*2.2. Different Excitations and Behaviour of Grape Cluster Fruit during Robotic Transportation and Placing*

When a grape cluster is transported towards a box after harvesting, the excitation is mainly caused by the start–stop of the mechanical system that transfers the gripper to the main rachis of the grape cluster, when the position of the main rachis of the cluster deviates from the point parallel to the gripper, as shown in Figure 2. Thus, the grape cluster starts to vibrate, and bending of the main rachis happens. In the operation of speedy robotic transportation, this bending of rachis would cause a severe load on the pedicel. When the load exceeds the connection strength, then the berry fall starts. During the speedy robotic placing of the grape cluster into the box, excitations come from the packaging materials, which is transmitted into the whole cluster, as shown in Figure 2. These excitations apply a load on the connection point between the pedicel and the berry so that berry shattering happens. Thus, the berry shatter of grape clusters is a highly complex problem of multiple loads during the whole robotic transportation placing cycle. Therefore, in this paper, the main focus is to analyze the vibration behavior of hanging grape clusters during vertical robotic transportation and placing cycles. The effect of different speed and acceleration excitations on the cluster during vertical transportation and the impact of different packaging materials on the cluster were observed and analyzed.

**Figure 2.** Different excitation transmissions and damage of grape cluster fruit during robotic transportation and placing cycles.

#### *2.3. Experimental Materials*

The experiment was carried out in the Key Laboratory of Modern Agricultural Equipment Engineering, designated by the Ministry of Education, Jiangsu University, Zhenjiang, China. Three artificial grape clusters with different shapes and masses (0.48, 0.50, 0.53 kg), measured with a digital weight balance (BP Professional Electronic Balance BP-6228, accuracy 0.01 g), were used as experimental materials. There were about 70 to 80 berries in each cluster that were filled manually with soil to maintain a similar mass to that of real berries, and each berry mass was 0.005 to 0.007 kg [63,64]. Since the real cluster will be damaged in experiments under different speeds and accelerations, which will lead to a change in conditions, the results of different excitation treatments cannot be put together to compare and analyze [62]. For 40 years, artificial fruits have been built similar to real agricultural produce in order to measure the mechanical load caused by harvest and postharvest handling systems [30]. Three different packaging materials—(a) a rigid plastic box, (b) a corrugated fiberboard box, and (c) an expandable polystyrene box—were used for the experimental placing test [35]. The experimental setup and materials are shown in Figure 3. A lead screw lathe with a fabricated 1 DOF (degree of freedom) actuator, a gripper, and a single-axis force sensor (model: MIK LCS1; weight range 0–5 kg with 0.03% FS) that was fixed in between the gripper and the hanging grape cluster were used for the measurement of magnitude of the cluster's vibration in terms of forces acting on the grape cluster before and after the impact in real-time. The behavior of grape cluster movement during and after the impact with the packaging materials was recorded with a high-speed camera system (Olympus, i-speed LT), as shown in Figure 3a [65]. The camera system was adjusted to 1000 fps (frames per second), with a black and white screen and a light source for high visibility. It was placed at a distance of 3.5 m from the hanging grape cluster.

**Figure 3.** Experimental materials: (**a**) experimental setup; (**b**) 3-grape clusters; (**c**) 3-packaging materials.
