VALVE APPARATUS

Abstract

The invention relates to a valve apparatus for setting and monitoring the clamping pressure of a clamping device (9) for workpieces which are to be clamped, in particular in lathes, having at least one pressure control valve (1A, 1B), via which the clamping pressure is set for the clamping device (9), and having at least one pressure sensor (6A, 6B) which detects the respective clamping pressure of the clamping device (9), which clamping pressure is to he adjusted in relation to a predefinable setpoint clamping pressure. It is possible by way of the valve apparatus to this effect to set the clamping pressure which is relevant in terms of safety, and also to monitor it, in particular to maintain or reduce it, during the machining in the sense of an adjustment.

Description

The invention relates to a valve apparatus for setting and monitoring the clamping pressure of a clamping device for workpieces which are to be clamped, particularly in lathes.

In modern machine tools, for example lathes, the workpieces to be machined are generally clamped by means of clamping devices which can be hydraulically actuated, particularly in the form of clamping cylinders, and/or are secured tightly by means of so-called tailstock spindle sleeves which can be hydraulically actuated, with the respective machine being released only after the clamping pressure is reached. If, at this point during machining with the machine tool, the clamping pressure on the clamping device is reduced due to a fault, this can lead to loosening of the clamping device, and the subsequently released workpiece can cause serious damage to the machine and constitutes a considerable safety risk for the machine operator.

In addition to this monitoring of the clamping pressure to ensure safe clamping forces, it can also be advantageous to reduce the clamping pressure, and therefore the clamping force, in order to prevent damage to the machined workpiece if it acquires a wall thickness geometry that has been reduced from “full bored,” for example, as a result of the type of machining and which, with the clamping force remaining the same relative first of all to the solid material used, would lead to the deformation of workpiece geometries that are reduced in wall thickness and therefore are weakened.

Proceeding from this prior art, the object of the invention is to increase safety in the clamping accommodation of workpieces to be machined in machine tools such as lathes, and to prevent inadvertent damage to the workpiece. This object is achieved by the valve apparatus with the features of claim 1 in its entirety.

The valve apparatus according to the invention is characterized in that it has at least one pressure control valve via which a clamping pressure adjustment for the clamping device takes place, there being at least one pressure sensor that detects the respective clamping pressure of the clamping device which is to be adjusted to a definable setpoint clamping pressure. With this valve apparatus, it is possible to set the clamping pressure which is relevant to safety engineering and also to monitor it during machining for purposes of adjustment, in particular to maintain or reduce it uniformly.

Using the respective pressure sensor, the current pressure of the clamping device is measured, whether in the form of the clamping cylinder which is to be hydraulically actuated or in the form of a tailstock spindle sleeve which is to be hydraulically actuated. This current clamping pressure should then correspond to a predefined setpoint clamping pressure which can be predefined by the control means, for example, in the form of a machine control for the machine tool. By triggering the pressure control valve, preferably in the form of a pressure reducing valve, the pressure of the clamping device can be set to constant pressure values or even reduced by means of triggering by means of the control means. Since, essentially for each workpiece to be machined according to the desired machining state, there are other clamping pressure constraints, they are defined in near real time as a setpoint clamping pressure by the control of the machine, that is to say, by the control means, as machining progresses. This ensures reliable clamping force monitoring in order to prevent the workpiece from unintentionally coming loose from the clamping device. Furthermore, it becomes possible, if necessary, to reduce the clamping force in order to protect the workpiece during machining against damage from a clamping-compressive force that has been set too high.

Other advantageous configurations of the valve apparatus according to the invention are the subject matter of the other dependent claims.

The valve apparatus according to the invention is detailed below using different exemplary embodiments as shown in the drawings. The figures are schematic in the manner of hydraulic diagrams.

FIG. 1 shows a first embodiment of the valve apparatus according to the invention using a pressure control valve;

FIG. 2 shows another embodiment as shown in FIG. 1 using two pressure control valves; and

FIG. 3 shows a third embodiment of the valve apparatus according to the invention as shown in FIGS. 1 and 2, but with a secondary pressure safeguard and with the elimination of the directional control valves.

In the three embodiments, fundamentally comparable components, in particular valve components, are used and designated with the same reference numbers. The main components are as follows:

• 1A, 1B pressure control valves with mechanical self-locking,
• 2 orifice,
• 4A, 4B directional control valves with latching (self-retaining) positions,
• 5 back pressure block in the form of a check valve,
• 6A, 6B pressure sensors,
• 7 rotary duct,
• 8 two check valves,
• 9 clamping cylinder made as a synchronous cylinder
• 10 clamping chuck with small transmission ratio (without self-locking)
• 11 hydraulic accumulator
• 12 control

The clamping cylinder, designated as 9 in the figures, is made as a so-called hydraulic synchronous cylinder, and the jaws of the clamping chuck 10 in one direction of motion are moved toward one another and in the opposite direction are moved away from one another. In this way, a workpiece to be machined (not shown) can be detachably fixed with a hydraulic actuation force both by way of the inside diameter and also in the other actuation direction by way of the outside diameter of the clamping jaws of the clamping chuck.

The rotary duct designated as 7 allows pivoting of the clamping device in at least one axis of motion or pivoting. These rotary ducts for hydraulic feed and drain lines are known in the prior art in a plurality of embodiments so that they will not be detailed any further here. In any case, in this way it is ensured by way of the rotary duct 7 that hydraulic supply of the working spaces of the clamping cylinder 9 takes place even when the clamping cylinder 9 is being pivoted with the clamping chuck 10. The clamping device which consists of the clamping cylinder 9 and the clamping chuck 10 is shown merely by way of example; different types of clamping devices (tailstock spindle sleeves) can likewise be used here for the valve apparatus which is still to be described.

The orifice designated as 2 on the output side of the respective pressure control valve 1A, 1B is used to adapt the volumetric flow to the volumetric size of the clamping cylinder 9, which, depending on the type of machining, can also be different for a machine tool. The fluid line designated as P is connected to a hydraulic supply means (not detailed), for example is formed from a hydraulic supply pump. The hydraulic accumulator, which is designated as 11 and which is connected to the pump line P, then allows pressure supply of the system when the power fails. The tank connecting line or tank line designated as T allows return of the working medium in the form of hydraulic oil into the tank, from where hydraulic supply can take place via the pump with the formation of a hydraulic circuit. This arrangement is also conventional so that it will not be detailed any further here.

In the embodiment as shown in FIG. 1, the clamping pressure for the clamping cylinder 9 can be set by way of the pressure control valve 1A with mechanical self-locking, and the value can be displayed on the digital display of a conventional electronic control 12, which display is not detailed. To set the predefinable clamping pressure value, this control 12, which is shown in FIG. 1 as a black box, therefore triggers the motor M of the pressure control valve 1A which moreover is connected to the pressure sensors 6A, 6B, in order in this way to detect the actual pressure prevailing in the utility connections A, B, which are, in turn, each connected to the pertinent working spaces of the clamping cylinder 9 to carry fluid via the check valves 8. By means of the control 12, the operator can therefore freely stipulate the corresponding pressure values for the pressure control valve 1A, or triggering takes place by way of a corresponding program for control 12; for different workpieces to be clamped, different programming is provided which, in turn, is freely selectable within a definable framework. The predefined pressure, set by hand or by way of the respective machine control program, is therefore accepted in this respect and is continuously monitored within the framework of further machining. If the clamping pressure on the clamping cylinder 9 then drops, for example, as a result of technical failure, this can be detected by way of the respectively assignable pressure sensor 6A, 6B, and a corresponding error message then travels to the control 12, with the result that it shuts off the assignable machine drive on the metal-cutting machine for the clamping device; this takes place in near real time. In this way, damage to the metal-cutting machine and/or the workpiece to be machined is avoided. Depending on the programming, the clamping pressure can be monitored both for internal clamping and also for external clamping by means of the clamping chuck 10 of the clamping cylinder 9.

While setting of the clamping pressure takes place on the valve 1A, the actual clamping takes place by actuating the valve 4A, while the valve 4B is not actuated. The valves 4A, 4B used are made in the form of directional control valves with locking (self-locking) positions, and they can be shifted into the respective actuating positions by way of assignable electrical control magnets S1, S2, S3, and S4 in order in this way to be able to move the clamping cylinder 9. If the valve 4A has been actuated, the clamping pressure is monitored by the pressure sensor 6A, conversely, at the same time there should not be any back pressure on the pressure sensor 6B; otherwise, this would be an indication of a malfunction. If the clamping cylinder 9 is to be relieved, in order, for example, to release the workpiece to be machined, then switching of valve 4B takes place while valve 4A is switched back into its initial position. As FIG. 1 shows, one output of the respective directional control valve 4A, 4B is blocked fluid-tight by way of a corresponding sealing plug since in this respect this output is not necessary for the valve function intended here.

According to the operating description as shown in FIG. 1, the two check valves 8 are interconnected such that they are connected to be able to be mutually unblocked and are connected on their blocking inlet side both to the assignable utility connection A and also to the utility ‘connection B. The back pressure block 5, which is made as a check valve, prevents a dynamic pressure which may build up in the tank line T from unintentionally changing the clamping force on the clamping cylinder 9. The valve components used for the valve apparatus according to the invention are standard components and can be economically made available and are moreover reliable in use. Furthermore, the pressure control valve 1A on the one hand is connected to the fluid line P with the hydraulic accumulator 11 and is connected to the directional control valves 4A and 4B respectively to carry fluid by way of the orifice 2.

With the valve apparatus which has been described in this way as shown in the circuit of FIG. 1, when the clamping pressure drops, the machine can be shut down in order thus to meet increased safety requirements. Moreover, the solution as shown in FIG. 1 allows a reduction of the clamping force in order to help avoid deformations of the workpiece which can arise, for example, as a result of the fact that during machining first a solid profile workpiece is clamped, which then becomes a hollow profile in metal cutting, with reduced wall thickness which could otherwise be deformed when the clamping force remains the same.

For this purpose, the exemplary embodiment as shown in FIG. 1, in turn, calls for setting the clamping pressure on the valve 1A which is preferably made as a proportional pressure reducing valve. A clamping process by way of the clamping cylinder 9 takes place by actuating the valve 4A, while the valve 4B remains in its position shown in FIG. 2. In the utility connection A then the clamping pressure is monitored on the pressure sensor 6A, while at the same time there should be little or no back pressure on the pressure sensor 6B. Relief then takes place by switching the valve 4B, while the valve 4A is, in turn, switched back into the initial position as shown in FIG. 1. Within the scope of this specification, it is fundamentally assumed that, by applying pressure in the utility line A with simultaneous discharge of hydraulic oil from the utility line B, a clamping process is initiated via the clamping cylinder 9 and the clamping chuck 10; by reversing this function, a relief process is carried out. When there is a change from inside clamping to outside clamping relative to the clamping jaws of the clamping chuck 10, the aforementioned statements then, however, apply in reverse.

For reducing the clamping pressure with only one pressure regulator 1A as shown in FIG. 1, as already described, the clamping pressure is set on the valve 1A by means of the control 12, and relief takes place by switching of valve 4A. At the same time, monitoring of the clamping pressure takes place by means of the pressure sensors 6A, 6B which relay their values to the control 12 of conventional design. If at this point the valve 4B is switched, the clamping pressure in the utility lines A, B is equalized, the check valves 8 are both opened, and pressure equalization takes place in the clamping cylinder 9. Since self-locking does not occur in the clamping chuck, the clamping force is lowered to zero.

The level of the clamping pressure on the pressure regulator 1A can now be lowered to the desired level, and the clamping pressure drops in lines A and B and, as a result of the opened check valve 8, also drops in the clamping cylinder 9. The clamping force then remains at zero. After completed switching back of the valve 4B, the pressure in the utility line B and on the relief side of the clamping cylinder 9 is reduced, and the clamping force is built up again at a lower level on the clamping chuck 10 by the prevailing pressure in the utility line A. In this way, the indicated minimization of the clamping force is achieved.

The solution as shown in FIG. 1 therefore uses two 4/2 directional control valves 4A, 4B, of which, viewed in the direction of looking at FIG. 2, the output on the left leads into a blind connection. Furthermore, the valves 4A, 4B are connected to the respectively assignable back pressure block 5 which is connected to the tank line T respectively. The outputs of the pressure sensors 6A, 6B are connected to the machine control 12 shown as a black box for reducing the clamping pressure force for evaluation of the respective measurement signal, the control 12 for stipulation of a pressure setpoint having a manual input which is not detailed or has a freely programmable flow diagram (program).

If it should not be possible to ensure that, when the clamping pressure is equalized, the friction is sufficient for actually holding the workpiece in the clamping chuck 10, the embodiment as shown in FIG. 2 with two pressure regulators 1A, 1B would be appropriate. This reduction of the clamping pressure then calls for a pressure just below the level in the utility line A to be set on the pressure control valve 1B. With the switching of valve 4B, a back pressure is then built up in the utility line B, and the check valves 8 are both opened. Since self-locking does not occur in the clamping chuck 10, the clamping force is reduced to a low value. As a result, the pressure on the valves 1A and 1B is lowered until the desired level is reached in the utility line A. The pressure difference between the valves 1A and 1B must be maintained in this process. Owing to the opened check valves 8, the clamping pressure also drops in the clamping cylinder 9 with the result that the clamping force remains at a constant low level.

By switching back the valve 4B, the pressure in the utility line B and on the relief side of the clamping cylinder 9 is reduced. The clamping force is then built up again at a lower level on the clamping chuck 10 by the pressure in the utility line A.

Instead of using 4/2 directional control valves, the embodiment as shown in FIG. 2 is equipped with motorized 3/2 directional control valves 4A, 4B. Furthermore, the 2-way pressure regulators shown in FIGS. 1 and 2 can also be replaced by 3-way pressure regulators.

The embodiment as shown in FIG. 3 differs from the two preceding embodiments in that neither directional control valves with latching positions as shown in FIG. 1 nor motorized 3/2 directional control valves according to the embodiment as shown in FIG. 2 are required. Rather in the solution as shown in FIG. 3, only two proportional pressure reducing valves 1A, 1B are used which acquire a secondary pressure safeguard via the respective back-pressure blocks 5. For the sake of simplicity, in FIGS. 2 and 3 in the embodiments there, the control 12 with its corresponding connection sites was not shown, but in this respect the embodiments relating to the solution as shown in FIG. 1 apply.

The valve apparatus according to the invention is advantageous in that in a modular construction it can also be retrofitted onto existing workpiece chucking fixtures in machine tools. As a result of the modular block structure of the valve apparatus, it takes up less installation space and is economical to implement because of the standard components which can be used.

Claims

1. A valve apparatus for setting and monitoring the clamping pressure of a clamping device (9) for workpieces which are to be clamped, particularly in lathes, with at least one pressure control valve (1A, 1B) via which a clamping pressure adjustment for the clamping device (9) takes place, and with at least one pressure sensor (6A, 6B) which detects the respective clamping pressure of the clamping device (9) which is to be adjusted to a definable setpoint clamping pressure.

2. The valve apparatus according to claim 1, characterized in that the respective pressure control valve is a pressure reducing valve (1), in particular a proportional pressure reduction valve (1A, 1B).

3. The valve apparatus according to claim 1, characterized in that the respective pressure control valve (1A, 1B) is provided with mechanical self-locking which is preferably formed by self-locking gearing of a positioning motor (M) which can be triggered by the control means.

4. The valve apparatus according to claim 1, characterized in that the respective pressure sensor (6A, 6B) is connected to an electronic control (12) or that the pressure sensor is part of an electronic pressure switch which can be freely programmed.

5. The valve apparatus according to claim 1, characterized in that at least two 3/2 directional control valves (4A, 4B) or two 4/2 directional control valves (4A, 4B) are used to supply the clamping device (9).

6. The valve apparatus according to claim 1, characterized in that two directional control (4A, 4B) valves and/or pressure control valves (1A, 1B) can be switched independently of one another.

7. The valve apparatus according to claim 5, characterized in that the respective directional control valve (4A, 4B) is connected to a hydraulic supply circuit between the assignable pressure control valve (1A, 1B) and the clamping device (9).

8. The valve apparatus according to claim 1, characterized in that the clamping device (9) has two check valves (8) which are connected to one another to carry fluid and which assume their blocking position in the direction of the respective pressure reducing valve (1A, 1B).

9. The valve apparatus according to claim 8, characterized in that the two check valves (8) are connected to the respective output of the assignable directional control valve (4A, 4B) to carry fluid.

10. The valve apparatus according to claim 1, characterized in that, to adapt to the volumetric size of the clamping device (9) used at the time, an orifice (2) is used which is located on the output side of the respective pressure reducing valve (1A, 1B).

11. The valve apparatus according to claim 1, characterized in that, with the omission of directional control valves, it has two pressure control valves (1A, 1B).