You will be positioned at our office in Sint-Denijs-Westrem, we develop the Materialise Control Platform, a software-driven, embedded hardware solution that allows you to take full control of laser-based AM machines.
Thesis subject: Automated ScanField Calibration for a 3D printer
Scan heads are used for laser control. They consist out of two galvanometers; one for movement in the x-direction and one for movement in the y-direction (see figure). An incoming laser beam enters the scan head through an entrance aperture. It is deflected by the first reflecting mirror (the mirror for the x-direction in the figure) and irradiates onto the second mirror (y-direction) which on his turn also deflects the laser beam. The mirrors are attached to galvanometers that can rotate around a certain axis. This way the laser beam is projected onto an image plane, which is the build platform in the case of an additive manufacturing machine. A single galvanometer can only deflect a laser beam along a line in the image plane and over a certain restricted angle (±5° to ±10°). This angle restriction is what defines the maximum size of a scan field.
Imagine a scan field image projected on a planar build platform using only a scan head without a dynamic focus or f-theta lens. The scan field as a result of such a set-up would have the shape shown in the left image below.
The scan field on the same setup, but adding either a dynamic focus or an f-theta lens would result in a scan field as shown in the right image. The red scan field might be rotated over a 90° angle, depending on the order of lenses of the scan head (if the lens for movement along the x-axis is the first lens in the scan head, or the second). The lens configuration can vary depending on the manufacturer of the scan head or the scan head type.
In order to understand where these scan field deviations originate from, let’s consider the XOZ plane of an AM machine. The input of the scan head is an angle for x and y. Rref is the working distance in the z direction. This is equal to the distance from the build platform to the center of the optics.
From the above image it can be stated:
x=Rref . tan(α) (1)
For small angles: tan(α) ≈ α
This assumption enables us to simplify formula (1): x=Rref . α
This simplification states that movement in the x direction is linear with the scan angle α. For small scan angles the error made by this simplification is very small, but the larger the scan angles the larger the error. From a certain angle (or distance away from the scan center (0,0)), the error becomes significant.
This is why scan field calibration is essential and has to be well performed.
Today, a scan field calibration is a manual, iterative process that consists out of four main steps: scanning a calibration grid (Ex. on paper), measurement of the error, calculation and generation of new calibration file and verification. The lack of accuracy in measurement tools results in a time consuming iterative process.
Qualifications & Experience
Your goal is to use a camera on the 3D printer that can automate the calibration process. An investigation will be needed to verify what cameras can be used, the accuracy that can be reached and what accuracy is needed. As a first requirement an accuracy of 50 µm on a scan field of 600mm x 600m can be used to check the feasibility. It will be needed to check the calibration of the camera and add this in the calibration process.
You will also implement a software that processes the camera image and generates a calibration file is required.
The algorithm that is used in the manual calibration procedure can be used. Also other algorithms to improve the accuracy or lower the overall cost of the system can be considered as an extension. Extensions: Multi Optics (> 1 scan field)
- You are an Industrial Engineering student: Electronics – ICT, electro- technics, Computer Science or mechanical engineering - electrical engineering
- You are in need of an incredibly interesting and challenging thesis subject;
- You have a passion for research, software, vision and mathematics;
- You are interested in the world of additive manufacturing;
- Please mention the thesis subject(s) of your interest when applying as subject
We offer an inspiring and challenging job with growth potential in an innovative market. You will be part of a dedicated team within a dynamic company that highly values openness, trust and team spirit.