robotmatrix.org

 Overview

The SCARA acronym stands for Selective Compliant Assembly Robot. It's also sometimes referred to as: Selective Compliant Articulated Robot Arm. Traditionally SCARA's are 4-axis robot arms, i.e., they can move to any X-Y-Z coordinate within their work envelope. There is a fourth axis of motion which is the wrist rotate (Theta-Z). The vertical motion is usually an independent linear axis at the wrist or in the base. By virtue of the SCARA's parallel-axis joint layout, the arm is slightly compliant in the X-Y direction but rigid in the 'Z' direction, hence the term: Selective Compliant.

One disadvantage of SCARA configuration is that it can be more expensive because the controlling software requires inverse kinematics for linear interpolated moves. On the other hand, the work envelope of the SCARA robot tends to be difficult to control, and restricted in volume coverage. Scara robots are tall, so they use a lot of headroom. Because they are headroom-intensive, Scara robots cannot be used to load press machines or for insertion and retrieval applications.

 Application

• The selective compliant feature of the SCARA robot which provides substantial rigidity for the robot in the vertical direction, but flexibility in the horizontal plane, makes it very suitable for many types of assembly operations, e.g., inserting a round pin in a round hole without binding.
• SCARA robots reportedly offer the best price/performance ratio as regarding speed. They are faster because they move less mass due to its configuration. Their single pedestal mount requires a small footprint and provides an easy, unhindered form of mounting. Thus, besides assembly, Scara is ideal for a variety of general-purpose applications requiring fast, repeatable and articulate point to point movements such as palletizing, de-palletizing, machine loading/unloading, pick-and-place and packaging applications. The electronic printed circuit board industry, in particular, use large numbers of SCARAs for placing semiconductor IC.
• Due to their ''elbow'' motions, SCARA robots are also used for applications requiring constant acceleration through circular motions like dispensing and in-place gasket forming.