The invention relates to a valve apparatus for setting and monitoring the clamping pressure of a clamping device for workpieces to be clamped, particularly in lathes.
In modern machine tools, for example lathes, the workpieces to be machined are generally clamped by clamping devices which can be hydraulically actuated, particularly by clamping cylinders, and/or are secured tightly by tailstock spindle sleeves which can be hydraulically actuated. The respective machine is 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 reduction can lead to loosening of the clamping device. 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, 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. 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.
An object of the invention is to provide an improved valve apparatus for clamping accommodation of workpieces to be machined in machine tools such as lathes, with increased safety and to prevent inadvertent damage to the workpiece.
This object is basically achieved according to the invention by a valve apparatus with at least one pressure control valve via which a clamping pressure adjustment for the clamping device takes place. At least one pressure sensor detects the respective clamping pressure of the clamping device 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 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, 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 triggering the control. 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 as machining progresses. This arrangement ensures reliable clamping force monitoring to prevent the workpiece from unintentionally coming loose from the clamping device. Furthermore, the clamping force can be reduced to protect the workpiece during machining against damage from a clamping-compressive force that has been set too high.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.
Referring to the drawings which form a part of this disclosure:
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:
The clamping cylinder 9 is made as a hydraulic synchronous cylinder. 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 the inside diameter and in the other actuation direction by the outside diameter of the clamping jaws of the clamping chuck.
The rotary duct 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, it is ensured by 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 includes 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 for the valve apparatus.
The orifice 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 P is connected to a hydraulic supply (not detailed), for example is formed from a hydraulic supply pump. The hydraulic accumulator 11 is connected to the pump line P and provides pressure supply to the system when the power fails. The tank connecting line or tank line 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.
In the embodiment as shown in
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. They can be shifted into the respective actuating positions by assignable electrical control magnets S1, S2, S3, and S4 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 back pressure 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, switching of valve 4B then takes place while valve 4A is switched back into its initial position. As
According to the operating description as shown in
With the valve apparatus described and as shown in the circuit of
For this purpose, the exemplary embodiment as shown in
For reducing the clamping pressure with only one pressure regulator 1A as shown in
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
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
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
The embodiment as shown in
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.
While various embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.
Number | Date | Country | Kind |
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10 2007 054 503 | Nov 2007 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2008/006976 | 8/26/2008 | WO | 00 | 5/10/2010 |
Publishing Document | Publishing Date | Country | Kind |
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WO2009/062558 | 5/22/2009 | WO | A |
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4747337 | Ohota | May 1988 | A |
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6003428 | Mundie et al. | Dec 1999 | A |
6038948 | Link et al. | Mar 2000 | A |
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38 36 453 | Jul 1989 | DE |
195 30 131 | Sep 1996 | DE |
1 068 932 | Jan 2001 | EP |
WO 2005005842 | Jan 2005 | WO |
Number | Date | Country | |
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20100229970 A1 | Sep 2010 | US |