The different characteristics of a material are determinative of its application. Because of this the materials used for a product are precisely determined during the development of this product. If the product needs to be light and strong, in an airplane for instance, a various range of composites can be used. Some of these composites are developed and tested at the aerospace faculty of the TUDelft, where students and science come together.
A composite consist of two main components, the vessel and the matrix. When these components are combined, the useful characteristics of each of the two are combined into the composite’s characteristics. This results in light but strong materials with a huge amount of applications. Sometimes these components are already combined, also known as pre-preg fibres, and can be used as tape. This tape can then be placed on a surface in any wanted direction and sequence. After placing the tape, it is treated with a combination of predetermined heat and pressure, resulting in the final composite material.
The placement of the tape by hand takes a lot of time and is very prone to mistakes. Because of this, the aerospace faculty has already developed a prototype tape laying head. This end-of-arm tool was developed to be used with an older robot which is no longer in use. We were asked to make the old prototype compatible with a new KUKA robotic arm and use the whole system to lay pre-preg fibres on an aluminium plate which is treated with release agent. To determine the position and orientation of this plate, a camera with vision-program is used.
To make the tape laying head compatible, all the interfaces have to be made compatible individually. This includes the electrical, pneumatical and mechanical interface, along with the needed programming. Whilst these different interfaces could be worked out alongside each other, they all needed to be fixed in order to start the main part of the programming. The programming needs to consist of different patterns, subroutines and a main program which ties these components together.
The approach of the vision aspect of the assignment changed a few times during the project due to the restrictions of the environment. To make the detection of the position and orientation of the mold reliable, a L-shaped mark needs to be applied in advance using a 3D-printed template. The vison-program will detect this mark and use it to determine the position and orientation of the mold.
After the project, the KUKA robotic arm is capable of laying different layers of tape on top of each other in a predetermined sequence and pattern. During this tape laying process, the different functions of the tape laying head are combined in order to make subroutines, such as cutting and heating, possible. These parts of the tape laying head are actuated using only signal cables. This is achieved by the use of different relays in the electrical box which is attached to the tape laying head. The voltage of the heating element can be adjusted to reach a different temperature in a different timeframe.
All the different electrical components of the tape laying tool are connected through the electric box in a professional and reliable way, whilst making sure that the safety of the electrical system can be guaranteed in every possible way. This electrical wiring is accompanied with updated electrical wiring diagrams in order to make it easily accessible in the future. All the components are controlled by the outputs of the KUKA robot, making them easy to incorporate into the programming.
In order to make the G-code compatible with the KUKA robot, a conversion technique had to be established. For this task, a free piece of software has already been created. This software can be adjusted to incorporate the different subroutines that have to be executed between movements.
After making a new mounting plate and fixing all the pneumatic couplings, the tape laying tool was ready to be attached to the robotic arm. This milestone was, apart from the end of the preparation phase, the start of the main part of the programming activities. The usable tape laying patterns consist of the converted G-code with the defined subroutines. These patterns can be executed by including them in the main program.
The main program features all the standard instruction such as the home position, base information and tool definition. The vision integration section of the main program creates a new base, based on the x, y and angle-value determined by the cognex camera. The different patterns can then be executed in a modular manner, giving the user full flexibility to choose the patterns they need for their sequence.
The whole system is now capable of laying predetermined layers of tape in any given sequence. It adjusts itself to the position and orientation of the mold and lays the tape accordingly. This makes the project a success as for meeting the set goals. The people that will need to further develop the system are provided with all the needed information and recommendations, paving the way for automating this time-consuming composite production method.
Article by: Coen Overvliet