Patent Abstract:
A human machine interface includes a capacitive sensor disposed on an interior side of a face plate. A control device is rotatably coupled to the face plate and is disposed on an exterior side of the face plate. The control device includes at least one electrically conductive element. The control device rotates about an axis substantially perpendicular to the face plate such that the at least one electrically conductive element follows the rotation of the control device. The capacitive sensor senses a rotational position of the at least one electrically conductive element.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to capacitive controls, and, more particularly, to capacitive encoders. 
     2. Description of the Related Art 
     Current control knobs, such as included in an automotive radio, have a mechanical encoder. A mechanical encoder requires a separate control circuit as well as a hole in the bezel/faceplate for the encoder. Current capacitive designs include a linear slider for volume control or a circular control requiring contact by a finger on the circular face of the control in order to actuate the control. 
     SUMMARY OF THE INVENTION 
     The invention may include a capacitive encoder which utilizes the same controller and patterns as capacitive touch buttons in a bezel or faceplate. This enables a rotating knob control of functions such as volume or tuning in a radio. A mechanical detent may engage the control ring structure in order to provide tactile feedback regarding how far the control ring has been rotated (i.e., in angular degrees) by the user. 
     The invention comprises, in one form thereof, a human machine interface including a capacitive sensor disposed on an interior side of a face plate. A control device is rotatably coupled to the face plate and is disposed on an exterior side of the face plate. The control device includes at least one electrically conductive element. The control device rotates about an axis substantially perpendicular to the face plate such that the at least one electrically conductive element follows the rotation of the control device. The capacitive sensor senses a rotational position of the at least one electrically conductive element. 
     The invention comprises, in another form thereof, a method of operating a human machine interface, including providing a face plate having an exposed exterior side and an unexposed interior side. A capacitive sensor is provided on the interior side of the face plate. A fixed knob housing is attached to the exterior side of the face plate. A control device is rotatably coupled to the knob housing. The control device includes at least one electrically conductive element. The control device is rotatable about an axis substantially perpendicular to the face plate such that the at least one electrically conductive element follows the rotation of the control device. The capacitive sensor is used to sense a rotational position of the at least one electrically conductive element. 
     The invention comprises, in yet another form thereof, a human machine interface including a first capacitive sensor disposed on an interior side of a face plate and having a substantially annular shape defining a central opening. A second capacitive sensor is disposed on the interior side of the face plate within the central opening of the first capacitive sensor. A knob is disposed on the exterior side of the face plate. The knob includes a housing fixedly attached to the exterior side of the face plate and including a central throughhole. A control device is rotatably coupled to the housing and includes at least one first electrically conductive element. The control device rotates about an axis substantially perpendicular to the face plate such that the at least one first electrically conductive element follows the rotation of the control device. A pushbutton is disposed in the central throughhole of the housing and is movable in a first axial direction toward the face plate and a second axial direction away from the face plate. A second electrically conductive element is disposed within the central throughhole of the housing and follows the movement of the pushbutton. A spring is disposed between the face plate and the pushbutton and biases the pushbutton in the second axial direction. The first capacitive sensor senses a rotational position of the at least one first electrically conductive element. The second capacitive sensor senses an axial position of the second electrically conductive element. 
     An advantage of the present invention is that the rotary knob enables the user to have a tactile feel and easily discern how far the knob has been rotated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an exploded view of one embodiment of a capacitive encoder of the present invention. 
         FIG. 2  is a top view of the capacitive encoder of  FIG. 1 . 
         FIG. 3  is a cross sectional view of the capacitive encoder along line  3 - 3  of  FIG. 2 . 
         FIG. 4  is an exploded view of another embodiment of a capacitive encoder of the present invention. 
         FIG. 5  is a top view of the capacitive encoder of  FIG. 4 . 
         FIG. 6  is a cross sectional view of the capacitive encoder along line  6 - 6  of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments hereinafter disclosed are not intended to be exhaustive or limit the invention to the precise forms disclosed in the following description. Rather the embodiments are chosen and described so that others skilled in the art may utilize its teachings. 
       FIG. 1  is an exploded view illustrating one embodiment of a human machine interface in the form of a capacitive encoder arrangement  10  of the present invention. Arrangement  10  may be included in a motor vehicle, and particularly in an audio system of a motor vehicle, for example. Arrangement  10  includes a dial or knob  12 , a face plate  14 , which may be made out of plastic, and a capacitive circular switch pattern  16 , which may be fixedly attached to face plate  14 . Knob  12  includes a housing  18 , a spring detent  20 , an outer ring bearing  22 , and a conductive element  24  in the form of a disc or other configuration. 
     Housing  18  may be attached to face plate  14 , such as by adhesive  25  ( FIG. 3 ) or a mechanical joint. Spring detent  20  may be attached to an underside  26  of an annular lip  28  of housing  18 . 
     Bearing  22  is rotatable in the plane of the page of  FIG. 2 , i.e., about its longitudinal axis  30 , which is substantially perpendicular to face plate  14 , in both a clockwise direction  32  and a counterclockwise direction  34 . Bearing  22  includes an annular detent  36  that engages with detent  20  as a user manually rotates bearing  22 . Thus, detents  20 ,  36  conjointly operate to provide the user with tactile feedback as he rotates bearing  22 . 
     Knob  12  does not include any wiring or electronics, but bearing  22  does include one or more capacitive elements such as conductive disc  24 , which may be made of any electrically conductive material, such as metal or carbon fiber. In the specific embodiment shown in the drawings, there is only one conductive disc  24  which, as shown in  FIG. 3 , is positioned opposite from capacitive circular switch pattern  16  relative to face plate  14 . 
     In operation, the user may manually rotate bearing  22 , detent  36  and conductive disc  24  relative to housing  18 , detent  20 , face plate  14  and capacitive circular switch pattern  16 . Capacitive circular switch pattern  16  may operate as a sensor to determine the position of conductive disc  24  along the rotational path of conductive disc  24 , as may be easily understood by those of skill in the art. Disc  24  may be disposed on the longitudinal end of bearing  22  that is adjacent to face plate  14  so as to be close to capacitive circular switch pattern  16  and thus be more easily capacitively sensed thereby. Capacitive circular switch pattern  16  may transmit a corresponding capacitance signal to a processor (not shown) which uses the capacitance signals to determine the rotational locations of conductive disc  24 . 
     Illustrated in  FIG. 4  is an exploded view of another embodiment of a human machine interface in the form of a capacitive encoder arrangement  110  of the present invention. Arrangement  110  may be included in a motor vehicle, and particularly in an audio system of a motor vehicle, for example. As in the embodiment of  FIGS. 1-3 , capacitive encoder  110  includes a knob, specifically knob  112 . Arrangement  110  also includes a face plate  114 , which may be made out of plastic, a capacitive circular switch pattern  116 , which may be fixedly attached to face plate  114 , and a capacitive button switch pattern  117 , which also may be fixedly attached to face plate  114 . Knob  112  includes a housing  118 , a spring detent  120 , a center push knob  121 , a first conductive element  123  in the form of a disc, a spring  125 , an outer ring bearing  122 , and a second conductive element  124  in the form of a disc. 
     Housing  118  may be attached to face plate  114 , such as by adhesive  119  ( FIG. 6 ) or a mechanical joint. Spring detent  120  may be attached to an underside  126  of an annular lip  128  of housing  118 . A head  127  of center pushbutton  121  is received in a central throughhole  129  of housing  128 . An annular shoulder  131  of center pushbutton  121  is too large to fit through throughhole  129 . 
     Spring  125  may be biased against face plate  114  by center pushbutton  121 , as best shown in  FIG. 6 . Spring  125  includes a central recess in which conductive disk  123  is received. Spring  125  includes a frusto-conically shaped body  133  and an annular base  135  extending radially outwardly from an interior end of body  133 . Conductive disk  123  is sandwiched between center pushbutton  121  and spring  125 . Spring may be of other configuration such as a wave form spring as an example. 
     Bearing  122  is rotatable in the plane of the page of  FIG. 5 , i.e., about its longitudinal axis  130 , which is substantially perpendicular to face plate  114 , in both a clockwise direction  132  and a counterclockwise direction  134 . Bearing  122  includes an annular detent  136  that engages with detent  120  as a user manually rotates bearing  122 . Thus, detents  120 ,  136  conjointly operate to provide the user with tactile feedback as he rotates bearing  122 . 
     Knob  112  does not include any wiring or electronics, but bearing  122  does include one or more capacitive elements such as conductive disc  124 , which may be made of any electrically conductive material, such as metal or carbon fiber. In the specific embodiment shown in the drawings, there is only one conductive disc  124  which, as shown in  FIG. 6 , is positioned opposite from capacitive circular switch pattern  116  relative to face plate  114 . Similarly, conductive disc  123  is positioned opposite from capacitive button switch pattern  117  relative to face plate  114 . 
     In operation, the user may manually rotate bearing  122 , detent  136  and conductive disc  124  relative to housing  118 , detent  120 , center pushbutton  121 , conductive disc  123 , spring  125 , face plate  114 , capacitive circular switch pattern  116 , and capacitive button switch pattern  117 . Capacitive circular switch pattern  116  may operate as a sensor to determine the position of conductive disc  124  along the rotational path of conductive disc  124 , as may be easily understood by those of skill in the art. Disc  124  may be disposed on the longitudinal end of bearing  122  that is adjacent to face plate  114  so as to be close to capacitive circular switch pattern  116  and thus be more easily capacitively sensed thereby. Capacitive circular switch pattern  116  may transmit a corresponding capacitance signal to a processor (not shown) which uses the capacitance signals to determine the rotational locations of conductive disc  124  in terms of rotational positions. 
     Similarly, capacitive button switch pattern  117  may operate as a sensor to determine the position of conductive disc  123  along longitudinal axis  130 , as may be easily understood by those of skill in the art. Capacitive button switch pattern  117  may transmit a corresponding capacitance signal to a processor (not shown) which uses the capacitance signals to determine the locations of conductive disc  123  along longitudinal axis  130 . That is, head  127  of center pushbutton  121  may be pushed by the user from the unbiased position in  FIG. 6  to a position in which conductive disc  123  is closer to face plate  114 . Conductive disc  123  may be received in a recess of spring  125 , as shown in  FIG. 6 . Conductive disc  123  may be biased by spring  125  back into the position of  FIG. 6  after the user takes his finger off of head  127  and stops pushing head  127  toward face plate  114 . 
     In the embodiments disclosed above, the rotational position of the bearing may be sensed. If the present invention is applied to an automotive application, then an operating parameter of an audio system, an HVAC system, or a navigation system, for example, of a motor vehicle may be adjusted dependent upon the sensed rotational position. 
     While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.

Technology Classification (CPC): 6