JPH0827227B2 - Surface hardness measuring instrument for fruits and vegetables and method for measuring surface hardness of fruits and vegetables - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface hardness measuring device for fruits and vegetables, and more particularly to a surface hardness measuring device for fruits and vegetables for measuring the surface hardness of soft fruits and vegetables which are easily scratched by being pressed. is there.

[0002]

2. Description of the Related Art Conventionally, in order to measure the surface hardness of soft fruits and vegetables which tend to be pressed and scratched, a method for measuring mechanical characteristics of fruits and vegetables by a vibration excitation method has been used.

In this method of measuring the mechanical characteristics of fruits and vegetables by the vibration excitation method, a vibrating section for vibrating the fruits and vegetables and a detecting section for detecting the vibrations by the vibrating section are separated, and It is designed to measure the wave propagation characteristics.

This surface vibration characteristic is evaluated mainly by the peak frequency of the power spectrum or the shift amount of the entire spectrum, and is used as an index of softening accompanying the maturity of fruits and vegetables. The correspondence between the measured power spectrum and the surface hardness of fruits and vegetables is as follows. (I) The higher the peak frequency of the measured power spectrum is, the higher the surface hardness of fruits and vegetables is (harder). (Ii) When observing the change in surface hardness with ripening of the same fruits and vegetables, it was confirmed that the peak hardness gradually shifts to the lower frequency side, and thus the surface hardness decreases, that is, becomes softer with ripening. Has been done.

[0005]

However, in such a conventional surface hardness measuring instrument for fruits and vegetables by the vibration excitation method,
There are the following problems. (1) Correct propagation characteristics cannot be obtained without considering the size of fruits and vegetables. (2) Since the vibrating section and the detecting section need to be brought into close contact with a wide portion of the fruit and vegetables, the vibrating section and the detecting section may be pressed too strongly against the fruit and vegetables, and the tissue may be damaged. (3) Since it is necessary to observe the vibration of the whole fruits and vegetables,
The wave propagation characteristics are likely to change depending on how the fruits and vegetables are fixed to the surface hardness measuring instrument, and thus the surface hardness measurement value is likely to change. (4) Since the mechanical characteristics of the vibration unit and the detection unit are also included in the data, it is necessary to use equipment with uniform characteristics.

[0006] The object of the present invention is to solve the above problems, and protects fruits and vegetables without pressing and scratching the fruits and vegetables, without being influenced by the size of the fruits and vegetables, and accurately by a simple structure. An object of the present invention is to provide a surface hardness measuring instrument for fruits and vegetables and a method for measuring the surface hardness of fruits and vegetables, which can measure the surface hardness of fruits and vegetables.

[0007]

In order to solve the above-mentioned problems, the invention of a surface hardness measuring instrument according to claim 1 provides a displacement imparting means (5) for locally displacing (x _i ) the fruit or vegetable to be measured. ), A displacement detecting means (3) for detecting the displacement (xi), and a reaction force detecting means (17) for detecting a local reaction force (p ₀ ) of the fruits and vegetables caused by the given displacement (xi). ) And the detected displacement (x _i ) and the detected reaction force (p ₀ ) as inputs, the local mechanical transfer function (H (s) = P ₀ (s) / X _i (s)) of the fruit and vegetables An anti-resonance frequency (fn) on the gain characteristic is calculated, and an analyzing means (23) for analyzing the surface hardness of the fruit or vegetables based on the correlation between the anti-resonance frequency (fn) and the surface hardness of the fruit or vegetables. To be done.

In the present invention, preferably, the displacement applying means has a contactor for contacting the fruit and vegetables, and the tip of the contactor is spherical.

[0009] invention the surface hardness measurement method according to claim 2 gives a displacement (x _i) in the local measurement target fruits or vegetables, the reaction force of the fruits or vegetables of the local generated by the given displacement (xi) (P ₀ ), and based on the displacement (x _i ) and the reaction force (p ₀ ), the local mechanical transfer function (H (s) = P ₀ (s) / X _i (s) of the fruits and vegetables. )) The antiresonance frequency (fn) on the gain characteristic is calculated, and the surface hardness of the fruit and vegetables is analyzed from the correlation between the antiresonance frequency (fn) and the surface hardness of the fruit and vegetables.

[0010]

According to the invention of the surface hardness measuring instrument described in claims 1 to 3, the displacement imparting means (5) locally applies a displacement (x _i ) to the fruit or vegetable (13) to be measured. ,
This displacement (x _i ) is detected by the displacement detecting means (3). When the displacement (x _i ) is given, a reaction force (p ₀ ) is locally generated in the fruits and vegetables (13). This reaction force (P ₀ ) is detected by the reaction force detection means (17). The detected displacement (x _i ) and reaction force (p ₀ ) are input to the analysis means (23). The analysis means (23), based on the input displacement (x _i ) and reaction force (p ₀ ), produces fruits and vegetables (1
3) Local mechanical transfer function (H (s) = P ₀ (s) /
The anti-resonance frequency (fn) on the gain characteristic of X _i (s) is calculated, and the surface hardness of the fruit or vegetable is analyzed from the correlation between the anti-resonance frequency (fn) and the surface hardness of the fruit or vegetable. Here, the measurement principle in the present invention will be described as follows. When a sinusoidal displacement (x _i ) is applied to the local area of the vegetable or fruit (13) to be measured while sweeping the frequency, the mass at the frequency determined by the constants of each element of the vibration system including the local area of the vegetable or fruit (13) to be measured is measured. The amplitude of the force applied to m increases or decreases. Where k is the elastic constant,
c represents a viscosity constant and is a parameter corresponding to the elastic modulus and the viscosity, respectively. k ₁ is a mechanical element on the measuring instrument side, k
₂ and c represent elements on the sample side. m is the sum of the masses of the detection part of the load detector and the part related to the vibration of the sample. x _i is the applied displacement, x is the displacement of the mass, p ₀ is the output of the load detector (that is, the reaction force of the fruit and vegetables), and each is a function with time as a variable. The equation of motion for the mass m of this dynamic system is expressed as the following equation. ^{_{m · d 2 x / dt 2}} = k 1 (x i -x) -k 2 x-c · dx / dt ...... (1) p 0 = k 1 (x i -x) ...... (2) then With respect to the equations (1) and (2), when Laplace transform is performed when the initial value is zero, It is expressed as However, s = jω (ω is an angular frequency and j is an imaginary unit), and P ₀ and X _i are Laplace transforms of p ₀ and x _i . H (s) is the displacement X _i given to the dynamic system
Is called, and the resulting expansion / contraction force of the spring k ₁ , that is, the reaction force P ₀ of the fruit (13) is output, and is called the transfer function of the dynamic system. The transfer function H (s) has a form in which the oscillating quadratic element is combined with the denominator and the numerator, and T and ζ are called the time constant and damping rate of the element indicated by the subscripts, respectively. The transfer function H (s) is derived by calculating the input / output ratio using the displacement x _i as an input and the reaction force p ₀ as an output. There are various methods for deriving the transfer function H (s), but instead of directly obtaining the function, FFT (Fast Fourier Transform) of the input / output signal is performed to calculate the frequency component of the input / output of the frequency. Generally, the frequency characteristic is obtained. The servo analyzer 23 is used as the analysis means for performing these calculations, and the servo analyzer 23 can easily obtain the frequency characteristic of the transfer function H (s). The servo analyzer 23 is generally used to analyze the input / output relationship of the control system in the frequency domain. Here, it should be understood that the task of obtaining the transfer function itself is not important, but what is known from the frequency characteristic of the transfer function (that is, the hardness index) is important. This transfer function H (s) is s = j
By substituting ω and rewriting it in polar coordinates, it is expressed by the product of the function representing the amplification factor and the function representing the input / output phase difference,
Generally, the common logarithm of the amplification factor is called a gain, and the input / output phase difference expressed by an angle is called a phase, which is used when expressing frequency characteristics in the Bode diagram. The gain of the transfer function H (s) is set as ωT ₁ = Ω ₁ and ωT ₂ = Ω ₂ , and the common logarithm is represented by Log as follows: Log | H (ω) | = Log {1-Ω ₁ ² ) ² + (2ζ ₁ Ω ₁ ) ² } -Log {1-Ω ₂ ² ) ² + (2ζ ₂ Ω ₂ ) ² } (6) Therefore, on the Bode diagram, At ω = T ₂ ^{−1 and} at ω = T ₂ ⁻¹ . T ₂ is a normal resonance point where the force amplitude shows a maximum, whereas T ₁
Is called the anti-resonance point because it is the minimum point of the amplitude.
Ζ in the equation (4) represents the sharpness of resonance at ω = T ₁ ⁻¹ and T ₂ ^−1. The smaller ζ is, the narrower the width of the resonance is, and the sharper the resonance is, the larger the gain is obtained. (7) As is apparent from equation is the square of the elastic constant k2 antiresonance frequency f _n of the fruits or vegetables (13) from the proportional, the use of anti-resonance frequency f _n to the hardness index of the fruit or vegetable (13) You can The anti-resonance frequency fn is defined as the strength of the transfer function, that is, the frequency at which the power spectrum theoretically becomes zero in the definition in control engineering. The anti-resonance frequency fn is determined by the dynamic system of the fruit and vegetables 13 and the dynamic system of the measuring instrument.
Is a value that reflects the mechanical characteristics of the fruits and vegetables 13. It can be considered that the reaction force (that is, hardness) that is felt when the local portion of the fruits and vegetables 13 is pushed slowly (that is, when the displacement speed is slow) depends on the elastic constant. In this case, "slowly" can be thought of as the speed at which humans normally touch objects. Furthermore, what corresponds to the elastic constant is the gradient of the force-deformation curve (that is, the breaking gradient) when the pulp of the fruit and vegetables 13 is locally compressed. It is clear that hardness is related to the elastic constant because there are many documents that report the relationship. Therefore, the elastic constant and the anti-resonance frequency f
From the relationship with n, it can be considered that there is a correlation between the anti-resonance frequency fn and the sense of hardness. However, the absolute amount of anti-resonance frequency and the absolute amount of perceptual hardness do not always have a one-to-one correspondence. The reason is that it is not possible at present to define the absolute amount of sensation, and academically it has not been achieved yet. The anti-resonance frequency fn is merely an index corresponding to the relative comparison of hardness. Next, regarding the relationship between the dynamic elastic modulus and the anti-resonance frequency, the elastic constant is a term used when expressing the static characteristics of a dynamic system. The equivalent is defined as the dynamic modulus. As shown in FIG. 2, the relationship between the anti-resonance frequency and the elastic constant (the breaking gradient in the case of fruits and vegetables) is the relationship between the anti-resonance frequency and the dynamic elastic modulus using a model sample whose dynamic elastic modulus is known. Is represented. The relationship between the actual elastic constant of the pulp ((breaking strength) and the anti-resonance frequency is shown in Fig. 4 regarding the breaking strength and the anti-resonance frequency. As described above, there is a correlation between the anti-resonance frequency fn and the hardness sensation. The anti-resonance frequency f _n
The surface hardness of 3) can be used as an index of hardness.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

The inventors of the present invention applied a local minute random vibration containing a frequency component of 20 Hz to 200 Hz to a surface of a fruit or vegetable as a sample by a vibration exciter. By this, it was found that the local mechanical characteristics of the surface of fruits and vegetables can be represented by anti-resonance frequency by detecting the displacement / contact pressure characteristics of fruits and vegetables and calculating the transfer function of the dynamic system. By calculating the transfer function of the dynamic system in this way, the influence of the mechanical characteristics of the vibration unit and the detection unit is eliminated.

At the same time, the inventors of the present invention found a correlation between the ripeness and freshness of fruits and vegetables, in particular fruits and vegetables such as tomatoes having a thin and soft skin, and the mechanical properties of the surface, and arrived at the present invention. It was

In the present invention, by measuring the mechanical properties of the surface of fruits and vegetables with a minute contact pressure, it is possible to obtain an index of hardness without scratching even soft fruits and vegetables such as tomatoes that are apt to be pressed and scratched. Provided is a surface hardness measuring instrument for fruits and vegetables capable of performing a so-called non-destructive quality evaluation method, and a method for measuring the surface hardness of fruits and vegetables.

Since the hardness of fruits and vegetables is an index of ripeness and freshness, the surface hardness measuring instrument for fruits and vegetables according to the present invention and the method for measuring surface hardness of fruits and vegetables are
High utility value at all stages of harvesting, distribution and processing of fruits and vegetables.

A preferred embodiment of the surface hardness measuring instrument for fruits and vegetables and the surface hardness measuring method for fruits and vegetables according to the present invention will be described with reference to FIG.

FIG. 1 shows a surface hardness measuring instrument for fruits and vegetables which should be called a surface hardness measuring system for fruits and vegetables.

A displacement gauge 3 and a vibrator 5 are set on the base 1. Further on the base 1, there is a fine movement device 7
The support member 9 is fixed.

The support member 9 has a sample of fruits and vegetables 1
A sample installation table 11 for mounting or setting 3 is provided. The sample setting table 11 has a simple structure, and preferably has an L-shaped cross section, on which the fruits and vegetables 13 are placed. In FIG. 1, this vegetable 13 is, for example, a tomato.

The fine movement device 7 can precisely position the fruits and vegetables 13 by moving the fruits and vegetables 13 placed on the sample installation table 11 in the horizontal direction along the arrow X direction by a small amount. .

The displacement meter 3 includes a vibrating rod 1 which penetrates the vibrating device 5.
5 is mechanically connected to the vibrating bar 15, and a small amount of horizontal displacement caused by the vibration locally applied to the fruit 13 is measured.

The vibrating rod 15 penetrating the vibration exciter 5 is
Also referred to as a vibrator oscillator, it is a displacement imparting means for imparting a displacement to the fruits and vegetables 13. This exciting rod 15 has
A load cell 17 is attached. A contact 33 is provided at the tip of the load meter 17.

The tip of the contact 33 is preferably spherical or hemispherical. The reason why the tip of the contactor 33 is formed into a spherical shape or a hemispherical shape in this way is to give a minute vibration to a local portion of the fruit and vegetables 13 by a minute contact pressure as described above.

The minute vibrations are local and minute random vibrations that preferably include frequency components up to 20 to 200 Hz, and are applied to the skin or surface of the fruits and vegetables 13 by the vibrator 5. This small random vibration
It is a combination of sine waves with a certain range of frequencies at a certain ratio.

As described above, the propagation characteristic is changed depending on how the fruits and vegetables 13 are fixed to the sample setting table 11 by giving a slight vibration to the local portion of the fruits and vegetables 13 with a minute contact pressure. The drawbacks can be eliminated. In addition, by adjusting the setting position of the fruits and vegetables 13 in the X direction by the fine movement device 7, the surface hardness of the fruits and vegetables 13 can be measured regardless of the size of the fruits and vegetables 13.

The load meter 17 is also called a load detector. The load meter 17 is a reaction force detecting means for detecting a reaction force due to a displacement generated on the skin or surface of the fruits and vegetables 13 when a minute vibration is applied to a local portion of the fruits and vegetables 13 by a minute contact pressure. Is.

Next, the calculation and measurement processing circuit 19 will be described.

A calculation / measurement processing circuit 19 is electrically connected to the displacement meter 3, the vibrator 5, and the load meter 17 described above.

An amplifier 21 is connected to the load meter 17, and the amplifier 21 is connected to a servo analyzer 23 and a voltmeter 25. The voltmeter 25 connects the contact 33 to the fruits and vegetables 13
It is provided for reference when adjusting the offset value of the contact pressure when it is brought into contact with the fine movement device 7.

The servo analyzer 23 is also called a digital spectrum analyzer, which is a displacement signal generator 27.
It is connected to the. The displacement signal generator 27 is connected to the vibration exciter 5 via a power amplifier 31.

As a result, the displacement signal generator 27 gives the displacement signal SD to the power amplifier 31 based on the signal from the servo analyzer 23. And this power amplifier 31
Is adapted to amplify the displacement signal SD and give it to the exciter 5. The vibration exciter 5 receives the amplified displacement signal SD.
Based on the load cell 17 and the contactor 33
Displacement can be given locally in 3.

Further, the displacement meter 3 is connected to the servo analyzer 23 via an amplifier 31. As a result, the displacement meter 3 measures the displacement generated in the fruits and vegetables 13, the signal PS of the measured displacement is amplified by the amplifier 29, and can be input to the servo analyzer 23.

Next, an experimental example in the embodiment of the surface hardness measuring instrument for fruits and vegetables of the present invention shown in FIG. 1 will be described. Experimental Example 1 First, the characteristics of a cylindrical model sample (simulated sample, not shown) were measured using the surface hardness measuring instrument for fruits and vegetables shown in FIG. 1 prior to measuring the surface hardness of the fruits and vegetables 13.

The cylindrical model sample is a cylindrical model made of silicone rubber in which the hardness is controlled by adjusting the amount of the curing agent, and the diameter is 20 mm and the length is 30 mm, for example.

The conditions for measuring the surface hardness of the model sample are as follows.

The amplitude control voltage applied from the power amplifier 31 of FIG. 1 to the exciter 5 is, for example, 0.02 V. By applying the amplitude control voltage to the exciter 5, the exciter 5 is loaded with a load meter. Random vibration having a maximum amplitude of 3 micrometers was applied as a displacement to the local portion of the model sample via 17 and the contact 33.

The offset output voltage of the reaction force or contact pressure applied to the servo analyzer 23 from the load meter 17 also called a load detector via the amplifier 21 is 2V to 4V, and this offset output voltage is the load meter. 1
Corresponding to a contact pressure of 3 to 8 gf at 7.

Further, the frequency of random vibration by the vibrator 5 is set to 20 to 200 Hz, and the room temperature (20 °
C) The measurements were made under

As a reference value for hardness, a dynamic viscoelasticity measuring instrument (manufactured by Toyo Seiki Co., Ltd.) for microscopic bodies was used, and longitudinal vibration mode, frequency 2 Hz, and amplitude 40 micrometer were set.
The dynamic elastic modulus measured at room temperature (20 ° C) was used.

The results of the above experiment are shown in FIG.

FIG. 2 shows the relationship between the anti-resonance frequency and the dynamic elastic modulus obtained as described above.
The anti-resonance frequency means a frequency at a place where resonance does not occur.

Dynamic elastic modulus of 1 × 10 ⁶ to 13 × 10 ⁶
The antiresonance frequency is 22 Hz to 61 Hz in the model sample in the range of dyn / cm2 (cm2 means square cm).
It was confirmed that there was a logarithmic relationship between the two, and that there was a change in the range.

Next, based on the experimental example 1, the experimental example 2 was performed. Experimental Example 2 Using the surface hardness measuring device for fruits and vegetables shown in FIG.
An experiment for identifying the hardness of a commercially available tomato (various name: Momotaro) as No. 3 was performed as follows.

First, 21 fruits and vegetables 13 were touched by hand and divided into three groups A, B and C having different hardness (surface hardness) as shown in FIG.

FIG. 3 shows the measurement items of the anti-resonance frequency, the breaking gradient, and the breaking force for each of the groups A, B, and C.

The breaking gradient and breaking force are determined by the following breaking test. First, divide the sample into two equal parts from the center,
Place the cut surface down on the sample table. Then, the plunger is vertically inserted into the portion where the surface hardness is measured. From the contact of the plunger with the sample to the displacement of 1 mm,
The rate of change of load with respect to displacement is called "breaking gradient", and the maximum load at the time when the peel peels is called "breaking force".

The rupture slope of the measurement items is a hardness index corresponding to the dynamic elastic modulus obtained in Experimental Example 1.

The hardest group A and the group A
For Group B, which is softer than that of No. 1, the equatorial portion of each of the fruits and vegetables 13 was measured at two locations using the surface hardness measuring instrument for fruits and vegetables shown in FIG. Further, in order to obtain an index of hardness at the equator of each fruit and vegetable 13, a breaking test was performed on the above two measurement points to obtain a breaking force.

On the other hand, the medium hardness group C was left in the environment of 20 ° C. for 5 days for softening, and then the two equator parts of each of the fruits and vegetables 13 of the group C were also shown in FIG.
Of the fruits and vegetables were subjected to a breaking test.

FIG. 4 is a graph showing the relationship between the anti-resonance frequency shown in FIG. 3 and the breaking gradient.

In FIG. 4, when a plunger (not shown) was pushed into the equator of the fruit and vegetables 13 based on the above-mentioned breaking test, the breaking gradient (gf / gf / mm) and the anti-resonance frequency (Hz). In the relationship of FIG. 4, a strong correlation of 0.899 was obtained between the breaking slope and the anti-resonance frequency. That is, it was found that the relationship between the anti-resonance frequency and the breaking slope was almost reproducible.

That is, it was confirmed that the anti-resonance frequency increased as the dynamic elastic modulus, which is the hardness index of the model sample, increased. Also in the experimental example using fruits and vegetables, as shown in FIG. 4, it was confirmed that the anti-resonance frequency increases as the breaking gradient (index corresponding to the dynamic elastic modulus) increases.

Moreover, as shown in FIG. 4, it was confirmed that there is a strong correlation between the antiresonance frequency and the breaking gradient.

As described above, the mechanical properties of fruits and vegetables are an important index for measuring the ripeness and texture of the fruits and vegetables. Particularly, the mechanical properties of the fruits and vegetables having a soft surface (the surface hardness of the fruits and vegetables) are measured as By obtaining the anti-resonance frequency from the given displacement and the reaction force (contact pressure) due to the displacement, the surface hardness of fruits and vegetables can be easily measured in an intact state.

The features of the embodiment of the present invention are as follows. (1) By attaching the load meter 17 also called a load detector to the vibrator 5 also called a vibrator, the vibrator 5 and the load meter 17 are located at almost the same location, and the fine movement device 7 makes X
You can adjust the position of fruits and vegetables 13 along the direction.
Fruit and vegetables 1 without being affected by the size of
The surface hardness of 3 can be measured. (2) The contact pressure of the contact 33 is very small (for example, several gf)
Therefore, it is possible to measure the surface hardness without pressing the fruits and vegetables 13. (3) Since the energy of the applied vibration is very small (for example, an amplitude of a few micrometers and the maximum frequency is 200 Hz), the vibration is attenuated at locations other than the measurement location, so that the propagation characteristics of the entire fruits and vegetables 13 are irrelevant. For this,
No special jig for fixing the fruits and vegetables 13 is required. (4) By describing the mechanical characteristics by the transfer function, which is the ratio of input and output, the characteristics of the surface hardness measuring instrument for fruits and vegetables can be excluded. That is, the surface hardness of fruits and vegetables can be measured regardless of the characteristics of the surface hardness measuring instrument for fruits and vegetables. (5) Since the contact surface of the contactor is spherical or hemispherical and the area thereof is minute, it is not easily affected by each variation in contact with the fruit or vegetable 13 as the object.

The present invention is not limited to the above embodiment.

[0057]

As described above, according to the present invention, the fruits and vegetables are protected without being pressed against the fruits and vegetables, and are not affected by the size of the fruits and vegetables, and the surface hardness of the fruits and vegetables can be accurately measured by a simple structure. Can be measured.

[Brief description of drawings]

FIG. 1 is a block diagram showing a preferred embodiment of a surface hardness measuring instrument for fruits and vegetables according to the present invention.

FIG. 2 is a diagram showing a relationship between an anti-resonance frequency and a dynamic elastic modulus.

FIG. 3 is a diagram showing an anti-resonance frequency, a breaking gradient, and a breaking force in each group of experimental examples.

FIG. 4 is a diagram showing a relationship between an anti-resonance frequency and a breaking gradient.

[Explanation of symbols]

 1 base 3 displacement meter 5 vibrator (displacement imparting means) 7 fine movement device 13 fruits and vegetables (sample) 17 load meter (reaction force detecting means) 19 arithmetic measurement processing circuit

Claims (2)

[Claims] 1. A local displacement (x _i ) of a vegetable or fruit to be measured
And a displacement detecting means for detecting the displacement (xi), and a reaction force detecting means for detecting a local reaction force (p ₀ ) of the fruits and vegetables caused by the given displacement (xi). , The detected displacement (x _i ) and the detected reaction force (p ₀ ) are input, and the local mechanical transfer function (H (s) = P of the fruits and vegetables is input.
The anti-resonance frequency (fn) on the gain characteristic of ₀ (s) / X _i (s) is calculated, and the surface hardness of the fruit or vegetable is analyzed from the correlation between the anti-resonance frequency (fn) and the surface hardness of the fruit or vegetable. A surface hardness measuring instrument for fruits and vegetables, comprising: 2. The local displacement (x _i ) of the fruit or vegetable to be measured
And a local reaction force (p ₀ ) of the fruits and vegetables caused by the given displacement (xi) is detected, and the displacement (x
_i ) and reaction force (P ₀ ) based on the local mechanical transfer function (H (s) = P ₀ (s) / X of the fruits and vegetables.
_{It is} characterized in that the anti-resonance frequency (fn) in the gain characteristic of _i (s) is calculated, and the surface hardness of the fruit or vegetable is analyzed from the correlation between the anti-resonance frequency (fn) and the surface hardness of the fruit or vegetable. Method for measuring surface hardness of fruits and vegetables.