Instrumentation Monthly Test | Measurement | Control
Chris Jones, managing director at Micro-Epsilon UK, takes a look into the development of non-contact displacement measurement solutions over the years, and then discusses future trends, where we will see more compact, smarter, sensors with integrated electronics that offer new features and functionality
Displacement can be measured in various ways by using a number of different physical measuring principles. Some years ago, displacement sensors were relatively large with separate, discrete electronics. Today, however, new technologies and production systems are enabling miniature sensors to be produced with integrated electronics.
Established in Hanover, Germany, in the same year that Instrumentation was first published, Micro-Epsilon was originally a supplier of strain gauges, the start of its displacement measurement product range. In the mid-1970s, it was recognised that the future lie in non-contact displacement measurement technology.
The S05, introduced in 1982, was the world’s first miniature eddy current displacement sensor; and was followed with further developments resulting in the launch of the U05 (08) in 1998. At that time, it was the world’s smallest eddy current displacement sensor, and was the result of a further reduction in size of the U05 standard sensor. This trend towards miniaturisation has been critical to this day.
The 1990s saw the constant progression of digital technologies, which made access to new electronics and optical components possible. In 1992, Micro-Epsilon launched the first fully digital optical sensor, the optoNCDT 2000. Rather than using PSD lines for acquiring measured values, innovative CCD elements were used, which achieved new levels of precision that had never been seen before.
In 1994 the LIP inductive sensor was developed, and was seen as a major innovation at the time. Compact and flexible, this enabled the company to manufacture cost-effective, customer-specific sensors for OEM displacement measurement applications.
From the turn of the Millennium, Micro-Epsilon has continued to develop its range of confocal measurement sensors. In 2006, for example, the company launched a confocal miniature sensor with an outer diameter of just 4mm.
Next-generation non-contact technologies
Current trends in displacement measurement technology indicate that smaller, more intelligent sensors with integrated electronics are now required. In mechanical engineering, the requirement for extremely compact sensors is always an important factor, especially if installation space is restricted or if the sensor needs to be lightweight. This is also the case in terms of integration of more electronics and intelligence in the sensor. As a result, sensors are more frequently required to perform the signal conditioning directly in the sensor, therefore reducing component count, whilst offering faster measuring speeds.
The next-generation of eddy current sensors use a patented embedded coil technology (ECT), which overcomes the previous limitations of discrete coil windings. The eddyECT sensor coil utilises new inorganic materials to embed the coil, which enables hermetically-sealed, ultra-compact designs. This provides almost unlimited scope in terms of the external design and geometrical shape of the sensors.
The sensors also offer extreme mechanical robustness, resulting in longer service intervals and higher temperature stability. The complete circuit electronics can be integrated into the sensor, providing an even more compact measurement solution. The sensors are also suitable for harsh operating environments, including high vibration, impact shocks and high operating temperatures (up to 650°C). Sensors have been produced with extremely low thermal drift and with temperature errors of less than 20 parts per million per degree Kelvin (20 ppm/K).
By integrating smart electronics in the sensor itself, laser triangulation sensors are a great example of how much smaller sensor systems are becoming. Most conventional sensors require a separate electronics unit as well as the sensor itself. The latest sensor designs have a very small housing in which the complete electronics are integrated without sacrificing sensor performance. Measuring ranges vary between 5mm and 2m.
Extremely high resolutions are possible when using confocal chromatic measurement technology, typically in the nanometre range. Confocal sensors have a very small measuring spot that enables measurements on particularly small objects, meaning even the finest scratches on a surface can be measured reliably. The beam path of the sensor is compact and concentric, so measurements inside bore holes or test tubes are possible. Thickness measurement of transparent films, boards or layers is also possible.
Communication standards
In industrial automation, there is a growing trend towards replacing existing first generation fieldbuses with industrial Ethernet. Manufacturing processes are becoming higher speed and more automated, so these industrial networks require sensors and measurement systems that support these faster, dynamic processes. As a result, Micro-Epsilon is integrating real time Ethernet technology into many of its laser displacement sensors and controllers, and is developing sensors and controllers that cater for these requirements.
EtherCAT is rapidly establishing itself within the market as a communications standard (protocol) that can offer true real time capabilities in automation technology. In line with this, sensors and controllers with EtherCAT capability have been developed, enabling them to be smoothly integrated into existing control and automation networks.
Micro-Epsilon
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