In mechanical engineering, compliant mechanisms are flexible mechanisms that transfer an input force and displacement at one port to an output force and displacement at another port through elastic body deformation. These may be monolithic (single-piece) or jointless structures.
Since many compliant mechanisms are single-piece structures, there is no need of assembly. With no joints, "rubbing" between two parts or friction as seen at the joints of rigid body mechanisms is absent. Compliant mechanisms are elastic.
Compliant mechanisms are usually designed using two techniques, the first being a pseudo-rigid-body model and the second, the topology optimization. Other techniques are being conceived to design these mechanisms. Compliant mechanisms manufactured in a plane that have motion emerging from said plane are known as lamina emergent mechanisms (LEMs).
The flexible drive or resilient drive, often used to couple an electric motor to a machine (for example, a pump), is one example. The drive consists of a rubber "spider" sandwiched between two metal dogs. One dog is fixed to the motor shaft and the other to the pump shaft. The flexibility of the rubber part compensates for any slight misalignment between the motor and the pump. See rag joint and giubo.
Research laboratories and researchers
A number of labs and researchers are explicitly researching compliant mechanisms:
- Prof. Larry Howell, Brigham Young University Compliant Mechanisms research
- Prof. Haijun Su at the Ohio State University
- Prof. Kota at University of Michigan Compliant Systems Design Lab
- Prof. Zentner at Ilmenau University of Technology
- Prof. Martin Culpepper at MIT Precision Compliant Systems Laboratory
- Prof. Just L. Herder at Delft University of Technology
- Prof. Engin Tanık and Prof. Volkan Parlaktaş at Hacettepe University
- Prof. Jonathan Hopkins at University of California, Los Angeles
- Prof. Dennis Brouwer at Twente University, the Netherlands
- Prof. Alexander Hasse at Chemnitz University of Technology
In addition, the following researchers may be doing compliant mechanism research:
- The Multidisciplinary and Multiscale Device and Design Laboratory (M2D2) at the Indian Institute of Science, Bangalore
- Prof. Sridhar Kota
- Prof. Shorya Awtar at University of Michigan
- Prof. G. K. Ananthasuresh at IISc, Bangalore
- Prof. Stephen L. Canfield at Tennessee Tech University
- Prof. Charles Kim at Bucknell University
- Prof. Anupam Saxena at IIT Kanpur, India
- Prof. Mary Frecker at The Pennsylvania State University, University Park
- Prof. Guimin Chen, Compliant Mechanisms & Precision Instruments Lab at Xidian University 
- Prof. Guangbo Hao, Compliant Mechanisms and Robotics Research Group at University College Cork, Ireland
- Prof. W.J. Zhang, Soft Body Mechanisms and Robots Research Group at University of Saskatchewan, Canada
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