The field of smart materials is an increasingly growing area of research. In aerodynamics applications especially, transducers have to fulfill a series of requirements such as light weight, size, energy consumption, robustness and durability. Piezoelectric transducers, devices which transform an electrical signal into motion, fulfill many of these requirements. Specifically, piezoelectric composites are of interest due to their added toughness and ease of integration into a structure. Resulting composites have a characteristic initial curvature with accompanying residual stresses that are responsible for enhanced performance, relative to flat actuators, when the active material is energized. A number of transducer designs based on composites have been developed. Two of these piezoelectric composites called Thunder® and Lipca are analyzed. Thunder is a composite of steel, polyimide adhesive, PZT, polyimide adhesive, and aluminum; and Lipca is a composite of fiberglass epoxy, carbon/epoxy, PZT, and fiberglass epoxy.Room temperature shapes of circular and rectangular Thunder® and Lipca actuators are predicted by using the Rayleigh-Ritz model. This technique is based on the assumption that the stable geometric configuration developed in the actuator after manufacturing, is the configuration that minimizes the total potential energy. This energy is a function of the displacement field which can be approximated by two functions, a four term model, and a twenty-three term model. The coefficients in the models are determined by minimizing the total potential energy of the actuator. The actuator deformations are assumed to obey the Kirchhoff hypothesis and the actuator layers are assumed to be in the state of plane stress.The four coefficient model produces results not comparable to three-dimensional surface topology maps. The twenty-three coefficient model however, is shown to have generally good agreement with the data for all studied actuators. To quantify the difference, at the cross section of each actuator, a profile is fitted by using a quadratic equation obtaining regression coefficients above 99%. For all actuators, the error between experimental and the calculated centerline data is less than 6%. For the 6R model however, the error is approximately 25%. One of the possible reasons for the error may be the tolerance of the thickness of the PZT layer. By changing the PZT thickness ±6% of the nominal value, over predicts the experimental dome height by 20%. Another possible reason for the discrepancy is the thickness of the actuator, thicker than all actuators used in this study, which might contradict the validity of the thin actuator assumption. Furthermore, by calculating the side-length-to-thickness ratio, 115 in this case, as stated by Aimmanee & Hyer (2004), may cause instability, and could result in unexpected behavior.The neutral axis position, calculated by using a force balance at equilibrium under the assumption of pure bending, for all actuators used in this study is determined and compared to the ceramic layer position. The results indicated that for all Thunder® models the neutral axis is located below the ceramic layer indicating that the PZT wafer may be in total tension. For the Lipca C2 device however, the neutral axis is found to be above the ceramic layer, indicating that the piezoelectric layer may be in total compression.Strain fields are also predicted with contradicting results when compared to the theory that the ceramic is in tension in the Thunder actuators. The contradiction on the strain calculations can be explained by the manner the strain field is derived: by differentiating and squaring the high-order polynomials of the approximated displacement component losing accuracy when it comes to predicting normal and shear strains.The Rayleigh-Ritz technique can become a tool to perform parametric studies of the key elements for manufacturing to optimize specific features of the actuators.

Thesis (M.S.)--University of Nevada, Reno, 2004. / "December 2004." Includes bibliographical references (leaves 107-109). Online version available on the World Wide Web.

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Balaji Panchapakesan, Dept. of Electrical and Computer Engineering. Includes bibliographical references.

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, 2002. / Word processed copy. Summary in English. Includes bibliographical references (leaves 81-83). Also available online.

A serial robotic manipulator arm is a complex electro-mechanical system whose performance is primarily characterized by the internal parameters of its actuators. The actuator itself is a complex nonlinear system whose performance can be characterized by the speed and torque capabilities of its motor and its accuracy depends on the resolution of the encoder as well as its ability to resist deformations in its gear train under load. The mechanical gain associated with the gear train transmission is critical to the overall performance of the actuator since it amplifies the motor torque thus improving the force capability of the manipulator housing it, reduces the motor speed to a suitable output speed operating range, dominates the inertia content of the manipulator and amplifies the stiffness improving the precision under load of the overall system. In this work, a basic analytic process that can be used to manage the actuator parameters to obtain an improved arm design based on a set of desired/required performance specifications is laid out. The key to this analytic process is the mapping of the actuator parameters (motor speed, motor torque, rotary stiffness, encoder resolution, transmission efficiency, mass, rotary inertia) to their effective values at the system output via the mechanical gains of the actuator transmissions as well as the effective mechanical gains associated with the manipulator geometry. This forward mapping of the actuator parameters allows the designer to determine how each of the actuator parameters influences the functional capacity of the serial manipulator arm. The analytic formulation is demonstrated to be effective in addressing the issue of configuration management of serial robotic manipulators where the goal is to assemble a system from a finite set of actuator modules that meets some required performance specifications. To this end, four design case studies demonstrating the solution of the configuration management problem are presented where the application domains include designing for light to heavy-duty force applications, designing for responsiveness and designing for Human-Robot Interactions (HRI). The design trade-offs for each of the application domains are analyzed and design guidelines are presented. This research also formulates a new approach to characterizing the dynamic behavior of serial chain mechanisms via the kinetic energy distribution. In any mechanism, the amount of kinetic energy in the system is a very important quantity to analyze. Since the inertial torques are directly related to the rate of change of the kinetic energy, better design (and operation) is achieved by having an understanding of how kinetic energy is distributed along the mechanism structure as well as how rapidly kinetic energy is flowing within it. In this work, a description of the Kinetic Energy Partition Values (KEPV) for serial chain mechanisms, as well as their rates of change, are presented. The KEPVs arise from the partitioning of the mechanism’s kinetic energy. Two design criteria, one based on the KEPVs and another based on their rates of change, are developed. These design criteria are indicators of both the dynamic isotropy of the system as well as the amount of kinetic energy flow within the system. A six-axis spatial manipulator is used to illustrate the solution of a design optimization problem where the goal is to demonstrate how the inertial parameters of the actuators and mechanical gains of the actuator transmissions alter the kinetic energy of the system which is “measured” via an effective mass criterion and its distribution which is measured via the KEPV criterion. It is demonstrated that the mechanical gains in the actuators significantly influence the magnitude of the kinetic energy as well as its distribution within the system. / text

Electromechanical actuators are becoming an increasingly popular alternative to traditional hydraulic actuators for ship, aircraft, vehicle suspension, robotic, and other applications. These actuators generally include an electric motor, gear train, bearings, shafts, sensors, seals, and a controller integrated into a single housing. This integration provides the advantages of a single shaft, fewer bearings, and ultimately, reduced weight and volume. Research has shown that the motor and gear train are the most critical, performance-limiting components in an actuator, and balancing the performance parameters (torque, weight, inertia, torque density, and responsiveness) among them is not trivial. The Robotics Research Group currently addresses this task by using intuitive rules of thumb and the designers’ experience, and this often requires multiple design iterations between the motor and gear train. In this regard, this research will provide preliminary guidelines for choosing the gear ratios and relative sizes of the motor and gear train when integrating a switched reluctance motor (SRM) with three different gear trains (hypocyclic gear train (HGT), star gear train coupled with a parallel eccentric gear train (Star+PEGT), and star compound gear train coupled with a parallel eccentric gear train (Star Compound+PEGT)) in the preliminary design stage. Research has also shown that there are cost benefits to developing actuator product families to meet the needs of a particular application domain. In this regard, scaling rules for the SRM, HGT, PEGT, and integrated actuators built from them (with diameters ranging from 6 to 50 inches and gear ratios from 100 to 450) will be developed. These scaling rules describe how the performance parameters vary as the size (diameter and aspect ratio) is varied and are useful for quickly sizing motor, gear train, and actuator designs. These scaling rules are useful for two purposes: 1) learning the relationships between the performance and dominant design parameters and 2) obtaining intermediate sizes not previously considered. The rules will be simple enough for designers to learn and use to make intelligent design parameter choices (purpose 1) but will also have sufficient accuracy for obtaining intermediate designs (purpose 2). The scaling rules are summarized in a series of three-dimensional design maps, with an emphasis on the development of visual decision-making tools. This research also formulates an actuator design procedure that incorporates the two central concepts of this research, balancing parameters and scaling, and this procedure is embedded within computational (MatLab) and solid modeling (SolidWorks) software programs. In addition to developing rules for scaling and balancing parameters, the procedure was also used for the following purposes. First, direct drive and geared actuators were compared in terms of their torque density and responsiveness to determine which alternative is superior for different gear ratio, diameter, and load inertia combinations. Second, alternative minimum sets of actuators were developed for an illustrative application, and the anticipated performance losses due to using common parameters among the sets were quantified. / text

Electromechanical actuators are highly complex non-linear devices that cannot be accurately modeled using only analytical formulations derived from first principles. When the application demands high model accuracy with a wide parametric range (and criteria) plus the need to take manufacturing/assembly variations associated with the asbuilt actuator into account, an empirical model based on extensive testing across the entire operating domain is the recommended approach. Since testing is an expensive, time consuming and laborious process, it is the aim of this research to determine efficient test methodologies (experimental designs) that would obtain the maximum information about actuator performance by means of a minimal number of tests. Current test standards are primarily designed to arrive at the actuator specifications by carrying out tests at either a single or a very limited set of test points. The results thus obtained are typically not valid across the entire operating domain of the actuator. Also these tests are performed for a very small set (one or two) of criteria. Furthermore most of this testing is conducted in terms of just one (occasionally two) control variables. As a result the full capability of the actuator is poorly represented. The research presented here addresses these limitations. To achieve the objective, the steps followed in this research are -- a) define a set of actuator performance criteria for testing, b) construct a test bed for actuator testing, c) develop a framework for testing actuators, d) conduct tests by applying principles from Design of Experiments, e) apply statistical techniques to identify empirical models and develop efficient experimental designs, and f) graphically present the actual capabilities of the actuator using performance maps. A commercially available permanent magnet synchronous motor-geartrain combination was chosen as the test actuator. This actuator has a nominal/peak rating of 43/86 lb-ft torque and 30/100 RPM speed. The criteria considered for characterizing the actuator’s operational capability includes noise, vibration, efficiency, current consumption, torque ripple, velocity ripple, backdriveability, and temperature. Control variables affecting the performance criteria were identified. Measurement of performance over the entire operating range of actuator requires that the actuator be operated at specific levels of these control variables and the concerned performance criteria be measured. Therefore to perform these actuator tests, a modular test bed was constructed. The test bed consists of an actuator loading mechanism (in the form of a magnetic particle brake or a geartrain-motor combination), an array of sensors, amplifiers, a signal conditioning unit, data acquisition modules, motion controller, and transformer. The measured sensor data is filtered through the signal conditioning unit (to remove noise) and digitized using the data acquisition modules. Statistical techniques were employed to process the sensor data and for each criterion, an empirical model relating the criteria to its control variables was determined. Model adequacy checks were carried out to ensure that the model did not violate important statistical assumptions and that it adequately represented the relationship between the input control variables and the output response (performance criteria). These models were used to generate performance maps for each criteria. Based on a predetermined set of run sizes, for each empirical model, alternate experimental designs were determined. Efficient experiment designs were identified by metrics such as -- Gefficiency, maximum prediction variance and average prediction variance. Besides the obvious advantage of arriving at complete and accurate performance profiles for the actuator undergoing tests (with minimal testing), the methodology could be applied to other actuators of a similar family. We might consider the methodology to be a subset of the general concept of metrology; i.e., the determination of as-built parameters vs. as designed parameters. Simplification techniques were applied to these models to remove unwanted model terms. / text

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