The rapid evolution of sensors, processors, and software is making unmanned ground vehicles (UGVs) viable in applications as diverse as mining and battlefields.
Military vehicles developed by Lockheed Martin and John Deere and mining vehicles made by Caterpillar have vastly different usage patterns, but they share many commonalities in electronic controls and sensors. Those controls combine a complex array of distributed microcontrollers that manage brakes, acceleration, and steering based on the input from a number of sensors that constantly build an image of the terrain along the vehicle’s route.
Among the many technologies needed to move vehicles autonomously or via remote control, the ability to process complex algorithms quickly is perhaps the most important. Design engineers are leveraging the advances of microprocessors and memory chips to handle the many control functions that occur every second.
“In this area of robotics, we’re really benefiting from Moore’s Law, which gives us the computing power to do things we couldn’t do before,” said Stuart Moorehead, Manager of Field Robotics for John Deere Moline Technology Innovation Center. “We also have enough memory to store maps and large amounts of data.”
Growth in memory sizes makes it possible to hold relevant map files, GPS data, and instructions, among other elements. The rapid capacity increases of flash memory also make it more cost-effective for engineers to house the complex programs that tell the vehicle when to slow down, speed up, and turn. This software is among the most important technology for autonomous transportation.
“Software is the big problem; this is where we solve the challenges,” Moorehead said. “The algorithms are very complex and very proprietary.”
These algorithms have to be handled at very high speeds to ensure that the vehicle makes good decisions as it travels through previously unseen terrain. At the same time, there is a strong need for error checking to ensure that a minor fault won’t cause problems that can quickly cascade into serious problems.
The continuing advances of multicore processors are helping on both counts. These processors provide high clock rates while they work in lockstep to ensure accuracy.
“Caterpillar uses several dual-core controllers for the autonomous system. These multiple controllers can be used to check that each controller is operating correctly,” said Craig Koehrsen, Autonomous Technical Steward for Caterpillar.
The modules in autonomous vehicles must communicate with each other continuously. The central controller is constantly receiving input from a broad range of sensor modules, and it must send commands to controllers as diverse as steering actuators and engine or brake control modules.
These multilayered computing structures are made of smaller controllers scattered throughout the vehicle. There are also higher-level computing modules that process data from sensors like cameras and radar.
“We’ve got a distributed architecture, with one module for perception, reading in data from sensors,” Moorehead said. “There’s also a module that keeps track of localization solutions, which include navigation and sensor input like GPS and odometry. That works with an inertial measurement unit.”
All these control modules rely on a host of sensors that provide information about the real world. Radar and lidar often augment IR and visible light cameras. GPS sensors work in conjunction with inertial sensors that provide odometry information that helps when GPS signals are lost.
At one time, these sensors used proprietary technologies. Some had specially designed sensing modules; others used extensive packaging to meet the harsh demands of vehicles moving through dusty or rainy areas with wide temperature ranges. But in the past few years, high-reliability sensors have been used by carmakers, making commercial off-the-shelf products readily available.
“Sensors are getting more ruggedized; the volumes of automotive have driven prices down,” Moorehead said. “We’re really gaining by utilizing technologies that have become popular in autos such as radar, ultrasonic, and cameras.”
UGV developers have also been aided by rapid advances driven by other fields such as unmanned aircraft. As drones have become one of the U.S. military’s most useful weapons, engineers have developed a number of different sensor technologies that give users more depth perception and different perspectives than simple photographs.
“One of the driving factors is the improvement of lidar, which we’re using as a primary means of obstruction detection and avoidance,” said Myron Mills, Program Manager for Lockheed Martin Missiles and Fire Control. “A number of companies make devices that are smaller and more ruggedized. These new devices also perform better.”