JPH05122979A - Rotational speed control circuit for motor - Google Patents

Abstract

PURPOSE:To provide a rotational speed control circuit for a motor in which the relationship between a manual operation amount and a rotating speed of the motor can be made substantially linearly irrespective of a rising delay of a supply current due to a self-inductance of a motor coil and hence a regulation of the speed can be facilitated. CONSTITUTION:A control signal having a duty width corresponding to a manual operation amount of an operation unit 44a is output from a rotational speed control circuit 40 to a driving circuit 10 for a motor M. The circuit 40 has regulating means 44 for so obtaining an operation amount-duty width characteristics as to reduce a variation in the duty width per unit operation amount of the unit 44a upon increasing of the duty width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for controlling the rotational speed of a motor such as a brushless motor by controlling the current supplied to the motor.

[0002]

2. Description of the Related Art A general brushless motor rotation speed control circuit includes a threshold voltage generation circuit for generating a threshold voltage, a triangular wave generation circuit for generating a triangular wave, and a comparator. The threshold voltage generating circuit has a variable resistor connected to the power supply. The movable contactor of the variable resistor is provided as an operation unit for setting the rotation speed of the brushless motor. The threshold voltage is output from the variable resistor according to the manual operation amount of the movable contact. The comparator receives a triangular wave at one input terminal, receives a threshold voltage at the other input terminal, and outputs a control signal having a duty width having a linear relationship with the threshold voltage. The drive circuit intermittently supplies a current to the coil of the motor in a very short cycle in response to the control signal from the comparator. As a result, the current supplied to the coil is controlled in accordance with the operation amount of the movable contact of the variable resistor, and thus the rotation speed of the motor is controlled.

Since the resistance value of the variable resistor changes linearly according to the operation amount of the movable contactor, the threshold voltage also changes linearly according to the operation amount of the movable contactor. As a result, the duty width of the control signal output from the comparator changes linearly according to the operation amount of the movable contact.

[0004]

By the way, a current flows through the coil of the motor during the period corresponding to the duty width of the control signal, but not a constant current.
That is, by the self-inductance action of the coil,
There is a tendency that the rising of the supply current is delayed and gradually increases to approach a predetermined current. Therefore, supply current (average value)
Does not have a linear relationship with the duty width of the control signal. Specifically, in the region where the duty width is small,
The change amount of the supply current is small with respect to the unit change amount of the duty width, and the change amount of the supply current with respect to the unit change amount of the duty width increases as the duty width increases.

As described above, since the duty width has a linear relationship with the operation amount of the movable contactor of the variable resistor, the supply current does not have a linear relationship with the operation amount of the movable contactor. More specifically, in the region where the duty width is small, the change in the supply current is small compared to the operation amount of the variable resistor, and in the region where the duty width is large, the supply current changes greatly due to the slight operation amount of the variable resistor. Resulting in. Therefore, there has been a problem in adjusting the rotation speed of the brushless motor by operating the movable contactor.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and its gist is to have an operating portion for setting the rotation speed of a motor, and a manual operation amount of this operating portion. In the rotation speed control circuit for controlling the supply current to the motor coil by outputting the control signal having the duty width corresponding to the motor drive circuit, and thus controlling the motor rotation speed, A rotation speed for a motor, which has an adjusting means for obtaining an operation amount-duty width characteristic such that a change amount of the duty width per unit operation amount is decreased with an increase in the duty width. It is in the control circuit.

[0007]

In the rotation speed control circuit of the present invention, the operation of the adjusting means causes the change amount of the duty width of the control signal corresponding to the unit operation amount of the operating portion to decrease as the duty width increases. It has a quantity-duty width characteristic. Therefore, this operation amount-duty width characteristic is defined as the duty width-supply current characteristic due to the self-inductance of the motor coil, that is, the larger the duty width, the larger the change amount of the supply current with respect to the unit change amount of the duty width. By combining them, the relationship between the operation amount and the supply current can be approximated to a linear relationship, and by extension, the relationship between the operation amount and the rotation speed of the motor can be approximated to a linear relationship.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a control system for controlling a brushless motor M. The brushless motor M is a three-phase brushless motor, for example, has three coils L ₁ ~L _3. These coils L _{1 to} L ₃ are connected to the drive circuit 10. The rotation of the brushless motor M is detected by the three Hall elements 20 (rotation detecting sensors). The rotation of the brushless motor M is controlled by the three-phase logic controller 30. The rotation speed of the brushless motor M is controlled by the rotation speed control circuit 40.

The drive circuit 10 includes a pair of transistors TR ₁ and TR ₂ connected in series, another pair of transistors TR ₃ and TR _4, and a further pair of transistors TR ₅ and TR ₆ , respectively. Battery V _{B in} parallel
It is configured by being connected to. Coil L ₁
Is connected between the transistors TR ₁ and TR ₂ , one end of the coil L ₂ is connected between the transistors TR ₃ and TR ₄ , and the coil L ₃ is connected between the transistors TR ₅ and TR ₆ . The other ends of the coils L _{1 to} L ₃ are connected to each other. The bases of the transistors TR ₂ , TR ₄ and TR ₆ are 3
The output terminals of the two comparators 11 are connected to each other.

The logic controller 30 receives the rotation detection pulse from the hall element 20. The logic controller 30 sequentially outputs a low-level coil selection pulse to the transistors TR ₁ , TR ₃ , and TR ₅ , and in synchronization with this coil selection pulse, the comparator 1
Other low-level coil selection pulses are sequentially output to the negative input terminal of 1. For example, a coil selection pulse is output to the base of the transistor TR ₁ to turn it on, and a coil selection pulse is output to the comparator 11 connected to the transistor TR ₄ to output the transistor T 4.
By turning on R ₄ , the current from the battery V _B is supplied to the coils L ₁ and L ₂ . Thus, the rotation of the brushless motor M is controlled by sequentially exciting the two coils in accordance with the rotation of the brushless motor M.

The rotation speed control circuit 40 includes a comparator 41, a triangular wave generation circuit 42 for supplying a high frequency triangular wave to one input terminal (minus input terminal in this embodiment) of the comparator 41, and the other input of the comparator 41. A threshold voltage generating circuit 43 for supplying a threshold voltage to the terminal (plus input terminal) is provided. The threshold voltage generating circuit 43 includes a variable resistor 44 connected to the battery V _B. As the movable contactor 44a (operating portion for setting the motor rotation speed) of the variable resistor 44 moves from the bottom to the top in FIG. 1, the threshold voltage rises, and the control signal output from the comparator 41 accordingly. The duty width, and consequently the duty ratio, are increased. This control signal is supplied to the positive input terminal of the comparator 11. As a result, in the above two selected coils,
A current of this duty width is supplied from the battery V _B ,
As a result, the rotation speed of the brushless motor M is controlled.

In the above structure, the rotation speed control circuit 40
When the drive circuit 10 supplies a current to the coil in response to the control signal from, as shown in FIG. 2, the self-inductance of the coil delays the rise of the current supplied to the coil. In the corresponding period, the supply current is not constant and gradually increases. The peak value of the supply current increases as the duty width increases to T ₁ , T ₂ , and T ₃ . As is clear from such a change in the supply current, the average value of the supply current (hereinafter, simply referred to as the supply current) does not have a linear relationship with the duty width. Specifically, in a region where the duty width is small, the change of the supply current is small with respect to the unit change amount of the duty width, and the larger the duty width is, the larger the change of the supply current is with respect to the unit change amount of the duty width.

In the present embodiment, the resistance value per unit length of the variable resistor 44 is the largest at the lower end of FIG. 1, gradually decreases as it goes upward, and becomes the smallest at the upper end. As a result, as shown in FIG. 4, the threshold voltage and the duty width proportional to the threshold voltage are
1 does not have a linear relationship with the movement amount (operation amount) of the movable contactor 44a from the lower end position in FIG. That is, the change amount of the duty width with respect to the unit operation amount gradually decreases from the region where the operation amount is small to the region where the operation amount is large. In the present embodiment, the adjusting means for obtaining the manipulated variable-duty width characteristic of FIG. 4 is composed of the variable resistor 44.

The operation amount-duty width characteristic of FIG. 4 and FIG.
As shown in FIG. 5, since the duty width and the supply current characteristic are combined, the relationship that the supply current is almost linear with the operation amount is obtained, and thus the relationship that the motor rotation speed is almost linear with the operation amount is obtained. Be done.

FIG. 6 shows another embodiment of the rotation speed control circuit of the present invention. In this embodiment, the same components as those in the above-mentioned embodiment are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the threshold voltage generating circuit 14
3 includes a variable resistor 144 and a threshold voltage adjusting circuit 145 (adjusting means). Variable resistor 144
Has the same resistance value per unit length over the entire length, and the output of the variable resistor 144 is the movable contact 144 from the lower end.
It has a linear relationship with the operation amount of a. The threshold voltage adjusting circuit 145 includes a microcomputer that stores the map of FIG.
A threshold voltage is output using the output of 44 as an address. The change amount of the threshold voltage with respect to the unit change amount of the output of the variable resistor 144 decreases as the output of the variable resistor 144 increases as shown in the map of FIG. 7. Also in this embodiment, the linear characteristic of the manipulated variable-supply current (motor rotation speed) shown in FIG. 5 can be obtained.

The present invention is not limited to the above-mentioned embodiment and various modes are possible. Contrary to that shown in FIGS. 1 and 6, the threshold voltage may be input to the negative input terminal of the comparator and the triangular wave may be input to the positive input terminal. In this case, the upper end of the movable contact of the variable resistor (Figs. 1 and 6)
The threshold voltage decreases, the duty width of the control signal from the comparator increases, and the rotation speed increases with an increase in the operation amount from. Therefore, when the threshold voltage generating circuit is composed of only the variable resistor, the resistance value per unit length of the variable resistor is decreased from the top to the bottom (FIG. 1). Further, when the threshold voltage generating circuit includes the variable resistor and the threshold voltage adjusting circuit, the threshold voltage adjusting circuit uses a map having a characteristic line which is convex downward in FIG.

[0017]

As described above, in the present invention, due to the action of the adjusting means, there is a delay in the supplied current due to the self-inductance of the motor coil.
The relationship between the manual operation amount and the current supplied to the coil can be approximated to a linear relationship, and the relationship between the manual operation amount and the motor rotation speed can be approximated to a linear relationship. As a result, the motor rotation speed can be adjusted. Can be facilitated.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a brushless motor control system incorporating a rotation speed control circuit of the present invention.

FIG. 2 is a diagram showing a change in supply current corresponding to a duty width.

FIG. 3 is a diagram showing a relationship between a duty width and a current (average value) supplied to a coil of a motor.

FIG. 4 is a diagram showing a relationship between an operation amount of a variable resistor and a duty width.

FIG. 5 is a diagram showing a relationship between an operation amount of a variable resistor and a supply current.

FIG. 6 is a circuit diagram showing another aspect of the rotation speed control circuit.

7 is a diagram showing the relationship between the output of the variable resistor of FIG. 6 and the output of the threshold voltage adjusting circuit.

[Explanation of symbols]

M ... motor _{L 1, L 2, L 3} ... coil 10 ... drive circuit 40 ... rotational speed control circuit 41 ... comparator 42 ... triangular wave generating circuit 43 ... threshold voltage generating circuit 44 ... adjustment means (variable resistor) 44a ... operation section (Movable contact) 144 ... Variable resistor 144a ... Operation part (movable contact) 145 ... Adjusting means (threshold voltage adjusting circuit)

Claims (1)

[Claims] 1. A motor having a manipulating section for setting a rotation speed of the motor, and outputting a control signal having a duty width corresponding to a manual operation amount of the manipulating section to a driving circuit of the motor. In the rotation speed control circuit for controlling the current supplied to the coil, and thus for controlling the rotation speed of the motor, the amount of change in the duty width per unit operation amount of the operation unit is reduced as the duty width increases. A rotation speed control circuit for a motor having an adjusting means for obtaining a manipulated variable-duty width characteristic.