Open-Loop Precision Grasping With Underactuated Hands Inspired by a Human Manipulation Strategy

Abstract

In this paper, we demonstrate an underactuated finger design and grasping method for precision grasping and manipulation of small objects. Taking inspiration from the human grasping strategy for picking up objects from a flat surface, we introduce the flip-and-pinch task, in which the hand picks up a thin object by flipping it into a stable configuration between two fingers. Despite the fact that finger motions are not fully constrained by the hand actuators, we demonstrate that the hand and fingers can interact with the table surface to produce a set of constraints that result in a repeatable quasi-static motion trajectory. Even when utilizing only open-loop kinematic playback, this approach is shown to be robust to variation in object size and hand position. Variation of up to 20 in orientation and 10 mm in hand height still result in experimental success rates of 80% or higher. These results suggest that the advantages of underactuated, adaptive robot hands can be carried over from basic grasping tasks to more dexterous tasks. Note to Practitioners-This work was motivated by the need for a means for robots operating in unstructured environments to robustly grasp and manipulate a wide range of objects using a multipurpose hand.To date, one of the most difficult tasks for a general-purpose hand has been grasping small, thin objects, which are typically found resting on a flat surface such as a table. The size of the object and the presence of the backing surface make it difficult to establish contact with the object resulting in a stable grasp. In previous work, we have shown how proper attention to the passive mechanics of the hand, including mechanical compliance and underactuated differential transmissions, can enable robust, open-loop "power" grasping of large objects. In this paper, we extend the same concept to "precision" grasping of small objects with the same demonstrated robustness and simplicity.

Exploitation of environmental constraints in human and robotic grasping

“…These works use environmental constraints for example to position the hand relative to the object [6], to cage objects [17,6,20], or to fixate an object during planar sliding [7,6]. Some pre-grasp manipulation relies on environmental constraints to improve grasp success.…”

Grasping and Manipulation of Unknown Objects Based on Visual and Tactile Feedback

“…Employing the outlined control basis framework to realize approaching motions for grasping and exploiting the passive compliance of modern, often underactuated hands [18,19], grasp planning is extremely simplified: The fingers will automatically wrap around the object due to the inherent compliance of the hand. Thus, the only task for grasp planning is to choose a suitable grasp prototype and to align the hand to the object during the approach phase.…”

Characterization of the precision manipulation capabilities of robot hands via the continuous group of displacements

“…This finger/palm layout has been normally used for power grasping (e.g. [24]); but, despite its simple architecture, it has been shown that this hand can be used for complex manipulation operations such as picking up small objects from a flat surface (flip-and-pinch tasks) [25].…”