How to Safely Retrofit a Woodworking Machine

To ensure that plant and machinery are always state of the art, retrofits have become increasingly established in the woodworking industry.

Safety defects that generally arise after many years of use, such as the lack of adequate safeguards, lead to a loss of machine safety. There are several immediate benefits a retrofit can bring: in addition to the updated safety technology, significant investment costs can be saved, because a new investment would cost considerably more. A retrofit will also increase the machine’s availability, as it will again be running smoothly and efficiently.  Pilz provides support in this area with tailor-made retrofit solutions.

For example, double-end tenoners – machines that process two sides of the work piece simultaneously. To increase their precision and availability, the first step is to determine whether the retrofit and increased availability need to be regarded as a significant change.

The width adjustment of these machines is critical: the implementation has to ensure that work piece transportation is safely guaranteed at all times, but that no hazards can arise for operating personnel as the adjustments are made.

The solution can be to use a safety light barrier, PSENopt, or the PSENslock / PSENsgate safety gate systems, both from Pilz. PSENopt provides protection where operator intervention is required as part of each cycle, such as insertion work, or the infeed and outfeed of material. PSENslock / PSENsgate, on the other hand, are integrated safety gate systems and cover functions such as safe monitoring, safe guard locking and control elements, including additional functions such as E-STOP and escape release, all in one unit. All components – whether mechanical or electronic - are integrated within one safety gate system.

Following the retrofit, operators now have the option in “Setup” mode to monitor the width adjustment process in the danger zone, via enable mode. Also, all the individual processing cabins are now secured in such a way that manual setup in “Setup” mode is possible at any time without risk. This gives the operator or tool setter the flexibility he or she needs for the task. “Set up” mode thus incorporates additional measures such as “Enable mode” and “Safely reduced speed”.

Hard real-time communication with RTFL

The RTFL transport layer of SafetyNET p is optimized for the fastest real-time applications. Typically the devices are networked in a linear structure, as with traditional fieldbus systems. All the bus subscribers have equal rights. Data is exchanged in accordance with the publisher/subscriber principle. As a publisher, each device can provide data to the other devices (subscribers) via SafetyNET p. In turn these subscribers can read
the published data from individual subscribers or all subscribers. This way it is possible to exchange data efficiently between all the subscribers. The communication mechanism used by RTFL is a very fast cyclical data transfer in one single Ethernet data frame or multiple data frames per cycle. Communication is initiated by a  special device called the Root Device (RD). The Ethernet frame generated within the Root Device is then  transferred to the other devices (OD – Ordinary Device). The ODs fill the Ethernet frame with data to be  published and extract from the Ethernet frame the data to be read. The devices are addressed via their MAC address. Each RTFL network requires just one Root Device. Each RTFL device has two Ethernet interfaces, which enables the familiar daisy chain wiring often found on fieldbuses.

UDP/IP-based communication with RTFN

The RTFN transport layer of SafetyNET p can be used at process control and manufacturing cell level, where standard Ethernet protocols are in demand and the real-time requirements are lower. RTFN is used to network the RTFL real-time cells and to connect standard Ethernet subscribers, such as visualization devices or service PCs. The RTFN level typically has a tree topology as used in office communication, i. e. with conventional Ethernet. Switches are used to connect the network subscribers in individual point-to-point connections.

RTFN can use two different mechanisms:
The Ethernet MAC frame is used in closed networks. The devices are addressed directly via their MAC address. Then there's the UDP protocol, which is available on most offi ce PCs. In this case the devices are addressed by their IP address. If IP based communication is used, the RTFN frames may also be routed from network to network.

What are the Changes to Europe’s Machinery Directive Every Manufacturer Must Know?

US manufacturers that export machinery to Europe need to be aware of the upcoming changes to the Machinery Directive.  When it comes to the design of safety related control systems the familiar standard EN 954-1 is set to be replaced by EN 62061 and EN ISO 13849-1. Pilz Automation Safety can help manufacturers understand this important change.

Where are the fundamental changes from EN 954-1? Previously the focus was on the architecture of the control system. Ultimately this was converted into “categories”. By contrast, the structure in the new standard EN ISO 13849-1 is simply stated on a qualitative basis. This means that quantitative variables such as the mean time to a dangerous failure (MTTFd), diagnostic coverage (DC) and common cause failures (CCF) have been added. Together, these parameters affect the performance level that can be achieved. Varying them also enables you to identify the optimum configuration. Due to these parameters, the new standard also considers aspects such as probability of failure and fault detection capabilities. These don’t just refer to the logic section. On a safety control system for example; the whole safety function is considered, from sensor to actuator. This overall assessment is nothing new in itself, but it does now have a different priority: as a result of the rigorous assessment in accordance with EN ISO 13849-1, it is now fully established and stipulated. The focus may now be on components such as valves for example, which were considered a lower priority under EN 954-1. In accordance with the new standard, these must now be included in the calculation with their characteristic data and reliability values.  

Machinery in the European Economic Area must comply with the Machinery Directive. The CE mark is the visible seal on the machine, which documents conformity with the Machinery Directive.   The change to the Machinery Directive takes place Dec 31, 2011. 

If a manufacturer does not want to use the standards to comply with the Machinery Directive, there is a more costly alternative, but for most manufacturers it is cost prohibitive and much slower to put into practice.

Rules for Exporting Machines to Europe Will Change Dec 31, 2011

 Companies that wish to export machinery to the European market need to make sure the machinery is safe and compliant with the Machinery Directive.  There are changes that will take place to this standard and they will take effect on December 31, 2011.  En 954-1 is the part of the Machinery Directive that will change.  EN 62061 and EN ISO 13849-1 are due to replace the familiar standard EN 954-1 when it comes to the design of safety related control systems.
The differences in the two standards can be summed up in the following:  EN ISO 13849-1 demands a probabilistic assessment of the safety functions, which goes beyond the “qualitative” approach of EN 954-1.  Pilz Automation Safety can help with making sure machinery is compliant with the new Machinery Directive.
There is no transition for this change.   In effect this means that if you continue to apply this standard, presumption of conformity as regards the Machinery Directive will no longer be triggered. To put it plainly: anyone who doesn’t get to grips with EN ISO 13849 will be running considerable risks as far as machine safety is concerned.
Machinery in the European Economic Area must comply with the Machinery Directive. The CE mark is the visible seal on the machine, which documents conformity with the Machinery Directive. Manufacturers use this to confirm compliance with the requirements of the Machinery Directive. In terms of actual implementation, the conformity process is supported by standards. In other words, when a standard is listed in the EU Official Journal, i.e. when the harmonized standard is available, you can benefit from presumption of conformity whenever it is applied. To put it another way: anyone who applies the relevant machine standards will have a safe machine, which may carry a CE mark provided all the other requirements have been considered.
There are more costly and slower alternatives to using standards to comply with the Machinery Directive, but they are generally cost prohibitive.

Why Ethernet in automation technology?

Automation technology is currently developing away from a centralized control system with simple binary sensors and actuators into complex, intelligent systems. The proportion of control and process capacity within the sensors and actuators is constantly growing. This trend changes the communication requirements dramatically: Instead of the usual master/slave system that we see today, in future, more and more data will be exchanged
directly between the network subscribers. Today's individual, largely passive bus subscribers will increasingly assume the function of bus masters, with their own computing capacity.

Modern IT technology – as seen in office communication with personal computers and office network technology such as switches, routers etc. – currently offers a wide range of system components at favorable prices. There is huge potential for innovation. That's why users are increasingly keen to modify this technology to make it usable for industrial automation technology. Ethernet, which is practically standard in today's office communication, has a prominent role to play. When developing modern fieldbus systems, the aim in future must be to exploit the benefits of Ethernet to a greater extent. The installation of Ethernet systems must become simpler; compared with current fieldbus systems, Ethernet in its current form is still too complex.

The requirements of the individual elements of a production plant also continue to grow. This affects scan times, precision/frequency of measurements, data amounts and processor power, to name but a few. As far as the automation system is concerned, the performance of the process computer and communication systems must satisfy these growing requirements. As a modern, Ethernet-based fieldbus system, SafetyNET p meets these new requirements. At the same time, SafetyNET p is as simple to install and as reliable as today’s available fieldbus systems.

SafetyNET p system description
Safety-related communication via Ethernet is explained below, using the real-time Ethernet communication system SafetyNET p as an example. SafetyNET p is a multi-master bus system, i. e. all devices on the network have equal rights. The bus scan time of SafetyNET can be adapted to suit the application requirements.

Security
The protocol includes a safe data channel, which is certified for data transfer in accordance with SIL 3 of IEC 61508. Both safety-related and nonsafety-related data is transferred via the same bus cable. Non-safety-related subscribers have direct access to safety-related data and can use it for further non-safety-related processing tasks.

Flexible topology and scan time selection
SafetyNET p is extremely flexible, not just when it comes to selecting a suitable bus scan time, but also on the issue of the appropriate topology: The multi-master bus system supports linear, star, tree and ring topologies. The RTFL communication principle (Real Time Frame Line) is suitable for intra-cell communication, as it allows the fastest scan times. A minimum bus scan time of 62.5 μs can be achieved. Jobs and events can be recorded and executed with high precision across the entire network. Absolutely essential for real-time applications: a jitter of around 100 ns must be achievable in real-time control loops. As a result, it’s even
possible to use SafetyNET p in a frequency converter control loop between a rotary encoder and a speed regulator. Other highly dynamic applications are also possible, of course. RTFN mode (Real Time Frame Network) is used at higher levels, as it offers maximum coexistence capability with existing services.

Application layer
The interface with the application is made via widely-used CANopen technology. Existing CANopen devices can be converted to SafetyNET p devices simply by changing the transport layer.

Standard Ethernet technology
SafetyNET p uses Ethernet technology. The interface depends on the required performance level: If fastest possible communication is required, the RTFL communication principle is used, which is based on Ethernet OSI Layer 2 (MAC Frames). For communication via mixed Ethernet-based networks, from cell to cell or in general networks, UDP/IP communication is used. Conventional, standard Ethernet infrastructures can be used if the performance is satisfactory. This includes connectors, cables, routers, switches, gateways or communication channels.

Industries, applications for SafetyBUS p®

Industries, applications
Today, safe bus systems such as SafetyBUS p are used worldwide in a wide range of industries and applications. The list below represents only a selection.

Automotive industry
The automotive industry uses SafetyBUS p tosafeguard and control presses. Applications range from small standalone presses to multi-stage transfer presses, demanding the very highest safety and performance  requirements of a safety bus. Even on the conveyor technology, where the safety and reaction time requirements are not so high, safety-related fi eldbuses are used to collect widely distributed, safe I/O signals such as  E-STOPs. Robot cells are frequently found in the automotive industry and normally require safety gates, light curtains and E-STOP pushbuttons as safety equipment. With SafetyBUS p, multiple robot cells can be networked together and monitored via a safety control system.

SafetyBUS p in a robot application

Airports
Airports contain baggage handling and conveying technology applications in which long distances have to be covered. Safety-related equipment such as E-STOP push buttons and grab wires are distributed across the whole route. SafetyBUS p collects the safety-related signals and makes them available to the safety control system, which shuts down the drives safely if necessary.

Passenger transportation
SafetyBUS p is also used for communication on cable cars: Safety-related signals are exchanged between the mountain and valley stations and signals are collected en route. Wireless or fiber-optic communication is used to cover the long distances.