Abstract: Taking a fully automatic solder paste printer as the research object, this paper proposes a hardware architecture for a PLC-based motion control system for the printer and completes the software design of the motion control system. The concept of state machine is introduced into the PLC program, which not only simplifies programming but also effectively ensures the stability and reliability of the system. The paper also solves the problem of absolute position positioning when the motor needs to switch frequency multiplication, thereby improving the system's operating speed and motion control accuracy.
Keywords: solder paste printer; motion control; PLC; state machine
0 Introduction
Fully automatic solder paste printers are one of the key pieces of equipment in SMT (Surface Mount Technology) production lines. As the first step in the surface mount production line, the quality of solder paste printing has a significant impact on the yield rate of SMT products. One of the most important factors affecting solder paste printing quality is the motion control precision of various parts of the printer. Currently, SMT product production is developing towards high output and "zero defects." During production, the printer must operate at high speed for a long time in a stable and uninterrupted manner, which places high demands on the operating speed, stability, and reliability of its motion control system.
1. Working process of a fully automatic solder paste printer
As shown in Figure 1, the solder paste printing machine mainly includes the following components: a vision system, a squeegee module, a PCB conveyor track, and a positioning platform. There are a total of 8 drive axes controlling the movement of each component. Specifically, the board width adjustment control moves the guide rail back and forth to adjust the PCB conveyor track to the width corresponding to the PCB to be processed; Camera X and Camera Y control the camera to move to the MARK point position; Platform X, Platform Y1, and Platform Y2 control the positioning platform to move back and forth, left and right, and rotate to accurately align the PCB with the stencil; Platform lifting control raises and lowers the positioning platform to switch the platform's working position; and Squeegee dragging control moves the squeegee module back and forth to complete the printing. All drive axis movements are point-to-point movements without any linkage requirements.
The workflow of the printing press is as follows: (1) After the PCB enters the printing press via the PCB conveyor track, the PCB clamping device installed on the PCB conveyor track fixes the PCB. (2) The vision system sends position feedback signals according to the two MARK points on the PCB and the stencil respectively. (3) The adjustment platform corrects the position and angle deviation between the PCB and the stencil, and accurately aligns the PCB and the stencil. (4) The alignment and positioning platform rises to the printing position, and the squeegee on the squeegee module moves back and forth to evenly print solder paste onto the pads of the PCB. (5) The alignment and positioning platform descends to its original position, the PCB clamping device is released, and the PCB conveyor belt sends the PCB out of the printing press, completing one work cycle.
For details, please click: Research on the Motion Control System of a Fully Automatic Solder Paste Printer
