Analysis of manipulator structures under joint-failure with respect to efficient control in task-specific contexts

Abstract — Robots are meanwhile able to perform several tasks. But what happens, if one or multiple of the robot’s joints fail? Is the robot still able to perform the required tasks? Which capabilities of the robot get limited and which ones are lost? We propose an analysis of manipulator structures for the comparison of a robot’s capabilities with respect to efficient control. The comparison is processed (1) within a robot in the case of joint failures and (2) between robots with or without joint failures. It is important, that the analysis can be processed independently of the structure of the manipulator. The results have to be comparable between different manipulator structures. Therefore, an abstract representation of the robot’s dynamic capabilities is necessary. We introduce the Maneu-verability Volume and the Spinning Pencil for this purpose. The Maneuverability Volume shows, how efficiently the end-effector can be moved to any other position. The Spinning Pencil reflects the robot’s capability to change its end-effector orientation efficiently. Our experiments show not only the different capabilities of two manipulator structures, but also the change of the capabilities if one or multiple joints fail. I

Knowledge-based automated mechanical design of a robot manipulator

Design methods have been improving with an increasing level of algorithmic support for some time. The most recent advances include generative design and various optimization methods. However, the automated design tools are often focused on a single stage of the design process, for example, kinematics design, mechanical topology, or drive selection. In this paper, we show the whole design process of a robotic manipulator in an automated workflow. The method consisted of two main parts: a genetic optimization of the kinematic structure and an iterative automated CAD design. The method was then applied to a case study in which a manipulator with five degrees of freedom for a handling task was designed.Web of Science1212art. no. 589

Optimization of a Reconfigurable Manipulator with Lockable Cylindrical Joints

This thesis presents a global optimization methodology to find the optimal Denavit-Hartenbeg parameters of a serial reconfigurable robotic manipulator maximizing a cost function over a pre-specified workspace volume and given lower and upper bounds on the design parameters. Several cost functions are investigated such as the manipulability measure, maximum force/torque capability of the manipulator at its end-effector, and maximum velocity capability of the manipulator, therefore improving the general kinetostatic performance of the manipulator. A modified global and posture-independent parameter of singularity (MPIPS) is presented, and a generic global optimization approach is proposed, using combined genetic algorithm (GA) and sequential quadratic programming (SQP). Different case studies are provided for a 3-DOF and a 6-DOF reconfigurable manipulator. Finally, a weighted objective function that balances between the opposing actions of the end effector velocity and force is proposed. The results are illustrated to demonstrate the performance of the generated manipulators, and are validated. Post-optimality analysis has also been conducted to investigate the sensitivity of the index to the variation in optimal parameters

A Two Dimensional Crystalline Atomic Unit Modular Self-reconfigurable Robot

Self-reconfigurable robots are designed so that they can change their external shape without human intervention. One general way to achieve such functionality is to build a robot composed of multiple, identical unit modules. If the modules are designed so that they can be assembled into rigid structures, and so that individual units within such structures can be relocated within and about the structure, then self-reconfiguration is possible. We propose the Crystalline Atomic unit modular self-reconfigurable robot, where each unit is called an Atom. In two dimensions, an Atom is square. Connectors at the faces of each Atom support structure formation (such structures are called Crystals). Centrally placed prismatic degrees of freedom give Atoms the ability to contract their outer side-length by a constant factor. By contracting and expanding groups of Atoms in a coordinated way, Atoms can relocate within and about Crystals. Thus Atoms are shown to satisfy the two properties necessary to function as modules of a self-reconfigurable robot. A powerful software simulator for Crystalline Atomic robots in two and three dimensions, called xtalsim, is presented. Xtalsim includes a high-level language interface for specifying reconfigurations, an engine which expands implicit reconfiguration plans into explicit Crystal state sequences, and an interactive animator which displays the results in a virtual environment. An automated planning algorithm for generating reconfigurations, called the Melt-Grow planner, is described. The Melt-Grow planner is fast (O(n2) for Crystals of n Atoms) and complete for a fully general subset of Crystals. The Melt-Grow planner is implemented and interfaced to xtalsim, and an automatically planned reconfiguration is simulated. Finally, the mechanics, electronics, and software for an Atom implementation are developed. Two Atoms are constructed and experiments are performed which indicate that, with some hardware improvements, an interesting self-reconfiguration could be demonstrated by a group of Atoms

Hierarchical Adaptive Control of Modular and Reconfigurable Robot Manipulator Platforms

Within the rapidly growing interest in today's robotics industry, modular and reconfigurable robots (MRRs) are among the most auspicious systems to expand the adaptability of robotic applications. They are adaptable to multiple industrial field applications but they also have additional advantages such as versatile hardware, easier maintenance, and transportability. However, such features render the controller design that manages a variety of robot configurations with reliable performance more complex since their system dynamics involve not only nonlinearities and uncertainties but also changing dynamics parameters after the reconfiguration. In this thesis, the motion control problem of MRR manipulators is addressed and hierarchical adaptive control architecture is developed for MRRs. This hierarchical structure allows the adjustment of the nominal parameters of an MRR system for system parameter identification and control design purposes after the robot is reconfigured. This architecture simplifies the design of adaptive control for MRRs which is effective in the presence of dynamic parameter uncertainty, unmodeled dynamics, and disturbance. The proposed architecture provides flexibility in choosing adaptive algorithms applicable to MRRs. The developed architecture consists of high-level and low-level modules. The high-level module handles the dynamic parameters changes and reconstructs the parametric model used for on-line parameter identification after the modules are reassembled. The low-level structure consists of an adaptive algorithm updated by an on-line parameter estimation to handle the dynamic parameter uncertainties. Furthermore, a robust adaptive term is added into this low-level controller to compensate for the unmodeled dynamics and disturbances. The proposed adaptive control algorithms guarantee uniformly ultimate boundedness (UUB) of the MRR trajectories in terms of robust stability despite the dynamic parameter uncertainty, unmodeled dynamics, changes in the system dynamics, and disturbance

Kinematic Design of Serial Link Manipulators from Task Specifications

One of the most important parameters to consider when designing a manipulator is the number of degrees-of-freedom (DOFs). This article focuses on the question: How many DOFs are necessary and sufficient for fault tolerance and how should these DOFs be distributed along the length of the manipulator? A manipulator is fault tolerant if it can complete its task even when one of its joints fails and is immobilized. The number of degrees-of-freedom needed for fault tolerance strongly depends on the knowledge available about the task. In this article, two approaches are explored. First, for the design of a General Purpose Fault Tolerant Manipulator, it is assumed that neither the exact task trajectory, nor the redundancy resolution algorithm are known a priori and that the manipulator has no joint limits. In this case, two redundant DOFs are necessary and sufficient to sustain one joint failure as is demonstrated in two design templates for spatial fault tolerant manipulators. In a second approach, both the Cartesian task path and the redundancy resolution algorithm are assumed to be known. The design of such a Task Specific Fault Tolerant Manipulator requires only one degree-of-redundancy.</p

Design Tool for Kinematics of Multibody Systems

This research provides a methodology and a tool for selection of appropriate robotic system based on the singularities in the workspace of the machines, suitable for both, designers and users. The kinematic problem solutions are managed through design methodology and represented with function modelling language, IDEF0. This novel approach specifies step by step activities on how to model robotic systems with math and programming tools, like Maple 17 and Matlab 2010. Symbolical and numerical solutions of kinematics, Jacobian matrix, singularities and workspace are successfully obtained for three types of multibody systems; general CNC machine, Mitsubishi MELFA RV-3SDB robot and Yaskawa Motoman DA-20, dual arm collaborative robot. CNC-R Global Reconfigurable Kinematic Model is developed for analyses of different types of manipulators. The main purpose of this design tool for kinematics of multibody systems is to help in kinematics problem solving, by providing visual representation of the workspace with the singularity locus of the same. It represents a set of iterative methods for kinematic design of manipulators, and so at the end, visual presentation of the effective work region, including singular configurations. The methodology is appropriate for any n-DOF multibody system, even for dual arm collaborativ

Reconfigurable Validation Model for Identifying Kinematic Singularities and Reach Conditions for Articulated Robots and Machine Tools

Automation has led to industrial robots facilitating a wide array of high speed, endurance, and precision operations undertaken in the manufacturing industry today. An acceptable level of functioning and control is therefore vital to the efficacy and successful implementation of such manipulators. This research presents a comprehensive analytical tool for downstream optimization of manipulator design, functionality, and performance. The proposed model is reconfigurable and allows for modelling and validation of different industrial robots. Unique 3D visual models for a manipulator workspace and kinematic singularities are developed to gain an understanding into the task space and reach conditions of the manipulator\u27s end-effector. The developed algorithm also presents a non-conventional and computationally inexpensive solution to the inverse kinematics problem through the use Artificial Neural Networks. Application of the proposed technique is further extended to aid in development of path planning models for a uniform, continuous, and singularity free motion