The Development And Key Technology Research Of High Precision Hydrostatic Rotary Table

With the rapid development of China’s military, wind power, automobilemanufacturing, mining machinery, shipbuilding and other industries, on the one hand,the size and weight of the products are becoming bigger and bigger, on the other hand,the precision and complexity are becoming higher and higher. Based on the abovereasons, the machine is moving in high speed, high precision and multi-axis direction.Precise turntable which is a key component of a large multi-axis CNC machine tools,for example, large aircrafts and ships with bearings and gears and other partsprocessing, the rotary table of high accuracy are required by vertical lathe machine andhobbing machine, while a lot of rotary tables are often drove by sliding bearing,rolling bearing or worm gear, resulting in movement accuracy and precision of rotarytable is difficult to have greatly improved. Therefore, the development of highprecision rotary table and the research of the mechanisms and measures to improve itsaccuracy, for the development of China’s large equipment manufacturing industry haveimportant theoretical and practical value.By means of analyzing the key technology of the large rotary table-drivingtype, bearing way and the angle measurement method, combined with direct drivemotor technology, hydrostatic guideway (bearing) technology and magnetic gridmeasurement technology, the thesis presents a design of the structure of a direct drivehydrostatic rotary table and put forward the development of high precision rotaryworktable four key techniques:(1) the turntable is driven by torque motor, thedecrease of the intermediate transmission link, thereby reduce the transmission error;(2) using liquid hydrostatic guideway, leveling rotary table loads and reduce friction,prevent turntable’s crawling and achieve slight angle of rotation, thus improve theaccuracy of the turntable;(3) in the circumferential direction using hydrostatic bearingway, improve the spindle rotation accuracy and rotary centering accuracy;(4) Magnetic grating ruler which is pasted in the circumferential direction and doublereading head’s angle are both larger than180degrees, in this way, we can achieveaccurate measurement of the turntable angle. In addition, the signal of double readinghead feedback direct controls the torque motor, forming a closed loop measurementand control system, so the turntable can realize the high precision.The key parameters of direct drive turntable structure involved in hydrostaticguideway and hydrostatic bearing are designed by using the theory of hydrostaticbearing theory. In addition, some key parameters are optimized by using the linearweighted coefficient method.Through analyzing the dynamic characteristics of hydrostatic direct driveturntable(including turntable starting characteristics, braking characteristics andvibration characteristics), the following conclusions are drawn as follows: the angularvelocity and angular acceleration of the turntable starts close to the time of stablevalue with the increase in guideway oil clearance and in part weight and extended; butthe time change of turntable needs to stabilize is not large with the increase inhydrostatic journal bearing oil clearance; angular velocity and angular acceleration ofthe turntable brakes time tend to be zero with the increase in guideway oil clearanceand in part weight and extended; but the time change of turntable needs to stop is notlarge with the increase in hydrostatic journal bearing oil clearance; vertical vibrationdisplacement of the turntable with the number of oil chamber increase and graduallydecreases, on the contrary, with the increase of the guideway oil film clearanceincrease and gradually increases, in addition, with the increase of the oil film dynamicviscosity increase and almost keep constant. The time of the turntable system from theinitial film thickness to a new equilibrium position with the number of oil chamberincrease and almost keep constant, but with the guideway oil film clearance and oilfilm dynamic viscosity increase and gradually increases. These conclusions provide abasis reference for future turntable control and parameter adjustment.