Robot Range of Motion
An industrial robot’s range of motion determines the movements it is capable of. Range of motion for a robot depends upon the degrees of freedom (DOF) it has. Each degree of freedom is represented by an axis. Each axis contains a motor that is responsible for producing a specific motion.
Most industrial robots have between three to six axes. Robots with fewer than six axes are considered to be low-DOF robots and therefore will have less range of motion than a six-axis robot. There are also articulated robots with greater than six axes and these are considered high-DOF robots. However, six-axis robots remain the most popular as they provide a full range of motion which allows them to access a unit of space from any angle. The range of motion of six-axis robots is most similar to that of the human arm, which is why they are able to automate a variety of manufacturing processes. The range of motion of six-axis robots allows them to operate on the x, y, and z planes as well as shift and rotate. The range of motion of each axis is defined as the following:
- • Axis 1 - Axis one allows the robotic manipulator arm to move 180 degrees from its center from left to right and vice versa for linear movements.
- • Axis 2 - Axis two controls forward and backwards motions of the robotic arm on the x and y planes. The FANUC R-2000ic is able to lift objects up and down because of the second axis.
- • Axis 3 - Axis three allows for the raising and lowering of the robotic arm, similar to axis 2, but on all three (x, y, and Z) planes.
- • Axis 4 - Axis four allows for the rotation of the robot wrist and EOAT.
- • Axis 5 - Axis five controls the pitch and yaw movements of the end-effector. With axis five robots can move their EOAT up and down or left and right.
- • Axis 6 - Axis six provides robots with the ability to change a part’s orientation a full 360 degrees. The sixth axis provides complete rotation of the robot’s wrist.
A robot’s range of motion is important as it determines the types and complexity of applications it can automate. More complex applications will require a greater range of motion. If parts need to be repositioned, a six-axis robot will be needed. The full range of motion of six-axis robots is one of the main reasons they are popular for robotic automation, as they can perform most applications.
Not every application will benefit or need a full range of motion. Those automating simpler processes can use a robot with less range of motion. Robots with fewer axes can be more affordable, easier to operate, and in some cases faster. A simple pick and place application that does not require part orientations to be changed can be automated by a three-axis robot. Automated palletizing applications are actually best for four or five-axis robots. Having a more limited range of motion provides greater stability for lifting heavy loads and part repositioning is often not required. The Motoman MPL160 is a four-axis robot designed specifically for palletizing. When selecting an industrial robot, it is important to consider the number of axes as this will determine the robot’s range of motion.