US2264532A

US2264532A - Hydraulic circuit for machine tools

Info

Publication number: US2264532A
Application number: US277651A
Authority: US
Inventors: Paul S Jackson
Original assignee: Rockford Machine Tool Co
Current assignee: Rockford Machine Tool Co
Priority date: 1939-06-06
Filing date: 1939-06-06
Publication date: 1941-12-02
Anticipated expiration: 1958-12-02

Description

Dec. 2, 1941. P. s. JACKSON 2,264,532

HYDRAULIC CIRCUIT FOR MACHINE-TOOLS Filed June 6, 1939 INVENTOR. Mk5: L/MSOWZ BY 5&2 n 8* RNEY twenty feet and less per minute.

Patented Dec. 2, 1941 2,264.53; 7 HYDRAULIC cmcurr Fon MACHINE TOOLS Paul S. Jackson, Rockford, assignor to Rockford Machine Tool Company, Rockford, 111., a corporation of Illinois Application June 6, 1939, Serial No. 277,651

9 Claims.

This invention relates generally to machine tools having a support actuated by a piston and cylinder device, such as planers, shapers, etc., and more particularly to a device'associated with the hydraulic circuit of such piston and cylinder device for the purpose of eliminating chatter of the support on its ways when operated at low speeds. to provide a new and improved mechanism for eliminating such chatter.-

Although liquids are generally characterized as solid bodies and non-compressible, it has been found in hydraulic circuits 'for machine tools that there is an appreciable compression of the oil, especially when used in large volumes, as is required in the long cylinders of large metal planers. This compressibility is frequently due to air which is entrained in the liquid, generally oil, either in a dissolved state or a slightly foamy condition. The use of a lubricating oil as the fluid medium in hydraulic circuits for machine tools is generally accepted, but the presence of air in the oil is a continuous source of annoyance and prevents smooth operation of the reciprocating support that is driven directly by the oil operating in a piston and cylinder device. The compressibility of the oil is evident, particularly on heavy loads and at slow speeds, such as from Apparently, during such heavy cuts the air in the oil is compressed to a certain point before the resistance of the tool on the work is overcome, whereupon the table lunges forward and the pressure of the oil drops, this cycle being repeated at a rela-' tively high rate on light machines, and at a relatively low rate on heavy machines. Although at It is the general object of the invention ment shown, it being contemplated that various and cylinder having one end of the cylinder connected to said hydraulic circuit adjacent one end of the main cylinder and having in the other end of the auxiliary cylinder a coil spring or other resilient element for resisting movement of the auxiliary piston therein when subjected to the fluid pressure of the hydraulic circuit.

Other objects will become readily apparent from the following detailed description taken in connection with the accompanying drawing, in which the figure illustrates a preferred form of the invention associated with the platen of a metal planer.

While I have illustrated in the drawing and shall hereinafter describe in detail a detailed form of .the invention with a metal planer, it is to be understood that .I do not intend to limit the invention-to the particular form and arrangechanges may be made by those skilled in the art without departing from the spirit and scope of the, appended claims.

As illustrated in'the drawing, numeral Ill represents platen or table of a planer on which a Work piece II is secured in position to be cut by a suitable tool l2, the supporting means for which is not illustrated. The table is arranged to be reciprocated by means of a main piston and cylinder device having a cylinder l3 suitably supported on the bed of the machine (not shown) and a piston Hi. The piston I4 is secured to one end of a piston rod l5, the other end of which extends out through oneend of the cylinder and higher cutting speeds, such as those above thirty feet per minute, this action of the table on its ways apparently does not exist and the accompanying chatter is absent, the chatter at the lower speeds and on heavy loads is extremely objectionable.

Another object is to provide a new and improved hydraulic circuit with a compensating device which is operable to eliminate such chatter of the driven support. During the operation of the machine, this compensator functions to maintain the pressure in the hydraulic circuit constant so that a very smooth out of the tool is obtained.

Another object is to provide in a hydraulic circuit for a machine tool support having a main piston and cylinder actuating the support, a hydraulio circuit including said cylinder and a compensating device comprising an auxiliary piston is secured to a' depending portion l6 of the tabl III by means including a nut l1.

The invention contemplates the reciprocation of the table Ill by means of a fluid, such as oil under pressure, the table generally being moved at a slow or feed rate toward the left during a cutting operation, and at a higher or traverse rate toward the right during the return stroke. The hydraulic circuit includes the main piston and cylinder device l3, l4, heretofore mentioned, a pumping mechanism l8 and valve mechanism designated generally IS. The pumping mechanism l8 and valve mechanism l9 maybe of any one of a number of commercial products as, for example, a type D-R pump manufactured by The Oilgear Company of Milwaukee, Wisconsin. This pump consists generally of a tank or reservoir 20 on which the pump casing 2! is mounted,

the pump casing having amongst other mechanisms, a' gear type pump 22 and a variable displacement piston type pump. Since the construction of the pumping mechanism It forms no part of the present invention, it will suflice to say that 23 indicates a means for adjusting the speed of the table during its cutting stroke toward the left, 2| indicates a means for adjusting the speed of the table during its return stroke toward the right, 25 indicates an automatic constant pressure relief valve in the return line to the

tank

20, and 26 indicates a high pressure relief valve in a return line to the tank 20. The output of the gear pump 22 is conducted to the valve mechanism I! through a conduit 3!, whereas the high pressure fluid from the variable displacement piston pump of the mechanism 13 is conducted to the valve mechanism by a conduit 3|. The right hand end of the main cylinder I3 is connected to the valve mechanism I! by means of a conduit 33, and the left hand end or the cylinder I3 is connected to the valve mechanism is by means of a conduit 33. A conduit 34 forms a return from the valve mechanism to the tank 20. and a conduit-35 forms a return from the valve mechanism to the pumping mechanism It. A conduit 36 connects at one end to the valve mechanism l9 and at the other end to the pumping mechanism I8, and functions to supply fluid to internal parts of the pumping mechanism when it is desired to obtain the maximum stroke of the variable stroke pump therein. The operation of the valve mechanism is controlled by means of a pilot having an operating member ID. This operating member is connected to one 'end of a lever 4| pivoted at 42, the other end of the lever being connected by means of a rod 43 to one arm ll of a bellcrank device pivotally supported at 45. The other arm 43 of the bellcrank carries a roller 41 positioned to be acted upon by a cam or dog 48 secured to the table II or by a cam or dog 49 secured thereto, the dogs being effective at the ends of the cutting and return strokes, respectively, to cause reversal of the table by actuation of the pilot valve.

More particularly, the invention in the form disclosed herein includes the provision of a means or compensating device I for eliminating chatter of the table on its ways when operating at relatively slow speeds. This compensating device comprises an auxiliary cylinder it having an auxiliary piston i2 therein. The right hand end 4 of the cylinder is connected to the hydraulic circuit by means of a conduit 65 which communicates with the conduit 33 adjacent the left hand end of the main cylinder I3. A risilient means in the form of a conically coiled spring 83 is positioned in the left hand end of the auxiliary cylinder SI to resist movement of the Dision 62 toward the left when subjected to the pressure of the fluid in the hydraulic circuit. In order to provide for adjustment of the resistance exerted by the coiled spring 63, a screw device it is threaded through the right hand end wall of the cylinder GI and carries a cupshaped member $1, between which and the piston 62 a coiled spring 3 is positioned.

Under certain circumstances and in order to obtain an elimination of chatter in both directions of operation of the table, a similar compensating device 53 may be provided for the right hand end of the main cylinder l3. This compensating device comprises an auxiliary cylinder having an auxiliary piston 52 therein. The left hand end 53 of the cylinder is connected to the hydraulic circuit by means of a conduit which communicates with the conduit 33 adjacent the right hand end of the main cylinder l3. A resilient means in the form of a coiled spring II is positioned in the ri ht hand end of the auxiliary cylinder ii to resist movement of the piston 52 toward the right when subjected to the pressure of the fluid in the hydraulic circuit. Preferably, a piston rod 53 is connected to the piston 52 when it is desired to observe the action of the piston 52 from a point externally of the cylinder. In order to avoid any build up of pressure in the right hand end of the cylinder 5| and the left hand end of cylinder 3| due to leakage of fluid past the pistons therein, a return conduit II is provided for the cylinder ii and a return conduit Si is for the cylinder il. These conduits serve to drain the portions of the auxiliary cylinders to which they are connected.

In order to permit the use of one compensating device or the other, or both, a suitable valve 65' is provided in the conduit ii and a valve 54' in the conduit 54 to permit of closing or opening said conduits. In practice, it is desirable that the conduits between the compensating device cylinders and main cylinder l3 be as short as possible. In the event only one com pensating device is used, it is preferable to use the one connected to that end of the main cylinder which is emptying during the cutting operation.

As mentioned hereinbefore, the preferred form of the invention is embodied in a hydraulic circuit for actuating the table of a metal planer. Such machine tool generally has a mechanism for feeding the tool I! laterally of the work at the beginning of each stroke. This may be accomplished by suitable means well known in the art, including a piston and cylinder device ll.

In operating the circuit disclosed herein, fluid is first supplied to the right hand end of the cylinder II for moving the table toward the left through a cutting stroke during which the fluid from the left hand end of the cylinder 3 passes back through the conduit 33 and valve mechanism It, thence through conduit 35 to the pumping mechanism II. A portion of the fluid passing through conduit 3! continues downwardly into the tank 23 past the automatic constant pressure relief valve 25, whereas the remainder of this fluid passes to the intake of the pumping mechanism so that only an amount of fluid equivalent to the volume of the piston rod I5 is caused to pass over the automatic constant pressure relief valve 25. Upon completion of the cutting stroke, the dog 43 engages the roller 41 so as to actuate the pilot valve member ll, whereupon the valve mechanism It is conditioned to direct fluid to the left hand and of the cylinder l3 through conduit 33 for the purpose of effecting a return stroke of the table II. fluid from the right hand end of the cylinder l3 then passes out through the conduit 32 to the valve mechanism It. The valve mechanism is then adjusted so as to connect the adjacent ends of the conduits 32, 33 and 3|, so as to obtain a fast return stroke of the table through the differential action thus obtained. The table-continues in its return stroke toward the right \mtil the dog 43 thereon engages the roller 41 and pivots the bellcrank in a counterclockwise direction to effect a cutting stroke toward the left. The table continues to reciprocate imtil the operator manipulates a stop valve I! provided in the valve mechanism II.

In practice, it has been found that the mechanism herein disclosed eiiectively eliminates chatter. Furthermore, the compensating devices operate to cushion the reversals of the table, as

well as the movement or the table in the event "hard spots'are encountered in the work by the tool. The invention has been particularly effective in connection with heavy tables or heavily loaded tables when operated at slow speeds, such as twenty feet per minute or less in planers.

Under such conditions, when heavy cuts are being taken, the oil in the hydraulic circuit or the air entrain therein compresses to a certain point where the resistance of the tool is overcome and then the table lunges ahead, whereupon the pressure of the oil and any entrained air drops, whereupon the table will momentarily stop until the necessary pressure is again built up. The rate at which this oscillation occurs is dependent to a considerable extent upon the weight oi the reciprocating table, oscillations and the attendant Q vibration of the table is effectively eliminated by the invention disclosed herein. This is accomplished by means of the compensator device because the piston thereof will oscillate in the auxiliary cylinder so as to maintain the pressure in the hydraulic circuit substantially constant and maintain a regular fluid flow from the pumping mechanism to the main cylinder.

A second compensating device may be incorporated when it is desired to efiect smooth operation during the return stroke of the table, as well as during the cutting stroke. When this compensating device is connected in the circuit, it has been found desirable to close the automatic constant pressure relief valve 25 entirely, with the result that any return flow of oil in excess of that passing through the intake of the pumping mechanism returns to the tank 20 over the hydraulic pressure relief valve 26.

I claim as my invention:

1. In a metal planer having a table, a main piston and cylinder device for actuating 'said table and a hydraulic circuit including pumping mechanism and valve mechanism for supplying and controlling the flow of fluid to and from the opposite ends of said cylinder, in combination, a compensating device comprising an auxiliary cylinder, a piston therein, a conduit connecting one end of said cylinder with said hydraulic circuit adjacent one end of said main cylinder and a spring in the other end of said auxiliary cylinder for resisting movement of the piston therein.

2. In a metal planer having a table, a main piston and cylinder device for actuating said table and a hydraulic circuit including pumping mechanism and valve mechanism for supplying and controlling the flow of fluid to and from the opposite ends of said cylinder, in combination, a compensating device comprising an auxiliary cylinder, a piston therein, a conduit connecting one end of said cylinder with said hydraulic circuit adjacent one end of said main cylinder and resilient means in the other end of said auxiliary cylinder for resisting movement of the piston therein.

3. In a metal planer having a table, a main piston and cylinder device for actuating said table and a hydraulic circuit including pumping mechanism and valve mechanism for supplying and controlling the flow of fluid to and from the opposite ends of said cylinder, in combination, a compensating device comprising an auxiliary cylinder, a piston therein, means connecting one end of said cylinder with said hydraulic circuit so as to subject the piston therein to the pressure of the fluid supplied to said main cylinder and resilient means in the other end of said auxiliary cylinder for resisting movement of the piston therein.

4. In a metal planer having a table, a mainpiston and cylinder device for actuating said table and a hydraulic circuit including pumping mechanism and valve mechanism for supplying and controlling the flow of fluid to and from the opposite ends of said main cylinder, in combination, a first compensating device comprising an auxiliary cylinder, a piston therein, means connecting one end of said cylinder with said hydraulic circuit adjacent one end of said main cylinder, resilient means in the other end of said auxiliary cylinder for resisting movement of the piston therein, and a second compensating device comprising a cylinder, a piston therein, resilient means in one end of said last mentioned cylinder for resisting movement of the piston therein, and means connectingthe other end of said cylinder to said hydraulic circuit adjacent the other end of said main cylinder.

5. In a metal planer having a table, a main piston and cylinder device for actuating said table and a hydraulic circuit including pumping mechanism and valve mechanism for supplying and controlling the flow of fluid to and from the opposite ends of said cylinder, in combination, a compensating device comprising an auxiliary cylinder, a piston therein, a conduit connecting one end of said cylinder with said hydraulic circuit adjacent the end of said main cylinder from which fluid discharges during a cutting operation, and a spring in the other end of said auxiliary cylinder for resisting movement of the piston therein.

6. In a metal planer having a table, a main piston and cylinder device for actuating said table and a hydraulic circuit including pumping mechanism and valve mechanism for supplying and controlling the flow of fluid to and from the opposite ends of said cylinder, in combination, a compensating device comprising an auxiliary cylinder, a piston therein, a conduit connecting one. end of said cylinder with said hydraulic circuit adjacent one end of said main cylinder, and means for draining fluid from the end of the auxiliary cylinder in which the resilient means is located.

'7. In a metal planer having a table, a main piston and cylinder device for actuating said table and a hydraulic circuit including. pumping mechanism and valve mechanism for supplying and controlling the flow of fluid to and from the opposite ends of said cylinder, in combination, a compensating device comprising an auxiliary cylinder, a piston therein, a conduit connecting one end of said cylinder with said hydraulic circuit adjacent one end of said main cylinder, and means for adjusting .the tension of said spring.

8. In a metal planer having a table, a main piston and cylinder device for actuating said table and a hydraulic circuit including pumping mechanism and valve mechanism for supplying and controlling the flow of fluid to and from the opposite ends of said cylinder, in combination, a compensating device comprising an auxiliary cylinder, a piston therein, a conduit connecting the head end of said cylinder with said hydraulic circuit adjacent one end of said main cylinder, a

draulic circuit adjacent one end of said main cylinder, resilient means in the other end of said auxiliary cylinder for resisting movement of the piston therein, and a second compensating device comprising a cylinder, a piston therein, resilient means in one end of said last mentioned cylinder for resisting movement of the piston therein, and a valve device in each of the connecting means between the cylinders of the compensating de- 10 vices and the hydraulic circuit.

PAUL S. JACKSON.