Abstract:
A variable resistor includes a resistor element having a first end and a second end, a slider sliding on the resistor element, an adjustable resistor portion having a first end connected to the first end of the resistor element and having a second end, a first terminal connected to the second end of the adjustable resistor portion, a second terminal electrically coupled to the second end of the resistor element, and a third terminal connected to the slider. The adjustable resistor portion is positioned outside of the sliding range of the slider. This variable resistor outputs a precise resistance having s small variation from a predetermined resistance.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a variable resistor used for operating various devices, and to a method of manufacturing the variable resistor.  
       BACKGROUND OF THE INVENTION  
       [0002]     As electronic devices, such as car air-conditioners, have recently had high performance, variable resistors is demanded to be capable of providing precise resistance output used for operating of the devices.  
         [0003]      FIG. 8  is a sectional view of conventional rotary variable resistor  5001 .  FIG. 9  is an exploded perspective view of variable resistor  5001 . Resistor board  1  includes an insulating substrate made of laminated substrate made of paper phenol resin or glass epoxy resin having circular hole  1 A formed in the center thereof. Resistor element  92  having a C-shape is provided on a top surface of resistor board  1  at an outer periphery of board  1 . Conductor  3  having a ring shape is provided on the top surface and inside the C-shape of resistor element  92 . Resistor element  92  and conductor  3  are formed by, for example, screen printing. Both ends of resistor element  2  and conductor  3  are electrically connected to terminals  4 A,  4 B, and  4 C, respectively. Terminals  4 A,  4 B and  4 C are fixed to resistor board  1 . Insulating case  5  made of insulating resin has an upper opening having a circular shape. Case  5  has hole  5 A having a size and a position substantially identical to those of engaging hole  1 A is formed in the center of the circular shape of the upper opening. Resistor board  1  is formed by insert molding so that resistor element  2  and conductor  3  expose on an inner bottom surface of the opening in insulating case  5 . Terminals  4 A,  4 B, and  4 C project outward from a side wall of plate portion  5 B extending from the side wall of insulating case  5 . Rotating body  6  has through-hole  6 A having an oblong shape provided in the central portion thereof Rotating body  6  has flange  6 B having a dusk shape in the upper portion of body  6 , and shaft  6 C having a cylindrical shape in the lower portion of body  6 . Slider  7  is fixed to a bottom surface of flange  6 B. Slider  7  slides on and contact resistor element  2  and conductor  3  provided on resistor board  1 . Shaft  6 C having the cylindrical shape is inserted in hole  1 A of resistor board  1  and engaging hole  5 A of insulating case  5  which overlap each other. Shaft  6 C has a thin tip. The tip is formed to have a trumpet shape on the bottom surface of insulating case  5  and attached rotatably to the bottom surface of case  5 .  
         [0004]     An operation of rotary variable resistor  5001  will be described below. A rotation operator is inserted in through-hole  6 A through rotating body  6  having a substantially oblong shape. When rotating body  6  rotates, slider  7  fixed to the bottom surface of flange  6 B slides on resistor element  92  and conductor  3  provided on resistor board  1 . A resistance in response to a position at which slider  7  contacts resistor element  2  is obtained from terminals  4 A,  4 B, and  4 C.  
         [0005]     Conventional rotary variable resistor  5001  may output a resistance varying from a predetermined resistance due to variations of resistor element  2  printed on resistor board  1  or displacement of components.  
         [0006]     Conventional variable resistor  5001  may reduce production yield rate of devices, such as vehicle-mounted devices, and audio visual devices, which require a precise resistance, and raises their production cost.  
       SUMMARY OF THE INVENTION  
       [0007]     A variable resistor includes a resistor element having a first end and a second end, a slider sliding on the resistor element, an adjustable resistor portion having a first end connected to the first end of the resistor element and having a second end, a first terminal connected to the second end of the adjustable resistor portion, a second terminal electrically coupled to the second end of the resistor element, and a third terminal connected to the slider. The adjustable resistor portion is positioned outside of the sliding range of the slider.  
         [0008]     This variable resistor outputs a precise resistance having s small variation from a predetermined resistance. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a plan view of a variable resistor in accordance with an exemplary embodiment of the present invention.  
         [0010]      FIG. 2  is a sectional view of the variable resistor at line  2 - 2  shown in  FIG. 1 .  
         [0011]      FIG. 3  is an exploded perspective view of the variable resistor in accordance with the embodiment.  
         [0012]      FIG. 4  is a plan view of a resistor board of the variable resistor in accordance with the embodiment.  
         [0013]      FIG. 5  shows a change of a resistance of the variable resistor in accordance with the embodiment.  
         [0014]      FIG. 6  shows a change of the resistance of the variable resistor in accordance with the embodiment.  
         [0015]      FIG. 7  shows a change of the resistance of the variable resistor in accordance with the embodiment.  
         [0016]      FIG. 8  is a sectional view of a conventional variable resistor.  
         [0017]      FIG. 9  is an exploded perspective view of the conventional variable resistor. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]      FIG. 1  is a plan view of rotary variable resistor  1001  in accordance with an exemplary embodiment of the present invention.  FIG. 2  is a sectional view of variable resistor  1001  at line  2 - 2  shown in  FIG. 1 .  FIG. 3  is an exploded perspective view of variable resistor  1001 .  FIG. 4  is a plan view of resistor board  11  of variable resistor  1001 .  
         [0019]     Resistor board  11  made of insulating resin has circular through-hole  11 A in the center thereof. Conductor  13  and resistor element  12  are formed on top surface  11 B of board  11  by screen printing. Conductor  13  is shaped in a ring concentric with circular through-hole  11 A. Resistor element  12  has substantially a C-shape concentric with circular through-hole  11 A at an outer periphery of conductor  13 .  
         [0020]     Resistor element  12  has both ends  112 A and  112 B. Conductor  13  has portion  113 A. Leads  12 A,  12 B, and  13 A are connected to ends  112 A,  112 B, and  113 A, and extend outward from resistor board  11  from ends  112 A and  112 B and portion  113 A, respectively. Terminals  14 A,  14 B, and  14 C are fixed to an end of resistor board  1 . Leads  12 A,  12 B, and  13 A are connected to terminals  14 A,  14 B, and  14 C, respectively.  
         [0021]     Lead  12 A is provided between end  112 A of resistor element  12  and terminal  14 A. Lead  12 A includes conductor  1112 A connected to end  112 A, conductor  2112 A connected to terminal  14 A, and adjustable resistor portion  16  that is provided between conductors  1112 A and  2112 A and that is connected to conductors  1112 A and  2112 A. Adjustable resistor portion  16  is connected in series with resistor element  12 . Adjustable resistor portion  16  includes three auxiliary resistor portions  16 A,  16 B, and  16 C connected between conductors  1112 A and  2112 A in parallel with each other. Auxiliary resistor portions  16 A,  16 B, and  16 C are formed on top surface  11 B of resistor board  11  equidistant from one another by screen printing. In other words, conductor  1112 A serves as an end of adjustable resistor portion  16  that is connected to end  112 A of resistor element  2 . Conductor  2112 A serves as an end of adjustable resistor portion  16  that is connected to terminal  14 A. Terminal  14 A is electrically coupled to end  112 A of resistor element  12 .  
         [0022]     Similarly to above, lead  12 B is provided between end  112 B of resistor element  12  and terminal  14 B. Lead  12 B includes conductor  1112 B connected to end  112 B, conductor  2112 B connected to terminal  14 B, and adjustable resistor portion  17  that is provided between conductors  1112 B and  2112 B and that is connected to conductors  1112 B and  2112 B. Adjustable resistor portion  17  is connected in series with resistor element  12 . Adjustable resistor portion  17  includes three auxiliary resistor portions  17 A,  17 B, and  17 C connected between conductors  1112 B and  2112 B in parallel with one another. Auxiliary resistor portions  17 A,  17 B, and  17 C are formed on top surface  11 B of resistor board  11  equidistant from one another by screen printing. In other words, conductor  1112 B serves as an end of adjustable resistor portion  17  that is connected to end  112 B of resistor element  2 . Conductor  2112 B serves as an end of adjustable resistor portion  17  that is connected to terminal  14 B. Terminal  14 B is electrically coupled to end  112 B of resistor element  12 .  
         [0023]     Insulating case  15  has circular opening  15 E allowing resistor element  12  and conductor  13  to expose through opening  15 E, and is formed by insert-molding resistor board  11  with insulating resin. Engaging hole  15 A is formed in bottom surface  15 D of insulating case  15 . Hole  15 A has a size and a position identical to those of circular through-hole  11 A formed in resistor board  11 . Engaging hole  15 A is concentric with circular opening  15 E. Insulating case  15  has plate portion  15 B extending in lateral direction  15 F. Terminals  14 A,  14 B, and  14 C project outward from plate portion  15 B in lateral direction  15 F. Insulating case  15  holds resistor element  12  via resistor board  11 . Holes  115 C and  215 C having rectangular shapes are formed in plate portion  15 B at positions corresponding to adjustable resistor portions  16  and  17 , respectively. Adjustable resistor portions  16  and  17  formed on resistor board  11  exposes from holes  115 C and  215 C, respectively. Auxiliary resistor portions  16 A to  16 C exposes from hole  115 C so as to be contacted from the outside of insulating case  15 . Similarly, auxiliary resistor portions  17 A to  17 C exposes from holes  215 C so as to be contacted from the outside of insulating case  15 . Each of holes  115 C and  215 C is provided on top and bottom surfaces of resistor board  11 . Thus, holes  115 C and  215   c  penetrate through plate portion  15 B of insulating case  15 . Instead of holes  115 C and  215 C, six holes which allows auxiliary resistor portions  16 A to  16 C and  17 A to  17 C to expose, respectively, may be formed in insulating case  15 .  
         [0024]     Through-hole  18 A having a substantially oblong shape is formed in the center of rotating body  18 . Flange  18 B having a disk shape is provided at the upper portion of rotating body  18  so as to cover opening  15 E of insulating case  15 . Slider  7  made of resilient conductive material is provided on bottom surface  18 E of flange  18 B facing opening  15 E. Slider  7  has portion  7 A operable to slide on resistor element  12  and portion  7 B operable to slide on conductor  13 . Sliding range L 1  which slider  7  (portion  7 A) slides on is resistor element  12 . Rotating body  18  includes accepter  18 C of a cylindrical shape located below flange  18 B, and shaft  18 D provided at the tip of accepter  18 C and having a diameter smaller than that of accepter  18 C. Shaft  18 D is inserted into circular through-hole  11 A provided in resistor board  11  and in engaging hole  15 A provided in insulating case  15  overlapping through-hole  11 A. Tip  18 F of shaft  18 D is expanded on the bottom surface of insulating case  15  and attached rotatably to insulating case  15 .  
         [0025]     An operation of rotating variable resistor  1001  will be described below. A rotation operator is inserted into through-hole  18 A in rotating body  18 . Upon rotating body  18  rotating, portions  7 A and  7 B of slider  7  slide on resistor element  12  and conductor  13 , respectively. A resistance between terminals  14 A and  14 C and a resistance between terminals  14 B and  14 C change according to the angle at which rotating body  18  rotates, i.e. to the position of slider  7 . Slider  7  does not slide on adjustable resistor portion  16  or adjustable resistor portion  17 . Adjustable resistor portions  16  and  17  are positioned outside of sliding range L 1  of slider  7 .  
         [0026]     A method of adjusting a resistance of rotating variable resistor  1001  with using adjustable resistor portions  16  and  17  will be described below.  FIG. 5  shows a change of the resistance between terminals  14 A and  14 B. Predetermined voltage V AB  is applied between terminals  14 A and  14 B, and voltage V AC  is measured between terminals  14 A and  14 C. The ratio V AC /V AB  of the measured voltage to the predetermined voltage indicates the change of the resistance indirectly. In  FIG. 5 , the horizontal axis represents an angle (rotation angle) at which rotating body  18  rotates, and the vertical axis represents the voltage ratio V AC /V AB . The rotation angle is expressed as the ratio to a full scale. Desired characteristic R 1  is a desired characteristic of the change of the resistance of variable resistor  1001 . Measured characteristic R 2  is the characteristic actually measured. Variable resistor  1001  has tolerance T 1  between lines in parallel with desired characteristic R 1 . The voltages between terminals  14 A,  14 B, and  14 C are measured in order to indirectly detect the resistance between at least two of these terminals changing according to the position of slider  7  (portion  7 A).  
         [0027]     If measured characteristic R 2  is within tolerance T 1 , as shown in  FIG. 5 , it is not necessary to adjust adjustable resistor portions  16  and  17 . If measured characteristic R 2  is not within tolerance T 1  due to displacement caused by variations or combinations of components, at least one of auxiliary resistor portions  16 A to  16 C of adjustable resistor portion  16  is left, and the remaining auxiliary resistor portions is disconnected so as to put measured characteristic R 2  within tolerance T 1   
         [0028]      FIG. 6  shows a change of the resistance of variable resistor  1001 . Measured characteristic R 3  deviates from tolerance T 1  at angle P closer to a rotation angle of 0% than to a rotation angle of 100%. In this case, auxiliary resistor portion  16 A of adjustable resistor portion  16  is punched for electrical disconnection so as to increase the resistance of adjustable resistor portion  16  from that before the disconnection of auxiliary resistor portion  16 A. While voltage ratios at angles close to the rotation angle of 100% are almost unchanged, voltage ratios at angles close to the rotation angle of 0% increase. This operation phenomenon causes measured characteristic R 3  to shift upward in the left side of  FIG. 6 , and allows measured characteristic R 3  of variable resistor  1001  to be adjusted to characteristic R 4  provided within tolerance T 1 .  
         [0029]      FIG. 7  shows a change of the resistance of variable resistor  1001 . Measured characteristic R 5  deviates from tolerance T 1  at angle Q closer to the rotation angle of 100% than to the rotation angle of 0%. In this case, auxiliary resistor portion  17 A of adjustable resistor portion  17  is punched for electrical disconnection so as to increase the resistance of adjustable resistor portion  17  from that before the disconnection of auxiliary resistor portion  17 A. While voltage ratios at angles close to the rotation angle of 0% are almost unchanged, voltages ratios at angles close to the rotation angle of 100% increase. This operation causes measured characteristic R 5  to shift downward in the right side of  FIG. 7 , and allows measured characteristic R 5  of variable resistor  1001  to be adjusted to characteristics R 6  provided within tolerance T 1 .  
         [0030]     Variable resistor  1001  has holes  115 C and  215 C each of which are provided on both the top and bottom surfaces of resistor board  11 . In other words, holes  115 C and  215 C penetrate through insulating case  15 . This structure allows adjustable resistor portions  16  and  17  to be easily punched. Insulating case  15  covers resistor board  11  around holes  115 C and  215 C, hence preventing resistor board  11  from damage due to the punching of adjustable resistor portions  16  and  17 .  
         [0031]     As described above, in variable resistor  1001  of this embodiment, auxiliary resistor portions  16 A to  16 C and  17 A to  17 C of adjustable resistor portions  16  and  17  exposing from holes  115 C and  215 C, respectively, are punched to allowing the change of the resistance of the variable resistor to be adjusted after the assembling of the variable resistor.  
         [0032]     Adjustable resistor portions  16  and  17  connected to ends  112 A and  112 B of resistor element  12  enables the change of the resistance at angles close to the rotation angle of 0, and the change of the resistance at angles close to the rotation angle of 100% to be adjusted separately. Thus, variable resistor  1001  has a wide adjustable range of the change of its resistance. The variable resistor according to the embodiment may have only one of adjustable resistor portions  16  and  17 , having the change of its resistance adjustable even after being completed.  
         [0033]     According to this embodiment, adjustable resistor portion  16  includes three auxiliary resistor portions  16 A to  16 C connected in parallel with each other. Adjustable resistor portion  17  includes three auxiliary resistor portions  17 A to  17 C connected in parallel with each other. The number of the auxiliary resistor portions is not limited to three. Their resistances may be determined appropriately to the resistance of variable resistor  1001 .  
         [0034]     Holes  115 C and  215 C in insulating case  15  may be provided only on adjustable resistor portions  16  and  17 , respectively, that is, only in surface  11 B of resistor board  11 . Insulating case  15  covers bottom surface  11 C opposite to top surface  11 B of resistor board  11 . In this case, auxiliary resistor portions  16 A to  16 C and  17 A to  17 C are trimmed by, for example, laser, so as to increase the resistances of adjustable resistor portions  16  and  17 .  
         [0035]     Variable resistor  1001  according to this embodiment is a rotary variable resistor. However, a sliding variable resistor including a resistor element and adjustable resistor portions provided at both ends of the resistor element can provide the same effects.