# Design of an Eye-in-Hand Smart Gripper for Visual and Mechanical Adaptation in Grasping
## 4 Mechanism Adaptive Results  
To validate the aforementioned kinematic analyses, a prototype design of an adaptive robotic gripper that can be used in various environments was presented and investigated in this section. In contrast to the design of a general-purpose robot gripper, the goal of the gripper is to assist industrial, commercial, and even home applications. To achieve this goal, the gripper was designed with maximum flexibility and high adaptivity for grasping objects, similar to a human hand. When humans attempt to grasp an irregular object, their fingers naturally cover the object according to the length of the object's surface. To achieve this humanoid grasping motion, the proposed adaptive robotic finger must be composed of several four-bar linkage structures to provide extra degrees of freedom for grasping. In addition to the finger linkage structures, the number of fingers is another key engineering design factor for robotic grippers. Evidentially, more fingers naturally offer a more stable gripping when grasping irregular objects. Interestingly, most industrial robotic  
Figure 14: Scatter plots (**top**) and input-output angle relationships (**bottom**) of the triple four-bar linkage structures when \(h_{1}=1.0L\) with different initial angle values (**a**) \(\varphi\) & \(\psi=45^{\circ}\), (**b**) \(\varphi\) & \(\psi=90^{\circ}\), and (**c**) \(\varphi\) & \(\psi=135^{\circ}\). Figure 13: Scatter plots (**top**) and input-output angle relationships (**bottom**) of the triple four-bar linkage structures when \(h_{1}=1.0L\) with length ratios (**a**) \(R=0.5\), (**b**) \(R=1.0\), and (**c**) \(R=1.2\). grippers are designed with two parallel rigid fingers. However, if the object's shape is irregular or asymmetric, gripper designs with more than two fingers are of a natural choice, as evidenced by [PERSON] and [PERSON] [19], to achieve stable grasping operations. The effects of the linkage parameters on the range of motion for double-section and triple-section structures are listed in Table 1. First, we denote the effect of the length ratio \(R\) between \(h_{2}\) and \(h_{1}\). With the same parameters, a larger \(R\) was found to decrease the range of motion for both the double- and triple-section structures. Second, with the change in initial angle \(\varphi\) and \(\psi\), a larger initial angle slightly decreases the range of motion at the endpoint. However, it obviously decreases the range of the input angle \(\delta_{1}\) as illustrated in Figures 12 and 14. Third, the length of \(h_{1}\) can slightly change the range of motion when different length ratios \(R\) are applied. When \(R\) is smaller than 1, a greater \(h_{1}\) value slightly increases the range of motion. However, when \(R\) is greater than 1, a larger \(h_{1}\) can decrease the range of motion. Finally, by comparing the double- and triple-section structures, the triple-section structures were found to be able to achieve a larger motion range in most cases. In this study, an adaptive gripper with three identical fingers was developed. Each finger of the gripper utilized three four-bar linkage structures to mimic the fingers of the human hand with MCP, PIP, and DIP joints. The parameters of the gripper finger structure are \(L=30\) mm, \(h_{1}=0.8\), \(R=0.5\), and \(=\psi=60^{\circ}\). We then analyzed its kinematics using the previously presented analytical model, as discussed in the previous sections. The gripper specifications are listed in Table 2. The range of motion of the gripper is illustrated in the scatter plot in Figure 15 to show the positions that the adaptive robotic finger can reach. The gripper can change its shape along the surface of the object, as illustrated in the simulations (top) and experiments (bottom), as shown in Figure 16. Using the cylindrical object in Figure 16a and different-sized boxes in Figure 16b-d as the target objects to be grasped, the adaptive feature of the gripper finger to the object's surface was demonstrated.