What Are Compliant Mechanisms?
Compliant Systems offer Optimal Performance through Flexibility
Mechanisms in nature customize their shape, their mechanical geometry, to maintain optimal performance under changing conditions in a dynamic environment. This is possible since natural bodies are essentially single-piece compliant mechanisms in that their various components grow out of one another or are bonded with self-renewing transitional surfaces. Such compliant designs are inherently robust since fatigue stresses are distributed throughout the entire form and thus strains are disbursed or absorbed during normal operation.
By comparison, conventionally engineered mechanisms have fixed geometry and are made up of rigid components connected by joints that are designed to be strong and stiff. With such designs, flexibility adds complexity both of design and part count. For this reason conventional mechanisms are typically optimized for peak performance within a specific operating envelope. Generally, these fixed designs sacrifice flexibility and compromise performance at all non-optimal conditions.
FlexSys, Inc, approaches mechanism design by replacing multi-body rigid linkages with compliant flexible elements within a single component. We accomplish this by exploiting the elasticity of conventional materials (including high-strength steels, aluminum, titanium and composites) to create flexure and motion without compromising the strength and resilience of the material at hand. FlexSys design technology initiates small forces within a proprietary internal geometry that morphs a single-body “monoform” from one desired shape to another and back again.
Our technology spreads actuator forces throughout the whole geometry to distribute compliance without localizing strains in any focused region. This enables FlexSys to achieve remarkably complex shape morphing with less weight while maintaining exceptional strength and reliability. Because of their strength, our designs stay safely within conventional life cycle limits, are highly reliable, and still very cost effectively while offering major enhancement and new functionality.
Among other enhancements shape morphing replaces conventional multi-body mechanisms with more precise and efficient alternatives. Compliant mechanisms formed within a single piece don’t require assembly so there’s no risk of assembly error. Also, as joint-less mechanisms, they don’t suffer from backlash in operation. And with the compliance designed-in, they move while maintaining higher levels of positional accuracy and repeatability.
Our designs don’t need lubrication, use less energy to function and can be made lighter in weight because lower stress loads distributed throughout the mechanism don’t require as much mass to compensate for localized strain locations that would wear and fail during operation. These features make our distributed compliance technology applicable to mechanisms of any scale from MEMS to wind turbine components.
Advantages of Compliant Mechanisms
- No joints: No joint friction, backlash or need for lubrication
- Easy integration: Can be coupled with modern actuators (piezoelectric, electromechanical, etc.)
- Scalable: equally effective at micro, meso or macro scale
- Materials-friendly: Wide range of applicable materials including steel, aluminum, titanium, polymers, GFRP, CFRP, and metal-matrix composites.
- Smaller and lighter: no need to accomodate springs, fasteners or hinges
- Fatigue resistant: stresses are distributed through the whole device.
Common Myths about Compliant Mechanisms
Myth: Flexible structures are prone to fatigue failure within a few cycles.
Fact: Life cycle optimization is a paramount design consideration with compliant structures. FlexSys has developed structures capable of 220 million morphing cycles while exposed to significant air loads and 600gs of inertial loads. Sandia National Labs tested a MEMS actuator (designed by Dr. S. Kota) structure to 10 billion cycles with no failure.
Myth: Flexible structures are not scalable and able to support realistic loads.
Fact: Compliant mechanisms are highly scalable, as demonstrated by our FlexFoil shape morphing technology (above left, dimensions in meters) and micro-scale devices (above right, dimensions in microns).
Myth: Compliant systems are difficult to manufacture.
Fact: FlexSys’ design approach and the associated software take into account a desired manufacturing method during structural design and optimization. These mass-manufacturing methods include stamping, casting, extrusion, injection molding, composite molding, etc.
Myth: The FlexSys technology is no different than previous monolithic mechanisms.
Fact: While it’s true that employing elastic strain to generate motions is not new and can be found in household products like shampoo-bottles where the lid and the cap are relatively rigid and flexion is concentrated in a thin flexural (living) hinge. Such designs employ “lumped compliance” that result in stress concentrations that limit fatigue life and are not suitable for high load bearing applications. The FlexSys approach utilizes ‘distributed compliance”, spreading elastic strains over a large region of the mechanism so that all elements share the load as many small deformations and results in high fatigue life. The illustrations below demonstrate these differences.
To learn more about how FlexSys can revolutionize your mechanism design while simplifying your assembly and performance needs, please contact us.