Safety lock-off throttle device

A safety device for a fluid operated tool features a throttle lever which is always freely movable but is normally rendered inoperable to effect tool actuation except in response to a consciously deliberate two step action wherein a first valve control must be actuated before an on-off valve controlling fluid flow may be operated by a second valve control in response to throttle lever operation to drive the on-off valve from a normally closed position to an open position establishing an open fluid flow condition for tool start-up.

BACKGROUND OF THE INVENTION 
To prevent accidental start-up of fluid operated tools such as grinders, 
nutsetters, buffers and similar tools having fluid motors, efforts have 
been directed to prevent accidental throttle lever actuation which in turn 
serves to operate a valve controlling fluid flow to effect motor start-up. 
This is particularly important in tools having a generally tubular body 
connected to a source of pneumatic pressure, e.g., through an attached 
pressurized air hose wherein the hose itself may whip and roll an 
unattended tool and accidentally effect tool start-up. 
Conventional approaches to date have sought to prevent accidental tool 
start-up by locking the throttle lever. Various types of safety throttle 
release devices have been proposed which first must be operated to release 
the initially locked throttle lever to permit tool operation. 
Such known devices normally are subject to abuse and, in the event of undue 
force being applied when the throttle lever is locked against movement, 
parts damage may occur. Moreover, the known devices conventionally have an 
externally located throttle valve lock which is subject to being tampered 
with or being removed in its entirety, thereby defeating the safety 
purpose of such devices. 
It is accordingly an object of this invention to provide a safety device of 
the type described which is tamper resistant and contained within an 
overall tool envelope of minimized size to permit maximum flexibility in 
the tool application and which features a freely movable throttle valve 
control requiring a purposeful two-step operating action to effect tool 
start-up while minimizing any possibility of inadvertent or accidental 
working of the tool which may cause accidental damage or injury upon 
unintended full throttle actuation of the tool. 
BRIEF SUMMARY OF THE INVENTION 
The safety device of this invention is particularly suited for use in a 
power tool having a fluid operated motor and a fluid supply passageway 
with an on-off valve controlling the fluid flow conditions in the 
passageway. The safety device itself features first and second 
independently operable valve controls which are respectively freely 
movable between starting and actuated positions. When the first valve 
control is deliberately moved into actuated position, the second valve 
control, which may be operated, e.g., by a throttle lever, is then and 
only then drivingly engaged in its starting position to the on-off valve 
for moving it between closed and open positions responsive to movement of 
the second valve control between its starting and actuated positions. The 
second valve control is rendered ineffective to actuate the on-off valve 
when the first valve control is in its normal starting position, thereby 
preventing accidental movement of the on-off valve from its normally 
closed position, while the second valve control is always permitted to be 
freely moved between its starting and actuated positions. This invention 
further features a selectively operable, tamper resistant locking 
mechanism between the second valve control and the on-off valve which 
locking mechanism is disposed in its entirety internally of the tool 
housing. 
Other details, objects and advantages of this invention will become 
apparent as the following description of a presently preferred embodiment 
of practicing the same proceeds.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawings in detail, a power tool 10 such as a 
nutsetter and the like having a fluid operated motor, not shown, will be 
understood to have a generally tubular motor housing 12 and a handle, not 
shown, to which an air inlet bushing 14 is adapted to be attached. It is 
to be understood that a fluid motor, preferably a conventional rotary vane 
type air motor, is mounted in the motor housing 12 for driving a spindle, 
not shown, operatively connected to a work engaging element of the power 
tool. 
Compressed air for driving the motor is supplied through a coupling at the 
rear of the handle and flows through the air inlet bushing 14 and through 
a suitable inlet screen 16 in a passageway generally designated 18, 
comprising a series of passages described more specifically below, leading 
to the motor. An air inlet passage 20 in bushing 14 communicates with a 
chamber 22 jointly defined by a bushing 24, fixed in one end of a bore 26 
diametrically extending across housing 12, and by an air regulator 
assembly 28 closing the other end of bore 26. The air regulator assembly 
28 includes an inner cup-like member 30 (FIGS. 5 and 6) having a shank 32 
of reduced diameter received in a hollow plug 34 screwed into bore 26. The 
inner cup-like regulator member 30 is retained against unintended axial 
movements by bushing 24 and an O-ring 36 encircling its shank 32 and 
seated on an inner end of plug 34. 
Inlet port 38 formed in wall 40 of the cup-like member 30 of the air 
regulator assembly 28 serves to connect the air inlet passage 20 and 
chamber 22. As described more specifically below, the volume of air 
admitted into chamber 22 is governed by rotatably adjusting the position 
of the inner cup-like member 30 of air regulator assembly 28 to vary the 
effective size of inlet port 38 which serves to connect the air inlet 
passage 20 and chamber 22. Assuming a load of an established value, an 
operator therefore may vary the motor power and spindle speed to suit the 
tool application. 
A generally tubular on-off valve 42 is received in chamber 22 and is shown 
having a radial flange 44 intermediate the ends of its valve body 46 with 
an annular seal 48 mounted on one side of flange 44 for engagement with an 
inner end 50 of the bushing 24 which serves as a valve seat for the seal 
48 which serves as a valve member. In a normally closed position depicted 
in FIG. 1, seal 48 engages the valve seat 50, and one end of the valve 
body 46 extends through a central opening 52 in the inner end of bushing 
24. An opposite end of valve body 46 extends coaxially through a central 
opening 54 of inner cup-like member 30 of air regulator assembly 28 and is 
supported therein for axial reciprocating movement by a suitable O-ring 56 
encircling valve body 46 and supporting it for shifting movements in 
opposite axial directions toward and away from its illustrated normally 
closed position in FIG. 1. Seals 36 and 56 accordingly provide a fluid 
tight construction preventing air leakage to atmosphere through the 
regulator end of bore 26. 
For controlling operation of on-off valve 42, valve control means is 
provided which includes a valve pin 58 received in chamber 22 and having 
an exposed stem 60 projecting through bushing 24 and a shank 62 of reduced 
size coaxially projecting from stem 60 through bushing 24 and a 
longitudinally extending axial opening 64 in body 46 of on-off valve 42 in 
coaxial alignment with these components. 
The valve control means further includes a hollow, generally cyindrical 
lock button 66 closed at an outer end which is exposed for manual 
manipulation at the end of valve bore 26 diametrically opposed from valve 
pin stem 60. An open terminal end 68 is formed on lock button 66 and 
disposed within the confines of air regulator assembly 28 in coaxial 
surrounding relation to valve body 46 and valve pin 58. A coil compression 
spring 70 is received within the hollow confines of lock button 66 with 
opposite ends of spring 70 seated against the closed end of lock button 66 
and an adjacent terminal end of valve body 46 for biasing lock button 66 
toward its starting position shown in FIG. 1 and on-off valve 46 toward 
its normally closed position. 
Lock button 66 has an intermediate external flange 72 which in starting 
position (FIG. 1) seats on an internal shoulder 74 of plug 34. The outside 
diameter of the open terminal end 68 of lock button 66 is of reduced size 
relative to its flange 72 and to the inside diameter of air regulator 
shank 32 such that the open terminal end 68 of lock button 66 may be 
received within the confines of the inner cup-like member 30 for axial 
shifting movement toward and away from the inside shoulder 74 of plug 34 
axially within bore 26. Spring 70 will be seen to not only bias valve body 
46 toward its normally closed position, wherein it is normally held in 
position with the assistance of air pressure, but also to urge lock button 
66 toward its illustrated position in FIG. 1 which will be understood to 
be a lock button starting position. 
As best seen in FIGS. 5-8, lock button 66 has a pair of diametrically 
opposed recesses or cut outs 76 in its side wall and flange 72 for 
receiving axially extending legs 32A of shank 32 of air regulator member 
30 to provide a rotary drive connection between lock button 66 and air 
regulator member 30. I.e., upon rotating lock button 66, its flange 72 
will engage and drive the shank legs 32A of the air regulator member 30 in 
a desired angular direction thereby to adjust the size of the effective 
inlet port 38 to the chamber 22, the adjustment being facilitated by a 
screw driver slot 78 which is easily accessible to an operator at the 
exposed closed end of lock button 66. 
To actuate the motor, a hand lever 80 is pivotally supported on the housing 
12 by pin 82 and engages the projecting end of valve pin stem 60 which may 
be depressed to drive the valve pin 58 axially from its starting position 
(FIG. 1) to its actuated position (FIG. 2). A second coil compression 
spring 84 is illustrated as having its opposite ends seated on an 
underlying shoulder of stem 60 and the adjacent terminal end of valve body 
46 and coiled about shank 62 of the valve pin 58 to serve as a valve pin 
return spring which biases the valve pin toward its illustrated starting 
position of FIG. 1. 
To minimize any accidental actuation of the fluid motor by inadvertent 
depression of valve pin 58, for whatever reason, selectively operable 
releasable locking means is provided for insuring that any motor actuation 
is effectively limited to an intentional sequential operation of the 
control valve means by an operator to positively effect motor operation 
under controlled conditions. More specifically, the releasable locking 
means of this invention is provided to selectively engage and lock the 
valve pin 58 and body 46 of on-off valve 42 only after lock button 66 
first has been deliberately depressed from starting position (FIGS. 1 and 
2) by manual actuation into actuated position (FIG. 3) before the operator 
depresses hand lever 80 controlling valve pin 58. 
In the specifically illustrated embodiment, body 46 of on-off valve 42 has 
a pair of sidewall openings 85 (FIG. 2) each of which receives a detent 
ball 86. Each ball 86, in the starting positions of valve pin 58 and lock 
button 66 as seen in FIG. 1, is trapped in registration with an enlarged 
inside diameter wall 88 (as best seen in FIG. 8) at the terminal open end 
68 of lock button 66 surrounding valve body 46, and an inner recess 
defined by a groove 90 circumferentially extending about the terminal end 
of valve pin shank 62. 
In the position shown in FIG. 1, the detent balls 86 are in disengaged 
relation to valve pin 58 and accordingly any depression of hand lever 80 
to drive valve pin 58 from its starting position (FIG. 1) to its actuated 
position (FIG. 2) will simply result in an axial movement of valve pin 
shank 62 past detent balls 86 with the on-off valve 42 and lock button 66 
remaining fixed in position. 
This construction accordingly serves as a safety feature in the event of 
accidental valve pin actuation, for no concomitant movement of body 46 of 
on-off valve 42 is effected. Thereafter, upon release of hand lever 80, 
valve pin 42 is restored to its starting position (FIG. 1) by the biasing 
action of valve pin return spring 84. 
With the air supply "on" and upon depressing lock button 66 from its 
starting position (FIGS. 1 and 2) into its actuated position (FIG. 3), 
detent balls 86 move into locked engagement within valve body 46 in 
abutment with valve pin shank 62 surrounding its groove 90 (FIG. 3). Such 
action is achieved by virtue of a camming action of a reduced intermediate 
diameter inside wall portion 92 (FIG. 8) of lock button 66 which drives 
detent balls 86 radially inwardly into locking engagement within mating 
groove 90 of valve pin shank 62. Thereafter, and only upon subsequent 
actuation of hand lever 80, an open fluid flow condition is established in 
the passageway 18 upon movement of valve pin 58 into an operative actuated 
position (FIG. 4). 
Upon actuating hand lever 80, the valve pin 58 accordingly is driven 
axially within the bore 26 away from its normally closed position to 
effect a following movement of body 46 of on-off valve 42 from its 
illustrated closed position (FIG. 3) into an open fluid flow position 
(FIG. 4) permitting air to flow into motor passage 94 via fluid outlet 96 
in bushing 24 at the downstream end of chamber 22. Lock button 66 may be 
released during such action to return to starting position (FIG. 4), and 
upon releasing hand lever 80, valve pin return spring 84 automatically 
drives valve pin 58 from its actuated position (FIG. 4) into starting 
position (FIG. 1) and the valve return spring 70 serves to restore on-off 
valve 42 into its normally closed position (FIG. 1) in unison with the 
return movement of valve pin 58. The valve return spring 70 additionally 
serves to maintain lock button 66 in its starting position (FIG. 1) in a 
ready condition for repeat operation with the tool 10 limited to a single 
cycling operation as described above by virtue of the disclosed 
construction. 
By virtue of the diametrically opposed disposition of the valve controls, 
accidental dropping or rolling of the tubular tool normally will not 
result in any undesired tool start-up but will require two separate, 
independent and purposeful movements for intentional tool operation. The 
coaxial arrangement of the disclosed safety device components is 
particularly suited for quick and easy assembly in a compact envelope for 
extended use under rugged operating conditions with minimized service 
requirements. Moreover, the free valve pin feature of this invention 
provides for depression of valve pin 58 without parts damage or tool 
actuation in the event the tool 10 were left on a workroom floor 
unattended and were rolled by the action of any attached pressurized hose, 
e.g., or if the lever 80 itself were otherwise actuated for whatever 
reason. 
While a presently preferred embodiment of this invention has been shown and 
described, and a preferred embodiment of practicing the same has been 
illustrated, it is to be understood that the invention is not limited 
thereto, but may be otherwise variously embodied within the scope of the 
following claims.