U.S. patent number 3,766,990 [Application Number 05/151,329] was granted by the patent office on 1973-10-23 for low torque automatic screwdriver.
Invention is credited to Richard E. Eckman, James C. Mitchell.
United States Patent |
3,766,990 |
Eckman , et al. |
October 23, 1973 |
LOW TORQUE AUTOMATIC SCREWDRIVER
Abstract
A pneumatic powered screwdriver adapted for moderately high
speed operation and automatic shutoff at relative low torque
turning resistance. An axially disengagable clutch unit
intermediately couples the motor drive to the output drive bit.
Contained in the clutch unit is a sear or cutoff member which is
cam shifted radially in response to clutch disengagement for
enabling air supply interruption to the motor.
Inventors: |
Eckman; Richard E. (Houston,
TX), Mitchell; James C. (Houston, TX) |
Family
ID: |
22538265 |
Appl.
No.: |
05/151,329 |
Filed: |
June 9, 1971 |
Current U.S.
Class: |
173/178;
192/150 |
Current CPC
Class: |
B25B
23/145 (20130101) |
Current International
Class: |
B25B
23/14 (20060101); B25B 23/145 (20060101); B25b
023/14 () |
Field of
Search: |
;173/12 ;192/150 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Purser; Ernest R.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A powered screwdriver comprising in combination:
a. an air motor having an inlet at which to receive a source of
high pressure supply air;
b. a drive end for work engagement with a fastener member to be
rotationally driven;
c. a clutch operative to couple the output of said motor to said
drive end and operative to effectively uncouple said drive end from
said motor output at an encountered fastener turning resistance
corresponding to a torque of predetermined value; and
d. disconnect means operative concomitantly and in parallel with
the uncoupling of said clutch to effect interruption of air supply
to said motor, said disconnect means including:
1. a shutoff valve in said air inlet adapted to open and close the
air supply to said motor;
2. a slidable throttle rod for operating said shutoff valve between
its open and closed positions;
3. sear means movable radially relative to the axis of tool
rotation between a first position effectively cocking said throttle
rod against movement in a direction for closing said valve and a
second position enabling said rod movement for closing said valve;
and
4. first cam means on said drive end operably independent of the
operation of said clutch for shifting said sear means from said
first to said second position.
2. A powered screwdriver according to claim 1 in which the centroid
of said sear is displaced from the axis of tool rotation whereby
rotational forces aid to maintain said sear in said first
position.
3. A powered screwdriver according to claim 2 in which said sear is
supported transversely intersecting the axis of said tool with its
centroid definitively located to one side of said axis and there is
included biasing means acting against said sear directionally of
said centroid urging the sear into said first position.
4. A powered screwdriver according to claim 3 in which said cam
means is rotationally supported on the axis of said tool and
includes a plurality of lobes displaced at angular intervals about
its periphery, at least one of said lobes being effective
concomitantly with uncoupling of said clutch to radially shift said
sear means from said first to said second positions in opposition
to said biasing means.
5. A powered screwdriver according to claim 4 in which said
throttle rod is supported on the axis of said tool extending
through an axially parallel bore in said sear means, said bore
being located radially offset with respect to said tool axis while
said sear means is in said first position to effect cocking of said
throttle rod and is shifted to relatively approach axial
coincidence when said sear means is shifted to said second position
for uncocking of said throttle rod.
6. A powered screwdriver according to claim 5 in which said
throttle rod includes a radial wall adjacent said sear means, and a
wall segment of said sear means contiguous to said bore axially
interferes with said throttle rod wall to effect said throttle rod
cocking.
7. A powered screwdriver according to claim 6 including a housing
supportably enclosing said motor, said drive end, said clutch and
said disconnect means, and in which said drive end is axially
slideable inward of said housing in response to a pressing work
engagement against a fastener to be driven and said throttle rod is
axially moveable in conjunction with said drive end to effect
opening of said shutoff valve.
8. A powered screwdriver according to claim 7 in which said
throttle rod operatively moves inwardly toward said drive end to
effect closing of said shutoff valve in response to shifting of
said sear means to said second position.
9. A powered screwdriver according to claim 8 including biasing
means to operatively effect a driving relation between said motor,
said drive end, said clutch and said disconnect means at the onset
of work engagement with a fastener and to restore said driving
relation on post-torqued removal from work engagement with the
fastener.
10. A powered screwdriver according to claim 1 in which said clutch
comprises a first annular member having a plurality of lobes
displaced at angular intervals about a radial face of said member
with adjacent of said lobes defining an axial recess therebetween,
a second annular member having a plurality of axial cutouts
circumferentially opposite the recesses of said first member,
interfitting means extending between each of said opposite recess
and cutout to effect a rotational coupling relation between said
first and second members, biasing means acting to urge one of said
members toward the other for maintaining said coupling relation and
second cam means operative to uncouple said first and second
members in response to encountering of said predetermined torque
value by said drive end.
11. A powered screwdriver according to claim 10 in which said
interfitting means comprise balls and said second cam means is
defined by a surface pitch merging at least one common end of said
recesses to its contiguous lobe.
12. A powered screwdriver according to claim 11 in which said first
annular member is operatively connected to said motor and said
second annular member is operatively connected to said drive
end.
13. A powered screwdriver according to claim 11 in which the
centroid of said sear is displaced from the axis of tool rotation
whereby rotational forces aid to maintain said sear in said first
position.
14. A powered screwdriver according to claim 13 in which said sear
is supported transversely intersecting the axis of said tool with
its centroid definitively located to one side of said axis and
there is included second biasing means acting against said sear
directionally of said centroid urging the sear into said first
position.
15. A powered screwdriver according to claim 14 in which said first
cam means is rotationally supported on the axis of said tool and
includes a plurality of lobes displaced at angular intervals about
its periphery, at least one of said lobes being effective
concomitantly with uncoupling of said clutch to radially shift said
sear means from said first to said second positions in opposition
to said second biasing means.
16. A powered screwdriver according to claim 15 including a housing
supportably enclosing said motor, said drive end, said clutch and
said disconnect means, and in which said drive end is axially
slideable inward of said housing in response to a pressing work
engagement against a fastener to be driven, and said throttle rod
is axially moveable in conjunction with said drive end to effect
opening of said shutoff valve.
17. A powered screwdriver according to claim 16 in which said
throttle rod operatively moves inwardly toward said drive end to
effect closing of said shutoff valve in response to shifting of
said sear means to said second position.
18. A powered screwdriver according to claim 17 including biasing
means to operatively effect a driving relation between said motor,
said drive end, said clutch and said disconnect means at the onset
of work engagement with a fastener and to restore said driving
relation on post-torqued removal from work engagement with the
fastener.
Description
BACKGROUND OF THE INVENTION
The field of art to which the invention pertains includes the art
of driving tools having a clutch for power stop control.
Powered screwdrivers of various types and capacities are well-known
and have been commercially used for many years. Popular among
consumers of such tools are those specifically adapted to interrupt
the power supply for automatic shutoff in contrast to those which
slip or ratchet on encountering a turning resistance of preset
torque value. Marketed tools exemplifying the shutoff type are
disclosed in U.S. Pat. Nos. 2,964,151; 2,986,052; and 3,242,996,
all of which have met with a large measure of commercial
success.
While fundamentally similar in purpose, construction of these
various shutoff tools is sufficiently different in order to render
each of them operationally suitable for their specific use
applications. As might be expected, tools suitable for torque
sensitivity on the order of 40 inch pounds and above are
substantially bulkier and heavier than such tools suitable for
delicate work requiring torque sensitivities on the order of 11
inch pounds and below. Moreover, by virtue of their respective
constructions, the higher torque tools are generally capable of
high speed operation on the order of 3,000 rpm whereas the low
torque tools have heretofore been subject to speed sensitivity
causing them to endure low speed limitations on the order of 1,000
rpm. Where used for mass production assembly, tool speed is
regarded as a significant factor in contributing toward the rate of
production output. Consequently, it has long been desired to
increase the speed of low torque tools, yet retain their
compactness and light weight features compatible with use on
delicate type work.
SUMMARY
This invention relates to pneumatically powered screwdrivers of the
automatic shutoff type suitable for low torque conditions of use.
More specifically, the invention relates to such low torque
screwdrivers capable of at least medium operating speeds on the
order of about 2,000 rpm and above while essentially retaining the
compactness and light weight features previously characteristic of
such tools. This is obtained in accordance herewith by means of a
novel clutch-cutoff construction connecting the motor output to the
drive bit. The clutch provides positive torque responsive
engagement and disengagement which is substantially insensitive to
speed at which the tool is operative. Without speed sensitivity,
previously imposed speed limitations are overcome thereby extending
the operational speed range for which such tools can be
constructed.
It is therefore an object of the invention to provide a novel
construction for powered screwdrivers of the automatic shutoff
type.
It is a further object of the invention to provide a novel
construction for an automatic shutoff powered screwdriver suitable
for low torque operation but capable of higher speed operation than
such similar purpose tools of the prior art.
It is a further object of the invention to provide a novel
construction for a low torque powered screwdriver as in the
aforementioned objects while essentially retaining the basic
compactness and light weight features characteristic of such tools
for delicate work suitability.
It is a still further object of the invention to provide a novel
power driven clutch mechanism for use in low torque powered
screwdrivers.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal view partially in section of a tool in
inoperative relation incorporating the construction hereof;
FIG. 2 is a fragmentary longitudinal section view of the tool of
FIG. 1 in its operative relation;
FIG. 3 is an enlarged longitudinal view partially in section of the
clutch mechanism;
FIG. 4 is an enlarged longitudinal fragmentary section through the
tool drive corresponding to the inoperative relation of FIG. 1;
FIG. 5 is a sectional elevation viewed substantially along the
lines of 5--5 of FIG. 4;
FIG. 6 is a sectional elevation viewed substantially along the
lines 6--6 of FIG. 4;
FIG. 7 is an enlarged longitudinal fragmentary section through the
tool drive corresponding to the operative relation of FIG. 2;
FIG. 8 is a sectional elevation viewed substantially along the
lines 8--8 of FIG. 7;
FIG. 9 is an enlarged longitudinal fragmentary section through the
tool drive in its post-torqued operative relation corresponding to
FIG. 2;
FIG. 10 is a sectional elevation viewed substantially along the
lines 10--10 of FIG. 9;
FIG. 11 is an enlarged isometric view of the cutoff sear as
enclosed within the dashed outlined in FIG. 4; and
FIG. 12 is a partial plan view as seen from the position 12--12 of
FIG. 1.
Referring now the drawings and specifically to FIGS. 1 and 2, the
tool hereof is generally comprised of an elongated longitudinal
housing formed of a rear section 11 enclosing the drive components
and telescopically threaded to a front section 13 enclosing the
work engaging and torque responsive elements. Within the latter is
included a screwdriver bit or the like 14 secured in output shaft
17 for rotationally driving a screw or other similar type fastener
element 15. It is understood of course that various forms of bits
can be substituted for that shown as required, including but not
limited to Phillips head, Allen head, socket, etc. Tool drive is
furnished by a conventional vane-type pressure fluid motor (not
shown) contained in housing section 11 and operationally supplied
with high pressure air received at inlet 18. Output from the motor
is transmitted to screwdriver bit 14 via an intermediate clutch
mechanism 19 to be described.
Tool actuation is initiated by a guide piece 22 adapted to engage
screw 15 and slideably contained within the necked-down work end 23
of housing section 13. For these purposes, there is provided a key
24 which rotationally interlocks the guide piece to work end 23,
but permits slideable inward movement thereof. Inward movement is
opposed by coil spring 26 and is limited in both directions to the
extent afforded by longitudinal key slot 25 as can be best
understood by contrasting the guide piece relation in FIGS. 1 and
2. Rearward guide piece displacement permits bit 14 to engage screw
15. Since the bit shank 36 is detachably mounted via a ball detent
37 to the full depth of output shaft bore 38, further rearward
movement carries with it clutch 19 and a throttle rod 40 for
admitting air received at inlet 18.
For a more detailed understanding of the various operating
components, attention is now also directed to FIGS. 3-8. As
thereshown, air inlet 18 is contained in a connector 28 screw
threaded to the rear of housing section 11 and fit pressure tight
with respect thereto by means of an annular o-ring seal 29. Fluid
pressure admitted through the connector is communicated into an
enclosed chamber 30 whereat it is exposed to the back face of
conically shaped throttle and shut-off valve 31. The shut-off valve
cooperates with an annular seat 32 for controlling fluid flow into
a chamber 33 which in turn feeds passage 34 for supplying air into
a motor inlet port 35. Opening and closing of valve 31 is governed
by axially slidable throttle rod 40 diametrically enlarged at 41,
reduced again at 42 and enlarged again at 43. The latter end is
received in axial bore 48 of output drive shaft 17 subjecting the
rod to urging in the other direction by compressed coil spring 50
in chamber 30 acting against the back face of valve 31. Air exhaust
is through muffler 44 and exhaust ports 45.
The motor is connected to a planetary gear train (not shown) the
output of which is rerpresented by a shaft 51 journalled in ball
bearing 52. Shaft 51 includes a central axial bore 53 of hexagonal
cross section in which to slidably receive a hexagonal input stub
shaft 54 of clutch 19 for a rotational driving interlock
therebetween. Clutch output, as will be described below, is through
radially extending annular flange 58 integral with a rearward
reduced diameter portion 59 of shaft 19. The latter shaft portion
is further reduced at its terminal end 60 at which it is formed of
polygonal cam acting cross section, preferably square, extending
inward of clutch 19 for reasons as will be understood.
Clutch 19, for rotatable coupling to output shaft 17, includes a
body 63 having a central bore 64 through which to slideably receive
section 41 of throttle rod 40. A counterbore 65 receives output
shaft section 59 to which it is axially coupled but rotatably free
by means of a plurality of small diameter balls 66. The balls are
adapted to seat between annular shaft groove 67 and corresponding
annular clutch groove 68 and are supplied for that purpose through
a radial bore 69 whereat they are retained by means of an
encircling spiral type spring retainer 70.
To transmit drive from the motor output to shaft 17 the leftward
end of clutch 19 (as viewed in the drawings) includes a cam 74
having a plurality of lobes 75. The lobes extend axially leftward
facing toward shaft 17 at angularly displaced intervals radially
outward of the shaft. Intermediate adjacent lobes, the cam is
axially recessed at 76 to receive a hardened steel ball 77. At its
circumferential ends each recess forms a rise 78 of gradual pitch
effective for screw tightening and an opposite rise 79 of
comparatively steeper pitch effective for reverse tool operation as
for untightening of a screw or the like. Balls 77, in turn, extend
axially inward of a plurality of radially open slots 82 formed in
shaft flange 58 and angularly matched to the location of cam
recesses 76.
For radially confining the balls while maintaining coupling
engagement between cam 74 and flange 58 there is provided a cup
shaped ball cage-retainer 83 constantly urged axially rearward by
means of a coil spring 84. The spring is axially compressed between
a follower 85 acting through thrust bearing 86 against the back
side of retainer 83 and an opposite follower 87 (FIG. 1) axially
slideable but rotationally secured to shaft 17 by means of opposite
keys 88. By this means, so long as a screw 15 is being free run
into torque position, balls 77 maintain clutch 19 rotationally
coupled to shaft 17. Upon encountering a turning torque resistance
at which the tool was set to operate, relative rotation begins to
occur between flange 58 and cam 74. At that point each ball 77
follows its respective cam rise 78 in forcing follower 85 and
bearing 86 increasingly rearward away from the cam in opposition to
spring 84 until coupling disengagement results.
Concomitantly operative with of clutch 19 but operably independent
disengagement thereof for effecting power interruption is a
radially movable sear or release pin 91 (see also FIG. 11) in a
radially extending cylindrical cavity 90 of body 63. The sear is
generally cylindrical, geometrically formed as to place its
centroid location 100 radially displaced from the rotational tool
axis 101. To achieve centroidal displacement, the pin as it appears
includes a relatively small top mass 102 and a comparative larger
bottom mass 103. Likewise, as arranged, the pin includes side faces
92 and 93 and a lateral bore 94 axially parallel to tool axis 101
and of diameter sufficient when appropriately positioned to
slideably pass throttle rod diameters 41 and 42. Inward of face 92
is a slot cutout 95 v-shaped at its top forming an apex 96 being
urged against the side flat 61 of shaft end 60 by means of
compressed coil spring 98.
On tool startup pin apex 96, by virtue of force exerted by spring
98, remains engaged with a shaft side flat 61 of shaft end 60. This
places a short segment 97 of pin side face 93 backed up to the
radial end face 99 of throttle rod portion 41 for precluding any
leftward movement thereof. With the pin mass center 100 being
eccentrically located opposite apex 96 relative to axis 101,
centrifugal force generated by tool rotation acts continuously in a
direction aiding spring 98 for maintaining apex 96 in the latter
relation. When, however, clutch disengagement occurs on the set
torque being encountered permitting rotation of shaft 17 relative
to the motor output being supplied to clutch 19, the same relative
rotation transmits a parallel reaction via corner 62 of shaft end
60 engaging apex 96 to shift pin 91 radially upward against spring
98 as best seen in FIGS. 9 and 10. On shifting of the pin, the axis
of bore 94 is similarly shifted to free rod 40 of leftward
interference and permitting axial movement leftward therethrough.
With the pin thus positioned, fluid force acting on the backside of
shutoff valve 31 assisted by spring 50 forces rod 40 leftward to
compress spring 49 until valve 31 seats to immediately interrupt
the motor drive. Spring 84 then acts to reset clutch balls 77
within their respective cam recesses 76. Valve 31 and rod 40 remain
in the closed position while clutch 19 remains rearward. On
subsequently removing the tool, springs 26, 49 and 98 restore the
components to their original startup relation of FIGS. 1 and 4.
Fluid pressure aided by spring 50 holds valve 31 against seat 32
while spring 49 urges guide piece 22 and consequently clutch 19
leftward allowing all components to reset.
In order to preset the torque valve at which clutch disengagement
is to be effected, there is provided an adjustment nut 106 as seen
in FIGS. 1 and 12 screw threaded onto shaft 17. Nut 106 has a
serrated radial end 107, facing toward angularly displaced pockets
108 in the back side of spring follower 87. Contained in the
uppermost pocket is a hardened steel ball 109 adapted to normally
seat in a serration valley 110 of the nut face. By means of a slot
112 formed in housing 13 in the vicinity of nut 106 access is
provided thereto whereby a Phillips screwdriver end or the like can
be inserted into an adjacent nut serration. Rotating the nut in
either direction will threadably advance or withdraw the nut along
shaft 17. This respectively increases compression or relaxation of
spring 84 in maintaining the desired coupling force to be overcome
in effecting clutch disengagement between shaft flange 58 and
clutch cam 74. A rotatably displaceable spring clip 113 normally
covers slot 112 and can be rotated for exposing nut 106 to render
adjustment in the manner just described.
In operation, the tool is supplied by flexible conduit or the like
with high pressure air from a suitable source connected to inlet
18. On pressing guide piece 22 against a fastener such as a screw
15, the tool is automatically centered on the fastener while guide
piece 22 is caused to slide axially rearward for the fastener to be
engaged by screwdriver bit 14. Continued pressing engagement
therebetween forces the screwdriver bit rearward carrying with it
drive shaft 17, clutch 19 and the operating components secured
thereto. Simultaneously, the same rearward movement likewise forces
throttle valve rod 40 rearward to open valve 31 whereby fluid
pressure in chamber 30, is admitted to chamber 33, passage 34 and
motor port 35 for energizing the motor. With the motor operating,
its output shaft 51 is caused to rotate whereby through its
connection with stub shaft 54 drive is transmitted to clutch 19. By
virtue of the engagement force imposed by spring 84, clutch balls
77 are restrained against the rise of cam pitch 78 thereby
transmitting the driving force through flange 58 to output shaft 17
and bit 14.
On screw 15 reaching its intended set torque, the turning
resistance exerted against bit 14, while the motor continues
operative, affords relative rotation between cam 74 and flange 58
forcing balls 77 axially outward on cam rise 78. Axial ball
movement in turn forces retainer cage 83 rearwardly in opposition
to the force of spring 84. With relative rotation occurring
therebetween, pin 91 is shifted by the reaction of shaft camming
corner lobe 62 against pin apex 96. By the latter, pin bore 94 is
re-positioned in cavity 90 until more nearly axially coincident
with rod section 41 permitting unimpeded axially leftward movement
of throttle rod 40. With axial throttle rod interference removed,
fluid force acting against shutoff valve 31 aided by the force of
spring 50 urges the valve in opposition to spring 49 to its shutoff
relation against seat 32. Fluid flow to the motor is immediately
interrupted as is tool rotation to complete the torquing cycle. On
tool removal from screw 15 the reacting spring forces restore the
various components to their startup relation for repeat of the
torquing cycle. For removing a screw greater cam pitch on rise 79
as compared to rise 78 increases the torque available for that
purpose and for which automatic cutoff is unnecessary.
By the above description there has been disclosed novel
construction for a power screwdriver adapted for automatic shutoff
on reaching a predetermined torque value at which the tool is
preset to operate. The novel clutch construction in accordance
herewith renders the tool readily capable of operating at low
torque values without speed sensitivity in the manner of such tools
of the prior art. To the contrary, by means of a sear disconnect
having a centroid offset from the rotational axis, tool rotation is
exploited to aid rather than impair engagement until such time as
desired torque resistance is encountered. Consequently, the
construction hereof achieves these results while retaining basic
compactness and light weight features characteristic of such tools
for delicate work suitability. At the same time, the tool instantly
affords a substantially higher torque for reverse operation as when
desired to remove a screw previously installed. Despite the
improvements afforded hereby, these features are effected in a
highly economical manner by the use of relatively simple and
inexpensive components.
Since many changes could be made in the above construction and many
apparently widely different embodiments of this invention could be
made without departing from the scope thereof, it is intended that
all matter contained in the drawings and specification shall be
interpreted as illustrative and not in a limiting sense.
* * * * *