Application of Linear Stepping Motor in Engine Speed Control of Road Roller
The full hydraulic double drum compactor is a construction equipment that compacts the road surface in modern pavement construction to meet the requirements of predetermined compactness and flatness. Since the road roller mainly uses its walking and vibration to work, its walking speed and exciting force determine the key to construction quality. As the main engine, the working condition and working efficiency directly affect the working performance and life of the roller; its working speed directly affects the output power of the whole machine. In order to improve the working performance and working efficiency of the whole roller and maximize the full-speed performance of the engine, we achieve the above purpose by controlling the engine speed by closed-loop control of the engine speed.
1 system structure and principle
1.1 Overview
In the application of traditional engineering machinery engines, most of the engine speed is adjusted by manual lever or foot pedal to adjust the engine speed, and the engine speed is not controlled. This not only affects its own performance but also gives the roller some original superior performance. Limited play: engine lift and deceleration are extremely inconvenient, it is difficult to achieve automatic and remote control. In addition, the roller has a large load change in the vibration and non-vibration modes; the engine speed fluctuates with load fluctuations, affecting the engine and The working efficiency of the hydraulic system; the engine is difficult to operate at a lower speed. If the load is large (walking or turning on the air conditioner at low speed), it is easy to cause the engine to slow down or even turn off; the engine speed cannot be automatically adjusted. In response to these situations, we developed a computer speed computer closed-loop control device to solve the above problems. The system hardware structure is shown in Figure 1.
1.2 Analysis of control principle
The double drum compactor has three states in normal operation: static rolling travel, vibration walking and high-speed running. These three states have different power output requirements for the engine. The travel handle, gear switch and vibration switch will be used. The three switch signals are input to the PLC, and the corresponding speeds of the engine can be respectively determined by the mutual logic relationship. At the same time, the PLC also receives the pulse signal of the speed sensor coming to the flywheel housing of the engine, and the two signals are sent to the PID adjustment in the PLC. Through a certain operation, a high-speed pulse and direction signal is output to the driver, and the driver converts it into two drive pulse trains with a phase difference of 180° to the linear stepping motor. The motor rotates at a certain rotation angle to cause a corresponding linear displacement of the spline shaft. And drive the engine throttle lever to accurately reach a given position, and finally make the engine run stably at a given speed, ensuring the best match between engine power output and power demand.
Considering the special requirements of the actual working conditions and the loss of the engine speed signal, the system has designed two modes of speed closed loop and open loop control, and can be freely switched by text display. In the open loop mode, the console is used. The speed reduction and speed increase control switch realizes stepless adjustment of engine speed from low idle to high idle.
1.3 hardware selection analysis
At present, the driving devices applied to the electronically controlled throttle device in the market are linear proportional electromagnets, swing stepping motors and linear stepping motors. The comparative analysis is as follows:
1) Linear proportional electromagnet: simple structure, maintenance-free, high reliability, fast response, accurate displacement control, PWM pulse signal control, low pulse frequency <200Hz; shortcoming is no self-locking ability, current consumption The current at the large and maximum position is 3.5A, and the coil heat causes poor thermal stability and linearity.
2) Swinging stepping motor: It can be controlled by PWM or PTO pulse signal, with fast response, strong anti-interference ability and low power consumption. The disadvantage is spur gear transmission, the structure is more complicated, there is no self-locking ability, and the stability in closed-loop control is poor.
3) Linear stepping motor: simple structure, maintenance-free, high reliability, accurate displacement control, PTO pulse signal control, if the stepper motor gets a pulse for a rotation angle of 5 ° ~ 12 °, converted into The linear displacement can reach the accuracy of 0.05~0.10mm, the response is fast, the moment of inertia is small, it is easy to achieve start, reverse and brake, strong anti-interference ability, self-locking ability, the disadvantage is that the pulse frequency is higher >500Hz There must be an extreme position overload protection device.
Based on the above analysis, we finally chose a straight line.
Stepper motor, by improving the accuracy of the mounting fit, high
Idle speed limit protection and program soft protection not only meet the constant speed precise control, the control accuracy is ±20RPM, the service life is also greatly improved, and the product has been used for 1000 hours without trouble.
