JPH05236796A - Driver for step motor - Google Patents

Abstract

PURPOSE:To set a constant conduction OFF time of coils for respective phases by outputting a primary switching signal(FS) when a detected phase current signal level exceeds a set current signal level and producing a secondary switching signal(SS) for turning a phase switching element OFF for a set time. CONSTITUTION:A comparator 23ac(23bd) receives a phase current signal Vac(Vbd) detected through a current limiting resistor Rac(Rbd) at the plus side terminal thereof while receives a set current signal Vref at the minus terminal thereof and produces (H level) an FSPSac(PSbd) if Vac(Vbd)>=Vref is satisfied. A monostable circuit 30ac(30bd) produces(H level) an SSSSac(SSbd) from the rising of FSPSac(PSbd). Duration(t) thereof is set by means of a resistor R and a capacitor C. Consequently, each element 22a-22d can be turned OFF for the set time(t) upon provision of the FSPSac(PSbd).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for a stepping motor, and more particularly to a driving device having a constant current control function.

[0002]

2. Description of the Related Art For example, four coils (CLa to CL
FIG. 3 shows a stepping motor (10) which has d) and which is driven to switch between the 1-2 phase excitation and its driving device (20).

In the figure, reference numerals 22a to 22d denote phase switching elements (drive transistors) serially connected to the drive power source (VM-PG) corresponding to the coils CLa to CLd of the stepping motor 1, respectively. PHa-P
ON / OFF control is performed in a predetermined procedure based on Hd. 21
NOR gates a and 21c (21b and 21d) form a constant current control circuit together with the comparator 23ac (23bd). In FIG. 3, 11 is a rotor, Rac (Rbd)
Is a current limiting resistor, and the phase current signal Vac (Vbd) is detected by this.

In the normal state, the comparator 23ac (23bd) cuts off the output of the switching signal PSac (PSbd) (H level), and the value of the detection phase current signal Vac (Vbd) is preset to the set current signal Vref. ． When the value is greater than or equal to the value, the output is generated (L level). That is,
The OFF time of the chopper, that is, the H level time of the switching PSac is determined by the balance of the resistance Rc of the comparator 23ac, the capacitor Cc, and the phase coil CLa of L.

This switching signal PSac (PSb
d) has phase switching signals PHa and PHc (PH
b, PHd) is connected to the NOR gate 21
It is input to the other terminal of a, 21c (21b, 21d).

In the driving device 20, for example, when the phase switching signal PHa is output (L level), the NOR gate 2
Since the output of 1a becomes H level, the phase switching element 22a becomes O
N, and a phase current flows through the energized coil CLa.
This phase current increases with time due to the inductance effect of the phase coil. Therefore, the phase current signal Vac detected by the current limiting resistor Rac rises as shown in FIG.

Thus, Vac ≧ Vref. Then,
Since the switching signal PSac becomes H level and the phase switching element 22a is turned off, the phase coil CLa is interrupted and the phase current signal Vac starts to decrease. After a lapse of a predetermined time, the phase switching element 22a is turned on again and this is repeated thereafter. Therefore, by the so-called constant current chopper drive control, the current flowing through the coil CLa can be made constant as shown in FIG. 4, and the stepping motor 1 can be rotationally driven with a predetermined torque continuously secured. That is, constant current control can be easily performed by appropriately setting the time constants of the comparators 23ac and 23bd.

[0008]

However, according to the above conventional structure, the capacitor Cc (C
Since the electric charge remains in c), O of the switching signal PSac
The FF (H level) time slightly changes, and the time tends to be short. Then, the phase current signal Vac (Vbd)
That is, as shown in FIG. 5, the phase currents of the coils CLa to CLd are set current signals Vref. Since the waveform becomes larger than the predetermined value determined by the above and becomes a waveform in the upper right, the generated torque increases and the temperature rises, and there is a strong possibility that the elements and the motor 1 are burned.

Nowadays, there is a strong demand for higher precision, smaller size, lighter weight, power saving, and cost reduction of a printer using the drive unit 20, and the influence of the residual charge cannot be ignored. ..

An object of the present invention is to provide a driving device for a stepping motor capable of controlling smooth rotation with a set constant current.

[0011]

A drive device for a stepping motor according to the present invention includes a comparator that compares a set current signal with each phase current signal to generate and output a switching signal. ON-O phase switching element
In a stepping motor drive device that performs FF to perform constant current control, the comparator is configured to be capable of outputting a primary switching signal when the detected phase current signal level is equal to or higher than a set current signal level, and A monostable circuit is connected between each phase switching element to input a primary switching signal, generate and output a secondary switching signal, and forcibly shut off the secondary switching signal after a set time has elapsed. ..

[0012]

In the present invention having the above structure, when the phase switching signal is input, the secondary switching signal is in the output cutoff state, so that the phase switching element is turned on and a current flows through the coil. The current value increases due to the inductance effect of the coil and reaches the set current value. Then, since the detected phase current signal level becomes equal to or higher than the set current signal level, the comparator generates and outputs the primary switching signal. Here, the monostable circuit receives the primary switching signal as an input, generates and outputs a secondary switching signal, and turns off the phase switching element. The time is determined by a preset time constant. That is, the OFF time of the phase switching element is constant. Therefore, when the phase switching element is turned on again after a certain time, a phase current flows.
By repeating this, the motor phase current value can be constantly controlled to the set current value.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the drive device (20) has the same basic configuration as that of the conventional example (FIG. 3), but the comparator 23a
c, 23bd and each phase switching element 22a, 22c, 22b,
22d, monostable circuits 30ac and 30bd are connected, and the output (H level) time of the secondary switching signals SSac and SSbd is forcibly made constant (t). The same components as those in the conventional example (FIG. 3) are designated by the same reference numerals, and the description thereof will be simplified or omitted.

In FIG. 1, the comparator 23ac (23b
d) is the positive side terminal input of the phase current signal Vac (Vbd) detected by the current limiting resistor Rac (Rbd) and the set current signal Vref. Is the negative terminal input, and Vac
(Vbd) ≧ Vref. In this case, the primary switching signal PSac (PSbd) is generated and output (H level). Capacitor C as in the conventional example (Fig. 3)
It is not held for a certain period of time using c.

Here, the monostable circuit 30ac (30bd)
Is formed of the LS123 element, and is configured to generate and output (H level) the secondary switching signal SSac (SSbd) at the rising edge of the primary switching signal PSac (PSbd) input to the B terminal. H
The level) time (t) is set by an external resistor R and a capacitor C. Therefore, Vac (Vbd) ≧ Vre
f. Becomes the primary switching signal PSac (PSb
It is possible to turn off the switching elements 22a to 22d for the set time t after the output of d).

In the drive device 20, as shown in FIG. 2, since the generation output (H level) time t of the secondary switching signal SSac is always constant, the phase coil current is accurately and stably controlled to the set current value. it can.

[0017]

According to the present invention, the comparator is configured to be capable of outputting the primary switching signal when the detected phase current signal level becomes equal to or higher than the set current signal level, and set with the primary switching signal as the input. The phase switching element is OF only for time
Since a monostable circuit that generates and outputs a secondary switching signal for F is provided, energization to each phase coil is turned off.
The time can always be kept constant, and smooth rotation drive with a constant torque can be performed while completely preventing motor overheating and burnout.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is likewise a timing chart for explaining the operation.

FIG. 3 is a circuit diagram showing a conventional example.

FIG. 4 is also a timing chart for explaining the operation.

FIG. 5 is also a timing chart for explaining the problem.

[Explanation of symbols]

 10 stepping motor 11 rotor 20 drive device 21a-21d NOR gate 22a-22d phase switching element 23ac, 23bd comparator 30ac, 30bd monostable circuit C capacitor R resistance CLa-CLd phase coil Rac, Rbd current limiting resistance Vac, Vbd phase current Signal Vref. Set current signal PSac, PSbd Primary switching signal SSac, SSbd Secondary switching signal PHa to PHd Phase switching signal

Claims (1)

[Claims] 1. A stepping device comprising: a comparator that compares a set current signal with each phase current signal to generate and output a switching signal, and turns on / off each phase switching element with the switching signal to perform constant current control. In a motor drive device, the comparator is configured to be capable of outputting a primary switching signal when the detected phase current signal level is equal to or higher than a set current signal level, and to provide a primary switching signal between the comparator and each phase switching element. A drive device for a stepping motor, characterized in that a monostable circuit is connected to which the secondary switching signal is input and which produces and outputs the secondary switching signal and which forcibly shuts off the secondary switching signal after a lapse of a set time.