3 608 878 300
Tightening Technology |
Bosch Rexroth AG 103
System 350
| 3 608 878 300/2019-03
4.3.4
Performance level (PL) within the Rexroth Tightening System 350
The basis of this section is that every machine manufacturer is obliged to identify possible dangers this
machine might pose for the operator and to remove the risk related to the danger. In situations in which
the danger cannot be removed, every machine manufacturer is obliged to reduce this danger to the
largest possible extent. The danger can be reduced by:
•
Safety functions of the machine in the sense of intrinsically safe construction
•
Protective equipment
•
Instructions for the user
Since the Machinery Directive 2006/42/EC came into effect on December 29, 2009, machine
manufacturers are obliged to make a quantitative statement regarding the probability of a dangerous
failure of the safety functions and/or the safety equipment of their machine. For the
Rexroth Tightening
System 350
, these characteristics have been determined by an independent, accredited organization.
Risk assessment
In the risk evaluation of a machine, the later is first of all dismantled into its partial functionalities. For each
partial functionality, the risk emanating from this partial functionality for the user is then analyzed
separately. In order to be able to design a safety function or safety equipment for a specific dangerous
situation, you first of all have to determine the contribution to the risk reduction that has to be made by
the protective equipment.
This contribution can be determined by applying the standard
DIN EN ISO 13849-1:2008 Safety of
machinery – Safety-related parts of control systems"
.
The contribution to the risk reduction depends on
•
The severity of the injury to be expected,
•
The frequency with which the user is exposed to the danger,
•
And the possibility to recognize an imminent danger in due time.
It is indicated as discrete level specifying the ability of safety-related parts of a control system to perform
a safety function under foreseeable conditions, the so-called Performance Level (PL). Here, the
performance level is divided into 5 levels "a" to "e", whereas the following applies:
•
PL = a
is the lowest level of requirements for the reliability of the safety function and/or the protective
equipment of the machine.
•
PL = e
is the highest level of requirements on the reliability of the safety function and/or the protective
equipment of the machine.
Functional safety in the Rexroth Tightening System 350
Depending on the machine design, the tightening spindle must - with tightening system - stop safely under
certain conditions and must not restart unexpectedly. This cannot be ensured by a tightening controller
consisting of hardware and software. (by definition of the machinery directive, industrial control systems
are generally not classified as safe. Exceptions are special safety control systems referred to as safety
PLCs.)
In order to still be able to guarantee safe stop and safe protection against unexpected restart, the
Rexroth
Tightening System 350
features a default emergency OFF interface. This interface is a safety function
within the
Rexroth Tightening System350
for which the probability of a dangerous failure has been
determined according to DIN EN ISO 13849-1.
Summary of Contents for Rexroth Tightening System 350
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