The goal of this project is to assemble a Four-Bar Mechanism with provided parts and perform a motion study on it to observe how the parts interact with each other. This includes obtaining quantitative data on metrics such as torque, power, and reaction forces.
The assembly of the mechanism consists of two bearings and three bars. The two bearings. which are fixed, can be replaced with one fixed bar while not affecting the function of the mechanism, thus the name "four bar". The main parts of the assembly are as follows with the image shown to the right:
- Bearing 1: Red part on the left *fixed*
- Bearing 2: Red part on the right *fixed*
- Crank: Blue part
- Extension: Green part
- Rocker: Magenta Part
The Motion Study
Before conducting the motion study, we first needed to verify that our assembled mechanism was properly constrained. This involved analyzing the assembly to check its degrees of freedom. Since this was a mechanism, it required exactly one degree of freedom to function correctly. In our case, we discovered some redundant mates (connections) that needed to be edited and eliminated to achieve this single degree of freedom.
Once we confirmed the proper constraint of the assembly, we proceeded to set it in its initial position. We then installed a motor at the junction between the crank and bearing one, which would enable the crank's rotation. The motor was configured to operate at 20 rpm for 6 seconds. With all preparations complete, we initiated the analysis and executed the motion study to observe the mechanism's movement.
Analysis
Motion studies enable us to collect data across multiple performance metrics. While traditional hand calculations for motion analysis can be challenging and time-consuming due to their complex combination of algebraic and classical physics equations, computer-aided analysis can perform these calculations almost instantly.
This computational power allows us to efficiently analyze specific performance targets. In our study, we focused on tracking the movement of a single point—specifically, the midpoint of the extension—throughout the simulation. The resulting motion data was then converted into graphical form for better visualization and analysis.
When compared to the time and angle of the crank, the instances of max torque could be determined.
From this data, it is easy to see that the maximum torque is about 20.4 N which occurs periodically when the crank is at its initial position, 0 degrees. While this dataset does not show this, negative motor torques are possible.
According to the motion study analysis, the maximum vertical forces on bearings 1 and 2 are 0.35 N and 0.17 N respectively. This is useful information for determining if the assembly can withstand such forces caused by its motion.