JPH0782381B2 - Absolute servo control method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an absolute servo control system using an absolute position detector.

[Conventional technology]

An incremental pulse generation type position detector is used as a position detection element of the servo motor in the conventional servo control system, and an incremental pulse train is generated according to the displacement of the servo motor. On the other hand, the data for commanding the target position is also given by an incremental pulse train (command pulse). The deviation counter counts the deviation between the command pulse and the position feedback pulse, and the deviation between the command position and the current position is calculated. Desired. Speed command data is generated according to the position deviation, and the servo motor is driven according to the speed deviation between the speed command data and the speed feedback signal of the servo motor.

Generally, the positioning target position of the servo motor is set by digital numerical data. The desired speed characteristic of the servo motor is also set by setting a steady speed (maximum speed), an acceleration point, a deceleration point, and the like. A sequence operation circuit is provided to generate the incremental command pulse based on the target position data and the speed setting data set by the digital numerical data. This sequence operation circuit includes a variable pulse oscillator whose oscillation frequency is variably controlled according to speed setting data, a pulse counter which counts the generated pulses, and a comparator which compares the count value of this pulse counter with the target position setting data. , And has a complicated configuration including a gate circuit which gates the pulse generated by the variable pulse oscillator according to the output of the comparator. The pulse output from the gate circuit is given as the command pulse.

[Problems to be Solved by the Invention]

Since the conventional servo control method as described above uses an incremental type position detector as the position detection means, if there is a power failure during control, the current position cannot be grasped and the control is performed by returning to the origin. There was a problem that I had to restart.

Further, the deviation counter for obtaining the position deviation comprises an up / down counter which inputs the command pulse train to the up count input and the position feedback pulse train to the down count input. This deviation counter generally does not operate when a pulse is simultaneously input to the up-count input and the down-count input, resulting in a miscount. This causes a response delay.

On the other hand, it is possible to configure the input circuit of the deviation counter so that the pulses are not simultaneously input to the up-count input and the down-count input of the deviation counter, but doing so makes the circuit configuration complicated. There was a problem.

In addition, there is a problem in that the circuit configuration becomes complicated because the sequence operation circuit has to be provided to generate the incremental command pulse train.

Furthermore, when a brushless motor is used as the servo motor, it is necessary to provide means for generating a commutator signal for phase switching, but when using an incremental position detector, absolute position is detected. Since it is not possible to generate a commutator signal based on the output of the incremental type position detector, a special commutator signal generating means using a hall element unit or the like must be further attached to the servo motor shaft.
There was a problem.

The present invention has been made in view of the above points, and an object of the present invention is to provide an absolute servo control system using an incremental type position detector to eliminate the drawbacks of the conventional servo control system.

[Means for Solving the Problems]

An absolute servo control system according to the present invention, a servo motor, an absolute position detector that detects the position of the servo motor by absolute, and the speed of the servo motor based on the position data detected by the absolute position detector. Speed calculating means for calculating, target position setting means for setting a target position absolute, speed setting means for setting speed characteristics, and the target position setting means from the start position according to the speed characteristics set by the speed setting means Calculating means for creating a time function pattern of the absolute command position of the servo motor up to the target position set in step 1, storage means for storing the time function pattern of the absolute command position created by this calculating means, and this storage means From the absolute command position data And reading means for reading in accordance with,
A speed command means for generating speed command data for the servo motor based on a deviation between the read out absolute command position data and the current position of the servo motor detected by the absolute position detector; and the absolute position detector. Phase switching signal generating means for generating a phase switching signal for the servomotor based on the position data detected by the servomotor, speed command data given from the speed commanding means, and the present state of the servomotor calculated by the speed calculating means. And a control circuit for controlling the servo motor on the basis of the deviation from the speed and for switching and controlling the phase of the servo motor on the basis of the phase switching signal generated by the phase switching signal generating means.

[Action]

The target position is set to an absolute value by the target position setting means, and the speed characteristic is set by the speed setting means.
The computing means creates a time function pattern of the absolute command position of the servo motor from the start position to the target position set by the target position setting means according to the set speed characteristic. This time function pattern is stored in the storage means. The reading means reads the data of the absolute command position from the storage means as time passes. Motor speed command data is generated based on the deviation between the read absolute command position data and the current motor position detected by the absolute position detector.The speed command data and the current motor position detected by the speed detection means are generated. The motor is servo-controlled based on the deviation from the speed.

Since the current position of the servo motor is detected by the absolute position detector, even if a power failure occurs during control, the current position can be immediately grasped when the power is restored, and the control returns to the origin and restarts control. There is no problem of having to.

Further, since the deviation between the commanded position data and the current position data of the motor is calculated by the absolute value calculation, the deviation counter is not necessary, and the inconvenience that has conventionally occurred is eliminated.

Further, since it is not necessary to generate the command pulse composed of the incremental pulse train based on the target position data set by the absolute value, the complicated sequence operation circuit for generating the incremental command pulse is also unnecessary.

Further, since the speed calculation means detects the speed of the servo motor based on the position data detected by the absolute position detector, a special speed detector using a tachometer or the like is further attached to the rotary shaft of the servo motor. No need. Further, since the phase switching signal generating means generates the phase switching signal of the servomotor based on the position data detected by the absolute position detector, the special phase switching signal generating means using the hall element unit, etc. No further attachment to the motor shaft is required.

In addition, since a time function pattern of the absolute command position from the start position to the target position is created and this occurs over time, the servo control is performed as command position data, so that the position from the start position to the target position is reached. It is possible to accurately grasp the movement locus of the motor up to and manage the locus. In particular, when simultaneously controlling a plurality of axes of a mechanical system, the servomotor control of each axis can be performed according to the present invention, and in that case, the movement locus of each axis motor can be managed. This is advantageous because the movement of each axis can be controlled in good synchronization.

〔Example〕

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, a target position setting unit 21 sets a desired target position Xp of a servo motor 42 (for example, a DC servo motor) which is a control target with an absolute value. In addition, a digital switch or the like may be used to manually set a digital value according to the target position Xp. Digital data indicating the target position Xp set by the target position setting unit 21 is given to the command position pattern creating unit 23.

The speed setting unit 20 is for setting a desired speed characteristic of the servomotor 42. For example, as is well known, the speed characteristic is set by setting a steady speed (maximum speed) and an acceleration section and a deceleration section. Is to be set. A typical example of the set speed characteristics is shown in FIG. That is, generally, the speed characteristics in servo control include steady speed (maximum speed) Vmax, acceleration section (acceleration time) ta from start to steady speed Vmax, and deceleration from deceleration start point to stop. It is well known that the interval (deceleration time) td is set, and this is also the case in the present embodiment. However, it goes without saying that the desired speed characteristic may be set by other factors. Set steady speed (maximum speed) Vmax data,
The data of the acceleration section (acceleration time) ta and the data of the deceleration section (deceleration time) td are given to the command position pattern creation unit 23.

The command position pattern creation unit 23 changes the start position Xo from the target position setting unit according to the speed characteristics set by the speed setting unit 20.
Performs calculation to create a time function pattern of the absolute command position of the servo motor rotation axis up to the target position Xp set in 21. An example of the time function pattern of the absolute command position created here is shown in FIG. The horizontal axis represents time, and the vertical axis represents the amount of movement of the motor 42 from the start position Xo, that is, the distance, which corresponds to the absolute command position of the servo motor rotation axis from the start position Xo to the target position Xp. As can be easily understood, since the target position Xp is set as an absolute value, the start position Xo may of course be a predetermined origin, and the start position Xo is not limited to the predetermined origin and any position can be set as the start position. You may make it possible to set it as an absolute value as Xo.

As shown in the example of FIG. 2, when the speed is increased by a linear function in the acceleration section (acceleration time) ta and is decreased by the linear function in the deceleration section (deceleration time) td, the acceleration section (acceleration time) The function of time vs. position in ta and deceleration section (deceleration time) td is the third
It becomes a quadratic function as shown in the figure. Further, in the section where the steady speed (maximum speed) Vmax is maintained between the acceleration section (acceleration time) ta and the deceleration section (deceleration time) td, the time-position function is a linear function as shown in FIG. Become. Of course, the form of this function is not limited to those shown in FIGS. 2 and 3.

In this way, the start position Xo and the target position Xp are absolutely specified, and the acceleration section (acceleration time) ta, the deceleration section (deceleration time) td, and the steady speed (maximum speed) Vm in between.
If the speed characteristic consisting of ax and the ax is specified, a time function pattern of the absolute command position of the servo motor rotation axis from the start position Xo to the target position Xp can be created according to the specified speed characteristic. That is,
The time function pattern of the absolute command position every moment as shown in FIG. 3 can be basically obtained by the definite integral calculation of the speed-time function as shown in FIG.

The created time function data of the absolute command position from the start position Xo to the target position Xp is stored in the readable / writable memory 24 with the data corresponding to the time as an address. The processing up to writing to the memory 24 is performed prior to starting the motor 42.

The read circuit 22 uses the start command of the motor 42 as a trigger,
It is for generating an address signal for reading the data of the absolute command position from the memory 24 as time passes. Here, the frequency of the clock for setting the reading speed every moment may be set variably, and the reading clock frequency may be set in the acceleration section and the deceleration section (and also in the constant speed section if necessary).
You may make it change with time.

The absolute command position data that is read from the memory 24 every moment is given to the positive input of the deviation calculator 25.
An absolute position detector that detects the absolute position of the rotation axis of the servo motor 42 is used as the negative input of the deviation calculator 25.
Output data Dθ of 60 is given.

The absolute position detector 60 detects the current position of the rotary shaft of the servomotor 42 by an absolute value from a predetermined limit point, and it is convenient to use an absolute position detector capable of detecting the absolute position over multiple rotations. But,
An absolute position can be detected within one rotation, and the number of rotations counted from the origin by a counter may be used.

The deviation calculator 25 subtracts the absolute current position data Dθ of the motor 42 given to the negative input from the absolute command position data given to the positive input to obtain the deviation between the commanded position and the current position. The position deviation data output from the calculator 25 is given to the speed command conversion table 26.

The speed command conversion table 26 generates speed command data according to the input position deviation data. This speed command data is converted into an analog speed command signal by the D / A converter 27 and given to the servo amplifier 30.

On the other hand, a speed detector 29 is provided to detect the speed of the servo motor 42. In this example, the speed detector
The reference numeral 29 is a speed calculation circuit which receives the current position data Dθ from the absolute position detector 60 and detects the speed by digital calculation based on the amount of change of the current position data Dθ per predetermined unit time.

The current speed data detected by the speed detector 29 is the D / A converter 28
Is converted into an analog signal and input to the servo amplifier 30 as a current speed feedback signal. Servo amplifier 30
Then, the deviation between the speed command signal input from the D / A converter 27 and the current speed feedback signal input from the D / A converter 28 is calculated, and the drive current given to the servo motor 42 is calculated according to this speed deviation. Control. The output of the servo amplifier 30 is given to the servo motor 42 via the power amplifier 41.

With the above configuration, the current position of the motor 42 is servo-controlled so as to follow the momentary absolute command position given from the memory 24. In this way, the motor 42 is controlled according to the time function pattern of the command position from the start position Xo to the target position Xp created by the command position pattern creation unit 23 and stored in the memory 24. As a result, the axis driven by the servo motor 42 is positioned at the target position Xp while the trajectory is managed according to the pattern.

As the absolute position detector 60, for example, an inductive type phase shift type position sensor may be used. An example of an absolute position detector 60 that employs such an inductive type phase shift type position sensor is shown in FIG. Since such an absolute position detector is known in Japanese Patent Laid-Open No. 57-70406, it will be briefly described below.

In FIG. 4, the absolute position detector 60 includes a sensor unit 61 and a signal conversion unit 62. The sensor unit 61 is
A plurality of poles A to D are arranged at predetermined intervals in the circumferential direction (for example, 90
) And a rotor 14 inserted in the stator space surrounded by the poles A to D. The rotor 14 is connected to the rotating shaft of the motor 42 and rotates in conjunction with the rotation of the motor 42. Rotor
Reference numeral 14 is made of a shape and material that changes the reluctance of each pole A to D according to the rotation angle, and is an eccentric cylindrical shape as an example. Primary coils 1A to 1D are attached to the poles A to D of the stator 13, respectively.
And the secondary coils 2A to 2D are wound respectively. The two poles A and C facing each other in the radial direction are coiled so as to operate differentially, and a differential reluctance change occurs. The same applies to the other pair of poles B and D. The primary coils 1A and 1C of one pole pair A and C are sinusoidal signals sinω
The primary coils 1B and 1D of the other pole pair B and D are excited by the tosine signal cosωt. As a result, the secondary coils 2A-2
A signal Y = sin (ωt−θ) obtained by phase-shifting the reference primary AC signal sinωt (or cosωt) by an electrical phase angle corresponding to the rotation angle θ of the rotor 14 as a synthetic output Y of D.
Can be obtained.

The signal conversion unit 62 supplies the primary AC signals sinωt, cosωt to the primary coils 1A to 1D of the sensor unit 61, and also the sensor unit 61.
Is for measuring the phase difference θ of the secondary output signal Y from the primary AC signal sinωt. The counter 16 counts a predetermined high-speed clock pulse CP, and the sine / cosine generation circuit 17 generates a sine signal sinωt and a cosine signal cosωt based on the output of the counter 16, and these are generated by the above-mentioned primary coils 1A, 1B, Apply to 1C and 1D respectively. On the other hand, the output signal Y = sin (ωt−θ) of the secondary coils 2A to 2D
Is supplied to the zero-cross detection circuit 18, and the siping pulse L is output in synchronization with the timing of the zero electric phase angle of the signal Y. The output pulse L of this circuit 18 is used as a latch pulse of the latch circuit 19. The latch circuit 19 latches the count output of the counter 16 in response to the rising edge of the pulse L supplied from the circuit 18. The period in which the count value of the counter 16 makes one cycle can be synchronized with one cycle of the sine signal sinωt. Then, in the latch circuit 19, the reference AC signal sinωt and the sensor output signal Y = sin (ωt−
The count value corresponding to the phase difference θ with respect to θ will be latched, and this will be output as digital absolute position data Dθ indicating the current position of the rotation axis of the motor 42. The sampling pulse L can be appropriately used as a pulse indicating the change timing of the absolute current position data Dθ.

For example, in the speed detection calculation in the speed detector 29,
It is convenient to use the sampling pulse L as the timing pulse for setting the calculation timing. Then, the speed detection calculation is performed in synchronization with the change timing of the absolute current position data Dθ.
Accurate speed detection calculation can be performed. If the speed detection calculation is performed at the calculation timing set by the fixed system clock pulse without doing so, the speed detection calculation is inaccurate because the change timing of the absolute current position data Dθ shifts from the speed detection calculation timing. May become. Therefore, in consideration of this point, it is convenient to dispose the speed detector 29 away from the arithmetic system unit including the command position pattern creating unit 23 and rather to be provided as an accessory to the circuit unit of the absolute position detector 60.

When a brushless motor is used as the servo motor 42, a commutator signal generation circuit 50 is provided, and absolute position data Dθ detected by the absolute position detector 60 is input to the commutator signal generation circuit 50 to rotate the motor 42. The commutator signal for phase switching is generated according to the angle. The power amplifier 41 is controlled by this commutator signal, and the phase of the motor 42 to which the drive current is to be supplied is switched.

In the example of FIG. 4, the absolute position detector 60 can detect the absolute position within one rotation, but a plurality of sensor units of the same principle are provided via a speed change gear and the like, and the outputs thereof are output. It is also known that it is possible to detect the absolute position over multiple rotations by calculating or combining, and in this respect, a detailed example is omitted.

Of course, as the absolute position detector 60, types other than the types described above (for example, resolver or other rotary encoder) can also be used. Further, not only the digital absolute type position detector but also an analog absolute type position detector can be used.

Further, the servo motor to be controlled is not limited to an electric motor, and may be hydraulic or any other motor. Further, it is not limited to the rotary type motor, and may be a linear drive type motor. In that case, as the absolute position detector 60,
It may be a linear sensor.

In the example of FIG. 1, the calculation for obtaining the speed deviation between the command speed and the feedback speed is performed in the servo amplifier 30 in an analog manner, but this portion should be changed as shown in FIG. You can also In FIG. 5, the digital speed command data output from the speed command conversion table 26 and the digital current speed data output from the speed detector 29 are converted into a digital deviation calculator 31.
To the digital signal, and the digital velocity deviation data is converted into an analog signal by the D / A converter 27. Servo amplifier 30, main amplifier 4 according to the analog speed deviation signal output from D / A converter 27
A drive current is applied to the motor 42 via 1. In this way, only one D / A converter can be used and the circuit becomes simple. In this case, since the D / A converter 27 can output an analog speed deviation signal with a desired conversion characteristic, the servo amplifier 30 is omitted and the analog speed deviation signal output from the D / A converter 27 is omitted. The speed deviation signal is sent to the main amplifier 41
You may input directly into.

〔The invention's effect〕

As described above, according to the present invention, since the current position of the servo motor is detected by the absolute position detector, even if a power failure occurs during control, it is possible to immediately grasp the current position when the power is restored. The problem of having to return to the origin and restart control does not occur.
Further, since the deviation between the commanded position data and the current position data of the motor is calculated by the absolute value calculation, the deviation counter is not necessary, and the inconvenience that has conventionally occurred is eliminated. Further, since it is not necessary to generate the command pulse composed of the incremental pulse train based on the target position data set by the absolute value, the complicated sequence operation circuit for generating the incremental command pulse is also unnecessary. Further, since the speed calculation means detects the speed of the servo motor based on the position data detected by the absolute position detector, a special speed detector using a tachometer or the like is further attached to the rotary shaft of the servo motor. No need. Further, since the phase switching signal generating means generates the phase switching signal of the servomotor based on the position data detected by the absolute position detector, the special phase switching signal generating means using the hall element unit, etc. No further attachment to the motor shaft is required. In addition, since a time function pattern of the absolute command position from the start position to the target position is created and this occurs over time, the servo control is performed as command position data, so that the position from the start position to the target position is reached. It is possible to accurately grasp the movement locus of the motor up to and manage the locus. In particular, when simultaneously controlling a plurality of axes of a mechanical system, the servomotor control of each axis can be performed according to the present invention, and in that case, the movement locus of each axis motor can be managed. Since it becomes possible to control the movement of each axis in good synchronization, various advantageous effects such as being advantageous are exhibited.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a servo motor control system according to the present invention, FIG. 2 is a graph showing an example of setting speed characteristics from start to stop, and FIG. 3 is a graph showing FIG. FIG. 5 is a graph showing an example of the command position pattern created by the command position pattern creating section of FIG. 1 corresponding to the speed characteristic, FIG. 4 is a block diagram showing an example of the absolute position detector in the same embodiment, and FIG. FIG. 4 is a block diagram showing a modified example of a speed data D / A conversion circuit portion and a speed deviation calculation circuit portion in FIG. 1. 20 …… Speed characteristic setting part, 21 …… Target position setting part, 22 ……
Readout circuit, 23 ... Position command pattern creation unit, 24 ... Memory, 25 ... Deviation calculator, 26 ... Speed command conversion table, 27, 28 ... Digital / analog (D / A) converter, 29 ...
… Velocity detector, 30 …… Servo amplifier, 41 …… Power amplifier, 42 …… Servo motor, 60 …… Absolute position detector.

Claims (2)

[Claims] 1. A servo motor, an absolute position detector for absolutely detecting the position of the servo motor, and speed calculation means for calculating the speed of the servo motor based on the position data detected by the absolute position detector. A target position setting means for setting the target position absolute, a speed setting means for setting the speed characteristic, and a target position set by the target position setting means from the start position according to the speed characteristic set by the speed setting means. Calculating means for creating a time function pattern of the absolute command position of the servo motor up to a position, storage means for storing the time function pattern of the absolute command position created by this calculating means, and the absolute command position from this storage means Reading means for reading data of A speed command means for generating speed command data of the servo motor based on a deviation between the read absolute command position data and the current position of the servo motor detected by the absolute position detector, and the absolute position Phase switching signal generating means for generating a phase switching signal of the servo motor based on the position data detected by a detector; speed command data given from the speed command means; and the servo motor calculated by the speed calculating means. Of the servomotor based on the deviation from the current speed of the servomotor and the control circuit for switching and controlling the phase of the servomotor based on the phase switching signal generated by the phase switching signal generating means. control method. 2. The absolute servo control system according to claim 1, wherein said speed setting means sets a speed characteristic by setting a steady speed and an acceleration section and a deceleration section.