Analytical and Computational Kinematic Analysis of a Four Bar Mechanism Actioned by a Pneumatic Actuator

Four bar mechanisms are widely used in mechanical engineering. These mechanisms consist of four bars, three of which can move freely and one of which is usually static. These mechanisms provide a way for designers to create a great variety of motion geometries and implement them on a wide variety of mechanisms and engineering applications. In this work, the motion of a scale backhoe excavator is developed with a four-bar mechanism and this motion is simulated and studied using computational methods and simulations to reproduce the motion of the pneumatic actuator.

Kinematic analyses of this mechanism were performed using a theoretical model and motion simulation analysis using the computational software SolidWorks® and Working Models. Additionally, experimental results were obtained using video tracking through the computational software Kinovea to follow the motion for each linkage bar and generate the corresponding experimental values of kinematic quantities. A comparison between the three methods was performed, in order to obtain the differences and similarities between them.

The theoretical model was developed using the relations for relative position, velocity and acceleration. Moreover, a relationship between the piston position and angular position of one of the bars was obtained using a geometric analysis of the system; this was necessary to get the relative positions in every instant of the motion and make the system solvable.

The simulation of the system was programmed such that the motion of the pneumatic actuator was sinusoidal. Meaning that the entire motion of the system could be represented by sine signals or combinations of sine signals. The generation of the backhoe excavator was the central focus point of this simulation and it can be seen that the obtained motion is highly approximated to that of the backhoe excavator. 

This sort of studies provides good approaches to these mechanisms. Moreover, it is a good tool for understanding and visualizing standard mechanisms. On the other hand, accelerations, and thus, forces, velocities and trajectories can be analyzed, allowing engineers to evaluate different kinds of operation strategies regarding the measurement of kinematic and kinetic quantities of the pneumatic pistons and the mechanism powered by it.

It is highly important to develop mechanical models that allow engineers to exemplify a variety of motions, besides developing measuring strategies, computational models, rapid prototyping through 3D printing and the integration of all these with pneumatic systems. Finally, this assembly of mechanisms also creates a direct impact on the learning processes of mechanical engineering students because it facilitates the comprehension and the integration of diverse complex concepts and it also provides different techniques and alternatives to the student, to analyze and propose pertinent and accurate solutions to real life problems.