Page 27 - EngineerIT September 2021

MEASUREMENT

channels. Thus, the requirements for a
safe sensor system are already fulfilled
when only one sensor unit is connected.
For signal output to a safety controller,
one signal output is available for each
sensor unit as well as safe OSSD (output
signal switching device) outputs with
short-circuit and cross-circuit monitoring.
If multiple AGVs are moving through
the warehouse and encounter each
other, interference between the ultrasonic
sensors of the different vehicles is
suppressed by dedicated software. Fixed
interference variables and reference
objects for tamper protection can be
hidden. Switching points, output logic,
the initialisation of periodic tests,
and safety- and ultrasound-specific
parameters can all be set intuitively using
the parameterisation software. This also the AGV. The parameterisation software can be used to quickly and easily adapt the
automatically generates safety records detection range of the sensor units to the conditions. The signal output can be used for
for the plant documentation. reduced speed or to output a warning signal, for example. The safety outputs reliably
trigger a stop in a hazardous situation.
Practical example: collision
avoidance in forklift arms Practical example: machine protection
In the case of automated guided In machines, critical areas are usually protected with photoelectric light grids. In some
vehicles, in addition to the main direction environments, such as the wood industry, such sensors often cause false triggering due to
of travel, the secondary directions — such the inevitable dust generation or airborne particles. The machine then switches to a safe
as travel in the fork direction and the state, after which the light grid must be cleaned and the system restarted.
lateral zone — are relevant for protection Alternatively, USi-safety produces a “sound curtain” that is unaffected by wood dust,
as well. The small sensor units of airborne particles, and adhered contamination. This technology reliably protects the
USi-safety can be integrated at any machine without any unnecessary interruptions in the production process. Machine parts
point, for example directly in the forks that extend into the measurement field can be learned by means of teach-in, and are also
of automated forklifts. The decoupled useful as a means of tamper protection. If such a reference target is no longer detected
control interface can be located further due to tampering, the system will go into a safe state. n
away in the chassis of the vehicle. The
three-dimensional sound field of the
sensor units thus secures the hazardous
area directly in front of the fork arms.
Airborne dust and other environmental
influences do not affect detection.

Practical example: personal safety
with track-guided AGVs
Track-guided AGVs follow markings
on the ground. The track is often
located in areas where people are also
moving around. Collisions must be
reliably avoided without unnecessary
interruptions to transport. Optical
systems, which are used for free
navigation and the protection of
personnel, can be supplemented or
even replaced by alternative protective USi-safety offers two independent channels,
equipment such as USi-safety. The each of which complies with ISO 13849
sensor units are flexibly integrated into Category 3 PLd

EngineerIT | September 2021 | 25