In order to place automated guided vehicles (AGVs) on the market in the European Economic Area, either individually or as part of an automated guided vehicle system (AGVS), the vehicles must meet the basic safety and health requirements of the Machinery Directive. In particular, non-contact protective devices such as safety laser scanners not only enable the safe and intralogistically efficient operation of these increasingly autonomous vehicles, but also detect contours and provide data for the navigation support of the vehicles. For example, safety-certified encoders can be used to provide the necessary speed information for the dynamic switching of the protective fields of the safety laser scanners. In addition, safe inductive sensors query vehicle parameters such as the steering angle or fork height and make them available to the safe control system of an AGV, for example a Flexi Soft from Sick.

The control system not only acts as a safe control center for the vehicle, but also intervenes directly in the monitoring and control of the travel drives via safety relays or a safe motion control module. Appropriate gateways then integrate the safety control system into the higher-level automation system - via Ethernet/IP or Profinet, for example.

EN ISO 3691-4 only a draft so far - what to do?

Safety solutions for AGVs must be able to detect people and objects in their path and reliably protect them from potential collisions, even under demanding operating conditions.

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So much for the technological state of the art. But what do the relevant standards say or require? By definition, AGVs are internal, floor-bound conveyor systems with one or more automatically controlled automated guided vehicles (AGVs) that have their own drive, can be used inside and outside buildings and are used for autonomous material transportation.

The safety requirements with the aim of protecting people and property are regulated by standards - actually. While various parts of the relevant DIN EN ISO 3691 are already in force, Part 4 of the standard - which deals specifically with the safety of ground transportation vehicles - is currently only available as a draft. The European C standard EN 1525, which has been used to date and was intended to be replaced by DIN EN ISO 3691-4, is not listed as a harmonized standard for the Machinery Directive (2006/42/EC). Until DIN EN ISO 3691-4 appears and is published in the Official Journal of the EU, it is therefore recommended that EN 1525, which is still valid, be used for vehicle safety issues.

Intelligent foresight on safety

Among other things, EN 1525 defines the requirements for industrial trucks, such as the braking system, speed limitation and stability. It also addresses the requirements for protective devices and operator information and, last but not least, provides information on testing and commissioning.

Autonomous machines, but above all machines that interact with humans, require new safety concepts that not only protect the worker, but also effectively support the flexibilization of production processes.

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In essence, AGVs as well as AGVs are the technological forerunners of cyber-physical production systems in the sense of Industry 4.0 and the smart factory - as AGVs that drive and work autonomously and as AGVs that organize, optimize and monitor themselves. The latter functionality must be implemented with the help of safety-oriented components after appropriate hazard analyses have been carried out in order to ensure the best possible accident protection during use and at the same time exclude possible liability risks for manufacturers and operators as far as possible.

Although safety is the most important aspect in this context, it is not the only one: safety devices must not impair the use of the vehicles - and intelligent additional functions should offer users additional benefits. Examples include safety laser scanners such as the compact S300 Expert or the S3000 Expert with CMS (CMS stands for Contour Meas-urement and Safety). These devices not only monitor the path of the AGV, but also provide geometric measurement data that enables the vehicle to independently pick up or set down pallets or containers in the correct position. The long range of an S3000 Expert of up to seven meters also makes it possible to detect position reflectors in a system and to record the distance and angle in relation to the vehicle position and use it for navigation support. In both examples, the intelligent functionality of the measurement data evaluation saves the use of additional sensors.

The safety control center that travels with you

In addition to safe sensor technology, the aforementioned safety control concept plays a central role in the efficient implementation of an AGV application. Concepts that offer flexibly combinable function modules, software-supported logic functions and extended options for fieldbus integration, for example via bidirectional gateways for common fieldbus connections, are a great advantage here. When used on an AGV, a solution such as Flexi Soft coordinates all sensors and functions that serve vehicle safety in its function as an on-board safety control center. Up to four sensors can be connected via the EFI interface (Enhanced Function Interface). In this way, for example, all-round AGV protection can be realized with several safety laser scanners.

In addition to the actual direction of travel, it is also necessary to monitor hazardous areas next to the vehicle during swivel movements or cornering, especially in the case of large AGVs. Flexi Soft uses the data from safe encoders to switch the protective fields of safety laser scanners depending on the speed. If information such as the steering angle or the height of the load handling attachment is relevant in terms of safety and control, safe inductive sensors can also be connected to the control system. Regardless of this, the latter can also process information from non-safety-related sensors in addition to the safe data, for example from light barriers, identification systems, 2D distance sensors or initiators - and thus generate additional added value.
Furthermore, such a modular concept with the corresponding modules enables safety-oriented monitoring of the travel drives. The FX3-MOC0 Drive Monitor from Sick, for example, uses the SSM (Safe Speed Monitor) and SLS (Safety Limited Speed) safety functions to enable safe monitoring of the speed of an AGV via encoders on the wheels. Depending on this, the warning and protective fields of the safety laser scanners attached to the vehicle can be switched. If warning fields are violated, a safe reduction in speed can be initiated automatically. If a protective field is violated, the drive monitoring functions SBC (Safe Brake Control) and SS1 (Safe Stop 1) or SS2 (Safe Stop 2) intervene, triggering and safely monitoring an emergency stop of the vehicle.

If the control system has triggered an emergency stop of an AGV, the safe direction of rotation detection SDI (Safe Direction) blocks the direction of rotation of the drive currently in use. This means that the vehicle can only make movements in one direction and thus safely move away from the obstacle. The safety-related monitoring of drives can therefore be fully integrated into the safety control system.

Data collector for Industry 4.0

Last but not least, safe sensors and safe control systems - especially when networked to form complete safety solutions - provide a wide range of additional data that can optimize the availability of individual AGVs as well as an entire AGV. Power consumption, operating hours, the onset of soiling or operating temperatures are examples of information that can be directly relevant for preventive or in-service maintenance as part of condition monitoring. It is provided by the sensors, evaluated and processed by the control system and sent to the vehicle control system via the gateway. From there, they are finally made available via radio data transmission, Bluetooth or NFC in superimposed or cloud-based applications. This not only enables process optimization in the sense of Industry 4.0, but also makes 'AGV 4.0' - in analogy to the cyber-physical production systems already mentioned - future-proof building blocks of intelligent production and warehouse logistics within the smart factory.

Author: Dennis Münich works in the Industrial Safety Systems division at Sick, Waldkirch.