Variable resistor

1. Field of the Invention

The present invention relates to a variable resistor for use in various electronic components.

2. Description of the Related Art

A conventional variable resistor is disclosed in Japanese Unexamined Patent Application Publication No. 2001-15308. As shown in FIG. 11A , this variable resistor includes an insulating substrate 51 having a substantially semi-circular resistor 58 provided on the surface and a sliding contact 56 rotatably attached to the insulating substrate 51 .

Into the insulating substrate 51 , metallic terminals 52 and 53 are insert-molded. The sliding contact 56 includes a driver plate 56 b rotationally operated by a tool, such as a screwdriver, and a body formed by folding the driver plate 56 b from the external edge to the backside. The body includes a contact arm 56 a sliding over the resistor 58 and a disk section 56 c supporting the contact arm 56 a . The sliding contact 56 is rotatably attached to the insulating substrate 51 by caulking the disk section 56 c.

A conventional variable resistor having a ceramic substrate as the insulating substrate is disclosed in Japanese Unexamined Application Publication No. 2002-231512.

Previously, the variable resistors disclosed in Japanese Unexamined Application Publication No. 2001-15308 and Japanese Unexamined Application Publication No. 2002-231512 have been required to reduce the height thereof, and to reduce the height, the height of the disk section 56 c of the sliding contact 56 is reduced.

However, as shown in FIG. 11B , if only the height of the disk section 56 c is reduced, the gap d between the top surface of the insulating substrate 51 and the sliding contact 56 is reduced. That is, the gap t between the contact arm 56 a and the driver plate 56 b is reduced. Therefore, a contact 56 d of the contact arm 56 a is likely to contact the driver plate 56 b due to manufacturing errors or deflection in use. When the contact arm 56 a is brought into contact with the driver plate 56 b , the contact pressure of the contact 56 d to the rotator 58 is changed, which results in fluctuations of the characteristics thereof (variations in resistance). If the contact 56 d contacts the rotator 58 with a large amount of pressure, the rotator 58 may be damaged.

To overcome the problems described above, preferred embodiments of the present invention provide a variable resistor in which contact between a contact arm and a driver plate is prevented even if the height of a disk section of a sliding contact is reduced so as to reduce the height of the variable resistor.

A variable resistor according to a preferred embodiment of the present invention includes an insulating substrate having a substantially arch-shaped resistor provided on a surface thereof, and a sliding contact rotatably attached to the insulating substrate, wherein the sliding contact includes a body including a contact arm sliding over the resistor and a disk section for supporting the contact arm and a driver plate overlapping the body for being operated by a tool, and wherein a step is disposed on a surface having the contact arm provided thereon and at a position of the contact arm opposing a contact such that a gap between the driver plate and the contact arm is increased.

According to preferred embodiments of the present invention, since the step increases the gap between the driver plate and the contact arm, even if the height of the sliding contact is reduced to reduce the height of the variable resistor, the contact arm does not contact the driver plate. Accordingly, contact between the driver plate and the contact arm caused by errors in manufacturing the sliding contact and the insulating substrate is prevented. As a result, the contact pressure between the contact of the contact arm and the resistor is stabilized, which suppresses fluctuations in electrical characteristics (changes in resistance). The step is preferably formed by folding the driver plate or by providing a recess in the driver plate. However, when the step is formed by the folding, since the height of the variable resistor is partially increased, it is preferable to form the step by providing the recess.

The above and other elements, characteristics, features, steps and advantages of the present invention will become clear from the following description of preferred embodiments taken in conjunction with the accompanying drawings.

FIG. 1 is an external perspective view of a variable resistor according to a first preferred embodiment of the present invention;

FIG. 2 is a plan view of the variable resistor shown in FIG. 1 ;

FIG. 3 is a side view of the variable resistor shown in FIG. 1 ;

FIG. 4 is a perspective view of an example of a manufacturing process of an insulating substrate shown in FIG. 1 ;

FIG. 5 is a perspective view of the manufacturing process continued from FIG. 4 ;

FIG. 6 is an expansion plan view of a sliding contact shown in FIG. 1 ;

FIG. 7 is a perspective assembly view of the variable resistor shown in FIG. 1 ;

FIG. 8 is a sectional view at the line VIII—VIII of FIG. 7 ;

FIG. 9 is a perspective assembly view of a variable resistor according to a second preferred embodiment of the present invention;

FIG. 10 is a side view showing another preferred embodiment; and

FIGS. 11A and 11B are side views of a conventional variable resistor.

Preferred embodiments of a variable resistor according to the present invention will be described below with reference to the attached drawings.

First Preferred Embodiment

FIGS. 1 to 3 are an external perspective view, a plan view, and a side view of a variable resistor, respectively. The variable resistor includes an insulating substrate 1 having metallic stationary-side terminals 2 and 3 and a metallic variable-side terminal 4 , which are integrally insert-molded, and a metallic sliding contact 6 attached to the variable-side terminal 4 by caulking.

After the stationary-side terminals 2 and 3 and the variable-side terminal 4 , which are attached to a coil strip 10 , as shown in FIG. 4 , are insert-molded with a resin as shown in FIG. 5 , the insulating substrate 1 is formed by cutting the molded product off the coil strip 10 . As the resin, a heat-resistant thermoplastic resin or a thermo-setting resin is used so as to resist heat from soldering and so as to enable stable operation at high temperature. For example, a liquid crystal (LPC) resin, modified nylon 6T, a polyphenylene sulfide (PPS) resin, a polyester resin, an epoxy resin, and a diallylphthalate resin may be used. Other suitable materials may also be used.

On the top surface of the insulating substrate 1 , conduction portions 2 a and 3 a of the stationary-side terminals 2 and 3 are exposed. External connection portions 2 b , 3 b , and 4 b , which are soldering portions for soldering the stationary-side terminals 2 and 3 and the variable-side terminal 4 to a printed circuit board, respectively, extend from the bottom surface of the insulating substrate 1 and folded upward along side surfaces of the insulating substrate 1 . The top surface of the insulating substrate 1 is coated with carbon (see FIG. 7 ) in a substantially arch-shaped arrangement so as to cover the conduction portions 2 a and 3 a of the stationary-side terminals 2 and 3 .

The carbon is dried so as to form a resistor 5 , which electrically connects the resistor 5 to the stationary-side terminals 2 and 3 . At one end of the variable-side terminal 4 , a cylindrical eyelet part 4 a is integrally formed and exposed from a central hole 1 a of the insulating substrate 1 . The stationary-side terminals 2 and 3 and the variable-side terminal 4 are made of a highly conductive thin plate, such as those made of a copper alloy and stainless steel. To improve solder wettability, at least surfaces of the conduction portions 2 a , 3 b , and 4 b are made by noble metal plating, such as plating of gold or silver, solder plating, and tin plating.

As shown in FIG. 6 , a sliding contact 6 includes an annular driver plate 6 a , which is a top surface, a disk section 6 c folded from an external edge of the driver plate 6 a backward along a dotted line L, and a semi-circular contact arm 6 d provided in an external edge of the disk section 6 c opposite to the folded portion thereof. The sliding contact 6 is formed by punching and drawing one metallic plate.

At the approximate center of the driver plate 6 a , a cross-shaped engagement hole (adjustment hole) 6 b is provided for being operated by a tool, such as a screwdriver. Furthermore, a step 6 e is disposed at an external edge of the back surface of the driver plate 6 a opposite to the folded portion, i.e., at a location in the disk section 6 c that is folded to the back surface of the driver plate 6 a and opposing a contact 6 f of the contact arm 6 d , such that a gap between the driver plate 6 a and the contact arm 6 d is increased.

The contact arm 6 d having a spring property is provided with the protruding contact 6 f provided at the approximate center. The contact 6 f is brought into contact with the resistor 5 of the insulating substrate 1 so as to slide thereon.

As shown in FIGS. 7 and 8 , the disk section 6 c is provided with a fitting hole 6 g at the approximate center thereof for fitting to the eyelet portion 4 a of the variable-side terminal 4 . After the eyelet portion 4 a of the variable-side terminal 4 is fitted into the fitting hole 6 g , the sliding contact 6 is rotatably attached to the insulating substrate 1 by outwardly caulking the eyelet part 4 a.

The sliding contact 6 is made of a thin metallic plate having high conductivity and spring characteristics, such as those made of a copper alloy, stainless steel, and a noble metal alloy.

To change the resistance of the variable resistor, the sliding contact 6 is rotated by inserting the edge of a Phillips screwdriver, for example, into the engagement hole 6 b . Thereby, the resistance between the stationary-side terminal 2 (or 3 ) and the variable-side terminal 4 is changed.

In the variable resistor, as shown in FIG. 3 , since the step 6 e increases the gap T 1 between the driver plate 6 a and the contact arm 6 d in size, even if the height of the disk section 6 c is reduced so as to reduce the height of the variable resistor, the contact 6 f of the contact arm 6 d does not contact the driver plate 6 a . Accordingly, contact between the driver plate 6 a and the contact arm 6 d caused by errors in manufacturing the sliding contact 6 and the insulating substrate 1 is reliably prevented. As a result, the contact pressure between the contact 6 f of the contact arm 6 d and the resistor 5 is stabilized, which suppresses fluctuations in electrical characteristics (changes in resistance). Also, when the step 6 e is formed by coining, the strength of the driver plate 6 a is increased by work hardening.

The depth T 2 of the step 6 e is set to a size such that the driver plate 6 a is not in contact with the contact arm 6 d in view of allowances of the sliding contact 6 and the insulating substrate 1 in the height direction. For example, in a variable resistor with an external size of about 2.7 mm by about 2.1 mm and a height of about 0.8±0.05 mm, if the thickness T 5 of the insulating substrate 1 is about 0.5 (+0.03/−0.05) mm, the thickness T 4 of a metallic plate of the sliding contact 6 is about 0.1 mm, the gap T 3 between the top surface of the insulating substrate 1 and the sliding contact 6 is about 0.1 mm, and the thickness of the resistor 5 is about 0.02 mm, preferably, the depth T 2 of the step 6 e is about 0.03 mm while the gap T 1 between the driver plate 6 a and the contact arm 6 d at the contact 6 f is about 0.08 mm.

Second Preferred Embodiment

FIG. 9 is an exploded perspective view of a variable resistor according to a second preferred embodiment. This variable resistor includes a ceramic insulating substrate 31 , a metallic variable-side terminal 20 , and the metallic sliding contact 6 attached to the variable-side terminal 20 , for example, by caulking. Since the sliding contact 6 is the same as in the first preferred embodiment, the detailed description thereof is omitted.

The insulating substrate 31 is obtained by baking a ceramic material such as alumina which is formed in advance. The top surface of the insulating substrate 31 is coated with cermet in a substantially arch-shaped arrangement about a central hole 31 a , and the cermet is dried so as to form a resistor 35 . At both ends of the resistor 35 , external electrodes 32 and 33 , which are formed from side surfaces to the back surface of the insulating substrate 31 , are connected. The external electrodes 32 and 33 are formed by printing, sputtering, or vapor deposition or other suitable process.

After an eyelet portion 21 of the variable-side terminal 20 , which is inserted into a central hole 31 a of the insulating substrate 31 , is fitted into the fitting hole 6 g provided at the approximate center of the disk section 6 c , the sliding contact 6 is rotatably attached to the insulating substrate 31 by outwardly caulking the eyelet part 21 . At one end of the variable-side terminal 20 , a stopper 22 is arranged so as to be upwardly folded along a side surface of the insulating substrate 31 .

The variable resistor as described above has the same functions and advantages as those of the first preferred embodiment.

The present invention is not limited to the preferred embodiments described above, and various modifications can be made within the scope of the invention. For example, as long as the step 6 e on the back surface of the driver plate 6 a prevents contact of the contact arm 6 d at the contact 6 f , the step 6 e may have any shape. Also, the step 6 e may be formed by coining or etching, alternatively, as shown in FIG. 10 , it may be formed by providing a folding part 41 in the driver plate 6 a.

The present invention is not limited to each of the above-described preferred embodiments, and various modifications are possible within the range described in the claims. An embodiment obtained by appropriately combining technical features disclosed in each of the different preferred embodiments is included in the technical scope of the present invention.