Design Of Truss-type Grasping Device And Finite Element Analysis Of Pinion-and-rack Gearing

As a device that can replace the arm to operate work piece,the grasping device greatly saves labor and improves the working efficiency.Pinion-and-rack gearing is an important part in truss-type grabbing device.It is mainly used to achieve straight-line movement of gripper of grasping device.The reliability and accuracy of rack-and-pinion gearing seriously affect stability,precision and service life of the whole grabbing device.In addition,due to the worse working environment of some grasping mechanism and difference of manufacturing technology,gears sometimes appear some small defects,and these defects always seriously affect transmission precision and service life of gears.With the increase of the volume and weight of work piece,working condition of rack-and-pinion gearing becomes more complex and severe.Therefore,the static analysis,dynamic analysis and defect analysis of rack-and-pinion gearing play very important role in the development and optimization of modern grasping device.According to the common working conditions,influences of different loads,speed,load and defects on gear and rack are studied based on WORKBENCH software.1.Based on the common working conditions,a truss-type grabbing device is designed.Based on that,the pinion-and-rack gearing in the design is analyzed by finite element method.2.The modal analysis of pinion-and-rack gearing is carried out to understand the natural frequency and corresponding mode of pinion-and-rack gearing,which provides reliable dynamic characteristic data to avoid resonance phenomenon.3.Based on WORKBENCH,the contact states of rack and pinion under different loads,different speeds and different friction coefficients are analyzed.The equivalent stress and contact stress of the gear are easy to increase with the increase of the load,but the increase of the speed is likely to have little effect on the fatigue strength of the gear,and the speed and the friction coefficient may have great influence on the contact fatigue of the gear.4.The fatigue life of pinion-and-rack gearing is analyzed.With the increase of load,the life of gear rack gradually decreases.With the increase of friction coefficient,the gear tooth is more prone to contact fatigue.In addition,through the rain-flow method and the Miners cumulative damage model,the fatigue life of gear is obtained by MATLAB software under different loads and friction coefficients.After that,compared those with the fatigue life of the gear obtained by the WORKBENCH simulation,the default that loads of gear are regarded as the full symmetrical cyclic loads maybe has some influence on calculation of life span.5.With different parts of the defective gear and the size of the different pits in the same part,the dynamic contact of the gears are analyzed.The stress of pit at the contact position between the rack and the gear is maximum relative to the other parts,and the stress concentration of the gear may be more obvious as the pit of the gear becomes larger.