US1955906A

US1955906A - Rheostat

Info

Publication number: US1955906A
Application number: US461975A
Authority: US
Inventors: George B Crouse
Original assignee: HARDWICK HINDLE Inc
Current assignee: HARDWICK HINDLE Inc
Priority date: 1930-06-18
Filing date: 1930-06-18
Publication date: 1934-04-24
Anticipated expiration: 1951-04-24

Description

April 24, 1934. G', B, CROUSE 1,955,906

RHEosTAT Filed June 18, 1930 '26 za /6 /f L75 INVENTOR @e0/'ya B. fraz/sa BY ff-a g ATTO E Patented Apr. 24, 1934 UNITED STATES PATENT OFFICE Hardwick llindle, Inc.,

ration of New Jersey Newark, N. J., a corpo- Application June 18, 1930, Serial No. 461,975

3 Claims.

This invention relates to rheostats particularly of the type having a sliding contact device adapted to be moved over a suitable resistance wire wound on a tubular member, provision being made for bothcoarse and fine adjustments of the contact device.

In rheostats of this type as heretofore constructed the fine adjustment of the contact device is obtained by a connection between it and a rotatable rod provided with a screw thread, the device being slidably mounted upon a guide rod placed parallel to the rotatable rod. For coarse adjustment whereby the contact device may be moved rapidly from one position to another, the connection to the threaded rod is of a detachable nature to permit it to be disengaged from the rod when desired. It is arranged to be held out of engagement with the rod or even locked in its disengaged position, while the contact device is being moved from one position to another. In the first case it is usually necessary to use both hands to manipulate the device, while in the latter case, the initial disengaging and locking operations must first be performed by manipulation of the devices provided for this purpose and then one must take hold of the entire contact device to alter its position.

Furthermore in such prior rheostats the contact device includes movable leaf springs which are attached to the device and the resiliency of which is depended upon te hold them against the wire with suilicient pressure to make good electrical contact. This resiliency is not however constant for the springs carry current and therefore become heated and gradually lose their resiliency. The leaves of the springs are flexible in the direction of movement of the contact device so that as the device is moved the leaves are deected and catch on the wire possible danger of damaging it or even breaking it.

The present invention has for its general object the provision of a rheostat in which the disadvantages of prior devices, particularly with respect to the contact device, are overcome, whereby it may be more quickly and conveniently manipulated when a coarse adjustment is desired and then by only one hand. The contact springs are movably mounted on the device and are held against the wire of the rheostat by other springs which do not carry current and therefore are not subject to changes in their resiliency. In other words, the functions of contact making and application of pressure to the springs are separated. This arrangement also avoids the tendency of the free ends of the contact springs to catch on the wire as the contact device is moved over it.

A further improvement resides in an arrangement for fastening in place the ends of the resistance wire and attaching thereto the wires of the external circuit.

The particular nature of the invention as well as other objects and advantages thereof will appear most clearly from a description of a preferred embodiment as shown in the accompanying drawing in which Fig. 1 is an elevation partly in section of the rheostat,

Fig. 2 is a plan View of the rheostat,

Fig. 3 is a transverse sectional view taken along the lines 33 of Figs. 1 and 2, and

Fig. 4 is a sectional view taken along the line 4-4 of Fig. 3.

The resistance unit of the device consists of a cylindrical tube 1 of a suitable heat resisting and electrically insulating material, such as porcelain. The tube is wound with wire 2 of the desired resistance and current carrying capacity for the circuit in which the rheostat is to be used. The insulation of the wire is formed by suitable oxidization of its surface. The wire is wound under the maximum tensile strength which the material will stand and at a slight angle to the axis of the tube so that the turns are snugly wedged together but insulated from each other by the oxide coating which however becomes worn oif in the path of the brushes of the contact device so that no resistance is interposed between the wire and the brushes.

The ends of the wire are held in place by bands 3 wide enough to embrace several turns of the wire at each end of the unit. As shown most clearly in Fig. 3, the ends of each band are turned outwardly and provided with

shoes

4 and 5 preferably Welded to the ends and having their inner edges shaped to conform to the bends of the bands at these points. A clamping screw 6 passes through the upper shoe 4 and is threaded into the lower shoe 5. The upper shoe is provided with a threaded extension 7 on which a pair of binding nuts 8 are screwed by which connection to the external circuit may be made.

The resistance unit is mounted between two end brackets 9 and l0 which serve as supports for the rheostat. The brackets are clamped against the ends of the tube 2 by a solid rod 11 having nuts 12 at its ends and a hollow rod 13 which is internally threaded for the reception of clamping screws 14. The hollow rod also serves as a guide for the contact device of the rheostat and for this purpose it must be insulated from the brackets 9 and 10. This is accomplished by means of insulating washers 15 and bushings 16. In order to allow for slight changes in the relative lengths of the tube and the rods when the rheostat becomes heated under load soft asbestos washers 17 are placed between the ends of the tube and the corresponding brackets 9 and 10.

In order to eliminate the necessity for accurately matching the length of the rod 13 to the length of the tube 1, the rod is made shorter than the tube and shimmed out to the correct length by washers 18. One of the clamping screws 14 is provided with a threaded extension 19 which carries a pair of binding nuts 20 for connection to an external circuit.

The outer surface of the hollow rod 13 is machined and carries a sleeve 21 which is accurately machined to slide freely on the rod, thus avoiding any appreciable lost motion between the rod and the elements of the Contact device which are mounted on the sleeve, such as occurs in prior rheostats of this general type in which machined parts are not used and springs or other devices are provided for taking up the lost motion between the parts.

The sleeve 2l serves to carry the elements of the contact device. The first of these is a member 22 provided with a pair of spaced lugs 23 which are machined to accurately t the sleeve 21. A corresponding member 24 is provided with a pair of spaced lugs 25 also accurately machined to fit the sleeve. Attached to the tops of the lugs 25 by screws 26 is a knob 27 formed of suitable insulating material, preferably in one piece. The lower flange 28 of the knob is provided with an aperture 29 through which passes a lever 30 having at one side an extension 3l lying between the lugs 25 and provided with an aperture through which the sleeve 21 passes. The upper end of the lever is normally forced outwardly by a coiled spring 32 having its ends set in recesses in the lever and the central portion or rib of the knob.

In assembling the device, one end of the sleeve 21 is initially spun outwardly to form a slight flange 33. The sleeve is then passed through the

lugs

23 and 25 and the aperture in the extension 31, after which the other end of the sleeve is also spun outwardly to form a corresponding flange to retain the

members

22 and 24 and the lever 30 in place on the sleeve.

The lower end of the lever 30 carries a pin 34 which under the influence of spring 32 normally enters the thread of a screw 35 mounted in holes in the end brackets 9 and 10, one end of the screw being provided with a knob 36 by which the screw may be rotated to shift the contact device along the rod 13. Washers 37 are employed for preventing end play of the screw without the necessity of forming the screw to fit accurately between the end brackets.

Each of the

members

22 and 24 is provided on the inner face of its depending portion with inwardly extending die cast rivets 38 which serve to hold in place a Contact spring 39 which as shown most clearly in Fig. 3 has a rounded projection 40 at its lower end which engages the wire 2 of the resistance unit and an inwardly extending portion 4l at its upper end. A pair of curved springs 42 are sprung into place beneath the lugs of the

members

22 and 24, with their ends bearing against the portions 41 of the contact springs 39, whereby the latter are held firmly against the wire 2 on account of the rotary connection between the sleeve 21 and the

members

22 and 24 to which the springs are attached which permits the springs 42 to force the contact springs inwardly against the wire. The ends of the springs 42 are turned upwardly as indicated at 43 to form rounded surfaces for engaging the portions 41 of the contact springs to produce most satisfactory operation.

For the usual fine adjustments of the contact device the elements of the latter occupy the positions shown in the drawing, that is, with the pin 34 held in engagement with the thread of the screw 35 by the effect of the spring 32 pressing outwardly the upper end of the lever. When the screw is rotated by the knob 36 the contact device will be translated along the wire 2 to vary the resistance of the rheostat as may be desired.

When however a coarse adjustment is desired, the operator takes hold of the knob 27 and with the thumb or a iinger of the same hand presses inwardly the upper end of the lever 30, thus disengaging the pin 34 from the screw 35 so that he may quickly move the contact device from one position to another. Thereafter by releasing the lever the normal condition of the apparatus is restored so that the contact device may be more accurately adjusted to the desired position.

While the apparatus of the invention has been referred to as a rheostat it will be understood that it is equally adapted to be used as a potentiometer, or for any purpose for which apparatus of this character may be used, by appropriately arranging the circuit connections. It will also be understood that while a preferred embodiment of the invention has been shown, it may be embodied in other forms and that various changes in structural details may be made Without departing from the principle of the invention as defined in the appended claims.

I claim:

1. In a rheostat, the combination of a resistance unit, a rod parallel to the axis of the unit, a member slidably mounted on the rod, a pair of devices rotatably mounted on the member, a contact element attached to each of the devices, a spring bearing at its centre against parts of the devices beneath the slidable member and at its ends against the cuter portions of said devices to hold the contact elements against the resistance unit and means associated with the slidable member and the devices for translating the contact elements with respect to the resistance unit.

2. In a rheostat, the combination of a resistance unit, a rod parallel to the axis of the unit, a contact device slidably mounted on the rod and co-acting with the unit, a screw parallel to the rod, a knob mounted on the device in fixed relation thereto, a lever movably mounted on the device and having its upper end adjacent to the knob, and its lower end adjacent to the screw,

a pin connected to the lower end of the lever,

a spring between the upper end of the lever and the knob for normally pressing the pin into engagement with the screw, whereby the contact device may then be translated by rotation of the screw or be moved rapidly from one position to another by simultaneous manipulation of the knob and disengagement of the pin and screw by pressure of the upper end of the lever against the spring.

3. In a rheostat, the combination of a resistlugs and their ends bearing against the extended portions of the devices to hold the Contact elements against the resistance unit and means associated with the sleeve for translating it and the devices and elements mounted thereon with respect to the resistance unit.

GEORGE B. CROUSE.