A flexure bearing is a category of

flexure A flexure is a flexible element (or combination of elements) engineered to be compliant in specific degrees of freedom (mechanics), degrees of freedom. Flexures are a design feature used by design engineers (usually mechanical engineers) for prov ...

which is engineered to be compliant in one or more angular

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 ...

. Flexure bearings are often part of

compliant mechanism In mechanical engineering, a compliant mechanism is a flexible mechanism that achieves force and motion transmission through elastic body deformation. It gains some or all of its motion from the relative flexibility of its members rather than fr ...

s. Flexure bearings serve much of the same function as conventional bearings or hinges in applications which require angular compliance. However, flexures require no lubrication and exhibit very low or no friction. Many flexure bearings are made of a single part: two rigid structures joined by a thin "hinge" area. A hinged door can be created by implementing a flexible element between a door and the door frame, such that the flexible element bends allowing the door to pivot open. Flexure bearings have the advantage over most other bearings that they are simple and thus inexpensive. They are also often compact, lightweight, have very low friction, and are easier to repair without specialized equipment. Flexure bearings have the disadvantages that the range of motion is limited, and often very limited for bearings that support high loads. A flexure bearing relies on the bearing element being made of a material which can be repeatedly flexed without disintegrating. However, most materials lose strength and eventually fail with repeated flexing and bending. For example, most metals will

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 ...

with repeated flexing, and will eventually snap. Thus, one part of flexure bearing design is the careful consideration of material properties to avoid fatigue with normal use. Flexure bearings can give very low friction and also give very predictable friction. Many other bearings rely on sliding or rolling motions (

rolling-element bearing In mechanical engineering, a rolling-element bearing, also known as a rolling bearing,ISO 15 is a bearing (mechanical), bearing which carries a load by placing rolling elements (such as balls, cylinders, or cones) between two concentric, Groove ...

s), which are necessarily uneven because the bearing surfaces are never perfectly flat. A flexure bearing operates by bending of materials, which causes motion at microscopic level, so friction is very uniform. For this reason, flexure bearings are often used in sensitive precision measuring equipment. Many types of flexure bearings are not limited to low loads, however. For example, the drive shafts of some sports cars replace cardan

universal joint A universal joint (also called a universal coupling or U-joint) is a joint or coupling connecting rigid shafts whose axes are inclined to each other. It is commonly used in shafts that transmit rotary motion. It consists of a pair of hinges ...

s with an equivalent joint called a

rag joint A rag joint refers to certain flexible joints ( flexure bearings) found on automobiles and other machines. They are typically found on steering column shafts that connect the steering wheel to the steering gear input shaft, usually at the stee ...

which works by bending rubberized fabric. The resulting joint is lighter yet is capable of carrying hundreds of kilowatts, with adequate durability for a sports car. Because flexure bearings do not rely on sliding or rolling motions, they do not require

lubrication Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubr ...

. Consequently, they can be employed in abrasive environments and environments hostile to

lubricant A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, ...

s: underwater, in a

vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...

and at elevated temperatures.

References

External links

NASA Tech Brief
*{{Cite report, url=http://www-personal.umich.edu/~awtar/PHD/Diaphragm.pdf, date=24 September 2006, title=Parasitic Error-free Symmetric Diaphragm Flexure, and a set of precision compliant mechanisms based it: Three and Five DOF flexible torque couplings, Five DOF motion stage, single DOF linear/axial bearing, first1=Shorya, last1=Awtar, first2=Alexander H., last2=Slocum, publisher=MIT
Kinematic Models for Design Digital Library (KMODDL)
- Movies and photos of hundreds of working mechanical-systems models at Cornell University. Also includes a
e-book library
of classic texts on mechanical design and engineering. * Weinstein, Warren D., "Flexure-Pivot Bearings", Machine Design, Part 1, June 10, 1965, Part 2, July 8, 1965 - Spring rates, bearing types, single and multi-strip design, material types, hysteresis and fatigue * Weinstein, Warren D., "Microperformance of Metals". Machine Design, September 11, 1969 - Material relaxation and rolamite
The Bal-tec Flexural Encyclopedia
Bearings (mechanical)

See also

References

External links