# Compliant mechanism

• tags: Machines CNC MTM Flexure
• Resources
• Notes
• Spring Stiffness
• Stiffness can be said as the derivate of the force with respect to the deflection. In a linear spring, this deflection will be a straight line.
• Ways to affect the stiffness,
• Topology
• Geometry, making the blades thinner, longer and wider.
• Material, Making the spring out of more compliant materials.
• Non linear springs
• Even though they can be considered linear, after certain deflection, the stiffness begins to increase appreciably.
• The stiffness changes almost immediately as the beams have to stretch and bend as they deform.
• Some springs can be designed to reduce the stiffness as they buckle.
• Most metals exhibit a linear stress strain relationship, but some elastomers have non linear elastic properties that change as the material is deformed. If we combine the stiffness properties of a design with a complementary material we can alter the design to have optimal stiffness along the range of motion.
• The nonlinear elastic properties of the spring are canceled by the nonlinear properties of the material.
• Elastic strain Energy
• Under elastic conditions and given the material is not permanently damaged, all the work under the force displacement graph is said to be stored in spring as Elastic strain energy.
• Bi Stable switch
• The stiffness of the two elements can be added together because they are parallel, ie they experience the same displacement of the shuttle.
• Axiomatic design
• Functional parameter only affect one area of the design parameter and the requirements are uncoupled from the design parameters.
• Compliant systems are inherently nonlinear and optimizing for all the variables is difficult and time-consuming. In nature, all systems are coupled and influence one another.
• For eg, if we wanted a circular motion about an axis, its easier to use rigid bodies and put a pin joint there, if we were to make it compliant then it becomes a non linear problem where the center of rotation will depend on the force, location and the material.
• Compliant clutches.
• 360 Robot joint
• These are rigidly constrained in all directions but offer zero stiffness in rotation. Used for robot joints. These can be taken a step further with engineered materials.
• Over running clutch
• Bi Stable Switch
• Lamina Emergent Systems
• Making things in 2D that can assemble on fold into 3D shapes.
• Flexure
• A flexure is a mechanism consisting of a series of rigid bodies connected together by compliant elements that is design to produce a geometrically defined motion upon application of force. - Stuart Smith
• Compliant mechanism

• Compliant mechanism

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