Degrees of freedom (DOF) is ” a term that describes a robot’s freedom of motion in three dimensional space”. Degree of freedom for a robot is defined as “the number of independent movements performed by the robot wrist in three dimensional space, relative to the robot’s base”. It refers to the ability of the robot arm to move forward and backward, up and down and to the left and to the right. For each degree of freedom, a joint is required. A robot requires six degrees of freedom to be completely versatile. The number of degrees of freedom defines the robot’s configuration. Many robotic applications require movement in all the three directions; i.e. X, Y and Z. These tasks require three joints, or three degrees of freedom.
The three degrees of freedom in the robot arm are 1 rotational and 2 linear.
Rotational movement: The rotational movement is about a vertical axis. Because of this, the robot can swivel its amr about its base.
Radial movement: The linear movement in horizontal direction allows the extension and retraction of the arm relative to the base. This movement allows the robot arm to cover large area along radial direction.
Vertical movement: The linear movement about the vertical axis provides vertical lift to the robot arm.
These degree of freedom of robots arm are shown in Fig. 6.1 (a). For applications that require more freedom, additional degrees can be obtained from the wrist, which can be obtained from the end effector. These additional three degrees of freedom in the wrist provide rotary motion to the arm.
These degree of freedom are named as: pitch, yaw and roll as shown in the Fig. 6.1 (b).
Pitch: The pitch, or bend, is the up-and-down movement Of the wrist about the horizontal axis.
Yaw: The yaw is the side-to-side movement, or swivel about the vertical axis in horizontal plane.
Roll: The roll is the rotation or swivel about the arm axis (horizontal).
- Degrees of Freedom of Robot Arm
- Degrees of Freedom of Robot Wrist
Fig. 6.1
Thus, the first three degrees of freedom are for arm movement while the remaining are for wrist movement. A robot requires a total of degrees of freedom to locate and orient its hand at any point in its work envelope, Fig. 6.2.
Fig. 6.2; Six Degree of Freedom
