On a laser anglemeter for mobile robot navigation

A laser anglemeter for use in a navigation system for mobile robots has been developed. The anglemeter measures heading angles to beacons made of vertical stripes of retroreflective tape. The anglemeter uses an- optical system with a rotating mirror. It scans a laser beam which illuminates the beacons and receives pulses of reflected light from them. The pulses are amplified by a low-noise amplifier and then fed to a comparator. When the comparator trips it is assumed that the laser beam has hit a beacon. Then the angle is measured with a counter which is fed with pulses from an incremental encoder fixed on the axis of the mirror. A navigation system using the anglemeter has been developed. The system includes an algorithm that associates measured angles with beacon identities. The algorithm has been patented by the author. The navigation system has been implemented on a test vehicle. The optical and electronic parts of the anglemeter have been thoroughly analysed and simulated. The performance limits of the anglemeter are stated and design criteria for the optical and electronic parts are proposed. Measurements support the simulations and the theoretical analysis. Some results of the analysis of the optical part of the anglemeter are: A Gaussian expression describing the bidirectional reflection distribution function (BRDF) of the beacons is proposed. The shape and power of the received light pulses from the beacons are found to be determined by the (Gaussian) intensity distribution and the divergence of the laser beam, the scan velocity, the width of the beacons and their BRDFs. No signal is received from beacons at close range. At long range the laser beam diameter is much larger than the width of the beacons which causes the range-dependence of the width of the received pulses to disappear. The shape of the pulses is approximately Gaussian in this region due to the intensity distribution of the laser beam. The width of the pulses is determined by the laser beam divergence and the scan velocity. Optical misalignments in the anglemeter cause the dominating systematic error in measured angles. Another important error source is the range dependence of the received signal. Furthermore a non-circular cross-section of the laser beam is a potential source of large systematic errors while random errors due to electronic noise are surprisingly small. Some results of the analysis of the electronic part of the anglemeter axe: A low-noise photodiode-amplifier circuit with the photodiode in the feedback path has been developed. No noise generating resistor is needed to provide a DC-path to ground for signal and bias currents at the amplifier input. It is possible to design the amplifier as a matched filter for square shaped pulses. An implementation of the amplifier was found to have a NEP~ 3 fW/√Hz at frequencies below 10 kHz.Godkänd; 1993; 20061125 (ysko

Lulea Turbo Turtle (LTT)

Godkänd; 1989; 20061125 (ysko

Competition - an efficient method to get students committed

The mechatronics course at Lulea University of Technology is divided into a traditional part with lectures, problem solving, lab exercises, and a project part. During 2002-2003, the project has been to design and build autonomous model race cars. A public race is arranged at the end of the course. The race track is an outdoor track. In year 2002, it was defined by a painted white line on asphalt. In 2003, it was defined by an electrical wire carrying 100 mA of current at 10 kHz frequency. The students had to design and build sensors, amplifiers, filters and interface circuits for the onboard PICI6F876 microcontroller as well as some power electronics to control the drive DC-motor. The race is obviously extremely challenging for the students and as a result, they spend much more time on the course than before.Godkänd; 2004; 20060929 (ysko

Lulea Turbo Turtle (LTT)

Godkänd; 1989; 20061125 (ysko

Single-stage photodiode op-amp solution suited for a self-mixing FMCW system

The current delivered by the photodiode in a self-mixing frequency modulated continuous wave or optical frequency domain reflectometry system consists of a dc-current resulting from the local oscillator, the reflected signal, dark current in the photodiode, and current generated from background light. The current also contains the useful harmonic signal with a beat frequency corresponding to the range and radial velocity of a target. To avoid saturation and clipping due to the dc current generated in the photodiode, it is desirable to minimize the gain at dc while maintaining a high gain in the beat frequency region. We have investigated some different solutions and present a modified current-to-voltage converter using bootstrapping and added voltage gain, which addresses this problem using only one OP-amp and no dc shorting inductors.Validerad; 2003; 20060929 (ysko)</p

Low-noise photodiode-amplifier circuit

A photodiode-amplifier circuit with the photodiode in the feedback path is presented. It is named the PIF-circuit. No resistor is needed at the amplifier input to provide a path to ground for the signal and leakage currents from the photodiode and the amplifier input bias current. Therefore, one potentially dominating noise source is eliminated. At frequencies below 10 kHz, the implemented PIF-circuit has an NEP&ap;3 fW/√HzGodkänd; 1994; 20061125 (ysko

GIMnet on the MICA wheelchair

This paper describes the implementation of GIMnet on the MICA wheelchair.Godkänd; 2010; 20100812 (hf

Advantages of a new modulation scheme in an optical self mixing frequency-modulated continuous-wave system

A new frequency-modulated continuous wave modulation scheme, which gives correct results even when the Doppler shift is larger than the frequency difference associated with the range, is presented and tested with a tunable laser diode and fiber-based system. By inserting a constant frequency region in the modulation scheme, both the magnitude and the sign of all beat frequencies can be determined. When they are known, the correct frequency difference as a result of the range can be calculated. This new scheme gives more freedom when choosing the modulation parameters of the laser, because increasing the modulation frequency, and/or the frequency sweep, to avoid ambiguities resulting from a large Doppler shift no longer becomes necessary. This is especially useful when using a somewhat cheaper laser diode source, since the maximum obtainable modulation frequency and frequency sweep can be somewhat limited. The suggested modulation scheme makes it possible to use some laser diodes in an application they otherwise would not be suited for.Validerad; 2002; 20061005 (ysko)</p

Using a discrete thermal model to obtain a linear frequency ramping in a frequency-modulated continuous-wave system

The lasing wavelength of a single-section distributed feedback (DFB) laser diode can be modulated by modulating the drive current. This makes it possible to utilize the DFB laser diode in a frequency-modulated continuous wave (FMCW) range and velocity measuring system. In FMCW, the frequency of the laser is ramped, and the frequency difference between the reflected wave and a local-oscillator wave is monitored. For maximum performance the frequency ramping should be linear. Due to thermal phenomena, a linear ramping of the current seldom results in a linear ramping of the optical frequency. We have derived a discrete thermal model, using resistors and capacitors, of our laser module. The thermal model was then used as a starting point to model the frequency behavior of the laser and to derive modulation currents that resulted in a linear frequency ramping at some different modulation frequencies.Validerad; 2005; 20060913 (ysko)</p

DE-Link, an antenna pointing system for stratospheric balloons

The DE-Link attitude determination and pointing system onboard stratospheric balloons provides a low cost, low weight and high accuracy method to increase the efficiency of WLAN communication between balloon and ground station. By determination of the 6-dimensional pose of the balloon gondola in real-time, the WLAN antenna can be pointed toward a known position on the ground. This removes the need for power-consuming omnidirectional antennas. It also gives an improvement in communication speed and reduction of overall weight by the removal of heavy RF power amplifiers. The design uses a combination of GPS receivers, accelerometers and magnetoresistive circuits to determine the absolute attitude and position of the gondola in real-time, and two DC motors to point the antenna in azimuthand elevation directions to compensate for the movements of the gondola. Ground based tests have shown the system to function well with a pointing error of less than ±2 deg.Godkänd; 2005; 20060922 (ysko