cazalea
[Seiko Moderator]
17077
Geneva drive or also known as Maltese Cross Drive
The name, Geneva drive, is derived from the device's earliest application in mechanical watches, which were popularized in Geneva, being the classical origin of watchmaking industry.
The Geneva drive is also called a "Maltese cross mechanism" due to the visual resemblance when the rotating wheel has four spokes. These mechanisms are frequently used in mechanical watches.
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 6 slots, it advances by 360°/6=60° per full rotation of the propeller wheel.
Geneva wheels having the form of the driven wheel were also used in mechanical watches, but not in a drive, rather to limit the tension of the mainspring, so it would not be overwound, or released too far. If one of the slots of the driven wheel is blocked, 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 counting machines, and many forms of indexable equipment used in manufacturing (such as the tool changers in CNC machines; the turrets of turret lathes, screw machines, and turret drills; some kinds of indexing heads and rotary tables; and so on). The Iron Ring Clock uses a Geneva mechanism to provide intermittent motion to one of its rings.
One application of the Geneva drive is in film movie projectors 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, which allows for fast-forwarding the film.) The first uses of the Geneva drive in film projectors go back to 1896 to the projectors of Oskar Messter and Max Gliewe and the Teatrograph of Robert William Paul. Previous projectors, including Thomas Armat's projector, marketed by Edison as the Vitascope, had used a "beater mechanism", invented by Georges Demenÿ in 1893, to achieve intermittent film transport.
=====
Cazalea
cool....i didn't know about such drives...
is it a concept from a watch maker ? thanks for sharing. Best, mahesh.,
Geneva drive or also known as Maltese Cross Drive
The name, Geneva drive, is derived from the device's earliest application in mechanical watches, which were popularized in Geneva, being the classical origin of watchmaking industry. The Geneva drive is also called a "Maltese cross mechanism" due to the v...
I think monsieur Ballouard
Likes those Geneva crosses a lot... The Upside down uses such mechanism to precisely rotate the hour markers when needed ...
