DE102014226727A1 - Method for driving a load device by a stepper motor - Google Patents

Abstract

The present invention relates to a method for driving a load device by a stepping motor, wherein preferably a well-defined torque curve is to be achieved by adapting actual step times to desired step times in a period following the measured deviation. The present invention also relates to a periodically operating device with which this method is carried out.

Description

The present invention relates to a method for driving a load device by a stepper motor, as well as a periodically operating device comprising a stepper motor and a load device, with which this method is executable.

Stepper motors usually have a non-uniform torque curve so far. These torque fluctuations are often referred to as torque ripple and lead to a step time variation. For example, they may be caused by the discrete number of steps of the stepper motor. In addition to the stepper motor, the torque curve of a load device can also comprise torque ripple. Cause can be, for example, an imbalance in the load device. If, for example, a load device is now operated with a stepper motor, the effect of the torque fluctuations of the stepper motor can be amplified by the torque ripples of this load device so that a common torque ripple occurs. If the stepping motor is operated at low speed, the stepping motor in such a case can increasingly run out of alignment or even be stopped or can no longer be controlled.

The prior art solves this problem by determining a respective step time of the last step and, based thereupon, correcting an immediately following step. So this is an adaptation from one step to the next.

Disadvantage of this method, however, is that the superimposed torque fluctuations of the respective directly successive steps can be so different that the regulation of the step time in each case controls in the wrong direction and thus the fluctuations in the torque curve are still amplified.

Starting from the prior art, it is therefore an object of the present invention to provide a method by which a stepper motor can operate a load device at a well-defined speed or well-defined torque, and also to provide a periodically operating device with which this method is executable.

This object is achieved by the method for driving a load device by a stepper motor with the features of claim 1, as well as by the periodically operating device having the features of claim 10. The respective dependent claims relate to advantageous developments of the method according to claim 1 and the periodically operating device according to claim 10.

The present invention relates to a method for driving a load device by a stepper motor. A stepper motor typically has a rotor, ie a rotatable motor part with shaft. The rotor can be rotatable by a step or its multiple by a controlled, stepwise rotating, electromagnetic field of stator coils in a non-rotatable motor part. The stepper motor may be, for example, a reluctance stepper motor, a permanent magnet stepper motor or a hybrid stepper motor.

The stepper motor may advantageously also be a DC motor or a synchronous motor. A DC motor is typically a DC rotary electric machine. A feature of the conventional DC motor is, for example, a mechanical inverter. This is also referred to as commutator or as Polwender. The commutator or Polwender can generate a speed-dependent alternating current by reversing or current application. The DC motor may advantageously be a brushless DC motor. In a brushless DC motor, electronic commutation, i. H. Umpolung be made dependent on the rotor position, the rotor speed and the torque or a Kommutierzeit be controlled. The commutation time is typically the time difference between two polarity reversals.

The generic term "stepper motor" may advantageously be used to designate, in particular, a permanent-magnet synchronous motor which, for example, is controlled electronically by a block commutation. Typically, in the synchronous motor, the rotor is moved by a variable magnetic rotating field in the stator, wherein the running synchronous motor performs a synchronous to the AC voltage movement.

The stepper motor goes through a plurality of steps each revolution. One step is typically a minimum angle by which the rotor can be rotated. The number of steps may be predetermined, for example, by the number of teeth of a toothed soft iron core in the reluctance stepper motor or, for example, by the number of poles or stator coils in the permanent magnet stepper motor. In the brushless DC motor, the number of steps may be predetermined, for example, by the number of commutations.

The stepper motor runs through the respective steps with a step time. The step times can be defined as time intervals from a start of execution of a step to a start of the execution of the next one Step. This time interval can also be given by a time which elapses, for example, between a start of supplying the energy supplied for carrying out the respective step and a start of supplying the energy supplied for carrying out the respective next step. The step times are, for example, commutation times.

A load device is usually a device that does work, such as a pump. Preferably, the pump is a fuel pump and / or a gerotor. A gerotor is a positive displacement pump having an inner and an outer rotor, the inner rotor having n teeth and the outer rotor having n + 1 teeth. The two rotors can each rotate toothed, wherein the inner rotor is mounted eccentrically to the outer rotor. Between the teeth of the inner and the outer rotor arise n different sized volumes due to the geometry of the gerotor. Due to the eccentrically mounted toothing of the inner and outer rotor, the volume between the teeth can respectively expand or contract during the rotation. Thus, by means of a resulting positive or negative pressure in the respective volumes, a liquid can be pumped.

The load device normally has torque fluctuations, also called torque ripple on. These can be predetermined by the design of the load device, for example, by an imbalance, by components or manufacturing tolerances. The torque ripple of the load device may interact with the torque ripple of the stepper motor so that common torque ripple may result.

The load device reaches after a certain number of revolutions of the stepping motor with a period recurring again an initial state. For the gerotor, for example, this may be the case after n × (n + 1) steps. Stepper motor and load device form a mechanical system. The initial state can be any well-defined state of this mechanical system. The one period may be defined as the time interval that begins at the time a particular state is entered and ends at the time this state is next taken. Normally, the same torque curve occurs in each such period when no correction is made. The load device can reach the initial state, for example, after each one revolution of the load device again, if the same torque curve occurs during each individual revolution of the load device. Also, the stepper motor, for example, have a construction-related number of m steps, which result in a mechanical rotation (360 °). For the exemplary overall mechanical system of stepper motor and gerotor, a number of m * n * (n + 1) steps in one period can then result in this example.

In each period, the stepping motor may undergo a certain number of revolutions each in a plurality of steps. In a period with N steps, N actual step times t ₁ , t ₂ ,..., T _i ,..., T _N can occur. For a multiplicity of steps of the stepping motor passing through in one of the periods, predetermined stepping times are predetermined. The desired step times t ₁ ', t ₂ ',..., T _i ',..., T _N ' can be specified for the N steps of a period, ideally a well-defined, preferably constant speed, and / or to achieve well-defined, preferably constant, torque. In a next process, the target step times t ₁ ', t ₂ ', ..., t _i ', ..., t _N ' in a period with the actual actual step times t ₁ , t ₂ , ... , t _i , ..., t _N are compared in this period. In the event of a deviation, a correction of the actual step times in a later period can optionally be brought about.

For this purpose, a multiplicity of actual actual step times, which occur in at least one of the periods, are determined which correspond to the respective desired step times. Let t ₁ , t ₂ , ..., t _i , ..., t _{N be} the actual actual step times measured in the at least one period and t ₁ ', t ₂ ', ..., t _i ', ..., t _N ' the predetermined target step times for this period, which has a plurality of N steps. Then the actual actual step times t _{i of} the respective steps i in one period and the predetermined set step times t _i 'of the respective step i in this period are considered to be corresponding.

In a period following those periods in which the plurality of N actual step times are determined, an energy supplied for executing the respective step i is reduced as long as 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 if the actual step time t _{i is} greater than the corresponding set step time t _i '.

The energy supplied for executing the respective step i is preferably adjusted by increasing or decreasing the energy supplied in step i itself. The energy supply in a step i, however, may also have effects on the execution of an adjacent step i-1 or i + 1. Due to a delay of the acceleration following the energy supply, the energy supplied for executing the respective step i can therefore also be supplied, for example, by an increase or decrease in the supplied energy Energy in an adjacent step i - 1 or i + 1 are adjusted.

Both speed and step time are typically dependent on the energy supplied to the stepper motor. Thus, the supplied energy can be reduced or increased, so as to achieve a correction of the actual step times. The reduction or increase in the energy supplied in each step i can in a later period, which follows the period in which the plurality of actual step times t ₁ , t ₂ , ..., t _i , ..., t _{N be} determined done. Preferably, the period in which the energy supplied to the stepper motor is increased or decreased in the respective step i directly follows the at least one of the periods in which the actual step time t _{i has been} determined. In the later period can, if appropriate, again the deviation .DELTA.t _i = t _i '- t _{i is} the actual step times t _1, t _2, ..., t _i, ..., _N t of the respective target step times t ₁ ', T ₂ ', ..., t _i ', ..., t _N ' are determined. This can be further reduced in an even later period. By adjusting the amount of power supplied over several periods, can thus ideally a convergence of the actual step times t _1, t _2, ..., t _i, ..., t _N and the corresponding target step times t ₁ ', t ₂ ', ..., t _i ', ..., t _N 'can be achieved. Thus, the predetermined, well-defined speed and / or the predetermined well-defined torque curve can be achieved.

Energy can be supplied to the stepping motor in the respective step, preferably by supplying an electric current with a determinable current intensity and / or voltage. The energy supplied to the stepping motor in the respective step is preferably reduced or increased by reducing or increasing the current intensity supplied to the stepping motor. Alternatively, for example, the voltage can be changed. In addition, the energy can also be supplied by a pulsed electric current. The actual step time is then preferably adjusted by reducing or increasing the pulse width of the pulsed electrical current.

The energy supplied for carrying out 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% are reduced if the actual step time is smaller than the corresponding desired step time, and / or increased, if the actual step time is greater than the corresponding desired step time.

Preferably, in addition to the regulation of the step times, a higher-level regulation of the rotational speed can be provided. This is advantageous, for example, when the correction of the individual step times t _1, t _2, ..., t _i, ..., t _N, in a period subsequent to that period in which the plurality of actual step times determined will result in an overall change in overall speed. For example, the total speed may be measured averaged over the duration of this later period. The regulation of the rotational speed preferably takes place in that an actual duration T of at least one of the periods is determined, a nominal duration T 'of this at least one period is predetermined, and the target step times t ₁ ', t ₂ ',... , t _i ', ..., t _N ' for this or a subsequent period be adapted so that the deviation .DELTA.T = T'-T the actual duration T is reduced by the target duration T '. The correction t _i '+ Δt _i ' of the desired step times t ₁ ', t ₂ ',..., T _i ',..., T _N ' can therefore be based on a deviation ΔT = T'-T of the actual Duration T is based on the target duration T '. For this purpose, for example, a base value of the target step time t _i `is corrected. This base value t <sub>i</sub> `is the value of the target step time from the at least one of the periods in which the actual duration of the period was determined. In a later period, the corrected value t _i '+ Δt _i ' can then be specified as the new setpoint 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 now preset. The correction Δt _i 'can be, for example, a relative correction Δt _i ' = ΔT / T * t _i ', which is proportional to the deviation ΔT.

Preferably, in determining the actual duration of the at least one period, the actual duration of at least one period, preferably at least three periods, more preferably at least five periods and / or at most twenty periods, preferably at most fifteen periods, especially preferably determined by at most ten periods.

The regulation of the energy supplied to the stepper motor can typically be done by a regulator. The controller can compare the setpoint step times, ie the reference variable, with the actual step times, ie the controlled variable, in an electrical control loop. From the difference, which can also be referred to as control deviation, the manipulated variable, ie preferably the supplied electrical energy, can be determined and adjusted accordingly. Preferably, the controller is a PI controller or a P controller.

For example, the PI controller is a standard linear controller with proportional and integral behavior, i. H. a superposition of a step response and a proportional response. For example, the P-controller has a characteristic step response.

In the following, the invention will be explained by way of example with reference to some figures without the To limit the invention to the embodiments shown there. The same reference numerals designate the same or corresponding features. The features described in the examples can also be combined between the examples and be realized independently of the specific example. Show it:

1 an exemplary stepper motor for driving a gerotor,

2 an exemplary course of the commutation time as a function of the rotation angle without correction,

3 an exemplary course of the commutation time as a function of the rotation angle with adaptation.

1 shows an example stepper motor for driving a gerotor. The gerotor has an inner ( 10 ) and an outer rotor ( 11 ), wherein the inner rotor n = 4 teeth ( 14 ) and the outer rotor has n + 1 = 5 teeth ( 14 ) Has. The two rotors ( 10 . 11 ) can each rotate toothed, with the inner rotor ( 10 ) eccentric to the outer rotor ( 11 ) is stored. Between the teeth ( 14 ) of the inner ( 10 ) and the outer rotor ( 11 ) arise due to the geometry of the gerotor n = 4 different sized volumes. Due to the interlocking of internal ( 10 ) and outer rotor ( 11 ), the volume between the teeth ( 14 ) each expand or contract on rotation. Thus, by means of a resulting positive or negative pressure in the respective volumes, a liquid can be pumped. The liquid is in the input ( 13 ) and then out of the exit ( 12 ). The gerotor rotates clockwise ( 15 ) and is in a round housing ( 16 ) that concentric with the axis of rotation of the inner rotor ( 10 ). In the case ( 16 ) are also holes for fixation.

2 shows an exemplary course ( 3 ) a step time, for example, a commutation ( 1 ), depending on a rotation angle ( 2 ) of a stepper motor. The history ( 3 ) the step time ( 1 ) as a function of the rotation angle ( 2 ) of the stepper motor shows slight fluctuations around the setpoint ( 4 ) on. After five turns ( 8th ) of the stepper motor, the load device has undergone a full cycle and returns to its initial state. In total, two full periods are shown, each five the setpoint ( 4 ) reaching maximums in the step time ( 1 ) and five each well below the setpoint ( 4 ) lying minima. These torque fluctuations are also called torque ripples ( 9 ). So there are a total of five torque ripple ( 9 ) on. Cause of the torque ripple ( 9 ) is, for example, an unbalance in the load device or the design of the stepper motor with multiple stator coils. The individual torque ripple ( 9 ) of the stepping motor and the load device couple to each other and thus give the five illustrated torque ripple ( 9 ).

3 shows an exemplary course ( 3 ) 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 course of commutation ( 1 ) in the first period is analogous to that in 2 structured. There are again five maxima and also five below the setpoint ( 4 ) located minima. However, there are now N = 9 control points ( 5 ), which may be, for example, individual steps of the stepping motor. The stepper motor goes through a plurality of steps each revolution. For a plurality of steps 1 to N = 9, setpoint values ( 4 ) t ₁ ', t ₂ ', ..., t _i ', ..., t ₉ ' or set step times. In addition, actual values of the step time ( 1 ) or commutation time t ₁ , t ₂ ,..., t ₉ , where t _{i is} the actually occurring actual step time or commutation time of step i. At the control points 1 to N = 9 now finds an adaptation ( 6 ) of the actual step times ( 1 ) or actual values of the commutation time t ₁ , t ₂ ,..., t ₉ to the setpoint values ( 4 ) or desired step times t ₁ ', t ₂ ', ..., t _i ', ..., t ₉ ' instead. In this case, the actual values t _i at the control point i are compared with the corresponding desired values t _i '. In accordance with the deviation Δt _i = t _i '- t _i , the commutation time ( 1 ) or actual step time are corrected. This process is preferably carried out by reducing or increasing the energy supplied during a commutation or a step i. If the actual step time or the actual value of the commutation time ( 1 ), for example, is less than the setpoint ( 4 ), the energy supplied can be reduced in a later period. If the actual step time or commutation time ( 1 ) is greater than the setpoint ( 4 ), the energy supplied can be increased. The energy supplied for executing the respective step i is preferably adjusted directly in step i. The energy supply in a step i, however, may also have effects on the execution of an adjacent step i-1 or i + 1. Due to a delay of the acceleration following the energy supply, the energy supplied for the execution of the respective step i can therefore alternatively be increased or reduced by increasing or decreasing the supplied energy in an adjacent step i-1 or i + 1. This correction of the supplied energy is preferably carried out in the period immediately following the measurement of the deviation. As a result, the second adapted period ( 7 ) significantly lower fluctuations in the actual step time or commutation time ( 1 ) around the setpoints ( 4 ) on. The torque ripple ( 9 ) are smoothed. The amount of energy supplied is preferably adjusted by varying the current intensity, the voltage or, in the case of a pulsed current, the pulse width, wherein the regulation is preferably effected by a PI regulator. In the adapted period ( 7 ), the actual actual duration of the period is preferably measured and adapted to a predetermined target duration. This can be done by changing the setpoints ( 4 ) or the predetermined target step times t ₁ ', t ₂ ', ..., t _i ', ..., t ₉ ' occur in a later period, wherein the change to the deviation of the actual duration of the target Duration of this period is based.

LIST OF REFERENCE NUMBERS

1

 Commutation time or actual step time

2

 Rotation angle of the stepper motor

3

 Course of the commutation time as a function of the rotation angle

4

 Setpoint or set step time

5

 Control points of the commutation time or steps

6

 Period with adaptation, d. H. Comparison actual step time / set step time

7

 Period with adapted commutation times or actual step times

8th

 Number of revolutions until the initial state is reached again

9

 torque ripple

10

 Inner rotor

11

 Outer rotor

12

Output of the pump

13

 Input of the pump

14

Teeth of the rotors

15

Direction of rotation in clockwise direction

16

 casing

Claims (12)

Method for driving a load device by a stepping motor, wherein the stepping motor passes through a plurality of steps in each revolution, the load device after a certain number ( 8th ) of revolutions of the stepping motor with a period recurring periodically reaches an output state, for a plurality of steps in one of the cycles of the stepping motor, target step times ( 4 ), a plurality of corresponding actual actual step times ( 1 ), which occur in at least one of the periods, 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 smaller than the corresponding target step time ( 4 ), and / or the energy supplied for carrying out the respective step is increased, if the actual step time ( 1 ) is greater than the corresponding target step time ( 4 ).  Method according to the preceding claim, wherein the load device is a pump, preferably a fuel pump, particularly preferably a gerotor.  Method according to one of the preceding claims, wherein the stepping motor is a DC motor, a synchronous motor and / or a reluctance stepping motor, a permanent magnet synchronous motor or a hybrid stepping motor. Method according to one of the preceding claims, wherein the energy supplied for carrying out the respective step by a percentage of at least 0.2%, preferably at least 0.5%, more preferably at least 0.8% and / or at most 5%, preferably at most 2 %, more 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 desired step time ( 4 ).  Method according to one of the preceding claims, wherein the energy supplied to the stepping motor is increased by increasing an electric current supplied to the stepping motor and / or a voltage supplied to the stepping motor and / or reducing the energy supplied to the stepping motor by applying a stepping motor supplied electric current and / or a voltage supplied to the stepper motor is reduced.  A method according to any one of the preceding claims, wherein the energy supplied to the stepping motor is supplied by means of a pulsed electric current, and the energy supplied to the stepping motor is increased by increasing a pulse width of the pulsed electric current and / or the energy supplied to the stepping motor thereby is reduced, that the pulse width of the pulsed electric current is reduced.  Method according to one of the preceding claims, wherein the energy supplied to the stepping motor is increased and / or reduced by means of at least one PI controller and / or at least one P controller. 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 ) are adjusted for this or a subsequent period so that the deviation of the actual duration from the target duration is reduced. 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, more preferably of at least five periods and / or of at most twenty periods, preferably from is determined at most fifteen periods, more preferably of at most ten periods, and preferably the periods used in determining the actual duration of the at least one period directly preceded by the time immediately determined at the time of determination period.  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 to an adjacent step, preferably in this step itself. A periodically operating device comprising a stepping motor and a load device, wherein the periodically operating device is arranged so that each step of the stepping motor passes through the stepping motor in a plurality of steps, after a certain number of ( 8th ) of revolutions of the stepping motor with a period recurring periodically an output state of the load device is reached again, for a plurality of in each of the periods traversed steps of the stepping motor target step times ( 4 ), a plurality of corresponding actual actual step times ( 1 ), which occur in at least one of the periods, are determinable, and in a period which follows 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 smaller than the corresponding target step time ( 4 ), and / or the energy supplied for carrying out the respective step can be increased if the actual step time ( 1 ) is greater than the corresponding target step time ( 4 ).  Device according to the preceding claim, wherein the device is a method according to one of claims 1 to 10 executable.

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