Research Areas

Smart Structures

Our focus in smart structures has been on the model-based control of distributed parameter systems. Distributed parameter models accurately represent the physics of many electromechanical systems. These models typically consist of partial differential equations (PDEs) for the distributed mechanical subsystem, boundary conditions, electromechanical coupling equations, and ordinary differential equations (ODEs) for the electrical subsystem. Applications include flexible cable cranes, high-speed machining spindles, active noise control systems, flexible robot arms, marine cable systems, and high-speed web and fiber handling systems. Traditionally, the distributed equations are discretized to a finite number (N) of low order modes, resulting in a set of ODEs that can be used for control design using standard tools. For systems with low damping, however, choosing N too small can cause spillover instabilities in the high order modes. Alternatively, choice of a large N may result in a high order compensator.

Using Lyapunov-based approaches that do not require discretization, we design controllers that asymptotically stabilize the distributed model. This mathematically elegant method eliminates the spillover instabilities associated with traditional control approaches, produces simple, low order, physically intuitive controllers, and is applicable to nonlinear systems. The approach applies mathematical tools based on functional analysis, semigroup theory, and Lyapunov's Direct Method to a specific mechatronic system. In addition, Lyapunov-based techniques such as adaptive and backstepping control can be used to account for parametric uncertainty and electrical dynamics, respectively. Unlike most researchers in this area who focus exclusively on mathematics, we experimentally implement the proposed controllers and demonstrate the improved performance provided by the control. This often requires the development of novel mechatronic sensing and actuation schemes to measure the required feedback variables and apply the required system inputs. The figure shows, for example, a distributed parameter model-based control experiment for repetitive learning force tracking in a whisker sensor for the Navy.

We also work in passive vibration control approaches such as multifunctional adaptive structure concept through investigating the unique and desirable characteristics of plants; including nastic (rapid plant motions) actuation with large force and stroke and self-sensing/reconfiguration/healing. More specifically, we propose to develop and investigate new bio-actuation/bio-sensing ideas building upon innovations inspired by the mechanical, chemical, and electrical properties of plant cells. We demonstrated that a fluidlastic cell coupled to a mass can isolate vibration at a specific frequency. The figure shows the theoretically predicted and experimentally demonstrated transmission isolation zero at around 28Hz.

Active Projects:
- eVTOL Active Vibration Control via Rotor Torque Modulation with Rotor Pitch-Lag Coupling

Previous Projects:
- Passive Helicopter Vibration Control Using F²MC Tubes
- Flutter Stability of Rotors with Fluidic Pitch Links

Advanced Actuators

Working with colleagues in the Electrical Engineering department, we developed small and lightweight actuators for vehicles and medical applications, including a recent project on piezoelectric (PZT) actuators and wings for Nano Air Vehicles (NAVs). We invented the T-beam actuators that provide two-axis displacement from bulk PZT structure. PZT actuators have been integrated with a polymer compliant mechanism to produce the shown flapping wing device. We modeled and experimentally tested the wing displacement, rotation, and lift generation. The PZT compliant mechanisms developed in this project are also being used in vibrational energy harvesting devices that generate power from the motion of the human body. EAP Actuators for Braille displays were developed using polymers that were cast into films, stretched to the desired thickness using a zone heating machine, placed on frames, sprayed with conductive polymer electrodes, laminated to form a bi-layer, cut and wound into tubes, thermally bonded in a vacuum oven, and metallically electroded on the top and bottom to form a longitudinal straining actuator. Many of the steps in this process were automated using mechatronic systems designed and fabricated in the MRL.

Active Projects:
Previous Projects:
- Designing Optimized Mechanical Structures for Body-Based Piezoelectric Harvesting