Abstract:
An input organ, being provided with means for detecting the touch of a fingertip, where said organ is provided with means for providing a tactile feedback to said fingertip to acknowledge an activation of said input organ, and where said means for providing a tactile feedback comprises an elongate object of shape memory metal.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of manually operable input organs or manoeuvre organs, such as keys, keyboards and touch sensors. In particular, it relates to such organs provided with means for providing a tactile feedback when activated. 
       STATE OF THE ART 
       [0002]    Keyboards for electronic devices, such as mobile phones etc, come in a wide variety. The keyboard forms part of the so called Man Machine Interface of the electronic device. It is an object of the present invention to develop better and/or more cost efficient keys, keyboards and touch sensors. 
         [0003]    Today many keyboards deliver a certain feel or sensation when a key is depressed. The response to the depressing action is often also accompanied with a click-sound or other sound to acknowledge the depressing. However, new and different methods to provide a user with feedback could give the manufacturer advantages on the market. 
       SUMMARY OF THE INVENTION 
       [0004]    It should be emphasised that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, elements, integers, steps, components or groups thereof. 
         [0005]    Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments. 
         [0006]    In the present invention, the problem of providing feedback from a touch sensor is solved by providing a touch surface of the touch sensor with a mechanical coupling to a so called muscle wire, which is a piece of memory metal, and means for activating the muscle wire when the touch sensor is touched, thereby creating a tactile feedback. 
         [0007]    According to one aspect of the present invention an input organ is provided, having means for detecting the touch of a fingertip, where said organ is provided with means for providing a tactile feedback to said fingertip to acknowledge an activation of said input organ, and where said means for providing a tactile feedback comprises a muscle wire. 
         [0008]    According to another aspect an input organ is provided, where a muscle wire is arranged to be energised when said organ is touched by a fingertip to such an extent that said wire contracts and mechanical energy resulting from said contraction is mediated to a touch surface of said input organ, arranged to make contact with said fingertip. Within this input organ, the muscle wire is arranged to convey a motion directed towards the fingertip. The input organ may also comprise a first and a second muscle wire, independently controllable, where the first muscle wire is arranged to convey mechanical energy as a motion via said touch surface towards the finger tip, and the second muscle wire is arranged to convey a motion of said touch surface away from said fingertip. The conveying of a motion is preferably achieved by arranging the first wire under and parallel to the touch surface and as a taut string between two supports and letting a key stem contacting the wire approximately at the middle of its length, conveying the increased tension in the muscle wire to the key stem, as would a bowstring to an arrow, and further to the touch surface. 
         [0009]    According to another aspect an input organ is provided, where a touch sensor is connected to a touch determination device for deciding when the input organ is touched, the touch determination device is further connected to an input of, and provides control signals to, a muscle wire heating unit having an output connected to the muscle wire for providing suitable heating current to the muscle wire. 
         [0010]    According to yet another aspect an input organ is provided where tactile feedback in the form of mechanical energy is mediated to a touch surface of said input organ as a mechanical energy selected from a tactile feedback patterns group consisting of: one short twitch, two or more short twitches, vibration of one or different frequencies, and vibration of rising and falling amplitude, and combinations thereof. 
         [0011]    According to another aspect a device is provided controlled from a keypad provided with tactile feedback where different events resulting from pressing the keypad give rise to different tactile feedback patterns. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention will be described in detail below with reference to the accompanying drawings, in which: 
           [0013]      FIG. 1  shows a key mechanically coupled to a muscle wire, according to one embodiment of the invention, 
           [0014]      FIG. 2  shows the key of  FIG. 1  arranged to close a switch, 
           [0015]      FIG. 3  shows a key mechanically coupled to two muscle wires according to another embodiment of the invention, 
           [0016]      FIG. 4  shows a touch sensor mechanically coupled to two muscle wires, 
           [0017]      FIG. 5   a  shows a cross sectional view of a touch sensible device according to yet another embodiment of the invention, 
           [0018]      FIG. 5   b  shows the touch sensible device of  FIG. 5   a,  in a view from below. 
           [0019]      FIG. 6  shows a general view of a keypad with muscle wire activated tactile feedback. 
           [0020]      FIG. 7  is a general diagram of a driving circuitry for a touch sensor with tactile feedback, and 
           [0021]      FIG. 8  is a flowchart describing a method for activating a touch sensor with tactile feedback. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0022]    Definition 
         [0023]    In this application the term muscle wire is used to denote an elongate object of shape memory metal, e.g. nickel-titanium alloy. Trademarks are Nitinol or Flexinol. 
         [0024]      FIG. 1  shows a key device  100  with a key  101  having a key stem  105  with a pin  110  sticking out from said stem, and a muscle wire  125  arranged between two attachment point  120 ,  115 , which attachment points also serve as electrical feeding points “+”, “−” for said muscle wire  125 . The muscle wire is arranged to run under the pin  110  of the key stem  105 , such that when the muscle wire contracts, as a result of an electrical current warming it up, the pin  110  is mechanically forced upwards, bringing the key stem  105  and key  101  with it, such that this in this way conveyed mechanical energy, is perceived as a sensation by the sense of touch of a finger tip  135  of a finger  130  of an operator. 
         [0025]      FIG. 2  shows the key device of  FIG. 1  further showing a mechanical switch  140  arranged to be engaged by the key stem  105  when the key  101  is depressed. 
         [0026]      FIG. 3  shows a key device with a key  301  mechanically coupled to two muscle wires  325 ,  327 . A key stem is provide with a pin approximately half way between a key end of said stem and attached to the key, and a far end  330  of said key stem  305  making contact with an object “C”, which “C” is a membrane which act both as an electrical switch and as membrane providing springback and/or resilient functionality to the key. 
         [0027]    A first muscle wire  325  is arranged between a first attachment point  320  and a second attachment point  315  provided on each side of said key stem  305 , such that said first muscle wire  325  runs from the first attachment point  320 , under a pin  310  attached to the key stem  305 , such that when the muscle wire is energised, i.e. an electrical current is made to flow from a first connection point A through the first wire  325  to a second connection point “−”, the first muscle wire contracts and forces the key stem upwards. Simultaneously a second wire, arranged to run from a third attachment point  322  to the second attachment point  315  over the horizontal pint  310 , is mechanically forced to adopt a longer shape and length due to the movement of the horizontal pin  310 . 
         [0028]      FIG. 4  shows a touch sensor mechanically coupled to two muscle wires. A touch sensitive membrane C is provided with a rod  405 , in contact with or attached to the underside of the touch sensitive membrane C, said rod being provided with a pin or another suitable organ having a contact surface suitable for a muscle wire to make contact to. The pin is preferably electrically isolating. In the alternative, a first muscle wire  425  and/or a second muscle wire  427  is provided with an electrically isolating cover. Preferably the muscle wires are non-isolated to facilitate cooling of said wires, and the pin is manufactured of a non-conducting material or covered or coated with a non-conducting material of a heat proof kind such as e.g. Teflon. As is explained below the first and second wires do not contact each other physically, but they are preferably arranged in different planes having a distance between them. 
         [0029]    In the same way as described above, the first muscle wire is energised when the touch sensitive membrane is touched. This is achieved by means of an energising organ (not shown here but in  FIG. 6 ) activated by the touch. 
         [0030]      FIG. 5   a,  and  5   b  shows a touch sensible device according to another embodiment of the invention. Here, supporting structures  545 ,  550  can be seen, supporting a key  501  with a key stem  505  and a pin  510 . A membrane or spring “C” provides a force upwards such that the key do not assume an undefined position when both muscle wires  525 ,  527  are in a non-active state, i.e., not energized. The spring “C” is provided under the key  501 , pressable between the key  501  and lower horizontal portions  551 ,  546  of the supporting structures  550 ,  545 . An electrical switch (not shown) is arranged to be engaged by the key  501 , the key stem  505  or the pin  510 . A preferred arrangement of the switch is under the key stem as shown in  FIG. 2 . 
         [0031]      FIG. 5   b  shows the device of  FIG. 5   a  from below. The key have a circular shape, i.e., the supporting structures  550 ,  545  are really the same structure. They do not connect in  FIG. 5   a  because  FIG. 5   a  shows a cross sectional view of the device. The muscle wires cross but do not contact each other because they are separated sideways as seen in  FIG. 5   b.  The pin  510  extends through a bore in the key stem  510 , or a pin can be arranged on each side of the key stem  512 , to provide suitable structures for muscle wires  525 ,  527  to engage. 
         [0032]    A first muscle wire  527  is arranged to run from a first attachment point A arranged at a first support structure (not shown here) below a first horizontal plane, the wire passing an upper bound  512  of the pin  510 , making contact to said upper bound  512  of said pin  510 , and the wire ending at a second attachment point  560  arranged at an opposite second support structure(not shown here) which second attachment point also is arranged below the first horizontal plane being tangent to the upper bound of the pin. The key stem being arranged between said first and second support structures. 
         [0033]    Correspondingly, a second muscle wire  525  is arranged to run from a third attachment point B arranged higher or over a second horizontal plane, which plane being tangent to a lower bound  513  of the pin  510 . The wire  525  further running under the pin, making contact to said lower bound  513 , and further to a fourth attachment point  561  also arranged higher than said second horizontal plane but opposite to the third attachment point B. 
         [0034]    The first attachment point may be equivalent to a first electrode A, capable of supplying the first muscle wire  527  with a first electrical current running from the first electrode A, through the first muscle wire  527  and to a second electrode “−” housing both the second and fourth attachment points  560 ,  561 . The third attachment point may be equivalent with a third electrode B. 
         [0035]      FIG. 6  schematically illustrates that a muscle wire unit  602  is provided to equip a keypad  606  with a single tactile feedback device according to the embodiment of  FIG. 5 . A complete continuous keypad can be activated by a single muscle wire device. The muscle wires provides a snap feeling, or a pluck feeling to the fingers in contact with the keypad  606 , and because the a user only depresses one single button, he or she will associate the feeling to that particular button. The muscle wires are preferably arranged to engage the keypad at its center, in this particular case close to the key “8”. Here, the keypad  606  may be of conventional type with electrical switches for each key, but it may also be a panel with touch sensors, or a display with touch sensors. 
         [0036]      FIG. 7  schematically shows how a muscle wire  720  is driven by muscle wire driving circuitry in a touch sensor with tactile feedback. A touch sensor  701  is connected to a touch determination device  705  in the form of a micro program controller  705  such that the micro program controller  705  receives an input signal from the touch sensor  701  when the touch sensor is touched. The micro program controller  705  is connected to a display for controlling the display based on the input signal. The micro program controller is also connected to a muscle wire heating unit in the form of an amplifier  715  for providing suitable voltage for controlling the activation of the muscle wire  720 . 
         [0037]    The micro program controller is provided with means for controlling the power and current to the muscle wire  720  such that a distinct tactile feedback is produced, see also below. 
         [0038]    The muscle wire is fabricated from a material that changes shape or size when the material is heated beyond a particular temperature. The particular temperature needed to change the shape/size depends on the particular material. In one implementation, muscle wire  720  may be made of an alloy that is designed to contract (i.e. a fixed length becomes shorter) when the wire  720  is heated beyond a threshold temperature. In addition, the alloy may be fabricated to have poor conductivity (e.g. have resistive characteristics). In this manner, when power is applied to wire  720 , the wire becomes heated beyond the threshold temperature, thereby causing wire  720  to contract. In an exemplary implementation, wire  720  may include alloys made from nickel and titanium that are known as “muscle wire” or “memory alloy”. For example, wire  720  may be fabricated using NITINOL, FLEXINOL or similar materials. 
         [0039]    Wire  720 , consistent with the invention, may contract about 3% to 5% when heated beyond the threshold temperature. In an exemplary implementation, the threshold temperature may range from about 88 to 98 degrees Celsius. The wire  720 , consistent with the invention, may also relax (i.e. return to the pre-heated state) at a temperature ranging from about 62 degrees to 72 degrees Celsius. 
         [0040]    The table below illustrates exemplary characteristics of wire  720  that may be used in implementations consistent with the invention. 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Wire diameter (millimeters) 
                 0.05 
                 0.125 
               
               
                   
                 Resistance (ohms/meter) 
                 510 
                 70 
               
               
                   
                 Typical power (watts/meter) 
                 1.28 
                 4.4 
               
               
                   
                 Contraction speed at typical power (seconds) 
                 1 
                 1 
               
               
                   
                 Maximum recovery force (grams) 
                 117 
                 736 
               
               
                   
                 Deformation force (grams) 
                 8 
                 43 
               
               
                   
                 Heat capacity (Joules/g) 
                 0.32 
                 0.32 
               
               
                   
                   
               
             
          
         
       
     
         [0041]    In a typical application, the electrical energy fed to a muscle wire is a pulse of amplitude 5 Volts, a current of 300 mA during 70 ms. 
         [0042]    The muscle wires in this application are preferably arranged to accomplish a suitable mechanical bias tension, such that taut wires are accomplished. This will facilitate fast reaction times of the tactile feedback. 
         [0043]    Also provided is a method for providing a tactile feedback of a touch sensor, the method comprising the steps of:
       Receiving an indication that a touch sensor is touched.   Providing, based on said indication, a signal for activating a muscle wire mechanically connected to the touch sensor for providing a mechanical influence on said touch sensor serving as a tactile feedback.       
 
         [0046]    Said mechanical influence may be a short twitch, i.e. a short mechanical pulse of 30-140 ms, resulting in a motion of whole of or part of the touch sensor surface of approximately 0.2-0.4 mm. Other suitable tactile feedback patterns may include two or more short twitches, vibration of one or different frequencies, and vibration of rising and falling amplitude. 
         [0047]    A device controlled from a keypad provided with tactile feedback according to the present invention may for example be a mobile station. Different events resulting from pressing the keypad may give rise to different tactile feedback patterns swiftly alerting the user of the equipment in question, of the result of a key being pressed. These mechanical patterns are controlled by feeding the muscle wires with appropriately varying voltages, causing the wires to heat up and contract in a way corresponding to the heating effect of the electrical current passing through the wire. Electrical current fed to the wire for causing a mechanical frequency may be an electrical current having alternating on and off periods corresponding to the desired frequency. A single twitch is generated by a single pulse.