JP2000107964A - Hydraulic clamp device for machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the equipment cost by making a high cost of variable displacement pump unnecessary, as well as to provide a clamp device for machine tool which can reduce an energy loss by using no large pump when the clamping condition is maintained. SOLUTION: In this hydraulic clamp device for machine tool, a hydraulic cylinder 1; and a hydraulic pressure source connected to the hydraulic cylinder 1 through a changeover valve 4; are provided, and an article 2 is held between the piston rod 1c of the hydraulic cylinder 1 and a fixing surface 3, by extending the hydraulic cylinder 1. In such a hydraulic clamp device, the hydraulic pressure source has a main pump P1 with a large capacity constant discharge amount; and a hydraulic pressure source P2 for leak conpensation; and the main pump P1 is driven in the extension and contraction operation time of the hydraulic cylinder 1, while only the hydraulic pressure source P2 for leak compensation is operated when the condition to clamp the article by the piston rod 1c of the hydraulic cylinder 1 is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic clamping device for a machine tool, which presses and fixes a workpiece to a worktable or a wall surface when machining with a machine tool, or grips the workpiece with a chuck mechanism.

[0002]

2. Description of the Related Art A conventional clamping device shown in FIG. 4 includes a hydraulic cylinder 1 which is operated by hydraulic pressure.
The workpiece 2 is pressed against the wall surface 3 to be clamped or released by the expansion and contraction of the workpiece 2. The ports 4a and 4b of the switching valve 4 are connected to the bottom chamber 1a and the rod chamber 1b of the hydraulic cylinder 1. The supply port 4c of the switching valve 4 is connected to a pump flow path 5 communicating with the discharge port of the variable discharge pump P.
The tank flow path 6 is connected to d. That is, the bottom chamber 1a and the rod chamber 1b are connected to the variable discharge pump P or the tank T via the switching valve 4. When the inclination of the swash plate is changed while maintaining a constant rotation speed by the motor M, the variable discharge pump P is a pump that changes its capacity and can control the discharge flow rate. In addition, this variable discharge pump P
It is equipped with a so-called constant horsepower control mechanism and has control characteristics shown in FIG.

Further, the switching valve 4 is an electromagnetic valve, which is maintained at a normal position shown by a spring 4e, but is switched to an offset position by energizing a solenoid 4f. The solenoid 4f is controlled by a control mechanism (not shown). When the switching valve 4 is in the normal position as shown in the figure,
The bottom chamber 1a of the hydraulic cylinder 1 has ports 4a, 4c
Is connected to the variable discharge pump P through the rod side chamber 1b.
Is connected to the tank T via the ports 4b and 4d. In this state, when the pressure oil is supplied from the variable discharge pump P to the bottom chamber 1a, the pressure oil is discharged from the rod chamber 1b to the tank T, and the hydraulic cylinder 1 is extended. Thus, when the hydraulic cylinder 1 is extended, the piston rod 1c presses the workpiece 2 against the wall surface 4 and clamps it.

On the other hand, when the switching valve 4 is switched to the offset position, the pressure oil is supplied to the rod side chamber 1b of the hydraulic cylinder 1, and the pressure oil in the bottom side chamber 1a is supplied to the tank T.
Is discharged to Then, the hydraulic cylinder 1 contracts and enters an unclamped state. In the above-described expansion and contraction operation of the hydraulic cylinder 1, the higher the speed, the higher the work efficiency. For this purpose, the variable discharge pump P
The discharge flow rate supplied from the hydraulic cylinder 1 to the hydraulic cylinder 1 must be increased. Therefore, during the expansion and contraction operation of the hydraulic cylinder 1, the swash plate of the variable discharge pump P is tilted greatly, and A in FIG.
Is supplied. However, at point A, the pressure is kept low. This is because if only the hydraulic cylinder 1 is to be moved quickly to the target clamping position, not much pressure is required.

On the other hand, when the hydraulic cylinder 1 is extended and clamps the workpiece 2, in order to maintain the clamped state, it is only necessary to maintain the pressure in the bottom chamber 1a of the hydraulic cylinder 1. That is, when the piston rod 1c of the hydraulic cylinder 1 has full stroke and clamps the workpiece 2, a large discharge amount of the variable discharge pump P is not required. Since only the leak amount needs to be supplied to the bottom side chamber 1a, B in FIG.
As shown in the figure, the capacity of the variable discharge pump P is set small, and the discharge amount is reduced. However, at this time, a high pressure is required because the hydraulic cylinder 1 must maintain the holding force. In the drawings, reference numeral 7 denotes a check valve, and reference numeral 8 denotes a relief valve. Therefore, when the pressure in the pump flow path 5 becomes equal to or higher than the set pressure, the pressure in the pump flow path 5 is reduced via the relief valve 8.
The pressurized oil is discharged to the tank T.

[0006]

In the above-described clamping device, the variable discharge pump P is operated so that the hydraulic cylinder 1 operates quickly when the operation of the hydraulic cylinder 1 is switched.
Is set to a low pressure and a large capacity, but when the hydraulic cylinder 1 maintains the extended clamp state, the pump P
Is set at a high pressure with a small capacity corresponding to the leak amount. Then, in order to change the capacity of the variable discharge pump P, the tilt angle of the swash plate is changed, but the variable discharge pump P and the motor M are constantly rotating. That is, even when the variable discharge pump P is set to a small capacity, a large pump must be rotated at a constant speed.

As described above, even when the discharge amount is small, the motor M must rotate the large variable discharge pump P. Therefore, energy loss is large. In addition, since a large-capacity variable discharge pump is expensive, there is a problem that the apparatus becomes expensive. An object of the present invention is to provide a machine tool clamping device that can reduce energy loss without using a large pump when maintaining a clamped state. Another object is to reduce the cost of equipment by eliminating the need for expensive variable displacement pumps.

[0008]

According to a first aspect of the present invention, there is provided a hydraulic cylinder and a hydraulic source connected to the hydraulic cylinder via a switching valve. A hydraulic clamping device for a machine tool for holding an object between a hydraulic pump and a fixed surface, wherein the hydraulic source includes a large-capacity constant-discharge main pump and a leak-compensating hydraulic source. Is driven so that only the leak compensating hydraulic source is operated when the state where the object is clamped by the piston rod of the hydraulic cylinder is maintained. The second invention is characterized in that the hydraulic pressure source for leak compensation is a small capacity constant discharge pump.
The third invention is characterized in that the hydraulic pressure source for leak compensation is an accumulator in which the discharge pressure of the main pump is accumulated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A clamp device according to a first embodiment shown in FIG.
This pump flow path 5 is branched into flow paths 5a and 5b on the upstream side, and through these flow paths 5a and 5b,
The first and second pumps P ₁ and P ₂ are connected in parallel.
The first pump P ₁ is a constant delivery pump of large capacity which is connected via a check valve 7 to the flow path 5a. Further, the second pump P ₂ is a constant delivery pump of small capacity connected through a check valve 9 into the flow path 5b. A motor M ₁ for rotating the _first and second pumps P ₁ and P ₂ ,
The driving of M ₂ is controlled by the controller 10.

[0010] The construction and operation of the hydraulic cylinder 1 and the switching valve 4 are the same as those of the conventional device. However, the piston rod 1c of the hydraulic cylinder 1 is provided with a detection unit 1d that moves integrally with the piston rod 1c. Further, switches 11 and 12 are provided around the piston rod 1c to output a signal to the controller 10 when the detection unit 1d comes into contact therewith.

These switches 11 and 12 operate as follows. As shown in the drawing, when the hydraulic cylinder 1 is extended and clamps the object 2, the detecting unit 1d
Contact Then, the switch 11 is connected to the controller 1
By outputting a signal to 0, the controller 10 recognizes that the clamp operation has been completed. Conversely, when the piston rod 1c moves in the direction in which the hydraulic cylinder 1 contracts, the detection unit 1d contacts the switch 12. This switch 12
Outputs a signal, the controller 10 recognizes that the unclamping operation has been completed. Then, the controller 10 is clamped state → unclamped state or, when switching unclamped → clamped state, i.e., only when the hydraulic cylinder 1 is expansion and contraction, so as to drive the first pump P ₁ ing.

Next, the operation of the clamp device will be described. A description will be given of a case where the hydraulic cylinder 1 is changed from the contracted state, that is, from the unclamped state to the clamped state. A switching valve 4 to the normal state, driving the first pump P _1. From this first pump P _1, a large discharge amount, because it is supplied to the bottom chamber 1a of the hydraulic cylinder 1, the hydraulic cylinder 1 is quickly extended. When the hydraulic cylinder 1 is extended and enters the clamp state, the switch 11 is turned on, and the controller 10 recognizes the end of the clamp operation. Upon detecting the completion of the clamping operation, the controller 10 stops the first pump P _1, to drive the second pump P ₂ instead.

[0013] As described above, in the clamped state, only the second pump P ₂ is driven. In order to maintain the clamped state, only the leak amount needs to be supplied to the cylinder 1 as described in the conventional example. Accordingly, the supply amount is sufficient only second discharge amount of the pump P ₂ of small capacity. At clamp drives only the second pump P _2,
A small amount of pressure oil is supplied to the bottom chamber 1a of the hydraulic cylinder 1. In this way, the workpiece 2 is processed while maintaining the clamped state. When the machining of the workpiece 2 is completed, the switching valve 4 is switched to the offset position, and the controller 10
₁ drives, stopping the second pump P _2.

When the switching valve 4 is at the offset position, a large discharge from the first pump P ₁ is supplied to the rod side chamber 1 b of the hydraulic cylinder 1. Then, the hydraulic cylinder 1 contracts quickly and enters an unclamped state. When the hydraulic cylinder 1 contracts, the detecting portion 1d provided on the piston rod 1c moves leftward in the figure.
Output a signal to 0. The controller 10, when detecting the unclamped state, stops the first pump P _1.

[0015] As described above, in the clamping device of the first embodiment, when expansion and contraction of the hydraulic cylinder, for driving the first pump P _1. Furthermore, when holding the clamp state, so that to drive the second pump P _2. In other words, as shown in FIG.
Different types of pumps are used. Therefore, unlike the conventional example, there is no need to drive a large pump even when a large discharge amount is not required, and energy loss is correspondingly small. Further, since the first pump P ₁ is also constant delivery pump of large capacity, which is less expensive than the variable discharge pump P of a large conventional. In addition, since it is compatible with low pressure, an inexpensive large capacity pump can be selected. In this first embodiment, the first pump P ₁ is the main pump of the present invention, the second
Pump P ₂ is a hydraulic source for leak compensation of the present invention.

[0016] In the first embodiment, the clamping operation is completed, only when this state is maintained, but so as to drive the second pump P _2, even when expansion and contraction of the cylinder, the the second pump P ₂ may be allowed to drive. By this way, at the time of expansion and contraction of the cylinder, so that the discharge amount of the sum of the first pump P ₁ and the second two pumps of the pump P ₂ is supplied to the hydraulic cylinder 1. Thus, the first displacement of the pump P _1, it is possible to reduce only the second capacity of the pump P _2. Although the second pump P ₂ has a high pressure, a small pump having a small capacity is sufficient.
It is cheap. In short, both pumps P ₁ and P ₂ can use relatively cheap pumps.

The second embodiment shown in FIG. 3 uses an accumulator 13 as a hydraulic pressure source for leak compensation. One flow path 5 a branched from the pump flow path 5 is provided with a large-capacity constant discharge pump P through a check valve 7.
₃ and the accumulator 13 is connected to the other flow path 5b.
Are connected. The pump P ₃ corresponds to the first pump 1 of the first embodiment, the main pump of the present invention. The accumulator 13 is provided with the pump P
_{When 3} is driven, a part of the discharge pressure can be stored. Further, the pressure sensor 1 is provided in the flow path 5b.
4 and the pressure sensor 14 is connected to the controller 1
0 is connected. Then, the pressure sensor 14 outputs a pressure detection signal of the flow path 5b to the controller 10.
This connects the motor M ₃ for rotating the pump P ₃ to the controller 10, the controller 10, the pump P ₃ so as to control the drive. Other, hydraulic cylinder 1
The configuration and operation of the switching valve 4 are the same as those of the first embodiment.

Next, the operation of the clamp device according to the second embodiment will be described. There switching valve 4 is in the normal position shown, the pump P ₃ is driven, a large discharge quantity is supplied to the bottom chamber 1a of the hydraulic cylinder 1. Then, the piston rod 1c moves quickly and clamps the workpiece 2.
In such a clamped state, the piston rod 1c
Does not move any further. Bottom side chamber 1 of hydraulic cylinder 1
while there is no change in the volume of a, since the discharge from the pump P ₃ is followed, the pressure in the pump passage 5 is increased. The pressure in the pump flow path 5 is stored in the accumulator 13 via the flow path 5b. Then, when the pressure sensor 14 detects a pressure equal to or higher than a predetermined pressure, the controller 10 detects that the extension operation of the hydraulic cylinder 1 has been completed and the hydraulic cylinder 1 has been clamped. Then, the controller 10 stops the pump P ₃ controls the motor M _3. At this point, a sufficient pressure is stored in the accumulator 13.

The pressure stored in the accumulator 13 compensates for the leak from the hydraulic cylinder 1. That is, in the clamped state where the pump P ₃ is stopped,
When a leak from the bottom chamber 1a of the hydraulic cylinder 1 to the tank flow path 6 side occurs, the pressures of the pump flow path 5 and the flow path 5b also decrease via the bottom chamber 1a. When the pressure in the flow path 5b decreases, the accumulator 13 releases the pressure. Thus, the pressure in the bottom chamber 1a of the hydraulic cylinder 1 is maintained by the pressure released by the accumulator 13, and the clamp state can be maintained.

[0020] Conversely, when unclamped from the clamp state, switches the the switching valve 4 to the offset position, for driving the pump P _3. A large amount of oil discharged from the pump P ₃ is the hydraulic cylinder 1 the rod chamber 1b
And the pressure oil in the bottom chamber 1a is discharged to the tank T. Therefore, the hydraulic cylinder 1 contracts quickly and enters the unclamped state. The piston rod 1c is
Even at full stroke to the left in the figure, if continues discharged from the pump P _3, as in the case of the clamped condition,
The pressure in the pump channel 5 increases. When the pressure in the flow path 5b exceeds a predetermined pressure, the detection signal is sent to the pressure sensor 1
4 to the controller 10. Controller 1
0 detects that the contraction operation of the cylinder becomes unclamped state ends, stopping the pump P _3. And
Even if the pressure oil leaks from the rod side chamber 1b of the hydraulic cylinder 1 and the pressure drops, there is no particular problem in maintaining the unclamped state, but the leak is compensated by the pressure of the accumulator 13. That is, in the second embodiment, the accumulator 13 serves as a hydraulic pressure source for leak compensation of the present invention.

[0021] As described above, the clamping device of the second embodiment, only during expansion and contraction of the hydraulic cylinder 1, and drives the pump P ₃ of large capacity. In order to maintain the clamped state, the accumulated pressure of the accumulator 13 is used. Therefore, unlike a conventional example, there is no need to constantly rotate a large pump, and energy loss is small. Further, it is possible to use an inexpensive constant-delivery pump P ₃ as compared with the variable discharge pump. Moreover, one constant discharge pump
Since only one unit need be provided, the driving energy is sufficient for one unit, and the control mechanism of the controller 10 can be simplified as compared with the first embodiment.

Although the first and second embodiments have described the table clamp, any type of clamp mechanism including the hydraulic cylinder 1 and the like may be used.
For example, it can be used for a device provided with a chuck.
Also, it can be used for a chuck mechanism of an NC lathe. In particular, in the chuck mechanism of the NC lathe, the cylinder must be rotated. In this rotating part, oil is intentionally leaked in order to enhance lubricity. Even in such a case, the main pump is stopped, and the leak amount can be dealt with only by the hydraulic pressure source for leak compensation, so that the cost is reduced accordingly.

[0023]

According to the first to third aspects of the present invention, the large-capacity main pump is driven only when the hydraulic cylinder is extended and retracted, and only the leak-compensating hydraulic source is operated when the object is clamped. Thereby, energy loss can be reduced. In addition, since a constant-discharge pump can be used for a large-capacity main pump, it is less expensive than a conventional large-sized variable discharge pump. In addition, since the main pump may be compatible with low pressure, an inexpensive large capacity pump can be selected. According to the second aspect, by using an inexpensive constant discharge pump as the main pump and the hydraulic pressure source for leak compensation, the hydraulic pressure source can be made inexpensive. In addition, the pump as a hydraulic pressure source for leak compensation has a high pressure, but a small one with a small capacity is sufficient.
It is cheap. Therefore, a relatively cheap pump can be used for both pumps. According to the third aspect, by using the accumulator as the leak compensating hydraulic source, the drive mechanism of the leak compensating hydraulic source can be simplified and energy-saving.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment.

FIG. 2 is a graph showing pressure flow characteristics of first and second pumps.

FIG. 3 is a circuit diagram of a second embodiment.

FIG. 4 is a circuit diagram of a conventional clamp device.

FIG. 5 is a graph showing pressure flow characteristics of a variable discharge pump.

[Explanation of symbols]

1 cylinder 2 workpiece 3 wall 4 changeover valve 10 controller 13 accumulator P ₁ first pump P ₂ second pump P ₃ pump

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naohiro Nagato 2-4-1 Hamamatsucho, Minato-ku, Tokyo World Trade Center Building Kayaba Industry Co., Ltd. F-term (reference) 3C016 BA03 BA05 CA03 CB03 CC01

Claims (3)

[Claims] 1. A machine tool hydraulic clamping device, comprising: a hydraulic cylinder; and a hydraulic source connected to the hydraulic cylinder via a switching valve, wherein the hydraulic source operates to hold an object. Equipped with a main pump for discharge and a hydraulic source for leak compensation, activates the main pump when the hydraulic cylinder expands and contracts, and activates only the hydraulic source for leak compensation when holding the object clamped A hydraulic clamping device for a machine tool, wherein the hydraulic clamping device is configured to cause the clamping. 2. The machine tool clamping device according to claim 1, wherein the leak compensating hydraulic source is a small capacity constant discharge pump. 3. The clamping device for a machine tool according to claim 1, wherein the hydraulic pressure source for leak compensation is an accumulator in which the discharge pressure of the main pump is accumulated.