KR20000033203A - Method of pr0cessing while keeping precision degree at corner upon processing at high speed - Google Patents

Abstract

PURPOSE: A method is provided to follow a designated speed within a range of satisfying an outline error that a user sets up at the corner and to precisely control at a high speed by automatically accelerating and decelerating. CONSTITUTION: After a machine having a capability of higher degree is approximated into a first system(10), a corner response of the first system is shown into a reference track and a system band width(20). An outline error is defined and an outline error function is obtained by using the outline error(30). In addition, the deceleration speed at the corner where the given outline error is satisfied is obtained by using the outline error function. Then a high-speed process is automatically performed at the corner based on the deceleration speed so that the range of the outline error is satisfied, and the automatic high-speed process is possible.

Description

How to process while maintaining precision at the corners during high speed machining of machine tools

The present invention relates to a method for high-speed processing while maintaining precision by automatically generating a speed trajectory satisfying a contour error set by a user at a corner in high-speed machining using a computer numerical control (CNC) machine tool. will be.

In general, the most important thing in the machining process using a computer numerically controlled machine tool is to reduce the machining time by transporting as fast as possible while maintaining constant accuracy at all times.

The contour error, which can represent the precision of the controller, appears largely at the corner where the processing shape changes rapidly. The feed speed and the contour error are proportional to the characteristics of the PID controller. Therefore, the contour error must pass through the corner at low speed to satisfy the accuracy. Therefore, if you do not use the functions such as in-position, dwell, etc., the processing time is increased by feeding at low speed even in the straight section that can be transferred at high speed. Inconvenient to determine the corners and there is an inefficient problem, because the uniform stop for various transfer conditions and the angle of the corners.

The present invention has been made to solve the problems of the prior art operating as described above, the main object is to follow the specified speed within the range that satisfies the contour error set by the user at the corner, while automatically accelerating and decelerating precisely and fast To provide a control method.

1A and 1B are graphs showing edge response comparisons between an actual higher order system and a first order approximated system,

2a and 2b is a graph showing the velocity trajectory at the preferred corner required by the present invention,

3A and 3B are graphs illustrating a method for defining contour errors at the corners of the present invention;

4 is a graph showing the trajectory used in the present invention,

5A and 5B are graphs comparing the values of the contour errors actually measured at the edges with those obtained in the present invention;

6 is a graph showing a velocity trajectory to which the control method according to the present invention is applied;

7 is a graph showing a corner trajectory error to which the control method according to the present invention is applied;

8A and 8B are graphs showing cornering responses with and without the control method according to the present invention;

9 is a flow chart showing a process of processing at high speed by applying the control method of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more apparent from the following detailed description based on the accompanying drawings in order to achieve the above object.

The method of maintaining the precision at the corners of the machine tool using the control of the present invention is to approximate the machine tool modeled as a higher order system to the primary system, and the corner response of the primary system is represented by the reference trajectory and the system bandwidth. We define the contour error and find the contour error function. In addition, by using numerically the contour error function, the deceleration speed at the corner satisfying the given contour error is obtained, and it is configured to perform the high speed machining automatically at the edge according to the deceleration speed.

Therefore, the method of approximating the machine tool to the primary system and calculating the contour error is as follows. The bed of a machine tool is modeled as a higher-order system of 2nd order from the servomotor input to the position of the bed. The response of such a system is expressed as a function of time, making it difficult to form a direct relationship between the X- and Y-axis responses. Therefore, the contour error must be measured or numerically obtained from an experimental or simulated experimental response. If the system is expressed as a primary, the time variable can be eliminated and the contour error can be calculated. In the present invention, the higher-order system is approximated as a primary system based on bandwidth. Since the mechanical servo system acts as a low pass filter, the corner response of the real system and the first-order approximation system is similar to the obtuse angle and the example. In another preferred embodiment of the present invention, the system used in the embodiment is a bed of Daewoo Heavy Industries ACE-V30 type and the closed loop transfer function of each axis is experimentally shown in equations (1) and (2).

The above embodiment configures a digital feedback controller having a temporarily sampled time of 0.1 ms and inputs a desired reference position trajectory as a sweep sine function using a dynamic signal analyzer. The closed loop system was then modeled using the measurement locations obtained at that time. In addition, the proportional controller is designed so that the bandwidth is 8Hz after calculating the transfer function from the input voltage of the servomotor to the bed position. Therefore, the transfer function of the first approximation system can be expressed as Equation 3.

As shown in FIG. 1, the responses of the secondary system and the approximation system with respect to the corners of the acute and obtuse angles are compared, and the two responses are almost identical.

The shape of the edge is as shown in Fig. 2a and the velocity trajectory at this time is given as the edge velocity as shown in Fig. 2b. V _c When the time variable is removed from the primary system response of each axis when decelerating to, it is expressed concisely as in Equation 4 below.

(CD section response)

C ₄ + C ₅ ln + C ₆ , n _D ≤n (DE interval response)

Here, (n, m) is a position in the m, n coordinate axis set as shown in Figure 2a, each coefficient and constant is represented by a constant constituting the reference trajectory and the bandwidth of the system.

Since the corner response of the primary system always moves inside the corner as shown in Equation 4, it shows the shape as shown in FIG. 3A. Therefore, the contour error at the edge is the minimum distance from point C to the response curve, E _c However, since it is difficult to obtain a clear solution, the present invention is approximately obtained as shown in FIG. 3B. As shown in the figure, the straight line p is the bisector of the corner angle, and the straight line q is in contact with the system's response during the straight line perpendicular to the straight line p. The contour error of the system is approximated by the distance between point C and the straight line q. The slope of the line q in the nm coordinate system is tan (- ), And the slope of the corner response is If we assume 결과 0, we get the same result as in Equation 5 below.

C ₅ + C ₆ , DE section

Contact point of straight line q and corner response ( n ₁ , m ₁ ), The straight line q is m = tan (- ) (n- n ₁ ) + m ₁ The contour error at this time is as shown in Equation 6 below.

In order to confirm the performance of the contour error prediction method proposed in the present invention, the reference figure of FIG. 4 is set. One embodiment for this is to start at the origin and to feed in a clockwise direction, the contour error measured when the feed speed is increased by 100mm / min from 200mm / min to 600mm / min and the contour error calculated by the new method Compared to FIG. The measured contour error is measured from the response obtained by simulating the system shown in equations (1) and (2). In the case of FIG. 5A which does not perform acceleration and deceleration and FIG. 5B which decelerates to half of the feed rate at the corner, it can be seen that the proposed method predicts the edge contour error of the actual model well.

In the above, the edge contour error using the reference trajectory, system bandwidth, and corner angle, E _c The function f for predicting is given in Equation 7 below.

E _c = f (a, V ₁ , V ₂ , V _c , A, θ)

When machining with a computer numerical control machine tool, the edge feed rate that satisfies the given contour error rather than predicting the error as shown in Equation 7 above. V _c Since we need to find the allowable contour error, E _c ^a Configure a function g that sets the edge deceleration rate that satisfies This is shown in Equation 8 below.

V _c = g (a, V ₁ , V ₂ , a, θ, E _c ^a )

In this case, since the function g of Equation 8 cannot be obtained from Equation 7, the condition given by the function f is satisfied. V _c Get the numerical value of In other words, the contour error at the edge V _c Minimum when = 0 ( E _c ^min ) V _c = min ( V ₁ , V ₂ ) When max ( E _c ^max ) Therefore, if the allowable contour error is equal to Equation 9,

E _c ^min ≤E _c ^a ≤E _c ^max

Corner deceleration speed to satisfy the given allowable contour error, V _c Is always in the range as shown in Equation 10 below.

0 ≤ V _c ≤ min (V ₁ , V ₂ )

Since the solution is limited in scope, use dichotomy to find the solution.

In confirming the performance of the control method for the corner, the control method of the present invention was applied to another preferred embodiment of the present invention by setting the allowable contour error to 0.03 mm with respect to the reference figure of FIG. 4. When the feed speed is 1000mm / min, the reference speed trajectory is shown in FIG. 6, but when the corner angle is large, the speed does not decelerate or decelerates a little and the speed decreases as the angle of the angle decreases. You can check the setting of the normal deceleration speed.

The edge contour error shown in FIG. 7 is measured from a response to an embodiment of the present invention, and even the corners of the same angle have a maximum value because of differences due to friction depending on the conveying direction. It can be seen that for various feed rates and edge angles, most edge contour errors are less than 0.03 mm permissible, and in some cases the tolerances of the feedback system are larger than expected due to unpredictable disturbances such as friction. Occurs. 8 shows enlarged corners of the acute angle and the obtuse angle, and it can be seen that the corner response is improved after application than when the corner deceleration is not applied.

As a result, as shown in FIG. 9, after approximating a machine tool modeled as a general higher order system to a primary system (10), the edge response of the primary system is represented by a reference trajectory and a system bandwidth (20). . Then, the contour error is defined and the contour error function is obtained using the contour error (30). The contour error function is numerically used to calculate the deceleration speed at the corner satisfying the given contour error (40). By performing the high-speed machining automatically at the corners (50), it satisfies the given contour error range and enables automatic high-speed machining.

The present invention can be variously modified and can take various forms and only the specific embodiments thereof are described in the detailed description of the invention. It is to be understood, however, that the present invention is not limited to the specific forms mentioned in the detailed description of the invention, but rather includes all modifications, equivalents, and substitutions within the spirit and scope of the invention as defined by the appended claims. It should be understood to do.

According to the present invention, a method for estimating edge contour error by reference trajectory and system bandwidth is proposed in order to maintain precision at corners with low precision during high-speed machining, and by using the method, the edge contour for edge response within an allowable contour error is used. By presenting the control method of the present invention, it is evident that the contour error of the edge is ensured, so that it is a very advantageous invention capable of high speed machining that satisfies a given contour error range without automatically requiring a separate operation at the corner and automatically accelerates and decelerates.

Claims (1)

In the method of maintaining the precision at the corners during high speed machining of machine tools, Approximating a machine tool modeled as a higher-order system to a primary system, representing edge responses of the primary system as reference trajectories and system bandwidths, defining contour errors and obtaining contour error functions, and numerically analyzing contour error functions Corners during high-speed machining of a machine tool, characterized by sequentially performing steps of obtaining a deceleration speed at an edge satisfying a given contour error and automatically performing a high-speed machining at the corner according to the obtained deceleration speed. How to process while maintaining precision.