Development of an analytical model of the safety brake system for a chainsaw
Sammanfattning: The safety braking system with the hand guard is the most important safety equipment for the user of a chainsaw. The safety system prevents serious injuries caused by a kickback. A kickback is when the running chain suddenly gets stuck e.g. by getting stuck in wood or hit a rock. Due to the potentially serious consequences of a kickback, the braking system has to fulfil strict requirements formulated by the authorities. In the present thesis, a generic analytical model of the braking system for a typical Husqvarna chainsaw is developed. The model is implemented as an Excel work sheet, which will facilitate future projects. The thesis includes sections of analytical calculations with information provided from both Catia and resources at Husqvarna. Several experiments were accomplished to strengthen and prove the analysis. The torque, index and activation force are tested. The static activation force is then completed in a simulation program to provide spread in the model. The parameters with most impact are also detected in the Excel simulation. A matrix of testing is constructed with parameters outside the tolerances for the dynamic experiment. Due to the collected data of the test, the relation between the two types of activation can be established. In comparison between samples of production with the simulation on equal numbers of 24 tests gave adifference on 4.75 % in mean value. 6 out of 32 tests could not be approved within the authorities’requirements for the acceleration with respect to the higher tolerances than production in the testing matrix. The most significant parameters for the static force were the brake spring and the angle of the knee joint. For the dynamic activation, the dimensions of the knee joint is crucial. Reasoning for errors are implemented in the discussion section e.g. the importance of data for the band. To improve the accuracy of the model a section of future work contains suggestments. One suggestion for improvement is to deliver more production values to ensure the comprehension of the experiments.
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