robotics, automation & assembly
Robot suppliers emphasise the ease of use of
modern programming, teaching and simulation
tools. But machine builders and system integrators
installing a robot for the first time need to be aware
of differences between the safeguarding of
conventional automation and robotic applications.
Safeguarding industrial robots
WHILE it is not compulsory to adhere to the
guidance provided in HSG43 - ‘Industrial Robot
Safety’, the Health and Safety Executives that
doing so will normally be enough to comply with
the law. HSG43 covers safety during installation,
commissioning, testing and programming, as
well as during use and maintenance. Other topics
include the principles of safeguarding robot
systems and safety at the design stage, through to
hazard identification, risk assessment, training
and interfacing with the controller. There is also a
useful appendix with case studies and another
that outlines the relevant health and safety laws.
The guide’s Reference lists relevant standards -
but HSG43 (second edition) was published in
2000, so it does not include all the latest standards
- such as EN ISO 13849-1 (Safety of machinery -
Safety-related parts of control systems - Part 1:
General principles for design), which supersedes
EN 954-1, or EN ISO 10218-1:2006 (Robots for
industrial environments - Safety requirements -
Part 1: Robot), which was recently harmonised to
the Machinery Directive to replace EN 775
(Manipulating industrial robots - Safety). A draft
for public comment of ISO 10218-2 (Robots for
industrial environments - Safety requirements -
Part 2: Robot system and integration) is expected
by mid-2008, and this is could pave the way for
substantial changes in the ways industrial robots
are used and safeguarded.
Hazardous situations can arise in unpredictable
ways when dealing with robots, so selecting
appropriate safeguards is more difficult than for
conventional automation - in which the
operating envelope, motions and other
performance parameters are more clearly defined.
Also, robots used for lifting, such as those in
handling or palletising applications, must meet
the requirements of LOLER (Lifting Operations
and Lifting Equipment Regulations) as well as
PUWER (Provision and Use of Work Equipment
Regulations). Following HSG43 minimises the
measures needed to comply with LOLER.
Industrial robots range from lightweight
benchtop units to large machines powerful
enough to manipulate objects weighing 1000kg.
The risks depend on the particular robot and its
application, so the starting point is risk
assessment. Potential for serious injury may be
high, so it’s best to design-out the hazards when
planning and designing the application. HSG43
recommends that hazard identification and risk
assessment is done jointly by user and supplier.
Robot programs are often prepared off-line,
but teaching - typically using a pendant
controller - still has a role to play in some
programming and position correction tasks. With
good visibility through the guarding, or using
CCTV, most teaching is achievable from outside
the enclosure. However, it may be necessary to
teach the robot or observe its movements from
close quarters, entering the robot enclosure while
the robot is powered. Step-by-step guidance in
HSG43 covers this, as well as for the program
verification procedure needed after teaching.
HSG43 overviews various safeguarding
methods while reminding readers that other
safeguards (eg the Pilz SafetyEYE 3D vision-based
safety monitoring system) can be used if they can
be demonstrated to provide a similar level of
safety. Methods covered include: perimeter
fencing; interlocking devices; electro-sensitive
safety systems; safety light curtains and light
beam devices; laser scanners; capacitance safety
devices; pressure-sensitive mats; two-hand
controls; trip devices; positive stops; brakes;
emergency stop actuators; and enabling devices.
Allied to safeguarding are controls for changing
operating mode from normal operation to
teach/setting, reduced-speed controls for
teaching/setting/troubleshooting, and the
indication of the robot’s swept area.
Control for robot systems is complex, especially
where multiple robots are synchronised to
operate together. Halting robots by cutting the
power supply to the servo drives is undesirable, as
recovery from the powered-down state can be
time-consuming and require human
intervention - and there can be costs associated
with damage to WIP. It is preferable to bring the
robot and other machinery to rest in a controlled
manner. Power to the servo drives may then be
52 MWP march 2008
removed, or power can remain connected (‘servo
hold’), provided the robot controller has adequate
built-in safety monitoring functionality or there
is a separate safety-related controller to monitor
the robot while it is stopped.
HSG43 outlines architectures for integrating a
robot controller with a safety-related control
system - which should include a programmable
electrical/electronic controller, so builders and
system integrators should avoid using BS EN 954-
1 - either EN 62061 (Safety of machinery,
Functional safety of safety-related electrical,
electronic and programmable electronic control
systems) or EN ISO 13849-1 would be more
appropriate. If there is any reliance on software -
or a programmable controller - for robot
safeguarding, it is advisable to work closely with
the supplier.
In all areas of machinery safety, including robot
applications, the following hierarchical approach
should be used:
■ Design out the hazards wherever possible
■ Provide safeguards for the hazards that cannot
be designed out
■ Use safe systems of work, training, personal
protective equipment (PPE) and warnings so that
residual hazards are as low as reasonably
practicable
With robotic installations, there is often a need
to rely on safe systems of work during
commissioning, programming, teaching,
troubleshooting and maintenance, and this is
covered in HSG43, together with formal permitto-work
systems.
Safeguarding of robots - and ISO 10218-2 in
particular - will be discussed at the two
Functional Safety Seminars being organised for
2008 by the Safety SIG (Special Interest Group)
within British Automation and Robot
Association. Copies of HSG43 ‘Industrial Robot
Safety, Your Guide to the Safeguarding of
Industrial Robots’ (ISBN 0717613100), priced at
£13.50, can be obtained directly from HSE Books.
www.hsebooks.co.uk
www.bara.org.uk
www.pilz.co.uk
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