Internal Geneva Mechanism

AIM – Motion Study of INTERNAL GENEVA MECHANISM using Solidworks Motion

Objectives – Our objective here is to do Motion Study of Internal Geneva Mechanism, while we vary the inputs in Motion Study viz.

• Creating 3D models for driver and driven wheels.
• Performing motion analysis by rotating the driver wheel at 10rpm and 20rpm.
• Obtain the following plots -
• Contact force (between driving and the driven wheel) as a function of time.
• Angular Displacement of the driven wheel.
• Comparing the contact forces with and without "Precise contact"

1 Modelling –

As per drawings given in Challenges, we have created solid MODLES of Geneva Wheels in Solidworks 2019 with the help of basic features in Sketch Tool. We have used very basic tools like,

• Sketch
• Extrude
• Extruded – Cut
• Power Trim etc.

2 Assembly –

In order to perform Motion Study, we have created Assembly consisting of 2 Parts (Driving and Driven Wheels of Geneva Mechanism).

2.1 Part Description –

There are two circular parts

• Driver Wheel
• Driven Wheel

2.2 Assembling the Parts Together –

Basically, we need two parts in such a way that they both can rotate.

In order to do that we have to fix the DOF (Degrees of Freedom) which are not needed, there are in total 6 Types of Degrees of Freedom –

• 3 Translation Motion (Along X, Y and Z-Axis)
• 3 Rotary Motion (Along X, Y and Z-Axis)

Now as we require only one DOF i.e. Rotation along Y-Axis (Considering that the Sketch is Done on Top Plane) so we need every other DOF to be Fixed. So, for that, we have used Mates (Co-Incident and Distance mates)

 

So, in order to do that, the following steps are followed –

Fig. 2.1

1. We need to fix the sliding motion along X and Y and Z axis, we will do so by selecting the axis and use Coincide mate with FRONT and RIGHT plane (This Fixes 2 Sliding Motion and 1 Rotating Motion)
2. Rest, we need to fix the one more Sliding and Rotating motion i.e. along Top plane, consider the figure shown,

Fig. 2.2

3. As shown above, this fixes 1 Sliding and 1 Rotary motion, now we have only one Rotary motion which is Free i.e. along Y-Axis.
4. Doing the same thing except giving coincide mate with Front we have provided Distance of 234.54mm from centre. This will give us the motion we want.

 

Fig 2.3 – Driving Wheel

 

 

Fig 2.4 – Driven Wheel

Fig 2.5 – Assembly

 

As shown above, in the Image the distance mate has shown which is the CD between the two so that the transition is smoother.

3 Motion Study – 

Now in order to perform the Motion Study, we need Solidworks Motion “ENABLED”

Fig 3.1 – Solidworks Motion

Next, we need to provide Motor to driving wheel and set it to 10 Rpm as shown,

Fig 3.2 – Assigning Motor

After this, we need to give contact,

Fig 3.3 – Contact between Driving and Driven Wheel

Next, we need to set the fps and make sure that Precise Contact is “Disabled”

Fig 3.4 – Setting fps

Next, we need to Calculate, and making sure we click “Motion Analysis” from the drop-down menu as shown,

Fig 3.5 – Calculation and Motion Analysis

After that, we need to see the results, for the Tasks given above by clicking on Results icon as shown,

Fig 3.6 – Results icon addressed

Now, we need to select the type of result we want, which is discussed in Conclusion Topic (1.6)

After that, we follow that same procedure with some changes viz,

Motor	10 RPM	10 RPM	20 RPM
FPS	60	60	120
Precise Contact	No	Yes	Yes

Table – 3.1

4 Conclusion –

So, For given tasks, we have performed the following –

1. Contact Force between Driving and Driven Wheel w/o Precise contact.
2. Contact Force between Driving and Driven Wheel w/ Precise contact.
3. Angular Displacement of Driven Wheel.
4. Angular Velocity of Driving Wheel.

Fig – 4.1

Fig – 4.2

As per the figures above, by visually inspecting both graphs, we can see that the magnitude of Contact Forces are different in both cases, it is higher when Precise Contact is enabled, which is because when precise contact is enabled the contact between the two selected surfaces is higher, meaning that the surfaces contacting with each other more as compared to non-precise contact. That’s why the magnitude of the force is higher in Precise Contact which results in more accurate values.

Fig – 4.3

Fig – 4.4

Fig – 4.5

Let us consider Fig – 4.3, the graph goes from 0 – (+180) and (-180) which shows that its rotating fully, the distortion between appears because of the ‘back and forth’ rotation of the wheel while driver spindle leaves the slot of the driven wheel, it is because when spindle leaves the slot the driven wheel is having no restriction of motion, there is no stiffness in the wheel through which it can stay at its place when there is no contact, it tries to retract itself, which results in back and forth motion of the wheel.

Now considering Fig -4.4 and 4.5 we can see that the angular motion stays linear, the reason because of which the Plot in Fig – 4.4,  looks distorted is because the values by which it is plotting are very-very small (5 to 6  points after the decimal) reason of which values along  Y-Axis is 60 what so ever.

The same does not happen with Fig – 4.5 is because for each second it is storing 120 values, which results in a greater number of values which results in more data and eventually very minor change, as we can see that the points on the line is extremely close to each other.

 The List of figures Shown above are attached below. 

 Link to view these Models

 https://drive.google.com/drive/folders/1fHIBm0UeAk-TVFtfup9vkL6VppabA-bZ?usp=sharing