Simulation and Experiment on Caging or Uncaging of a 3-D Object Using a Three-Pin Gripper We conduct two experiments involving a caging grasp and an uncaging grasp. Caging Grasp We assume the initial caging configuration as in Figure 15(c). Then we conduct the simulation of the caging process using ADAMS, as shown in Figure 17(a)-(d). The actual experiment using the three-pin gripper is demonstrated in Figure 18(a)-(b). (a) (b) Uncaging Grasp We assume the initial uncaging configuration as in Figure 16(c). Then we perform the simulation of the entire caging grasping process using ADAMS, as shown in Figure 19(a)-(d). The actual grasping experiment is demonstrated in Figure 20(a)-(b). Conclusions This article investigates the relationship between a cage and the form-closure grasp (full immobilization) of a single DoF two-pin or three-pin gripper. Thus, an object being caged would finally arrive at a stable state, which is of practical importance for industrial applications of the gripper. The detection of the form-closure grasping cage based on the attractive region formed by the constraints of the gripper is as follows: We first construct a special function in the configuration space and denote it by the attractive function. We then detect the minimum and the boundary of the attractive function. The minimum of the attractive function denotes a form-closure grasp. The boundary of the attractive function encloses the cage set on the attractive region. Therefore, we can select an initial caging grasp that will finally achieve a (c) (d) Figure 19. (a) The initial uncaging configuration, (b) the gripper squeezing the bolt with (c) an unstable grasp, (d) resulting in the bolt not being picked up. form-closure grasp on the attractive region. For caging of the 3-D object, we divide the attractive function in the highdimensional configuration space into two subfunctions in the low-dimensional subspaces. The proposed method can be used for grasping of polygon-like or polyhedron-like objects with a 1-DoF industrial gripper. The attractive region formed by the gripper is used to eliminate the uncertainty of the gripper and to achieve a stable grasp. Similar constrained regions can be obtained in the configuration space of other manipulation systems. Gripper Gripper Gripper Gripper Bolt (a) Bolt Bolt Bolt (b) (a) Figure 18. (a) The gripper is being moved to the caging configuration and (b) the object after it has been picked up. (b) Figure 20. (a) The gripper moving to the uncaging configuration and (b) the object after it has escaped from the gripper. SEPTEMBER 2017 * IEEE ROBOTICS & AUTOMATION MAGAZINE * 95