JPH04208099A - Method of controlling stepping motor - Google Patents

Abstract

PURPOSE:To facilitate reduction of an effective current applied to the coil of a stepping motor and suppress the temperature rise of the surface of the stepping motor by a method wherein simple circuits are added so as to provide a plurality of constant current set values. CONSTITUTION:Comparators 16a and 16c and resistors 19a, 19b, 20a and 20b are additionally provided so as to facilitate selection of not only a constant current set value of 4A but also a constant current set value of 2.5A. In order to change the set value of the current applied to the coil of a stepping motor 14, when the current set value is switched from a small value to a large value, the switching is performed earlier than the timing of the switching of an operation mode by a time corresponding to the several driving pulses of the stepping motor 14 and, when the current setting value is switched from a large value to a small value, the switching operation is performed later than the timing of the switching of the operation mode by a time corresponding to the several driving pulses of the stepping motor 14. With this constitution, the effective current applied to the coil can be reduced and the temperature rise of the surface of the motor M can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a constant current control method for a driver for driving a stepping motor.

[Background of the invention]

Constant current control of a conventional stepping motor driver will be explained with reference to FIGS. 3, 4, and 5. Third
The figure shows a constant current control circuit of a driver for driving a two-phase stepping motor.

Stepping motor control data stored in the ROM 4 is sequentially read out and commands are executed.

RAM 5 and CPU 2 for freely reading and writing data necessary for CPU 2 and CPU 2 to execute instructions
The data output from the microcomputer unit 1, which consists of a port 3 for outputting data to peripheral elements and inputting data from the peripheral elements, enters the pulse generator 6 as an input signal. The pulse generator 6 sequentially outputs pulses (signal name CLK-N) for rotating the stepping motor 14 to the phase generator 7 .

The operation of the phase generator 7 will be explained with reference to FIG. When the signal DRV-N from I10 port 3 is at TTL level "L II", the phase generator 7 becomes active.The output signal A-P of the phase generator 7
goes “H” at the TTL level every time it detects the falling edge of the pulse CLK-N from the pulse generator 6 twice.
Repeat "L".The phase is 90 with respect to this signal A-P.
The signal B-P changes with a delay of 180 degrees, the signal -P changes with a delay of 1806 degrees, and the signal 10-P changes with a delay of 270 degrees. The period of the pulse from the pulse generator 6 is 71 to t2 (t1>t2) from t2 to t3.
(t2>t3), the signals A-'P, B-P
, A-P, and B-P also become shorter.

When the signal DRV-N is set to “Hu” at TTL level, the output signals A-P, B-P, λ-P of the phase generator
, B-P are all "L II" at TTL level.

Next, the driver section 8 shown in FIG. 3 will be explained. The names of the excitation phases of a stepping motor are A phase, B phase, A phase, and 1.
When the phase is set, the AND gate 9a is a power transistor l for passing current to the A phase coil of the stepping motor.
This is to make la ○N10FF. The AND gate 9a has two inputs, one of which is connected to the phase generator turf signal A-P. The other is connected to the output of the comparator 16b. When the two inputs are both at TTL level and trH"', the power transistor lla is ONL, and current flows to the A-phase coil of the stepping motor 14. One of the two inputs of the AND gate 9a is at the TTL level LL L II When , the power transistor lla turns off. When the power transistor lla turns on and current flows through the A-phase coil of the stepping motor 14, a voltage is generated across the resistor 13a. This voltage is determined by the current flowing through the coil. As it becomes larger, it becomes larger in proportion to it.AND gates 9b, 9
c, 9d, power transistor llb, llc, 11d
The same applies to

Resistors 21a and 22a are connected to the positive input of the comparator 16b for determining the upper limit of the current flowing through the A-phase coil and the human-phase coil of the stepping motor 14. One end of the resistor 13a is connected to the negative input, and a voltage generated across the resistor 13a when current flows through the A phase and the human phase is input. The resistor 12a is the comparator 16b
This is a current suppression resistor to prevent large current from flowing to the negative input of the When the upper limit of the current flowing in the A phase and the input phase is I, the voltage that appears across the resistor 13a is I
X (resistance value of the resistor 13a). If the values of the resistor 22a and the resistor 21a are determined so that this value is equal to 5×(resistance value of the resistor 22a)/((resistance value of the resistor 21a)+(resistance value of the resistor 22a)), the stepping motor 14 When the current flowing through the A-phase coil and the A-phase coil is smaller than the current, the output of the comparator 16b is "HII" at the TTL level, and "L" at the TTL level when it becomes larger than ■.
It becomes jl. That is, during the period when the signal A-P is 'H' at the TTL level to cause current to flow from the phase generator 7 to the human phase of the stepping motor 14, the current flowing through the resistor 1-3a is lower than the upper limit value I. When it is small, the output of comparator 16b is at TTL level.
pr, the power transistor lla turns on, and current flows to the A phase of the stepping motor 14. When the current flowing through the resistor 13a becomes larger than the upper limit value I, the output of the comparator 16b becomes ttL" at the TTL level, the power transistor lla becomes 0FFL, and the current flowing to the A phase of the stepping motor 14 stops flowing. Regarding the comparator L6d The same is true.

As described above, the current flowing through each phase of the stepping motor 14 is controlled to be constant so as not to exceed the upper limit value (■).

FIG. 5 shows the general operation of the stepping motor 14. CLK- output from pulse generator 6 on the vertical axis
The driving frequency PPS of the stepping motor 14 is determined by the period of N, and time is shown on the horizontal axis.

The stepping motor 14 operates from a stopped state in the order of startup, constant speed, and fall, which is considered as one sequence. Start-up means that the cycle of CLK-N from the pulse generator 6 is gradually increased from the lowest to the highest, so that the driving frequency of the stepping motor 14 reaches a constant speed of 2.
It ends when it reaches 200 PPS. The time required for this is approximately 20cm5ec. Falling down is the reverse sequence of acceleration. The time required for this is approximately 33ms
It is e c. Further, when the stepping motor 14 is stopped, detent is performed so that the stepping motor 14 does not operate independently of the signal from the phase generator 7 due to the force applied from the load. That is, by turning DRV-N output from I10 port 3 ON10FF at an arbitrary period, the phase generator tough signals A-P, B-P, λ-P, and signal-P are passed, and the TTL The level is set to It L I+, but by setting any two phases to tt Hpt, current is caused to flow through the two phases of the stepping motor 14, and the motor shaft is fixed. The detent time is approximately 61 m5ec. Further, the time for operating at constant speed is 326 m S e Q.

The torque required to operate the stepping motor 14 is larger at startup and shutdown than at constant speed and detent by the amount of acceleration torque. Therefore, when determining the upper limit of the current flowing through each phase of the stepping motor 14, the required operating torque is the maximum. In other words, it was necessary to match the timing of startup and shutdown, when the current flowing through the coil of the stepping motor 14 is maximum. The current required at this time is 4A.

4 in the same way as starting and falling during constant speed and chopping.
If a current of A is applied, the surface temperature of the stepping motor 14 will rise due to heat generated by the stepping motor 146. For example, when using a stepping motor with a rated current of 6 A, set the constant current to 4 A. Then,
The surface temperature of the motor increased by 50d, eg. Generally, the environment in which a motor is used is 0 to 50℃, and the surface temperature of this motor is MAX 100℃, and the insulation type is E class (
For those with a rated temperature of 130°C, there is no margin. Furthermore, in order to protect nearby cables and the like from damage due to heat, the motor had to be forcibly cooled with a cooling fan. Alternatively, it was necessary to select one with an even larger rated current of 8A.

[Purpose of the invention]

An object of the present invention is to eliminate the drawbacks of the prior art, reduce the effective current of the current flowing through the coil, and reduce the surface temperature rise of the motor while supplying sufficient current to generate the necessary operating torque of the stepping motor. An object of the present invention is to provide a constant current drive circuit that can perform a constant current drive circuit.

[Summary of the invention]

The present invention has the following features: 1. The required operating torque of the stepping motor (in other words, the current flowing through the coil) can be smaller during constant speed and detent than during startup and shutdown.

2. One operation sequence of a stepping motor is at a constant speed compared to the time required for startup and shutdown.

The time during detent is much longer.

(-As an example, the total time for startup and shutdown is 53m5e.
c, constant speed, day tent time is 387m5
It is ec. ) Focusing on the above two points, when starting up and stopping the stepping motor, increase the constant current setting value, lower the speed,
The relationship between the operating mode of the stepping motor and the current flowing through the motor coil has been devised so that the constant current setting value is lowered during detent.

Furthermore, in order to switch the constant current setting value, we focused on the fact that even if the command data is output from the microcomputer, the switching operation is not performed immediately because there is a time delay due to the operation of the hardware. When switching the current setting value from a low value to a high value, switch it earlier than the timing when switching the operating mode, and when switching the current setting value from a higher value to a lower value, switch it later than the timing when switching the operating mode. The relationship between the current setting value switching timing and the operation mode switching timing has been devised so that the current setting value can be switched.

[Embodiments of the invention]

Examples of the present invention are shown in FIGS. 1 and 2 (a), (b), and (c).
, will be explained using FIG. FIG. 1 is a circuit diagram of a constant current control system for a stepping motor showing an embodiment of the present invention. FIGS. 2(a), 2(b), and 2(c) are flowcharts of FIG. 1.

In Fig. 1, the same parts as in Fig. 3 are indicated by the same symbols,
Explanation of common parts will be omitted. An improvement over the conventional technology is that it has a plurality of constant current setting values and can be switched arbitrarily.

In this example, the constant current setting value in the conventional circuit is 4A.
In addition, comparators 16a, 16c and resistors 19a, 19b are installed so that a constant current setting value of 2.5A can be selected.
, 20a, and 20b have been added.

Also, constant current setting values 4A and 2.5A are connected to ■/○ port 3.
The signal CURRENT DW for selecting one of
N-N has been added.

This CURRENT DWN-N signal and the signal inverted by the inverter 15 are connected to the AND gates 17b and 1.
7d, 17a, and 17c, and further input to the driver section 8 through OR gates 18a and 18b.
It is connected to the. In other words, when selecting a constant current setting value of 2.5A, the CURR output from I10 port 3
ENTDWN-N signal at TTL level LL L IT
shall be.

At this time, comparators 16a and 16c connected to AND gates 17a and 17c are selected. Resistor 19a, 1
When the current flowing through the coil of the stepping motor 14 is smaller than the reference value 2.5A set by 9b, 20a, 20b, the power transistors lla, llb, llc
, the lid can be turned on, and the current flowing through the coil is
When it is larger than 2.5A, the power transistor lla,
llb, 11c, and 11d are turned off. CURRENT
When the DWN-N signal is set to "H" at the TTL level, the comparators 16b and 16d are selected, and the current flowing through the coil of the stepping motor 14 is kept constant at 4A.

In other words, the constant current setting value can be switched by the CURRENT DWN-N signal output from the I10 port 3.

Next, a series of operation sequences of the stepping motor 14 will be explained according to the flowchart of FIG.

To start the stepping motor 14, the DRV-N signal output from I10 port 3 is set at TTL level.
LIT and activate phase generator 7. Next, convert the CURRENTDWN-N signal to TTLLzVerte11
Hgg, and the constant current setting value is 4A. Next, start-up CLK data is input to the pulse generator 6 to start-up the stepping motor 14. The start-up operation is equivalent to 12 steps of the phase of the stepping motor 14, and the C L output from the pulse generator 6
The start-up operation continues until 12 K-'N are counted. The time required for the start-up operation is approximately 20 m5ec.

When the start-up mode is finished, the blowing mode shifts to the constant speed mode. First, low-speed CLK data is input to the pulse generator 6. The stepping motor drive frequency at constant speed is 2
It is 200pps. After entering the low speed mode, the number of CLK-H signals output from the pulse generator 6 is counted (6), and then the constant current setting value is switched from 4A to 2.5A.

After switching the constant current setting value to 2.5A and counting 701 CLK-Ns output from the pulse generator 6, the current setting value is switched to 4A again. In other words, with a current setting value of 2.5A, the stepping motor 14 operates at a constant speed for one CLK-N70, approximately 319m.
It is 5ec. Furthermore, after counting 10 CLK-Ns, the constant speed mode ends.

Next, shift to shutdown mode. First, the pulse generator 6 is provided with falling CLK data. The falling operation takes about 33 msec for CLK-N51 force count.
When 51 signals CLK-N from the pulse generator 6 (c) are counted, the falling mode ends.

Next, shift to detent mode. First, the constant current setting value is switched from 4A to 2.5A. Next, 6KHz (
7) Switch the signal DRV-N of I10 boat 3 at the TTL level to "HII tL L 11" at the cycle.
The motor shaft of the stepping motor 14 is fixed at the excitation phase that stopped last.

The above is the operation sequence of the stepping motor 14. In this example, the cycle in which the series of operations of the stepping motor 14 is repeated is approximately 440 msec.
Therefore, the detent period is about 61 m5ec.

With the above control, when the required operating torque is large (that is, the current that must be passed through the coil of the stepping motor 14 is large), the constant current setting value is set to 4 A, and the required operating torque is small (that is, the stepping motor When the current that must be passed through the coil of the motor 14 is constant (low current) and detent, the constant current setting value is switched to 2.5A. In addition, after issuing the constant current setting value switching mode from the microcomputer section 1, there is a wait for the hardware to actually switch.
K-N signal 6 pulses (about 2.7m5ec), 10 pulses before moving from constant speed to falling (about 4.5m5ec),
A difference is provided between the timing of switching the operating mode of the stepping motor 14 and the timing of switching the constant current setting value.

In this embodiment, the stepping motor 14 is
The effective current is 3.4 A, and the surface temperature rise value is 50
d e g, respectively 2.4A and 25d
eg, no external forced cooling fan is required, and a motor with a rated current of 4A can be used. (It is no longer necessary to use a motor with a rated current of 8A.)
[Effects of the Invention] According to the present invention, the effective current flowing through the coil of a stepping motor can be reduced by simply adding a simple circuit, so when selecting a stepping motor with the same temperature rating (for example, , E class 130° C.), it is possible to select a small motor with a current rating. Furthermore, even if the motor requires forced air cooling using an external cooling fan, the need for an external cooling fan is eliminated. Furthermore, since the capacity of the power supply for feeding the stepping motor can be reduced, the power supply can be made smaller and lower in price.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a constant current drive circuit for a stepping motor according to the present invention. 2(a), 2(b), and 2(c) are flowcharts for explaining FIG. 1. FIG. 3 is a circuit diagram of a conventional constant current drive circuit for a stepping motor. ,
FIG. 5, a time chart for explaining the operation of the phase generator, is a schematic diagram showing an example of an operating motor of a stepping motor and a state of constant current setting in the conventional and embodiments of the present invention. In the figure, 6 is a pulse generator, 7 is a phase generator, 8 is a driver section, 9a to 9d are AND gates, 11a to 1lcl are power transistors, 13
a and 13b are resistors, and 14 is a stepping motor. Name of patent applicant Hitachi Koki Co., Ltd.
μ2-dp゛) 6k) lZ/lff1fi DRV-N1 'H”L
'Ji1 Kidney included. 24 countries RVLN

Claims (1)

[Claims] A pulse generator that generates drive pulses, a phase generator that determines the order of the excitation phases of the power transistors using the drive pulses, and outputs them; and a drive circuit that drives the power transistors based on the output from the phase generator, and a current that flows to the coil of the stepping motor. It has a control circuit that keeps the current flowing through the stepping motor coil constant by cutting off the excitation signal of the power transistor when the current value exceeds a certain level. In a constant current drive circuit for a stepping motor that performs detent operation, when changing the setting value of the current flowing through the stepping motor coil in each operation mode of startup, constant speed, fall, and detent. , when switching the current setting value from small to large, the switching time is equivalent to several stepping motor drive pulses earlier than the timing of switching the operating mode, and when switching the current setting value from large to small, the operating mode Rather than the timing to switch
A method for controlling a stepping motor characterized by switching a current setting value late by a time corresponding to several pulses of the stepping motor drive pulse.