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Ultrasonic/Sonic Jackhammer Advantages Include Low Noise, Low Vibration, and Low Average Power Demand

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Ultrasonic/Sonic Jackhammer Advantages Include Low Noise, Low Vibration, and Low Average Power Demand Ultrasonic/Sonic Jackhammer Advantages include low noise, low vibration, and low average power demand. NASA’s Jet Propulsion Laboratory, Pasadena, California An ultrasonic/sonic jackhammer (USJ) the USJ would offer several advantages situations in which there is a need to is the latest in a series of related devices, the over conventional pneumatic jackham- cut through concrete or asphalt with- first of which were reported in “Ultra- mers, as discussed below. out damaging such embedded objects sonic/Sonic Drill/Corers With Integrated In the USJ (see figure) as in the previ- as pipes, cables, and reinforcing steel Sensors” (NPO-20856), NASA Tech Briefs, ously reported ultrasonic/sonic drill/ bars. Vol. 25, No. 1 (January 2003), page 38. corers (USDCs) and related devices, the In contrast, even a full-scale USJ would Each of these devices cuts into a brittle ma- actuator assembly includes a piezoelec- generate much less noise and much less terial by means of hammering and chisel- tric stack and a horn for mechanical am- back-propagating vibration. The full- ing actions of a tool bit excited with a com- plification of the piezoelectric displace- scale USJ would also demand less average bination of ultrasonic and sonic vibrations. ment. A cylindrical shank of a power. Moreover, on the basis of experi- A small-scale prototype of the USJ has been chisel-shaped tool bit is mounted on the ence with the USDCs, it is expected that demonstrated. A fully developed, full-scale lower end of the horn. A bobbin-like such relatively flexible materials as wood, version of the USJ would be used for cut- cylindrical mass is free to move axially plastics, metals, and human tissues will ting through concrete, rocks, hard asphalt, through a limited range between the not be damaged by brief contact with the and other materials to which conventional lower end of the horn and the upper end tool bit of the operating USJ. Yet another pneumatic jackhammers are applied, but of the blade portion of the tool bit. The advantage is that like a USDC as de- sharp edge of the bit is placed in contact scribed in the noted prior NASA Tech with the rock or other hard material to Briefs article, the USJ could be instru- Actuator be cut. Unlike a pneumatic jackhammer, mented with mechanical-impedance sen- sors that could be used to obtain feed- Handle the USJ need not be heavy because its principle of operation does not require a back to optimize the electrical excitation large contact force. for cutting and/or to utilize the vibra- The piezoelectric stack is electrically tions to probe the hard material in the driven at its resonance frequency, and a vicinity of the tool bit. Horn bolt holds the stack in compression to This work was done by Yoseph Bar-Cohen prevent fracture during operation. The and Stewart Sherrit of Caltech and Jack Herz free mass bounces between hard stops at of CTC for NASA’s Jet Propulsion Labora- the limits of its range of motion at a sonic tory. Further information is contained in a frequency. The impacts of the free mass TSP (see page 1). on the hard stops create stress pulses that In accordance with Public Law 96-517, the propagate along the horn, to and contractor has elected to retain title to this in- through the tool bit, to the tool-bit/rock Free Mass vention. Inquiries concerning rights for its interface. The rock becomes fractured commercial use should be addressed to: when its ultimate strain is exceeded. Innovative Technology Assets Management A conventional pneumatic jackham- JPL mer generates enormous amounts of Mail Stop 202-233 noise, along with severe vibrations that 4800 Oak Grove Drive Tool Bit propagate back into the operator’s Pasadena, CA 91109-8099 body and that are so strong as to some- (818) 354-2240 times injure the operator. Every object E-mail: [email protected] The Ultrasonic/Sonic Jackhammer is driven elec- trically instead of pneumatically. It offers several encountered by the tool bit is dam- Refer to NPO-40771, volume and number advantages over a conventional pneumatic jack- aged. This indiscriminate cutting ac- of this NASA Tech Briefs issue, and the hammer. tion is particularly disadvantageous in page number. NPO-40771 ABPI 06-03-04 LE 20 NASA Tech Briefs, May 2005.
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