DE20208990U1 - Electro-hydraulic clamping device - Google Patents

Description

GRÜNECKER KINKELDEY STOCKMAIR & SCHWANHÄUSSER

LAW FIRM

GKS & S MAXIMILIANSTRASSE 58 D-80538 MUNICH GERMANY

Applicant:

HEILMEIER & WEINLEIN FACTORY F.
OIL-HYDRAULIK GMBH & CO. KG
STREITFELDSTRASSE 25
81673 MUNICH

LAWYERS

MUNICH

DR. HELMUT EICHMANN

GERHARD BARTH

DR. ULRICH BLUMENRÖDER, LLM.

CHRISTA NIKLAS-FALTER

DR. MAXIMILIAN KINKELDEY, LLM.

DR. KARSTEN BRANDT

ANJA FRANKE, LL.M.

UTE STEPHANI

DR. BERND ALLEKOTTE, LL.M.

DR. ELVIRA PFRANG, LLM.

KARIN LOCHNER

BABETT ERTLE PATENT ATTORNEYS EUROPEAN PATENT ATTORNEYS

MUNICH

DR. HERMANN KINKELDEY PETER H. JAKOB WOLFHARD MEISTER HANS HILGERS DR. HENNING MEYER-PLATH ANNEUE EHNOLD THOMAS SCHUSTER DR. KLARA GOLDBACH MARTIN AUFENANGER GOTTFRIED KUTZSCH DR. HEIKE VOGELSANG-WENKE REINHARD KNAUER DIETMAR KUHL DR. FRANZ-JOSEF ZIMMER BETTINA K. REICHELT DR. ANTON K. PFAU DR. UDO WEIGELT RAINER BERTRAM JENS KOCH, M.S. (U of PA) M.S.

BERND ROTHAEMEL DR. DANIELA KINKELDEY DR. MARIA ROSARIO VEGA LASO THOMAS W. LAUBENTHAL DR. ANDREAS KAYSER DR. JENS HAMMER DR. THOMAS EICKELKAMP

PATENT ATTORNEYS

EUROPEAN PATENT ATTORNEYS

BERLIN

PROF. DR. MANFRED BÖNING DR. PATRICK ERK, M.S. (MIT)

COLOGNE

DR. MARTIN DROPMANN

CHEMNITZ MANFRED SCHNEIDER

OF COUNSEL PATENT ATTORNEYS

AUGUST GRÜNECKER DR. GUNTER BEZOLD DR. WALTER LANGHOFF

DR. WILFRIED STOCKMAIR (-1996)

YOUR REF.

OUR REF.

G 4736-25/Sü DATE / DATE

10.06.02

Electro-hydraulic clamping device

GRÜNECKER KINKELDEY j ··** .·*· · JEL J · J Vf? 89*&idigr;} 23Sp · * * * I DEUTSCHE BANK MUNICH

STOCKMAIR & SCHWANHÄJJSER ^&khgr; (GR 3) **+*49 89*22 02 87** No. 17 51734

MAXIMIUANSTR. 58 _{FAX (GR 4)} +49 89 21 86 92 93 ^{Bank code 7u0 700 10}

D-80538 MUNICH http://www.grunecker.de SWIFT: DEUT DE MM

RFRMAMY H-mailr nnstmait-erannmcrker He

Electro-hydraulic clamping device

The invention relates to an electro-hydraulic clamping device of the type specified in the preamble of claim 1.

In the electro-hydraulic clamping device known from DE 44 23 585 A, an electrical switch is assigned to the clamping pressure valve, which signals when the set clamping pressure has been reached depending on the pressure-dependent position of the control piston, which is acted upon by its setting spring depending on the pressure set in the control chamber. In particular, when the clamping pressure is set electrically, the signal from the electrical switch is not sufficiently reliable information about the clamping pressure. This is because it is assumed that the correct pressure is present in the control chamber. However, unwanted electrical influences can lead to deviations in the pressure in the control chamber, so that the electrical switch acknowledges an incorrect clamping pressure. As is usual, a pressure gauge can provide a visual clamping pressure display for the personnel; however, this does not give the control device any opportunity to react. Despite the acknowledgement by the electrical switch, damage to the machine tool or workpieces due to incorrect clamping pressure cannot be ruled out. Furthermore, it is hardly possible to set the clamping pressure correctly without a clamped workpiece, because hydraulic medium must flow for the adjustment to be made.

The invention is based on the object of specifying an electro-hydraulic clamping device whose clamping pressure can be reliably adjusted electrically and which is very reliable in operation.

The stated problem is solved with the features of claim 1.

The analogue position sensor of the actuating piston reports the relative position of the actuating piston as an equivalent to the pressure in the control chamber, so that the preload of the actuating spring of the control piston indicates which clamping pressure corresponds to the pressure in the control chamber. The higher-level control device can use the signal from the analogue position sensor as an actual value/target value comparison.

not only to set the correct clamping pressure, but also to permanently adjust the clamping pressure, whereby unwanted electrical influences that could affect the pressure in the control chamber can be immediately detected and compensated. This increases operational reliability when setting and permanently regulating the clamping pressure. Another advantage is that the clamping pressure can be set without a workpiece by setting the position of the actuating piston in accordance with the target clamping pressure based on the message from the analogue position sensor, without the need for hydraulic medium to flow.

The analogue position sensor is simply integrated into a head section of the control chamber in order to directly measure the travel of the adjusting piston.

A reliable analogue displacement signal is achieved with an analogue Hall sensor and a bar magnet, the rod axis of which at least roughly corresponds to the adjustment direction of the adjustment piston and which moves with the adjustment piston relative to the analogue Hall sensor. The analogue Hall sensor in particular scans at least one transition area between a strong and a weak magnetic field of the bar magnet and thus precisely indicates the relative position of the adjustment piston along its adjustment path.

In electro-hydraulic clamping devices, leakage occurs particularly in the clamping element. The extent of this leakage is highly dependent on the pressure. In addition, clamping elements from different manufacturers have significantly different leakages. Pressure fluctuations in the system can occur due to leakage, among other things, when setting the clamping pressure and during operation. It is even possible that the clamping element is stationary due to leakage, but the control device cannot detect this standstill, or that the clamping element is moving although the control device assumes that the clamping element is stationary. Such pressure fluctuations must be automatically compensated for by the control piston of the clamping pressure valve, e.g. in the well-known electro-hydraulic clamping device. However, the control piston is fitted relatively tightly and has considerable breakaway resistance. In the case of such, often relatively large, fluctuations and/or pressures in a storage/charging system,

operation, the control piston cannot move reliably enough to compensate for the pressure fluctuations. Because the position of the control piston is adjusted depending on the pressure, the electrical switch assigned to the control piston can then report that the target clamping pressure has been reached even though this is not actually the case, or that the target clamping pressure has not been reached even though it has already been set. For these reasons, the signal from the electrical switch is not sufficiently informative for the control device and under certain operating conditions. To eliminate this disadvantage, it is therefore advisable to assign a pressure compensator to the clamping pressure valve in the main circuit, which keeps the pressure difference across the control piston constant and can easily be designed to be so smooth that it automatically compensates for even small pressure fluctuations. The pressure compensator relieves the control piston of the task of compensating for pressure changes and also has the important advantage that the switching point position of the control piston is no longer pressure-dependent but purely quantity-dependent and the signal derived from this position from the electrical switch assigned to the control piston always provides a reliable statement for the control device. Using the signal from the analogue position sensor and the signal from the electrical switch, operational reliability when setting and adjusting the clamping pressure is significantly improved.

The pressure compensator is conveniently located in the main circuit upstream of the clamping pressure valve and the control piston cooperates with the electrical switch at a precisely predetermined switching point position that is related to the clamping pressure via the quantity. The compensating influence of the pressure compensator allows the switching pressure position to be predetermined very precisely, so that the electrical switch can be adjusted exactly to the switching point position.

The operational reliability can be further increased if an analogue pressure sensor is provided for the actual clamping pressure signal and connected to the control device. This is because the directional control valve usually provided between the clamping pressure valve and the clamping element and/or leakage in the clamping element can have an uncontrollable influence on the fact that the target clamping pressure set by the clamping pressure valve does not correspond to the actual clamping pressure prevailing in the clamping system.

Any such deviation is immediately detected via the analogue pressure sensor and reported to the control device, which can then make a correction.

A further increase in operational reliability can be achieved by ensuring that the safety valve, which has to maintain the pressure in the control chamber, is leak-tight in both flow directions in its shut-off position. This not only prevents the pressure in the control chamber from being lowered or increased in the event of an unwanted change in current and the resulting adjustment of the proportional pressure control valve, but also prevents the pressure in the control chamber from being increased unintentionally in the event of a pump malfunction. This design of the safety valve can even be used to set a control routine in which the proportional pressure control valve is completely relieved after the clamping pressure has been adjusted and is only built up again when the clamping pressure is readjusted or changed.

The proportional pressure control valve, the safety valve and the analog position sensor are conveniently arranged on the head part of the control chamber in order to achieve a compact design, and the proportional magnet and the switching magnet are combined to form a compact double magnet.

The actual clamping pressure signal, which the analog pressure sensor picks up and reports to the control device, is conveniently and structurally simply picked up in the directional control valve between the clamping pressure valve and the clamping element.

An embodiment of the subject matter of the invention is explained with reference to the drawing. They show:

Fig. 1 is a symbolic block diagram of an electro-hydraulic clamping device for a machine tool,

Fig. 2 shows a partial section of a concrete embodiment of the electro-hydraulic control of the clamping device, and

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Fig. 3 is a section along the plane III-III in Fig. 2, with some internal components omitted for clarity.

An electro-hydraulic clamping device S (Fig. 1) is used to actuate (e.g. release and clamp) a clamping element 1 of a machine tool and contains a hydraulic control 2 to which a higher-level electronic control and/or monitoring device 3 is assigned. A signaling device 4 can be provided to indicate a good or faulty state. An adjustment device 5 is used to electrically adjust the clamping pressure for the clamping element 1.

In the hydraulic control 2, a pump P is connected to a main circuit 6. A pressure compensator DW is arranged upstream of a clamping pressure valve V (e.g. pressure reducing valve). In a directional control valve W downstream of the clamping pressure valve V, working lines 27, 26 lead to the clamping element or clamping group 1. A return line 13 leads from the directional control valve W to a pressure medium reservoir. Downstream of the clamping pressure valve V, a line 21 branches off from the main circuit 6 to a pressure gauge M. The pressure compensator DW is acted upon in the closing direction by the pressure in the line 21 and the force of a spring 22, but in the opening direction by the main circuit pressure between the pressure compensator DW and the clamping pressure valve V. It compensates for pressure fluctuations and keeps the pressure difference in a control piston K of the clamping pressure valve V constant.

An electrical switch 8 can be assigned to the clamping pressure valve V, which, for example, emits a good signal when the target clamping pressure is reached and transmits it to the control device 3. In the clamping pressure valve V, the control piston K is loaded by an adjusting spring 11 for adjusting the size of an aperture 7. The adjusting spring 11 is acted upon by an adjusting piston 10 arranged in a control chamber 9.

The directional control valve W can be adjusted from the neutral position shown into two control positions by magnets 24, 25. A clamping pressure signal line 12 branches off in the directional control valve W, which contains an actual clamping pressure signal and transmits this to the control piston K in the pressure valve V in opposition to the force of the adjusting spring 11.

. An adjustment pilot control circuit branches off from the main circuit 6 between the pressure compensator DW and the clamping pressure valve V, which leads to the control chamber 9 via a proportional pressure control valve B and a safety valve D arranged downstream of this. The proportional pressure control valve B is adjusted against the force of a control spring 16 by a proportional magnet 15, for example with a current that is set using the adjustment device 5 in the control device 3. The safety valve D is adjusted by a black/white switching magnet 14 against the force of a spring 16 from the shown shut-off position O to a through position c. The safety valve 14 contains a shut-off device C, which seals leak-free in both flow directions in the shut-off position O, i.e. prevents any flow from the control chamber 9 to the proportional pressure control valve B, and vice versa.

An analog pressure sensor A can be connected to the actual clamping pressure signal line 12, which, like the other electrically operated components of the hydraulic control system 2, is connected to the control device 3. The analog pressure sensor A reports the actual clamping pressure that prevails in one of the working lines 26, 27 when the directional control valve W is switched. The electrical switch 8 sends a signal to the control device 3 at a predetermined switching point position of the control piston K. The switching point position is precisely matched to the target clamping pressure. Since the pressure compensator DW keeps the pressure difference at the control piston K constant regardless of pressure fluctuations, the signal emitted by the electrical switch 8 is quantity-dependent and unambiguous.

The adjusting piston 10 is connected to an analogue position sensor R, which is connected to the control device 3 and permanently reports the position of the adjusting piston 10, as equivalent to the pressure in the control chamber 9 or to the preload of the adjusting spring 11 or to the target clamping pressure.

Function:

The clamping element 1 is in its release position. The directional control valve W is switched to its neutral position. The target clamping pressure is set electrically with the setting device 5. The aperture y has its largest opening. The proportional magnet

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15 is energized according to the set target clamping pressure. The switching magnet 14 has moved the safety valve D to the through position c. The travel control valve W is moved to a control position in order to clamp a workpiece that is offered to the clamping element 1. A pressure that corresponds to the target clamping pressure is built up in the control chamber 9. The analogue travel sensor R monitors the adjustment movement of the adjustment piston 10 and reports its position to the control device 3. By means of the actual clamping pressure signal transmitted in the signal line 12, the control piston K is moved against the force of the adjustment spring 11 in order to adjust the size of the aperture 7 so that the target clamping pressure is generated. As soon as the target clamping pressure is set, the electrical switch 8 responds and sends an acknowledgement signal to the control device 3 (or shortly before the target clamping pressure is reached). The analog pressure sensor A reports the actual clamping pressure to the control device 3. The pressure compensator DW compensates for pressure fluctuations upstream of the control piston K. To monitor correct functioning, at least the pressure in the control chamber 9 is controlled by the control device 3, taking into account the signal from the analog position sensor R, so that the adjustment piston 10 reaches a position equivalent to the target clamping pressure. The signal from the switch 8 and/or the analog pressure sensor A can also be used for monitoring and/or control or regulation.

If the target clamping pressure is brought into line with the actual clamping pressure, then the safety valve D is first moved to its shut-off position O and then the pressure control valve B is relieved by de-energizing the proportional magnet 5. If the clamping pressure and/or the pressure in the control chamber 9 should change again later due to external influences, then a readjustment is made by re-energizing the magnets 14, 15, again taking the existing signals into account.

To release the clamping element 1, the directional control valve W is switched. The pressure in the control chamber 9 can be controlled in an analogous manner to set a specific release speed and/or a specific release pressure.

In addition, it is possible to adjust the clamping pressure without a workpiece by adjusting the pressure corresponding to the target clamping pressure in the control chamber 9 by means of the analogue displacement sensor R, for example with regard to a workpiece series to be machined in the future.

The hydraulic control 2 is explained in detail using Fig. 2 and 3. It should be emphasized that the pressure compensator DW and/or the analog pressure sensor A are not absolutely necessary, but are convenient options.

The hydraulic control 2 shown is composed of several interconnected blocks, with the main circuit 6 leading to the pressure compensator DW in the lower block in Fig. 2. The control spring 22 of the pressure compensator DW acts on a pressure compensator piston 23 in its opening direction parallel to the pressure fed in from line 21 behind the pressure compensator piston 23, while at the same time the main circuit pressure acts upstream of the clamping pressure valve V in the closing direction.

The control piston K of the clamping pressure valve V, which can be moved linearly in the middle block, is relieved on its side loaded by the adjusting spring 11 towards the return line 13, and receives the actual clamping pressure signal from the signal line 12 on the opposite side. It moves into the switching point position in which it sets the amount for the target clamping pressure via the orifice 7 through the cooperation of its control edge with a housing edge, whereby the end of the control piston K actuated by the clamping pressure signal then actuates the electrical switch 8. The switching point of the electrical switch 8 is adjusted exactly to the switching point position of the control piston K, for example by inserting or removing supports 18, so that the electrical switch 8 responds exactly to the amount set by the size of the orifice 7. Depending on the current supply to one of the magnets 24, 25, the directional control valve W connects the main circuit 6 to one or the other working line 26, 27. The actual clamping pressure prevailing in the respective working line 26 or 27 is also permanently tapped by the analog pressure sensor A via the signal line 12.

In the middle block, the preload of the adjusting spring 11 is preselected by the adjusting piston 10 using the pressure set in the control chamber 9. The safety valve D and the proportional pressure control valve B are conveniently placed next to each other in a head section 19 of the control chamber 9. The proportional magnet 15 can be combined with the switching magnet 14 to form a double magnet, which is mounted on the head section 19 and has a common plug connection 20 for both functions. This is symbolized by the labels SW and PROP in Fig. 3. The two magnets can be designed and mounted separately. The valves B, D can also be installed separately, if necessary with their own blocks.

The proportional pressure control valve B (Fig. 3) is expediently a screw-in valve which is installed in the head part 9 in a chamber between a connection bore 28 of the adjustment pilot circuit and a channel 29 to a further chamber in the head part 19 which accommodates the safety valve D. The safety valve D can also be a screw-in valve which is designed as a seat valve and has a closing element 31 with a spherical or conical sealing surface and a matching valve seat 30. The valve seat 30 is formed in a hollow housing insert in which the switching magnet 14 can lift the closing element 31 against the force of the spring 17 and the pressure in the channel 29 from the shut-off position shown from the valve seat 30 and bring it into the through position. The closing element 31 is acted upon in the closing direction by the pressure in the channel 29. A channel leads from the housing insert of the safety valve D into the control chamber 9. The closing element 31, together with the valve seat 30 and the closing spring 17, forms the shut-off device C of the safety valve D, which, thanks to the seat valve function, is leak-tight in both flow directions in the shut-off position.

The analogue displacement sensor R is also arranged in the head part 19. It has an analogue Hall sensor 35, which is mounted in a cutout 34 on a non-magnetic wall 37 of the head part 19, preferably longitudinally adjustable, and a bar magnet 33, which is housed in a tubular body 32 of the adjusting piston 10. The output signal of the analogue displacement sensor R is tapped at a connection 36. The analogue Hall sensor 35 is designed in such a way that it expediently detects a

transition area between a strong and a weak magnetic field of the bar magnet 33.

Claims (10)

1. Electrohydraulic clamping device (S), in particular for a machine tool, with a clamping pressure valve (V) in a main circuit ( 6 ) which can be hydraulically adjusted via a pilot control circuit from a higher-level electronic control device ( 3 ), the clamping pressure valve (V) being a pressure reducing valve with a linearly adjustable control piston (K) loaded by an adjusting spring ( 11 ), which changes an aperture ( 7 ) arranged in the main circuit as a function of an actual clamping pressure signal against the adjusting spring, and with an adjusting piston ( 10 ) for the adjusting spring ( 11 ) which is hydraulically acted upon from the pilot control circuit in a control chamber, characterized in that an analogue displacement sensor (R) connected to the control device ( 3 ) is provided for the adjusting piston ( 10 ). 2. Electrohydraulic clamping device according to claim 1, characterized in that the analogue position sensor (R) is arranged in a head part ( 19 ) of the control chamber ( 9 ) of the adjusting piston ( 10 ). 3. Electrohydraulic clamping device according to claim 2, characterized in that the analogue displacement sensor (R) has an analogue Hall sensor ( 35 ) mounted in the head part ( 19 ), preferably adjustable, outside the control chamber ( 9 ) and a bar magnet ( 33 ) connected to the adjusting piston ( 10 ) in the control chamber ( 9 ), the bar axis of which coincides at least approximately with the adjustment direction of the adjusting piston ( 10 ). 4. Electrohydraulic clamping device according to at least one of claims 1 to 3, characterized in that a pressure compensator (DW) is assigned to the control piston (K) in the main circuit ( 6 ). 5. Electrohydraulic clamping device according to claim 4, characterized in that the pressure compensator (DW) is arranged in the main circuit ( 6 ) upstream of the clamping pressure valve (V) and is acted upon in the opening direction by a spring ( 22 ) and the main circuit pressure downstream of the clamping pressure valve (V), but in the closing direction by the main circuit pressure upstream of the clamping pressure valve (V). 6. Electro-hydraulic clamping device according to at least one of the preceding claims, characterized in that the clamping pressure valve (V) has an electrical switch ( 8 ) which can be actuated by the control piston (K) at a predetermined switching point position related to the clamping pressure. 7. Electrohydraulic clamping device according to at least one of the preceding claims, characterized in that an analog pressure sensor (A) is provided for the actual clamping pressure signal and is preferably connected to the control device ( 3 ). 8. Electro-hydraulic clamping device according to claim 1, characterized in that a proportional pressure control valve (B) and a safety valve (D) which can be actuated from a shut-off position into a through position by a switching magnet ( 14 ) are provided in the pilot circuit, and that the safety valve (D) is leak-tight in both flow directions in the shut-off position. 9. Electrohydraulic clamping device according to claim 8, characterized in that the proportional pressure control valve (B) and the safety valve (D) are arranged next to one another in the head part ( 19 ), that a signal tap ( 36 ) of the analogue position sensor (R) is arranged on the head part ( 19 ), and that the proportional magnet ( 15 ) and the switching magnet ( 14 ) are combined in a double magnet mounted on the head part ( 19 ). 10. Electro-hydraulic clamping device according to claim 1, characterized in that the actual clamping pressure signal originates from a directional control valve (W) arranged in the main circuit ( 6 ) between the clamping pressure valve (V) and a clamping element ( 1 ).