MULTI-BODY DYNAMICS SIMULATION OF INTERNAL GENEVA MECHANISM IN SOLIDWORKS

AIM: MULTI-BODY DYNAMICS SIMULATION OF INTERNAL GENEVA MECHANISM IN SOLIDWORKS.

THEORY:

Geneva mechanism is the mechanism through which continuous rotation motion is converted into intermittent rotation motion. In this, the driver wheel rotates continuously and the driven wheel has rotation in regular intervals not continuously.

The driver wheel is equipped with a pin that goes into the slot created in the driven wheel so that it advances a step at a time.

The Geneva drive has two versions: External Geneva Mechanism and Internal Geneva Mechanism.

EXTERNAL GENEVA MECHANISM:

INTERNAL GENEVA MECHANISM:

OBJECTIVE:

• To obtain contact force between driver and driven wheel for rpm of 10 and 20.
• Compare results with and without precision contact.
• To plot angular displacement and angular velocity.

3-D MODELLING OF GENEVA COMPONENTS

• First, the sketch of the driven wheel cross-section was created.
• A slot was created in the driven wheel as per the dimensions specified.
• The slot allows the intermittent motion of the driven wheel on the rotation of driver wheel.
• The sketch was finally extruded to make it a 3-D part.
• Similarly, a sketch of driver wheel created as per dimensions specified and then extruded to make the 3-D part.
• A pin was created on the drive wheel that goes in the slot in the driven wheel to make it rotate in regular intervals.

DRIVEN WHEEL

DRIVER WHEEL

ASSEMBLY

• Both the created parts were taken into SolidWorks assembly.
• All the required constraints (mate) were applied to fix the motion of the mechanism.
• We need to make sure that the driven wheel only rotates about its axis when the pin of the driver wheel goes inside the slot.
• To restrict the translation movement of the driver wheel, centre to centre distance between the driver and driven wheel fixed to 225.

MOTION ANALYSIS:

• Now after creating the assembly, we move to motion analysis.
• To set up the motion analysis, go to SolidWorks MBD add on and select motion analysis.
• In motion analysis study, set up the motor of 10 rpm on the centre axis of driver wheel.
• Then, go to contact selection, select the contact surfaces and apply material as dry steel.
• Under the setting icon, set the frames per second to be 60 for 10 rpm case study.
• Set the time of the motion to 20 seconds and calculate the motion.
• Export the results of contact force, angular displacement and angular velocity to excel and plot graphs.
• Repeat the steps by setting precision contact under the setting icon.
• Similarly, perform the motion study for rpm of 20 with frame per sec as 120.
• Total of 4 study to be performed, results of all 4 studies are shown below.

1. At RPM=10 and with precision Contact

CONTACT FORCE: (between driver and driven wheel)

Angular Displacement of the driven wheel

Angular velocity of driver wheel

2. At RPM=10 and without precision Contact

CONTACT FORCE: (between driver and driven wheel)

Angular Displacement of driven wheel

Angular velocity of driver wheel

3. At RPM=20 and without precision Contact

CONTACT FORCE: (between driver and driven wheel)

Angular Displacement of driven wheel

Angular velocity of driver wheel

4. At RPM=20 and with precision Contact

CONTACT FORCE: (between driver and driven wheel)

Angular Displacement of driven wheel

Angular velocity of driver wheel

OBSERVATION :

Sn. no	Motion Type	Max. Contact force (N)
1	Rpm = 10 (without precision contact)	870
2	Rpm = 10 (with precision contact)	1013
3	Rpm = 20 (without precision contact)	1431
4	Rpm = 20 (with precision contact)	2258

Explanation of plots:

• As we can see that at rpm of 20 the contact force acting between driver and the driven wheel is more than rpm of 10. This is because of an increase in angular velocity of driver wheel which imparts more momentum to the driven wheel on contact, therefore the contact force increased.
• By applying precision contact, we can see that the value of contact force increases in both cases (rpm=10 and 20). This is because the contact accuracy increases on with precision contact and we get a better solution of the governing equation of the motion analysis.
• In angular displacement plot of the driven wheel, we can observe that for some time the angular displacement remains constant with time on regular intervals. This id because of the intermittent motion of the driven wheel.

ANIMATION: https://youtu.be/V0cnIDkNunc

CAD MODEL OF PARTS AND ASSEMBLY: https://drive.google.com/drive/folders/1sSiBRfghMEd4I_veoCXajZb862if7-S3?usp=sharing

CONCLUSION:

The motion analysis of the Geneva mechanism gives us important results. By observing the contact forces, we can choose the optimum value of rpm and also design the components of the mechanism according to that. It also gives us validation that our mechanism is working correctly. We can monitor the angular displacement of the driven wheel to accomplish the target value.