What are Industrial Robot Joints?

FANUC R2000ib 125L R30ia Motoman MA1400 FANUC M710ic 50 Motoman HP6 NX100 FANUC Arcmate 120ic
Industrial robots are comprised of multiple links that are connected to one another. These link connections are the joints of an industrial robot, also commonly referred to as axes. Robot joints are essential to provide and ensure robotic arm movement. Each joint contains a motor or actuator, that powers the joint to perform a relative motion. Each robotic joint has its own specific movement or degree of freedom. The more joints an industrial robot has the more degrees of freedom it has which means it will be capable of accessing greater amounts of space.

Most industrial robots have between three to six joints or axes. Six-axis robots are the standard and have a full range of motion. With six joints, the FANUC Arcmate 120ic can access space from any angle due to its six degrees of freedom. There are robots with seven or more joints. 7-axis robots are relatively new, but their extra degree of freedom allows them to maneuver their arm around objects and eliminates the need for positioners. Industrial robots featuring double digit joint configurations are usually designed with dual robotic arms. Robots with greater than six joints are classified as high-DOF (degree of freedom) robots while those with less than six joints are considered low-DOF robots. The number of joints your robot will need will depend upon the complexity of the application you are automating. More complex applications generally require a broader range of motion and will likely need at least a six-axis robot. Less complex applications typically involve more straightforward movements which can be automated by a low-DOF robot.

Types of Robot Joints

There are five main types of robotic joints. Two of these types feature linear motions while the other three feature rotary motions. Industrial robots may be configured with one joint type or a combination of joint types.

  • • Linear Joint - The relative motion of linear joints is parallel, meaning the two joint links slide linearly. SCARA robots are configured with two linear parallel joints. The FANUC Sr-3ia is a SCARA robot. These may also be called type L joints.

  • • Orthogonal Joints - Orthogonal, or type O joints are another type of linear moving joint. The difference between this type and linear joints is that instead of running parallel they run perpendicular. Cartesian robots feature this type of robotic joint.

  • • Rotational Joints - Rotational joints produce rotational relative motions and are referred to as type R joints. With these joints the rotational axis runs perpendicular to the two links.

  • • Twisting Joints - Twisting joints, also called type T, produce rotary motions. Like rotational joints, the axis of rotation runs perpendicular to the two links.

  • • Revolving Joints - Revolving joints or type V joints, allow for rotational relative motion between two links. With this type one link runs parallel while the other runs perpendicular.

Articulated industrial robots feature a combination of joint types, as do delta robots. Articulated robots may feature multiple rotary joints depending upon their complexity. Most articulated robots like the Yaskawa MA1440 are built with twisting and rotational joints. Delta robots feature a combination of rotational and linear joints.

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