Safety engineering: The main aim of safety engineering is to protect people

Functional safety is an indispensable component in modern machine and plant construction. It is important to comply with guidelines and thus make future-proof applications possible.

We have compiled a wealth of information on the subject of functional safety for you and present current guidelines such as the Machinery Directive 2006/42/EC and EN ISO 13849-1.

Both guidelines have been in force since the end of 2009 - we inform you about details and the steps that EN ISO 13849-1, for example, provides for in principle in order to design a safe machine.

From the safety function to the product: Our products with safety engineering

An essential aspect of a safe machine is its "Functional Safety". This means having a safety function, e.g. the machine switching off when a safety door is opened, that is always implemented or ensuring that an error is uncovered in the implementation of a safety function before it causes any injury to people.

The complexity and failure risk increases with each additional component in a machine. Deep integration of "Functional Safety" into the products and engineering tools will provide the necessary safety. The safety functions thus correspond to one element of the uniform standards.However, they are more convincing if they have application-specific functions that considerably reduce the engineering expenditure and provide additional benefits, such as reducing the need for large buffer zones in storage and retrieval units.

Table: Lenze products with safety technology

			Frequency inverters				Servo inverters		Controls
			i550	8400	8400 motec	8400 protec	i700	9400	c250-S
Safe stop and brake functions	STO	Safe torque off	●	●	●	●	●	●	○
	SS1	Safe stop 1				●		●	○
	SS2	Safe stop 2						●	○
	SOS	Safe operational stop						●	○

Safe basic motion functions	SLS	Safely limited speed						●	○
	SS1	Safe stop 1				●		●	○
	SS2	Safe stop 2						●	○
	SLP	Safely limited position						●	○

Safe extended motion functions	SCA	Safe cams						●	○
	SSM	Safe speed monitoring						●	○
	SDI	Safe motion direction						●	○
	SLI	Safely limited increment						●	○

Additional safety functions	SSE	Emergency stop				●		●	○
	OMS	Operating mode selector switch with enable switch (ES)				●		●	○
	SMS	Safe maximum speed						●	○
		Safe monitor						●	○
	SCAS	Cascading of the STO safety function						●	○
	PDSS	Position-dependent safely limited speed						●	○
		PLC open TC 5 functions							●

Safe communication		Safety bus PROFIsafe				●		●
		Safety bus FSoE						●	●
		Safe transmission of current position and speed data						●	●
		Connection of safety sensors	●	●	●	●	●	●	●
		Operation with safety PLC				●		●

● Safety function integrated
○ Activation/deactivation of the safety function

Five steps to a safe machine

The Machinery Directive comprises the following elements:

Carrying out a risk assessment: this enables you to identify applicable safety and health protection requirements.

Design and construction of the machine that takes into account the results of the risk assessment.
Following the risk assessment, you will know what measures you need to implement to reduce the risks.

If you cannot implement these measures in the design phase, then it will be necessary to integrate them into the control technology and set them down in writing in the specifications for the safety functions.

When using a control system, the Performance Level (PL) determines the requirements that the measures will need to meet in order to reduce risk. Following the implementation of safety functions, the real achieved PL will be checked and must be at least the same or greater than that worked out in theory beforehand.

1. Assessment of risk and risk reduction

The first step to a safe machine is establishing the limits of the machine and in particular its application as directed. This includes, for example, its application area, operating modes, service life and the interface between people and machine.

Using these specifications, you can identify points of danger and evaluate the risk of each individual danger. If it turns out that the risk would be too great without implementing additional measures, then the said risk must be reduced to an acceptable level.

The measures taken should prevent the danger entirely or reduce it by using an inherently safe design. Only if these measures do not lead to sufficient reduction of the risk should you rely on technical protective measures and - as a last resort - the documentation.

2. Safety concept

If the technical protective measures require the use of a control system, then the safety functions to be controlled by the control system should be described in precise detail. The required Performance Level (PL) for each safety function will then be established according to the DIN EN ISO 13849-1 graphs.

Following selection of the control system and all components that influence the safety function, checks will be carried out to see if the identified Performance Level is adhered to during implementation and verification.

3. Validation planning

Following selection of the control system and components, you will plan the validation.

In doing so, you will need to specify the following:

How documents are identified and updated?
In which ambient conditions the validation should take place?
Which checks and measuring tools are to be used?
Which standards should be used (e.g. DIN EN ISO 13849-2 for control systems)?
Who are the people responsible?

4. Implementation and verification

The implementation of the planned measures must then be carried out e.g. the safety control should be programmed and the safe drive parameterised.

As part of verification, you should check whether the planned measures have been correctly implemented. If they have, it should be confirmed that the Performance Level of the implemented safety functions is better or equal to the Performance Level identified when drawing up the safety concept.

5. Validation

Validation is carried out according to the specified planning. If checks are not passed, rectification will be required.

All validation activities must be documented. Successful validation is concluded with a validation report.

Guidelines and standards

The application of the Machinery Directive is a legal requirement in all countries that are part of the European Union. It does not contain specifications as to technical details, but defines the essential requirements that machines must meet, such as the results that must be achieved or the dangers that must be prevented. It does not specify what the technical solution should look like in concrete terms.

The Machinery Directive (2006/42/EC) applies to:

Machines
Safety components
Incomplete machines (partial machines)

Once the machine has been manufactured, the manufacturer will confirm that all essential requirements have been taken into account and the machine therefore conforms by applying the CE mark and drawing up the Declaration of Conformity.

The uniform standards offer guidance in meeting essential requirements. If a uniform standard covers all the risks associated with the machine, you may assume the machine conforms to it. In this case, we talk about the presumption of conformity.