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Timestamp: 2020-02-22 08:01:12
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Monitoring tags - Guidance Monitoring Limited
United States Patent 7612678
Potter, John Ian (Leicestershire, GB)
Paterson, Graeme Lindsay Jonathan (Somerset, GB)
11/194390
Guidance Monitoring Limited (Leicester, GB)
2/338, 24/16PB, 340/568.2, 340/573.1, 340/573.4
24/562, 340/573.1, 340/568.2, 24/543, 24/178, 2/336, 2/338, 2/195.1, 24/16PB, 2/312, 340/539.15, 24/3.12, 340/573.4, 24/302, 340/572.8, 24/72.1
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7084764 System and method for monitoring location of an object 2006-08-01 McHugh et al. 340/568.2
20060048275 Headwear having exposed stitches to fix a lower hem thereof 2006-03-09 Cho 2/195.1
20020190864 Surveillance and remote alarm system for persons subject to limitation of freedom of movement 2002-12-19 Boccacci
20020130776 Fiber optic based security system 2002-09-19 Houde
5680104 Fiber optic security system 1997-10-21 Slemon et al.
5650766 Wearable transmitter with optical tamper detection 1997-07-22 Burgmann
5543780 Monitoring tag with removal detection 1996-08-06 McAuley et al.
5523740 Wearable transmitter assembly 1996-06-04 Burgmann
5184274 Adjustable, elastic static control wristband 1993-02-02 Weiss 361/220
5069957 Fire resistant elastic strap 1991-12-03 Vandermeersch 442/184
5013908 Break detection system using optical fibers having unique frequency modulated light 1991-05-07 Chang
4691924 Golfer's arm movement control device 1987-09-08 Strong 473/212
WO2002073561A1 2002-09-19 FIBER OPTIC BASED SECURITY SYSTEM
One known way of trying to remove the monitoring tag is to heat the strap and stretch it. In many cases the optical fibre will stretch with the rest of the strap so there is no critical interruption of the optical signal. To prevent this from happening, a thread, yarn, braid or tape of a thermally inelastic material such as Kevlar® material (supplied by DuPont Corporation of Wilmington, Del., United States of America) can be embedded in the strap. However, the applicant has found in the referenced instances that unless this thread, yarn, braid or tape is mechanically bonded to the rest of the strap and/or mechanically secured to the housing (either directly or indirectly through the clips mentioned below) then it is still possible to stretch the strap because there is relative movement between the thermally inelastic material and the surrounding material of the strap.
FIG. 1 shows a monitoring tag including a housing 20 having a central cavity 22 and pair of oppositely extending arms 24a and 24b. The cavity 22 is sized and shaped to receive a self-contained transmitter module (not shown) in a particular orientation. The transmitter module includes an antenna and control and tamper detection circuitry mounted on a printed circuit board. Signals are transmitted by the antenna to a base unit (not shown) but they are only received when the monitoring tag is a within a certain range. If the individual wearing the monitoring tag moves too far away from the base unit then the signals transmitted by the antenna will no longer be received and this can be logged or recorded by the base unit. The base unit can also trigger an alarm or automatically notify an authorised person. The optical tamper detection circuit includes an optical transmitter 8 (see FIGS. 6 and 10) (optionally a light emitting diode (LED)) and an optical receiver (not shown) (optionally a photodiode detector).
With reference to FIG. 2, the housing 20 is secured around the ankle of the individual (not shown) using a flexible elongate strap 40 made of a Elastollan® (a thermoplastics polyurethane (TPU) supplied by BASF Corporation of Florham Park, N.J., United States of America). The strap 40 is provided in a number of different lengths and both ends of the strap include a series of four holes 42 arranged in a rectangular configuration. The strap 40 is about 2.2 centimeters (⅞ inch) wide and about 0.4 centimeters ( 5/32 inch) thick.
The ends of the strap 40 are secured to the arms 24a and 24b of the housing 20 using integrally-formed plastic clips 50. Each clip 50 includes a pair of edge parts 52a and 52b, a first plate part 54 and a second plate part 56. Each of the edge parts 52a and 52b includes a resilient engaging barb 58. A front part 60 of the clip 50 includes an opening 62 (best seen in FIG. 5) for receiving an end of the strap 40. When the clip 50 is located on the end of the strap 40 as shown in FIG. 4, the edge parts 52a and 52b are positioned alongside the rounded sides of the strap 40 and the first plate part 54 and the second plate part 56 are positioned alongside the planar surfaces 40a and 40b of the strap.
The first plate part 54 includes a pair of holes 64. The second plate part 56 includes four holes 66 arranged in a rectangular configuration. When the end of the strap 40 is received through the opening 62, the four holes 42 are aligned with the four holes 66 in the second plate part 56. The pair of holes in the strap 40 that are located furthest away from the end of the strap are also aligned with the pair of holes 64 in the first plate part 54. A clip 50 can therefore be secured to each end of the strap 40 using a locking member 68. The locking member 68 has a substantially planar part with four extending projections or pins 70 arranged in a rectangular configuration. These pins 70 are a clearance fit through the pair of holes 64 in the first plate part 54, a press fit through the four holes 42 in the end of the strap 40 and are finally received in the four holes 66 in the second plate part 56. The holes 42 in the strap 40 also extend through the ends of the woven braids 46 so that the braids are mechanically secured to the clips 50 once the locking member 68 is engaged. The pins 70 of the locking member 68 can be made of a plastics material or made of metal. The latter is preferred in some situations where there is a risk that a sharp object such as a knife or blade might be inserted between the planar surface 40a of the strap and the locking member 68 to cut through the pins 70 and release the strap from the housing 20. If the remainder of the locking member 68 is made of a plastics material then moulded metal pins can be inserted in the plastics part. Alternatively, the whole of the locking member 68 can be made of a metal such as die cast aluminium.
The surface of the substantially planar part of the locking member 68 facing the strap 40 in use has a stepped configuration such that a narrow part 68a comes into contact with an outer surface of the first plate part 54 and a wide part 68b comes into contact with the planar surface 40a of the strap. The wide part 68b includes a number of ridges or teeth 68c (FIG. 13) that press into the planar surface 40a of the strap. The inner surface of the second plate part 56 also has a number of ridges or teeth 72 that press into the other planar surface 40b of the strap.
The edge parts 52a and 52b of the clip 50 are connected to each other and to the first and second plate parts 54 and 56 by an annular member 74 (best seen in FIG. 5) that extends around the opening 62 for receiving the end of the strap 40. The annular member 74 includes at outwardly extending flange 76. The purpose of the flange 76 will be explained in more detail below.
The arms 24a and 24b include openings 78a and 78b that communicate with the central cavity 22 of the housing 20. The openings 78a and 78b are sized and shaped at their open ends to receive the clips 50 such that the ends of the strap 40 can be fixedly secured to the housing 40 around the item. FIG. 6 shows part of one of the arms 24a in cut out so that the internal features of the opening 78a can be seen. The self-contained transmitter module (not shown) is located inside the cavity 22 such that the optical transmitter 8 is accurately aligned with an optically-transparent plastics cap 80 that includes a recess 82 that is shaped and sized for receiving the end of the strap 40 that protrudes beyond the clip 50. The cap 80 is welded to the surrounding parts of the housing 20 to completely close the opening 78a and includes a curved lens part 84 that couples the optical signals from the optical transmitter 8 into the end of the optical fibre 44. Projection parts (not shown) of the cap 80 are received in corresponding apertures in the housing 20 for the purpose of better fixing the cap in the opening 78a. The cap located in the other arm 24b includes an identical lens part that couples the optical signals from the other end of the optical fibre 44 to the optical receiver (not shown). Each end of the compressible strap 40 is a compression interference fit in the recess 82 of the associated cap 80 so that an annular water-tight seal is established completely around the end of the strap 40 in the region denoted generally by the reference numeral 86 (also shown in FIG. 10). This prevents any liquid such as water, sweat or ink from being drawn through the gap between the cap 80 and the end of the strap 40 by capillary action and then collecting between the end of the optical fibre 44 and the lens part 84 of the cap. If liquid is allowed to collect in this area then it can be drawn up the optical fibre, again by capillary action, where it can cause serious damage. The liquid also interferes with the transmission and receipt of the optical signals and can produce false triggers in the optical tamper detection circuit.
The barbs 58 provided on the edge parts 52a and 52b of the clip are designed for one-way snap-fit engagement with locking recesses 88 that are formed in opposite inner side surfaces of the openings 78a and 78b. These locking recesses 88 can be seen in FIG. 6. Once the clip 50 has been inserted into an opening in one of the arms and the barbs 58 have engaged with the corresponding locking recesses 88 then the barbs cannot be disengaged unless the clip 50 is broken apart. Frangible regions 90 located between the edge parts 52a and 52b of the clip 50 and the first and second plate parts 54 and 56 provide the primary mode of failure if a force is applied to the strap 40 to try and pull the ends of the strap away from the housing 20.
The frangible regions 90 will be described in more detail with reference to FIGS. 7 and 8. The frangible regions 90 extend from the ends of v-shaped channels 92 that are formed between the edge parts 52a and 52b and the first and second plate parts 54 and 56. In other words, the edge parts 52a and 52b and the first and second plate parts 54 and 56 are only connected together by the annular member 74 and the flange 76 and these are narrowed in the regions adjacent the ends of the v-shaped channels 92. The narrowing is shown in FIG. 7 by the dashed line that extends into the annular member 74 and the flange 76. If the clip 50 is viewed from any direction other than that shown generally in FIG. 8 then the frangible regions cannot be seen. (For example, the frangible regions 90 cannot be seen in FIG. 5, which shows the end of the clip 50 that is visible in use.) This is because the outer surface 76a of the flange is continuous and the frangible regions 90 are defined by channels or recesses that are spaced inwardly from the outer surface of the flange.
To protect the frangible regions 90 and provide additional strength and rigidity to the clips 50 as they are inserted into the openings in the arms of the housing 20, thin u-shaped webs 94 are provided between the edge parts 52a and 52b and the second plate part 56. These webs 94 are folded down into suitably shaped recesses 96 in the edge parts 52a and 52b and the second plate part 56 when the clips 50 are inserted into the openings in the housing. The process of folding the webs 94 effectively destroys their structural integrity so that they are easily broken if sufficient force is applied to the strap 40 to break the frangible regions 90.
If sufficient force is applied to the strap 40 then the frangible regions 90 will break allowing the first plate part 54 and the second plate part 56 to separate from the edge parts 52a and 52b. The end of the strap 40 is therefore released from the housing 20. In practice, the first plate part 54 and the locking member 68 remain secured to the end of the strap 40 but the second plate part 56 will readily detach as shown in FIG. 9 because the pins 70 of the locking member 68 and the holes 66 in the second plate part 56 are a clearance fit. The edge parts 52a and 52b will remain at least temporarily inside the respective opening in the housing with the barbs 58 engaged with the locking recesses 88.
FIGS. 10 and 11 show a clip 50 that is engaged in the opening 78a in the arm 24a of the housing. The alignment between the optical fibre 44 the lens part 84 of the cap 80 and the optical transmitter 8 can be clearly noted. The flange 76 of the clip 50 is received in an annular recess 98 that extends around the mouth of the opening 78a. The addition of the flange 76 helps to prevent anyone from pushing a thin probe through the gap between the outside of the clip 50 and the inside surface of the opening 78a. The close interference fit between the end of the strap 40 that protrudes beyond the clip 50 and the cap 80 can also be seen. No liquid, dirt or debris can get past the cap 80 and into the central cavity 22 of the housing 20. It will be readily appreciated that instead of being welded across the opening, the cap can also be formed as an integral optically-transparent part of the housing itself. FIG. 10 also shows that the locking member 68 is inaccessible when the clip 50 is engaged in the opening 78a so that it cannot be tampered with or removed.
Two additional features of the openings 78a and 78b in the arms of the housing 20 can be seen with reference to FIGS. 12 and 13. The first feature is a pair of ramps 100 that are located on opposite surfaces (only one surface is shown in FIG. 12 but the other is the same) of the opening 78a. When a clip 50 is inserted into the opening 78a the ramps 100 progressively force the first and second plate parts 54 and 56 together so that the pattern of ridges or teeth 72 dig into the planar surfaces 40a and 40b of the strap to provide additional friction grip between the clip 50 and the strap 40. The force applied by the ramps 100 also helps to stop anyone from inserting a thin probe through the gap between the planar surfaces 40a and 40b of the strap and the first and second plate parts 54 and 56. The second feature is a series of ribs 102 that are located on the same opposite surfaces of the opening 78a and are received in the v-shaped channels 92 of the clip 50 when it is inserted into the opening. This is best seen in FIG. 13 where the first plate part 54 of the clip and the locking member 68 are shown in their engaged position. The ribs 102 help to position the clip 50 and provide support to the edge parts 52a and 52b of the clip when the monitoring tag is in use. More particularly, they prevent the v-shaped channels 92 from closing when a force is applied to the strap 40. Such a movement, if unchecked, might disengage the barbs 58 from their locking recesses 88 and release the clip or weaken the frangible regions 90.
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