6.2 Industrial engineering applications
6.2.12 Automation/Robotics
Automation is beginning to emerge as an important method for addressing the negative aspects of construction; then industry is associated with the “three Ds,” i.e., many of its tasks are perceived as Dirty, Dangerous, and Dull. Automated systems have been devel- oped to perform such tasks, but they have yet to obtain wide acceptance. One obstacle to acceptance is a relatively low cost of labor in many countries, including the United States.
In Japan, the aging of the workforce and the high cost of labor have facilitated the partial adoption of automated systems.
The Robotics Industry Association defines a robot as a reprogrammable multifunc- tional manipulator designed to move material, parts, tools, and specialized devices for the performance of a variety of tasks.
A study by Slaughter (1997) reviewed 85 robotics/automation technologies used in the construction environment. In keeping with a worldwide pattern, over two-thirds of the tech- nologies in the sample had originated in Japan, while the remainder were distributed between the countries of Europe and the United States, with one each from Israel and Australia.
Industrial robot manipulators are devices that can control both position and move- ment, and can utilize tools to perform a variety of complex tasks with great precision. They are capable of interfacing via a range of communications devices and are capable of force control and visual serving.
Warzawski and Navon (1998) point out that the construction industry faces a number of problems that may favor the application of robotics and automation: labor efficiency and productivity are low, quality levels are low, construction safety and accident rates are a major concern, skilled workers are in increasingly short supply.
On the other hand, the low cost of labor in some countries such as Portugal limits the via- bility of large investments to facilitate construction robot applications (Pires and Pereira, 2003).
Gambao and Balaguer (2002) point out that construction automation is low relative to the state of technology. Research in automation and robotics falls into two groups—
civil infrastructure and house building. Examples of civil infrastructure projects have been carried out in the European Union (EU) include the EU Computer Integrated Road Construction project of 1997 to 1999. Road paving robots were developed to operate auton- omously, using GPS technology for navigation purposes. Automated systems have been developed for compaction of asphalt in road construction.
Japanese companies have been active in several robotics/automation applications—
in tunnel construction, excavation machines are equipped with sensor-based navigation devices such as gyrocompasses, lasers, level gauges, and inclinometers. Shield-type tun- nels are constructed with automatic drive systems; bolt-tightening robots install the tunnel segments. Tunneling through mountains is facilitated via concrete spraying by a shotcrete machine. The Japanese have also developed automatic/semi-automatic systems for bridge and dam construction—a column to column welding robot has been used for column field welding. A robotic bridge maintenance system has been developed at North Carolina State Univresity based on a truck-mounted inspection robot with four degrees of freedom.
Japanese companies have been very active in residential/commercial building appli- cations—the SMART system was used in the 1990s to construct buildings of 30 stories
129 Chapter six: Industrial engineering applications in the construction industry
and higher. The system comprises a robotic factory on the top floor (see www.cv.ic.ac.uk/
futurehome). It elevates the construction plant floor-by-floor as the building is erected.
Robots have been developed for interior-finishing applications, such a mobile floor finishing and interior painting, where close tolerances have to be maintained. The KIST floor robotic system involves the network-based actions of a fleet of robots to compact and control the thickness of flooring concrete. Painting robots developed at Technion are used for coating interior building surfaces.
Pires and Periera (2003) give several reasons why it is difficult and often impractical to utilize robots on construction sites: construction sites are unique in nature with varied topography. They involve the conduct of many simultaneous tasks; they represent a hos- tile environment with dust, debris, and uneven surfaces. In the majority of instances, each building is unique; hence there is little repetition in the construction process. Construction sites are inherently dynamic—several tasks are interlinked, but compete for the same resources. The performance of tasks generally requires complex motions in several planes and moving from one location to another, literally to bring materials and labor to the building in process. The unstructured nature of building sites would make it difficult for robots to sense the environment, interpret the data and carry out the necessary complex tasks. The irregular terrain would also be an obstacle to the robot’s mobility.
Pires and Pereira list a number of attributes that robots would need for the construc- tion environment:
Locomotion—the ability to navigate obstacles, climb ladders, and traverse open areas.
For robot operations to be feasible, the site would have to be provided with guidance systems, predefined routes, or reference points that are recognizable by robots.
Vision—robots would need artificial vision to recognize and interpret a wide variety of elements involved in construction sites.
Adaptability to hostile environments—construction robots would need to be weather proof, resistant to heavy falling objects as well as withstanding falls from heights. They would need to maintain precision of movement and manipulation when subjected to vibration dust, and abrasive/corrosive agents.
Capacity to handle a wide range of materials—construction materials cover a wide range of sizes, shapes, weights, configurations, and textures. Heavy loads may include beams and precast panels. Fragile loads may include glass, ceramic tiles, and bathroom fixtures.
Pires and Pereira (2003) express the view that robotic systems are immediately adaptable to construction activities in a factory setting, such as in the manufacture of prefabricated building components.
6.2.12.1 Layered fabrication technology—contour crafting
Khoshnevis (2004) describe the development of the contour crafting (CC) system that promises to take automation in construction from the component level to the fabrication of entire structures. Khoshnevis points out that automation has seen limited application due to the lack of suitable technologies for large-scale products, limitations in building materi- als and design approaches, economic viability, and managerial issues. Khoshnevis et al.
(2001) describes CC as a superior layer fabrication technology as it produces better surface quality, higher fabrication speed, and provides a wider choice of materials.
Contour crafting is achieved through the use of computer control of troweling tools to create smooth and accurate planar and free-form surfaces. It applies computer control
to the traditional practice of industrial model building with surface shaping knives; it also combines this technology with an extrusion process and a filling process to build an object core. As shown in the diagram, a material feed barrel supplies the material to a nozzle for layering, while a top and a side trowel shape the deposited material incrementally.
The CC technology is extended to large structures, such as complete houses, as indi- cated in Figure 6.5. Khoshnevis describes a gantry system which carries a nozzle on two parallel lanes mounted at the construction site. As shown in the figure, the CC machine moves along the parallel lanes and laterally between the gantry supports as the nozzle deposits the ceramic mix. The process is very effective for building the exteriors of build- ing systems, which can subsequently be filled with concrete. The process is also very effective with adobe-type structures that include domes and vaults in their configuration.
These designs are typical of CalEarth (www.calearth.org).
Conventional designs can be constructed by incorporating other devices with the gan- try system such as a picking and positioning arm; the system can, in a single run, produce a single house or a colony of houses, all of different designs.
Automated reinforcement—the picking and positioning arm complements the extru- sion nozzle and trowel system by incorporating modular reinforcement components, which are imbedded between the layers of walls built by CC. The steel reinforcement may be supplied by a module feeder, which may be combined with the concrete filler feeder.
This system can simultaneously position internal reinforcement and create a wide variety of smoothly finished exterior surfaces.
6.2.12.2 Benefits of contour crafting
According to Khoshnevis (2004), the CC system has many e-design flexibility benefits: the system makes possible the construction of architecturally complex shapes that are difficult to realize with conventional construction.
6.2.12.3 Material flexibility
A variety of materials may be used for external materials as well as fillers between sur- faces. The system makes it possible to combine materials that normally interact just before
Material feed barrel
Nozzle
Top trowel
Side trowel control machanism
Side trowel
Figure 6.5 Contour crafting process. (With permission from B. Khoshnevis, University of Southern California.)
131 Chapter six: Industrial engineering applications in the construction industry
they are deposited. This contrasts with the use of concrete, which has a very limited time window for use before it becomes unworkable.
“Smart materials,” such as carbon-filled concrete, may be configured to create floor and wall heating elements with specified electric resistance. Similarly, strain sensors may be incorporated into the construction. Nonmetallic materials such as glass or carbon fibers may be extruded to create fiber-reinforced plastics (FRP) in one step (Figure 6.6).
Posttensioning can be used with the CC system—ducts can be built into the structure and metal or FRP lines can be threaded through and tensioned to provide the necessary structural strength.
6.2.12.4 Minimal waste
Whereas the construction of a typical single family generates 3–7 tons of waste material, CC is an additive process that produces very little or no material waste. Also, the process may be electrically driven and consequently produce few emissions.
6.2.12.5 Simplified building utility systems
Utility conduits defined in a CAD system can be constructed in the field through CC, as material is deposited layer by layer. In the case of plumbing, wall layers are installed and conduit chases are created; lengths of piping are inserted that have joints, which have been pretreated with solder and provided with heating elements. As the height of a wall is built further, the robotics system uses robotic grippers to add lengths of pipe. Each length of pipe is placed in the respective coupling of its predecessor, and a heater ring is used to melt the solder, bonding the pipes together to form a pressure tight joint. The components to be installed may be prearranged in a tray or magazine for easy manipulation by the robotics system.
In the case of electrical and communications wiring, the conductors may be imbed- ded in insulating material and designed to interconnect in modular fashion. As done in
Extrusion nozzle assembly Gantry support Mortar conveyor
system
Figure 6.6 Construction of conventional building using counter crafting. (With permission from B.
Khoshnevis.)
plumbing systems, the electrical modules may be inserted into conduits fabricated in the walls of a structure. This technology requires the use of specialized robotic grippers work- ing in conjunction with a delivery tray or magazine.
6.2.12.6 Automated trades
In addition to the CC technology, several skilled trades activities can be integrated with the gantry hardware.
Tiling of walls and floors can be accomplished by having the CC equipment deposit the adhesive material to the respective surfaces. A robotic arm can retrieve the tiles from a stack and place them in the locations where the adhesive has been applied. The arm may be installed on the system that bears the CC nozzle assembly.
Painting may be carried out with a mechanism attached to a robotics manipulator; this mechanism may be a spray nozzle or an ink-jet-based system that can paint very complex patterns.
6.2.12.7 Mobile robotics approach
Khoshnevis explains that the gantry robot system has significant limitations—the gantry has to be large enough to accommodate the finished structure within its oper- ating envelope, which results in a large structure. It also requires extensive site prepa- ration. In contrast, a system of multiple, mobile robots has several advantages—it is easier to transport and set up, and several robots may work on the same building simultaneously.
The mobile robot may be equipped with material tanks, material delivery pumps; its end effector would be provided with a CC nozzle. Mobile robots may be used to build supportless structures such as domes and vaults. In the case of planar roofs it is preferable to incorporate roof beams in the design. The erection process would involve having two robots lift the beams at either end and place them on the structure.
The delivery of materials to the roof is challenging—mobile robots may be positioned inside a structure and move materials over the roof beams, in succession as they are placed over each beam. After all beams are mounted, the robots would work from the exterior of the structure.
The NIST RoboCrane system offers a special application—it may be attached to a con- ventional crane and hoisted overhead where it can manipulate structural members with much great precision than the master crane. The RoboCrane may be provided not only with a gripper for beams, but also may be equipped with a material tank and a CC nozzle for delivering materials to the roof.
6.2.12.8 Information technology systems
As described by Khoshnevis several support activities are required to make CC and other automated systems feasible.
A planning system generates proposed alternatives; these are tested for feasibility for CC applications. Engineering models and simulation tools establish the feasibility of using CC. The construction of a vaulted roof may be tested using fluid dynamics and materials science models. This test may identify the required specifications of appropriate materials as well as the configurations to be implemented.
Multirobot coordination may be required with complex structures. In order to opti- mize the use of automation in the construction environment that involves a variety of materials and equipment, logistics planning is necessary to ensure that work activities can proceed without interruption.
133 Chapter six: Industrial engineering applications in the construction industry