Internal Geneva Mechanism
Aim : -To Create 3D models of the internal Geneva mechanism and perform motion analysis.
Genava mechanism : - The Geneva drive is a gear mechanism that translates a continuous rotation movement into intermittent rotary motion.The rotating drive wheel is usually equipped with a pin 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.
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
2D CAD drawings to create the 3D model of the internal Geneva mechanism
Steps :-
- Open new part file and form a sketch of driven wheel in front plane and then extrude it to 40mm and then save it as driven wheel
- Open new part file and from a sketch a circle of diameter 420 then extrude it to 20mm then on the top face of extruded surface form a circle of diameter 40 at a distance of 160mm from center and then extruded it to 40mm then save it as driving wheel
- Open New Assembly file and insert both the driving wheel and driven wheel then right click on first added file and select float .
- Select front plane of driven wheel and coinside it with front plane of assembly then coinside the axis of wheel to top and right plane so that wheel and rotate only.
- Calculate the distance between two wheel by making the position of driving wheel in driven wheel sketch
- Select back plane of driven wheel and coinsie it with fornt plane of driving wheel make a centre distance of 226.27mm between two wheel and the coinside driving wheel with top or right plane.
- For motion study go to motion study enable solidworks motion and select motion analysis.
- Add a motor to driving and wheel give rpm of 10 or 20 .
- Add solid body conact as dry steel for both the wheels.
Driving wheel at 10rpm
Animation
Plot of angular displacement of driven wheel vs time
The driven wheel goes from -50 degree to - 180 degree and then from 180 degree to 50 degrees
Plot of contact force without precise contact vs time.
Contact force is negligible except at the time when pin of driving wheel is entering the slot of driven wheel
Plot of contact force with precise contact vs time
Using the precise contact we can get the accurate result but the calculation time is increased and the contact force is high
Plot of driver wheel's angular velocity vs time
Angular velocity of driving wheel is constant at 60deg/sec
Driving wheel at 20rpm
Animation
Plot of angular displacement of driven wheel vs time
The driven wheel complete its one rotation from 180 degrees to -180 degrees in 12 sec
Plot of contact force without precise contact vs time
Contact force is negligible except at the time when pin of driving wheel is entering the slot of driven wheel
Plot of contact force with precise contact vs time
Using the precise contact we can get the accurate result but the calculation time is increased and gives high value of contact forces
Plot of driver wheel's angular velocity vs time
Angular velocity of driving wheel is constant at 120deg/sec
Precise contact selection
- click on motion study properties
- set frames per second (120 for 20rpm and 60 for 10rpm) and check precise contact option
Result
By using the precise contact accurate result is obtained with high contact force but it will increase calculation time and make study low