Investigation On The Identification Method Of Heat Source Power For Ball Screw Feed Systems

As the most common manufacturing and processing tool in the industry,the development of CNC machine tools greatly affects the leading level of the equipment manufacturing industry.As a transmission mechanism widely used in CNC machine tools,the ball screw pair has the characteristics of high efficiency,high precision and high stability.However,during the work of the machine tool,the contact surface of each motion pair of the ball screw feed system will continue to generate heat due to friction,which will affect the pre-tightening and lubrication state of the mechanism,resulting in insufficient machining accuracy and reduced machine tool life.Although scholars at home and abroad have done a lot of research work on the thermal characteristics of the ball screw feed system,due to the particularity of the working mode and the time-variability of the working conditions,the research difficulty is increased.However,most scholars assume that the heating rate of the heat source is a constant value,which cannot describe the time-varying characteristics of the working conditions,which increases the solution error of the thermal characteristics such as temperature and deformation of the system.Aiming at the above problems,this paper studies the time-varying characteristics of the heating rate of each heat source in the ball screw feed system.The specific content is as follows:(1)Taking the Z-axis ball screw feed system of the CNC machine tool HTC2050i as the research object,a thermal characteristic measurement test bench was established,which realized the continuous detection of the temperature of the key points of the system,the detection of the thermal deformation of the key points at the working time point,and the thermal image detection at the time point.Three working conditions with different feed speeds are selected,and the thermal characteristics of the system are tested separately,and the time-varying law of temperature rise and thermal error at each key point of the feed system is obtained,as well as the thermal image of the system with the running time.The law of change.(2)Use ANSYS software to construct a three-dimensional finite element model of the ball screw feed system;consider the movement characteristics of the heat source and the feed speed of the nut caused by the change of the table position on the heat transfer coefficient of the screw,and write it through the APDL parameterized design language The nut heat source position and the screw heat transfer coefficient command flow program are implemented to realize the dynamic loading of the nut heat source and heat transfer coefficient during the finite element calculation process;the objective function of the sum of squares of the simulated temperature and the actual detection temperature of the system is established,based on the golden section The method adjusts the temperature of each heat source,and proposes an identification algorithm for the heating rate of the system.Through numerical calculation,the time-varying characteristics of the heating rate of the system heat source at three different feed speeds are obtained.(3)Based on the heat network method,the heat transfer path of the feed system is analyzed,the distribution diagram of the temperature node of the system is determined,and the heat resistance network of the feed system is established;According to the material parameters and geometry of each part of the system,the heat resistance,heat transfer resistance and heat capacity between nodes are calculated;Based on the energy balance theory,the partial differential equations of heat conduction of each node isolation network are derived,and the partial differential equations of heat conduction of feed system are established;Based on the transient heat transfer equation,the central implicit difference processing is carried out,and the relationship between the temperature of the feed system detection point at each sampling time point and the heating rate of each heat source is derived.The identification algorithm of the heating rate of the feed system is proposed;The MATLAB program is written to identify the heating rate of each heat source,and the law of the heat rate of each heat source with the system operation time is obtained.(4)According to the finite element method and the thermal network method to obtain the dynamic change value of the heating rate of each heat source,the two are fitted by the least square method;Based on the numerical heat transfer equation of the finite difference method,the ball is calculated according to the one-dimensional long rod heat transfer calculation theory The lead screw feed system has been simplified reasonably to complete the separation of its space area and time area;and considering the real-time change of heat source heating rate,a thermal error prediction model is established.Through the comparison of simulation calculation and measured data,the validity of the model is verified,which provides a basis for the thermal error compensation of the feed system,and indirectly proves the accuracy of the identification result of the heat source heating rate.