JP7019445B2 - Indentation test equipment - Google Patents

Description

The present invention relates to an indentation test device for indenting an indenter into a food such as kamaboko or ham or a soft tissue of a human and measuring the softness of the indenter.

The following Patent Document 1 discloses an indentation test device for measuring the softness of a flexible food, a human body tissue, or the like as a subject.
As shown in FIG. 5, this device includes an indenter 10 pushed into the subject, a force sensor 30 that detects the force acting on the indenter 10 when the indenter 10 is pushed into the subject, and the softness of the subject. It is provided with a calculation unit 40 that calculates Young's modulus for evaluating Young's modulus 10 based on the force acting on the indenter 10, and a housing 20 in which they are arranged.
The indenter 10 is arranged in the housing so that a certain amount of the hemispherical portion at the tip protrudes from the pressing surface which is the end surface 21 of the housing 20.

この(数１)を用いて、力センサ３０で検出された押込荷重Ｆから被検体のヤング率Ｅを求めることができる。 The operator who operates this device grips the housing 20 portion and pushes the indenter 10 into the subject until the end face 21 of the housing 20 comes into contact with the subject.
At this time, the force (pushing load) detected by the force sensor 30 when the end face 21 of the housing 20 comes into contact with the subject is F, and the protrusion amount of the indenter 10 protruding from the end face 21 of the housing 20 (that is, that is). Let δ be the amount of indenter 10 pushed into the subject, φ be the diameter of the hemisphere of the indenter 10, E be the Young's modulus of the subject, and ν be the Poisson's ratio peculiar to the subject. There is a relationship represented by (Equation 1).

Using this (Equation 1), the Young's modulus E of the subject can be obtained from the indentation load F detected by the force sensor 30.

This indentation test device can measure the softness of a subject at the place where the subject should be (so-called “in-situ measurement”), and can be expected to be used in a wide range of fields.

WO2017 / 164426

However, in this indentation test apparatus, when the indenter 10 is pushed into the subject, in the initial stage, only the indenter 10 protruding from the housing 20 comes into contact with the subject, so that the housing 20 is the subject. It is difficult to push in the direction perpendicular to the surface of.
When the traveling direction of the housing 20 when the indenter 10 is pushed into the subject is tilted from the vertical direction of the subject surface, the following situation occurs.

FIG. 6A shows a state in which the indenter 10 is not tilted with respect to the surface of the subject, and FIG. 6B shows a state in which the indenter 10 is tilted by θ with respect to the surface of the subject. There is.
Assuming that the load detected by the force sensor 30 in the case of FIG. 6A is F, the component force F'of F detected by the force sensor 30 in the case of FIG. 6B is
(Equation 2) F'= Fcosθ
Will be. If the absolute value of θ is 5 ° or less, the error between F and F'is 0.4% or less, which is not a problem in practice.

However, in this indentation test device, when the indenter 10 is tilted with respect to the surface of the subject, not only the error between F and F'but also the indenter when the end surface 21 of the housing 20 comes into contact with the subject. The pushing amount of 10 is different.
As shown in FIG. 6 (c), when the indenter 10 is not tilted with respect to the surface of the subject, the amount of the indenter 10 pushed in until the end surface 21 of the housing 20 comes into contact with the subject is defined as δ. do. In addition, r is a radius in the outer diameter of the end face 21 of an annular shape.
When the indenter 10 is tilted by θ with respect to the surface of the subject, as shown in FIG. 6D, the pushing amount δ'of the indenter 10 when the end surface 21 of the housing 20 comes into contact with the subject is
(Equation 3) δ'= δ-rsinθ
Will be.
Therefore, in (Equation 1), F and δ are replaced with F'and δ', so that the error of Young's modulus E becomes large.
Note that y in FIG. 6D shows the distance between the subject and the end face portion at a position symmetrical to the contact position when a part of the end surface 21 of the housing 20 comes into contact with the subject.

FIG. 7 shows the relationship between the inclination of the indenter 10 and the error of Young's modulus E, with the angle corresponding to θ on the horizontal axis and the error of Young's modulus E on the vertical axis. It can be seen that the inclination of the indenter 10 must be maintained within 0.2 ° in order to make the error of Young's modulus E 1% or less.

The present invention has been devised in consideration of such circumstances, and an object of the present invention is to provide an indentation test apparatus capable of accurately measuring the softness of a subject by anyone.

In the present invention, an indenter pushed into a subject, a force sensor for detecting a force acting on the indenter, the force sensor, and a connecting member connecting the force sensor and the indenter are housed, and the indenter is housed. A housing arranged so that at least a part thereof protrudes outward from the end face, and a plurality of contact detection sensors provided at positions separated from the end face of the housing to detect contact with a subject. The plurality of contact detection sensors project from the end face by the same length at the position that divides the circumference centered on the indenter by approximately equal distances, and protrude outward from the end face. The distance to the tip of the indenter is longer than the length of the plurality of contact detection sensors protruding from the end face, and when the housing is operated so as to push the indenter into the subject, the contact detection sensor operates. The force acting on the indenter at the time of contact with the subject is detected by the force sensor, and the softness of the subject is calculated based on the detection result.
In this device, it is possible to know whether or not the indentation test device is tilted with respect to the surface of the subject from the contact state of the plurality of contact detection sensors with the subject.

Further, in the indentation test apparatus of the present invention, each time each of the plurality of contact detection sensors detects contact with the subject, the value of the softness of the subject is used by using the detection value of the force sensor at the time of detection. May be calculated and the obtained plurality of said values may be averaged.
In this device, even if the pushing direction of the indenter deviates from the vertical direction of the surface of the subject, the softness of the subject can be calculated with high accuracy by taking an average value.

Further, in the indentation test apparatus of the present invention, the indentation speed of the indenter into the subject and the time difference between the times when a plurality of contact detection sensors detect contact with the subject are used to obtain the housing of the housing with respect to the subject. The inclination in the pushing direction is calculated, and the inclination is used to calculate the pushing amount of the indenter when one of the contact detection sensors first contacts the subject, and the pushing amount and the force sensor detect at the time. The value of the softness of the subject may be calculated using the detected value.
In this device, even if the pushing direction of the indenter deviates from the vertical direction of the surface of the subject, it is possible to correct the error due to the deviation.

Further, in the indentation test apparatus of the present invention, the contact detection sensor may have a pin shape.
In this device, the length of the indenter protruding from the end face of the housing is set longer than the length of the pin-shaped contact detection sensor.

Further, in the indentation test apparatus of the present invention, a plurality of contact detection sensors may be configured by a vibrating body whose vibration state changes when in contact with a subject.
When the vibrating body comes into contact with the subject, the vibration of the vibrating body stops or the amplitude becomes small, so that the contact with the subject can be detected.

With the indentation test apparatus of the present invention, the softness of the subject can be determined with high accuracy.

The figure which shows the contact detection sensor position of the indentation test apparatus which concerns on embodiment of this invention. The figure which shows the pin type contact detection sensor (A) A diagram showing a change in Young's modulus when the indentation test device is indented into a subject at a constant speed, and (b) a diagram showing a relationship between an inclination and an error when calculating Young's modulus by the method of the embodiment. A flow chart showing a procedure for calculating Young's modulus by the method of the embodiment. The figure which shows the conventional indentation test apparatus Diagram explaining the effect of indenter slope on Young's modulus calculation The figure which shows the relationship between the inclination and the error when calculating Young's modulus using the conventional indentation test equipment.

As shown in FIG. 1, the indentation test apparatus of the present invention includes a plurality of contact detection sensors 22 projecting from the end face 21 of the housing 20. In this device, a plurality of contact detection sensors 22 form a contact portion with the subject. The plurality of contact detection sensors 22 are arranged at positions that divide the circumference around the indenter at substantially equal distances. The protrusion lengths of the plurality of contact detection sensors 22 from the end faces 21 are all the same.
The contact detection sensor 22 may be any as long as it can detect contact with the subject, and the pressure-sensitive rubber whose electric resistance value changes due to contact with the subject or the vibration state changes due to contact with the subject. Various things such as vibrating bodies can be used.

When the vibrating body is used as a contact detection sensor, a plurality of piezoelectric bodies are arranged at the positions of the contact detection sensor 22 in FIG. 1, an AC voltage having a resonance frequency is applied to each piezoelectric body, and resonance vibration is applied to each piezoelectric body. Let me do it. When the piezoelectric body comes into contact with the subject, the vibration of the piezoelectric body stops or the amplitude becomes small, so that contact with the subject can be detected.
Further, FIG. 2 shows a device in which a pin-type contact detection sensor 221 whose frequency characteristic of an applied electric signal changes due to contact with a subject is arranged around an indenter 10.
The tip of the indenter 10 protrudes from the tip of the contact detection sensor 221. Therefore, when the indenter 10 is pushed into the subject, the plurality of contact detection sensors 221 come into contact with the subject behind the indenter 10.

In this indentation test device, the softness of the subject may not be detected unless it is detected that all of the plurality of contact detection sensors 22 are in contact with the subject. By doing so, it is possible to ensure the detection of softness in a state where the periphery of the indenter evenly contacts the subject and the pushing direction of the indenter is maintained in the vertical direction of the subject surface.

FIG. 3A shows the results of measuring the transition of the Young's modulus of the subject while pushing the tip of the apparatus into the subject at a constant speed using a push-in test device equipped with two pin-type contact detection sensors. There is. The horizontal axis of FIG. 3A is time, and the vertical axis is Young's modulus.
Point A in FIG. 3A shows the magnitude of Young's modulus when one of the contact detection sensors comes into contact with the subject, and point B in FIG. 3A shows the other of the contact detection sensors on the subject. It shows the magnitude of Young's modulus at the time of contact. Here, since the indentation test device is slightly tilted with respect to the surface of the subject, the time points when the two contact detection sensors come into contact with the subject do not match.
During the time period until the point A, none of the contact detection sensors were in contact with the subject, and only the indenter was pushed into the subject, so that the Young's modulus increased.
In the time zone between points A and B, Young's modulus increases because one of the contact detection sensors and the indenter are pushed into the subject. Further, in the time zone from the point B to the peak of Young's modulus, the Young's modulus is increased by pushing the two contact detection sensors and the indenter into the subject.
After the peak, the pushing force is released and Young's modulus decreases.

In this case, the Young's modulus when the indentation test device is not tilted with respect to the surface of the subject and the two contact detection sensors come into contact with the subject at the same time is the Young's modulus at point A and the Young's modulus at point B. It can be calculated as an average value.
In this way, the Young's modulus is calculated using the indentation load detected by the force sensor when each of the plurality of contact detection sensors comes into contact with the subject, and the Young's modulus is averaged to obtain the Young's modulus of the subject. As shown in FIG. 6D, it is possible to calculate the Young's modulus with high accuracy even if the indenter's pressing direction is slightly tilted with respect to the surface of the subject.

FIG. 3B shows the relationship between the error (vertical axis) of Young's modulus of the subject obtained by this method and the slope (horizontal axis) corresponding to θ in FIG. When the magnitude of the inclination is within 2 °, the error of Young's modulus is 3% or less, and it can be seen that the measurement result with extremely high accuracy can be obtained as compared with the characteristics of FIG. 7.

The flow chart of FIG. 4 shows a procedure for calculating Young's modulus of a subject by this method.
When there is a contact detection sensor that newly detects contact with the subject among multiple contact detection sensors (Yes in step 1), Young's modulus is calculated by (Equation 1) using the pushing load at the time of detection. And record in the recording unit (step 2). This procedure is repeated until all contact detection sensors detect contact with the subject, and when all contact detection sensors detect contact with the subject (Yes in step 3), multiple Young's modulus recorded in the recording unit. Is averaged (step 4).

Here, the average value of a plurality of Young's modulus is calculated, but each time there is a contact detection sensor that newly detects contact with a subject among a plurality of contact detection sensors, it is pushed in at the time of detection. The load is recorded in the recording unit, and after all the contact detection sensors detect contact with the subject, the average value of multiple indentation loads recorded in the recording unit is calculated, and the Young's modulus is calculated using the average value. You may do so.

In addition, when a push-in test device equipped with a plurality of contact detection sensors is pushed into a subject at a known push-in speed, the tilt of the push-in test device with respect to the surface of the subject is caused by the deviation of the contact detection points of the plurality of contact detection sensors (Fig.). 6 (d), the angle corresponding to θ) can be calculated.
Now, as shown in FIG. 6D, a push-in test device in which two contact detection sensors are arranged at positions that divide the circumference of the housing end face into two is pushed into the subject at a constant push-in speed V. It is assumed that the time difference between the times when one contact detection sensor detects contact with the subject is t.
At this time, the distance corresponding to y in FIG. 6 (d) is
(Number 4) y = Vt
And the slope θ is
(Equation 5) θ = sin ^-1 (y / 2r)
It is represented by.
Using this θ, it is possible to calculate δ'of (Equation 3).
Then, according to (Equation 1), if the Young's modulus E is calculated using the indentation load F detected by the force sensor when the contact detection sensor detects the contact with the subject for the first time and the indentation amount δ', the indentation is performed. Even if the pushing direction of the test device is slightly tilted with respect to the surface of the subject, the softness of the subject can be calculated with high accuracy.

The number of contact detection sensors constituting the contact portion may be 2 or more.
Further, although an indenter having a hemispherical surface is shown here, the shape of the indenter is not limited to this. It may be a cylinder, a cylinder, a cube, or the like.

The indentation test apparatus of the present invention can measure the softness of a subject with high accuracy, and is used in a wide range of fields such as a food field, a medical field, and a field dealing with materials that require measurement of softness. be able to.

10 Indenter 20 Housing 21 End face 22 Contact detection sensor 30 Force sensor 40 Calculation unit 221 Pin type contact detection sensor

Claims (4)

The indenter pushed into the subject and
A force sensor that detects the force acting on the indenter, and
A housing in which the force sensor and a connecting member connecting the force sensor and the indenter are housed, and the indenter is arranged so that at least a part thereof protrudes outward from the end face.
A plurality of contact detection sensors for detecting contact with the subject, which are provided at positions separated from the end faces of the housing, and
Equipped with
The plurality of contact detection sensors project from the end face by the same length at the position where the circumference centered on the indenter is divided by a substantially equidistant distance.
The distance to the tip of the indenter protruding outward from the end face is longer than the length of the plurality of contact detection sensors protruding from the end face.
When the housing is operated so as to push the indenter into the subject, each time each of the plurality of contact detection sensors detects contact with the subject, the detection value of the force sensor at the time of detection is detected. A push-in test device in which the softness value of the subject is calculated using the above, and the obtained plurality of the obtained values are averaged . The indenter pushed into the subject and
A force sensor that detects the force acting on the indenter, and
A housing in which the force sensor and a connecting member connecting the force sensor and the indenter are housed, and the indenter is arranged so that at least a part thereof protrudes outward from the end face.
A plurality of contact detection sensors for detecting contact with the subject, which are provided at positions separated from the end faces of the housing, and
Equipped with
The plurality of contact detection sensors project from the end face by the same length at the position where the circumference centered on the indenter is divided by a substantially equidistant distance.
The distance to the tip of the indenter protruding outward from the end face is longer than the length of the plurality of contact detection sensors protruding from the end face.
When the housing is operated so as to push the indenter into the subject, the time difference between the pushing speed of the indenter into the subject and the time when the plurality of contact detection sensors detect contact with the subject. Using the above, the inclination of the housing in the pushing direction with respect to the subject is calculated, and the amount of pushing of the indenter at the time when one of the contact detection sensors first contacts the subject is calculated by using the inclination. A push-in test device that calculates the softness value of the subject using the push-in amount and the detection value detected by the force sensor at the time point. The indentation test apparatus according to claim 1 or 2 .
An indentation test device in which the contact detection sensor has a pin shape. The indentation test apparatus according to any one of claims 1 to 3 .
A push-in test device including a vibrating body whose vibration state changes when the contact detection sensor comes into contact with the subject.

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