The Difference between Cartesian, Delta, SCARA and Six-axis Robots

The use of Cartesian and six-axis robots, as well as selective-compliance-articulated robot arms (SCARAs) is on the rise. They automate tasks to accelerate cycle times, increase throughput, and eliminate bottlenecks. Advanced controls make the robots user-friendlier than ever, with fewer backend-programming requirements. And in some cases, online tools let end users and OEMs quickly choose and configure robot features.
Cartesian robots, sometimes called gantry robots, are mechatronic devices that use motors and linear actuators to position a tool. They make linear movements in three axes, X, Y, and Z. Physical scaffolding forms a framework that anchors and supports the axes and payload. Certain applications, such as machining tightly toleranced parts, require full support of the base axis, usually the X axis. In contrast, other applications, such as picking bottles off a conveyor, require less precision, so the framework only needs to support the base axis in compliance with the actuator’s manufacturer recommendations. Cartesian-robot movements stay within the framework’s confines, but the framework can be mounted horizontally or vertically, or even overhead in certain gantry configurations.
In contrast, SCARAs and six-axis robots typically mount on a pedestal. SCARAs move in the X, Y, and Z planes like Cartesians, but incorporate a theta axis at the end of the Z plane to rotate the end-of-arm tooling. This makes SCARAs good for vertical assembly operations, such as inserting pins in holes without binding. However, the arm is essentially a lever, and that limits SCARAs’ reach: The joints are load points that need robust bearings and high-torque motors to handle the loads when the arm extends.
Almost all Scara robots have a dead zone beneath the robot. Phil Baratti of Epson Robotics demonstrates their new model Scara robot that has no dead zone.
Six-axis robots (6 DOF) move forward and back, up and down, and can yaw, pitch, and roll to offer more directional control than SCARAs. This is suitable for complex movements that simulate a human arm — reaching under something to grab a part and place it on a conveyor, for example. The additional range of movement also lets six-axis robots service a larger volume than SCARAs can. Six-axis robots often execute welding, palletizing, and machine tending. Programming their movements in 3D is complex, so software typically maps the motion to a set of world coordinates in which the origin sits on the pedestal’s first joint axis.
Parallel robots are also known as delta robots. They are built from jointed parallelograms connected to a common base. The parallelograms move a single end of arm tooling in a dome-shaped envelope. They are used primarily in the food, pharmaceutical, and electronic industries. The robot itself is capable of precise movement, making it ideal for pick-and-place operations.