Abstract:Pitting is an essential step for producing litchi lantern flesh, while the variable pit size poses a challenge for efficient and successful mechanical pitting. To solve this problem, an adaptive pitting tool and mechanism was designed by measuring the physical properties of litchi fruit, and the spatiotemporal changes of equivalent stress and cutting stress during the pitting process of litchi at three different rotational speeds were investigated, based on the LS-DYNA dynamic simulation and bench tests. Furthermore, it quantified and compared the success rates and pulp loss rates of adaptive pitting for litchi fruit with variable pit sizes at different rotational speeds, and evaluated the overall pitting performance. Lychee fruit and kernel sphericity coefficients of 0.95 and 0.74 were obtained, and their three-dimensional radial dimensions showed normal distributions. The simulation results indicated the effects of rotational speed on the distribution of effective stress and the extreme values of cutting stress in litchi fruit was consistent with the bench test results. As rotational speed increased, both the maximum equivalent stress and maximum cutting stress in the litchi were decreased, leading to improved success rates for adaptive pitting of litchi with variable pit size. Among the three tested rotation speeds (feed with speeds of 100 mm/min and 20 mm depth), pitting at 292 r/min demonstrated the best overall pitting performance, with a 100% success rate and a pulp loss rate of 22.4%, respectively. The revealed adaptive pitting mechanism were significant for developing high-quality and efficient pitting devices for stone fruits, including but not limited to litchi.
