Mohammad Motamedi

Robust adaptive control of a micro telemanipulation system using sliding mode-based force estimation

Piezoelectric actuators are widely used in micro manipulation applications. However, hysteresis nonlinearity limits the accuracy of these actuators. This paper presents a novel approach for utilizing a piezoelectric nano-stage as the slave manipulator of a teleoperation system based on a sliding mode controller. The Prandtl-Ishlinskii (PI) model is used to model actuator hysteresis in feedforward scheme to cancel out this nonlinearity. The presented approach requires full state and force measurements at both the master and slave sides. Such a system is costly and also difficult to implement. Therefore, sliding mode unknown input observer (UIO) is proposed for full state and force estimations. Furthermore, the effects of uncertainties in the constant parameters on the estimated external forces should be eliminated. So, a robust adaptive controller is proposed and its stability is guaranteed through the Lyapunov criterion. Performance of the proposed control architecture is verified through experiments.

Robust control of a piezoelectric stage under thermal and external load disturbances

Piezoelectric actuators are widely used in micromanipulation tasks such as Atomic Force Microscopy and Cell Manipulation. However, the hysteresis nonlinearity and the creep reduce their fidelity and cause difficulties in the micromanipulation control procedure. Besides, variation of temperature and external loads could change the model parameters identified for the piezo actuator. In this paper, a novel feedforward-feedback controller is proposed. The Prandtl-Ishlinskii model is utilized to linearize the actuator hysteresis in feedforward scheme and a sliding mode based impedance control with perturbation estimation is used to cancel out the thermal and external load disturbances in feedback scheme. The efficiency of the proposed controller is verified by experiments.

Transparency Enhancement of Haptic Systems Based on Compensation of Device Dynamics

Transparency is a measure of performance in haptic devices. In order to improve transparency and reduce the difference between the impedance transmitted to the user and the target impedance it is necessary to compensate for the dynamics of the haptic device. Due to stability reasons improvement of transparency is limited. Passivity as a stability criterion has been used widely in design and analysis of haptic devices. Since passivity is a conservative criterion, it acts as an obstacle in improving transparency of the haptic interfaces. In this paper instead of passivity, robust stability of the interaction is studied in the presence of parametric uncertainties due to variations in user hand dynamics. Two design methods are implemented and their performance and stability are evaluated. The first strategy is based on H-infinity controller synthesis technique applied to a generalized control plant which involves the target impedance as a performance weighting function. Human hand dynamics is not present in the controller synthesis stage, because it does not affect the robot impedance and consequently has no effect on performance. The obtained results depend on the weighting function parameters. In the second approach a controller is designed based on the inverse model of the device. The advantage of the latter method is that it can reduce the device impedance in a wide frequency range and results in non-passive robot impedance which is much more transparent than the impedances obtained by passivity based methods. Simulation results confirm the effectiveness of the proposed methods.Copyright

Performance Control of a Tape Transport Mechanism Using Entire Eigenstructure Assignment

To achieve high rate of data transfer, tape mechanisms must be able to transport the tape with a constant velocity for scanning. During this process, it is desired to make the rise time minimized without timing and data transfer errors. In this paper, three servo systems including the take-up and supply reel servos for tape tension control and capstan servo for speed control are considered. So, tape transport mechanisms can be described with a nonlinear multi-input multi-output system (MIMO). After state-space representation of the problem, feedback control is designed for tracking objective. It should be mentioned that an increase in the speed of time response of system corresponds to an increase in the control signal and leads to additional cost. So, the eigenvalues and eigenvectors are chosen optimally until an appropriate response is achieved while the gains of feedback matrix remain small simultaneously.Copyright

The Impact of Dam‐Reservoir‐Foundation Interaction on Nonlinear Response of Concrete Gravity Dams

To study the impact of dam‐reservoir‐foundation interaction on nonlinear response of concrete gravity dams, a two‐dimensional finite element model of a concrete gravity dam including the dam body, a part of its foundation and a part of the reservoir was made. In addition, the proper boundary conditions were used in both reservoir and foundation in order to absorb the energy of outgoing waves at the far end boundaries. Using the finite element method and smeared crack approach, some different seismic nonlinear analyses were done and finally, we came to a conclusion that the consideration of dam‐reservoir‐foundation interaction in nonlinear analysis of concrete dams is of great importance, because from the performance point of view, this interaction significantly improves the nonlinear response of concrete dams.

Control Design and Passivity Analysis for Scaled One-Dimensional Bilateral Teleoperated Nanomanipulation

In this paper, a novel control approach for one-dimensional bilateral teleoperated nanomanipulation system is proposed. While manipulating objects with a nanomanipulator, real time visual feedback is not available. So, force feedback is used to compensate for the lack of visual information. Since nanometer scale forces are dominated by surface forces instead of inertial forces as in macro world, scaling of nanoforces is one of the major issues of teleoperation system. The Hertz elastic contact model is used to model the interactions between the slave robot and the environment. The proposed approach uses the simple proportional derivative control, i.e., the master and slave robots are connected via a virtual spring and damper. The passivity of the combination of control blocks and communication is demonstrated via the control passivity concept. The outcome is a robust platform to enforce master-slave position coordination and perform teleoperated nanomanipulation on a broad range of materials. Simulations are performed to confirm the proposed control approach.Copyright

H∞ Robust Control of Continuous Fluidized Tea Bed Dryer

During drying processes, moisture control of food products, such as dried tea, is of great importance. Improving dryer control, results in consistent production and reduction of energy consumption. However, the dryer is a complex system associated with model uncertainties. In this paper, a realistic uncertain model of a fluidized tea bed dryer is considered. Moisture content and temperature of tea leaves (or other products) are controlled at desired values by manipulating tea leaves heating rate. Developing a code by Robust Control Toolbox of MATLAB and modeling uncertainties, a robust controller is designed based on μ-synthesis with DK-iteration algorithm. Results show that in the presence of model uncertainties, designed controller guarantee robust performance of the system; with appropriate behavior in tracking desired set points.Copyright