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Motorised Neck Brace for client with MND

The client needs to lean their head forwards in order to swallow. However, they have very weakened neck muscles, due to MND, and their head falls forward uncontrollably. The client is then unable to bring it back up without help from her carers.

This motorised brace has given the client the independence to move their head up and down as required, by squeezing a switch between their knees.

The Challenge

The client’s head control is very weak. They have little control when dropping their head forwards to allow swallowing; their head simply flops forward. Once in this position the client has insufficient neck strength to lift their head back up. A carer must do this for them.

A variety of collars have been tried by the OT. Most of these collars and head supports are designed to prevent the person from dropping their head at all. Those that allow forward movement have insufficient restorative force to help the client lift their head back to the horizontal. Any stiffer and they can’t push down against it.

Typical NHS chin support, with very weak springs

Based on the collars that had been previously tried (see above) a number of spring loaded “test” braces were built. These had adjustable stiffness and different shaped “levers”, but nothing met the requirement. Even if the client could only just press down against the brace there was still insufficient restorative force to help the client lift their head back to the horizontal.

3D printed support with adjustable springs

It was agreed with the OT that a powered solution should be tried. This became a motorised neck brace.

The main safety concerns were around the speed at which the client’s head would move and how the motors were going to be set in motion. The client has very limited movement.

The client is very adept at using an Eye-gaze so consideration was giving to interfacing with this, but while downward movement could be initiated, once down, the client can on longer use the Eye-gaze to bring the brace back up. Timers were considered to bring the brace up after a predetermined time, but eventually it was agreed that a large switch between the client’s knees, that could be squeezed, would be used to initiate both directions of travel.

The solution

The brace is fabricated entirely from 3D printed parts.

The basis of the design is a hinged, “horse-shoe” shaped, support that the client’s chin could rest on. This is fixed to the client’s head with Velcro straps.

Initial Trial brace showing “scissor jack” arrangement

The position of the brace is controlled by an electric motor on each side of the brace and the lift mechanism is based on a scissor-jack; frequently used to lift a car while changing a wheel.

The design was a significant challenge due to the large range of movement required in such a small space and the fact that the mechanism was hinged, unlike a standard jack where the movement between the two halves of the jack move in parallel.

The biggest challenge was the interconnection with the motor. Because the mechanism was hinged, and despite using left-hand and right-hand threaded rods on each side, the centre of the jack moved significantly in relation to the hinge.

The solution, to reduce this movement, was to use linkages of different lengths. Through trial and error a set of linkage lengths were selected.  This can be seen in the image above. This didn’t remove the change in position totally, but greatly reduced it to about 5mm. This movement could be accommodated using a sliding connection and a universal joint (gimbal) to accommodate the angular changes with the fixed motor.

Motor with gimbal and sliding coupling

The knee switch used a standard 65mm Buddy Button enclosed in 3D printed spacers to fit the gap between the client’s knees in their natural resting position.

Large knee switch. Approx 150mm wide.

The neck brace is controlled by a miniature microprocessor (ATtiny84) that is able to detect the action of the knee switch and 4 micro-switches on the neck brace. This controls the subsequent motion of the motors, the direction of which is dependant upon their previous state.

  • If the neck brace is moving & the knee switch is pressed, the motors will stop.
  • If the neck brace if stationary & the knee switch is pressed, the motors will start moving in the opposite direction to that previously moved.
  • This applies whether the neck brace is in mid-travel or at one of the end stops.

Each motor is controlled independently, with their own upper and lower limit switches. This is to allow for the possibility of one motor reaching an end stop before the other and the two motors becoming out of sync.

The software is bespoke and is about 500 lines of code.

The software monitors the knee switch, the 4 limit switches, the battery voltage and has an alarm output to warn the client and the carers that the battery requires charging.

The alarm is based on a “novelty” voice recorder chip. When the batteries require recharging the voice says “please charge the batteries”. This is played through a very small loudspeaker in one of the motor mount enclosures.

When not being used the processor enters a sleep mode during which time the current drawn from the batteries is only 200nA. In this state the batteries will last many years! The self-discharge rate of the batteries will probably cause an issue before the “sleeping” processor does.

It is estimated that in normal use the batteries will last a couple of days between charges.

The benefit

The main benefit is independence; the client can now swallow whenever needed.

The client’s reaction, in the photos above and the video below, when the brace was first used said it all.

 

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