JPH06106040B2 - Driving circuit for step motor - Google Patents

Description

The present invention relates to a drive circuit for a step motor connected to a storage battery, such as a storage battery mounted on a vehicle, which has large fluctuations in power supply voltage.

[Prior Art] In recent years, step motors have been widely used as servomotors for NC machinery and automobiles rapidly with the digitization of electronics. For example, in automobiles, idle speed control, throttle valve drive, etc. Used for control, control rack control for injection pump, etc.

Generally, a step motor is composed of a rotor, a plurality of sets of stators that are mounted to face each other around the rotor, and stator windings wound around each stator. Then, by sequentially supplying a pulse voltage to these stator windings, the rotor rotates by an angle corresponding to the number of input pulses. In this way, in the step motor, since the rotation angle is proportional to the input pulse, without using a device such as a shaft encoder or potentiometer for detecting the position,
Position control can be performed using the open loop control as it is.

By the way, as the performance of the step motor, it is desirable that the step motor has a high responsiveness, that is, one that starts its rotation as quickly as possible and rotates at a high speed, but at the time of start-up, the rotor is vigorously raised from stop to high-speed rotation. If this is attempted, a large load due to inertia will be applied to the step motor, which may cause so-called step-out, which causes a deviation between the number of input pulses and the actual rotation angle, resulting in instability. To prevent this, generally, a pulse with a relatively long cycle is input in the initial stage of starting the step motor to slowly start the rotation,
After that, by shortening the pulse cycle with time,
A slow-up that leads the step motor to high speed rotation is used.

When driving the step motor, there are a method of driving with a constant voltage and a method of driving with a constant current depending on the difference in the power supply. When using a storage battery with large voltage fluctuation as the power supply, constant current drive is more suitable. .

Furthermore, when driving the step motor at a constant current, we want to increase the rotation speed as much as possible in accordance with the slow-up described above in order to improve the responsiveness.However, as the step motor rotates faster, the winding impedance of the step motor also increases. Therefore, constant current drive cannot be maintained unless the supply voltage is high. Therefore, the maximum value of the rotation speed of the step motor needs to be set firmly.

Particularly, when an attempt is made to drive a stepper motor by using a storage battery of an automobile or the like as a power source, the storage battery has a large voltage fluctuation, and thus requires further consideration. In other words, assuming that the voltage of the storage battery will be higher than the rated voltage, if the maximum value of the rotation speed is set to a high value and constant current driving is performed, when the voltage drops, the constant current driving of the step motor rotating at high speed Cannot be maintained, and the torque against the load is weak even if the speed is increased, causing step-out. Therefore, conventionally, the maximum value of the rotation speed is set in accordance with the low voltage when the voltage of the storage battery is lower than the rated voltage, and constant current driving is performed, or as described in JP-A-57-189554. The stable rotation of the step motor is maintained by detecting the position of the rotor by monitoring the phase voltage of the step motor and by using the encoder to perform closed loop control.

[Problems to be Solved by the Invention] However, in the conventional step motor drive circuit in which the maximum value of the rotation speed is set on the assumption that the voltage of the storage battery becomes lower than the rated voltage, the rated voltage or higher voltage is exceeded. However, even if it is possible to achieve rotation above the set maximum rotation speed, the rotation speed will be suppressed, and it will not be possible to improve responsiveness. There is a problem such as.

On the other hand, position detection using the winding of the step motor,
In the case of a closed-loop control step motor drive circuit that incorporates an encoder, etc., even if the power supply voltage fluctuates, it is possible to satisfactorily rotate at high speed while checking the position of the step motor rotor. There is a problem that the configuration of the drive circuit provided in the above becomes complicated and expensive, and the great advantage of the step motor, which is originally capable of performing open loop control with a simple configuration, is lost.

Therefore, the present invention has been made for the purpose of providing a stepper motor drive circuit capable of driving the stepper motor stably and at high speed even if the voltage of the storage battery fluctuates in the open loop control.

[Means for Solving Problems] The configuration of the present invention made to solve the above problems is as follows.
As shown in the basic configuration diagram of FIG. 1, a constant current circuit for receiving a power supply from a storage battery to generate a constant exciting current for driving a step motor and a pulse signal for sequentially switching the exciting phase of the step motor are provided. When a pulse signal generating means to be generated and a step motor acceleration or deceleration command are externally received, the pulse rate of the pulse signal generated by the pulse signal generating means is gradually increased or decreased in a predetermined pattern. A pulse rate increasing / decreasing means, a detecting means for detecting the exciting current or the output voltage of the storage battery, and an upper limit for setting the upper limit value of the pulse rate based on the exciting current or the output voltage of the storage battery detected by the detecting means. When the value setting means and the pulse rate increasing / decreasing means increase the pulse rate of the pulse signal according to an acceleration command from the outside. ,
When the pulse rate reaches the upper limit value set by the upper limit setting means, the pulse rate limiting means for stopping the increase of the pulse rate by the pulse rate increasing / decreasing means, and the pulse rate generating means for outputting the pulse rate The upper limit of the pulse rate is limited by the limiting means. The driving means is provided for sequentially switching the excitation phase for supplying a constant excitation current generated by the constant current circuit according to the pulse signal, and driving the step motor. The gist is a drive circuit for a step motor, which is characterized in that

[Operation] In the stepper motor drive circuit of the present invention configured as described above, the drive means is an excitation device that applies a constant excitation current generated by the constant current circuit in accordance with a pulse signal input from the outside. The step motor is driven with a constant current by sequentially switching the phases. The pulse signal input to this driving means is generated by the pulse signal generating means,
The pulse rate of the pulse signal is gradually increased / decreased or decreased in a predetermined pattern by the pulse rate increasing / decreasing means in accordance with an acceleration or deceleration command input from the outside.

That is, the drive circuit of the step motor of the present invention controls the rotation of the step motor by the constant current drive, and when the rotation of the step motor is increased according to an acceleration command from the outside, such as when the step motor is started. By gradually increasing the pulse rate of the pulse signal in a predetermined pattern, the so-called slow-up drive is performed to gradually increase the rotation speed of the step motor, and conversely, when the step motor is stopped, etc., according to an external deceleration command. When reducing the rotation of the step motor, the so-called slow-down drive is performed in which the rotation rate of the step motor is gradually reduced by gradually reducing the pulse rate of the pulse signal.

In the step motor drive circuit of the present invention, the detection means detects the exciting current supplied from the constant current circuit to the step motor or the output voltage of the storage battery, and the upper limit value setting means detects the detected exciting current or The upper limit value of the pulse rate of the pulse signal is set based on the output voltage of the storage battery. Then, when the pulse rate increasing / decreasing means increases the pulse rate of the pulse signal in accordance with an acceleration command from the outside, when the pulse rate reaches the upper limit value set by the upper limit value setting means, the pulse rate limiting means However, the increase of the pulse rate by the pulse rate increasing / decreasing means is stopped.

That is, in the present invention, when the pulse rate increasing / decreasing means increases the pulse rate of the pulse signal output from the pulse signal generating means to increase the rotation speed of the step motor, the pulse rate is equal to the exciting current or When the upper limit value set based on the output voltage of the storage battery is reached, the pulse rate limiting means determines that the rotation speed of the step motor has reached the upper limit value at which constant current driving is possible, and the pulse rate increasing / decreasing means changes the pulse rate The increase is stopped and the rotation speed of the step motor is kept at its upper limit value. As a result, the step motor is rotated at a constant speed at the maximum rotation speed that can be driven with a constant current until the deceleration command is input from the outside and the pulse rate increasing / decreasing means reduces the pulse rate of the pulse signal. Become.

[Embodiment] An embodiment of a drive circuit for a step motor according to the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram showing the structure of the drive circuit of the step motor of the first embodiment. As shown in the figure, the drive circuit 1 of the present embodiment is for driving a four-phase step motor 3 using a battery 2 of an automobile as a power supply.

The drive circuit 1 is supplied with power from the battery 2 through the stabilized power supply 4, and has a pulse signal (hereinafter referred to as a phase switching signal) for sequentially switching the excitation phases of the step motor,
And a microcomputer 5 including a detecting means, an upper limit value setting means, a pulse rate limiting means, a pulse rate increasing / decreasing means, and a pulse signal generating means for generating a signal for determining the rotation direction of the step motor, and output from the microcomputer 5. The control circuit 6 as a drive means for sequentially controlling ON / OFF of the exciting currents flowing in the exciting phases A, B, C, D of the step motor 3 by the phase switching signal and the like. It is composed of a constant current circuit 7 for making the flowing exciting current constant.

The microcomputer 5 has a read-only memory (hereinafter, also simply referred to as ROM) 10 in which a control program for driving the step motor and data necessary for control are written in advance, and a microprocessor for executing sequential execution according to this program. (Hereinafter, also simply referred to as CPU.) 11
And an AD converter 12 (corresponding to the detecting means) for converting the power supply voltage value required for execution processing into a digital value, and the converted voltage value or command value of the acceleration / deceleration switching SW13a or the rotation direction switching SW13b. , A random access memory (hereinafter, also simply referred to as RAM) 14 for temporarily storing various data necessary for processing, a signal for determining a rotation direction according to execution processing, and a phase switching signal for the control circuit 6 It is composed of an output unit 15 for outputting to. The operation of the microcomputer 5 will be described later in detail.

Next, every time the phase switching signal from the microcomputer 5 is input, the control circuit 6 generates a phase excitation signal for each phase A to D in the order of two-phase excitation in the rotation direction designated by the microcomputer 5. And the NPN type transistors 18a to 18d which perform switching operation so that an exciting current flows through the stator windings 17a to 17d of the step motor 3 which are collector-connected by the phase exciting signal.

The constant current circuit 7 is an NPN transistor 18a or 18c.
The current detection resistor 20ac connected to the emitters of the NPN type transistors 18a and 18c and the same NPN type transistor 1 so as to detect the exciting current flowing as a voltage value when the
A current detection resistor 20bd that detects the exciting current flowing as a voltage value when 8b or 18d is on, and the current detection resistor 20ac
And a current detection comparator 21ac and 21bd that outputs the result of comparison between the voltage value detected by 20bd and the reference voltage value set in advance according to the required torque output, and excitation according to the comparison result. When it is determined that the current value is large, a high level signal is output, and when it is determined that the exciting current value is low, a switching signal generators 22ac and 22bd that output a low level signal and the low level signal of the signal generator 22ac are output. A PNP that performs switching operation so that the excitation current value flowing in the stator winding 17a or 17c connected to the collector becomes a predetermined current value by turning on with a level signal and turning off with a high level signal.
Type transistor 23ac and switching signal generator
A PNP that performs a switching operation so that the exciting current flowing in the stator winding 17b or 17d with a 22bd signal has a predetermined current value.
Type transistor 23bd and these PNP type transistors 23a
stator winding 17a when c and 23bd are turned from on to off
Each of the elements is composed of diodes 24ac and 24bd connected to the collectors of the PNP type transistors 23ac and 23bd so as not to be destroyed by the back electromotive force generated at 17d to 17d.

The operation of the drive circuit of the step motor of the present embodiment configured as above will be described. FIG. 3 shows the control circuit 6
However, receiving the rotation direction signal and the phase switching signal from the microcomputer 5, the excitation phases of the step motor 3 are sequentially changed to 2
It is a timing chart showing the phase excitation signal which carries out phase excitation.

As shown in the figure, every time a phase switching signal is input to the distribution circuit 16 in the control circuit 6, the distribution circuit 16 outputs AB phase, BC phase, CD
The phase excitation signal is set to high level cyclically in the order of phase and DA phase. When the signal indicating the rotation direction is switched from the high level to the low level by the microcomputer 5, the distribution circuit 16 similarly turns the phase excitation signal to the high level in the order of the DA phase, the CD phase, the BC phase, and the AB phase. To In addition, as the cycle of the phase switching signal gradually shortens, the switching of the phase excitation signal becomes faster, and the rotation speed of the step motor increases. In this way, slow-up is performed to increase the rotation speed with a large load from the initial state of the step motor starting and stopping to the constant speed rotation.

When attempting to reverse the step motor that has reached bottom speed rotation, the drive circuit first performs a slowdown by gradually increasing the cycle of the phase switching signal, then changes the rotation direction, and the same as at startup. Slow down,
Guide the stepper motor to constant speed rotation. The above operation will be described in accordance with a control program for driving a step motor, which is executed by the microcomputer 5 shown in FIG.
In advance, when executing this program, the RAM 14 is assigned a slow-up counter for determining the cycle of the phase switching signal, in other words, the pulse rate of the phase switching signal,
The contents of the slow-up counter change according to the execution of the program. Further, the cycle data of the phase switching signal corresponding to the count value of the slow-up counter is written in the ROM 10, and the cycle becomes shorter (that is, the pulse rate increases) as the count value increases. There is.

Now, as the rotation speed of the step motor gradually increases, the impedance of the stator winding of the step motor also increases, so there is a lower limit to the cycle of the phase switching signal that can be driven with a constant current. In other words, in order to increase the rotation speed of the step motor, it suffices to shorten the cycle of the phase switching signal and increase its pulse rate. However, if the pulse rate is increased too much, the stator winding of the step motor will be increased. Since there is a case where the step motor cannot be driven with a constant current due to an increase in the impedance of, there is a limit in shortening the cycle of the phase switching signal and increasing the pulse rate thereof. The maximum current that can be supplied to the step motor is the battery 2
The lower limit value of the cycle of the phase switching signal (that is, the upper limit value of the pulse rate) varies depending on the output voltage of the battery 2.
It changes according to the output voltage of. Therefore, in this embodiment, RO
A map of the maximum value N of the slow-up counter with respect to the battery voltage having the characteristic shown in FIG. 5 is written in M10. By setting the maximum value N using this map, the cycle of the phase switching signal is changed. The lower limit value, that is, the upper limit value of the pulse rate can be set.

When the program is executed, first, step 101 is performed to clear the value Cs of the slow-up counter allocated in the RAM 14 and set it as the initial value. Next Step 103
Then, the battery voltage value is read through the AD converter 12 of the input unit 13, and in step 105, the maximum value N of the slow-up counter corresponding to the read battery voltage value is set by referring to the map shown in FIG. . In addition,
In this embodiment, the processing of steps 103 and 105 for reading the battery voltage value and setting the maximum value N of the slow-up counter corresponding to this value corresponds to the above-mentioned upper limit value setting means.

Subsequently, in step 107, the command values of the rotation direction changeover switch 13b and the acceleration / deceleration changeover switch 13a are read from the input unit 13, and in the next step 109, it is determined whether or not the rotation direction is changed, and the rotation direction is changed. If it is determined that the deceleration mode is not set, the process further proceeds to step 111, and it is determined whether the deceleration mode is set. If it is determined in step 111 that the mode is not the deceleration mode, that is, if the mode is the acceleration mode or the constant speed mode, the process proceeds to step 113, and if the data in the ROM 10 indicated by the value Cs of the slow-up counter is set as the cycle, the phase switching signal Is output from the output unit 15 to the distribution circuit 16 to perform processing as pulse signal generation means. Then Step 115
Then, as the pulse rate increasing / decreasing means, the value Cs of the slow-up counter is incremented to update the cycle data so that the cycle of the phase switching signal at the next output becomes short (that is, the pulse rate increases). Execute the process. Further, in step 117, it is determined whether or not the incremented value Cs of the slow-up counter is larger than the maximum value N, and the slow-up counter Cs has the maximum value N.
If it is determined that the value is Cs or less, the value of Cs remains unchanged, and if it is determined that the value is greater, the process proceeds to step 119 and the value of Cs is set to the maximum value N. Then, the process returns to the beginning of the routine indicated by and the process from step 103 is repeated. Eventually, the value of Cs reaches the maximum value N, and the step motor 3 rotates at a constant speed. The processing of steps 117 and 119 corresponds to the pulse rate limiting means of the present invention.

On the other hand, during driving, when the acceleration / deceleration switching SW13a is switched to deceleration in order to stop the step motor 3, the deceleration command value is read in step 107, and in the determination processing of step 111,
It is determined to be the deceleration mode. Then, the process proceeds to step 121 and the process as the pulse signal generating means for outputting the phase switching signal is executed in accordance with the cycle of the slow-up counter Cs as in step 113, but this time, the cycle is gradually lengthened with time. In other words, in other words, the pulse rate of the phase switching signal is gradually decreased, and in step 123, the value of the slow-up counter Cs is decremented in order to decelerate the step motor. Further, in step 125, it is determined whether or not this value is smaller than zero. If it is determined that it is not small, it is kept as it is, and if it is determined that it is small, the process proceeds to step 127, the value of Cs is set to zero, and it is indicated again by. The routine returns to the beginning of the routine described above and is repeated, and the step motor 3 is stopped.

Similarly, if the rotation direction switching SW 13b is switched while the step motor 3 is being driven, it is determined in step 109 that the rotation direction has been switched, and the process proceeds to step 131 to output the phase switching signal and reduce the speed. Similar to the mode, the slow-up counter is decremented so that the cycle becomes longer (that is, the pulse rate becomes smaller) in step 133, and the processing in steps 131 and 133 is repeated until the value of Cs reaches zero in step 135. . Then, returning to the beginning of the routine indicated by again, the rotation direction is changed, and the slow-up is started similarly to the start-up.

When this program is executed in this manner, the pulse rate of the phase switching signal increases with time as shown by the solid line in FIG. 6, and when the value Cs of the slow-up counter becomes equal to the maximum value N set previously, the phase switching signal Is maintained, and the step motor 3 starts rotating at a constant speed.

If the battery voltage value read by the AD converter 12 is, for example, 18 V, which is higher than the rated voltage 12 V, the step motor 3 can be driven with a constant current up to a higher rotation speed, so the maximum value N of the slow-up counter is N. Is set to a value larger than the above-mentioned value, and the pulse rate at constant speed is high
This is indicated by the one-dot chain line in FIG. For the same reason, when the battery voltage value becomes low, for example, when it drops to 5V, it becomes as shown by the broken line in FIG.

As described above, in the present embodiment, the step motor 3 is always driven with a constant exciting current so that the torque does not change as shown in FIG.

As described above, according to the drive circuit of the step motor of the present embodiment, the maximum rotation speed commensurate with the battery voltage can be realized without changing the open loop control. Further, since a constant exciting current is supplied regardless of the battery voltage value, the torque becomes equal, and an unstable phenomenon such as step out is unlikely to occur and stable rotation can be performed.

Further, since the step motor is driven according to the same cycle data regardless of the battery voltage from acceleration to constant speed, the slow-up can be stably performed, and the slow-up and slow-down cycle data are common, and the memory of the memory can be stored. You can also save money.

As described above, in the first embodiment, the battery voltage value is read as a digital value by the AD converter, and the lower limit value of the constant current drive period is set in order to determine the maximum rotation speed of the step motor. Without reading, the lower limit value of the cycle of the phase switching signal when the exciting current flowing in the stator winding of the step motor falls below a predetermined current value, in other words, the upper limit value of the pulse rate of the phase switching signal,
Also good. A stepper motor drive circuit constructed in this manner will be described below as a second embodiment of the present invention.

As shown in FIG. 8, the step motor drive circuit of this embodiment is realized by using a programmable timer module 30 instead of the AD converter used in the detection means of the first embodiment. It should be noted that the numbers of the respective parts of the present embodiment are represented by adding a dash to the numbers of the respective parts shown in the aforementioned embodiments in order to correspond to the aforementioned embodiments.

The programmable timer module (hereinafter also simply referred to as PTM) has an output unit 15 'of the microcomputer 5'.
A predetermined time proportional to the cycle of the phase switching signal is set through the data bus, and a clock serving as a reference for time measurement is also supplied to the CLOCK terminal of PTM30 from the output unit 15 '. Then, at the same time as the start, the PTM30 starts measuring the clock, and if the output of the switching signal generator 22'ac connected to the terminal of the PTM30 becomes active low before it reaches the set time, the microcomputer 5 is connected from the ▲ ▼ terminal of the PTM30. It is configured to output an active low signal to the'input section 13 '.

In this embodiment using such a PTM30, when the step motor is driven and the phase excitation signal of a predetermined excitation phase becomes high level, the excitation current begins to flow and the constant current circuit 7'is excited as shown in FIG. The current is increased until the current reaches a predetermined current value. When the current detection comparator 21'ac determines that the current value has reached the predetermined value, the switching signal generator 22'ac starts the switching operation and controls the exciting current to be constant. This switching operation is the ninth
If it is within the set time of the PTM 30 shown by the solid line in the figure, the PTM 30 outputs an active low signal from the terminal and the microcomputer 5'determines that the constant current has been reached. Then, as in the above-described embodiment, a phase switching signal having a shorter cycle than before is output to increase the acceleration of the step motor 3 ', and a predetermined time proportional to the cycle is set in the PTM30 again.
Repeat. When the set time becomes short as shown by the broken line in FIG. 9, the switching operation of the switching signal generator 22'ac does not occur within this set time. At this time, the microcomputer 5'determines that the constant current has not been reached, and thereafter stops updating the cycle, and the step motor 3 '
Enters constant speed rotation.

As described above, according to the drive circuit of the step motor of the present embodiment, it is not necessary to know the relationship between the battery voltage and the lower limit value of the cycle in advance, and the cycle of the phase switching signal corresponding to the battery voltage value is automatically calculated. The lower limit value of, that is, the upper limit value of the pulse rate of the phase switching signal can be set.

Further, since the exciting current value is directly read, stable constant current driving can be performed without problems even if the resistance value of the stator winding changes in temperature due to heat generation or the like.

In the above embodiment, the acceleration / deceleration switching SW and the rotation direction switching SW are provided for control, but sensor signals such as the number of revolutions and the position are input to the microcomputer to automatically determine the acceleration / deceleration and the rotation direction. It may be controlled.

[Effects of the Invention] As described in detail above, the drive circuit of the step motor of the present invention performs constant current drive of the step motor. When accelerating or decelerating the step motor, a constant exciting current is applied. The pulse rate of the pulse signal for sequentially switching the excitation phase for energizing is gradually increased or decreased in a predetermined pattern, and further, when the step motor is accelerated to increase the pulse rate, it is based on the excitation current or the output voltage of the storage battery. The upper limit of the pulse rate is limited by the set upper limit.

Therefore, according to the present invention, when accelerating the step motor to increase the pulse rate of the pulse signal, when the pulse rate of the pulse signal reaches the upper limit value capable of constant current driving the step motor, the increase of the pulse rate, In other words, it becomes possible to stop the acceleration of the step motor. Therefore, even if the voltage of the storage battery fluctuates, the step motor can be driven at the maximum rotation speed corresponding to the fluctuation. Further, in the present invention, since such control can be realized by open loop control that does not require a feedback system, it can be realized with a simple circuit configuration.

On the other hand, according to the present invention, on the other hand, the step motor is accelerated and decelerated (slow up, slow down) by gradually increasing and decreasing the pulse rate of the pulse signal within a range in which the step motor can be driven with a constant current. The step motor can always be stably driven without causing step-out during acceleration or deceleration of the step motor. In the present invention, the step motor can always be driven with a constant current by limiting the upper limit of the pulse rate, so that the pulse rate for slow-up and slow-down is always increased or decreased in a constant pattern. Even if the output voltage of the storage battery changes, it is only necessary to change the upper limit. That is, according to the present invention, it is not necessary to change the pulse rate increase / decrease pattern itself when the output voltage of the storage battery changes. Therefore, according to the present invention, one pattern data may be set in advance as the pattern data for increasing / decreasing the pulse rate, and the pattern for increasing / decreasing the pulse rate is changed according to the voltage fluctuation of the storage battery. The capacity of the recording medium for storing the pattern data can be made smaller than that of.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram showing a configuration of the present invention, FIGS. 2 to 7 show a first embodiment of the present invention, and FIG. 2 is a block diagram showing a configuration of a drive circuit of a step motor. ,
FIG. 3 is a timing chart showing a phase excitation signal when the step motor is driven by two-phase excitation, FIG. 4 is a flowchart showing a control program for driving the step motor, and FIG. 5 is a slow-up counter for the battery voltage. 6 is a characteristic diagram showing the change of the maximum value N of FIG. 6, FIG. 6 is a timing chart showing the operation of the slow-up according to the battery voltage, and FIG. 7 is a graph showing the change of the torque with respect to the pulse rate corresponding to FIG. FIGS. 8 and 9 show a second embodiment of the present invention. FIG. 8 is a block diagram showing the configuration of a step motor drive circuit corresponding to FIG. 2, and FIG. 9 is an exciting current. 3 is a timing chart showing signals such as “A”. 1 ... Step motor drive circuit, 2 ... Battery, 3 ... Step motor 5 ... Microcomputer, 6 ... Control circuit, 7 ... Constant current circuit 10 ... ROM, 11 ... CPU, 12 ... A / D converter, 13 ... Input Part 14 ... RAM, 15 ... output part, 30 ... programmable timer module

Claims (1)

[Claims] 1. A constant current circuit for receiving a power supply from a storage battery to generate a constant exciting current for driving a step motor, and a pulse signal generating means for generating a pulse signal for sequentially switching the exciting phases of the step motor. Pulse rate increasing / decreasing means for gradually increasing or decreasing the pulse rate of the pulse signal generated by the pulse signal generating means in a predetermined pattern when an acceleration or deceleration command of a step motor is received from the outside, Detecting means for detecting the exciting current or the output voltage of the storage battery; upper limit setting means for setting the upper limit value of the pulse rate based on the exciting current or the output voltage of the storage battery detected by the detecting means; When the rate increasing / decreasing means is increasing the pulse rate of the pulse signal according to an acceleration command from the outside,
When the pulse rate reaches the upper limit value set by the upper limit setting means, the pulse rate limiting means for stopping the increase of the pulse rate by the pulse rate increasing / decreasing means, and the pulse rate generating means for outputting the pulse rate Drive means for sequentially switching the excitation phase for energizing the constant excitation current generated by the constant current circuit according to the pulse signal whose upper limit of the pulse rate is limited by the limiting means, and driving the step motor. A drive circuit for a step motor, characterized in that