Precision Design And Study Of Mechanism With Clearances

For the general machinery and equipment,precision and cost are the two most critical indicators.So far our focus have lain in the processing process in which we try to improve the machining precision of parts within budget,but this control method has great blindness and can't achieve a perfect balance between precision and cost.In this paper,it is taken as the research objects for the serial mechanism,6-DOF parallel mechanism and lower-mobility parallel mechanism with clearances.In the design phase of the equipment,we can determine the tolerance grade of parts,reduce the cost effectively through precision design and analyze the error source for the prototype,which all have important theoretical guiding meanings on the precision design,cost control and error detection of the general mechanism.The main contents of this paper are as follows:The precision design of mechanism with clearances is analyzed theoretically.Combined with fuzzy theory and multi postures simulation analysis and measurement,the error source detection method of mechanism with clearances is analyzed.According to the output precision index of the antenna folding device,the distribution of contact point of a rotating pair with clearance is analyzed in the design stage,what's more,the effective length model and mechanism error models with clearances and length error are established and the cost model is set up combining with linear and nonlinear restrictions.The precision synthesis of the mechanism is carried out by Monte Carlo method and the combination method of machining precision of parts which meets the requirement of precision and the cost is obtained.Based on the results,the antenna folding prototype is processed and the theoretical study and analysis of the error source detection of prototype is also carried out.By using the vector method,the branch error models and the mechanism error models of the Stewart parallel mechanism with tolerance are established.Based on Monte Carlo,the influence of all kinds of errors on the pose accuracy of moving platform is analyzed under the extreme posture,and the maximum pose error in workspace issimulated.The cost model of single branch is established,and the optimal combination of machining precision of parts is obtained by the accuracy allocation.The theoretical error detection method of Stewart is preliminarily studied,Meanwhile,taking the 3-CUR parallel mechanism with less freedom as an example,the law of mapping between the error and the output error of the moving platform is established,which can be used to detect the error sources and guide the processing.Based on the conclusion of precision design method for crank slider mechanism with clearances and Stewart parallel mechanism with clearances,the error models of3-CUR parallel mechanism with clearances are built.Combined with the cost model,the precision synthesis and processing of the mechanism are completed.The experimental results meet the requirements,which prove the correctness of the method of precision design and the detection results of the error source also testify the feasibility of the error identification method.