ARTICULATED ARMS

In robotics, it is important to have control over articulated mechanisms. What is the reach of the “arms” of a certain robot? The space of possible positions of these mechanisms is often intricate.

NASA use of articulated arms.

In the mechanism we present below, we use colors to understand the reach of each arm. If it were not connected to the others, each arm would allow positioning the red dot along a circular ring, which is represented on the board by one of the primary colors red, green or blue.

In the positions allowed to the 3 arms simultaneously the color is white (the mixture of the 3 colors in equal proportions). In positions where none reaches, the color is black. And in those where only two can, it is the mixing (by addition) of the two corresponding colors. Therefore, the white region, which is a kind of hexagon with circular edges, is the set of points accessible to the mechanism.

Image: Alisson Ricardo.
Image: Alisson Ricardo.

This RepRap page talks about Delta Geometry, which relates to the idea of reaching the articulated arm, from a more geometric point of view. The page is in English, but it has some drawings that make it easier to understand!


This type of joint is very present in robotics, with very advanced technology. This Citisystems page shows the six main types of industrial robots. One of them is the "articulated robot", which has numerous advantages and has a lot of its basis in mathematics!

This page of the DMG Lib portal - Digital Mechanism and Gear Library - brings several models of mechanisms and machines, explaining their structural and functional characteristics. This type of mechanism has a lot of joints, so it's a great way to see them in action!