Jiao et al. / J Zhejiang Univ SCIENCE A 2006 7(10):1772-1776 1772 A laser shaft alignment system with dual PSDs * JIAO Guo-hua †1,2 , LI Yu-lin 1 , ZHANG Dong-bo 3 , LI Tong-hai 1 , HU Bao-wen 1 ( 1 Xi’an Institute of Optics and Precision Mechanics of CAS, Xi’an 710068, China) ( 2 Graduate School of the Chinese Academy of Sciences, Beijing 100039, China) ( 3 The 16th Institute of CATEC, Xi’an 710100, China) † E-mail: ghjiao@opt.ac.cn Received Mar. 3, 2006; revision accepted July 6, 2006 Abstract: Shaft alignment is an important technique during installation and maintenance of a rotating machine. A high-precision laser alignment system has been designed with dual PSDs (Position Sensing Detector) to change traditional manual way of shaft alignment and to make the measurement easier and more accurate. The system is comprised of two small measuring units (laser transmitter and detector) and a PDA (Personal Digital Assistant) with measurement software. The laser alignment system with dual PSDs was improved on a single PSD system, and yields higher measurement accuracy than the previous design, and has been successful for designing and implements actual shaft alignment. In the system, the range of offset measurement is ±4 mm, and the resolution is 1.5 µm, with accuracy being less than 2 µm. Key words: Rotating machine, Shaft alignment, Laser alignment, Position sensing detector (PSD), Laser micro-displacement measurement doi:10.1631/jzus.2006.A1772 Document code: A CLC number: TH741.4 INTRODUCTION Precise alignment occurs when the centerlines of rotation of two shafts are essentially collinear with each other. The degree to which two machines are misaligned can be determined by examining the amount of offset and angularity that exists between them. Offset is the distance between the two rota- tional centerlines, and angularity is the angle between the centerlines created by the misalignment of the two centerlines. The traditional precise shaft alignment method is dial indicator alignment (Piotrowski, 1995), and the two most popular methods are the rim and face method and the reverse indicator method. With the traditional technique, the measurement results must be graphed out manually and the calcu- lations must yield the corrections required. With the laser alignment system all these are done automati- cally. Real time alignment values are displayed as the machine moves. The laser alignment system cuts the measurement time at each coupling by 50% compared to the previous method of taking 16-point rim and face dial readings (Perry, 1998). The improved ac- curacy of the laser also minimized the number of subsequent bearing alignment corrections required. The laser alignment system has been adopted for more and more precise shaft alignments, such as rotor system (Brommundt and Krämer, 2005), vibration (Lee, 2004), cooling tower fans (Luedeking, 2003), gas turbine (Luedeking, 2005), Link Coupling (Pan et al., 1998), turbine driven feed water pump (Parry, 2001), etc. The single PSD laser alignment system designed by us has been applied in actual shaft alignment (Jiao et al., 2006). Dual PSDs method is based on the single PSD laser alignment system, and has evidently im- proved the system measurement accuracy through some modification in the light road, circuits, and software. * Project (No. 60337030) partly supported by the National Natural Science Foundation of China Journal of Zhejiang University SCIENCE A ISSN 1009-3095 (Print); ISSN 1862-1775 (Online) www.zju.edu.cn/jzus; www.springerlink.com E-mail: jzus@zju.edu.cn