Method for driving a load device using a stepper motor

Abstract

Method for driving a load device by a stepper motor, wherein the stepper motor performs a plurality of steps in each revolution, the load device periodically returns to an initial state after a certain number (8) of revolutions of the stepper motor with a period, target step times (4) are specified for a plurality of steps of the stepper motor performed in one of the periods, a plurality of corresponding actual step times (1) occurring in at least one of the periods are determined, and in a period following those periods in which the plurality of actual step times are determined, the energy supplied for the execution of the respective step is reduced if the actual step time (1) is less than the corresponding target step time (4), and / or the energy supplied for the execution of the respective step is increased.provided that the actual step time (1) is greater than the corresponding target step time (4), wherein an additional control of the rotational speed is provided, wherein an actual duration is determined for a period under consideration and a comparison is carried out with a predetermined target duration of the period, wherein the target step times of the period under consideration or the target step times of the period following the period under consideration are adjusted in such a way that the deviation between the actual duration and the target duration is minimized.

Description

[0001] The present invention relates to a method for driving a load device by means of a stepper motor, and to a periodically operating device comprising a stepper motor and a load device with which this method can be carried out.

[0002] Stepper motors typically exhibit an uneven torque curve. These torque fluctuations, often referred to as torque ripple, lead to variations in step time. They can be caused, for example, by the discrete number of steps performed by the stepper motor. Besides the stepper motor itself, the torque curve of a load device can also exhibit torque ripple. This can be caused, for example, by an imbalance in the load device. If a stepper motor is used to drive a load device, the effect of the stepper motor's torque fluctuations can be amplified by the torque ripple of the load device, resulting in a combined torque ripple. If the stepper motor is operated at low speed, it can run increasingly unevenly in such a case, or even stall or become uncontrollable.

[0003] The current state of the art solves this problem by determining the step time of the last step and correcting the immediately following step based on this. This is therefore an adjustment from one step to the next.

[0004] However, a disadvantage of this method is that the superimposed torque fluctuations of the respective directly successive steps can be so different that the control of the step time regulates in the wrong direction each time, thus further increasing the fluctuations in the torque curve.

[0005] Document US 4,879,502 A discloses a speed control device and a speed control method for an electric motor.

[0006] Based on the prior art, the object of the present invention is therefore to provide a method by which a stepper motor can operate a load device at a well-defined speed or torque, and also to provide a periodically operating device with which this method can be carried out.

[0007] This problem is solved by the method for driving a load device by a stepper motor with the features of claim 1, and by the periodically operating device with the features of claim 11. The respective dependent claims relate to advantageous embodiments of the method according to claim 1 and of the periodically operating device according to claim 11, respectively.

[0008] The method according to the invention relates to a method for driving a load device by a stepper motor, wherein the stepper motor executes a plurality of steps in each revolution, the load device periodically returns to an initial state after a certain number of revolutions of the stepper motor, target step times are specified for a plurality of steps of the stepper motor executed in one of the periods, a plurality of corresponding actual step times occurring in at least one of the periods are determined, and in a period following those periods in which the plurality of actual step times are determined, the energy supplied for the execution of the respective step is reduced if the actual step time is less than the corresponding target step time, and / or the energy supplied for the execution of the respective step is increased.provided that the actual step time is greater than the corresponding target step time, wherein additional speed control is provided, wherein an actual duration is determined for a period under consideration and a comparison is made with a predetermined target duration of the period, wherein the target step times of the period under consideration or the target step times of the period following the period under consideration are adjusted in such a way that the deviation between the actual duration and the target duration is minimized.

[0009] The device according to the invention relates to a periodically operating device comprising a stepper motor and a load device, wherein the periodically operating device is configured such that, with each revolution of the stepper motor, the stepper motor executes a plurality of steps, after a certain number of revolutions of the stepper motor with a period, an initial state of the load device is periodically reached again, target step times can be specified for a plurality of steps of the stepper motor executed in one of the periods, a plurality of corresponding actual step times occurring in at least one of the periods can be determined, and in a period following those periods in which the plurality of actual step times are determined, the energy supplied for the execution of the respective step can be reduced, provided that the actual step time is less than the corresponding target step time.and / or the energy supplied for the execution of the respective step can be increased, provided that the actual step time is greater than the corresponding target step time, wherein additional control of the rotational speed is provided, wherein an actual duration can be determined for a period under consideration and a comparison with a predetermined target duration of the period can be carried out, wherein the target step times of the period under consideration or the target step times of the period following the period under consideration can be adjusted in such a way that the deviation between the actual duration and the target duration is minimized.

[0010] The present invention relates to a method for driving a load device by means of a stepper motor. A stepper motor typically has a rotor, i.e., a rotatable motor part with a shaft. The rotor can be rotated by one step or a multiple thereof by a controlled, stepwise rotating electromagnetic field of stator coils in a non-rotating motor part. The stepper motor can, for example, be a reluctance stepper motor, a permanent magnet stepper motor, or a hybrid stepper motor.

[0011] The stepper motor can advantageously also be a DC motor or a synchronous motor. A DC motor is typically a rotating electrical machine that operates on direct current. One feature of a conventional DC motor is, for example, a mechanical inverter. This is also called a commutator or polarity reverser. The commutator, or polarity reverser, can generate a speed-dependent alternating current by reversing the polarity or current. The DC motor can advantageously be a brushless DC motor. In a brushless DC motor, electronic commutation, i.e., polarity reversal, can be made dependent on the rotor position, rotor speed, and torque, or a commutation time can be controlled. The commutation time is typically the time difference between two polarity reversals.

[0012] The term "stepper motor" can advantageously refer in particular to a permanent magnet synchronous motor, which is, for example, electronically controlled by block commutation. Typically, in a synchronous motor, the rotor is moved by a rotating magnetic field in the stator, with the running synchronous motor performing a movement synchronous with the alternating voltage.

[0013] The stepper motor completes a number of steps with each revolution. A step is typically the minimum angle by which the rotor can be rotated. The number of steps can be determined, for example, by the number of teeth on a toothed soft iron core in a reluctance stepper motor, or by the number of poles or stator coils in a permanent magnet stepper motor. In a brushless DC motor, the number of steps can be determined, for example, by the number of commutations.

[0014] The stepper motor executes each step with a step time. Step times can be defined as the time interval between the start of one step and the start of the next. This time interval can also be the time that elapses, for example, between the start of the energy supply required to execute the current step and the start of the energy supply required to execute the next step. Step times are, for example, commutation times.

[0015] A load device is typically a device that performs work, such as a pump. Preferably, the pump is a fuel pump and / or a gerotor. A gerotor is a positive displacement pump with an inner and an outer rotor, the inner rotor having n teeth and the outer rotor having n+1 teeth. The two rotors can rotate in a toothed fashion, with the inner rotor mounted eccentrically to the outer rotor. Due to the geometry of the gerotor, n different volumes are created between the teeth of the inner and outer rotors. Because of the eccentric toothing of the inner and outer rotors, the volume between the teeth can expand or contract during rotation. Thus, a liquid can be pumped by means of the resulting overpressure or underpressure in the respective volumes.

[0016] The load device typically exhibits torque fluctuations, also known as torque ripple. These can be inherent to the load device's design, for example, due to imbalance, component design, or manufacturing tolerances. The torque ripple of the load device can interact with the torque ripple of the stepper motor, potentially resulting in combined torque ripple.

[0017] After a specific number of revolutions of the stepper motor, the load device periodically returns to its initial state. For the gerotor, this could occur, for example, after n·(n+1) steps. The stepper motor and load device form a single mechanical system. The initial state can be any well-defined state of this mechanical system. A period can be defined as the time interval that begins when a specific state is reached and ends when that state is reached again. Normally, the same torque profile occurs in each such period if no correction is made. The load device can, for example, return to its initial state after each revolution of the load device if the same torque profile occurs during each individual revolution.The stepper motor, for example, can have a design-related number of m steps, which result in one mechanical revolution (360°). For the exemplary overall mechanical system consisting of the stepper motor and gerotor, this could then result in a number of m·n·(n+1) steps per period.

[0018] In each period, the stepper motor can complete a specific number of revolutions, each with a plurality of steps. In a period with N steps, N actual step times t1, t2, ..., t are possible. i , ..., t N The following occur. Target step times are specified for a large number of steps of the stepper motor that occur in one of the periods. The target step times are t1', t2', ..., t i ', ..., t N' can be specified for the N steps of a period to ideally achieve a well-defined, preferably constant, rotational speed and / or a well-defined, preferably constant, torque. In a subsequent process, the target step times t1', t2', ..., t i ', ..., t N ' in a period with the actual step times t1, t2, ..., t i , ..., t N The actual step times will be compared during this period. If there is a discrepancy, a correction of the actual step times can be made in a later period.

[0019] For this purpose, a large number of actual step times, occurring in at least one of the periods, are determined, corresponding to the respective target step times. Let t1, t2, ..., t be denoted by these values. i , ..., t N the actual step times measured in at least one period and t1', t2', ..., t i ', ..., t N'The specified target step times for this period, which has a plurality of N steps. Then the actual step times t are calculated. i the respective steps i in a period and the specified target step times t i ' of the respective step i in this period is considered to be corresponding.

[0020] In a period following those periods in which the multitude of N actual step times are determined, the energy supplied for the execution of the respective step i is reduced, provided that the actual step time t i is smaller than the corresponding target step time t i ', and / or the energy supplied for the execution of the respective step i is increased, provided that the actual step time t i is greater than the corresponding target step time t i '.

[0021] The energy supplied for the execution of each step i is preferably adjusted by increasing or decreasing the energy supplied in step i itself. However, the energy supply in a step i can also affect the execution of an adjacent step i-1 or i+1. Due to a delay in the acceleration following the energy supply, the energy supplied for the execution of each step i can therefore also be adjusted, for example, by increasing or decreasing the energy supplied in an adjacent step i-1 or i+1.

[0022] Both rotational speed and step time are typically dependent on the energy supplied to the stepper motor. Therefore, the supplied energy can be decreased or increased to correct the actual step times. The decrease or increase of the energy supplied in the respective step i can then be applied in a later period following the period in which the multitude of actual step times t1, t2, ..., t1 are recorded. i , ..., t N The determination process is carried out. Preferably, the period in which the energy supplied to the stepper motor is increased or decreased in the respective step i follows directly after at least one of the periods in which the actual step time t is determined. i has been determined. In a later period, the deviation Δt can thus be determined again if necessary. i =t i '-t i the actual step times t1, t2, ..., t i , ..., t N of the corresponding target step times t1', t2', ..., ti ', ..., t N ' can be determined. This can be further reduced in a later period. By adjusting the amount of energy supplied over several periods, a convergence of the actual step times t1, t2, ..., t can ideally be achieved. i , ..., t N and the corresponding target step times t1', t2', ..., t i ', ..., t N ' can be achieved. This allows the specified, well-defined speed and / or the specified, well-defined torque curve to be achieved.

[0023] Energy can preferably be supplied to the stepper motor in each step by applying an electric current with a definable current and / or voltage. The energy supplied to the stepper motor in each step is preferably decreased or increased by decreasing or increasing the current supplied to the stepper motor. Alternatively, the voltage can also be changed, for example. Furthermore, the energy can also be supplied by a pulsed electric current. The actual step time is then preferably adjusted by decreasing or increasing the pulse width of the pulsed electric current.

[0024] The energy supplied for the execution of the respective step can be reduced by a percentage of at least 0.2%, preferably at least 0.5%, particularly preferably at least 0.8% and / or at most 5%, preferably at most 2%, particularly preferably at most 1.3% if the actual step time is less than the corresponding target step time, and / or increased if the actual step time is greater than the corresponding target step time.

[0025] Preferably, in addition to controlling the step times, a higher-level control of the rotational speed can be provided. This is advantageous, for example, if the correction of the individual step times t1, t2, ..., t i , ..., t NIn a period following the period in which the multitude of actual step times are determined, this results in a change in the overall rotational speed. The overall rotational speed can, for example, be measured as an average over the duration of this subsequent period. The rotational speed is preferably controlled by determining an actual duration T of at least one of the periods, specifying a target duration T' for this at least one period, and determining the target step times t1', t2', ..., t i ', ..., t N ' for this or a subsequent period so that the deviation ΔT=T'-T of the actual duration T from the target duration T' is reduced. The correction t i '+Δt i ' of the target step times t1', t2', ..., t i ', ..., t N ' can therefore be based on a deviation ΔT=T'-T of the actual duration T from the target duration T'. For this purpose, for example, a base value of the target step time t is used. i' corrected. This base value t i ' is the target step time value from at least one of the periods in which the actual duration of the period was determined. In a later period, the corrected value t can then be used. i '+At i ' as the new target step time. Preferably, the target step times are corrected in a period immediately following the period of the actual duration T, and the corrected value is then specified. During the correction Δt i ' could, for example, be a relative correction Δt i '=ΔT / T * t i ', which is proportional to the deviation ΔT.

[0026] Preferably, when determining the actual duration of at least one period, the actual duration of at least one period, preferably of at least three periods, particularly preferably of at least five periods and / or of at most twenty periods, preferably of at most fifteen periods, particularly preferably of at most ten periods, is determined.

[0027] The energy supplied to the stepper motor can typically be regulated by a controller. In an electrical control loop, the controller compares the target step times (i.e., the reference input) with the actual step times (i.e., the controlled variable). From the difference, which can also be called the control deviation, the manipulated variable (preferably the supplied electrical energy) can be determined and adjusted accordingly. Preferably, the controller is a PI controller or a P controller.

[0028] The PI controller, for example, is a standard linear controller with proportional and integral behavior, i.e., a superposition of a step response and a proportional response. The P controller, for example, exhibits a characteristic step response.

[0029] The invention will now be explained by way of example with reference to several figures, without limiting the invention to the embodiments shown therein. Identical reference numerals denote identical or corresponding features. The features described in the examples can also be combined between the examples and implemented independently of the specific example. The figures show: Fig. 1 an exemplary stepper motor for driving a gerotor, Fig. 2 an exemplary curve of the commutation time as a function of the rotation angle without correction, Fig. 3 an exemplary progression of the commutation time as a function of the rotation angle with adaptation.

[0030] Fig. Figure 1 shows an example stepper motor for driving a gerotor. The gerotor has an inner (10) and an outer rotor (11), where the inner rotor has n = 4 teeth (14) and the outer rotor has n+1 = 5 teeth (14). The two rotors (10, 11) can rotate in a toothed fashion, with the inner rotor (10) being mounted eccentrically to the outer rotor (11). Due to the geometry of the gerotor, different volumes are created between the teeth (14) of the inner (10) and outer rotor (11). Because of the toothed engagement of the inner (10) and outer rotor (11), the volume between the teeth (14) can expand or contract during rotation. A liquid can thus be pumped by means of the resulting overpressure or underpressure in the respective volumes. The liquid is drawn into the inlet (13) and then pushed out of the outlet (12).The gerotor rotates clockwise (15) and is mounted in a round housing (16) that is concentric to the axis of rotation of the inner rotor (10). The housing (16) also has holes for fixing it in place.

[0031] Fig. Figure 2 shows an exemplary curve (3) of a step time, which is, for example, a commutation time (1), as a function of a rotation angle (2) of a stepper motor. The curve (3) of the step time (1) as a function of the rotation angle (2) of the stepper motor exhibits slight fluctuations around the target value (4). After five rotations (8) of the stepper motor, the load device has completed one full period and returns to its initial state. A total of two full periods are shown, each with five maxima in the step time (1) reaching the target value (4) and five minima significantly below the target value (4). These torque fluctuations are also referred to as torque ripple (9). Thus, a total of five torque ripples (9) occur. The cause of the torque ripple (9) is, for example, an imbalance in the load device or the design of the stepper motor with multiple stator coils.The individual torque ripples (9) of the stepper motor and the load device couple to each other, resulting in the five torque ripples (9) shown.

[0032] Fig. Figure 3 shows an exemplary curve (3) of the step time or commutation time (1) as a function of the rotation angle (2) of the stepper motor. Again, two periods are shown. The curve of the commutation time (1) in the first period is analogous to that in Figure 3. Fig. The structure shown in Figure 2 is as follows. Again, there are five maxima and five minima below the setpoint (4). However, N=9 control points (5) are now shown, which can, for example, be individual steps of the stepper motor. The stepper motor completes a plurality of steps with each revolution. Setpoints (4) t1', t2', ..., t are defined for a plurality of steps 1 to N=9. i', ..., t9' or target step times are specified. In addition, actual values ​​of the step time (1) or commutation time t1, t2, ..., t9 are determined, where t i The actual step time or commutation time of step i is the actual step time occurring. At control points 1 to N=9, an adaptation (6) of the actual step times (1) or actual values ​​of the commutation time t1, t2, ..., t9 to the setpoint values ​​(4) or setpoint step times t1', t2', ..., t now takes place. i ', ..., t9' instead. The actual values ​​t are used. i at control point i with the corresponding setpoint values ​​t i 'Compared. According to the deviation Δt i =t i '-t iThe commutation time (1) or actual step time can be corrected. This process is preferably carried out by decreasing or increasing the energy supplied during a commutation or step i. For example, if the actual step time or the actual value of the commutation time (1) is less than the target value (4), the supplied energy can be reduced in a later period. If the actual step time or commutation time (1) is greater than the target value (4), the supplied energy can be increased. The energy supplied for the execution of the respective step i is preferably adjusted directly in step i. However, the energy supply in a step i can also affect the execution of an adjacent step i-1 or i+1. Due to a delay in the acceleration following the energy supply, the energy supplied for the execution of the respective step i can therefore alternatively also be adjusted by increasing or decreasing the energy supplied during a subsequent step i.The energy supplied in an adjacent step i-1 or i+1 is increased or decreased, respectively. This correction of the supplied energy is preferably performed in the period immediately following the measurement of the deviation. Consequently, the second adapted period (7) exhibits significantly smaller fluctuations in the actual step time or commutation time (1) around the setpoints (4). The torque ripples (9) are smoothed. The amount of supplied energy is preferably adjusted by varying the current, the voltage, or, in the case of a pulsed current, the pulse width, with the control preferably being carried out by a PI controller. In the adapted period (7), the actual duration of the period is preferably measured and adjusted to a predetermined setpoint duration. This can be achieved by changing the setpoints (4) or the predetermined setpoint step times t1', t2', ..., t. i', ..., t9' will occur in a later period, with the change being based on the deviation of the actual duration from the target duration of that period. Reference symbol list 1 Commutation time or actual step time 2 Rotation angles of the stepper motor 3. Commutation time as a function of the rotation angle 4. Target value or target step time 5 control points of the commutation time or steps 6 periods with adaptation, i.e., comparison of actual step time / target step time 7 Period with adapted commutation times or actual step times 8 Number of revolutions until the initial state is reached again 9 torque ripples 10 Inner rotor 11 Outer rotor 12 Pump output 13 Pump inlet 14 teeth of the rotors 15. Rotation direction: clockwise 16 cases

Claims

[1] Method for driving a load device by a stepper motor, wherein the stepper motor runs through a plurality of steps with each revolution, the load device periodically reaches an initial state again after a certain number (8) of revolutions of the stepper motor with a period, target step times (4) are predetermined for a plurality of steps of the stepper motor run through in one of the periods, a plurality of corresponding actual step times (1) occurring in at least one of the periods are determined, and in a period following those periods in which the plurality of actual step times are determined, an energy supplied for executing the respective step is reduced if the actual step time (1) is less than the corresponding target step time (4), and / or the energy supplied for executing the respective step is increased,if the actual step time (1) is greater than the corresponding target step time (4), an additional control of the speed is provided, an actual duration being determined for a period under consideration and a comparison being made with a predetermined target duration of the period, the target step times of the period under consideration or the target step times of the period following the period under consideration being adjusted in such a way that the deviation between the actual duration and the target duration is minimized. [2] Method according to the preceding claim, wherein the load device is a pump, preferably a fuel pump, particularly preferably a gerotor. [3] Method according to one of the preceding claims, wherein the stepper motor is a DC motor, a synchronous motor and / or a reluctance stepper motor, a permanent magnet synchronous motor or a hybrid stepper motor. [4] Method according to one of the preceding claims, wherein the energy supplied for carrying out the respective step is reduced by a percentage of at least 0.2%, preferably at least 0.5%, particularly preferably at least 0.8% and / or at most 5%, preferably at most 2%, particularly preferably at most 1.3%, if the actual step time (1) is less than the corresponding target step time (4), and / or increased if the actual step time (1) is greater than the corresponding target step time (4). [5] Method according to one of the preceding claims, wherein the energy supplied to the stepper motor is increased by increasing an electrical current supplied to the stepper motor and / or a voltage supplied to the stepper motor and / or the energy supplied to the stepper motor is reduced by reducing an electrical current supplied to the stepper motor and / or a voltage supplied to the stepper motor. [6] Method according to one of the preceding claims, wherein the energy supplied to the stepper motor is supplied by means of a pulsed electric current, and the energy supplied to the stepper motor is increased by increasing a pulse width of the pulsed electric current, and / or the energy supplied to the stepper motor is reduced by reducing the pulse width of the pulsed electric current. [7] Method according to one of the preceding claims, wherein the energy supplied to the stepper motor is increased and / or decreased by means of at least one PI controller and / or at least one P controller. [8] Method according to one of the preceding claims, wherein an actual duration of at least one of the periods is determined, a target duration of this at least one period is specified, target step times (4) for this or a following period are adjusted such that the deviation of the actual duration from the target duration is reduced. [9] Method according to the preceding claim, wherein, in determining the actual duration of the at least one period, the actual duration of at least one period, preferably of at least three periods, particularly preferably of at least five periods and / or of at most twenty periods, preferably of at most fifteen periods, particularly preferably of at most ten periods, is determined, and preferably the periods used in determining the actual duration of the at least one period directly precede the period immediately traversed at the time of the determination. [10] Method according to one of the preceding claims, wherein the energy supplied for carrying out the respective step is supplied in this step itself and / or in an adjacent step, preferably in this step itself. [11] A periodically operating device comprising a stepper motor and a load device, wherein the periodically operating device is configured such that with each revolution of the stepper motor, the stepper motor runs through a plurality of steps, after a certain number (8) of revolutions of the stepper motor with a period, an initial state of the load device is reached again in a periodically recurring manner, target step times (4) can be specified for a plurality of steps of the stepper motor run through in one of the periods, a plurality of corresponding actual step times (1) that occur in at least one of the periods can be determined, and in a period following those periods in which the plurality of actual step times are determined, an energy supplied for executing the respective step can be reduced, provided that the actual step time (1) is less than the corresponding target step time (4),and / or the energy supplied for executing the respective step can be increased if the actual step time (1) is greater than the corresponding target step time (4), wherein an additional control of the speed is provided, wherein an actual duration can be determined for a period under consideration and a comparison with a predetermined target duration of the period can be carried out, wherein the target step times of the period under consideration or the target step times of the period following the period under consideration can be adapted in such a way that the deviation between the actual duration and the target duration is minimized. [12] Device according to the preceding claim, wherein a method according to one of claims 1 to 10 can be carried out with the device.

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