Using Xsens MTi and MTi-G in autonomous and remotely operated vehicles

Transcription

1 Using Xsens MTi and MTi-G in autonomous and remotely operated vehicles Document MT0314P, Revision A, 01 Mar 2012 Xsens Technologies B.V. phone fax internet

2 Revisions Revision Date By Changes A March MHA First version 2012, Xsens Technologies B.V. All rights reserved. Information in this document is subject to change without notice. Xsens is a registered trademark of Xsens Technologies B.V. MTi, MTx and MTi-G are trademarks of Xsens Technologies B.V. Xsens [ii] Using Xsens MTi and MTi-G in autonomous and remotely operated vehicles

3 Table of Contents 1 XSENS MOTION TRACKERS XSENS MTI AND MTI-OEM XSENS MTI-G USE OF MEMS IN NAVIGATION AND CONTROL & STABILIZATION OF (UN)MANNED VEHICLES MTI SPECIFICATIONS INTERFACING CONTROL SYSTEMS DiOS EXAMPLE APPLICATIONS GROUND VEHICLES AERIAL VEHICLES SENSE AND AVOID... 8 Xsens [iii] Using Xsens MTi and MTi-G in autonomous and remotely operated vehicles

4 1 Xsens Motion Trackers Xsens is the industry standard in accurate MEMS Attitude and Heading Reference Systems (AHRS s), Inertial Measurement Units (IMU s) and GPS/INS s. Xsens has two brands offering these capabilities: the MTi AHRS and the MTi-G GPS/INS. The MTi is also available as OEM board. 1.1 Xsens MTi and MTi-OEM The MTi is a miniature size and low weight 3DOF Attitude and Heading Reference System (AHRS).The MTi contains accelerometers, gyroscopes and magnetometers in 3D, and as such is an Inertial Measurement Unit (IMU) as well. Its internal low-power signal processor provides real-time and drift-free 3D orientation as well as calibrated 3D acceleration, 3D rate of turn and 3D earthmagnetic field data. The MTi is an excellent measurement unit for stabilization and control of cameras, robots, vehicles and other (un)manned equipment. The orientation accuracy of the MTi is 0.5 deg static and 2.0 deg RMS under dynamic conditions. With a size of 58x58x22 mm, it fits in almost any application. 1.2 Xsens MTi-G The MTi-G is a miniature size and low weight 6DOF Attitude and Heading Reference System (AHRS). The MTi-G contains accelerometers, gyroscopes, magnetometers in 3D, an integrated GPS receiver, a static pressure sensor and temperature sensor. Next to the data that the MTi delivers, it outputs 3D orientation that is compensated against long-term accelerations typical in high-dynamics applications as well as 3D position and 3D velocity data. The position and velocity is stabilized by the inertial sensors, so it can bridge GPS outages, increase heading and position accuracy and reject GPS outliers. The orientation accuracy of the MTi-G is 0.5 deg static and 1.0 deg RMS under dynamic conditions. The position accuracy is 2.5 meter CEP covering for GPS outages up to 10 sec. Xsens [4] Using Xsens MTi and MTi-G in autonomous and remotely operated vehicles

5 2 Use of MEMS in navigation and control & stabilization of (un)manned vehicles Inertial sensors, IMU's and AHRS's are excellent sensors for use in systems controlling unmanned vehicles. They can be combined with GPS, odometers (wheel speed sensors) and even vision. Tests and competitions that have shown this proof of principle are abundant at technical and agricultural universities all over the world. Also browse through the section Applications at the Xsens website for more information. In the past years commercial companies also started working on autonomous systems and these companies have progressed steadily. Xsens can accurately measure the state of vehicles. Once this data is in the CPU of the autonomous vehicle, the data needs to be interpreted and together with the input from the user or the mission details, the control system needs to act accordingly. In order to accurately measure the state of a vehicle, Xsens spends much effort and time in making the MTi and MTi-G fit for the purpose of doing so. This yields the following specifications that are 2.1 MTi and MTi-G specifications Using MEMS sensors in unmanned vehicles is not always straightforward. MEMS IMU s and AHRS s are cost-effective technologies, but the cost reduction has a downside when not properly engineered. Xsens MTi s and MTi-G s offer three technologically advanced features making sure that the most performance is gained from the MEMS sensors. Latency: in order to be able to control a vehicle directly based on the orientation and position sensors, the latency between the physical event and the output to the user has to be as low as possible. The well-engineered signal processing pipeline and a powerful processor with compact sensor fusion algorithms make the latency of Xsens Motion Trackers the lowest in the industry. The latency of the MTi is <2.5 ms, the latency of the MTi-G is <5 ms Vibrations: All unmanned vehicles have engines on it and often the structure of an unmanned vehicle is kept as light as possible to accommodate for a higher payload. This makes vibrations on unmanned vehicles extremely violent. The MTi and MTi-G feature antialiasing filters and robust signal processing so that vibrations are attenuated as much as possible. Magnetic distortions: The MTi and MTi-G both have a 3D magnetometer onboard. This magnetometer is very helpful for a good heading reference in a homogenous magnetic field. Often however, the magnetic field is disturbed by the vehicle itself, which means that compensating or calibrating for these disturbances is needed. The MTi and MTi-G offer a Magnetic Field Mapping algorithm, which can bring the heading accuracy back to better than 1 deg. Next to the Magnetic Field Mapper, the sensor fusion algorithm of the MTi and MTi-G are tuned to compensate for temporal magnetic distortions, such as passing vehicles. Xsens [5] Using Xsens MTi and MTi-G in autonomous and remotely operated vehicles

6 2.2 Interfacing The MTi and MTi-G have an open source industry standard communication protocol and API. The extensive software development kit (SDK) includes an intuitive GUI, examples for Windows and Linux, as well as source code for various communication levels that can be used in e.g. embedded systems. Because of the onboard processing capabilities of the MTi and MTi-G, it is often not needed to write extensive code on a host PC or laptop. CMT-1: hardware interface The hardware interface allows for direct low level (binary) communication with the MTi. CMT-2: Message interface The message interface is an implementation of the hardware interface that turns the bit stream of CMT-1 to messages CMT-3: Device interface This CMT level allows for logging data and extended functionality and ease of use in addressing the devices. CMT-4: Application interface CMT-4 can read in raw data from the sensors and reprocess it into orientation and position. This level needs Windows to operate. Xsens [6] Using Xsens MTi and MTi-G in autonomous and remotely operated vehicles

7 2.3 Control systems Manufacturers of autonomous vehicles know their vehicle well, but they often rely on other companies to interpret the AHRS data and convert the required trajectory and/or behavior of the vehicle into actuator commands. This work is often done by external consultancy, either in collaboration with a University or with commercial (robotic) companies. The latest development in this field however is that software packages can be purchased from dedicated companies who have a lot of experience in this field. These software packages can then be configured according to the user s wishes and easily distributed in the onboard CPU of the vehicles. One example of such a robot operating system, that is tuned for Xsens' MTi's and MTi-G's is DiOS (Distributed Operating System) from AeroSpy, based in Linz, Austria DiOS DiOS (Distributed Operating System) is a system with OS like functionality for complex distributed systems. DiOS is a tool which allows a rapid integration of different sensors into existing or new developed autonomous systems. Such systems are typically highly complex having different computers onboard. Base module and interface libraries The base module contains the DiOS control center which enables the control of distributed system. An installation routine installs all necessary components on the predefined network setup. A distribution routine copies the code to computers. Interface libraries are available and can easily be tuned. DiOS Control Center Time Synchronization and data collection During the integration process data collection of all sensor information and states plays a critical role in order to verify the functionality and integrity of the whole system. This requires an independent tool which guarantees the time synchronization of all sub-systems so that the data are available with only one timestamp. DiOS provides this a system independent synchronization and distributed data collection in order to avoid overflow of the network. Software development, filter library and model library DiOS allows for integration based on pre-compiled libraries or via simulation tools, such as Matlab. A filter library including various filters (linear Kalman filter, EKF, UKF, PF and RBPF) is available to diminish development time. For different systems, there are different dynamic models available in a model library. Examples are point mass models, attitude models (decoupled or coupled, 2D or 3D), Dubins vehicle etc. Xsens [7] Using Xsens MTi and MTi-G in autonomous and remotely operated vehicles

8 3 Example applications There are many system integrators in the unmanned systems application area that use Xsens MTi's and MTi-G's already. One could think of e.g. unmanned agricultural vehicles. The MTi-G can aid the navigation next to trees that stand close to the field. It can also compensate for the position error caused by slopes in a field (position of the antenna then differs from the position of the vehicle). Another use of the MTi-G in agriculture is to be able to measure fast heading changes that cannot be measured with GPS, for example at the end of the field. 3.1 Ground vehicles The predictive behaviour of the MTi-G and the easy-to-use framework of DiOS, make the combination of the MTi-G and DiOS ideal for all kind of robots. Especially the DiOS feature that code can be copied from one main programming environment to embedded environments makes it very suitable for swarm robotics. The MTi-G provides 3D orientation that can be used to stabilize for example the on board camera. Also, combining the odometers with the orientation sensors and GPS, the MTi-G and the DiOS are excellent for navigation. 3.2 Aerial vehicles The MTi-G and DiOS are not only used for ground robotics, but serve as an excellent system for unmanned aerial vehicles. AeroSpy has extensive experience in this area, with amongst other solutions the Sense and Avoid system. The MTi and MTi-G both have a temperature rating of -40 to 85 deg C, so they can be used at high altitudes and in extreme climates. Many MTi-G s are already used in unmanned aerial vehicles for reconnaissance, inspection, aerial photography and target practice. 3.3 Sense and avoid Sense and Avoid is the enabling technology for the integration of UAVs into civil airspace. Besides that Sense and Avoid can be used as a pilot assistant and a tracking enhancement system for manned aviation. It uses a 360 deg panoramic camera setup to sense and avoid other objects in the surrounding airspace. The system can keep track of these actions and recommend actions to the operator or pilot. Xsens [8] Using Xsens MTi and MTi-G in autonomous and remotely operated vehicles

9 About Xsens Xsens is a leading developer and global supplier of 3D motion tracking products based upon miniature (MEMS) inertial sensor technology. Since its foundation in 2000, thousands of motion sensors and motion capture solutions have successfully been deployed for 3D character animation, movement science, control of autonomous vehicles and stabilization. Clients of Xsens include Electronic Arts, NBC Universal, INAIL Prosthesis Centre, Daimler, Saab, Kongsberg Defence Systems and many other companies and institutes throughout the world. Xsens is working with several industry partners, including Autodesk, Sagem (Safran Group) and Siemens. Xsens research department has created unique intellectual property in the field of multi-sensor data fusion algorithms, combining inertial sensors with GPS and RF positioning and biomechanical modelling. Xsens and its products have received several awards and five consecutive entries in Deloitte s ranking of fastest growing technology companies in Europe. Xsens is a privately held company with its headquarters in Enschede, the Netherlands and a US subsidiary in Los Angeles, California. -- About AeroSpy AeroSpy is one of the leading technology suppliers in the field of navigation, motion tracking, and mobile robotics in the air, on the ground, and in the water. Since its foundation in 2006 we have integrated several navigation and motion tracking systems for various customers. The fast integration of our technology, based on DiOS into customer products creates an essential technological advantage due to our experience of integrating our technology and our high technological know-how. To maintain a high level of technology we have filed several patents in the field of autonomous navigation and sensor fusion. Our daily business is based on high technology, know-how and the flexibility to adapt our products to each customer s specifications. AeroSpy is privately owned company located in Linz, Austria. We do not simply provide products; we provide specific navigation solutions that are in line with your needs. Xsens [9] Using Xsens MTi and MTi-G in autonomous and remotely operated vehicles