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United States Patent	3,614,704
Fujii ,   et al.	October 19, 1971

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Foreign Application Priority Data

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Oct 23, 1968 [JA]			191932/1968

Current U.S. Class:	338/140 ; 338/170; 338/190
Current International Class:	H01C 10/48 (20060101); H01C 10/00 (20060101); H01C 10/34 (20060101); H01C 10/08 (20060101); G01R 1/20 (20060101); G01R 1/00 (20060101); H01c 009/04 ()
Field of Search:	338/72,95,97,122,123,138,140,142,185,190,191,192,193 323/43.5 336/150

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References Cited

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U.S. Patent Documents

297324	April 1884	Weston
432131	July 1890	Flemming
743607	November 1903	Wright
2632831	March 1953	Pritikin et al.
3111639	November 1963	Ploke
3270135	August 1966	Schaeffer et al.

Primary Examiner: Goldberg; E. A.
Assistant Examiner: Tone; D. A.

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Claims

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We claim:

1. A variable electrical resistor which comprises:

a slider;

a plurality of contacts provided in parallel on said slider;

a main resistance consisting of a plurality of thin film resistance layers, said thin film-resistance layers having widths which are varied along the track of movement of said contacts on said slider and being connected in series for obtaining a wide range of resistance; and

a plurality of tap electrodes extending from said main resistance into the track of said slider, said tap electrodes being of stripe shape and made from a thin film layer of relatively low resistance, the direction of the contact train formed by said contacts and the extending direction of electrodes forming an electrode train almost parallely provided within the track of said slider being inclined relatively to each other so as to change the contacting point of said electrodes and said contacts in accordance with the movement of said slider whereby at least three contacts on said slider are simultaneously engageable with respective electrodes, with the contact closest to said main resistance being engaged with a tap electrode extending from the higher resistance portion of said main resistance and the contact furthest from said main resistance being engaged with a tap electrode extending from a lower resistance portion of said main resistance.

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Description

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This invention relates to a sliding member and electrodes for measuring instruments, and more particularly to tap electrodes consisting of resistive bodies capable of forming low-resistance layers on a thin film sliding variable resistor and sliding contacts therefore.

A conventional contacting mechanism between tap electrodes and a slider of a thin film sliding resistor for measuring instruments is shown in FIGS. 3 through 7, in which 8 is a slider, 9 are tap electrodes, and 10 is a baseplate. The tap electrodes 9 are fixed on the baseplate 10 by means of evaporation etc. The slider makes contact with and slides on the tap electrodes along a guide (not indicated). The transversal width of the sliding surface of the slider is so designed that the surface is wide enough to make contact with at least two adjacent tap electrodes regardless of its position. With the increase in the number of sliding times the surfaces of the slider and tap electrodes become worn out, and the shape of their cross section becomes that as shown in FIG. 4. Although the slider makes contact with two tap electrodes at the position shown in FIG. 4, it is in the state of making contact with only one tap electrode at the position shown in FIG. 5. At the position as shown in FIG. 6, the projection of the slider that has been produced by the deformation due to wear makes contact with the baseplate and the slider is prevented from making contact with any tap electrode. Thus an unstable change in resistance occurs at a comparatively early stage. This is particularly true in the case in which the slider is designed to make contact with three or more than three tap electrodes as shown in FIG. 7, and the aforementioned deformations are produced in very earlier stage.

In the case of electrodes having resistance, if the slider is not constructed to make contact with two or more than two electrodes, or with three or more than three electrodes simultaneously, a temporary increase in resistance appears when the slider slides in resistance decreasing direction by making or breaking its contact with the electrode on the higher resistance side; and a temporary decrease in resistance is observed when the slider slides in a resistance-increasing direction. Similarly, when the electrode itself possesses a resistance, a smooth resistance change is hard to get near the junction of two series-connected resistance layers.

The object of this invention is to overcome the above-mentioned defects of the conventional structure and to provide a set of tap electrodes of thin film resistors for measuring instruments having a plurality of resistance layers connected in series, different in width before and after each junction and a slider comprising numerous of small slider contacts provided in parallel. The aforementioned tap electrodes are provided in parallel within the track of the slider. The direction of the contact train formed by each contact of the aforementioned small contacts and the direction of the electrode train are such that the contacts near the low resistance in the direction perpendicular to the direction in which the slider advances extend farther from the resistance layers within the track of the said slider and the contacts near the high resistance are closer to the resistance layers. The directions of the contact train and the electrode train are made relatively inclined to each other by tilting one or both of them. By this inclination, one of the parallel smaller contacts on the slider are always maintained on two or more than two adjacent electrodes, making contact with them.

The present invention will be more apparent from the following description referring to an illustrative embodiment and conventional structure for comparison sake as shown in the accompanied drawings in which:

FIG. 1 is a plan view of an embodiment of this invention;

FIGS. 2A and B show a plan and side views, respectively of an embodiment of slider according to this invention;

FIGS. 3 to 7 show explanatory cross-sectional views of a conventional slider contacting with electrodes;

FIG. 8 is a graph showing the relationship between the positions of electrodes and the resistance value; and

FIG. 9 is a graph showing the relationship between the positions of slider and the resistance value.

In FIG. 1, 1 is a contact train comprising contacts 11 through 17; 4 and 2 are the electrode sections comprising low-resistance layers, and the electrode section 2 comprises tapped electrodes a through o; 3 and 3' are high-resistance layers, on which the layer 3 has a lower surface resistance than the layer 3' has and each of them connecting electrodes, and 5 is a baseplate that holds electrodes and resistance layers. The single dotted lines show the tracks of individual contacts. In this case, the slider rotates around the center O.sub.1 of the baseplate. The slider consists of spring wire material held by the holding part 7 as shown in FIG. 2. A part A of the arc at the tip of the spring wire 6 forms a train of contacts 11 through 17. The direction of electrodes of tapped electrode sections a through o of the electrode section 2 is inclined within the slider tracks 18 and 19 against the slider contact train 1 as shown in FIG. 1. The angle of inclination is so set that one of the contacts 11 through 17 is always maintained on three or more than three electrodes to make contact with them. In other words, in this embodiment the contacts are so arranged that between the contact 17 which is positioned closer to the highest resistance side of the parallel contacts of the slider and the contact 11 which is closer to the lowest resistance there exist three or four electrodes depending on the position of the slider, including the electrode which is making contact with the contact 17 or 11. Between the aforementioned contacts 11 and 17 there always are at least two contacts on and between any two adjacent electrodes, and at least one contact stays on and makes contact with each electrode. With such a construction, when for example the contact train 1 is in the position indicated by the arrow in FIG. 1, four electrodes g, h, i, and j exist between the contacts 11 and 17, and the three contacts 11, 12, and 13 are present between the electrodes g and h, four contacts 13, 14, 15, and 16 are between the electrodes h and i, and three contacts 15, 16, and 17 between electrodes i and j. As is clear from this example, in an arbitrary position of the slider some of the contacts 11 through 17 make contact with at least three electrodes and there exist at least two contacts on adjacent electrodes and within the space between these electrodes. As for the resistance change between the electrode 4 and the slider, when the contact train is at the same position as indicated by the arrow in FIG. 1, resistance decreases temporarily when the slider slides in the direction to increase the resistance and increases temporarily when the slider slides in the direction to decrease the resistance, depending on whether the contact 17 on the high-resistance side makes or breakes contact with the electrode j. However, since the indicated resistance is dependent on each contact and is more dependent on the contacts closer to the electrode 4 such as the contacts 11 and 12, even when the electrode 2 is composed of a resistance layer having a resistance value that cannot be completely ignored, the shift in the resistance can be made negligibly small in such a construction by selecting the number of contacts and the inclination between the contact train and the electrode train according to the electrode and the resistance value of the resistance layer. As for the other contacts 11 through 16, the aforementioned phenomena does not take place even when the electrode 2 itself has a significant resistance, because when one contact makes contact with the next electrode in case the slider slides in the resistance--increasing direction, the preceeding contact has already made contact with the contact, and in the case in which the slider slides in the resistance--decreasing direction, when a contact leaves an electrode, the succeeding contact has made contact with the electrode.

Special advantages brought about by the aforementioned properties to the junction of the resistance layers will be discussed in the following. Degree of change in the resistance obtained will be described referring to FIG. 8 and 9. FIG. 8 is a graph representing the resistance of this example. The vertical axis represents the resistance and the horizontal axis represents the electrode position. FIG. 9 is a graph representing the resistance of this example where the vertical axis shows the resistance and the horizontal axis represents the slider position. When two resistance layers 3 and 3' are connected in series as shown in FIG. 1, and when the tip of the resistance layer 3 is narrow and the part of the resistance layer 3' that connects to said tip is wide, the resistance at each electrode position is as shown by the solid line in FIG. 8. The change in the resistance is great near the electrodes h and i as indicated by 20. This is a phenomenon which occurs noticeably when the electrode has a resistance that cannot be ignored. Electric current flows through a narrow path between g and h, and a wide path between i and j, and the aforementioned phenomenon appears near the midway between these two paths. Against this, the arrangement of the contacts as shown in FIG. 1 for an example of this invention is advantageous. Here the contact 11 positioned closer to the low resistance side is placed apart from the resistance layers, the contact 17 positioned closer to the high-resistance side is placed near the resistance layers, and the contacts in between them are placed sequentially between the contacts 11 and 17. The resistance varies along a gentle slope as indicated by 21 in FIG. 8. Macroscopically, the change indicated by the line 22 of FIG. 9 becomes like the one shown by the line 23. It is of course permissible to move each of the contacts 11 through 17 along direction of the electrode, as long as some of the contacts are making contact with at least three electrodes and at least two contacts are present on and between two adjacent electrodes.

Moreover, when making the electrodes having the shapes as shown in the embodiment by evaporation, sputtering, or etching, there is of course no increase in the cost because the working time is independent of the shapes. As have been described, according to this invention, it is possible to obtain tap electrodes capable of forming low resistance layers of thin-film sliding variable resistors for use in measuring instruments, comprising a plurality of resistance layers connected in series and having different widths before and after their junctions, and a slider which has the property of: not increasing the resistance temporarily when the slider slides in the resistance-decreasing direction; not decreasing the resistance temporarily when the slider slides in the resistance-increasing direction; changing the resistance ideally stepwise without any rapid change at the junction of two resistance layers; and holding a steady stepwise resistance change over a long period of time against the increase in the number of times the slider is rotated. There is no increase in production cost and manufacturing is easy.

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