The Geneva drive or Maltese cross is a

gear A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic ...

mechanism that translates a continuous rotation movement into intermittent rotary motion. The ''rotating drive'' wheel is usually equipped with a

pin A pin is a device used for fastening objects or material together. Pin or PIN may also refer to: Computers and technology * Personal identification number (PIN), to access a secured system ** PIN pad, a PIN entry device * PIN, a former Dutch ...

that reaches into a slot located in the other wheel (''driven wheel'' that advances it by one step at a time. The drive wheel also has an elevated circular blocking disc that "locks" the rotating driven wheel in position between steps.

History

The name, Geneva drive, is derived from the devices earliest application in

mechanical watches A mechanical watch is a watch that uses a clockwork mechanism to measure the passage of time, as opposed to quartz watches which function using the vibration modes of a piezoelectric quartz tuning fork, or radio watches, which are quartz watches ...

, which were popularized in

Geneva , neighboring_municipalities= Carouge, Chêne-Bougeries, Cologny, Lancy, Grand-Saconnex, Pregny-Chambésy, Vernier, Veyrier , website = https://www.geneve.ch/ Geneva ( ; french: Genève ) frp, Genèva ; german: link=no, Genf ; it, Ginevr ...

, being the classical origin of watchmaking industry. The mechanism is frequently used in mechanical

watch A watch is a portable timepiece intended to be carried or worn by a person. It is designed to keep a consistent movement despite the motions caused by the person's activities. A wristwatch is designed to be worn around the wrist, attached b ...

es, since it can be made small and is able to withstand substantial mechanical stress. The ''Geneva drive'' is also called a " Maltese cross mechanism" due to the visual resemblance when the rotating wheel has four spokes. In the most common arrangement of the Geneva drive, the client wheel has four slots and thus advances the drive by one step at a time (each step being 90 degrees) for each full rotation of the master wheel. If the steered wheel has ''n'' slots, it advances by 360°/''n'' per full rotation of the propeller wheel. Because the mechanism needs to be well lubricated, it is often enclosed in an oil capsule.

Uses and applications

One application of the Geneva drive is in film

movie projector A movie projector is an opto-mechanical device for displaying motion picture film by projecting it onto a screen. Most of the optical and mechanical elements, except for the illumination and sound devices, are present in movie cameras. Mod ...

s and movie cameras, where the film is pulled through an exposure gate with periodic starts and stops. The film advances frame by frame, each frame standing still in front of the lens for a portion of the frame cycle (typically at a rate of 24 cycles per second), and rapidly accelerating, advancing, and decelerating during the rest of the cycle. This intermittent motion is implemented by a Geneva drive, which in turn actuates a claw that engages sprocket holes in the film. The Geneva drive also provides a precisely repeatable stopped position, which is critical to minimizing jitter in the successive images. (Modern film projectors may also use an electronically controlled indexing mechanism or

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 ...

, which allows for fast-forwarding the film.) The first uses of the Geneva drive in film projectors date to 1896, with the projectors of

Oskar Messter Oskar Messter (21 November 1866 – 6 December 1943) was a German inventor and film tycoon in the early years of cinema. His firm Messter Film was one of the dominant German producers before the rise of UFA, into which it was ultimately merg ...

and Max Gliewe and the ''Teatrograph'' of

Robert William Paul Robert William Paul (3 October 1869 – 28 March 1943) was an English pioneer of film and scientific instrument maker. He made narrative films as early as April 1895. Those films were shown first in Edison Kinetoscope knockoffs. In 1896 he s ...

. Previous projectors, including

Thomas Armat Thomas J. Armat (October 25, 1866 – September 30, 1948) was an American mechanic and inventor, a pioneer of cinema best known through the co-invention of the Edison Vitascope. Biography Armat studied at the Mechanics Institute in Richmond, Vir ...

's projector, marketed by Edison as the ''Vitascope'', had used a "beater mechanism", invented by

Georges Demenÿ Georges Demenÿ (12 June 1850 in Douai – 26 October 1917 in Paris) was a French inventor, chronophotographer, filmmaker, gymnast and physical fitness enthusiast. Main publications *''L’Éducation physique en Suède'', Paris, Société d' ...

in 1893, to achieve intermittent film transport. Geneva wheels having the form of the driven wheel were also used in mechanical

es, but not in a drive, rather to limit the tension of the

spring Spring(s) may refer to: Common uses * Spring (season) Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of ...

, such that it would operate only in the range where its elastic force is nearly linear. If one of the slots of the driven wheel is occluded, the number of rotations the drive wheel can make is limited. In watches, the "drive" wheel is the one that winds up the spring, and the Geneva wheel with four or five spokes and one closed slot prevents overwinding (and also complete unwinding) of the spring. This so-called Geneva stop or "Geneva stop work" was the invention of 17th or 18th century watchmakers. Other applications of the Geneva drive include the pen change mechanism in plotters, automated sampling devices,

banknote A banknote—also called a bill (North American English), paper money, or simply a note—is a type of negotiable promissory note, made by a bank or other licensed authority, payable to the bearer on demand. Banknotes were originally issued ...

counting machines, and many forms of indexable equipment used in manufacturing (such as the tool changers in

CNC 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 a p ...

machines; the turrets of

turret lathe The turret lathe is a form of metalworking lathe that is used for repetitive production of duplicate parts, which by the nature of their cutting process are usually interchangeable. It evolved from earlier lathes with the addition of the ''turre ...

s, screw machines, and turret drills; some kinds of

indexing head An indexing head, also known as a dividing head or spiral head, is a specialized tool that allows a workpiece to be circularly indexed; that is, easily and precisely rotated to preset angles or circular divisions. Indexing heads are usually use ...

s and

rotary table A rotary table is a precision work positioning device used in metalworking. It enables the operator to drill or cut work at exact intervals around a fixed (usually horizontal or vertical) axis. Some rotary tables allow the use of index plates ...

s; and so on). The

Iron Ring Clock The McMaster Faculty of Engineering is a faculty located at McMaster University in Hamilton, Ontario. The faculty was established in 1958 and was the first engineering program to developed problem-based learning curriculum. It currently has seven ...

uses a Geneva mechanism to provide intermittent motion to one of its rings. A Geneva drive was used to change filters in the

Dawn mission ''Dawn'' is a retired space probe that was launched by NASA in September 2007 with the mission of studying two of the three known protoplanets of the asteroid belt: Vesta and Ceres. In the fulfillment of that mission—the ninth in NASA's Di ...

framing camera used to image the asteroid

4 Vesta Vesta ( minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of . It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, t ...

in 2011. It was selected to ensure that should the mechanism fail at least one filter would be usable.

Internal version

An internal Geneva drive is a variant on the design. The axis of the drive wheel of the internal drive can have a bearing only on one side. The angle by which the drive wheel has to rotate to effect one step rotation of the driven wheel is always smaller than 180° in an external Geneva drive and always greater than 180° in an internal one, where the switch time is therefore greater than the time the driven wheel stands still. Croix malte interne - filled.svg, Internal Geneva drive Internal Geneva wheel ani.gif, Animation showing an internal Geneva drive in operation The external form is the more common, as it can be built smaller and can withstand higher mechanical

stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...

es.

Spherical version

Another variant is the spherical Geneva drive. Croix malte spherique - filled.svg, Spherical Geneva drive

Kinematics

Chronogrammes croix malte 4 branches complet

The figure shows the motion curves for an external four-slot Geneva drive, in arbitrary units. A discontinuity appears in the acceleration when the drive pin enters and leaves the slot, occurring at the instant the rigid bearing surfaces make contact or separate. This generates an "infinite" peak of jerk ( Dirac peak), and therefore vibrations.

References

External links

* . * . * . * – ''Quickermittent''. Modified starwheel for fast pulldown. * {{Citation , type = animation and instructions for building , url = http://www.brickengineer.com/pages/2007/10/07/geneva-mechanism/ , contribution = LEGO Geneva Mechanism , title = Brick engineer , date = Oct 7, 2007 Gears Watches Rotating machines Mechanisms (engineering)