Abstract:
A hinge position sensor comprises first and second members connected together to provide a hinge, and an optical fiber or wave-guide connected between the first and second members to provide a communication link between the first and second members. A laser or LED is coupled to the optical fiber or wave-guide to transmit optical signals between the first and second members and the optical signal is received by a photo-detector. The optical fiber or wave-guide is physically distorted by actuation of the hinge such that light escapes from the optical fiber or wave-guide. The optical power level received by the photo-detector is used to determine the position of the hinge.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an optical position sensor, particularly, but not exclusively, to a fibre optic position sensor for sensing the position of a hinged lid of a portable electronic device such as a mobile telephone or a lap-top computer. 
     BACKGROUND TO THE INVENTION 
     It is common for a portable electronic device such as a lap-top computer or a mobile telephone to comprise a base, which includes the device&#39;s keypad, and a lid, which includes the device&#39;s screen or user display. In this type of device, the base and the lid are connected together by a hinge section such that the user display can be hinged to lie flat against the keypad when the device is not in use. By detecting when the hinge is closed, the device is able to detect when it may safely switch to a power-saving mode. This function allows the device to conserve battery power when the device is not in use. 
     It is known to detect the open/closed state of this type of hinge using a mechanical sensor, such as a boss-type media detection switch or a rotary-type position detection switch. However, the use of a mechanical sensor often imposes design constraints on the electronic device and may also require that bosses be fitted to the device&#39;s exterior. A mechanical sensor often also requires extra space on the motherboard of the device for the inclusion of a detector switch. 
     Alternatively, the position of the hinge may be detected using a solid-state relay. For example, it is known to magnetically detect the position of a lid with a system employing a Hall Integrated Circuit. However, this type of detector requires both space on the motherboard of the device and a level of standby power. In addition, magnetic switches of this type are liable to interfere with other types of sensor which may be integrated into the device, such as those employed by global positioning systems. 
     The use of optical proximity sensors is also known. However the surfaces of a proximity sensor&#39;s emitter and receiver must be kept clean in order for the sensor to function reliably. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a hinge-position detection apparatus comprising a first member and a second member rotationally connected to one another so as to provide a hinge, a first optical fibre, a light emitter to transmit light through the optical fibre and a light detector to detect a power level of light emitted from the optical fibre, wherein the optical fibre is physically distorted by actuation of the hinge and the detected power level is used to determine the position of the hinge. 
     Preferably, a physical distortion in the optical fibre causes light to escape from the optical fibre and affects the optical power level detected by the light detector. 
     Preferably, the optical fibre is connected between the first member and the second member so as to traverse the hinge. 
     Preferably, the determined position of the hinge is used to control the operation of an electronic device. 
     More preferably, if the hinge is determined to be in a closed position, the apparatus is configured to switch one or more components of an electronic device to a power saving mode. 
     Preferably, the hinge is determined to be in a closed position if the detected optical power level reaches a predetermined threshold level. 
     Preferably, the light emitter is included in the first member, the light detector is included in the second member and the optical fibre is coupled between the light emitter and the light detector. 
     Preferably, the light detector is positioned to directly detect the emission of light from the optical fibre, the emission of light being caused by a physical distortion in the fibre. 
     More preferably, the apparatus includes a further optical fibre operable to direct the emission of light from the optical fibre to the detector. 
     Preferably, the light emitter comprises an LED or a laser, and the light detector comprises a photo-sensitive device, such as a photo-diode, photo-transistor or photo-resistor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In order that the invention may be more fully understood, embodiments thereof will now be described by way of illustrative example with reference to the accompanying drawings in which: 
         FIG. 1  is an illustration of a mobile telephone handset comprising a base and a lid connected together by a hinge joint. 
         FIG. 2  is a block diagram illustrating components of the handset shown in  FIG. 1 . 
         FIG. 3  is cross-sectional illustration of an optical fibre traversing the hinge joint of the handset. 
         FIG. 4  is a cross-sectional illustration showing the coupling of the optical fibre between a laser and photo-diode. 
         FIG. 5  is a cross-sectional illustration showing the escape of light from the optical fibre. 
         FIG. 6  is an illustration of the direct detection of light escaping from the optical fibre. 
         FIG. 7  is an illustration showing the direct detection of light escaping from the optical fibre via a second optical fibre. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a hinge position detection apparatus is part of a mobile telephone handset  11 . The mobile telephone handset  11  comprises a first member in the form of a base  12  and a second member in the form of a lid  13 . The base  12  and lid  13  are connected together by a hinge joint  14 , allowing the handset  11  to be movable between a closed position and an open position. 
     The telephone handset  11  is configured to operate in a cellular radio network, such as a GSM network, although it could be configured for use with other networks such as a 3G network or I-mode. 
     The telephone handset  11  is provided with a user display  15 , for example in the form of a liquid crystal display (LCD) panel. The handset  11  is additionally provided with a loudspeaker  16 , which is located in the lid  13  and is on the same surface as the user display  15 . The base  12  of the handset  11  houses the remainder of the telephone&#39;s principal components, including a keypad  17 . 
     The keypad  17  is located on the surface of the base  12  such that, when the hinge joint  14  is in the closed position, the keypad  17  directly faces the user display  15 . Thus, the user display  15  and keypad  17  are not visible to the user when the hinge  14  is closed. An antenna  18  is located inside the base  12  such that it does not form part of the handset&#39;s exterior. 
     Referring to  FIG. 2 , in addition to the user display  15 , the loudspeaker  16 , the keypad  17  and the antenna  18 , the handset  11  comprises a microphone  21 , a SIM card  22 , a SIM card reader  23 , amplifiers  24  and  25 , an rf subsystem  26 , a codec  27 , a micro-controller  28  and a memory  29 . 
     The rf subsystem  26  contains the circuits of the telephone&#39;s transmitter and receiver. The rf subsystem  26  is coupled to the antenna  18  for the reception and transmission of radio signals in a cellular mobile network. 
     The antenna  18  is connected through the rf subsystem  26  to the codec  27 , which is configured to process signals under the control of the micro-controller  28 . 
     The micro-controller  28  operates according to a program stored in the memory  29  and controls the operation of the handset  11 . It is coupled to the rf subsystem  26  for supplying tuning instructions to a frequency synthesizer. 
     The user display  15  is connected to the micro-controller  28  for receiving control data and the keypad  17  is connected to the micro-controller  28  for supplying user input data. In  FIG. 2 , the memory  29  is shown separately from the micro-controller  28 . However, the memory  29  and the controller  28  may also be included together in an integrated unit. 
     The amplifier  24  amplifies demodulated audio from the codec  27  and applies it to the loudspeaker  16 . Acoustic signals, detected by the microphone  21 , are pre-amplified by the amplifier  25  and sent to the codec  27  for coding. 
     Information concerning the identity of the user is held on the smart card  22  in the form of a GSM SIM card which contains the usual GSM international mobile subscriber identity (IMSI) and an encryption key K i  that is used for encoding the radio transmission in a manner that is well known. The SIM card is removably received in the SIM card reader  23 . 
     Referring to  FIG. 3 , the handset  11  further comprises an optical wave-guide, for example an optical fibre  31 , which is connected between the base  12  and the lid  13  via the hinge joint  14 . The optical fibre  31  is connected so as to provide a transmission medium for optical communication between electronic circuits located in the base  12  and the lid  13 . 
     Referring to  FIG. 4 , the base  12  of the handset  11  further includes a light emitter, for example a laser  41 , which is adapted to emit red laser light in the wavelength range 630-670 nanometres. However, other suitable wavelengths could also be used. The laser  41  is coupled to the base-end of the optical fibre  31  and, as such, light emitted from the laser  41  enters the optical fibre  31  and is transmitted to the lid  13 . The term “light” is used herein to mean electromagnetic radiation in the visible, infra-red and ultraviolet spectrum. 
     The optical fibre  31  comprises a central core  31   a  surrounded by a cladding layer  31   b . The refractive index of the core  31   a  is of a different refractive index to that of the cladding  31   b , meaning that light is confined to the core  31   a  by total internal reflection and is guided along the optical fibre  31 . The optical fibre  31  may be either a graded optical fibre or a step-index optical fibre. The light transmitted through the optical fibre  31  may carry, for example, signals for controlling the operation of the user display  15  or loudspeaker  16 . Alternatively, light transmitted through the optical fibre  31  may comprise control data for illumination at the lid side of the handset  11 . In an alternative embodiment, the laser  41  could be replaced by a light-emitted diode (LED). 
     Further referring to  FIG. 4 , the lid  13  of the handset  11  includes a light detector, for example a photo-diode  42 , which is coupled to the lid-end of the optical fibre  31 . The photo-diode  42  is adapted to detect light transmitted through the fibre  31  from the laser  41  and is coupled to electronic circuits located in the lid  13  of the handset  11 . Alternatively, instead of the photo-diode  42 , the handset may comprise another type of photo-sensitive device such as a photo-transistor or photo-resistor. 
     The optical fibre  31  is fabricated from suitable plastics and is flexible in such a way that it is able to bend with the hinge joint  14  of the telephone handset  11 . The use of plastics allows the optical fibre  31  to be adapted such that it may be bent to a very small radius. This is convenient as the optical fibre  31  should be able to comfortably bend to a radius enabling it to traverse the hinge joint  14  when the handset  11  in the closed position. The use of plastics also provides advantages in terms of transmission speed and is inexpensive in comparison to alternative materials. However, it will be appreciated that materials other than plastics can be used. 
     Referring to  FIG. 5 , as the optical fibre  31  is bent to the a radius enabling it to traverse the hinge joint  14  in the closed position of the handset  11 , some of the light being transmitted through the fibre  31  does not meet the conditions for total internal reflection within the fibre  31  at the bend. The light which does not meet the conditions for total internal reflection escapes from the fibre  31 , as illustrated schematically in  FIG. 5  by arrows A. In consequence, the light not meeting the conditions for total internal reflection is not detected by the photo-diode  42 . As the radius of the bend decreases, as the lid  13  is hinged to the closed position on the base  12 , the amount of light escaping from the optical fibre  31  increases. Accordingly, for an optical signal of constant power transmitted from the laser  41 , the optical power detected by the photo-diode  42  is a function of the radius of the bend in the optical fibre  31  and, therefore, is also a function of the position of the hinge joint  14 . 
     The optical power detected at the photodiode  42  can be used to calculate the position of the hinge joint  14 . Information concerning the position of the hinge joint  14  may then be processed to determine whether the handset  11  is open or closed and, accordingly, may be used to control the operational mode of the handset  11 . 
     As shown in  FIG. 3 , the laser  41  and the photo-diode  42  are coupled to the controller  28 , which is adapted to control the operational mode of the components of the handset  11  in dependence of the optical power level detected by the photo-diode  42 . These components may include, for example, the user display  15  and loudspeaker  16 . Accordingly, if the optical power level detected by the photo-diode  42  falls below a predetermined threshold, the handset is determined to be closed and the operational mode of the lid  13  is switched to a power-saving mode. Alternatively, the optical power level may be used to monitor the precise angle of the hinge and may be used for more complex control of the handset  11 . 
     In an alternative embodiment, the laser  41  is comprised as part of the lid  13  and is coupled to the lid-end of the optical fibre  31 . In this embodiment, the photo-diode  42  is comprised as part of the base and is coupled to the base-end of the optical fibre  31 . Light transmitted through the optical fibre  31  may carry control signals for controlling the operation of the handset  11 . The user display  15  may be a touch-sensitive display and may be operated by a user to select menu options from the display for operating the handset  11 . Accordingly, the control signals transmitted through the optical fibre  31  may comprise, for example, information concerning a menu option selected by a user touching the display  15 . This information may then be relayed to the micro-controller  28  and used for controlling the operation of the handset  11 . 
     The photo-diode  42  is configured to detect the optical power received from the laser  41 . Information concerning the optical power level detected at the base-end of the optical fibre  31  by the photo-diode  42  is supplied to the micro-controller  28  for controlling the operational mode of the handset  11 . If the detected optical power level falls below the predetermined threshold value previously described, the handset  11  is determined to be closed and the micro-controller  28  switches the operational mode of the handset  11  to a power-saving mode. Alternatively, optical power level information supplied by the photo-diode  42  may be processed to control the operation of one or more components of the handset  11  directly. 
     Therefore, the optical power level detected by the photo-diode  42  is compared against a predetermined threshold value in order to determine whether the handset  11  is in the open or closed position. If the handset  11  is determined by the hinge-position detection apparatus to be in a closed position, the components of the handset  11  are configured to operate in a power saving mode. The handset  11  is thus able to increase the efficiency of its use of power and, accordingly, is able extend the standby time provided by a single charge of its battery (not shown). 
     Referring to  FIG. 6 , in an alternative embodiment, a second light detector, for example a second photodiode  61 , is located in the hinge joint  14  of the handset  11  to detect light escaping from the optical fibre  31 . The second photodiode  61  is positioned in the area of maximum light emission from the bend in the optical fibre  31  to maximise the efficiency of detection of the light escaping from the fibre  31 . 
     The second photodiode  61  is coupled to the micro-controller  28  such that information concerning the power of the optical light escaping from the fibre  31  may be relayed back to the controller  28  and processed to determine whether the handset  11  is in the open or closed position. Alternatively, the photodiode  61  may be configured to communicate the detected power level back to the controller  28  by wireless means, for example via a Bluetooth connection. In contrast with the previously described embodiments of the invention, the optical power level detected by the photo-diode  61  is inversely proportional to the radius of the hinge joint  14 ; as the radius of the bend in the optical fibre  31  decreases, the optical power level detected by the photo-diode  61  increases. By sensing the emitted light directly, the apparatus is able minimise the effect of errors due to losses caused by temperature fluctuations and aging of the optical fibre  31 . In addition to determining whether the hinge joint  14  is open or closed, the relationship between the power level detected by the photo-diode  61  and the radius in the bend of the optical fibre  31  may be used to provide detailed information regarding the position of the hinge joint  14 . For example, the optical power level detected by the photo-diode  61  may be used for calculating the angle of the hinge joint  14 . 
     Alternatively, instead of the second photo-diode  61 , the handset may comprise a different type of photo-sensitive device such as a photo-transistor or photo-resistor. 
     The controller  28  processes the optical power level information supplied by the photo-diode  61  to control the operational mode of the handset  11 . If the optical power level detected by the photo-diode  61  increases above a predetermined threshold value, the handset  11  is determined to be closed and the micro-controller  28  switches the operational mode of the handset  11  to a power saving mode. Alternatively, the optical power level detected by the photo-diode  61  may be used to control the operational mode of one or more individual components of the handset  11  directly. 
     Referring to  FIG. 7 , in an alternative embodiment, the second photo-diode  61  is comprised as part of the base  12  of the handset  11  and a second optical wave-guide, for example a second optical fibre  71 , is positioned to receive light escaping from the bend in the first optical fibre  31  and to direct the light. Alternatively, instead of the second optical fibre  71 , the handset may comprise alternative means for directing the light. The alternative means may comprise, for example, a light pipe comprising a length of plastic without cladding in which the plastic/air interface confines light to the light pipe. The optical fibre  71 , optical wave-guide or light pipe may be used either with or without a light-collecting apparatus  72 , for example comprising lenses, for collecting light escaping from the optical fibre  31 . 
     The light inlet to the optical fibre  71  is positioned adjacent to the point of maximum emission of the first optical fibre  31  during bending thereof. The optical power level detected by the photo-diode  61  is used, either by the controller  28  or directly, to control the operational mode of the handset  11 . If the optical power level detected by the photo-diode  61  increases above a predetermined threshold, the handset  11  is determined to be closed and the handset  11  is switched to a power saving mode. 
     The inclusion of the second optical fibre  71  provides more flexibility in the design of the handset  11  as the position of the second photo-diode  61  is not dictated by the position of maximum light emission from the first optical fibre  31 . Accordingly, the photo-diode  61  may be positioned at a convenient position in the base  12  of the handset  11 . Alternatively, the photo-diode  61  may be positioned in the lid  13  of the handset  11 . 
     The optical fibre  31  may be surrounded by a protective jacket (not shown). In the described embodiments where light escaping from the bend in the fibre  31  is detected directly, if an LED is used instead of the laser  41 , the jacket is removed at the point of maximum emission in order to allow the photo-diode  61  to detect the power level of the light escaping from the fibre  31 . However, if the laser  41  is used as described, the protective jacket may be adapted such that the laser light is partially transmitted through the jacket. In this case, there is no need to remove the jacket in order for the photo-diode  61  to detect the light. 
     The control of the operational mode of the handset  11  has been described as being dependent on a detected power level of light at a photo-diode. However, the control of the handset could equally be dependent on a calculated signal-loss. 
     The implementation of the described hinge position detection apparatus involves minimal adaptation of the hardware of the handset  11 . The components used for detection of the hinge&#39;s position are largely already present in many otherwise conventional mobile telephone handsets. Furthermore, apart from the optical fibre  31 , no moving parts are used and, thus, the hinge-position detection apparatus can be considered to be extremely reliable. The hinge-position detection apparatus is not sensitive to electric or magnetic fields and will also not interfere with surrounding equipment, for example a GPS system, making use of such fields. 
     The above-described embodiments and alternatives may be used either singly or in combination to achieve the effects provided by the hinge-position detection apparatus. Although the hinge-position detection apparatus has been described with reference to a mobile telephone handset  11 , the system is equally applicable to other types of electronic device which include a hinge section. These types of device include, for example, hand-held and lap-top computers, hand-held video games and personal digital assistants.