JP2002272160A - Motor rotation control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor rotation control method which enables automatic adjustment with the highest resolution of a control system and a quick response, at a low cost. SOLUTION: A counter is reset at specific one or a plurality of points in one rotation of a motor, and has one or a plurality of control target values of a motor rotation period. Certain periods, while the moor is in an on-state, are provided after the resets of the counter, before and after the ends of the one or plurality of target periods.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for controlling the rotation of a motor.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing an example of a conventional motor rotation control device for controlling the rotation of a three-phase brushless motor. The operation of each unit will be briefly described with reference to the drawings. First, the frequency divider 2 divides the frequency of the clock output from the oscillator 1 by a frequency division ratio according to the setting of the rotation speed of the motor, and outputs a count clock.

The counter 3 counts the count clock and outputs a count value. Further, the frequency divider 2 and the counter 3 are reset by a reset pulse output from a speed comparing unit 4 described later. The count value output from the counter 3 is input to the speed comparison unit 4.

The speed comparing section 4 compares a predetermined reference value with the output (count value) of the counter 3 at the rising edge of the output of the rotation sensor output from the A-phase detection Hall sensor 13 to be described later. The PWM duty control unit 5 outputs difference information of the rotation speed of the motor with respect to the control target value, and based on the difference information, increases / decreases the PWM duty data given to the PWM generator 7. Further, the speed comparison unit 4 performs a speed comparison process at the rising edge of the output of the rotation sensor, and then generates a reset pulse to reset the frequency divider 2 and the counter 3, and
The rotation speed detection sequence starts.

[0005] The output of the counter 3 is also input to the PWM generator control unit 6, which generates a PWM start pulse at appropriate intervals.

[0006] The PWM generator 7 outputs a PWM waveform for one cycle, triggered by the PWM start pulse.

The motor 12 is a three-phase brushless motor, and has an A-phase detection Hall sensor 13 disposed at equal intervals along the outer or inner circumference of the rotor in a direction facing a magnetic field generated by the rotor. Hall sensor 1 for B phase detection
The rotation angle of the rotor, that is, the rotation phase of the motor is detected by detecting the magnetic pole of the rotor by the Hall sensor 15 for detecting the C and C phases. These phase detection Hall sensors 1
The outputs from 3 to 15 are input to the phase switching control unit 9 and provide a phase switching signal to the power control unit 10 so as to excite an appropriate coil according to the rotation angle of the rotor.

The power control unit 10 is composed of, for example, a MOSFET array and its control logic.
The motor 12 is turned on or off in accordance with the WM waveform to supply electric power proportional to the high-level duty of the PWM waveform
Supply to When the overcurrent is detected by the overcurrent detection unit 11, the power supply to the motor is turned off until the PWM cycle in which the overcurrent is detected ends.

The high-level duty of the PWM waveform is determined by a rotation sensor (phase detection Hall sensor 13).
Is increased / decreased by the PWM duty control unit 5 so that the counter value at the rising edge of the output of FIG. 4 coincides with the reference value, so that the feedback control is performed so that the rotation speed of the motor 12 becomes equal to the control target value.

[0010]

A conventional motor rotation control method, for example, the power supplied to the motor is controlled by digital PWM capable of counting the ON time in units of one clock and changing the PWM duty in 256 steps. Assuming that the PWM cycle is about one-tenth of the rotation cycle of the motor in the method of controlling the rotation of the motor, the PWM duty itself can be changed in one clock unit. If it is changed, the ON time of the motor will change by several tens of clocks per rotation of the motor, and the ON time of the motor cannot be changed in units of 1 clock which is the maximum resolution inherent in the system. There is a problem that the rotation speed control becomes coarse.

In addition, one PWM cycle during one rotation of the motor
If the resolution of power control per unit time by digital PWM is improved by dispersing the on-time of the motor in clock units, the on-time of the motor should be changed in 1-clock units, which is the maximum resolution of the system. However, under such a condition that the PWM cycle for changing the motor on-time exists at the end of the cycle of one rotation of the motor starting from the rotation speed detection point of the motor, a slight change in the motor on-time may be generated. Since it takes time until the rotation speed is reflected in the rotation speed of the motor, there is a problem that the followability to the rotation speed fluctuation is poor, and the rotation speed is difficult to stabilize in a system having a short rotation speed fluctuation period.

When the difference between the motor rotation speed and the control target value is directly reflected on the PWM duty,
At least it is necessary to add a change to the reference duty, and in some cases, it is necessary to multiply the change. When such operations are performed at high speed by hardware, there is a problem that the circuit scale becomes large.When performed by software, a unit for executing the operations such as a microprocessor or a digital signal processor is required, and rotation speed fluctuations are required. Since it takes time from the detection to the reflection of the calculation result, there is a problem that the followability to the rotation speed fluctuation is poor. In both cases, there is a problem that the cost is increased.

An object of the present invention is to provide a motor rotation control method capable of automatically adjusting the maximum resolution of a control system.

Another object of the present invention is to provide a motor rotation control method which can be performed with a simple circuit configuration and has a quick response.

[0015]

SUMMARY OF THE INVENTION A feature of the present invention is that the counter is reset at a specific point or points during one rotation of the motor and is reset from a reset of a counter that sets the control target value of the motor rotation period to one or more periods. The control is to provide a period for turning on the motor for a certain period of time before and after the end of one or a plurality of cycles of the counter.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a control device for executing a motor rotation control method according to the present invention. The motor in this embodiment can be applied to drive control of a rotary polygon mirror in an optical scanning device of a laser printer or a copying machine, for example.

In this embodiment, the motor 12
It is a three-phase brushless motor. The rotation control device includes an oscillator 1 that outputs a clock, a frequency divider 2 that divides the clock and outputs a count clock, a counter 3 that counts a count clock, and a difference between a motor rotation speed and a control target value. , A speed comparison unit 4 that outputs difference information and outputs a reset pulse, a PWM duty control unit 5 that increases and decreases the PWM duty based on the difference information, and a PWM that outputs a PWM start pulse.
M generator control unit 6 and PWM for outputting a PWM waveform
An M generator 7, an additional on signal control unit 8 for outputting an on signal of the motor independently of the PWM control, an A phase detection Hall sensor 13 for detecting the rotational position of the motor,
A phase detection Hall sensor 14, a C-phase detection Hall sensor 15, and a phase switching control unit 9 that outputs a phase switching signal for selecting an excitation coil of the motor based on the output of each phase detection Hall sensor. A power control unit 10 for supplying power to an appropriate coil of the motor from a phase switching signal, a PWM output, and an additional on signal, and an overcurrent detection for detecting an overcurrent by comparing a current flowing through the coil of the motor with a set value. A section 11 is provided.

Next, the operation of the rotation control device will be described.

The frequency divider 2 divides the frequency of the clock output from the oscillator 1 by a frequency division ratio according to the motor speed setting, for example, 1/20 in the case of a reference motor speed.
Count clock divided by 1/16 for 1.25x speed, divided by 15 for 1.33x speed, and divided by 14 for 1.43x speed , And is reset by a reset pulse output from the speed comparison unit 4 described later.

The counter 3 is a lower counter (not shown) for counting the count clock from 0 to 39.
And a high-order counter (not shown) that counts from 0 to 127 with one cycle of the low-order counter as one count. The total counts from 0 to 5119 and outputs it as a count value. Reset by output reset pulse. The upper counter of the counter 3 has a count value of 127.
When it reaches, it is configured to stop until it is reset. The counter 3 is configured as described above in order to further increase the stability of the motor rotation speed, as described later, by setting the PWM cycle to an integer fraction of the control target value of the motor rotation cycle. It is.

Here, the output of the counter 3 is input to a speed comparison unit 4 serving as speed detection means, and the speed comparison unit 4 receives a predetermined reference value, for example, 2560, and an A-phase detection Hall sensor 13 described later. Is compared with the output of the counter 3 at the rising edge of the output of the rotation sensor, to detect a difference in the motor rotation speed with respect to the control target value, and gives the difference to the PWM duty control unit 5 as difference information. The speed comparison unit 4 performs a speed comparison process at the rising edge of the rotation sensor output, and then performs a reset
Generate a pulse to reset the divider 2 and counter 3,
Enter the rotation speed detection sequence in the next one rotation,
The circuit configuration is such that the time from the rising edge of the rotation sensor output to the fall of the reset pulse is shorter than one cycle of the clock output from the oscillator 1.

The output of the counter 3 is also input to the PWM generator control unit 6, and in this embodiment, the lower counter of the counter 3 is set to the PWM period defining means PWM
It is used as a counter for the M cycle, and when the lower counter of the counter 3 becomes 0, the PWM generator control unit 6 generates a PWM start pulse and outputs the PWM start pulse for 64 cycles of the PWM cycle.
The period is set to match the control target value of the rotation period of the motor.

Further, P serving as PWM duty adjustment means
The WM duty control unit 5 increases or decreases the PWM duty data given to the PWM generator 7 based on the difference information. Note that the PWM duty data is
It is composed of 15 bits, and the count number represented by the upper 9 bits, that is, 0 to 511 counts, is used as the basic PWM duty commonly used in each PWM cycle, and the count number represented by the lower 6 bits, that is, 0 to 63 counts Is distributed and assigned by one count to each PWM cycle, and 1
The on-time of the motor can be controlled in clock units.

When the PWM start pulse is input, the PWM generator 7 changes its output to a high level,
Clock counting is started after the PWM start pulse falls, and when the count number specified by the PWM duty data is counted, the output goes low. By repeating such an operation, the PWM generator 7 outputs a PWM waveform.

As described above, the motor 12 is a three-phase brushless motor, and is an A-phase detection motor arranged at equal intervals along the outer or inner circumference of the rotor in a direction facing the magnetic field generated by the rotor. The position of the magnetic pole of the rotor is detected by the Hall sensor 13 for detection, the Hall sensor 14 for B-phase detection, and the Hall sensor 15 for C-phase detection, and the rotation angle of the rotor, that is, the rotation phase of the motor is detected. These rotation sensor outputs are input to a phase switching control unit 9 to provide a phase switching signal to a power control unit 10 so as to excite an appropriate coil according to the rotation angle of the rotor.

The power control unit 10 as a power control means is composed of, for example, a MOSFET array and its control logic, and turns on or off the channel of the MOSFET array corresponding to the phase switching signal in accordance with the PWM waveform. The electric power proportional to the high-level duty of the waveform is supplied to the motor 12.

The overcurrent detecting section 11 includes a MOSFET
The current flowing through the array is monitored, and an overcurrent detection signal is output when the current flowing through the MOSFET array exceeds a set value. This overcurrent detection signal is input to the power control unit 10, and the power control unit 10 turns off the MOSFET array until the end of the PWM cycle in which the overcurrent is detected. Here, the high-level duty of the PWM waveform is increased or decreased by the PWM duty control unit 5 so that the output of the counter 3 at the rising edge of the output of the rotation sensor coincides with the reference value. Feedback control is performed so as to be equal to the control target value.

The above is the basic operation in this embodiment, which is the same as the conventional control technique described above.
Next, the following control technology which is a feature of the present invention is added.

The additional ON signal control section 8 receives the output of the counter 3 and outputs the upper counter of the counter 3 to 0, 1
6, 32, 48, 64, 80, 96, 112 and the lower counter of the counter 3 is 0, 1, 38, 39,
An additional on signal for turning on the motor 12 is output independently of the PWM control. Here, when the counter 3 is reset, both the upper counter of the counter 3 and the lower counter of the counter 3 become 0, which is included in the above conditions.

Since the additional ON signal is input to the power control unit 10, the motor 12 is turned ON by the additional ON signal in addition to the PWM waveform.

In this embodiment, the additional ON signal control section 8 is constituted by AND logic and OR logic, and the upper counter of the counter 3 is set to 0, 16, 32, 48, 64, 80, 96 and 112 and the lower counter of the counter 3 is 0, 1, 38 and 39.

As described above, the additional ON signal control unit 8 can be realized at low cost by adding a small number of logic circuits. Further, by setting the cycle for generating the additional ON signal to be a time obtained by equally dividing the control target value of the motor rotation cycle, if the rotation speed of the motor is near the control target value, the motor is turned on by the additional ON signal. Since the periods are arranged at substantially equal intervals during one rotation of the motor, it is possible to suppress variations in torque distribution during one rotation of the motor due to the provision of the additional ON signal.

Similarly, by setting the PWM cycle to an integral fraction of the control target value of the motor rotation cycle, when the motor rotation speed coincides with the control target value, the motor ON period by the PWM control is reduced. Since the motors are arranged at equal intervals during one rotation of the motor, the stability of the rotation speed during one rotation of the motor can be improved.

Further, as in this embodiment, the counter serving as a reference of the cycle for generating the additional ON signal is PW
By also using the M cycle defining means, the period related to the automatic adjustment effect by the motor ON period by the additional ON signal does not occur during the motor ON period by the PWM waveform. Can be obtained.

In this embodiment, the counter 3
Is composed of a lower counter that counts the count clock from 0 to 39 and an upper counter that counts from 0 to 127 with one cycle of the lower counter as one count. The combination of the lower counter and the upper counter is The counter 3 may be constituted by a combination or a single counter.

In this embodiment, the speed comparison unit 4
Although the configuration is such that the output of the counter 3 is compared with the reference value at the rising edge of the rotation sensor output, it may be modified so that the comparison is performed at the falling edge of the rotation sensor output.

In this embodiment, the speed comparison unit 4
The reference value to be compared is set to 2560, but may be another value.

Further, in this embodiment, the PWM period is set so that 64 PWM periods coincide with the control target value of the rotation period of the motor. It is sufficient that the relationship is such that

Further, in this embodiment, the PWM duty data is composed of 15 bits, but may be composed of 14 bits or another number of bits.

In this embodiment, the power control unit 10 controls the motor 12 at a high-level duty of the PWM waveform.
Although the configuration is such that the power supplied to the power supply is controlled, the control may be performed at a low level of the PWM waveform.

In this embodiment, the power control unit 1
Although 0 is configured by a MOSFET array and its control logic, another configuration such as a transistor and its control logic may be used.

In this embodiment, the timing at which the additional ON signal is output is such that the upper counter of the counter 3 is 0, 16, 32, 48, 64, 80, 96, 112 and the lower counter of the counter 3 is 0, Although the case of 1, 38, and 39 has been described, for example, an additional ON signal may be output every PWM cycle, or a PWM cycle with another counter value may be used.

Further, in this embodiment, the additional ON signal control section 8 is constituted by AND logic and OR logic.
Another logic element may be used, or the additional ON signal may be temporarily latched and then used.

Next, the effect obtained by the additional ON signal will be described with reference to FIG. For simplification of the drawing, in FIG. 2, four PWM cycles are set as control target values of the motor rotation cycle.

FIG. 2 (a) shows the case where Δt, which is the difference between the rotation cycle of the motor and its control target value, is 0, that is, the motor is turned on when the rotation speed of the motor and the control target value match. 6 is a timing chart showing signals.

The PWM cycle counter goes around at a fixed cycle and returns to 0, but is also reset by a reset pulse output at every rising edge of the rotation sensor. Here, when the PWM cycle counter is 0, PWM
It is configured to output a start pulse.
The PWM output becomes high level at a timing obtained by adding a time delay of _{Td to} the rise of the PWM start pulse.
The PWM output is kept at the high level for the period of T _{PWM after} the fall of the PWM start pulse and becomes the low level. The additional ON signal is configured to be at a high level when the PWM cycle counter is equal to or more than m ₁ or m ₂ , and from the rising of the additional ON signal to the rising of the PWM start pulse in FIG. To T ₁ ,
From the rising of the PWM start pulse until the fall of the add-on signal and T _2. Motor on-time T _on the condition of FIG. 2 (a), becomes a _{T on = T 1 + T d} + T PWM, since T ₁ and T _d is constant, the difference of T _on for each PWM period, T _PW to _M only to dependent. That is,
If the PWM duty is constant, the motor-on time per one rotation of the motor is constant.

Next, FIG. 2B shows that the rotation period of the motor is
Δt <T for the control target value₁Just short
This signal indicates the power-on signal and extends before and after the reset pulse.
It is a great timing chart. In this case, the PWM
Period counter is set when the rotation sensor output rises.
Therefore, it is reset in a cycle shorter by Δt compared to the normal case.
In order for the PWM
The time to the auto pulse is reduced by Δt. But
The motor-on time T before and after the reset pulse _onIs T_on= T₁−Δt + T_d+ T_PWM The motor-on time per motor rotation is shown in FIG.
It becomes shorter by Δt than in the case of (a).

Next, FIG. 2C shows a motor-on signal when the rotation period of the motor is longer than the control target value by Δt <T ₂ , and is a timing chart in which before and after the reset pulse are enlarged. It is. In this case, when the output of the rotation sensor rises, the PWM cycle counter
Since the reset is performed in a cycle longer by Δt than in the normal case, a PWM start pulse is once generated and the PWM start pulse is generated.
After the output goes high, the PWM start
A pulse will be generated. T _PWM is the last PWM
Since the time after the start pulse falls, the motor- _on time T _on before and after the reset pulse is T _on = T ₁ + Δt + T _d + T _PWM , and the motor-on time per one rotation of the motor is shown in FIG.
It becomes longer by Δt than in the case of (a).

From the above relationship, as in this embodiment,
By adding the additional ON signal to the control, if the rotation period of the motor is shorter than the control target value, that is, if the rotation speed of the motor is faster than the control target value, the difference between the rotation speed of the motor and the control target value is obtained. If the motor-on time per one rotation of the motor becomes shorter in proportion to the control target value, on the contrary, if the rotation period of the motor is longer than the control target value, that is, if the rotation speed of the motor is lower than the control target value, The motor-on time per motor rotation increases in proportion to the difference between the speed and the control target value. Therefore, in the range of Δt <T ₁ and Δt <T ₂ , the on-time of the motor is automatically adjusted in proportion to the difference from the control target value even if the rotational speed of the motor fluctuates, and the rotational speed of the motor is reduced. It is controlled to be stable. In addition, since the on-time of the motor is increased or decreased immediately after the speed comparison, the follow-up to the rotation speed fluctuation is improved.

[0050]

According to the present invention, the counter is reset at a specific point or a plurality of points during one rotation of the motor and has a control target value of the motor rotation cycle of one or more cycles. By providing a period during which the motor is turned on for a fixed time before or after the end of one or more cycles, the motor on time is automatically adjusted at the highest resolution of the system in proportion to the difference between the control target value and the motor rotation speed. In addition, since it is not necessary to perform an arithmetic operation on the data which is the set value of the PWM duty, it is possible to control the rotation of the motor with a simple circuit configuration and a quick response.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a control device that implements a motor rotation control method according to the present invention.

FIG. 2 is a timing chart showing a relationship between an additional ON signal and a motor ON signal in the control device shown in FIG. 1;

FIG. 3 is a block diagram of a control device that implements a conventional motor rotation control method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Oscillator, 2 ... Divider, 3 ... Counter, 4 ... Speed comparison part, 5 ... PWM duty control part, 6 ... PWM generator control part, 7 ... PWM generator, 8 ... Additional ON signal control part, 9 ... Phase Switching control unit, 10 ... power control unit, 11
... Overcurrent detector, 12 ... Motor, 13 ... Hall sensor for A-phase detection, 14 ... Hall sensor for B-phase detection, 15 ... Hall sensor for C-phase detection.

Claims (3)

[Claims] 1. A speed detecting means for detecting a motor rotating speed, a PWM duty adjusting means for increasing and decreasing a PWM duty according to a difference between the motor rotating speed with respect to a control target value, and a PWM duty set by the PWM duty adjusting means. Power control means for controlling the power supplied to the motor by means of a motor, PWM cycle defining means for defining a PWM cycle having a plurality of control target values of the motor rotation cycle, and a specific point or a plurality of points during one rotation of the motor. A motor rotation control method provided with a counter that is reset and sets a control target value of the motor rotation cycle to one or more cycles. Motor rotation control characterized by providing a period for turning on the motor for a certain period of time before and after the end Method. 2. The motor rotation control method according to claim 1, wherein an interval of the period during which the motor is turned on is a time obtained by equally dividing a control target value of a motor rotation cycle. 3. The motor rotation control method according to claim 1, wherein said counter also functions as said PWM cycle defining means.