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A striped-down (simplified) drawing showing the essentials needed for kinematics analysis. All links are numbered while the joints are lettered. Kinematic ...
Typology: Lecture notes
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A striped-down (simplified) drawing showing the essentials needed for kinematics analysis. All links are numbered while the joints are lettered.
Mechanism to open and close a window Kinematic diagram
Ao
B
Bo
A
E, F
X
D
C B
A
1
Link 2 Link 3
It allows pure rotation between the two links that it connects (R joints)
The sliding and rotational motions are related by the helix angle of the thread (H joint)
It permits both angular rotation and an independent sliding motion (C joint)
It permits rotational motion about the Z axes axis and sliding motion in x and y axes (F joint), used seldom in design
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
Degrees of Freedom (DOF) โ Type of Joints, Lower Pairs
Each pin connection removes two degrees of freedom of relative motion between two successive links.
A slider is constrained against moving in the vertical direction as well as being constrained from rotating in the plane.
Two degrees of freedom joints are sometimes called a half a joint (Norton).
A spheric pair is a ball and socket joint, 3 DOF.
The helical pair has the sliding and rotational motion related by the helix angle of the screw.
Planar pair is seldom used
the link AB, x A, y A, and angle ๏ฑ
DOF = degree of freedom or mobility
L = number of links, including ground link
J 1 = number of 1 DOF joints (full joints)
J 2 = number of 2 DOF joints (half joints)
Degrees of Freedom (DOF) โ trench hoe
Number of links, L = 12, (^) Number of one DOF joints, J 1 = 12 (pins) + 3 (slider) = 15,
Number of two DOF joints, J 2 = 0
12 11 10
9 8 7 6 5 1
2
3
4
11, 12
1 2
3
4
6 5
7 (^98)
10
3 hydraulics are used to control the position of the bucket.
Degree of Freedom (DOF) - example Number of links, L = 7,
1
1
1
2
3
4
5 6
7
Number of one DOF joints, J 1 = 6 (pins) + 1 (slider) = 7, Number of two DOF joints, J 2 = 1 (fork joint)
DOF = 3( L โ 1) โ 2 J 1 โ J 2 = 3(7-1) โ 2(7) โ 1 = 3
Fork Joint
Slider
Spring
Three input sources are needed to control the mechanism
