MOTION CONTROL FEATURE
To help machine builders develop integrated solutions capable of
meeting today’s precision and throughput
requirements, a recent collaboration between ACS Motion Control and SCANLAB has come up with a new approach.
Ofer Ben-Ari, outbound marketing manager at ACS Motion Control, and Cliff Jolliffe, head of segment marketing for Automation at Physik Instrumente (PI), explain
C
onnectivity between equipment and systems is an essential feature
of industrial automation solutions, and is almost always treated as a key design element right from the start of the development process. A notable exception to this approach is micropositioning systems, which have generally been regarded as highly specialised standalone units with different operating principles and control requirements. The rise of the internet of things
and Industry 4.0 have brought this issue to the fore, and now machine builders need to reconsider the control requirements of these systems – in terms of programming language, parameters and capabilities – in order to develop integrated solutions capable of meeting today’s precision and throughput requirements.
CHALLENGES One area where this is a significant challenge is laser machining. High speed laser galvanometer scanners are increasingly being used to provide high throughput, accurate and flexible laser machining for a wide range of processes. However, the limited field of view (FoV) of these scanners requires them to be used in combination with machine tooling platforms or XY-stages to provide sufficient range of movement for high throughput applications such as cutting, welding or marking. The challenge with this set-up is that the different operating principles of the galvanometer scanner and the machine
CONNECTING THE dots in automation
tooling table – very high speed, short travel motions versus variable speed, longer travel movements and accurate stand-still position – mean that these devices generally need to be controlled in isolation, using a ‘step and scan’ approach to coordinate operation of the two separate systems. Simple
communication between the two systems is achieved via little more than ‘handshake’ processes, where the automation controller instructs the motorised axes to move a part to an appropriate position under the galvanometer scanner, then informs the scanner controller to carry out its operation. Once this operation has been performed, the galvanometer scanner controller informs the automation controller, and the process repeats until machining is complete.
LIMITATIONS Unfortunately, there are numerous limitations to this approach in terms of throughput and precision. The most obvious drawback of a step and scan approach is that only the galvanometer scanner or the machine tooling table is in operation at any given time. Requiring numerous sequential steps to complete each machining process, this limits throughput. While parallel, co-ordinated operation of the galvanometer scanner and tooling table has the potential to significantly increase throughput by eliminating this idle time, it requires sophisticated, coordinated, high speed movements to achieve the necessary precision. The second issue with step and scan
approaches is stitching errors. Each time the machine tooling platform moves the workpiece, there can be misalignment at the junction between scanning operations due to the precision and repeatability of the motion control systems. One way to minimise this
phenomenon is to increase the FoV of the galvanometer scanner. This increases the area of the workpiece that can be assessed, but the oblique angle at which the laser strikes the workpiece towards the circumference of the FoV leads to variations in the shape of the laser at the contact surface and reduced accuracy.
A BETTER WAY TO CONNECT A recent collaboration between
The solution combines the galvanometer scanner and tooling table or XY-stage into an integrated automation platform that allows simultaneous control and movement of both systems
ACS Motion Control and SCANLAB has
come up with an alternative approach - combining the galvanometer scanner and tooling table or XY-stage into an integrated automation platform that allows simultaneous control and movement of both systems. The platform, a laser marking solution called XLSCAN, can be operated via a standard industrial network, such as EtherCAT (IEC 61158). The system uses any ACS control system and bespoke software to co- ordinate the movements of SCANLAB’s excelliSCAN 14 galvanometer scanner
“The result is robust, high precision, motion control without the need for highly specialised systems –offering
seamless integration and communication with other equipment across the production line or shop floor”
Left: Step and scan approaches can result in stitching errors. Each time the machine tooling platform moves the workpiece, there can be misalignment at the junction between scanning operations due to the precision and repeatability of the motion control systems
system with a high precision XY-stage from Physik Instrumente. This set-up effectively overlays the FoV of the scanner with the longer travel of the tooling table, allowing continuous scanning without stitching errors to significantly improve accuracy and increase throughput by up to 40%. The result is robust, high precision, motion control without the need for highly specialised systems – offering seamless integration and communication with other equipment across the production line or shop floor.
Physik Instrumente (PI)
www.physikinstrumente.co.uk/en/
DESIGN SOLUTIONS | JULY/AUGUST 2018 27
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