Mom_Lect_2_Kinematic link, Kinematic Diagrams.pdf

Kinematic pair, kinematic link, mechanics of machines

1. Ken Youssefi Mechanical Engineering Dept 4
Type of Joints –Kinematic Pairs
Lower Pairs–motion is transmitted through an
area contact, pin and slider joints.
Higher Pairs–motion is transmitted through a
line or a point contact; gears, rollers, and
spherical joints.

2. Ken Youssefi Mechanical Engineering Dept 5
Joints
The Revolutejoint (pin or hinge joint) -one degree
of freedom
It allows pure rotation between the two links that it connects (R joints)

3. Ken Youssefi Mechanical Engineering Dept 6
Joints
The Slidingjoint (prism or piston joint) -one degree
of freedom
It allows linear sliding between the two links that it connects (P joint)

4. Ken Youssefi Mechanical Engineering Dept 7
Joints
The Helicaljoint (helix or screw joint) -one degree of
freedom
The sliding and rotational motions are related by the helix angle of the
thread (H joint)

5. Ken Youssefi Mechanical Engineering Dept 8
Joints
The Cylindrical(cylindric) joint -two degrees of freedom
It permits both angular rotation and an independent sliding motion (C joint)

6. Ken Youssefi Mechanical Engineering Dept 9
Joints
The Spherical (spheric)-Three degree of freedom
It permits rotational motion about all three axes, a ball-and-socket joint (S joint)

7. Ken Youssefi Mechanical Engineering Dept 10
Joints
The Planar (flat)-Three degree of freedom
It permits rotational motion about the Zaxes axis and sliding motion in x and y
axes (F joint), used seldom in design

8. Ken Youssefi Mechanical Engineering Dept 11
Joints
A cam joint allows both rotation
and sliding between two links. A gear connection also
allows both rotation and
sliding as the gear teeth
mesh

9. Classification of Kinematic Pairs
1. Sliding pair / Prismatic pair (P)
Whenthetwoelementsofapairareconnectedin
suchawaythatonecanonlysliderelativetothe
other,hasacompletelyconstrainedmotion.
E.g.:Thepistonandcylinder,Cross-headandguidesofa
reciprocatingsteamengine,ramanditsguidesinshaper,tail
stockonthelathebed
According to the type of relative motion between the elements
DOF = 1

10. 2. Turning Pair / Revolute Pair (R)
Whenthetwoelementsofapairareconnectedinsuchawaythatonecanonly
turnorrevolveaboutafixedaxisofanotherlink.
ExamplesLathespindlesupportedinheadstock.
cyclewheelsturningovertheiraxles.
DOF = 1

11. 3. Spherical pair (S)
Whenthetwoelementsofapairareconnectedinsuchawaythatoneelement
turnsorswivelsabouttheotherfixedelement.
Eg:Theballandsocketjoint.
Attachmentofacarmirror.
Penstand.
DOF = 3

12. 4. Screw pair
Whenthetwoelementsofapairareconnectedinsuchawaythatoneelementcan
turnabouttheotherbyscrewthreads.
Examples:
•The lead screw of a lathe with nut
•Bolt with a nut
DOF = 1

13. 5. Cylindrical pair
If the relative motion between the pairing elements is the combination of turning
andsliding, then it is called as cylindrical pair.
DOF = 2

14. 6. Rolling Pair
Whenthetwoelementsofapairareconnectedinsuchawaythatonerollsover
anotherfixedlink.
E.g.: Ball and roller bearings, railway wheel rolling over a fixed rail
Belt and pulley
DOF = 1

15. According to the type / nature of contact between the elements / links.
Classification of Kinematic Pairs
1. Lower pair
When the two elements of a pair have a surface contact, and the surface of one
element slides or rolls over the surface of the other.
E.g. sliding pairs, turning pairs and screw pairs form lower pairs.

16. According to the type / nature of contact between the elements / links.
Classification of Kinematic Pairs
2.Higherpair
Whenthetwoelementsofapairhavealineorpointcontact,andthemotion
betweenthetwoelementsispartlyturningandpartlysliding.
E.g.:toothedgearing,beltandropedrives,ballandrollerbearingsandcamand
follower.

17. According to the Mechanical arrangement.
1.Self closed pair
When the two elements of a pair are connected together mechanically in such a
way that only required relative motion occurs.
E.g.Lower pairs are self closed pair.
2. Force -closed pair
Whenthetwoelementsofapairarenotconnected
mechanicallybutarekeptincontactbytheactionof
externalforces,thepairissaidtobeaforce-closedpair.
E.g.: Cam and follower
Classification of Kinematic Pairs

18. KinematicChain
Whenthekinematicpairsarecoupledinsuchawaythatthelastlinkisjoinedto
thefirstlinktotransmitdefinitemotion(i.e.completelyorsuccessfullyconstrained
motion),itiscalledakinematicchain.
Or
Assemblyoflinks(Kinematiclink/element)andKinematicpairstotransmit
required/specifiedoutputmotion(s)forgiveninputmotion(s)

19. Kinematic diagram
Schematiclinediagramshowingthearrangement of links and
their inter-connection
It reveals the kinematics chain
Dimensions are secondary

25. Kinematic Diagram
❖Schematic line diagram showing the arrangement of links and their inter-
connection
❖A stripped-down (simplified) drawing showing the essentials needed for
kinematic analysis
❖Reveals the kinematic chain
❖Dimensions are secondary
❖All links are numbered while the joints are lettered
❖A kinematic diagram should be drawn to a scale proportional to the actual
mechanism

26. Kinematic Diagram

27. Kinematic Diagram

28. Kinematic Diagram

29. Kinematic Diagram

30. Kinematic Diagram
Clamping Jaw

31. Kinematic Diagram
Clamping Jaw

32. Kinematic Diagram

33. Kinematic Diagram

34. Kinematic Diagram

35. Kinematic Diagram

36. Kinematic Diagram

37. Kinematic Diagram

38. Kinematic Diagram

39. Kinematic Diagram

40. Kinematic Diagram

41. Kinematic Diagram