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A third robotic arm controlled by the diaphragm

A child in one arm, shopping in the other, who has never dreamed of having a third appendage to open the front door of the house? Rejoice: owning a robotic arm and controlling it with your diaphragm is now possible! Or almost.

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A third robotic arm controlled by the diaphragm

A child in one arm, shopping in the other, who has never dreamed of having a third appendage to open the front door of the house? Rejoice: owning a robotic arm and controlling it with your diaphragm is now possible! Or almost... Researchers have developed a digital interface to capture the movements of the muscle located under the last ribs, to control this additional arm.

And to become this augmented human, no need for surgery! This is what a study published in Science Robotics in December 2003 by researchers from the École Polytechnique Fédérale de Lausanne (EPFL) shows. A respiratory belt placed on the upper part of the abdominals captures the movements of the diaphragm, and transmits them to the 3rd arm motor. During voluntary contraction of the diaphragmatic muscle, the robotic arm extends; conversely, during muscle relaxation it retracts into the rest position. Humans are capable of adapting and allocating part of the brain to this new function.

In previous work, the feet and/or legs were fitted with sensors allowing an additional limb to be tamed. But this limited the normal use of these arms or legs. It was therefore necessary to find an organ with contraction capacities, but little or not exploited by the body, so that its use did not hinder the other functions of the body.

The diaphragm is a muscle located under the last ribs separating the thorax and abdomen. It is used when we breathe “through the stomach”: the reflex contraction of this muscle causes air to enter the lungs during inspiration. Its release ensures expiration, the exit of air. But most of us use thoracic ventilation instead, contracting the costal and intercostal muscles. The diaphragm is therefore little used on a daily basis, leaving it partly free to be used by robotics.

In order to adjust the device, the experiment began with a virtual reality headset. We first had to ensure that the brain was capable of managing a third arm, while using the two already existing ones. The sensor placed at the level of the diaphragm controlled an arm visible on the headset screen, and the participant had to reach different targets with each of his three arms; amusing detail: the virtual “hand” had six fingers and was perfectly symmetrical, so that the user did not favor the right or left of their brain...

They added another element to it. At any moment, we know how to position our limbs in space (this is proprioception), and our brain receives information about what we touch (this is sensory feedback). These senses are essential for modulating the movements of our limbs, in order to make them precise. A sensory device placed on the volunteer's chest gave him information on the position of the robotic arm (the more tense it was, the more pressure was applied to the chest, and grasping the target object triggered a vibration).

The researchers then placed a robotic arm attached to the volunteer's chest by a harness, and controlled by their diaphragm. The sensitive feedback device by pressure and vibration on the chest, however, was not used in the real version of the robotic arm, because it did not really bring any improvement in performance.

The researchers show that despite some arm direction errors, particularly when the person must speak at the same time or visualize different shapes in their environment, the use of this 3rd arm does not generally hinder the ability to speak and see their own. environment. Maintaining these capabilities is essential for effective human augmentation. The mental load imposed by this extra arm is, however, very present, particularly on first use.

It also remains to question the usefulness of this third arm... The researchers believe that this technique could be used for amputees or quadriplegics, but they also imagine its use for augmented humans. “I use technology to compensate amputees. I don't work on augmented humans but for treated humans. I would never operate on someone to increase it,” judges Dr. Edward de Keating-Hart, hand surgeon at the Jules Verne Clinic in Nantes and pioneer of bionic prosthesis surgery in France. On the other hand, he concedes, this type of device could allow “quadriplegic people, via movements of the neck or ear muscles, to answer the telephone or use a tablet in order to be less dependent”.

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