With
a continued trend towards ever greater automation of final assembly techniques,
there have remained tasks which can still only be performed by humans. In
sensitive scenarios the inherent intelligence and dexterity of human fingers
are often more capable and attuned than even some of the most advanced robotic
equipment at present. Noting irregularities or testing of ergonomic products
often necessitates the gripping and feeling capabilities that only a human can
contribute.
This
last bastion of manufacturing and product development, where human hands are
needed, is however in decline. The use of infrared sensors enables the
recognition of the smallest changes on the active surface of elastomers and
guarantees that even the slightest imperfections are detected by the sensor
surface and passed on.
These
transducers also need to be rugged enough to withstand challenging operating
environments over long periods of time where they could be exposed to
significant temperatures swings and other conditions such as vibration and
exposure to fluids or dust.
In
order to develop equipment for industrial automation and product development,
it is crucial to seek solutions which are able to build upon the sensitivity
and properties of specific sensor technology.
Optical force sensing Vs strain gauge technology
In
simple terms, force sensing is the measurement of the deformation and deducting
of a given applied load within the sensor itself. Since 1938 strain gauge
technology has been seen as the most capable means to achieve these aims. The
most common type of strain gauge sensor makes use of an insulated and flexible
backing which supports a metallic foil pattern. The gauge is attached to the
object and the electrical resistance felt by the sensor is then used to measure
the deformity.
However,
this pre-existing technology has been limited in its take-up by practical
limitations surrounding the brittle and delicate structure of sensors, their
susceptibility to environmental conditions such as humidity and electro static
discharge (ESD), additional weight that they can add, and the high cost of manufacturing
them. Furthermore, in some applications, strain gauges add mass and damping to
the vibration profiles of the hardware they are intended to measure.
As
such their usage has been limited to applications where their high cost and
potential fragility can either be absorbed or accepted. What is required
instead are sensors capable of dealing with the harsh environmental conditions
which would be encountered in many industrial settings.
Three-axis
optical force sensing technology makes use of photodiodes, instead of foil
based circuity, to measure the quantity of reflected light originally emitted
by an LED upon the X, Y and Z axes. By comparing these measured values, and
their effect upon the photodiodes, it is possible to accurately recreate the acting
forces in a 3D model, which not only measures the magnitude, but also the
direction of force.
If
a cluster of these three-axis sensors are coupled together they have the
ability to measure not only the lateral forces upon them, but also the torque which
is acting on the X, Y and Z axes, thus creating a 'six-axis sensor'.
A touch of intelligence
The
Internet offers no shortage of videos featuring robotic hands, claws and vices,
gripping fragile objects such as eggs and lightbulbs and seeking to demonstrate
their capabilities. The reality is that few of these products have the ability
to do so without prior preparation.
For
a sensor node to be able to pick up on the most subtle forces and pressures, it
is necessary for the sensor to feature a more advanced method of measuring and
responding to forces. In order to achieve this feat straight away, without
pre-preparation, requires not only a more intelligent sensor and indeed a more
intelligent material for the sensor to be made from.
Silicone,
with its varied manufactured textures and shapes, offers a material which can
be custom designed to offer the most accurate measurements of deformities and
deflections. This 'optical grade' silicone is not only able to detect a force
of only a few hundred nanometres but also to withstand temperatures ranging
from -40°C to +100°C
Automation and autonomy
While
automation is nothing new to the manufacturing industry there still remain
techniques and applications where humans offer a higher degree of quality
assurance than machines. 3D sensors offer the capability to meet these
parameters, however they are often limited by their fragility or great cost.
Typical
applications for 3D sensors include: grinding, polishing, finishing tasks with
force control, robotic assembly and machine guidance. Furthermore, their
sensing capabilities can easily be turned to advanced safety features such as
ensuring collision detection from various angles.
Multi-actual force sensors
Sensors
such as those from leading Hungarian manufacture OptoForce are able to respond
effectively and with a high degree of accuracy to pressures of even the
smallest magnitude. These sensors are capable of detecting the force of a
feather being dragged across their surface, or even air movements.
While
other manufacturers have successfully developed and sold multi-actual force
sensors, OptoForce have developed sensors that offer the robust characteristics
that enable them to match the requirements of applications across the
automation, manufacturing and development sectors. By offering a cost-efficient
development kit it is possible to find markets and use for these sensors which
would have been prohibitive before.
Concurrently,
the more rugged the sensor, the greater number of tasks it is capable of. Such applications
in the industrial world could include polishing, grinding, deburring and
assembly tasks. Indeed any task where the manufacturing equipment is required
to follow the curvature of an object, while exerting the same amount of force
or when it needs to detect if the object it is holding is in the right place.
This
even allows the potential for more advanced and capable walking robots. Prior
to the development of this technology, force sensors were incapable of
providing the required resistance to the shocks that are generated when the
legs of such robots come into contact with the ground. With the greater degree
of accuracy and durability these sensors offer the chance for robotic
technology to be developed with a more intuitive sense of motion and balance.
Conrad and force sensors
It
is the responsibility of distributors and retailers of advanced technologies to
not only follow the curve of technological advancement but sometimes to also
lead. As such, Conrad Business Supplies, has sought to offer its customers a
range of force sensors including OptoForce's complete offering of 3D
sensor-development kits.
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