Robotic Grasping Using Proximity Sensors for Detecting both Target Object and Support Surface

The robustness of the positioning and posturing of robot hands relative to target object and support surface is an important issue for autonomous grasping. For example, to perform a grasping action such as picking up thin objects from a table top, the position and posture of the hand must be controlled to keep adequate relative posture and distance to the support surface besides those between the hand and the target object. Because slight errors in the posture and position are enough to cause grasping failure, the positioning and posturing of the hand must be precise enough, specially when the hand is close to the target object and support surface. To improve the robustness of robotic grasping, in this paper we present a method by grasping control based on the relative posture and position between hand and support surface besides those between hand and target object, using proximity sensors. Proximity sensors are newly installed on fingernails besides on the fingertips. As the fingernail sensor, an integration of Time-of-Flight (TOF) sensor and photo-reflector is designed to realize long range detection, as well as with precise and high-speed detection regardless of the reflectance of support surfaces when approaching the support surface. By the sensors, the hand can approach the object and support surface coarsely first, and then can be controlled fast and precisely to realize adequate grasping motion along the support surface but without contact with the support face. The method has been implemented to a manipulator system, and successful grasping experiments have demonstrated the effectiveness of the proposed method.