Abstract: Addressing the problems and potential hazards of ultrasonic cleaning machines, this paper systematically analyzes the equipment's defects from the perspectives of electrical control hardware and software and mechanical structure. A modification scheme using a rotary encoder to replace proximity switches is proposed, and the control circuit hardware and software are designed. Keywords: Ultrasonic cleaning machine, PLC encoder, high-speed counter 1. Process Flow The PTO-7032TJ fully automatic ultrasonic cleaning machine is a key piece of equipment for our company's ceramic shell cleaning. The positioning positions are arranged in a row from left to right: 0 is the feeding platform; 1 is the ultrasonic hot water washing tank; 2 is the ultrasonic cold water washing tank; 3 is the clean water rinsing tank; 4 is the spray tank; 5 is the air pumping tank; 6 is the water cutting tank; 7 is the hot air drying tank; and 8 is the discharge platform. Guide rails, racks, and other accessories are installed parallel above and in front of each tank. The robotic arm positioning system (up, down, left, and right directions) moves and positions itself on the guide rails. In the left and right directions, the motor shaft drives the gear to mesh and move on the rack. In the up and down direction, another motor shaft, gear, and sprocket complete the up and down movement. The baskets containing the products are moved sequentially from left to right (positions 0 to 8 above) to complete the cycle, so that the products enter each tank in turn to complete various cleaning processes until they are placed on the discharge platform to complete the entire cleaning process. 2 Analysis of existing problems (1) Since there are two proximity switches fixed on the guide rail above each tank as the positions for the robot to put and take the baskets, the position of the robot is identified by a counter in the program. After a year and a half of use, the robot arm positioning system showed an increased deviation in the left and right directions. That is, it did not stop immediately after reaching the position of the proximity switch. Sometimes the product basket could not be placed on the V-shaped positioning port on the tank. Sometimes the robot arm moved left and right when it should have risen but did not, causing the robot arm to hit the inner tank wall. Moreover, there was an incident where the product basket was pushed against the tank due to positioning error, causing the entire robot arm assembly to tilt. Fortunately, it was discovered in time and the accident was not amplified. This type of positional motion control requires the robotic arm to have strict positioning and sequence; otherwise, it is very likely that the process will be disordered or "tilting" will occur (the product basket is placed on the tank wall or in the tank with an existing basket, or the robotic arm moves left and right before it is raised, thus tilting the robotic arm functional components). If the machine is not stopped in time, it will seriously damage the equipment and the product. (2) Use a programmer to call up the program, carefully analyze the control software and mechanical system, and determine that the equipment has certain design defects: ① All the original left and right position identification devices are two-wire proximity switches; because of the leakage current, it may cause false input phenomenon. ② After the equipment has been used for a period of time, due to the running-in of the mover and the components, the frictional resistance is reduced, and the inertial movement of the left and right motion motor after power failure is increasing. There is no measure in the control software to eliminate this inertial movement. For details, please click: Fully Automatic Ultrasonic Cleaning Machine Robotic Arm PLC Control System