Abstract:
The invention relates to methods and arrangements for actuating electromechanical transducers, in particular electric motors (3) having a voltage or a current, the optimum curve shape of which is previously determined from the data of a model transducer and which data are stored in a function memory (30). In this way, a prescribed power or torque characteristic, for example without fluctuations, can be achieved.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for actuating electromechanical transducers for the purpose of generating a prescribed power characteristic or torque characteristic, in particular for reducing angle-dependent torque fluctuations in electric motors, in which time-dependent or position-dependent (travel-dependent or angle of rotation-dependent) data sets are stored in a function memory, which data sets are called up as a function of the travel or angle of rotation covered in operation or with timing control and are logically connected in an arithmetic switching unit to an input variable to form momentary values, and in which, as a function of the momentary values, voltages or currents with corresponding time-dependent or position-dependent curve shape are impressed into the electrical terminals of the transducer. In addition, an arrangement for carrying out such a process is a subject of the present invention. 
     An important property, for example of an electric motor, is its concentricity quality (or the uniform power characteristic of an electromechanical transducer). It influences both the accuracy and the stability of a drive system. In order to be able to suppress the disturbing torque pulsations in motors, it is first necessary to localize the cause. Four factors are essentially responsible for the torque fluctuations: 
     Already with a currentless armature, permanent-magnet torque fluctuations arise, triggered by the interaction of the permanently magnetic materials and the winding grooves or other ferromagnetic components, in motors with permanent-magnet excitation or in motors with iron parts having high residual induction. A rotation of the rotor leads to fluctuations of the overall energy of the magnetic circuit and thus to angle-dependent torques with alternating stable and unstable extreme values. 
     In contrast with this, the electromagnetic torque fluctuations arise from the interaction of the armature electric loading and the magnetic field. The electromagnetic fluctuations are a result of the special distribution of magnetic fields in the air gap, the winding arrangement and the armature electric loading curve shape as a function of the angle of the rotor. 
     An angle-dependent change in the motor inductance, as occurs for example with a non-uniform air gap, with partial iron saturation, with a non-uniform material distribution, with respect to the magnetic permeance, and other effects, leads in conjunction with the armature currents to reluctance torque fluctuations. 
     Torque pulsations in the motor can also have mechanical causes. The mechanical torque fluctuations, as they will be referred to below for the sake of simplicity, are triggered for example by unsymmetrical stresses of the motor shaft such as axle shifts at couplings, eccentric bearing seats etc. They can also result from the load coupled to the motor (or generally transducer). 
     As a rule, all four types of torque fluctuation referred to occur together in the electric motor but usually with a different order of magnitude of the individual components. There are cases in which individual components are negligible with respect to the others. 
     Efforts have already been made to improve the concentricity quality of electric motors by constructional measures. 
     The portion of the permanent-magnet torque fluctuations can be eliminated for example by using a non-iron-containing winding with an annular magnetic yoke (for example: bell-type armature motors). A considerable reduction is already achieved by placing the iron laminated core at an angle, for example by one slot pitch, and by a suitable design of the shape of the magnet and of the slot, tooth or poleshoe geometry. Drive motors which are designed for steady-state motor speeds are frequently equipped with an additional flyweight (for example, record players). 
     The electromagnetic pole sensitivity (pole cogging) can be favorably influenced for example by means of a selection of the winding design matched to the air gap field and the current curve and thus also by inclining the slot pitch. 
     The reluctance torque fluctuations can be considerably reduced, inter alia, by using rotationally symmetrically arranged low-retentivity and high-retentivity materials. 
     However, these known constructional measures for improving the concentricity quality or corresponding measures for achieving a uniform power characteristic of a general, electromechanical transducer (for example linear motor, loudspeaker or the like) come up against limits without achieving complete uniformity. Moreover, such constructional measures frequently make the design more expensive and involve additional tolerance problems or a worsening of the data of such electric motors or transducers. 
     A different possible way of improving the synchronism is the electrical compensation of the torque pulsations. In the simplest case, an automatic control device ensures improved synchronism, running up or positioning. Further, the demands made on the controller with respect to adaptive control parameters, rapidity and stability cannot always be satisfactorily fulfilled with this method. Therefore, it is suitable to relieve the controller of the oscillatory moments and to generate the current harmonics required for constant torque in accordance with a characteristic line which has been previously determined from the motor data. 
     A method frequently used with brushless DC motors is to vary the ratio of the switch-on and switch-off range of the square-wave actuation. By means of a corresponding selection of the switch-on range of the different phases, an improved synchronism characteristic is achieved. 
     A universal and even better matched actuation is obtained by superimposing defined current harmonics. The required summing current curves can deviate considerably from a sinusoidal or square-wave shape. In this way, without external intervention in the motor, the synchronism quality can be considerably improved in a purely electronic manner. The motor developer is now presented with the possibility of optimizing the drive according to other viewpoints (for example, a more favorable production method). However, the greater outlay, in terms of control and power electronics, required for this should not be overlooked. The most recent progress in microelectronics and power transistors makes it considerably easier today to realize such high-quality servodrive systems. 
     Previous work on the aforementioned subject area is restricted merely to the electronic compensation of the electromagnetic torque fluctuations. This is usually only sufficient for an electric drive if the generated useful torque is very much greater than the other angle-dependent interfering pulses. Generally, this requirement is not fulfilled. Instead, a drive is required here which supplies in an angle-independent manner a constant moment over the entire torque range, i.e. a simultaneous reduction of permanent-magnet torque fluctuations, electromagnetic torque fluctuations, reluctance torque fluctuations and mechanical torque fluctuations or a selection of the latter if one or more components are negligible. 
     In addition, it is already known from EP-A-180 083 to generate a defined angle-dependent torque by means of corresponding actuation with currents of a particular curve shape. However, with this known measure only reluctance torque fluctuations are reduced, and to be precise also not very extensively since the actuation curves used are symmetrically trapezoidal or sinusoidal with a flattened maximum range. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the object of proposing a method and an arrangement for actuating electromechanical transducers for the purpose of generating a prescribed power or torque characteristic in which all the components, at least the most important and most strongly manifest ones affecting the power or torque characteristic and possibly other interfering variables in other directions also are taken into account in order to achieve in particular a good concentricity quality in electric motors, for which purpose it is not necessary to carry out any constructional measures on the motor. 
     This object is achieved with a method of the type mentioned at the beginning by a plurality of different data sets, determined from the power or torque characteristic of the transducer and possibly from a connected load and taking into account different influences, being stored in the function memory in particular in the form of tables, regulations, equations or functions, by these data sets being called up out of the function memory in a position-dependent manner (for example in the case of a self-controlled synchronous motor) or time-dependent manner (for example in the case of a step motor) and being logically connected in sets, divided up according to the influences, to in each case at least one input variable, and by these logical connection results obtained in this way being combined to form the position-dependent and time-dependent momentary values. 
     The method according to the invention and a corresponding arrangement have the advantage that a more simple design of the transducer with lower tolerance requirements is obtained and that in the event of the position-dependent power and torque fluctuations being reduced noise reductions are obtained in electric motors and special flywheels in the drives can be dispensed with. 
     Depending on the type of motor design, it is possible for the purpose of simplifying the actuation to take into account only a number of the influences on the power or torque characteristics. However, in an electromagnetic transducer preferably one of the influences a), c) or d) or at least two of the subsequent influences are taken into account: 
     a) electromagnetic influences, 
     b) reluctance influences, 
     c) permanent-magnet and mechanical influences, 
     d) mechanical influences (in the transducer and possibly also the connected load). 
     If, with the corresponding transducer design, one or more of the influences have only a small influence on the power or torque characteristic, these can then be ignored. 
     In order to be able to compensate interfering forces occuring in other directions than the useful force or the useful torque, in this respect in particular the radial and the axial interfering forces in rotation motors should be mentioned, this can be taken account of by impressing additional, special voltage or current components. 
     The data sets which take into account the power or torque characteristic of the transducer and possibly the load can be calculated either from the given design and material data or they are calculated indirectly from parameters and/or characteristic lines measured on a model. In the first case, neither a test bench not other measurements are required. 
     However, it is also possible to determine the data sets which take account of the power or torque characteristic of the transducer and possibly of the load, by measuring passes on a measuring and test bench for optimization for the purpose of achieving the randomly prescribed power or torque characteristic of a model. Although this solution requires a test bench, it permits individual fine adjustment independently of manufacturing and material tolerances, which is not possible by means of calculations. For this solution there are two processes, specifically the direct one (measurement, determining the data sets, operation of the transducer with the data sets) and the iterative process in which the steps of the direct process are followed by the renewed measurement, the correction of the data sets and the operation of the transducer with the corrected values, these subsequent steps being repeated as often as desired. 
     An expedient arrangement for carrying out the method according to the invention is characterized by a function memory having in each case one memory section per influence to be taken account of for storing the associated data set, an arithmetic switching unit for logically connecting data sets read out of the memory sections to in each case at least one input variable and for combining the logic connection results to form momentary values, a position or time generator assigned to the electromechanical transducer for controlling the position-dependent or time-dependent reading out of the data in the function memory and a power controller for impressing voltages or currents into the electrical terminals of the transducer in accordance with the momentary values. 
     If the transducer is a multi-phase transducer, for example a multi-phase electric motor, data sets can be stored for each of the individual phases and corresponding momentary values can be derived therefrom, in which case for each of the individual phases corresponding function memories, arithmetic switching units and power controllers or corresponding sections are provided or the latter are operated with time-division multiplexing. In such a case, asymmetries and other deviations between the individual phases of the transducer can be taken account of. However, a simpler solution consists in common data sets being stored for all the phases and either these data sets being read out with a phase shift for the individual phases and logically connected for the individual phases by means of the arithmetic switching units to form momentary values or common momentary values being derived from these common data sets and a phase shifting unit being provided which derives from the common momentary values the momentary values, shifted by the corresponding phase angles, for all the phases. This latter solution requires a smaller degree of outlay but cannot take into account asymmetries between the individual phases as is the case for the first solution. 
     Further advantageous embodiments of the invention can be found in the further subclaims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in greater detail below by means of exemplary embodiments and with reference to the enclosed drawings, in which: 
     FIG. 1 shows the equivalent circuit diagram of a permanent-magnet-excited synchronous motor; 
     FIG. 2 shows a flow diagram for determining the phase currents for the electric motor for the purpose of reduction of the electromagnetic torque fluctuations; 
     FIG. 3 shows an illustration of the induced voltage in a phase of a four-phase motor in standardized form; 
     FIG. 4 shows the circuit diagram of a device for the direct measurement of the static torque of a model motor; 
     FIG. 5 shows the circuit diagram for an indirect measurement of the static torque of a model motor; 
     FIG. 6 shows a flow diagram for iteratively determining the phase currents for the reduction of the permanent-magnet and mechanical torque fluctuations of a motor, divided up into three parts (FIG. 6a, 6b and 6c); 
     FIG. 7 shows an illustration of the current curve, determined iteratively in accordance with the flow diagram of FIG. 6 for a phase in standardized form; 
     FIG. 8 shows an illustration of the permanent-magnet and mechanical torque fluctuations of the test motor in the static state before an electronic correction (without frictional moment); 
     FIG. 9 shows an illustration of the torque fluctuations similar to FIG. 8 but after the electronic corrections; 
     FIG. 10 shows the block circuit diagram in a simplified illustration of an arrangement for actuating an electromechanical transducer in the form of an electric motor; and 
     FIG. 11a-c show illustrations of the phase current curves of the test motor in the currentless state with a current of 0.1 A and with a current of 0.5 A. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The term &#34;electromechanical transducer&#34; is to be understood to refer to any transducers which produce a mechanical effect from an electric current or a voltage, or vice versa, for example electromagnetic transducers, piezoelectric transducers, electret transducers, thermo transducers. Rotating electric motors and generators (ideal brake) as well as linear motors and loudspeaker drive systems, relays, actuators and pull magnets are important. 
     Since the mechanical behavior of loads (for example rotating transmissions and general lever transmissions and other transmissions) coupled to the transducers influence the power characteristic or torque characteristic, these can also be taken into account in combination with the transducers. 
     Power fluctuations can also have effects in directions other than the useful force or the useful moment and are taken into account as required. This applies, for example, to axial or radial interfering forces in rotating transducers which have a indirect rather than direct effect on the operating behavior or cause additional wear or additional noises. 
     Firstly, the torque or torque fluctuations will be derived from the motor energy balance by means of the electrical equivalent circuit diagram according to FIG. 1. The torque equation for the equivalent circuit diagram according to FIG. 1 is as follows: ##EQU1## where: T is the resulting torque 
     T r  is the sum of the permanent-magnet and the mechanical moment fluctuations, 
     E is the induced phase voltage, 
     I is the phase current 
     L is the motor inductance 
     ω is the rotor angle speed 
     δ is the rotor angle 
     m is phase number and 
     i and k are control variable for the motor phases. 
     As can be recognised from the torque equation, the current change speed is not a contributory factor to the formation of torque. The entire torque consists of four constituents: 
     a) the electromagnetic component, 
     b) the reluctance component, 
     c) the permanent-magnet component, and 
     d) the mechanical component. 
     The first term of the torque equation contains the electromagnetic torque constituent. It is determined by the interaction between the magnetic coil fluxes and the associated armature currents. The electromagnetic constituent consists of a constant useful moment and a superimposed pulsation moment. 
     The second term of the torque equation describes the reluctance moment. An angle-dependent change of the motor inductance, as occurs for example with a non-uniform air gap, leads in conjunction with the armature currents to a resulting torque which, depending on the current supply and design, consists of a constant useful moment and pulsation moment. 
     The third term of the torque equation shows the permanent-magnet and the mechanical constituent. The latter generates locking moments, due to the interaction between armature slots and permanent-magnets, and thus interfering pulsations. The size of these four components is influenced by the principle and the design of the motor. 
     If the electromagnetic torque constituent of the torque main equation (1-15) is isolated from the other components, the following is obtained: ##EQU2## with the desired condition 
     
         T.sub.el =const.                                           (2 -2) 
    
     the relations for the required phase currents shall now be derived. 
     The equation system (2 -1 . . . 2) is underdefined in its present form. An expedient additional condition can be imposed. Here, the requirement for minimum winding losses were selected: ##EQU3## 
     In order to solve this extreme value task with m variables and the secondary condition (equation 2 -1 and -2), the necessary conditions are determined with the aid of the Lagrangian multiplicator λ from the following formulation: ##EQU4## This formulation applies for an independent control of the phase currents. A further additional condition, for example the requirement ##EQU5## requires the introduction of a further Lagrangian multiplicator. However, the dissipated power may rise as a result of this additional condition. 
     From this the following is obtained: ##EQU6## If equation (-6) is inserted into the torque equation (-1), the following is obtained ##EQU7## 
     The Lagrangian multiplicator is thus determined by ##EQU8## 
     From the relations (-6) and (-8), the desired current equations of the phases k=1 . . . m are obtained in order to reduce the electromagnetic torque fluctuations: ##EQU9## 
     These phase currents can be determined on a computer-controlled motor test bench (which is explained later) in accordance with the flow diagram in FIG. 2. The current curve shapes for the reduction of the electromagnetic torque fluctuation have been determined for the example of a two-pole electronically commutated motor with four phases. Here, a motor is selected as the example which has both very high electromagnetic and permanent-magnet torque pulsations. 
     The phase voltage characteristic for a phase of the motor is shown in FIG. 3. The induced voltages were recorded at a very high motor speed (5000 rpm) so that interfering influences due to motor speed fluctuations are negligible. If these measurements have to be carried out at low motor speeds, an additional flyweight would be required. If this motor is fed with the phase current curves determined according to the flow diagram in FIG. 2, a very uniform torque characteristic without fluctuations is obtained. Possible residual interference can be revealed by means of a measurement and can be eliminated by correspondingly matched current curves in a second step or in additional following steps. 
     In addition to the process described above for calculating the motor phase currents, it is also possible to use a process which is based on the harmonic analysis. In order to compensate the individual torque harmonics the ordinal number of the current harmonics was selected in such a way that they interact with the largest voltage harmonics (fundamental harmonic). The interfering moments occuring here which arise from the interaction of the calculated current harmonics with voltage components whose ordinal number deviates from the fundamental harmonics are calculated and eliminated in steps by means of an iterative correction process. 
     A comparison of the two calculation methods shows that pratically the same results are achieved, the more rapid and simpler method in terms of solution structure is the direct method described first. 
     The permanent-magnet locking moment from the torque equation (Eq. 1-15) is a function of the rotor angle δ. 
     
         T.sub.r =T.sub.r (δ);                                (3 -1) 
    
     In contrast with the electromagnetic torque pulsations, this component is current-independent. The determination of the moment characteristic can occur by means of a field calculation or directly by means of a measurement. The way using the (numeric) field calculations leads, for the already mentioned reasons, partially to very unreliable results. This is compounded by ignorance of the previous history of the rotor magnets which may already be partially demagnetized as a result of excessively high thermal loading or excessively high armature reactive effect. The result of these effects are directly detected in a torque measurement. Two methods are suitable for torque measurement: 
     
                       TABLE______________________________________comparison of two measurement principlesfor ascertaining the static moment.     measuring methodselection   direct        indirectcriteria    (ω = 0) (ω ≠ 0)______________________________________duration of the       proportional to                     independent ofmeasurement the number of angle                     angle resolution;       increments;   very short measuring       a high resolution                     time (dependent on       leads to a large                     the rotor speed).       measuring time.Measured variables       *motor current and                     in addition:required for       *torque-current                     *overall inertiadetermining the       characteristic of                     moment of thestatic moment       the drive motor;                     test system;       *angle position;                     *speed dependence                     of the frictional                     moment;                     *determining the                     angle speed and                     acceleration from                     φ (t).Unreliability of       very small;   more unreliable duethe measurement           to additonally re-result                    quired measurement                     parameters.overall     more extensive                     larger computingoutlay      hardware;     outlay for evalution.______________________________________ *the direct measurement of the static moment T.sub.r (δ), and *the indirect determination of the static moment by means of a dynamic torque measurement (where ω ≠ 0). 
    
     The functional blocks of the two variants are set out opposite one another in FIGS. 4 and 5. A comparison of the above table leads to the result that both methods are justified depending on the priorities selected. 
     For the following description, the method of dynamic torque measurement is selected. Further details regarding the test bench can be found in a patent application entitled: &#34;Measuring and Test Bench for Electromechanical Transducers&#34; (same inventor, same applicant, same day of application). 
     The derivation of the equation system for the compensation of the permanent-magnet and mechanical constituent begins with the illustration of the dynamic motion equation for the measurement system according to FIG. 5. The drive servomotor is controlled by means of a controllable voltage source in such a way that at the smallest possible motor speed the permanent-magnet tilt moment of the currentless test motor is just overcome. The moment which occurs can be measured in the stationary state by means of the armature current of the drive motor. 
     
         T=f(I(δ));                                           (3 -2) 
    
     For a DC bell-type armature motor with a very high number of collector laminars, the relationship between moment and armature current is linear to a very good approximation. The equation 3 -2 is simplified by using the torque constants k T  as: 
     
         T=k.sub.T I(δ);                                      (3 -3) 
    
     The measurable torque is composed of three components which are considered below. 
     The first term is formed by the angle-dependent torque: 
     
         T.sub.1 =T.sub.r (δ);                                (3 -4) 
    
     The locking moment T r  is triggered by a superimposition of the permanent-magnet moment fluctuations, the mechanical moment fluctuations and the motor speed-independent frictional moment constituent. 
     The second term is determined by motor speed-dependent moment constituents: ##EQU10## 
     Depending on the motor design and operating range, the function T 2  (ω) may depend on the motor speed in a linear or even strongly non-linear fashion. Influencing variables are bearing and brush friction, air friction, eddy current moments and hysteresis brake moments. 
     Finally, the third term is the acceleration moment dependent on the mass inertia moment of the entire rotating system. ##EQU11## where 
     J p  : inertia moment of the test motor, 
     J b  : inertia moment of the brake, 
     J o  : other inertia moments (e.g. clutch, angle generator). 
     The torque balance from the equations (3 -2, -4, -5 and -6) is as follows: ##EQU12## After conversion, the angle-dependent locking moment is obtained as: ##EQU13## 
     Therefore, the following condition equation is to be fulfilled for the compensation of the permanent-magnet and mechanical torque fluctuations: 
     
         T.sub.r (δ)+T.sub.c (δ)=0;                     (3 -9) 
    
     The relation for the phase currents which generate the electromagnetic compensation moment T c  can be derived by using equation (2 -9). The exact solution using the secondary condition of minimum losses is: ##EQU14## where T r  (δ) is in accordance with equation (3 -8). 
     Here, as in the compensation of the electromagnetic torque fluctuations, the current curve can also be alternatively determined on the basis of a harmonic analysis. 
     The sequence of calculation of the phase current curves can be seen from the flow diagram according to FIG. 6 (with the components FIGS., 6a, 6b and 6c). The measurements on the motor which are required for the calculation are carried out fully automatically on a measuring and test bench so that the motor can then be operated and tested with the determined correction curve. 
     FIG. 7 shows in standardized form the current curve for a motor phase determined with the iterative method according to the flow diagram in FIG. 6, for the compensation of permanent-magnet and mechanical torque fluctuations. FIGS. 8 and 9 show curves for the static torque before and after the electronic correction. 
     FIG. 10 shows an exemplary embodiment in a diagrammatic illustration of an arrangement for actuating electromechanical transducers, in the present case of an electric motor. The circuit arrangement according to FIG. 10 contains a motor controller 10, an arithmetic switching unit 20, a function memory 30 and a power supply for the motor 3 which consists in the present example of a current controller 5, an output stage 6, a DC voltage power supply 7 and a current measuring device 4. The arithmetic switching unit contains two multipliers 21 and 22 and a logical connection circuit in the form of an accumulator (summing device) 23, the output signal of which actuates the current controller 5. The function memory 30 contains in the present case two curve memories 31 and 32 so that two different terms can be taken into account. If further terms have to be processed, for example for compensating reluctance interfering influences or interfering influences acting in directions other than the useful force or the useful torque, the arithmetic switching unit 20 and the function memory 30 are to be expanded with the corresponding elements. In such a case, it is possible that the logical connections do not occur multiplicatively and additively, as shown in FIG. 10, but rather by means of different corresponding functional logical connections. 
     Even if, in the circuit arrangement according to FIG. 10, in each case only one memory section 31, 32 per influence variable is shown in the function memory 30, each of the memory sections can be divided up into several components so that different data sets can be stored per influencing variable. These different data sets are then selected by means of an input variable 33. 
     In the present case, the motor controller 10 contains a torque control 11, a motor speed controller 12 and a position controller 13, the output signals of which are connected optionally via a change-over switch to an input 25 of the arithmetic switching unit 20, as well as a motor speed and direction of rotation detecting device 14. In addition, an input 24 is provided for the arithmetic switching unit. The motor 3 is coupled to an angular position encoder 2 in order to supply corresponding angular position signals for the function memory 30 and for the motor controller 10. 
     In a way which is representative of a multiplicity of correction or control elements (input variables), the input 26 or 27 is labeled for a possible evaluation of the multiplication factors 24 or 25. The input variable 33 makes a decision by selecting special curves for taking into account different operating states (non-linear operation due to iron saturation and armature reactive effects, temperature) and motor operating modes (e.g. uniform operation or pulsing operation as step motor). 
     The following input variables are of interest with respect to the circuit arrangement: control variables for the amplitudes of the stored, standardized curve or of the curve generator, possibly a signal variable which makes it possible to read out the curves in a time-dependent manner or as a function of the rotor position, control or signal variables for selecting the curves and possibly for changing the curve shape in particular with a non-linear motor characteristic, in which case the curve shape is to be matched to the operating state. Furthermore, control variables, for example, for an arithmetic switching unit 20 can occur which control the sequence of the logical connection of control variables and curves or change the logical connection function in accordance with the operating state of the motor. Digital, analog or other signal variables which possibly impress defined currents or voltages on the motor phases by means of a power controller in order to improve the concentricity quality of the motor or generally the operating characteristic are produced as output variables. 
     The data for curves which lead to the compensation of the individual torque fluctuation modes is deposited in the function memory 30. The data can be stored in the form of tables, regulations (e.g. limitation on the maximum current amplitude), equations or functions. Depending on the symmetry of the magnetic and electric circuit, it is necessary to deposit the curves for all the phases separately or only one curve per torque fluctuation mode. In the latter case, the curves are read out shifted by the phase shift angle. Curve generators which generate the defined curves can also take the place of the function memories 30. 
     An arithmetic switching unit 20 now logically connects the curve amplitudes, made available in a time-dependent or rotor angle-dependent manner, to the input control variables in accordance with defined functions. However, in the present case the logical connection elements 21, 22 or adding elements 23 are employed; under certain circumstances other logical connection elements are necessary for taking into account other influencing variables. 
     In the circuit arrangement according to FIG. 10, the current curve values, calculated for a rotor rotation, of the individual phases, for the purpose of reducing the electromagnetic torque fluctuation (curve memory 32) and the permanent-magnet fluctuation, including the mechanical fluctuation (curve memory 31) are separated and deposited in standardized form. 
     In accordance with the rotor angle φ, the current curve of the curve memory 31 is read out and multiplied by a current amplitude i A  (input 24). The amplitude i A  is selected in such a way that the permanent-magnet torque fluctuations are minimal. The amplitude i A  is also contained in the stored data set. In motors with a non-saturated iron circuit and negligible armature reactive effect the amplitude can be kept constant. Otherwise, the value is to be adjusted in accordance with conditions. The current curve generated in this way flows unchanged into the individual phase windings independently of the operating state of the motor and thus compensates the torque pulsations which have permanent-magnet and mechanical causes. 
     On the condition that the motor has a linear current-torque characteristic, which is usually the case with permanent-magnetic-excited motors, the actual operating curve can now be superimposed additively on the current curve: 
     
         i.sub.permanent =i.sub.A A(φ) 
    
     It arises from the product of the controller-current amplitude and the current curve B (φ) intended for compensating the electromagnetic torque fluctuations: 
     
         i.sub.el -magn=i.sub.B B(φ) 
    
     If the respective motor has a non-linear behavior, it is expedient to use different curves per type of torque fluctuation for different operating areas. This can occur for example by implementing a curve selection switch as a function of the operating state of the motor, which switch selects via an input 33 the corresponding sections of the memory sections 31, 32 etc. or the curves are changed in an appropriate way so that they are better matched to the respective operating state. Matching can however also occur by changing the input control variables 26, 27. 
     If the reluctance torque fluctuations or other influences are not negligible, a further third path or other further paths consisting of an additional memory section and a logical connection element (not shown) can be added to the circuit according to FIG. 10, said path permitting the reluctance fluctuations to be reduced by appropriate current circuits. 
     It is apparent from the torque equation given at the beginning that this term can be dependent on the self-inductances and mutual inductances as well as on the individual phase currents. It is possible to deposit the necessary information for the current curve generation as data sets in the form of table values, regulations, equations or functions or to calculate the information directly from the respective operating state. 
     The electrical circuit can be realized in different ways. It can be constructed, for example purely in hardware terms, from analog and/or digital components or it can also be realized in software terms by means of a computing program. In addition, a moment control and a position control, speed control or acceleration control can be superimposed on the electrical circuit. In the case shown, the overall circuit has the structure of a cascade control. In the motor controller 10, internally there is a speed controller 12 subordinate to the position controller 13 and externally a current controller 5 subordinate to the said speed controller 12. 
     The essential difference with respect to other position, speed, acceleration and moment controls resides in the fact that due to the selected current curve control any possible moment fluctuations are already suppressed at the start and thus the superimposed control circuits are relieved to a very great extent. The controllers only still have to be configured for a fine correction. One controller for impressing a torque can be dispensed with entirely. 
     By means of these measures which have been presented, the operating behavior of the motor with respect to moment fluctuations and also speed fluctuations is substantially improved. Further improvements are a lower generation of noise, better efficiency and lower operating temperatures. 
     The proposed electronic circuit is suitable for actuating motors with any desired current curves. If an additional pulse generator with controllable frequency is added parallel to the angular-position encoder 2, this circuit is suitable for the universal operation of all types of small electrical motors, that is to say for remote-controlled and non-position-controlled motors such as general synchronous motors, step motors, asynchronous motors etc. For the fedback operation, the angular-position encoder 2 is connected into the electrical circuit and for the controlled operation the pulse generator is connected into the electrical circuit. 
     FIGS. 11a, 11b and 11c now show for one phase current curves for achieving different constant nominal torques, such as are applied for example by means of the circuit arrangement according to FIG. 10 to the motor 3. These curves take into account both constituents of torque fluctuations, namely the electromagnetic and the permanent-magnet fluctuations. Phase current curves for three different operating states of the motor 3 are shown, specifically for the currentless state (FIG. 11a) for a current of 0.1 A (FIG. 11b) and for a current of 0.5 A (FIG. 11c). In these cases, a very uniform torque characteristic without fluctuations is obtained.