System Integration & Control Systems Design


Accelerating high-precision assembly of micro-optics

January 2022 System Integration & Control Systems Design

German-based Aixemtec develops automated solutions for the precision assembly of electro-optical systems. Founded in 2016 as a spin-off from the Fraunhofer Institute for Production Technology (IPT), the high-tech company offers customised solutions based on a modular system, covering everything from material feeding and handling to micromanipulation and measurement for ultra-precise assembly, rounded off with quality assurance. PC-based control from Beckhoff, including TwinCAT Vision software, ensures both accurate and rapid process workflows.

Optical systems are used in a wide range of products with application examples found in sensors and cameras for autonomous driving (e.g., LiDAR and driver assistance cameras), for gesture recognition and for beam shaping of high-power lasers. The accuracy demands for the assembly of these optical systems range from a few micrometres to a few hundred nanometres. Combined with cycle times of less than one second and the production of several million components per machine per year, special demands are placed on the automation system.

Compact and flexible automation technology

Aixemtec offers assembly solutions for various application areas based on a comprehensive modular system platform. A scalable housing design concept is applied to each machine. Highly precise and highly dynamic linear drives are frequently used. Automation components from Beckhoff help optimise space utilisation across the platform, while also minimising the system footprint.

The high-performance C6032 ultra-compact industrial PC is another key factor in reducing system size: Until now, a separate PC for image processing, HMI and sequential control was used alongside the CX5130 Embedded PC for machine control, whereas the C6032 now takes over all of these tasks. The compact drive technology from Beckhoff, such as the EL72xx EtherCAT servo terminals with AM8100 servomotors, as well as the high-density (HD) EtherCAT Terminals, also ensures that space is saved on the DIN rail.

On the software side, TwinCAT Vision is used alongside TwinCAT PLC, TwinCAT NC PTP, TwinSAFE and TwinCAT HMI and it plays a key role in connecting up to eight industrial cameras.

Dynamic pick-and-place process for micro-lenses

A prime example of the high demand for accuracy is seen in the pick-and-place process for micro-lenses: To prepare them, they must first be arranged in a specific orientation on a tool carrier. The aim is to position these fragile components quickly and precisely in a workpiece magazine.

The lenses are fed in bulk on a backlit surface, which is scanned with a camera via XYZ kinematics. The result is a 2D panorama of the area being examined. By means of precise time synchronisation of TwinCAT NC axis control with TwinCAT Vision, image capture can be precisely aligned with axial positioning. Where before a time-consuming PTP process was used, TwinCAT Vision can reduce the setup time of this process by at least a factor of eight.

The individual images created in this way during the ‘fly-over’ are inserted into an overall image with pixel accuracy in real-time. Using this overall image, the micro-lenses are identified by image processing and their current orientation is measured. This results in an efficient work plan for how the pick-and-place system should pick up the individual lenses, orient them in all spatial dimensions and place them. The linear axes enable highly dynamic yet highly precise movement of the entire kinematics.

The micro-lenses that have been prepared for assembly are bonded with a light source in a subsequent step. For this purpose, an adhesive dispenser applies a fixed amount of adhesive. Precise dosing is essential for correct assembly, which is why the drop flow is continuously monitored and adjusted by a camera system during the dispensing process. In the future, this task will also be taken over by TwinCAT Vision, as drop triggering, image capture and exposure can be ideally synchronised with the EL2596 LED strobe control terminal and the distributed clock function. Before the adhesive cures, the optical function of the system to be assembled is optimised with the help of a 6D manipulator in a closed control loop.

Sebastian Sauer, head of machine development at Aixemtec, summarises: “This is an ideal solution for us as we are able to retain our modularity by using distributed clocks and XFC technology. TwinCAT Vision allows us to remain completely in the real-time environment even in the context of image processing.”

For more information contact Dane Potter, Beckhoff Automation, +27 79 493 2288, danep@beckhoff.com, www.beckhoff.co.za


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