Fabric Formwork1.0 (Shuangying Xu, Yuxin Qiu, Min Deng)

Traditional rigid formwork has distinct disadvantages for casting complex forms from concrete. Moreover, the wood formwork of a specific component can hardly be reused after disassembly. This project focuses on developing a mean of replicable linear concrete (cement) component manipulation utilizing robotically-controlled, flexible fabric formworks.

• Flex Sensor - Measure the Curvature

-Model: RP-C10-ST

-Pressure measuring range: 20 g ~ 2 kg

-Activation time: less than 0.01 S

-Response time: <10 ms

-Waterproof

• Pressure Sensor - Check if casting finishes

-Model: SEN0064

-Flat Resistance: 10K Ohms ±30%

-Bend Resistance Range: 60K to 110K Ohms

-Power Rating : 0.50 W continuous/ 1 W Peak

-Waterproof

• 180° Servo
• Lycra

Lycra has been chosen as the formwork fabric with a seam length of 40cm reaching a maximum length of 75cm before failure, representing elasticity of c.a. 187.5%. In addition, Poland cement (CEM I 42,5 R) has been used as manipulating material because of a proper processing time of 2 hours/ 20 °C, with the density of 1860 kg/m3. In order to get the real-time shape information, a flex sensor (SEN0064) has been introduced to measure the maximum curvature at the bottom of the element while a pressure sensor (RP-C10-ST) to check if the formwork has been filled up.

The proposed system allows for a complex geometry to be realized in discrete elements that are fabricated and later assembled into the final composition. In the first step, a free multi-curve was shaped digitally in Grasshopper, which will be divide into several single-curves. The lowest point of each curve followed by the maximum curvature are measured according to the geometry as target curvature in manipulation. The horizontal distance between endpoints of the single curve is recorded as a reference to the horizontal length of the proposed element. Lycra is sewn into a long tube ending by two wood pieces that is stretched and positioned by a robot arm as the formwork into which concrete is casted, which enables the translation from flexibility of fabric into flexibility in pre-defined shape. A frame is used to fix the free end of the Lycra tube to maintain the length of the formwork. A Valve controlled by a servo is set inside the casting pipe, which is utilized to enable and disable the casting motion. 

Before we start the prototype we use rice as a simulation tool to test the relationship between our curvature and the position of the two endpoints.

We control our whole system through two sensors. First is the flex seneor to control the position of robot. The second is the pressure seneor to control the casting on/off by detecting the presence of pressure.

Therefore, our end effector is built according to this principle. We use the 180° servo as a controller for our value. It is mounted on the left side of the framework, above the framwork is which the cement is placed, and the right side of the framework is connected to the robot.

In the robot online control approach, the flow control is realized by using an Ethernet shield between an Arduino board and the KUKA robot controller. The current curvature value is obtained by the flex sensor attached at the lowest point of the target shape, and then transferred to the computer through Grasshopper plug-in Firefly, where the TCP position of KUKA Robot Arm is remapped and calculated according to the real time value of flex sensor. Meanwhile, the pressure sensor at the end of the formwork will keep monitoring if the fabric formwork is filled up and the valve will stop casting when the pressure sensor reaches the boundary. As the water will be filtered out of the fabric while the cement still left in, the volume and weight of the casting material will shrink. Consequently, the void in the formwork will cause the reduction in the pressure value and curvature, thus the valve will open again and the Robot Arm move back. This repeated process will draw the shape as close to the defined curvature as possible, which ensure the accuracy of element production.

Test Shape

Test Value

Test Value/Sensor

The robotically cast components have the potential for deployment as constituents of a compound structure in complex shapes that can also be realized on a building scale, such as load-bearing façade and freestanding walls and sculptures.