JPS6043753B2 - Motor speed control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a motor speed control device suitable for servo systems such as tape recorders (including VTRs).

Conventionally, when using a DC motor in the servo system that controls the rotational speed of the motor described above, an AC signal of a frequency corresponding to the rotational speed of the motor is extracted from a frequency generator connected to the rotational shaft of the motor. The above-mentioned frequency change of the alternating current signal is rectified to form a direct current control signal, which is appropriately amplified and then supplied to the motor to control the rotational speed of the motor.

When using an AC motor, insulate the control signal system from the motor connected to the AC power supply using an isolation transformer, for example, and control the variable impedance element connected in series to the motor to The rotation speed is controlled.

In the above-mentioned products, the motor has poor response characteristics and lacks color. In addition, a signal whose pulse width changes depending on the rotational speed of the motor is defined as a speed signal pulse, and the output obtained by this speed signal pulse and an indicator pulse that instructs charging or discharging for a predetermined period of time is A sample-and-hold type that is held in a capacitor has the advantage of fast response speed, but it is unstable as a servo system, and various compensation circuits are provided to compensate for the above instability. There is. In order to compensate for the instability of the above-mentioned system, the detection signal corresponding to the rotational speed of the motor is converted into a pulse, and the pulse is appropriately processed to have a pulse width corresponding to the rotational speed. In devices that extract a signal and convert it into DC, a considerably high F-V (frequency-voltage) conversion gain can be obtained during the pulse processing process, but it is difficult to generate negative feedback and stabilize the servo system. It was difficult to obtain compensation for this. The present invention has been made in view of the above points, and aims to provide a motor speed control device that stabilizes a servo system and has excellent response characteristics.The present invention can be summarized as follows. In other words, the configuration is such that the charging or discharging of the hold capacitor of the sample and hold circuit described above is made constant using a speed signal pulse whose pulse width changes according to the rotational speed of the motor. It aims to stabilize the system by removing positive feedback factors in the system.

Below, referring to FIG. 1, it will be explained how the positive feedback factor can be eliminated by making the charging or discharging of the hold capacitor in the sample hold circuit described above constant current. In FIG. 1, 1 is a detection signal detected according to the rotational speed of the motor, and when the rotational speed of the motor is fast, its period T. If it is slow, it will be shorter, and if it is slower, it will be longer. 2 is a speed signal pulse whose pulse width changes according to the rotational speed of the motor, and this pulse width ζ becomes narrower when the rotational speed of the motor is fast, and conversely becomes wider when the rotational speed of the motor is slow.

Reference numeral 3 indicates an indicator pulse for instructing discharge of the hold capacitor, and a predetermined constant pulse width is output according to the rotational speed of the motor.

That is, t1 described above is a variable constant, and T2 is a constant. Further, 4 is the sample hold output υ, the leading value at that time is indicated by e, and the initial value is indicated by V. is displayed. Considering the case where the charging of the hold capacitor is made constant current using the speed signal pulse (pulse width tl) described above, the leading value e of the sample hold output shown in (4) is e=υo+Ktl (K: constant),
The sample hold output V1 is (τ2: discharge time constant)
becomes.

A in formula (1). ．． B is a positive or negative constant
1T2l, respectively A=v♂】complete, B=
Ke7.

It is. Further, the sample hold output υ2 when the current is not constant is (τ1: charging time constant 5).

(2) C in formula, . D is a positive or negative constant, C=E−e, D=−(E−v −T2O)・e, respectively
]7. Equation (1) above (sample and hold output when constant current is used) shows that the sample and hold output υ1 is proportional to the pulse width of the speed signal pulse, and in this case it is stable as a servo system. A negative feedback closed loop can be constructed.

Further, in equation (2) (sample and hold output υ2 when the current is not made constant), the following equation is obtained by performing a Taylor expansion near 0 from the condition τ1)t1.

The second term in parentheses in equation (3) above is the output term for the servo.

However, the third term (10″ (÷P゜) is the second term (−
Since the sign is opposite to that of +2, the above-mentioned three-term component acts in the opposite direction to the servo, that is, causes positive feedback, and is a factor that makes the servo system unstable. In other words, the third term component above. The change in the bee is blocked by the square of t1.
It is a component that gives 1t1, and (+-(1)2
) becomes a positive feedback component because it changes in the opposite way to (1 y) and 2 γ1.

Therefore, in a device that is equipped with a sample hold circuit and controls a servo system by the output of the circuit, the sample hold circuit is controlled by a speed signal pulse whose pulse width changes according to the rotational speed of the motor as described above. By making the charging or discharging of the hold capacitor of the circuit a constant current, it is possible to eliminate the positive feedback factor that causes instability in the servo system, thereby making it possible to stabilize the servo system.

In addition, in the above-mentioned FIG. 1, 2 is explained as a speed signal pulse, but 3 may be used as a speed signal pulse to make it a constant current, and in the above, discharge is performed after charging, but It can also be implemented with a sample-and-hold circuit configured to discharge first and then charge.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment in which a DC motor is used, and its operation will be explained with reference to the waveform diagram shown in FIG. 3.

In the figure, M is a DC motor whose rotational speed is controlled as described later, and FG is a frequency generator connected to the rotating shaft of the DC motor M.

The frequency power generator PG outputs an alternating current signal S1 having a substantially sinusoidal waveform as shown in FIG. 3, the frequency of which changes depending on the rotational speed of the motor M. Frequency generator FG
The above-mentioned AC signal S1 is applied to an AC amplifier composed of three stages of transistor Q1 and inverters 11 and 12, where it is amplified, waveform-shaped, and limited, and its output is shown in FIG. A rectangular wave pulse S2 having a constant amplitude is extracted. The above-described pulse S2 from the inverter 12 is delayed by a required amount by a delay circuit composed of a resistor R1 and a capacitor C1, and is supplied to the inverter 13 as a signal S3 shown in FIG. Note that L1 in the figure indicates a threshold level. A signal S4 shown in FIG. 3 is outputted from the inverter 13. The diodes D1 and D2 constitute an OR circuit, and the diode D1 receives the output signal S4 from the inverter 13, and the diode D1 receives the output signal S4 from the inverter 13.
The output signal S2 from the inverter 12 described above is applied to the inverter 12, and the logical sum of the above respective signals is taken and the signal S shown in FIG. 3 is supplied as an input signal to the inverter 14. The output of the inverter 14 becomes a signal S6 shown in FIG. 3, and this signal S6 is directly connected to two stages of inverters 15 and 16 via a diode D3 and a charging/discharging element consisting of resistors R3 and R4 and a capacitor C2. is supplied to the buffer amplifier. The input signal to the inverter 15 is shown at S7 in FIG. 3. L in the diagram
2 indicates the threshold level. In addition, the above resistance R3
The variable resistor R2 connected in series with the above-mentioned signal S6
The pulse width τs can be arbitrarily set. The output of the inverter 16 constituting the buffer amplifier mentioned above is the S red signal shown in FIG. 3, and τυ in the figure is supplied as a speed signal pulse to the base of the transistor Q2. The width of τ shown in the above-mentioned signal S8 becomes wider when the rotational speed of the motor M is high, and conversely becomes narrower when the rotational speed of the motor M becomes slow, and the width of τυ is as described above. is the opposite. This is because the period of the AC signal S1 obtained from the frequency power generation ladder G becomes shorter when the rotational speed of the motor M becomes faster, and conversely becomes longer when the rotational speed of the motor M becomes slower. It can be easily understood. During the τ period of the signal S8, the transistor Q2 is off, but the speed signal pulse τυ
During this period, the transistor Q2 is turned on, and a constant current is supplied from the power supply +B via the emitter resistor R5 and the transistor Q2, and the hold capacitor C3 is charged.
Then, the output signal S8 from the inverter 14 mentioned above is applied as an indicator pulse to the base of the transistor Q3 to instruct the discharge of the hold capacitor C3, and along with the application of the indicator pulse S6, the output signal S8 of the transistor Q3 is applied to the base of the transistor Q3.
is turned on, and the charging voltage of the hold capacitor C3 is discharged via the resistor R6 and the transistor Q3.
The discharge time at this time is the period of the pulse width of the above-mentioned indicator pulse S6 (the pulse width of S6 shown in FIG. 3 and 6).
That is, the transistors Q2 and Q3 described above constitute a sample-and-hold circuit, and the transistor Q2 is a switching element for charging the holding capacitor C3, and is turned on only during the τυ period of the signal S8 shown in FIG. 38. . The transistor Q3 is a switching element for discharging the hold capacitor C3, and is turned on only during the pulse width of the indicator pulse S6 shown in FIG. 3. In this way, the sample-and-hold output from the hold capacitor C3 becomes an output signal shown as S9 in FIG. The rotational speed of the motor M is controlled to be constant. Note that the well-known Zener diode Dz inserted in the power supply +B line in the figure is for constant voltage. According to the above-mentioned device, when the rotational speed of the motor M increases,
The pulse width of the speed signal pulse τυ described above becomes narrower, and the charging time of the hold capacitor C-3 becomes shorter (
Charging time becomes shorter for a given discharging time.

) the sample and hold output (shown in Figure 3, 9) decreases;
Composed of transistors Q4 and Q5, the current supplied to the motor M from the DC amplifier decreases, and the speed of the motor M decreases to 7.
Decrease. In addition, when the rotational speed of the motor M becomes slow, the operation is opposite to the above, that is, the pulse width of the speed signal pulse τυ becomes wider, and the charging time of the hold capacitor C3 becomes longer (for a given discharge time). (The charging time becomes longer.) The sample hold output increases and the disturbance PC
The current supplied to the motor M from the amplifier increases, and the rotational speed of the motor M increases. Therefore, according to the device of the present invention described above, the rotational speed of the motor M is always controlled to be constant. Furthermore, actual measurements have confirmed that the ripple component of the sample-and-hold output is smaller in the device of the present invention than in the conventional device. It should be noted that even if the speed signal pulse and indicator pulse described above are interchanged, it can be implemented simply by taking into account the polarity of the DC amplifier described above, and the sample hold circuit can be replaced with a configuration that charges and then discharges as described above. Alternatively, the battery may be configured to be charged after being discharged.

Furthermore, although the present invention has been described above in the case of controlling the speed of a DC motor, the gist of the present invention can also be applied and implemented in the case of an AC motor. Next, the case where an AC motor is used will be explained using the circuit diagram shown in FIG. 4, together with the waveform diagram shown in FIG. 5, but its operation is not much different from that shown in FIG. 2.

In FIG. 4, 1 is an AC power supply, and 2 is a full-wave rectifier composed of a diode bridge. A motor (AC motor) M is connected to one end of the AC power supply 1, L1 is its main winding, L2 connected in parallel to the main winding L1 is a phase splitter winding, and C is a phase splitter. It is a capacitor. Similarly, the above-mentioned frequency generator FG is connected to the motor M. Therefore, S in Figure 5 1
An alternating current signal with a frequency corresponding to the rotational frequency of the motor M, indicated by ll, is obtained from the frequency generator FG, and the alternating current signal Sll is amplified, waveform-shaped, and limited by the transistors Qll and Ql2, and then transmitted to the transistor Q.
A rectangular wave pulse Sl2 with a constant amplitude as shown in FIG. 5 is obtained as the output of l2.

The pulse Sl. are applied to a differentiating circuit composed of a capacitor Cll and a resistor Rll interposed on the output side of the transistor Ql2, and are differentiated in the differentiating circuit, and the leading and trailing edges of the above-mentioned pulse Sl2 are respectively shown in FIG. Differential pulses Sl3 and Sl4 are generated as shown. The above fruit. In the implementation circuit example, in order to drive the transistor Ql3,
Although the above-mentioned positive polarity differential pulse Sl3 is used,
Of course, it is also possible to use the differential pulse Sl4 of negative polarity as appropriate. The above-mentioned positive polarity differential pulse Sl3
is applied to the base of the transistor Ql3, the transistor Ql3 is turned on at a portion above the threshold level Lll. By turning on the transistor Ql3, the charge in the capacitor Cl2 is discharged through the resistor Rl2, the diode D, and the transistor Ql3 only during the on period. When the transistor Ql3 is in an off state, the capacitor Cl2 is charged. The anode side of the diode D mentioned above (point A in the diagram)
The voltage waveform of is shown as Sl5 in FIG. still,
The slope of the waveform of the signal Sl5 when the capacitor Cl2 is charged is the same as that of the capacitor Cl2 and the resistor Rl2.
It is possible to change the time constant by making variable the time constant obtained by multiplying by, for example, by making the above-mentioned resistor Rl2 variable. By doing so, the pulse width of the speed signal pulse, which will be described later, can be arbitrarily set. Also,
The cathode side of the diode D (point B in the figure), that is, the collector output of the transistor Ql3 becomes a signal Sl6 shown in FIG. This signal Sl6 is supplied as an indicator pulse to the base of the transistor Ql6 in order to instruct discharge of the sample and hold capacitor Cl3 for a certain period of time, as will be described later. Transistor Ql4 is connected to resistor Rl
3" and Rl4, the emitter voltage of the transistor is E, and the base-emitter forward bias voltage is the sum of 2 (this is the input above the threshold level Ll2 shown in ) is supplied to the base, the transistor Ql4 turns on, and a signal Sl7 shown in FIG. 5 is obtained at the output of the transistor Ql4.This signal S
17 is supplied to a transistor Q15, and a signal Sl8 shown in FIG. 5 is obtained at its collector output. This signal Sl8 is supplied to the base of transistor Ql7 as a speed signal pulse. Pulse width τυ of the speed signal pulse
As described above, ? changes depending on the rotational speed of the motor M. That is, when the rotation speed of motor M becomes faster, the pulse width τυ becomes narrower, and conversely, when the rotation speed of motor M becomes faster, the pulse width τυ becomes narrower.
When the rotation speed of τ decreases, the width of τυ increases.
The above-described transistors Ql6 and Ql7 are a sample and hold circuit, and the above-mentioned speed signal pulse Sl8 is applied to the transistor Ql7, and the transistor Ql7 is in an on state for a period of τυ shown in the figure, and the hold capacitor Cl3 is connected to the power supply 1B. A constant charging current flows through the transistor Ql7 and the resistor Rl5.
In addition, the above-mentioned indicator pulse Sl is applied to the transistor Ql6.
6 is supplied, the transistor Ql6 is turned on only during the period of τS shown in the figure, the above-mentioned hold capacitor Cl3 is discharged via the transistor Ql6 and the resistor Rl6, and the output of the transistor Ql7 is a sample-and-hold output. 5. Output Sl9 shown in FIG. 8 is obtained. That is, the above-mentioned transistor Ql6 serves as a switching element for discharging the holding capacitor Cl3, and the transistor Ql7 serves as a switching element for charging the above-mentioned capacitor Cl3, respectively.
and operates for a predetermined period by supplying the speed signal pulse Sl8. The above sample hold output Sl9 is supplied to the motor (AC motor) M via the transistor Ql8, and is further amplified in power by the transistor Ql9,
The rotational speed of the motor M is limited so as to be constant. still,
The transistor Q2O and the Zener diode Dz in FIG. 4 are interposed for the purpose of constant voltage. In the circuit shown in FIG. 4 described above, the pulse width τv of the speed signal pulse Sl8 changes depending on the rotational speed of the motor M, and it is not possible to control the motor M to a constant speed according to the change in the pulse width. Since the operation is exactly the same as that of the circuit shown in FIG. 2 described above, detailed explanation of the invention will not be repeated.

As described above, according to the present invention, in a motor speed control device equipped with a sample and hold circuit, the rotational speed of the motor is controlled by pulse processing a signal from a frequency generator connected to the rotational shaft of the motor. In addition to obtaining a speed signal pulse whose pulse width changes according to the rotation of the motor, by similarly pulse-processing the signal from the frequency generator, a pulse with a fixed time width is output according to the rotation of the motor, and the sample and hold circuit and an indicator pulse instructing the discharge or charge of the hold capacitor, and the speed signal pulse causes the charge or discharge of the hold capacitor to be constant current,
Since the holding capacitor is discharged or charged at a predetermined period of time using the indicating pulse, a stable servo system can be constructed regardless of the type of motor, and the motor can be used with excellent response characteristics and versatility. A speed control device can be provided.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the present invention, Fig. 2 is a circuit diagram when the present invention is applied to speed control of a DC motor, and Fig. 3 is a waveform diagram contributing to explanation of its operation. FIG. 4 is a circuit diagram when the present invention is applied to speed control of an AC motor, and FIG. 5 is a waveform diagram contributing to explanation of its operation.

Claims (1)

[Claims] 1. In a motor speed control device equipped with a sample and hold circuit, the speed at which the pulse width changes according to the rotational speed of the motor by pulse processing a signal from a frequency generator connected to the rotational shaft of the motor. In addition to obtaining signal pulses, by similarly pulse-processing the signal from the frequency generator, a pulse of a certain time width is output in accordance with the rotation of the motor, instructing the discharge or charging of the hold capacitor of the sample and hold circuit. The speed signal pulse causes the holding capacitor to be charged or discharged at a constant current, and the indicator pulse causes the holding capacitor to be discharged or charged at a predetermined period of time. A motor speed control device characterized by the following features: