Vibration Feature Analysis Of Grape Cluster In Different Stages For Robotic Harvesting

Berry falling is one of the main loss of fresh grapes during harvest and post-harvest handling.It has also become one of the bottleneck problem in the application of robotic grape harvesting.Analyzing the features and laws of grape cluster vibration during robotic harvesting is very important for realizing efficient and low-loss harvesting.Therefore,in this study the vibration features and berry falling mechanism during horizontal,vertical transportation and placement of fresh grape cluster were analyzed.This thesis includes three main parts:(1)The vibration features of grape cluster during robotic horizontal transportation stage was studied.Therein,the effect of different excitations on the vibration of the hanging grape cluster was investigated.The experimental results showed that the swing angle of the cluster increased linearly with the hanging force,both for the accelerating and deaccelerating phases,respectively.The multi-stage cluster’s vibration during robotic transportation was observed,and the behavior of cycled damping after a sudden stop of the actuator was found.The modeling calculation results in damping phase were agreed with experimental results with R~2 more than 0.90 at an optimum acceleration of 10 m/s~2.It was concluded that start(accelerating)and stop(deaccelerating)phases of the actuator during transportation caused more vibration of the cluster,resulting more chances of berry fall.(2)The effect of a cluster’s vibration on berry fall mechanism during robotic vertical transportation and the impact of different placing materials was then analyzed.In experiment,three grape clusters(0.48,0.50,0.53 kg),three placing materials(rigid plastic box,corrugated fiberboard box,expandable polystyrene box),four speeds(0.4,0.6,0.8,1.0 m/s),and four acceleration excitations(6,8,10,12 m/s~2)were set.It was concluded from experiment that with the increase of speed and acceleration excitations,the change of hanging force increased positively(R~2=0.92).Additionally,the force after the striking of the grape cluster with placing materials decreased negatively(R~2=0.97),and the corresponding index of berry deflection increased.It was observed that the deflection of the upper berries is due to the excitations coming from bending of the main rachis,and the deflection of lower berries is due to the torsional load on the junction between the pedicel and the berry during placing.It was also concluded that rigid plastic box caused the maximum deflection of the grape berries,with the highest change in force of 8.6 N after the impact,resulting more berry fall.(3)The third part deals with vibration simulation analysis of grape cluster.Therein,firstly different properties of fresh grape berries i.e.physical,physiological and mechanical properties(skin hardness,compression and detachment force)were determined.Simulation study was carried out to investigate vibration mechanism of grape cluster during robotic transportation and placing phases.During horizontal transportation,the magnitudes of the hanging forces and swing angle were observed higher in the deaccelerating phase(i.e.8.2 N and 72.40 respectively)compared to that in accelerating phase(i.e.7.3 N and 60.34 respectively)for input excitation speed of 1 m/s(with 10 m/s~2 acceleration value),while,during vertical transportation,there is no significant impact observed due to less vibration of the cluster.Moreover,the maximum value of hanging force,and tensile and bending loads were found associated with the rigid plastic material,which causes more berry fall.The simulation results for all these phases are found in agreement with the experimental results.Summarizing all,this study provides technical and theoretical support for the damage-free control of fresh-eating cluster fruits during different stages of robotic harvesting,and suggests safe zones,placing material and excitations at which chances of damage would be minimum.The knowledge and understanding about the vibration mechanism of cluster during different stages of robotic harvesting has a great value to improve the performance and reliability at both industrial and field level.