Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H51/00—Electromagnetic relays
  • H01H51/28—Relays having both armature and contacts within a sealed casing outside which the operating coil is located, e.g. contact carried by a magnetic leaf spring or reed
  • H01H51/287—Details of the shape of the contact springs
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H11/00—Apparatus or processes specially adapted for the manufacture of electric switches
  • H01H11/005—Apparatus or processes specially adapted for the manufacture of electric switches of reed switches
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/64—Protective enclosures, baffle plates, or screens for contacts
  • H01H1/66—Contacts sealed in an evacuated or gas-filled envelope, e.g. magnetic dry-reed contacts
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H11/00—Apparatus or processes specially adapted for the manufacture of electric switches
  • H01H11/04—Apparatus or processes specially adapted for the manufacture of electric switches of switch contacts

Definitions

• the invention relates to a method of adjusting the mutual separation of the overlapping metallic cantilever members within the vitreous envelope of a reed switch.
• two lightweight metallic rods are hermetically sealed through opposite ends of an elongated hollow glass tube in such a manner that they extend substantially parallel to the longitudinal axis of the tube.
• a portion of each rod within the tube is flattened out, and these flattened portions (referred to as "reeds") are mutually positioned in such a way as to face each other across a narrow intervening gap (of the order of a fraction of a millimeter) and to overlap each other.
• Each rod behaves as a cantilever, since it is fixed at one end into the wall of the glass tube, but is free at its flattened end.
• a portion of each rod protrudes outward through the wall of the tube, to facilitate electrical contact with the portion located within the tube.
• the rods, or at least their flattened portions comprise a soft-magnetic material such as NiFe.
• a soft-magnetic material such as NiFe.
• the flattened portions Under the influence of an appropriate external magnetic field, which can penetrate the vitreous tube, the flattened portions thus become magnetised and mutually attracted, and will converge and physically contact one another if the external field is strong enough.
• the assembly can act as a magnetically-triggered electrical switch.
• the reed switch can be used as an electrical relay.
• the value of the external magnetic field strength at which the reeds are caused to contact each other is referred to as the AW-value of the reed switch.
• the term "AW” is an abbreviation for "Ampere Winding", in reference to the fact that the magnetic field strength generated along the longitudinal axis of a current-carrying coil is determined both by the magnitude of the electrical current in the coil and by the fashion in which the coil is wound (number of turns per axial unit of length, and the radius of the turns).
• the AW-value of the reed switch is inter alia a sensitive function of the size of the gap between the flattened portions.
• Reed switches are usually manufactured in batches according to the specifications of a given customer, and a particular customer's stipulated admissible range o AW-values is generally the most crucial quality-control factor in meeting each order. Despit exercising the greatest of care and accuracy in the manufacturing process, however, the very nature of the reed switch itself results in inevitable deviations from the desired gap-value (and thus AW-value) for a given batch, since automated sealing of lightweight and easily- pliable metallic rods into the walls of a tiny glass envelope can hardly be expected to occur with an absolute guarantee of a strictly maintained mutual orientation, degree of overlap and intervening gap. As a result, a typical batch of reed switches will demonstrate a (Gaussian) distribution of gap-values around the intended gap-value.
• a method of adjusting the mutual separation of the overlapping metallic cantilever members within the vitreous envelope of a reed switch characterised in that a beam of radiant energy to which the envelope is substantially transparent is directed for a controlled period of time through the envelope onto a localised area of at least one of the members, thereby effecting permanent thermally- induced bending of that member about the irradiated area.
• the inventors directed a controlled, sharply-focused burst of laser radiation through the glass envelope of a reed switch and onto the "back" of one of the reeds therewithin, i.e. onto that surface of the flattened portion facing away from the opposing reed.
• the metallic material in the highly- localised irradiated area was hereby abruptly heated and caused to expand, forcing the reed- back to temporarily bend away from the irradiating beam.
• the reed-back bent back through its original position, and became permanently bent towards the original line of the irradiating beam. It is postulated that this change in bending- direction was caused by the occurrence of plastic deformation in the metallic material within the irradiated area, whereby cooling of the irradiated material caused it to undergo a net contraction.
• the same method can also be successfully used to obtain a decrease in the switch-gap, by directing the irradiating beam onto the "front" of one of the reeds (i.e. onto that surface of the flattened portion facing toward the opposing reed) instead of onto its back.
• This is made possible by the fact that the flattened portions (generally) only overlap to a slight extent, so that a relatively large portion of each can be accessed from all sides.
• the obtained change ⁇ g in the gap-value can be tailored by appropriate choice of a number of parameters. These include:
• the energy fluence E j of the employed irradiating beam The wavelength of the radiation in the beam;
• the area of the localised irradiated region on the reed determined by the extent to which the irradiating beam is focused onto the reed surface. This in turn affects the delivered power per unit area;
• ⁇ g is approximately proportional to Xj via the relationship ⁇ g *> ⁇ x 2 (this relationship holds with a high degree of accuracy for relatively small values of a (less than about 10°) and for values of Xj whic significantly exceed the amount of longitudinal overlap of the reeds (by about a factor of ten, or more); such requirements are easily met in common practice);
• a particular embodiment of the inventive method is characterised in that the beam of radiant energy is embodied as a pulsed laser beam.
• the beam of radiant energy is embodied as a pulsed laser beam.
• the beam By pulsing the beam, its energy content is concentrated into successive short bursts, in which the delivered power is consequently much greater than in the case of a continuous energy output.
• Particularly suitable pulsing for this purpose can be achieved, for example, by optically pumping the employed laser device with a flash source. It should be noted in this context that use of too high a laser fluence can have a detrimental effect on the quality of the inventive adjustment procedure.
• the pulse-length of the employed laser radiation is chosen to lie in the range 0.1-2.0 ms, and the delivered radiative energy per pulse is chosen to lie in the range 0.05-1.0 J. Values within these ranges typically result in ⁇ g-adjustments of the order of 10-20% per radiative "shot" (for X j in the range 0.5-4.5 mm), with negligible production of evaporated metallic material. ⁇ g-adjustments of this size are quite practical, since smaller adjustments (e.g. 5%) generally fall within the tolerances quoted by the customer anyway.
• the manner in which the reed bends under the influence of irradiation is inter alia a function of y
• y j is zero (i.e. when the reed is irradiated at some point along its longitudinal axis)
• the bending motion of the reed occurs linearly in a direction substantially perpendicular to the plane of the flattened portion.
• y 2 has a value other than zero (i.e. when the reed is irradiated at a point to one side of its longitudinal axis)
• the bending motion of the reed will additionally contain a degree of torsion about the longitudinal axis.
• Such torsion decreases the homogeneity of the switch-gap, since it causes one edge of the irradiated flattened portion to be twisted towards die opposing reed, whilst the facing edge is twisted away from the opposing reed.
• this effect can be prevented by ensuring that the reed is irradiated symmetrically with respect to its longitudinal axis, e.g. by successively (or simultaneously) irradiating it at two points which are mirror images of one another in the longitudinal axis.
• the homogeneity of the change ⁇ g in the switch-gap improves even further when the irradiated region on the reed's surface extends across the full width of the reed (measured substantially at right angles to the reed's longitudinal axis).
• One way of achieving such irradiation is to quickly scan a sharply focused laser beam across the width of the reed, thereby creating a narrow "score mark" instead of a spot-like burn.
• typically suitable scan speeds of the laser beam across the reed surface generally lie in the range 20-60 m/s.
• an advantageous embodiment of the inventive method is characterised in that the employed laser radiation has a wavelength in the range 525-540 nm, to which the commonly used green glasses are highly transparent. Radiation of this wavelength, and of sufficient intensity, can be conveniently derived from a (pulsed) frequency-doubled Nd:YAG laser, for example.
• the inventors have developed an apparatus for accurately positioning the reed switch with respect to the irradiating beam.
• This apparatus employs an electromagnetic coil both to orient the reed switch and to determine its AW- value, whilst a television camera is used to accurately aim the irradiating beam with respect to the reed's free extremity (thereby determining X j , and ultimately a).
• Figure 1 shows an elevation of a reed switch in which the switch-gap ha been adjusted using a method in accordance with the present invention
• Figure 2 is a plan view of the subject of Figure 1;
• Figure 3 depicts a detail of Figure 1;
• Figure 4 shows a plan view of Figure 3.
• Embodiment 1
• FIGS 1-4 render various views of a reed switch whose switch-gap has been adjusted in accordance with the current inventive method.
• Corresponding features in th various Figures are denoted by identical reference symbols.
• the Figures are not drawn to scale, so as to facilitate clear illustration of the various aspects of the inventive method.
• FIG 1 shows an elevation of a reed switch 1 in which the switch-gap has been adjusted using the method according to the invention.
• the switch 1 comprises an oblong green glass envelope 3 (in practice, of the order of 10 mm long) into which two metallic cantilever members 5, 7 have been sealed at opposite ends.
• These members 5, 7 a comprised of a soft-magnetic NiFe alloy (permalloy). They are substantially parallel, and have flattened portions 9, 11 which overlap in the region 17.
• Figure 2 renders a plan view of th same reed switch 1.
• Figure 3 depicts the central region of Figure 1 in more detail.
• the switch is in its relaxed state, with an open gap between the flattened portions 9, 11.
• Each of these portions 9, 11 has a "back" surface 9a, 11a and a "front” surface 9b, lib.
• the portions 9, 11 had an original switch-gap of size g, but this has since been increased by an amount ⁇ g using the inventive method.
• a localised region of the back surface 1 la was briefly irradiated at a location p situated at a distance x 2 from the free extremity 19 of the flattened portion 11, thereby causing the free end of the portion 11 to bend slightly about point p through an angle ⁇ with respect to the longitudinal axis 15, in a direction away from opposing portion 9.
• the irradiating beam 21 is here schematically illustrated via a dashed outline.
• a further possibility is to irradiate a localised region of the front surface lib of the portion 11, in which case the free end of that portion 11 can be caused to bend towards the opposing portion 9.
• Figure 4 renders a (partial) plan view of the flattened portions 9, 11 as depicted in Figure 3.
• the mark 23 made by the irradiating beam 21 is schematically depicted.
• the mark 23 extends across the full width of the reed-back 11a along the axis 25, and was made by rapidly drawing the (sharply focused) irradiating beam 21 across the surface 11a along the axis 25.
• the reed-back 11a can also be irradiated at one or more distinct points along the axis 25. It is then preferable to position these points symmetrically with respect to the longitudinal axis 15, e.g. by irradiating at a single point at the intersection of axes 15 and 25, or by irradiating at two points on the axis 25 which are mirror images of each other in the axis 15, etc.
• the glass tube 3 has a length of about 14 mm and a diameter of about 2.5 mm.
• the flattened portions 9, 11 are each approximately 4.5 mm long, 1.2 mm wide and 0.15 mm thick.
• the amount of longitudinal overlap 17 is about 0.2 mm, and the gap-value g is approximately 30 ⁇ m (depending on the exact specifications of a given batch).
• the inventors irradiated the back 1 la of each flattened portion 11 using a beam 21 from a frequency-doubled Nd:YAG laser, with a wavelength of 532 nm and a pulse-length of 0.5 ms.
• the beam 21 was focused to an approximate diameter of 200 ⁇ m, and each reed switch was subjected to a single "shot" at some point along its longitudinal axis 15.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Manufacture Of Switches (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=19865186

Family Applications (1)

Country Status (4)

Cited By (2)

Families Citing this family (5)

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• 1995
  • 1995-09-20 WO PCT/IB1995/000771 patent/WO1996010833A1/en active IP Right Grant
  • 1995-09-20 EP EP95929989A patent/EP0731978B1/de not_active Expired - Lifetime
  • 1995-09-20 JP JP51155896A patent/JP3645266B2/ja not_active Expired - Lifetime
  • 1995-09-20 DE DE69502928T patent/DE69502928T2/de not_active Expired - Lifetime

Non-Patent Citations (1)

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