Study On The Influence Upon Structural Constraint And Kinematics Performance Of A Family Of Parallel Mechanisms With Three Degree Of Freedom Affected By Kinematic Chain Layout

Kinematic chain layout has a great impact on structural constraint and kinematicperformance of the lower m obility parallel mechanisms. However, researches in thisarea are scarce, and published literatures on this problem are still on case study phase.This dissertation investigates a f amily of lower mobility parallel mechanisms withthree degree of freedom, and reveals the influential action of kinem atic chain layouton structural constraint and kine matic perform ance of t his type m echanism. Thefollowing contributions have been made.(1) Based upon the identification of single joint space layout param eters, thelocality arrangem ent param eters of dif ferent kinem atic chains, w hich includedimensional parameters and structural para meters, are identified. By virtual of theseparameters, the variation of the arrangement of the kinematic chains can be convertedform a geom etry pro blem to a m athematical problem concerned with takingparameters values and their combinations. Through this method, different mechanismconfigurations with identical kinematic chain can be enumerated, which of importanttheoretical meaning and practical value to propose new type parallel mechanisms.(2) The o verall Jaco bin m atrix of lo wer mobility par allel m echanisms isformulated by use of s crew theory, the forw ard and inverse veloci ty models of themechanisms are established. Based upon these work, the velocities of the end of thekinematic chains are achieved. By investig ating the orientation relationships betweenthe active forces of the kinematic chains and the velocities of the end of the kinematicchains, the transmission pressure angle of the kinem atic chains are proposed as aperformance index to evaluate the kinem atic performance of the m echanisms. Theperformance index provides an ef fective way to evaluate the kinem atic performanceof the lower mobility parallel mechanisms having coupled translational and rotationalmovement capabilities.(3) Accord ing to dif ferent layou t param eters values and their com binations,different configurations of3-RPS,3-PRS,3-SPR and3-PSR parallel mechanisms are enumerated respectively based on RPS, PR S, SPR and PSR kinem atics chains. Thestudies on influential action of kinem atic chain layout on structur al constraint andkinematic perform ance of the m echanisms m entioned abo ve are carried out. Thekinematic perform ances of di fferent t ypes of3-RPS,3-PRS,3-SPR and3-PSRparallel mechanisms are analyzed and comparatively studied though the transmissionpressure angle index. These works lay a theore tical foundation for configurationselection and optimization of the parallel mechanisms.The research results has great practical significance and important th eoreticalvalues for enriching and developing lower mobility parallel mechanism design theoryand for promoting engineering application of parallel robot technology.