Dragan Kostic

Learning-based identification and iterative learning control of direct-drive robots

IEEE Transactions on Control Systems Technology, 2005

A combination of model-based and iterative learning control (ILC) is proposed as a method to achi... more A combination of model-based and iterative learning control (ILC) is proposed as a method to achieve high-quality motion control of direct-drive robots in repetitive motion tasks. We include both model-based and learning components in the total control law, as their individual properties influence the performance of motion control. The model-based part of the controller compensates much of the nonlinear and coupled robot dynamics. A new procedure for estimating the parameters of the rigid body model, implemented in this part of the controller, is used. This procedure is based on a batch-adaptive control algorithm that estimates the model parameters online. Information about the dynamics not covered by the rigid body model, due to flexibilities, is acquired experimentally, by identification. The models of the flexibilities are used in the design of the iterative learning controllers for the individual joints. Use of the models facilitates quantitative prediction of performance improvement via ILC. The effectiveness of the combination of the model-based and the iterative learning controllers is demonstrated in experiments on a spatial serial direct-drive robot with revolute joints.

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Modeling Robot "Psycho-Physical" State and Reactions - A New Option in Human-Robot Communication Part 2: Modeling and Simulation

Journal of Intelligent and Robotic Systems, 2002

This part of the paper examines numerically the possibility of modeling “robot fatigue” being rep... more This part of the paper examines numerically the possibility of modeling “robot fatigue” being representative of a human psychophysical state that can be applied to robots. Temperatures of driving motors are suggested as analogs to fatigue in muscles. Simulation of robot behavior is performed on a typical human task, namely handwriting. Three phases of task execution, characteristic for humans, are observed, i.e. regular motion, reconfiguration after symptoms of fatigue, and degeneration caused by the too long, hard work.

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Robust attenuation of direct-drive robot-tip vibrations

This paper suggests and employs a method for reducing vibrations at the tip of a robot. The vibra... more This paper suggests and employs a method for reducing vibrations at the tip of a robot. The vibrations, caused by structural flexibility, are detected using accelerometers. The robot control system consists of two complementary sub-systems: a nominal motion controller and a vibration compensator. The former one realizes joint motions in accordance with a prescribed tip trajectory. The latter one robustly attenuates oscillations at the tip that are due to structural flexibility. The benefits of this set-up are experimentally verified for a spatial directdrive robot with 3 revolute degrees of freedom.

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Experimentally supported control design for a direct drive robot

We promote the idea of an experimentally supported control design as a successful way to achieve ... more We promote the idea of an experimentally supported control design as a successful way to achieve accurate tracking of reference robot motions, under disturbance conditions and given the uncertainties arising from modeling errors. The H ∞ robust control theory is used for design of motion controllers. Potential of the theory is additionally enhanced by incorporating a disturbance-based control design cycle. Within each iterative cycle we experimentally evaluate effects of designed H ∞ controllers on a direct-drive robotic set-up. The controllers resulting from such iterative design are indeed specialized for this robot, but they significantly improve both performance and robustness against disturbances and modeling errors, as compared with conventional industrial motion controllers. Superior performance is experimentally demonstrated in both configuration (joint) and task (Cartesian) spaces of the robot.

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Modeling and identification of an RRR-robot

A dynamic model of a robot with 3 rotational degrees of freedom is derived in closed form. A syst... more A dynamic model of a robot with 3 rotational degrees of freedom is derived in closed form. A systematic procedure for estimation of model dynamic parameters is suggested. It consists of the following steps: (i) identification of friction model parameters for each joint; (ii) calculation of optimal exciting trajectories, required for estimation of the remaining dynamic model parameters; (iii) estimation of these parameters using a least-squares method. The estimated model satisfactory reconstructs experimental control signals, justifying its use in model-based nonlinear control.

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Humanlike behavior of robot arms: general considerations and the handwriting task—Part I: mathematical description of human-like motion: distributed positioning and virtual fatigue

Robotics and Computer-integrated Manufacturing, 2001

This paper (Part II) investigates the motion of a redundant anthropomorphic arm during the writin... more This paper (Part II) investigates the motion of a redundant anthropomorphic arm during the writing task. Two approaches are applied. The "rst is based on the concept of distributed positioning which is suitable to model the`writinga task before the occurrence of fatigue symptoms. The second approach uses the concept of`virtual fatiguea (<F) which is a variable that dynamically behaves in a way analogous to the biological fatigue. <F enables the arm to recon"gure itself and take postures appropriate for the current level of fatigue. The study includes the analysis of legibility and inclination of handwriting, and a set of simulation results that show most practical aspects of robot human-like performance.

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Estimator-based sliding mode control of an optical disc drive under shock and vibration

A more robust servo control system using Sliding Mode Control to handle shock and vibration distu... more A more robust servo control system using Sliding Mode Control to handle shock and vibration disturbances for optical disc drive systems is presented in the paper. An estimator-based SMC controller is used in the radial servoloop instead of the traditional PID controller. Simulation and experimental results show a significant improvement of the drive's anti-shock performance in the radial direction. The same algorithm can be applied to the focus servo-loop.

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Concerning the primary and secondary objectives in robot task definition — the “learn from humans” principle

Mathematics and Computers in Simulation, 2000

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Dynamics of anthropomorphic painting robot: Quality analysis and cost reduction

Robotics and Autonomous Systems, 2000

KNAW Narcis. Back to search results. Publication Dynamics of Anthropomorphic Painting Robot: Qual... more

Motion in human and machine: A virtual fatigue approach

IEEE Transactions on Systems, Man, and Cybernetics, 2002

Achieving human-like behavior of a robot is a key issue of the paper. Redundancy in the inverse k... more Achieving human-like behavior of a robot is a key issue of the paper. Redundancy in the inverse kinematics problem is resolved using a biological analogue. It is shown that by means of "virtual fatigue" functions, it is possible to generate robot movements similar to movements of a human arm subject to muscle fatigue. Analytic method enabling control of robot motions in a human-like fashion is described. An example of an anthropomorphic robot arm performing a screw-driving task illustrates the method.

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Data-based design of high-performance motion controllers

Electronics Letters, 2004

This paper presents a data-based design of a linear feedback controller which realizes desired cl... more This paper presents a data-based design of a linear feedback controller which realizes desired closed-loop sensitivity and complementary sensitivity transfer functions. These transfer functions are specified via a single model-based performance cost. The data-based equivalent of this cost is derived, and its utility for the feedback design is demonstrated. A designer can prescribe the controller structure and complexity. Experimental results obtained in a direct-drive robot motion control problem show the quality of the design.

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Humanlike behavior of robot arms: general considerations and the handwriting task—Part II: the robot arm in handwriting

Robotics and Computer-integrated Manufacturing, 2001

This paper (Part II) investigates the motion of a redundant anthropomorphic arm during the writin... more This paper (Part II) investigates the motion of a redundant anthropomorphic arm during the writing task. Two approaches are applied. The "rst is based on the concept of distributed positioning which is suitable to model the`writinga task before the occurrence of fatigue symptoms. The second approach uses the concept of`virtual fatiguea (<F) which is a variable that dynamically behaves in a way analogous to the biological fatigue. <F enables the arm to recon"gure itself and take postures appropriate for the current level of fatigue. The study includes the analysis of legibility and inclination of handwriting, and a set of simulation results that show most practical aspects of robot human-like performance.

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Illustrating man-machine motion analogy in robotics - The handwriting problem

IEEE Robotics & Automation Magazine, 2003

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Representation of robot motion control skill

IEEE Transactions on Systems, Man, and Cybernetics, 2000

Development of skilled robotics draws clues from model-based theories of human motor control. Thu... more Development of skilled robotics draws clues from model-based theories of human motor control. Thus, a comprehensive anthropomorphic background is given in the introductory part of the paper. Skills in robotics are viewed as a tool for fast and efficient real-time control that can handle complexity and nonlinearity of robots, generally aiming at robot autonomy. Particularly, a skill of redundancy resolution is addressed through skill representation problem based on Function Approximator. The task of the robot is approximated by a set of parameterized motion primitives. Adopted parameters are also parameters of the function approximator, i.e., skill used. Redundancy is resolved during skill learning based on available expert knowledge, yielding parameterized joint motions. Approximation procedure-Successive Approximations, a major contribution of the paper, is used for batch compilation of parameterized examples resulting in a parameterized skill model. Such skill enables a user inexpert in redundancy resolution to gain benefits from redundant robots. All properties of the Successive Approximations procedure such as accuracy in interpolation and extrapolation, acceleration in redundancy resolution and upgrading to new skill regarding the task variation, will be discussed in the example of five Degrees-of-Freedom planar redundant robot, performing parameterized ellipse as motion primitive.

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Learning of Inverse Kinematics Behavior of Redundant Robot

Acceleration in redundancy resolution has been achieved by model-based learning. Parameterized jo... more Acceleration in redundancy resolution has been achieved by model-based learning. Parameterized joint motions generated by pseudoinverse of parameterized motion primitives in operational space are taken as learning examples. The method of successive approximations (SA) as a function approximator generalizes given examples resulting in a parameterized model, termed redundancy resolution skill. The SA method results in an analytical solution of joint motions. This particular property enables extension of the universality of skills to tasks never experienced by learning. Moreover, a proper addressing of skills output results in paths completely different from learned ones. In practice, this means that a segment as a motion primitive suffices in acquiring skill in the learning domain. The example emphasises this property of SA-based redundancy resolution. Highly compressed skill, acquired on segments only, is applied in RR along two test-trajectories-an `H'-character and a rosette. The gained acceleration of RR recommends this procedure for online redundant robot control and easy robot programming

Model-based support for integration and testing of a multi-disciplinary industrial system

* This work has been carried out as part of the TANGRAM project under the responsibility of the E... more

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