Page 26 - EngineerIT September 2021

MEASUREMENT

Compact ultrasonic sensors for

safety applications

By Matthias Sollmann, Pepperl+Fuchs

he protection of personnel in a point or a scan line. It is therefore unaffected by holes and recesses in the target object.
industrial environments places high Dust, vapours and precipitation have little effect on the sound. In addition, ultrasonic sensors
Tdemands on safety engineering: are almost entirely unaffected by contamination or coatings adhering to the surface.
protection systems must be robust and
completely reliable while also meeting Elliptical sound beam
strict guidelines and standards. The The sound beam of an ultrasonic sensor is usually radially symmetrical. By contrast, in
higher the degree of automation, the USi-safety, it is very wide in one axis and very narrow in the other. This asymmetry gives
more important this aspect becomes. the sound beam a distinctly elliptical shape and enables the sensor to cover a large area.
An example of this is in production and The resulting safety zone is 80 cm wide at a distance of 1,5m. The various adjustment
warehouse logistics, where automated options offered by the device also make it possible to detect small objects or body parts
transport systems are being used more from a long distance. The maximum detection range is 2,5m, which allows the AGV to
and more. They move in areas where monitor the entire space in its direction of travel.
people work and therefore need to be The ultrasonic transducer itself is extremely compact, at just 27×21×13mm, meaning
able to stop quickly at any time to avoid that it can be readily installed in forklift arms, for example. This miniaturisation is possible
collisions. Since multiple automated because the actual sensor is separated from the control interface and can be placed up
guided vehicles (AGVs) are often moving to a cable length of three metres away. It has connections for two sensors, allowing both
around at once, safety technology is also forklift arms to be protected during forward and reverse travel. The high IP69K degree of
used to protect the vehicles themselves in protection makes the ultrasonic transducers particularly resistant to dust, and they can
the case of encounters with other vehicles. even withstand high-pressure cleaning.

Robust measuring principle Reliable electronics, intuitive parameterisation
It is essential for obstacles to be Each ultrasonic sensor unit is assigned two fail-safe outputs via the electronics. Two
detected by the sensor system under microcontrollers in the control interface monitor both the sensor function and each other.
all circumstances. This is where the Noticeable deviations of the sensor units or between the controllers automatically trigger
design of ultrasonic sensors has an the safety circuit. Reliable protection is possible from each of the two independent sensor
advantage over other technologies
such as photo-electrics. Optical sensors
rely on the unimpeded dispersion of
light. If their light beam is obstructed,
deflected or insufficiently reflected, they
cannot reliably detect the target object.
In outdoor use, vapour and dust or fog,
rain and snow can “swallow” the light
pulse. Object-specific properties such as
irregular contours, holes and recesses in
the surfaces can also cause the optical
measurement to be disrupted.
Ultrasound is almost completely
unaffected by these interference factors.
By definition, the optical properties of a
surface are not relevant. When detecting
irregular contours, design-related
properties are helpful. The sound beam
always hits the target object on a surface,
and the sensor detects far more than just

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