Indexing gear
Step gears convert a continuous rotary movement into an intermittent rotary movement, i.e. the gear output stands still between the individual steps until the next step begins. Index drives can be implemented with almost any type of gearbox .
A special form is the so-called pilgrim step , in which every step forward is not followed by a real pause, but a short backward movement. Such a gear is particularly important in the manufacture of seamless pipes using the so-called pilgrim step process .
Designs
Step gears can be implemented, among other things, by means of gear gears , gear coupling gears or coupling gears , but also cam gears and special gear designs.
One design of stepper drives is the Geneva cross gear, in which the determining gear part (depending on the form) can take the form of a Geneva cross. It is driven by a roller rotating on a crank. A distinction is made between internal and external Maltese gearboxes, depending on where the role occurs.
Further designs are cylinder cam gears or globoidal cam gears. Both with the cylinder cam gear and the globoidal cam gear, both the law of motion (e.g. modified sinoids, trapezoid or polynomial) and the ratio between switching and holding angles can be varied during construction and determined during production. Cam gears have lower acceleration values and thus lower inertia forces than Geneva cross gears.
One type of gear train is the so-called star gear train , in which the number of steps, step length and pause length per cycle can be varied over a wide range.
Indexing drives based on linkage gears are essentially modifications of linkage ratchet gears .
A typical example of a curve-step transmission is in internal combustion engines, the actuation of the valves from the cam shaft via rocker arms , finger followers or tappets . The up and down movement is interrupted by a pause.
Applications
Maltese cross gears and star gears were mainly used in earlier times for various technical processes. They were used very frequently, especially in textile machines and in film projectors. Due to increasing electronic automation, they are rarely found in such machines these days. They have been almost completely replaced by mechanical cam drives with optimized movement and acceleration or electronically controlled electric motors. Cam index drives in the form of camshafts are now the most common application.
literature
- Kurt Luck, Karl-Heinz Modler: Transmission technology. Analysis Synthesis Optimization, Springer Verlag Wien GmbH, Vienna 1990, ISBN 978-3-7091-3890-8 .
- Johannes Volmer: Transmission technology. Guide, Friedrich Vieweg & Sohn Verlagsgesellschaft, Braunschweig 1978.
Web links
- Disc cam indexer - Taktomat (accessed on May 12, 2016)
- CF3 index drive (accessed May 12, 2016)