To create the main shell of the final structure, the second robot, the Grip Robot, attaches to the foundation footprint. Its four rollers clamp on to the upper edge of the structure allowing it to move along the previously printed material, depositing more layers. The nozzle moves dynamically allowing for greater accuracy of material deposition. To create a curved surface the material output will be incrementally offset. Heaters, integrated into the robot’s structure increase the local air temperature to influence the curing process. Controlled by custom software the robot follows a predefined path, but can also adjust its path to correct errors
within the printing process. Rotational actuators control height above the previous layer to maintain a consistent layer.
The Grip Robot size 40*27*12 cm, weighs 4.6kg.
Tools and materials:
-Dynamixel ax-12 servos *9
-6mm metal shaft
-6mm linear motion
-Waterjet aluminum for body and gears
-Plastic gears -18/6/6mm bearing
-3D printed wheel core
-Rubber to cast wheel and rollers
-Heat gun stripped for heat element, sensors and fans.
-3D printed pulley and belt from hobbycar shop
-4mm acrylic for laser cutting
The print-head positioning system comprises of a front-back linear motion system (11),
side linear motion system (12), front-back motion actuation system (13), side motion actuation system (14) and actuators for print-head or multiple print-heads. The connection of print-heads to the material supply is illustrated in (15). The device positioning system consists of feet (5) each attached to a further four or more legs (4) that are attached to the frame. Legs are connected to the frame via a linear motion system (9). Linear motion bearings (10) allow smooth movement relative to the frame. This motion can be actuated either by springs or by linear actuators (8). Feet are attached to legs via rotary joints that allow rotation relative to the legs. This rotation can be controlled and is actuated by the foot actuation system (7). Wheels (3) are mounted on the feet and are moved using the wheel actuation system (6). The surface is coated with a durable, flexible material to reduce vibration of the device during movement and to increase its grip to the structure on which the device is attached.
In the case the printing path is closed without openings, the movement of the robot is continuous and front-back print-head motion may not be used. The device is placed on the footprint at a desired position, once material is extruded through the aperture of the print-head and the device starts moving in the desired direction, print without pausing is to use one continuous spiral path. In this case the wheels are not in their centralized position during the printing process, the device is constantly moving upwards; every complete rotation the device moves up by the height of one layer.
Having the print-head fixed in a fixed position would cause a number of problems, on any curved path the print-head center would deviate from the center of the path, where the center position of the nozzle is marked with a dashed line. In this case each preceding path would deviate accumulatively from the desired shape thus printing a different structure than programmed.
This can be solved by introducing linear side to side motion to the print-head, it can be used to correct the deviation and control the path of the print head. To position the print-head correctly a mechanical sensor calculates the deviation and adjusts accordingly. If the position of the device and path curvature are known - deviation can be pre calculated geometrically without the need for additional sensors.
If the print-head was confined to only following the previous layer, printed structures could only be shaped as extruded versions of their footprints. This would exclude forms such as vaults, and cantilevers. Shifting the print-head provides an opportunity to alter the curvature of the wall during the printing process. When layers shift relative to their previous layers the curvature of the wall changes. The amount of shift should be precalculated, varying dependent on the position of the device. In the case that the position of the robot is incorrect or an error is detected - curve deviation should be taken into account and either added or subtracted from the shift. The position of the robot in relation to previous layers can be abstracted in various ways, for example different types of sensors from Local Positioning Systems to rotation counters attached on the wheels leading to many possibilities.