US3222480A - Thermal switch with calibration means - Google Patents

Abstract

957,826. Thermal switches; cam-operated switches. KING-SEELEY THERMOS CO. Dot.12, 1962 [Nov. 3, 1961], No. 38665/62. Heading H2B. The initial calibration of the thermally operated contacts of switch generally similar to that disclosed in Specification 895,264 (but without the rapid separation bimetal and without ambient temperature compensation) is performed by rectilinear pressure on a frictionheld member 58 which replaces the adjusting screw in the earlier disclosure. The member 58 is pressed into the hole 56 until lug 58a displaces rigid member 46 to apply torsion to bracket 45 carrying assembly of bimetal 40 and heater strip 42 such that contact 32 engages contact 33. The dial 15a is then set to a preselected temperature and the switch placed in a jig where the bimetal 40 is maintained at the preselected temperature while a tool is inserted through a hole 59 in the front plate 11 to press on the end 58b of member 58, which is thus moved against friction until the contacts 32, 33 just open. The tool is preferably power-driven via an electric clutch which is in circuit with contacts 32, 33 so that the drive ceases immediately the contacts open (Figs. 8, 9 and 10, not shown). The bimetal 40 may be heated by its surroundings instead of heater 40 and it may close instead of open the contacts when heated. In the latter case member 58 is first set to open the contacts and then adjusted to just close them.

Description

1965 D. E. CLAPP THERMAL SWITCH WITH CALIBRATION MEANS 2 Sheets-Sheet 1 Filed Nov. 5, 1961 d 2 7 7 9 6 RP M. 0 4 5 m H EL A w l L Q n E m m m 4 D 2 a B 7 F J m. fl 3 F IGI.

1965 D. E. CLAPP THERMAL SWITCH WITH CALIBRATION MEANS 2 Sheets-Sheet 2 Filed Nov. 5. 1961 INVENT 0R. DANIEL E. CLAPP BY WW ATTYS.

United States Patent 3,222,480 THERMAL SWITCH WITH CALIBRATION MEANS Daniel E. Clapp, Churchville, Pa., assignor, by mesne assignments, to King-Seeley Thermos Co., Ann Arbor, Mich., a corporation of Michigan Filed Nov. 3, 1961, Ser. No. 149,970 8 Claims. (Cl. 200-122) This invention relates to method and means for calibrating electric control switches, and more particularly adjusting the initial relationship of the contacts of a thermally actuated switch.

In a thermally actuated switch, a thermomotive member is provided which is adapted to move one contact either toward or away from its opposed contact when heated. In its more usual form, the thermomotive memher is arranged to tend to separate the contacts when heated, the heat being derived either from the controlled heating element or from an auxiliary resistance heater connected in circuit with the contacts and arranged to be in heat transfer relationship with the thermomotive member. The form employing an auxiliary resistance is known as an infinite switch. In order to select the temperature to be maintained by the heating element, adjustment means is provided which conveniently takes the form of a cam arranged to adjustably resiliently displace one contact by the other contact, which displacement is commonly called contact overclosure. The angular position of the cam is indicated by a dial, or the like, including calibration legends. The accuracy of these legends, as indicators of the temperature level selected, depends on the initial calibration of the switch. Basically such initial calibration is accomplished by adjusting the initial position of one contact in relation to the other.

Accurate calibration is particularly diflicult in the case of an infinite switch in which the heating element is intermittently energized, the temperature level being established by the ratio of closed to open contact time, which determines the percentage input, and this is particularly true in the lower range of adjustments. To assure maximum accuracy throughout the whole range, calibration is ordinarily performed at some specific low setting. In the prior art, a screw has been used for this purpose, either threaded though the mounting and arranged to engage the contact-carrying arm, or threaded through a member interconnected with the contact-carrying arm and extending through a clear hole in a portion of the mounting, with the head of the screw engaging the outer surface of that portion.

For close adjustment, the use of a screw leaves much to be desired. There is a limit to the fineness of thread pitch that is commercially obtainable, so that adjustment is coarser than is desirable. Even an extremely fine pitch thread has a certain amount of clearance at the pitch line, with the result that the longitudinal position of the screw may immediately change when the pressure of the screw-driver is removed. A slight bend can result in a wobble whereby a small turning of the screw may cause a relatively large change in calibration. There are problems of thread uniformity, possibly stripped threads, and/ or eccentricity. In addition, the position of the screw may be altered as a result of vibration.

By this invention, calibration is accomplished by pressing into position a specially constructed adjusting pin adapted to frictionally engage the walls of an aperture in the mounting. A novel device is utilized to exert pressure on the pin, arranged to automatically release the pressure at the exact position representing the temperature level for which the dial is set. In contrast to a screw, such an adjusting pin is not affected by eccentricity or lack of straightness, since it is not rotated. It

obviates all of the defects of a threaded part, including lack of thread uniformity, stripped threads, and pitch-line clearance. It is not affected by vibration, since it is held tightly in its mounting by frictional engagement.

For illustrative purposes, the present invention is described as it is applied to an infiinite switch, although its use is not intended to be limited thereto.

In the accompanying drawings:

FIGURE 1 is a perspective view of the exterior of a housing for a thermally actuated switch;

FIGURE 2 is a plan view of the contents of the housing, with cover plate removed;

FIGURE 3 is a sectional view taken along line 33 of FIGURE 2 showing the infinite switch construction;

FIGURE 4 is a plan view of the rear of the housing;

FIGURE 5 is a fragmentary perspective view of a detail of the switch mounting;

FIGURE 6 is a perspective view of the calibration adusting pin;

FIGURE 7 is a fragmentary section on the line 7-7, FIG. 3 through the aperture for the adjusting pin with the pin in place;

FIGURE 8 is a front elevational view of a device used for setting the adjusting pin;

FIGURE 9 is a sectional view taken along line 99 of FIGURE 8; and

FIGURE 10 is a detailed view partially in section showing operation of the device of FIGURES 8 and 9 on the pin structure of FIGURES 4, 6 and 7.

Referring to FIGURES 1-4 and particularly to FIG- URE l, the switch is preferably enclosed in a hollow housing 10, a box-like enclosure having an open side and various element supporting appendages integral therewith. The housing may be composed, for example, of arigid phenolic resin which is molded into the desired shape. Closing the open side of the housing is a cover plate 11, held in place by suitable fastening means 12' and 13 (see FIGURE 3). Extending through the cover plate and across the switch housing to a suitable bearing is a shaft 14 to the outer end of which is secured a knob 15 and a dial 15a whose indicator legends, indicating selected temperature level, may be compared with a reference mark 16 on the cover plate.

Within the housing are a pair of switch structures generally designated 17 and 18 (see FIGURE 2). Switch structure 17 provides two switches, each including one fixed and one movable contact. The movable contacts have a common support 20 one end of which is bifurcated to provide struts 20a and 20!) supporting at their ends, respectively, contacts 21 and 22. Support 20 is fixed to housing 10 at the end opposite from the contacts by a rivet 23 which also secures terminal tab 24, part 24a of which extends through the bottom of the housing. Strut member 20a includes a cam follower portion 25. Cooperating with contact 21 is contact 26 fixed to a metallic support 27 having a terminal tab 27a extending through the bottom of the housing. The other strut 20b provides contact 22 by having its end bent downwardly so that its narrow end provides the movable contact which cooperates with fixed contact 28. Contact 28 is affixed to terminal 29, which is fixed to the housing so that its integral terminal tab 29a extends through the bottom of the housing. The switch provided by contacts 21, 26 is preferably an on-oflF switch for energizing a heating unit, while the switch provided by contacts 22 and 28 serves to lCIllntrOl an auxiliary circuit including a pilot light or the As seen in some detail in FIGURE 3, switch 18 comprises a composite thermomotive member 31. One end of member 31 is secured to the housing and the free end carries a contact 32 which cooperates with an adjustable contact 33. Contact 33 is aflixed to the free end of resilient blade 34 whose other end is attached by rivet 35 to plate 36, which is aifixed in turn to the housing. Plate 36 also provides a terminal tab 36a. (See FIGURE 4). One end of adjusting blade 37 is secured to the free end of blade 34 while its other end bears against plate 36. Follower portion 38 of adjusting blade 37, is provided to adjust the position of contact 33 in relation to contact 32.

Composite thermomotive member 31 comprises a bimetallic member 40 and an associated heater strip 42 separated from each other by insulation 43. The elements 40, 42 and 43 are secured together at the supported end of member 31 by rivet 44 which secures member 31 to the housing by means of angle bracket 45 and to one end of rigid adjusting blade 46. Heater strip 42 is connected in series with the switch contacts and with the heating load, and its association with the bimetallic member is such that the successive heating and cooling of the heater strip by the intermittent closing and opening of the contacts controlled by the bimetallic member serves to augment the closing and opening of the switch contacts by imparting an additional force due to successive expansion and contraction of the heater strip following closing and opening respectively. To assist in this functioning, a force-transmitting member 47 is attached between the free end of heater strip 42 and the free end of bimetallic member 40, as by spot welding. Member 47 is formed to include a spring loop or bight 47a. Member 47, bimetallic member 40, contact 32 and tab 48 are rigidly secured together as by spot welding. The assembly of heater strip 42, insulation 43 and bimetallic member 4-0 is bound together by a winding of fiberglass cord 49.

The structure of switch 18 thus far described forms a current-operated infinite switch which is adapted to operate cyclically to supply an average input to the heating element according to the setting of an adjusting cam 50 connected to move with knob 15 by shaft 14. In operation, when cam 50 is rotated from off to a position calling for energization of the heating element, inner cam race 51 bears against cam follower 25 and closes the contacts of on-off switch 17, which remain closed in every on position. At the same time, cam race 52 bears against follower 38 and causes switch 18 to close. Upon the closing of switch 18 (contacts 32;, 33) current flows through heater strip 42 and heats bimetal member 40. The orientation of the high expansion side of bimetallic member 41}, is such that the contacts will open in response to the heating after an interval of time. The bimetal member 46 then cools until contacts 32, 33 again close and the cycle is repeated, the ratio of on to off time being determined by the extent of overclosure of the contacts under the influence of cam 50.

As shown in FIGURES 4, and 6, one end of composite thermomotive member 31 is attached to angle bracket 45 which is fixed to housing and extends transversely to terminal 54. The bracket is divided into three planar elements, to wit, transversely extending member 45a fixed to the housing and tab 45b and 450 arranged preferably in a common plane at 90 to the plane of member 45a. Rivet 55 affixes terminal 54 to tab 45c. Rivet 44 fastens composite member 31 to tab 45b. Also bound by rivet 44 is the rigid member 46 which is spaced from the exterior of the housing by oflfset 46a, and extends laterally of the housing and member 31 by diagonal portion 46b.

The free end of rigid member 46 includes a notched portion 46c which brackets an aperture 56 provided in boss 57 of housing 11). For calibration, an adjusting pin 58 is extended through aperture 56. Referring to FIG- URE 6,, pin 58 is constructed of strip steel having a generally L-shaped tab extension 58a at one end and a tapered portion 58b at the other end. The sheet metal of which pin is formed into a half circle having a larger radius than that of aperture 56, to cause an interference fit when the pin is forced into the aperture. In assembly,

the tapered end 58b of the pin enters aperture 56 through the notched portion 460 in member 46. It is then pressed inward until the L-shaped portion 58a engages member 46 and causes contact 32 to close against contact 33 through the torsion of resilient strip 45a which acts as a hinge, biased toward open contact position. The housing is then reversed, and pressure is applied to the tapered end 58b of the pin until the contacts just open, which establishes the initial calibration. Access to the pin is provided by a hole 59 in cover lid 11 (see FIGURE 1).

FIGURES 8, 9 and 10 illustrate a novel device for setting the adjusting pin and the method of adjustment of the pin. The device comprises a support frame 60 supporting in suitable bearings a shaft 61 connecting cam 62 through electric clutch 63 to a motor drive coup ling 64 also supported on the frame. Cam 62 engages a roller 65 rotatable about pin 66 which is secured to roller-support 67. Support 67 is carried by a plunger 68 adapted for vertical movement in bearings 69 and 70 on the support frame 60. Supported by the lower end of plunger 68 and aligned therewith is a hardened pin driving tool 71, having a smaller outside diameter than hole 59 in the cover lid 11. A fixture 72 is mounted on base 73 integral with frame 60. The fixture 72 is arranged to accept the switch housing 10 and to retain it in a position in which hole 59 is aligned with tool 71. A compression spring 74 surrounds plunger 68 and extends between the bearing supporting stationary bracket 75 and key 76 on the frame 60. Key 76 is secured to plunger 68, and its free end 76a extends through slot 77 in the frame.

Attached to cam supporting shaft 61 is stop means 77 which rotates with the shaft and is arranged to engage pin 78 to limit the rotation of shaft 61 and to thereby establish the zero position of cam 62. Extending between stop means 77 and pin 78 is a torsion spring 79. The contour of cam 62 has a gradual rise from zero position so as to cause plunger 68 to be urged slowly downward against the spring 74 when the cam is rotated.

Fixture 72 includes two electrical contact strips so positioned as to engage terminal tabs 36a and 54 of the switch to be calibrated whereby the contacts of that switch are in circuit with the driving motor and the electric clutch. For this purpose, the contact strip engaging one of these tabs is connected directly to one side of the line, and the contact strip engaging the other tab is connected to the other side of the line in series with the driving motor and clutch.

In calibrating, pin 58 is first pressed in so that contacts 32, 33 are in closed position, as previously described and the assembly completed. The dial 15a is then set at a preselected point, preferably representing a given low temperature, the closed switch housing is placed in fixture 72 and bimetallic member 40 is held at a predetermined temperature represented by the dial setting. In infinite switches the heater element is built into the switch assembly, but in other types of switches a separate heater may be employed to achieve the same effect. The circuit including the switch to be calibrated, the driving motor and the clutch is controlled and closed by means of an auxilary switch. As shaft 61 rotates it rotates cam 62, thereby moving tool 71 downward against the bias of spring 74 until it engages the end of pin 58 and moves it toward a position where the contacts can separate. As the cam rotates, torsion spring 79 is also stressed. When the contacts separate, the driving motor and clutch are deenergized. The release of the clutch permits torsion spring 79 to quickly return the cam to its zero position established by stop 77 and pin 78. Since roller 65 is immediately released spring 74 acting through plunger 68 withdraws tool '71 from contact with pin 58. As a result of this procedure there is no looseness or overtravel by tool 71 so that the pin is located at the exact position represented by the dial setting, achieving a reliability not heretofore obtainable.

The proportions of pin 58 and aperture 56 are such that approximately pounds pressure is required to move the pin, hence it is held firmly against any of the much smaller forces encountered in use of the switch tending to displace the pin. With age, and the accompanying shrinkage of the phenolic resin, the pin becomes increasingly tighter.

In the case of an infinite switch, such as the one described, heating of the bimetal may be accomplished conveniently by energizing the resistance heater associated with it. For thermostatic switches that do not include a resistance heater, separate heating means may be provided in fixture 72.

It is obvious that similar means may be used to calibrate a thermally actuated switch whose thermomotive member is adapted to close the contacts when heated. In such case, the pin is initially located at a point at which the contacts are in open position, and tool 71 is applied in such manner as to move the contacts toward closed position, with provisions for automatically opening the circuit when such closure is accomplished. Other modifications will occur to those skilled in the art, and it is intended that the appended claims shall cover such modifications as do not depart from the scope and spirit of this invention.

I claim:

1. A thermally actuated switch including a pair of cooperating contacts at least one of which is supported by a blade which is in turn supported by deflectable mounting means, housing means supporting said mounting means and enclosing said switch, calibration means comprising walls defining an aperture through a portion of said housing means, a control lever connected to said deflectable mounting means, and an adjusting member movably mounted in said aperture and being interconnected with said control lever so that movement of said adjusting member fixedly deflects said mounting means and moves the contacts in a direction to change the relative position of the contacts, said member being frictionally compressed by said walls and frictionally retained therein in any of a plurality of fixedly adjusted positions.

2. Calibration means in accordance with claim 1, wherein the adjusting member comprises a portion of a resilient cylinder having a greater outside radius than the radius of said aperture.

3. Switch means having a pair of relatively movable contacts, deflectable blade means supporting one contact for movement relative to the other contact, heating means associated with said deflectable blade means to cause movement of said one contact by deflection of said blade means, calibration means for selectively positioning said deflectable blade means and said one contact comprising support bracket means for said deflectable blade means, said support bracket beans being resiliently deflectable, control lever means connected to said support bracket means, housing means for said switch means, calibrating means fixedly frictionally retained in said housing means and being selectively movable between a plurality of fixedly frictionally retained positions under the application of calibrating forces, and said calibrating pin means being operatively connected to said control lever means and holding said support bracket means in a resiliently deflected fixed position whereat said movable contact is selectively positioned to obtain a predetermined set of operating characteristics.

4. The invention as defined in claim 3 and wherein: said pin means comprises an elongated resilient shank portion capable of being inwardly compressed and gripping means provided in said housing means to squeeze and hold said pin means in fixed position during use of said switch means.

5. The invention as defined in claim 3 and wherein: one end of said pin means protrudes outwardly on one side of said housing means and the other end of said pin means protrudes outwardly on an opposite side of said housing means, and access means provided in said housing means to enable said pin means to be adjustably moved from either side of said housing means.

6. The invention as defined in claim 5 and wherein: said pin means has a tapered end portion, and a hook portion formed on the opposite end portion and engaging and holding said control lever means.

7. Switch means having an enclosing housing, support bracket means, one end of said support bracket means being fixed to said housing, a resilient deflectable leg portion formed on the other end of said bracket means, blade means fixed to said other end of said bracket means and being deflectable relative thereto, a pair of relatively movable contacts, one contact being mounted on said blade means and being movable therewith relative to the other contact, lever means connected to said other end of said bracket means, retainer means in said housing, pin means fixedly frictionally held by said retainer means and being rectilinearly movable relative thereto under application of calibrating forces between a plurality of fixedly held positions, and one end of said pin means engaging and holding said lever means in a deflected posi tion causing deflection of said other end of said bracket means and causing said switch means to be maintained in a predetermined deflected position under certain operating conditions.

8. The invention as defined in claim 7 and wherein the other end of said pin means extends beyond said retainer means, said housing means enclosing said other end of said pin means, and access means provided in said housing means to permit application of calibration forces to said other end of said pin means by force applying means located outside of said housing means.

References Cited by the Examiner UNITED STATES PATENTS 2,584,016 1/1952 Hild 200-139 2,839,640 6/1958 Epstein 200-122 3,048,028 7/-1962 Slocum 73-1 3,099,878 10/1963 Woods 29-15555 3,141,322 7/1964 Himelsbaugh 73--1 3,167,643 1/1965 Turner 200-l22 3,167,852 2/1965 Stengl 29-405 BERNARD A. GILHEANY, Primary Examiner.

Claims (1)

1. A THERMALLY ACTUATED SWITCH INCLUDING A PAIR OF COOPERATING CONTACTS AT LEAST ONE OF WHICH IS SUPPORTED BY A BLADE WHICH IS IN TURN SUPPORTED BY DEFLECTABLE MOUNTING MEANS, HOUSING MEANS SUPPORTING SAID MOUNTING MEANS AND ENCLOSING SAID SWITCH, CALIBRATION MEANS COMPRISING WALLS DEFINING AN APERTURE THROUGH A PORTION OF SAID HOUSING MEANS, A CONTROL LEVER CONNECTED TO SAID DEFLECTABLE MOUNTING MEANS, AND AN ADJUSTING MEMBER MOVABLY MOUNTED IN SAID APERTURE AND BEING INTERCONNECTED WITH SAID CONTROL LEVER SO THAT MOVEMENT OF SAID ADJUSTING MEMBER FIXEDLY DEFLECTS SAID MOUNTING MEANS AND MOVES THE CONTACTS IN A DIRECTION TO CHANGE THE RELATIVE POSITION OF THE CONTACTS, SAID MEMBER BEING FRICTION-

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