Portable Sit-to-Stand Device

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Adults suffering from muscular diseases, such as muscular dystrophy (MD) and inclusion body myositis (IBM), suffer muscular weakness, particularly in the quads, that renders standing from a seated position difficult or impossible. Subjects typically need assistance from caregivers in transfer operations, such as between a bed and a wheelchair, wheelchair and other chair or car seat, and wheelchair and toilet. In some cases, once raised high enough, subjects can lock their knees to stand and support their own weight, work at a countertop, or walk with the aid of a walker.

The primary issue to be addressed in this project is raising the subject from the seated position to standing. For typical subjects and typical seated positions, this involves lifting the center of mass of the subject approximately 12 inches (30 cm). For a subject weighing 150 lbs (67 kg), this means adding 67 kg x 9.8 m/s^2 x 0.3 m = 200 J of potential energy.

This energy often comes from a caregiver who helps to lift the subject. The problem is that the caregiver may not be strong, or that the caregiver may be injured (e.g., in the lower back) over time. While the caregiver must apply other forces to the subject (e.g., to stabilize their position), the primary force is simply to overcome gravity. It is this force that should be assisted, so that the caregiver need only apply small forces.

Various equipment, electrically powered or human powered (e.g., cranks, levers, hydraulics, etc.) exist to assist the caregiver in this operation. However this equipment is often not portable, making travel difficult for the subject.

Contents

Goal and specifications

Develop a portable electrically powered device that assists the caregiver with the sit-to-stand operation. A single device should work with a wheelchair, lounge chair, or other seat, so that only one extra device need be carried on trips. The device should be capable of lifting a subject weighing 200 lbs at least 6 inches. The less time the better, but 10 seconds for the full lift is a decent target time. The weight of the entire device should be 20 lbs or less and it should be small enough to be carried on a plane. You can assume a caregiver is present to help stabilize the operation, but the major lifting force is provided by the device.

Concept 1

Subjects often carry a lightweight padded seat to allow them to sit higher, so that the sit-to-stand distance is shorter. A 6 inch padded seat means that a typical sit-to-stand operation only involves raising the center of mass 6 inches or so, instead of 12.

This concept involves putting a lift mechanism inside the padded seat, allowing the seat to extend in height from 6" to 12". The seat's width should be about 16" in each direction (to fit in most standard wheelchairs), be comfortably padded on top and in the front (where the legs are), have a carrying handle, weigh no more than 20 lbs, and extend from 6" or less retracted height to 12" or more full height, operated by a switch, carrying up to 200 lbs.

The device could begin with a modified commercially-available mini scissor jack

outfitted with a motor, or with an electrically powered car jack

Since the device has to be portable, the electrically powered jack needs a rechargeable battery and charger. These are common in electric scooters, for example, so that's a good place to start. The car jack is driven by a 12V motor, so a 12V rechargeable battery could be

at 3.2 lbs, or perhaps a lower weight one that stores less energy would suffice:

For a charger, perhaps CHR-S12V3AHS

with charging/charged LED and a power cord that allows the pad to be recharged overnight. You should double-check with the manufacturers that your charger and battery combination work together.

The jack should be retrofitted with a lightweight frame that makes a sturdy seat. Car jacks have a lift capacity that is overkill; production models of this concept could involve lighter materials and a smaller motor.

Optionally the lift pad could be outfitted with a telescoping handle and wheels like carry-on luggage, allowing it to be rolled instead of carried.

Here are some pictures of a typical Invacare wheelchair, some showing a seating pad: picture 1, picture 2, picture 3, picture 4.

Concept 2

A modified version of the above could be used for a lift toilet seat. The top of the device would be a toilet seat, and the whole device could be rested on an existing toilet. The subject could be transferred to the toilet with the device in the raised position, then lowered to a comfortable seated position. The device should work with most common toilets, perhaps after removing the existing toilet seat.

Concept 3

A portable device that can be placed under a "standard" manual wheelchair or transport chair to safely lift the entire chair and subject.

Some existing equipment for sit-to-stand and transfer operations

This is not an exhaustive list, but gives a good idea of what's available. Further research is needed. A great resource are the clinicians at the Rehabilitation Institute of Chicago (RIC). An interview should be arranged.

Some of the devices below are expensive, not portable, or don't assist with helping the subject stand.

Upeasy lift devices

These products come in unpowered (9 lb) and powered (12 lb) versions and are similar to concept 1. One big difference is that it rotates forward, which may carry the danger of pushing the subject off the seat before the knees have locked. Also, the powered version must be plugged in to operate. Concept 1 uses a rechargeable battery and so can be used anywhere.

manual Hoyer lift

powered lift

EasyPivot manual lift for transfers

A smaller device similar to the EasyPivot

the Japanese "skylift"

Power toilet aid

This device has a telescoping frame and a linear actuator as seen in this picture.

Standing frames to assist bringing from a seated position to a standing position

Bounder wheelchair

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