The document discusses replacing a ballscrew-driven XY stage used to place semiconductors with a ServoBelt system. The stage required long travel moves at 400 mm/sec and short, high-speed moves of 13 mm that must settle within 150 milliseconds. The ballscrew technology could not achieve these moves or the desired throughput. ServoBelt was chosen as it could meet the dynamic requirements with zero backlash, inherent damping allowing for high gains and settling times, and at a lower cost than linear motors which would have required a long coil. The ServoBelt solution exceeded all dynamic and cost targets for the application.

1. Semiconductor
Packaging
Replace a ballscrew-driven stacked XY stage
that places tested and diced semiconductors
in output trays.
Technical Requirements:
The stage required a linear drive system versatile enough to
make two very different types of moves. One is a long travel
move at 400 mm/sec. The other is a short, high-speed move of
13 mm that must settle to 10 microns in 150 milliseconds.
The customer’s incumbent ballscrew technology could not
make either of the desired moves, making the goal throughput
impossible. Linear motors and higher-performance ballscrew
drives, while capable of meeting the motion requirements,
would have exceeded the customer’s cost targets by [40-50%].
The short index moves and accuracies were not
achievable by the incumbent ball-screw stage
without the addition of a linear encoder, and a
higher pitch screw would be required to achieve
the higher speed without screw whip.
The moving mass seen by the lowest axis in the system was
38Kg with a bi-directional accuracy goal of ± 5 microns based
on the positioning reference from a 1-micron Renishaw optical
linear encoder. Ultimately, the only way to achieve the fast
index moves was to close the servo loops using the linear
encoder, which requires a true backlash-free drive line from
motor to payload.
Low-cost drives, whether ballscrew or rack-and-
pinion, have too much backlash to deliver the
stable, high-gain control loop required by this
application.
The ServoBelt Solution
After an extensive engineering evaluation [that included linear
motors], the customer successfully applied our ServoBelt in a
new XY stage design exceeds all dynamic and cost requirements.
ServoBelt, controlled in a single-loop mode that takes feedback
just from the linear encoder, won the job over more expensive
linear motor solutions by providing:
• A zero backlash solution. ServoBelt has no backlash, which
proved essential when tuning a control system that would
meet the customer’s dynamic requirements.
• Inherent damping ServoBelt inherently offers excellent
mechanical damping, which allows for very high tuning
gains, typically 4 times the velocity and positional gains,
which translates into extremely low settling times. Linear
motors, by contrast, must simulate this damping servo-
amplifier electronics, which inherently reduces the
possible positional gain.
A linear motor could have succeeded at this
job. But achieving the power density needed to
produce the required 300N of continuous force
would have resulted in an unacceptably long
motor coil and high costs. ServoBelt offered
both a cost and size advantage.
Conclusion
In high-performance applications such as semiconductor,
position ServoBelt as a “linear motor killer.” ServoBelt offers
zero backlash, excellent mechanical damping and a high
power density at a lower cost and smaller form factor than an
equivalent linear motor.
82 Aero Camino, Goleta, CA (805) 685-1029 www.bell-everman.com
ServoBelt
Application Note 1
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