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24 October, 2021

Switching into safety engineering - The future of safety engineering

05 October, 2021

Recent developments relevant to safety engineering come in many guises.  In the fifth of a six-part series, Andy Pye reviews some of the significant ones.

OEE (Overall Equipment Effectiveness) is the gold standard for measuring manufacturing productivity. It identifies the percentage of manufacturing time that is truly productive. An OEE score of 100% means you are manufacturing only Good Parts, as fast as possible, with no Stop Time.

The advent of Industry 4.0 technologies has improved the ability of production managers to obtain more data about the operation of their machines and processes. Measuring OEE is a manufacturing best practice. By measuring OEE and the underlying losses, important insights are unearthed on how to systematically improve the manufacturing process.
It transpires that a manufacturing process where safety considerations are paramount are often the most productive, because there are fewer shutdowns due to machine stoppages.

Safety on the bus

For years, it has been normal to ensure safety at machines by means of extensive wiring and related switches. Wiring is visible and therefore tangible, which reinforces the feeling of safety. The safety logic intercepts any faults that occur in the wiring and thus the safety requirements are met in full.

This begs the question "Why change this?" However, there are some very good reasons for considering the use of a safety bus system. One is the significantly reduced wiring work. At least as much safety can be achieved by using a bus system as with conventional wiring.
There are many bus systems for every conceivable automation task. Often which bus system is used depends on the control system technology used. In Europe, above all PROFIBUS - and its successor PROFINET - is dominant, while ASI and EtherCAT are significant.

Conversely, DeviceNet or its successor EtherNet/IP dominate in the USA. On the Asian market there is no one really dominating bus system. The more European companies can gain a foothold in the Asian and American markets, the more the related bus systems will spread in these markets.

Security Issues

Systems that are connected to a bus network are potentially at risk of intrusion. A cyber- attack could lead to the safety system being degraded or disabled. The safety of a machine is directly dependent on authorised access to functions and danger zones.
Over time, various approaches have been developed to ensure that personnel can only obtain access to potentially dangerous machine functions under certain conditions. Safety guards on many machines and installations still must be overridden for maintenance and servicing work. Thus, service engineers have more access rights than machine operators.
Providing a variety of operating modes allows the operator to select the required operation mode (eg setup) and activate the suitable safety guard (eg enabling switch).
A very common method is the use of keys that permit the holder to use certain functions on a machine. An alternative is restriction via password. Both approaches have weaknesses: both keys and passwords can be exchanged between personnel. Passwords can easily be forgotten, or compromised very quickly.

Electronic-Key-System (EKS)

Euchner's Electronic-Key-System (EKS) acts as a replacement for both. It consists of a read station and at least one Electronic-Key. The Electronic-Key contains a writable memory.

With the EKS, applications such as access to control systems/operating parameters and entry of an expiration date can be realised in addition to selection of operation mode. The Electronic-Key data are transmitted from the read station to the control system via the data interface (e.g. ProfiNet, Profibus, USB, Ethernet TCP/IP).

Unlike passwords or conventional keys, EKS Electronic-Keys cannot be easily copied. With EKS, management always retain an overview of its group of users. If a key should be lost, it can be blocked.

EKS Electronic-Keys can be allocated to individual people. Responsibility is thereby visibly transferred to the Electronic-Keyholder, effectively preventing Electronic-Keys from being passed along or left inserted.

On many installations, there are particularly dangerous tasks that can be performed only with open safety doors and, in some cases, only at full speed. Persons must be specially trained to perform these tasks. The EKS with data interface offers the option of storing verification of training on the Electronic-Key. The dangerous work can then be performed only with valid verification.

The EKS Light, can perform only a single function such as controlling access to selection of operation mode.

The EKS FSA (For Safety Applications) offers additional options for improving selection of operation mode and making it safer. FSA devices have a second channel, which is generally available in the form of an additional output. This output is always evaluated for safety purposes.

Using the EKS FSA, it is possible to develop a procedure permitting selection of operation mode on a touch panel without additional mechanical controls.

The procedure was approved by the Institute for Occupational Safety and Health of the German Social Accident Insurance (Institut für Arbeitsschutz, IFA). This Institute confirms that selection of operation mode with a touchscreen is possible up to PL e according to EN ISO 13849-1. This requires using the EKS FSA in combination with suitable software in the failsafe PLC. The procedure also allows so-called softkeys
to be used instead of a touchscreen, also up to PL e.

Industry 4.0 and Smart Machines

As manufacturers are continuing to enter the age of Industry 4.0, the requirements for information transparency and machine interconnectivity is ever increasing. Intelligent monitoring capabilities make it possible for an operations manager to see the status of a production facility at any moment in time, or the equipment manufacturer to receive condition updates to replenish consumables automatically.
Safety interlocks and guard locking devices are now capable of transmitting key information. Process data is sent to the control system, including status signals, such as the position of the door or guard locking, indication of whether a switch is out of alignment. Moreover, other services can be used to collect data such as the switch temperature, the applied voltage and number of operating cycles.
With these advances, it is now very easy for a factory maintenance team to key into a machine’s maintenance programme and schedule maintenance and repair and from an external position, and for the machine manufacturer to remotely monitor the safety aspects of the machine, its guards and other safety elements. This results in positive accounting rather than disaster management, optimising plant uptime and reducing unwanted costs.

Collaborative robot safety

Increasingly forming part of the production environment, collaborative robots (cobots) share tasks with humans. Integrated safety features allow them to work with or close by humans. Despite these, safe implementation based on comprehensive risk assessments is crucial.

The area in which a collaborative robot operates, including any tooling or additional equipment, is known as the collaborative workspace, the space within the safeguarded area where the robot and human can perform tasks simultaneously during production operations. It is extremely important to review the entire area for any circumstances where an operator could be trapped or clamped by the robot and surrounding pieces of equipment.

The safety standard ISO 10218 and technical specification RIA TS 15066 define the safety functions and performance of a collaborative robot.

Safety devices are generally quite easy to integrate into a collaborative robotic application. These include:
Open area safety guarding (eg safety area scanners and mats).
Gated/limited area safety guarding solutions (eg light curtains and safety switches)
Active hazards safety guarding (eg a “deadman” switch that automatically goes back to the “off” position if the user fails to exert pressure.

References
• Euchner Safety Book, pp85-102
https://www.euchner.de/en-us/service/eks-application-examples/
https://assets.euchner.de/uploads/127382_07-07-18_Flyer-EKS-Betriebsartenwahl.en-us.pdf

This is the fifth part of our ‘Switching into safety engineering’ series which will include comprehensive articles and follow-up Zoom Q&A sessions – to register for the series or to request a copy of the free machinery safety guidebook, please visit www.drivesncontrols.com

Are wireless systems safe?

Wireless communication is often proposed as a key enabling technology for the implementation of advanced manufacturing systems. Factory operators could control operations in ways that are cost-prohibitive with wires.

However, there are technical challenges, including time synchronisation, reliability, latency determinism, resilience to interference from factory-generated noise and other transmission security vulnerabilities.

Over time, it is expected that new protocols for future automation systems will address these challenges.




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