JPH02246794A - step motor drive circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant current chopping drive circuit for a step motor.

[Conventional technology]

As a method of driving a step motor, chopping drive uses a switching element such as a transistor connected in series to the excitation coil to control the current flowing through the excitation coil by periodically switching the excitation coil between energization and de-energization. The method is widely used. Switching control of the switching elements in this chopping drive is performed using a periodic waveform signal generated by an oscillation circuit or the like, or according to a coil current detected using a resistor.

When driving a step motor by chopping in this way, the larger the current flowing through the excitation coil, the higher the torque can be obtained, but on the other hand, heat generation in the motor and switching elements becomes a problem, and failures due to overcurrent are also a problem. This becomes a problem.

In addition, the higher the switching frequency of the switching element, the more stable the torque can be obtained because the current flowing through the coil is averaged over time, but heat generation due to switching loss in the switching element becomes a problem, and when the step motor is on standby, switching If the frequency is set low, the noise generated by the motor becomes a problem.

JP-A-62-110496 proposes an oscillation circuit that controls the amount of current flowing through the coil and the switching frequency of the switching element, and a coil current detection circuit that uses a resistor to solve these problems during chopping drive with a step motor. By comparing the respective outputs of the step motor and switching with the switching element accordingly, when the step motor is operating, the current can be increased and the switching frequency can be lowered to suppress heat generation due to switching loss. When the step motor is on standby, reduce the current to the extent that sufficient holding force can be obtained.

They also propose switching the output waveforms of each oscillation circuit so that the frequency exceeds the audible frequency. [Problems to be Solved by the Invention] The above-mentioned conventional technology controls the current flowing through the coil and the switching frequency by setting the energizing time and non-energizing time of the excitation coil in advance based on the output waveform of the oscillator circuit. This limits the maximum level of current.

However, since the rise time of the current when the excitation coil is energized varies depending on the energy remaining in the excitation coil, etc., it is necessary to accurately set the current flowing through the coil to a predetermined level at the energization time set by the output waveform of the oscillation circuit. It was difficult.

Furthermore, when limiting the amount of current flowing through the coil using the current detection circuit, it has not been possible to control the frequency at which the switching element is switched between energization and de-energization.゛An object of the present invention is to accurately control the current flowing through the coil to a constant level in order to efficiently obtain stable and high rotational torque when chopping a step motor, and to provide a simple circuit and control system. This provides a step motor drive circuit that can accurately set the current flowing through the coil and the switching frequency to arbitrary levels depending on the operating state of the step motor.

(Means for solving the problem) The above object is to provide a current comparison means that converts the amount of current flowing through the excitation coil into a voltage level using a resistor, etc., and compares it with a reference voltage that can be set arbitrarily; The energizing time is C
Non-energized time comparison means converts the voltage level into a voltage level using an R integration circuit or the like and compares it with an arbitrarily settable reference voltage, and sets the amount of current flowing through the exciting coil and the non-energized time of the exciting coil to respective predetermined levels. This is realized by a switching means that switches between energization and de-energization of the excitation coil so as to set the excitation coil.

(Operation) When the current comparison means detects that the current flowing through the exciting coil exceeds a preset current level, the switching means is turned off to de-energize the exciting coil, thereby reducing the current flowing through the exciting coil. The amount can be controlled to a certain level.

Furthermore, when the non-energizing time comparing means detects that the non-energizing time of the excitation coil exceeds a preset time, the switching means is turned on to energize the excitation coil. The switching frequency of energization can be controlled.

As described above, according to one aspect of the present invention, the current and frequency for chopping driving of the step motor can be set using a simple circuit and control without worrying about the rise time of the current in the excitation coil.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a schematic diagram of a constant current chopping drive circuit for a four-phase step motor using the present invention.

In FIG. 1, numerals 1 and 2 are a pair of excitation coils in a step motor. Switching between energization and de-energization of the excitation coil 1 is performed by MO8FET3, which is a switching element.
When O8FET3 is on, current flows from the vl power source to excitation coil 1, MO8FET3. Current detection resistor 5.
Flows to GND.

4 in Fig. 1 is a flywheel diode that allows the regenerative current I2 due to the back electromotive force generated when the exciting coil 2 switches from the energized state to the non-energized state to flow from the GND side of the exciting coil 1 to the voltage #1v i. can be.

This regenerative current control can prevent a decrease in torque in the motor during constant current chipping.

6 and 10 in Figure 1 are current setting comparators, respectively;
This is a comparator for setting the de-energized time.

If both (-) input voltages are higher than (+) input voltages, the output will be at GND level, and conversely, if (-) input voltages are (
+) When the voltage is lower than the input voltage, the output becomes a high impedance state.

In the current setting comparator 6, the voltage drop due to the current 11 flowing through the exciting coil 1 at the current detection resistor 5 is inputted to the (-) input, and the output of the D/A conversion circuit 7 is inputted to the (+) input.

In addition, the comparator 10 for setting the de-energization time.

The output of the D/A conversion circuit 11 is input to the (-) input, and the output of the current setting comparator 6 is input to the (+) input.

By adding an integrating circuit consisting of a resistor 8 and a capacitor 9 to the output of the current setting comparator 6, the output voltage is set to GND when the (-) input voltage of the current setting comparator 6 is lower than the (+) input voltage. It is made to gradually rise from the level to the voltage V.

A control signal 27 and a control signal 28 are inputted to the D/A conversion circuits 7 and 11, respectively, and output two types of voltage levels depending on whether these signals are 'High level or 'Low' level.

Reference numeral 12 in FIG. 1 is an AND gate, which includes a phase switching signal for selecting the exciting coil 1 and a comparator 10 for setting the non-energization time.
The output of
MO8FET3 is turned on when the current level is low.

The second diagram shows the operating waveforms of each part of the step motor drive circuit shown in FIG.

In Fig. 2, the phase switching signal 20 becomes 'High' at time L.
When the level reaches the level, the output voltage 26 of the AND gate 12 becomes 'v
2 level, MO8FET3 is turned on and the excitation coil 1 starts to be energized. As the current flowing through the exciting coil increases, the (-) input voltage 21 of the current setting comparator 6 increases.

When it becomes higher than the (+) input voltage 22 at time t3, the output voltage 23 of the current setting comparator 6 becomes the 'GND level. Accordingly, the output voltage 25 of the de-energization time setting comparator 10 goes to the GND level, the output voltage 26 of the AND gate 12 goes to the GND level, the MO8FET 3 is turned off, and the exciting coil 1 becomes de-energized.

As a result, the (-) input voltage 21 of the current setting comparator 6 falls to the GND level, so that the output voltage 23 is increased by the resistor 8. It gradually increases due to the action of the integrating circuit consisting of the capacitor 9, and when it becomes higher than the (+) input voltage 24 of the de-energization time setting comparator 10 at time t3, the output voltage 25
becomes 'High' level, and the output voltage 26 of AND gate 12 becomes 'V, 'L/to/L/to 1M08FET.
3 is turned on again, and the excitation coil 1 starts to be energized again.

The period when the phase switching signal 20 is at the 'High' level (from t to t
In i), the excitation coil 1 is energized as described above.

De-energization switching is performed repeatedly. MO8F at this time
The switching frequency at ET3 is 1/(t4- tz
), but this frequency can be switched in two stages by switching the period from time t2 to t in FIG. 2, that is, the non-energization time, using the control signal 28.

Next, a case will be described in which the amount of current flowing through the excitation coil and the switching frequency are switched at time t.

In this embodiment, when the step motor is on standby, the current amount is reduced and the switching frequency is increased above the audible frequency. By lowering both 24,
This can be easily done by the action of the current comparison comparator 6 and the non-energized time ratio comparison comparator.

The operation of the step motor drive circuit of FIG. 1 from time t7 to t8 DEG is performed in the same manner as from time t to time t.

In this embodiment, for example, when the excitation coil 2 is in a de-energized state, a regenerative current I2 flows due to the function of the flywheel diode 4, so even if the de-energized time is changed, the driving torque of the step motor is not greatly affected. .

Furthermore, in this embodiment, one switching element was used to switch between energization and de-energization by constant current chopping and to switch the excitation phase, but the same effect can be obtained when two switching elements are used. . Furthermore, although the output voltage of the D/A converter circuit that sets the current amount and non-excitation time is switched in two stages in this embodiment, it can easily be changed to more stages.

〔Effect of the invention〕

According to the present invention, in a constant current drive circuit for a step motor, the amount of current flowing through the excitation coil and the switching frequency for switching between energization and de-excitation can be set arbitrarily using a simple circuit and control. Sometimes, the amount of current is set to obtain sufficient drive torque, and the switching frequency is set low enough to minimize heat generation due to switching loss in the switching element, and when the step motor is on standby, it is necessary to The step motor can be driven more efficiently depending on driving conditions, such as by setting the amount of current to be small so as to obtain torque and setting the switching frequency to exceed the audible frequency.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a step motor drive circuit according to an embodiment of the present invention, and FIG. 2 is an operation waveform diagram of each part of the step motor drive circuit of FIG. 1. 1.2...Step motor excitation coil, 3...M
OSFET, 4... Flywheel diode, 5.
...Current detection resistor, 6.10...Voltage comparator,
7゜11...D/A conversion circuit, 8,9...CR integration circuit. 12...AND gate, 20-28...signal waveform.

Claims (1)

[Claims] 1. A switching means for switching between energization and de-energization of the excitation coil in the step motor, a current comparison means for converting the amount of current flowing through the excitation coil into a voltage level, and comparing it with a reference voltage that can be set arbitrarily; and non-energized time comparing means for converting the non-energized time into a voltage level and comparing it with an arbitrarily settable reference voltage, and based on the respective comparison results of the current comparing means and the non-energizing time comparing means. A step motor drive circuit characterized in that the amount of current flowing through the excitation coil and the switching frequency of the switching means can be arbitrarily controlled by switching the excitation coil to a de-energized state and a energized state, respectively.