GPS World, August 2013

COVER STORY Autonomous Navigation A HUMAN OPERATOR is easily accomodated within the drop in actuator kit The positioning requirement derives from the testers need not only for accurate location data of each vehicle but for precise knowledge of how far apart they are while performing realtime control to orchestrate repeatable scenarios intersecting vehicle and robot paths to determine whether the vehicle acts to prevent a collision Safety Systems There is a driver in the test vehicle and there are personnel present at the test site who could be injured by a test vehicle or target robot platform In addition to wireless e stop remotes the test vehicle and target robot systems can be disabled and stopped by a number of events In the target robot an e stop causes the battery pack to be completely disconnected from all vehicle systems and a springload is released applying mechanical braking to stop the vehicle Under normal conditions the spring is held back with a pneumatic system and air is dumped upon e stop event A target robot e stop is triggered by remote e stop controller a command issued by control software loss of communication with external systems failure of or loss of communication with internal systems loss of power Aside from fail safe remote and onboard e stop systems additional safety measures are employed by means of safety controllers that monitor safetycritical regions of software implement a wide range of robot safety checking rules and ensure that the robot is operating within safe parameters of the environment such as by staying within an invisible fence and pre defined operation boundary Common MAX UGV Robot Logic A common instrumentation and control system CICS for both the target robot platforms and test vehicle instrumentation and robotic assist platforms is illustrated in FIGURE 2 Embedded Controller The heart and soul of the vehicle hosts and runs the algorithms receives sensor data and executes actuation commands to the motor controllers based on desired route plans and dynamic sensor information This controller runs the MAX software platform MAX UGV framework and various MAX drivers I O Controller Handles inputs from sensors for temperatures voltages and currents as well as monitoring limit switches and actuating relays Certain controls are planned such as mock brake lights on target robots and warning lights in test vehicles Locata A constellation of nine LocataLite units on towers covers the existing track for Phase I of the project Phase 2 will require additional units to add coverage to the covered track some towers will provide coverage to both tracks Each target robot vehicle and each drop in kit for the test vehicles carries a Locata rover Locatas new software essentially adds some capability from its indoor software to its outdoor software to deal with reflections multipath issues caused by the metal buildings at the test site The new software also allows the rover to perform real time calculations on board required for the less than 10 cm accuracy Previously this had to be done on a separate system and data had to be transferred back and forth which worked against meeting real time position update requirements for controlling speed position and relative position of robots and test vehicles In test vehicles and target robots the Locata rover position updates are merged with the output of Locata Antenna E stop Antenna Wireless Estop Interface Locata Rover Wireless Antenna Wireless Communications Adapter AHRS Safety Controller Embedded Controller I O Controller I O Sensing Control Electronics Hi Power Electronics and Motors FIGURE 2 Target robot logic flow an attitude heading and reference system AHRS AHRS The CICS in the robots and test vehicles includes an AHRS that provides the required heading position and velocity updates Accuracy requirements are heading 1 degree position less than 10 centimeters velocity 1 mph Our required position update rate is 10 Hz We expect to achieve 100 Hz in our system which improves self nav capability and overall performance This rate also applies to other measured logged data A Kalman filter computes data from sources within the AHRS and from external sources GPS and Locata Wireless Adapter Antenna On our critical channel we exchange messages between vehicles to effect proper trajectory and relative positioning Our e stop controllers and safety systems also use this network The non critical channel is used for test setup and supervisory control decimated data transmission for HMI monitoring and logged data transmission Wireless E stop Interface This interface is for remote shutdown of a vehicle The e stop triggers are similar for the test vehicle systems but the driver can also disable the robotic system Rather than brake the test vehicle an e stop of the test vehicle systems disables the steering brake and throttle actuators into limp mode and releases control of the test vehicle to the driver Safety Controller A separate watchdog See ROBOT page 44 GPS World August 2013 www gpsworld com 32