Electrohydraulic clamping module

Details Electrohydraulic clamping module Electrohydraulic clamping module

1999-04-29

2001-03-20

Michalsky, Gerald A. (Department: 3753)

Fluid handling

Systems

Supply and exhaust

C060S431000, C091S446000, C091S447000

Reexamination Certificate

active

06202685

ABSTRACT:

The invention relates to an electrohydraulic clamping module as disclosed in the following.
Similar clamping modules are known from DE 297 10 129 (FIG.
2
), DE 297 10 127 and DE 297 10 128. The direction control valve responsible for controlling the direction of the clamping element is leakage-proof in its locking position. A separately provided electrical pressure switch is surveying the pressure in the pump line and is switching the pump on and off upon demand. The clamping pressure for the clamping element is regulated by means of a pilot controlled 3/2-pressure regulating valve having a slider valve design, to which within a pilot circuit, a safety valve and a pilot valve are associated, The pressure surveillance of the clamping pressure is carried out by a separate pressure difference valve actuated by the pilot pressure of the pilot valve and a reference pressure derived from the clamping pressure. Said pressure difference valve is co-operating with a switch. The pressure regulating portion of said clamping module is complicated. Leakages, e.g. towards the tank, occur in rest periods and during operation, e.g. in the 3/2-pressure regulating valve and lead, particularly in resting periods, to the effect that then the pump is frequently switched on and off via the pressure switch surveying the pressure line. For that reason a high capacity pump is needed.
DE 42 37 901 discloses a pressure reducing valve having an integrated pressure switch and serving as a clamping pressure regulating valve within a clamping module. The control piston, operating with leakage and like a slider without seat valve function leads during operation and its blocking position, particularly in case of high system pressure, to leakage, e.g. towards the tank, so that said pressure reducing valve cannot be used in a clamping module where leakage-proofness is needed. The control piston controlling the working flow is activating an electrical switch directly or indirectly by means of a parallel piston or cam mechanism, respectively.
A pressure reducing valve according to DE 296 15 498 allows pressure regulation independent from pressure variations of the non-regulated pressure since the control piston adjusting the closure member in relation to the valve seat only is displaced by the regulated pressure counter to the regulating force which regulating force is determining the value of the pressure which is to be regulated. Such pressure reducing valve designed as seat valves are used in high pressure hydraulic applications if beside the pressure regulation the requirement of a leakage-free or leakage-proof function has to be fulfilled, since seat valves contrary to slider valves even in their blocking position are leakage-proof. A surveillance of the regulated pressure is not provided.
Further prior art can be found in DE 44 46 538A, DE 32 04 955A, WO 87/01171A.
It is an object of the invention to provide a clamping module of the kind as disclosed at the beginning being structurally simple, leakage-proof and having a reliable pressure surveillance feature.
Said task can be achieved with the features hereinafter described.
Untypically for a clamping module as the pressure relating valve a simple and directly regulating seat valve is used without a connection to the tank (two-ways) which seat valve in connection with the leakage-proof directional control valve can avoid any leakages. A complicated pilot circuit operating with leakage is eliminated. Since with the directly regulating seat valve control piston actuated counter to the regulating force exclusively by the regulated pressure the pre-determined value of the regulated pressure always is reached at a certain position of the control piston, which position is independent from the magnitude of the selected regulating force, the pressure surveillance can be designed structurally simply when the control piston is used to actuate the pressure surveying sensor. Despite the structural simplification of the clamping module the necessity is avoided to readjust the pressure surveying sensor in case of a new adjustment of the value for the regulated pressure or the clamping pressure by varying the regulating force. Thanks to the leakage-proofness furthermore a compact pump or a precisely dimensioned pumping system (multiple stage pump) can be used. Particularly for tooling machines having a leakage-proof clamping device this is a fair price and optimal combination.
In a preferred embodiment the seat valve with its pressure surveying sensor is provided in the pump line branch of the respective directional control valve in order to survey the clamping pressure by means of its pressure surveying sensor already upstream of the directional control valve and for the clamping element controlled by it. Further consumers connected to the pump line can receive the unregulated pressure nevertheless.
In a further embodiment for all clamping elements connected to the same pump line the same regulated pressure is adjusted and surveyed centrally.
In a further embodiment not only the clamping pressure is regulated and surveyed in at least one consumer line of the clamping element, but even for a selected moving direction of the clamping element which direction might be critical in view to the clamping pressure. This leads to very strong signals for a higher ranking control unit of a tooling machine.
In a further embodiment upstream of the first directional control valve a pressure switch is connected to the pump line serving to switch on or off the pressure source. Due to the leakage-proofness of the directional control valve and/or the seat valve even with a simple design of the supply circuit it is avoided that the pump will be switched on and off during resting periods.
In a further embodiment the pressure surveying sensor is constituted by an electrical switch or microswitch which is actuated by means of the control piston via the mechanical coupling. Such switches are available for fair prices, are reliable and need only small mounting space. The control piston could even directly actuate the switch.
In a further embodiment the mechanical coupling is provided outside the working flow path such that it does not need specific sealing measures.
In an advantageous embodiment the switching point of the electrical switch is associated to the position of the control piston at which the value of the regulated pressure or an intentionally selected, somewhat lower pressure value will be reached, in order to transmit an okay-signal or a error-signal, respectively, to a higher ranking control unit. Said position at which the switch is switching is reached by the control piston independent from the value of the adjusted regulating force. Due to this the pressure surveying sensor does not need to be re-adjusted when changing the value of the regulated pressure by an adjustment of the regulating force.
Advantageously said regulating force is generated either by means of at least one regulating spring or by means of a proportional magnet. A proportional magnet generates the regulating force like a magnetic spring depending on its current supply.
In another embodiment the electrical switch is situated at an exterior side of the housing of the seat valve or sidewards of the component generating the regulating force. The plunger is connecting the control piston with an actuating element of the switch. This saves mounting space and is advantageous for manufacturing reasons.
Expediently the electrical switch or its actuating element is provided adjustably at the housing. Instead or additionally the effective length of the plunger can be varied. This simplifies the adjustment of the switching point.
An vital aspect of the invention of particular importance is the use of a seat valve being leakage-free at least in its blocking position and having an integrated pressure surveillance feature for the pressure regulation and for maintaining the regulated pressure in a clamping module of a tooling machine, such that the pressure surveillance feature automatically adapts to an intended change of t

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