A flexure is a flexible element (or combination of elements) engineered to be compliant in specific

degrees of freedom In many scientific fields, the degrees of freedom of a system is the number of parameters of the system that may vary independently. For example, a point in the plane has two degrees of freedom for translation: its two coordinates; a non-infinite ...

. Flexures are a design feature used by

design engineer A design engineer is an engineer focused on the engineering design process in any of the various engineering disciplines (including civil, mechanical, electrical, chemical, textiles, aerospace, nuclear, manufacturing, systems, and struct ...

s (usually

mechanical engineer Mechanical may refer to: Machine * Machine (mechanical), a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement * Mechanical calculator, a device used to perform the basic operations o ...

s) for providing adjustment or compliance in a design.

Flexure types

Most compound flexure designs are composed of three fundamental types of flexure: * Pin flexure - a thin bar or cylinder of material, constrains three degrees of freedom when geometry matches a notch cutout * Blade flexure - thin sheet of material, constrains three degrees of freedom * Notch flexure - thin cutout on both sides of a thick piece of material, constrains five degrees of freedom Since single flexure features are limited both in travel capability and degrees of freedom available, compound flexure systems are designed using combinations of these component features. Using compound flexures, complex motion profiles with specific degrees of freedom and relatively long travel distances are possible.

Design aspects

In the field of

precision engineering Precision engineering is a subdiscipline of electrical engineering, software engineering, electronics engineering, mechanical engineering, and optical engineering concerned with designing machines, fixtures, and other structures that have except ...

(especially high-precision

motion control Motion control is a sub-field of automation, encompassing the systems or sub-systems involved in moving parts of machines in a controlled manner. Motion control systems are extensively used in a variety of fields for automation purposes, includi ...

), flexures have several key advantages. High precision alignment tasks might not be possible when

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...

stiction Stiction (a portmanteau of the words '' static'' and ''friction'') is the force that needs to be overcome to enable relative motion of stationary objects in contact. Any solid objects pressing against each other (but not sliding) will require some ...

are present. Additionally, conventional bearings or linear slides often exhibit positioning

hysteresis Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...

due to

backlash Backlash may refer to: Literature * '' Backlash: The Undeclared War Against American Women'', a 1991 book by Susan Faludi * ''Backlash'' (Star Wars novel), a 2010 novel by Aaron Allston * Backlash (Marc Slayton), a comic book character from ...

and friction. Flexures are able to achieve much lower resolution limits (in some cases measured in the

nanometer 330px, Different lengths as in respect to the Molecule">molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm), or nanometer (American spelling Despite the va ...

scale), because they depend on

bending In applied mechanics, bending (also known as flexure) characterizes the behavior of a slender structural element subjected to an external Structural load, load applied perpendicularly to a longitudinal axis of the element. The structural eleme ...

and/or torsion of flexible elements, rather than surface interaction of many parts (as with a

ball bearing A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this ...

). This makes flexures a critical design feature used in

optical instrument An optical instrument is a device that processes light waves (or photons), either to enhance an image for viewing or to analyze and determine their characteristic properties. Common examples include periscopes, microscopes, telescopes, and camera ...

ation such as

interferometer Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...

s. Due to their mode of action, flexures are used for limited range motions and cannot replace long-travel or continuous-rotation adjustments. Additionally, special care must be taken to design the flexure to avoid material yielding or

fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

, both of which are potential failure modes in a flexure design.

Design examples

* Living hinge: Flexure which acts as a hinge. Preferred for their simplicity, as they can be included as a feature in a single piece of material (as in a

Tic Tac Tic Tac (stylized in lowercase) is a brand of small, hard mint manufactured by the Italian company Ferrero. They were first produced in 1969 and are now available in a variety of flavors in over 100 countries. Tic Tacs are typically sold in s ...

box's lid). *

Leaf spring A leaf spring is a simple form of spring (device), spring commonly used for suspension (vehicle), suspension in wheeled vehicles. Originally called a ''laminated'' or ''carriage spring'', and sometimes referred to as a semi-elliptical spring, e ...

: Leaf Springs are commonly used in

vehicle suspension Suspension is the system of tires, tire air, spring (device), springs, shock absorbers and Linkage (mechanical), linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems must support b ...

s. Leaf springs are an example of a flexure system with one compliant

degree of freedom In many scientific fields, the degrees of freedom of a system is the number of parameters of the system that may vary independently. For example, a point in the plane has two degrees of freedom for translation: its two coordinates; a non-infinites ...

. * Flex Pivot: Frictionless pivoting component, for use in precision alignment applications. *

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

Mars Exploration Rover NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, ''Spirit (rover), Spirit'' and ''Opportunity (rover), Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rove ...

s and the Mars Science Laboratory rover

Curiosity Curiosity (from Latin , from "careful, diligent, curious", akin to "care") is a quality related to inquisitive thinking, such as exploration, investigation, and learning, evident in humans and other animals. Curiosity helps Developmental psyc ...

have engineered flexures in their wheels which act as vibration isolation and suspension for the rovers.

References

{{reflist Mechanical engineering

Flexure types

Design aspects

Design examples

See also

References