BRICK LABYRINTH GARDEN BUILD BY ROBOTICS ARMS
Professor Xu Weiguo invented the "Automatic Masonry System by Robotic Arms". Unlike the existing bricklaying systems, this integrative system combines bricklaying and 3D printing mortar process together to achieve fully automatic smart construction method; and for the first time in the world, the system is used on the actual construction site instead of a laboratory: a brick labyrinth garden was built with this system in Zhangjiakou.
The automatic masonry system changes the conventional way of picking up bricks, using vacuum lifters instead of clamps, which can lay bricks in variegated walls without collision; meanwhile, the mortar can be printed more accurately.
The garden is located in Wujiazhuang Village (Dingfangshui, Xiahuayuan, Zhangjiako), a village featuring in brick buildings specially designed for the 2022 winter Olympics. The village owns the only brick factory in the neighboring area, so red bricks have been used widely in the renovation as construction and decoration in recent years, making the village famous in Zhangjiakou. The garden locates in a triangle site near the entrance of the village. After its completion, it becomes a place for villagers to gather and relax.
Concept of design
The base of this garden is a circle with a diameter of 13m with irregular carved areas. Three winding brick walls laying on the circle form continuous drapes in the plan and adopt the curved form in the vertical direction too. With more changes in bricks’ position and angles, these walls form a labyrinth both in vision and space. Bamboos and grass are planted in the outer area of the curved walls, while the inner space is designed for the villagers’ activities, which presents the relativity relationship of Chinese Yin and Yang in complexity.
The design of the garden is based on digital generation technology. Firstly, a curved shape is generated in the rhinoceros software. It is shaped like a flowing ribbon, and the shape of the surface is optimized to make sure that it meets the basic requirements of circulation flow and human scale. The base curve was then introduced into Grasshopper to arrange the bricks. We extract curves in a series of profile heights of the surface as the reference lines for each row of bricks; then divide the lines to arrange bricks and ensure staggered position in adjacent rows; at last, use additional reference lines to generate changes in bricks’ position perpendicular to the surface, making gradient patterns on the curved surface.
After the digital model of brick walls is generated, the design team designs the robot arm’s movement path in combination with the construction method and uses KUKA|PRC to export it as program codes recognizable by the robotic arm. The process includes picking up bricks by vacuum lifters, releasing bricks in designated positions, flipping the tool to print mortar and print mortars according to the designed path. The codes also integrated commands for external devices like air pump issued by the robotic arms’ IO module, and pass the obstacle avoidance test in simulation. After simulation in the program, the PRC exports program for robotic arm execution, so that we can achieve accurate conversion from the digital model to the actual building.
There are two robotic arms working together in the construction process, one is KUKA KR210 with the arm length of 2.7m; the other one is KUKA KR120 with the arm length of 3.9m. The positions of construction and their procedure have been designed in order to maximize the efficiency of this automatic system and avoid any collision the robots or the walls. The two robotic arms were moved 7 times in total to complete the whole process, and each course has been simulated in the PRC program.
In the experimental phase, a brick wall damage test was also carried out to test whether it reaches the standard of the design and construction specifications of the brick walls. We used different types of mortar according to the environment temperature which can satisfy demands for both winter and summer construction, and their fluidity and early strength time can meet the requirements of 3D printing. The mortar used 425# cement, while the water-cement ratio was about 0.7, and the mortar strength was up to 45MPa. After the maintenance period, sandbags were used to destroy two experiment walls, and their strength is up to the standard of China’s specification.
The construction process includes measuring, foundation construction, wall masonry, landscape construction, and ground paving etc. After we used the total station to measure the site, we used the robotic arm to cut 30cm-thick foam blocks to make molds for the outer curved green area and poured reinforced concrete inside the forms to make a slab for brick walls and activity areas. As for the masonry process by the smart construction system, at least two workers are needed. One of them will operate the system, and the other one will move mortar and bricks. Forklift is used to move the robotic arm to designed positions. In order to ensure construction precision, robotic arm positioning calibration will be conducted after each movement. After the completion of the walls, we remove the foam surrounded and refill soil and plant grass and bamboo in the future. Concurrently, inside the wall, hollow bricks are used to pave the garden.
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