In drive applications, linear servomotors are popular due to their excellent characteristics in terms of dynamics and synchronous
operation. They are particularly advantageous if the installation of rotary motors is not possible due to the mechanical specification. The
linear motors are not subject to mechanical wear and are easy to commission. These advantages are partly weakened by the higher costs for the
feedback systems. The new magnetic encoder system from Beckhoff complements the linear technology market with an inexpensive alternative. The
feedback system for the AL2000 series linear motors is scaleless and therefore independent of the length of the magnetic plates.
For the operation of linear motors, the feedback
system is installed parallel to the travel path. It
consists of a reader head, usually mounted on
the motor slide, and a scale mounted parallel to
the travel path. A distinction is made between
absolute and incremental systems; both are subdivided
into magnetic and optical systems, with
precision and sensitivity playing a crucial role.
Magnetic encoders do not quite reach the resolution
of the optical models, but they are slightly
cheaper.
However, the displacement measuring systems described above have the disadvantage that
their costs increase with the length of the measuring section. Linear motors are also increasingly
used, for example, in gantry systems involving large distances. Here, the additional expenditure
for the displacement measuring system is excessive and may make the whole machine concept
financially questionable. Costs are also the reasons why the use of the above systems is
often not justified for other applications with moderate precision requirements, for example
for wood or Pick & Place machines.
For this reason, automation specialist Beckhoff has developed a measuring system that monitors
the magnetic field of the permanent magnets of the magnetic plate and provides the
AX2000 series servoamplifier with incremental transducer signals for commutation, speed and
position control. The measuring system provides 1000 increments per logical motor revolution.
A logical motor revolution corresponds to the distance between two homopolar magnets, i.e.
for example between two north poles. With 24 mm, this distance is very short for the AL2000
series linear motors, resulting in very high resolution. This leads to particularly synchronous
operation and low running noise.
A resolution of 0.1 mm is adequate for simple positioning tasks
A maximum resolution of 24 µm is adequate for simple positioning tasks. The achievable precision
ranges between ±0.1 mm and largely depends on the mechanical precision and
position of the travel path magnets. The influence of temperature fluctuations and external
interference fields is compensated.
However, the crucial advantage is the absence of the scale; this means no comprehensive alignment
and installation is required, since the measuring system can be mounted directly on
the motor. If the travel path is extended, no reinstallation or replacement of the scale is
required. The magnetic encoder system for AL2000 series linear motors is only 36 mm wide
and is mounted in front of the linear motors. The process is further facilitated by the use of preassembled
cables. This means that the price remains constant, no matter what measuring
length is required. Another advantage is the maximum possible travel path. With AX2000
servoamplifiers, this is 50 m.
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Estimated market release 1st quarter 2003. We reserve the right to make technical changes. |
