Study On Firmness Evaluation Of Korla Pear Using Vibration Spectrum Characteristics

Nondestructive testing of internal quality of Korla pear has been paid more attention in the process of sorting. In this work the focus is on firmness evaluation of Korla pear based on vibration spectrum characteristics in order to realize the nondestructive testing of firmness. Firstly, the suitable excitation conditions were determined by means of low frequency excitation test. Secondly, the suitable firmness index for Korla pear with different fruit shapes was established by finite element modal analysis and experimental modal analysis. Finally, the firmness of Korla pear with different internal qualities was evaluated using new firmness index. The fitting relationships between firmness index values and Magness-Taylor (M-T) measurements of Korla pear were also obtained. The results in the study can provide research foundation and scientific basis for nondestructive testing of Korla pear internal qualities. The main contributions are as follows:(1) Effects of excitation and detections points, exaction materials and exaction forces on vibration spectrum characteristics of Korla pear were studied. The results show that effects of corresponding detection positions or exaction positions in same position on natural frequencies were not significant when a Korla pear was excited or detected in cheek or stem shoulder (calyx shoulder). Only the Korla pear was excited or detected in cheek, the difference of natural frequencies between cheek and stem shoulder or calyx shoulder was significant. So any points in same position can be used to detect when a Korla pear was excited in cheek or stem shoulder (calyx shoulder). The effects of excitation materials and excitation forces on natural frequencies were not significant. However, the bigger force should be selected from3-15N range which causes no damage for Korla pear in practice to get enough exaction energy for reducing the effects of noise.(2) Effects of fruit shape and density on firmness evaluation of Korla pear were studied by means of finite element modal analysis and experimental modal analysis. Firmness index f2w2/3qt was determined using the natural frequency (f) of first five vibration modes, mass (m) and fruit shape factor (q). The natural frequency range and suitable t values for different vibration modes were obtained, namely32.50-95.00Hz,5.76for the first mode,97.50-128.16,1.57for the second mode,142.56-210.97Hz,2.11for the third mode,487.50-593.80Hz,1.06for the fourth mode and699.35-1782.06Hz,0.60for the fifth mode.(3) Vibration spectrum characteristics of Korla pear with different internal qualities were analyzed and firmness was evaluated using the index f2m2/3qt. The results show that firmness of green maturity fruit and yellow maturity fruit of Korla pear can be evaluated by index f2m2/3q5.87and stem shoulder was the suitable excitation and detection section. The fitting relationships between firmness index values and M-T measurement values of Korla pear with two maturities are:FI=254.20-3.53F,R2=0.8608for green maturity fruit, and FI=-67.47+1.81F,R2=0.8350for yellow maturity fruit. Firmness of Korla pear with normal and rough peels can be evaluated by index f2m2/3q1.57and calyx shoulder was the suitable excitation and detection section. The fitting relationship between firmness index values and M-T measurement values of Korla pear with normal and rough peels are:FI=-92.02+2.05F, R2=0.8398for normal fruit and FI=-25.81+0.91F,R2=0.9173for rough peel fruit.