27 April 2001
Coring machine with integrated sensors
By Bob Felton
Assess engineering properties of drilled material while drilling.
An ultrasonic coring machine designed for sampling the surface of Mars provides real-time data about the sampled material before the core exits the sampling barrel, courtesy of onboard sensors. Further, it draws little power, extracts a core having any of multiple cross-section shapes, operates from very low to very high temperatures, and does not rely on large axial force to advance the bit. NASA’s Jet Propulsion Laboratory developed the machine.
According to the inventor’s report to NASA, "The USDC [Ultrasonic/Sonic Drill/Corer] advances into the material of interest by means of a hammering action and a resulting chiseling action at the tip of the corer. The combination of ultrasonic vibrations (typically at a frequency of about 20 kilohertz) and sonic vibrations (typically at a frequency between 60 hertz and 1 kilohertz) gives rise to a hammering action that is more effective for drilling than the microhammering action of ultrasonic vibrations alone. The hammering and chiseling actions are so effective that, unlike in conventional twist drilling, a negligible amount of axial force is needed to make the USDC advance into the material. Also, unlike a conventional twist drill, the USDC operates without need for torsional restraint and can easily be made to drill into a material at an oblique angle."
Because the corer is advanced sonically instead of by rotating a cutting edge, drilling work is unaffected by the shape of the barrel cross section. Further, sensors may be mounted inside the barrel so the properties of the sampled material may be assessed as it is drilled.
Though originally developed for extraterrestrial subsurface sampling, the technology is adaptable to medical and manufacturing uses. According to the researchers, "In its role as a hammering mechanism, the USDC also acts as a sounding source for geophysical or physiological sonar to examine drilled objects and the surrounding ground or tissue. When the tip of the corer first touches an object, the acoustic impedance (and hence the electrical impedance) of the piezoelectric actuator changes; these impedances can serve as additional sensory quantities for probing the object and/or for feedback control of the excitation." Further, "The drill bit extensional and transverse motions cause the formation of a hole that is larger than the bit size and thus protect it from jamming."
When fitted with electrodes or inductive coils on the tip or core barrel, the USDC measures electric grounding properties, conductivity, electrostatic charges, and dielectric constant. Using electrodes made of different materials permits evaluation of oxidation properties. Measuring the force corresponding to microindentation of solids provides quantitative information about the hardness of the penetrated material.
Researchers at NASA’s Jet Propulsion Laboratory developed the USDC. For further information, access the Technical Support Package online at www.nasatech.com under the Machinery/Automation category. IT
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