A method to improve the precision of grinding. That is, the relationship curve of each linkage axis command with time (herein referred to as the command curve) is optimized while keeping the linkage relationship between the axes unchanged. Find an optimal command curve, under the premise of satisfying a certain productivity, make the metal wear rate fluctuation, servo axis speed, acceleration and acceleration change rate as small as possible, and make the frequency component of the input curve as single as possible.
In this case, accuracy can be improved without changing the productivity and without changing the hardware. The forming motion of the camshaft is composed of a reciprocating linear (X-axis) motion of the grinding wheel frame and a rotational motion (C-axis) of the workpiece. This paper mainly considers the following factors affecting the machining accuracy: grinding point line speed, servo axis speed, acceleration and acceleration rate, frequency component of the command curve. From the perspective of improving the precision of grinding, the linear velocity of the grinding point should be changed as small as possible. The absolute value of the servo axis speed should not be too large. The absolute value of the acceleration and acceleration rate should be small. The frequency of the input curve should be small. The composition should be as small as possible. If the frequency component of the input curve cannot be reduced, the amplitude of the high frequency component should be as small as possible. Many of the above factors are related to each other. One of the reductions may cause another increase. It is necessary to comprehensively consider all the above factors to obtain a better result. At the same time, some effects must be considered in the actual grinding process. Other factors in the precision of grinding.
The system has a total of 8 performance indicators, and a unified objective function is synthesized by weighted addition. The purpose of optimizing the command curve is to minimize the equation so that each factor has the least impact on the accuracy of the grinding process. In summary, the optimization model of the system is written as min(F(a1, a2,...an) where the parameters to be optimized are the parameters for determining the command curve. Minimize the formula and find the best by a1, a2,...an The expression curve reduces the negative factors affecting the precision of grinding processing, so as to improve the processing precision. The description of the command curve uses the function to express the curve cluster that satisfies certain constraints. This is called the description of the curve. The parameters a1, a2, ... an to be optimized are used to express a set of curves, and the expression should be simple and can approximate the curve of any shape. This paper uses a relatively simple polynomial expression.
Optimization results and impact on grinding accuracy The optimization object in this paper is more complicated, so it is carried out by genetic algorithm. In order to compare the results of workpiece constant line speed grinding, constant angular speed grinding and optimization, the same camshaft model and the same machining efficiency are selected. The average workpiece speed during machining is 1r/s, and the selected one is Wuxi. The camshaft of the camshaft factory. Before optimization, the weight parameters in the objective function must be determined. The weight parameters are mainly determined based on the measured acceleration dimensions and the parameters of the servo motor. The command curve of the C axis is described using a seventh degree polynomial. Considering the grinding of this type of camshaft, the linear velocity of the grinding point changes relatively small, the acceleration is relatively large, and the rate of change of acceleration and acceleration will be the main consideration. No other factors are considered for grinding. The influence of quality, in addition to the influence of the dimension, the main parameters selected are as follows: A = 0.5, B = 1, C = 1, D = 0.001, E = 0.001, F = 1, G = 1, H After the =0 command curve is optimized, the dynamic parameters such as speed, acceleration and acceleration of the servo axis change. The maximum acceleration of the C-axis is greatly reduced compared to the constant-line speed grinding, which is only 5% of the workpiece's constant line speed grinding. The angular acceleration rate of change is more reduced, and the X-axis acceleration is also reduced by nearly 30%, which will reduce the error caused by insufficient rigidity of the grinding wheel frame system. The proportion of the high frequency components of the command curve is greatly reduced. The maximum speed has increased, but the speed is still very low. The line speed of the grinding point has a certain change, and the ratio of the maximum minimum speed is 1.34.
(Finish)
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