Research On The Self-adaptive Preloading Mechanism Of Electric Spindle Based On Piezoelectric Ceramics

The electric spindle has the characteristics of wide speed range and high rotation precision.It is widely used in high-speed,high-torque,low-speed and high-power conditions,and is the core component of the machine tool.The preloading force is the key parameter to ensure the normal operation of the electric spindle.In the low speed section,it is necessary to apply a large preload to the bearing to increase the rigidity of the spindle unit.In the high speed section,a small preload is required to reduce the bearing temperature rise.Therefore,the electric spindle unit should have the ability to adaptively adjust the preload force according to the speed.At present,the commonly used fixed-position and constant-pressure preloading mechanism can't meet the requirements meet the needs of modern processing due to the lack of such capability.In view of the current research status of preloading mechanism,this paper proposes an adaptive preloading mechanism of electric spindle based on piezoelectric ceramics.The main research contents include:(1)Based on the Hertz elastic contact theory,the statics and mimetic dynamics calculation formulas of angular contact bearings are established and analyzed by Matlab.Finally,the relation curve between preloading force,rotational speed,contact angle approaching amount and frictional heat,etc.has been obtained,which lays a theoretical foundation for the adaptive preload of the spindle.(2)Taking AC8230026100 high-speed electric spindle as the research object,the spindle unit stiffness,rotation accuracy,bearing heat generation,etc.are taken as control targets,and finally the preloading law at different speeds is obtained Finally,the law of preloading at different speeds is obtained.Compared with the constant pressure preloading mechanism,it is proved that the adaptive preloading mechanism can meet the requirements of increasing the spindle stiffness in the low and medium speed sections and reducing the bearing temperature in the high speed section;According to the heat generation mechanism of the electric spindle and the energy transfer process between different parts of the electric spindle,the spindle heat generation model is established.By analyzing the influence of factors such as motor power and spindle speed on the heat generation of the spindle,the calculation formula of the thermal displacement of each part of the spindle can be obtained.(3)According to the deformation mechanism of piezoelectric ceramics and its basic characteristics,the theoretical basis for the application of piezoelectric ceramic preloading mechanism has been laid.Piezoelectric ceramic output force,displacement and pressure tests were carried out to verify its feasibility of applying to the spindle preloading mechanism.Compared with other smart materials,it tests and verifies that it has more superiority in output stress,frequency response,reciprocating precision than other materials.Finally,based on the previous research,a new preloading mechanism—the adaptive preloading mechanism of the electric spindle based on piezoelectric ceramics is proposed.The thermal displacement of each part of the spindle and the output displacement of the preloading mechanism are combined to obtain the variation law of the output force and displacement of the voltage and the preloading mechanism at different speeds of the spindle.The application of an appropriate preload force to the bearing according to the rotational speed and the stability of the preloading force is achieved.