Abstract:
A neuromuscular stimulation device is described having a plastic casing housing a printed circuit board bearing control electronics, with the casing including an external integral flexible portion which is capable of being flexed into the interior of the casing so as to cause an electrically insulative substrate on which is carried an electrically conductive pathway to be pushed into contact with the PCB in order to complete an electrical circuit. Such a switch is relatively inexpensive to produce, as it has few moving parts, can be formed in a usual manufacturing process, and is robust.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a switch configuration for incorporation into an electronic device. Aspects of the invention relate to an electronic device including such a switch. In particular, the switch is useful in disposable medical devices, for example an electronic neurostimulator device. 
       BACKGROUND TO THE INVENTION 
       [0002]    Low cost, disposable electronic devices are used in many fields, including the medical device field. The present applicants have previously described an electronic neurostimulator device, in international patent application WO2010/070332. The device described therein incorporates a control unit housing the necessary electronics to drive the device, and to allow a user to operate the device; these typically include a PCB and an electrical cell. A pair of electrodes driven by the control unit are printed onto a flexible electrically insulative substrate (such as BoPET [Biaxially-oriented polyethylene terephthalate], for example Mylar®) along with electrically conductive tracks leading to the control unit. The substrate is mounted onto a more robust elongate tongue made from, for example, a flexible plastics material. 
         [0003]    Such devices incorporate electrical switches to activate or deactivate the device, or to allow a user to adjust the intensity or other characteristics of the electrical stimulation. Incorporating suitable switches and their attendant moving parts into a low cost unit can be problematic, particularly when the unit is intended to be sealed or disposable. It is among the objects of embodiments of the present invention to provide an alternative switch configuration. 
       SUMMARY OF THE INVENTION 
       [0004]    According to a first aspect of the present invention, there is provided an electronic device comprising:
       a plastic casing defining an interior and exterior, the interior housing a printed circuit board having an electrical contact point, the casing incorporating an external integral flexible portion which is capable of being flexed into the interior of the casing;   a flexible electrically insulative substrate on which is carried an electrically conductive pathway;   wherein at least a portion of the flexible substrate is retained by the casing such that said portion is adjacent to but spaced from the PCB;   such that when the integral flexible portion is flexed into the interior of the casing, it urges said portion of the flexible substrate into contact with the PCB, such that the electrically conductive pathway contacts the electrical contact point, thereby completing an electrical circuit.       
 
         [0009]    This arrangement allows a switch to be formed from a substrate bearing a printed circuit in combination with a printed circuit board (PCB) bearing control electronics. The printed circuit on the substrate and the PCB are arranged with respect to one another such that the two are brought into contact on actuating the integral flexible portion of the casing, which completes an electrical circuit. This may be used to activate or deactivate a device, or to adjust operating parameters. The switch is relatively inexpensive to produce, as it has few moving parts, and can be formed in the usual manufacturing process, and is robust. 
         [0010]    In a preferred embodiment, the external integral flexible portion is resilient, such that when force is applied to the integral flexible portion it is flexed into the interior of the casing, and when force is not applied, it is no longer so flexed. This allows the flexible portion to act as a spring, and to reopen the switch after closure. There is thus no need to include an additional spring to reopen the switch. 
         [0011]    Preferably the external integral flexible portion is formed in a dome shape. This feature also gives tactile feedback when pressed. This occurs when the dome is deformed during activation. Both the overall form of the dome and the properties of the polymer help the button/dome to restructure into its original state. 
         [0012]    Preferably the portion of the flexible substrate is retained by the casing under tension. For example, the flexible substrate may be disposed within a tortuous path formed within the casing, such that the substrate is retained by the casing. Keeping the substrate under tension also allows the substrate to act somewhat as a spring, as well as retaining it fast within the casing to prevent or reduce unwanted movement. The casing may be formed from two portions which are secured together (for example, by welding, such as ultrasonic welding), and the tortuous path is formed between the two portions. 
         [0013]    The flexible substrate may extend beyond the casing. This allows electrical signals to be taken outside the casing; for example, to drive electrodes mounted beyond the casing for use as neuromuscular stimulation devices. 
         [0014]    The flexible substrate may be a polymeric substrate, preferably a biaxially-oriented polyethylene terephthalate film, for example Mylar®. 
         [0015]    The integral flexible portion may comprise an internal protrusion, sized and shaped to assist in urging the flexible substrate into contact with the PCB; for example, a pin or pins extending from an inner surface of the flexible portion on the casing. 
         [0016]    The device may further comprise an electrical cell within the casing. 
         [0017]    The device may comprise a plurality of external integral flexible portions, and a corresponding plurality of electrical contact points on the PCB—that is, the device includes multiple switches. 
         [0018]    Preferably the casing is substantially sealed against moisture ingress. 
         [0019]    Preferably the casing is injection moulded. 
         [0020]    The device is preferably a medical device, for example an electrical neuromuscular stimulator. However, the switch may be incorporated into any number of devices, as will be readily apparent to the skilled person. 
         [0021]    Also provided by the present invention is an electrical switch comprising:
       a plastic casing defining an interior and exterior, the interior housing a printed circuit board having an electrical contact point, the casing incorporating an external integral flexible portion which is capable of being flexed into the interior of the casing;   a flexible electrically insulative substrate on which is carried an electrically conductive pathway;   wherein at least a portion of the flexible substrate is retained by the casing such that said portion is adjacent to but spaced from the PCB;   such that when the integral flexible portion is flexed into the interior of the casing, it urges said portion of the flexible substrate into contact with the PCB, such that the electrically conductive pathway contacts the electrical contact point, thereby completing an electrical circuit.       
 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0026]      FIG. 1  shows an electronic neuromuscular stimulation device, taken from WO2010/070332. 
           [0027]      FIG. 2  shows a section of the control module of a device, incorporating a switch arrangement in accordance with an embodiment of the present invention. 
           [0028]      FIG. 3  shows the control module of  FIG. 2 , when being activated by a user. 
           [0029]      FIG. 4  shows an enlarged view of a portion of  FIG. 3 . 
           [0030]      FIGS. 5 and 6  show an alternative device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    Shown in  FIG. 1  is a neuromuscular stimulator device  10  as described in WO2010/070332, The device comprises a flexible, non-stretchable thermoplastic elastomer substrate  12  which includes an elongate tongue  14  at one end, and a moulded recess  16  at the other. 
         [0032]    On the tongue  14  are printed positive  18  and negative  20  electrodes. The positive is slightly larger than the negative. Each electrode includes a conductive track  22 ,  24  leading from the electrode to a respective contact point  26 ,  28  located in the recess  16 . Not shown in the figures are an insulative strip arranged between the positive track  22  and the negative electrode  20 , and similar strips at the edges of the tongue, to prevent unwanted leakage of current. 
         [0033]    Within the recess  16  are placed an electrical cell (not shown), and a PCB (not shown) including suitable circuitry to control the electrodes. Together with the conductive tracks  22 ,  24  and contact points  26 ,  28 , this forms a complete circuit. A plastic cover is then sonically welded over the recess  16  to seal the components. A layer of gel is then placed over the whole device  10 ; this provides an electrical contact with a user&#39;s limb and helps keep the device adhered to a user. The gel may be protected in transit by a peelable backing layer. 
         [0034]    The outer surface of the recess  16  is formed with an integral diaphragm button  30  and an aperture  32  for displaying an LED. The button  30  is arranged to contact a corresponding button on the battery housing or PCB to activate the device. The aperture  32  displays an LED which indicates whether the device is operating. 
         [0035]    In order to incorporate the switch arrangement as described herein, the device  10  is modified in a number of ways. The positive  18  and negative  20  electrodes are printed on a BoPET (eg, Mylar®) flexible substrate, which is itself affixed to the elongate tongue  14 . The substrate also carries conductive tracks for connecting the electrodes to the control circuitry on the PCB. Further, the button  30  does not itself contact a corresponding button on the battery housing or PCB, as will be described. 
         [0036]    An alternative device is shown in external view in  FIGS. 5 and 6 . This is generally similar in operation to the device shown in  FIG. 1 , but has a slightly different configuration, in that the recess/enclosure is located towards the centre of the flexible tongue. The presence of two dome-shaped push buttons can be seen on the upper surface of the device, in  FIG. 5 . A view of the device from the lower surface is shown in  FIG. 6 . 
         [0037]      FIG. 2  shows a section of the modified device of  FIGS. 5 and 6 , in accordance with an embodiment of the invention. The figure shows a housing  30  forming an enclosure (corresponding to the recess  16  of  FIG. 1 ). The housing  30  is formed of two injection moulded plastic parts ( 32 ,  34 ), forming upper and lower portions of the housing. The elongate tongue  14  can be connected to flanges formed at either end of the housing  30 . Within the housing  30  are located an electrical cell  36  and a PCB  38 . The two portions of the housing are welded together to form a watertight seal: for example, by ultrasonic welding. 
         [0038]    The housing  30  includes a tortuous path  40  formed therein between the upper and lower portions  32 ,  34 , with the path being formed as a gap between the portions. Within this path  40  is placed the Mylar flexible substrate  42 , which extends beyond the housing where it may be fixed to the tongue  14 . On the lower surface (as seen in the figure) of the substrate  42  are printed a pair of electrodes and electrically conductive tracks for connecting the substrate to the PCB  30  and cell  36 . The tortuous path  40  serves to retain the substrate  42  under tension, such that it is suspended above the PCB  38 , and such that it does not move with respect to the housing. 
         [0039]    On the upper external surface of the upper portion  32  of the housing  30  are formed a pair of switches in the form of flexible protruding domes  44 ; each dome  44  includes an inwardly extending pin  46 . The domes  44  and pins  46  are integrally formed within the housing. The domes  44  in particular are formed of a resilient material, such that they deform under pressure, but return to their original position upon removal of that pressure. In some embodiments of the invention, the domes may merely be formed of a deformable material, such that they do not revert to their original position. 
         [0040]    In order to actuate the switches, a user will exert pressure on the domes  44  (shown in  FIGS. 3 and 4 ) with their finger. The dome  44  deforms and extends inwardly into the housing  30 ; this in turn urges the pin  46  into contact with the substrate  42  which is thus pressed into contact with the PCB  38 . A portion of the conductive track printed on the substrate  42  thus contacts a conductive portion formed on the PCB, thereby forming a complete electrical circuit and closing the switch. When the user releases the switch, the resilience of the plastics material will allow the dome  44  to revert to the original position, while the tension in the substrate  42  also assists by acting as a spring. This separates the substrate  42  from the PCB  38 , thereby opening the switch. The dome shape of the switch, in combination with the resilient nature of the substrate and the presence of the pin will together provide tactile feedback to the user. 
         [0041]    In certain embodiments, the domes  44  may not be resilient, such that the switch will remain closed; this might be of use for a single-use button or circuit. 
         [0042]    Although the switch has been described in the context of a medical device for neuromuscular stimulation, it will be apparent that its applicability is not so limited. In particular, the switch arrangement it ideally suited for low cost, disposable applications, in that there are relatively few moving parts, and the switch can be formed out of those components (casing, substrate, PCB) which will be used in an electronic device anyway. Further, the casing may be sealed to result in a largely waterproof device. The present inventors particularly envisage the switch as being of benefit in mobile telephones, watches, control panels, or keyboards, among others.