Showing papers by "Asif Sabanovic published in 2009"

Scaled Bilateral Teleoperation Using Discrete-Time Sliding-Mode Controller

Abstract: In this paper, the design of a discrete-time sliding-mode controller based on Lyapunov theory is presented along with a robust disturbance observer and is applied to a piezostage for high-precision motion. A linear model of a piezostage was used with nominal parameters to compensate the disturbance acting on the system in order to achieve nanometer accuracy. The effectiveness of the controller and disturbance observer is validated in terms of closed-loop position performance for nanometer references. The control structure has been applied to a scaled bilateral structure for the custom-built telemicromanipulation setup. A piezoresistive atomic force microscope cantilever with a built-in Wheatstone bridge is utilized to achieve the nanonewton-level interaction forces between the piezoresistive probe tip and the environment. Experimental results are provided for the nanonewton-range force sensing, and good agreement between the experimental data and the theoretical estimates has been demonstrated. Force/position tracking and transparency between the master and the slave has been clearly demonstrated after necessary scaling.

SURALP: A new full-body humanoid robot platform

Abstract: SURALP is a new walking humanoid robot platform designed at Sabanci University - Turkey. The kinematic arrangement of the robot consists of 29 independently driven axes, including legs, arms, waist and a neck. This paper presents the highlights of the design of this robot and experimental walking results. Mechanical design, actuation mechanisms, sensors, the control hardware and algorithms are introduced. The actuation is based on DC motors, belt and pulley systems and Harmonic Drive reduction gears. The sensory equipment consists of joint encoders, force/torque sensors, inertial measurement systems and cameras. The control hardware is based on a dSpace digital signal processor. A smooth walking trajectory is generated. A variety of controllers for landing impact reduction, body inclination and Zero Moment Point (ZMP) regulation, early landing trajectory modification, and foot-ground orientation compliance and independent joint position controllers are employed. A posture zeroing procedure is followed after manual zeroing of the robot joints. The experimental results indicate that the control algorithms presented are successful in improving the stability of the walk.

Motion control systems with network delay

Abstract: In this paper motion control systems with delay in measurement and control channels are discussed and a new structure of the observer-predictor is proposed. The feature of the proposed system is enforcement of the convergence in both the estimation and the prediction of the plant output in the presence of the variable, unknown delay in both measurement and in the control channels. The estimation is based on the available data — undelayed control input, the delayed measurement of position or velocity and the nominal parameters of the plant and it does not require apriori knowledge of the delay. The stability and convergence is proven and selection of observer and the controller parameters is discussed. Experimental results are shown to illustrate the theoretical predictions.

Force feedback pushing scheme for micromanipulation applications

Abstract: Pushing micro-objects using point contact provides more flexibility and less complexity compared to pick and place operation. Due to the fact that in micro-world surface forces are much more dominant than inertial forces and these forces are distributed unevenly, pushing through the center of mass of the micro-object may not yield a pure translational motion. In order to translate a micro-object, the line of pushing should pass through the center of friction. In this paper, a semi-autonomous scheme based on hybrid vision/force feedback procedure is proposed to push micro-objects with human assistance using a custom built tele-micromanipulation setup to achieve translational motion. In the semi-autonomous pushing process, velocity controlled pushing with force feedback is realized along x-axis by the human operator while y-axis orientation is undertaken automatically using visual feedback. In this way the desired line of pushing for the micro-object is controlled to pass through the varying center of friction. Experimental results are shown to prove nano-Newton range force sensing, scaled bilateral teleoperation with force feedback and pushing operation.

Novel observers for compensation of communication delay in bilateral control systems

Abstract: The problem of communication delay in bilateral or teleoperation systems is even more emphasized with the use of the internet for communication, which may give rise to loss of transparency and even instability. To address the problem, numerous methods have been proposed. This study is among the few recent studies taking a disturbance observer approach to the problem of time delay, and introduces a novel sliding-mode observer to overcome specifically the effects of communication delay in the feedback loop. The observer operates in combination with a PD+ controller which controls the system dynamics, while also compensating load torque uncertainties on the slave side. To this aim, an EKF based load estimation algorithm is performed on the slave side. The performance of this approach is tested with computer simulations for the teleoperation of a 1-DOF robotic arm. The simulations reveal an acceptable amount of accuracy and transparency between the estimated slave and actual slave position under both constant and random measurement delay and variable and step-type load variations on the slave side, motivating the use of the approach for internet-based bilateral control systems.

Hybrid vision/force feedback control for pushing micro-objects

Abstract: In 2D microassembly applications, it is inevitable to position and orient polygonal micro-objects lying on a flat surface. Point contact pushing of micro-objects provides a feasible way to achieve the task and it is more flexible and less complex compared to pick and place operation. Due to the fact that in micro-world surface forces are much more dominant than inertial forces, and tend to be unevenly distributed, these dominant forces obstruct the desired motion of the micro-object when using point contact pushing alone. Thus by adopting an hybrid vision/force feedback scheme, it is possible to attain a translation motion of the object as the uncertainties due to varying surface forces and disorientation of the micro-object is compensated by force and vision feedback respectively. In this paper, a hybrid vision/force feedback scheme is proposed to push micro-objects with human assistance using a custom built tele-micromanipulation setup to achieve translational motion. The pushing operation is divided into two concurrent processes: In one human operator acts as an impedance controller alters the velocity of the pusher while in contact with the micro-object through scaled bilateral teleoperation to compensate for varying surface forces. In the other process, the desired line of pushing for the micro-object is determined continuously using visual feedback procedures so that it always compensate for the disorientation. Experimental results are demonstrated to prove nano-Newton range force sensing, scaled bilateral teleoperation with force feedback and pushing micro-objects.

Sensorless torque estimation in multidegree-of-freedom flexible systems

Abstract: This paper presents a sensorless torque estimation algorithm for multidegree-of-freedom flexible systems. The proposed algorithm makes it possible to estimate externally applied torques due to flexible system's interaction with the environment without taking any measurement from the system. The algorithm is based on modifying the disturbance observer in order to decouple the reflected torque waves out of the total disturbance on the actuator. Then Reflected torque waves are used along with the actuator's current and velocity to estimate flexible system parameters, dynamics and the external torques or disturbances. Several experimental results are included in order to confirm the validity of the proposed torque estimation algorithm.

Sensorless wave based control for flexible structures using actuator as a single platform for estimation and control

Abstract: —In this paper we present a wave based control approach for flexible structures using the actuator as a single platform for measurement and control without picking any measurements from the system. using the reflected wave to the actuator from the system along with the actuator parameters as the current and velocity to estimate the flexible system’s parameters. and using those estimated parameters to achieve robust controllers keeping the system free from any measurements and attached sensors. in this paper all the sensors attached to the system were used just to verify the performance of the controller not to have feed back from the system.

Estimation Based PID controller-Sensorless Wave Based Technique ?

Abstract: This paper presents a sensorless estimation algorithm for estimating flexible system parameters, dynamics and externally applied forces or torques due to system interaction with the environment. The proposed algorithm makes it possible to design a chain of observers that require measuring actuator's current and velocity along with performing two off-line experiments that do not require any additional measurement from the flexible system. The output of these observers are estimates of the system parameters, estimates of the system dynamics in configuration, motion and acceleration level. Eventually, the estimated positions are used to control the motion and vibration of the flexible lumped system without taking any measurement from the system. Experimental results show the validity of the proposed sensorless estimation algorithm and the possibility of controlling motion and vibration of flexible systems by focusing all the measurements on the actuator side keeping the system free from any attached sensors.

A novel algorithm for sensorless motion control, parameter identication and position estimation

Abstract: This article demonstrates that an actuator can be used as a single platform for measurement, control and estimation by designing a chain of estimators and performing simple off-line experiments. Making use of the fact that rejected torque from the dynamical system consists of all the system dynamics beside all external disturbances. The rejected torque waves are estimated using the actuator parameters, and used for an off-line experiment for parameter estimation, then the estimated rejected torque is used along with the estimated parameters to estimate the positions of any multi-degree of freedom flexible dynamical system. That makes it possible to use those estimates to achieve sensorless motion and vibration control without using actual measurement. Moreover, all the estimated parameters and system dynamics can be used in order to estimate any external disturbance on the system when it starts to interact with the environment.

Force control in multi-degree-of-freedom flexible systems — Sensorless technique

Abstract: This paper presents a novel sensorless force control algorithm for Multi-degree-of-freedom flexible systems which enables controlling the interaction forces with the environment without using force sensors. The coupled nature of flexible system dynamics makes it possible to estimate externally applied forces or torques that arise due to system's interaction with the environment. Disturbance and flexibility are simultaneously utilized to estimate system parameters, dynamics and externally applied forces or torques. The interaction torque estimate is then used to accomplish sensorless torque control assignment. This paper attempts to keep the flexible plant free from any measurement while performing a torque control assignment. However, actuator's parameters and variables are assumed to be available.

Semi-autonomous scheme for pushing micro-objects

Abstract: In many microassembly applications, it is often desirable to position and orient polygonal micro-objects lying on a planar surface. Pushing micro-objects using point contact provides more flexibility and less complexity compared to pick and place operation. Due to the fact that in micro-world surface forces are much more dominant than inertial forces and these forces are distributed unevenly, pushing through the center of mass of the micro-object will not yield a pure translational motion. In order to translate a micro-object, the line of pushing should pass through the center of friction. In this paper, a semi-autonomous scheme based on hybrid vision/force feedback is proposed to push microobjects with human assistance using a custom built tele-micromanipulation setup to achieve pure translational motion. The pushing operation is divided into two concurrent processes: In one process human operator who acts as an impedance controller alters the velocity of the pusher while in contact with the micro-object through scaled bilateral teleoperation with force feedback. In the other process, the desired line of pushing for the micro-object is determined continuously using visual feedback procedures so that it always passes through the varying center of friction. Experimental results are demonstrated to prove nano-Newton range force sensing, scaled bilateral teleoperation with force feedback and pushing microobjects.

Estimation based control of flexible systems-sensorless wave based technique

Abstract: This paper presents an algorithm for parameters and positions estimation of lumped flexible systems. As soon as the parameters and the positions are estimated they can be used to design virtual sensors that can be moved along the system to estimate the position of any lumped mass keeping the system free from any attached sensors. The virtual sensors are nothing but a chain of estimators that are connected at the end of each other, starting with two actuator's measurements and ending up with system parameters and all the system lumped positions. An estimation Based PID controller is presented based on the feedback of the virtual sensor's estimates instead of the actual measurement.

On Fraction Order Modeling and Control of Dynamical Systems

Abstract: This paper demonstrates the feasibility of modeling any dynamical system using a set of fractional order difierential equations, including distributed and lumped systems. Fractional order difierentiators and integrators are the basic elements of these equations representing the real model of the dynamical system, which in turn implies the necessity of using fractional order controllers instead of controllers with integer order. This paper proves that fractional order difierential equations can be used to model any dynamical system whether it is continuous or lumped.

Central controller for hybrid control over network

Abstract: In this paper, a central controller for position/force hybrid control over network is proposed In the proposed method, the central controller receives position and force information from each plant Then, the central controller generates acceleration references for each plant by using a hybrid controller and a dead time compensator As an application, bilateral control with communication delay is implemented And some simulations and experiments verify the validity of the proposed method

Control systems with network delay

Abstract: In this paper motion control systems with delay in measurement and control channels are discussed and a new structure of the observer-predictor is proposed. The feature of the proposed system is enforcement of the convergence in both the estimation and the prediction of the plant output in the presence of the variable, unknown delay in both measurement and in the control channels. The estimation is based on the available data - undelayed control input, the delayed measurement of position or velocity and the nominal parameters of the plant and it does not require apriori knowledge of the delay. The stability and convergence is proven and selection of observer and the controller parameters is discussed. Experimental results are shown to illustrate the theoretical predictions.

Microassembly System Design: A Case Study

Abstract: With the miniaturization of products to the levels of micrometers and the recent developments in microsystem fabrication technologies, there arises a great need for an assembly process for the formation of complex hybrid microsystems. Integration of microcomponents, manufactured from different materials using different micro fabrication techniques, is still a primary challenge since some of the fundamental problems originating from the small size of parts to be manipulated, high precision necessity and the physics of the micro world are still not fully investigated. In this book, design and development of an open-architecture and modular microassembly workstation for efficient and reliable assembly of micromachined parts is presented through detailed inspection of the necessities for design and problems which arise as a result of the nature of the microworld. The analysis of the design process will be useful for the investigation of the inevitable technology of near future, microassembly, with the increasing trend towards miniaturization in every aspect of our lives and will be especially helpful to professionals in Microsystems Technologies.

Algılayıcısız dalga tabanlı parametre sezimi ve konum kestirimi

Abstract: In this work, mechanical waves are used in order to estimate dynamics of any flexible lumped system along with its parameters without taking any measurement from the system. By considering mechanical waves that propagate through the dynamical system as a natural feedback that carries all system information back to one of the system boundary conditions. And instead of attaching any sensor or performing any parameter identification process to obtain certain information from the system, mechanical waves are estimated, analyzed and decoupled in order to extract system dynamics and parameters. In this paper, waves are used in order to estimate flexible system parameters and states.

İki yönlü denetimde iletişim kanalındaki gecikmenin kayan kipli gözlemcikullanarak telafisi

Abstract: In bilateral control applications, time delays in the communication channel have destabilizing effects. In this paper, a new sliding mode observer based compensation technique is presented. Disturbance observer is utilized to make this sliding observer more robust to parameter changes. Simulation and experimental results show that the proposed method is successful as far as avoiding instability due to time delays and providing transparency between master and slave sides.

Gürbüz bir tutma kuvveti denetleyicisi

Abstract: This paper includes modeling and simulation of a new grasping control structure using bilateral actuators. A priori knowledge of parameters for the object is assumed to be existing. The controller is designed by considering accurate tracking of the force and position according to the proposed model.