3.2.1. Design of the Finger End

The human finger pulp has the biological characteristics of a thicker cuticle and subcutaneous fat pad. In grasping small fruits, the last finger pulps gradually form the concave geometric surface that are fitted to the fruit surface. Hand-picking realizes the grasping characteristics of large contact areas, strong envelopment, and flexible contact. Therefore, the finger ends were designed as the geometric surface close to the spherical surface of the cherry tomato. The parameters of the geometric surface are shown in

Equation (7) (unit: mm). The model is shown in Figure 6. Its surface was covered with the 3 mm soft material called Dragon Skin 10 for flexible contact.

$$\begin{cases} x^2 + y^2 + z^2 = 40\\ -5 \le x \le 5\\ y > 0\\ -10 \le z \le 10 \end{cases} \tag{9}$$

**Figure 6.** The design of finger end surface. Note: the yellow area is the surface.
