End-effector

An end-effector is the working end of a robot arm, the part that actually touches and manipulates the world. Depending on the job, it might be a simple two-fingered gripper, a dexterous multi-fingered hand, a suction cup, or a specialized tool like a welding torch or a screwdriver. Whatever its form, the end-effector is where the robot's intentions meet reality. The rest of the arm exists largely to carry the end-effector to the right place and hold it at the right angle so it can do its job.

Because the end-effector is what interacts with objects, its position, orientation, and state are usually the things a control policy cares about most. When a robot is told to pick up a cup, what matters is getting the gripper to the cup, oriented correctly, and closing it at the right moment. For this reason, actions are often expressed in terms of the end-effector, describing where it should go and what it should do, rather than in terms of every individual joint. Its state, such as whether a gripper is open or closed, is also a key part of the robot's proprioceptive self-sensing.

A robot arm's joints work together to position and orient the end-effector, so controlling the arm is often framed as deciding where the end-effector should be and letting the joint motions follow from that. The end-effector's pose is its position and orientation in space, and its state captures what it is doing, such as how far a gripper is open. A control policy frequently outputs targets for the end-effector, and the system then figures out the joint movements needed to achieve them. Proprioceptive sensing reports the end-effector's current pose and state so the controller always knows where the working point of the robot is.

The end-effector matters because it is where a robot's work actually gets done, which makes it the natural focus for both control and evaluation. For anyone reasoning about manipulation, thinking in terms of the end-effector clarifies what a task really requires, since most manipulation goals are ultimately statements about where the gripper or tool needs to be and what it needs to do. Understanding this helps explain why so much of robot control and robot data is organized around the end-effector rather than around individual joints.

Because most tasks are really about what the working point of the robot does, such as reaching and grasping an object. Specifying the end-effector's target pose captures the goal directly, and the system can then work out the joint motions needed to achieve it.

Its pose is its position and orientation in space, describing where it is and which way it faces. Its state describes what it is doing, such as whether a gripper is open or closed. Both are important for control.

Yes. A gripper, a dexterous multi-fingered hand, a suction cup, or a specialized tool all count as end-effectors. The term covers whatever device sits at the end of the arm and interacts with the world.

Embodiment, Degrees of freedom (DoF), Proprioception, Action head / action decoder, Teleoperation.