JP7461638B2 - Tactile evaluation device, tactile evaluation method, and program - Google Patents

Description

The present invention relates to a tactile evaluation device, a tactile evaluation method, and a program.

For various products that come into contact with people, such as writing utensils, balls, and clothing, the tactile sensation (roughness, smoothness, etc.) greatly affects the commercial value, so evaluation of the tactile sensation is considered important in the development of these products.

For example, the device disclosed in Patent Document 1 has been developed as a tactile evaluation device. The evaluation device in Patent Document 1 moves an elastomer formed to cover a three-axis force sensor while in contact with a test object, and evaluates the tactile characteristics of the test object.

JP 2012-520451 A

To perform accurate tactile evaluation, it is necessary to perform an evaluation using minute displacements that take into account the initial slippage between the finger and the subject. Furthermore, the tactile sensation is affected not only by linear sliding motions, but also by curved motions, rotational motions, etc. With the evaluation device of Patent Document 1, which uses a three-axis force sensor, it is difficult to perform accurate tactile evaluation based on these minute displacements, rotational motions, etc.

The present invention has been made in consideration of the above circumstances, and aims to provide a tactile evaluation device, a tactile evaluation method, and a program that can respond to minute movements and rotational movements between a subject and a pseudo-finger and can evaluate tactile sensation with high accuracy.

In order to achieve the above object, a tactile evaluation device according to a first aspect of the present invention comprises:
a force sensor that measures a force and a moment acting on a test object when the test object or the artificial finger is moved in a state where the test object is in contact with a artificial finger that is an elastic body;
and an evaluation unit that evaluates the subject's sense of touch based on a movement amount of a center of pressure calculated using the force and moment measured by the force sensor and the thickness of the subject.

Moreover, the force sensor is a six-axis force sensor.
This may also be the case.

Moreover, the evaluation unit
using a plurality of evaluation results as training data, and using an estimation model generated by machine learning to estimate the tactile sensation from the amount of movement of the center of pressure, the tactile sensation of the subject is estimated.
This may also be the case.

Further, a tactile evaluation method according to a second aspect of the present invention includes:
a measuring step of measuring a force and a moment acting on a test object when the test object or the artificial finger is moved in a state where the test object and the artificial finger are in contact with each other;
The method includes an evaluation step of evaluating tactile characteristics of the subject based on a movement amount of a center of pressure calculated using the force and moment measured in the measurement step and a thickness of the subject.

Moreover, a program according to a third aspect of the present invention comprises:
Computer,
a force sensor control unit that acquires a force and a moment acting on a test object when the test object or the artificial finger, which is an elastic body, is moved in a state where the test object is in contact with the artificial finger;
an evaluation unit that evaluates a tactile characteristic of the subject based on a movement amount of a center of pressure calculated using the force and moment acquired by the force sensor control unit and a thickness of the subject;
Function as.

The tactile evaluation device, tactile evaluation method, and program of the present invention evaluate the tactile characteristics of the subject based on the force and moment acting on the subject measured by a force sensor and the amount of movement of the center of pressure calculated using the thickness of the subject, making it possible to perform a highly accurate tactile evaluation.

1 is a front view showing the appearance of a tactile evaluation device according to an embodiment of the present invention. 1A and 1B are diagrams showing a schematic configuration of a tactile evaluation device according to an embodiment, in which (A) is a front view and (B) is a side view. 1 is a block diagram of a tactile evaluation device according to an embodiment. 1 is a conceptual diagram showing measured forces, moments, and resultant forces related to a test object. FIG. 1 is a flowchart showing a flow of tactile evaluation according to an embodiment. 1A is a conceptual diagram showing a contact surface between a dummy finger and a test subject, and FIG. 1B is a conceptual diagram showing a relationship between a tangential force and a sticking area. 11 is a graph showing an example of the relationship between the amount of movement of the center of pressure and the tangential force. 11 is a graph showing an example of the relationship between the amount of movement of the center of pressure and the tangential force when Young's modulus is changed.

(Configuration of tactile evaluation device)
Hereinafter, a tactile evaluation device 1 according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, FIG. 2(A), and FIG. 2(B), the tactile evaluation device 1 according to this embodiment includes an artificial finger 10, an artificial finger driving unit 11, a force sensor 12, a stage 13, and a control unit 20.

In the diagrams explaining the various parts of the tactile evaluation device 1, an orthogonal coordinate system is set up in which the left-right direction in a front view of the tactile evaluation device 1 shown in FIG. 2(A) is the x-axis direction, the depth direction of the tactile evaluation device 1, i.e., the direction perpendicular to the paper surface of FIG. 2(A), is the y-axis direction, and the up-down direction of the tactile evaluation device 1 is the z-axis direction, and is referred to as appropriate. Note that the right direction in FIG. 2(A) is the +x direction, the depth direction is the +y direction, and the upward direction is the +z direction.

The artificial finger 10 is a semi-spherical elastic member that imitates a human finger. The material of the artificial finger 10 is not particularly limited, but a gel with a hardness close to that of human skin, such as soft urethane resin, can be used.

The pseudo finger driving unit 11 is a slider or the like that moves the pseudo finger 10. The pseudo finger driving unit 11 according to this embodiment includes a linear actuator that operates in the z-axis direction to press the pseudo finger 10 against the surface of the subject S. This allows the pseudo finger driving unit 11 to press the pseudo finger 10 in a direction perpendicular to the subject S that is placed on the x-y plane (hereinafter also referred to as the normal direction).

The pseudo finger driving unit 11 also includes a linear actuator for pressing the pseudo finger 10 against and in contact with the surface of the subject S and moving it in a direction parallel to the surface of the subject S. Specifically, the pseudo finger driving unit 11 is arranged to operate in the x-axis direction and the y-axis direction, which are parallel directions (hereinafter also referred to as tangential directions) to the surface of the subject S arranged on the x-y plane. This allows the pseudo finger driving unit 11 to operate the pseudo finger 10 parallel to the subject S.

The stage 13 is a base on which the measurement material to be the specimen S is placed and fixed. The specimen S is an object to be evaluated for tactile sensation, and is, for example, a sheet-like member such as leather, rubber, or paper.

The force sensor 12 is attached below the stage 13 (in the -z direction) so as to support the stage 13, and measures the forces and moments acting on the subject S. The force sensor 12 in this embodiment is a six-axis force sensor that measures forces in the x-, y-, and z-axis directions and moments about the x-, y-, and z-axes.

The control unit 20 is, for example, a computer device, and includes a control unit 21, a memory unit 22, a display unit 23, and an input unit 24, as shown in the block diagram of FIG. 3.

The control unit 21 is composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a crystal oscillator, etc., and controls the operation of the tactile evaluation device 1, and calculates the center of pressure (COP) of the contact surface between the artificial finger 10 and the subject S based on the force and moment acting on the subject S measured by the force sensor 12, the thickness of the subject S, etc. The control unit 21 also estimates the tactile sensation of the subject S based on the amount of movement of the calculated center of pressure.

The control unit 21 loads various operation programs and data stored in the ROM, memory unit 22, etc. of the control unit 21 into the RAM and operates the CPU, thereby realizing each function of the control unit 21 shown in FIG. 3. As a result, the control unit 21 operates as a force sensor control unit 211 and an evaluation unit 212.

The force sensor control unit 211 controls the force sensor 12 to acquire force and moment measurement data from the force sensor 12. The force sensor control unit 211 also transmits the acquired measurement data to the memory unit 22 for storage.

The evaluation unit 212 calculates the center of pressure of the contact surface between the dummy finger 10 and the specimen S at each measurement time t based on the measurement data of the force and moment acquired from the force sensor 12. Fig. 4 is a diagram showing the force and moment measured by the force sensor 12, the resultant force acting on the specimen S, etc. As shown in Fig. 4, when the resultant pressure force applied from the dummy finger 10 is F, the coordinates (X _COP , Y _COP ) of the center of pressure, which is the point of action of the resultant pressure force, are calculated by the following formulas (1) and (2).

where _Fx , Fy, _{and Fz} are forces in the three axial directions, _Mx , _My , and _Mz are moments about the three axes, and h is the thickness of the subject S.

The evaluation unit 212 also stores the calculated movement of the center of pressure, i.e., the time change of the pressure center coordinate, in the storage unit 22. The evaluation unit 212 also reads out the time change of the pressure center coordinate stored in the storage unit 22 and evaluates the tactile sensation of the subject S. The evaluation of the tactile sensation represents the roughness and other tactile sensations felt by a person due to the unevenness, slipperiness, etc. of the surface of the subject S.

The storage unit 22 is a non-volatile memory such as a hard disk or a flash memory, and stores a calculation algorithm for calculating the center of pressure of the contact surface between the artificial finger 10 and the subject S from the force and moment measured by the force sensor 12, a learned model for estimating the tactile sensation based on the amount of movement of the center of pressure, etc.

The display unit 23 is a display device provided in the control unit 20, which is a computer device, and is, for example, a liquid crystal panel. The display unit 23 displays the force and moment acting on the subject S measured by the force sensor 12, the tactile evaluation results estimated by the evaluation unit 212, etc.

The input unit 24 is an input device for inputting instructions to start and end evaluation in the tactile evaluation device 1, changes to various evaluation conditions, etc. The input unit 24 is a keyboard, touch panel, mouse, etc. provided in the control unit 20.

(Tactile evaluation method)
Next, a tactile evaluation method using the tactile evaluation device 1 will be specifically described with reference to the flowchart of FIG.

First, the subject S, who is to be evaluated for tactile sensation, is placed on the stage 13 (step S11). After the subject S is placed, the measurement step is started, and the control unit 21 controls the artificial finger driving unit 11 to lower the artificial finger 10 in the -z direction and press the subject S with a predetermined force that has been set in advance (step S12).

After the descent of the artificial finger 10 is completed, the control unit 21 controls the force sensor 12, which is a six-axis force sensor, to start measuring the force and moment acting on the subject S due to contact between the artificial finger 10 and the subject S (step S13).

Then, the control unit 21 controls the pseudo finger driving unit 11 to operate the pseudo finger 10 (step S14). The operation of the pseudo finger 10 is not particularly limited as long as it is performed while maintaining contact between the pseudo finger 10 and the subject S, and may be, for example, a linear operation (tangential direction) on the x-y plane, a rotational operation, etc. When the operation is started, the force sensor control unit 211 starts acquiring measurement data of the force and moment acting on the subject S from the force sensor 12 (step S15).

The evaluation unit 212 also calculates the center of pressure of the contact surface between the pseudo finger 10 and the subject S based on the measurement data acquired from the force sensor 12 (step S16). The evaluation unit 212 stores the coordinates of the calculated center of pressure and the measurement time t in the storage unit 22. If a predetermined measurement end condition has not been reached (NO in step S17), the control unit 21 repeats the acquisition of measurement data and the calculation of the center of pressure for each predetermined time step. The measurement end condition is, for example, that the measurement time, the number of measurement steps, the amount of movement of the pseudo finger 10, etc. have reached a predetermined value.

When a predetermined measurement end condition is reached (YES in step S17), the measurement step ends and the process proceeds to the evaluation step. In the evaluation step, the evaluation unit 212 of the control unit 21 evaluates the tactile sensation based on the amount of movement of the center of pressure calculated from the time change in the pressure center coordinate (step S18). The tactile sensation evaluation is performed, for example, using a correlation table that shows the correlation between the amount of movement of the center of pressure and tactile characteristics, which are stored in advance in the storage unit 22, a trained model that estimates tactile characteristics from the amount of movement of the center of pressure, etc.

The control unit 21 stores the evaluation results in the memory unit 22 and displays them on the display unit 23 (step S19), and ends the evaluation process.

(Numerical example)
Next, an example of a case where a tactile evaluation is performed on a specimen S having beads of different particle sizes applied to its surface will be described.

The characteristics of the film as the specimen S are as shown in the table below.

In order to perform tactile evaluation with high accuracy, it is necessary to take into account the relationship between force and displacement at the initial slip when the artificial finger 10 starts to move relative to the subject S, so in this example, tactile evaluation is performed based on the movement at the initial slip.

Figures 6(A) and (B) show the relationship between pressure and displacement during initial slippage when the dummy finger 10 starts to move relative to the subject S. As shown in Figures 6(A) and (B), during initial slippage, there are slippage areas where slippage occurs between the dummy finger 10 and the subject S, and sticking areas where no slippage occurs.

In the tactile evaluation at the initial slip according to the present embodiment, an evaluation is performed based on the relationship between the tangential force and the amount of movement of the center of pressure. In this example, the normal force _fg with which the dummy finger 10 presses the subject S in the z-axis direction is 10 N. The dummy finger 10 also moves 15 mm in the x-axis direction at 2.5 mm/s.

The small displacement of the artificial finger 10 during the initial slip can be expressed by the following formula (3) using the normal force f _g and the tangential force f ₁ applied to the subject S.

where μ is the static friction coefficient, a is the radius of the contact surface, G is the rigidity modulus, and ν is the Poisson's ratio.

The graph in Fig. 7 shows the relationship between the theoretical value of the small displacement derived from the above formula or the amount of movement of the center of pressure calculated from the calculated _XCOP and _YCOP , and the tangential force _f1 . As shown in formula (3), in the theoretical value of the small displacement, the whole is multiplied by μ, and the tangential force _f1 is multiplied by 1/μ. That is, the shape of the graph differs depending on the magnitude of the friction coefficient μ, and the larger the friction coefficient μ, the larger the graph shape becomes in the vertical and horizontal directions.

7, in this example, it is found that the experimental values and the theoretical values are in good agreement for a plurality of specimens S having different friction coefficients μ. That is, the relationship between the tangential force f _l measured by the force sensor 12 and the amount of movement of the center of pressure calculated based on the measurement data of the force sensor 12 is close to the theoretically calculated relationship between the tangential force f _l and the small displacement.

Therefore, the friction coefficient μ can be estimated based on the amount of movement of the center of pressure calculated based on the measurement data of the force sensor 12. Furthermore, by storing a correlation table showing the correlation between the friction coefficient μ and the tactile sensation in the memory unit 22 in advance, the control unit 21 can derive the tactile evaluation result corresponding to the calculated friction coefficient μ based on the correlation table.

Here, the modulus of rigidity G in formula (3) is expressed as G = E / 2 (1 + v) using Young's modulus E. In general, the modulus of rigidity G, which is a characteristic parameter of the artificial finger 10, is greatly affected by the shape of the artificial finger 10, the composition of the material, etc., so it is difficult to make the catalog value derived from the design match the actual value. For example, in the calculation of the theoretical value in FIG. 7, Young's modulus E = 0.31 GPa is used, but as shown in FIG. 8, if Young's modulus E is E = 0.23 GPa, the measured value and the theoretical value will deviate. Therefore, it is preferable to set a value close to the actual value by fitting the modulus of rigidity G or Young's modulus E in advance through an experiment.

In addition, the tactile evaluation is performed by storing a correlation table showing the correlation between the friction coefficient μ and the corresponding tactile characteristic in advance in the storage unit 22, and outputting the tactile characteristic corresponding to the calculated friction coefficient μ as the evaluation result, but this is not limited to this. For example, the tactile evaluation may be performed using a trained model that has been trained using multiple forces and moments related to a subject S with various tactile sensations as teacher data.

In this case, the trained model may be an estimation model generated by machine learning to calculate the center of pressure from the force and moment and estimate the tactile sensation of the subject S. The trained model is stored in advance in the memory unit 22, and the evaluation unit 212 inputs the force and moment acquired from the force sensor 12 into the trained model adjusted according to the thickness of the subject S, thereby calculating the amount of movement of the center of pressure within the trained model and performing tactile evaluation. In addition, the machine learning algorithm for generating the trained model is not particularly limited, but a machine learning algorithm using a neural network, for example, can be used.

For example, in the case of the above numerical example, the amount of movement of the center of pressure and the change in the magnitude of the tangential force f _l acting on the specimen S, i.e., the force in the direction parallel to the xy plane, can be used as training data to estimate the surface roughness, etc. of the specimen S and evaluate the sense of touch.

As described above, the tactile evaluation device, tactile evaluation method, and program of the present invention evaluate the tactile characteristics of the subject S based on the force and moment acting on the subject S measured by the force sensor 12 and the amount of movement of the center of pressure calculated using the thickness of the subject S. Therefore, it is possible to perform a highly accurate tactile evaluation even in the range of minute displacements associated with initial slippage.

In this embodiment, the tactile sensation is evaluated by moving the pseudo finger 10 in one direction along the x-axis, but this is not limited to the above. For example, the pseudo finger 10 may be moved in two directions along the x-axis and y-axis, or the pseudo finger 10 may be rotated. In this case, the pseudo finger driving unit 11 may be provided with a motor that rotates the pseudo finger 10. This allows for a multifaceted evaluation, resulting in a more accurate tactile evaluation.

In addition, in this embodiment, the artificial finger 10 is moved in the x-axis direction at a constant speed, but this is not limited to this. For example, the moving speed of the artificial finger 10 or the stage 13 may be changed in stages, or may be a curved movement such as a sine wave, or a movement that causes a change in acceleration such as a reciprocating movement. This allows for more accurate tactile evaluation based on complex movements.

In addition, the artificial finger 10 according to this embodiment is hemispherical in shape to imitate a human finger, but is not limited to this. Any shape suitable for acquiring data such as force and moment by the force sensor 12 may be used, for example, an elliptical cylinder with an R-shaped tip, or a shape with different curvatures on the nail side and the pad side like a human finger. Furthermore, the direction in which the artificial finger 10 is pressed against the subject S is not limited to a direction perpendicular to the subject S, and the artificial finger 10 may be pressed obliquely against the subject S. This allows for a tactile evaluation close to that when a person actually touches the subject S.

The tactile evaluation of the artificial finger 10 is not limited to a dry state, and may be performed in a wet state. For example, after a series of data acquisition for tactile evaluation is performed using the dry artificial finger 10, the artificial finger 10 may be brought into contact with a sponge wet with water, data may be acquired using the wet artificial finger 10, and tactile evaluation may be performed based on these data. This allows for a more accurate tactile evaluation that takes into account the different tactile sensations depending on the degree of dryness of the finger surface.

In addition, in this embodiment, the tactile sensation is evaluated based on the minute displacement of the artificial finger 10 at the initial slippage relative to the subject S, but this is not limited to this. For example, the tactile sensation may be evaluated by combining a range of minute displacement with a range of a larger amount of displacement without a sticking region.

The tactile evaluation method according to this embodiment can be realized using a normal computer system. For example, a computer program for executing the above operations can be stored and distributed on a computer-readable recording medium such as a USB memory or a DVD-ROM, and the computer program can be installed on a computer to cause the computer to function as the control unit 20 of the tactile evaluation device 1 that executes the above tactile evaluation method.

The present invention is suitable for use in a tactile evaluation device that evaluates the tactile sensation of a subject with high accuracy. In particular, the present invention is suitable for use in a tactile evaluation device that performs tactile evaluation when a finger or palm is slid across the surface of a subject as if stroking the surface.

1 Tactile evaluation device, 10 Artificial finger, 11 Artificial finger driving unit, 12 Force sensor, 13 Stage, 20 Control unit, 21 Control unit, 211 Force sensor control unit, 212 Evaluation unit, 22 Memory unit, 23 Display unit, 24 Input unit, S Subject

Claims (5)

a force sensor that measures a force and a moment acting on a test object when the test object or the artificial finger is moved in a state where the test object is in contact with a artificial finger that is an elastic body;
and an evaluation unit that evaluates the tactile sensation of the subject based on a movement amount of a center of pressure calculated using the force and moment measured by the force sensor and a thickness of the subject.
A tactile evaluation device characterized by: The force sensor is a six-axis force sensor.
The tactile evaluation device according to claim 1 . The evaluation unit is
using a plurality of evaluation results as training data, and using an estimation model generated by machine learning to estimate the tactile sensation from the amount of movement of the center of pressure, the tactile sensation of the subject is estimated.
3. The tactile evaluation device according to claim 1 or 2. a measuring step of measuring a force and a moment acting on a test object when the test object or the artificial finger is moved in a state where the test object and the artificial finger are in contact with each other;
and an evaluation step of evaluating a tactile characteristic of the subject based on a movement amount of a center of pressure calculated using the force and moment measured in the measurement step and a thickness of the subject.
A tactile evaluation method comprising: Computer,
a force sensor control unit that acquires a force and a moment acting on a test object when the test object or the artificial finger, which is an elastic body, is moved in a state where the test object is in contact with the artificial finger;
an evaluation unit that evaluates a tactile characteristic of the subject based on a movement amount of a center of pressure calculated using the force and moment acquired by the force sensor control unit and a thickness of the subject;
A program that functions as a