Irregular Bamboo Knot Weaving End-effector

Bamboo has amazing structural properties. Its tensile strength can be higher than that of steel, especially its weight-specific strength properties are very good and it grows super fast (up to 30 to 50cm per day!). However due to its inhomogeneous geometrical nature, construction with this material can be a challenge.

There are many solutions to this problem. Two of theses solutions are the fabrication of custom node connection (custom steel nodes, or even 3d-printed ones) and the way of connecting bamboo rods with traditional knots using laces. A highly interesting approach to connecting wooden elements is presented in the paper Three- Dimensional Fibre Placement in Wood for connections and reinforcements in timber structures, which involves a minimal subtractive CNC milling operations and the insertion of continuous fibrous materials (in this case CFRP tows, which are then cured by applying an electrical current). With the way of connecting bamboo rods with a traditional knot, as well as with the novel 3D-FPW method, a lot if manual labor is still necessary. Our CDDF project aim to solve this by developing an end-effector for a 6-axis industrial robot, which is capable of producing both types of fibrous connections mentioned before. A successful implementation of this could enable a whole spectrum of new possibilities including the economical production of pre-fabricated building elements (wall panels, slabs & columns).

The first end effector prototype consists of 5 main parts:

- The frame, on which all the actuating parts are mounted onto and which itself is mounted onto the industrial 6-axis robot.

- The pin, which is the element that pulls the thread through the pre-milled wholes. It is symmetrical and chamfered on both sides, as it is moved back and forth and thus a turn of the pin is not necessary. It itself is hollow, so that:

- The laser paired with a laser receiver, can confirm that a hole has been reached. If not, the laser beam is interrupted and the receiver sends a corresponding signal.

- Two driving units paired with respective limit switches, that are moving the pin back and forth. At any given time point, the pin is held by at least one driving unit.

- Guiding rails at the driving units and guidances at the pin, which make sure that the pin is always aligned orthogonally to the frame plane.

With our first prototype we were able to demonstrate: the pin moving through a pre-drilled bamboo hole, stopping as soon as the laser signal was interrupted and moving back again as soon as the limit switch was hit on one side.

- stepper motors with respective drivers

- laser

- laser receiver

- limit switch

- 3d-printed parts

- bamboo test rod

Print the uploaded parts from below and assemble the driving unit using M3 screws.

Print and assemble the laser and laser receiver box using M3 as well as M2 screws. Make sure to align the laser precisely, so that it can pass through the pin to the receiving end.

Mount everything onto a base platform, again making sure that everything is aligned correctly. Ideally this platform will be mounted to a moving frame (6 axis robot :).

Wire everything together according to the fritzing diagram. Ideally you are installing 2 stepper motors per side, however 1 is also sufficient.

Get the test bamboo rod and let the pin attached with the rope run through the pre-drilled bamboo holes!