Flexures and Compliant Mechanisms
Flexures, also known as compliant mechanisms, are mechanical elements that are designed to provide flexibility and compliance in a system whereby compliance means the ability of a material or structure to deform elastically under an applied load and return to its original state once the force is removed and to do that without any permanent deformations caused by an applied force.
I was transfixed by a series by Dan Gelbart called “Building Prototypes Dan Gelbart”, a proficient inventor with over 100 patents to his name. One of the videos that caught my eye is about flexures and their properties. If you have ever wondered how super, and I mean super, to the 0.0001 mm or about 1000 times less than the thickness of human hair, precise measurements are made check the following video.
In the context of flexures and compliant mechanisms, the term "compliance" refers to the ability of a mechanical element to deform or bend in response to applied forces. A compliant mechanism is one that is able to flex or bend in a controlled and repeatable manner, allowing it to transmit forces without introducing errors or inaccuracies into the system and to do that without any change or deformation as all flexing is done below its permanent deformation based on Young's modulus. This means that any design of such mechanisms needs to take into account the point at which the material exceeds its elastic deformation load and permanently deforms. If loads are kept under control for the desired operation the mechanism will run forever.
There are no moving parts to wear out as we are taking the material’s natural elasticity as a feature to create the desired outcome.
Flexures are used in a wide variety of applications, including robotics, microelectromechanical systems (MEMS), and optical systems. In these applications, flexures can provide a number of benefits, such as improved precision, reduced weight and size, and increased durability.
Our modern world is built upon MEMS devices, devices such as accelerometers that count our steps, or DLP chips inside video projectors among others.
One of the key advantages of flexures is their ability to transmit forces while maintaining high levels of precision and accuracy. This is because flexures are able to deform in a controlled and repeatable manner, allowing them to compensate for any misalignments or deformations in the system.
In addition to their use in precision systems, flexures are also commonly used in applications that require high levels of compliance, such as in robots and other mechanical systems. The flexibility of flexures allows them to absorb shock and vibrations, reducing wear and tear on the system.
For more about flexures check out “The FACTs of Mechanical Design!” youtube channel by professor Jonathan Hopkins.
For some of the software used to construct flexures check out DAS 2D which is a MatLab script but you can get it as a standalone with included MatLab runtime.
Another more focused app would be Vink System Design & Analysis.
This post is more of a primer into fixtures as there is a lot that goes into making a good flexure. If you are interested in mode check out these free resources:
Modeling and Design of Flexure Hinge-Based Compliant Mechanisms, Sebastian Linß, Stefan Henning, and Lena Zentner
A Design Method for Flexure-Based Compliant Mechanisms on the Basis of Stiffness and Stress Characteristics, Ing. Qiaoling Meng
Flexures, Marcel Thomas