JPH0719180B2 - Feed axis position control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a position control method for a feed axis in a numerically controlled (hereinafter simply referred to as NC) machine tool, etc., in particular, for lost motion of a motor when reversing a moving direction. The present invention relates to a position control method for a feed axis that shortens the moving time of the robot and reduces the trajectory error during multi-axis synchronous operation.

(Prior art) Conventionally, for the position control of the feed axis, which requires high-precision control of the position of NC machine tools, etc., an inductosyn or optical device that can directly detect the position of the controlled object as a position detector While adopting a direct type position detector such as a formula scale,
A so-called full-closed loop control system, which constitutes a closed loop of the position by using the detection output of the direct type position detector as a position feedback signal, is widely used.

FIG. 7 shows a block configuration example of the feed axis drive system adopting the fully closed loop control system. The subtracter 1 subtracts the position feedback signal X _I from the position command X _C, and calculates the position error X _e . calculate. Position feedback signal X
_I is a position signal in which the machine position of the table 11 to be controlled is directly detected by the inductins 12 and 13. The position error X _e is amplified by the amplifier 2 and the amplifier 2
The output of becomes the speed command V _C. The speed detection signal of the detector 7 that detects the rotational position and the rotational speed of the electric motor 6 mechanically connected to the electric motor 6 is input to the subtractor 3 as a speed feedback signal V. The subtractor 3 subtracts the speed feedback signal V from the speed command V _C to obtain the speed error V _e
To calculate. The speed error V _e is amplified by the PID amplifier 4 and becomes the torque signal T _C of the electric motor 6. The torque command T _C is power-amplified by the power amplifier 5, and its output is a current for generating a torque corresponding to the torque command T _C in the electric motor 6.
I _C. The torque generated in the electric motor 6 by the current I _C is transmitted to the ball screw 10 via the gear trains 8 and 9. The ball screw 10 converts this transmitted torque into the propulsive force of the table 11 via the nut member 11A.

As explained above, the fully closed loop control method is suitable for a highly accurate positioning system because it controls so that the position command X _C and the position feedback signal X _I indicating the actual table position finally match. . In general, the feed shaft drive system is configured to transmit the output torque of the electric motor 6 to a control target through a mechanism such as gear trains 8 and 9 and a ball screw 10 as shown in FIG. Occurrence of lost motion due to backlash of rows 8 and 9, expansion and contraction of ball screw 10, twist deformation, etc. cannot be avoided.

FIG. 8 is a model diagram showing the movement of the feed shaft drive system having a lost motion in the torque transmission mechanism. That is, in FIG. 8, when the table is moving in the N direction, the rotational positional relationship of the electric motor with respect to the table position is the position (a). When the table is next reversed in the P direction from this state, the rotation direction of the electric motor is reversed, and the table does not move even if the rotational position relationship of the electric motor with respect to the table position becomes as shown in (b). Only when the rotational position relationship of the electric motor is as shown in (c), the table starts the reverse movement in the P direction. In this way, in the feed shaft drive system having the lost motion, a dead zone corresponding to the lost motion amount occurs when the moving direction is reversed,
At the time of reversing the axis movement, the electric motor has to operate by an extra lost motion amount relative to the actual table movement amount.

FIG. 9 shows the position command X _C when the moving direction is reversed (time t ₁ ).
Is a time chart showing the relationship among the change amount (position command speed) per unit time, the motor output torque T _C , the motor speed V, and the table speed. When the reversal of the moving direction is instructed at the time point t ₁ , the sign of the position error X _{e in} FIG. 7 is reversed at the time point t ₅ when the reversing operation actually starts, and the motor output torque T output from the PID amplifier 4 is output. _C begins to decline. Torque “-T
_L ″ represents a friction torque required to move the table in the direction before the inversion, and when the absolute value of the motor output torque T _C becomes smaller than T _L , the movement of the table 11 and the rotation of the electric motor 6 are stopped. the quiescent period t _r of (= t ₂ -t ₅₎ is equal to the sign inversion time of the motor output torque T _C, the electric motor 6 from the time t ₂ when the motor output torque T _C is sign inversion starts to rotate in the opposite direction. is time t ₂ ~t ₃ becomes travel time lost motion amount in the dead zone during movement direction reversal in FIG. 8, the area of this period the motor speed V becomes lost motion amount. in addition, the sign-inverted at time t ₂ The motor output torque T _C continues to increase until time t ₃ because the table 11 is stopped.At the time t ₃ , the motor output torque T _C exceeds the friction torque + T _L required to move the table in the reverse direction. And table 11 is in the reverse direction Starts moving. To regain the time t ₃ after the operation delay time _{t d (= t 3 -t 5} ) delays the table position relative to the position command X _C generated in the temporary table speed is faster than the position command speed Becomes, motor output torque
T _C also increases temporarily.

As described above, in the feed shaft drive system adopting the full closed loop control system, the operation delay time t _d is generated when the moving direction is reversed due to the lost motion generated in the torque transmission mechanism. Such a feed axis drive system (X axis, Y
When an arc command is given to the (axis), the locus relationship between the position command and the actual table position is shown on the XY coordinates as shown in FIG. As is apparent from FIG. 10, after the quadrant switching point A of the circular arc, the X-axis operation continues the P-direction operation, so the table position in the X-axis direction is set to the X-axis position command as before A point. Although it can follow accurately, the movement direction of the Y-axis operation is reversed from the P-direction operation to the N-direction operation, so a reversal operation delay time occurs due to the amount of lost motion. The position lags behind the position command. As a result, the table position locus on the XY coordinates becomes a locus having an error of the convex portion as shown in the figure with respect to the position command locus.

(Problems to be Solved by the Invention) That is, in the feed axis drive system adopting the fully closed loop control system, an operation delay time occurs due to the lost motion of the mechanical system when the moving direction is reversed. For this reason,
When operating multiple axes including direction reversal axes in synchronization,
A trajectory error occurs between the position command trajectory and the actual feed axis position trajectory. The occurrence of such a locus error can be suppressed by increasing the amplification factor of the amplifier 2 shown in FIG. This is because the sign reversal time t _r of the motor output torque T _{C in} FIG. 8 and the operation delay time t _d including the movement time for lost motion are reduced by the increase in the amplification factor of the control system. However, the mechanical rigidity of the feed shaft drive system inevitably limits the increase of the amplification factor of the amplifier 2. Increasing the amplification factor beyond this limit causes instability of the operation of the feed shaft. Therefore, it is very difficult to minimize the trajectory error while maintaining the stability of the operation of the feed shaft.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a feed axis control system that realizes a quick reversal of the direction of the feed axis while maintaining the stability of the operation of the feed axis drive system. To provide.

(Means for Solving the Problems) The present invention relates to a position control system for a feed shaft by an electric motor, and the above object of the present invention is to provide an output signal of an electric motor position detection means coupled to the electric motor and a feed shaft. An error signal obtained by subtracting the output signal after adding the position detection increment amount of the electric motor to the output of the feed axis position detecting means for directly detecting the position is obtained, and the output signal and the error signal are used as a position feedback signal. This is achieved by simultaneously performing the position control of the electric motor according to the electric motor position command increment and the position control of the feed shaft according to the feed shaft position command.

(Operation) In the present invention, when the movement direction of the feed shaft is reversed, the movement position command for the lost motion is given only to the electric motor from the outside of the feedback loop, so that the electric motor is operated as fast as the lost motion, and the feed shaft is moved. This is intended to reduce the final table inversion operation time while maintaining the stability of the drive system.

(Example) The Example of this invention is described below with reference to an accompanying drawing.

FIG. 1 shows an example of a block configuration of a feed shaft drive system according to the present invention in correspondence with FIG. 7. The lost motion correction amount generator 15 has a previously measured lost motion amount LM of the feed shaft drive system. _C is set. The lost motion correction amount generator 15 inputs the moving direction reversal detection signal SP from the moving direction reversal detector 14, starts the generation of the lost motion correction amount LM in synchronization with this input, and generates the lost motion correction amount. LM is added to the control loop by adder 16. The moving direction reversal detection signal SP is a pulse signal generated at the timing when the moving direction reversal detector 14 detects the reversal of the moving direction of the feed shaft position command X _C. When the amplification factor of the amplifier 2 is extremely high, the timing of reversing the moving direction can be detected only by the position command X _C. However, when the amplification factor of the amplifier 2 is low, the timing of actually reversing the electric motor 6 is the position command X _C. It will be behind the reversal timing. Therefore, the moving direction reversal detector 14 uses the actual motor speed command V _C to generate the moving direction reversal detection signal SP based on the sign reversal of the speed command V _C.

FIG. 2 shows the generation of the movement direction reversal detection signal SP on the Y axis and the generation of the lost motion correction amount LM when the arc command as shown in FIG. 3 is given to the feed axis drive system X and Y axes. 3 is a time chart showing the operation of the electric motor associated with. In a third diagram, the position command X _C (see FIG. 2) at the timing t ₄ when reaching the arc quadrant switched point A, Y arc quadrant switched point-axis direction of the table movement position instruction A The movement is still continuing in the P direction toward, and the reverse movement in the N direction is actually required at the timing t ₅ when the actual table position reaches the quadrant switching point A of the circular arc. Therefore, the moving direction inversion detection signal SP is generated at the timing of time t ₅ as shown in FIG. 2, and this causes the lost motion correction amount generator 15 to generate the lost motion correction amount LM. Lost motion correction amount
As the LM generation method, the set lost motion amount
LM _C may be instantaneously to generate, but lost motion amount L
When M _C is large, the occurrence time t _LMC of the lost motion correction amount LM is usually set as shown in FIG. 2 in consideration of the response limit of the motor 6, and the occurrence amount is interpolated within this occurrence time t _LMC . Output. In this case, the lost motion correction amount LM for generating end t _6, the lost motion correction amount LM is equal to the lost motion amount LM _C that has been set.

Next, when the moving direction of the feed axis is reversed to the P direction, the lost motion correction amount generator 15 generates the lost motion correction amount LM = -LM _{C at} the above-mentioned generation timing. After that, similarly, the lost motion correction amount generator 15 becomes N
Generates a lost motion correction amount of LM = LM _C when reversing the direction and LM = -LM _C when reversing the P direction. The lost motion movement amount detector 18 latches the position detection signal X _M of the detector 7 at the generation timing of the movement direction inversion detection signal SP,
The difference lm from the subsequent position detection signal X _M is calculated. The calculated difference lm is the lost motion movement amount of the electric motor 6 which indicates where the positional relationship of the electric motor 6 with respect to the table 11 corresponds to between (a) and (c) in FIG. Lost motion movement amount lm is "0" when N direction movement is reversed.
The more the final lost motion correction amount LM = LM _C increases. In this case, the lost motion movement amount lm calculated by the lost motion movement amount detector 18 is lm <LM
_{Performed in} the _C range. In the range of lm ≧ LM _C , the motor 6 has finished moving for the lost motion, so lm = LM _C
Is the limit. Further, even when the P direction movement is reversed, the lost motion movement amount detector 18 starts calculating the lost motion movement amount lm at the timing of generation of the movement direction reversal detection signal SP, and thereafter is performed within the range of lm> -LM _C. Be done.
In the range of lm ≤ -LM _C , lm = -LM _C is the limit. Direction detection when the moving direction is reversed by the lost motion movement amount detector 18 can be performed by the sign of the lost motion correction amount LM.

The lost motion movement amount lm calculated in this way is
In order to move the electric motor 6 within the lost motion range quickly and accurately, it is incorporated into a position feedback loop. Subtractor 19 subtracts the lost motion movement amount lm from the position detection signal X _M of the electric motor 6. This embodiment basically has two signals as position feedback signals except for lost motion correction processing.
One is the position detection signal X _M of the electric motor 6, and the other is the position detection signal X _I of the table 11 by the inductors 12 and 13.
Is a signal X _r indicating the difference between the position detection signal X _M of the electric motor 6 and the position detection signal X _M subtracted by the subtractor 20. In this embodiment, the subtractor 17
The position error X _e, which is the output of, becomes X _e = X _C + LM− (X _r + X _M ) ... (1). Since the signal X _r is X _r = X _I − (X _M −lm) (2), substituting the expression (2) into the expression (1), X _e = X _C + LM- {X _I -X _M -lm) + X _M } = X _C -X _I + (LM-lm)
… (3) In other words, the position error X _e becomes X _e = X _C -X _I in the one-way moving state in which the lost motion correction amount LM becomes equal to the lost motion moving amount lm, and the control system uses the actual position command X _C as the actual position command X _C. It operates so that the table position X _I follows.
In addition to the difference between the position command X _C and the actual table position X _I , the difference between the lost motion correction amount LM and the lost motion movement amount lm is added, and as a result, the control system causes the lost motion movement amount lm to be lost motion correction. It will operate to be equal to the quantity LM.

FIG. 4 is a time chart showing the relationship among the position command speed, the lost motion correction amount generation speed, the motor output torque T _C , the motor speed V, and the table speed when reversing the moving direction in this embodiment. When the movement direction reversal is instructed at the time point t ₁ , the generation of the lost motion correction amount LM is started at the time point t ₅ when the reversing operation is actually started. Position error at time t ₅
According to the conventional method, X _e is X _e = X _C −X _I (4), but according to the present invention, the position error X _e is the above-mentioned expression (3). The lost motion movement amount lm of the electric motor 6 follows the lost motion correction amount LM, so that the position error X _e does not increase. As a result, the motor output torque T _C rapidly reverses and increases in sign, and the rotation stop time t _r of the motor 6 and the travel time t _d of the lost motion amount including the rotation stop time t _d are significantly reduced as compared with the conventional case. You can

FIG. 5 shows the locus relationship between the position command and the table position when an arc command is given to the feed shaft drive system (X, Y axes) according to the present invention. Lost motion amount movement time
Due to the drastic decrease of t _d , after the quadrant switching point A of the arc,
Since the delay amount of the table position in the Y-axis direction with respect to the position command is small, the track error of the table position track with respect to the position command track is significantly reduced compared to the track error generated by the conventional control method shown in FIG. I have a little.

In the present embodiment, when the moving direction is reversed, the actual electric motor 6
Lost motion movement amount lm is the lost motion correction amount
When it is smaller than LM, a position error X _e is generated to compensate for this, and the electric motor 6 is rotated at a speed V _C determined by this position error X _e and the amplification factor of the amplifier 2 to cause a lost motion movement amount.
lm is controlled so as to approach the lost motion correction amount LM. Therefore, the actual lost motion movement is delayed by t _LMCD as shown by the lost motion movement speed (1) in FIG. 2 with respect to the generation of the lost motion correction amount LM.

FIG. 6 shows another embodiment of the present invention in correspondence with FIG. FIG. 6 has a configuration in which a differentiator 21 and an adder 22 are added to the embodiment of FIG. The differentiator 21 temporally differentiates the lost motion correction amount LM generated by the lost motion correction amount generator 15, and the differentiated output is the lost motion correction amount generation speed LMC _V. Lost motion compensation amount generation speed LMC _V is speed command by adder 22
It is added to V _C and becomes the final speed command V _CN of the electric motor 6. In the configuration example of FIG. 1, assuming that the speed of the motor 6 is V and the amplification factor of the amplifier 2 is K _P , the position error X _e is X _e = V / K _P , and the position error X _e proportional to the motor speed V is On the other hand, in the embodiment shown in FIG. 6, the speed error V _e can operate at V _e ≈0 due to the high amplification factor of the PID amplifier 4.
Therefore, in the present embodiment adopting the feedforward control in which the lost motion correction amount generation speed LMC _V is added to the speed command V _C , the actual lost motion moving speed lm of the electric motor 6 is changed to the lost motion moving speed in FIG. (2)
As shown in, the lost motion compensation amount generation speed LMC _V can be almost matched. That is, the lost motion correction amount LM of the actual lost motion movement amount lm of the electric motor 6
The delay t _{LMCD for} is almost never generated.

(Effect of the Invention) In the feed axis drive system that employs the fully closed loop control, a delay occurs in the operation due to the lost motion of the system when the axis movement direction is reversed. However, according to the present invention, since the movement command for the lost motion is directly applied only to the electric motor at the time of the axis movement reversal, the stability of the feed axis operation is maintained and the axis movement reversal time is shortened and accordingly. It is possible to reduce the trajectory error during multi-axis synchronous operation. Further, by significantly shortening the moving time corresponding to the lost motion of the electric motor when reversing the moving direction, it is possible to significantly reduce the trajectory error during the multi-axis synchronous operation. Further, in the present invention, since the loop sensitivity of the control system does not change, the stability of the operation of the feed shaft is not hindered.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
5 to 5 are diagrams for explaining the operation, FIG. 6 is a block diagram showing another embodiment of the present invention, FIG. 7 is a block diagram showing a conventional control device, and FIGS. FIG. 10 is a diagram for explaining the operation. 1,3,19,20 ... Subtractor, 2 ... Amplifier, 4 ... PID amplifier, 5 ...
Power amplifier, 6 ... Motor, 10 ... Ball screw, 11 ... Table, 14 ... Moving direction reversal detector, 15 ... Lost motion correction amount generator, 16, 22 ... Adder, 18 ... Lost motion movement amount detector, 21 ... Differentiator.

Claims (3)

[Claims] 1. A feed shaft position control system using an electric motor, wherein the output signal of a motor position detecting means coupled to the electric motor and the output of a feed shaft position detecting means for directly detecting the position of the feed shaft are used as the output signals. An error signal obtained by subtracting the output signal after adding the position detection increment amount of the electric motor,
By using the output signal and the error signal as the position feedback signal, the position control of the electric motor according to the electric motor position command increment amount and the position control of the feed shaft according to the feed shaft position command can be performed at the same time. A feed axis position control method characterized by the above. 2. An electric motor which generates a position command increment amount of the electric motor according to an amount set from the outside of the control device by generation of a reversal detection signal in the moving direction of the feed shaft or an amount set in advance inside the control device. Is generated by the inversion detection signal generation by adding the feed axis position command value and the position detection increment amount of the electric motor after the inversion detection signal generation to the position feedback signal. 2. The position control method for the feed shaft according to claim 1, wherein control is performed so that the operation command amount of the electric motor and the operation amount of the electric motor after the generation of the inversion detection signal become equal. 3. The operation command amount of the electric motor is an amount set from the outside of the control device or an amount preset in the inside of the control device, a time set from the outside of the control device or inside the control device. The operation command amount of the electric motor interpolated and generated by performing an interpolation process at a preset time is temporally differentiated and added to the speed command value as the operation speed command amount. The position control system of the feed axis described in 2.