Kinematic Pairs (Joints) and Constraints
When we connect bodies (called links) together using joints, we introduce constraints, which reduce the total DOF of the system. Each joint allows certain motions and restricts others.
Common Joint Types and Their DOF
|
Joint Type |
Symbol |
Description & Motion Allowed |
DOF (Spatial) |
Constraints |
|---|---|---|---|---|
|
Revolute |
R |
Hinge-like, allows only rotation about one axis. |
1 |
5 |
|
Prismatic |
P |
Sliding, allows only linear motion along one axis. |
1 |
5 |
|
Cylindrical |
C |
Allows rotation and translation about the same axis. |
2 |
4 |
|
Spherical |
S |
Ball-and-socket, allows 3 rotational motions. |
3 |
3 |
|
Screw |
H |
Coupled rotation and translation (like a nut on a bolt). |
1 |
5 |
|
Planar |
E |
One surface sliding on another. |
3 |
3 |