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Laser scanners put safety first
The safety laser scanner is one development in machinery safety which has had a transforming impact on productivity and machinery development. Since its introduction in the mid 1990s, it has proved to be a true enabling technology in production environments, says Seb Strutt, senior product manager at Sick UK
T
he safety laser scanner has cre- ated new opportunities to protect personnel at affordable costs and, in particular, according to Strutt, its versatility has offered increased collision protection from driverless guided vehicles. At the same time, the technology has enabled the speed and production throughput of vehicles to be dramatically increased, while downtime and vehicle maintenance have been reduced.
Recent technological advances, that have made the safety laser scanner more compact, have delivered major advances in the use of Automated Guided Vehicles (AGV). They have achieved safe non-contact detection of personnel in the path of moving vehi- cles travelling along complex paths and production layouts.
Before the advent of laser tech- niques, contact bumpers physically detected obstacles by deformation and activated an associated mechanical switch. The approach speed of an AGV had to be limited to the impact force required to activate the collision detec- tion system before it could cause harm. The introduction of the laser scan- ner immediately allowed the AGV to travel faster as it was a collision pre- vention system which could detect oncoming obstacles way before impact. Thus the AGV could travel faster, increasing its hourly load capacity and ensuring safety. Safety laser scanners scan their sur- roundings in a fan shape and measure distances using the time-of-flight mea- surement principle. As soon as a safety laser scanner detects an object in the pre-programmed hazardous area, it switches off the OSSD (Output Signal Switching Device) causing the vehicle to stop. Warning fields can be also defined so that objects are detected before reaching the hazardous area.
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Above: A graphic of an AGV in operation
JBT Automated Systems unmanned counterbalance AGV with Sick inset
Laser scanners on mobile vehicles usually have three zones configured to form the field set. If a pedestrian enters the outer zone, a warning alarm may be sounded, in the middle zone the vehicle may decelerate and in the inner zone only would an emergency stop be triggered. The need to stop the vehicle and impact production effi- ciency is therefore minimised. Scanners now have increased detec- tion ranges allowing safety fields up to seven metres. Multiple fields up to 64 zones can be configured to provide high-performance and flexibility for complex vehicle paths as the AGVs turn and change direction to follow their routes.
Safety laser scanners are a machine safety product which have had a transforing impact on produc- tivity and machin- ery development
The ability to integrate laser scan- ners with other sensing technologies can also be a major advantage. In par- ticular, laser scanners have the ability to safely measure the speed of a vehi- cle via inputs from encoders fitted to the vehicle. Based on the measure- ment, the detection field is automati- cally adjusted.
Right inset:
Sick’s safety laser scanners
Sick UK T: 01727 831121
www.sickuk.com Enter 350
Such advances have enabled more controlled deceleration of vehicles which has reduced wear and tear on vehicles caused by harsh braking. As technology has developed, the size and power requirements have reduced allowing application of the technology on to smaller guided vehi- cles. One example is the compact machines developed by the AGV man- ufacturer, JBT. JBT’s guided vehicles are used in hospitals, manufacturing plants and warehouses and minimising vehicle size can be important for those who want to minimise aisle widths. As technology has developed, so has the functionality of the scanners. Even on a small AGV there may be between two and five laser scanners to provide the required protection. This means the complexity of the AGV control system has also increased.
A significant degree of expertise is needed to integrate all the necessary control signals as well as the laser scan- ner itself, in order to reach the Safety Integrity Level required to comply with the essential Health and Safety require- ments of such machinery.
The complexity of cabling encoders, field switching signals, and safety sig- nals to and from each device could incur significant cost, so the latest developments to technology have focused on integrating complex sen- sors and safety-related controls. Sick has developed a package that utilises the power of a safety controller (Flexi Soft) connected to four laser scanners using a two wire bus called EFi (Enhanced Function interface). A two wire network cable is used to control all aspects of the scanner via safe protocols that ensure PLd confor- mance. Field switching, control and status signals can be connected cen- trally to the local Flexi Soft controller. The safety-enable function from the Flexi controller is then easily inte- grated with the speed and direction control of the AGV to allow interven- tion during hazardous events. The high-performance of the central controller also enables diagnostic functions to be set up to monitor the system and review any incidents. This concept can be applied to transfer cars and shuttles as well as complex access control applications where field switching is required.
NOVEMBER/DECEMBER 2012 Materials Handling & Logistics
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