Sensor Technology
Fig 2: A wide range of fibre optic sensor heads is available
Fig 3: Use
Case: Precisely detecting the location of small components surface-mounted on an electronics board
Fig 5: Use case: High-speed detection and counting of small components falling into a defined area.
also have little or no detection ‘dead zones’ so are suitable for tight machine spaces. There’s no electrical circuitry or mechanical parts and, because they require little power, fibre optic systems can reach very high switching speeds. They are highly reliable even under severe environmental conditions, such as extreme temperatures, vibration, shock, moisture, corrosive chemicals or electro-magnetic ‘noise’. The detection principle is independent of object colour, shape or surface, so it can detect virtually any material, and even transparent glue beads.
Some fibres can withstand repeat bending without degradation of the signal, making them useful, e.g. in robotic gripper applications (Fig 6).
What should I consider when specifying a fibre optic sensor? First, look for an amplifier that minimises inventory. For example, by being able to switch between PNP, NPN or push-pull outputs on the same device, users need only one type of Sick WLL80 fibre optic amplifier for all machine controls.
Ensure the amplifier is compatible with common bus protocols and that sensors can be networked together, without the risk of interference. SICK WLL80 sensors can be organised in banks in a master-slave configuration to enable automatic cloning of parameter settings for multiple devices. Look for an amplifier with an OLED pushbutton display to make setting or adjusting the sensor in situ quick and
easy. There should be detailed setting options for detection parameters and switch points, enabling accurate detection and repeatability.
Using IO-Link could be an advantage in some applications for diagnostics and troubleshooting, as well as rapid replacement. By using Smart Tasks for pre-defined parameter configurations, reliable detection of fast-moving, small or transparent objects can be assured within minimal load on the machine control. The SICK WLL80 also
Fig 6 Use case: reliably verifying the presence of a product in a robot gripper throughout a dynamic process
offers the advantage of continuous threshold adaption (CTA) which adapts the signal strength, e.g. in a dusty environment, or because of contamination build-up on the fibre heads, to maximise periods between maintenance.
Fig 4: Through-beam system
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There are some limitations associated with using fibre optic sensors: it can take a little more effort to install and set the sensor parameters, for example. Also, because they use an energetic detection principle, there is no real background suppression available with fibre optic sensors. However, fibre optic sensors are
versatile for a wealth of applications in almost any industry. So, it’s always worth considering whether they are the best solution.
With so many specification options for fibre optic sensors, choosing and installing them may seem daunting. However, vendors should now offer easy specification guidance on their website, as well as technical sales support to guide you to a reliable and successful application.
www.sick.co.uk Components in Electronics November 2022 39
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