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Pilz discusses safety requirements for packaging machines

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article image Packaging machinery

Safety is gaining ground in modern engineering.

Every day new functions are being added to packaging machinery automation, in order to cope with the different types of product in terms of design, size, and container.

Machinery can be much more flexible as a result of decentralised drive technology.

Further disciplines have been added over the last few years. The demands on safety including the implementation of the relevant safety functions have increased.

The question, how much safety does a machine actually need, is easy to answer: The protection of man and machine must be guaranteed, as must the ability to design production processes individually.

Short product life cycles, high variability and modern packaging mean that machines are ever more flexible and place heavy demands on technology and process alike.

Everyday life is governed by the frequent interchange of contents and packaging.

Automation technology with individual drives meets this requirement for flexibility, dynamics, fault reaction and changeover at the touch of a button. Generally it offers even greater availability while still increasing performance. In doing so, the limits of automation are often reached. The operator and his capabilities must also be considered as part of the production process.

Safety devices protect operating personnel:

Even on packaging machinery with high quantity output, the operator often plays no more than a subordinate role.

Interaction with the machine is mostly limited to packaging refills or brief interventions in the case of a fault. For this reason, not too much importance is attached to the use of qualified personnel to operate the machine.

Covers, fences and gates are used as safety devices to prevent direct access and exclude the possibility of injury.

Hazards arise when the machine is run outside of production mode, during setup or cleaning for example, or when the process requires some intervention while the machine is active. In this case, machine safety must be designed to enable human errors to be intercepted to a certain extent.

Safety in the classical sense will always refer to personal safety: risk must be kept to a minimum.

To exclude the risk completely you would actually need to stop using operating personnel all together.

However, the huge increase in machine flexibility has only come about as a result of improved interaction between man and machine.

Complete automation, including during setup and cleaning, would increase costs and labour exponentially. Over the next few years, this interaction between man and machine will result in even more developments in the area of safe sensor technology and safe data communication.

How much safety is necessary?

Each industry and machine has its own specific requirements.

For large areas of the packaging sector the safety requirements are limited to safety gate and E-STOP concepts.

As soon as an operator has to interact with an active part of the machine, the safety requirements increase.

A general statement that Category 3 of EN 954-1 is always sufficient for packaging machinery may often be correct, but does not apply across the board.

One thing must always be considered: Safety is not a self-contained function but needs to be designed individually for each machine.

As far as the machine builder is concerned, he either needs to have precise knowledge of the relevant standards and their implementation or he can call upon the extensive range of services and consultancy opportunities available from safe automation technology manufacturers such as Pilz .

Status of the standards:

The C standard applicable for the respective machine type describes the potential hazards and the measures required to avoid them.

In the case of packaging machinery this is EN 415 1-3. Additional standards apply if the safety functions are transferred to the machine control system.

The generic standard describing the safety-related parts of the control system is still EN 954, with its classification into categories (Cat. B to Cat. 4). It has been in use since 1996 and is being replaced by ISO 13849-1, which also assesses safety-related control systems in terms of their probability of failure. This is where the performance level (PL a - PL e) is used. ISO 13849-1 is predominantly used on pneumatic, hydraulic or mechanical systems.

EN IEC 62061 developed as a machinery sector standard under IEC 61508, is restricted to electrical and (programmable) electronic systems for control system and drive technology. This standard also considers the probability of a hazardous event occurring.

These parameters are used to determine a value, the level of which represents a benchmark for each hazardous situation. This value is classified into Safety Integrity Level 1 to 3.

The classification into SIL (0 – 3) refers to IEC 62061, which was written specifically for electronic control systems and drive technology.

It does not matter whether classification is by category, safety integrity level or performance level – what is important in each case is that the applied control technology is designed in such a way that the potential hazard to an operator from a machine is reduced to an acceptable minimum or is excluded entirely, based on the assessment resulting from the hazard analysis.

Safe operational stop brings drives to a standstill:

On a packaging machine designed to fill containers, foil lids regularly fall out of the magazine during production and drop on to the containers, which at this point are still open.

Although it is not actually necessary to intervene in the process because the containers are inspected later, it is common practice to stop the machine briefly, open the safety gate and remove the surplus lid.

Particularly on the lid placer, it would be out of the question to shut down the drive for such an incident, as the synchronicity of the whole machine would be lost as a result.

So the object of the exercise is to stop the drives synchronously when the safety gates are opened, to transfer to a safe operational stop and to restart the machine without delay by pressing the reset button once the gates have closed.

In this industry it is quite common to stop the machine via the safety gate because staffs are busy working around the machine during operation. If a fault is detected, the process can be halted by opening the next safety gate.

When the safety gate is opened, the hazard analysis must show whether there is enough time to stop the drives before staff come into contact with moving parts.

Although the enormous plate conveyor represents a high potential risk, it is quite sufficient to comply with the requirements of SIL 2 or PL d (previously Category 3) due to the frequency of occurrence and the probability of a hazardous situation arising.

A safe operational stop function (SOS in accordance with IEC 61800-5-2) is required to solve this task. It guarantees that, once stopped, the position of the drives is monitored until the safety gate is closed again and the process has been reset.

Scalable solutions, tailored to the specific application:

As a supplier of complete automation solutions with a focus on safety and motion control, Pilz supplies a safety solution within the servo amplifier, as part of the PMC system series. This solution also takes into account the requirements of the packaging industry.

A scalable solution offers different levels of safety, depending on the user’s requirements. The basis for all safety functions is the safe stop, which is included even in the basic version.

If additional safety functions are required, the user can implement these simply by inserting a safety card. So additional functions can be added in the future such as safely reduced speed, safe operational stop or safe standstill.

In the above example for container filling, the servo amplifier PMCprotego D enables the individual drives to be easily upgraded with extended safety functions for E-STOP and safety gate circuits, and parameters to be set for the time to machine standstill.

When the complete function range of the safety card is used to monitor the drive and with the planned expansions up to Category 4 in accordance with EN 954, Pilz offers a safe drive solution for interaction between man and machine.

For multi-axis applications, networking via SafetyNET p will be the future. So Pilz can completely cover all the specific safety functions of the packaging industry.

Safety as a guarantee of greater availability:

The safety of man and machine is of key importance. Operating personnel need to be protected from hazards during dynamic packaging processes.

Modern concepts integrate safety directly within the drive. The example shows that small modifications can considerably increase a machine’s efficiency and availability, while at the same time providing greater protection for operating personnel. Even bridged gate contacts may now be consigned to the past.

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