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Precision Positioning with High Throughput: Automation Platforms for Laser Material Processing

Today, numerous business sectors profit from the advanced capabilities of laser material processing.

Today, numerous business sectors profit from the advanced capabilities of laser material processing. However, process, material, work cycle, ambient conditions, and criteria such as throughput, precision, geometry tolerances, size of the machining surface make very different demands on the motion control system. As solution supplier for drive technology and positioning systems, PI (Physik Instrumente) accepted the challenges in laser processing for cutting, drilling, welding, marking or structuring and can now offer automation platforms according to requirements for laser processing that allow both high quality and high throughput. The spectrum ranges from single and multi-axis systems without scanner to multi-axis positioning systems where the motion of galvanometer scanners where positioning systems have to be synchronized and are also able to run simultaneously.

Long version:

Cutting, drilling, welding, marking or structuring – lasers are used in a wide variety of processes in many different industrial sectors to optimize manufacturing processes and ensure the high quality of components (image 1). This for example, is how the electronics business sector or semiconductor industry benefits from the advanced capabilities for laser material processing. Process, material, work cycle, ambient conditions, and criteria such as throughput, precision, geometry tolerances, size of the machining surface, and contours, all make different demands on the motion control system. For example, as far as throughput and precision is concerned, it is possible to achieve this when system components such as the mechanics, laser control, and laser beam steering complement each other and communicate via high-performance control solutions.

Laser processing is a broad field and the respective applications are correspondingly varied. Because the laser performance is normally not a limiting factor as far as throughput is concerned, the speed and dynamics of the platforms used today are decisive for the achievable productivity.

As solution supplier for drive technology and positioning systems, PI (Physik Instrumente) accepted the challenges in laser processing and is now able to offer automation platforms for industrial laser processing that allow both high quality and high throughput. The spectrum ranges from single- and multi-axis systems without galvanometer scanners to multi-axis positioning systems where control of laser motion and the positioning systems have to run simultaneously.

Engraving Diamonds

Engraving diamonds is one of the applications for multi-axis position systems. For example, the certificate number is engraved onto the diamond by the laser beam (image 2). The motion of the workpiece in the X, Y direction and positioning of the laser objective in the Z-direction is done with high dynamics linear stages that work with magnetic direct drives. They achieve high velocities as well as scanning frequencies of over 10 Hz. Thanks to their crossed roller guides, submicrometer accuracy is possible using motors with high repeatability and suitable encoders. The integrated direct-measuring, optical linear encoder allows reliable position control. A motion controller, which allows both position and speed-dependent triggering of the laser, controls the precision labeling for certifying the diamonds.  This allows motion of the positioning system and the laser pulse to be matched exactly to each other when cutting edges, arcs, circles, and complex patterns. An optimized algorithm in the controller synchronizes the motion of the workpiece with the laser pulses so that the gap between adjacent points and their size in the patterns remains the same (image 3).

Wafer Dicing

Segregating wafer dies also depends on the high accuracy. The cutting width must remain constant and vertical intersections are necessary. In addition, the absolute accuracy is important in order not to damage the individual dies during cutting. The permissible tolerances along the travel range amount to only a few micrometers per meter.

The A-322 air bearing planar stage, which is moved by magnetic direct drives, is a suitable positioning system for such applications (image 4). It has a magnetic direct drive that makes high velocities and accelerations of 20 m/s² possible. At the same time, sine-commutated control makes a high positioning resolution of one nanometer possible. The positioning system was designed to both maximize the throughput and ensure the highest precision.

Producing Stencils and Printed Circuit Boards

The requirements for production and processing stencils and printed circuit boards are similar (image 5). Workpieces and structural density are particularly large here. That is the reason why longer travel ranges and micrometer precision are required from positioning systems. Gantry systems (image 6) with their high stiffness but light motion platforms offer a good basis for this. Cable management and operation are optimized so that vertical motion axes, autofocus sensors, and an infeed system for the laser can be added. The design also makes it possible to hold the part to be processed at a standstill and only move the laser together with the optics. The absolute measuring systems implemented by PI simplify system initialization because this makes it unnecessary to perform a reference move after switching on.

Marking with the Laser Beam

In the case of laser engraving, multi-axis positioning systems with a galvanometer scanner are often combined for steering the laser beam (image 7). This leads to good results with respect to dynamics and precision when for example, dials are to be written onto functional components. Motion in the XY direction is then taken over by a positioning stage from the V-731 series, which is set up as an XY roller stage.

It achieves a repeatability of 0.1 μm and the minimum incremental motion is 0.02 μm. Its linear motors require no additional mechanics and they drive the platform directly. This makes high velocities possible. It can be combined with a linear axis for motion in the Z axis direction that also provides high travel accuracy (image 8).

EtherCAT Laser Control Module and HMI

In the case of the laser processing process described, it is often possible to control complex processes easily with a special laser module. It allows direct control of the laser source in order to increase the precision and throughput.

The EtherCAT slave module of the LCM series (image 9) offers a broad range of functions, which includes digital pulse modulation for dynamic power control, output impulses or gating signals (on/off signals) that are synchronized to positions along a two to six-dimensional motion path or programmable operation zones. The control module can control virtually any laser via universal electrical interfaces. In addition to the high-speed laser signal output, the module is also equipped with a special lock system, an error input, and an enable output. Eight digital I/Os are also available for laser specific functions.  The challenges during development of a robust and scalable laser processing or micro manufacturing machine platform can be solved much better and faster with this type of laser module. HIM platforms provide further simplification (image 10a, b). This particularly applies to optimizing the accuracy and repeatability of laser control for motion and for developing the associated HMI software. Machine developers, system integrators, and users benefit equally from this because at the same time, the result means higher machine performance and reduced expenditure on development.

Scanning Process in XL Format

In the case of the laser processing process with galvanometer scanners described previously, scanners and positioning systems do not operate simultaneously but one after the other in a stitching process. Large areas with many small details cannot be marked efficiently in this way.

Smaller details require high accelerations and larger require longer travel ranges. It is therefore recommended to separate the trajectories for smaller, easier, and therefore faster positioning systems with shorter ranges, and for larger, more difficult, and therefore relatively slow motion components with longer travel ranges. Both systems then need to be synchronized.

Basically, laser marking then functions in a similar way to human writing. The arm, as slow musculoskeletal system, provides gross manual dexterity while the hand and fingers accurately form the individual letters, which corresponds to the motion of the galvanometer scanner. Analogous to this, the motion patterns from the XY stage and scanner are synchronized by a controller and run simultaneously during scanning. This process allows efficient marking of large areas with many small details and therefore increases the throughput.

Because laser beam deflection by the scanner needs to be kept small and therefore keep optical errors low, higher processing accuracy is achieved when compared to the stitching process; at the same time, stitching errors are also eliminated.

In conjunction with laser technology, positioning systems from PI have already been tried and tested in a variety of different precision applications in research and industry. A corresponding positioning system is even being used on Mars for “processed” chemical analysis with a laser.


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