Internal Geneva Mechanism
Aim:-1. Create 3D models for driver and driven wheels using the given drawings
2. Perform motion analysis by rotating the driver wheel at 10rpm.
3. Obtain the following plots:
a) Contact force (between driving and the driven wheel) as a function of time.
b) Angular Displacement of the driven wheel.
4. Compare the contact forces with and without "Precise contact"
a) Show image for precise contact selection
b) Use 60 Frames per second for 10 rpm and then 120 Frames per second for 20 Rpm
5. Export the results that you get to Excel and make the plots over there
6. Make a plot of the driver wheel's angular velocity and discuss the results.
Theory:-The Geneva mechanism is a gear mechanism in which a rotary motion is converted into intermittent rotary motion. It has a driving and driven gear, where the driving wheel has the rotational motion and the driven wheel undergoes intermittent rotation. The driving wheel is attached to a motor and consist of a pin which transfers the motion to the driven wheel. The driven part has a number of slots provided, which accommodates the pin of the driver to receive the input rotation motion. An internal Geneva mechanism is a variant of this, where the slots on the driven wheel are provided inside its periphery. Common application of this mechanism comes in the automotive industry, mechanical watches, stepper motors, indexing mechanisms, and so on.
Step 1: Creation of 3D Models and Assembly
All the dimensions were used as per the drawings given. For assembling the parts, the following constraints were given:
Driving wheel: The front plane (the plane in which the body was modelled) was made coincident with the front plane of the assembly. The centre axis of the wheel was made coincident with the top and right planes of the assembly, giving it freedom to rotate only along its centre axis.
Driven wheel: The centre axis of the part was made coincident with the right plane of the assembly and the front plane was constrained to a distance of 20mm with the front plane of driving wheel.
Also, the centres of both the wheels were constrained to a distance of 226.27mm, such that the required motion is generated.
Step 2: Motion analysis of the assembly.
The driving wheel was given a constant rotation condition and a solid body contact was defined between the two bodies and the material was assigned as Steel (dry).
Motion analysis of the assembly at 10rpm.
The contact force between the bodies and the angular displacement of the driven wheel was calculated. All the results were exported into excel and the plot were generated.
This plot shows the angular displacement of the driven wheel. From the plot it can be seen that at 10rpm, the driven wheel takes 24 seconds to complete one entire revolution (360 deg).
Analysis of the contact forces with and without precise contacts at 10rpm
Comparison of angular velocities of the bodies at 10rpm and 20rpm
The following figures shows the angular velocities of the driver at 10rpm (60 fps) and 20rpm (120 fps). The first figure under each specification is the one without precise contacts and the second one is with precise contacts. It can be seen that the values remains the same with or without precise contacts. The driver wheel exhibits constant angular velocity because the wheel is rotated at constant speeds and it undergoes a continuous rotary motion. On the other hand, the driven wheel exhibits an angular velocity which exhibits cyclic increase and decrease in the values. This is because it undergoes an intermittent rotary motion. As the driver pin enters the slot, the angular velocity of the driven wheel increases and attains a maximum, then to decrease and fall to zero as the pin exit the slot. It is also to be noted that the angular velocity values are higher at 20rpm.
Driver wheel:
a) 10rpm
b) 20rpm