JPH01251112A - Absolute servo control system - Google Patents

Abstract

PURPOSE:To instantaneously grasp the present position of a servomotor at recovery of a power failure even if the power failure occurs during the control by detecting the present position of the servomotor via an absolute position detector. CONSTITUTION:A target position of a servomotor 42 is set by a target position setting means 21 in the form of the absolute value. While the speed characteristics are set by a speed setting means 20. An arithmetic means 25 produces a time function pattern for the absolute command position of the servomotor 42 up to the target position set by the means 21. The produced time function pattern is stored in a memory 24. Then a reading means 22 transmits the speed command data on the servomotor 42 based on the deviation between the absolute command position data read out of the memory 24 and the present position of the servomotor 42 detected by an absolute position detector 60.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an absolute servo control system using an absolute position detector.

[Conventional technology]

As a position detection element for a servo motor in a conventional servo control system, an incremental pulse generation type position detector is used, and is designed to generate an incremental pulse train in accordance with 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), and a 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 using a deviation counter. Desired. Speed command data is generated according to this positional deviation, and the servo motor is driven according to the speed deviation between this speed command data and a speed feedback signal of the servo motor.

Generally, the positioning target position of a servo motor is set using digital numerical data. Desired speed characteristics of the servo motor are also set by setting a steady speed (maximum speed), acceleration point, deceleration point, etc. A sequence calculation circuit is provided to generate the incremental command pulses based on target position data and speed setting data set by digital numerical data. This sequence calculation circuit counts the variable pulse oscillator whose oscillation frequency is variably controlled according to the speed setting data and the generated pulses. A pulse counter, a comparator that compares the count value of this pulse counter with target position setting data,
It has a complicated configuration including a gate circuit that gates the pulses 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.

[Problem to be solved by the invention]

The conventional servo control method described above uses an incremental position detector as a means of detecting one position, so if there is a power outage in the middle of control, the current position cannot be determined and the control returns to the origin. The problem was that it had to be restarted.

The deviation counter for determining the positional deviation is an up/down counter that inputs a command pulse train to an up-count input and inputs a position feedback pulse train to a down-count input. Generally, this deviation counter does not operate when pulses are input to the up-count input and the down-count input at the same time, resulting in a miscount. This has caused a problem in that a response delay occurs.

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

Furthermore, since the sequence calculation circuit described above must be provided in order to generate the incremental command pulse train, there is a problem in that the circuit configuration becomes complicated.

Furthermore, when using a brushless motor as a servo motor, it is necessary to provide a means to generate a commutator signal for phase switching, but when using an incremental position detector, it is necessary to provide a means to generate a commutator signal for phase switching, but when using an incremental position detector, it is necessary to provide a means for generating a commutator signal for phase switching, but when using an incremental position detector, it is necessary to provide a means to generate a commutator signal for phase switching. Therefore, it is not possible to generate a commutator signal based on the output of the incremental position detector, and a special commutator signal generation 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 it is an object of the present invention to provide an absolute servo control method that eliminates the drawbacks of the conventional servo control method using an incremental position detector.

[Means for Solving the Problems] The absolute servo control system according to the present invention includes a servo motor, an absolute position detector that detects the position of the servo motor in an absolute manner, and a speed detection means that detects the speed of the servo motor. a target position setting means for setting a target position in an absolute manner, a speed setting means for setting a 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. a calculation means for creating a time function pattern of the absolute command position of the motor up to the position; a storage means for storing the time function pattern of the absolute command position created by the calculation means; reading means for reading data over time; and a speed command for generating speed command data for the motor based on a deviation between the read absolute command position data and the current position of the motor detected by the absolute position detector. and a control circuit that controls the motor based on the deviation between the speed command data given from the speed command means and the current speed of the motor detected by the speed detection means.

[For production]

The target position is set as an absolute value by the target position setting means, and the speed characteristic is set by the speed setting means.

The calculating 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 out data of the absolute command position from the storage means over time. Motor speed command data is generated based on the deviation between the read absolute command position data and the motor's current position detected by the absolute position detector, and this speed command data and the motor's current position detected by the speed detection means are generated. The motor is servo controlled based on the deviation from the speed.

The current position of the servo motor is detected by the absolute position detector, so even if there is a power outage during control, the current position can be immediately determined when the power is restored, and the control can be resumed by returning to the origin. The problem of having to do this does not occur.

A deviation counter is not required, thereby eliminating the disadvantages encountered heretofore.

Further, since there is no need to generate command pulses consisting of an incremental pulse train based on target position data set as absolute values, there is no need for a complicated sequence calculation circuit for generating incremental command pulses.

In addition, since the current rotation angle of the servo motor can always be grasped using the absolute position detector, even when using a brushless motor as the servo motor, the commutator signal for phase switching can be determined based on the output of this absolute position detector. Since this can be easily generated, there is no need to further attach a special commutator signal generating means using a Hall element unit or the like to the servo motor shaft.

In addition, we created a time function pattern for the absolute command position from the start position to the target position, and this is generated over time and used as command position data to perform servo control, so that the absolute command position can be reached from the start position to the target position. It is possible to accurately grasp the movement trajectory of the motor up to the point in time, and to perform trajectory management. In particular, when controlling multiple axes of one mechanical system simultaneously, the servo motors of each axis can be controlled according to the present invention. In that case, the movement locus of each axis motor can be managed, so for example, This is advantageous because it allows the movement of each axis to be controlled with precise synchronization.

[Embodiment] 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 section 21 sets a desired target position XP of a servo motor 42 (for example, a DC servo motor) to be controlled using an absolute value. Alternatively, a digital value corresponding to the target position XP may be manually set using a digital switch or the like. Digital data indicating the target position XP set in the target position setting section 21 is given to the command position pattern creation section 23.

The speed setting unit 20 is for setting desired speed characteristics of the servo motor 42, and for example, as is well known,
The speed characteristics are set by setting a steady speed (maximum speed), an acceleration section, and a deceleration section. A typical example of the set speed characteristics is shown in FIG. That is, in general, speed characteristics in servo control include a steady speed (maximum speed) vrsax, an acceleration period (acceleration time) ta from the start to the steady speed Vmax,
Deceleration period from deceleration start point to stop (deceleration time)
td is well known, and the present embodiment also follows this.

However, it goes without saying that the desired speed characteristics may be set using other factors. Data of set steady speed (maximum speed) Vmax, acceleration period (acceleration time)
The data of ta and the data of deceleration period (deceleration time) td are given to the command position pattern creation section 23.

The command position pattern creation unit 23 creates the absolute command position of the servo motor rotation axis from time to time from the start position XO to the target position Xp set by the target position setting unit 21 according to the speed characteristics set by the speed setting unit 20. Perform operations to create time function patterns. An example of the time function pattern of the absolute command position created here is shown in FIG. 3. The horizontal axis is time, and the vertical axis is the amount of movement of the motor 42 from the start position Xo, that is, the distance.
This corresponds to the absolute command position of the servo motor rotating shaft moment by moment 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, it goes without saying that the start position Xo may be a predetermined origin. [X o may be set as an absolute value.

As in the example in Figure 2, if the speed is increased by a linear function in the acceleration period (acceleration time) ta and decreased by a linear function in the deceleration period (deceleration time) td, then the acceleration period (acceleration time) ta
The function of time versus position in the deceleration section (deceleration time) td is a quadratic function as shown in FIG. In addition, the acceleration section (
In the section where the steady speed (maximum speed) Vmax is maintained between the acceleration time (acceleration time) ta and the deceleration section (deceleration time) td, the function of time versus position becomes a linear function as shown in FIG. In addition,
Of course, the shape of this function is not limited to that shown in FIGS. 2 and 3.

In this way, the start position XO and the target position XP are absolutely specified, and the acceleration period (acceleration time) ta
If the speed characteristic consisting of the deceleration section (deceleration time) td and the steady speed (maximum speed) V+*ax during that period is specified,
According to the specified speed characteristic, a time function pattern of the absolute command position of the servo motor rotating shaft from time to time from the start position XO to the target position Xp can be created. That is, the time function pattern of the absolute command position from moment to moment as shown in FIG. 3 can basically be obtained by definite integral calculation of the speed versus time function as shown in FIG.

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

The readout circuit 22 is triggered by a command to start the motor 42 and generates an address signal for reading absolute command position data from the memory 24 over time. Here, the frequency of the clock that sets the readout speed from time to time may be set variably, or the readout clock frequency may be set in the acceleration section and deceleration section (and even in the constant speed section if necessary). It may be changed over time.

The momentary absolute command position data read from the memory 24 is given to the positive input of the deviation calculator 25. The negative input of the deviation calculator 25 is given output data Dθ of an absolute position detector 60 that detects the absolute position of the rotating shaft of the servo motor 42 .

The absolute position detector 60 detects the current position of the rotating shaft of the servo motor 42 using an absolute value from a predetermined origin, and it is convenient to use one that can detect the absolute position over multiple rotations. However, absolute position detection within one rotation is possible,
The number of rotations from the origin may be counted by a counter.

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 find the deviation between the commanded position and the current position.

The device deviation data constituted by this calculator 25 is given to a speed command conversion table 26.

The speed command conversion table 26 generates speed command data according to input positional deviation data.

This speed command data is converted into an analog speed command signal by a D/A converter 27 and is provided to a servo amplifier 30.

On the other hand, a speed detector 29 is provided to detect the speed of the servo motor 42. In this embodiment, the speed detector 29 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 in the current position data Dθ per predetermined unit time. It consists of a speed calculation circuit. However, the present invention is not limited to this, and it is also possible to attach a dedicated speed detector such as a tachometer to the rotating shaft of the motor 42 as in the conventional case.

The current speed data detected by the speed detector 29 is converted into an analog signal by the D/A converter 28 and inputted to the servo amplifier 30 as a current speed feedback signal. The servo amplifier 3o determines 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, and provides it to the servo motor 42 according to this speed deviation. Controls drive current. The output of this servo amplifier 30 is given to a servo motor 42 via a power amplifier 41.

With the above configuration, the motor 42 is configured to follow the absolute command position given from the memory 24 from time to time.
The current position of is servo controlled.

In this way, from the start position Xo created by the command position pattern creation unit 23 and stored in the memory 24 to the target position
The motor 42 is controlled according to the time function pattern of commanded positions up to P. As a result, the axis driven by the servo motor 42 is positioned at the target position Xp while its trajectory is managed according to the pattern.

As the absolute position detector 60, for example, an inductive phase shift type position sensor may be used. An example of the absolute position detector 60 employing such an inductive phase shift type position sensor is shown in FIG. . Such an absolute position detector is disclosed in Japanese Patent Application Laid-Open No. 57-704.
Since it is publicly known in No. 06, etc., it will be briefly explained below.

In FIG. 4, the absolute position detector 60 includes a sensor section 61 and a signal conversion section 62. The sensor section 61 includes a stator 13 in which a plurality of poles A-D are provided at predetermined intervals (for example, 90 degrees) in the circumferential direction, and various poles A-D.
The rotor 1 inserted into the stator space surrounded by
Contains 4. The rotor 14 is connected to a rotating shaft of a motor 42 and rotates in conjunction with the rotation of the motor 42. The rotor 14 has various types of A-
D consists of a shape and material that changes the glue roughtance,
- Eccentric cylindrical shape, for example. Various A- of stator 13
D has primary coils IA to ID and secondary coils 2A to 2D.
are wound around each other.

Coils are wound around two radially opposed poles A and C so that they operate differentially, and differential roughtance changes occur. The same goes for the other pair of poles B and D. One polar pair A.

The primary coils IA and IC of C are excited by a sine signal sinωt, and the primary coils IB and ID of the other pole pair B and D are excited by a cosine signal cosωt. As a result, the composite output Y of the secondary coils 2A to 2D is a signal Y=sin(ωt −θ) can be obtained.

The signal conversion unit 62 converts the primary coils IA to I of the sensor unit 61 into
This is for supplying the primary AC signals sinωt and cosωt to D, and measuring the phase difference θ in the secondary output signal Y of the sensor section 61 with respect to the primary AC signal sinωt. A predetermined high speed clock pulse CP is sent to counter 1.
6, and based on the output of this counter 16, a sine/cosine generating circuit 17 generates a sine signal sinωt and a cosine signal cosωt, respectively, and these are sent to the aforementioned primary coils LA and IB.

Apply to IC and LD respectively. On the other hand, secondary coils 2A~2
The output signal Y=sin (ω is - θ) of D is given to the zero cross detection circuit 18, and the sampling pulse L is outputted in synchronization with the timing of the electrical phase angle of this signal Y being zero. The output pulse L of this circuit 18 is used as a latch pulse of the latch circuit 19. Latch circuit 19 is circuit 18
The counter 16 responds to the rising edge of the pulse L given from
Latch the count output. It is possible to synchronize the period in which the count value of the counter 16 makes one cycle with one cycle of the sine signal sinωt. Then, the latch circuit 19 receives the reference AC signal sinωt and the sensor output signal Y=sin
A count value corresponding to the phase difference θ with (ω = θ) is latched, and this is output as digital absolute position data Dθ indicating the current position of the rotating shaft of the motor 42. Note that 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 a timing pulse for setting the calculation timing. By doing so, the speed detection calculation will be performed in synchronization with the change timing of the absolute current position data Dθ, and accurate speed detection calculation can be performed. If you don't do that.

If the speed detection calculation is performed at the calculation timing set by a fixed system clock pulse, the speed detection calculation may become inaccurate due to a difference between the change timing of the absolute current position data Dθ and the speed detection calculation timing. Therefore, in consideration of this point, it is convenient to separate the speed detector 29 from the arithmetic system unit including the command position pattern generation section 23, and rather to provide it attached to the circuit unit of the absolute position detector 60.

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

In the example of FIG. 4, the absolute position detector 60
Although it is possible to detect the absolute position within one rotation, it is also possible to detect the absolute position over multiple rotations by installing multiple sensor units based on the same principle via a transmission gear, etc., and calculating or combining their outputs. is possible. This is also well known, and detailed illustrations of this point will be omitted.

Of course, as the absolute position detector 60, it is also possible to use a type other than the above-mentioned type (for example, a resolver or other rotary encoder). Moreover, it is also possible to use not only a digital absolute type position detector but also an analog absolute type position detector.

Further, the servo motor to be controlled is not limited to an electric motor, but may be a hydraulic or other type of motor.

Further, the motor is not limited to a rotary type motor, and may be a linear drive type motor. In that case, the absolute position detector 60
Alternatively, a linear type sensor may be used.

In the example shown in FIG. 1, the calculation for determining the speed deviation between the command speed and the feedback speed is performed in analog in the servo amplifier 30, but this part can be changed as shown in FIG. You can also do it. In FIG. 5, digital speed command data output from the speed command conversion table 26 and digital current speed data output from the speed detector 29 are input to a digital deviation calculator 31, and the speed difference between the two is is obtained as a digital value, and this digital speed deviation data is sent to the D/A converter 27.
Convert it to an analog signal. In response to the analog speed deviation signal output from the D/A converter 27, the servo amplifier 30. A drive current is applied to the motor 42 via the main amplifier 41.

In this way, the number of D/A converters can be reduced to one, and one circuit can be simplified. In this case, since the D/A converter 27 can output an analog speed deviation signal with desired conversion characteristics, the servo amplifier 30 can be omitted and the analog speed deviation signal output from the D/A converter 27 can be output. The speed deviation signal may be input directly to the main amplifier 41.

〔Effect of the invention〕

As described above, according to the present invention, the current position of the servo motor is detected by the absolute position detector, so even if there is a power outage during control, the current position can be immediately determined 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 command position data and the current position data of the motor is calculated by calculating an absolute value, there is no need for a deviation counter, thereby eliminating the conventional inconvenience. Further, since there is no need to generate command pulses consisting of an incremental pulse train based on target position data set as absolute values, there is no need for a complicated sequence calculation circuit for generating incremental command pulses. Also.

Since the current rotation angle of the servo motor can always be grasped using the absolute position detector, even when using a brushless motor as the servo motor, the commutator signal for phase switching can be easily generated based on the output of this absolute position detector. Therefore, there is no need to further attach a special commutator signal generating means using a Hall element unit or the like to the servo motor shaft.
In addition, we created a time function pattern for the absolute command position from the start position to the target position, and this is generated over time and used as command position data to perform servo control, so that the absolute command position can be reached from the start position to the target position. It is possible to accurately grasp the movement trajectory of the motor up to the point in time, and to perform trajectory management. In particular, when controlling multiple axes of a mechanical system simultaneously, the servo motors of each axis can be controlled according to the present invention. In that case, the movement locus of each axis motor can be managed, for example, This provides various excellent effects, such as being advantageous in that the movement of each axis can be controlled in perfect synchronization.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the servo motor control method according to the present invention, Fig. 2 is a graph showing a general example of speed characteristics from start to stop, and Fig. 3 is the speed of Fig. 2. A graph showing an example of a command position pattern created by the command position pattern creation section shown in FIG. 1 in accordance with the characteristics, FIG. FIG. 2 is a block diagram showing an example of a modification of the speed data D/A conversion circuit section and the speed deviation calculation circuit section in FIG. 1; 20... Speed characteristic setting section, 21... Target position setting section, 22... Readout circuit, 23°... Position command pattern creation section, 24... Memory, 25... Deviation calculator,
26... Speed command conversion table, 27.28... Digital/analog (D/A) converter, 29... Speed 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 that detects the position of the servo motor in absolute terms, a speed detection unit that detects the speed of the servo motor, a target position setting unit that sets the target position in absolute terms, and speed. a speed setting means for setting characteristics; and creating a time function pattern of an absolute command position of the motor from a start position to a target position set by the target position setting means according to the speed characteristics set by the speed setting means. a calculation means; a storage means for storing the time function pattern of the absolute command position created by the calculation means; a readout means for reading out data of the absolute command position from the storage means over time; and the read absolute. speed command means for generating speed command data for the motor based on a deviation between command position data and the current position of the motor detected by the absolute position detector; speed command data given from the speed command means and the speed; An absolute servo control system comprising: a control circuit that controls the motor based on a deviation from the current speed of the motor detected by a detection means. (2) The absolute servo control method according to claim 1, wherein the speed setting means sets the speed characteristic by setting a steady speed, an acceleration section, and a deceleration section. (3) The absolute servo control method according to claim 1, wherein the speed detection means calculates the speed based on position data detected by the absolute position detector.