Research On Variable Structure Control Theory Of Rotary Type Non-circular Parts Grinding Process

The rotary non-circular parts such as camshaft, crankshaft and the rotor cavity in the engine are the key components in the engine, and the profile accuracy of this kind of parts affects the performance of the engine directly. The grinding process of such parts is performed through X-C biaxial linkage motion, more exactly, it is the linear motion of X axial, which followed the rotary motion of C axial, that formed the non-circular profile. There are many factors that influence the contour accuracy of these parts, such as tracking position error, the shock of velocity and acceleration, the fluctuation of grinding force, etc. In order to improve the profile accuracy of non-circular parts, it is important to research the control methods of the non-circluar contour error.The rule of non-circular contour grinding force which changed with non-circular profile curvature is revealed. The griding force of an abrasive as a cutting tool is analyzed and the cutting volume is calculated. Based on the X-C linkage grinding theory, the grinding force model of Non-circular parts is built. The curvature of non-circular contour is an important factor that affects X-C linkage grinding force, the relationship between the grinding force and the curvature of non-circular contour is analyzed quantitatively. The non-circular grinding force such as Cam, elliptical, and rotor cavity in the engine are calculated and simulated respectively. The X-C linkage grinding force is studied on the influence of the non-circular profile grinding process, the relationship between the two axis motion position and X-C linkage grinding force is discussed.The position error of X and C axis tracking control are studied respectively. In order to improve the tracking performance of the servo axis, sliding mode variable structure control strategy is proposed to apply to the grinding machining of non-circular parts. The SMVSC is compared with the conventional PID control by simulation, including the control accuracy and anti-disturbance ability. The SMVSC can provide the high tracking accuracy and strong anti-interference capability. The strong robustness of the sliding mode variable structure control method makes the axis motion of non-circular grinding machine have better tracking performance.The method of fuzzy control is applied to the variable structure control in the non-circular parts grinding process. To solove the problem of chattering in SMVSC, the fuzzy controller which adjusts the switch control coefficient real-time is applied.According to analysis with Matlab/simulink simulation, the conclusion can be made that equivalent sliding mode control, which is based on fuzzy adaptive exponential reaching law, can restrain the chattering effectively. The fuzzy SMVSC has the ability to perform high accuaracy grinding, and retain the features of strong robustness in non-circular grinding process. It is a good idea to research the way of variable structure control for the high precision grinding of non circle contour.The relationship between the error of the non-circular contour and the position error of the two servo axis is studied. By analyzing the contour feature of non-circular parts, the error model of the non-circular contour caused by the single servo axis lag is constructed.The controll method of coupling-enhanced is proposed. The method is suitable for X-C linkage motion machine. Because the X-C linkage motion is different from the X-Y linkage motion, according to the idea of cross coupling control and the principle of X-C linkage motion, the coupling enhanced controller which is based on the variable structure control is designed. The X axis and C axis tracking error are calculated into the non-circular profile error and compared with each other, the compared result is applied to slower axis so that it can follow the faster one quickly. This coupling-enhanced controller can reduce the contour error of non-circular parts effectively.The error measurement tests are completed on the NC camshaft grinding machine. In order to verify the validity of simulation results, the datas of the X axis and the C axis tracking delay in the cam grinding process are obtained. The experimental platforms of X axis and C axis are established. The PID control and sliding mode variable structure control and fuzzy sliding mode variable structure control method are verified on the experimental platforms. The conclusion is that fuzzy SMSVC can provide high precision in the servo-axis position tracking. The X-C linkage coupling enhanced controller based on the variable structure and fuzzy variable structure are designed and simulated. The control method of X-C linkage coupling enhanced can accelerate the X axis tracking speed and decrease its lag so that the motion of X-C is synchronous.