A detent is a mechanical or magnetic means to resist or arrest the movement of a

mechanical device A machine is a physical system that uses power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromolec ...

. Such a device can be anything ranging from a simple metal pin to a machine. The term is also used for the method involved. Magnetic detents are most often used to divide a shaft rotation into discrete

increment Increment or incremental may refer to: *Incrementalism, a theory (also used in politics as a synonym for gradualism) * Increment and decrement operators, the operators ++ and -- in computer programming * Incremental computing * Incremental backup ...

s. Magnetic detents are inherent in some types of electric motors, most often

stepper motor A stepper motor, also known as step motor or stepping motor,Clarence W. de Silva. Mechatronics: An Integrated Approach (2005). CRC Press. p. 675. "The terms ''stepper motor'', ''stepping motor'', and ''step motor'' are synonymous and are often u ...

Mechanics

Arresting movement

Ratchet and pawl

The ratchet-and- pawl design arrests movements by employing a small

gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

- or spring-actuated

lever A lever is a simple machine consisting of a beam (structure), beam or rigid rod pivoted at a fixed hinge, or '':wikt:fulcrum, fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, l ...

paired with a notched wheel. The lever is mounted on a pivot point in proximity to the

wheel A wheel is a rotating component (typically circular in shape) that is intended to turn on an axle Bearing (mechanical), bearing. The wheel is one of the key components of the wheel and axle which is one of the Simple machine, six simple machin ...

. The vertical angle of the sides of the notches that face the direction of rotation desired is generally very acute (45 degrees or less), so that as the wheel rotates in that direction, the end of the lever is easily lifted or pushed out and over the top of a notch. Following this, the lever drops into the next notch and the next et cetera as the wheel or shaft continues to spin. The angle of the backside of the notch is severe (usually 90 degrees or greater to the end of the lever) so that the lever cannot be pushed up or out of the notch if wheel attempts to turn in the opposite direction. The lever is jammed between the back of the notch and its pivot point, stopping movement in that direction against any force that the materials used can withstand. The wheel has little resistance moving in the direction desired, other than that required to lift or push the lever over the next notch.

Resisting movement

To resist movement (or when creating incremental steps), methods are employed which include a spring-loaded ball detent that locates in small incremental depressions, or a piece of

spring steel Spring steel is a name given to a wide range of steels used in the manufacture of different products, including swords, saw blades, springs and many more. These steels are generally low-alloy manganese, medium-carbon steel or high-carbon stee ...

that snaps into position on flat surfaces or shallow notches milled into the shaft or wheel.

Motor detents

Stepper motor A stepper motor, also known as step motor or stepping motor,Clarence W. de Silva. Mechatronics: An Integrated Approach (2005). CRC Press. p. 675. "The terms ''stepper motor'', ''stepping motor'', and ''step motor'' are synonymous and are often u ...

s rely on magnetic detents to retain step location when winding power is removed. They are well suited to be used in printers and

numerical control Computer numerical control (CNC) or CNC machining is the automated control of machine tools by a computer. It is an evolution of numerical control (NC), where machine tools are directly managed by data storage media such as punched cards or ...

(CNC) devices.

Examples

A well-known example of a detent can be seen on the popular

game show A game show (or gameshow) is a genre of broadcast viewing entertainment where contestants compete in a game for rewards. The shows are typically directed by a game show host, host, who explains the rules of the program as well as commentating a ...

''Wheel of Fortune'', which employs rubber flippers to help disambiguate on which wedge the wheel has stopped after being spun by a contestant. Other common examples include: * A balance control on a piece of

stereo Stereophonic sound, commonly shortened to stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configurat ...

equipment which seems to "click" or "snap" into the center position of its rotation, indicating the point where the volumes of the left and right channels are equal or "balanced", or volume controls with a separate detent to match each of the digits on the

control knob {{more citations needed, date=January 2017 A control knob is a rotary device used to provide manual input adjustments to a mechanical/ electrical system when grasped and turned by a human operator, so that differing extent of knob rotation corres ...

(typically 10). * Rotary switches typically employ detents to keep the control shaft properly aligned with the appropriate contact. * Any spring-powered wind-up toy employs one, in order to disallow unwinding of the spring. * The ratchet wrench, which is employed to intentionally use force against the detent and comes in an increasing variety of types. It was designed to allow one to keep the wrench engaged with the bolt or nut which it is turning, in an area where the swing arc of the wrench is limited, while being able to continue to turn it in one direction by simply pulling the handle back and letting the detent reposition itself. The repositioning allows the wrench to be forcibly turned again. * The

scroll wheel A scroll wheel is a wheel used for scrolling. The term usually refers to such wheels found on computer mouse, computer mice (where they can also be called a mouse wheel). It is often made of hard plastic with a rubbery surface, centred around a ...

s on many

computer mice A computer mouse (plural mice; also mouses) is a hand-held pointing device that detects Plane (mathematics), two-dimensional motion relative to a surface. This motion is typically translated into the motion of the Cursor (user interface)#Po ...

employ detents to divide scrolling into discrete steps. * The shutter button on many

camera A camera is an instrument used to capture and store images and videos, either digitally via an electronic image sensor, or chemically via a light-sensitive material such as photographic film. As a pivotal technology in the fields of photograp ...

s has a detent to selectively activate autofocusing and exposure calculation. Further pressure on the button then passes the detent and activates the shutter. * Many

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

have detents on the

thrust lever Thrust levers or throttle levers are found in the cockpit of aircraft, and are used by the Pilot in command, pilot, copilot, flight engineer, or autopilot to control the thrust output of the aircraft's aircraft engine, engines, by controlling th ...

for pre-set thrust values e.g. climb or

reverse thrust Reverse or reversing may refer to: Arts and media *Reverse (Eldritch album), ''Reverse'' (Eldritch album), 2001 *Reverse (2009 film), ''Reverse'' (2009 film), a Polish comedy-drama film *Reverse (2019 film), ''Reverse'' (2019 film), an Iranian cr ...

References

{{Reflist Mechanisms (engineering)