US2984217A - Feedback mechanism for servo control of hydraulic press - Google Patents

Description

y 1961 c. D. CLlNE 2,984,217

FEEDBACK MECHANISM FOR SERVO CONTROL OF HYDRAULIC PRESS Filed July 20, 1959 2 Sheets-Sheet 1 I H I I l-"- mu INVENTOR. (2/14 J. (10v! United States Patent FEEDBACK NIECHANISM FOR SERVO CONTROL OF HYDRAULIC PRESS Charles D. Cline, Mount Gilead, Ohio, assignor to Koehr ing Iompany, Milwaukee, Wis., a corporation of Wiscousin Fiied July 20, 1959, Ser. No. 828,288

8 Claims. (Cl. 121-411) This invention relates generally to servo control mechanisms and'more particularly to feed back mechanisms for servo control of hydraulic presses and other apparatus employing a power driven axially movable member.

One advantage of using hydraulic presses for various manufacturing operations is that the press operator is enabled to apply a force which is many times the force he could apply by his own efforts. However for those operations requiring precise control of ram movement it is difiicult to use such presses unless means are provided for correlating control lever movement and ram or force applying member movement. Without such means the operator would not have the sense of feeling he has, for example, in a mechanical press operated by his own effort.

Various mechanical feed back mechanisms have here tofore been provided for preserving the desired correlation, but in so far as I am aware none of them has been entirely satisfactory, either because of their complexity or because of their inability to function throughout the ram stroke regardless of stroke length.

An object of the invention, therefore, is to provide for hydraulic presses or the like a simple and effective mechanism for correlating control lever and ram movement and which is effective throughout ram stroke regardless of the length of the ram stroke.

Another object of the invention is to provide for hydraulic presses or the like a direct acting feed back mechanism which gives the press operator complete control of ram position and pressure during the full range of ram stroke and without necessity for compensating adjustmerits.

Another object of the invention is to provide a feed back mechanism which is built into the press control rod so that the press linkage more closely resembles that of a conventional hand-operated press.

Further objects and advantages of the invention will be readily apparent from the following description, reference being had to the drawings showing a preferred embodiment of the invention.

Fig. 1 is a perspective view of a hydraulic press provided with a preferred embodiment of the present invention, appropriate parts being broken away to show the mechanism.

Fig. 2 is a fragmentary side elevational view of the press partially broken away to show portions of the control mechanism and partly in vertical section to show details of the control valve for the press ram.

Fig. 3 is a fragmentary view taken along plane 33 of Fig. 2.

Fig. 4 is a fragmentary view partly in section and taken along plane 44 in Fig. 2.

Referring more particularly to the drawings, the press includes a frame 1 having a base portion 2 and an upper portion 3. The base portion includes a platen 4 for holding the workpieces and a control handle 5 for the operator. The upper portion 3 which extends over the platen contains a hydraulic cylinder (shown schematice ically in Fig. 2) and ram 11. A motor driven pump for the hydraulic fluid operating the cylinder and a hydraulic reservoir or tank are also located within the press frame 1 but are not shown as these are conventional components for the hydraulic system and are well known to those skilled in the art.

A four-way spool valve 20 having a movable spool 30 to control the supply of pressure fluid to the ram 11 is located in the upper portion 3 of the press adjacent cylinder 10.

The mechanical actuating and feed back linkage for the valve 20 comprises a control rod arrangement, between the valve 20 and the manual control handle 5, having a spool section 40 and a rotatable cam section 60. A cam actuator 12 for driving or rotating cam section 60 is attached to ram 11.

The spool section 40 is connected on the upper end to the spool 30 by pin 41 and is further provided with a female multiple fast thread coupling 42 on its lower end. A coil spring 43 for biasing the spool 30 downward is retained between the lower end of the valve 20 and an adjustable collar 44 on spool section 40 secured by set screw 45. The spool section 40 is further provided with another collar 46 secured by a set screw 47. The collar 46 has a groove 48 which engages a pin 51 fastened in a guide block which is fastened to the press frame 1 by screws 52. The guide block 50 and collar 46 are best illustrated in Fig. 3. The pin 51 and groove 48 arrangement prevent any rotation of the rod section 49 while allowing it to move up and down. The multiple fast thread coupling 42 at the lower end of the section 4% is engaged with a male multiple fast thread coupling 61 on the upper end of the cam section 60. The cam section has a cam portion 62 having two spiral grooves 63 in its outer periphery spaced 180 apart. The cam section 60 has an extension 64 which passes vertically through bracket 6 affixed to the frame 1 and also through the frame 1 where it terminates in the base portion 2.

It is to be understood that spool section 44] need not be a separate section but could be an integral extension of spool 30, coupled by a thread to cam section 60. It is also possible, of course, to reverse the male and female threaded coupling 61, 42. The female end could be on cam section 60 and the male end on spool section .40.

The operators control handle 5 is secured to a shaft 7 which is pivotally mounted in base portion 2. A control lever 8 which moves simultaneously with the control handle 5 is also attached to the shaft 7. Two thrust bearings for lever 8 are secured to extension 64. One bearing 65 is contained by collar 66 above lever 8; and another bearing 67 is located below lever '8. Depressing the handle 5 moves sections 60 and 4t) upward by the action of lever 8 against bearing 65, also moving spool 30 upward. Movement of handle 5 upward allows sections 60 and 40 to move downward by action of spring 43 pulling spool 30 downward. If the control rod mechanism fails to move downwardly by the action of spring 43, the bearing 67 will be engaged by lever 8 for positively moving the rod mechanism downwardly. Bearing 67 is necessary only to insure that the rod arrangement can be pulled down with operating handle 5 in case spring 43 fails to reverse valve spool 30. Normal operation would not require bearing 67.

The cam actuator 12 is attached to the lower end of ram 11 by means of a collar 13 and screws 14. The cam actuator 12 includes a collar section 16 encircling spiral cam 62. The collar 16 has rollers 17, as shown in Fig. 4, attached by pins 18. The rollers engage the spiral grooves 63 for the full length of the stroke of ram 11. The actuator 12 also includes a bifurcated end 19 which overlaps a guide bar 9 attached to the press frame 1 in line with ram 11. The guide bar 9 prevents actuator 12 from tending to twist or rotate by the action of rollers 17 in spiral grooves 63 and thus keeps the cam actuator in position with respect to cam section 60. To prevent an unnecessary strain and to provide better alignment a slip joint 15 is provided at the mid portion of actuator 12.

An adjustable collar 68 is provided at the lower end of the cam portion 62. It may be adjusted to any position on cam portion 62 and provides a stop limit for cam actuator 12 and thus limits downward stroke of the ram 11. Another adjustable collar 69 is provided on extension 64. The bracket 6 on press frame 1 provides a stop limit for the collar 69 to limit downward movement of cam section 60 and thus limit upward travel of the ram 11.

The leads of threads 42, 61 and spiral grooves 63 are such that movement of the cam actuator 12 downward by the ram 11 will cause cam section 62 to rotate section 60 in a counter-clockwise direction, turning thread 61 into thread 42. Section 40 will thus move downward pulling spool 31) downward. Movement of ram 11 upward will cause a reverse rotation of section 60 and thread 61 will turn out of thread 42 causing section 44) and spool 30 to move upward. The leads of the threads 42, 61 and spiral grooves 63 are also proportioned so that for each increment of linear movement of the ram 11 there is a proportional linear movement of spool 30 which returns spool 30 to the same position as it was when ram movement commenced.

Although the flow of pressure fluid to the ram cylinder is here shown as controlled by a spool valve or regulator 20, any valve or regulator providing the equivalent functions of the valve disclosed herein would be satisfactory. An example of such a regulator would be an electric switch having a movable control element. The four-way spool valve or servo-valve shown has a body 21 with a bore 22 containing spool 30 for control of passages or ports 23, 23b, 24, 25 and 26. Passages 23 and 23b are connected to the tank (not shown) by line 23a shown in Fig. 1. Passage 24 is connected to the crowd side of cylinder 10 or the main cylinder by line 24a. Passage 25 is connected to the opposite end of the cylinder 10 or the pull back side by line 25a. Passage 26 is connected to a pump (not shown) by line 26a. The valve 20 also includes a cap 27 containing a piston 28 the topside of which is connected by passages 29, 29a to main cylinder port 24. The piston 28 exerts a downward force on the spool 30 which is proportional to the force on the ram 11 when pressure fluid flows through port 24.

The spool 30 is provided with a cap 31 and lands 32, 33. It is employed to control flow of hydraulic fluid between the various ports 23, 24, 25, 23b, 26. The cavity 34 which surrounds spool cap 31, limits the stroke of the spool 31 The valve spool 30, as shown in Fig. 2, is in a neutral position. Land 32 is a few thousandths of an inch narrower than main cylinder passage 24. Hydraulic fluid, therefore, can flow from pump passage 26 past the lower portion of land 32 into tank passage 23. Land 33 is so arranged that full flow of hydraulic fluid into the pull back cylinder is shut oflf, however, sufiicient fluid will be forced past land 33 into passage 25 in sufficient quantity to stabilize ram 11 and hold it up. The tolerances of the lands 32 and 33 with respect to the bore 22 and passages described are such that movement of the spool 34) upward or downward only several thousandths of an inch will cause ram movement. Movement of the spool upward causes the ram to descend most position. To make the ram 11 descend, the operator depresses handle 5 which through lever 8 raises the valve spool 30 by raising the control rod sections 60 and 40. The stroke of the valve spool 30 is of course limited by the cap or land 31 as explained above. Upon raising of the spool 30 oil passes from the pump port 26 past land 32 to the main cylinder through port 24. Land 32 prevents flow of oil from port 24 into tank port 23, at the same time oil can flow from pull back cylinder through port 25 to tank port 23b because of upward movement of land 33. Oil under pressure in the main cylinder thus forces the ram 11 downward.

As soon as the ram 11 begins to descend cam section 60 begins to turn due to the action of rollers 17 located in the cam actuator 12 acting in grooves 63. The multiple thread 61 threads or turns into multiple thread 42. As long as the handle 5 is urged downward the ram 11 will descend and section 60 will continue to move upward and at the same time will continue to rotate and thread itself into coupling thread 42. If the handle 5 is held stationary at any point the rod section 60 will cease to move vertically upward but will continue to rotate. The section 60 will continue to thread itself into thread 42 and section 40 will move downward pulling valve spool 30 into idle or neutral position. Thus for each position of operators handle 5 there is a corresponding position for ram 11.

A similar action takes place when the ram ascends. As long as the operating handle 5 is allowed to move upward the control rod mechanism 60 and comprising section 40 are free to move downward by action of spring section 43 and the action of lever 8 against bearing 67. As the spool 30 moves downward oil under pressure flows to the pull back cylinder and the ram 11 ascends. If the operating handle 5 is held stationary the control rod section 60 will not move vertically downward but will continue to revolve causing multiple thread 61 to thread out of coupling thread 42 causing the rod section 40 to rise which allows valve spool 30 to reach its neutral position.

The ram 11 can be controlled in its upward or downward movement in increments of infinite degree by very slight changes in the position of the spool 30. It is possible for the ram 11 to just contact a workpiece or some resistance without actually exerting force on the workpiece or resistance. In its neutral position the valve spool allows oil to be bypassed to the tank or reservoir at very low pressure. Thus, by depressing handle 5 it is possible to gradually raise the spool 30 such that pressure gradually is diverted to the main cylinder through port 24 and flow to the tank through ports 23 and 23b will cease. As the pressure increases in the main cylinder some oil under pressure is transferred through passages 29, 29a and acts against piston 28 as explained above. This pressure against the spool 30 and thus the operating handle 5 tends to give a sense of pressure to the operator so that the ram 11 force exerted on a workpiece is sensed at the operating handle 5. If the ram 11 descends far enough so that the actuator 12 contacts collar 68 the vertical upward motion of rod section 60 stops and the ram 11 through actuator 12 will actually pull the rod section 60 and section 40 downward causing valve spool 30 to go to its neutral position. Similarly when the ram ascends if collar 69 reaches the bracket 6 the cam section 60 will cease vertical downward motion and the spool 30 will be restored to neutral position by the action of cam 62 and threaded couplings 42, 61 as explained heretofore.

There are variations of this type of press that can employ the novel feed back mechanism described. The lead of the spiral on the control rod and the lead of the threaded coupling arrangement can be changed in various degrees so that the rate of response to movement of the operating lever or handle can be varied over a wide range. The device or press can therefore be made extremely sensitive or less sensitive to suit the particular or special application desired.

The land of the spiral and threads may be reversed or one may be left-hand and the other right-hand. One continuous right-hand or left-hand thread or spiral may be used. It is also possible for two separate spirals to be used in place of a spiral and threaded coupling as shown and described herein.

Having described the invention, what is claimed as new 1s:

1. Control mechanism for use with a motor having a reciprocally movable ram, said mechanism comprising; regulating means for controlling the actuation of said motor; a rotatable and axially movable control rod for effecting movement of said regulating means from a given control position, said control rod having an axis substantially parallel to the axis of said ram; a threaded coupling connecting said control rod and said regulating means; and means for rotating said control rod in relation to ram movement to vary the length of said threaded coupling whereby upon movement of said regulating means from a given position by axial movement of said control rod and said coupling, said regulating means will thereafter be automatically returned to said given position by rotary movement of said control rod and consequent change in the length of said threaded coupling.

2. Control mechanism for use with a motor having a reciprocally movable ram, said mechanism comprising; regulating means for controlling the actuation of said motor; a rotatable and axially movable control rod for eifecting movement of said regulating means from a given control position, said control rod having an axis substantially parallel to the axis of said ram; a threaded coupling connecting said control rod and said regulating means; a spiral cam defined on a portion of said control rod; and cam follower means for effecting rotation of said control rod to vary the length of said threaded coupling in proportion to ram movement whereby upon movement of said regulating means from a given position by axial movement of said control rod and said coupling said regulating means will thereafter be automatically returned to said given position by rotary movement of said control rod and consequent change in the length of said threaded coupling.

3. Control mechanism for use with a motor having a reciprocally movable ram, said mechanism comprising; regulating means for controlling the actuation of said motor; a reciprocally movable control element in said regulating means; a rotatable and axially movable control rod for effecting movement of said control element from a given position, said control rod having an axis substantially parallel to the axis of said ram; a threaded coupling connecting said control rod and said movable control element; a spiral cam defined on a portion of said control rod; and a cam actuator for efiecting rotation of said control rod to vary the length of said threaded coupling in proportion to ram movement whereby upon movement of said control element from a given position by axial movement of said control rod and said coupling, said control element will thereafter be automatically returned to said given position by rotary movement of said control rod and consequent change in the length of said threaded coupling.

4. Control mechanism for use with a hydraulic motor having a reciprocally movable ram, said mechanism comprising; a valve for controlling flow of hydraulic fluid to said motor; an axially movable spool in said valve disposable in a given position; means for biasing said spool in one direction; an operating lever; an axially movable control rod connected between said operating lever and said spool; a threaded coupling in said control rod for varying the length of said control rod when one portion of said control rod is rotated with respect to the other portion; spiral cam means defined on said one portion of said control rod; means for pred venting rotation of said other portion of'said control rod; and a cam actuator for effecting rotation of said one portion in relation to ram movement whereby said spool is automatically returned to said given position by the variance in the length of said control rod subsequent to axial movement of said spool by said control rod.

5. Control mechanism for use with a hydraulic press having a reciprocally movable ram, said mechanism comprising; a valve for controlling flow of hydraulic fluid to said press; an axially movable spool in said valve disposable in a neutral position; a spring for biasing said spool in one direction; an operating lever; an axially movable control rod connected between said operating lever and said spool, said control rod comprising a spool section and a control section; a threaded coupling between said sections for varying the length of said control rod when said control section is rotated in respect to said spool section; pin and groove means operatively associated with said spool section for preventing rotation thereof; stop means secured on said control section for limiting axial movement of said control rod; spiral cam means defined on a portion of said control section; and a cam actuator for etfecting rotation of said control section in relation to ram movement whereby said spool is automatically returned to said neutral position by the variance in the length of said control rod subsequent to axial movement of said spool by said control rod in response to movement of said operating lever.

6. A hydraulic press comprising, in combination, a fluid pressure actuated ram; valve means for regulating supply of fluid pressure to said ram; a manually movable control handle; an axially movable control rod connected between said control handle and said valve, said control rod having an axis substantially parallel to said ram; a threaded coupling in said control rod for varying the length of said control rod when one portion of said control rod is rotated with respect to another; spiral cam means secured to a portion of said control rod for effecting rotation thereof; and cam follower means connected between said ram and said spiral cam means for etfecting in relation to ram movement rotation of said portion of said control rod and consequent variance in the eflective length thereof.

7. A hydraulic press comprising in combination a fluid pressure actuated ram; valve means for regulating supply of fluid pressure to said ram; a movable spool in said valve means; a manually movable control handle; an axially movable control rod connected between said movable spool and said control handle, said control rod comprising a spool section and a control section; a threaded coupling connecting said sections for varying the length of said control rod when said control section is rotated with respect to said spool section; means for preventing rotation of said spool section; spiral cam means defined on said control section for etfecting rotation thereof; cam actuating means connected between said ram and said spiral cam means for etfecting rotation of said control section of said control rod in relation to ram movement and consequent variance in the effective length of said control rod; and stop means secured on said control sec tion for limiting axial movement of said control rod.

8. A hydraulic press comprising in combination a fluid pressure actuated ram; a valve for regulating supply of fluid pressure to said ram; a manually movable control handle; an axially movable spool in said valve means disposable in a neutral position; an axially movable control rod connected between said control handle and said spool, said control rod comprising a spool section and a control section; a threaded coupling connecting said sections for varying the length of said control rod when said control section is rotated with respect to said spool section; pin and groove means operatively associated with said spool section for preventing rotation thereof; stop means secured on said control section for limiting axial movement thereof; spiral cam means defined on said 17 8 control section for effecting rotation thereof; and cam References Cited in the file of this patent actuating means connected between said ram and said spiral cam means for effecting rotation of said control UNITED STATES PATENTS section in relation to ram movement whereby the efiec- 465,730 Russell Dec. 22, 1891 tive length of said control rod varies in relation to ram 5 786,652 Larsson Apr. 4, 1905 movement automatically returning said spool to said neu- 1,942,189 Shepard I an. 2, 1934 tral position subsequent to movement of said spool and 2,610,614 Sedgwick Sept. 16, 1952 said ram in response to axial movement of said control rod by said control handle.

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