Research On Dynamic Characteristics Of SPECT Mechanical System

As an advanced nuclear medicine imaging equipment,human SPECT has a wide range of applications in disease diagnosis and organ functional imaging.The mechanical system of SPECT has the characteristics of high load-bearing,multiple degrees of freedom,and multiple working modes,which makes the difficult to detect gaps,looseness,and other issues in the motion mechanism a hidden danger that causes SPECT equipment failures,and even threatens personal safety.Therefore,in-depth research on the dynamic characteristics of SPECT mechanical systems,especially under clearance excitation,is of great significance for SPECT equipment operation status evaluation and fault diagnosis.On the basis of analyzing the working principle and mode,a three-dimensional model of the SPECT mechanical system was established.Based on the multi body dynamics simulation platform Adams,dynamic models of the SPECT main rotation mechanism and the detector translation mechanism were established.Using the multi rigid body dynamics analysis method,dynamic simulation analysis was conducted on typical motion mechanisms of SPECT,such as planetary gear reducers,worm gear reducers,spur cylindrical gear drives,screw drives,etc.The dynamic characteristics of the main rotary transmission gear and the detector translation mechanism were analyzed in detail for the 90° mode and 180° mode operating conditions.Based on Hertz contact theory,study the dynamic characteristics of the main rotary gear transmission mechanism and lead screw transmission mechanism under clearance excitation.We investigated the changes in contact force between the main rotary gear and the driving gear,as well as between the screw nut and the nut sleeve,as well as the variation pattern of contact force with increasing clearance.The results show that when the clearance value between the main rotary gear and the driving gear exceeds 0.5 mm,the contact force generated by the clearance collision begins to rapidly increase,and the load sensitive tangential contact force is significantly greater than the radial contact force;As the gap between the screw nut and the nut sleeve increases,the contact force generated by the gap collision shows an exponential growth trend.Using the rigid flexible coupling dynamic analysis method to analyze the stress of the main rotary gear,driving gear,and nut sleeve in the translation mechanism,and determine the stress concentration of each component under different clearance conditions.Based on the stress analysis results,the fatigue life analysis of the main rotary gear,driving gear,and nut sleeve was completed using the S-N curve method.The variation of fatigue life with clearance was observed for different clearance conditions.The results indicate that,under the premise of ensuring the safety of equipment use,the clearance between the main rotary gear and the driving gear should be controlled within 0.5 mm;The clearance of the X-direction nut sleeve should be controlled within 0.17mm;The clearance of the Y-direction nut sleeve should be controlled within 0.19 mm.