2. Digital bodies¶

This week I worked on developing a mannequin using different digital fabrication techniques.

Introduction¶

Using mannequins is one of the oldest and the best ways to display customs due to the fact that they provide a semi- real look for the garments when they are worn (refer to the link). There are so many techniques that can be used to build and model mannequins such as vacuum forming, molding and casting also using digital fabrication techniques. With digital fabrication, 3D models for mannequins can be obtained using technologies such as 3D scanning or some special softwares that can develop 3D models for the human body. Then the 3D body can be manufactured using 3D printing or it can be sliced to be fabricated using 2D machines such as the laser cutter and the CNC milling machine.

This week, I have explored how to use 3D scanning to obtain the 3D mesh and then how to get the same result using human modeling software like MakeHuman. Also, I have used Slicer for Fusion 360 software to obtain the 2D sliced pieces of the 3D model. Finally, I have used the laser machine to fabricate the mannequin.

3D Scanning¶

3D scanning is a process of determining the shape of an object’s surface or its volume in three-dimensional space.

3D Scanner¶

A 3D scanner is a device for creating high resolution, accurate digital 3D models from real-world objects. The scanner is built around stereo-vision (normally two digital imagers) and structured light projection in order to generate 3D. The scanner is controlled by 3D scanning software that runs on a computer. A 3D scanner is also capable of capturing the color map of an object. By merging the color map onto the 3D model, a color 3D digital model is created.

3D Mesh¶

A 3D mesh is the structural computarized version of a 3D model consisting of polygons. 3D meshes use reference points in the X, Y and Z axes to define shapes dimensions in terms of height, width and depth. It was very interesting for me to realize from where the 3D mesh came and how the computer analyzes every single point. The following figure illustrates the composition of the mesh.

Generally a 3D model is consisting of many polygon meshes making up the mesh surface. By increasing the resolution of the polygon mesh, the 3D object will tend to look smoother and close to the real object.

This is quite similar to the idea of Analog to Digital Conversion when it comes to electronics particularly when interfacing sensors with a microcontroller in a circuit. Based on the resolution/ number of bit of the microcontroller, the number of steps for quantization will be more or less and the quality of the digitized signal. With the ADC resolution, the shape and quality of the analog signal will be sustained or lost.

Practical Process¶

Used Equipment and Software¶

Kinect 3D Scanner
Kscan 3D Software
Mehsmixer Software
Slicer for Fusion 360
Gweike LC 1390S Laser Machine
Laser Cut Software
Transparent Acrylic (9mm)
Cardstock Paper (A0 size)

Preparing the 3D Model Using 3D Scanner¶

I have used the Kinect 3D scanner and KScan 3D software to scan my friend Saad. The following steps illustrate the scanning process.

1- Preparing the setup I have made the Kinect scanner connected on to of a shelf cart to have it fixed at a high level. Saad was getting ready to be scanned and he sat on a rotating stool in front of a black background to obtain the best scanning results. The scanner was positioned at 95cm - 1m distance from Saad to get the head and the torso detected by the scanner camera.

2- The scanning process

In order to get the full 3D model for Saad, he was sitting in a rotation stool to ease taking pictures from different angles. KScan 3D was an easy software to use for the scanning process. I have reffered to this video tutorial to understand how to use the software with Kinect 3D scanner.

3- Finishing the 3D scanned model

Combining all the scanned images together to obtain the final 3D model.

4- Exporting the 3D model

Obtaining the STL file for the 3D model.

5- Closing the 3D mesh using Meshmixer software

The export 3D model is complete but not 100% solid as it have opening from the top of the head and the bottom of the torso as these parts were not scanned. In order to have a mesh that is printable or can be fabricated by any other digital fabrication technique, the mesh should be closed or in other words the 3D model should be made solid. Many 3D meshing softwares such as Meshmixer and Meshlab can be used to make the object solid. I have used Meshmixer software to close the loop.

Simply I have imported the STL file obtained from the KScan 3D software then I closed the mesh from the "Edit" menu.

Finally, I have got the solid model ready :)

Obtaining the 3D Model from MakeHuman Software¶

Makehuman is a free and open source 3D computer graphics software particularly designed for the prototyping of human body. It was developed in 2017 by a group of different programmers, artists, and academics interested in 3D character modeling. This software is an easy interface to model and render mannequins by simply providing the demnsions and editting the different body features. The following figure shows the tool bar of the software. Note that this bar has different parameters to edit the model body.

To make changes to the model features, you should be in the second tap labeled "modeling".

1- When the software is opened it will give a defualt female model. I have edited the model by changing the customs as follows.

2- From the main menu, I have reduced the musculane feature and the weight to have the model body slim.

3- As I am interested to fabricate the head and the torso of the model, I have opened the torso features to make the body look slimmer and made some editing to highlighted features.

4- From the measure tap, the measurement of the different parts of the body can be edited.

5- After finishing with all the different features editting, the model was exported as an STL file as follows.Go to file then export and then select the format to be "STL".

From the right side of the window, select the measurement unit and then export.

Finally, choose the location to save your file, name it and save it as an STL file.

6- Since I am interested in the torso, the rest of the lower body can be deleted using Meshmixer software.

First, import the STL file using Meshmixer. The file will open with a small scale, inside the build plate of Makerbot 3D printer.

Then I have modified the orientation of the axis for the model (rotating the x-axis by 90 degrees) and edited the dimensions to the real size in cm as follows.

Click on "Select" to select the parts of the lower body and the arms then to be deleted from the model.

After deleting the extra parts, the bottom of the amdomin and the upper arms will result in a hollow model from indside. To have the 3D model closed, I selected "Make Solid" from "Edit" -as done to close the mesh for the scanned object-.

Then I made the model looks neat from the edges of the cut parts (legs and arms) using "Plane Cut" option from "Analyze". Cutting the bottom part of the abdomin.

After cutting the bottom part of the abdomin, the object will be hollow and should be made solid again.

Cutting the arms properly using the same method and making the object solid after each cutting step.

7- Final step will be to export the STL file for the new editted model.

Slicing the 3D Model¶

In order to fabricate the 3D model using the laser machine, the model should be sliced into 2D parts. I have used Slicer for Fusion 360 to do the slicing. This software requires the type of material, material sheets size and the thickness of the material to determine the number of sheets needed for fabrication and to determine the size of the slots for joints that will give the best fit. When you open the software the following window will show.

Slicing the 3D model for the model obtained from MakeHuman software¶

1- Import the STL model.

When the model is open, double check that the size is kept as the original size of the real 3D model.

2- The first step and the most important step is to determine the size of the material that will be used for the fabrication. This will enable the software to analyze how the slices will be designed and to determine how many sheets will be needed to fabricate the model. Since the material for fabrication was unlisted, I have added a new material by simply clicking on "+" then I defined the different paramaters such as length, width and thickness. For the model, I would like to use clear acrylic of 9mm thickness. The tool diameter is made 0mm as I will use the laser machine (however, the tool diameter will matter when using CNC milling machine as there will be drill bit used).

3- Then for the slicing, there are different styles and techniques, I am interested to do "Interlocked Slices".

By default, there are two axises for slicing 1st = horizontal slices and 2nd axis = vertical slices. When the number of the slices per axis is low with respect to the size of the model, the details of the model will not show. By increasing the number of axises, the model details will start to reveal clearly. First, I have changed the direction of slicing from "Slice Direction" option I have rotated the 1st axis by 90 degrees to get a better slicing. Then, I have changed the number of axises to get a clear sliced model.

It is noticed that by changing the number of axises, the number of parts and sheets have increased consequently.

4- After I finished with the slicing parameters, I opened the assembly preview and guide from "Assembly Steps" to have an idea how the model slices will be assembled by simply sliding the winder.

5- The final step will be to get the assembly plan with sheets of material and the different parts for assembly labeled. By selecting the format for the export file to "DXF" files to be saved to the computer.

The exported files will be downloaded as a zip file where each file represet one sheet of material. Since the final number of sheet after editing was 2 sheets, there are exported 2 DXF files.

Slice Saad's 3D model¶

For Saad's scanned model, I have used a different strategy for slicing which was "Folded Panels" using cardtock paper as the material to be cut.

1- I have imported the STL file in Slicer software.

2- I have added cardstock paper as a new material for cutting.

3- I have selected the slicing strategy to be "Folded Panels" and modified the parameters in terms of the number of vertices and the joint type to get the parts with minimal modelissues.

4- Finally I exported the two sheets as DXF files ready for laser cutting.

Using the Laser Cutter for the Fabrication¶

When using the laser machine it is very essential to follow the safety precuations and to make sure that the material used for cutting is safe with the machine type. I have used clear acrylic of 9mm thickness to cut the model and cardstock paper to cut Saad's model. For the laser machine, it is very important to select the proper cutting parameters in terms of laser power and speed of cutting. We have pre-tested the laser machine with many materials.

Cutting Saad's Model¶

After preparing the laser file and setting the machine, I have inserted the material inside the machine. I wanted the design to have two colors, white and blue. I have started with the first DXF file and used the white sheet to be cut.

From LaserCut software, I defined the cutting parameters for the paper to be Speed = 100% and Power = 20%; however, this was for cutting not for engraving. For engraving the folding lines, the speed should be much more than 100% I made it = 200% and power was made very weak = 10% to ensure that the laser will not cut through. Before downloading the laser file, the priorities of the cutting should be defined. Generally, the engraving and inner cuts need to be done before cutting the outer most edges. Therefore, the order was made to do first the gray and red lines first which are the folding lines and then to do the blue lines which represent the cuts for the outer edges.

The machine started first with engraving for all edges and then it cut the outer edges.

However, when I used the blue paper sheet, the laser machine did not cut it properly as the cooling air coming out from the laser head has resulted in slightly moving the sheet. This has affected the design completely especially when cutting the outer edges.

A clearer picture for the issue.

Then I have decided to proceed with the fabrication for the mannequin and to get back later for Saad's model.

Cutting the Mannequin¶

One very challenging task was to be smart about resources and to use only one sheet of acrylic to build my mannequin. I have spent some time to nest the parts together with a minimum gaps between them to sustain the material. I have used LaserCut software to group the parts together, to edit the laser cutting parameters for cutting the 9mm acrylic which was Speed = 5% and Power = 100% and also to prepare the laser file. I could use only one sheet of acrylic with 130cm x 175cm only.