U.S. patent application number 12/667143 was filed with the patent office on 2010-09-09 for noise elimination brake for automatic spindle locking mechanism.
Invention is credited to Daniel Brogli, Yeo Joanne, Chi Hoe Leong, Thomas Mathys, Andreas Schwieger, Eng Hock Tan, Olivier Zeiter.
Application Number | 20100224382 12/667143 |
Document ID | / |
Family ID | 38740301 |
Filed Date | 2010-09-09 |
United States Patent
Application |
20100224382 |
Kind Code |
A1 |
Leong; Chi Hoe ; et
al. |
September 9, 2010 |
NOISE ELIMINATION BRAKE FOR AUTOMATIC SPINDLE LOCKING MECHANISM
Abstract
A rotary power tool of the invention has a motor, a motor shaft
driven by the motor, an output shaft coupled to the motor shaft via
an automatic spindle locking mechanism, a housing portion
surrounding the output shaft, and a braking member that is
non-rotatable relative to the housing portion. The braking member
exercises a braking torque on the output shaft whenever it
rotates.
Inventors: |
Leong; Chi Hoe; (Bayan
Lepas, MY) ; Joanne; Yeo; (Penang, MY) ; Tan;
Eng Hock; (Penang, MY) ; Mathys; Thomas;
(Lyss, CH) ; Zeiter; Olivier; (Biberist, CH)
; Brogli; Daniel; (Penang, MY) ; Schwieger;
Andreas; (Penang, MY) |
Correspondence
Address: |
RONALD E. GREIGG;GREIGG & GREIGG P.L.L.C.
1423 POWHATAN STREET, UNIT ONE
ALEXANDRIA
VA
22314
US
|
Family ID: |
38740301 |
Appl. No.: |
12/667143 |
Filed: |
May 30, 2008 |
PCT Filed: |
May 30, 2008 |
PCT NO: |
PCT/EP08/56658 |
371 Date: |
May 3, 2010 |
Current U.S.
Class: |
173/164 |
Current CPC
Class: |
B25F 5/001 20130101 |
Class at
Publication: |
173/164 |
International
Class: |
E21B 3/00 20060101
E21B003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2007 |
EP |
07111436.7 |
Claims
1-11. (canceled)
12. A rotary power tool comprising: a motor; a motor shaft driven
by the motor; an output shaft coupled to the motor shaft via an
automatic spindle locking mechanism; a housing portion surrounding
the output shaft; and a braking member that is non-rotatable
relative to the housing portion, which the braking member exercises
a braking torque on the output shaft whenever the output shaft
rotates.
13. A rotary power tool according to claim 12, wherein the output
shaft is stabilized by at least two bearing members and the braking
member is positioned between the at least two bearing members.
14. A rotary power tool according to claim 12, wherein the braking
member is ring-shaped and contacts the output shaft along its inner
surface.
15. A rotary power tool according to claim 13, wherein the braking
member is ring-shaped and contacts the output shaft along its inner
surface.
16. A rotary power tool according to claim 12, wherein the braking
member is in direct contact with the housing portion.
17. A rotary power tool according to claim 15, wherein the braking
member is in direct contact with the housing portion.
18. A rotary power tool according to claim 12, wherein the braking
member and the housing portion are coupled by an interference
fit.
19. A rotary power tool according to claim 17, wherein the braking
member and the housing portion are coupled by an interference
fit.
20. A rotary power tool according to claim 12, wherein an inner
surface of the braking member has a chamfer-shaped surface.
21. A rotary power tool according to claim 20, wherein an inner
surface of the braking member has a chamfer-shaped surface.
22. A rotary power tool according to claim 12, wherein an outer
surface of the braking member has a structure complimentary with an
inner surface of the housing portion.
23. A rotary power tool according to claim 21, wherein an outer
surface of the braking member has a structure complimentary with an
inner surface of the housing portion.
24. A rotary power tool according to claim 12, wherein the braking
torque is of sufficient magnitude so that in an absence of an
external torque urging the output shaft to rotate, a rotating
velocity of the output shaft is always less than or equal to a
rotating velocity of the motor shaft.
25. A rotary power tool according to claim 23, wherein the braking
torque is of sufficient magnitude so that in an absence of an
external torque urging the output shaft to rotate, a rotating
velocity of the output shaft is always less than or equal to a
rotating velocity of the motor shaft.
26. A rotary power tool according to claim 12, wherein the braking
member is made of a flexible non-metal material.
27. A rotary power tool according to claim 25, wherein the braking
member is made of a flexible non-metal material.
28. A rotary power tool according to claim 12, wherein the braking
member is composed of felt.
29. A rotary power tool according to claim 27, wherein the braking
member is composed of felt.
30. A rotary power tool according to claim 12, wherein the braking
member is composed of plastic, rubber or foam.
31. A rotary power tool according to claim 27, wherein the braking
member is composed of plastic, rubber or foam.
Description
PRIOR ART
[0001] The present invention relates to rotary power tools and in
particular those tools which are configured with an automatic
spindle locking mechanism (ASLM). When the motor is inactive, an
ASLM blocks a rotary tool output shaft from rotating in response to
an external applied torque, for example resulting from rotation of
a tool-holding chuck coupled to the output shaft. Through the years
many different coupling arrangements have been employed, but
usually the structure is such that rotation of the motor shaft will
drive the output shaft, but rotation of the output shaft will not
drive the motor shaft, and instead leads to engagement of the
ASLM.
[0002] The motor shaft and output shaft of a power tool with an
ASLM are typically coupled but with some rotational play remaining
between the coupling parts. An undesirable consequence of this ASLM
configuration arises when the motor shaft slows after the motor has
been shut off. Due to its inertia, the output shaft tends to
overtake the slowing motor shaft. Relatively speaking, an output
shaft that is rotating faster than the motor shaft is in effect
attempting to drive the motor shaft, and this leads to engagement
of the ASLM. The locking action triggers a reactive force which
slows the output shaft and disengages the ASLM. However the motor
shaft continues to slow down more rapidly until its speed is once
again less than the output shaft, and the process repeats. Repeated
engagements, disengagements, and reengagements generate an
undesirable chattering noise.
[0003] U.S. Pat. No. 6,311,787 describes several means for
counteracting this phenomenon, including an automatic brake and an
automatic drag system. These are mediated by output shaft-coupled
members which make frictional contact either with housing-coupled
members or with motor shaft-coupled members, respectively. In both
cases, this serves to slow the rotation of the output shaft
relative to the motor shaft so that the frequency of chattering
noise is reduced or eliminated altogether.
ADVANTAGES OF THE INVENTION
[0004] A disadvantage of the prior art solution is that the
described structures comprise integral aspects of the design, and
they cannot be readily incorporated into an existing rotary power
tool without requiring an extensive redesign. What is needed is a
simpler and less expensive means of achieving a similar outcome,
and particularly a solution that can be implemented on an existing
rotary power tool design, thereby requiring no redesign of the
power train. It is also advantageous if the invention provides for
an intuitive and predictable adjustment, so that the process of
optimizing the solution for a particular rotary power tool is
simplified.
[0005] These advantages are realized by providing a rotary power
tool comprising a motor, a motor shaft driven by the motor, an
output shaft coupled to the motor shaft via an ASLM, a housing
portion surrounding the output shaft, and a braking member that is
non-rotatable relative to the housing portion, wherein the braking
member exercises a braking torque on the output shaft whenever it
rotates. This invention can be conveniently retrofitted to existing
rotary power tools without requiring a detailed redesign.
[0006] If the output shaft is stabilized by at least two bearing
members, a preferred and advantageous place for incorporating the
braking member is in a position between the two bearing members,
since this provides greater consistency to the amount of braking
torque exercised by the braking member on the output shaft.
[0007] For ease of assembly, it is advantageous if the braking
member is ring-shaped, thereby allowing the output shaft to
position it radially. This shape is also preferable for ensuring
consistent and uniform contact with the output shaft and the
housing portion via its inner ring surface and outer ring surface,
respectively.
[0008] It is advantageous if the braking member is in direct
contact with the housing portion to provide means for immobilizing
the braking member relative to the rotating output shaft.
[0009] This contact is advantageously accomplished via an
interference it (i.e., a friction fit), since this requires no
additional coupling parts, provides some flexibility and tolerance
during assembly and minimizes assembly and material costs.
[0010] It is advantageous if the braking torque exercised by the
braking member is of sufficient magnitude so that in the absence of
an external torque urging the output shaft to rotate, the rotating
velocity of the output shaft is always less than or equal to the
rotating velocity of the motor shaft. When this is the case, all
chattering noise created by the ASLM is eliminated.
[0011] It is advantageous when optimizing the design to pursue a
braking torque that is neither too small nor too great to achieve
the correct balance between removing the chattering noise without
dissipating too much power. A predictable way of optimizing the
forces of friction and adhesion is by adjusting the width of the
inner surface of the braking member independently of the overall
width by providing this inner surface with a chamfer-shape.
[0012] An additional way that the braking member can be kept in
non-rotational contact with the housing portion is by providing the
outer surface of the braking member with a structure that is
complimentary with an inner surface of the housing portion.
[0013] So that the braking member can be easily fitted to the
housing by an interference fit and not require additional members
to stabilize the braking member against rotation, the braking
member is advantageously composed of a flexible, non-metal
material, such as felt, plastic, rubber or foam. In comparison with
metals, these materials may have lesser material and manufacturing
costs.
DRAWINGS
[0014] FIG. 1 is a schematic section view of a portion of a rotary
tool according to the present invention.
[0015] FIG. 2 is a partial schematic section view taken along
section line A-A of FIG. 1.
[0016] FIG. 3 is a perspective view of a braking member according
to a first embodiment of the invention.
[0017] FIG. 4 is a perspective view of a braking member according
to a second embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] A portion of a rotary power tool and particularly a
drill/driver according to the present invention is illustrated in
schematic form in FIG. 1. The power source for such tools is
typically either AC current or a DC battery. Positioned within the
housing 10 of the rotary power tool are a motor 12 driven by this
power source and its associated motor shaft 14.
[0019] As is typical, a transmission 16 modulates the speed and
torque conveyed by the motor shaft 14 to downstream elements in the
power train.
[0020] An automatic shaft locking mechanism (ASLM) 18 is positioned
downstream of the transmission 16. ASLM's are well known in the
art, and the details of how they operate will not be described in
detail in the present description. For examples of different
ASLM's, readers are referred instead to U.S. Pat. No. 6,311,787 and
U.S. Patent Publication No. 2006/0131043 A1 which are hereby
incorporated by reference. As is typical in the art, the
transmission 16 may not necessarily be discrete from the ASLM 18.
That is, there may be components that function as both part of the
transmission 16 and the ASLM 18.
[0021] Downstream from the ASLM 18 is an output shaft 20. The
output shaft 20 may interact directly with the ASLM 18 or it may be
coupled to one or more other elements in between.
[0022] A housing portion 28 comprises the portion of housing 10
that is coaxial with and surrounds the output shaft 20. The output
shaft 20 is coupled with this housing portion 28 via two
ring-shaped ball bearings 22 and 24 which serve to stabilize the
shaft. At the end of the output shaft 20 is an output interface 26
for attaching a tool holder such as a drill chuck or the like.
Alternatively tools can be attached directly to the output shaft 20
itself.
[0023] A braking member comprising a felt ring 30 is positioned
between the two ball bearings 22 and 24. It surrounds the output
shaft 20 and preferably is secured by an interference (friction)
fit with housing portion 28. The resulting friction between the
felt ring 30 and the housing portion 28 is much greater than the
friction between it and the output shaft 20. As a result, the
braking member will not rotate relative to the housing portion 28
when the output shaft 20 is rotating at typical operating speeds in
the range of 400-1400 RPM. The friction can be of sufficient
magnitude so that no means for maintaining the position of the
braking member in the axial direction are necessary. However, even
if the braking member were free to move axially, the bearings 22
and 24 would serve to confine the braking member to the generally
appropriate axial location around the output shaft 20, which is
preferably at any axial point that is between the two bearings. Any
friction resulting from contact of the braking member with the side
of the ring-shaped ball bearing 22 is negligible in comparison to
the frictional force exerted on the output shaft 20.
[0024] It is preferred that the braking member is positioned in the
space between the bearings 22 and 24, but it may alternatively be
positioned outside of them provided there is sufficient axial space
to accommodate the braking member and there is no interference with
other structures.
[0025] The felt ring 30 is seen in isolation in FIG. 3 and is
characterized by an inner diameter 32, an outer diameter 34, and a
thickness 36. The inner diameter 32 and the outer diameter 34 are
chosen so as to satisfy the preferred frictional conditions
discussed above. However, particular care has been taken to adjust
the inner diameter 34 so as to control the frictional force between
the inner surface 38 of the felt ring 30 and the output shaft 20.
In a preferred scenario, this braking torque is just exactly enough
so that the down-coasting velocity of the output shaft 20 is slowed
to a rate exactly equal to that of the motor shaft 14. When this
condition is satisfied, there is no engagement of the ASLM 18 when
the power is cut to the motor.
[0026] However, this preferred scenario does not define the
preferred embodiment, since with repeated use of the tool, there is
wear on the felt ring 30, and this may alter the amount of friction
between the braking member and the output shaft 20. In our tests,
we find that the frictional force decreases with repeated use.
Therefore the preferred embodiment has just enough friction to
compensate for anticipated decreases in friction due to wear over
the lifetime of the tool. In our tests, it appears that the
frictional force decreases approximately 20 to 45% over the tool
lifetime.
[0027] Though not described explicitly above, it is understood that
too much friction between the braking member and the output shaft
20 is undesirable. As is well known, friction causes power to be
dissipated as heat without providing mechanical advantage. As such
it is desirable to minimize the frictional force. Also, while a
secure friction fit is desirable, too great an outer diameter 34
makes it more difficult to assemble the housing halves that
comprise the housing portion 28 surrounding the braking member.
[0028] Even a bearing that is designed to minimize friction will
exert some frictional force on a shaft that it is supporting,
thereby exerting a theoretical braking torque on the shaft. The
braking member described here is not intended to provide support
for the output shaft 20. It is intended to be of inexpensive
construction, and is designed not for minimizing friction, but for
introducing friction. The amount of braking torque it exerts is
preferably adjustable and the alternative embodiment described
below provides one manner of achieving precision in controlling
this parameter during design of the tool. A second embodiment for a
braking member, comprising an elastic ring 40 made of soft
resilient material is shown in isolation in FIG. 4. The elastic
material may be a rubber, such as nitrile butadiene rubber (NBR), a
plastic, such as acetal polyoxymethelene (POM), or a cellular
urethane foam, such as Poron.RTM. (a registered U.S. trademark of
Rogers Corporation), each of which could have the appropriate
combination of elasticity and strength to serve as the braking
member.
[0029] Note that the outer surface 41 of the elastic ring 40 is
configured to have what can be generally characterized as
protrusions 42 and recesses 44. In this case, these features are
intended to cooperate with complementary recesses 46 and
protrusions 48 respectively that may be present on the inner
surface 49 of the housing portion 28 (see FIG. 2). Such cooperation
would potentially lessen the extent to which a friction fit between
the elastic ring 40 and the housing portion 28 is necessary.
[0030] Alternative means for securing the braking member against
rotation include configuring the housing portion 28 with pin-like
structures (not shown) that would puncture and deeply penetrate the
braking member during the housing assembly process. Alternatively,
even if the housing portion 28 is configured with recesses 46 and
protrusions 48, a braking member without cooperating features can
be used (see FIG. 3) since the braking member is composed of
compliant material. In any case, through whatever means, it is
preferred that the braking member does not rotate during operation
of the rotary tool, since this results in wear on the braking
member and housing portion 28, heat generation, and adds
variability to the system, so that it may be more difficult to make
predictions when optimizing the braking member dimensional
parameters.
[0031] Protrusions and recesses could also be provided on the felt
ring 30. However this may be more complicated or costly from a
manufacturing standpoint versus an elastic ring 40 which can be
made from a variety of materials that lend themselves well to
injection molding. Hence when more complicated surface contours are
desired, the braking member is preferably manufactured from
moldable materials.
[0032] Changing the contact area with the output shaft 20 by
varying the inner surface 50 of elastic ring 40 is one way to
optimize the amount of braking provided by the brake member. The
inner surface 50 of the elastic member 40 can be chamfered to
create a chamfered surface 52. Alternatively such a surface, though
only appearing to be chamfered, can be achieved through injection
molding. This rather simple constructional manipulation allows one
to make predictions in adjusting the braking torque since the
forces of friction and/or adhesion appear to be related to the
contact area between the braking member and the output shaft
20.
* * * * *