Taking on the challenge of mobile robot safety

9th August 2024

TÜV SÜD

Caitlin Gittins

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Automatic guided vehicles (AGV) and automated vehicle systems are becoming increasingly indispensable for automated operations. As they provide continuous service around the clock and can be flexibly assigned for a variety of applications, their contribution to increased efficiency and productivity is significant.

By Stewart Robinson MIET MInstMC, Principal Engineer and Functional Safety Expert at TÜV SÜD

The primary task of AGVs is to transport materials, both within industrial buildings and across company premises, helping to automate and optimise logistics processes. They consist of the following elements: one or more automated guided vehicles, a master control system, equipment for location determination and position detection, equipment for data transmission, infrastructure, and peripheral equipment.

However, this equipment poses hazards to humans with risks growing alongside increasing human interaction with AGVs. Manufacturers, suppliers, integrators and operators must therefore assess and validate robot compliance against a range of different standards, as well as considering application-specific requirements.

Safety guidelines

ISO 3691-4:2023 – Industrial trucks – safety requirements and verification - Part 4:Driverless industrial trucks and their systems marks a crucial advance in autonomous vehicle safety guidelines.

Regarding machinery safety, ISO and EN standards are categorised in three types:

Type-A: basic safety standards containing principles of design and general aspects that can be applied to all machinery

Type-B: group safety standards that cover a safety aspect or protective device relevant to a wide range of machinery

Type-C: contain the safety requirements for a specific machine or type of machine. A Type-C standard has priority over Type-A and Type-B.

ISO 3691-4 is a Type-C standard because it containsthe safety requirements for a specific type of machine, and it applies to all stakeholders – machinery manufacturers, integrators and operators. This ensures there isco-responsibility to create a unified approach towards AGV safety and risk management. It outlines the safety requirements for driverless industrial vehicles and their systems, as well as how to check that they meet those requirements.

Three key aspects must be taken into account:

Operating environment (different zones where the truck operates and interacts with humans)

Associated hazards and risks

Correct implementation of safety systems (protection)

To give an example, an AGV navigating towards a machine in an operating area with a human presence represents a ‘collision risk’. According to ISO 3691-4, this risk may be mitigated by using three safety measures incorporated in AGV design:

Personnel detection system

Speed control system

Braking system control

In current practice, speed limitations due to a human presence are therefore applied even if there are no humans in the actual AGV operating area.

Likewise, in a confined area, with no human presence allowed, an AGV making its final approach to a machine for docking may pose a collision risk between two industrial assets. This unsafe docking event risk may be mitigated by using two safety measures incorporated in AGV design:

Speed control system

Parking braking system control

The condition of the operating environment has a significant effect on the safe operation of a truck. So, Annex A, which covers the requirements for the preparation of the operating zones, must be used to eliminate hazards when preparing the operating zone.

Annex B lists all significant hazards, hazardous situations or hazardous events that must be considered during the life of the truck. Not only should this include hazards relevant to the machine when it is being used as intended, this should also cover conditions of misuse that are considered reasonably foreseeable by the manufacturer. The Performance Level (PL), found in ISO 13849, for the different safety functions are based on the hazards listed in this annex.

When designing the safety functions, it is vital that the complete system is taken into account so that the interrelationships between the multiple functions of the AGV are considered to optimise safety, for the protection of operators and other assets around them. For example, the AGV’s control system must manage both safety and non-safety functions, so it must be taken into account that some safety functions may not only impact safety, but also non-safety functions.

While Industry 4.0 sees reduced risk in several areas, the range and flexibility of connected interfaces introduce a new set of risk issues. For now, ISO 3691-4 takes us a step further as it is well aligned with ISO 13849. This is a safety standard which applies to parts of machinery control systems that are assigned to providing safety functions. It provides safety requirements and guidance on the principles of design, and the integration of safety-related parts of control systems (hardware or software). This means it provides invaluable guidance for carrying out safety assessments for the complete AGV. It is therefore clear that ISO 3691-4 should not be seen a standalone document to assume conformity with other AGV standards and the EU’s Machinery Directive, its new Machinery Regulation, or the UK’s Supply of Machinery (Safety) Regulations.

This article originally appeared in the July'24 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.