Design Of Nondestructive Testing Device Of Korla Pear Firmness Based On Acoustic Response Method

Korla pear is one of the characteristic fruits in Xinjiang. With the pear plant area expanding, the differences in internal quality become larger. The firmness is one of the important indicators reflecting the differences of internal quality. Conducting the research of Korla pear firmness nondestructive testing device is significant for the pear internal quality identification and classification technology development.Therefore, in this paper the pear acoustic exciting and sensing components, signal acquisition and processing hardware circuit as well as software system were designed based on acoustic response method.PFT-1 type Korla pear firmness testing device was developed. The specific research contents and results are as follows:(1) Two Q220-A4-303 YB type bending bimorph sensors were chosen as the pear acoustic signal exciting and sensing components. The pear acoustic exciting and sensing components assembly was developed. The spring to adjust the distance of the sensor exciting and sensing point is YA 1.0 x 5 x 115 and its helix angle is 5.82. The maximum load is 15 N and the minimum load is 1.39 N. KS103 S type ultrasonic wave sensor was chosen to measure the distance between exciting point and sensing point. Its precision is 0.5 mm, with 1 ~ 520 cm range.(2) The circuit board for acoustic response signal acquisition and processing of Korla pear is mainly composed of the power supply module, the PA78 DK type voltage amplifying module, the signal conditioning module and the data storage module and display module with the core TMS320F28335 circuit board. According to the debugging analysis, 2.5V sharp wave pulse was amplified to 49.7 V by the voltage linear amplification module, attenuated to 31.8 V with the pear transmission. This voltage declined to 1.29 V by the ratio transformation and the second order active filter of the acoustic signal conditioning circuit,which met the work requirements of the circuit board.(3) The software system for acoustic response signal acquisition and processing of Korla pear was developed in Altium Designer programming environment providing the C language as well as assembly language, containing software system main program and subroutines including acoustic signal data acquisition, response signal FFT and the sound velocity value calculation, the sound velocity value display.This software system can acquire signal with 5120 Hz sampling frequency and 512 sampling points. Pear acoustic signal is calculated by the FFT function. Then the value of sound velocity is calculated, displayed on the liquid crystal display screen.(4) PFT-1 type Korla pear firmness testing device was developed. The relative error is 14.2% through the comparative analysis of this device testing results and exact results of the M-T puncture method.