US 7,321,113 B2
Precision material-handling robot employing high-resolution, compact absolute encoder
Alva E. Hare, Marlborough, Mass. (US); Keith M. Hinrichs, Natick, Mass. (US); and William G. Thorburn, Whitinsville, Mass. (US)
Assigned to GSI Group Corporation, Billerica, Mass. (US)
Filed on May 25, 2005, as Appl. No. 11/137,675.
Prior Publication US 2005/0258986 A1, Nov. 24, 2005
This patent is subject to a terminal disclaimer.
Int. Cl. H03M 1/48 (2006.01)
U.S. Cl. 250—231.13  [341/116] 11 Claims
OG exemplary drawing
 
1. A precision material-handling robot, comprising:
a motor-driven shaft mechanically coupled to an end effector to impart motion thereto;
an annular scale affixed to the motor-driven shaft, the annular scale including periodic first and second tracks, the period of the second track exceeding the period of the first track by a track ratio;
detector circuitry operative in response to first and second periodic energy patterns from the first and second tracks respectively to generate corresponding first and second sets of analog signals representing respective amplitudes of the first and second periodic energy patterns at predetermined spatial locations; and
processing circuitry operative in response to the first and second sets of analog signals to:
(i) generate first and second position sample values of the first and second tracks respectively, each position sample value being modulo the period of the respective track, the second position sample value having sufficient resolution that a predetermined number of least significant digits of the second position sample value are overlapping digits representing nominally the same position information as corresponding most significant digits of the first position sample value, the predetermined number being determined by the magnitude of uncertainty of a spatial phase relationship between the first and second tracks over a predetermined portion thereof;
(ii) scale the second position sample value by a number corresponding to the track ratio to form a second position estimate value having the overlapping digits occupying the same digit positions as the corresponding most significant digits of the first position sample value;
(iii) subtract the first position sample value from the second position estimate value to create a corrected second position estimate value; and
(iv) combine the first position sample value with a non-overlapping most significant part of the corrected second position estimate value.