US3662651A

US3662651A - Hydraulic system for limiting deflection of a piston stop

Info

Publication number: US3662651A
Application number: US885891A
Authority: US
Inventors: Henry L Cunningham
Original assignee: Hardinge Brothers Inc
Current assignee: Hardinge Brothers Inc
Priority date: 1969-12-17
Filing date: 1969-12-17
Publication date: 1972-05-16
Anticipated expiration: 1989-05-16
Also published as: GB1306119A

Abstract

This invention relates to a hydraulic system for machine tool operation which limits deflection of a stop at the end of machine tool travel. The hydraulic system includes a cylinder, a piston, a fluid line connected to one end of the cylinder, with the fluid lines being alternately pressure and exhaust lines. Fluid under pressure is introduced alternately in one of the fluid lines for moving either a piston or a cylinder housing relative to the piston and a means for reversing fluid flow in the lines acts to move either the piston or cylinder housing back and forth. Maximum flow pressure is maintained in one of the fluid lines when used as a pressure line, and a minimum fluid pressure is maintained in one of the fluid lines when used as an exhaust line. The cylinder housing includes a stop whereby said minimum fluid pressure on one side of the piston acts against the maximum fluid pressure on the other side of the piston for limiting deflection of the stop.

Description

United States Patent Cunningham [451 May 16, 1972 [54] HYDRAULIC SYSTEM FOR LIMITING DEFLECTION OF A PISTON STOP [72] Inventor:

[73] Assignee: I-Iardinge Brothers, Inc., Elmira, N.Y.

[22] Filed: Dec. 17, 1969 [21] App]. No.: 885,891

Henry L. Cunningham, Horseheads, N.Y.

Primary Examiner-Edgar W. Geoghegan Assistant Examiner-Irvin C. Cohen AttorneyShlesinger, Arkwright & Garvey ABSTRACT This invention relates to a hydraulic system for machine tool operation which limits deflection of a stop at the end of machine tool travel. The hydraulic system includes a cylinder, a piston, a fluid line connected to one end of the cylinder, with the fluid lines being alternately pressure and exhaust lines. Fluid under pressure is introduced alternately in one of the fluid lines for moving either a piston or a cylinder housing relative to the piston and a means for reversing fluid flow in the lines acts to move either the piston or cylinder housing back and forth. Maximum flow pressure is maintained in one of the fluid lines when used as a pressure line, and a minimum fluid pressure is maintained in one of the fluid lines when used as an exhaust line. The cylinder housing includes a stop whereby said minimum fluid pressure on one side of the piston acts against the maximum fluid pressure on the other side of the piston for limiting deflection of the stop.

4 Claims, 1 Drawing Figure ll? 5P "919710 3 I38 I44 .IOB I220 124 ME 2200 I46 2'80 Tp now? we zozf 2l4u J26 PRESSURE I28 REDUCING I32 126 VALVE PITENT'Enm 1a m1 ATTORNEYS HYDRAULIC SYSTEM FOR LIMITING DEFLECTION OF A PISTON STOP This invention relates to hydraulic systems to be used in an automatic chucking machine" for automatic precision finishing of work pieces.

PRIOR ART DEVELOPMENTS Machine tools which include a hydraulically motivated piston device for moving a machine part into working position are old in the art. Cunningham, U.S. Pat. No. 3,224,070, Dec. 21, 1965, discloses one of those machine tool devices. The Cunningham patent, issued to the inventor of the hereindescribed invention, generally discloses the basic mechanical structure, machine tool operation, and electric circuitry used in this invention. This invention, although it could be applied to the machine described in the Cunningham patent, is designed primarily for use in an automatic chucking machine.

Significant problems arise in the operation of the automatic chucker when this invention is not included in the hydraulic circuitry. When the cross slide and turret carriage are moved into position by their respective piston devices, their pistons near the end of movement toward their respective work pieces, contact a solid stop. Before the present invention is applied to those operations, both the cross slide and turret carriage hit their respective solid stops and then very slowly creep into final position. This consumes from two to ten seconds depending on the rate of feed at which the controlling feed valve is set.

This time lag is caused by the mechanical deflection of the solid stops as the pressure differential between the two sides of the piston changes. Upon metering the fluid exhausting from the cylinder when distance between the piston and its stop is decreasing, pressure on the exhaust side remains slightly under pressure on the pump side until the piston hits the solid stop. When the solid stop is contacted the pressure in the exhaust side slowly bleeds off, the length of time depending on the feed valve setting. With pump pressure remaining constant the pressure exerted by the piston device against the solid stop gradually increases as the exhaust side pressure is reduced, thereby slowly deflecting the solid stop and changing the position of the cross slide and turret carriage which, in turn, moves the machine tool. This change of position occurs until the exhaust side pressure bleeds down to atmospheric pressure at which time the movement ceases.

The above-described situation makes it difficult to machine close-turned diameters and bores on work pieces without a relatively long time delay to allow the machine tool to settle into its final position against the stop. That time delay considerably lengthens the cycle time of an automatic machine tool mechanism.

Additionally, when the four-way valve controlling fluid movement shifts to reverse the direction in which the cross slide or turret carriage moves, the cross slide or turret carriage takes a momentary jump caused by the stop moving back to its pre-deflection position. If the tool is in contact with the work piece, a mark is cut into the work piece, which is in many cases objectionable. This jump is caused by no pressure being present in the exhaust side of the cylinder through the fourway valve between the cylinder and the choke valve.

The subject matter of this invention discloses a workable solution to the hereinbefore described problems.

OBJECTS AND SUMMARY it is therefore, an object of this invention to provide a hydraulic system for machine tool operation which reduces the time that it takes for a carriage and cross slide of a machine such as an automatic chucker to move into final working position.

Another object of this invention is to provide a hydraulic system for machine tool operation which reduces the cycle time of an automatic chucker.

Still a further object of this invention is to provide a hydraulic system for machine tool operation which considerably reduces the time required by a machine tool slide to creep into a final accurate position.

A further object of this invention is to provide a hydraulic system for machine tool operation which creates a condition in the exhaust side of a piston so the fluid pressure on the exhaust side will not have to bleed down to atmospheric pressure for piston controlled slides to reach a final accurate position.

Still another object of this invention is to provide a hydraulic system for machine tool operation which maintains an adjustable constant minimum hydraulic pressure in fluid exhaust lines.

Yet a further object of this invention is to provide a hydraulic system for machine tool operation which limits mechanical deflection of a solid stop once it is contacted by a piston device moved under relatively high pressure.

Still a further object of this invention is to provide a hydraulic system for machine tool operation which utilizes a pressure reducing valve to maintain an adjustable constant minimum pressure in fluid exhaust lines.

Yet another object of this invention is to provide a hydraulic system for machine tool operation which prevents the momentary jump of a machine tool caused by the stop jumping back to its pre-deflection position when pressure exerted by a piston device against the stop is relieved.

To summarize, it is therefore an object of this invention to provide a hydraulic system for machine tool operation which provides a pressure differential between the pump side and the v exhaust side of a piston which moves a cross slide or turret carriage, the pressure differential being great enough to allow the piston to move a machine tool into working position and small enough to prevent excessive deflection of a solid stop when contacted by the piston under pressure.

These and other objects of this invention and advantages and capabilities will be apparent from the following description and appended claims and accompanying drawings in which:

The FIGURE is a simplified hydraulic diagram typical for use in the operational control of the herein-described invention.

THE FIGURE The invention hereinafter described specifically relates to a hydraulic control circuit for operation of a turret carriage and cross slide for an automatic chucker, but may be adapted for use in other generally similar machines.

The condition of the machine parts and their working mechanisms shown in the FIGURE is that the turret carriage and cross slide are in their non-working or back positions. The turret carriage and the cross slide are both retracted away from the work piece. All of the hydraulic valves are in positions that they assume when their solenoids are de-energized, the valves being returned to this position by return springs. Altemately, the hydraulic valves, instead of being returned to their back positions by return springs, could include another solenoid that would control the valves by being alternately energized and de-energized with respect to the first solenoid.

Hydraulic pump A, having been energized by 'a hydraulic pump motor (not shown), delivers hydraulic fluid under pressure to to pressure line 100. To maintain the turret carriage TC in its retracted position, fluid flows through line 100, through control valve 102 in its de-energized state, and into line 104. Fluid flows from line 104, through fluid passage 106, and into cylinders which are connected by the cylinder port 108. Piston rods 107 extend from both sides of pistons TP so that pistons TP will be of equal areas on both sides.

As pistons TP move turret carriage TC to the right in the FIGURE to reach the position shown, fluid in cylinders 110 on the left side of pistons TP in the FIGURE, connected by port 112, exhausts through fluid passage 114 into line 116. As the exhaust fluid from line 116 flows through control valve 102 in its position shown in the FIGURE, the exhaust fluid enters line 118. A two-way valve 122, shown in the FIGURE in its fluidpassing position, is connected by line 120 to line 118. When two-way valve 122 is in its fluid-passing position, the exhaust fluid from line 118 flows through line 120, through two-way valve 122, through line 124, and into sump 126. When twoway valve 122 is in its fluid-blocking position, exhaust fluid in line 118 flows to a plurality of solenoid-operated two-way valves, as described in detail in the hereinbefore mentioned Cunningham patent, for controlling the feed rates for each turret position.

Pressure reducing valve 128 is connected on one side to line 100 by line 130, and is connected on the other side to line 118 by line 132. A check valve 134 is positioned on line 132 to prevent fluid flow from line 118 into line 132 when fluid pressure in line 118 is greater than fluid pressure in line 132, while allowing fluid to flow from line 132 into line 118 when fluid flowing in line 132 is under greater pressure than fluid flowing from line 118. The positioning of pressure reducing valve 128 as just described allows a minimum fluid pressure to be maintained in line 116 when four-way control valve 102 is in the position shown in the FIGURE. When four-way control valve 102 is energized line 1 16 becomes a pressure line and line 104 becomes an exhaust line resulting in pressure reducing valve 128, through line 118a, maintaining a minimum fluid pressure in line 104. Check valve 134a performs the same function as described for check valve 134 except with respect to line 1 18a.

When four-way control valve 102 is energized, it changes its position and fluid flows through line 110 and into line 116. The fluid then flows through fluid passage 114 and into cylinders 110 on the left side of pistons TP in the FIGURE, cylinders 110 being connected by port 112, thereby resulting in pistons TP moving turret carriage TC to the left in the FIGURE. Fluid is discharged from cylinders 110 on the right side of pistons T? in the FIGURE, connected by port 108, through fluid passage 106, through line 104, through four-way control valve 102, and into line 118a. Two-way valve 122a is l the counterpart of two-way valve 122 and when in its fluid passing position, as shown in the FIGURE, it allows exhaust fluid in line 118a to flow intosump 126. However, when twoway valve 122a is in its fluid-blocking position, exhaust fluid flowing through line 118a is diverted to line 138. Line 138 is connected to a plurality of solenoid-operated two-way valves, as described in the Cunningham patent in detail,'for controlling the feed rates for each turret position.

As fluid under pressure enters cylinders 110 on the left side of pistons TP in the FIGURE, pistons TP cause turret carriage TC to move to the left in the FIGURE. When turret carriage TC reaches the end of its travel, pistons TP contact solid stops 109 which are the end of cylinders 1 10, but may be recognized devices such as protuberances extending into the path of piston travel. As pistons TP contact the right end of cylinders 110, the relatively high pressure exerted by hydraulic fluid on pistons TP normally causes the solid stops 109 to deflect slightly. The minimum fluid pressure maintained in exhaust line 104 by pressure reducing valve 128 limits considerably deflection of the solid stops 109 by creating a pressure differential high enough to move turret carriage TC to the left in the FIGURE, but low enough to prevent excessive deflection of the solid stops 109.

With the preceding description being limited to movement of the turret carriage TC, the following will describe the operation of cross slide 200. The hydraulic configuration shown in the FIGURE shows piston 201 in its back position with the cross slide 200 away from the work piece (not shown). Piston rod 205 extends on both sides of piston 201 so that both sides of piston 201 are of equal area. The automatic chucker (not shown) is arranged so that the cross-slide 200 can be fed against stop 207 while the tool is facing a shoulder on the work piece, after which the carriage slide moves the tool axially to either turn a close diameter or bore a close hole. If this invention is not incorporated into the hydraulic circuitry for the automatic chucker and the time-consuming bleeding of exhaust pressure down to atmospheric pressure is present, the longitudinal slide would be moved before the cross slide settles into its final accurate work position, producing a tapered diameter or bore.

To maintain piston 201 in the position shown, fluid under pressure from pump A flows through line 202, through fourway control valve 203 in its de-energized position, through line 204, and into cross slide cylinder 206. Fluid exhausted from cylinder 206 on the right side of piston 20] in the FIGURE flows through line 208, through four-way control valve 203, and into line 210. Two

choke valves

212, 214 are arranged in parallel on line 210 and the flow of exhaust fluid to one or the other of

choke valves

212, 214 is controlled by two-

way valves

216 and 218, respectively. When two-way valve 216 is in a fluid-blocking position, two-way valve 218 is in a fluid-passing position thereby allowing the exhaust fluid to flow through choke valve 214 and into sump 126., When

twoway valves

216 and 218 are reversed, the exhaust fluid flows from line 210, through choke valve 212, and into sump 126. The selectively restricted passing positions of

choke valves

212 and 214 act to control movement speed of the cross slide 200.

When solenoid 219 is energized, four-way control valve 203 shifts its position for moving the cross slide into working position. When the position of four-way control valve 203 is thus changed, fluid under pressure from line 202 flows through control valve 203, through line 208, and into cylinder 206 on the right side of piston 201 as shown in the FIGURE, thereby moving cross slide 200 to the right in the FIGURE. As piston 201 moves to the right in the FIGURE, fluid from cylinder 206 is exhausted into line 204, through control valve 203, through line 210a, and selectively through two-way valve 216a and choke valve 212a or through two-way valve 218a and choke valve 214a, depending on the positions of two-way valves 216a and 218a.

Similar to the hydraulic configuration described for the turret charriage TC, pressure reducing valve 128 connects to lines 210 and 2100 through lines 220 and 220a, respectively. Check valves 222 and 2220 are positioned on lines 220 and 220a, respectively, to prevent fluid flow from

lines

210 and 210a, respectively, into lines 220 and 220a, respectively, when fluid pressure in

lines

210 and 210a respectively, is greater than fluid pressure in lines 220 and 220a, respectively, while allowing fluid to flow from lines 220 and 220a, respectively, into

lines

210 and 210a, respectively, when fluid flowing in lines 220 and 220a, respectively, is under greater pressure than fluid flowing in

lines

210 and 210a, respectively. As hereinbefore described for the turret carriage TC, pressure reducing valve 128 maintains a minimum fluid pressure at all times in line 204 or line 208, whichever is acting as an exhaust line, depending on the position of four-way control valve 203.

Similar to the situation described with respect to the turret carriage TC, as cross slide piston 201 reaches the end of its travel in cylinder 206, piston 201 comes in contact with a solid stop 207. That stop 207 can either be an end of cylinder 206 in the FIGURE or a protuberance extending into the path of piston travel. As piston 201 contacts the left end of cylinder 206, the relatively high pressure exerted by hydraulic fluid on piston 201 normally causes the solid stop 207 to deflect slightly. The minimum fluid pressure maintained in exhaust line 204 by pressure reducing valve 128 limits deflection of the solid stop 207 by creating a pressure differential high enoughto move cross slide to the right in the FIGURE, but low enough to prevent excessive deflection of the solid stop 207.

Cam switches (not shown) similar to the ones disclosed in the Cunningham patent, control the position of four-way control valve 203 by selectively energizing and de-energizing solenoid 219.

OPERATION For an automatic chucker, the hydraulic system described herein best operates when the fluid from pump A is introduced into the hydraulic system at approximately 300 p.s.i., and pressure reducing valve 128 is set at 175 p.s.i. A differential pressure of approximately 125 p.s.i. has been found adequate in most instances providing a minimum pressure substantially above atmospheric pressure, but this will of course vary somewhat depending upon the job to be accomplished and the type of machine used. The minimum pressure above atmospheric pressure in exhaust lines is significent in that when a piston contacts its respective solid stop the pressure on the exhaust side of the piston will only have to bleed down to 175 p.s.i. before the check valve will open allowing the 175 p.s.i. from the pressure reducing valve to enter the exhaust line. With the pressure against the opposite side of the piston being 300 p.s.i., the carriage is held against the solid stop by the pressure differential of 125 p.s.i. in a satisfactory manner. The time for the pressure on the exhaust side of the piston to bleed to 175 p.s.i. is relatively small at any feed valve setting and the carriage quickly reaches its final accurate position with a minimum creepage caused by deflection of the solid stop. Until pressure in the exhaust line drops to 175 p.s.i. the check valve keeps the higher pressure from flowing back through the pressure reducing valve.

While this invention has been described in connection with the preferred embodiment, it will be understood that this invention is capable of further modification. This application is intended to cover any variations, uses, or adaptations of the invention following, as well as the principles of the invention in general including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and further including such departures as may be applied to the essential features hereinbefore set forth and fall within the scope of the invention or the limits of the appended claims.

Having thus described my invention, What I claim is:

1. A hydraulic system for precision machine tool operation for limiting deflection of a stop means at the end of machine tool travel comprising:

a. piston and cylinder means,

b. a first fluid line connected near one end of said cylinder means,

c. a second fluid line connected to the other end of said cylinder means,

d. said fluid lines being alternately pressure and exhaust lines,

e. valve means for reversing fluid flow in said fluid lines for moving said piston means back and forth relative to said cylinder means,

f. a pressure reducing valve,

g. means for introducing fluid into said first fluid line and said pressure reducing valve at a first predetermined pressure,

b. means for conveying fluid at a second predetermined pressure lower than said first predetermined pressure and substantially above atmospheric pressure from said pressure reducing valve to said valve means and said second fluid line, and

i. said conveying means including check valve means permitting fluid passage from said pressure reducing valve to said valve means and preventing fluid passage from said valve means to said pressure reducing valve.

2. A hydraulic system as in claim 1 and wherein:

a. said valve means includes a four-way valve means, and

b. means for positioning said four-way valve means.

3. A hydraulic system as in claim 2 and including:

a. a plurality of choke valve means,

b. each of said choke valve means including a choke valve and a two-way valve having fluid blocking and fluid passing positions and being in fluid commumication with said choke valve,

c. means for selectively positioning said two-way valves, and d. a sump connected to said choke valves.

4. A hydraulic system for precision machine tool operation for limiting deflection of a stop means at the end of machine tool travel comprising:

a. piston and cylinder means,

b. a first fluid line connected near one end of said cylinder means,

c. a second fluid line connected to the other end of said cylinder means,

d. said fluid lines being alternately pressure and exhaust lines,

f. a pressure reducing valve,

g. means for introducing fluid into said first fluid line and said pressure reducing valve at a first predetermined pres sure,

h. means for conveying fluid at a second predetermined pressure lower than said first predetermined pressure and substantially above atmospheric pressure from said pressure reducing valve to said valve means and said second fluid line,

i. said conveying means including first and second check valves for receiving fluid from said pressure reducing valve,

j. said first check valve being in fluid communication through said valve means with one of said fluid lines and said second check valve being in fluid communication through said valve means with the other of said fluid lines, and

k. said check valves preventing fluid flow from said valve means to said pressure reducing valve.

Claims

1. A hydraulic system for precision machine tool operation for limiting deflection of a stop means at the end of machine tool travel comprising: a. piston and cylinder means, b. a first fluid line connected near one end of said cylinder means, c. a second fluid line connected to the other end of said cylinder means, d. said fluid lines being alternately pressure and exhaust lines, e. valve means for reversing fluid flow in said fluid lines for moving said piston means back and forth relative to said cylinder means, f. a pressure reducing valve, g. means for introducing fluid into said first fluid line and said pressure reducing valve at a first predetermined pressure, h. means for conveying fluid at a second predetermined pressure lower than said first predetermined pressure and substantially above atmospheric pressure from said pressure reducing valve to said valve means and said second fluid line, and i. said conveying means including check valve means permitting fluid passage from said pressure reducing valve to said valve means and preventing fluid passage from said valve means to said pressure reducing valve.

2. A hydraulic system as in claim 1 and wherein: a. said valve means includes a four-way valve means, and b. means for positioning said four-way valve means.

3. A hydraulic system as in claim 2 and including: a. a plurality of choke valve means, b. each of said choke valve means including a choke valve and a two-way valve having fluid blocking and fluid passing positions and being in fluid commumication with said choke valve, c. means for selectively positioning said two-way valves, and d. a sump connected to said choke valves.

4. A hydraulic system for precision machine tool operation for limiting deflection of a stop means at the end of machine tool travel comprising: a. piston and cylinder means, b. a first fluid line connected near one end of said cylinder means, c. a second fluid line connected to the other end of said cylinder means, d. said fluid lines being alternately pressure and exhaust lines, e. valve means for reversing fluid flow in said fluid lines for moving said piston means back and forth relative to said cylinder means, f. a pressure reducing valve, g. means for introducing fluid into said first fluid line and said pressure reducing valve at a first predetermined pressure, h. means for conveying fluid at a second predetermined pressure lower than said first predetermined pressure and substantially above atmospheric pressure from said pressure reducing valve to said valve means and said second fluid line, i. said conveying means including first and second check valves for receiving fluid from said pressure reducing valve, j. said first check valve being in fluid communication through said valve means with one of said fluid lines and said second check valve being in fluid communication through said valve means with the other of said fluid lines, and k. said check valves preventing fluid flow from said valve means to said pressure reducing valve.