FI72414B - COUPLING SYSTEM FOR GENERATING AV STEGPULSER FOR DRIVNING AND STEGMOTOR - Google Patents

Description

[uSSr ^ l ANNOUNCEMENT

• ISIM? (11) UTLÄGGNINGSSKRIFT 7241 4 C (45) Pa tantti rryönr.c tty (51) Kv.lk//lnt.CI.4 H 03 K 5/13, H 02 P 8/00 (21) Patent application - Patentansökning 78 1 4 7 3 (22) Application date - Ansökningsdag 10.05-78 (EN) (23) Starting date - Giltighetsdag 10.05-78 (41) Published public - Blivit off e nti ig 12.11.78

National Board of Patents and Registration Date of display and publication - 30.01.87

Patent and registration authorities', Ansökan utlagd och utl.skriften publicerad (86) Kv. application - Int. ansökan (32) (33) (31) Privilege claimed - Begärd priority 1 1.05.77 ll.O5.77 Federal Republic of Germany Förbunds-republiken Tyskland (DE) P 2721282.4, P 2721240.4 (71) Siemens Aktiengesel1schaft, Ber1in / Munchen, DE ; Wittelsbacherplatz 2, Munich, Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) (72) Oskar Eisenmann, Milnchen, Dietmar Pohlig, Munchen,

Federal Republic of Germany Förbundsrepubliken Tyskland (DE) (74) Berggren Oy Ab (5 * 0 Coupling arrangement for generating stepper motors for use with a stepper motor - Koppiingsanordning för generering av stegpulser för drivning av en stegmotor

The invention relates to a switching arrangement for generating step pulses for use in a stepper motor, wherein a frequency divider generates step pulses from clock pulses of a certain frequency, the repetition frequency of which is selectable by data words depending on the calculation words, give data words.

From "Celerate the Digital Stepping Motor" Electronic Design 1, Jan. 4, 1973, pages 84-87, a circuit is known for generating step pulses for the operation of a stepper motor, which includes a frequency divider to which clock pulses at a given frequency are input and output. step pulses The repetition frequency of step pulses is the frequency of clock pulses multiplied by a specified factor, which is usually less than 1. The factor determines the data word currently input to the frequency divider. During the calculation, the counting pulses, the frequency of which is substantially lower than the frequency of the clock pulses, step the counter forward from the predetermined initial state to the final state.The repetition frequency of the step pulses increases continuously depending on the current state of the counter elements due to the variable value . When the counter unit has reached its final state, the continuation of the counting is prevented and the repetition frequency of the step pulses remains the same. When the stepper motor decelerates, the counter is stepped back again with counting pulses. In a manner similar to the acceleration of a stepper motor, the frequency of the step pulses decreases again depending on the current state of the counter.

With this known switching arrangement, the repetition frequency of the step pulses can be set to change linearly, logarithmically or exponentially during the acceleration and deceleration of the stepper motor. However, the stepper motor will not operate in its optimal load-angle range. However, if the stepper motor is used in positioner operation, the settling time must often be as short as possible. The higher the settling time, the shorter the settling time. The torque depends not only on the stepper motor used, but also on how it is used. In known switching arrangements, the repetition frequency of the step pulses changes symmetrically during acceleration and deceleration. However, in certain use cases, it may be advantageous to use other, and in particular asymmetric, variations in the repetition frequency of the step pulses over time.

The invention is thus based on the object of providing a switching arrangement by means of which an arbitrary time dependence of the repetition frequency of the step pulses can be developed and which in particular gives step pulses at which the stepper motor accelerates at maximum dynamic torque.

According to the invention, the task is solved in a switching arrangement such as that mentioned in the introduction by storing in the memory an acceleration program for determining the time course of stepper motor acceleration, a second number of data words. during acceleration or deceleration of the stepper motor, the data words of the acceleration program or the deceleration program, respectively, are connected to the frequency divider.

3 7241 4

The advantage of the coupling arrangement according to the invention is that the acceleration and deceleration curves of the stepper motor can be set arbitrarily in a simple manner. For example, the acceleration curve can be set so that the stepper motor operates in the optimal load angle range during the entire setting movement, and the setting can take place in a shorter time even when only a few steps are available. The theoretical maximum output power of the stepper motor is then fully utilized. In addition, the connection arrangement is simple and is particularly well suited for manufacture as an integrated circuit.

If the stepper motor is designed so that the half cycle of the static torque characteristic corresponds to an odd step number s, it is advantageous if the number of starting pulses is (S + 1) / 2.

The dynamic torque is quickly optimized if the repetition frequency of the starting pulses is substantially higher than the repetition frequency of the control pulses at the beginning of the acceleration.

In order to brake the stepper motor as quickly as possible with the maximum possible torque, it is advantageous if the braking of the stepper motor is started by a series of step pulses bringing an optimal negative load angle range close to the stepper motor according to its torque characteristic.

The asymmetric characteristic curve, i.e. the different acceleration and deceleration curves, is obtained in a simple manner so that the data words given during acceleration are different from the data words obtained during deceleration when the same calculation words are entered.

In order to obtain different data words when entering the same calculation words during acceleration and deceleration, it is advantageous if the memory includes a toggle switch which, during acceleration or deceleration of the stepper motor, connects to the frequency divider the data words corresponding to acceleration or deceleration.

If the contents of the memory do not need to be changed, it is advantageous if the memory is read-only memory.

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If the deceleration duration of the stepper motor is shorter than the acceleration duration, and thus less information words are required for the deceleration than for the acceleration, it is advantageous if the counter unit is set at a certain fraction of the counter state reached before deceleration. A particularly simple connection is obtained by setting the counter unit to half the counter space reached before the stepper motor decelerates.

In order to obtain the deceleration and acceleration characteristics of the stepper motor which are independent of the absolute value of the repetition frequency of the step pulses, it is advantageous if step pulses are applied to the counter unit as calculation pulses.

An embodiment of the switching arrangement of the invention will now be described in more detail with reference to the drawing, in which Fig. 1 shows a time diagram of angular velocity and step pulses, Fig. 2 shows the course of a static torque characteristic curve; Fig. 6 is a circuit diagram of the counter unit.

The time diagram in Figure 1 shows the time t as the abscissa and the step pulses SI as the ordinate and the angular velocity ω of the stepper motor. The stepper motor is accelerated between the idle times tO and t1 from the idle state to the angular velocity ω. The step pulses are initially two start pulses and then three control pulses. The repetition frequency of the start pulses is selected to be substantially higher than the repetition frequency of the control pulses at the beginning of the start. At time t1, the angular velocity of the stepper motor has reached its holding value ω and the motor is given control pulses with a constant repetition frequency.

Between times t2 and t3, the stepper motor is decelerated and the repetition frequency of the step pulses S1 is reduced accordingly. The negative additional step pulse given after time t2 immediately sets the load angle to the optimum range for braking. If the stepper motor is controlled via an amplifier by a ring counter, 5 7241 4 the direction of rotation of the ring counter is reversed during the occurrence of a negative step pulse. The direction of rotation is shown in Figure 1 at d. After time t3, the stepper motor stops with a damping oscillation.

In the static torque characteristic curve shown in Fig. 2, the abscissa has a load angle β. The load angle refers to the angle at which the stepper motor shaft, when loaded with a certain static torque, rotates with respect to the unloaded state, i.e. the magnetic rest position. In this case, no control pulses are applied to the stepper motor. The ordinate is the static torque compared to the holding torque MH. The holding torque then means the maximum torque at which the excited stepper motor can be loaded statically without causing continuous rotation. In the following, it is assumed that the torque curve is sinusoidal.

The dynamic torque of a stepper motor is obtained from a static torque-torque characteristic curve. Dynamic torque in this case means the average torque available on the motor shaft during rotation of the angle Δφ. In this case, it is assumed that the next control pulse is always given after exactly one step of rotation. It can be seen from the torque curve that the stepper motor gives its maximum dynamic torque Mmax when rotating by a step angle a when the load angle between the two control pulses is symmetrical about the peak value, i.e. the holding torque MH. A simple calculation gives the maximum dynamic torque - MH - a

Mmax = · 2 · sm p j and the minimum dynamic torque - MH / T —7

Mmm = - · / 1 - cos pa / p · a - where p is the pole pair number of the stepper motor and a is the step angle.

Examining how the repetition frequency of the control pulses and the rotation angle f of the stepper motor rotor change with time, when a constant dynamic torque M must be obtained continuously from the shaft, it is found that when starting the stepper motor from magnetic sleep, a steadily accelerating motion is obtained when the repetition frequency f follows 6 - 24 · · T> J a where J is the total moment of inertia.

If, on the other hand, the repetition frequency increases more slowly, the rotor does not turn the angle α between the two control pulses, so that the conditions for constant torque are no longer fulfilled.

If the repetition frequency f increases, albeit linearly, faster than this, it may happen that after a few control pulses the motor drops out of phase and stops because the load angle β exceeds the unstable equilibrium state in the static torque curve.

As the repetition frequency f increases linearly with time, the acceleration capacity provided by the stepper motor will not be fully utilized because the difference between the minimum and maximum dynamic torque can be very large.

In principle, the stepper motor can be accelerated by the repetition frequency SI of the control pulses £ _ Mmax .1 _ ^ J "a However, this repetition frequency represents a theoretical limit case and this frequency must not be exceeded.

When only very few steps are available to start the stepper motor, a linear increase in the repetition frequency f is no longer satisfactory or possible due to the small number of steps. In this case, it is not advantageous to allow the repetition frequency f to increase as a monotonically increasing function, but in this case it must be ensured that the load angle is obtained as quickly as possible for the optimal operating range obtained from the equation - - = o _ _JL, et 2p 2 ~ p - 2p + 2

In the time diagram shown in Fig. 3, the load angle β is obtained for the optimal operating range as quickly as possible by initially giving two start pulses close in time at times 7 72414 t0 and t1. The time interval of the pulses is so short that during this time the motor of the stepper motor does not have time to rotate at all or it rotates only very little compared to the magnitude of the step. The number n of these consecutive starting pulses must be such that the load angle 31 = ^ 2p 2 is reached exactly or almost so that the inequality <1 - π a, n a 2p + 2 'where n is an integer is valid. At the latest at the t + n start pulse at time t2, the stepper motor accelerates to the maximum possible acceleration torque Mmax. The ordinate of the time diagram is the angle of rotation <p as measured by the step angle α. The figure also shows the step pulses S1, which at time t1 and t1 consist of start pulses and after time t2 control pulses. In addition, the repetition frequency f of the step pulses is shown. The time diagram shows that the repetition frequency of the start pulses is substantially higher than the repetition frequency of the subsequent control pulses.

If an odd number of steps s are required in the torque characteristic curve corresponding to Fig. 2 to bypass the half cycle of the static torque curve, the equals sign is valid in the latter expression, so the number n of starting pulses is given by the equation n = 5 · <25 * 2> = -

The following control pulses are given when the rotor of the stepper motor has turned by an average of a step angle a. The motor then starts at a steadily accelerating speed with a torque of Mmax.

For example, if a four-pole motor (p = 2) is equipped with a three-part winding and its step angle a = 30 °, the number of starting pulses is then n = 2. Thus, two starting pulses are given at the beginning of the start. Figure 3 shows this case.

If the number s is even, the number n is obtained according to the equation 1 π s a 2p 2 7241 4. The first following control pulses are given in contrast to the case where p is an odd number, the time when the rotor is rotated half a step angle. All subsequent control pulses are given so that the torque Mmax is reached. The stepper motor then operates in the optimum load angle range.

Thus, a stepper motor in which s is an even number can, just like a stepper motor in which the value of s is odd, be accelerated from the outset by the maximum possible torque Mmax.

The equivalent is also true for the deceleration of a stepper motor, which can be considered a negative acceleration. In this case, the load angle can be set to optimal either by omitting a number of step pulses or by giving negative step pulses. The step pulses SI usually control a ring counter in the motor amplifier, which is used to control the private windings of the step motor. If the ring counter is normally stepped in the positive direction, the negative step pulses will step it in the deceleration in the negative direction. In this way, the deceleration also takes place at the maximum torque Mmax, when the number of negative step pulses is selected so that the load angle β = - is obtained as accurately as possible.

The switching arrangement shown in Fig. 4 for generating step pulses for the operation of a stepper motor is included as an example in the remote control carriage return control. The trolley must be returned in the shortest possible time and the repetition frequency of the step pulses must therefore be as high as possible. The return movement of the wagon consists of three parts, namely acceleration, running at constant speed and deceleration. The carriage reset command, which is given, for example, by closing switch SW1, initiates carriage reset. Switch SW1 outputs a signal SI corresponding to the carriage reset command to the frequency divider FT. The clock pulses T generated by the clock TG are applied to the frequency divider FT. From the output of the frequency divider FT, step pulses S1 are obtained, which are applied to the stepper motor SM via the amplifier stage V. The repetition frequency of the step pulses SU is the frequency of the clock pulses T multiplied by a specified factor. The coefficient, which is usually less than 1, is determined by the data word DW, which is also imported into the FT inputs of the frequency divider.

The data words DW are stored in the memory SP, for example a read-only memory. The addresses DW of the data words in the memory SP are transmitted by calculation words ZW, which are brought to the memory SP from the counter unit ZS. The memory SP includes an address decoder which generates signals corresponding to the calculation plane ZW to obtain the addresses of the data words in the memory SP. The memory SP also has a changeover switch UM, which, under the control of the signal S3 given by the switch SW3, is set to either a first or a second position, in which the memory SP reads the data words related to either the acceleration or deceleration of the stepper motor. The data related to the acceleration of the As film motor have been compiled into the acceleration program BP and the data related to the deceleration DW into the deceleration program VP. Other details of the switching arrangement will be explained below in connection with the time diagram of Fig. 1.

At time to, a carriage reset command is given by closing switch SW1. Switch SW1 outputs the signal SI to the frequency divider FT and sets it to operation. The switches SW2 and SW3 are open and the changeover switch UM controlled by the signal S3 is in the position shown in Fig. 3 by a solid line. The counter unit ZS is in the counting state 0 and gives the counting word ZW associated with this state to the memory SP. The address decoder AD searches for the data word DW stored in the address 0 in the memory. However, only the data word DW included in the acceleration program BP is read and routed to the input of the frequency divider FT via the changeover switch UM.

The frequency divider FT includes, for example, a counter which is made to count from an adjustable initial state determined by the information word DW onwards to an unchanged final state. Whenever the counter reaches its final state, the frequency divider FT issues a step pulse S1 and again sets the initial state of the counter to the value determined by the data word DW.

The signal S3 controls the counter unit ZS so that when the switch SW3 is open, i.e. during acceleration, it counts forward. The step pulses SI are input to the counting unit ZS as counting pulses. After the first step pulse S1 given by the frequency divider FT, the calculation state of the counter unit ZS proceeds by one unit, and the corresponding count plane ZW is given to the memory SP. The memory SP gives a new data word DW depending on this calculation plane ZW to the frequency divider FT, and thus the repetition frequency of the as-pulses changes according to the new data word.

At each step pulse, the counter unit ZS is stepped forward by one calculation unit and at its time t1 reaches its predetermined maximum calculation state. Memory SP address decoder AD

10 7241 4 detects this counting state and the memory SP gives a signal S4 to the counter unit ZS, which prevents the forward counting from continuing. Thus, between the time instants t1 and t2, the calculation word ZW does not change and the same data word DW is continuously obtained from the memory SP. The repetition frequency of the step pulses SI thus remains constant and is dimensioned to correspond to the maximum speed of the stepper motor SM.

The carriage of the remote printer thus reaches its maximum speed at time t1 and maintains this speed until at time t2 the carriage itself closes the switch SW3 in the vicinity of the left stop to start the deceleration of the stepper motor SM.

When the switch SW3 closes, the signal S3 turns the toggle switch UM to the position shown by the broken line in Fig. 4, and the counter unit ZS is set to count backwards. With the following step pulses S1, the calculation state of the counter unit ZS decreases by one unit and, as well as between times t1 and t2, the data words DW corresponding to the desired deceleration curve are read from the memory SP between times t3 and t4. However, due to the second position of the toggle switch UM, the data words DW stored in the deceleration program VP are now read from the memory, and the repetition frequency of the step pulses SI is reduced according to the deceleration curve.

At time t3, shortly before the left limiter of the remote printer carriage, the counter unit ZS again reaches the counting state O, and the address decoder AD outputs a signal S5 by which the counting state 0 is detected and the counting down of the counter unit ZS is prevented from continuing. The data DW corresponding to the low repetition frequency of the step pulses SI may be stored in the memory at address 0. Since the calculation state of the counter unit ZS does not change, the same data word DW is continuously obtained from the memory SP, as well as between the times t1 and t2, and the carriage of the remote printer then moves at a low constant speed deviating from the time diagram shown in Fig. 1.

When the remote printer carriage reaches the left limiter and closes the switch SW2, the signal S2 given by this puts the frequency divider FT in the inhibit state and no new step pulses S1 are received. At the same time, the stepper motor SM stops.

If the acceleration curve and the deceleration curve are symmetrical, only one program is needed in the memory SP and the toggle switch UM can be omitted 11 7241 4. In this case, the calculation words ZW always correspond to the same data words regardless of acceleration or deceleration.

However, if the deceleration of the stepper motor requires a shorter time, the counter stage ZS can be set at the beginning of the acceleration to a calculation mode equal to the number of data words required in the representation of the deceleration curve. For example, if the counter unit ZS reaches its maximum possible counting state 63 at time t2 and if the deceleration of the stepper motor lasts only half the acceleration time, the counter unit can be set to 31 at time t2. In this case, the deceleration ends already after 31 step pulses S1 and the deceleration curve is substantially steeper.

The circuit diagram of Fig. 5 shows the implementation of the changeover switch of the frequency divider FT and the memory SP.

The frequency divider FT comprises a counter ZA1, two AND members UI and U2 and a flip-fl1 F1. The counter ZA1 is, for example, eight bits. The signal SI sets the flip-fl1 F1 and its output signal releases the AND element UI, which switches the clock pulses T to the counter ZA1. The counting mode of the counter ZAl advances by one unit for each clock pulse from the initial setting. When the counter ZA1 has reached the counting state 254, the AND member U2 outputs a step pulse S1, which is fed on the one hand through the amplifier stage V to the stepper motor SM and on the other hand to the setting input of the counter ZA1. The step pulse SI sets an initial setting in the counter ZA1, which is determined by the signals DW1-DW8 corresponding to the data word DW. The higher the value of the data word, the faster the counter ZA1 reaches the counting state 254 and thus the higher the repetition frequency of the step pulses S1.

At the end of the carriage reset, the signal S2 returns the flip-fl1 F1.

The output signal of the flip-flop F1 sets the AND element Ui to the closed state and the clock pulses can no longer reach the counter ZA1, so it can no longer give step pulses SI to the stepper motor.

The changeover switch UM of the memory SP includes eight AND / OR members U01-U08 and a flip-flop F2. The signal S1 sets the flip-flop F2 at the beginning of the carriage reset, and the signal of this non-inverting output then sets the left AND gates of the AND / OR members U01-U08 to operation. In this case, the data words included in the acceleration program BP, represented by the signals BP1-BP8, become connected as output signals 12 7241 4 of the AND / OR elements U01-U08 to the frequency divider FT. When the deceleration of the stepper motor begins, the signal S3 returns the flip-flop F2 and the signal at its inverting output activates the right-hand AND gates of the AND / OR members U01-U08 when the left-hand AND gates are in the closed state. Thus, during the deceleration, the data words represented by the signals VP1-VP8 included in the deceleration program VP become connected as output signals DW1-DW8 of the AND / OR elements U01 to U08 to the frequency divider FT.

The counter unit ZS shown in Fig. 6 includes a counter ZA2, an AND member U3, an OR member N, and a flip-flop F3, which may be similar to the flip-flop F2. At the start of the acceleration of the stepper motor, the signal S1 sets the flip-flop F3 and its output signal S1 sets the counter ZA2 to count forward with the step pulses S1 coming through the AND member U3. For example, the counter ZA2 is six bits and counts from the initial state 0 to the final state 63. When the counter reaches the count state 63, the address decoder AD gives a signal S4 and sets the OR member U3 to the closed state via the N-OFF member N, so that the step pulses S1 no longer enter to the calculation input of counter ZA2. When the deceleration of the stepper motor begins, the signal S3 resets the flip-flop F3 and thus sets the counter ZA2 to count backwards with the step pulses S1. The signal S3 further sets the counter ZA2 to an initial setting which is a fraction of the maximum calculation state 63, for example 31.

This can be carried out in a particularly simple manner in such a way that the outputs of the counter ZA2 are connected to the setting inputs on the left next to the counter ZA2 in each case. When the counter ZA2 has reached its initial state 0, the address decoder AD of the memory SP gives a signal S5 and the AND member U3 enters the closed state again, so that no step pulses can enter the counting input of the counter ZA2. To prevent the counter ZA2 from locking due to the closing of the AND member U3 caused by the signals S4 and S5, S4 is removed as soon as the counter ZA2 is stepped down and the signal S5 is removed as soon as the counter ZA2 is stepped up.

Claims (4)

13 7241 4 A switching arrangement for generating step pulses for use in a stepper motor (SM), wherein a frequency divider (FT) generates step pulses from clock pulses having a predetermined frequency, the repetition frequency of which is selectable by data words (DW), during stepper motor (SM) acceleration and deceleration, respectively. correspondingly, the counter unit (ZS) counting down the counting pulses provides counting words related to its counting state, and wherein the memory (SP) outputs data words (DW) depending on the counting planes, characterized in that a first motor is formed in the memory (SP); (SM) acceleration timing program (BP), and a second, smaller number of data words (DW), a stepper motor (SM) deceleration timing program (VP), and that the memory includes a changeover switch (UM), the position of which, depending on the position of the stepper motor SM) during acceleration or deceleration of the acceleration program (BP) i Correspondingly, the data words (DW) of the deceleration program (VP) are connected to a frequency divider (FT). Switching arrangement according to Claim 1, characterized in that the counter unit (ZS) for initiating the deceleration of the stepper motor (SM) can be set to a counting state which is a certain fraction of the counting state reached before the deceleration. Switching arrangement according to Claim 2, characterized in that the counter unit (ZS) is set to half the calculation state reached before the stepper motor (SM) is decelerated. Switching arrangement according to one of Claims 1 to 3, characterized in that the values of the memory data words (DW) for initiating acceleration in the acceleration program (BP) are considerably greater than the values corresponding to linear acceleration.