Tech Briefs Magazine - November 2021 - 52

Mechanical &
Fluid Systems
seamless integration with the rest of the
automation system (Figure 3).
DC stepper drives and motors contain
relatively few components, while electronically
commutated DC servo motors
possess the advantage of no wear parts
like fans or brushes. These attributes help
both DC stepper and servo systems hold
up over long periods of time with minimal
maintenance. Both drive types are
well suited for a wide range of variable
speed, positioning, synchronous axis, and
gearing applications.
In many cases, engineers and designers
look first to traditional AC drives for industrial
applications. But extra-low-voltage
industrial DC stepper and servo drives provide
reliable and highly configurable
motor control and when properly selected,
they meet industrial application needs.
This article was written by Kevin Wu,
SIMATIC motion controller product marketing
manager for Siemens Industry, Norcross,
GA. For more information, visit http://info.
hotims.com/79419-124.
Servo Motor
or
Sensor
Stepper Motor
Figure 3. The F-TM StepDrive and ServoDrive snap into a PLC rack, consuming minimal cabinet
space, and they may be safely wired to their motors directly. (Photo courtesy of Siemens)
Color-Changing Dyes Visualize Stress in Plastics
Directly visualizing external stresses of plastics is useful in development of materials with
improved mechanical properties.
Chemnitz University of Technology, Germany
research team constructed a new
dye molecule from the area of
mechanophores. Thanks to this molecule,
stress of different magnitudes in
plastic components can be visualized
continuously by color changes.
The concept of such dyes is not new but
most previous mechanophores were able
to only indicate the presence or absence
of stress in plastics. The new molecule
enables the differentiation between stresses
of different magnitudes. This is important
to map stress distributions in macroscopic
plastic components to monitor
integrity of the material at all times. The
team is developing this form of deformation
and damage analysis, bringing it closer
to practical applications.
The dye shows stress of different magnitudes in plastic components. The dye was investigated
using mechanical experiments on test specimens containing the dye. (Photo: Maximilian
Raisch/Professorship of Polymer Chemistry, Chemnitz University of Technology)
nal load is taken off, the dye molecule
returns into its original state - a molecular
spring that stretches and springs,
depending on external tension.
Compared to existing molecular
switches that translate stress in plastics
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ToC
by changing color, the advantages with
the new technology lie in the stepless
mapping of forces of different magnitudes
as well as the spring-like behavior
of the molecule, which can be used
again and again.
Tech Briefs, November 2021
A
By combining a molecularly designed
dye with a suitable and non-brittle plastic,
macroscopic forces can now be
brought down to the molecular scale.
These acting forces can be, for example,
external pressure or tension. The dye
molecule thus " feels " the force acting
within the plastic components and continues
to indicate changes in force by
increasing changes in color. If the exter52

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Tech Briefs Magazine - November 2021

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