STANDSTILL CONTROL WITH MANIPULATED VARIABLE FEEDFORWARD

Abstract

In order to specify a method for the standstill control of a drive body on which a friction force acts, by means of which a controlled reduction in undesirably stored potential energy is possible, an activation manipulated variable is specified which changes a setting manipulated variable which does not overcome the friction force to a relaxation manipulated variable, and the relaxation manipulated variable is converted by an actuator into a relaxation drive force acting on the drive body, wherein the activation manipulated variable is specified in such a way that the relaxation drive force overcomes the friction force, acting on the drive body, at least temporarily during the standstill control.

Claims

1. A method for the standstill control of a drive body on which a friction force acts, a setting manipulated variable being determined and converted, utilizing an actuator, into a drive force acting on the drive body in order to bring the drive body to a standstill and/or to keep it at a standstill, wherein a setting manipulated variable is determined for the drive body to be brought to a standstill or for the drive body that has been brought to a standstill or for the drive body that is held at a standstill, which setting manipulated variable alone results in a drive force that does not overcome said friction force, wherein an activation manipulated variable is specified and the determined setting manipulated variable is changed by the activation manipulated variable to a relaxation manipulated variable, and wherein the relaxation manipulated variable is converted, utilizing the actuator, into a relaxation drive force acting on the drive body for moving the drive body, the activation manipulated variable being specified such that the relaxation drive force at least temporarily overcomes the friction force acting on the drive body during the standstill control.

2. The method according to claim 1, wherein the setting manipulated variable is determined utilizing a controller from a deviation between at least one movement variable of the drive body and a standstill set point specified for the at least one movement variable, in order to set the at least one movement variable of the drive body to the specified standstill set point, or wherein the setting manipulated variable is determined utilizing a control system from a standstill set point specified for the at least one movement variable, without taking the at least one movement variable into account when determining the setting manipulated variable.

3. The method according to claim 2, wherein a movement of the drive body resulting from the relaxation drive force leads to a deviation of the at least one movement variable from the standstill set point specified for it, which, during the standstill control, does not exceed a specified maximum deviation of 10% of a value of the specified standstill set point or 5% of a value of the specified standstill set point or 1% of a value of the specified standstill set point or 0.5% of a value of the specified standstill set point.

4. The method according to claim 1, wherein the friction force acting on the drive body is caused by a static friction or a sliding friction or a rolling friction or a combination of the static friction, rolling friction, and sliding friction.

5. The method according to claim 1, wherein the activation manipulated variable is only determined and used to change the setting manipulated variable when the drive body has been held at a standstill for a specified minimum standstill period.

6. The method according to claim 1, wherein the activation manipulated variable is determined in the form of a periodic signal with a specified activation amplitude and/or a specified activation frequency.

7. The method according to claim 1, wherein the activation manipulated variable is used for a specified activation time period to change the setting manipulated variable.

8. The method according to claim 1, wherein a time average value of the activation manipulated variable corresponds to the value zero.

9. The method according to claim 2, wherein a position of the drive body is determined as a movement variable of the drive body, and a target position for the determined position is specified as a standstill set point, or wherein a speed of the drive body is determined as a movement variable of the drive body, and a vanishing target speed for the determined speed is specified as a standstill set point.

10. The method according to claim 2, wherein a position of the drive body is determined as a movement variable of the drive body, and a target position for the determined position is specified as a standstill set point, and wherein the activation manipulated variable is only determined and used to change the setting manipulated variable if a magnitude of a position deviation between the position of the drive body and the specified target position when the drive body is at a standstill is above a specified deviation threshold value.

11. The method according to claim 9, wherein the sign of the activation manipulated variable is selected as a sign opposite to the sign of the position deviation or as a sign corresponding to the sign of the position deviation.

12. The method according to claim 9, wherein the change in the setting manipulated variable by the activation manipulated variable is terminated as soon as the magnitude of the position deviation falls below the specified deviation threshold value.

13. The method according to claim 1, wherein the drive body is mechanically coupled to a number n of further bodies on each of which a friction acts, in particular to a coupling body on which a friction acts, and forms an oscillating multi-body system with at least n resonance frequencies with the number n of further bodies.

14. The method according to claim 13, wherein the activation manipulated variable is specified in the form of a periodic signal with a specified activation amplitude and/or a specified activation frequency, wherein the activation frequency is selected to be greater than the largest of the n resonance frequencies of the resonant multi-body system, or is selected to be greater than or equal to the smallest of the n resonance frequencies of the resonant multi-body system, or equal to one of the n resonance frequencies of the resonant multi-body system, and/or wherein a magnitude of a drive force resulting from a conversion of the relaxation manipulated variable by the actuator overcomes, at least temporarily, a sum of the friction force acting on the drive body and the friction forces acting on the number n of further bodies, which friction forces result from the respective acting frictions.

15. The method according to claim 1, wherein a position and a speed of the drive body in a first coordinate direction are determined as movement variables, and the drive force generated by the actuator acts on the drive body along the first coordinate direction, wherein a second position of the drive body in a second coordinate direction different from the first and a second speed of the drive body along the second coordinate direction are determined as further movement variables, and wherein the activation manipulated variable is only determined and used to change the setting manipulated variable if a magnitude of a second position deviation between the determined second position and a second target position specified for the second position is above a specified second position threshold value.

16. A drive system comprising a movable drive body on which a friction force acts, wherein a control unit, which, in order to control the standstill of the drive body, is configured to determine a setting manipulated variable, and an actuator are provided, the actuator being configured to convert the determined setting manipulated variable into a drive force acting on the drive body in order to bring the drive body to a standstill and/or to keep it at a standstill, wherein the control unit is further configured to determine a setting manipulated variable for the drive body to be brought to a standstill or for the drive body that has been brought to a standstill or for the drive body that is held at a standstill, which setting manipulated variable alone results in a drive force that does not overcome said friction force, wherein the control unit is further configured to specify an activation manipulated variable and to change the determined setting manipulated variable utilizing the activation manipulated variable to a relaxation manipulated variable, and wherein the actuator is further configured to convert the relaxation manipulated variable into a relaxation drive force, acting on the drive body, for moving the drive body, the activation manipulated variable being specified such that the relaxation drive force at least temporarily overcomes the friction force acting on the drive body during the standstill control.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present disclosure is described in greater detail below with reference to FIGS. 1 to 7, which show schematic and non-limiting advantageous embodiments of the disclosure by way of example. In the figures:

[0024] FIG. 1 shows a control loop for a multi-body system according to the prior art,

[0025] FIG. 2 shows a friction model known from the prior art,

[0026] FIG. 3 shows a two-body system which is degenerated to form a locked single-body system,

[0027] FIG. 4 shows a control circuit with manipulated variable feedforward according to the disclosure,

[0028] FIG. 5a, 5b, 5c show possible time courses of the activation manipulated variable according to the disclosure,

[0029] FIG. 6 shows a portion of a long stator linear motor,

[0030] FIG. 7 shows an application of the disclosure for solving a tilting of a shuttle of a linear motor.

DETAILED DESCRIPTION

[0031] FIG. 1 shows a control loop 1 for controlling a movement variable BG of a multi-body system MKS according to the prior art. In the case shown, the multi-body system MKS to be controlled is a two-body system with two bodies J.sub.A, J.sub.K, a drive body J.sub.A, and a coupling body J.sub.K mechanically coupled to the drive body J.sub.A. It should already be noted at this juncture that a multi-body system MKS, which is controlled by means of a control loop 1 as shown in FIG. 1, can also have more than two bodies J.sub.A, J.sub.K, and can be given, for example, as a three-, four-, or five-body system, but also only one bodyspecifically, only one drive body J.sub.A. The problem of unintentionally stored potential energy solved by the present disclosurecan occur in all of these cases.

[0032] It should also be noted that the closed control loop 1 shown in FIG. 1 is to be regarded as purely exemplary and in particular serves to provide a clear and comprehensible representation of the disclosure. The standstill control presented below could also be implemented without closed feedback. The term standstill control therefore includes, in the context of this application, both a regulation system in the classical sense with feedback and a control without feedback. For the implementation of the disclosure explained below, there are no restrictions arising from the use of a control system or from the use of a classic regulation system.

[0033] A multi-body system MKS as shown in FIG. 1 can be a rotary or a translatory multi-body system MKS, i.e., a multi-body system MKS, whose bodies J.sub.A, J.sub.R perform translational movements, rotational movements, or superimpositions of translational and rotational movements. It is also possible that one body of the multi-body system MKS moves rotationally and another body moves translationally. In the following discussion, we will therefore use the generic terms body, speed, force, wave force, etc. With regard to rotary multi-body systems (MKS), this should also include the analogous terms inertia, rotational speed or angular speed, torque, shaft torque, etc. Concrete examples of multi-body systems (MKS) include drive axes of machine tools, drive trains, test benches with a loading machine and a test object connected to the loading machine via a mechanical shaft (e.g., an internal combustion engine to be tested), printing rollers, or other multi-body systems (MKS).

[0034] In the case shown in FIG. 1, the mechanical coupling of the drive body J.sub.A and the coupling body J.sub.K is achieved via a spring element c and a damper element d (corresponding to the usual designation of stiffness with c or damping with d). The spring element c and the damper element d thereby form an elastic, mechanical shaft. In a known manner, relative movements between the drive body J.sub.A and the coupling body J.sub.K result in shaft forces F.sub.W transmitted via the spring element c and the damper element d, i.e., shaft forces F.sub.W transmitted via the mechanical shaft formed by the spring element c and the damper element d, which influence the movements of the bodies J.sub.A, J.sub.K in a known manner.

[0035] For the following explanations, it is assumed that a non-negligible friction .sub.1, .sub.2 acts on both the drive body J.sub.A and the coupling body J.sub.K, which in a known manner cause non-negligible friction forces F.sub.r1, F.sub.r2 (possible and sufficiently known friction mechanisms are discussed below with reference to FIG. 2). However, this restriction does not represent a necessary requirement in the context of this disclosure, since in particular drive systems with only one drive body J.sub.A alone can be suitable applications for the disclosure (see in this regard FIG. 6 and FIG. 7), where no second coupling body J.sub.K exists, or the coupling body J.sub.K could be completely or almost friction-free. However, the relationships relevant to the disclosure are particularly clear and easy to see on the basis of the friction dual-mass oscillator under consideration.

[0036] Friction can occur for different reasons, so that the frictions .sub.1, .sub.2 considered here can be static friction or sliding friction or rolling friction or a combination of these frictions. For a variety of reasons, the friction .sub.2 acting on the coupling body J.sub.K can be much stronger than the friction .sub.1 acting on the drive body J.sub.A. To illustrate the frictions mentioned, a friction model known from the prior art is shown in FIG. 2, in which Coulomb friction .sub.C and viscous (speed-dependent) friction .sub.v act in combination. The frictions .sub.1 and .sub.2 shown in FIG. 1 can therefore correspond to a Coulomb friction .sub.C, a viscous (speed-dependent) friction .sub.v, or a combination of these frictions.

[0037] The frictions .sub.1 and .sub.2 cause friction forces F.sub.r1, F.sub.r2 acting on the bodies in a known manner, e.g., in the case of speed-proportional friction, according to a product of friction and speed (.Math.v), in the case of Coulomb friction .sub.C, according to a product of friction and the sign of the speed (.Math.sign(v)), in the case of static friction, according to a friction force compensating for a drive force, etc. These relationships are well known to a specialist in the field of drive technology (cf., e.g., The Mechatronics Handbook, R. H. Bishop, CRC Press, 2002), so details will not be discussed here.

[0038] With regard to the drive body J.sub.A and the coupling body J.sub.K mechanically coupled to it, it is assumed in the present connection that only the drive body J.sub.A is subjected to a drive force F.sub.A which can be specified by a controller R. This is also in no way mandatory in the context of this disclosure, so that a force specified by a controller R could also act on the coupling body J.sub.K. However, the restriction of drive forces F.sub.A acting only on the drive body J.sub.A facilitates the explanation of the inventive principle in question, since, with a drive force F.sub.A acting only on the drive body J.sub.A, the movement of the coupling body J.sub.K is influenced only by the shaft force F.sub.W transmitted via the mechanical shaft and by the friction .sub.2 acting on the coupling body J.sub.K.

[0039] In the block diagram shown in FIG. 1, in particular a position x of the drive body J.sub.A can be determined as a movement variable BG, or a speed v of the drive body J.sub.A or an acceleration a or a force, etc. Various possibilities for determining positions and/or speeds and/or accelerations and/or forces are known in the prior art, which are sufficiently known to a person skilled in the field of drive technology, e.g., the use of sensors, such as rotary encoders or translatory encoders. In the course of the following explanations, it is assumed, without loss of generality, that a position x of the drive body J.sub.A is determined and controlled as a movement variable BG.

[0040] Specifically, in the context of this disclosure, a position x can be measured directly as a movement variable BG, e.g., by a position sensor, which immediately generates a position measurement signal and consequently no longer requires any further processing of a signal generated by a sensor to determine a speed measurement signal. However, a position x can also be determined from another measurement signal, e.g., by integrating a speed signal, or it can be calculated from other signals using the observer technique well known from control engineering, e.g., from measured electrical currents or voltages or from magnetic fluxes, etc. For the present disclosure, it is irrelevant how a processed movement variable BG of a drive body J.sub.A is specifically determined.

[0041] The position x determined as movement variable BG is fed to the controller R in the case shown in FIG. 1. The controller R uses the movement variable BG and a standstill set point B.sub.soll specified as the target position x.sub.soll to determine an adjustment manipulated variable u.sub.S for adjusting the position x to the target position x.sub.soll. A deviation e between the target position x.sub.soll and position x is usually determined within the controller R, and the setting manipulated variable u.sub.S is determined from the determined deviation e, the control error e, using a predefined control law. Such a control law can involve a variety of approaches known from control engineering, such as approaches from the areas of sliding mode control, backstepping control, model predictive control, or flatness-based control. In practice, cascaded control loops are often used in this connection, in which a higher-level position controller specifies a target speed v.sub.soll for a lower-level speed controller R.sub.v as a manipulated variable, which the lower-level speed controller R.sub.v subsequently regulates by means of a comparison with a speed v of the drive body J.sub.A. In such a case, two or more movement variables BG can be used in the control.

[0042] As is known, in a control loop 1 as shown in FIG. 1, the setting manipulated variable u.sub.S determined by the controller R does not act directly on the multi-body system MKS, specifically on the drive body J.sub.A and ultimately on the movement variable BG to be controlled, but the setting manipulated variable u.sub.S (information signal) is still converted by an actuator A into a corresponding power variable F.sub.A, i.e., into a real (drive) force, a real torque, a real current, such as a drive current i.sub.A to generate a drive force, etc.

[0043] For practical implementation, a controller, such as a controller R in particular, for controlling a movement variable can be realized on suitable microprocessor-based hardware, which, in some embodiments, forms a control unit, such as, for example, on a microcontroller, or in an integrated circuit (ASIC, FPGA). The prior art also offers a variety of options for an actuator A for converting a setting manipulated variable u.sub.S (information signal) into a drive force F.sub.A (power signal), such as servo motors or electric motors in general (asynchronous motor, synchronous motor, stepper motor), linear motors, hydraulic actuators, etc. As is usual with multi-body systems MKS driven by servo motors, a body of the multi-body system MKS can be a component of the servo motorfor example, its rotor. The aforementioned microprocessor-based hardware for implementing controllers, etc., can also be part of the servo motor and be wired to the aforementioned sensors, encoders, or rotary encoders. These relationships are well known to the person skilled in the art of control and/or drive technology, which is why these specifications are not discussed in more detail at this point.

[0044] In order to explain the problems solved by the present disclosure in more detail, FIG. 3 first shows a topological change of the multi-body system MKS shown in FIG. 1, which occurs in the context of the exemplary position control considered in the present case, especially at low speeds of the bodies J.sub.A, J.sub.K. Low to zero speeds can occur during operation of a multi-body system MKS for a variety of reasons, e.g., due to a corresponding specification by an operator or due to a specified target profile (target speed=0) or towards the end of a positioning process in which a position x of the drive body J.sub.A is already close to a target position x.sub.soll specified for the position x, and the target position x.sub.soll is slowly approached with the aim of coming to a stop in the target position x.sub.soll. Small deviations between position x and a target position x.sub.soll, especially in combination with speeds that are also low in terms of magnitude, typically lead to small setting manipulated variables F.sub.s required by the controller R, which results in low drive forces F.sub.A, which in turn results in low shaft forces F.sub.W transmitted via the shaft.

[0045] If the coupling body J.sub.K of the multi-body system MKS is subjected to a friction .sub.2 that cannot be overcome by the wave force F.sub.W, the coupling body J.sub.K is braked, despite a drive force F.sub.A that is other than zero and despite a wave force F.sub.W that is other than zero, comes to a standstill, and possibly also remains at a standstill. From the perspective of the controller R, which specifies a drive force F.sub.A and only perceives a coupling body J.sub.K that follows this drive force F.sub.A less and less, the coupling body J.sub.K behaves like a body with very high or infinitely high inertia or with very high or infinitely high mass. In this case, the multi-body system MKS can be represented in a first approximation as a constrained single-body system, as shown in FIG. 3.

[0046] If the coupling body J.sub.K is subsequently already fixed, while the drive body J.sub.A is still moving, e.g., because it has not yet reached the target position x.sub.soll intended for it, the mechanical shaft connection between the drive body J.sub.A and the coupling body J.sub.K twists. According to Hooke's law, the potential energy E.sub.pot=c.Math.(xx.sub.R).sup.2/2 is stored in the mechanical coupling, or the potential energy E.sub.pot=c.Math.(x.sub.sollx.sub.R).sup.2/2, when the position x has finally reached the specified target position x.sub.soll. In addition to the stored potential energy E.sub.pot, a shaft connection tensioned in this way also involves a shaft restoring force F.sub.W=c.Math.(x.sub.sollx.sub.R) which must be compensated for when the system is at a standstill, since the drive body J.sub.A to be positioned would otherwise move away from the target position x.sub.soll. Corresponding compensation setting manipulated variables, which lead to compensation forces F.sub.S=c.Math.(x.sub.sollx.sub.R) for compensation of a remaining restoring force, are contrary to the intention of energyefficient systems.

[0047] The value of a permanent setting manipulated variable F.sub.S=c.Math.(x.sub.sollx.sub.R) can depend on stationary and dynamic factors, as well as on previous system states, and is therefore usually difficult to model or estimate. In practice, precise modeling often presents the problem that such models are mathematically complex and time-consuming, and therefore real-time use is often not possible. In addition to the problem of oscillations and vibrations described at the beginning, which can result from the dissipation of potential energy E.sub.pot as just described, the restoring forces mentioned are another reason to avoid unnecessarily stored potential energy, which is stored during the shutdown, i.e., the standstill control, of a drive body J.sub.A.

[0048] According to the disclosure, an activation manipulated variable u.sub.akt is provided for this purpose to change the controller manipulated variable u.sub.S, which is explained in more detail below with reference to FIG. 4. The statements made previously with regard to FIG. 1, e.g., with regard to the multi-body system MKS or controller R or control unit for implementing the controller R, remain unchanged for the block diagram shown in FIG. 4. With regard to the block diagram shown in FIG. 4, it also applies that, in addition to a position x, a speed v or an acceleration a can be captured as the movement variable BG to be controlled.

[0049] In order to realize a tension-free standstill control, the control circuit shown in FIG. 4 is initially provided for determining a setting manipulated variable u.sub.S from a deviation e between at least one movement variable BG of the drive body J.sub.A and a standstill set point B.sub.soll specified for the at least one movement variable BG, wherein the determined setting manipulated variable u.sub.S is converted by means of an actuator A into a drive force F.sub.A, acting on the drive body J.sub.A, in order to set the at least one movement variable BG to the standstill set point B.sub.soll, so that the drive body J.sub.A is brought to a standstill and/or held at a standstill if the drive body J.sub.A was already at a standstill. During standstill control, constant target positions, i.e., those that remain constant over time, are, in some embodiments, specified as standstill set points B.sub.soll, which, in the case of position control, can, however, have values other than zero. In the case of speed control, standstill set points B.sub.soll are typically provided, which correspond to a vanishing target speed, i.e., a target speed with the value zero.

[0050] Since the drive body J.sub.A is brought to a standstill and/or held at a standstill, it usually follows that a setting manipulated variable u.sub.S determined from the specified standstill set point B.sub.soll by the controller R alone only leads to a drive force F.sub.A which no longer overcomes the friction force F.sub.r1 acting on the drive body J.sub.A, i.e., in a known manner no longer overcomes the friction forces resulting from the friction .sub.1 in terms of magnitude. Based on this, in the context of the disclosure, the already mentioned activation manipulated variable u.sub.akt is now specified, and the determined setting manipulated variable u.sub.S is changed by the activation manipulated variable u.sub.akt to a relaxation manipulated variable u.sub.ent. The relaxation manipulated variable u.sub.ent is subsequently converted by the actuator A into a relaxation drive force F.sub.ent, acting on the drive body J.sub.A, to move the stationary drive body J.sub.A, wherein the activation manipulated variable u.sub.akt is specified in such a way that the relaxation drive force F.sub.A at least temporarily overcomes the friction force Fr, acting on the drive body J.sub.A, during the standstill control.

[0051] In the context of this disclosure, changing the setting manipulated variable u.sub.S by the activation manipulated variable u.sub.akt means generating a new manipulated variable, specifically the relaxation manipulated variable u.sub.ent, from the setting manipulated variable u.sub.S and the activation manipulated variable u.sub.akt. For this purpose, the activation manipulated variable u.sub.akt can be added to the setting manipulated variable u.sub.S, as shown in FIG. 4, or the activation manipulated variable u.sub.akt can be multiplied by the setting manipulated variable u.sub.S, or the activation manipulated variable u.sub.akt and the setting manipulated variable u.sub.S can be linked to one another by means of a specified mathematical relationship, e.g., by both manipulated variables acting as inputs into a dynamic, multi-variable system and being mapped to a common output, which then corresponds to the relaxation manipulated variable u.sub.ent. In this context, a suitably trained specialist can make a suitable selection to determine the relaxation manipulated variable u.sub.ent. Changing the setting manipulated variable u.sub.S by the activation manipulated variable u.sub.akt naturally also includes the case that the setting manipulated variable u.sub.S disappears, i.e., assumes the value zero, and the relaxation manipulated variable u.sub.ent is then formed entirely by the activation manipulated variable u.sub.akt (the relaxation manipulated variable u.sub.ent then usually corresponds to the activation manipulated variable u.sub.akt). Such scenarios usually occur in the case of a summation of activation manipulated variable u.sub.akt and setting manipulated variable u.sub.S.

[0052] The afore-mentioned steps according to the disclosure take place in the embodiment shown in FIG. 4 in the block V representing a pilot control unit, whereby the determination of the activation manipulated variable u.sub.akt can also take place in the controller R. Like the controller R, the block V can of course also be implemented on a suitable control unit. In the case shown in FIG. 4, three further signals are made available to block V, a movement variable BG of the drive body J.sub.A, a standstill set point B.sub.soll specified for this movement variable BG of the drive body J.sub.A, and the derivative BD of the movement variable BG determined by differentiation, which can correspond, for example, to a speed. Depending on the application, it may be advantageous to also form further derivatives of the movement variable BG, such as a second derivative, if, for example, an acceleration is to be taken into account, or a third derivative, if, for example, a jerk is to be taken into account.

[0053] It should be noted that it is by no means mandatory to supply all of these quantities to block V. What is crucial is that, in block V, it can be detected whether the drive body J.sub.A is at a standstill or not, or at least is close to reaching a standstill. This can be done, for example, by monitoring whether a speed v.sub.x corresponds to the value zero for a specified duration or is already very low, or by monitoring whether a position corresponds to a target value x.sub.soll for a specified duration, depending on which variables are selected as movement variables.

[0054] By including an activation manipulated variable u.sub.akt, which in conjunction with the setting manipulated variable F.sub.S results in a relaxation drive force F.sub.ent being generated that overcomes the sum of all acting friction forces, it is ensured that there is at least a brief, repeated movement of the bodies J.sub.A, J.sub.K of the multi-body system. This relieves any tension that may exist in the mechanical coupling between the bodies J.sub.A, J.sub.K.

[0055] In some embodiments, suitable control measures are taken to ensure that a movement of the drive body J.sub.A resulting from the relaxation drive force F.sub.ent leads only to a repeated deviation e between the controlled movement variable BG and the standstill set point B.sub.soll specified for it, which, during the standstill control, does not exceed a specified maximum deviation e.sub.max of 10% of a value of the standstill set point B.sub.soll specified during the standstill control, or 5% of a value of the standstill set point B.sub.soll specified during the standstill control, or 1% of a value of the standstill set point B.sub.soll specified during the standstill control, or 0.5% of a value of the standstill set point B.sub.soll specified during the standstill control. A person with average training in control engineering knows which steps can be taken for this purpose, such as a manipulated variable limitation that means that the relaxation manipulated variable F.sub.ent can only slightly overcome the acting friction forces, e.g., that the relaxation manipulated variable F.sub.ent is only 1% or 5% or 10% greater than the acting friction forces.

[0056] In order to avoid having to switch on an activation manipulated variable u.sub.akt every time the drive body J.sub.A is at a standstill, the change of the setting manipulated variable u.sub.S by an activation manipulated variable u.sub.akt can be linked to further conditions. Specifically, in the context of the disclosure and of course in the context of the block diagram shown in FIG. 4, it can be provided that the activation manipulated variable u.sub.akt only be determined and used to change the setting manipulated variable u.sub.S if the drive body J.sub.A has remained at a standstill for a specified minimum standstill period t.sub.0,min. The minimum downtime t.sub.0,min can be adapted to specific application cases and can, for example, be 0.01 seconds or 0.1 seconds or 1 second or 10 seconds, or it can also correspond to a longer or shorter period of time.

[0057] Possibilities for the concrete design of the activation manipulated variable u.sub.akt according to the disclosure are shown in FIGS. 5a-5c. What the curves shown have in common is that the activation manipulated variable u.sub.akt is other than zero only for a given activation time period t.sub.akt. The activation time duration t.sub.akt can also be selected differently, depending on the application, in order to ensure that the activation manipulated variable u.sub.akt is not applied for an unnecessarily long time, but also not too short, in order to achieve the desired goal of reducing potential energy. A person skilled in the art is aware of the time limitations required for this, which vary from application to application.

[0058] In the curve shown in FIG. 5a, the activation manipulated variable u.sub.akt is selected in the form of a periodic signal with a specified activation amplitude A.sub.F and a specified activation frequency f.sub.F, whereby in particular the time average value during the activation period t.sub.akt corresponds to the value zero, which is often of great advantage in practice, since such curves alone do not usually result in permanent deflections of the moving bodies. In FIG. 5b, the activation manipulated variable u.sub.akt is realized as a random signal and, in FIG. 5c, as a signal with increasing amplitude A.sub.F, which increases until the bodies of the multi-body system MKS execute a movement, and the stored potential energy E.sub.pot is reduced.

[0059] In a particularly advantageous embodiment, an activation amplitude A.sub.F and/or an activation frequency f.sub.F and/or an activation time duration t.sub.add of the activation manipulated variable u.sub.akt, but also other characterizing parameters of an activation manipulated variable u.sub.akt, such as, for example, a ramp gradient in the time course of the activation manipulated variable u.sub.akt, can be changed by means of an adaptation method during the movement of the drive body J.sub.A, wherein different algorithms from the field of adaptive systems can be used, such as least squares methods or maximum likelihood methods or other suitable algorithms. In the same way, a course of an activation manipulated variable u.sub.akt can also be fixed a priori, e.g., by using prior knowledge about occurring friction forces , etc., and the same time course of an activation manipulated variable u.sub.akt can always be used. It is also conceivable to make a selection from a finite number of predefined time courses of an activation manipulated variable u.sub.akt during the standstill control, which can be randomly based or can also depend on the state of the actuator A and/or the drive body J.sub.A. There are various options for specifying or determining the activation manipulated variable u.sub.akt, which a specialist knows how to use appropriately.

[0060] With regard to the choice of the activation frequency f.sub.F, it should be noted that, in the present embodiment, the drive body J.sub.A and the coupling body J.sub.K coupled to the drive body J.sub.A form an oscillating system, which in any case has at least one resonance frequency. In a particularly advantageous manner, care can be taken here to ensure that no resonance frequencies of a given multi-body system MKS are excited, which can be ensured, for example, by choosing the activation frequency f.sub.F to be larger, an in some embodiments, significantly larger, e.g., twice or five times or ten times larger, than the resonance frequency of the oscillating multi-body system MKS. As mentioned earlier, in certain applications, it can also be useful and advantageous to tune the activation frequency f.sub.F exactly to a resonance frequency of the multi-body system MKS and thus to activate it at a resonance point, whereby a given activation amplitude A.sub.F of the activation manipulated variable u.sub.akt achieves the greatest possible effect. A conscious choice between resonance frequencies can also be advantageous, especially in so-called stiff systems whose resonance frequencies are far apart, and where, in this way, the most uniform possible excitation of all bodies of the multi-body system MKS is possible.

[0061] In an advantageous manner, the activation frequency f.sub.F and the activation amplitude A.sub.F of the activation manipulated variable u.sub.akt are chosen such that the multi-body system MKS is not able to completely follow the dynamics of the activation manipulated variable u.sub.akt. The movements generated by the activation manipulated variable u.sub.akt serve exclusively to compensate for tensions in the drive train which are caused by the described frictions .sub.1, .sub.2, such as in particular static friction, usually at the end of a positioning process when stopping. After a short relaxation phase, the additional activation manipulated variable u.sub.akt can be removed again when the system then comes to a standstill.

[0062] In a further advantageous aspect, further quantities shown in FIG. 1 and FIG. 4 can be incorporated to implement the disclosure, as explained below. Specifically, it can be provided that the activation manipulated variable u.sub.akt is only determined and used to change the setting manipulated variable u.sub.S if a magnitude of the deviation e between the movement variable BG and the standstill set point B.sub.soll is above a specified deviation threshold value e.sub.min, or it can be provided that the sign of the activation manipulated variable u.sub.akt be selected as a sign opposite to the sign of the deviation e between the movement variable BG and the standstill set point B.sub.soll or as a sign corresponding to the sign of the deviation e.

[0063] In a particularly advantageous manner, the change of the setting manipulated variable u.sub.S by the activation manipulated variable u.sub.akt can be terminated as soon as the magnitude of deviation e between the movement variable BG and the standstill set point B.sub.soll falls below the specified deviation threshold value e.sub.min again. Since the disclosure reduces any existing tension and thus allows unnecessary restoring forces to be compensated for, energy can be saved in this way, especially in applications with long downtime phases.

[0064] An important practical application of the present disclosure, which is in particular an application of the disclosure with only a single drive body J.sub.A alone, which is not coupled to any other bodies, is shown below with reference to FIG. 6 and FIG. 7. Here, FIG. 6 shows an example of a transport device 1 in the form of a long stator linear motor (LLM) 10 for moving transport units T.sub.1, . . . , T.sub.k. The LLM 10 consists of a plurality of separate stator segments S.sub.1, . . . , S.sub.p, of which only the segment S.sub.1 with the transport unit T.sub.1 is shown in FIG. 6. Following on from the above statements, the mechanical body of a transport unit T.sub.1 corresponds to a drive body J.sub.A according to the disclosure. In an LLM 10, several stator segments S.sub.1, . . . , S.sub.p are usually assembled to form a stationary long stator 2. The stator segments S.sub.1, . . . , S.sub.p can for this purpose be arranged on a stationary support structure SK. Furthermore, the stator segments S.sub.1, . . . , S.sub.p can be designed in different geometric shapes, e.g., as straight segments or curved segments, in order to realize different transport paths.

[0065] Electrical drive coils L.sub.m1, . . . , L.sub.mn are arranged along the long stator 2 in a known manner for each stator segment Sm in the longitudinal direction (shown in FIG. 6 only for the stator segment S.sub.1, n is an integer greater than one), which interact with drive magnets Y.sub.1, . . . , Y.sub.L of the transport units T.sub.1, . . . , T.sub.k. In an equally well-known manner, based on coil control units 101, 102, a drive force F.sub.A for each of the transport units T.sub.1, . . . , T.sub.k is generated by controlling/setting coil voltages U.sub.L1, . . . , U.sub.Ln dropping across the drive coils L.sub.m1, . . . , L.sub.mn, in order to move the transport units T.sub.1, . . . , T.sub.k and the drive bodies J.sub.A1, . . . , J.sub.Ak linked to them along the long stator 2. As a rule, a plurality of drive coils L.sub.m1, . . . , L.sub.mn act simultaneously on a transport unit T.sub.1, . . . , T.sub.k, which together generate the drive force F.sub.A. For reasons of clarity, only two coil control units 101, 102 are shown in FIG. 1. Of course, each coil voltage U.sub.L1, . . . , U.sub.Ln of each drive coil L.sub.m1, . . . , L.sub.mn in each stator segment S.sub.m is controlled by a coil control unit 101, 102, wherein a plurality of coil control units 101, 102 can also be combined into one control unit. Possible implementations of a coil control unit 101, 102 include microprocessor-based hardware, such as microcontrollers and integrated circuits (ASIC, FPGA). Following on from the above statements, the system of drive magnets Y.sub.1, . . . , Y.sub.L and drive coils L.sub.m1, . . . , L.sub.mn arranged on the long stator 2 forms an actuator A which converts a manipulated variable F.sub.S required by a controller R, for example, by a position controller R, for the controlled movement of a transport unit T.sub.1 into a drive force F.sub.A moving the transport unit T.sub.1.

[0066] In the embodiment of an LLM 1 shown in FIG. 6, each of the transport units T.sub.1, . . . , T.sub.k can be moved individually (speed, acceleration, path, direction) and independently (except for the avoidance of possible collisions) of the other transport units T.sub.1, . . . , T.sub.k by means of a transport controller 100 that is superordinate to the coil control units 101, 102. For this purpose, the transport controller 100 can continuously predefine a position specification (equivalently also a speed specification) for each transport unit T.sub.1, . . . , T.sub.k to be moved, which is converted by the coil control units 101, 102 into coil voltages U.sub.L11, . . . , U.sub.Lpn required for the movement of the transport unit T.sub.1, . . . , T.sub.k. The coil control units 101, 102 receive set points SG.sub.1, . . . , SG.sub.n for the control from the transport control 100, which can in particular be corresponding target positions x.sub.soll or corresponding target speeds v.sub.soll. Since this basic principle of an LLM is sufficiently well known, it will not be discussed in detail here. In the transport control 100, in particular the blocks position controller R.sub.x and pilot control unit V discussed with reference to FIG. 1 and FIG. 4 can be implemented.

[0067] How the present disclosure can be advantageously used in an LLM 10 as shown in FIG. 6 is described below with reference to FIG. 7. Specifically, FIG. 7 shows four sequential scenarios a), b), c), and d). In the case of scenario a), the transport unit T.sub.1 and thus the drive body J.sub.A moves in the coordinate direction xR with a decreasing speed v towards a specified target position x.sub.soll (to the left). As can be seen from scenarios a) and b), the upper side OS of the long stator 2 is subject to a large friction .sub.1, which holds back the drive body J.sub.A. In the case of LLM 10, so-called V-rollers or V-groove guide rollers are often attached to the upper sides, which often lead to increased friction. Typically, in transport units T.sub.1 of LLM's, a position sensor is attached at a selected and arbitrary point, e.g., in the geometric center of the transport unit T.sub.1for example, a magnetoresistive AMR sensor well known from the prior art. If a position x given in the middle of the transport unit T.sub.1 is now recorded as a movement variable BG and converted into a standstill set point B.sub.soll specified as a target position x.sub.soll, but a part, facing the upper side OS, of the transport unit T.sub.1 is held back due to friction forces, the transport unit T.sub.1 tilts, as shown in scenario b). Although the position x in the coordinate direction xR corresponds to the desired target position x.sub.soll, due to the aforementioned tilting, the transport unit T.sub.1 or the mechanical part of the transport unit T.sub.1, i.e., the drive body J.sub.A, is twisted, which leads to undesired stored potential energy and the associated disadvantages.

[0068] According to the disclosure, however, in scenario c), after the transport unit T.sub.1 has come to a standstill, an activation manipulated variable u.sub.akt is switched on, whereby the transport unit T.sub.1is set into vibration, the said potential energy is removed from the system by averaging effects, and the tilting in question is resolved. The result of this procedure is scenario d), in which the transport unit T.sub.1 is in the specified target position X.sub.soll in the x-direction xR, but the tilting described is eliminated.

[0069] Since a tilting as described in scenarios a), b), c), and d) of FIG. 7 does not manifest itself in the direction of movement xR, but, rather, in a direction of movement yR that differs from the direction of movement xR, e.g., when a point on the upper side OS on the transport unit T.sub.1 lies above or below a target value y.sub.soll specified for this point in the coordinate direction yR, the following procedure can be used to handle such cases in the context of this disclosure.

[0070] Specifically, it may initially be intended to determine a second position y of the drive body J.sub.A in a second coordinate direction yR, which is different from the first coordinate direction, and a second speed v.sub.y of the drive body J.sub.A along the second coordinate direction yR. Based on this, it can be provided that the activation manipulated variable u.sub.akt only be determined and used to change the setting manipulated variable u.sub.S if a magnitude of a second position deviation e.sub.y between the determined second position y and a second target position y.sub.soll specified for the second position y is above a specified second position threshold value y.sub.min, so that, in the present case of the LLM 10 shown in FIG. 6 and FIG. 7, intervention is only carried out if a tilting as discussed above is present.