Motion analysis of Internal Geneva mechanism by using SOLIDWORKS
AIM
To create a internal geneva mechanism with analyse the motion of the model and post processing it.
METHODOLOGY/FLOW OF CONTENT
OBJECTIVE
1) Create from 2D drawing to 3D part in individually and assemble it.
2) Provide the physical parameter for that assembly.
3) Test it the assembly body motion with 10 RPM AND 20 RPM in individually.
4) Plot the contact force between driver and driven wheel with and without precision.
5) Plot the angular velocity of driver wheel at which both 10 and 20 RPM.
6) Plot the angular displacement of driven wheel at which both revolution per minute.
INTRODUCTION
The geneva drive is a gear mechanism that 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 advancing it by one step. The drive wheel also has a circular blocking disc that locks the driven wheel in position between steps. Such a mechanism is used in film projectors, watches and indexing tables among others.
Classification of geneva mechanism
1) External geneva mechanism
In this type of mechanism, the geneva cross is connected with cam drive externally which is the most popular and can withstand higher mechanical stresses. The driver grove lock the the driven wheel pin during dwell. During movement, the driver pin mates with the driven wheel slot.
2) Internal geneva mechanism
In this type of mechanism, the geneva cross and driver wheel pin are connected internally in the closed driven model. The driver and driven wheel rotate in same direction. The ratio of rotation of driven and driver wheel is 1:4 for in our case this is appropriate ratio. Because of, we have only four slot in the driven wheel.
3) Spherical geneva mechanism
In this type of mechanism, the geneva cross is in spherical shape and cam drive are connected in externally, which is extremely are rare. The driver and driven wheel are on perpendicular shafts. The duration of dwell is exactly `180^o` of driver rotation.
Working of geneva mechanism
In the most common arrangement, the driven wheel has four slots and thus advances by one step of 90 degree for each rotation of driver wheel. If the driven wheel has n slots, it advances by `360^o/n` per full rotation of the drive wheel.
Advantages of geneva mechanism
1) Geneva mechanism may be the simplest and least expensive of all intermittent motion mechanisms.
2) They come in a wide variety of sizes, ranging from those used in instruments, to those used in machine tools to index spindle carriers weighing several tons.
3) They have good motion curves characteristics compared to ratchets, but excibit more jerk or instantenous change in acceleration, than better cam systems.
Applications and Uses
1) It is applicable in production industries and in industries for mass production.
2) Modern film projectors may also use an electronically controlled indexing mechanism or stepper, which allow the fast forwarding the film.
3) Geneva wheels having the form of driven wheel were also used in mechanical watches, but not in drive, rather to limit the tension of the spring, such that it would operate only in the range where the elastic force is nearly linear.
4) Indexing tables in assembly lines, tool changers for CNC machines ans so on.
CREATE A MODEL FROM 2D DRAWING TO 3D MODEL
2D PART OF DRIVEN WHEEL 2D PART OF DRIVER WHEEL
We create a three dimensional part in individually by using two dimensional sketch. Most common tools are circle, line and fillet these are used create a two dimensional part in individually with appropriate dimensions. At the stage, we has to make a three dimensional from drawn two dimensional sketch, by using extrude boss base command it help us to make the three dimensional part for both sketches driven wheel and either it's driver wheel.
ANALYTICAL FORMULAUS
Angular velocity`omega`
Angular velocity is the rate of change of the position angle of an object with respect to time.
`omega = (2piN)/60` rad/sec
Where,
N = Number of revolution of driver wheel in our case
Upon 60 has been converting from revolution per minute to revolution per second. In our plot angular velocity is radians per minute.
Angular displacement
Angualr displacement of a body is the angle in radians or degrees through which a point revolves around a centre or line has been rotated in a specified sense about a specified axis. Thus the rotation of a rigid body over a fixed axis is referral to as rotational motion.
Instantenous angular velocity `omega = (d theta)/(d t)`
CREATE A INTERNAL GENEVA MECHANISM DRIVEN WHEEL
Open new file and select the part, create a driven wheel in our solidworks design software with appropriate dimensions. and save it the model with proper name.
CREATE A INTERNAL GENEVA MECHANISM DRIVER WHEEL
Open new file and select the part, create a driver wheel in our solidworks design software with appropriate dimensions. and save it the model with proper name.
ASSEMBLED MODEL OF INTERNAL GENEVA MECHANISM
Import the driver and driven wheel on the assemble file in our solidworks software. First of all, the driven wheel is fixed, so we put float option for unfixing the driven wheel. Driver wheel is mate into the assembly plane of front and mate into concentric circle, in same manner do in driven wheel as well.
ASSIGN THE INPUT PARAMETRES
Case 1
1) To provide power to driver wheel axis at 10 Revolution per minute, clockwise roation.
2) Material for both parts is steel in our case.
3) Moreover, we provide the frames per second is 60 and also calculating the results with and without precision.
Case 2
1) In case 2 we provide power to driver wheel axis 20 RPM instead of 10RPM, clockwise roatation.
2) Material has to be same in both cases.
3) In this case, we provide the frames per second is 120 and also calculating the results with and without precision.
MOTION VIDEO IN BOTH CASES
Motion analysis of internal geneva mechanism at 10 RPM
Youtube video link 1 : https://www.youtube.com/watch?v=HY_5AO_zga4
Motion analysis of internal geneva mechanism at 20 RPM
Youtube video link 2 : https://www.youtube.com/watch?v=p8DIKVFrLR4
POST PROCESSING
Post processing means extracting useful data from that calculating model.
Case 1
Contact force between the driver and driven wheel with precision at 10 RPM
1) Contact force or reaction force it actually a Newton's third law "Every force there is an equal and opposite reaction force". Not only third law, it always obeys the three laws of Newton. To comparing the both plots there is an little variation of reaction of that components.
2) The pin is strike on the driven wheel, that more resist force has producing. After some time the resist force has drop due to first law of newton's.
3) When we enable the precision option, results has more accurrate. Disable the precision option, the results has less accurate compare to previous one.
4) Driver wheel had complete four revolution so that contact force heaps at four times.
Contact force between the driver and driven wheel without precision at 10 RPM
Contact selection location
The driver wheel is rotates clockwise direction so that I can select the bottom face of slot. Actually, pin has been hit on the selected location. The reaction force also replies on that location.
Angular displacement of driven wheel at 10RPM
Ratio of angular displacement of the driven wheel is 1 : 4 that means one revolution of driver wheel is equal to quarter revolution of driven wheel and also function of time.
Angular velocity of driver wheel at 10RPM
We provide constant speed of 10 RPM, the driven wheel have some inertial force on it. From Newton's first law, sometimes the appling force is morethan or equal. That's the reason heaps have appeared.
Case 2
Contact force between driver and driven wheel with precision at 20 RPM
1) In this case, we change the RPM instead of previous RPM. The system has calculating the results in same manner for in this case.
2) Ratio also be same, there is no change in no of slots.
3) The revolution was increased so that heaps also be proprotional.
Contact force between driver and driven wheel without precision at 20 RPM
Angular displacement of driven wheel at 20 RPM
Angular velocity of driver wheel at 20 RPM
Initially, the driven wheel have some amount of inerial force also driver wheel take some time to overcome these inertial forces on the driven wheel.
CONCLUSION
Finally, we done the motion analysis of internal geneva mechanism and also done the post processing.