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12:35 Uhr
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General information
Special operating modes for
set-up mode and process observation
w w w. s c h m e r s a l . c o m
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Autor:
Frank Schmidt,
Key Account Automotive der
K.A.Schmersal GmbH, 42279 Wuppertal
How can the job of the machine setter or
operator be facilitated, whilst it is still
guaranteed that he works safely during the
set-up or after a size change on the one
hand and that he has the best visibility on
the process so that he can intervene in
case of an emergency on the other hand?
The new Machinery Directive provides –
under strictly defined conditions – the possibility to use special operating modes; an
opportunity, which the machinery builder
should take advantage of.
CNC machining centres”; German version)
provides an additional operating mode, the
“extended manual intervention”, which is also
known as operating mode 3. Its application is
covered by a clause in Appendix I to the new
Machinery Directive (2006/42/CE; 1.2.5: “Selecting the control and operating modes“):
when the conditions set forth for the available
operating modes are not operationally feasible, a safe workplace still can be guaranteed
A machine generally is equipped with two
operating modes, which are defined in the
harmonised C-standards, e.g. DIN EN 12417.
During the production process, i.e. when it is
used for its actual purpose, the machine runs
in automatic mode with the safety guards closed. For set-up and adjustment activities
after a tool replacement or a size change, the
machine runs in set-up mode with the safety
guards open, at considerably reduced speed
and with additional safety measures. In this
situation, the operator can intervene in the
process to prepare the machine for automatic
mode (image 1). The larger part of machines
requiring set-up offers this possibility.
Two operating modes available, more required
Actual practice however has revealed that
this selection was insufficient for many machine types as well as for particular set-up
and parameter setting tasks, especially on
CNC machining centres. The manufacturers
and especially the users of these machines
requested extended possibilities. After reflection, the standardization bodies took adequate measures: a supplement (amendment
1:2006) to DIN EN 12417 (“Machine tools –
Bild 1: machine operation with open safety guard:
new operating modes offers larges degrees
of freedom for set-up mode and process
observation.
Safety in system. Protection for man and machine.
1/3
K. A. Schmersal GmbH
Industrielle Sicherheitsschaltsysteme
Postfach 24 02 63, 42232 Wuppertal
Möddinghofe 30, 42279 Wuppertal
Telefon: +49-(0) 2 02-64 74-0
Telefax: +49-(0) 2 02-64 74-1 00
E-Mail: info@schmersal.com
Internet: http://www.schmersal.com
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is interrupted, which could lead to problems
or even failures of the tool.
Bild 2: with the RFID key selector switch, individual
selection rights can be assigned for specific
operating modes.
using other safety measures, which are triggered through the control or operating mode
selector switch.
Operating mode 3: extended manual intervention
Provided that he has been adequately trained
and instructed, the user can run the machine
with the safety guards open in operating
mode 3. In this situation, he can activate a limited number of machine functions by keeping an enabling switch, installed on the
hand-held controller, pushed down (image 2).
Although the speed of the hazardous movements is reduced, it is still higher than in operating mode 2 and automatic feeds, e.g. for
the work piece change or the tool replacement are not operational.
In this way, the operator can process individual work pieces with the machine, whilst he
observes the process and sets up the machine functions for instance without his visual
range being restricted by the separating safety guard. As he needs to keep the enabling
switch pushed down with one hand and operates the control unit of the machine with his
other, he is unable to reach within the hazardous area. The prescribed training and instruction also increase his awareness of the
risks.
Not all wishes fulfilled
Operating mode 3 already constituted an essential facilitation of the operator’s work without the safety level being jeopardized. But
the machinery builders and users had other
needs as well, which were not covered by
operating mode 3. More precisely: when the
machine was used, it revealed that there still
were problems for specific applications, for
instance when the operator of a large CNC
machining centre must actuate a concealed
reference point or set up the machine for undercuts or counter drafts on the work piece.
In these situations, the process to be observed can continue for a longer period of time.
The operator however continuously must
keep the enabling switch pushed down and
taking the realistic timeframes for the set-up
activities into account, his hand could slip off
the enabling switch or becomes cramped due
to the permanent pressing. The process then
Complex processes cannot always be represented
Carrying out the parameter setting at reduced
speed furthermore is not always recommended, especially on high-quality machining
operations and for high-speed processing.
These processes often require particular
speeds. Last but not least, the operator
needs to use his both hands for preparing the
highly complex machining operations. For instance, when he is setting the angle of attack
and the path feed rate of the tool at the same
time, his both hands are occupied and he can
no longer keep the enabling switch pressed.
Operating mode 4: process observation
Starting from these reflections and objections
formulated by the manufacturers and users,
the legislative bodies have agreed to accept
an additional operating mode, provided that
adequate safety measures are implemented.
This fourth operating mode is defined as
“process observation” and enables running
the machine with open safety guards, without
the need to keep the enabling switch pressed.
Operating mode 4 however is not discussed
in the standards yet. A document from the
technical committee “Machine Building, Production Systems and Steel Construction” of
the professional metal works association
North-South however defines the framework
conditions for the application of the new operating mode.
Differences between operating mode 3 and 4
A significant difference between the two operating modes for instance is that in operating
mode 3 (compared to operating mode 2) extended however absolute upper limits are
prescribed for the rotation speeds and the
feed rates, whereas the maximum limits for
operating mode 4 are determined by the process needs and therefore can be higher as
well. This is the so-called process-required
speed.
Only for trained staff
The safety measures include, in addition to
the disabling of automatic functions such as
the automatic tool replacement and the safely
monitored reduced speeds, the necessity to
allow only especially trained staff to work
with this operating mode. This requirement
must be met by the availability of a separate
feature to select this operating mode, e.g. a
second key selector switch. This operating
mode furthermore may only be selected in
case of compelling technological requirements, when the task concerned cannot be
satisfactory be realised with the operating
modes 1 to 3. The linguistic proscription stipulates that in this case, the “unavoidability”
of this operating mode must be proven.
Safety in system. Protection for man and machine.
2/3
K. A. Schmersal GmbH
Industrielle Sicherheitsschaltsysteme
Postfach 24 02 63, 42232 Wuppertal
Möddinghofe 30, 42279 Wuppertal
Telefon: +49-(0) 2 02-64 74-0
Telefax: +49-(0) 2 02-64 74-1 00
E-Mail: info@schmersal.com
Internet: http://www.schmersal.com
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Seite 3
The user is responsible
Operating mode 4 therefore reminds the machine user of his duties – which is entirely in
accordance with the Machinery Directive. The
additional operating mode enables the trained
and instructed operator setting up the tools in
the immediate range of vision of the process,
for instance by means of a hand-held controller, or observing whether the process parameters are correct.
Electronic key for individual operating
modes
For the practical implementation of these regulations, the Schmersal Group has developed a new key selector switch, which is
equipped with an additional RFID transponder
(image 3). With this transponder, the machine
can be switched from automatic mode to a
special operating mode.
The authorisation for the switchover can be
individually defined through the RFID coding.
For instance, one operator can use a key
enabling the switchover to set-up mode (operating mode 3), whereas another operator,
who is adequately trained and instructed, can
also run the machine in operating mode 4
with his key. Other authorisation levels can
also be assigned through the key selector
switch. This “electronic key” therefore is a
simple yet safe system for a differentiated assignment of access rights.
Larger degree of freedom with Wireless
technology
The safety-related radio link - which the
Schmersal Group, who was the first provider
of this technology, has developed for seriesproduction (image 4) - offers considerable advantages especially for the special operating
modes. The operator can observe the process
immediately on site, without being restricted
by the cable. This feature is a distinctive advantage, especially on large machines such
as interlinked plants in sheet-metal working
or in the printing and the paper and pulp industry.
New degrees of freedom for machine builders and operators
Both new operating modes show that the directives and standards regarding machine safety generally fulfil the desires of the user
with regard to productivity and practical suitability. The machine builder should purposefully use these possibilities to facilitate the
handling of the machine by the operator –
also because he has safety switchgear at his
disposal, enabling the integration of the operating modes in the safety and operating concept.
The operating modes 3 and 4 however can be only
selected, when specific conditions are fulfilled and
provided that many additional safety-related measures, including the instruction and training of the
staff, have been implemented. For operating mode
4, the necessity of use also must be proven – this
is understandable, considering that the misuse of
this operating mode can only be avoided when the
operators are aware of their responsibility. An even
more important issue is a clearly arranged assignment of the authorization rights as enabled by the
“electronic key” with RFID technology.
Bild 3: ergonomic alternative to wired systems: the
mobile ESALAN Wireless control terminals
High-level safety and productivity
Machinery builders willing to implement these
operating modes in their machines are especially recommended to thoroughly study the
harmonised standards and, if necessary, to
consult engineering companies, which have
specialised in issues regarding machinery safety. The costs related to that are worth-wile,
considering that safety concepts using the
new operating modes will result in safer and
simultaneously more productive machines,
which can be set up and parameterized more
easily; this in turn is a considerable competitive advantage to the manufacturer.
Photos:
K.A. Schmersal GmbH, Wuppertal
Autor:
Autor: Frank Schmidt, Key Account Automotive
der K.A.Schmersal GmbH, 42279 Wuppertal
Note:
This article was first published in the specialised magazine “S&I-Kompendium, Heft
01/08”. With the kind authorisation of the
editorial staff and the authors.
Safety in system. Protection for man and machine.
3/3
K. A. Schmersal GmbH
Industrielle Sicherheitsschaltsysteme
Postfach 24 02 63, 42232 Wuppertal
Möddinghofe 30, 42279 Wuppertal
Telefon: +49-(0) 2 02-64 74-0
Telefax: +49-(0) 2 02-64 74-1 00
E-Mail: info@schmersal.com
Internet: http://www.schmersal.com