Measurement of six-degree-of-freedom planar motions by using a multiprobe surface encoder

Xinghui Li, Yuki Shimizu, Takeshi Ito, Yindi Cai, So Ito, Wei Gao

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)


A multiprobe surface encoder for optical metrology of six-degree-of-freedom (six-DOF) planar motions is presented. The surface encoder is composed of an XY planar scale grating with identical microstructures in X- and Y-axes and an optical sensor head. In the optical sensor head, three paralleled laser beams were used as laser probes. After being divided by a beam splitter, the three laser probes were projected onto the scale grating and a reference grating with identical microstructures, respectively. For each probe, the first-order positive and negative diffraction beams along the X- and Y-directions from the scale grating and from the reference grating superimposed with each other and four pieces of interference signals were generated. Three-DOF translational motions of the scale grating Δx, Δy, and Δz can be obtained simultaneously from the interference signals of each probe. Three-DOF angular error motions θX, θY, and θZ can also be calculated simultaneously from differences of displacement output variations and the geometric relationship among the three probes. A prototype optical sensor head was designed, constructed, and evaluated. Experimental results verified that this surface encoder could provide measurement resolutions of subnanometer and better than 0.1 arc sec for three-DOF translational motions and three-DOF angular error motions, respectively.

Original languageEnglish
Article number122405
JournalOptical Engineering
Issue number12
Publication statusPublished - 2014 Dec


  • angle
  • displacement
  • measurement
  • multidegree of freedom
  • planar motions
  • surface encoder


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