US3505884A

US3505884A - Rotation limit device

Info

Publication number: US3505884A
Application number: US733893A
Authority: US
Inventors: Robert M Ford; David W Friday
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1968-06-03
Filing date: 1968-06-03
Publication date: 1970-04-14
Anticipated expiration: 1987-04-14

Description

April 14, 1970 R. M, FORD ETAL 3,505,884

ROTATION LIMIT DEV-ICE Filed June 5, 1968 \\l 1. f 30 nvvewroe ROBERT M. FORD oawo m FRIDAY if 82W 3 AGE/VT United States Patent O 3,505,884 ROTATION LIMIT DEVICE Robert M. Ford and David W. Friday, Framingham,

Mass., assignors to Raytheon' Company, Lexington, Mass., a corporation of Delaware Filed June 3, 1968, Ser. No. 733,893 Int. Cl. F16h 35/18 US. Cl. 74-10.2 5 Claims ABSTRACT OF THE DISCLOSURE.

A knob mounted on the end of a rotatable shaft which extends through a control panel from an adjustable device supported on the rear side of the panel, the knob having a circular series of equally spaced holes in the panel side thereof, two of said holes containing removable pins which protrude from the panel side of the knob to define the maximum limits of clockwise and counterclockwise rotation of the knob. An anti-rotate washer orientates the adjustable device on the control panel and has a right angle tab which extends out from the control panel into the rotational path of the roll pins which protrude from the panel side of the knob.

BACKGROUND OF THE INVENTION This invention relates generally to knobs for control devices and, more particularly, is concerned with an adjustable means for selecting the desired limits of clockwise and counterclockwise rotation of the knob.

The operation of equipment today is controlled, to a great extent, by adjustable devices, such as valves, rheostats, potentiometers, variable capacitors, gang switches and the like. Generally, these devices are mounted in a control panel on the rear side thereof and have a rotatable control shaft which extends through a hole in the panel to protrude from the front side thereof. A knob is mounted on the end of the shaft and is attached thereto in binding fashion, such as by journalling a radially extending screw in the knob against a flat surface on the shaft of the control device. Thus, turning the knob rotates the shaft and varies the setting of the adjustable device.

Since some of the commercially available control devices allow continuous rotation of the control shaft, a problem arises when limits must be set on the rotational adjustment of the control device. Instances occur where an operator can exceed critical limits and cause damage to the associated operating equipment. For example, the entire output of a potentiometer, applied across the terminals of a circuit, could be excessive and burn out valuable components in the circuit. In many cases, when the control device is provided with rotational limits, the stoppingmechanism is located internally in the body of the device, which is often potted. Control devices of this type do not provide means for adjusting the maximum limits of rotation to conform with the critical limits required by the associated operating equipment.

One solution disclosed by the prior art provides a control knob having a fixed extension tab which will strike an object protruding from the control panel in the rotational path of the tab. Usually, screws or the like are installed in the control panel to engage the extension tab at the selected limits of clockwise and counterclockwise rotation. However, this solution does not provide a convenient means for adjusting the limit stops. If a change in the location of the limit stops is required, the only alternative is to drill additional holes in the panel so that the screws or like objects may be installed at the newly selected points of maximum rotation.

3,505,884 Patented Apr. 14, 1970 Therefore, the solution to this problem not only requires a means to limit the rotation of the control knob but also a means for adjusting the location of the limit stops should a change of this type be required by the associated operating equipment. Furthermore, the change in maximum rotation should be accomplished easily and quickly; therefore the means of adjusting the limit stops should be readily accessible to the operator.

SUMMARY OF THE INVENTION In accordance with these objectives, this invention provides a control knob having a circular series of equally spaced cavities in the panel side thereof, two of the respective holes containing respective removable pins which protrude outwardly from the panel side of the knob and an anti-rotate washer having a right angle tab which extends into the rotational path of the aforementioned pins.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing may be more fully understood from the description when read together with the accompanying drawing wherein:

FIG. 1 is an exploded, perspective view partly in axial section of the preferred embodiment of this invention;

FIG. 2 is an. elevational view, partly in axial section, of the preferred embodiment of this invention; and

FIG. 3 is an axial sectional view taken along lines 3-3 of FIG. 2 looking in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, wherein like characters of reference designate like parts throughout the several views, there is shown in FIGS. 1 and 2 an adjustable control device 10, such as a potentiometer for example, which is mounted in a control panel 12 from the rear side thereof. The rotatable shaft 14 and threaded collar 16 of control device 10 extend through a hole 18 in panel 12 and protrude from the front side thereof. An antirotate washer 20 is placed over collar 16 and has a radial, inwardly extending, tab 22 which fits into a longitudinal slot 24 on the outer diameter of the collar 16 and a right angle tab 26 which extends rearwardly into a hole 28 in panel 12. Thus, the anti-rotate washer 20 orientates the body of control device 10 with respect to the panel and prevents the device from turning when the shaft 14 is rotated. A nut 30 is journalled onto the threaded collar 16 to hold the body of control device 10 and the anti-rotate washer 20 tightly against the panel 12. As shown in FIG. 3, cavity 35, centrally located in the panel side of control knob 32, receives and slidingly engages the end of the rotatable shaft 14. Knob 32 is bindingly attached to a shaft 14 by any convenient means, as by journalling a screw 34 into a radially disposed hole 33 in knob 32 until screw 34 bears against the flat surface of a landing 36 on shaft 14. Thus, turning the control knob 32 rotates the shaft 14 and varies the setting of control device 10.

Since the entire output of the control device 10., such as a potentiometer for example, may damage the operating equipment associated with it, maximum limits of clockwise and counterclockwise rotation of the shaft 14 are required. As shown more clearly in FIG. 3, the panel side of knob 32 is provided with a circular series of equally spaced cavities 40. A removable spring pin 42, protruding from the rear or panel side of knob 32, is press-fitted into a cavity 40 which cavity is located at the selected limit of clockwise rotation of knob 32. Another removable spring pin 42 similarly carried by knob 32, is press-fitted into another cavity 40, which cavity is located at the selected limit of counterclockwise rotation of knob 32. When one of the pins 42 is engaged by an object which extends outwardly from panel 12 and into the rotational path of the pins 42, rotation of the knob 32 will be stopped. One method of providing a fixed stop is shown in the drawing and comprises a tab 44 which extends outwardly or forwardly from the antirotate washer and protrudes into the rotational path of the pins 42. Rotation of the knob will be stopped in either the clockwise or counterclockwise direction when the respective pin 42 strikes against the tab 44. Thus, the pins 42 in knob 32 and tab 44 on anti-rotate washer 20 determine the maximum clockwise and counterclockwise movement of control knob 32. Accordingly, the arcuate distance between pins 2 determines the maximum rotary movement of shaft 14 and, consequently, the variable range of control device 10.

The rotary movement of the control knob 14 can be increased or decreased by loosening the set screw 34 and sliding the knob 32 off the end of shaft :14 whereupon the spring pins 42 can be removed from the cavities into which they have been press-fitted and reinstalled into other cavities which conform more closely to the newly selected limits of maximum clockwise and counterclockwise rotation. The pins 42 can be removed entirely if continuous rotation of the shaft 14 is desired. The knob is replaced on the end of the shaft 14, the set screw 34 in knob 32 is tightened and the control device is back in operation in a very short time, with rotary movement of the shaft 14 restricted to the new limits of maximum rotation. Having the adjustable means on the knob 32 is a most convenient arrangement because the knob is the closest element of the assembly to the operator and is the first unit removed in gaining access to any other element of the assembly.

Although fifteen cavities are shown in the circular series on the panel side of the knob in FIG. 3, it is apparent that the number of holes could be increased or decreased as required by the associated operating equipment. Although right angle tab 44, extending outwardly from the anti-rotate washer, provides the illustrated positive limit stop, other fixed means would function as well, such as a screw journalled into the panel. The arrangement of this invention would not require moving the screw to change the limits of rotation of the knob because the adjustable feature of the invention is located on the panel side of the knob. Although the knob has been shown attached to a rotatable shaft by means of a radially disposed screw, the knob may be attached by other means, such as press-fitting it onto the end of the rotatable shaft. These and other modifications which may occur to those skilled in the art are within the spirit and scope of this invention.

We claim:

1. A control knob having a panel side with a central opening located therein for receiving an end of a rotatable shaft and a circular series of equally spaced holes radially spaced from said central opening, and two pins interfitting into respective holes of said circular series and protruding from the panel side of the knob, said pins being removable from said holes and reinsertable in other selected holes of said circular series.

2. A control knob attached to an end of a rotatable shaft protruding from a panel, said knob having in the panel side thereof a series of uniformly spaced holes concentric with the rotatable shaft, at least one of said cavities carrying a removable member which protrudes from the panel side of the knob, and fixed stop means located in the rotatational path of said member for defining the maximum limit of rotation of said knob.

3. A control knob as set forth in claim 2 wherein said fixed stop means includes an anti-rotate washer fixedly attached to the panel, and a tab extending outwardly from said washer.

4. In combination, a control knob bindingly attached to one end of a rotatable shaft, said shaft protruding from a panel and extending through a hole in the panel to an adjustable device mounted on the opposite side of the panel, said knob having in the panel side thereof a circular series of equally spaced cavities radially spaced from the rotatable shaft, two pins, each having an end disposed within a respective cavity and having an opposite end extending outwardly from the panel side of the knob, said pins being removable from said respective cavities and insertable into other respective cavities of the circular series, and an anti-rotate washer between said panel and knob and having a portion thereof interlocked with said device, another portion interlocked with the panel, and a tab extending outwardly from the panel into the rotational path of said pins, thereby defining the maximum limits of clockwise and counterclockwise rotation of said knob.

5. A control knob having a rear side with a central opening for receiving a shaft therein, spaced holes in said rear side of the knob and radially spaced from said central opening, said holes being greater than two in number, and two members in two of said holes and projecting outwardly from said rear side of the knob, said members being removably mounted in said holes for reinsertion in other selected holes as desired.

References Cited UNITED STATES PATENTS 2,444,485 7/1948 Aitcheson 74-553 3,214,985 11/1965 Danek et al 74-526 X MILTON KAUFMAN, Primary Examiner US. Cl. X.R. 74526