Electrical contactless switch

An electrical contactless switch that includes a housing, a moveable element and a magnetic field sensor. The moveable element is made of a ferromagnetic material and is slidably mounted in the housing. The moveable element is adapted to move relative to the housing between a resting position and an engaged position, the moveable element is elastically biased towards the resting position. The moveable element includes a plurality of magnetized legs spaced from each other and at least part of the magnetized legs is slidably guided in the housing. The magnetic field sensor is secured to the housing and positioned to face the plurality of magnetized legs. The magnetic sensor is configured to detect a magnetic field generated by the magnetized legs as the moveable element is in the engaged position. The moveable element is closer to the magnetic field sensor in the engaged position than in the resting position.

The present disclosure generally relates to a magnetic based contactless switching device suitable for push buttons and selectors.

BACKGROUND

Conventionally, switching devices utilize a mechanically controlled contacts that wear out after a given number of operations and limit a longevity of the switching devices. Further-more, such switching devices are not suitable for an operation in a humid environment because the mechanically controlled contacts would be exposed to the entry of humidity and degrade prematurely.

With a progress of technology, the mechanical controlled contacts of the switching devices have been gradually replaced by contactless solid-state switches controlled by a magnetic or an electrical field. In some cases, such contactless solid-state switches utilize a permanent magnet to provide a source of a magnetic field for switching control. A utilization of traditional permanent magnets as a source of a magnetic field in mid to high volume production of switching devices bears manufacturing disadvantages caused by challenges in handling and assembly of permanent magnets that drives overall product cost.

Therefore, it would be advantageous to have a simple, low-cost contactless switching device that is easy to manufacture.

SUMMARY OF THE INVENTION

One aspect of the present disclosure is directed to an electrical contactless switch. The electrical contactless switch comprises a housing, a magnetic field sensor and a moveable element. The moveable element is made of a ferromagnetic material and slidably mounted in the housing. The moveable element is adapted to move relative to the housing between a resting position and an engaged position. The moveable element is elastically biased towards the resting position. The moveable element comprises a plurality of magnetized legs spaced from each other and at least part of the magnetized legs is slidably guided in the housing.

The magnetic field sensor is secured to the housing and positioned to face the plurality of magnetized legs. The magnetic element is configured to detect a magnetic field generated by the magnetized legs as the moveable element is in the engaged position. The moveable element is closer to the magnetic field sensor in the engaged position than in the resting position.

Additionally, the legs of the plurality of magnetized legs may protrude in parallel from one side of the moveable element.

Additionally, the plurality of magnetized legs may be magnetized such that at least one leg of the plurality of magnetized legs is magnetized in an opposite direction than the rest of the plurality of magnetized legs.

Additionally, the plurality of magnetized legs may comprise two side legs and a middle leg between the two side legs, wherein the middle leg is magnetized in an opposite direction than the two side legs.

Additionally, each of the two side legs may be terminated by a hook protruding laterally outwards.

Additionally, the housing may comprise a slot in which the moveable element may be slidably guided and the side legs may be snap-fitted in the slot and maintained in the slot by the hooks cooperating with an abutment belonging to the slot.

Additionally, the switch may further comprise a resilient element positioned at least partially between the plurality of magnetized legs and the magnetic field sensor, wherein the resilient element may be configured to elastically bias the moveable element towards the resting position and counteract a movement of the moveable element from the resting position to the engaged position.

Additionally, the resilient element may be a compression type coil spring.

Additionally, the moveable element may be made of an annealed semi-hard ferromagnetic metal or hard ferromagnetic metal.

Additionally, the annealed ferromagnetic metal may be a cobalt based metal.

Additionally, the moveable element may have a plate shape with a thickness of 1 mm to 3 mm.

Additionally, the magnetic field sensor may comprise a Hall-effect or a magneto-resistive sensor.

A further aspect is directed to a method of manufacturing a moveable element for the electrical contactless switch and/or its alternatives as defined above. The method comprising: providing a moveable element made of a ferromagnetic material and comprising a plurality of legs spaced from each other, and magnetizing the legs by abutting a magnet against one of the legs.

Additionally, the plurality of magnetized legs may comprise two side legs and a middle leg between the two side legs and magnetizing the legs may be performed by abutting the magnet against the middle leg only.

Additionally, the magnet may be a permanent magnet and the moveable element may be made of an annealed semi-hard ferromagnetic metal or hard ferromagnetic metal.

Further areas of applicability will become apparent from the description herein. The description and specific examples in the summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DETAILED DESCRIPTION

In the figures, the same references denote identical or similar elements, unless stated oth-erwise. In the drawings, the size of each element or a specific portion constituting the element is exaggerated, omitted, or schematically shown for convenience and clarity of description. Thus, the size of each component may not entirely reflect the actual size. In the case where it is judged that the detailed description of the related known functions or constructions may unnecessarily obscure the gist of the present disclosure, such explanation will be omitted.

InFIG.1is depicted a first embodiment of an electrical contactless switch1. The first embodiment comprises a housing2, a moveable element3and a magnetic field sensor7. The moveable element may move relative to the housing between a resting position and an engaged position as depicted by an arrow12. The moveable element may slidably move in a slot11,10within the housing2. The moveable element3may have a plurality of magnetized protrusions that may form a plurality of magnetized legs4and6spaced from each other by having a gap5therebetween. Whilst there are two legs of the plurality of magnetized legs depicted inFIG.1, the moveable element3may have three or more legs. The magnetized legs4and6may protrude in parallel from one side of the moveable element3. The magnetic field sensor7may be secured to the housing and positioned to face the plurality of magnetized legs4and6. The magnetic field sensor7may be coupled to a printed circuit board8that may be attached (not shown) to the housing2. The magnetic field sensor7detects a magnetic field generated by the plurality of magnetized legs4,6as the moveable element3is in the engaged position. The moveable element3is closer to the magnetic field sensor7in the engaged position than in the resting position. The magnetic field sensor14may comprise a Hall-effect or a magneto resistive sensor. The magnetic field sensor14may be a Hall-effect switch. The moveable element is elastically biased towards the resting position via a resilient element9that may be positioned at least partially between the plurality of magnetized legs4and6and the magnetic field sensor7. The resilient element9may counteract a movement of the moveable element from the resting position to the engaged position. The resilient element9may be made of an elastomer and have variety of shapes.

FIGS.2and3depict a second embodiment of the electrical contactless switch13,25.FIG.2depicts the second embodiment of the electrical contactless switch13in an engaged position andFIG.3depicts the second embodiment of the electrical contactless switch13in a resting position. The second embodiment comprises a housing24, a moveable element18and a magnetic field sensor14. The moveable element may move relative to the housing between a resting position and an engaged position as depicted by an arrow30. The moveable element18may have a plurality of magnetized protrusions that may form plurality of magnetized legs16,19and21spaced from each other by having a gap therebetween. The moveable element18as depicted inFIGS.2and3has three legs, however, the moveable element may have other number of legs than three. The magnetized legs16,19and21may protrude in parallel from one side of the moveable element18. The moveable element18may have two side legs16,21and a middle leg19located between the two side legs. Each of the two side legs16,21may be terminated by a hook29and26protruding laterally outwards as depicted inFIG.3. The housing24may have a slot28,27in which the moveable element18is slidably guided. The side legs16and21may be snap-fitted in the slot and maintained in the slot by the hooks26,29cooperating with an abutment20,17belonging to the slot.

The magnetic field sensor14may be secured to the housing and positioned to face the plurality of magnetized legs16,19and21. The magnetic field sensor14may be coupled to a printed circuit board15that may be attached (not shown) to the housing24. The magnetic field sensor14may detect a magnetic field generated by the plurality of magnetized legs16,19and21as the moveable element18is in the engaged position23. The moveable element18may be closer to the magnetic field sensor14in the engaged position which is depicted as a gap23than in the resting position. The magnetic field sensor14may comprise a Hall-effect or a magneto resistive sensor. The magnetic field sensor14may be a Hall-effect switch.

There may more than one magnetic sensor secured to the housing to provide redundancy in sensing of the magnetic field generated by the plurality of magnetized legs16,19and21as the moveable element18is in the engaged position23. For instance, an additional magnetic sensor31may be coupled to the same printed circuit board15. The printed circuit board15may be a single or a double-sided printed circuit board15and the magnetic sensor15may be soldered to a one side of the printed circuit board15. The additional magnetic sensor32may be advantageously coupled to the opposite side of the printed circuit board15than a first magnetic sensor14. The both magnetic sensors14,32may be placed at substantially same location having only the printed circuit board in between so that they both detect a magnetic field generated by the plurality of magnetized legs16,19and21as the moveable element18moves to the engaged position23. The both magnetic sensors may comprised of identical sensors or they may be comprised of different types of sensors for instance a Hall effect and a magneto resistive sensor.

The printed circuit board15may bear other electronic components13such as without limitation processing and or protecting circuitry, communication and/or connecting circuitry and so forth.

The moveable element18may be elastically biased towards the resting position via a resilient element22that may be positioned at least partially between the plurality of magnetized legs16,19and21and the magnetic field sensor7. The resilient element22may counteract a movement of the moveable element from the resting position to the engaged position. The resilient element22as depicted inFIGS.2and3may be a compression type coil spring. However, other types of resilient elements may be used. A non-limiting example of such resilient element may be an elastomer having variety of shapes, leaf spring, volute spring, extension spring and so forth.

The moveable element18may be made from a ferromagnetic material. The ferromagnetic material may be a metal. The metal may be a semi-hard or hard ferromagnetic metal. The metal may be made from a cobalt based metal. The moveable element18may be initially not magnetized. The semi-hard or hard ferromagnetic metal may be selected from materials having a coercivity Hc e.g. between 25 to 700 A/m. The ferromagnetic material may be in the shape of a metal sheet or metal plate. The ferromagnetic material may be ductile and suitable for pro-ducing the moveable element by a stamping or punching from the metal sheet or the metal plate. One benefit of such type of production is a low-cost production of the moveable element. Another benefit of such production is that the moveable element when punched from not magnetized metal sheet which simplifies its transport and handling. In general, ductile relates to a material property expressing a capacity to sustain and/or withstand plastic deformation.

When made of the metal sheet or the metal plate the moveable element18may form a plate shape with a thickness comprised between of 1 mm to 3 mm as depicted inFIG.7that shows an exemplary perspective view of such a plate shape63moveable element62. Stamping or punching method enables a production of features such as for instance protrusions61termi-nating legs of the moveable element62. The moveable element may also be made by an alter-native method for instance from powder pressed metal via for instance metal injection molding or other methods involving different types of metal additive or metal subtractive manufacturing.

Once the moveable element18is shaped a heat treatment may be performed. The heat treatment may be an annealing. One benefit of annealing may be is that it makes the ferromagnetic material of the moveable element18harder than before annealing and in annealed state the ferromagnetic material of the moveable element18may exhibit well defined, robust and repeatable magnetic properties.

FIGS.4,5and8depict an exemplary magnetization process of the moveable element18as described in either of the two embodiments.FIG.4depict the moveable element18being initially in an unmagnetized condition and a source of magnetic field36that may be formed by a permeant magnet37. Alternatively, the source of magnetic field may be an electromagnet (not shown). The permanent magnet37may have a magnetic South pole on its first end38and magnetic North pole on its second end opposite to the first end38.

The first end38of the permanent magnet37may be set to face an end39of the middle leg19of the moveable element18. As depicted inFIG.5the first end38of the permanent magnet may be moved in the direction of arrow40inFIG.4towards the end39of the middle leg45of the moveable element18until the first end38of the permanent magnet37becomes abutted against the end39of the middle leg of the moveable element45. The moveable element48consequently may become magnetized by the permanent magnet magnetic field36generated by the permanent magnet37. One benefit of such magnetizing operation is in its simplicity and ability to be turned into an automatic industrial process.

The magnetizing of the legs may be performed by abutting67the magnet against the middle leg only. Then the magnetic lines may travel through the side legs46,47of the moveable element48and close the magnetic circuit through the middle leg45of the moveable element48. Hence, the middle leg45of the magnetized moveable element48may become magnetized in an opposite direction than the side legs46,47of the magnetized moveable element48. Provided the first end38of the permanent magnet bears a South magnetic pole as depicted inFIGS.4and5then the middle leg45of the magnetized moveable element48may become magnetized as a North magnetic pole and the side legs as having a South magnetic pole.

FIG.6depicts magnetic field lines that may be produced when the moveable element48is magnetized, as described above, by abutting67the permanent magnet37against the middle leg45of the moveable element48only. The magnetic field lines51may then flow from the middle leg45of the magnetized moveable element48to the side legs46and47. The magnetic force lines flowing through the gaps52,53between the middle leg45and each of the side legs46,47of the moveable element48may be denser than the magnetic field lines51that close between middle leg45and each of the side leg46,47through the magnetic field sensor14.

One benefit of such flat and focused shape of the movable element48is that it enables to design a compact size yet robust electrical contactless switch.