Kevin Steele
Bosch Rexroth Corp
Pleasanton, Calif.
Consider manufacturing or assembly processes set up inside
a clean room or vacuum environment. The transport systems
used in these settings face far
more critical demands then those
used to assemble toasters. To
meet those demands, the Electric
Drives and Controls group from
Bosch Rexroth Corp. worked
with Tecnotion to produce a special transportation system.
The system has proven itself
for the OTB Group (www.otb.nl),
a maker of solar cells in the Netherlands. Solar-cell fabrication
requires a high-vacuum environment in which precision parts
move continuously. The transport
system must maintain great accuracy while the delicate assembly
and manufacturing operations
take place in vacuum.
The Linear Motion System
(LMS) fosters accuracy by using
intelligent coils placed outside
the vacuum environment. Only
the moving parts that convey the products sit in vacuum. The
transportation system is modular, expandable, and easily adapts
to transported items. There are
no mechanical or electrical feedthroughs from the external control system to penetrate the vacuum environment.
The basic concept is that of a
linear motor. A standard linear motor has fixed magnets attached to
a frame while a coil travels along
the magnets. The same principle
can work the other way around:
Fix the coils in position and let
the magnet move from coil to
coil. With the magnet attached to
a carrier, the carrier follows the
magnet motion. The carrier can
move over long distances when
the spacing between multiple
coils is less than the length of the
carrier magnet.
Possible applications that
could make use of this design
include manufacturing lines
for displays, optical equipment, and solar cells as well as
any process done in a vacuum,
clean-room, aseptic, or gas-sensitive environment.
While the basic technical concept is brilliantly simple, implementation involved complex
technical issues. One problem
concerned measuring the true
position of each carrier without
physical contact. Likewise, the
transition from coil to coil must
take place as smoothly as possible. Each carrier had to have individual speed control with the ability to stop at specific points for the next process
step. With differing
speeds comes the
possibility of collision. A precollision
detector prevents
one carrier from
bumping another,
especially critical
when operations
take place at the
nanometer level on
the stopped carrier. Finally, multiple carriers should
move like a "train"
to transport larger
products.
Different applications dictate
different types of linear
motors, so the carrier
system can use either
standard iron core or
ironless linear motors.
This versatility lets engineers at Tecnotion
and Bosch Rexroth
adapt the carrier system to specific needs.
Carrier temperature
can reach 110°C while
working in a vacuum of
10-7 mbar and IP62 environments. Speeds can
hit 5 m/sec and forces
10,000 N, depending on
motor configuration
and system design.
Analog Hall-effect
sensors built into the
linear-motor core monitor the position of the magnet plate within an accuracy
of 200 μm. Resolution is typically
10 to 20 μm with repeatability
within 40 μm.
The carrier uses NYCe4000 integrated motion controllers from
Bosch Rexroth connected via a
network to a PC or PLC to run the
user interface part of the control
software. Each controller handles up to 10 coils with the coil drive
electronics integrated in the
NYCe4000.
MAKE CONTACT
Bosch Rexroth Corp.,www.boschrexroth-us.com
Tecnotion B.V., www.tecnotion.com