Abstract:
A handset having a keypad structure for inputting information is described. The keypad structure includes a keypad assembly having a plurality of keys being interconnected by a foil, the plurality of keys being provided with activation pins, a keypad base part having a switching device that is activated by an associated activation pin when a respective key is depressed, and a support device arranged in between the keypad assembly and the keypad base part supporting the foil of the keypad in between the keys.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The invention relates to a keypad structure for a communication terminal. In particular the keypad assembly has a plurality of keys being interconnected by a foil. The keys have activation pins cooperating with switching means whereby the switching means are closed when the respective key is depressed. 
     BACKGROUND OF THE INVENTION 
     This kind of keypads is very attractive because the manufacturing costs are low. However this kind of keypad has a drawback because the foil is very flexible but not extensible. Therefore the depression of one key will cause a movement of the neighbouring keys due to the stiffness of the foil when the key is pressed. Therefore the keypads will have a cheap appearance. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a support structure for a keypad. The structure shall allow use of a plastic film keypad with in-moulded keys without affecting the overall quality appearance. 
     This purpose is obtained by a keypad structure for a communication terminal comprising a keypad assembly having a plurality of keys being interconnected by a foil, said plurality of keys are provided with activation pins, a keypad base part having switching means being activated by an associated activation pin when a respective key is depressed, and support means arranged in between the keypad assembly and the keypad base part supporting the foil of the keypad in between the keys. Hereby the depression of one key will cause a sideways movement of the neighboring key due to the force applied to the foil when the key is pressed. The keys will extend through openings in the front cover and will therefore not move due to the sideways draw. Instead the draw in the foil will be absorbed by elastic deformation of the foil surrounding the intermoulded keys. 
     The invention furthermore relates to a handset having such a keypad. The cost of the keypad may therefore by reduced substantially without negatively affecting the feel and appearance. 
     According to the preferred embodiment keypad is used in a cellular phone having exchangeable covers. The keypad assembly is maintained in a sandwich structure in between the releasable front cover and an inner housing cover. The user will be allowed to handle the keypad when he changes the front cover and the foil cover is very robust and therefor very attractive in this situation. 
     Preferably the support means are formed as pins and support areas on the inner housing, and said pins and support areas are raised relatively to the surrounding part of the inner housing cover. The switching means may advantageously be provided as switches on a printed circuit on a Printed Circuit Board covered by a resilient metallic dome means, whereby the switches are closed when the metallic dome means are depressed by means of the depression of the associated key. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     For a better understanding of the present invention and to understand how the same may be brought into effect reference will now be made, by way of example only, to accompanying drawings, in which: 
     FIG. 1 illustrates a preferred embodiment of a hand portable phone according to the invention. 
     FIG. 2 schematically shows the essential parts of a telephone for communication with a cellular or cordless network. 
     FIG. 3 shows in exploded view the individual parts of the phone shown in FIG.  1 . 
     FIGS. 4 and 5 shows how the light guide and the front cover shell are assembled in the phone shown in FIG.  1 . 
     FIG. 6 shows in perspective the keymat assembly of the phone shown in FIG.  1 . 
     FIG. 7 shows a rear view of the keymat assembly shown in FIG.  6 . 
     FIG. 8 shows a cross section of the keymat assembly along the line VIII—VIII in FIG.  7 . 
     FIG. 9 shows schematically a cross section view of the keymat structure according to a preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a preferred embodiment of a phone according to the invention, and it will be seen that the phone, which is generally designated by  1 , comprises a user interface having a keypad  2 , a display  3 , an on/off button  4  FIG.  3 ), a speaker  5  (only openings are shown in FIG.  1 ), and a microphone  6  (only openings are shown in FIG.  1 ). The phone  1  according to the preferred embodiment is adapted for communication via a cellular network, but could have been designed for a cordless network as well. 
     According to the preferred embodiment the keypad  2  has a first group  7  of keys as alphanumeric keys, a soft key  8 , and a navigation key  10 . Furthermore the keypad includes a “clear” key  9 . The present functionality of the soft key  8  is shown in separate fields in the display  3  just above the key  8 . This key layout is characteristic of the Nokia 311™ phone and the Nokia 511™ phone. 
     The phone  1  has an inner housing of which gripping areas  23  are visible. An exchangeable front cover  21  and rear cover  22  are snapped onto the inner housing. 
     FIG. 2 schematically shows the most important parts of a preferred embodiment of the phone, said parts being essential to the understanding of the invention. The preferred embodiment of the phone of the invention is adapted for use in connection with the GSM 900 MHz and GSM 1800 MHz network, but, of course, the invention may also be applied in connection with other phone networks. The processor  18  controls the communication with the network via the transmitter/receiver circuit  19  and an antenna  20  that will be discussed in details below. 
     The microphone  6  transforms the user&#39;s speech into analog signals formed thereby are A/D converted in an A/D converter (not shown) before the speech is encoded in an audio part  14 . The encoded speech signal is transferred to the processor  18 , which i.a. supports the GSM terminal software. The processor  18  also forms the interface to the peripheral units of the apparatus, including a RAM memory  17   a  and a Flash ROM memory  17   b , a SIM card  16 , the display  3  and the keypad  2  (as well as data, power supply, etc.). The audio part  14  speech-decodes the signal, which is transferred from the processor  18  to the earpiece  5  via a D/A converter (not shown). 
     The Preferred Mechanical Concept 
     The individual parts of the phone are shown in exploded view FIG. 3. A bezel assembly  101  is adhered to the front cover shell  104  by means of a double-sided adhesive tape  102 . A speaker net  103  is sandwiched in between the bezel assembly  101  and the front cover shell  104 . A speaker gasket  105  and a dust seal  106  for the display are glued to the inner surface of the front cover shell  104 . This assembly is named as the front cover  21  in FIG.  1 . 
     A keymat assembly  107  constitutes the keypad  2  in FIG.  1 . 
     A release button  126  is snapped into a rear cover shell  125  and a logo label is glued onto the rear side of the rear cover shell  125 . This assembly is named as the rear cover  22  in FIG.  1 . 
     The phone  1  has a replaceable battery pack  124  that can be replaced when the rear cover  22  is removed from the phone. 
     The display assembly will be described in the following. The rear side of a light guide  113  is coated with a reflector  114  and an LCD module  110  is adhered to the front side of the light guide  113  by means of two LCD adhesive strips  112 . A display frame  109  is mounted on the front side of the LCD module  110  and a zebra strip (connector)  111  connects the complete display assembly  128  (FIG. 5) to a Printed Circuit Board  118  of the Phone  1 . 
     A multi gasket  115  for carrying a speaker unit  116  and a not shown buzzer is mounted in a front cover  108  of an inner housing. Then the display assembly is placed in the front cover  108 . A dome sheet  117  is inserted in between the Printed Circuit Board  118  carrying the electrical components of the phone and the rear side of the light guide  113 . Finally a bottom connector  119  is positioned and a metallic rear cover  120  of the inner housing by means of four screws  123  closes the front cover shell  108  of the inner housing. A SIM gate  121  is mounted on the rear cover  120  prior to the final assembly. An internal antenna  122  is snapped onto the assembled inner housing. 
     The essential purpose of the dome sheet  117  is to transform the movement of the key  7 - 10  into an elastically switching connection on the Printed Circuit Board  118 . Furthermore the dome sheet  117  gives a tactile feeling when the keys  7 - 10  is pressed. In addition to this the dome sheet  117  acts as reflector for the light guide in order to provide back light for the keys  7 - 10 . According to the preferred embodiment the dome sheet is provide as a 0.055 mm thick white polyester film adhered to a 0.085 mm thick wax coated paper sheet (for insulation). The domes have a diameter of 5.5 mm and are made of stainless steel and have a center pin underneath for better contact to the switching circuit on the Printed Circuit Board  118 . When a key is pressed the center pin closes a contact by short-circuiting two terminals. This is state of the art and no further description is needed for a man skilled in the art in order to understand the inventive concept. 
     In FIGS. 4 and 5 it is shown how the light guide  113  and the front cover shell  108  are assembled in order to support the keymat assembly  107 . It is seen that the light guide  113  and the front cover shell  108  has a plurality of holes  133  and  134  through which activation pins from the keypad assembly extends for cooperation with the domes of the dome sheet  117 . The light guide  113  has a cover part  129  constituting a part of the front surface of the inner housing when assembled. This cover part  129  carries some pins  130  supporting the keymat assembly  107  when a key is pressed. The front surface of the front cover shell  104  has some semi-spherical raised portions  131  to support the keymat assembly  107  between the keys  8 - 10 , and some rails  132  supporting the periphery of the keymat assembly  107 . The height and the diameter of the pins  130  is approximately 0.9 mm. The distance between two pins  130  through the center of a key is approximately 19 mm. 
     The keymat assembly  107  is shown in detail in FIG. 6 and 7. The keymat assembly  107  has four flaps  137  for being snapped into a recess in the front cover  21 . Furthermore the keymat assembly  107  has a hole  138  for receiving a guiding pin (not shown) extending from the front cover  21 . In FIG. 8 in-moulded bodies  135  are marked by dotted lines. When the foil and the in-mould bodies are produced by the same material the two parts of the keymat will be well integrated and the dotted lines mark only the change in the thickness of the material. Pins  139  expand from the in-mould bodies  135 . 
     FIG. 8 shows a cross section along the line VIII—VIII in FIG.  7 . Two keys  141  are visible and the foil  145  connecting the two keys  145  is clearly illustrated. Furthermore it is seen how pins  139  extend from the main body of the key  145 . The pin  139  has a bore  140  in order to establish a ring shaped contact with the domes  142  of the dome sheet  117  as seen in FIG.  9 . The domes  142  have contact pins  143  facing towards the metallic pads (illustrated with the referral number  144 ) on the Printed Circuit Board  118 . 
     When one key  141  is pressed the support pin  130  transfers the force (FIG. 9; arrow a) in the pressing direction into a lateral force (FIG. 9; arrow b), and the key holes in the front cover  104  transfers this lateral force into an elastically deformation of the key parts  150  shown in FIGS. 8 and 9. 
     The support means may have any appropriate form according to the invention. However the support means have to support the keymat foil in a distance from the keys corresponding to preferably 2-3 times the the thickness of the keymat foil. Preferably the in-mould resin material is a PC (Poly Carbonate) blend. The foil or film is a 0.125 mm PC sheet with matt texture (e.g. Baybol from Bayer).