Mircea Badescu

Efficient Electromechanical Network Models for Wireless Acoustic- Electric Feed-throughs

There are numerous engineering design problems where the use of wires to transfer power and communicate data thru the walls of a structure is prohibitive or significantly difficult that it may require a complex design. Such systems may be concerned with the leakage of chemicals or gasses, loss of pressure or vacuum, as well as difficulties in providing adequate thermal or electrical insulation. Moreover, feeding wires thru a wall of a structure reduces the strength of the structure and makes the structure susceptibility to cracking due to fatigue that can result from cyclic loading. Two areas have already been identified to require a wireless alternative capability and they include (a) the container of the Mars Sample Return Mission will need the use of wireless sensors to sense pressure leak and to avoid potential contamination; and (b) the Navy is seeking the capability to communicate with the crew or the instrumentation inside marine structures without the use of wires that will weaken the structure. The idea of using elastic or acoustic waves to transfer power was suggested recently by Y. Hu, et al.1. However, the disclosed model was developed directly from the wave equation and the linear equations of piezoelectricity. This model restricted by an inability to incorporate head and tail mass and account for loss in all the mechanisms. In addition there is no mechanism for connecting the model to actual power processing circuitry (diode bridge, capacitors, rectifiers etc.). An alternative approach which is to be presented is a network equivalent circuit that can easily be modified to account for additional acoustic elements and connected directly to other networks or circuits. All the possible loss mechanisms of the disclosed solution can be accounted for and introduced into the model. The circuit model allows for both power and data transmission in the forward and reverse directions through acoustic signals at the harmonic and higher order resonances. This system allows or the avoidance of cabling or wiring. The technology is applicable to the transfer of power for actuation, sensing and other tasks inside sealed containers and vacuum/pressure vessels.

Wireless piezoelectric acoustic-electric power feedthru

There are numerous engineering applications where there is a need to transfer power and communication data thru the walls of a structure. A piezoelectric acoustic-electric power feedthru system was developed in this reported study allowing for wireless transfer of electric power through a metallic wall using elastic waves. The technology is applicable to the transfer of power for actuation, sensing and other tasks inside sealed containers and vacuum/pressure vessels. A network equivalent circuit including material damping loss was developed to analyze the performance of the devices. Experimental test devices were constructed and tested. The power transfer capability and the transfer efficiency were measured. A 100W feed though capability with 38 mm diameter device and 88% transmission efficiency were demonstrated. Both analytical and experimental results are presented and discussed in this paper.

Studies of acoustic-electric feed-throughs for power transmission through structures

There are numerous engineering design problems where the use of wires to transfer power and communicate data thru the walls of a structure is prohibitive or significantly difficult that it may require a complex design. Using physical feedthroughs in such systems may make them susceptible to leakage of chemicals or gasses, loss of pressure or vacuum, as well as difficulties in providing adequate thermal or electrical insulation. Moreover, feeding wires thru a wall of a structure reduces the strength of the structure and makes the structure prone to cracking due to fatigue that can result from cyclic loading and stress concentrations. One area that has already been identified to require a wireless alternative to electrical feedthroughs would be the container of any Mars Sample Return Mission, which would need wireless sensors to sense a pressure leak and to avoid potential contamination. The idea of using elastic or acoustic waves to transfer power was suggested recently by [Y. Hu, et al., July 2003]. This system allows for the avoidance of cabling or wiring. The technology is applicable to the transfer of power for actuation, sensing and other tasks inside any sealed container or vacuum/pressure vessel. An alternative approach to the modeling presented previously [Sherrit et al., 2005] used network analysis to solve the same problem in a clear and expandable manner. Experimental tests on three different designs of these devices were performed. The three designs used different methods of coupling the piezoelectric element to the wall. In the first test the piezoelectric material was bolted using a backing structure. In the second test the piezoelectric was clamped after the application of grease. Finally the piezoelectric element was attached using a conductive epoxy. The mechanical clamp with grease produced the highest measured efficiency of 53% however this design was the least practical from a fabrication viewpoint. The power transfer efficiency of conductive epoxy joint was 40% and the stress bolts (12%). The experimental results on a variety of designs will be presented and the thermal and non-linear issues will be discussed.

Lemur IIb: a Robotic System for Steep Terrain Access

Purpose – Introduces the Lemur IIb robot which allows the investigation of the technical hurdles associated with free climbing in steep terrain. These include controlling the distribution of contact forces during motion to ensure holds remain intact and to enable mobility through over‐hangs. Efforts also can be applied to further in‐situ characterization of the terrain, such as testing the strength of the holds and developing models of the individual holds and a terrain map.Design/methodology/approach – A free climbing robot system was designed and integrated. Climbing end‐effector were investigated and operational algorithms were developed.Findings – A 4‐limbed robotic system used to investigate several aspects of climbing system design including the mechanical system (novel end‐effectors, kinematics, joint design), sensing (force, attitude, vision), low‐level control (force‐control for tactile sensing and stability management), and planning (joint trajectories for stability). A new class of Ultrasonic/S...

High-power piezoelectric acoustic-electric power feedthru for metal walls

Piezoelectric acoustic-electric power feed-through devices transfer electric power wirelessly through a solid wall using elastic waves. This approach allows for the elimination of the need for holes through structures for cabling or electrical feed-thrus . The technology supplies power to electric equipment inside sealed containers, vacuum or pressure vessels, etc where holes in the wall are prohibitive or may result in significant performance degradation or requires complex designs. In the our previous work, 100-W of electric power was transferred through a metal wall by a small, piezoelectric device with a simple-structure. To meet requirements of higher power applications, the feasibility to transfer kilowatts level power was investigated. Pre-stressed longitudinal piezoelectric feed-thru devices were analyzed by finite element modeling. An equivalent circuit model was developed to predict the characteristics of power transfer to different electric loads. Based on the analytical results, a prototype device was designed, fabricated and successfully demonstrated to transfer electric power at a level of 1-kW. Methods of minimizing plate wave excitation on the wall were also analyzed. Both model analysis and experimental results are presented in detail in this paper.

Rotary hammer ultrasonic/sonic drill system

Subsurface sampling systems for future planetary robotic missions which include reliable methods of generating, acquiring, and delivering samples to a scientific instrument for analysis are of extreme importance to the success of future in situ and sample return missions. Operating at remote locations the sampler needs to deal with a variety of disparate rock sources while being essential to deliver samples in different forms and to accommodate the requirements of a wide range of scientific instruments. Existing highly efficient terrestrial drilling techniques have limited space applications due to their need for large axial forces and holding torques, high power consumption and inability to efficiently duty cycle, and the use of rigid handling platforms. This paper describes the work performed at Jet Propulsion Laboratory (JPL) and Honeybee Robotics for the development of a rotary percussive drill that uses an ultrasonic/sonic drill/corer as the hammering device integrated in a sampling system capable of automatic operation in a Mars environment.

Subsurface sampler and sensors platform using the ultrasonic/sonic driller/corer (USDC)

The search for existing or past life in the Universe is one of the most important objectives of NASAs mission. For this purpose, effective instruments that can sample and conduct in-situ astrobiology analysis are being developed. In support of this objective, a series of novel mechanisms that are driven by an Ultrasonic/Sonic actuator have been developed to probe and sample rocks, ice and soil. This mechanism is driven by an ultrasonic piezoelectric actuator that impacts a bit at sonic frequencies through the use of an intermediate free-mass. Ultrasonic/Sonic Driller/Corer (USDC) devices were made that can produce both core and powdered cuttings, operate as a sounder to emit elastic waves and serve as a platform for sensors. For planetary exploration, this mechanism has the important advantage of requiring low axial force, virtually no torque, and can be duty cycled for operation at low average power. The advantage of requiring low axial load allows overcoming a major limitation of planetary sampling in low gravity environments or when operating from lightweight robots and rovers. The ability to operate at duty cycling with low average power produces a minimum sample temperature rise allowing for control of the sample integrity and preventing damage to potential biological markers in the acquired sample. The development of the USDC is being pursued on various fronts ranging from analytical modeling to mechanisms improvements while considering a wide range of potential applications. While developing the analytical capability to predict and optimize its performance, efforts are made to enhance its capability to drill at higher power and high speed. Taking advantage of the fact that the bit does not require rotation, sensors (e.g., thermocouple and fiberoptics) were integrated into the bit to examine the borehole during drilling. The sounding effect of the drill was used to emit elastic waves in order to evaluate the surface characteristics of rocks. Since the USDC is driven by piezoelectric actuation mechanism it can designed to operate at extreme temperature environments from very cold as on Titan and Europa to very hot as on Venus. In this paper, a review of the latest development and applications of the USDC will be given.

Power loss consideration in wireless piezoelectric acoustic-electric power feedthru

Piezoelectric acoustic-electric power feedthru devices that are able to transfer electric power through metallic/ferromagnetic wall are investigated. Electric energy is converted to acoustic energy by piezoelectric transducer at one side of the wall. The acoustic wave propagates through the wall and, then, it is converted back to electric energy by another transducer on the other side. For high efficient transmission, it is critical that all the energy loss should be minimized. In addition to the electrical, mechanical and electromechanical loss in the transducers and the thickness of the wall, Lamb (plate) waves are excited by the transducers in the wall and they also result in energy losses. In this study, the energy loss caused by the Lamb waves are analyzed analytically and by finite element simulations. The results and the methods to reduce the loss are presented and discussed in this presentation.

New Performance Indices and Workspace Analysis of Reconfigurable Hyper-Redundant Robotic Arms

In this paper, we introduce new performance indices to characterize the workspace of reconfigurable hyper-redundant robotic arms. These indices are then used to analyze the workspace of a type of hyper-redundant robotic arm using as modules lower mobility parallel platforms. The modules of the reconfigurable robotic arm are the three-legged translational universal-prismatic-universal (UPU) and orientational universal-prismatic-spherical (UPS) parallel platforms. Each arm is composed of a large number of these modules having a very large number of degrees of freedom. Results of the workspace analysis are presented in tabular and graphical forms and the corresponding best designs are identified. All possible arm assembly configurations with two, three, and four parallel platform modules and one configuration with five parallel platform modules have been taken into consideration, analyzed, and compared.

Deep Drilling and Sampling via the Wireline Auto-Gopher Driven by Piezoelectric Percussive Actuator and EM Rotary Motor

The ability to penetrate subsurfaces and perform sample acquisition at depths of meters is critical for future NASA in-situ exploration missions to bodies in the solar system, including Mars, Europa, and Enceladus. A corer/sampler was developed with the goal of acquiring pristine samples by reaching depths on Mars beyond the oxidized and sterilized zone. The developed rotary-hammering coring drill, called Auto-Gopher, employs a piezoelectric actuated percussive mechanism for breaking formations and an electric motor rotates the bit to remove the powdered cuttings. This sampler is a wireline drill that is incorporated with an inchworm mechanism allowing thru cyclic coring and core removal to reach great depths. The penetration rate is optimized by simultaneously activating the percussive and rotary motions of the Auto-Gopher. The percussive mechanism is based on the Ultrasonic/Sonic Drill/Corer (USDC) mechanism, which is driven by a piezoelectric stack, demonstrated to require low axial preload. The Auto-Gopher has been produced taking into account the lessons learned from the development of the Ultrasonic/Sonic Gopher that was designed as a percussive ice drill and was demonstrated in Antarctica in 2005 to reach about 2 meters deep. A field demonstration of the Auto-Gopher is currently being planned with the objective of reaching as deep as 3 to 5 meters in tufa formation.