Dr. Ezzat G Bakhoum

In the recent years, robotic devices have been widely used to interact with human beings in various scenarios, including healthcare, education, tourism, and manufacturing applications. These applications of robotic devices have also been expanded to many social activities. These social robots can take the form of a traditional mobile robot or a humanoid system that provide one-on-one interaction. Among different types of robotic devices, the bio-inspired humanoid robotics has received extensive attention in therapeutic settings by providing psychological and physiological benefits. With the social benefits, humanoid type of social robots can be an important tool to assist people in many different situations.
To allow social robotic devices to better interact with human being, it is desired that these robotic systems can identify ongoing human motions and respond to the motions by mimicking human movements. Thus, these systems need to acquire human motions and predict the types of these movements in real-time. Such a technique has been investigated by various research groups. Once the human motions have been identified, corresponding reactions of the robots can be determined accordingly, which usually requires the involved joints to move along specific trajectories. To synthesize such an interactive robotic system, a platform of a multi-axial robotic device, a motion identification model of human motions, a reference generator based on the identified motions, the sensors used for real-time motion measurements, and an adequate control strategy need to be integrated as a single system. The major bottleneck of such a system is that the processing and control units might not be efficient enough and can cause dramatic legacy. To validate the overall process, a simplified system was developed to investigate the feasibility of such an interactive robotic system.
In this study, an experimental multi-axial robotic arm was adopted. A developed motion identification model was used to determine the on-going motions of the interacting person. Once the motion being identified, the responding motion of robotic device can be determined based on a pre-selected motion library. The trajectories of individual joints of the robotic arm can then also be generated accordingly. The robotic arm was then following the pre-selected trajectories for corresponding interactions. To compensate for the nonlinear factors caused by existing mechanical/electrical components and the cross-coupled dynamics among the mechanical components, a control strategy that integrates an adaptive robust control method and a linear controller for motion tracking was applied. With the proposed control scheme, an adequate controlled outcome can be achieved.

In this paper, we propose to design, develop, and study a cyber-physical system that enables patients and therapists to virtually interact for rehabilitation activities with assistive robotic devices. The targeted users of this system are post stroke patients. On the patient's side, an assistive robotic device can generate the force that the therapist applies to the patient. On the therapist's side, another robotic device can reproduce the responsive force generated by the patient. With this system, the interaction can be virtually established. In addition, by integrating real human trajectories, the proposed assistive robotic system can help patients to perform rehabilitation activities in their own pace. Such an assistive robotic system and virtual interacting scheme can minimize both patient's and therapist's traveling time. The assistive functions of this light weight design can also help patients to in their ADLs.

In this paper, an assistive robotic device that integrates the consideration of human motion and algorithm of multi-axial control using a dual twisted-string actuation was designed and fabricated. To derive arm trajectories, subjects with different heights were recruited to identify the impacts to arm motions with various physical conditions. In addition to the identification of arm movements, an adaptive robust control (ARC) algorithm was used to compensate for the rotational movement of shoulder joint with an external load attached to the palm of the fabricated robotic device. With the ARC controller, the robotic device demonstrates an excellent tracking and synchronization performance.

In this paper, an adaptive robust controller of assistive robotic device using a dual twisted-string actuation devices was synthesized. With the consideration of system uncertainties, nonlinear dynamics, and operational dead-zones, a compensation strategy for high accuracy motion control is integrated in the controller. The proposed controller not only accounts for the tracking performance but also minimizes synchronization errors of the dual-axial system. A test platform was designed to validate the performance of the proposed ARC controller, which can achieve tracking performance of individual twisted-string actuation and minimize the synchronization error simultaneously. The performance of the proposed ARC controller was compared with the outcome of regular PID controller as well.

In the past, most of the operating strategies of energy harvesting devices focus only on the resonant frequency of its first mode. The resonant frequency in this mode is fine tuned with an attached proof mass. This paper presents a new approach of operating energy harvesting devices in different vibration modes. With this operation strategy, the harvested power can be increased. The resonant frequencies of adopted piezoelectric devices in different modes can be fine tuned with the same mechanism. A mathematical model that estimates resonant frequencies of piezoelectric cantilevers is proposed for various scenarios. The theoretical results have also been validated by experiments with different mass moving along the experimental cantilever. Other important factors, such as resistive loads, that affect output power are discussed as well.

Piezoelectric devices have been widely used as a means of transforming ambient vibrations into electrical energy that can be stored and used to power other devices. This type of power generation devices can provide a convenient alternative to traditional power sources used to operate certain types of sensors/actuators, MEMS devices, and microprocessor units. However, the amount of energy produced by these devices is in many cases far too small to directly power an electrical device. Therefore, much of the research into power harvesting has focused on methods of accumulating the energy until a sufficient amount is present, allowing the intended electronics to be powered.
Due to the tiny amount of harvestable power from a single device, it is critical to collect vibration energy efficiently. Many research groups have developed various methods to operate the harvesting devices at their resonant frequencies for maximal amount of energy. Different techniques of conversion circuits are also investigated for efficient transformation from mechanical vibration to electrical energy. However, efforts have not been made to the analysis of array configuration of energy harvesting elements. Poor combination of piezoelectric elements, such as phase difference, cannot guarantee the increasing amount of harvested energy. To realize a piezoelectric energy-harvesting device with higher volume energy density, the energy conversion efficiencies of different array configurations were investigated. In the present study, various combinations of piezoelectric elements were analyzed to achieve higher volume energy density. A charging circuit for solid-state batteries with planned energy harvesting strategy was also proposed. With the planned harvesting strategy, the required charging time can be estimated. Thus, the applicable applications can be clearly identified.
In this paper, optimal combination of piezoelectric cantilevers and different modes of charging methods were investigated. The results provide a means of choosing the piezoelectric device to be used and estimate the amount of time required to recharge a specific capacity solid-state battery.

This paper investigates motion synchronization of a multiple axes system. Three different control schemes: a cross-coupling controller in feedback loop, a linear quadratic optimal controller and an adaptive controller, were used to synthesize the synchronization compensator with the cross-coupling dynamics among the axes for both nominal and coefficient varying systems. With these strategies, the asymptotic convergence of both tracking and synchronization errors can be achieved. Simulation and experimental results of a three-axis motion system illustrate the effectiveness of the proposed approaches.

This paper investigates on motion synchronization of a multiple axes system. An adaptive robust control scheme was used to synthesize the synchronization compensator with cross-coupling dynamics among axes. By using the adaptive robust strategies, the asymptotic convergence of both tracking and synchronization errors are achieved. The robust control scheme also guarantees the satisfaction of transient performance, tracking errors, and synchronization errors. Experimental results of a three-axis motion system that include system uncertainties are also illustrated to verify the effectiveness of the proposed approach. The results indicate the excellent transient and both tracking and synchronization accuracies.

With the computation power of the state-of-the-art processors and digital electronics, fast microprocessors and combination-logic devices, such as CPLD and FPGA, have become dominant in control engineering. Engineers usually expect that designed controllers can be realized accurately with fast processing speed. However, though the speed of digital electronics has been increased dramatically in the past decade, the resolution has not been improved significantly. As the demand of precision control increases with faster response, calculated outputs of the synthesized controller with fast sample rate but insufficient resolution will not only be distorted, but it can also lead to undesired results or become unstable. This paper provides a guideline to estimate the required wordlength for digital controllers in state-space realization.

This paper investigate on motion synchronization of multiple axes systems. Two different control strategies, a cross-coupling controller in feedback loop and an adaptive controller, were used to synthesize the synchronization compensator with the cross-coupling dynamics among the axes. By using these strategies, the asymptotic convergence of both tracking and synchronization errors are achieved. The comparison of the two controllers of the nominal plant is discussed. Experimental results of a three-axis motion system that include system uncertainties are also illustrated to verify the effectiveness of the proposed approach.