Since the whole assembly process has typical phase transitions between control laws driven by the environment event, the techniques of hybrid control can be employed to specify the hybrid control properties. Finally a hybrid controller and corresponding hybrid control programs are designed using the HCSP language to describe a peg-in-hole problem.

Hybrid control approach to the peg-in hole problem

This paper presents a minimalist, four-finger hand comprised of two pairs of tendon-driven, underactuated fingers decoupled by an independent, central, rotating axis. This mechanical configuration allows for finger-gaiting while also retaining the passive adaptability and other capabilities of the underactuated finger pairs. As a result, the hand, requiring only four actuators, is capable of a unique set of dexterous manipulation primitives, including finger-gaiting and precision manipulation, while retaining the robust, adaptive precision and power grasping behavior of underactuated hands. The low-cost, compact design is built with rapid-prototyping techniques and off-the-shelf components, enabling quick and inexpensive fabrication that can be produced using even desktop FDM 3D printers.

An underactuated hand for efficient finger-gaiting-based dexterous manipulation

The paper discusses the scale-dependent grasp. Suppose that a human approaches an object initially placed on a table and finally achieves an enveloping grasp. Under such initial and final conditions, he (or she) unconsciously changes the grasp strategy according to the size of objects, even though they have similar geometry. We call the grasp planning the scale-dependent grasp. We find that grasp patterns are also changed according to the surface friction and the geometry of cross section in addition to the scale of object. Focusing on column objects, we first classify the grasp patterns and extract the essential motions so that we can construct grasp strategies applicable to multifingered robot hands. The grasp strategies constructed for robot hands are verified by experiments. We also consider how a robot hand can recognize the failure mode and how it can switch from one to another.

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Scale-dependent grasp

A practical procedure for achieving an, enveloping grasp is presented especially for cylindrical objects. It is composed of three phases, the approach phase, the lifting phase and the grasping phase. For the grasping phase, we introduce the natural computation mode in which a preset torque is commanded to each joint, so that both the equilibrium position and the contact forces may be determined automatically. A sufficient condition for achieving the enveloping grasps is shown for the given procedure. Experimental results are also shown to verify the effectiveness of the proposed grasping procedure.

On three phases for achieving enveloping grasps-inspired by human grasping

In this paper, we perform a quantitative and qualitative analysis of human peg-in-hole operations in a tele-operating setting with a moderate degree of dexterity. Peg-in-hole operation with different starting configurations are performed with the aim to derive a strategy for performing such actions with a robot. The robot is a 6 DoF robot arm with the dexterous 3 finger SDH-2 gripper. From the extracted data, we can distill important insights about (1) feasible grasps depending on the peg's pose, (2) the object trajectory, (3) the occurrence of a particular force-torque pattern during the monitoring of the action and (4) an appropriate insertion strategy. At the end of the paper, we discuss consequences for using these insights for deriving algorithms for robot execution of peg-in-hole actions with dexterous manipulators.

Analysis of human peg-in-hole executions in a robotic embodiment using uncertain grasps

This paper discusses the peg-in-hole task performed by a system integrating a dextrous hand, a 6-DOF robot and a camera. It is shown how the starting conditions of the final insertion only performed by the fingers are affected by the previous stages. Based on the experimental findings, some criteria for the overall system design and the required manipulation capabilities of the gripper are derived. With respect to this performance evaluation a modular concept for solving insertion tasks with a multifingered gripper is presented. The object manipulation is realized by primitives which are executed in dependence on various assembly states. The implementation of this approach is described and beside a theoretical characterization, experimental results are given.

A modular approach for solving the peg-in-hole problem with a multifingered gripper

Whereas the emphasis of precision grasping only using the fingertips is placed on dexterity and sensitivity, power grasps guarantee high security and stability. But even if the task requires a power grasp, in the initial configuration the complete enveloping by the fingers is often impossible due to the position of the object in the workspace and only a fingertip grasp can be applied. Then a transition from precision to power grasping has to be performed. Based on an experimental study this paper discusses several possibilities to realize this transition by using a three-fingered dextrous hand mounted on a 6DOF robot. In particular it is distinguished between strategies requiring a coordination of robot and hand and strategies performing the transition only by the fingers like humans do.

K.P. Kleinmann

Papers

A modular approach for solving the peg-in-hole problem with a multifingered gripper

Object manipulation by a multifingered gripper: on the transition from precision to power grasp