Using Laser Scanners for Automated Guided Vehicle - AGV - Safety

Seb Strutt

By Seb Strutt, Senior Product Manager and Safety Specialist at SICK (UK)

The safety laser scanner is an established and universal tool for machinery safety.  It’s versatility and value-for-money capability has created unprecedented new opportunities to better protect machine operators.  It has been the foundation without which other automation advances in industries such as automotive, steel and metal working and materials handling could not have taken place.

Advanced laser scanners such as those from SICK provide collision protection from Automated Guided Vehicles (AGV).   Developments in the safe use of unmanned vehicles are based on more compact safety laser scanners such as the SICK S3000 series which have enabled the safe non-contact detection of personnel in the path of a moving vehicles travelling along complex paths and production layouts.

We have seen how the technology has helped our customers dramatically increase their speed and production efficiency by using driverless vehicles, while downtime and maintenance have been reduced.

 

No contact needed

Prior to the advent of laser techniques, obstacles were physically detected by deformation of contact bumpers, which activated an associated mechanical switch. Thus, the approach speed limited the impact force required to activate the collision detection system before the AGV could cause harm.  

By introducing a compact safety laser scanner, the AGV was immediately allowed to travel faster as the collision prevention system could detect oncoming obstacles some distance before impact. Thus the AGV could increase its hourly load capacity and still ensure safety.

 

Detection at speed

The principle of safety laser scanners is scanning their surroundings in a fan shape to measure distances using the time-of-flight measurement principle.  With detection of an object in the pre-programmed hazardous area, a safety laser scanner switches off the OSSD (Output Signal Switching Device) causing the vehicle to stop. 

Laser scanners on mobile vehicles usually have three zones configured to form the field set, two warning and one emergency:

  • outer zone, if a pedestrian enters, a warning alarm may be sounded,
  • middle zone, here the vehicle may decelerate 
  • inner zone, only if this is entered would an emergency stop be triggered 

The need to stop the vehicle for every object detection, and affect production efficiency, is therefore minimised.

Complex protection for complex systems

Continuing development means increased detection ranges allowing safety fields up to 7 metres.   High-performance and flexibility for complex vehicle paths are enabled by multiple fields up to 64 zones to allow the AGVs to turn and change direction while following their routes.

 

Speed measurement integration

By integrating laser scanners with other sensing technologies, further advantages can be realised.  For example, with encoders fitted to the vehicle (such as the SICK ATM60/90), laser scanners have the ability to safely measure the speed of a vehicle via inputs from the encoders. 

Based on the measurement, the detection field is automatically adjusted and, with more controlled deceleration of vehicles, the wear and tear on vehicles caused by harsh braking is reduced.  In addition, technology developments have reduced size and power requirements to enable application to much smaller guided vehicles.  Minimising vehicle size can be very important for customers who want to minimise the aisle widths.  Such vehicle are used in hospitals, manufacturing plants and warehouses.

Functionality of the scanners has also developed so that 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.

 

Achieving safe operation

In order to reach the Safety Integrity Level (SIL) required to comply with the essential Health and Safety requirements of such machinery, a significant degree of expertise is needed to integrate all the necessary control signals as well as the laser scanner itself. For a safety slow down and stop function in the direction of travel, the performance level of the stop function should be category 3, PLd.

The latest developments in the technology have focused on integrating complex sensors and safety-related controls to reduce the costs of the complexity of cabling encoders, field switching signals, and safety signals to and from each device.

 

Reducing cabling and cost

For example, Sick has developed a package that utilises the power of a safety controller (SICK Flexi Soft) connected to 4 laser scanners using a 2 wire bus called EFi (Enhanced Function interface) in order to reduce wiring in applications where several scanners are used.

The concept reduces the requirement for 10 or more core cables to be connected to each scanner. Instead, a two wire network cable is used to control all aspects of the scanner via safe protocols that ensure PLd conformance.

By centrally connecting field switching, control and status signals to the local Flexi Soft controller, the safety-enable function from the Flexi Soft controller is then easily integrated with the speed and direction control of the AGV to allow intervention during hazardous events.

 

Vehicle, car and shuttle safety

With a high-performance central controller, diagnostic functions can be set up to monitor the system and review any incidents. As well as AVGs, this concept can be applied to transfer cars and shuttles as well as complex access control applications where field switching is required. Existing (retrofit) or new machinery can benefit from the technology.

Laser scanning technology is likely to see even more developments in compactness and systems integration, which will make AGVs an ever more common sight, not only in factory environments and warehouses, but in environments such as hospitals, airports or large commercial buildings.