A detent is a mechanical or magnetic means to resist or arrest the movement of a mechanical device. 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 increments. 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, is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can be commanded to move and hold at one of these steps without any posi ...

Mechanics

Arresting movement

Ratchet and pawl

The ratchet-and-

pawl A pawl is a movable lever that engages a fixed component to either prevent movement in one direction or restrain it altogether. As such, it is a type of latch and can also be considered a type of dog. It typically consists of a spring-loaded ...

design arrests movements by employing a small

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

- or

spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of water * Spring (mathematics), a geometric surface in the shape of a h ...

-actuated

lever A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or '' fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is d ...

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

wheel A wheel is a circular component that is intended to rotate on an axle bearing. The wheel is one of the key components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be ...

. The

vertical angle In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the ''vertex'' of the angle. Angles formed by two rays lie in the plane that contains the rays. Angles a ...

of the sides of the notches that face the direction that rotation is desired is generally very

acute Acute may refer to: Science and technology * Acute angle ** Acute triangle ** Acute, a leaf shape in the glossary of leaf morphology * Acute (medicine), a disease that it is of short duration and of recent onset. ** Acute toxicity, the adverse ef ...

(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 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, is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can be commanded to move and hold at one of these steps without any posi ...

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 Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, grinders, routers and 3D printers) by means of a computer. A CNC machine processes ...

(CNC) devices.

Examples

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

game show A game show is a genre of broadcast viewing entertainment (radio, television, internet, stage or other) where contestants compete for a reward. These programs can either be participatory or demonstrative and are typically directed by a host, ...

''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, or more commonly 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 configuration ...

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 (typically 10). * Rotary switches typically employ detents to keep the control shaft properly aligned with the appropriate contact. * Any spring-powered

wind-up toy A wind-up toy is an automaton toy powered by a clockwork motor. Background Automata built for the sake of art, amusement, and simulation have been described since antiquity, in cases such as Heron of Alexandria designing clockwork birds durin ...

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 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 mice (where they can also be called a mouse wheel). It is often made of hard plastic with a rubbery surface, centred around an internal rota ...

s on many

computer mice A computer mouse (plural mice, sometimes mouses) is a hand-held pointing device that detects two-dimensional motion relative to a surface. This motion is typically translated into the motion of a pointer on a display, which allows a smoot ...

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

camera A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with ...

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

References

{{Reflist Mechanisms (engineering)