Abstract:
An angular offset sensing device includes an optical encoder having a light generating element and a light sensor. An armature includes a reflective surface having a generally semicircular shape and a surface height continuously increasing from a first end of the surface to a second end of the surface. A housing encloses both the optical encoder and the armature and rotationally supports the armature. An electrical voltage is generated when light from the light generating element is reflected back to the sensor from the reflective surface. The voltage is proportional to a wavelength of the reflected light and is indicative of an angular rotation of the armature relative to the optical encoder. The voltage is corrected for linearity and used for example to signal a vehicle transfer case shift.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. patent application Ser. No. 11/010,729 filed on Dec. 13, 2004 now U.S. Pat. No. 7,138,623. The disclosure of the above application is incorporated herein by reference. 

   FIELD 
   The present disclosure relates in general to rotational sensor systems and more specifically to angular rotational sensor systems used to direct operation of power transfer devices. 
   BACKGROUND 
   Systems for determining the position of rotating shafts are known. Existing systems including sensors which determine a relative position between a gear tooth and a reference tooth are known. Other systems include variable reluctance sensors, multiple element tone rings, inductive magnetic sensor systems and systems which utilize one or more brushes to physically make contact between a rotating part and a reference point. 
   Known systems for determining angular rotation are susceptible to damage from environmental conditions such as dirt, grease and oil products. Systems utilizing brushes for contact are additionally susceptible to wear and/or oxidation of the brushes which leads to a decreased accuracy of the system as well as increased maintenance costs. 
   Optical sensors used for determining torque or rotational speed are also known. Optical encoders having two outputs are capable of determining both a shaft movement and a direction of shaft movement. Incremental encoders having a third output are also known which can locate a unique angular position on a rotating shaft. 
   A disadvantage of known systems using optical encoders is that the number of light sources such as light emitting diodes (LED) increases as the complexity of the measurement type increases. This increases the cost of the system and increases the complexity of the circuitry required to receive and correlate all of the received signal data. There is therefore a need for a system for determining angular rotation which reduces the number of components required and simplifies the overall circuitry. 
   SUMMARY 
   An angular rotation identification device with a contactless optical encoder and pitched reflective surface according to several embodiments of the present disclosure includes an optical device having an angular rotation identification device. An optical device includes a light generating element and a light sensor. A reflective surface has a generally semicircular perimeter shape and a continuously varying surface height from a first end of the surface to a second end of the surface. An electrical voltage generated by light from the light generating element being reflected back to the sensor upon angular rotation of the reflective surface with respect to the optical device is proportional to a wavelength of the reflected light and directly proportional to a distance between the reflective surface and the optical device. 
   According to another aspect of the present disclosure, an optical angular offset sensing device includes an optical encoder including a light generating element and a light sensor. An armature includes a reflective surface, the reflective surface having a generally semicircular shape and a continuously varying surface height from a first end of the surface to a second end of the surface. A housing enclosing both the optical encoder and the armature rotationally supports the armature. An electrical voltage generated by light from the light generating element being reflected back to the sensor from the reflective surface is proportional to a wavelength of the light reflected from the reflective surface to the optical encoder and is indicative of an angular rotation of the armature relative to the optical encoder. 
   According to yet another aspect of the present disclosure, an optical angular offset sensing system has an optical device including a light generating element and a light sensor. A reflective surface has a generally semicircular perimeter shape and a continuously varying surface height from a first end of the surface to a second end of the surface. A rotatable shaft operably supports the reflective surface. An electrical voltage generated by light from the light generating element being reflected back to the sensor from the reflective surface is proportional to the wavelength of the light reflected to the optical device during rotation of the rotatable shaft. 
   According to yet another aspect of the present disclosure, an optical angular offset sensing system includes an electrical voltage generated by light from the light generating element is received by the sensor after reflection from the reflective surface. A discrete circuit separate from the optical device converts the electrical voltage to a linear voltage indicative of a device angular offset. 
   According to yet another aspect of the present disclosure, a method for controlling a power transfer device using an optical device having a light generating element and a photoelectric device, and a reflective surface includes: producing an output light from the light generating element; continuously increasing a height of the reflective surface from a first end of the reflective surface to a second end of the reflective surface; rotatably positioning the reflective surface to reflect the light from the reflective surface to the photoelectric device such that a wavelength of the reflected light continuously increases as the optical device changes position between the first and second ends; generating an electrical voltage using the photoelectric device, the electrical voltage being proportional to the wavelength of the reflected light; and utilizing the electrical voltage to control a shift position of the power transfer device. 
   A power transfer device with contactless optical encoder of the present disclosure provides several advantages. By using an optical encoder to both transmit light and collect the light after reflection from a reflective surface, brushes previously known for the application of sensing angular rotation are eliminated, which reduces maintenance and improves sensor life. By continuously increasing a height of the reflective surface, a distance from the optical encoder to the reflective surface as the reflective surface rotates changes at a predetermined rate. Rotational motion is thereby sensed as changing reflected light frequency which is converted to a substantially linear analog signal. 
   Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating several embodiments of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a flow diagram of a power transfer system with contactless optical encoder according to a preferred embodiment of the present disclosure; 
       FIG. 2  is a flow diagram of the optical encoder components for the system of  FIG. 1 ; 
       FIG. 3  is an electrical diagram identifying the components for a sensor of the present disclosure; 
       FIG. 4  is an electrical diagram similar to  FIG. 3  further identifying an LED output path as well as a reflected light path returning to a detector of the present disclosure; 
       FIG. 5  is a plan view of an optical encoder device of the present disclosure; 
       FIG. 6  is a side elevational view of the optical encoder of  FIG. 5 ; 
       FIG. 7  is a plan view of a base member according to a preferred embodiment of the present disclosure; 
       FIG. 8  is a side elevational view of the base member of  FIG. 7 ; 
       FIG. 9  is a plan view of a circuit board according to a preferred embodiment of the present disclosure; 
       FIG. 10  is a side elevational view of the circuit board of  FIG. 9 ; 
       FIG. 11  is a perspective view of an armature providing a reflective surface for the optical encoder of the present disclosure; 
       FIG. 12  is a plan view of the armature of  FIG. 11 ; 
       FIG. 13  is a cross sectional view taken at section  13 — 13  of  FIG. 12 ; 
       FIG. 14  is a plan view of a cover element for the optical encoder of the present disclosure; 
       FIG. 15  is a bottom plan view of the cover element of  FIG. 14 ; 
       FIG. 16  is a side elevational view of the cover element of  FIG. 14 ; 
       FIG. 17  is an electrical diagram similar to  FIG. 4  further identifying an LED output path as well as a reflected light path returning to a detector from a curved reflective surface; 
       FIG. 18  is a plan view of an optical encoder device of further embodiments of the present disclosure; 
       FIG. 19  is a side elevational view of the optical encoder of  FIG. 18 ; 
       FIG. 20  is a plan view of a base member similar to the base member of  FIG. 7 ; 
       FIG. 21  is a bottom plan view of the base member of  FIG. 20 ; 
       FIG. 22  is a side elevational view of the base member of  FIG. 20 ; 
       FIG. 23  is a perspective view of an armature providing a continuously curving reflective surface for another optical encoder of the present disclosure; 
       FIG. 24  is a side elevational view of the armature of  FIG. 23 ; 
       FIG. 25  is a plan view of the armature of  FIG. 23 ; 
       FIG. 26  is a cross sectional view taken at section  26 — 26  of  FIG. 25 ; 
       FIG. 27  is a cross sectional view taken at section  27 — 27  of  FIG. 25 ; 
       FIG. 28  is a plan view of a cover element for a second optical encoder of the present disclosure; and 
       FIG. 29  is a side elevational view of the cover element of  FIG. 28 . 
   

   DETAILED DESCRIPTION 
   The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. 
   Referring generally to  FIG. 1  and according to a preferred embodiment of the present disclosure, an optical encoding system  10  includes an optical encoder  12  connectible to a gear train  14 . The gear train  14  is subsequently connected to an electric motor  16 . Optical encoder  12  is also connected to an electronic control module (ECM)  18  to feed electrical output signals from optical encoder  12  to ECM  18  via a communication path  20 . Optical encoder  12  is connected to a shaft  21  of gear train  14  such that angular rotation of shaft  21  can be determined by optical encoder  12 . Electrical signals from optical encoder  12  sent to ECM  18  are used to control the rotational speed of motor  16 . Gear train  14  is used to convert the relatively high rotational speed and low torque of motor  16  to a relatively lower speed, high torque output. Gear train  14  is also used to control the shift position of a movable actuation device  19  associated with the power transfer device  22  which in one embodiment of the present disclosure includes a transfer case for an automobile vehicle (not shown). Such actuation devices  19  may include, without limitation, a range shift mechanism of a multi-speed gearset or a clutch actuator used to apply a clutch engagement force on a friction clutch. 
   Referring generally to  FIG. 2 , optical encoder  12  includes a sensor  23  positioned adjacent to an armature  24 . Light generated by sensor  23  is transmitted to armature  24  as input light  26 . Light reflected by armature  24  is returned to sensor  23  as reflected output  28 . A discreet external circuit  30  is connected to sensor  23  via a circuit input line  32  and a circuit output line  34 . A microcontroller  36  is also connected to sensor  23  via an input line  38  and an output line  40 , respectively. Electrical signals generated by microcontroller  36  are forwarded to ECM  18  as output electrical signals  42  via a microcontroller output line  44 . Electrical power for sensor  23  is provided from ECM  18  to sensor  23  via a sensor input voltage line  46 . 
   Referring next to  FIG. 3 , individual components of sensor  23  include an anode  47  which connects electrical voltage to a light emitting diode (LED)  48 . Current from anode  47  flows through LED  48  and is discharged via a cathode  50  to ground. Sensor  23  further includes a collector  52  which also receives a current input to supply a photo-transistor or photoelectric detector  54 . Current from collector  52  transferred via photoelectric detector  54  is discharged via an emitter  56 . 
   Referring now specifically to  FIG. 4 , the operation of sensor  23  is further identified. Current from anode  47  to LED  48  generates a light output which is transmitted via a light transparent surface  58  to a reflective surface  60  of armature  24 . The input light  26  is reflected by reflective surface  60  and returned as reflected output  28  to photoelectric detector  54 . As reflected output  28  reaches photoelectric detector  54 , the voltage across photoelectric detector  54  increases in proportion to the amount and frequency of reflected light received. A separation distance “A” is normally provided between light transparent surface  58  of sensor  23  and reflective surface  60 . In one preferred embodiment of the present disclosure separation distance “A” is approximately 1.5 millimeters. 
   Referring generally to  FIGS. 5 and 6 , optical encoder  12  according to one preferred embodiment of the present disclosure is constructed with armature  24  having reflective surface  60  enclosed between a base member  62  and a cover member  64 , respectively. Base member  62  and cover member  64  can be provided of a polymeric material which is preferably molded to the shapes identified in  FIGS. 5 and 6 . A circuit board  66  is disposed between base member  62  and cover member  64 . Circuit board  66  functionally supports sensor  23 . Sensor  23  is connected to circuit board  66  by known techniques such as using conductive adhesive or by soldering. Sensor  23  is thereby fixedly connected to circuit board  66 . Armature  24  is rotatably received between cover member  64  and circuit board  66  such that armature  24  can be coupled to shaft  21  (shown in  FIG. 1 ). Base member  62  is connected to cover member  64  via a perimeter wall  68  of base member  62  being slidably received within an annular slot  70  of cover member  64 . Separation distance “A” is clearly distinguishable in reference to  FIG. 6 . An assembly width “B” of base member  62  and cover member  64  is approximately 11.2 mm in one preferred embodiment of the present disclosure. A plurality of electrical leads  72  are connected to circuit board  66  and in the embodiment shown in  FIG. 5  extend outward from optical encoder  12  for connection to external electrical connections. Electrical connections made to leads  72  include a voltage supply such as sensor input voltage line  46  as well as ground connections and sensor  23  voltage/current output connections. 
   Referring generally now to  FIGS. 7 through 9 , base member  62  further includes a through aperture  74  with a through aperture diameter “E” provided through a sleeve  75  having a sleeve outer diameter “F”. An opposed pair of engagement wall surfaces  76  have a wall spacing “G” defining a cavity  78  there-between. Cavity  78  has a cavity width “H”. Annular slot  70  is provided between perimeter wall  68  and an inner perimeter wall  77 . Perimeter wall  68  has an outer diameter “J”. Annular slot  70  is defined between a base perimeter wall inner diameter “K” and an inner wall outer diameter “L” of inner perimeter wall  77 . 
   In one preferred embodiment of the present disclosure, through aperture diameter “E” is approximately 22.3 millimeters, sleeve outer diameter “F” is approximately 25.3 millimeters, wall spacing “G” is approximately 25.1 millimeters and cavity width “H” is approximately 22.6 millimeters. It is further noted that in one preferred embodiment of the present disclosure, base outer diameter “J” is approximately 58.65 millimeters, base perimeter wall inner diameter “K” is approximately 56.15 millimeters and inner wall outer diameter “L” is approximately 53.5 millimeters. Through aperture diameter “E” provides clearance for slidably mounting armature  24  to sleeve  75 . These dimensions are exemplary of one preferred embodiment of the present disclosure. It should be obvious that the dimensions provided herein can be varied for any application of an optical encoding system  10  of the present disclosure. 
   Referring generally now to both  FIGS. 10 and 11 , circuit board  66  includes a perimeter  79  having a diameter “M”. A circuit board aperture  80  is also provided having an aperture diameter “N”. Sensor  23  is directly connectible to a surface  82  of circuit board  66  by forming a connecting joint  84 . As previously noted, connecting joint  84  can be made using a conductive adhesive, a solder joint or other known electrical contact joining techniques.  FIG. 11  also identifies that a substantial portion of leads  72  extend outwardly beyond perimeter  79  of circuit board  66 . Leads  72  are also connected to surface  82  similar to sensor  23 . 
   In one preferred embodiment of the present disclosure, diameter “M” is approximately 53 millimeters such that circuit board  66  is captured within base perimeter wall inner diameter “K” and physically retained against inner perimeter wall  77  as shown in  FIG. 5 . Circuit board  66  further includes a circuit board thickness “P”. According to one preferred embodiment of the present disclosure, circuit board thickness “P” is approximately 1.1 millimeters. 
   Referring now to  FIG. 12 , armature  24  includes reflective surface  60  formed on a first side of a semispherical flange portion  86 . A reduced diameter flange portion  88  is oppositely positioned from semispherical flange portion  86 . An engagement tooth  90  is provided within a sleeve  92  which longitudinally extends through armature  24  and is coaxially aligned with an armature axis of rotation  94 . Shaft  21  (shown in reference to  FIG. 1 ), is slidably received within sleeve  92 . A suitable receiving slot (not shown) is formed within shaft  21  which receives engagement tooth  90 . Any rotation of shaft  21  therefore provides an equivalent rotation of armature  24 . 
   Referring generally now to both  FIGS. 13 and 14 , sleeve  92  provides a sleeve inner wall  96  to slidably receive shaft  21 . At least one color  97  is disposed as a spectrum of color or as a color scale on reflective surface  60 . In the embodiment shown, color  97  starts at a first end  98  of semispherical flange portion  86  and extends to a second end  100  of semispherical flange portion  86 . Color  97  can be provided as shown ranging from a violet to a red color spectrum. In another embodiment of the present disclosure (not shown) color  97  is formed as varying intensities of a color such as black beginning at first end  98  as a light black or gray and extending to a fully black color adjacent second end  100 . Semispherical flange portion  86  is defined within an angle θ. Angle θ can vary at the discretion of the designer and to suit a desired angular rotation of shaft  21 . In one preferred embodiment of the present disclosure, angle θ is approximately 180°. In an alternate embodiment of the present disclosure angle θ is approximately 155°. 
   Semispherical flange portion  86  includes a semishere radius “Q”. Reduced diameter flange portion  88  includes a radius “R”. In one preferred embodiment of the present disclosure, semisphere radius “Q” is approximately 22.28 millimeters and radius “R” is approximately 15.2 millimeters. 
   Referring now to  FIGS. 4 ,  5  and  13 , light from sensor  23  is emitted by LED  48 , reflected from reflective surface  60  and received by photoelectric detector  54 . The light reflected from reflective surface  60  has a wavelength which is determined by the particular color or intensity of color disposed along reflective surface  60 . An electrical voltage produced by photoelectric detector  54  is therefore directly proportional to a wavelength of the reflected light. Optical encoding system  10  therefore provides an electrical signal from optical encoder  12  which is directly proportional to the wavelength of reflected light. As armature  24  rotates with respect to sensor  23 , the output voltage of sensor  23  varies with the wavelength of the reflected light. This permits a direct correlation between the output voltage of sensor  23  and an angular rotation of shaft  21 . Because armature  24  and circuit board  66  are substantially enclosed between base member  62  and cover member  64 , contaminants are prevented from contacting reflective surface or sensor  23 . This reduces the chance that reflected light from reflective surface  60  will vary in wavelength based on surface contamination. 
   Referring next to both  FIGS. 15 and 16 , cover member  64  includes a perimeter wall  102  which when assembled with base member  62  as seen in  FIG. 6 , extends outwardly of perimeter wall  68 . Cover member  64  also includes an aperture  104  having an aperture diameter “U”. An opposed pair of engagement surfaces  106  are created at one location of perimeter wall  102 . A clearance dimension “V” is provided between engagement surfaces  106 . In one preferred embodiment of the present disclosure, cover diameter “S” is approximately 55.6 millimeters, cover inner diameter “T” is approximately 53.6 millimeters, aperture diameter “U” is approximately 20.8 millimeters and clearance dimension “V” is approximately 18.3 millimeters. 
   As armature  24  rotates relative to circuit board  66  and sensor  23 , sensor  23  receives reflected light in wavelengths in the visible light region of the electromagnetic spectrum between approximately 35 nanometers to approximately 1,000 nanometers. In one preferred embodiment of the present disclosure, the received wavelengths range between approximately 35 nanometers to approximately 750 nanometers and correspond to an angle θ of approximately 155°. A voltage produced by sensor  23  ranges from zero to approximately 5 volts DC. A linear output voltage of sensor  23  is desirable to provide quantifiable ranges of voltages corresponding to desired shift points of power transfer device  22 . Both external circuit  30  and microcontroller  36  are therefore provided to convert the output voltage of sensor  23  to a linear output voltage. 
   Referring back to  FIGS. 1 through 4 , sensor  23  receives input voltage from ECM  18  which is distributed to both anode  47  and collector  52 . Light generated by LED  48  is directed towards reflective surface  60 . The color or spectrum of colors provided on reflective surface  60  reflects light back to sensor  23  at a wavelength of the color at the relative position on reflective surface  60  directly adjacent to sensor  23 . The received light is converted to an electrical voltage having a range of approximately 0 to 5 volts DC by photoelectric detector  54  and emitted by emitter  56 . This voltage is corrected by external circuit  30  and/or microcontroller  36  to a linear output voltage. The linear output voltage is forwarded by microcontroller  36  to ECM  18  where the voltage signal is used to direct motor  16  and gear train  14  to reposition power transfer device  22 . 
   ECM  18  receives an operator&#39;s command for shifting power transfer device  22  to a desired position. ECM  18  generates a pulse width modulation signal which supplies power to motor  16  and gear train  14  to move power transfer device  22  to an appropriate position. Rotational movement of motor  16  and gear train  14  determines an angular position of optical encoder  12 . The output of motor  16  is used as the input to gear train  14  to convert the relatively high speed, low torque output of motor  16  to the relatively low speed, high torque ouput from gear train  14 . The low speed, high torque output of gear train  14  is used to shift the actuation devices  19  within power transfer device  22  and also to define a position of motor  16  via optical encoder  12 . Typical shift positions associated with a power transfer device  22  having a two-speed gear reduction unit and an adaptive transfer clutch include 4 HI, AWD, 2 HI, neutral, and 4 LO. These positions are representative of an all-wheel drive vehicle. Similar positions can also be obtained for a power transfer device of a two-wheel drive and/or a four-wheel drive vehicle. 
   A power transfer device with contactless optical encoder of the present disclosure provides several advantages. By using an optical encoder to both transmit light and collect the light after reflection from a reflective surface, brushes previously known for this application of sensing angular rotation are eliminated. This reduces maintenance and improves system operational life. By varying a range of colors or varying a single color intensity along the reflective surface, a substantially linear voltage output from the encoder and encoder circuitry is used to direct the shifting of, for example, a power transfer case. The reflective surface is created on an armature. A distance from the optical encoder to the reflective surface as the reflective surface rotates is maintained at a substantially constant value. Rotational motion is thereby sensed as a changing reflected light frequency which is converted to a substantially linear analog signal without the need for physical contact between the sensor and armature. 
   Referring now generally to  FIG. 17 , according to several embodiments of the present disclosure, an armature  124  is substituted for armature  24 , to modify the operation of optical encoder  12 . Thicknesses and several other dimensions of base member  62  and cover member  64  are modified as required to incorporate a greater depth of armature  124 , which will be described in greater detail as follows. Other aspects of operation using armature  124  with respect to sensor  23  are similar to operation using armature  24 . Similar to operation of armature  24 , voltage supplied by anode  47  to LED  48  generates a light output which is transmitted via light transparent surface  58  to a continuous pitch reflective surface  126  of armature  124 . The input light  128  is reflected by continuous pitch reflective surface  126  and returned as reflected output  130  to photoelectric detector  54 . As reflected output  130  reaches photoelectric detector  54 , the voltage across photoelectric detector  54  increases in proportion to the amount and frequency of reflected light received. A separation distance “W” varies between light transparent surface  58  of sensor  23  and continuous pitch reflective surface  126 . According to several embodiments separation distance “W” varies between approximately 2.0 millimeters to approximately 5.0 millimeters from light transparent surface  58 . 
   Referring generally to  FIGS. 18 and 19 , an optical encoder  132  according to several embodiments of the present disclosure is constructed with armature  124  having reflective surface  126  enclosed between a base member  134  and a cover member  136 , respectively. Base member  134  and cover member  136 , similar to base member  62  and cover member  64  can also be provided of a polymeric material which is preferably molded to the shapes identified in  FIGS. 18  and  19 . Circuit board  66  is also used in optical encoder  132  and is disposed between base member  134  and cover member  136 . Armature  124  is rotatably received between cover member  134  and circuit board  66  such that armature  124  can be coupled to shaft  21  (shown in  FIG. 1 ). Base member  134  is connected to cover member  136  via a perimeter wall  138  of base member  134  being slidably received within an annular slot  140  of cover member  136 . Separation distance “W” is distinguishable in reference to  FIG. 19  as each of a separation distance W 1  and a separation distance W 2 . In several embodiments, separation distance W 1  corresponds to the greatest separation distance between light transparent surface  58  and sensor  23 , and creates an output of 5 volts from sensor  23 . In several embodiments, separation distance W 2  corresponds to the minimum separation distance between light transparent surface  58  and sensor  23 , and creates an output of θ volts from sensor  23 . An assembly width “X” of base member  134  and cover member  136  is approximately 12.2 mm in several embodiments of the present disclosure. The plurality of electrical leads  72  are connected to circuit board  66  and similar to the embodiment shown in  FIG. 5  extend outward from optical encoder  132  for connection to external electrical connections. Electrical connections made to leads  72  include a voltage supply such as sensor input voltage line  46  as well as ground connections and sensor  23  voltage output connections. 
   Referring generally now to  FIGS. 20 through 22 , base member  134  is generally similar except in depth to base member  62 . Base member  134  includes a through aperture  142  having through aperture diameter “E” provided through a sleeve  144  having sleeve outer diameter “F”. An opposed pair of engagement wall surfaces  146  have wall spacing “G” defining a cavity  148  there-between. Cavity  148  has cavity width “H”. Annular slot  140  is provided between perimeter wall  138  and an inner perimeter wall  148 . Perimeter wall  138  has outer diameter “J”. Annular slot  140  is defined between base perimeter wall inner diameter “K” and inner wall outer diameter “L” of inner perimeter wall  148 . 
   In several preferred embodiments of the present disclosure, through aperture diameter “E”, sleeve outer diameter “F”, wall spacing “G”, cavity width “H”, base outer diameter “J”, base perimeter wall inner diameter “K”, and inner wall outer diameter “L” are equivalent dimensions with base member  62 . Similar to base member  62 , through aperture diameter “E” provides clearance for slidably mounting armature  124  to sleeve  144 . These dimensions can be varied for any application of an optical encoding system  10  of the present disclosure. 
   Referring now to  FIG. 23 , armature  124  includes continuous pitch reflective surface  126  formed on a first side of a semispherical-shaped flange  150 . A reduced diameter flange portion  152  is oppositely positioned from semispherical-shaped flange  150 . An engagement tooth  154  is provided within a through aperture  156  which longitudinally extends through armature  124  and is coaxially aligned with an armature axis of rotation  158 . Shaft  21  (shown in reference to  FIG. 1 ), is slidably received within through aperture  156 . A suitable receiving slot (not shown) is formed within shaft  21  which receives engagement tooth  154 . Any rotation of shaft  21  therefore provides an equivalent rotation of armature  124 . A shoulder  160  is created at junction with semispherical-shaped flange  150 . A first tubular body portion  162  extends axially from flange portion  152 , and a second tubular body portion  164 , generally smaller in diameter than a diameter of first tubular body portion  162 , extends axially from first tubular body portion  162 . 
   Referring generally now to  FIGS. 24 through 27 , a third tubular body portion  166  extends axially opposite with respect to flange portion  152  from first and second tubular body portions  162 ,  164 . First, second, and third tubular body portions  162 ,  164 ,  166  have diameters “Y”, “Z” and “AA” respectively. Through aperture  156  defines a sleeve inner wall  167  to slidably receive shaft  21 . Armature  124  has a total depth “BB” which according to several embodiments is approximately 13.2 mm. Continuous pitch reflective surface  126  has a continuously changing pitch or surface height “CC” with respect to sensor  23 . In the embodiment shown, continuous pitch reflective surface  126  has a surface height “CC” that varies between zero up to approximately 3 mm from a first end  168  to a second end  170  of continuous pitch reflective surface  126 . The outer extents of semispherical-shaped flange  150  are defined within an angle θ. Angle θ can vary at the discretion of the designer and to suit a desired angular rotation of shaft  21 . In several embodiments of the present disclosure, angle θ is approximately 180°. In several other embodiments of the present disclosure angle θ is approximately 155°. Semispherical-shaped flange  150  includes semi-sphere radius “Q”. Reduced diameter flange portion  152  includes radius “R”. An output voltage of reflected light is increased as light reflects from first end  168  to second end  170  of continuous pitch reflective surface  126 . 
   Referring now to  FIGS. 17 ,  18  and  25 , light from sensor  23  is emitted by LED  48 , reflected from continuous pitch reflective surface  126  and received by photoelectric detector  54 . The light reflected from continuous pitch reflective surface  126  has a wavelength which is determined by the value of the separation distance “W” between sensor  23  and continuous pitch reflective surface  126 . An electrical voltage produced by photoelectric detector  54  is therefore directly proportional to the wavelength of the reflected light. Optical encoding system  10  therefore provides an electrical signal from optical encoder  132  which is directly proportional to the wavelength of reflected light. As armature  124  rotates with respect to sensor  23 , the output voltage of sensor  23  varies with the wavelength of the reflected light. This permits a direct correlation between the output voltage of sensor  23  and an angular rotation of shaft  21 . Because armature  124  and circuit board  66  are substantially enclosed between base member  134  and cover member  136 , contaminants are prevented from contacting continuous pitch reflective surface  126  or sensor  23 . This reduces the chance that reflected light from continuous pitch reflective surface  126  will vary in wavelength based on surface contamination. 
   Referring next to both  FIGS. 28 and 29 , cover member  136  includes a perimeter wall  172  which when assembled with base member  134  as seen in  FIG. 19 , extends outwardly of perimeter wall  138 . Cover member  136  also includes an aperture  174  having aperture diameter “U”. An opposed pair of engagement surfaces  176  are created at one location of perimeter wall  172 . A depth “DD” of cover member  136  according to several embodiments is approximately 5.2 mm, which is greater than a corresponding depth of cover member  64  to permit installation of armature  124 . A clearance dimension “V” is provided between engagement surfaces  176 . Similar to optical encoder  12 , in several preferred embodiments of optical encoder  132 , cover diameter “S” is approximately 55.6 millimeters, cover inner diameter “T” is approximately 53.6 millimeters, aperture diameter “U” is approximately 20.8 millimeters and clearance dimension “V” is approximately 18.3 millimeters. 
   As armature  124  rotates relative to circuit board  66  and sensor  23 , sensor  23  receives reflected light in wavelengths of the electromagnetic spectrum between approximately 35 nanometers to approximately 1,000 nanometers. In one preferred embodiment of the present disclosure, the received wavelengths range between approximately 35 nanometers to approximately 750 nanometers using an angle θ of approximately 155°. A voltage produced by sensor  23  ranges from zero to approximately 5 volts DC. A linear output voltage of sensor  23  is desirable to provide quantifiable ranges of voltages corresponding to desired shift points of power transfer device  22 . Both external circuit  30  and microcontroller  36  are therefore used to convert the output voltage of sensor  23  to a linear output voltage. 
   Referring again to  FIGS. 1 through 3  and  17 , sensor  23  receives input voltage from ECM  18  which is distributed to both anode  47  and collector  52 . Light generated by LED  48  is directed towards continuous pitch reflective surface  126 . The continuously changing pitch or curvature of continuous pitch reflective surface  126  reflects light back to sensor  23  at a wavelength corresponding to the relative position where the light strikes continuous pitch reflective surface  126  directly opposed to sensor  23 . The received light is converted to an electrical voltage having a range of approximately 0 to 5 volts DC by photoelectric detector  54  and emitted by emitter  56 . This voltage is corrected by external circuit  30  and/or microcontroller  36  to a linear output voltage. The linear output voltage is forwarded by microcontroller  36  to ECM  18  where the voltage signal is used to direct motor  16  and gear train  14  to reposition power transfer device  22 . 
   ECM  18  receives an operator&#39;s command for shifting power transfer device  22  to a desired position. ECM  18  generates a pulse width modulation signal which supplies power to motor  16  and gear train  14  to move power transfer device  22  to an appropriate position. Rotational movement of motor  16  and gear train  14  determines an angular position of optical encoder  132 . The output of motor  16  is used as the input to gear train  14  to convert the relatively high speed, low torque output of motor  16  to the relatively low speed, high torque ouput from gear train  14 . The low speed, high torque output of gear train  14  is used to shift the actuation devices  19  within power transfer device  22  and also to define a position of motor  16  via optical encoder  132 . Typical shift positions associated with a power transfer device  22  having a two-speed gear reduction unit and an adaptive transfer clutch include 4 HI, AWD, 2 HI, neutral, and 4 LO. These positions are representative of an all-wheel drive vehicle. Similar positions can also be obtained for a power transfer device of a two-wheel drive and/or a four-wheel drive vehicle. 
   A power transfer device with contactless optical encoder of the present disclosure provides several advantages. By using an optical encoder to both transmit light and collect the light after reflection from a reflective surface, brushes previously known for this application of sensing angular rotation are eliminated. This reduces maintenance and improves system operational life. By continuously varying a pitch or curvature of the reflective surface, a substantially linear voltage output from the encoder and encoder circuitry is used to direct the shifting of, for example, a power transfer case. The reflective surface is created on an armature. A distance from the optical encoder to the reflective surface as the reflective surface rotates is continuously varied to produce a change in the reflected light wavelength and therefore the voltage output of the sensor. Rotational motion is thereby sensed as a changing reflected light frequency which is converted to a substantially linear analog signal without the need for physical contact between the sensor and armature. 
   The description of the present disclosure is merely exemplary in nature and, thus, variations that do not depart from the gist of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.