A system has been developed using sound to detect problems on rovers or other remote platforms autonomously. It consists of a sensor array of microphones and accelerometers that uses the differences in the sounds generated by the motors, gears, instruments, or other devices being monitored to determine abnormal operation conditions.
In general, to locate a sound source in a given volume requires at least three sensors. In the case of a vehicle, however, a combination of vibration sensors needs to be used to monitor the amplitude of local vibrations in the structure. The microphones monitor the local pressure changes in the atmosphere to determine the noise location. The arrangement could be simple with three accelerometers and three microphones. Ideally, the microphones would be decoupled from local vibrations in the support structure to reduce interference of structure vibrations.
A series of accelerometers and microphones is attached to the mobility platform’s mechanical subsystems, chassis, suspension, wheel mounts, mast, instrument deployment device, etc. The sensors monitor ambient sound and record what it sounds like to drive on Mars, for example, and also transmit to Mission Operations sounds that are abnormal or may have destructive implications (grinding, fractures, pops, etc.) that can be analyzed and potentially processed by using the waveforms from a variety of the sensors to determine the location of the source.
Traditional accelerometers are made from piezoelectric materials by fixing the piezoelectric to the body of the sensor and attaching a reaction mass to the other surface. As the sensor is accelerated, the reaction mass produces a force on the piezoelectric, and charge is generated. These simple accelerometers can act as vibration sensors and be distributed at pre-determined locations to allow for the localization of the noise source via timing the acoustic signal in the structure.
In addition, the system could be used to determine the ground integrity and hardness as well as ambient winds. This system could be used to create another dimension in planetary exploration. Current rover systems have a plethora of cameras and imagers. Of the five senses that a human uses to explore, sound can be used to determine a variety of information on a faraway planet and assist in diagnosis of potential problems in a reliable manner.
This work was done by Stewart Sherrit, Xiaoqi Bao, Yoseph Bar-Cohen, and Phillip E. Walkemeyer of Caltech for NASA’s Jet Propulsion Laboratory. NPO-49405