Test Stand for Checking Rotary Converter Accuracy

Abstract

S. M. Latyev, UDC 681.7 S. S. Mitrofanov, and G. V. EgorovMethods and equipment are considered for automated checking of rotary encoder accuracy using highprecision transducers and accurate devices for their integration, as well as a method of compensating for certain checking errors. An improved test stand is presented that provides improved rotary encoder calibration accuracy.Analog and digital rotary encoders manufactured by a number of companies in the form of standardized (modular) devices are widely used in machine and instrument engineering [1-3]. Such transducers have different principles of operation. Each transducer must undergo periodic checks and calibration tests during their manufacture and operation. Many methods and devices are known for checking transducer accuracy [4][5][6]. High-precision transducers exhibit high accuracy and resolution, which requires the use of measurement devices with even stricter accuracy characteristics, as well as the performance of checks in a greater number of positions, approaching the number of pulse-generating elements (lines) on the encoder's reference scale. For example, off-the-shelf high-precision photoelectric transducers of accumulating and absolute type that use circular rasters and code scales (18-24 bits) have an error of 1-5ʺ and 18000-36000 lines on the controlled path.The error of checked transducers is normally evaluated by comparing them against linked reference rotary encoders. In most cases, the shafts of the encoder being checked and the reference encoder are connected by an accurate compensation coupling that brings them into synchronous rotation and compares conversion codes from shaft rotary motion. Here, the reference encoder must exhibit a three-fold (or higher) accuracy margin as compared to the encoder being tested.A shortcoming of such a checking method is that the compensation couplings transmit movement from one shaft to the other with errors, which depend on the accuracy of the mutual position of the connected shafts, determined by axial misalignment, skew, as well as axial and radial rotational errors [7]. Before the check is performed, the shafts must be closely aligned with each other. The best domestically produced high-precision couplings (LIR-805 and LIR-807 [1]) exhibit an error of ±(0.5-1)ʺ provided the connected shafts exhibit no greater than 0.05 mm axial misalignment and 0.09° skew.Quite often, errors associated with compensating coupling rotary transmission are greater than those exhibited by the encoders being checked, and it does not appear feasible to consider their impact on accuracy checking. For this reason, the accuracy of certain transducers and angular encoders is checked using a reference polygonal prism (mirrored polygon) and automated autocollimator mounted on the shaft (table, spindle) [8]. In such a checking method, shaft rotation angles specifi ed by the prism are compared to the angles determined by the encoder (device). However, in doing so, checking may be accomplished at a number of points that is limited by...