Tecnico

Document Type: Tutorial NI Supported: Yes Publish Date: Mar 29, 2012

A Layered Approach to Designing Robot Software
Table of Contents 1. 2. 3. 4. Driver Layer Platform Layer Algorithm Layer User Interface Layer

Robot software architectures are typically a hierarchical set of control loops, representing high-level mission planning on high-end computing platforms, all the way down tomotion-control loops closed with field-programmable gate arrays (FPGAs). In between, there are other loops controlling path planning, robot trajectory, obstacle avoidance, and many other responsibilities. These control loops may run at different rates on different computing nodes, including desktop and real-time OSs, and custom processors with no OS. At some point, the pieces of the system must cometogether. Often, this is accomplished by predetermining very simple interfaces between the software and the platform—perhaps as simple as just controlling and monitoring direction and speed. Sharing sensor data across different layers of the software stack is a good idea, but comes with considerable integration pain. Each engineer or scientist involved in designing a robot brings a different view ofthe world, and an architecture that works well for the computer scientist may not work well for the mechanical engineer, for example. The proposed software architecture for mobile robotics, shown in Figure 1, takes the form of a three- to four-layer system represented by the following graphic. Each layer in the software depends only on the specific system, hardware platform, or end goal of therobot and remains completely blind to the contents of the layer above or below it. A typical robot’s software contains components in the driver, platform, and the algorithm layers; however, only applications with some form of user interaction include the user interface layer (fully autonomous implementations might not need this layer).

Figure 1. Robotics Reference Architecture In this specificexample, the architecture represents an autonomous mobile robot with a manipulator that is designed to execute tasks including path planning, obstacle avoidance, and mapping. This type of robot might be used in several real-world applications, including agriculture, logistics, or search and rescue. The onboard sensors include encoders, an inertial measurement unit (IMU), a camera, and several sonarand infrared (IR) sensors. Sensor fusion is used to combine the data from the encoders and IMU for localization and to define a map of the robot environment. The camera is used to identify objects for the onboard manipulator to pick up, and the position of the manipulator is controlled by kinematic algorithms executing on the platform layer. The sonar and IR sensors are used for obstacle avoidance.Finally, a steering algorithm is used to control the mobility of the robot, which might be on wheels or treads. The NASA robots shown in Figure 2 illustrate a mobile robot architecture.

Figure 2. Mobile Robots Designed by SuperDroid Robots Developers can implement these mobile robot platform layers using NI LabVIEW system design software. LabVIEW is used to design sophisticated roboticapplications—from robotic arms to autonomous vehicles. The software increases the productivity of engineers and scientists by abstracting I/O and integrating with a wide variety of hardware platforms. A commonly used hardware platform for robotics is NI CompactRIO, which includes an integrated real-time processor and FPGA technology. The LabVIEW platform includes built-in functionality for communicatingdata between each layer, and for sending data across a network and displaying it on a host PC. Driver Layer As the name suggests, the driver layer handles the low-level driver functions required to operate the robot. The components in this layer depend on the sensors and actuators used in the system as well as the hardware that the driver software runs on. In general, blocks in this level take...