Research On Variable Stiffness Mechanism Of Two New Types Of Probes Based On Pressure Bar Instability And Magnetron Constraint

The coordinate measuring machine is generally used to measure parts with small and complex surface topography.The micro-nano probe is a key component of the coordinate measuring machine,and its performance directly affects the measurement accuracy and stability of the CMM.Stiffness is essential property of the micro-nano probe,which affects the contact force of measurement,stability,processability and dynamic response of the micro-nano probe.It has great significance to improve the proformance of the micro-nano probe by selecting the appropriate stiffness.On the one hand,the stiffness is raised,the measurement force will be increased,then destroying the surface of the workpiece;on the other hand,the stiffness is reduced,it will bring troubles,such as slow response speed,poor stability and manufacturing ect.Based on the instability characteristics of the pressure bar,a pressure bar type variable stiffness probe with a cross beam is constructed.The parallel guiding compliant mechanism is driven by the piezoelectric actuator to squeeze the constraint support beam to reduce the stiffness,then achieve the purpose of adjusting the stiffness of the probe.Based on the principle of minimum potential energy,the stiffness model of the pressure-rod variable stiffness probe is established,and the relationship between stiffness and piezoelectric driving force is obtained.The established stiffness model is verified by finite element simulation.At the same time,the dynamic characteristics of the mode,harmonic response and transient response of the probe under isotropic stiffness are simulated.Analogous to the high static and low dynamic isolation device,a three-beam magnetron variable stiffness probe is constructed.The dynamic stiffness is generated by the electromagnetic-permanent-electromagnetic structure,paralleled to the probe constraining support mechanism to achieve the purpose of stiffness adjustment of the probe.Based on the stiffness matrix method,the static stiffness model of constrain support beam of the probe is established,then the constraint condition of the isotropic stiffness of the probe is obtained.By finite element simulation,the established static stiffness model is verified,and the variation range of dynamic stiffness is obtained,as well as the modal,harmonic response and transient response of the probe under static stiffness.Through the genetic algorithm,the pressure-type variable stiffness probe and the magnetron variable stiffness probe are optimized for the size parameters from the natural frequency,mass and isotropic stiffness.Through the optimization,the specific size parameters of the two types of variable stiffness probes are obtained,then compared and analyzed the advantages and disadvantages of the two probes.Figure [55] table [18] reference [71]...