Jeremy Harris wrote:Being the technically inclined lot that we are, couldn't we come up with a means to do this automatically? How about a little gadget with a low frequency contact microphone (or maybe an accelerometer on a contact pad) coupled with a thumper that provides a preset tap to the melon? Some means of capturing and analysing the waveform, using a µcontroller perhaps, would be needed, together with a way to recognise the unique signature of a ripe melon.
Calibration would be needed, maybe by testing a few melons, recording the waveform and then comparing the perfect, ripe, melon with the recordings to try and see what the signature looks like.
The internal quality of fruit can be non-invasively tested using systems based on vibrational characteristics. In this work, acoustic impulses were used to detect internal hollows in watermelons; the change in the signal revealing the problem. Frequency spectrum variables were analysed for their potential as non-destructive predictors of this defect. The band magnitude variables, obtained from the integral of the spectrum magnitudes between two frequencies, best predicted internal disorders. Experimental modal analysis was used to investigate the vibrational performance of watermelons and to determine the best positions for the impact point and response measurement microphone. A firsttype spherical mode and its resonant frequency was the best indicator of internal quality problems. Finite element modal analysis was performed to establish a watermelon shape/characteristics model and to compare theoretical and experimental results.
The assessment of watermelon ripeness on the basis of its apparent properties, such as size or skin colour, is very difficult as traditional methods have various problems and limitations. These include lack of uniformity, concentration of excitation energy within narrow bands and need for physical contact between a fruit and the measuring device. In this study a new method making use of Laser Doppler Vibrometry technology (LDV) has been applied to evaluate the ripeness of watermelons, without many of those limitations. At first a watermelon is excited by a shaker as vibration generating device within a range of frequencies. At the same time, the vibrating response of the upper side of the fruit is measured by LDV. The device emits a laser beam on a spot above the sample. The beam reflected from that point is received by the LDV and finally the vibration response of the sample is measured and the signal is sent to the computer. Using a fast fourier transform algorithm and the ratio of input to response signals, the frequency response of the fruit sample was processed and the desired results extracted.
fechter wrote:Then they do the Watermelon ripeness destructive test That's got to be the best part.
bigmoose wrote:. My secret? I wait for a 60 ish year old woman to start picking through the watermelon pile. As she appears about done, I ask her: "Could you pick one for me?" She usually points to one of the last 4 she discarded and says: "That's a pretty good one." I thank her, pick it up, pay for it, go home and enjoy it!