# Design of an Eye-in-Hand Smart Gripper for Visual and Mechanical Adaptation in Grasping
## 1 Introduction  
With the advancement of technology, robots have been widely incorporated into industrial, commercial, and even home applications. For applications in daily life or smart manufacturing environments, a robotic gripper that can universally grasp objects is of utmost importance. Owing to the needs of high accuracy, high repeatability, and strong gripping force, an industrial robotic gripper is commonly designed to possess a single-degree-of-freedom actuation. Despite the aforementioned advantages, it is difficult to adapt to different objects. As such, to maximize the flexibility in grasping, changing the adaptors in this single-degree-of-freedom gripper is necessary. Currently, the most dexterous gripper available is the human hand, and its flexibility is too hard to achieve by a robotic gripper. To mimic the characteristics of a human hand, [PERSON] et al. designed a humanoid hand with multiple degrees of freedom and five fingers [1], and [PERSON] et al. also developed a 3D-printed humanoid hand control with fivefingers and four motors embedded in the hand [2]. They attempted to design a humanoid robotic hand to imitate human motion. Although a humanoid gripper has good flexibility, its accuracy and payload capacity are limited. [PERSON] and [PERSON] used springs and belts to control multiple finger joints by using a single motor to build an under-actuated gripper [3]. This under-actuated gripper adapted the surface of an object by the force-limit characteristics of a driven chain, during which certain finger joints would stop while the others kept moving to adaptively cover the object. To reduce the number of actuation elements, such as motors, in a robotic gripper, [PERSON] et al. proposed an adaptive structure that contained redundant degrees of freedom [4]. This gripper utilized a single driving source to control its finger, which consisted of linkage structures with multiple degrees of freedom. [PERSON] and [PERSON] proposed a gripper finger that used multiple four-bar linkages in series [5] to reduce the number of driving sources while maintaining or even improving the adaptability of the gripper. Based on this design concept, they attempted to derive mathematical functions for each adaptive gripper finger joint [6]. Conversely, [PERSON] and [PERSON] reported that the adaptability of the adaptive gripper is affected by external forces applied to the structure, which eventually led to bending of the finger structures [7]. To properly design an adaptive gripper, a design concept with multiple redundant degrees of freedom was investigated in our previous study [8]. To take it further, systemic and detailed analytical parameter studies and integration with visually adaptive algorithms are conducted and examined in this paper. Experimental validations were conducted by prototyping an eye-in-hand adaptive three-finger robotic gripper through mechatronics integration. In addition to the mechanical-adaptive feature, robotic arms with computer vision systems are widely used in pick-and-place and visual-tracking control applications. Three types of camera installation are typically used, as illustrated in Figure 1. The first type is an eye-to-hand system, in which the frames of the camera and gripper are in different coordinate systems. The second type is the eye-on-hand system, where the camera and gripper are mounted at the end of the manipulator, but the coordinate system of the camera is offset from that of the gripper. The third type is the eye-in-hand system, where the camera and gripper are again mounted at the end of the manipulator but share the same coordinate system. In other words, the camera is part of the gripper module in the eye-in-hand configuration. For an eye-to-hand system, the camera's view can be obstructed by another object that is neither part of the target nor the arm of the manipulator itself. However, eye-on-hand and eye-in-hand systems can solve this problem because the camera can move along with the manipulator.