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Circle Sector Expansions for On-Line Exploration

A novel and effective method denoted circle sector expansion (CSE) is presented that can be used to generate reduced Voronoi diagrams. It is intuitive and can be used to efficiently compute possible paths for a vehicle. The idea is to model free space instead of the features in the environment. It is easy to implement and can be used while a vehicle moves and collects new data of its surrounding. The method is directly applicable and has properties for fast computations of safety margins while at the same time having low complexity. We have successfully implemented the algorithm and its methods and performed real-life tests using an autonomous wheelchair equipped with a range scanning laser, a rate gyro, and wheel-encoders. Tests showed good results for supporting the use of CSE. The results are applicable for example to improve assistive technology for wheelchair users.

A MATLAB/Java Interface to the MICA Wheelchair

Abstract In the MICA (Mobile Internet Connected Assistant) project a high tech wheelchair has been controlled remotely with MATLAB/Java software client-server implementations. Sensor servers that read, time stamp and store sensor device measurements to databases, runs concurrently on an embedded PC running Linux. The network clients used to read sensor values from the servers are written in Java. That gives them portability between different platforms and architectures. MATLAB client programs runs on stationary computers. These are used to process andvisualize collected data from the wheelchair. MATLAB programs are also used to control and make the wheelchair run semi-autonomously. The combination of MATLAB/Java software is good for fast development, implementation and testing of algorithms in both education and research. With the client/server approach it is possible to have one computer to run a complex and power consuming control algorithm and another one to handle the GUI. Both computers execute MATLAB programs and they run concurrently and have mutual exchange of data over the Internet. When a program works properly in MATLAB it can be ported to Java for faster execution speed and portability.

Remote CAN operations in MATLAB over the Internet

This paper describes the implementation of a CAN server that acts as a CAN tool to a client. It can be used to monitor, observe and send messages to a distant CAN network over IEEE802.11b (Wave-LAN). The CAN server is controlled by one or several clients that can connect to it by TCP/IP. It is possible to send and receive CAN messages over Internet from a MATLAB environment since the client software is written in Java. The CAN server collects CAN messages and stores them into a ring buffer. The messages in the ring buffer are classified by their identifier and stored into a database. The CAN tool has been used in a demonstrative application example that consist of a remotely controlled wheelchair. In the example the wheelchair was programmed to run in a square. The positions obtained by odometric CAN messages are compared with the position from the navigation system onboard the wheelchair.

CSE+: Path planning amid circles

This paper presents a method for obstacle avoidance and path-finding amid circular objects.

On passing a doorway with an autonomous Internet connected wheelchair using MATLAB

If a wheelchair for disabled is used for semi-autonomous navigation indoors it must be able to navigate through doors. A door and doorway can be parameterized with five parameters. A divide and conquer implementation of the Hough transform is used to segment outlines from range scans. The client software remote controls the wheelchair from the MATLAB environment. The software consists of several Java threads that run concurrently. Sensor data are polled by threads and put into databases to reduce the network lag. The databases are used by a controller and a Kalman filter. Since most of the implementation is coded in Java it is possible to run it as a stand alone program on a computer that has Java installed. From 10 runs the trajectory offset was calculated to 0.9 cm with a standard deviation of 1.4 cm. The standard deviation of the heading was 2.2 degrees. This performance is essentially independent of the initial starting pose.

Winter tests of a quad-bike rollover prevention system

We made a quad-bike teleoperated to be able to test a developed rollover prevention system. The vehicle was equipped with onboard computers, power steering, throttle control, emergency power cutoff, an IMU module, pneumatic actuators, and retractable outriggers. The onboard computer system tracks the vehicle orientation and velocity in real time. When the vehicle is predicted to overturn the system activates functions to prevent a rollover. The functions are: — activation of retractable outriggers — decrease the throttle for motor brake — activation of rear wheel brakes. The system has no active steering. The system was field tested in winter conditions in mars 2010, and was able to prevent rollover situations sideways and backwards.

On filtering of laser range data in snowfall

This paper is towards reducing the clutter from snowflakes for outdoor robots. There are three basic cases: 1. normal operation of the laser with objects within range for detection. 2. close range with objects close to the laser i.e. shorter than the pulse length. 3. Free space as background i.e. all detects are false. The findings are summarized as: The two lasers used were a pulsed wide beam laser and a modulated narrow beam laser. The narrow beam laser has much better penetration between the snowflakes. We did not use snow and rain threshold setting for the wide beam laser. Median filtering shows a substantial reduction in snowflake detects. The gamma distribution describes fairly well the distribution of detected snowflakes.

Signature Graphs for Effective Localization

We present a novel method for the localization of an autonomous vehicle in two dimensions. Instead of focussing on properties of obstacles, we emphasize the description of free-space. We introduce the concept of signature graphs which is a compact data structure describing available free-space of an environment. It therefore also represents a map of the environment. A signature is an edge in the graph and is defined by seven parameters. An edge indicates that it is possible for the vehicle to move between two graph nodes. The signature graph is flexible and can easily be updated as new information about the environment is collected. We have with an autonomous wheelchair implemented our methods and tests them with successful results

Using Modern Software and the ICE Approach When Teaching University Students Modelling in Robotics

This paper presents a robotic course that was revised with the ICE (Ideas-, Connections-, Extensions levels) approach of teaching in mind. It includes practical labs where the students have to deri ...

Field tests of a roll-over prevention system for quad-bikes

A quad-bike has relative short wheelbase, high ground clearance, large wheels, a powerful engine, and can become lethal if it is used inappropriately. Each year many drivers are killed or seriously injured in different types of rollover accidents, where the driver may face choking, internal bleeding, and crushing. We have thus developed and tested an active system to prevent rollover accidents. It is based on inertial sensors, pneumatic actuators, and mechanical retractable legs. The system tracks the vehicle orientation and velocity in real time. If the vehicle is predicted to overturn the system activates functions to prevent a rollover. The system was field tested in snowy conditions, in a sand pit, and in a steep slope. The system was able to prevent rollover accidents both sideways and backwards.