# Spindle Error Movements and Their Measurement
## 4 Commercial Systems for Testing Error Movements of High-Speed Spindles  
### System SEA (Spindle Error Analyzer)--Lion Precision  
Lion Precision is one of the few systems that developed a comprehensive system for testing spindle error movements (current version SEA 8.5). The system is designed in such a way that, without expert knowledge, the intermediate user can easily perform measurements on a machine tool located in the production hall, in a real environment in which the user works. This allows for calculation of how spindle error movements affect the tolerance of the workpiece. The configuration of the sets proposed by Lion Precision is based on the traditional measurement method. A typical configuration is shown in Figure 12[22]. Figure 11: The basic method of measuring error movements using a precise measuring pattern with a spherical reference surface and a set of: (**a**) three displacement sensors; (**b**) five displacement sensors. The company states that, by measuring machines with the SEA system before purchase, the user can avoid buying a machine (which is not cheap) that is unable to produce items with a strictly defined tolerance. The basic measuring elements of the SEA system are contactless, precise capacitive displacement sensors. The system may use three or five sensors depending on the tested rotational speed of the spindle. Additionally, you can connect up to seven temperature sensors and the output from the encoder for measuring the spindle's rotation angle. The signals from the sensors and the encoder, after passing through the filters and amplification, are fed to the inputs of the National Instruments DAQ card. The copyrighted software from Lion Precision interprets the sensor outputs as changes in the dimensions of the position and displays the results digitally and graphically. For detailed information, especially that needed for FFT analysis, many samples per revolution are required. Five measuring channels are available for testing faster spindle speeds (in the range of 120-180 thousand (rpm)). Along with development of the software, more and more attention is paid to the ease of use of the device. In the new version, manufacturer's support during operation of the measuring system is practically redundant. In addition, problems related to the sampling rate of the device and software installation have been resolved. New versions of the system focus on two types of errors:  
* related to ambient temperature and operation of the machine itself (Figure 13)
* related to spindle error movements. Figure 12: Stand for testing spindle error movements [22]. Figure 13: View of the Spindle Error Analyzer (SEA) system screen during examination of the influence of temperature on the position of the tool in the spindle (without revolutions) (e.g., influence on the dimension of depth for the made hole) [22]. To measure spindle error movements, sensors positioned perpendicular to each other, preferably parallel to the main axes of the machine, measure the distance to a precisely machined sphere or cylinder, with known non-roundness, mounted in the spindle's holder. Arrangement of sensors is shown in Figure 14.  
Depending on the type of machine and the tested rotational speed of the spindle, the set comes with several options (Table 1). SEA 8.5 System Software  
The software included with the system is an original development of Lion Precision. It is a proprietary software; the algorithms are not described, and the source version is not available to the user. According to the manufacturer, the software enables comprehensive spindle tests. Figure 15 shows the program menu with available tests and analyses.