JPH04299087A - Digital servo controller - Google Patents

Abstract

PURPOSE:To improve follow-up performance of digital servo controller regardless of the operating condition. CONSTITUTION:Proportional gain and integrating time of proportional/ integrating operation are set in speed feedback loop according to the servo lock state, accelerating/decelerating state or constant speed state of a commanded control shaft. Thus set proportional gain and integrating time are applied to the speed difference between a target speed and a current speed and the time integration thereof, thus operating a target current for current feedback loop through proportional/integrating operation. Consequently, vibration is prevented under servo lock state and overshoot is prevented at the time of transfer to constant speed.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] The present invention relates to a digital servo motor that obtains optimal control characteristics according to operating conditions such as servo lock, acceleration/deceleration, and constant speed of a servo motor. Regarding a control device. 2. Description of the Related Art In recent years, digital servo control devices have come into use to overcome the drawbacks of analog control systems. This digital servo control device provides a target value and a feedback value as digital values, calculates the deviation between the two using a digital computer, provides a command value corresponding to the deviation as a digital value, and controls the control amount according to that value. It is digitally controlled. Such servo controllers generally include position, velocity, and current feedback loops. In the speed feedback loop, in order to calculate the target current, the q-axis component of the target current for the current feedback loop is obtained by proportional/integral calculations regarding the speed deviation. [0003]Problems to be Solved by the Invention In the proportional/integral calculations in the speed feedback loop described above, how to determine the proportional gain and integral time is an important issue in terms of control performance. . For example, the optimum proportional gain and integration time are determined from the transfer function of the velocity feedback loop. However, these values are determined assuming a steady state in which the servo motor is rotating at a constant speed under a predetermined load state. That is, since the proportional gain is set large so that the control characteristics are optimal at steady speed, backlash vibration occurs when the servo motor is in a servo-locked state with a reduced load. In addition, since the integration time is set small so that the control characteristics are optimal at steady speed, there is no overshoot or overshoot in the tracking characteristics when transitioning from an acceleration state to a constant speed state or from a deceleration state to a stop state. There were problems such as undershoot. The present invention has been made to solve the above problems, and its purpose is to improve the control performance of a servo motor. Means for Solving the Problems As shown in FIG. 12, the configuration of the invention for solving the above problems has a position feedback loop, a speed feedback loop, and a current feedback loop, and has a command value and a feedback loop. In a digital servo control device that servo-controls a control axis by giving a value in a digital quantity, there is a target position output means that outputs the target position that the control axis should be in every moment, and a servo lock state of the control axis commanded by the target position. , a proportional integral coefficient setting means for setting a proportional gain and an integral time of proportional/integral calculations in the speed feedback loop according to an acceleration/deceleration state or a constant speed state; a current position detecting means for detecting the current position of the control axis; A target speed calculating means for calculating a target speed according to a positional deviation between the target position and the current position, a current speed detecting means for detecting the current speed of the control axis, and a speed deviation between the target speed and the current speed and the speed deviation thereof. A target current calculation means is provided which calculates a target current by proportional/integral calculation by applying a set proportional gain and integration time to the integral with respect to time. [0006] The target position output means outputs the target position of the control shaft from time to time, and the current position detection means detects the current position of the control shaft from time to time. Next, the target speed calculation means calculates the position deviation of the control axis from this target position and the current position of the control axis detected by the current position detection means, and the target speed of the control axis is calculated according to the position deviation. Ru. On the other hand, the proportional integral coefficient setting means controls the proportional integral coefficient in the speed feedback loop according to the servo lock state, acceleration/deceleration state, and constant speed state of the control axis commanded by the target position outputted every moment by the target position output means. - The proportional gain and integration time of the integral operation are determined. Next, the target current calculation means applies a set proportional gain and integral time to the speed deviation between the target speed and the current speed detected by the current speed detection means and the integral of the speed deviation with respect to time, The target current is calculated by proportional/integral calculations. The actual load current is controlled in a current feedback loop so that it follows this target current. [Examples] The present invention will be explained below based on specific examples. FIG. 1 is a block diagram showing the configuration of a digital servo control device according to the present invention. The digital servo control device 10 mainly includes a CPU 11, a ROM
12, RAM 13, digital signal processor (hereinafter referred to as "DSP") 14, common RAM 17, ROM 2
0, A/D converters 15a, 15b and current value counter 1
It consists of 6. A keyboard 21 and a CRT display device 22 are connected to the CPU 11 via an interface 19. [0009] The ROM 12 stores a processing program executed by the CPU 11. Also, RAM13
includes a flag area for storing the operation command state of the servo motor 31 (servo lock state, acceleration/deceleration state, constant speed state) and a command data area for storing movement command data for giving positioning, rotation commands, etc. of the servo motor 31. It is provided. Further, the common RAM 17 is set with a target position output from the CPU 11 every moment, and a proportional gain and integral time in a speed feedback loop determined by the CPU 11 according to the operating state of the servo motor 31 are set. The output of the DSP 14 is input to an inverter 25, and the inverter 25 drives the servo motor 31 in accordance with the output signal of the DSP 14. A synchronous motor is used as the servo motor 31, and the load current of the servo motor 31 is controlled by PWM voltage control of the inverter 25, and as a result, the output torque is controlled. U-phase and v-phase load currents of the servo motor 31 are detected by CTs 32a and 32b, and amplified by amplifiers 18a and 18b. The outputs of the amplifiers 18a and 18b are connected to the A/D converters 15a and 18b.
15b, sampled at a predetermined period, and converted into a digital value. The sampled value is input to the DSP 14 as a feedback value of the instantaneous load current, ie, current current. A pulse encoder 33 is also connected to the servo motor 31 to detect its current position. The output of the pulse encoder 33 is connected to the current value counter 16 via a waveform shaping/direction determining circuit 34. The output signal from the pulse encoder 33, which is input to the current value counter 16 via the waveform shape/direction discrimination circuit 34, increases or decreases the value of the current value counter 16. The value of the current value counter 16 is read by the DSP 14 as the feedback value of the position feedback loop, that is, the current position. Then, the DSP 14 compares the current position with the target position output from the CPU 11 and calculates a positional deviation. Then, the DSP 14 calculates a target speed based on the positional deviation. Furthermore, the current position input to the DSP 14 is differentiated with respect to time, and the feedback value of the speed feedback loop, ie, the current speed, is calculated. DSP1
4, the target speed determined according to the positional deviation and the current speed are compared to calculate the speed deviation. and,
The q-axis component (effective current) of the target current for control in the current feedback loop is calculated by proportional/integral calculation using the speed deviation and the time integral (accumulation) of the speed deviation. Further, the d-axis component (reactive current) of the target current is set to zero. The DSP 14 converts the q-axis and d-axis components of the target current into feedback values of a current feedback loop detected by the CTs 32a and 32b via amplifiers 18a and 18b and A/D converters 15a and 15b. That is, compared with the q-axis component and d-axis component of the current current,
The current deviation of each component is calculated. Then, the proportional equation using this current deviation and the time integral (cumulation) of the current deviation
Through the integral calculation, the q-axis component and d-axis component of the command current at that time are calculated. The q-axis component and d-axis component of the command current are inversely converted into command currents for each phase. The command current for each phase is compared with a high-frequency triangular wave, and a voltage control PWM signal that controls the on/off of transistors for each phase of the inverter 25 is generated. The voltage control PWM signal is inverter 2
5, and the transistors of each phase of the inverter 25 are respectively driven. By switching the inverter 25, the load current is controlled to the target current. Note that the positioning of the servo motor 31 is performed using the CP
The process is completed when it is determined by U11 that the output value of the current value counter 16 has become equal to the target position value. Also, A
The u-phase and v-phase load currents sampled by the /D converters 15a and 15b are subjected to dq conversion by the DSP 14. The digital servo control device of this embodiment is as follows:
As mentioned above, it is composed of three feedback loops: position, velocity, and current. The lower the feedback loop is, the higher the response is required, for example, the lowest current feedback loop is 100 μs.
, the velocity feedback loop is synchronized with a time interval several times that amount, and the position feedback loop is synchronized with a time interval several times that amount, and the processing of each feedback loop is executed. Next, the operation of the apparatus of this embodiment will be explained. FIG. 2 is a flowchart showing a program stored in the ROM 12 and executed by the CPU 11. Before this program is executed, the servo motor 31 is in a stopped state. In step 200, one block of movement command data is read from the RAM 13, and in step 2
At 02, the acceleration/deceleration flag in the flag area of the RAM 13 is turned on. Next, in step 204, an interpolation target position in an acceleration region for accelerating the servo motor 31 from a stopped state to a commanded constant speed is calculated, and the interpolation target position is momentarily output to the common RAM 17 and stored there. Ru. Next, when the acceleration is finished, step 206
At step 20, the acceleration/deceleration flag is turned off, and the next step 20
At step 8, the constant speed flag in the flag area of the RAM 13 is turned on. Next, in step 210, an interpolation target position in the constant speed region is calculated, and the interpolation target position is momentarily outputted to the common RAM 17 and stored therein. Next, in step 212, it is determined whether one block of movement command data includes a command to temporarily stop at the command target position. If a stop command has not been given, move command data for the next block is input in step 214, and an interpolation target position in the constant speed region is calculated in step 210. Step 21
By repeating 0 and 214, the target position can be sequentially updated at a constant speed, and the interpolated target position can be sequentially output. If it is determined in step 212 that the movement command data includes a stop command, the acceleration/deceleration flag is turned on in step 216, and the constant speed flag is turned off in the next step 218. Then, in step 220, interpolation target positions of the deceleration area are sequentially calculated, and the interpolation target positions are stored in the common RAM 1 every moment.
7 and stored there. Next, after the deceleration interpolation is completed, the servo lock flag in the flag area of the RAM 13 is turned on in step 222 to indicate the servo lock state. Then, in step 224, the same target position is outputted to the common RAM 17 from time to time, and the target position is stored there. As a result, the servo motor 31 is held at the same position in a servo-locked state, that is, in an energized state. After the temporary stop for the time specified by the movement command data is completed, the process returns to step 200, the movement command data of the next block is read, and the position control of the servo motor is performed in the same manner as in the above step. be exposed. In this way, the position of the servo motor is commanded. On the other hand, the CPU 11 interrupts the execution of the program shown in FIG.
The program shown in FIG. 3 stored in 2 is executed. In step 300, it is determined whether the servo lock flag in the RAM 13 is on. If the servo lock flag is on, the process moves to step 302 and the common RAM1
7, a relatively small value KpL is set as the proportional gain Kp. Further, if the servo lock flag in step 300 is off, the process moves to step 304 and the common RA
A relatively large value of KpH is set in M17 as a proportional gain Kp. As a result, the proportional gain is reduced in the servo lock state compared to the constant speed state, so backlash vibrations are prevented. Next, in step 306, the RAM 13
It is determined whether the acceleration/deceleration flag set in is on. If the acceleration/deceleration flag is on, step 30
8, a relatively large value of TiH is stored in the common RAM 17.
is set as the integration time Ti. Also, step 30
If it is determined in step 6 that the acceleration/deceleration flag is off, a relatively small value TiL is set in the common RAM 17 as the integral time Ti in step 310. As a result, the integration time is set longer in the acceleration/deceleration state than in the constant speed state, so the damping coefficient becomes larger, and the tracking characteristics when transitioning from the acceleration state to the constant speed state or from the deceleration state to the stop state This prevents overshoot and undershoot from occurring. In this way, the servo motor 3 at that time
According to one command control state, that is, a servo lock state, an acceleration/deceleration state, and a constant speed state, the optimal proportional gain Kp and integral time Ti are set in the common RAM 17 for each state. These proportional gain Kp and integration time Ti are accessed by the DSP 14, which will be described later, and used to calculate the target current in the speed feedback loop. Next, the DSP 14 executes the programs shown in FIGS. 4 and 5 stored in the ROM 20 to control the position, speed, and torque of the servo motor 31. The programs shown in FIGS. 4 and 5 are repeatedly executed by the DSP 14 at predetermined minimum cycles. In step 100, it is determined whether or not the actual execution cycle is the position deviation calculation timing, and if it is the position deviation calculation timing, the process moves to step 102, and the target position θ(i)( interpolation target position) is input and stored. Also, the target position within a certain amount of time in the past is a common RA.
It is stored in M17. Next, in step 104, the current position (electrical angle) θa(i) held in the current value counter 16 is read. Next, in step 106, the positional deviation Δθ(i) between the target position θ(i) at the current time (i) and the current position θa(i) is calculated. Next, in step 108, the target speed V(i) is changed to the position deviation ΔP(i
), that is, calculated using the following formula. [Formula 1] V(i) =k·ΔP(i) This position feedback control is executed at the timing shown by the signal S1 in FIG. Next, in step 110, it is determined whether the actual running cycle is the speed deviation calculation timing. If it is speed deviation calculation tuning, the process moves to step 112 and the current position θa(n
) is loaded. Next, the process moves to step 114, where the current speed Va(n) at the current time (n) is calculated. The current speed Va(n) is calculated using the following formula based on the current position θa(n-1) read at the previous speed deviation calculation timing, the current position θa(n) input this time, and the speed control cycle D. It is calculated by [Formula 2] Va(n) = (θa(n) - θa(n-1)
) /D Next, in step 116,
The deviation between the target speed V(i) calculated in step 108 and the current speed Va(n), that is, the speed deviation ΔV(n) is calculated. Further, the cumulative value (integral) S of the speed deviation ΔV(n) is calculated by S=S+ΔV(n). next,
In step 118, the speed deviation ΔV(n) calculated in step 116 and the integral S of the speed deviation, and the common RAM
Using the proportional gain Kp and integration time Ti corresponding to the control state at that time, which are set to It is calculated by Note that the d-axis component (reactive current) of the target current is zero. This speed feedback control is executed at the timing shown by signal S2 in FIG. [Equation 3] Iq(n)=Kp(ΔV(i)+S/Ti)
Next, in step 120, it is determined whether the actual cycle is the current deviation calculation timing. If it is the current deviation calculation timing, the process moves to step 122. Step 122 and subsequent steps are current feedback control, and this control is executed at the timing shown by signal S3 in FIG. In step 122, the current detection time Δt1 measured from the beginning of the current control period, the load current control time Δt2 measured from the beginning of the current control period, and the current speed Va(n) are used to determine the electrical angle corresponding to that time. The electrical angle θ1 during current detection and the electrical angle θ2 during control are calculated by interpolation. [Equation 4] θ1 = θa(n)+Va(n)・Δt1
Equation 5] θ2 = θa(n)+Va(n)・Δt2 0
[033] These times Δt1, Δt2 and the electrical angle θ1,
They correspond to θ2 as shown in FIG. Next, the process moves to step 124, and the current values of the u-phase and v-phase load currents, that is, the current currents Iu and Iv are input to the A/D converter 15a.
, 15b. Then, in step 126, the current current Iu,Iv is dq transformed to d
The axis component Iad and the q-axis component Iaq are calculated by the following equation. [Formula 6] Iad=21/2 {lusin(θ1+2π
/3)-Ivsinθ1} [Formula 7] Iaq=21/2
{Iucos(θ1+2π/3)−Ivcosθ1}[
[0034] As is well known, the dq coordinate system is d
This is a coordinate system in which the axis is in phase with the excitation magnetic field, and the q-axis is at a phase difference of 90 degrees in electrical angle from the excitation magnetic field. The d-axis component represents an invalid component, and the q-axis component represents an active component. Next, in step 128, the d-axis component Id(n) and q-axis component Iq(n) of the target current obtained in step 118 and the d-axis component Iad and q of the current current obtained in step 126 are calculated.
The deviation from the axis component Iaq, that is, the d-axis component deviation and the q-axis component deviation are determined. Then, based on the d-axis component deviation and q-axis component deviation, the d of the command current is calculated by proportional and integral calculations.
Axis component Id* and q-axis component Iq* are calculated. Next, in step 130, the d-axis component and q-axis component Id*, Iq* of the command current are inversely dq-transformed using the following equation to obtain each phase current command value Iu*, Iv*, Iw.
* is calculated. [Formula 8] Iu* = (2/3)1/2 ・{Id* c
osθ2 −Iq*sinθ2} [Formula 9] Iv* = (2/3)1/2 ・{Id* cos(θ
2 +2π/3) −Iq*sin(θ2+2π/3)
} Note that Iw* is calculated by Iw*=-(Iu*+Iv*). Next, in steps 132 and 134,
A series of PWM signals within one control period are generated using the level relationship between each phase current command value Iu*, Iv*, Iw* and a high-frequency triangular wave, that is, using the average voltage method. . A series of PWM signals can be represented by a voltage vector indicating the voltage application state of each phase, as shown in FIG. The rotating magnetic field vector is expressed as an integral of this voltage vector. Therefore, as shown in FIG.
The locus of the tip of the rotating magnetic field vector is drawn by the sum of each voltage vector x duration time. In order to position the rotating magnetic field to a point on the circumference at every angle of 2π/n by the shortest path, three vectors, two adjacent voltage vectors and a zero vector V0 shown in Fig. 8, are used for each control period. Inverter 25
needs to be controlled. The combination of these three voltage vectors and the phase of the rotating magnetic field uniquely correspond. Correspondence table of combinations of rotating magnetic field phase and voltage vector (zero vector V
0 is always one element of the combination, so only a set of two voltage vectors is required) is stored in advance in the ROM 12, as shown in FIG. In step 132, the electrical angle θ2 during control is
(phase of rotating magnetic field) The above table in the ROM 12 is searched to find the combination of voltage vectors at that time. At step 134, the durations t1, t2, and t3 of each voltage vector are calculated. For example, as shown in FIG. 11, the combination of voltage vectors is Vn = (
1,1,0), V1 = (1,0,0), V2 =
(0, 0, 0), the duration times t1, t2, t3 of each voltage vector are calculated. In this embodiment, the well-known average voltage method is used as the calculation method. That is, each phase current command value Iu*, Iv*
, Iw*, the two with the largest absolute values are I
1, I2, the durations t1, t2, t3 are determined by the following equations. [Formula 10] t1 = |2I2*+I1*|・T/Vdc
[Formula 11] t2 = |I1*-I2*|・T/Vdc[
Equation 12: t3 = T - (t1 + t2) where T is the period and Vdc is the applied DC voltage. Next, in step 136, a PWM signal based on a set of voltage vectors is generated for durations t1, t2,
Only t3 is output. For example, as shown in FIG. 11, V6 = (1, 1, 0), V1 = (1, 0, 0),
In the order of V0 = (0, 0, 0), the duration t1, t2,
Only t3 is output. In other words, the U phase is t1
A voltage is applied for +t2, a voltage is applied for t1 to the V phase, and no voltage is applied to the W phase during the control period. In this way, the processing of one execution cycle is completed. This execution cycle is executed with the minimum control period, and the current feedback loop is controlled at an integral multiple n1 of the minimum control period, the velocity feedback loop is controlled at an integral multiple n2 of the minimum control period, and the position feedback loop is controlled at an integral multiple n3 of the minimum control period. Step 100
, 114, and 124 set the number of times that serves as a criterion for determination. However, n1<n2≦n3. By repeating the above cycle, feedback control of position, speed, and current is performed at the timing shown in FIG. 7. However, the timing shown in FIG. 7 is detected by timing from the time when the CPU 11 executes the program. By the servo control as described above, when a movement command with a speed as shown in FIG. 6 is given, the servo motor 31 accurately follows the target speed. In the acceleration region and deceleration region, the integral time Ti of the velocity feedback loop
Since the damping coefficient is set longer than the value in the constant speed region, the damping coefficient becomes large, and overshoot, undershoot, and vibration do not occur when reaching constant speed or stopping. Furthermore, in the servo lock state, the proportional gain Kp of the speed feedback loop is set smaller than its value in the constant speed region, so that backlash vibrations are prevented from occurring. In the above embodiment, as shown in FIG.
The integration time is set long in the entire section of the acceleration region or deceleration region, but the integration time is set to the integration time of the constant speed region a little before going from the acceleration region to the constant speed region or a little before reaching the stop from the deceleration region. You may do so. In this way, it is possible to improve the followability in the constant speed region from the initial stage without causing overshoot or undershoot. Effects of the Invention [0043] The present invention adjusts the proportional gain and integral time of proportional/integral calculations in the speed feedback loop according to the servo lock state, acceleration/deceleration state, or constant speed state of the control axis commanded by the target position. a proportional integral coefficient setting means for setting, and a proportional gain and an integral time set by the proportional integral coefficient setting means to act on the speed deviation between the target speed and the current speed and the integral regarding the time of the speed deviation, and target load current calculation means for calculating a target load current for the current feedback loop by proportional/integral calculations. Therefore, the proportional gain and integral constant of the speed feedback loop are appropriately set depending on the control state of the control axis, that is, the servo lock state, acceleration/deceleration state, or constant speed state, and the backlash vibration in the servo lock state , overshoot and undershoot when shifting to constant speed after acceleration are prevented, and appropriate servo control is achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a digital servo control device according to a specific embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure for commanding a target position processed by the CPU 11 of the apparatus of the embodiment.

FIG. 3 is a flowchart showing a procedure for setting a proportional gain and an integral time according to a commanded control state processed by the CPU 11 of the device of the embodiment.

FIG. 4 is a flowchart showing a processing procedure by the DSP used in the device of the embodiment.

FIG. 5 is a flowchart showing a processing procedure by the DSP used in the device of the embodiment.

FIG. 6 is an explanatory diagram showing the relationship between the target speed commanded by the CPU 11 and the follow-up speed by the control device of the present embodiment.

FIG. 7 is a timing chart showing the timing of position, speed, and current feedback control.

FIG. 8 is a vector diagram showing voltage vectors corresponding to PWM signals.

FIG. 9 is a vector diagram showing the relationship between a voltage vector and a rotating magnetic field.

FIG. 10 is an explanatory diagram showing the correspondence between pairs of rotating magnetic field phases and voltage vectors.

FIG. 11 is a timing chart showing a PWM signal.

FIG. 12 is a block diagram showing the overall configuration of the present invention.

[Explanation of symbols]

10...Digital servo control device 11...CPU 12...ROM 13...RAM14...
DSP (digital signal processor) 15a, 15
b...A/D converter 16...Current value counter 25...Inverter 31...Servo motor 32a, 32
b...Current transformer (CT) 33...Pulse encoder

Claims (1)

[Claims] Claim 1: Comprising a position feedback loop, a velocity feedback loop, and a current feedback loop,
A digital servo control device that servo-controls a control axis by giving a command value and a feedback value in digital quantities, comprising: target position output means for outputting a target position that the control axis should be at every moment; proportional-integral coefficient setting means for setting a proportional gain and integral time of proportional/integral calculations in the speed feedback loop according to a servo lock state, an acceleration/deceleration state, or a constant speed state of the control axis; and a current position of the control axis. current position detection means for detecting the current position; target speed calculation means for calculating a target speed according to a positional deviation between the target position output by the target position output means and the current position output from the current position detection means; a current speed detection means for detecting the current speed of a control axis; a speed deviation between the target speed calculated by the target speed calculation means and the current speed detected by the current speed detection means; and an integral of the speed deviation over time. target current calculation means for calculating a target current for the current feedback loop through proportional and integral calculations by applying the proportional gain set by the proportional integral coefficient setting means and the integral time to Control device.