Internal Geneva Mechanism
Aim:- Multi body dynamics analysis of internal Geneva mechanism.
Introduction:- In this project, I have done motion analysis of internal Geneva Mechanism.
Theory:- The Geneva drive or Maltese cross is a gear mechanism that translates a continuous rotaion movement into intermittent rotary motion. 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.
Application:
- 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.
- Other applications of the Geneva drive include the pen change mechanism in plotters, automated sampling devices, banknote counting machines, and many forms of inaxable equipment used in manufacturing (such as the tool changers in CNC machines; the turrets of turret lathe, screw machine, and turret drills; some kinds of indexing hrad and rotary table and so on). The iron ring clock uses a Geneva mechanism to provide intermittent motion to one of its rings.
Motion study setup:- In internal Geneva mechanism, there is a driver wheel which rotates at 10RPM. Driven wheel rotates after particuler interval of time. There is a physical contact between driver and driven wheel.
Constraints for Driver wheel:
1. Axis of rotation in Right plane of assmbly.
2. Axis of rotation in Top plane of assmbly.
3. Front plane of driver wheel part coincides with front plane of assembly.
Constraints for Driven wheel:
1. Front plane of part distance mate with front plane of assmebly.
2. Loctaion of Axis of rotation is calculated by formula.
Animation:-
Plots And Results:-
Plots are drawn on various conditions:
Condition1
Speed of driver wheel 10RPM
Frames per Second 60
Precise contact is considered
Contact force between driving and the driven wheel as a function of time.
Angular Displacement of the driven wheel:
Condition2
Speed of driver wheel 10RPM
Frames per Second 60
Precise contact not considered
Contact force between driving and the driven wheel as a function of time.
Angular Displacement of the driven wheel:
Selecting the option precise contact:-
Condition3
Speed of driver wheel 20RPM
Frames per Second 120
Precise contact is considered
Contact force between driving and the driven wheel as a function of time.
Angular Displacement of the driven wheel:
Condition4
Speed of driver wheel 20RPM
Frames per Second 120
Precise contact not considered
Contact force between driving and the driven wheel as a function of time.
Angular Displacement of the driven wheel:
Results:- From the above simulation we study and analysis the motion of the internal geneva wheel and graph are plotted from different condition . we can also note that reaction force increases at time of contact of shaft and slot and thus decreases gradually and displacement takes place faster with increase in speed . The precises contact can be used for approximate results . This mechanism has a wider range of application as mentioned above.