Fully automated assembly
lines and integrated robotics are an essential part of modern automobile
production. To ensure a high level of productivity, assembly, painting and
welding tasks are all handled by anthropomorphic robots which must meet the
highest demands for round-the-clock operation.
For automobile manufacturer Alfa Romeo, part of the Fiat group,
robotics is a key component in the successful introduction of new cars such as
the MiTo, its latest compact car. Working with COMAU
Robotics, Alfa Romeo is using industrial robots for production of the MiTo
that rely on dual core PCs, tightly integrated drives and high-speed Ethernet
POWERLINK communications to fully synchronize drives and I/O every 400 µsec.
"One of the highlights of the application is that we actually
developed a PC that plugs directly into our drive rack," says Robert
Muehlfellner, automation director for B&R
Industrial Automation. "The architecture allows for control of all the
drives in a single drive rack instead of separate motion and/or robot
This hardware approach
simplifies the system architecture by using one power supply and a common
backplane where the user can plug in all the individual drive modules as well
as the PC that controls the entire robot right in the rack. All of the
additional components required are only just a handful of separate I/O nodes.
Driven by Processors
In the past, COMAU relied on customer-specific automation
solutions. But with the quest for continuous improvement and fast development
times, specific solutions quickly appeared outdated, because any adjustments or
improvements reflected negatively in the total costs.
Because the most important aspect of a robot is its drive
technology, COMAU decided in favor of standard components with interpolation of
the axes processed centrally on a dual core processor PC. One advantage of the
dual core architecture is its ability to intelligently share tasks, and
dedicate one core to the run time system and the other core to support Windows.
"One core can be dedicated to visualization and the other to
perform processing such as trajectory calculations for the robotics motion
and/or other control systems functions," says Muehlfellner. The real-time
operating system for the control system is VX Works-based, with Windows serving
an active front end and running in the idle time of the RTOS which has full
control over all the system resources and is given absolute priority. By
dedicating one core for use by Windows which runs in parallel with the
real-time operating system, if Windows has a performance issue, the real-time
system continues running.
The industrial PC and Core 2 Duo processor offers sufficient
computing power for path calculations that are communicated to the ACOPOSmulti
modular drive system. Set values are sent cyclically using Ethernet POWERLINK
to the servo drives every 400µs and provides enough bandwidth to tunnel two
complete robots with additional axes, I/O data, diagnostics data, safety
information, as well as fieldbus systems. POWERLINK also enables COMAU to
integrate combinations of Profibus, DeviceNet or CANopen master/slaves as
needed - an important capability so the robots can be connected to an existing
infrastructure in the production plants.
The complete control solution made it possible for COMAU to
reduce its already optimized switching cabinet by an additional 30 percent, in
part by controlling the robot's six axes with just three dual-axis drive
modules. A feed-through model, one of three ACOPOSmulti cooling models, also
makes it possible for the heat sink to be placed outside of the switching
cabinet. This reportedly saves even more space and prevents additional heat in
the switching cabinet.
Another feature developed specifically for this
application was a redundant induction braking capability within the ACOPOSmulti
drive to provide additional safety. When power is switched off, the robot arm
is suspended by motor brakes. Otherwise, gravity would pull the arm toward the ground without any braking
which could cause mechanical damages to both the robot and the surrounding
To prevent that from happening,
B&R and COMAU developed a Safe Brake Control function which provides an
additional, redundantly designed motor brake control. If the motor brake fails, the ACOPOSmulti drive system
detects it and prevents the arm from dropping rapidly by absorbing the energy
in the drive system's power supply. The potential energy of the robot arm is
converted in a controlled manner to heat as it drops slowly toward the ground
and prevents damage.
"Even if the robot is powered off and a brake fails, the
potential energy stored in the robot would be used to reactivate the entire
drive control system and provide control braking," says Muehlfellner. "The
robot would sag toward the ground, but it would be a slow and somewhat
controlled motion versus crashing into the ground."