Internal Geneva Mechanism
Aim:Study of Internal Geneva Mechanism using Solidworks
Introduction
Geneva mechanism is used to convert rotary motion into intermittent rotary motion.Geneva mechanism is widely used for it's ease in design,low cost.There are primarily 3 types of geneva mechanisms
- External Geneva Mechanism
- Internal Geneva Mechanism
- Spherical Geneva Mechanism
Each of the mechanism has its own advantage and disadvantage.
External and internal gennava mechanism are used when drive and driven axis are parallel.On the other hand Spherical Gennava Mechanism is used when axis of drive and driven are perpendicular to each other.
D:Dwell time
n=number of slots
External Gennava is used when dwell time more than 180 degree is requred
Given by the following formula
`D=180°+(360°)/n`
Internal Gennava is used when dwell time is less than 180degree is requred
Given by the following formula
`D=180°-(360°)/n`
Spherical Gennava is used when dwel time of exact 180 degree is required
D =180°
Solidwords Setup for the Internal Gennava Mechanism
Setup for analysis consists of the following steps
- Construction of Drive and Driven
- Assembly of Drive and Driven
- Conduction MBD on the assembly
Construction of Drive and Driven
The following are the drawing of model for study along with their Solidworks model.
Drawing of the Driven Component
Drawing of the Driver Component
Model of Driven Component in SolidWorks
Model of Driver Component in Solidworks
Assembly of Drive and Driven
The assemby should be done in such a way that the DOF of the entire assembly is 1
Thus each component must have only one degree of freedom
As,`F=3(N-1)-2P`
N=2
F=1 if only if P=2
The only freedom to each component as well as the assembly is rotation alng one axis
Clip showing rotation of drive
Clip showing rotation of driven
The next task in assembly was to find the center to center distance between the drive and driven.
The following picture shows the entire assembly drawing in solidworks.
According to following Diagram below .The Centre to centre distance can be analytically calculated
Alpha :-Input angle by Drive
O3 :- Centre of driven
O2 :- Centre of Drive
P :- Centre of Roller Pin
R :- Distance of Roller pin from Centre of Drive
n :- no of slots
Thus O2O3=`(R)/(sin(180/n))`
Conduction MBD on assembly.
Gennava mechanism is used for converting of rotary motion into interidiatery motion.Thus driver is given an clockwise Tourque using motor in Solidworks.
The contact between the Drive and driven is given using Solid contact present in the MBD ribbon.
The clip showing the motion of entire assembly.
Analysis Contraints
Motor speed =10 RPM
Difference between precise and non precise contact
In Precise contact software calculates parameters(Forces,Velocity) using analytical equations whereas,in non Precise contact software take approximations.
The graph shows Contact force wrt Time
Non-Precise Contact
Precise Contact(60 fps)
Graph Consisting of Both Precise and non Precise Contact
In above Graph it is clearly visible there are peak of forces in certain interval of time.The peak in forces are time when the Roller pin gets into the slot .It is clearly visible that there exists a difference between analytical an approximate solutions.
Motor speed= 20RPM
The graph shows Contact force wrt Time
Non-Precise Contact
Precise Contact(120 fps)
Graph representing 20 rpm Precise and Non precise Contact
In above Graph it is clearly visible there are peak of forces in certain interval of time.The peak in forces are time when the Roller pin gets into the slot .It is clearly visible that there exists a difference between analytical an approximate solutions.
Angular Displacement of the driven wheel
The above graph shows the variation in Angular velocity of Driven.It is clearly visible that linear motion is converted to non linear motion.
Driver Wheel Angular Velocity
Since we gave Motor constant velocity the graph is approximately strainght.However it is visible graph is not ideal beacuse Angular velocity is indeed fluctuating to some extent due to resisting torque generated due to engagement between drive and driven
Conclusion
Thus MBD of Internal Geneva Mechanism has been completed