Patent Publication Number: US-2023160763-A1

Title: Pressure sensor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Chinese Utility Model number 2020 20671744.7, filed on 24 Apr. 2020, the whole contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a pressure sensor, and a key structure including a pressure sensor. 
     Existing pressure sensors are generally made of polymers and flexible substrates. However, after the pressure is removed, the response speed is slow due to the viscoelasticity of the polymers and flexible substrates, and it takes a certain time to return to the original position. Obvious creep and hysteresis are generated, and therefore, the sensitivity and the reliability of the pressure sensor are low. 
     BRIEF SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a pressure sensor, characterized in that it comprises: a base layer, a supporting structure arranged on the base layer, an elastic layer disposed above the base layer and the supporting structure, having a curved lower surface that is recessed away from the base layer, wherein the curved lower surface, the supporting structure and the base layer define a cavity with an arched top wall, a first electrode, a second electrode, and an elastic body, all arranged within the cavity, such that when the elastic layer is elastically deformed in the direction of the base layer, the elastic body electrically connects the first electrode with the second electrode, so as to generate a first signal related to the elastic deformation of the elastic body. 
     By designing the elastic layer in the pressure sensor to be curved in the direction away from the base layer, the stiffness of the elastic layer can be increased, thereby solving the problem that the existing pressure sensor needs a certain time after the pressure is removed. The problem of low sensitivity and reliability brought about by restoring to the original position improves the efficiency of elastic layer rebound, thereby improving the sensitivity and reliability of the pressure sensor. 
     According to a second aspect of the present invention, there is provided a button structure comprising a pressure sensor of the aforementioned type and a pressing mechanism, said pressing mechanism comprising a pressing portion arranged above the elastic layer and above the cavity, wherein the pressing portion is configured to be depressed by manual action, such that the pressing portion engages with the elastic layer to move it towards the base layer. 
     According to a third aspect of the present invention, there is provided an apparatus comprising either a pressure sensor or a button structure of the aforementioned type, and a processor connected to the electrodes of the pressure sensor, wherein the processor is configured to generate the first signal related to the amount of elastic deformation of the elastic body when the electrodes are connected through the elastic body. 
     According to a fourth aspect of the present invention, there is provided a method of generating a key press signal, comprising the steps of: obtaining a pressure sensor comprising a base layer, a supporting structure arranged on the base layer, an elastic layer disposed above the base layer and the supporting structure, having a curved lower surface that is recessed away from the base layer, wherein the curved lower surface, the supporting structure and the base layer define a cavity with an arched top wall, and a first electrode, a second electrode, and a variable resistance elastic body, all arranged within the cavity; applying a force to the elastic layer to move the elastic layer towards the base layer; compressing the variable resistance elastic body in response to the force; and contacting the first and second electrodes to generate a signal in response to elastic deformation of the variable resistance elastic body. 
     Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings. The detailed embodiments show the best mode known to the inventor and provide support for the invention as claimed. However, they are only exemplary and should not be used to interpret or limit the scope of the claims. Their purpose is to provide a teaching to those skilled in the art. Components and processes distinguished by ordinal phrases such as “first” and “second” do not necessarily define an order or ranking of any sort. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG.  1    illustrates a computer and keyboard in which the invention may be deployed; 
         FIG.  2    is a diagram of the keyboard shown in  FIG.  1   ; 
         FIG.  3    is a diagrammatical cross section of a key shown in  FIG.  1   ; 
         FIG.  4    is a cross section of a second embodiment of a pressure sensor; 
         FIG.  5    is a cross section of a third embodiment of a pressure sensor; 
         FIG.  6    shows the pressure sensor of  FIG.  5    with an additional elastic sponge; 
         FIG.  7    is a cross section of a fourth embodiment of the invention; 
         FIG.  8    is a cross section of a fifth embodiment of the invention; 
         FIG.  9    is a cross section of a sixth embodiment of the invention; 
         FIG.  10    shows an arrangement of electrodes; and 
         FIG.  11    shows an alternative arrangement of electrodes. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
       FIG.  1    illustrates an environment in which the invention described herein may be deployed. A computer  101  is wirelessly connected to a keyboard  102 . Manual input is provided to computer  101  by operation of keys indicated generally at  103 , including key  104 , on keyboard  102 . 
     Many different designs of keyboard are available, which may connect wirelessly or using a wire. Alternatively, a keyboard may be integral to a computer, such as a laptop computer. The invention described herein may be used for any type of keyboard. It may also be used for any other type of input device that requires depression of a button, or any other pressure sensor application. For example, a device that uses a pressure sensor such as a scale body. 
     FIG.  2   
     A simplified block diagram of keyboard  102  is shown in  FIG.  2   . Keyboard  102  includes a number of keys  103 . A key signal generation circuit  201  connects to keys  103  and also to an interface  202 , which in this example is a wireless interface. 
     Circuit  201  receives electrical signals from keys  103  and generates key signals for provision to computer  101  via interface  202 . Any circuit or alternative electronics that provides this functionality could be used. In this example, circuit  201  includes a processor, provided by CPU  203 , and a number of further components not shown here. 
     FIG.  3   
       FIG.  3    is a cross section of key  104 . Other keys  103  are similar, though may be of a different size and shape. Key  104  is an embodiment of a button structure according to the invention herein described, comprising a pressure sensor  301  and a pressing mechanism  302 . Connections to key signal generation circuit  201  are shown diagrammatically. 
     Pressure sensor  301  includes a base layer  303 , a support structure  304  provided by two supports  305   a  and  305   b , an elastic layer  306 , an upper electrode  307 , a lower electrode  308 , and a variable resistance elastic body  309 . The two supports  305   a  and  305   b  are arranged on the base layer  303  at intervals, and elastic layer  306  covers and is in contact with support structure  304 . Thus, support structure  304  and elastic layer  306  define a cavity  310  on base layer  303 . 
     Elastic layer  306  has a lower surface  311  that is curved, with a concave curvature with respect to base layer  303 . Cavity  310  therefore has an arched top provided by surface  311 . 
     In other embodiments, the support structure may comprise only one or more than two supports, and the supports may be arranged in any suitable way that creates a cavity on the base layer. The supports may be made of rubber or other elastic material, or may be a structure that fixedly connects the elastic layer and the base layer. A layer of glue may be used, to support the elastic layer at a certain distance from the base layer to form the cavity. 
     Upper electrode  307  is arranged on the lower surface  311  of elastic layer  306 . Lower electrode  308  is arranged on the upper surface  312  of base layer  303 , opposite upper electrode  307 . Both are located within cavity  310 . Variable resistance elastic body  309  is disposed on the upper surface  313  of lower electrode  308 , and therefore opposite upper electrode  307  and within cavity  310 . 
     Upper electrode  307  is connected to circuit  201  by connection  314 , and lower electrode  308  is connected to circuit  201  by connection  315 . It will be understood that all the keys  103  are connected to circuit  201 , and that this may be done using any suitable number of connections. 
     The material of variable resistance elastic body  309  is an elastomer. In this example it is a carbon-based quantum tunnelling composite such as that sold by the applicant Peratech Holdco Limited under the name QTC®, although it may be any carbon-based polymer material, for example, graphene. The elastic matrix of this material is an insulator in its normal form, and under compression or elastic deformation, it transforms from an insulator to a conductor. When it electrically connects two electrodes in this way, the resistance of the elastic body is related to the magnitude of the force applied, or the amount of elastic deformation it experiences. 
     The principle by which the material of elastic body  309  produces conductivity can be called the field-induced quantum tunnelling phenomenon, as follows: the metal particles in the material are very tightly distributed in the matrix under normal conditions, but there is no contact between them. When the material is pressed or deformed, the distance between the metal particles is reduced to the point where electrons can be transferred between the metal particles, thereby becoming conductive. 
     Pressing mechanism  302  includes a pressing portion  317 , an abutment portion  318  and two support portions  319  and  320 . the upper ends of the two support portions  319  and  320  are connected to the lower surface of pressing portion  317  at intervals, and their lower ends are respectively arranged on opposite sides of cavity  310 . Abutment portion  318  is disposed on the lower surface of pressing portion  317  and is located between the two supporting portions  319  and  320 , and abutment portion  318  is opposite to cavity  310  for pressing elastic layer  306  into the cavity. 
     In use, pressure is applied to the top of pressure sensor  301  using pressing mechanism  302 . In other embodiments in which pressing mechanism is absent, pressure may be applied directly to elastic layer  306 . Alternative pressing mechanisms may also be used. Elastic layer  306  undergoes elastic deformation to compress the space in cavity  310 , and then elastic body  309  is compressed and deformed elastically between the two electrodes  307  and  308 . When electrodes  307  and  308  are turned on, a connection is made between the electrodes via elastic body  309 , which is sensed by circuit  201 . Processor  203  generates a key signal  316 , which is output to computer  101  via interface  202 . Key signal  316  is related to the amount of deformation of elastic body  309 . 
     Due to the different pressure or elastic deformation of the elastic substrate, the resistance value is different, and the generated key signal is also different, so that the adjustment of the force change of the key can be realized. 
     Since the lower surface  311  of elastic layer  306  is concave relative to base layer  303 , the rigidity of layer  306  can be increased under the condition that the starting force is considered, and the problem that the base material of the elastic layer cannot rebound in time after a touch is solved. 
     A pressure sensor of this type can have an elastic layer with an increased stiffness, by designing the elastic layer in the pressure sensor to be concave in the direction away from the base layer. This solves the problem that known pressure sensors need a certain time to recover after the pressure is removed. In the invention described herein, the rebound efficiency of the elastic layer is improved, thereby improving the sensitivity and reliability of the pressure sensor. 
     Various alternative embodiments of the pressure sensor are envisaged, some of which are described with reference to  FIGS.  5  to  11   , all of which may be used with or without a pressing mechanism similar to mechanism  302  or any other pressing mechanism. In each embodiment, the electrodes can be connected to a circuit such as circuit  201  in order to generate the key signal, but these connections are not shown. 
     FIG.  4   
     A second embodiment of the invention herein described is shown in  FIG.  4   . Similarly to pressure sensor  301 , pressure sensor  401  has a base layer  402 , support structure  403 , and elastic layer  404 , defining a cavity  405  in which electrodes are arranged. Upper electrode  406  is arranged on the lower surface of elastic layer  404 . Arranged in cavity  405  on the upper surface of base layer  402  are a first lower electrode  407  and second lower electrode  408 . First elastic body  409  is arranged in cavity  405  on the upper surface of first lower electrode  407 , and second elastic body  410  is arranged in cavity  405  on the upper surface of second lower electrode  408 . 
     The lower surface  411  of elastic layer  404  defines two arches  412  and  413 . Upper electrode  406  is arranged at the surface where the two arches  412  and  413  meet. This achieves the effect of increasing the rebound stiffness of the elastic layer. 
     In use, pressure sensor  401  works in the same way as pressure sensor  301  to generate a key signal. 
     FIG.  5   
     A third embodiment of the invention herein described is shown in  FIG.  5   . Similarly to pressure sensor  301 , pressure sensor  501  has a base layer  502 , support structure  503 , and elastic layer  504  with a concave lower surface, defining a cavity  505 . Electrodes are arranged in pairs in cavity  505  on the lower surface of elastic layer  504 , each covered by an elastic body. For example, first electrode  506  and second electrode  507  are adjacent, and elastic body  508  is arranged on the lower surface of both electrodes. In this embodiment there are three such pairs of electrodes, but any suitable number could be used. 
     It has been described above that an elastic body of a carbon-based polymer material, such as elastic body  508 , is an insulator in a normal form, and is transformed from an insulator to a conductive body under pressure or elastic deformation, such that two electrodes can be electrically connected through the body. 
     However, due to the difference in particle distribution in the material, elastic body  508  has a difference in longitudinal conductivity and lateral conductivity, which in turn makes the structure of first electrode  506  and second electrode  507  different. Elastic body  508  is used as the lateral conductivity. 
     In use, force is applied to the top of pressure sensor  501 . Elastic layer  504  is pressed and flexed to drive the electrode pairs, such as electrodes  506  and  507 , and elastic body  508 , to move downwards towards base layer  502 . Elastic body  508  contacts base layer  502  and is compressed, such that it undergoes elastic deformation and is converted from an insulator to a conductor. Electrodes  506  and  507  are thus connected, and the electron transfer path is from first electrode  506 , via elastic body  508 , to second electrode  507 . 
     FIG.  6   
     As an addition to pressure sensor  501 , there may be a resilient elastic sponge  601  filling cavity  505  and wrapping around each electrode pair and corresponding elastic body, such as electrodes  506  and  507  and elastic body  508 . 
     In use, after pressure has been released on pressure sensor  501 , elastic sponge  601  resiles back to its original state, thus pushing upwards on elastic layer  504  and assisting its restoration to its original position. 
     FIG.  7   
     A fourth embodiment of the invention herein described is shown in  FIG.  7   . Similarly to pressure sensor  501 , pressure sensor  701  has a base layer  702 , support structure  703 , and elastic layer  704  with a concave lower surface, defining a cavity  705 . Electrodes are arranged in pairs in cavity  705  on the lower surface of elastic layer  704 . For example, first electrode  706  and second electrode  707  are adjacent. In this embodiment there are three such pairs of electrodes, but any suitable number could be used. A single elastic body  708  is arranged in cavity  705  on the top surface of base layer  702 , and thus in this embodiment it is not arranged on any of the electrodes. 
     In use, force is applied to the top of pressure sensor  701 . Elastic layer  704  is pressed and flexed to drive the electrode pairs, such as electrodes  706  and  707 , to move downwards towards base layer  702 . The electrodes contact elastic body  708  which is compressed, such that it undergoes elastic deformation and is converted from an insulator to a conductor. Electrodes  706  and  707  are thus connected, and the electron transfer path is from first electrode  706 , via elastic body  708 , to second electrode  707 . 
     FIG.  8   
     A fifth embodiment of the invention herein described is shown in  FIG.  8   . Similarly to pressure sensor  701 , pressure sensor  801  has a base layer  802 , support structure  803 , and elastic layer  804  with a concave lower surface, defining a cavity  805 . Upper electrodes are arranged in pairs in cavity  805  on the lower surface of elastic layer  804 . For example, first upper electrode  806  and second upper electrode  807  are adjacent. In this embodiment there are three such pairs of upper electrodes, but any suitable number could be used. A lower electrode  808  is arranged in cavity  805  on the top surface of base layer  802 , opposite the upper electrodes, and an elastic body  809  is arranged in cavity  805  on the top surface of lower electrode  808 . 
     In use, force is applied to the top of pressure sensor  801 . Elastic layer  804  is pressed and flexed to drive the electrode pairs, such as electrodes  806  and  807 , to move downwards towards base layer  802 . The electrodes contact elastic body  809  which is compressed, such that it undergoes elastic deformation and is converted from an insulator to a conductor. Electrodes  806 ,  807  and  808  are thus connected, and the electron transfer path is from first upper electrode  806 , via elastic body  809 , to lower electrode  808 , to second upper electrode  807 . 
     FIG.  9   
     A sixth embodiment of the invention herein described is shown in  FIG.  9   . Similarly to pressure sensor  801 , pressure sensor  901  has a base layer  902 , support structure  903 , and elastic layer  904  with a concave lower surface, defining a cavity  905 . Upper electrodes are arranged in pairs in cavity  905  on the lower surface of elastic layer  904 . For example, first upper electrode  906  and second upper electrode  907  are adjacent. In this embodiment there are three such pairs of upper electrodes, but any suitable number could be used. A lower electrode  908  is arranged in cavity  905  on the top surface of base layer  902 , opposite the upper electrodes. 
     In this embodiment an elastic body  909  is arranged in cavity  905  such that it can contact all the electrodes when force is applied to pressure sensor  901 . Body  909  includes a horizonal elastic member  910  which is arranged on lower electrode  908 . Upstanding from and integral with horizontal elastic member  910  are six vertical elastic members, such as vertical elastic members  911  and  912 . The number of vertical elastic members is equal to the number of upper electrodes. Vertical elastic member  911  defines, at its top, a channel  913 ; the remaining vertical elastic members are similar. Channel  913  has a substantially U-shaped cross section to correspond with the shape of first upper electrode  906 . First upper electrode  906  is arranged within channel  913  but is spaced away from the walls of the channel so that it is not in contact with elastic body  909  when pressure sensor is in its uncompressed form. The other upper electrodes are similarly each arranged within one of the channels. 
     A resilient elastic sponge  915  fills cavity  905  and wraps around elastic body  909 . 
     In use, force is applied to the top of pressure sensor  901 . Elastic layer  904  is pressed and flexed to drive the upper electrodes, such as electrodes  906  and  907 , to move downwards towards base layer  902 . The upper electrodes contact the bottom of their respective channel, for example electrode  906  contacts the bottom wall of channel  914 . This compresses the bottom of each channel, each vertical elastic member, and horizontal elastic member  910 . In this way the electrodes contact and compress elastic body  909 , such that it undergoes elastic deformation and is converted from an insulator to a conductor. The upper and lower electrodes are thus connected, and a key signal can be generated. 
     After pressure has been released on pressure sensor  901 , elastic sponge  915  resiles back to its original state, thus pushing upwards on elastic layer  904  and assisting its restoration to its original position, such that the electrodes are no longer connected to each other. 
     FIG.  10   
       FIG.  10    shows an arrangement of upper electrodes suitable for use in a pressure sensor, such as pressure sensor  501 ,  701 ,  801  or  901 . In this embodiment, there are two upper electrode layers  1001  and  1002  arranged on the lower surface of an elastic layer  1007 . Each electrode layer comprises a trunk conductive rod and a plurality of branch conductive strips. 
     Electrode layer  1001  comprises trunk conductive rod  1003  and a set  1004  of four branch conductive strips  1004 . Similarly, electrode layer  1002  comprises trunk conductive rod  1005  and a set  1006  of four branch conductive strips that are attached to rod  1003  at one end. Trunk conductive rods  1003  and  1005  are opposite to each other, and the sets of branch conductive strips  1004  and  1006  are spaced apart from each other and arranged alternately, such that the strips are interdigitated. 
     Trunk conductive rods  1003  and  1005  are arc-shaped, such that the shape formed by the two electrode layers is substantially circular, with the branch conductive strips located within the circumference. 
     In each of pressure sensors  501 ,  701 ,  801  and  901 , each electrode pair comprises one of branch conductive strips  1004  and one of branch conductive strips  1006 . 
     FIG.  11   
       FIG.  11    shows an alternative arrangement of electrode layers  1101  and  1102 . It is similar to the arrangement of  FIG.  10    save that the trunk conductive rods  1103  and  1104  are rectangular and elongated, and arranged in parallel, rather than arced. The entire arrangement forms a rectangular or square shape. 
     In this description, it should be noted that the orientation or positional relationship indicated by the terms “within”, “above”, “below” and similar is based on the orientation or positional relationship shown in the drawings, or the way the product is usually placed when used. The orientation or positional relationship is only for the convenience of describing the application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the application. 
     It should also be noted that, unless otherwise clearly specified and limited, the terms “disposed”, “arranged” and “connected” should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection. The connection can also be indirectly connected through an intermediate medium, and it can be the internal communication between two components.