The position control system is composed of a PLC, expansion modules, a PPI pulse comparison and output amplifier, an AAI signal conversion unit, a hydraulic servo valve controller, a hydraulic cylinder displacement sensor (magnetic scale), an amplifier, a phase detector, and a human-machine interface touch screen. It operates as a closed-loop feedback control system. Due to the failure of the original OMRON C200H computer, the system has been upgraded with a Siemens S7-CPU226, along with digital input/output expansion modules EM223 and EM222, and an analog input/output module EM235. The touch screen has also been replaced, and the control software has been reprogrammed to enhance functionality.
Previously, the load sorting was divided into two categories: qualified and unqualified. Now, it has been expanded to four qualified grades plus one unqualified grade, providing more detailed classification. The CPU 226 features DC input and output, with 24 input points and 16 output points. The EM223 and EM222 are 16-channel DC input and 16-channel relay output modules, while the EM222 is an 8-channel relay output module. The EM235 is used for processing analog signals from the load cell. All parameters are entered and displayed through the touch screen, which is configured using dedicated software.
The PPI board is responsible for pulse comparison and amplification. It receives pulse width modulation (PWM) signals and direction signals from the PLC outputs Q0.10 and Q0.11, compares them with the position signal from the displacement sensor, and then generates an analog output to the hydraulic servo valve, driving the hydraulic cylinder to move to the desired position.
In terms of motion control, the process begins with the hydraulic piston returning to the origin (O), where its position is verified by a sensor. Next, it moves to the working point (W) using PWM signals from Q0.10, which is detected by a hardware sensor. From there, it moves to detection point 1 (X1), controlled by a pulse train (PTO) output from Q0.10. Software calculates whether the movement is complete based on the number of pulses set. The same process is repeated when moving from X1 to X2. At both X1 and X2, the piston remains stationary for a set time to capture stable load cell readings.
Finally, the piston returns to the working point (W). The first half of the movement uses PTO control, while the second half uses PWM, which is sensed by the position sensor at W. This cycle repeats for each spring, completing the load detection process. The control program is written in ladder logic, and the system has been successfully tested on a spring testing table, later applied to the intake and exhaust valve springs of real motorcycle engines, achieving excellent results.
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