JPH01228005A - Feed shaft position control system - Google Patents

Abstract

PURPOSE:To stabilize the action and to shorten the reversing time by directly adding the moving command of a lost motion part only to a motor at the time of shaft movement and reversal. CONSTITUTION:For a full closed loop control system, a subtracter, etc., calculates a position error Xe with a position command Xc, obtains a speed command Vc through an amplifier 2, and subtracts a speed feedback signal V to calculate a speed error Ve. The speed error Ve becomes a torque signal Tc of a motor 6 for driving forward a table 11. At this time, a lost motion correcting quantity generator 15 is provided, and a lost motion quantity LMc of the feed shaft driving system measured beforehand is set in the generator. The corrector 15 inputs a detection signal SP from a moving direction reversal detecting device 14, synchronizes to this, starts the generation of a lost motion correcting quantity LM and the generated said correcting quantity LM is added to the control loop in an adder 16.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for controlling the position of a feed axis in a numerically controlled (hereinafter simply referred to as NC) machine tool, etc. The present invention relates to a position control method for a feed axis that reduces the travel time of the feed axis and the trajectory error during multi-axis synchronous operation.

(Conventional technology) Conventionally, in the position control of feed axes that require high-precision control of the position of NG machine tools, etc., inductors and optical sensors that can directly detect the position of the controlled object have been used as position detectors. A so-called full-closed-loop control system is widely used, which employs a direct position detector such as an equation scale and uses the detection output of the direct position detector as a position feedback signal to form a closed position loop.

FIG. 7 shows an example of a block configuration of a feed shaft drive system that employs a full closed loop control system, in which the subtracter 1 is used for position command x. The position feedback signal x1 is subtracted from the position error signal X to calculate the position error X.

The position feedback signal X is a position signal obtained by directly detecting the mechanical position of the table 11 to be controlled by the induction sins 12 and 13. The position error x6 is amplified by the amplifier 2, and the output of the amplifier 2 is the speed command v
c. Further, an electric motor 6 mechanically connected to the electric motor 6
A speed detection signal from a detector 7 for detecting the rotational position and rotational speed of the motor is input to the subtracter 3 as a speed feedback signal V. The subtracter 3 subtracts the speed feedback signal (■) from the speed command ve to calculate the speed error V.

The speed error Ve is amplified by the PID amplifier 4 and becomes the torque signal Tc of the electric motor 6. The torque command Te is power amplified by the power amplifier 5, and its output is the torque command T.
The current I for the electric motor 6 to generate a torque corresponding to c
c. The torque generated in the electric motor 6 by the current IC is transmitted to the ball screw lO via a gear train 8.9.

The ball screw lO transfers this transmitted torque to the nut member 11A.
It is converted into the propulsion force of the table 11 via.

As explained above, the full closed loop control method performs control so that the position command xc and the position feedback signal XI indicating the actual table position finally match.
It is passed through a high-precision positioning system. Generally, as shown in Fig. 7, the feed shaft drive system is configured to transmit the output torque of the electric motor 6 to the controlled object through mechanical parts such as a gear train 8.9 and a ball screw IO. The occurrence of lost motion due to backlash of the row 8.9, expansion/contraction, torsional deformation of the ball screw 1O, etc. cannot be avoided.

FIG. 8 is a model showing the movement of a feed shaft drive system that has lost motion in its 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 at position (a). When the table is next reversely moved in the P direction from this state, the rotational direction of the electric current m is reversed, and the table does not move even if the rotational positional force of the electric motor relative to the table position becomes as shown in (b). , the table starts to reversely move in the P direction only when the relationship between the table position and the rotational position of the electric motor becomes as shown in (C). In this way, in a feed axis drive system that has lost motion, a dead zone corresponding to the amount of lost motion occurs when the direction of movement is reversed, and when the axis movement is reversed, the electric motor must operate an extra amount of lost motion relative to the actual amount of table movement. Must be.

FIG. 9 shows the position command x when the moving direction is reversed (time 1+). The relationship among the amount of change per unit time (position command speed), motor output torque Tc, motor speed V, and table speed is expressed in a time chart. When the reversal of the movement direction is commanded at time t1, the position error X in FIG.
The motor output torque Tc, which is the output of the amplifier 4, begins to decrease. Torque '-TL' indicates the friction torque required to move the table in the direction before reversal, and the motor output torque TC
When the absolute value of becomes smaller than TL, the movement of the table 11 and the rotation of the electric motor 6 stop. This rotation stop time 1r (-12・-ts) of the electric motor 6 is the motor output torque Tc
The electric motor 6 starts rotating in the opposite direction at time t2 when the sign of the motor output torque Tc is reversed, which is equal to the sign reversal time of . Time points t and ~t are the travel time of the amount of lost motion that corresponds to the dead zone when the direction of movement is reversed in FIG.
The area of the motor speed V during this time becomes the amount of lost motion. Note that the motor output torque T whose sign is reversed at time t2
, continues to increase until time t3 because table 11 is stopped. At time t3, when the motor output torque Tc exceeds the friction torque ◆TL necessary for moving the table in the reverse direction, the table 11 starts moving in the reverse direction.

Immediately after time t, in order to recover the delay in the table position relative to the position command xc that occurred within the operation delay time td (・t3-ts), the table speed at - time becomes faster than the position command speed, and the motor output torque Tc also temporarily increases. do.

As explained above, in the feed shaft drive system employing the full closed loop control system, an operation delay time t occurs when the moving direction is reversed due to lost motion generated within the torque transmission mechanism. When an arc command is given to such a feed shaft drive system (X-axis, Y-axis), the locus relationship between the position command and the actual table position is shown on the X-Y coordinates as shown in Fig. 1O. As is clear from this 1θ diagram, after the quadrant switching point A of the arc, the X-axis operation continues in the P direction, so the table position in the X-axis direction is determined by the X-axis position command as before point A. Although accurate tracking is possible, for Y-axis motion, the direction of movement is reversed from P direction motion to N direction motion, so a reversal motion delay time occurs due to the amount of lost motion, and after point A, the table moves in the Y jTtb direction. The position lags behind the position command. As a result, the table position locus on the X-Y coordinates becomes a locus with 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 a feed shaft drive system that employs a full closed loop control method, an operation delay time occurs due to lost motion of the mechanical system when the direction of movement is reversed. For this reason,
When operating multiple axes synchronously, including direction-reversing axes,
A trajectory error occurs between the position command trajectory and the actual feed axis position trajectory.

The occurrence of such a trajectory error can be suppressed by increasing the amplification factor of the amplifier 2 shown in FIG. This is due to the sign inversion time 1. of the motor output torque Tc in FIG. and operation delay time t, including travel time for lost motion.
This is because d decreases as the amplification factor of the control system increases. However, there is inevitably a limit to the increase in the amplification factor of the amplifier 2 due to the mechanical rigidity of the feed shaft drive system, and increasing the amplification factor beyond this limit will lead to instability of the feed shaft operation. For this reason, it has been extremely difficult to maintain stability in the feed axis operation and to minimize trajectory errors.

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a feed axis control method that achieves quick direction reversal of the feed axis while maintaining operational stability of the feed axis drive system. Our goal is to provide the following.

(Means for Solving the Problems) The present invention relates to a method for controlling the position of a feed shaft using an electric motor, and the above object of the present invention is to control the output signal of a motor position detection means coupled to the electric motor and the feed 11! Ill
An error signal is obtained by adding the position detection increment amount of the motor to the output of the feed shaft position detection means that directly detects the position of the motor, and then subtracting the output signal. This is achieved by simultaneously controlling the position of the electric motor in accordance with the increment amount of the motor position command and controlling the position of the feed shaft in accordance with the feed axis position command.

(Function) When the direction of movement of the feed axis is reversed, the present invention provides a moving position command for the lost motion from outside the feedback loop to the electric motor, so that the electric motor operates faster by the lost motion, and the feed axis This is designed to shorten the final table reversal operation time while maintaining the stability of the drive system.

(Example) Embodiments of the invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an example of the block configuration of the feed shaft drive system according to the present invention in correspondence with FIG. 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 generating the lost motion correction amount LM in synchronization with this input, and generates the generated lost motion correction amount. LM is added to the control loop in 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 moving direction reversal of the position command xc of the feed axis. If the amplification factor of the amplifier 2 is extremely high, the timing of the reversal of the moving direction can be detected only by the position command xc, but if the amplification factor of the amplifier 2 is low, the timing to actually reverse the motor 6 is the timing of the reversal of the position command xc. It will be later than that. Therefore, the movement direction reversal detector 14
is the actual motor speed command ve, and this speed command v
A moving direction reversal detection signal sp is generated based on the sign reversal of e.

Figure 2 shows the generation of the movement direction reversal detection signal SP in the Y axis when the arc command shown in Figure 3 is given to the X and Y axes of the feed axis drive system, the generation of the lost motion correction amount LM, and this. 3 is a time chart showing the operation of the electric motor associated with. In Fig. 3, at timing t4 when the position command xc reaches the quadrant switching point A of the circular arc (see Fig. 2)
, the table movement in the Y-axis direction is still moving in the P direction toward the quadrant switching point A of the circular arc of the position command, and the actual table position requires reverse movement in the N direction. This is the timing of time ts when the arc reaches the quadrant switching point A. Therefore, the moving direction reversal detection signal sp is generated at the timing t, as shown in FIG.
The lost motion correction amount LM begins to be generated. As a method of generating the lost motion correction amount LM, the set lost motion amount LMC may be instantaneously generated, but if the lost motion amount LMC is large, the second As shown in the figure, a generation time tLMc: of the lost motion correction amount LM is provided, and the generation amount is interpolated within this generation time tLMC and output. In this case, at time t6 when the generation of the lost motion correction amount LM ends, the lost motion correction amount LM becomes equal to the set lost motion amount LMc.

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 -- LMc at the generation timing described above. Thereafter, similarly, the lost motion correction amount generator 15 generates a lost motion correction amount of LM-LMC when reversing in the N direction and LM-LMC when reversing in the P direction. The lost motion movement amount detector 18 latches the position detection signal XM of the detector 7 at the generation timing of the movement direction reversal detection signal SP, and calculates the subsequent position detection signal X and the difference ILm. The calculated difference numerator 1m has a positional relationship between the electric motor 6 and the table 11 as shown in FIG. 8(a).

(c) This is the amount of lost motion movement of the electric motor 6 that corresponds to a position between . When reversing movement in the N direction,
The lost motion movement amount 1m increases from O" toward the final lost motion correction amount LM - LMC. In this case, the lost motion movement amount detector 18 calculates the lost motion movement amount 2m as J2m<LMc
It is carried out within the range of

In the range of ILm≧LMc, the electric motor 6 has finished moving by the amount of lost motion, so the limit is 1-LMC. Also, even when reversing the movement in the P direction, the lost motion movement amount 4 is determined by the lost motion movement amount detector 18.
The calculation of 2+11 is started at the timing of generation of the moving direction reversal detection signal SP, and thereafter I1. This is carried out in the range m>-LMc. Also, in the range of 1-≦-t, MC is 11
The limit is m-LMc. The lost motion movement amount detector 18 can detect the direction when the moving direction is reversed based on the sign of the lost motion correction amount LM.

Lost motion movement amount j2+ calculated in this way
is incorporated into a position feedback loop to quickly and accurately move the electric motor 6 within the lost motion range. A subtracter 19 subtracts the lost distortion movement amount 11 va from the position detection signal x 2 of the electric motor 6.

In this embodiment, except for lost motion correction processing, there are basically two signals as position feedback signals. One is the position detection signal x of the electric motor 6, and the other is the position detection signal xM of the electric motor 6 subtracted by the subtracter 20 from the position detection signal x1 of the table 11 by the inductors 12 and 13. A signal X indicating the difference between
.

It is. In this embodiment, the position error x8, which is the output of the subtracter 17, is expressed as: Xe = XCφLM - (Xr*XJ ・
・””・・’ (1). Here, the signal x1 is Xr-L-(XM-flIn)..."
...”' Since (2), by substituting equation (2) into equation (1), we get Xe−Xc+LM −(XI−(X+++−
um) ”XM)・Xc-XI”(LM-u m
) ---(:l). In other words, position error x. is X, -Xc-XI in the unidirectional movement state where the lost motion correction amount L'l is equal to the lost motion movement amount l1I11, and the control system follows the position command XC with the actual table position x 1. It works like this. In addition, in addition to the difference between the position command It will work so that it is equal to .

FIG. 4 is a time chart showing the relationship among the position command speed, lost motion correction amount generation speed, motor output torque Tc, motor speed (2), and table speed when the moving direction is reversed in this embodiment. When a movement direction reversal is commanded at time t, the generation of lost motion correction ffi L, M is started at time t5 when the reversal operation actually begins.

Position error X at time t5.

According to the conventional method, is ×e-Xe-xI (4), but
According to the present invention, since the position error x 6 is expressed by the above-mentioned equation (3), the control system allows the actual lost motion movement amount 11 of the electric motor 6 to follow the lost motion correction ffiLM, thereby increasing the position error It works like it doesn't. As a result, the motor output torque Tc rapidly reverses its sign and increases.
The rotation stop time tr of the electric motor 6 and the travel time td of the lost motion amount including the rotation stop time tr can be significantly reduced compared to the conventional art.

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. Due to a significant reduction in the travel time td of the lost motion amount, the delay amount of the table position in the Y-axis direction relative to the position command becomes smaller after the quadrant switching point A of the circular arc, so the trajectory error of the table position trajectory with respect to the position command trajectory becomes , is significantly reduced compared to the trajectory error generated by the conventional control method shown in FIG. 1O.

In this embodiment, when the moving direction is reversed, the actual electric motor 6
Lost motion movement amount j! + is smaller than the lost motion correction amount LM, a position error x6 is generated to compensate for this, and this position error X.

The electric motor 6 is rotated at a speed vc determined by the amplification factor of the amplifier 2, and lost motion movement! ! Jl: it 42
Control is performed so that m approaches the lost motion correction amount LM.

Therefore, with respect to the generation of the lost motion correction amount LM, the actual lost motion movement is delayed by < ttvco as shown in the lost motion movement speed (1) in FIG.

FIG. 6 shows another embodiment of the present invention corresponding to FIG. FIG. 6 has a configuration in which a differentiator 21 and an adder 22 are added to the embodiment shown in FIG.

The differentiator 21 temporally differentiates the lost motion correction iLM generated by the lost motion correction amount generator 15, and the differential output becomes the lost motion correction amount generation speed LMCV. Lost motion correction amount generation speed L
MCV is added to speed command vc by adder 22,
This becomes the final speed command vcN for the electric motor 6. In the configuration example shown in FIG. 1, the position error x8 becomes Xs-V/2, assuming that the speed of the motor 6 is V and the amplification factor of the amplifier 2 is 2.
Whereas a position error x6 proportional to the motor speed ■ occurs, in the embodiment of FIG. Therefore, the lost motion correction amount generation speed LMC
In this embodiment, which employs feedforward control in which V is added to the speed command VC, the actual lost motion moving speed ILm of the electric motor 6 is corrected as shown in lost motion moving speed (2) in FIG. The amount generation rate LMCV can be made to almost match the amount generation rate LMCV. That is, the delay tLMCD of the actual lost motion correction amount 11m of the electric motor 6 with respect to the lost motion correction amount LM hardly occurs.

(Effects of the Invention) In a feed shaft drive system employing full closed loop control, a delay in operation occurs due to lost motion of the system when the axis movement direction is reversed. However, in the present invention, a movement command for the lost motion is directly applied to the electric motor only when the axis movement is reversed, so while maintaining the stability of the feed axis operation, the axis movement reversal time can be shortened and this problem can be solved. It is now possible to reduce trajectory errors during multi-axis synchronous operation. Further, by significantly shortening the travel time corresponding to the lost motion of the electric motor when the moving direction is reversed, it is possible to significantly reduce trajectory errors during multi-axis synchronous operation. Further, in the present invention, since the loop sensitivity of the control system does not change, there is no problem with the stability of the feed axis operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one 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. 1O is a diagram for explaining the operation. 1.3.19.20...Subtractor, 2...Amplifier, 4
... PID amplifier, 5 ... power amplifier, combination ... electric motor, lO ... ball screw, 11 ... table, 1
4... Movement direction reversal detector, 15... Lost motion correction amount generator, 16.22... Adder, 18...
-Loss tomotion displacement detector, 21...differentiator. Applicant's representative Yasugata Yu Mito Watata 1 Houki 2 Diagram number 4 Diagram Nn Hyakuhoki 8th 1st O8

Claims (1)

[Claims] 1. In a method for controlling the position of a feed shaft using an electric motor, an output signal of a motor position detection means coupled to the electric motor;
An error signal is obtained by adding the position detection increment amount of the electric motor to the output of the feed shaft position detecting means that directly detects the position of the feed shaft, and then subtracting the output signal. A feed axis characterized in that by using a feedback signal, it is possible to simultaneously control the position of the motor according to the motor position command increment and the position control of the feed shaft according to the feed shaft position command. position control method. 2. The increment amount of the position command for the electric motor is determined by an amount set from outside the control device by generation of a reversal detection signal in the direction of movement of the feed axis, or an operation command for the motor generated according to an amount preset inside the control device. By adding the amount to the feed axis position command value and adding the incremental amount of position detection of the motor after the generation of the reversal detection signal to the position feedback signal, the electric motor generated by the generation of the reversal detection signal is 2. The feed shaft position control system according to claim 1, wherein control is performed so that the amount of operation command and the amount of operation of the electric motor after the generation of the reversal detection signal are equal. 3. The operating command amount of the electric motor is an amount set from outside the control device or an amount preset inside the control device at a time set from outside the control device or a amount set in advance inside the control device. 3. The interpolated motor operation command amount is generated by performing interpolation processing using the time, and the interpolated motor operation command amount is differentiated over time and added to the speed command value as the operation speed command amount. The position control method of the feed axis.