Dr. D. Y. Patil Institute Of Engineering, Management & Research, Akurdi, Pune

1. Subject – Theory of Machines - I Sub-subject – kinematic pair Prof. SushantPande Assistant Professor Department of Mechanical Engineering Dr. D. Y. Patil Institute Of Engineering, Management & Research, Akurdi, Pune

2. Kinematic pair The geometrical forms by which two members of a mechanism are joined together, so that the relative motion between these two is consistent are known as pairing elements and the pair so formed is called kinematic pair. Each individual link of a mechanism forms a pairing element. Definition of kinematic pair Fig. Kinematic pair

3. Types of kinematic pairs (i) Based on nature of contact between elements: -Lower Pair -Higher Pair(ii) Based on relative motion between pairing elements: -Sliding Pair -Rolling Pair -Turning Pair/Pin joint/Revolute pair -Screw Pair (or Helical Pair) -Spherical Pair -Cylindrical Pair

4. (iii) Based on the nature of mechanical constraint. -Self Closed Pair -Force Closed Pair

5. (i) Based on nature ofcontact between elements: 1. Lower Pair:-A kinematic pair is said to be a lower pair if the links in the pair have surface or area contact between them. Along with a cylinder, a piston forms a lower pair

6. pin joints, shaft rotating in bush, slider in slider crank mechanism are the example of lower pair. Fig. Lower pairs

7. 2. Higher Pair:A higher pair is a kinematic pair in which the links have point or line contact. Ball bearings, cam and follower are examples of higher pair. Ball Bearings

8. Fig. Higher pairs

9. II. Based on the type of mechanical constraint: 1. Self Closed Pair: A pair is said to be self closed if the links in the pair have direct mechanical contact, even without the application of external force. 2. Force Closed Pair A kinematic pair is said to be force closed if the links in the pair are kept in contact by the application of external forces. A good example of this type of pair is ball and roller bearings.

10. Fig. Closed pair Fig. Force closed pair (cam & follower)

11. III. Based on the type of relative motion between the elements of the pair

12. 1. Sliding Pair:As the name suggests, a sliding pair is a kinematic pair in which each element has sliding contact with respect to the other element. Some good examples of sliding pairs are piston inside a cylinder, spur gear drive and square bar in a square hole Square Bar in a Square Hole – An example of Sliding Pair

13. 2. Rolling Pair:In a rolling pair, one element undergoes rolling motion with respect to the other.

14. When the pairing elements have rolling contact, the pair formed is called rolling pair. Eg. Bearings, Belt and pulley. DOF = 1 Fig. Belt and pulley Fig. Ball bearing

15. 3. Turning Pair:In a turning pair, one link undergoes turning motion relative to the other link. Example is a shaft with collars in a circular hole. Fig. Turning pair

16. 4. Screw pair:A screw pair consists of links that have both turning and sliding motion relative to each other. Bolt and Nut – An Example of Screw Pair

17. When the nature of contact between the elements of a pair is such that one element can turn about the other by screw threads, it is known as screw pair. Eg. Nut and bolt. DOF = 1 Fig. Screw pair

18. 5. Cylindrical Pair:A cylindrical pair is a kinematic pair in which the links undergo both rotational and translational motion relative to one another.Example: A solid cylindrical bar inside a hollow shaft. Fig. Cylindrical pair

19. 6. Spherical Pair:In a spherical pair, a spherical link turns inside a fixed link.A spherical pair has three degrees of freedom. Fig. Ball and socket joint

20. Thank You !!