Proposed packages called "remote engineering units" (REUs) would contain all the electronic circuitry needed to implement a subset of the design of the motor-control system of a robot. The REUs were conceived, specifically, for incorporation into small robotic vehicles (the Mars '03/05 Athena Rovers) to be used in exploring the surface of Mars. Some of the characteristics that make REUs attractive in the Mars Rover applications may also make them attractive for terrestrial robotic applications. These characteristics include modularity, amenability to a distributed motor-control architecture, and adaptability of both design and function.
The REUs would provide interfaces among (1) a control computer; (2) regulated and unregulated external power supplies; and (3) motors and analog and digital input/output (I/O) circuits. More specifically, each REU (see figure) would contain circuits for controlling two dc motors equipped with optical shaft-angle encoders; for receiving and processing the analog and digital outputs of motor-current sensors, temperature sensors, force sensors, potentiometers, and other sensors; and for controlling two dc power switches. Each REU would also contain an internal power regulator, plus two heaters to enable operation at low ambient temperature.
Within each REU, circuits connected to regulated sources of power would be electrically isolated from sources connected to unregulated sources of power by means of optocouplers, capacitors, inductors, and/or differential interfaces with sufficient common-mode rejection to prevent adverse effects of ground loops. There would be separate digital and power grounds, which would be brought together at a system-level single ground point. Except for the connection at the system level, electronic circuits connected to digital ground would be electrically isolated from those connected to power ground.
Each REU would contain a field-programmable gate array (FPGA) for processing digital command, data, and clock input and output signals. The REU would communicate with the control computer via a bidirectional interrupt-request serial data bus. The REU would function as a slave interface; that is, the control logic of the REU would support only the slave receiving and slave transmitting modes of bus operation.
An REU would be capable of operating according to any of three motor-control modes. In one, pulse-width modulation would be used to control the speeds of the two motors. The other two modes would involve closed-loop proportional/integral/derivative control implemented in hardware; the closed-loop controller would be capable of functioning in both rate- and position-control modes, using shaft-angle feedback from either optical or potentiometric shaft-angle encoders.
This work was done by Sung Park, Ken Mehaffey, Dave Hykes, John Waters, Gary Bolotin, Michelle Bell, and Edward Kopf of Caltech for NASA's Jet Propulsion Laboratory.