Fall 2024, MIT
Compliant Mechanism Design - Pseudo Rigid Body Model
Scroll ↓
Designing a Compliant Egg Gripper
For a class in compliant mechanisms, my team designed and built an egg gripper that safely holds an egg and whose motion has no sliding or rolling parts. We designed it with Pseudo-Rigid Body Modelling (PRBM) theory that allows an engineer to create compliant mechanisms that mimic the motion of rigid-body mechanisms that have bearings and sliding parts.
Functional Requirements
We developed a set of measurable requirements that our device would need to meet to be functional. These requirements were used as inputs into the mechanical theory to design the device.
Mechanical Calculations
Once we decided on a general design, I used mechanics theory to determine the stiffness of the design based on the geometry and material properties. This, along with other equations we derived, were compiled in a spreadsheet to guide the design of the gripper.
Model “Pressure Test”
To ensure the model made sense, we “pressure tested” it by plugging in extreme values to the inputs and testing if the outputs made logical sense. With the model pressure tested, we employed it for the design of our prototype.
Prototype Testing
We built the prototype and collected data on its performance to ensure it met our functional requirements. It also held the egg without breaking it!
Validation with PRBM
Part of the purpose of the project was to employ pseudo-rigid body modelling (PRBM) so we could design a compliant, single-piece 4-bar mechanism that mimicked the motion of a rigid 4-bar mechanism with bearings. In this picture, we attached rigid bars with bearings that overlapped the compliant bars. The bearings overlapped where we expected the compliant bars to bend based on the theory. The fact that the overlapping bars can move together illustrates that we applied the modelling theory correctly.