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ACTIVE SPEED CONTROL – CAMERA-BASED SENSOR SYSTEM FOR
CLOSED-LOOP FEED REGULATION IN LASER CUTTING

> Dr. Boris Regaard
TRUMPF Werkzeugmaschinen GmbH + Co. KG
Ditzingen, Germany

Active Speed Control marks a milestone towards autonomous laser cutting. Its innovative camera- Machine operators frequently reduce the machine’s feed rate as a safety measure to allow for
based sensor looks through the nozzle at the cutting zone. The melt pool and cutting kerf are variations in the material. In many cases this does make the process more reliable; however,
analyzed in real-time and the feed rate is constantly regulated for optimal results. Thus, maximum besides productivity loss it can also have a negative impact on the cutting process and the quality
cutting speed and a more reliable process are ensured, which leads to optimized productivity as of the cut. As an example, a lower feed rate can cause heat to accumulate within the material. This
well as reduced scrap and rework. For example, Active Speed Control immediately responds to built-up heat can cause the material to melt in an uncontrolled fashion, reducing the reliability of
changes in material composition, thickness and temperature as well as surface defects, pollution, the machining process. By automatically controlling the feed rate, Active Speed Control increases
or rust. Also, machine tolerances like laser power or focal position can have an influence on the the feed rate at higher material temperature, thus maintaining high cut quality and at the same
process performance and are compensated for by adjusting the feed rate. time increasing cutting speed, sometimes well above the default value specified in the cutting data.
The heart of Active Speed Control is a camera-based sensor system inside the cutting head. A TRUMPF machines use predefined cutting data sets to tell the machine how to process a certain
dichroic mirror separates the beam paths of the laser and the camera, allowing to observe the material and thickness. This data includes a buffer to compensate for material deviation and other
process area coaxially with the laser beam (Figure 1). Additionally, the sheet surface and the inner parameter tolerances. Ultimately, this means the machine is cutting at a lower feed rate than it is
surface of the cutting nozzle are illuminated, allowing on-line measurement prior and during capable of. Active Speed Control eliminates the need for this buffer, as the feed rate is controlled in
piercing and cutting. Real-time image processing analyses the camera data and evaluates the real time. The sensor system allows the machine to always work as fast as it can while maintaining
process stability, using information from thermal radiation inside the melt pool and from radiation the required levels of process reliability. In many cases, Active Speed Control achieves speeds that
reflected at the illuminated material surface. are significantly higher than the default values specified in the cutting data.

The determined process stability is used as a feedback signal to a closed-loop controller, which As an add-on, Active Speed Control also monitors important machine and process parameters and
constantly adapts the feed rate and thus ensures a constant process stability (Figure 2). If e.g. the informs the operator if adjustment work or replacements are necessary. If monitored parameters
material thickness is increasing, the process stability declines and in return the controller reduces are critical for safe operation or if a cut failure is detected, Active Speed Control automatically stops
the feed rate until the process stability reaches the desired value. This also works for most of the the machine and informs the operator how to fix the problem. A live image of the cutting zone as
other usual variations in material composition, ambient conditions and condition of the cutting tool. seen from the sensor camera including additional status information can be displayed on the HMI
Due to a high control bandwidth of several 100 Hz, a constant process result is ensured. to observe the cutting process from outside the machine (Figure 3).

Active Speed Control was first introduced to the public at the EuroBLECH 2018 in Hannover and won
the EuroBLECH Award 2018 in the category “Measuring and test technology”.

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