WO2018044227A1 - Stretchable pressure mapping sysytem - Google Patents

Stretchable pressure mapping sysytem Download PDF

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Publication number
WO2018044227A1
WO2018044227A1 PCT/SG2016/050307 SG2016050307W WO2018044227A1 WO 2018044227 A1 WO2018044227 A1 WO 2018044227A1 SG 2016050307 W SG2016050307 W SG 2016050307W WO 2018044227 A1 WO2018044227 A1 WO 2018044227A1
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WO
WIPO (PCT)
Prior art keywords
status
electrodes
col
rij
pressure sensing
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Application number
PCT/SG2016/050307
Other languages
French (fr)
Inventor
Qinghua Xia
Weibiao GU
Joshua GOFMAN
Original Assignee
Yoggzee Corporation Pte Ltd
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Priority to PCT/SG2016/050307 priority Critical patent/WO2018044227A1/en
Publication of WO2018044227A1 publication Critical patent/WO2018044227A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/18—Measuring force or stress, in general using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
    • G01L1/205—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using distributed sensing elements
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/0414—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means using force sensing means to determine a position
    • G06F3/04146—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means using force sensing means to determine a position using pressure sensitive conductive elements delivering a boolean signal and located between crossing sensing lines, e.g. located between X and Y sensing line layers
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/0416—Control or interface arrangements specially adapted for digitisers
    • G06F3/04166—Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2203/00—Indexing scheme relating to G06F3/00 - G06F3/048
    • G06F2203/041—Indexing scheme relating to G06F3/041 - G06F3/045
    • G06F2203/04102—Flexible digitiser, i.e. constructional details for allowing the whole digitising part of a device to be flexed or rolled like a sheet of paper

Definitions

  • the present disclosure describes piezoresistive sensors, complex programmable logic devices (CPLDs), multiplexer, switch, electronic circuit, microcontroller, and firmware to construct a pressure mapping system.
  • CPLDs complex programmable logic devices
  • a pressure mapping system with the capability to sense pressures at multiple points on a flat or curved surface can find variety of applications in the fields of fitness, health care, sports, surgery, and augmented reality etc.
  • Small size pressure mapping systems are common and purchased easily, but large format system is rare and expensive.
  • One of the reasons is the complicated interelectrode crosstalk issue associated with a large format system that consists of many rows and columns of sensor points. If not designed and handled properly, crosstalk problem will cause erroneous readings.
  • U.S. Pat. No. 5,505,072 discloses a scanning circuit to enhance interelectrode isolation from hardware level.
  • the objective of the present invention is to develop a pressure mapping system that can mitigate crosstalk problem from both hardware and software levels, resulting in a simpler electronic circuit with lesser components, as compared with a system solving the problem from hardware level alone.
  • Some applications require a pressure sensing layer of the system to be stretchable. Such product is still rare in the market due to challenges of making it stretchable.
  • Another objective of the present invention is to develop a pressure sensing layer that can be stretchable.
  • a pressure mapping system consists of either through-type or shunt- type pressure sensing layer, electronic circuit for changing electrode status and capturing voltage reading, and firmware to derive applied pressure on all the sensor points.
  • a stretchable pressure sensing layer is constructed with stretchable substrates, electrodes, and adhesive Z-axis electrically conductive transfer film.
  • the Z-axis transfer film allow current to flow through the film but not the surface of the film. This feature also helps reduce the amount of stray current flowing along the surface of electrodes, thus reduce interelectrode interference.
  • status on each electrode of pressure sensing layer can be set by GPIO pins of two CPLDs.
  • a GPIO pin of a CPLD can be set at either Status "1 " that outputs a test voltage Vcc, Status "0" with 0V voltage, or Status "X" at high impedance status.
  • proper status setting on electrodes prevents current from flowing to unwanted portion of sensor points and circuit, thus mitigates interelectrode crosstalk issue.
  • the arrangement of sensor points in strip, square or rectangular patterns on force sensing layer also prevents stray current from flowing between electrodes.
  • FIG. 1 shows sketch of the pressure mapping system
  • FIG. 2 shows through-type pressure sensing layer construction
  • FIG. 3 shows shunt-type pressure sensing layer construction
  • FIG. 4 shows shunt-type sensor points arrangement patterns
  • FIG. 5 shows construction of adhesive Z-axis electrically conductive transfer film
  • FIG. 6 shows a through-type stretchable pressure mapping system construction
  • FIG. 7 shows a shunt-type stretchable pressure mapping system construction
  • FIG. 8 shows an embodiment of pressure mat's control board and pressure sensing layer
  • FIG. 9 shows equivalent circuit of pressure sensing segment
  • FIG. 1 0 shows the circuit to obtain V xx reading for the embodiment in FIG . 8
  • FIG. 1 1 shows the circuit to obtain V 21 reading for the embodiment in FIG . 8
  • FIG. 12 shows the circuit to obtain V ml reading for the embodiment in FIG. 8
  • FIG. 13 shows the circuit to obtain V llf reading for the embodiment in FIG . 8
  • the pressure mapping system consists of top cover 1 01 , pressure sensing layer 102, the base 1 03, and control board 104.
  • the thin top cover 101 is used to protect the pressure sensing layer 102, yet does not affect pressure sensing.
  • the pressure sensing layer 102 maybe constructed with through-type or shunt-type sensor points arrangement, as shown in FIGs 2 and 3.
  • FIG. 2 shows through-type arrangement.
  • the sensing layer consists of lower electrodes covered with force sensing resistor strips, and upper layer electrodes covered or not covered with force sensing resistor strips.
  • the force sensing resistor strips are slightly wider than the electrode, and the lower and upper electrodes are arranged perpendicular to each other, or at an angle.
  • the force sensing segment sandwiched between each intersection of the lower and upper electrodes acts as a pressure sensor point, which decreases in electrical resistance when a force or pressure is applied on it.
  • FIG. 3 shows shunt-type arrangement of the pressure sensing layer.
  • the electrode layer consists of horizontal and vertical electrodes. At each junction of horizontal and vertical electrodes is a pair of interdigitated traces that are isolated with each other. By putting force sensing resistor over each pair of traces, the traces are connected with the resistor. The electrical resistance between the traces becomes a function of how much pressure is applied on the force sensing resistor.
  • the arrangement pattern of force sensing resistors placed on top of the electrode layer can be in strip, square or rectangular shapes.
  • FIGs. 5, 6, and 7 illustrate construction of stretchable pressure sensing layers.
  • FIG . 5 shows a thin stretchable adhesive transfer film that has anisotropic electrical conductivity property. It is filled with tiny conductive particles which allow interconnection between substrates through the adhesive thickness (the "Z- axis") but are spaced far enough apart for it to be electrically insulating in the plane of the adhesive.
  • FIG. 6 illustrates a through-type stretchable pressure sensing layer construction.
  • the lower and upper electrodes are printed or put onto stretchable substrates.
  • the force sensing resistors arranged in matrix array shown at the right hand side of FIG . 4 are sandwiched between lower and upper adhesive stretchable Z-axis transfer film shown in FIG . 5. All the layers are stacked together to form a stretchable pressure mat. With this arrangement, current will flow through the lower and upper transfer films along the Z-axis and not along the surface.
  • FIG. 7 illustrates a shunt-type stretchable pressure sensing layer construction.
  • the lower electrodes, printed onto lower stretchable substrates, consists of pairs of interdigitated traces that are isolated with each other.
  • the force sensing resistors arranged in matrix array shown at the right hand side of FIG . 4 are sandwiched between upper adhesive and lower adhesive stretchable Z-axis transfer film shown in FIG . 5. All the layers are stacked together to form a stretchable pressure mat. With this arrangement, each pair of traces is connected with the force sensing resistor above it through the lower Z-axis transfer film.
  • FIG. 8 shows one embodiment of control board 104 and pressure sensing layer 1 02.
  • the control board 104 consists of two CPLDs, a multiplexer, a microcontroller or MCU, a signal amplifier that is connected to the analog input of the MCU.
  • the pressure sensing layer 102 consists of m rows of horizontal and n columns of vertical electrodes, with pressure sensing points at the intersections of electrodes. Status on vertical and horizontal electrodes is set by GPIO pins of CPLD1 and CPLD 2, respectively. Switches Si to Sn of the multiplexer Mux 1 are connected to Col 1 to Col n of vertical electrodes respectively.
  • the two CPLDs and Mux 1 are connected and controlled by the MCU.
  • a GPIO pin of a CPLD can be set at either Status "1 " that outputs a test voltage Vcc, Status "0” with OV voltage, or Status "X” at high impedance status.
  • a switch status of Mux 1 can be set at either open or close status.
  • FIG. 9 shows equivalent circuit of the pressure sensing segment, for either through-type or shunt- type, stretchable or non-stretchable pressure sensing layer.
  • the force sensing resistors at the intersections of rows and columns are modeled as variable resistors that change resistance with applied pressure.
  • R represents the sensor point resistor at the junction of the ith row and the jth column of electrodes. For each sensor point, there is certain relationship between its electrical resistance and the applied pressure on it. By obtaining resistance value of each sensor point, the corresponding applied pressures will also be derived.
  • Col 1 of vertical electrodes is set to Status "X", and the rest of the vertical electrode columns are set to Status "1 " by CPLD 1 .
  • Row 1 of horizontal electrodes is set to Status "1 ", and the rest of horizontal electrode rows are set to Status "0” by CPLD 2.
  • the status setting for the vertical electrodes guides the current from the GPIO pin of CPLD 2 connecting to Row 1 to flow through Col 1 alone, but not through the rest of vertical electrodes, thus to mitigate interelectrode crosstalk issue.
  • So is set to close, Si of the multiplexer Mux 1 is set to close, and the rest of the switches of Mux 1 are set to open status.
  • the equivalent measurement circuit is shown in FIG. 10. Under the status setting, the following two equations can be obtained, with voltage reading Vn at Vin pin of the MCU:
  • V " T T ⁇ Vcc - (fiq. 2m)
  • FIG. 13 Another embodiment of method to obtain all the force sensing resistor values is shown in FIG . 13. From the status setting to get Eqs.1 & 2, now maintain all the status setting except So, which is now changed to open status as shown in FIG . 13, voltage reading V f can be obtained:

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Human Computer Interaction (AREA)
  • Force Measurement Appropriate To Specific Purposes (AREA)

Abstract

A pressure mapping system that can sense applied pressure on a flat or curved surface. It consists of pressure sensing layer with piezoresistive sensor points at intersections of horizontal and vertical electrodes, complex programmable logic devices (CPLDs), multiplexer, measurement circuit, a microcontroller and firmware. The piezoresistive sensor is made of force sensing resistor, which decrease in electrical resistance when a force or pressure is applied on it. The CPLDs that is controlled by the microcontroller change statuses in certain sequence on all the rows and columns of the electrodes, causing current to flow through piezoresistive sensor points in controlled directions. By measuring voltages caused by current flow variations via the measurement circuit, electrical resistances, hence the applied pressures, at all the sensor points can be derived by the firmware inside the microcontroller. Interelectrode crosstalk issue is mitigated with proper status setting on electrodes that prevent current from flowing to the unwanted portion of electronic circuit.

Description

STRETCHABLE PRESSURE MAPPING SYSTEM
TECHNICAL FIELD
The present disclosure describes piezoresistive sensors, complex programmable logic devices (CPLDs), multiplexer, switch, electronic circuit, microcontroller, and firmware to construct a pressure mapping system.
BACKGROUND ART
A pressure mapping system with the capability to sense pressures at multiple points on a flat or curved surface can find variety of applications in the fields of fitness, health care, sports, surgery, and augmented reality etc. Small size pressure mapping systems are common and purchased easily, but large format system is rare and expensive. One of the reasons is the complicated interelectrode crosstalk issue associated with a large format system that consists of many rows and columns of sensor points. If not designed and handled properly, crosstalk problem will cause erroneous readings.
To mitigate crosstalk issue, U.S. Pat. No. 5,505,072 discloses a scanning circuit to enhance interelectrode isolation from hardware level. The objective of the present invention is to develop a pressure mapping system that can mitigate crosstalk problem from both hardware and software levels, resulting in a simpler electronic circuit with lesser components, as compared with a system solving the problem from hardware level alone.
Some applications require a pressure sensing layer of the system to be stretchable. Such product is still rare in the market due to challenges of making it stretchable. Another objective of the present invention is to develop a pressure sensing layer that can be stretchable.
SUMMARY
According to the invention, a pressure mapping system consists of either through-type or shunt- type pressure sensing layer, electronic circuit for changing electrode status and capturing voltage reading, and firmware to derive applied pressure on all the sensor points.
According to the first aspect of the present invention, a stretchable pressure sensing layer is constructed with stretchable substrates, electrodes, and adhesive Z-axis electrically conductive transfer film. The Z-axis transfer film allow current to flow through the film but not the surface of the film. This feature also helps reduce the amount of stray current flowing along the surface of electrodes, thus reduce interelectrode interference.
According to the second aspect of the present invention, status on each electrode of pressure sensing layer can be set by GPIO pins of two CPLDs. A GPIO pin of a CPLD can be set at either Status "1 " that outputs a test voltage Vcc, Status "0" with 0V voltage, or Status "X" at high impedance status. By changing statuses on electrodes in certain sequence, voltage readings at a measurement point can be obtained. Based on the voltage readings and their corresponding equivalent measurement circuit for each status setting, all the force sensing resistor values can be derived.
According to the third aspect of the present invention, proper status setting on electrodes prevents current from flowing to unwanted portion of sensor points and circuit, thus mitigates interelectrode crosstalk issue. The arrangement of sensor points in strip, square or rectangular patterns on force sensing layer also prevents stray current from flowing between electrodes.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows sketch of the pressure mapping system
FIG. 2 shows through-type pressure sensing layer construction
FIG. 3 shows shunt-type pressure sensing layer construction
FIG. 4 shows shunt-type sensor points arrangement patterns FIG. 5 shows construction of adhesive Z-axis electrically conductive transfer film
FIG. 6 shows a through-type stretchable pressure mapping system construction
FIG. 7 shows a shunt-type stretchable pressure mapping system construction
FIG. 8 shows an embodiment of pressure mat's control board and pressure sensing layer
FIG. 9 shows equivalent circuit of pressure sensing segment
FIG. 1 0 shows the circuit to obtain Vxx reading for the embodiment in FIG . 8
FIG. 1 1 shows the circuit to obtain V21 reading for the embodiment in FIG . 8
FIG. 12 shows the circuit to obtain Vml reading for the embodiment in FIG. 8
FIG. 13 shows the circuit to obtain Vllf reading for the embodiment in FIG . 8
DETAILED DESCRIPTION
As shown in FIG . 1 , the pressure mapping system consists of top cover 1 01 , pressure sensing layer 102, the base 1 03, and control board 104.
The thin top cover 101 is used to protect the pressure sensing layer 102, yet does not affect pressure sensing.
The pressure sensing layer 102 maybe constructed with through-type or shunt-type sensor points arrangement, as shown in FIGs 2 and 3. FIG. 2 shows through-type arrangement. The sensing layer consists of lower electrodes covered with force sensing resistor strips, and upper layer electrodes covered or not covered with force sensing resistor strips. The force sensing resistor strips are slightly wider than the electrode, and the lower and upper electrodes are arranged perpendicular to each other, or at an angle. The force sensing segment sandwiched between each intersection of the lower and upper electrodes acts as a pressure sensor point, which decreases in electrical resistance when a force or pressure is applied on it.
FIG. 3 shows shunt-type arrangement of the pressure sensing layer. The electrode layer consists of horizontal and vertical electrodes. At each junction of horizontal and vertical electrodes is a pair of interdigitated traces that are isolated with each other. By putting force sensing resistor over each pair of traces, the traces are connected with the resistor. The electrical resistance between the traces becomes a function of how much pressure is applied on the force sensing resistor. As shown in FIG . 4, on the force sensing layer, the arrangement pattern of force sensing resistors placed on top of the electrode layer can be in strip, square or rectangular shapes.
Some applications require a pressure sensing layer to be stretchable. FIGs. 5, 6, and 7 illustrate construction of stretchable pressure sensing layers. FIG . 5 shows a thin stretchable adhesive transfer film that has anisotropic electrical conductivity property. It is filled with tiny conductive particles which allow interconnection between substrates through the adhesive thickness (the "Z- axis") but are spaced far enough apart for it to be electrically insulating in the plane of the adhesive. FIG. 6 illustrates a through-type stretchable pressure sensing layer construction. The lower and upper electrodes are printed or put onto stretchable substrates. The force sensing resistors arranged in matrix array shown at the right hand side of FIG . 4, are sandwiched between lower and upper adhesive stretchable Z-axis transfer film shown in FIG . 5. All the layers are stacked together to form a stretchable pressure mat. With this arrangement, current will flow through the lower and upper transfer films along the Z-axis and not along the surface.
FIG. 7 illustrates a shunt-type stretchable pressure sensing layer construction. The lower electrodes, printed onto lower stretchable substrates, consists of pairs of interdigitated traces that are isolated with each other. The force sensing resistors arranged in matrix array shown at the right hand side of FIG . 4, are sandwiched between upper adhesive and lower adhesive stretchable Z-axis transfer film shown in FIG . 5. All the layers are stacked together to form a stretchable pressure mat. With this arrangement, each pair of traces is connected with the force sensing resistor above it through the lower Z-axis transfer film.
FIG. 8 shows one embodiment of control board 104 and pressure sensing layer 1 02. The control board 104 consists of two CPLDs, a multiplexer, a microcontroller or MCU, a signal amplifier that is connected to the analog input of the MCU. The pressure sensing layer 102 consists of m rows of horizontal and n columns of vertical electrodes, with pressure sensing points at the intersections of electrodes. Status on vertical and horizontal electrodes is set by GPIO pins of CPLD1 and CPLD 2, respectively. Switches Si to Sn of the multiplexer Mux 1 are connected to Col 1 to Col n of vertical electrodes respectively. The two CPLDs and Mux 1 are connected and controlled by the MCU. A GPIO pin of a CPLD can be set at either Status "1 " that outputs a test voltage Vcc, Status "0" with OV voltage, or Status "X" at high impedance status. A switch status of Mux 1 can be set at either open or close status.
FIG. 9 shows equivalent circuit of the pressure sensing segment, for either through-type or shunt- type, stretchable or non-stretchable pressure sensing layer. The force sensing resistors at the intersections of rows and columns are modeled as variable resistors that change resistance with applied pressure. R represents the sensor point resistor at the junction of the ith row and the jth column of electrodes. For each sensor point, there is certain relationship between its electrical resistance and the applied pressure on it. By obtaining resistance value of each sensor point, the corresponding applied pressures will also be derived.
Based on the embodiment shown in FIG. 8, to derive resistance values of all the m number of sensor points along Col 1 , firstly, Col 1 of vertical electrodes is set to Status "X", and the rest of the vertical electrode columns are set to Status "1 " by CPLD 1 . Row 1 of horizontal electrodes is set to Status "1 ", and the rest of horizontal electrode rows are set to Status "0" by CPLD 2. The status setting for the vertical electrodes guides the current from the GPIO pin of CPLD 2 connecting to Row 1 to flow through Col 1 alone, but not through the rest of vertical electrodes, thus to mitigate interelectrode crosstalk issue. Meanwhile, So is set to close, Si of the multiplexer Mux 1 is set to close, and the rest of the switches of Mux 1 are set to open status. The equivalent measurement circuit is shown in FIG. 10. Under the status setting, the following two equations can be obtained, with voltage reading Vn at Vin pin of the MCU:
Figure imgf000004_0001
Secondly, maintain the statuses at vertical electrodes, Mux 1 and So, change Row 2 of horizontal electrodes to Status "1 ", and the rest of horizontal electrode rows to Status "0". The equivalent measurement circuit is shown in FIG. 1 1 . Similarly, the following two equations can be obtained:
Figure imgf000004_0002
Thirdly, still maintain the statuses at vertical electrodes, Mux 1 and So, progressively change the status of Row i (i=3,4, ...,m) to Status "1 ", the rest of horizontal electrode rows to Status "0", and then obtain V31 till Vmi . The equivalent measurement circuit to get Vmi is shown in FIG. 12. Similarly, the following two equations can be obtained: Eq. 2m 1)
(m-l)l Ύ
V" = T T \ Vcc - (fiq. 2m)
\Kmi Ktmi)
Based on Eqs. 1 - 2m. All the sensor resistance values along Col 1 can be derived by the following two equations. Vai = V11 + V21 + - + Vml (Eq. 2m + 1)
Figure imgf000005_0001
Similarly, to get all the m number of sensor resistance values along Col j (j=2,3, ... ,n) , now set Col j (j=2,3, ... ,n) of vertical electrodes to Status "X", and the rest of the vertical electrode columns to Status "0" progressively. Meanwhile, So is still at close status, Mux 1 switch Sj set to close status, and the rest of the Mux 1 switches to open status. Repeat the same status settings from Row 1 to Row m described above to get Eqs 1 - 2m, the resistance values along Col j can be derived by the following two equations.
Figure imgf000005_0002
Till now, all the values of force sensing resistors at the interactions of rows and columns of electrodes are derived, thus the corresponding pressure obtained.
Another embodiment of method to obtain all the force sensing resistor values is shown in FIG . 13. From the status setting to get Eqs.1 & 2, now maintain all the status setting except So, which is now changed to open status as shown in FIG . 13, voltage reading V f can be obtained:
Figure imgf000005_0003
From Eqs.1,2, 2m + 5, 2m + 6, Ri 1 can be derived as:
Vcc(Vu - Vii f)
fi - V ./ Rf (Eq. 2m + 7)
1/ii1/ 11/
Repeat the same sequence for all the rows (i=1 ,2, ... ,m) and columns (j=1 ,2, ... ,n), all the resistance values of sensor points can be derived.

Claims

1 . A pressure mapping system's through-type pressure sensing layer shown in FIG. 2
comprising:
lower electrodes covered with force sensing resistor strips, upper layer electrodes covered or not covered with force sensing resistor strips, with strips slightly wider than electrodes, and the lower and upper electrodes arranged perpendicular to each other, or at an angle.
2. A pressure mapping system's shunt-type pressure sensing layer shown in FIG. 3 comprising: horizontal and vertical electrodes, pairs of interdigitated traces isolated with each other at junctions of horizontal and vertical electrodes, and force sensing resistors in strip, square or rectangular shapes over the pairs of interdigitated traces.
3. The through-type pressure sensing layer of claim 1 can be made stretchable with:
lower and upper electrodes printed or put onto stretchable substrates, and strips of force sensing resistors sandwiched between lower and upper adhesive stretchable Z-axis transfer film. The thin Z-axis transfer film has anisotropic electrical conductivity property, filled with tiny conductive particles which allow interconnection between substrates through the adhesive thickness (the "Z-axis") but are spaced far enough apart for it to be electrically insulating in the plane of the adhesive. With this arrangement, current will flow through the lower and upper transfer films along the Z-axis and not along the surface.
4. The shunt-type pressure sensing layer of claim 2 can be made stretchable with:
electrodes printed or put onto lower stretchable substrates, isolated pairs of interdigitated traces, and force sensing resistors in strip, square or rectangular shapes sandwiched between upper adhesive and lower adhesive stretchable Z-axis transfer film. The thin Z-axis transfer film has anisotropic electrical conductivity property, is filled with tiny conductive particles which allow interconnection between substrates through the adhesive thickness (the "Z-axis") but are spaced far enough apart for it to be electrically insulating in the plane of the adhesive. With this arrangement, each pair of traces is connected with the force sensing resistor above it through the lower Z-axis transfer film.
5. For the stretchable pressure sensing layer of claims 3 and 4, the Z-axis transfer film allow current to flow through the film but not the surface of the film, which helps reduce the amount of stray current flowing along the surface of electrodes, thus reduce interelectrode interference.
6. For the pressure sensing layer of claims 1 , 2, 3 and 4, the arrangement of sensor points in strip, square or rectangular patterns prevents stray current from flowing between electrodes.
7. The control board for the pressure sensing layer of claims 1 , 2, 3 and 4 comprising:
two complex programmable logic devices (CPLDs), a multiplexer, a switch, and a signal amplifier connected to the analog input of the MCU, as shown in FIG. 8. The pressure sensing layer is constructed with m rows of horizontal and n columns of vertical electrodes, with pressure sensing points at the intersections of electrodes. Status on vertical and horizontal electrodes is set by GPIO pins of CPLD1 and CPLD 2, respectively. Switches Si to Sn of the multiplexer Mux 1 are connected to Col 1 to Col n of vertical electrodes respectively. The two CPLDs and Mux 1 are connected and controlled by the MCU. A GPIO pin of a CPLD can be set at either Status "1 " that outputs a test voltage Vcc, Status "0" with 0V voltage, or Status "X" at high impedance status. A switch status of Mux 1 can be set at either open or close status.
8. For the pressure sensing layer of either claim 1 , 2, 3 or 4, the force sensing resistors at the intersections of rows and columns are modeled as variable resistors that change resistance with applied pressure. Rij represents the sensor point resistor at the intersection of the ith row and the jth column of electrodes. For the control board of claim 7, to derive all the m number of sensor points' resistance values along Col j (j=1 ,2, ...,n), firstly, So is set to close, Sj of Mux 1 is set to close, and the rest of the switches of Mux 1 are set to open status. Col j of vertical electrodes is set to Status "X", and the rest of the vertical electrode columns are set to Status "1 " by CPLD 1 ; secondly, Row i (i=1 ,2, ...,m) of horizontal electrodes is set to Status "1 ", and the rest of horizontal electrode rows are set to Status "0" by CPLD 2, then m number of voltage readings V (i=1 ,2, ...,m) at the analog input Vin pin of the MCU is obtained, and the following equations can be derived:
1 - 1 + 1 + + 1 + 1 +
Rtij Rij ¾y Rmj Rf
Rtij
li = (Rij + Rtij) Vcc
Where Rtij (i=1 ,2, ...,m, and j=1 ,2, ...n) represents the parallel connected resistors of Rf and all the Rij along Col J except Rij.
Based on equations above and Vy readings captured, the resistance values along Col j can be derived by the following equations:
mj
Figure imgf000007_0001
Repeat the same sequence for all the columns j (j=1 ,2,... ,n), all the resistance values of sensor points can be derived. For each sensor point, there is certain relationship between its electrical resistance and the applied pressure on it. By obtaining resistance value of each sensor point, the corresponding applied pressures will also be derived.
For the pressure sensing layer of claims 1 , 2, 3 and 4, Rij represents the sensor point resistor at the intersection of the ith row and the jth column of electrodes.
For the control board of claim 7, to derive the resistance values of the sensor point at the intersection of Row i (i=1 ,2,...,m) and Col j (j=1 ,2, ...,n), firstly, So is set to close, Sj of Mux 1 is set to close, and the rest of the switches of Mux 1 are set to open status. Col j of vertical electrodes is set to Status "X", and the rest of the vertical electrode columns are set to Status "1 " by CPLD 1 ; secondly, Row i (i=1 ,2, ...,m) of horizontal electrodes is set to Status "1 ", and the rest of horizontal electrode rows are set to Status "0" by CPLD 2, a voltage reading V at Vin pin of the MCU is obtained, and the following equations can be derived:
Figure imgf000007_0002
Where Rtij (i=1 ,2, ...,m, and j=1 ,2, ...n) represents the parallel connected resistors of Rf and all the Rij along Col J except Rij.
Thirdly, maintain all the status setting except So, which is now changed to open status, voltage reading Vijf can be obtained from Vin pin of the MCU, and the following equations can be derived: Rtijf
Figure imgf000008_0001
Where Rtijf (i=1 ,2, ...,m, and j=1 ,2,...n) represents all the parallel connected resistors Rij along Col J except Rij.
Based on the four equations, Rij can be derived as:
_ Vcc (Vij - Vijf) p
vUv f
Repeat the same sequence for all the rows (i=1 ,2,... ,m) and columns (j=1 ,2,... ,n), all the resistance values of sensor points can be derived. For each sensor point, there is certain relationship between its electrical resistance and the applied pressure on it. By obtaining resistance value of each sensor point, the corresponding applied pressures will also be derived.
10. For the control board of claim 7, the purpose of setting Col j at Status "X" and the rest of the columns at Status "1 " is to guides the current from CPLD 2's GPIO pin at Status "1 " to flow through Col j alone, but not through the rest of vertical electrodes, thus to mitigate interelectrode crosstalk issue.
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