Garnett C. Horner

A linear piezoelectric motor

The development of a linear hybrid transducer type piezoelectric motor is shown. This design has the advantages of light weight, macro- and micro-positioning, and large force/velocity output. The motor consists of a longitudinal actuator that provides output displacement and force, and two alternating clamping actuators which provide the holding force. The advantages of this design over other types of piezoelectric motor are shown. Significant design considerations for the development of a piezoelectric motor (including material choices, shear loads on piezoelectric materials, and contact surface interaction) are discussed. A simulation, including a finite element analysis of the system, is used to predict the motor response to various input sets. A prototype motor is built and its characteristics are compared to theoretical predictions.

Aircraft Morphing program

In the last decade smart technologies have become enablers that cut across traditional boundaries in materials science and engineering. Here we define smart to mean embedded actuation, sensing, and control logic in a tightly coupled feedback loop. While multiple successes have been achieved in the laboratory, we have yet to see the general applicability of smart devices to real aircraft systems. The NASA Aircraft Morphing program is an attempt to couple research across a wide range of disciplines to integrate smart technologies into high payoff aircraft applications. The program bridges research in seven individual disciplines and combines the effort into activities in three primary program thrusts. System studies are used to assess the highest-payoff program objectives, and specific research activities are defined to address the technologies required for development of smart aircraft systems. In this paper we address the overall program goals and programmatic structure, and discuss the challenges associated with bringing the technologies to fruition.

Adaptive structural systems and compliant skin technology of morphing aircraft structures

Morphing aircraft design - the design of aircraft capable of macroscale shape change for drastic in-flight performance variation - is an extremely broad and underdefined field. Two primary means of developing new concepts in morphing exist at Cornell University: design of broad test platforms with generalized motions that can provide future insight into targeted ideas, and specifically adapted aircraft and shape change mechanisms attempting to accomplish a particular task, or hybridize two existing aircraft platforms. Working with both schools of thought, Cornell research has developed a number of useful concepts that are currently under independent analysis and experimentation, including three devices capable of drastically modifying wing structure on a testbed aircraft. Additional concerns that have arisen include the desire to implement ornithological concepts such as perching and wingtip control, as well as the necessity for a compliant aerodynamic skin for producing flight-worthy structural mechanisms.

Precision cryogenic magnetostrictive actuator using a persistent high TC magnet

Cryogenic magnetostrictive materials, such as rare earth zinc crystals, offer high strains and high forces with minimally applied magnetic fields, making the material ideally suited for deformable optics applications. For cryogenic temperature applications, such as Next Generation Space Telescope, the use of superconducting magnets offer the possibility of a persistent mode of operation, i.e., the magnetostrictive material will maintain a strain field without power. High temperature superconductors (HTS) are attractive options if the temperature of operation is higher than 10° Kelvin (K) and below 77 K. However, HTS wires have constraints that limit the minimum radius of winding, and even if good wires can be produced, the technology for joining superconducting wires does not exist. In this article, the design and capabilities of a rare earth zinc magnetostrictive actuator using bulk HTS is described. Bulk superconductors can be fabricated in the sizes required with excellent superconducting properties. E...

Actuator concepts and mechatronics

Mechatronic design implies the consideration of integrated mechanical, electrical, and local control characteristics in electromechanical device design. In this paper, mechatronic development of actuation device concepts for active aircraft aerodynamic flow control are presented and discussed. The devices are intended to be embedded in aircraft aerodynamic surfaces to provide zero-net-momentum jets or additional flow-vorticity to control boundary layers and flow- separation. Two synthetic jet device prototypes and one vorticity-on-demand prototype currently in development are described in the paper. The aspects of actuation materials, design approaches to generating jets and vorticity, and the integration of miniaturized electronics are stressed.

Linear traveling wave motor

The objective of this research is to design and develop a working prototype of a linear traveling wave motor that utilizes Thin-layer composite-Unimorph piezoelectric Driver (THUNDER) technology. THUNDER technology is used to create curved actuators from piezoceramic wafers. These flexures are arranged alternatively bowed towards and away from a flat surface. The basis of motion rest on the fact that upon actuation the flexures will change both chord length and radius of curvature. This allows the flexures to either grip the driving rod or extend axially. Motion is achieved through sequential operation of individual flexures. This method yields a lightweight actuator with power off holding capability and a larger step size than motors that use stacked actuators. The simple design lends itself to inexpensive fabrication. A finite element model was used to predict the initial curvature and the height displacement of a single flexure. The model takes into account material properties, physical layout, fabrication techniques and driving voltage. These theoretical predictions were compared to experimental results. A prototype was developed but no movement has been realized in this configuration. However, it is shown that the flexures have the capability to achieve step sizes 1-2 orders of magnitude greater than other similar linear actuators.

Integration issues for high-strain actuation applications

Strain actuators, used to induce a relative structural displacement, are most effective when integrally embedded into the host structure. The paper summarizes progress and challenges in the field of embedding smart materials into structures. The difficulties of embedding active elements within composite structures are described from a system design perspective. Issues associated with the application of strain actuators in primary aircraft structure are discussed. Development of new embedding technology to combat the difficulties with high strain applications is advocated.

On incorporating reliability considerations into control system designs

This paper considers reliability in designing control systems for large orbital structures that are expected to have appreciable flexibility. Reliability is considered for both the control configuration (i.e. selecting sensor and actuator locations over an admissible set) and the ultimate operation of the system. The approach presented is to construct a cost function that indicates the absolute goal of the system and, for a given structural design, to determine the lowest achievable costs conditioned on the failure states of the system (i.e. which actuators and sensors are operational). These costs are then weighted and summed to provide an overall system performance measure. This measure is then minimized over the set of admissible control configurations. The approach is illustrated using a beam that has four actuators with the goal of achieving a given parabolic shape.

Flex-Patch: a highly flexible piezoceramic composite with attached electrical leads

A new packaging technique for piezoceramic wafers is presented in which encapsulation of the piezoceramic incorporates the electrical leads. This technique for encapsulation produces a hermetically sealed package that also is flexible. The resulting product is called Flex-Patch because of the high flexibility. Micro-graphs of the flexed piezoceramic show that despite micro-cracking within the ceramic there is little, if any, loss in performance. Flex-Patch may be surface mounted or embedded into composites.

Single-axis piezoceramic gimbal

This paper describes the fabrication, testing, and analysis of a single axis piezoceramic gimbal. The fabrication process consists of pre-stressing a piezoceramic wafer using a high-temperature thermoplastic polyimide and a metal foil. The differential thermal expansion between the ceramic and metal induces a curvature. The pre-stressed, curved piezoceramic is mounted on a support mechanism and a mirror is attached to the piezoceramic. A plot of gimbal angle versus applied voltage to the piezoceramic is presented. A finite element analysis of the piezoceramic gimbal is described. The predicted gimbal angle versus applied voltage is compared to experimental results.