Compression modulus estimation system, method, and program

Abstract

The purpose is to estimate the compressive modulus of flexible materials such as human skin. [Solution] A compression modulus estimation system for estimating the compressive modulus of a sample using a compression force measuring device having a support stand for supporting the sample, a contactor whose tip shape is at least spherical and which contacts the sample, an actuator for pressing the contactor into the sample, a speed control unit for controlling the speed at which the sample is compressed using the contactor, a force sensor for measuring the compressive force of the sample, and a displacement sensor for measuring the compressive displacement of the sample, comprises a speed setting unit for setting the speed, a definition unit for defining a function of the compressive modulus with unknown coefficients, an input unit for inputting the radius of the sphere and the thickness of the sample, a timing setting unit for setting the timing for the compression force measuring device to measure the compressive force and compressive displacement for each unknown coefficient, a storage unit for storing the measured compressive force and compressive displacement for each unknown coefficient, and a calculation unit for calculating unknown coefficients using the data stored in the storage unit.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a technique for estimating the compressive modulus of elasticity of flexible materials. [Background Art]

[0002] With the progress of aging and labor shortage, development is ongoing for service robots used in places where humans coexist, such as homes, stores, and factories, or collaborative robots that work in cooperation with humans. Along with this, techniques for achieving contact safety between humans and robots are required. In particular, techniques for measuring the mechanical properties (such as modulus of elasticity) of flexible materials like human skin form the foundation of contact safety.

[0003] Patent Document 1 discloses that an apparatus for measuring the elasticity of soft materials present at a high depth calculates a Young's modulus coefficient from the load value and displacement value at the time when a contactor reaches the target after setting a predetermined maximum load value. [Prior Art Literature] [Patent Literature]

[0004] [Patent Document 1] Japanese Unexamined Patent Publication No. 2011-117920 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] However, although Patent Document 1 can obtain the elasticity of a measurement object under a predetermined load value, it has the problem that it cannot estimate the compressive modulus of elasticity of flexible substances.

[0006] The present invention was completed through intensive research focusing on such problems, and an object of the present invention is to estimate the compressive modulus of elasticity of flexible materials. [Means for Solving the Problem]

[0007] To solve the above problems, the present invention provides a compressive modulus estimation system for estimating the compressive modulus of a sample, which uses a compressive force measuring device having a support base for supporting a sample to be estimated, a contactor whose tip shape is at least spherical and which contacts the sample, an actuator for pressing the contactor into the sample, a speed control unit for controlling the speed at which the sample is compressed using the contactor, a force sensor for measuring the compressive force of the sample, and a displacement sensor for measuring the compressive displacement of the sample, the system comprising: a speed setting unit for setting the speed; a definition unit for defining a function of the compressive modulus with unknown coefficients; an input unit for inputting the radius of the sphere and the thickness of the sample; a timing setting unit for setting the timing for the compressive force measuring device to measure the compressive force and the compressive displacement for the number of unknown coefficients; a storage unit for storing the measured compressive force and compressive displacement for the number of unknown coefficients; and a calculation unit for calculating the unknown coefficients using the data stored in the storage unit.

[0008] Another aspect of the present invention is a method for estimating the compressive modulus of a sample, using a compression force measuring device having a support stand for supporting a sample to be estimated, a contactor whose tip has a shape of at least a spherical surface that contacts the sample, an actuator for pressing the contactor into the sample, a speed control unit for controlling the speed at which the sample is compressed using the contactor, a force sensor for measuring the compressive force of the sample, and a displacement sensor for measuring the compressive displacement of the sample, the method comprising: a speed setting step for setting the speed; a definition step for defining a function of the compressive modulus with unknown coefficients; an input step for inputting the radius of the sphere and the thickness of the sample; a timing setting step for setting the timing for the compression force measuring device to measure the compressive force and the compressive displacement for the number of unknown coefficients; a storage step for storing the measured compressive force and compressive displacement for the number of unknown coefficients; and a calculation step for calculating the unknown coefficients using the data stored in the storage unit.

[0009] Another aspect of the present invention is a computer-executable program for estimating the compressive modulus of a sample, which uses a compression force measuring device having a support stand for supporting a sample to be estimated, a contactor whose tip has a shape of at least a spherical surface that contacts the sample, an actuator for pressing the contactor into the sample, a speed control unit for controlling the speed at which the sample is compressed using the contactor, a force sensor for measuring the compressive force of the sample, and a displacement sensor for measuring the compressive displacement of the sample, the program comprising: a speed setting step for setting the speed; a definition step for defining a function of the compressive modulus with unknown coefficients; an input step for inputting the radius of the sphere and the thickness of the sample; a timing setting step for setting the timing at which the compression force measuring device measures the compressive force and the compressive displacement for the number of unknown coefficients; a storage step for storing the measured compressive force and compressive displacement for the number of unknown coefficients; and a calculation step for calculating the unknown coefficients using the data stored in the storage unit. [Effects of the Invention]

[0010] According to the present invention, the compressive modulus of a flexible material can be estimated. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of the compression modulus estimation system according to an embodiment of the present invention. [Figure 2] This diagram illustrates the positional relationship of the spherical tip of the contactor according to this embodiment before it sinks into the sample. [Figure 3] This diagram illustrates the positional relationship of the spherical tip of the contactor according to this embodiment after it has sunk into the sample. [Figure 4] This is a schematic flowchart for estimating the compressive modulus according to this embodiment. [Figure 5] This is a detailed flowchart for estimating the compressive modulus according to this embodiment. [Figure 6] This table shows the compressive force and displacement according to this embodiment. [Figure 7] This table shows the compressive modulus coefficients according to this embodiment. [Figure 8] This figure illustrates the estimation results according to this embodiment. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described with reference to the drawings. This description assumes that the compressive modulus estimation system according to this embodiment consists of a compressive force measuring device composed of hardware and a compressive modulus estimation device composed of software.

[0013] (Compression modulus estimation system according to this embodiment) Figure 1 is a schematic diagram of a compressive modulus estimation system according to an embodiment of the present invention. The compressive modulus estimation system consists of a compressive force measuring device 100 and a compressive modulus estimation device 200 for estimating the compressive modulus of a sample 110. The sample 110 is assumed to be a flexible material such as human skin. Therefore, a system is needed that can estimate the compressive modulus of a flexible material in a minimally invasive manner without taking a test piece from a human.

[0014] The compression force measuring device 100 is a device for measuring the compressive force applied to a flat plate-shaped sample 110. The compression force measuring device 100 comprises a support base 120 for supporting the sample 110, a contact element 130 whose tip that contacts the sample has a shape of at least a spherical surface, an actuator 140 for pushing the contact element 130 into the sample 110, a speed control unit 150 for controlling the speed at which the sample 110 is compressed using the contact element 130, a force sensor 160 for measuring the compressive force of the sample 110, and a displacement sensor 170 for measuring the compressive displacement of the sample 110. The sample 110, support base 120, and actuator 140 are easily identifiable from their appearance and are therefore represented by solid lines, while the speed control unit 150, force sensor 160, and displacement sensor 170 are not easily identifiable from their appearance and are therefore represented by dotted lines. As shown, the tip of the contact element 130 is in contact with the upper surface of the flat plate-shaped sample 110 and has a shape of at least a spherical surface.

[0015] The actuator 140 is a linear actuator. The dotted arrow above the actuator 140 indicates the direction in which the actuator operates (vertically downward in this case). The actuator 140 enables pressing the spherical tip of the contact 130 into the sample 110.

[0016] The speed control unit 150 has a mechanism for controlling the operating speed of the actuator 140. Since the sample 110 is assumed to be human subcutaneous tissue, the sample 110 has viscous properties in addition to elasticity. In order to cancel the effect of viscosity, in the present embodiment, the speed control unit 150 moves the actuator 140 at an ultra-low speed.

[0017] The force sensor 160 is used to measure the compressive force applied to the sample 110, and may be provided on the actuator 140 side (that is, the upper side) or on the support base 120 side (that is, the lower side). Here, it is illustrated as being provided on the upper side, which is effective when measuring with a force smaller than the weight of the sample 110. In addition, when provided on the lower side, there is an advantage that force data is easy to measure.

[0018] The displacement sensor 170 measures the distance that the contact 130 moves downward in order to measure the compressive displacement of the sample 110.

[0019] The compressive elastic modulus estimating apparatus 200 includes a speed setting unit 210 that sets the speed of the actuator 140, a function defining unit 220 that defines a function of the compressive elastic modulus of the sample 110 with the coefficients of the function being unknown, an input unit 230 that inputs the radius of the spherical tip of the contact 130 and the thickness of the sample 110, a timing setting unit 240 that sets timings for the compressive force measuring apparatus 100 to measure the compressive force and compressive displacement by the number of unknown coefficients, a storage unit 250 that stores the compressive force and compressive displacement measured by the number of unknown coefficients, and a calculating unit 260 that calculates the unknown coefficients using the data stored in the storage unit 250. Each of the functional blocks 210 to 260 of the compressive elastic modulus estimating apparatus 200 is configured by software, and cannot be recognized from the external appearance, so they are represented by dotted lines.

[0020] Before describing each functional block 210 to 260, the positional relationship of the tip spherical surface of the contactor 130 before and after it sinks into the sample 110 will be explained using Figures 2 and 3. Figure 2 is a diagram illustrating the positional relationship of the tip spherical surface of the contactor 130 before it sinks into the sample 110. Figure 3 is a diagram illustrating the positional relationship of the tip spherical surface of the contactor 130 after it sinks into the sample 110.

[0021] In Figure 2, the z-axis represents the direction in which the contactor 130 is pressed (i.e., the longitudinal central axis of the contactor), the x-axis is perpendicular to the z-axis, and the xz coordinate plane represents the longitudinal cross-section passing through the center of the contactor 130. Also, T represents the thickness of the sample 110, and r represents the spherical radius of the contactor 130. Point O represents the center of the tip of the spherical surface of the contactor 130 as it sinks into the sample 110. Here, the coordinates of the state in which the contactor 130 is in contact with the sample 110 (just before sinking) can be represented as (x,z)=(0,0).

[0022] In Figure 3, δ represents the displacement (or compressive displacement) of the contact element 130, and F(δ) represents the contact force on the entire contact sphere (the arc at z=0, and the arc from intersection b to intersection b', as Figure 3 is a 2D diagram). The contact force on the entire contact sphere from the sample 110 is the same in magnitude as the compressive force exerted by the contact element 130 on the sample, although its direction is different. Here, when the contact element 130 is displaced by δ, the intersection of the circles obtained by cutting the contact element 130 in the plane at z=0 is b, and the distance on the x-axis from x=0 to intersection b is a. As will be described later, a is the half-width of the pressure distribution. That is, the contact force F(δ) is the value obtained by line integral from the maximum pressure at z=0 to the minimum pressure at intersection b (or b'). Furthermore, the tip of the contact element 130 only needs to have a circular cross-section when cut at the point where it sinks most deeply into the sample 110 (i.e., the maximum compressive displacement). Therefore, the lower limit of the range in which the shape of the tip of the contact element 130 is at least spherical is the maximum compressive displacement. The contact element 130 may be a perfect sphere as shown in Figure 1, or it may be approximately two-thirds spherical as shown in Figures 2 and 3.

[0023] Figure 4 is a schematic flowchart for estimating the compressive modulus according to this embodiment. The schematic flowchart will be explained while describing its relationship with each functional block shown in Figure 1. In S100, the function definition unit 220 defines the function for the compressive modulus of the sample 110, with the coefficients of the function unknown. In S200, the input unit 230 receives input for the spherical radius r of the contactor 130 and the thickness T of the sample 110.

[0024] In S300, the compression force and compression displacement are measured using the speed setting unit 210, the timing setting unit 240, and the storage unit 250. The speed setting unit 210 transmits a setting signal to the speed control unit 150 to control the speed of the actuator 140 to an extremely low speed. The timing setting unit 240 sets the timing for measuring the compression displacement for the number of unknown coefficients and transmits these timings to the force sensor 160 and the displacement sensor 170. The storage unit 250 stores the data for the number of unknown coefficients measured by the force sensor 160 and the displacement sensor 170, respectively.

[0025] In S400, the calculation unit 260 uses the data stored in the storage unit 250 to construct a system of simultaneous equations for the function of the compressive modulus of elasticity, where the coefficient is unknown. In S500, the calculation unit 260 solves the constructed system of simultaneous equations to calculate the coefficient of the compressive modulus of elasticity.

[0026] Figure 5 is a detailed flowchart for estimating the compressive modulus according to this embodiment. The detailed flowchart will be explained while describing its relationship to the schematic flowchart shown in Figure 4. Figure 5 begins with the step (S200) in which the sample thickness T and sphere radius r are input. The relationship with the definition step S100 and the measurement step S300 will be described later.

[0027] In construction step S400, width calculation step S400-1 takes the spherical radius r as input and calculates the pressure distribution half-width a from equation (1). Shape function calculation step S400-2 takes the spherical radius r as input and calculates the shape function f(x) of the tip sphere of the contactor 130 at z=0 (i.e., the contact surface with the sample 110) from equation (2). Compression strain calculation step S400-3 takes the sample thickness T and spherical radius r as input and calculates the strain ε(x) at position x from equation (3).

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[0028] In step S400-4, the compression modulus calculation step, the strain ε(x) is input to the compression modulus function E(ε(x)) defined in S100. E(ε(x)) is expressed by equation (4). In this embodiment, the compression modulus function E(ε(x)) was defined in S100 as a quadratic function of strain ε(x). The coefficient of the quadratic term is defined as a, the coefficient of the linear term as b, and the coefficient of the constant term as c. Note that the coefficient a of the quadratic term is different from the pressure distribution half-width a mentioned above.

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[0029] In the compressive stress calculation step S400-5, the pressure p(ε(x)) at position x can be expressed as equation (5) as the product of the compressive modulus E(ε(x)) and the strain ε(x). The pressure p(ε(x)) can be expressed as a quadratic function that is maximum at x=0 and minimum at x=a (half-width of the pressure distribution).

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[0030] The contact force F(δ) can be obtained by line integrating the pressure p(ε(x)) as shown in equation (6). In the contact force calculation step S400-6, line integration is performed over the integration interval [0, pressure distribution half-width a] in x. This constructs the system of equations in S400. That is, a system of equations for the contact force F(δ) and displacement δ related to the compressive modulus considering nonlinearity can be constructed.

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[0031] The system of equations constructed in S400-6 has three unknowns: a, b, and c. Therefore, in the measurement step of S300, three sets of test data (F, δ) are measured.

[0032] In S500, the solution to the system of equations S400-6 is obtained using the three sets of test data (F1,δ1), (F2,δ2), and (F3,δ3) shown in equation (7). The obtained solution is the compressive modulus coefficients a, b, and c.

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[0033] (Example: Estimation of compressive modulus using artificial skin) As an example, the estimation of the compressive modulus using artificial skin will be explained. A commercially available artificial skin will be used as sample 110. Two types of artificial skin with different hardnesses (softer So and harder Ha) will be prepared, each with a thickness of 10 mm. The material of the contact element 130 will be stainless steel. The material of the contact element 130 should be harder than the material of sample 110. The diameter of the contact element is 20 mm. The radius of the spherical tip of the contact element 130 should be greater than the thickness T and compressive displacement of sample 110. The actuator 140 will compress sample 110 at a low speed of 0.01 mm / s, such that the viscosity of sample 110 can be ignored.

[0034] Figure 6 is a table showing the compressive force and displacement according to this embodiment. It shows the displacement and force obtained by measuring two samples 110 using the compressive force measuring device 100. Since there are three unknowns in the simultaneous equations described above, three pairs of (displacement, force) were measured for materials So and Ha.

[0035] Figure 7 is a table showing the compressive modulus coefficients according to this embodiment. The coefficients of the compressive modulus function were determined for materials So and Ha using the compressive modulus estimation method described above.

[0036] Figure 8 is a diagram illustrating the estimation results according to this embodiment. Figure 8(a) shows the actual measurement results (solid lines) and estimation results (dotted lines) for materials So and Ha, respectively. Figure 8(b) shows the force estimated using the compression modulus function estimated for materials So and Ha, with six displacement values ​​δ set between 1 mm and 6 mm, the pressure distribution half width a of S400-1, and the force F(δ) of S400-6. Here, while actuator 140 is compressing sample 110 at 0.01 mm / s, a data logger (not shown) measures the value of displacement sensor 170 in real time. Sampling during measurement is acquired at 10 kHz, resulting in a large number of samples. Therefore, the data that has been thinned after measurement is used. Please note that in this case, the displacement data δ is not a round value such as 1.000 mm.

[0037] For materials So and Ha in Figure 8(a), the actual measurement results (solid lines) and estimated results (dotted lines) are in good agreement. According to this embodiment, the compressive modulus can be estimated up to a displacement of approximately 6 mm for a flexible material with a thickness of 10 mm, that is, up to approximately 60% of the finite thickness.

[0038] (Effects and Benefits) The compressive modulus estimation system of this embodiment defines the compressive modulus of a flexible material possessing both elastic and viscous properties as a nonlinear function. The compression force measuring device is controlled to press a contactor into the material at an extremely low speed, and the compressive force and displacement are measured. The coefficients of the nonlinear function are calculated from the measurement results. By determining the nonlinear function in this way and modeling the compressive modulus of flexible materials such as human skin with this nonlinear function, the compressive modulus of the flexible material can be estimated. Furthermore, it is possible to understand the compressive characteristics of flexible materials up to high compressibility levels, even with minimal invasiveness.

[0039] (modified version) In S100, the function of compressive modulus E(ε(x)) described above was defined as a quadratic function of strain ε(x). The function of compressive modulus E(ε(x)) may also be a piecewise linear function. That is, the strain ε(x) may be a linear function with a predetermined slope up to a certain point, and thereafter a linear function with a steeper slope, and the function as a whole may be nonlinear.

[0040] In this embodiment, the speed control unit 150 moves the actuator 140 at an extremely low speed (0.01 mm / s), and the contact element 130 compresses the sample 110. However, the contact element 130 may pause after slightly pushing the sample 110. In this way, a predetermined time may elapse until the viscous effect of the sample 110 subsides, and then the compression may be repeated. When measuring the compressive force and compressive displacement, it is also preferable to measure them after a predetermined time has elapsed.

[0041] Although embodiments (including modifications) of the present invention have been described above, two or more of these embodiments may be combined and implemented. Alternatively, one of these embodiments may be partially implemented. Furthermore, two or more of these embodiments may be partially combined and implemented.

[0042] Furthermore, the present invention is not limited in any way to the embodiments described above. Various modifications are also included in this invention, provided they do not depart from the scope of the claims and are easily conceivable by those skilled in the art.

[0043] (Examples of application) Examples of applications of the present invention will now be described. According to the present invention, it becomes possible to mathematically formulate the property that the elastic modulus changes depending on the amount of compression, without creating test specimens. For this reason, it can be applied to the design of flexible materials and flexible covers for protection from contact with collaborative robots and mechanical devices. Furthermore, it becomes possible to consider the elastic modulus and thickness of a cover that satisfies pain tolerance values ​​based on the contact shape and the braking distance of the robot.

[0044] Although the compressive modulus of human soft tissue is unknown, obtaining basic data can be used in material and dummy development, enabling an understanding of human body surface rigidity and the development of highly bio-fidelity artificial skin. Furthermore, it will be possible to develop medical bio-phantoms using gel-like materials, as well as general consumer goods that utilize the elastic modulus of human tissue. [Explanation of Symbols]

[0045] 100 Compression force measuring device 110 samples 120 Support stand 130 Contactor 140 Actuators 150 Speed ​​control unit 160 force sensor 170 Displacement Sensor 200 Compression modulus estimation device 210 Speed ​​setting section 220 Function Definition Section 230 Input section 240 Timing setting section 250 Storage section 260 Calculation Unit

Claims

1. A compression modulus estimation system for estimating the compressive modulus of a sample, comprising: a support base for supporting a sample to be estimated; a contactor having a tip shape of at least spherical that contacts the sample; an actuator for pressing the contactor into the sample; a speed control unit for controlling the speed at which the sample is compressed using the contactor; a force sensor for measuring the compressive force of the sample; and a displacement sensor for measuring the compressive displacement of the sample, wherein the system estimates the compressive modulus of a sample. A speed setting unit for setting the aforementioned speed, A definition unit defines the function of the compressive modulus while the coefficients of the function are unknown, An input unit for inputting the radius of the sphere and the thickness of the sample, The compression force measuring device includes a timing setting unit that sets the timing for measuring the compression force and the compression displacement for the number of unknown coefficients, A storage unit that stores the compressive force and compressive displacement measured for each unknown coefficient, A compression modulus estimation system comprising: a calculation unit that calculates an unknown coefficient using data stored in the memory unit.

2. The compressive modulus estimation system according to claim 1, wherein the material of the contactor is harder than the sample.

3. The compressive modulus estimation system according to claim 1, wherein the radius of the sphere is greater than the thickness of the sample and the compressive displacement.

4. The compressive modulus estimation system according to claim 1, wherein the lower limit of the range in which the shape of the tip of the contactor is at least spherical is the maximum value of the compressive displacement.

5. The compression modulus estimation system according to claim 1, wherein the speed setting unit sets the speed to a low speed such that the viscosity of the sample can be ignored.

6. The compression modulus estimation system according to claim 1, wherein the speed setting unit pauses at the timing set by the timing setting unit, and the compression force measuring device measures the compression force and compression displacement of the sample after a predetermined time has elapsed since the pause.

7. The calculation unit described above, A strain calculation unit calculates compressive strain from the radius of the sphere, the thickness of the sample, and the compressive displacement, A stress calculation unit that calculates compressive stress from the aforementioned compressive strain and the aforementioned function, A width calculation unit calculates the half-width of the pressure distribution from the radius of the sphere and the compression displacement, A compressive force calculation unit calculates the compressive force from the compressive stress and the pressure distribution half width, A construction unit that constructs a system of simultaneous equations for the function in a state where the coefficients are unknown, using the compressive strain, compressive stress, pressure distribution halfwidth, and compressive force, The compression modulus estimation system according to claim 1, further comprising a calculation unit for calculating the solution to the simultaneous equations.

8. A method for estimating the compressive modulus of a sample, comprising a support base for supporting a sample to be estimated, a contactor having a tip shape of at least spherical that contacts the sample, an actuator for pressing the contactor into the sample, a speed control unit for controlling the speed at which the sample is compressed using the contactor, a force sensor for measuring the compressive force of the sample, and a displacement sensor for measuring the compressive displacement of the sample, wherein the compressive modulus of a sample is estimated using a compressive force measuring device, A speed setting step for setting the aforementioned speed, A definition step in which the function of the compressive modulus is defined while the coefficients of the function are unknown, An input step in which the radius of the sphere and the thickness of the sample are input, A timing setting step in which the timing for measuring the compression force and the compression displacement of the compression force measuring device is set for the number of unknown coefficients, A storage step of storing the compressive force and compressive displacement measured for the number of unknown coefficients, A method for estimating the compressive modulus of elasticity, comprising: a calculation step of calculating an unknown coefficient using data stored in the memory unit.

9. A compressive modulus estimation program for estimating the compressive modulus of a sample, using a compressive force measuring device having a support base for supporting the sample to be estimated, a contactor with a tip shape of at least spherical that contacts the sample, an actuator for pressing the contactor into the sample, a speed control unit for controlling the speed at which the sample is compressed using the contactor, a force sensor for measuring the compressive force of the sample, and a displacement sensor for measuring the compressive displacement of the sample, A speed setting step for setting the aforementioned speed, A definition step in which the function of the compressive modulus is defined while the coefficients of the function are unknown, An input step in which the radius of the sphere and the thickness of the sample are input, A timing setting step in which the timing for measuring the compression force and the compression displacement of the compression force measuring device is set for the number of unknown coefficients, A storage step of storing the compressive force and compressive displacement measured for the number of unknown coefficients, A computer-executable program for estimating the compressive modulus of elasticity, comprising: a calculation step of calculating an unknown coefficient using data stored in the memory unit.

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