US1620573A - Rheostat - Google Patents

Description

Patented Mar. 8, 1927.

UNITED JOSEPH A. ROSTRON, OF CAMBRIDGE, MASSACHUSETTS.

RHEOSTAT.

Application filed March 7, 1922'.

This invention relates to improvements in rheostats. While the invention may be applied in various connections, the apparatus is illustrated more particularly as it may be applied for use with *acuum tube units in sending and receiving wireless messages. In a so called wireless installation it is necessary to be able to adjust the resistance with great delicacy. Although various devices have been proposed heretofore to accomplish this purpose they have always, so far as I am aware, entailed the addition of elements and construction which introdu'ced more complications and cost. It is a purpose of the present invention to provide for such delicacy of adjustment while retain ing extreme simplicity of parts. And whereas it has been .attempted to attain delicacy heretofore by providing a considerable number of convolutions, and making these convo'lutions small, so that the step from one to another would be small, the present invention provides for making the resistance wire convo'lutions of any size, with a micrometer adjustment instantly available along any of them,

These objects are accomplished by providing a straight helix of resistance wire in which the convolutions are separated from each other a small distance, as, for example about 1/64 or 1/32 of an inch, and providing a rod which is mountedslidably and rotat ably .at its axis carrying a brush or contact member which is capable both of sliding to and fro crosswise of the convolutions, moving in the direction of the axis, and also is capable of moving around in the (llI'CtlOII of the convolutions, circling around the axis following the thread of the helix. The parts are so constructed that the brush is frictionally held at any of its positions, preferably by friction of the brush on the coil. Specifically, this is accomplished by making the brush of a flat spring metal strip, which strip is arranged outside of the coil, extending in a direction parallel to the axis and close over the threads of the coil, with a shoe atits end which is convex toward the coil and rests in contact therewith, with the convexity of the shoe pressing into the space between two adjacent convolutions of the coil and making contact with both of them. This brush is mounted on a rod which is set at the axis of the coil and is slidable to and fro in the direction of the axis, moving Serial No. 541,760.

the shoe with it from one convolution to another when the rod is so slid by the operator, on which occasion the convexity of the shoe allows it easily to ride up over each successive convolution and spring into the valley or depression beyond it. It is a feature of the invention that the shoe sinks deeply enough between the adjacent convolutions to tend definitely to remain between them, and consequently to remain between them when the rod on which it is mounted 1S rotated without being pushed in the direction of the axis. A control button being provided for the operator to grasp the rod, he can both push the rod so that any desired number of convolutions of the resistance wire are included in the circuit, and can rotate the same control means to add thereto or subtract therefrom any desired fraction of a convolution. The shoe may be formed by the extremely simple device of making a bend in the thin sheet metal which constitutes the brush. Variations may however be made in this respect and in other respects without departing from the scope of the invention. It is intended that the patent shall cover, by suitable expression in the appended claims, whatever features of patentable novelty exist in the invention disclosed.

In the accompanying drawings,

Figure 1 is a rear view of a rheostat constructed in accordance with the present invention Figure 2 is a side view of the device as seen from the right in Figure 1;

Figure 3 is a section on line 33 of Figure 1;

Figure 4c is a section, somewhat enlarged, through a portion of the coil showing the contact relation of the brush and the wires; and

Figure 5 is a section on line 55 of Figure t on the same scale as is used in that figure.

Referring to the drawings, the device is shown assembled on a base or panel 10 which may be considered to be the equivalent of any portion of a wireless apparatus adapted to support a rheostat. The circuit whose resistance is to be controlled by the apparatus of the invention leads through a terminal and contact plate 12 to which is attached, by a screw 16, one end 18 of a coil 18 of resistance wire wound helically about an insulating cylindrical surface 19,

preferably formed of heat resisting material. Each turn of wire of this helix is a short distance away from the next, thereby forming between each two adjacent convolutions a sort of helical groove around the cylindrical surface.

In the embodiment of the invention illustrated, this surface 19, upon which the coil is wound, is a sleeve 22 of non-conductive material placed around a barrel or drum 24 which may be of any size suitable to the requirements of the apparatus being served, so that much or little resistance wire may be wound about it as needed. Within the drum at each end, and secured to it, is a diametrical cross bar. One of these, 26, in conjunction with the screws 30, serves to hold the drum firmly on the panel 10, and the other, 28, serves several purposes, among which is the reinforcing of the drum and the providing of a convenient place for attachment of the other end 18 of the coil, there being a screw 82 on the cross bar for this purpose. The drum may be made of any suitable material, but the cross arm 26 should be of conducting material and the cross arm 28 of insulating material, so that upon the attachment of the end 18 to the latter the path of current, thus far described is terminated. It is also desirable to stop the windings a short distance from the end of the cylindrical surface 19, as will more particularly appear hereinafter and to this end a hole 33 through the drum is provided for passage of the wire to the arm 28. If the drum is of conductive material provision should be made for insulating the walls of this hole to prevent any contact with the wire. The cross bar 26, is connected by a short conductor 34 to the other contact plate and terminal 20, and it only remains to describe the means by which the current is conducted from the coil to the cross bar 26 and to show how these means may be utilized to regulate the length of the current path; first by changing the number of complete convolutions of the coil traversed by the current, and second by adding or subtracting a portion of a single convolution to or from the number of complete turns in the path. This is accomplished by providing a brush or wiper member 36 which can be moved axially along the surface of the drum from one turn of the wire to the next and circumferentially around the helix along any one convolution. The brush is preferably made of flat spring metal with a curved foot or shoe 36 formed by bending the end of the brush to provide a convex ridge on the side of the brush next to the wires. This shoe dips into the space or groove between two successive turns of the wire and is held there by its own spring pressure or resiliency. The curvature of the surface of this foot is about an axissubstantially at right angles to the axis of the coil, and the radius of curvature is sufficiently large to enable the shoe to be moved across the wires with little effort, yet is small enough for the shoe to drop into each groove and thus prevent undue slippage. When thus resting in a groove the shoe is tangent to the surface of the wire, see Fig. 4L, which enables it to be turned around the helix, in either direction with little friction. The arm of the contact brush rearward, extends approximately parallel to the axis of the coil, a distance slightly greater than the length of the drum, and then turns toward the axis where it is fastened to a rod 38 which lies along the axis of the drum. This rod passes through a hole in the rear cross bar 28, which helps support it, and thence through the drum and the other cross bar 26, and the panel and is movable rotatably and longitudinally. The end of the rod projecting on the front of the panel is provided with a knob 40 by which the rod can be pulled out or pushed in or rotated in any of its axial positions. The axial rod is made of conducting material and makes sliding fit with the cross bars so that when the foot is in contact with the helix the rear part of the coil is short circuite'd through the brush and its arm to the axial rod 38 and thence through the arm 26 and conductor 3% to the terminal 20. The circuit will be broken at any time when the shoe of the brush rests on the insulated surface 19 beyond the last convolution. This simple provision enables the rheostat to perform the function of a switch, and in this form it is especially adapted for certain uses such as dimming lights, the complete extinguishment being a natural step just beyond the maximum dimming.

It is obvious that any movement of the rod axially or in rotation must move the contact brush similarly. If toward or from the panel the length of resistance wire in circuit will be successively shortened or lengthened by units equalling the length of I a convolution. A fairly close adjustment of the rheostat can be made by simply mov ing the rod axially. The exact resistance needed is then attained by turning the knob in either direction so as to wipe the foot of the contact brush around the helix, thereby increasing or decreasing the path of the current through the coil by whatever fractional part of a single convolution is thus added or subtracted. The dotted positions of the contact arm shown in Figure 1 illustrate two of the various positions in which this arm may be rotated about the coil. drum surface may be made in any size practicable it follows that the greater the circumference, the finer will be the attainable adjustment of resistance, for thereby a smaller proportion of the total length of As the one convolution can be added or cut oif by the same amount of circumferential movement of the foot. Great speed and delicacy of adjustment is accordingly provided, in apparatus of extreme simplicity of construction, by the present invention inasmuch as the mere sliding of the shoe across the successive windings gives a setting of the shoe on the turns of wire which is almost correct so that but little movement around the winding is required to add or subtract the necessary amount of resistance to make the adjustment perfect.

Although the preferred embodiment of the invention is herein illustrated as comprising a fixed coil and a movable brush, it is obvious that the principles could be applied as Well with a fixed brush and a movable coil. Furthermore the invention is not limited to a coil arrangement, but its scope embraces any conductor having a series of adjacent lines continuously connected and means whereby a second conductor may be moved relative to the first from one line to another for large increase or decrease of current path, and along any one line of the series for minute changes.

I claim as my invention:

1. A rheostat comprising a continuous resistance element, arranged in successive connected lines, combined with a brush element adapted to engage the resistance element palpably between any pair of adjacent lines thereof; one of said elements being mounted fixedly and the other of them being mounted movably with respect to the fixed element and being manually movable in its said mounting so that, by its movement alone, the location of engagement of brushwith resistance is adjustable both across and along said lines; the said engagement being such that when the location of contact is adjusted along the lines the said engagement may cause the contact to continue between the brush and the particular pair of said lines which are at the moment engaged by the brush.

2. A rheostat comprising a resistance coil, a brush; a support for the brush; and axial mounting means for the support wherein the support is movable longitudinally and rotatably, and whereby the brush is movable in three dimensions of space to various parts of the surface of the coil; said brush and resistance material having surfaces which are convex to each other making tangential contact in each of said directions.

3. A vernier rheostat having a helical resistance coil, a longitudinally movable and rotary shaft arranged concentrically thereto, and a yielding contact carried by the shaft and movable thereby transversely and concentrically with respect to the convolutions of the helical coil for the coarse and fine regulation of the current, respectively.

4. A vernier rheostat having an insulating spool, a helical resistance coil thereon, a longitudinally movable and rotary shaft passing through the center of the spool, a knob on the shaft, and a yielding contact carried by the shaft and removable there by transversely and concentrically with respect to the convolutions of the helical coil for the coarse and fine regulation of the current, respectively.

Signed at Boston, Massachusetts, this second day of March, 1922.

JOSEPH A. ROSTRON.

Certificate of Correction.

Patent No. 1,620,573. Granted March 8 1927, to JOSEPH A. ROSTRON.

It is hereby certified that error appears in the printed specification of the abovenumbered patent requiring correction as follows: Page 3, line 71, claim &, for the Word removable read movable; and that the said Letters Patentshould be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 19th day of April, A. D. 1927.

[SEAL] M. J. MOORE,

Acting Commissioner of Patents.

Certificate of Correction.

Patent No. 1,620,573. Granted March 8, 1927, to JOSEPH A. ROSTRON.

It is here-by certified that error appears in the printed specification of the abovenumbered patent requiring correction as follows: Page 3, line 71, claim 4, for the Word removable read movable; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the ease in the Patent Office.

Signed and sealed this 19th day of April, A. D. 1927.

[SEAL] M. J. MOORE,

Acting Cowvmz'ssioner of Patents.

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