Small roll angle is hard to be measured directly by commercial interferometer instruments due to their low sensitivities in axial direction. A method for its measurement based on a heterodyne interferometer is presented, which adopts accessories including a half wave plate, a multiple-reflector, and a phase meter to achieve test by detecting phase differences between the measurement and reference arms. Mathematical model reveals the resolution will be improved by increasing pass times through the half wave plate. The theoretical resolution is up to 0.19 in. when the pass times increase to three and the phase meter resolution is 0.01°. The proposed method is proved by the experiment.
Plane mirror interferometer is a common way for the precision displacement measurement. However, during the measurement, it still suffers from disturbances such as misalignments, rotations and air refractive index fluctuations, which lead to poor accuracy. Traditional error analysis is rather limited in the static state and separation of the disturbances. In this paper, displacement measurement errors are analyzed, which are caused by the disturbed factors for a plane mirror interferometer. Then error modeling, which based on the geometric optical paths, is carried out by the partial differentiation theory. Moreover, the characteristics of the error are discussed by using this model. It is suggested that this model can release the measurement accuracy reduction brought by coupling effects between adjustment factor of the optical paths and the rotary error of the measured object (e. g. a guideway).
The roll angle measurement is difficult to be achieved directly using a typical commercial interferometer due to its low sensitivity in axial direction, where the axial direction is orthogonal to the plane of the roll angular displacement. A roll angle measurement method combined diffraction gratings with a laser heterodyne interferometer is discussed in this paper. The diffraction grating placed in the plane of a roll angular displacement and the interferometer arranged in the plane's orthogonal direction, constitute the measurement pattern for the roll angle with high resolution. The roll angular displacement, considered as the linear, can be tested precisely when the corresponding angle is very small. Using the proposed method, the angle roll measurement obtains the high resolution of 0.002″. Experiment has proved its feasibility and practicability.
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