Specialized Mechanisms – GENEVA WHEEL 51026
The Geneva drive or Maltese cross is a gear mechanism that translates a continuous rotation into an intermittent rotary motion. The rotating drive wheel has a pin that reaches into a slot of the driven wheel advancing it by one step. The drive wheel also has a raised circular blocking disc that locks the driven wheel in position between steps.
The name derives from the device’s earliest application in mechanical watches, Switzerland and Geneva being an important center of watchmaking.The Geneva drive is also commonly called a Maltese cross mechanism due to the visual resemblance when the driven wheel has four spokes. They are used in watches and for the main reason of being made small and can withstand mechanical stress.
In the most common arrangement, the driven wheel has four slots and thus advances for each rotation of the drive wheel by one step of 90°. If the driven wheel has n slots, it advances by 360°/n per full rotation of the drive wheel.
DESIGN ALTERNATIVES -Internal Geneva Drive 1
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.
The external form is the more common, as it can be built smaller and can withstand higher mechanical stresses.
The ratio of dwell period to motion period is 1/3. Angle of each rotation of the driven shaft is 90 degrees.
DESIGN ALTERNATIVES – Internal Geneva Drive 2
The ratio of dwell period to motion period is 1/5. Angle of each rotation of the driven shaft is 60 degrees.
DESIGN ALTERNATIVES – Internal Geneva Drive 3
The ratio of dwell period to motion period is 1/3. Angle of each rotation of the driven shaft is 90 degrees.
DETAILS OF GENEVA WHEEL
Download This PDF: 51026_Geneva_Wheel_Document.pdf
DESIGN ALTERNATIVES – Inverted Geneva Mechanism
Inspired by mechanism #169 from 1800 Mechanical Movements, Devices and Appliances by Gardner D. Hiscox.
Republication by Dover Press, 2007. Simulation created in Autodesk Inventor 2012 Professional.
Video Links:
Featured Video – http://youtu.be/-6YArfCFUQw
Internal Geneva Drive 1 – http://youtu.be/w1oT0Zx_xcU
Internal Geneva Drive 2- http://youtu.be/MQP7yNxx3ag
Internal Geneva Drive 3 -http://youtu.be/ReXprJUMqF4
Inverted Geneva Mechanism – http://youtu.be/GeqaONpiI0M
