Sabri Tosunoglu

A control structure for fault-tolerant operation of robotic manipulators

Failure of any robotic system component during operation is a matter of concern. Internal shock phenomena due to the failure of joint actuation, and a recovery algorithm for both serial and parallel mechanisms under such circumstances are investigated. A control algorithm is studied that consists of a model reference algorithm and a simple proportional integral derivative (PID) controller in the feedback process. Simulation results illustrate the effectiveness of this recovery algorithm which attempts to reduce the internal shock when failure occurs, and accomplish the continued tracking of the given end-effector trajectory.<<ETX>>

On Extending the Wave Variable Method to Multiple-DOF Teleoperation Systems

It is well known that providing a human operator with contact force information can significantly improve task performance in a teleoperation system. Unfortunately, time delay is a serious problem for such systems. Even a small time delay in a bilateral teleoperation system will generally degrade the systems performance and cause instability. Consequently, without some form of compensation for time delay, latencies in a teleoperation system would preclude the use of force feedback. Fortunately, there are approaches based on scattering theory and passivity that can compensate for time delay and allow the use of force feedback in teleoperation systems with latencies. In particular, the wave variable method is a passivity-based approach that guarantees stability for any fixed time delay. Since its introduction, the wave variable method has been augmented with predictors to compensate for variable time delay. The wave variable formalism has also been extended to multiple-DOF systems by replacing scalar damping constants with a family of impedance matrices. In this paper, the authors generalize this last approach to include a larger family of impedance matrices. The paper includes a complete derivation of the extended family of impedance matrices as well as simulation and experimental results to illustrate the approach.

Architectures for fault-tolerant mechanical systems

Fault tolerance is an increasingly important specification for advanced mechanical and electronic systems. In this paper we consider the architectural features of a technology that can realize this stringent specification in the domain of mechanical systems. We examine elements of a fault-tolerant mechanical architecture and a failure-responsive control system architecture that operates over it from the perspective of robotic manipulator systems.<<ETX>>

Control algorithms for fault-tolerant robots

When a fault-tolerant robot fails, its fault responsive system detects and identifies the failure. During the recovery process, reconfiguration of the system isolates the fault, and a new system model and a suitable controller attempt to completely compensate for the faulty condition without interrupting the robots operation. In this paper, the authors address the recovery process for fault-tolerant serial robots when they experience actuator failure. For this purpose, the authors consider three controllers based on PID feedback, sliding control, and parameter adaptation methods. It is shown that the sliding control implemented with a boundary layer reduces the system errors efficiently when the errors are large, and the controller behaves like an ordinary PID feedback as the errors get smaller. Additionally, when failures cause uncertainty in system parameters, inclusion of parameter identification capability in the controller design is suggested. Although the work is valid for a general robot, simulation results are presented on a four-axis robot.<<ETX>>

Kinematic and Structural Design Assessment of Fault-Tolerant Manipulators

ABSTRACTFault tolerance technology promises higher system reliability even under unexpected component failure. Such capability is attained by developing a structural system design that can deliver fault tolerance, and by designing controllers that can take advantage of the fault-tolerant structure. This paper reviews fault-tolerant design issues from a kinematic and structural viewpoint. This is accomplished by studying the kinematic design of a fault-tolerant robotic system at four levels: (1) Joint level (Single and dual actuators); (2) Link level (Serial and parallel modules); (3) Sub-system level (Non-redundant and redundant manipulators); (4) System level (Multiple cooperating manipulators). This work addresses the four levels from a structural design viewpoint. A measure is developed to determine the relative fault-tolerant capacity gained from one manipulator to another. Other criteria are also reviewed in evaluating various manipulators as design alternatives in an effort to identify the most effi...

Control of a six-degree-of-freedom flexible industrial manipulator

A controller design is proposed for manipulators modeled with joint and link compliances. First, nonlinear feedforward and PID state feedback components are used in the controller, and manipulator dynamics are converted into error-driven system dynamic equations. Then, the error-driven dynamic equations are stabilized using the second method of Lyapunov. The special structure of the Lyapunov matrix equation is exploited, and an explicit solution to this equation is presented. The analysis shows that controller performance can be enhanced through the modulation of this solution. The controller was numerically implemented on the model of a six-degree-of-freedom Cincinnati Milacron T3-776: industrial manipulator that is modeled with three joint and four link flexibilities. The simulations show satisfactory path tracking and oscillation rejection properties.<<ETX>>

A survey of telesensation and teleoperation technology with virtual reality and force reflection capabilities

Abstract A telesensation system implies the ultimate goal of teleoperation. Such a system provides the operator with the sensational feelings of the remote site as if he/she were working in the actual environment. Thus, the performance of the system is greatly improved. This paper mainly reviews some of the existing units of the three most important elements in a telesensation system. These units are force-reflecting manual controllers, virtual reality units, and an advanced operator interface. The feel of touch is provided by the force-reflecting manual controller, while the virtual reality unit gives the operator the 3-D view of the working environment. The telesensation system, also implemented with the advanced operator interface, allows the operator to easily control, model, plan, and simulate remote systems. These features have proven to be the most significant feedback of telesensation systems.

Complete Accessibility of Oscillations in Robotic Systems by Orthogonal Projections

The current practice of controller development for flexible robotic systems generally focuses on one-link robotic arms and is valid for small oscillations. This work addresses the control of n-link, serial, spatial robotic systems modeled with m1 joint and m2 link flexibilities such that n≥m1 +m2 . System compliance is modeled by local springs and nonactuated prismatic and revolute type pseudo joints. The coupled, nonlinear, error-driven system equations are derived for the complete model without linearization or neglecting certain terms. For this system, the complete accessibility of vibrations is studied by orthogonal projections. It is shown that under some configurations of a robotic system, the induced oscillations may not be accessible to the controller. Given accessibility, the controller developed in this work assures the global asymptotic stability of the system. Example numerical simulations are presented based on the model of a six-degree-of-freedom Cincinnati Milacron T3-776 industrial robot. One example models the system compliance in four joints, while another case study simulates four lateral link oscillations. These examples show that this controller, even under inaccurate payload description, eliminates the oscillations while tracking desired trajectories.

State of the art in adaptive control of robotic systems

An up-to-date assessment of adaptive control technology as applied to robotics is presented. Although the field is relatively new and does not yet represent a mature discipline, considerable attention for the design of sophisticated robot controllers has occurred. In this presentation, adaptive control methods are divided into model reference adaptive systems and self-tuning regulators with further definition of various approaches given in each class. The similarity and distinct features of the designed controllers are delineated and tabulated to enhance comparative review. >

Fault-tolerant control of mechanical systems

Fault tolerance attempts to provide for uninterrupted system operation even when one or more of a systems components fail. This is accomplished by continuously monitoring the state of each of the components. Upon detection of a failure, the recovery process makes decisions for the reallocation of the resources, and then announces the new task assignments in order to recover the system from failure as gracefully as possible. While the recovery process takes place, usually the post-failure system is not the same system before failure. Hence, a new controller design is usually required in the recovery process. This work examines controllers based on adaptive parameter estimation, sliding control and computed-torque method for their potential use in fault-tolerant controller design of mechanical systems such as serial and parallel mechanisms.