| Hydraulic transmission has the advantages of large power density ratio,large output force,high upper limit of response speed,and impact resistance.The liquid resistance full bridge network system composed of 5 two-way two-position electric fluid proportional valves,with independent control of load terminals,which can meet the composite control function requirements of the direction,flow and pressure of the electro-hydraulic valve by the joint compliance control of the hydraulic robot in the future.In this paper,an electro-hydraulic axis control system controller is designed for the liquid-resistance full-bridge network.First of all,the controller uses the STM32H7 series as the core board to expand the sensor signal sampling circuit,current sampling circuit and proportional valve drive circuit.According to the output characteristics of pressure and displacement sensor signals,a first-order RC low-pass filter circuit is designed and matched with an operational amplifier to achieve signal filtering and impedance matching.According to the-10V-10 V voltage signal output by the force sensing signal amplifier,the voltage conversion of 0-3V is realized through the dual op amps.The INA180A2 chip senses current by amplifying the sampling resistor voltage by a factor of 50.The characteristics of single-tube unloading drive circuit and reverse unloading drive circuit are analyzed,and the single-tube unloading drive circuit is used to drive the proportional valve.Based on the effect of optocoupler load resistance on switching delay in the drive circuit,and the duty cycle usage range under optocoupler load of 1KΩand PWM frequency of 1KHZ is given.By calculating the maximum power consumption of the controller components,the switching power supply is determined to operate at 50%-80% of the load,which improves the reliability of the power supply system.Secondly,the overall software framework of the controller is divided into three parts: Main function entry,interrupt running task,and Free RTOS real-time task.Set the interrupt sampling task preemption priority to 5 and the interrupt current closed-loop task preemption priority to 6,which improves the program execution efficiency by planning the running time of each real-time task in Free RTOS.The improved PID current closed-loop algorithm is used to realize the proportional valve current control,and the current step time is reduced by about 10 ms compared with the classical PID current closed-loop algorithm.Based on the underlying current loop control,the outer loop position controller is set to realize the position tracking of the hydraulic cylinder.Finally,the controller sampling circuit and proportional valve drive circuit are experimented.The amplitude-frequency attenuation characteristics of RC low-pass filters and current closed-loop are analyzed.Experiments show that the trend of current changing with duty cycle at PWM frequency of 1KHZ-5KHZ is basically the same,and the peak difference of the current gradually decreases with the increase of frequency.Through the current closed-loop control and hydraulic cylinder position tracking experiment,the feasibility of the controller is verified. |
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