Motion analysis of Internal Geneva Mechanism using Solidworks

Aim:

To create the cad models of the driver and driven wheel and set up the motion analysis for the internal Geneva mechanism using the Solidworks motion.

Objective:

1. To create 3D models for driver and driven wheels using Solidworks.
2. Then Perform motion analysis by rotating the driver wheel at 10rpm and then at 20rpm.
3. Then to Obtain the following plots,
4. Contact force (between driving and the driven wheel) as a function of time with and without "Precise contact"
5. Angular Displacement of the driven wheel.
6. Compare the contact forces with and without "Precise contact"
7. Finally to Export the results to Excel and make the plots over there

Introduction:

The Geneva drive or Maltese cross 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 main 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, where the switch time is therefore greater than the time the driven wheel stands still.

Procedure:

1. Initially open the Solidworks sketch window and set the unit system to ‘MMGS’.
2. The internal Geneva mechanism consists of two parts namely driving wheel and driven wheel
3. Both the parts separately created with proper dimensions

Driven wheel:

1. Two concentric circles of 240 mm and 1120 mm diameter are created.
2. From the smaller circle a slot of length 260 mm and width of 20 mm is made.
3. Using circular sketch pattern 4 slots are created.
4. Trim the unwanted extension and extrude it to a length of 40 mm.
5. Then create fillet of 50mm radius around the center hole and slots.
6. Therefore the driven wheel is created.

Driving wheel:

1. Then next step is to create the driving wheel. For that a circle of 420 mm diameter is created and extruded the circle for 20 mm.
2. Another circle of 40 mm diameter is sketched at an offset of 160 mm and extruded to 40mm which is the pinion.
3. Therefore the driving wheel is created.

Assembly:

1. Finally assemble both the wheels to form the final assembled component.
2. Assemble both the parts using proper mating conditions to form the product
3. The proper assembly is made using the convert entities option in solidworks through which two concentric circles of 240 mm and 1120 mm diameter are created.
4. Then the concentric mate is applied to both the parts. Which allows them to rotate on their own axis.

Motion Analysis:

1. Then the motion analysis is done using the SolidWorks motion.
2. Then the Rotary motor is added to the driving wheel. The rpm is set.
3. Then the Solid body contact is established between the parts.
4. For 10 rpm, 60 frames per second are selected and for 20 rpm, 120 frames per second are selected.
5. Various plots were created for the contact forces with respect to time with and without precise contact and angular displacement for both the speeds of the Component.

Output Plots:

All the results are exported to Excel as said in the challenge and the plots are made in Excel.

1.PLOT FOR THE ROTATION AT 10 RPM:

1.1 Contact force w.r.t time(without precise contact):

1.2 Angular Displacement of the driven wheel:

1.3 Contact force w.r.t time(with precise contact):

2.PLOT FOR THE ROTATION AT 20 RPM:

2.1 Contact force w.r.t time(without precise contact):

2.2 Angular Displacement of the driven wheel:

2.3 Contact force w.r.t time(with precise contact):

3.Image for precise contact selection:

Video link for the motion of internal Geneva mechanism:

https://youtu.be/eBy2KBNoZrA

Conclusion:

Results acquired from precision contact are more accurate than non-precise contact. Due to the movement of driven wheel in slot the contract force is getting to its crest.The maximum peek value is appears when the driving wheel gets in contact with driven wheel.Thus the motion analysis of the internal Geneva mechanism is done and the various results are obtained using the motion study.