Force sensing

David Sanders

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    A young child can explore and learn and compensate for unknown dynamics by
    prodding, pushing, touching, grasping and feeling. Force sensing and software
    research could soon allow artificial mechanisms to do the same.

    Force sensing has its roots in strain gauges, piezoelectrics, Wheatstone
    bridges, automation, robotics, grippers and virtual reality.

    That force sensing research has now become commonplace and has expanded from those roots to include so much more: video games, athletic equipment, drug delivery, braking, computer aided design, autonomous machines such as steerable needles and sensing on flexible printed circuits and at the atomic-scale.

    The haptic system in humans includes sensing of muscle and tendon states as well as tactile sensing of skin deformation. New artificial haptic interfaces attempt
    to mimic those systems by detecting the motion of a human operator without
    impeding that motion, and to feed-back forces from a teleoperated robot or
    virtual reality environment.

    Robots typically lack the ability to operate in unstructured and unknown
    environments but force sensing and compliance can help. That work could lead to robots that work alongside us, providing assistance to a worker on a production line or helping around the house. To achieve this, robots will need to perform their tasks within our human world. But our environments are complicated, changing, uncontrolled and difficult to detect reliably and then understand.

    New generations of force sensors can help to overcome many of these
    difficulties. Indeed, force sensing is already making surgical robots a more
    common sight in hospital operating theatres and many procedures requiring
    accuracy and precision are moving to surgical robots. These surgical systems can
    be more dexterous (and have better vision), but when they are mixed with
    realistic haptic feedback then they may outperform the best human surgeons.
    An aim in all this and other force feedback systems is that the operator or
    controlling computer is provided with high fidelity forces and torques. That
    requires compact devices with conflicting capabilities such as low apparent mass
    and inertia and, therefore, low friction (especially static friction) but while
    having structural stiffness and a wide range to provide an even feel to a human
    operator or understandable feedback to a computer.

    To achieve this, new robots are being created for force- controlled applications
    with direct-drive brushless motors and crank-rod mechanisms to provide
    low-friction joints without gearboxes. That makes it possible to control forces
    without any extra force sensor as the motors can become the transducer by
    monitoring and then regulating the currents to the motors.

    The nano-mechanical properties of materials has become an area of increasing
    importance and at the atomic-scale, structure and reactivity of single crystal
    semiconductor surfaces are being investigated along with the interaction forces
    between molecules. From this work, force sensors for chemicals, viruses, and
    bacteria are being developed along with intelligent surfaces. These can use
    micro-fabricated transducers to detect minute forces.

    Ultra-thin, flexible printed circuit force sensors can already be constructed
    with layers of substrate with conductive material and layers of
    pressure-sensitive ink.

    As all this moves out from the research laboratories and into the real world,
    then some of the research can be expected to move on to addressing the high
    bandwidth and natural learning required to integrate visual sensors with
    compliant force sensors; all in real time. Those systems will also have to
    provide robust precision without having to rely on complicated perceptual
    modeling and explicit planning. And of course both those sensor systems may only have low level signals to work with in a noisy and changing environment.
    Original languageEnglish
    Pages (from-to)177
    Number of pages1
    JournalIndustrial Robot: An International Journal
    Issue number3
    Publication statusPublished - 2007


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