ABSTRACT
Virtual garmenting technique involves advanced software (like CAD) in creating a 3D representation of garments and also creating a virtual feeling of fabrics to satisfy the consumers taking advantage of state-of-the-art algorithm from the field of mechanical simulation, animation and rendering. This system is mainly targeted towards higher accuracy, shortened design process and wider versatility required by a garment designer and also offers a very high level of interactivity for the designer. The main process involved in this technique are flat pattern generation from digitizer, marker making, file conversion to Photoshop, matching fabrics and pattern adjustment, digital printing and automated cutting. This involves large number of techniques such as mechanical simulation, collision detection and response, simulation of dynamic meshes, real time animation of garments and virtual try-on of the garment for the customers. In mechanical simulation, the accurate reproduction of the mechanical behaviour of the material is carried out. In collision detection and response, the geometrical contacts between the complex moving surfaces and the way in which these geometrical contacts alter the mechanical behaviour of the cloth are analysed. The next step is the construction of dynamic meshes that would automatically adapt to the shape and feature changes of the garment patterns during their design. The real-time animation of the garment provides real-time visualization of the garment on the animated body. With the virtual try-on, customers can choose garment and try on 3D mannequins that are adjusted to their body measurements and are assisted to conduct proper online purchase of the apparels. Thus advancements in computer sector reflect in our textile industry by improvising the present trend of technology to meet international standards.
INTRODUCTION:
In the modern era, greatest challenge faced by textiles at the e-customer end is the quality and the selection of garment in a short span of time. Virtual garment simulation is one of the methods available for cloth simulation. This enables the three dimensional construction of a garment from its cloth panels. Animation is the key issue in garment prototyping, as the motion of garments accounts a lot for the final visual look-and-feel of a dressing style. This however requires the simulation to reach a higher level of accuracy. The important features provided by this system are pattern design with interactive garment fitting evaluation, high quality animation previews on moving characters, along with the possibility of managing dressing styles, compared by several complex multilayer garments with many different material and seams.
REPRESENTING THE MECHANICS OF CLOTH
1) Mechanical Properties of Cloth
Cloth being approximated as a thin surface, its mechanical behavior is decomposed in in-plane deformations (the 2D deformations along the cloth surface plane) and bending deformation (the 3D surface curvature).The in-plane behavior of cloth is described by relationships relating, for any cloth element, the stress to the strain (for elasticity) and its speed (for viscosity) according the laws of viscoelasticity.
For cloth materials, strain and stress are described relatively to the weave directions weft and warp following three components: weft and warp elongation and shear stress. Assuming to deal with an orthotropic material, usually resulting from the symmetry of the cloth weave structure relatively to the weave directions, there is no dependency between the elongation components and the shear component .
2) Simulation using Particle Systems
The issue is now to define a model for representing these mechanical properties on geometrical surfaces representing the cloth. These curved surfaces are typically represented by polygonal meshes, being either triangular or quadrangular, and regular or irregular. Continuum mechanics are one of the schemes used for accurate representation of the cloth mechanics. Another option is to construct a model based on the interaction of neighboring discrete points of the surface. Such particle systems allow the implementation of simple and versatile models adapted for efficient computation of highly deformable objects such as cloth.
· Spring-Mass Models
The simplest particle system one can think of is spring-mass systems. In this scheme, the only interactions are forces exerted between neighboring particle couples, similarly as if they were attached by springs. Spring-mass schemes are very popular methods, as they allow simple implementation and fast simulation of cloth objects.The simplest approach is to construct the springs along the edges of a triangular mesh describing the surface. This however leads to a very inaccurate model that cannot model accurately the anisotropic strain-stress behavior of the cloth material, and also not the bending. More accurate models are constructed on regular square particle grids describing the surface. This model is still fairly inaccurate because of the unavoidable cross-dependencies between the various deformation modes relatively to the corresponding springs. It is also inappropriate for nonlinear elastic models and large deformations.
· An Accurate Particle System Model
Because of the real need of representing accurately the anisotropic nonlinear mechanical behavior of cloth in garment prototyping applications, spring-mass models are inadequate, and we need to find out a scheme that really simulates the viscoelastic behavior of actual surfaces. For this, we have defined a particle system model that relates this accurately over any arbitrary cloth triangle through simultaneous interaction between the three particles which are the triangle vertices.
a)Definition in Fabric Coordinates b)Deformation in World Coordinates c)Deformed fabric triangle
(left): A triangle of cloth element defined on the 2D cloth surface (left) is deformed in 3D space (center) and its deformation state is computer from the deformation of its weft-warp coordinate system (right).
(right): Drape accuracy between a simple spring-mass system along the edges of the triangle mesh (left) and the proposed accurate particle system model (center). Color scale shows deformation. The spring-mass model exhibits inaccurate local deformations, along with an excessive "Poisson" behavior. This is not the case with the accurate model, which may still model the "Poisson" effect if needed. The spring-mass model is also unable to simulate anisotropic or nonlinear models accurately.
3) Validation of the Model
Accuracy of a model has been tested by reproducing a "virtual" tensile test using an isotropic material featuring nonlinear metric behavior described with various piece-wise polynomial curves. With elongations up to 50%, the matching accuracy between the original curve and the measured curve did not exceed 0.1% when measured along thread directions, and 1% when measured along arbitrary directions. The error amount was mainly related to the nonlinearity of the curve and the roughness of the mesh.
Virtual elongation test
Virtual elongation test:
A square sample of fabric, attached along its opposite edges, is extended. Its mechanical properties are defined using polynomial spline approximations of real material (curves). The forces measured on the edges against elongation are then compared to the initial curves. The model has been extended to handle anisotropic curvature stiffness through bending momentums applied along
edges, for which the angle between the adjacent elements give an evaluation of the local surface curvature along the orthogonal direction.
The proposed model simulates accurately anisotropic bending stiffness, with possible rest curvature defined on the surface (left).Rest curvature may also be defined along precise lines (center). Lines may also carry additional stiffness with their own custom rest length (right). All these features bring lot of potentialities for designing complex garment models.
4) AN INTERACTIVE SYSTEM FOR GARMENT PROTOTYPING
While essential, computational techniques alone are not sufficient for producing a powerful tool allowing accurate and convenient creation and prototyping of complex garments. We have integrated all these techniques into a garment design and simulation tool aimed at prototyping and virtual visualization, and allowing fashion designers to experiment virtually new collections with high-quality preview animations, as well as pattern makers to adjust precisely the shape and measurements of the patterns to fit the body optimally for best comfort.
The high level of interactivity required by these features necessitates simultaneous computation of the 3D garment updated immediately to each design modification done to the patterns. Our design and simulation tool provides a dual view of the garment, featuring both the 2D view of the pattern shapes cut on the fabric and the 3D view of the garment worn by a virtual character, with tight synchronization. Any editing task carried out in one view is directly displayed in the other view.
Between real and virtual
Between real and virtual:
This system offers high-quality garment simulation, along with highly interactive pattern 2D-3D design and preview tools allowing complex garment models to be designed efficiently with many features such as seams, buttons, pockets, belts...
Interactive Garment Editing Tools:
The system features a fast Constrained Delaunay triangulation scheme that allows the discretization of complex patterns described as polygonal lines of control points (2D locations on the fabric). The system allows variable discretization densities over the mesh, as well as size anisotropy (elements elongated in a given direction), for representing adaptively complete garments from large surfaces to intricate details.
The interactivity of the system is based on two main features:
· Mesh mapping update:
The 2D displacement of any control point of the pattern shape on the cloth surface immediately updates the mesh of that pattern on the cloth, while leaving the 3D drape position of the cloth constant. For obtaining this, each vertex of the mesh keeps track of a weighted sum of the pattern control points, which is computed during the triangulation process. This allows any measurement or shape editing to be directly taken into account by the mechanical simulation without any heavy recomputation, for immediate feedback of any pattern sizing adjustment.
· Mesh topology reconstruction:
When the topology of the pattern mesh is changed (rediscretization, new features,etc), the 3D drape position of the new mesh is automatically recomputed from the drape position of the old one.During this process, advanced algorithms compute, for each mesh vertex of the new mesh, the location of the surfaceof the old mesh having identical 2D coordinates on the fabric. Extrapolation methods are used for computing the location of vertices which are located outside the old surface. This allows pattern design changes (new features, darts, seams...) to be added and modified without needing re-assembling and re-draping the garment on the virtual body.
ASSEMBLING 2D PATTERNS ON THE MANNEQUIN
Modaris 3D Fit (M3DF) is the software used for the simulation of garments, from the patterns prepared and sewn in Modaris. To drape and simulate a garment in M3DF, we first start with the importation of the scanned body of the customer (format .wrl), once the importing of the body is done, the various morphological points should be marked on the body, for example neck, wrist, thigh etc. After the marking of the morphological points comes the stage on creating lines of measurement on the body, using the anthropological line tab. Now to covert this marked body into a mannequin, it needs to be saved as a mannequin (format .mnq). Doing this makes the body with the markings a standard and hence can be used for several garments, without repeating the initial process again. Now that the mannequin has been created, the actual process of draping the garment begins. Load the garment to be simulated/ draped in the window (format .mdl), then associate the various slip on points present on the garment to the various positions of the mannequin respectively, this enables the software to understand the positioning of the various parts constituting the garment. To visualize the seams used in the garment, we can use the seam tab and all the seams in the garment are seen.
The next stage in this process is the Fabric stage, in this stage we select the fabric of the customer's choice and use that fabric while draping. From the various paths given in the Fabric Command Bar, select the File containing the fabric and load it. After the fabric stage, the Assembling of the garment parts is done. Once the assembling of the garment is done, we drape the garment, which takes into account the various mechanical properties to the fabric, unlike the assembly part. If there are any problems relating to collision, then the changing of the size of the mesh and re-simulating the garment would resolve the issue, or else the tools of Inflation/ deflation can also be used. Once the draping is done, using the pull fabric tool we adjust the position of the garment on the mannequin. Layers need to be added when simulating the other parts of the garment like pockets, loops etc i.e. the parts which are not the main body of the garment. Now that the garment is draped, we can measure the ease provided in the garment, using the Ease tab and verify it. Verification of the grain line and the deviation of the grain line can also be checked by the tools in the Control Command Bar. To verify and control the proportion of the garment, in terms of garment, pieces, fabric type and seam types we can use the proportion tab in the
Control Command Bar. After this, save the whole assembly in the type of format preferred, usually in .Url for purpose of importing it into the Virtual Shop.
CREATING THE VIRTUAL SHOP
We needed to create a virtual shop in our project so as to enable the import of the draped mannequins in it. The software that we used in this process was Media Machine’s FLUX STUDIO 2.0 .Flux Studio is an easy to use, inexpensive, general purpose, visually oriented, 3D modeling and animating application that creates and exports real-time 3D web content in X3D, VRML97, and several other open and special file formats.
Flux studio accepts a wide range of 3d formats like X3D, VRML, .DAE, .KLM, 3D STUDIO, DXF etc. Using this software a virtual shop with a capacity to store and display garments was created. An effort was made so as create a shop that would facilitate movement and allow the customers to easily browse all the garments displayed.
The mannequins with garments were imported from the 3D Fit with the latest styles draped on them. This would allow the users to check out the current collections of a brand online thus saving time and effort and thereby making the entire process more efficient. Making the shop interactive is another important task.
CREATING THE WEBSITE & LINKING THE VIRTUAL SHOP WITH IT
A website is the most important link between the customers and the retailers. It was imperative for this project to design a website which efficiently hosted the virtual shop within and allowed the customers to easily interact and place orders simultaneously.
However this involved dealing with critical problems like the size of the virtual shop and the 3 D plug in required to visualize the shop once placed in the website. Inclusion of mannequins with simulated garments on them greatly increases the file size of the shop making it difficult to navigate as well as to upload the file. Thus it is crucial for the smooth functioning of the shop to reduce the file size to the extent possible. This could be achieved by utilizing the minimum required number of mannequins and other objects inside the virtual shop. Besides it is important for the customers to have special plug in installed on their computers which would enable them to view the virtual shop.
CREATION OF WEBSITE AND LIKING WITH VIRTUAL SHOP
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These special plug-in used in combination with explorers enable the visualization of 3D objects on the internet. Some of the commonly used plug in include Cortona VRML Client, Vcom 3D Venues Beta 3.0, Octaga Player, Flux Player and BS contact to mention a few.With the inclusion of appropriate coding a link between the virtual shop and website is created and hence it is possible to access the virtual shop through the website
FLEXIBLE MANUFACTURING
Incorporation of a mass customization approach would have intense impacts on various processes involved in the apparel business. It might require the entire restructuring or reformulation of procedures and strategies. As a well known fact the traditional manufacturing practices do not entail or are not adapted to accept frequent changes in styles. The production of garments in bulk has always been a key factor for bringing down the aggregate manufacturing cost and thus resulting in high profit margins.
However, in a mass customization scenario, where every garment being made would differ from the other. Frequent style changes would require highly flexible manufacturing facility which would enable a large number of frequent changes over. This could be attained by using the principles of component commonality, postponement strategies as well as delayed differentiation.
The basic motive being standardizing the work flow to the maximum extent and creating small modules for customization which could be swiftly swapped and replaced for flexible manufacturing.
FIG 6: MANUFACTURING PROCESS, WITH TWO STYLES
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AUTOMATION OF PRODUCTION SYSTEM
Implementing a micro-controller based single system to interface sewing machines and multi-drop net working to transmit the machine performance and production data to a computer system to store, process and generate reports. These reports will be used by the managers or supervisors to take timely action to increase productivity, to improve logistics and to generate quick response. It is a low cost system with a payback period of about 1 year
PROPOSED SYSTEM DESCRIPTION
System consists of several single board microcomputers and a host computer. Each sewing machine has one single board microcomputer. Each microcomputer is connected to the host computer through twisted pair wire. Microcomputer collects data like machine ON time, piece-handling time, piece stitching time, bundle entry and exit time etc. from each station, stores data in memory and on demand from host computer, it offloads the stored data to the host computer. It analyses the data and generates various reports like production, material on shop-floor location of each piece, efficiency of operator, status of job on hand etc. These reports provide valuable and important information to the managers, supervisors and customers at any time. It also provides cost effective logistics of material movement to meet a planned schedule. It also builds up the data bank for generating norms for standard stitching time of various processes.
Single Board Microcomputer - It is 8-bit micro controller based system with 64KB programme memory to store monitor programme with keyboard for inputting data manually. It has 16 characters, 2 line LCD display-to-display information like on going bundle number, pending bundle number etc. It has got RS485 serial communication port for data Trans-receive. It has also Real Time clock to get various event times.
Sensor - It is a non-contact optical reflectance type sensor, which senses the status of sewing machine i.e. whether the machine is ON or OFF. A reflective strip is mounted on the wheel of the machine and the sensor, which consists of infrared light transmitter and receiver, is mounted in front of it at 5 mm distance. Whenever reflective strip comes in front of sensor, light transmitted from sensor returns and output voltage level of sensor changes. Thus sensor changes its output state whenever machine is running above certain speed and maintains it as long as machine is running at that speed.
Networking - Movement of data is handled using serial communication method. It is a specialized interface that would not be considered standard equipment on today’s home PC but is very common in the data acquisition world. It supports 32 drivers and 32 receivers and with repeater it supports another 32 receivers and with repeater it supports another 32 drivers and receiver. Maximum cable length can be as much as 4000 feet because of the differential voltage transmission system used. Using RS485 technique, single PC is connected to several addressable microcomputer boards sharing cable. Thus it saves cable cost. Since it employs differential voltage transmission technique, data are transmitted efficiently.
Software - Software has been developed in assembly language, which runs on single board microcomputer and keeps track of various events like machine on time, machine off time, piece completion time, piece handling time etc. It stores these events data in data memory and sends stored data to host computer on demand. Software has been developed in VB as well as in Access, which collects data generated at each station at regular interval, analyzes the collected data and upgrades various reports. It also allows user for inputting various other data manually.
CONCLUSION
The system described above has already been used for creating fashion models that have enough realism for reproducing accurately the behavior of real garments. More than draping, this system is able to compute realistic animations. The core technologies of this system are now being adapted to actual needs of the garment industry through collaborative projects, which deal on mechanical characterization of fabrics, virtual prototyping, manufacturing processes, e-commerce. Although some advances are still welcome in the area of efficiency and accuracy of mechanical simulation techniques, the challenge is now to create new tools that will ensure to the garment industry a smooth transition from tradition to novel possibilities offered by virtual simulation |
