JP2007058278A - Position controller with lost motion correcting function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-price position controller, capable of lost motion correction with high precision, which solves the problem that a lost motion quantity LM in case of repetition of fine inversion etc., can not completely be corrected only by corrections having conventionally considered gradual increase type characteristics. <P>SOLUTION: A displacement quantity calculating unit 3 calculates a displacement quantity Δx of a position command after inversion detection with an inversion signal detected by an inversion detector 2 and a position command. A correction quantity calculating unit 5 sums up an acceleration component correction quantity, a friction component correction quantity, and a displacement quantity component correction quantity of lost motion and outputs the result as a position command correction quantity. An inverting operation of a machine tool is not always only an arc movement, but an inverting operation including a stop without fail. Especially, during cutting such as metal mold machining, the problem that fine inversion including a stop state is repeated is solved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a position control device for a feed shaft in a machine tool or the like.

  In a semi-closed loop position control device of a machine tool, a moving body such as a table of a machine tool is moved by converting a rotary motion of a servo motor into a linear motion by a feed drive mechanism using a ball screw. There is backlash due to play between the ball screw used in the feed mechanism and the nut on the table side. This backlash generates a position error between the forward direction command and the backward direction command.

  When using a ball screw and a nut that are pressurized in order to eliminate this backlash, backlash due to backlash between the ball screw and the nut is eliminated, but the frictional resistance of the ball screw portion is generated by applying the pressure. Further, there are guides in the feed mechanism of the machine tool, and guides such as rolling guides and sliding surface guides are used, and friction resistance is also generated in these guide portions. It has been a problem to correct the position error caused by the lost motion due to the frictional resistance.

  In conventional semi-closed position control, lost motion correction data obtained by dividing the amount of lost motion generated during arc motion at multiple position intervals is calculated at a pulse rate corresponding to the command speed and the divided position and supplied to the speed control system. Is used (Patent Document 1).

  FIG. 15 is a block diagram illustrating an example of the numerical control device disclosed in Patent Document 1. A drive signal for the motor 12 is created from the command data 17 by the data analysis unit 18. This drive signal is supplied to the motor 12 via the speed control unit 8, and the ball screw 13 is rotated to move the moving body 14 to the command position. The speed control unit 8 performs general feedback control using the detector 11. The correction data sections 15a to 15n include correction data obtained by dividing the lost motion amount generated during arc motion as shown in FIG. 17 at a plurality of position intervals, and corrections supplied to the speed control section according to the divided positions. The pulse rate data for calculating the pulse rate corresponding to the feed rate of the amount and the correction amount data are accumulated. The correction amount calculation unit 16 reads the correction data from the correction data storage unit corresponding to the command speed, and calculates the correction amount from the pulse rate data corresponding to the command speed and the division position.

  FIG. 16 is a diagram showing the contents of correction data stored in the correction data portions 15a to 15n. F1 to Fm are feed speeds, and D0 to Dn are division positions. The correction amount data is correction data indicated by BL0 to BLn and pulse rate data indicated by L0 to Lm.

  According to this method, it is possible to considerably improve the biting phenomenon in arbitrary arc cutting, but there are the following problems.

JP 08-263117 A

  When a reverse operation is performed by changing the command by 1 μm by pulse feed, the lost motion amount LM increases gradually according to the position displacement amount. Moreover, it is clear from the experimental results that even if the reversal in the continuous motion such as the arc motion is similar to the gradually increasing type. For this reason, conventionally, the lost motion amount LM has been corrected by a gradually increasing characteristic with respect to the displacement amount of the position command as shown in FIG.

  However, when the reversal operation including the stop state is performed and the lost motion amount LM is measured using the feed speed as a parameter, the result shown in FIG. 7 is obtained. Also in the arc motion, the lost motion amount LM does not increase to a simple incremental type according to the position displacement amount, but has a characteristic as shown in FIG. When the feed rate is slow, it gradually increases. However, as the feed rate increases, the lost motion amount LM that increases gradually increases as the position displacement amount Δx increases.

  Next, FIG. 8 shows the lost motion amount LM when the acceleration is a parameter when the feed rate is relatively slow. FIG. 9 shows the lost motion amount LM when the acceleration is a parameter when the feed speed is relatively fast. 8 and 9, a1, a2, and a3 are acceleration parameters, and a3> a2> a1.

  As described above, the reversing operation of the machine tool includes not only a circular motion but also a reversing operation in which a stop always occurs. In particular, in cutting such as mold processing, there is a case where minute inversion with a stopped state is repeated. The lost motion amount LM generated in such an operation cannot be completely corrected only by a correction having a gradual increase type characteristic which has been conventionally considered.

  The present invention relates to a servo motor to which a position detector is attached, and a position control device for controlling the position of a feed shaft driven by the servo motor and performing feedback control based on a difference between a position command and a position detection value of the position detector. , The direction reversal detector for detecting the direction reversal of the feed shaft or the servomotor from the position command value or the position detection value, and the displacement amount of the position command value or the position detection value after the direction reversal is calculated. A displacement amount calculator, and a correction amount calculator that calculates a command correction value by inputting the displacement amount, the acceleration of the feed shaft or the motor and the speed of the feed shaft, and the correction amount calculator calculates the speed. A friction speed calculator that calculates a first-order lag friction component calculation speed as an input, a friction component calculator that outputs a friction component of a lost motion amount according to the friction speed, and the acceleration An acceleration component calculator that outputs an acceleration component of the lost motion amount according to the displacement amount correction component calculator that outputs a displacement amount correction component of the lost motion amount according to the position displacement amount, and the lost motion An amount of friction component, the acceleration component, and a displacement amount correction component are added to obtain a command correction value, and the command correction value is added to the position command value to perform lost motion correction.

The present invention also provides a position for controlling a position of a servo motor to which a position detector is attached and a feed shaft driven by the servo motor, and performing feedback control based on a difference between a position command and a position detection value of the position detector. In the control device, a direction reversal detector that detects whether or not the feed shaft or the servo motor is reversed and stopped for an arbitrary time from the position command value or the position detection value, and the position command value or A displacement amount calculator that calculates a displacement amount of the position detection value; and a correction amount calculator that calculates a command correction value by using the displacement amount and the acceleration of the feed shaft or motor and the speed of the feed shaft as input. The quantity calculator uses the equations Xc = sign (Δx) × (A + B (1−exp [− | Δx | / C]))
A position command corrector for calculating the command correction amount Xc, and the lost motion correction is performed by adding the position command correction value Xc to the position command value.

  Further, it is desirable that the displacement amount calculator outputs the displacement amount = 0 as the amount of arbitrary displacement after the inversion, and outputs the subsequent displacement amount as Δx.

  According to the position control device having the lost motion correction function according to the present invention, the lost motion can be appropriately corrected not only in the reversing operation of the arc motion on the feed axis of the machine tool but also in the reversing operation in which the stop always occurs. it can. Further, since the correction data can be varied according to the speed or acceleration without having a huge amount of data, a position control device having a relatively inexpensive and highly accurate lost motion correction can be provided.

  FIG. 1 shows an embodiment of the present invention. The same components as those of the conventional position control device shown in FIG. 15 are denoted by the same reference numerals, and the description thereof is omitted. Reference numeral 7 in FIG. 1 is a position controller that outputs a speed command based on the position command and the position feedback value detected by the detector 11. Reference numeral 8 denotes a speed controller, which outputs a torque command based on a speed detection value obtained by differentiating the speed command and the position detection value with a differentiator 10. A current controller denoted by reference numeral 9 controls the current based on the torque command.

  Next, the components surrounded by the dotted line in FIG. 1 will be described. The differentiator 1 differentiates the position command or the position detection value and outputs a speed command or speed detection value. The inversion detector 2 detects inversion based on the speed command or the speed detection value, and outputs an inversion detection signal. The displacement amount calculator 3 calculates the displacement amount Δx of the position command after the inversion detection based on the inversion signal detected by the inversion detector 2 and the position command. The differentiator 4 differentiates the speed command and outputs an acceleration command. The correction amount calculator 5 outputs a position command correction amount Xc based on the displacement amount Δx, the acceleration command α, and the speed command v.

Next, the correction amount calculator 5 will be described. FIG. 2 shows an embodiment of the correction amount calculator 5. The displacement amount component calculator 24 outputs the displacement amount correction amount Xcx of the lost motion when the shaft is moved at a slow speed such as pulse feed with the displacement amount as an input. The acceleration component correction amount calculator 21 receives the acceleration of the feed axis or the acceleration of the motor and outputs an acceleration component correction amount Xca of the lost motion. The friction speed calculator 26 receives the speed of the feed shaft or the speed of the motor as an input, and outputs an absolute value of the first-order lag friction force calculation speed. The frictional force calculator 22 receives the frictional force calculation speed as an input, and calculates the frictional force Fμ using a cubic function or the like with respect to the absolute value | v | of the speed as shown in FIG. A function for calculating the frictional force is shown in equation (1).
Fμ = sign (Δx) × [h (| v | −v1) ³ + i (| v | −v2) ²
+ J (| v | −v3) + μ0] (1)
Here, v: speed, v1, v2, v3: arbitrary speed, h, i, j: coefficient, μ0: constant, sign (Δx): sign of displacement, sign 28 in FIG. It is.

  The friction component calculator 23 calculates a correction amount of the friction component lost motion according to the friction force, and multiplies the sign by the accumulator 27 to output Xcμ. The adder 25 adds the displacement component Xcx of the correction amount of the lost motion, the acceleration component Xca, and the friction component Xcμ, and outputs a position command correction amount Xc.

  When the weight of the moving body of the feed shaft to be controlled is Mg, the acceleration after reversal is α, and the friction coefficient of the entire shaft system is μ, the friction force Fμ is Fμ = Mg · μ, which is necessary after reversal The strong force Fg is Fg = Mg · α + Fμ. The force required after reversal is that the tension of the spring system of the feed shaft is Fl = k · LM, where k is the spring coefficient of the feed shaft and LM is the amount of lost motion. The force required after reversal and the force of the spring system of the feed shaft are the same (Fl = Fg). That is, k · LM = Mg · α + Fμ, and the lost motion amount LM becomes LM = (Mg / k) · α + Fμ / k.

Here, the acceleration component correction amount Xca of the lost motion in FIG. 2 is equivalent to (Mg / k) · α. The lost motion friction component correction amount Xcμ in FIG. 2 is equivalent to the frictional force Fμ / k. The displacement component correction amount Xcx is a gradually increasing function, for example, as shown in equation (2), where A and B are coefficients that vary according to speed and C is a coefficient that varies according to acceleration.
Xcx = sign (Δx) × (A + B (1−exp [− | Δx | / C]))
... (2)

  For example, when the lost motion LM is measured when the moving body is moved from the stopped state at a very slow feed rate such as pulse feed, the result is as shown in FIG. The horizontal axis in FIG. 4 is the position command CON, and the vertical axis is the position APA of the moving body. The dashed line in FIG. 4 indicates a position command at the time of the reverse motion, and is a diagram showing that the lost motion LM is generated not in one direction but in both directions. The position before reversal in the reversing motion is indicated by a dotted line, and the position after reversal is indicated by a solid line. The position error when the position error before and after reversal is constant is the command position.

  In this case, the position command correction amount Xc for correcting the lost motion is a function as shown in FIG. 5 where A when approximated by the above equation (2) is A0 and the coefficient B is B0. A0 in FIG. 5 includes the lost motion component other than the frictional resistance, for example, the backlash component of the ball screw and the nut portion. Further, the relationship with the time of the lost motion LM when the reversing operation is repeated is as shown in FIG.

  The coefficient of friction μ in the machine tool has the characteristics shown in FIG. In FIG. 10, the area (1) is a boundary lubrication area, the area (2) is a mixed lubrication area, and the area (3) is a fluid lubrication area. The characteristics shown in FIG. 7 are very similar to the speed-dependent characteristics of the friction coefficient μ shown in FIG.

  Further, when the shaft moves, the boundary lubrication region shifts to the mixed lubrication state, and further shifts to the fluid lubrication region. When the moving body stops, the fluid lubrication state is shifted to the mixed lubrication region and the boundary lubrication state with a delay. Therefore, in the reversal in the continuous operation such as the circular motion, the fluid lubrication region (3) shown in FIG. 10 or the mixed lubrication region (2) is changed to the boundary lubrication region (1) shown in FIG. The reversal operation is performed in the respective lubrication areas without returning. The speed of the arc motion of the machine tool is mostly in the mixed lubrication region, and the frictional force calculation speed | v | is a function of the first order lag of the speed v as described above, so the friction coefficient remains in the mixed lubrication state. The reversal operation is performed without shifting to the normal lubrication state, and the characteristics shown in FIG. 18 are obtained. Further, when the feed rate is relatively slow, such as pulse feed, the boundary lubrication region remains, and no transition is made to the mixed lubrication region or the fluid lubrication region. Therefore, the gradual increase characteristic as shown in FIG. 8 is obtained.

  FIG. 3 shows another embodiment of the correction amount calculator 5. The displacement amount calculator 34 shown in FIG. 3 receives the displacement amount | Δx | and outputs a displacement compensation component Xcx for the lost motion according to the above (Equation 4). The acceleration component calculator 21 receives the acceleration of the moving body or the acceleration of the motor and outputs an acceleration component correction amount Xca for the lost motion. The coefficient C calculator 31 varies the coefficient C according to the acceleration of the moving body or the motor. The coefficient A calculator 32 changes the coefficient A with the speed of the moving body or the speed of the motor as an input. The displacement component Xcx of the lost motion and the acceleration component Xca are added to output a position command correction amount Xc.

  For example, assuming that the acceleration of the moving body is α and C∝1 / α, the incremental increase in the lost motion position command correction amount Xc with respect to the displacement amount Δx increases as the acceleration increases even at the same feed rate, as shown in FIG. In a machine tool feed shaft or the like, the amount of lost motion immediately after reversal becomes a problem only in the velocity region of the boundary lubrication region (1) and the mixed lubrication region (2) shown in FIG. Therefore, the coefficient A is a function that varies according to the speed as shown in FIG. Vhtl in FIG. 11 is a speed at which the boundary lubrication region shifts to the mixed lubrication region. The correction amount calculator shown in FIG. 3 can perform correction equivalent to the correction amount calculator shown in FIG.

  Furthermore, in the rolling guide machine, the lost motion when the moving body of the feed shaft is moved from the stopped state by pulse feed is as shown in FIG. The contents overlapping with those described in FIG. 4 are omitted.

In this case, the position command compensation amount Xc for correcting the lost motion is as shown in the equations (3-1) to (3-4).
When Δx ≧ Δx1,
Xcx = A + B (1-exp [(− | Δx | −Δx1) / C]) (3-1)
When Δx ≦ −Δx1,
Xcx = −A−B (1−exp [(− | Δx | + Δx1) / C]) (3-2)
When 0 <Δx <Δx1, Xcx = −A−B (3-3)
When −Δx <Δx <0, Xcx = A + B (3-4)
Here, A, B, and C are coefficients. When A is approximated by the above equations (3-1) to (3-4) and A0 is set, and the coefficient B is B0, the function is as shown in FIG. Further, the relationship with the time of the position command correction amount Xcx when the reversing operation is repeated is as shown in FIG.

  As described above, according to the position control device having the lost motion correction function according to the present invention, the lost motion is not only in the reversing operation of the circular motion in the feed axis of the machine tool but also in the reversing operation in which the stop always occurs. It can be corrected appropriately. Further, since the correction data can be varied according to the speed or acceleration without having a huge amount of data, a position control device having a relatively inexpensive and highly accurate lost motion correction can be provided.

It is a block diagram which shows embodiment of this invention. It is a block diagram which shows the correction amount calculator of this invention. It is a block diagram which shows the other correction amount calculator of this invention. It is the figure which measured the position command and position of the feed axis of a machine tool. It is the figure which showed the displacement amount correction | amendment component of the lost motion of this invention. It is the figure which showed the displacement amount correction | amendment component of the lost motion of this invention, and the relationship of time. This is a measurement result of displacement and lost motion with speed as a parameter. This is a measurement result of displacement and lost motion with acceleration as a parameter. This is a measurement result of displacement and lost motion with acceleration as a parameter. It is a speed characteristic figure of a friction coefficient. It is a figure which shows the function of the coefficient A of this invention. It is the figure which measured the position command and position of the feed axis of a machine tool. It is the figure which showed the displacement amount correction | amendment component of the lost motion of this invention. It is the figure which showed the displacement amount correction | amendment component of the lost motion of this invention, and the relationship of time. It is a block diagram which shows a prior art example. It is a figure explaining a prior art example. It is a figure explaining a prior art example. It is a figure explaining a prior art example.

Explanation of symbols

  1, 4, 10 Differentiator, 2 Inversion detector, 3 Displacement calculator, 5 Correction calculator, 6, 19, 20, 25, 35 Adder, 7 Position controller, 8 Speed controller, 9 Current control , 11 detector, 12 motor, 13 ball screw, 14 moving body, 15a, 15b, 15c, 15n correction data section, 16 correction amount calculation section, 17 command data, 18 data analysis section, 21 acceleration component correction amount calculator, 22 friction force calculators, 23 friction component calculators, 24 displacement amount component calculators, 26 friction speed calculators, 31 coefficient C calculators, 32 coefficient A calculators, 34 displacement amount component calculators.

Claims (3)

In a position control device for controlling a position of a servo motor to which a position detector is attached, and a position of a feed shaft driven by the servo motor, and performing feedback control from a difference between a position command and a position detection value of the position detector,
A direction reversal detector for detecting a direction reversal of the feed shaft or servomotor from the position command value or the position detection value;
A displacement amount calculator for calculating a displacement amount of the position command value or the position detection value after direction reversal;
A correction amount calculator for calculating a command correction value by inputting the displacement amount and the acceleration of the feed shaft or motor and the speed of the feed shaft;
With
The correction amount calculator is
A friction speed calculator for calculating a first-order lag friction component calculation speed using the speed as an input;
A friction component calculator that outputs a friction component of the lost motion amount according to the friction speed;
An acceleration component calculator that outputs an acceleration component of a lost motion amount according to the acceleration;
A displacement amount correction component calculator that outputs a displacement amount correction component of the lost motion amount according to the position displacement amount; and
Have
Add the friction component of the lost motion amount, the acceleration component, and the displacement correction component as a command correction value,
A position control device having a lost motion correction function, wherein the lost motion correction is performed by adding the command correction value to the position command value. In a position control device for controlling a position of a servo motor to which a position detector is attached, and a position of a feed shaft driven by the servo motor, and performing feedback control from a difference between a position command and a position detection value of the position detector,
A direction reversal detector for detecting whether the feed shaft or the servomotor is reversed in direction and stopped for an arbitrary time from the position command value or the position detection value;
A displacement amount calculator for calculating a displacement amount of the position command value or the position detection value after direction reversal;
A correction amount calculator for calculating a command correction value by inputting the displacement amount and the acceleration of the feed shaft or motor and the speed of the feed shaft;
With
The correction amount calculator has the following formula: Xc = sign (Δx) × (A + B (1−exp [− | Δx | / C]) where A and B are coefficients that vary according to speed, and C is a coefficient that varies according to acceleration. )
A position command corrector that calculates the command correction amount Xc by
A position control device having a lost motion correction function, wherein the lost motion correction is performed by adding the position command correction value Xc to the position command value. 3. The position according to claim 1, wherein the displacement amount calculator outputs a displacement amount = 0 as an arbitrary displacement amount after inversion, and outputs the subsequent displacement amount as Δx. Control device.

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