Servodrives with integrated safety functions - User-friendly safety in mechanical engineering
Virtually all machine movements in an industrial environment present a hazard to the operating and maintenance staff. Typical situations requiring safe machine states are startup, setup, troubleshooting or any situation where persons are in direct proximity of the production process. Servodrives using amplifiers with the appropriate approvals and certifications help the mechanical engineer to comply with the applicable safety requirements. Safety functions integrated in the drive technology ensure optimal protection for employees in critical situations and reduce the workload of the controller – as this example shows.
ESAB GmbH, which is based in Solingen and has approximately 30 production sites across the globe, manufactures welding equipment and consumables as well as cutting systems for virtually all welding and cutting processes. Thanks to its wide product range, the company is well represented throughout the entire steel-manufacturing and steelprocessing industry. The head office of the cutting machinery division is located in Karben near Frankfurt am Main. The portal machines with movable bridges are available for laser, oxy and plasma cutting. Depending on the design, they are suitable for a wide range of sheet metals, in particular structural steel, stainless steel and aluminium. The blow-torch machines are adapted precisely to the relevant requirements: As a rule, ESAB uses sample material provided by the user to determine all cutting parameters – that is, the best cutting process as well as the processing speed, nozzle type, process gases etc.
Servodrives with integrated safety functions
|Safety requirement level||IEC 61508<br />IEC 62061||SIL 2<br />SILCL2|
|Performance level||EN ISO 13849-1||PL-d|
|Stop functions||IEC 60204-1||Stop category 0/1/2|
|Functional safety||IEC 61800-5-2||STO/SS1/SS2/SLS|
An important topic: employee and property protection
When manufacturing its machines, the company has always focused on the protection of employees and property and considers itself a pioneer of integrated safety technology in the industry. The servodrives used in the blow-torch machines are just one example of these efforts. In this context, ESAB has already enjoyed ten years of successful cooperation with the drive experts from YASKAWA, and both sides intend to maintain this relationship for years to come. Not only have the drive solutions always offered highest levels of reliability and durability but, with its integrated safety functions, the latest generation of drives offers maximum safety without restricting user friendliness. The altered conditions brought about by the new Machinery Directive have also changed the safety requirements, but this advancement in protection is not to make things any more difficult for the operator. At the same time, the controller is relieved of all drive-specific safety tasks, because YASKAWA Sigma-5 drives possess all of the properties required by the applicable safety standards and were certified accordingly by TÜV Süd.
Since the introduction of the standard EN ISO 13489 - 1:2008 “Safety of machinery – Safety-related parts of control systems”, the control components used to build safe machines are either evaluated according to their Performance Level (PL a–e) or their Safety Integrity Level (SIL 1–4). IEC 61800-5-2 defines the safety functions for adjustable speed drives.
Safe workflows during practical operation
ESAB uses two of these advanced safety functions for their blow-torch machines: SLS (Safely Limited Speed) and SS1 (Safe Stop 1). STO (Safe Torque Off, i.e. safe disconnection from the mains) is already standard in all Sigma-5 series servo amplifiers. The safety functions SS1 and SLS can be integrated by means of an option board. The same applies to SS2 (Safe Stop 2, safe stop with position monitoring), which is essential for stamping and die-cutting machines, for example. In the worst-case scenario, the tool must not only be stopped safely, it must also be held in position safely to rule out injury to persons or damage to property.
The following example shows how blow-torch machines benefit specifically from integrated safety technology: If a safety door is opened for configuration or machine maintenance, the motion controller integrated into the servo amplifier restricts the speed of the motion to a safe speed. The Sigma-5 safety module monitors compliance with the preset speed (SLS = Safely Limited Speed). If the safely limited speed is exceeded, the drive is switched off directly, e.g. via STO (Safe Torque Off). The reaction is similar if the machine is shut down due to a light barrier signal or because an emergency stop switch is activated, for example. The safety function SS1 monitors the controlled shutdown. The STO function safely disconnects the drives from the power supply so that the maintenance or configuration staff can work on the machine without danger. All of these safety-relevant functions are performed by the Sigma-5 servo controller; the machine’s upper control is not affected.
Overall, depending on the size of the respective blow-torch machine, at least three servodrives are used – two to drive the moving bridge on the x-axis and another to move the cutting tool on the y-axis. The motors used must each provide 400 W of power in the application described for small blow-torch machines. However, in order to cope with higher mass moments of inertia, they are designed for a maximum power of 800 W. In principle, other power ranges are also no problem for the Sigma-5 servodrives. The complete series covers motor capacities from 50 W to 15 kW, which means that the outputs required even for large blow-torch machines can be easily achieved. All conventional bus systems can be used to connect the units to higher-level control networks quickly and simply. The drive technology can therefore be incorporated into the user’s automation environment seamlessly. This opens up interesting possibilities for mechanical engineering.
ESAB GmbH, Karben, Germany
Steel/Metal processing industries
Cutting and welding machines
Sigma-5 Servo Drives
Integrated Safety Functions