Markus Simon, head of system consulting, PI miCos
Cutting, drilling, welding, marking or structuring—lasers are used in a wide variety of processes in many different industrial sectors to optimise manufacturing processes and ensure the high quality of components (Figure 1). This, for example, is how the electronics business sector or semiconductor industry benefits from the advanced capabilities for laser material processing.
Figure 1: Lasers are used in a wide variety of processes in many different industrial sectors to optimise manufacturing processes and ensure the high quality of components.
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 instance, as far as throughput and precision are concerned, it is possible to achieve this when system components such as 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. Laser performance is not normally a limiting factor as far as throughput is concerned, therefore the speed and dynamics of the platforms used today are decisive for the achievable productivity.
As a seasoned drive technology and positioning systems solutions provider, PI (Physik Instrumente) is able to offer automation platforms for industrial laser processing that deliver both high quality and high throughput. The spectrum ranges from single- and multi-axis positioning systems to multi-axis positioning systems with galvanometer scanners where control of laser motion and the positioning systems must run simultaneously.
Multi-axis positioning systems
Diamond engraving
Diamond engraving is a prime example of an application for multi-axis positioning. A laser beam is used to engrave certificate numbers onto diamonds; the motion of the workpiece in the X, Y direction and positioning of the laser objective in the Z direction are performed using highly dynamic linear stages that work with magnetic direct drives (Figure 2). They achieve high velocities as well as scanning frequencies of over 10 Hz. Owing to their crossed roller guides, sub-micrometre accuracy is possible using motors with high repeatability and suitable encoders.
Figure 2: The motion of the workpiece in the X, Y direction and positioning of the laser objective in the Z direction is performed using highly dynamic linear stages that work with magnetic direct drives.
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 labelling 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 optimised algorithm in the motion controller synchronises the motion of the workpiece with the laser pulses so that the gap between adjacent points and their size in the patterns remains consistent (Figure 3).
Figure 3: An optimised algorithm in the motion controller synchronises the motion of the workpiece with the laser pulses so that the gap between adjacent points and their size in the patterns remains consistent.
Wafer dicing
Wafer dicing, the separation of semiconductor wafers into dies, also depends on high accuracy. The cutting width must remain constant and vertical intersections are necessary. Accuracy is essential in order not to damage the individual dies during cutting. The permissible tolerances along the travel range amount to only a few micrometres per metre.
The A-322 PIglide HS planar air-bearing stage, which is moved by magnetic direct drives, is a suitable positioning system for such applications (Figure 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 nanometre possible. The positioning system was designed to both maximise throughput and ensure exceptional precision.
Figure 4: Segregation of wafer dies depends on high accuracy. The permissible tolerances along the travel range amount to only a few micrometres per metre. The A-322 PIglide HS planar air-bearing stage, which is moved by magnetic direct drives, is a suitable positioning system for such applications.
Producing stencils and printed circuit boards
The requirements for producing and processing stencils and printed circuit boards are similar. Workpieces are particularly large and structurally dense, and this is why longer travel ranges and micrometre precision are required from positioning systems (Figure 5). Gantry systems, with their high stiffness but light motion platforms, are a good basis for this (Figure 6).
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Figure 5: Workpieces are particularly large and structurally dense during the production and processing of templates, and this is why longer travel ranges and micrometre precision are required from positioning systems. (Source: TRUMPF)
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Figure 6: Gantry systems, with their high stiffness but light motion platforms, offer high throughput. Cable management and operation are optimised so that vertical motion axes, autofocus sensors and an infeed system for the laser can be added.
Cable management and operation are optimised 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 initialisation because this makes it unnecessary to perform a reference move after switching on.
Multi-axis positioning systems with galvanometer scanners
Marking
For marking applications, a multi-axis positioning system often incorporates a galvanometer scanner for steering the laser beam. 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 X, Y direction is then taken over by the V-731 PIMag positioning stage, which is set up as an X, Y roller stage.
This positioning stage achieves a repeatability of 0.1 μm and minimum incremental motion of 0.02 μm. Its linear motors require no additional mechanics and they drive the platform directly, making high velocities possible. Furthermore, it can be combined with a linear axis for motion in the Z axis direction, which also provides high travel accuracy (Figure 7).
EtherCAT laser control module and human machine interface (HMI)
In the case of all the aforementioned laser processing processes, it is often possible to control their complexity easily via a special laser module. This allows direct control of the laser source in order to increase the precision and throughput.
The EtherCAT slave LCM (laser control module) offers a broad range of functions, including digital pulse modulation for dynamic power control (DPC) and output impulses or gating (on/off) signals that are synchronised to positions along a two to six-dimensional motion path or programmable operation zones. The module can control virtually any laser via universal electrical interfaces (Figure 8).
Figure 8: The EtherCAT slave LCM (laser control module) offers a broad range of functions. The module can control virtually any laser via universal electrical interfaces. (Source: ACS Motion Control)
In addition to a high-speed laser signal output, the module affords a special lock system, an error input and an enable output. Eight digital input/outputs (I/Os) are also available for laser specific functions. The challenges during development of a robust and scalable laser processing or micromanufacturing machine platform can be solved much better and faster using this type of laser module. HMI platforms provide further simplification (Figures 9a and b). This applies particularly to optimising 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.
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Figures 9a and b: The human machine interface (HMI) is an important subsystem of the machine and normally falls into one of two classifications. There are HMIs that are CNC in style, which import and execute machine-coded programs (typically G-code) created by a CAM software post-processor (a). The second type is integrated graphical HMIs, which allow importing as well as processing of CAD files and offer integrated functionality for post-processing of CAM data (b). (Source: ACS Motion Control)
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Figures 9a and b: The human machine interface (HMI) is an important subsystem of the machine and normally falls into one of two classifications. There are HMIs that are CNC in style, which import and execute machine-coded programs (typically G-code) created by a CAM software post-processor (a). The second type is integrated graphical HMIs, which allow importing as well as processing of CAD files and offer integrated functionality for post-processing of CAM data (b). (Source: ACS Motion Control)
Scanning process in XL format
Again, in the case of all the aforementioned laser processing processes, 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 higher accelerations and larger details 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 synchronised (Figure 10).
Figure 10: For the XL format scanning process, smaller details require higher accelerations and larger details require longer travel ranges. The motion of the X, Y stage and galvanometer scanner is synchronised for this purpose.
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 X, Y stage and scanner are synchronised 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.
As laser beam deflection by the scanner needs to be kept small and therefore keep optical errors low, higher processing accuracy is achieved when compared with 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.
PI miCos