Micromotors

Exoskeleton for the lumbar spine

Exoskeleton for the lumbar spine

Exoskeleton for the lumbar spine

Exoskeleton for the lumbar spine

Exoskeleton for the lumbar spine

Exoskeleton for the lumbar spine

Today, microdrives perform remarkably well in a wide variety of applications. Not only in industrial automation technology are the requirements compact, high-torque, dynamic with precise control and as silent as possible. The same properties are also in demand, for example, in robotics and laboratory or medical technology. A good example are innovative exoskeletons that relieve the spine when lifting heavy loads. Here, too, powerful DC microdrives are the driving force.

Unfavourable strain and permanent overloading of the spine are by far the most common causes of back pain. Countless people are affected and many sick leaves and early retirements are the result, especially when the complaints become chronic. The consequential costs for the economy and health systems of industrialised countries are enormous. However, it is actually easy to avoid the wrong kind of strain if you stick to one simple basic rule: Always lift loads from the legs and only with the upper body upright.

However, this is often impossible to follow in everyday life for many tasks. If you help a patient out of bed, lift a parcel out of a delivery van, handle heavy parts in manufacturing or work with large hand machines in construction, the movements are by no means always ergonomically correct. The lifted weight then inevitably presses on the bent spine. The lifting effect that results is considerable: depending on the degree of flexion, a 10-kilo package can then press up to 50 kilograms on the lumbar intervertebral discs of the lower spine. Although these natural shock absorbers made of fibrous cartilage are extremely tough and resistant, they age over the years and can also wear out prematurely with frequent incorrect loading. This often has painful consequences, such as a slipped disc.

Protect the intervertebral discs from unfavourable stress

"If the incorrect load cannot be consistently avoided, you should think about relieving the load," says Antoine Noel. The robotics engineer founded the company Japet in Lille in 2015 together with Amelie Blondeaux and Damien Bratic. "Our goal was to develop an active support corset for the lumbar spine. Unfavourable loads should be compensated by motor force so that the intervertebral discs are protected." The result of the development work is the Japet.W exoskeleton.

The innovative support corset for the lumbar spine essentially consists of two belts connected by four actuators - two on each side of the body. The upper strap supports the back, the lower strap rests on the hips. The actuators are so-called serial elastic actuators (SEA). They "sense" a force acting on them and then work against it with their motor force. Their most important elements are a motor, a spindle and a spring. A potentiometer measures the acting force, for example when the wearer of the exoskeleton bends forward and lifts a weight. This measurement signal controls the motor, which is coupled to the drive spindle via a gear. The spindle rotates and thus transmits the motor force to the spring. The spring then presses from the lower to the upper belt, thereby supporting the upper body and relieving the lumbar spine. The wearer of the exoskeleton can select the degree of relief in four stages. The control unit and the battery of the device are integrated into the double belt.

"The hips are only slightly stressed by the additional pressure; anyway, they can tolerate heavier weights without any problems," adds Antoine Noel. "The force on the lumbar spine, on the other hand, is greatly reduced. Above all, the excessive strain on the intervertebral discs in a bent position is significantly reduced or even completely avoided. At the same time, the posture of the upper body is also improved

Ready for series production with the right motors

The founders of Japet met the drive specialists from Faulhaber at a trade fair. At that time, the French company was still a technical test laboratory in an adjoining room of a clinic in northern France and far from having products ready for series production. In their first test devices, the three young entrepreneurs had installed noisy cheap motors that were also difficult to control. The experts at Faulhaber liked the idea and supported the innovative development work with intensive advice and free samples of high-quality motors that could cope with the demanding application. "This was an important contribution to making our product ready for series production," emphasises Antoine Noel.

Compact, lightweight and powerful

In the Japet.W exoskeleton, four DC motors with precious metal commutation from the 1524...SR series now provide the supporting force to relieve the spine. The precious metal commutated DC motors are only 24 mm long with a diameter of 15 mm, making them very compact and requiring little installation space, which of course suits the application described. They deliver a continuous torque of up to 2.8 mNm at speeds of up to 4,500 rpm. The DC micromotors differ from conventional designs mainly in the rotor. This is not wound on an iron core, but consists of a self-supporting copper coil produced in an inclined winding. The light rotor convinces with its low moment of inertia and cogging-free running, which in turn benefits the dynamics.

Power transmission is provided by 15A series planetary gears with a reduction ratio of 52:1. Since the unit is naturally worn on the body, which should also be relieved, every gram counts. Here, too, the drives score points. With only 18 grams per motor, they make up only a fraction of the total mass. Nevertheless, they are strong enough to take the weight of three to four medium-sized cars off the discs of the wearer over the course of a working day. The corresponding control system could also be easily integrated into the exoskeleton's control system.

Quality and reliability

In addition to the relationship between volume and force, quality and reliability are also decisive criteria for Japet: "The exoskeleton is a certified medical device," explains Antoine Noel. "The highest requirements apply here. In addition, the device must support its wearer in continuous operation, over a long period of time and preferably without any maintenance. This becomes possible with the drives from Faulhaber."

In the meantime, the innovative exoskeleton is used in numerous industries, including the railway industry, construction and medical care. Here everywhere its use counteracts the possible development of chronic back pain. But it is also used by people who have already developed this syndrome and are looking for a way to still be able to continue working. "75 per cent of wearers who had previously developed back pain at work report effective pain reduction," Antoine Noel is pleased to report. "This is a remarkable figure from a medical point of view, especially as chronic back pain is a very stubborn and difficult to treat disease. As we all tend to work longer and longer, and at the same time the know-how of older employees becomes more and more valuable, the exoskeleton also has great potential from an economic point of view."

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