Does anyone know what this is in the lab Cartesian Coordinate Robot, what is it for?

The following is a classification of industrial robots, please refer to: 1, plane multi-joint robots (SCARArobots): in a plane, there are two parallel rotary joints to work on the robot (see below). 2, multi-jointed robots (Articulatedrobots): more than three rotary joints of robots (see below). 3, coordinate robots (sit< /p>