Automation and Visualization in Modular and Prefab Construction Industry

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Automation and Visualization in Modular and Prefab Construction

Industry

A u t o m a t i o n i n M o d u l a r a n d P r e f a b I n d u s t r y

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Automation in Modular and Prefab Industry

Joseph Neelamkavil

Table of Contents

Introduction ...4

Automation Research in Prefab & Modular Construction...5

The FutureHome Project ...5

The ManuBuild Project: ...8

Making of the Construction Components – Role of Robotics Automation ...9

Precast automation ...11

Automated Construction Site ...12

Crane Selection and Movement Automation ...16

Virtual Reality and Simulation in Modular Construction ...17

Planning for Automated Building Assembly ...19

Scheduling Automation and Sensor-based Control ...20

Order Processing Automation ...21

Conclusion & Future Directions for the Prefab Industry ...22

Prefab Factory – A Stage for Construction Productivity Enhancement ...22

Prefab Building – An Example of Quality and Functionality...24

List of Figures

Figure 1. FutureHome Robotized Crate – Source Balaguer et al [17]...5

Figure 2. Assembly Using Cones Connector – Source: Diez et al [18] ...7

Figure 3. AUTMOD3 Assembly Planner – Source Padron et al [19] ...7

Figure 4. NCC Apartment Building – Source: www.manubuild.org/downloads [23] 9

Figure 5. Gantry-type Robots for Precast Panel Production – Source: Bock [32] .10

Figure 6. Robotized Manufacturing of Precast Panels - Source: Peñin et al [3]....11

Figure 7. Software Spec. System Architecture – Source: Eastman et al [24] ...12

Figure 8. Crane Handling Tool – Source: Martinez et al [7] ...13

Figure 9. SMART System – Source: Reference [16]...14

Figure 10. ‘Big Canopy’ Parallel Delivery System - Source: Hamada et al [37] ....15

Figure 11. Modular Assembly – Source: Olearczyk et al [26]...16

Figure 12. 3D AUTOCAD Model of Building - Source: Manrique [5] et al ...17

Figure 13. Virtual Construction Environment – Source: Murray et al [8] ...18

Figure 14. ProModel Graphics Library – Source: Nasereddin et al [6] ...19

Figure 15. Bespoke Production Planner – Source: Benjaoran & Dawood [34] ...21

Abstract

The construction industry at-large is dominated by numerous small and specialized sub-contractors who typically are not technologically advanced enough to embrace

automation. The sector that represents factory built housing (the modular, panelized and prefabricated, precast, etc.) is perhaps an exception. Since these are built in factories, the principles of mass production that are the norm in manufacturing, applies. This will also make it easy to adapt to automation, integration and optimization. In this scenario, the constructability aspects can easily be verified prior to being built, and an optimum plan for construction (similar to a manufacturing process plan) can be chosen. Newer materials can be applied, and tight tolerances achieved, while the built products are not affected by outside climatic conditions, as is the case for site built housing. This report provides an overview and the type of automation that is prevalent in the factory-built and prefab industry. It will also provide some background information for the researchers to further their research on this important topic.

Introduction

Automation in the construction sector, inclusive of factory-built housing, mostly means the automation of the on-site construction process, and the automated component making operation [1]. Generally speaking, the construction process falls into one of three

categories: 1) components making process, (parts, panels, precast, formwork, etc.) which deal primarily with the construction of the building blocks; 2) assembly process in which the construction components (from many different suppliers) are assembled/installed to form the buildings, houses, etc., by an array of sub-contractors, with sometimes conflicting workflows; 3) construction business processes – most business and support processes (project management, workflow management, supply chain management, document management, change management, planning & scheduling, etc.)

Traditionally, the bulk of the construction tasks are realized via manual methods. Hence, prior to deciding to automate the component making process, it is prudent to evaluate and decide on whether it is even worthwhile to launch modular or factory-built operations. Jongchul Song et al [11] has developed a tool that helps decide on the viability of prefabrication, preassembly, modularization, and off-site fabrication, etc. - collectively termed as pre-work (PPMOF). It facilitates the decision-making process for evaluating the use of PPMOF on any specific projects. Automating an operation that doesn’t make any business sense is not at all advisable. Similarly, creating islands of automation does very little to the efficient functioning of the business. Sheer et al [12] has presented the key issues for improving integration of the automation systems pertaining to the whole construction process - from design to component making through the assembly of these components to the end product – house, building, etc.

A key catalyst for success in implementing automation is that the suppliers, designers and clients work collaboratively in fully integrated teams. As reported by Summers [13] on various aspects regarding the case of construction of terminal 5 at Heathrow airport, a high-level supervisory system needs to control what is in production at the factory, track delivery and storage inventory, and monitor quality at various levels. At a higher

technology level, it is analogous to the requirements summarized by Alan M. Lytle et al [30] during a NIST workshop on construction automation, namely: a) Robotics and process integration in the fabrication shop, b) Materials tracking using radio frequency identification (RFID) tags, bar codes, etc., c) Design of connections for compliant

assembly, d) Pre-assembly to minimize field connections, e) Integrated project processes, databases and 4-D models, f) Positive control of members and sub-assemblies using manipulator arms, inverse Stewart platforms, etc., g) Automated welding, bolting, adhesion, etc., and h) Global positioning and locating systems. The NIST workshop focused on automation in steel construction, yet many of these technologies are also equally applicable in precast, pre-fabricated and/or modular type housings.

Automation Research in Prefab & Modular Construction

Europe has seen two mega research projects being undertaken in the prefab domain, with automation as the core. These are the FutureHome and ManuBuild projects. The

FutureHome project [17, 18, 19, 20, 21] started in 1998 and was completed in 2002. The ManuBuild project [22, 23] started in 2005 and is due to be completed in 2009.

T h e F u t u r e H o m e P r o j e c t

The European segment of this project is known as FutureHome, and the Japanese segment is designated as IF7. The main objective of the FutureHome project is the development of integrated construction automation (ICA) concept and associated

technologies for all stages of the house-building construction process, from the architect’s desk to site robots. This includes: a) modular design of buildings with planned robotic erection, b) automatic planning and real-time re-planning of offsite prefabrication, transportation, and onsite assembly and c) onsite automatic and robotic transportation, manipulation, and assembly of the buildings’ prefabricated parts.

Figure 1. FutureHome Robotized Crate – Source Balaguer et al [17]

The present-day prefabricated structures can only be taken apart with loss of functionality, either due to unavoidable damage or irreversible jointing. Whereas the FutureHome

building system derives from a Kit-of-Parts approach, which is a specific implementation of prefabrication. The distinction is that such structures follow an assembly, disassembly,

parts replacement, re-assembly sequence as required during their life-cycle. In this project, standardization plays a major role in achieving economies from the many variations allowed in the parts set. The stakeholders of the FutureHome project chose light steel framing for the pre-fabrication; the rationale comes from transportation logistics and the requirement to use automation tools both in the factory and on site. This demands guaranteed dimensional precision and avoidance of problems like warping and shrinkage. The project custodians took the approach to erect a building complex that consisted of several buildings. Each building is erected using three-dimensional (3-D) modules and two-dimensional (2-D) panels (facades). These modules and panels are prefabricated offsite in a factory. Using beams, panels, installation elements, etc., the 3-D modules are assembled in a flexible production line. Frames, panels, windows, doors, etc., are used to build the 2-D facade panels.

A noteworthy feature of the construction modules from this project is their ability to be automatically assembled. Several assembly connectors had been developed for the assembly of the modules, the structural connection, and electrical and service pipes connections. These connectors ensure automatic performance of complete assembly between modules. Another important element of the project is the development of a tool called AUTMOD3, which is an automatic modular construction software environment [18, 19, 20]. This system seamlessly integrates architectural design, planning and simulation tools in a commercial CAD program. Special purpose software modules, menus and libraries are linked to the CAD system, and a library of several types assists and guides the designer through the process. It contains structural 3D modules, 2D façade modules, 3D roof modules, and so on. The automatic modularization feature is invoked for deciding the number and types of modules, which depends on several criteria, like the minimum number of modules, module-size limitation due to pre-fabrication, transportation, etc. There are two methods of modular design in the AUTMOD3 tool. The first method is based on traditional architectural design. Architects design and draw architectural plans in a CAD system, and these drawings are processed using a modular division procedure to obtain the modules needed for the house. If there is any problem during the modular division due to the complexity of the design, the system requires the architect to make appropriate corrections. In the second method, the design is performed using a catalogue of 3D parametric modules. The library of modules is updated taking into account customer and architect requirements and also the development of new materials, accessories and fabrication techniques. All information is stored in a central database, which allows its access from other processes in the system.

The planning segment of the AUTMOD3 tool features production planning and on-site modular assembly planning. Here, the assembly planning element generates the trajectories, which can be applied directly to a robotized crane developed as part of the project. The onsite assembly processes are expected to be performed by robots, autonomous cranes and/or other automated machines. The planning segment is considered four-dimensional (4-D), which takes into account not only the geometrical constraints of the assembly, but also the time constraints. That is, it determines the sequence in which different building components are assembled and plans the robot or crane trajectories to assemble them.

A prime feature in arriving at a successful automated assembly system in this project is the integration of the planning process with the design and execution processes. For this to happen, pre-fabricated modules are vertically assembled using the cone connectors

system (as shown in figure above). This system allows auto-centering of the modules during the insertion, as well as a bigger tolerance in the precision of the crane

movements. The assembly, by means of cones connectors, ensures that assembling motions occur essentially in a single direction, usually up-and-down.

Figure 2. Assembly Using Cones Connector – Source: Diez et al [18]

As noted, the production sequence and the on-site modular assembly planning are the objectives of the AUTMOD3 planner (see the interface below). It defines the sequence, in which pre-fabricated modules should be produced, transported and finally assembled on the construction site. It generates programs for the automated devices involved in the on-site assembly. It also defines the assembly operations and their sequence, the fixture design, the tool selection and the workspace layout, to ensure satisfaction of a set of technical and economical requirements.

In addition, as described by Wing and Atkin [21], visualization methods provide support on several levels in the FutureHome project. Virtual reality is employed to complement the Kit-of-Parts, providing a common virtual environment that can be shared by clients, architects, engineers, constructors, maintenance providers, etc. The clients can be led through the virtual design of their house, created on-line using “prefabricated”

components. In addition, a simulation of the construction process is provided, allowing examination of cost, quality and time aspects. It is an environment within which the user creates a design from its constituent prefabricated components. A 3D window lists a library of available components. The user selects a component and views it in 3D; he/she then chooses to add the component to the design, using collision detection and constraint- based modeling techniques to ease the interaction process. As the design progresses, a window within the environment keeps the user updated with the total component cost of the design. The user then moves to the construction environment for a simulation of the construction process, which includes a tower crane and other virtual site equipment.

T h e M a n u B u i l d P r o j e c t :

The ManuBuild project [22, 23] is due to be completed in 2009, and has set its vision such that customers will be able to purchase high quality manufactured buildings that have a high degree of design flexibility at relatively low costs. Enabling business processes, ICT systems, new materials/technologies and smart components are the major features of this project. ManuBuild targets a shift from the traditional "craft and resource-based

construction" to ‘open building manufacturing’. It combines efficient manufacturing in factories and on the sites with an open system for products and components that offers diversity of supply in the market. It has set its vision: ‘Customers will be actively engaged in the design of their buildings, using state of the art interactive tools; it incorporates mass customization, and offers customers increased choice and design flexibility; the efficient, flexible and scalable manufacturing concept enables production efficiencies of production scale; an open system for products and components gives diversity of supply at

competitive costs. Potential impacts include significant reductions in waste, costs, time to construct and the number of construction related accidents.

Striving to achieve automation, one of ManuBuild’s goals is to provide ICT support for distributed building manufacturing. Several decision support tools have been developed ranging from catalogues of products via information delivery, design, custom

configuration, and assembly planning. Some of the highlights are:

• Market analysis method taking into account economic models, demography and cultural conditions; reactions to market changes can be set in motion in advance, and this enables to focus production according to customer demand.

• Intelligent component catalogues for parametric, intelligent building products – here the term ‘parametric’ refers to the customizability for the end-user needs, and ‘intelligent’ refers to built-in design/logic and life cycle information of the objects. • Design and configuration tools for customer driven design and configuration of

buildings, based on intelligent catalogues and stored building templates. • Assembly planning and monitoring tool to integrate production planning and

component delivery scheduling having visual features of 3D assembly. The use of RFID is also being experimented with for efficient tracking of components.

• Open ManuBuild System Platform: the solutions are made available on a common portal, which permits access to all developed tools by the partner stakeholders.

As a visible outcome, ManuBuild is about to complete demonstration projects (see figure below) across several European cities, including two large residential buildings in Madrid (led by EMV3, the City Council of Madrid), a low-rise apartment building in Stockholm (led by NCC4) and a residential project and a healthcare or school building in the UK (led by Taylor Woodrow Construction, TWC5).

Figure 4. NCC Apartment Building – Source: www.manubuild.org/downloads [23]

Making of the Construction Components – Role of Robotics

Automation

Robots were first introduced in construction in the production of industrialized building components and modular housing. Later, mobile robots were developed for special on-site construction tasks. As reported by Bock [15], robots played a very active role at the

production line of Sekisui Chemical Sekisui Heim in Japan, where more than 85 percent of the houses are prefabricated. The steel frames of the box unit are assembled from the roof, floor, and end wall frames which are welded together in a totally automated process using arc- and spot welders. The production process starts with cutting the prescribed length of highly rust resistant fused galvanized steel. Robots then weld connecting fittings to the columns. At the ceiling frame production line, 2" x 4" beams are attached to the ceiling frame and electric wiring is installed. In the floor-frame production line, insulation is laid on the floor-frame and an automatic nailer installs the floor boards. Another

automated process assembles columns fitted with connecting lugs to form a column frame. The frames are spot welded together in a fully automated process. The frame supports also serve as jigs establishing the frame's dimensions. After the exterior wall panels that are manufactured on a different line are fitted to the structure, the interior items and partitioning panels are installed.

Recently humanoid construction robots have been developed and tested. The evolution of robots in the construction industry is further elaborated by Bock [32]. For example, a robotic precast concrete panel factory uses a multipurpose unit which allows flexible production of unique concrete floor, wall and roof panels. Here, first the robotic cleaning unit cleans the production table and then sets regular spacers. Next the multi functional

gantry type robotic unit with two vertical arms places magnetos on the steel production table according to the CAD supplied design data. In a third step the robotic unit attaches shutters on top of the magnetos and then places horizontal, vertical and triangular

reinforcement bars, according to structural engineering data. Next, a CADCAM controlled concrete distributor spreads the right amount of concrete while controlled by a CAD layout plan, which takes into account installation, window or door openings. The whole system is very flexible and can create any layout, or be run by rush order or optimal panel layout on the steel production pallet (see figure 5).

Figure 5. Gantry-type Robots for Precast Panel Production – Source: Bock [32] Kye-Young Lee et al [9] has proposed the human-robot cooperative (HRC) system to cope with the construction environment via real-time interaction with a human and robot simultaneously. The physical power of a robot system helps a human to handle heavy materials with a relatively scaled-down load. The human can feel and respond to the force reflected from the robot end-effecter acting with the working environment. The human-robot relation is modeled with a target dynamic system which describes physical

behaviors with impedances. The HRC system feature is the power-assistance and force-reflection. The effect of force-reflection is realized by the feedback of force reflected from an external force-sensor. The study also presents the experiments and evaluations to verify the proposed human-robot cooperative system for robotic applications in construction giving the performance tests, like force assistance, force reflection, and position-tracking in a two axes manipulator.

Engelbert Westkamper et al [14] have developed a robotic system for the automatic laying of tiles within certain tolerances on prefabricated modules. The pilot system consists of the following features:

• A tile laying system consisting of tile positioning equipment, centering and measuring system and laying unit;

• An adhesive application system consisting of adhesive preparation, adhesive transport and adhesive application;

• A tile supply system consisting of a store and a measuring unit; • Systems for generating process parameters, and

• Handling and positioning systems having industrial robot and process control. The supply system consists of two laser triangulation sensors moved by a linear motor to measure the tiles. The laying equipment is composed of vacuum grippers on pneumatic cylinders having limit switches and a mechanical centering unit with a linked electronic measuring system. The adhesive application tool consists of a reusable container with a plunger for the supply of the adhesive, a hose pump for transporting the adhesive, and a nozzle for applying the adhesive.

P r e c a s t a u t o m a t i o n

Peñin et al [3, 4] has developed a robotized cell for the manufacturing of pre-fabricated glass reinforced cement (GRC) panels for a Spanish construction company. The system is primarily developed for the automatic programming and control of facade panel

manufacturing. A CAD based 3D-drawing of the building facade serves as the input, and from the CAD design, the optimum facade to the panel’s partition is obtained. In order to manufacture each panel, automatic task and path planning are performed for the available equipment in the manufacturing cell, such as the spraying robot, PLCs, control computer, etc.

Figure 6. Robotized Manufacturing of Precast Panels - Source: Peñin et al [3] Where concrete is used as a structural building material, the modular formwork systems aid in automating the formwork operation and also improves productivity. However, proper planning for the form reuse schemes in the design as well as the construction phases of a building, including resource allocations and the construction sequence, is vital for

successful use of modular formwork systems. Rong-yau Huang [10] et al has employed computer process simulation to study different form reuse schemes and to use gang forming systems in construction. Five form reuse schemes are identified, and to develop computer models for each scenario, a technique known as CYCLONE modeling

methodology is employed. Simulations and sensitivity analyses of the schemes, using different numbers of form sets, cranes, and crews, are then conducted for real cases to assess their impact on the productivity and the cost-effectiveness of the operation.

Eastman et al [24] has reported on the effort to integrate advanced design and

engineering information technologies in the North American precast/pre-stressed concrete industry. The project was undertaken by a consortium of precast producer companies formed specifically for the task. The effort involves significant process modeling work. This has led to the development of a specification for an advanced precast concrete design and engineering application platform implemented by a major building modeling software company. The platform, developed on top of a general parametric modeling CAD platform, is meant to provide the geometric modeling capabilities to support the definition of a precast concrete structure, all of its pieces and connections, and the reinforcing and other components embedded in the pieces. It provides the required geometric modeling,

parametric capabilities, and information handling capabilities of the system architecture. The platform supports the engineering design of precast building assemblies, including whole buildings, like parking garages or the precast components of an office building.It supports top-down parametric modeling, allowing the full building to be defined as sets of precast assemblies that could be updated and automatically revised. Each piece in the assembly is defined, based on its relationship to the overall assembly. The architecture for the software specification is shown in the figure below.

Figure 7. Software Spec. System Architecture – Source: Eastman et al [24]

Automated Construction Site

Automated construction sites use robotics for logistics and assembly. Four major reasons contribute to the use of robots at a construction site: 1) Health & safety risk reduction, 2) Improving the working environment, 3) Improvement of quality and productivity, and 4) Cost reduction. Yet, the development and use of robotic systems for on-site construction faces many barriers. These barriers can be technological barriers or economical barriers. The technological barriers are that a construction robot must cope with the complexity of the construction process involving an unstructured and continuously evolving site,

together with the need for performing multiple tasks with differing characteristics. This is in addition to the replacement of human labor, which necessitates the system to have a

certain level of intelligence in the form of an advanced control system and sensory system. As detailed by Zied [31], robotics research in construction has moved to address the technological barriers via:

• Development of mobile platforms and manipulators • Development of advanced control systems

• Sensory systems integration

• Re‐engineering of processes to suit robotic systems

• Software development to help in the above aspects of development

• The use of advanced IT systems to enhance the whole system performance. The driving force for the final implementation of the robotic system to perform construction tasks is economics. Economical barriers are:

• The direct cost or benefits

• The effect of the new system on the organization – like the technology strategy to comply with factors such as health & safety regulations and labor organizations. • Changes required for implementing the new system.

• Martinez et al [7] has described their research, carried out in the robotization and industrialization of the construction process, with the following objectives: a) Modular design of buildings, with robotic erection as a means for construction; b) automatic planning and real-time re-planning of the offsite prefabrication, transportation, and onsite assembly; c) onsite automatic and robotic transportation, manipulation, and assembly of the buildings’ prefabricated components.

Figure 8. Crane Handling Tool – Source: Martinez et al [7]

They have developed tools for the assembly of building modules, which consist of three main parts:

• The used gantry crane is a low-cost commercially available system with some modifications. Its main characteristics are 4m of span and 500 kg of payload.

• The control system consists of vector control drivers for all motors, and a PC with a multi-axis controller PMAC that allows handling complex motion trajectories, difficult servo filters, advanced computation algorithms, and sophisticated I/O logic

simultaneously.

• A square shaped metallic platform was designed and built to lift and assemble the modules. The conical shape of the electromagnets facilitates the assembly, due to the auto-centre facility.

SMART (Shimizu Manufacturing system by Advanced Robotics Technology) represents modern attempts at computer-integrated construction, which claims to reduce the person-hours required to complete a multi-storey office building by as much as 30% (refer 16). System set-up takes a few weeks, after which the building's top floor and roof are erected on top of four jacking towers. The jacking towers are used to push up the several-ton heavy top floor assembly - the main work platform - as well as lifting their own bases from floor to floor in a cycle time of around two and a half hours. The heart of the system is composed of lifting mechanisms and automatic conveying equipment which are installed on the work platform (this may later become the roof of the building). Overhead gantry cranes are connected to the underside of the roof structure in a way that very much resembles a factory production facility. Trolley hoists are used to lift and position construction components which are introduced at ground level. The whole process is computer-controlled, though workers are still involved in overseeing operations. Simplified connections between construction components facilitate rapid erection times. Floors emerge from under the top floor, and the weather factor is excluded from the site by a mesh fabric hung around the work area. The SMART system automates a range of production processes including:

• erection and welding of steel frames

• placement of precast concrete floor planks

• exterior and interior wall panels

• installation of various prefabricated units.

Koji Hamada et al and others [39, 40, and 41] have described a similar construction system for high-rise reinforced concrete buildings, which is often referred to as the ‘Big Canopy’. As shown in the figure below, the Big Canopy set up consists of a parallel delivery system with three automated overhead cranes and one large construction lift under an all-weather synchronously climbing temporary roof frame. A modern material management system becomes a major part of it with linkage to databases and seamless communication with a CAD system, which draw resources based on prefabricated construction materials, and uses versatile workers.

Figure 10. ‘Big Canopy’ Parallel Delivery System - Source: Hamada et al [37] Essentially, the Big Canopy construction system can be divided into the following subsystems:

• a roof supported by four tower crane posts, which are situated outside the building; • a complex hoist system with three cranes mounted against the roof;

• a jib crane on the roof to mount and to dismantle the tower crane posts; • a high-speed constructions lift to all floors;

• use of prefabricated components with easy identification (RFID, bar-coded etc.); • a material management and delivery system to manage the flow of materials and

components.

The work sequence itself follows something like this: Assemble the temporary roof frame and proceed with basement work under the roof. Raise the temporary roof two floors at a time, and skeleton work is performed using an efficient delivery system under the roof, and complete finishing and equipment work. After the skeleton work is completed, the temporary roof is lowered onto the roof of the actual building in order to dismantle it. Separate the perimeter of the temporary roof frame and lower it in the reverse sequence to the ground so as to dismantle it. The temporary roof is transported to the next project, or may be left as, for instance, a heliport.

C r a n e S e l e c t i o n a n d M o v e m e n t A u t o m a t i o n

Olearczyk et al [26] have elaborated on a construction case based on field experience. Modules are fabricated in factories and transported for the assembly on site. These modules incorporate utilities, furniture and even painted walls, and are stacked together in the required configuration to create a multi-storey building. Presented also is the use of 3D modeling to solve problems of equipment interference, as an approach to the

development of mathematical algorithms for crane position optimization, and to optimize sequential lifting patterns. Algorithms are also used to optimize different construction assembly scenarios, with the most efficient option being selected based on an evaluation of the kinematics movements for each module lift, via a series of simulation sequences. The 3D/4D models are utilized for the training of the operating crew, and for

constructability verification and improvement. To implement the operation schedule, task duration to the minute scale is assigned, which is rarely the case in construction, but is the norm in the automotive industry.

Figure 11. Modular Assembly – Source: Olearczyk et al [26]

Manrique [5] et al. have presented a concept involving the construction of a somewhat complex residential tilt-up-panel structure utilizing 3D modeling and animations. The residence is comprised of 108 precast concrete panels of varying rectangular shapes with “dog legs” and window and door “cutouts”, resembling an assembled jigsaw puzzle. 3D animations were used primarily to experiment with the construction process on the computer screen prior to construction to avoid potential conflicts and on-site errors, as well as a training tool for the contractors. The authors describe a methodology to integrate the crane selection algorithm and optimization model with 3D modeling and animation for the selection, utilization, and location of cranes on construction sites. Over 50 different types of cranes were tested in order to select the equipment with enough capacity to lift the 108 concrete panels, while considering the lowest rental cost and the space

Figure 12. 3D AUTOCAD Model of Building - Source: Manrique [5] et al

Virtual Reality and Simulation in Modular Construction

The use of virtual prototyping technology (VP) in the construction industry is somewhat recent. Virtual reality (VR) enables real-time viewing of, and interaction with, spatial information. Virtual prototyping technology can assist planners to verify their plans so that construction risks can be eliminated before the commencement of the actual project. It enables contractors to “construct the building many times” in the computer, and reuse the model at different stages of the construction process. Different scenarios can be

previewed and potential problems identified in advance in visualization process. The visualization can perform such tasks as production, transportation, handling and assembly of different construction components, including all the associated operational processes. Li et al [27] described an integrated framework and process for general contractors to apply the VP technology. In this framework, an expert (process modeler) accepts the BIM model from the designer, and decomposes it into formats required by the main contractor, subcontractors and consultants. At the same time, the process modeler integrates

information provided by the construction team into the BIM model to create a virtual prototyping of the construction processes. Through an iterative process, the process modeler enables the construction team to conduct ‘what-if’ analyses of different

construction methods in the virtual prototyping environment, until a satisfactory method is obtained.

Typically, the construction companies use virtual models only on large and complex buildings and infrastructure projects. The lead users are concerned with reducing risk, increasing technological innovation and improving business processes; that is, the visualization is seen as a means rather than an end. Some VR applications in the construction domain include [2]:

• Recognition of design errors and clashes early in the process, • Improve design and reduce waste in the construction process,

• Constructability analysis and demonstrating with clients before the project starts, • Helps in bidding for the construction of a facility,

• Customer interface – offer the customer a greater understanding of the ‘product’, • Reusing the modules across many different construction projects and with the

advantage of being able to sell from a virtual plan as it reduces the development risks.

Murray et al [8] described a virtual environment that supports the design as well as the construction process of buildings assembled from prefabricated components and simulates the construction sequence according to a schedule. The design environment imports a library of 3-D models of prefabricated modules that can be used to interactively design a building. The construction schedule of the designed building can be altered, and the information may be fed back to the construction simulation environment. Within this environment the order of construction can be visualized using virtual machines. It provides a single 3-D environment where the user can construct their design through automatic constraint recognition and view the real-time simulation of the construction process within the environment. A visualization tool such as the one just described could assist the site manager in obtaining a better perception of the project which could be achieved by integrating the schedule management of the project with an animated virtual environment display.

Figure 13. Virtual Construction Environment – Source: Murray et al [8] In this environment, the model creation requires very minimal user interaction as it

supports automatic constraint recognition between the components so that when the user constructs the model, the system automatically detects whether the components that being manipulated can be linked. An object database holds the types of modules that are used in the building and any relevant information applicable to the component, such as price, size, construction methods, etc. It also holds information relevant to the construction site, such as stock, resources and delivery information. As the user creates the building, the construction information is stored within the object database along with the order of construction and any dependencies between the tasks. One may review the building being constructed from within the virtual environment; the construction order of the 3-D model can be replayed to provide an animated 4-D model, combined with virtual machines (a crane, for instance) to simulate the construction process. Using a project plan, the

construction schedule can be altered and fed back into the virtual construction environment to explore alternative schedules.

Nasereddin et al [6] described an automated approach for developing discrete event simulation models, very much applicable to the prefab industry. The paper describes elements commonly found in modular manufacturing, and summarizes an approach for automating the model development process using ProModel and Visual Basic. A case study is presented to verify advantages that included a reduction in model development time and improved modeling consistency. In ProModel, work locations must be defined and presented on the simulation canvas. The animation data which was done manually includes the graphics library that they created for the modular home manufacturing industry (see figure below). The library is used to show animation changes to the module as it is processed through the production line (example: after the wall set process is done, the simulation model will show the graphic with the walls installed). The simulation

analysis is reported to have helped the clients to choose a factory layout that increased the overall production capacity by as much as 50%.

Figure 14. ProModel Graphics Library – Source: Nasereddin et al [6]

Planning for Automated Building Assembly

Automatic planning of construction process is an important premise of construction automation. In this context, construction of a prefabricated building can be considered analogous to the assembly of a manufactured product where the assembly is the reverse of disassembly in most cases. And in manufacturing, through the disassembly of a product, the disassembling process can be planned and based on which assembly

process plan can be inferred. Drawing on a similar parallel, components are basic units of a building, and a building is comprised of a number of components assembled according to certain rules and constraints. The assembly of building components is dependent not only on geometric properties of components, but also on the assembly relationship of the

components. Accordingly, a computer model of construction in a prefabricated building will consist of relationship information of components and spatial restriction information. With these in mind, Hu [33] has presented a method for the automatic determination of a construction sequence from a connection graph representing a pre-fabricated building through the extraction of components. The extraction is based on the recursive extraction of components by a simultaneous verification of disassemblability. Components that are tightly connected together geometrically and physically, but loosely connected to the rest of the assembly, are selected as a preferred super-component. The process of extracting components not only makes it possible to reduce the problem space by early pruning of infeasible construction sequences, but also explicitly defines temporal and spatial parallelism in construction.

Scheduling Automation and Sensor-based Control

An efficient production schedule can drive the automation process in the making of prefab components. Several scheduling prototypes are reported to be developed addressing this issue. For example, adecision support system for coordinated prefabrication production scheduling has beendescribed by Weng-Tat Chan [28]. The system supports key elements of production (re)scheduling, namely, conflict detection, determination of the priority for conflict resolution, generation and evaluation of alternatives forconflict resolution, and ranking of outcomes for negotiation. Itcombines the use of an explicit constraints-based scheduling model, geneticalgorithms for the determination of

scheduling parameters and conflictresolution priorities, as well as constraint programming to facilitate the rapiddetermination of several alternative schedules with minimum

disruption of existing plans. Note that genetic algorithms (GA) have been popularly used in many areas: constrained or unconstrained optimization, sequencing, transportation, reliability optimization, artificial intelligence, and many others. A (GA) based searching technique is adopted in a mixed precast flow-shop scheduling system proposed by Leu and Hwang [35] to provide the optimal or near-optimal combination of production

sequences, resource utilization, and minimum make-span while complying with resource constraints and mixed production.

To help automate the planning segment of ‘bespoke’ precast production, Benjaoran and Dawood [34] have developed an innovative planning system called ‘Artificial Intelligence Planner’ (AIP). It has two major functionalities. The first is a data integration system that encourages automation in the planning process. The second is a decision support system for planners to improve the efficiency of the production plans. These functionalities

complement each other to deliver optimum benefits to precast manufacturers. The AIP system adopts artificial intelligence technologies (neural network and genetic algorithm) to assist the process of production planning. The figure below shows the major elements of the system, which are: information inputs, main production processes, and information outputs. Primary information inputs for the system are fetched from external sources (project designers and contractors of construction projects). These can be project drawings, product specifications, and construction schedules. The production process includes product design, productivity estimation, production planning, and component manufacturing. Three major AIP components have been developed, which are: ‘Graphic

data Extractor’ to assist the product design; ‘Processing-Time Estimator’ for the

productivity estimation; and ‘Production Scheduler’ for the production scheduling. The AIP system implements data integration technology through the central database to manage historical and current project data. The outputs of the system can be a quality production

schedule that satisfies short customer lead-time, effective factory resource utilization, and satisfaction of delivery requirements.

Figure 15. Bespoke Production Planner – Source: Benjaoran & Dawood [34]

Geetha Gajamani and Koshy Varghese [29] have presented a system on the use of RFID for automated schedule and inventory monitoring in real time, in the context of

construction that involved precast/ prefabricated components. Note that in the fabrication phase of these components, details of the material composition need to be documented. Data of where they are stored are documented to identify and transport them with

minimum time loss. In the construction phase, the components delivered to the site have to be inspected and stored, and then located and tracked prior to installation. Similarly, details related to installation have to be recorded. During all these activities, the real time data regarding the component identification, its location in the structure, and details of the installation are required. And this necessitates automated data collection, not only for the control but also for the field material management. Addressing these issues, RFID technology is employed to indentify and track building components used in the site, and the data collected in real time is converted using software technology for any future use.

Order Processing Automation

Shin et al [25] described an order configuration system for the construction industry, which is targeted for the automated selection of pre-fabricated housing modules. The order management program (OMP) reported in this project runs on a PC, and offers the customer important information in real time about finishing materials, unit prices,

specification of materials, an installation diagram, final price, etc. In contrast to common practice, which support only limited information through pamphlets and/or visits to the model house, customers can select proposed options directly, and look at the combination of selected options and their pictures in one place. When all the selections have been made, customers are provided with information on the total cost of the chosen finishing materials and the overall contract price in real time as well as the contract itself. The order is sent to the site-office server via intranet or anywhere the customer can access it. The OMP program provides customers with a user interface (see below) to place orders on

finishing materials. The customer can make selections on various combinations of finishing materials in a virtual reality environment.

Figure 16. Option selection for Order Configuration – Source: Shin et al [25]

Conclusion & Future Directions for the Prefab Industry

The type of automation technologies reviewed in this study revolves around actual

projects and research activities related to constructing a real product: that is, construction components, fabricated modules, panels, houses etc. And, it appears that three areas of automations are becoming dominant in the prefab domain – automating the business processes (includes planning and scheduling), the design, and the material handling (robots, etc.). It is reasonable to conclude that the use of some form of automation will be the norm in all factory-built housings of the future. Based on this study, and on our

understanding of the type of automation that already exists in other domains like

manufacturing, a roadmap of the future for the prefab industry is outlined. The vision on future direction details primarily productivity issues of a factory setting (where the prefab components are built), and the quality and functionality of the products being made (the components, assembly of the buildings etc.). The technological and infrastructure issues related to transporting the components to the construction site, and/or technologies related to foundations of the house/building, etc. are not considered.

P r e f a b F a c t o r y – A S t a g e f o r C o n s t r u c t i o n

P r o d u c t i v i t y E n h a n c e m e n t

The ultimate objective of automation is to improve on productivity and quality, which will also contribute to substantial cost reduction. A detailed vision for the prefab industry is carved out based on the ideas given in Mullens [36], the technology roadmap given in manufactured housing research alliance [40], and the findings of the Altus Clayton consultant report [41] as the following:

Embracing those technologies that revolutionized manufacturing industry, prefab builders can radically improve the efficiency with which it produces homes and commercial

buildings. The prefab builders of the future will evaluate ways to improve productivity through the application of lean production, information and automation technologies. It will develop efficient methods for warehousing, inventorying and accessing products in the plant. It will develop strategies to reduce construction waste, and adopt techniques for

recycling. It will develop and deploy technologies for defect-free transportation of the homes and prefab components. It will develop and test alternative transportation system features that are high performance, low cost and more fully integrated into the home's structural system.

The prefab factory will produce high quality custom homes from entry level through luxury. It will provide a productive and safe environment that will offer excellent value and timely delivery for the homebuyer, a safe and rewarding career for employees and a profitable investment for owners. Ample capacity will be available in the factory to accommodate short-term growth. The factory design will be modular and flexible to facilitate expansion to accommodate rapid or longer-term growth. Materials will arrive in the factory just in time to support production, and be stored close to the point of use on the production line.

Materials and production items will be identified and tracked in real time to monitor the exact location and status of all items. Automation will be provided when justified, for both material handling and manufacturing processes to eliminate injuries, minimize excessive physical exertion, assure capacity and boost productivity. Production documentation will be accurate and timely and can be accessed from remote locations. Employees will know the status of any order, recognize the restrictions at any workstation or work group, and be able to react so that schedule and customer demands can be profitably met. Rework will be minimal and production flow will be smooth and synchronous with demand.

Employee work groups will be actively engaged in continuous improvement and will share in the resulting profits.

Synthesizing these ideas, it can be inferred that achieving a smooth flow of production is one of the outcomes of automation within the factory that builds prefab components. Production flow is a function of many parameters, like the factory line length, location of facility-constrained workstations, module sequencing, and task process times. Whereas, the process times are driven by module design, process/material handling technologies, workforce levels, and location of material staging and support workshops. Accordingly, the key drivers of production flow fall into four areas: module design, process and material

handling technology, factory configuration, and shop floor planning & control. These

factors are interrelated, and are areas that require more investigation.

Module design and advanced process & material handling technology have a major impact on production flow. Modular manufacturers seek designs, materials, equipment and systems that are engineered specifically for their factory production, and that provide obvious advantages over site built houses. Factory configuration also plays an important role in reducing the impact of bottlenecks in the production line. It requires an adequate number of line workstations to provide a total flow time in which all critical path activities may be completed. A critical path activity requires detailed examination to see if certain sub-activities can be taken off the critical path by moving off-line. Effective shop floor planning & control, like the factory configuration, begins with the acquisition of data. Real time data collection tools such as automatic identification (e.g., bar code scanning, radio frequency identification) should become the standard practice. Challenges also lie in developing systems that work in dirty, rough, open (even outdoor) environments. Using these tools on a continued basis can provide the data needed for real time planning, shop floor control and longer-term continuous improvement. Bottleneck management will also require the development of decision support systems that assist in scheduling and labor assignment. Support technologies are likely to include optimization, simulation,

P r e f a b B u i l d i n g – A n E x a m p l e o f Q u a l i t y a n d

F u n c t i o n a l i t y

Technological considerations on how to enhance the quality of the actual product being constructed (i.e. constructed components, houses, etc.) in terms of its function, is also an important factor. Forward thinking on how the product of the future will look and behave can give good insight.

In future, the prefab components and houses will adopt a systems integration approach to the design, engineering and construction. It will incorporate fully integrated structural systems that resist the forces applied during home transport and site installation. Included will be new building envelope systems (roof, wall and floor, etc.) that maximize integrated performance. It will integrate plumbing and mechanical systems within the whole module. It will develop new wiring and cabling systems that optimize whole-house performance. It will also incorporate the range of functions that wired and wireless technologies and systems can offer. It will develop new assemblies and subassemblies that improve performance, which could be applied with ease in the factory setting. It will pinpoint the reasons for failure of materials and systems attributable to manufacturing and/or installation problems. It will develop new manufacturing, installation and joining (eg: fasteners, adhesive joints, etc.) techniques, and new component designs to minimize failures. A virtual and/or simulation environment that supports the design of the modules and components, as well as the assembly of these to simulate the construction process respecting certain schedule will become the standard practice. The simulation

environment likely will import a library of 3-D design models of prefab modules that will be used (re-used) to interactively design the whole house/building.

It will test and evaluate the performance of new materials and building systems under extreme conditions, including accelerated aging. It will improve the life expectancy and in-place performance of the materials, products, systems and assemblies that go into prefab modules, beginning with the exterior envelope (walls and roof). It will develop next

generation mechanical equipment and air distribution systems. The design and operation of all its homes promote and contribute to the health of their occupants. It will develop and deploy methods for controlling sources of contamination, techniques for improving

ventilation, and systems & procedures for controlling moisture. The built units will be the most energy efficient choice of housing, and annual energy costs of these homes will be as low, or even lower than comparable site-built homes. It will develop and deploy new and existing energy conservation and renewable energy technologies and strategies.

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