EP0471695B1 - Hydraulic drive - Google Patents

Abstract

A hydraulic drive (10) for the adjustment, feed and return movements of a tool head of a machine tool comprises a hydraulic motor (11) and an after-running adjustment valve (12). The reference value of the position is set and the actual value indicated by means of a threaded spindle (39) and spindle nut (37) in the form of a hollow shaft. One of these two elements can be driven by an electric motor (41) in order to set the reference value of the position. The other of these two elements can be driven in order to indicate the value of the actual position. A rotational and angular position indicator system (68, 74, 75 and 69, 77) produces an output which is a direct measure of the total number of revolutions executed by the preset reference value shaft and of the azimuthal position of the preset reference value shaft within each revolution. An electronic position sensor system (71, 78 and 71', 78'; 71'') produces an output which is a measure of the contouring error ΔS. The actual position of the tool head or of the drive element of the hydraulic motor (16) is therefore phase-retarded in relation to its reference position by said contouring error.

Description

The invention relates to a hydraulic drive device for the infeed and feed and the retraction movements of a tool head of a machine tool and with the other generic features mentioned in the preamble of claim 1.

Such a hydraulic drive device is known from DE-A-3438 600.

In the known drive device, the piston of a hydraulic motor, which is firmly coupled to the tool, is controlled by means of a follow-up control valve which works with an electromechanically controllable position setpoint specification for the movable drive element of the hydraulic motor and with mechanical actual position feedback. In this case, a threaded spindle and a spindle nut which meshes with its thread are provided for the position setpoint specification and actual value feedback, one of these two elements - the spindle nut system - being drivable by means of an electric motor in the sense of the position setpoint specification and the other of these two elements can be driven in the sense of the actual position feedback, such that that when the rate of change of the position setpoint specification and the position actual value feedback are balanced, the spindle and the nut rotate at the same speed and do not perform any relative axial movements with respect to one another. As part of the overrun control valve, a valve actuator is provided which, when the spindle and the nut rotate at different speeds, also carries out relative movements of the nut against the spindle and thereby the valve in the sense of an increase in the flow cross sections of supply paths via which the pressure medium Achievement of the desired direction of movement flows, controlled when the rate of change of the actual position is smaller than the change in the position setpoint specification, and keeps these flow cross-sections constant if and as long as these rates of change are the same. The signals required for the motion control of the electric motor are generated by an electronic control unit which is provided with an interface which enables a signal transition and / or data exchange between an NC or a CNC control and the electronic control unit. In order to be able to determine whether and / or when the tool driven by the drive device has reached a certain position, be it to determine whether the tool has actually carried out its working stroke, or to be able to determine exactly the end point of its working stroke, for example If the result of the work depends on the fact that a defined end position is actually reached, as in the case of a press or embossing machine, a monitoring device is provided in which the distance of the control valve actuating element from its basic position is monitored and if this distance defines a predefinable, defined one Falls below the minimum value, which is equivalent to the fact that the tool approaches the dead center, triggers a position-characteristic monitoring signal from a proximity switch. As a result, a sufficiently precise determination of the "programmed" Achieved dead center of the tool, which indicates that the tool has completed its working stroke. To set the device to a certain lifting height of the tool and a certain material thickness of the workpiece or depth of deformation of the same, all that is required is appropriate programming of the setpoint specification device. The detection of the dead center itself takes place with the aid of a proximity switch which responds when a rotary wing which is driven by the valve actuating element via a step-up gear reaches a defined, preset position which corresponds to the "central position" of the valve actuating element which it occupies , when the target and actual positions are equal, which is equivalent to reaching the dead center of the tool.
In the known device, it is also recognized when the overrun control valve is fully open, that is, when the following error ΔS of the control loop becomes very large, which can be taken as an indication that there is a collision between the drive element and an obstacle, and it the drive device is then switched off. The direction of the movement of the drive element is also taken into account here, that is to say it can be seen from the signal combinations generated by the monitoring device whether a collision has taken place in the “forward” or “backward” direction.

In the known drive device, it is entirely possible to adapt its monitoring device so that it can be set to different threshold values of the following error ΔS for different purposes, but it is not possible to determine the amount of the following error as long as it is below the mentioned threshold value , with the consequent disadvantageous consequence, that a change in the tracking error occurring in the operation of a machine equipped with the drive device, e.g. B. in the sense of an enlargement of the same, can not be detected.

The object of the invention is therefore to improve a drive device of the type mentioned in such a way that a continuous and continuous detection of the following error ΔS is possible.

This object is achieved by the characterizing features of claim 1.

Thereafter, the monitoring device comprises a rotary position transmitter which, e.g. generates output signals in digital format which are a direct measure of the total number of revolutions carried out by the setpoint specification element and their azimuthal position within each revolution, and an electronic displacement sensor is also provided, the output signals of which are a direct measure of the axial deflection of the setpoint value Default element relative to the neutral position of the same or the neutral position of the valve actuating element and thus a measure for the following error ΔS are by which the actual position of the tool or the drive element of the hydraulic motor lags behind its target position.

The resulting advantageous properties of the device according to the invention are at least the following:

Because the position of the setpoint input element is monitored - in the sense of a measurement - it is currently for the Operating state of the drive device relevant position setpoint exactly "known" and not affected by inaccuracies that, z. B. with a pulse control of a provided for driving the setpoint input step motor can occur in that the stepper motor, if the pulse repetition frequency of the control should be too high, "overlooks" a control pulse.

Due to the permanent measurement of the deflection of the valve actuating member of the overrun control valve from its rest position, i.e. the measurement of the drag error of the control device, which can be converted into units of the position of the tool driven by the drive device, its actual position is also known at the same time, so that in each phase of a machining process that is carried out using the drive device according to the invention, it can be seen exactly how far the machining process has progressed.

A meaningful and in this respect simple use of this knowledge can, for. B. consist in a large number of similar machining operations, which are repeated periodically, evaluates how large the following error ΔS is at a certain desired position of the tool driven by the drive device. If it is shown here that the following error Δs, based on this specific target position of the tool, increases continuously over several work processes, this is an indication that the tool is "bad" - blunt - and must therefore be replaced immediately.

In this respect, the drive device according to the invention offers the possibility of recognizing an impending malfunction of the machine equipped with it as a whole and of course also the - timely - avoidance of this malfunction, which could be linked to damage to the machine.

On the other hand, in the drive device according to the invention, such phases of machining can also be recognized in which the following error ΔS increases, but this increase is always the same in the case of periodically repeated machining processes, which can be interpreted as an indication that the machining process is controlled by the position setpoint specification control seen here is not optimally "programmed", d. H. the position setpoint specification for the considered processing phase is too fast.

• i Konstanthaltung des Schleppfehlers und/oder
• ii Verringerung des Schleppfehlers durch Änderung der Kreisverstärkung des Regelkreises, und/oder
• iii Abschaltung der Antriebsvorrichtung, wenn der Schleppfehler ΔS einen einstellbar vorgegebenen, werkzeugspezifischen Wert überschreitet.

Both from the point of view of early detection of tool wear and from the point of view of optimal control - programming - the machining sequence, it is therefore advantageous if - according to claim 2 - an electronic control and processing unit is provided, which consists of processing the outputs of the rotary position encoder and can generate control signals for the following functions as required:

• i keeping the following error constant and / or
• ii reduction of the following error by changing the loop gain of the control loop, and / or
• iii Shutdown of the drive device when the following error ΔS exceeds an adjustable, tool-specific value.

This control unit enables the drive device z. B. in the sense of the best possible compromise between desired high dynamics and nonetheless gentle operation.

The preferred design of the rotary position sensor provided for monitoring the position setpoint value and the arrangement of its rotating sensor elements on the setpoint value shaft of the overrun control valve of the drive device has the advantage of very precise detection of the relevant position setpoint value - ultimately - The tool, since no gears or transmission elements, which may be subject to slip or play, are connected between the position setpoint input shaft and the rotary position transmitter.

The same applies with analogous reference to the accuracy of the following error measurement also for the design of the displacement sensor system provided by the features of claim 4, with which the axial deflections of the setpoint input shaft of the follower control valve can be monitored.

Due to the arrangement of the position feedback feedback spindle of the follower control valve, the drive device can be implemented with advantageously small axial dimensions.

Due to the arrangement of the control motor of the follow-up control valve in its leakage oil chamber, which is completely filled with hydraulic oil during operation of the drive device, the working medium of the drive device can be used in a simple manner for cooling the control motor, which is thereby controlled with higher electrical power can, which in turn benefits the dynamics of the entire drive device.

Furthermore, a considerable constructive simplification of the drive device - saving of seals and sealing surfaces required for such, which can be machined with high precision - can be achieved in that, according to claim 7, the rotational position and following error measuring system "in oil", that is, in one with the Receiving space of the control motor is housed in communicating connection housing space of the drive device. It is then only necessary to seal the housing part containing the above-mentioned measuring systems, the motor and the leak oil chamber of the follow-up control valve, but not also to seal the corresponding receiving spaces within the housing from one another. Also provided for the direct control of the control motor power output stage of the electronic control device provided for the operational control of the drive device can be accommodated in a - unpressurized - leakage oil chamber of the device and thereby cooled in a simple manner, it being understood, of course, that the electrical supply - And control lines as well as the signal lines, via which the sensor elements of the rotary position transmitter and the travel sensor are connected to the electronic control unit, must be isolated and liquid-tight from the housing of the drive device, but this is technically problem-free.

The features of claim 8 indicate a preferred, special design of the rotary position transmitter provided for monitoring the position setpoint specification, which enables an angular resolution of the rotary position of 3.6 · 10⁻²⁰.

By the features of claim 9 the basic structure is gradually specified by those of claim 10 in terms of a preferred embodiment of the displacement sensor, by means of which the following error ΔS of the drive device can be detected, the following error ΔS being accurate to at least 1/100 of its maximum amount is measurable.

The evaluation of the displacement sensor output signal provided in accordance with claim 11 means that the neutral position of the valve actuating element of the follower control valve can not be assigned to a specific output signal level of the displacement sensor, so that time-consuming adjustment and calibration processes can be dispensed with.

Fig. 1

ein bevorzugtes Ausführungsbeispiel einer erfindungsgemäßen hydraulischen Antriebsvorrichtung mit einem Meßsystem für den Sollwert der Kolbenposition und für den Schleppfehler der Regelung.

Fig. 2a

Einzelheiten einer Drehstellungsgebereinheit des Meßsystems gemäß Fig. 1,

Fig. 2b

Eizelheiten eines Referenzsignalgebers des Meßsystems gemäß Fig. 1 und

Fig. 2c

Einzelheiten eines Schleppfehlergebers des Meßsystems gemäß Fig. 1, jeweils in vereinfachter, teilweise abgebrochener Ansicht.

Further details and features of the invention will become apparent from the following description of a specific embodiment using the drawing. Show it:

Fig. 1

a preferred embodiment of a hydraulic drive device according to the invention with a measuring system for the setpoint of the piston position and for the following error of the control.

Fig. 2a

Details of a rotary position transmitter unit of the measuring system according to FIG. 1,

Fig. 2b

Details of a reference signal transmitter of the measuring system according to FIGS. 1 and

Fig. 2c

Details of a tracking error transmitter of the measuring system 1, each in a simplified, partially broken view.

The hydraulic drive device according to the invention shown in FIG. 1, to the details of which is expressly referred to, is designated overall by 10 and consists of a hydraulic motor 11, a follow-up control valve 12 which, with an electrically controlled specification of the desired value of the position of a tool (not shown) , which is brought into its working positions by means of the hydraulic motor 11, and mechanical position actual value feedback operates, an electronic control unit 13 for the position setpoint specification control, which is only indicated schematically, and a measuring system, designated overall by 14, by means of which, on the one hand, the controlled one The desired position value of the tool or the drive piston 16 can be measured and, on the other hand, the following error ΔS can be detected, by which the tool or the drive piston 16 lags the controlled position desired value.

In the drive device 10 explained in this respect by the designation of its functionally essential components 11 to 14, its hydraulic motor 11, the follow-up control valve 12 and the measuring system are designed as a compact structural unit accommodated in a common housing 17, the follow-up control valve 12 along the seen central axis 18 of the assembly 11, 12, 14, "between" the hydraulic motor 11 and the measuring system 14 is arranged.

The hydraulic motor 11 in the particular embodiment shown is designed as a linear hydraulic cylinder, the piston 16 of which is fixedly connected to the piston rod 19 within a section forming the housing 17 'of this hydraulic cylinder 11 The housing 17 defines two drive pressure chambers 21 and 22 of the hydraulic cylinder 11 so that they can be moved in a pressure-tight manner, by means of their alternative connection to the high-pressure (P) outlet 23 of the pressure supply unit 24, which is only schematically indicated, or its pressure-free tank, which is controlled by the follow-up control valve 12 (T) port 26 of the drive piston 16 in the directions of movement represented by the arrows 27 and 28 - feed movement and retraction movement - can be driven.

The follow-up control valve 12 is a 4/3-way valve in its function, the neutral basic position 0 is its blocking position, in which both drive pressure chambers 21 and 22 of the hydraulic motor 11 both against the P connection 23 and against the T connection 26 of the pressure supply unit are blocked.

In the function position I of the follow-up control valve 12 assigned to the feed operation of the drive device 10, the one, according to the drawing left drive pressure chamber 21 of the hydraulic cylinder is connected via a flow path 29 of the follow-up control valve 12 to the P-pressure outlet 23 of the pressure supply unit 24, while the other drive pressure chamber 22 is relieved of pressure via the further flow path 31 to the tank 26 of the pressure supply unit. In this functional position I of the follow-up control valve 12, the piston 16 of the hydraulic cylinder 11 moves in the direction of the arrow 27, according to FIG. 1 to the right.

In the functional position II of the follow-up control valve 12 assigned to the withdrawal operation, the drive pressure chamber 21 on the left according to FIG. 1 is via a flow path 32 of the follow-up control valve 12 connected to the - unpressurized - tank connection 26 of the pressure supply unit 24, while the other drive pressure chamber 22 of the hydraulic cylinder 11 is connected to the P-pressure outlet 23 of the pressure supply unit 24 via the second flow path 33 which is effective in the functional position II of the overrun control valve 12. In this functional position II of the follow-up control valve 12, the drive piston 16 of the hydraulic motor 11 moves in the direction of the arrow 28, according to FIG. 1, to the left.

The overrun control valve 12, which - for the purpose of explanation - is required as a slide valve according to the semi-schematic illustration of FIG. 1, the "piston" 34 of which is represented by the 4/3-way valve symbol, is designed as a proportional valve , seen from its blocking basic position 0, with an increasing displacement of its valve piston 34 to the "left"; i.e. in the sense of an action on the hydraulic motor 11 in the feed direction 27, increasingly larger cross sections of the flow paths 29 and 31 are released and with an increasing displacement of its valve piston 34 to the "right", i.e. in the sense of acting on the hydraulic motor in the retraction direction 28, increasingly larger cross sections of the flow paths 32 and 33 are released, the valve piston 34 moving in the opposite direction to the direction of movement of the drive piston 16.

In order to be able to control the follow-up control valve 12 explained in this way in terms of the movement control of the piston 16 of the hydraulic motor 11 and the tool driven with it in its various functional positions 0 and I or II, the following functional elements are further provided:

A hollow shaft 37 is mounted rotatably and axially displaceably in a central bore 36, coaxial with the longitudinal axis 18 of the drive device 10, of a block-shaped central section 17 ″ of the housing 17 which forms on the housing of the follow-up control valve 12 and which on its side faces the hydraulic motor 11 End portion is provided with an internal thread 38, via which it is in meshing engagement with a central, elongated threaded spindle 39 which is fixedly connected to the drive piston 16 of the hydraulic motor 11. This hollow shaft 37 can be driven - for specifying the position setpoint of the drive piston 16 of the hydraulic motor 11 - by means of an electric motor designated overall by 41, the power supply of which is controlled by electrical output signals of the electronic control unit 13 in the sense of the position setpoint specification.

In the special embodiment shown, this electric motor has a stator 42 arranged fixed to the housing and an axially reciprocable rotor 43, the rotor shaft of which is formed by a section of the hollow shaft 37, which is connected to the rotor 43 so as to be fixed in terms of rotation and displacement. The rotor 43 of the electric motor 41 is thus in a central position via the section 44 of the hollow shaft 37 axially penetrated by the threaded spindle 39 on the block-shaped central section 17 ″ of the housing 17, on the one hand, and on the other hand with a further section 46 of the hollow shaft 37 carrying the rotor 43 Bore 47 of an intermediate wall 48 of the housing 17 is rotatably mounted, which essentially delimits the space 49 occupied by the motor 41 and the overrun control valve 12 from the housing space 51 provided for accommodating the measuring system 14, these spaces 49 and 41 not being pressure-tight are closed against each other, but overall form the leak oil chamber of the drive device 10. In the central part 17 '' of the housing 17 of the drive device 10 which receives the follow-up control valve 12, axially displaceable but non-rotatable is a generally designated 52 yoke-shaped valve actuating member, which has two parallel yoke legs 53 and 54 has that through a parallel to! Central longitudinal axis 18 of the drive device extending guide rod 56, which passes through a radially lateral guide bore 57 of the block-shaped, central housing part 17 '', are firmly connected to one another and engage axially on each of the opposite sides of the valve piston 34 via an actuating pin 58 or 59 , wherein this support of the yoke legs 53 and 54 on the actuating pins 58 and 59 and the valve piston 34 is a positive fit.

The two yoke legs 53 and 54 have aligned, with the central longitudinal axis 18 of the drive device 10 coaxial bores 61 and 62, the diameter of which is slightly larger than the outer diameter of the hollow shaft 37, so that this with a sufficient for their smooth rotation through these holes 61 and 62 of the yoke legs 53 and 54 of the valve actuating member 52 can pass through.

The valve actuating member 52 is axially free of play between radial driving flanges 66 and 67 of the hollow shaft 37 via ball bearings 63 and 64, which impart smooth rotation of the hollow shaft 37 relative to the valve actuating member 52.

For the purpose of explaining the function of the components of the drive device 10, as far as their basic structure is concerned, it is first assumed that the hydraulic motor, starting from a rest position in which the follow-up control valve 12 assumes its blocking position 0, e.g. B. the rest position shown, should perform a feed movement in the direction of arrow 27.

For this purpose, the electric drive motor 41 is driven by output signals from the electronic control unit 13 with that direction of rotation - the motor 41 can be driven in alternative directions of rotation - that its rotor 43 and with it the hollow shaft 37 - because of their thread engagement with the initially unoccupied spindle 39 - undergoes an axial displacement in the direction 28 opposite to the feed direction 27, which is also transmitted to the valve piston 34 of the follow-up control valve 12 via the valve actuating member 52, which also carries out this initial axial displacement of the hollow shaft 37, which thereby moves into its Function position I assigned to feed operation arrives. Due to the resulting - increasing - pressurization of the one drive pressure chamber 21 of the hydraulic motor 11, as shown in FIG. 1 on the left, with simultaneous pressure relief of its other drive pressure chamber 22, the piston 16 of the hydraulic motor 11 now experiences a displacement in the feed direction 27, which is due to the form-fitting intermeshing engagement between the threaded spindle 39 and the internal thread 38 of the hollow shaft 37 also on this and thus the valve piston 34, which thereby again in the direction of its basic position 0, ie in the sense of a reduction in the effective cross sections of the flow paths 29 and 31 of the follow-up control valve is moved. After the control system has "settled" in only a short period of time The result is a stationary state in which the hollow shaft 37 is driven at the speed that the axial displacement of the two elements 37 and 39 relative to the rotational relative movement of the hollow shaft 37 relative to the threaded spindle 39 is equal to the feed speed of the piston 16. In this stationary, ie constant feed speed of the piston 16, corresponding operating state of the drive device 10, the equality of the actual value corresponds to the feed speed of the drive piston 16 and the target value of the feed speed, the valve actuator 52 is "at rest" and the overrun control valve 12 in its functional position I is opened so far that the oil volume flow dV / dt, which is fed into the pressurized drive pressure chamber 21 of the hydraulic cylinder or discharged from the pressure-relieved pressure chamber 22, has exactly the value F * dS / dt , where F is the value of the pressurized surface of the drive piston 16 and dS / dt the feed speed in the direction of arrow 27.

The mode of operation of the drive device 10 in the retracting operation of the hydraulic motor 11 - when the electric motor 41 is actuated in the opposite direction of rotation - is analogous, with only the effective cross-sectional area of the piston 16 being smaller in the particular exemplary embodiment shown.

However, in the steady state of operation of the drive device 10, which corresponds to the actual value and the target value corresponding to the speed of movement of the piston 16, there is a difference between the currently relevant target value of the position of the drive piston 16 and its actual value, which is the same as that for maintaining the stationary one Condition Required deflection stroke of the follower control valve piston 34 from its basic position is 0 and corresponds to the following error ΔS of the control by which the actual position value of the drive piston 16 or the tool lags behind the target value

The measuring system 14, for the explanation of which reference is now also made to the details of FIGS. 2a and 2b and 2c, comprises a total of 3, basically rotationally symmetrical encoder elements 68, 69 and 71, which can be seen from FIG. 1 Arrangement at an axial distance from one another in a rotationally and displaceably fixed manner are arranged on the end section 72 of the hollow shaft 37 which projects into the receiving space 51 of the measuring system 14.

The first mechanical transmitter element 68 has the shape of a gearwheel with teeth 73 running parallel to the central longitudinal axis 18, which trigger pulse-shaped AC voltage output signals of these sensor elements 74 and 75 when passing past electronic sensor elements 74 and 75 arranged fixed to the housing, i.e. Consequences of voltage pulses varying between a maximum and a minimum level, the pulse shape of which corresponds to the hollow shaft 37 or the rotor 43 of the electric motor 41 in a very good approximation of a sine wave at a predetermined speed.

So-called field plate sensors of a type known per se are used as sensor elements 74 and 75, in which the amplitudes of the output signals are independent of the rotational speed of the mechanical encoder elements 68, that is to say the signal level of their output signals varies between defined - upper and lower - extreme values, so that the output signals the level of the two sensor elements 74 and 75 can also be easily evaluated.

The two sensor elements 74 and 75 are arranged at such an azimuthal distance Δφ from one another that there is a phase shift of 90 ° between their output signals, so that continuous monitoring of the time profile of the output signals of the two sensor elements 74 and 75 and the temporal changes (temporal Differential quotients) the same also the sense of rotation of the hollow shaft 37 can be detected.

This evaluation of the sensor output signals takes place according to known algorithms in the electronic control unit 13, to which the output signals of the two sensor elements 74 and 75 are fed.

The gear-shaped transmitter element 68 and the sensor elements 74 and 75 associated therewith thus form an angular position measuring system, the accuracy of which is greater, the greater the number of teeth 73 equidistantly distributed over the circumference of the transmitter element 68 and the higher the accuracy the output signal amplitudes of the two sensor elements 74 and 75 can be measured. The relevant measuring accuracy allows the angular distance of two teeth that follow one another to be recorded precisely to 1/100 of its amount. With an angular distance of 3.6 ° between two successive teeth 73, the accuracy of the angular position measuring system is 68.74.75 3.6 x 10⁻² °.

The second - with the hollow shaft 37 - rotating - mechanical encoder element 69 is designed as an annular flange-shaped element, which has only a single, for example V-shaped, slot 76 on its circumference, alternatively a - pointed - projection 76 ', by advancing on one assigned to this transmitter element 69, arranged fixed to the housing electronic sensor element 77 a reference pulse is triggered.

By the occurrence of the reference pulse of this electronic sensor element 77, the structure of which is analogous to that of the sensor elements 74 and 75 of the angular position measuring system 68, 74, 75, a reference plane is marked, as it were, to which the two sensor elements 74 and 75 within one revolution of the Hollow shaft 37 detectable angular positions of this shaft can be obtained. Due to the angular position and number of revolutions impulses which occur in a certain direction of rotation of the hollow shaft 37 and which are emitted by the sensor elements 74 and 75 and possibly 77, the desired position value can be obtained in a simple manner - by appropriate evaluation in the electronic control unit 13 Specification for the drive piston 16 of the hydraulic motor 11 can be checked.

The gear-shaped transmitter element 68 and the annular flange-shaped transmitter element 69 and the associated electronic sensor elements 74 and 75 and 77 are arranged and designed so that the output signals of at least the two sensor elements 74 and 75 of the angular position measuring system 68, 74, 75 by the in operation possible axial displacements of the hollow shaft 37 - and thus also of the transmitter elements 68 and 69 - of the drive device 10 are not influenced, since the output signals of the two sensor elements 74 and 75 should also be able to be evaluated as precisely as possible with regard to the amounts of their amplitudes (signal level).

This is not absolutely necessary for the reference measuring system 69, 77, but it is also expedient here if the amplitudes of the output signals generated by the sensor element 77 do not vary, at least not drastically, with axial displacements of the ring-flange-shaped transmitter element 69.

In contrast to this, the subsystem of the measuring system 14 comprising the third rotating sensor element 71 and at least one further electronic sensor element 78 which is also arranged fixed to the housing is designed such that the output signal level of the output signals generated by this third electronic sensor element 78 is significant, preferably in a linear relation with axial ones Displacements of the encoder element 71 or the hollow shaft 37 vary in order to be able to determine with sufficient accuracy from the relevant variation or the respective amount of the output signal of the sensor element 78 the following error ΔS which is relevant in the operation of the drive device 10.

For this purpose, the simple design of the following error measuring system 71, 78, which can be seen in FIG. 1, has its mechanical encoder element 71 formed as an annular rib with conical flanks 79 and 81, which adjoin one another along a sharp ring edge 82, by their axial displacements relative to the sensor element 78 whose output signal level is influenced.

An element of the type is again provided as sensor element 78, as already explained for the angular position measuring system 68, 74, 75. In terms of a simple evaluation of the level of the output signals of the sensor element 78 in units of the tracking error ΔS, it is favorable if a position of the mechanical transmitter element 71 is linked to the - blocking - basic position O of the overrun control valve 12, in which the output signal of the sensor element 78 of the following error measuring system 71, 78 corresponds to a - high or low - extreme value, so that changes in the output signal level of the sensor element 78 are in each case monotonously related to the following error ΔS in one direction or the other.

A necessary adjustability of the following error measuring system 71, 78 can be realized in that its transmitter element 71 can be screwed onto a thread 83 of the hollow shaft end section 72 and can thus be displaced in the axial direction and can be fixed by means of a locking nut (not shown).

As an alternative to the configuration of the encoder element 71 shown in FIG. 1, which is symmetrical with respect to the plane of the ring edge 82, a single-conical ring 71 'can also be provided as a mechanical encoder element, as a mechanical encoder element, in order to create a monotonous relationship to achieve the output signal level of the sensor element 78 with the following error ΔS. In the embodiment of the mechanical encoder element 71 'of the following error measuring system 71', 78 provided in accordance with FIG. 2c, it can be calibrated in units of the following error ΔS in a simple manner by switching on the drive device, i.e. As long as the hollow shaft 37 or the encoder element 71 'has not yet undergone any displacement, the output signal level of the sensor element 78 is stored as a reference point for the following error measurement and is thus taken into account as a correction variable for the following error measurement.

The implementation of a necessary correction or An evaluation circuit is readily possible for a person skilled in the art with conventional electronic circuit technology if the purpose is known, so that details in this regard do not appear to require explanation.

In combination with a device which can recognize the change in the following error ΔS, it can also be advantageous to increase the accuracy of the following error measurement if, as shown in the lower part of FIG. 2c, In the context of the following error measuring system, a mechanical encoder element 71 'is provided, the radius of which varies periodically between a minimum value r and a maximum value R, preferably, as shown, linearly within the axial length L of the encoder element 71''used for the following error. A sensor system which detects the direction of the following error change can then be implemented in a simple manner with two sensor elements 78 'and 78''of the same type as the sensor element 78, which are arranged at a distance ΔL from one another which is dimensioned such that their output signals, based on the periodic structure of the encoder element 71 '', have a phase shift of 90 ° or an odd multiple thereof, so that - in analogy to the angular position measuring system 68, 74, 75, here too, in addition to the absolute value of the following error ΔS, its sense of change can be seen from the axial displacements of the encoder element 71 ″. A relevant arrangement of the two sensor elements 78 'and 78''is, for example, the one in which their axial distance ΔL has the value 1/4 l, where l denotes the periodicity length of the periodic structure of the transmitter element 71''. With this configuration of the following error measuring system 71 ″, 78 ′, 78 ″, “calibration” is possible in that the output signal combination of the two sensor elements 78 ′ and 78 ″ is stored before or with the start of the regulation and monitoring operation and as Reference values for the further measurements are taken into account.

Claims (12)

1. Hydraulic drive for the adjustment and feed as well as return movements of a toolhead of a machine tool with

   a) a hydraulic motor (11) comprising a movable drive element (16,19) fixedly connected to the toolhead, this drive element being drivable by alternative pressurization and pressure relief of drive pressure chambers (21,22) along the lines of the tool movements,

   b) a follow-up control valve (12) operating with electromechanically controllable reference position value setting for the movable drive element (16), as well as with mechanical actual position value return indication thereof, wherein

   c) for setting the reference position value and return indication of actual position value, a threaded spindle (39) is provided and a spindle nut fashioned as a hollow shaft (37) and meshing with the thread of the spindle is also provided, and one of the two elements of this spindle-nut system can be driven by means of an electric motor (41) along the lines of setting the reference position value, and the other (39) one of these two elements is driven by means of the drive element (16) along the lines of actual position value return indication, and wherein

   d) the signals required for the motion control of the electric motor (41) are produced by an electronic control unit (13) with interface for an NC or a CNC control,

   characterized by the following features:

   e) a rotational and angular position pickup system (68, 74,75,69,77) is provided which produces output signals constituting the information of the number of revolutions executed in total by the reference value setting shaft (37), as well as for the azimuthal position of the reference value setting element (37) within each revolution, and

   f) an electronic displacement pickup system (71, 78;71', 78',71'') is provided, the output signals of which are a direct measure for the axial deflections of the reference value setting element (37), and of a valve operating member (52) of the follow-up control valve (12) also executing these axial deflections with regard to the rest position thereof, and providing a measure for the lag error ΔS by which the actual position of the toolhead and/or of the drive element (16) of the hydraulic motor (11) trails with respect to its reference position.
2. Hydraulic drive according to claim 1, characterized in that the hollow shaft (37) is used as the position reference value setting element, and that the threaded spindle (39) is used as the actual position return indication element.
3. Hydraulic drive according to claim 1 or claim 2, characterized in that an electronic control and processing unit (13) is provided which causes activation of the electric motor (41) along the lines of setting the reference position value, to which control and processing unit there can be fed as the input also the output of the rotational and angular position pickup system (68,74,75,69,77) as well as of the displacement pickup system (71,78;71,78';71'', 78''), this electronic control unit (13) producing, from the processing thereof, correction signals for an at least partial lag error compensation and/or for maintaining the lag error ΔS constant and/or for cutting off the drive (10) when the lag error ΔS exceeds an adjustably preset threshold value.
4. Drive according to one of claims 1 - 3, characterized in that the rotational and angular position measuring system (68,74,75) has a rotating pickup element (68) with a contour which, as seen in the peripheral direction, is of a periodically wavy or periodically toothed shape, the voltage output signals characteristic for the angular position of the reference value setting shaft (37) being produced by the passage of this rotating pickup element past at least one sensor element (74 and/or 75), and that this pickup element (68) in coaxial arrangement with the central axis (18) of the reference value setting shaft 837) and the actual value return indication spindle (39) is nonrotationally and nondisplaceably connected with the reference value setting shaft (37) while the sensor element (74 and/or 75) is arranged fixedly at the machine and/ or that a further pickup element (69) nonrotationally and nondisplaceably connected with the reference value setting shaft (37) is provided, the circumference of which only exhibits a radial projection (76') or a radial recess (76), the passage of this projection or recess past a further electronic sensor element (77) fixedly arranged at the machine making it possible to trigger reference signals for the number of completely executed revolutions by the reference value setting shaft (37).
5. Hydraulic drive according to one of claims 1-4, characterized in that the displacement measuring system (71, 78;71',78';71'',78'') provided for detecting axial deflections of the reference position value setting shaft (37) of the follow-up control valve (12) includes a pickup element (71;71';71'') nonrotationally and nondisplaceably connected with the reference value setting shaft 837), the axial deflections of this pickup element with respect to at least on noncontactually responding electronic sensor element (78;78' and/or 78'') arranged fixedly at the machine changing the output signal of this sensor element to the extent characteristic for the deflection, and that the rotor (43) of the electric motor (41) provided for the setting of the reference position value is connected nonrotationally and nondisplaceably with the reference value setting shaft (37) and is arranged to be shiftable together with this shaft axially relatively to the stator (42) of the motor (41) fixedly mounted to the housing.
6. A hydraulic drive according to one of claims 1-5, wherein the hollow shaft (37) the reference position value setting element and the threaded spindle (39) forms the actual position value element, said threaded spindle being nondisplaceably connected to the drive element (16) of the hydraulic motor (11), characterized in that threaded spindle (39) is surrounded by the hollow shaft 837) along a section of a length thereof corresponding at least to the displacement path of the drive element (16) of the hydraulic motor (11).
7. Hydraulic drive according to one of claims 1-6, characterized in that the electric motor (41) provided for controlling the setting of the reference position value is arranged in a leakage oil chamber (49,51) of the drive (10).
8. Hydraulic drive according to claim 7, characterized in that also the rotational and angular position measuring system (68,74,75,69,77) and/or the lag error measuring system (71,78;71',78';71'',78'') is and/or are arranged in the leakage oil chamber (49, 51) of the drive (10).
9. Hydraulic drive according to one of claims 1-8, characterized in that the rotational and angular position measuring system (68,74,75) comprises, as the mechanical pickup element, a toothed rim (68) with 100 teeth (73) distributed equidistantly over the rim circumference and extending in the axial direction, and that two electronic sensor elements (74 and 75) are provided, the azimuthal distance Δφ of which is an odd-number multiple of one-fourth of the angular distance of neighboring teeth (73) of the toothed rim (68), and that the two electronic sensor elements (74 and 75) are fashioned as field plate sensors of a conventional type of structure.
10. Hydraulic drive according to one of the preceding claims, characterized in that the mechanical pickup element (71;71';71'') of the lag error measuring system has at least one ramp surface (79 and/or 81) extending obliquely to the central longitudinal axis (18), the variation of the distance of this ramp surface from the respective sensor element (78;78';78''), linked with an axial shift of this pickup element (71;71';71''), yielding a shift-proportional change of the output signal of the respective sensor element (78;78';78'').
11. Hydraulic drive according to claim 10, characterized in that the mechanical pickup element (71'') of the lag error measuring system, as seen over its length, has a periodically varying diameter, and that two electronic sensor elements (78' and 78'') are provided which are located at an axial distance ΔL from each other which is an odd-number multiple of l/4, wherein l means the length of periodicity of the diameter variation of the pickup element 71''.
12. Hydraulic drive according to one of claims 1-11, characterized in that the electronic control unit (13) comprises a correction or evaluating circuit, by means of which the output of the rotational and angular position measuring system (68,74,75,69,77) produced in the basic position of the follow-up control valve (12) and/or of the lag error measuring system (71,78;71',78';71'',78'') can be taken into account as reference values for the rotational and angular position measurement and, respectively, for the lag error measurement.

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