U.S. patent application number 10/027767 was filed with the patent office on 2002-12-12 for control module for flywheel operated hand tool.
Invention is credited to Adams, Shane, Garvis, Conrad, Leimbach, Richard.
Application Number | 20020185514 10/027767 |
Document ID | / |
Family ID | 22978767 |
Filed Date | 2002-12-12 |
United States Patent
Application |
20020185514 |
Kind Code |
A1 |
Adams, Shane ; et
al. |
December 12, 2002 |
Control module for flywheel operated hand tool
Abstract
A control module advantageously reduces cost and enhances
reliability, design flexibility, ease of assembly, and performance
of a flywheel operated hand tool. The control module includes a
thin film printed circuit with non-contact speed sensing of a
flywheel to more accurately set the target speed and control
transfer kinetic energy thereof to a fastener, achieving a desired
depth regardless of variations in component performance and battery
voltage. The printed circuit also includes long service life thin
film switches for responding to trigger and safety inputs.
Furthermore, the control module responds to a user speed selection
and to preset speed selection ranges to reconfigure the controls as
appropriate to constraints of a fastener drive assembly and to user
preferences.
Inventors: |
Adams, Shane; (Lebanon,
OH) ; Garvis, Conrad; (Mason, OH) ; Leimbach,
Richard; (Cincinnati, OH) |
Correspondence
Address: |
FROST BROWN TODD LLC
2200 PNC Center
201 E. Fifth Street
Cincinnati
OH
45202-4182
US
|
Family ID: |
22978767 |
Appl. No.: |
10/027767 |
Filed: |
December 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60258022 |
Dec 22, 2000 |
|
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|
Current U.S.
Class: |
227/2 ;
227/131 |
Current CPC
Class: |
B25C 1/008 20130101;
H02P 3/08 20130101; B25C 1/06 20130101; H02P 27/047 20130101 |
Class at
Publication: |
227/2 ;
227/131 |
International
Class: |
B25C 005/06 |
Claims
What is claimed is:
1. A control module for an electrically power hand tool having a
rotary member; comprising: a speed adjustment circuit; a speed
sensor operable to sense a rotary speed of the rotary member; and a
controller responsive to the speed adjustment circuit to set a
speed target and operably configured to command the rotary member
in response to a comparison of the sensed rotary speed and the
speed target.
2. The control module of claim 1, wherein the speed sensor
comprises a noncontact transducer.
3. The control module of claim 1, wherein the rotary member
includes magnetic poles, the speed sensor comprises an inductive
pickup operable to sense the magnetic poles on the rotary
member.
4. The control module of claim 1, further comprising: a mechanical
control for receiving a user input for operating the hand tool; and
a thin film switch in physical communication with the mechanical
control and in electrical communication with the controller.
5. A method of controlling a electrically powered rotary member of
a hand tool, comprising: in respone to receiving a user command,
accelerating the rotary member; sensing a rotary speed of the
rotary member; decelerating the rotary member in response the
rotary speed of the rotary member exceeding a speed target.
6. The method of claim 5, wherein the hand tool comprises a
fastener driving tool having a safety switch and a trigger switch,
the receiving a user command comprises: receiving a safety signal
from the safety switch indicating a nose assembly of the tool is
against a workpiece; accessing a safety time-out value; timing a
duration of depression of the safety signal; activating the tool to
drive a fastener in response to receiving a trigger signal from the
trigger switch before the timed duration of the safety signal
exceeds the safety time-out value.
7. A portable hand tool, comprising: an electric motor; a rotary
member turned by the electric motor; a speed adjustment circuit; a
speed sensor operable to sense a rotary speed of the rotary member;
and a controller responsive to the speed adjustment circuit to set
a speed target and operably configured to command electric motor to
turn the rotary member in response to a comparison of the sensed
rotary speed and the speed target.
8. An electric powered hand tool, comprising: an electric motive
device; at least one mechanical control positioned by a user; a
controller operably configured to command the electric motive
device in response to an electrical command; and a thin film switch
in mechanical communication with the mechanical control and in
electrical communication with the controller and operable to
provide an electrical command in response to positioning of the
mechanical control.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority of Provisional Patent
Applicant serial No. 60/258,022, filed on Dec. 22, 2000 and
incorporates herein, by reference, the totality of the invention
disclosure therein.
[0002] This application is related to three commonly-owned,
co-pending U.S. non-provisional patent applications filed on even
date herewith and respectively titled, "FLYWHEEL OPERATED TOOL" to
Conrad Gravis, et al; "FLYWHEEL OPERATED NAILER" to John Burke, et
al; and "RETURN MECHANISM FOR A CYCLICAL TOOL" to Kevin Harper, et
al. This application further relates to the commonly-owned,
co-pending U.S. non-provisional patent application to Shane Adams,
et al., filed on even date herewith and titled "CONTROL MODULE FOR
FLYWHEEL OPERATED HAND TOOL".
FIELD OF THE INVENTION
[0003] This invention generally relates to a hand-held
electromechanical fastener driving tool, and more particularly to a
fastener driving tool having an inertial member for imparting
kinetic energy to drive a fastener into a work piece.
BACKGROUND OF THE INVENTION
[0004] In the past, where relatively large energy impulses have
been required to operate a fastener driving tool, such as an
industrial nailer or stapler, it has been common practice to power
such tool pneumatically. Such tools are capable of driving a 3" or
longer nail, or staple, into framing wood such as 2.times.4s, for
example. However, pneumatic driving tools require an on-site air
compressor, which is often unavailable or not desired. Also,
dragging the pneumatic umbilical is often an impediment to the
user.
[0005] Corded AC electrical fastener driving tools are often used
instead of pneumatic power since electrical power is more often
available than air compressors. In particular, much effort has been
expended in the prior art in providing heavy duty, high powered,
fastener driving tools employing a flywheel as a means of
delivering kinetic energy sufficient to drive a heavy duty
fasteners. Examples of such systems are disclosed in U.S. Pat. Nos.
4,042,036; 4,121,745; 4,204,622; 4,298,072; and 5,511,715. Use of a
flywheel is an attempt to limit the large current draws to actuate
a solenoid to drive a fastener. A DC motor is activated over a
non-instantaneous period and then the kinetic energy thus developed
in the flywheel is clutched to the driver in an "energy dump".
[0006] While such corded electrical fastener driving tools may
perform well, in many instances an AC outlet is not available. Even
if an AC outlet is available, many users find dragging the
electrical cord to be an impediment to use. To address these
preferences, it is further known to employ a portable power source
such as a battery, such as solenoid-operated fastener driving
tools. These portable fastener driving tools are primarily used in
light-duty applications such as in driving one inch brad nails, for
example, rather than the larger 2" to 4" staples or nails used in
framing.
[0007] One approach to an efficient portable electrically driven
tool is a multiple impact tool, such as described in U.S. Pat. No.
4,625,903, wherein a linear inertial member is repeatedly raised by
a cam against a compression spring and released to impact a
fastener. An electrical motor and portable battery pack are
operated in a more efficient manner by running the motor for a
period of time rather than providing a surge of power to a device
such as a solenoid. The relatively small amount of energy stored in
the spring each cycle typically requires a large number of impacts
to drive a staple or nail into a workpiece. During this time, the
user is required to maintain an appropriate position and force on
the fasten and to gauge the appropriate length of time to achieve
the desired depth. However, while the multiple impact tool is
efficient and effective in driving fasteners, some users prefer a
single driving action comparable to pyrotechnic or compressed air
systems. The multiple impact tools also can damage a wood surface
due to the vibrations the tool generates while stroking.
[0008] It would be desirable to use a battery to power a flywheel
operated hand tool to provide a portable fastener driver that can
drive larger fasteners in a single drive. However, using a battery
has been thwarted by a number of challenges. First, each specific
application generally requires a fastener drive assembly and motor
customized for the type of fastener. In particular, the size of
flywheel, the desired rotary speed of the flywheel, and the type of
electric motor to accelerate the flywheel to the desired rotary
speed are generally specifically sized for the type of fastener and
work piece into which the fastener is typically driven. Thus, each
specific application was thought to require a custom control
module, with the increased costs of design, manufacture and
support.
[0009] Even assuming that various types of fasteners could then be
used with a family of flywheel operated hand tools, each tool would
suffer the disadvantages inherent in using battery power. The
battery voltage varies as a function of the amount of charge
remaining and the amount of electrical current being drawn. The
rotary speed of the flywheel varies with the battery voltage, and
thus the depth of drive of the fastener would unacceptably vary.
The generally known controllers for corded flywheel operated hand
tools are unable to accommodate these power variations.
[0010] Furthermore, even for a specific application, the desired
depth of drive is affected by the type of work piece into which the
fastener is driven and to user preferences. However, flywheel
operated hand tools rely upon a given amount of kinetic energy
imparted by the flywheel to achieve a desired depth of travel.
Thus, when the work piece is more or less dense, the depth of the
drive will vary. Moreover, the user may prefer in some instances to
sink the fastener below the plane of the work piece or to leave the
head of the fastener exposed for easy removal.
[0011] Other types of hand tools, such a pneumatic powered hand
tools, generally rely on driving the fastener to a specific
position in order to achieve a desired depth. For example, in U.S.
Pat. Nos. 4,679,719, 5,732,870 and 5,918,788 a control module is
described that advantageously determines the mode of operation for
the trigger. In particular, a microprocessor provided additional
capabilities by receiving two signal inputs initiated by the user
and by selectively activating an electronic solenoid in response
thereto. Although the increased functionality of the control module
in such pneumatic tools has advantages, these control modules are
not responsive to changes in operating conditions to vary the depth
of drive.
[0012] Other tools employing a rotary member (e.g., drill)
generally require the user to determine the proper speed of the
tool. The user provides the closed loop control of the tool,
monitoring the tool for binding and proper operation and depressing
the trigger an appropriate amount. However, consistent operation of
the tool is thus dependent upon the skill level and attentiveness
of the user. Due to the speed in which a fastener must be driven
into the workpiece, the user would only learn after the fact
whether the rotary member (in this case a flywheel) was accelerated
to an appropriate speed prior to firing.
[0013] Therefore, a significant need exists for a control module
that drives medium and large fasteners into a work piece with a
single driving action, yet has the increased portability of battery
power. It would be further desired to have such a tool that
consistently provides a depth of fastener regardless of the state
of charge of the battery. It would be yet further desired to have a
control module readily adapted to a family of hand tools.
BRIEF SUMMARY OF THE INVENTION
[0014] These and other problems in the prior art are addressed by a
control module that is responsive to a rotary speed of a rotational
member of an electrically powered hand tool and is responsive to an
adjustable target speed for the rotational member. Thereby, the
control module more consistently controls the hand tool, avoiding
human error and the inconvenience of relying upon the user to
modulate the speed of the tool.
[0015] In one aspect of the invention, a control module for a hand
tool includes a speed setting that is used for presetting the
control module to an operating range of the intended rotational
member of the hand tool. Thus, the control module is readily
adjusted to the operating environment, using the speed setting as a
target for comparing a sensed speed.
[0016] In another aspect of the invention, a method of controlling
a fastener-driving tool enforces a user input sequence to ensure
that a fastener is driven into a workpiece. In particular, a safety
signal is received from a safety switch indicating a nose assembly
of the tool is against a workpiece. A safety time-out value is
accessed. The duration of depression of the safety signal is timed.
Then, the tool is activated to drive a fastener in response to
receiving a trigger signal from a trigger switch before the timed
duration of the safety signal exceeds the safety time-out value. By
so enforcing this sequence, a user is less likely to inadvertently
drive a fastener in instances where the trigger is inadvertently
squeezed and the tool contacts a surface.
[0017] In yet another aspect of the invention, an electrically
powered hand tool is provided a reliable interface to a control
module through use of a thin film switch interface to user controls
(e.g., safety and trigger) and through use of noncontact speed
sensing.
[0018] These and other objects and advantages of the present
invention shall be made apparent from the accompanying drawings and
the description thereof.
BRIEF DESCRIPTION OF THE DRAWING
[0019] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention, and, together with the general description of the
invention given above, and the detailed description of the
embodiments given below, serve to explain the principles of the
present invention.
[0020] FIG. 1 presents a left side elevational view of a hand held
nailing tool, embodying the present invention, having a portion of
its left side removed to show the general positioning of a fastener
drive assembly and control module.
[0021] FIG. 1A presents a generally rearward elevated view of the
control module of the nailing tool of FIG. 1
[0022] FIG. 2 presents a top view of the fastener drive assembly
removed from the main body of the hand held nailing machine as
illustrated in FIG. 1.
[0023] FIG. 3 presents a left side elevational view of the fastener
drive assembly as removed from the nailing machine illustrated in
FIG. 1.
[0024] FIG. 4 presents a bottom view, looking upward from the
handle of the fastener drive assembly as removed from the nailing
machine outer shell illustrated in FIG. 1 and having the electrical
control module removed for clarity.
[0025] FIG. 5 presents an end elevational view of the fastener
drive assembly as removed from the nailing machine illustrated in
FIG. 1 and having the electrical control module removed for
clarity.
[0026] FIG. 6 presents a pictorial view of the fastener drive
assembly, having the electrical control module removed for clarity,
showing the general arrangement the clutch drive assembly
components.
[0027] FIG. 7 presents an exploded pictorial view showing the
components of the fastener drive assembly illustrated in FIGS. 2
through 6.
[0028] FIG. 8 presents a sectional view taken along line 8-8 in
FIG. 3.
[0029] FIG. 9 presents a sectional view taken along line 9-9 in
FIG. 4.
[0030] FIG. 10 presents an enlarged view of the circled section in
FIG. 8.
[0031] FIG. 11 is a sectional view taken along line 11-11 in FIG.
4.
[0032] FIG. 12 is a sectional view taken along line 12-12 in FIG.
4.
[0033] FIGS. 13A through 13C present a schematical presentation of
the ball/cam action between the fixed plate and the activation
plate.
[0034] FIG. 14 presents a graph showing the distance x between the
fixed plate and the actuation plate as a function of degrees of
rotation of the actuation plate.
[0035] FIG. 15 presents an expanded pictorial view of the solenoid
camming plates.
[0036] FIG. 16 presents an expanded pictorial view of the
activation camming plates.
[0037] FIG. 17 is a cross-sectional view taken along line 17-17 in
FIG. 9.
[0038] FIG. 18 presents a block diagram of a control system for the
fastener-driving tool of FIG. 1.
[0039] FIG. 19 presents a flow diagram for a sequence of steps, or
main routine, for a controller of FIG. 18 to operate the
fastener-driving tool.
[0040] FIG. 20 presents a flow diagram of a diagnostic routine,
referenced by the main routine of FIG. 19.
[0041] FIG. 21 presents an intermittent mode portion of the main
routine of FIG. 19.
[0042] FIG. 22 presents a continuous mode portion of the main
routine of FIG. 19.
[0043] FIGS. 23A-23F present illustrative timing diagrams for
sequencing of safety and trigger signals for a valid command,
referenced in the main routine of FIGS. 19-22.
[0044] FIGS. 24A-24B present illustrative timing diagrams for motor
activation and solenoid actuation in response to variations in
battery charge and clutch wear, referenced in the main routine of
FIGS. 19-22.
[0045] FIG. 25 presents an illustrative control circuit for the
control system of FIG. 18.
[0046] FIG. 26 presents an indexing control circuit for the control
circuit of FIG. 25.
DETAILED DESCRIPTION OF THE INVENTION
[0047] With reference to FIG. 1, wherein like numbers refer to like
components throughout the several views, a portable flywheel
operated hand tool, depicted as a hand-held nailing tool 10,
includes a control system 12 that advantageously provides
consistent speed control throughout a range of operating
conditions. In particular, the nailing tool 10 generally comprises
a housing or main body 14 enclosing a fastener drive assembly 16
and a control module 18, and further includes and a gripping handle
20. Attached to the end of handle 20 is a removable, rechargeable
battery 22 for providing the necessary electrical energy to operate
a DC motor 24 and a solenoid 26 of the fastener drive assembly 16,
as well as the electrical control module 18. Unlike generally known
batteries that are required to handle large current influxes (e.g.,
Nickel Cadmium), the present invention advantageously may utilize
other types of batteries (e.g., Nickel Metal Hydride (NiMH),
lithium Polymers).
[0048] The DC motor 24, when accelerated by the control module 18,
turns a flywheel 28 to build kinetic energy in the form of
rotational inertia. Thereafter, the control module 18 actuates the
solenoid 26 in response to user inputs and a sensed parameter of
rotational speed of the flywheel 28 to impart the kinetic energy of
the flywheel 28 to a fastener, which is described in further detail
below
[0049] A user input to the nailing tool 10 are depicted as a
trigger 30 of the handle 20, which mechanically communicates with
the control module 18 via a trigger linkage 32. Another user input
is depicted as a safety device 34 of a nose assembly 36 that
mechanically communicates with the control module 18 via a safety
linkage 38. Yet another user input is depicted as a speed adjust
knob 40.
[0050] The nailing tool 10 includes a fastener supplying magazine
assembly 42, which is typically attached to the main body 14 and
handle 20, as illustrated, for supplying a strip of fasteners (not
shown) to the nose assembly 36. It will be appreciated that the
control system 12 may be advantageously operated with different
types of magazine assemblies 42 to include different numbers, types
and sizes of fasteners. Moreover, the control system 12
advantageously enhances use of indexed magazine assemblies, as will
be described in more detail below.
[0051] Control Module.
[0052] With reference to FIGS. 1 and 2, the control module 18 of
the control system 12 advantageously enhances reliability, design
flexibility, ease of assembly, and performance of the nailing tool
10. In particular, the control module 18 includes user speed
selection capability, depicted as a potentiometer 44 that is
adjusted by knob 40. By being responsive to the user speed
adjustment knob 40 enables the nailing tool 10 to adjust a target
speed of the flywheel 28. In addition to any preset target speed of
the control module 18, the user may adjust the knob 40 to
compensate for variations in the workpiece or the desired depth of
fastener insertion.
[0053] The control module 18 further includes a thin film printed
circuit 46 that provides an extremely reliable electrical interface
to the mechanical user inputs of the safety device 34 and the
trigger 30. Moreover, the printed circuit 46 is readily adapted to
various three-dimensional orientations with the support of a molded
bridge 48. Thus, a trigger switch 50 and a safety switch 52 are
readily positioned to receive the respective trigger and safety
mechanical linkages 32, 36. It will be appreciated that thin film
switches 50, 52 provide a service life that exceed generally known
trigger and safety switches and at a reduced cost.
[0054] The molded bridge 48 further supports and orients a portion
of the printed circuit 46 that forms a rotary speed transducer 54.
Two inductive pickups 56, 58 of the printed circuit 46 are oriented
to register to respectively to alternating north and south magnetic
poles on a ring magnet (not shown in FIGS. 1 and 2) of the flywheel
28, forming a rotary speed sensor 60. The non-contact nature of the
rotary speed sensor 60 avoids degradation due to wear. In addition,
by sensing rotary speed directly, the sensor 60 provides an
accurate measurement representative of the kinetic energy of the
flywheel 28. By contrast, if electrical current drawn by the motor
was sensed instead, the resulting measurement may contain
variations due to friction, motor component degradation, etc. More
accurate speed sensing allows more accurate transfer of kinetic
energy to the fastener and thus a more consistent result.
[0055] Before discussing the control system 12 in greater, the
mechanical aspects of the fastener drive assembly 16 are discussed
in greater detail.
[0056] Fastener Drive Assembly of the Flywheel Operated Hand
Tool
[0057] The fastener drive assembly 16 is described that has
features of efficiently uses DC electrical power by accelerating
the flywheel 28 with the DC motor 24. A clutching technique is
advantageously used that avoids the need for a manual reset. In
addition, components are described below that advantageously couple
to the flywheel during acceleration to increase the inertial load
prior to driving the fastener and then disengage after driving the
fastener. Furthermore, resetting the fastener drive assembly 16
with a vacuum return approach further conserves electrical power
and avoids the generally known techniques that require a manual
reset key.
[0058] FIGS. 2, 3, 4, and 5 illustrate top, left side, bottom and
rear views of the fastener drive assembly 16 as positioned within
the main body 14 of the nailing tool 10 illustrated in FIG. 1.
FIGS. 2, 4, and 5 have electrical control module 18 removed for
clarity. As illustrated in FIG. 6, the primary operational elements
of fastener drive assembly 16 comprise the flywheel 28 for
providing kinetic energy, for driving a fastener into a workpiece,
energized by an electric motor 24. Flywheel 28 is freewheeling upon
a fixed central shaft 62. Upon achieving the required revolutions
per minute (RPM), a clutch drive assembly 64 (see FIGS. 7 and 9)
causes engagement of a clutch plate 66 and flywheel 28 thereby
transferring a portion of the kinetic energy of flywheel 28 to a
linearly moving fastener driver 68 for driving a fastener into a
workpiece. The flywheel 28 is thereafter allowed to continue
spinning with any remaining kinetic energy between cycles to
further conserve electrical power and to reduce cycle time.
[0059] Referring now to FIGS. 2, through 9, the elements and
operation of the fastener drive assembly 16 will be discussed. The
fastener drive assembly 16 comprises clutch drive assembly 64 and
flywheel 28 gear driven by electric motor 24. Although a gear drive
between motor 24 and flywheel 28 is primarily illustrated herein,
it is understood that a belt drive may also be used between motor
24 and flywheel 28 or any other suitable drive mechanism. As an
alternative to having the motor axis of rotation parallel to the
axis of rotation of flywheel 28, as illustrated herein, it may be
preferable to position motor 24 such that its axis of rotation is
perpendicular to the axis of rotation of flywheel 28 and shaft 62,
thereby employing a bevel gear drive between the motor output shaft
and the flywheel periphery.
[0060] Referring particularly to FIG. 9 and additionally to FIGS. 6
through 8, the mechanical structure of flywheel 28 and clutch drive
assembly 64 will be operationally described.
[0061] Clutch drive assembly 64 and flywheel 28 are axially aligned
upon central shaft 62 as best illustrated in FIG. 9. Central shaft
62 is threadingly affixed to end plate 70 which in turn is rigidly
attached to a frame 72 by an integral boss 74 extending axially
from end plate 70 and received within a slotted groove 76 such that
end plate 70 and central shaft 62 are non-rotatable. The opposite
end of central shaft 62 is received within supporting groove 78 in
frame 72.
[0062] Flywheel 28 is rotatingly positioned at the end of central
shaft 62, as best illustrated in FIG. 9, upon a deep groove ball
bearing 80, whereby flywheel 28 freely rotates about central shaft
62 when energized by motor 24.
[0063] Flywheel 28 includes a conical cavity 82 for receiving
therein a conical friction surface 84 of conical clutch plate 66.
Clutch plate 66 and an activation plate 86, although they are
separable members, are geared to a drum 88 by interlocking
projections 90 and 92 respectively, whereby clutch plate 66,
activation plate 86 and drum 88 rotate freely about shaft 62 as a
single unitary assembly. Roller bearings 94a and 94b, positioned on
the inside diameter of drum 88, are provided to assure the free
rotational characteristic of activation plate 86, drum 88 and
clutch plate 66 as a unitary assembly.
[0064] Adjacent activation plate 86 is a fixed plate 96. Fixed
plate 96 and activation plate 86 are connected to one another by
three equally spaced axially expandable ball ramps 98a, 98b, 98c,
98a', 98b', and 98c' as illustrated in FIG. 16. The operation of
the ball ramps 98 between fixed plate 96 and activation plate 86 is
described in greater detail below. Fixed plate 96 is fixed to frame
72 such that fixed plate 96 is free to move axially upon central
shaft 62, but not free to rotate about central shaft 62 by an
anti-rotation tang 100 slidably received within an axially aligned
slot 102 within frame 72. See FIG. 17.
[0065] Fixed plate 96 includes a circular projection 104 receiving
thereon freely rotatable thrust bearing 106 positioned between
fixed plate 96 and a retarder plate 108. A pair of nested, parallel
acting, Belleville springs 110 are positioned, as illustrated in
FIG. 9, between retarder plate 108 and a solenoid plate 112 the
function of which is described in greater detail below. Axially
expandable ball ramps 113, see FIG. 15, connect end plate 70 and
solenoid plate 112, the function of which is also described in
greater detail below.
[0066] Positioned upon central shaft 62, between clutch plate 66
and flywheel 28, is a compression spring assembly 114 comprising
washers 116 and 118 having a coil spring 120 therebetween the
function of which is described in further detail below.
[0067] Upon start of the fastener work, or driving, cycle, the
control module 18 causes motor 24 to "spin up" flywheel 28, in the
counter clockwise direction as indicated by arrow A in FIG. 7, to a
predetermined RPM. Upon flywheel 28 achieving its desired RPM, or
kinetic energy state, the control module 18 activates solenoid 26
which, through a flexible wire solenoid cable 122 extending from a
solenoid plunger 124 and affixed to the periphery of solenoid plate
112 causes solenoid plate 112 to rotate clockwise, as indicated by
arrow B in FIG. 7. As solenoid plate 112 rotates clockwise,
solenoid plate 112 is caused to move axially away from end plate 70
by action of the corresponding ball ramps 98 in end plate 70 and
solenoid plate 112. See FIG. 15. As end plate 70 and solenoid plate
112 axially separate, the remaining elements of clutch drive
assembly 64 are thereby caused to move axially toward flywheel 28
compressing coil spring 120 whereby clutch surface 36 preliminarily
engages flywheel cavity 44. Engagement of clutch plate 66 with
flywheel 28 causes counter clockwise rotation of clutch plate 66,
drum 88 and activation plate 86, as an assembly. By action of
corresponding ball ramps 98, between fixed plate 96 and activation
plate 86, see FIG. 16, rotation of activation plate 86 causes axial
separation of clutch plate 66 and activation plate 86. Belleville
springs 72 are thus compressed against solenoid plate 112 thereby
providing an opposite axial force, forcing clutch plate 66 into
tighter engagement with flywheel 28.
[0068] As drum 88 rotates counter clockwise, cables 126a and 126b
wrap about peripheral grooves 128 and 130 in drum 88 and clutch
plate 66 respectively, thereby drawing a vacuum return piston
assembly 132 downward, within a cylinder 134, in a power, or
working, stroke whereby the attached fastener driver 68 is likewise
driven downward, through guide block 108 and opening 135 within
frame 72, thereby driving a selected fastener into a targeted
workpiece.
[0069] FIGS. 13A through 13C sequentially illustrate the action
between fixed plate 96 and activation plate 86 as plate 86 rotates
during the power stroke of clutch drive assembly 64. Although ball
ramps 98 of fixed plate 96 and activation plate 86 are helical as
illustrated in FIG. 16, ramps 98 are illustrated as being linear in
FIGS. 13A through 13C for simplicity of explanation.
[0070] FIG. 13A illustrates fixed plate 96 and activation plate 86
at the beginning of the tool's work cycle. As flywheel 28 drives
activation plate 86 counter clockwise (to the left in FIG. 13A)
balls 136, following the profile of ramp 98, cause a fast and
sudden separation x, between activation plate 86 and fixed plate 96
as illustrated in FIG. 13B. Separation x is maintained throughout
the power stroke of fastener driver 68, as illustrated in FIG. 13B,
thereby affecting the transfer of the kinetic energy, stored within
flywheel 28, to a driver 68 as described above. At the end of the
power stroke, as illustrated in FIG. 13C, plates 96 and 86 suddenly
close together thereby causing the rapid disengagement of clutch
plate 66 from flywheel 28.
[0071] FIG. 14 presents a representative graphical plot of the
separation x between activation plate 86 and fixed plate 96 as a
function of the angle of rotation of activation plate 86. A
combination driver guide and resilient stop block 138 is preferably
positioned at the bottom of cylinder 134 to stop piston assembly
132, within cylinder 134, at the end of the power stroke.
[0072] Upon disengagement of clutch plate 66 from flywheel 28, coil
spring 120 urges all elements of clutch drive assembly 64 back
toward end plate 70. The resulting axial force and pressure now
being applied to solenoid plate 112, by action of coil spring 120
and Belleville springs 74, cause solenoid plate 112 to close upon
end plate 70. The pressure being exerted, by solenoid plate 112,
upon balls 140 cause solenoid plate 112 to rotate,
counterclockwise, towards its original start position whereby
solenoid cable 122, being wrapped about solenoid plate 112, stops
the rotation of solenoid plate 112 when solenoid plunger 124
returns to its start position as illustrated in FIG. 12. In order
to decrease the tensile stress applied to solenoid cable 122 as it
stops, the counterclockwise rotation of solenoid plate 112 and
retarder plate 108 is provided. By action of the axial force
remaining within Belleville springs 72, retarder plate 108 and
solenoid plate 112, as an assembly, exhibit a combined mass and/or
inertia greater than that of solenoid plate 112 alone. Thus, during
the short period of time during which the combined solenoid plate
112 and retarder plate 108 assembly is rotationally accelerated the
rotational velocity achieved has been reduced and upon separation
of retarder plate 108 from solenoid plate 112, solenoid plate 112
has a lower angular momentum resulting in a lower tensile stress
being applied to solenoid cable 122 as it stops rotation of
solenoid plate 112. Once retarder plate 108 is uncoupled from
solenoid plate 112, retarder plate 108 freely rotates about central
shaft 62 until its kinetic energy dissipates. By use of retarder
plate 108 the mass and/or inertia of solenoid plate 112 may be
selectively chosen so as not to unnecessarily stress solenoid cable
122 upon stopping the rotation of solenoid plate 112.
[0073] By constructing the clutch drive assembly 64, as taught
hereinabove, clutch plate 66 disengages from flywheel 28 thereby
allowing flywheel 28 to continue spinning after clutch drive
assembly 64 has reached the end of its power stroke. Thus in the
event it is desired to successively drive additional fasteners, the
remaining kinetic energy is available for the subsequent operation
thereby economizing battery power and saving the drive assembly
elements and/or the frame 72 from having to absorb the impact that
would otherwise occur by bringing flywheel 28 to a full stop
immediately after the power stroke. This feature also permits "dry
firing" of the tool.
[0074] The clutch drive system as taught herein also provides for
automatic compensation for clutch wear in that the expansion
between end plate 70 and solenoid plate 112 will continue until
clutch plate 66 engages flywheel 28 thereby allowing solenoid plate
112 to take up the difference at the start of every power
drive.
[0075] Referring now to FIG. 10. Vacuum return piston assembly 132
comprises piston 142 slidably received within cylinder 134. Spaced
from the top of piston 142 is a circumscribing groove 144 having
positioned therein a sealing O-ring 146. Positioned toward the
bottom of piston 142 are two axial stabilizing bands 148 and
150.
[0076] The inside diameter D, of cylinder 134, is flared outward to
diameter D' at the top of cylinder 134 as illustrated in FIG. 10.
Diameter D' is slightly greater than the outside diameter of O-ring
146 thus creating an annular gap 152 between O-ring 146 and inside
diameter D'.
[0077] As piston assembly 132 is drawn axially into cylinder 134,
during the power stroke of fastener driver 68, O-ring 146 slidingly
engages the inside wall diameter D of cylinder 134 thereby forming
a pneumatic seal between inside wall 153 of cylinder 134 and piston
assembly 132. As piston assembly 132 progresses into cylinder 134,
a vacuum is created within the top portion of cylinder 134, between
advancing piston assembly 132 and the sealed end cap 154.
[0078] Upon disengagement of friction clutch plate 66 from flywheel
28, the vacuum created within the top portion of cylinder 134 draws
piston assembly 132 back toward an end cap 154 thereby resetting
activation plate 86, drum 88, and clutch plate 66, as an assembly,
to their restart position.
[0079] As O-ring 146 passes from inside diameter D to diameter D',
on its return stroke, any air that may have by passed O-ring 146,
during the power stroke, is compressed and permitted to flow past
O-ring 146 through annular gap 152 and to the atmosphere through
cylinder 134, thereby preventing an accumulation of entrapped air
above piston assembly 132. A resilient end stop 156 is preferably
positioned within end cap to absorb any impact that may occur as
piston assembly 132 returns to its start position at the top of
cylinder 134.
[0080] As drum 88 returns to its start position tang 157 radially
extending from drum 88 engages abutment block 158 affixed to frame
72, see FIG. 11, thereby preventing over travel of drum 88 as it
returns to its start position.
[0081] It will be appreciated that the above-described fastener
drive assembly 16 is illustrative and that aspects of the invention
have application in other types of fastener drive assemblies.
[0082] Additional structural and operational details of the
fastener drive assembly 16 is completely described within the two
co-pending patent applications identified in the "Related Patent
Applications" section above and are incorporated herein by
reference.
[0083] Speed Controller
[0084] FIG. 18 depicts a control system 200 for a nailing tool 10
that advantageously uses rotary speed sensing of a inertial member,
depicted as a flywheel 202, to more consistently and efficiently
drive a fastener into a workpiece. The control system 200 responds
to input signals 204 received and processed by an electronic
control module 206 to command a motive device, such as a flywheel
motor 208, to accelerate the flywheel 202. The control module 206
further commands a clutch actuator 210 to transfer kinetic energy
from the flywheel 202 to a fastener.
[0085] A signal representative of the rotational rate (e.g., RPM)
that a plurality 212 of radially arrayed pairs of magnetic poles
rotate with the flywheel 202 is generated by a transducer 214 that
senses each closest pair of registered magnetic poles 216, 218 of
the plurality 212. In addition to flywheel speed signal, the
control system 200 responds to other types of inputs. For example,
the input signals 204 may include a trigger input 220, a safety
input 222, a user speed adjustment input 224, a continuous flywheel
mode switch input 226, a fastener type sensor input 228, and a
fastener transducer input 230 for sensing the presence of a
fastener positioned for driving.
[0086] A fastener indexer 232 may advantageously respond to an
electrical command from the control module 206. The electric
interface to a separable indexing magazine (not shown) may be
readily designed and assembled with electrical interconnects. This
advantageously compares to pneumatic power tools with indexing
wherein more complicated pneumatic plumbing at the interface of the
magazine and main body is required.
[0087] The control module 206 may respond to an enabling condition
input 234. In some instances, the availability of electrical power
in combination with actuation of a trigger or depression of a
safety may be deemed an enabling condition for powering the nailing
tool 10. Alternatively or in addition, the enabling condition input
234 may represent other input signals that enable or disable the
nailing tool 10. For instance, the enabling condition input 234 may
include a sensed motor overheat condition, an ON/OFF switch, a
battery power voltage level, or presence of an AC electrical power
input. The latter may cause the control module 206 to switch power
source, or to charge a battery.
[0088] Battery input 236 may represent a source of power for the
control module 206. In addition, the control module 206 may respond
to the voltage level of the battery input 236 by altering time-out
values when the control module expects to see acceleration and
actuation performed. For example, for a given battery voltage
level, the flywheel motor 208 should accelerate to a given target
speed in a certain time range, whereas this time range would be
expected to change in relation to the voltage level. Thus,
mechanical failures would be more accurately detected by more
accurately predicting the performance thereof.
[0089] The electronic control module 206 includes interfaces
240-256 for these input signals 204. A speed sensor 240 may convert
the speed signal from the transducer 214 into another form. For
instance, the speed sensor may convert an analog signal into a near
DC signal (digital signal) suitable for digital signal processing.
A thin film switch "A" 242 converts a mechanical trigger input 220
into an electrical trigger signal. A thin film switch "B" 244
converts a mechanical safety input 222 into an electrical safety
signal. A preset speed range interface 246 may fully comprise a
speed selection or define a flywheel speed range for user speed
adjustment input 224. The present speed range interface 246 may
define a range constrained by a combination of the operable range
of the flywheel motor 208 and/or clutch actuator 210 and the force
requirements expected for the fastener and type of workpiece. A
continuous mode input 248 receives a selection for continuous or
intermittent mode for the flywheel. It should be appreciated that
continuous mode or intermittent mode may be used at the exclusion
of the other mode. Alternatively or in addition, the selection may
be determined based on another consideration such as state of
charge of the battery (e.g., switching to intermittent mode to save
electrical power when a battery is partially discharged). A
fastener type input interface 250 senses or accepts a selection
from the fastener type sensor input 228, which may advantageously
adjust speed and timing considerations. A fastener sensor interface
252 responds the fastener transducer input 230 to convert the
signal into a form suitable for digital processing. The control
module 206 may respond to the presence or absence of a fastener
ready for driving in a number of fashions. For example, dry firing
may be prevented to avoid wear or a jam of a partially loaded or
improper fastener; an indication of the need to load the magazine
may be given, a continuous mode for the flywheel may be
discontinued, etc. For applications with an indexing magazine, an
index control interface 254 provides an index signal suitable for
the fastener indexer 232.
[0090] The control module 206 is depicted as including a power
supply 256 that responds to the enabling condition input 234 and
the battery input 236. It should be appreciated that the power
supply may comprise a power source for the control module 206 only,
wherein power drain on the battery is prevented by shutting down
the control module 206 except when commanded to drive a fastener or
when in continuous mode and the tool 10 is enabled. The power
supply 256 may further represent logic to select a source of
electrical power and/or to charge an attached battery. In addition,
the power supply 256 may represent additional safety features to
prevent electrical power from inadvertently reaching actuating
components.
[0091] The electronic control module 206 provides a motor control
interface 260 to convert a control signal into a form suitable for
the flywheel motor 208 (e.g., a logic signal to a pulse width
modulated (PWM) power signal). A clutch control interface 262
converts a control signal into a form suitable for the clutch
actuator 210 (e.g., a logic signal to power signal).
[0092] The control system 200 may advantageously include additional
features to the user to include an aim indicator 264 that is
controlled by an indicator control interface 266 in the control
module 206. For example, in response to an enabling condition such
as depression of the safety against a workpiece, a focused light or
laser pointer may be directed at the expect point of the fastener.
The illumination thereof may assist the user in seeing the
workpiece more clearly in dim lighting or to better appreciate the
aim of the tool.
[0093] The electronic control module 206 advantageously includes a
digital controller 300 that is programmed for additional features.
To that end, a processor 302 accesses instructions and data by
indirect addressing through a pointer 304 of a Random Access Memory
306. The processor and/or memory access analog-to-digital (A/D)
inputs 308, such as from the speed sensor 240, that are used and
stored in digital form. Although not depicted, another example may
be the speed adjustment input 224 and preset speed range interface
246 as being analog inputs. The memory 306 includes instructions
310; a switch timer 312 for monitoring a stuck or inadvertently
held switch; interrupts code 314 for handling time sensitive
signals or abnormal processing; a motor timer 316 for monitoring
overlong motor operation that could result in overheating; a switch
debounce buffer 318 for precluding inadvertent or spurious switch
signals from being acted upon; a speed target register 320 for
holding a preset or calculated value for a desired or appropriate
flywheel speed; an actuation timer register 322 for holding a
preset or calculated value for monitoring for abnormally long time
for transfer kinetic energy to the driver by actuation; a
no-operation (no op) timer 324 for timing when to deactivate; or
other data structures or unused memory 326
[0094] It will be appreciated that the instructions 310 include
diagnostic code to perform RAM checking, verifying that all memory
locations are working properly prior to use and that the program
counter 304 is indexing correctly. The diagnostic code further
checks that jumps and returns from subroutine locations return back
to the correct location. In addition, the diagnostic code checks
that when the processor 302 tells a pin to go high or low that the
line attached to the pin responds accordingly.
[0095] The control module 206 includes a watch dog timer circuit
330 that prevents a processing failure. Throughout processing, it
will be appreciated that the watch dog timer circuit 330 is
periodically reset by the processor 302, lest a time limit be
reached that initiates resetting or disabling the control module
206.
[0096] In FIG. 19, an illustrative sequence of steps for utilizing
the control system 200 to affect control of the tool 10 is depicted
as a main routine 400. Before driving a fastener, user settings are
available (block 402). For instance, a user setting may include an
enabling condition such as an ON setting or a momentary actuation
of a control (e.g., trigger, safety). A user setting may include a
MODE setting, such as continuous, intermittent, or automatic (e.g.,
the control system determines the appropriate mode). The user
setting may include a speed adjust setting, to include a factory
preset range appropriate for the fastener drive assembly, a range
appropriate for the type of fastener sensed, or a user selected
range.
[0097] In the illustrative embodiment, a user input, such as
depression of the safety switch, begins processing (block 404) by
enabling the control system (block 406). Immediately, the control
module performs diagnostics to preclude failures that may cause an
inadvertent activation and actuation of the tool (block 408),
discussed in more detail below. It will be appreciated that certain
diagnostic features continue to be performed throughout
operation.
[0098] Once diagnostics are complete, with a determination is made
as to whether the safety is depressed (block 410). If so, an aim
indicator is activated (block 412). This feature is included to
illustrate features that may be performed to give visual
indications to the user about the operation or condition of the
tool.
[0099] Thereafter, a determination is made as to whether the tool
is in continuous mode (block 414). This determination may be
preset, user selected, or automatically selected based on
considerations such as battery voltage. If in continuous mode in
block 414, then a further determination is made as to whether an
input has been made to ready the tool for actuation, for instance a
depression of the trigger (block 416). And if so, the continuous
mode is initiated as described below. Otherwise, an additional
determination is made as to whether a no op timer has expired
(block 418). If no operations have been received within a suitable
time, then the control module is disabled (block 420) to prevent
battery drain and preclude inadvertent actuation. If in block 418
the no op time-out has not occurred, then processing continues to
wait for a trigger command to initiate the continuous operating of
the flywheel.
[0100] Returning to block 414, if continuous mode is not selected
or appropriate, then the main routine 400 is in an intermittent
mode that advantageously accelerates the flywheel to a target speed
each time a fastener is to be driven. Thus, battery power is
conserved between driving cycles. Since residual kinetic energy of
the flywheel is conserved by the fastener drive assembly, the cycle
time is still short even in intermittent mode. In intermittent
mode, a determination is made as to whether a valid command to
drive a fastener has been received (block 422), and if so,
initiating intermittent acceleration of the flywheel will be
discussed below, as well as the forced sequence of the safety and
the trigger for a valid command. If a valid command is not received
in block 422, then a further determination is made as to whether a
no op time-out limit has been reached (block 424), and if so the
control module is disabled (block 420) and routine 400 is
complete.
[0101] FIG. 20 depicts the diagnostics routine 500 referenced in
FIG. 19. Certain diagnostic tests are performed upon powering up
the control module and other tests continue in background during
operation of the tool. For example, a watchdog timer (block 502) is
depicted, wherein a dedicated circuit times the period since the
last update from the processor. If the watchdog timer is not
updated before timing out, the control module is assumed to be
processing abnormally and the tool is placed in a safety lockout
mode (block 503). This watchdog timer continues operation
throughout the main routine 400.
[0102] Also, digital parameters are initialized and any
calibrations are performed (block 504). For example, interrupt
vectors are set so that any resets will be appropriately handled.
Also, analog devices like oscillators are calibrated. Then the
processor memory is tested by checking for any failure to toggle
and to read a memory location (Z BIT) (block 505). If Z BIT fails
(block 506), then safety lock-out mode is set (block 503), else any
unused memory is loaded with a reset code (e.g., interrupt vector)
(block 508). In addition, a check is made as to whether the program
counter (pointer) is corrupt (block 510), and if so safety lockout
mode is set (block 512). If the program is not corrupt in block
510, then a delay occurs to allow for the power supply to the
control module to stabilize (block 514). If not stable (block 516),
then safety lockout mode is set (block 518). If stable in block
516, then the trigger time-out counter is set up so that overly
long trigger commands due not result in actuation (block 520).
Also, switch debounce code is set up so that momentary or spurious
signals are ignored (block 522). Thereafter, routine 500 returns to
the main routine 400 of FIG. 19.
[0103] FIG. 21 depicts the intermittent mode from block 416 of FIG.
19. In particular, this portion of the main routine 400 begins with
a valid command from the user indicating that the flywheel is to be
accelerated to the target speed and the driver is to be driven by
the flywheel. To that end, the speed target is determined (block
600), which could be based on a preset value, a user selection, a
preset speed range adjusted by a user selection, a selection based
on a sensed fastener type, or a range based on a sensed fastener
type as adjusted by a user selection. With the target set, a motor
command is initiated (block 602).
[0104] Advantageously, the motor command begins with a Pulse Width
Modulated (PWM) soft start is used. Thus, the duty cycle of the PWM
command ramps up to a full command level, reducing the initial
electrical current demand on the battery and surge to the motor.
Thereby, power consumption is greatly reduced and the service life
of the motor is extended.
[0105] With the flywheel accelerating in response to the motor
command, a determination is made as to whether the safety is still
held (block 604). Withdrawal of the safety from the workpiece
causes the motor command to be deactivated (block 606) and the
control module to be disabled (block 608).
[0106] If the command is still valid in block 604, then a further
determination is made as to whether the motor time-out has expired
(block 610). If so, due to a failure in the fastener drive assembly
(e.g., stuck clutch, motor failure, weak battery), the safety
lockout mode is set (block 612). If the motor has not timed out in
block 610, then the current sensed speed is compared to the target.
If the target is not reached (block 614), then processing returns
to block 602, continuing with a full motor command. If the target
speed is reached in block 614, then the motor command is
deactivated (block 616).
[0107] A speed reduction threshold is determined for imparting or
transferring kinetic energy from the flywheel to the linearly
moving fastener driver. Thus, not only is a known amount of kinetic
energy available in the flywheel, but a known amount is transferred
to the driver and thus to the fastener for a consistent depth of
drive. Moreover, since the flywheel is not completely stopped
during or after transferring the kinetic energy, the remaining
kinetic energy is available for a subsequent operation. The speed
reduction may be based on a look-up table for the given conditions,
based on a fixed ratio of a current speed, or a fixed scalar amount
below the target, or other measures.
[0108] The clutch is engaged to transfer the kinetic energy to the
driver (block 620). Then a determination is made as to whether the
threshold is reached (block 622). If not reached, then a further
determination is made as to whether the actuation time-out has been
reached (block 624), and if so, safety lock-out mode is set (block
626). If in block 622 the time-out is not reached, then actuation
is still in progress by returning to block 620. Returning to block
622, if the reduction threshold is reached, then the clutch is
deactivated (block 628). If installed and enabled, the fastener
index is actuated (block 630). Then the control module is disabled
(block 632) and main routine 400 ends.
[0109] FIG. 22 depicts the continuous mode portion after a trigger
command in block 416 of the main routine 400 of FIG. 19. In
particular, the speed target is determined (block 700) and the
motor is started (block 702) in a manner similar to that described
respectively for blocks 600 and 602. Then a determination is made
as to whether the motor time-out has expired, indicating an
inability to accelerate the motor in the expected time (block 704).
If expired, then safety lockout mode is set (block 706). If not
timed out, then a further determination is made as to whether the
target has been reached (block 708). If not, then flywheel
acceleration continues by returning to block 702.
[0110] Advantageously, continuous mode allows addition
safety/trigger sequcnces for a valid command. For instance, rather
than requiring the safety signal to precede the trigger signal,
("trigger fire"), the trigger signal may precede the safety signal
("bottom fire"). Again, a trigger time-out (e.g., 3 seconds) is
applicable just as is the safety time-out (e.g., 3 seconds) to
minimize inadvertent actuation. Bottom fire is included as an
option in continuous mode for applications wherein the user desires
very short cycle time between drives or has a personal preference
for this technique.
[0111] If the target is reached in block 708, then the speed is
held (block 710). For example an operating range may be entered
wherein the motor command is recommenced when a lower limit is
reached and removed when an upper limit is reached. Then, a
determination is made as to whether a valid command has been
received from the user (block 712). If not, a check is made as to
whether the no op time-out has occurred (block 714), and if not,
the flywheel speed is continuously maintained by returning to block
710. If the no-op timer has expired in block 714, then the motor
command is deactivated (716) and the control module is disabled
(block 718).
[0112] Returning to block 712 wherein a valid command has been
received, then the clutch is actuated in a manner similar to that
described above for the intermittent mode, wherein blocks 720-734
correspond respectively to block 616-630. However, after
deactuating the clutch in block 732 and actuating a fastener index
in block 634, control returns to block 710 to continue holding
speed in a continuous fashion awaiting the next valid command to
drive a fastener.
[0113] FIG. 23A graphically illustrates a valid user command that
initiates acceleration of the motor 24 and actuation of the
solenoid 26 of FIG. 1 over a time period of "t0" to "t7". At time
"t1" , an enabling event, depicted as depression of the safety,
provides power to the control system. The "Power or Safety" remains
on throughout the depicted time scale to time "t7". At time "t2",
trigger signal is received, which also remains present throughout
the remainder the graph, representing the tool placed against the
workpiece followed by depression of the trigger. Also at time "t2",
the motor command ("Motor Signal") begins.
[0114] The portion of the motor signal between times "t2" and "t3"
of FIG. 23A are depicted in greater detail in FIG. 23B, which shows
the soft start portion of the motor signal. In particular, the PWM
motor signal begins with an on time of 2 .mu.sec and off time of
510 .mu.sec, incrementing each cycle by 10 .mu.sec until reaching a
full command of 510 .mu.sec on time and 10 .mu. off time. It will
be appreciated that other approaches to soft starting the motor may
be implemented as well as omitting soft start.
[0115] Returning to FIG. 23A, with the motor signal beginning at
time "t2", the parameter of rotational speed of the flywheel and
motor is sensed ("motor speed"). The initial value of motor speed
at time "t2" may be nonzero if the flywheel has residual kinetic
energy from a previous driving cycle. At about time "t3", the
sensed speed enters the lowest speed of the speed range available
for actuation. At time "t5", the sensed speed reaches the target
speed, whereupon several changes occur. The motor command is
deactivated. In addition, a solenoid signal commands actuation,
transferring the kinetic energy from the flywheel to the linearly
moving driver to the fastener as shown by the decreasing motor
speed. At time "t6", the motor speed is sensed at having reduced to
a threshold indicating the desired actuation, and thus the solenoid
signal is deactivated.
[0116] FIGS. 23C-23F depict instances where an invalid command is
given, resulting in no actuation of the tool. FIG. 23C presents a
trigger signal at time "t1" that precedes the safety signal at time
"t2", which in the illustrative embodiment precludes activating the
motor and actuating the solenoid. FIG. 23D presents a safety
depressed at time "t1", but the safety signal reaches a time-out at
time "t4" before the trigger signal is received, thus precluding
activation and actuation. FIG. 23E presents a safety signal at time
"t1" and a trigger signal at time "t2", which is the required
sequence and within the time-out value for the safety. Although the
safety signal remains present, the trigger signal is withdrawn
after time "t4" before the motor speed has reached the speed target
("speed set point"). Without a valid command being removed, the
motor signal is removed and actuation does not occur. FIG. 23F
presents a situation similar to FIG. 23E except that the safety
signal is the one that is removed after time "t4" before the motor
speed reaches the speed target. Again, the motor signal is removed
and actuation does not occur.
[0117] FIGS. 24A-24B illustrate the adaptability of the control
system to a wide operating range of fastener types and battery
charge. FIG. 24A graphically illustrates a scenario where the
flywheel accelerates rapidly with a fully charged battery and a low
speed set point for the speed target. Thus at time "t1" the low
speed set point is reached and the solenoid signal is present for a
relatively short period until time "t2". Then, between time "t4"
and "t5", the battery voltage is shown as reaching a fully
discharged level and the tool having been set to a high-speed set
point. Thus, the acceleration of the motor speed from time "t5" to
time "t6" to the high-speed set point takes longer. Moreover, the
solenoid signal is required to be present for a longer period from
time "t6" to "t7" by actuating more slowly with a lower solenoid
signal.
[0118] FIG. 24B illustrates a feature of the control system to
accommodate increased tolerance within the clutch components due to
wear or manufacturing variation yet still detect a failure
condition. In the first trace representing a clutch with a low gap,
the motor accelerates the flywheel to the target speed at time
"t1". Then, a brief solenoid signal starts at time "t1". After a
brief period, the flywheel has slowed to the necessary speed drop
off and the solenoid signal is deactivated, having provided the
necessary amount of kinetic energy to the driver. In the second
trace representing a clutch with a high gap, the motor accelerates
the flywheel to the target speed at time "t6", prompting the
solenoid signal to start. The solenoid signal last for a longer
period than the first trace. At time "t7", the necessary speed drop
off is reached and the solenoid signal is deactivated. The third
trace represents a clutch that fails to engage. At time "t10", the
motor has accelerated the flywheel to the target speed and the
solenoid signal starts. With the clutch failing to engage, the
motor speed drops off slowly, still higher than the expected value
at time "t11" . Then, at time "t12", the clutch time-out value is
reached, indicating the failure, and the solenoid signal is
discontinued.
[0119] FIG. 25 depicts an exemplary control circuit 800 for a
flywheel operated hand tool, such as the nailing tool 10 of FIG. 1
that advantageously provides selectable continuous or intermittent
modes and economical speed sensing.
[0120] A speed sensor 802 is picks up alternating north and south
magnetic fields 804 on a ring magnet with an inductive transducer
806. In particular, a series pair of coils 808 have their shared
node is grounded and their opposite ends connected to a
differential amplifier, or comparator U1, such as model no.
TA75S393F. Thus, as each pair of fields 804 of the 32 alternating
poles are encountered, the push-pull arrangement or differential
arrangement enhances signal integrity and noise immunity of the
differential speed signal of about 10-15 mV. The comparator U1 is
biased between power supply VDD and ground. The positive bias is
also coupled to ground via capacitor C1 suppress high frequency
noisy disturbances from the power supply.
[0121] The output node of the comparator U1 is coupled to ground
via a capacitor C2 to rectify and low pass filter the differential
speed output that is passed to the +T input of a monostable
multivibrator (one shot) U2, such as model no. MM74HC4538 by
Fairchild Semiconductor Corporation. The one shot U2 is an
integrated circuit that, when triggered, produces an output pulse
width that is independent of the input pulse width, and can be
programmed by an external resistor-capacitor (RC) network to set
the pulse width. To that end, the RC input of the one shot U2 is
coupled to the common node of a series resistor R1 and capacitor
C3, the series coupled between power supply VDD and ground,
respectively. The inverted input CS of the one shot U2 is coupled
to the common node of a series resistor R2 and capacitor C4, the
series coupled between power VDD and ground, respectively. The
inverted output {overscore (Q)} of the one shot U2 is connected to
the inverted input -T. The bias V+ of the one shot U2 is coupled to
power supply VDD and to ground via capacitor C5. Thus configured,
the one shot U2 outputs at noninverted output Q a series of pulses,
the spacing between pulses being a function of the rate that the
poles of ring magnet pass by the speed transducer 808.
[0122] The pulse train at output Q of one shot U2 is connected to a
node 810 via a resistor R3. The node 810 is also coupled to ground
via capacitor C6. Thus, the signal at node 810 is low pass
filtered, creating a near DC signal whose amplitude is related to
rate of pulses. Thus, the sensed speed signal has been converted to
a form suitable for digital processing.
[0123] A controller U3, such as an 8-pin RISC microprocessor
performs the digital processing, model PIC12C671. The analog input
GP 1 of the controller U3 receives the near DC signal from node
810. This near DC signal is compared to a speed target reference
signal at analog input GPO. The controller U3 changes the analog
reference signal into a digital signal to be compared to the
digitized speed signal with a resolution of one bit. The speed
target reference signal is produced by preset speed adjust range
formed by a voltage divider of trimmable resistors R4 and R5
coupled between power supply VDD and ground. Inserting an
infinitely variable potentiometer 812 between resistors R4 and R5
advantageously provides a user speed adjustment. The pick off point
of the potentiometer 812 is coupled to the analog input GPO and
also coupled to ground via capacitor C7 for noise suppression. It
will be appreciated that the resistors R4 and R5 may be selected
for a desired speed range within which the potentiometer 812
selects a target speed. The voltage thus produced at analog input
GPO may advantageously be selected for a desired voltage level
corresponding to a target speed. When enabled by a safety signal at
input GP2, the processor U3 awaits a trigger signal at input GP3,
as described above in the timing diagrams of FIGS. 23A-23F before
producing a motor signal at output GP5 and thereafter a solenoid
actuation signal at output GP4.
[0124] The user initiates these actions by selecting a mode, either
continuous or intermittent, at mode select switch 814, enabling the
tool with safety switch 816, and then commanding the driving of a
fastener with a trigger switch 818.
[0125] The safety signal is received in either continuous or
intermediate mode, which affects the manner of operation of
processor U3. Specifically, in continuous mode, switch 814 couples
battery voltage VBATT to a resistor R6 whose value is selected to
scale the battery voltage to the desired voltage VDD for the
control system 800. The resulting power supply voltage VDD is
further regulated by being coupled to ground via the parallel
combination of a capacitor C8 and zener diode ZI. Thus, in
continuous mode, the control system remains enabled, awaiting a
safety and trigger signal to initiate the tool.
[0126] To that end, the mode switch 814 in continuous mode also
couples the battery voltage to a first input of an AND gate 820,
such as an SN74AHC1G08. The other input to the AND gate 820
receives battery voltage VBATT when the safety switch 816 is
closed, inverted by inverter 822, such as an SN74AHC1G04. The
output of the AND gate 820 controls the input GP2 via a biasing
circuit 824. In particular, the output of the AND gate 820 is
connected to input GP2 via resistor R7. The input GP2 is also
coupled to power supply VDD via a resistor R8 and to ground via
capacitor C9. When the trigger switch is closed, ground is coupled
the input GP3 of the processor U3 via resistor R9. The input GP3 is
connected to power supply VDD via resistor R10 and to ground via a
capacitor C10.
[0127] When the mode switch 812 is in intermittent mode, the
resistor R6 is connected to battery voltage VBATT when the safety
switch 816 is closed. Also, the first input of the AND gate 820 is
connected to ground.
[0128] The processor U3 commands a DC motor 826 with a motor signal
at output GP4 that is coupled via resistor R11 to the base of a
buffer, depicted as a small signal transistor Q1 such as a 2N4401.
The base is also coupled to ground via resistor R12 to ensure that
the transistor will be off if voltage is not applied to the base.
The collector is connected to power supply VDD. The emitter is also
connected to the base of a rectifier Q2, such as an IRL3803 that
advantageously has a low RDS (on) characteristics minimizing energy
dissipation, that is heat shielded. The emitter is also coupled to
ground via resistor R13 to ensure that rectifier Q2 if off when not
supplied with a signal. The turned-on rectifier Q2 thereby couples
to ground a negative terminal respectively of a DC motor 826, a
MOSFET configured as a diode Q3 (such as a model MTD20N03HDL) that
advantageously has a high current carrying capacity in a small
package. A positive terminal respectively of the diode Q3 and the
DC motor 826 are coupled to battery voltage VBATT. Thus, the DC
motor 826 is activated when rectifier Q2 closes.
[0129] The processor U3 commands a solenoid 828 with a solenoid
signal at output GP5 that is coupled via resistor R14 to the base
of a MOSFET configured as diode Q4 (such as a model MTD20N03HDL).
The base is also coupled to ground via resistor R15 to ensure that
the transistor will be off if voltage is not applied to the base.
The rectifier Q4 has a negative terminal coupled to ground and a
positive terminal coupled to a negative terminal of the solenoid
828. The positive terminal of the solenoid 828 is coupled to
battery voltage VBATT, thus solenoid 828 activates when rectifier
Q4 is closed by the solenoid signal. The rectifier Q4
advantageously withstands the electrical current spikes associated
with inductive loads of solenoids.
[0130] FIG. 26 presents an index circuit 830 for providing an
electrical index signal, thereby avoiding the additional complexity
of pneumatic index approaches. Moreover, the index circuit
advantageously uses a one shot U4 that is part of the same package
as one shot U2. The index circuit 830 is triggered by the solenoid
signal from GP4 of the processor U3 to an inverted -T input, as
would be appropriate for a solenoid that is triggered on a falling
edge of a solenoid signal rather than a rising edge. The one shot
U4 is configured with a positive bias V+ to power supply VDD and
also coupled to ground via capacitor CO. A negative bias V- is
grounded. A noninverted output Q is connected to input +T to place
the device into a non-retriggerable, monostable mode of operation.
An inverted input R is coupled to a shared node of a series
combination of a resistor R18 and capacitor C11 that are connected
across power supply VDD and ground, providing a reset RC network to
hold the device in reset until power supply VDD is up and stable.
Similarly, an input RC of the one shot U4 sets up the output
timing, i.e. time the output pulse is high. In particular, the
input RC is coupled to a shared node of a series combination of a
resistor R19 and capacitor C12 connected between power supply VDD
and ground, respectively. The one shot U4 has an output pulse of
appropriate duration and delay from the solenoid signal to advance
the next fastener after the previous fastener is driven. The index
pulse from output Q is given an appropriate voltage by passing
through a series resistor R16 to a base of a rectifier Q5 (a MOSFET
configured as a diode such as a model MTD20N03HDL. The base is also
coupled to ground through a resistor R17 to ensure that rectifier
Q5 is off when no voltage is applied. A negative terminal of the
rectifier Q5 is grounded. A positive terminal rectifier Q5 is
connected to a negative terminal of an indexing solenoid 832. A
positive terminal of the indexing solenoid 832 is connected to
battery voltage VBATT. Thus, when the indexing signal closes the
rectifier Q5, the indexing solenoid 832 is activated.
[0131] In use, a user loads the magazine 42 of the nailing tool 10
with a strip of fasteners, and installs a charged battery 22. The
tool is in a mode, such as Intermittent, conserving battery power
by accelerating a flywheel each time that a fastener is to be
dispensed or driven. As the nose assembly 36 is placed against a
workpiece, closing a safety device 34, the safety mechanical
linkage 38 contacts a highly reliable thin film safety switch 52,
powering the control module 18. A trigger 30 is depressed,
activating another highly reliable thin film trigger switch 50 via
a trigger mechanical linkage 32. If the safety and trigger switches
are actuated within appropriate time intervals and sequence (e.g.,
safety depressed and held no more than 3 seconds prior to trigger),
then the processor U3 calculates a target speed for the flywheel
set as appropriate for the fastener drive assembly 16 and/or an
appropriate setting for the fastener and workpiece. As the flywheel
accelerates, the speed signal from a noncontact speed sensor 60 is
compared to the target speed. Once reached, the motor 24 is
de-energized and then a solenoid actuation signal couples a clutch
to the flywheel 28 to impart kinetic energy to a linearly moving
fastener driver 68. The processor U3 uses a reduction threshold to
determine when the flywheel 28 has imparted an appropriate amount
of kinetic energy, thereafter allowing the flywheel 28 to continue
spinning with any remaining energy available for the next cycle. By
monitoring flywheel speed, fault conditions are detected such as a
slow motor acceleration that could be due to low battery voltage,
motor degradation or a stuck clutch. Similarly, by detecting an
actuation time-out, the failure of the clutch drive assembly 64 to
engage is detected, preventing jamming of the tool 10 if attempting
to cycle again.
[0132] By virtue of the foregoing, a portable tool 10 provides a
consistent drive in a single stroke, yet efficiently uses
electrical power from the battery 22 without detrimental surges by
using a DC motor 24 to accelerate a flywheel 28. Moreover,
consistent drives are ensured across a range of battery voltages
and component tolerance variations (e.g., clutch wear). The
consistent rotary sensing and control of a rotary member (e.g.,
flywheel 28) has application more broadly to hand tools in
accurately and robustly setting a desired speed.
[0133] While the present invention has been illustrated by
description of several embodiments and while the illustrative
embodiments have been described in considerable detail, it is not
the intention of the applicant to restrict or in any way limit the
scope of the appended claims to such detail. Additional advantages
and modifications may readily appear to those skilled in the art.
For example, aspects of the invention are applicable to other
sources of power, such as corded power tools or pneumatic power
tools. As another example, although a programmed approach is
described herein, it will be appreciated that digital logic or
analog controls may be used.
[0134] As a further example, although a noncontact speed sensor is
disclosed, applications of the present invention may include other
types of speed sensing. For instance, an optical encoding approach
may be used, weigan sensor, variable reluctance sensors, Hall
effect sensors, feedback from the motor such as a tachometer
signal, and other techniques.
[0135] As yet a further example, the described control circuit 800
employs a battery voltage VBATT having a nominal value with
resistors and a zener diode Z1 being used to step down the battery
voltage to the power supply voltage VDD. However, it will be
appreciated that a power supply (e.g., a switching power supply)
capable of regulating the voltage to the integrated circuit
components may be used while providing a battery voltage signal to
a processor. Thereby the processor may adapt its command, timing,
and other features to accommodate a wider range of battery voltage,
thus extending service life. For instance, a processor having
additional available inputs such as an 18-pin processor, model
PIC16C71 may be used.
[0136] As an addition example, a speed adjustment circuit may
employ other types of voltage references, such as a sized digital
resistor. In addition, the processor may calculate or lookup in a
table a digital reference against which the sensed speed signal is
compared.
[0137] As another example, although a specific safety and trigger
sequence is described, other sequences and time-out schemes may be
employed. Moreover, even a single trigger scheme without a safety
may be employed.
* * * * *