The Study And Development Of A Computer Control System For The Increment Type Digital Hydraulic Valve

Hydraulic transmission and controlling system are widely usedin industry and agriculture fields for their unique advantages overmechanical and electrical systems. As an important branch ofhydraulic technique, hydraulic servo controlling system has importantpart in the control area, and has been constantly improved by thepractice. The hydraulic control components are improved rapidlyeither. Modern hydraulic technique has become a collection of manysciences. As the development of information and electronic computer,people has realized more and more deeply the change caused by usingelectronic technique. A tendency to be numerical controlled comesbefore us.To keep step with the trend, and based on the requirement ofdrawing tester we studied most of works and thesis about numericalcontrol and computer control, analyzed the working condition andmade out this plan to modify the normal hydraulic loading controllingsystem on a material tester, which uses digital signal to control theloading process. But we did not re-fabricate the whole system. Just dothe more necessary. In other words, we still use the main poweramplifying part of the control valve and only replaced theelectro-magnetic proportional control unit with the increment digitalcontrolling system. In this thesis, the requirement to the digital controlelement has been putted forward after the analysis of the hydraulicvalve performance, and pulse number and frequency modulationmethod are established in the developing computer control system.You can find the characteristic of the pulse modulation in this thesisthat is every pulse input will result in a corresponding outputstep-angle of the stepper motor. This angle is further transmitted todrive the spring of guide valve to move. In this way, the spring iscompressed or relaxed for a definite amount and the loading pressureof hydraulic system is changed.For the tester, a main working is to maintain the pressure at acertain value and for a period of time. In order to diminish theaffection caused by the non-linear factors of the control and drivingdevices, which would lead to the offset between the real displacementof driven part and the desired value, we use the detecting elements toform a closed loop control. Thus the problem can be solved effectively.The detecting system feeds back the detected quantity to controller;the controller adjusts the input pulse number and frequency to ensurethat the step motor is operated dynamic and proper according to thedetected value and speed. This auto-compensate can decrease theaffect of operator for it needs no manual adjustment in this process.This system uses pressure sensor to obtain the acting message ofthe valve. That message is then processed into a digital signal and fedback to the controller, which keeps the total system working inpre-designed regulation according to the error of the two values---thedetected and the desired. By this means, the system pressure iscontrolled to follow the instruction tightly. And the pulse generatingcircuit converts the digital signal into instruction pulse.For being conveniently used and maintain, all programs are builtinto function blocks, including a main program and several routineprograms. Every routine program can return to the host in short timewithout the problem such as longer time consuming. The routines dealwith the corresponding events according to the flag bit and judge bit.The main program fulfills such initialization processes by using theroutines as the start-state settings for the SCM ports, the controlstorage, the timer, and the RAM unit. It has the responsibility to openthe timing interrupt. The routines finish their tasks by the functionalelements.Digital filter use the method of median mean. The value ofmeasured is saved in special memory. Fuzzy subprogram deals withthe measurement data according to fuzzy controlling need. Thecalculating result of pressure error and variety is prepared for fuzzyreasoning.There are two kinds of analog signal processing ways in thissystem, one is by traditional A/D converter, and the other is V/Fconverter. In practice, the use can be selected by comparison in orderto diminish the interference. As an A/D converter, TLC2543 canprovide 16-bit accuracy, and with a serial data transition. It increasesthe accuracy and saves the ports resource. In the step motor controlcircuit, the light electrical coupling is adapted which can fill out theinduction interference.Display circuit uses dynamic design, uses chip CD4511. Thissystem allows the user to modify some parameter away from themaster controller by the keyboard on slave controller. The settingparameters and the dynamic real-time detected value can be indicatedon the LED according user ask.In this controlling system, we programmed five automationprocesses for convenient use and multi-working-point setting. Andyou can pre-draw a curve to ask the system to follow.When the manual adjustment is needed, the single-run form canbe selected. Thus the running way of single-step or multi-step can bedelivered either from the master controlling computer or the slavecomputer keyboard.After the overall design finished, every mode and systemsoftware have been manipulated and the control process have beensimulated. Seen from the result, this system could finish the controltask by step increment manner, and this system (principle) can beused on other machineries where an accurate movement or a rotationposition is needed. And this system has a bright prospect because thecenter computer can control many components or systems at the sametime.