Robotic Sewing
Robotic Sewing
ABSTR ACT
Unlike any other building material, timber has seen numerous innovations in design, manufacturing, 1 Interior view of the ICD/ITKE
Research Pavilion 2015-16. The
and assembly processes in recent years. Currently available technology not only allows architects
finished large-scale prototype
to freely shape building elements but also to define their micro- or macroscopic material make-up building serves as an architectural
demonstrator for research into
and therefore the material itself. At the same time, timber shells have become a focus of research in
robotic sewing.
wood architecture by rethinking both construction typologies and material application. Their main
advantage, however, also poses a challenge to its construction: As the shell is both the load-bearing
structure as well as enclosure, its segmentation and the individual segment’s connections become
increasingly important. Their complex and often differentiated geometries do not allow for stan-
dardized timber joints, and with decreasing material thickness, conventional connection techniques
become less feasible.
The research presented in this paper investigates textile strategies for the fabrication of
ultra-lightweight timber shells in architecture. Specifically, a robotic sewing method is developed
in conjunction with a computational design method for the development of a new construction
system that was evaluated through a large-scale prototype building.
224
INTRODUCTION due to the comparatively high effort necessary for their in-situ
The development of new building products such as Laminated construction, which involves the manufacturing of complex
Veneer Lumber (LVL) and Cross-Laminated Timber (CLT) not formwork and extensive manual labor, even with today’s high
only enabled the use of planar elements but also drove timber degree of automation. An alternative is the construction of thin
construction towards a homogenization of wood properties for timber shells made from segments, as demonstrated in previous
the sake of calculability. The unique and specific characteristics of work in the Landesgartenschau Exhibition Hall (Krieg et al. 2015)
wood, such as its anisotropy and elasticity—which both depend and the ICD/ITKE Research Pavilion 2011 (Menges and Schwinn
on grain direction—are leveled out through the cross-lamination 2012). However, the dimensional limitations of plywood, as well
of individual anisotropic layers. Whereas conventional timber as the subsequent need for transportation, limits the size of the
construction relies on thick cross sections and metal fasteners segments from which the shell is to be constructed. In addition,
for connections, the aim of this research is to construct very thin as the previous case studies have demonstrated, the planarity
shells made from plywood by taking advantage of the specific of the available timber sheet material leads to the requirement
material characteristics in the design and fabrication process of elaborate planarization strategies in order to approximate
and by using alternative connection strategies suited for very complex double-curved surfaces while respecting fabrication
thin sheet material. Consequently, form-finding principles have constraints (Schwinn et al. 2014; Schwinn et al. 2013).
to be established that incorporate materiality and fabrication
possibilities. Another major challenge in the development of segmented shells
is the design of the joints, as the stiffness continuity of the shell
New developments in digital fabrication, particularly in robotics, is interrupted (Li and Knippers 2015). Therefore, a particular
allow for the implementation of design principles such as focus of any design approach for segmented shells has to be
heterogeneity, hierarchy, or anisotropy in architecture, which the joint design. This has led to a considerable research effort
are characteristic principles found in nature (La Magna et al. directed towards the design and fabrication of so-called inte-
2013). Enabled by computational design strategies, the premise grated joints (Krieg et al. 2015; Robeller and Weinand 2015).
of these high-level principles is that, similar to biology, more Contrary to conventional timber construction, the complexity of
geometric variability can lead to higher performance of the struc- the joint is integrated into the element through elaborate digital
ture, given that its elements are individually adapted to specific fabrication techniques. However, this poses a problem for thin
requirements and less energy and material is required in their shells with a highly reduced material thickness. Not only can
construction. Consequently, the research presented in this paper the geometric complexity of integral joints not be embedded
is to a large extent based on the abstraction and transfer of within an element’s edge below a certain material thickness, but
morphological principles from biology to the design and fabrica- building codes also regulate the required distance between metal
tion of thin shells in architecture. fasteners like screws and the material surface. Both aspects limit
the further reduction of shell thickness. Furthermore, although
The availability, analysis, and abstraction of relevant biological integrated connectors such as finger and dovetail joints are
principles and the aspects related to structural analysis and form- and force-fit connections, they are usually the result of
simulation, both of which are discussed in Bechert et al. (2016), subtractive fabrication processes such as CNC milling. In these
lie outside the scope of this paper. Rather, this paper focuses processes, the continuity of the cellulose fibers in the wood is
on the technical transfer of these principles and on its methods disrupted, potentially weakening the material, particularly where
of implementation in the design and fabrication of thin shells; the main forces are transferred between building elements.
specifically, on the joint design and custom robotic fabrication These aspects have led to the search for alternative joining
approaches. Its main hypothesis is that the design and construc- techniques for thin timber and to the investigation of a possible
tion of very thin, geometrically differentiated timber shells transfer of textile processing techniques into timber construction.
requires alternative connection and fabrication methods and
that, consequently, they can be built entirely without the need of Textile Techniques
traditional timber fasteners (Fig. 1). From a microscopic point of view, wood, like most biological
constructions, can be considered a natural fiber composite
CONTEXT AND RELATED WORK exhibiting similar properties to man-made composites such as
Thin Timber Shells fiber-reinforced polymers (FRP). In both cases, the fiber direc-
Continuous thin concrete shells have been a popular typology tion in the lay-up determines the anisotropic material behavior.
in architecture and engineering from the 1930s to the 1980s. In the case of technical textiles, this allows users to design the
However, they seem to have lost their appeal in recent decades material properties to meet structural or other requirements in a
3a 3b 4
bottom-up manner. This is why FRPs play such a crucial role in usually preferable to few large connectors (Herzog et al. 2003),
automotive and aerospace industries, where a high stiffness-to- which lead to force concentrations and possibly material failure.
self-weight ratio is required. In the case of wood, however, the While textile approaches have previously been proposed by
anisotropic material behavior is usually considered undesirable Weinand and Hudert (2010), as well as Fleischmann et al. (2012),
in the context of the building industry, leading to the devel- they have mainly been limited to weaving and intersecting
opment of plywood or fiberboards with mostly homogeneous plywood strips.
characteristics.
Despite the possible benefits and advantages of sewing timber,
The objective of this research is consequently to re-consider examples seem extremely rare. The Couture armchair by Färg and
and re-interpret the material properties of wood in light of its Blanche (2015) is made with a stationary industrial grade sewing
textile nature. The field of technical textiles and in particular the machine used to connect layers of plywood of approximately
field of fiber-reinforced polymers provides established methods 4 mm each. The fabrication is restricted to two-dimensional
for manipulating anisotropic sheet material with the potential sewing in the plane on a large table and the work piece is guided
of being transferred into an application in timber architecture. manually. However, it proves the viability to sew plywood
Sewing is identified as a particularly promising approach, where using machines from the leather and upholstery industry and
initially planar sheets are connected along their edges using indicates the high quality of sewing that can be achieved. An
thread, resulting in complex three-dimensional forms based on industrial example of robotic sewing with applications mostly
two-dimensional cut patterns. The goal is therefore to apply in the automotive industry is the 3D-Robot Sewing unit by KSL
techniques such as patterning, sewing, lacing, and lamination to for the “application of decorative seams to automotive interiors”
the fabrication of lightweight building components made from (Keilmann 2014). In general, however, sewing has mostly eluded
timber, and to exploit the material’s elasticity during fabrication, automation, most likely due to the complications of simulating
resulting in self-supporting and stable structures. the complex behavior of textiles. It remains a process where
human sensory capacity and manual dexterity cannot be easily
The parallels between timber and textiles become more evident replaced by mere robotic precision.
at material thicknesses much lower than those usually used in
timber construction. Given the thickness of rotary sliced veneer Yet, robotic sewing does provide the opportunity to sew three-di-
of about 1 millimeter, the material can be manipulated like a mensionally, unconstrained by any work plane, and with high
textile. Furthermore, sewing has similar advantages in timber precision. It opens up areas of application thatin turn would lie
construction as it has in textiles, as many small connections are outside the range of human capacity. Using an industrial robot for
handling timber veneer through a stationary sewing machine was 1. Transferring textile processing methods from the field of technical
therefore investigated as a fabrication approach in this research textiles to digital fabrication and construction in architecture;
project. 2. Utilizing the specific material characteristics of wood as drivers for
the development of a construction system including multi-material
Biomimetics joints;
In previous research, biology has been an extensive concept 3. Investigating alternative approaches to planarization for segmenting
generator for the design of segmented shells (Grun et al. 2016). shell surfaces taking the bending elasticity of wood into account;
Biomimetics serves as a design strategy to analyze and transfer 4. Synthesizing the design principles, material characteristics, and textile
the mechanical behavior, constructional morphology, and methods in an integrated computational design and robotic fabrica-
functional properties of load-bearing systems from nature to tion approach; and finally
technology. Different biological role models have been repeat- 5. Testing the above hypotheses through the construction of a full-scale
edly used as concept generators for the design of thin shells. architectural prototype.
This includes the aforementioned timber shells, the ICD/ITKE
Research Pavilion 2011 and the Landesgartenschau Exhibition METHODS
Hall, but also the ICD/ITKE Research Pavilions 2012 (Reichert et Biomimetic Design
al. 2014) and 2013–14 (Dörstelmann et al. 2014). In the latter Biological examples of segmented shells as they can be found
two examples, the fibrous morphology of natural fiber composite in the regular and irregular sea urchins in the class of Echinoidea
shells of lobsters and flying beetles, which consist of chitin fibers have been investigated and analyzed with a focus on the struc-
in a protein matrix, was translated into extremely lightweight tural morphology of the shells on different levels of hierarchy,
shell structures. ranging from the microscopic level to the whole organism. In the
context of this research, the most relevant novel principles that
Research Objectives have been identified and translated into design principles for
Based on the observations regarding the architectural and struc- segmented shells include (1) the fibrous connections between the
tural potential of segmented thin shell structures, the anatomy plates in the test (Fig. 2); (2) internal supports, which connect the
of wood, the textile approaches in lightweight constructions upper and lower shell layers of irregular sea urchins (Fig. 4); (3)
using FRP, as well as the opportunities provided by a biomimetic shell openings, which can be found in irregular sea urchins in the
design approach, the objectives of the research within the scope form of lunules; and (4) the growth principle of plate accretion
of this paper are as follows: and addition was transferred for the design process of the shell.
The fibrous collagenous material acts as an additional connecting An initial challenge for the design of the loops’ edge curves
element, which can be observed in the joints between the plates was the approximation of elastic curves of different radii that
of some sea urchins. It is hypothesized that it plays an important result from varying the material stiffness of the bent plywood.
role in maintaining the shell integrity during growth as well However, as the required stiffness can be calculated from the
as for dynamic forces throughout the sea urchin’s life (Chakra desired curvature radius, discretized stiffness values could
and Stone 2011). This principle of a multi-material connection be deduced from the digital model, resulting in a database of
has been translated on the level of the connection between element-specific lamination instructions (Fig. 6). The resulting
elements as well as on the level of connection of layers of veneer tri-looped segments each consist of three developable surface
during lamination using robot sewing. patches of varying curvature.
Computational Design and Simulation The digital model at this point not only captures the architectural
An integrative computational design approach is essential design intent, and the material specifics of bending custom-lam-
in order to incorporate different requirements of fabrication, inated plywood, but also the constraints of fabrication resulting
material characteristics, biological principles, architectural design from the specific robotic fabrication setup. These are continu-
intentions, structural analysis, and ultimately also constraints of ously monitored by simulating the robotic fabrication process
time and budget. There are different computational strategies to within the digital design environment, which allows for checking
control and evaluate interdependent parameters within a form- for out of reach positions and collisions (Fig. 5). In order to
finding process. In this research project, the aforementioned arrive at a configuration that integrates these constraints, design
procedural biomimetic principle of plate accretion and addition iterations of the parametric model allowed us to locally adjust
was used as a basis for the development of a design tool. curvature of the design domain, the spacing and location of the
input points for the segment generation, and control the curva-
In a first step, the design of the spatial configuration of the shell ture of the segments through the shape of their edge curves.
structure—that is, its orientation on site, its span, and its support Additionally, each design iteration has been analyzed structur-
points—is defined parametrically as a design domain in the form ally. The structural analysis has been informed by material tests
of a non-uniform rational b-spline (NURBS) surface. In the subse- described in Bechert et al. (2016). This informed model then
quent step, the design domain is populated by a particle system forms the basis for the generation of the fabrication data: the
originating at the supports, which represents the segment center lamination instructions, the generation of the finger joints along
points and implements the growing radii of the segments over the edge loops where the segments are connected to each other,
time. The result is an evenly spaced arrangement of input points the NC-code necessary for their 3-axis milling, and finally the
with tangent circles indicating the increasing radius of separation generation of the robot code based on the sewing lines (Fig. 5).
between segments away from the seeding origins. This process
terminates as soon as the design domain is filled with input Textile Methods: Material Design
points and the kinetic energy of the system is minimized (Fig. 3A). Similar to textile fabrication methods, the grain direction and
The third step constitutes the generation of a topological relation lay-up of the laminate ultimately defines the material’s charac-
between previously generated input points on the design domain teristics. In order to approximate the required curvature along
using a Delaunay triangulation of the UV parameter space. The one of the elastically bent strips, their bending stiffness has to be
edges in the resulting mesh form the basis for the generation of programmed through an individualized lamination process (Tamke
the segment loops in the shell (Fig. 3B). et al. 2012). The relation between varying grain directions and
layers of veneer, and the resulting bending stiffness was evalu- Textile Methods: Robotic Sewing
ated through physical bending tests with beech plywood (Fig. 6). The robotic prefabrication process is developed not only to
These experiments also established the lower bound of curvature connect three elastically bent strips into a segment, but also to
that the laminate would tolerate before failing. Summarizing, in assist in their assembly beforehand. In this first step, the robot
areas of higher curvature, the material stiffness has to be low, is used as a positioning aid in order to assemble the three strips
resulting in low material thickness and the grain direction of the in their correct elastically bent shapes. As there is otherwise
laminate running mostly perpendicular to the bending direction. no information on the relative position of the upper and lower
Conversely, in areas of low curvature, a high stiffness is required, base plane of the segment where all three strips meet, the robot
resulting in a material thickness of about twice as high and the positions its variable effector accordingly (Fig. 8). All three strips
predominant grain direction in the laminate running parallel to are then glued and connected to the effector, which in turn is
the bending direction. fixed in its predefined position in order to stabilize the segment
for sewing.
Each strip is divided into 100-mm-wide areas of discretized stiff-
ness and carries information on the number of veneer layers and An industrial grade sewing machine is used as an external tool
their grain direction, depending on the required radius. The strips through which the robot then guides the segment (Fig. 9). It
are then unrolled and nested on the bounding box of available is integrated into the robot control and activated through
beech veneer and plywood stock material. From here on, the a command in the robot code. When the sewing machine
production information is connected to a sheet of stock material controller receives a command, it initiates a stitch and sends back
that usually includes two to four individual strips. In order to a signal once the stitch is complete. This method ensures that
guarantee a precise and efficient lamination process, the instruc- there is no lateral movement of the segment while the needle
tions are transferred to the stock material using a projector. is penetrating the material. Instead, the segment is only moved
Since the resulting laminates have locally differentiated material in between stitches. Even with the communication between
thickness, lamination is achieved through vacuum pressure. The robot control and sewing machine, one stitch only takes about
individual strips are then cut out from the laminated sheet using 500 milliseconds. Sewing lines are predefined in the digital
a 3-Axis CNC cutting process. The finger joints along the looped model based on the size of the segment and the robot effector
edges are shaped to accommodate the varying angles between position in order to ensure a distributed connection, and as a
segments. As these range from coplanar to perpendicular, the consequence, evenly distributed pressure between the strips. In
finger joints vary in width and length (Fig. 7). order to accommodate minor differences between the simulated
segment model and the actually bent segment, a path correction
routine has been incorporated into the sewing process that development of the described textile connection approaches.
allows the online control and adjustment of the robot position Consequently, the entire shell has been constructed without the
during fabrication. need for traditional timber fasteners. The structure ultimately
weighs 780 kg while covering an area of 85 square meters and
As the robotic sewing ensures that the three strips are tightly spanning 9.2 meters. With an average material thickness / span
connected while the glue is curing, even after the segment has ratio of 1/1000, the building has a structural weight of 7.85 kg/
been taken off the robot effector, it is also used to attach an m² shell.
additional membrane element along the segment edges, which
allows the connection of neighboring segments through lacing. The large-scale building prototype is not only a demonstrator
As a second hierarchy of textile connection, this conventional for the developed construction system, but is also designed
and well-proven membrane technique ensures easy accessibility to incorporate surrounding site conditions. The pavilion opens
during assembly. up towards the campus area and provides a view towards the
university buildings and the neighboring park. It provides shade
On-Site Assembly and forms a point of attraction for an otherwise rarely used part
After varnishing the segments in order to protect the wood of the campus (Fig. 11).
against moisture and to prevent fungi growth, the 151 pre-fab-
ricated segments where assembled on site in 12 days. While the Similar to the biological role model, the structure not only
finger joints could be used as a positioning aid, the lacing tech- functions as a pure shell, but allows for structural situations with
nique allowed the gradual tightening of the connection between higher bending moments through the introduction of columns
two segments during the assembly process, and thereby adjusted (internal supports) as an integral part of the construction system.
already connected segments when necessary. The overall struc- All forces are ultimately translated locally into membrane forces
ture not only showed a high flexibility but also enough rigidity to in the plywood segments, but globally, the system allows a
be built from the ground up without large-scale support, even transition from a shell system to a column and slab system. This
during critical assembly phases (Fig. 10). offers entirely new architectural possibilities by expanding the
catalogue of structural types and possibly constitutes one of
RESULTS the main contributions to the field of segmented shells. The
Each of the 151 segments is between 0.5 and 1.5 meters synthesis of the many different and sometimes-conflicting design
in diameter and has a material thickness between 3 and 6 requirements allows for the exploration of a specific domain of
mm. The extremely low thickness of the material required the the solution space that would not be accessible otherwise.
10
DISCUSSION AND OUTLOOK gets more complex, adaptive robot control is being investi-
Multi-material fibrous connections have proven to be a valuable gated through the integration of a sensor-based control loop.
technique for thin, segmented timer shells. Being exposed to In order to achieve highly adaptive sewing techniques for thin
rain and UV-light, delamination has been expected to be a major and flexible materials, sensor input is essential to react to, or
concern. However, the sewn connections within each segment encourage and build upon the inherent material behavior during
have proven to prevent delamination even after the employed the fabrication process.
glue was heavily exposed to the weather. Instead, the preten-
sion in the elements derived from elastic bending was lost faster
than expected due to creeping of the wood. This was presum- ACKNOWLEDGEMENTS
ably due to the unusually wet spring and the repeated wetting The work presented in this paper was partially funded by the German
and drying of the wood, resulting in the sagging of the structure Research Foundation (DFG) as part of the Collaborative Research Centre
in the mostly horizontal slab area of the shell. Although the TRR 141 “Biological Design and Integrative Structures.” The project was
construction system has not been developed as a weather- also supported by GettyLab.
proof shell, the integration of membranes already hints at the
The authors would like to thank their fellow investigators from the
possibility for integrating larger membrane elements, such as a
Institute of Building Structures and Structural Design (ITKE)—Prof. Jan
secondary layer functioning as a constructive wood protection,
Knippers, Simon Bechert, and Daniel Sonntag—and the work group
which is expected to mitigate the creeping effect.
Paleontology of Invertebrates of the department of Geosciences at the
University of Tübingen (IPPK)—Prof. Oliver Betz, Prof. Nebelsick, and
The described robotic fabrication process is based on a large-
Tobias Grun—as well as their colleagues Long Nguyen, Michael Preisack,
range industrial robot arm with the material attached to the
and Lauren Vasey for additional support during design development.
robot flange and a stationary sewing machine. An alternative
robotic sewing setup has been tested as part of the Robots in The presented research was conducted at the intersection between
Architecture workshop, “Robotic sewing of timber veneer lami- research and teaching together with students of the ITECH MSc
nates,” where two cooperating robots handle the work piece and programme. The authors would like to express their gratitude towards
guide it through an industrial sewing machine. Another alter- the students Martin Alvarez, Jan Brütting, Sean Campbell, Mariia Chumak,
native setup where the sewing machine is carried by the robot Hojoong Chung, Joshua Few, Eliane Herter, Rebecca Jaroszewski, Ting-
as an effector is currently under investigation. In each case, the Chun Kao, Dongil Kim, Kuan-Ting Lai, Seojoo Lee, Riccardo Manitta, Erik
robot’s reach and the orientation of the sewing machine define Martinez, Artyom Maxim, Masih Imani Nia, Andres Obregon, Luigi Olivieri,
the resulting design solution space. As the fabrication process Thu Nguyen Phuoc, Giuseppe Pultrone, Jasmin Sadegh, Jenny Shen,
11
Michael Sveiven, Julian Wengzinek, and Alexander Wolkow, who strongly Fleischmann, Moritz, Jan Knippers, Julian Lienhard, Achim Menges,
contributed to the development of this work. and Simon Schleicher. 2012. “Material Behaviour: Embedding Physical
Properties in Computational Design Processes.” Architectural Design 82
(2): 44–51.
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