JPH07111645B2 - Arc trajectory control method for multi-axis feed drive mechanism - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an arc locus control method for a multi-axis feed drive mechanism such as an NC machine tool or a laser beam machine, and particularly to improvement of locus accuracy.

[Prior Art] In order to obtain good machining accuracy in multi-axis feed mechanisms such as NC machine tools and laser beam machines, it is necessary to minimize the trajectory error in the trajectory control of each feed drive axis.

FIG. 9 is a control block diagram showing the control of each axis of the conventional multi-axis feed mechanism. As shown in the figure, the position control device 1, the speed control device 2, the adder 3, and the feed drive mechanism 4 of the control device are shown. And form a closed-loop control system.

In the control system shown in FIG. 9, the NC device (not shown) sends the position command x _ir for each axis to the position control device 1 via the adder 3, and the position control device 1 sends the position command x _ir for each axis. A speed command for each feed drive shaft is calculated based on _ir and sent to the speed control device 2. The speed control device 2 drives the drive motor of each feed drive mechanism 4 based on a predetermined speed command to give a predetermined feed. At this time, the tacho generator of the feed drive mechanism 4 detects the rotation speed of the drive motor, and the pulse generator of the feed drive mechanism 4 detects the response position of each axis and feeds it back. In such a control system, the position control device 1 normally uses proportional control so that the actual position x _i does not overshoot the target position x _ir .

[Problems to be Solved by the Invention] In such a conventional control method, as shown in FIG. 10, the actual position x _i of the feed drive shaft is steady with respect to the target position x _ir of each axis every moment. Follows with a delay of speed deviation. Due to this tracking delay, for example, when driving two axes on an arc locus, the actual response locus 6 becomes smaller than the command locus 5 as shown in FIG. 11, and a locus error 7 occurs. However, there is a problem in that good processing accuracy cannot be obtained.

In order to solve such a problem, a circular arc trajectory control method characterized by performing comparative example control using the square of the circular arc center angle deviation as a feedback amount in addition to the independent control for each axis is provided. Proposed by the applicant (filed on February 24, 1987, Japanese Patent Application No. 62-39264).

FIG. 12 is a block diagram showing an example of the two-axis control of the arc locus control method X, Y. X as shown
The actual position x in the X-axis direction and the actual position y in the Y-axis direction during driving, which are respectively detected by the pulse generators of the X-axis and Y-axis feed drive mechanisms 4X and 4Y, are sent to the arc center angle deviation calculator 8 and the arc center angle The deviation calculator 8 uses the actual response positions x and y and the command positions x _r and y _r sent from the NC unit 9 to determine the center angle θ of the response position of the arc locus, the arc center angle deviation Δθ, and the arc center angle deviation Δθ.
calculating a square ([Delta] [theta]) ² of theta, proportional control device 10X of the center angle theta and the square of the arc center angle deviation (Δθ) ² X-axis and Y-axis, 10
Send to Y. The proportional control devices 10X and 10Y perform proportional calculation processing based on these values, and the calculation results are added to the adders 11X and 11Y.
Send to. Each adder 11X, 11Y is the speed command _r , for each axis calculated based on the position command and the response position by the position control device 1X, 1Y, respectively.
_r proportional controller 10X, adds the calculation value calculated by the 10Y, the speed command value to zero in the X-axis component and a Y-axis component of the arc contour deviation Is calculated and the speed control devices 2X and 2Y are controlled so that the feed trajectory error becomes zero.

However, in the case of this method, it is necessary to add a new signal into the conventional position control loop through the adders 11X and 11Y, and in order to implement this method using the conventional control device, It is necessary to change the control system, and there is a problem in that it costs a lot to change the position control system.

The present invention has been made to solve the problems according to the present invention, and an object thereof is to propose an arc locus control method for a multi-axis feed drive mechanism that can improve locus accuracy with a simple configuration. is there.

[Means for Solving Problems] According to an arc locus control method of a multi-axis feed drive mechanism according to the present invention, a target arc center angle in a target arc locus and a radius of the target arc locus are calculated from position target values given to the multi-axes. Then, using the calculated target arc center angle, the arc center angle and arc center angle deviation in the arc locus control system are estimated, and the estimated arc center angle predicted value and the arc center angle deviation are 2
Using the predicted value of the power, the amount obtained by multiplying the radius of the target arc locus by the predicted value of the square of the arc center angle deviation and 1/2 is distributed to each axial direction based on the predicted value of the arc center angle. The axis component is obtained as a position correction value of the position target value of each axis, and by adding these various position correction values to the position target value, feedforward compensation of the position control system and speed control system of each axis is performed. It is characterized by being controlled by performing.

[Operation] In the present invention, the position target value of the time function given to each axis is corrected on the basis of the predicted value of the arc center angle in the arc locus and the predicted value of the square of the arc center angle deviation. Feed-forward compensation of the position control system and speed control system of each axis with the position correction value of the axis to cancel in advance the radial error as shown in the second term on the right side of the equation (4) described later. You can Therefore, the influence of the disturbance is canceled out without changing the position control system, and the trajectory error in the radial direction of the arc trajectory is reduced.

[Embodiment] First, in explaining an embodiment of the present invention, the principle of arc locus control of the multi-axis feed drive mechanism of the present invention is as shown in FIG. 1, a biaxial feed drive mechanism composed of an X axis and a Y axis. It will be explained based on.

In FIG. 1, 5 is a command locus, 6 is a response locus,
Command trajectory 5 is an arc having a radius r ₀ around the coordinate origin 0 Consider the ideal case. Now, as shown in FIG. 1, the angle formed by the radial direction of the command position P ₀ (x _r , y _r ) on the command locus 5 in the X-axis direction, that is, the central angle is θ ₀ , and the response on the response locus 6 The radius of the position P (x, y) is r, the central angle is θ, and the central angle deviation θ ₀ −θ between the command position P ₀ and the response position P is Δθ.

Now, for example, what is generally used as the position control devices 1X and 1Y used in the conventional control device shown in FIG. 9 is a proportional control device, and if the proportional gain is K _p , the output from this proportional control device is is the response position P (x, y) command speed _r of the command speed _r and Y-axis direction of the X-axis direction in is expressed by the following equation. _{r = K p (x r -x} ) ...... (1) r = K p (y r -y) ...... (2) command speed _ref in the radial direction in response position P (x, y) is the orthogonal coordinate system Considering the conversion of the commanded speed expressed by to the polar coordinate system, it is expressed by the following equation.

Substituting equations (1) and (2) into equation (3) and converting to polar coordinate system Therefore, the command speed _{ref in the} radial direction is expressed by the following equation.

Considering the equation (4), a block diagram of the control system in the radial direction is shown in FIG. Expression (4) is an expression expressing only the portion surrounded by the dotted line in the control system of FIG. That is, FIG. 2 is a block diagram for analyzing how the radius of the arc locus behaves when performing the arc locus control using the orthogonal two-axis feed drive mechanism. The single-axis feed drive mechanism does not physically exist. From this equation (4), the control system in the radial direction is compared with the system with the constant command value r ₀ . The disturbance is added. Therefore, the response value r is the command value r ₀
There is a deviation with respect to, and this deviation becomes the trajectory error.

Therefore, the central angle deviation Δθ of the response position P can be calculated by the equation (5). Equation (6) is calculated for the command speed _{ref in the} radial direction using the calculated central angle deviation Δθ. If u _r is added, the disturbance can be canceled and the trajectory error can be reduced.

If u _r obtained by the above equation (6) is transformed from the polar coordinate system (r, θ) to the orthogonal coordinate system (x, y), u _x and Y of the X axis component
U _y axis components following equation (7), obtained in (8).

These u _x and u _y are command speeds shown in equations (1) and (2),
It is possible to improve the accuracy of the arc locus by adding to each of the above. The X and Y axes Is determined by the following equations (9) and (10).

The expressions (9) and (10) are represented by block diagrams as shown in FIGS. 3 (a) and 3 (b). In FIG. 3, (a) shows an X-axis block diagram, and (b) shows a Y-axis block diagram.

As shown in FIG. 12, the arc locus control method previously proposed by the applicant of this application is based on the above principle. However, in order to implement the control method shown in FIG. 12 in a conventional control system, it is necessary to change the X-axis position control loop 12X and the Y-axis position control loop 12Y. Therefore, the X-axis and Y-axis block diagrams shown in FIGS. 3 (a) and 3 (b) are modified as shown in FIGS. 4 (a) and 4 (b), respectively. That is, the X-axis Signal and Y axis By sending the signal of and to the command position x _r , y _r of each axis and then sending it to the position control loop 12X, 12Y, It is not necessary to add the above signal to the position control loops 12X and 12Y, and it is not necessary to change the position control system.

On the other hand, the command speed _ref in the central angle direction is expressed by the following equation.

Expression (1), Expression (2) and Expression (12) below are added to Expression (11). Substituting and transforming Then, using the approximate expression of sin (θ ₀ −θ) = (θ ₀ −θ), and approximating r ₀ / r = 1, the command speed in the central angle direction
_ref is expressed by the following equation. _ref = K _p (θ ₀ −θ) (13) Considering this equation (13), a block diagram of the control system for the central angle is shown in Fig. 5. Expression (13) is an expression that expresses only the portion surrounded by the dotted line in the control system of FIG. That is, FIG. 5 is a block diagram for analyzing how the radius of the arc locus behaves when performing the arc locus control using the orthogonal two-axis feed drive mechanism. The single-axis feed drive mechanism of No. does not physically exist. From the equation (13), the control system in the radial direction is 1 with respect to the known target value θ ₀ of the arc center angle.
It is the next control system. Therefore, if the relationship shown in FIG. 5 is used on the basis of the target value θ ₀ of the arc center angle at every moment, the predicted value of the arc center angle at every moment is calculated. And predicted value of arc center angle deviation Can be asked.

That is, when the transfer function of the velocity control system in the central angle direction is G (S) in FIG. With the relational expression Can be asked.

Therefore, instead of θ and Δθ, the predicted values As shown in FIGS. 6 (a) and 6 (b), respectively.
If a control system including the target position generators 13X and 13Y for the axes and the position control loops 12X and 12Y for the X and Y axes is configured, the arc locus error can be greatly reduced as in the control method shown in FIG.

The control system shown in FIGS. 6 (a) and 6 (b), in the stage of generating the target position given to the position control loop of each axis, and Original position target value
x _r, it comes to control how to modify the y _r.

In addition, this and Is the ideal case and the compensation value and And the arc locus error can be reduced even if k is a constant close to 1/2. Also, Instead of, cos θ ₀ , sin θ ₀ may be used.

An embodiment of the present invention based on the principle of arc locus control of the multi-axis feed mechanism will be described below with reference to the block diagram shown in FIG. 7 and the flow chart shown in FIG. 7th
In the figure, 1X, 1Y to 4X, 4Y are exactly the same as the conventional control system shown in FIG.

First, from NC device 9, arc center angle and arc center angle predicted value calculator
The target values x _r and y _r that change momentarily at time t are input to 14 (step S1). Arc center angle / arc center angle predicted value calculator
14 is an arc center angle target value θ ₀ and a target arc locus radius r _{0 is} calculated from the input X axis and Y axis target values x _r and y _r (step S
2) Based on the calculated target value θ ₀ , use the relationship shown in FIG. And arc center angle deviation predicted value Calculated and calculated predicted value And the radius r ₀ of the target arc locus are sent to the compensation value calculator 15 (step S3). Compensation value calculator 15 predicts arc center angle deviation And the radius r ₀ of the target arc locus The momentary value of is calculated (step S4). this Value and arc center angle predicted value X-axis feed-forward compensator 16X Value is calculated, and Y is calculated by the Y-axis feedforward compensator 16Y.
Axis feedforward compensation value Is calculated (step S5). These X-axis and Y-axis feedforward compensation values are added to target values x by adders 17X and 17Y, respectively.
_r, are summed to y _r, every moment of the corrected target value ▲ x
^* _r ▼, ▲ y ^* _r ▼ are calculated (step S6), and the calculated correction target values ▲ x ^* _r ▼, ▲ y ^* _r ▼ are stored in the correction target value storage device 18 (step S7).

The correction target values ▲ x ^* _r ▼ and ▲ y ^* _r ▼ that are stored in the correction target storage device 18 every moment are input to the machining time t when the X and Y axes are driven (step S8). It is sent to the position control system and the Y-axis position control system (step S9) to control the X-axis and Y-axis feeds to cancel the trajectory error.

In the above embodiment, the case where the target value correction is performed in advance before the driving of the X axis and the Y axis and is stored in the corrected target value storage device 18 has been described. The target value correction process is performed at the time of actual driving without using the device 18, and the corrected target values ▲ x ^* _r ▼ and ▲ y ^* _r ▼ corresponding to the driving time are obtained to determine the X-axis position control system and the Y-axis. Even if it is sent to the position control system, the trajectory error can be canceled as in the above embodiment.

Further, in the above embodiment, the case of the two-axis feed drive mechanism has been described, but the case of the three-axis feed drive mechanism can be applied in the same manner as the above-mentioned embodiment.

EFFECTS OF THE INVENTION As described above, according to the present invention, the position target value of each axis is corrected in advance based on the predicted value of the arc center angle and the predicted value of the square of the arc center angle deviation. Since the same result can be obtained by canceling the disturbance applied in the radial direction of, the trajectory accuracy of the arc trajectory can be significantly improved.

Further, since the trajectory accuracy is improved by correcting the position target value of each axis, it is not necessary to change the conventional position control system, and the trajectory accuracy can be improved easily and at low cost. Have.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the operating principle of the present invention, FIG. 2 is a block diagram of a control system relating to the radial direction of the arc locus shown in FIG. 1, and FIGS. 3 (a), (b) and 4 Figure (a),
(B) is a block diagram showing a control system based on the above operation principle, (a) is an X-axis block diagram, (b) is a Y-axis block diagram, and FIG. 5 is shown in FIG. Block diagram of the control system relating to the central angle of the arc locus, FIG. 6 (a),
(B) is a block diagram of a control system based on the operation principle of the present invention, (a) is an X-axis block diagram, and (b) is Y.
FIG. 7 is a block diagram of a shaft, FIG. 7 is a block diagram showing an embodiment of the present invention, FIG. 8 is a flow chart showing the operation of the embodiment shown in FIG. 7, and FIG. 9 is each conventional multi-axis feed mechanism. Control block diagram for each axis, FIG. 10 is a tracking delay characteristic diagram of the feed drive shaft, FIG. 11 is an explanatory diagram of a trajectory error according to a conventional example, and FIG. 12 is an arc trajectory previously proposed by the applicant of this application. It is a block diagram which shows control. 1X, 1Y …… Position control device, 2X, 2Y …… Speed control device, 3X, 3
Y, 17X, 17Y …… Adder, 4X, 4Y …… Feed drive mechanism, 9 ……
NC device, 14 ... Arc center angle / arc center angle predicted value calculator,
15 ... Compensation value calculator, 16X ... X-axis feedforward compensator, 16Y ... Y-axis feedforward compensator, 18 ...
... modified target value storage device.

Claims (1)

[Claims] 1. A circular arc control for moving a tool or a work table in an arc shape by independently controlling the positions of orthogonal multi-axis feed drive mechanisms and giving a position target value of each axis as a function of time. , In the arc control method of the multi-axis feed drive mechanism in which the position control system includes the speed control system as a minor loop and the control operation of the position control system and the speed control system is proportional operation, the target arc is calculated from the position target value given to each axis. The target arc center angle in the trajectory and the radius of the target arc trajectory are calculated, the arc center angle and the arc center angle deviation in the arc trajectory control system are estimated using the calculated target arc center angle, and the estimated arc center angle is calculated. 2 of predicted value and arc center angle deviation
Each axis that is obtained by multiplying the radius of the target arc locus by the squared predicted value of the arc center deviation and 1/2 by using the predicted value of the squared power and distributed in each axial direction based on the predicted value of the arc center angle. Is calculated as a position correction value of the position target value of each axis, and by adding these various position correction values to the position target value, feedforward compensation of the position control system and speed control system of each axis is performed. A method for controlling an arc locus of a multi-axis feed drive mechanism, which is characterized in that: