JPH08205582A - Circuit for controlling speed of dc motor - Google Patents

Abstract

PURPOSE: To select at least two preset speeds of a DC motor, by presetting through a simple circuit configuration the controlling signal (voltage) for the applied voltage to the motor while using an inputted power supply voltage for driving the motor and a predetermined voltage, and by altering the control signal (voltage) through an external signal. CONSTITUTION: The emitter terminal of a transistor TR2 is earthed, and its base terminal is connected with an external switching circuit 28. By the external switching circuit 28, the inputted signal to the base terminal of the transistor TR2 can be switched from a low level to a high level, and vice versa. Hence, the state between the collector and emitter of the transistor TR2 can be made to be OFF or ON-state according to the case of the circuit 28 outputting the low or high level signal, and thereby, the voltage fed to a comparator 20 can be altered. By this alteration, the preset speeds of a DC motor 12 can be swiched to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a bridge circuit including an internal resistance of a DC motor, and a speed control circuit of the DC motor for maintaining a rotation speed at a predetermined speed regardless of a load applied to the DC motor. Regarding

[0002]

2. Description of the Related Art Conventionally, in a paper feeding motor (DC motor) used in a copying machine or the like, it is necessary to prevent speed fluctuation due to load fluctuation. A bridge servo system is generally used as an electronic governor system for electrically detecting load fluctuations without using a sensor device such as a rotation sensor for speed fluctuations based on the load fluctuations.

In the bridge servo system, the voltage generated by the rotation of the DC motor is compared with a preset reference voltage, and the voltage applied to the DC motor is changed based on the comparison result (voltage difference). The rotation speed is kept constant. As a conventional technique to which this bridge servo system is applied, Japanese Patent Laid-Open No. 3-49586 (hereinafter, referred to as
Prior art 1), JP-A-5-91778 (hereinafter, referred to as
JP-A-5-2119773 (hereinafter referred to as prior art 3) and the like are disclosed.

In the prior art 1, the voltage drop of the diode is used as the reference voltage. However, since the value of the voltage drop of the diode changes greatly depending on the flowing current, the diode may be changed depending on the load depending on the load. The accuracy of speed control deteriorates significantly.

Further, in the prior art 2, the speed is set by the Zener diode, and the Zener diode also changes the Zener voltage depending on the magnitude of the current. Therefore, when the load change is large, the accuracy is lowered. As a method of switching the speed of the motor, a configuration is disclosed in which two types of Zener diodes are selectively switched by a switch.

As described above, the comparison circuit using the diode and the Zener diode cannot be applied to a load fluctuation such as a paper feeding motor of a copying machine.

Next, in the prior art 3, the reference voltage is fixed and the potential difference between the bridges is compared with the divided voltage. By adjusting this voltage division ratio, the set rotational speed is finely adjusted. The prior art 3 has a built-in dedicated reference voltage generating circuit and is relatively good in accuracy. Further, the speed of the motor can be controlled with good responsiveness to load fluctuations.

[0008]

However, in the prior art 3, the division ratio is adjusted in order to finely adjust the set rotational speed, but the impedance matching is not performed, so that the adjustment work is not performed. It becomes complicated. Further, when switching the speed of the motor, it is necessary to readjust it from the beginning, which is unsuitable for, for example, a device in which the motor needs to be operated at a two-speed shift.

In the present invention, in consideration of the above facts, by matching the impedance of the circuit, a signal (voltage) for controlling the voltage applied to the motor with a simple circuit configuration is supplied with a predetermined power supply voltage for driving the motor and a predetermined voltage. It is possible to obtain a speed control circuit of a DC motor that can be set by a voltage and that can select at least two kinds (binarized signals in the case of two kinds) of set speeds by an external signal. Is the purpose.

[0010]

The invention according to claim 1 has a bridge circuit including an internal resistance of a DC motor,
A speed control circuit of a DC motor for maintaining a rotation speed at a predetermined speed irrespective of a load applied to the DC motor, and a voltage V across which is generated by driving the DC motor.
_The comparison result includes a first input end to which ₃ is input and a second input end to which a voltage V ₁ based on a power supply voltage to the DC motor and a predetermined reference voltage V ₂ are input. comparison means and the applied voltage control means for controlling a voltage applied to the DC motor based on the control voltage V _O output from the comparison means for outputting a control voltage V _O in accordance with,
The predetermined voltage switching means for changing the reference voltage V ₂ in at least two stages and the control voltage V _O are V ₀ = n (V ₃ −
V ₂ −V ₁ ) [n: positive number] Impedance constructed by combining a plurality of resistors in order to set the values of the voltages V ₁ and V ₂ input to the second input terminal And a matching circuit.

[0011]

According to the first aspect of the present invention, the voltage V ₃ between both ends which changes according to the driving state of the DC motor is input to the first input of the comparison means. On the other hand, the voltage V ₁ based on the power supply voltage and a predetermined reference voltage V ₂ which is determined in advance are input to the _second input terminal. By comparing the voltages input to the first and second input terminals, the comparison means outputs the control voltage V ₀ .

The control voltage V ₀ is supplied to the applied voltage control means, and the voltage applied to the DC motor is set based on the control voltage V ₀ . For example, when the load applied to the DC motor increases, the counter electromotive voltage decreases and the voltage V ₃ across the voltage decreases. Due to this voltage drop, the control voltage V
₀ decreases, and the voltage V ₁ is increased in inverse proportion to this decrease. Conversely, when the load on the DC motor decreases, the control voltage V ₀ increases and the voltage V ₁ decreases.

As a result, the DC motor can keep the current substantially constant regardless of the load increase / decrease, and can maintain a predetermined rotation speed.

Here, the predetermined rotation speed is determined by the voltages V ₁ and V ₂ , but the predetermined voltage switching means can change the reference voltage V ₂ in at least two stages. . For example, as a means for easily changing the reference voltage V ₂ , an NPN type switching transistor is used, and a binarized signal (L, H) is supplied to the base of the switching transistor so that E-
The conduction and non-conduction between C are controlled to divide the reference voltage.

By the way, when a predetermined rotation speed, that is, a voltage applied to the DC motor is set, if the impedance matching of the entire circuit is ignored, the setting work becomes complicated, and the desired rotation speed cannot be easily obtained. . Therefore, in the impedance matching circuit of the present invention, the control voltage V _O is V ₀ = n (V ₃ −V ₂ −V ₁ ) [n: positive number]
It is configured by combining a plurality of resistors so as to obtain. Thus, the values of the voltages V ₁ and V ₂ input to the second input terminal (in particular, the setting of the reference voltage V ₂ by the predetermined voltage switching means) can be easily performed.

[0016]

【Example】

(First Embodiment) FIG. 1 shows a DC motor speed control circuit 10 according to the first embodiment.

One end of the DC motor 12 is grounded,
The other end is connected to the collector terminal of the PNP transistor TR1 via the resistor R9. This transistor TR
A signal line 14 for applying a power supply voltage (+ 24V) is connected to the emitter terminal of 1. Therefore, the transistor TR1 can control the voltage applied to the DC motor 12 according to the control voltage V ₀ input to the base terminal via the resistor R10.

The collector terminal of the transistor TR1 is
One end of the resistor R7 is connected in parallel with the resistor R9, and the other end of the resistor R7 is connected to one end of the resistor R8. The other end of the resistor R8 is grounded, so that the bridge circuit 16 is constituted by the DC motor 12 and the resistors R7, R8, R9. By comparing the signal based on the voltage V ₃ across the DC motor 12 in the bridge circuit 16 with the signal based on the voltage V ₁ between the resistors R7 and R8, the current flowing to the DC motor 12 can be recognized.

Therefore, the DC motor 12 and the resistor R9 are
One end of the branch line 18 is connected from between and, and the other end of the branch line 18 is connected to the brass side input end (first input end) of the comparator 20 via the resistor R1. As a result, the voltage V across the DC motor 12 is applied to the positive input terminal.
A signal proportional to ₃ will be input. The positive input terminal is grounded via a resistor R5.

On the other hand, one end of the branch line 22 is also connected between the resistors R7 and R8, and the other end is connected to the minus side input end of the comparator 20 via the resistor R2. As a result, a signal based on the voltage V ₁ which is a part of the comparison voltage is input to the negative input terminal. Further, the signal line 24 for supplying the reference voltage V ₂ (+5 V) is connected to the negative side input terminal of the comparator 20 via the resistors R6 and R3 (the resistors R6 and R3 are connected in series). Further, the output terminal of the comparator 20 has a resistor R4.
Is connected to the minus side input end via. As a result, a signal based on the voltage V ₂ which is the comparison voltage together with the voltage V ₁ is input to the negative input terminal.

As a result, as shown in FIG. 2, in the comparison circuit 26 centered on the comparator 20, the current i ₁ ,
i ₂ , i ₃ and i _A will flow, the value of which can be defined by the resistors R1, R2, R3, R4.

Here, in the first embodiment, when the values of the resistors are set, the impedances are matched so that the following conditions are satisfied between the resistors.

R2 = nR1 (where n is a positive number) ... (1) R1 = R3 ... (2) R4 = {n / (1-n)} / R1 (where n is a positive number) (3) By satisfying the above conditions, the control voltage V ₀ output from the output end of the comparator 20 can be obtained by the voltages V _{1 to} V ₃ input to the input end. That is, the control voltage V ₀ can be expressed by the following equation.

V ₀ = n (V ₃ −V ₂ −V ₁ ) ... (4) (where n is a positive number) One end of the output end of the comparator 20 is connected to the base terminal of the transistor TR 1. It is connected to the other end of the resistor R10. In the transistor TR1, when the control voltage V ₀ input to the base terminal increases, the emitter-collector voltage decreases, and when the control voltage V ₀ decreases, the emitter-collector voltage increases, so that the control voltage V ₀ changes. Accordingly, the voltage applied to the DC motor 12 can be controlled.

[0025] Incidentally, to decrease the control voltage V ₀ is when the counter electromotive voltage across voltage decreases decreased by the rotation speed load consuming large to the DC motor 12 is lowered, the control voltage V ₀ Increases when the load decreases.

A variable resistor V is provided between the resistors R6 and R3.
It is connected to one end of R1. The other end of the variable resistor VR1 is grounded. One end of the variable resistor VR1 is connected to the collector terminal of the NPN-type transistor TR2 via a resistor R _11. This transistor TR2
The emitter terminal is grounded and the base terminal is connected to an external switch circuit 28. Switch circuit 28
Is capable of switching the signal input to the base terminal to a low level and a high level. When outputting a low level signal, the collector-emitter is turned off, and when outputting a high level signal, the collector-emitter is turned on. Therefore, the voltage supplied to the comparator 20 can be changed. By this change, it becomes possible to switch the set speed of the DC motor 12.

The operation of the first embodiment will be described below. Well
Switch to set the rotation speed of the DC motor 12.
The low circuit or high level signal is operated by operating the H circuit 28.
No. is output. Here, a low level signal is output
Then, since the transistor TR2 is turned off, the resistance R
The voltage between 6 and the variable resistor VR1 is between the variable resistor VR1.
It becomes the voltage of. Also, a high-level signal is output
Then, since the transistor TR2 is turned on, the resistance R
The voltage between 6 and the variable resistor VR1 is
It becomes a voltage between the resistors combined with the resistor R11. As a result,
Reference voltage input to the negative input terminal of the palator 20
V ₁Can be changed in two steps, and the DC motor 12
The comparison value with the driving voltage can be changed.

Here, since the reference voltage is taken in from the outside and is input to the minus side input terminal of the comparator 20 via the variable resistor VR1, and the switching transistor TR2 is provided, a low or high level signal is externally applied. Only by inputting, the speed of the DC motor 12 can be switched.

Further, by changing the value of the variable resistor VR1, fine adjustment of each speed of high speed rotation and low speed rotation can be performed, but in the first embodiment, impedance matching by other resistance can be achieved. Therefore, the comparator 20
Each voltage V ₁ , V ₂ , V that is the reference of the signal input to
_The control voltage V ₀ output from the comparator 20 can be predicted based on ₃ , and the adjustment work to the desired rotation speed can be easily performed.

While the DC motor 12 is rotating and being driven by a normal load, the control voltage V ₀ output from the comparator 20 holds the emitter-collector voltage of the transistor TR1 at a predetermined voltage. The motor 12 rotates at a constant speed.

Here, when the load becomes high, the DC motor 12
Since a large amount of current flows in the motor, the number of revolutions decreases, the back electromotive force decreases, and the voltage across the motor decreases.

This decrease is due to the positive side of the comparator 20.
It is transmitted to the input end. Here, according to the formula (4),
Pressure V₁And V₂Is constant and voltage V₃When the
Pressure V ₀Will decrease, and this decreased control voltage V
₀Are supplied to the base of the transistor TR1.

As a result, the emitter-collector voltage of the transistor TR1 increases and the voltage applied to the DC motor 12 increases. That is, since the voltage increases as the load increases, the current value eventually becomes constant, and the DC motor 12 continues to rotate at a speed equivalent to that under normal load.

On the other hand, when the load decreases from the high load state,
It can be seen from the equation (4) that the voltage across the motor increases and the control voltage V ₀ increases. As a result, in the transistor TR1, the emitter-collector voltage is reduced and the motor applied voltage is reduced. That is, since the applied voltage is reduced when the load is reduced, the DC motor 12 is rotated at a constant speed as in the case where the load is increased.

In this way, by controlling the speed of the DC motor 12 by the bridge circuit 16 and the comparison circuit 26, it is possible to always rotate the DC motor 12 at a constant rotation speed even if a load is applied to the DC motor 12.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to FIG. In the second embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and the description of the configuration will be omitted.

In the second embodiment, the DC motor 12 is set to PW.
The circuit is characterized in that it is configured to perform M control (pulse width control).

Therefore, as shown in FIG.
Control voltage V output from the motor 20 ₀Is the resistance R12
Is input to the positive side input terminal of the comparator 30 via
There is. In addition, at the negative side input end of the comparator 30
Is the signal from the sawtooth wave (triangular wave) generation circuit 32.
The control voltage V₀Depending on the size of the saw
The time to cross the re-wave is changed and the pulse width is changed.
Can be.

The pulse wave output from the comparator 30 is input to the base terminal of the NPN transistor TR3 via the resistor R13. The emitter terminal of the transistor TR3 is grounded, is connected to one end and the base terminal of the transistor TR ₁ of the resistor collector terminal via the resistor R10 R14. Resistance R
The other end of 14 is connected to the emitter terminal of the transistor TR ₁ .

The collector terminal of the transistor TR1 is connected to the anode side of the diode D1 and the cathode side is connected to the emitter terminal.

Further, the emitter terminal is connected to the cathode side of the diode D2 and one end of the coil L1. The other end of the diode D2 is grounded, and the other end of the coil L1 is connected to the positive electrode of the electric field capacitor C1 and also to the resistor R9. The negative electrode of the capacitor C1 is grounded.

The above-mentioned diodes D1 and D2 and coil L
1. The capacitor C1 prevents the time delay of the current change with respect to the voltage change due to the chopper drive (PWM control).

As described above, in the second embodiment, the control voltage V
₀ is not used as it is, but is applied as a pulse width control voltage, the operation of the transistor TR1 is chopper-driven to reduce noise, and the coil L1 and the capacitor C1 are particularly used for smoothing. The speed control can be performed more efficiently and accurately.

In the second embodiment, the PWM drive section (the portion surrounded by the chain line in FIG. 3) is constructed by actually forming a circuit, but as shown in FIG.
By using the C circuit 34, the circuit configuration can be significantly simplified.

[0045]

As described above, the DC motor speed control circuit according to the present invention receives a signal (voltage) for controlling the motor applied voltage with a simple circuit configuration by matching the impedance of the circuit. Can be set by the motor drive power supply voltage and a predetermined voltage, and
It has an excellent effect that at least two kinds (binarized signals in the case of two kinds) of setting speeds can be selected by a signal from the outside.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a DC motor speed control circuit according to a first embodiment.

FIG. 2 is an enlarged view showing a current flow state in a comparison circuit.

FIG. 3 is a schematic diagram of a DC motor speed control circuit according to a second embodiment.

FIG. 4 is a schematic diagram of a DC motor speed control circuit in which an IC chip is partially applied (a PWM drive unit) according to a modification of the second embodiment.

[Explanation of symbols]

 10 DC motor speed control circuit 12 DC motor 16 Bridge circuit 20 Comparator 26 Comparison circuit 28 Switch circuit

Claims (1)

[Claims] 1. A speed control circuit for a DC motor, comprising a bridge circuit including an internal resistance of the DC motor, for maintaining a rotation speed at a predetermined speed regardless of a load applied to the DC motor. A voltage V ₁ based on the power supply voltage to the first input terminal and the DC motor, to which the voltage V ₃ generated at the driving of the motor is input, and a predetermined reference voltage V
A second input terminal ₂ and is input, applies the comparator comparing means for outputting a control voltage V _O in accordance with the result, to the direct current motor based on the control voltage V _O output from the comparison means Applied voltage control means for controlling the voltage to be applied, predetermined voltage switching means for changing the reference voltage V ₂ in at least two stages, and the control voltage V _O is V ₀ = n (V ₃ −V ₂ −V ₁ ).
To set the values of the voltages V ₁ and V ₂ input to the second input terminal as obtained by [n: positive number],
A speed control circuit for a DC motor, comprising: an impedance matching circuit configured by combining a plurality of resistors.