CN203133033U - Fruit firmness nondestructive detection device based on laser doppler vibrometry - Google Patents

Abstract

The utility model discloses a nondestructive detection device for fruit hardness based on laser Doppler vibration measurement. It mainly includes a vibration control system composed of a computer, a vibration control module, a power amplifier, a vibration generator, an extension table and a charge-type acceleration sensor; it mainly includes a vibration control system composed of a laser Doppler vibration measurement module, an ICP acceleration sensor, a data acquisition card and a tripod. Signal acquisition system. Collection of representative fruit composition modeling sample sets; determination of sample quality; collection of vibration signals; processing of vibration signals; determination of hardness standard values; establishment and verification of hardness prediction models. Use the signal analysis software that comes with the laser Doppler vibration measurement module to perform filtering, calculus, FFT, and amplitude-frequency response on the output signals of the laser Doppler vibration measurement controller and the ICP acceleration sensor. The utility model has the advantages of not being affected by environmental noise, not destroying the free vibration of the fruit, good adaptability, etc., and realizes the nondestructive detection of the fruit hardness.

Description

A non-destructive testing device for fruit firmness based on laser Doppler vibration measurement

technical field

The utility model relates to a nondestructive detection device for fruit hardness, in particular to a nondestructive detection device for fruit hardness based on laser Doppler vibration measurement.

Background technique

China is known as the "Kingdom of Fruits in the World". Almost all kinds of fruits are produced and the output is high. However, due to backward testing and grading equipment, the competitiveness of fruits in the international market is still not enough, and the export rate is low. Fruits are stored and transported after harvesting. There are problems of ripening, softening and decay in the process. Fruit hardness, also known as firmness, refers to the strength of the pulp against pressure, and can be used as an important indicator for judging maturity and quality. Accurate detection of fruit firmness is of great significance for determining the appropriate harvest period, post-harvest storage, evaluating the best edible period, and product grading.

The traditional fruit hardness test method is mainly sampling. Usually, several test points are selected at the equator of the sample, and then the skin is peeled at the test point, and a texture analyzer or hardness tester is pressed into the fruit for a certain distance to measure. This is a destructive method. Sexual detection, the inspection rate is low, time-consuming and labor-intensive, and cause a lot of waste. At present, the non-destructive testing methods for fruit firmness are mainly acoustic testing methods, and some studies have mentioned near-infrared spectroscopy and hyperspectral spatial scattering curve methods. The signal of the acoustic detection method is easily interfered by environmental noise, resulting in low detection accuracy, and some methods of tapping may cause certain damage to the fruit; near-infrared technology is related to its chemical substances, and the hardness of the fruit is mainly related to its physical structure. The results of near-infrared detection are not very ideal, and for samples with defects on the fruit surface, the detection point needs to avoid the defect location; while hyperspectral technology is greatly affected by environmental factors such as light sources, and the detection conditions are harsh. the

Laser Doppler Vibrometry (LDV) technology is a technology used to detect the mechanical vibration characteristics of objects. The measurement of mechanical vibration characteristics of fruits can be divided into two ways: contact and non-contact. The traditional measurement method needs to attach the acceleration sensor to the surface of the object to be measured, and use the output signal to realize the related measurement of "acceleration-velocity-displacement". This contact installation method will destroy the original vibration state, and even in many Occasions cannot be applied, thus limiting its scope of application. As a non-contact measurement method, laser Doppler vibration measurement technology integrates optics, electromechanics, and is not affected by environmental noise. Sensitive and other advantages, it is also very effective for detecting vibrations with small amplitudes, and its characteristics meet the needs of fruit vibration measurement. In fruits with different textures, the transmission of vibrational energy must be different, so theoretically speaking, the mechanical vibration characteristics of fruits can be detected by using this technology to establish the relationship with hardness. the

Contents of the invention

In view of the problems existing in the above-mentioned background technology, the purpose of this utility model is to provide a non-destructive testing device for fruit hardness based on laser Doppler vibration measurement. The vibration signal of the fruit is obtained through the device, and the signal is processed to obtain the characteristic frequency, and the hardness prediction model is established, so as to realize the non-destructive detection of the fruit hardness.

The technical scheme that the utility model adopts is:

Including vibration control system and vibration signal acquisition system, among which:

1) Vibration control system: including computer, vibration control module, power amplifier, vibration generator, expansion platform and charge type acceleration sensor; the vibration control module is installed in the PCI slot of the computer, and the expansion platform is rigidly connected to the vibration generator. The charge-type acceleration sensor is fixed on the expansion platform with mounting screws, and the output end of the vibration control module is connected to the vibration generator through the power amplifier;

2) Vibration signal acquisition system: including laser Doppler vibration measurement module, ICP acceleration sensor, data acquisition card and tripod; the laser Doppler vibration measurement module is composed of laser detection head and laser Doppler vibration measurement controller; laser The detection head is placed vertically downward on the tripod, the laser beam is projected on the apex of the upper surface of the fruit perpendicular to the extended table, the vertical distance between the focusing lens and the apex of the upper surface of the fruit is greater than the minimum working distance of the laser detection head, and the ICP acceleration sensor is fixed with mounting screws On the extension platform, the two input ends of the data acquisition card are respectively connected to the output ends of the laser Doppler vibration measurement controller and the ICP acceleration sensor, and the output end of the data acquisition card is connected to the computer;

The signal analysis software that comes with the laser Doppler vibration measurement module performs filtering, integration, FFT, and amplitude-frequency response on the output signals of the laser Doppler vibration measurement controller and the ICP acceleration sensor.

A non-destructive testing method for fruit firmness based on laser Doppler vibration measurement:

Step (1) Collect a representative sample set for fruit composition modeling;

Step (2) Determination of sample mass: weigh the mass of each sample with an electronic balance;

Step (3) Acquisition of vibration signals: place the sample at the center of the vibration generator extension table and apply an excitation signal of frequency change to it, and measure the vibration velocity signal at the apex of the upper surface of the sample with a laser Doppler vibration measurement module , using the ICP acceleration sensor to measure the vibration acceleration signal of the extended table, the obtained two-way vibration signal is collected by the data acquisition card and sent to the computer for storage, and the sampling frequency is 5120 Hz;

Step (4) Vibration signal processing: filter, integrate, and fast Fourier transform the collected two-way vibration signals, then calculate the amplitude-frequency response, and extract the characteristic frequency;

Step (5) Determination of hardness standard value: measure the maximum force/force area (N/cm ² ) of each sample on a universal mechanical testing machine, and use it as the hardness standard value;

Step (6) Establishment and verification of the hardness prediction model: divide the samples into a calibration group and a verification group, and divide the calibration group and the verification group into a ratio of 3:1, and use the linear regression method to establish the relationship between the mechanical vibration characteristics and the hardness of the samples in the calibration group. and verify the obtained prediction model based on the verification group, compare the predicted value and standard value of sample hardness, and optimize the model according to the actual production requirements.

In the step (3), the computer outputs the vibration control signal through the vibration control module, which is amplified by the power amplifier to excite the vibration generator to work. The excitation signal is a sinusoidal frequency sweep signal of 5-2000 Hz, and the starting frequency is 5 Hz. Linear growth, the sweep rate is 600 Hz/min, the 5-32 Hz amplitude is constant at 0.5 mm, and the 32-2000 Hz acceleration is constant at 1 g; the fruit is placed at the center of the extension table on the vibration generator, and the laser detection head is vertical Put it straight down on the tripod, the laser beam is projected on the apex of the upper surface of the fruit perpendicular to the extended table, adjust the focusing lens of the laser detection head, so that the laser beam is focused on the apex of the upper surface of the fruit through the lens; The reflected laser light is received by the laser detection head, processed by the laser Doppler vibrometer controller and output voltage signal, then collected by the data acquisition card, and transmitted to the computer for storage, and finally the vibration velocity signal at the top of the fruit surface is obtained ; The ICP acceleration sensor is fixed on the extension table of the vibration generator, and the vibration acceleration signal of the extension table is obtained and collected by the data acquisition card, and transmitted to the computer for storage. the

In the step (4), first, the high-frequency interference noise is filtered out from the collected two vibration signals through a low-pass filter with a cutoff frequency of 2 kHz, and then the vibration acceleration signal measured by the ICP acceleration sensor is converted into The velocity signal is used as the input signal, and the vibration velocity signal measured by the laser Doppler vibrometer module is used as the output signal, and the input and output signals are respectively subjected to fast Fourier transformation to calculate the amplitude-frequency response, and extract it from the amplitude-frequency response curve characteristic frequency. the

Compared with the background technology, the utility model has the beneficial effects as follows:

1. Non-destructive testing. Using the laser Doppler vibrometer technology, just put the fruit on the expansion platform, and use the acceleration sensor and the laser Doppler vibrometer module to detect the excitation and response signals. At the same time, the vibration method will not cause damage to the fruit. Keep the original state of the fruit intact.

2. Do not destroy the free vibration of the measured object. As a non-contact measurement technology, laser Doppler vibration measurement technology will not destroy the original free vibration state of the fruit, and has a fast dynamic response, making the vibration signal accurate and reliable. the

3. Good adaptability. There are no special requirements for the test environment, it is not affected by environmental noise, and does not require a special test space. the

Description of drawings

Fig. 1 is the method flowchart of the present utility model.

Fig. 2 is a schematic diagram of the device structure of the present invention. the

In the figure: 1. Computer; 2. Vibration control module; 3. Power amplifier; 4. Vibration generator; 5. Expansion platform; 6. Charge type acceleration sensor; 7. ICP acceleration sensor; 8. Fruit; 9. Laser detection 10. Laser Doppler vibration measurement controller; 11. Data acquisition card. the

Fig. 3 is the engineering diagram of the expansion platform of the utility model. the

Fig. 4 is the linear regression model diagram of the elastic coefficient and the hardness of the correction group papaya in the embodiment of the present invention. the

Fig. 5 is a scatter diagram of the predicted value and standard value of papaya hardness of verification group in the embodiment of the present invention. the

Detailed ways

Below in conjunction with accompanying drawing and embodiment the utility model is further described. the

As shown in Figure 2 and Figure 3, the device of the present utility model includes a vibration control system and a vibration signal acquisition system, wherein:

1) Vibration control system: including computer 1, vibration control module 2 (such as Amber multi-functional vibration controller), power amplifier 3 (such as PA-1200), vibration generator 4 (such as ES-05), extension table 5 and electric charge type acceleration sensor 6 (DL-24100); the vibration control module 2 is installed in the PCI slot of the computer 1; The acceleration sensor 6 is fixed on the expansion platform 5 with M5 mounting screws, and the output end of the vibration control module 2 is connected with the vibration generator 4 through the power amplifier 3;

2) Vibration signal acquisition system: including laser Doppler vibrometer module (such as LV-S01), ICP acceleration sensor 7 (such as LC0159), data acquisition card 11 (such as NI USB-4431) and tripod; the laser Doppler The vibration measurement module is composed of a laser detection head 9 and a laser Doppler vibration measurement controller 10; the laser detection head 9 is placed vertically downward on a tripod, and the laser beam is projected on the apex of the upper surface of the fruit 8 perpendicular to the extension table, and the focusing lens The vertical distance from the vertex on the upper surface of the fruit 8 is greater than the minimum working distance of the laser detection head 9. The ICP acceleration sensor 7 is fixed on the expansion platform 5 with M5 mounting screws. The output end of controller 10 is connected with ICP acceleration sensor 7, and the output end of data acquisition card 11 is connected with computer 1;

The signal analysis software included with the laser Doppler vibrometer module performs filtering, integration, FFT, and amplitude-frequency response on the output signals of the laser Doppler vibrometer controller 10 and the ICP acceleration sensor 7 .

The working process of the above device:

The computer sends a sine frequency sweep signal to the power amplifier through the vibration control module. After the signal is amplified, the vibration generator is stimulated to work, and the fruit placed on the extension table vibrates together. At the same time, the actual vibration acceleration signal measured by the charge type acceleration sensor Feedback to the vibration control module to form a closed-loop control; the fruit vibration velocity signal measured by the laser Doppler vibration measurement module is sent to channel 2 of the data acquisition card, and the vibration acceleration signal of the expansion table measured by the ICP acceleration sensor is sent to the channel of the data acquisition card 1. Finally, the data acquisition card sends the collected two-way vibration signals to the computer, and processes them with the signal analysis software that comes with the laser Doppler vibration measurement module.

The expansion table is rigidly connected with the vibration generator by screws, and in the utility model, the function of stably placing the fruit and driving its vibration is realized. The material of the expansion table is magnesium-aluminum alloy; there is a diameter of 60 mm in the middle of the expansion table, and a depth of It is a 3 mm pit, and a layer of frosted paper is pasted on the bottom of the pit to prevent the fruit from shifting and rotating when it is vibrated. the

The detection of the hardness of the fruit of the utility model has universality. Taking the papaya as an example, the implementation process of the detection of the hardness of the papaya of the utility model is introduced. Other fruits can refer to the method of this embodiment to establish a corresponding hardness prediction model, which can be used for different The firmness of the fruit is tested non-destructively. the

Embodiment: the papaya hardness non-destructive detection based on laser Doppler vibration measurement, carries out according to the step as shown in Figure 1:

1. Papaya sample collection:

Collect 100 papayas in the market, try to select representative papayas to form the modeling sample set, and make the sample hardness range as large as possible.

2. Determination of sample mass: Weigh the mass of each sample with an electronic balance with an accuracy of 0.01 g. the

3. Acquisition of vibration signals:

As shown in Figure 2, put the papaya (that is, the fruit 8) on the extension platform 5, the computer 1 outputs the vibration control signal through the vibration control module 2, and after being amplified by the power amplifier 3, the vibration generator 4 is amplified to work, and the control signal is 5 -2000 Hz sinusoidal frequency sweep vibration signal, the starting frequency is 5 Hz, increasing in a linear form, the sweep rate is 600 Hz/min, the amplitude of 5-32 Hz is constant at 0.5 mm, and the acceleration of 32-2000 Hz is constant at 1 g . The papaya is placed at the center of the expansion platform 5 above the vibration generator 4, the laser detection head 9 is placed vertically downward on the tripod, and the laser beam is projected on the top surface of the papaya perpendicular to the expansion platform 5. 9 focusing lens, the laser beam is focused on the apex of the upper surface of the papaya through the lens. The laser light reflected back from the vibrating papaya upper surface apex is received by the laser detection head 9, and the output voltage signal is processed by the laser Doppler vibration measuring controller 10, and then the vibration velocity signal of the papaya is collected by the data acquisition card 11; The ICP acceleration sensor 7 is fixed on the expansion platform 5 above the vibration generator 4, and the vibration acceleration signal of the expansion platform 5 is obtained and collected by the data acquisition card 11. The two vibration signals are collected by the data acquisition card 11 and then sent to the computer 1 for storage.

4. Determination of hardness standard value:

Select 4 points at equal intervals to measure the hardness at the maximum diameter between the papaya fruit stalk and the fruit stem, and take the average value as the hardness value of the sample. The hardness measurement method is: peel off a thin layer of skin at the selected position, the test surface should be flat, the thickness of the peeled peel should not be too large, and the pulp should be damaged as little as possible, and the peeled area is slightly larger than the area of the indenter of the universal mechanical testing machine used. , and then put the sample on the universal mechanical testing machine, press the indenter at a speed of 1 mm/s, and stop at 10 mm, the hardness at this point is the maximum force/force area (N/cm ² ), this The diameter of the indenter used in the examples is 6 mm. The hardness range of papaya measured in the experiment is 1.02-10.71 N/cm ² .

5. Processing of vibration signal:

First, the signal is filtered out by a low-pass filter with a cutoff frequency of 2 kHz to remove high-frequency interference noise, and then the vibration acceleration signal measured by the ICP acceleration sensor is converted into a velocity signal by an integral, which is used as an input signal. The laser Doppler vibration measurement module The measured vibration velocity signal is used as the output signal, and fast Fourier transform (FFT) is performed on the input and output signals respectively to obtain the amplitude-frequency response, and the characteristic frequency is extracted from the amplitude-frequency response curve.

6. Establishment and verification of hardness prediction model:

For 100 papaya samples, 6 outliers were first eliminated according to the standardized residual of the hardness value, and the remaining 94 samples were divided into a calibration group and a verification group according to a ratio of 3:1. The statistical values of the indicators in the two parts after division are shown in Table 1.

Table 1 Statistical value of hardness index of calibration group and verification group samples sample set Number of samples Hardness range (N/cm ² ) Average hardness (N/cm ² ) Standard deviation (N/cm ² ) Calibration group 71 1.02-10.71 4.86 2.25 verification group twenty three 2.20-9.44 5.16 1.93

Then, calculate the elastic coefficient EI of each sample according to the following formula:

Where: f ₂ is the second resonance frequency, m is the mass of papaya.

The linear regression model of elastic coefficient EI and hardness was established based on the calibration group, that is, the hardness prediction model. The coefficient of determination of the model was R ² =0.631, as shown in Figure 4. Then use the verification group samples to verify the established hardness prediction model. Comparing the predicted value with the standard value, the results are shown in Figure 5. It can be seen that the correlation coefficient between the predicted value and the standard value in the verification group is r=0.724, and the standard error of prediction SEP=1.055, indicating that the established prediction model can be compared with Accurately predict the firmness of papayas.

As can be seen from the foregoing embodiments, the utility model detects the vibration response of papaya under the action of a certain excitation vibration signal based on laser Doppler vibration measurement technology, and calculates after extracting the second resonance frequency from the amplitude-frequency response of the input and output signals. The elastic coefficient of papaya, using linear regression to establish a prediction model of papaya hardness, so as to realize the non-destructive testing of papaya hardness. the

The above-mentioned specific embodiments are used to explain the utility model, rather than to limit the utility model. Within the spirit of the utility model and the scope of protection of the claims, any modifications and changes made to the utility model fall into the scope of the utility model. scope of protection. the

Claims (1)

1. A fruit hardness non-destructive testing device based on laser Doppler vibration measurement, characterized in that: the device includes a vibration control system and a vibration signal acquisition system; wherein: 1) Vibration control system: including computer (1), vibration control module (2), power amplifier (3), vibration generator (4), extension table (5) and charge type acceleration sensor (6); vibration control module ( 2) Installed in the PCI slot of the computer (1), the expansion platform (5) is rigidly connected to the vibration generator (4), the charge type acceleration sensor (6) is fixed on the expansion platform (5) with screws, and the vibration The output end of the control module (2) is connected to the vibration generator (4) via the power amplifier (3); 2) Vibration signal acquisition system: including a laser Doppler vibration measurement module, an ICP acceleration sensor (7), a data acquisition card (11) and a tripod; the laser Doppler vibration measurement module consists of a laser detection head (9) and a laser multiple Composed of the Puler vibration measurement controller (10); the laser detection head (9) is placed vertically downward on the tripod, the laser beam is projected on the apex of the upper surface of the fruit (8) perpendicular to the extended table, the focusing lens and the fruit (8) The vertical distance of the vertex on the upper surface is greater than the minimum working distance of the laser detection head (9). The ICP acceleration sensor (7) is fixed on the expansion platform (5) with mounting screws. The two input ports of the data acquisition card (11) are respectively connected to the laser multiple The output end of the Puler vibration measurement controller (10) is connected to the ICP acceleration sensor (7), and the output end of the data acquisition card (11) is connected to the computer (1); the signal analysis software that comes with the laser Doppler vibration measurement module The output signals of the laser Doppler vibrometer controller (10) and the ICP acceleration sensor (7) are filtered, integrated, FFTed, and the amplitude-frequency response is obtained.

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