# Comparison of Current Five-Point Cylindicity Error Separation Techniques
## 4 Conclusions  
Three five-point ESTs used for in situ cylindricity measurement were analyzed to determine their characteristic features as well as main benefits and drawbacks. The following are conclusions drawn about the parallel scan EST:  
1. Measurement of cylindrical profile was performed with five displacement probes. Outputs from five probes were used to measure radius deviations and roundness deviations of sequential cross-sectional profiles, as well as the LSC vectors of sequential cross-sectional profile, with which spatial curved median line profile of the cylinder was determined. Further, cylindrical profile could be accurately reconstructed by assembling each obtained cross-sectional profile onto the spatial curved median line. 2. The completeness of the measurement model in theory is promising. Accurate detection of the spatial curved median line of the cylinder highlights its novelty, and the error motions of the cylinder and carriage in measuring system are fully eliminated. 3. Detecting full harmonic components of sequential cross-sectional profiles is dependent on how the three probes in one cross-section are located relative to each other. Therefore, to ensure good anti-interference capability, angular arrangement of the three probes should be carefully selected so as to obtain large transfer function \(\mathbf{\Omega}(p)\)\((p=0,2,\cdots,15)\). 4. The probes should be strictly calibrated and carefully chosen. Especially, inconsistencies of sensitivity and linearity among five probes should be overcome as much as possible, which is a main factor impacting on the precision of spatial curved median line of the cylinder. 5. Accuracy of the method has not been verified by calibration. 6. The method is suitable for on-machine measurement of cylindrical profile. Where, the carriage can be mounted onto the tool carriage. Measurement cost is relatively low. 7. The parallel four-point scan EST is more suitable for in situ cylindricity measurement of large-scale roller, where the tilt error motions of the cylinder are negligible because the roller is long and the rotation speed is low. The conclusion about spiral scan EST can be summarized as follows:  
1. Measurement of cylindrical profile is performed with five displacement probes, which are arranged in a spiral scanning-path. Cylindrical profile measurement is transformed to one-dimensional straightness measurement by the multi-point straightness EST based on DFT. 2. The multi-point straightness EST based on DFT is built in an assumption that the straightness profile is end-to-end. The actual spiral profile on the cylinder is impossible to achieve. Therefore, direct adoption of straightness EST based on DFT to measure and reconstruct spiral profile on the cylinder would weaken the theoretical completeness. 3. The way to fill a segment of data of Probes 2-4 at the tail end of measurement becomes a crucial factor to determine measurement accuracy. In light of the authors' experience, if straightness errors of actual spiral profile are significant in the outputs of the probes, it may be a good solution that a segment of data of Probes 2-4 at the tail end of measurement are assigned by the data collected by Probe 1 at the head end of measurement. 4. The \(M\)th harmonic suppression of the EST will not impact measurement accuracy of the spiral line profile. It only causes a slight shift of the measured spiral line profile. 5. Because a segment of data of Probes 2-4 at the tail end of measurement is uncertain, the accuracy of the measured spiral line profiles at both ends of the cylinder deteriorated significantly. Therefore, the shortened effective measurement length of the spiral line profile is a weakness. 6. Accuracy of the method has not been verified by calibration. 7. If this EST is employed in situ measurement of cylindricity, motion accuracy of the guideway and spindle should be high. The conclusions about V-block scan method can be summarized as follows:
1.