Harald Staab

Extrinsic dexterity: In-hand manipulation with external forces

“In-hand manipulation” is the ability to reposition an object in the hand, for example when adjusting the grasp of a hammer before hammering a nail. The common approach to in-hand manipulation with robotic hands, known as dexterous manipulation [1], is to hold an object within the fingertips of the hand and wiggle the fingers, or walk them along the objects surface. Dexterous manipulation, however, is just one of the many techniques available to the robot. The robot can also roll the object in the hand by using gravity, or adjust the objects pose by pressing it against a surface, or if fast enough, it can even toss the object in the air and catch it in a different pose. All these techniques have one thing in common: they rely on resources extrinsic to the hand, either gravity, external contacts or dynamic arm motions. We refer to them as “extrinsic dexterity”. In this paper we study extrinsic dexterity in the context of regrasp operations, for example when switching from a power to a precision grasp, and we demonstrate that even simple grippers are capable of ample in-hand manipulation. We develop twelve regrasp actions, all open-loop and hand-scripted, and evaluate their effectiveness with over 1200 trials of regrasps and sequences of regrasps, for three different objects (see video [2]). The long-term goal of this work is to develop a general repertoire of these behaviors, and to understand how such a repertoire might eventually constitute a general-purpose in-hand manipulation capability.

Structured collaborative behavior of industrial robots in mixed human-robot environments

In mixed human-robot environments safety and productivity are two important factors for the design of robotic collaborative behaviors. The collaborative behavior should be able to uphold productivity as far as possible while respecting safety constraints for varying collaboration modes and evaluation criteria. In this paper, a concept of using a finite state automaton for structuring the collaborative behavior of industrial robots is proposed to systematically handle the following exceptions. Safety and productivity (S&P) exceptions which either interfere with productivity or compromise workers safety are caught by the corresponding exception reaction. The regular production operation after an exception reaction is restored with exception recovery strategies. The state automaton model for an industrial assembly scenario is finally presented to illustrate this concept. A demonstration realizing the example for interaction between an ABB Dual-Arm Concept Robot and a human is discussed.

Regrasping objects using extrinsic dexterity

This video presents the application of Extrinsic Dexterity to change the pose of an object in the hand, i.e., to regrasp the object. Gravity, inertia, arm motions and external contacts can be exploited to manipulate an object in the hand. As such dexterity does not depend solely on the intrinsic capability of the hand, but rather is derived from external resources, we call it as “Extrinsic Dexterity”. The video showcases a repertoire of regrasps developed for a simple gripper and presents one of the sequences regrasps designed to explore border manipulation capability by connecting different regrasps.

A two-phase gripper to reorient and grasp

This paper introduces the design of novel two-phase fingers to passively reorient objects while picking them up. Two-phase refers to a change in the finger-object contact geometry, from a free spinning point contact to a firm multipoint contact, as the gripping force increases. We exploit the two phases to passively reorient prismatic objects from a horizontal resting pose to an upright secure grasp. This problem is particularly relevant to industrial assembly applications where parts often are presented lying on trays or conveyor belts and need to be assembled vertically. Each two-phase finger is composed of a small hard contact point attached to an elastic strip mounted over a V-groove cavity. When grasped between two parallel fingers with low gripping force, the object pivots about the axis between the contact points on the strips, and aligns upright with gravity. A subsequent increase in the gripping force makes the elastic strips recede into the cavities letting the part seat in the V-grooves to secure the grasp. The design is compatible with any type of parallel-jaw gripper, and can be reconfigured to specific objects by changing the geometry of the cavity. The two-phase gripper provides robots with the capability to accurately position and manipulate parts, reducing the need for dedicated part feeders or time-demanding regrasp procedures.

The DOHELIX-Muscle: A Novel Technical Muscle for Bionic Robots and Actuating Drive Applications

In this paper a new concept of a technical muscle is presented. The proposed muscle is based on standard components and is scalable in many respects: size, weight, power, speed, price, and quality. It is composed of a turning shaft with small diameter and a high-strength and highly flexible plaited cord. The shaft may be driven by a small DC-motor, possibly in combination with a gearbox. This makes design, power supply, and control quite easy compared to other types of artificial muscles such as pneumatic, hydraulic, shape memory alloy, and electro-active polymer muscles. With appropriate measures in design it will be able to meet various application requirements such as wide temperature range and high IP rating. Moreover, with careful selection and dimensioning of components a very high degree of efficiency, a very high power to weight ratio, and high dependability may be achieved. The muscle is applicable as an actuating drive in industrial environments as well as for bionic robot mechanisms with biomimetic and undulatory motion. The name DOHELIX is an acronym for double helix, a shape resulting from contraction of the muscle.

Ultra-flexible production systems for automated factories

Conveyor based transportation systems are used in today manufacturing environments. The main concept we introduce in this paper is using mobile platforms to move parts, tools and fixtures between workstations in a manufacturing environment instead of conveyors. A conveyor-based production system is a fixed transportation system, hard mounted and not reconfigurable, any change in the conveyors path is costly, time-consuming and difficult. Mobile platforms allow for a more flexible manufacturing environment as it only requires a change in the software to reroute the transportations paths and accommodate the changes to the production flow and workstations. This concept paper addresses two objectives: 1) describe some of the existing mobile platform used in industry today 2) introduce the concepts and a simulation of the ultra-flexible production system.