Electricity and Control December 2021-January 2022

SAFETY OF PLANT, EQUIPMENT + PEOPLE

Ultrasonic sensors for safety applications Matthias Sollmann, Pepperl+Fuchs The protection of personnel in industrial environments places high demands on safety engineering. Protection systems need to be robust and completely reliable and they need to meet strict guidelines and standards. Pepperl+Fuchs recognises that the higher the degree of automation, the more important this aspect becomes. Examples of this are in production and warehouse logistics, where automated transport systems are being used increasingly.

A utomated guided vehicles (AGVs) and other au- tomated transport systems move in areas where people work and therefore need to be able to stop quickly at any time to avoid collisions. As multiple AGVs may often be moving around at the same time, safety tech- nology is also used to protect the vehicles when they en- counter other vehicles. The USi-safety ultrasonic sensor system from Pepperl+Fuchs combines the robustness of ultrasonic sensors with intrinsically safe electronics. It is therefore suitable for the safe control of machines and AGVs, among other things. It meets the requirements of Category 3 PL d of ISO 13849 and is the only safe ultrasonic sensor on the market. A robust measuring principle It is essential that sensor systems should be able to de- tect obstacles under all circumstances. This is where the design of ultrasonic sensors has an advantage over other technologies, such as photoelectrics. Optical sensors rely on the unimpeded dispersion of light. If the light beam is obstructed, deflected, or insufficiently reflected, they can-

not 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 such 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 more than a single point or a scan line. It is therefore unaffected by holes and recesses in the target object. Dust, vapours and precipitation have little effect on the sound. In addition, ultrasonic sensors are almost entirely unaffected by contamination or coatings adhering to the surface. An elliptical sound beam The sound beam of an ultrasonic sensor is usually radially symmetrical. By contrast, in USi-safety it is wide in one axis and narrow in the other. This asymmetry gives the sound beam a distinctly elliptical shape and enables the sensor

to cover a large area. The resulting safety zone is 80 cm wide at a distance of 1.5 m. Various adjustment options make it possible to detect small objects or components from a long dis- tance. The maximum detection range is 2.5 m, which allows an AGV to monitor the entire space in its direction of travel. The ultrasonic transducer itself is particularly compact, at just 27×21×13 mm, which means it can be installed in forklift arms, for example, and other compact applications. This ‘minia- turisation’ is possible because the sensor is separated from the control interface and can be placed a cable length of up to three metres away. The USi device has connections for two sensors, allowing both forklift arms to be pro- tected during forward and reverse travel. The high IP69K degree of protection makes the ul- trasonic transducers resistant to dust, and they can also withstand high-pressure cleaning.

The elliptical sound beam of the USi-safety sensor system monitors an optimal area.

20 Electricity + Control DECEMBER 2021-JANUARY 2022