US2752438A - Infinitely variable control switch - Google Patents

Description

June 26, 1956 M. J. LEWIS E'TAL 2,752,438

INFINITELY VARIABLE CONTROL SWITCH Filed Dec 28, 1953 2 1 JNVENTORS U X f MERLE J. LEWIS &

2 N gwg MILTON .WILLIAMS.JR. s M THEIR AT ORNEY United States Patent INFINITELY VARIABLE CONTROL SWITCH Merle J. Lewis, Clinton, Iowa, and Milton S. Williams,

Jr., Louisville, Ky., assignors to General Electric Company, a corporation of New York Application December 28, 1953, Serial No. 400,541

8 Claims. (Cl. 200-31) This invention relates to electric switches and more particularly to switches of the type adapted to control the power supplied to an electric heating element or the like.

While not limited thereto, our improved control switch is particularly adapted to control the surface units of an electric range so that the wattage output of these units may be varied in small increments from zero to a predetermined maximum.

Infinitely variable heat control switches wherein the amount of current supplied to the heating unit is regulated by intermittently interrupting the circuit and varying the duration or frequency of the interruption are of course well known in the art, an important advantage of such switches (as compared with heat control switches of the type having a limited number of separate and distinct positions to produce separate heats) being the flexibility of control afforded thereby. As disclosed and claimed in application Serial No. 400,642, filed December 28, 1953 by Merle J. Lewis and Thomas H. Lennox, and assigned to the assignee of the present application, even greater flexibility and more precise control in the low heat range may be achieved by providing a circuit interrupter mechanism including switching means for switching the heating element controlled thereby from a relatively low voltage in one heat range to a relatively higher voltage in another heat range. The present in vention is an improvement over the prior invention of the Lewis and Lennox application, and therefore we do not claim as our invention anything shown or described in the aforesaid Lewis and Lennox application, which is to be regarded as prior art with respect to this present application.

A primary object of our invention is to provide an improved switch of the type disclosed in the aforementioned patent application having means for positively preventing destructive arcing between the contacts of the voltage changing switch means.

Another object of our invention is to provide an infinitely variable control switch having switch means for changing the voltage in the circuit controlled thereby and means for positively preventing actuation of the switch means during the intervals when current is flowing in the circuit.

Further objects and advantages of our invention will become apparent as the following description proceeds, and the features of novelty which characterize our invention will be pointed out with particularity in the claims appended to and forming a part of this specification.

Briefly stated, in one embodiment of our invention we provide a pair of movable cooperating contacts adapted to be connected in circuit with a heating element, a constant speed cam arranged to constantly engage and disengage the contacts, a manually adjustable cam for independently positioning one of the contacts so as to selectively vary the intervals during which they are in engagement, and a switch device operable between one position in which the heating element is connected to the outer 2,752,438 Patented June 26, 1956 'ice conductors of a three conductor power source and another position in which the heating element is connected to an outer conductor and the neutral conductor. The manually adjustable cam includes two portions each providing separate ranges of adjustment, and an actuator for the switch device so arranged that the heating element is energized at a relatively high voltage in one range of adjustment and a relatively lower voltage in the other range of adjustment. To prevent actuation of the switch device during the intervals when current is flowing in the circuit controlled by the movable cooperating contacts, we provide mechanical interlock means periodically actuated by a member carried by the shaft supporting the constant speed cam.

For a better understanding of our invention reference may be made to the accompanying drawing in which:

Fig. l is a fragmentary top plan view of a control switch constructed in accordance with our invention, the cover and control knob being removed.

Fig. 2 is a fragmentary sectional view taken along the line 2-2 of Fig. 1.

Fig. 3 is a plan view of another embodiment of our invention.

Fig. 4 is a side elevation view of the switch illustrated in Fig. 3.

Control switches of the character to which this invention relates are particularly adapted to control surface heating units of electric ranges, and as each surface unit must be individually controlled a separate circuit interrupter mechanism is required for each surface unit. These interrupter mechanisms may be conveniently arranged around a motor operated actuator as shown in Newell Patent 2,275,918, for example, so that the member serves as a common actuator for all the interrupter mechanisms. Electric ranges usually have four surface units and accordingly the four separate circuit interrupter mechanisms may be located respectively in the four corners of a case or housing at the center of which is a motor driven common actuator by which the four interrupter mechanisms are operated, each interrupter mechanism, however being individually adjustable by a control knob to regulate the supply of power to the particular surface unit which it controls.

Referring to the drawing, in which Fig. 1 shows one of the circuit interrupter mechanisms of such a multiple unit arrangement the reference numeral 1 designates a case or housing including a bottom wall 2 and a surrounding side wall 3 which support and enclose the various elements of the device. The housing 1 and the cover (not shown) are preferably of insulating material so that the various electrical conductors and terminals attached thereto are thereby electrically insulated from one another.

Centrally located in housing 1 is a cam 4 secured on a shaft 5 which is operated by a constant speed motor (not shown) at a slow constant rate of speed such as one revolution per minute. Each of the circuit interrupter mechanisms mounted in housing 1 includes a switch arm 6 supported at one end on the housing by means of a flange 7 and having at its free end a cam follower 8 in operative engagement with cam 4. Cam follower 8 is biased against earn 4 by the resilience of switch arm 6 and since cam 4 includes two semicircular portions the movement of arm 6 is a reciprocating movement at the rate of two cycles per revolution of shaft 5. Mounted in spaced parallel relation with respect to switch arm 6 is a cooperating switch arm 9 supported at one end on housing 1 by means of a flanged portion 10, its free end being biased by its own resilience into engagement with a pin 11 secured to the end of a link member 12. Mounted on switch arms 6 and 9 respectively are a pair of movable cooperating contacts 13 and 14, contact 13 being constantly reciprocated during rotation of cam 4 toward and away from contact 14.

Link member 12 is pivotally mounted on a shaft 15 secured to housing 1 and is biased so that it tends to rotate in a clockwise direction, as viewed in Fig. l, by a biasing spring 16 coiled about shaft 15 and supported at one end in an aperture in wall 3. Link member 12 includes an arm portion 17 terminating in an enlarged portion 18 in which an adjusting screw 19 is mounted for engagement with the flange 20 of another link member 21. Link member 21 carries a cam follower 22 secured thereto for engagement with a manually adjustable cam member 23. From the preceding description it will be evident that cam follower 22 is moved in an arc about shaft 15 upon rotation of carn member 23 and by means of a linkage mechanism comprising link members 12 and 21 functions to position contact 14 so as to selectively vary the intervals during which contacts 13 and 14 are in engagement during rotation of earn 4. Cam member 23 is supported for rotation on a shaft 24 on which is also mounted a control knob 25. Inasmuch as cam follower 22 is biased into engagement with cam member 23 by spring 16 acting through link members 12 and 21, and switch arm 9 is biased'into engagement with pin 11 on link 12, counterclockwise movement of dam follower 22 about pivot shaft 15 as a result of rotation of cam 23 causes switch contact 14 to move away from switch contact 13, thus shortening the intervals during which these contacts are in engagement. As contact 13 reciprocates toward and away from contact 14 switch arm 9 is free to move away from pin 11 during the intervals of engagement but its initial position is always determined by the position of link member 12.

As disclosed in the. aforementioned Lewis and Lennox application the configuration of cam member 23 is such that it provides two ranges of movement of switch arm 9 and contact 14 The. cam surface of cam 23 includes one portion 26 providing a plurality of contact positions including a continuously disengaged position, and another portion 27 providing a plurality of positions including a continuously engaged position. The continuously disengaged position, which of course corresponds to the ofF position of the mechanism, is provided by a high portion 28 on cam 23 while the continuously engaged position is provided by a low portion 29 which permits switch arm 9 to move into a position in which contact 14 is continuously engaged with contact 13 regardless of the re cipr'ocating movement of switch arm 6. It will be observed that portion 26 of the cam surface becomes progressively lower from high portion 28 to the beginning of portion 27, and that likewise portion 27 becomes pro gressively lower from its juncture with portion 26 to low portion 29.

In addition to switch arm 9, a contact arm 30 which moves in a plane perpendicular to the plane of movement or switch arms 6 and 9 is operated by rotary movement of control knob 25. Contact arm 30 is fixed at one end to a support 31 integral with side wall 3 of the housing and extends inwardly toward the central portion of the housing. The free end of arm 30 extends between a pair of spaced fixed contact members which as shown in the drawing may be a pair of spaced ring members 32 and 33 supported by a suitable insulating means (not shown). Contact arm 30 is normally biased into engagement with fixed contact 32 but may be moved into engagement with fixed contact 33 by means now to be described.

Formed on the top surface of cam member 23 is a switch actuator 34 comprising a raised flat arcuate cam surface extending in an are substantially equal to the arc. encompassed by carnsurface portion 27. Cooperating with switch actuator 34 is a follower 35 secured to the mid portion of arm 30. It will be noted that the two ends of actuator 34 terminate in inclined portions 36 and 37 which permit follower 35 to travel from the top surface of cam 23 to the raised surface of the actuator and vice versa upon rotation of cam 23. Actuator 34 is positioned on cam 23 so that follower 35 rides on the top surface of the cam (between the two inclined portions 36 and 37) when follower 22 engages cam surface portion 26, and on actuator 34 when follower 22 engages cam surface portion 27. Thus actuator 34 cooperates with follower 35 to move contact arm 30 from a first position in engagement with fixed contact 32 when cam follower 22 engages cam portion 26 to a second position in engagement with fixed contact 33 when cam 23 is rotated to a position in which follower 22 engages cam portion 27. In the drawing the parts are shown in the position in which arm 30 is held in engagement with fixed contact 33 and cam 23 is in the range of movement in which follower 22 engages cam portion 27.

Referring now to the electrical circuit arrangement shown in Fig. 1, a resistance heating element 38 is connected to the control switch mechanism described above by means of wire 39 connected to terminal 40 of switch arm 6 and wire 41 connected to terminal 42 of contact arm 30. Terminal 43 of switch arm 9 is connected to one of the outer conductors of a three conductor source of power, while terminal 44 of fixed contact ring 32 and terminal 45 of fixed contact ring 33 are connected to the neutral conductor and the other outer conductor of the power source respectively. Thus it will be observed that contacts 13 and 14 are connected in series with heating element 38 and that the heating element may be energized at a relatively high voltage or a relatively low voltage de pending upon whether contact arm 30 is in engagement with fixed contact 32 or fixed contact 33. While the ar-. rangement is not shown in the drawing it will be apparent to those skilled in the art that the constant speed motor which drives shaft 5 and thus cam 4 may be connected in circuit with an eelctric switch operated by roation of shaft 24. With such an arrangement the motor driven shaft 5 would be deenergized whenever cam 23 is in the off position but automatically energized upon the movement of control knob 25 to any heating position.

From the preceding description it will be evident that contact arm 30 is switched from engagement with fixed contact 32 into engagement with contact 33 upon movement of cam 23 so that cam follower 22 engages cam surface portion 27 rather than portion 26, and that arcing between contacts 32 and 33 may occur if contacts 13 and 14 are closed during switching movement of arm 30. Further, contacts 13 and 14 may or may not be in engagement when arm 30 is actuated depending on the position of cam 4 at the time.

To overcome this difliculty and positively eliminate any possibility of destructive arcing between contacts 32 and 33, we provide a stop member which may take the form of a flexible arm 46 normally interposed between fixed contacts 32 and 33 so that the contact arm 30 is prevented from moving therebetween. Flexible arm 46 is secured at one end to suitable supporting means as-. sociated with housing 1 such as an insulating ring member 47 supported on the housing by a plurality of column member 48. Arm 46 projects radially inwardly toward the center of housing 1 and normally occupies a position between fixed contact ring members 32 and 33 in the path of movement of the free end of contact arm 30. Arm 46 is relatively narrow as compared with distance between ring members 32 and 33 and is spaced midway between the ring members so that when arm 30 is actuated it is disengaged from one of the rings but is prevented from engaging the other ring by arm 46.

Flexible stop member 46 is arranged for movement out of the path of movement of contact arm 31 during each cycle of operation of contacts 13 and 14, and for this purpose a rotating member 49 is secured to shaft 5 for rotation therewith into periodic engagement with arm 46. Inasmuch as the cam 4 shown in Fig. 1 provides two cycles of operation per revolution of shaft 5, member 49 is arranged to actuate arm 46 twice during each revolution, and thus includes two oppositely disposed actuating portions 50 and 51. Actuating portions 50 and 51 rotate in a circular path intersecting the free end of flexible arm 46 and thus are carried into periodic engagment with arm 46 so as to periodically move it out of the path of movement of contact arm 30. Member 49 is oriented on shaft 5 with respect to cam 4 so that arm 46 is moved to permit actuation of contact arm 30 during the intervals when contacts 13 and 14 are disengaged.

In considering the operation of the embodiment of our invention described above it will first be assumed that cam 23 is in the off position, i. e. that high portion 28 is in engagement with cam follower 22, and that a low heat output from heating element 38 is desired. This is obtained by rotating control knob 25 clockwise sufficiently to cause cam surface portion 26 to engage follower 22 thus permitting switch arm 9 and contact 14 to move toward contact 13 sufliciently to permit periodic engagement of the contacts as cam 4 is rotated. With cam 23 in this position follower 35 engages the top surface of the cam between the two ends of actuator 34 and thus the free end of contact arm 30 is in engagement with fixed contact ring 32. With control knob 25 in this position heating element 38 is periodically energized at a relatively low voltage, 118 volts for example, the duration of the intervals of engagement being dependent on the exact position of cam 23. As knob 25 is rotated clockwise the intervals of engagement of contacts 13 and 14 are lengthened since contact 14 is moved progressively toward contact 13 by the accompanying movement of cam 23.

If a relatively high heat output is required clockwise rotation of knob 25 is continued until cam portion 27 engages cam follower 22 and contact arm 30 is actuated by actuator 34 into engagement with fixed contact ring 33. With the cam 23 in this range of positions heating element 38 is periodically energized at a relatively high voltage, 236 volts for example, the duration of the intervals of engagement of contacts 13 and 14 depending upon the exact position of the cam 23.

During movement of cam 23 from its high voltage range to its low voltage range the free end of contact arm 30 is disengaged from contact 33, but prevented from moving into engagement with contact 32 by flexible stop member 46 until the heating circuit is interrupted by disengagement of contacts 13 and 14. Likewise, during movement of cam 23 from the low to high voltage range stop member 46 performs a similar function. As cam 4 rotates to the position in which these contacts are momentarily disengaged one of the actuating portions of member 49 engages the free end of stop member 46 and flexes it out of the path of movement of contact arm 30. If cam 23 had previously been rotated by the operator from a position in the low heat range to a position in the high heat range, for example, contact arm 30 would be biased upwardly by engagement of actuator 34 and follower 35 and the free end of arm 30 would move upwardly into engagement with contact ring 33 as soon as flexible arm 46 was withdrawn from its path of movement.

Referring now to the embodiment of the invention shown in Figs. 3 and 4, we have shown a control switch suitable for controlling a single heating element but it will be evident that a plurality of switch mechanisms as disclosed in Fig. 1 might be incorporated in a device utilizing the form of our invention now to be described. Referring to Fig. 3 the numeral 52 designates a base of insulating material on which a contact arm supporting member 53 is securely mounted. At the opposite end of base 52 is a cam 54 secured on a shaft 55 operated by a constant speed motor (not shown) at a slow constant rate of speed such as one revolution per minute. Cam 54 co operates with a switch arm 56 supported at one end on member 53 and having at its free end a cam follower 57 in operative engagement with the cam surface of cam 54. Cam follower 57 is biased -against the cam by the resilience of arm 56, and since cam 54 includes two semicircular portions the movement of arm 56 is a reciprocating movement at the rate of two cycles per revolution of shaft 55. Mounted in spaced parallel relation with respect to switch arm 56 is a cooperating switch arm 58 supported at one end on member 53, its free end being biased by its own resilience into engagement with a projection 59 secured to the end of a link member 50. Mounted on switch arms 56 and 58 respectively are a pair of movable cooperating contacts 61 and 62, contact 61 being constantly reciprocated during rotation of cam 54 toward and away from contact 62.

Link member 60 is pivotally mounted on a shaft 63 secured base 52 and is biased so that it tends to rotate in a clockwise direction, as viewed in Fig. 3, by a biasing spring 64 coiled about shaft 63 and supported at one end on member 53. Link member 60 carries a cam follower 65 secured thereto for engagement with a manually ad-- justable cam member 66. From the preceding description it will be evident that cam follower 65 is moved in an are about shaft 63 upon rotation of cam member 66, and by means of link member 60 functions to position contact 62 so as to selectively vary the intervals during which contacts 61 and 62 are in engagement during rotation of cam 54. Cam member 66 is supported for rotation on a shaft 67 on which is also mounted a control knob 68. Inasmuch as cam follower 65 is biased into engagement with cam member 66 by spring 64 acting through link member 60, and switch arm 58 is biased into engagement with projection 59 on link 60, counterclockwise movement of cam follower 65 about pivot shaft 63 as a result of IO tation of cam 66 causes switch contact 62 to move away from switch contact 61, thus shortening the intervals during which these contacts are in engagement. As contact 61 reciprocates toward and away from contact 62 switch arm 58 is free to move away from projection 59 during the intervals of engagement but its initial position is always determined by the position of link member 60.

Cam member 66 is similar in all respects to cam member 23 of the embodiment illustrated in Fig. l and described above. Thus the cam surface of cam 66 includes one portion 69 providing a plurality of contact positions including a continuously disengaged position and another portion 70 providing a plurality of positions including a continuously engaged position. The continuously disengaged position, which of course corresponds to the off position of the mechanism, is provided by a high portion 71 while the continuously engaged position isprovided by a low portion 72 which permits switch arm 58 to move into a position in which contact 62 is continuously engaged with contac 61 regardless of the reciprocating movement of switch arm 56.

In addition to switch arm 58, a contact arm 73 which moves in a plane perpendicular to the plane of movement of switch arms 56 and 58 is operated by rotary Formed on the top surface of cam member 66 is a switch actuator 76 comprising a raised fiat arcuate cam surface extending in an are substantially equal to the arc encompassed by cam surface portion 70. Cooperating with switch actuator 76 is a follower 77 secured to the mid portion of arm 73. Actuator 76 is positioned on cam 66 so that follower 77 rides on the top surface of the latter, between the two ends of the actuator, when follower 65 engages cam surface portion 70 and on actuator 76 when follower 65 engages cam surface portion 69. Thus actuator 76 cooperates with follower 77 c arm 73 from a first position in engage- "contact- 74' when ca'm follower ss'gen ion 71516 a second position in engagement 'fcdnta'ct 75"when 'cam '66' isrotat'ed to 5150-:

to move contact men "with with sitio n fir which answer '65" engages cam portion '69.

Referring now'to'the electrical circuit arrangement shod 1'1" ih' FigI '3, a' resistance heating elementi7g is connected to the control switch mechanism described asave by means'of wire '79 connected to terminal 81) of 10 and l, 62 fare iconnectedinf series with heating element 78 and that the heating element maybe energized at a relatively high voltage or a relatively low voltage depend fixed contact fitter fixed contact 75.

From the-preceding description it will be evident that ing upon whethen contact arm 73 is in engagement with contact arm 73 is switched from engagement with fixed' contact7d into engagement with contact 75 upon movement"of cam"66 so that cam follower 65 engages cam surface portion 70 rather than portion 69, and that arcing between contacts 74 and 75 might occur of contacts 61 and 62 are closed during switching movement of arm 73 Further, contacts 61 and 62'may or may not be in engagement when arm 73 is actuated depending on the position of cam 54 at the time. In the present embodiment of our invention we overcome this dilficulty and positively eliminate any possibility of destructive arcing between contacts 74 and 75 by providing a stop member 86 carried by shaft 55 and rotated into the path of a movement of the free end of contact arm 73 during each interval when movable contacts 61 and 62 are in engag'ement, thus restraining arm 73 from moving'between fixed contacts 74 and 75 when current is flowing in arm 73.;f As shown in Fig. 3 stop member 86 may be generally oval-in form with oppositely disposed flattened sides'87 and 88, the lon'g dimension of themember being great'enough so that its curved periphery overlies the path o'fmovement of arm 73 However when'either of flattened portions 87 or 88 are perpendicular to arm 73 thearm is free to'move between fixed contacts 74 and 75 Stop member 86 is oriented on shaft 55 with respect to-cam 54 so that actuation of contact arm 73 is permitted-during the intervals when contacts 61 and 62 are disengaged.

While we have shown and described two specific embodiments of ourinvention, we do not desire our inven tion to be limited to the particular constructions shown and described and we intendby the appended claims to cover all modifications within the true spirit and scope of'ourinvention.

What we claim as new and desire Patent-of the United States is:

1.; In a device for periodically supplying current to a heating element or the like for selectively variable intervals of time,-the combination of first and second movabl e cooperating contacts adapted to be connected in circuit with said heating elementjcontinuously operable means for periodically moving said first contact toward and away from said second contact, manually adjustable means for positioning said second contact so as to selec tively vary the intervals during which said contacts are in'engagementfsaid adjustable means including means providing first and second-ranges of movement in each of which said second contact is movable to a plurality of pos itionsfswitch means operable bysaid adjustable to secure by Letters means as; connecting said heating element to a 'rela tivelylow voltage source of energy when said adjustable means isin said first range of movement and to a respectively. Thus it will be observed that contact (Sijustable means is in secondlrange ot m c vemer tt, amt meanso'pei'ated by 'said continuously operable means rend ringsaidgswitc'h means inoperable during the in-- tefv'alswhen'said contacts are mana emen 21" Ina 'd'e'vice' for periodically supplying current to a heating element 'or the 'like'for selectively variable intervals of time, the combination of first and second movablefcooperating contacts adapted to be connected in circuit 'withYsaid heating element, continuously operable means for periodically moving said first contact toward I and away from said second contact, manually adjustable means for positioning said second contact so as to selectively vary' the intervals during which said contacts are in engagemenh said adjustable means including means provi'dinghfi r st and second ranges of movement in each of whichsaid second contact is movable to'a plurality of 7 positions, switch means operable by said adjustablemeans for connecting said heating element-to a relatively lo w-' voltage source of energy when said adjustable means is in said first range of movement and to a relatively high voltage source of energy when said adjustable means is;

in said second range offmovement, and means including a member carried by said continuously operable meansfor rendering said switch means inoperable except when said contacts are disengaged. 1

3. In a device for periodically supplying current to a heating element or the like for selectively variable intervals of time, the combination of first and second movable cooperating contacts adapted to be connected in circuit with said heating element, continuously operable means for periodically moving said first contact toward and away from said second contact, manually adjustable means for positioning said second contact so as to'selectively vary the intervals during which said contacts are in engagement, said adjustable means including means providing first and second ranges of movement in eachof which said second contact is movable to a plurality of po'- sitions, a switch actuator'movable with said adjustable means, first andsecond fixed contacts adapted to be con-' nected to a relatively low and a relatively high voltage source respectively, a movable contact arm operable by said actuator between a first position in engagement with said first fixed contact and a second position in engagement with said second fixed contact, said contact arm being adapted to be connected in circuit with said -heat-' ing element, said actuator being constructed and arranged so that said contact arm is insaid first position when said adjustable means is in said first range of'movement and in said second position when said adjustable means is in said second range of movement, a stop member normally mterposed m the-path of movement of said contact armso as to prevent movement thereof between said first and second positions, and means for withdrawing said stop member from said path-of movement each 'time said first contact 1s m'oved'away from said second contact.

4. In'a device for periodically supplying current toa heating elementor the like for selectively variable 'intervals oftimejthe combination of first and second movable cooperating contacts adapted to be connected'in circuit with said heating element, continuously operable means for periodically moving said first contact toward and away first'and second fixed contacts adapted to be connected to 'a'relatively low and a relatively high voltage source respectively, a movable contact arm operable by said actuator between a fi'rst position in engagement with said first fixed contactand'a second position in engagement with said' second fixed-contact, said contact arm being adapted to be connected in circuit witl r said heat-ing ele ment, and said actuator being constructed and arranged so that said contact arm is in said first position when said adjust-able means is in said first range of movement and in said second position when said adjustable means is in said second range of movement, a stop member normally interposed in the path of movement of said contact arm so as to prevent movement thereof between said first and second positions, and a continuously operable member arranged to engage and move said stop member from said path of movement during the intervals when said first and second contacts are disengaged.

5. In a device for periodically supplying current to a heating element or the like for selectively variable intervals of time, the combination of first and second movable cooperating contacts adapted to be connected in circuit with said heating element, continuously operable means for periodically moving said first contact toward and away from said second contact, linkage means including a cam follower for positioning said second contact so as to selectively vary the intervals during which said contacts are in engagement, a manually adjustable cam member including a cam surface in operative engagement with said cam follower, said cam surface including a first portion providing a plurality of positions of said second contact and a second portion also providing a plurality of said positions, first and second fixed contacts adapted to be connected to a relatively low and a relatively high voltage source respectively, a movable contact arm operable between a first position in engagement with said first fixed contact and a second position in engagement with said second fixed contact, said contact arm being adapted to be connected in circuit with said heating element, and an actuator for said contact arm carried by said cam member and arranged so that said contact arm is moved into said first position when said first portion of said cam surface is in engagement with said cam follower and into said second position when second portion of said cam surface is in engagement therewith, a flexible arm normally positioned between said fixed contacts and in the path of movement of said contact arm so as to prevent movement thereof between said first and second positions, and a member carried by said continuously operable means into periodic engagement with said flexible arm so as to move it out of said path of movement during the intervals when said first and second contacts are disengaged.

6. In a device for periodically supplying current to a heating element or the like for selectively variable intervals of time, the combination of first and second movable cooperating contacts adapted to be connected in circuit with said heating element, continuously operable means for periodically moving said first contact toward and away from said second contact, manually adjustable means for positioning said second contact so as to selectively vary the intervals during which said contacts are in engagement, said adjustable means including means providing first and second ranges of movement in each of which said second contact is movable to a plurality of positions, and switch means operable by said adjustable means for connecting said heating element to a relatively low voltage source of energy when said adjustable means is in said first range of movement and to a relatively high voltage source of energy when said adjustable means is in said second range of movement, and stop means carried by said continuously operable means and engageable with said switch means to render the switch means inoperable during the intervals when said contacts are in engagement.

7. In a device for periodically supplying current to a heating element or the like for selectively variable intervals of time, the combination of first and second movable cooperating contacts adapted to be connected in circuit with said heating element, continuously operable means for periodically moving said first contact toward and away from said second contact, manually adjustable means for positioning said second contact, manually adjustable means for positioning said second contact so as to selectively vary the intervals during which said contacts are in engagement, said adjustable means including means providing first and second ranges of movement in each of which said second contact is movable to a plurality of positions, a switch actuator movable with said adjustable means, first and second fixed contacts adapted to be connected to a relatively low and a relatively high voltage source respectively, a movable contact arm operable by said actuator between a first position in engagement with said first fixed contact and a second position in engagement with said second fixed contact, said contact arm being adapted to be connected in circuit with said heating element, and said actuator being constructed and arranged so that said contact arm is in said first position when said adjustable means is in said first range of movement and in said second position when said adjustable means is in said second range of movement, and a stop member carried by said continuously operable means into the path of movement of said contact arm during each interval when said movable contacts are in engagement, whereby said contact arm is restrained from moving between said fixed contacts when current is flowing therethrough.

8. In a device for independently controlling the supply of current to a plurality of heating elements or the like, the combination of a continuously operable cam, a separate pair of movable contacts for each heating element, each pair of contacts having a member operable by the cam to cause intermittent engagement and disengagement of the respective pairs of contacts, said members being uniformly spaced about the cam, separate linkage means each including a cam follower for positioning one of each of the pairs of contacts so as to selectively vary the intervals during which they are in engagement, a manually adjustable cam for each of the linkage means including a cam surface in operative engagement with its cam follower, said cam surface including a first portion providing a plurality of positions of the contact positioned by said cam follower including a continuously disengaged position and a second portion providing a plurality of said positions including a continuously engaged position, first and second fixed contact members adapted to be connected to a relatively low and a relatively high voltage source respectively, separate movable contact arms each adapted to be connected in circuit with one of said plurality of heating elements, said contact arms being separately operable between a first position in engagement with said first fixed contact member and a second position in engagement with said second fixed contact member, separate actuators for said contact arms carried by said manually adjustable cams and arranged so that each contact arm is moved into said first position when the first .cam surface portion of the cam on which its actuator is carried is in engagement with its cam follower and into said second position when the second cam surface portion thereof is in engagement with said cam follower, and separate flexible arms each normally positioned between said fixed contact members and in the path of movement of one of said contact arms so as to prevent movement thereof between said first and second positions, and a member carried by said continuously operable cam into periodic engagement with said flexible arms so as to move them out of said paths of movement during the intervals when the pairs of contacts respectively associated therewith are disengaged.

References Cited in the file of this patent UNITED STATES PATENTS 2,194,587 Brown et al. Mar. 26, 1940 2,215,404 Myers Sept. 17,1940 2,294,573 Potter Sept. 1,1942 2,503,082 Tuttle Apr. 4,1950 2,572,553 Wojcik Oct. 23,1951

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