[Abstract] This thesis studies the mathematical motion model for cam grinding based on open architecture. The hardware and software of the control system based on open architecture are designed. Some control algorithms are presented for canl grinding. Key words: open architecture; NC; cam grinding . For camshaft grinding, the traditional machining method is to use ordinary grinding wheels and a template for machining. This method has shortcomings in terms of grinding process, control method, and machining accuracy. With the development of CNC technology, especially since the 1990s, with the development of open architecture CNC technology, camshaft grinding methods have been continuously updated. A new machining method is to use superhard CBN grinding wheels as grinding tools to perform fully CNC high-speed grinding of camshafts. The principle is as follows: By establishing a mathematical relationship model between the grinding point on the cam profile and the workpiece rotational angular displacement, a computer-controlled grinding wheel tracks the corresponding curve while ensuring a certain feed motion to complete the grinding of the cam surface profile. All processes are completed in one operation. 1 Mathematical Model of Two-Axis Linkage in Cam Grinding In Figure 1, the center of the base circle in the cam profile is taken as the origin 0. The cam workpiece rotates around point 0, while the grinding wheel feeds horizontally to ensure that the grinding wheel and workpiece are in contact grinding at every moment of workpiece rotation. Assuming that the grinding point is M after the workpiece has rotated through a certain angle, the coordinates of the corresponding grinding wheel center 0 (distance from the grinding wheel center point to the cam rotation center point 0) are: Where: pμ and aμ are the rotation radius and deflection angle of the corresponding grinding point on the cam profile. It is assumed that the initial positioning angle is 0. 2 Design of Camshaft Grinding Control System Based on Open CNC The camshaft grinding CNC system uses a PC bus industrial control computer (IPC) as the hardware platform. With the development of PC technology, including software and hardware, the powerful programming software resources provided by PCs have shortened the development cycle of CNC systems. The rapid data processing capabilities of PC hardware greatly enhance the ability to perform complex calculations, trajectory processing, graphics processing, and real-time communication. Because PCs have an open bus, PC-based CNC system hardware is characterized by its openness, modularity, and embeddability. Delta Tau, an American company, has developed an open CNC system based on PCs. Its PMAC motion controller, based on a high-speed DSP, can handle real-time control functions such as interpolation, servo control, and PLC control, and can also utilize a PC interface to perform non-real-time functions such as human-machine interaction and status display. The PMAC motion controller adopts an advanced modular design and a fully open structure, allowing for the selection of appropriate options and accessories based on different applications. Applying the PMAC motion controller to camshaft grinding, its control system configuration is shown in Figure 2. In the figure, the MACRO workstation is connected to the PMAC 4-axis motion controller via fiber optic cable. Its main functions are as follows: ① 4 analog output ports, 4 encoder outputs; ② 144-bit I/O points; ③ Complete motion control; ④ Built-in PLC program control. In Figure 2, the computer-controlled AC servo motor realizes the x-axis movement of the grinding wheel head for transverse feed and the c-axis for controlling the rotation of the workpiece spindle to realize the cam profile machining without a template. The z-axis motor controls the gear shifting during the grinding process to complete the grinding of each cam on the camshaft. The hand-cranked pulse generator is used for manual adjustment of each axis. 144 I/O points are used for PLC program control to complete various status detection and auxiliary actions. 3 Implementation of system software The system software can be divided into the following according to real-time performance: (1) Main control module, which is a non-real-time module, completes human-machine interaction and status display, and can also perform offline coarse interpolation of the processed contour line before sending it to the PMAC motion controller; (2) Motion control and PLC control module. This is a real-time module that performs real-time control of the workpiece rotation and grinding wheel tracking and feed linkage during the grinding process, as well as the completion of corresponding actions during grinding, such as opening and closing the protective door, workpiece loading, clamping and positioning, and cooling water on/off. The software composition is shown in Figure 3. The main control module includes user interface design, parameter management, communication, and verification of the machining motion mathematical model. It mainly handles user operation, real-time communication, management of controlled system parameters and machine tool parameters, and system fault diagnosis. The main control module also includes: inputting geometric parameters such as cam lift table, phase, position, and base circle radius; curve fitting of the lift table; establishment of the polar coordinate equation of the cam surface contour; offline coarse interpolation of the surface contour; establishment of the motion mathematical model; error analysis; and static machining simulation. During system operation, the main control module is in the foreground, while the motion control and PLC modules are in the background. 4 Control Algorithm (1) Tracking Control Based on the constant rotation speed or constant linear speed of the workpiece, combined with the cam lift table and grinding wheel radius, offline calculation is performed to calculate the correspondence between each rotation angle of the workpiece and the grinding wheel feed. Then, the rotation angle and the grinding wheel feed amount are sent to the memory of the PMAC motion controller in the form of increments. During real-time control, only the required data needs to be read from the memory without calculation. In this way, the time used for data calculation within the sampling period can be minimized, and the interruption time can be reduced accordingly, thereby improving the processing speed and reducing the profile processing error. (2) Feed Control For each cam on the camshaft, the machining allowance of each cam is called the total feed amount of the cam. Within the total feed amount, it can be divided into up to 8 stages. The feed amount of each stage is selected according to the accuracy of the workpiece being processed. The sum of the feed amounts of each stage is equal to the total feed amount. (3) Rotation speed control: The rotation speed of the C-axis is different in each grinding stage. At the same time, since the entire cam profile is formed by the synchronous movement of the grinding wheel head (x-axis) and the workpiece spindle (C-axis) in one stage, in order to keep the grinding amount basically constant when machining the entire cam profile and to ensure the grinding surface finish, the angular velocity of the workpiece must be controlled according to the cam profile so that the linear velocity of each grinding point is basically constant. [References] [1] Gong Shihua, et al. Key technologies of CNC system for cam grinding. Manufacturing Automation, 2000, (4): 14-15 Click here to download the original text