| Bulldozer is one of earthwork engineering machine, and its working environment is atrocious. During working period, the driver needs to adjust the position of working device, and change the speed and the direction of bulldozer continually. At present, centralized connecting lever and flexible shaft manipulating mechanism is used in most steering and barking system of bulldozers which are produced at home and abroad. This kind of structure needs more joy sticks, each of which need biggish force to move. In the case of frequently steering and barking, the driver has to pay more attention to change the joy sticks, which will affect the working quality, and make the driver more tired. For the narrow space of cab, simplifying structure is against to setting all joy sticks reasonable. Furthermore, connecting levers and adjusting bolts related to the steering and braking system must be adjusted. If there is any nonconformance in dimension and adjustment, steering or braking failure may be caused. Also the failure may be caused by the abnormal dimension of pull lever for long time relative movement. So it is necessary to improve the steering and barking system of bulldozers and make it be electric control single stick system which is easier to be installed and manipulated. Developing new type steering and barking system will improve the control performance, reliability and automation of bulldozers, and make basis for future distance control of special occasion.In this system, electro-hydraulic proportional control technology is adopted without change the transmission system of bulldozer, and steering or braking can Fig. 1 Control principles block diagrambe realized by controlling the current through the proportional valve. The control principles refer to Fig.1. Based on the above control principles, system hydraulic loop is designed in this article. In the system, two hydraulic rams are used to control the steering and braking valves in both sides of bulldozer, one electromagnetic direction valve to select controlling side, and proportional reduced valve to control the pressure of hydraulic ram. At the same time, PIC16C73B single chip processor is used in the controller which can produce PWM signals. By adjusting the duty factor of PWM signals, the pressure output by the proportional reduced valve is controlled. For hardware design, reliable and well-rounded circuit is adopted as much as possible, to make the electric unit have high reliability.In order to have good control performance, mathematical model is established, and the system is simulated in the article. According to the result, we analyze and research the algorithm of the control system. According to feature of the system, the integral separation PID control algorithm is deduced, and self-adjusting method based on ITAE principle is adopted. So in the case of time variation, good control performance can be obtained. Furthermore, we design fuzzy control algorithm, build up the membership functions, establish fuzzy control regulation, and get the fuzzy control table in chapter 5. Based on the control requirements and algorithm, system software is designed and control program is worked out.Integral separation PID control algorithm with self-adjusting parameter and fuzzy control algorithm have been simulated and experimented in the article to test their control effect. And the results show that Integral separation PID control algorithm with self-adjusting parameter has shorter adjusting time and lower overshoot than conventional PID control algorithm and it has simple structures which make it realized, and the fuzzy control algorithm enhances the flexibility and robustness of the system and has good control effect too. Both kinds of algorithms can improve the static and dynamitic characteristics of the system, and meet the design requirements.Considering the actual operating condition, mid position dead zone of the stick angle is set in the software and hardware to avoid false operation. In order to meet the frequency requirement of valve, the freq...
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