DE102006020058A1 - Electrical stepper motor e.g. two-phase-claw pole-stepper motor, operating method for motor vehicle, involves activating determination of blocking condition only after free run of stepper motor for predetermined period is sensed in advance - Google Patents

Abstract

The method involves supplying a control signal to an electrical stepper motor. A blocking condition of the stepper motor is determined during supplying of the stepper motor with the control signal. The determination of the blocking condition is activated only after a free run of the stepper motor for a predetermined period is sensed in advance. The stepper motor is controlled in a half-stepping operation, where the stepper motor has two coils that are electrically separated from each other. Independent claims are also included for the following: (1) a control device for operating an electrical stepper motor (2) a headlight assembly for a motor vehicle.

Description

The The present invention relates to a method for operating a electric stepping motor, wherein the stepping motor by means of at least a drive signal is applied and at least temporarily while the application of the stepping motor with the at least one drive signal a blocking state of the stepping motor is detected.

The Invention also relates a control unit for operating an electric stepper motor, wherein the controller is the stepper motor acted upon by at least one drive signal and at least temporarily during the application of the stepping motor with the at least one drive signal detects a blocking condition of the stepping motor.

• – mindestens einen Scheinwerfer; und
• – Variationsmittel zur Variation der Charakteristik eines von dem mindestens einen Scheinwerfer ausgesandten Lichtbündels, wobei die Variationsmittel
• – einen elektrischen Schrittmotor zur Variation der Lage des Scheinwerfers oder eines Bauteils des Scheinwerfers, welches die Charakteristik des Lichtbündels beeinflusst, und
• – ein Steuergerät zum Ansteuern des elektrischen Schrittmotors umfassen.

Finally, the present invention also relates to a headlamp assembly for a motor vehicle. The headlamp assembly includes:

• - at least one headlamp; and
• Variation means for varying the characteristic of a light beam emitted by the at least one headlight, wherein the variation means
• An electric stepping motor for varying the position of the headlamp or a component of the headlamp, which influences the characteristic of the light beam, and
• - Include a control unit for driving the electric stepping motor.

Out the motor vehicle sector, it is known the characteristics of a from a motor vehicle headlight emitted light beam by means of a Actuator, for example, designed as a stepper motor is to vary. For example, it is known for headlamp leveling or for the realization of a cornering light function in motor vehicle headlights to use so-called linear actuators. These are based, among other things on stepper motors, often as so-called 2-phase stepper motors, in particular as 2-phase claw-pole stepper motors are formed. such Stepper motors are characterized by having two separate, comprise mutually electrically separate coils. The two coils are by two each phase-shifted from each other Actuated control signals. The stepper motor has a rotor with a permanent magnet on. Due to the phase shift of the two Control signals and the resulting electromagnetic Fields is the permanent magnet or the rotor in one offset corresponding rotational movement.

The Stepper motors of a motor vehicle are by means of a control device in the Usually over one Triggered output stage. The control unit is capable of the rotor of the stepper motor by driving one or more coils the stepper motor by a specific pulse pattern to a certain Number of steps to move. An internal counter of the controller counts the Pulse of the drive signals, which is usually the number of covered Steps corresponds, so the position of the stepper motor always is known. Over a Spindle or another translator becomes the rotational movement the stepper motor then into a linear movement to adjust the Characteristic of the light beam emitted by the headlamp implemented.

The Variation of the characteristic of the light beam can, for example, by Adjusting the orientation of the entire headlight or merely a part of the headlight can be realized. It is conceivable, for example an adjustment of a diaphragm, a reflector, an imaging optics (e.g., in the form of a lens), or an additional optically active Elements (for example in the form of a prism or an additional Lens). It is particularly important to the adjustment of such parts of the Headlamps thought to be the characteristics of the headlamp generated and emitted light beam in any way can influence. As a characteristic of the light beam can, for example, its orientation (headlight range control: up and below; Bend light: to the left and right), the shape of the light beam (width, Height), the light distribution within the light beam or any combination these characteristics are varied.

Of the Rotor of the stepper motor is over the converter with the entire headlight and / or the adjustable Part of the headlamp directly or indirectly, for example via a Control rod, preferably articulated in connection.

Due to external or internal influences acting on the headlight or on the adjusting device, it may happen that the mechanical force necessary for a movement of the rotor is greater than the electromagnetically achieved adjusting force and that the rotor does not follow the intended rotational movement, the means that the drive pulses do not have the desired stepwise rotational movement result, and there are so-called step losses. External influences that can lead to an impairment of the rotational movement of the rotor, for example jamming of the part to be adjusted, a stiffness of the adjustment due to mechanical friction, inertial forces, impacts by acceleration forces, for example, due to road bumps, etc. Corresponding external influences can also Act, when the stepper motor is used to vary the orientation of the entire headlamp. Internal influences, by which a free rotational movement of the rotor can be affected, are, for example, spent bearing grease, an operating temperature of the motor outside of a specified temperature range, etc.

A Logic or a scheduler in the controller may do the undesirable Not immediately recognize the operating state of a step loss because the internal counter of the control unit no longer with the actual Actual position of Rotor or the adjustable by the stepper motor Component of the headlamp matches. The finally has with the result that the headlight emits a faulty light beam, that, for example, in a headlight range adjustment coming Road user fades (too long range of the light beam) or but insufficient long-distance illumination of the road (too low Light range of the light beam) or that, for example, in a curve light function not the curve a roadway on which the motor vehicle drives, corresponds.

Out In the prior art it is known the actual value of the mechanical Position of the rotor of a stepper motor or that of the stepper motor adjustable component of the headlamp by means of a sensor to capture and forward to the controller for further processing. The sensor is designed, for example, as a Hall sensor. Of the Target value of the mechanical position of the rotor can be determined by the control signals for the stepper motor be determined. By comparing the detected by the sensor Actual value with the target value of the mechanical position of the rotor can be permanent Step losses of the stepping motor can be detected. So it will be the difference between the actual value and the target value of the mechanical position of the rotor observed. The use of a sensor to capture the actual value However, the mechanical position of the rotor is complicated and expensive. About that In addition, the sensor used claimed a relatively large amount of space in the headlamp or other parts of the headlamp assembly and leads to an increase in weight the entire headlamp assembly.

From the prior art (for example, from the DE 198 123 487 A1 ), it is also known to make an initialization of the headlamp assembly after switching on a headlamp assembly and at various other predetermined times. In this case, the stepping motor and thus also the headlight of the headlight assembly or the adjustable by the stepper motor component of the headlight is set in a defined starting position. In the cited document, it is proposed to control the stepping motor in such a way that the rotor is moved in at least the maximum possible number of steps in one direction. Depending on the starting position of the rotor, sooner or later it drives against a mechanical stop. Due to the impulse of the impact on the stop, the rotor bounces back from the stop and rotates due to the rebound by a few half or full steps back, and then again to drive due to the electromotive force against the stop.

Of the Rotor is therefore driven against the stop until it at least the maximum possible Number of steps in one direction. This should be sure that the rotor, even if the initial position the rotor is far away from the mechanical stop which Rotor definitely reached the mechanical stop. After graduation the initialization is the rotor of the stepper motor on or near of the mechanical stop. This initialization process will referred to as referencing of the headlamp. The referencing is executed at least after each activation of the headlights.

The The type of referencing known from the prior art leads to vibrations of the stepping motor, because the rotor is repeatedly against the mechanical Stop moves. The vibrations are both from the occupants of a motor vehicle acoustically (there is a loud rattling sound) and tactile disturbing. Furthermore It may be due to the vibrations to a regular (periodic) or irregular light shivering as a result of referencing, which is at least irritating to the driver and the riders is. Cause for Light shaking is the unwanted turning back of the rotor of the stepper motor by a few half or full steps as soon as the mechanical stop is reached. Both the noise as well as turning back hanging from the rotor strongly depending on the design of the stepper motor, but will be in each Case perceived as extremely disturbing. After all to lead the vibrations also lead to a high mechanical load on the adjusting device and even the entire headlight assembly.

A method and a control device for driving an electric stepping motor in half-step operation, for example, from DE 102 25 610 A1 The stepping motor has at least two electrically separated coils and the blocking state of the stepping motor is detected by means of a current flowing through at least one of the coils or by means of a voltage applied to at least one of the coils. However, it is disadvantageous that, for example, a blocking state of the stepping motor, not on the achievement of a mechanical stop, but is due to other causes, leads to an error detection. Such causes that can lead to misrecognition, for example, a freezing of the stepper motor, the adjustable component or the entire adjustable headlamp. Also conceivable, for example, mechanical impairments of the free mobility of the stepping motor, the adjustable headlight or the adjustable by the stepper motor components.

adversely is also that while a generator operation of one of the coils of the stepping motor on the coil voltage is measured only once. If, for example, due to the transient of the voltage curve or due to disturbances, which affect the voltage curve, to an untypical Voltage course comes, it can be in the state of the art that the only measurement of stress is performed at exactly the time to which the voltage curve due to the unfinished Transient or due to other disturbances of its actual Value deviates, which can also lead to an error detection.

Especially when using stepper motors to vary the characteristic a light beam emitted by a headlight of a motor vehicle must be misrecognized However, to a minimum, preferably even completely be excluded, otherwise the risk of malposition of the Headlamps, a misalignment of the emitted light beam, a faulty light distribution and thus endangerment of others Road user exists. The reduction of false identifications to a minimum is therefore an essential prerequisite for admission the headlamp assembly according to the invention and requirement for an acceptance of such headlight assemblies by customers. These Requirements can the known method and the known control unit not fulfill.

outgoing of the known prior art is the present invention Thus, the object underlying the control of a stepper motor in half-step operation to design and develop that load changes the stepping motor, in particular a blocking state of the stepping motor, safe and reliable detected and error detections are reduced to a minimum.

to solution This object is based on the method of the aforementioned Art suggested that the blocking state detection enabled first will, after previously for a predetermined period of time a freewheel of the stepping motor has been detected.

Advantages of invention

Of the mechanical stop is outside of normal adjustment range of the servomotor, during the intended operation of the servomotor to vary the characteristic of the light beam. Only in the initialization mode for referencing the servomotor the normal adjustment range is left and the mechanical stop approached. In this respect, it can be ruled out that a servomotor while the intended use at the mechanical homing stop comes to the plant. Consequently it is also excluded that a servomotor to be referenced Already at the beginning of the homing on the mechanical stop is applied. Rather, the servomotor is in the context of referencing at a error-free servomotor always first for a certain period of time can be moved in the freewheel, before reaching the mechanical stop. This travel of the original one Position of the servomotor at the beginning of the referencing process until reaching the mechanical stop is at a fault working servomotor in free-running. The original Position of the servomotor usually corresponds to the position in which the headlight or actuator before in normal operation was turned off.

To Beginning of the referencing process is so first the Freewheel of the stepper motor detected before the blocking state detection is activated. The freewheel is at least for the duration of a zero-current half-step a drive signal detected during the by a with the Actuator signal applied coil of the servomotor no current flows and the Coil is thus operated in generator mode.

With the present invention can be prevented that in case of malfunction of the servo motor or the headlamp blocking the servo motor, which is not caused by the mechanical stop, leads to an error detection and thus to a faulty referencing of the servomotor. As a result, the reliability of the headlamp assembly according to the invention can be increased. In addition, the traffic safety can be increased because dazzling oncoming road users can be excluded by too high set or by too far on the opposite lane radiating headlights due to the faulty referencing. In addition, the safety for the driver of the motor vehicle is increased with the headlamp assembly according to the invention, since a unzurei chte apron and / or remote illumination due to a faulty referencing of the servomotor can also be excluded.

The the blocking state detection upstream freewheel detection is therefore of great importance in the present invention, because the blocking state detection has the task of shaking the Actuator against a blockage, especially against a mechanical Reference stop, to prevent. This has the advantage that annoying noises and Vibrations are prevented. On the other hand, it will also a free shake of the servomotor of a weak blocking, another one Cause as the mechanical stop has prevented. Much more is used in the referencing process after recognition of the Blocking condition - regardless of whether this on the mechanical stop, on a faulty Servomotor or due to a faulty headlight - the position, at which the blocking state occurs, as a stop for the referencing used the servomotor. With the present invention is it possible determine whether the detected blocking condition is actually on the driving against the reference stop is due or not.

When Another embodiment of the invention, it is conceivable that after the Detection of a blocking state of the homing process completed and immediately afterwards a new referencing process is started becomes. If then at the beginning of the new referencing process during the predetermined free-running time of the stepping motor can be detected can, it can be assumed that in the frame the previous referencing did not detect blocking to a blockage due to the mechanical stop, but to a blockage due to a fault or damage of the servomotor or of the headlamp.

According to one advantageous development of the present invention is proposed that the stepper motor is driven in half-step mode, wherein the stepper motor at least two electrically isolated from each other Coils and the blocking state of the stepping motor based a current flowing through at least one of the coils of the stepping motor or by means of a voltage applied to at least one of the coils is recognized.

• – Erzeugen von zwei phasenversetzt zueinander verlaufenden Ansteuersignalen für den Schrittmotor; und
• – Beaufschlagen des Schrittmotors mit den Ansteuersignalen,
• – Erkennen eines Betriebszustands des Schrittmotors, zu dem mindestens eine der Spulen des Schrittmotors als Generator betrieben wird;
• – Ermitteln einer an der mindestens einen Spule im Generatorbetrieb anliegenden Spannung;
• – Vergleichen der ermittelten Spannung mit mindestens einem vorgebbaren Schwellwert; und
• – Erkennen eines Blockierzustands des Schrittmotors, falls der Betrag der ermittelten Spannung kleiner als der Betrag des Schwellwerts ist.

It is further proposed that the method comprises the following method steps:

• - Generating two phase-shifted drive signals for the stepper motor; and
• - Applying the stepping motor with the drive signals,
• Detecting an operating state of the stepping motor to which at least one of the coils of the stepping motor is operated as a generator;
• - Determining a voltage applied to the at least one coil in the generator mode voltage;
• - comparing the determined voltage with at least one predefinable threshold value; and
• Detecting a blocking state of the stepping motor, if the amount of the detected voltage is smaller than the amount of the threshold value.

• – während eines Betriebszustands des Schrittmotors, zu dem wenigstens eine Spule als Generator betrieben wird, die an der Spule im Generatorbetrieb anliegende Spannung ermittelt wird;
• – die ermittelte Spannung mit einem vorgebbaren Schwellwert verglichen wird; und
• – ein Freilauf des Schrittmotors erkannt wird, falls der Betrag der ermittelten Spannung größer als der Betrag des Schwellwerts oder gleich dem Betrag des Schwellwerts ist.

According to another preferred embodiment of the invention it is proposed that a freewheel of the stepping motor is detected by

• - During an operating state of the stepping motor, to which at least one coil is operated as a generator, which is determined on the coil in generator operation voltage is detected;
• - The determined voltage is compared with a predetermined threshold value; and
• - A freewheeling of the stepping motor is detected, if the amount of the detected voltage is greater than the amount of the threshold value or equal to the magnitude of the threshold value.

The Freewheel detection is thus preferably during a zero-current half-step executed by one or more drive signals. The circumstance exploited, that while of the zero-current half-step, the corresponding coil in the generator mode is operated. The coil operated in generator mode applied voltage can either directly to the terminal contact tapped off the coil or indirectly via a through the coil over a Measuring resistor flowing current be determined, in which case the falling over the measuring resistor Voltage either directly as a measuring voltage or as a measure of the measuring voltage is used. The threshold value with which the determined voltage is compared to the freewheel detection, either equal to the threshold be to the blocking state detection or deviating from this Be threshold.

According to a preferred embodiment of the present invention, it is proposed that a freewheel of the stepping motor is detected only if the magnitude of the determined voltage during a plurality of successive operating states, to which the voltage applied to at least one of the coils in the generator mode voltage, in the plurality of Cases greater than or equal to the magnitude of the threshold. According to this embodiment, therefore, not only during a single zero-current half-step, but during several, preferably immediately successive zero-current half-steps, the voltage applied to the coil in generator operation is determined. Only if in a majority of the considered zero-current half-steps a freewheel of the Stepping motor is detected, it is assumed that the stepper motor is actually in the freewheel. It is conceivable, for example, that for the considered zero-current half steps, a majority decision is made and only one freewheel of the stepping motor is detected if, for example, in two of three or in three of four zero-current half steps respectively, the amount of the determined voltage greater than the amount or is equal to the magnitude of the threshold.

According to one Another advantageous embodiment of the present invention suggested that to determine the on the coil in the generator mode voltage applied to the voltage applied to the coil during the Duration of generator operation of the coil measured several times in succession becomes. This means that in each zero-current half-step not just a single measurement, but a series of measurements comprising several measurements is performed. It is conceivable that a blocking state of the stepping motor detected If all measurements of the measurement series are below the specified threshold value lie. Alternatively, it is also conceivable that a blocking state the stepping motor is detected, if the majority of the measurements a measurement series are below the threshold value.

advantageously, is used to determine the voltage applied to the coil in generator mode Voltage the voltage applied to the coil during the duration of the generator operation the coil measured a total of three times in succession. A series of measurements thus preferably comprises three individual measurements. Before the beginning of the measurement series, this means before the first single measurement, a predefinable period of time is waited for, so that the voltage to be measured operated in the generator mode Coil the possibility has to settle on the value in the zero current half step. The transient begins at the moment in which the previous half-step begins flowing through the coil current on the value 0 or to a value close to 0 while of the zero current half step to fall.

According to one another preferred embodiment The vorlie this invention is proposed that a blocking state the stepping motor is detected only if the amount of the detected voltage while several consecutive operating states, to those at the coil in the generator operating voltage is determined, in the majority of the cases is less than the amount of the threshold. So that means that also for the blocking state detection not only during a zero-current half-step the voltage applied to the generator operated coil is measured, but in several, preferably directly to each other following zero-current half steps each measured the voltage becomes. It can during during each zero-current half-step either a single measurement or a Measurements taken with several measurements. For blocking state detection it is according to the proposed embodiment required that in the majority of considered zero-current half-steps of Amount of the determined voltage smaller than the amount of the threshold value is. So it becomes a majority decision on the considered zero current half steps carried out. A blocking state of the stepping motor is detected only if for example, the voltage measurement in two out of three or in three from four zero-current half steps to a blocking of the stepping motor indicate.

The inventive method is preferably used to vary the characteristic of one of Headlight of a motor vehicle emitted light beam means the stepper motor used. In this case, the stepper motor, preferably articulated, on the entire headlight or on one or more certain components of the headlamp, by which the characteristic of the light beam can be influenced, articulated. In particular, it is thought that the stepper motor on a reflector for varying the beam range and for realizing a cornering light function, on a diaphragm for Switching the light beam between different lighting functions, in particular between low beam and high beam, but also between motorway light, city light and other light functions, or on one lens or another optical element of the headlamp is articulated.

Especially It is proposed that the method for detecting a blocking state the stepper motor during a referencing of the stepping motor at the beginning of an operation of the headlamp and / or after starting the motor vehicle. Of course it is also conceivable, the inventive method to arbitrary Times during the intended use the headlight and / or the motor vehicle to one or more Stepper motors of the headlamp apply. When the inventive method every time you start the motor vehicle or the internal combustion engine carried out of the vehicle It does not necessarily have to be every time you turn on the headlights accomplished become. As a result, the optimally adjusted light bundle stands with the optimal light distribution already immediately after activation the headlight available, especially when entering tunnels, where at short notice one optimum illumination of the roadway must be ensured, great benefits Has.

According to one another solution The object of the present invention is based on the control unit of the above mentioned type that the control unit further means for activation the lock state detection and means for detecting a freewheel the stepping motor, wherein the activating means the blocking state detection only activate after the freewheel detection means previously for a predefinable Time have recognized a freewheeling the stepper motor.

According to one preferred embodiment of the present invention is proposed that the controller Means of execution the method according to the invention having.

Finally will as another solution the object of the present invention, starting from the headlamp assembly for a Motor vehicle of the type mentioned proposed that the headlamp assembly a control device according to the invention, which only activates the lock state detection after it previously for a predetermined period of time detects a freewheel of the stepping motor Has.

According to one advantageous development of the present invention is proposed that the stepper motor of the headlamp assembly as a 2-phase stepping motor, in particular as a 2-phase claw-pole stepper motor is.

preferred embodiments The present invention will be described below with reference to FIGS explained in more detail. It demonstrate:

1 the course of the adjustment speed of a stepper motor;

2 the course of applied to a coil of the stepping motor current and voltage applied during a freewheel of the stepping motor;

3 the course of applied to a coil of the stepping motor current and applied voltage when hitting a mechanical stop;

4 a system representation of an automatic headlamp leveling of a motor vehicle headlight;

5 a sectional view of a 2-phase claw pole stepper motor;

6 two mutually phase-shifted drive signals of the two coils of the stepping motor; and

7 a flow diagram of the method according to the invention.

The present invention relates to a method and a control device for operating an electric stepping motor, as exemplified in 5 is shown. It is a so-called 2-phase claw-pole stepping motor, which in 5 in its entirety by the reference numeral 1 is designated. The stepper motor 1 includes a stator 2 and a relative to this rotatable rotor 3 , The stator 2 includes two excitation coils 4 . 5 , as well as claws 6 , which are designed as a bracket and in the interior of the stator coils 4 . 5 protrude. The claws 6 take over the leadership of the magnetic flux. The two coils 4 . 5 are arranged on top of each other so that a rotating, indexed magnetic field can be generated. The generation of the magnetic fields takes place by acting on the coils 4 . 5 with drive signals, for example with drive currents, via electrical supply lines 7 . 8th , The rotor 3 includes a cylindrical permanent magnet and a shaft 9 , The magnetization of the permanent magnet is based on the arrangement of the claws 6 aligned. The motor 1 has as many claws 6 like the rotor 3 Pole has.

The stepper motor 1 rotates when the stator magnetic field is stepped and the rotor 3 moves synchronously with this field. The continuation of the stator field is effected by applying corresponding control signals to the stator coils 4 . 5 ,

Stepper motors convert electrical pulses into incremental mechanical movements. They are particularly well suited for positioning tasks, since it is possible to count the drive pulses by means of a counter and thereby to the current position of the motor 1 close. stepper motors 1 are very robust and have a long life. The in 5 illustrated 2-phase claw-pole stepper motor 1 is particularly suitable for smaller power, for example, less than 10 watts.

In 6 the course of the two drive signals is shown, with which the two coils 4 . 5 of the stepper motor 1 be driven in the uncompensated half-step mode. The drive signals are in 6 represented in the form of the pulsed phase currents I ₁ , I ₂ . Down in 6 are half steps 1 ... 8th shown. It can be clearly seen that the two drive signals I ₁ , I ₂ are offset by two half steps relative to each other. A special feature of the uncompensated half-step operation of the servomotor 1 is that there are states in which only one of the two coils 4 . 5 energized. Thus results from the control signals 6 a bipolar control in which the operating states + I _operation , 0, -I _{operation are} possible. To the below in 6 turned recorded time at half step 1 there is the first coil 4 through which the string current I ₁ flows, for example in an operating state in which no current flows through the coil 4 flows and this is operated as a generator. Accordingly, for example, at the time of half-step 3 the second coil 5 of the stepper motor 1 , through which the phase current I ₂ flows, in the generator operating state. In the 6 The time steps shown below correspond to the half steps, which form the basis for the control of the stepping motor 1 form.

In 4 is a preferred embodiment for the use of the stepping motor 5 represented in the context of the present invention. It is a device for controlling the headlight range (LWR) of one or more motor vehicle headlights (not shown). 4 shows the pure system engineering of such a LWR system. The system initially includes the stepper motor 1 which is articulated to an adjustable headlamp or to an adjustable part of the headlamp to vary by adjusting the position and / or orientation of the headlamp or the component, the characteristic of a light beam emitted by the headlamp. In the present example of a LWR system, the range of the light beam is varied, for example, by adjusting the entire headlight or by adjusting only the reflector or another component of the headlight. The headlamp or the reflector are therefore adjustable in inclination. The headlamp inclination when the headlamp is adjusted is in 4 with the reference number 10 designated.

The activation of the stepper motor 1 takes place by means of control signals (cf. 6 ), in a control unit 11 calculated and, for example via a driver stage (not shown) to the stepper motor 1 or the coils 4 . 5 of the stepper motor 1 be created.

At the entrance of the LWR system off 4 is a target value for the headlight range, with the reference numeral 12 is designated. The LWR target value 12 becomes the output signal of an axis angle sensor 13 added and the controller 11 fed. The axis angle sensor 13 is on or on an axis 14 of the motor vehicle is arranged and registers movements of the axle 14 relative to the vehicle body 15 as a result of a load change or changed driving dynamics 17 , Movements of the body 15 result in a so-called pitch angle, denoted by the reference numeral 16 is designated.

At the output of the stepper motor 1 is the actual value 18 the position of the stepper motor 1 at. The sum of pitch angle 16 and actual position 18 of the stepper motor 1 gives the resulting headlight inclination 10 with adjusted headlight. In order to allow optimal control of the headlamp range of the headlamp, it would be advantageous if the actual position 18 of the stepper motor 1 would be detected by a suitable sensor, such as an absolute encoder, which is the actual position 18 or one of the actual position 18 appropriate size to the controller 11 could forward. However, such a sensor costs money, space and weight and is therefore often saved in practice. For this reason, the absolute encoder is for determining the actual motor position 18 in 4 also shown in dashed lines.

In the implementation of the present invention, such an absolute value encoder is therefore not used. In the invention, the actual position 18 rather, by an internal counter of the control unit 11 emulates the drive pulses of the drive signals I ₁ , I ₂ for the two coils 4 . 5 of the stepper motor 1 count and from this to the actual position 18 back closes. It is particularly important that the proposed method safe and reliable states of the stepper motor 1 detects or compensates in which the stepper motor 1 Although it is controlled by appropriate control signals, but due to internal and / or external circumstances no or no complete rotational movement executes, so that a conclusion from the number of drive pulses to the actual position 18 of the stepper motor 1 only conditionally or no longer possible. In such a case, the proposed method offers the possibility of step losses, that is, differences between the state of the ECU internal counter or the resulting emulated position of the stepper motor 1 and the actual actual position 18 of the stepper motor 1 recognize and take appropriate action. These measures can, for example, consist in a compensation of the lost steps, a new referencing of the headlight or simply in the output of a corresponding error message.

A flow chart of the method according to the invention is shown in FIG 7 shown. With the reference number 20 is the start of the procedure called. In a functional block 21 then an activation of the stepping motor takes place 1 in the manner described above. In particular, the coils 4 . 5 of the stepper motor 1 with the drive signals I ₁ , I ₂ whose course is exemplified in 6 is shown, applied. In the function block 22 a blocking state detection takes place in a manner known per se (compare, for example DE 102 25 610 A1 ). In this case, in a zero-current half-step (half steps 1 and 5 for the first drive signal I ₁ and half steps 3 and 7 for the second drive signal I ₂ in 6 ) on the corresponding coil 4 or 5 measured in the generator operation voltage, compared with a threshold and depending on the result of the comparison to a blocking state of the stepping motor 1 closed or not. This is then done in a query block 23 a check whether a blocking condition exists or not. If so, appropriate action will be taken. For example, simply in the function block 24 branches and the process is terminated. If there is no blocking state, it becomes the function block again 21 branches, with the control 21 and the lock state detection 22 be continued and run until either a blocking detected or the process is otherwise terminated.

According to the invention, it is proposed that the blocking state detection 22 upstream freewheel recognition 25 is performed. Thus, when the inventive method is started (function block 20 ), always first a freewheel detection 25 executed and the blocking state detection 22 only activated, if in advance in fact for a predetermined period of time, a freewheeling of the servomotor 1 was determined (compare query block 26 ). This will prevent being stuck in a stepper motor 1 the stuck position is erroneously recognized as the position of a mechanical reference stop and the servomotor 1 it is referenced.

The inventive method is thus carried out as follows: The operation of the servomotor 1 starts and the coils 4 . 5 be with drive signals I ₁ , I ₂ , as they are for example in 6 are shown acted upon.

The goal is to use the servomotor 1 For referencing, first move against a mechanical reference stop and use the position of the servomotor at this reference stop as a zero position or zero position for the subsequent LWR. In this way, step losses that have occurred in the context of a previous operation of the headlamp or the LWR system can be compensated. By applying the coils 4 . 5 with the drive signals I ₁ , I ₂ moves the stepper motor 1 ie starting from any starting position in the direction of the mechanical reference stop. In a faultless servomotor 1 this reaches the reference stop freewheeling. The start position of the stepper motor 1 corresponds to the position in which the LWR system or the headlamp was turned off at the end of the previous phase of operation. The starting position is in any case within a normal adjustment range, that of the servomotor 1 can be passed through as part of its intended use to the LWR. By contrast, the mechanical reference stop is outside the normal adjustment range. This means that in a faultless servomotor 1 starting from the starting position always for several half steps a freewheel of the servomotor 1 is given before the reference stop is reached. This freewheel during the predeterminable period corresponding to at least one, but preferably a plurality of half steps, is in the function block 25 detected the method of the invention.

With a faulty stepper motor 1 where either the stepper motor 1 itself or the adjustable headlight or an adjustable component of the headlamp is fixed, there is no freewheel. That means that in the query block 26 it is found that a freewheel of the stepper motor 1 immediately after the start of the procedure has not occurred and thus that a defect of the stepping motor 1 or the adjustable headlamp or the adjustable component of the headlamp must be present. The procedure is ended. Of course, alternatively or additionally, any other measures can also be initiated if there is no freewheel.

Particularly important in the present invention is that the position in which the stepper motor 1 or the adjustable headlamp or the adjustable component of the headlamp is fixed, not as a reference position for initialization of the stepping motor 1 is used to zero position for the subsequent LWR. Instead, the faulty jam condition is detected and appropriate countermeasures can be taken. A suitable measure could be, for example, initially to prevent activation of the headlights or a light emission of the headlights and the inventive method at a later time after reaching a higher operating temperature of the stepping motor 1 or the headlight (for example, warmed up by the waste heat of the internal combustion engine of the motor vehicle or by a heater), perform again. If the specified stepper motor 1 caused by freezing, the blocking state could possibly be remedied in this way. Another measure could be, for example, the driver visually and / or acoustically on the fixed servomotor 1 so that they can then choose and initiate further measures themselves.

In 1 is the adjustment speed v in the unit half steps (Hs) per second (sec) over the path s in the unit half steps (Hs) plotted. The maximum total travel 30 of the stepper motor 1 lies in a range between 0 Hs (external mechanical reference stop) and 1,000 Hs (mechanical reference stop inside). The overall adjustment path 30 includes both the normal adjustment range 30 ' which can be passed through as part of a normal operation of the LWR system as well as an external area 3 '' , which only in the context of referencing the servomotor 1 of the LWR system. The external area 30 '' can be any size. He can even run to zero, with the mechanical reference stop then directly to the normal adjustment range 30 ' followed.

At the beginning of the method according to the invention is the stepper motor 1 in a random position 31 within the range 30 , The random starting position is in 1 with the reference number 31 designated; For example, it is 500 Hs. Starting from the starting position 31 becomes the stepper motor 1 along an acceleration ramp 32 accelerated to a typical adjustment speed v _typ , for example, to 300 Hs / sec. Once the typical adjustment v _type is reached, the stepper motor drives 1 at constant speed - in the error-free case in free-running - up to the mechanical reference stop at 1,000 Hs, which is used to refer to the stepper motor 1 serves. The constant travel with the adjustment speed v _typ is in 1 with the reference number 33 designated. During the constant journey 33 is the freewheel recognition (blocks 25 and 26 in the flowchart 7 ) is activated.

Once for one or more half steps of the freewheel during the constant drive 33 was detected, the blocking state detection (function blocks 22 and 23 in 7 ) is activated. Once then the stepper motor 1 against the mechanical reference stop at 1000 Hs travels, the blocking is detected. The position of the stepper motor 1 in abutment with the reference stop is used as a zero position for the subsequent LWR. The procedure of the blocking state detection is described below on the basis of 2 and 3 explained in more detail.

At the mechanical reference stop falls the adjustment speed v of the stepping motor 1 v typical of the _type of adjustment to the value 0. On the basis of the referenced zero position of the servomotor 1 then becomes the desired position 34 of the servomotor 1 approached. This is the servomotor 1 initially for some half steps from 0 to an operating speed v _betr , for example, accelerated to 80 Hs / sec. The corresponding acceleration ramp is denoted by the reference numeral 35 designated. Then the servomotor moves 1 at constant speed v _betr up to the desired position 34 , This cruise is in 1 with the reference number 36 designated. The target position 34 can therefore be approached very precisely, as previously the referencing of the servomotor 1 was carried out on the mechanical reference stop at 1,000 Hs, whereby any step losses were compensated.

In 2 the process of blocking state detection is shown in detail, with in the left half of 2 the course of a drive current I, and the course of the corresponding voltage U for the constant speed 33 is shown. In the right half of 2 on the other hand, the drive current I and the corresponding voltage U are shown after hitting the mechanical reference stop. It can be clearly seen that during the cruise 33 there is a high voltage level in the zero-current half-step (abs (U ') >> 0). In contrast, the voltage level in the zero-current half-step has collapsed to nearly 0 volts when hitting the mechanical reference stop. This change in the voltage level is made according to the present invention both for freewheel detection (see function blocks 25 and 26 in 7 ) as well as to the blocking state detection (compare function blocks 22 and 23 in 7 ) advantage.

In 3 is the left half off 2 during the constant journey 33 shown enlarged again. Both the freewheel recognition and the blocking state detection are carried out in the method according to the invention during a zero-current half-step, for example in the range between (d) and (f) in 3 , Strictly speaking, the zero-current half-step already starts before point (d) and continues beyond point (f). However, the range between the point (c) and the point (d) serves to settle the current value I from the value + I _operation during the previous half-step to the value 0 during the zero-current half-step. Also, the range from the point (f) to the point (g) for settling the current value I from the value 0 or approximately 0 during the zero-current half-step to the value -I _operation during the subsequent half-step. At the beginning of the zero-current half-step, it is first waited for a predefinable time period ((e) - (d)) before, for example, the measurement of the voltage U is started at point (e). The point (e) is after the point (d), since the transient for the voltage U lasts longer than the transient process for the current I. Only after the voltage U has settled to the end value for the respective half-step, with the measurement to be started.

The measurement of the voltage U at the time (e) gives a negative voltage value U '. On the other hand, the measurement of the voltage U during the preceding zero-current half-step at the time (h) and during the subsequent zero-current half-step at the time (i) gives a positive voltage value U '. For detection of the freewheel it is checked whether the magnitude of the measured voltage value U 'is greater than a predefinable threshold value U ₁ . The measurement of the voltage U 'is preferably carried out at any time between the times (e) and (f), ie at steady state voltage curve U.

According to the invention, during the measurement period between the point (e) and the point (f), it is proposed to record not only one measurement, but one measurement series with several measurements, for example three measurements per measurement interval. In order to detect a freewheel for the considered zero-current half-step, either all or the majority of the measured voltage values U ' ₁ , U' ₂ , U ' _{3 must be} greater in magnitude than the threshold value U ₁ . Likewise, it is envisaged to carry out measurement series with one or more measurements not only during a single zero-current half-step (between (d) and (f)), but during several preferably immediately consecutive zero-current half-steps. The consecutive series of measurements can either always use the same coil 4 ; 5 or alternately both coils 4 . 5 affect. Even with the various zero-current half-steps considered, it can be used to detect a freewheel of the stepping motor 1 be required that either one freewheel is detected at each zero-current half steps or only to a majority of the considered zero-current half steps. Preferably, four consecutive zero-current half-steps are considered, wherein for each considered zero-current half-step, a freewheel of the stepping motor 1 must be detected in order to arrive at the end to the end result, that in fact a freewheel of the stepping motor 1 is present.

The blocking state detection (see function blocks 22 and 23 out 7 ) likewise takes place during the zero current half steps. Also in the blocking state detection, the measurement is preferably carried out within the measuring interval between the points (e) and (f). As with the freewheel recognition also, several measurements, preferably three measurements, are preferably recorded per zero-current half-step. Also, preferably, a plurality of zero-current half-steps are successively, in particular immediately consecutive zero-current half-steps of the same coil 4 ; 5 or both coils 4 ; 5 alternately considered. So that ultimately a blocking state of the stepper motor 1 At least three out of four considered zero-current half-steps must indicate a blocking state, each of the considered zero-current half-steps indicating a blocking state only if all the voltage measurements U ' ₁ , U' ₂ , U recorded during the considered zero-current half-step ₃ each indicate a blocking state individually, that is, when each of, for example, three recorded measurements lies below a predefinable threshold value U ₂ .

Of course, the threshold value U ₂ for the blocking state detection and the threshold value U ₁ for the freewheel recognition can also be the same threshold value. Furthermore, the stepper motor can of course be used not only for LWR, but also for otherwise varying the characteristics of the light beam. In particular, the stepper motor is being considered 1 to implement an adaptive curve light function or other adaptive light distribution. Likewise, the stepper motor 1 be used to switch the headlamp between different lighting functions, for example, between low beam, high beam, city light, motorway light, fog light, etc.

Claims (15)

Method for operating an electric stepping motor ( 1 ), wherein the stepper motor ( 1 ) is acted upon by at least one drive signal (I ₁ , I ₂ ) and at least temporarily during the application of the stepping motor ( 1 ) with the at least one drive signal (I ₁ , I ₂ ) a blocking state of the stepping motor is detected ( 22 ), characterized in that the blocking state detection ( 22 ) is activated only after a free run of the stepping motor ( 1 ) was detected ( 25 ). Method according to Claim 1, characterized in that the stepping motor ( 1 ) is driven in half-step mode, wherein the stepper motor ( 1 ) at least two electrically isolated coils ( 4 . 5 ) and the blocking state of the stepping motor ( 1 ) by means of at least one of the coils ( 4 . 5 ) of the stepper motor ( 1 ) flowing current (I ₁ , I ₂ ) or based on at least one of the coils ( 4 . 5 ) voltage applied (U) is detected. Method according to Claim 2, characterized in that the method comprises the following method steps: - generating two drive signals (I ₁ , I ₂ ), which are out of phase with each other, for the stepping motor ( 1 ); and - applying the stepping motor ( 1 ) with the drive signals (I ₁ , I ₂ ); - detecting an operating state of the stepping motor ( 1 ), to which at least one of the coils ( 4 . 5 ) of the stepper motor ( 1 ) is operated as a generator; Determining one at the at least one coil ( 4 ; 5 ) voltage applied in generator operation (U '); - comparing the determined voltage (U ') with at least one predefinable threshold value (U ₂ ); and - detecting a blocking state of the stepping motor ( 1 ) if the magnitude of the detected voltage (U ') is less than the threshold (U ₂ ). Method according to one of claims 1 to 3, characterized in that a freewheel of the stepping motor ( 1 ) is detected by - during an operating state of the stepping motor ( 1 ), to which at least one coil ( 4 ; 5 ) is operated as a generator attached to the coil ( 4 ; 5 ) voltage applied in generator operation (U ') is determined; - The determined voltage (U ') is compared with a predetermined threshold value (U ₁ ); and - a freewheel of the stepping motor ( 1 ) is detected if the magnitude of the detected voltage (U ') is greater than the threshold value (U ₁ ) or equal to the threshold value (U ₁ ). A method according to claim 4, characterized in that a freewheel of the stepping motor ( 1 ) is detected only if the magnitude of the detected voltage (U ') during several consecutive operating conditions, to those at the coil ( 4 ; 5 ) in generator operation voltage (U ') is determined, in the majority of cases greater than or equal to the threshold value (U ₁ ). Method according to one of claims 3 to 5, characterized in that for determining the at the coil ( 4 ; 5 ) voltage applied in generator operation (U ') to the coil ( 4 ; 5 ) voltage (U ') during the period of generator operation of the coil ( 4 ; 5 ) is measured several times in succession. A method according to claim 6, characterized in that for determining the at the coil ( 4 ; 5 ) voltage applied in generator operation (U ') to the coil ( 4 ; 5 ) voltage (U ') during the period of generator operation of the coil ( 4 ; 5 ) is measured three times in succession. Method according to one of claims 3 to 7, characterized in that a blocking state of the stepping motor ( 1 ) is detected only if the magnitude of the detected voltage (U ') during several consecutive operating conditions, to those at the coil ( 4 ; 5 ) Applied voltage (U ') is determined in the generator mode, small in the majority of cases than the threshold value (U _2). A method according to claim 8, characterized in that the at the coil ( 4 ; 5 ) voltage applied during generator operation (U ') during four consecutive operating states, to those at the coil ( 4 ; 5 ) voltage applied in generator operation (U ') is determined, in three of four cases smaller than the threshold value (U ₂ ). Method according to one of claims 3, to 9, characterized in that the method for varying the characteristic of a light beam emitted by a headlight of a motor vehicle by means of the stepping motor ( 1 ) is used. A method according to claim 10, characterized in that the method for detecting a blocking state of the stepping motor ( 1 ) during referencing of the stepping motor ( 1 ) is used at the beginning of an operation of the headlamp and / or after starting the motor vehicle. Control unit ( 11 ) for operating an electric stepping motor ( 1 ), whereby the control unit ( 11 ) the stepper motor ( 1 ) acted upon by at least one drive signal (I ₁ , I ₂ ) and at least temporarily during the application of the stepping motor ( 1 ) with the at least one drive signal (I ₁ , I ₂ ) detects a blocking state of the stepping motor ( 22 ), characterized in that the control unit ( 11 ) Means for activating the blocking state detection and means for detecting a freewheel of the stepping motor ( 1 ), wherein the activating means the blocking state detection ( 22 ) only after the freewheel detection means previously for a predetermined period of time a freewheel of the stepping motor ( 1 ) have recognized. Control unit ( 11 ) according to claim 11, characterized in that the control unit ( 11 ) Comprises means for carrying out a method according to one of claims 2 to 11. Headlamp assembly for a motor vehicle, the headlamp assembly comprising: - at least one headlamp; and - variation means for varying the characteristic of a light beam emitted by the at least one headlight, the variation means comprising an electric stepping motor ( 1 ) for varying the position of the headlamp or a component of the headlamp, which influences the characteristics of the light beam, and a control device ( 11 ) for driving the electric stepping motor ( 1 ), characterized in that the control unit ( 11 ) is formed according to claim 12 or 13. Headlamp assembly according to claim 14, characterized in that the stepping motor ( 1 ) is designed as a 2-phase stepping motor, in particular as a 2-phase claw-pole stepping motor.