JPS62118784A - Speed controller for dc motor - Google Patents

Abstract

PURPOSE:To eliminate a D/A converter by outputting a reset pulse prior to a control pulse having a pulse width responsive to a speed deviation. CONSTITUTION:A speed detecting pattern 11 outputs the rotating speed of a rotor in the form of an induced voltage to inputs 12a, 12b of an amplifier 13, and input the speed through the amplifier 13 to the interrupt terminal 19 of a muCPU 18. The muCPU 18 outputs a control pulse CTL having a pulse width responsive to the positional difference between the speed signal and a reference signal, and outputs a reset pulse RST prior to the pulse CTL. A D/A converter 22 discharges a capacitor on the pulse RST, charges the capacitor on the pulse CTL to convert a digital signal to an analog signal, and applies it to a driver circuit 17.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a DC motor speed control circuit for controlling the rotational speed of a DC motor used in a floppy disk drive or the like.

[Conventional technology]

2. Description of the Related Art In file devices in electronic computing devices such as floppy disk drives, DC motors, particularly brushless DC motors, are often used to rotate media.

As shown in Figure 6, the brushless DC motor is a magnets I motor.
It consists of a rotor 1 and a stator 2 including a plurality of stator coils, and the position of the rotor 1 is detected by a magnetic sensing element (hereinafter referred to as a Hall element) arranged in each stator coil. The rotor 1 is rotated in a fixed direction by selectively exciting a fixed coil.

FIG. 7 is a plan view showing the stator 2 of the brushless DC motor, and FIG. 8 is a plan view showing the rotor 1 of the brushless DC motor, which has a three-phase stator coil.

In this case, the stator 2 is provided with stator coils 3X, 3Y, and 3Z corresponding to the three phases x, y, In step 1, the rotor magnet 5 is divided and magnetized.

Here, each Hall element 4X, 4Y of the stator 2.

4Z sequentially detects the polarity of the rotor 1, and the respective outputs are sent to third amplifiers 6X and 6Y in FIG.

6Z and input port 8X to a microcomputer (hereinafter referred to as μCPU) 7 as a control unit.

Input from 8Y and 8Z. μCPU7 is Hall element 4
The position of the rotor is identified by the polarity of each output of X, 4Y, and 4Z, and φX1 φ
Output Y1 φZ, stator coils 3X, 3Y, 3Z
The rotor rotates in one direction.

Incidentally, this type of DC motor must be speed controlled in order to rotate at a constant speed with a constant rotational speed.

In general, this speed control is usually performed by detecting the rotational speed of the rotor and using this feedback.

Although this feedback control can be performed using analog hardware, recently a μCPU is often used because the cost of the element itself is low and it allows flexibility in control.

A conventional DC motor speed control circuit will be described below. FIG. 9 is a circuit diagram showing an example of a conventional DC motor speed control circuit.

For control, first, the rotational speed of the rotor is detected. There are various detection methods, but here, as shown in Fig. 10, a speed detection magnet 10 is placed around the outer circumference of the rotor magnet 5, and the resulting magnetic flux is transferred to a copper foil placed on a substrate on the stator side. This method uses a zigzag speed detection pattern 11 according to the present invention. As a result, an output of, for example, 72 cycles can be obtained in one rotation, and the rotation speed can be determined by the period of the output.

This causes the speed control operation to begin. The rotation of the rotor is caused by the voltage induced by the speed detection pattern 11 at the terminals 12a,
12b, is converted into a vT pulse through the first amplifier 13, and is input to the interrupt terminal 14 of the μCPU 7. Accordingly, the μCPU 7 calculates the rotational speed of the DC motor, compares it with the reference speed, and detects the feedback amount.
This is converted into an 8-bit binary code, bO to b7. These bO to b7 are input to the D/A converter 15 in order to convert them into analog quantities. The output of the D/A converter is amplified by the second amplifier 16 and becomes the supply voltage for the coil drive circuit. Thereby, the voltage applied to the coil is controlled so that the rotation speed is constant.

This is based on a phase locked loop method (PLL method), that is, the output of the speed detector is made to follow an accurate phase pulse serving as a reference. The phase reference is created by rotating a counter inside the μCPU.

This is shown in a time chart as shown in FIG.

Detect the change point of the input from high level to low level, calculate the phase shift θ from the reference at this point and the period T of vT and the speed W as W = 1/'rω,
The phase shift amount Klθ and the speed feedback amount for damping are increased by 2W to the feedback amount (Klθ− is 2W
) is calculated. Convert this quantity to an 8-bit binary number b
(, -b7 is digitally transmitted. In response, the output vo of the D/A converter 15 is set as an analog amount between 0 and +5v. The output v□ is for each fixed coil 3X, 3Y.
, 3Z to perform feedback, and fixed coil 3X.

Control the applied voltages of 3Y and 3Z.

[Problem that the invention seeks to solve]

However, according to the above-mentioned conventional technology, an inverter is required to calculate the feedback amount using the μCPU and convert the result into an analog amount.

This D/A converter requires a 4 to 8-pit input line as input, and the output port of the μCPU, which is limited in number, is used exclusively for it, which has the problem of reducing the number of mechanisms that can be controlled by the μCPU. .

Furthermore, although this D/A converter is usually a one-chip IC, there is a problem in that it is more expensive than logic ICs and the like.

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC motor speed control circuit that uses fewer output ports of a μCPU and does not use a D/A converter.

[Means to solve all problems]

The present invention includes a speed detector connected to a drive circuit of a DC motor to detect the rotational speed of the rotor, and a control section that calculates a shift feedback amount from the output of the speed detector and outputs it as a signal. , a DC motor speed control circuit that converts a signal output from the control unit into a voltage value and applies this as feedback to the drive circuit to control the applied voltage of the DC motor, wherein the control unit controls the output of the speed detector. It is configured to convert the calculated feedback amount into a pulse width and output it as a control pulse, and to output a reset pulse with a constant pulse width prior to this control pulse, and this output reset pulse reduces the charge on the capacitor. While the discharge and second control pulses are on, this capacitor is charged through a resistor and a capacitor terminal voltage corresponding to the control pulse width is output.
The present invention is characterized in that it is equipped with a complete circuit that maintains this terminal voltage while both the reset pulse and the control pulse are off, thereby obtaining an output voltage value that controls the voltage applied to the DC motor.

[Effect]

According to the above configuration, the present invention calculates the rotational speed of the rotor detected by the speed detector in the μCPU, obtains the feedback amount, converts it into a pulse width, and outputs it as a control pulse. A reset pulse with a constant pulse width is output prior to the reset pulse, the output reset pulse discharges the charge in the capacitor, and then, while the control pulse is on, this capacitor is charged through the resistor and the charge is adjusted according to the control pulse width. A capacitor terminal voltage is output, and this terminal voltage is held while both the reset pulse and the control pulse are off.

By applying the output of this terminal voltage to the drive circuit of the DC motor and performing feedback, the voltage applied to the first-current motor can be controlled.

〔Example〕

Examples will be described below according to the drawings.

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a time chart of the entire embodiment, and Fig. 3 is a D/A diagram of the embodiment.
FIG. 4 is a circuit diagram of the converting section, FIG. 4 is a time chart of the D/A converting section, and FIG. 5 is a flow chart of the operation within the μCPU of the same embodiment.

It should be noted that although this embodiment also has a three-phase stator coil like the conventional example, it is not limited to this.

In the figure, 3X, 3Y, and 3Z are stator coils 4X.

4Y, 4Z are Hall elements, 18 is μCP as a control unit
It is U.

In this embodiment, the circuit for controlling the current flowing through the stator coils 3X, 3Y, and 3Z is the same as that of the conventional example. That is, 6X, 6Y, 6Z are Hall elements 4X, 4Y, 4Z
8X, BY, 8Z are the third amplifiers that amplify the output of
Input ports 9X, 9Y input the output amplified by the amplifier to μcptr1B.

9z is an output port that outputs φX, φY, and φ2 that completely determine the driving of the stator coils 3X, 3Y, and 3Z.

In the circuit diagram of FIG. 1, the configuration of the portion related to speed control in this embodiment will be explained below.

Reference numeral 11 denotes a well-known speed detection pattern, which detects the rotational speed of the rotor using the method described in the prior art section, and outputs this as an induced voltage to 12a and 12b. 13 is a first amplifier that amplifies this output induced voltage.

The μCPU 13 has an interrupt terminal 19, a CTL signal output port 20 that outputs a control pulse (hereinafter referred to as a CTL signal), and an R8T signal output port 21 that outputs a reset pulse (hereinafter referred to as an R8T signal). The signal input to the interrupt terminal 19 is calculated and the CTL is calculated from this.
A program shown in the flowchart of FIG. 5 is implemented to transmit the signal and, in response, to transmit the R8T signal.

The explanation of FIG. 5 will be given later together with the explanation of the operation.

22 is a D/A converter that converts the CTL signal 20 and R3T signal 21 transmitted from the μcpty 18 into analog voltage values and outputs them as a terminal voltage OUT.

As shown in detail in FIG. 3, the D/A converter 22 is an RC integrating circuit composed of a resistor 23 and a capacitor 24.

25 is a second amplifier, and the terminal voltage OUT outputted from the A/A converter 22 is amplified through the second amplifier 25. Reference numeral 17 denotes a drive circuit that applies a voltage to the stator coil, and the terminal voltage OUT amplified by the second amplifier 25 becomes the supply voltage of the drive circuit 17.

The operation of this embodiment with the above configuration will be explained.

The rotation of the rotor is output as an induced voltage by the speed detection pattern 11 to 12a and 12b, and is input to the interrupt terminal 19 of the μcpty 18 through the first amplifier 13. This signal is input for 75 cycles for 7 rotations of the rotor, and μCP
U113 detects as an input when the input changes from high level to low level.

μcpu1B calculates the feedback amount based on this. In this embodiment, a PLL system with good rotational speed accuracy is adopted.

The outline is that first, an internal counter accurately generates a reference speed detection cycle that produces a desired rotation speed within the μCPU 18, and then the output of the actual speed detector is controlled to match this cycle. be.

That is, as shown in FIG. 2, the μcpty 18 calculates the position difference θ from the phase reference from the counter value, and also calculates the speed W from the period Tω of vT as w=17″rω.

Then, multiply each of θ and W by a coefficient (Klθ− is 2
W) is calculated. Kl and K2 are values determined from the stability conditions of the servo system, taking into account conditions such as the DC motor's torque constant, time constant, rotation speed, and load torque rotation fluctuation rate.

(Klθ-2W) is then converted into a pulse width Tc having a time value of minimum 01 maximum nt. n is an equal fraction of about 16 or 32, t is the unit time of division, and μCPU 11
3 instruction cycle time.

Using the above method, the μCPU 18 calculates the input signal and transmits the CTL signal to the Dekaport 20 as a CTL signal. This is sent to the D/A converter 22.

In parallel with this CTL signal output operation, the μCPU 18 outputs an R8T signal having a constant pulse width. R8T
The signal must be sent to the CT of μCPU 18 before outputting the CTL signal.
It is output from the L signal output port 20.

The above operation within the /LCPU 18 will be explained according to the flowchart shown in FIG. 71 Human power monitors the change point from high level to low level Sl, and if there is a change, detects the position difference θ with the phase reference S2, then detects the speed W by checking τω, S5, Position difference θ and speed W (Kl
2W for θ-) is calculated, SLl, this result is converted to pulse width Tc and the calculation is completed S5゜Next, pulse i of constant pulse width as R3T signal
1 is outputted in step S6, followed by step S7 in which the CTL signal is immediately outputted from the CTL signal output port 20 with a pulse width Tc, and this is performed as a series of sequences for each interrupt.

Next, the operation of converting the pulse signal transmitted from the μCPU 18 into a voltage value in the voltage conversion section 22 will be explained.

First, by the operation of the μCPU 19 described above, the R8T signal is inputted as a constant pulse width Tr, and the CTL signal is inputted as a pulse width Tc depending on the amount of feedback.

On the other hand, in the spindle motor of the floppy disk 1 drive device, the rotation speed must be controlled to 30 Orpm, so Tω#2.78 ms, for example, Tr+
Tc is T (less than 1/10 of IJ, i.e. Tr#10μ
s.

Select Tcmax#100μs.

When the R8T signal is turned on, the transistor 26 is turned on, and the charge on the capacitor 24 is rapidly discharged, so that the terminal voltage OUT of the capacitor 24 becomes O.

Next, when the CTL signal turns on (low level), the transistor 27 turns on and the υ capacitor 24 is charged from +5V through the resistor 23, and the terminal voltage OUT rises as shown by curve 8 in FIG.

The rise value is determined by the time constant RC. This time constant RC is set to be larger than T'cmax, but it needs to be selected to an optimum value in relation to the gain of the second amplifier 25 in the next stage.

Since the CTL signal is turned off during the rise of the voltage of the terminal voltage OUT, the voltage of the terminal voltage OUT does not rise any further. and R8TXCT
When both L signals are turned off, the charging and discharging path is cut off, so C
The voltage at the time the TL signal is turned off is held.

As a result, a voltage approximately proportional to the pulse width Tc is set as the terminal voltage OUT.

As described above, the pulse width Tc is converted into a voltage value.

The voltage value of the terminal voltage OUT is as shown by OUT in FIG.

Note that the OUT waveform momentarily drops to 0 every cycle of vT, so the control voltage is not smooth. However, this voltage drop molecule is very short compared to the Tω length, so
The currents in the stator coils 3X, 3Y, and 3Z cannot follow this, so it has no effect on the actual operation.

As described above, the R8T signal and CTL signal which are multiple outputted from the μCPU 18 are input to the D/A converter 22 and converted into voltage values, which are all amplified by the second amplifier 25 and applied to the drive circuit 17. do.

As for the applied voltage, as shown by vO in FIG. 2, when the rotation becomes slow, vo becomes a high voltage, and when it becomes fast, the voltage becomes low, and feedback is applied to maintain a constant rotation speed.

As described above, the position difference θ with respect to the phase reference is fed back to control the voltages of the stator coils 3X, 3Y, and 3Z.

〔Effect of the invention〕

As explained in detail above, according to the present invention, the μCPU converts the feedback amount calculated from the output of the speed detector into a pulse width and outputs it as a CTL signal, and this CTL
Prior to the signal, a constant pulse width R8T signal is output, a circuit is provided to integrate both signals, and this is used as a D/A converter, and the voltage applied to the DC motor is controlled by the converter. Since a voltage value output is obtained, there is no need to use an expensive /A converter to convert the result of digital calculation by the μCPU into an analog value as in the conventional method, resulting in an effect of reducing costs.

In addition, according to the present invention, only two control lines are required to control the D/A conversion section, so the output ports of the μCPU, which are limited in number, are not monopolized as in the past, and the usage efficiency of the μCPU is improved. It has the effect of rising.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a time chart of the entire embodiment, and Fig. 3 is a D/A diagram of the embodiment.
A circuit diagram of the converting section, FIG. 4 is a time chart of the D/A converting section, FIG. 5 is a flow chart of the operation inside the μCPU of the same embodiment, and FIG. 6 is a side sectional view of the brushless DC motor.
Fig. 7 is a plan view showing the stator of the brushless DC motor shown in Fig. 6, Fig. 8 is a plan view showing the rotor of the same brushless DC motor, Fig. 9 is a circuit diagram showing a conventional example, and Fig. 10. 1 is a plan view showing a rotor of a brushless DC motor used in the conventional example, and FIG. 11 is a time chart of the conventional example. 3X, 3Y, 3z--Stator coil, 4X, 4Y
. 4z...Hall element, 17...2 drive circuit, 18.
...μCPU. 20...CTL signal output port, 21...R8T signal output port, 22...conversion unit. Patent Applicant Oki Electric Industry Co., Ltd. Agent Patent Attorney Takashi Kanakura Nisuke 2 Circuit diagram of the D/A converter of the Kunimoto Example 'T''f Flowchart of the operation inside the μCPU of the Example in bold 5
Mouth pongee 6 l @ 7 Mouth @ 9 Plan view showing the mouth rotor Conventional time chart 11 [i

Claims (1)

[Scope of Claims] A speed detector connected to a drive circuit of a DC motor to detect the number of rotations of a rotor, and a control unit that calculates a feedback amount from the output of the speed detector and outputs it as a signal. A DC motor speed control circuit that converts a signal output from the control unit into a voltage value and applies this as a feedback to the drive circuit to control the voltage applied to the DC motor, wherein the control unit includes a speed detector. It is configured to convert the feedback amount calculated from the output of The charge is discharged, and then, while the control pulse is on, this capacitor is charged through the resistor and a capacitor terminal voltage corresponding to the control pulse width is output, and while the reset pulse and control pulse are both off, this terminal voltage remains unchanged. What is claimed is: 1. A DC motor speed control circuit, comprising: a circuit configured to hold the voltage applied to the DC motor;