Patent Publication Number: US-2005115087-A1

Title: Optical torque and angle sensor

Description:
FIELD OF THE INVENTION  
      The present invention relates to a method and an apparatus for determining the position of at least one surface having patterned regions.  
     BACKGROUND INFORMATION  
      A plurality of optical sensors currently are used in vehicle applications to detect the positions of moveable components of the vehicle. Optical sensors replace a mechanical switching element and may allow the establishment of a digital communication concept within a vehicle. Optical sensors may be used to measure the revolutions of a crankshaft of an internal combustion engine or to count the revolutions of a vehicle driver&#39;s steering wheel to detect the angle of the front wheels of a vehicle with respect to the vehicle&#39;s body.  
      U.S. Pat. No. 5,930,905 discusses a method and device for angular measurement of a rotatable body. That rotatable body is mounted to be rotated by more than 360° and includes a number of uniform angular markers or teeth. The rotatable body cooperates with at least two further rotatable bodies, which have another number of uniform angular markers or teeth, that angles 0 and v of this two further rotatable bodies are determined and the angular position φ of the rotatable body whose angle is to be measured, is calculated from the angles 0 and ψ, taking into consideration the prevailing geometric conditions. In a first step the whole number k is determined by forming the difference between the number of the teeth M of a gear wheel, multiplied by the angle 0 and the number of teeth of the gear wheel multiplied by the angle ψ. This number is divided by the angle Ω whereas in a second step the angle φ which is to be tacted, is determined starting from this k-value by evaluating the equation  
       φ   =         m   ·   ψ     +       (     m   +   1     )     ·   θ     -       (       2   ⁢   m     +   1     )     ·   k   ·   Ω         2   ⁢   n           
 
 and, in case of negative angles φ, subsequently the full angle period is added to this value. German Published Patent Document No. 100 41 095 discusses a device for measuring the angle and/or a torque on a rotatable body. The angle of rotation is detected by means of magnetic or optical sensors. In an exemplary embodiment two devices are provided, each being provided with two optical readable code traces. The two code traces of each device are embodied in the same manner and are arranged in such a manner that said devices are off-set against each other to allow allocated sensors to output a digital signal. The angle of rotation is calculated from the off-set of two digital signals. In another exemplary embodiment a torsional element having a certain stiffness and is arranged between the two devices. A torque which is transmitted by the rotatable body may thus be calculated from the different angles of the two devices. The device according to the disclosure of German Published Patent Document No. 100 41 095 may be used in the steering column shaft of a motor vehicle. 
 
      International Published Patent Application No. WO 00/28285 discusses an optical sensor. This sensor is used for determining the position of a moveable surface having patterned regions of high and low reflectivity to EMR, the sensor including an application specific integrated circuit (ASIC) at least one lens and at least one EMR-source. The ASIC includes at least one array of EMR-sensitive detectors and processing arrangement, the EMR-source facilitating illumination of the surface and the at least one lens facilitating the focusing of reflected EMR from the surface and generating an image on the at least one array of EMR-sensitive detectors corresponding to the pattern on the surface. Said ASIC, the at least one lens and the at least one EMR-source are enclosed in a single housing providing for accurate optical alignment of these elements with respect to each other and integrated as a single replaceable module. The processing arrangement of the ASIC facilitates processing of the image to determine the position of the pattern on the surface.  
      For single turn applications (360°) torque and angle sensors (TAS) are frequently used. To detect a plurality of rotations, i.e. multiturns of the rotatable element this TAS is operated to electrically count the number of turns. That implies that the TAS is switched with respect to the battery voltage and, on ignition of the internal combustion engine of the vehicle, is connected to supply voltage. At ignition on, the sensor (TAS) measures in a approximately 500 μs an actual position and counts the number of turns. After ignition has been switched off the sensor works in an inactive mode (i.e. sleeping mode). In this inactive mode the refreshing time of said TAS increases to decrease the average of the supply current to operate the TAS. However, the TAS counts the turns in the inoperative mode as well.  
      The multiturn-operation strategy of the TAS provides that the supply current for the TAS, even in its inoperative mode, discharges the battery and decreases the time between two ignition-cycles which may cause motor starting problems. Thus, the recovery period for the vehicles battery is considerably decreased causing significant problems on ignition of the internal combustion engine, which is extremely critical at low ambient temperatures.  
     SUMMARY OF THE INVENTION  
      According to the present invention, a torque and angle module (TAS) is disclosed for detection of multiturns of a moveable component in a vehicle which does not discharge the battery of the respective vehicle. Instead, a gear is provided between a standard code disk having patterned surface regions thereon and a further additional code disk. By means of one sensor element, packaged within the TAS-module, at least two code carriers such as disks may be surveyed contactless, transferring optical signals from the respective surface patterned regions of the code carriers into digital processable information. The number of multiturns of a moveable vehicle component, such as a steering wheel and its associated steering column shaft are detected by means of a modified nonius-calculation or an n-dimensional nonius calculation.  
      An optical system and an illumination system are arranged within a TAS-module&#39;s housing. The illumination system may allow for sequential illumination of different code carriers such as code disks, being arranged on a rotating shaft or another rotating component. Due to the small size of ASIC and sensor, said components fit into a housing of small size as well, which may be packaged close to the movable component the number of turns of which are to be detected. According to different exemplary embodiments of the present invention, a sequential illumination of input code-carrier and a multiturn information carrier may be achieved as well as a sequential illumination of output code carrier and a multiturn information carrier, depending on the respective spatial conditions. The multiturn disk-element may be arranged either assigned to a bearing&#39;s side on a shaft or on a shaft&#39;s circumferential torsion in a distance from a bearing or at a side of the torsion bar.  
      The TAS-multiturn imaging and illumination principle according to the present invention provides for measurement of three different code carriers such as code disks, having 12 tracks, by means of two detective arrays ( 8  tracks) on the ASIC&#39;s surface. The respective carriers provided with code patterns include different reflectivity characteristics to enhance contrast-generation of the ASIC, provided on top of the TAS-module&#39;s housing.  
      Maximum contrast generation is important to enhance distinction between non-symmetrical turning marks and surfaces of laser marks.  
      To increase robustness of the measurement principle, sequential measurement of two code carriers such as code disks may be performed at the same time. This improves reliability of the TAS-module-application.  
      The movement principle as disclosed may be used for single turn sensor arrangements, as well as electrical multiturns sensors. Further, the measurement principle according to the present invention may be used in connection with a mechanical multiturn sensor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows an illumination system of a rotating surface having patterned regions according to known systems.  
       FIG. 2  shows the mechanical configuration of a torque/angle-sensor (TAS) cooperating with two code surfaces having patterned regions thereon.  
       FIG. 3 . 1  shows output phase signals according to the nonius principle for various gear issues.  
       FIG. 3 . 2  shows output phase signals according to the nonius principle for various gear issues.  
       FIG. 4 . 1  shows sequential measurements of code carriers such as disks.  
       FIG. 4 . 2  shows sequential measurements of code carriers such as disks.  
       FIG. 4 . 3  shows sequential measurements of code carriers such as disks.  
       FIG. 5  shows a gear assembly providing a multiturn disk in a first exemplary embodiment according to the present invention.  
       FIG. 6  shows a gear assembly providing a multiturn disk in a second exemplary embodiment according to the present invention.  
       FIG. 7  shows a gear assembly with a bevel-gear assembly in a third exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  shows an illumination system of a rotating surface having patterned regions according to known systems, being assigned to respective surfaces of code carrying elements.  
      As may be seen from  FIG. 1 , a printed circuit board  1  includes a first light emitting diode (LED)  2  and a second LED  3 . Between said light emitting diodes  2 ,  3 , respectively, an ASIC is arranged. Said ASIC  4  includes a surface  5  which is oriented towards a lens  8 . Said ASIC-surface  5  of the ASIC  4  includes a first array  6  and a second array  7 . Below said first LED  2  and said second LED  3  a first light guide  9  and a second guide  10  are provided, each of which detects a first coded pattern  12  and a second coded pattern  14 , each of which are provided on circumferential surfaces of a first code disk  11  and a second code disk  13 . According to the exemplary embodiments given in  FIG. 1  the first code disk  11  and the second code disk  13  are mounted to a shaft  15  which is only given schematically here. Reference numeral  16  identifies reflected rays from the first coded pattern  12 , arranged on the surface of the first code disk  11 , whereas reference numeral  17  identifies reflected rays from the second coded pattern  14  of the second code disk  13 . By means of the lens  8  arranged between the first coded pattern  12  and the second coded pattern  14  and the ASIC  4  arranged at the bottom of the printed circuit board  1 , the reflected rays  16 ,  17  are focused on the first array  6  and the second array  7  arranged on the surface  5  of the ASIC  4 . The profile and the shape of the first coded pattern  12  and the second coded pattern  14  provided on the surfaces of the first code disk  11  and the second code disk  13  are given in greater detail in an enlarged view  18 .  
      Reference numerals  19 ,  20 , respectively, identify a first turning mark and a second turning mark. The first turning mark  19  and the second turning mark  20  are shaped in a saw-teeth-profile  21  including a curved surface  22 . The profile  21  further includes an inclined surface  23 . A first beam  24  results in a reflected first beam  25 . A second beam  26  reaching the curved surface  22  of the profile  21  results in a reflected second beam  27 . The reflected first beam  25  and the reflected second beam  27  generate a optical ASIC-information  28  on the surface  5  of the ASIC  4  mounted between the first LED  2  and the second LED  3 . The optical ASIC-information  28  includes bright/dark-profile  29  on the respective first array  6  and the second array  7  on the ASIC&#39;s surface  5 . By means of the ASIC  4 , the bright/dark-profile  29  is turned into digital information which may be processed further in components not given in greater detail in  FIG. 1 .  
      An optical ASIC information  31  given on the left hand side of  FIG. 1  is generated according to the radiation reflected by the surface of the second coded pattern  14  of the second code disk  13 . The arrow  32  identifies reflected radiation, resulting from irradiation of flat surface  33  of the second coded pattern  14 .  
       FIG. 2  shows the mechanical configuration of a torque/angle-sensor (TAS) cooperating with two coding surfaces having patterned regions.  
      The printed circuit board  1  is mounted within a TAS-module  40 , including the ASIC  4  having a surface  5  oriented towards the lens  8 . On a shaft  45  an output-code-disk  46  and an input-code-disk  47  are arranged, defining a detection area  48 . Within the detection area  48 , the surfaces of the output-code-disk  46  and the input-code-disk  47 , respectively, are detected and focused by means of the lens  8  on the respective first array  6  and the second array  7  on the surface  5  of the ASIC  4 .  
      Within the hollow interior  44  of the shaft  45  a torsion element  43  is mounted. Said shaft  45  is rotatably mounted by means of a first ball bearing  41  and a second ball bearing  42 .  
      The arrangement of  FIG. 1  and  FIG. 2  provides that the TAS module  40 , according to this configuration, discharges a vehicle&#39;s battery even if the TAS module  40  is not in use, i.e. in a “sleeping” mode.  
       FIGS. 3 . 1  and  3 . 2  show output phase signals according to the nonius principle for various gear ratios according to the present invention.  
       FIG. 3 . 1  shows an input code signal  100  of the input-code-disk  47  having a saw-profile. Reference numeral  101  depicts a saw-profile of an output code signal  101 . According to the present invention a multiturn code signal  102  is generated by means of an additional multiturn disk  149 ,  155 , respectively. Said multiturn-code-disks  149 ,  155 , respectively, are mounted by means of an intermediate gearing which has a preselected gear ratio  103 . By the preselected gear ratio  103  a plurality of single multiturn signals  110  according to the selected first gear ratio may be generated. Said single multiturn signals  110  each includes a multiturn signal  110  according to a first gear-ratio  103 , and generates according to the signal sequence given in  FIG. 3 . 1  19 signal peeks  112 . Each single multiturn signal  110  is defined by a signal peak  112  and a signal end  113 . Summarized over 4 turns  106 ,  107 ,  108  and  109  the input-code-disk  47  generates 20 input signals, whereas the output-code-disk  46  generates 16 output signals. However, due to the first gear ratio  103  the multiturn code signal  102  includes 19 single multiturn signals.  
      In  FIG. 3 . 2  the input code signal  100  is the same as given in the example relating to the first gear ratio, i.e. 20 single input code signals. Further, the output code signal  101  includes 16 single output signals summarized over the period of 4 turns  106 ,  107 ,  108  and  109 . According to a second gear ratio  104 , the second multiturn code signal sequence includes 15 single multiturn signals  110  which according to the nonius-principle may allow calculation of the number of turns of a respective rotatable element such as steering wheel shaft  152  (see  FIGS. 5, 6  and  7 ). The second multiturn-code-disk signal sequence  105  is generated by means of multiturn disk arrangements  149 ,  155  (see  FIGS. 5, 6  and  7 ).  
      Due to the different gear ratios  103  and  104  in relation to the multiturn code signal sequences  102  and  105 , the single multiturn signals  111  of the sequence  105  in  FIG. 3 . 2  are longer as compared to the signal duration of the single multiturn signals  110  according to the gear ratio given in  FIG. 3 . 1 .  
      The bright images on the ASIC are produced at positions in which the light may reach the ASIC. This happens, when the light is reflected at the turning marks and focused by the lens. The dark images on the ASIC are produced when the light is reflected at a laser mark and does not reach the lens and the ASIC.  
       FIGS. 4 . 1 , 4 . 2  and  4 . 3  show sequential measurement arrangements for code-carriers, having patterned surface-regions.  
      According to the first solution given in  FIG. 4 . 1 , a turning mark profile  120  of the output-code-disk  46  and the input-code-disk  47 , respectively, is arranged in the same orientation, whereas the turning mark profile  120  of the multiturn-code-disks  149 ,  155  is oriented in opposite direction as compared to the turning marks  120  of the output-code-disk  46 , and the input-code-disk  47 , respectively.  
      On the bottom of a printed circuit board the ASIC  4  is mounted in between a first port  128  and a second port  129 . Below that first port  128  and said second port  129  a first angled light guide  122  and a second angled light guide  123  is arranged. By means of the second angled light guide  123  the turning mark profile  120  of the multiturn disk  149 ,  155  is detected. The reflected arrays from the turning mark profile  120  arranged on the surface of the multiturn-code-disks  149 ,  155 , respectively, is focused by a first lens  125  of the lens combination  124  on an array—not given in greater detail here—of ASIC  4 . The reflected arrays of the light, emitted by the first angled light guide  122  is focused by a second lens  126  of the lens combination  124  on respective arrays on the surface of the ASIC  4  oriented towards the lens combination  124 .  
      According to the measurement arrangement given in  FIG. 4 . 2  a first port  128 , a second port  129  and a third port  133  are arranged on the lower surface of the printed circuit board. Between said first port  128  and said second port  129  the ASIC  4  is mounted. As given in the exemplary embodiment shown in  FIG. 4 . 1  a lens combination  124 , including a first lens  125  and a second lens  126  is mounted in between the ASIC  4  and the turning mark profile  120 . The first angled light guide  122 , assigned to the first port  128 , directs light to the turning marks  120  of the input-code-disk  47 . A combined light guide  127 , assigned to the second port  129  and the third port  130 , directs its light to the surfaces of the output-code-disk  46  and the multiturn-code-disk  149 ,  155 .  
      The first lens  125  focuses the reflected rays from the code pattern of the surface of multi-turn-code-disk  149 ,  155 , respectively, on of an assigned array of ASIC  4 . The reflections of the surfaces of the input-code-disk  47 , and the output-code-disk  46  are focused by second lens  126  on the surface  131  of the ASIC  4 .  
       FIG. 4 . 3  shows a third solution of a measuring arrangement in which first port  128 , second port  129  and third port  130  arranged on the lower surface of a printed circuit board. According to this exemplary embodiment a first angled light guide  122  emits light onto the surface of the input-code-disk  47 , whereas the single light guide  132  emits a light only to the surface of the multiturn-code-disk  149 ,  155 , respectively. A second angled light guide  123 , assigned to the third port  130  of the printed circuit board emits light onto the surface of output-disk  46 .  
      The structure of the code of the multiturn-code disc and the input-code disc have the same orientation in relation to the angle based laser marks. The orientation of the turning marks are not afflicted therefrom. The turning marks only shall reflect the light to the lens. The angle of the turning marks only depends on the light guide and the position of the LED and the positions of the lenses. That means, that in the solutions 1, 2 and 3 the code disks including the code are imaged to the same region of the ASIC by the two lenses. Therefore the ASIC is able to read both codes, the code of the turning mark and the code of the laser mark or the combination thereof.  
       FIG. 5  shows a gear assembly providing a multiturn disk in a first exemplary embodiment according to the present invention.  
       FIG. 5  shows a TAS-module  140  assigned to the outer circumference of a steering wheel shaft  152 . Within the TAS-module  140  the ASIC  4  is arranged above a lens combination  124 , including the first lens  125  and the second lens  126 . Below the lens arrangement  125 ,  126  a detecting area  148  is identified.  
      Assigned to the outer circumference of the steering wheel shaft  152  is the input-code-disk  47  a distance  150  from the output-code-disk  46 , also arranged on the outer circumference of the steering wheel shaft  152 . Further, according to the first exemplary embodiment of the present invention a first multiturn disk  149  is mounted to or assigned with respect to the outputcode-disk  46 .  
      The first multiturn-code-disk  149  includes an inner gearing  143 , having arranged a plurality of teeth  153  on its circumference. The inner gearing  143  cooperates with an outer gearing  144  having a plurality of outer teeth  154  arranged thereon. A meshing zone of the inner teeth  153  with the respective outer teeth  154  is identified with reference numeral  145 . Opposite the meshing zone  145 , reference numeral  146  identifies the maximum eccentricity  146  of the gearing  142  assigned to the first multiturn-code-disk  149 . Said gearing  142  is integrated into a combined bearing  141  which is arranged on the outer circumference of the steering-wheel-axle  152 . A sealing element  147  (O-ring) is mounted on the respective side of the gearing  142  which is oriented to the output-code-disk  46 . This may be derived from  FIG. 5 , the arrangement of which is similar to the arrangement given in previously mentioned  FIG. 4 . The outer circumference of the first multiturn-code-disk  149  reflects light which is focused by first lens  125  on the surface  131  of ASIC  4 . The reflected light generated by an illuminating system which is not given in greater detail in the exemplary embodiment according to  FIG. 5 , is focused by second lens  126  onto the surface  131  of ASIC  4 . Due to the eccentricity  146  between the inner gearing  143  and the outer gearing  144  of the gearing  142  a different number, depending on the gear ratio of multiturn signals is detected by the first lens  129  and focused on the respective array on the ASIC  4  assigned into the TAS-module  140 . The input-code-disk  47  and the output-code-disk  46 , respectively, however, rotate without eccentricity and reflect radiation onto the second lens  126 , which focuses the reflected rays onto the ASIC  4  of the TAS-module  140 . The solution given in  FIG. 5  may allow sequential measurement of two code disks at the same time. The measurement of two code disks at the same time enhances the reliability and the performance of the measurement principle.  
       FIG. 6  shows a gear assembly providing a multiturn disk in a second exemplary embodiment according to the present invention.  
      According to the exemplary embodiment given in  FIG. 6 a  second multiturn-code-disk  155  is assigned to the input-code-disk  47 . The second multiturn-code-disk  155  includes plurality of inner teeth  153  cooperating with a plurality of outer teeth  154  in a meshing zone  145 . Opposite the meshing zone  145  the maximum eccentricity between the inner teeth  153  and the outer teeth  154  is depicted by reference numeral  146 . According to the eccentricity, defining the gear ratio between the inner gearing  143  and the outer gearing  144  of the gearing  142  a code pattern sequence is generated which is focused by first lens  125  on ASIC  4  added in TAS-module  145 . In this exemplary embodiment a ball bearing is assigned to a second multiturn-code-disk  155 . The distance between the output-code-disk  46  and the input-code-disk  47  is identified by reference numeral  150 . The surface patterns of the input-code-disk  47  and the output-code-disk  46 , respectively, is detected by the second lens  126  which focuses the reflected light rays onto the lower surface  131  of the ASIC  4 .  
      On the right hand side of  FIGS. 5 and 6 , respectively, a side-elevation of gearing  142  is shown. Within meshing zone  145  the inner teeth  143  of inner gearing  143  mesh with outer teeth  154  of outer gearing  144  of the gearing  142 . Opposite the meshing zone  145  the maximum eccentricity is labeled with reference numeral  146 . The turning ratios 1:1,05 (i.e. 4 turns), 1:1,025 (8 turns) according to  FIG. 3 . 1  and the gear ratios given in  FIG. 3 . 2 , i.e. 1:1,0625 (4 turns) and 1:1,03125 (8 turns) are defined by the eccentricity  146  the number of inner teeth  153  assigned to the inner gearing  143  and consequently the number of outer teeth  154  assigned to the outer gearing  144  of the gearing  142 . In both exemplary embodiments according to  FIGS. 5 and 6  of the present invention, the hollow interior of the steering wheel shaft  152  surrounds a torsion element  43 , which is not given in greater detail in this figures.  
      According to the first and second exemplary embodiment of the present invention given in  FIGS. 5, 6 , respectively, the measurement of the surfaces of the first multiturn disk  149 , and the second multiturn disk  155 , respectively, is performed without an additional ASIC  4 , i.e. by sequential illumination of input-/output-code-disk  47 , 46  and the multiturn-code-disk  149 ,  155  a second ASIC device  4  is superfluous. Since the nonius-measurement principle is integrated to calculate the number of multiturns of the rotatable component, i.e. in this case a steering wheel shaft  152  no discharge of a vehicle battery may occur.  
       FIG. 7  shows the gear assembly with the bevel-gear assembly in a third exemplary embodiment of the present invention.  
      This exemplary embodiment of the present invention distinguishes over the first and second exemplary embodiments of the present invention as given in  FIGS. 5, 6 , respectively, as a bevel gear arrangement  159  is provided. On the outer circumference of a steering wheel shaft  152  an inputcode-disk  47  is spaced in a distance  150  from an output-code-disk  46 . The output-codedisk  46  is provided with a bevel gear which cooperates with a bevel gear code disk  160  arranged in a modified TAS-module  140 . Within meshing zone  145  the bevel gear assigned to the outer circumference of the output-code-disk  46  cooperates with the bevel gear code disk  160 .  
      Within the housing of the modified TAS-module  140  a lens combination  124  is arranged, which cooperates with ASIC  4  arranged on the sealing of the respective housing. Below said lens arrangement  124  the light reflections of the circumferential surfaces  156 ,  157  of the input-code-disk  47  and the output-code-disk  46  are focused and transferred to the ASIC  4  arranged in the modified TAS-module  140 . The code structure of the multiturncode-disk  160  (angle based transmission holds) and the respective input-code-disk  47  (having angle-based laser mark) is the same. In the arrangement according to  FIG. 7  of the present invention a prism  161  is assigned to or incorporated in the ASIC  4  within the modified TAS-module  140 . On a lower plane  162  of the prism  161  light is reflected to a receiving unit  163 , being arranged within the modified TAS-module  140 . Sealing elements  164  are arranged between the moving components of the arrangement according to  FIG. 7  to prevent humidity from entering the hollow interior of the modified TAS-module  140 . A further sealing element  151  is assigned to a ball bearing arranged on the outer circumference of the steering wheel shaft  152 .  
      According to the present invention the nonius-principle with phase-angle behavior is based on the modified nonius calculation of the multiturn-code-disk  149 ,  155  using 2 code-disk&#39;s information. The n-dimensional nonius calculation principle makes use of 3-code-disks in information, i.e. the pattern information of the input-code-disk  47 , the output-code-disk  46  and the multiturn-code-disk  149 ,  155 , respectively. The modified nonius calculation using 2-code-disk information is performed by sequential measurement of the respective 2-code-disks  47 ,  46  or  47 ,  149 ,  155  or  46 ,  149 ,  155 , respectively. The first multiturn-code-disk  149  and the second multiturn-code-disk  155  may be assembled on an steering-wheel axle of a vehicle having three laser marks assigned thereto. The sequential measurement of the patterned regions of the different code disks  46 ,  47 ,  149 ,  155  is performed by sequential illumination of the respective disks the surfaces of which are detected in different sequential modes.