Method and apparatus for configuration control of redundant robots

A method and apparatus to control a robot or manipulator configuration over the entire motion based on augmentation of the manipulator forward kinematics is disclosed. A set of kinematic functions is defined in Cartesian or joint space to reflect the desirable configuration that will be achieved in addition to the specified end-effector motion. The user-defined kinematic functions and the end-effector Cartesian coordinates are combined to form a set of task-related configuration variables as generalized coordinates for the manipulator. A task-based adaptive scheme is then utilized to directly control the configuration variables so as to achieve tracking of some desired reference trajectories throughout the robot motion. This accomplishes the basic task of desired end-effector motion, while utilizing the redundancy to achieve any additional task through the desired time variation of the kinematic functions. The present invention can also be used for optimization of any kinematic objective function, or for satisfaction of a set of kinematic inequality constraints, as in an obstacle avoidance problem. In contrast to pseudoinverse-based methods, the configuration control scheme ensures cyclic motion of the manipulator, which is an essential requirement for repetitive operations. The control law is simple and computationally very fast, and does not require either the complex manipulator dynamic model or the complicated inverse kinematic transformation. The configuration control scheme can alternatively be implemented in joint space

Geometric Perspective on Kinematics and Singularities of Spatial Mechanisms

This doctoral dissertation deals with the kinematics and singularity analyses of serial and parallel manipulators with multiple working modes. The inverse kinematics of 6R architectures with non-spherical wrists were solved using simple geometric considerations; the problem was reduced to the solution of a trigonometric equation in one variable, the sixth joint angle. The direct kinematic analysis of the parallel manipulator, namely the Exechon, was conducted; it involves using a standard numerical tool to solve the system of equations in platform\u2019s angle variables. Both kinematics analyses took advantage of the standard numerical solver to obtain the solutions. The singularities of the Exechon were studied with the geometrical interpretation. By using the theory of reciprocal screws, the input-output velocity equations were introduced. This led to the investigation of the Jacobian matrices, which is an essential part when working with any manipulator. A method for obtaining the singularity loci and the numerical example was provided. The formulations presented in this dissertation are general and effective enough to be applicable for many other similar architectures

A novel closed-form solution for the inverse kinematics of redundant manipulators through workspace analysis

© 2017 Elsevier Ltd This work addresses the inverse kinematic problem for redundant serial manipulators. Its importance relies on its effect in the programming and control of redundant robots. Besides, no general closed-form techniques have been developed so far. In this paper, redundant manipulators are reduced to non-redundant ones by selecting a set of joints, denoted redundant joints, and parametrizing its joint variables. This selection is made through a workspace analysis which also provides an upper bound for the number of different closed-form solutions for a given pose. Once these joints have been identified several closed-form methods developed for non-redundant manipulators can be applied for obtaining the analytical solutions. Finally, particular instances for the parametrized joints variables are determined depending on the task to be executed. Different criteria and optimization functions can be defined for that purpose.Peer ReviewedPostprint (author's final draft

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

Task based synthesis of serial manipulators

Computing the optimal geometric structure of manipulators is one of the most intricate problems in contemporary robot kinematics. Robotic manipulators are designed and built to perform certain predetermined tasks. There is a very close relationship between the structure of the manipulator and its kinematic performance. It is therefore important to incorporate such task requirements during the design and synthesis of the robotic manipulators. Such task requirements and performance constraints can be specified in terms of the required end-effector positions, orientations and velocities along the task trajectory. In this work, we present a comprehensive method to develop the optimal geometric structure (DH parameters) of a non-redundant six degree of freedom serial manipulator from task descriptions. In this work we define, develop and test a methodology to design optimal manipulator configurations based on task descriptions. This methodology is devised to investigate all possible manipulator configurations that can satisfy the task performance requirements under imposed joint constraints. Out of all the possible structures, the structures that can reach all the task points with the required orientations are selected. Next, these candidate structures are tested to see whether they can attain end-effector velocities in arbitrary directions within the user defined joint constraints, so that they can deliver the best kinematic performance. Additionally least power consuming configurations are also identified

Human-like arm motion generation: a review

In the last decade, the objectives outlined by the needs of personal robotics have led to the rise of new biologically-inspired techniques for arm motion planning. This paper presents a literature review of the most recent research on the generation of human-like arm movements in humanoid and manipulation robotic systems. Search methods and inclusion criteria are described. The studies are analyzed taking into consideration the sources of publication, the experimental settings, the type of movements, the technical approach, and the human motor principles that have been used to inspire and assess human-likeness. Results show that there is a strong focus on the generation of single-arm reaching movements and biomimetic-based methods. However, there has been poor attention to manipulation, obstacle-avoidance mechanisms, and dual-arm motion generation. For these reasons, human-like arm motion generation may not fully respect human behavioral and neurological key features and may result restricted to specific tasks of human-robot interaction. Limitations and challenges are discussed to provide meaningful directions for future investigations.FCT Project UID/MAT/00013/2013FCT–Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020