Global Identification of Joint Drive Gains and Dynamic Parameters of Parallel Robots

International audienceOff-line robot dynamic identification methods are based on the use of the Inverse Dynamic Identification Model (IDIM), which calculates the joint forces/torques (estimated as the product of the known control signal-the input reference of the motor current loop-with the joint drive gains) that are linear in relation to the dynamic parameters, and on the use of linear least squares technique to calculate the parameters (IDIM-LS technique). Most of the papers dealing with the dynamic parameters identification of parallel robots are based on simple models, which take only the dynamics of the moving platform into account. However, for advanced applications such as output force control in which the robot interaction force with the environment are estimated from the values of the input reference, both identifications of the full robot model and joint drive gains are required to obtain the best results. In this paper a systematic way to derive the full dynamic identification model of parallel robots is proposed in combination with a method that allows the identification of both robot inertial parameters and drive gains. The method is based on the total least squares solution of an over-determined linear system obtained with the inverse dynamic model. This model is calculated with available input reference of the motor current loop and joint position sampled data while the robot is tracking some reference trajectories without load on the robot and some trajectories with a known payload fixed on the robot. The method is experimentally validated on a prototype of parallel robot, the Orthoglide

Single-Loop Full R Joints of Multi-Mode Omnidirectional Ground Mobile Robot

In order to solve the problem of loss of locomotion ability due to overturning and instability during the movement of a mobile robot, a multi-mode omnidirectional ground mobile robot with a deformable structure is proposed. Single-loop is used as the unit, and the three-direction geometric deformation can be realized by controlling its R joints in time sharing. The 4-RRRRRR parallel mobile robot formed by two closed-loops orthogonally has four different rolling modes, and each mode can be switched between each other. Once the robot is overturned and unstable during the movement, it can be deformed into other modes and continue to move. After the description of the robot, the DOF (degree-of-freedom) is calculated based on the screw theory. Gait planning and locomotion feasibility analysis indicate that the robot can realize four locomotion modes and their mutual switching. Finally, the simulations and prototype experiments are presented to verify the feasibility of the different locomotion modes and the ability of the obstacle crossing

Experimental Identification of the Inverse Dynamic Model: Minimal Encoder Resolution Needed Application to an Industrial Robot Arm and a Haptic Interface

Ce chapitre de livre, accessible par internet, décrit une méthode pour connaître l'influence de l'erreur de mesure sur le résultat final. Elle revient à utiliser une méthode classique utilisée dans l'évaluation de la robustesse des simulations numériques vis à vis de la troncature liée au codage des réels par les ordinateurs. (la méthode CESTAC :Contrôle et Estimation Stochastique des Arrondis de Calculs)

Parallel Manipulators

In recent years, parallel kinematics mechanisms have attracted a lot of attention from the academic and industrial communities due to potential applications not only as robot manipulators but also as machine tools. Generally, the criteria used to compare the performance of traditional serial robots and parallel robots are the workspace, the ratio between the payload and the robot mass, accuracy, and dynamic behaviour. In addition to the reduced coupling effect between joints, parallel robots bring the benefits of much higher payload-robot mass ratios, superior accuracy and greater stiffness; qualities which lead to better dynamic performance. The main drawback with parallel robots is the relatively small workspace. A great deal of research on parallel robots has been carried out worldwide, and a large number of parallel mechanism systems have been built for various applications, such as remote handling, machine tools, medical robots, simulators, micro-robots, and humanoid robots. This book opens a window to exceptional research and development work on parallel mechanisms contributed by authors from around the world. Through this window the reader can get a good view of current parallel robot research and applications

A randomized kinodynamic planner for closed-chain robotic systems

Kinodynamic RRT planners are effective tools for finding feasible trajectories in many classes of robotic systems. However, they are hard to apply to systems with closed-kinematic chains, like parallel robots, cooperating arms manipulating an object, or legged robots keeping their feet in contact with the environ- ment. The state space of such systems is an implicitly-defined manifold, which complicates the design of the sampling and steering procedures, and leads to trajectories that drift away from the manifold when standard integration methods are used. To address these issues, this report presents a kinodynamic RRT planner that constructs an atlas of the state space incrementally, and uses this atlas to both generate ran- dom states, and to dynamically steer the system towards such states. The steering method is based on computing linear quadratic regulators from the atlas charts, which greatly increases the planner efficiency in comparison to the standard method that simulates random actions. The atlas also allows the integration of the equations of motion as a differential equation on the state space manifold, which eliminates any drift from such manifold and thus results in accurate trajectories. To the best of our knowledge, this is the first kinodynamic planner that explicitly takes closed kinematic chains into account. We illustrate the performance of the approach in significantly complex tasks, including planar and spatial robots that have to lift or throw a load at a given velocity using torque-limited actuators.Peer ReviewedPreprin

Six-DOF Spacecraft Dynamics Simulator For Testing Translation and Attitude Control

This paper presents a method to control a manipulator system grasping a rigid-body payload so that the motion of the combined system in consequence of externally applied forces to be the same as another free-floating rigid-body (with different inertial properties). This allows zero-g emulation of a scaled spacecraft prototype under the test in a 1-g laboratory environment. The controller consisting of motion feedback and force/moment feedback adjusts the motion of the test spacecraft so as to match that of the flight spacecraft, even if the latter has flexible appendages (such as solar panels) and the former is rigid. The stability of the overall system is analytically investigated, and the results show that the system remains stable provided that the inertial properties of two spacecraft are different and that an upperbound on the norm of the inertia ratio of the payload to manipulator is respected. Important practical issues such as calibration and sensitivity analysis to sensor noise and quantization are also presented

Kinematically redundant parallel robots for high performance applications

This thesis addresses the development of kinematically redundant parallel robots for high performance applications and methods of kinematic analyses tailored towards them. Parallel robot manipulators are well known to hold various advantages over serial manipulators, including having better speeds, accuracies, and power-to-weight ratios. However, a major disadvantage they have is that they suffer from limited workspaces and rotational capabilities; indeed, it can be argued that this is the main reason serial robots are used more frequently in many industries. This thesis aims to address this major shortcoming of parallel robots, whilst maintaining all of their advantages, by concentrating on the solution of kinematic redundancy. Firstly, an introduction to the topic of kinematically redundant parallel robots for high performance applications is presented and a review of the relevant literature is given. In the second section, a novel kinematically redundant architecture of parallel robot is presented. The kinematic redundancy of the mechanism allows it to achieve full cycle rotations of the end-effector without encountering kinematic singularities, a feat that is not possible for non-redundant systems. The third section addresses the issue with current methods of singularity analyses of parallel robots when applied to kinematically redundant architectures. It is shown that conventional Jacobian-based methods of singularity analysis are unreliable when applied to kinematically redundant architectures. In the fourth section a novel, more robust, method of singularity analysis is presented, which is then used to develop a method of singularity avoidance. The fifth section presents a kinematically redundant architecture that is dynamically balanced, meaning that the shaking forces and moments imposed on the base by the manipulator are nullified. An issue for manipulators moving at high speeds is that shaking forces and moments generated can cause vibration and inhibit the performance of the system. By dynamically balancing the system, the manipulator is able to move at high speeds without experiencing these drawbacks. The aim of this PhD thesis is that the work presented here can provide some of the building blocks for developers of robot manipulators to create high performance parallel robots which exhibit high speed, strength, and dexterity, through the use of kinematic redundancy

Kinematic Design and Optimisation of a Quadruped Robot with Six Actuated DoF

While legged robots hold many advantages over wheeled robots, especially regarding dynamic capabilities and mobility, they often suffer from lower energy efficiency and reliability due to the use of more actuators. Many classic approaches to quadruped design rely on designs with 12 actuated degrees of freedom - three in each leg - which allows the feet to be freely placed with respect to the body. One obvious solution to this problem is a reduction in the number of actuators, but this usually comes at the cost of functionality reduction. In terms of simple locomotion, however, the robot’s center of mass can be sufficiently moved by freely placing each foot with respect to the world, thus changing the robot’s contact points. It should then be possible to achieve locomotion with free foot placement using only six actuated degrees of freedom if the existing functions are appropriately combined and/or reduced. The aim of this thesis is therefore to design a full quadruped kinematic structure with only six actuators which is capable of simple locomotion through free placement of its feet. A review of existing literature regarding legged locomotion and reduced-DoF quadrupeds is performed to form a basis for new concepts, and a novel kinematic structure is proposed which relies on two types of leg couplings to reduce the degrees of freedom. A kinematic analysis then provides representations of the model in terms of forward, inverse and differential kinematics, and a control algorithm with position error feedback is proposed for task-space trajectory following. The proposed model is implemented in Creo Parametric and simulated with the help of the LucaDynamics library in MATLAB. A few tests are performed in the simulated environment which show that the proposed robot is indeed capable of stable static walking with free placement of all four feet, with the task-space position errors remaining very low for all tested trajectories and no indications of singular or near-singular poses

Modeling and control of a Delta-3 robot

This Master Thesis describes the mathematical modeling of a Delta-3 robot actuated by motors and drive units developed by ELAU GmbH. A given model of the ELAU GmbH drive unit and motor is used when building the Delta-3 robot model including three drive units, one for each motor to be able to actuate the three upper arms. The Delta-3 robot model is divided into kinematics and dynamics parts. The kinematics is used to calculate the trajectories for the three robot arms (joint space) and the corresponding motion of the robot travelling plate (Cartesian space). The Thesis also looks into the robot dynamics, so the coupling effect between the three arms is taken into account in the Simulink model. Different trajectories created with ELAU GmbHs own software are imported to Matlab workspace and simulated with the Simulink model. The results from the Simulink model are compared with the results from a real Delta-3 robot driven by ELAU GmbH hardware and software. The Jacobian matrix for the Delta-3 robot is also calculated to be used in the equations for the coupling effect between the three arms. The Jacobian matrix is also implemented in ELAU GmbH software to be able to calculate the joint velocity or joint acceleration when the TCP velocity or TCP acceleration is known and vice versa. These results can then be used in equations for calculating the torque which is needed for each of the three motors to actuate the upper arms along with the desired TCP trajectory. The torque calculations can be done offline so the real robot don't have to be running, which gives the opportunity to see how much torque each motor needs so the robot is able to follow the desired trajectory for the robots travelling plate. Experiments with comparison between the Simulink model and the real robot are done and the results of the measured values are shown in the Thesis. Also the experiments for the implementation of the Jacobian matrix in ELAU GmbH software are shown in the Thesis

Design and Development of a Tele-operated Surgical Simulation Environment

With the introduction of robots into laparoscopic surgery, surgeons have difficulties in selecting the placement of the incisions required to insert the robots instruments into the body and also determine which patients are suitable for robotically assisted surgery. Poor selection of these two items mentioned above can result in a conversion to a more invasive form of surgery during the procedure. This work introduces the design and development of a surgical simulation environment to assist in the research for optimal incision placement and patient selection. The simulator allows importing any serial link robot that was designed in a computer aided modelling package. With minimal added information, the imported robot can be controlled using a multi-degree of freedom user input device. The simulator allows for importing patient geometries along with the robot to allow for the simulation of surgical procedures. A Jacobian transpose algorithm was added onto the simulator in a modular format to control the simulated robots, as well as to allow for other control systems to be created and implemented. Experiments were performed to determine the effects of patient geometry models on rendering speeds. The control system could control the tested robots with a maximum lag time of 15 ms between moving the input device and the simulated robot moving to the correct desired position. The simulator makes importing and controlling robots a simple and intuitive matter, without putting a large restriction on the type of robots to be simulated. The simulator also allows for importing models of a patient, to make real world analysis of a patient possible. Further improvements on the presented simulator include the addition of collision detection and more testing on the control system for stability and response over a larger range of robots