JP2525248B2 - Motor control voltage calculator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a motor control voltage calculation device, and more particularly to a PWM signal calculation device in the case of controlling a motor rotation speed by a PWM signal.

<Prior Art> Some motor rotation speed control devices are controlled by a PWM signal.

Such a rotation speed control device is also used in a DC servo motor control device for driving an optical system in a document reading device such as a copying machine.

In the servo motor control device for driving the optical system, in particular, even if the frictional resistance or the like changes with the movement of the optical system and the motor load fluctuates, the servo motor can be kept at a constant speed with good followability and the optical system It is necessary to move at a constant speed.

Conventionally, in order to keep the servomotor at a constant speed, proportional control has been performed in which a PWM signal is obtained by a voltage proportional to the speed difference between the target speed and the actual detected speed.

<Problems to be Solved by the Invention> However, in the conventional proportional control, the acceleration when increasing the motor speed from the actual detected speed to the target speed is
The target speed varies depending on the size of the target speed. The larger the target speed is, the smaller the acceleration is, the longer it takes to reach the target speed, and the poorer the followability is.

 A more specific description will be given.

The equation of motion when a voltage V is applied to a motor is generally Becomes

Solving this for n, if t = 0 and n = Np, Also, Becomes

From this equation, when the sampled speed is Ns, the acceleration a at the time when the voltage V is applied is calculated by substituting Np = Ns, t = 0. Given in.

By the way, the target speed is N and the sampled speed is N
s, and the difference is ΔN, the acceleration a when V = KΔN = K (N-Ns) is applied by normal proportional control is as follows: V = KΔN, Ns = N-ΔN Substituting, From this equation, it can be seen that even if ΔN has the same value, the acceleration a is small when the target speed N is large, and a is large when N is small.

Therefore, the present invention has been made to solve such a drawback, and an object of the present invention is to provide a control signal calculation device capable of controlling a motor with good followability.

<Means for Solving the Problem> The present invention is a device for calculating a control voltage for controlling a rotation speed of a motor, wherein a voltage applied to the motor is a difference between a target rotation speed and an actual rotation speed. And a value obtained by multiplying the actual rotation speed by a second constant,
A means for calculating the sum of the predetermined offset voltage, a target phase detecting means for detecting the phase of the target speed, a rotation phase detecting means for detecting the phase of the actual rotation speed, and a phase difference between the target phase and the rotation phase. A control voltage calculation device for a motor, comprising: an applied voltage correction unit that corrects the calculated applied voltage based on

In the motor control voltage calculation device, the target phase detection means includes a phase reference value calculation means for adding or subtracting a predetermined phase reference value at each predetermined timing, and the phase reference value calculation means. It is characterized in that the target phase is grasped by the value of.

<Operation> When the control voltage is obtained according to the present invention, the acceleration is determined by the speed difference between the target speed and the actual speed, regardless of the target speed, and the acceleration constant is selected to be an arbitrary value. A desired acceleration can be obtained with respect to the speed difference.

In addition, it is possible to apply a control voltage that produces a constant acceleration regardless of the target speed, and a voltage that corrects the phase difference between the phase of the target speed and the phase of the detected speed is further added. It is possible to follow the target speed in a short time.

<Embodiment> In the following, as an embodiment of the present invention, a case where the present invention is applied to a drive control circuit of a DC servo motor for driving an optical system (illumination unit and reflecting mirror) of a copying machine will be described.

FIG. 1 is a block diagram showing a configuration example of a drive control circuit of a DC servo motor for driving an optical system of a copying machine. This control circuit is a circuit that uses a PWM signal as a voltage applied to the DC servo motor.

The DC servomotor 10 is of a permanent magnet field type and is rotationally driven by a driver unit 11 to move an optical system 17.

A rotary encoder 12 is connected to the rotary shaft of the servomotor 10. As is well known, the rotary encoder 12 outputs a rotation pulse each time the servo motor 10 rotates a predetermined minute angle. The rotary encoder 12 of this embodiment outputs, for example, 200 rotation pulses when the servo motor 10 makes one rotation.

Further, the rotation pulse of the rotary encoder 12 includes at least an A-phase rotation pulse and a B-phase rotation pulse. Both rotation pulses have the same number (200 per motor rotation) and their phases are 90 degrees. The pulses are out of phase.

The rotation pulse output from the rotary encoder 12 is
It is given to the encoder signal input unit 13. The encoder signal input section 13 is a rotary encoder, as described in detail later.
Servo motor based on rotation pulse given from 12
This is a circuit for detecting 10 rotations. The detection output of the encoder signal input unit 13 is given to the control unit 14.

The control unit 14 is a center for controlling the entire circuit,
The calculation of the control signal of the servomotor 10 and other arithmetic processing are performed.

The control unit 14 includes a memory and a timer used in the control operation described later.

The control unit 14 is also provided with an operation command signal and a command speed. The command speed is supplied to the control unit 14 by applying a speed command clock from a control unit (not shown) of the copying machine main body to the speed command signal input unit 15 for signal processing. The details will be described later.

The control unit 14 performs arithmetic processing based on each of these input signals, calculates PWM (pulse width modulation) data and supplies it to the PWM unit 16, and also supplies a driver unit drive signal to the driver unit 11 described above.

The PWM unit 16 outputs the PW based on the supplied PWM data.
This is a unit for changing the pulse width (output duty) of the M signal. The rotation speed of the servomotor 10 is controlled by the PWM signal output from the PWM unit 16. In addition, the driver drive signal determines the rotation direction of the servomotor 10 and brakes.

By the way, in order to accurately rotate the servomotor 10 at a desired speed, it is necessary to accurately detect the rotation speed of the servomotor 10 as a premise.

Therefore, in this drive control circuit, the encoder signal input section 13 is configured as shown in FIG. 2 and the signal reading by the control section 14 is devised so that accurate speed detection can be performed.

Referring to FIG. 2, the encoder signal input section will be described.
13 includes an edge detection circuit 131 to which the A-phase rotation pulse output from the rotary encoder 12 is applied.
The edge detection circuit 131 detects the rising edge of the applied rotation pulse and derives its detection output.

The encoder signal input unit 13 also includes a free running counter 133 of, for example, a 16-bit configuration that counts up a given reference clock, and a capture register 134. The capture register 134 uses the edge detection output of the edge detection circuit 131 as a capture signal, and the free running counter 133 using the capture signal as a trigger.
The count number of is read and held.

The reference clock is a reference clock that serves as a reference for the operation timing of the entire circuit shown in FIG. 1, and a machine clock is used when the circuit is configured by a microcomputer.

If there is no such reference clock, a reference clock generation circuit may be provided.

The input unit 13 further includes an up / down detection unit 135 and an up / down counter 136. The up-down detection unit 135 determines the level of the B-phase rotation pulse when the A-phase edge detection output is given, and determines whether the B-phase rotation pulse is at the high level or the low level.
10 (FIG. 1) is to determine whether it is rotating normally or reversely. The up / down counter 136 uses the edge detection circuit 1 based on the discrimination output of the up / down detection unit 135.
The detection output of 31 is up-counted or down-counted.

 Next, the operation of the circuit shown in FIG. 2 will be described.

The contents of the capture register 134 are the capture signal,
That is, it is updated by the rising edge detection signal of the A phase. The up / down counter 136 counts the edge detection signal (the number of rotation pulses).

Therefore, while the up / down counter 136 counts n rotation pulses, the free running counter 13
Measure the count number of the reference pulse counted in 3,
The rotation speed N can be calculated based on this. The rotation speed N is The relationship between the rotation speed N and the error N ′ is Becomes

A graphical representation of these relationships is shown in Figure 3A.

In this embodiment, paying attention to the relationship between the rotational speed N and the error N ′, the control unit 14 devises a sampling timing for reading the count numbers of the capture register 134 and the up / down counter 136, and the rotational speed N is By increasing the rotation pulse number n for calculating the rotation speed N in accordance with the increase, the error N ′ that tends to increase at a square rate with the increase of the rotation speed N is calculated by the formula (7). As shown in the figure, the error N'is suppressed by limiting the increase to the first power so that the rotational speed N can be accurately detected.

More specifically, one sample time from a certain sample timing to the next sample timing is Δt.
Then, in order to detect the rotation speed N, at least one rotation pulse, that is, the output of the edge detection circuit 131 must be derived within the sample time Δt.

For that purpose, the above-mentioned formula (6) must satisfy the condition of X ≦ Δt, and in the end, the rotation speed N and the error N ′ are N ′ ≧ (1 / Δt) N (8) It is necessary to meet the relationship. The relationship of the equation (8) is on the upper side of the straight line N ′ = (1 / Δt) N as shown in FIG. 3B.

Therefore, by setting the sampling time Δt to an appropriate constant time that satisfies the relationship of the equation (8), the thick line portion in FIG. 3B, that is, the range in which the error N ′ is relatively small with respect to the rotational speed N is successfully used. Then, the rotation speed N can be detected.

FIG. 4 is a flowchart showing a control operation for the control unit 14 to read the contents of the capture register 134 and the up / down counter 136 at every sampling time Δt to calculate the rotation speed N.

Next, a description will be given with reference to FIG. 2, FIG. 3B and FIG.

The control unit 14 resets the timer (step S2) and reads the contents of the capture register 134 and the up / down counter 136 (step S3) every time the internal timer reaches a certain sample time Δt (step S1).

Then, after subtracting the count number CPT _n-1 of the previously read capture register 134 stored in the memory A from the read count number CPT _n of the capture register 134 to obtain the reference clock number X within one sampling time Δt, CPTn
Is stored in the memory A (step S4).

Further, the count number UDC _n-1 of the previously read up / down counter 136 stored in the memory B is subtracted from the read count number UDC _n of the up / down counter 136 to obtain 1
After obtaining the number of rotation pulses within the sampling time Δt, UDCn is stored in the memory B (step S5).

Then, based on the equation (6) described above, the servo motor
The rotation speed N of 10 is obtained (step S6).

In steps S5 and S6, if the rotation speed N of the servo motor 10 increases, the rotation pulse speed n also increases stepwise within the sampling time Δt. Therefore, the servo motor 10 using the thick line portion in FIG. 3B is used. As described above, the number of rotations N can be detected.

Next, the speed command signal input unit 15 will be described in detail.

FIG. 5 is a block diagram showing a specific configuration example of the speed command signal input unit 15. The speed command signal input unit 15 includes an edge detection circuit 151 for detecting a rising edge of the speed command clock, a free running counter 152, a capture register 153, and an up counter 15.
Includes 4 and.

The free-running counter 152 is, for example, a 16-bit counter that counts up a given reference clock. This free running counter 152
It may be shared with the free running counter 133 of the encoder signal input unit 13 described above.

The capture register 153 uses the edge detection output of the edge detection circuit 151 as a capture signal, and uses the capture signal as a trigger to read and hold the count number of the free running counter 152.

The up counter 154 is for up counting the output pulse of the edge detection circuit 151.

 The operation of this circuit is as follows.

A speed command clock output from the apparatus main body side, for example, the control side microcomputer of the copying machine main body is given to the edge detection circuit 151, and the rising edge is detected. Since the output of the edge detection circuit 151 is given to the free running counter 152 as a capture signal, the content of the capture register 153 is updated in response to the rising edge of the speed command clock. Therefore, the content of the capture register 153 is read based on a certain edge detection signal, the content of the capture register 153 is read based on the next edge detection signal, and if the difference is obtained, the free running counter 152 in one cycle of the speed command clock. It is possible to measure the count number of. That is,
The target rotation speed data can be obtained.

Note that in this embodiment, each time the contents of the capture register 153 are updated, it is not the method of obtaining the count number of the difference between the count number after update and the count number before update, but in order to further improve the detection accuracy. A reading method similar to the reading of the count number of the capture register 153 in the encoder signal input unit 13 is used.

That is, the control unit 14 controls the contents of the capture register 153 and the up counter 1 at every predetermined sampling time Δt.
The content of 54 is read, the difference between the count number read this time in the capture register 153 and the count number read last time is calculated, and it is divided by the difference between the count number read this time in the up counter and the count number read last time. Thus, a more accurate number of reference clocks within one cycle of the speed command clock is obtained.

Further, the control unit 14 detects the phase difference between the command speed given from the speed command signal input unit 15 and the detected speed given from the encoder signal input unit 13 by the control described below.

That is, the control unit 14 reads the count number of the free running counter 152 in response to the edge detection signal from the edge detection circuit 151 of the speed command signal input unit 15, and sets the number as the phase reference value PPI. .

On the other hand, the edge detection circuit 131 of the encoder signal input unit 13
Even in response to the application of the edge detection signal from, the count number of the free-running counter 152 is read and the number is used as the phase comparison value PDT.

If the phase of the command speed, that is, the phase of the speed command clock and the phase of the rotation pulse of the encoder 12 are the same, the count number of the free running counter 152 is read at the same time, so the phase reference value PPI Is equal to the phase comparison value PDT. However, when both phases are deviated, the two values are not equal.

Therefore, the control unit 14 calculates the phase difference PHDT between the speed command clock and the phase detection pulse of the edge detection circuit 131 by the following equation.

However, SPD: number of reference clocks in one cycle of speed command clock The detection of the phase difference between the command speed and the detected speed may be performed by a detection procedure as described below instead of the above-described detection procedure. In this example, the following procedure is more preferred.

Each time an edge detection signal is given from the edge detection circuit 131 of the encoder signal input unit 13, the count number of the free running counter 152 is read, and the number is read as the phase comparison value P.
DT.

On the other hand, from the start of the phase comparison, the reference clock number SPD (SPD is a fixed value) in one cycle of the speed command clock is added every time the edge detection signal is output from the edge detection circuit 151, and the phase is increased. Use the standard value PPI.

Therefore, the phase reference value PP at a certain read timing n
A relationship of PPIn = PPI _n-1 + SPD is established between In and the phase reference value PPI _n-1 at the previous read timing n-1.

Therefore, the phase difference PHDT between the speed command clock and the phase detection pulse is Can be obtained by

Since the phase reference value is calculated by calculation without relying on such a phase difference detection procedure, there is an advantage that the phase reference value can be set more accurately than that based on the actual measurement value. In the above case, subtraction may be performed instead of addition.

The phase difference PHDT detected as described above is fed back to the PWM data as follows.

That is, since the PWM data is calculated by the equation (12) described below, the output voltage V is calculated by adding / subtracting the detected phase difference data PHDT to a constant α. V is corrected.

V _OUT = V ± α · PHDT (11) By changing α in the equation (11) above, the ratio of the phase difference can be investigated, and the servomotor 10 can be controlled at a constant speed with better followability.

 Next, a method of calculating the output voltage V will be described.

The control unit 14 is the servo motor detected as described above.
The applied voltage represented by the following equation is calculated from the difference between the actual rotation speed Ns of 10 and the command rotation speed N given from the speed command signal input unit.

The acceleration when the voltage expressed by this formula is applied is
Substituting equation (12) into equation (4) above and substituting Ns = N-ΔN, The value obtained by dividing the speed difference ΔN by Δt is the acceleration,
By optimizing Δt, a constant optimum acceleration can be obtained for ΔN.

Next, the process of deriving the above equation (12) will be described.

FIG. 6 is an equivalent circuit diagram of a permanent magnet field type DC servo motor.

When the signal voltage V is applied to the motor armature and the angular displacement θ of the rotating shaft is obtained as the output, the transfer function of the motor is Is led.

Since the induced voltage E of the motor is proportional to the angular velocity ω of the rotating shaft, However, K _E : Induced voltage constant Since the generated torque is proportional to the amateur current I, T = K _T I (16) where K _T : Torque constant Now, the sum of the sensitivity moments of the rotor and the load is J, and the bearing loss is Assuming that the motor braking load including B is B, the load torque T _L is Since the torque generated by the motor is equal to the load torque, Becomes

In general, the inductance La of the amateur circuit is designed to be smaller than the moment of inertia J, so that La = 0, and since the braking load B can be ignored, B = 0. 19) Equation (17) is Becomes

As for the moment of inertia J [Kg msec ² ], it is more convenient to actually use GD ² [Kg m ² ], so change to GD ² .

GD ² ＝ Mg (2k) ² … (21) Where, G ＝ Mg: Weight of object [Kg] M: Mass g: Gravitational acceleration [9.8m / sec ² ] k: Radius of gyration Physical moment of inertia J [ Kgmsec ² ], given that the total mass is collected at a certain distance, it is expressed as J = Mk ² (22). Therefore, GD ² = 4gJ (23)

From equation (20) and equation (23), From equation (24) and equation (25), Becomes

This equation (26) represents the torque required to obtain the rotation speed change amount ΔN during the time period Δt.

Since the required load torque is the torque generated by the motor,
From equation (16) and equation (26), Is obtained.

Here, although the generated torque and the current are proportional expressions with K _T being a constant from the expression (16), there is a necessary current (no-load current) even in a no-load state.

Now, assuming that the no-load current is I _O Becomes

Next, since the actual drive control method is the voltage drive type by PWM, from equation (19) and equation (28), Becomes

Here, the induced voltage E is E = K _E N where K _{E is the} induced voltage constant, so equation (29) is Becomes

By the way, the equation (30) does not include the terms of the sliding load and the braking load on the motor. Therefore, letting this sliding load and braking load be T _BL , Motor braking load T calculated from no-load current I _O
BM is And the braking load T _B (Bω) in equation (17) is Becomes

Thus, equation (30) becomes Becomes

From the above, when rearranging, when the speed difference ΔN with respect to the target speed N occurs, The voltage V obtained in step 3 may be applied to the motor.

Here, the constant that is determined by determining the actual load and motor is Ra: Amateur resistance [Ω] K _T : Torque constant [kgm / A] K _E : Induced voltage constant [V / rpm ] I _O : No load current [A] GD ² : Inertia moment due to load and motor [kg cm ² ] T _BL : Sliding load [kgm].

 Therefore, N, ΔN, and Δt are variables during control.

FIG. 7 is a block diagram showing a specific configuration example of the PWM unit 16, and FIG. 8 is a timing chart for explaining the operation of the PWM unit 16.

The PWM unit 16 includes a set signal generator 161, a PWM data register 162, a down counter 163, and an RS flip-flop 164.

The set signal generator 161 generates a set signal at regular intervals. The set signal generation unit 161 is composed of, for example, a ring counter, and is configured to generate a set signal every time a constant number of reference clocks are added.

The PWM data register 162 is a PW provided by the control unit 14.
It is for holding M data. The PWM data given from the control unit 14 is the voltage data obtained by the above-mentioned equation (11). That is, it is the voltage V _{OUT obtained} by correcting the voltage of Expression (12) with the phase difference data PHD. This PWM
The data is used to determine the duty of the PWM output signal output from the PWM unit 16.

The down counter 163 counts down each time a PWM reference clock (in this embodiment, the PWM reference clock shares the reference clock used by the encoder signal input unit 13 and the speed command signal input unit 15). And
When the set number is measured, a reset signal is output.

 The operation of the PWM unit 16 is as follows.

When the set signal generator 161 outputs the set signal, the contents of the PWM data register 162, that is, the PWM data given from the controller 14 is set in the down counter 163, and the flip-flop 164 is set by the set signal. To be done. Therefore, the output of flip-flop 164,
That is, the PWM signal becomes high level.

Next, the down counter 163 counts down based on the PWM reference clock, and when the set count value becomes “0”, gives a reset signal to the flip-flop 164. Therefore, the output of the flip-flop 164 is inverted to the low level.

As a result, from the PWM unit 16, the PWM data register
The duty is determined by the value held in 162, that is, the voltage data calculated by the equation (11), and the PWM signal is derived.

The present invention is not limited to controlling the optical system of a copying machine,
It can be used for a reading device control motor of a facsimile machine and other general motor control circuits.

The present invention can also be applied to the case where the applied voltage is calculated using a signal other than the PWM signal.

<Effects of the Invention> Since the present invention is configured as described above, it is possible to calculate a control signal capable of keeping the acceleration constant regardless of the target speed. Therefore, regardless of the target speed, it is possible to control the speed of the motor with good followability.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a drive control circuit of an optical system driving DC servo motor to which an embodiment of the present invention is applied. FIG. 2 is a circuit block diagram showing a main configuration of a rotation speed detecting device for a DC servo motor for driving an optical system according to an embodiment of the present invention. 3A and 3B are graphs showing the relationship between the motor rotation speed N and the error N '. FIG. 4 is a flow chart showing the rotational speed detecting operation in the embodiment of the present invention. FIG. 5 is a block diagram showing a specific configuration example of the speed command signal input unit. FIG. 6 is an equivalent circuit diagram of a permanent magnet feed type DC servo motor. FIG. 7 is a block diagram showing a specific configuration of the PWM unit. FIG. 8 is a timing chart showing the operation of the PWM unit. In the figure, 10 ... DC servo motor, 11 ... Driver section, 12
… Rotary encoder, 13… Encoder signal input section, 14
... Control unit, 15 ... Speed command signal input unit, 16 ... PWM unit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshihiko Araki 1-2-2 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka Mita Industry Co., Ltd. (56) Reference JP-A-58-119790 (JP, A) JP Flat 2-76686 (JP, A) Actual Open Flat 1-120217 (JP, U)

Claims (2)

(57) [Claims] 1. A device for calculating a control voltage for controlling a rotation speed of a motor, wherein a voltage applied to the motor is obtained by multiplying a difference between a target rotation speed and an actual rotation speed by a first constant. Value, a value obtained by multiplying the actual rotation speed by the second constant, and a predetermined offset voltage, a target phase detection means for detecting the phase of the target speed, and an actual rotation speed phase. A control voltage calculation device for a motor, comprising: a rotational phase detection means for detecting; and an applied voltage correction means for correcting the applied voltage calculated based on the phase difference between the target phase and the rotational phase. 2. The motor control voltage calculation device according to claim 1, wherein the target phase detection means adds or subtracts a predetermined phase reference value at every predetermined timing. And the target phase is grasped by the value of the phase reference value calculation means.