Compliant three-axis force sensor and method of making the same

Abstract

A compliant three-axis force sensor that can be included in a soft robot or electronic skin is disclosed. The sensor includes: a first electrode layer, including column electrodes in a first orientation; a second electrode layer, including column electrodes in a second orientation orthogonal to the first orientation; a force-related active layer, provided between the first electrode layer and the second electrode layer and configured to change at least one property, such as quantum tunneling, conductivity, resistivity or charge, when subjected to force; at least one three-dimensional protrusion, arranged to transmit an externally applied force through the active layer; and at least one spacer, arranged to maintain separation between two or more layers in the sensor until an external force is applied.

Description

Technical Field

[0001] The present invention relates to a compliant three-axis force sensor and a method of manufacturing the same. Background Art

[0002] In order for robots and machines to interact with the world around them in a human-like way, they must also have a highly sensitive sense of touch similar to that of humans. One of the most difficult areas for robots to mimic is the palm, as it has one of the highest densities of nerve receptors in the human body. In addition, the skin has multiple mechanoreceptors for sensing different forces / pressures as well as vibration frequencies. Static sensing of pressure is most important for a robot’s ability to handle delicate objects. For this purpose, a variety of tactile sensors have been manufactured to provide pressure data.

[0003] Most sensors currently on the market include single force sensors or other transducers. These only provide a scalar value for pressure over what is considered a relatively large surface area. Other sensors that provide more advanced tactile information include sensors that are robust but require the replacement of the entire robot finger.

[0004] However, force is a vector with two components (magnitude and direction). For many years, directional information / data has been an important factor in improving robotics. Sensors that can determine both magnitude and direction are generally referred to as three-axis force sensors. These force-torque (F / T) sensors are primarily used as part of robotic end-effector arms (see reference 1 listed at the end of this specification), or more recently to measure the directional component of force on robotic fingertips (see reference 2 listed at the end of this specification). Historically, there have been many attempts to make such sensors, and some recent sensors have achieved relatively high densities, but they are made using solid-state materials and / or micromachining techniques. Not only are force readings sensitive to bending around a given surface, but many of them cannot bend and can only be integrated into robotic hardware. Recently, both human and robot monitoring have realized the need for compliant tactile systems. Many compliant / conformable pressure sensing systems can be classified as electronic skin (e-skin) types.

[0005] Some recent electronic skins and data gloves have been produced that can provide multi-point or high-density tactile information (see references 3 and 4 listed at the end of this specification), however most do not provide directional information that is critical for measuring some phenomena. This allows robots to grasp objects, detect the mass of objects in a gravity environment such as the Earth, and measure ground reaction forces in shoe insoles for gait analysis, among other physical phenomena.

[0006] There have been many attempts recently to make fully compliant three-axis force sensors. Various esoteric approaches have been used, including various compliant strain gauge designs using liquid metals such as eGaIn (eutectic gallium indium) (see Reference 5 listed at the end of this specification), some of which are similar to rosette strain gauges (which are difficult to make and can result in toxic leaks), others are based on bulky pneumatic chambers, and others are self-aligning carbon nanotube (CNT) arrays.

[0007] When any of these sensing systems need to be integrated at high density, a matrix array is necessary because it reduces wiring considerations and thus the space they take up on the electronic skin. While this is largely achieved through capacitive sensing, whether using metal, conductive liquids, or other materials (see references 6, 7, and 8 listed at the end of this specification), this type of sensing is sensitive to the substrate it is used on (e.g., human skin, metal robots) due to the capacitive coupling that can occur between the surface and the sensor. In addition, capacitive sensing requires complex readout electronics and is susceptible to background electromagnetic (EM) noise, which makes it impractical in many applications. Other methods have also been used, but all have certain disadvantages; piezoelectric sensing (see reference 9 listed at the end of this specification), which has the potential for actuation and detection (see reference 10 listed at the end of this specification), is susceptible to significant background electromagnetic compatibility (EMC) noise and cannot perform static sensing; magnetic sensing (including Hall effect and induction methods) (see references 11 to 14 listed at the end of this specification) is also affected by background EMC and ambient magnetic fields, some of which may be generated by the robot's own actuators.

[0008] Furthermore, it is of utmost importance to make the electronic skin as thin as possible so that it does not interfere with the device it is to be retrofitted to, while also having a compact electronic readout system, which is lacking in most solutions / systems. Very promising but costly manufacturing processes have recently been developed that utilize self-aligning carbon nanotube arrays to read out the three-axis information in an integrated array generated on the sidewall during the manufacturing process with good cycle repeatability (see reference 15 listed at the end of this specification).

[0009] Quantum tunneling materials have been used before, as well as piezoresistive composites, but none of the proposed systems were highly integrable or packageable. Often, the flexible wiring is not flexible or compliant enough, either because the material is too stiff or compliant in only 1 axis, or the layer is not thin enough. The structure of such a device typically involves placing a "bump" that converts force into torque, which is placed directly above 4 orthogonally arranged pressure sensors or pressure sensing pixels (sensor elements). When the top of the post is subjected to a force from a given direction, this translates into a downward force and a lateral torque. Therefore, the 4 pressure sensors are subjected to different forces / pressures. The measurement of the change in resistance on each of these sensors can then be used to resolve the force into its 3D Cartesian components (F x 、F y and F z ). Various electrode configurations can be used to read signals from piezoresistive materials (see reference 16 listed at the end of this specification).

[0010] To date, the materials that come closest to making arrays of piezoresistive three-axis sensors include interlocking structures with sidewalls embedded in polydimethylsiloxane (PDMS) and micro-pyramid array structures (see reference 17 listed at the end of this specification). The former has the advantage of being able to be deployed in a relatively dense 3×3 array, but can only operate at very low loads of 0-225Pa. The latter has the advantage of having a wide dynamic range from 128Pa to 44kPa. However, it requires a lot of wiring because it is not suitable for being deployed as a matrix, and also has an overall structure that is several millimeters thick, which means it cannot be wrapped around a surface, and due to its complexity, large-scale production will be very difficult.

[0011] Quantum tunneling composites Discovered by David Lussey in 1996. They are composite materials consisting essentially of metallic particles and a non-conductive elastomeric binder or matrix. These materials have a high resistance to electric current and are essentially insulators in the absence of applied pressure. Once pressure is applied, their resistance drops exponentially, which can be measured using the correct circuit. The reason for this is that the metal particles are dispersed in the material at a specific concentration, but are not in physical contact with each other. After the pressure is applied, the metal particles come close to each other and, despite not being able to touch each other, electrons begin to be able to jump from one particle to another through a phenomenon called quantum tunneling. The higher the pressure, the closer the particles are to one another, which in turn enhances this tunneling effect and reduces the resistance of the material. In order for this to work well, a good dispersion of the particles within the binder and their small size are necessary, as the tunneling effect only works on a small scale. For this reason, the particles are usually micron or nanometer sized and made of a conductive material, usually a metal such as silver, gold or magnetite. They are also often nano-patterned, for example "pointy" nanoparticles show better tunneling behavior than round nanoparticles, due to the fact that the tips of the microscopic spikes enhance the tunneling current even when the particles are at a greater distance from each other. This improves sensitivity and overall performance.

[0012] Peratech Pills have been used in attempts to create three-axis sensors, but these devices suffer from miniaturization and other issues such as sensor hysteresis. Pellets lack the ability to be integrated during large-scale production processes, and have a large thickness and minimum diameter, making them bulky and not particularly sensitive.

[0013] In summary, commercial flexible force sensors on the market can only give the scalar value of force, but not its direction or shear force. They cannot withstand significant bending and change their value during bending. In addition, array technology including three-axis technology is needed to obtain the necessary data to realize a variety of advanced applications. This is particularly important in gait analysis of humans and robots, robots manipulating objects in complex ways, robots manipulating precision objects without damaging them, using wearable clothing to monitor physiological forces such as muscle activity and blood flow on the human body, sensing the flow of fluids such as air or water on tidal tops and wind turbines, and allowing surgeons to "touch" tissues with surgical robots, etc.

[0014] Compliant, three-axis sensors can be formed (in research laboratories) using a variety of transmission mechanisms such as piezoresistive (e.g. using strain gauges or nanocomposites); capacitive; piezoelectric; inductive; optical or magnetic. Piezoresistive and capacitive sensors dominate because of their superior performance. However, capacitive sensors are sensitive to the substrate on which they are placed (due to capacitive coupling to that surface) and require more complex readout electronics (a barrier due to space requirements and implementation complexity). Disadvantages of other sensors include: piezoelectric sensors cannot sense static contact forces because the induced charge in the material dissipates quickly; most such sensors are temperature sensitive and are generally not rugged; lack a dynamic force sensing range; are sensitive to EMC noise (especially in magnetic and piezoelectric sensors); and some piezoelectric sensors are photosensitive. In addition, most known processes for manufacturing these sensors are inherently low-yield, inconsistent, and not scalable. Typically, measurements made with such sensors are not repeatable, resulting in unreliable sensors.

[0015] Of all the available sensors, none are robust enough to be able to perform functions in an ideal manner in a realistic setting. There is a pressing need in the industry for a robust sensor made of durable materials that can withstand thousands to millions of cycles, that is insensitive to temperature and harsh environmental conditions, and that is able to perform three-axis force sensing. The sensor must also be very thin so that it can be added to existing devices without interfering with its functionality, and the operation of the sensor is insensitive to bending so that it can also perform functions on soft surfaces such as soft robots or human skin.

[0016] It is therefore an object of the present invention to provide a compliant three-axis force sensor and method of making such a sensor that addresses at least some of the problems discussed above with current technology use. Summary of the invention

[0017] In a first aspect of the present invention, there is provided a compliant three-axis force sensor comprising:

[0018] a first electrode layer having an array of column electrodes in a first orientation;

[0019] a second electrode layer having an array of column electrodes in a second orientation orthogonal to the first orientation;

[0020] a force-dependent active layer configured to change at least one property when subjected to a force and disposed between the first electrode layer and the second electrode layer;

[0021] at least one three-dimensional protrusion arranged to transmit an externally applied force through the active layer; and

[0022] Therein, at least one spacer is provided, and the at least one spacer is arranged to maintain the separation between two or more layers in the sensor until an external force is applied. Therefore, an embodiment of the present invention includes a compliant three-axis force sensor, which can be made of thin layers of material to allow it to be completely compliant and flexible, but it includes one or more spacers to maintain the spacing between specific layers so that the bending of the sensor itself does not cause erroneous force readings, and the sensor can therefore be rugged, reliable and repeatable. Therefore, the sensor can withstand thousands to millions of cycles without failure and can therefore operate effectively in an industrial environment. The consistent output also eliminates the large amount of time that may be required to calibrate each sensing element individually. This is particularly useful in some embodiments where 4 sensors are used for each tactel, i.e., a protrusion. In addition, the sensor is less sensitive to background noise and can be easily configured with different force sensing ranges depending on the application (i.e., by increasing or decreasing the thickness of the active layer).

[0023] Advantageously, the sensor can be configured as a thin, stretchable, conformable, nanocomposite-based tactile device that can measure forces on three different axes (x, y, and z). Embodiments of the present invention can be sufficiently compliant to be wrapped around very small bend radii or soft robots, but with minimal impact on signal integrity or response, allowing accurate measurement of force magnitude as well as direction. Therefore, the sensor performance is insensitive to bending. Flexible connections and electrical wiring are integrated into the sensor through layer and electrode structures, and the sensor has a "bump" layer on top that converts force into torque. In addition, the sensor is suitable for large-scale production using any of a variety of existing simple mass production processes, such as screen printing and roll-to-roll printing using customizable materials while maintaining high yields. Therefore, it can be deployed in large-scale arrays, such as electronic skin applications may require such arrays. Currently, there is no universal electronic skin of this type. The sensor can be highly integrated into different devices, products or clothing and can be reinstalled on hard, soft and stretchable surfaces. In addition, environmentally friendly materials can also be used.

[0024] Each layer can be printed (e.g., by screen printing or inkjet printing) to enable high miniaturization (at least to the ideal 1mm×1mm three-axis pixel density required for a robotic end effector). In some embodiments, the first electrode layer and / or the second electrode layer can be formed from a conductive ink deposited on an underlying layer.

[0025] All of the above advantages enable embodiments of the present invention to provide a commercially viable sensor suitable for industrial applications in a controlled laboratory environment or "real world" outside of academia.

[0026] The active layer includes at least one of a quantum tunneling material, a piezoresistive material, or a piezoelectric material. Thus, when the active layer is subjected to a force, the at least one property that can be changed is the amount of: quantum tunneling; conductivity; resistivity or charge. Thus, embodiments of the present invention may employ a composite material that utilizes a quantum tunneling conduction mechanism or a piezoresistive conduction mechanism to convert an applied force into a sensing signal. Due to the properties of the material, the active layer is conveniently anisotropic, making it more selective in its response to normal forces when deposited in a thin layer.

[0027] The at least one three-dimensional protrusion may have a footprint that extends at least partially over at least two column electrodes in the first electrode layer and at least partially over at least two column electrodes in the second electrode layer, such that a force applied to the protrusion can be transmitted through the active layer in at least four discrete regions. In this way, each tactel is connected to four sensors or pixels, and the strength of the force on each sensor can be used to determine the magnitude and direction of the applied force (i.e., generating a combination of shear and compressive forces).

[0028] In other embodiments, the at least one three-dimensional protrusion has a footprint contained within the space between two column electrodes in the first electrode layer and between two column electrodes in the second electrode layer. In this case, one or more spacers may be used to redistribute the force applied to the protrusion to each of the four sensors.

[0029] The active layer may include a first active layer and a second active layer, with a gap between the first active layer and the second active layer.

[0030] The sensor may also include one or more of the following: a base layer below the first electrode layer, a top layer above the second electrode layer, a first carbon layer between the first electrode layer and the active layer, a second carbon layer between the second electrode layer and the active layer, and a covering layer on at least one three-dimensional protrusion.

[0031] The first carbon layer and / or the second carbon layer may be continuous over a plurality of column electrodes in the first electrode layer and / or the second electrode layer.

[0032] At least one spacer may be provided within the active layer; between the base layer and the top layer; or on or through the first electrode layer or the second electrode layer.

[0033] The at least one spacer may be in the form of a point, a post, a rod, a cylinder, a tube, a pyramid or a grid.

[0034] At least one spacer may have a solid or hollow cross-section in the form of a circle, square, rectangle, diamond, pentagon, hexagon, or honeycomb lattice.

[0035] The sensor may include an array of said spacers. The spacers in said array may have a plurality of different sizes.

[0036] The active layer may form a continuous layer on the plurality of column electrodes in the first electrode layer and / or the second electrode layer.

[0037] The active layer may form a discontinuous layer on the pillar electrodes in the first electrode layer and / or the second electrode layer.

[0038] The sensor may include an insulator between adjacent electrodes in the first electrode layer and / or the second electrode layer.

[0039] At least one spacer may take the form of an adhesive provided between the active layer and the first electrode layer and / or the second electrode layer, wherein the adhesive is provided in gaps between adjacent pillar electrodes and extends between respective edges of the active layer and said adjacent pillar electrodes.

[0040] The sensor may include an adhesive layer provided between one or more adjacent layers.

[0041] At least one of the three-dimensional protrusions may include a polymer having a different elasticity than the remainder of the sensor.

[0042] The at least one three-dimensional protrusion may be in the form of a platform, a dome, a hemisphere, a hemisphere segment, a cone, a cone segment, a cuboid, a cylinder, a half cylinder, a pyramid, a pyramid segment, a tetrahedron, a tetrahedron segment, a hexahedron, a triangular prism or a polyhedron.

[0043] The height of at least one three-dimensional protrusion can be at least twice the height of the rest of the sensor. In some embodiments, the protrusion can be significantly taller than the rest of the sensor (e.g., up to 3 mm in height) to convert shear forces into sufficiently high moments to compress the underlying active layer material with varying pressures. In some embodiments, the active layer can have a width of 1 mm between electrodes, and each tactel can consist of 4 pixels in a matrix array, with a spacing of 2 mm between each pixel, resulting in a sensing area of ​​3 mm×3 mm=9 mm 2 However, with a more sensitive active layer, better resolution can be achieved. The spacing between the tactile element and the sensor element can be very small to improve resolution (e.g., 500 μm or less), as long as they are not touching and tunneling does not occur between them. Separating the electrodes in this way helps reduce crosstalk in the sensor.

[0044] The sensor may comprise an array of said three-dimensional protrusions.

[0045] According to a second aspect of the present invention, there is provided a method for manufacturing a sensor according to the first aspect, comprising:

[0046] providing a first electrode layer having an array of column electrodes in a first orientation;

[0047] providing a second electrode layer having an array of column electrodes in a second orientation orthogonal to the first orientation;

[0048] providing a force-dependent active layer, the active layer being configured to change at least one property when subjected to the force and being provided between the first electrode layer and the second electrode layer;

[0049] providing at least one three-dimensional protrusion arranged to transmit an externally applied force through the active layer; and

[0050] At least one spacer is provided and arranged to maintain a separation between two or more layers in the sensor until an external force is applied.

[0051] Thus, embodiments of this aspect of the invention provide a method of manufacturing a sensor that can be easily mass-produced using a variety of existing techniques.

[0052] Each layer, protrusion or spacer may be provided by one of printing, screen printing, roll-to-roll printing, inkjet printing, 3D printing, electrospinning, deposition, droplet dispensing, casting, coating, molding, spinning or weaving.

[0053] The method may include forming at least a first electrode layer and the second electrode layer on a single substrate; separating the substrate into two parts; and stacking the two parts together.

[0054] The method may comprise forming at least one spacer on at least one of the portions prior to said separating and / or stacking. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Non-limiting embodiments of the present invention will now be described for purposes of illustration only with reference to the following drawings, in which:

[0056] Figure 1A shows a top perspective view of a compliant three-axis force sensor including a dome-shaped protrusion according to a first embodiment of the present invention;

[0057] Figure 1B Shows Figure 1A A side view of the sensor;

[0058] Figure 1C Shows Figure 1A A plan view of the sensor;

[0059] Figure 2A shows a top perspective view of a compliant three-axis force sensor including a cube-shaped protrusion according to a second embodiment of the present invention;

[0060] Figure 2BShows Figure 2A A side view of the sensor;

[0061] Figure 2C Shows Figure 2A A plan view of the sensor;

[0062] Figure 3A A top perspective view of a compliant three-axis force sensor including a cylindrical shaped protrusion according to a third embodiment of the present invention is shown;

[0063] Figure 3B Shows Figure 3A A side view of the sensor;

[0064] Figure 3C Shows Figure 3A A plan view of the sensor;

[0065] Figure 4 is a flow chart of a method for manufacturing a sensor according to an embodiment of the present invention;

[0066] FIG. 5A to FIG. 5I Illustrate the steps of a method for manufacturing a sensor according to another embodiment of the present invention;

[0067] FIG. 6A to FIG. 6I Illustrate the steps of a method for manufacturing a sensor according to yet another embodiment of the present invention;

[0068] FIG. 7A to FIG. 7G Illustrate the steps of a method for manufacturing a sensor according to yet another embodiment of the present invention;

[0069] Fig. 8A and Figure 8B A plan view showing a portion of a sensor including different cylindrical support post configurations according to an embodiment of the present invention;

[0070] Fig. 9A and Fig. 9B A plan view showing a portion of a sensor including a different diamond-shaped support post configuration according to an embodiment of the present invention;

[0071] Fig. 10A and Fig. 10B A plan view showing a portion of a sensor including a different square support post configuration according to an embodiment of the present invention;

[0072] Fig.11A , Fig. 11B and Fig. 11C A plan view showing a portion of a sensor including a different hexagonal support post configuration according to an embodiment of the present invention; and

[0073] Fig. 12AA top perspective view showing a single tactel of a sensor according to an embodiment of the present invention;

[0074] Fig. 12B Show Fig. 12A Side perspective views of a tactile element before and after application of an oblique force and corresponding force versus time graphs; and

[0075] Fig. 12C Show Fig. 12B A side view of a tactile element when an oblique force is applied. DETAILED DESCRIPTION

[0076] according to Figure 1A , Figure 1B and Figure 1C , shows a compliant three-axis force sensor 100 including four three-dimensional dome-shaped protrusions 102 according to a first embodiment of the present invention. The sensor 100 includes a base layer 104 in the form of a bottom film packaging layer; a first (bottom) electrode layer 106 having an array of column electrodes 106a in a first orientation; a second (top) electrode layer 108 having an array of column electrodes 108a in a second orientation orthogonal to the first orientation; a force-dependent active layer 110 in the form of a quantum tunneling material layer, which is configured to change at least one property when subjected to force and is disposed between the first electrode layer 106 and the second electrode layer 104; and a top layer 112 in the form of a top film packaging layer. The dome-shaped protrusions 102 are disposed on the top layer and are arranged to transmit externally applied forces through the active layer 110. Although in Figure 1A , Figure 1B and Figure 1C Although not shown, at least one spacer is provided, which is arranged to maintain the separation between two or more layers in the sensor 100 until an external force is applied. Figures 4 to 11C The spacer is described in more detail.

[0077] like Figure 1A and Figure 1B As shown, an optional array of insulators 114 is disposed between pillar electrodes 106a in the first electrode layer 106. A similar array of insulators 116 is disposed between pillar electrodes 108a in the second electrode layer 108. Each protrusion 102 has a circular base 102a and a curved sidewall 102b extending to a flat top 102c.

[0078] In this embodiment, each of the base layer 104, the first electrode layer 106, the active layer 110, the second electrode layer 108 and the top layer 112 is 0.10 mm thick to form a sensor body of 0.50 mm thickness. In addition, each column electrode 106a, 108a is 1 mm wide, and the height of each protrusion 102 is 1 mm and has a maximum diameter of 3 mm. There is a gap of 1 mm between each adjacent protrusion 102. In other embodiments, other sizes can be used to suit specific applications. However, it is conceivable that the sensor body is usually composed of relatively thin layers to allow the sensor to be compliant and can be applied to curved or other shaped surfaces. As shown here, in some embodiments, the protrusion 102 can be significantly higher than the sensor body to convert the shear force into a sufficiently high moment, which in turn compresses the active layer 110 below with different pressures.

[0079] like Figure 1C As shown, each three-dimensional dome-shaped protrusion 102 has a footprint extending at least partially over at least two column electrodes in the first electrode layer 106 and at least two column electrodes in the second electrode layer 108, so that a force applied to the protrusion 102 can be transmitted through the active layer 110 in at least four discrete regions. In this way, each protrusion 102 can be considered to be connected to four sensing elements (sensels) or tactile elements (tactels) of a pixel, and the strength of the force at each sensor can be used to determine the location, magnitude, and direction of the applied force (i.e., to generate a combination of shear force and compressive force), as described below with reference to Fig. 12A , Fig. 12B and Fig. 12C Further explanation. Note that Figure 1C In FIG. 1 , the pillar electrodes 106 a , 108 a are shown in dashed lines as if the layers of the sensor 100 were transparent.

[0080] Although sensor 100Neo is shown having an array of four protrusions 102, the sensor body may be extended and may include any number of protrusions 102 desired for any given application.

[0081] In any of the embodiments described, the sensor may be formed from any selection of the materials listed below.

[0082] The base layer 104 and the top layer 106 may be formed from any suitable substrate and may include one or more of the following: polyethylene (para-xylelene) polymer (Parylene), 2,8-dichlorotricyclo[8.2.2.2 4,7] Hexadecane-1(12),4,6,10,13,15-hexene (Parylene-C), polydimethylsiloxane (PDMS), polyimide (PI), polybutyrate, polyethylene (methyl methacrylate) (PMMA / Acrylic), acrylate, polyethylene (PE), high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyethylene terephthalate (PET), thermoplastic polyurethane (TPU), polyurethane (PU), polysiloxane (Silicone), polyvinyl chloride (PVC), polyethyleneimine (PEI), polyethylene naphthalate (PEN), polypropylene (PP), polystyrene (PS), aliphatic or 30 semi-aromatic polyamide (PI), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), non-woven fabric or a mixture thereof. Low Young's modulus polymers can help to achieve higher consistency, for example a Young's modulus of up to 1.5 MPa (megaPascals), more preferably up to 1.2 MPa, still more preferably up to 1 MPa and preferably at least 500 kPa, for example in the range of 700 kPa to 1 MPa, for example 700 to 800 kPa. This is particularly applicable to PDMS; the disadvantage of these low Young's modulus polymers is that they are often too brittle or not heat-resistant enough for certain applications. For this purpose, a mixture such as silicone coated with TPU can be used. Many of the harder polymers in the list (such as PEN) have high flexibility at a thickness of 25 microns. Some exemplary thicknesses of different possible substrates are: Parylene-C, 500-10000 nm; PEN, 25-100 microns; PET, 36-125 microns; Silicone, 5-500 microns; TPU, 50-75 microns.

[0083] The column electrodes 106a, 108a of both the first electrode layer 106 and the second electrode layer 108 can be formed of a conductive composite material containing ink such as metal filler particles (micrometer or nanometer scale). Carbon, silver, gold and copper are the most commonly used. If the substrate is not stretchable or particularly thin, or if the metal has a curvature when the substrate is stretched rather than stretching the metal itself, a metal film (e.g., gold / copper) can be used. All of these need to have high conductivity, and the best metal used is gold, because it is the most ductile and tough of all metals. Some example materials that can be used for the column electrodes 106a, 108a are conductive inks (CI) of Engineered Materials Solutions, Inc. (EMS) (e.g., CI-1036, which is a silver conductive ink with a sheet resistivity of <0.010Ω / area (square) at a thickness of 25.4 microns; or CI-2051, which is a carbon-based conductive ink with a sheet resistivity of <50Ω / area (square) at a thickness of 25.4 microns). Other suitable materials include Asahi TM ink and gold film, which has a thermal conductivity of 2.44×10 -8 Resistivity of Ωm.

[0084] The active layer 110 may include a quantum tunneling material, a piezoresistive material, or a piezoelectric material. Due to the quantum tunneling effect, the resistance of the quantum tunneling material will decrease exponentially, which results in a value as high as 10 12 The huge resistance change of Ω spans a very large dynamic force range. In some embodiments, the force range that can be sensed can be as low as 0.003N to 200N, and this can be extended to higher if more rigid materials are used in the sensor. Examples of suitable quantum tunneling materials are quantum tunneling composite materials. It includes a binder material plus nickel or silicon (semiconductor) filler particles with high aspect ratio tips (e.g., rounded, pointed, or needle-shaped). Particles composed of dielectric materials (such as titanium dioxide or fumed silica particles) can also be used in this material. Metals or metal alloys with void-bearing structures can also be used with a variety of different binders. Another suitable quantum tunneling material is It contains pointed or needle-shaped magnets and / or nickel particles and a polyurethane adhesive. The particles do not touch each other, but the current can pass through them through the quantum tunneling mechanism. Zero-dimensional, one-dimensional or two-dimensional nanoparticle materials may be ideal due to their enhanced dynamic range and sensitivity. Part of the reason for this may be that the local electric field at its tip is concentrated to enhance the quantum tunneling effect and the lower percolation threshold (and therefore the quantity) of the required material. Advantageously, quantum tunneling materials are most sensitive to the compressive pressure between the electrodes measuring the resistance, which allows, for example, significant selectivity that strain gauges do not provide. Compared with many other sensors and materials, quantum tunneling materials are also less sensitive to temperature and environmental electromagnetic compatibility noise.

[0085] Suitable piezoresistive materials include nanocomposites and electrostatically spun microfibers or nanofibers. When different voltages are applied to the piezoresistive material and pressure is applied to the material, the piezoresistive material regulates the current. These include active fillers (micrometers / nanometer particles), which can be carbon, carbon nanotubes (CNTs), multi-walled carbon nanotubes (MWCNTs), graphene, borophene, silver, quantum dots or any other conductive or semiconductor micrometers / nanometer particles. They can also include surfactants that usually perform functions on the surface of nanoparticles to increase dispersion and reduce agglomeration due to, for example, van der Waals forces. Adhesives such as PDMS, silicones, tetrafluoroethylene (TFE), propylene, PVDF (all of which are not piezoelectric), other polymers such as those contained in substrates or concrete are also used. Polymers can be thermosetting (i.e., permanent crosslinking reactions occur due to heat, moisture, light or air) or non-thermosetting (i.e., melting). They can also be fluoropolymers. Piezoresistive materials can also include solvents to control viscosity (e.g., during printing), but the solvents are usually mostly evaporated in the air or during curing. The nanoparticles are ideally arranged vertically (and well dispersed) to enhance the anisotropic behavior of the material, thereby sensing the pressure generated in the normal direction due to bending and stretching of the material and the minimum pressure reading. Some particles in the piezoresistive material can be electrically aligned or magnetically aligned (by applying a static or changing electric and / or magnetic field to the material before and / or during curing and / or deposition). For example, this can be achieved by using dielectrophoresis alignment by changing the AC (alternating current) electric field through the material before curing, by applying a DC (direct current) current through the material and using DC alignment, or purely by a DC electric field (wherein a static field exists in the material without current flowing through its conductive particles). This alignment can be performed to make the piezoresistive material more anisotropic or light-transmitting. If the conductive particles in the piezoresistive material themselves do not respond to the applied field, they can use other nanoparticles (e.g., ferromagnetic iron oxide nanoparticles) to perform functions to be aligned. Other potentially suitable piezoresistive materials include films of any fillers used in the nanocomposites listed above.

[0086] Suitable piezoelectric materials also include nanocomposites and electrostatically spun microfibers or nanofibers. These may include active fillers (micro / nanoparticles) that exhibit charge separation due to external stress, which may include but are not limited to zinc oxide (ZnO), polyvinylidene fluoride (PVDF), polyethylene (vinylidenefluoride-co-trifluoroethylene) P (VDF-TrFE), lead zirconate titanate (PZT), barium titanate (BaTiO3), lead (II) titanate (PbTiO3), lithium tantalate (LiTaO3), aluminum nitride (AlN), borosilicate minerals containing complex elements (tourmaline), lead magnesium niobate-lead titanate (PMN-PT) or any combination thereof, plus a binder such as those listed above. Other potentially suitable piezoelectric materials include films of any filler used in the nanocomposites listed above.

[0087] The protrusions 102 may include a polymer, such as a dielectric polymer, polysiloxane, rubber, silicone, or an amorphous crystalline material such as glass.

[0088] Figure 2A , Figure 2B and Figure 2C A compliant three-axis force sensor 200 including four three-dimensional cuboid protrusions 202 according to a second embodiment of the present invention is shown. The sensor 200 includes the same sensor body as the sensor 100 described above, but the four dome-shaped protrusions 102 are replaced by four cuboid protrusions 202. Therefore, similar reference numerals will be used for similar components. As described above, each protrusion 202 has a footprint extending onto two column electrodes 106a in the first electrode layer 106 and onto two column electrodes in the second electrode layer 108, so that the force applied to the protrusion 202 can be transmitted through the active layer 110 in at least four discrete areas.

[0089] Figure 3A , Figure 3B and Figure 3C A compliant three-axis force sensor 300 including four three-dimensional cylindrical protrusions 202 according to a third embodiment of the present invention is shown. The sensor 300 includes the same sensor body as the sensor 100 described above, but the four dome-shaped protrusions 102 are replaced by four cylindrical protrusions 302. Therefore, similar reference numerals will be used for similar components. As described above, each protrusion 302 has a footprint extending over two column electrodes 106a in the first electrode layer 106 and two column electrodes in the second electrode layer 108, so that a force applied to the protrusion 302 can be transmitted through the active layer 110 in at least four discrete areas.

[0090] It should be understood that the above three-dimensional protrusions are only examples. In other embodiments, each protrusion may be in the following forms: platform, dome, hemisphere, hemispherical segment, cone, cone segment, cuboid, cylinder, semi-cylinder, pyramid, pyramid segment, tetrahedron, tetrahedron segment, hexahedron, triangular prism, polyhedron or other shapes. In addition, the sensor may include protrusions of different shapes and / or materials to suit any given application.

[0091] Figure 4 is a flow chart of a general method 400 for manufacturing a sensor as described above according to an embodiment of the present invention. The method 400 includes a step 402 of providing a first electrode layer 106 having an array of column electrodes 106a in a first orientation; a step 404 of providing a second electrode layer 108 having an array of column electrodes 108a in a second orientation orthogonal to the first orientation; a step 406 of providing a force-dependent active layer 110, the active layer 110 being configured to change at least one characteristic when subjected to a force and being disposed between the first electrode layer 106 and the second electrode layer 108; a step 408 of providing at least one three-dimensional protrusion 102, 202, 302 arranged to transmit an externally applied force through the active layer 110; and a step 410 of providing at least one spacer arranged to maintain separation between two or more layers in the sensor until an external force is applied. As described above, the spacer will be shown and described in more detail below.

[0092] Each layer, protrusion or spacer may be provided by one of the following: printing, screen printing, roll-to-roll printing, inkjet printing, 3D printing, electrospinning, deposition, droplet dispensing, casting, coating, molding, spinning or weaving. The method 400 may include forming at least a first electrode layer 106 and a second electrode layer 108 on a single substrate 104; separating the substrate into two parts; and stacking the two parts together, as will be explained in further detail below. The method 400 may also include forming at least one spacer on at least one part before said separation and / or stacking.

[0093] FIG. 5A to FIG. 5I The steps of a specific method 500 of manufacturing a sensor according to an embodiment of the present invention are illustrated. Figure 5A In the process, the base layer 504 is spin coated, deposited, cast or sprayed into a thin film that forms the bottom polymer encapsulation layer. Ideally, the base layer 504 is made of an insulating polymer (such as PDMS or Parylene-C) with the required elastic properties, which can also form part of the adhesive material of the active layer. If spin coating, it can be done on a silanized silicon wafer so that the polymer does not get stuck and the device can be peeled off after production. Figure 5BIn the embodiment of the present invention, the first electrode layer 506 is screen printed, cast, sputter coated, or spin coated (e.g., using photolithographic patterning) into the matrix array of bottom column electrodes. The first electrode layer 506 can be composed of a conductive adhesive, such as a carbon impregnated elastomer, an intrinsically conductive polymer such as polyethylene (3,4-ethyldioxythiophene) polystyrene sulfonate (PEDOT:PSS), or a metal such as gold or silver. Figure 5C An optional step of adding an insulating layer 514 between each column electrode in the first electrode layer 506 for additional stiffness or robustness using screen printing or photolithographic patterning is shown. In this case, the insulating layer 514 can be made of the same material as the base layer 504. Figure 5D The attachment of a thin active layer 510 of, for example, a quantum tunneling material (such as those described above) is shown by screen printing, casting, spin coating, spray coating, or the like. The thickness of the active layer 510 can determine the sensitivity of the sensor and can vary from tens of microns to several millimeters. The type of metal and the bonding matrix material can vary depending on the desired application, and the composition of the material can be in liquid or solid form. For example, the active layer 510 can include gold nanoparticles and PDMS, or alternatively include a magnet and a water-based polymer ink. It can be a known material or a custom formulated material. Figure 5E Screen printing, casting, sputter coating or spin coating (e.g., using photolithographic patterns) is shown to create a thin layer (~10-100um thick) of adhesive material so that spacers 520 are formed only in the areas between the electrodes to be deposited so that the electrode edges are on top of the spacer edges. These spacers form small air gaps between the electrodes. Standard micromachining or chemical techniques can be used to create the air gaps, such as patterning a partially soluble layer using, for example, a photocurable polymer. Fig. 5F A matrix array of top electrodes in a second electrode layer 508 perpendicular to the first electrode layer 506 is shown formed on top of the spacer 520 by screen printing, casting, sputter coating, spin coating or attaching (e.g., using photolithographic patterns). The second electrode layer 508 can be composed of a conductive adhesive, such as a carbon impregnated elastomer, an intrinsically conductive polymer such as PEDOT:PSS, or a metal such as gold or silver. Optionally, a support layer is provided between the spacers 520 on which the top electrodes are formed. Figure 5G An optional step of adding an insulating layer 514 between the top electrodes of the second electrode layer 508 using screen printing or photolithographic patterning techniques to obtain additional stiffness or robustness is shown. As described above, the insulating layer 514 can be the same material as the base layer 504. Figure 5H In the embodiment, the top layer 512 is spin coated, deposited, cast or sprayed into the film to form the top polymer encapsulation layer. The top layer 512 can be made of an insulating polymer with the required elastic properties, such as PDMS or Parylene-C, and can ideally be formed of the same material as the adhesive material of the active layer 510. Fig.5IIn the method 500, four three-dimensional surface protrusions 502 are added to the top layer 512 by casting a polymer layer on each group of four overlapping electrodes or sensors to form the protrusions 502. It is worth noting that the protrusions 502 have different elasticity and stiffness from the rest of the sensor (for example, the protrusions 502 may be more rigid than the sensor body). For example, the three-dimensional shape of each protrusion 502 can be a cube, a cone, or a platform / hemisphere, and its corners should overlap with the four lower electrodes to a certain extent. This gives each group of 4 electrodes (i.e., sensor elements) in the array the ability to become a single three-dimensional or three-axis force sensing tactile element (tactel). After each step described in method 500, an optional oxygen plasma layer, a thiol layer, or other chemical adhesive layer can be added to improve the robustness of the sensor. If the base layer 502 has been spin-coated, further steps may be required to peel the entire assembly off the wafer by peeling it off.

[0094] If the adhesive material of the above method is a stretchable elastomer, the entire sensor array can also be made stretchable to further increase its potential applications.

[0095] The substrate or base layer 504 used to create the sensor depends to some extent on the application. Conventional flexible electronic substrates that are compliant in only one axis can be used, such as PET (polyethylene terephthalate) with a thickness varying between 25-125 microns and PEN (polyethylene naphthoate) with a thickness varying between 10-100 microns (typically 25 microns). These materials may be needed when high resolution is required, or when the device needs to withstand harsh external environments (such as underwater). For less harsh conditions, substrates that are compliant in more than one axis, such as TPU (thermoplastic polyurethane) or silicone, can be used. Or TPU-coated silicone to reduce shrinkage caused in silicone during thermal curing of the nanocomposite ink after deposition. The thickness of these materials can also be between 25-125 microns. Non-woven fabrics as well as paper and various rubbers or latexes can also be used as substrates. Various other polymers can also be used as substrates. Parylene-C can be used in the 10 nm-1 μm range, for example, for biocompatible applications or those requiring extreme compliance and / or complete sealing from the outside. In addition, if necessary, ink can be placed on top of the substrate to facilitate the spreading of the ink for the electrodes during printing.

[0096] A first layer of conductive ink can be printed, which serves as a conductive track for the first electrode layer 506 and has a high conductivity. To define the matrix pattern of the first electrode layer 506, a stencil or mask or screen printing mesh with appropriate openings by cutting or cleaning with a solvent can be used, through which the ink can be spread onto the substrate using a squeegee commonly used in screen printing or roll-to-roll printing. The sheet resistivity is 0.05 ohm / mm 2Such electrode layers within the range are made of nanocomposites and can be flexible or stretchable. Stretchable inks work with substrates such as TPU or silicone that can allow a certain proportion of stretching. Such inks contain conductive particles that are usually nanometer-sized and generally micrometer-sized in total size, which are embedded in a polymer matrix that is usually mixed with solvent chemicals and surfactants for ensuring uniform dispersion between particles in the ink. The particles are usually composed of silver or carbon, but can also be composed of gold, graphene, copper, tungsten, zinc, etc. In screen printing, the thickness of the deposited ink can be on the order of 10-50 microns (sometimes 100 microns), but if inkjet printing is used, the thickness can be even smaller. The width of some electrodes can be as low as 20 microns to 1 mm.

[0097] After the electrode ink is deposited, it must usually be cured at a temperature between 80-120° C. During curing, part of the solvent evaporates while curing the polymer composite.

[0098] The trace compositions that may be required to connect the sensor to the readout electronics and the electrodes themselves may be the same composition or made of different compositions. Alternatively, the electrodes may be printed with an ink having a different composition on top of the conductive traces that extend to the area under each electrode.

[0099] One or more of the sensitive (potentially anisotropic, ie sensitive only to the normal direction, either by material thickness or its intrinsic properties) active layers are provided in each sensor.

[0100] Additionally, spacers composed of dielectric polymers can be printed or deposited onto the sensor using a droplet dispensing method. These spacers are ~10-50 microns in height and ~1-200 microns in diameter or width and are used to keep the sensor's grid layers separated from each other until a specific force is applied. They also serve to redistribute the force and prevent the sensor skin from wrinkling or wrinkling when bent, which in turn could create localized pressure points or "bubbles" that could result in pressure readings on the sensor.

[0101] Once the sensor is printed, reinforcements can be added to the ends of the connected electrode traces or tracks if the material is highly compliant and stretchable or if the material is very thin such as 25 microns or less so that normal solder tabs or cables can be crimped onto them and the sensor electronics can be connected to a rigid electronic processing circuit.

[0102] FIG. 6A to FIG. 6I The steps of a method 600 for manufacturing another sensor according to another embodiment of the present invention are illustrated. In each step, the sensor is shown in three-dimensional and two-dimensional views. Fig. 6AIn the embodiment, a suitable substrate material 604 is selected (e.g., PEN, PET, TPU, PDMS, silicone coated with TPU, latex, etc.) and manufactured to the desired thickness. In this case, the substrate 604 will form the base layer and top layer of the sensor, as will be described in more detail below. In this embodiment, the substrate 604 is PET with a thickness of 36 microns. Figure 6B The steps of printing (e.g., screen printing or inkjet printing) the first electrode layer 206 and the second electrode layer 608 in a matrix array having row electrodes and column electrodes perpendicular to each other are shown. The electrodes are formed of inks that generally contain silver or low-resistance carbon. In the present embodiment, the electrodes are made of CI-1036 stretchable silver-based conductive ink with a sheet resistivity of <0.010Ω / area (Ω / square) at a thickness of 25.4 microns. In this example, the electrodes are screen printed as emulsion thickness, so that the electrodes have a thickness of 14 to 25 microns before curing. Each electrode has a width of 2 mm, and three electrodes are provided in each of the first electrode layer 606 and the second electrode layer 608 to form a sensor that will be 1 cm wide × 1 cm long when assembled. A gap of 2 mm is provided between the first electrode layer 606 and the second electrode layer 608 on the substrate 604 to allow each layer to be easily separated, as will be described below. Figure 6C An optional step of screen printing a carbon layer 607, 609 on each of the first electrode layer 606 and the second electrode layer 608 is shown. Fig.6D The step of depositing (e.g., screen printing, inkjet printing, electrospinning) an active layer 610 on each of the first electrode layer 606 and the second electrode layer 608 is shown. The active layer may include a layer of piezoresistive and / or quantum tunneling and / or piezoelectric material and can be deposited on top of each other as a single layer or more layers to control the layer thickness. The active layer may include a continuous piece or discrete portions, for example, in the form of lines, squares, dots, or other shapes. In this embodiment, the active layer consists of a quantum technology super sensor. The C75 piezoresistive ink is formed, which is printed only on top of the electrode columns and rows on the grid area and has a similar thickness to the previous layers. Fig. 6EIn the embodiment, a dielectric, insulating or conductive material is used to deposit a spacer layer 620. The spacer layer 620 can be deposited, for example, by screen printing, inkjet printing or using a droplet dispenser. In this embodiment, a spacer layer 620 is formed only on one side of the substrate 604 in the gap between the electrodes forming the second set of electrodes 608. In this example, the spacer layer 620 includes an array of cylindrical columns, each having a diameter of 50 microns and a height of 100 microns and arranged at a spacing of 1 mm on the substrate 604. The material used for the spacer layer 620 in this example is a dielectric such as EMS DI-7548 that is both stretchable and flexible. The spacer layer 620 can be printed on one side of the sensor in a single thickness layer, more layers applied on top of each other, or if the layer is thin, it is printed on both sides of the sensor (although this requires precise alignment).

[0103] exist Fig. 6F In the process, the substrate 604 is cut, for example, using scissors, laser, knife plotter or electron beam lithography to separate the first electrode layer 606 and the second electrode layer 608 into two parts. The two parts are then folded inward so that the second electrode layer 608 is stacked on top of the first electrode layer 606 to form a Figure 6G The conductive matrix grid is shown. In this configuration, the substrate 604 attached to the second electrode layer 608 forms the top layer of the sensor. In addition, the posts of the spacer layer 620 extend between the substrate 604 forming the base layer and the substrate 604 forming the top layer, so that there is an air gap 622 in the portion of the active layer 610 that is disposed between the first electrode layer 606 and the second electrode layer 608. When similar to Figure 6G When stacking the sensors, the spacer layer 620 serves to distribute the force when the sensor is bent, and in this case also serves to maintain an air gap between the active layers 610 to ensure that an open circuit exists until a given offset force is applied. In some embodiments, the sides of the sensor can be bonded using an adhesive paste (e.g., silicone PDMS) applied along the edges of the device and around the sensing layer area to seal it from the external environment and laminate the sensor sides to each other in a durable manner. In addition, vapor deposition of APTES (3-aminopropyltriethoxysilane) linker can be applied to the top layer for 1 hour. In some embodiments, the sensor can be completely coated with a compliant polymer, such as latex, at this stage. For extremely thin sensors, dip coating techniques can be used.

[0104] like Figure 6HAs shown, the protrusion 602 is then applied to the top surface of the sensor to convert the force into a torque. In order to sense the direction and magnitude of the force, the protrusion should be placed at the center of each group of 4 orthogonally arranged electrodes (sensels), which can convert any force applied into a torque when pressed. Then, the torque will compress some sensor elements more heavily than other sensor elements, which can be read by the attached electronic circuit. Multiple dielectric layers can be printed by using various printing techniques (including 3D printing or silicon etching), or by casting the protrusion in a mold (in this case, when the polymer used is in a liquid or partially cured state, the sensor needs to be inverted on the mold, and then the entire assembly must be cured). In this embodiment, the original mold is made of PLA for four cubic protrusions 602 (height is 2mm, length and width are 6mm). Then liquid PDMS (or silicone / latex / TPU / rubber) is cast into the mold (the weight ratio of elastomer to curing agent is 10: 1) and cured in an oven at 80 degrees Celsius for 1 hour. After this, the PDMS is treated with UV ozone or oxygen plasma to further increase adhesion before bonding it to the top layer of PET on substrate 604. The assembly is left overnight to form a strong bond between the PDMS protrusions and the PET. The protrusions 602 themselves can be rigid or compliant, as long as they allow the device to bend at a given thickness. Thinner protrusions 602 and protrusions made of highly compliant materials will distort the measurements less when bent, thus providing better anisotropic selectivity for the normal force when the device is in a bent state.

[0105] like Fig.6I As shown, a final optional step may include laminating or insulating the top of the sensor or the edge of the sensor or the entire sensor structure to form a cover layer impermeable to external elements 624. Lamination may be performed using, for example, a fully conformable Parlene coating (more specifically, Parlene-C with a thickness of 1 nm to 1 μm), and insulation may be achieved using silicone, rubber, polyurethane or other blended polymers.

[0106] It will be appreciated that any suitable printer may be employed for any layer in the sensor. However, an example of a suitable screen printer is the Horizon Dek i3™.

[0107] The sensor readings can be taken using the known zero potential method. This minimizes crosstalk between adjacent sensors within a large array. In a resistor array circuit, large interference currents can be generated when the resistance of one sensing element approaches the resistance of the other elements around it. In the negative piezoresistive sensor described herein, the resistance of the sensing element decreases from a high resistance as pressure is applied. This means that in the described sensor, low pressures produce higher interference due to the high resistance of the material at rest. These are provided below. FIG. 12A to FIG. 12C More details on the operation of the relevant sensors.

[0108] FIG. 7A to FIG. 7G The steps of a method of making a sensor according to yet another embodiment of the invention are illustrated. This sensor can be considered a 4-wire single point sensor, which operates differently from the other sensors described above. In particular, this sensor differs in that it measures the "center of mass" of the pressure applied within the resistive region between the 4 wires in the electrode grid. Since the location of the center of mass can provide us with the direction of the force, the protrusion of this sensor functions in a similar manner to a joystick.

[0109] like Fig. 7A As shown, select a suitable material and thickness of substrate 704. In this embodiment, substrate 704 is formed of PET with a thickness of 36 microns. Figure 7B The screen printing of the first electrode layer 706 and the second electrode layer 708 on the same substrate 704 is shown, wherein the electrodes in each layer are positioned perpendicular to each other. In this embodiment, the electrodes are made of EMS CI-1036 TM The electrodes are made of a stretchable silver-based conductive ink having a low sheet resistivity of <0.010Ω / square at a thickness of 25.4 microns. In this embodiment, the electrodes are screen printed at an emulsion thickness such that the ink thickness before curing is 14 to 25 microns. The electrodes are 2 mm wide and only two electrodes are provided along the edge of each of the first electrode layer 706 and the second electrode layer 708 to form a 1 cm x 1 cm footprint sensor.

[0110] Figure 7C The screen printing of a first high resistance carbon layer 707 deposited on top of and extending between two electrodes in the first electrode layer 706 and a second high resistance carbon layer 709 deposited on top of and extending between two electrodes in the second electrode layer 709 is shown. In this embodiment, both high resistance carbon layers are made of two Henkel inks called ECI 7004HR and NCI 7002 inks. TMThe inks are mixed (80% / 20% mixture by weight) to give a sheet resistivity of ~10,100 Ω / square / ml at 10 microns thick after curing. Deposition is done through a web with an emulsion thickness of about 20-40 microns. In other embodiments, EMS may be used. TM CI-2050LR (1,500-2,500 Ω / area / ml at 25.4 μm) and / or HR (>10 MΩ / area / ml at 25.4 μm) form a high resistive carbon layer. In some embodiments, the first high resistive carbon layer 707 and the second high resistive carbon layer 709 may be different.

[0111] For this type of sensor, it is important that the resistance of the high resistance carbon layers 707, 709 is much higher than the sum of the lead resistance within the device and the contact resistance of the interface to the outside world. The reason for this is that when a voltage is applied to the top electrode layer 708 or the bottom electrode layer 706 of the device, most of the voltage drop is expected to occur in the resistive carbon area. This ensures that the location of the pressure center of the torque applied to the raised layer can be measured: when pressure is applied to the device, the two active layers 710 are in contact with each other around a given point. If a potential difference is applied to the electrodes on one side of the device (top or bottom) and the voltage is measured from either electrode on the other side of the device, a voltage divider circuit is formed. The voltage reading from one of the electrodes opposite the carbon plane (to which the potential difference is applied) will give the pressure position between the two electrodes to which the pressure is applied (on one axis). This electrical configuration can be flipped to read the position of the other axis, with the electrodes / carbon layers on the other side of the device.

[0112] Fig.7D The screen printing, inkjet printing or electrospinning of the active layer 710 on each of the first high resistance carbon layer 707 and the second high resistance carbon layer 709 is shown. In this embodiment, the active layer 710 is made of a quantum technology super sensor. C75 piezoresistive water-based ink is formed.

[0113] exist Fig. 7E In the embodiment, a spacer layer 720 comprising a square array of short cylindrical spacer dots is provided on the active layer 710 on one side (first side) of the substrate. Each spacer dot is 200 microns in height and is spaced 2 mm apart from its neighboring dots. In this embodiment, the spacer layer 720 is provided using the Stratasys Tango TM (TangoPlus TM , FLX930) material (which is a PolyJet that simulates a rubber thermoplastic elastomer TMThe spacer layer 720 is printed using a printable material). Typical properties of this material are a Shore stiffness of 26-28 and an elongation at break of 170-220%. Therefore, even if pressure is applied when the device itself is flat, the spacer is able to withstand the difference between the tensile stress and the compressive stress at the top and bottom of the device when it is bent. The substrate 704 is then cut, for example using scissors, a laser, a knife plotter, or electron beam lithography, to separate the first electrode layer 706 and the second electrode layer 708 into two parts. The two parts are then folded inward so that the second electrode layer 708 is stacked above the first electrode layer 706 to form a Fig. 7E The conductive matrix grid is shown. In this configuration, the substrate 704 attached to the second electrode layer 708 forms the top layer of the sensor. In addition, the posts of the spacer layer 720 extend between the active layer 710 on the first electrode layer 706 and the active layer 710 on the second electrode layer 708, so that there is an air gap in the middle of the active layer 710, as shown in FIG. Figure 7F As shown. Once the device was cut and folded, the sides were bonded using a silicone PDMS adhesive coated around the edges of the device. Vapor deposition of APTES (3-aminopropyltriethoxysilane) linker was then applied to the upper surface of the device for 1 hour to promote PDMS adhesion as described below.

[0114] exist Figure 7G In the embodiment, the projection 702 is arranged in the middle of the sensor, spaced apart from the electrode grid. The projection 702 can be cast or printed, and a variety of polymers can be used for this purpose, such as more flexible PDM or inflexible SU8. Depending on the desired application, the projection 702 can have various shapes, sizes and heights. In the present embodiment, the original mold for the rectangular projection 702 is made of PLA, and its height is 2mm, and the length and width are 6mm. Liquid PDMS is cast into the mold (the weight ratio of elastomer to curing agent is 10: 1) and cured in an oven at 80 degrees Celsius for 1 hour. After this, before being pasted to the top layer of the substrate 704, the PDMS is treated with UV ozone or oxygen plasma to further increase adhesion. The assembly can be placed overnight to form a firm bond between the PDMS projection and the substrate 704.

[0115] For this type of sensor, the reading of each protrusion 702 consists of three separate readings. One reading is required for the X position and another for the Y position, as explained below. Each time, a voltage (and current) is applied to the electrodes on one plane (i.e., the first electrode layer 706 or the second electrode layer 708) and a voltage is read using one of the electrodes on the opposite plane (i.e., the other of the first electrode layer 706 or the second electrode layer 708). This forms a voltage divider circuit in which the voltage read corresponds to the (x or y) position where the two planes touch (which is where the force is applied). Importantly, the resistance of the high-resistance carbon layer is much higher than the lead resistance and contact resistance that connects the device to the outside world, making them essentially negligible. Otherwise, the position reading is limited as some significant voltage drop will occur in the leads.

[0116] In order to read the force itself, the current must flow from one plane to another plane, where the active layer 710 (i.e., the piezoresistive material) is located between the two planes. This can be achieved by applying a potential difference between one electrode on the top plane (i.e., the second electrode layer 708) and another electrode on the bottom plane (i.e., the first electrode layer 706). In this case, the applied pressure affects the resistance of the active layer, which in turn changes the current through the device. Therefore, the total voltage drop on the active layer 710 will also change. By using opposite electrodes (not used to transmit current) on two planes, it is possible to measure the voltage at two locations. This corresponds to what is called a four-point probe measurement in the electronics literature, because it does not measure the contact resistance or, in this case, the voltage drop in the electrodes of the device and their corresponding leads. However, since we are measuring the voltage drop, it is not perfect. Depending on the location where the pressure is applied, different distances on the high resistance plane will require the current to pass through, which causes a variable resistance and therefore a variable voltage drop in the resistance layer due to the location where the pressure is applied. Knowing the resistance and uniformity of the high resistance layer can understand how much the resistance measurement should be adjusted based on the location and through the device calibration. Thus, when a force is applied to the protrusion 702 on top of the sensor, its shear component creates a moment on the protrusion 702, which concentrates the center of pressure to a specific area of ​​the device. Measuring the location and magnitude of this force allows the average direction and magnitude of the force to be measured.

[0117] The spacer in any of the embodiments of the present invention serves to distribute the force and prevent wrinkles from forming in the sensor that would be erroneously registered as pressure, while ensuring that an open circuit exists when no biasing force is applied. FIG. 8A to FIG. 11C Various exemplary spacer arrangements for use in embodiments of the invention are shown. For illustration purposes, only a portion of a sensor is shown in each case.

[0118] Fig. 8A and Figure 8BA plan view of a portion of a sensor including different cylindrical spacer configurations according to an embodiment of the present invention is shown. In both cases, a substrate 804 is provided with three horizontal electrodes in a first electrode layer 806 and three orthogonal electrodes in a second electrode layer 808. An active material 810 is provided between the electrodes in the first electrode layer 806 and the second electrode layer 808. In both cases, the spacer is formed by a cylindrical rod, post or dot.

[0119] exist Fig. 8A 8, spacers 820a are printed on both sides of substrate 804 and are arranged to extend from or through each electrode layer to substrate 804 between overlapping portions of the electrode matrix.

[0120] exist Figure 8B 8, spacers 820b are printed on only one side of substrate 804 and are arranged to extend between the lower and upper portions of substrate 804 between the electrode matrix overlaps.

[0121] Fig. 8A and Figure 8B The spacers in the sensor may be formed of a polymer, such as a dielectric polymer, polysiloxane, rubber or silicone, or an amorphous crystalline substance such as glass. The shape of the spacers may be cylindrical, conical or conical segment, pyramidal or pyramidal segment, cuboid, hemispherical or hemispherical segment, semi-cylindrical, tetrahedron or tetrahedron segment, hexahedron, triangular prism, polyhedron, other shapes. In some embodiments, the spacers may be graded so that their height, shape, size, or spacing on the sensor varies. In one example, the spacers may be cones with a width of 50 microns, a height of 25 microns, and a spacing of 1 mm.

[0122] Fig. 9A and Fig. 9B A plan view of a portion of a sensor according to an embodiment of the present invention is shown, the sensor including different diamond spacer configurations. In both cases, the substrate 904 is provided with three horizontal electrodes in the first electrode layer 906 and three orthogonal electrodes in the second electrode layer 908. The active material 910 is provided between the electrodes in the first electrode layer 906 and the second electrode layer 908. In both cases, the spacer is composed of a diamond or square grid.

[0123] exist Fig. 9A In the embodiment of the present invention, the spacers 920a are printed on only one side of the substrate 904 and are arranged to extend from or through each electrode layer between the electrode matrix overlaps.

[0124] exist Fig. 9B, spacers 920b are printed on both sides of substrate 904 and are arranged to extend on and / or between upper and lower portions of substrate 904 between overlapping portions of the electrode matrices.

[0125] Fig. 9A and Fig. 9B The spacers in may be formed from a fabric mesh or a flexible / rubbery polymer mesh, for example, 3D printed using any of a variety of soft polymers.

[0126] Fig. 10A and Fig. 10B A plan view of a portion of a sensor including different square spacer configurations according to an embodiment of the present invention is shown. In both cases, a substrate 1004 is provided with three horizontal electrodes in a first electrode layer 1006 and three orthogonal electrodes in a second electrode layer 1008. An active material 1010 is provided between the electrodes in the first electrode layer 1006 and the second electrode layer 1008. In both cases, the spacers consist of hollow square pillars.

[0127] exist Fig. 10A , the spacers 1020a are printed on only one side of the substrate 1004 and are arranged to extend around a large sensor area, for example, surrounding nine electrode overlaps with a single square.

[0128] exist Fig. 10B In the embodiment shown in FIG. 1 , spacers 1020b are printed on only one side of substrate 1004 and are arranged to extend around a small sensor area, for example, between each electrode matrix overlap.

[0129] Fig. 10A and Fig. 10B The spacers in can be made of materials similar to the cylindrical or diamond-shaped spacers mentioned above.

[0130] Fig.11A , Fig. 11B and Fig. 11C Plan views of a portion of a sensor including different hexagonal spacer configurations according to embodiments of the present invention are shown. In each case, a substrate 1104 is provided with three horizontal electrodes in a first electrode layer 1106 and three orthogonal electrodes in a second electrode layer 1108. An active material 1110 is provided between the electrodes in the first electrode layer 1106 and the second electrode layer 1108. In each case, the spacer is composed of a hollow hexagonal (i.e., honeycomb) grid of different sizes.

[0131] exist Fig.11A In FIG. 1 , spacers 1120a are printed on only one side of substrate 1104 and are arranged to extend between overlapping portions of the electrode matrix.

[0132] exist Fig. 11B , spacers 1120b are printed on only one side of substrate 1104 and are arranged to extend around a small sensor area over and / or between each electrode matrix overlap.

[0133] exist Fig. 11C In the embodiment of the present invention, the spacers 1120c are printed on only one side of the substrate 1104 and are arranged to extend between and constrain the electrode matrix overlaps.

[0134] Fig.11A , Fig. 11B and Fig. 11C The spacers in the can be formed by extruded or printed grids. These can be in the shape of honeycombs, triangles, quadrilaterals, diamonds, diamonds with loops, squares or flat surfaces. A variety of different fabrics can be selected depending on the application and it must be ensured that enough of the sensor's active layers can be in contact with each other. The purpose of the woven grid is the same as the other spacer layers. In addition, plain Dutch weave, twill weave, plain weave, twill Dutch weave, lock crimp, inner crimp, twill Dutch double weave or twisted weave can also be used. The grid can be made of non-conductive textile thread or conductive thread (for example, silver or titanium) and can be used to distribute pressure within the sensor while increasing sensitivity.

[0135] To make a completely compliant flat sensor, there are multiple challenges: the sensor must be thin, the electrodes must be compliant, and the sensor must not react to forces other than those required. The quantum tunneling active layer material has a very high resistance (~10 9 The contacts of this material can be made of a variety of different materials, but the electrodes must be compliant and slightly elastic so that the material can be used to wrap around objects. One approach is to make stretchable silver electrodes or alternatively use conductive adhesives, even if they change slightly depending on the pressure.

[0136] As explained above, a grid / matrix of these sensors can be made by sandwiching the active layer between row and column electrodes that move in perpendicular directions on both sides. This has been achieved before with non-compliant electrodes and electronics, and even with "flexible" electronics that have a limited bending radius but are not completely compliant on any macroscopically observable surface. To read from the matrix, a multiplexer is required that reads each sensor element (sensing pixel) in the array one by one and is attached to a microcontroller or other signal processing hardware and software.

[0137] In an embodiment of the present invention, a simple device is presented wherein not only is the entire device itself compliant, but each cluster of 4 sensor elements in the grid can be converted into a 3D force sensing "tactel" by including a "bump" or shape of a force transfer structure as the top layer of the device.

[0138] The device is designed for mass production using printing such as roll-to-roll printing, screen printing or similar microfabrication techniques.

[0139] The main working mechanism of the above sensor is as follows: the resistance of each of the four sensor elements and their normal distribution are changed to estimate the three-dimensional force on the sensor. Each protrusion is used as a force transmission structure. By applying a directional force on each protrusion, stress is generated by deforming the "protrusion". The normal component of the force compresses each sensor element below it uniformly (causing a symmetrical resistance change), while the shear component generates a moment in the active layer that compresses some sensor elements more than others (causing an asymmetric resistance change). Its sensitivity can be adjusted by changing the thickness and bonding material of the active layer, as well as the height and stiffness of the "protrusion" and the underlying substrate material.

[0140] Individual grid lines can be made as small as 10 microns, and the spacing between them as small as possible without creating tunnels between layers that could create crosstalk and short circuits.

[0141] To read out the signal, each column electrode and each row electrode must be connected to an appropriate electronic readout circuit. When reading out the signal, the resistive crosstalk noise is significantly reduced because each electrode is spatially separated from each other. However, to further reduce the crosstalk or improve the signal-to-noise ratio (SNR) of each sensor element, one of the following methods can be used: i) the Pubrick voltage mirror method, in which the drive line not considered at the measurement point is set at a potential equal to the output voltage, or ii) the simpler zero potential method, in which the voltage of the scan electrode is set to zero. These form equipotential areas that eliminate the effects of crosstalk. In practice, there are multiple ways to configure the above circuit.

[0142] Calibration of the device is necessary, however, if provided with appropriate training data, machine learning or artificial intelligence algorithms are also able to "learn" how the sensor works. The range of forces that can be measured using such a sensor varies from 0.01N to a theoretically infinite amount, depending on the formulation of the active layer, its binder, and the overall thickness of the sensor.

[0143] No one layer has a preferred thickness, but to make the overall device compliant, they are expected to be no thicker than 1 mm and no thinner than 10 nm. The bumps on the surface may include shapes other than those listed, however the limit of 1 bump per 4 sensor elements applies in most cases.

[0144] Fig. 12AA top perspective view of a single tactel 1200 of a sensor according to an embodiment of the present invention is shown. The tactile element has a dome-shaped protrusion 1202 disposed on four sensor elements C1, C2, C3, and C4 representing the pixels to be read. Table 1 below shows the resistance change experienced by each of the four sensor elements when subjected to different forces. Thus, it can be determined how the electronic readings of such a sensor can be converted into a measurement of the location, magnitude, and direction of the applied force.

[0145]

[0146] Table 1: Sensor element changes in response to force direction

[0147] Fig. 12B Show Fig. 12A 1 and 12. A side perspective view of the tactile element 1200 of FIG. 1 and 12 and a corresponding force versus time graph before and after an oblique force is applied to the protrusion 1202. This illustrates the difference in forces experienced on the x, y, and z axes when an oblique force is applied.

[0148] Fig. 12C When an oblique force is applied to the protrusion 1202 Fig. 12B 12 is a side view of a tactile element 1200. For ease of illustration, this shows a simplified sensor layer structure, which includes an active layer 1210 sandwiched between an upper substrate and a lower substrate 1204. In this example, sensor element C3 experiences a small deformation when a force is applied while sensor element C4 experiences a large deformation. This is converted into a weaker change in C3 than in C4, which helps to accurately determine the direction of the applied force.

[0149] The described sensors have a variety of applications. These come from the large industrial, domestic and medical needs for compliant triaxial force sensors that work reliably. Examples include robotics (hard and soft robots, slip detection), electronic skin, prosthetics, human-computer interaction, tactile systems and surfaces such as walls and floors, virtual reality, gaming, structural integrity monitoring (wings, buildings), smart clothing (e.g., gloves), gait analysis insoles (ground reaction force direction, overall pressure, diabetic foot ulcer monitoring, etc., which can replace force sensing plates), sports impact monitoring (can detect direction and magnitude of impact), implantable devices, wearable devices (e.g., for smart homes), biomedical devices, drug delivery patches / systems, stretchable electronic circuits, adult and sex toy industry (e.g., toys or dolls with real-time performance / feedback and / or adaptive devices), pillows that sense movement, beds that monitor bedsores, blood pressure monitoring and detection (e.g., for use through, for example, clothing or wearables wearable devices to monitor blood pressure and flow), muscular strength / exertion, fatigue monitoring and detection, tidal or wind turbines to monitor flow characteristics around blades to increase service life or power generation, all areas where autonomous robots might be envisioned and require a high degree of dexterity and tactile information (e.g., warehouse sorting, space exploration, search and rescue, elderly care, cooking, electronics assembly, fishing, social robotics, etc.), aircraft wings (monitoring loads / forces helps reduce weight and costs as well as better wing designs), force monitoring in construction work environments, saddle pressure monitoring, muscular force mapping / monitoring, tissue stiffness / density monitoring (e.g., breast cancer diagnosis / how close a woman is to giving birth), prosthetics (e.g., for amputees, but also for tremor compensation in certain diseases such as Parkinson's, ALS, etc.), and others.

[0150] In some embodiments, piezoresistive and piezoelectric layers may be stacked prior to applying the bump layer to better mimic high and low frequency mechanoreceptors in the skin.

[0151] Furthermore, the device may be used inverted (ie, with the protrusions abutting the user's skin and forces applied through the base layer), which may be particularly beneficial if aerodynamic or fluid dynamic properties are to be maintained on the surface of the device.

[0152] Although the foregoing description has described exemplary embodiments, those skilled in the art will appreciate that multiple changes of embodiments may be made within the scope of the invention defined in the claims. In addition, the features of one or more embodiments may be mixed and matched with the features of one or more other embodiments.

[0153] References:

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Claims

1. A compliant three-axis force sensor comprising: a first electrode layer having an array of column electrodes in a first orientation; a second electrode layer having an array of column electrodes in a second orientation orthogonal to the first orientation; a force-dependent active layer configured to change at least one property when subjected to a force and provided between the first electrode layer and the second electrode layer; at least one three-dimensional protrusion arranged to transmit an externally applied force through the force-dependent active layer; wherein at least one spacer is provided, the at least one spacer being arranged to maintain a separation between two or more layers in the compliant three-axis force sensor until an external force is applied; and wherein the at least one spacer is in the form of an adhesive provided between the active layer and the first electrode layer and / or the second electrode layer, wherein the adhesive is provided in a gap between adjacent column electrodes and extends between respective edges of the force-related active layer and the adjacent column electrodes; or wherein the force-related active layer comprises a first active layer and a second active layer having a gap therebetween, and wherein the at least one spacer is provided within the force-related active layer.

2. The compliant three-axis force sensor of claim 1, wherein the force-dependent active layer comprises at least one of a quantum tunneling material, a piezoresistive material, or a piezoelectric material.

3. The compliant three-axis force sensor of claim 1, wherein the at least one property is: quantum tunneling; conductivity; resistivity or charge.

4. A compliant three-axis force sensor according to claim 1, wherein the at least one three-dimensional protrusion has a coverage area that extends at least partially over at least two column electrodes in the first electrode layer and at least partially over at least two column electrodes in the second electrode layer, so that a force applied to the protrusion can be transmitted through the force-related active layer in at least four discrete regions.

5. The compliant three-axis force sensor of claim 1, wherein the at least one three-dimensional protrusion has a footprint contained within a space between two adjacent column electrodes in the first electrode layer and between two adjacent column electrodes in the second electrode layer.

6. The compliant three-axis force sensor according to any one of claims 1 to 5, further comprising one or more of the following: a base layer below the first electrode layer; a top layer above the second electrode layer; a first carbon layer between the first electrode layer and the force-related active layer; a second carbon layer between the second electrode layer and the force-related active layer; and a covering layer on the at least one three-dimensional protrusion.

7. The compliant three-axis force sensor of claim 6, wherein the first carbon layer and / or the second carbon layer is continuous over a plurality of column electrodes in the first electrode layer and / or the second electrode layer.

8. A compliant three-axis force sensor according to any one of claims 1 to 5, wherein the at least one spacer is provided between a base layer and a top layer; or on the first electrode layer or the second electrode layer, or through the first electrode layer or the second electrode layer.

9. The compliant three-axis force sensor according to any one of claims 1 to 5, wherein the at least one spacer is in the form of a point, a post, a rod, a cylinder, a tube, a pyramid or a grid.

10. The compliant three-axis force sensor according to any one of claims 1 to 5, wherein the at least one spacer has a solid or hollow cross-section in the form of a circle, square, rectangle, diamond, pentagon, hexagon or honeycomb lattice.

11. The compliant three-axis force sensor of any one of claims 1 to 5, wherein the at least one spacer comprises an array of the spacers.

12. The compliant three-axis force sensor of claim 11, wherein the spacers in the array have a plurality of different sizes.

13. The compliant three-axis force sensor according to any one of claims 1 to 5, wherein the force-dependent active layer forms a continuous layer over a plurality of column electrodes in the first electrode layer and / or the second electrode layer.

14. The compliant three-axis force sensor according to any one of claims 1 to 5, wherein the force-dependent active layer forms a discontinuous layer on the column electrodes in the first electrode layer and / or the second electrode layer.

15. The compliant three-axis force sensor according to any one of claims 1 to 5, wherein an insulator is provided between adjacent electrodes in the first electrode layer and / or the second electrode layer.

16. A compliant three-axis force sensor according to any one of claims 1 to 5, wherein an adhesive layer is provided between one or more adjacent layers.

17. The compliant three-axis force sensor of any one of claims 1 to 5, wherein the at least one three-dimensional protrusion comprises a polymer having a different elasticity than the remainder of the compliant three-axis force sensor.

18. A compliant three-axis force sensor according to any one of claims 1 to 5, wherein the at least one three-dimensional protrusion is in the form of a platform, a dome, a hemisphere, a hemispherical segment, a cone, a cone segment, a cuboid, a cylinder, a half cylinder, a pyramid, a pyramid segment, a tetrahedron, a tetrahedron segment, a hexahedron, a triangular prism or a polyhedron.

19. The compliant three-axis force sensor of any one of claims 1 to 5, wherein the height of the at least one three-dimensional protrusion is at least twice the height of the remainder of the compliant three-axis force sensor.

20. The compliant three-axis force sensor of any one of claims 1 to 5, wherein the at least one three-dimensional protrusion comprises an array of the three-dimensional protrusions.

21. A method of manufacturing a compliant three-axis force sensor according to any one of claims 1 to 5, comprising: providing a first electrode layer having an array of column electrodes in a first orientation; providing a second electrode layer having an array of column electrodes in a second orientation orthogonal to the first orientation; providing a force-dependent active layer, the force-dependent active layer being configured to change at least one property when subjected to a force and being provided between the first electrode layer and the second electrode layer; providing at least one three-dimensional protrusion, the at least one three-dimensional protrusion being arranged to transmit an externally applied force through the force-dependent active layer; providing at least one spacer arranged to maintain separation between two or more layers in the compliant three-axis force sensor until an external force is applied; as well as The at least one spacer is provided in the form of an adhesive between the active layer and the first electrode layer and / or the second electrode layer, wherein the adhesive is provided in the gap between adjacent column electrodes and extends between the respective edges of the force-related active layer and the adjacent column electrodes; or the force-related active layer is provided as a first active layer and a second active layer with a gap therebetween, and the at least one spacer is provided within the force-related active layer.

22. The method of claim 21, wherein each layer, protrusion or spacer is provided by one of printing, screen printing, roll-to-roll printing, inkjet printing, 3D printing, electrospinning, deposition, droplet dispensing, casting, coating, molding, spinning or weaving.

23. The method according to claim 21 or 22, comprising forming at least the first electrode layer and the second electrode layer on a single substrate; separating the substrate into two parts; and stacking the two parts together.

24. The method of claim 23, comprising forming said at least one spacer on at least one portion prior to said separating and / or stacking.

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