JP3337058B2 - Position control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position control device for a motor used in a robot, a machine tool, or the like, and particularly to a position control device required to suppress vibration at the time of stoppage induced by digital control.

[0002]

2. Description of the Related Art A conventional position control device for stopping a motor at a target position has the following configuration widely and generally used. As shown in FIG. 1, the configuration includes a command generation unit 11 that generates a position command Pref (i) by a position control device.
A position control unit 12 for inputting the position command Pref (i) and the detected position Pfb (i) of the motor and outputting a speed command Vref (i) to perform position control; and a speed command Vref.
(I) The motor speed Vfb (i) calculated by the differentiator 17 based on the position Pfb (i) and the torque command Tr
Speed control unit 13 that outputs ef (i) to perform speed control
And a current control unit 14 that controls the current supplied to the motor based on the input torque command Tref (i). Then, the speed command V
A subtractor for subtracting the speed Vfb (i) from the ref (i) to obtain a speed deviation Ve (i), and a time integration of the speed deviation Ve (i) with a time constant Ti to perform a speed deviation integrated value SVe (i).
And the speed command Vref (i) as γ (0.
0 ≦ γ ≦ 1.0) to obtain a signal γVref (i), a signal γVref (i) and a speed deviation integral S
An adder / subtractor for adding Ve (i) and reducing the speed Vfb (i); and a multiplier for calculating a torque command Tref (i) by multiplying the output of the adder / subtractor by a speed loop gain Kv. In this configuration, the position was controlled in the main loop while the speed was controlled in.

[0003]

In the prior art, however, the position Pfb (i) is detected by an encoder and the position Pfb (i) is detected.
Since the speed Vfb (i) is obtained from b (i),
When the motor stops, there is a variation of ± 1 pulse, which is the position detection resolution. Control is performed so as to suppress the deviation of this ± 1 pulse. There was a problem that the width of remains. Therefore, an object of the present invention is to provide a position control device that solves this problem.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a command generating unit for generating a motor position command Pref (i) at a current time i, and a detected motor rotation axis. A difference calculator that calculates a difference between the position Pfb (i) and outputs a motor speed Vfb (i), and a position deviation Pe (i) obtained by subtracting the position Pfb (i) from the position command Pref (i). A position control unit for outputting a speed command Vref (i) and controlling the position so that the position deviation becomes zero; and a speed Vf based on the speed command Vref (i).
a speed control unit that outputs a torque command Tref (i) based on the speed deviation Ve (i) obtained by subtracting b (i) and controls the speed so that the speed deviation becomes zero;
A current control unit that controls a current supplied to the motor based on (i), wherein the position control unit is configured to execute a position deviation Pe (im) before m samplings where m is a natural number. And the absolute values of the position deviations Pe (i) and Pe (im) are all equal to or smaller than a predetermined constant N (N ≧ 0), and the position command Pref
(I) increment value dPref (i) (dPref (i) =
When Pref (i) -Pref (i-1)) is zero, a predetermined deviation α (α> 1) is output, and when it is not zero, α = 1 is output. The control unit calculates the speed deviation Ve (i) as Ve (i) = Ve
(I) / α.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on specific embodiments. FIG. 1 is a block diagram of a motor control system to which the present invention is applied. In the figure, reference numeral 11 denotes a command generator, which outputs a position command Pref (i) at the current time i. The position control unit 12 receives the position command Pref (i) and the position Pfb (i), performs position control so that the position command Pref (i) and the position Pfb (i) match, and performs a speed command Vref (i) and a signal. α (α ≧ 1) is output to the speed control unit 13. The speed control unit 13 outputs the speed command Vref
(I), the signal α, and the speed Vfb output by the differentiator 17
(I) to input the speed command Vref (i) and the speed Vfb
Speed control is performed so that (i) matches, and a torque command Tref (i) is output. The current control unit 14 receives the torque command Tref (i) and supplies a current corresponding to the torque command Tref (i) to the motor 15 to drive the motor. 16 is motor 1
This is a detector for detecting the position of No. 5, and an encoder is suitable in the present application. The detector 16 has a motor position P
fb (i) is outputted as a pulse as a digital signal. 1
Reference numeral 7 denotes a differentiator for calculating the difference between the motor position Pfb (i) and the motor speed Vfb (i). Next, the position control unit 12 and the speed control unit 13 will be described in detail with reference to FIG. In the figure, a position control unit 12 includes a subtractor 12
1, a position deviation judging unit 122, an adder 123, and a coefficient unit 124. The position command Pref (i)
And the motor position Pfb (i), and outputs a signal α and a speed command Vref (i). The signal α is a signal indicating a constant, and the subtracter 121 subtracts the motor position Pfb (i) from the position command Pref (i) to obtain a position deviation Pe (i).
Is output, and the position deviation determiner 122 outputs the position command Pref.
(I) and the position deviation Pe (i) are input, and signals α and β are output. The signal β is a signal indicating a constant, and the position deviation Pe
Set to (の) the resolution of (i). Position deviation judgment device 1
22 is a position deviation Pe (i) before m sampling when m is a natural number parameter for setting conditions of α and β.
-M) is internally provided, and receives a position command Pref (i) and a position deviation Pe (i), and inputs Pe
It is determined whether the absolute values of (i) and Pe (im) are all equal to or less than a predetermined constant N (N ≧ 0) pulses, and whether or not the position command increment dPref (i) is zero. Values are all less than or equal to N pulses and said increment value dPref
If (i) is zero, the signals α (α> 1) and β (β> 0)
, And otherwise outputs the signal as α = 1, β = 0. The adder 123 adds the position deviation Pe (i) and the signal β, and the coefficient unit 124 receiving the signal multiplies the coefficient Kp by a factor Kp and outputs a speed command Vref (i). Here, the function of β will be briefly described. When the position deviation Pe (i) is stopped within ± 1 pulse and stopped, it means that it stops somewhere in three pulses having a pulse width of +1 pulse, 0 pulse, and -1 pulse.
Here, if, for example, 0.5 pulse is added to Pe (i),
e (i) = 0 is Pe (i) = 0.5, Pe (i) = − 1
Is Pe (i) =-0.5, so that the speed command Vref (i) is generated so as to eliminate this deviation. Accordingly, although the pulse width originally has a width of three pulses at the time of stopping, the width can be suppressed to two pulses by adding β. The speed control unit 13 includes a subtractor 131, coefficient units 134 and 138, dividers 132 and 136, a subtractor 135, and an integrator 133.
And a speed command Vref (i) and a motor speed Vf
b (i), the signal α is input and the torque command Tref (i) is input.
Is output. The subtractor 131 subtracts the speed Vfb (i) from the speed command Vref (i) to output a speed deviation Ve (i), and the divider 132 receives the speed deviation Ve (i) and the signal α and divides the signal to obtain a speed deviation. Ve (i) is multiplied by 1 / α. The integrator 133 receives this signal and performs time integration with the time constant Ti. The coefficient unit 134 converts the speed command Vref (i) into a coefficient γ
(0.0 ≦ γ ≦ 1.0), and the subtractor 135 is a coefficient unit 1
The speed Vfb (i) is subtracted from the signal of No. 34. Divider 13
6 inputs the signal of the subtractor 135 and the signal α, and
Is divided by α, and the adder 137 adds the output of the integrator 133 and the signal of the divider 136. The coefficient unit 138 multiplies the signal of the adder 137 by the speed loop gain Kv and outputs a torque command Tref (i) to the current control unit 14. Here, the coefficient γ corresponds to the control method of the speed control loop,
By designating this coefficient γ, if 0, IP control, 1 if PI control, and if 0.5, an intermediate control method is formed.

With such a configuration, the control method of the speed control loop is selected according to the value of γ, and the absolute values of the position deviation Pe (i) and the position deviation Pe (im) up to m samples before are all predetermined. If smaller than the magnitude N, the speed deviation V
The speed control loop is configured by correcting e (i) to 1 / α times, and if it is larger than N, the correction is not performed in the transient state where the response to the position command has a large deviation. The feature that this correction works and it is difficult to vibrate is obtained. Next, an operation example when the AC servomotor is driven will be described with reference to FIG. In the figure, (a) is a response using the conventional example, (b) is a response using claim 1 of the present invention, and (c) is a response using claim 2. Position loop gain kp, which is a control parameter,
The velocity loop gain kv, the time constant Ti and γ (= 0) are set the same in all cases, and the other parameters are α = 8 (β = 0.0) and N = M = 1,
In (c), α = 8, β = 0.5, and N = M = 1. In the figure, A is a position command, B is a motor position, C is a position deviation, D is an enlarged version of C, and E is a torque command. As can be seen from the figure, in the conventional example, the vibration of ± 1 pulse frequently occurs at the time of stoppage, but the invention of claim 1 shown in FIG. From this, it can be seen that there is an effect of suppressing vibration at the time of stop. Further, in the invention of claim 2 or claim 3 shown in FIG. 3C, the vibration at the time of stop is 0 or 1, and the width of ± 1 pulse (+1, 0, −
Since the width is 2/3 of the width of 1), the positioning accuracy at the time of stopping is increased to 2/3 times.

[0007]

As described above, according to the present invention, fine vibrations when the motor is stopped can be suppressed, and the positioning accuracy can be increased more than ± 1 pulse. Has the effect of improving practicality.

[0008]

[Brief description of the drawings]

FIG. 1 is a block diagram of a motor control system to which the present invention is applied.

FIG. 2 is a block diagram of a main part of the present invention.

FIG. 3 shows an operation example when an AC servomotor is driven using the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Command generator 12 Position control part 13 Speed control part 14 Current control part 15 Motor 16 Detector 17 Difference machine 121, 131, 135 Subtractor 122 Position deviation judgment machine 123, 137 Adder 124, 134, 138 Coefficient unit 133 Integrator 132, 136 Divider

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G05D 3/00-3/20 G05B 19/18-19/46

Claims (1)

(57) [Claims] 1. A motor position command Pr at a current time i.
ef (i), a difference generator for calculating a difference between the detected position of the rotating shaft of the motor Pfb (i) and outputting the speed Vfb (i) of the motor, and the position command Pr.
a position control unit that outputs a speed command Vref (i) based on a position deviation Pe (i) obtained by subtracting the position Pfb (i) from ef (i), and controls the position so that the position deviation becomes zero; From the command Vref (i), the speed Vfb
A speed control unit for outputting a torque command Tref (i) based on the speed deviation Ve (i) obtained by subtracting (i) and controlling the speed so that the speed deviation becomes zero;
A current control unit that controls a current supplied to the motor based on (i), wherein the position control unit is a position deviation Pe (im) before m samplings where m is a natural number. , And the absolute values of the position deviations Pe (i) and Pe (im) are all equal to or smaller than a predetermined constant N (N ≧ 0), and the increment dPref of the position command Pref (i). (I) (dPre
If f (i) = Pref (i) -Pref (i-1)) is zero, a predetermined constant α (α> 1) is output, and if not, α = 1 is output. With
The speed control unit calculates the speed deviation Ve (i) as Ve
(I) = Ve (i) / α is corrected.