Gsi Group Corporation

Microe, Inc.

Novanta Corporation

Gsi Lumonics Corporation

William G Thorburn

Donald K Mitchell

Keith M Hinrichs

Andrew M Goldman

Alva E Hare

Joel Mikael Petersen

Bruce A Horwitz

Christopher Chapman Rich

Donald L Grimes

Douglas A Klingbeil

Stuart A Dodson, Ii

Marc A Bernard

Norman J Tobey

Melvin J J Teare

Ralph A Kelliher

A rotary optical position encoder includes a source of a linear-polarized light beam, a polarization-sensitive detector, and a rotating retarder disposed for rotation between the source and the detector. The retarder is configured and operative to produce a polarized exit beam whose polarization state rotates at a rate greater than a rotation rate of the retarder, thereby for increased resolution over a similar encoder using a rotating polarizer element. In an example, when polarized light is incident upon a rotating half-wave retarder, the transmitted beam's polarization axis rotates at twice the rate of retarder rotation, resulting in an electrical detector output that varies four times per revolution. Resolution is improved accordingly, as a given detected increment at the output is produced by only one-half the physical rotation increment required for a simple polarizer.

Rotary position encoder based on polarization

An optical position encoder includes a scale having multiple tracks separated in a direction perpendicular to travel, the tracks including an incremental track and an absolute track, the scale interacting with an incident first light beam to generate a second light beam having components carrying respective optical patterns produced by the incremental track and absolute track respectively. The encoder further includes a set of optical detectors including at least first and second detector arrays of differing properties to detect the respective optical patterns produced by the incremental track and absolute track respectively, each of the first and second detector arrays spanning multiple tracks of the scale and configured to respond to a respective detector-specific component of the second light beam more strongly than to another component of the second beam specific to another of the detector arrays.

Multi-track absolute encoder

An absolute encoder employs multiple sub-encoders of different resolutions and a linking algorithm for combining the sub-encoder outputs to form an accurate, high-resolution position estimate. The sub-encoders can utilize edge modulation of a main grating track, sloped patterns of successively higher periods, and other types of scale patterns. The sub-encoders can also use a variety of detector types suitable for the patterns being used. In one linking approach, pairs of tracks are linked together successively by applying a phase shift to the coarser track and then combining it with the finer track such that the transitions of the coarse track estimates become aligned with those of the finer track, whereupon the values can be combined to form a linked position estimate. In another approach, beat tracks are calculated from physical tracks of similar period, and the beat tracks are used as the coarser tracks in the linking process.

Absolute encoder employing linked sub-encoders and beat track

A flexible optical marker is applied to an optical scale substrate to make an optical scale assembly for an optical position encoder. The marker may be a limit marker, index marker, or other type of marker. The marker substrate may be a plastic film such as polyester, singulated from a 'recombine' roll created by a web process. The marker has a microstructured pattern on one surface that is covered with a reflective metal coating. The marker also has an adhesive layer and is affixed to the optical scale substrate by a process of aligning the marker to an edge of the scale and then applying pressure to the upper surface of the marker. The marker may be applied with a handle portion that is separated from the marker after the marker is affixed. The marker may be especially useful with a flexible scale substrate such as a metal tape substrate. By affixing the marker to the scale substrate as a separate step of making an encoder scale, various benefits such as reduced inventory, cost, and lead time may be achieved.

Scale assembly for optical encoder having affixed optical reference markers

An optical encoder includes a source of a light beam, an optical grating that generates a spatial pattern of interference fringes, and an optical detector which includes generally elongated detector elements that sample the interference fringe pattern at spatially separated locations along the direction of motion of the grating. Each detector element has one or more segments slanted along the direction of motion of the grating by an integer multiple of the period of an undesirable harmonic component of the fringe pattern, thereby spatially integrating the harmonic component and suppressing its contribution to an output of the detector. One specific detector type includes parallel elongated rectangular elements in a rectangular array that is rotated slightly about a Z axis; another type includes detector elements arranged to form a non-rectangular parallelogram. Another type of detector includes detector elements that each have multiple elongated rectangular segments which may be arranged into two non-parallel sets. The two sets can be further arranged in an alternating fashion so as to impart a zig-zag or chevron shape to each detector element.

Optical encoder having slanted optical detector elements for harmonic suppression

An absolute encoder employs multiple sub-encoders of different resolutions and a linking algorithm for combining the sub-encoder outputs to form an accurate, high-resolution position estimate. The sub-encoders can utilize edge modulation of a main grating track, sloped patterns of successively higher periods, and other types of scale patterns. The sub-encoders can also use a variety of detector types suitable for the patterns being used. In one linking approach, pairs of tracks are linked together successively by applying a phase shift to the coarser track and then combining it with the finer track such that the transitions of the coarse track estimates become aligned with those of the finer track, whereupon the values can be combined to form a linked position estimate. In another approach, beat tracks are calculated from physical tracks of similar period, and the beat tracks are used as the coarser tracks in the linking process. A wafer-handling robot employs the absolute encoder for controlling rotation of multiple joints.

Precision material-handling robot employing high-resolution, compact absolute encoder

Absolute encoder employing concatenated, multi-bit, interpolated sub-encoders

A rotary position sensor employs an offset beam forming optical element such as a tilted mirror or a diffraction grating. The axis of the light beam from a source can be parallel to the rotational axis or tilted at a predetermined angle. One or multiple spots of light from reflected/diffracted beam(s) are located on a generally elliptical path on an array of detectors. A detector that is photosensitive only along the elliptical path may be employed, the detector being divided into multiple regions to enable a processor to identify the azimuthal angle of the spot. When a diffraction grating is employed, return beams corresponding to positive first and negative first diffracted orders are generated, and these are displaced substantially symmetrically with respect to the axis of the source. The use of multiple beams can reduce sensitivity to mis-alignment errors. Some aspect of one or more of the beams, such as optical intensity or radial displacement, can be made unique to enable the processor to identify the angular position modulo 360 degrees.

Rotary position sensor with offset beam generating element and elliptical detector array

An encoder calculates position error values and applies compensation values to encoder position measurements in-situ. The encoder includes a scale and a multi-section detector for detecting a spatially periodic pattern, such as an optical interference pattern, produced by the scale. The detector includes spatially separated first and second sections. A signal processor estimates respective phase values from detector sections and calculates a phase difference reflecting a spatial position error in the scale. A compensation value is calculated from the phase difference and included in the estimate of the scale position to compensate for this spatial position error. The compensation values may be calculated and used on the fly, or calculated and saved during an in-situ calibration operation and then utilized during normal operation to compensate uncorrected measurements.

Encoder scale error compensation employing comparison among multiple detectors

An optical encoder includes an optical source, a scale, an optical detector and signal processing circuitry. The scale is operative with a light beam from the source to generate an optical pattern such as a line pattern extending in an X direction of relative movement between the scale and the source. The detector generates analog detector output signals indicative of the location of the optical pattern on the detector in an alignment direction orthogonal to the X direction. The detector may include two bi-cell elements spaced apart in the X direction, each element including two cells of complementary shape, such as a sharks-tooth. The signal processing circuitry operates in response to the detector output signals to generate an alignment value indicating a polarity and a magnitude of misalignment between the detector and the scale in the alignment direction. A method of providing information to a user regarding alignment of a detector and an encoder scale employs a graphical alignment indicator displayed on a computer display. The graphical alignment indicator has a bipolar indicator scale and a marker whose location on the scale is based on the alignment values such that the magnitude and polarity of misalignment is indicated.

Optical position encoder having alignment indicators providing quantitative alignment indications

The disclosed optical encoder includes a scale and a sensor head. The scale includes an optical grating and an optical element. The sensor head includes a light source, a detector array, and an index detector all of which are disposed on a substrate. The scale is disposed opposite the sensor head and is disposed for movement relative to the sensor head. The distance between the scale and the sensor head is selected so that the detector array lies near a talbot imaging plane. The light source emits a diverging beam of light, which is directed towards the scale. Light from the diverging beam of light is diffracted by the grating towards the detector array. Light from the diverging beam of light is diffracted by the optical element towards the index detector. The detector array provides a measurement of the position of the sensor head relative to the scale. The index detector provides a reference measurement of the position of the sensor head relative to the scale.

Reference point talbot encoder

Position of a diffusely scattering surface is detected by interfering backscattered light from respective input beams which illuminate a common spot. Through polarization of the input beams and appropriate filtering, backscattered light is isolated from specularly reflected light and interfered to form a fringe pattern on a detector. The position sensor has particular applicability as a push pin sensor in a hard disk servo system.

Diffuse surface interference position sensor

The apparatus disclosed herein employs a grating (13) which concentrates light at a preselected wavelength into the positive (33) and negative (35) first orders while minimizing the zeroth order (31). The grating (13) is illuminated with monochromatic light of the selected wavelength and a poly-phase periodic detector (25) has its sensing plane spaced from the grating a distance less than ##EQU1## where W is the width of the illuminated region of the grating. The period of the poly-phase detector is equal to P/2 so that each detector element (51) or phase responds principally to the natural interference between the positive and negative first orders without requiring magnification or redirection of the diffracted light. Preferably, the distance of the sensing plane from the grating (13) is greater than ##EQU2## so that the detector response does not include substantial components from diffraction orders higher than the first. Various embodiments of the invention are described including a wavefront compensation approach which greatly increases design freedom in the selection of grating and detector characteristics in implementing the present invention in practical and manufacturable devices.

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Whitinsville, MA, United States of America

William G Thorburn