JPH1019813A - Method and device for automatically selecting vegetables and fruits using nuclear magnetic resonance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for automatically selecting vegetables and fruits using a nuclear magnetic resonance which can select vegetables and fruits with high precision even when measurement is made using the nuclear magnetic resonance while moving a specimen. SOLUTION: A high frequency magnetic field and a slope magnetic field in the same direction as a conveying direction of a specimen are applied to the specimen, whereby a slice face which is vertical to a conveying direction of the specimen, and which has a specific thickness in the conveying direction is selectively excited, and when a nuclear magnetic resonance signal from its are is obtained, a static magnetic field correcting magnetic field is applied so as to have a strength proportional to the product of three items of strength G of the slope magnetic field applied to the specimen, an applying time t of the slope magnetic field and a conveying speed v of the specimen, and to have a magnetic field distribution which is substantially same as and uniform in a static magnetic field in the area where the specimen is moved during measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for automatically sorting fruits and vegetables such as watermelons and melons by non-destructively inspecting the internal quality of fruits and vegetables using nuclear magnetic resonance.

[0002]

2. Description of the Related Art In recent years, a method of automatically sorting fruits and vegetables without using the experience of an experienced person has been introduced. The main purpose of the introduction is to quantify the criteria for grade selection to increase the reliability in the market, to be able to identify high quality ones, and to select grades according to the demands of the shipping destination And to rationalize the sorting operation.

[0003] In order to achieve such an object, a method of applying a shock to fruits and vegetables, detecting a shock wave emitted from the fruits and vegetables, analyzing the waveform, and performing a comprehensive grade judgment from a plurality of measurement items related to internal quality ( For example, JP-A-3-95455),
A method of observing the internal state by irradiating with X-rays has been proposed. However, the former cannot be said to be non-destructive, and the latter has a poor measurement accuracy and a bad impression in the market. At present, non-destructive inspection methods using nuclear magnetic resonance are becoming mainstream.

As this kind of inspection method, for example, Japanese Patent Laid-Open No.
No. 110358 discloses a method for measuring an internal cavity using the nuclear magnetic resonance phenomenon of protons in a watermelon. As an examination method using nuclear magnetic resonance, a nuclear magnetic resonance tomography apparatus (MRI) for image diagnosis in the medical field is well known, and the principle and configuration of such an apparatus are described in the document "N.
MR Medicine -Basic and Clinical- (Japan Magnetic Resonance Medical Association);
Maruzen 1991 ".

According to such an inspection method, a tomographic image inside the object to be inspected can be obtained with high resolution without destruction.
When applied to, for example, watermelon as a fruit or vegetable, the presence or absence of an internal cavity can be easily determined. However, in the method of performing such image diagnosis, usually, imaging takes time in units of minutes, thereby increasing the measurement cost per hour. Therefore, there is no practical use in selecting fruits and vegetables.

[0006] Under such circumstances, in the conventional inspection method using fruits and vegetables using nuclear magnetic resonance, two-dimensional image diagnosis is not performed, but the object to be inspected is a layered region having a certain thickness. And process the nuclear magnetic resonance signal from the cross section as a profile projected in a certain direction, and determine a cavity from the shape of the processed profile.

[0007] In an environment where a large amount of fruits and vegetables must be processed, such as a fruit sorting place, it is indispensable to increase the sorting speed in order to improve work efficiency. For example, in a large-scale watermelon sorting plant in Kumamoto Prefecture, 3 per day
After sorting up to 40,000 watermelons, they are packed and shipped. Therefore, for an automatic sorter applied to such a purpose, a large-scale rapid processing is required. In consideration of such points, for example, Japanese Patent Application Laid-Open No. 2-110360 discloses a method for automatically sorting fruits and vegetables in consideration of the movement of a test subject.

[0008]

However, a method has not yet been established which is capable of accurately sorting fruits and vegetables using nuclear magnetic resonance while transporting an object to be inspected by a conveyor or the like. is there.

The reason is that, when selectively exciting a layered region with respect to the object to be inspected, since the object to be inspected is moving, it is not possible to correctly excite the region to be previously excited. Is mentioned. More specifically, when a high-frequency magnetic field and a gradient magnetic field are applied to selectively excite a certain region of the object to be inspected conveyed at a high speed and a nuclear magnetic resonance signal from the region is observed, a high-frequency The movement of the test object during application of the magnetic field and the gradient magnetic field must be considered. This is because, when a nuclear magnetic resonance signal is to be selectively obtained from a certain region of the test object, as shown in the above-mentioned document, the frequency of the high-frequency magnetic field applied to the test object and the gradient magnetic field This is because the size needs to satisfy a certain relationship. This relationship is shown as follows. _{2πf = γΒ 0 + γG x (} 1) where f: frequency of the high-frequency magnetic field gamma: gyromagnetic ratio beta _0:磁速density of the static magnetic field G: gradient magnetic field strength x: is the position of the region to be measured. Further, in reality, since the region to be measured has a certain width Δx, the frequency f of the high-frequency magnetic field also has a width Δf corresponding thereto.

As described above, when the object to be inspected is moving, a method fundamentally different from observing a nuclear magnetic resonance signal from a stationary object to be inspected must be realized. On the other hand, in the conventional inspection method as disclosed in Japanese Patent Application Laid-Open No. 2-110360, the disturbance of the phase of the nuclear magnetic field resonance signal is corrected by adjusting the gradient magnetic field, and a plurality of excitation pulses are applied. In forming a high-frequency magnetic field, the displacement of the selective excitation surface due to the movement of the object to be inspected between pulses is merely prevented.

Therefore, even if a nuclear magnetic resonance signal of a moving test object is observed by the method described in the publication, a signal from a set area cannot be observed. The reason is that, although the time during which the high-frequency magnetic field and the gradient magnetic field are applied is short (usually several ms), the object to be inspected moves during this time. Specifically,
If the time for applying the high-frequency magnetic field and the gradient magnetic field is 10 msec, and the moving speed of the test object is 40 cm / sec, the test object moves 4 mm while applying the magnetic field. Therefore,
When a plane perpendicular to the moving direction of the test object is excited, a signal from a region having a thickness of 4 mm is lost. If the thickness of the area to be excited is 10 mm
If this is the case, a signal from an area near half of the area cannot be obtained.

The present invention has been made in consideration of the above-mentioned problems of the conventional automatic fruit and vegetable sorting method. Even when the subject to be inspected is moved and the sorting using nuclear magnetic resonance is carried out, the present invention is highly effective. An object of the present invention is to provide a method and an apparatus for automatically sorting fruits and vegetables using nuclear magnetic resonance capable of sorting fruits and vegetables with high accuracy.

[0013]

According to the automatic fruit and vegetable sorting apparatus of the present invention, a static magnetic field is formed on a conveyed test object, and a gradient magnetic field is superimposed on the static magnetic field. In the automatic fruit and vegetable sorting method for non-destructively inspecting the internal quality of a test object by detecting and processing nuclear magnetic resonance signals, the test object has the same orientation as the high-frequency magnetic field and the transfer direction of the test object. By applying a gradient magnetic field, a slice plane having a predetermined thickness in the transport direction perpendicular to the transport direction of the test object is selectively excited,
When attempting to obtain a nuclear magnetic resonance signal from the region, the intensity is proportional to the product of the intensity G of the gradient magnetic field applied to the test object, the application time t of the gradient magnetic field, and the transport speed v of the test object. The gist of the present invention is to apply a static magnetic field correction magnetic field that has the intensity I and that can have substantially the same and uniform magnetic field distribution as the static magnetic field in a region where the object moves during measurement. The intensity I of the nuclear magnetic resonance signal is required to satisfy the following relationship: I = a.G.v.t (-0.8 <a <-1.2).

According to the automatic fruit and vegetable sorting apparatus of the present invention, a static magnetic field is formed on a conveyed test object, a gradient magnetic field is superimposed on the static magnetic field, and a nuclear magnetic resonance signal emitted from the test object is generated. In an automatic fruit and vegetable sorting apparatus that non-destructively inspects the internal quality of a test object by detecting and processing, the intensity G of the gradient magnetic field applied to the test object, the application time t of the gradient magnetic field, and the transport speed of the test object a static magnetic field correction magnetic field coil having an intensity I proportional to the product of v and generating a magnetic field distribution that is substantially the same as the static magnetic field and uniform in a region where the test object moves during measurement. The gist is to become

In the above apparatus, a power supply for supplying a current to the static magnetic field correction magnetic field coil, a waveform storage unit for providing the power supply with a signal waveform for correcting the static magnetic field, and a timing for outputting the signal waveform And a pulse control unit that controls

That is, in the present invention, when measuring a moving test object, even if the moving test object is measured by applying a static magnetic field correction magnetic field which is a function of a gradient magnetic field, a moving speed and an application time, A nuclear magnetic resonance signal can be collected with the same accuracy as the measurement of a stationary test object.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. FIG. 1 shows an embodiment of an apparatus used in the automatic fruit and vegetable sorting method of the present invention. This automatic sorting apparatus is configured to determine the presence or absence of an internal cavity by collecting a nuclear magnetic resonance signal from protons inside a watermelon and analyzing the signal. In the following description, a central axis of a bore of a static magnetic field generator described later is defined as a z-axis, a vertically upward direction orthogonal to the z-axis is defined as a y-axis, and a horizontal direction is defined as an x-axis.

In FIG. 1, reference numeral 1 denotes a transport conveyor for transporting a watermelon 3 as an object to be inspected, and reference numeral 2 denotes a watermelon 3.
Tray for holding the sheet on the conveyor 1, reference numeral 4
Is a static magnetic field generator which is a measuring unit of the automatic sorting device,
The watermelon 3 conveyed by the conveyor 1 can pass through the static magnetic field generator 4. Therefore, the transport conveyor 1 and the dedicated tray 2 are made of a non-magnetic material and an insulator. More specifically, in the present embodiment, of the components of the conveyor 1, a portion arranged in the static magnetic field generator 4 and a portion passing therethrough are made of FRP, and the dedicated tray 2 is made of hard rubber. I have.

The static magnetic field generator 4 is composed of a plurality of superconducting coils in order to realize a high uniformity of the static magnetic field. The region in the static magnetic field generator 4 where the static magnetic field is generated is a cylindrical space, and is usually called a bore. The uniformity of the static magnetic field is adjusted until the inside of the 30 cm sphere at the center of the bore becomes about 10 ppm. The static magnetic field uses a relatively low magnetic field of 0.2 Tesla. This is because the watermelon, which is the test subject, is rich in water, and thus a proton nuclear magnetic resonance signal can be observed with a relatively low magnetic field. Further, the use of such a low magnetic field is desirable from the viewpoint of making the static magnetic field generator 4 compact and minimizing the leakage magnetic field around the apparatus. Further, in order to suppress the leakage magnetic field to the periphery and to avoid the adverse effect of the surrounding ferromagnetic material on the uniformity of the static magnetic field, the periphery of the static magnetic field generator 4 is shielded by a magnetic shield 5 made of carbon steel. Have been. A gradient magnetic field coil 6 for applying a magnetic field gradient in each of the z-axis direction, the y-axis direction, and the x-axis direction is arranged inside the bore of the static magnetic field generation device 4, and further corrects a static magnetic field described later. Static magnetic field correction magnetic field coil 7 for generating a magnetic field for the purpose is provided.

Further on the center side of the static magnetic field generator 4, a high frequency magnetic field generating / receiving coil (hereinafter referred to as RF) having a passage through which the conveyor belt 1 on which the watermelon 3 is placed can be inserted.
8) are disposed. Reference numeral 9 denotes a photoelectric sensor for accurately detecting the position of the watermelon 3 passing through the static magnetic field generator 4, and correspondingly reflects the light emitted from the photoelectric sensor 9 to the dedicated tray 2. Reflector 10 is attached.

Reference numerals 11 and 12 denote power supplies for supplying a current having a predetermined waveform to the gradient magnetic field coil 6 and the static magnetic field correction magnetic field coil 7. A matching network 13 for efficiently transmitting and receiving signals is connected to the RF coil 8.
A preamplifier 14 for amplifying minute nuclear magnetic resonance signals is connected to 3 via a duplexer 15 for preventing a high-intensity high-frequency magnetic field from entering.

The output of the preamplifier 14 is connected to a radio frequency (hereinafter referred to as RF) transceiver 16 for supplying high-frequency power to the RF coil 8 and amplifying a signal received by the RF coil 8 and then detecting the amplified signal. ing. The output of the RF transceiver 16 is connected to the duplexer 15.

The pulse programmer 17 includes the RF transceiver 1
The timing of sending a waveform stored in the waveform memory 19 in advance to the power supply 6 and the two power supplies 11 and 12 is controlled. Reference numeral 18 denotes data or commands to the pulse programmer 17 or R
This is a central information processing device (hereinafter, referred to as a CPU) that digitizes a signal provided from the F transceiver 16 and performs data processing. The pulse programmer 17 is provided with an inspection object detection signal output from the photoelectric sensor 9. If one automatic sorting apparatus having the above configuration is installed for one transport line, automatic sorting of watermelons becomes possible.

Next, the automatic sorting method according to the present embodiment will be described in comparison with a method for selecting a test object at rest. FIG. 2 shows a pulse sequence of a gradient magnetic field and a high-frequency magnetic field applied to a stationary test object. The obtained nuclear magnetic resonance signal is supplied to the matching network 13, the duplexer 15,
Amplified via a preamplifier 14 and an RF transceiver 16,
CPU 18 after digitization by A / D converter 20
The CPU 18 performs processing according to a predetermined algorithm.

FIG. 3 shows data processed by the CPU 18. This waveform is a sliced surface with a certain thickness of watermelon (this surface is a surface perpendicular to the Z direction)
Are selectively excited, and a nuclear magnetic resonance signal therefrom is projected in the X direction or the Y direction, and is called a profile. If there are no cracks or cavities in the slice plane, the shape of the profile becomes parabolic as shown in FIG. However, if cracks or cavities exist in the slice plane, they cause signal loss, and therefore appear as depressions in the profile as shown in FIG. 3B.

When such a slice plane is scanned over the entire watermelon, the presence or absence of a cavity can be determined.
However, stopping the watermelon 3 to be inspected at the center of the static magnetic field generator 4 in order to detect a nuclear magnetic resonance signal imposes a heavy burden on the conveyor 1 and restarts the conveyor 1 after signal detection. It takes time to make
Inspection time will be significantly extended. To realize the automatic sorting method, it is necessary to eliminate this point.

On the other hand, in the automatic sorting method of the present invention,
By making appropriate corrections, it is possible to obtain a nuclear magnetic resonance signal from a moving subject as well as a nuclear magnetic resonance signal from a stationary subject. Hereinafter, a method of acquiring a nuclear magnetic resonance signal while transferring the watermelon 3 and accurately selecting the watermelon 3 based on the signal will be described in detail.

The watermelon 3 is moved at a speed vm / s by the conveyor 1
When the beam reaches the predetermined measurement position in the static magnetic field generator 4, the beam emitted from the photoelectric sensor 9 is reflected by the reflector 10 attached to the dedicated tray 2. This inspection object detection signal is sent to the pulse programmer 17, which triggers the measurement.

In this embodiment, since the measurement is started on the basis of the test object detection signal detected by the photoelectric sensor 9 as described above, there is no displacement between the measurement start time and the watermelon 3. Measurement without errors becomes possible. When the measurement of one watermelon 3 is completed, the measurement waits until the next watermelon 3 is detected by the photoelectric sensor 9.

In the conventional method in which the sequence used for the selective excitation of the slice plane combines the high-frequency magnetic field and the gradient magnetic field for slice plane excitation shown in FIG. 2, the following problems occur. For selective excitation of the slice plane, it is usually necessary to simultaneously apply a high-frequency magnetic field pulse having a SINC function as an envelope and a gradient magnetic field for a certain period of time.

If the time for applying the high-frequency magnetic field pulse is 10 ms, the time for applying the gradient magnetic field is 20 ms, and the watermelon transfer speed v is 0.4 m / s, the watermelon 3 is excited during the slice plane, ie, 20 ms. It will move as much as 8mm. This moved area will deviate from the set slice plane, so that no nuclear magnetic resonance signal can be obtained from this area. If the thickness of the slice surface for obtaining a nuclear magnetic resonance signal is 20 mm, no signal can be obtained for almost half the thickness. This state will be described in detail with reference to FIG.

The horizontal axis of the figure indicates the position of the watermelon, which is the object to be inspected, and the vertical axis indicates the angular frequency of the applied high-frequency magnetic field and the intensity of the corresponding gradient magnetic field. In general, the following relationship is satisfied when a slice plane having a certain thickness ΔX is selectively excited when the object to be inspected is stationary. 2πf ₁ = γ (H ₀ + G × X ₁₀ ) (2) 2πf ₂ = γ (H ₀ + G × X ₂₀ ) (3) where f ₁ and f ₂ : frequency of the high-frequency magnetic field (center f ₀ , f ₁ >) f
₂ ) γ: magnetic rotation ratio H ₀ : magnetic flux density of static magnetic field G: intensity of gradient magnetic field (G> 0) X ₁₀ , X ₂₀ : (position of slice surface end portion X ₁₀ > X ₂₀ ). Wherein the frequency of the RF magnetic field has a bandwidth of f ₁ ~f ₂ is a high-frequency magnetic field applied, but have SINC function like envelope.

When the object to be inspected is stationary, the above equation (2)
, (3) is maintained while the high-frequency magnetic field and the gradient magnetic field are applied, so that the set slice plane (FIG.
Nuclear magnetic resonance signals from the entire region (0) are accurately obtained.

However, when the test object has a constant speed v
When moving with (> 0), since the position of the slice plane is a function of the time t, the above equations (2) and (3) do not hold. For example, the time when the application of the high-frequency magnetic field and the gradient magnetic field is started is t = 0, the time when the application is completed is t = t ₁ , and the position of the end surface of the set slice plane in the sample traveling direction is X ₁
(T), assuming that the position of the other end face is X ₂ (t), X ₁
(T) and X ₂ (t) are expressed as X ₁ (t) = X ₁₀ + v · t ₁ (4) X ₂ (t) = X ₂₀ + v · t ₁ (5) and correspond to these. The frequency f ₁ ′ of the high-frequency magnetic field,
f ₂ ′ is obtained from 2πf ₁ ′ = γ (H ₀ + G × ₁₀ + G × v ・ t ₁ ) (6) 2πf ₂ ′ = γ (H ₀ + G × X ₂₀ + G × v ・ t ₁ ) (7) Desired.

If f ₂ ′ <f ₁ , the following occurs. That is, the slice plane represented by area (1) in FIG. 4, every moment, but moves while changing a resonance frequency, the portion overlapping the region (2) at _{t = t 1, 0 <t} <t The resonance frequency deviates from the range of the frequency included in the high-frequency magnetic field applied during ₁ , and the resonance phenomenon can occur only for a shorter time than in the region (3). Therefore, for example, the intensity I (X ₀ ) of the nuclear magnetic resonance signal from the portion located at the position X ₀ at t = 0 in the region (2) is smaller per unit volume than the signal from the region (3). I (X ₀ ) = sin (β · (t ₁ −X / v)) / sin (β · t ₁ ) (8) (β is an arbitrary real number). Usually β is β
Since the setting is made so that t ₁ ≦ 90 °, the above equation (8) means that the signal decreases, and in the cavity judgment based on FIG. 3, the cavity existing in the area (2) is overlooked. There is fear.

If f ₂ ′ ≧ f ₁ , the measurement conditions are further degraded, and there is no longer a region (region (3) in FIG. 5) within which the signal can be accurately collected within the set slice. This may lead to erroneous cavity determination for the entire slice.

On the other hand, in the present invention, the above formulas (6) and (6)
A method of applying a high-frequency magnetic field that can eliminate the “Gvt” term in (7) is realized. That is, a magnetic field B (t) that satisfies 2πf = γ (H ₀ + G · X ₁₀ + G · v · t) + γB (t) (9) is applied. This B (t) is given by the following equation (10). B (t) = a ・ G ・ v ・ t (10)

The magnitude of the magnetic field “a · G · v · t” is a function of time t, but does not depend on the position of the slice plane.
Therefore, this magnetic field needs to have the same spatial homogeneity as the static magnetic field H ₀ . “A · G · v” in the above equation (9)
The magnetic field t ″ corresponds to a uniform offset of the static magnetic field H _0. Such an offset magnetic field can be obtained by applying an external current to the static magnetic field correction magnetic field coil 7, which is a feature of the present invention. Can be.

That is, the gradient magnetic field coil 6 generates a magnetic field (the direction of the magnetic field is the same as the static magnetic field) whose magnitude changes in the traveling direction of the conveyor 1, whereas the static magnetic field coil 6 generates the magnetic field. The correction magnetic field coil 7 is capable of generating a uniform magnetic field in the traveling direction of the conveyor 1 and is indispensable for correcting a static magnetic field in the present invention.

FIG. 5 shows an example of a pulse sequence for applying a high-frequency magnetic field, a gradient magnetic field, and a static magnetic field correction magnetic field for exciting the slice plane according to the above embodiment. In the pulse sequence shown in the figure, the above-described reduction in the signal on the slice plane can be prevented by correcting the static magnetic field. Therefore, according to this pulse sequence, even when the watermelon 3 as the object to be inspected is moving, a signal from a preset slice plane can be obtained correctly.

FIG. 6 shows the relationship between the signal intensity and the proportionality constant a experimentally examined. From this result, it can be seen that practically, the condition of -0.8 <a <-1.2 is required.

[0042]

As is apparent from the above description, according to the present invention, in the method for sorting fruits and vegetables using nuclear magnetic resonance, while transferring an object to be inspected, the method is as accurate as in a stationary state. The internal quality can be measured, and the inspection time can be greatly reduced to improve the efficiency of sorting.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a sorting device used in an automatic sorting method according to the present invention.

FIG. 2 is a time chart showing a pulse sequence when the object to be inspected is stationary.

FIG. 3 is a comparison graph of profiles obtained from watermelons without and with cavities.

FIG. 4 is an explanatory diagram showing a relationship between a gradient magnetic field and a high-frequency magnetic field applied to a test object in a stationary state and a moving state.

FIG. 5 is a pulse sequence according to the present invention when the test object is moving.

FIG. 6 is a graph showing a relationship between a nuclear magnetic resonance signal and a proportionality constant a.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conveyor 2 Dedicated tray 3 Watermelon 4 Static magnetic field generator 5 Magnetic shield 6 Gradient magnetic field coil 7 Static magnetic field correction magnetic field coil 8 RF coil 9 Photoelectric sensor 10 Reflector plate 11, 12 Power supply 13 Matching network 16 RF transceiver 18 Central information processing Device 19 Waveform memory

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Motofumi Suzuki 630 Shinagase-cho, Hamamatsu-shi, Shizuoka Machi Works, Ltd. (72) Inventor Kazunori Saito 1-5-5 Takatsukadai, Nishi-ku, Kobe City Inside Kobe Research Institute, Kobe Steel Co., Ltd. (72) Takashi Miki 1-5-5, Takatsukadai, Nishi-ku, Kobe City Shares Kobe Steel, Ltd.Kobe Research Institute (72) Inventor Seiji Hayashi 1-5-5 Takatsukadai, Nishi-ku, Kobe City, Kobe Research Institute Kobe Research Institute

Claims (4)

[Claims] 1. A static magnetic field is formed on a transported test object, a gradient magnetic field is superimposed on the static magnetic field, and a nuclear magnetic resonance signal emitted from the test object is detected and processed. In the automatic fruit and vegetable sorting method for nondestructively inspecting the internal quality of the test object, the method comprises applying a high-frequency magnetic field and a gradient magnetic field in the same direction as the transfer direction of the test object to the test object. When the slice plane perpendicular to the transport direction of the test object and having a predetermined thickness in the transport direction is selectively excited to obtain a nuclear magnetic resonance signal from that region, the test object Has an intensity I proportional to the product of the intensity G of the gradient magnetic field to be applied, the application time t of the gradient magnetic field, and the transport speed v of the test object, and the test object moves during measurement. And the static magnetic field Fruit or vegetable automatic sorting method using nuclear magnetic resonance and applying a static magnetic field correction field such that it can have the same qualitative and uniform magnetic field distribution. 2. The automatic fruit and vegetable sorting method according to claim 1, wherein the intensity I of the nuclear magnetic resonance signal satisfies the following relationship: I = aGvt (-0.8 <a <-1.2). . 3. A static magnetic field is formed on the transported test object, a gradient magnetic field is superimposed on the static magnetic field, and a nuclear magnetic resonance signal emitted from the test object is detected and processed. In the automatic fruit and vegetable sorting apparatus for non-destructively inspecting the internal quality of the inspection object, the intensity G of the gradient magnetic field applied to the inspection object, the application time t of the gradient magnetic field, and the transport speed v of the inspection object A static magnetic field correction magnetic field coil having an intensity I proportional to the product of the three, and generating substantially the same uniform magnetic field distribution as the static magnetic field in a region where the test object moves during measurement. An apparatus for sorting fruits and vegetables, comprising: 4. A power supply for supplying a current to the static magnetic field correction magnetic field coil, a waveform storage unit for providing the power supply with a signal waveform for correcting a static magnetic field, and a timing for outputting the signal waveform. The fruit and vegetable sorting device according to claim 3, further comprising a pulse control unit for controlling.