Types of Joints Used in Robot Wrists

Much like the human wrist, the robot wrist serves to help rotate and move the robot’s grip or hand to properly position it for the task at hand. For that reason, it needs to be able to move in complex ways. To accomplish this, normally, two or three types of joints are used in the assembly. The joints are simply where two parts are connected to allow movement.

Which types of joints are best for use in different robot wrists depends on the nature of the work the robot will do. Some things that should be considered are if it needs to move horizontally or vertically or both as well as if it needs to rotate. Finally, what types of grips or tools need to be attached may also play a role in determining which type of robotic wrist is best for a job.

Different Robot Wrist Joints

  • Linear Joints – also known as type L joints, these slide along a linear axis.
  • Orthogonal Joints – also known as type O joints, these also slide along a linear axis, however the output is at a 90 degree angle to the input.
  • Rotational Joints – also known as type R joints, these allow rotational movement perpendicular to the input and output axes, allowing the output to swing up and down or left and right.
  • Twisting Joints – also known as type T joints, these allow a rotational movement parallel to the axes input and output of the axis, allowing the output to rotate like a screw.
  • Revolving Joints, also known as type V joints, these allow a perpendicular output link to rotate around the input link.

The Joint Notation System

As stated above most robot wrists will have two or three joints in them, allowing for several degrees of freedom of movement, or ways the wrist can move the attached gripper or tool to where it needs to be. The letter types mentioned above are used to define the configuration of an assembled robot system. First the body-and-arm configuration is listed and then comes the wrist configuration. For example: in the configuration LRT : RT, the robotic wrist has two joints, a rotational joint, followed by a twisting joint. It is important to consider how the robot wrist will need to position itself when deciding on which configuration is best.