Internal Geneva Mechanism
MOTION SIMULATION OF INTERNAL GENEVA MECHANISM
AIM: Use the following 2D CAD drawings to create the 3D model of the internal Geneva mechanism.
Objective:
1) prepare 3-D model driver and driven part of internal Geneva mechanism.
2) create the assembly of a Geneva mechanism.
3) simulation of the Geneva mechanism at 10 and 20 RPM
4) compare the graph for the precise contact and non-precise contact force.
5) compare the graph of the angular velocity of the driver and driven at 10 and 20 RPM
6) get the graph of angular displacement.
THEORY:
The Geneva drive is also commonly called a Maltese cross mechanism. The Geneva mechanism translates a continuous rotation into an intermittent rotary motion. The rotating drive wheel has a pin that reaches into a slot of the driven wheel. The drive wheel also has a raised circular blocking disc that locks the driven wheel in position between steps.
There are three basic types of Geneva motion mechanisms namely external, internal and spherical. The spherical Geneva mechanism is very rarely used. In the simplest form, the driven wheel has four slots and hence for each rotation of the drive wheel it advances by one step of 90°. If the driven wheel has n slots, it advances by 360°/n per full rotation of the drive wheel.
In an internal Geneva drive the axis of the drive wheel of the internal drive is supported on only 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 is always greater than 180° in an internal one. The external form is the more common, as it can be built smaller and can withstand higher mechanical stresses.
3-D CAD MODEL
DRIVER WHEEL
DRIVEN WHEEL
ASSEMBLY
PLOTS
Condition-1 - AT 10 RPM and 60 FPS
1. CONTACT FORCES WITHOUT PRECISE CONTACT
2. CONTACT FORCES WITH PRECISE CONTACT
3. ANGULAR DISPLACEMENT OF DRIVEN WHEEL
4. ANGULAR VELOCITY OF DRIVER WHEEL
CONDITION-2 - AT 20 RPM AND 120 FPS
1. CONTACT FORCES WITHOUT PRECISE CONTACT
2. CONTACT FORCES WITH PRECISE CONTACT
3. ANGULAR DISPLACEMENT OF DRIVEN WHEEL
4. ANGULAR VELOCITY OF DRIVER WHEEL
IMAGE FOR PRECISE CONTACT SELECTION
EXPLANATION OF RESULTS
1. CONTACT FORCES WITH AND WITHOUT PRECISE CONTACT
About the contact force graph where we got a peak in the graph at a different point because when the pin of driver moves inside the driven member slot there some clash occurs in between the driver and driven. comparatively, we have a higher reaction force in the 20 RPM rotation speed. But in the same force decreases simultaneously. Whereas in the 10 RPM rotation speed from the starting to end our force is increasing. In the precise contact I got the less fluctuation and points were near to each other and accuracy of the result is higher.
When the driver tries to enter in the slot of the driven wheel it faces a jerk as the entry is not smooth therefore,we can see also from the plot that at the entry to the slot gives rise to a suddent increase in the contact force which decreases as the driver enters into the slot. We can also see from the contact force plots of the 2 RPM's that as we increase the rotation of the driver the jerk force/contact force at the entry also increases and then it drastically decreases.
2. ANGULAR DISPLACEMENT OF DRIVEN WHEEL
The angular displacement of the driver and the driven member in the graph of 10 RPM and at 20 RPM, we can see a clear difference that at the higher RPM we get the higher angular displacement.In the 20 RPM graph, we have lines nearer to each other than the 10 RPM graph.
3.ANGULAR VELOCITY OF DRIVER WHEEL
The angular velocity plot reveals that at first, there is a jerk felt by the driven wheel and we see peak in the angular velocity plot and then when it enters the slot there is an acceleration in the driven wheel but as the motion progresses there is reduction in the velocity and hence retardation occurs.The maximum velocity is at the point where the pin of the driver reaches the bottom point of the driven wheel.
The angular velocity of the driven wheel also increases if we increase the rotation of the driver which is seen from the plot.
RESULT:
From the above simulation we study and analysis the motion of the internal geneva wheel and graph are plotted from different condition . we can also note that reaction force increases at time of contact of shaft and slot and thus decreases gradually and displacement takes place faster with increase in speed . The precises contact can be used for approximate results . All CAD models are also attached.