3.2.2. Effect of Acceleration Excitations during Vertical Transportation

It was observed from the experiments that at input acceleration excitations (6, 8, 10, 12 m/s2), the amplitude of the cluster's vibration was maximum at the start of the actuator movement. It was due to the sudden motion of the actuator and the friction of the guide rails [66] on which the actuator moves. It was observed, secondly, from the experimental analysis, that the magnitude of the cluster's hanging force in the starting phase of the actuator was positively correlated with the input acceleration and mass of the cluster. The magnitude of hanging force was observed to be high at the acceleration excitation of 12 m/s<sup>2</sup> at the following speeds of the actuator, i.e., (0.4, 1.0 m/s), as shown in Figure 8. It was also observed from the experimental analysis that the optimized acceleration excitation was 10 m/s2, at which the deflection of the berries was minimum. This is due to the cluster swinging in one direction, with minimum twisting of the main rachis. Therefore, the chances of berry deflection will be minimized. These results suggest that the acceleration phase causes serious vibrations of the grape cluster during robotic vertical transportation, and more berry deflection occurs in this phase. In robotic vertical transportation, the acceleration excitations did not affect the vibration of the grape cluster too much, so the cluster's vibration is always low in vertical downward transportation compared to horizontal transportation of the hanging grape cluster, as measured in our previous research [62].

**Figure 8.** Effect of acceleration excitations on the peak force of the cluster during vertical transportation at different speeds, such as (**a**) 0.4 m/s; (**b**) 1.0 m/s.

#### 3.2.3. Effect of Packaging Materials on the Berry Deflection of Cluster

In the placing phase of the grape cluster, the time interval of the stop or deaccelerating phase of the actuator was too short, so the berry dropping mechanism of the whole cluster could not be observed properly. Therefore, a high-speed photography camera was used for the analysis. It was observed from the high-speed photography images that the deflection of the cluster's berries in terms of torsion from the bottom and bending from the upper side increases with an increase in speed and acceleration excitations of the actuator. It was also observed from Figure 9 that the effect of the rigid plastic box on the deflection of the upper and lower berries was at a maximum, and it showed small force signals, i.e., 8.8 N, compared to expandable polystyrene and corrugated fiberboard boxes (9.6 and 9.35 N). This is due to the maximum excitations that transmit from the rigid box surface towards the whole grape cluster. It can also be seen from Figure 9 that the fluctuations in the force signals are more after striking with the rigid plastic box due to the large deflection of the whole cluster. These force signal results indicate that the choice of packaging materials can significantly reduce the possibility of berry drop damage during the robotic placing of cluster fruits.

**Figure 9.** *Cont.*

(**a**)

**Figure 9.** High-speed camera-based determination of cluster deflection and force signals after striking with different placing materials: (**a**)force change signals with corrugated fiberboard; (**b**) force change signals with expandable polystyrene; (**c**) force change signals with a rigid plastic box.

3.2.4. Effect of the Cluster's Mass on Berry Deflection during Placing

Figure 10 shows the high-speed camera images of three different grape clusters (0.48, 0.50, 0.53 kg) during placing on a rigid plastic box, along with the corresponding results of the force sensor. According to the results, with the increment in the mass of the grape cluster, the deflection of the berries was observed to be less. This was due to the excitations absorbed by the grape cluster after colliding with the packaging material; it decreased with the increase in the mass of the cluster. The grape cluster with a mass of 0.48 kg showed the maximum change of force or load, i.e., 8.20 N from the calibrated force value of that sample, 10.8 N after colliding with the rigid plastic box, as compared to two other grape cluster samples with different masses, i.e., 0.50 and 0.53 kg, with changes in force signals of 8.75 and 9.28 N. The calibrated force of these two cluster samples was 11 and 11.15 N respectively. These results suggest that fruit mass is an important component of the momentum that affects the detachment forces of the berries; the higher the fruit mass, the higher the momentum and hang force, and the lower the berry shattering during placing due to the compactness of the berries.

Force signal for three different clusters

**Figure 10.** Effect of the cluster's mass on force change during placing of grape clusters: (**a**) 480 g; (**b**) 500 g; (**c**) 530 g.

3.2.5. Behavior of Top and Bottom Berries during Placing

Figure 11 shows the behavior of the top berry and the bottom berry during the placing of the grape cluster at an excitation speed of 1.0 m/s. The selected top berry is shown in red color; the bottom berry is in yellow. It can be seen from Figure 11 that at the start of the placing, there is no bending of the main rachis; hence, a small deflection of the berries at the top and bottom sides of the cluster was observed. When the cluster collided with the packaging material, the top berry deflected from the initial position due to the load coming from the bending of the main rachis; the bottom berry was also displaced from the initial position due to torsion between the pedicel and the berry. At the end of the placing phase, the top berry continued to deflect in some other direction. These continuous changes in the position of the berries decrease the connection strength between the berry and the pedicle and become the reason for berry drop in speedy robotic placings of grape clusters on both

industrial and farm levels. These dropping of berries due to deflection during placing can be controlled by a force feedback mechanism.

**Figure 11.** Behavior of berry deflection during robotic placing. Top berry in (red color) and bottom berry (yellow color).

3.2.6. Relationship between the Cluster's Force before and after Impact

It was observed from the experimental analysis that with the increase of speed, i.e., (0.4, 0.6, 0.8, and 1.0 m/s) of the actuator, the corresponding average magnitude of hanging force for all three grape cluster samples increased linearly (with *R*<sup>2</sup> = 0.92, 0.97, 0.98) at the start of the actuator's motion. Additionally, the magnitude of the force after impact with all three packaging surfaces decreased linearly (with *R*<sup>2</sup> = 0.99, 0.97, 1), as shown in Table 2 and Figure 12. This was due to the reason that the packaging surface bears the weight of the grape cluster during the stop of the actuator, which caused the berries' deflection from both the top and bottom sides of the cluster. It is easy to conclude that the higher the hanging force of the grape cluster, the greater the deflection of the cluster after striking the packaging surface, and more berry deflection occurs. There is a negative correlation between hang force and force after the impact of the cluster with a goodness

of fit of *R*<sup>2</sup> = 0.95 at different speeds, as shown below in Figure 13. These results show that the cluster with high mass showed a high magnitude of hang force, but it strikes the packaging material with low deflection of the berries due to the compactness of the berries in the cluster with high mass.


**Table 2.** Hang and impact force under different speed intensities.

**Figure 12.** Effect of different speeds on the changes of forces during transportation and impact: (**a**) hanging force; (**b**) impact force.

**Figure 13.** Relationship between hang force and impact force.
