Planetary Potentiometer Assembly

This invention relates broadly to ganged, variable resistance elements and specifically to multiple elements within a small area, also having vernier capability.

Very early in the history of communications devices it became evident that a need existed for multiple controls which could be adjusted simultaneously. Many solutions have been developed, possibly the most satisfactory being the most obvious, i.e., using a common shaft to turn the rotors of several axially aligned but individual controls. With the move toward microelectronics has come a demand for all components to be reduced in size without affecting other characteristics. The development of four-channel sound has given new impetus to the search for smaller multiple controls for adjusting tone or volume of the individual channels simultaneously as desired.

It is therefore an object of this invention to provide multiple ganged variable resistance units in a relatively small area.

It is an additional object to provide vernier capability in a multiple control.

In the present invention, these objectives are achieved by the use of a planetary arrangement of cylindrical contact elements which are supported between two spaced apart insulating members mounted on a single control shaft. The contact elements are spaced around the shaft and are driven by a friction drive surface affixed to the shaft between the insulating support members. Each resistance is made up of two parallel strips of resistance material mounted on the inside of the curved wall of the housing. Electrical contact with the resistance material is made through the curved housing wall. No terminals are connected to any moving part. As the cylindrical contact is driven by the friction surface, it shunts across the two strips, thus increasing or decreasing the effective resistance between the terminals. The ratio of the diameter of the friction drive portion of the shaft to the inside diameter of the housing determines approximately the degrees of rotation of the shaft for full range resistance variation.

FIG. 1 is a perspective view of a complete multiple control according to a preferred embodiment of the invention.

FIG. 2 is an exploded view of the control of FIG. 1.

FIG. 3 is a perspective view of a section of the interior of the control of FIGS. 1 and 2.

FIG. 4 is an exploded partial perspective view of another embodiment of the contact for the control of FIGS. 1-3.

FIG. 5 is a set of wiring diagrams for various applications of the invention.

The invention will be best understood by reference to the accompanying drawing in which like reference numerals designate like parts in the various figures. FIG. 1 is an overall view of an embodiment of the invention generally designated as reference numeral 10, wherein turning shaft 11 changes either the resistances or moves voltage taps in the several circuits of an electronic apparatus (not shown). Terminals 12 are connected to the ends of the resistance elements 13 (FIGS. 2 and 3) and pass through the curved wall 14a of the housing 14, the wall preferably being made of a sturdy insulating material. The bottom 14c of the housing may be of any suitable material but should preferably seal the contents from the environment and support the end of the shaft 11. The top 14b of the housing is of standard potentiometer construction. The entire housing can be made of metal, but, provision must then be made to insulate the terminals from the housing. In either case, slight resilience of the curved housing wall is desirable for best contact between the rolling contacts and the resistance elements. FIG. 2 is an exploded view showing the parts of the invention in detail. A four-unit control is illustrated but no such limitation is implied or should be construed. Around a narrowed portion of the shaft 11 is tightly affixed a friction drive surface 15 and at each end of the drive surface an insulating disc 16a is mounted on the shaft in a loose fit. Supported by the discs 16a and spaced evenly around the shaft 11 are a number of cylindrical contacts 17. If one of the contacts 17 is to act as a shunt it will preferably be made of a non-oxidizing metal such as brass. If, as described below, electrical contact is not desirable, any suitable insulating material may be used. The resistance elements 13 may be of any material having the desired characteristics, a preferred material being a mylar ribbon with a resistance coating, which is highly tolerant flexing. A spacific example is RESISTOFILM made by New England Instrument Company. For simplicity in the drawing, the elements 13 are shown as rectangular. However, as is known in the art, the shape would depend on the resistance characteristic desired. some form of detent or shaft rotation limiting device would normally be required, but since such devices are well known in the art and form no part of the novelty of the invention, they are omitted from the drawing in the interest of clarity. In FIG. 3 is shown a portion of the interior of the curved wall 14a of the housing 14. Shown in this view are parts of four of the resistance elements 13 which make up two of the four ganged control units in this embodiment, along with the conductive cylindrical contact 17 of one control unit. Three terminals 12 are shown for each control unit but two or four may be used, depending on the application of the controls according to the invention. As the shaft 11 is rotated, each cylindrical contact 17 will constitute a moving shunt across the two resistance elements 13 of one control unit. Thus, depending on the wiring, as will be described more fully below, a rheostat or potentiometer function is provided.

In FIG. 4 another embodiment of the contact portion is shown wherein each of the cylindrical contacts is a coiled spring 18 (one shown). The insulating discs 16b have projections which support the springs. Since the coils are under some compression when installed, a slight wiping action is provided as the control shaft is turned. Under certain operating conditions this may be a desirable or even necessary feature. The resistance elements 13 of FIG. 3 would be used for this embodiment. FIG. 5 includes four possible wiring diagrams for any one of the ganged controls, FIG. 5a providing potentiometer capability wherein A represents one pair of terminals and B represents another pair of terminals. FIGS. 5c and 5d providing rheostat or variable resistance capability. The circuit of FIG. 5b might be desirable in some applications. The circuit of FIG. 5a is a typical potentiometer arrangement as far as the remainder of the circuit is concerned, except that the portion marked (b) of one of the resistance elements 13 is included in the output circuit. It should be noted here that all values of resistance are within the scope of the invention including values down to essentially zero for any individual resistance strip. FIGS. 5c and 5d are essentially identical rheostats but the end connection of FIG. 5d might be advantageous if the cylindrical contact should momentarily be inadvertently separated from the resistance elements, as by physical shock.

From the above, it is clear that the invention teaches a multiple, ganged variable resistor or potentiometer within a space as small or smaller than that usually occupied by a single equivalent unit. A second feature is that there is no moving contact which must be connected to a non-moving terminal. Another feature is that the ratio of the inside diameter of the housing to the diameter of the friction drive portion of the shaft determines the ratio of the degrees of rotation of the shaft to degrees of arc of one pair of resistance elements traversed by one contact means, i.e., ##EQU1## Thus, a vernier capability is obtained which is somewhat dependent on the number of ganged control units. For four units, the optimal design provides approximately 250.degree. rotation of the shaft for a 70.degree. arc element. For a single control unit in one housing having one conductive cylindrical contact and one non-conductive contact and a small diameter drive surface, the resistance element could cover approximately 330.degree. of arc and shaft rotation could be as much as eight times that. It is also obvious that electrical contacts or taps may be made available at any point along any of the resistance elements by means of additional terminals.