Tech Briefs Magazine - August 2023 - MD-7

the cobot to indicate when a new blank
was required or when a finished part was
ready for removal. The cobot would
need to communicate via a common bus
network and share the same communication
protocol (e.g., EtherCAT, Sercos,
Profinet, or similar).
Ease of Use
Since cobots, as designed, work in
conjunction with humans in the manufacturing
environment, they must be
easy to operate by workers of various skill
levels. The software solutions designed
for cobots have advanced considerably
over the past decade.
An interface for a cobot (Figure 2)
should be designed to accommodate
the human operators with graphical
user interfaces that are intuitive and
easy to learn.
The purpose of a cobot is to assist an
operator, such as a welder, operate a
welding machine. The experienced
welder will need to operate the cobot
without an in-depth understanding of
each of its elements. Selection of a cobot
that can be pre-programmed with the
knowledge of the welding profession will
provide an easier transition into the
work cell.
Safety Features
Safety is paramount in the selection of
any cobot. Since cobots collaborate with
humans in a shared space, they must be
equipped with many inherent safety
functions. A thorough risk assessment is
essential to determine if a specific cobot
design meets the intended safety needs.
Typical safety functions include limits
that prevent excessive force, torque, or
speed based on sensors integrated into
the design. Safe Motion configurations
are determined by the outcome of a
safety risk assessment that defines the
stop modes associated with specific
safety events.
Many cobot controllers allow the creation
of specific safe zones where
pre-determined actions are activated,
such as reduced speed, lower torque
limits, or other collision avoidance routines.
Since cobot applications include
humans in close proximity, system designers
must run a thorough safety analysis
and the appropriate Safe Motion
and Safe Machine SIL recommendations
must be incorporated.
ISO/TS
15066 provides guidelines for design
Motion Design, August 2023
Saftey-rated
monitored stop
Robot stops when
human enters
collaborative space
Hand
guiding
Robot motion is
controllered by human
hand
Speed and
separation
monitoring
Robot maintains
specifed distance and
speed
Power and
force limiting
Inherent design and
controls limit impact at
contact events
Figure 3: Basic safety measures for collaborative robots to meet TUV SUD certification. (Image: TUV SUD)
and implementation of a collaborative
workspace (Figure 3).
Mobile Cobot in a Palletizing
Application
In a palletizing example, the components
to consider depend on what palletizing
actions are required. Consider the
functions the cobot will perform, including
how the product will be loaded or
unloaded, where the cobot will be positioned,
and what sensor techniques will
be used for motion and product locating.
In this example, the maximum payload
is as high as 55 lbs and the desired
reach is 1.7 m. The package pick-up device
will be a lightweight vacuum gripper
weighing approximately 6.5 lbs. The
cobot will use a touchable PC under a
windows operating system.
The software must include specific
palletizing application programs with a
simplified GUI. The vertical lift system
should incorporate a servo actuator and
wheels will be added to provide a mobility
element to the cobot. A radar sensor
with 3 axes of freedom (up, down, left,
and right) will be used for range detection
for enhanced safety. This application
specific collection of requirements
begins to cover the functionality, sizing,
and ease of use considerations. The compatibility
element will tie into the PC operations
and how it is networked into the
factory operations.
The most important consideration is
safety. The safety risk assessment in this
example might consider the stop event
and safety conditions below.
* SIL3, PL e CAT4, including safe torque
off (STO), Safe brake control (SBC),
and Emergency Stop.
* SIL2, PL d CAT3, including Tool Center
Point (TCP)/Robot Position Limit, TCP
Orientation limit, TCP Speed Limit,
TCP Force Limit, Robot Momentum
Limit, Robot Power Limit, Collision
Detection, Safety I/vO, and Reflex Stop.
All these safety events are tested in accordance
with the appropriate IEC or ISO
standards, with the results certified by a
Machine Safety Specialist. A document
that certifies the cobot has met all applicable
safety standards is required prior to
introducing the cobot into production.
Cobots continue to play a critical role
in supplementing the human workforce.
Their use in applications enhances production
and makes the work environment
safer for humans. When designing
a cobot into an application, following
these key considerations will lead to a
successful implementation and a strong
return on investment.
This article was written by Stephanie
Callaway, Marketing Development
Manager, Doosan Robotics Americas
(Plano, TX). For more information, visit
www.doosanrobotics.com.
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http://www.doosanrobotics.com

Tech Briefs Magazine - August 2023

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