WO2004102225A2 - Dispositif de codage d'angle de polarisation optique sans contact - Google Patents

Dispositif de codage d'angle de polarisation optique sans contact Download PDF

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Publication number
WO2004102225A2
WO2004102225A2 PCT/US2004/013958 US2004013958W WO2004102225A2 WO 2004102225 A2 WO2004102225 A2 WO 2004102225A2 US 2004013958 W US2004013958 W US 2004013958W WO 2004102225 A2 WO2004102225 A2 WO 2004102225A2
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WIPO (PCT)
Prior art keywords
angle
light
signal
rotation
polarizer
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Application number
PCT/US2004/013958
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English (en)
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WO2004102225A3 (fr
Inventor
Geert Johannes Wijntjes
Constantine T. Markos
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Visidyne, Inc.
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Application filed by Visidyne, Inc. filed Critical Visidyne, Inc.
Publication of WO2004102225A2 publication Critical patent/WO2004102225A2/fr
Publication of WO2004102225A3 publication Critical patent/WO2004102225A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/344—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells using polarisation
    • G01D5/345—Polarising encoders

Definitions

  • This invention relates to a non-contact optical angle of rotation encoding system and method and more particularly to a system which enables measurement of the angle of rotation of a rotating or fixed object.
  • Magnetic encoders are susceptible to interference when used in high-speed systems, such as turbines. Also, magnetic encoders of the two phase (resolver) or the three phase (synchro) transmitter design, are expensive, have a limited maximum RPM and require an AC power source that further increases their cost. Hall effect sensors provide relatively low signal levels and have temperature limitations, making them vulnerable to electro-magnetic interference (EMI).
  • EMI electro-magnetic interference
  • angle of rotation encoders have significant mass and are required to be attached to a rotating object, such as a rotating shaft, resulting in a substantial Umitation upon smaller mechanical systems (such as disk drives or medical devices, etc.). Angle of rotation encoders may also be limited in their ability not to reduce the size of holes in their encoders since light will not adequately pass through the holes if the holes are too small.
  • angle of rotation encoders such as interferometric based units and potentiometer based units. These devices are cost prohibitive and are limited with respect to the number of rotations of an object that can be accurately encoded.
  • the subject invention results from the realization that an improved method of measuring and encoding the angle of rotation of a stationary or rotating target object is achieved by employing a light source and a rotatable polarizer having an angle of rotation that is synchronous with the angle of rotation of a target object, by employing a plurality of analyzers (fixed polarizers), a plurality of light detectors configured to output a signal in response to at least one attribute of the light polarized by each respective one of the plurahty of analyzers, and a phase processor configured to compute a value representing the angle of polarization of light directed from the rotatable polarizer in response to the input of a signal from each of the plurality of light detectors.
  • a plurality of analyzers fixed polarizers
  • a plurality of light detectors configured to output a signal in response to at least one attribute of the light polarized by each respective one of the plurahty of analyzers
  • a phase processor configured to compute a value representing the
  • an angle of rotation encoder includes a first plurality of analyzers, each responsive to light originating from a light source and configured to polarize the light at a unique angle of polarization, a first plurality of light detectors, each configured to receive light polarized by a unique one of the first plurality of analyzers and configured to output a signal in response to at least one attribute of the polarized light and a phase processor configured to compute a value representing an angle of polarization attribute of the light originating from the hght source in response to the input of the electrical signal from each of the first plurality of light detectors.
  • the at least one attribute of the polarized light includes a measurement of the optical power.
  • the phase processor simultaneously samples the electrical signal from each of the first plurality of light detectors.
  • the angle of rotation encoder can further include a second light detector configured to receive light not being polarized by any of the first plurality of analyzers.
  • the angle of rotation encoder further includes a polarizer configured to rotate synchronously with a first object, configured to be responsive to hght originating from the light source and configured to direct hght originating from the hght source to the first plurahty of analyzers.
  • the first object is rotatable and the polarizer is configured to rotate synchronously with the first object.
  • the angle of rotation encoder further includes a polarizer configured to have an angle of rotation that is synchronous with a first object, configured to be responsive to light originating from the light source and configured to direct light originating from the light source to the first plurality of analyzers.
  • the polarizer is disposable or detachable and re-usable on at least a second object.
  • the first plurality of analyzers includes at least three analyzers that each have a unique angle of polarization.
  • the first plurality of analyzers includes three analyzers having angles of polarization approximately 120 degrees apart.
  • the polarizer is attached to the first object and reflecting light originating from the light source towards the first plurality of analyzers. In another embodiment, the polarizer is attached to the first object and allows the passage of light originating from the light source towards the first plurality of analyzers.
  • the light originating from the light source is transmitted to the polarizer through an optical fiber.
  • the first plurality of light detectors receives light from a unique one of the first plurality of analyzers through an optical fiber.
  • the angle of rotation encoder further includes a non- polarizing light beam splitter configured to receive light from the polarizer and to output at least a first plurality of light beams, each of the hght beams being directed to a unique one of the first plurality of analyzers.
  • a non- polarizing light beam splitter configured to receive light from the polarizer and to output at least a first plurality of light beams, each of the hght beams being directed to a unique one of the first plurality of analyzers.
  • at least one of the at least a first plurahty of light beams is output directly towards the second light detector.
  • the invention provides a method of encoding the angle of rotation of an object including the steps of providing a first plurality of analyzers, each responsive to light originating from a light source and configured to polarize the light at a unique angle of polarization, providing a first plurality of light detectors, each configured to receive light polarized by a unique one of the first plurality of analyzers and configured to output a signal in response to at least one attribute of the polarized light; and providing a phase processor configured to compute a value representing an angle of polarization attribute of the light originating from the light source in response to the input of the electrical signal from each of the first plurality of light detectors.
  • Fig. 1 is a simplified block diagram illustrating the basic principals of encoding an angle of rotation of an object, such as a polarizer, using an analyzer (fixed polarizer) and a light detector;
  • Fig.2 illustrates the intensity of light received by the hght detector of Fig. 1 as a function of the relative angle of polarization of the polarizer as compared to the angle of polarization of each or any analyzer;
  • Fig. 3 illustrates the intensity of hght received by the hght detector of Fig. 1 as a function the relative angle of polarization of the polarizer as compared to a reference angle ofpolarization;
  • Fig.4 is a simplified block diagram, in accordance with the subject invention, of a system for high precision and non-contact encoding of an angle of rotation of an object, such as a polarizer;
  • FIG. 5 is simplified block diagram illustrating, in accordance with an embodiment of the subject invention, the system shown in Fig.4 utilizing a reflective polarizer;
  • Fig. 6 is simplified block diagram illustrating, in accordance with an embodiment of the subject invention, the system shown in Fig. 5 optical fiber links;
  • Fig. 7 is simplified block diagram illustrating, in accordance with an embodiment of the subject invention, the system shown in Fig.4 utilizing a transmissive polarizer;
  • Fig. 8 is a simplified block diagram illustrating, in accordance with an embodiment of the subject invention, a system for non-contact encoding of the angle of rotation of an object utilizing a non-polarizing beam splitter;
  • Fig. 9 is a simplified block diagram illustrating, in accordance with an embodiment of the subject invention, a system for non-contact encoding of the angle of rotation (orientation) of multiple stationary (non-rotating) objects;
  • Fig. 10A is simplified block diagram, in accordance with another embodiment of the subject invention, of a system for high precision and non-contact encoding of an angle of rotation of an object, such as a polarizer;
  • Fig. 10B is a graph of the three signals output from the three detectors of the system of Fig. 10A;
  • Fig. 11 is a graph showing the top, middle and bottom signals at time ti for the signals that are output from the system of Fig. 10 A;
  • Fig. 12 is a graph that shows the reference amplitude and measured amplitude signals for the signals shown on the graph of Fig. 11 ;
  • Fig. 13 is a block diagram of an analog to digital converter for the system of 10 A;
  • Fig. 14 is one embodiment of a polarizing wheel that includes a 2 bit encoder for use with the system of Fig. 10A;
  • Figs. 15A-15C are schematic views of another embodiment of a polarizing wheel for use with the system of Fig. 10 A;
  • Figs. 16A and 16B are block diagrams of one example of the electronic subsystems for the system of Fig. 10 A.
  • Fig. 1 is a simplified block diagram illustrating the basic principals of encoding an angle of rotation of an object, such as a polarizer 114, using an analyzer 116 (fixed polarizer) and a light detector 120.
  • the position of the polarizer 114 may be fixed or rotating.
  • a light source 110 projects light 115 through a lens 112 and towards a rotating polarizer 114.
  • the hght 117 passes through the rotating polarizer 114 and towards the analyzer 116.
  • the analyzer 116 is a fixed polarizer.
  • Light 119 passes through the analyzer 116 and through a lens 118 and towards a light detector 120.
  • the light detector 120 generates an electric signal 122 that represents at least one attribute of the light 119 received by the light detector 120.
  • the rotating polarizer 114 and the analyzer 116 each polarize light at a particular angle ofpolarization.
  • the angle ofpolarization of each device, 114 or 116 is dependent upon the angle of rotation of each device 114 or 116, respectively.
  • the maximum amount of hght passes through both the polarizer 114 and the analyzer 116.
  • both devices 114 and 116 are positioned at the same angle ofpolarization, they are positioned at the same angle of rotation.
  • the minimum amount of hght passes through the rotating polarizer 114 and the analyzer 116.
  • the intensity of the hght 119 received by the hght detector 120 is indicative of the amount of light passing through the polarizer 114 and the analyzer 116 and indicative of the relative difference between the angles the polarization (rotation) between the rotating polarizer 114 and the analyzer 116.
  • the amplitude of the electrical signal 122 expressed in terms of signal current, is also indicative of the intensity of the hght received by the hght detector 120.
  • Fig.2 illustrates the intensity 124 of light received by the hght detector 120 as a function of the relative angle ofpolarization (rotation) of the polarizer 114 as compared to the angle ofpolarization (rotation) of the analyzer 116.
  • the intensity of the light 119 is measured by the light detector 120 after the light 119 has passed through the polarizer 114 and the analyzer 116.
  • Each half turn of the polarizer 114 alters its angle ofpolarization (rotation) and alters the relative difference between the angle ofpolarization (rotation) of the polarizer 114 and of the analyzer 116, by 180 degrees.
  • Each half turn of the polarizer 114 causes the intensity of the hght 119 to oscillate through one full sinusoidal cycle of hght intensity 124 as shown.
  • the intensity 124 of the hght 119 is maximized when the angle ofpolarization (rotation) of the polarizer 114 differs from the angle ofpolarization (rotation) of the analyzer 116 by a value of 0 degrees or by a multiple of 180 degrees.
  • the angle of polarization (rotation) difference values that maximize the intensity of the light 119 include 0, 180, 360 and 540 degrees etc.
  • the intensity 124 of the hght 119 is niinimized when the difference between the angle ofpolarization (rotation) of the polarizer 114 and of the analyzer 116 is a an odd multiple of 90 degrees.
  • angle ofpolarization (rotation) difference values that nrinimize the intensity of the light 119 include 90, 270 and 450 degrees etc.
  • the hght detector 120 includes aphotodiode (not shown) that produces an electrical signal 122 having a current that is proportional to the intensity 124 of the light 119 received by the light detector 120.
  • the electrical signal current (I) 122 generated by the light detector 120 expressed as a function of the relative angle of polarization (rotation) ( ⁇ ) between the polarizer 114 and a reference angle ofpolarization (rotation), is as follows:
  • (K) is a constant
  • (P 0 ) is an optical power value
  • (m) is a modulation efficiency value
  • ( ⁇ ) is a relative angle ofpolarization (rotation) value
  • ( ⁇ o ) is a relative angle ofpolarization (rotation) offset value.
  • Fig. 3 illustrates the amplitude of the current I ( ⁇ ) 122 generated by the light detector 120 as a function of the relative angle ofpolarization (rotation) of the polarizer 114 as compared to a reference angle ofpolarization (rotation) 134.
  • the amplitude of the current I ( ⁇ ) 122 generated by light detector 120 is proportional to the intensity 124 of hght 119 received by the light detector 120.
  • the reference angle ofpolarization (rotation) 134 is depicted as being 45 degrees offset (counter clockwise) from a vertical angle ofpolarization (rotation) 136.
  • the amplitude of the current I ( ⁇ ) 122 generated by light detector 120 is equal to (K) (P 0 ).
  • the amplitude of the current I ( ⁇ ) 122 generated by hght detector 120 is equal to (K) (P 0 ) + (K)(m)(P 0 ).
  • the amplitude of the current I ( ⁇ ) 122 generated by the light detector 120 is again equal to (K) (P 0 ).
  • the amplitude of the current I ( ⁇ ) 122 generated by the light detector 120 is again equal to (K) (P 0 ) - (K)(m)(P 0 ).
  • the amplitude of the current I ( ⁇ ) 1 2 generated by the light detector 120 is again equal to (K) (P 0 ).
  • angles ofpolarization (rotation) of the polarizer 114 span one entire 180 degree sinusoidal cycle of electrical current amplitude, which is proportional to the intensity 124 of light received by the light detector 120, as shown.
  • the reference angle ofpolarization (rotation) of the polarizer is 45 degrees apart (counter clockwise) from a position that is aligned with the angle ofpolarization (rotation) of the analyzer 116.
  • ⁇ o 0 degrees
  • the angle ofpolarization (rotation) difference values ( ⁇ ), which maximize the amplitude of the current of the electrical signal 122 include 45, 225, and 405 degrees etc.
  • the amplitude of the current I( ⁇ ) 122 generated by the light detector 120 includes a direct current (DC) component and an alternating current (AC) component.
  • the AC component transitions through 2 complete cycle per revolution, (1 complete cycle per half revolution), of the polarizer 114.
  • the maximum or minimum amplitude of the electrical signal current I( ⁇ ) 122 may not be a constant value.
  • the maximum current may differ between the angle ofpolarization (rotation) values of 0, 180 and 360 degrees.
  • the minimum current may differ between the angle ofpolarization (rotation) values of 90, 270 and 450 degrees.
  • the amplitude of the sine wave representing the electrical signal current I( ⁇ ) 122 is measured from the "middle" current value of the sine wave (KP 0 ) and not from the lowest current value to (K) (P 0 ) - (K)(m)(P 0 ).
  • the DC component may raise both the minimum and maximum current values of the sine wave, but not necessarily the amplitude of the sine wave, because in theory, the DC component raises both the rmnimum and the maximum equally and at any one instant in time.
  • the value (K) is a constant that converts an optical power value of the light 119 detected by the light detector 120, expressed in units of watts, to an electrical current expressed in units of amperes.
  • the optical power of the light 119 received by the hght detector 120 is proportional to the intensity 124 of the light 119 received by the light detector 120.
  • the variable (P 0 ) is an optical power value, detectable by the light detector 120, that causes the light detector 120 to generate the underlying direct current (DC).
  • the underlying DC current is represented by (K) (P 0 ).
  • the modulation efficiency variable (m), is expressed as a value between 0 and 1 and represents the efficiency of the light detector 120 with regard to its modulation of the output current 122 based upon the measured optical power of the light 119.
  • the relative angle ofpolarization (rotation) ( ⁇ ) and ( ⁇ o) both express the rotational position of an object, such as the rotational position of the polarizer 114, expressed in terms of the number of whole and/or fractional rotations.
  • the variables (P 0 ), (m) and ( ⁇ ) are time dependent and can change independently from each other. Consequently, the underlying DC component (KP 0 ) and the AC component (m P 0 sin (2 ( ⁇ + ⁇ o))), both being dependent upon (P 0 ), are also time dependent and can change independently from the rotation of the polarizer 114.
  • the AC component (m Po sin (2 ( ⁇ + ⁇ o))) is additionally dependent upon (m), and can change independently from the DC component and independently from the rotation of the polarizer 114.
  • Fig.4 is a simplified block diagram, in accordance with the invention, of a system for high precision and non-contact encoding of an angle ofpolarization (rotation) of an object, such as a polarizer 114.
  • the position of the polarizer 114 may be fixed or rotating.
  • This embodiment employs three analyzers (fixed polarizers) 116A-116C, four hght detectors 120A-120D outputting electrical signals 122A-122D into a phase processor 130.
  • the phase processor 130 outputs a value represented by a signal 132 that encodes the angle of rotation of the rotating object 114 over time.
  • the phase processor 130 is capable of simultaneously sampling the electrical signals 122A-122D at a rate of 5 MHz. Sampling the angle of rotation of a rotating object at 5 MHz far exceeds the sampling rates provided by the prior art.
  • a light source 110 projects light 119 through a lens 112 towards a rotating polarizer 114.
  • the hght 119 passes through a rotating polarizer 114 towards the analyzers 116A-116C.
  • the analyzers 116A-116C are fixed polarizers.
  • the light 119 passes through the analyzers 116 A-l 16C and is directed through a lens 118 and towards light detectors 120A-120D.
  • the light detectors 120A-D each generate an electric signal 122A-122D that represents at least one attribute, possibly only an intensity attribute, of the light 119 received by the light detectors 120A-120D.
  • Each of the analyzers 116A, 116B and 116C are configured to polarize the light 119 at a unique and different angle ofpolarization. Preferably, the angles ofpolarization of the analyzers 116A, 116B and 116C are 120 degrees apart.
  • Each of the light detectors 120A, 120B and 120C are configured to receive the light 119 polarized by a unique one of the analyzers 116 A, 116B and 116C, respectively.
  • Light detector 120A receives light only passing through analyzer 116 A.
  • Light detector 120B receives light only passing through analyzer 116B.
  • Light detector 120C receives hght only passing through analyzer 116C.
  • Light detector 120D is configured to receive hght 119 that passes through the polarizer 114 but that does not pass through the analyzers 116A-116C.
  • Each of the light detectors 120A-120D output an electrical signal having a current amplitude that is proportional to the intensity (power) of the light 119 received by it 120A- 120D.
  • These electrical signals 122A-122D are simultaneously transmitted to the phase processor 130.
  • the phase processor 130 in response processes these signals 122A-122D and outputs a signal 132 representing the angle of rotation of the polarizer 114 for each instance in time over a period of time.
  • the phase processor 180 is configured to compute a value representing an angle ofpolarization attribute of the hght originating from the light source in response to the signal output from each of the hght detectors 120A-120C.
  • Each of the three simultaneous electrical signals 122A-122C are dependent upon the same instantaneous value of (P 0 ), (m) and ( ⁇ ) at one instance in time.
  • Each of the simultaneous electrical signals depends upon a unique and different ( ⁇ o) which is dependent upon the unique angle ofpolarization of the analyzer 116 A-l 16C associated with the particular electrical signal 122A-122C.
  • the 3 simultaneous electrical signals 122A-122C provide 3 independent equations for I( ⁇ ) that each have 3 unknown variables (P 0 ), (m) and ( ⁇ ).
  • the 3 equations that model each of the electrical signals 122A-122C are listed below.
  • these three signals can be transformed (condensed) into a pair of quadrature signals, sine and cosine by the algebraic step, the equivalent of a Schott-T transformation.
  • quadrature signals are listed below.
  • ⁇ is the encoded angle of rotation of the polarizer 114.
  • the angle of rotation calculation is expressed in terms of modulo QA a shaft turn), and absolute within that increment of Vz a shaft turn. Absolute encoding over a full rotation requires indexing.
  • a light and dark ring 342A, 342B are marked on the exterior of the polarizer 314 to act as an index.
  • Each ring 342A, 342B identifies a particular Vi of a rotation of the polarizer 314. This index information resolves the modulo of l A- a rotation ambiguity of the polarizer 314 and facilitates the encoding of the absolute angle of rotation over 360 degrees, a full rotation of the polarizer 314.
  • Light detector 120D is configured to detect hght reflecting off of the light 342A and the dark ring 342B.
  • the hght reflecting off of the light 342A and the dark ring 342B originates from the light source 110.
  • the light reflecting off of the light 342 A and the dark ring 342B originates from a source other than the light source 110.
  • the phase processor 130 processes the intensity of the hght received by the light detector 120D in order to determine which half of a full rotation of the polarizer 314, that the polarizer position currently resides in at a particular instant in time.
  • (P 0 ), (m) and ( ⁇ ) can be solved for mathematically, for each instance in time over a period of time. Solving for ( ⁇ ) reveals the angle ofpolarization (rotation) of the polarizer 114, and of any rotating object (not shown) rotating synchronously with the polarizer 114, at each instance in time over a period of time.
  • Fig. 5 is simplified block diagram illustrating, in accordance with an embodiment of the invention, the system shown in Fig.4 utilizing a reflective polarizer 314.
  • the reflective polarizer 314 is disposed perpendicular to the longitudinal axis of a rotating shaft 340.
  • the polarizer 314 rotates synchronously with the rotating shaft 340.
  • Light 115 emitted from a light source 110 and the lens 112 is directed towards the reflective polarizer 314.
  • the reflective polarizer 314 reflects the light 117 emitted from the light source 110 and the lens 112 and redirects it towards the three analyzers 116A-116C.
  • Light 117 reflected from the reflective polarizer is polarized according to the angle ofpolarization (rotation) of the reflective polarizer 314.
  • Light 115 emitted from the light source 110 and the lens 112 is preferred to be unpolarized.
  • Each rotation of the rotating shaft 340 causes one rotation of the reflective polarizer 314.
  • Each rotation of the reflective polarizer 314 reflects light 119 that generates two full sinusoidal cycles of light intensity 124 as measured by the hght detectors 120A-120C.
  • Electrical signals 122A-122D are transmitted to the phase processor 130 via communications channels 124.
  • the index rings 342A, 342B are markings that provide information that identifies which half of a rotation that the angle of rotation of the polarizer 314 is currently residing in. Each half of a rotation corresponds to one sinusoidal cycle of light intensity 124 of the hght 119 as measured by each hght detector 120A-120C.
  • Fig. 6 is simplified block diagram illustrating, in accordance with an embodiment of the invention, the system shown in Fig. 5 utilizing optical fiber links 344, 346 and 348.
  • Optical fiber 344 transmits light 115 emitted from the light source HO to the lens 112.
  • Optical fiber 346 transmits light passing through each analyzer 116A- 116C to each respective light detector 120A-120C.
  • Optical fiber 344 is preferably a non-polarizing optical fiber.
  • Optical fiber 346 transmits a signal output from each respective hght detector 120A-120D to the phase processor 130.
  • optical fibers Use of the optical fibers enables the light source 110 and the light detectors 120A- 120D to be placed outside of an extreme environment. This enables the more sensitive portions of the system to be protected from electromagnetic interference (EMI) and RFI related problems.
  • EMI electromagnetic interference
  • Fig. 7 is simplified block diagram illustrating, in accordance with an embodiment of the invention, the system shown in Fig. 4 utilizing a transmissive polarizer 414.
  • the transmissive polarizer 414 is disposed pe endicular to the longitudinal axis of a rotating shaft 340.
  • the polarizer 414 rotates with the rotating shaft.
  • the hght source 110 may or may not rotate with the rotating shaft 340.
  • the light 119 emitted from a hght source 110 and passing through the lens 112 is directed through the transmissive polarizer 414 and towards the three analyzers 116A-116C.
  • the light 119 passing through the transmissive polarizer 414 is polarized by the transmissive polarizer 414 according to its current angle ofpolarization (rotation).
  • the hght 119 emitted from the hght source 110 and passing through the lens 112 is preferred to be non-polarized.
  • Each rotation of the rotating shaft 340 causes one rotation of the transmissive polarizer 414.
  • Each full rotation of the transmissive polarizer 314 transmits hght 119 with two full cycles ofpolarization. After passing through each analyzer 116 A-l 16C, the light 119 transitions through 2 full sinusoidal cycles of hght intensity as measured by each hght detector 120A-120C.
  • the index ring 342 is a marking that provides information that identifies which 180 degree half of the polarizer rotational cycle that the polarizer 414 currently resides in. Each half of a rotation corresponds to one sinusoidal cycle of transmitted light intensity as measured by each light detector 120A-120C.
  • fiber optic cables can be employed for the embodiment shown in Fig. 7.
  • An optical fiber can transmit light emitted from the light source 110 to the lens 112.
  • An optical fiber 346 can transmit light passing through each analyzer 116A-116C to each respective light detector 120A-120C.
  • An optical fiber 346 can transmit a signal output from each respective light detector 120A-120D to the phase processor 130.
  • Fig. 8 is a simplified block diagram illustrating, in accordance with the invention, a system for non-contact encoding of the angle of rotation of an object utilizing a non- polarizing beam splitter 552.
  • the reflective polarizer 514 may or may not be rotating.
  • Non-polarizing beam splitter 552 Light 519 passing through the non-polarizing beam splitter 552 reflects off of the reflective polarizer 514 and is redirected back towards the non-polarizing beam splitter 552.
  • the non-polarizing beam splitter 552 redirects some of the light 519 reflected from the rotating polarizer 514 towards the light detectors 120A-120D.
  • some of the light reflected from the polarizer 514 passes through (not shown) the non-polarizing beam splitter 552 towards the lens 112 while some of this light is reflected upward (not shown) by the non-polarizing beam splitter 552.
  • Light passing through the analyzers 116A-116C from the non-polarizing beam splitter 552 is optionally communicated via fiber optic cable 346 to the hght detectors 120A- 120C.
  • the signals generated by the hght detectors 120A-120D are optionally communicated to the phase processor 130 via fiber optic cables 348.
  • Light emitted from the hght source 110 is optionally communicated to the lens 112 via a fiber optic cable 344.
  • Fig. 9 is a simplified block diagram illustrating, in accordance with the invention, a system for non-contact encoding of the angle of rotation of a non-rotating object.
  • Various objects 652A-652C are being transported along a conveyor belt 650.
  • a polarizer 654A- 654C is associated with and disposed onto each of the objects 652A-652C.
  • Each polarizer 654A-654C is disposed onto an object 652A-652C at an angle of rotation that represents an attribute, such as the orientation of its associated object 652A-652C.
  • light 115 emitted from a hght source 110 and lens 112 is directed towards and reflected off of the polarizer 654A-654C associated with and disposed onto the object 652A-652C.
  • the light 117 that is reflected by the polarizer 654A-654C is directed towards the analyzers 116A-116C.
  • Light detectors 120A-120D and the phase processor 130 function in accordance with the description of Fig.4.
  • the polarizers 654A-654C are detachable and reusable.
  • the polarizers 654A-654C can be deployed and disposed onto other objects 652A-652C to indicate their orientation.
  • the polarizers 654A-654C are disposable.
  • the embodiments described have various applications including but not limited to, motion control and measurement for various types of motors used for hybrid electric vehicles (HEV), elevators, radar antenna, pick and place applications, cut-to-length of spooled materials such as wires and plastics, programmable logic control units (PLC).
  • HEV hybrid electric vehicles
  • elevators elevators
  • radar antenna pick and place applications
  • cut-to-length of spooled materials such as wires and plastics
  • PLC programmable logic control units
  • the invention can also be applied to the design of a Linear Variable Differential Transformer (LVDT) and a Rotary Variable Differential Transformer (RVDT) and smart toys.
  • LVDT Linear Variable Differential Transformer
  • RVDT Rotary Variable Differential Transformer
  • non-contact optical polarization angle encoder 700, Fig. 10A implements a second phase measurement algorithm within the phase processor.
  • the second phase measurement algorithm does not require the computation of the arctangent
  • Angle encoder 700 includes an LED 702 and a head detector 704 that includes three polarizers 116A', 116B', 116C', and three detectors 120A', 120B', and 120C'- Detectors 128'-128C detect the light from LED 702 that transmits through a
  • LED 702 and head detector 704 are shown as being on opposite sides of polarizing wheel 114', they could otherwise be located on the same side of polarizing wheel 114' if it is capable of reflecting light from LED 702 back to head detector 704.
  • the output of detectors 120A'-120C' respectively provide three output signals 122A', 122B', and 122C', Fig. 10B.
  • Each of the three simultaneous electrical signals 122A'-122C', Fig. 11, are sampled at multiple points in time.
  • a top signal 710 is identified as having the highest amplitude
  • a bottom signal 712 as having the lowest amplitude
  • a middle signal 714 as having an amplitude not higher than the top signal and not lower than the bottom signal.
  • a measured amplitude is determined by subtracting bottom signal 712 from middle signal 714.
  • a reference amplitude is determined by subtracting bottom signal 712 from the top signal 710.
  • An amplitude ratio is determined by dividing the measured amplitude by the reference amplitude.
  • Signals 720 and 722, Fig. 12, represent the reference amplitude and the measured amplitude, respectively, for signals 122A'-122C' Fig. 11.
  • the amplitude ratio is proportional to the rotational position of the rotating polarizing wheel 706 within a 180 degree range.
  • the amplitude ratio equals zero at 724, Fig. 12
  • the measured amplitude equals zero
  • the middle signal amplitude equals the bottom signal amplitude.
  • the middle signal amplitude equals the top signal amplitude.
  • the reference amplitude signal 720, Fig. 13, and the measured amplitude signal 722 are input on lines 730 and 732, respectively, to an analog to digital converter (ADC) to obtain a digital phase data output on line 736.
  • ADC analog to digital converter
  • the digital phase data output signal on line 736 corresponds to the amplitude ratio, which may be used to determine the phase of polarizing wheel 114'.
  • the rotating polarizer 114' is aligned (parallel) with the one of the analyzers 116A'- 116C' that is associated with the top signal.
  • the rotating polarizer 114' is 90 degrees orthogonal (maximally mis-aligned) with the one of the analyzers 116A'-C' that is associated with the bottom signal.
  • the rotating polarizer 114' has a rotational position halfway between the rotational positions at which the amplitude ratio equals zero and one.
  • a complete rotation of the rotating polarizer 114' equals 360 degrees of rotational movement.
  • the rotating polarizer 114' cycles between an amplitude ratio of zero and one every 180 degrees of rotational movement. Consequently, the rotating polarizer 114' rotates through two 180 degree ranges of rotational movement to complete one 360 degree complete rotation.
  • a polarizing wheel 114A which constitutes an embodiment of the rotating polarizer, includes a 2 bit encoder wheel.
  • the 2-bit encoder wheel is a circular area having a black background 750 that resides within the interior of the polarizing wheel.
  • the 2-bit encoder wheel 114A includes 2 semi-circular lines 752 and 754 (shts) that are adjacent to each other in one 90 degree upper right quadrant.
  • One semicircular line (754) resides interior, closer to the center of the polarizing wheel, than the other semi-circular line 752.
  • Each line 752, 754 allows light to be transmitted therethrough, but in another embodiment would reflect hght.
  • Each quadrant of the polarizing wheel can be identified by a unique combination of semi-circular lines.
  • Upper left quadrant 756 includes only the interior semi-circular line 754
  • upper right quadrant 758 includes both semi-circular lines 754 and 752
  • the lower right quadrant 760 includes only the exterior semi-circular line 752
  • lower left quadrant 762 includes neither of the semi-circular lines.
  • rotating polarizer 114B has a surface configured to deflect light from LED 702 to either or both of photo detectors 770 and 772 to resolve any ambiguity between the two 180 degree ranges of rotational movement. If LED 702 shines hght on spot 774 of polarizing wheel 114B, a light will be reflected only to detector 770. However, if LED 702 shines hght on spot 776 once polarizing wheel 114B rotates 180 degrees, then light LED 702 would be reflected only to detector 772 as shown by phantom line 778.
  • polarizing wheel 114B can include angled surfaces 780 to reflect light in a desired manner. Surfaces 780 are similar to those typically used in the production of compact discs.
  • 2-bit photo detectors 802A, 802B, Fig. 16A are used to determine at any point in time, which of the two possible 180 degree ranges of rotational movement that the rotating polarizer 114A resides within.
  • Each 2-bit photo detector 802 A, 802B is aligned with a unique one of the two semi-circular lines to detect the presence or absence of reflected light associated with the unique one semi-circular line.
  • the absence of reflected light indicates the presence of the associated semi-circular line 752 or 754.
  • the presence of reflected light indicates the absence of the associated semi-circular line 752 or 754.
  • the amplitude ratio indicates the approximate position of the rotating polarizer 114A within one of two possible 180 degree ranges.
  • the 2-bit polarizers 802 A, 802B indicate within which of the two possible 180 degree ranges of rotational movement the amplitude ratio corresponds to and the rotating polarizer 114A resides. Consequently, the combination of the amplitude ratio and information provided by the 2-bit polarizers indicates the approximate position of the rotating polarizer 114A within one complete 360 degree revolution.
  • a block diagram 800, Fig. 16A, ofpolarization angle encoder uses the outputs from 2-bit photo detectors 802A and 802B and inputs it into digital machine 804.
  • the outputs of three photodetectors 120A', 120B', and 120C' are input into comparators 806A, 806B and 806C to determine which of these signals is the top, bottom or middle signal.
  • the output of comparators 806A-C are input digital machine 804.
  • the outputs of photodetectors 120A'-C are also input into multiplexers 808A, 808B and 808C which select the corresponding input signals as either the top, bottom or middle signal, respectively, and output four signals into ADC 734.
  • Digital machine 804 is shown in greater detail in Fig. 16B, in which a multiplex control decoder 810 is responsive to the outputs of comparators 806A-C and outputs a control signal to control the operation of multiplexers 808A-C.
  • a magnitude comparator 812 is responsive to 12 bit data from ADC 734 and is used to provide information relating to the incremental advance of polarizing wheel 114A.
  • Magnitude comparator 812 is also responsive to a feedback loop that includes state machine 814 and counter 816 so that it can compare the current value of 12 bit data with the prior value of 12 bit data to determine if the value of the 12 bit data has gone up or down.
  • the 12 bit data from ADC 734 represents a decoded phase angle that may be preliminary and is the approximate rotational position of the rotating polarizer 114A within the 360 degree range. If the decoded phase angle is prehrninary, it is modified by EEPROM 820 with a calibration error value associated with the preliminary decoded phase angle to determine a corrected or final decoded phase angle.
  • the calibration error value is typically determined after the factory assembly of the angle of rotation encoder.
  • the correction (or cahbration) values are stored in EEPROM 820 which is set by factory calibration and can be programmed through interface 822.
  • the calibration error value is determined by measuring the difference between the true angle of rotation of the rotational polarizer 114A and the prehminary decoded phase angle associated with the true angle of rotation of the rotational polarizer 114A. This difference is a cahbration error value that is recorded in association with the preliminary decoded phase angle.
  • the calibration error value compensates for multiple sources of inaccuracies including mis-alignment of the assembled angle of rotation encoder components and the non-linearity of the middle signal which interferes with the complete accuracy of the second algorithm.
  • the preliminary decoded phase angle is modified with a calibration error value associated with the prehrmnary decoded phase angle to determine a corrected decoded phase angle.
  • the corrected decoded phase angle most accurately represents the true angle of rotation of the rotational polarizer 114A based upon the preliminary decoded phase angle.
  • Encoder data interface 824 includes a 12-bit parallel data output 825 which provides signals representing an absolute rotational position and also includes an A/B index data output 827 which provides a signal representing an incremental rotational position.
  • the A/B index data output 827 generates a series of pulses over time, each pulse representing a unit of rotational movement, that can be counted via a counter.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optical Transform (AREA)

Abstract

L'invention concerne un dispositif de codage rotatif à couplage optique permettant de mesurer et de coder l'angle de rotation d'un objet en rotation ou stationnaire. Un polariseur tourne de manière synchrone avec l'objet en rotation et entre une lumière non polarisée large bande ou monofréquence. Le polariseur produit en sortie une lumière polarisée et la dirige vers une pluralité d'analyseurs fixes et de détecteurs de lumière. Chaque analyseur fixe produit en sortie une lumière repolarisée et la dirige vers l'un des détecteurs de lumière. Chaque détecteur de lumière produit en sortie un signal électrique en direction d'un processeur de phase sur la base d'un attribut de la lumière repolarisée. Le processeur de phase produit en sortie un angle de phase présentant une haute résolution (> 12 bits) avec une haute précision et une fréquence élevée (5 MHz). Ce dispositif peut fonctionner dans des conditions extrêmes caractérisées par de hautes températures, de la poussière et des débris, et n'est pas sujet à une perturbation électromagnétique/radioélectrique.
PCT/US2004/013958 2003-05-05 2004-05-05 Dispositif de codage d'angle de polarisation optique sans contact WO2004102225A2 (fr)

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Cited By (8)

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Publication number Priority date Publication date Assignee Title
FR2916042A1 (fr) * 2007-05-07 2008-11-14 Apticod Soc Par Actions Simpli Capteur optique de mesure d'une position angulaire.
WO2011054392A1 (fr) 2009-11-06 2011-05-12 Nokia Siemens Networks Oy Collimateur électriquement contrôlable dans un résonateur laser
EP2388557A1 (fr) * 2010-05-21 2011-11-23 Codechamp Capteur optique de position angulaire absolue utilisant la technique de la polarimétrie
US8345240B2 (en) 2007-04-10 2013-01-01 Renishaw Plc Rotation detection kit
DE102012109221A1 (de) * 2012-09-28 2014-04-03 Deutsches Zentrum für Luft- und Raumfahrt e.V. Opto-elektronischer Sensor
US10209101B2 (en) 2013-08-01 2019-02-19 Renishaw Plc Rotation detection apparatus
US10816649B1 (en) 2017-09-14 2020-10-27 The United States Of America As Represented By The Secretary Of The Air Force Temporally multiplexed LADAR polarimeter
WO2023139014A1 (fr) 2022-01-18 2023-07-27 Danfoss Power Solutions Inc. Détecteur de position angulaire amélioré

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DE102015107908A1 (de) * 2015-02-25 2016-08-25 Günter Grau Vorrichtung zur Messung von Drehwinkeln in Zählwerken und mehrstufigen Drehgebern sowie zugehörige Sensoren

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US3306159A (en) * 1963-06-19 1967-02-28 North American Aviation Inc Angle transducer employing polarized light
US5424535A (en) * 1993-04-29 1995-06-13 The Boeing Company Optical angle sensor using polarization techniques
US6437318B1 (en) * 1999-02-03 2002-08-20 Logitech, Inc. Encoder using polarized filters

Patent Citations (3)

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Publication number Priority date Publication date Assignee Title
US3306159A (en) * 1963-06-19 1967-02-28 North American Aviation Inc Angle transducer employing polarized light
US5424535A (en) * 1993-04-29 1995-06-13 The Boeing Company Optical angle sensor using polarization techniques
US6437318B1 (en) * 1999-02-03 2002-08-20 Logitech, Inc. Encoder using polarized filters

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8345240B2 (en) 2007-04-10 2013-01-01 Renishaw Plc Rotation detection kit
US8368887B2 (en) 2007-04-10 2013-02-05 Renishaw Plc Rotation detection kit
FR2916042A1 (fr) * 2007-05-07 2008-11-14 Apticod Soc Par Actions Simpli Capteur optique de mesure d'une position angulaire.
WO2011054392A1 (fr) 2009-11-06 2011-05-12 Nokia Siemens Networks Oy Collimateur électriquement contrôlable dans un résonateur laser
EP2388557A1 (fr) * 2010-05-21 2011-11-23 Codechamp Capteur optique de position angulaire absolue utilisant la technique de la polarimétrie
FR2960292A1 (fr) * 2010-05-21 2011-11-25 Codechamp Capteur optique de position angulaire absolue utilisant la technique de la polarimetrie
DE102012109221A1 (de) * 2012-09-28 2014-04-03 Deutsches Zentrum für Luft- und Raumfahrt e.V. Opto-elektronischer Sensor
US10209101B2 (en) 2013-08-01 2019-02-19 Renishaw Plc Rotation detection apparatus
US10816649B1 (en) 2017-09-14 2020-10-27 The United States Of America As Represented By The Secretary Of The Air Force Temporally multiplexed LADAR polarimeter
WO2023139014A1 (fr) 2022-01-18 2023-07-27 Danfoss Power Solutions Inc. Détecteur de position angulaire amélioré

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