Abstract:
A device for the determination of the degree of relative rotation between two parts or members with respect to each other about a main axis, the device comprising a first detector arrangement, which includes a rotation-imparting element and produces precise information indicating a relative angular position of the two members within the range of 0° and 360°, and comprising a second detector arrangement, which produces approximate information in order to be able to distinguish between full rotations. The second detector arrangement comprises a gear drive ( 40, 45, 75, 71 ) driven by the relative rotary motion of the two members and an absolute position sensor ( 23, 73 ) for the determination of the position of a measuring element ( 76 ) moved by the gear drive ( 40, 45, 75, 71 ). The dimensions of the gear drive ( 40, 45, 75, 71 ) are such that the maximum possible range of relative rotation between the two members parts corresponds to a range of motion of the measuring element ( 76 ), within which range all positions can be distinguished from each other in a geometric manner and which range can be resolved by the position sensor ( 23,73 ) at a resolution corresponding at least to the full rotations between the two members.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     MICROFICHE APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a device for the determination of the degree of relative rotation between two parts or members with respect to each other about a main axis, said device comprising a first detector arrangement, which includes a rotation-imparting element and produces precise information indicating a relative angular position of the two parts within a range of 0° and 360° C. and comprising a second detector arrangement, which produces information in order to be able to distinguish between full rotations. 
     Many such devices have been known and are used for the detection of actual values in control and regulating systems, whereby, a first part represents a stationary “stator,” in which the second part, the “rotor,” is supported in a rotatable manner. The rotor may be the rotor of any motor or the shaft of any gear drive or measuring device; and, the stator may be the stator of the motor or a housing or a mount. The preferable, however, not exclusive field of application of the invention herein, is the determination of the relative rotation of the steering wheel of a motor vehicle. In a steering wheel application, the rotor is the steering wheel shaft and the stator is the steering wheel mount or steering column. 
     Generally, rotation-imparting elements with analog or digital angle sensors are used for the determination of an angle of rotation. Digital angle sensors principally consist of a pattern-bearing arrangement and a pattern-sensing sensor arrangement, which rotate relative with respect to each other corresponding to the relative motion of the two parts. In the case of incremental sensors the pattern-bearing arrangement is a disc or a wheel with marks distributed uniformly over the periphery, the marks being detected by the sensor arrangement and indicated by the generation of corresponding pulses. Successive pulses are counted as a function of the direction of rotation to determine the angle of rotation based on the accumulated sum. In order to use the latter for the determination of the actual position, a reference position must be pre-set and used as reference for the counted value. Usually, this reference position is identified by a separate reference or zero mark, which can be detected by the sensor arrangement. In the case of absolute sensors, however, the pattern is coded as a function of location so that for each angular position an individual sensor signal can be generated, thereby clearly indicating the respective position. 
     If the range of relative motion is greater than 360°, i.e., greater than one full rotation, the indication of an angular position produces ambiguous information concerning the actual degree of relative rotation. The same angular positions within successive full rotations cannot be distinguished from each other geometrically. In order to obtain an unambiguous indication, additional measures are required to allow the distinction between full rotations. 
     An appropriate known measure is a counting of passes as a function of the direction of rotation by means of a reference or zero angle position, as has been disclosed, for example, by literature references DE-C2-3,700,876 and DE-C1-19,508,607 in conjunction with a steering wheel sensor device. These latter known arrangements create particular problems, inasmuch as there is the risk that the counted value is lost when electrical power is shut off or altered due to counting errors; therefore, the entire counter must be initialized periodically in order to calibrate it to zero for a specific reference steering position. 
     In the known arrangements the selected reference point for initialization is that zero pass, which occurs when the center of the range of relative rotation of the steering wheel is passed and represents the straight-line driving direction. In the arrangement of reference DE-C2-3,700,876, the straight-line driving direction is identified by historical evaluation: a detected zero pass is considered the middle of the range of torsion, unless another zero pass is determined within a predetermined time after the former detection. In the arrangement of DE-C1-19,508,607, the straight-line driving direction is detected by a separate sensor, which recognizes the straight-line position of the steered wheels of the vehicle. 
     These above-described known devices are complex and susceptible to problems, inasmuch as counting errors, or even counting value losses, occur between initializations; and, therefore, a factor of uncertainty remains. 
     Reference WO-96/11514 discloses a spiral/pin gear drive. Provided on a stationary disc, concentric to the axis of rotation of the steering wheel, is a spiral groove, in which slides a pin revolving with the steering wheel shaft and which is movable in radial direction. The position of the pin comes into approximate alignment with a mark when the steering wheel reaches the center of its total range of relative rotation. This mark is located either directly on the path of movement of the pin or on the end of a rotary indicator, to which the pin motion is transmitted by means of a lever arm. The ends of the spiral grooves represent the stops for the steering wheel rotation. This known mechanism serves as a positioning aid during assembly of the steering system. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention solves the problem of providing a device for the determination of the degree of relative rotation between two parts or members in such a manner that the device is less prone to trouble; and, the degree of relative rotation between the two parts or members is indicate&amp;reliably, even over more than one full rotation. 
     In the present invention the second detector device, which provides information permitting the distinction between full rotations, comprises a gear drive driven by the rotation of the two parts with respect to each other and an absolute position sensor for the determination of the position of a measuring element moved by the gear drive. The gear drive has dimensions such that the maximum possible range of the relative rotation of the two parts corresponds to a range of motion of the measuring element, within which all positions can be distinguished from each other by geometric means and which can be resolved by the position sensor at a resolution corresponding to the full rotations between the two parts or members. 
     The present invention has the advantage that a repeated initialization of the second detector arrangement is not required. When full rotations of the parts occur, the movement of the measuring element remains within a range, the locations of which can be differentiated directly and absolutely. As rotary movements greater than 360° occur, an absolute position sensor on the measuring element is capable of making a direct distinction between individual full rotations. The position sensor can be relatively compact and simple, because its resolving capabilities need to correspond only to the number of maximum possible full rotations of the two parts or members. 
     In one advantageous embodiment of the present invention the gear drive comprises a spiral groove extending concentrically to the main axis on the surface of a disc mounted to a first part and having a number of convolutions corresponding at least to the number of possible full rotations. A pin engages with the spiral groove, the pin being supported on the second part in such a manner that the radial position of the pin changes with respect to the main axis during the movement of the two parts with respect to each other. Mechanical means are used for the connection of the pin with the measuring element. 
     In the present invention the available absolute position sensor preferably comprises an array of sensor elements mounted to the second part and a sensor object connected with the measuring element. The sensor object moves past the sensor element array when the measuring element is moving, in order to affect, i.e., energize or deenergize, an individual selection of sensor elements in the same manner for each position range, corresponding respectively to a specific full rotation between the parts. 
     The sensor elements may be light barriers, for example, bifurcated light barriers, whereby the sensor object represents a light-blocking diaphragm array for the selective deenergization of the photoreceivers, or reflected-light barriers, whereby the sensor object is a reflecting array for the selective energization of the photoreceivers. The sensor elements may also be configured as a CCD camera or as specific optical ASICs. Instead of optoelectric sensor elements, it is also possible to use inductive or capacitive elements or elements operating with ultrasound. 
     The range of motion of the measuring element may be kept relatively narrow because its determination of location may occur with relatively minor resolution. On the other hand some sensor elements such as, for example, light barriers or inductive sensors cannot be configured as small as desired. In one advantageous embodiment of the present invention it is permissible, measured in the direction of movement of the sensor object, for the detection range of the sensor element array and the length of the sensor object to be considerably greater than the maximum deflecting range of the sensor object. In order to permit the absolute determination of location, the sensor object in this case has several partial divisions spaced along its length. These divisions are different from those of the sensor elements such that, for each position range of the sensor object corresponding to a specific full rotation range between the parts, an individual selection of sensor elements is affected in the same sense. 
     In an alternative embodiment of the present invention, the sensor object may be undivided in its direction of movement and have a length such that it may extend over a number of two or more adjacent sensor elements. This number, preferably, is smaller by 1 (one) than the total number of sensor elements, which, in turn, is preferably smaller by 2 (two) than the number of possible full rotations between the parts. This reduces the risk of ambiguities along the boundaries between respectively two full rotations. 
     The position sensor can be located directly on the path of movement of the pin sliding in the spiral groove in order to monitor a measuring element placed directly on the pin. In an alternative embodiment, however, the pin movement is transmitted to a measuring shaft by rigidly mounting the pin to the end of an arm, which, in turn, is rigidly connected with the measuring shaft. The latter is rotatably supported in the second of the two parts or members and its axis extends parallel to the main axis; and, the position sensor is designed to determine the position of rotation of the measuring shaft. In this case the sensor object, for example, an aperture array with bifurcated light barriers as sensor elements, preferably is an arcuate element, which is mounted to the measuring shaft and extends in concentric direction to the shaft axis, whereby the sensor elements are arranged appropriately in the manner of a circular arch. 
     The rotation-imparting element of the first detection arrangement, which indicates the angular position of the two parts or members relative to each other within one full rotation, may be configured in any manner. It may operate with an incremental or any analog or digital absolute angle sensor. In a particular embodiment of the present invention, an angle sensor is used, which comprises a sensor object configured as a pattern disc mounted to the first part or member and having on its periphery a rim with a detectable pattern, and comprises an array of sensor elements mounted to the second part or member for the generation of electrical pulses as the pattern passes. One of the advantages of this embodiment is that the spiral groove can be provided on a surface of the pattern disc. Design advantages may result when the patterned rim projects in the axial direction from the edge of the pattern disc. 
     The sensor elements of the angle sensor of the first detector arrangement and the sensor elements of the position sensor of the section detector arrangement preferably are located on opposite surfaces of a support disc retained on the second part. 
     Preferably, the second part is stationary and the first part is rotatable. This applies in particular to the use of the invention for the determination of the relative rotation of the steering wheel of a motor vehicle; in this case the steering wheel shaft constitutes the rotatable of the two parts or members while the support of the steering wheel shaft constitutes the second of the two parts or members. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pulled-apart perspective illustration of the essential parts of one form of embodiment of an inventive rotation-measuring device, viewed at an angle from the top; 
     FIG. 2 is the parts shown in FIG. 1, viewed at an angle from the bottom; and 
     FIG. 3 is an assembled device, viewed in section along line A—A of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The illustrated rotation-measuring device is configured such that it can be mounted to the steering column of a vehicle in order to determine the degree of relative rotation of the steering wheel. The parts of the steering wheel and its shaft, as well as the support for the steering wheel, are not illustrated to avoid confusion. The dashed line denoted X—X represents the steering wheel axis. 
     The device has a lower housing part indicated generally at  10  with a circular bottom  11 , whereby a cylindrical exterior wall  12  extends in upward direction from the exterior edge of the bottom  11 . An adjoining cylindrical sleeve or inner wall  13  extends through the center of bottom  11  and upwardly to the same height as exterior wall  12 . Between sleeve  13  and exterior wall  12  there extends concentrically a central or radially intermediate wall  14 , which has the same height and is also an integral part of bottom  11  and is not completely closed in peripheral direction but, instead, has two ends. Between the ends of central wall  14 , bottom  11  has a cutout  15  having the shape of a circular arc. This circular arc extends in space concentric relationship to a hole  16  close to exterior wall  12 , the hole  16  being provided in bottom  11  and adjoined on the underside of bottom  11  by an integral relatively small support collar  17 . 
     The annular space between exterior wall  12  and central wall  14  of lower housing part  10  accommodates an essentially annular support disc  20  fixed in the housing. The upper side of said support disc  20  has arranged on it a plurality of first bifurcated light barriers  21  distributed in peripheral direction. Support disc  20  has an inwardly-extending arcuate segment  22  at a location, which corresponds to the position of arcuate cutout  15  in bottom  11  of the lower housing part. On the lower side of arcuate segment  22  is mounted an array comprising a plurality of second arcuate bifurcated light barriers  23  concentric to a notch  26  provided on the external edge of support disc  20 . In the assembled condition of the device, light barriers  23  extend downwardly out of cutout  15  of housing bottom  11 . 
     A guard ring indicated generally at  30 , essentially having the same exterior and interior diameters as support disc  20 , is positioned in a non-rotatable manner on support disc  20 . Guard ring  30  is composed of two connected concentric parts  31  and  32  surrounding light barrier array  21  on the outside and inside. An annular gap  33  is formed in the upper side of guard ring  30  between parts  31  and  32 , the gap  33  providing peripheral access to the detection area of bifurcated light barriers  21 . 
     A disc indicated generally at  40  located on the same axis as guard ring  30  can be rotated relative with respect to the housing and, therefore, also with respect to guard ling  30  and support disc  20 . Disc  40  has a central opening  42  and is provided on its external edge with a cylindrical rim  43  extending in a downward direction and having a pattern of slits  44  or castellations distributed over its periphery. From the top, this rim  43  comes into engagement with annular gap  33  of guard ring  30  and extends into the detection range of light barriers  21 . The upper side of disc  20  is provided with a spiral groove  45  consisting of several complete convolutions about the center point of disc  40 . The illustrated embodiment has five convolutions. 
     A sliding pin  75 , being a component of a gear drive mechanism indicated generally at  70 , comes into engagement with spiral groove  45 . Mechanism  70  will be described later in detail. 
     An upper housing part indicated generally at  50  has an annular cover wall  51 , from the external edge of which a cylindrical, lateral or side wall  52  extends in downward direction. Cover wall  51  has a large central opening  53 . Lateral wall  52  is slipped, from the top, over the lateral wall  12  of lower housing part  10  and retained there by suitable means at such a height that a certain free space remains between the upper side of disc  40  and the underside of cover wall  51 . 
     Another housing part in the form of a cap  60  is provided and which covers the area of the arcuate cutout  15  in bottom  11  of lower housing part  10 ; and, thus cap  60  covers the array of light barriers  23  from the bottom. 
     Hereinafter, the details of the mentioned gear drive mechanism  70  will be described. This mechanism comprises an arm  71 , with sliding pin  75  mounted to one end thereof. The other end of arm  71  is rigidly connected with a measuring shaft  76  extending parallel to main axis X—X. A lower section of measuring shaft  76  is rotatably supported in hole  16  in support collar  17  at the bottom  11  of lower housing part  10 . The upper end of measuring shaft  76  is supported rotatably in hole  56  formed in cover wall  51  of upper housing part  50 . 
     Notch  26  on the exterior rim of support disc  20  is designed for engagement with measuring shaft  76 . This engagement secures support disc  20  against rotation and ensures that the arcuate array of second light barriers  23  on the underside of support disc  20  is aligned concentric with measuring shaft  76 . A similar notch  36  on guard ring  30  secures this element against rotation. 
     In the range of detection of the arcuate light barrier array, i.e., the location of the circular line between emitters and receivers of the bifurcated light barrier  23 , extends an arcuate light-blocking member  73 , which is connected by spoke-like strips  77  in a rigid manner with the lower end of measuring shaft  76  and extending out of the support collar  17  and having several spaced slits  74 . Light-blocking member  73  represents the “sensor object” of light barrier array  23 . 
     For operation, lower housing part  10  is non-rotatably connected with a first part, i.e., with the support of a steering wheel, in that sleeve  13  is locked together with the (not illustrated) steering column collar. Lower housing part  10  also retains upper housing part  50 , the location of measuring shaft  76 , support disc  20  and guard ring  30 . However, disc  40  having the patterned rim remains rotatable. A second part (not illustrated) steering wheel, is connected in a non-rotatable manner with disc  40 , for example, by locking it together with a projection  47  of disc  40 , whereby the steering wheel shaft extends through central opening  42  of disc  40 . 
     If disc  40  is rotated by rotating the steering wheel, the pattern of slits  44  moves as the sensor object through the detection ranges of bifurcated light barriers  21 , which, as a result, are opened and closed in order to produce electrical signals as a function of rotary motion. The actual rotary position can be deduced from the evaluation of the electrical signals. Disc  40  and light barriers  21  form a rotation-imparting element. In the illustrated embodiment, this rotation-imparting element is configured as an absolute angle sensor. To accomplish this, the pattern of slits  44  over the periphery of rim  43  has a so-called chain code, i.e., the division of the slits is not uniform but varies over the periphery corresponding to a cyclically permutated chain code. In the illustrated embodiment, there are 9 (nine) permutation cycles over the periphery; and, the number of light barriers  21  distributed over the periphery of support disc  20  corresponds thereto. Upon appropriate decoding, output signals of light barriers  21  produce an absolute indication of the angular position of disc  40  in the range between 0° and 360°. 
     During each full rotation of disc  40 , the light barrier signals repeat identically so that individual full rotations cannot be distinguished from each other based on these signals. The additional sensor system, which consists of the arrangement of two light barriers  23 , permits such a distinction. 
     Arm  71  and light-blocking member  73  are arranged relative to each other on measuring shaft  76  in such a manner that light-blocking member  73  assumes its central position on the arcuate light barrier array  23 , when sliding pin  75  on the end of arm  71  is located in the center of the length of spiral groove  45 . In the illustrated example, in which spiral groove  45  has exactly 5 (five) full convolutions, this location represents the center of the third convolution. At the time the device is assembled, before sliding pin  75  is set in spiral groove  45 , the rotary position of measuring shaft  70  and the rotary position of disc  40  are aligned appropriately with respect to each other. 
     During the rotation of disc  40 , pin  75  sliding in spiral groove  45  travels toward the inside or outside, depending on the direction of rotation. In so doing, pin  75  describes a circular path concentric to measuring shaft  76  and rotates shaft  76  accordingly. It will readily be seen that, care must be taken that this circular path crosses all the convolutions of spiral groove  45 . The rotation of measuring shaft  76  results in a corresponding deflection of light-blocking element  73  in the detection range of light barriers  23 . 
     The arrangement of light barriers  23  and the arrangement of slits  74  in light-blocking member  73  are selected in such a manner that no absolute position sensor is created. In the simplest form of the invention, it may be sufficient to provide one single slit  44  and a number of light barriers  23  equal to the number of convolutions of spiral groove  45 . The divisions of light barriers  23  must then be such that they correspond to the moving path of light-blocking member  73  for each full rotation of disc  40 , so that for each full rotation respectively one unambiguously associated unit of light barriers  23  is opened. However, this may involve design problems when the moving path of the light-blocking member is relatively small and in the event correspondingly small light barriers are not available or are too expensive. 
     In order to eliminate this problem in the illustrated embodiment, several slits  44  are provided in the light-blocking member  73 , these being distributed over a length essentially greater than the moving path of light-blocking member  73 . Therefore, the length of the light barrier array is correspondingly greater and so is the distance between light barriers  23 , which, therefore, need not be very small. As a result of the specific dimension of the division of slits  44  in relation to the division of light barriers  23 , it can be ensured that in the different positions of light-blocking member  73 , which correspond to different full revolutions of disc  40 , respectively, different combinations of light barriers  23  are opened and/or closed. As a result of this “coding,” the light barrier signals provide an unambiguous distinction between the individual full rotations of disc  40 . 
     One alternative suitable for longer paths of movement and requiring only relatively few light barriers  23  for the absolute position sensor is to configure light-blocking member  73  without slits and provide light barriers  23  with a length in the direction of movement long enough that said light-blocking member can block respectively two or more adjacent light barriers  23  at the same time. If, for example, five full rotations need to be distinguished, three light barriers A, B and C are adequate, provided the length of the light-blocking member is large enough that it can cover respectively two adjacent light barriers. Considering five different full rotation ranges, the following distinguishable situations can be created: 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Light Barrier: 
                 A 
                 B 
                 C 
               
               
                   
                   
               
             
             
               
                   
                 Rotation 1: 
                 Light 
                 Light 
                 Light 
               
               
                   
                 Rotation 2: 
                 Dark 
                 Light 
                 Light 
               
               
                   
                 Rotation 3: 
                 Dark 
                 Dark 
                 Light 
               
               
                   
                 Rotation 4: 
                 Light 
                 Dark 
                 Dark 
               
               
                   
                 Rotation 5: 
                 Light 
                 Light 
                 Dark 
               
               
                   
                   
               
             
          
         
       
     
     If a distinction needs to be made among six full rotations, four light barriers A, B, C, and D are adequate, provided that the length of the light-blocking member is selected large enough that it can cover respectively three adjacent light barriers. Considering six different full rotation ranges, the following distinguishable situations can be created: 
     
       
         
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Light Barrier 
                 A 
                 B 
                 C 
                 D 
               
               
                   
                   
               
             
             
               
                   
                 Rotation 1: 
                 Dark 
                 Light 
                 Light 
                 Light 
               
               
                   
                 Rotation 2: 
                 Dark 
                 Dark 
                 Light 
                 Light 
               
               
                   
                 Rotation 3: 
                 Dark 
                 Dark 
                 Dark 
                 Light 
               
               
                   
                 Rotation 4: 
                 Light 
                 Dark 
                 Dark 
                 Dark 
               
               
                   
                 Rotation 5: 
                 Light 
                 Light 
                 Dark 
                 Dark 
               
               
                   
                 Rotation 6: 
                 Light 
                 Light 
                 Light 
                 Dark 
               
               
                   
                   
               
             
          
         
       
     
     Generally, the following is applicable: The number n of light barriers is selected smaller by 2 than the number of possible full rotations and the length of the light-blocking member is selected in such a manner that it may reach over n−1 light barriers. The combination of the absolute position sensor, which consists of the light-blocking member on mechanism  70  and light barriers  23 , with the rotation-imparting element, which consists of peripheral rim  43  and light barriers  21 , produces information regarding the degree of relative rotation of the steering wheel in the range of more than one full rotation. Position sensor  73 ,  23  identifies approximate information for various full rotations; and, rotation-imparting element  43 ,  21  indicates as precise information the angular position within each full rotation. After a one-time alignment of the angular position of disc  40  at the time the device is assembled, only one single adjustment is required when the device is locked on the steering mechanism; this permits that the center of the total rotation range of the steering wheel, i.e., the steering position for straight-line driving, is positioned on the center of the adjustment range of the position sensor. 
     In connection with the steering apparatus of a motor vehicle, the inventive device provides a relatively trouble-free means for the production of reliable information regarding steering deviations. This information can be used, for example, in systems for steering assistance, navigation assistance, motor vehicle dynamics control and the like. 
     The present invention is not restricted to the embodiment shown by the drawings, but leaves room for modifications, some of which have already been suggested. The rotation-imparting device may also be provided with a different code pattern than the described one; an incremental angle sensor without coding may be used in conjunction with a counter. 
     The information provided above regarding the bifurcated light barriers and the diaphragm array can be applied in the same manner to different types of sensor elements or matching sensor objects as have already been described as examples herein. However, the absolute position sensor can also be an analog sensor such as, for example, a potentiometer. In this case the measuring element can move the sliding potentiometer element; furthermore, it is also possible to configure the measuring element as moving potentiometer path. In the latter case the potentiometer path may be a resistive coating in one spiral groove provided on a disc similar to disc  40 , while the sliding element is configured as a pin in engagement with the groove similar to sliding pin  74 . In such an arrangement, the electrical leads of the potentiometer would be partially flexible and could be wound in such a manner that they provide play for several full rotations between the two parts or members. 
     The invention herein is not restricted to the use on a motor vehicle steering mechanism but may be used advantageously wherever the relative rotation of any two parts or members over a limited number of full rotations is to be determined in a precise and reliable manner.