U.S. patent application number 14/495311 was filed with the patent office on 2015-03-19 for safety mechanisms for power tools, including magnetorhelogical brake for blade.
The applicant listed for this patent is Frank Buhrmann, Andy Butler, Edward Cooper, Peter Domeny, John Gilbert, Brian Lamb, Clinton Lazzari, Eric Edward Schultz, William Scott, Chris Tacklind, David Titzler. Invention is credited to Frank Buhrmann, Andy Butler, Edward Cooper, Peter Domeny, John Gilbert, Brian Lamb, Clinton Lazzari, Eric Edward Schultz, William Scott, Chris Tacklind, David Titzler.
Application Number | 20150075343 14/495311 |
Document ID | / |
Family ID | 42198494 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150075343 |
Kind Code |
A1 |
Butler; Andy ; et
al. |
March 19, 2015 |
SAFETY MECHANISMS FOR POWER TOOLS, INCLUDING MAGNETORHELOGICAL
BRAKE FOR BLADE
Abstract
Various safety systems for power tools, and in particular table
saws include detection systems for detecting a dangerous condition
relative to a blade of the power tool, reaction systems for taking
mitigation action in response to detection of a dangerous
condition. The safety system may detect, prevent, and/or mitigate a
dangerous condition associated with the power tool.
Inventors: |
Butler; Andy; (Palo Alto,
CA) ; Lamb; Brian; (Belmont, CA) ; Tacklind;
Chris; (Menlo Park, CA) ; Lazzari; Clinton;
(Mountain View, CA) ; Cooper; Edward; (Lafayette,
CA) ; Schultz; Eric Edward; (Los Altos Hills, CA)
; Buhrmann; Frank; (San Francisco, CA) ; Gilbert;
John; (Applegate, OR) ; Titzler; David; (Palo
Alto, CA) ; Scott; William; (Palo Alto, CA) ;
Domeny; Peter; (Peachtree City, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Butler; Andy
Lamb; Brian
Tacklind; Chris
Lazzari; Clinton
Cooper; Edward
Schultz; Eric Edward
Buhrmann; Frank
Gilbert; John
Titzler; David
Scott; William
Domeny; Peter |
Palo Alto
Belmont
Menlo Park
Mountain View
Lafayette
Los Altos Hills
San Francisco
Applegate
Palo Alto
Palo Alto
Peachtree City |
CA
CA
CA
CA
CA
CA
CA
OR
CA
CA
GA |
US
US
US
US
US
US
US
US
US
US
US |
|
|
Family ID: |
42198494 |
Appl. No.: |
14/495311 |
Filed: |
September 24, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13129948 |
May 18, 2011 |
8919231 |
|
|
PCT/US09/65083 |
Nov 19, 2009 |
|
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14495311 |
|
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|
61116098 |
Nov 19, 2008 |
|
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Current U.S.
Class: |
83/62 |
Current CPC
Class: |
Y10T 83/141 20150401;
Y10T 83/7788 20150401; Y10T 83/613 20150401; Y10T 83/081 20150401;
Y10T 83/7697 20150401; Y10T 83/089 20150401; B27B 5/222 20130101;
Y10T 83/088 20150401; B23D 45/067 20130101; B27B 5/38 20130101;
Y10T 83/773 20150401; Y10T 83/8773 20150401; B27B 5/243 20130101;
B23D 47/10 20130101 |
Class at
Publication: |
83/62 |
International
Class: |
B27B 5/38 20060101
B27B005/38; B27B 5/22 20060101 B27B005/22 |
Claims
1. A table saw comprising: a cutting surface; a motor-driven
rotatable shaft positioned below the cutting surface; a blade for
cutting a workpiece on the cutting surface, wherein the blade spins
when the shaft rotates, and wherein a portion of the blade is
extendable above the cutting surface; a detection system for
detecting a dangerous condition relative to the blade; a reaction
system in communication with the detection system for taking a
reaction in response to detection of the dangerous condition,
wherein the reaction system comprises a magnetorheological rotary
brake connected to the shaft that brakes the shaft to thereby brake
the spinning of the blade in response to detection of the dangerous
condition by the detection system.
2. The table saw of claim 1, wherein the blade is mounted on the
rotatable shaft
3. The table saw of claim 1, wherein the magnetorheological rotary
brake comprises: a rotor fixed to the shaft; a housing, wherein the
housing and the rotor define a spacing; magnetorheological fluid in
the spacing; and a magnetic field-producing coil that is energized
in response to detection of the dangerous condition by the
detection system to produce a magnetic field that causes the
magnetorheological fluid to increase its viscosity to brake the
rotor, thereby braking the shaft, thereby braking the blade.
4. The table saw of claim 3, wherein the blade is mounted on the
rotatable shaft.
5. The table saw of claim 1, further comprising a kickback
detection system for detecting kickback of the workpiece during
cutting of the workpiece.
6. The table saw of claim 5, wherein the reaction means further
comprises a downstream kickback mitigation means for mitigating
kickback of the workpiece in response to detection of kickback of
the workpiece.
7. The table saw of claim 1, further comprising a clutch coupled to
the rotatable shaft, such that when the clutch is engaged and the
motor is running, the blade shaft is rotated, and wherein the
reaction means comprises a motor shut-down circuit connected to the
clutch and the brake system, wherein the motor shut-down circuit
disengages the clutch and actuates the brake system to brake the
blade when the motor is turned off.
8. The table saw of claim 1, further comprising a blade-spin
detection means for detecting whether the blade is rotating based
on energy from the blade, wherein the blade-spin detection system
is in communication with the reaction means and provides an output
to arm the reaction means when the blade-spin detection system
detects that the blade is spinning.
9. The table saw of claim 1, further comprising an electrical
generator connected by one or more gears to the rotatable shaft,
wherein the electrical generator is further connected to the
reaction means and generates electricity when the shaft rotates to
power at least one of the reaction means and the detection
means.
10. The table saw of claim 1, wherein the blade comprises: an outer
peripheral portion that comprises a first material; and an inner
portion that comprises a second material that is different from the
first material, wherein the first material is denser than the
second material.
11. The table saw of claim 1, further comprising a passive
downstream safety member for mitigating kickback of the workpiece,
wherein the passive downstream safety member is not actuated by the
detection means.
12. The table saw of claim 11, wherein the passive downstream
safety member comprises angled snells that impede kickback of the
workpiece.
13. The table saw of claim 1, wherein the detection means comprises
a blade contact sensor means for sensing contact with by a foreign
object with the blade, wherein the blade contact sensor is in
communication with the reaction means, and wherein the reaction
means is for taking the reaction in response to detection of
contact by a foreign object with the blade upon detection by the
blade contact sensor means.
14. The table saw of claim 13, wherein: the blade comprises: a
first electrically conductive blade portion; a second electrically
conductive blade portion that comprises teeth for cutting the
workpiece; and a dielectric between the first and second
electrically conductive blade portions, and the blade contact
sensor means is connected to the first electrically conductive
blade portion and drives the first electrically conductive blade
portion with a drive signal, and wherein the blade contact sensor
means comprises a processor for detecting contact with the blade by
the object based on an electrical signal from the first
electrically conductive blade portion.
15. The table saw of claim 1, further comprising a blade proximity
sensor means for sensing proximity of a foreign object to the
blade, wherein the blade proximity sensor means is in communication
with the reaction means, and wherein the reaction means is for
taking the reaction in response to detection of proximity by a
foreign object to the blade upon detection by the blade proximity
sensor means.
16. The table saw of claim 1, further comprising sensor means
connected to the cutting surface for sensing a characteristic of
the workpiece during cutting of the workpiece.
Description
PRIORITY CLAIMS
[0001] The present application claims priority as a divisional
under 35 U.S.C. .sctn..sctn.120-121 to U.S. nonprovisional patent
application Ser. No. 13/129,948, filed May 18, 2011, now U.S. Pat.
No. ______, which claims priority to PCT application
PCT/US09/65083, filed Nov. 19, 2009, which claims priority to U.S.
provisional application Ser. No. 61/116,098, filed Nov. 19, 2008,
all of which are incorporated herein by reference in their
entirety.
BACKGROUND
[0002] Many types of power tools have exposed blades, such as table
saws and other cutting tools. Contact between the blade and an
object other than the workpiece can be dangerous. Safety systems to
mitigate potentially dangerous conditions are continually being
developed.
SUMMARY
[0003] Various new and improved safety systems for power tools,
such as table saws, are disclosed herein. The disclosed safety
systems include detection systems for detecting a dangerous
condition relative to a blade of the power tool, reaction systems
for taking mitigating action in response to detection of a
dangerous condition, systems for detecting whether the blade is
spinning, systems for detecting kickback of the workpiece, and
others. Generally, the embodiments described herein may detect,
prevent, and/or mitigate a dangerous condition associated with the
power tool.
[0004] In one general aspect, embodiments of the present invention
are directed to a table saw that comprises a cutting surface and a
motor-driven, rotatable blade for cutting a workpiece on the
cutting surface. In one embodiment, the table saw comprises a
kickback detection system for detecting kickback of the workpiece
during cutting of the workpiece. In addition, the table saw
comprises reaction means in communication with the kickback
detection system for taking a mitigating reaction in response to
detection of kickback of the workpiece during cutting of the
workpiece by the kickback detection system. According to various
implementations, the kickback detection system comprises an
acoustic sensor and a processor in communication with the acoustic
sensor. The processor is programmed to recognize a condition
indicative of kickback of the workpiece during cutting of the
workpiece based on input from the acoustic sensor. In another
implementation, the kickback detection system comprises a torque
sensor mounted on the rotatable blade shaft and a processor in
communication with the torque sensor, where the processor is
programmed to recognize a condition indicative of kickback of the
workpiece during cutting of the workpiece based on input from the
torque sensor.
[0005] In another general aspect of the present invention, the
table saw comprises a blade-spin detection system for detecting
whether the blade is rotating based on energy from the blade. The
blade-spin detection system may be in communication with the
reaction means and may provide an output to arm the reaction means
when the blade-spin detection system detects that the blade is
spinning. According to various implementations, the blade-spin
detection system comprises a static electricity charge sensor in
proximity to the blade for sensing the static electricity build-up
on the blade. In another implementation, the blade-spin detection
system comprises: (i) a transmitter proximate to the blade for
transmitting radio signals; (ii) a passive electronic circuit on
the blade that transmits responsive radio signals when passively
energized by the radio signals transmitted by the transmitter; and
(iii) a receiver, proximate to the blade, for detecting the
responsive radio signals from the passive electronic circuit on the
blade. In another implementation, the blade-spin detection system
comprises an acoustic sensor and a processor, where the processor
is programmed to determine whether the blade is rotating based on
input from the acoustic sensor.
[0006] In another general aspect of the present invention, the
table saw comprises a sensor connected to the cutting surface for
sensing a characteristic of the workpiece during, prior to, and/or
after cutting of the workpiece. In various implementations, the
sensor comprises a height sensor for sensing a height of the
workpiece relative to the cutting surface. In such an embodiment,
the table saw further comprises a height adjustment circuit that
receives an input signal from the height sensor indicative of the
height of the workpiece relative to the cutting surface and outputs
a signal to a blade height adjustment mechanism to adjust the
height of the blade based on the height of the workpiece as sensed
by the height sensor. In another embodiment, the sensor comprises a
workpiece conductivity sensor on the cutting surface that detects
electrical conductivity of the workpiece. In such an embodiment,
the table saw further comprises contact detection means for
detecting contact with the blade by an object other than the
workpiece. The contact detection means receives an input from the
workpiece conductivity sensor, which input is used to determine
when to trigger the mitigating reaction means.
[0007] In another general aspect of the present invention, the
blade comprises a first electrically conductive blade portion, a
second electrically conductive blade portion, and a dielectric
between the first and second electrically conductive blade
portions. In such an embodiment, the table saw may comprise a
contact detection system for detecting contact with the blade by an
object other than the workpiece. The contact detection system may
be connected to the first electrically conductive blade portion and
drive the first electrically conductive blade portion with an
electrical drive signal. The processor of the contact detection
system may detect contact with the blade by a foreign object based
on an electrical signal from either the first or second blade
portions. For example, the processor may detect contact with the
blade by a foreign object based on an electrical signal from the
first electrically conductive blade portion.
[0008] In yet another general aspect of the present invention, the
table saw comprises a reaction system for taking a mitigating
reaction in response to detection of a dangerous condition relative
to the blade when detected by the detection system. In various
embodiments, the reaction system comprises a magnetorheological
rotary brake connected to the blade shaft that brakes the shaft to
thereby brake the blade in response to detection of the dangerous
condition by the detection system.
[0009] These and other advantageous safety systems for power
cutting tools will be apparent from the description below.
FIGURES
[0010] Various embodiments of the present invention are described
herein by way of example in conjunction with FIGS. 1 to 54,
wherein:
[0011] FIG. 1 is a diagram of a table saw:
[0012] FIG. 2 is a block diagram of a table saw according to
various embodiments of the present invention;
[0013] FIGS. 3 and 4 are block diagrams of table saws with
blade-spin detection sensors according to various embodiments of
the present invention;
[0014] FIGS. 5A and 5B illustrate a table saw blade with magnets
according to various embodiments of the present invention;
[0015] FIG. 6 is a diagram of a table saw with an electric
generator according to various embodiments of the present
invention;
[0016] FIG. 7 is a block diagram of a table saw with a static
charge detection circuit according to various embodiments of the
present invention;
[0017] FIGS. 8A and 8B are diagrams illustrating a table saw blade
with passive electronic components according to various embodiments
of the present invention;
[0018] FIG. 9 is a block diagram of a table saw with a variable
speed motor according to various embodiments of the present
invention;
[0019] FIGS. 10A and 10B are diagrams illustrating a table saw
blade connected to a motor;
[0020] FIG. 11 is a diagram illustrating a table saw with a
counter-rotating flywheel according to various embodiments of the
present invention;
[0021] FIG. 12 is a diagram illustrating a table saw blade
comprising multiple pieces with different masses according to
various embodiments of the present invention;
[0022] FIG. 13 is a diagram of a high-mass flywheel according to
various embodiments of the present invention;
[0023] FIG. 14 is a diagram of a table saw with a moveable throat
plate according to various embodiments of the present
invention;
[0024] FIG. 15 is a diagram of a table saw with a tabletop that
pops up according to various embodiments of the present
invention;
[0025] FIG. 16 is a diagram of a table saw blade with elongate,
moveable members according to various embodiments of the present
invention;
[0026] FIG. 17 is a diagram of a table saw blade with pivoting
teeth members according to various embodiments of the present
invention;
[0027] FIG. 18 is a block diagram of a table saw with remote
warning systems according to various embodiments of the present
invention;
[0028] FIGS. 19A and 19B are diagrams illustrating a table saw
blade with a reaction system that uses an air bag according to
various embodiments of the present invention;
[0029] FIG. 20 is a block diagram of a magnetorheological brake for
a table saw according to various embodiments of the present
invention;
[0030] FIGS. 21A-B are flowcharts of a process according to various
embodiments of the present invention;
[0031] FIG. 22 is a diagram of a table saw blade and motor with a
clutch and brake system according to various embodiments of the
present invention;
[0032] FIG. 23 is a block diagram of a table saw according to
various embodiments of the present invention;
[0033] FIG. 24 is a diagram of a table saw with a trailing edge
sensor assembly according to various embodiments of the present
invention;
[0034] FIG. 25 is a diagram of a table saw with a conductivity
sensor according to various embodiments of the present
invention;
[0035] FIGS. 26 and 27 are diagrams of table saws with a sensing
table top surface according to various embodiments of the present
invention;
[0036] FIG. 28 is a diagram of a segmented table saw blade
according to various embodiments of the present invention;
[0037] FIGS. 29 and 30 are diagrams of a table saw blade capacitor
according to various embodiments of the present invention;
[0038] FIG. 31 is a diagram of a table saw blade with whiskers
according to various embodiments of the present invention;
[0039] FIG. 32 is a diagram of a segmented table saw blade
according to various embodiments of the present invention;
[0040] FIG. 33 is a diagram of a table saw with a overhead sensor
assembly according to various embodiments of the present
invention;
[0041] FIGS. 34-42 are diagrams of table saws with downstream
safety members according to various embodiments of the present
invention;
[0042] FIG. 43 is a block diagram of a table saw with a height
sensor and blade height adjustment circuit according to various
embodiments of the present invention;
[0043] FIGS. 44-46 are diagrams of table saws with a workpiece
height sensor assembly according to various embodiments of the
present invention;
[0044] FIG. 47 is a block diagram of a table saw with an installed
retrofit package according to various embodiments of the present
invention;
[0045] FIGS. 48, 49 and 50 are diagrams of a push stick that can be
used with a table saw according to various embodiments of the
present invention;
[0046] FIG. 51 is a top view of a table saw with a suction feed
assembly according to various embodiments of the present
invention;
[0047] FIGS. 52 and 53 are diagrams of a kick back detection
mechanism according to various embodiments of the present
invention; and
[0048] FIG. 54 is a block diagram of a table saw with a torque
sensor according to various embodiments of the present
invention.
DESCRIPTION
[0049] The embodiments of the present invention relate generally to
safety systems for power tools having an exposed, moving cutting
instrument or blade, such as a table saw. Before describing the
various new safety features, an example table saw is described.
FIG. 1 shows one type of exemplary table saw 10. It includes a
table (or tabletop) 12 through which a circular blade 14 extends
from beneath the table. The table 12 includes a throat plate 13,
which includes an elongated slot through which a portion of the
circular blade 14 extends. A workpiece (not shown) may be placed on
the cutting surface of the tabletop 12 and be cut by the portion of
the blade 14 extending above the cutting surface. The table 12 and
blade 14 are supported by a housing 16 and legs 18. The housing 16
may enclose the mechanics that support, position, and drive the
blade 16. The housing 16 may also comprise processor-based systems
for detecting a dangerous condition relative to the blade, as
described below, and/or processor-based systems for detecting the
condition of the blade (e.g., whether it is spinning). A motor to
drive the blade can be positioned in or outside of the housing. A
switch 20 may be used to turn the saw on and off, causing blade 14
to spin when turned on. A handle 22 may be used to adjust manually
the position of the blade 14 relative to the table 12. For example,
using the handle 22, an operator of the saw 10 may adjust how far
the blade 14 extends above the table 12 or how the blade 14 tilts
relative to the top (or cutting surface) of the table 12. A user
places a workpiece on the table 12 and slides it into the blade 14
to cut the workpiece. Of course, table saws take many different
configurations, from large saws sized for industrial use to small
saws that can be placed on a bench top or counter, and table saws
come with various types of tables and housings. The safety and
other mechanism described below may be employed in most any type of
table saw, as will be apparent from the description below.
[0050] FIG. 2 is a diagram showing certain features of a table saw
10 according to various embodiments of the present invention. FIG.
2 shows that the table saw 10 may comprise a detection system 30
that may be used to detect a potentially dangerous condition with
respect to the blade 14. In the illustrated embodiment, the
detection system 30 may be a processor-based capacitive contact
sensing system that detects contact of a foreign object with the
blade 14 based on a change in an electrical signal on the blade 14
due to the change in capacitance when the foreign object contacts
the blade 14. The processor of the detection system 30 may be, for
example, a digital signal processor, a microprocessor, a
microcontroller, or some other type of processor. In such an
embodiment, the detection system 30 operates by driving an
excitation voltage onto the blade 14 and detecting the current
drawn from the blade 14. This current and/or excitation voltage may
show changes in amplitude and phase when the blade 14 comes into
contact with an electrically conductive foreign object (such as an
operator's hand or finger, as well as work pieces). The
characteristics of these changes can be used to trigger selectively
the operation of a reaction system 32, which takes one or more
actions to mitigate the detected dangerous condition. The
excitation voltage may be driven onto the blade 14 via an
excitation plate 34, which is capacitively coupled to the blade 14.
In such an embodiment, a shield 37 may guard the blade 14 from
outside electrical interference, including the tabletop 12.
[0051] More details regarding such capacitive contact sensing
detection systems 30 may be found in U.S. patent application Ser.
No. 11,481/549, entitled "Capacitive sensing system for power
cutting tool," filed Jul. 6, 2006, and U.S. patent application Ser.
No. 12/244,994 entitled "DETECTION SYSTEM FOR POWER TOOL," filed
Oct. 3, 2008, both of which are incorporated herein in their
entirety. In other embodiments, the detection system 30 may
comprise two electrodes capacitively coupled to the blade 14. In
such embodiments, the drive signal may be copied to one of the
electrodes. Contact by an object with the blade may be detected by
analyzing the signal from one or both of the electrodes. The
detection system 30 may also be a proximity sensing system that
detects when a foreign object comes near (or proximate) to the
exposed blade 14. Examples of proximity sensing systems are
disclosed in U.S. Pat. No. 7,421,932, issued Sep. 9, 2008, and U.S.
patent application Ser. No. 11/444,712, both of which are
incorporated herein by reference in their entirety. Other types of
detection systems may also be used, and this application discloses
other types of detection systems.
[0052] The blade 14 may be mounted to an arbor or rotatable blade
shaft 38. A motor 40 may drive the arbor 38 to spin the blade 14.
The motor 40 may drive the arbor 38 via one or more belts or gears,
or it may use a direct drive.
[0053] The blade 14 may be directly driven by the motor or
indirectly driven through the use of one or more drive belts or
gears. The saw 10 may also comprise (under the table 12) a bevel
adjustment mechanism (not shown) to adjust the angular orientation
of the blade 14 relative to the table top 12 by pivoting the saw
blade 14 and motor. The saw 10 may also comprise a height
adjustment mechanism (not shown) to adjust the cutting depth of the
saw blade 14 by vertical movement of the saw blade 14 and motor.
Example embodiments of the bevel adjustment mechanism and the
height adjustment mechanism are provided in U.S. Pat. No.
6,595,096, which is incorporated herein by reference in its
entirety.
[0054] The reaction system 32 may serve to mitigate the potentially
dangerous condition detected by the detection system 30 by, for
example, braking the blade 14, dropping the blade 14 below the
tabletop 12, or any other suitable reaction, several of which are
described in more detail below. One example reaction system 32 may
use an explosive charge to drive a stopper (or brake) (not shown)
into the blade 14, arresting its motion. In addition, or instead,
an example reaction system 32 may drop or collapse a blade support
member (not shown) causing the blade 14 to fall below the surface
of the table 12. An example blade-drop reaction system is described
in U.S. patent application Ser. No. 11/374,319, filed 13 Mar. 2006,
which is incorporated herein by reference in its entirety.
[0055] In a table saw having a reaction system 32, it is often
important to keep the reaction system 32 operative when the motor
40 powering the blade 14 is turned off, but the blade 14 is still
spinning. This is because the spinning blade 14, even though the
motor is turned off, still represents a potentially dangerous
condition. In one embodiment, as shown in FIG. 3, the table saw 10
may comprise an acoustic sensing system 300, comprising an acoustic
sensor 301, such as a microphone, and a processor 302 (e.g., a DSP
or microprocessor). The output of the acoustic sensor 301 may be
connected to the processor 302, which may characterize the audible
and inaudible acoustic energy picked up by the acoustic sensor 301
to detect various operating conditions of the table saw. For
example, the acoustic sensor 301 could be positioned near, but
spaced from, the blade 14, preferably under the tabletop 12 as
shown in FIG. 3, to detect whether the blade 14 is spinning. The
acoustic sensing system 300 may be in communication with the
reaction system 32. In operation, the processor 302 may compare the
acoustic waveforms detected by the sensor 301 to a database of
signature waveforms indicative of various conditions of the table
saw 10 in order to detect various states or conditions of the table
saw, such as whether the blade 14 is spinning or not. If, for
example, the acoustic sensing system 300 determines that the blade
14 is still spinning based on the comparison of the signals from
the acoustic sensor of the database of signature waveforms, the
acoustic sensing system 300 may signal the reaction system 32 to
remain powered on and operative (e.g., armed). On the other hand,
if the acoustic sensing system 300 detects that the blade 14 is
spinning slowly, slowing down, or no longer spinning, or if it
detects that the blade 14 is about to come to a complete stop, the
acoustic sensing system 300 may signal the reaction system 32 to
disarm.
[0056] The acoustic sensing system 300 also may be used to detect
other conditions, such as potentially dangerous conditions. If the
acoustic sensing system 300 detects such a dangerous condition, the
acoustic sensing system 300 may send a signal to the reaction
system 32 to cause the reaction system to take its mitigating
action. Again, the processor 302 may compare the input waveforms
from the acoustic sensor 301 to a database of signature waveforms
to detect a dangerous condition. For example, the acoustic sensing
system 300 may be programmed to detect kickback conditions
involving the workpiece being cut by the blade 14. If it detects a
kickback condition, the acoustic sensing system 300 may output a
signal to the reaction system 32 that triggers the mitigating
reaction of the reaction system 32. The acoustic sensing system
300, based on the output from the sensor 301, could also be
programmed to detect various other conditions, such as: (i) motor
on with no load; (ii) cutting various types of material (e.g.,
wood, metal, plastic); and (iii) motor off. The detection of these
various states could be used to control different systems of the
table saw 10. For example, if the acoustic sensing system 300
detects that the motor is off and the blade is not spinning, the
acoustic sensing system 300 may disarm the reaction system 32 so
that, for example, maintenance of the table saw 10 may be performed
without activating the reaction system 32. Of course, in various
embodiments, the acoustic sensing system 300 may comprise a number
of acoustic sensors 301 that supply input to the processor 302. The
data base of the signature waveforms (for blade spin and/or
kickback or the other conditions) may be stored in a memory unit
that is in communication with the processor 302. The memory unit
may be, for example, a read-only memory (ROM). In various
embodiments the ROM may be integrated with the processor 302.
[0057] In another embodiment, as shown in FIG. 4, the table saw 10
may comprise a blade-generated airflow sensing system 400 to detect
whether the blade 14 is spinning or not. The blade-generated
airflow sensing system 400, as shown in FIG. 4, may comprise one or
more sensors 401 and a processor 402 in communication with the
sensors 401. The sensor 401 may include one or more airflow
detection sensors, such as, for example, pressure sensors or hot
wire anemometers, that detect airflow generated by the blade 14. To
enhance the airflow from the blade 14, the blade 14 may comprise a
number of off-center holes therethrough (i.e., holes that are not
in the center of the blade and that are not used for the blade
shaft). The sensors 401 may detect the airflow generated by the
blade teeth and/or the holes in the blade. The processor 402 may be
programmed to detect conditions based on the output signals from
the sensors 401, such as whether the blade 14 is spinning or not.
If the blade 14 is spinning, the blade-generated airflow sensing
system 400 may signal the reaction system 32 to remain armed. If
the blade-generated airflow sensing system 400 determines that the
blade 14 is not spinning, it may signal the reaction system 32 to
disarm. Again, the processor 302 may detect whether the blade is
spinning by comparing the signals from the airflow sensors 401 to a
database of signature waveforms that are indicative of whether the
blade is spinning or not.
[0058] In another embodiment, one or more vibration sensors (e.g.,
accelerometers) may be used to detect whether the blade is
spinning. Such vibration sensor may be mounted to the saw 10 in a
position relative to the blade so that they vibrate in a detectable
manner when the blade spins.
[0059] In another embodiment, as shown in FIGS. 5A-B, one or more
magnets 502 may be embedded in or placed on the exterior of the
blade 14. In addition, an inductor 504 may be positioned near the
blade 14, such as in the tabletop 12 or under the tabletop 12. As
the blade 14 spins, the spinning magnets 502 will induce a voltage
across the inductor 504. The level of the voltage across the
inductor 504 may be used to control whether the reaction system 32
is armed or not. For example, the inductor voltage may be coupled
to a control circuit 505 (analog or digital) that controls whether
the reaction system 32 is armed based on the inductor voltage. If
the inductor voltage level exceeds a threshold level, the reaction
system 32 may be armed. If the inductor voltage level does not
exceed the threshold level, the reaction system 32 may be
disarmed.
[0060] In another embodiment, the inductor voltage may directly
power the detection system 30 and/or the reaction system 32 with a
power converter (not shown) that converts the inductor voltage to
input voltage for the detection system 30 and/or the reaction
system 32. That way, the detection system 30 and/or the reaction
system 32 are only powered on so long as the blade 14 is spinning.
In such embodiments, the detection system 30 and/or the reaction
system 32 may comprise their own, respective, energy storage device
to maintain sufficient continuous power levels.
[0061] In another embodiment, as shown in FIG. 6, an electric
generator 602 may be positioned under the tabletop 12 and
mechanically powered by the spinning blade 14. The generator 602
may convert this mechanical energy to electricity, which may be
used to power the detection system 30 and/or reaction system 32. As
shown in the embodiment of FIG. 6, the arbor 38 may include a gear
604, which is geared into a gear 606 for the generator 602. As
shown in FIG. 6, there may be one or more intermediary gears 608
between the arbor 38 and the generator 602. When the arbor rotates
the armature of the generator 602 is rotated (via the gears
604-608) to thereby generate electricity. The electricity generated
by the generator 602 may be used to electrically power the
detection system 30 and/or the reaction system 32. By using such a
generator 602, the detection system 30 and/or reaction system 32
would be powered when the blade 14 is spinning. That way, the
detection system 30 and/or reaction system 32 could be powered
independently of the motor 40 used to spin the blade 14. As such,
the detection system 30 and/or reaction system 32 could be powered
even when the motor 40 used to rotate the blade 14 is turned off,
as long as the blade/arbor is spinning. This would keep the
detection system 30 and/or reaction system 32 enabled even when the
power to the blade 14 is turned off. Also, the detection system 30
and/or reaction system 32 would not be enabled when maintenance is
being performed on the saw 10 and/or blade 14, as the blade/arbor
would not be spinning in such a mode. In other embodiments, the
generator 602 may not be geared to the arbor, but may use a drive
belt or some other drive mechanism to drive the generator 602 when
the arbor rotates.
[0062] In another embodiment, as shown in FIG. 7, the static
electricity that accumulates on the blade 14 may be used to detect
a spinning condition for the blade 14. The static electricity
build-up on the blade may also be used to detect contact between
the blade 14 and foreign objects. As shown in the embodiment of
FIG. 7, a static charge detection circuit 702 may be coupled to,
and receive as an input a signal from, the excitation plate 34 that
is capacitively coupled to the blade 14. As the blade 14 spins,
static charge is generated and accumulated on the blade 14. The
static charge detection circuit 702 may monitor the static charge
on the blade 14, via the excitation plate 34, to detect various
conditions pertaining to the blade 14. For example, as the blade 14
slows down, the static charge decreases. The static charge
detection circuit 702 may interpret the decrease in the static
charge as an indication that the blade 14 is slowing down.
Similarly, by monitoring the static charge on the blade 14, the
static charge detection circuit 702 can detect when the blade 14
stops spinning. The detection system 30 and/or reaction system 32
may be enabled (e.g., powered on) based on the determination by the
static charge detection circuit 702 of whether the blade 14 is
still spinning. For example, the static charge detection circuit
702 may be in communication with a controller circuit (not shown)
that outputs control signals to arm or disarm the detection and/or
reaction systems based on the output from the static charge
detection circuit 702 regarding the static charge build-up on the
blade 14. In addition, as contact between the blade 14 and foreign
objects (such as the material to be cut by the blade) will affect
the static charge on the blade 14, the static charge detection
circuit 702 can be used to detect contact between the blade 14 and
a foreign object. The detection system 30 may use this information
from the static charge detection circuit 702 to determine whether
there exists a dangerous condition that warrants triggering of the
reaction system 32. The static charge detection circuit 702 may be
implemented with analog circuitry, and may also include digital
circuitry in various implementations.
[0063] In another embodiment, as shown in FIGS. 8A-B, the blade 14
may comprise one or more embedded passive electronic components or
circuits 801. The passive circuit components 801 may be embedded in
or positioned on one or both of the sides of the blade 14. In one
embodiment, the electronic component 801 may be powered passively
by incoming radio frequency signals from a transmitter 803 near the
blade 14, such as embedded in the tabletop 12, under the tabletop
12, etc. The emitted signals from the transmitter 803 may be at a
relatively low power so that the passive circuit components 801 are
only passively powered when the circuits 801 rotate past the
transmitter 803. In one embodiment, the electronic component 801
may comprise a burst RF circuit that, when energized passively,
emits a burst RF signal to a receiver 805, that may, like the
transmitter 803, be near the blade 14. The output signal from the
circuit component 801 may indicate that the RF circuit 801 is "on"
due to the fact that the RF circuit is powered due to the fact that
the blade 14 is spinning. Based on the signal received from the RF
circuit 801, the receiver 805 may output a signal to the detection
system 30 and/or the reaction system 32 to remain enabled. In
addition, the receiver 805 may be able to determine the speed of
the rotating blade 14 based on the number of burst signals received
per time period (e.g., minute or second). That way, the receiver
805 can detect whether the blade 14 is speeding up or slowing down.
In other embodiments, the circuit 801 may comprise a passively
powered accelerometer or other motion sensor, with a transmitter
(e.g., an RF transmitter) for transmitting sensor data to the
receiver 805. That way, based on the sensor data, the receiver 805
may determine whether the blade 14 is spinning or not.
[0064] In another embodiment, as shown in FIG. 9, the saw 10 may
include a variable speed motor 901 for powering the blade 14. In
such an embodiment, when the detection system 30 detects a
condition that approaches the threshold level that triggers the
reaction system 32, the detection system 30 may output a signal to
the variable speed motor 901 to reduce the speed of the motor 901,
to thereby reduce the rate at which the blade 14 is spinning. That
way, the motor speed may be at a reduced level if and when the
reaction system 32 is triggered. In such an embodiment, therefore,
the detection system 30 may have at least two trigger levels: a
first trigger level that causes the motor speed of the variable
speed motor 901 to reduce and a second trigger level that triggers
the reaction system 32. The second trigger may be dropping or
braking the blade 14, or some other mitigating reaction as
described herein. Some time after the condition returns below the
first trigger level, the motor 901 may be returned to full speed.
The detection system 30 may be a proximity-based or contact-based
detection system. An advantage of using a variable speed motor 901
is that the speed of the motor may provide feedback to the user
regarding potentially dangerous conditions. For example, the
reduction in motor speed may provide the user with advanced warning
of a dangerous condition, and the user could react to the advanced
warning, to thereby potentially avoid the mitigating reaction of
the reaction system 32.
[0065] In another embodiment, as shown in FIGS. 10A and 10B, when a
dangerous condition is detected, the detection system 30 may output
a signal to change, or reverse, the direction of the motor 40. Such
a mitigating reaction to a detected dangerous condition may be
combined with other reaction systems 32, such as a braking reaction
system (see, e.g. U.S. Pat. No. 6,920,814, which is incorporated
herein by reference in its entirety), a drop mechanism (see, e.g.,
U.S. patent application Ser. No. 11/589,344, which is incorporated
herein in its entirety), or other types of reaction systems, such
as described herein. In particular, for a drop reaction system, the
change in angular momentum of the blade 14 due to the change in
motor direction could be leveraged to increase the rate at which
the blade 14 drops beneath the tabletop 12.
[0066] As another type of reaction system, as shown in FIG. 11, the
saw 10 may comprise a counter-rotating flywheel 1101, which may
rotate in a direction opposite the rotational direction of the
blade 14. When the dangerous condition is detected by the detection
system 30, the reaction system 32 may cause a clutch 1103 to engage
the flywheel 1101 with the drive for the blade 14. Preferably, the
flywheel 1101 has a mass and speed such that the angular momentum
of the flywheel is equal to the angular momentum of the blade 14.
That way, the stored energy of the flywheel 1101 may stop the blade
14 from spinning when the clutch 1103 is engaged. If the angular
momentum of the flywheel 1101 is greater than the angular momentum
of the blade 14, the blade 14 may reverse direction when the clutch
1103 is engaged. In such an embodiment, a blade-braking system may
be used to stop the blade 14 from reverse spinning. If the angular
momentum of the flywheel 1101 is less than the angular momentum of
the blade 14, the blade 14 may slow down when the clutch 1103 is
engaged. Similarly, a blade-braking system may be used in such an
embodiment to completely stop the blade 14 from spinning. In one
embodiment, the motor 40 may power both the blade 14 and the
flywheel 1101, with a transmission being used to provide the
reverse rotational direction for the flywheel 1101. In another
embodiment, a second motor may be used to power the flywheel 1101.
The flywheel 1101 may be located below the tabletop 12.
[0067] In another embodiment, the blade 14 may be made out of less
massive materials and/or the blade 14 may have a geometry that
lessens the mass of the blade 14 (while still providing sufficient
structural strength). Using a less massive blade reduces the stored
energy in the blade when spinning, thus allowing the lightweight
blade to be stopped or braked faster in response to the detection
of a dangerous condition. FIG. 12 shows three such exemplary blades
14a-c. In the first embodiment, the blade 14a comprises an interior
portion 1201 and a peripheral portion 1202. The interior portion
1201 may be made from a material that is less dense than the
peripheral portion 1202, yet still sufficiently strong and durable.
For example, the interior portion 1201 may comprise lightweight,
strong metals, such as magnesium or titanium, or composite
materials. Suitable composite materials include, but are not
limited to, fiber reinforced polymers, carbon-fiber reinforced
plastic, glass reinforced plastic, metal matrix composites, ceramic
matrix composites, organic matrix/ceramic aggregate composites,
thermoplastic composite materials, or any other suitable composite
material. In addition, other lightweight, strong materials could be
used. The peripheral portion 1202 of the blade 14 may comprise, for
example, conventional blade materials, such as steel, and the
material of the peripheral portion 1202 may be more dense than the
interior portion 1201.
[0068] In other embodiments, the blade may comprise one or more
off-center holes or openings, as shown in blades 14b-c, to reduce
the mass of the blade. The holes/openings 1207 shown in the example
blades 14b-c are off-center in the sense that they are not the
blade center-hole through which the blade 14 is mounted to its
rotatable shaft. In addition, the teeth of the blades 14a-c could
comprise less massive materials, such as carbide, titanium,
aluminum, composite plastics, etc. Blades of the type shown in FIG.
12 may be used in saws having an airflow-based blade-spin detection
system 400 (See FIG. 4).
[0069] In embodiments using a low mass blade, such as described
above, the low mass blade may be coupled to a high-mass flywheel
1301, as shown in FIG. 13. The high-mass flywheel 1301 may provide
added momentum to the blade 14 to aid in cutting workpieces. When a
dangerous condition is detected, the reaction system 32 may
disengage a clutch that couples the flywheel 1301 to the blade
drive. That way, the reaction system 32 can more easily stop, drop,
or otherwise react the lightweight blade, and not have to
additionally stop the high-mass flywheel 1301.
[0070] In another embodiment, as shown in FIG. 14, once a dangerous
condition is detected, the reaction system 32 may cause a throat
plate 1401, positioned around the blade 14 on the tabletop 12, to
pop up. In such an embodiment, the throat plate 1401 may be caused
to pop up by a number of suitable actuators under the throat plate
1401 that are actuated when the dangerous condition is detected,
such as for example: pyrotechnic actuators; springs; solenoids;
hydraulic actuators; pneumatic actuators; etc. By popping up, the
throat plate 1401 may create a guard around the blade 14 and/or
knock foreign objects out of the vicinity of the blade 14. The
throat plate 1401 may be made from a thin piece of metal (e.g.,
steel or aluminum), wood, or plastic, for example. As such, it may
take less energy to cause the throat plate 1401 to pop up than it
might take to employ other types of reaction systems. In addition,
the pop-up throat plate 1401 could be combined with other reaction
systems, such as braking reaction systems or blade-drop reaction
systems. In addition, according to various embodiments, one side of
the throat plate 1401, such as the side at the back of the blade
14, may be pivotably connected to the tabletop 12. In such an
embodiment, when the dangerous condition is detected, the other end
(e.g., the front end or a side) of the throat plate 1401 may be
popped up by the actuators causing the throat plate 1401 to rotate
into the blade 14 and jam the blade 14, potentially making it stop
spinning.
[0071] In another embodiment, as shown in FIG. 15, when a dangerous
condition is detected by the detection system 30, the tabletop 12
may pop up. Preferably, the tabletop 12 may be lifted or popped up
to an elevation level that is the same as, close to, or greater
than the elevation level of the top of the blade 14. That way, the
tabletop 12 can remove objects from around the vicinity of the
exposed blade 14. In one embodiment, the tabletop 12 may be
actuated, for example, by pyrotechnic charges in response to
detection of the dangerous condition by the detection system 30,
although other suitable actuation means may be used, such as
pneumatic actuators, hydraulic actuators, magnetic actuators (e.g.,
solenoids), etc. Preferably, the tabletop 12 is moveably connected
to the remainder of the base 16 of the table saw 10 by connectors
1501 that prevent the tabletop 12 from coming loose from the base
16 when the tabletop is elevated in response to detection of a
dangerous condition.
[0072] The number of actuators will depend on, among other things,
the force supplied by each actuator, their placement, and the
mass/size of the tabletop 12. In one embodiment, actuators are
placed in each corner of the tabletop 12, near the connectors 1501.
In other embodiments, the actuators are located in two corners of
the tabletop 12, so that the tabletop 12 effectively hinges upward
when the dangerous condition is detected. The pop-up tabletop 12
could be combined with other reaction systems, such as a dropping
blade. Also, the pop-up tabletop 12 preferably is combined with a
guard system that prevents the workpiece from flying away when the
tabletop 12 pops up.
[0073] In another embodiment, the reaction system 32 may cause the
geometry of the blade 14 to change in response to detection of a
dangerous condition by the detection system 30. As shown in the
example of FIG. 16, the blade 14 may comprise an elongate, moveable
member 1601 between each tooth 1603 of the blade 14. The members
1601 may be connected at a pivot point 1604 to the blade 14, such
that the members 1601 have one free end and one fixed, or pivoting,
end. In normal operating conditions, the moveable member may be in
the normal or stored position, as shown by moveable member 1601a in
FIG. 16. In this position, the member 1601a is tucked behind the
tooth 1603 in front of it so that the moveable member 1601 does not
interfere with the cutting operation. When the dangerous condition
is detected, the moveable member may transition to the deployed
position, as shown by moveable member 1601b in FIG. 16. As can be
seen in FIG. 16, the deployed moveable member 1601b may pivot about
the pivot point 1604 to extend in front of, and preferably beyond,
the cutting member 1605 of the tooth 1603 when deployed. That way,
the deployed moveable member 1601b will reduce the impact of the
cutting member 1605 relative to the object being cut by the blade
14.
[0074] In various embodiments, the moveable members 1601 may
comprise a magnetic material or a shape memory material (or alloy).
For an embodiment using magnetic moveable members 1601, when the
dangerous condition is detected, the reaction system 32 may apply a
magnetic field in the vicinity of the blade 14 to cause the
magnetic moveable members 1601 to deploy. In an embodiment
employing shape memory material moveable members 1601, the reaction
system 32 may activate the shape memory moveable members 1601, such
as through heat or electrical current, for example, to cause the
moveable members 1601 to deploy. In other embodiments, the moveable
members 1601 may have other actuating means, such as pyrotechnic
charges, etc.
[0075] In another embodiment, as shown in FIG. 17, the blade 14 may
comprise pivoting teeth members 1701. In such an embodiment, the
pivoting teeth members 1701 may be connected to the blade interior
1703 at a pivot 1705. FIG. 17 shows a pivoting tooth member 1701 in
the open or normal position. In this position, the cutting
instrument 1707 on the tooth member 1701 can cut effectively a
workpiece being fed to the blade 14. When a dangerous condition is
detected, the pivoting tooth member 1701 pivots forward,
counter-clockwise in FIG. 17, so that the cutting instrument 1707
is shielded completely or partially by the blade peripheral portion
1709 in front of the pivoting tooth member 1701. In this
embodiment, therefore, the pivoting tooth member 1701 rotates in
the direction that the blade 14 is spinning. In other embodiments,
the pivoting teeth members 1701 could be configured to pivot or
rotate in the direction opposite the direction of rotation of the
blade 14.
[0076] The pivoting teeth members 1701 may be actuated by an
electrical circuit, a pyrotechnic charge, or any other suitable
means. In addition, in an embodiment where the blade 14 is braked,
the stored rotational energy of the blade 14 may be sufficient to
actuate the pivoting teeth members 1701. In any event, the pivoting
teeth members 1701 preferably may be combined with another type of
reaction system to mitigate the danger of the spinning blade 14,
even if the teeth have retracted to a less dangerous position. For
example, a blade braking system or a blade drop mechanism may also
be employed.
[0077] In another embodiment, as shown in FIG. 18, the reaction
system 32 may activate one or more visual and/or audible alarm
systems when a dangerous condition is detected by the detection
system 30. For example, the reaction system 32 may be in
communication, via wired and/or wireless data links, to the alarm
system(s). Example alarm systems may comprise warning light systems
1801 and audible alarm systems 1802 that are in the building where
the table saw 10 is located and/or in the table saw 10 itself. The
audible alarm system 1802 may comprise a speaker. The warning light
system 1801 may comprise one or more illumination devices, such as
LEDs or lamps. Where wireless data links are used, the data links
between the reaction system 32 and the alarm systems 1801, 1802 may
be, for example, rf or infrared data links. In one embodiment, the
reaction system 32 may communicate with the alarm systems 1801,
1802 using, for example, Powerline communication (PLC), Wi-Fi,
Ethernet, or some other suitable communication standard. In
addition, the reaction system 32 may be in communication with an
automated call center 1803, which may place an automated call when
the dangerous condition is detected. For example, the automated
call center may place an automated call to an emergency response
center (i.e., 9-1-1), relevant supervisors, or employees of the
shop where the power tool 10 is located, etc. In addition,
automatic text messages, e-mails, instant messages, etc. may be
placed to supervisors, etc. when the dangerous condition is
detected, according to various embodiments.
[0078] In another embodiment, the reaction system 32 may comprise
an air bag 1901, as shown in FIGS. 19A-B. In one embodiment, the
air bag, when it is in a non-deployed condition, may be stored in
or under the throat plate 1902 that surrounds the blade 14 on the
tabletop 12. When the dangerous condition is detected, the reaction
system 32 may actuate the air bag 1901, as shown in FIG. 19B. The
air bag 1901 may be inflated using, for example, a solid propellant
that burns extremely rapidly to create a large volume of gas to
inflate the bag 1901, much like an air bag in automobiles. In other
embodiments, a canister of compressed gas may be used to inflate
the air bag 1901 in response to detection of the dangerous
condition. Activation of the air bag 1901 in response to detection
of the dangerous condition may cause objects that are in the
vicinity of the blade 14 to be knocked away from the blade 14. In
addition or alternatively, an air bag could be positioned under the
tabletop 12 at the side of the table saw 10 where an operator
normally stands to operate the table saw 10. When activated in
response to detection of the dangerous condition, such an air bag
may push the operator away from the tabletop 12 and the blade 14.
In addition or alternatively, the operator may wear an air bag,
such as on a bracelet or belt, that is activated by the reaction
system 32. In such embodiments, the wearable air bag may have a
wired or wireless connection to the reaction system 32. Deployment
of such a wearable air bag may knock the operator and attached
extremities thereof away from the tabletop 12 and/or blade 14.
[0079] In another embodiment, as shown in FIG. 20, the reaction
system 32 may comprise a magnetorheological (MR) rotary brake 2001
to brake the blade 14 in response to detection of a dangerous
condition by the detection system 30. The MR rotary brake 2001, as
shown in FIG. 20, may comprise a rotor 2003 fixed to the shaft 2006
that rotates the blade (not shown). The shaft 2006 is placed in a
bearing 2005 and can rotate in relation to a housing 2004 for the
MR rotary brake 2001. Wires 2010 are connected, and supply
electrical current, to a coil 2002. Between the rotor 2003 and the
housing 2004 there may be a spacing 2007 that is filled with MR
fluid 2008. The MR fluid 2008 in the gap or spacing is physically
near the coil 2002 such that when the coil 2002 is energized by
electrical current from the wire 2010, in response to detection of
a dangerous condition, the magnetic field from the coil 2002 causes
the MR fluid to greatly increase its apparent viscosity to the
point of becoming a viscoelastic solid, thereby braking the rotor
2003, which brakes the shaft 2006, which brakes the blade 14 (not
shown) connected to the shaft 2006. That is, for example, when a
dangerous condition is detected by the detection system 30, the
detection system 30 may output a control signal to a current supply
connected to the coil 2002. In response to the control signal from
the detection system 30, the current supply may be coupled to the
coil 2002 to energize the coil 2002. Such a MR brake reaction
system could be combined, for example, with a blade drop
mechanism.
[0080] In other embodiments, a MR clutch could be used to disengage
the blade drive mechanism. For example, in normal operating
conditions, the MR fluid in the clutch could be energized by an
electromagnetic field to create a friction lock to couple the drive
mechanism to the blade. When a dangerous condition is detected, the
electromagnetic field is removed, causing the MR fluid to convert
to its fluid state, effectively disengaging the drive mechanism
from the blade.
[0081] In various embodiments, the table saw 10 may have numerous
operating modes, including "on," "off," and "maintenance." An
operator of the table saw 10 may transition between the modes using
switches, such as one three-state switch for each of the modes, or
a plurality of switches that provide similar functionality.
According to various embodiments, the table saw 10 may undergo
automated procedures, as shown in FIG. 21A, when the table saw
transitions to various modes. If the table saw 10 transitions to
the Off mode (e.g., the operator flips the on/off switch to the off
position), the table saw may take the following actions
automatically: (i) the blade 14 retracts below the tabletop 12;
(ii) the power to the motor 14 is cut; and (iii) the reaction
system 32 is turned off. These steps may be performed in various
orders, although preferably the reaction system 32 should be turned
off last. If the table saw 10 transitions to the On mode, the table
saw may take the following actions automatically: (i) the power to
the motor 40 is turned on; (ii) the reaction system 32 is turned
on; and (iii) the blade 14 is raised. Again, these steps may be
performed in various orders, although preferably the reaction
system 32 is turned on prior to the raising of the blade. A
processor-based controller 2120, as shown in FIG. 21B, may control
and initiate these automatic reactions. An automated, motorized
blade height adjustment system 2122 may be used to raise and lower
the blade height in such table saws. If the table saw 10
transitions to the maintenance mode, such as if the operator hits
the "maintenance" button or switch 2124 in order to change the
blade, for example, the reaction system 32 is turned off. Also, the
controller 2120 may output a signal to the motor control circuit
2130 to turn the motor 40 on or off. Other convenience and safety
features may be provided or monitored in the maintenance mode. For
example, a sensor may detect whether the nut holding on the blade
is over-torqued or not. Also, in the maintenance mode, the blade
drive shaft may be automatically locked to aid in the blade removal
process.
[0082] As an alternative to automated blade height adjustment
system, side panels in the tabletop 12 may rise automatically to
surround the blade 14 when the saw is turned off. Also, the throat
plate 13 (see FIG. 1) could rise automatically to surround the
blade when the saw is turned off.
[0083] FIG. 22 shows an embodiment of a system that may be used to
stop the blade 14 when the saw 10 is turned off. As shown in FIG.
22, the system may include a clutch 2201 that couples the motor 40
to the blade shaft 2202. The illustrated embodiment shows a direct
drive for the blade 14, although a belt drive or gear drive could
be used to power the blade 14 as well. The system also includes a
brake system 2204 that, when actuated at turn off of the saw 10,
grips an interior portion of the blade 14 to stop the blade 14 from
spinning, preferably in a manner that is not destructive to the
blade 14. That way, when the saw 10 is turned off, the clutch 2201
may disengage the motor 40 from the blade 14, and the brake system
2204 may stop the blade 14 from spinning. Such an embodiment
effectively eliminates the need to detect whether the blade 14 is
still spinning after the motor 40 is cut in order to keep the
reaction system 32 enabled because the blade 14 is braked by the
brake system 2204 immediately at turn-off. Alternatively, some of
the blade spin-down detection mechanisms described herein could be
used to detect blade spin down to keep the reaction system 32
active and armed, although spin down detection techniques based on
the motor 40 will not be effective in such an embodiment because
the power to the motor is cut.
[0084] According to various embodiments, it may be desirable to
know the conductivity of the wood or other workpiece being cut by
the table saw and adjust detection systems accordingly. For
example, in a capacitive detection system the baseline current
and/or voltage drawn from the blade 14 during normal operations
(e.g., when the blade is in contact with the workpiece, but not in
contact with a foreign object) may depend on the conductivity of
the workpiece. Some other types of detection systems may also
utilize the conductivity of the workpiece to determine when the
blade has come into contact with a foreign object.
[0085] FIG. 23 illustrates one embodiment of a table saw 10 having
a conductivity sensor 2302 for measuring the conductivity of a
workpiece to be cut by the blade 14. The conductivity sensor 2302
may provide to the detection system 30 a signal indicative of the
conductivity of the workpiece being cut (or to be cut). The
detection system 30 may comprise one or more processors for
receiving and processing the signal from the sensor 2302. The
detection system 30 may process the conductivity data from the
sensor 2302 in determining whether a foreign object has come into
contact with the blade 14. For example, if the workpiece has a high
conductivity, its electrical behavior in contact with the blade may
be closer to that of a human body part. Accordingly, the detection
system 30 may adjust its sensitivity and/or disable capacitive
foreign object sensing. For example, the saw 10 may instead use
other foreign object sensing mechanisms including, for example,
those discussed herein below. In addition, the detection system may
provide an alert (e.g., a visual or audible alert) to the user that
the workpiece has a high conductivity.
[0086] The conductivity sensor 2302 may be physically embodied as
one or more sensors that may be placed at various locations on the
saw 10. For example, FIG. 24 illustrates one embodiment of the
table saw 10 with a trailing edge sensor assembly 2408. The blade
14 of the table saw 10 is shown in contact with a workpiece 2406,
which may be moved across the table saw 10 in the direction
indicated by arrow 2404. After being cut by the blade 14, the
workpiece 2406 may contact the sensor assembly 2408. The sensor
assembly 2408 may include any suitable type of sensor for measuring
the conductivity of the workpiece 2406. For example, the sensor
assembly 2408 may include one or more probes made of a conductive
material positioned to contact the workpiece 2406 after it has been
cut and fed past the blade 14. The probes may be used to cause a
current to flow through the workpiece 2406. The voltage drop across
the workpiece 2406 may then be used to determine its conductivity.
Any suitable assembly may be used to bring the sensors into
operational contact with the workpiece 2406. For example, as
illustrated in FIG. 24, the sensor assembly 2408 may comprise a
wheel 2410 positioned behind the blade 14. The wheel 2410 may be
slightly narrower than the kerf of the blade 14, allowing the wheel
2410 to fit within the cut to the workpiece 2406 made by the blade
14. The wheel 2410 may comprise spikes (or probes) 2412 that
protrude towards the workpiece 2406. As the wheel 2410 passes
through the cut in the workpiece 2406, the spikes 2412 may come
into contact with the portion of the workpiece 2406 that has just
been cut by the blade 14. The spikes 2412 may be, or may comprise,
sensor leads for measuring the conductivity of the workpiece 2406.
Sensing the conductivity of the workpiece 2406 within a fresh cut
may give a reading that is indicative of the interior of the
workpiece 2406.
[0087] FIG. 25 illustrates another embodiment of the table saw 10
where the conductivity sensor 2302 comprises a leading edge
conductivity sensor assembly 2504 positioned at the front or
leading edge of the blade 14. No workpiece is shown in FIG. 25. In
use, however, a workpiece would be moved towards the front or
leading edge of the blade 14 in the direction of arrow 2507. The
sensor assembly 2504 is illustrated upstream of the blade 14. The
sensor assembly 2504 may comprise one or more spiked wheels 2506.
The wheels 2506 may be configured to rotate about an axis parallel
to the arbor 38 of the blade 14. The spikes on the wheels 2506 may
come into contact with the workpiece before it contacts the blade
14. The spikes may be, or may comprise, leads for conductivity
sensors for sensing the conductivity of the workpiece. In some
embodiments, the spikes may be sharp, allowing them to slightly
puncture the exterior of the workpiece and provide a conductivity
reading from below the surface of the workpiece. According to
various embodiments, one or more wheels 2506 on the table saw 10
may be adjustable along their axis of rotation. This may allow an
operator of the table saw 10 to adjust the wheels 2506 based on a
width of the workpiece.
[0088] FIG. 26 illustrates one embodiment of the table saw 10 where
the sensor 2302 comprises a sensing table top surface 2604. The
surface 2604 may comprise a metallic or other conductive material.
When the surface 2604 is in contact with a workpiece (not shown), a
current may be passed through the workpiece to measure its
conductivity. According to various embodiments, an operator of the
table saw 10 may place the workpiece on the surface 2604, allowing
the saw 10 to measure the conductivity of the workpiece prior to or
during a cut. FIG. 27 illustrates one embodiment of the table saw
10 where the sensor 2302 comprises a sensing surface 2704 that is
less than all of its table top 2706. The sensing surface 2704 may
be positioned upstream of a blade 14 as shown in FIG. 27, or in
other embodiments it could be located at different locations of the
tabletop including at a trailing edge of the blade 14. The sensing
surface 2704 may operate according to principles similar to that of
the surface 2604 described above. In use, a workpiece (not shown)
may be brought into contact or proximity with the sensing surface
either as the workpiece is pushed towards the blade 14 or before a
cut is begun. This sensing surface 2704 may sense the conductivity
of the workpiece and adjust the operation of the detection system
30 and/or the reaction system 32 accordingly. The sensing surface
2704 may be electrically insulated from the rest of the tabletop
12.
[0089] According to various embodiments, the conductivity sensor
2302 may comprise all or a portion of a blade 14 of the table saw
10. In embodiments that monitor changes in the blade capacitance to
determine whether a foreign object is in contact with the blade, it
may not be desirable to use the entire blade 14 to detect the
conductivity of a workpiece. FIG. 28 illustrates one embodiment of
a segmented blade 2802 that may be used both to detect the
conductivity of a workpiece and to capacitively detect foreign
objects in contact with the blade. The blade 2802 in such
embodiments may comprise conductive sensing teeth 2804 and
capacitive sensing teeth 2808 at different regions of the blade 14.
Although the respective teeth 2804, 2808 are shown in contiguous
sections in FIG. 28, it will be appreciated that they may be
interspersed around the blade 2802 in any suitable pattern. The
conductive sensing teeth 2804 and capacitive sensing teeth 2808 may
be electrically insulated from one another and placed in a separate
circuit paths.
[0090] In use, the capacitive sensing teeth 2808 may be used by the
detection system 30 to determine whether a foreign object is in
contact with the blade 2802. For example, the detection system 30
may monitor a change in an electrical signal applied to the
capacitive sensing teeth 2808 due to a change in capacitance in the
teeth 2808 caused by contact with a foreign object. The conductive
sensing teeth 2804 may be used as a conductivity sensor, or a
portion thereof. For example, all or part of each conductive
sensing tooth 2804 may serve as a probe. An additional probe (not
shown) may be otherwise placed in contact with the workpiece. For
example, the operator may secure the additional probe to the
workpiece. In various embodiments, the additional probe may be
embedded in the saw's table top. Also, according to various
embodiments, an adjacent or other nearby conductive sensing tooth
2804 may serve as the additional probe. In use, a current may be
passed from the first conductive sensing tooth 2804, through the
workpiece and through the second conductive sensing tooth 2804. The
voltage drop in the signal may be indicative of the resistance
and/or conductivity of the workpiece. Because the blade 2802 may
measure the conductivity of material that it is in contact with, it
may be used to detect contact between the blade and a foreign
object. For example, if the blade 2802 senses a large increase in
the conductivity of the materials in contact with the blade 2802,
it may indicate that a foreign object, such as a conductive body
part, is in contact with the blade 2802. In such situations, the
detection system 30 may trigger the reaction system 32.
[0091] In the embodiment described in FIG. 2, the blade 14 acts as
one element of a capacitor. The excitation plate 34 is separated
from the blade 14 by a dielectric (e.g., air) and serves as a
second element of the capacitor. FIGS. 29 and 30, however,
illustrate one embodiment of a blade 2900 that serves as a complete
capacitor. The blade 2900 comprises a blade body 2902, a plate
2904, and a dielectric 2906. The blade body 2902 may comprise the
teeth 2908 of the blade 2900, and may also define a hollow cavity
2910 for receiving the dielectric 2906 and the plate 2904. Within
the cavity 2910, the dielectric 2906 may be positioned between the
blade body 2902 and the plate 2904 and may cause electrical
insulation of the body 2902 and plate 2904. In this way, the blade
body 2902 and plate 2904 may serve as elements of a capacitor. When
the blade 2900 is used in a detection system, such as the detection
system 30 described above, the excitation plate 34 may be omitted.
Instead, the excitation voltage may be driven onto the blade body
2902 via the capacitor plate 2904. The capacitor plate 2904 may be
connected to a voltage drive source via a connection through the
blade shaft that is insulated from the shaft and the blade body
2902. Because the blade 10 itself makes up the entire capacitor,
its capacitance may be more easily set during manufacture. In
contrast, the capacitance of the blade 14 and excitation plate 34
capacitor described above is dependent on various unpredictable
environmental conditions, and therefore, its capacitance at any
given time may be difficult to control or adjust. For example, the
dielectric 2906 may be selected to achieve a desirable blade
capacitance. Also, the surface area of the body 2902 and the plate
2904 may be manipulated. Manipulating the blade capacitance may
lead to superior detection performance as well as an improved
signal-to-noise ratio.
[0092] FIG. 31 illustrates one embodiment of a blade 3100
comprising a plurality of blade whiskers 3102 radiating generally
from the center of the blade 3100. The blade 3100 may be used with
any saw having a detection system, such as the saw described in
FIG. 2 above. The blade whiskers 3102 may extend radially from the
blade 3100, creating a contact radius beyond the teeth 3104. In one
example embodiment, the whiskers 3102 may extend up to about 1 mm
beyond the teeth 3104. In this way, a foreign object contacting the
blade 3100 may contact the whiskers 3102 before contacting the
teeth 3104. The whiskers 3102 may be short enough to avoid wrapping
around a foreign object, such as the finger of an operator, and
thus pulling it into the blade 3100. According to various
embodiments, the whiskers 3102 may be electrically conductive and
electrically coupled to all or a portion of the blade 3100. When
the foreign object contacts the whiskers 3102, the capacitance, and
thus the signal drawn from the blade 3100, may begin to change.
Because this change begins to occur before the foreign object
contacts the teeth 3104 of the blade 3100, the effective reaction
type of the saw may be improved. According to various embodiments,
the length of the whiskers 3102 may be selected based on the
reaction type of the detection and reaction systems of the saw 10.
For example, if the typical reaction time of the saw 10 without the
whiskers 3102 results in a cut 0.6 mm in depth, then the whiskers
may be 0.6 mm or longer to prevent any cut in the event of a
foreign object contacting the blade.
[0093] When the blade 3100 is used to cut a workpiece, the whiskers
3102 may be designed to bend or retract out of the path of the
teeth 3104. In this way, the teeth 3104 may cut the workpiece
without interference from the whiskers 3102. The whiskers 3102 may
be made, for example, from a metal wire (e.g., steel, aluminum,
etc.). Also, for example, the whiskers 3102 may be made from a
conductive carbon composite or other electrically conductive
material. According to various embodiments, the whiskers 3102 may
comprise a non-capacitive sensor. For example, each whisker 3102
may comprise one or more probes for measuring the conductivity of
materials in contact with the blade 3100. Also, according to
various embodiments, the blade 3100 may include a mechanism for
replenishing the length of the whiskers 3102. In use, individual
whiskers 3102 may be broken or torn as they contact the workpiece.
Accordingly, one or more of the whiskers 3102 may comprise a reel
(not shown) of additional whisker material. The reel may be
actuated by centripetal force to extend additional whisker material
when its corresponding whisker 3102 is lost or shortened.
[0094] FIG. 32 illustrates a diagram of one embodiment of a
segmented blade 3200 that may be used with the saw embodiment shown
in FIG. 2. The blade 3200 is shown in the process of cutting a
workpiece 3210. Arrow 3212 indicates the direction of movement of
the workpiece 3210 relative to the blade 3200. Arrow 3214 indicates
the rotation direction of the blade 3200. In FIG. 32, the blade
3200 is shown with four electrically insulated segments 3202, 3204,
3206, 3208. Each of the segments 3202, 3204, 3206, 3208 may form a
capacitor (e.g., in conjunction with an excitation plate 34 and/or
utilizing a laminate design such as described above with respect to
FIGS. 29 and 30). Because the segments are electrically insulated,
each capacitor (e.g., each blade segment 3202, 3204, 3206, 3208)
may be capable of being separately monitored by the detection
system 30.
[0095] As the blade spins, each of the segments 3202, 3204, 3206,
3208 is alternately in contact with a leading portion of the
workpiece 3210 (in FIG. 32, segment 3204), a trailing portion of
the workpiece 3210 (in FIG. 32, segment 3202) and no portion of the
workpiece (in FIG. 32, segments 3206 and 3208). The capacitance of
each segment (e.g., as measured by an excitation current and/or
voltage) may reflect the properties of the material in contact with
the respective segment. This may enable a variety of useful
features. For example, the segmented blade 3200 may enable the
detection system 30 to re-calibrate on-the-fly. Portions of the
blade cycle where a given segment 3202, 3204, 3206, 3208 is not in
contact with the workpiece 3210 may be used as baseline
measurements for recalibration of the segment. Also, for example,
the detection system 30 may be able to track whether the saw is at
the beginning, middle, or end of a cut. This may allow the
detection system 30 to calibrate its sensitivity accordingly. Also,
use of the blade 3200 may allow the detection system to compare
differences in properties between the leading portion and the
trailing portion of the workpiece 3210.
[0096] FIG. 33 illustrates one embodiment of the table saw 10
having an overhead sensor assembly 3304. The overhead sensor
assembly 3304 may comprise one or more sensors, which may be active
or passive. For example, an active sensor may comprise an emitter
as well as a receiver. Sensors that are passive may not comprise an
emitter. According to various embodiments, the transmitter and
receiver may be separate, with one or both of them located on the
saw 10 at a location different from the overhead sensor assembly
3304. When the saw 10 is in use, its blade 3302 and a workpiece
3308 may be in the field of view of at least one of the sensors of
the sensor assembly 3304.
[0097] According to various embodiments, the sensor assembly 3304
may comprise a radar sensor. A radar sensor may comprise an emitter
that generates electromagnetic waves (e.g., radio waves,
microwaves, etc.) and directs the electromagnetic waves toward the
blade 3302. The waves may reflect off of the blade 3302, the
workpiece 3308 and any foreign objects that may be present. A
receiver may sense the reflected waves and provide an output signal
to a processor-based detection system 30. The detection system 30
may glean various information from the input signal about the
reflected waves. For example, the reflected waves may provide an
indication of the direction and speed with which the workpiece 3308
is moving relative to the blade. If the workpiece 3308 reverses its
motion, that may indicate a kickback event, which may cause the
detection system 30 to activate the reaction system 32. If a
foreign object is detected within a predetermined distance from the
blade 3302, then a reaction system 32 may be activated. For
example, if a foreign object is detected between the blade 3302 and
the sensor assembly 3304, the reaction system 32 may be activated
by the detection system 30. More details regarding a radar sensing
system may be found in U.S. Pat. No. 7,421,932, which is
incorporated herein by reference in its entirety.
[0098] According to various embodiments, the sensor assembly 3304
may comprise an infrared (IR) receiver. The IR receiver may sense
the IR signature of the blade 3302, the workpiece 3308, and any
foreign objects present in its field-of-view. The IR signature of
the blade 3302 and workpiece 3308 may be distinguishable from the
IR signature of a body part or other foreign object that may
inadvertently come near the blade. The detection system 30 may
monitor the output of the IR receiver. If the IR receiver indicates
that a foreign object is within a predetermined distance from the
blade 3302, a reaction system may be activated. For example, if a
foreign object is detected between the blade 3302 and the sensor
assembly 3304, the reaction system 32 may be activated.
[0099] In other embodiments, the sensor assembly 3304 may include
emitters and receivers for measuring backscatter off of the blade
3302, the workpiece 3308 and any foreign objects that may be
present near-by. Any suitable frequency of electromagnetic
radiation may be used to measure backscatter. According to various
embodiments, however, a frequency or frequencies may be selected
based on the difference in backscatter profiles between typical
workpieces 3308 and typical foreign objects, such as human body
parts. In use, backscatter techniques may be able to differentiate
between workpieces 3308 and foreign objects. For example, a foreign
object, such as the skin on a body part, may scatter back a first
quantity of radiation, while a workpiece 3308 of the same surface
area may scatter back a second quantity of radiation. This may
allow the detection system 30 to differentiate between the two. If
a foreign object is detected within a predetermined distance of the
blade 3302 (e.g., if the foreign object is over the blade 3302 or
between the blade 3302 and the sensor assembly 3304), then the
reaction system 32 may be activated by the detection system 30,
which is in communication with the sensor assembly 3304.
[0100] In some embodiments, the sensor assembly 3304 may include an
optical camera (e.g., a CCD camera). The optical camera may have a
resolution fine enough to allow it to determine a distance between
a foreign object and the blade 3302. If the distance is less than a
predetermined amount, the reaction system 32 may be triggered by
the detection system 30. Various image processing algorithms may be
used by the detection system 30 to distinguish the blade, a typical
workpiece, and a foreign object.
[0101] In various embodiments, the sensor assembly 3304 may include
an emitter and receiver for measuring differential reflection.
Differential reflection may be a measure of difference in
reflection between surfaces. For example, a foreign object may
reflect more or less electromagnetic radiation as compared to a
typical workpiece 3308 and/or the blade 3302. The emitter for
differential reflection may be any suitable emitter of
electromagnetic waves including, for example, a laser. The
detection system 30 is in communication with the sensor assembly
3304 and determines whether the reaction system 32 should be
triggered based on the differential reflection detected by the
sensor assembly 3304.
[0102] FIGS. 34-42 illustrate embodiments utilizing downstream
safety members (e.g., safety members that are positioned near the
trailing or rear edge of the blade 14). A downstream safety member
is a component of a table saw that is positioned parallel to and
downstream from the blade 14. Specific examples of downstream
safety members include riving knives and splitters. Different
downstream safety members may serve different purposes, for
example, as described herein. Generally, a downstream safety member
may serve to steady a workpiece and/or to mitigate the risk of a
kickback event by preventing a cut from closing around the blade
14.
[0103] FIG. 34 illustrates one embodiment of a downstream safety
member 3400 having directional snells 3402. The snells 3402 may
extend outwardly at an angle from the downstream safety member
3400. The snells 3402 may be configured so that a workpiece may
smoothly pass over the snells 3402 in the downstream direction, but
is impeded if the workpiece is kicked-back in the upstream
direction. FIG. 35 illustrates a top view of the downstream safety
member 3400. A workpiece 3406 is illustrated being pushed
downstream, as indicated by arrow 3408. When the workpiece 3406
contacts the snells 3402 moving downstream, it may slide along the
snells 3402 without significant resistance because the snells are
pointed generally away from the blade and in the direction that the
workpiece is being fed. In the event of a kickback, however, the
workpiece 3406 may be thrust upstream. In this case, the snells
3402 may dig into the workpiece 3406, either preventing the
workpiece from moving upstream or impeding its upstream motion.
[0104] The snells 3402 may take any suitable form and may be made
of any suitable material (e.g., steel, another suitable metal,
engineered plastic, etc.). For example, in various embodiments, the
snells 3402 may be flexible flaps formed into or secured to the
downstream safety member 3400. When the workpiece 3406 passes in
the downstream direction, the flaps may flex, allowing the
workpiece 3406 to pass. When the workpiece is thrust upstream, the
flaps may not flex and may instead dig into the workpiece 3406,
impeding its upstream movement. According to various embodiments,
the snells 3402 may be actuatable by the reaction system 32. For
example, each snell 3402 may be extendible from a rest position,
where the workpiece 3406 is allowed to pass without significant
resistance, to an extended position, where the motion of the
workpiece 3406 is impeded. When a kickback condition is detected,
the reaction system 32 may extend the snells 3402 to prevent the
workpiece 3406 from being thrust back towards the operator and/or
the blade 14. The snells 3402 may be actuated according to any
suitable mechanism. For example, a mass of nitinol or another shape
memory allow may be actuated to lift each snell 3402 to the
extended position. In other embodiments, each snell 3402 may be
spring loaded from the rest position to the extended position. In
still other embodiments, the snells 3402 may be extended using
solenoids, pneumatics, hydraulics, magnets, pyrotechnics, or any
other suitable method.
[0105] FIGS. 36-38 illustrate one embodiment of the table saw 10
including a downstream safety member 3602 comprising one or more
wing members 3604. The wing members 3604 may extend roughly
parallel to the table surface 3614 and roughly perpendicular to a
body 3608 of the downstream safety member 3602. A workpiece 3610
being acted upon by a blade 14 may pass under the wing members 3604
when extended. In this way, the wing members 3604 may serve to
prevent the workpiece 3610 from lifting off of the table surface.
This may prevent and/or mitigate a kickback event. During a typical
kickback event, the motion of the workpiece 3610 relative to the
blade 14 is stopped or slowed (e.g., when the blade 14 contacts a
knot or hard portion of the workpiece 3610, by a pinching off of
the cut behind the blade 14, etc.). When the workpiece 3610 is
stopped or slowed, the motion of the blade 14 pushes the workpiece
3610 up, where it contacts the top of the blade 14 and is thrust
back towards the operator. Wing members 3604 may prevent or
mitigate a kickback event by preventing the workpiece 3610 from
riding upwards relative to the blade 14.
[0106] According to various embodiments, the wing members 3604 may
be movable from a resting position to a deployed position when
triggered, such as by turn-on of the motor/blade. In the resting
position, the wing members 3604 may be parallel to a body 3608 of
the downstream safety member 3602. In some embodiments, the
combined width of the body 3608 and the wing member or members 3604
may be less than the kerf of the blade 14, allowing the downstream
safety member 3602 to pass through the cut in the workpiece formed
by the blade 14 if the wing members 3604 are in the resting
position. Normally, the wing members 3604 are deployed when the saw
is being operated. FIGS. 36 and 37 illustrate one embodiment where
the wing members 3604 fold down against the body 3608 of the
downstream safety member 3602 when in the resting position. FIG. 38
illustrates another embodiment where the wing members 3604 fold
upwards when in the resting position. In such an embodiment, the
wing members 3604 may transition to the deployed position, parallel
to the tabletop when triggered by a kickback detection system.
According to various embodiments the downstream safety member 3602
may comprise a height adjustment mechanism 3616 for raising and
lowering the downstream safety member 3602. This may allow an
operator to adjust the height of the wing members 3604 based on the
height of the workpiece 3610.
[0107] According to various embodiments, the downstream safety
member 3602 may be actuated from the resting position to the
deployed position by the reaction system 32 upon detection of a
kickback event by the detection system 30. The kickback event may
be sensed according to any suitable method including, for example,
those described herein below. Upon detection of the kickback event,
the reaction system 32 may cause the wing members 3604 to be
transitioned, such as from the upright resting position shown in
FIG. 38, to the deployed position using any suitable mechanism or
method. For example, the wing elements 3604 may be actuated by a
spring element, solenoids, pneumatics, hydraulics, pyrotechnics,
etc.
[0108] According to various embodiments, a downstream safety member
can be used as a component of the reaction system 30. For example,
the downstream safety member may be used to cover the exposed
portion of the blade 14 or otherwise prevent or stop contact
between the blade 14 and a foreign object. FIGS. 39 and 40
illustrate one embodiment of the table saw having a downstream
safety member 3904. The downstream safety member 3904 has a resting
position, shown in FIG. 39, and a deployed position, shown in FIG.
40. In the resting position, a portion of the downstream safety
member 3904 may extend above the table top 3906 and serve as a
standard downstream safety member, such as a splitter.
[0109] The detection system 30 may detect a dangerous condition
according to techniques described herein, including contact between
the blade 14 and a foreign object or proximity of the foreign
object to the exposed portion of the blade 14. When the condition
is detected, the detection system 30 may trigger the reaction
system 32. The reaction system 32 may, in turn, trigger an
actuating mechanism 3910, which may rapidly transition the
downstream safety member 3904 from the resting position, shown in
FIG. 39, to the deployed position, shown in FIG. 40. In this way,
the safety member 3904 may prevent the foreign object from
contacting the blade 14, or if the foreign object has already
contacted the blade 14, the safety member 3904 may push or knock
the foreign object away from the blade 14.
[0110] The downstream safety member 3904 may be transitioned from
the resting position to the deployed position according to any
suitable actuation mechanism or method. In some embodiments, the
saw may include tracks (not shown) for directing the downstream
safety member 3904 from the resting position to the deployed
position. The actuating mechanism 3910 may comprise any suitable
mechanism for moving the safety member 3904 along the tracks
including, for example, spring loading, pneumatics, hydraulics,
explosive charges, etc. Also, in some embodiments, the downstream
safety member 3904 may be directed from the resting position to the
deployed position by a series of pivotable bar members (not shown).
In these embodiments, the actuating mechanism 3910 may be
configured to pivot the downstream safety member 3904 about the
bars again using any suitable mechanism (e.g., spring loading,
pneumatics, hydraulics, pyrotechnics, etc.).
[0111] FIG. 41 illustrates another embodiment of the saw 10 having
a downstream safety member 3952 that may be used as part of a
reaction system 32. Upon detection of a triggering condition
involving a foreign object and the blade 14 by the detection system
30, the downstream safety member 3952 may be split into two or more
sections. The actuating mechanism 3910 may propel a first section
along track 3958, and a second section along track 3956. As shown
in FIG. 41, the tracks may run generally parallel to the blade 14
on opposite sides of the blade 14. In this way, the downstream
safety member 3952 may cover the blade 14 to prevent and/or
mitigate contact between the blade 14 and a foreign object. In some
embodiments, the downstream safety member 3952 may not split in
two, but instead the entire downstream safety member 3952 may be
propelled down a track on one side of the blade 14. The actuating
mechanism 3910 may utilize any suitable propelling mechanism
including, for example, spring loading, pyrotechnics, solenoids,
pneumatics, hydraulics, etc.
[0112] FIG. 42 illustrates one embodiment of a saw 10 having a
downstream safety member 4202 with a material sensor 4204 thereon.
The material sensor 4204 may be any suitable type of sensor for
sensing a property of a workpiece (not shown). For example, the
sensor 4204 may be a conductivity sensor for sensing the
conductivity of the workpiece which, as described above, may be an
indicator of its moisture content. The sensor 4204 may be
positioned at any suitable location on the downstream safety member
4202, and may take any suitable physical form. For example, the
sensor 4204 may include probes that extend perpendicularly from the
downstream safety member 4202 to contact material within a cut on a
workpiece created by the blade 14. The sensor 4204 may be in
communication with the detection system 30 in a manner similar to
that described above with respect to FIG. 23.
[0113] In some table saws, the blade height is manually adjustable,
such as by using a crank. An operator of the table saw may adjust
the blade height to match the height of the workpiece being cut.
Many operators, however, neglect to adjust the blade height for
each cut. Instead, operators sometimes set the blade to a height
that is high enough to allow them to cut a number of workpieces. As
a result, the blade is sometimes too high for certain cuts,
creating a potentially unsafe condition. FIG. 43 illustrates a
block diagram of a table saw 4300 with an automatically adjustable
blade 14. The blade 14 may be adjustable with a mechanical
adjustment mechanism 4320. The mechanism 4320 may be any suitable
type of mechanism including, for example, known manual blade height
adjustment mechanisms. The mechanism 4320 may be powered by an
actuating mechanism 4321, such as a stepper motor or other suitable
device. A height sensor 4324 may be used to sense the height of the
workpiece currently being cut by the blade 14. The sensor 4324 may
be any suitable type of sensor including, for example, an optical
sensor. The sensor 4324 may be positioned so that it can measure
the height of workpieces at a location in front of the leading edge
of the blade 14. The height sensor 4324 may provide an output
signal indication of the height of the workpiece to a
processor-based height adjustment circuit 4322. From the output
signal of the sensor 4324, the circuit 4322 may determine the
height of the workpiece and whether the blade height needs to be
adjusted or not given the height of the workpiece. The circuit 4322
may then signal the actuating mechanism 4321 to adjust the
mechanism 4320 to raise or lower the blade 14 based on the height
of the workpiece. For example, the blade 14 may be raised such that
its top is a predetermined distance above the top of the workpiece.
In some embodiments, the blade height adjustment mechanism 4320 may
also raise or lower the motor 40 as well.
[0114] FIGS. 44-46 illustrate one embodiment of the table saw 10
according to other embodiments. The blade 14 and table top surface
4304 are shown in FIGS. 44-46. The height sensor 4324 may comprise
a fan emitter 4308 and a detector array 4306 (shown in FIG. 44).
The fan emitter 4308 may emit a laser or other electromagnetic beam
across the table top 4304 and workpiece 4307 towards the detector
array 4306. The beam may be `fanned` or shaped to disperse
vertically. When the workpiece 4307 breaks the beam, a portion of
the beam may be prevented from reaching the sensor array 4306.
Based on the portion of the beam that reaches the detector array
4306, the height adjustment circuit 4322 may determine the height
of the workpiece and send appropriate signals/instructions to the
actuating mechanism 4321. FIGS. 45 and 46 illustrate the operation
of the saw 10 with two workpieces, 4307' and 4307''. As shown in
FIG. 45, the workpiece 4307' has a first height. In FIG. 45, the
blade 14 is shown relative to the table top 4304 at a height
roughly corresponding to that of the workpiece 4307'. As shown in
FIG. 46, the workpiece 4307'' has a second height that is greater
than that of the workpiece 4307'. Accordingly, FIG. 46 shows the
blade 14 at a greater height relative to the tabletop than is shown
in FIG. 45. The height of the blade 14 relative to the tabletop in
FIG. 46 may roughly correspond to the height of the workpiece
4307''.
[0115] Various embodiments of the present invention are also
directed to retrofitting existing table saws with detection and
reaction systems. FIG. 47 illustrates one embodiment of the saw 10
with a retrofit package 4702 installed. The retrofit package 4702
may comprise a detection system 30, a reaction system 32 and a
power system 4704. The detection system 30 may be any suitable type
of detection system including, for example, those described herein.
For example, in one embodiment, the retrofit package 4702 may
comprise an excitation plate 34 that is installed next to the blade
14, as shown. The detection system 30 may drive a signal onto the
excitation plate and monitor changes in the resulting blade current
or signal due to changes in the capacitance between the blade 14
and the plate 34 to detect contact between the blade 14 and a
foreign object. In some embodiments, the blade 14 may be replaced
with a blade that does not require an excitation plate such as, for
example, blade 2900 described herein. Other non-capacitive
detection systems 30 may be used including, for example, the radar,
backscatter, and/or video-based embodiments described herein.
[0116] The reaction system 32 may comprise any suitable type of
reaction mechanism. According to various embodiments, however,
reaction systems 32 requiring a minimum of modification to the saw
10 may be selected. Examples of such systems include those
utilizing actuatable throat plates, actuatable table tops, airbags,
changes to the blade shape, blade brakes, etc. The reaction system
32 and detection systems 30 of the retrofit package 4702 may be
powered by a power system 4704. The power system 4704 may comprise
a connection to a power source of the saw 10. According to various
embodiments, the power system 4704 may comprise a blade-driven
generator, such as those described with reference to FIGS. 5-6. In
this way, the reaction and detection systems 32, 30 may continue to
operate until the blade 14 completely spins down.
[0117] Operators of table saws sometimes use push sticks to guide
or feed the workpieces towards the blade. Use of a push stick may
allow the operator to keep their hands farther away from the blade
14 when feeding a workpiece toward the blade 14. FIGS. 48 and 49
illustrate one embodiment of a push stick 4802 according to various
embodiments of the present invention. The push stick 4802 may
comprise a handle and an end effector, separated by a shaft. The
operator may grasp the push stick 4802 by the handle and use the
end effector to push the workpiece, as shown in FIG. 49. FIG. 50
illustrates a block diagram of the push stick 4802 in communication
with an example saw 4820. According to various embodiments, the
push stick 4802 may comprise one or more accelerometers 4810. The
accelerometer(s) 4810 may be in communication with a transmitter
4824, which may transmit signals indicative of the acceleration of
the push stick 4802 to the saw 4820 (e.g., via receiver/detector
4822). The detection system 30 of the saw 4820 may monitor the
acceleration of the push stick 4802, as this may be indicative of
the acceleration of the workpiece 4804 and/or the operator's hand.
If the acceleration of the push stick 4802 falls outside of
acceptable bounds, the detection system 30 may trigger the reaction
system 32. For example, the acceleration of the push stick may be
outside of acceptable bounds if the stick accelerates too quickly
in the direction of the blade 14. In addition, a sudden
acceleration away from the blade 14 may indicate a kick back
condition. The push stick 4802 may also comprise devices and/or
sensors allowing the detection system 30 to estimate its location.
For example, the push stick 4802 may comprise a Radio Frequency
(RF) transmitter 4812 that may periodically transmit RF pulses. The
saw 4820 (e.g., via the detector/receiver 4822) may receive the RF
pulses. Based on the strength of the RF pulses, the detection
system 30 may estimate the distance between the push stick 4802 and
the blade 14. In some embodiments, the push stick 4802 may comprise
an infrared (IR) pulse generator. The IR pulses may be received by
the saw 4820. For example, the saw 4820 may comprise a plurality of
IR receivers positioned at different locations on the saw 4820.
These may allow the saw to use triangulation to estimate the
position of the push stick 4802 relative to the blade, for
example.
[0118] FIG. 51 is a top view of a table saw 10 with a suction feed
assembly 5102 for feeding workpieces towards the blade 14 according
to various embodiments of the present invention. The suction feed
assembly may comprise a plurality of suction elements 5104 located
on the table at the leading edge of the blade 14. Each suction
element 5104 may comprise one or more suction generated devices.
When actuated, the suction generating devices may create a vacuum
between the section element 5104 and any object in contact with the
section element 5104 (e.g., the workpiece). Each suction element
5104 may reciprocate towards and away from the blade, for example,
as shown by arrows 5106. Adjacent section elements 5104 may
reciprocate 180.degree. out of phase. Accordingly, the suction
elements 5104 may be selectively actuated and de-actuated to move a
workpiece towards or away from the blade 14. In this way, it may
not be necessary for an operator to place their hand near the blade
14. Instead, the suction elements 5104 may feed the workpiece
toward the blade 14. The state of the feedback from the suction
elements 5104 can be used to detect hazardous conditions.
[0119] FIG. 52 illustrates a top-down view of one embodiment of a
kick back detection mechanism 5200. As shown in the illustrated
embodiment, the blade 14 and arbor 38 may be mounted in a kick back
frame 5202 that is pivotable relative to the remainder of the table
saw about the joint 5204. Arrow 5208 indicates the direction of
movement of a workpiece. The kick back mechanism 5200 may serve a
variety of purposes. For example, many kickback conditions occur
when a cut is pinched or otherwise knocked out of alignment,
causing the cut portion of a workpiece to contact a rear portion of
the blade 14. Because the kick back mechanism 5200 allows the blade
14 some freedom of motion around the pivot 5204, it may prevent
many kickback conditions. In some embodiments, the kick back
mechanism 5200 may comprise a sensor (not shown) positioned to
sense movement of the kick back frame 5202 about the joint 5204.
The sensor may be in communication with the detection system 30.
Movement of the kick back frame 5202 about the joint 5204 may
indicate a kickback condition. Accordingly, when the detection
system 30 receives a signal from the sensor indicating that greater
than a predetermined amount of motion has occurred about the joint
5204, it may trigger a reaction system 32. FIG. 53 illustrates an
alternative embodiment of the kick back mechanism 5200'. With the
mechanism 5200', the blade 14 and arbor 38 are mounted to a
four-bar linkage frame 5210, which is shown rigidly mounted to a
portion 5214 of the saw. The four-bar linkage frame 5210 may allow
the blade 14 to move from side-to-side, as illustrated by arrow
5216. This may serve to prevent kickback conditions, as described
above. Also, for example, a sensor may be positioned to sense
movement of the linkage frame 5210, which, if greater than a
predetermined threshold, may indicate a kickback condition. The
sensor (not shown) may be positioned at any location allowing it to
sense movement of the frame 5210, but may be positioned at one of
the joints 5212 of the frame 5210. In another embodiment, strain
measurements, from a strain sensor, on the kickback frame 5202 can
be used to detect a kickback condition, without having to use a
pivot.
[0120] FIG. 54 illustrates one embodiment of the saw 10 having
torque-based kick back detection mechanism. When a kickback event
occurs, the workpiece may come into contact with a trailing or rear
portion of the blade 14. This may increase the torque that the
motor 40 must produce to maintain a constant rotation of the blade
14. Accordingly, in such embodiments, the saw 10 comprises one or
more torque sensors 5402 mounted on a shaft between the motor 40
and the blade 14. For example, the torque sensor 5402 may be
mounted on the arbor shaft to which the blade 14 is secured, or
some other drive shaft between the motor 40 and the blade 14. The
detection system 30 may be in communication with the torque
sensor(s) 5402. If the torque sensor(s) 5402 indicates that the
torque on the shaft has increased by more than a predetermined
amount, it may indicate that a kickback condition has occurred.
Accordingly, the detection system 30 may trigger the mitigating
reaction of the reaction system 32. Any suitable torque sensor 5402
may be used, such as strain gauge torque sensors or surface
acoustic wave (SAW) torque sensors.
[0121] According to various embodiments, embodiments of the present
invention are directed to a table saw that comprises: a cutting
surface; a motor-driven, rotatable blade for cutting a workpiece on
the cutting surface, wherein a portion of the blade is extendable
above the cutting surface; a kickback detection system for
detecting kickback of the workpiece during cutting of the
workpiece; and reaction means in communication with the kickback
detection system for taking a mitigating reaction in response to
detection of kickback of the workpiece during cutting of the
workpiece. According to various implementations, the kickback
detection system comprises: an acoustic sensor; and a processor in
communication with the acoustic sensor, wherein the processor is
programmed to recognize a condition indicative of kickback of the
workpiece during cutting of the workpiece based on input from the
acoustic sensor. The processor may be further programmed to
determine whether the blade is rotating based on input from the
acoustic sensor, and, when it is determined that the blade is
rotating, maintain the reaction means in an armed state. In
addition, the kickback detection system may comprise: a torque
sensor mounted on the rotatable blade shaft; and a processor in
communication with the torque sensor, wherein the processor is
programmed to recognize a condition indicative of kickback of the
workpiece during cutting of the workpiece based on input from the
torque sensor. In other embodiments, the table saw further
comprises: a motor positioned below the cutting surface; a
rotatable blade shaft positioned below the cutting surface on which
the blade is mounted; a clutch coupled to the blade shaft, such
that when the clutch is engaged and the motor is running, the blade
shaft is rotated; a brake system for braking the blade; and a motor
shut-down circuit connected to the clutch and the brake system,
wherein the motor shut-down circuit disengages the clutch and
actuates the brake system to brake the blade when the motor is
turned off.
[0122] According to other embodiments, the table saw comprises: a
cutting surface; a motor-driven, rotatable blade for cutting a
workpiece on the cutting surface, wherein a portion of the blade is
extendable above the cutting surface; detection means for detecting
a dangerous condition relative to the blade; reaction means in
communication with the detection means for taking a reaction in
response to detection of the dangerous condition; and a blade-spin
detection system for detecting whether the blade is rotating based
on energy from the blade, wherein the blade-spin detection system
is in communication with the reaction means and provides an output
to arm the reaction means when the blade-spin detection system
detects that the blade is spinning. In various implementations, the
blade-spin detection system comprises a static electricity charge
sensor in proximity to the blade for sensing the static electricity
build-up on the blade. In other implementations, the blade-spin
detection system comprises: a transmitter proximate to the blade
for transmitting radio signals; a passive electronic circuit on the
blade that transmits responsive radio signals when passively
energized by the radio signals transmitted by the transmitter; and
a receiver, proximate to the blade, for detecting the responsive
radio signals from the passive electronic circuit. In yet other
implementations, the blade-spin detection system comprises: an
acoustic sensor; and a processor in communication with the acoustic
sensor, wherein the processor is programmed to determine whether
the blade is rotating based on input from the acoustic sensor. In
yet other implementations, the blade-spin detection system
comprises: an airflow sensor that senses airflow generated by the
plurality of off-center holes of the blade when the blade spins;
and a processor in communication with the airflow sensor, wherein
the processor is programmed to determine whether the blade is
rotating based on input from the acoustic sensor. In yet other
implementations, the blade-spin detection system comprises: one or
more magnets mounted on the blade; and an inductor proximate to the
blade, wherein the magnets, when spinning with the blade, induce a
voltage across the inductor, wherein the reaction means is
connected to the inductor. In addition, the table saw may further
comprise a power converter having an input connected to the
inductor for converting the voltage across the inductor to an
output voltage used to power the reaction means and/or the
detection means.
[0123] According to various implementations, the blade comprises a
plurality of off-center holes that extend through the blade. In
addition, the table saw may further comprise an electrical
generator connected by one or more gears to the rotatable blade
shaft, wherein the electrical generator is further connected to the
reaction means and generates electricity when the shaft rotates to
power the reaction means and/or the detection means. In addition,
the reaction means may comprise: a clutch coupled to the blade
shaft, such that when the clutch is engaged and the motor is
running, the blade shaft is rotated, and wherein the clutch is
disengaged when the detection means detects the dangerous
condition; and a brake system for braking the blade when the
detection means detects the dangerous condition. Additionally, the
blade may comprise an outer peripheral portion that comprises a
first material, an inner portion that comprises a second material
that is different from the first material, wherein the first
material is denser than the second material. In addition, the table
saw may further comprise: a flywheel that rotates in a direction
that is the same as a direction of rotation for the blade, wherein
the flywheel is coupled to the rotatable shaft by a clutch, and
wherein the reaction means disengages the clutch when the dangerous
condition is detected. In addition, the table saw may further
comprise kickback mitigation means downstream from the blade for
mitigating kickback of the workpiece and/or a suction feed assembly
that feeds the workpiece to the blade for cutting.
[0124] According to other embodiments, the table saw comprises: a
cutting surface; a motor-driven, rotatable blade that is partially
extendable above the cutting surface for cutting a workpiece
positioned on the cutting surface; and a sensor connected to the
cutting surface for sensing a characteristic of the workpiece
during cutting of the workpiece. In various implementations, the
table saw further comprises a blade height adjustment mechanism for
adjusting a height of the blade relative to the cutting surface,
the sensor comprises a height sensor for sensing a height of the
workpiece relative to the cutting surface, and the table saw
further comprises a height adjustment circuit that receives an
input signal from the height sensor indicative of the height of the
workpiece relative to the cutting surface and outputs a signal to
the blade height adjustment mechanism to adjust the height of the
blade based on the height of the workpiece sensed by the height
sensor. In other implementations, the sensor comprises a workpiece
conductivity sensor on the cutting surface that detects electrical
conductivity of the workpiece. In such an implementation, the table
saw may further comprise: contact detection means for detecting
contact with the blade by an object other than the workpiece,
wherein the contact detection means receives an input from the
workpiece conductivity sensor and detects contact with the blade by
the object based on the input from the workpiece conductivity
sensor; and reaction means in communication with the contact
detection system for taking a mitigating reaction in response to
detection of contact with the blade by the object. The workpiece
conductivity sensor may comprise a wheel positioned adjacent to a
trailing and/or leading edge of the blade, wherein the wheel
comprises one or more probes that extend into the workpiece to
sense the electrical conductivity of a portion of the workpiece
after cutting of the portion by the blade.
[0125] According to other embodiments, the table saw comprises: a
cutting surface; a motor-driven, rotatable blade for cutting a
workpiece on the cutting surface, wherein a portion of the blade is
extendable above the cutting surface; a contact detection system
for detecting contact with the blade by an object other than the
workpiece; and reaction means in communication with the contact
detection system for taking a mitigating reaction in response to
detection of contact with the blade by the object. The blade
comprises: a first electrically conductive blade portion; a second
electrically conductive blade portion; and a dielectric between the
first and second electrically conductive blade portions. The
contact detection system is connected to the first electrically
conductive blade portion and drives the first electrically
conductive blade portion with a drive signal, and wherein the
contact detection system comprises a processor for detecting
contact with the blade by the object based on an electrical signal
from the first electrically conductive blade portion. For example,
the contact detection system may detect contact with the blade by a
foreign object based on the current drawn by the first electrically
conductive blade portion.
[0126] According to other embodiments, the table saw comprises: a
cutting surface; a motor-driven rotatable shaft positioned below
the cutting surface; a blade for cutting a workpiece on the cutting
surface, wherein the blade is mounted on the shaft, and wherein a
portion of the blade is extendable above the cutting surface; a
detection system for detecting a dangerous condition relative to
the blade; a reaction system in communication with the detection
system for taking a reaction in response to detection of the
dangerous condition, wherein the reaction system comprises a
magnetorheological rotary brake connected to the shaft that brakes
the shaft to thereby brake the blade in response to detection of
the dangerous condition by the detection system. In various
implementations, the magnetorheological rotary brake comprises: a
rotor fixed to the shaft; a housing, wherein the housing and the
rotor define a spacing; magnetorheological fluid in the spacing;
and a magnetic field-producing coil that is energized in response
to detection of the dangerous condition by the detection system to
produce a magnetic field that causes the magnetorheological fluid
to increase its viscosity to brake the rotor, thereby braking the
shaft, thereby braking the blade.
[0127] While various embodiments of the present invention have been
shown and described, it should be understood that other
modifications, substitutions and alternatives are apparent to one
of ordinary skill in the art. Such modifications, substitutions,
and alternatives can be made without departing from the spirit and
scope of the invention, which should be determined from the
appended claims.
* * * * *