Robot Dos and Don'ts: Glossary of Robotics Terms

Accuracy: the ability of a robot to move to a specified X, Y and Z value in space.

Actuator: a device that converts electrical, hydraulic or pneumatic energy into robot motion.

Articulated: a robot whose arm has at least three rotary joints.

Cartesian: a robot whose arm has three prismatic joints and axes that are coincident with a Cartesian coordinator.

Cylindrical: a robot whose arm has at least one rotary and at least one prismatic joint, and whose fixed axes form a cylindrical coordinate system.

Degrees of freedom: each direction a joint can go gives a robot arm one degree. To reach any possible point in space within its work envelope, a robot needs a total of six degrees of freedom. Contiguous points are represented along six axes: X, Y, Z, yaw, pitch and roll. With a six-axis robot, the arm is positioned in three axes and the robot wrist is positioned in the other three.

End effector: a device or tool that attaches to the robot wrist to enable the robot to perform its intended task.

Envelope: a volume of space that encompasses all working or reaching movements of a robot.

Force control: a new method for robotic control. Traditionally, robots use a position-based control strategy. But, this can be ineffective as an assembly tool in cases where the assembly tolerance is less than the positional uncertainty. To achieve assembly performance levels comparable to humans, a new breed of robots direct forces in a controlled way and react to contact information gained through a force and torque transducer.

Gripper: a mechanical- or vacuum-actuated device located at the end of a robot arm that manipulates parts and other objects.

Humanoid: a humanlike robot that walks upright and features two arms, two legs and a head.

Manipulator: a machine, the mechanism of which usually consists of a series of segments jointed or sliding relative to one another, for the purpose of grasping and moving objects, pieces or tools in several degrees of freedom.

Idle time: refers to any time that a robot is idle and not performing a value-added maneuver.

Machine vision: a guidance system that gives a robot the ability to see what it is doing and react, as a human would, to changes in positioning.

Maximum envelope: the volume of space encompassing the maximum designed movements of all robot parts, including the end effector, workpiece and attachments.

Operating envelope: that portion of the restricted envelope that is actually used by the robot while performing its programmed motions.

Parallel: a robot whose arms (primary axes) have three concurrent prismatic or rotary joints.

Repeatability: the ability of a robot to return repeatedly to a given position.

Restricted envelope: that portion of the maximum envelope to which a robot is restricted by limiting devices. The maximum distance that the robot can travel after the limiting device is actuated defines the boundaries of the restricted envelope of the robot.

SCARA: a Selective Compliance Articulated Robot Arm that has two parallel joints to provide compliance in a plane. It is also referred to as a Selective Compliance Assembly Robot Arm, because most of these robots are used for assembly applications.

Single point of control: the ability to initiate robot motion from one source of control. Motion is possible only from that source and cannot be overridden from another source.

Spherical: a robot whose arms have concurrent prismatic or rotary joints.

Wrist: an interconnected set of links and powered joints between the arm and end effector that supports, positions and orientates the end effector.

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