| The research object of this paper is the 1480 D digital hydraulic cylinder which is applied to the rocker arm of coal mining machine for the first time in engineering practice.This paper combines the advantages of the digital hydraulic cylinder,replaces the original electro-hydraulic proportional height adjustment system and ordinary reversing valve height adjustment system with the digital hydraulic cylinder,and on this basis,conducts an in-depth study on the influence of the clearance of the coal miner automatic height adjustment system on the control characteristics of the system,so as to provide a theoretical basis for the performance optimization of the coal miner automatic height adjustment system.(1)Firstly,the principle of the composition of the digital hydraulic control system for the rocker arm of the coal mining machine is introduced.the interaction mechanism of the feedback mechanism of the prismatic pair,a screw nut pair,two gear pairs,a ball screw pair,their clearance in the feedback process is analysed,the dead zone clearance model is adopted,a non-linear dynamics model of the feedback mechanism is established,and then a servo motor control model and an asymmetric valve-controlled asymmetric cylinder hydraulic power mechanism model are established respectively to obtain a digital hydraulic cylinder model with the nonlinear characteristics of the feedback mechanism clearance,and a block diagram of the system with the nonlinear characteristics of the feedback mechanism clearance is drawn.(2)Based on the descriptive function method,the influence of the feedback mechanism clearance on the stability of the digital hydraulic cylinder is investigated by comparing the negative inverse frequency curves of the four drive clearances of the feedback mechanism with the position of the linear part of the Nyquist curve.The static analysis method is used to simplify the model of the digital hydraulic cylinder with the nonlinear characteristics of the feedback mechanism clearance,and the clearance is equated to the disturbance quantity to derive the expression of the static error caused by each clearance,so as to study the influencing factors and laws of the static error caused by the feedback mechanism clearance.(3)Build the AMESim simulation model of digital hydraulic cylinder according to the test parameters,verify the analysis results of the influence of feedback mechanism clearance on the stability of the system and the correctness of the static error expression caused by the deduced clearance,and determine the influence of different feedback mechanism parameters on the static error of the clearance.Then the influence of feedback mechanism clearance on tracking error,step signal response characteristic and sinusoidal signal response characteristic are analyzed by simulation.Finally,the validity of the AMESim simulation model and the correctness of the theoretical analysis are verified by the test curve and simulation curve.(4)Add the rocker arm model to the AMESim simulation model of the digital hydraulic cylinder,consider the constant load force,and obtain the load force applied to the rocker arm when the digital hydraulic cylinder pushes it through the simulation.The load forces obtained from the simulation were compared with those calculated by MATLAB programming to verify the correctness of adding the rocker arm model to the AMESim simulation model.On this basis,the influence of feedback mechanism clearance on step signal response characteristics and static difference is studied by simulation when the piston rod pushes the load at different positions.(5)When the feedback mechanism clearance is ignored,the influence of the rocker mechanism clearance on the system stability when the clearance is large is studied.The effect of the rocker mechanism clearance on the response characteristics of the step signal and on the resulting static difference is,then investigated when the plug rod is pushing the load at different positions.There are 61 pictures,6 tables and 60 references. |
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