Internal Geneva Mechanism

“Motion Analysis of Internal Geneva Mechanism Using Solidworks”.

1. AIM: TO ANALYSE THE MOTION ANALYSIS OF INTERNAL GENEVA MECHANISM USING SOLIDWORKS.

2. OVERVIEW:

The Geneva drive or Maltese cross is a gear mechanism that translates a continuous rotation movement into intermittent rotary motion. The difference between Geneva Drive mechanisms and other gears is that Geneva Drive mechanisms have unusual teeth. Unlike in typical gears, the interaction between the part being driven and the part doing the driving is not continuous and the resultant motion is intermittent. Geneva Drives work by having the driving part, or wheel, interlocking with the driven part intermittently. The number of spokes that the driven part has and the speed with which the driving part rotates determines the frequency and distance of travel. There is an elevated segment on the driving wheel which keeps the driven part in position till the next revolution is complete. The external Geneva Drive is by far the most common type, although there are other variations possible in the design. The external drive can be built to withstand higher levels of stress and are generally more robust and sturdy than other variants. The Internal Geneva Drive has the driving part below the driven wheel, with the driving part often being much smaller than the driven wheel. 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.

Fig 1. External Geneva Mechanism

Fig 2. Internal Geneva Mechanism

3. OBJECTIVE:

• To create 3D models for driver and driven wheels.
• Perform motion analysis by rotating the driver wheel at 10rpm.
• Obtain the following plots:
• Contact force (between driving and the driven wheel) as a function of time.
• Angular Displacement of the driven wheel.
• Compare the contact forces with and without "Precise contact."
• Showing image for precise contact selection.
• Export the results that we get to Excel and make the plots over there.

4. Procedure:

To do motion analysis of internal Geneva mechanism first we need to design 3D parts of the Geneva mechanism. Hence, to do that we are going to design individual part in Solidworks i.e first part is the driving wheel and the second part is a driven wheel based on the following 2D drawing.

Fig 3. 2D Drawing of Driver Wheel

Fig 4. 2D Drawing of Driven Wheel

To do part design, open Solidworks software > choose a new option > choose a part design option.[Note:before designing a part we need to verify our unit system which is as MMGS (i.e Millimeter, Gram, Second).

• Driving Wheel:

We are going to design our first 2D drawing of Driving Wheel. The procedure of making the 2D drawing of Driving Wheel is as follows:

• First select the front plane and choose the option for sketching.
• Draw a circle at Axis with 420 mm of diameter.
• After that similarly draw a small circle with 40 mm of diameter at a distance of 160 mm from the centre.
• After completing 2D Drawing we are going to use the Extrude option to make the 2D Drawing into 3D.

At the last step extrude the larger circle with 20 mm and smaller circle with 40 mm to get the final result.

The final result of Driving Wheel is as shown below.

Fig 5. Driving Wheel

• Driven Wheel:

Now we are going to design our Driven Wheel. The procedure of making the driven wheel is as follows:

• First choose the front plane and draw three circle with diameter of 1120 mm, 1040 mm and 120 mm respectively(make sure that 1040 mm diameter circle should be construction circle).
• After that we are going to draw x and y axis(Should be construction line) as a reference to draw the slot in the driven wheel.
• Then by using offset with 20 mm we are going to make four slots.
• There after we are going to make fillet with 50 mm radius in the inner circle which has radius of 120 mm.
• At last we are going to extrude the design with 40 mm.

The Final result of Driven Wheel is as shown below.

Fig 6. Driven Wheel

5. Assembly Design:

To do the motion analysis at first we have to assemble of Driving and Driven Wheel. The Process of the assembly design is as follows:

• At first we have to import our driving wheel and make it float so that it can move.
• Then we have to go for mate option.
• After that we have to mate the front plane of the assembly with the front plane of the driving wheel.
• Next we have to enable the temporary axis visible so that we can see the centre axis of the driving wheel.
• Next we have to mate the centre axis of the driving wheel with the right plane of the assembly and also with top plane of the assembly. Now we can see that our driving wheel is fully constraint and it can do circular motion at its own axis.
• Now we have to import our Driven Part. Next we have to constraint our driven wheel also.
• After that we have to mate the centre axis of the driven wheel with the right plane of the assembly.
• Now we have to mate the front plane of the assembly with the front plane of the driven wheel.
• At last we have to do the distance mate between the centre axis of driving wheel and driven wheel. Now we can see that the driven mechanism is also fully constraint and it can do only circular motion at its axis.
  

6. Simulation and analysis:

The following process of the motion analysis of internal Geneva mechanism is as follows:

• To do the motion analysis first we have to do choose the solidworks motion .
• Next we have to choose the motor and place it at the axis of driving wheel and set the rpm at 10.
• Next we have to do the contact between driving wheel and driven wheel and make them as same material.
• Next we put a value 60 frame per second to do the motion analysis at 10 RPM with 60 fps.

After doing the motion analysis at 10 RPM we will change the value at 20 RPM and also 120 frame per second and will do the motion analysis again.

• Analysis at 10 RPM:

Contact Force:-

The plot of contact force between driving wheel and driven wheel is given below:

Angular displacement of driven wheel:-

The plot of angular displacement of driven wheel is given below:

Contact force with precise contact:-

The plot of contact force between driving wheel and driven wheel with precise contact is given below:

• Analysis at 20 RPM:

Contact Force:-

The plot of contact force between driving wheel and driven wheel is given below:

Angular displacement of driven wheel:-

The plot of angular displacement of driven wheel is given below:

Contact force with precise contact:-

The plot of contact force between driving wheel and driven wheel with precise contact is given below:

• Angular velocity of Driver wheel at 20 RPM:-

The plot of Angular velocity of Driving wheel is given below:

• Surface selection for contact force:

The surface selection for conatct force of motion analysis of internal geneva mechanism is shown below:

• Conclusion:

The motion analysis of internal geneva mechanism has performed and also we can see that to get the accurate results of motion analysis we have to do the exact calculation of the distance of centre axis between driving wheel and driven wheel.

Reference:

https://en.wikipedia.org/wiki/Geneva_drive