In 2020, NASA plans to go to the moon to explore its varied surfaces. It needed to develop a vehicle that was capable of traveling over the extremely rough terrain of the moon, as well as be able to climb 40-degree slopes. This required wheel assemblies that could perform "crab-like" crawling maneuvers. Thus, the "Lunar Rover" was designed featuring six wheel assemblies containing two tires each. The wheel assemblies can work and move independently from one another. Additionally, each tire can be raised, lowered or moved side to side. The wheel assemblies can even "kneel" so astronauts may closely observe the moon's surfaces without leaving the Rover.
"During the development phase of the project, NASA is using five absolute encoders from SICK¦STEGMANN Inc. on each wheel assembly to provide precise feedback of how the Rover's drive and control systems are working," says Jon Whittelsey, application engineer for SICK¦STEGMANN. "Specifically, they are being used to help determine how the wheel and drive assemblies react to path planning, as well as managing obstacles that may be on its path when the Rover is traveling over the moon's surface."
Absolute encoder feedback provides a unique shaft position. The root of this positional information is the code disc, which has 12 to 15 bits (4,096 to 32,768 positions) of resolution within a single turn. The multi-turn units have several miniature gear stages which provide 12-bits of turn information, which equals 4,096 turns of feedback capability. This is useful to the drive system, as it provides information to determine the heading, the rate of travel and the position of the suspension arms relative to the chassis. Another key feature of these absolute encoders is that if power is removed from the absolute encoder and restored at a later time, the true absolute position is immediately available without a homing sequence or use of memory from an external device. This improves the reliability, start-up time and confidence of the position information received from the encoders compared to the incremental variety of encoders.
Five phases for the NASA Lunar Rover project are planned. Each phase of this program will mature the technologies related to drive systems, motion control, sensing and power systems. The end result will be an electric vehicle with a long drive time that can effectively traverse and study the moon. The development of this technology will benefit other U.S. industries ... according to information on NASA's website, "For each advancement NASA makes in the Lunar Electric Rover's capabilities, the world will be one step (and 12 wheels) closer to returning to the moon and one step closer to having highly reliable and efficient electric vehicles on Earth."