Configuration Transformation and Flow Control of Equal-coded Digital Flow Control Unit

doi:10.3901/JME.2024.02.287

Abstract

Abstract: The digital flow control unit(DFCU) based on parallel on/off valves is the core component of digital hydraulics. The on/off combinations of DFCU increase exponentially with the coded bits under the coding-based on/off control, which faces the problems of large control calculations and limited flow resolution. Therefore, the coding transformation method of equal-coded DFCU is proposed by reducing the number of coded bits to narrow the search space for the best on/off combination and decrease the control calculation, The coding-based on/off control based on the cost function, pulse width modulation(PWM) control, and their compound controllers are designed to improve the flow resolution and ensure control accuracy. The mathematical model of flow-duty-pressure of the high-speed on-off valve is established by tests and fitting. The 7-bit equal-coded DFCU composed of high speed on/off valves is the research objective, which is converted to 4-bit Fibonacci-coded and 3-bit Binary-coded DFCU utilizing the combined control for different numbers of on/off valves and analyze the flow control characteristics under the designed pulse number modulation(PNM), pulse code modulation(PCM), PWM and compound controllers. The comparison results from control accuracy, calculation and switching numbers show that the DFCU can achieve the discrete flow output with less switching number under the coding-based on/off control, and the calculation can be effectively reduced after the coded configuration transformation, while the switching number and pressure shock are slightly increased; the PWM control can achieve the nearly continuous flow output, but the pressure pulsation and switching number are much higher than the coding on/off control; the transformed coding-based on/off control with PWM compound control not only improves the flow control accuracy similar to flow output of PWM control, and the switching number is much smaller than the PWM control and reduce the amount of computation in the control duty.

Key words: DFCU, PWM, PCM, PNM, coding configuration, flow control

CLC Number:

TH137

WANG Pei, CHENG Yuwang, LI Xinhao, YAO Jing, WU Liujie. Configuration Transformation and Flow Control of Equal-coded Digital Flow Control Unit[J]. Journal of Mechanical Engineering, 2024, 60(2): 287-301.

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