Thumbnail Image

Dynamic Analysis of Flexible Mechanisms with Clearance

Ahmedalbashir, Mona Abdullah Hassan
A Master of Science thesis in Mechanical Engineering by Mona Abdullah Hassan Ahmed albashir entitled, "Dynamic Analysis of Flexible Mechanisms with Clearance," submitted in November 2016. Thesis advisor is Dr. Lotfi Romdhane. Soft and hard copy available.
This research is focused on studying the dynamic behavior of a four-bar mechanism with clearance. The presence of clearance in a revolute joint induces impacts between the journal and the sleeve. Therefore, it causes vibration, noise and decreases the efficiency of the mechanism. Two different methods are proposed to eliminate the undesirable effects of clearance in the joint through simulations and experiments. The first method, that is used to eliminate these impacts, relies on attaching a spring to a rigid four-bar mechanism. The impacts are predicted by monitoring the moment of the reaction force in the joint with clearance using MATLAB software simulations. It is shown that the impacts could be easily eliminated using adequate and optimized spring parameters. The optimization of the spring parameters is performed to keep the positive effects of adding the spring (eliminating the impacts) and to minimize its negative effects (high maximum input torque and its high fluctuations). The second method aims at studying the dynamic behavior of the mechanism with a flexible coupler link. The dynamic analysis of the flexible mechanism is investigated using two different materials of the coupler link (aluminum and steel) with two different thickness values for each material (3 and 4 mm for aluminum and 1.5 and 2 mm for the steel). The rigid mechanism is considered in this case with a coupler link made of steel with 5 mm thickness to highlight the difference between flexible and rigid mechanisms. The deformation of the flexible coupler links (using ideal joints) is investigated by measuring the strain values at three different speeds (277, 415 and 554 rpm). The obtained results show that the strain values are significantly affected by the crank speed and the thickness of the links. Experimental tests are performed to measure the accelerations for the follower of the four-bar mechanism using rigid and flexible coupler links. These measurements are done for the case of ideal joint (no clearance) and realistic joint with a clearance of 0.5 mm and 1 mm sizes at the three mentioned speeds for each case. The experimental results are validated through simulation tests using ADAMS software. These results confirm that the flexibility of the coupler has thus a role of a suspension for the mechanism.
External URI