Method and circuit arrangement for operating stepper motors

Translation of description of equivalent WO 03105332 A1

Method and circuit arrangement for operating stepper motors

The invention relates to a method and a circuit arrangement for operating stepper motors, or other suitably dimensioned synchronous motors.

Stepper motors can be precisely controlled and known move position controlled. The rotational position of a magnet rotor follows a magnetic field that is generated by phase-shifted currents of a plurality of coils that are arranged around the rotor. If a stepper motor is used not only for the relative, but also to the absolute position of an object, it is necessary first to determine a reference position to which the absolute position can be obtained. A controlled absolute positioning is then possible as long as the control of the stepper motor acceleration takes into account his characteristic movement parameters such as angle of rotation, speed and loading.

For determining a reference position alternatives are essentially two known. These are, firstly, the mechanical zero, in which the motor against a mechanical, serving as a reference position limit or a stop is being driven, and on the other the reference electric drive, in which a sensor (for example, an electromechanical switch or a light barrier) when reaching a generates reference position, a corresponding signal.

Both alternatives have advantages and disadvantages. While the mechanical homing is expected noise and increased wear by the mechanical stress, is the realization of the electrical homing due to the sensors with higher costs, an increased constructive effort for the integration of sensors into a mechatronic system, as well as with additional associated cabling work, in particular in harsh environments also can be a problem, the reliability of the sensors themselves.

Furthermore, it should be noted that by specific operating conditions such as sudden load changes through obstacles o. Ä. During operation of a stepping motor may step or losses, the stepper motor may even stop, so that a new reference run is necessary. However, there are applications tions where a homing on the fly is not possible, so that in addition to the one-time determination of the reference position also monitoring the operating state of the stepping motor during operation - especially without any additional sensors - is desirable.

From EP 0182490 a method for controlling a rotation detector circuit arrangement is known, is determined by whether a driving pulse which is fed to a stepper motor causes the rotor rotates in the correct direction. The rotation detection is carried out substantially in that an element of high or low impedance is electrically connected to a winding of the motor upon actuation of a first and second switching means and that the first, second and third signals are fed in the first and second switching means to the element with the low impedance of the coil to separate, while the high impedance element is connected at the time of rotation detection by the winding.

From EP 1017159 a method for controlling a voltage / frequency converter controlled single or multi-phase electric motor is known, with a phase shift between an EMF voltage and a BEMF voltage other hand the difference between the zero crossing of the phase current determined and the voltage generated by self-induction and the frequency of the inverter is adjusted correspondingly. The measurement of the intrinsic induction takes place at the zero crossing of the current course of the associated phase, wherein during the measurement phase is separated from the supply network.

The invention is based on the general object of the invention to provide a method and a circuit arrangement for operating a stepping motor (or other suitably dimensioned synchronous motor), in a simple manner, an operating state of the engine can be monitored with the / key.

In particular, the invention provides a method and a circuit arrangement for operating a stepping motor (or other suitably sized synchronous motor) are created, identifier a Laster- with the / key in a simple manner and thus is also a determination of a reference position of the motor possible borrowed. This object is achieved according to claim 1 comprising a method of operating a stepping motor in a first mode for normal motor operation in which an alternating current is impressed into at least one of the coils of the stepping motor, and in a second mode for detecting an operating or Lastzu - state of the motor based on the level of a current flowing in the shorted coil measuring current generated by a counter-induced by a rotor of the motor in the coil voltage substantially, wherein the second operating mode is activated for the coil within a time window of the first mode when the embossed into the coil concerned AC approximates to a zero crossing.

The object is further according to claim 6 achieved by a circuit arrangement for operating a stepping motor, in particular by a method according to the invention, which has a means provided to detect an operating and load condition of the engine based on the level of a current flowing in a short-circuited coil measuring current is generated by a counter-induced by a rotor of the motor in the coil voltage substantially when the impressed alternating current in the coil in question is approaching a zero crossing.

A general advantage of these solutions is that no sensors are required, and a relatively simple and low-cost implementation is possible, especially when the motor is driven by pulse width modulation (PWM) of a voltage which an appropriate current to the motor coil (coil current) imprints, as allow the evaluation of the measuring current (short circuit current) components required in a PWM circuit are already largely in place.

Another advantage of this solution is that the beginning of the measuring current (current lobe) due to the control of the coil current (target current) by the PWM voltage is highly reproducible and largely independent of the magnitude of this voltage. This results in an at least extensive independency of component tolerances.

Furthermore, it has been found that at least largely linear relationship between the level of the measuring current and confiscated by a mechanical load capacity is. This means in particular that the measuring current so becomes smaller the higher the mechanical load on the engine.

The background is the fact that with an increasing engine load, and thus increasing load angle (angle between the rotor and the main direction of the generated by the coil magnetic field) the phase shift between the impressed into the coil inductor current and the counter induced by the rotor voltage is less (and in the engine is zero).

Since the mechanical power of the motor at a constant speed proportionally to the engine power or engine torque is, represents the height of the measuring current (current lobe) at a constant speed directly the amount of torque of the engine load and together with the torque characteristics of the engine in question indirectly the load angle represent.

In particular, a Referenzpositi- on the engine can be detected without sensors by driving the motor against a mechanical stop and the resultant change in operating or load condition. The problems associated with a conventional sensorless determination of a reference position disadvantages as mechanical wear and noise do not occur or occur only to a considerably lesser extent in appearance.

An advantage of the above-mentioned almost direct load or torque measurement means of the (mechanical) reference run is that this is largely independent of the modulus of elasticity of the mechanical stop.

The dependent claims relate to advantageous developments of the invention to the content.

Further details, features and advantages of the invention will become apparent from the following description gen a preferred embodiment with reference to the drawings: FIG.

FIG. 1 is a schematic diagram of a first circuit of the invention; 2 shows a first diagram of the voltage and current curves in the region of a zero crossing of the coil current.

Fig. 3 shows a second diagram of the voltage and current waveforms in the field a zero crossing of the coil current; 4 shows a third diagram of the voltage and current curves in the region of a zero crossing of the coil current. and Fig. 5 is a schematic diagram of a second inventive circuit arrangement.

Figure 1 shows a block diagram of a circuitry with a switch S between a first mode for normal engine operation (switch position 1) and a second mode for detecting an operating state and in particular a reference position of the motor (switch position 0) can be switched, by measuring a mechanical change in load when driving the stepper motor is determined against a mechanical stop.

The stepping motor itself is shown only in the form of one of its coils L with a serial internal resistance RL, wherein a plurality of these coils is arranged in a known way a circle around a magnetic rotor. Alternatively, it may be a linear stepper motor, however, also.

Parallel to the coil L (or mutually associated coil groups), a voltage source for generating a supply voltage (PWM voltage) is respectively connected with that in the first mode, a particular target current (coil current) II in the relevant ^) coil (s) L is impressed. In series with each coil L is a further measuring resistor Rs, on which a measurement voltage U_$ in response to a current actually flowing through the coil L (measurement) drops stream.

Ideally, such a step motor driver operates at a sufficiently high supply voltage as a quasi ideal current source, provided that the current reduction is not only passively ( "Slow Decay"), but active ( "Fast Decay") takes place.

The circuit arrangement furthermore comprises a measuring circuit M to the input of the measurement voltage applied U§ and a comparator K for comparing the measurement voltage U_$ with a reference voltage UR which, as well as a digital / analog converter DAC for generating the comparison voltage supplied from one of the measuring circuit M digital signal. The reference voltage U_R may be supplied in other ways, or in analog form. Furthermore, a control circuit C is provided, which generates the digital signal to the digital / analog converter DAC, and fed to the output signal of the comparator K. The control circuit C can be controlled via an interface I to 0 and 1 switch the switch S between its two switch positions depending on the output of the comparator K or to provide this output to a further processing.

The measuring circuit M and the control circuit C, in the case of a pulse width modulation (PWM) controlled coil current II generally already present, so that the circuit of the invention can be implemented inexpensively and with relatively little additional expense.

In normal engine operation (first mode), the coil L are phase shifted with alternating currents fed that in a known manner a progressive magnetic field is created, which the magnetic rotor follows stepwise or quasi-continuously in micro movements in the switch is No.1.

To impress a defined target current II in the coil L (coil current), may at the measuring resistance R_$ are falling measurement voltage Us evaluated and used in a known manner for controlling the supply voltage UM-generating power source.

By the movement of the rotor and the thus caused changes in magnetic flux, an electrical voltage UE K (counter) is induced in the coil L, which counteracts the supply voltage, and in terms of their course largely on the speed of the rotor and its instantaneous position relative to the coil depends. In the diagram of Figure 1, this voltage is represented by a series-connected to the coil L voltage source, the voltage U_EMκ generated.

With no mechanical load (that is, at a load angle of substantially 0 ° and an idealized internal resistance RL of the coil of 0 ohms), the voltage U across the terminals of the coil L from the impressed coil current I by 90 ° out of phase (ie, at a wattage of Zero). The average over a period electric power is then equal to zero. With increasing load angle this phase shift decreases between the voltage UL and the coil lenstrom II- At maximum load angle (that is, just before a step loss), the phase shift ultimately substantially zero, and the power is maximum.

In a mechanically unloaded stepping motor which is fed with sinusoidal and cosinusförmi- gene coil currents I a constant frequency, the induced voltages against UEMK i^m Ideally, also sinusoidal and cosinusformig and opposite the coil currents II moved to the respective coils L by 90 ° in phase. Phase shifts of constant kind and other courses of voltages UEMK but can by the design of the engine and caused particular the geometric shape of the rotor and stator and their magnetization.

Further occur by a non-zero load angle (angle between the rotor and the main direction of the magnetic field) supply decreased phase shifts between the voltage and the coil current UEMK II particularly in a mechanical load on the motor.

When the stepping motor is mechanically loaded beyond a limit, so it has the ability to jump to one or more integer multiples of the current period (four full steps in a 2-phase stepper motor) and thus lose steps. It occurs between the coil current II and the counter induced voltage U MK also a phase shift, which also shows the voltage UEMK due to the jumps significantly change. The phase of the GE geninduzierten voltage UEMK thus essentially represents the rotor position.

The time course of the target current II through the coil L is not necessarily sinusoidal and cosinusformig. Depending on the type of the stepping motor can be achieved with bear pez- or triangular Bestromungsmustem or mixed forms, a better operation behavior.

In a second mode the counter induced voltage UEMK however is nevertheless suitable for determining the above-mentioned movement and load states of the stepper motor, ie its operating state, and therefore also for the detection of a mechanical stop for example at a Set reference tion, since the height of the voltage UEMK ^U.Nd, the phase position is dependent not only on the speed of the rotor in particular by the load angle of the rotor and thus the load state of the engine to the coil current II.

Specifically, the amplitude of the induced voltage against UEMK is proportional to the speed of the rotor. The phase of this voltage UEMK relative to the impressed coil current II is essentially determined by the mechanical load. With a maximum load, this phase shift substantially reduced to 0. This is clear from the figures 2 to 4 and is explained in detail later.

The voltage U MK could be measured in a non-energized coil L directly on the terminals of the coil. However, because such a coil L does not contribute to the torque of the engine, this type of detection is not desirable worth seeing. Also a quick change between energized and not bestrom- tem state is not desirable due to the occurring, relatively high induction voltages.

According to the invention, therefore, the counter induced voltage UEMK is determined in the second mode by disconnecting the coil of the supply voltage U and short-circuiting the coil, in each case periodically within such a time windows in which the impressed into the respective coil L II is relatively low, the ie shortly before and after the change of polarity of this current or this einprägenden supply voltage U -

For this purpose, the switch S is switched into the switch position 0th

The beginning of the time window does not need this to be determined by monitoring the input voltage Us and compared with a reference voltage. Rather is the beginning and the length of the time window through the known and fixed course, the supply voltage U or the course of the impressed into the coil current I concerned_L given, so that the control circuit C can be driven for switching the switch S directly via the interface I accordingly.

The induced voltage against UEMK drives in the characterized shorted coil directing rice now a measuring current IS.EMK (current lobe) which generates at the measuring resistance R§ a corresponding voltage drop US.EMK.

This voltage U_SEMK is again evaluated with the measuring circuit M to determine the operating condition of the engine and determine whether the engine is running under a more or less high mechanical load or even against a mechanical stop to it if necessary disable for avoiding wear immediately.

For this purpose, the voltage US₍EMK ^m the comparator K with different threshold values ​​Uso_, Usu compared to that determined in dependence on the rotational speed of the engine and are referred to as digital values ​​via the interface I and the control circuit C to the digital / analog converter DAG (or also analog), respectively.

This evaluation will be explained with reference to the diagrams of Figures 2 to 4. FIG. Here, the vertical axis denotes the magnitude of the current or the voltage, while the horizontal axis represents the period is plotted.

The around the time window Z (UM = 0) flowing through the coil L coil current II is respectively represented by a solid line. This coil current II is within the time window Z in which the coil circuit is short-circuited by switching the switch S in the switch position 0, zero. Instead, flows within the time window Z essentially by the counter induced voltage U_eMK induced measuring current IS, EMK (shown in dashed lines, current lobe), through to the sensing resistor Rs, a measuring voltage US₍EMK.

Furthermore, in these diagrams with a dashed line, the course of the counter induced voltage UEMK entered.

Figure 2 shows the trend of these currents and voltages for a substantially unloaded state, that is, at a minimum load angle, while the gradients at a medium load and a medium load angle are shown in FIG. 3 Figure 4 shows the courses of the currents and voltages at a maximum load and a maximum load angle.

As already explained, decreases with increasing load, the phase- shift between the coil current and II - during the second mode - between the measuring current IS_,EMK through the coil L and the counter induced voltage UEMK-

For completeness, it should be mentioned that as generally known the counter induced voltage UEMK opposite phase to the supply voltage UM in polarity.

The amount of current flowing during the time window Z measuring current IS, EMK (Stromzip- fei) and thus the height of the measurement voltage generated by this during the time window Z US, EMK is ^from the rotational speed and the load caused by a load angle of the motor dependent and thus also represents the effective power.

A load change leads to a phase shift of the counter induced voltage UEMK ud thus to a change in the by this into the coil circuit current. This change, in turn, a change of the current flowing during the time window Z measuring current IS, EMK (current lobe) which, by evaluating the measuring voltage US_.EMF is detected.

Thus, by comparing the measured voltages US, EMK ⁿ consecutive time windows are detected Z is a change in the load of the engine. In particular, it is possible to detect when driving against a mechanical stop occurring load changes and fixed down in this way, a reference position or define.

Load changes are preferably detected by a comparison of the measurement voltage U, electromotive force within the time window Z with threshold values ​​which are set in dependence on the speed of the motor.

For example, according to the figures 2 to 4, an upper and a lower threshold value U_so, Usu for measuring voltage US, EMK ^SO stipulates that at a certain speed and relatively low load of the engine the measuring voltage US.EMK is greater than the upper threshold value Uso while under at a mechanical load increase caused by driving against a mechanical stop the measuring voltage US, EMK the lower threshold value Usu lies. Figure 2 shows the case in which a measurement current IS, EMK flows within the time window by the Z coil, through which a measuring voltage U_,EMF is generated which corresponds to the upper threshold value Uso.

According to FIG 3 a measuring current IS, EMK flows through the coil, through which a measuring voltage US.EMK drops, corresponding to the lower threshold value Usu.

According to Figure 4, the load finally is so large that the measuring current IS.EMK and thus also the voltage drop US_;Emf is substantially zero.

With the measuring circuit of Figure 1 therefore the measuring voltage US, EMK is within a time window Z with the two threshold values ​​Uso_, Usu compared with the measured voltage value present at an input of the comparator K and each represents a threshold at the other input of the comparator K. The thresholds Uso_, Usu are fed via the interface I and the control circuit C to the digital / analog converter DAC.

If the measured voltage US, EMK is smaller than the lower threshold value Usu_,^so a signal is generated by the control unit C and the interface I, with the reaching of a reference position is displayed at a mechanical stop.

If the measured voltage US_;Emf between the two thresholds Uso_, Us is so can in a corresponding manner a signal can be generated with an increased engine load is displayed.

Finally, when the measuring voltage US_,EMF is greater than the upper threshold value Uso_,^so k^ann a signal can be generated, is displayed with the that the engine runs at relatively low load.

For the realization of the invention is to demand as constraints that the internal resistance RL of the respective coils L is of the order of the measuring resistor Rs, so that the measured voltage US.EMK when measuring the load sufficiently large, that is in the field of measuring voltage Us is in normal operation. If a switchable measuring resistor Rs is provided the solution according to the invention can also be applied to high-impedance motors. In contrast, when R ' Rs is, the measuring circuit M should have a sufficiently high gain.

Particular advantages of the invention consist in that the signal voltage US, EMK is independent of the supply voltage UM, as it is recorded during a time window, in which the supply voltage (PWM) is not applied. The resulting from short-circuiting the coil circuit current loop is low, so that the measuring spam ung US.EMK is relatively insensitive to interference. In addition, the measurement resistor Rs causes a current limitation for short-circuited coil circuit.

Due to the regulation of the coil current I during the first mode (normal operation) of the measuring current IS, EMK (current lobe) are created particularly well reproducible conditions during the second mode for measuring the level. In contrast, when the stepping motor can be operated at a voltage source the would, so the level of the current lobe of the magnitude of the supply voltage would be dependent, which would be taken into account.

Figure 5 shows a schematic diagram of a second circuit of the invention, are provided in the same or corresponding components as in Figure 1 with the same designations.

In contrast to the embodiment according to Figure 1 can here the PWM supply voltage UM via a first and a second switch Sl, S2, which are switched by the control circuit C, be reversed. The second mode, during which the measuring current generated by the counter induced voltage UEMK IS_;EMF is detected and evaluated according to the above explanation, will be, that is immediately after the switching of the two switches Sl, S2 is activated in this case, immediately after the polarity reversal of the PWM supply voltage, before the measurement current may not be position controlled (Slow Decay Mode ).

Furthermore, as indicated in this embodiment that led to the comparator measuring voltage need not necessarily be generated by a voltage drop by means of a resistor Rs. Rather, also the Hall sensors, power divider in MOSFET switches or other elements, optionally at other locations of the circuit arrangement is used, with which a signal proportional to the measurement current through the coil L signal is generated which corresponding to the can be compared thresholds.

As already explained, can be detected with the illustrated circuit arrangements not only a mechanical stop, but also a load and optionally a suddenly occurring obstacle, so that a monitoring of the driving operation of the motor is possible. Also, a load angle measurement is possible in principle.

Unlike many known ways to stop detection, it is not necessary here that the engine returns.

The short-circuited in the region of the zero crossing of the supply voltage and the impressed coil current coil circuit also possible resonance vibrations (comparable with the principle of the eddy current brake) attenuates described.

The phase shift and the amplitude reduction of periodic coil current II are very sensitive to a change in load, at the same time, however, both variables are very insensitive to other disturbances which are not so related, such as the exposure of electrical energy. This provides a very accurate detection and low load changes is possible. Moreover, smoothes the coil in the coil circuit of any electrical noise, so that their influence is further reduced.

The measuring conditions are very well defined within the time window Z, is highly reproducible. The current flowing during the time window Z current IS, EMK is only dependent on the rotational speed of the motor, the load angle and motor constants, but no, or only very slightly dependent on parameters that drift or vary due to manufacturing tolerances.

Finally, it should be noted that the inventive method and the inventive circuit arrangement is also suitable for use with other synchronous motors, provided that they are dimensioned so that at least one of the coil circuits may be short-circuited.