JPH0279798A - Step motor - Google Patents

Abstract

PURPOSE:To simplify the constitution of a circuit by measuring the ON-duty width of a chopped signal with a voltage which is detected at the coil-current detecting resistor of a chopper driving type step motor, and detecting a speed signal. CONSTITUTION:A coil L of a motor is connected to the output terminals of a bridge circuit comprising transistors(Tr) Q1 to Q4 which are connected in an inverter type. A coil-current detecting resistor Rs is connected between the bridge circuit and the ground. The voltage across both ends of the resistor Rs is compared CP2 with a reference voltage Vref2. AND operation of the result of comparison and a high frequency clock 5 is performed. The output of the AND circuit 6 is binary-counted 7. Timing control 9 is performed. Then, D/A conversion is carried out. Thus a speed signal is detected. A chopper control circuit 2 chops the gate voltages of the Trs Q1 to Q4 based on the voltage generated by the resistor Rs. The same processing is carried out for other phases. Thus the speed signal is obtained with a simple circuit.

Description

[Detailed Description of the Invention] +SS Field of Application] The present invention relates to a chopper-driven step motor having a rotor equipped with a magnet.

[Prior Art 1] Step motors have the advantage of being able to accurately control position in an open loop, but have the disadvantages of slow speed, large vibrations when stopped, and difficulty in applying braking.

Therefore, in recent years, even though it is a step motor, a speed sensor is installed, a detection coil is installed in the same place as the winding to detect the back electromotive voltage of the rotor, or a coil that is not excited is used for detection in a 4-phase motor. A method has been proposed in which the rotor is quickly stopped by controlling the current of the excitation coil' based on this speed information to perform stop control with less vibration. FIG. 5(a) shows the drive control system, in which the rotational speed of the step motor M is detected by a speed sensor S, the output of this speed sensor S is amplified by an amplifier AMP, and the drive circuit 20
feedback is applied to the input. A block diagram of this system is shown in Fig. 5(b)6.
), J is the moment of inertia of the rotor, B is the coefficient of viscous friction, D is the feedback coefficient, K is the constant of the motor (excluding the component (■)), θe is the input electrical angle, and θS is the output mechanical angle. Further, FIG. 6(a) shows the vibration state when the motor is stopped +Ir when the above-mentioned control is not performed, and FIG. 6(b) shows the vibration state when the motor is stopped when the control is performed.

However, in a step motor equipped with a magnet in the rotor, the method of detecting the speed by detecting the back electromotive force as described above requires multiple sensing coils outside or inside the motor, resulting in high costs. In addition, the method of using the unexcited fill of the 4-phase motor for sensing has the advantage of not requiring a separate sensing coil, but this is only possible with the unipolar drive method. In the bipolar system, all coils are always excited, so this method is not used.

Incidentally, in recent years, a chopper drive system has been often used to speed up the operation of a step motor, but this system has a problem in that the braking effect is particularly poor when the rotor stops, and the rotor does not stop smoothly. In other words, in a normal step motor, the rotor is braked by a change in the fill current due to the back electromotive force generated in the rotor, but since the chopper control circuit operates to flow a constant current through the excitation fill, the flicker tilJ is controlled. The circuit cancels out the current change, and the braking force is reduced to frictional force only, making it difficult to stop. Therefore, in order to apply braking in the 1,000-lapper drive system, feedback of the speed signal is essential, and in the past, a speed sensor was always required.

[Problem to be Solved by the Invention 1] The present invention has been made in view of the above points, and its purpose is to eliminate the need for a special speed sensor or sensing coil for speed sensing. The first object is to provide a step motor whose speed can be detected using a circuit.

[Means for Solving the Problems 1] In order to achieve the above object, the present invention provides a speed signal detection circuit that detects the on-duty of a chop signal from a coil current detection resistor and calculates the on-duty width to obtain a speed signal. It is equipped with

(Function) In the present invention, the speed change can be controlled by J! Arriving at the point appearing in the on-duty width of the chip signal that is varied in order to keep the current flowing through the I-magnetic coil constant, this on-duty width is detected from the voltage across the coil current detection resistor to obtain the speed signal. This is how it was done.

(Example) An embodiment of the present invention is shown in FIGS. 1 to 4.

First, a chopper drive type step motor, which is the basis of this embodiment, will be explained with reference to FIG. The drive circuit 1 that drives the excitation coil T- is connected to the drive circuit 1 (source VDD).
Two transistors Q1, Q, and Q in series across the
2, Q, and the series-connected transistors Q, ,Q, and zotrannostar Q2. Q.

This circuit uses an inverter type circuit configured by connecting an excitation coil I- between the connection points of the excitation coil By passing a current through the excitation coil I, an alternating current is caused to flow through the excitation coil I.

Note that 1. The normal drive power supply V I+r+ is a power supply voltage higher than the rated voltage of the excitation coil L, and the transistors Q , , Q ,
And when the transistors Q 2 and Q 3 are turned on, the rise time of the current flowing through the excitation filter L is made faster, so that the motor can rotate at high speed. Note that the transistor Q3. of the drive circuit 1 described above. A fill current detection resistor Rs for detecting the current flowing through the excitation coil is provided between the commonly connected emitters of Q and 7. The control circuit 3 creates an excitation phase switching signal for the step motor from clock pulses, CW/CCW switching signals, etc. output from a control device such as a microcomputer.
This excitation phase switching signal is used to turn on and off the transistor Qt+Q2, and this excitation phase switching signal is also output to drive circuits for other phases. The transistors Qff, Q of the drive circuit 1 are on/off controlled by a chopper control circuit 2. The ticktsuba control circuit 2 includes a comparator CP that compares the voltage across the resistor Rs with a reference voltage Vref.
, and R6 is reset by the output of comparator CP.
An oscillation circuit O8 that generates a pulse signal that determines the 7 rip 70 knob FF and the chopping frequency, and sets the R87 rip 70 knob FF at the rising edge of this pulse signal.
The output of the R87 lip 70-tube FF becomes the Natsubui δ.

The operation of this basic circuit is as follows. Now, a case will be described in which the trannostar Q is turned on by the htra magnetic phase switching signal. In this case, when the transistor Q is turned on by the output of the R87 lip 7C77 FF, that is, the output of the oscillation circuit 4 turns on the R87 lip 70 FF.
When F is set, current flows through the exciting coil L.

In this way, the excitation coil 1. When a current flows through, the resistance Rs
A voltage drop occurs across the . At this time, the voltage across the resistor Rs is compared with the reference voltage Vref by the comparator CPl, and when the voltage across the resistor becomes higher than the reference voltage Vref+, the output of the comparator CP becomes low level.
At this time, the fan plater CP shown in #1IJ8 diagram (b)
At the fall of the output of 1, R as shown in Figure 8(C)
Reset the 87-lip 70-tube FF and reset the transistor Q.
, turn off. Then, as shown in FIG. 8(d), the RS 7 U tube 70 tube FF is set by the output of the oscillation circuit 3, and the transistor Q is activated again.

turns on and repeats the above operation. Note that the same operation occurs when the transistor Q2 is on.

In other words, the on-duty of the R87 lip 70 tube FF is controlled so that a constant current flows through the excitation filter L in accordance with the reference voltage VreL set by the volume VR, as shown in FIG. 8(a). In this case, as explained in the section on the conventional example, when the rotor is stopped, the taper control circuit 2 cancels out the back electromotive force generated by the vibration of the rotor, resulting in poor braking characteristics.

Therefore, in the present invention, the fact that the tipper control circuit 2 has the function of canceling out the back electromotive force generated by the motor and keeping the current constant means that changes in the speed of the motor are caused by changes in the on-duty of the chipper control circuit 2. This focuses on the fact that it appears in Rs.

The following will explain how speed changes appear as on-duty changes. The equation of motion of the motor is: (2) A#I electrical equation... (3) B phase electrical equation Among these, focusing on the electrical equation (2) or (3), d
θ・Nφ−1~91rlθ is the velocity data, and L is ignored because dt is small.If you transform the equation as follows, it becomes ・−1 1A−−(e＾N16”5in19) Rdt.i If 8 is constant, Nφ'-'-s i n
You have to hit 0 minutes. FIG. 2(a) shows the vibration of the rotor, and FIG. 2(b) shows the speed change. In other words, in order for the current i to remain constant, the voltage must change to create the back electromotive force (see Figure 2).
This means canceling the speed signal shown in b). Here, since the change in voltage is nothing but a change in the on-duty of the chopper control circuit 2, the speed can be detected from this on-duty.

In this embodiment, the speed detection circuit 4 that detects the speed from the on-duty is connected to the voltage across the resistor Rs and the reference voltage Vr.
A comparator CP2 that compares ef2, a clock generation circuit 5 that generates a high-frequency clock signal, an AND date 6 that ANDs the output of the comparator CP2 and the output of the clock generation circuit 5, and the output of the AND date 6 is counted. A binary counter 7, a D/A converter 8 that converts the output of the binary counter into an analog value, and a timing control circuit 9 that controls the timing of the above-mentioned circuit.
It consists of

In this speed detection circuit 4, the voltage across the resistor R8 is compared with one reference voltage Vrefz by the comparator CP2, and a third
The on-duty of the chopper control circuit 2 shown in Figure (a) is detected. The output of this comparator CP2 and the output of the high frequency clock generation circuit 5 ((+3) in the tjS3 diagram) are ANDed at AND date 6. Then, by counting the output of the AND date 6 shown in FIG. 3(c) at this time, the pulse width of the on-duty is counted, and the output value of the binary counter 7 is A/D converted. A speed signal shown in No. 31(f) is obtained.

In addition, FIG. 3(d) shows the rear 2F output from the timing control circuit 9 in order to reset the binary counter 7.
The signal (e) in the figure shows a D/A conversion start signal.

The speed signal detected by the speed signal detection circuit 4 of this embodiment is shown by A in FIG. Note that the opening in the figure indicates the speed signal obtained by the tough generator. In this way, in this embodiment, a speed signal equivalent to a speed sensor or the like can be obtained without using a speed sensor or the like in terms of circuitry. Therefore, by integrating the circuit of this embodiment with the drive circuit or the diving control circuit into an IC, the cost can be reduced.

Note that the clock frequency of the clock generation circuit 5 and the resolution of the D/A converter 8 are appropriately adjusted according to the desired speed signal to obtain desired characteristics.

[Effect of the Invention 1] As described above, the present invention has the following advantages:
Equipped with a speed signal detection circuit that detects the on-duty of the knob signal and measures the on-duty width to obtain the speed signal, so it is possible to obtain the speed signal using a circuit without using a speed sensor or sensing coil. This has the effect of reducing costs. Also, if this method is used,
It is possible to detect the speed signals of all chipper-driven step motors that have magnets in their rotors, and if a diving control circuit is provided that applies braking based on this speed signal, the step motors can be stopped at high speed.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 (a) 1 and (b) explain the operation of the same as above, and Fig. 3 (a) to (f) explain the operation of the speed signal detection circuit. Figure 4 is a signal waveform diagram showing the speed fH obtained in the above, Figure 5 (a) is an explanatory diagram of a conventional step motor drive control system, Figure 5 (b) is a block diagram of the same as above, FIGS. 6(a) and 6(b) are explanatory diagrams showing vibrations of the rotor with and without guiping control, FIG. 7 is a circuit diagram of a conventional example, and FIG. 1 is a drive circuit, 2 is a chopper control circuit, 4 is a speed signal detection circuit, L is an excitation coil, [(S is a resistor for detecting fill current. Agent: Patent Attorney Ishi 1) Ai Shichi

Claims (1)

[Claims] (1) The rotor is equipped with a magnet, and the drive circuit that flows the excitation current to the excitation coil is driven chopper, and the current flowing to the excitation coil is detected by a coil current detection resistor, and the on-duty of the chop signal is varied to coil the coil. In a chopper-driven step motor that maintains a constant current,
A step motor comprising a speed signal detection circuit that detects the on-duty of the chop signal from the coil current detection resistor and measures the on-duty width to obtain a speed signal.