Patent ID: 12196626

While various embodiments discussed herein are amenable to modifications and alternative forms, aspects thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the disclosure to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure including aspects defined in the claims. In addition, the term “example” as used throughout this application is only by way of illustration, and not limitation.

DETAILED DESCRIPTION

Aspects of the present disclosure are applicable to a variety of different types of apparatuses and methods involving a sensor apparatus that senses forces applied thereto and that defines both the magnitude and type of the force. In certain implementations, aspects of the present disclosure have been shown to be beneficial when used in the context of a skin-like tactile sensor for robotic or prosthetic application, such as robotic hands, but it will be appreciated that the instant disclosure is not necessarily so limited. Various aspects may be appreciated through the following discussion of non-limiting examples which use exemplary contexts.

Accordingly, in the following description various specific details are set forth to describe specific examples presented herein. It should be apparent to one skilled in the art, however, that one or more other examples and/or variations of these examples may be practiced without all the specific details given below. In other instances, well known features have not been described in detail so as not to obscure the description of the examples herein. For ease of illustration, the same reference numerals may be used in different diagrams to refer to the same elements or additional instances of the same element. Also, although aspects and features may in some cases be described in individual figures, it will be appreciated that features from one figure or embodiment can be combined with features of another figure or embodiment even though the combination is not explicitly shown or explicitly described as a combination.

Embodiments of the instant disclosure are directed to methods and apparatuses (e.g., systems, devices and circuitry) configured for providing tactile sensing by measuring and discriminating between normal and shear forces. Tactile sensing can be used for a variety of purposes, such as for dexterous manipulation of objects in robotics. Distinguishing between such forces in real time can be beneficial for slip detection and interaction with fragile objects. Embodiments in accordance with the present disclosure include a sensor apparatus that uses impedance-based sensing to measure and discriminate between normal and shear forces in real time. The sensor apparatus includes an array of capacitors formed by top and bottom electrodes, such as carbon nanotubes (CNTs)-based electrodes. The sensing ability is provided by a three-dimensional structure that can mimic the interlocked dermis-epidermis interface in human skin. For example, the top electrode can include pyramid-shaped CNT microstructures arranged along phyllotaxis spirals, with one spiral per dome-shaped CNT microstructure of the bottom electrode, and that results in a skin-like sensor apparatus with increased sensitivity, minimal hysteresis, excellent cycling stability and response time in the millisecond range. In specific embodiments, the skin-like sensor apparatus can be used to control a robot arm for a variety of tasks and/or provide tactile feedback, although embodiments are not limited to robotics and the sensor apparatus can be used for a variety of purposes.

In accordance with a number of embodiments, the array of capacitors is formed by a first substrate and a second substrate. The first substrate and second substrate are formed of an elastomer material and have embedded thereon a plurality of microstructures. The plurality of microstructures of the first elastomer substrate are formed in a pattern and can include three-dimensional shapes, such as pyramid-shaped microstructures. The plurality of microstructures of the second elastomer substrate are formed in a pattern and can include three-dimensional shapes, such as dome-shaped microstructures. The dome-shaped microstructures can be hill-like, such as semi-spheres, and/or semi-spheroids. An intermediate substrate or material of dielectric is formed between the first and second elastomer substrates, with the respective microstructures positioned to contact the dielectric material. The dielectric material provides electrical insulation of the capacitors. In specific embodiments, the microstructures are formed using CNTs, and can be referred to as CNT microstructures, although embodiments are not so limited and the microstructures can be formed using a variety of material, such as rubber and/or of both rubber and CNTs.

The patterns of microstructures on the top and bottom elastomer substrates can be positioned orthogonally to one another, such that a subset of the three-dimensional structures on the top elastomer substrate respectively form an array of capacitors with a dome-shaped structure on the bottom elastomer substrate. For example, the first and second substrates with microstructures are aligned perpendicular to one another such that each dome-shaped microstructure on the second elastomer substrate corresponds or otherwise aligns with a subset of the plurality of pyramid-shaped microstructures. In specific embodiments, each dome-shaped microstructure corresponds with twenty-five pyramid-shaped microstructures (one on top of the dome, four on the slopes of the dome, four on the corners of the dome, and sixteen surrounding the dome) forming the array of capacitors, sometimes referred to as a “sensor array”, although embodiments are not so limited and the subset may include sixteen or nine pyramids per dome. Such alignment results in the pyramid-shaped microstructures being positioned according to a grid, such as a phyllotaxis spiral grids with one spiral per dome.

Turning now to the figures,FIGS.1A-1Bshow example sensor apparatuses, consistent with embodiments of the present disclosure. The sensor apparatus100include a plurality of capacitors coupled to sensor circuitry110and used to detect both the type and magnitude of force applied is flexible for application on surfaces that are not smooth.

As shown byFIG.1A, the sensor apparatus100includes a plurality of capacitors formed of at least two substrates102,104. The substrates102,104each include at least one electrode108,106and are separated from one another by a dielectric substrate or material103. In specific embodiments, the substrates102,104are formed of a flexible elastomer material and the electrodes106,108can be formed on or embedded with the flexible substrates. The first substrate102can include a plurality of first electrodes108and the second substrate104can include one or more second electrodes106(e.g., such as illustrated byFIG.1B) forming a plurality of electrode pairs.

The dielectric substrate or material103and the substrates102,104can include a structure formed of a stretchable elastomer, such as Polydimethylsiloxane (PDMS), Polyurethane (PU), poly(styrene-butadiene-styrene) (SBS), styrene butylene styrene (SEBS), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), although embodiments are not so limited.

The plurality of first electrodes108of the first substrate102may be aligned with the second electrode106of the second substrate such that each of plurality of first electrodes108form one of the plurality of capacitors with the second electrode106. The second electrode106thereby forms a plurality of capacitors with the plurality of first electrodes108, which is sometimes interchangeably herein referred to as “an array of capacitors” or “a sensor array”. The plurality of first electrodes108and/or the second electrode106may be formed of an elastomer material and/or CNTs. For example, the first and second substrates102,104are formed of PU and the respective electrodes106,108are embedded thereon and formed of PU with a coating of CNTs, although embodiments are not so limited.

The plurality of first electrodes108include three-dimensional microstructures embedded on the first substrate102and the second electrode106includes a three-dimensional microstructure embedded on the second substrate104. As used herein, a microstructure includes or refers to a structure formed of a physical material that has one or more dimensions in the micron range. In various embodiments, the plurality of first electrodes108each include pyramid-shaped microstructures and the second electrode106includes a dome-shaped microstructure. The pyramid-shapes may include a triangular pyramid, a square or rectangular pyramid, a pentagonal pyramid, among others. A dome-shape may include or be hill-like, such semi-spheres, and/or semi-spheroids. Each of the electrodes106,108may be solid or may be hollow. In some embodiments, the pyramid-shaped microstructures are positioned orthogonally with respect to the dome-shaped microstructure. In other embodiments, the pyramid-shaped microstructures are positioned in a spiral pattern with respect to the dome-shaped microstructure.

The sensor apparatus100further includes sensor circuitry110coupled to the plurality of capacitors formed by the first and second substrates102,104. The sensor circuitry110may be used to detect the magnitude and direction of a force, such as a randomly-combined force including normal, shear, and rotation forces with high sensitivity and sensing range. In various specific embodiments, the sensor apparatus100is used to measure a capacitive transduction system that takes advantage of the unique geometry of capacitive electrodes, e.g., the different shaped microstructures of the first substrate102and the second substrate104.

More specifically, the sensor circuitry110differentiates between normal and shear forces applied to the sensor apparatus100based on a pattern of impedance responses of each of the plurality of capacitors formed by the second electrode106and the plurality of first electrodes108. The pattern of impedance (e.g., capacitance or resistance) responses may include or be used to generate an impedance map indicative of the impedance changes of different electrode pairs of the plurality of capacitors. The impedance map may include pixels or boxes that provide an indication of the impedance response of a respective electrode pair. In specific examples, the impedance map includes a grid of pixels. For example, the sensor circuitry110is to differentiate between normal, shear, and tilt forces by generating the impedance map that is indicative of the pattern of impedance responses and comparing the impedance map to predetermined patterns.

The sensor circuitry110may include at least one capacitance-to-digital converter (CDC) circuitry that connects the electrodes to an input channel of the CDC circuitry. The sensor circuitry110can measure capacitance at a sampling rate using the CDC circuitry and connected processing circuitry, such as a controller. To measure dynamic force by such a sampling rate, the sensor uses two CDC circuitry (Capacitance-to-Digital Converter chips) to connect the electrode pairs to 2 of the 12 analog input channels of each chip, since a high sampling rate (>500 Hz) can be obtained from a lower number of capacitor inputs to the chip. The CDC chip consists of a sigma-delta-based CDC with 12 analog input channels and communicates with a microcontroller via an I2C bus, measuring capacitance in 0.3-1.2 kHz sampling rate, and cancelling noise from capacitors through active shield function. For more information on CDC chips and active shield function, reference is made to AD7147, Analog, http://www.analog.com/media/en/technical-documentation/data-sheets/AD7147.pdf, which is fully incorporated herein by reference.

Additionally and/or alternatively, the apparatus100includes one or more additional electrodes used as a part of a transducer circuit and further including a passively or inductively powered circuit configured to provide power to at least the sensor circuitry110. The apparatus100, in specific aspects, includes a wireless communication circuit for wirelessly communicating signals from the sensor circuitry. The sensor circuitry110and/or the apparatus100further include a power circuit to provide an electric potential across the terminals of the plurality of capacitors. Alternatively and/or in addition, the apparatus100can further include a computer (e.g., CPU and/or microcontroller) to provide or assess the forces based on signals provided from the sensor circuitry.

Although only one second electrode106is illustrated, embodiments are not so limited and the second substrate104may include a plurality of second electrodes arranged in a pattern. In such embodiments, for each of the plurality of second electrodes, a respective subset of the plurality of first electrodes108of the first substrate102are positioned to align with the respective one of the plurality of second electrodes such that the plurality of first electrodes and plurality of second electrodes form a plurality of arrays of capacitors.

FIG.1Billustrates a specific example sensor apparatus, which is consistent with the sensor apparatus ofFIG.1A. The sensor apparatus111has first and second substrates102,104that each include a plurality of electrodes and are separated from one another by a dielectric substrate or material103.

The electrodes of the first substrate102include pyramid-shaped microstructures and the electrodes of the second substrate104include dome-shaped microstructures, as respectively illustrated by the particular pyramid-shaped microstructure108and the dome-shaped microstructure106. Each of the plurality of dome-shaped microstructures align with a subset of the plurality of pyramid-shaped microstructures, thereby forming a plurality of arrays of capacitors. Each array of capacitors includes a plurality of electrode pairs formed by the respective dome-shaped microstructure and the respective subset of pyramid-shaped microstructures of the plurality of pyramid-shaped microstructures. The subset of pyramid-shaped microstructures may be aligned to effectively surround or center the respective dome-shaped microstructure.

The first and second substrates102,104may be formed of an elastomer material, such as PU. The pyramid-shaped microstructures and dome-shaped microstructures may include CNTs coated on the elastomer. For example, the structures are formed of PU elastomer and coated with CNTs. The elastomer may elastically deform in response to pressure applied thereto, and may store and release energy reversibly. The dielectric substrate or material103may be thinner than the first and second substrates102,104and provides electrical insulation to the capacitors. In a further specific embodiment, the plurality of pyramid-shaped microstructures are arranged in a grid pattern on the first substrate with a distance between of b and having a length of a, wherein the ratio of b/a is from 0.4-4.0.

The pyramid-shaped microstructures and dome-shaped microstructures (e.g., the top and bottom electrodes) may be aligned. For example, respective subsets of the pyramid-shaped microstructures are aligned with each of the dome-shaped microstructures. In specific examples, the pyramid-shaped microstructures are aligned perpendicularly with each of the dome-shaped microstructures aligned perpendicularly, such that an array of capacitors is formed. Sensor apparatuses having a plurality of dome-shaped microstructures may include a plurality of array of capacitors, which each array being associated with one of the plurality of dome-shaped microstructures.

In specific embodiments, the first substrate102has twenty-five pyramid-shaped microstructures of the first substrate102for each of the one dome-shaped microstructures of the second substrate104, such that there are twenty-five electrode pairs, or twenty five capacitors, per dome-shaped microstructure of the second substrate104. In such embodiments, each subset includes twenty-five pyramid-shaped microstructures associated with one of the plurality of dome-shaped microstructures, resulting in the twenty five electrode pairs per dome. As a specific example, each subset of pyramid-shaped microstructures are arranged with respect to the respective dome-shaped microstructure such that a first pyramid-shaped microstructure of the subset is arranged with respect to a top of the dome-shaped microstructure, four of the pyramid-shaped microstructures of the subset are arranged with respect to slopes of the dome-shaped microstructure, four of the pyramid-shaped microstructures of the subset are arranged with respect to corners of the dome-shaped microstructure, and sixteen of the pyramid-shaped microstructures are arranged surrounding the dome-shaped microstructure.

The impedance may be measured between each of the pyramid shaped-microstructures or electrodes at the first substrate102and the corresponding dome-shaped microstructure or electrode of the second substrate104and across the dielectric substrate or material103. The electrodes store electric charges which leads to change in impedance. An intermediate dielectric substrate or material103provides separation and electrical insulation of capacitors and is polarized by an applied electric field on the electrode layers. The microstructures allow the elastomer to elastically deform when an external pressure is applied, storing and releasing the energy reversibly, thus minimizing undesirable viscoelastic behavior and resulting in enhanced sensitivity.

Although not illustrated byFIG.1B, the sensor apparatus111may further include sensor circuitry coupled to the plurality of arrays of capacitors and configured and arranged to measure and differentiate between normal and shear forces applied to apparatus based on a pattern of impedance responses of each of the plurality of arrays of capacitors. Sensor circuity, in accordance with the present disclosure, can discriminate forces with a spatial signal processing on the grid at each time step, so that the controller's bandwidth (therefore the performance) can be higher.

FIGS.2A-2Cshow an example sensor apparatus under different forces and patterns of the respective microstructures, consistent with embodiments of the present disclosure. More specifically,FIGS.2A and2Billustrate the first and second substrates212,218having an array of capacitors as illustrated by the top down views213,215of the apparatus. For example, subsets of the microstructures of the first substrate212form a plurality of capacitors with a respective one of the microstructures of the second substrate218. The first and second substrates212,218are separated by a dielectric substrate214.FIGS.2A-2Bshow additional side views217,219of one of the dome-shape structures222of the second substrate218and the subset of pyramid-shapes microstructures (as illustrated by one of the pyramid-shaped microstructures216) of the second substrate218with different types of forces applied to the first substrate212and which cause different impedance patterns. As shown, the first substrate212flexes in response to the force applied, and the dome-shaped microstructures cause different changes in impedance for respective electrode pairs and which depend on the type of force. The distinction between the different forces can be based on the shape of the impedance response curve as a function of time that differs from one mechanical stimulus to the other. As shown byFIGS.2A-2B, a power source206may be coupled to the terminals of the capacitors, as previously described.

FIG.2Cillustrates an example pattern of the pyramid-shaped electrodes as aligned with a dome-shaped electrode to form a plurality of capacitors. For example,FIG.2Ccan include a top-down view of the first and second substrate ofFIGS.2A-2B.

The forces may be distinguished based on patterns of impedance response of the electrode pairs using coupled sensor circuitry. The pattern of impedance responses can be represented as a map, with a pixel representing an impedance value between the dome-shaped microstructure and one of the pyramid-shaped microstructures.

As previously described, the magnitude of normal and shear static forces can be measured by measuring, monitoring and/or analyzing changes in impedance derived from changes in distances between respective electrode pairs (e.g., the gap distance) and changes in overlapping areas of the electrode pairs, respectively. The normal and shear forces can be distinguished based on the comparison of impedance from each electrode pairs of one (or more) arrays of capacitors of the apparatus. As used herein, normal forces includes or refers to pressure or compression forces on the sensor circuitry. Shear forces includes or refers to unaligned forces pushing in different directions. Tilt includes or refers to the combination of normal and shear forces.

FIGS.3A-3Cshow an example sensor apparatus under different forces, consistent with embodiments of the present disclosure. More specifically,FIG.3Ashows a resulting pattern of impedance responses to a normal force applied to the first and second substrate of the sensor apparatus300, as is consistent withFIG.2A.FIGS.3B-3Cshow resulting patterns of impedance responses to a shear force and tilt forces applied to the first and second substrate of the sensor apparatus300, as is consistent withFIG.2A. As may be appreciated, a tilt force may include a combination of normal and shear forces.

The patterns of impedance responses may change depending on both the type of force, the direction of the force, and the amount of force applied. The distinction between the different forces can be based on the shape of the response curve as a function of time and that differs from one mechanical stimulus to the other. Shown byFIGS.3A-3C, the pattern of capacitive responses of the electrode pairs may include or be generated as an impedance map301,302,303having pixels, with each pixel (e.g., box) representing one of the electrode pairs associated with a dome-shaped microstructure of the apparatus300. In the specific example, an array of capacitors associated with one of dome-shaped microstructure of the apparatus300includes an array of 5×5 sensing pixels represented in a grid. An intensity of the impedance value is presented by each sensing pixel. The impedance maps301,302,303show different patterns for different forces. For example, the impedance map301ofFIG.3Aillustrates an example response to a normal force, the impedance map302ofFIG.3Billustrates an example response to a shear force, and the impedance map303ofFIG.3Cillustrates an example response to a tilt force, all forces being applied to the apparatus300.

Although various embodiments are described as including twenty-five electrode pairs represented by 5×5 pixels, examples are not so limited and may include different numbers of electrode pairs and/or pixel representations. For example, in the case of a robotic application, the data of a fraction of the twenty-five pixels can provide sufficient information (for instance, nine of them, one on the top of the dome/hill, four on the sides, and four in the corners). For example, embodiments may include sixteen electrode pairs represented by 4×4 pixels and/or nine electrode pairs represented by 3×3 pixels.

FIGS.4A-4Bshow an example of fabricating a sensor apparatus, consistent with embodiments of the present disclosure. The assembly of the sensor apparatus may involve a benchtop process involving the lamination of the bottom electrode layer with the dome-shaped microstructures, the intermediate dielectric layer, and the top electrode layer with pyramid-shaped microstructures.

The fabrication process for the sensor apparatus can include electrode formation, dielectric layer formation, and bonding. The fabrication processing can include forming (e.g., printing) electrode pairs on one or more flexible substrates, building a dielectric layer on a first (or more) of the flexible substrates, bonding the dielectric layer of the first flexible substrate to a second flexible substrate. To print electrode patterns on flexible substrates, photolithography, laser ablation, inkjet printing or three-dimensional (3D) printing can be employed on flexible substrate. To build dielectric layers on these patterned electrodes, a dielectric structure is made with various methods; such as photolithography, laser ablation, laser additive, inkjet printing, 3D printing, dissolvable material frame, emulsion droplet frame to sponge frame technique. This solidified dielectric structure can bond to a patterned electrode by chemical bond (e.g., chemical glue). Further, the dielectric layer bonded to the electrode is bonded to another electrode by plasma treatment and, optionally, the process may be repeated to stack two electrode pairs. In various specific embodiments, the fabrication process can automate alignment of electrode pairs within the sensor circuitry.

More specifically,FIG.4Aillustrates an example method which includes forming a first substrate414of elastomer having a plurality of pyramid-shaped microstructures embedded thereon. Forming the first substrate may include patterning a silicon wafer with pyramid shapes (e.g., patterned with pyramids of different sizes by lithography followed by HF oxide etching and finally an anisotropic potassium hydroxide (KOH) etching, at428. The silicon wafer may be coated with a CNT layer, at430. After the coating, the first elastomer substrate is formed (e.g., casted) on the wafer with the carbon-nanotube adhering to the elastomer, at432. The first elastomer substrate may then be released from the wafer to form the first substrate414having the plurality of pyramid-shaped microstructures embedded thereon, at434.

The method further includes forming a second substrate412of elastomer having a plurality of dome-shaped microstructures embedded thereon. For example, a silicon wafer is patterned, at416, and then coated with a CNT layer, at418, which may include a pattern of CNTs (e.g., not continuous). After the coating, the second elastomer substrate is formed (e.g., casted) on the wafer with the carbon-nanotube adhering to the elastomer, at420, and the second elastomer substrate with the CNT layer may then be released from the wafer to form the second substrate, at422. The dome-shapes may be generated on the elastomer substrate using a vacuum process. For example, a vacuum is applied and released to the second substrate412to form the plurality of dome-shaped microstructures embedded thereon the second substrate which are proximal to the CNT layer, at424and426.

The method further includes combining the first substrate414and the second substrate412, with a dielectric substrate between, at436, such that each one of the plurality of dome-shaped microstructures is aligned with a different subset of plurality of pyramid-shaped microstructures, and the plurality of pyramid-shaped microstructures and dome-shaped microstructures form a plurality of arrays of capacitors. For example, the dielectric substrate may be bonded to one of the first and second substrates, and then the second and first substrate are bonded together. The method may include laminating the aligned first substrate, dielectric substrate and second substrate.

The second substrate412may be thicker than the first substrate414, and the dielectric substrate may be thinner than both the first and second substrates412,414. As an example, the first substrate414may include a PU material having a thickness in the μm range (such as 60 μm-thick) and has the array of pyramid-shaped microstructures. The second substrate412may include a PU material that has a thickness in the mm range (such as 1 mm-thick) with an array of dome-shaped microstructures. The domes may have a diameter in the mm range and a height in the μm, such as a diameter of 1 mm and height of 200 μm. The dielectric material may have a thickness in the μm range, such as 10 μm thick. In specific embodiments, the dielectric substrate or material is polyhydroxybutyrate/polyhydroxyvalerate (PHB/PHV) and used as a spacer between the first and second substrates412,414. The electrodes are made of spray-coated and photolithography-patterned conducting CNTs embedded into the PU matrix (electrodes width 300 μm, separation distance between two electrodes 50 μm). The construct may reinforced with tape at the sides, to mitigate or prevent sliding of the substrate layers when shear force is applied. If the sensor array is scaled, proper adhesion between layers can be implemented to ensure mechanical stability. For example sensor sizes, tape is sufficient to stabilize the system for lab experiments.

FIG.4Billustrates an optical image showing the CNTs-PU interconnects for signal recording LCR (inductance-capacitance-resistance) meter and scanning electron microscopy (SEM) image of the top e-skin layer with molded pyramids, showing CNTs-PU and PU areas (inset).

The above described fabrication process may be scaled readily, and results in a geometrical configuration with several benefits. The resulting sensor apparatus presents a high density of mechanoreceptor-like sensors. Each dome corresponds to twenty-five capacitors each 90,000 μm2in size (e.g., one capacitor at the top of the dome, four on the slopes, four on the corners of the dome and sixteen surrounding the dome), and the location of each sensing pixel is controlled and ensured by proper alignment. As may be appreciated, embodiments are not limited to twenty-five capacitors per dome and may include other numbers such as sixteen and nine.

In accordance with various embodiments, the proposed design has the ability to detect the direction of applied force. Because of the 3D geometry of the domes/hills and the anisotropic deformation of the top layer with applied tilt force, the capacitors located on the side of the dome are exposed to a greater pressure can have a larger increase in impedance than those located on the other side opposite to the applied force direction.

The sensor circuitry can measure dynamic force by using the same transduction technology used for the static force by applying a high sampling rate (>500 Hz). As previously described, to measure dynamic force by such a sampling rate, the sensor uses two CDC chips to connect the two electrode pairs to two of the twelve analog input channels of each chip.

In some specific embodiments, the sensor apparatus is formed of a flexible metalized mylar, hundreds nm-thick conductive material is ablated or printed on top of a micron-thick flexible film, including Polyethylene terephthalate (PET), Polylmide Kapton (PI), and ITO film, and a stretchable elastomer having the apertures. The elastomer may be Polydimethylsiloxane (PDMS), Polyurethane (PU), poly(styrene-butadiene-styrene) (SBS), styrene butylene styrene (SEBS), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), among other elastomers. These materials are selected by considering mechanical and electrical properties of the target application. The electrode material is flexible and the dielectric material is flexible and stretchable, such that the resulting sensor is responsive to multi-axis force. Higher dielectric elastomer is also expected to be more sensitive.

Sensor apparatuses in accordance with the present disclosure may have a variety of dimensions. For example, the first substrate with the first electrodes or the pyramid-shaped microstructures may have a thickness in a range of 0.1 nanometer (um) to several centimeters (cm) (e.g., a thickness not less than about 0.1 um and not more than several cm, such as 2 cm, 3 cm, 4 cm, 10 cm and more). The second substrate having a second electrode or a plurality of second electrodes/the dome-shaped microstructures may have a thickness in a range of 0.1 um to several cm, and which in specific embodiments includes a range of 0.1 um and 3 cm or 4 cm (e.g., a thickness of not less than about 0.1 um and not more than several cm). The dielectric material may have a thickness in a range of 0.1 um to several millimeters (mm) (e.g., a thickness of not less than about 0.1 um and not more than several mm or less in other embodiments), with the thickness of the dielectric material impacting the impedance measured. In a specific example, the dielectric material is 10 um thick and the second substrate is 3 mm thick, although embodiments are not so limited. The total thickness of the first substrate, the second substrate and the dielectric material may be in a range of 50 um to several cm, and in some specific examples, 100 um to 10 cm or to 200 cm (e.g., a thickness of not less than about 50 um and not more than several cm). The first electrodes or pyramid-shaped microstructures may have a (pyramid) width in a range of 1 um to several hundreds of um, a (pyramid) height in a range of 1 um to several hundreds of um, and a distance between respective pyramids (e.g., two consecutive pyramids) in a range of 1 um and several hundreds of um, and in more specific embodiments in a range of 3 um and 900 um or about 999 um. For example, the pyramid-shaped microstructures may exhibit a width of not less than about 1 um and not more than about several hundreds of um, a height of not less than about 1 um and not more than about several hundreds of um, and a distance between of not less than about 1 um and not more than several hundreds of um. The second electrode(s) or dome-shaped microstructures may have a (dome) diameter in a range of 2 um to several cm, and a (dome) height of 2 um to about half of the diameter (or one half of several cm). In a specific embodiment, the domes have a diameter of around 800 um with a height of a 200-900 hundred um. For example, the dome-shaped microstructures may exhibit a diameter of not less than 2 um and not more than several cm, and in some specific embodiments, not less than 3 um and not more than 6 um. The dome-shaped microstructures may exhibit a height of not less than 2 um and not more than 5 cm, and in specific embodiments not less than 2 um and not more than 3 um.

As used herein, several includes or refers to 2 or more, such as 2-4, 2-5 2-6, 2-7, 2-9, 2-10, 2-15, 2-25, 2-50, 2-90, 2-99, and 2-100 in various examples. For example, several hundreds may include 200-700, 200-900, 200-999, and 2-1000, among other ranges. Similarly, several cm, mm, and/or um may include 2-4, 2-5, 2-6, 2-7, 2-9, 2-10, 2-15, 2-25, 2-50, 2-90, 2-99, and 2-100, among other ranges. Although embodiments are not limited to the above dimension ranges, and sensor apparatuses may be formed in a variety of dimensions for different applications.

Various specific embodiments can include integrating the above-described sensor apparatus with robotics and prosthetics. For example, the sensor apparatus can be applied on target surfaces of robots for a robotic tactile sensing system as the mechanoreceptors of robot skin. On the robot skin or other prosthetic, a flexible three-axis capacitive tactile sensor is freely applicable and indispensable for three distinct kinds of dexterous activities: response, manipulation, and exploration; which include the activity of response of detection and reaction to external agents, manipulation of contact location and force control, and exploration of surface texture and local features. In specific implementations, the sensor circuitry is formed as part of a robotic hand and is used to detect slip of an object being held or touched by the robotic hand. In related specific aspects, the sensor circuitry is formed as part of an apparatus (e.g., robotics, prosthetics and other implementations) having a plurality of different types of sensors including the sensor circuitry, pressure sensor circuitry, strain sensor circuitry, and/or temperature sensor circuitry, among other types of sensors.

Embodiments in accordance with the present disclosure are not limited to a sensor circuitry that is placed on an exterior surface (e.g., proximal to the environment) of robotics or prosthetics apparatus and can be directed to implants or other applications. In some specific embodiments, the sensor circuitry and/or an apparatus including the sensor circuitry can be implanted under an external surface of the skin of a user or other animal, e.g., is subdermal, and/or below a surface of the robotics or prosthetic, similar to or including a passive radio frequency (RF) pet implant. For example, the sensor circuitry can be implanted at a depth below the surface of the skin sufficient to be subcutaneous but not in muscle (e.g., within interstitial space of a user or other animal and/or prosthetic) and/or below a surface or the exterior surface of the robotics/prosthetic. In various embodiments, the implant is located below the surface of the skin, robotic and/or prosthetic sufficient for the implant including the sensor circuitry to communicate with external circuitry (e.g., to receive and output communications such as RF or other wireless signals).

Experimental/More Detailed Embodiments

In various embodiments, the above-described sensor apparatuses may be used for robotic type applications. Tactile sensing can be used for the dexterous manipulation of objects in robotic applications. In particular, the ability to measure and distinguish, in real time, between normal and shear forces is useful for slip detection and interaction with fragile objects. Embodiments in accordance with the present disclosure are directed to a biomimetic soft electronic skin composed of an array of capacitors, capable of measuring and discriminating in real time both normal and tangential forces. The electronic skin (e-skin) apparatus can include a 3D structure that mimics the interlocked dermis/epidermis interface in human skin. Moreover, pyramid microstructures arranged along phyllotaxis spirals result in an e-skin with increased sensitivity, minimal hysteresis, excellent cycling stability and response time in the millisecond range. The e-skin is used to control a robot arm in various tasks, illustrating its potential application in robotics with tactile feedback. Such an e-skin can use multiple levels of biologically inspired patterning, capable of discriminating both normal and tangential forces. The following more detailed/experimental embodiments describes an e-skin formed by layers of elastomer (e.g., PU) material having CNT microstructures thereon, however embodiments are not limited to such material.

FIGS.5A-5Ishow an example sensor apparatus under different forces and resulting capacitive patterns, consistent with embodiments of the present disclosure. The sensor apparatus may be consistent with that described byFIGS.1A-1B and3A-3Cand has a first substrate with a plurality of pyramid-shaped microstructures, a second substrate with a plurality of dome-shaped microstructures and a dielectric substrate between. Each of the dome-shape microstructures pair with a subset of the plurality of pyramid-shaped microstructures.

FIGS.5A-5Cillustrate the different patterns of impedance responses to normal force (FIG.5A), shear force (FIG.5B) and tilt force (FIG.5C). The impedance pattern, which is illustrated as the impedance map521,523,525indicative of impedance values of electrode pairs associated with a dome, provides the ability to differentiate several types of applied forces, while an individual pixel alone is not able to provide this information. The impedance maps include pixels (e.g., the boxes) associated with each electrode pair formed by one of the subset of pyramid-shaped microstructures and the respective dome-shaped microstructure. In the specific example, a 5×5 sensor array is associated with each dome, however examples are not so limited. The impedance values of the 5×5 capacitors, centered around the dome, are characterized by measuring the pressure response curve upon applied normal force.

FIG.5Aillustrates a cross-sectional view515of at least a portion of an apparatus that includes a subset of pyramid-shaped microstructures centered around one dome-shaped microstructure and with normal force applied, as illustrated by the arrows. The relative change in impedance, such as changes in capacitance (ΔC/Cmin=(C700 kPa−Cmin)/Cmin, where Cminand C700 kPaare the capacitances without and with applied pressure, respectively) is shown for the twenty-five capacitors, as shown by the impedance map521. The measured pressure response curves are shown by the graph527for three capacitors (e.g., one located at the top of the dome/hill and two located at the bottom, surrounding the dome/hill). The circle represents the location of the dome-shaped microstructure. The normal force may be applied and measured multiple times.

FIG.5Billustrates a cross-sectional view517of the at least portion of the apparatus, as illustrated byFIG.5A, and with shear force applied and which may include a normal force of 5-10 kPa, the shear force being illustrated by the arrows. The relative change in impedance (ΔC/Cminwith ΔC=(C340 kPa−Cmin)) is shown for the twenty-five capacitors, as shown by the impedance map523. The patterns for normal and shear forces are distinct, as shown byFIGS.5A and5B. The measured pressure response curves are shown by the graph529for three capacitors at different locations. The circle represents the location of the dome-shaped microstructure. The normal force may be applied and measured multiple times.

FIG.5Cillustrates a cross-sectional view519of the at least portion of the apparatus, as illustrated byFIG.5A, and tilt force applied, the tilt force being illustrated by the arrows. The relative change in impedance (ΔC/Cminwith ΔC=(C340 kPa−Cmin)) is shown for the twenty-five capacitors, as shown by the impedance map525. The pattern for the tilt force includes a combination of the pattern for normal and shear forces, as shown byFIGS.5A-5C. The measured pressure response curves are shown by the graph531for three capacitors at different locations. The circle represents the location of the dome-shaped microstructure. The normal force may be applied and measured multiple times.

FIG.5Dillustrates example impedance graphs533,535. The capacitors of the array have a different pressure response curves (and sensitivity) depending on their location. The first graph533illustrates capacitive response characteristics, for applied normal force, for two capacitors located at the top and at the bottom of the dome-shaped microstructure, respectively. The second graph535illustrates normalized response curves for the two capacitors. The slopes are used to calculate the sensitivities in various pressure ranges.

The pressure sensitivity S is defined as the slope of the traces, S=δ(ΔC/Cmin)/δP, where C and Cminare the impedances with and without applied pressure, and P is the applied pressure. The normal pressure sensitivity for the capacitors located at the top of the domes, is 0.19±0.07 kPa−1in the low-pressure regime (P<1 kPa), 0.10±0.01 kPa−1in the range 1<P<10 kPa, and 0.04±0.001 kPa−1in the range 10<P<20 kPa. The pressure sensitivity is on average 68% and 30% of these values for the capacitors located on the slope and at the bottom of the domes, respectively. Moreover, the measured response time may be within the millisecond range (as further illustratedFIGS.11A-11B).

In specific experimental embodiments, the sensitivity to shear force, for the capacitors located at the top and side of the dome-shaped microstructure exposed to shear force, is 3.0±0.5 Pa−1(10<P<20 kPa). The sensitivity of the capacitors located on the side of the dome-shaped microstructure not exposed to shear force is on average 30% that of the exposed side. Each capacitor associated a respective dome-shaped microstructure, depending on its location on the dome-shaped microstructure, reacts differently to the same applied force. For example, the dome-shaped microstructure concentrate forces onto the receptors differently depending on the direction of applied force as shown byFIG.5D. At pressures below 70 kPa, the capacitors at the top of the dome-shaped microstructure can have a higher sensitivity than the capacitors at the bottom of the dome-shaped microstructure, due to the short capacitor gap and the deformation of the pyramid-shaped microstructures upon applied pressure. On the other hand, the capacitors located at the side of the dome-shaped microstructure can have a better ability to measure larger forces without reaching saturation: above 70 kPa, the capacitors surrounding the dome-shaped microstructures can have a pressure sensitivity 9% higher (range 100 to 600 kPa) than the capacitors at the top of the dome-shaped microstructures, because of the deformation of the top membrane.

As shown byFIGS.5E-5I, because of the stretchability of elastomer, the sensor apparatus enables the detection of a force exerted on a localized area with limited effect on nearby pixels, as demonstrated with a 9×9 sensor array. In a specific example, the sensor apparatus is designed to work in a range up to a maximum of 100 kPa, a little higher than the typical human touch sensitive range (˜10 kPa). Such a sensor in robotic application also can be robust to high-pressure events, such as shown byFIG.5H. For several consecutive runs of pressures 0 to 1800 kPa, the sensor output is reproducible and the characteristic of the device may not be altered by the high pressures. Further, the sensor apparatus is sensitive and can detect small weights of 15 mg, as shown byFIG.5G, corresponding to pressure <0.5 kPa. In such experimental embodiments, a real-time signal-to-noise ratio (SNR) of 3 is calculated. In a number of embodiments, the baseline signal is higher and a greater SNR is obtained. Moreover, the pressure response of the sensors can be reproducibly cycled thousands of times, as shown byFIG.5I. After applying a pressure of 70 kPa and releasing to 15 kPa for more than 30,000 cycles (duration of 1 cycle: 4 seconds), Cminand Cmaxincrease by 2.3% and 0.2%, respectively.

FIGS.5E and5Fillustrate three dimensional plots541,543of the measured relative change in impedance for a sensor array537,539of 9×9 capacitors, where each shaded band corresponds to a variation ΔC/Cmin=5%. Normal force applied on the entire 9×9 array, as shown by the sensor array537and on the bottom left corner, as shown by the sensor array539. The pixels (e.g., capacitors) located proximal to the top of the dome-shaped microstructures have a measured standard deviation on ΔC/Cminbelow 20%.

FIG.5Gillustrates example repeated measurements related to an object. The sensor apparatus may be sensitive enough to measure objects as small as the illustrated 1 mm-diameter plastic bead542(15 mg, corresponding to less than 0.5 kPa). The bead542is placed on the sensor array (zone 2) and removed several times, and the pressure response signal is measured for capacitors located at the top (as illustrated by the first graph544), at the slope (as illustrated by the second graph546) and at the bottom (as illustrated by the third graph548) of the dome-shaped microstructure.

FIG.5Hillustrates a graph547of sensor apparatus responses at applied pressures in the range 0 to 1800 kPa (normal force, pyramids width a=30 μm, separation distance between the pyramids b/a=2 where a+b is the distance between the centers of 2 pyramids). The robustness of the sensor is illustrated by the unaltered pressure response curves after several runs at various pressures (shown in inset).FIG.5Iillustrates a graph549showing results of a cycling test which illustrate the stability of the pressure response over 30,000 cycles (a=30 μm, b/a=2). A small signal drift is measured, illustrated by the fact that C15 kPa(capacitance measured when 15 kPa is applied) increases by 2.3% and C80 kPa(capacitance measured when 80 kPa is applied) increases by 0.2% after 30,000 cycles. In all figures, the pyramids are arranged in a 2D orthogonal grid, the width of the pyramids is a=30 μm and the separation distance between the pyramids is b/a=4 unless stated otherwise.

The differing behaviors allow for sensor circuitry to differentiate between normal, shear, and tilt forces. The sensor circuitry may be used to identify the type of force, the direction of the force, and the magnitude of the force based on the resulting patterns illustrated by a respective array of capacitors and/or of a plurality of arrays.

The sensor circuitry can measure dynamic force by using the same transduction technology used for the static force by applying a high sampling rate (>500 Hz). In specific embodiments, the sensor circuitry includes at least one CDC circuitry that connects at least some of the electrodes to an input channel of the CDC circuitry. The sensor circuitry can measure dynamic forces by measuring impedance at a sample rate using the CDC circuitry and connected processing circuitry (e.g., microcontroller). To measure dynamic force by such a sampling rate, the sensor uses two CDC circuitry (e.g., CDC chips) to connect the four electrode pairs to 2 of the 12 analog input channels of each chip, since a high sampling rate (>500 Hz) can be obtained from a lower number of capacitor inputs to the chip. The CDC chip consists of a sigma-delta-based CDC with 12 analog input channels and communicates with a microcontroller via an I2C bus, measuring capacitance in 0.3-1.2 kHz sampling rate, and cancelling noise from capacitors through active shield function. For more information on CDC chips and active shield function, reference may be made to AD7147, Analog, http://www.analog.cm/media/en/technical-documentation/data-sheets/AD7147.pdf.

In various embodiments, the sensor apparatus is configured to be in contact with a finger. For example,FIGS.4A-4Bof the underlying provisional application show an example experimental sensing apparatus, consistent with embodiments of the present disclosure. More specifically,FIG.4Aof the underlying provisional application illustrates sensor circuitry in contact with a human finger. The sensor circuitry is thin and flexible such that it can cover the curved finger surface.FIG.4Bof the underlying provisional application illustrates sensor circuitry in communication (wired or wireless) with processing circuitry. The sensor circuitry can be connected to the processing circuitry, such as a laptop computer, by a printed circuit board. The processing circuitry can receive the signal data from the sensor circuitry and provide a graphical display of the resulting applied force on the sensor circuitry (e.g., the graph).

FIGS.6A-6Hshow an example of a sensor apparatus under different forces, consistent with embodiments of the present disclosure. More specifically,FIGS.6A-6Dillustrates an example of sensor apparatus designed with the objective to maximize the sensitivity, the signal-to-noise ratio (SNR) and the time-response. The geometry of the pyramid-shaped microstructures may be optimized based on geometry of the pyramids (e.g., size, ratio b/a) for the deflection of the top membrane in zone 1, corresponding to the capacitors located on the slopes and at the bottom of the dome-shaped electrodes. For this purpose, various pyramid sizes (e.g., width 10, 20, 30, 40 and 50 μm) and separation distances (e.g., ratio b/a=0.4, 0.8, 1.2, 1.6, 2 and 4, where a+b is the distance between the centers of two pyramids) are investigated. Zone 1 capacitors are located on the slopes and bottom of the domes/hills and zone 2 capacitors are at the top of the domes/hills.FIG.6Hillustrates the different changes in structure, as well illustrating as zone 1 and zone 2.

FIG.6Aillustrates a cross sectional view of the first substrate having pyramid-shaped electrodes in zone 1. A 1 kPa uniform pressure is applied (normal force). The initial and deformation patterns are shown, respectively.FIG.6Billustrates the cross sectional view of the deformation pattern of the first substrate with the pyramid-shaped electrodes in response to applying the 1 kPa uniform pressure. Additionally shown is zone 1661.FIGS.6C-6Eillustrate simulations performed for pyramid widths of 10, 20, 30, 40 and 50 μm, and separation distances between the pyramids of b/a=0.4, 0.8, 1.2, 1.6, 2 and 4 (a+b is the distance between the centers of two pyramids).

COMSOL simulations for zone 1 and zone 2 are performed with the objective to maximize the deflection of the top membrane upon applied pressure. Following the parallel plate capacitor definition of C, this results in larger ΔC/Cmin:
C=εrε0A/d(1)
where εris the relative static permittivity, co is the permittivity of vacuum, A is the area of overlap of the two electrodes and d is the separation between the electrodes.

FIGS.6F-6Gshow results for total displacement (e.g.,FIG.6F) and stress (e.g.,FIG.6F). The distance evaluated for total displacement is indicated with arrows. The stress is evaluated at the point indicated with the circle613. Then the circle611identifies optimized conditions for high sensitivity. The influence on ΔC/Cmin, when comparing worst case scenario (a=50 μm, b/a=0.4) and the optimized scenario (a=10 μm, b/a=4, applied pressure 1 kPa) is ˜4%.FIGS.6F-6Gshow that higher top membrane deformation is achieved in zone 1615with smaller pyramids and larger separation distance, resulting in larger ΔC/Cminand larger sensitivity. Moreover, according to equation (1), in zone 2616, larger Cminand therefore better SNR are achieved with smaller pyramids and smaller separation distance between the pyramids, as further illustrated byFIGS.12A-12D. In addition, it is shown that faster response time is achieved with smaller separation distance between the pyramids.

FIG.6Hshows a summary for an optimized sensor apparatus, in terms of pyramids microstructure design. To optimize the sensor apparatus, the positions of pyramids are adjusted in order to fulfill the requirements for both zone 1 and 2615,616. A spiral grid or pattern gives a good combination of high sensitivity in zone 1615, and high Cminand fast time response in zone 2616. This distribution offers a smooth transition of pyramids density from zone 1 to 2, from large to small ratio b/a, respectively. Spiral grids may include so-called phyllotaxis spirals. An example phyllotaxis spiral is shown by a capitulum of sunflower (e.g.,FIG.5dof the underlying Provisional Application), where multiple spirals run both clockwise and anticlockwise. Mathematically, phyllotaxis spirals can be calculated using the planar model proposed by Helmut Vogel. This model is based on an analysis of the Fibonacci suite converging at infinity towards the golden number, where every number is the sum of the two preceding ones. The position of each pyramid from the center is defined with the formula:
φ=n*137.5°, r=c n1/2(2),
where n is the numbering order of each single pyramid. The scaling parameter controls the phyllotaxis pattern. Based on this formula, sensor apparatuses are fabricated, where the pyramids are not positioned according to orthogonal grids, but according to phyllotaxis spiral grids with one spiral per dome (e.g.,FIGS.7A-7G). The top electrode with pyramids are seen to be organized along a phyllotaxis spiral grid (e.g.,FIG.7H), ready for sensor assembly.

FIGS.7A-7Gshow example microstructure patterns, consistent with embodiments of the present disclosure.FIGS.7A and7Billustrate microscope images of the Silicon (Si) masks used to mold the PU top electrode, with pyramids arranged along orthogonal grid.FIGS.7D and7Eillustrate microscope images of the Si masks used to mold the PU top electrode, with pyramids arranged along spiral grids.FIGS.7C and7Fillustrate the domes shown at the same scale as the top electrode with pyramids. As previously described the top electrode layers are positioned on the 1 mm-diameter domes shown at the same scale.FIG.7Gillustrates an SEM image showing the PU top electrode layer with pyramids arranged along phyllotaxis spiral grid. The CNTs-PU conducting electrodes appear as stripes of light grey (stripes of darker grey correspond to PU without CNTs between the electrodes).

FIGS.8A-8Dshow an example sensor apparatus under different forces and resulting capacitive response patterns, consistent with embodiments of the present disclosure. The response characteristics of the sensor apparatus, for sensor arrays of 5×5 capacitors with orthogonal and spiral pyramids grids are shown inFIGS.8A-8D. More specifically,FIG.8Aillustrates 30 μm-wide pyramids positioned along an orthogonal grid with ratio b/a=4.FIG.8Billustrates 30 μm-wide pyramids positioned along an orthogonal grid with ratio b/a=0.4.FIG.8Cillustrates 30 μm-wide pyramids positioned along a phyllotaxis spiral grid (ratio b/a=0.4 and 4 at the spiral center and border, respectively).FIG.8Dillustrates 10 μm-wide pyramids positioned along a phyllotaxis spiral grid (ratio b/a=0.4 and 4 at the spiral center and border, respectively). Each ofFIGS.8A-8Dillustrate a cross-sectional side view821,823,825,827of the sensor array with κ×5 capacitors, and with a normal force illustrated by the arrow. Further,FIGS.8A-8Dillustrates capacitive maps822,824,826,828showing the relative change in capacitance ΔC/Cminfor the twenty-five capacitors of each array. And, the graphs831,833.835,837illustrates the response curves for the twenty-five capacitors of each array.

Considering zone 1, larger ΔC/Cminare measured with devices inFIGS.8A and8C, where the separation distance between the pyramids is large (ratio b/a=4 vs. 0.4 inFIG.8B). This result is in agreement with simulations (e.g.,FIGS.6A-6G). Moreover,FIGS.8C and8Dshow the response curves for two sensor arrays with spiral grids, with pyramids width 30 μm and 10 μm, respectively. The difference in concentration or intensity between the center and edge is less distinct with spiral grids (e.g.,FIGS.8C and8D) than orthogonal grids (e.g.,FIGS.8A and8B), corresponding to larger response curves and ΔC/Cminmeasured at the border of the hills in the context of spiral grids. In addition, larger Cminand better SNR are achieved with smaller pyramids (e.g.,FIG.8D). These results illustrate the superiority of the spiral grids compared to orthogonal grids.

FIGS.9A-9Fshow example performance of a sensor apparatus, consistent with embodiments of the present disclosure. Robotic experiments may be performed, as shown, with the objectives to demonstrate the use of the e-skin to control a robot arm in real time, and that the high sensitivity of the nature-inspired e-skin for normal force and shear force stimuli enables tasks requiring high dexterity.

FIG.9Ashows example experimental set-up which includes a sensor array mounted on an artificial hand and fixed on a gripper that is attached to a robot arm. The limitations of a single pixel detection experimental set-up prevents integration of the full directional sensing capabilities in robotic application, which requires developments of a multiplexing acquisition platform. An LCR (inductance (L), capacitance (C), resistance (R)) meter is recording the capacitance signal from sensor array. Data is stored on a server and retrieved by the robot controller to be used in a closed-loop feedback scheme to control the movement of the robot arm in real time.

This design has the advantage of making the mechanical structure of the sensor independent from the movement of the arm, thus the only measurement obtained is the contribution of the pressure and shear forces.FIG.9B(as well asFIG. S7of the underlying provisional application) show an example test-plate with holes, and the pre-programmed consecutive movements executed by the robot arm, unless tactile feedback prevents the execution of the entire movement downwards. The sensor array951is either exposed to normal force (e.g., arrows952) or shear force (e.g., arrows953). Illustrated is an example test-plate with holes (e.g., either 8 holes, 4 holes, or no hole, as illustrated inFIGS.9D and9F). The lines show the consecutive movements executed by the robot arm, unless tactile feedback prevents the entire execution of the down movement.

When the sensor array is solely exposed to normal force, the robot arm correctly executes a premature movement in upwards direction as soon as the finger touches the test plate at a location with no hole due to sensing of a normal force (arrow952), as shown byFIGS.9C-9D. More specifically,FIG.9Cillustrates a set of experiments where the sensor array is solely exposed to normal force is reproduced three times. The arrows show the movement executed downwards, unless normal force feedback952is detected and prevents the entire execution of the movement downwards.FIG.9Dillustrates example experiments performed with 4 different test-plate with holes. The robot arm goes consecutively from position 1 to position 8. For each experiment, the position of the robot arm in z-direction and the measured capacitance C are plotted as a function of time. The arrows in the graph indicate the successful detection of normal force when the finger touches the plate (in the absence of a hole), and the corresponding close-loop control feedback movement in upwards direction.

FIG.9Eillustrates a second set of experiments in which the sensor array is solely exposed to shear force, reproduced three times. If the sensor array is solely exposed to shear (tangential) force with a light object (ping pong ball, weight 2.7 g) placed between the two artificial fingers, shear force (e.g., arrow953) is exerted on the sensor array as soon as the robot arm goes vertically down and the ball is pressed on the table. The arrows show the movement executed downwards, unless shear (tangential) force feedback953is detected and prevents the entire execution of the movement downwards. Because of the light weight, only a negligible tangential force contribution due to the weight (gravity) is initially present.FIG.9Fshow example experiments performed with four different test-plates with various numbers of holes. The arrows in the measured capacitance plots indicate the successful detection of shear force. When the ping pong ball touches the table below, it is observed that it is not sliding between the fingers because of the initial small normal force applied to hold it and because of the surface interaction between polyurethane and the ball. It is therefore the tangential force that is measured by the sensor array that is used to control the robot movement. As soon as tangential force is measured the robot stops its movement downwards, goes back up and continue the experiment to the next position.

It is shown inFIG.9Fthat the robot arm correctly interrupts its pre-programmed movement in downward direction as soon as shear force is detected and the ball touches the test plate at a location with no hole.FIGS.6gto6iof the underlying Provisional Application also illustrate the high sensitivity of the sensor and demonstrate the tactile sensing capabilities allowing to interact with deformable and delicate objects such as a fresh raspberry. The tactile feedback may be used to prevent the raspberry from being flattened.

Embodiments in accordance with the present disclosure include a biomimetic flexible e-skin composed of an array of capacitors, capable of measuring and discriminating in real time both normal and shear forces. The e-skin is used to control a robot arm in various tasks as a first step towards integration of its high-sensitivity directional sensing capabilities, illustrating its potential future application in various fields of robotics including personalized domestic help, ambulatory and inpatient health care, medical diagnosis, surgery, industry, and exploratory missions in hard to reach places.

In various experiments shown inFIGS.5A-9Fdata collection rules are based on pressure ranges predefined prior to each experiment. A pressure gauge or the robotic hand controller automatically reverses upon detection of a pressure maxima. Outliers are identified by analyzing SNR of the response curve, which allows for identification of faulty sensor fabrication or bad connectivity at the interfaces. In those cases, either the sensor is eliminated from the test batch, the two electrode layers are realigned, or connectivity with LCR is adjusted. Experiments are then reproduced with the new sensor.

Fabrication of the silicon (Si) wafer with pyramid grids may include Si wafers patterned with pyramids of different sizes by lithography followed by HF oxide etching and finally an anisotropic potassium hydroxide (KOH) etching.

Patterning of the CNT electrodes on polyurethane substrate may include a fabrication step applied to both the top and bottom PU electrodes. Si wafers are cleaned with O2-plasma. A CNTs-layer is spray-coated on the wafers from a CNTs dispersion (12 mg of P2-SWNT from Carbon Solutions and 70 mL of N-methyl-2-pyrrolidone ultrasonicated for 30 minutes followed by collecting the supernatant after centrifugation for 30 minutes at 8000 rpm, 18 degrees C.). The CNT electrodes are lithographically patterned using S1813 photoresist. For the top electrode with pyramid grid, the photolithography mask is aligned with the pyramids, to ensure a proper positioning of the CNT electrodes. A subsequent oxygen plasma etching is used to remove the CNTs without photoresist protection. The remaining photoresist is then removed using acetone, isopropanol and water. On this wafer, polyurethane elastomer (Tecoflex SG-80A from Lubrizol Co.) is cast from chloroform solution (10 mg/mL) by spin-coating at 1000 rpm, followed by another layer of polyurethane from chloroform solution (60 mg/mL) at 1000 rpm. The first layer is used to promote adhesion to CNTs, while the thicker layer (˜10 μm) allows for manipulation of the electrodes. The PU films with CNTs-patterned electrodes are then released from glass substrate for sensor assembly.

Fabrication of the domes/hills arrays may involve CNTs-patterned PU electrode film (without pyramids) being placed on a grid with 1 mm holes, with the CNTs lines aligned with the grid (three lines per hole, one line in between each hole, as shown inFIGS.1band3b(inset) of the underlying Provisional Application). Vacuum (˜250 Torr) is applied to create the hill shape in PU. A Polydimethylsiloxane layer (ratio 1:10, thickness˜3 mm, PDMS Sylgard from Dow Corning Co.) is cast onto the electrode film, then oven-baked for 30 min at 80 degrees C. The final bottom electrode with domes/hills is then released and ready for assembly.

The sensor is assembled by laminating the bottom electrode with hills, the 10 μm-thick polyhydroxybutyrate-polyhydroxyvalerate (PHB-PHV) dielectric layer, and the top electrode with pyramids. During lamination, the two electrodes are aligned perpendicular to each other so that each dome/hill corresponds to twenty-five capacitors (one on the top of the dome/hill, four on the slopes, four on the “corners”, and sixteen shared capacitors surrounding the dome/hill). The alignment is made manually using an optical microscope. Moreover, PHB-PHV is selected as dielectric because it combines good mechanical resistance at low thickness and moderate dielectric constant to maximize for capacitance, as described in Equation 1.

As shown byFIG.9A-9F, force response measurement setup may involve and/or consists of a motorized vertical stage used in combination with a force gauge, while the capacitance of each sensor was measured with an LCR meter.

The e-skin is fixed on a mock-up flexible hand, which is attached to a Schunk WSG50gripper mounted on a robot arm (KUKA IIWA). The robot is programmed to perform series of predefined movements, as defined by the experimental protocol, with a controller that can stop the movement depending on the signal recorded on the e-skin. The control algorithm takes as input the signal from the e-skin through the LCR and stops the movement of the robotic arm if the signal reaches a predefined capacitance threshold. A redis interface is used for the communication between the LCR and the computer controlling the robot.

FIGS.10A-10Cshow an example of a sensor apparatus under different forces, consistent with embodiments of the present disclosure. A sensor array of 5×5 capacitors, centered on one dome, is characterized by measuring the pressure response curve upon an applied normal force (as shown byFIG.10A), an applied shear force (as shown byFIG.10B), and an applied tilt force (as shown byFIG.10C).FIGS.10A-10Cshow respective 3D plots where each color band corresponds to a variation ΔC/Cmin=(C700 kPa−Cmin)/Cmin==5%, where Cminand C700 kPaare the capacitances without and with applied pressure, respectively.

FIGS.11A-11Dshow example performance of a sensor apparatus, consistent with embodiments of the present disclosure, such as using the experimental set up illustrated byFIG. S3of the underlying provisional. More specifically.FIGS.11A-11Dshow an immediate response of the sensor array when a constant pressure is applied and then released (here 20 kPa for about 10 s). The underlying provisional application illustrates an example experimental set up for applying normal, shear, and tilt forces to a sensor array.

FIGS.12A-12Dshow example microstructure patterns, consistent with embodiments of the present disclosure. For example,FIGS.12A-12Dillustrate the optimization of the separation distance between the top and bottom electrodes of the capacitors in zone 2 (capacitors located at the top of the domes).FIG.12Aillustrates a comparison of various sizes of pyramids (from 10 to 50 μm). If the pyramid is smaller, the separation distance between the top and bottom electrodes is smaller. According to equation 1, it results in a larger value of the capacitance Cmin, which directly (positively) impacts the signal-to-noise ratio.FIGS.12B-12Dillustrate a comparison of various separation distances between the pyramids (ratios b/a from 0.4 to 4), and how it influences the value of Cmin. More and smaller pyramids result in higher Cmin. The CNTs conducting layer is marked in a solid black line. The equivalent separation distance between the bottom and top electrodes is marked by the arrows. It is calculated as the average distance between the top and the bottom electrode, taking into account the 3D geometry of both electrodes. Higher Gun, and therefore better SNR are achieved with a smaller separation distance between the pyramids, which corresponds to a smaller equivalent separation distance. In both figures the conditions resulting in the highest Cminare marked with a circle.

FIGS.13A-13Cshow example microstructure patterns, consistent with embodiments of the present disclosure. For example,FIGS.13A-13Cillustrate the optimization of the time-response (zone 2, capacitors located at the top of the domes/hills) by changing the separation distance between pyramids. For example,FIG.13Aillustrates a separation distance between the pyramids ranging from b/a of 4,FIG.13Billustrates a separation distance b/a of 1.2, andFIG.13Cillustrates a separation distance b/a of 0.4. For each condition, a cross-sectional view showing the pyramids and the equivalent mechanical circuit model are provided. When pressure is applied on the sensor, the pyramids deform reversibly. Each pyramid can be modeled as a spring (constant K) in series with a damper (constant B). The equivalent circuit for several pyramids in parallel and the corresponding system time constant τ are calculated for each condition, indicating that shorter time-response is achieved with b/a=0.4 (best-case scenario, indicated with a circle).

Specific sensor apparatuses in accordance with the present disclosure can measure and distinguish combined normal and shear pressure during different object manipulation as applying different normal pressure and shear pressure. The sensor responds to normal pressure as impedance changes in all and the average impedance is used to analyze the normal pressure. On the other hand, the sensor responds to shear pressure, even with normal pressure, as differences in impedance s that increase in two electrodes while impedance s decrease in others, so the subtraction of the impedance is used to analyze the shear pressure. The demonstration illustrated tactile sensing capabilities of the device, which allows the robotic device to interact with deformable, even stretchable, and fragile objects by manipulating tofu and/or a berry.

Various embodiments are implemented in accordance with the underlying Provisional Application (Ser. No. 62/750,951), entitled “Skin-Like Sensor for Normal and Shear Stress Detection,” filed Oct. 26, 2018, to which benefit is claimed and which are both fully incorporated herein by reference for their general and specific teachings. For instance, embodiments herein and/or in the Provisional Application be combined in varying degrees (including wholly). Reference may also be made to the experimental teachings and underlying references provided in the underlying provisional application. Embodiments discussed in the Provisional Application are not intended, in any way, to be limiting to the overall technical disclosure, or to any part of the claimed disclosure unless specifically noted. The Provisional Application illustrates a general sensor apparatus, and specific implementations of the first and second substrates including patterns of microstructures, and experimental embodiments used to optimize the same. It is recognized that the various figures and descriptions herein can be used in combination with a variety of different structures and technical applications as described in the above-referenced Provisional Application, which is fully incorporated herein by reference for all it contains.

Terms to exemplify orientation, such as top view/side view, before or after, upper/lower, left/right, top/bottom, and above/below, may be used herein to refer to relative positions of elements as shown in the figures. It should be understood that the terminology is used for notational convenience only and that in actual use the disclosed structures may be oriented differently than the orientation shown in the figures. Thus, the terms should not be construed in a limiting manner.

As examples, the Specification describes and/or illustrates aspects useful for implementing the claimed disclosure by way of various circuits or circuitry which may be illustrated as or using terms such as blocks, modules, device, system, unit, controller, and/or other circuit-type depictions. Such circuits or circuitry are used together with other elements (robotics, electronic devices, prosthetics, processing circuitry and the like) to exemplify how certain embodiments may be carried out in the form or structures, steps, functions, operations, activities, etc. For example, in certain of the above-discussed embodiments, one or more illustrated items in this context represent circuits (e.g., discrete logic circuitry or (semi)-programmable circuits) for implementing these operations/activities, as may be carried out in the approaches shown in the figures. In certain embodiments, such illustrated items represent one or more circuitry and/or processing circuitry (e.g., microcomputer or other CPU) which is understood to include memory circuitry that stores code (program to be executed as a set/sets of instructions) for performing a basic algorithm (e.g., inputting, counting signals having certain signal strength or amplitude, classifying the type of force including a magnitude and direction using impedance values output by the sensor circuitry, sampling), and/or involving sliding window averaging, and/or a more complex process/algorithm as would be appreciated from known literature describing such specific-parameter sensing. Such processes/algorithms would be specifically implemented to perform the related steps, functions, operations, activities, as appropriate for the specific application.

Based upon the above discussion and illustrations, those skilled in the art will readily recognize that various modifications and changes may be made to the various embodiments without strictly following the exemplary embodiments and applications illustrated and described herein. For example, methods as exemplified in the Figures may involve steps carried out in various orders, with one or more aspects of the embodiments herein retained, or may involve fewer or more steps. Such modifications do not depart from the scope of various aspects of the disclosure, including aspects set forth in the claims.