Mehrdad Moallem

Design and Implementation of Modular FPGA-Based PID Controllers

In this paper, modular design of embedded feedback controllers using field-programmable gate array (FPGA) technology is studied. To this end, a novel distributed-arithmetic (DA)-based proportional-integral-derivative (PID) controller algorithm is proposed and integrated into a digital feedback control system. The DA-based PID controller demonstrates 80% savings in hardware utilization and 40% savings in power consumption compared to the multiplier-based scheme. It also offers good closed-loop performance while using less resources, resulting in cost reduction, high speed, and low power consumption, which is desirable in embedded control applications. The complete digital control system is built using commercial FPGAs to demonstrate the efficiency. The design uses a modular approach, so that some modules can be reused in other applications. These reusable modules can be ported into Matlab/Simulink as Simulink blocks for hardware/software cosimulation or integrated into a larger design in the Matlab/Simulink environment to allow for rapid prototyping applications.

Simulation of a Wind Turbine With Doubly Fed Induction Generator by FAST and Simulink

In order to fully study the electrical, mechanical, and aerodynamic aspects of a wind turbine with a doubly fed induction generator, a detailed model that considers all these aspects must be used. A drawback of many works in the area of wind turbine simulation is that either a very simple mechanical model is used with a detailed electrical model, or vice versa. Hence, the effects of interactions between electrical and mechanical components are not accurately taken into account. In this paper, three simulation programs - TurbSim, FAST, and Simulink - are used to model the wind, mechanical and electrical parts of a wind turbine, and its controllers. Simulation results obtained from the model are used to observe the interaction of all three factors affecting the operation of a wind turbine system. For example, it is shown how an electrical disturbance can cause dangerous tower vibrations under high speed and turbulent wind conditions, which may not be feasible using a simple model of the wind and wind turbine.

High-Fidelity Bilateral Teleoperation Systems and the Effect of Multimodal Haptics

In master-slave teleoperation applications that deal with a delicate and sensitive environment, it is important to provide haptic feedback of slave/environment interactions to the users hand as it improves task performance and teleoperation transparency (fidelity), which is the extent of telepresence of the remote environment available to the user through the master-slave system. For haptic teleoperation, in addition to a haptics-capable master interface, often one or more force sensors are also used, which warrant new bilateral control architectures while increasing the cost and the complexity of the teleoperation system. In this paper, we investigate the added benefits of using force sensors that measure hand/master and slave/environment interactions and of utilizing local feedback loops on the teleoperation transparency. We compare the two-channel and the four-channel bilateral control systems in terms of stability and transparency, and study the stability and performance robustness of the four-channel method against nonidealities that arise during bilateral control implementation, which include master-slave communication latency and changes in the environment dynamics. The next issue addressed in the paper deals with the case where the master interface is not haptics capable, but the slave is equipped with a force sensor. In the context of robotics-assisted soft-tissue surgical applications, we explore through human factors experiments whether slave/environment force measurements can be of any help with regard to improving task performance. The last problem we study is whether slave/environment force information, with and without haptic capability in the master interface, can help improve outcomes under degraded visual conditions.

A layered goal-oriented fuzzy motion planning strategy for mobile robot navigation

Most conventional motion planning algorithms that are based on the model of the environment cannot perform well when dealing with the navigation problem for real-world mobile robots where the environment is unknown and can change dynamically. In this paper, a layered goal-oriented motion planning strategy using fuzzy logic is developed for a mobile robot navigating in an unknown environment. The information about the global goal and the long-range sensory data are used by the first layer of the planner to produce an intermediate goal, referred to as the way-point, that gives a favorable direction in terms of seeking the goal within the detected area. The second layer of the planner takes this way-point as a subgoal and, using short-range sensory data, guides the robot to reach the subgoal while avoiding collisions. The resulting path, connecting an initial point to a goal position, is similar to the path produced by the visibility graph motion planning method, but in this approach there is no assumption about the environment. Due to its simplicity and capability for real-time implementation, fuzzy logic has been used for the proposed motion planning strategy. The resulting navigation system is implemented on a real mobile robot, Koala, and tested in various environments. Experimental results are presented which demonstrate the effectiveness of the proposed fuzzy navigation system.

A force reflective master-slave system for minimally invasive surgery

Minimally invasive surgery involves inserting special instruments into the body cavity through tiny incisions in order to perform surgical procedures. In this paper, the design of a robotic master-slave system for use in minimally invasive surgery is discussed. This system is capable of providing haptic feedback to the surgeon in all available degrees of freedom. System design as well as master and slave bilateral control and communication issues are discussed.

Transparent Time-Delayed Bilateral Teleoperation Using Wave Variables

Besides stability, a high degree of transparency is also an essential requirement in order to enable operators to safely and precisely perform bilateral teleoperation tasks. An existing approach based on the wave transformation technique can make a two-channel teleoperation system insensitive to time delays by making the time-delayed communication channel passive. In this paper, we propose a novel method for incorporating this technique in a four-channel architecture, which is the optimal architecture from a transparency point of view, and derive the corresponding absolute stability condition. It is analytically demonstrated that the proposed teleoperation architecture is capable of providing ideal transparency when transmission delays are present, and criteria for its stable operation are derived. We also show that a three-channel variant of the proposed four-channel control architecture can offer a comparable performance with less implementational complexity. Experimental results in support of the developed theory are provided.

Attitude estimation and stabilization of a rigid body using low-cost sensors

We consider the attitude and gyro-bias estimation as well as the attitude stabilization problem of a rigid body in space using low-cost sensors. We assume that a biased measurement of the angular velocity of the rigid body is provided by a low-cost gyroscope, and the attitude measurements are obtained using low-cost (low-pass) sensors such as accelerometers and magnetometers. We provide an attitude and gyro-bias estimation algorithm using the biased gyro measurement and the attitude measurements - which represent the true attitude only at low frequencies - provided by the low-cost attitude sensors. Finally, the proposed estimation algorithm is coupled with a quaternion-based attitude stabilization scheme, and simulation results are provided to show the effectiveness of the proposed algorithm.

An integral manifold approach for tip-position tracking of flexible multi-link manipulators

In this paper, a nonlinear control strategy for tip position trajectory tracking of a class of structurally flexible multilink manipulators is developed. Using the concept of integral manifolds and singular perturbation theory, the full-order flexible system is decomposed into corrected slow and fast subsystems. The tip-position vector is similarly partitioned into corrected slow and fast outputs. To ensure an asymptotic tracking capability, the corrected slow subsystem is augmented by a dynamical controller in such a way that the resulting closed-loop zero dynamics are linear and asymptotically stable. The tracking problem is then redefined as tracking the slow output and stabilizing the corrected fast subsystem by using dynamic output feedback. Consequently, it is possible to show that the tip position tracking errors converge to a residual set of O(/spl epsiv//sup 2/), where /spl epsiv/ is the singular perturbation parameter. A major advantage of the proposed strategy is that the only measurements required are the tip positions, joint positions, and joint velocities. Experimental results for a single-link arm are also presented and compared with the case when the slow control is designed based on the rigid-body model of the manipulator.

A Novel Manipulator for Percutaneous Needle Insertion: Design and Experimentation

In this paper, we present the design of a novel 5-DOF manipulator for percutaneous needle insertion. The requirements of the manipulator have been instigated by a relatively common medical procedure: low-dose rate brachytherapy of the prostate. The manipulator can perform orientation, insertion, and rotation of the needle and linear motion of the stylet to drop radioactive seeds contained in a thin hollow needle (cannula) at targeted locations. The key features of the manipulator such as backdrivable joints, a fault-tolerant needle driver, stationary actuators, and redundant sensors enhance overall safety and reliability of the mechanism, a critical requirement for surgical manipulators. The manipulator is an integral part of a system utilizing a mechanically rotated side-firing transducer to create 3-D ultrasound images of the organ and utilizing 3-D SLICER software to visualize those images. Experimental results in agar phantoms prove that the manipulator is capable of positioning the needle tip at the targeted locations with good accuracy.

Brief Nonlinear tip-position tracking control of a flexible-link manipulator: theory and experiments

This paper presents an observer-based inverse dynamics control strategy that results in small tip-position tracking errors while maintaining robust closed-loop performance for a class of multi-link structurally flexible manipulators. This is done by defining new outputs near the end points of the arms as well as by augmenting the control inputs by terms which ensure stable operation of the closed-loop system. As part of the control design, a nonlinear observer is introduced to estimate the rates of change of flexible modes. Experimental results are given for the case of a two-link manipulator with a flexible link that further confirm the theoretical and simulation results.