Understanding: Linkages and Joints for Robotics

PLANAR MECHANISMS

The planar mechanism is the most common type of mechanism. The trajectory of one point on the planar mechanism lies on a plane during motion. The trajectory of all points on the planar mechanism lies on planes which are parallel to each other. For example, a door is a simple planar mechanism that consists of a moving link and a ground link. This mechanism can be described on a plane. There are basically three type of planar joints :

  • Revolute: permits rotational motion with respect to a fixed axis. It has only one degree of freedom.
  • Prismatic joint: permits translational motion between of a pair of links. It has only one degree of freedom.
  • Direct contact joint: permits both rotation and slide between links. It has two degrees of freedom.

Linkages and Joints for Robotics

Spatial mechanisms In a spatial mechanism, the motion of the links is not planar. For example, the spherical mechanism form concentric spheres trajectories of the links in a spherical mechanism form concentric spheres o Cylindrical joint: it consists of a shaft and a sleeve, and permits two-DOF motion. o Helical joint: it is a one-DOF joint consists of a screw nut and a bolt. o A universal joint: is a spherical joint which provides three-DOF motion. o Direct contact joint: in a spatial mechanism can have 5 DOF (point contact), 4 DOF (line contact) or 3 DOF (surface contact).

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