HK1258799B - Method for detecting a blockage of electrically commutated electric motors - Google Patents

Description

The invention relates to a method for detecting a signal of possible blocking for electrically switched electric motors of various types and number of turns and in particular for unipolar and bipolar stepper motors and for three-phase stepper motors.

The positioning of stepper motor systems is known by various means, depending on the state of the art, for example by means of absolute position sensors, which can directly detect the position of the powered component.

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The characteristic of stepper motors, which perform discrete steps, i.e. angular increments, makes it possible to determine position simply by monitoring the number of steps taken from a spatially defined starting point by means of an electronic counter, i.e. counting.

These two conditions can be controlled by external sensors, such as terminal switches and encoder discs, which is however expensive and expensive. Alternatively, sensorless steps detection methods are known, in which the feed flow or feed voltage is analyzed during the flow of the motor windings.

A method and device for sensorless motion detection of a multiphase stepper motor is known, for example, from the DE 40 35 970 A1. It evaluates the voltages of two phases, i.e. the voltages attached to the motor windings, by means of a microcomputer. In particular, in the event of a blockage, voltage breaks occur at the phase voltages that are recorded. Although the method is supposed to be insensitive to high frequency disturbances, it has a number of other disadvantages: motion detection is only possible on multiphase, unipolar stepper motors and not on bipolar stepper motors.

EP-A-0 462 050 also describes a method and circuit for detecting the failure of a stepper motor. The current flowing through the motor windings is taken and evaluated at a shunt resistor. Similarly to the above printed document, the problems arising from the use of the shunt resistor have been solved. Another difficulty is that current measurements under certain operating conditions, for example voltage fluctuations, as are often found in on-board networks of motor vehicles, are relatively error-prone, which can only be compensated by costly interference and stabilisation measures.

EP-A-0402 220 and EP-A-0574 339 describe other steps detection methods for stepper motors, but these also have the shortcomings mentioned above.

It is known from DE-C-38 36 240 and US-B-6 285 156 that, in order to estimate the angle of rotor position, a sampling impulse is applied to each unexcited wind which causes a change in current in the unexcited phases.

However, the application of the latter method is limited to multiphase Reluctance engines and provides only an approximate estimate.

DE-C-196 53 460 is a method for the sensorless step detection of step motors by analysis of the motor current, whereby the various motor winding connections are switched on at high voltage during operation and the duration of the response signals at the high voltage motor winding connections is evaluated to determine whether the step motor has moved by one step.

EP-A-1460757 describes a bi-polar stepper motor with a velocity sensor by means of bi-polar control.

Finally, US-A-2006/0049791 and US-A-2008/0224639 provide information on the methods of switching and operating stepper motors.

The purpose of the invention is to specify a method for detecting blocks in electrically switched electric motors which can be used in all types or configurations of electrically switched motors mentioned above.

To solve this problem, a method is proposed for detecting an indication of a blockage in a 3-phase stepper motor by analysis of the motor current, which has the steps described in claim 1, according to the invention.

The invention is particularly apparent in the fact that the flow diagram and signal detection are adapted to the stepper motor types proposed herein, which makes it possible to use the block detection method according to the invention on a 3-phase stepper motor with other flow forms than those described in DE 196 53 460 C2 and US-B-6 285 156.

The invention provides that, in the event of alternating variations in the lengths of time intervals by more than one predictable difference, a first indication of a possible blockage is detected.

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In addition, the various embodiments of the invention provide for one or more of the following characteristics: (a) Types of engine The following shall be considered: the implementation for x-phase, in particular 2-phase unipolar stepper motors forCommon node = negative supply,Common node = positive supply,Common node of one pair of coils at negative supply of the other pair of coils at positive supply, Other (This allows the same control circuit to be used for unipolar and bipolar motors, and this type of control can be done without block detection for all current types) for single-strand block current with and without PWM, for two-strand block current with and without PWM,half-step method with and without PWM,microstepping with PWM (sinus, trapezoid, other curve shapes),microstepping with PWM with torque and/or speed control),Other Successful. the implementation for x-phase, in particular 3-phase motors inStern circuits,Triangle circuits (with and without virtual star point),all current types with:block commutation,PWM micro stepping (sinus, trapezoid, other curve shapes),PWM micro stepping (especially for spatial vector modulation),PWM micro stepping with torque and/or speed control independent of the type of modulation (s.a.), (b) reference training (b.1) the supply (positive, negative, GND) or other reference voltages serve as a comparator reference potential (e) or as a basis for the formation of reference potentials,optionally measurement and reference potentials are subdivided,b.2) Optionally, voltage losses are detected via drivers by capacitive coupling and optionally, a capacitive voltage distribution is used;b.3) - the reference potential is x times the supply potential,b.4) in particular in the form that x is essentially chosen to be 2,b.5) in particular in the form,that a positive or negative offset is added to the base reference,b.6) - the reference formation in operation is dynamically switched depending on environmental parameters (such as operating voltage, temperature, engine situation); c.1) - optional preamplification of the signal (usually analogue); (d) the pre-amplifier is designed in analogue technology or the pre-amplifier is designed in SC technology; d.1) - the comparator is designed in analogue technology orerd.2) - the comparator is designed in SC technology,d.3) - the preamplification and comparator are realized in a common SC technology,d.4) - the comparator is formed by means of a single transistor against a base load, whereby the voltage failure is accepted by the transistor threshold voltage, in particular by using existing,For the purpose of this Regulation, the following definitions shall apply: e.1) - the measuring signal is clamped at this threshold when the reference is reached,e.2) - the measuring signal is not clamped when the reference is reached,e.3) - the type of clamping function in operation is also dynamically switchable,e.4) the voltage limitation (clamping) is achieved by one or more diodes and/or other semiconductors,e.5) - the voltage limitation is achieved in such a way that a voltage defect is first applied to the components described in d) above, which then activates a power supply that carries a large part of the current load,e.6) - the power driver for clamping is a driver existing for the motor control,e.7) - the power driver is specifically implemented for this purpose,e.8) - the power driver is a component present to protect the assembly (e.g. ESD protection transistor),e.9) - the current flow is monitored by these components,e.10) - only the current flow is monitored at one of these components,e.11) - for monitoring the voltage at one or more components an additional load (current source or resistor) is attached to these components, which ensures a defined signal level in case of variation (voltage limitation not active);) with time group (time-meter): f.1) - the length of the comparator signal is determined by a time counter,f.2) - the counter is run in logic gates,f.3) - a TMU (Time Measurement Unit) is used for the calculation,f.4) - a controller/processor directly performs the time counting,f.5) - the counter works logarithmically, i.e. counts more slowly with increasing counting time (to significantly reduce the size of the counter and simplify subsequent evaluation),f.6) - the logarithm is performed in rough steps (adapted to the application) and thus controlled error tolerance may be low to keep production costs as low as possible,g) variant with a time counter (construction group: evaluation and filter) g.1) - a logic that evaluates and/or filters time counts,g.2) - a controller/processor that evaluates and/or filters time counts,g.3) - evaluation and/or filtering is done by software,g.4) - the software can be reprogrammed in the system (e.g. by FLASH),(h) Direct conversion by ADC h.1) - the voltages without a comparator are digitised by means of an ADC with or without pre-amplification,h.2) - the ADC is evaluated by a logic,h.3) - the ADC is evaluated by a controller or processor,h.4) - the evaluation is done by software,h.5) - the software can be reprogrammed (e.g. by FLASH) to allow adaptation to different engine types,i) determination of the engine load The following shall be applied: - the time of the turbulence phase as shown can be used not only to analyse the engine's locking but also to determine the current load on the engine38), - the knowledge of the load is used to adjust the engine's flow to the required level by PM control (to reduce:(i.2) - knowledge of the load is used to achieve maximum torque and maximum dynamics when the engine is accelerated and brake;i.3) - knowledge of the load is used to reduce the engine torque in specific and appropriate operating situations;i.4) - knowledge of the load is used to compensate for the dependence of the engine torque on the supply voltage;i.5) - knowledge of the load is used to compensate for the dependence of the engine torque on the temperature.

A further advantageous design of the invention provides for filtering the results of the evaluation of the lengths of the time intervals for suppression of the influence of disturbances.

A further advantage of the invention is that the current rotational position of the stepper motor or its anchor is determined at the time of the locking detection and/or that the flow of the stepper motor is stopped at a locking detection to reduce noise formation and/or minimize mechanical overload on the stepper motor, a gearbox and/or other components connected to it.

A further advantageous design of the invention provides that the transition from the flow of a motor winding to the flow of the counter-motor winding is not simultaneous but is carried out with a predefined timing, in particular in the case of PWM sine/trapezoid etc. commutation with a predefined timing related to the zero-pass, and that, in particular, at a certain time before the zero-pass, the remaining current deviating from the curve shape characteristic of the flow variant is interrupted and the motor winding connection is connected in a high-speed manner (similar to Fig. 5).

The advantageous development of the invention is that, for the purpose of detecting the response signals, a peak detector determines the peak of the response signal and compares the peak signal with a threshold that is independent of and in particular in a certain ratio to the peak voltage of the peak detector.

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The advantageous development of the invention is that the threshold and, especially in the case of unipolar stepper motors, the clamp characteristic in operation, are dynamically switched to capture the response signals, independent of parameters (such as operating voltage, temperature and engine situation).

A further advantageous design of the invention provides that, in order to save costs, the determination of the duration of time intervals is performed by means of a logarithmic and therefore shorter counter, whereby subsequent mathematical operations can be performed in a cost-saving linear calculus (plus/minus calculus) instead of in point calculus (multiplication/division).

The advantageous development of the invention is that the response signal is recorded by an ADC, whereby the threshold-setting, response-duration, differential-setting and filtering functions can be performed in whole or in part by logic or by software controller.

A further advantageous design of the invention provides that, when deviations first occur, the instantaneous position values (in steps or angles or the like) are stored in between (Fig. 4), that, when a block or other load condition is detected later, this intermediate value is used to compensate for or minimize the position error caused by the filter response delay (Fig. 4), that, when a block or other block condition is detected later, a fixed or variable correction value is optionally added to or subtracted from the intermediate non-stored position value in order to minimize remaining errors in the process and to eliminate the residual value of the delayed position when the block is detected.

The advantageous development of the invention is that the measurement of the duration of the time intervals, depending on the operating condition, starts either with the start of the high-frequency circuit or with the detection of the start of the time interval.

A further advantageous aspect of the invention is that it is characterized by: Avoidance of high-output switching of a winding connection,Monitoring of the polarity of the voltage drop (similar to Fig. 7) via the switch and determining the time of change of polarity,Determining the duration of the difference time interval by determining the time difference between the motor commutations and the times of change of polarity and evaluating as described in the claims above.

The invention is explained in more detail below by means of several examples of execution and by reference to the drawing, which show in detail: Figures 1 to 3 - Schematic representations and signal paths to explain the process of detection of blocks in a unipolar stepper motor (no example of the invention),Figures 4 - Schematic representation of the (response) signal path which can be used to detect a blockage regardless of the type of motor,Figures 5 and 6 - Schematic representations and signal paths to explain the process of detection of blocks in a 3-phase stepper motor as an example of the invention,Figures 7 - Schematic representations and signal paths to explain the process of detection of blocks in a bipolar stepper motor (no example of the invention).

Description of a variant not in conformity with the invention when used for a unipolar motor: Other In order to detect a blockage of a unipolar motor, the winding current is monitored in the commutation phase according to the invention.

Figure 1 shows that a low-side switch of a winding pair (in this case with centre-inlet) of a unipolar motor drives a current from one supply voltage connection 1 (in this case VBAT) to the other supply voltage connection 2 (in this case GND) through the winding.

The evaluation phase of the process begins in the second time period (see Figure 2) when the switch or transistor which switches the winding connection to supply voltage connection 2 (in this case GND) is switched off.

In this phase, the winding current remains constant due to the inductivity of the motor winding. As a result, the voltage at the winding connection (here OUT) jumps not only to the potential of the supply voltage connection 1 (here VBAT), but beyond. The final value of the winding connection voltage (here OUT) depends on the amount of currents previously flowed through the winding and the rotation of the motor, but is additionally limited by other conditions of the system, e.g. clamping condition by optional ten-diode.

Since the voltage drop over the inductance or over the motor winding is the reverse sign, when the second time interval is reached, the winding current begins to decrease.

Once the winding current has disappeared (0 amperes), this causes the voltage at OUT to move towards supply voltage connection 1 (here, for example, VBAT).

This condition is detected by observing the voltage at OUT and recording the time for which the voltage at OUT is equal to or at least equal to a reference voltage, usually about 2* the voltage at supply voltage connection 1.

The accuracy of the threshold is relatively insignificant, but should not be too far below 2* VBAT or 2* of the voltage at supply connection 1 as this is below the feedback voltages of the open winding connection due to the generating effect of the motors.

If the threshold is within this range, the generative effect would overlap the detection of I=0A and therefore the procedure would be rather uncertain.

A free-running, i.e. unlocked motor produces comparatively constant values for the time periods for which the voltage at OUT is equal to or at least equal to a reference voltage, usually 2 times the voltage at supply voltage connection 1.

Thresholds, duration measurements and evaluations can be performed with comparators plus digital technology including microcontrollers and software, but it is equally possible to record the voltages of the winding connections with an ADC and to perform thresholds, duration measurements and evaluations with digital technology and/or microcontrollers and software.

Figure 5 shows the schematic signal paths when the invention is applied to a 3-phase stepper motor.

Finally, the signal paths in Fig. 7 represent the non-inventional application of the process in a bipolar stepper motor.

Claims (12)

1. A method for detecting an indication of a possible blockage of a three-phase stepper motor by analyzing the motor current supply, comprising the following method steps:

   - impressing an operating current according to a current supply variant for the operation of the three-phase stepper motor into the one or more motor windings thereof which are either in star connection or in delta connection with virtual star point or without virtual star point by means of one switch half-bridge circuit per motor winding terminal, wherein the switch half-bridge circuit connects the motor winding terminal alternately to one of two supply voltage terminals of the motor winding,

   - commutating the motor windings by means of pulse width modulation of a sinusoidal or trapezoidal waveform of the operating current course,

   - wherein the current supply variant is modified such that shortly before a zero crossing of the current, i.e. with a residual current still remaining, at a motor winding terminal the latter is switched to high impedance for a specific period of time, but at least until the end of the time interval mentioned below,

   - detecting the voltage at a motor winding terminal switched to high impedance at least for the high-impedance time period and comparing said voltage to a threshold that is near the magnitude of the voltage at the one or the other of the two supply voltage terminals depending on the polarity of the voltage,

   - detecting the time period from when the motor winding terminal is switched to high impedance until the residual current is reduced to zero, by detecting the time interval for which the voltage at the motor winding terminal switched to high impedance crosses the threshold value,

   - comparing the length of the intervals for a plurality of motor winding terminals each switched to high impedance, and

   - detecting a possible blockage based on the comparisons of the lengths of the intervals by detecting alternating variations of the lengths of the time intervals by more than a predeterminable difference as an indication for a possible blockage.
2. The method according to claim 1, characterized in that the results of the evaluation of the lengths of the time intervals are filtered to suppress the influence of interferences.
3. The method according to claim 1 or 2, characterized in that the present rotational position of the stepper motor and the armature thereof, respectively, is determined at the point of time when the blockage is detected, and/or that the current supply of the stepper motor is stopped when a blockage is detected to reduce generation of noise and/or to minimize a mechanical overload of the stepper motor, a gearbox operatively connected to said motor and/or other components.
4. The method according to any one of claims 1 to 3, characterized in that for detecting the response signals a peak detector determines the peak of the response signal and the comparison for determining the end of the response signal is carried out using a threshold which depends on the peak voltage of the peak detector and in particular shows a specific division ratio to said voltage.
5. The method according to any one of claims 1 to 4, characterized in that for detection of the response signals the threshold and, in particular in unipolar stepper motors, the clamping characteristic during operation, if necessary, is/are connected such that it/they is/are adapted to be dynamically switched depending on operating parameters.
6. The method according to claim 5, characterized in that the operating parameters are the operating voltage, the temperature and the motor situation.
7. The method according to any one of claims 1 to 6, characterized in that for the purpose of cost-saving implementation the determination of the duration of the time intervals is carried out by means of a logarithmic and thus shorter counter, wherein the subsequent mathematical operations can be carried out via cost-saving addition/subtraction, i.e. plus and/or minus calculation, instead of multiplied by/divided by calculation, i.e. multiplication and/or division.
8. The method according to any one of claims 1 to 7, characterized in that the detection of the response signal is carried out by an ADC, wherein the tasks of threshold value generation as well as the determination of the duration of the response signal, the difference generations as well as filter functions can be fully or partly carried out through a logic and/or with the aid of a controller through a software.
9. The method according to any one of claims 1 to 8, characterized in

   - that, when deviations occur for the first time, the momentary position values are buffered,

   - that during later detection of a blockage or another load condition this buffered value is used to compensate for or to minimize the position error caused by the response delay of the filter,

   - that during later detection of a blockage or another load condition optionally a fixed or a variable correction value is added to the buffered momentary position value or subtracted from said value to minimize remaining residual errors of the process, and

   - that during later non-detection of a blockage the buffered values are discarded.
10. The method according to any one of claims 1 to 9, characterized in that the measurement of the duration of the time intervals starts either at the beginning of switching to high impedance or at the time of detection of the beginning of the time interval, depending on the operating condition.
11. The method according to any one of claims 1 to 10, characterized by

    - omission of switching to high impedance of a winding terminal,

    - monitoring of the polarity of the voltage drop across the switches and determination of the point of time of the polarity reversal,

    - determination of the duration of the difference time interval by determining the time difference between the motor commutations and the points of time of the polarity reversal, and

    - evaluation as described in the claims above.
12. Use of the method according to any one of the preceding claims for time optimizing of initialization processes of the stepper motor or a unit provided with said stepper motor, comprising turning the stepper motor shaft or an actuator operatively connected to said motor against a limit stop, and/or for using the detected time intervals for influencing the stepper motor control, in particular with regard to motor speed and/or torque.