Patent Publication Number: US-6338562-B1

Title: Light fitting unit having releasable immobilizer

Description:
The present invention is generally concerned with light fittings comprising a base adapted to be mounted on a support of any kind, for example, and a diffuser mobile relative to the base and able to move between two positions, namely a closed position in which it prevents access to the interior volume of the unit and an open position in which it enables such access. A closure device operative between the diffuser and the base releasably locks the diffuser to the base. A safety switch controlling the electrical power supply to the unit is open when the diffuser is in its open position. 
     The present invention is more particularly directed to the situation in which the closure device includes a slider operated by actuator means accessible to the user from the outside and moving longitudinally on the base between a closed position and an open position respectively corresponding to the closed position and the open position of the diffuser. Coupling means operative at least locally on the path of movement of the slider enable the diffuser to be hooked onto the slider. 
     Such light fittings are used in explosive atmospheres, for example. 
     When a light fitting of this kind is opened, for example to carry out a maintenance operation, its power supply is normally systematically isolated as soon as it opens and is normally not reconnected until it has been closed. 
     Thus the operative can normally work in complete safety and there is normally no risk of any sparks occurring while the operative is working. 
     In practice, however, the means provided for this purpose can be faulty. 
     The safety switch may be inadvertently closed when the diffuser is in the open position, for example. 
     Or the safety switch may be stuck in the closed position when the diffuser is opened. 
     Such incidents can obviously have serious consequences. 
     A general object of the present invention is a totally safe way to prevent such incidents. 
     To be more precise, the present invention consists in a light fitting of the above kind which is generally characterized in that the slider is associated with releasable immobilizing means operated by the diffuser and adapted to oppose movement of the slider in the direction toward its closed position when the diffuser is in its open position and in that the safety switch is itself operated by the slider. 
     This prevents unintentional movement of the slider when the diffuser is in the open position and the slider is therefore prevented from operating the safety switch when the diffuser is in the open position. 
     In one preferred embodiment of the invention, the slider carries a ramp which positively opens the safety switch when it is in its open position. 
     In other words, in this embodiment of the invention, the slider holds the safety switch open when it is in its open position. 
     In other words, and in contrast to the usual arrangements, the safety switch is operated when the diffuser is open instead of unoperated. 
     This advantageously prevents all risk of the safety switch being stuck in the closed position when the diffuser is opened, which is to the benefit of safety. 
     Likewise, the slider covers the safety switch when the diffuser is in the open position and therefore prevents operation of the switch, which prevents all risk of unintentional operation of the safety switch when the diffuser is in the open position, which is again beneficial to safety. 
     In another preferred embodiment of the invention, when the slider operating means include a pinion rotating on the base and meshing with a rack fastened to the slider, which is the usual arrangement, the height of the teeth of the rack progressively decreases at one end at least of the rack. 
     The pinion can therefore escape from the rack at the end of its travel, which has the advantage of limiting the loads applied to the system and that the resulting rasping noise tells the operator that the rack has reached the end of its travel if the operator has failed to notice this by any other means. 
    
    
     The features and advantages of the invention emerge from the following description which is given by way of example and with reference to the accompanying diagrammatic drawings, in which: 
     FIG. 1 is a locally cut-away view in elevation of a light fitting of the invention, 
     FIG. 2 shows to a larger scale and in its entirety the part of FIG. 1 which is exposed by virtue of the partial cut-away therein and concerns the closure device of the light fitting, shown in the configuration it assumes when the diffuser of the light fitting is in the closed position, 
     FIG. 3 is a partial view of the slider of the closure device in cross section taken along the line III—III in FIG. 2, 
     FIG. 4 is a partial elevation view derived from that of FIG.  2  and showing only the rack of the slider, 
     FIGS. 5A,  5 B are partial views analogous to that of FIG.  2  and showing respective successive phases of operation of the closure device of the invention as the diffuser moves from its closed position to its open position, and 
     FIG. 6 is a partial elevation view which is also analogous to that of FIG.  2  and which shows how the slider of the closure device is immobilized when the diffuser is in the open position. 
    
    
     As shown in FIG. 1, and in a manner that is known in itself, the light fitting  10  of the invention includes a base  11  adapted to be attached to a support of any kind, not shown, or to be coupled to suspension members of any kind, also not shown, and a diffuser  12  made of a translucent or transparent material and mobile relative to the base  11  between two positions, namely a closed position in which, as shown in FIG. 1, it prevents access to the interior volume  13  of the unit and an open position, not shown, in which it enables such access. 
     In practice the base  11  and the diffuser  11  are elongate, generally parallelepiped-shaped and nest one within the other in a sealed manner. 
     For example, the diffuser  12  is articulated to the base  11  along one longitudinal edge of the unit by hinges which can also enable it to be removed, if required. 
     A light fitting  10  of this kind, which is intended for use in explosive atmospheres, for example, is well known in itself and is therefore not described in detail here. 
     Only its components necessary for understanding the invention are described. 
     In a manner that is known in itself, the light fitting  10  includes a closure device  14  operative between the diffuser  12  and the base  11  and adapted to releasably lock the diffuser  12  to the base  11 . 
     In practise the closure device  14  includes a slider  15  operated by means  16  accessible to the user from the outside and mobile longitudinally on the base  11  between a closed position and an open position respectively corresponding to the closed position and the open position of the diffuser  12 , and, as described in more detail later, coupling means  18  operative at least locally on the path of movement of the slider  15  and adapted to enable the diffuser  12  to be hooked onto the slider. 
     In practise the slider  15  is within the interior volume  13  of the unit, extending along the longitudinal edge thereof opposite that along which the diffuser  12  is articulated to the base  11 . 
     In a manner that is known in inself, and as shown diagrammatically in FIG. 2 in particular, the light fitting  10  of the invention includes a safety switch  20  which controls the electrical power supply to the unit and which is open when the diffuser  12  is in the open position. 
     For example, and as shown diagrammatically in FIG. 2, the safety switch  20  includes one or more mobile contacts  21  controlled by a sliding plunger  22  and included in an electrical circuit  23  powering various electrical components within the interior volume  13  of the unit, such as a lampholder, ballast, etc. 
     In practise, and as shown in FIG. 2, the direction D in which the slide  15  moves is its lengthwise direction. 
     The slider  15  is of course engaged with guide means fastened to the base  11 . 
     The guide means, which will be obvious to the skilled person, are not shown in the figures. 
     For example, they include spaced studs projecting from the base  11  engaged in slots in the slider  15 . 
     In the embodiment shown, and in a manner that is known in itself, the coupling means  18  operative between the slider  15  and the diffuser  12  include at least one hook  24  on the slider  15  and which is elongate substantially parallel to the direction D in which the slider  15  moves and has an entry chamfer  25  at one end, and at least one lug  26  on the diffuser  12 , in corresponding relationship to the hook  24 , on the path of movement of the hook  24  and adapted to inter-engage therewith. 
     In practise, and as shown in FIG. 1, there is a plurality of hooks  24  spaced along the slider  15  and the diffuser  12  includes as many lugs  24  in corresponding relationship thereto, i.e. one lug  26  per hook  24 . 
     In the embodiment shown, the means  16  for operating the slider  15  include a pinion  27  rotating on the base  11  and meshing with a rack  28  fastened to the slider  15 . By means of a pin  29  the pinion is constrained to rotate with an operating nut  30  accessible to the user from outside the unit (see FIG.  1 ). 
     For example, and as shown here, the rack  28  is formed in a slot  31  in the slider  15  and the pinion  27  is inside the slot  31 . 
     In practise the resulting operating means  16  are substantially in the middle area of the base  11 . 
     According to the invention, the slider  15  is associated with releasable immobilizing means  32  operated by the diffuser  12  which, as described in more detail later, are adapted to oppose movement of the slider  15  toward its closed position when the diffuser  12  is in its open position, and the safety switch  20  is operated by the slider  15 . 
     In the embodiment shown, the releasable immobilizing means  32  include at least one elastically deformable lug  34  on the slider  15  and carrying a transverse detent  35  and at least one abutment  36  on the base  11  which is on the path of movement of the elastically deformable lug  34  and cooperates with the detent  35 . 
     In practise the elastically deformable lug  34  is elongate parallel to the direction D in which the slider  15  moves and its detent  35 , which is preceded by an entry chamfer  37 , faces toward the closed position of the slider  15 . 
     For example, and as shown, the elastically deformable lug  34  lies within a slot  38  in the slider  15 , projecting cantilever fashion from one transverse edge of the slot  38 , and the abutment  36  fastened to the base  11  projects into the volume delimited by the slot  38 . 
     In the embodiment shown, the elastically deformable lug  34  has a tail portion  39  with a relatively small cross section attached to the slider  15  and a larger head  40  which forms the detent  35  and the entry chamfer  37  and with projects laterally out of the slot  38  toward the interior volume  13  of the unit (see FIG.  3 ). 
     The diffuser  12  carries a finger  42  in corresponding relationship to the elastically deformable lug  34  and for actuating it. 
     In practise the finger  42  extends beyond the opening of the diffuser  12  and enters the interior volume of the base  11 . 
     As is the case in the embodiment shown, the releasable immobilizing means  32  preferably include a plurality of elastically deformable lugs  34  spaced along the slider  15  and the same number of abutments  36  on the base  11 , with the same number of fingers  42  on the diffuser  12 , i.e. one abutment  36  and one finger  42  for each elastically deformable lug  34 . 
     Again as is the case in the embodiment shown, the height of the teeth  43  of the rack  28  fastened to the slider  15  preferably decreases progressively at one end thereof at least, i.e. at one end at least of the rack  28 . 
     For example, and as shown, the height of the teeth  43  of the rack  28  decreases progressively at both ends. 
     It is therefore exactly as if the teeth  43  were leveled off with a curved profile (the envelope of their crests) with its convex side facing toward the interior of the slot  31  in the slider  15 . 
     In the embodiment shown, the number of shorter teeth  43  at one end of the rack  28  is different from the number of shorter teeth  43  at its other end. 
     To be more precise, in this embodiment, and for reasons that will become apparent hereinafter, this number is greater at the end of the rack  28  corresponding to the open position of the slider  15  (FIGS. 5A and 5B) than at the end of the rack  28  corresponding to the closed position of the slider (FIG.  2 ). 
     Again as is the case in the embodiment shown, the slider  15  preferably carries a ramp  45  which positively opens the safety switch  20  when it is in its open position. 
     In practise the ramp  45  is formed by the edge of a boss  46  projecting for this purpose from the slider  15  and whose path of movement impinges on the plunger  22  of the safety switch  20 . 
     For simplicity, it has been assumed in the figures that the boss  46  is in the same general plane as the slider  15 . 
     However, it could equally be in the form of a right-angled rim on the slider  15 , for example, if required. 
     Be this as it may, in the embodiment shown, the ramp  45  has a straight portion  47  substantially parallel to the direction D in which the slider  15  moves and an oblique entry portion  48  at the end of the straight portion  47  nearer the safety switch  20 . 
     When the diffuser  12  is in the closed position the hooks  24  on the slider  15  are engaged with the lugs  26  on the diffuser  12 , as shown for two of them in FIG. 2, and the diffuser  12  is therefore held firmly in its closed position on the base  11 . 
     As shown in FIG. 2, the safety switch  20  is in its closed position at this time. 
     When the slider  15  is moved from its closed position to its open position by the operating means  16 , as symbolized by an arrow F 1  in FIGS. 2 and 5A, each of its elastically deformable lugs  34  impinges as it moves on the corresponding finger  42  of the diffuser  12 , which obliges it to flex elastically, as shown in the case of one of them in FIG. 5A, and enables it to pass under the corresponding abutment  36  of the base  11  without interfering with the abutment  36 . 
     The hooks  24  on the slider  15  are disengaged from the lugs  26  on the diffuser  12 , as shown for two of them in FIG.  5 A. 
     This releases the diffuser  12  which can therefore be opened, as symbolized by an arrow F 2  in FIG.  5 B. 
     Because of the resulting disengagement of the fingers  42  of the diffuser  12 , each of the elastically deformable lugs  34  of the slider  15  resumes its original configuration, because of its inherent elasticity, as a result of which its detent  35  engages behind the corresponding abutment  36  of the base  11 , as shown in the case of one of them in FIG.  5 B. 
     As will become apparent hereinafter, this prevents excessive retrograde movement of the slider  15 . 
     The slider  15  also opens the safety switch  20  when its ramp  45  depresses the plunger  22  of the switch (FIGS.  5 A and  5 B). 
     The immobilized slider  15  positively holds the safety switch  20  in the open configuration. 
     Thus the safety switch  20  is operated when the diffuser  12  is in the open position. 
     In other words, the return spring acting on its mobile contact (s)  21  is compressed. 
     In practise, when the slider  15  is in the open position, the rack  28  is substantially at the end of its travel relative to the pinion  27  with which it meshes. 
     Because of the shorter teeth  43  of the rack  28  at the corresponding end thereof, the pinion  27  escapes from the teeth  43  if it is rotated further, which limits the forces transmitted by the pinion  27  to the slider  15  and has the advantage of protecting the pinion  27  and the slider  15 , and also produces a rasping noise to catch the attention of the operative. 
     There can be a clearance between the detent  35  of the elastically deformable lugs  34  of the slider  15  and the corresponding abutment  36  on the base  11  in the end of travel position of the rack  28 , as shown for one of the elastically deformable lugs  34  in FIG.  5 B. 
     If retrograde movement of the slider  15  is then attempted, even though the diffuser  12  is in the open position, each of the elastically deformable lugs  34  of the slider  15 , or at least one of them, bears on the abutment  36  on the base  11 , as symbolized by an arrow F 3  in FIG. 6, after taking up the corresponding clearance, as shown for one of the elastically deformable lugs  34  in FIG. 6, which immediately opposes further retrograde movement of the slider  15 . 
     The releasable immobilizing means  32  provided for this purpose therefore hold the slider  15  in its open position for as long as the diffuser  12  is itself in its open position. 
     The length of the straight portion  47  of the ramp  45  on the slider  15  is made sufficient for the safety switch  20  to remain open in the event of any such small retrograde movement of the slider  15 . 
     For the same reasons as previously, a rasping noise alerts the operative to the fact that greater retrograde movement of the slider  15  is impossible. 
     For the slider  15  to be able to return to the closed position, the diffuser  12  must be returned to its closed position first. 
     As shown in FIG. 5A, when the diffuser  12  is in its closed position, the fingers  42  of the diffuser  12  again act on the elastically deformable lugs  34  of the slider  15 , which enables each of the lugs to escape from the corresponding abutment  36  on the base  11 . 
     Of course, the present invention is not limited to the embodiment described and shown, but encompasses any variant execution thereof. 
     In particular, if the coupling means operative between the diffuser and the slider include hooks and lugs, as described and shown, the hooks and the lugs on the slider and the diffuser can be interchanged. 
     Likewise the elastically deformable lugs and the abutments of the releasable immobilizing means can be interchanged between the slider and the base on which the slider moves.