US3869688A

US3869688A - Customer adjustment switch assembly

Info

Publication number: US3869688A
Application number: US436282A
Authority: US
Inventors: George C Aldous
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1974-01-24
Filing date: 1974-01-24
Publication date: 1975-03-04
Anticipated expiration: 1992-03-04

Abstract

A thermal cycling switch mounted on a control panel for a surface cooking unit with calibration means attached to the switch and extending forwardly of the control panel for customer access. Abutment means in the path of movement of the extension determine the maximum adjustment that can be made by the user. The extension is disposed so as to normally be covered by the forwardly projecting control knob of the switch which must first be axially displaced some distance from the control panel for access to the extension.

Description

United States Patent 1 Aldous CUSTOMER ADJUSTMENT SWITCH ASSEMBLY [75] Inventor: George C. Aldous, Mansfield, Ohio [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Jan. 24, 1974 [21] Appl. No.: 436,282

[52] US. Cl 337/82, 337/57, 337/94, 337/347, 337/369 [51] Int. Cl. H0lh 61/00 [58] Field of Search 337/44, 51,57, 64, 82, 337/94, 347, 369, 101

[56] References Cited UNITED STATES PATENTS 2,979,597 4/1961 Karlen 337/44 X [in 3,869,688 Mar.4, 1975 Turner 337/44 X Aldous 337/101 Primary Examiner-J. D. Miller Assistant Examiner-Fred E. Bell Attorney, Agent, or FirmF. A. Winans [57] ABSTRACT A thermal cycling switch mounted on a control panel for a surface cooking unit with calibration means attached to the switch and extending forwardly of the control panel for customer access. Abutment means in the path of movement of the extension determine the maximum adjustment that can be made by the user. The extension is disposed so as to normally be covered by the forwardly projecting control knob of the switch which must first be axially displaced some distance from the control panel for access to the extension.

9 Claims, 2 Drawing Figures CUSTOMER ADJUSTMENT SWITCH ASSEMBLY BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a thermal cycling switch and more particularly to such a switch mounted on the control panel and having a forwardly projecting calibration means for calibrating the switch, within certain predetermined limits, by the customer.

2. Description of the Prior Art Thermal cycling switches are well known in the prior art (see for example U.S. Pat. No. 3,634,802 of common assignee) and are extensively used to control the energization of surface cooking units on a range or the like. Such switches typically include two spatially separated electrical contacts carried on movable leaf spring arms with one of the arms in intimate facing relationship with a bimetal extending over a substantial length of the arm. The bimetal in turn is in intimate contact with a resistance heater. The other contact carrying arm is moved in response to a rotatable cam, controlled by a shaft extending from the switch casing. The cam, in its various positions at which the switch is on forces the contacts together with varying deformation of the bimetal.

Closing the contacts, in addition to energizing the surface unit, energizes the heater in the switch which in turn causes the bimetal to be deformed. The amount of initial deformation by the cam determines the amount of deformation required by heating the bimetal to open the contacts, deenergizing thesurface unit and the heater, permitting bimetal to cool down whereupon the contacts again close and the cycle is repeated.

It is noted that this switch does not respond to the temperature of the surface unit but controls the percent of time there is power to the unit which in turn is correlated to a relative cooking temperature, such as low, medium, high, etc., indicated by the manual control knob on the shaft.

These switches also typically include an ambient responsive bimetal to compensate for variations in the ambient temperature causing variations in the percent of on" time at the same setting. Also, a calibration member provided for adjusting the initial operation of the switch so that at certain settings of the control shaft the switch maintains the surface unit energized a predetermined percentage of time within accepted tolerances.

Although such switches have generally been satisfactory, it has been found that for various reasons, after a period of use, the switches require recalibration. This is critical primarily at the lowest setting where, in switching from the of position to the initial on position, the surface unit is maintained energized a greater percentage of the time than desirable. (One accepted criteria is for the unit to just melt butter at this lowest setting, which is accomplished when the unit is energized about 5 percent of the time, with the permissible range being 3 to 8 percent at this setting.) At any higher setting of the switch and change in the percentage of on time can be accommodated merely by altering the setting of the control knob; however, at the initial setting there is no way to decrease the on time without turning the unit off." Such a change in the operating characteristic of the switch has resulted in customer complaint. And, although the switch is capable of being corrected by a service call for recalibration by the calibration member, it has been found to be less expensive to simply replace the switch rather than recalibrate it.

SUMMARY OF THE INVENTION The invention provides a thermal cycling switch of well known construction and further including a customer accessible calibration extension projecting forwardly through the panel mounting the switch to be disposed in a generally unobtrusive position sub-adjacent to the control knob of the switch. Abutment means are provided to limit the calibration permitted the customer through this device to an amount that is empirically known to accommodate at least the majority of switches that require recalibration.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of a thermal cycling switch;

FIG. 2 is a perspective view of the switch mounted on a panel associated with a surface cooking unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is associated with a thermal cycling switch such as fully described in U.S. Pat. No. 3,634,802 which is herein incorporated for its more detailed description of such a switch. However, reference is made to FIG. 1 which shows such a switch for the purpose of identification of its part. Thus, the switch 10 is enclosed in a box like casing 12 of rigid insulating material housing the

switch contacts

14, 16. It is seen that the switching contacts are, in the off position shown, in opposed facing spaced relationship as carried at the free end ofa pair of conducting arms 18, 20 cantilevered from the casing. Arm 18 is anchored as by welding at its opposite end to a terminal 24 extending to the exterior of the casing and includes an offset intermediate portion 22 forming a cam following projection.

Arm 20 carrying contact 16 and likewise anchored at the end opposite the contact to another terminal 26, is associated with a bimetal 28 along its length, separated by a strip of insulating material so that when arm 20 is conducting current, an energized resistance heater 27 causes the bimetal to expand in a direction to move contact 16 away from contact 14 (i.e, clockwise as viewed in FIG. 1).

An ambient compensating bimetal arm 30 is also anchored to the terminal 26 and extends for a short distance in generally the same direction as arm 20. The free end of arm 30 has a threaded aperture 32 therein that receives an adjusting screw 34 extending in the plane of movement of both arms 20 and 30. Access to the adjusting screw 34 is provided by an opening 36 in the sidewall of the casing.

The lead end of the adjusting screw abuts arm 20 and through its relative position adjust the spatial separation of

contacts

14, 16 for calibrating the switch to operate within a predetermined acceptable range for the surface unit energization.

A manual control shaft 32 is rotatably mounted in the casing and extends forwardly therefrom transverse to the plane of movement of contacts l4, l6 and carries a camsurface 34 in contact with the cam following portion of arm I8. Rotation of shaft 32 and thus cam 34 from its off" position, moves arm 18 to the left (as viewed in FIG. 1) closing contact 14 on contact 16. Because of the configuration of the cam, the contacts are closed under various degress of deformation of the arms. The amount of deformation set by the cam determines the amount of deformation the bimetal must assume before it can move its associated arm 20 to a position where the contacts open. Thus, at any on setting, the contacts are closed until movement of the bimetal opens them whereupon the heater is deenergized and the bimetal cools to the contacts again become closed,'resulting in the surface unit, controlled through these contacts being intermittently energized a certain percentage of time. The elapsed time that the contacts remain close is thus dependent upon the setting of the cam. For the purpose of controlling a surface cooking unit, it is desirable, at the lowest on setting, that the contacts remain closed only about 5 percent of the time, with the percentage of closed time increasing gradually through the various higher settings of the control shaft to approximately 50 to 60 percent. Any setting beyondthe 60 percent will maintain the unit continuously energized as there is no needto provide any variability between 60 to 100 percent as there is no appreciable distinction in the type of cooking by the unit over this range.

The switch is initially calibrated after assembly by the screw 34 setting the spatial separation of the two contacts to a position wherein the switch operates in the above parameters. However, after a period of use it is possible for the switch to require readjustment. It is pointed out that it is not necessary for the switch, at any of its intermediate setting, to always provide the same amount of energized time which that particular setting has provided heretofore for the reason that any change in the on time at any particular intermediate setting can be compensated for by adjusting the control knob in eitherdirection to accommodate the change. However, at the lowest setting of the switch to an on position, where it is desirable to have the switch energized a surface unit only about 5 percent of the time, any change in the switch characteristics which causes the lowest setting of the switch to maintain the burner .energized above the acceptable limit for that setting (8 percent being the largest percentage of energized time permissible at the lowest setting to have the switch provide the range of cooking abilities desired) cannot be compensated for as turning the control shaft to a lower setting turns the switch off. This type of failure is the most common user complaint of such a switch. Further, it has been found less expensive to completely replace the switch in the field than have a serviceman recalibrate it as the lead wires are easily removed and only two screws are employed in mounting the switch. This is less time consuming than recalibration through the use of the screw and then testing the unit to determine if it is energized within the range of 3 to 8 percent of the time at the lowest setting.

Thus the present invention provides a means for the user to easily turn the adjusting screw to recalibrate the switch to an acceptable operation. Referring to both FIGS. 1 and 2, it is seen the adjusting screw 34 of this switch has a manually accessible turning member 40 engaging the screw 34 and extending outwardly through the access aperture in the side wall of the casing. Member 40 includes a portion 42 projecting forwardly in the same general direction as the control shaft so that it extends through an appropriately sized aperture 44 in the control panel. The turning member 40 also includes an abutment projection '46 that at contacts adjacent stationary structure, such as the side wall of the casing (also, it is obvious that the portion 42 abutting the ends of the elongated aperture 44'could serve the same purpose) to limit the permissible customer adjustment.

The screw threads and the positioning of the adjustment screw against the arm 20 of the commcrcial'embodiment of the above-described switch results in changing the energization 1 percent for every l0 rotation of the screw. The abutment means of the present invention permit 50 rotation thereby allowing a 5 percent change. Preferably, after the initial factory calibration, the turning mechanism would be mounted on the screw head such that the abutment portion was in one extreme position permitting only outward axial movement of the screw to increase the spatial separation of the contacts. Thus, should the switch subsequently require recalibration to a lower setting, an adjustment of up to 5 percent could be accommodated. Thus, assuming the lowest setting after a period of use results in an on time of 10 to 13 percent which is too high for this setting, the customer could readjust the switch to within the 5 to 8 percent range which is then in the acceptable limits. It has been found that such ad justment would correct at least percent of the switches previously requiring replacement.

Externally on the forward side, the control shaft has a manual knob 48 which carries indicia cooperating with indicia on the panel to inform the user of the relative setting of the switch in relation to the type of cooking temperature the surface unit will have. In the preferred embodiment, the control knob has a flared base portion which extends radially outwardly a sufficient distance to cover the extended portion 42 of the manually accessible turning member 40. Thus, when an adjustment of the switch is required, the control knob can be telescopically pulled outwardly, revealing the extended portion for access, the correction made, and the knob (indexed to the shaft by a complementary flat surfaces) replaced.

I claim:

1. In an electric cooking apparatus comprising a surface heating unit supported on a counter member and including panel for supporting switch means associated with said unit, a thermal cycling switch enclosed in a housing mounted on the back face of said panel having a pair of opposed relatively movable contact carrying arms and a rotatable control shaft mounted with one end adjacent said arms and including means for controlling the closed position of said contacts, the opposite end of said shaft extending forwardly through said panel to be manually accessible for rotating said shaft between an off position and any various on positions to vary the energization time of said heating unit over a predetermined range in accordance with the closed position of said contacts for maintaining a relative cooking temperature identified by indicia associated with said position and wherein the improvement comprises:

switch calibration means for correlating, within limits, the relative temperature of said unit maintained at one of said positions of said shaft to the indicia relating to said position, said calibration means comprising means for adjusting the initial position of one contact with respect to the other, said adjusting means being incrementally movable and including a portion extending from adjacent one of said contact carrying arms to exteriorly of said switch housing, and forwardly through said panel for manual access for moving said adjusting means from the same side of said panel as the manual movement of said shaft, and abutment means for limiting the movement of said adjusting means.

2. In a thermal cycling switch for controlling the energization of a surface cooking unit, said switch housed within a casing mounted on the back face of a control panel associated with said cooking unit and including a manual control means extending forwardly through an aperture in said panel for setting said switch to energize said cooking unit to a preferred relative cooking range generally corresponding to indicia associated with said control means, said switch further including within said casing a pair of opposed contact carrying arms and means for adjusting the relative spatial separation of said arms for calibrating said switch to respond within a preferred range of energizing characteristics, said last named means being accessible from exteriorly of said casing and wherein the improvement comprises:

a manually accessible member operatively connected to said adjusting means and extending forwardly through an appropriately sized aperture in said panel for turning said adjustment means from forwardly of said panel; and,

abutment means operatively associated with said turning means for limiting the movement of said turning means to less than one full turn.

3. Structure according to claim 2 wherein said control means includes a rotatable shaft extending from said casing forwardly of said panel and a control knob received by said shaft and having indicia thereon coopcrating with indicia on said panel for indicating the relative setting of said switch, the portion of said knob generally adjacent said panel having a sufficient radial dimension to normally cover said turning means and its associated aperture in said panel.

4. Structure according to claim 3 wherein said abutment means limits the movement of said turning means so that the operational characteristics of said switch can be altered only within a minimal range.

5. Structure according to claim 4 wherein said adjustment range permitted by said abutment means is sufficient to recalibrate a majority of said switches, subsequent of the factory calibration, to within the previously determined acceptable operational characteristics.

6. A thermal cycling switch electrically connected to a surface cooking unit and housed Within a casing mounted on a control panel associated with said unit, said switch having a pair of opposed independently movable contact carrying arms, means for moving one of said arms to any of various positions for closing said contacts with variable amounts of bias and means associated with the other of said arms for opening and closing said contacts in response to an elapsed time at either previous condition of said contacts determined by said biasing force thereby resulting in said contacts cy clically energizing said cooking unit at any on setting with the elapsed time of energization variable in accordance with the setting of said moving means of said one arm, said last named means including a rotatable shaft extending forwardly through said panel and an indicia carrying knob attached to the extending end and indicating the relative setting of said switch and wherein the improvement comprises:

a forwardly accessible switch calibration means for correlating the relative cooking temperature produced by said cyclical energization to that indicated by said indicia, said calibration means including a screw and means for mounting said screw adjacent said other of said arms for movement in the plane of movement of said contacts, said screw having one end contacting said last named arm to vary the normal position of said arm, and the opposite end of said screw connected to a turning member extending outwardly of said casing and forwardly through said panel through an appropriately sized aperture; and,

means for limiting the permissible rotation of said turning member to a predetermined amount less than one full turn.

7. Structure according to claim 6 wherein said forwardly projecting moving member and associated apertures are normally covered by said control knob.

8. A thermal cycling switch for controlling a surface cooking unit mounted on the back of a.control panel associated with said unit, said switch comprising a casing housing a pair of spatially opposed movable contact carrying arms, movable in a plane generally parallel to the plane of said psnel and a rotatable control shaft including means for moving said arms to various positions, the axis of said shaft disposed generally perpendicular to said plane of movability and having a portion extending forwardly through said panel for manual accessibility, said forward portion supporting a control knob having indicia indicating the relative setting of said switch with respect to the energization of said cooking unit; and,

means for adjusting the spatial relationship between said arms, said adjusting means comprising and adjusting screw threadably received in support means for axial movement of said screw in the plane of movability of said arms, said screw having one end abutting one of said arms, the opposite end of said screw supporting means for turning said screw exteriorly of said casing, said turning means including a portion extending forwardly through said panel in a plane generally perpendicular thereto; and,

means for limiting the rotation of said screw to less than one revolution thereof, said limiting means comprising abutment means disposed in the normal path of said turning means.

9. Structure according to claim 8 wherein said turning means extending through said panel is normally covered by said control knob.

Claims

1. In an electric cooking apparatus comprising a surface heating unit supported on a counter member and including panel for supporting switch means associated with said unit, a thermal cycling switch enclosed in a housing mounted on the back face of said panel having a pair of opposed relatively movable contact carrying arms and a rotatable control shaft mounted with one end adjacent said arms and including means for controlling the closed position of said contacts, the opposite end of said shaft extending forwardly through said panel to be manually accessible for rotating said shaft between an ''''off'''' position and any various ''''on'''' positions to vary the energization time of said heating unit over a predetermined range in accordance with the closed position of said contacts for maintaining a relative cooking temperature identified by indicia associated with said position and wherein the improvement comprises: switch calibration means for correlating, within limits, the relative temperature of said unit maintained at one of said positions of said shaft to the indicia relating to said position, said calibration means comprising means for adjusting the initial position of one contact with respect to the other, said adjusting means being incrementally movable and including a portion extending from adjacent one of said contact carrying arms to exteriorly of said switch housing, and forwardly through said panel for manual access for moving said adjusting means from the same side of said panel as the manual movement of said shaft, and abutment means for limiting the movement of said adjusting means.

2. In a thermal cycling switch for controlling the energization of a surface cooking unit, said switch housed within a casing mounted on the back face of a control panel associated with said cooking unit and including a manual control means extending forwardly through an aperture in said panel for setting said switch to energize said cooking unit to a preferred relative cooking range generally corresponding to indicia associated with said control means, said switch further including within said casing a pair of opposed contact carrying arms and means for adjusting the relative spatial separation of said arms for calibrating said switch to respond within a preferred range of energizing characteristics, said last named means being accessible from exteriorly of said casing and wherein the improvement comprises: A manually accessible member operatively connected to said adjusting means and extending forwardly through an appropriately sized aperture in said panel for turning said adjustment means from forwardly of said panel; and, abutment means operatively associated with said turning means for limiting the movement of said turning means to less than one full turn.

3. Structure according to claim 2 wherein said control means includes a rotatable shaft extending from said casing forwardly of said panel and a control knob received by said shaft and having indicia thereon cooperating with indicia on said panel for indicating the relative setting of said switch, the portion of said knob generally adjacent said panel having a sufficient radial dimension to normally cover said turning means and its associated aperture in said panel.

6. A thermal cycling switch electrically connected to a surface cooking unit and housed within a casing mounted on a control panel associated with said unit, said switch having a pair of opposed independently movable contact carrying arms, means for moving one of said arms to any of various positions for closing said contacts with variable amounts of bias and means associated with the other of said arms for opening and closing said contacts in response to an elapsed time at either previous condition of said contacts determined by said biasing force thereby resulting in said contacts cyclically energizing said cooking unit at any ''''on'''' setting with the elapsed time of energization variable in accordance with the setting of said moving means of said one arm, said last named means including a rotatable shaft extending forwardly through said panel and an indicia carrying knob attached to the extending end and indicating the relative setting of said switch and wherein the improvement comprises: a forwardly accessible switch calibration means for correlating the relative cooking temperature produced by said cyclical energization to that indicated by said indicia, said calibration means including a screw and means for mounting said screw adjacent said other of said arms for movement in the plane of movement of said contacts, said screw having one end contacting said last named arm to vary the normal position of said arm, and the opposite end of said screw connected to a turning member extending outwardly of said casing and forwardly through said panel through an appropriately sized aperture; and, means for limiting the permissible rotation of said turning member to a predetermined amount less than one full turn.

8. A thermal cycling switch for controlling a surface cooking unit mounted on the back of a control panel associated with said unit, said switch comprising a casing housing a pair of spatially opposed movable contact carrying arms, movable in a plane generally parallel to the plane of said psnel and a rotatable control shaft including means for moving said arms to various positions, the axis of said shaft disposed generally perpendicular to said plane of movability and having a portion extending forwardly through said panel for manual accessibility, said forward portion supporting a control knob having indicia indicating the relative setting of said switch with respect to the energization of said cooking unit; and, means for adjusting the spatial relationship between said arms, said adjusting means compRising and adjusting screw threadably received in support means for axial movement of said screw in the plane of movability of said arms, said screw having one end abutting one of said arms, the opposite end of said screw supporting means for turning said screw exteriorly of said casing, said turning means including a portion extending forwardly through said panel in a plane generally perpendicular thereto; and, means for limiting the rotation of said screw to less than one revolution thereof, said limiting means comprising abutment means disposed in the normal path of said turning means.