JPH0471382A - Dc motor control circuit - Google Patents

Abstract

PURPOSE:To realize easy and reliable constant speed control of motor by providing a current/voltage converting means and a voltage amplifying circuit and setting the amplification factor of the voltage amplifying circuit at a predetermined value which is equal to the ratio between DC voltage to be applied on a DC motor and the starting current. CONSTITUTION:A DC motor 1 is connected in series with an emitter follower NPN transistor Q1, a current/voltage converting resistor R1 and a power MOS transistor Q2 for switching control. A control signal CONT is fed through a resistor R2 to the gate of the power MOB transistor Q2. The current/voltage converting resistor R1 has resistance of 10OMEGA and produces a 10V voltage for 1A current which means gain of '10' and since an inverting amplifier 2 has gain of '2', total amplification factor of '20' (constant) is obtained. When a voltage proportional to such driving current is fed back to the DC motor 1, constant speed control can be realized within a predetermined load range.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a control circuit for a DC motor, and in particular to constant speed control of a motor used for paper feed control of a copying machine.

(Background of the Invention) In copying machines, laser beam printers, etc., the motor that drives the optical system is usually controlled with high precision using a PLL circuit, etc. However, the motor that controls paper feeding is Constant speed control of the motor by the negative feedback circuit is not performed. This is because paper feeding control does not require much precision, and desired precision can be guaranteed as long as the timing of motor drive is accurate.

(Problems to be Solved by the Invention) In a type of copying machine in which a paper feed cassette is set on the side of the apparatus, the paper feed path is short, and the accuracy of paper feed control is not so important.

However, in recent years, small, low-cost front-loading type copiers (a type in which transfer paper is set at the bottom of the device and fed to the top where the photoreceptor is located during transfer) have become popular, and the paper feed path is is long, and therefore paper feeding accuracy becomes a problem. For example, if the rotation of the paper feed motor changes depending on the type or condition of the transfer paper that is the load, the error will be magnified during paper feeding, and it may become outside the device's tolerance range, resulting in false detection of a jam, etc. Malfunctions will occur.

Therefore, in such a case, constant speed control is also required for the paper feed motor. However, it is not allowed to make the system complicated, and the required accuracy is not so high, so it is necessary to adopt a simple and reliable motor control method. Conventionally, such studies have not been made, and there has been no suitable motor control method.

The present invention was made based on the results of such studies, and it is an object of the present invention to provide a novel motor control circuit that is capable of simple and reliable constant speed control of a motor.

(Means for Solving the Problems) The present invention includes a current/voltage converter that converts a current flowing through a DC motor into a voltage, and a voltage generated from the current/voltage converter that is amplified and supplied to the DC motor. and a voltage amplification circuit, the amplification factor of the voltage amplification circuit being a predetermined value, and the predetermined value being a ratio of the DC voltage supplied to the DC motor and the starting current. It is characterized by

(Function) A simple control system for a motor, which was studied by the inventor before the present invention, will be explained with reference to FIGS. 3 and 4.

In Figure 3, the horizontal axis is the load (torque) T of the DC motor, and the vertical axis is the rotation speed N and the current I flowing through the DC motor.
It is a figure showing the relationship.

The T-■ characteristic when the measured voltage (voltage supplied to the DC motor) is 24 V is represented by a straight line α, and the conditions for performing constant speed control of a DC motor having such a characteristic will be discussed.

Originally, this DC motor has a rotation speed of 360 in no-load condition.
Orpm, as the load T becomes heavier, the rotation speed decreases and reaches zero at 960 (g-Cm) (r-N characteristic β).Even if the load T increases, the rotation speed decreases. is constant within a predetermined range (characteristic δ indicated by a thick line)
Think about creating.

For convenience of explanation, a case will be considered below in which the rotational speed N is kept constant when the load changes from point A to point B.

In this case, the supply voltage may be increased from point A as the load (drive current I) increases.

Point A is a point on the TN characteristic γ when 16V is applied to the motor, and point B is a point on the TN characteristic β when 24V is applied to the motor. When the load T changes from A to B, the drive current I changes from A to A as the load increases.

At this time, if the voltage is increased in proportion to the increase in current, a flat characteristic such as an appropriate gain δ can be obtained. This gain is (V, -V,): (Iaay)
It is determined by This means (supply voltage): (starting current)
This means that it is a value that can be easily calculated from the motor characteristic curve.

In this way, when the measured (supply) voltage is changed, the ratio between each supply voltage and the starting current (current at the time of starting) remains constant at each supply voltage. In other words, when performing constant speed control, the relationship between supply voltage and drive current is 24V÷1.2 A=20 (constant)...
...(1) is satisfied (the no-load rotation speed is proportional to the voltage).

Therefore, in order to replace the change in load with current and compensate for the increased torque of the load with the supply voltage, (current value) x (constant) = (voltage applied to motor).

Based on the above study results, a model circuit as shown in FIG. 4 is considered, and necessary gains and constants for controlling the DC motor 1 at a constant speed are determined.

The supply (applied) voltage VM is V,-@RΦIM+bias-RφIM-(K-1,
)R・■8+bias, and (K-1)R=20 (constant). Bias is a term that determines the set rotation speed, and the rotation speed can be determined by measuring the voltage applied to the motor in a no-load state. The set rotation speed N is N-3f100x (bias/24) rpm.

The above method is not limited to constant speed control from point A to point B of the load, but if the circuit parameters are set appropriately, when there is no load (load - It is also possible to perform constant speed control from point 0) to point B. However, in actual motor control, if constant speed control from point A to point B is achieved, it is considered to be sufficiently practical.

The present invention is based on such studies, and by detecting the current flowing through the motor, changes the voltage applied to the motor in an analog manner, thereby achieving approximately constant speed control.

(Example) Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention.

In this embodiment, an emitter follower NPN transistor Q1 and a current/voltage conversion resistor R1 are connected in series with the DC motor 1.
and a power MOS transistor Q for switching control.
Connect 2. A control signal C0NT is supplied to the gate of the power MOS transistor Q2 via a resistor R2.

In addition, an inverting amplifier 2 having resistors R3, R4, R5, and a capacitance C is connected to the connection point between the resistor R1 and the DC motor 1,
The output voltage of this inverting amplifier 2 is further increased by resistors R6 and R7.
, R8, and is supplied to the base of an emitter follower NPN transistor Q1. Further, a protection diode D1 is connected in parallel to the DC motor 1. In addition, the resistance RIO
, R11, and R12 are for setting the bias voltage of the non-inverting terminal of the inverting amplifier 3.

The resistance value of the current/voltage conversion resistor R1 is 10Ω, and since it generates a voltage of IOV with respect to the current IA, the gain
10'' and the gain of the inverting amplifier 2 is 2'', so the overall amplification factor is 20°' (constant).

By adopting such a configuration in which a voltage proportional to the drive current is fed back to the DC motor 1, constant speed control is possible within a predetermined load range, based on the above study.

FIG. 2 is a circuit diagram showing the configuration of another embodiment.

In this embodiment, the DC motor 1 is connected between the power supply and the emitter of the emitter follower PNP transistor Q3, and the output voltage of the inverting amplifier 4 is connected to the emitter follower PNP transistor Q3.
) is supplied to the base of transistor Q3. The operation is the same as that of the previous embodiment, and the resistor R]4 allows DC
The current flowing through the motor 1 is converted into a voltage, inverted and amplified by an inverting amplifier 4, and then supplied to the base of a transistor Q3. D
As the current flowing through the C motor 1 increases, the potential difference between the power supply and the emitter of the transistor Q3 increases, increasing the voltage supplied to the motor so that a proportional relationship is maintained.

(Effects of the Invention) As explained above, the present invention converts the current flowing through the motor into voltage, amplifies this voltage, and returns it while maintaining the proportional relationship between the current and voltage, and converts the voltage applied to the motor into analog form. By changing to , the following effects can be obtained.

(1) Constant speed control within desired accuracy can be achieved by a circuit with a simple configuration.

(2) It is easy to apply to actual equipment, and the equipment does not become complicated at all.

(3) These can improve the reliability of, for example, small and inexpensive front-loading type copying machines.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of one embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of another embodiment of the present invention, and FIG. 3 is a study made by the inventor of the present invention before inventing the present invention. Characteristic diagram of DC motor to explain the contents, Figure 4 is Figure 3
FIG. 3 is a circuit diagram showing a model circuit when determining control conditions based on the results of the study shown in the figure. 1...DC motor 2,, 3.4...Inverting amplifier Q1...Emitter follower N P N l- transistor Q2... Control power MO5) Transistor Q3...
・Emitter follower PNP transistor R1, R1,
4... Current/voltage conversion resistor ONT

Claims (1)

[Claims] Current that converts the current flowing through the DC motor (1) into voltage/
a voltage conversion means (R1); and a voltage amplification circuit (2) that amplifies the voltage generated from the current/voltage conversion means (R1) and supplies it to the DC motor (1).
, 3), and the amplification factor of the voltage amplification circuit (2, 3) is a predetermined value, and this predetermined value is the D supply to the DC motor.
A DC motor control circuit characterized in that the ratio between the C voltage and the starting current is set.