State-of-the-art robotic grippers, grasping and control strategies, as well as their applications in agricultural robots: A review

Grasping, carrying and placing of objects are the fundamental capabilities and common operations for robots and robotic manipulators. Grippers are the most essential components of robots and play an important role in many manipulation tasks, since they serve as the end-of-arm tools, as well as the mechanical interface between robots and environments/grasped objects. Gripper developments are motivated by the great number of different requirements, diverse workpieces and the desire for well adapted and reliable systems. Grippers provide temporary contact with the grasped objects in manipulations. Secure grasping not only requires contacting the objects, but also avoiding the risk of potential slip and damage while the objects are picked and placed. To offer secure grasping for objects with a wide variety of shapes, sizes and materials, various sensors and control strategies are also needed. With the developments of technologies, labor shortage caused by the population aging, as well as the requirements of high automation degree, agricultural robots will find their increasing applications in agricultural and food industries. As the end-of-arm tools for the robots, grippers can be seen as the hands of robots, almost all automatic manipulations are conducted directly by robotic grippers. This paper gives a detailed summary about the state-of-the-art robotic grippers, grasping and sensor-based control methods, as well as their applications in robotic agricultural tasks and food industries. Different from workpiece in industrial environment, agricultural products are fragile and damageable. The requirement for grasping agricultural products is higher than that of grasping of industrial workpieces, various sensors are needed to be installed to the grippers to make them less aggressive, and more flexible and controllable. Therefore, particular attention has been paid to the sensors that used in the grippers to improve their sensing and grasping capabilities. The advantages and disadvantages of the grippers are discussed and summarized. Finally, the challenges and potential future trends of grippers in agricultural robots are reported.