Objective :
1. crating the part design of driver and driven part of the geneva mechanism .
2. creating assembly of the geneva mechanism.
3. plot the various aspects like contact force ,angular velocity at diffrent rpm .
Intoduction :
Geneva mechanism one of the most commonly used devices for producing intermittent rotary motion, characterized by alternate periods of motion and rest with no reversal in direction. It is also used for indexing (i.e., rotating a shaft through a prescribed angle).
In the Figure the driver A carries a pin or roller R that fits in the four radial slots in the follower B. Between the slots there are four concave surfaces that fit the surface S on the driver and serve to keep the follower from rotating when they are fully engaged. the pin is entering one of the slots, and, on further rotation of the driver, it will move into the slot and rotate the follower through 90°. After the pin leaves the slot, the driver will rotate through 270° while the follower dwells.thisis the basic operation of geneva mechanism.
Applications:
1. Early motion-picture projectors used Geneva mechanisms to give the film a quick advance while the shutter was closed, followed by a dwell period with the shutter open.
2. Geneva drive include the pen change mechanism in plotters, automated sampling devices, banknote counting machines, and many forms of indexable equipment used in manufacturing (such as the tool changers in CNC machines; the turrets of turret lathe and turret drills;and so on).
Part modeling :
Driving part :
so from the above drawing we can make the driving part of the geneva mechanism as per the required dimensions . the model view will be as below ,
Driven part :
From above drawing we can draw the driven part of the geneva mechanism and the following is the model view of the driven part ,
Assembly :
so here we can see the assembly view of the geneva assembly here we turn on the temporary axis of the parts which will helps us to create the assembly the procedure is given as below for the assembly ,
1. first we import both parts .
2. now the first part in assembly is by default fix so we have to float that part which we can do by the right mouse key and click on the float to free the first part .
3. now driving parts front plane and assembly front plane coincident
4. now same for right plane
5. now btoh for parts front plane should have distance mate of 10 mm and should be parallal .
6. both parts should have center distance of 111.02 mm .
above are the steps for the assembly operation for the geneva mechanism .
Motion Analysis :
now to set up the motion analysis we use the foloowing steps ,
1. we provide the motor (constant RPM) to the driver axis as shown by red arrow which shows the direction of the rotation .
2. then we provide the contact force between the driver and driving part as follows,
now our set up is almost set now we have to start the study and it will show the animation and after compliting the study we can get the various plots regarding contact force and angular velocity and angular acceleration , here we have set the frames to 120 and we have use precise contact in setting .
Results:
1. plot of contact force between face of driven slot and the driving pin.
here we can see that there is spike in force which is cause of jerk when the contiues moving pin is inserted into slot there will be higher jerk which increase the reaction contact force between slot and pin thats why at pin entry into slot there will be higher force value shows.
2. angular velocity of driving pin
below is the graph for the angular velocity which is constant line which correct because we provide the constant RPM to the driving part hence it is constant value is justified that our set up analysis is ok.
3. Angular velocity of the slotted driven part .
here we can see that velocity is intermittent means our slotted disc which is driven mechanism is rotated at intermittent level which is also justifiablw whixh is basically the principal of GENEVA mechanism which convert our continuous rotary motion into intermittent motion .
here our max velocity of driven part is 891 rad/sec . and for 90 degree it has velocity and then for other 270 degrees it has no angular velocity .
Animation link :
https://drive.google.com/file/d/1CHW_UZghQ-S1PYJn2JIJob9I2HXEAvv0/view?usp=sharing