From: veritasium
Compliant mechanisms are devices that achieve motion through the bending and flexing of their components, rather than relying on traditional rigid-body joints like hinges and bearings [00:00:06]. This approach leverages the inherent flexibility of materials to perform mechanical functions [00:00:36]. Professor Larry Howell, who authored a highly cited book on the subject, highlights how this seemingly “bad” characteristic of flexibility can be used to advantage [00:00:40] [00:00:26].
Compliant mechanisms offer several advantages over traditional mechanisms, including reduced part count, lower cost, and precise motion without backlash [00:02:27] [00:02:42] [00:05:20].
Examples in Everyday Objects and Common Applications
Compliant Gripper
An early example of a compliant mechanism is a simple gripper designed to hold objects [00:01:33]. This gripper is a single piece of plastic that can generate significant force, capable of breaking chalk [00:01:45] [00:01:51]. It can amplify force by approximately 30-to-1, meaning one pound of input force can produce 30 pounds of output force [00:03:01]. Unlike traditional vice grips, which have many separate components like hinges and bearings, this compliant gripper achieves a similar function with a single, flexible piece [00:02:51] [00:02:57]. Its simple design makes it extremely inexpensive to produce, potentially costing mere cents if injection molded or extruded [00:03:10] [00:03:22].
Plastic Switches
Many modern switches utilize compliant mechanisms [00:03:35]. These switches are often made from a single piece of plastic, replacing the multiple springs, hinges, and rigid parts found in conventional switch designs [00:03:38]. This integration into a single component simplifies manufacturing and reduces costs [00:03:30]. Such compliant switches have demonstrated impressive durability, withstanding over a million cycles in fatigue testing without failure [00:03:46].
Tactile Clicking Device
A popular demonstration of compliant mechanism principles is a small, satisfying clicking device [00:06:02]. This device, inspired by microscopic compliant mechanisms built on silicon chips, offers a pleasing tactile and auditory “snap” when operated [00:06:11] [00:06:18]. The ability to create such mechanisms from brittle materials like silicon or less-than-ideal materials like PLA demonstrates the versatility of compliant design [00:06:27] [00:06:43].
Centrifugal Clutch
Another application is the centrifugal clutch, which uses compliant principles for engagement [00:09:05]. As the device spins at a certain speed, its flexible outer part expands outwards due to centrifugal force [00:09:09] [00:09:39]. This expansion allows it to engage with an outer drum, transferring power [00:09:14] [00:09:19]. This mechanism is similar to those found in chainsaws, where the chain only engages once the engine reaches a sufficient RPM [00:09:30]. While often demonstrated in plastic, these clutches can be manufactured from materials like steel for real-world applications [00:09:42] [00:09:46].
Specialized Applications
Nuclear Weapons Safing and Arming Device
One critical application of compliant mechanisms is in the safing and arming of nuclear weapons [00:00:53] [00:01:05]. These devices are designed to prevent accidental detonation, ensuring that random vibrations (e.g., from an earthquake) do not inadvertently disarm the weapon [00:10:21] [00:10:23].
A key requirement for this device was extreme miniaturization [00:10:30]. Using compliant mechanisms, engineers created a device from hardened stainless steel with components as fine as a human hair [00:10:43] [00:10:49]. The device features a rotor wheel with a hole that rotates when specific inputs are given [00:11:00] [00:11:06]. An arming laser beam must align with this hole to initiate the arming sequence [00:11:00] [00:11:08]. The design ensures predictable and reliable performance, even if the device remains unused for decades [00:11:17].
Space Technology
Compliant mechanisms are well-suited for space applications due to their lightweight and simplified designs [00:07:32] [00:07:37].
- Solar Panel Hinges: NASA has explored using compliant hinges, often 3D-printed from titanium, to replace traditional bearings for deploying solar panels [00:07:41] [00:07:46]. A single piece of titanium can achieve a 180-degree deflection, demonstrating remarkable flexibility in a solid material [00:07:58] [00:08:03].
- Thruster Director: A complex compliant mechanism designed for NASA allows a single thruster to be directed in any direction using two motor inputs [00:08:33] [00:08:44]. The entire motion relies on bending, and the design ensures no pinch points for critical fuel or electrical lines [00:08:49] [00:08:54]. This innovation allows one thruster to perform the function of two, further optimizing space systems [00:09:01].