Photoelectric Theodolite Large-size Bearing Rings Roundness Error Testing Techniques

Roundness of bearing ring is an important form parameter. It affects the radialaccuracy and the angle swing of shafting of optoelectronic theodolite.To accomplish the task of measuring the roundness of the large dimension andheavy workpieces, an overall design project of measuring large dimension bearing ringhas been developed, by using modular overall structure. The bearing rings withdimension larger than worktable are measured by rotating the sensors, and otherworkpieces including heavy axial workpieces are measured by rotating the worktable.To solve the conflicts between range of measurement and accuracy, a large rangegrating micrometer is used to center the workpiece roughly, a small range and highaccuracy inductive micrometer is used to center the workpiece accurately and makes theultimate measurement of roundness.When evaluating the roundness, a mathematic model of discriminant rule has beenestablished. A new cross-discriminant arithmetic has been designed. It can be used todistinguish cross-discriminant of the four extremums points of the minimum zone circle,a sharp angle triangular of the three extremums points and the radial symmetry of twoextremums points of the minimum inscribing circle and maximum circumscribing circleat the same time. The mathematic model based on cross-discriminant arithmetic candistinguish the new extremums when moving the center of circle, reducing thecalculating.Roundness of the spindle of worktable has been measured, a comparison has beenmade between rotation of sensor and rotation of worktable by measuring the sameworkpiece. The effect of temperature drift error of inductive micrometer on themeasurement has been analysed, and two methods of share the error and using thesubtracting of two sensors have been proposed to reduce the effect of temperature drifterror on the measurement.The uncertainty of measurement of experimental equipment has been evaluated,and a comparison of the results measured by the experimental equipment with theresults measured by Talyrond 290 XL roundness measuring instrument has been made. The reason of the error of polar radius overtop combined standard uncertainty has beenanalysed, a method of using the means of points of several rounds to evaluate theroundness has been proposed, the result is very close to the results measured byTalyrond 290 XL roundness measuring instrument.The overall structure of the roundness measuring system has been designed, thetechnical data of every part have been determined according to the experiments and theuncertainty of measurement has been evaluated. The expanded uncertainty is 0.5μm,reaching the requirement of the task.