The invention relates to a hydraulic actuator for the hydraulic actuation of a mechanism, such as the clamping rod of a vise, whereby a hydraulic housing is equipped with an outward projecting pump plunger, which pump plunger can be displaced to pressurize the hydraulic fluid in the hydraulic housing; furthermore, the hydraulic housing is equipped with an outlet through which hydraulic fluid pressurized by the pump plunger can be discharged. In addition to clamping vises with an essentially linear clamping action, the above-mentioned mechanism can also be a radially clamping chuck.

Mechanisms of this type are disclosed in German Patent Application P 43 39 439.6 and are the subject of unpublished German Utility Model Application 295 02 702.9. The content of these applications is fully incorporated into this application, including for the purpose of incorporating the features of these older applications into the claims of this utility model application.

The object of the invention is to design a hydraulic actuator as a universal device. To achieve this object, the invention teaches that there is a check valve to hold the pressure of the pressurized hydraulic fluid and that the pump plunger is retracted by means of a switch-actuated by-pass of the check valve that allows the force accumulator of the impinged mechanism to force hydraulic fluid back to the actuator. So long as the by¬ pass is not actuated, the hydraulic fluid remains

pressurized and the clamping mechanism remains open independent of the displacement of the pump plunger. Both automatic or hand/foot actuation is possible. In the latter case, there is no dependence on a connection to a power supply. Added to this is the advantageous utilization of the internal force accumulator for the return of the hydraulic fluid to the depressurized state. With an actuator not equipped with a check valve, the hydraulic fluid and the retraction of the pump plunger by means of the discharge of the force accumulator of the impinged mechanism occurs immediately after release. This can also be useful in certain situations.

With such self-enclosed hydraulic system, the interface for the attachment of an optional actuating mechanism is exposed in both cases. Everything can be easily reached by simple structural means, even in the event of a system expansion, because a pump chamber for the pump plunger is realized in the actuator and a reservoir containing the hydraulic fluid is connected to the pump chamber via a line protected by the check valve. A reservoir of this type makes it possible for the hydraulic actuator to control larger or a greater number of such mechanisms. The invention also teaches that a further hydraulic connection is equipped with a relief valve and that the relief valve is set to a maximum pressure for the pressurized hydraulic fluid. The latter prevents operational outages due to overload and increases the service life of the hydraulic actuator. It

has also proven to be advantageous that the actuator be equipped with a pilot valve for the return of the hydraulic fluid to the actuator. An advantageous configuration with respect to variability can be achieved in that the actuator consists of multiple plate-like elements. By this means, the actuator can be equipped to meet a wide variety of demands. For example, the first plate can be equipped with the hydraulic discharge port, a hydraulic supply port which can be closed as necessary and a hydraulic connecting port, whereby the hydraulic supply port is connected to the hydraulic discharge port and the second hydraulic connecting port is connected to the pump chamber for the pump plunger.

The invention also teaches that the second plate has a second hydraulic connecting port which is likewise connected to the pump chamber. A spatially advantageous configuration specifies that the second plate be equipped with the hydraulic fluid reservoir. The invention also teaches that the hydraulic fluid reservoir is connected to the pump chamber, isolated on the pump side by means of a second check valve. Also, the second, pump-side check valve is located between the pump chamber and the fluid reservoir in a second hydraulic connection, whereby the second check valve opens in the opposite direction of the first check valve. It is also advantageous that the second plate have a third hydraulic connecting port which is connected via a separate connection to the hydraulic fluid reservoir.

Further, there is a third plate which is equipped with the pilot valve and two connecting ports connected to the pilot valve. With an actuated mechanism such as the clamping rod of a vise having a hydraulic actuator, it has proven advantageous that the force accumulator have a receptacle filled with an elastic, compressible fluid, in particular silicone oil, and that the fluid can be compressed or decompressed by the displacement of a moving part. Force accumulators of this type are reliable, can be precisely adjusted with respect to pre-tension and, above all, require little maintenance. The invention further teaches that the hydraulic fluid flowing out of the hydraulic discharge port impinges a piston of a mechanism, and that this piston is also impinged by a compressible fluid, such as silicone oil, for charging and discharging the force accumulator. It is advantageous with respect to actuation that the discharge valve be foot-actuated.

Finally, the invention also teaches that the actuator is remotely located from the mechanism, whereby there is a hydraulic line forming the connection between the hydraulic discharge port and the mechanism. The invention is described in greater detail below with reference to the attached drawings of several embodiments.

Figure 1 shows, in the simplest possible schematic representation, a mechanism in the form of a clamping rod of a linearly operated vise and equipped with a hydraulic

actuator, foot-actuated with respect to the relief valve, as claimed by a first embodiment;

Figure la shows the hydraulic actuator as claimed by a second embodiment, with hand-actuated pilot valve (the mechanism to be controlled is not shown here) ;

Figure 2 shows a longitudinal section through the mechanism in form of the clamping rod of a vise, having a feed connection for actuation of the force accumulator integrated into the mechanism; Figure 3 shows this region and the docked hydraulic actuator;

Figure 4 shows the section along Line IV-IV in Figure 3;

Figure 5 shows the section along Line V-V in Figure 4 and

Figure 6 shows a machine tool, shown in the simplest possible representation, whereby the actuating force is applied by means of a plunger motion along the z-axis of the machine tool. The actuator shown, the whole of which is designated

1, serves to operate a clamping mechanism 2, for instance a machine tool, which is represented schematically as a machining center and designated 3 (see Figure 6) . The actuator 1 is a hydraulic device having as its core a pump 4. The latter is machine actuated.

The mechanism 2, realized as a spring-force clamping mechanism, is influenced in the context of a release by means of the pump 4 of the actuator, which mechanism is

realized in this embodiment as the clamping rod 5 of a vise 6. The embodiment shown is illustrative but not restrictive. The clamping force is applied linearly by means of the discharge of a force accumulator 7. The latter contains silicone oil as a compressible fluid 8, which can be precisely pre-tensioned as a function of the respective application.

With respect to the structural details of the force accumulator 7: the device in question is an oblong cartridge whose pressure vessel 9 is located in the base portion 10 of the vise 2. A moving part 11 in the form of a plunger and having sealed guides passes through the force accumulator 7 of the manifold-shaped pressure vessel 9. The moving part 11 is realized as a differential piston, whose right end as shown in Figure 2 is connected to a moveable clamping jaw 12. The left end of the seating enclosure 9 engages a moveable clamping jaw 13 at this location. In the plane of movement between these points is a fixed clamping jaw 14. Intermediate seats 15, formed in equal measure by the clamping jaws 12 through 14, actively clamp the workpieces 16 for machining. The step piston configuration is disclosed in P 43 39 439.6.

The gliding motion of the moveable clamping jaws 12, 13 is achieved by means of drivers 17 carried on sleds relative to the seating receptacle 9, each of which drivers extends into a cavity 18 in the bottom of said clamping jaws 12, 13. The drivers 17 are braced against

rod-side abutments 19, 20. 21 designates a fluid receptacle.

On the left, a cylindrical chamber 22 is located upstream from the receptacle 21 containing the pre-tensioned fluid 8. A piston 23 connected to the moving part 11 moves inside this chamber. The piston 23 forms an extension of said moving part 11 or plunger which extends outside of the receptacle 21. The facing away from the plunger is impinged to the right to unclamp the workpieces 16. This occurs against the force of the silicon oil tension spring, i.e. the force accumulator 7. The moveable clamping jaws 12, 13 move away from the intermediate fixed clamping jaws 14. The hydraulic fluid making up the working medium is designated 24. This outside energy, which is only briefly needed, can be applied by the machine tool itself. For example, the spindle box, which generally performs the advance motion along the Z axis, moves to a certain point, such as the clamping table, and actuates the pump 4. An integral component of said pump 4 is a hydraulic housing 25. The latter contains a pump plunger 26 which is sealed off to the outside. In its base position, the plunger 26 projects upward and can be displaced vertically downward to generate a high pressure within the hydraulic fluid 24 in the hydraulic housing 25 (Arrow P indicates the direction of pressure) . That pump chamber of the pump 4 whose volume can be reduced in this manner is designated 27.

The hydraulic housing 25 is also equipped with a hydraulic discharge port 28, which delivers this non- or only slightly compressible hydraulic fluid 24 in such a manner as to exert a pressure. The working medium is passed through this outlet port into the cylindrical chamber 22, i.e. to a location in front of the outward cross-sectional area of the piston 23 which forms a pressure base. This opening cylinder or cylindrical chamber 22 is supplied centrally so that an even pressure is applied to the piston 23. Distribution of the hydraulic fluid can be optimized by means of radial feed indentations resembling grooves, be it in the end face of the piston, in the opposing end face, i.e. that transverse wall 29 of the cylindrical chamber 22 containing the hydraulic discharge port 28, or both end faces. The transverse wall 29 is a screw plate with a central bore. The hydraulic discharge port 28 is formed by a nipple 30 extending from the hydraulic housing 25 and inserted into the bore to form a seal. This embodiment of the actuator 1 utilizes the recoil force of the force accumulator 7 to return the pump plunger 26 to its original position as indicated in Figures 1 and la. Such an actuator 1 is suitable for use without check valves. The force accumulator 7 simply forces the hydraulic fluid 24 back through the feed line and impinges the pump plunger 26 to achieve the appropriate return displacement. The workpieces can then be changed and reclamped.

If it is not possible to use the machine to keep the pump plunger 26 depressed, i.e., the spindle box must retreat and the seats 15 must remain open, a check valve VI is installed in the pressure line. This keeps the working medium, i.e. hydraulic fluid 24, in a pressurized state until deliberately released. In other words, the check valve VI prevents the hydraulic fluid 24 from flowing back into the pump chamber 27 when the spindle box retreats. The check valve VI is installed in the pressure line 31 of the actuator 1 and sits in a valve seat which leads to the pump chamber 27. This valve is a spring-mounted ball valve with a housing-side valve face. The latter is located on the pump-side of the ball.

If such a check valve Vl is specified to hold the hydraulic fluid 24 in a highly pressurized state, the pump plunger 26 is returned by means of spring force. An appropriate spring with sufficient pre-tension can be mounted in the pump plunger 26 and braced against the bottom of the pump chamber 27. Also installed in the hydraulic housing 25 is a reservoir 32 to receive/hold the hydraulic fluid 24, which reservoir is connected to the pump chamber 27 by means of a line protected against reflux. The working charge is deliberately discharged into this reservoir or the hydraulic fluid is held in a circulatory loop. For this purpose, there is another hydraulic connection with a safety valve V2 which works in the opposite direction, which valve is located in a very short channel bridge

between the pump chamber 27 and the reservoir 32 for the hydraulic working medium. Both chambers 27, 32 can also be realized as parallel bores. The valve V2 also assumes a safety function in that its response threshold is set to the maximum system pressure for the pressurized hydraulic fluid 24. It discharges into the reservoir 32. The safety valve V2 is shown as schematically as possible. Classic, prior art means are used to support the spring, etc. The connections forming the above-mentioned, switch-actuated bypass, realized as a channel, is designated 33. It is shown schematically in Figure 3 and corporeally in Figure 5.

Hydraulic fluid 24 returns to the actuator 1 through this by-pass via a pilot valve V3, which is deliberately manipulated. This valve is realized as a slide. The pilot valve V3 is springloaded in the direction of its blocking position, which is also its base position, by means of a convoluted pressure spring 34. This sits at the exposed, actuation-accessible contact region 35 of a slide actuating rod 36, whose free end is compressed into the shape of a knob. One end of the convoluted pressure spring 34 is braced against the underside of the knob forming the contact region; the other is braced against the hydraulic housing. The slide of the pilot valve V3 is moved into a congruent position relative to the corresponding ends of the lines to form a hydraulic bridge between the pressure line 31, the adjoining

hydraulic connection 33 and the reservoir; the pilot valve thus clearly functions as a relief valve.

In addition to the hand actuation shown in Figure 3, the relief valve, i.e. pilot valve V3, can also be equipped for foot actuation as is shown in Figure la. In this case, the entire actuator 1 is located remotely from the mechanism 2. As a result, a hydraulic line 37 in the form of a compression-proof hose, etc. is used as the connection between the hydraulic discharge port and the mechanism 2. If a hydraulic actuator 1 is used to service several stations, i.e. mechanisms 2, the hydraulic line 37 is equipped with a branch or branches 38. By this means, an entire series of mechanisms 2 can be serviced, in which case a relatively large reservoir 32 becomes increasingly important.

The reservoir 32 is also accessible to permit the targeted addition of hydraulic fluid 24. To this end, the top of the hydraulic housing 25 is covered by a screw-down cover 39. This cover 39 includes the necessary seals, as well as the recesses and openings for mounting the pump plunger 26, which was described in detail above. The cover 39 holds a guide sleeve 40 which overlaps the joints to the hydraulic housing 25, the rest of which sleeve is located in the hydraulic housing 25 itself. The sleeve is housed half in one and half in the other. This conveys the sleeve 40 with a fitting function which facilitates assembly. The fastening screws holding the cover 39 are designated 41.

The free end of the pump plunger 26 forms a head 42 which protrudes clearly from the cross-section of the plunger shaft and serves simultaneously as an enlarged actuating surface and as a stop to limit insertion depth. The stop in the other direction is realized as a locking ring 43 which contacts the underside of the above-mentioned, axially fixed guide sleeve 40.

The foot actuation (Figure 1, bottom right) also functions in the context of the desired depressurization of the working medium, i.e. the hydraulic fluid 24. In terms of function, the same configuration can be used here as at the pilot valve V3. With respect to the foot actuation, a more extensive remote control can be achieved if two compression-proof hoses 45 are used between the actuator 1 and the foot valve mechanism to provide the connection between the actuator 1 and the foot valve mechanism 44 as the pilot valve V3.

The fact that the pilot valve V3 can be installed at a variety of locations with respect to the actuator 1 and even the mechanism 2 can be of advantage in that edges which can interfere with the tool are eliminated. The separation/variability is also of fundamental significance. It is in no small part for this reason that the hydraulic actuator 1 is realized using a modular attachment design, leaving it up to the operator whether actuation will be by means of the attachment module or by means of a built-in hydraulic actuator. As can be seen from the drawings, the actuator 1 comprises several

plate-like elements. Working back from the hydraulic discharge port 28, the individual plates, which have essentially the same circumference, are designated I, II and III. The plates have a rectangular horizontal projection.

The first plate I contains the above-mentioned hydraulic discharge port 28, realized in the nipple 30; a hydraulic supply port a which can be closed, if necessary, and a hydraulic connecting port b to the pressure line 31.

The hydraulic supply port a can be directly supplied by the machine tool or similar unit. In this case, the plate I functions as a connecting cover to the clamping rod 5 of the machine mechanism 2. Docking is by means of four anchor bolts 46. That side of the first plate I facing away from the clamping rod is equipped with recesses for the heads which are of sufficient depth that, if additional plates are installed, the heads of the anchor bolts 46 do not project beyond the adjoining joint to the next plate.

The hydraulic supply port a and the hydraulic connecting port b are in hydraulic communication with the hydraulic discharge port 28. This is also true if such hydraulic supply ports a are supplied from a variety of directions to ensure the greatest possible independence for feed lines to the pressure line 31. The pressure line 31 consequently leads via several channel sections coming from the various narrow edges to the center of the

hydraulic discharge port 28, which branches off perpendicular thereto. This network of channels simultaneously ensures that the connecting port b is in hydraulic communication with the pump plunger pump chamber 27.

The entire pump assembly and associated reservoir is located in the adjoining second plate II. The second plate II is equipped with a second hydraulic connecting port c. It is congruently oriented to, and adjoins, the hydraulic connecting port b of the first plate I. Here, too, the second hydraulic connecting port c leads to the pump chamber 27. It crosses the valve bore of the first check valve Vl. The latter rises under the operating pressure from its corresponding valve seat and permits the pressurized hydraulic fluid 24 to impinge the force accumulator 7. As can be seen in Figure 4, the reservoir 32 is in hydraulic communication with the pump chamber 27, here protected by means of a check valve V4. The hydraulic connection controlled by means thereof is designated 47. Together with the valve chamber located there, it forms a U-shaped channel connecting an opening d in the floor of the pump chamber 27 with an opening e in the floor of the reservoir 32. The latter is used to direct the hydraulic fluid 24 into the circulatory loop. The second plate II is fastened by means of anchor bolts 46 with correspondingly longer shafts.

With reference to the pump 4, i.e. essentially with reference to second plate II, the valves are arranged in

such a manner that the second check valve V4 relative to the pump is located in the second hydraulic connection 47 between the pump chamber 27 and the hydraulic fluid reservoir 32. This second check valve V4 opens in the opposite direction of the first check valve Vl of the reservoir 32. Figure 3 shows that the second plate II has a third hydraulic connecting port f, which itself is separately connected to the hydraulic reservoir 32 via the hydraulic connection designated 33. The third plate III, which is fastened in the same manner, includes the compactly docked pilot valve V3. The respective connecting ports are designated g and h. All line transitions and bushings between plates are, of course, sealed and those not in use can be closed with plugs.

With reference to the plate designated I, it must be remembered that the connecting port b located there is diverted as a channel via a reversing plate 48 into a channel section at a higher elevation (see Figure 5) , by means of which the connection to the section of the pressure line 31 crossing the discharge port 28 can be cleverly realized while preserving the desired plate thinness. Depending on the application, all or only the unused hydraulic supply ports a in plate I are closed by means of screwed plugs.

Function is summarized below: if the first plate I is used as a connecting cover, the working medium, i.e. hydraulic fluid 24, enters by means a hydraulic supply

port a. The clamped workpieces 16 are released when the pressure is increased. After changing workpieces, the workpieces can be reclamped by decreasing the pressure of this working medium. The pump 4 is used if the machine does not have a built-in oil feed system. The actuator 1 for the pump can be either docked or mounted remotely as a function of the available mounting options. If the machine has the appropriate equipment, such as a die, the pump plunger 26 is displaced inward (Arrow P indicates the direction of pressure) . The hydraulic fluid 24 in the lines then impinges the force accumulator 7, which uses the hydraulic fluid 24 to return the pump plunger 26 to its original position when the actuating pressure is released, reclamping the workpieces. Release can be maintained by preventing the hydraulic fluid 24 from flowing back. This is done by means of the check valve VI. By by-passing the same, the pre-tensioned force accumulator 7 can be discharged when impingement of the mechanism 2 is discontinued. This occurs by means of either hand or foot actuation, locally or remotely.

All of the disclosed features are fundamental to the invention. The disclosure of the application incorporates the complete disclosed content of the associated/enclosed priority documents (copy of the pre-application) , including for purposes of incorporating features of these documents into the claims of this application.