JPH0722873B2 - Position control device for feed axis - Google Patents

Description

TECHNICAL FIELD The present invention relates to a position control device for a feed shaft (table) in a numerical control (hereinafter, simply referred to as NC) machine tool or the like.

(Prior Art) Conventionally, in the position control of the feed axis, which requires highly accurate position control in NC machine tools, etc.,
A position detector that can directly detect the position of the controlled object such as an optical scale is adopted, and the so-called full-closed loop control method that forms a position feedback loop using the output of this position detector as a position feedback signal is widely used. ing.

An example of the feed axis position control device adopting the full closed loop control system will be described with reference to FIG. In FIG. 7, the position command value X _C generated by the position command generator 1 is
It is input to the feed axis control unit 10 that controls the position and speed of the feed axis (table). The subtractor 11 in the feed axis control unit 10 is
The position deviation Xe is calculated by subtracting the position feedback signal X _I from the position command value X _C. The position feedback signal X _I is a position detection value obtained by directly detecting the machine position of the table 5 to be controlled by the inductins 6 and 7. The position deviation Xe is amplified by the amplifier 12 having an amplification factor of the position loop gain Kv, and the amplified signal becomes the feed shaft speed command value V _C. The position detection value X _M output from the position detector 3 coupled to the electric motor 2 is the speed detection unit 16
Is differentiated by time to be converted into a motor speed and becomes a speed feedback signal V _M. The subtractor 13 subtracts the speed feedback signal V _M from the speed command value V _C to calculate the speed deviation Ve. It is output from the subtractor 13. The speed deviation Ve is amplified by the PID amplifier 14 and becomes the torque command value T _C of the electric motor 2. The torque command value T _{C is} power-amplified by the power amplifier 15, and its output becomes a current I for causing the electric motor 2 to generate a torque corresponding to the torque command value T _C. The torque generated in the electric motor 2 by the drive based on the current I is transmitted to the ball screw 4, and the transmitted torque is transmitted to the table 5 by the ball screw 4.
Converted to propulsion.

In such a position control device for the table 5, the operation of the table 5 when the position command including the reversal of the moving direction of the table 5 is performed will be described with reference to FIGS. 8 and 9. As an example, the time change amount of the position command value X _C (hereinafter, referred to as position command speed) dX _C / dt is Consider the position response of Table 5 when it changes linearly.

The position response of the position control device shown in FIG. Can be expressed as Here, generally, the amplification factors of the PID amplifier 14 and the power amplifier 15 are high, and the speed control with the speed deviation Ve≈0 is possible. Further, the motor speed V _M and the table speed dX _I / dt (hereinafter simply referred to as V _I ) during one-directional movement are V _M =
From V _I , the above equation (2) becomes Can be replaced with Then, by substituting the position command speed dX _C / dt given by the equation (1) into the equation (3),
If you solve this Becomes However, this is the speed of the table 5 within the time t ≦ t ₁ satisfying the condition during the movement in one direction.

Next, consider the correspondence at time t> t ₁ . Time t ₁
After that, the moving direction of the table 5 has to be reversed, but since the backlash generally exists in the mechanical portion such as the ball screw 4, the motor 2 has to perform a reversing operation corresponding to the backlash in order to start the reversal of the table 5. It must be finished, and the table 5 is stopped until the reversing operation is finished. Then, the position deviation Xe occurring during the stop time t ₁ after the table, the position deviation at time t ₁ Xe
Since Xe = 0 from the expressions (3) and (4), if the elapsed time after the time point t ₁ is t, And the resulting motor speed V _M and motor reversal operation amount
P _M is Becomes Here, when the backlash amount of the mechanical portion is B, the time T _O until P _M = B is the table stop time (see FIG. 8). _Assuming that the time point at which the table 5 starts the reversing operation after the stop time T _O has elapsed is t ₂ , the speed of the table 5 increases after the time point t ₂ , and the speed is constantly given by the equation (4). . Figure 8 shows the position command speed in this example.
Fig. 9 shows the relationship between dX _C / dt and table speed V _I. Fig. 9 shows the relationship between position command speed dX _C / dt and motor speed V _M, and RC shows ideal response. The hatched area AR in FIG. 9 indicates the backlash amount B.

(Problems to be Solved by the Invention) The above-described feed axis position command is used for synchronous tapping of the quadrant switching part, the spindle and the feed axis during arc shape machining by multi-axis synchronous operation of a plurality of feed axes. Frequently occurs at the screw bottom, etc., where the operation is reversed.

FIG. 10 shows the shape error of the quadrant switching portion caused by the response delay of the table 5 when machining the circular arc shape. For each of the X and Y axes that drive the XY table, Position command is issued, the X-axis position command speed dX _C /
Since dt = −Rω · sinωt, the position command speed dX _C / dt at ωt≈π / 2 is Can be approximated by That is, in a time around t = π / 2ω, a linear position command speed dX _C / dt including reversal of the moving direction with respect to the X axis is given. Time point
During the X-axis stop time from t ₁ to time t ₂ , the Y-axis can accurately follow the command, resulting in a shape error ε as shown in FIG.

The above is a description of the case where the position command speed dX _C / dt changes linearly including the sign reversal, but during multi-axis synchronous machining including the reversal operation of the feed axis, backlash of the mechanical part is generally caused. A shape error occurs in the axis reversal portion due to the occurrence of the axis stop time. As can be seen from the above equation (7), the shape error of this type can be reduced by increasing the position loop gain K _V, and the feed shaft stop time can be shortened. However, since the position loop gain Kv is limited by the rigidity of the feed shaft mechanism portion, there is a problem that it cannot be increased in a machine with low axial rigidity such as a large machine. Further, the lost motion including the deflection in the backlash of the feed shaft mechanism part is accurately grasped in advance, and the correction amount corresponding to the lost motion is given as the position command of the electric motor 2 at the time of the reversing operation of the feed shaft. A method of realizing the reversing operation of the feed axis is also conceivable. However, when the sliding resistance or the load fluctuates greatly, the deflection changes, so that it is difficult to accurately grasp the lost motion of the mechanism section.

The present invention has been made under the circumstances as described above, and an object of the present invention is to shorten the feed axis stop time during the axis reversing operation in the multi-axis synchronous operation of the feed axes of NC machine tools and the like. The purpose of the present invention is to provide a position control device for the feed shaft of an NC machine tool that can reduce the shape error that occurs in the axis reversing part.

(Means for Solving the Problem) The present invention relates to an electric motor, a first position detector (or a speed detector) coupled to the electric motor, a feed shaft driven by the electric motor, and a feed shaft. The present invention relates to a feed shaft position control device comprising a second position detector coupled to the feed shaft and a feed shaft control unit for controlling the position and speed of the feed shaft,
The object of the present invention is to provide a speed feedback signal calculation determining means, and to obtain a motor speed obtained from the first position detector (or speed detector) according to a calculation method or a calculation constant obtained by the calculation determining means, This is achieved by performing a composite calculation with the feed shaft speed calculated by the second position detector to obtain a composite speed of the electric motor and the feed shaft, and performing speed control using this composite speed as the speed feedback signal. It

(Operation) The present invention performs the speed control by using the composite speed of the motor speed and the feed shaft speed, which eliminates the influence of the feed shaft speed or the feed shaft speed, as the speed feedback signal when the movement of the feed shaft is reversed. This realizes a quick reversing operation of. That is, it has a speed calculation unit that calculates a composite speed of the motor and the feed shaft speed in a composite manner,
In addition, the calculation method of the speed calculation unit is (1) the position command value of the feed axis, (2) the position error between the position command value and the feed axis position,
(3) It is possible to determine the position control state of the feed axis based on the feed axis speed, and select the optimum calculation method according to the control state and the rigidity of the feed axis drive system.

By using the composite speed obtained from such a structure as the speed feedback signal, the position control that flexibly responds to changes in lost motion while maintaining the stability of the control system and realizes a quick reversal operation of the feed axis The device can be obtained.
As a result, the operation stop time at the time of the feed axis reversing operation is shortened, so that the shape error generated in the quadrant switching portion at the time of arcuate shape machining can be suppressed to be small.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention in correspondence with FIG. 7, and the same components are designated by the same reference numerals and described.

In the present invention, the position X _I of the table 5 detected by the inductors 6 and 7 is time-differentiated by the speed detector 19 in the feed axis controller 10A to obtain the table speed (feed axis speed) V _I. There is. Motor speed V _M and table speed
Each V _I is input to the speed calculation unit 18, a composite calculation is performed by the motor speed V _M and the table speed V _I, and the composite speed V is output from the speed calculation unit 18. This composite speed V becomes a speed feedback signal and is input to the subtractor 13.
The speed calculation determination unit 17 inputs the position command X _C , the position deviation Xe, and the table speed V _I , determines the control state of the position of the table 5 based on these, and the composite speed V in the speed calculation unit 18 is determined.
Or the signal PRM corresponding to the operation constant that defines the characteristic of the speed operation unit 18 is output when the operation method is previously determined by the speed operation unit 18.

The operation of such a configuration will be described.

The speed calculation determination unit 17 reverses the sign of the position command immediate dX _C / dt, which is the time derivative of the position command value X _C generated by the position command generator 1, and the position deviation Xe position command speed dX _C / dt. The sign inversion in the same direction changes the calculation method for obtaining the composite speed V which is the speed feedback signal in the speed calculation unit 18. As shown in FIG. 2, the speed calculation unit 18 is a switching circuit selection circuit 181 that selects either the motor speed V _M or the table speed V _I , and when the sign inversion is detected, the speed calculation determination unit 17 sets the table. The speed V _{I is} selected and becomes the speed feedback signal V. Select the table speed V _I in Table 5
Is continued until the reversing operation is started, and when the reversing operation is actually started, the speed calculation determination unit 17 detects this from the table speed V _I , and the selection circuit 181 selects the speed feedback signal V to the motor speed V _M. To change. After that, the selection of the electric motor speed V _M is continued until time elapses and the position command speed dX _C / dt and the position deviation Xe generate the sign inversion opposite to the above.

FIG. 4 and FIG. 5 explain the table operation in the quadrant switching section when an arc shape machining command is given to the position control device of the table 5 to which the present invention is applied. t <
Within ₁ hour, the speed feedback signal V is used as the motor speed.
Since V _M is selected, the table operation is the same as when the conventional position control device is adopted. And time t
= T ₁ , the table speed V _I is selected as the speed feedback signal V by the operation of the speed calculation determination unit 17.
Time until table 5 starts reversing operation t ₁ <t <t ₂
Table 5 is in a stopped state. Here, the amplification factor of the PID amplifier 14 for determining the speed Fupugein Kv Because normally be set high, the electric motor 2 in the table stop time T _O continues to generate a large torque. As a result, the electric motor 2 rapidly reverses. Then, when the time reaches t = t ₂ , the table 5 starts the reversing operation, so that the motor speed V _M is selected as the speed feedback signal V.

As described above, in the reversing operation of the electric motor 2 within the table stop time T _O at the time of the table movement reversing command, the high speed loop gain Kv is not utilized in the conventional method, and the position loop as shown in the above expression (7) is used. While it is determined only by the gain Kv, in the present invention, the control is performed with the amplification factor obtained by multiplying the position loop gain Kv by the high speed loop gain, so that the reversing operation of the electric motor 2 is completed in a shorter time than the conventional method. Can be made.

Therefore, according to the present invention, as shown in FIG. 6, it is possible to reduce the shape error .epsilon. Further, according to the present invention, since the motor reversing operation corresponding to the backlash of the table drive system is forcibly performed in the speed control loop, it is not necessary to grasp the lost motion of the drive system, and the sliding motion is eliminated. There is an advantage that it can flexibly cope with the change of the lost motion amount due to the change of resistance.

FIG. 3 shows many structural examples of the speed calculation unit 18 in the present invention. Generally, when the table speed V _I is used as the speed feedback signal V, the responsiveness of the table position should tend to improve, but since the table drive system is included in the speed control loop, the speed control system includes a drive system. There is a problem that the resonance phenomenon due to the natural frequency of is likely to occur, and as a result, the velocity loop gain Kv cannot be set high and the responsiveness cannot be improved. FIG. 3 is an example of the configuration of the speed calculation unit 18 in consideration of such a problem. When the transfer function of the signal converter 182 is G (ω), the speed feedback signal V is represented by the following equation.

V = V _M + G (ω) · (V _I −V _M ) = G (ω) · V _I + (1-G) · V _M (10) Here, the signal converter 182 is a first-order delay circuit. Then, Therefore, the time constant T becomes a calculation constant PRM that defines the characteristics of the speed calculation unit 18. In this example, the smaller the time constant T, the greater the influence of the table speed V _I on the speed feedback signal V.

In the example of FIG. 3, in the example in which the speed calculation unit 18 is the selection circuit 181 of FIG. 2 described above, the resonance phenomenon does not occur under the condition that the motor speed V _M is selected. By selecting a large time constant T according to the natural frequency and a small time constant T under the condition that the table speed V _I is selected in the example of FIG. 2, a rapid table reversing operation is performed. According to the configuration of the speed calculator 18 as shown in FIG. 3, not only the movement and reversal of the table 5 but also a part of the table speed V _I is used as the speed feedback signal even when the table 5 is moved in one direction. It can be expected that the response and the like in the case of reducing the position error caused by the change in the amount of flexure will be improved.

The transfer function of the signal converter 182 is not limited to the first-order lag system. It is natural for the purpose of the signal converter 182 that the function of the characteristic is such that the influence of the table speed V _I is large in the low frequency region.

In the embodiment described above, the position detector 3 is attached to the electric motor 2.
, And the position detection value X _M obtained thereby is time-differentiated by the speed detection unit 16 to obtain the electric motor speed V _M. However, the speed detector is connected to the electric motor 2 to directly obtain the electric motor speed. Is also good.

(Advantages of the Invention) As described above, according to the position control device of the feed shaft of the present invention, the response delay at the time of the feed shaft reversing operation when generating the position command including the movement reversal on the feed shaft becomes small, It is possible to accurately follow the movement of the feed axis with respect to the position command.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 3 and FIG. 3 are circuit diagrams showing the detailed configuration of the speed calculation unit, FIGS. 4 to 6 are diagrams for explaining the operation of the present invention, and FIG. 7 is a block configuration diagram showing an example of a conventional device. 8 to 10 are diagrams for explaining the operation. 1 ... Position command generator, 2 ... motor, 3 ... position detector, 5 ... table, 10,10A ... feed axis control, 11,13
…… Subtractor, 14 …… PID amplifier, 16 …… Speed detection unit, 17
...... Speed calculation determination unit, 18 ・ ・ ・ Speed calculation unit, 19 ・ ・ ・ Speed detection unit.

Claims (3)

[Claims] 1. A motor, a first position detector coupled to the motor, and a feed shaft driven by the motor.
In a feed axis position control device including a second position detector coupled to the feed axis and a feed axis control unit for controlling the position and speed of the feed axis, a speed feedback signal calculation determining means is provided. The motor is obtained by compositely calculating a motor speed obtained by the first position detector and a feed speed calculated by the second detector according to a calculation method or a calculation constant obtained by the calculation determining means. And a feed shaft position control device, wherein a composite speed of the feed shaft is obtained, and the composite speed is used as the speed feedback signal to perform speed control. 2. The calculation determining means calculates a calculation method or a calculation constant of the speed feedback signal based on a position command value of the feed axis, a deviation between the position command value and a position detection value, and the feed axis speed. Claim 1 to be decided
The position control device for the feed shaft described in. 3. The position control device for a feed shaft according to claim 1, wherein a speed detector is used in place of the first position detector.