-The parameters of the KLM and Mason's equivalent circuits in the thickness mode are presented to include dielectric, elastic and piezoelectric loss. The models are compared under various boundary conditions with and without acoustic layers to the analytical solutions of the wave equation. We show that in all cases equivalence is found between the analytical solution and the KLM and Mason's equivalent circuit models. It is noted that in order to maintain consistency with the linear equations of piezoelectricity and the wave equation care is required when applying complex coefficients to the models. The effect of the piezoelectric loss component on the power dissipated in the transducer is presented for loaded and unloaded transducers to determine the significance of the piezoelectric loss to transducer designers. The effect of the piezoelectric loss on the insertion loss was found to be small.
Drilling consists of 2 processes: breaking the formation with a bit and removing the drilled cuttings. In rotary drilling, rotational speed and weight on bit are used to control drilling, and the optimization of these parameters can markedly improve drilling performance. Although fluids are used for cuttings removal in terrestrial drilling, most planetary drilling systems conduct dry drilling with an auger. Chip removal via water-ice sublimation (when excavating water-ice-bound formations at pressure below the triple point of water) and pneumatic systems are also possible. Pneumatic systems use the gas or vaporization products of a high-density liquid brought from Earth, gas provided by an in situ compressor, or combustion products of a monopropellant. Drill bits can be divided into coring bits, which excavate an annular shaped hole, and full-faced bits. While cylindrical cores are generally superior as scientific samples, and coring drills have better performance characteristics, full-faced bits are simpler systems because the handling of a core requires a very complex robotic mechanism. The greatest constraints to extraterrestrial drilling are (1) the extreme environmental conditions, such as temperature, dust, and pressure; (2) the light-time communications delay, which necessitates highly autonomous systems; and (3) the mission and science constraints, such as mass and power budgets and the types of drilled samples needed for scientific analysis. A classification scheme based on drilling depth is proposed. Each of the 4 depth categories (surface drills, 1-meter class drills, 10-meter class drills, and deep drills) has distinct technological profiles and scientific ramifications.
-JPL has a requirement for telerobotic tools for planetary sample acquisition, which require low power and have the ability to work in harsh environments. We are currently investigating the possibility of using ultrasonic horns to develop a family of ultrasonic tools for these environments. In an effort to determine control parameters a one-dimensional Mason's model for a stepped ultrasonic horn assembly was developed which includes the effects of mechanical and electrical losses in the piezoelectric material and acoustic elements. The model is separated into three regions; the piezoelectric stack including stress bolt the backing layer and the horn. The model is found to predict the impedance data of the horn assembly very accurately up to the first coupled (radial) resonance. The model also allows for the calculation of the velocity and force and power delivered to each acoustic element. FEM modeling and accelerometer data from the horn tip were used to corroborate the model. The difficulties associated with modeling the load impedance of various devices will be discussed and current directions noted.
Force feedback from remote or virtual operations is needed for numerous technologies including robotics, teleoperated surgery, games and others. To address this need, the authors are investigating the use of electrorheological fluids (ERF) for their property to change the viscosity under electrical stimulation. This property offers the capability to produce feedback haptic devices that can be controlled in response to remote or virtual stiffness conditions. Forces applied at a robot endeffector due to a compliant environment can be reflected to the user using such an ERF device where a change in the system viscosity in proportion to the force to be transmitted. This paper describes the analytical modeling and experiments that are currently underway to develop an ERF based force feedback element.
Abstract-Future NASA exploration missions to Mars, Europa, Titan, comets, and asteroids will perform sampling, in-situ analysis and possibly the return of material to Earth for further tests. One of the major limitations of sampling in low gravity environments is that conventional drills need high axial force. An ultrasonic/sonic driller/corer (USDC) mechanism was developed to address these and other limitations of existing drilling techniques. The USDC is based on an ultrasonic horn that is driven by a piezoelectric stack. The horn drives a free-mass, which resonates, between the horn and drill stem. Tests have shown that this device addresses some of the key challenges to the NASA objective of planetary in-situ sampling and analysis. The USDC is lightweight (450 g), requires low pre-load (< 5N) and can be driven at low power (5W). The device was operated from such robotic platforms as the Sojourner rover and the FIDO robotic arm and it has been shown to drill various rocks including granite, diorite, basalt and limestone. The drill can potentially operate at high and low temperatures and does not require sharpening. Although the drill is driven electrically at 20 kHz, a substantial sub-harmonic acoustic component is found that is crucial to drilling performance. Models that explain this low frequency coupling in the horn, free-mass, drill stem and rock are presented. Efforts are currently underway to integrate the models and experimentally corroborate the predictions.
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