ANALYSIS OF GENEVA MECHANISM

The Geneva drive or Maltese Cross is a gear mechanism that translates a continous rotation into an intermittant rotary motion. The roating drive has a pin that drives in to the slot of driven wheel advancing it by one step at a time. The driver wheel also has a circular blocking disc in position between steps.

Generally Geneva Mechanism is of two types-

a. Internal Type Geneva Mechanism

b. External Type Geneva Mechanism

c. Spherical Type Geneva Mechanism

a. External Type Geneva Mechanism-

In this type of mechanism, the geneva cross is connected with cam drive externally hich is the most popular and can withstand higher mechanism stresses.

The driver grooves lock the driven wheel pins during dwell. During movement, the driver pin mates with the driven wheel slot.

The image of external type mechanism is shown below-

B. Internal Type Geneva Mechanism-

In this type of mechanism, the geneva cross and the cam drive are connected internally in the closed box.

The driver and the driven wheel rotate in the same direction. The dwell is more than 180 degree of the driver rotation.

The image of internal type mechanism is shown below-

c. Spherical Type Geneva Mechanism-

In this type of mechanism, the Geneva cross is in Spherical shape and the cam drive are connected in externally, which is extremenly rare.

The driver and driven wheel are on perpendicular shafts.The duration of the dwell is exactly 180 degree of driver rotation.

Motion or Working description of Geneva Mechanism-

In the most comman arrangement, the driven wheel has four slots and thus advances by one step of 90 degrees for each rotation of the drive wheel. If the driven wheel has n slots, it advances by 360 degree per full rotation of the drive wheel.

Geneva is also combined with variety of other mechanism, such as four bar linkages, clutch brake combinaions, non circular gears etc. to modify the motion curves and dwell moition ratios obtained from pure Geneva Mechanism.

Here the Geometry is provided in the .STEP file format. Hence by importing the step file with the help of Tools>import FEA or Geometry tool, we get a new dialogue box through which we are able to change different parameters along with very important mesh parameters.

Importing the Geometry keeping the properties and Moment of intertia and mass as it is which is associated to the graphics.

After importing-

For the model, the following parameters are used:
Gravity= -9810 mm/s^2 (Y direction)
Length units: mm
Force Units: Newton (N)

which are default values which are set.

After it is imported into motionview, bodies are assigned to the graphics of the geneva wheel and the driver disc. The geneva wheel body has its COM at (0,111,15) and the driver disc has its COM at (0,0,15).

2 joints are defined:
Driver spindle (Revolute Joint defined at the Driver disc COM)
Table spindle (Revolute Joint defined at the Geneva wheel COM)

1 motion is defined on the driver spindle given by the expression 20*TIME where TIME denotes the total simualtion time.

Here, initial angular velocity is given to the Boss extrude 3 joint which is driver disc body which is 10 rad/sec.

Total DOF of the system:
DOF due to 2 rigid bodies (driver and the geneva wheel)= 2*6= 12
Constraints due to 2 revolute joints 2*5=10
Constraints due to motion element= 1
Total DOF= 12-10-1=1
Thus this model has no redundancy.

Now the model is run and it is ensured that it has no errors before adding in the contact.

3D contact is added further, deactivating edit normal force option and enabling Edit force option and choosing Dynamic option and keeping the values default-

The rest of the contact parameters and the simulation settings are kept as default and the simulation is run.

The animation is shown below-

Angular velocity plot for the analysis-

Angular Velocity on Driven body-

Here, we observe, we get maximum angular velocity in the time range of 3.8 Sec- 4 sec, which is around 39 Rad/sec.

Angular Velocity on Driving body-

Torque Output after analysis-

Torque output on Driven Body-

Torque output on Driving Body-

Contact Force Analysis

Contact Force analysis on Body extrude 1 (Driven Body)

Contact Force analysis on Body extrude 3 (Driving Body)

Overall Analysis overview is shown below-

After Generating report-

We get Contour Penetration depth-

The Session files along with animations and screenshot are attached the google drive, the link to which is given below-

https://drive.google.com/drive/folders/19wJ7nF8RamTP9pCKQBcU3IXUOjOEtAv3?usp=sharing