Abstract:
An optically coupled rotary encoder that is capable of measuring and encoding the angle of rotation of a rotating or stationary object. A polarizer rotates synchronously with the rotatable object and inputs broadband or single frequency unpolarized light. The polarizer outputs and directs polarized light towards a plurality of fixed analyzers and light detectors. Each fixed analyzer outputs and directs further polarized light towards one of the light detectors. Each light detector outputs an electrical signal to a phase processor based upon one attribute of the further polarized light. The phase processor outputs a phase angle with high resolution (&gt;10 bit) with high accuracy and frequency (5 Mhz). The system and method can operate in harsh environments having high temperatures, dirt and debris and is not susceptible to EMI/RFI.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims priority to and incorporates by reference U.S. Provisional Application No. 60/333,288 filed on Nov. 6, 2001 titled OPTICAL ANGLE ENCODERS FOR ADVANCED POWER TRAINS. 
     
    
     GOVERNMENT LICENSE RIGHTS  
       [0002] The U.S. Government has a paid up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of SBIR contract number NSF00-48/CFDA#47.041, award number 0109171. 
     
    
     
       FIELD OF THE INVENTION  
         [0003]    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.  
         BACKGROUND OF THE INVENTION  
         [0004]    Most prior art angle of rotation encoders involve the use of code wheels, magnetic encoders or hall effect sensors. The manufacturing of code wheels requires stamping or lithographic etching, which are both expensive processes. Furthermore, the function of a code wheel is limited to optical diffraction. This constrains the size of code wheels to larger devices.  
           [0005]    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 electromagnetic interference (EMI).  
           [0006]    Also, 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 limitation upon smaller mechanical systems (such as disk drives or medical devices, etc.).  
           [0007]    There are other types of 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.  
         SUMMARY OF THE INVENTION  
         [0008]    It is therefore an object of this invention to provide a non-contact optical system and method of measuring and encoding the angle of rotation of an object, that is more accurate, of higher frequency and of greater tolerance to environmental extremes than the prior art.  
           [0009]    It is a further object of this invention to provide a system and method of accurately measuring and encoding the angle of rotation of an object with a sampling frequency substantially in excess of the prior art.  
           [0010]    It is a further object of this invention to provide a system and method of accurately measuring and encoding the angle of rotation (orientation) of multiple stationary (non-rotating) objects.  
           [0011]    It is a further object of this invention to provide a system and method of accurately measuring and encoding the angle of rotation of a crankshaft of an advanced automotive powertrain, such as a crankshaft of an electric or hybrid electrical vehicle.  
           [0012]    This 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 plurality 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.  
           [0013]    In a preferred embodiment, 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 light source in response to the input of the electrical signal from each of the first plurality of light detectors.  
           [0014]    Preferably, the at least one attribute of the polarized light includes a measurement of the optical power. Preferably, the phase processor simultaneously samples the electrical signal from each of the first plurality of light detectors.  
           [0015]    Optionally, 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.  
           [0016]    In one embodiment, the angle of rotation encoder further includes a polarizer configured to rotate synchronously 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. In this embodiment, the first object is rotatable and the polarizer is configured to rotate synchronously with the first object.  
           [0017]    In one embodiment, 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. Optionally, the polarizer is disposable or detachable and re-usable on at least a second object.  
           [0018]    In one embodiment, the first plurality of analyzers includes at least three analyzers that each have a unique angle of polarization. Preferably, the first plurality of analyzers includes three analyzers having angles of polarization approximately 120 degrees apart.  
           [0019]    In one embodiment, 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. Optionally, the light originating from the light source is transmitted to the polarizer through an optical fiber. Optionally, the first plurality of light detectors receives light from a unique one of the first plurality of analyzers through an optical fiber.  
           [0020]    In some embodiments, 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 light beams being directed to a unique one of the first plurality of analyzers. Optionally, at least one of the at least a first plurality of light beams is output directly towards the second light detector.  
           [0021]    In another embodiment, 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. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:  
         [0023]    [0023]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.  
         [0024]    [0024]FIG. 2 illustrates the intensity of light received by the light detector as a function of the relative angle of polarization of the polarizer as compared to the angle of polarization of the analyzer.  
         [0025]    [0025]FIG. 3 illustrates the intensity of light received by the light detector as a function the relative angle of polarization of the polarizer as compared to a reference angle of polarization.  
         [0026]    [0026]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 of rotation of an object, such as a polarizer.  
         [0027]    [0027]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.  
         [0028]    [0028]FIG. 6 is simplified block diagram illustrating, in accordance with an embodiment of the invention, the system shown in FIG. 5 optical fiber links.  
         [0029]    [0029]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.  
         [0030]    [0030]FIG. 8 is a simplified block diagram illustrating, in accordance with an embodiment of the invention, a system for non-contact encoding of the angle of rotation of an object utilizing a non-polarizing beam splitter.  
         [0031]    [0031]FIG. 9 is a simplified block diagram illustrating, in accordance with an embodiment of the invention, a system for non-contact encoding of the angle of rotation (orientation) of multiple stationary (non-rotating) objects. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]    Aside from the preferred embodiment or the embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description of the invention or illustrated in the drawings in accordance with the invention.  
         [0033]    [0033]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 light  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 .  
         [0034]    The rotating polarizer  114  and the analyzer  116  each polarize light at a particular angle of polarization. The angle of polarization of each device,  114  or  116 , is dependent upon the angle of rotation of each device  114  or  116 , respectively. When both the rotating polarizer  114  and the analyzer  116  are positioned at the same angle of polarization, the maximum amount of light passes through both the polarizer  114  and the analyzer  116 . When both devices  114  and  116  are positioned at the same angle of polarization, they are positioned at the same angle of rotation.  
         [0035]    When the polarizer  114  and the analyzer  116  are positioned at angles of polarization (rotation) that are 90 degrees apart from each other, the minimum amount of light passes through the rotating polarizer  114  and the analyzer  116 . The intensity of the light  119  received by the light 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 . Likewise, the amplitude of the electrical signal  122 , expressed in terms of signal current, is also indicative of the intensity of the light received by the light detector  120 .  
         [0036]    [0036]FIG. 2 illustrates the intensity  124  of light received by the light detector  120  as a function of the relative angle of polarization (rotation) of the polarizer  114  as compared to the angle of polarization (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 of polarization (rotation) and alters the relative difference between the angle of polarization (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 light  119  to oscillate through one full sinusoidal cycle of light intensity  124  as shown.  
         [0037]    The intensity  124  of the light  119  is maximized when the angle of polarization (rotation) of the polarizer  114  differs from the angle of polarization (rotation) of the analyzer  116  by a value of 0 degrees or by a multiple of 180 degrees. For example, the angle of polarization (rotation) difference values that maximize the intensity of the light  119  include 0, 180, 360 and 540 degrees etc.  
         [0038]    The intensity  124  of the light  119  is minimized when the difference between the angle of polarization (rotation) of the polarizer  114  and of the analyzer  116  is a an odd multiple of 90 degrees. For example, angle of polarization (rotation) difference values that minimize the intensity of the light  119  include 90, 270 and 450 degrees etc.  
         [0039]    In one embodiment, the light detector  120  includes a photodiode (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) (Ω) between the polarizer  114  and a reference angle of polarization (rotation), is as follows:  
           I (Ω)= K[P   o   +m P   o  sin(2(Ω+Ω o ))] 
         [0040]    where (K) is a constant, (P o ) is an optical power value, (m) is a modulation efficiency value; (Ω) is a relative angle of polarization (rotation) value and (Ω o ) is a relative angle of polarization (rotation) offset value.  
         [0041]    [0041]FIG. 3 illustrates the amplitude of the current I (Ω)  122  generated by the light detector  120  as a function of the relative angle of polarization (rotation) of the polarizer  114  as compared to a reference angle of polarization (rotation)  134 . The amplitude of the current I (Ω)  122  generated by light detector  120  is proportional to the intensity  124  of light  119  received by the light detector  120 .  
         [0042]    The reference angle of polarization (rotation)  134  is depicted as being 45 degrees offset (counter clockwise) from a vertical angle of polarization (rotation)  136 . In this illustration, the analyzer  116  is positioned at the vertical angle of polarization (rotation)  136 , corresponding to Ω o =0 degrees.  
         [0043]    When the polarizer  114  is positioned at the reference angle of polarization (rotation)  134 , the amplitude of the current I (Ω)  122  generated by light detector  120  is equal to (K) (Po). When the polarizer  114  is positioned at the vertical angle of polarization (rotation)  136 , 45 degrees offset from the reference angle of polarization, the amplitude of the current I (Ω)  122  generated by light detector  120  is equal to (K) (Po)+(K)(m)(Po).  
         [0044]    When the polarizer  114  is positioned at 90 degrees (clockwise) offset  138  from the reference angle of polarization  134 , equal to 45 degrees (clockwise) offset from the vertical angle of polarization (rotation)  136 , the amplitude of the current I (Ω)  122  generated by the light detector  120  is again equal to (K) (Po).  
         [0045]    When the polarizer  114  is positioned at 135 degrees (clockwise) offset  140  from the reference angle of polarization  134 , equal to 90 degrees (clockwise) offset from the vertical angle of polarization (rotation)  136 , the amplitude of the current I (Ω)  122  generated by the light detector  120  is again equal to (K)(Po)−(K)(m)(Po).  
         [0046]    When the polarizer  114  is positioned at 180 degrees (clockwise) offset  142  from the reference angle of polarization  134 , equal to 135 degrees (clockwise) offset from the vertical angle of polarization (rotation)  136 , the amplitude of the current I (Ω)  122  generated by the light detector  120  is again equal to (K) (Po).  
         [0047]    The aforementioned angles of polarization (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.  
         [0048]    In summary, when Ω o =0, the reference angle of polarization (rotation) of the polarizer is 45 degrees apart (counter clockwise) from a position that is aligned with the angle of polarization (rotation) of the analyzer  116 . When Ω o =0 degrees, the amplitude of the current of the electrical signal  122  is maximized at Ω=45 degrees and at any multiple of 180 degrees plus 45 degrees. For example, the angle of polarization (rotation) difference values (Ω), which maximize the amplitude of the current of the electrical signal  122 , include 45, 225, and 405 degrees etc.  
         [0049]    The amplitude of the current I(Ω)  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 .  
         [0050]    The maximum or minimum amplitude of the electrical signal current I(Ω)  122  may not be a constant value. For example, the maximum current may differ between the angle of polarization (rotation) values of 0, 180 and 360 degrees. Likewise, the minimum current may differ between the angle of polarization (rotation) values of 90, 270 and 450 degrees.  
         [0051]    The amplitude of the sine wave representing the electrical signal current I(Ω)  122 , is measured from the “middle” current value of the sine wave (Kpo) and not from the lowest current value to (K)(Po)−(K)(m)(Po). 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 minimum and the maximum equally and at any one instant in time.  
         [0052]    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 light detector  120  is proportional to the intensity  124  of the light  119  received by the light detector  120 .  
         [0053]    The variable (Po) 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) (Po).  
         [0054]    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 .  
         [0055]    The relative angle of polarization (rotation) (Ω) and (Ω 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.  
         [0056]    The variables (Po), (m) and (Ω) are time dependent and can change independently from each other. Consequently, the underlying DC component (KPo) and the AC component (m P o  sin (2 (Ω+Ω o )), both being dependent upon (Po), are also time dependent and can change independently from the rotation of the polarizer  114 . The AC component (m P o  sin (2 (Ω+Ω o )), is additionally dependent upon (m), and can change independently from the DC component and independently from the rotation of the polarizer  114 .  
         [0057]    [0057]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 of polarization (rotation) of an object, such as a polarizer  114 . The position of the polarizer  114  may be fixed or rotating.  
         [0058]    This embodiment employs three analyzers (fixed polarizers)  116 A- 116 C, four light detectors  120 A- 120 D outputting electrical signals  122 A- 122 D 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.  
         [0059]    The phase processor  130  is capable of simultaneously sampling the electrical signals  122 A- 122 D at a rate of 5 Mz. Sampling the angle of rotation of a rotating object at 5 Mhz far exceeds the sampling rates provided by the prior art.  
         [0060]    Like shown in FIG. 1, a light source  110  projects light  119  through a lens  112  towards a rotating polarizer  114 . The light  119  passes through a rotating polarizer  114  towards the analyzers  116 A- 116 C. The analyzers  116 A- 116 C are fixed polarizers. The light  119  passes through the analyzers  116 A- 116 C and is directed through a lens  118  and towards light detectors  120 A- 120 D. The light detectors  120 A-D each generate an electric signal  122 A- 122 D that represents at least one attribute of the light  119  received by the light detectors  120 A- 120 D.  
         [0061]    Each of the analyzers  116 A,  116 B and  116 C are configured to polarize the light  119  at a unique and different angle of polarization. Preferably, the angles of polarization of the analyzers  116 A,  116 B and  116 C are 120 degrees apart. Each of the light detectors  120 A,  120 B and  120 C are configured to receive the light  119  polarized by a unique one of the analyzers  116 A,  116 B and  116 C, respectively. Light detector  120 A receives light only passing through analyzer  116 A. Light detector  120 B receives light only passing through analyzer  116 B. Light detector  120 C receives light only passing through analyzer  116 C. Light detector  120 D is configured to receive light  119  that passes through the polarizer  114  but that does not pass through the analyzers  116 A- 116 C.  
         [0062]    Each of the light detectors  120 A- 120 D output an electrical signal having a current amplitude that is proportional to the intensity (power) of the light  119  received by it  120 A- 120 D. These electrical signals  122 A- 122 D are simultaneously transmitted to the phase processor  130 . The phase processor  130  processes these signals  122 A- 122 D and outputs a signal  132  representing the angle of rotation of the polarizer  114  for each instance in time over a period of time.  
         [0063]    Each of the three simultaneous electrical signals  122 A- 122 C are dependent upon the same instantaneous value of (Po), (m) and (Ω) at one instance in time. Each of the simultaneous electrical signals depends upon a unique and different (Ωo) which is dependent upon the unique angle of polarization of the analyzer  116 A- 116 C associated with the particular electrical signal  122 A- 122 C.  
         [0064]    The 3 simultaneous electrical signals  122 A- 122 C provide 3 independent equations for I(Ω) that each have 3 unknown variables (Po), (m) and (Ω). The 3 equations that model each of the electrical signals  122 A- 122 C (I R , I S , I T ) are listed below.  
           I   R (Ω)= K[P   o   +m P   o  sin(2(Ω+0))] 
         I S (Ω)= K[P   o   +m P   o  sin(2 (Ω+⅓))] 
           I   T (Ω)= K[P   o   +m P   o  sin(2(Ω+⅔))] 
         [0065]    The orientation of the angle of polarization for each analyzer  116 A- 116 C are offset by 60°, (120° electrical), thereby producing 3 signals that in principle are equal except for a 120° ⅓ cycle phase difference. Having three independent equations with three unknowns allows for an unambiguous solution for Ω, modulo (½ cycle or shaft turn).  
         [0066]    Mathematically, 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. These quadrature signals are listed below.  
           I   X ={square root}{fraction (3/2)}( S−T )= Km P   o  sin 2 Ω 
           I   Y   =R− ½( S+T )= Km P   o  cos 2 Ω 
         [0067]    These two quadrature signals are without the DC component and are thus centered on zero. The angle of rotation of the polarizer  114  and of an associated object is then given by  
         Ω=tan −1 ( I   X   /I   Y )  
         [0068]    where Ω is the encoded angle of rotation of the polarizer  114 . The angle of rotation calculation is expressed in terms of modulo (½ a shaft turn), and absolute within that increment of ½ a shaft turn. Absolute encoding over a full rotation requires indexing.  
         [0069]    As shown in FIG. 5, a light and dark ring  342 A,  342 B are marked on the exterior of the polarizer  314  to act as an index. Each ring  342 A,  342 B identifies a particular ½ of a rotation of the polarizer  314 . This index information resolves the modulo of ½—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 .  
         [0070]    Light detector  120 D is configured to detect light reflecting off of the light  342 A and the dark ring  342 B. In some embodiments, the light reflecting off of the light  342 A and the dark ring  342 B originates from the light source  110 . In other embodiments, the light reflecting off of the light  342 A and the dark ring  342 B originates from a source other than the light source  110 .  
         [0071]    The phase processor  130  processes the intensity of the light received by the light detector  120 D 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.  
         [0072]    Hence, (Po), (m) and (Ω) can be solved for mathematically, for each instance in time over a period of time. Solving for (Ω) reveals the angle of polarization (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.  
         [0073]    [0073]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  116 A- 116 C.  
         [0074]    Light  117  reflected from the reflective polarizer is polarized according to the angle of polarization (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 light detectors  120 A- 120 C. Electrical signals  122 A- 122 D are transmitted to the phase processor  130  via communications channels  124 .  
         [0075]    The index rings  342 A,  342 B are markings that provides 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 light  119  as measured by each light detector  120 A- 120 C.  
         [0076]    [0076]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  110  to the lens  112 . Optical fiber  346  transmits light passing through each analyzer  116 A- 116 C to each respective light detector  120 A- 120 C. Optical fiber  344  is preferably a non-polarizing optical fiber. Optical fiber  346  transmits a signal output from each respective light detector  120 A- 120 D to the phase processor  130 .  
         [0077]    Use of the optical fibers enables the light source  110  and the light detectors  120 A- 120 D 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.  
         [0078]    [0078]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 perpendicular to the longitudinal axis of a rotating shaft  340 . The polarizer  414  rotates with the rotating shaft. The light source  110  may of may not rotate with the rotating shaft  340 .  
         [0079]    The light  119  emitted from a light source  110  and passing through the lens  112  is directed through the transmissive polarizer  414  and towards the three analyzers  116 A- 116 C. The light  119  passing through the transmissive polarizer  414  is polarized by the transmissive polarizer  414  according to its current angle of polarization (rotation). The light  119  emitted from the light source  110  and passing through the lens  112 , is preferred to be non-polarized.  
         [0080]    Each rotation of the rotating shaft  340  causes one rotation of the transmissive polarizer  414 . Each full rotation of the transmissive polarizer  314  reflects light  119  with two full cycles of polarization. After passing through each analyzer  116 A- 116 C, the light  119  transitions through 2 full sinusoidal cycles of light intensity as measured by each light detector  120 A- 120 C.  
         [0081]    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  120 A- 120 C.  
         [0082]    Like shown in FIG. 6, 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  116 A- 116 C to each respective light detector  120 A- 120 C. An optical fiber  346  can transmit a signal output from each respective light detector  120 A- 120 D to the phase processor  130 .  
         [0083]    [0083]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 . Some of the light emitted from the light source  110  and directed through the lens  112 , passes through the non-polarizing beam splitter  552  and towards the reflective polarizer  514 . The reflective polarizer  514  may or may not be rotating.  
         [0084]    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  120 A- 120 D. Likewise, 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 .  
         [0085]    Light passing through the analyzers  116 A- 116 C from the non-polarizing beam splitter  552  is optionally communicated via fiber optic cable  346  to the light detectors  120 A- 120 C. The signals generated by the light detectors  120 A- 120 D are optionally communicated to the phase processor  130  via fiber optic cables  348 . Light emitted from the light source  110  is optionally communicated to the lens  112  via a fiber optic cable  344 .  
         [0086]    [0086]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  652 A- 652 C are being transported along a conveyor belt  650 . A polarizer  654 A- 654 C is associated with and disposed onto each of the objects  652 A- 652 C. Each polarizer  654 A- 654 C is disposed onto an object  652 A- 652 C at an angle of rotation that represents an attribute, such as the orientation of its associated object  652 A- 652 C.  
         [0087]    When an object  652 A- 652 C arrives at a particular location  656  along the conveyor belt, light  115  emitted from a light source  110  and lens  112  is directed towards and reflected off of the polarizer  654 A- 654 C associated with and disposed onto the object  652 A- 652 C. The light  117  that is reflected by the polarizer  654 A- 654 C is directed towards the analyzers  116 A- 116 C. Light detectors  120 A- 120 D and the phase processor  130  function in accordance with the description of FIG. 4.  
         [0088]    In some embodiments, the polarizers  654 A- 654 C are detachable and reusable. The polarizers  654 A- 654 C can be deployed and disposed onto other objects  652 A- 652 C to indicate their orientation. In some embodiments, the polarizers  654 A- 654 C are disposable.  
         [0089]    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).  
         [0090]    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.  
         [0091]    Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments.  
         [0092]    Although specific features of this invention are shown in some drawings and not in other drawings, this is for convenience only, as each feature may be combined with any or all of the other features in accordance with the invention.  
         [0093]    Other embodiments will occur to those skilled in the art and are within the following claims: