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UoM E S1

Mechanisms

Mechanism

An assembly of rigid bodies or links designed to obtain a desired motion from an available motion while transmitting appropriate forces and moments. Motion of the links have definite relative motion with other links.

Simple mechanisms

  • Lever
  • Pulley
  • Gear trains
  • Belt and chain drive
  • Four bar linkage

Other complex mechanisms

  • Lock stitch mechanism (used in sewing machine)
  • Geneva mechanism
    Constant rotational motion to intermittent rotational motion. mostly used in watches.
  • Scotch yoke mechanism
    Constant rotational motion to linear motion (vice versa.). Mainly used as valve actuators in high pressure gas pipelines.
  • Slider crank mechanism
    Used in internal combustion engines

Method of instantaneous centre of rotation

  • Find the instantaneous centre of the rotation from known velocities at known points
  • Use the instantaneous centre to find velocities at other points

Kinematic chain

An arbitrary collection of links (forming a closed link) that is capable of relative motion and that can be made into a rigid structure by an additional single link.