Arm for electric switches controlled by electricity

Abstract: This invention relates to an arm (10) preferably for electric switches the arm being controlled by electricity and having a first fixed end and the other end of which is movable mainly perpendicular to the length direction of the arm. The arm comprises two mainly parallel parts (16) separated by an air gap (17) or some other heat insulating material and which are secured to each other at each end. At least one of the parts can be heated by electricity and through longitudinal heat expansion with respect to the other part achieve said movement. The parts are so shaped that they adjacent the fixed end (at 45) with respect to the rest of the parts have a reduced bending resistance about an axis which is perpendicular to the length direction of the arm and with respect to said direction of movement.

Description: This invention relates to an arm which is controlled by electricity and having a first fixed end and a second end which is movable mainly perpendicular to the length direction of the arm, the arm comprising two mainly parallel elongated parts being separated by an air gap or some other heat insulating material, that at least one of the parts can be heated by electricity in order to effect said movement by longitudinal heat expansion with respect to the other part. Devices of the above mentioned type are known and are used for controlling electric switches. US patent 3 716 814 describes such a device where two leafshaped elongated elements are placed at a distance from each other one of the elements being heated up by means of an electric circuit applied on it. The longitudinal expansion of the element which occurs is transferred to a turning motion of a contact holder which is parallel to the arm this motion being used for breaking or closing a contact means. The device shown is however complicated and comprises several details cooperating with each other which means that it is troublesome to assemble the device. There also is a large risk that malfunctions will occur in the device because of the complexibility. Moreover the device has to be adjusted with particular adjusting screws which are placed on the contact means. The large amount of details also means that the device will get large dimensions which is a drawback for such occasions where the space is a limiting factor. Moreover, the contact holder operates with a creeping motion i.e. the motion is comparatively slow which means that arcs can be created and affect the contact surfaces. The purpose of this invention is to achieve a device having small dimensions and mainly having the same function as the device described above and which can be used to replace conventional relays in such apparatus where rapidity when transferring signals is of minor interest. Such apparatus are for instance household appliances of different kinds such as ranges, washing-machines, dishwashers and so on. The device according to the invention is more simple and hence cheeper to manufacture than previously known devices. The device is also so designed that even small expansions i.e. such expansions which are achieved by means of small effect circuits are transferred to comparatively large motions to be used for manipulating snap action type mechanisms and to control a contact means. This is achieved by means of a device having the characteristics mentioned in the claims. Serveral embodiments of the invention will now be described with reference to the accompanying drawings where Fig. 1 and 2 in a vertical section show the basic function of the device whereas Fig. 3 is a partly broken perspective view of a second embodiment of the invention. Fig. 4 shows a vertical section through a third preferred embodiment of the Invention whereas Fig. 5 is a partly broken plan view of the device shown in Fig. 4. Figs. 6 - 8 are sections on the lines VI-VI, VII-VII and VIII-VIII in Fig. 4. As appears from Fig. 1 and 2 the device comprises an arm generally denoted 10 which cooperates with a contact means 11, a spring 12 being clamped between the arm 10 and the contact means 11. The arm 10 as well as the contact means 11 are fixed at a holder 13. The arm 10 comprises a support 14 which is fixed at the holder 13 the support continuing into two elongated parts 15, 16 which are separated by an air gap 17 via a, with respect to the parts 15, 16, reduced section 18. Since the parts 15, 16 have this reduced section they will at this section have a less bendning resistance about an axis perpendicular to the plane of the paper compared to the other sections of the parts. The outer ends of the part 15 and 16 are joined to each other via an end part 19 in which there is a recess 20 in which the spring 12 rests. The parts 15 and 16 support a heating source which is a strip shaped material 21, 22 for instance a film enclosing an electric circuit 23, 24 through which current can be directed. The strip shaped material 21, 22 is fastened to the parts 15 and 16 by means of gluing or in any other suitable way. The strip shaped material can as well be replaced by a printed circuit or the like which is produced in a conventional manner. The two parts 15 and 16 are of the same material which preferably is metal. The contact means 11 comprises an upper and a lower contact plate 25, 26 and an intermediate flexible plate 27 these plates being of metal and fixed to the holder 13 and projecting outwards from the holder in order to form contact pins for electric conduits. The contact strips 25, 26 are at their inner ends and at the sides facing towards each other provided with a contact surface 28, 29 and the intermediate metal plate 27 has a contact surface 30, 31 at each side. The inner edge of the intermediate plate has a recess 32 supporting the spring 12, the plate 27 by snap action moving between an upper position in which the contact surfaces 28, 30 are abutting each other and lower position where the contact surfaces 29 and 31 cooperate. The spring 12 comprises two arched thin metal plates 33, 34 who are connected to each other so that the concave sides are facing each other the plates being joined to each other at the outer parts resting in the recesses 20 and 32 respectively. The device operates in the following way. In the position shown in Fig. 1 the arm 10 projects horisontally from the holder 13 the spring 12 pressing the metal plate 27 downwards so that the contact surface 31 abuts the contact surface 29 of the strip 26. This means that current can flow between the strips 26 and 27 to the associated conduits. In order to change the position of the switch a control current is directed through the circuit 23 which means that the part 15 is expanded longitudinally whereas the parts 16 mainly maintains its length. A part of the heat is carried through the sections 18 and the part 19 to the part 16 but the heat transferred is small compared to the heat supplied through the circuit 23. The expansion difference between the part 15 and 16 and caused by the heat means that the outer end of the arm 10 is bent downwards to the position shown in Fig. 2 the bending mainly taken place in the reduced section 18 whereas the part 15 and 16 maintain their straight shape. Since this shape is maintained during the movement no separating bending tension is created between the material 21 enclosing the circuit 23 and the parts 15, 16. When the arm has taken the position shown in Fig. 2 with full lines and hence acts on the spring 12 so that an upwardly directed force component is created on the metal plate 27 the metal plate 27 will snap upwards to the position shown with dashed lines. This means that the electric connection between the contact plates 26 and 27 is disconnected and instead an electric connection is established between the plates 25 and 27 and the electric conductors connected thereto. If the current through the circuit 23 then is cut off the contact plate 27 will remain in the dashed line position although the arm 10 returns to the position shown in Fig. 1. In order to return the contact strip to the original position a current is directed through the circuit 24 which means that the arm 10 is bent upwards and thus snaps over the metal plate 27 to the original position. At the embodiment shown in Fig. 3 there is a holder 13 which preferably has a box like shape the holder enclosing the arm 10 the contact means 11 and the spring 12. The arm 10 and the spring 12 in this case are intergrated and comprise three sheet metal parts. One of these parts consists of an elongated frame shaped metal plate 35 with a rectangular opening 36, one end 37 of the metal plate 35 being provided with a contact surface 38 at each side. From the end 37 three parallel tongues 39a, 39b, 39c extend into the opening in a way which will be described below. From the end 37 also two parallel edge parts 40 extend to the other end 41 of the metal plate 35 the end 41 via a pin 42 being connectable to an electric circuit not shown. The two other sheet metal parts 43 are identical and comprise a flat end 44 who is pressed against the two sides of the end 41 by the holder 13. The metal plate surfaces of the ends 41 and 44 might be separated from each other by means of an electrically insulating layer not shown. The flat end 44 continues towards the interior of the holder and forms a - compared to the rest of the metal plate - weakened section 45 and projects outside the holder as a pin 46. The weakened section 45 continues into an elongated stiff profile shaped part 47 which is U-shaped in section. The upper thin sheet metal plate part is turned so that the U-shape is inverted and the two parts are separated by an air gap 17. The profile shaped part 47 continues into a flat part 48 with an outer upwardly and downwardly resp. bent edge 49 the two flat parts 48 being fixed to each other for instance by spot welding. Each sheet metal part 43 has a printed circuit 50 which is placed on the elongated profile shape part 47 and has conductive paths 51 connected with the pin 46 so that a control current can flow through the printed circuit thereby heating the upper or the lower part 47. The upwardly resp. downwardly bent edges 49 together form an abutting surface for the tongues 39a, 39b, 39c these tongues having such a length and being so fastened that they are arced. The tongues 39a and 39c have their concave side turned downwards and the tongue 39b has its concave side turned upwards which means that a snap action is achieved when the flat part 48 of the metal part 43 is moved upwards or downwards with respect to the end 37 of the sheet metal plate 35. The contact means 11 in this case comprises two sheet metal plates 52 and 53, which are fixed into the holder 13 each having a contact surface 54 with which the contact surface 38 of the end 37 of the sheet metal plate cooperates. The ends of the sheet metal plates 52 and 53 are shaped as pins to which electric conduits can be connected in a conventional manner. This device operates so that a current which is directed through the pin 42 flows through the metal plate 35 and possibly through the sheet metal parts 43 to the contact surface 38 which in the Figure shown abuts the contact surface of the sheet metal plate 53 which means that current can be taken out by the sheet metal plate 53. In order to switch over the current to the sheet metal plate 52 a control current is directed through the printed circuit 50 on the upper elongated part 47 which means that the upper part 47 is heated up and expands whereas the corresponding lower part mainly keeps its shape. Since the part 47 has a comparatively large bending resistance about and axis which is perpendicular to the length direction of the arm and which also is perpendicular to the direction of movement of the arm the expansion difference between the two parts 43 will cause a downwards bending movement of the arm 10 the bending taking place at the weakened section 45 which with respect to the sheet metal parts 43 has a comparatively small bending resistance in said direction. The downwardly directed movement of the outer free ends of the parts 43 and hence of the flat part 48 means that the tongues 39a, 39b, 39c are pressed together. When the force component on the end 37 of the metal plate 35 and created by the tongues at a certain position is directed upwards the end 37 will snap over to an upper position where the contact surface 38 will abut the contact surface 54 of the sheet metal plate 52 which means that current can be taken out from the sheet metal plate 52. In a corresponding way the sheet metal plate can be returned by directing a control current through the circuit 50 or the lower sheet metal plate part 43. In should be observed that it according to this embodiment is possible to temporarily achieve a switch on effect of the sheet metal plate 52 with an automatic returning function when the control current is switched off. By placing the sheet metal plate 52 at a lower level than what is shown which means that the snap action of the spring is not activated when the control current is switched on the contact surface 38 will abut the contact surface 54 of the upper sheet metal plate 52 as long as a control current is directed to the circuit 50 in the upper sheet metal plate part 43. Hence, this means that the lower sheet metal plate part not has to be equipped with a printed circuit. At the embodiment shown Figs. 4 - 8 there is as in previously decribed embodiments a holder 13, an arm 10, a spring 12 and a contact means 11. As in the last mentioned embodiment the arm 10 and the spring 12 comprise cooperating sheet metal plate parts, one part 55 with tongues 56 who strain against the outer end of the two other parts 57 which at this end are secured to each other. The two parts 57 are separated from each other by means of an air gap 17 and have an elongated stiff part 58 which in section is U-shaped this part near the holder continuing into a flat section 59 which has reduced bending resistance. This section continues into the pin 60 to which a connection means for a control current is attached. At each pins 60 there is a conductive path 61 to which a printed circuit 62, applied on the elongated stiff part 58, is connected so that a control current can heat one of the parts 58. The sheet metal plate part 55 is as in the lastmentioned embodiment frame shaped and is at its middle part at both sides supported by studs 63 projecting from the holder 13. These studs limit the necessary vertical space in the holder for the movement of the arm and the spring. The outer free end of the arm has a fork 64 surrounding a flexible sheet metal plate 65 with a contact surface 66 on its upper and under side. The contact surfaces 66 may cooperate with corresponding contact surfaces on an upper and a lower sheet metal plate 67 and 68 respectively. All of the sheet metal plates 65, 67 and 68 are fixed to the holder and extend outside it where they continue into pins which can be connected to electric conduits. The device mainly operates in the same manner which has been described with respect to the firstmentioned embodiment i.e. current which is supplied through the sheet metal plate 65 can flow either through the sheet metal plates 66 or 67 by directing a control current to the upper or the lower printed circuit 62 from the pin 60. The heat expansion difference which will follow is converted into a bending moment of the arm 10 the bending taking place at the weakened section 59. The bending means that the snap action of the spring 12 is activated and at the fork 64 moves the sheet metal plate 65 from an upper to a lower position or vice versa. It should be observed that several devices for instance of the type which is shown in Fig. 5 preferably are placed beside each other for creating a complete chain of relay functions.

Claims: Arm for electric switches which is controlled by electricity and having a first fixed end and a second end being movable mainly perpendicular to the lenght direction of the arm, the arm comprising two mainly parallel parts (15, 16, 47, 57) which are separated by an air gap (17) or some other heat insulating material, that at least one of the parts can be heated by electricity and by longitudinal heat expansion with respect to the other part achieve said movement, characterized in that the parts are so shaped that they adjacent the end which is fixed (at 18, 45, 59) with respect to the rest of the parts have a reduced bending resistance about an axis which is perpendicular to the length direction of the arm and to said direction of movement. Arm according to claim 1, characterized in that it comprises two sheet metal plate parts (43, 58) which are fixed to each other at the ends. Arm according to claim 2, characterized in that the parts (43, 58) between the major part of the distance between said ends are profile shaped in order to increase the bending resistance. Arm according to claim 3, characterized in that the profile is a U-profile. Arm according to any of claims 2-4, characterized in that the parts at the area (45, 59) with the reduced bending resistance are flat and abut each other. Arm according any of the preceding claims, characterized in that it when being moved acts on a contact means via a spring (12). Arm according to claim 6, characterized in that the spring (12) is a compression spring which is inserted between said arm (10) and the contact means (11), the movement of the arm causing a snap action of the contact means so that it is moved stepwise between two positions at a certain bending movement by the arm. Arm according to claim 6 or 7, characterized in that the spring (12) comprises at least two arced tongues the concave sides of which are facing each other and the ends of which are tensioned between the contact means (11) and the arm (10). Arm according to claim 8, characterized in that the tongues (39a, 39b, 39c) are a part of a frame shaped metal plate (35) one end (41) of which is placed between the metal plates (43, 58) who form the arm and the other end (37) of which supports at least a contact surface (38) of the contact means and that the parts (40) which connect said ends (37, 41) are situated at each side of the arm. Arm accordning to any of the preceding claims, characterized in that at least one of said parts (15, 16, 43, 57) supports an electric circuit (23, 24, 50, 62) through which a control current can flow to heat the part.

Inventors: BERGQUIST PER-MARCUS, TROBERG HENRIK EVALD, BERGQUIST, PER-MARCUS, TROBERG, HENRIK EVALD
Applicants: ELECTROLUX RES & INNOVATION, ELECTROLUX RESEARCH & INNOVATION AB
Application year: 1990
Main classification: H01H61
IPC codes: H01H61