Dual Shaft Rotary Electric Device

1. Field of the Invention

The present invention relates to a dual shaft electric device and particularly to such a device in which a dual shaft arrangement is formed by concentric inner and outer shafts, and in which slider supports provided with sliders respectively fixed thereto are attached to the inner and outer shafts for engagement with respective contact patterns.

2. Description of the Prior Art

Conventionally, a dual shaft variable resistor includes an inner shaft connected to a slider carrying contacts adapted to slide across resistance elements carried on a substrate, and an outer shaft also carrying a slider. The slider of the outer shaft carries contacts adapted to slide along resistance elements formed on another substrate, and the two substrates are separated axially of the shafts by a spacer. Recently, such dual shaft variable resistors are assembled by stacking the respective parts on the concentric shafts by means of an automatic machine. However, this method of assembly results in a disadvantage in that the insulating substrate of the variable resistor first placed on the shaft may ride along the shaft with the insulator spacer because it is pushed along the shaft by a spring or the like provided for the slider, so as to make it difficult to position the substrate of the next variable resistor, resulting in difficulty in automatic assembling.

An object of the present invention is, therefore, to eliminate the disadvantage as mentioned above for the prior art.

Another object of the present invention is to provide a dual rotary electric device in which an insulating substrate disposed initially on the shafts during assembly is prevented from moving along the shaft to thereby facilitate automatic assembling of the device.

FIG. 1 is an exploded perspective view of a dual shaft variable resistor according to an embodiment of the present invention;

FIG. 2 is a cross-sectional side view of the assembled dual shaft variable resistor of FIG. 1; and

FIG. 3 is a side view of the dual shaft variable resistor of FIG. 2.

Referring to the drawings, an embodiment of the present invention will be now described.

A shaft bearing 1 formed by zinc die casting includes a bearing portion 1a integrally molded with a cup-like frame portion 1b. An outer shaft 2 made of an insulating material such as glass polyacetal is loosely inserted into the bearing portion 1a of the shaft bearing 1. The outer shaft 2 has at its inner end a disc-like slider support 3 integrally molded therewith. An insulating substrate 4 of a lower stage (right stage in FIG. 2) is disposed so as to cover the opening side of the frame portion 1b so that a slider 5 fixed on the inner surface of the slider support 3 may be slid along a resistive element 6 formed on the insulating substrate 4 by rotation of the outer shaft 2. A U-shaped front side plate 7 having a pair of arms 7a and 7b is provided at the side of the frame portion 1b such that the pair of arms 7a and 7b are fitted into a pair of grooves 8a and 8b formed at opposite sides of the frame portion 1b. A pair of protrusions 11a and 11b formed at the opposite sides of an insulating spacer 11 are inserted into a pair of small holes 9 and 10 formed in the arms 7a and 7b of the side plate 7 respectively, so that the insulating spacer 11 may be fixed at the inner surface of the insulator substrate 4 so as to hold the insulating spacer 11 in place. An inner shaft 12 is loosely inserted into the outer shaft 2, and a slider support 13 is fixed by a washer 19 to the inner end of the inner shaft 12. An insulating substrate 14 of the upper stage (left stage in FIG. 2) is arranged such that as the inner shaft 12 rotates, a slider 15 provided on the slider support 13 is slid along a resistive element 16 provided on the insulating substrate 14 to thereby vary the resistance value. A switch mechanism 17 is provided on the insulating substrate 14 and is actuated by being pushed by the inner shaft 12.

Assembling of the dual shaft variable resistor according to the embodiment will be described. First, the bearing portion 1a of the shaft bearing 1 is inserted into a fitting hole 7c formed in the U-shaped front side plate 7 with the arms 7a and 7b fitted into the grooves 8a and 8b of the frame portion 1b. Then, the outer shaft 2, to which the slider support 3 with the slider 5 attached thereto has been previously fixed, is loosely inserted into the shaft bearing portion 1b, so that the slider support 3 fixed to the outer shaft 2 is mounted on the bottom of the frame portion 1b through a spring 18. Next, the insulating substrate 4 of the lower stage is mounted on the open side of the frame portion 1b in the state that the insulating substrate 4 is held by the pair of arms 7a and 7b of the front side plate 7, and then the protrusions 11a and 11b formed at the opposite sides of the insulating spacer 11 are respectively inserted into the small holes 9 and 10 of the insulating spacer 11 so as to fix the insulating spacer 11 in place.

The insulating substrate 14 of the upper stage is next mounted on the insulating spacer 11 in the state that the insulating substrate 14 is held by the arms 7a and and the inner shaft 12 to which the slider support 13 has been fixed by the washer 19 is loosely inserted into the outer shaft 2 so that the slider 15 fixed on the slider support 13 is placed in contact with the resistive element 16 on the insulator substrate 14 of the upper stage to vary the resistance value of the resistive element 16 on the insulating substrate 14 as the inner shaft 12 rotates. Finally, the switch mechanism 17 is attached by caulking at its upper surface (left surface in FIG. 2) with the forward ends of the pair of arms 7a and 7 of the front side plate 7.

In the thus arranged dual shaft variable resistor according to the embodiment of the present invention, even when the parts are successively stacked upward from the lowermost one to the uppermost one in the longitudinal direction of the shafts to assemble the variable resistor by utilizing an automatic machine or the like, the insulating substrate 4 of the lower stage is prevented by the insulating spacer 11 from moving up toward the upper stage, so that the positioning of the insulating substrate 14 of the upper stage can be performed very smoothly and the automatic assembling by using an automatic machine can be progressed very satisfactorily. Owing to the existence of the insulating space 11, there is no risk of the dielectric breakdown accident or the like even when the two insulator substrates 14 and 4 of the upper and lower stages respectively are arranged close to each other and to doubly assure against the dielectric breakdown, the portion 11c of the insulative spacer 11 opposed to rivets 20 of the insulating substrates 4 and 14 is made thin. Although the embodiment has been described above with respect to a dual shaft variable resistor by way of example, the application of the present invention is not restricted to such a variable resistor but can be widely applied to any dual shaft rotary electric device, for example an encoder.