A Field-Reconfigurable Manipulator for Rovers
- Created: Friday, 01 August 2014
Applications include bomb disposal, disaster recovery, search and rescue, and law enforcement.
Lyndon B. Johnson Space Center, Houston, Texas, and Ames Research Center, Moffett Field, California
Robotic technologies will be deeply involved in any future human mission to the Moon. Prior to human arrival, robots will survey and explore the lunar surface, establish infrastructure, and assemble and test habitat modules. Once humans have arrived, the robots must be able to assist human exploration activities. After the humans depart, robots will perform cleanup, maintenance, and documentation tasks. All these various robotic activities will require sensing and manipulation of the environment, but in quite different ways: a survey robot has very different requirements from a habitat assembly robot. It would be inefficient to launch a different robot for each task, yet a single robot capable of performing all of them would be ungainly and impractical. Instead, what is needed is a “kit” of robot parts that can be assembled into the desired robot for each task.
A prototype Reconfigurable Modular Manipulator (RMM) was developed to fill this need, designed to be mounted on terrestrial testbed rovers for exploring planetary surface activities. The RMM comprises seven low-power joints, each containing a motor, failsafe brake, absolute position encoder, gearing, all control and power electronics, data passthrough, and a novel magnetic brake release.
All manipulator components share a common connector, called a Universal Mating Adapter (UMA), which provides a strong mechanical coupling, data line for commanding joints, power connections, and an independent data line for communicating with a COTS end effector or sensor. Every joint has a UMA Socket at one end and a UMA Plug at the other end. The UMA can be coupled or decoupled by hand with no additional tools, enabling easy reconfiguration of the device with up to seven joints plus an end-effector.
UMA Sockets may be installed in various convenient locations on the exterior of a rover. In the ones that are not physically connected to a joint, a circuit in the Socket disconnects power, eliminating the risk of accidental short-circuits. A protective cap may also be screwed onto the unused Sockets. Because all drive and control electronics are embedded in the joints, the rover need only provide DC power and data connections.
Each end effector is equipped with a UMA Plug. Motors in the end effector may be actuated through the same control architecture as the other joints, or through a dedicated communication line. This allows the RMM to be used with end effectors from third-party vendors. In addition to the more traditional grippers as end effectors, other devices such as drills, camera platforms, or other sensors, can be equipped with UMA Plugs and used either at the end of a manipulator arm or mounted directly to an unused Socket on a rover. Mobility options, such as wheel modules, treads, or legs, can be equipped with UMA Plugs for quick change-out on a vehicle.
An innovative automatic attach/detach (AAD) mechanism in the wrist joint enables the manipulator to detach from one end effector and attach to another without a human present. If a payload is equipped with a UMA Plug, the RMM can use the AAD to form a rigid mechanical connection with the payload and move it into position while also providing power and data. After the payload is positioned, the AAD can release it.
Apart from the RMM system, a second innovation is a software control system that coordinates the motion of the manipulator with that of the vehicle to which it is mounted. This software effectively extends the robot’s dexterous workspace, provides a more unified, intuitive interface for the operator, and enables the robot to move the end effector gracefully along trajectories that are much longer than the workspace of the manipulator by itself.
This work was done by Robert Burridge of TRACLabs, Inc. for Johnson Space Center and Ames Research Center. MSC-24463-1/5122-1