Absolute position Moiré type encoder for use in a control system

A two dimensional Moiré encoder system, comprising:

• a) a plurality of surfaces, each surface comprising a first pattern which varies in a predetermined manner over said surface;
• b) a radiation source for emitting radiation having at least one second pattern;
• c) means for substantially simultaneously projecting one or more images of radiation from said radiation source onto each of said plurality of surfaces for interaction therewith;
• d) a radiation detection system operative to separately detect radiation which has interacted with each of said surfaces and to produce a corresponding plurality of electronic signals;
• e) a control system connected to determine a position in two dimensions for each surface based on:
• the plurality of electronic signals, the first pattern associated with each surface and the at least one second pattern;
• and
• f) at least one moveable element,
• wherein motion of said at least one moveable element creates relative motion between the one or more images of radiation from said radiation source and a corresponding one of said plurality of surfaces.

A method of implementing a two dimensional encoder, the method comprising:

• providing a radiation source comprising a plurality of radiation emitting devices capable of being addressed to create a pre-determined radiation pattern;
• projecting said radiation pattern from said radiation source onto a reticle surface, said reticle surface comprising transmissive and non-transmissive portions positioned and sized to generate Moiré interference at said surface;
• and
• detecting said Moiré interference to determine relative motion between said surface and said radiation pattern projected onto said reticle surface.

A method of implementing a two dimensional encoder, the method comprising:

• providing a radiation source comprising a plurality of radiation emitting devices capable of being addressed to create a pre-determined radiation pattern;
• projecting said radiation pattern onto a reticle surface, said reticle surface comprising reflective and non-reflective portions disposed to generate Moiré interference at said surface;
• and
• detecting said Moiré interference to determine relative motion between said surface and said radiation pattern.

A system for determining a position of an object, the system comprising:

• a reticle coupled to move with the object, the reticle having a spatially varying pattern of interaction with radiation incident on the reticle;
• a pattern projector configured to project a first group comprising at least three distinct radiation patterns onto the reticle, the three distinct radiation patterns of the first group each comprising a plurality of elongated stripes extending generally parallel to a first axis;
• and
• a radiation sensor associated with the reticle, the radiation sensor located to generate a sensor signal indicative of an intensity of radiation of each radiation pattern which has interacted with the reticle.

An apparatus for determining a position in two dimensions comprising:

• an optical element having optical properties which interact with incident radiation in a manner that varies according to a two-dimensional incidence position of the radiation on the element;
• an imaging optical system which projects a plurality of radiation patterns onto the element;
• and
• at least one radiation detector positioned to measure intensities of the plurality of radiation patterns after they interact with the element,
• wherein the measured intensities of the plurality of radiation patterns may be used to determine a position of the element in two dimensions.

An apparatus for determining a position in two dimensions, comprising:

• a plurality of radiation sources which emit a corresponding plurality of radiation beams;
• an optical element comprising optical properties which interact with incident radiation in a manner that depends on a two-dimensional incidence position of the radiation on the element;
• an imaging optical system interposed between the plurality of radiation sources and the element, so as to direct the plurality of radiation beams toward the element and to create images of the plurality of radiation sources on the element;
• at least one radiation detector capable of measuring intensities of the plurality of radiation beams after they interact with the element;
• and
• a controller connected to receive the measured intensities of the plurality of radiation beams and to use the measured intensities of the plurality of radiation beams to determine a position of the element in two dimensions.

A method of determining a two-dimensional position comprising:

• providing an optical element having optical properties which interact with incident radiation in a manner that varies according to a two-dimensional incidence position of the radiation on the element;
• projecting a plurality of radiation patterns onto the element;
• measuring intensities of the plurality of radiation patterns after they interact with the element;
• and
• determining a position of the element in two dimensions based on the measured intensities of the plurality of radiation patterns.

A method of determining a two-dimensional position comprising:

• providing an optical element, which comprises at least one first optical feature that is spatially periodic in a first direction and at least one second optical feature that is spatially periodic in a second orthogonal direction;
• generating Moiré interference by projecting a plurality of radiation patterns onto the element, such that when projected onto the element, each radiation pattern is spatially periodic in at least one of:
• the first direction and the second orthogonal direction;
• measuring aspects of the Moiré interference produced by each radiation pattern;
• and
• determining a position of the element in two dimensions using the measured aspects of the Moiré interference.

An apparatus for determining a position in two dimensions, comprising:

• an optical element, which comprises at least one first optical feature that is spatially periodic in a first direction and at least one second optical feature that is spatially periodic in a second orthogonal direction;
• a plurality of individually addressable radiation sources, each of which is spatially periodic in at least one of:
• the first direction and the second orthogonal direction;
• an imaging optical system interposed between the plurality of radiation sources and the element, so as to image the plurality of radiation sources onto the element in a manner that generates Moiré interference;
• a radiation detector positioned to measure aspects of the Moiré interference;
• and
• a controller connected to receive the measured aspects of the Moiré interference and determine therefrom a position of the element in two dimensions.