Page 12 - EngineerIt June 2021

AUTOMATION AND CONTROL

Safety light curtain installation boosts

productivity case study

safety light curtain installation for a Cape Town-based, non- of removing the existing hand-operated hydraulic valves,
metallic mineral product manufacturer resulted in operator simplifying the hydraulic circuit to a single solenoid-controlled
A efficiency improvement of almost 20%. The manufacturer, valve and installing sensors to measure stroke movement and
IWT Abrasives, approached ElectroMechanica (EM) in 2019 for a the force applied by the press. A new control cabinet to house the
system that would improve safety around its hydraulic press, and new PLC-based control system was supplied, as was a human
simultaneously enhance press productivity. This installation has machine interface (HMI) to enable operator feedback.
continued to prove itself, two years later. The combination of sensor feedback and light curtain
IWT specialises in the weaving and impregnation of glass protection enabled the press to perform its action autonomously
fibre rovings used in the reinforcement of cutting and grinding and to automatically reset. This allows operators to prepare the
wheels. Its hydraulic press shapes flexible material into the form next product for pressing safely and efficiently, contributing to
of grinding disks. To operate the press, the operator uses two increased production. “The extra time gained has added a lot of
hand lever valves. This mechanism ensures operator safety, but it value for IWT,” says Cameron.
slows throughput. A further concern for IWT was the high energy The use of a PLC in the solution created smarter press
consumption of the hydraulic press due to its constantly operating control, resulting in an improvement in operator efficiency and
hydraulic pump, which also heated the oil, reducing its lifespan. reduced waste, as well as energy savings. In terms of production,
“IWT wanted a solution that would address these concerns the biggest improvement over the last two years has been
while also improving operation productivity”, explains William quality consistency and subsequent waste reduction, since the
Cameron, EM product manager. “We proposed our ReeR light PLC limits the force and movement of the press. The improved
curtains to replace the two hand lever safety mechanisms, which control provides the hydraulic pump with the ability to switch off
automatically and swiftly halts any press movement if the light automatically when the press has been idle for a specified period,
beam is interrupted”. increasing system longevity.
IWT had previously installed similar light curtains from EM “Safety in manufacturing enterprises is often overlooked due
on their Chiesa cutting machines. After doing some research on to the expected loss in productivity and complexity of adoption.
the ReeR brand, IWT agreed that the positive market feedback, However, safety solutions can be implemented in a phased
affordability and recognised quality made this the ideal solution approach with minimal disruption, and can lead to significant
for their requirements. productivity returns,” concludes Cameron. n
EM supplied all required products for the scope of work,
which was undertaken by IWT engineers. The project consisted WHAT IS A SAFETY LIGHT CURRENT?

afety light curtains are an advanced method of safeguarding personnel
around many hazardous machines. Safety light curtains offer
Sfreedom, flexibility and reduced operator fatigue when compared with
traditional guarding methods such as mechanical barriers, sliding gates and
pull-back restraints.
How they work
A photo-electric transmitter projects an array of synchronised, parallel
infrared light beams to a receiver unit. When an opaque object interrupts
one or more beams in the sensing field, the control logic of the light curtain
sends a stop signal to the guarded machine.
The transmitter unit contains light emitting diodes (LEDs) that emit
pulses of invisible infrared light when energised by the light curtain’s timing
and logic circuitry. The light pulses are both sequenced – one LED is
energised after another – and modulated – pulsed at a specific frequency.
Corresponding photo-transistors and supporting circuitry in the receiving
unit are designed to detect only the specific pulse and frequency designated
for it. These techniques offer enhanced safety and rejection of external light
sources. The control logic, user controls and diagnostic indicators may be
contained in a separate enclosure or be enclosed in the same housing as the
receiver electronics. n

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