Laser rangefinder | EPFL Graph Search

A laser rangefinder, also known as a laser telemeter, is a rangefinder that uses a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in a narrow beam towards the object and measuring the time taken by the pulse to be reflected off the target and returned to the sender. Due to the high speed of light, this technique is not appropriate for high precision sub-millimeter measurements, where triangulation and other techniques are often used. It is a type of scannerless lidar. Pulse The pulse may be coded to reduce the chance that the rangefinder can be jammed. It is possible to use Doppler effect techniques to judge whether the object is moving towards or away from the rangefinder, and if so, how fast. Precision The precision of an instrument is correlated with the rise time, divergence, and power of its laser pulse, as well as the quality of its optics and onb

Experimental indoors localization using distance measurements obtained from visual data

Yuan Yao

In recent years, the emergence of artificial intelligence increases the demand of automatic and robust localization outdoors and indoors. While GPS provides enough accuracy in most outdoor cases, there is still a lack of robust and efficient indoor localization systems available on the market. In this report, an experimental framework for indoor localization is developed and tested. To operate an automatic robot owned by LCAV laboratory, two different operation modes have been successfully implemented, including controlling a robot in real-time or with extra input containing a list of commands. Also, a new visual fiducial system have been developed, and is able to capture the locations of Apriltags inside a room accurately. Multidimensional scaling (MDS) and Squared range least square (SRLS) algorithms containing distance information will also be introduced and the final localization result is within 2% error of tolerance compared with the ground truth results measured by a laser meter.

2017

Evaluation of Cost-Effective Technologies for Highly Efficient Silicon-Based Solar Cells

Luca Gautero

The work underscores the feasibility of highly efficient silicon solar cell structures manufactured with high throughput machines. The main challenge consists in the implementation of more performant structures of intrinsic higher complexity. These structures are meant to be fabricated within similar constraints on time and on cost as for conventional devices of industrial manufacture. Achievements in this direction foster larger economical deployment of this kind of renewable energy. The structure chosen for the implementation of "high efficiency" concepts requires an advanced machining of the silicon substrate. Etching techniques, dielectric coating preparations, and metal to semiconductor contact formation were evaluated for their integration in a complete silicon solar cell fabrication sequence. These sequences were later tested to gain knowledge regarding the effects of the aforementioned advanced processing. Prototypes were created using the fabrication sequence. They were analysed to acquire a further understanding of the advanced processing influences. Statistical interpretation of the data obtained was used to support physical interpretation of the observed phenomena. For one particular implementation of a surface passivation (floating junction passivation) an attempt of modelling aiming to unveil its specific dynamics is reported. A resulting solar cell concept compatible with high throughput equipment achieved a certified efficiency of 18% (VOC = 635 mV, JSC = 37.3 mA/cm2, FF = 76 %) on substrate with a reduced thickness (120 µm). The resulting sequence prepares the back surface with a thermal oxidation for passivation purposes and with a laser technique to locally contact the bulk. The thickness is compatible with the intent of cost reduction through the decrease in material consumption. Other approaches performed on the same substrate achieved 17.1% efficiency (VOC = 617 mV, JSC = 36.1 mA/cm2, FF = 75 %). In this case the passivation was achieved with deposited dielectric layers on the back surface. Furthermore, the investigated dynamics of the floating junction passivation allows for better insight into its traits. The proposed solution has an interesting ratio of efficiency versus costs. The general consequence is a higher market appeal of this particular renewable source on the energy market. The study on the floating junction passivation allows a better exploitation of this particular implementation towards more performant silicon solar cells.

EPFL2010

Study of polyvinylidene fluoride (PVDF) based bimorph actuators for laser scanning actuation at kHz frequency range

Hannes Bleuler, Ricardo Pérez Suárez

This work focuses on some promising applications of polyvinylidene fluoride (PVDF) based bimorph actuators in microengineering. The actuator of several centimeters in length and 100 mu m in thickness takes advantage of the structural and electromechanical capabilities of the PVDF. These characteristics make the proposed PVDF based bimorph ideal for a laser scanner/switcher where high speed laser beam manipulation is feasible. This domain requires light and efficient actuators capable of actuating the mirror surface at kHz frequency range and having a weight of less than 200 mg and volume of less than 150 mm(3). Analytical and finite element (FE) modeling were used to design the bimorph actuator with an attached mirror on the tip. Results of the modeling were also used to establish dimension criteria for the proposed bimorphs with an attached mirror. Some clean and gray room processing was needed to fabricate the bimorph actuators. Static and dynamic characterization was carried out to validate the response of the proposed actuator. Other bimorph based configurations were analyzed and compared to the proposed one. Results indicate that the PVDF bimorph actuator responds conveniently in a range up to 3 kHz for beam scanning tasks. The same principle may be implemented to 2 DoF actuators. Results obtained from modeling tools indicate a similar performance in terms of displacement. In addition, due to the intrinsic properties of the PVDF, the actuation system is compact which is advantageous for other domains such as biomedical and aerospace. (C) 2012 Elsevier B.V. All rights reserved.

Elsevier Science Sa2012

Evaluation of Cost-Effective Technologies for Highly Efficient Silicon-Based Solar Cells

Luca Gautero

EPFL2010