Robot end effector
In robotics, an end effector is the device at the end of a robotic arm, designed to interact with the environment. The exact nature of this device depends on the application of the robot.
In the strict definition, which originates from serial robotic manipulators, the end effector means the last link (or end) of the robot. At this endpoint the tools are attached. In a wider sense, an end effector can be seen as the part of a robot that interacts with the work environment. This does not refer to the wheels of a mobile robot or the feet of a humanoid robot which are also not end effectors—they are part of the robot's mobility.
End effectors may consist of a gripper or a tool. The gripper can be of two, three or even five fingers.
The end effectors that can be used as tools serve various purposes, such as spot welding in an assembly, spray painting where uniformity of painting is necessary, and for other purposes where the working conditions are dangerous for human beings. Surgical robots have end effectors that are specifically manufactured for the purpose.
Mechanism of gripping
Generally, the gripping mechanism is done by the grippers or mechanical fingers. Generally only two finger grippers are used for industrial robots as they tend to be built for specific tasks and can therefore be less complex. The fingers are also replaceable whether or not the gripper itself is replaced. There are two mechanisms of gripping the object in between the fingers (for the sake of simplicity, the following explanations consider only two finger grippers).
Shape of the gripping surface
The shape of the gripping surface of the fingers can be chosen according to the shape of the objects that are to be manipulated. For example, if the robot is designed to lift a round object, the gripper surface shape can be a concave impression of it to make the grip efficient, or for a square shape the surface can be a plane.
The end effector of an assembly line robot would typically be a welding head, or a paint spray gun. A surgical robot's end effector could be a scalpel or others tools used in surgery. Other possible end effectors are machine tools, like a drill or milling cutters. The end effector on the space shuttle’s robotic arm uses a pattern of wires which close like the aperture of a camera around a handle or other grasping point.
When referring to robotic prehension there are four general categories of robot grippers, these are:
- Impactive – jaws or claws which physically grasp by direct impact upon the object.
- Ingressive – pins, needles or hackles which physically penetrate the surface of the object (used in textile, carbon and glass fibre handling).
- Astrictive – suction forces applied to the objects surface (whether by vacuum, magneto- or electro-adhesion).
- Contigutive – requiring direct contact for adhesion to take place (such as glue, surface tension or freezing).
|Examples of end effectors|