Lecture - 3 (Kinematics pairs)

KINEMATIC PAIRS
any connection between two links is always known as joint or a pair but this pair will only be a kinematic pair when the relative motion between the links is a constrained motion.
Classification of kinematic pairs
1. According to the type of relative motion

  • TURNING PAIR - relative motion between two links is pure turning forms a turning pair. these pairs are also called revolute pair or pin joint pair
  • SLIDING PAIR - Relative motion between two links is pure sliding forms a sliding pair. These pairs are also called as prizmatic pair.
  • ROLLING PAIR - Relative motion between two links is pure rolling forms a rolling pair. Pure rolling means rolling without slipping. 
      In figure a ball is rolling over the ground, here we see two motion that's pure rolling and translational motion but still it is a kinematic pair because translational motion is dependent motion, it depends on rotational motion. So we have only one independent motion and that's rotational.

In below figure of a ball bearing, inner race ( link 1 ) and ball ( link 2 ) forms a rolling pair. Similarly ball ( link 2 ) and outer race  ( link 3 ) forms a rolling pair. But inner race ( link 1 ) and outer race ( link 3 ) of bearing forms a turning pair

  • SCREW PAIR - relative motion over the threads forms a screw pair. Example is Nut and bolt
  • SPHERICAL PAIR - when relative motion between two links is 3-dimensional rotation than it forms a spherical pair. For example, spherical pair is used in side mirror of cars & bikes for adjustment. 
2. According to type of contact
  • LOWER PAIR - when there is surface contact between two links then its called lower pair.
  • HIGHER PAIR - when there is a point or line contact between two links then its called as higher pair
In below figure of cam and follower, the contact between fixed link (consider as link 1) and follower (consider as link 2) forms a lower pair. Contact between fixed link (link1) and cam (consider as link 3) forms a lower pair. Contact between cam (link 3) and follower (link 2) forms a higher pair because it is point contact.

3. According to type of closure

  • SELF CLOSED PAIR OR CLOSED PAIR -  the permanent contact between 2 links forms a self closed pair. Examples are turning pair, rolling pair, sliding pair.
  • FORCED CLOSED PAIR OR OPEN PAIR - the forceful contact between 2 links forms a forced closed pair. Examples are higher pair in cam & follower, door closer, automatic clutch operation system

Comments

  1. Shubham Bhavsar31 January 2019 at 18:54

    in case of cam and follower example how cam and fixed link forms a lower pair?

    ReplyDelete
    Replies
    1. Aakash ahlawat1 February 2019 at 12:47

      Cam and fixed link is connected with a turning pair, which is cylindrical pin and the surface of this cylindrical pin is in contact. Whenever there is surface contact lower pair is formed.

      Delete

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