| In recent years, people have an increasing demand for fruits with the help of improvement of life level ,and varieties and output of fruits have greatly increased too. There is an increasing demand for the quality of all kinds of fruits. Therefore , considerable research about the measurement of quality of fruits have been carried out The results of many researches show that firmness is a very important factor which is used to determined the quality of fruits and mature stage. Up to now there are several types of the laboratory techniques for measuring the firmness of fruits. However, at present the Magness-Taylor firmness test remains the sole commercially applied approach for the monitoring of the fruit firmness in growing and post-harvest storage. The intactness of fruit will be damaged in this method, and the speed of measurement is not fast. So it is not suit for on-line test For overcoming these flaws, many researchers have studied the non-destructive measurement techniques of firmness of fruit by using the physical property of fruit such as optics, acoustics, electrics and so on.. Nevertheless, these approaches are not widely used in commercial. This research is focused on the characteristics of frequency-spectrum of pear and peach under lower height or light knocking, Then obtain the frequency-time and frequency-spectrum curve. The correlation between response frequency and physical property parameter of pear or peach has been analyzed, and Prediction models of firmness have been established.1 data acquisition systemIn this experiment, a high-power acceleration sensor and high-speed and large data acquisition card are applied. These equipments are safe and credible, which can assure the data acquisition card acquire sample data rapidly. This solves the problem that data is acquired low-speedly and acquisition of experiment parameters are not precise enough. The acquisition software applies interrupt control. The auto-trigger mode is carried out through value of the channel port voltage. It can acquire data without delay, and the DMA mode was used with ZOOHz, so the signal obtained under it was precise and credible.2 studying on characteristics of frequency spectrum of pearpears of different mature stage are harvested and grouped for performing different experiments through dropping impact and knocking , and experiment datum are obtained. Then the time-domain characteristic curves of acceleration signal are drawn .At the same time , Fast Fourier transformation on the acceleration signal are performed ,and frequency response curves are drawn, and frequency response curve under different experiment conditions is analyzed .The SAS software is applied to analyze the correlation between different parameter and the main frequency. The result of analysis shows that different experimental method can not affect the conclusion as following : 1) The main frequency increases with the increase of firmness . There is high correlation (R=0.88)between them. The main frequency of unripe pear is larger than ripe one; 2) The main frequency decreases with prolongation of storage time after harvest; 3) The main frequency is correlated with sugar contained in pear, and it will decrease with the increase of sugar, 4) Mass has significant effect on the main frequency . The main frequency increases with the decrease of mass. There is good negative correlationbetween them; 5) Density has little effect on the main frequency ,so it is not important factor affecting the main frequency; 6) Position near equator has little effect on the main frequency.3 studying on characteristics of frequency spectrum of peachpeaches of different mature stage are harvested and grouped for performing different experiments through dropping impact and knocking , and experiment datum are obtained Then the time-domain characteristic curves of acceleration signal are drawn .At the same time , Fast Fourier transformation on the acceleration signal are performed ,and frequency response curves are drawn, and frequency response cur...
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