**Testing**

**Testing**

## PUPS4

Part1 - Design a 3D kinematic coupling (for example that could be used as a tool or fixturing holder on your machine)

Please refer to this page for complete description of design and prototyping of a 3-groove kinematic coupling

Part2 - Test Stiffness, Repeatability and Accuracy

Please refer to this page for complete description of design and prototyping of a 3-groove kinematic coupling

Part2 - Test Stiffness, Repeatability and Accuracy

__REPEATABILITY__

To test the repeatability of the 3-groove kinematic coupling I built, I attached a laser pointer on the top plate using tape and pointed it at a graph paper attached to the wall. Coupling is taken apart and placed for five times and the point where laser hits the paper is marked using a pen and its repeatability is measured

Over five cycles, the average distance between each of the dots marked on the paper is 1.2mm and the distance between the laser pointer and the paper attached on the wall is 45mm

__Repeatability:__Over five cycles, the average distance between each of the dots marked on the paper is 1.2mm and the distance between the laser pointer and the paper attached on the wall is 45mm

STIFFNESS |

Next, to measure the stiffness of the kinematic coupling, I placed a book of known dimensions and weight (which is considerable) and repeated the process described above. With known raise in height and taking note of the markings for five repetitions, its stiffness is computed.

Measured thickness of the book is 60mm and measured distance between the two cluster of points with and without the weight of the book is 55mm. Measured weight of the book is 5lb~2.27Kg~22.7N.

Hence the stiffness can be estimated to be 4.5 N/mm.

Measured thickness of the book is 60mm and measured distance between the two cluster of points with and without the weight of the book is 55mm. Measured weight of the book is 5lb~2.27Kg~22.7N.

Hence the stiffness can be estimated to be 4.5 N/mm.

Part3 - Compare tests to predictions

Computations predict very high stiffness of the coupling. The discrepancies are because of the fact that the balls used here are hallow and the spreadsheet assumes solid balls. Given that the thickness of shell for pingpong balls will be considerably lower than the stiffness of a solid ball made from the same material, difference between observed and calculated stiffness of coupling is justified.

If I were to reiterate the design, I would replace the current balls with solid plastic balls and redo the experiments and analysis to find the differences

If I were to reiterate the design, I would replace the current balls with solid plastic balls and redo the experiments and analysis to find the differences