A system for indoor navigation of a mobile robot includes (1) modulated infrared beacons at known positions on the walls and ceiling of a room and (2) a cameralike sensor, comprising a wide angle lens with a position-sensitive photodetector at the focal plane, mounted in a known position and orientation on the robot. The system also includes a computer running special-purpose software that processes the sensor readings to obtain the position and orientation of the robot in all six degrees of freedom in a coordinate system embedded in the room.
For a given beacon imaged on the focal plane, the output of the sensor comprises two parameters that depend in a known way on the characteristics of the lens and the direction to the beacon in a coordinate system attached to the sensor and robot. If at least three beacons are within the field of view of the sensor, then the sensor outputs from observations of all three beacons can be combined to obtain six parameters indicative of the directions to all three beacons. These directions, in combination with the known positions of the beacons, uniquely determine the position and orientation of the robot in the room. Equivalently, the six parameters constitute, in principle, sufficient data to locate the robot in all six degrees of freedom by solving the equations that express the applicable geometric relationships summarized above.
The nature of a position-sensitive photodetector is such that it is not possible to measure the centroids of two beacon images simultaneously. Therefore, it is necessary to provide for illumination of the beacons in rapid succession and to provide means for the image-data-processing software to recognize which beacon is under observation at a given instant. To satisfy this need, the beacons are turned on and off in a sequence that coincides with a predetermined code. The sensor subsystem accumulates beacon readings and their times until it begins to recognize the code sequence. Thereafter, the computer processes the readings from the recognized beacons within the field of view of the sensor.
The equations for the geometric relationships are nonlinear. The software includes a module that solves these equations by means of an iterative optimization procedure, in which it strives to find a position and orientation that, when inserted in the equations, minimizes a measure of the difference between the actual sensor readings and the sensor readings predicted by the equations.
Another software module provides an initial guess of position and orientation to start the optimization procedure. Knowing which beacons are in view, this module applies to the equations for a number of postulated robot poses and determines which pose, when inserted in the equations yields the closest match to the sensor readings. The closest match becomes the initial guess for the optimization procedure.
This work was done by Joel Shields and Muthu Jeganathan of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-40730
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Indoor navigation using direction sensor and beacons
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Overview
The document is a technical support package from NASA, specifically focusing on indoor navigation using direction sensors and beacons. It is part of the NASA Tech Briefs and aims to disseminate results from aerospace-related developments that have potential applications beyond their original context.
The primary subject of the document is the Formation Control Testbed (FCT), a ground-based robotic testbed designed to simulate the dynamic interactions of spacecraft formations in a six-degree-of-freedom (6-DOF) environment. This testbed utilizes linear and spherical air bearings to replicate a zero-gravity space environment, allowing for the testing of autonomous robotic systems equipped with advanced avionics. Each robot in the testbed is fully autonomous and includes a suite of onboard navigation sensors, an inertial measurement unit (IMU) with three-axis gyros and accelerometers, wireless communication capabilities, cold-gas thrusters, reaction wheels, and an integrated power unit.
A key feature of the FCT is its use of infrared (IR) beacons, which are mounted on the walls and ceiling to create an artificial star field for inertial attitude sensing. The document discusses the design and requirements for these beacons, emphasizing the importance of synchronization and signal integrity. The beacon system is designed to ensure that the signals from the detectors are sampled simultaneously to avoid errors caused by temporal variations, which could arise from robot motion or thermal transients.
The document also outlines the technical specifications for the beacon system, including the need for a minimum signal level for synchronization recognition and the importance of maintaining signal quality to prevent saturation of the analog-to-digital (A2D) inputs. It highlights the necessity of averaging multiple samples to improve the reliability of the measurements and discusses the implications of current levels on the efficiency of the IR beacons.
In summary, this technical support package provides a comprehensive overview of the FCT's design, focusing on the integration of direction sensors and beacons for indoor navigation. It serves as a resource for understanding the technological advancements in autonomous navigation systems and their potential applications in various fields. The document also includes contact information for further inquiries and access to additional resources from NASA's Scientific and Technical Information Program Office.
