Robot Types

The hands and arms of early robots were pneumatically powered (air pressure) or hydraulically powered (fluid pressure). Flexible tubes carried the pressurized substances to the joints. Now, electrical motors located at the joint give the robot greater precision and control, but slow down its movements.

Most robots are equipped with one hand and one arm of several articulated joints. Some of these joints swivel in smooth arcs mimicking the behaviour of the human shoulder, wrist, and elbow. Other robots move in straight lines similar to a crane. Robots are grouped into classes according to the combination of joints used in their construction.

There are five types of robot arms that are used today. Degrees of freedom are the axes around which it is free to move. The area a robot arm can reach is its work envelope.

Rectangular arms are sometimes called "Cartesian" because the armīs axes can be described by using the X, Y, and Z coordinate system. It is claimed that the cartesian design will produce the most accurate movements. 

A cylindrical arm also has three degrees of freedom, but it moves linearly only along the Y and Z axes. Its third degree of freedom is the rotation at its base around the two axes. The work envelope is in the shape of a cylinder.

The sperical arm, also known as polar coordinate robot arm, has one sliding motion and two rotational, around the vertical post and around a shoulder joint. The spherical arm's work envelope is a partial sphere which has various length radii.

The SCARA (Selection Compliance Assembly Robot Arm) is also known as a horizontal articulated arm robot. Some SCARA robots rotate about all three axes, and some have sliding motion along one axis in combination with rotation about another.

The last and most used design is the jointed-arm., also known as an articulated robot arm. The arm has a trunk, shoulder, upper arm, forearm, and wrist. All joints in the arm can rotate, creating six degrees of freedom. Three are the X, Y, and Z axes. The other three are pitch, yaw, and roll. Pitch is when you move your wrist up and down. Yaw is when you move your hand left and right. Rotate your entire forearm, this motion is called roll.

Arc Welding Robot             Spot Welding Robot




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Last updated: Tuesday, November 12, 2001

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