Method for operating a parallel kinematic system

Abstract

The invention relates to a method for operating a parallel kinematics (1) comprising at least two adjustment units (2a-2f) for generating positioning movements along a respective adjustment direction (VR1-VR6), - wherein the parallel kinematics (1) comprises a base body (3) and an adjustable body (4) and wherein the adjustable body (4) is adjustable with respect to its actual position (X_actual) in a first coordinate system (K1) relative to the base body (3) by means of the adjustment units (2a-2f, 2c), - wherein the parallel kinematics (1) also includes a sensor system (5) by means of which an adjustment of the adjustable body (4) in a second coordinate system (K2) can be determined, - wherein the parallel kinematics (1) comprises a control / regulation device (10) that can be switched between a first and a second operating mode (BM1, BM2), - wherein, according to the procedure, a predetermined target position (X_target) of the adjustable body (4) in the first coordinate system (K1) is set and controlled in the first operating mode by means of the control / regulation device (10) by controlled adjustment of the adjustment units (2a-2f), - wherein, according to the procedure, in the second operating mode, a respective actual adjustment position (V_ist) of the adjustment units (2a-2f) is determined by means of the control / regulation device (10) and at least one actual adjustment position (V_ist) is regulated.

Description

[0001] The present invention relates to a method for operating a parallel kinematics system with at least two adjustment units and to a parallel kinematics system that is set up or programmed for carrying out this method.

[0002] Parallel kinematic systems are available with up to six degrees of freedom and, due to their typically low inertia, possess high dynamics in all axes.

[0003] Against this background, DE 198 58 154 A1 describes a method and a device for calibrating devices with at least one partially indeterminate geometric parameter. A test specimen is arranged in the device, and a test element is attached to a part that is movable relative to the test specimen. The device is moved until the test element has assumed a defined position with respect to a measuring point on the test specimen. The parameters representing the position of the device are then recorded at the measuring point. This process is repeated for several measuring points. From known actual dimensions of the test specimen and the recorded position parameters, correction values ​​are determined for manufacturing- and assembly-related deviations in the geometric parameters of the device that affect its movement behavior. These correction values ​​are used to correct the geometric parameters, thereby calibrating the device.

[0004] A disadvantage of such conventional parallel kinematic systems is that when energy is deactivated, i.e., when the parallel kinematics are deactivated to set or reach a park position, an undesirable change in the system's position – albeit only a slight one – can occur, so that its actual position deviates from the desired park position.

[0005] It is therefore an object of the present invention to provide an improved method for operating a parallel kinematic system in which the aforementioned disadvantage is at least partially, preferably completely, eliminated.

[0006] This problem is solved by the subject matter of the independent patent claims. Preferred embodiments are the subject matter of the dependent claims.

[0007] The basic idea of ​​the invention is therefore to design a parallel kinematic system with an adjustable body in such a way that it can be operated in two different operating modes, between which the parallel kinematic system can be switched during operation. The two operating modes differ in that the adjustment units are controlled and regulated in different coordinate systems. In the first operating mode, the position or orientation of the adjustable body relative to a fixed base body in the first coordinate system can be regulated. Preferably, the adjustable body can be considered a rigid body.The position of the adjustable body can then be conveniently defined by six coordinates. The first, second, and third coordinates can be spatial coordinates, defining the position of the adjustable body relative to an origin of the coordinate system, typically defined by the base body. These can conveniently be x, y, and z coordinates of a Cartesian coordinate system with an x-axis, a y-axis, and a z-axis, respectively. The fourth, fifth, and sixth coordinates can each be angular coordinates, defining the rotational position or orientation of the adjustable body relative to the base body or the coordinate axes. These angular coordinates can conveniently be Euler angles.In the first operating mode, the position of the adjustable body, defined by, in particular, six coordinates, can be set by specifying a target position and controlled using a parallel kinematic control loop.

[0008] In the second operating mode, in contrast to the first, the basis vectors for the second coordinate system are those direction vectors along which the individual adjustment units are adjustable, preferably linearly, in order to change the (adjustable) position of the adjustable body relative to the base body. In the second operating mode, the adjustment units can also be adjusted and controlled as in the first. Since the position of the respective adjustment units can be directly controlled in the second operating mode, this mode is particularly suitable when the parallel kinematics are to be de-energized to set a park position; because the second operating mode allows the last adjustment position set, especially in the first operating mode, to be controlled and thus maintained.Thus, to deactivate the parallel kinematics, it is possible to successively de-energize the individual adjustment units and, using sensors within the parallel kinematics to determine the position of the adjustable body, to verify whether the electrical de-energization resulted in an undesired adjustment of the respective unit exceeding a maximum acceptable tolerance limit, or whether the undesired adjustment of the respective unit remained within the specified tolerance limit. In the former case, the respective adjustment unit can be reactivated, i.e., supplied with electrical energy again, and the de-energization process can be repeated. In the latter case, the process can continue with the next adjustment unit, proceeding as described above.In this way, all individual adjustment units can be successively set without energy with very high positional accuracy, which can preferably be ≤ 70nm.

[0009] Finally, the method according to the invention allows for an individual analysis or fault analysis of a single adjustment unit in the parallel kinematic system, i.e., in a state installed in the parallel kinematic system.

[0010] Following the above inventive concept, the method according to the invention serves to operate a parallel kinematic system comprising at least two adjustment units for generating positioning movements along a respective adjustment direction. Preferably, at least one adjustment unit can comprise a piezoelectric actuator, in particular one that is linearly length-adjustable along a specific adjustment direction. Particularly preferably, all adjustment units of the parallel kinematic system can comprise such a piezoelectric actuator.

[0011] At least one actuator, preferably each actuator, can have a plurality of layers of a piezoceramic material, the individual layers being separated by electrical electrodes arranged between them. Such a configuration is known to those skilled in the art as a "multilayer structure".

[0012] An electrical voltage can be applied between any two adjacent electrodes to generate the desired electric field within the piezoceramic material. The stacking direction of the layers of piezoceramic material and the electrodes arranged between them extends along the adjustment direction of the respective actuator. The adjustment direction of each actuator is therefore essentially perpendicular to the planes in which the electrodes are arranged. However, in one variant, it is also conceivable that the adjustment direction of the respective actuator runs parallel to the plane of a specific electrode.

[0013] The parallel kinematics according to the invention further comprises a base body and a body adjustable relative to the base body by means of at least two adjustment units. Each of the adjustment units can be designed to be length-adjustable along an individual adjustment direction. In particular, the respective adjustment unit or its piezoelectric actuator can be length-adjusted by utilizing the known piezoelectric effect by supplying or applying an electrical voltage to the respective adjustment unit or, optionally, the respective piezoelectric actuator.

[0014] In the parallel kinematics according to the invention, all adjustment units act on the adjustable body, which is preferably designed as a common platform. This allows the dynamic properties of the individual adjustment units to be designed identically, and the moving mass of the adjustable body can be kept small.

[0015] Parallel kinematics, in this context, refers to a system in which at least two adjustment units act on the same adjustable body. Advantageously, the parallel kinematics can be formed by a so-called hexapod, which has six adjustment units acting on the adjustable body and allowing its adjustment relative to the base body in three translational degrees of freedom and three additional rotational degrees of freedom. The adjustable body can be moved relative to the base body in a first coordinate system by means of these adjustment units.

[0016] Furthermore, parallel kinematics includes a sensor system by which a change in the position of the adjustable body in a second coordinate system can be determined.

[0017] The parallel kinematics further comprises a control / regulation device that can be switched between a first and a second operating mode. According to the invention, in the first operating mode, a predetermined target position of the adjustable body in the first coordinate system is set and regulated by means of the control / regulation device through controlled adjustment of the adjustment units. In the second operating mode, a respective adjustment position of the adjustment units along the adjustment directions is determined by means of the control / regulation device, and at least one actual adjustment position is regulated.

[0018] In a preferred embodiment, at least two actual positions of the at least two adjustment units can be controlled independently of one another in the second operating mode. Particularly preferably, the actual positions of all available adjustment units can be controlled independently of one another. This allows the individual adjustment units to be successively de-energized in such a way that de-energizing one adjustment unit does not negatively affect the positions of the other adjustment units due to their continued active control. In this way, it can be avoided that individual adjustment units change their position when de-energized, which would in turn lead to the aforementioned undesirable adjustment of the adjustable body when the parallel kinematics are deactivated or "parked".

[0019] According to a further preferred embodiment, in the first operating mode, a deviation of the target position from the actual position is transformed into a respective setpoint of the at least two adjustment units by means of an output transformation matrix to control the position of the adjustable body. Furthermore, in this embodiment, the adjustment of the adjustable body determined by the sensors is transformed into the actual position of the adjustable body by means of an input transformation matrix. Thus, a coordinate transformation between the first and second coordinate systems is effectively realized by means of the two matrices.

[0020] In the second operating mode of this embodiment, the adjustment of the adjustable body, determined by the sensors, is transformed into an actual adjustment position using a further transformation matrix to control at least one adjustment position. This transformation matrix is ​​calculated by matrix multiplication of the input transformation matrix and the output transformation matrix. The control values ​​of the at least two adjustment units are determined without transformation from the deviation of the actual adjustment position from the target adjustment position.

[0021] According to a further advantageous embodiment, two measures, a) and b), can be implemented to de-energize the first of the actuators. In the first measure, a), the control device is switched to the second operating mode, and all actual positions of the at least two adjustment units are controlled. In the second measure, b), the first adjustment unit is de-energized by appropriate control. Thus, the individual adjustment units can be switched from the nominal first operating mode, in which the adjustable body can be moved and positioned relative to the base body as desired during operation of the parallel kinematics, to the second operating mode when the parallel kinematics are to be "parked" with high positional accuracy and therefore de-energized.

[0022] Preferably, after de-energizing according to measure b), a further measure c) can be taken to check whether the actual adjustment position is outside a predefined tolerance range. If measure c) determines that this is the case, i.e., the actual adjustment position of the relevant actuator is outside the predefined tolerance range, the first actuator is classified as having been unsuccessfully de-energized, and therefore the position control for this actuator is reactivated. Following this reactivation of the position control, measures b) and c) can then be repeated at least once, and preferably multiple times or N times, if necessary.

[0023] If, however, step c) determines that the actual adjustment position is within the specified tolerance range, the first adjustment unit is classified as successfully de-energized. In this case, the process of de-energizing the next adjustment unit can continue until all existing adjustment units have been successively de-energized.

[0024] According to a beneficial further development, after the first adjustment unit has been successfully de-energized, the remaining adjustment units are successively de-energized using the same procedure as measures b) and c). In this way, all existing adjustment units can be de-energized one after the other with high positional accuracy.

[0025] In a further preferred embodiment of the method according to the invention, the de-energizing process can be aborted if one of the adjusting units is unsuccessfully relaxed more than N times consecutively according to measures b) and c) or if a predetermined time period is exceeded. Here, N is a natural number. Particularly preferably, said time period can be between two seconds and 10 seconds.

[0026] Particularly preferably, the de-energizing in measure b) comprises controlling the adjustment unit to reduce its creep behavior by generating at least one electrical voltage pulse, preferably at least two or more successive electrical voltage pulses, which causes a remanent change in length of the adjustment unit.

[0027] The invention further relates to a parallel kinematic system comprising at least two adjustment units for generating positioning movements along a respective adjustment direction.

[0028] Preferably, at least one adjustment unit can include a piezoelectric actuator. Particularly preferably, all existing adjustment units can include such a piezoelectric actuator.

[0029] Furthermore, parallel kinematics comprises a base body and a body that can be adjusted relative to the base body. The adjustable body can be moved relative to the base body in a first coordinate system with respect to its actual position by means of adjustment units.

[0030] In this context, parallel kinematics refers to a system in which at least two adjustment units act on the same adjustable body.

[0031] The parallel kinematics can expediently be formed by a hexapod which has six adjustment units that act on the adjustable body and allow adjustment of the adjustable body relative to the base body in three translational degrees of freedom and also in three further rotational degrees of freedom.

[0032] Furthermore, the parallel kinematics system includes sensors by means of which a change in the position of the adjustable body in a second coordinate system can be determined. The parallel kinematics system also includes a control device that can be switched between a first and a second operating mode. This device is configured and programmed to carry out the method according to the invention described above. The advantages of the method according to the invention, as explained above, therefore also apply to the parallel kinematics system according to the invention.

[0033] In the first operating mode, a predetermined target position of the adjustable body in the first coordinate system can be set and controlled by the control device through controlled adjustment of the adjustment units. This is preferably also set and controlled during operation of the parallel kinematics. In the second operating mode, the control device can determine the respective adjustment position of the adjustment units along the adjustment directions defined in the second coordinate system, and at least one actual adjustment position can be controlled. This determination and control preferably takes place during operation of the parallel kinematics.

[0034] As explained above, in another preferred embodiment, at least one adjustment unit can comprise a piezoelectric actuator whose length can be adjusted linearly along a specific adjustment direction. The length of the piezoelectric actuator is measured along an adjustment direction along which the length of the factor can be varied.

[0035] Further important features and advantages of the invention will become apparent from the dependent claims, the drawings and the associated description of the figures based on the drawings.

[0036] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0037] Preferred embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components.

[0038] They show, schematically: Fig. 1 in perspective view an example of a parallel kinematics according to the invention, Fig. 2. A circuit diagram-like representation illustrating the functioning of a control loop of the parallel kinematics when the parallel kinematics is in the first operating mode. Fig. 3. A circuit diagram-like representation illustrating the functioning of the control loop when the parallel kinematics is in the second operating mode. Fig. 4 a flowchart explaining the method according to the invention.

[0039] The Fig. Figure 1 shows in perspective an example of a parallel kinematics system according to the invention. Fig. In the example, parallel kinematics 1 comprises a base body 3 and also a body 4 that is adjustable relative to the base body 3. Furthermore, in the example, parallel kinematics 1 comprises six adjustment units 2a to 2f for generating linear positioning movements along a respective adjustment direction VR1 to VR6. In the example, each of the adjustment units 2a to 2f comprises a piezoelectric actuator that is length-adjustable, i.e., linearly adjustable, along the respective adjustment direction VR1 to VR6 (in Fig. 1 not shown in detail). In the example of the Fig. 1 is the parallel kinematics 1 designed as a hexapod 6.

[0040] Each of the actuators, i.e., each actuating unit 2a-2f, has a plurality of layers of piezoceramic material, the individual layers being separated by electrical electrodes arranged between them. Such a configuration is known to those skilled in the art as a "multilayer structure".

[0041] An electrical voltage can be applied between any two adjacent electrodes to generate the desired electric field within the piezoceramic material. The stacking direction of the layers of piezoceramic material and the electrodes arranged between them extends along the adjustment direction VR1-VR6 of the respective actuator 2a-2f. The respective adjustment direction VR1-VR6 of the respective actuator 2a-2f thus runs essentially perpendicular to the planes in which the electrodes are arranged. However, in one variant, it is also conceivable that the respective adjustment direction VR1-VR6 of the respective actuator 2a-2f runs parallel to the plane of a specific electrode. The respective actuator 2a to 2f, or its piezoelectric actuator, can therefore utilize the piezoelectric effect by supplying or applying an electrical voltage to the respective actuator 2a to 2b.The length of the respective piezoelectric actuator can be adjusted. This is accompanied by an adjustment of the position and / or orientation of the adjustable body 4 relative to the base body 3.

[0042] The adjustable body 4 is simplified and considered as an ideal rigid body. The adjustable body 4 can be adjusted relative to the base body 3 in a first coordinate system K1 by means of the six adjustment units 2a to 2f with respect to its current actual position X_actual in the first coordinate system K1. The first coordinate system K1 is a coordinate system fixed with respect to the base body 3. Advantageously, the first coordinate system K1 can be a Cartesian coordinate system, and an origin U of the first coordinate system K1 can be defined by the position of the fixed base body 3. The position of the adjustable body 4 in the first coordinate system K1 can thus be defined by three translational coordinates x, y, z and by three rotational coordinates u, v, w (in Fig. (1 not shown) must be fully defined.

[0043] Furthermore, the parallel kinematics 1 includes a sensor system 5, by means of which an adjustment of the adjustable body 4 in a second coordinate system K2 different from the second coordinate system K1 (in Fig. (1 not shown) can be determined. In the example scenario, the sensor system 5 comprises three sensors 5a to 5c arranged on the adjustable body 4. Each of the three sensors 5a-5c can detect an adjustment or movement of the respective sensor 5a to 5c and thus an adjustment or movement of the adjustable body 4 along a respective measuring direction. These measuring directions generally differ from the adjustment directions VR1 to VR6.

[0044] The parallel kinematics 1 further comprises a control unit 10 for controlling the six adjustment units 2a to 2f. The six adjustment units 2a to 2f can thus be adjusted by the control unit 10. In addition, the control unit 10 is connected to the sensor system 5 or sensors 5a to 5c for data transmission, so that it can receive and process sensor data that reflects a movement detected by a respective sensor 5a to 5c along the respective measuring direction.

[0045] Furthermore, the control / regulating device 10 includes a control loop 20, the structure of which is in Fig. 2 is represented in a circuit diagram format. The control loop 20 is according to Fig. 2 is subdivided into a first partial circle 20a, which operates in the first coordinate system K1, and into a second partial circle 20b, which operates in the second coordinate system K2. The control loop 20 comprises, in a known manner, a controlled system 21 extending over both partial circles 20a and 20b, as well as a feedback loop 22 also extending over both partial circles 20a and 20b.

[0046] The control / regulating device 10 can be switched between a first and a second operating mode BM1, BM2 (see also Fig. 1).

[0047] In the first operating mode BM1, a predetermined target position X_target of the adjustable body 4 in the first coordinate system K1 is set and controlled by means of the control / regulation device 10 by controlled adjustment of the adjustment units 2a-2f.

[0048] In the second operating mode BM2, the control / regulation device 10 determines a respective adjustment position VP1-VP6 of the adjustment units 2a to 2f along the adjustment directions VR1 to VR6 defining the second coordinate system K2, and the actual adjustment positions V_actual are regulated to a setpoint V_target.

[0049] The functionality of the first operating mode BM1 is explained below using the controller diagram. Fig. 2 explained. In the first operating mode, to control the position of the adjustable body 4 relative to the base body 3, a control value X_set is determined from a control deviation A of an externally specified target position X_target of the moving body 4 in the first coordinate system K1 (=reference variable in the first operating mode BM1) from the actual position X_actual using a control algorithm 23. The control algorithm 23 thus calculates a control value vector X_set from the control deviation A as the control variable, with the control values ​​x_set, y_set, z_set, u_set, v_set, w_set of the six coordinates x, y, z, u, v, w.

[0050] The transition from the first sub-circle 20a to the second sub-circle 20b is now carried out using a first transformation matrix, which is referred to below as the output transformation matrix O.

[0051] Is X_set therefore the vector of the control values ​​X_set calculated by the control algorithm 23 for the six coordinates x, y, z, u, v, w, i.e. X_set=(x_sety_setz_setu_setv_setw_set), These can be transformed using the two-dimensional output transformation matrix O to the setpoints v1_set to v6_set of the six control units 2a-2f along the respective adjustment direction VR1 to VR6.

[0052] Is V_set the vector with the six position values ​​v1_set to v6_set as vector components, i.e. V_set=(v1_setv2_setv3_setv4_setv5_setv6_set), Therefore, the following applies: V_set=O*X_set.

[0053] The setpoints V_set, i.e. v1_set to v6_set, can be output as control signals Sig1 to Sig6 and converted into electrical voltages U1 to U6 by means of an electrical amplifier 24, which are supplied to the individual actuating units 2a-2f and determine the adjustment position or length extension of the respective actuating unit 2a-2f or of the respective actuator.

[0054] The sensor data or sensor signals S1-S3 provided by sensors 5a to 5c regarding the movement of sensors 5a to 5c along the respective measurement direction are further processed as a control variable by the control loop 20 in its feedback loop 22. This further processing can be achieved by linearizing the sensor signals S1-S3 using a linearization unit 25 following the sensor system 5 in the feedback loop 22 of the control loop 20. In the example scenario, this unit is configured in two stages. A first stage of the linearization unit 25 electrically linearizes the sensor system 5 with its three sensors 5a to 5c. A second stage of the linearization unit 25 mechanically linearizes the sensor signals. An electrical sensor filter 26 can be provided downstream of the linearization unit 25. This filter can be configured as a low-pass filter and, in this case, suppresses or at least attenuates unwanted high-frequency components.

[0055] The linearized and filtered sensor signals S1 to S3, and thus the adjustment of the adjustable body 4 determined by sensors 5 and 5a to 5c, are transformed in a subsequent section of the control loop 20 into the actual position X_actual of the adjustable body 4 using a second transformation matrix, the input transformation matrix I. The transition from the second sub-circuit 20b to the first sub-circuit 20a is therefore performed using the input transformation matrix I.

[0056] Is X_ist the vector of the actual position of the adjustable body 4 in the first coordinate system K1, i.e. X_ist=(x_isty_istz_istu_istv_istw_ist), and S_ist is a vector whose vector components s1_ist to s3_ist represent the sensor positions of the respective sensor 5a-5c resulting from the sensor data, i.e. S_ist=(s1_ists2_ists3_ist), These sensor positions s1_ist to s3_ist can thus be transformed into the actual position of the adjustable body 4 in the first coordinate system K1 using the input transformation matrix I. Therefore, the following applies: X_ist=I*S_ist.

[0057] The actual position X_actual can thus be compared again with the reference variable X_target, and the control loop 20 is closed.

[0058] In the second operating mode BM2, the actual adjustment positions v1_ist to v6_ist of the adjustment units 2a to 2f are determined along the adjustment directions VR1-VR6 defining the second coordinate system K2, i.e. V_ist=(v1_istv2_istv3_istv4_istv5_istv6_ist), and the six actual adjustment positions v1_ist to v6_ are controlled independently of each other. This control is explained below using the controller diagram assigned to the second operating mode BM2. Fig. 3 explained. In the second operating mode BM2, the actual adjustment positions v1_actual to v6_actual, and thus also the setpoints v1_set to v6_set, last set in the first operating mode BM1, are maintained by controlling the individual adjustment positions or length expansions of the actuating units 2a-2f, so that the adjustable body 4 remains in the position last set in the first operating mode BM1. These setpoints V_set, set in the first operating mode BM1, therefore form the target adjustment positions v1_set to v6_set of the actuating units 2a-2f in the second operating mode BM2.

[0059] Furthermore, in the second operating mode BM2, the sensor positions s1_ist to s3_ist determined by means of sensor 5 are displayed. S_ist=(s1_ists2_ists3_ist) by means of a further, third transformation matrix T, it is transformed into the respective actual adjustment position v1_ist to v6_ist. so V_ist=(v1_istv2_istv3_istv4_istv5_istv6_ist)=T*S_ist=(s1_ists2_ists3_ist)=S_ist The transformation matrix T is calculated by matrix multiplication T = O * I of the input transformation matrix I with the output transformation matrix O.

[0060] Therefore, it is true that V_ist=O*I*S_ist

[0061] As the diagram of Fig. As can be seen from 3, the setpoints V_set of the adjustment units 2a-2f can be determined without transformation, i.e. without applying a further transformation matrix, from the control deviation A' between target adjustment position V_target and actual adjustment position V_actual, i.e. for example V_set = V_target - V_actual.

[0062] The second operating mode, BM2, can be used to de-energize the individual actuator units 2a-2f while maintaining their last set position V_actual before de-energizing. Due to the active control of the individual positions of actuator units 2a-2f in the second operating mode, BM2, the actuator units 2a-2f can be de-energized independently. To determine the current actual positions V_actual of actuator units 2a to 2f, X_actual is first set equal to X_set. X_set=X_ist.

[0063] It follows: I*S_ist=O−1*V_set.

[0064] V_set is in turn equated with V_ist, so V_set=V_ist, and thus calculated as follows: V_set=T*S_ist=O*I*S_ist.

[0065] Using the two operating modes BM1 and BM2 of the parallel kinematics 1, it is possible to de-energize the adjustment units 2a-2f while maintaining their current actual position X_actual. In other words, it is possible to prevent the current actual position X_actual of the respective adjustment units 2a-2f from changing beyond a maximum permissible, predefined tolerance during the de-energizing process. For this purpose, the individual adjustment units 2a to 2f are successively de-energized, as illustrated below in the flowchart of the Fig. 4 is explained using an example: To de-energize the first 2a of the six adjustment units 2a to 2f, two measures a) and b) are carried out successively.

[0066] According to a first measure a), the control / regulating device 10 is switched from the first operating mode BM1 to the second operating mode BM2, and the actual adjustment positions X_ist of the six adjustment units 2a-2f are initially regulated.

[0067] In a second step (b) following the first step (a), the first adjustment unit 2a is de-energized by appropriate control. For this purpose, the actuator of the first adjustment unit 2a can be disconnected from the electrical control voltage Sig1, or this electrical control voltage can be set to zero. This also sets the electrical output voltage U1 to zero. This also deactivates the control system for the first adjustment unit 2a.

[0068] After de-energizing according to measure b), a further measure c) checks whether the actual adjustment position V_ist lies outside a predefined tolerance range TB. If measure c) determines that the actual adjustment position lies outside the predefined tolerance range, the first adjustment unit 2a is classified as unsuccessfully de-energized and therefore the control for this adjustment unit 2a is reactivated.

[0069] In the event of such an unsuccessful classification, measures b) and c) will be repeated (see arrows P1, P2 in Fig. 4) This can be repeated up to N times, where N is a natural number >= 1. In the example scenario, N = 10. During this repetition(s), a subsequent action c1) can check whether actions b) and c) have already been repeated N times (= condition 1). It can also check whether a predetermined maximum time t_max has been exceeded since switching from the first operating mode BM1 to the second operating mode BM2 (= condition 2). In the example, this time can be between two and ten seconds. If at least one of the two conditions 1 or 2 is true, the procedure is terminated in a subsequent action x) (see arrow P3). Otherwise, another repetition of both actions b) and c) is performed (see arrow P2).

[0070] If, however, step c) determines that the actual adjustment position V_actual is within the specified tolerance range, the first adjustment unit 2a is classified as successfully de-energized. In this case, step c1) described above is not performed. Instead, step c2) checks (see arrow P4) whether the previously described de-energizing process, according to steps b) and c), and, if applicable, c1), has already been carried out for all existing adjustment units 2b to 2f. If this condition is met, the procedure is terminated according to step x) (see arrow P5). Otherwise, the procedure continues, and steps b) and c) are continued for another adjustment unit 2b to 2f that has not yet been de-energized (see arrow P6).

[0071] Therefore, after the first adjustment unit 2a has been successfully de-energized, the remaining adjustment units 2b to 2f are successively de-energized, each following the same procedure as measures b) and c). In other words, for each of the remaining adjustment units 2b to 2f, measures b) and c) are carried out sequentially (see the dashed outline in the figure). Fig. 4).

[0072] In measure b), the de-energizing process in the example scenario involves controlling the adjustment units 2a-2f to reduce their creep behavior. For this purpose, several successive electrical voltage pulses can be applied to each adjustment unit, causing a permanent change in length of the respective adjustment unit 2a-2f.

[0073] Preferably, the electrical voltage pulses can each have a pulse duration between 50 ms and 150 ms, more preferably between 70 ms and 120 ms. Particularly preferably, the rise and fall times at the edges of the individual voltage pulses can each be between 5 ms and 20 ms, and more preferably between 8 ms and 12 ms.

[0074] For example, electrical voltage pulses with an amplitude of at least +80 volts can be applied. Detailed experimental investigations have shown that no discernible change in length occurs in the electromechanical adjustment units 2a-2f when electrical voltage pulses with an amplitude below a positive electrical voltage of +80 volts are applied. If several successive voltage pulses are generated, a certain increase in length occurs with each individual pulse when the voltage pulse has an amplitude of at least +80 volts. This increase is greater for the initial pulses and decreases with an increasing number of pulses.

[0075] Experimental investigations have shown that a relatively large change in length occurs at the beginning of each voltage pulse, but this change then drops sharply towards the end of the pulse, followed immediately by a further, relatively slow decrease over a longer period. This expansion behavior of the respective adjustment unit 2a-2f along the adjustment direction VR1-VR6 is due to the fact that, initially, at the beginning of the voltage pulse, both a permanent and a labile reorientation of domains occur, as well as an excitation of the inverse piezoelectric effect within the electromechanical element. Only the permanent reorientation of the domains and the corresponding remanent expansion are effectively usable.

[0076] The term "stable reorientation of domains" describes the fact that an electrical voltage pulse initially causes a certain number of domains to reorient, but this reorientation is not stable, only unstable, so that a return to the previous state occurs. This process, known as "creep," requires a certain amount of time, which explains the slower decrease in size in this area. The remaining increase in size or thickness after subtracting the creep process is therefore due to the permanent alignment of a certain number of dipoles in the individual domains of the piezoceramic material of the respective actuator 2a-2f. With an increasing number of applied voltage pulses at an electrical voltage of +80 volts, the piezoceramic material of the respective actuator 2a-2f experiences increasing electrical polarization, whereby this polarization is permanent.causes residual elongation, which persists even after the electrical voltage is removed.

Claims

[1] Method for operating a parallel kinematic system (1) comprising at least two adjustment units (2a-2f) for generating adjustment movements along a respective adjustment direction (VR1-VR6), - wherein the parallel kinematics (1) comprises a base body (3) and an adjustable body (4) and wherein the adjustable body (4) is adjustable with respect to its actual position (X_actual) in a first coordinate system (K1) relative to the base body (3) by means of the adjustment units (2a-2f), - wherein the parallel kinematics (1) also includes a sensor system (5) by means of which an adjustment of the adjustable body (4) in a second coordinate system (K2) can be determined, - wherein the parallel kinematics (1) comprises a control / regulation device (10) that can be switched between a first and a second operating mode (BM1, BM2), - wherein, according to the procedure, a predetermined target position (X_target) of the adjustable body (4) in the first coordinate system (K1) is set and controlled in the first operating mode by means of the control / regulation device (10) by controlled adjustment of the adjustment units (2a-2f), - wherein, according to the procedure, in the second operating mode, a respective actual adjustment position (V_ist) of the adjustment units (2a-2f) is determined by means of the control / regulation device (10) and at least one actual adjustment position (V_ist) is regulated. [2] Method according to claim 1, characterized by , that in the second operating mode (BM2) at least two actual adjustment positions (V_ist) are controlled independently of each other. [3] Method according to claim 1 or 2, characterized by , that - in the first operating mode for controlling the position of the adjustable body (4): - a deviation of the target position (X_target) from the actual position (X_actual) is transformed into a respective setpoint (V_set) of at least two adjustment units (2a-2f) using an output transformation matrix (O), - the adjustment of the adjustable body (4) determined by means of the sensor (5) is transformed into the actual position (X_actual) of the adjustable body (4) by means of an input transformation matrix (I); - in the second operating mode (BM2) for controlling at least one adjustment position: - the adjustment of the adjustable body determined by means of the sensor (5) is transformed into an actual adjustment position (V_ist) by means of a transformation matrix (T), where the transformation matrix (T) is the result of a matrix multiplication (T = O * I) of the input transformation matrix (I) with the output transformation matrix (O), - the setpoints (V_set) of at least two adjustment units (2a-2f) are determined without transformation by forming the difference between the target adjustment position (V_target) and the actual adjustment position (V_actual). [4] Method according to any one of claims 1 to 3, characterized by , that to de-energize a first (2a) of the adjustment units (2a-2f) in order to maintain its adjustment position (V_ist) in a de-energized state, the following measures are carried out: a) Switching the control / regulating device (10) to the second operating mode (BM2), whereby all actual adjustment positions (V_ist) of the at least two adjustment units (2a-2f) are controlled, b) De-energizing the first adjustment unit (2a) by deactivating the control for this adjustment unit (2a). [5] Method according to claim 4, characterized by , that - after the energy is de-energized according to measure b), in a further measure c) it is checked whether the actual adjustment position (V_ist) is outside a specified tolerance range; - if in measure c) it is determined that the actual adjustment position is outside the specified tolerance range, the first adjustment unit (2a) is classified as unsuccessfully de-energized and therefore the control for the first adjustment unit (2a) is reactivated and measures b) and c) are repeated at least once. - if in measure c) it is determined that the actual adjustment position is within the specified tolerance range, the first adjustment unit (2a) is classified as successfully de-energized. [6] Method according to claim 5, characterized by, that after successful energy de-energization of the first adjustment unit (2a), the remaining adjustment units (2b, 2c) are successively de-energized in the same manner as measures b) and c). [7] Method according to claim 5 or 6, characterized by , that the de-energizing of a respective actuating unit (2a-2f) is aborted if this actuating unit (2a-2f) is unsuccessfully relaxed more than N times in succession according to measures b) and c) or if a predetermined time period, which is preferably between 2 seconds and 10 seconds, is exceeded. [8] Method according to claim 7, characterized by, that the de-energizing in measure b) includes controlling the adjustment unit (2a-2f) to reduce its creep behavior by applying at least one electrical voltage pulse, preferably a plurality of successive voltage pulses, which causes a remanent change in length of the adjustment unit (2a-2f). [9] Method according to claim 8, characterized by , that - an amplitude of at least one electrical voltage pulse, preferably of all electrical voltage pulses, is at least 80 volts, and / or that a pulse duration of at least one generated electrical voltage pulse, preferably of all electrically generated voltage pulses, is between 50 ms and 150 ms, preferably between 70 ms and 120 ms. [10] Parallel kinematics (1), - with at least two adjustment units (2a-2f) for generating positioning movements along a respective adjustment direction (VR1-VR6), - with a base body (3) and with an adjustable body (4), wherein the adjustable body (4) is adjustable with respect to its actual position (X_actual) in a first coordinate system (K1) relative to the base body (3) by means of the adjustment units (2a-2f), - wherein the parallel kinematics (1) also includes a sensor system (5) by means of which an adjustment of the adjustable body (4) in a second coordinate system (K2) can be determined, - wherein the parallel kinematics (1) comprises a control / regulation device (10) switchable between a first and a second operating mode (BM1, BM2), which is set up / programmed to carry out the method according to one of the preceding claims. [11] Parallel kinematics (1) according to claim 10, characterized by , that the parallel kinematics (1) is switchable between a first (BM1) and a second operating mode (BM2), - wherein in the first operating mode (BM1) a predetermined target position (X_target) of the adjustable body (4) in the first coordinate system (K1) can be set and controlled by means of the control / regulation device (10) by controlled adjustment of the adjustment units (2a-2f), - wherein in the second operating mode (BM2) a respective adjustment position (VP1-VP6) of the adjustment units (2a-2f) is determined by means of the control / regulation device (10) along the adjustment directions (VR1-VR6) defined in the second coordinate system (K2) and at least one actual adjustment position (V_ist) is controllable. [12] Parallel kinematics (1) according to claim 11, characterized by , that at least one adjustment unit (2a-2f), preferably all adjustment units (2a-2f), comprises a piezoelectric actuator that is linearly length-adjustable along the relevant adjustment direction (VR1-VR6).

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