Rotary Electric Component

The present invention relates to a rotary electric component such as a semifixed variable resistor or a rotary switch.

Conventional semifixed variable resistors often include an insulating substrate and a cover mounted on a rotatable shaft. The cover typically has a skirt spaced apart from the insulating substrate by a gap. Dust or soldering flux tends to find its way through the gap into the cover and cause malfunctions of the semifixed variable resistor.

It is an object of the present invention to provide a rotary electric component which has a simple construction for preventing dust from entering through a gap between a cover and an insulating substrate.

According to the present invention, a molded body of synthetic resin is mounted on an insulating substrate by outsert molding and has a portion formed as a dust wall covering a gap between a cover and the insulating substrate.

The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.

FIG. 1 is a front elevational view of an insulating substrate in a conventional semifixed variable resistor;

FIG. 2 is a side elevational view of a conventional semifixed variable resistor;

FIG. 3(A) is a front elevational view of an insulating substrate in a semifixed variable resistor according to an embodiment of the present invention;

FIG. 3(B) is an enlarged cross-sectional view taken along line B--B of FIG. 3(A);

FIG. 3(C) is an enlarged cross-sectional view taken along line C--C of FIG. 3(A);

FIG. 4 is a perspective view of the insulating substrate shown in FIG. 3(A);

FIG. 5(A) is a fragmentary cross-sectional view of an insulating substrate according to another embodiment of the present invention; and

FIG. 5(B) is a fragmentary cross-sectional view of an insulating substrate according to still another embodiment of the present invention.

FIGS. 1 and 2 show a conventional semifixed variable resistor. The semifixed variable resistor has an insulating substrate 1 made of a laminated sheet of phenolic resin or the like. The insulating substrate 1 has a central shaft hole 1a and a semicircular resistor 2 deposited on a surface thereof concentrically around the shaft hole 1a, the resistor 2 being formed of carbon or the like printed on the insulating substrate 1. The resistor 2 has on ends thereof a pair of electrodes 3a, 3b of such conductive material as silver deposited on the insulating substrate 1 by printing or evaporation. A pair of grommets 4a are fixed respectively to ends of the electrodes 3a, 3b by grommets 4a, 4a staked around attachment holes defined in the insulating substrate 1. The insulating substrate 1 has a slot 1b located centrally between the electrodes 3a, 3b and extending contiguously to the shaft hole 1a. The slot 1b serves to prevent migration of silver which would be caused when the electrodes 3a, 3b are deposited, thereby avoiding shortcircuiting between the electrodes 3a, 3b.

For assembling the semifixed variable resistor, a shaft 5 is rotatably mounted in the shaft hole 1b, as shown in FIG. 2. Then, a movable contact 6 is attached to an upper portion of the shaft 5, and a terminal 7 is attached to the reverse side of the insulating substrate 1 in electric connection to the shaft 5. A support spacer 8 of synthetic resin is fitted around the shaft 5 between the movable contact 6 and the insulating substrate 1 for supporting the shaft 5 in position. A cap-shaped cover 9 is fixted to the upper end of the shaft 5, the cover 9 being made of an insulating material such as synthetic resin and doubling as a control knob for rotating the shaft 5. When the semifixed variable resistor is to be actuated, the shaft 5 and the movable contact 6 are rotated by operating the cover 9 to cause a distal end of the movable contact 6 to slide on the resistor 2. When the movable contact 6 is stopped at a desired position, a resistance is established between the terminal 7 electrically connected to the movable contact 6 and either one of the terminals 4.

With the conventional construction, an effort has been made to render the electric component smaller in overall size by locating an attachment end 4b of the terminal 4 closely to the shaft 5 and hence immediately below a skirt 9a of the cover 9, resulting in the necessity of providing a gap h between the skirt 9a of the cover 9 and the attachment end 4b of the terminal 4b. With the gap h, however, the skirt 9a of the cover 9 and the upper surface of the insulating substrate 1 must be spaced apart from each other by a greater gap H. The gap H tends to allow dust and soldering flux to enter the cover 9, a condition which leads to failure of the electric component. Furthermore, the known semifixed variable resistor is also disadvantageous in that the slot 1b reduces the mechanical strength of the insulating substrate 1, which is liable to get damaged under external forces. A conventional solution to this problem has been a collector integral with the terminal 7 and having grip fingers engaging in grooves 1c defined in opposite edges of the insulating substrate 1 to reinforce the latter.

FIGS. 3(A) through 3(C) and 4 show an insulating substrate according to an embodiment of the present invention.

The insulating substrate, designated by the reference character 1, is in the form of a laminated sheet of phenolic resin, and has a shape substantially as shown in FIG. 1. More specifically, the insulating substrate 1 has a central shaft hole 1a and a slot 1b extending contiguously to the central shaft hole 1a and serving to prevent shortcircuiting between electrodes 3a, 3b. A resistor 2 of carbon is deposited on the insulating substrate 1. The electrodes 3a, 3b are made of silver and deposited on the insulating substance 1 and connected respectively to ends of the resistor 2. Terminals 4 are fixed by grommets 4a, 4b and connected respectively to ends of the electrodes 3a, 3b.

A molded body 10 is molded on the insulating substrate 1 by way of outsert molding, the molded body 10 being formed of a synthetic resin material different from that of the insulating substrate 1. A portion of the molded body 10 is formed as an annular dust wall 10a extending around the outer periphery of the resistor 2. As shown in FIG. 3(B), the dust wall 10a is positioned outside of and adjacent to a skirt 9a of a cover 9 disposed over the insulating substrate 1 and covers a gap between the skirt 9a and the insulating substrate 1. The molded body 10 also has a portion serving as a connector 10b extending radially inwardly of the dust wall 10a and an annular support spacer 10c on a distal end of the connector 10b. The annular support spacer 10c extends around the shaft hole 1a as shown in FIG. 3(B). The support spacer 10c has a central support hole 10d coaxial with the shaft hole 1a. The molded body 10 has another portion extending as a protective cover 10e over attachment portions 4b of terminals 4. As shown in FIG. 3(C), the protective cover 10e extends through the grommets 4a and the slot 1b to the reverse side of the insulating substrate 1. The terminal attachment end portions 4b are protected by the protective body 10e on the both surfaces of the insulating substrate 1. The end portions of the insulating substrate 1 on both sides of the slot 1b are retained and reinforced by the protective cover 10e to make up for a reduction in the mechanical strength of the insulating substrate 1 which results from the slot 1b.

In assembly of a semifixed variable resistor using the insulating substrate 1, a rotatable shaft similar to the rotatable shaft 5 shown in FIG. 2 is inserted into the support hole 10d in the support spacer 10c. Then, the the movable contact 6 and the cap-shaped cover 9 of insulating material are fixedly mounted on the upper portion of the shaft 5. Terminals are attached to the reverse side of the insulating substrate 1 and connected to the rotatable shaft. Since the slot 1b defined in the insulating substrate 1 is filled for reinforcement with a synthetic resin material, the end portions of the insulating substrate 1 on which the electrodes 3a, 3b are mounted are completely free from the danger of spreading laterally away from each other and of being damated. Accordingly, there is no need to provide grooves such as the grooves 1c in the opposite lateral edges of the insulating substrate as shown in FIG. 1, and to place a collector for engagement in such grooves.

In operation of the semifixed variable resistor, the cap-shaped cover 9 is rotated by fingers to rotate the rotatable shaft and the movable contact supported thereon. When the distal end of the movable contact is stopped at a desired position on the resistor 2, a resistance is established between either one of the terminals 4 and the terminal connected to the rotatable shaft. The skirt 9a of the cover 9 also angularly moves inside of the dust wall 10a, which prevents dust from entering the gap between the skirt 9a and the insulating substrate 1.

While in the illustrated embodiment the dust wall 10a is disposed outside of and closely adjacent to the skirt 9a of the cover 9 as shown in FIG. 3(B), the dust wall 10a may be positioned inside of and closely adjacent to the skirt 9a as shown in FIG. 5(A). Alternatively, the dust wall 10a may be disposed immediately below the skirt 9a as illustrated in FIG. 5(B).

Although in the illustrated embodiments a semifixed variable resistor has been described as being a rotary electric component by way of example, the present invention is also applicable to other electric components such as rotary switches or small-size rotary switches.

With the arrangement of the present invention, a molded body of synthetic resin is fixedly mounted on an insulating substrate and has a portion formed as a dust wall covering a gap between a cover skirt and the insulating substrate. Thus, dust or soldering flux used when connecting wires to terminals is prevented by the dust wall from entering into the cover, so that a rotary electric component incorporating such an insulating substrate is protected against malfunctions. Since the dust wall is fixedly molded on the insulating substrate by way of outsert molding, the number of parts to be assembled is not increased and so is the number of assembling steps. Outsert molding allows the dust wall to be simply fabricated in any desired shape and mass-produced. Furthermore, the dust wall permits the gap (indicated at h in FIG. 2) between the cover skirt and the insulating substrate to be widened, so that the terminal attachment end portions can be located closely to the support for the rotatable shaft, and the insulating substrate is smaller in size.

With the terminal attachment end portions covered by a portion of the molded body, the terminals are prevented from contacting terminals of other electric components or lead wires for shortcircuiting.

The synthetic resin material of the molded body filled in the slot 1b serves to compensate for a reduction in the mechanical strength of the insulating substrate which is caused by the slot 1b.

Although certain preferred embodiments have been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.