JPH0642791B2 - DC motor speed control circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a DC motor speed control circuit for controlling the rotation speed of a DC motor used in a floppy disk drive or the like.

[Conventional technology]

A DC motor, particularly a brushless DC motor, is often used for rotating a medium in a file device in an electronic computer such as a floppy disk drive.

As shown in FIG. 6, the brushless DC motor is composed of a rotor 1 using a rotor and a stator 2 including a plurality of stator coils, and a magnetic sensitive element (hereinafter referred to as a hall element) arranged in each stator coil. By detecting the position of the rotor 1 and selectively exciting each fixed coil, the rotor 1 is rotated in a fixed direction.

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, showing a case having a three-phase stator coil.

In this case, the stator 2 is provided with stator coils of 3X, 3Y, 3Z corresponding to the three phases of X, Y, Z, and Hall elements 4X, 4Y, 4Z are arranged at the center of each coil. A rotor macnet 5 is divided into magnets for the rotor 1.

Here, the polarities of the rotor 1 are sequentially detected by the Hall elements 4X, 4Y, 4Z of the stator 2, and the respective outputs are amplified by the third amplifiers 6X, 6Y, 6Z of FIG. Is input to the microcomputer 7 (hereinafter referred to as μCPU) 7 from the input ports 8X, 8Y, 8Z.
The μCPU 7 identifies the position of the rotor by the polarities of the outputs of the Hall elements 4X, 4Y, and 4Z, and the output ports 9X, 9Y, and 9Z so that rotational torque is always generated in the same direction.
Outputs φX, φY, and φZ, respectively, and determines driving of the stator coils 3X, 3Y, and 3Z, and the rotor rotates in one direction.

By the way, this type of DC motor must be speed-controlled in order to rotate at a constant speed with a constant number of rotations.

Generally, for this speed control, it is usual to detect the rotational speed of the rotor and perform the control by this feedback.

This feedback control can be done by analog hardware, but recently, μCPU is often used because the cost of the device itself is low and the control is flexible.

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.

First, the rotational speed of the rotor is detected for control. There are various detection methods, but here, as shown in FIG. 10, the speed detecting magnet 10 is arranged around the outer circumference of the rotor magnet 5 and the magnetic flux generated thereby is arranged on the substrate on the stator side. It is based on the method of detecting by the zigzag speed detection pattern 11 made of copper foil. As a result, for example, 72 cycles of output are obtained per revolution, and the rotation speed can be known from the cycle.

This starts the speed control operation. First, the rotation of the rotor is the induced voltage due to the speed detection pattern 11 as a terminal 12a,
It is output to 12b, is converted into a pulse of V _T through the first amplifier 13, and is input to the interrupt terminal 14 of the μCPU 7.
With this, μCPU7 calculates the rotation speed of the DC motor,
The feed back amount is detected by comparing with the reference speed, and this is converted into an 8-bit binary code, b _{0 to} b ₇ . These b _{0 to} b ₇ are input to the D / A converter 15 for conversion into analog quantities. The output of the D / A converter is amplified by the second amplifier 16 and becomes the supply voltage of the coil drive circuit. As a result, the voltage applied to the coil is controlled so that the rotation speed becomes constant.

This is a phase locked loop system (PLL system)
That is, that is, the output of the speed detector is made to follow the accurate phase pulse serving as a reference. The phase reference is created by rotating the counter inside the μCPU. This is shown in time chart as shown in FIG.

The change point of the V _T input from the high level to the low level is detected, and the speed W is calculated as W = 1 / Tω from the phase shift θ from the reference at this point and the period Tω of V _T , and the phase shift amount K ₁ θ and the amount of velocity feedback for damping
K ₂ W calculates the fed back amount _{(K 1 θ-K 2 W} ) than.
This amount is converted into an 8-bit binary number and digitally transmitted to b _{0 to} b ₇ . In response to this, the output V ₀ of the D / A converter 15 is 0 ^V
Set as an analog amount between ~ +5 ^V. The output V ₀ is applied to the drive circuit 17 of each fixed coil 3X, 3Y, 3Z to perform feedback back, and the applied voltage to the fixed coils 3X, 3Y, 3Z is controlled.

[Problems to be solved by the invention]

However, according to the above-mentioned conventional technique, the D / A converter is required to calculate the feedback amount using the μCPU and convert the result into the analog amount.

This D / A converter requires an input line of 4 to 8 bits for input, and the μCPU output port, which has a limited number, is used exclusively for it, which reduces the controllable mechanism of the μCPU. It was

Further, although this D / A converter is normally a one-chip IC, there is a problem that it is expensive as compared with a logic IC or the like.

The present invention uses a small number of μCPU output ports, and
An object of the present invention is to provide a DC motor speed control circuit that does not use an / A converter.

[Means for solving problems]

The present invention comprises a drive circuit for a DC motor, a speed detector for detecting the number of revolutions of the rotor of the DC motor, and a control unit for calculating a feedback amount from the output of the speed detector and outputting this as a signal. A direct current motor speed control circuit which controls the applied voltage of the direct current motor by converting the signal output from the control part into a voltage value and applying it as a feedback to the drive circuit. So that the pulse width is shorter than the rotation cycle of
The feedback amount calculated from the output of the speed detector is converted into a pulse width corresponding to this feedback amount and is output as a control pulse, and short before the control pulse as compared with the rotation cycle of the DC motor. The control section is configured to output a reset pulse having a constant pulse width, and the control section is provided with a CTL signal output port for outputting the control pulse and an RST signal output port for outputting the reset pulse.
Connected to the L signal output port and the RST signal output port,
It discharges the charge on the capacitor while the reset pulse is on, charges the capacitor while the control pulse is on, and charges it while the control pulse is on while both the reset and control pulses are off. It is characterized in that it is provided with an integrating circuit for holding the electric charge of the capacitor, thereby obtaining an output of a voltage value for controlling the applied voltage of the DC motor.

[Action]

With the above configuration, the present invention obtains a feedback amount from the number of rotations of the rotor detected by the speed detector in the control unit, and based on this feedback amount, the feedback amount is compared with the rotation cycle of the DC motor. A control pulse with a short pulse width is obtained and output from the CTL signal output port, and immediately before this control pulse, a reset pulse with a constant pulse width shorter than the rotation cycle of the DC motor is output from the RST signal output port. .

In the integration circuit, the charge of the capacitor is discharged while the reset pulse is on, and the charge is charged to the capacitor while the control pulse input immediately after that is on, and the capacitor terminal voltage corresponding to the pulse width of the control pulse is discharged. Therefore, the capacitor terminal voltage is held while both the reset pulse and the control pulse are off.

Then, by applying the output of this terminal voltage to the drive circuit of the DC motor and performing feedback, the applied voltage of the DC motor can be controlled.

〔Example〕

 Embodiments will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a time chart of the same embodiment, FIG. 3 is a circuit diagram of a D / A converter of the same embodiment, and FIG. A time chart of the / A converter, FIG. 5 is a flow chart of the operation in the μCPU of the embodiment.

Incidentally, this embodiment also has the case of having a three-phase stator coil as in the conventional example, but the present invention is not limited to this.

In the figure, 3X, 3Y and 3Z are stator coils 4X and 4
Y and 4Z are Hall elements, and 18 is a μCPU as a control unit.

In this embodiment, the circuit for controlling the current flowing through the stator coils 3X, 3Y, 3Z is the same as that of the conventional example. That is, 6X, 6Y and 6Z are Hall elements 4X, 4Y and 4Z.
Third amplifier for amplifying the output of 8X, 8Y, 8Z is the third
Input ports for inputting the output amplified by the amplifier to the µCPU 18, 9X, 9Y and 9Z are stator coils 3X, 3Y and 3
These are output ports for outputting φY, φY, and φZ that determine the driving of Z.

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

Reference numeral 11 is a known speed detection pattern, which detects the rotation speed of the rotor by the method described in the section of the prior art and outputs this to 12a and 12b as an induced voltage. Reference numeral 13 is a first amplifier for amplifying the output induced voltage.

The μCPU 18 has an interrupt terminal 19, a CTL signal output port 20 for outputting a control pulse (hereinafter referred to as CTL signal), and an RST signal output port 21 for outputting a reset pulse (hereinafter referred to as RST signal), The signal input from the interrupt terminal 19 is calculated and the CTL is calculated from this.
A program shown by a flow chart in FIG. 5 is provided so as to emit a signal and, correspondingly, an RST signal. The explanation of FIG. 5 will be given later together with the explanation of the operation.

22 is the STL signal 20 and RS transmitted from the μCPU 18
The T signal 21 is converted into an analog voltage value to obtain the terminal voltage O
It is a D / A converter that outputs as a UT.

The D / A converter 22 is an RC integrating circuit including a resistor 23 and a capacitor 24, as shown in detail in FIG.

Reference numeral 25 denotes a second amplifier, and the terminal voltage OUT output from the D / A converter 22 is amplified through the second amplifier 25. Reference numeral 17 denotes a drive circuit for applying a voltage to the stator coil, which is a terminal voltage O amplified by the second amplifier 25.
UT becomes the supply voltage of the drive circuit 17.

The operation of this embodiment having the above configuration will be described.

First, the rotation of the rotor is output as induced voltage by the speed detection pattern 11 to 12a and 12b and is input to the interrupt terminal 19 of the μCPU 18 through the first amplifier 13. This signal is input for 75 cycles for 7 revolutions of the rotor, and μCPU18
Detects as an input when the input changes from high level to low level.

The μCPU 18 calculates the feedback amount by this.
In this embodiment, a PLL system with good rotation speed accuracy is adopted.

The outline is that first, a reference speed detection cycle that achieves a desired rotation speed in the μCPU 18 is accurately generated by an internal counter, and the actual output of the speed detector is controlled to match this. is there.

That is, as shown in FIG. 2, the μCPU 18 calculates the position difference θ from the phase reference from the counter value, and also calculates the speed W from the cycle Tω of V _T as W = 1 / Tω. Then, each of θ and W is multiplied by a coefficient to calculate (K ₁ θ−K ₂ W). K ₁ and K ₂ are values obtained from the stable condition of the servo system in consideration of conditions such as torque constant, time constant, rotation speed, load torque rotation fluctuation rate of the DC motor.

(K ₁ θ-K ₂ W) is then converted to a pulse width T _C with time values of minimum 0 and maximum nt. n is an even fraction of about 16 or 32, and t is a unit time of division, which is taken as the instruction cycle time of the μCPU 18.

With the above method, the μCPU 18 calculates the above-mentioned input signal and uses this as the CTL signal, and the CTL signal output port 20.
Send more. This is sent to the D / A converter 22.

The μCPU 18 operates in parallel with this CTL signal output operation,
The RST signal having a constant pulse width is output. The RST signal is always output from the RST signal output port 21 of the μCPU 18 before the output of the CTL signal.

The above-described operation in the μCPU 18 will be described with reference to the flow chart of FIG. The change point of the V ₁ input from the high level to the low level is monitored S ₁ , and if there is a change, the position difference θ from the phase reference is detected S ₂ , and then the speed W is detected by checking T ω to detect S _3. , From the position difference θ and the velocity W (K ₁ θ−
K ₂ W) is calculated and S ₄ , and the result is converted into a pulse width T _C and the calculation is ended S ₅ . Next, a pulse having a constant pulse width is output from the RST signal output port 21 as the RST signal S ₆ , and immediately thereafter, the CTL signal is immediately transmitted to the CTL with the pulse width T _c .
S ₇ output from the signal output port 20.

This is performed for each interrupt as a series of sequences.

Next, the operation of converting the pulse signal transmitted from the μCPU 18 into a voltage value in the D / A converter 22 will be described.

First, by the operation of the μCPU 18, the RST signal is input as a constant pulse width T _r and the CTL signal is input as a pulse width T _c according to the feedback amount.

On the other hand, in the spindle motor of the Floppy disk drive, the number of revolutions must be controlled to 300 rpm, so Tω ≈ 2.78 ms. For example, T _r + T _c is this Tω.
Of 1/10 or less, that is _{T r} ≒ _10μs, Tcmax ≒ _100μs
Select in.

Transistor 26 is turned on when the RST signal is turned on, the terminal voltage OUT of the capacitor 24 charges are rapidly discharge of the capacitor 24 becomes O ^V.

Next, when the CTL signal is turned on (low level), the transistor 27 is turned on, the capacitor 24 is charged from +5 ^v through the resistor 23, and the terminal voltage OUT rises as shown by the e curve in FIG. The rise value is determined by the time constant RC. This time constant RC is set to be larger than Tcmax,
It is necessary to select the optimum value for the second amplifier 25 in the next stage because of the gain.

The voltage of the terminal voltage OUT does not rise any further because the CTL signal is turned off during the rise. And RST, CT
When both L signals are turned off, the charge / discharge path is cut off.
The voltage at the time when the TL signal is turned off is held.

As a result, a voltage substantially proportional to the pulse width T _c is set as the terminal voltage OUT.

As described above, the pulse width T _c is converted into the voltage value. The voltage value of the terminal voltage OUT is as shown by OUT in FIG.

The OUT waveform is instantaneously lowered to 0 ^v in each cycle of V _T , which is not a smooth control voltage. However, since the reduced part f of this voltage is very short compared to the Tω length,
Since the currents of the stator coils 3X, 3Y, 3Z cannot follow this, they have no effect on the actual operation.

As described above, when the RST signal and the CTL signal output from the μCPU 18 are input to the D / A converter 22 and converted into a voltage value, the voltage value is amplified by the second amplifier 25 and applied to the drive circuit 17. .

As shown by V ₀ in FIG. 2, the applied voltage is fed back so that V ₀ becomes a high voltage when the rotation is slow and becomes a low voltage when the rotation is fast so that the rotation speed is constant.

As described above, the position difference .theta. From the phase reference is fed back and the voltages of the stator coils 3X, 3Y, 3Z are controlled.

〔The invention's effect〕

As described in detail above, according to the present invention, in the DC motor speed control circuit, the control unit controls the rotor of the DC motor so that the pulse width is shorter than the rotation cycle of the DC motor to be controlled. The feedback amount calculated from the output of the speed detector that detects the number of revolutions is converted into a pulse width according to this feedback amount and this is output as a control pulse, and immediately before this control pulse, the DC motor rotation cycle is set. The control unit is configured to output a reset pulse having a shorter constant pulse width by comparison, and the control unit is provided with a CTL signal output port for outputting the control pulse and an RST signal output port for outputting the reset pulse. Also, the controller is connected to the CTL signal output port and the RST signal output port, discharges the electric charge of the capacitor while the reset pulse is on, and charges the capacitor while the control pulse is on to reset the reset pulse. And a control pulse are both OFF, an integrating circuit for holding the charge of the capacitor charged while the control pulse is ON is provided as a D / A conversion unit. Since the output of the voltage value for controlling the voltage applied to the motor is obtained, it is not necessary to use an expensive D / A converter as in the past to convert the digital calculation result into an analog amount in the control unit, and the cost is reduced. There is an effect of doing.

Further, according to the present invention, since the number of control lines for controlling the D / A conversion unit is only two, it is not necessary to occupy the limited number of output ports of the control unit as in the conventional case, and the use of the control unit is possible. This has the effect of increasing efficiency.

Furthermore, according to the present invention, since the integrating circuit is an RC integrating circuit including a set of a resistor and a capacitor, the voltage is 0V.
However, since the pulse width of the reset pulse and the control pulse is shorter than the rotation cycle of the DC motor, the reset pulse is output immediately before the control pulse.
The voltage drop portion is very short compared to the rotation cycle of the DC motor, and even if an integrating circuit consisting of a pair of resistance capacitors is used, there is no effect on the operation of the DC motor. .

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a time chart of the same embodiment, and FIG. 3 is a D / A of the same embodiment.
A circuit diagram of the converter, FIG. 4 is a time chart of the D / A converter, FIG. 5 is a flow chart of the operation in the μCPU of the embodiment, FIG. 6 is a side sectional view of a brushless DC motor, and FIG. 6 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 brushless DC motor, FIG. 9 is a circuit diagram showing a conventional example, and FIG. 10 is the same. FIG. 11 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 coils, 4X, 4Y, 4Z ...
Hall element, 17 ... Driving circuit, 18 ... μCPU, 20 ... C
TL signal output port, 21 ... RST signal output port, 2
2 ... Converter.

Claims (1)

[Claims] 1. A drive circuit for a DC motor, a speed detector for detecting the rotational speed of a rotor of the DC motor, and a control unit for calculating a feedback amount from the output of the speed detector and outputting the feedback amount as a signal. A DC motor speed control circuit for controlling a voltage applied to the drive circuit by converting the signal output from the control unit into a voltage value and applying the voltage value as feedback to the drive circuit, wherein the control unit includes the DC The feedback amount calculated from the output of the speed detector is converted into a pulse width corresponding to the feedback amount so that the pulse width is shorter than the rotation period of the motor, and this is output as a control pulse, and Immediately before this control pulse, a reset pulse with a constant pulse width shorter than the rotation cycle of the DC motor is output. And a CTL that outputs this control pulse to the control unit.
A signal output port and an RST signal output port for outputting a reset pulse are provided, which are connected to the CTL signal output port and the RST signal output port of this control unit, discharge the electric charge of the capacitor while the reset pulse is ON, and It is equipped with an integration circuit that charges the capacitor while it is on and holds the charge of the capacitor that was charged while the control pulse is on while both the reset pulse and the control pulse are off. A DC motor speed control circuit, which obtains a voltage value output for controlling a voltage applied to a motor.