DE19721282A1 - Stepping motor driving method - Google Patents

Abstract

A method of driving a stepping motor, includes microstep driving in a low-frequency acceleration/deceleration area and supplying an exciting current to each phase formed into a chopping wave current in these microsteps during one step of switching respective phases by bipolar driving in order to make it possible to make current ripple small and to control generation of heat of the stepping motor and also to control vibration in a low-frequency acceleration/deceleration area at the time of low-speed rotation and at the time of high-speed rotation. The stepping motor may be used for driving a printer.

Description

The invention relates to a method for driving a stepper motor, in particular also a method for driving a stepper motor, the as a drive source for a carriage drive mechanism with one a carriage equipped printer or as a drive source for one Paper transport mechanism of a printer is used.

A so-called serial printer in which a predetermined Recording takes place while a carriage is carrying a printhead is moved along a printer abutment, the print head is selective is driven to a line section on a recording print carrier, the record carrier is transported line by line if one line is printed, then the next Printing a line primarily serves as an output device for one Calculator or a word processor.

In such a serial printer is generally a Stepper motor used to drive a carriage and / or to control a paper transport mechanism. The step Motor is particularly suitable because it has the following special Has advantages:

• 1. The angle of rotation of the motor is proportional to the number of Input pulses, there is no accumulative error.
• 2. The speed of the motor is proportional to the input pulse fre quenz, and it is a precise synchronous operation in a large Tax area possible.  
• 3. Starting and stopping behavior are excellent; the operation at constant frequency is at or below the self-start frequency possible.
• 4. The response behavior is very good, as is the starting line tung.
• 5. You can control the position by just one Inputs input pulse corresponding to a target position.
• 6. Digital control is possible.

A stepper motor is shown in FIG. 9 mainly provided with a stator 6, a first (A), a second (B), a third (C) and fourth (D) magnetic pole (phase) 2, 3, 4 and 5 has, which are arranged at intervals of 90 degrees, and a rotor 7 , which consists of a rotating permanent magnet with an N and an S pole with a 180 degree offset. Furthermore, this rotor 7 is coupled to an output shaft, not shown. A first coil 8 is wound around the first and third magnetic poles 2 and 4 , and a second coil 9 is wound on the second (B) and fourth (D) magnetic poles 3 and 5 .

If in the coils 8 and 9, an excitation current with corresponding phases for the stator is fed in order to set the stepping motor 1 in rotation, a magnetic field is generated by this current, so that electromagnetic attraction or between the stator 6 and the rotor 7 Repulsive forces arise. The electromagnetic force between the stator 6 and the rotor 7 is switched over by successively reversing the excitation current, thereby generating a torque for rotating the rotor.

Figure 10 is a block diagram of a motor driver IC for driving a general stepper motor. As is apparent from Fig. 10, the motor driver IC 10 is constructed by a control circuit 11, a dri berschaltung 12 and a supply source 13. The control circuit 11 has the functions of controlling as a whole, for example changing the input voltage, the rotational speed and the direction of rotation, a distance and an angle different from an input interface, and it carries out the control of the times for the pulses which are supplied to the stepping motor 1 . In addition, the driver circuit 12 is a circuit for distributing pulse-shaped signals coming from the control circuit 11 , and for amplifying these signals to excite the respective phases of the stepping motor 1 in a determined sequence. Two types are required as supply source 13 , one for driving the stepper motor, the other for a typical integrated circuit (IC).

In addition, there are basically two types of driver systems, namely a unipolar and a bipolar driver system for controlling the stepper motor 1 .

The unipolar driver system corresponds to a method in which a current is fed into respective coils in one direction by only switching on a corresponding transistor 21 , 22 , 23 or 24 , which are connected to the associated coils, as can be seen from FIG. 11 the. In contrast, in a bipolar driver system, a plurality of transistors 25 , 26 , 27 and 28 are connected to associated coils, as shown in FIG. 12. For example, if only phase A is considered, a current flows in the direction A when the first transistor 25 and the fourth transistor 28 are switched on, while a current flows in the reverse direction A by the second transistor 26 and the third transistor 27 turns on. In the unipolar driver system, a simplified circuit structure compared to the bipolar driver system is possible because the number of transistors is only half as large. However, the bipolar driver system has the advantage of a larger motor torque compared to the unipolar driver system, based on the same electrical input power. The method according to the invention for driving a stepping motor 1 is explained in the present context with reference to bipolar control.

The feed system for an excitation current contains the 1-phase excitation gung, the 1-2-phase excitation, the 2-2-phase excitation and so on.

The above-mentioned method for driving a stepping motor 1 by means of 1-phase excitation is the most basic driving method for energizing the respective phases in phases in order to rotate the stepping motor by a basic step angle. Although the angular accuracy is high, this method has the disadvantage that the drive torque is low and the power efficiency is low. This is why this method is not used so often. In addition, with the 1-phase excitation, a step angle corresponds to a basic step angle.

The above-described method for driving a stepping motor 1 by 2-2-phase excitation is a method in which two adjacent phases are constantly excited at the same time and the excitation of one phase is switched over at a certain time. Since two phases are always excited, the power efficiency is high and a high output torque is obtained with the same voltage supply. In addition, the stepper motor is advantageously well protected against vibrations, such as arise when the rotor rotates beyond the desired position. Therefore, this method is widely used for driving a stepping motor 1 .

In addition, there is the procedure for Driving a stepper motor by 1-2 phase excitation. With this type the 1-phase excitation mentioned above becomes the motor control performed alternately with the 2-2 phase excitation. Because the Anhal position of the rotor in 1-phase excitation and the stopping position with 2-2 phase excitation against each other by 1/2 of the basic step  are offset at an angle, the output variable can be done in one step get angle, 1/2 of the step angle of the 1-phase excitation and of 2-2 phase excitation by making these two excitation states can be set alternately. So the resolution doubles compared to the other control methods, so you get a fine step setting of the stepper motor reached. In addition, the Stepper motor with little noise and in a stable manner at high Ge drive speed. The procedure is then primarily used if an exact rotation size is to be obtained.

However, if in this method of driving a step motor tors the input power is increased to operate at high Speed to reach a correspondingly high torque, so in generates excessive torque in the lower speed range, which leads to vibrations and noise.

In order to avoid this inadequacy, use is made of a driver method, which is referred to as the micro-step driver method, and in which a constant current chopper system is used, in which a step angle, which is mechanical due to the structure of the stepper motor 1 is set, is also subjected to a fine division, with the help of an electronic circuit's, via which the rotor of the stepping motor 1 is controlled so that it is rotated smoothly. In the present case, it should be described that the control takes place according to the micro-step driver method by means of bipolar control with 2-2-phase excitation.

The state changes of a driver current in the full step control as well as in the micro step control are shown in FIG. 13. If the torque-angle characteristic curve of the stepping motor 1 has an approximately sinusoidal curve, a smooth rotation with small torque fluctuations is possible if one feeds a sinusoidal excitation current, as shown in FIG. 13. This sinusoidal excitation current is obtained by dividing a period into several periods with a control circuit. Fig. 13 shows the case of dividing a period into forty sections, but since this means that the basic step angle is divided into ten sections, the resolution becomes ten times as high as before. Apart from that, the number of subdivisions can be selected optionally.

In a conventional constant current chopper system, a constant current is obtained in the micro step driving by using one of the methods explained below. The constant current chopper driver is designed to provide the current waveform shown in Fig. 14, after which a constant current is maintained by establishing a current-off state for a predetermined period of time when the supply current reaches a set value , and the current is then switched on again so that the feed current reaches the set value.

According to a first method for obtaining the constant current, in a driver circuit of the type shown in FIG. 12, a first transistor 25 and a fourth transistor 28 are switched on when the voltage supply is switched on, and when the supply current reaches a set value, the first transistor 25 becomes in turned off a state in which the fourth transistor 28 remains turned on. Although the exciting current gradually decreases, an operation is repeatedly performed in which the first transistor 25 is turned on, the current is raised to a set value, and the first transistor 25 is turned off again after a predetermined period of time has passed. 12, the first transistor 25 and the fourth transistor 28 will drive according to a second Ver in the driver circuit of FIG. Turned on, then the first Transistor is stor 25 turned off and the fourth transistor 28 is also turned off to the time at which the supply current reaches the set value, then the current is drastically reduced, the first transistor 25 and the fourth transistor 28 are turned on to increase the current to the set value, and the first transistor 25 and the fourth transistor 28 are turned off again when a predetermined Period of time has passed. This process is repeated.

Only the course of the excitation current in phase A was explained tert, but a similar control is also carried out for the others Phase coils with offset excitation times.

In the first method explained Although the current ripple can be shown in FIG. 15 decrease, but the exciting current is distorted, so that the attack increases from heat in the stepping motor.

In the second method, there is a shortcoming that the current ripple increases as shown in FIG. 16, so that the motor losses increase, and at the same time the torque is reduced.

Because the micro-step driver method is also used at high times Speeds there is a need to step (impulse) into further To subdivide fine steps, a driver pulse receives a high frequency quenz component, what the structure of the driver circuit and its Control complicated.

In a known control method for a stepper motor Overcoming the problems of the prior art by one method the control of a stepper motor in which the Motor at high speeds with a normal excitation system system is controlled, while at low speeds the micro Step control takes place, the current during the switch-off time clamp in chopper mode to achieve a constant current in the micro step driver method is reduced by using a High speed damping combined with a low speed damping kidney.  

With this control method there is the possibility of rippling the current to reduce the amount of heat and vibra tion when rotating the motor at low speed without thereby complicating the control circuit.

However, in such a driving method for a stepper motor, the first coil 8 wound on phases A and C and the second coil 9 wound on phases B and D are the reference voltage of a motor driver IC 10 corresponding to sine waves, as shown in FIG. 17A and 17B is shown while the microstep driving is taking place while the excitation currents fed into the coils 8 and 9 are also sinusoidal waves based on the reference voltage, as shown in FIGS. 18A and 18B. If one examines the sum of the excitation currents in the first coil 8 and the second coil 9 , it can be seen that a current ripple has arisen, as shown in FIG. 18C. Fig. 19 shows an enlarged view of Fig. 18C, and it can be seen that the current sum has a peak each time the excitation current of the first coil 8 and the excitation current of the second coil 9 overlap. Such a current ripple leads to a torque ripple of the stepper motor and was a cause for the development of vibrations in the microstep control.

The object of the invention is to provide a method for driving a stepper motor that is able without the need a complicated control circuit vibrations at the To master micro-step control of the stepper motor.

Another object of the invention is to provide a method for Driving a stepper motor in which vibrations in the low frequency Acceleration / deceleration range in low speed operation number or can be controlled at high speed.  

This problem is solved by the one specified in the claims Invention.

The present invention provides a method for driving a Stepper motor created, in which a micro-step control in low frequency acceleration / deceleration range during the Operation at low speed and during operation at high Speed of the stepper motor when switching the phase during bipolar control is performed so that the rotor core of the Stepper motor rotates round (smooth), in the lower acceleration / Deceleration range at high and low speeds so that Vibrations are suppressed to a minimum.

The invention also provides a method for controlling a Stepper motor created, which is able to sum a current to prevent ripple from arising and vibrations at the time of Suppress microstep control without a complicated Control circuit would be required by an excitation current for each lige phases is formed by having a chopper current wave With the help of microstep control is generated.

The invention is also intended to provide a method for actuating a Stepper motor are created in which the vibration level of the Mo tors is improved by feeding an excitation current that is composed of a chopper current wave, which in turn is obtained by applying a bias current to the respective coils of the stepper motor.

In the following, exemplary embodiments of the invention are described with reference to the Drawing explained in more detail. Show it:

Fig. 1A is a diagram illustrating a speed change of a stepper motor in the lower speed range according to the inven tion;

Fig. 1B is a diagram showing a change in voltage for each phase of an engine in the lower speed area (of the portion of the sawtooth wave illustrates the Treiberpo sitions by micro-step driving);

Fig. 2A is a diagram of a speed change of a stepping motor in the high speed range according to the invention;

FIG. 2B is a diagram showing a change in voltage for each phase of a motor in the high speed range (the illustrated Sägezahnwellenbereich shows the driving positions by micro-step driving);

Fig. 3 is a waveform diagram of a coil current in accordance with an embodiment of a driving method for a stepping motor according to the invention;

FIG. 4A is a waveform diagram of a reference voltage accordingly a first coil of a motor driver ICs according to an embodiment of a driving method for a stepping motor according to the invention;

4B is a waveform diagram of a second coil of a motor driver IC similarly illustrates a reference voltage as illustrated above.

Fig. 5A is a waveform chart showing an excitation current to the first coil in accordance with an embodiment of the driving method according to the Invention for a stepping motor;

5B is a waveform diagram which shows the similar exciting current of the second coil of the above representation.

5C is an explanatory diagram illustrating a current sum of exciting currents of the first and the second coil veran.

Fig. 6 is an enlarged diagram of Fig. 5C;

Fig. 7A is a waveform diagram of the reference voltage, which is applied with a corresponding bias to the first coil of the motor driver IC according to a further embodiment of a driver method according to the invention for a stepper motor;

FIG. 7B is a waveform diagram showing a reference voltage that is biased to the corresponding second coil of the motor driver IC, similar to FIG. 7A;

FIG. 8A is a waveform diagram of an excitation current, of a further embodiment is fed an inventive method for driving a stepper motor with bias in the first coil in accordance with;

8B is a waveform diagram of an excitation current, which is fed with pre-tension in the second coil.

8C is a view showing a sum current of the exciting currents which are supplied with bias voltage in the first and the second coil.

Fig. 9 is a basic diagram illustrating the structure of a stepping motor;

Fig. 10 is a block diagram of a stepper motor driver;

FIG. 11 is an explanatory view showing a driver circuit for a stepper motor of a unipolar system;

FIG. 12 is an explanatory diagram of a drive circuit for a stepping motor of a bipolar system;

FIG. 13 is an explanatory diagram for explaining the change of an excitation current in the full-step driving a hand, and at the micro-step drive the other;

FIG. 14 is a waveform diagram for an excitation current at a constant current chopping system;

FIG. 15 is a waveform diagram of an excitation current during the time of low-speed damping according to a conventional driving method;

FIG. 16 is a waveform diagram of an excitation current at the time of high-speed damping according to a convention tutional driving method;

FIG. 17A is a waveform diagram of a reference voltage accordingly the first coil of the motor driver IC according to a conventional driving method for a stepping motor;

Fig. 17B is a waveform diagram showing a reference voltage corresponding to the second coil of the motor driver IC similar to Fig. 17A;

FIG. 18A is a waveform diagram of an excitation current to the first coil according to a conventional driving method for a stepping motor;

FIG. 18B is a waveform diagram of an excitation current for the second coil, similar to FIG. 18A;

FIG. 18C is an explanatory diagram for a total current of exciting currents of the first and the second coil; and

Fig. 19 is an enlarged diagram of Fig. 18C.

A driver method for a stepper motor according to the invention is based on the chopper control with the bipolar driver circuit explained above. In a first embodiment of the present invention, the control takes place with normal 1-2-phase excitation or 2-2-phase excitation during high speeds of the stepping motor, while in the lower speed range and in the high speed range of the stepping motor 1, a microstep control takes place low-frequency acceleration / deceleration range is made.

In a second embodiment of the invention, the control takes place tion with normal 1-2-phase excitation or 2-2-phase excitation at high speeds, while at low speeds the micro step control takes place and for the fed into each phase Excitation current a chopped current is used.

In a third embodiment of the invention, a stepper motor driven by an excitation current as in the second embodiment is fed in, but with a corresponding bias current.

The period of low speed mentioned here means the Period of control or driving in which one Driver pulse width per step from about 650 microseconds to 10 Lasts milliseconds.

Fig. 1 and 2 to the rotating speed of a motor and the voltage applied to each phase at that time for a voltage Ver drive of driving a stepping motor according to the first execution form to illustrate the invention.

Fig. 1A shows the speed of the stepping motor 1 at the time of slow rotation, that is, low speed, Fig. 1B shows the voltage applied to each phase at that time. Furthermore, 2A, FIG. 1, the rotational speed of the stepping motor during high speed rotation and Fig. 2B shows the voltage applied to each phase voltage then. In FIGS. 1B and 2B, the saw tooth-shaped trace the portion in which the control is implemented by the micro step drive.

As is apparent from Fig. 1, when the stepping motor 1 is rotated at a low speed, the motor is controlled to be in the whole range from the acceleration range (time t0 to t1) to the constant speed range (time t1 to t2) and the delay area (time t2 to t3) is operated according to the microstep driving method.

On the other hand, the stepper motor is controlled according to FIG. 2 so that in the high speed range of the stepper motor 1, the drive by micro-step control occurs only in an area in which the driver pulse width per step between three times the self-starting frequency of the stepper motor 1 (about 650 Microseconds) and 10 milliseconds is while the rotation is accelerated to a predetermined constant Ge speed and there is a delay from the predetermined constant speed to stop, that is, only in the time period t0 to t1 and t4 to t5 while in the other acceleration / speed ranges at high speed and in the low speed ranges, control is carried out according to the normal exciter.

At this time, the current is fed with a constant current chopper system, and a first transistor 25 is turned off when a current reaches a set value in a driver circuit shown in FIG. 12 at a split time while the on and off state of the fourth transistor 28 is selected can be while the first transistor 25 is turned off, and the fourth transistor 28 can also be turned off together with the first transistor 25 when the current reaches a set value. The excitation current is then drastically reduced (high-speed damping). Then, when the exciting current is lowered to a predetermined value (predetermined time period), the fourth transistor 28 is turned on. The reduction of the excitation current is slow (low speed damping). Furthermore, when the current level drops to a second set value (a predetermined period of time has passed), the first transistor 25 is turned on again, thereby increasing the current level. When the current increases to the set value, the above-mentioned control for the first transistor 25 and the fourth transistor 28 takes place . This chopper operation is regulated with a division time by repeating the control in several periods.

A current waveform obtained by the above-described control operation is shown in FIG. 3. By repeating this control at respective partial times, the excitation current has a smooth course with suppressed distortions or ripples of the current, so that it becomes possible to control the generation of heat in the stepper motor 1 and also to reduce the power loss of the stepper motor 1 small hold. This avoids a reduction in the torque, and the rotation of the rotor 7 of the stepping motor 1 becomes round and shows no vibrations or fluctuations. The transistor is switched on and off with the aid of a CPU contained in the control circuit 14 .

Next, a second embodiment of the invention will be explained will. This second embodiment differs from that above explained first embodiment by the fact that as a pathogen current a chopped current wave is used, each phase one Microstep control in the lower speed range is supplied.  

The waveforms of the reference voltage given to the motor driver IC 10 and the excitation currents for the respective coils 8 and 9 in such a control are shown in FIGS. 4 and 5. FIG. 4A shows the reference voltage corresponding to the first coil 8 A, which corresponds to phase A and phase C, the reference voltage being supplied to the motor driver IC 10 , FIG. 4B shows the reference voltage corresponding to the second coil 9 for phase B and phase D. Furthermore, FIG. 5A shows the excitation current that is fed into the first coil 8 based on the reference voltage according to FIG. 4A, and FIG. 4B shows the excitation current that flows into the second coil 9 based on that in FIG. 4B shown reference voltage is fed. As can be seen from these figures, by shaping the wave form of the reference voltage supplied to the motor driver IC 10 into a chopped wave with a straight rise or descent, it is possible to excite the currents for the first coil 8 and the second coil 9 also to make a chopped wave that rises or falls in a straight line. In FIG. 6, the sum of the respective excitation currents for the first coil 8 and the second coil 9 is also shown graphically as an enlargement of FIG. SC. As can be seen from these diagrams, the total current from the excitation currents for the first coil 8 and the second coil 9 becomes constant. In other words, no current ripple is generated.

Accordingly, because there is no torque ripple or torque fluctuations, the vibration of the stepping motor 1 can be controlled even more effectively.

Next, a third embodiment of the invention will be presented with reference to FIGS. 7 and 8.

In this embodiment, a bias current is fed in when the excitation current is supplied to the first coil 8 and the second coil 9 in a microstep control according to the second embodiment described above. Applying a bias voltage or feeding a bias current means that the zero crossing point of the voltage is shifted to the plus side or to the minus side by applying a direct voltage to the alternating voltage, or that the zero crossing point of the current is shifted towards the plus or minus side, by applying a direct current to an alternating current to set a predetermined operating point.

It is assumed that a reference voltage is applied to the excitation current with a bias current on the reference voltage for the motor driver IC 10 , as shown in Fig. 7.

FIGS. 7A and 7B show waveforms of the reference voltage Motortrei over IC 10 according to the first coil 8 and the second coil 9, and in addition, they show that a bias voltage is applied to the embodiment shown in Fig. 2 the reference voltage. Thus, according to FIG. 8A and 8B, where a bias current for the exciter currents flowing in the first coil 8 and the second coil are fed 9, and if this exciting currents are summed, the sum current is constant without a Stromsummenwelligkeit arises, as apparent from Fig. 8C.

So if the excitation current is applied with bias current, the vibration level of the stepper motor 1 improves, and you achieve a ver improved and stabilized rotation control.

The invention is not based on the exemplary embodiments explained above limited, but can be modified in numerous ways, depending according to the circumstances.

The microstep control is e.g. B. controlled so that during the Time of rotation at low speed is done. However, a considerable effect when turning at high speed Vibration avoidance and the like in the acceleration range achieve if the microstep drive in the above Constant current chopper system is used.  

A similar effect is not only seen in a system with 2-2 phase excitation achieved, but also in the case of a 1-2-phase excitation.

As can be seen from the above description, one can stand out the influence of improvement for the vibration in microstep control achieve without requiring a complex control circuit would.

Claims (4)

1. A method for driving a stepper motor, in which a stator ( 6 ) with a plurality of phases wound with coils ( 8 , 9 ) is arranged around a rotor ( 7 ), an electromagnetic attraction or repulsion force being generated between the stator and the rotor , in that an excitation current is fed into the coils ( 8 , 9 ), and the electromagnetic force is switched over by successively switching over the excitation currents for the respective phases, thereby rotating the rotor, characterized in that the excitation current in the low-frequency acceleration / deceleration -The range during the rotation of the motor at low speed and during the time of rotation at high speed of the motor is controlled by means of microstep control. 2. The method according to claim 1, wherein the control by means of a normal excitation system in high frequency acceleration / ver deceleration range and in the constant speed range, when the engine is rotating at high speed. 3. Method for driving a stepper motor, in which a stator ( 6 ) with a plurality of phases wound with coils ( 8 , 9 ) is arranged around a rotor ( 7 ), an electromagnetic attraction or repulsion force being generated between the stator and the rotor by feeding an excitation current into the coils ( 8 , 9 ) and switching the electromagnetic force by successively switching over the excitation currents for the respective phases, thereby rotating the rotor, characterized in that the excitation current is controlled with microstep control, and that during the time of rotation of the motor at low speed, the exciting current is formed as a chopped current wave. 4. The method of claim 3, wherein the excitation current to the motor is supplied with a bias current.