KR20190047959A - Apparatus for Stiffness Measurement - Google Patents

Abstract

The present invention relates to a hardness measurement apparatus. According to the present invention, the hardness measurement apparatus comprises: a pressing unit including a pressing needle pressing a material to be measured and a force sensor measuring a force applied to the material to be measured by the pressing needle; one or more contact sensors spaced apart from the front end part of the pressing needle at a predetermined distance; and a controller reading a force value of the force sensor to derive the hardness of the material to be measured when the force sensor senses contact with the material to be measured; a contact unit for supporting the contact sensor; and a distance adjustment unit adjusting a horizontal distance between the contact unit and the pressing unit. Accordingly, the horizontal distance can be adjusted in accordance with a predicted hardness of the material to be measured, thereby performing hardness measurement in a high-sensitive operation area of the force sensor.

Description

[0001] Apparatus for Stiffness Measurement [

The present invention relates to a hardness measuring apparatus, and more particularly, to a hardness measuring apparatus capable of measuring a hardness of a soft material by measuring a compressive force required to make a compressive displacement of a certain size on a contacting object.

Elastic materials such as fabrics, leather, rubber and polymers are used in many areas of our life. In particular, the hardness and elasticity of the skin or muscle tissue present various information about the aging or health condition of the body. Therefore, in the medical and cosmetic fields, it is necessary to measure hardness of skin and tissues as well as elastic substances. In addition, there is a need for a hardness measuring device capable of miniaturization and high integration to be used as a part of a tactile sensor applied to a hand of a medical robot or a medical robot due to the recent development of robot technology.

Such an elastic material can measure the hardness by measuring elastic deformation. That is, the hardness value is derived by measuring the restoring force proportional to the compressed distance. Therefore, conventional hardness measurement devices require a displacement sensor for measuring the distance over which the measurement substance is compressed. A hardness measuring apparatus requiring a separate displacement sensor is difficult to be miniaturized and highly integrated. Therefore, there has been an attempt to replace the displacement sensor with an acceleration sensor. However, since the noise value of the output signal of the acceleration sensor relative to the minute displacement is too large, accurate displacement can not be calculated.

In addition, a force sensor or a pressure sensor for measuring the restoring force has a threshold at which a force or a pressure value to be measured is saturated, and there is a problem that the sensitivity of a hardness measured when a force of a threshold value or more is applied is reduced do. When measuring at low force values in order to measure low hardness materials, it is impossible to obtain the exact hardness due to the noise generated in the force sensor or pressure sensor. Therefore, in order to measure materials having different hardness, there is a demand for a hardness measuring apparatus equipped with a sensor suitable for each case.

Accordingly, there is a need for a hardness measuring device that can be used in a water-reducing and medical robot, and can measure the hardness of various materials.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a hardness measuring device capable of precisely measuring hardness values of materials having various hardnesses by having contact portions including a pressing portion including a force sensor and a contact sensor.

According to an aspect of the present invention, there is provided a pressure measuring apparatus comprising: a pressing unit including a pressure needle for pressing a measuring material and a force sensor for measuring a force applied to the measuring material; And a controller for reading the force value of the force sensor to derive the hardness of the measurement substance when the contact sensor senses contact with the measurement substance.

According to an embodiment of the present invention, the hardness measuring apparatus may further include a contact portion for supporting the contact sensor and a distance adjusting portion for adjusting a horizontal distance between the contact portion and the pressing portion.

At this time, two or more contact portions may be symmetrically disposed at the same horizontal distance with respect to the pressing portion, and when two or more contact portions are disposed, The final hardness at which the error is minimized can be derived.

Wherein the distance adjusting unit adjusts the horizontal distance between the pressing unit and the contacting unit to be small when the expected hardness of the measuring material is high and controls the horizontal distance between the pressing unit and the contacting unit to be large when the expected hardness of the measuring material is low So that the force value can be measured in the high sensitivity driving area of the force sensor, and the hardness can be measured more sensitively.

According to another embodiment of the present invention, one or more contact sensors may be disposed on the surface of the body of the pressure ulcer, with the touch sensor being spaced a certain distance around the tip of the pressure ulcer.

The pressing may be selected from various forms such as a hemispherical shape, a conical shape, a cylindrical shape, a cylindrical shape, and a polygonal shape depending on the elasticity and plasticity of the measurement material.

An elastic body contractible by the repulsive force of the measurement material may be attached to one end of the pressure probe, and the elastic body may be adjusted to have a different elastic modulus depending on the expected hardness of the measurement material according to the main use purpose of the hardness measurement apparatus .

The present invention can obtain a precise hardness value without a separate displacement sensor for measuring the distance the measured material is pressed by measuring the force applied to the force sensor of the pressed portion at the moment when the contact sensor of the contact portion contacts the measured substance.

According to an embodiment of the present invention, the contact portion supporting the contact sensor can be spaced apart by a certain horizontal distance by the distance adjusting portion about the pressing portion. There is a problem in that it is difficult to reduce the accuracy due to the saturation of the output characteristic in the high force region exceeding the threshold value and the noise generated in the low force region. By adjusting the horizontal distance between the contact part and the crimping part, it is possible to adjust the force measured when the contact part contacts with the measuring material, and therefore, when necessary, the hardness value can be measured within the sensor operating range .

In one embodiment, the contact portions may be spaced apart from each other by a predetermined distance about the crimping portion, and two or more of the contacting portions may be symmetrically disposed. When the hardness measuring device is made portable or small, it can be in contact with the measuring material at a constant angle with the direction perpendicular to the surface of the measuring material when it is pressed against the measuring material. The final hardness value that minimizes the error due to the twist can be derived by using the average of the hardness values at the moment when each contact portion contacts the surface of the measurement material.

The technical effects of the present invention are not limited to those mentioned above, and other technical effects not mentioned can be clearly understood by those skilled in the art from the following description.

1 is a sectional view showing a hardness measuring apparatus according to an embodiment of the present invention.
2 is a block diagram showing components of a hardness measuring apparatus according to an embodiment of the present invention.
3 is a schematic view for explaining a measuring method of the hardness measuring apparatus according to an embodiment of the present invention.
4 is a graph for explaining a driving region of the force sensor.
5 is a sectional view showing a hardness measuring apparatus according to an embodiment of the present invention.
6 is a schematic view for explaining a measuring method of a hardness measuring apparatus according to an embodiment of the present invention.
FIG. 7 is a graph showing the hardness difference according to the adjustment of the horizontal distance between the pressing portion and the contact portion according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. Rather, the intention is not to limit the invention to the particular forms disclosed, but rather, the invention includes all modifications, equivalents and substitutions that are consistent with the spirit of the invention as defined by the claims.

It will be appreciated that when an element such as a layer, region or substrate is referred to as being present on another element "on," it may be directly on the other element or there may be an intermediate element in between .

Although the terms first, second, etc. may be used to describe various elements, components, regions, layers and / or regions, such elements, components, regions, layers and / And should not be limited by these terms.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. In the following description, the same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.

Example 1

1 is a sectional view showing a hardness measuring apparatus according to an embodiment of the present invention.

Referring to FIG. 1, a hardness measuring apparatus according to an embodiment of the present invention includes a contact portion 10 including a contact sensor 11 on a surface contacting with a measurement material, A distance adjusting unit 30 for adjusting the horizontal distance between the contact unit 10 and the pressing unit 20, and a distance adjusting unit 30 for adjusting the distance between the contact unit 10 and the contact unit 20, And a controller (not shown) that reads the force value to derive the hardness of the measurement material when the sensor 11 detects contact with the measurement material.

The contact portion 10 includes a support portion 13 connected to the distance control portion 30 and a contact sensor 11 formed on a contact surface where the measurement material contacts the support portion 13.

The support portion 13 may have a wide contact surface to help the crimping portion 20 be introduced perpendicularly to the surface of the measurement material.

The touch sensor 11 can use a known touch sensor as a sensor capable of recognizing the contact between the measurement material and the contact surface of the contact portion 10 and generating a signal. For example, the touch sensor 11 may be a resistive touch sensor, a capacitive touch sensor, an Infra-Red touch sensor, and a surface acoustic wave touch sensor .

Optionally, the contact sensor 11 may be connected to a linear bearing formed at the bottom of the support 13 for fine distance adjustment. The contact sensor 11 can move along the linear bearing and further adjust the horizontal distance to the crimping portion 20. [

The pressing part 20 includes a pressing part 21 for applying a force to the measuring material in contact with the measuring material, an elastic body 23 attached to one end of the pressing part 21 and contracted by a repulsive force of the measuring material, A force sensor 25 for measuring a force applied to the measurement material by the elastic body 23 and a supporter 27 for fixing the pressure hand 21, the elastic body 23 and the force sensor 25 .

The pressure ulcer 21 may protrude a predetermined distance x _i from the contact surface where the contact portion 10 is in contact with the measurement substance. Therefore, before the contact portion 10 contacts the measuring material yet, the pressing tool 21 contacts the measuring material to apply a force and the measuring material is squeezed.

One end of the elastic body 23 is selectively disposed between the pressure ulcer 21 and the auxiliary portion 27. The elastic body 23 can use various materials having elasticity. For example, the elastic body 23 may be a spring, a rubber and a polymer compound, and in some cases, a sealed gas having a constant force may be used. It is also possible to use an apparatus such as a solenoid capable of applying a repulsive force by using an electromagnetic device. The elastic body 23 contracts by the restoring force of the measuring material when the pressing tool 21 presses the measuring material so that the measuring material does not undergo plastic deformation or permanent deformation. Therefore, the elastic body 23 can be selected according to the type of the substance to be measured. When the material to be measured is easily plastic-deformed, the elastic body 23 may have a very low modulus of elasticity and be easily deformed.

The force sensor 25 measures a force applied to the measurement material by the pressure ulcer 21 and the elastic body 23. Therefore, the force sensor 25 can be formed at a position capable of measuring the force applied by the pressing tool 21 and the elastic body 23. [ That is, as shown in the figure, the force sensor 25 may be positioned between the elastic body 23 and the auxiliary portion 27, but may be located between the pressure hand 21 and the elastic body 23 or between the pressure hand 21 As shown in FIG. The force sensor 25 may be replaced by a pressure sensor. When using a pressure sensor, the contact area A of the pressure sensor can be converted to a force value F by multiplying the measured pressure value P. The force sensor 25 may be one of a Piezoresistive force sensor, a capacitive force sensor, an optical force sensor, a resonance force sensor, and an electric inductive force sensor.

And may include an auxiliary portion 27 for fixing the pressure needle 21, the elastic body 23, and the force sensor 25. The end of the auxiliary portion 27 may be at the same height as or higher than the contact surface of the contact portion 10 from the surface of the measurement material. The auxiliary portion 27 may guide the pusher 21 and the elastic body 23 to move in the vertical direction by covering the outer circumferential surfaces of the pusher 21 and the elastic body 23. Therefore, the error of the hardness caused by the flexure of the elastic body 23 in the horizontal direction can be minimized.

The distance adjusting unit 30 fixes the contact unit 10 and the pressing unit 20 at a predetermined distance. The horizontal distance between the contacting portion 10 and the pressing portion 20 can be adjusted so that the force applied to the measuring material is located within the optimum driving region of the force sensor. The distance adjuster 30 may include a linear bearing that can move along a predetermined orbit. In this case, the contact portion 10 can be moved to a desired position using a linear bearing to adjust the horizontal distance to the contact portion 20.

According to an embodiment of the present invention, the hardness measuring apparatus may include a plurality of contact portions 10a and 10b.

The plurality of contact portions 10a and 10b may be arranged symmetrically at the same horizontal distance about the press portion 20. The contact portions 10a and 10b are spaced apart from each other by the same horizontal distance as the contact portion 20 and the contact portions 10a and 10b and the contact portion 20 are on the same straight line . When there are three or more contact portions 10, each contact portion 10 may be positioned so as to divide the circle formed by points having the same horizontal distance from the contact portion 20 at the same angle.

The hardness measuring apparatus according to the embodiment of the present invention averages or arithmetically processes the values of hardness derived from the moment when each contact portion 10 contacts the surface of the measuring material so that the hardness measuring apparatus measures the surface It is possible to minimize an error in the hardness caused by not being introduced perpendicularly.

2 is a block diagram showing components of a hardness measuring apparatus according to an embodiment of the present invention.

2, a hardness measuring apparatus according to an embodiment of the present invention includes a pressing portion 20 including a force sensor 25, a contact portion 10a including a first contact sensor 11a, A contact portion 10b including a sensor 11b and a controller 40. [

The controller 40 includes an operation unit 41 that receives the contact signals of the contact sensors 11a and 11b and the force value of the force sensor 25 and computes and transmits the hardness value and a power source unit 43 And a display unit 45 for outputting the derived hardness. In the case where the hardness measuring apparatus is a portable apparatus, the communication module 47 for transmitting a value to an external apparatus may be included in the display unit 45 or may be included together with the display unit 45. It may further comprise an amplifier 49 for making the force measurement of the force sensor 25 more sensitive.

When the first contact sensor 11a generates a signal indicating that the first contact portion 10a contacts the surface of the measurement material, the calculation portion 41 receives the signal and outputs the signal to the force sensor 25 1 Stores the force value. Calculates the first hardness from the stored first force value and stores the value.

When the second contact sensor 11b generates a signal indicating that the second contact portion 10b contacts the surface of the measurement material, the calculation unit 41 similarly receives and stores the second force value from the force sensor 25 , And calculates a second hardness therefrom.

Alternatively, the calculating unit 41 may adjust the distance adjusting unit based on the hardness values so that the horizontal distance between the pressing unit 20 and the contact unit 10 has an appropriate distance.

The values of the first hardness and the second hardness are averaged to obtain the final hardness that minimizes the error caused by the fact that the crimping portion 20 is not introduced perpendicularly to the surface of the measurement material. The calculation unit 41 transmits the final hardness to the display unit 45 or the communication module 47. [

The display unit 45 or the communication module 47 may output the received final hardness value to a display or an external device.

3 is a schematic view for explaining a measuring method of the hardness measuring apparatus according to an embodiment of the present invention.

3, when the contact sensor 11 is brought into contact with the surface of the measurement material 50, the measurement material 50 is pressed by the protruding pressure needle 21 of the press portion 20 to a predetermined depth .

The vertical distance u (d, 0) between the surface of the measuring material 50 and the original surface before being compressed is defined by the curvature of the surface of the measuring material 50 as the measuring material 50 is squeezed, Can be calculated by the following equation.

(Equation 1)

a _pressure : the radius of the pressure needle 21

h: Depth at which the measuring substance 50 is pressed by the pressing tool 21

According to the Sneddon solution, h is determined by the inherent physical properties of the measuring substance 50 as follows.

(Equation 2)

P: pressure applied to the measuring substance 50

ν: Poisson ratio of the measuring substance (50)

E: Young's modulus of the measuring substance (50)

Where v is the Poisson ratio and represents the ratio between the vertical strain and the horizontal strain when the material is stretched in that direction due to the action of the tensile force. E in the above equation is a modulus of elasticity, which is a modulus of elasticity indicating the relationship between strain and force occurring in the measuring material 50.

The following equation (2), which is a general equation relating to the force and the Young's modulus, can be applied to Formula 2 to calculate the depth u (d _{contact sensor} , 0) of the position where the contact sensor 11 contacts the measuring material 50.

(Equation 3)

Apchim 21 in the state in which forming a repulsive force and the balanced by the compression of the test substance (50), apchim 21 is a touch sensor as in the initial protruding length x _i elastic body 23 is obtained by subtracting the compressed distance x _elastomers length ( 11 protrude from the surface of the contact portion 10 where the contact portion 10 is located. Therefore, the depth h at which the measuring material 50 is pressed by the pressing tool 21 has the following relationship with the depth u (d _{contact sensor} , 0) of the touch sensor 11:

(Equation 4)

According to Hook's law and Newton's third law, the force of the elastic body 23 pressing the pressing tool 21 and the repulsive force due to the pressing of the measuring material 50 can be approximated by the following relation .

(Equation 5)

Expression 3, Expression 4 and Expression 5 can be expressed as follows in the expression for h.

(Equation 6)

F _{force sensor} : a force value measured by the force sensor 25 when the contact sensor 11 is contacted

x _i : the initial protrusion length before the pressing tool 21 contacts the measuring material 50

a _pressure : the radius of the pressure needle 21

d _{touch sensor} : the contact portion 10 is horizontally spaced from the center point of the pressing portion 20 by a horizontal distance

k _{Elastic body} : The modulus of elasticity of the elastic body (23)

k _{material (part)} : the modulus of elasticity of the point of compression of the measuring material (50)

When Equation 6 is summarized for the k _{material (portion)} , the hardness of the measurement material 50 can be calculated by the following equation.

(Equation 7)

Therefore, the partial hardness of the pressed portion of the measured material can be derived from the force (F _{force sensor} ) measured by the force sensor 25 when a contact signal is generated from the contact sensor 11 using the above equation.

The above-described formula 1 and formula 2 are applied when the pressure hand 21 is cylindrical, and the pressure hand 21 can have various forms such as a cone, a hemisphere, a cylinder and a polygonal pyramid. In this case, Can be appropriately modified to derive the hardness of the measured material.

The partial hardness of the measured material derived from Equation 7 can be used to derive the Young's modulus of the measured material and the overall hardness of the material.

(Expression 8)

The relationship between force and pressure can be expressed as Eq. (8). A is the area to which the force is applied. In the present hardness measuring system, it can be calculated through the radius (a) of the bob 21.

The following equation can be derived by substituting equation (8) into equation (3).

(Equation 9)

The value of h can be obtained using the k _{material (portion)} of Equation 7. Therefore, applying the derived h value to Eq. 9 can calculate the Young's modulus of the measured material. Snellen's law assumes that the material to be measured is semi-infinite, but it is applicable if the thickness of the material is greater than 3 cm. In general materials, the Poisson's ratio (v) has a value of 0 to 0.5. In the present invention, (1-v ² ) can be fixed to a value between 0.8 and 0.9 for convenience of calculation.

(Equation 10)

A _substance : total area of the _{substance to be} measured

T: thickness of the measuring material

The hardness k _{material (total)} of the _{entire material} can be derived by substituting the Young's modulus derived from Equation 9.

4 is a graph for explaining a driving region of the force sensor.

Referring to FIG. 4, most force sensors currently used have a high sensitivity driving area as shown in the graph. The high sensitivity drive area is a region where the sensor output sensitively changes due to the applied force, and is a region having a high slope on the graph.

If the force applied to the force sensor is too low, the output of the force sensor will not be adequate due to the noise. Also, when the force applied to the force sensor is too high, the output of the force sensor shows a saturated graph, so that the increase in force can not be measured sensitively.

In the present invention, the hardness of the measurement material can be measured in the high-sensitivity driving region of the force sensor by adjusting the horizontal distance between the pressing portion 20 and the contact portion 10. [

Equation (7) is summarized for the F _{force sensor} as follows.

(Expression 11)

The arcsin (a / d _{contact sensor} ) decreases as the size of the d contact sensor increases, and increases sharply as it decreases. Therefore, when the hardness of the measurement material is high, the horizontal distance between the crimping portion 20 and the contact portion 10 is adjusted to be close to the horizontal distance between the crimping portion 20 and the contact portion 10, The hardness of the force sensor can be measured within an appropriate driving range.

Example 2

The hardness measuring apparatus according to another embodiment of the present invention may be provided with a contact sensor 11 (not shown) on the body of the pressure hand, which is spaced a certain distance around the tip of the pressure hand 21, ) Directly. This structure is suitable for miniaturization of the hardness measuring apparatus.

5 is a sectional view showing a hardness measuring apparatus according to an embodiment of the present invention.

5, a hardness measuring apparatus according to an embodiment of the present invention includes a pressing tool 21 for pressing a measuring material and a force sensor 25 for measuring a force applied to the measuring material by the pressing tool 21 At least one contact sensor 11 disposed at a distance from the tip of the pressure probe 21 and spaced a predetermined distance from the tip of the pressure probe 21 and when the contact sensor 11 senses contact with the measurement material, And a controller (not shown) for reading the force value of the force sensor 25 and deriving the hardness of the measurement material. At this time, the contact sensor 11 may be disposed on the body of the pressure ulcer 21 around the tip of the pressure ulcer 21.

At this time, the body of the pressure probe 21 may be various shapes such as a cylinder shape, a cone shape and a polygonal shape depending on the hardness and the degree of plasticity of the measurement material as well as the hemispherical shape.

Further, at one end of the pressure ulcer 21, an elastic body 23 having a known hardness may be provided. The elastic body 23 can be compressed due to the repulsive force of the measuring material when the pressing tool 21 applies a force to the measuring material.

The force sensor 25 may be disposed between the pressure hand 21 and the auxiliary portion 27 or at the tip end of the pressure hand 21.

6 is a schematic view for explaining a measuring method of a hardness measuring apparatus according to an embodiment of the present invention.

According to the Hertzian solution, when the hemispherical pressure ulcer 21 is employed, the displacement of the surface of the measuring substance in contact with the pressure ulcer 21 can be expressed by the following equation.

(Expression 12)

a: radius of the surface where the pressing tool 21 and the measuring material 50 are in contact with each other

h: Displacement of material at r = 0

When the hardness measuring device is introduced into the measuring material and the contact sensor 11 contacts the measuring material 50, the radius a of the surface with which the measuring material 50 contacts the pressing tool 21 becomes a d _{contact sensor} .

Therefore, the displacement u (r) of the measurement material 50 by the pressure ulcer 21 when the contact sensor 11 generates the contact signal can be expressed as follows.

(Expression 13)

Therefore, the displacement of the measuring material 50 at the position of the contact sensor 11 (r = d _{contact sensor} ) is h / 2 and the vertical distance difference x _i between the tip end of the pusher 21 and the contact sensor 11, Can be expressed by the following equation.

(Equation 14)

The displacement (x _material ) of the measuring material deformed by the pressing tool 21 can be approximated as follows in consideration of the hemispherical shape of the pressing tool 21.

(Expression 15)

The force, which is detected by the force sensor according to Hooke's law. F The hardness of the _{force sensor} and the measured material has the following relationship.

(Expression 16)

Equation (14) and Equation (16) can be summarized by the following equation.

(Equation 17)

As described above, Equation 17 shows a method of deriving the hardness when the pressure hand 21 is hemispherical, and Equations 12 to 15 can be suitably modified and applied depending on the shape of the pressure hand 21.

Experimental Example

In order to test the hardness measurement principle of the present invention, a hardness measuring device having symmetrical contact pairs spaced apart from each other with a constant horizontal distance on both sides of the crimping portion was manufactured. A prefabricated module capable of attaching a touch sensor was used as a distance control unit to adjust the horizontal distance. The horizontal distance was adjusted to 6 mm and 20 mm using the assembled module. As an elastic body to be inserted into the crimping portion, two springs, which are known as spring constants of 2.1 N / mm and 0.4 N / mm, respectively, were alternately used. The radius of the pusher is 5 mm, and the length of the pusher protruding from the contact is 3 mm.

Sponges, rubbers, black foams, blue foams and skin, which are known to have different hardnesses, were measured under three conditions by varying the horizontal distance and the spring constant of the springs.

FIG. 7 is a graph showing the hardness difference according to the adjustment of the horizontal distance between the pressing portion and the contact portion according to an embodiment of the present invention.

Referring to FIG. 7, when the horizontal distance between the pressed portion and the contact portion is as small as 6 mm and the spring constant is 2.1 N / mm in FIG. 7A, the hardness difference of the five kinds of materials is not large, N / mm. In FIG. 7B where the horizontal distance between the pressed portion and the contact portion increased to 20 mm, it can be seen that the hardness difference between the respective materials was large.

In FIG. 7C, when the horizontal distance between the crimping portion and the contact portion is maintained at 20 mm and the spring constant is reduced to 0.4 N / mm, the difference in hardness between rubber, black foam and blue foam having a relatively high hardness in comparison with the spring constant is reduced, And the difference in hardness between rubber and rubber increased significantly. Therefore, the sensitivity can be improved by determining the spring constant according to the hardness of the material to be measured.

13: Support part 20:
21: tumbler 23: elastomer
25: force sensor 27:
30: distance adjustment unit 40: controller
43: power supply unit 45: display unit
47: Communication module 49: Amplifier
50: Measuring material

Claims (8)

A pressing part including a pressing tool for pressing the measuring material and a force sensor for measuring a force applied to the measuring material by the pressing tool;
At least one contact sensor disposed at a predetermined distance from the tip of the pressure needle; And
And a controller for reading the force value of the force sensor to derive a hardness of the measurement substance when the contact sensor senses contact with the measurement substance. The method according to claim 1,
A contact portion for supporting the contact sensor; And
And a distance adjusting unit for adjusting a horizontal distance between the contact unit and the crimping unit. 3. The method of claim 2,
Wherein the contact portions are symmetrically disposed at equal horizontal distances centering on the crimping portions,
And derives a final hardness at which the error is minimized from each force value measured by the force sensor at the moment when the contact portion contacts the measurement material. 3. The method of claim 2,
Wherein the distance adjuster adjusts the horizontal distance between the crimping portion and the contact portion to be small when the expected hardness of the measurement material is high,
And adjusts the horizontal distance between the pressing portion and the contact portion to be large when the expected hardness of the measurement material is low. The method according to claim 1,
Wherein at least one of the contact sensors is disposed on a surface of a body of the pressing tool, the contact sensor being spaced a predetermined distance from the tip of the pressing tool. The method according to claim 1,
Wherein the pressing force has one of a hemispherical shape, a conical shape, a cylindrical shape, a cylindrical shape, and a polygonal pyramid shape. The method according to claim 1,
And an elastic body contracted by the repulsive force of the measurement material is attached to one end of the pressure probe. 8. The method of claim 7,
Wherein the elastic body can have a different modulus of elasticity depending on the expected hardness of the measurement material.

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