JPH11183443A - Measuring method for ripeness degree of fruit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring method, for the ripeness degree of a fruit, in which the ripeness degree of the fruit in which the elastic modulus of sarcocarp is changed as a tomato, a kiwi fruit, an apple or the like ripens is measured nondestructively. SOLUTION: A vibration whose frequency (f) is changed sequentialliy is applied to a fruit 2, to be measured, by a vibration generator 4. The magnitude and the phase of the vibration of the fruit 2 at the applied vibration frequency (f) are measured sequentially. The maximum value of a peak in the measured vibration magnitude in which the phase difference between an applied vibration phase and a measured vibration phase is situated between -270 deg.±90 deg. is found. An elastic coefficient E is found by E=m.EXP(2/3).f.EXP (2) on the basis of the frequency (f) of the applied vibration indicating the maximum value and on the basis of the weight (m) of the fruit 2. The ripenss degree of the fruit 2 is measured on the basis of the value of the elastic coefficient E.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for non-destructively measuring the ripeness of fruits, such as tomatoes, kiwifruits and apples, whose pulp elasticity changes as they ripen. is there.

[0002]

2. Description of the Related Art The Magness-Taylor fruit hardness tester is widely used as an apparatus for measuring the degree of maturity from the hardness of fruit pulp. The fruit hardness tester has the drawback that the plunger penetrates the fruit under specified conditions, and the stress is measured to measure the fruit hardness. It was appropriate.

[0003] In order to solve this drawback, nondestructive methods for measuring the ripeness of fruits, such as a method for measuring a change in fruit color and a method for measuring the hardness of the fruit surface, have been tried.
However, the method of measuring the change in the color of a fruit cannot be applied to a fruit such as kiwifruit or pear that does not change color as it ripens. In addition, since there is no device capable of measuring the hardness of the surface in a non-destructive manner, the hardness is determined solely by human hands, and there is a problem that objective measurement cannot be performed.

[0004] In order to solve such a problem, utilizing the fact that the hardness of fruit pulp has a strong correlation with the elastic modulus,
Abbott et al. (1968a. Food Technol. 22) tried to measure the pulp hardness of fruits by measuring the natural frequency of the fruits by applying vibrations of various cycles to the fruits and calculating the elastic modulus.
(5): 635-646) and Finney et al. (1972. J. Texture studies)
2 (1): 62-74). Further Cooke
(1972. Trans of ASAE.15 (6): 1075-1080) theoretical analysis of fruit vibration was performed, and the natural frequency f of fruit and the weight m of fruit obtained from the measurement were used to determine the elastic modulus E of the pulp. E = m
It was reported that EXP (2/3) ・ f ・ EXP (2) can be calculated.

[0005]

However, this elastic modulus
In order to obtain E, the natural frequency f of the fruit must be obtained. However, conventionally, the natural frequency is determined by human eyes by detecting the vibration of the fruit and outputting it to an XY plotter or the like. Therefore, it was not a practical technique for measuring the degree of maturity.

[0006]

According to the present invention, there is provided a method for measuring ripeness of a fruit, which comprises calculating a frequency response function between a vibration applied to the fruit and a vibration of the fruit, and having a phase of -27.
When the angle is between 0 ° and ± 90 °, the maximum value of the peak of the measured vibration of the fruit is obtained, and the maximum value is recognized as the natural frequency. ADVANTAGE OF THE INVENTION According to this invention, the ripeness of a fruit can be measured nondestructively at high speed and accurately by automatically recognizing the natural frequency of a fruit.

[0007]

According to the first aspect of the present invention, a vibration whose frequency f changes sequentially is applied to a fruit to be measured, and the magnitude and phase of the vibration of the fruit at each applied vibration frequency f are sequentially measured. Then, a maximum value of a peak value of the magnitude of the measured vibration is determined in which a phase difference between the phase of the applied vibration and the phase of the measured vibration is located between −270 ° ± 90 °. From the applied vibration frequency f indicating the maximum value and the weight m of the fruit, the elastic modulus E is calculated as E = m · EXP (2/3) ·
It is characterized in that the ripeness of the fruit is measured by f · EXP (2) and the value of the elastic coefficient E is measured.

(Embodiment) The first aspect of the present invention will be described below.
The embodiment of the invention described in FIG.
This will be described with reference to FIGS. FIG. 1 shows a gain characteristic of a frequency response function of a fruit. From FIG. 1, it can be confirmed that many peaks exist. These peaks are referred to as a primary peak and a secondary peak in order from the lowest frequency. Abbott et al. Reported that the natural vibration that greatly affects the fruit pulp hardness is a secondary peak (hereinafter, natural frequency). I have. As shown in FIG. 1, the natural frequency shifts from immature to overripe and low-frequency as the fruit softens. FIG. 2 shows the relationship between the natural frequency and the phase. Even if the natural frequency changes, its phase is largely distributed around -270 °. This can be explained by vibration theory.

That is, since the peak is generated by the second-order lag element, the phase of the peak is advanced by 90 ° in the direction of the low frequency and delayed by 90 ° in the direction of the high frequency around the peak frequency. When there are a large number of first and second order peaks in the frequency response function, if the peaks are sufficiently separated, each peak may be considered as a linear combination of second order delay elements. At this time, since there is a phase difference of 180 ° between the peaks,
The phase of the next peak frequency occurs at -90 °, and the frequency of the second peak occurs at -270 °, further delayed by 180 °. Actually, the phase of the secondary peak varies due to an error at the time of measurement or the like. Therefore, in practice, it may be determined that the secondary peak exists in the range of -270 ° ± 90 °. The maximum value of the gain peak within this range is the fruit natural frequency.
The elastic modulus E of the fruit is calculated from the natural frequency and the weight of the fruit thus obtained, and the ripeness of the fruit can be measured.

FIG. 3 shows a maturity measuring apparatus using the above measuring method. In FIG. 3, a weight scale 3 is for measuring the weight of the fruit 2 to be measured, and is connected to the microprocessor 11. The vibration generator 4 is a vibration source for giving a predetermined vibration to the fruit 2 to be measured, and is composed of, for example, a permanent magnet and an electromagnetic coil, and converts a given electric signal into mechanical vibration. The vibration generator 4 includes
A gantry 6 for mounting the fruit 2 to be measured is mechanically connected. The vibration signal given to the fruit is given to the vibration generator 4 via the power amplifier 7 by the signal generator 8 connected to the microprocessor 11. The laser Doppler vibrometer 1 is placed immediately above the fruit 2 to be measured. The laser Doppler vibrometer 1 detects the vibration of the surface of the fruit 2 in a non-contact manner and outputs a beat signal proportional to the speed. The demodulator 9 converts the output of the laser Doppler vibrometer 1 into a vibration signal and inputs the vibration signal to the FFT 10. The gantry 6 is provided with vibration detecting means 5 such as an acceleration sensor for detecting vibration applied to the fruit. The output of the vibration detecting means 5 is F
Input to FT10. In the FFT 10, the signal from the demodulator 9 and the signal from the vibration detection means 5 are each subjected to fast Fourier transform and output to the microprocessor 11. The display device 12 is connected to the microprocessor 11 and displays a measurement result.

FIG. 4 shows a measurement procedure performed by the microprocessor 11 in the maturity measuring device shown in FIG. First, the fruit 2 is put on the weight scale 3 and the weight m of the fruit 2 is input to the microprocessor 11. Thereafter, the fruit 2 is placed on the gantry 6, and the microprocessor 11 instructs the signal generator 8 to generate a sine wave at a first frequency (for example, 20 Hz). The oscillation output of the signal generator 8 is sent to the vibration generator 4 via the power amplifier 7 to vibrate the fruit 2 on the gantry 6. At this time, the vibration of the gantry is detected by the acceleration sensor 5 and input to the microprocessor 11 via the FFT 10. At the same time, the surface vibration of the fruit 2 is detected by the laser Doppler vibrometer 1 and input to the FFT 10 via the demodulator 9. The output of the FFT 10 is input to the microprocessor 11. The microprocessor 11 calculates a frequency response function based on the input from the FFT 10. In this manner, the microprocessor 11 commands the signal generator 8 to output a sine wave having an appropriate frequency interval up to a second frequency (for example, 3 KHz) higher than the first frequency, and inputs the input from the FFT each time. The frequency response function is calculated based on the frequency response function.

Next, the microprocessor 11 detects the peak value of the frequency response function whose phase information is in the range of -270 {± 90} in the calculated frequency response function. From the obtained peak values, the frequency f at which the gain becomes maximum is detected. The detected frequency f and weight m
Then, the elastic modulus E is calculated as E = m2 / 3 · f2. The elastic modulus E calculated in this way is displayed on the display device 12. Although a sine wave is used as the excitation signal in this example, a similar result can be obtained by using a random wave or a swept sine wave in a band including the first frequency and the second frequency.

[0013]

As described above, according to the method for measuring the ripeness of a fruit of the present invention, the fruit is destroyed by detecting the natural frequency of the vibrated fruit and calculating the elastic modulus of the flesh from the fruit weight. It is possible to provide an instrument for measuring the ripeness of fruits and vegetables, which can quickly and accurately measure the ripeness of fruits without performing the method.

[Brief description of the drawings]

FIG. 1 is a diagram showing gain characteristics of a frequency response function of a fruit;

FIG. 2 is a diagram showing a relationship between a natural frequency and a phase of a fruit.

FIG. 3 is a block diagram showing a ripeness measuring apparatus to which the method for measuring ripeness of fruit of the present invention is applied.

FIG. 4 is a flowchart showing a measurement procedure performed by a microprocessor in the same maturity measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser Doppler vibrometer 2 Fruit to be measured 3 Weight scale 4 Vibration generator 5 Vibration detection means 6 Mount 7 Power amplifier 8 Signal generator 9 Demodulator 10 FFT 11 Microprocessor 12 Display device

Claims (1)

[Claims] 1. A vibration whose frequency f changes sequentially is applied to a fruit to be measured, and the magnitude and phase of the vibration of the fruit at each of the applied vibration frequencies f are sequentially measured, and the phase of the applied vibration and the measurement are measured. The maximum value of the peak of the magnitude of the measured vibration whose phase difference between the phase and the applied vibration is located between -270 ° ± 90 ° is determined, and the applied vibration frequency f indicating the maximum value is obtained. And the elastic modulus E from the weight m of the fruit,
E = m ・ EXP (2/3) ・ f ・ EXP (2)
And measuring the ripeness of the fruit according to the value of (1).