Research On Soft Start Control Characteristics For Belt Conveyor Based On Automated Mechanical Transmission

The common soft starters of the belt conveyor are expensive and have high maintenance costs. So soft starter with lower cost is becoming the demand of the market. Heavy AMT has been widely used in heavy vehicles because of its large torque and low cost. It is an innovation to use AMT as the soft starter of belt conveyor in the application field of AMT which has huge market value.Supported by the National Natural Science Foundation of China (Grant No. 51174126), the starting process control and shifting process control of AMT softly starting belt conveyor are deeply researched. The main work and contributions are summarized as follows:(1) Mechanical model has been established for AMT softly starting belt conveyor. Dynamic equations of AMT’s transmission system are established according to the power transmission principle of AMT softly starting belt conveyor. The non-slip conditions for the belt and the materials are analyzed with the help of the mechanical model. The motion equations of the belt are also analyzed. The models of the clutch, the transmission brake and the solenoid valve are established which are used to analyze the time delay characteristics of AMT pneumatic system. The mechanical model of AMT system can describe the power transmission process of the belt conveyor and reflect the time delay characteristics of AMT pneumatic system which lays a foundation for the following research of starting process and shifting control method.(2) Starting acceleration control curves of AMT softly starting belt conveyor have been researched. The trapezoidal and orthogonal trapezoidal soft starting acceleration curves are proposed which suit AMT softly starting belt conveyor through analyzing the advantages and disadvantages of common five soft starting curves. AMESim is used to establish the dynamic simulation model of AMT softly starting belt conveyor. Comparative analysis is made between the dynamic responses of AMT softly starting belt conveyor with trapezoidal soft starting acceleration curves and that with orthogonal trapezoidal soft starting acceleration curves. The two soft starting curves can meet the requirements of soft starting according to the velocity, acceleration, jerk and tension of the belt.(3) Estimation method of load parameters has been researched during starting process. According to the influence of load parameters on shifting process control, an estimation method of load resistance torque based on semi joint of the starting process is proposed. A recursive estimation method of load inertia based on recursive least square algorithm is also proposed. According to the location of the semi joint of the starting process and the clutch characteristic of torque and displacement, the load resistance torque estimation is obtained. According to the clutch displacement and the speed of the output shaft during acceleration stage, the estimation model of load inertia is established, and the load inertia is estimated on line with the help of the recursive least square algorithm.(4) Controllers of the clutch engagement stages during starting process have been designed for AMT softly starting belt conveyor. According to the requirements of soft starting, the evaluation indicators of starting quality and control requirements are given. Control tasks for each stage are determined through analyzing the starting process. Controllers for different stages are designed separately including the empty stroke stage, resistance stage and acceleration stage. In order to decrease the belt jerk and sliding friction loss while starting, CFDL-MFAC control algorithm based on parabolic displacement curve is used to track the clutch displacement during resistance stage. For the convenience of AMT control, the control of belt acceleration and jerk is replaced by the control of output shaft’s angular acceleration and jerk during acceleration stage. A fuzzy PID control algorithm with jerk compensation is used to track the orthogonal trapezoidal acceleration curve.(5) Synchronous shifting control strategy for AMT without synchronizer has been researched. Synchronous rotational speed difference upshift control strategy is proposed which is based on the braking of the input shaft. Synchronous downshift control strategy is also proposed which makes the input shaft always wait for the output shaft to decelerate. Control algorithm of the input shaft is designed through theoretical analysis of synchronous upshift and synchronous downshift. The synchronous rotational speed difference is taken as the basis to decide the shifting time because of actuator’s hysteresis. According to transmission brake’s property, a kind of PD control algorithm with limiting the amplitude is used to control transmission brake. The rule of the input shaft’s deceleration curve is tracked which is got through the desired speed of the input shaft until the required synchronous rotational speed difference is reached.(6) Controllers of the clutch engagement stages during shifting process have been designed for AMT softly starting belt conveyor. According to the requirements of soft start, the evaluation indicators of shifting quality and control requirements are given. In order to control the belt jerk, CFDL-MFAC control algorithm based on parabolic displacement curve is used to track the clutch displacement during resistance stage. Based on the load parameters identification, a fuzzy PID control method based on engagement position prediction and correction is used to track the orthogonal trapezoidal angular acceleration control curve of the output shaft during acceleration stage.(7) Electronic control system has been designed for AMT softly starting belt conveyor. The overall scheme of AMT’s electronic control system and the software design frameworks of the bottom layer, the middle layer and the upper layer are given which provides software and hardware support for the test.(8) The control schemes of AMT softly starting belt conveyor have been verified. Several experiments have been designed including clutch engagement and disengagement characteristic experiment, clutch’s characteristic experiment of torque and displacement, transmission braking characteristic experiment, control experiment of starting process and control experiment of shifting process. It is verified that the control schemes of starting process and shifting process of AMT softly starting belt conveyor are feasible.