JPS6159070B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a control device for rotating a DC motor at a constant speed at an arbitrary set speed.

[Prior art]

Conventionally, constant speed control methods for DC motors include: 1. A method in which a resistance bridge circuit is constructed using a back electromotive force in the windings, which is generated in proportion to the rotational speed of the motor, and equilibrium conditions regarding resistance are used.

2 Using a rotation speed detection means that generates a signal with a voltage or frequency proportional to the rotation speed of the motor, converts this signal from frequency to voltage, and applies an amount of current to the motor that is proportional to the difference between the voltage and the voltage corresponding to the set speed. How to add.

3 A method in which the same rotational speed detection means as in 2 is used to compare the phase of this signal with a reference frequency corresponding to the set speed, the phase difference signal is passed through a loop filter, and this signal is used to control the amount of current to the motor. .

etc.

However, in method 1, the temperature characteristics of the back electromotive force are poor and temperature compensation is difficult. Although the second method is not affected by the temperature of the detection signal, there is a delay in response depending on the time constant of the low-pass filter that constitutes the frequency/voltage converter. The third method is
It is used for fine adjustment when the motor rotation speed is close to a set value, and is used to control up to the phase difference with the reference signal, and is often used in combination with control 2. However, this method also has the same drawbacks as 2. In order to speed up the rise response, there is a method of forcibly switching the filter output to a fixed value, but in order to vary the set speed over a wide range, it is necessary to switch the timing or change the filter time constant. The configuration becomes complicated.

〔the purpose〕

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks, and to provide a control device with a simple configuration that allows speed settings over a wide range and has a short response time. Furthermore, the present invention is a system suitable for microcomputers that have high performance and are becoming inexpensive, and by using a microcomputer, the configuration can be extremely simplified.

[Summary of the invention]

In general, a DC motor exhibits a constant acceleration determined by the motor torque and load when approximately a constant current is applied over a narrow rotational speed range. Furthermore, when the power to the motor is turned off, it exhibits a constant negative acceleration determined by the friction of the load.
If this acceleration is αON and αOFF, control as shown in FIG. 4 is possible by storing these values in advance in the microcomputer. That is, at the speed V, the motor is energized for a certain period of time T _ON , and the motor is accelerated to a rotational speed higher than the set speed V by a certain speed ΔV ₁ . Thereafter, until an encoder pulse for detecting the speed of the motor is input, the power to the motor is cut off, and the speed is decelerated to a speed ΔV ₂ lower than the set speed V. and Δ
A computer predicts and determines the energization time T _ON to the motor based on the accelerations αON and αOFF so that V ₁ and ΔV ₂ are equal. Through such control, the average speed of the motor can be set to the set speed V.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example in which the present invention is used to drive an optical scanning system of a variable magnification copying machine having multiple stages of copying magnification. 1 is a scanning system including an illumination system, and 2 is a DC motor for driving the scanning system. 3 is an encoder for detecting the rotation speed of the DC motor 2, and a pulse having a frequency proportional to the rotation speed of the DC motor 2 is obtained.

FIG. 2 shows the configuration of a control circuit for controlling the speed of the DC motor 2. Numeral 10 is a switching circuit for turning on and off the power supply to the DC motor, which can also switch between forward and reverse rotation.

11 is a control unit using a microcomputer for controlling the switching circuit 10,
This control section 11 has an 8-bit internal timer.

The control unit 11 includes a set speed V of the motor 2 which is set in accordance with the copying magnification of the copying machine, a scanning command S to rotate the scanning system 1 forward or reverse, and a stop (brake).
Various control signals required for copying the command B etc. are applied, and pulses having a pulse interval corresponding to the actual speed v of the motor are applied from the encoder 3 for speed detection of the DC motor 2 via the waveform shaping circuit 12. is applied, and a fixed frequency reference pulse for measuring the pulse interval from the encoder 3 is further applied from the reference oscillator 13. Then, in the control section 11, the signal is generated from the encoder 3. During two adjacent pulse intervals, the reference oscillator 1
Count the number of pulses generated from 3 with an internal timer,
The rotational speed of the DC motor 2 is calculated from the counted value _T1 . In this example, the encoder generates 50 pulses per revolution of the DC motor 2, while the oscillation frequency of the reference oscillator is 200 KHz. For example, when the DC motor 2 is rotating at a constant speed of 400 rpm, the number of reference oscillation pulses counted by the control unit 11 is set to 600. As the rotational speed of the DC motor 2 increases, the pulse interval from the encoder 3 becomes shorter, making it impossible for the microcomputer to follow the process, resulting in a decrease in the accuracy of the detected speed of the DC motor 2. In order to prevent such problems, a frequency divider may be provided on the output side of the encoder 3, for example.

The control unit 11 stores the programs shown in FIG. 3A to D for controlling the speed of the DC motor 2 according to the principles of the present invention, and also stores a program for executing normal copying operations. There is. Note that the copying operation is not related to the present invention, so a description thereof will be omitted.

In addition, the memory of the control unit 11 contains data representing the acceleration αON that occurs when a constant current is passed through the armature of the DC motor 2 for a short time, and the negative acceleration αOFF that occurs in relation to the load when the current is suddenly interrupted. and the set speed V
Predetermined speed deviations for ΔV ₁ and ΔV ₂
and the motor such that |ΔV ₁ |= |ΔV ₂ |
A calculation formula F (V, v) for predicting the ON time T _ON is stored.

And when the DC motor 2 is rotating at a certain speed, one pulse Pi from the encoder 3
As shown in the figure, when the voltage is applied to the control unit 11, the control unit 11 outputs the αON, αOFF pulse Pi and the previous pulse Pi.
_-1 , the motor speed v and the motor energization time T _ONi from the set speed V to F(V,
v), the switching circuit 10 is turned on according to the time T _ONi , a predetermined voltage V _ONi is supplied to the DC motor 2, and the DC motor 2 is accelerated. After time T _ONi , the motor speed is V + Δ
When V ₁ is reached, the switching circuit 10 is turned off.

As a result, the current supply to the DC motor 2 is interrupted, and the DC motor 2 is decelerated.

Next, when the next pulse Pi+1 is applied from the encoder 3 to the control unit 11, the time T _(ONi+1) for which the motor speed becomes V+ΔV ₁ is calculated by the same operation as described above, and this T _{ON(i+ 1)} is calculated and this TON _(i+1)
During the time, the switching circuit 10 is turned on again to supply power to the DC motor 2 and accelerate it. Thereafter, the same operation is performed to drive the motor every time a pulse is received from the encoder 3 to maintain the DC motor 2 at the set speed.

The above control operation will be explained in further detail with reference to FIGS. 3A to 3D.

The control unit 11 is controlled in synchronization with other processes by another microcomputer that controls other processes of the copying machine. Hereinafter, this process control microcomputer will be referred to as a master.
When the control section 11 is reset, it initializes itself in a step and then waits for a command from the master. During a certain process, the master controls the control unit 11 at the document scanning timing.
A scan signal indicating that it is scan timing and data of the set scan speed V are output.

When the control unit 11 receives the scan signal and the set scanning speed V in step 1, it clears the interval timer T _I for measuring the pulse interval of the encoder 3 in step 1, and stops the motor 2 currently used for scanning. Therefore, the motor on timer T that regulates the motor on time (energization time)
Set a sufficiently large initial value for _ON , and also clear the timer register Treg of the control unit 11,
Register 1 indicating the initial value of this timer register
Set the maximum value of T reg to . The internal timer register T reg of the microcomputer used in this example is an 8-bit up counter, so the timer register T reg contains zero,
Timer I is set to 2 ⁸ =256. When the setting of the initial value of the timer is completed, processing INT-E is started by an external interrupt signal in step .
The timer interrupt INT-T is enabled, the switching circuit 10 is set to normal rotation, and the motor 2 is started. Thereafter, in the main routine, the scan signal is turned off and the process continues to wait for the scanning end timing (step). Of these interrupts, INT
-T, an interrupt occurs when the internal timer register T reg of the microcomputer counts up the pulses of the reference oscillator 13 connected to the external clock terminal ECK and overflows. The timer register T reg is
After the flow, the external clock terminal starts again from zero.
Continue counting every time a pulse comes to ECK. The other interrupt INT-E is the external interrupt terminal INT
An interrupt occurs when a pulse from the encoder 3 is input. When each interrupt occurs, execution of the main routine for the copying operation is temporarily interrupted, control is transferred to the corresponding interrupt processing routine, and after the processing is completed, control is returned to the original main routine. Also, if an interrupt occurs while one interrupt is being processed by another, it will be suspended until the former interrupt processing is completed, and after the previous processing is completed,
Control is not returned to the main routine, but is transferred to a later interrupt processing routine. Furthermore, if interrupts occur at the same time, external interrupts are given priority.

When the switching circuit 10 is set to normal rotation in step, the DC motor 2 starts rotating in the normal rotation direction, and the encoder 3 starts outputting pulses at a frequency proportional to the rotational speed of the DC motor 2. However, when the DC motor 2 starts rotating, the rotation speed is still low, so the pulse interval from the encoder 3 is long, and the timer register T
reg overflow occurs first. This causes a timer interrupt, which causes the main routine to
Control is transferred to INT-T. At INT-T in FIG. 3C, first, in step T-1, the current DC motor 12 is
If it is on, the motor on timer T is checked in step T-2.
From _ON , the initial value T of the timer register T reg
decrease. Then, in step T-3, if T _ON becomes negative or zero, the motor 2 is turned off in step T-4.
Turn off. When motor 2 starts up, timer T _ON
This condition does not hold because is set to a sufficiently large value. Next, in step T-5, T is added to the interval timer T _I to update T _I.
Finally, in step T-6, T is the maximum value of T reg t _n
Set _ax (here 2 ⁸ ), end the process,
Return control to the main routine. Timer register T
Since reg continues counting from zero even after overflow, the next timer interrupt occurs when the external clock pin ECK pulses 2 ^{to 8} .
= after 256 counts. This is equivalent to setting t _nax (=2 ⁸ ) in the timer register T reg. In this example, the external clock terminal
The oscillation frequency of the reference oscillator connected to ECK is
Since it is 200KHz, this time is 1.28ms.
In this way, only INT-T occurs for a while.

After that, a pulse from encoder 3 is generated,
When an external interrupt occurs, control is transferred to INT-E. In INT-E, first, in step E-1, the current value of the timer register T reg is added to the interval timer T _I to find the current encoder pulse interval. Then, in step E-2, the current speed v of the DC motor 2 is determined.
Then, in step E-3, the motor-on timer T _ON is temporarily set to zero. Next, in step E-4, this speed v and the preset set speed (target speed) V are converted into the optimal time function F(v,
V). F(v,V) is a function as follows. A DC motor exhibits a constant acceleration determined by the motor torque and load when an approximately constant current is applied over a narrow range of rotational speeds. Furthermore, when the power to the motor is turned off, it is determined by the friction of the load. Indicates constant negative acceleration. If this acceleration is αON and αOFF, by storing these values in advance in the microcomputer, control as shown in FIG. 4 is possible. At speed v, the motor is energized for a certain time T _ON and accelerated to a rotational speed higher than the set speed V by a certain speed ΔV ₁ . After that, the motor is turned off until the next encoder pulse is input, and from the set speed V, Δ
Decrease speed by V ₁ . and ΔV ₁ and ΔV ₂
Predict and determine T _ON so that they are equal. In the steady state of this kind of control, it becomes as shown in Figure 5,
The average speed when the motor is on and the average speed when the motor is off are both the set speed V. With this method, it is not possible to keep the speed at all times equal to the set speed V, but by setting the pulse frequency of the encoder 3 sufficiently high and suppressing speed fluctuations in a steady state, the scanning system of the copying machine can be controlled. As such, it can be made sufficiently practical. The value of the function F(v, V) is not always fixed, but when the speed v increases beyond a certain value, the average speed until the next pulse from the encoder comes will become the set speed even if the motor is not turned on at all. V will be exceeded (Step E-4-NO). In such a case, the value of F(v, V) cannot be determined. Therefore, in such a case, step E-
At step 7, set the interval timer T to keep the motor off until the next pulse from the encoder arrives.
The value of _ON should be set to zero. For this reason, if NO in step E-4, the processing in steps E-5 and E-6 is skipped, and the T _ON set in step E-3 is
=0 is used. When F(v,V) is determined,
In step E-5, the function F(v, V) is set in the motor-on timer T _ON , and in step E-6, the switching circuit 10 is set to turn the motor on. Then, in step E-7, to measure the time until the pulse from the encoder 3 arrives, the interval timer T _I is set to zero, and the timer register T _reg is divided by the maximum time t _nax of the timer register T reg. The remainder at that time is set in timer T, and its complement is set in timer register T reg. Therefore, the time determined by the function F(v, V) is a value converted to the count value of the reference oscillation frequency. After setting data to T, T reg, T _I and T _ON , the INT-E processing is terminated and control is returned to the main routine.

In this way, the interval between encoder pulses is measured with INT-T, and each time a pulse is input from encoder 3, the optimum motor on time T _ON is determined from the current rotation speed and set speed with INT-E. .
In INT-T, the on-time is managed while measuring the interval of the next encoder pulse, and the motor is turned off after the on-time has elapsed. By repeating this process, the average rotational speed of the motor is maintained at the set value.
In this example, when the set speed is 400 rpm, 1
The variation in average speed per second was within 0.3%, and the width of speed fluctuation was within 5%.

In this way, constant speed control is performed during document scanning. Thereafter, the scan signal from the master is turned off, and the end of the scan is detected in the steps of the main routine. As a result, in the step of the main routine, the INT-E and INT-T interrupts are prohibited and the constant speed control is ended, and in the step, the switching circuit 10 is set to reverse rotation, and the optical scanning system is directed to the scanning start position. and return it. At this time, constant speed control is not performed. Thereafter, when the scanning start position is approached, the master outputs a brake signal in steps. As a result, in the step of the main routine, the switching circuit 10 is set to regenerative braking,
Decrease the reverse speed. Thereafter, when the optical scanning system returns to the scanning starting position, the brake signal from the master is turned off in step. When this is detected in the main routine step, the motor is turned off and the process returns to waiting for the scan signal.

Although the above embodiment is an example of an optical scanning system of a copying machine, the present invention is not limited to this.
Application to a DC motor for driving other devices such as a paper feeder or a photosensitive drum drive is also possible. In such a case, if the microcomputer used for control has sufficient capability, it is possible to control multiple motors or control other processes in parallel. Also, if the microcomputer has an accurate reference oscillation, there is no need for an external reference oscillation. Furthermore, with current semiconductor technology,
By combining the control section, reference oscillation section, waveform shaping section, and switching section into one chip, it is possible to reduce the size and cost.

In addition, in the above embodiment, control was explained in which the DC motor 2 is turned on every time a pulse is generated from the encoder 3. However, this control cuts off the current to the motor with the generation of a pulse, and sets the OFF time T _OFF to meet the above conditions. It is also possible to calculate it as shown below.

However, in this case, there is a risk that the motor will stop if an overload is applied to the motor during motor speed control (INT-T, E permission), so the above embodiment is not implemented. This can be said to be the preferred method.

When the copying magnification of the copying machine is changed, the value of the set speed V input to the control section 11 changes, and therefore the value of the function F (V, v) also changes, and the motor on time calculated by the control section 11 changes. T _ON changes. Thereby, the speed of the DC motor 2 can also be changed.

〔effect〕

As described in detail above, the present invention performs intermittent operation at a high speed in controlling the speed of a DC motor, and the pulse interval and on-time are determined by pulses corresponding to the speed of the motor. Since the motor was operated at a constant speed, there was no need for a complicated feedback control device, and digital equipment such as a microcomputer could be used to
It has the advantage of being able to control speed with a simple configuration.

ON time T of the DC motor used in the above example
An example of _{the ON} calculation formula F(V, v) will be explained below. (See Figure 4) As a condition, consider the case where the next motor ON time T _ONi is determined when the i-th pulse Pi occurs.

When the speed at the time of pulse Pi generation (time ti) is vti, if the motor is energized by T _ONi , then (101) v (ti + T _ONi ) = v _ti + T _ONi , αON {αON: acceleration αOFF: deceleration} (102 )v(ti+T _I(i+1) ) =v(ti+T _ONi )+(T _I(i+1) −T _ONi )・αOFF =v _ti +T _ONi , αON+ (T _I(i+1) −T _ONi ). αOFF In the above equation, it corresponds to ( _TI(i+1) −T _ONi )=T _OFFi .

Here, if we give the condition that the increasing speed ΔV ₁ when the T _ONi motor is energized is equal to the decreasing speed ΔV ₂ after T _OFFi , then (103)v(ti+T _ONi )−V=V−v(ti+T _{I( i+1)} ), so (104)T _ONi =2V-2v _ti -T _I(i+1)・αOFF
/2αON−αOFF Here, T _{I (i+1)} is unknown and is calculated by the following formula.

That is, the average speed during T _ONi during T _{I (i+1)} is V(ti+T _ONi +Vti/2, and the average speed during T _OFF is V, so if the moving distance during that time is a, then (105) a=T _OFFi ,V +v(ti+T _ONi )+v _ti /2・T _ONi =T _OFFi ,V +v _ti +T _ONi .αON+v _ti /2T _ONi Therefore, (106)T _I(i+1) = 1/2V {2a+2T _ONi (V-v _ti ) −T ² _ONi αON} Therefore, T _ONi is the solution to the simultaneous equations of equations (104) and (106). However, v _ti is the previous pulse It is calculated from T _{ON (i-1)} and T _Ii when the interval T _Ii is used. (Described later) However, if the above processing is performed using a microcomputer, there is a risk that the time required for calculation will be too long. Therefore, after the motor reaches a steady speed, it can be approximated as (107)T _I(i+1) = a/V.

Then, when the motor starts up, using the previous measured pulse interval T _Ii as an approximate value, (108) T _ON =2V-2v _ti -T _Ii・αOff/
2αON-αOFF (at rise) 2V-2v _ti -aαOFFV-1/2αO
N-αOFF (at steady state).

However, (109)v _ti =a/T _Ii +T _ON ² _(i-1) (αON-αOFF) +T ² _Ii 〓 _Off /2T _Ii .

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a scanning mechanism of a copying machine to which the present invention is applied, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIGS.
FIG. 4 is a waveform diagram showing the operation of the embodiment shown in FIG. 2, and FIG. 5 is a diagram illustrating that the average motor speed is constant. 2...DC motor, 3...Encoder, 10...
...Switching circuit, 11...Control section.

Claims (1)

[Scope of Claims] 1. Pulse generating means for generating a pulse signal with a frequency proportional to the rotational speed of a DC motor, means for detecting the rotational speed of the motor from the pulse interval of the pulse generating means, and a predetermined energization time. means for storing the acceleration of the motor and the acceleration of the motor when the current is cut off, and when the motor rotates,
The rotational speed of the motor when the motor is _energized for a predetermined period of time is V + ΔV ₁ with respect to the target value V,
If the rotational speed when the current is then cut off for a predetermined period of time T _OFF is V - ΔV ₂ (ΔV ₁ and ΔV ₂ are positive numbers), then the above is set so that T _ON + T _OFF = pulse interval ΔV ₁ = ΔV ₂ . T _ON or T using the detected rotational speed of the motor and the stored acceleration.
_OFF , and T _ON or T _O every time the above pulse occurs.
A speed control method for a DC motor, characterized in that energization to the motor is controlled by _{an FF} to obtain a constant speed V on average.