When selecting an industrial robot there are many things which need to be considered, such as: what is its purpose, how fast does it need to move, what precision of movement does it need, will it be a collaborative robot? All of these considerations, and many others, determine the type of industrial robot which is best for a job.
One of the major factors which determines how an industrial robot will move and what limits its workspace is its robot configuration. There are six major types of robot configurations: Cartesian, Cylindrical, Spherical, Selective Compliance Articulated Robot Arm (SCARA). Articulate, and Delta (Parallel).
Some industrial robots may not be able to scratch the back of their forearm with the same hand, just like most people can not perform this task. However, through the attention to axes and the selection of a configuration, industrial robots can be designed to move their tools quickly, accurately, and repetitively to any point within a three dimensional workspace.
| Robot Configuration | Explanation | Common Uses |
|---|---|---|
| Cartesian | Has the robot’s tool moving in a linear motion along each of the Cartesian coordinates (x, y, z). This type of configuration can sweep out a box-like work envelope. | Many 3D printers have their print nozzles mounted on a Cartesian configuration. |
| Cylindrical | Allows its tool to rotate around a central axis. The tool can also move towards and away from the central axis, plus up and down the central axis. This configuration creates a work-volume in the shape of a cylinder. | This configuration is typically used for assembly operations, handling of machine tools and die-cast machines, and spot welding. |
| Spherical | The tool motion created by this configuration sweeps out a workspace shaped like a sphere. It has its tool rotate around a central axis, and the tool can also rotate around a second axis which is placed at a 90 degree angle on the central axis. In addition, the tool can move back and forth along an axis. | They are commonly used for die casting, injection molding, welding, and material handling. |
| Selective Compliance Articulated Robot Arm (SCARA) | Uses pivot points to allow its tool to move in a combination of the Cartesian and the cylindrical motions. This allows the tool to move more quickly, and move more easily in certain motions, such as moving in an arc. | SCARA robots are used for assembly and palletizing, as well as bio-medical applications. |
| Articulated | This type of robot is the most commonly pictured when referring to an industrial robot. As a minimum, it needs to have at least a shoulder joint, an elbow joint, and a wrist joint. Many examples of these configurations can have both major and minor axes. | Typical applications for articulated robots are assembly, arc welding, material handling, machine tending, and packaging. The VEX V5 Workcell is an example of an Articulated configuration. |
| Delta (Parallel) | Can move the robot’s tool the fastest of all of the robot configuration types. It uses parallel linkages to allow its tool to quickly sweep out its workspace. | A Delta can nimbly and quickly pick and place items in a sorting task, as well as serve in many other functions. |
Calibration and Defining Movement
In order to define a movement in space, the movement needs to be measured. Measurements require a starting point or zero point, called a calibration point. It is important for robots to be calibrated so they can use a standard point to measure their movements. Moving to a calibration point is called calibration.
Let’s say a foreman wants to write a set of instructions with measurements for an employee to draw a circle on the whiteboard in the exact place that they have just drawn one. If the instruction’s measurements do not include a specific starting point, there is almost no chance the circle will be drawn in the same location. This starting point would be known as the calibration point for the drawing.
When robots are moving, their axes define their motion. The workspace they sweep through is known as the robot’s work-volume or work envelope. With the arm mounted on the V5 Workcell, its work-volume or work envelope includes all the space it can move through, in all directions.
A robot’s work-volume is not only defined by the robot’s axes, but the structure of the robot can also define its motion. For instance, a robot’s wrist might be able to make a full rotation, but its arm might block a tool on the wrist from making a full turn. An area in which the robot can not move is called a singularity.
For example, the arm mounted on the V5 Workcell can pivot up and down at the shoulder. However, there is a post which holds the shoulder bracket together which limits the arm’s height. The area above the limit of the arm would be considered a singularity.