Patent Publication Number: US-6909355-B2

Title: Illumination-type rotary variable resistor

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to illumination-type rotary variable resistors used for controlling the temperature and wind direction of car air conditioners and the sound volume and quality of video and audio equipment. 
   2. Background Art 
   Rotary variable resistors with an annular cross section are commonly used as equipment controls. The increasing sophistication of equipment and the trend for centralization of operating units have led to building switches and other electronic components into rotary variable resistors and mounting them on equipment wiring boards. 
   Concerning rotary variable resistors, illumination-type rotary variable resistors which have a light-emitting diode (LED) built into the operating unit are increasingly used. The LED is built in to indicate the position to which the resistor has been rotated when in use. 
   An LED built-in rotary variable resistor is described next as a conventional illumination-type rotary variable resistor, with reference to  FIGS. 9  to  12 . 
     FIG. 9  is a side sectional view,  FIG. 10  is an exploded perspective view,  FIG. 11  is a sectional view of a key part showing a section taken along Line  11 — 11  in  FIG. 10  in its center portion, and  FIG. 12  is a plan view illustrating the relation of an insulating substrate and slider which are key parts of the conventional rotary variable resistor with built-in LED. 
   In  FIGS. 9  to  12 , housing  1  has an approximately round center hole  1 A at its center. Housing  1  is an insulating resin housing with an annular cross section. 
   A wall surrounding center hole  1 A protrudes upward to form cylinder  1 B. 
   An annular portion of housing  1  is cavity with an open top. In other words, cylinder  1 B, round bottom plate  1 C, and outer wall  1 D create cavity  1 E. 
   Annular insulating substrate  2  is housed and held in cavity  1 E. 
   LED conductive film  3  including anode conductive film  3 A and cathode conductive film  3 B are printed to be formed on a top face of insulating substrate  2  at the inner radius. 
   Resistor film  4  including resistance film  4 A and conductive film  4 B are concentrically printed to be formed on insulating substrate  2  at the outer radius of LED conductive film  3 . 
   Terminal  5  for coupling to an outer electrical circuit (not illustrated) of the illumination-type rotary variable resistor is connected to the end of each film. 
   Insulated resin operating knob  6  has flange  6 B on its outer radius beneath cylindrical operating member  6 A. An inner face of operating member  6 A is fitted in rotatable fashion to an outer face of cylinder  1 B of housing  1 . 
   When operating member  6 A and cylinder  1 B are fitted together, flange  6 B is housed in cavity  1 E of housing  1 . Resistor slider  7  which resiliently contacts and slides on resistor film  4 , and anode slider  8  and cathode slider  9  which resiliently contacts and slides on LED conductive film  3  are provided on the bottom face of flange  6 B. 
   The top face of operating knob  6  assembled in rotatable fashion on housing  1  as described is supported by cover  10 . This cover  10  is attached in a way such as to cover cavity  1 E of housing  1  containing flange  6 B. 
   Cylindrical operating member  6 A and cylinder  1 B of housing  1  protrude upward from center hole  10 A in cover  10 . 
   As shown in  FIG. 10 , spring member  14  is attached to cover  10 . Spring member  14  has retainer  14 B at its center. This retainer  14 B engages tooth  6 G created on flange  6 B of operating knob  6 . Retainer  14 B is pressed against tooth  6 G by springs  14 A on both its sides. This allows operating knob  6  to be held reliably at the rotated position to maintain the set resistance. 
   As shown in  FIGS. 10 and 11 , LED through hole  6 C is created such as to pass vertically through in a radial thickness of cylindrical operating member  6 A of operating knob  6 . 
   A portion of anode slider  8  perpendicularly bent upward is further processed to create dogleg LED contact  8 B. In the same way, a portion of cathode slider  9  perpendicularly bent upward is further processed to create dogleg contact  9 B. 
   LED contact  8 B and LED contact  9 B are inserted into LED through hole  6 C in such a way that these contacts  8 B and  9 B face each other inside LED through hole  6 C. Projection  6 D provided on a bottom face of flange  6 B is flattened and deformed such as to secure anode slider  8  and cathode slider  9 . In this way, anode slider  8  and cathode slider  9  are fixed to the bottom face of flange  6 B. 
   LED  11  is inserted from the top into LED through hole  6 C in operating member  6 A. Bottom ends of two LED terminals  11 A, the anode and cathode of LED  11 , are cut at a bevel to a predetermined length from the end so as to form a sharp point at each tip. These two LED terminals  11 A bend the top of dogleg LED contacts  8 B and  9 B, and resiliently contact anode slider  8  and cathode slider  9 . 
   LED conductive film  3  and resistor film  4  are disposed on annular insulating substrate  2 . 
     FIG. 12  shows further details of substrate  2 . Cathode conductive film  3 B and anode conductive film  3 A are disposed as LED conductive film  3 , and conductive film  4 B and resistance film  4 A are printed to be formed as resistor film  4  in these sequences from the inner radius. 
   Each film is annular, with the same center, and disposed electrically insulated from each other. 
   Anode slider  8  has conductive film contact  8 A whose tip is split into two contacts and which slides on anode conductive film  3 A. Contact  8 A extends away from the insertion position of LED  11  in the direction opposite to the circumferential direction of LED contact  8 B. 
   Cathode slider  9  has conductive film contact  9 A whose tip is split into two contacts and which slides on cathode conductive film  3 B. Contact  9 A extends away from the insertion position of LED  11  to the direction opposite to the circumferential direction of LED contact  9 B. 
   Resistor slider  7  has conductive film contact  7 A whose tip is split into two contacts and resistance film contact  7 B whose tip is split into three contacts. Each contact resiliently contacts and slides on conductive film  4 B and resistance film  4 A. 
   Conductive film contact  7 A and resistance film contact  7 B resiliently contact conductive film  4 B and resistance film  4 A respectively at radially aligned positions. 
   In the above configuration, resistor slider  7  slides on resistance film  4 A and conductive film  4 B when operating knob  6  is rotated so that a predetermined resistance is gained from electrically coupled terminal  5 . 
   LED  11  emits light when powered by the current passing between anode conductive film  3 A and cathode conductive film  3 B through anode slider  8  and cathode slider  9  so as to clearly indicate the operating position of operating knob  6 . 
   One known prior technical document related to the conventional illumination-type rotary variable resistor described above is the Japanese Laid-open Application No. 2001-305259. 
   This conventional illumination-type rotary variable resistor provides a dogleg bend on LED contacts  8 B and  9 B of LED sliders  8  and  9 . In addition, LED sliders  8  and  9  are bent approximately perpendicularly to the attachment face that is the bottom face of flange  6 B. 
   Furthermore, LED contacts  8 B and  9 B are inserted and fixed to LED  11  through hole  6 C in operating knob  6  in a way not to deform contacts  8 B and  9 B when attaching LED sliders  8  and  9 . 
   With respect to workability, the above processing and attachment are not always efficient. 
   In addition, it is often preferable to cut the tip of LED terminal  11 A at a bevel before inserting LED  11 . This is because a beveled tip makes it easy to bend dogleg LED contacts  8 B and  9 B of LED sliders  8  and  9  using two LED terminals  11 A when LED  11  is inserted into LED through hole  6 C in operating knob  6 . 
   SUMMARY OF THE INVENTION 
   The present invention offers an illumination-type rotary variable resistor with stable quality that demonstrates good placement and attachment workability for a light-emitting diode (LED) and LED slider. 
   The illumination-type rotary variable resistor of the present invention is configured as below. 
   (a) A housing includes a round bottom plate, cylinder, and cylindrical outer wall. 
   The cylinder is attached to an inner radius of the bottom plate, and protrudes in the first direction along its center axis. 
   The cylindrical outer wall surrounds the bottom plate, and protrudes in the first direction. 
   (b) An annular insulating substrate is housed in the housing facing the bottom plate. A resistor film and light-emitting diode (LED) conductive film are disposed on the surface of the insulating substrate facing in the first direction. 
   (c) An insulating resin operating knob has a cylindrical operating member and flange. 
   The operating member has a through hole passing through in the first direction, and is fitted in rotatable fashion around the outer radius of the cylinder. 
   The flange is attached to the operating member at the side of the second direction that is the direction opposite to that of the first direction. A resistor slider and LED slider are disposed on the flange at a face facing in the second direction. 
   (d) A cover is attached to the housing, and covers the flange. 
   (e) A surface-mount LED is fitted in a through hole at the end in the second direction. 
   In the above resistor, the resistor slider resiliently contacts and slides on the resistor film. The first contact of the LED slider resiliently contacts an electrode of the surface-mount LED. A second contact of the LED slider slidably and resiliently contacts the LED conductive film. 
   The above configuration allows fitting of the surface-mount LED to the bottom end of the LED through hole provided on the cylindrical operating member of the operating knob, i.e., the end facing in the second direction. Still more, the contact of the LED slider resiliently contacts the electrode on the bottom face of the LED by fixing the LED slider on the bottom face of the flange of the operating knob. This eliminates the need for preparatory work to cut the LED terminal, and facilitates attachment of the LED and LED slider. The present invention thus offers the illumination-type rotary variable resistor with reliable quality and fewer assembly steps. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side sectional view of a rotary variable resistor with a built-in LED, which is an illumination-type rotary variable resistor in accordance with a preferred embodiment of the present invention. 
       FIG. 2  is an exploded perspective view of the illumination-type rotary variable resistor in accordance with the preferred embodiment of the present invention. 
       FIG. 3  is a sectional view of a key part of the illumination-type rotary variable resistor in accordance with the preferred embodiment of the present invention, which shows a section taken along Line  3 — 3  in  FIG. 2  in its center portion. 
       FIGS. 4A and 4B  illustrate attachment of a surface-mount LED which is a key part of the illumination-type rotary variable resistor in accordance with the preferred embodiment of the present invention. 
       FIG. 5  is a plan view illustrating the relation of an insulating substrate and slider of the illumination-type rotary variable resistor in accordance with the preferred embodiment of the present invention. 
       FIG. 6  is a bottom view of an operating knob with fixed slider of the illumination-type rotary variable resistor in accordance with the preferred embodiment of the present invention. 
       FIG. 7  is a magnified sectional view of a fitted portion of a housing and operating knob of the illumination-type rotary variable resistor in accordance with the preferred embodiment of the present invention. 
       FIG. 8  is a sectional view of a key part of the illumination-type rotary variable resistor in accordance with the preferred embodiment of the present invention, which shows, in its center portion, a section where a transparent bar is fitted to a LED through hole. 
       FIG. 9  is a side sectional view of a conventional rotary variable resistor with built-in LED. 
       FIG. 10  is an exploded perspective view of the conventional rotary variable resistor with built-in LED. 
       FIG. 11  is a sectional view of a key part of the conventional rotary variable resistor with built-in LED showing a section taken along Line  11 — 11  in  FIG. 10  in its center portion. 
       FIG. 12  is a plan view illustrating the relation of the insulating substrate and slider of the conventional rotary variable resistor with built-in LED. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A preferred embodiment of the present invention is described next with reference to  FIGS. 1  to  8 . 
     FIG. 1  is a side sectional view of a rotary variable resistor with a built-in light-emitting diode (LED), which is an illumination-type rotary variable resistor in the preferred embodiment of the present invention. 
     FIG. 2  is an exploded perspective view of the illumination-type rotary variable resistor in the preferred embodiment of the present invention. 
     FIG. 3  is a sectional view of a key part centering on a section taken along Line  3 — 3  in  FIG. 2  of the illumination-type rotary variable resistor in the preferred embodiment of the present invention and its surrounding area. 
   In  FIGS. 1 ,  2 , and  3 , housing  21  has round center hole  21 A at its center, and thus a cross section of the outline of housing  21  is annular. Housing  21  can also be made of an insulating resin. Cylinder  21 B protrudes upward, which is the first direction parallel to its center axis, and surrounds center hole  21 A. Cylindrical outer wall  21 D protruding upward, round bottom plate  21 F, and cylinder  21 B form cavity  21 E with an open top face. 
   Annular insulating substrate  22  is housed in housing  21  such as to face bottom plate  21 F on the bottom of cavity  21 E. LED conductive film  23  and resistor film  24  are printed to be formed in annular shapes, having the same center respectively, on the top face of insulating substrate  22 , which is facing in the first direction. Ends of films  23  and  24  are coupled to terminals corresponding to terminals  25 . 
   Operating knob  26  includes cylindrical operating member  26 A and flange  26 B. This flange  26 B is formed on the bottom, which is a part toward a second direction opposite to the first direction, of operating member  26 A, and protrudes outside operating member  26 A. The inner face of operating member  26 A rotatably fits with the outer face of cylinder  21 B. 
   Operating knob  26  and housing  21  are assembled so as to house flange  26 B inside cavity  21 E of housing  21 . Resistor slider  27 , anode slider  28 , and cathode slider  29  are fixed to the bottom face of flange  26 B, which is facing in the second direction. Resistor slider  27  is used for sliding resistor film  24  formed on insulating substrate  22 . Anode slider  28  and cathode slider  29  are used for sliding anode conductive film  23 A and cathode conductive film  23 B of LED conductive film  23 . 
   Cover  30  is attached to housing  21  such as to cover cavity  21 E of housing  21 . Cylinder  21 B of housing  21  and operating member  26 A of operating knob  26  protrude upward from center hole  30 A in cover  30 . 
   As shown in  FIG. 2 , spring member  34  is attached to cover  30 . This spring member  34  has retainer  34 B which engages tooth  26 G created on flange  26 B of operating knob  26 . Retainer  34 B is pressed against tooth  26 G by springs  34 A on both sides. This assures the firm holding of operating knob  26  in the position to which it has been rotated and maintains the set resistance. 
   As shown in  FIGS. 1 and 3 , LED through hole  26  is created so as to pass vertically through, i.e., along the first direction, in a radial thickness of operating member  26 A. Surface-mount LED  31  is fitted to the bottom end of the LED through hole  26 C, which is the end facing in the second direction. 
     FIGS. 4A and 4B  illustrate attachment of the surface-mount LED. 
   As shown in  FIGS. 4A and 4B , the bottom end, i.e., the end facing in the second direction, of the LED through hole  26 C is stepped to match the outline of LED  31 . LED  31  fitted to a position such that its bottom face, i.e., that facing in the second direction, is approximately level with the bottom face of flange  26 B. In addition, protrusions  26 D provided on longer sides of an opposing bottom end of LED through hole are flattened and deformed to anchor LED  31  in place. 
   In this way, the bottom end of LED through hole  26 C is stepped to match the outline of LED  31 . Surface-mount LED  31  is thus positioned stably without any rattling. Still more, protrusions  26 D on the bottom end of LED through hole  26 C are flattened and deformed to secure LED  31 . This eliminates the need for preparations such as cutting the LED terminal. Moreover, LED  31  can remain firmly in place even if subjected to vibration. 
   Furthermore, this configuration facilitates automated attachment of LED  31 . 
     FIG. 5  is a plan view illustrating the relation of the insulating substrate and slider. 
   As shown in  FIG. 5 , the positional relationship of films formed on annular insulating substrate  22  disposed inside cavity  21 E of housing  21  from the center is opposite to that of the conventional configuration described in the Background Art. 
   More specifically, resistor film  24  includes conductive film  24 B formed in the innermost radius and resistance film  24 A on its outer radius. LED conductive film  23  is formed on the outer radius of resistor film  24 , and includes anode conductive film  23 A and cathode conductive film  23 B on the outermost radius. Conductive film  24 B, resistance film  24 A, anode conductive film  23 A, and cathode conductive film  23 B are printed to be formed concentric to the center axis of cylinder  21 B, and are electrically insulated from each other. 
     FIG. 6  is a bottom view of the operating knob where sliders are fixed. 
   As shown in  FIG. 6 , resistor slider  27 , anode slider  28 , and cathode slider  29  are attached to the bottom face of flange  26 B by flattening and deforming projections  26 E on the bottom face of flange  26 B. 
   Anode slider  28  and cathode slider  29  electrically couple LED  31  and LED conductive film  23  on insulating substrate  22 . 
   Anode slider  28  and cathode slider  29  respectively have LED contacts  28 A and  29 A as the first contact and conductive film contacts  28 B and  29 B as the second contact. 
   LED contacts  28 A and  29 A as the first contact resiliently contact anode electrode  31 A and cathode electrode  31 B of surface-mount LED  31 . 
   Conductive film contacts  28 B and  29 B as the second contact slidably and resiliently contact LED conductive films  23 A and  23 B of insulating substrate  22 . 
   Conductive film contact  28 B is formed such that its two arms face each other. Each tip of these two arms is slidably disposed on corresponding anode conductive film  23 A on the same circumference. 
   Conductive film contact  29 B is also formed such that its two arms face each other. Each tip of these two arms is slidably disposed on corresponding cathode conductive film  23 B on the same circumference. 
   The tip of each arm can be split into two or more. 
   The above-described configuration of conductive film contacts  28 B and  29 B allows sliding of contacts  28 B and  29 B on anode conductive film  23 A and cathode conductive film  23 B while maintaining contact at two or more points. The width of anode conductive film  23 A and cathode conductive film  23 B in the radial direction is the same as when only one contact exists. However, the contact stability of the slider and conductive film is better than when only one contact exists. 
   In other words, contacts slide on more than one point on the same rotation radius of the LED conductive film so that they can maintain firm contact with the conductive film of the slider. This is because there are two or more contacts, and contacts  28 B and  29 B contact facing each other. Accordingly, contacts  28 B and  29 B slide on film  23 B and  23 A in almost the same contact condition for both clockwise and counterclockwise rotations. 
   On the other hand, if the contact and film only contacts at one point, the contact condition differs depending on the direction of rotation, failing to achieve stable contact condition. 
   On the other hand, resistor film  24  includes conductive film  24 B and resistance film  24 A disposed on the top face of annular insulating substrate  22 , which is facing in the first direction. Resistor film  24  is formed on the circles right under the position where LED  31  is fitted. In other words, resistor film  24  is formed annularly centering on the center axis of insulating substrate  22 . A cross point of the line passing through hole  26 C along the first direction and insulating substrate  22  exists between the inner radius end and outer radius end of resistor film  24 . 
   Resistor slider  27  slides while resiliently contacting conductive film  24 B and resistance film  24 A. Resistor slider  27  is attached to a deviated rotating circumference to achieve a rotating angle that avoids contacting LED sliders  28  and  29 . Resistor film  24  is also printed to be formed on the deviated rotating circumference to conform to this deviated angle. 
   Resistor slider  27  and LED sliders  28  and  29  are disposed on almost the same circles under LED  31  with the angle deviated in the rotating direction. Accordingly, the size of insulating substrate  22  is not restricted by the size of resistor slider  27  or LED sliders  28  and  29 . The outline of insulating substrate  22  can thus be reduced. This enables downsizing the illumination-type variable resistor of the present invention. 
   In addition, resistor slider  27  can be disposed at an innermost radius on insulating substrate  22 . Still more, resistor slider  27 , anode slider  28 , and cathode slider  29  can be disposed to be aligned in the circumferential direction. This allows reduction of insulating substrate  22  in radial width, enabling downsizing of the variable resistor. 
   The above configuration also facilitates provision of anode slider  28  and cathode slider  29  close to anode electrode  31 A and cathode electrode  31 B on the bottom face of surface-mount LED  31 , which is facing in the second direction. Accordingly, LED contacts  28 A and  29 A, which are respectively the first contacts of LED sliders  28  and  29 , can be bent upward, i.e., in the first direction, for a shorter length. 
   On the other hand, anode slider  28  and cathode slider  29 , which are respectively the second contacts of the LED slider, are bent downward, i.e., in the second direction, to form conductive film contacts  28 B and  29 B. As described above, LED contacts  28 A and  29 A need to be bent only slightly. Accordingly, anode slider  28  and cathode slider  29  can be easily processed even though conductive film contacts  28 B and  29 B are bent downward and LED contacts  28 A and  29 A are bent upward. In addition, attachment of anode slider  28  and cathode slider  29  to the bottom face of flange  26 B of operating knob  26  can be automated, achieving efficient assembly. 
   In attaching LED sliders  28  and  29  to operating knob  26 , the risk of deforming one of contacts  28 A,  29 A,  28 B, and  29 B is also very small. In addition, LED contacts  28 A and  29 A can be attached resiliently after LED  31  is fixed to anode electrode  31 A and cathode electrode  31 B, which are the electrodes of surface-mount LED  31  fixed to operating knob  26 . Accordingly, LED contacts  28 A and  29 A firmly contact the LED. 
     FIG. 7  is a magnified sectional view of a fitted portion of the housing and the operating knob in the preferred embodiment of the present invention. 
   As shown in  FIG. 7 , padding  21 C is provided at  8  points, forming equal central angles to the center axis of cylinder  21 B, on the outer face of cylinder  21 B of housing  21  at the lower part, which is in the second direction side. 
   The top of padding  21 C contacts the inner face of operating knob  26 . This contact is roughly a point contact. 
   Conversely, padding  26 F is disposed at  8  points, forming equal central angles to the center axis of operating member  26 A, on the inner face of operating member  26 A of operating knob  26  at the upper part. Paddings  26 F contact the outer face of cylinder  21 B of housing  21 . This contact is also roughly a point contact. 
   As described above, paddings  26 F and  21 C are respectively provided at the upper part of the outer face of cylinder  21 B of housing  21  or the inner face of operating knob  26 , i.e., in the first direction side, and provided at the lower part of the other sides, i.e. in the second direction side, at positions having equal central angles to the center axis of cylinder  21 B. This enables sliding of the fitted portion of cylinder  21 B and operating knob  26  in point contact at both upper and lower parts. Accordingly, the present invention offers a rotary variable resistor with good tactile feedback such that the user does not feel any uneven rotation. Rattling of the fitted portion can also be suppressed. The sliding positions of sliders  27 ,  28 , and  29  attached to the bottom face of flange  26 B of operating knob  26  are thus unlikely to deviate from positions where resistor film  24  and LED conductive film  23  are printed on insulating substrate  22 . 
   Uneven rotation can be further reduced by providing a longer distance between paddings  21 C and  26 F by disposing them as far as possible from each other toward the top and bottom ends. 
   Since both housing  21  and operating knob  26  are cylindrical, distortion often occurs at the fitted portion due to shrinkage of resin after molding. Accordingly, dies for molding housing  21  and operating knob  26  are adjusted in some cases to prevent the occurrence of distortion. In the preferred embodiment, paddings  21 C and  26 F are provided on housing  21  and operating knob  26 . Accordingly, only a portion of the die for molding paddings  21 C and  26 F needs to be corrected when adjusting the die. The operation required for correction is thus easily implemented. 
   In the above preferred embodiment, padding is provided at 8 points each on cylinder  21 B and operating knob  26 . However, padding can be disposed at 3 or more points with equal central angles to the center axis of cylinder  21 B and operating knob  26 . This achieves the same effect as above described. 
   In the illumination-type rotary variable resistor in the preferred embodiment, resistor slider  27  slides on resistance film  24 A and on conductive film  24 B when operating knob  26  is rotated. At this point, a predetermined resistance is gained from terminal  25  electrically coupled to resistor slider  27 . In addition, surface-mount LED  31  emits light when the current passes through anode conductive film  23 A, anode slider  28 , cathode slider  29 , and cathode conductive film  23 B. Accordingly, the light clearly indicates the operating position of the operating knob  26 . 
     FIG. 8  is a sectional view of a key part where a transparent bar is fitted to the LED through hole. 
   As shown in  FIG. 8 , bar  32  made of a transparent material such as acryl is fitted and anchored to LED through hole  26 C in the upper part of LED  31  attached to the bottom end of LED through hole  26 C of operating knob  26 , which is the end facing in the second direction. This leads the light from LED  31  efficiently to the top of operating member  26 A. The present invention thus offers an illumination-type rotary variable resistor that indicates the rotating position even more brightly. 
   As described above, in the present invention, the surface-mount LED is fitted at the bottom end of the LED through hole created in the cylindrical operating member of the operating knob. Further, the contact of the LED slider resiliently contacts the electrode on the bottom face of the LED by fixing the LED slider on the bottom face of the flange of the operating knob. Accordingly, preparations, such as cutting the LED terminal, are eliminated, and attachment of the LED and the LED slider is facilitated. The present invention thus offers an illumination-type rotary variable resistor with reliable quality and fewer assembly steps.