Machine builders in the European market know that their machines must meet the requirements of the machinery directive if they want to be CE marked and sold. This is not news to anyone. But are you aware that the requirements are written provided that new technical solutions are constantly developed over time?
The Machinery directive, 2006/42/EC, states:
(14) The essential health and safety requirements should be satisfied in order to ensure that machinery is safe; these requirements should be applied with discernment to take account of the state of the art at the time of construction and of technical and economic requirements.
State of the art is a moving target, and it will always be a challenge for machine manufacturers to keep up with the latest developments. Technical solutions evolve and open up new ways of making machines more safe in comparison to the past.
The early days of programmable electronics for machineryParker launched IQAN, programmable electronics to help make machinery more safe by enabling smarter safety interlocks in the mid-90s. Examples of its safety functions include load moment limitations on cranes and stopping of all movement when the driver leaves the cab. At that time, the key characteristics of best-in-class systems were robust hardware built for harsh environments and electromagnetic compatibility. These are now considered basic requirements. In the case of IQAN, software specific for developing application software made machines less prone to implementation errors, but there was no established method that machine manufacturers could use to objectively evaluate software. The standards for safety of machinery that existed at this time was very focused on different levels of redundancy, with little consideration of software aspects and analysis of electronics. Standardized solutions could be both cost-prohibitive and fail to address important control system aspects.
With the release of ISO 13849-1:2006 Safety of Machinery, designers received guidance on how to methodically develop a control system with safety functions by focusing on hardware reliability, diagnostics and software quality to reach a desired performance level (PL). The requirements in the standard adapted to the increasing experience of using programmable electronics and the growing availability of component reliability data. The ISO 13849-1 standard allows machine designers to choose the best solution for each part of a safety function. For example, sensors with redundant signals, off-the-shelf controllers certified to IEC 61508 and well-tried reliable hydraulic components.
When Parker introduced the IEC 61508 SIL2 certified controller IQAN-MC3 in 2010, they gave machine manufacturers an effective way to implement SIL2 / PLd safety functions. The IQAN-MC3 controller is designed around the concept that in-depth knowledge of the components is the key to efficient hardware diagnostics. The core diagnostics package includes a technique called challenge-response, a set of cyclic tests that give a good diagnostic coverage without adding too much extra hardware. This gives a realistic hardware cost, but the extensive self-diagnostics firmware does take its toll in calculation speed.
An example of an application where the technology has been deployed is the load moment control of a reach stacker, where stability of a machine is calculated to prevent a machine from overturning. Another example is wheel steering on lift trucks.
As manufacturers of mobile machinery gain experience from using standards for the most critical safety functions, the next step is to bring this structured approach to normal operating functions. In mobile, it has always been difficult to distinguish some of the normal operating functions from the safety functions. Load moment limitations and stopping of all movement when the driver leave the cab are examples of functions whose primary purpose is to achieve safety. Stopping the implement hydraulics when the operator lets go of the lever is part of normal machine operation, but it can also be a safety function. As mobile machinery controllers with safety certification become more affordable, it makes sense to step up the requirements on all motion controlling functions.
State-of-the-art technology joins safety and performance
The new series of IQAN-MC4xFS is a perfect example of how state of the art is changing.
IQAN-MC4xFS builds on the experience of the IQAN-MC3, reusing the proven IQAN software platform that is the foundation for all IQAN masters. It has also inherited the concept for power driver outputs with a combined high-side and low-side switching and detection of wiring faults for safety related loads. The core electronics has also evolved. A key component is the Infineon microcontroller designed for both automotive and machinery applications. This is designed from the start with hardware supported self-diagnostics. Compared to its predecessor the IQAN-MC3, this makes the IQAN-MC4xFS more run-time efficient; it can execute larger applications at a shorter cycle time.
With one of the larger modules IQAN-MC42FS or IQAN-MC43FS, the machine designer has a choice to use one certified controller of on all sections on a hydraulic directional control valve. This gives a cost-effective way to meet safety function Performance Level c without adding extra hydraulic components. For functions requiring the higher Performance Level d, IQAN-MC4xFS can be used to read spool position sensors and actuate pump unloading valves to have a second hydraulic shutdown path.
Conclusion
The MC4xFS gives the possibility to meet current and future requirements of functional safety without compromising the performance of the machine functionality. It makes it possible to create both safe and user-friendly functionality in a cost-efficient way. The technology development on electronics has taken us to a state of the art level that makes it possible to implement safety functions in and on virtually all motion control functions in a machine. It lets you focus on what matters most - machine functionality. Learn more.
Article contributed by Gustav Widén, systems engineer electronics, Parker Hannifin Manufacturing Sweden AB.
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