Seeing robots process large work area with high precision

The special feature: robots place the components with high absolute accuracy to a working area of five by three meters in a ISO 6 clean room environment. This accuracy is made possible by machine vision.

Increasing productivity, relieving humans of physically demanding tasks and improving quality – these are the major benefits of robot-based automation.

A specialist in the implementation of robot-based automation solutions in combination with machine vision is the company AKEOPLUS. Based in Château-Gaillard, France, the company is considered a pioneer in the field of robotics. Founded in 2006, AKEOPLUS supports customers from a wide range of industries with applications for optimising industrial robots. As part of its robotics solutions, AKEOPLUS uses advanced vision systems and advanced algorithms. A system that combines the strengths of robotics and machine vision was developed at AKEOPLUS, in coordination and on behalf of Thales Alenia Space’s site in Cannes, in the south of France. Thales Alenia Space is a global space manufacturer delivering high-tech solutions for telecommunications, navigation, Earth observation, environmental management, exploration, science, and orbital infrastructures. Thales Alenia Space’s engineers have developed an innovative bonding process allowing the automation of optical solar reflectors (OSR) placement, while increasing thermal and weight performance. Experts from AKEOPLUS then worked alongside with Thales Alenia Space teams to develop a robotic solution for a satellite panel manufacturing process.

In the cell called ‘SOLAR’, robots place OSR to satellite panels. The goal in the development for this consortium was to enable the robots, under clean room conditions, to place the OSRs to the panel, which measures up to five by three meters, with an absolute accuracy bellow 0.2 millimetres. The ratio of positioning accuracy to the size of the work area is 1:40,000, which was a major challenge in implementation. To meet the requirements, AKEOPLUS relied on MVTec HALCON machine vision software to assist with inspection tasks and alignment of the OSRs.

Benefits of automation: reduced workload for employees, higher productivity, increased quality

Optical solar reflectors are used in the space industry, for example, to protect satellites in geostationary orbits from the high radiation levels prevailing there. A corresponding panel used as an outer wall is equipped with up to 7,000 reflectors, with one OSR measuring around 40 by 40 millimetres. Until now, the OSRs were mounted to the panel purely manually. Two or more workers lying on mats had the task of gluing and positioning the OSR stripes with their arms stretched downward and ensuring they were correctly aligned.

"The production of large panels has increased and working such surfaces was not ideal for the employees for ergonomic reasons. Thales Alenia Space is a major player in space equipment, and they constantly strive for excellence in work conditions and quality of their process. Therefore, we decided together to automate the whole process. The robotic cell has been designed to speed up the process and thus increase productivity. Our customer can now manufacture much faster, even though we have implemented additional steps for traceability and quality assurance," explains Maxime Motisi, Chief Operating Officer and project manager of the SOLAR robotic cell at AKEOPLUS.

Two robots work autonomously thanks to machine vision

For the new automated production process, AKEOPLUS has jointly designed with Thales Alenia Space the SOLAR robot cell. Two robots are integrated into it, as well as a positioning table on which the satellite panels are placed. For absolute accuracy guidance: a laser tracker is dedicated to the six axis robotic arm, and for industrial image processing three high-resolution 2D cameras are used on the hardware side. The HALCON machine vision software is responsible for the quality inspection of the OSR, fine positioning, human-machine-interface, and visualisation.

The manufacturing process is as follows: the small and fast robot takes an OSR from the tray and places it on a vacuum backlight under the first camera station. The camera takes a picture, which is inspected for breaks and scratches using HALCON. In addition, the machine vision method ‘Shape Matching’ is used to determine the exact position of the OSR and to check whether the size and shape of the component correspond to the model provided in the design plan. Position determination is so important because the robot grips each optical solar reflector minimally differently. It is therefore aligned using machine vision in order to transport it to the next production step with an accuracy close to 0.2 millimetre. When the component is ‘OK,’ it is placed under the glue dispenser nozzle. After the glue pattern has been applied, the small robot picks up the OSR again and places it in a post so that the larger robot can grab it for further processing.

The robot with the larger work envelope now moves the part in front of the next image processing station, where the second camera captures images of the applied glue. The captured image of the glue pattern is analysed by HALCON, which checks whether the glue is evenly distributed and respects a very specific pattern that Thales Alenia Space’s thermal engineers have developed, and which must be rigorously reproduced.

This is followed by the precise alignment of the OSR to the arm of the robot. This is the first step in being able to place the reflector with high accuracy at the intended location on the satellite panel. To do this, the third high-resolution camera again takes images of the OSR. The alignment is done by HALCON's algorithms determining the three-dimensional transformation between the coordinates of the OSR corner and the coordinate system of the robot’s gripper that holds the OSR by a vacuum gripping system. The corners of the OSR are determined by the intersection of the edges. From this, a coordinate system can be defined where the corner of the OSR is centred and aligned with the edges of the OSR. The coordinate system of the robot effector was determined in advance by hand-eye calibration of the robot. Determining the coordinate systems is important for two reasons: first, for 3D alignment as the reflector on the gripper might be tilted. Therefore, the corners of the OSR are compared with that of the effector, where each corner are known and hence acts as a reference point. Thus, even minimal tilts or shifts can be compensated. Secondly, the corner of the OSR serves as a reference point for placing to the panel.

However, since the robot's 2.4-meter-long gripper arm is not 100% accurate, but the reflectors must be gripped with a very high accuracy, any inaccuracies must be compensated. With the support of the laser tracker and the HALCON machine vision software, AKEOPLUS has developed an iterative serving process. This enables the robot to mount the OSR to the exact location on the 18-square-meter panel with the required accuracy.

Aligning the OSR on the panel with sub-millimeter accuracy

"We have been working with MVTec for many years. Therefore, we knew that with HALCON we have the powerful machine vision software we need for the SOLAR robotic cell," reports Motisi. AKEOPLUS relies on the C# programming language to operate its equipment. With the help of HDevelop, the development environment integrated in HALCON, seamless process integration is possible. AKEOPLUS managed to load the HALCON script into the plant control system.

Then the human-machine-interface from AKEOPLUS can display each HALCON procedure as a function with the inputs and outputs to be used in the process cycle. This is helpful to not mix the job of the C# developers and the machine vision expert: the vision process takes place inside a capsule, uses images, and parameters as input and returns results or values. Another important factor for the implementation was the speed and possibility to quickly develop or adjust powerful algorithms, which in turn can be easily integrated into the host system.

On the other hand, powerful machine vision software such as HALCON offers technologies to perform, for example, three-dimensional positional determinations or detect defective components. Specifically, matching methods can reliably find objects with an accuracy greater than 1/20 pixel, even if they are partially occluded. In addition, images can be suitably aligned. Subpixel-accurate ShapeMatching is one of the most important technologies in this regard. It enables objects to be found precisely, robustly, and very quickly. With regard to quality control, in addition to checking for defects, determining dimensional accuracy is also essential. This involves checking whether the components are within the defined tolerance ranges. Lastly, machine vision enables the subpixel-accurate measurement of edges along lines or circle segments in less than a millisecond.

Application also serves as a showcase

The SOLAR robotic cell is already in operation.

"The implementation was not quite easy. Especially the work on and with the glue was challenging, but we were able to find solutions together thanks to the know-how of Thales Alenia Space in thermal adhesives. We can now be very satisfied with the result, because the requirements in terms of quality, productivity, and employee satisfaction were all achieved," says a pleased Motisi.

In practice, this means that the cycle time for gluing and positioning an OSR has been reduced to less than 45 seconds, and a OEE of less than 95%. As a result, a large panel can now be completely covered with solar reflectors in five days with just one employee. Previously, it took around two employees and seven days to complete the same panel. In addition, the work environment for employees has improved by eliminating long hours of working lying down and reducing contact with the chemical glue. A new quality assurance process was successfully introduced, namely checking the OSR for breakage and scratches.

In addition, the robotic cell serves another purpose.

Motisi explains: "The SOLAR robotic cell is not only used to produce satellite panels for actual use. The application is also a showcase of Thales Alenia Space’s robotic solutions, demonstrating its capabilities and expertise. And we, at AKEOPLUS, are very proud of this use-case, I would say that it is a condensed of all our skills and know-how, and this allows us to get more customers excited about our innovative technologies."

For AKEOPLUS, the combination of robotics and machine vision has always been a necessity in order to meet needs never realised before.

“Our value lies in the association of cutting edge technologies with robots, MVTec offers one of these key technologies, and has been a partner for more than eight years already,” says Motisi in conclusion.