In this paper a method is developed for straightness measurement of a linear guide by using a straightness self-compensating stage with an optical straightness measuring system, an eddy current sensor, and a cross-roller type compensation stage. Both the compensation stage and the optical straightness system were set up on a scanning stage to measure the straightness error of the scanning stage. The measured straightness error was fed back to the control system to compensate directly in real time. Thus, straightness of a linear guide without the added straightness error of the scanning stage could be measured. The Hewlett Packard laser straightness calibration system was used to verify the real-time compensated results. Straightness error of the scanning stage was compensated from the worst straightness error of 20 μm/150 mm to 0.9 μm/150 mm. The eddy current sensor measured straightness of the linear guide and the measured result matched the result obtained by the coordinate measuring machine.

At present, the accuracy of precision manufacture is most affected by straightness errors, so the measurement and compensation of these errors are very important. In the current paper, three measurement systems for straightness are presented; they are characterized by simple set-up, online measuring, low cost, and sub-micrometre accuracy achieving 0.2 μm. Experimental results show that these three measurement systems can be applied to implement a compensation system which comprises one among them, an Elmo controller, and a dSPACE controller, and accomplish static compensation and dynamic compensation in the dual linear-axis stage. The accuracies of the static and dynamic compensation achieve ± 1 μm and ± 2.5 μm, respectively.

Stress in components will lead to the change of material properties and even failure. Therefore, the assessment for the stress state of components is play an important role in testing industry. As a non-contact and multi-physical field nondestructive testing method, eddy current thermography (ECT) can be applied to detect non-homogeneous electromagnetic characteristics parameter distribution in conductive materials. Internal stress and its distribution in a material will affect the value of electromagnetic characteristic parameters. If induction current applied on conductive material, the Joule’s heat, which generate in the sample will lead to the temperature rise on the surface of the specimen by induction heating process. The temperature distribution on the specimen surface can be recorded by infra camera and stored as IR images or videos. The feature of the temperature distribution and its variation can be used to express the stress state in the specimen. It is concluded that there is an approximate linear relationship between the surface temperature appreciation and the loading force when the excitation source condition remains unchanged.