A Modulus Sensor

Disclosed is a device for measuring a property of a material. The device comprises a base; a sensor, the sensor being in a fixed coupling with the base; an indenter, the indenter being slidably coupled to the base to move relative to the base in an axial direction in response to a first abutment of the indenter with a surface of the material such that the indenter provides a push force to the sensor in the axial direction; and a locking device, the locking device being configured to releasably lock the indenter in a locked state in response to a second abutment of the base with the surface of the material, wherein the indenter in the locked state is prevented from moving relative to the base in the axial direction. Also disclosed is a new method of measuring Young's modulus of a material.

The present application claims priority from the Singapore patent application no. 10202012110R, the contents of which are incorporated herein in entirety by reference.

TECHNICAL FIELD

The present disclosure relates to the field of measurement, and more particularly to a device and method of measuring a softness-related property of a material.

BACKGROUND

Haptic perception of softness enables humans to feel the mechanical properties of objects. Artificial haptics or recreation of our sense of touch has many applications ranging from robotics, virtual and augmented reality to clinical diagnosis. Among several types of haptics, softness perception is common in our daily lives, for example, when handling soft objects like tofu or during diagnosis by medical professionals, where palpations are used for disease prognosis. Conventionally, the measurements of softness or degree of softness of a material require stabilized samples and well-cut samples with known sizes, which makes it difficult to perform in-situ measurement rapidly in many scenarios including haptics, robotics, clinics, and cosmetics.

SUMMARY

In one aspect, the present disclosure provides a device configured to measure a property of a material. The device comprises a base; a sensor, the sensor being in a fixed coupling with the base; an indenter, the indenter being slidably coupled to the base to move relative to the base in an axial direction in response to a first abutment of the indenter with a surface of the material such that the indenter provides a push force to the sensor in the axial direction; and a locking device, the locking device being configured to releasably lock the indenter in a locked state in response to a second abutment of the base with the surface of the material, wherein the indenter in the locked state is prevented from moving relative to the base in the axial direction.

Preferably, the sensor is configured to operably provide a measurement signal in response to receiving the push force. Preferably, the sensor is configured to operably provide a measurement signal concurrently with the indenter being in the locked state. Preferably, the measurement signal corresponds to a quantitative measure of the property of the material. Preferably, the measurement signal corresponds to a Young's modulus value of the material. Preferably, the measurement signal is directly correlatable to the Young's modulus value of the material. Preferably, the measurement signal corresponds to a quantitative measure of a haptic sensation of the material.

In some embodiments, the sensor comprises a strain gauge, the strain gauge having opposing edges in the fixed coupling with the base such that the strain gauge is disposed in a transverse plane in an undeformed state, the transverse plane being normal to the axial direction, and wherein the strain gauge is deformable into a deformed state by the indenter pushing against the strain gauge, the strain gauge in the deformed state being partially displaced out of the transverse plane by an offset in the axial direction. Preferably, the indenter is configured to contact the strain gauge. Preferably, the strain gauge is deformed by the indenter in the locked state to provide a strain gauge reading corresponding to a Young's modulus value of the material. Preferably, the sensor comprises a pressure sensor resiliently coupled to the indenter.

In some embodiments, the indenter comprises a first end, the first end being disposed beyond the base and configured to be brought into contact with the surface of the material; and a second end, the second end being disposed proximal to the sensor, wherein the indenter defines an indenter axis extending through the first end and the second end, and wherein the indenter axis is parallel to the axial direction when the indenter is in the locked state. Preferably, the first end is characterized by a Young's modulus value that is larger than a Young's modulus value of the material. Preferably, the first end comprises a hemispherical tip.

In some embodiments, the locking device comprises a cap, the cap being coupled to the base; and at least one clamp element, the at least one clamp element being resiliently coupled to the base, wherein the at least one clamp element is configured to be displaced by the cap in a clamping direction non-parallel to the axial direction such that the at least one clamp element releasably locks the indenter in response to the second abutment. Preferably, the locking device comprises at least two clamp elements, the at least two clamp elements being diametrically disposed about the indenter and configured to cooperatively releasably lock the indenter. Preferably, each clamp element defines a sloped surface inclined relative to the clamping plane. Preferably, each clamp element defines an increasing thickness towards the indenter. Preferably, the cap is biased apart from the base by a spacing if the indenter is in an unlocked state, and wherein the cap is responsive to a force to move relative to the base opposite the axial direction. Preferably, the cap is slidably engageable with the sloped surface such that a movement of the cap opposing the axial direction relative to the base is translated to a movement of the at least one clamp element in the clamping direction to releasably lock the indenter.

In some embodiments, the cap comprises a tab; and at least one actuating leg extending from the tab parallel and opposite to the axial direction, the at least one actuating leg being slidably engageable with the sloped surface, wherein the cap and the base are telescopically moveable to releasably lock the at least one clamp element with the indenter. Preferably, a displacement of the at least one clamp element in the clamping direction brings the at least one clamp element into an abutment with the indenter at a locking location, wherein the locking location is one selected from a continuum of potential locking locations along an indenter body of the indenter. Preferably, the indenter body defines an indenter axis extending through a first end of the indenter and a second end of the indenter, and wherein the abutment of the at least one clamp element with the indenter disposes the indenter axis to be parallel to the axial direction. Preferably, the device is configured to be attachable to an end-effector or a user.

Also disclosed is a haptic device. The haptic device comprises the device as disclosed above; and a processor coupled to the sensor and configured to acquire a measurement signal corresponding to the property of the material. Preferably, the processor is configured to determine a Young's modulus value of the material based on the measurement signal. The haptic device may further comprise a user interface coupled to the device, the user interface being configured to output a Young's modulus value of the material. The haptic device may further comprise a telemetry device coupled to the device, the telemetry device being configured to perform a method of acquiring at least one measurement signal from the sensor; and based on the at least one measurement signal, transmit a Young's modulus value and/or a trend of a plurality of Young's modulus values to a user interface and/or a computing device.

Also disclosed is a tool for quantifiable palpation. The tool comprises the device as disclosed above; an attachment, the attachment being attachable to the cap; and a user interface coupled to the device, wherein the user interface is configured to display data based on a corresponding plurality of measurement signals from the device.

In another aspect, the present disclosure includes a method of measuring a degree of softness of a material. The method comprises bringing an indenter of a device into contact with a surface of the material, wherein the indenter protrudes from a contact surface of the base, and wherein the indenter is configured to retract inwardly relative to the base such that the indenter provides a push force to the sensor in an axial direction; and obtaining a measurement signal from the sensor corresponding to a relative displacement between the indenter and the base, wherein the relative displacement is limited by the contact surface being brought into contact with the surface of the material. The method may further include: before obtaining the measurement signal, locking the indenter relative to the base in response to the contact surface contacting the surface of the material. Preferably, the measurement signal corresponds to a quantitative measure of the degree of softness of the material. Preferably, the measurement signal corresponds to the Young's modulus value of the material.

In some embodiments, the device configured to measure a property of a material, the device configured according to any described above, in which the sensor comprises a strain gauge disposed in a transverse plane in an undeformed state, the transverse plane being normal to the axial direction, wherein the strain gauge is deformable into a deformed state by the push force, wherein the strain gauge in the deformed state is partially displaced out of the transverse plane by an offset in the axial direction.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment”, “another embodiment” or “an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the use of “in one embodiment” or “in an embodiment” or the like in various places throughout this specification may refer to more than one embodiment. Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, that the various embodiments be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, some or all known structures, materials, or operations may not be shown or described in detail to avoid obfuscation.

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. As used herein, the singular ‘a’ and ‘an’ may be construed as including the plural “one or more” unless apparent from the context to be otherwise.

Terms such as “first” and “second” are used in the description and claims only for the sake of brevity and clarity, and do not necessarily imply a priority or order, unless required by the context. The terms “about” and “approximately” as applied to a stated numeric value encompasses the exact value and a reasonable variance as will be understood by one of ordinary skill in the art, and the terms “generally” and “substantially” are to be understood in a similar manner, unless otherwise specified.

For the sake of brevity, the terms “Young's modulus”, “material elasticity”, “material stiffness”, and “resilience of material” refer to a material property, and may be used interchangeably in the present disclosure.

Conventionally, measurement of the Young's modulus of a material requires the measurement of the full stress-strain curve, as well as knowledge of other properties of the material being tested. In addition to the bulky systems resulted from multi-parameter/multi-variable calculations involved, the requirements of stabilized and well-cut samples prevent rapid measurements in-situ and on-demand. Such conventional methods are clearly not applicable to in-situ measurement on non-standard materials such as a part of a patient's body. It will be understood that some materials are generally considered “soft” but, conventionally, “softness” has been difficult to objectively define or to quantify. The terms “haptic response”, “haptic sensation”, and “haptic feedback” may be interchangeably used herein to refer to a softness perception or a tactile sensation experienced by a user. For example, such softness perception may be a softness of an object when the user touches the object. This softness perception is conventionally only perceivable by the user's finger, in which mechanoreceptors in the user's skin, muscles, tendons, and joints generate neural signals in response to the pressure on the finger. The softness perception is thus conventionally understood to be a subjective feeling or sensation. The following describes a new method of measuring a Young's modulus of a material, including but not limited to soft materials. According to embodiments of the present disclosure, non-limiting examples of a device and a method of measuring a softness-related property (here generally referred to as “softness”) of a material are described below to illustrate haptic sensation or haptic feedback in the form of a single quantitative measure such as a Young's modulus value of the material. The device and method are applicable to soft materials, including but not limited to materials having a Young's modulus value from several tens of kPa to a few MPa.

The term “palpation” refers to a clinical diagnostic method involving a trained medical personnel using fingers or hands to touch the patient and to feel for swelling, turgidity, hard lumps under the skin, softness of human body/muscle/tissue, etc. Conventionally, the amount of palpation force exerted on a target area varies from one touch to another, and it takes a trained and experienced medical professional to exert a consistent palpation in order to correct diagnose the patient's condition. Measurement of the softness of a material can serve as the basis for a wide range of applications, including but not limited to, palpation (such as for clinical diagnosis), massage tools (such as for physiotherapy or cosmetic purposes), haptic sensitive tools (such as for surgical instruments, application of medications and/or creams for medical or cosmetic purposes), monitoring conditions such as elasticity of skin (for medical or cosmetic purposes), tools for product quality assessment, classification and/or quality control (such as for checking ripeness of fruits), etc. The term “measure” as used herein is to be understood broadly and not to limit the potential applications that may be enabled by measuring a softness-related property of a material (e.g., of an object or a subject).

FIG.1Aillustrates a modulus sensor200(interchangeably referred to as a device200) according to one embodiment of the present disclosure. The modulus sensor or device200is useful in a variety of applications, including but not limited to providing a quantitative measure corresponding to the Young's modulus of a material. The device200is optionally coupled to a handle/attachment400to form a hand-held or portable haptic device300. The device200is configured to be operable by a user20bringing the device200into contact with a surface50of a material or a target to be sensed for its softness and/or to palpate the target area. A telemetry device320may be provided in the haptic device300. The haptic device300may be configured to communicate by a cable or wirelessly (as shown) with a computing device (not shown) such that measurement signals obtained by the device200may be stored, displayed, and/or used. The haptic device300may be configured as a tool for quantifiable palpation, such as one suitable for use by a medical professional. A user interface, such as a display500, may be provided on the attachment400to provide real-time and/or essentially instantaneous indication or readings based on the measurement signals obtained from the device200. As will be described in the following, the device200is configured to provide a more consistent and quantifiable palpation, and hence a more accurate clinical diagnosis. The haptic device300is also configured to provide real-time measurements such that the haptic device can serve as a practical tool for bedside clinical diagnosis.

FIG.1Billustrates another embodiment of the haptic device300including the device200configured for use to measure softness and/or provide palpation, etc. The device200may be coupled with an attachment400that serves as a handle for a user20as well as to house a telemetry device320. The haptic device300may be configured to communicate wirelessly or by a cable502(as shown) with a computing device (not shown) such that measurement signals obtained by the device200may be stored, displayed, and/or used.

The device200advantageously enable the haptic device300to be held by hand in different poses in the course of use. For example, the haptic device300may be held, e.g., be used while held in various different poses. For example, the haptic device300may be held like a brush (FIG.1A) or like a pen (FIG.1B). As will be described in the following, the device200is configured such that it can self-correct to provide a meaningful measurement signal even if the haptic device300and the surface50are not strictly orthogonally aligned. This enables the haptic device300to be hand-held and portable, and suitable for use in bedside clinical diagnosis.

FIG.1Cis a schematic block diagram of a system100according to another embodiment of the present disclosure. The system100includes a haptic device300. The haptic device300includes the device200operably coupled to a processor310. The processor310may be configured to acquire from the device200a measurement signal corresponding to the property of the material. In some embodiments, the processor310is configured to determine a Young's modulus value of the material based on the measurement signal. The haptic device300may further include a telemetry device320. In some embodiments, the telemetry device320is configured to acquire at least one measurement signal from the device200; and based on the at least one measurement signal, transmit a Young's modulus value and/or a trend of a plurality of Young's modulus values to a computing device504for records, calculations, display, and/or other uses. The computing device504may be provided with a user interface500configured to display measurement data and/or diagnostic information. In this example, the haptic device300may be coupled to a detachable or interchangeable attachment400. In some examples, the computing device504may be a mobile electronic device, such as a smart phone, etc. In some embodiments, the attachment400may be an end-effector. In other examples, the attachment may be wearable by a user. In some examples, the haptic device300may be configured as a laboratory equipment to measure softness perception of objects/subjects52.

FIGS.2to4illustrate a non-limiting embodiment of the device200to aid understanding.FIG.2shows a base210coupled with a cap250. The cap250may be configured with a tab254and actuating legs252. In some embodiments, the cap250may include a tab254and at least one actuating leg252extending from the tab254parallel to and opposite to an axial direction82. In this example, the actuating legs252are provided with flanges256. The device200may be coupled with an attachment400via the tab254of the cap250. In some examples, tab254may be formed as an integral part of the attachment400. The tab254may be configured in different forms to suit the application and/or ergonomics. For example, in the pen configuration ofFIG.1AorFIG.1B, the body of the pen (the handle/attachment400) can also serve as the tab254.

As shown inFIGS.3A,3B, and4, the base210includes a contact end215with an opening212defined by the contact end215. The contact end215provides an external face211and an opposing internal face213. A wall217extends from the contact end215along the axial direction82. The wall217may be configured with a set of pothooks216which are releasably engageable with the actuating legs252. The cap250and the base210are prevented from being axially pulled apart from one another by the cooperative engagement of flanges256and the pothooks216.

In some embodiments, the device200includes a locking device240having at least one clamp element242. One or more clamp elements242may be provided in the device200. In some examples, one of the clamp elements242is displaceable relative to the indenter230, while other of the clamp elements242are fixed relative to the indenter230. In this example, two clamp elements242are disposed on the internal face213. The clamp elements242may be diametrically disposed about the indenter230and configured to cooperatively and releasably lock the indenter230. Both of the clamp elements242are configured to be displaceable relative to the indenter230to lock the indenter230. The actuating legs252rest on the respective clamp elements242such that the cap250and the base210are biased to be axially spaced apart. In some examples, at least one of the clamp elements242are resiliently coupled to the base210and moveable relative to the opening212. In some examples, a layer of polymer is provided between each of a pair of the clamp elements242and the internal face213of the base210. The layer of polymer serves as an elastic adhesive providing a resilient/elastic coupling between the clamp elements242and the base210. In some examples, the device200is formed by 3D printing using a support material such as FullCure705. A layer243of FullCure705of about 200 μtm thickness may be retained after the 3D printing process, between the base210and the clamp elements242. The FullCure705layer243can serve as an elastic/resilient coupling between each of the clamp elements242and the internal face213of the base210. In other examples, a resilient member in the form of a spring may be coupled between at least one clamp element242and the base210. The resilient coupling between each clamp element242and the base210is configured to bias the clamp element242away from the opening212, while permitting a relative movement of the clamp element242toward the opening212.

Each of the clamp elements242may define a sloped surface244inclined relative to a clamping plane76. The sloped surface244may be one of or a combination of a straight/flat surface, a concave surface, or a convex surface. Each clamp element242may define an increasing thickness towards the indenter230. In some embodiments, each clamp element242may define a sloped surface244with an increasing height toward the indenter230and relative to the clamping plane76, with or without an increasing thickness. For example, the clamp element242may be configured as a hollow element with a relatively constant thickness throughout, while still presenting a sloped surface244as described. The clamping plane76may be parallel to the transverse plane74.

The actuating legs252extending from the tab254are disposed substantially parallel to the axial direction82. At least one actuating leg252may be slidably engageable with the sloped surface244of the respective clamp elements242. The cap and the base are telescopically moveable88to releasably lock the at least one clamp element242with the indenter230. A movement of the cap250may push onto sloped surface244of the clamp elements242, to displace the clamp elements to move towards the indenter230. Therefore, the cap250is slidably engageable with the sloped surface244such that a movement of the cap250opposing the axial direction82relative to the base210is translated to a movement to each of the clamp element242in the clamping direction84to releasably lock the indenter230. A displacement of one or more of the clamp elements242in the clamping direction84brings the clamp elements242into an abutment with the indenter230at a locking location. The locking location may be one selected from a continuum of potential locking locations along the indenter body233of the indenter230. In some embodiments, the abutment of respective clamp elements242with the indenter disposes the indenter axis86to be parallel to the axial direction82. In other words, the clamp elements242clamps onto the indenter230to align the indenter axis86parallel to the axial direction82. This advantageously prevents the indenter230from being in a tilted orientation relative to the base210or the surface50.

A sensor220is disposed in a cavity defined by the cap250and the base210. The sensor220is configured to be in a fixed coupling227with the base210, that is, at least a part of the sensor220is coupled to be immovable relative to the base210. In some examples, the sensor220may include a strain gauge, such as a polydimethylsiloxane (PDMS) based piezoresistive strain sensor. The strain gauge may be a multilayer structure. Opposing ends221of the strain gauge are fixedly coupled227to respective supports214of the base210such that the strain gauge is substantially disposed in a transverse plane74when the strain gauge is in an undeformed state. The transverse plane74is configured to be substantially normal to the axial direction82.

The device200includes an indenter230slidably coupled to the base210. In this example, the indenter230is slidable through the opening212defined by the contact end215of the base210. The indenter230is configured to move relative to the base210in the axial direction82. The indenter230may be configured with an indenter body233that defines an indenter axis86extending through a first end232and a second end234.

The indenter230is disposed relative to the base210such that the first end232extends outside the device200, i.e., with the first end232disposed beyond the base210. In use, device200is brought towards a surface50of a material/object to be tested such that the first end232of the indenter230can be brought into contact with the surface50. The first end232of the indenter230may be shaped with a rounded tip or a substantially hemispherical tip. Preferably, the first end232is made of a relatively hard material characterized by a Young's modulus (e.g., in a range of more than 1 GPa) that is significantly larger than a Young's modulus of the material/object to be tested (e.g., in a range of less than 1 MPa).

The second end234of the indenter230is disposed proximal to the sensor220. In this example where the sensor220includes a strain gauge, the indenter230and the sensor220are disposed such that the second end234of the indenter230can come into contact with a part of the strain gauge that is deformable as a result of the second end234pushing on the strain gauge.

Reference will be made toFIGS.5to10to describe the device200in operation or in use.FIG.5illustrates a cross-sectional view of the device200when it is brought into contact with a surface50, andFIG.6is a magnified partial view ofFIG.5. Initially, the first end232of the indenter230contacts the surface50and the external face211of the base210does not contact the surface50. As illustrated, the indenter230is configured such that in response to a first abutment60in which the indenter230abuts a surface50of the material, the indenter230pushed along the axial direction82. When the indenter230contacts the sensor220, the indenter230provides a push force72to the sensor220. In some embodiments, the strain gauge of the sensor220is deformable into a deformed state (as shown inFIG.9) by the indenter230pushing against the strain gauge. The strain gauge in the deformed state is partially displaced out of the transverse plane74by an offset224in the axial direction82. The push force72may be in the axial direction82. Alternatively, the push force72may be substantially parallel to the axial direction82. The sensor220is configured to operably provide a measurement signal in response to receiving the push force72. The indenter body233and the opening212are sized such that the indenter230is freely slidable through the opening212. A clearance62is provided between the indenter230and the respective clamp element242, such that the locking device240is not engaged with the indenter. The indenter230is in an unlocked state230aand is slidable relative to the base210. The cap250may be biased apart from the base213by a spacing21when the indenter230is in the unlocked state230a, such that the cap250is responsive to the pressing force to move relative to the base210opposite the axial direction82.

FIG.7illustrates the device200when the indenter230is retracted (at least partially retracted) into the device200with the first end232indenting the surface50and the external face211of the base210contacting the surface50. The base210is in a second abutment65with the surface50, or more specifically, the external face211of the base210abuts the surface50. The device200is configured such that upon a second abutment of the base210with the surface50, the indenter230is locked and prevented from further displacement relative to the base210. At least one of the clamp elements242are configured to be displaced by the cap250in a clamping direction84, closing the clearance62, such that the clamp elements242releasably lock the indenter230in response to the second abutment65. The clamping direction84may be in a radial direction towards the indenter230, and is non-parallel to the axial direction82.

This automatic locking advantageously makes the device200easy to use and yet robust enough to provide consistent and meaningful measurements. The user may apply the device200to the surface50without a need to carefully regulate the amount of force applied (via the cap250and hence via the device200) to the surface. Referring also toFIG.8which shows a magnified partial view ofFIG.7, when base210is in the second abutment with the surface50, any further pressing of the cap250opposite the axial direction (e.g., when a pressing force is provided on the cap250by a fingertip), the actuating legs252in slidable engagement with the respective sloped surfaces244will squeeze the clamp elements242toward the indenter230until there is a releasable engagement or releasable locking63between the indenter230by the clamp element242of the locking device240. In the locked state230b, there is no clearance62between the indenter and the clamp element242, and the indenter axis is aligned with the axial direction82. The locking device240releasably locks the indenter230in a locked state230b(as shown inFIGS.7to9), in response to a second abutment65where the base210abuts with the surface50. The indenter230in the locked state230bis prevented from further movement relative to the base210in the axial direction82.

FIG.9shows that the second end234of the indenter230pushes against the sensor220(in this example, a strain gauge). The strain gauge in the deformed state is partially displaced out of the transverse plane74by an offset224in the axial direction82. A push force from the indenter230bears on the sensor220to give a measurement signal which corresponds to a quantitative measure of the property of the material. As an example, the measurement signal corresponds to a Young's modulus value of the material. The clamp elements242are forced into a tight grip on the indenter body233, which concurrently and automatically brings the indenter axis86into substantially co-axial alignment with the axial direction82. In some embodiments, the lock device240disposes the indenter axis86parallel to the axial direction82when the indenter230is in the locked state230b. In some embodiments, the strain gauge is deformed by the indenter230in the locked state230bto provide a strain gauge reading corresponding to a Young's modulus value of the material. The deformation of the sensor220and hence the measurement signal provided by the sensor220can be held constant or substantially constant when the indenter230is in the locked state230b. The user need not be very careful to manually check and adjust for alignment as the device200is configured to ensure the alignment and consistent measurements. The self-alignment of the device200is also of practical use in clinical diagnosis where it is often impossible to orientate the patient's body such that the surface to be tested is perfectly horizontal.

FIG.10illustrates an example where the device200is further brought towards the surface50of the material to form a third abutment67, in which the base210depresses or deforms a surface55. This may be the case where the user presses on the device200with any pressing forces (even if the user intends to use only a gentle touch). The actuating legs252are prevented by the clamp elements240from moving further opposite the axial direction82. The sloped surface244of a clamp element240also result in a stronger locking/clamping force between the clamp element240and the indenter230if the user continues to press on the device200. The locking device240locks the indenter230in the locked state230b, and the indenter230does not further deform the strain gauge. Any depression of the device200into the soft material will not change in measurement signal from the strain gauge. The user may consistently obtain useful softness perception by using the device200, without a need to carefully regulate the amount of pressing forces applied and without a need to carefully ensure correct orientation of the device relative to the surface.

An alternative embodiment is shown inFIGS.11and12. The sensor220includes a pressure sensor222resiliently coupled to an indenter230. For example, the pressure sensor222may be coupled between a rigid plate224and a resilient member226. The rigid plate224may be fixedly coupled to the base210. The resilient member226may be configured to resiliently deform along the axial direction82. When the indenter230moves in the axial direction82from an unlocked state230a(as shown inFIG.11) to a locked state230bas shown inFIG.12), the resilient member226is deformed and a push force from the indenter230bears on the pressure sensor222to give a measurement signal which corresponds to a quantitative measure of the property of the material. As an example, the measurement signal corresponds to a Young's modulus value of the material.

In other embodiments as illustrated inFIG.13, one or both of the actuating legs252may define slopped surface258slidably engageable with a corner246of respective clamp elements242. Similarly, a movement of the cap250opposing the axial direction82relative to the base210is translated to a movement to each of the clamp element242in the clamping direction84to releasably lock the indenter230.

The device200is useful in many applications including robotics, prosthetics, and clinical diagnosis.FIG.14(not drawn to scale) shows an example of how the device200may be positioned in relation to a fingertip21of a user, an artificial finger, or an end-effector of a robot. The device200may be releasably attachable or fixed to the fingertip21via the cap250. In this example, the fingertip is positioned at a top surface259of the tab254. The cap250may be configured with a curved top surface259in compliance with a curvature of the fingertip. In another example, the cap250may be coupled to an attachment400, such as a finger glove or a prosthetic. In the course of the user/end-effector performing various activities, the device200may serve as a haptic sensor, generating electrical signals in which each single electrical signal (measurement signal) can be transformed or correlated to a haptic perception of softness. The device200can be used to heighten or provide touch sensory perception to the user/robot.

The device200is advantageously configured such that a humanoid softness perception is achievable without force or movement feedback. The device200is configured to enable in-sensor signal transformation, such that the Young's modulus of a material is univariate with and can be determined from a measurement signal from the sensor220. The device200is also configured such that the measurement signals obtained are independent of the forces pressing on the surface/the device200. This is especially relevant in light of the results of a survey summarized by the histogram plot ofFIG.15. The survey was conducted in which gentle touch forces applied by 20 persons were recorded. Each survey participant pressed on a force sensor 10 times with an intention to apply a gentle touch each time, but otherwise without intentional control of the amount of strength of the force used. The histogram ofFIG.15shows the wide range of force values collected in the survey. It is difficult for the same person to deliver a consistent palpation, and it is even more difficult for different persons to deliver similar amounts of forces during palpation. It is therefore an advantage that the device200can be used without regard to the amount of force or the direction of force applied by a user (or a robot) to the cap250of the device200. The device200can be used to provide a way for advanced clinical skills like palpation to be delivered more consistently as well as in other applications.

One example of a method800of obtaining Young's modulus of a material using based on a measurement signal of the sensor220from the device200will be described. The method assumes a rigid indenter230and a soft material such that Ei>>Es, where Eiis the Young's modulus of the indenter (more specifically, of the first end232of the indenter230) and Esis the Young's modulus of the material50under test.

The Hertzian contact model provides a way to calculate the Young's modulus of a material, assuming that a uniform distribution of pressure between the rigid and spherical indenter, and assuming elastic deformation from an initially flat surface of the material. The Young's modulus of the material may be expressed as shown below:

where Esand vsare respectively the Young's modulus and the Poisson's ratio of the material (as an example, vsis a constant and approximately 0.5 for incompressible materials such as PDMS and human tissue), Fi-sis the contact force between the indenter and the material, riis the radius of the first end of the indenter, and hsis the material deformation (FIG.9).

Conventionally, the calculation of the Young's modulus requires two values Fi-sand hsto be known. Conventionally, the laboratory setup for measuring the contact force Fi-sand material deformation hsis bulky and requires a specially cut out sample of the material. In practice, such laboratory setups are not practical for prosthetics or clinical applications.

The device200of the present disclosure is configured to transform the two variables contact force Fi-sand material deformation hsinto one new variable. The device200is configured such that the single new variable is measurable by the sensor220, doing away with the need to measure the contact force Fi-sand the material deformation hs.

Before the device200is brought into contact with a surface of a material, the first end232of the indenter230is configured to extend beyond the base (i.e., protrude from the base) by a tip length represented by Lp(FIG.3B). When the device200is pressed onto the surface, the first end232of the indenter is pushed in the axial direction by a tip displacement z, causing the second end234of the indenter to activate the sensor220. The sensor220registers a change or produces a measurement signal in response to being pushed in the axial direction by the indenter230. In the example where the sensor220is a stretchable strain sensor, the strain sensor undergoes a change in resistance. Both the tip displacement z and the contact force Fi-smay be derived from the strain CI of the strain sensor (FIG.9). At a time when the external face211just touches the surface, the material deformation hsis equal to the tip length (the length of the indenter230outside the base210, or the length of the indenter230extending beyond the external surface211). Therefore, at this instance, both the contact force Fi-sand the material deformation hsmay be expressed as follows:

where t is the thickness of the strain sensor, w is the width of the strain sensor, and Egis the Young's modulus of the strain sensor. L is the transverse distance between the indenter230and the base210. Substituting equation (2) and equation (3) into equation (1), the Young's modulus of a material may be expressed in equation (4) below as:

where εtis determined by the performance of the strain sensor,

With this configuration, the Young's modulus of the material becomes univariate with the resistance of the strain sensor:

To give a sense of the relative size of the values, in some embodiments where the device is used for soft materials, non-limiting exemplary values for Lpmay be in the range of 0.7 mm (millimeters) to 1.1 mm and the transverse distance L may be around 1 mm. In some examples, the radius riof the first end of the indenter may be about 2.5 mm. In some examples, a thickness t of the strain gauge may be about 350 μm (micrometers), a width w of the strain gauge may be about 2 mm, and a Young's modulus of strain sensor is about 818 kPa. The device200may be used on food items, e.g., to test for the ripeness of fruits, and in some measurements taken, the material deformation hsexhibited by the food item is in a region of about 1 mm.

The device200is configured such that it will automatically provide a measurement signal corresponding to the time instant when the external face211of the base210just begins to touch the surface50. Thereafter, even if the user should continue to press the device200against the surface, the device200will not provide a different measurement signal. This was experimentally verified using a prototype of the device200.FIG.16illustrates a plot of a resistance of sensor220in relation to pressing forces on the device200. Plot92corresponds to resistance values read from a strain gauge that was not configured to provide force-independent readings. To apply the Hertzian contact model, it would be desirable to acquire the strain gauge reading at the inflexion point P2. However, using a conventional strain gauge, it is not possible to acquire the reading at P2without plotting out the changes in resistance over a range of forces. As the pressing forces on the strain gauge increases, the resistance values read from the strain gauge increases. If the strain gauge reading is obtained when the pressing force is too large (e.g., at point P3′), the readings obtained will be inaccurate. In practice, as shown inFIG.15, it is difficult to deliver just the right amount of “gentle touch” forces.

Plot90ofFIG.16corresponds to the measurement signals obtained from the device200which includes a locking device240. It can be seen that for the device200of the present disclosure, constant measurement signal values are output by the device200from the point P2onwards. Point P2corresponds to the instance when the external face211of the base210of the device200contacts the material. In other words, the device200is configured such that the useful reading at P2is automatically obtainable. Even if the “gentle touch” forces applied on the object/subject via the device200is too large, the device200is configured to output a useful measurement signal corresponding to the point P2. The device200is therefore described as being configured to be force-independent.

FIGS.17A to17Fare plots showing the performance of the device of the present disclosure.FIG.17Ashows that the sensor220of the device200shows good linearity (R2=0.999) and a high sensitivity (gauge factor, GF=155) over a large rage of strain (0˜50%). In this example, the sensor is a carbon nanotube-based strain sensor, R0is the initial resistance, and ΔR is the change in resistance from the initial resistance.FIG.17Bshows that the strain sensor is coupled to rest of the device200such that it is sensitive to stretching and less sensitive (or not sensitive) to bending forces exerted thereon.FIG.17Cshows the strain readings obtained from a device200of the present disclosure when used in relation to different materials.FIG.17Cshows results that experimentally verify the force-independent nature of the measurement signals obtained from the device200. In contrast,FIG.17Dshows the strain readings where there is no force-independent feature, for different materials in cases where the reading obtained were not independent of the forces applied. The different materials tested ranged from and included the softer Ecoflex at 37 kPa and 89 kPa respectively to the relatively harder PDMS at 170 kPa and 1 MPa respectively.FIG.17Eshows that the measurement errors1751for the device200are significantly smaller (and practically negligible) compared to those of a strain gauge setup that is not force-independent1752.FIG.17Ealso shows that the device200outperforms other setups especially for softer materials.FIG.17Fcompares the measurement signals obtained from the device200when a gentle touch1761is applied to different materials via the device200, and when a heavy touch1762is applied to the same. A touch was considered gentle if it does not deform a soft sponge, and a touch was considered heavy if it clearly deforms the sponge.FIG.17Fshows that consistent measurement signals are obtainable independent of the touch being gentle or heavy. It is thus demonstrated that the device200can be used to provide a single quantitative measure that is consistent to the multi-parametric result from a conventional TA. It is also demonstrated that the device200can be used on a wide range of materials, for example, including but not limited to materials with Young's modulus ranging from 37 kPa to 3.3 MPa. Advantageously, the device200performs well on materials with Young's modulus of around 1 MPa and below. The measurement range and accuracy can be tuned by changing the fabrication parameters such as the sizes of each elements and the Young's modulus of the sensor.

FIGS.18A to18Fare plots comparing theoretical and experimental Young's modulus obtained using the device200of the present disclosure.FIGS.18A to18Cshow theoretical calculations of strain sensor response of the device200at different tip lengths (Lp) and different indenter-to-base transverse distances (L). The plots suggest that the device200is particularly suitable for use with soft materials, e.g., materials with relatively lower Young's modulus). The sensitivity of the device200may be tuned by providing a longer Lpor a shorter L.FIG.18Dshows that the measurement signals of the device200correspond to resistance values that are consistent with Young's modulus measured using a conventional apparatus.FIG.18Eshow that experimental results (dots) and theoretical analysis (curve) of the relationship between the measurement signals and Young's modulus agree well.FIG.18Fshow a good correlation between the Young's moduli measured by the device200and those measured using the conventional apparatus.

FIG.19is a non-limiting example of a prototype according to an embodiment of the present disclosure. This prototype was used in experiments to test the performance of the device200and system100in providing quantifiable palpation. The system100includes the device200coupled to an attachment400(such as a prosthetic finger glove that can be worn on a user's fingertip21). The system100includes a processor310, a Bluetooth transmitter320, and a power bank330. The system100was configured such that the haptic device300was configured to communicate wirelessly with a computing device (not shown) having a user interface. Other computing devices may be used, e.g., laptops, tablets, etc. In the experiments, the computing device used was a mobile phone. The user interface500is configured to display the Young's modulus value in real-time to facilitate clinical diagnosis. Also illustrated is the user interface showing a Young's modulus determined for a healthy instep512and for a swollen instep514.

The system100was employed to palpate and assess the status of swollen tissues in patients suffering from joint damage.FIG.20shows the Young's modulus measurements of both the swollen and healthy instep of a patient obtained from the system100. The system100shows that the swollen instep subsided after four days and surgery is recommended on the fifth day, this matched a medical professional's assessment. The error bars inFIG.20are standard deviations calculated from at least five measurements. Besides surgical recommendations, the quantitative data obtained using the system100may also be used for any study that requires monitoring changes in softness. For example, to assess the effects of drugs on swelling, or the progression of tumours.

FIG.21illustrates another embodiment wherein the device200is employed as a convenient artificial haptic for distinguishing softness of a variety of soft materials, such as jelly, glue pudding, marshmallow, cake, ham sausage, etc. Young's moduli (bar inFIG.21) measured by the device200corresponds to the trend of peak forces (dots inFIG.21) measured by a commercial texture analyzer (TA) for measuring softness of various foods.FIG.22shows a good correlation between Young's moduli obtained using the device and peak forces measured using a TA, which demonstrates accuracy of the device200. Dots are experimental data fromFIG.21and the dashed line represents theoretical results calculated from equation (1) of the Hertzian contact model (ri=2.5 mm, hs=1 mm, =0˜700 mN). Error bars inFIGS.21and22are standard deviation calculated from nine measurements.

FIG.23shows a method800of measuring a degree of softness of a material. The method800includes bringing an indenter of a device into contact with a surface of the material810, with the indenter protruding from a contact surface of the base, and the indenter being configured to retract inwardly relative to the base such that the indenter provides a push force to the sensor in the axial direction. The method800includes obtaining a measurement signal from the sensor corresponding to a relative displacement between the indenter and the base820, in which the relative displacement is limited by the contact surface being brought into contact with the surface of the material. The method800may further include, before obtaining the measurement signal, locking the indenter relative to the base in response to the contact surface contacting the surface of the material830. In some embodiments, the measurement signal corresponds to a quantitative measure of the degree of softness of the material. In some embodiments, the measurement signal corresponds to the Young's modulus value of the material.

In various embodiments described above, a device for measuring a property of a material is disclosed. The property of the material may be a measure of a softness of the material. The softness of the material may be quantitatively determined based on a Young's modulus value of the material. In some embodiments, the device is configured to operably provide a measurement signal concurrent with a locked state. The measurement signal may correspond to a quantitative measure of the property of the material, for example, the measurement signal corresponds to a Young's modulus value of the material. In some embodiments, the measurement signal is directly correlatable to the Young's modulus value of the material. In other embodiments, measurement signal corresponds to a quantitative measure of a haptic sensation of the material. The quantitative measure may be representative of different haptic sensations such as “soft”, “stiff”, “swollen”, etc. The device may be employed in various applications such as for medical diagnosis, for virtual and augmented reality applications, or even for daily tasks such as determining softness of food.

To aid understanding and not to be limiting, one exemplary method of fabricating a device200will be described with the aid ofFIG.4andFIGS.24A to24D.

In this non-limiting example, the sensor220includes a strain sensor or a strain gauge. To form a linear and highly sensitive stretchable strain sensor, a silicon wafer is first treated with oxygen plasma902(150 Watts, 60 seconds, 450 mTorr) and then treated by the vapor of (tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-trichlorosilane on a hot plate at 180° C. for 2 h (FIG.24A). PDMS 904 (available as Sylgard 184 from Dow Corning) is prepared by mixing a base with a crosslinker (in a mass ratio of 10:1), degassed (centrifuge at 5000 revolutions per minute for 5 minutes), and spin coated (500 revolutions per minute for 45 seconds) on the silicon wafer, followed by baking at 60° C. for 4 hours. After curing, the PDMS is peeled off and then covered by a metal mask906with a predetermined pattern908, followed by hydrophilic treatment with oxygen plasmonic (150 Watts, 90 seconds, 450 mTorr). The exposed area thus becomes hydrophilic. Next, a carbon nanotube (CNT) solution912(P3-SWNT, Carbon solution) is dropped onto the hydrophilic area918of the PDMS (FIG.24B). When the CNT solution has evaporated for several hours at room temperature, a coffee ring (CNT ring930) is formed along the edge of the hydrophilic area, with the same pattern of the metal mask. The PDMS is cut along a cutting profile922as shown by the dashed lines inFIG.24C. The PDMS is then covered by another PDMS strip (a pre-cured PDMS with the same thickness)940. The upper PDMS strip has two holes942at its ends which are used to attach Gallium-Indium eutectic (EGaIn) as electrodes of the sensor. After a further bake at 60° C. for 4 hours, the resulting product is cut into a strip with a width of 2 mm, a thickness of about 350 μm, and a CNT straight line950can be found located at the center of the sandwich structure.

It will be understood that while the method of making an intrinsically large-deformation strain sensor has been described as a method of providing a sensor220, other types of sensors may be selected for use as part of the device200. While strain sensors and pressure sensors are examples of sensors that may be selected for use as part of the device200, the device200advantageously is operable with a wide range of sensors to suit different applications. For example, the sensor220may include a strain sensor (also referred to as a large-deformation strain sensor or a stretchable strain sensor) as described above, i.e., one that is intrinsically characterized by a relatively large deformation upon a relatively small push force or a relatively small displacement. Alternatively, the sensor220may include a strain sensor selected from conventional strain gauges. In other embodiments, the sensor220may include a strain sensor resiliently coupled to an indenter with a resilient member, such as a leaf spring or a cantilever spring, coupled between the indenter and the strain sensor. When the indenter is displaced towards the strain sensor, the resilient member is deformed and a push force from the indenter bears on the strain gauge to give a measurement signal. Conventional strain gauges may be configured such that they can only deform slightly or deform less than a large-deformation strain sensor, and may be selected for applications where availability and cost efficiencies are more important considerations than having a more sensitive sensor. Alternatively, the sensor220may include a pressure sensor, i.e., a sensor configured to provide a measurement signal in response to receiving a pressure (with or without a resulting mechanical deformation). In some examples, the sensor220includes a pressure sensor that is intrinsically characterized by a relatively large deformation upon receiving a relatively small pressure (also referred to as a large-deformation pressure sensor or a stretchable pressure sensor). Alternatively, the sensor220may include a conventional pressure sensor with a deformable structure that undergoes a relatively small deformation (such as the example ofFIGS.11and12). The pressure sensor may be one deformable into a deformed state by the indenter pushing against the pressure sensor to operably provide a measurement signal in response to receiving the push force. In some alternative embodiments, the pressure sensor may be a thin film pressure sensor or a resistive ink pressure sensor. The sensor220may be configured to provide measurement signals based on resistance values, capacitance, voltages, etc.

Examples of different embodiments of the device200include but are not limited to those schematically illustrated inFIGS.25A to25C.FIG.25Ais a partial schematic diagram showing the tab254with an actuating leg252in interface with a sloped surface of a clamp element242. The clamp element242is coupled to the base210via a resilient coupling243. The resilient coupling243may include but is not limited to a leaf spring. The resilient coupling243may be oriented differently from the schematic representation shown inFIG.25A. The sensor220is in a fixed coupling227with the base210, with part of the sensor220being deformable by the indenter230from an undeformed state (in which the sensor220is substantially disposed in the transverse plane74) to a deformed state by an offset224. Movement of the indenter230in the axial direction82is limited. The actuating leg252causes the corresponding at least one clamp element242to move in the clamping direction84and releasably lock the indenter230such that the locked state230bcorresponds to a deformed state.FIG.25Bschematically illustrates part of another embodiment of the device200with some components omitted for the sake of clarity. The sensor220includes a beam225in a fixed coupling227with the base210and a sensing element223(such as but not limited to a pressure sensor222) coupled to the beam225. The sensing element223may be coupled to the indenter230via a resilient member226.FIG.25Cis a partial schematic diagram of yet another embodiment of the device200. The sensor220includes a beam225in a fixed coupling227with the base210and a sensing element223(such as but not limited to a strain gauge) coupled to the beam225. The beam225is cantilevered relative to the base210. A free end of the beam225is coupled to the indenter230via the resilient member226.

To fabricate the rest of the device200, methods including but not limited to additive manufacturing or 3D printing may be used. For example, for some of the experiments conducted, parts of the device200were printed using a commercial 3D printer (Eden 260V available from Stratasys). The materials used include RGD525and VeroClear, and the supporting material used is FullCure705. The indenter230was printed with RGD525so as to provide a rounded or substantially hemispherical tip (first end232) with a Young's modulus (E) in a region of 2˜3 GPa. That is, so that the indenter230can be considered as a rigid indenter compared with the targeted material to be measured (Young's modules (E)<4 MPa).

The method of assembling the device200may depend on the manner in which the parts are 3D printed. The method may include, for example but is not limited to, inserting the indenter230into a base210with the tip (first end232) extending beyond the base210. was inserted. The base210, the indenter230, and the sensor220were then treated by oxygen plasma (150 Watts, 90 seconds, 450 mTorr) to increase the surface energy. Next, the sensor220(such as the linear stretchable strain sensor described above) was coupled to the respective supports214of the base210, e.g., by an adhesive. The second end234of the indenter230may be coupled to a deformable/displaceable/sensing part of the sensor220, e.g., by an adhesive. The adhesive used may be an epoxy resin adhesive, and the parts may be kept at room temperature for 24 hours for curing. Finally, the cap250was assembled with the base210. The cap250and the base210may be prevented from separating from one another by two pairs of pothooks or flexible fasteners. A microcontroller unit (e.g., an Arduino Nano module such as ATmega328P) may be added to read the measurement signals and a Bluetooth transmitter module (e.g., HC-06 Bluetooth module) may be added to communicate the measurement signals.

Alternatively described, making reference toFIG.4, a method of fabricating a device200according to embodiments of the present disclosure may include: coupling a strain gauge/sensor220to a base210such that the strain gauge in an undeformed state has a first planar surface disposed in a transverse plane74; assembling an indenter230with the base210such that a first end232of the indenter protrudes from a contact surface/contact end215of the base210and a second end234of the indenter is proximal the first planar surface of the strain gauge/sensor220, the indenter230being configured for relative displacement with the base along a displacement axis/axial direction82normal to the transverse plane74such that the second end234deforms the strain gauge/sensor220out of the transverse plane by an offset224along the displacement axis/axial direction82; and disposing a pair of clamps/one or more clamp element242about the indenter230, the pair of clamps/one or more clamp element242being configured to be actuated by a cap250in slidable engagement with the base210, such that the offset224is limited. Making reference toFIGS.24A-24D, the method as described above, wherein the sensor220includes a strain gauge, the strain gauge being made by a process comprising: providing a metal mask906on a first polymer film904(991); treating an exposed portion908of the polymer film with oxygen plasma902to form a hydrophilic area918(991); disposing an aqueous mixture of carbon nanotube (CNT)912on the hydrophilic area918to form a CNT coffee ring930(992/993); and sealing the CNT coffee ring930with a second polymer film940to form a layered structure960(994).

The device200is useful in a wide range of applications. For example, the device200may be part of a cosmetic tool or beauty aid. The device200may be integrated in mobile cosmetic devices to monitor or test skin elasticity. Since the device200can provide meaningful measurement signals even in situations where the user is not a trained professional, the device200can be configured as a consumer product suitable for daily use by the average consumer. The device200may also be provided in the form of medical instruments for use in clinical diagnosis or in the form of surgical instruments. The device200may also be provided in the form of a mechanical characterization instrument that is more portable, cost efficient, and easier to use, compared to conventional material characterization instruments found in the typical laboratory. From the above description, it can be understood that the term “measuring” a property of a material can be understood broadly to include providing a quantitative measurement, an indication of whether the property is above or below a threshold, an indication of whether the property is within a range, etc. The device200can be configured to measure materials with Young's modulus larger than 1 MPa.

All examples described herein, whether of apparatus, methods, materials, or products, are presented for the purpose of illustration and to aid understanding, and are not intended to be limiting or exhaustive. Various changes and modifications may be made by one of ordinary skill in the art without departing from the scope of the invention as claimed.