Four Bar Mechanism

Project Description

Goals:

Use SolidWorks Motion to analyze a four-bar mechanism and understand its dynamic behavior.
Fully define the linkage to ensure a single degree of freedom for accurate motion studies.
Evaluate motor torque, crank angle, bearing forces, and power requirements under different speeds and with gravity applied.
Gain insight into how the mechanism responds to loading and what factors influence its overall performance.

Solidworks Analysis

4 bar linkage.mp4

Motion Analysis

The 4-bar linkage was built through Solidworks by mating parts. In order to do a correct analysis, the Gruebler Count was used to ensure there was only 1 degree of freedom. The attached video demonstrates the motion analysis of the 4-bar linkage system operating at 20 RPM without gravity, along with the trace path of the extension’s center point.

Maximum Value of the Motor Torque

0.678 N-m at 1.32s and 4.32s

Angle of Crank at Max Torque

The angular displacement of the crank affects the motor torque. When the crank is almost horizontal to the left, or at an angle of 45° above the positive x-axis at 1.32s and 4.32s, the torque reaches its maximum . The linkage opposes motion the most in this position, therefore the motor must exert greater torque.

Max Vertical Force on Bearings

The max vertical force on the bearins is 1.2429E+01 N at 2.32s and 5.32s.

Minimum motor power to move Crank at constant angular speed 600 rpm

The motor’s power rises and falls as the crank goes through its cycle and the torque changes and the demand isn’t constant at 600 rpm. To hold that 600 rpm speed, the motor needs at least 668.4 W as it needs to be able to cover the highest positive power peaks in the graph. At some points in the cycle, the power dips below zero, showing that the linkage is giving energy back to the motor.

Explain the meaning of the negative motor torque values and how they are related to the motion of the mechanism links.

Negative motor torque occurs when the mechanism’s motion drives the motor instead of the motor driving the mechanism. This happens because inertia and gravity in certain link positions assist the crank’s rotation. Positive torque corresponds to the motor working against gravity or resisting the linkage motion. The alternating positive and negative values reflect the changing mechanical advantage of the four-bar linkage throughout its cycle.

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