JPS6210114B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotation speed control device for a small DC motor widely used in audio equipment, magnetic recording and reproducing devices, and the like.

Compact DC motors are widely used in tape recorders, record players, magnetic recording and reproducing devices, etc., and are equipped with a rotation speed control device to maintain a constant rotation speed even when load torque fluctuates. Drive controlled. FIG. 1 is a functional block diagram of a general rotational speed control device. 1 is a voltage comparator, 2 is an amplifier, 3 is a motor, 4 is a rotation speed detector, 5 is a frequency-to-voltage converter, and 6 is a reference power source. In FIG. 1, power is supplied from an amplifier 2 to rotate a motor 3, and a frequency-to-voltage converter 5 converts the output of a rotation speed detector 4, which outputs a frequency proportional to the rotation speed of the motor, to the rotation speed. Convert this voltage to a proportional DC voltage and combine this voltage with the voltage of the reference power supply 6.
If negative feedback is applied so that this differential voltage becomes smaller compared to Vr, the rotation speed will be approximately determined by the voltage Vr of the reference power source 6, and the rotation speed will be controlled to be constant even with load fluctuations. That is, voltage comparator 1
G ₁ and G 2 are the gains of the amplifier 2, G ₃ is the conversion rate of the rotation speed to the applied voltage of the motor, G ₄ is the conversion rate of the rotation speed to frequency of the rotation speed detector 4, _and conversion of the frequency-to-voltage converter 5. If the rate is G ₅ , the rotation speed ω
is, ω=G ₁ G ₂ G ₃ /1+G ₁ G ₂ G ₃ G ₄ G ₅ Vr
Vr/G ₄ G ₅ However, 1<< _{G 1} G ₂ G ₃ G ₄ G ₅ can be considered, and by varying the voltage Vr of the reference power source 6, it is possible to control the rotation speed to a constant value at any rotation speed. To explain in detail, when the rotation speed decreases due to load torque, the output of the frequency-to-voltage converter 5 changes as the rotation speed decreases, and the voltage of the reference power supply 6 changes.
The error voltage with respect to Vr increases, which eventually operates to increase the motor drive voltage and keep the rotation speed constant. However, in this configuration, in addition to the motor drive amplifier 2, a rotation speed detector 4, a frequency-to-voltage converter 5, a reference power source 6,
The voltage comparator 1 must be installed, making the circuit configuration complicated and expensive to implement.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a rotation speed control device for a small DC motor with a simple circuit configuration.

The main objective of the present invention is to control the rotation speed by actively utilizing the generator function that the motor inherently has, and by keeping the back electromotive force of the motor, which is proportional to the rotation speed, constant.

The present invention will be explained in detail below with reference to Examples. FIG. 2 is a circuit diagram showing the principle of the present invention, and FIG. 3 is an explanatory diagram of the operation. In Fig. 2, 11 is constant current I ₀
7, 8 are limiters, 9, 1 are constant current sources that supply
0 is a reference power source having voltages of opposite polarity and equal magnitude, and 3 is a motor. Constant current is applied to motor 3 without limiters 7, 8 and reference power sources 9, 10.
When I ₀ is supplied, the motor 3 is given a starting torque τ ₀ proportional to the constant current I ₀ and starts rotating. When driving a motor with a constant current source, unlike constant voltage driving, a constant power can be supplied regardless of the back electromotive force that accompanies rotation, so the rotation speed can be maintained until the torque loss caused by rotation and the supplied power are balanced. Rise. Therefore, the rotation speed characteristic with respect to the external load is a straight line connecting the no-load rotation speed No. and the starting torque τ ₀ , as shown by 12 in FIG. At this time, constant current source 11
Since the internal resistance of the motor is extremely large compared to the stator coil of the motor, a sine wave voltage with an amplitude proportional to the rotational speed is generated at the stator coil input terminal 16 of the motor. In order to control the rotational speed one after another, a case will be described in which a limiter represented by a reversely connected diode that limits the amplitude of positive and negative voltages and reference power supplies 9 and 10 that determine the conduction voltage level thereof are connected. At startup, since the motor is not rotating, no back electromotive force is generated, and there is no conduction between limiters 7 and 8, so all constant current I ₀ is supplied to motor 3.
Rotation is started at the desired starting torque τ ₀ . Next, as the rotation speed increases, the back electromotive force increases, and the positive and negative amplitudes of this back electromotive force signal become
When the limiter level determined by the voltage of 0 and the value voltage of the limiter is exceeded, the limiters 7 and ₈ start conducting, a part of the constant current I0 flows through the limiters 7 and 8, and the drive current to the motor decreases. , operates to prevent the rotational speed from increasing. Furthermore, even if the rotational speed is to increase, the back electromotive force will increase by that amount, and the amount of constant current _I0 sent to the limiters 7 and 8 will only increase, and the amount of flow into the motor will remain constant. The rotation speed remains constant. Therefore, by adjusting the values of the voltages -Vr and Vr of the reference power supplies 9 and 10, the desired rotation speed can be set. Can be controlled. Straight lines 13, 14, and 15 in Figure 3 are reference power supplies. Desired rotation speed setting for a decrease in the absolute value of voltage |Vr|. This shows how the control works. By inserting the limiters 7 and 8 as described above, the rotation speed is maintained constant even in response to fluctuations in load torque.
Here, when diodes are used for limiters 7 and 8, the internal resistance of the diodes is the applied voltage, in this case,
Since it operates so as to decrease as the back electromotive force increases, the internal resistance at the start of conduction cannot be said to be sufficiently small compared to the internal resistance of the motor coil, and it does not necessarily operate as an ideal limiter. In this case, the straight lines 13, 14, and 15 in FIG. 3 have characteristics shown by broken lines at the start of conduction. However, if the internal resistance of the coil is appropriately selected, it can be made close to the solid line of 13 to 15. The limiters that conduct with each other with opposite phase signal amplitudes have been described above, but even if there is only one limiter, the effect will be reduced, but the same effect will occur.

The same applies to the case where an NPN transistor 17 and a PNP transistor 18 are used instead of the limiters 7 and 8 as shown in FIG. Can be set. Power supplies 19 and 20 are bias sources that apply to transistors 17 and 18 to operate them. Here, since a diode or a transistor generally has its own conduction start voltage, in the case of a diode, the voltage between the anode and the cathode is V _F. In the case of a transistor, the voltage between the base and emitter is V _BE , In some cases, by appropriately selecting the internal resistance of the coil, it is possible to set and control the rotation speed to a desired value even if the conduction start voltage is not set.

The above explained constant current source drive, but even with a constant voltage source, it is difficult to realize an ideal constant voltage source and always has an internal resistance r _0. Therefore, at startup, the internal resistance rc of the motor coil It is possible to keep the rotation speed constant by flowing a current determined by the power supply internal resistance r ₀ and constant voltage V ₀ and making the limiter conductive as the rotation increases. At this time, the back electromotive force current to the limiter is shunted by the power supply's internal resistance r ₀ and the limiter's conduction resistance, so it does not necessarily operate as a perfect limiter, but if a resistor is inserted into the output of the constant voltage power supply, the limiter can be made more complete. can be operated. Furthermore, as in FIG. 1, if the voltages of the reference power supplies 9 and 10 in FIGS. 2 and 4 are controlled using a DC voltage proportional to the rotation speed, more precise rotation speed control can be achieved. That is, as shown in FIG. 5, the rotation speed detector 4 and the frequency-to-voltage converter 5 convert it into a DC voltage proportional to the rotation speed, and the output of the differential amplifier 21 which outputs mutually opposite phase voltages is used to control the limiter. 7,
By controlling the conduction start voltage of the frequency-to-voltage converter 5, the voltage sum of the voltage of the output of the frequency-to-voltage converter 5 and the offset power supply 23 becomes equal to the voltage of the reference power supply 22.
Here, the offset power supply 23 is for setting a desired rotation speed. With this configuration, in addition to controlling the rotational speed of the limiters 7 and 8, the conduction start voltage is also controlled, thereby compensating for imperfections in the limiters and allowing more precise control.

Although the limiter has been described above using a diode transistor, it is clear that a limiter that conducts by a back electromotive force generated depending on the rotational speed and in which the motor drive current is shunted will have the same effect.

As described above, according to the present invention, not only can a rotation speed control device be easily realized by installing a limiter at the output of a motor drive power source, but also the limiter can be controlled with a DC voltage proportional to the rotation speed. By controlling the conduction start voltage, more precise rotational speed control is possible.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional rotation speed control device.
FIG. 2 is a circuit diagram showing a principle embodiment of the present invention, FIG. 3 is a characteristic diagram for explaining the operation, and FIGS. 4 and 5 are circuit diagrams showing other embodiments of the present invention. 1...Comparator, 2...Amplifier, 3...Motor,
4... Rotation speed detector, 5... Frequency-to-voltage converter, 6... Reference power supply, 7, 8... Limiter, 9,
10...Reference power supply.

Claims (1)

[Claims] 1. A motor drive power supply means for supplying a constant current to the motor coil, a limiter circuit connected to a connection point between the motor coil and the motor drive power supply means and for limiting the voltage value, and a control means for varying the limiter level of the limiter circuit. A rotational speed control device, characterized in that the rotational speed of the motor is controlled by changing the limiter level of the limiter circuit by the control means.