Polar robots, while simple in construction, have drawbacks that limit their use compared with other topologies like articulated, Cartesian, and SCARA robots: ■ The spherical coordinate system makes programming more complex. ■ They typically have a more limited payload capacity than other types of robots. ■ They are slower than other robots. The main benefits of polar robots include a large workspace and high precision. They are used for machine tool tending, assembly operations, material handling in automotive assembly lines, and gas and arc welding. SCARA robot (from "selectively compliant arm for robotic assemblies") is a manipulator with two parallel rotary joints to provide compliance in a selected plane. A basic SCARA robot has three degrees of freedom, the third from a rotating end effector. SCARA robots are also available with an additional rotary joint for a total of four degrees of freedom, enabling more complex motions. SCARA robots are often used in pick-and-place or assembly applications where high speed and high accuracy are needed. For example, Dobot's M1-PRO is a 4-axis SCARA robot with a working radius of 400 mm, a maximum
payload of 1.5 kg, and a repeatability of ±0.02 mm. It has sensor-free collision detection and drag-to- teach programming, making it suitable for use as a cobot as well as a standalone robot (Figure 5).
Figure 5: Four-axis SCARA robot with a repeatability of ±0.02 mm. (Image source: DigiKey)
Conclusion All industrial robots meet the ISO 8373 requirement to be automatically controlled with a reprogrammable, multipurpose manipulator. However, not every design has a defined number of axes for a specified topology. Delta and Cartesian robots are available with fewer than the defined number of axes, while some SCARA robots have more axes than defined by IFR.
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