Measurement of range of motion of human finger joints, using a computer vision system

Assessment of finger range of motion (ROM) is often required for monitoring the effectiveness of rehabilitative treatments and for evaluating patients' functional impairment. There are several devices which are used to measure this motion, such as wire tracing, tracing onto paper and mechanical and electronic goniometry. These devices are quite cheap, excluding electronic goniometry; however the drawbacks of these devices are their lack of accuracy and the time- consuming nature of the measurement process. The work described in this thesis considers the design, implementation and validation of a new medical measurement system utilized in the evaluation of the range of motion of the human finger joints instead of the current measurement tools. The proposed system is a non-contact measurement device based on computer vision technology and has many advantages over the existing measurement devices. In terms of accuracy, better results are achieved by this system, it can be operated by semi-skilled person, and is time saving for the evaluator. The computer vision system in this study consists of CCD cameras to capture the images, a frame-grabber to change the analogue signal from the cameras to digital signals which can be manipulated by a computer, Ultra Violet light (UV) to illuminate the measurement space, software to process the images and perform the required computation, a darkened enclosure to accommodate the cameras and UV light and to shield the working area from any undesirable ambient light. Two calibration techniques were used to calibrate the cameras, Direct Linear Transformation and Tsai. A calibration piece that suits this application was designed and manufactured. A steel hand model was used to measure the fingers joint angles. The average error from measuring the finger angles using this system was around 1 degree compared with 5 degrees for the existing used techniques

Bir krank biyel mekanizmasının ön kalibreli, 2 ticari kamera kullanılarak geliştirilen görüş sistemi vasıtasıyla kinematik analizi.

There are two main objectives of this study. The first objective is to develop a vision system consisting of 2 inexpensive commercial cameras. In general, by self – calibration methods reconstruction of a scene by using uncalibrated images is performed up to a scale only. However, in this thesis reconstruction of a scene is to be performed such that one obtains the actual values of the distances in the scene. For this purpose, it is assumed that the extrinsic parameters of the cameras are known. Therefore, one needs to determine the intrinsic parameters of the cameras only. In order to calculate the intrinsic parameters, two methods, that take advantage of the simplified Kruppa equations and the equal eigenvalue theorem, are used. The results obtained via the two methods are compared with the results obtained by using a calibration pattern. A triangulation process is then performed to calculate several known distances in the scene by using the method that gives better results for the intrinsic parameters. The actual and estimated distances obtained via the vision system are then presented and compared. The second objective of this study is to perform kinematic analysis of a slider crank mechanism by using the developed vision system. The position, velocity and acceleration analyses of the slider crank mechanism are realized by using several markers that are attached on the moving links of the mechanism. The positions of the markers are calculated by using the vision system. This data is then utilized to determine the joint variables, joint velocities and joint accelerations of the slider crank. The results thus obtained via an encoder attached to the input link of the mechanism are compared with the results obtained via the developed vision system. The effects of the locations of the markers and the effects of the number of markers used on the accuracy of the results are also investigated.M.S. - Master of Scienc

Calibração de um sistema de visão estéreo: de correspondências de pontos à reconstrução euclideana

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia ElétricaUma imagem fornece uma representação em duas dimensões de uma cena. Durante o processo de formação desta representação, todas as informações 3D são perdidas. Contudo, tais informações podem ser recuperadas, através da visão estéreo, se duas imagens de uma mesma cena, mas de perspectivas diferentes, estão disponíveis. No entanto, isto só é possível se o sistema estiver calibrado. Por isso, a calibração de câmeras é indispensável em diversas aplicações. Neste trabalho, realiza-se uma análise crítica das diversas técnicas de calibração existentes na literatura. Além disso, novos métodos de calibração de um sistema de visão binocular são propostos. Basicamente, as técnicas propostas consistem em, inicialmente, recuperar a geometria epipolar e realizar uma calibração projetiva. Em seguida, os pontos de um gabarito de uma única dimensão são utilizados para atualizar da calibração projetiva para a euclideana. Como é utilizado um gabarito de dimensões reduzidas e de fácil confecção, os métodos de calibração propostos são bastante flexíveis e de fácil execução. Para auxiliar a tarefa de calibração, novos algoritmos de correspondência de pontos e estimação da matriz fundamental também são propostos. Em especial, o algoritmo de estimação da matriz fundamental utiliza um conjunto de correspondências virtuais que definem um plano também virtual. Evidentemente, tal plano induz uma homografia entre as imagens estéreo. O paralaxe de correspondências que não satisfazem tal homografia permite estimar um dos epipolos do sistema e, portanto, caracterizar a matriz fundamental. A principal vantagem do método proposto é obter uma boa estimação utilizando uma parametrização com apenas cinco incógnitas. Experimentos em imagens reais e sintéticas validam as técnicas propostas, mostrando como seu desempenho varia quanto a quantidade de ruído e número de correspondências existentes