Degrees of Freedom and Axis of Movement

Two terms which are often confused when considering Robot configuration are " Degrees of Freedom " and " Axes or Degrees of Movement". The distinction is important as they relate to different aspects of the Robots capability. The term Degrees of Freedom relates to the locating or positioning of a body in space. Any body in space has six degrees of freedom. It can have linear movement along three mutually perpendicular axes and rotational movement about the same three axes. ( Fig 1) The three linear movements, often termed Translational movements, allow the body to be moved to a desired position in space and the three rotational movements allow the body to be orientated about that position.

In order for a Robot to reach all sides of a component, its movements should include all six degrees of freedom. It is not necessary for the Robot configuration to provide all six as us usually three are provided by the end effector.

The term Axes of Movement relates to the number of axes in which the Robot may move. In one particular Robot configuration the axes of movement coincides with the joints of the human body indeed they are called waist, shoulder, elbow and wrist movements.

In the jointed arm shown in fig 2a, the arm has two axes of movement represented by the two rotary joints A and B. The joints when actuated are capable of moving the end of the arm through three degrees of freedom. Adding more joints to the arm as in fig 2b does not necessarily increase degrees of freedom. Adding more joints to a Robot increases its degrees of movement and may increase its reach and accessibility.

Robot ConfigurationDegrees of Movement Degrees of Freedom