Title:
PISTON LOCK FOR POWER CYLINDERS
United States Patent 3576151


Abstract:
A power cylinder having means for holding and locking the piston at one end of its travel and operative to maintain a constant augmented force on the piston tending to move the latter in the direction of travel.



Inventors:
SENDOYKAS JACK J
Application Number:
04/806194
Publication Date:
04/27/1971
Filing Date:
03/11/1969
Assignee:
JACK J. SENDOYKAS
Primary Class:
Other Classes:
91/45, 92/28, 254/93R
International Classes:
B23Q5/58; F15B15/26; (IPC1-7): F15B15/26
Field of Search:
92/27,28,23,24,25,17,15 188
View Patent Images:
US Patent References:



Foreign References:
GB608704A
CA650040A
Primary Examiner:
Schwadron, Martin P.
Assistant Examiner:
Payne, Leslie J.
Claims:
I claim

1. The combination with

2. The combination as set forth in claim 1 wherein said piston is provided with a part having a shoulder; and wherein said locking mechanism comprises a powered actuator movable into and out of position behind said shoulder, at least one of said shoulder and said actuator having a beveled surface and said actuator being operative through said beveled surface to lock said piston in the held position and to exert said axial pressure against said piston.

3. The combination as set forth in claim 2 wherein the mentioned part of said piston is in the form of headed pin means carried by and projecting axially from said piston; and wherein said powered actuator interfits with said headed pin means to lock and exert axial pressure against said piston.

4. The combination as set forth in claim 2 wherein the mentioned part of said piston comprises a plurality of headed pins on and projecting axially from said piston; and wherein said cylinder is provided in the mentioned end thereof with sockets disposed to receive said headed pins and operative to position the latter for engagement by said powered actuator.

5. The combination as set forth in claim 4 wherein said powered actuator comprises a rotatably movable ring mounted in the mentioned end of the cylinder and a fluid motor including a plunger operatively connected to said ring to oscillate the same, said ring having a plurality of keyhole slots disposed to receive said headed pins in one oscillatory position of said ring and to engage behind the headed portions of said pins in another oscillatory position of said ring, at least one of said pins and said keyhole slots having beveled surfaces operable by oscillating movement of said ring to exert axial pressure on said piston through said pins.

6. The combination as set forth in claim 5 wherein the operative connection between said plunger and said ring comprises a pivot on and movable with said ring, and a bearing block journaled on said pivot and carried by and slidable transversely relative to said plunger; and wherein one of said headed pins and the socket associated therewith is relatively longer than the other of said pins and operative to position said ring and said piston selectively rotatably in said cylinder properly with respect to said plunger.

7. The combination with a cylinder and a piston reciprocable in said cylinder between predetermined limit positions by a fluid medium under pressure, of

8. The combination with a cylinder and a piston reciprocable in said cylinder of

9. The combination with a cylinder and a piston reciprocable in said cylinder between predetermined limit positions by a fluid medium under pressure of

10. The combination with a cylinder and a piston reciprocable in said cylinder of

11. The combination with a cylinder and a piston reciprocable in said cylinder of

Description:
BACKGROUND OF THE INVENTION

It is contemplated that the power cylinder of this invention be operated either by hydraulic pressure or by pneumatic pressure, and the need to hold the piston securely in either the fully advanced or fully retracted position exists in either mode of operation. However, the need for a piston holding and locking means is particularly present in the case of a pneumatically operated cylinder. Air-operated power cylinders and the auxiliary equipment which supplies air under pressure to the cylinder are much less expensive to install and maintain than their hydraulically operated counterparts. However, in practice, pneumatically operable and hydraulically operable power cylinders are not necessarily interchangeable.

As a typical example of a situation where an ordinary pneumatic cylinder cannot be properly substituted for a hydraulic cylinder, one might cite the cylinder which advances the slide of a tool head in a machine tool so as to bring the cutting tool to a position to operate on a workpiece. If a hydraulic cylinder is used, hydraulic liquid under pressure in the cylinder behind the piston usually holds the slide solidly when the cutting tool is advanced into the work although this may not be true if air is in the line as often is the case. On the other hand, if a pneumatically operated power cylinder is used to advance the slide, air is compressible and compression of air behind the piston in the cylinder causes the tool to bounce back and forth or chatter when it is moved against and into the work. The present invention permits either a pneumatically or an hydraulically operated cylinder to be used in the above situation to advance the slide and to lock and hold the piston mechanism in the fully advanced position during the feed stroke of the cutting tool and the piston holding and locking means holds the piston positively and solidly under these conditions to prevent any vibrating or chattering of the tool due to yielding or bouncing of the piston in the power cylinder as the tool moves forward on its feed stroke. Thus, the piston holding and locking feature of this invention permits the use of either type of power actuator but more particularly, it permits the use of the less expensive air-operated power actuator in the above situation without the disadvantages described which necessarily obtain and normally attend this type of actuator.

Another example is found in the case of power cylinders conventionally used to operate work holding clamps. It is essential in these situations that the cylinder hold the workpiece securely and that it maintain a holding force on the work sometimes for long periods of time and sometimes regardless of variations in the size of the work due to permissible work tolerances or other factors.

In this first connection, parts such as aircraft wings or the like are sometimes clamped in position and left for days while different machining and assembling operations are performed thereon. It is important in these cases that the power clamps used to hold the part maintain full pressure continuously and that pressure not be relieved or even reduced appreciably at any clamp during the entire period. In these situations, loss of pressure in the line supplying the clamps would be fatal if that pressure alone were relied upon to hold the clamp cylinders. However, if the clamps are equipped with power cylinders of this invention, the pressure in the line can be completely shut off after the locking has taken place.

In a typical situation embodying the second contingency is one where clamps are used in machine tools to hold a workpiece for a machining operation. In this particular environment, any condition or circumstance that results in a loss or significant reduction of pressure in the power cylinder--as, for example, a leak or a loss of pressure in the line which supplies fluid to the power cylinder--causes a corresponding reduction in the holding force exerted by the cylinder against the workpiece; and this, of course, permits the work to fly out of the machine with attendant danger to personnel and damage to the machine. The positive piston holding and locking means of this invention permits either an hydraulically operated power cylinder or a considerably less expensive air-operated power cylinder to be used to operate a work-holding clamp in a fixture of the type described above; and the piston locking and holding feature assures that full clamping pressure is maintained at all times regardless of minor variations in the size of different workpieces and regardless of whether a loss of pressure in the fluid supply line or other contingency occurs which otherwise would result also in a loss of pressure in the power cylinder and a loss of holding force against the work.

The situations hereinabove described are given by way of example only; and it will be appreciated that the power cylinder of this invention and particularly the piston clamping and holding feature which is a part of this invention has greater utility and can be used for many different purposes and to achieve many different advantages.

SUMMARY OF THE INVENTION

According to the present invention, the piston of the power cylinder is provided with headed pins or studs which extend axially therefrom in at least one direction and the cylinder is provided at least at one end thereof with a power-operated part which is movable into and out of locking engagement with the pins. It is contemplated that the interlocking part be normally positioned to permit free travel of the piston in the cylinder and that it be movable to interfit with the pins when the piston approaches or reaches the limit of its travel. If desired, actuation of the locking part can be controlled by suitable automatic means so that the piston is locked immediately after it reaches the limit of its travel and until the occurrence of some subsequent event causes the reverse actuation of the locking means to release the piston. It is a feature of this invention, also, that the locking means and the piston-locking pins are uniquely constructed and mutually cooperable to exert a continuing positive force on the piston in the direction of its travel toward the locking means so that the piston is capable of exerting a considerably greater force on the part attached thereto and operated thereby than otherwise would be the case and of assuring a positive and continuing lock on the piston even though a loss of pressure should occur in the system which supplies fluid to the cylinder.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing parts in section and parts in elevation of a power cylinder embodying the invention and illustrating the piston in the fully retracted position and the locking and holding mechanism released from the piston;

FIG. 2 is a transverse sectional view taken on the line 2-2 of FIG. 1;

FIG. 3 is a view similar to FIG. 1 but showing the piston in the fully advanced position and the locking and holding mechanism engaged with the piston;

FIG. 4 is a transverse sectional view taken on the line 4-4 of FIG. 3;

FIG. 5 is a fragmentary, longitudinal sectional view taken on the line 5-5 of FIG. 3;

FIGS. 6, 7 and 8 are fragmentary sectional views showing progressive positions of the piston locking and holding member and illustrating how the latter functions to hold the piston locked and under full pressure in different axial positions in the cylinder;

FIG. 9 is a side elevational view showing a power cylinder embodying this invention incorporated as part of a work-holding clamp and illustrating the clamp in a work-holding position;

FIG. 10 is a view similar to FIG. 9 but showing the clamp in a work-releasing position; and

FIG. 11 is a side view showing parts in section and parts in elevation of a power cylinder embodying the invention and illustrating the same as part of a machine tool for advancing and retracting a slide which carries a tool head.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The power cylinder 18 of this invention comprises a tubular body 20 one end of which is closed by a header 22 and the other end of which is closed by a header 24 and an intermediate mounting ring 26. The header 22 is generally square and relatively thick and is formed with a peripheral, axially inwardly extending annular flange 28 which surrounds and snugly fits the end portion 30 of the body 20. An O-ring 32 disposed within an inner annular recess 34 in the flange 30 seals the joint between the body and the header 22. The ring 26 surrounds and snugly fits the other end portion 36 of the housing 28 and it has a radially inwardly extending flange 38 at the outer end thereof that overlays and butts against the end face of the housing. At the opposite or inner end of the ring 26 is a radially outwardly extending flange 40 that seats the header 24 and positions the latter axially on the body 20. An O-ring 42 disposed within an inner annular recess 44 provided in the ring 26 seals the joint between the ring and the housing 20. The header 24 preferably is of the same or substantially the same shape as the header 22 and it also is essentially thick. An axially extending annular flange 46 on the header 24 surrounds and snugly fits the ring 26 and butts endwise against the flange 40 as hereinabove described. An O-ring 50 disposed in an inner annular recess 52 in the header flange 46 hugs the periphery of the ring 26 and seals the joint between the header flange and the ring. Tie bars 54 (FIG. 9) connect the headers 22 and 24 exteriorly of the housing 20 to hold the parts hereinabove described securely together and to provide and assure a fluidtight cylinder unit 56.

Mounted for reciprocation within the cylinder unit 56 is a piston 58 having a piston rod 60 which extends through a central opening 62 in the header 24, and the projecting end of the piston rod is formed with a threaded extension 64 which adapts the rod for attachment to a part to be actuated by the piston. An O-ring 66 mounted in an annular recess 68 provided in the header 24 around the opening 62 bears on the piston rod 60 to seal the joint between the rod and the header, and a second seal 70 mounted in an annular recess 72 provided in the outer face of the header 24 around the opening 62 also bears on the rod 60 to prevent dirt and other foreign matter from being drawn into the cylinder 56 by reciprocation of the piston rod 60. The piston 58 is equipped with the usual ring 74, here shown in the form of an O-ring, which is mounted in a recess 76 provided in the periphery of the piston for sealing the joint between the piston and the cylinder wall 20 so that fluid introduced into the cylinder 56 at one side or the other of the piston causes the latter to advance or retract in the cylinder.

The piston rod 60 may be connected to the piston 58 in any suitable or conventional manner but, in the particular form of the invention here shown by way of illustration, the piston is provided with a central opening 78 having a counterbore 80 in the rod or inner side of the piston and a counterbore 82 at the opposite or outer side of the piston. The end of the rod 60 has a portion 84 of reduced diameter which extends into and snugly fits the counterbore 80 and a portion 86 of the still smaller diameter which extends into and snugly fits the central opening 78. A threaded stud portion 88 on and extending from the rod portion 86 carries a nut 90 which fits within and is entirely received by the outer counterbore 82. As shown in FIG. 3, the rod portion 84 seats on the bottom of the counterbore 80 and when the nut 90 is tightened on the threaded stud 88, the portion of the piston 58 between the two counterbores 80 and 82 is clamped solidly between the rod portion 84 and the nut 90 to hold the piston rod 60 attached securely to the piston. A collar 92 of a relatively soft metal such as brass or the like is provided around the rod portion 84 and confined between the inner face of the piston 58 and a radial shoulder 94 provided at the juncture of the rod portion 84 and the main body of the piston rod 60.

Fluid under pressure is introduced into the cylinder 56 behind the piston 58 through a passage 96 in the header 22, and fluid under pressure is introduced into the cylinder in front of the piston through a passage 98 in the header 24. As suggested, it is contemplated that the power cylinder 18 of this invention be operated either hydraulically or pneumatically, and it is contemplated also that either liquid or air under pressure be supplied to the passages 96 and 98 from any suitable conventional source of fluid pressure (not shown). To this end, the outer ends of the passages 96 and 98 preferably are threaded to receive fluid supply pipes (not shown) in the usual manner. Also, it is contemplated that the fluid supply means include a conventional valve means (not shown) which is operable to direct fluid under pressure either to the passage 96 or to the passage 98 while simultaneously venting the passage not so connected to a sump or the like (not shown). In this connection, it will be readily appreciated that since the fluid supply means comprises no part of the present invention and since this equipment is conventional and well known, it is not necessary to show the same in association with the power cylinder 18.

A primary feature of this invention is the provision of means for holding and mechanically locking the piston 58 at one or both ends of its travel in the cylinder 56. In the particular form of the invention here shown by way of illustration, the holding means comprises headed pins on the piston and a locking ring on one of the headers which is operable to engage or release the pins when the piston is at the end of its travel. In order to simplify the disclosure, a holding and locking means of the type described is shown for holding the piston 58 in the fully advanced position only. Thus, a locking ring and operating means therefor is mounted in and associated with the header 24 and the piston 58 is provided with forwardly extending pins which interlock with the ring to hold the piston fully advanced However, it will be readily apparent that a locking ring can be mounted similarly in the header 22 and that the piston can be provided with pins which extend rearwardly rather than forwardly for engagement with the ring to hold the piston in the fully retracted position. Similarly, if it should be necessary for the piston 58 to be held in both the advanced and the retracted position, locking rings and operating means therefor can be provided in both of the headers 22 and 24 and the piston can be provided with two sets of pins which extend both forwardly and rearwardly. In this instance, one set of pins engages and cooperates with a locking ring in the header 22 to maintain the piston fully retracted and the other set of pins engages and cooperates with a locking ring in the header 24 to maintain the piston fully advanced. Since the holding and locking means is identical in both instances and since the lock ring and the pins coact in the same manner to hold the piston 58 at the end of its travel, a detailed description of but one of these arrangements will suffice.

As suggested, the holding and locking mechanism is here shown in the header 24, and it comprises a locking ring 100 which is mounted in a central recess 102 provided in the inner face of the header 24. The locking ring 100 fits the recess 102 peripherally relatively snugly but with sufficient clearance to permit free rotational movement or oscillation thereof; and the peripheral portion of the ring 100 is confined between the bottom of the recess 102 and the inner flange 38 of the mounting ring 26, so as to prevent significant axial movement of the ring. Rotational movement is imparted to the locking ring 100 by a piston or plunger 104 which is mounted in a bore or cylinder 106 provided in the header 24 outwardly of the ring 100. As shown in FIG. 4, the bore which forms the cylinder 106 extends transversely entirely through the header 24; and the ends thereof are closed by plates 108 and 110 which are fastened to the header by screws 112 and 114, respectively. Fluid from any suitable source is admitted to one end or the other of the cylinder 106 through pipes 116 and 118 having connecting nipples 120 and 122 screwed into holes 124 and 126 in the plates 108 and 110, respectively. The plunger 104 is here shown in the form of a relatively elongate rodlike or cylindrical member and the opposite ends thereof are sealed against the cylinder 106 by suitable rings such as the O-rings 128. A generally square or rectangular slide 130 mounted on a pivot 132 carried by and extending forwardly from the locking ring 100 is snugly but slidably received in a transverse slot 134 in the plunger 104. As clearly shown in FIG. 4, the plunger 104 has limited reciprocable travel in the cylinder 106 and as it travels it acts through the slide 130 pivot 132 to rotatably actuate the locking ring 100. As the locking ring 100 rotates, movement of the pivot 132 transversely of the piston is accommodated by movement of the slide in the slot 134. Manifestly, the limited travel of the plunger 104 results in a correspondingly limited rotational movement of the locking ring 100 so that full movement of the plunger 104 back and forth in the cylinder 106 produces an oscillatory movement of the locking ring 100.

The piston 58 is provided with a plurality (here shown as 3) of equispaced, axially forwardly extending headed pins 136, 138 and 140 which are adapted to be received in correspondingly spaced and positioned arcuate keyhole slots 142, 144, 146 respectively. As shown in FIG. 5, the large diameter portion 148 of each keyhole slot 142, 144, 146 extends entirely through the locking ring 100 and the relatively narrow portion 150 of each keyhole slot has a countersink 152 in the outer face of the locking ring 100 which extends from and is of substantially the same width as the large diameter portion 148. When the plunger 104 is at one end of its movement in the cylinder 106, it positions the locking ring 100 with the large diameter portions 148 of the keyhole slots 142, 144, 146 in position to receive the headed pins 136, 138, 140 respectively. Thus, when the piston 58 is fully advanced with the locking ring 100 in the mentioned position, the headed pins 136, 138, 140 are received in the large diameter portions 148 with the enlarged head portions of the pins aligned laterally with the countersinks 152. If the plunger 104 is then moved toward the other end of its cylinder 106, the locking ring 100 is rotated or oscillated to move the relatively narrow portions of the keyhole slots 142, 144, 146 along the shank portions of the headed pins 136, 138, 140. During this movement of the locking ring 100, the enlarged head portions of the pins 136, 138, 140 are accommodated in the countersinks 152; and, as the head portions of the pins move into the countersinks 152, they extend laterally of the narrow portions of the keyhole slots to lock the piston 58 to the ring 100 and to provide positive interlocking of the pins with the ring which prevents retraction of the piston 58 in the cylinder 56. Manifestly, the piston 58 is held positively in the advanced position until the plunger 104 is returned to its initial position to rotatably actuate or oscillate the locking ring 100 in a reverse direction to bring the large diameter portions 148 of the keyhole slots 142, 144, 146 into registration with the heads of the pins 136, 138, 140.

In connection with the foregoing, it is of particular significance that the bottom surfaces 154 of the countersinks 152 are beveled or inclined from the large diameter ends 148 of the keyhole slots 142, 144, 146 toward the outer side 156 of the locking ring 100. Thus, the countersinks 152 become increasingly shallower in a direction away from the large diameter portions of the keyhole slots 142, 144, 146. Also, the undersides 158 of the head portions of the pins 136, 138, 140 are tapered or beveled, as shown in the drawings, so that the head portions are of reduced thickness toward the peripheries thereof. The taper angles of both the countersinks 152 and the under surfaces of the pin head portions is relatively flat; but it is particularly desirable that the bottom surfaces 154 of the countersinks 152 provide a locking angle which will prevent fluid pressure in the cylinder 56 ahead of the piston 58 from acting through the pins 136, 138, 140 to rotate the locking ring 100 independently of the plunger 104. An angle of approximately 7° between the beveled surfaces 154 and a plane at right angles to the axis of the ring 100 is suitable for this purpose. The primary reason for beveling the undersurfaces of the head portions of the pins 136, 138, 140, of course, is to increase the area of contact between the head portions and the beveled seating surfaces 154. Thus, when the locking ring 100 is rotated to move the relatively narrow portions of the keyhole slots 142, 144, 146 over the shank portions of the headed pins 136, 138, 140 and to interlock the piston 58 with the ring 100, the head portions of the pins seat on the keyhole countersinks 152 some place along the length of the latter which then acts as a thread or helix so that continued pressure on the plunger 104 tending to rotate the locking ring 100 farther simply wedges the bottom surfaces 154 of the countersinks more tightly against the head portions of the pins and this wedging action tends to hold the piston 58 in the cylinder 56 all the more securely. Also, it will be apparent that the force exerted in this manner by the locking ring 100 against the piston 58 through the pins 136, 138, 140 augments the holding force exerted on the piston 58 by fluid under pressure in the cylinder 56 behind the piston. THe total force tending to hold the piston 58 under these conditions is the force against the face of the piston by fluid pressure in the cylinder 56 plus the force exerted by the locking ring 100 against the heads of the pins 136, 138, 140.

It is a special feature of this invention that one of the pins 136, 138, 140 (here shown as the pin 140) is made relatively longer than the others to aid in orienting or positioning the parts properly at assembly. In the particular form of the invention here shown by way of illustration, the head portions of the pins 136 and 138 are entirely accommodate in the countersinks 152 of the keyhole slots 142 and 144 with which they are associated in all rotative positions of the locking ring 100, as shown in FIGS. 6, 7 and 8, whereas the head portion of the pin 140 is relatively considerably longer and extends beyond the countersink 152 of the keyhole slot 146 and into a hole or socket 160 in the header 24 which preferably is provided with a bushing 162 or hardened steel or the like. The socket 160 is here shown to be a part of the fluid passage 98 and the head of the pin 140 is formed with peripheral flats 164 which provide free flow of fluid from the passage 98 to the keyhole slot 146 and thence to the cylinder 56 ahead of the piston 58. Of particular significance, however, is the fact that the socket 160 receives the projecting end portion of the pin 140 and thus rotatably positions the piston 58 in the cylinder 56 at assembly and assures a proper rotative position of the piston and of the locking ring 100 with respect to the plunger 104 so that the latter is automatically positioned at assembly properly to turn the locking ring so as to engage and release the piston through the pins 136, 138, 140 as the plunger 104 moves back and forth in the cylinder 106. Also, the relatively long pin 140 serves to take any rotational tendency out of the piston due to the wedging action of the locking ring 100 thus eliminating deflection in a long piston rod.

Attention is now directed to FIGS. 9 and 10 which show a typical environmental situation in which a power cylinder 18 equipped with the piston-locking feature of this invention has particular utility. Specifically, these FIGS. of the drawings show the power cylinder 18 of this invention operatively associated with a form of work clamp having a U-shaped body 166. The clamp body 166 is fixed to a suitable supporting surface 168 such as the bed of a machine tool, for example, and a clamping bar 170 is mounted on a pivot 172 extending between and carried by the upstanding sides of the body 166. As shown in the drawing, the clamping bar 170 has a T-shaped head portion which is arranged generally vertically between the sides of the body 166 and the lower arm of the head portion is journaled on the pivot 172. The power cylinder of this invention also is mounted between the upstanding sides of the body 16 behind the clamping arm 170 with the front header 24 attached to the upstanding sides of the body by pivots or trunnions 174. The piston rod 160 extends in the direction of the clamping arm 170 and a clevis 176 on the threaded end 64 of the rod is pivoted at 178 to the upstanding arm portion of the clamping arm head portion. A work-clamping member 180 adjustably fastened to the forward end of the work-clamping arm 170 by a threaded shank 182 and held in a selected adjusted position by lock nuts 184 and 186 is adapted to clamp a workpiece 188 against the surface 168. The power cylinder is free to rock on the trunnions 174; and, when the piston rod 60 is retracted, as shown in FIG. 10, it holds the clamping arm 170 raised to release the work 188. Contrariwise, when the piston rod 60 is advanced, as shown in FIG. 9, it holds the clamping arm 170 in a generally horizontal position with the member 180 clampingly engaging the workpiece 188. Manifestly, as the piston rod retracts it swings the clamping arm 170 in a clockwise direction, as viewed in the drawing, around the pivot 172 and the power cylinder rocks on the trunnions 174 to the substantially horizontal position shown in FIG. 10. On the other hand, as the piston rod 60 advances it swings the clamping arm 170 in a counterclockwise direction to the position shown in FIG. 9 and during this motion of the piston rod, the power cylinder rocks on the trunnions 174 to the slightly inclined position shown in the drawing.

A special problem exists in the case of work-clamping fixtures of the type here shown in that the clamp is required to engage and hold a succession of workpieces and is essential that the clamp hold each workpiece exceedingly securely Very often machining or other operations are performed on a workpiece while the latter is held by clamping fixture; and, if the workpiece is not secure, it may fly out of the fixture during the machining operation and injure personnel or damage equipment. A problem arises, however, from the fact that workpieces invariably differ somewhat in size due to permissible manufacturing tolerances or other causes and from the fact that a loss of pressure in the line which supplies the power cylinder and which serves to maintain clamping pressure on the work may result in such a loss of clamping pressure as to permit the workpiece to fly out of the fixture in the manner described. The piston-locking feature of this invention offers a solution to both of these problems. It holds and locks the piston 58 in the fully advanced position; and, as the locking ring 100 engages the piston-carried pins 136, 138, 140, it exerts a wedging force in a direction to advance the piston in the cylinder 56 and thus augments the force exerted by the fluid pressure in the cylinder behind the piston. Thus, the compounded forces exerted both by the piston-locking ring 100 and the fluid pressure in the cylinder 56 is utilized in clamping the workpiece 188. In addition, the piston-locking ring 100 holds the work clamping member 180 against the work 188 with full clamping force even though a loss of pressure should occur in the fluid line which supplies the power cylinder 18. This full clamping pressure will be maintained notwithstanding the loss of fluid pressure in the supply line until the piston-locking ring 100 is disengaged and the piston is retracted in the power cylinder. The need for toggle arms or other form of pressure applying and holding means on the clamping fixture is eliminated.

In describing the particular operation of the work-clamping fixture shown in FIGS. 9 and 10, it will be assumed that the plunger 104 is all the way to the right, as shown in FIG. 2, to position the large diameter portions of the keyhole slots 142, 144, 146 in alignment with the headed pins 136, 138, 140. The pins 136, 138, 140 are thus released by and disengaged from the locking ring 100. Fluid pressure introduced into the cylinder 56 ahead of the piston 58 through the passage 98 holds the piston retracted, as shown in FIG. 1 and the work-clamping bar 170 raised in the open position shown in FIG. 10.

To begin the operating cycle, fluid under pressure is admitted into the cylinder 56 behind the piston 58 through the passage 96 and the opposite passage 98 is vented. This action causes the piston 58 to advance in the cylinder 56 and the work-clamping arm 170 to swing to the closed position shown in FIG. 9. When the work-clamping member 180 engages the work 188, the piston 58 is in or substantially in the fully advanced position shown in FIG. 3 with the headed pins 136, 138, 140 in the large diameter portions of the keyhole slots 142, 144, 146. If it is assumed that the piston 58 is 1 3/4 inches in diameter and that fluid is supplied to the cylinder 56 at a line pressure of 50 pounds, a total force of 430 pounds is exerted on the piston 58 by fluid pressure in the cylinder 56 tending to hold the member 180 against the workpiece 188.

Now, fluid is admitted to the cylinder 106 to the right of the plunger 104, as viewed in FIG. 2, to move the plunger to the left and to the position shown in FIG. 4. As this action takes place, the locking ring 100 is rotatably actuated or oscillated in a counterclockwise direction, as viewed in the drawing, to engage the relatively narrow portions of the keyhole slots 142, 144, 146 behind the head portions of the pins 136, 138, 140. In practice, the locking ring 100 will turn until the beveled or inclined surfaces 154 wedge solidly against the heads of the pins 136, 138, 140. If the workpiece 188 is on the high side or relatively large side within its permissible tolerance range, the surfaces 154 wedge relatively quickly against the headed pins 136, 138, 140, as shown in FIG. 6. On the other hand, if the workpiece 188 is about average in size within the permissible tolerance range, the wedge surfaces 154 wedge against the headed pins 136, 138, 140 about midway, as shown in FIG. 7. Finally, if the workpiece 188 is relatively undersize within the permissible tolerance range, the wedge surfaces 154 do not wedge against the headed pins 136, 138, 140 until the locking ring 100 has made a complete or substantially complete oscillatory movement, as shown in FIG. 8. It is contemplated that, in a power cylinder of the size hereinabove described, the wedge surfaces 154 have a length of at least 1 inch although this dimension, of course, can be varied depending on the existencies of the particular situation. In a typical work-clamping fixture having relatively dimensional parts as shown and having relatively long wedge surfaces 154 inclined at angles of approximately 7°, an adjustment of approximately one-eighth inch is provided at the clamping end of the arm 170. Further, the same wedging force will be exerted by the surfaces 154 against the headed pins 136, 138, 140 in all positions of the locking ring 100 in which the wedge surface exerts a wedging action against the heads of the pins.

In a power cylinder 18 of the type and size described above, fluid at 50 pounds line pressure in the cylinder 106 exerts sufficient force against the plunger 104 so that, acting through the wedge surface 154, an additional force of approximately 400 pounds is exerted on the piston 58 tending to advance the latter. Thus, in the supposititious situation here under consideration, there is a total force of approximately 830 pounds tending to advance the piston 58 and the bevel angle of approximately 7° locks the ring 100 with the surfaces 154 jammed against the pins 136, 138, 140 so that no amount of counterforce or vibration against the work clamping member 180 by a machining or other operation on the work 188 or other factors can react through the mechanism to loosen the ring 100 sufficiently to permit the piston 58 to retract even slightly even though there is a complete loss of power in the line which supplies fluid to the cylinders 56 and 106.

Attention is next directed to FIG. 11 which shows by way of example another typical environmental situation in which a power cylinder 18 is equipped with the piston lock feature of this invention can be used to advantage. This view shows a typical tool head of a machine tool wherein a slide 190 is mounted for reciprocation on a base 192 and in the present instance is actuated by the power cylinder 18. Mounted on the slide 190 is a tool head 196 having a rotatable and reciprocable spindle 198 which carries a drill 200. The spindle 198 is rotatably driven by a motor 202 through the endless belt 204, and a power cylinder 206 is operatively connected to the spindle 198 to advance and retract the same relative to a workpiece 208. It will be understood that suitable means (not shown) normally is provided to detachably clamp the workpiece 208 on the base 192 or other suitable support so that it is held solidly when the spindle 198 is advanced to move the tool 200 into the work as shown in the drawing. In the particular arrangement here shown by way of illustration, the slide 190 has a forwardly extending part 210 that carries a guide bushing 212 which is positioned closely adjacent to the work 208 during the drilling operation and which steadies and guides the drill in its feed stroke.

In practice, the slide 190 normally is retracted to permit the workpiece 208 to be mounted in the machine. To initiate the drilling operation, the slide 190 is advanced by the power cylinder 18 of this invention until it engages a fixed stop 214 to position the guide bushing 212 is proximity to the workpiece 208. This positioning of the bushing 212 reduces the amount of overhanging of the drill as it moves from the guide bushing into the work. In a typical operation, the motor 202 is energized as soon as the slide 190 engages the fixed stop 214; and the power cylinder 206 operates to advance the spindle 198 and to feed the tool 200 in to the work 208.

If a conventional air-operated power cylinder were used in place of the cylinder 18, the force of the drill 200 against the work 208 would cause the slide 190 to move or bounce back and forth due to the compression of the air in the cylinder behind the piston. This action in turn would give a poor finish to the hole which is drilled in the work 208 and would make it impossible to hold the diameter of the hole to a close tolerance. However, if the power cylinder 18 of this invention is used to actuate the slide 190 the locking ring 100 holds the main piston 58 solidly in the fully advanced position and effectively prevents any bouncing or chattering of the slide during the drilling operation. At the same time, it permits relatively inexpensive air to be used to operate the cylinder.

Almost every shop is equipped with an air line which carries air under pressure sufficient to operate the power cylinder of this invention; and this source of air pressure can by utilized inexpensively to operate the power cylinder for any job or use that may be required of it. Thus, the need to operate the cylinder 56 by oil or other kind of hydraulic liquid and the need to supply a correspondingly higher priced and more expensive oil-pumping unit for the cylinder is eliminated.