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5 August, 2021

Switching into safety engineering - the basics and fundamentals of safe machinery

31 March, 2021

Introducing a programme of feature articles and webinars sponsored by Euchner, covering the philosophy behind safe machinery and the role that the various types of safety switches and devices can provide.

At the start of the machine age, machinery was significantly simpler than today. Most machine parts moved slowly and the processes undertaken by the machine were clear to the operator - only the main spindle was powered, while the axes were actuated manually by the operator. The situation changed as it became possible to equip all the axes with separate drives, so inattentiveness during operation could be dangerous for the operator and the machine could also be damaged.

Therefore, the significance of machinery safety has steadily increased in recent years. Due to modern, high-speed, highly automated work equipment, hazards to personnel and processes lurk in all machinery and installations, many not apparent at first glance. A further trend that has increased the importance of considered machinery safety design is the way people interact with the equipment; gone are the days when it was adequate to simply shut down the entire machine when an operator required access. Motive power is often needed for setting up or optimising the equipment during regular production and this must be done safely.

For this reason, various directives, standards and laws have been introduced to define suitable safety measures. Worldwide safety standards and regulations are increasingly applied, even in countries where in the past little value was placed on safety standards. Through the use of the applicable standards, we can ensure the safety of people at work, while addressing the requirements of globalised trade based on consistent standards for machinery. The appetite for this globalised consistency is demonstrated by the immense number of ISO (International Standards Organisation) standards in publication, numbering over 23,000 to date.

We start the six-part series with a look into some of the main topics facing machinery builders and operators today:

Machine safety components may look similar to the standard equipment used on the factory-floor but they are often very different. A failsafe PLC utilises a whole host of technologies to ensure it has a known failure mode. Safety switches of various types monitor gates and doors, as well as any other movable physical guards. If a guard has been opened or removed, or is out of alignment, safety-switches send a signal to the machine control system. These switches often monitor themselves to ensure they are able to switch off when required. Even the simple roller-plunger limit switch is redesigned for safety applications to help prevent a contact-weld or a failed spring leading to a dangerous condition.

Personnel safety or process safety?

Historically, there has been a perception that safety decreases productivity - in other words, it aims to stop everything and stopping movement creates downtime. But if safety is designed in correctly, this negative impact of safety can be minimised. Whereas safety used to be added in as an afterthought at the end, designers are now encouraged to consider functional safety at the outset, an approach echoed in a number of the safety standards we will be discussing in the upcoming features.

Important though the safety of personnel is, in many cases the process must also be protected. Opening a door may cause a process to jam up and take several hours of downtime to sort out the resulting mess. The answer is to keep the door locked until the machine is stationary.

Safety or security?

Safety and security may need rethinking in industrial plants, now that Industry 4.0 is advancing networking and digitalisation. The future is digital.

The term "safety" refers to the hazard for personnel due to a machine; "security" on the other hand is protection against intrusion either from within or outside of an organisation. At first glance, machinery safety and security do not appear to have much to do with each other. But on more detailed consideration, there are big overlaps. The safety of a machine is directly dependent on factors such as selection of functions, access to danger zones and authorisation. Safe automation must now encompass more than just emergency shutdown and worker protection, but also provide effective protection against deliberate manipulation, cyber attacks or accidental misuse.

The need for personnel to interact closely with the complex machines in our modern factories is increasing and this requires more flexible safety systems, yet at the same time ensuring the operators remain well-protected. Over time, various approaches have been developed to ensure that personnel only obtain access to potentially dangerous machine functions under certain safe conditions.

A common method is the usage of keys that permit the holder to use certain functions on a machine. Service engineers then have more access rights than machine operators. Another very frequently used method is restriction via password.

However, both solutions have weaknesses: keys and passwords can be exchanged between personnel, which makes tampering easier. Passwords can easily be forgotten and, if they are written down, they are also compromised.

Possible solutions

  • Safe ‘mode’ selection that can only be operated by authorised users
  • Reduced speed or force
  • ‘Hold-to-run’ or hand-held enable controls
  • Individually ‘paired’ safety switches
  • Euchner has created the Electronic Key System (EKS), which is a replacement for keys and passwords, which also opens up other application areas

As manufacturing organisations adopt the benefits of Industry 4.0 next generation automation there is a greater need for secure and robust factory automation networks to carry both standard and safety related information. The ISO standard 62443 (industrial communication networks, network and systems security) deals with IT security and automation. It currently offers the best orientational guide for both operators and device manufacturers when it comes to implementing security efficiently, the range of topics or topics within that standard, our risk analysis, requirements of safe operation.

Tamper-proofing & manipulation

The early safety devices only had low levels of coding whereby any actuator worked with any switch. This allowed a user to easily manipulate the safety device. This can be done by someone who carries a spare actuator with them and uses it to keep the door open while running the machine, for example. Thankfully, technology and standards have addressed this and suitable solutions might include non-contact safety switches where the actuator is embedded in the guarding or a uniquely coded RFID-monitored safety switch. With a high-coded version of an RFID safety switch the sensor actuates when only the paired actuator is detected.

* This is the first 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.




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