Choosing A Wheelchair
Category: Mobility. Author: Daniel Gómez Peciña, Aids Dynamics
MOBILITY AND FRICTIONChoosing A Wheelchair
A wheelchair should aim to allow the user maximum functionality, comfort and mobility. To meet this goal, the chair should be designed to fit the person, not the person who must adjust to his chair.If an inappropriate wheel chair is chosen, it can be uncomfortable or for example have a seat in which the user slipping forwards or to tilt to one side. The result is that the user will be wasted energy unnecessarily due to continued efforts to change their stance.
Improper wheel chair can even cause extra disabilities.
It is often considered that what most affects the maneuverability of the chair are its weight and the material it is made structure. However, there are more important factors such as the seat and the position that it is derived, the wheelbase of the wheels, the position and size of the wheels, even the way the chair has been set or mounted, which can decisively influence the functionality and user mobility.
We started analyzing the factors affecting the MOBILITY-FRICTION:
The greater the friction, rolling resistance of the chair will be higher, and therefore the user will require more energy for propulsion.
In this section we discuss how they affect the ease to roll the following factors:
The weight distribution between front and rear wheels. More weight on the front wheels causing greater friction, but also makes the chair more stable. A standard wheelchair has a weight distribution of 50/50%, while a slight adjustable chair (setting) has a weight distribution of 80% at the rear wheel and the front 20% (approximately). This makes better than a standard roll but is less stable.
• The land on which the chair is to be used. The soft soil produces a higher friction and therefore requires more effort to propel the chair. The friction is smaller in land or hard surfaces.
• Size and composition of the wheels: pneumatic wheels are more comfortable cushion better but oppose increased rolling resistance for being softer. Resistance is lower wheel covers massive to be tougher. Small wheels have a lower friction surface having less contact with the ground, but this makes it worse present grip. Larger wheels are better grip by having a larger contact surface but also produces a higher friction.
• Front Wheel Size: Large wheels are more suitable for outdoor use, and difficult terrain. Small wheels are best for indoor use and sports to greater speed of rotation on smooth and hard surfaces. However the right size, is determined by the combination of the surface on which it will be used and the weight distribution in the chair. Therefore, a small wheel in a chair with a weight distribution 50/50% would give a high friction.
• Centre of gravity of the chair: By moving the center of gravity back and up the weight on the rear wheels is increased and makes the chair easier to handle but more unstable. If the center of gravity moves downward and forward, the chair wins in stability but harder to handle. (Normally you can reach a compromise according to user needs. It may be necessary to introduce safety devices such as anti-tip wheels). • Distance between front and rear wheels: A long wheelbase best maintains the course (why racing chairs are very elongated). A short wheelbase is softer and easier to handle (why basketball chairs tend to have the shortest distance).
• angulation of the rear wheels: If the wheels have a positive angle (greater width at the base) chair better stay the course, will be more stable and posture shoulders better (more close to the body to propel arms). (The downside is that so the total width of the chair is increased, so is only used for sports chairs). A neutral angle (parallel to the wheel chair) is less effective from the point of view of easiness to roll. A negative angle (smaller width at the base) makes the position worse shoulders and the chair will be more unstable.
• angle of the front wheels: After any change to the rear wheels or the height of the frame, always check that the front are to 90º. if the angle is more open (greater than 90) rotate faster chair but tend to go to stop back and front of the frame will be higher. If the angle is less than 90 ° rotation is difficult. When you want to stop the wheelchair, it tends to keep rolling, and the front of the chair is lower than the rear.
FACTORS OF PROPULSION
The assembly of the wheelchair must ensure efficient propulsion with a minimum expenditure of energy. Each user due to their personal circumstances has a capacity of different propulsion and sometimes limited. Therefore it is important to note the following important factors that allow you to search the composition of chair that each user needs, to optimize the propulsion within their means.
1. RANGE OF MOTION
The degree of mobility that has the user in the column. Shoulder, elbow, wrist and fingers delimit the possibility of making the whole journey optimum propulsion. Should have good mobility in these joints, the most effective route is starting behind the trunk to finish up to the thighs. Thus flexing arm muscles that allow applying force is used.
To propel correctly and harness all the energy of this drive, the user must be correctly seated (upright) in a symmetrical sitting position. Only then can properly reach the handrims and perform the full movement of the arm, to start the drive wheel from behind, using force throughout the tour.
If the user slides the seat, the rings will be too high and would be very uncomfortable start propulsion from behind, so we tend to advance in the journey log. Propulsion thus be shorter and less efficient.
3. HEIGHT AND POSITION OF THE WHEELS
To achieve more efficient propulsion, the rear wheels must be located so that the user with the relaxed and dropping his arm stretched shoulder, can touch the tip of your fingers the axis of the rear wheel. If the wheel axle is higher than indicated, the thrust ring will also be high, and you must bend your arms to propel too.
The propulsion will be more awkward and inefficient. The same applies if the axis of the wheel is lower than the fingertips. The user should perform propulsion with arms overstretched and can not make the necessary strength for proper propulsion.
This same rule also marks the optimum position of the wheel. If the wheel is advanced and the axis lies ahead of the fingers, the user starts the propulsion too far back and can not complete the tour.
If the shaft is behind the fingers, the user starts the advance propulsion and therefore have a (less efficient) shortest path.
The position of the rear wheel also affects the stability of the chair. If the wheel is rearmost seat will be more stable (for standard chairs) but also requires more energy for propulsion. Lightweight chairs tend to have the rear more advanced than standard wheel chair. Thus lever requires less force and less energy for propulsion.
4. WHEEL SIZE
The smaller rear wheel lets you apply less effort to propel, but also takes a shorter route. They typically use lower wheels 600 mm (24 “) in users with difficulty of movement in the shoulders or quifótica column. Smaller wheels are also used in pushchairs for the thrust ring is at a more appropriate height to length his arms.
A long distance between front and rear axles keeps a straight course, but also roam farther wheels so more energy is needed for propulsion. A short distance axis turns more easily and handled easier by requiring less energy for propulsion.
6. ANGULATION WHEEL
The optimum propulsion is performed parallel to the seat rear wheels. Thus the distance of the arms to the body is appropriate to apply the energy needed for proper propulsion.
If the wheels are wider at the base, the chair is more stable, but the arms are closer to the body. And further shoulder abduction so propulsion is more difficult and less effective occurs.
If the wheels are closer together at the base, arms away from your body will be very difficult to apply the necessary force for propulsion. Besides the chair is unstable.
TYPES OF COMPONENTS IN A WHEELCHAIR
Before adjusting a wheelchair to the needs of its user, it is important to know the wide range of possibilities in the various components of a wheelchair. Thus we can choose each component, which best suits the user and thus maximize their functionality in the chair.
As key parts of a wheelchair, we will discuss the different types of frames, wheels, brakes, footrest and armrest, and the advantages and disadvantages of each.
The frame of a wheelchair may be rigid (fixed) or folding. Harnessing the power to propel the user applies is twice in a chair with rigid frame (15-20% of the pulse is used) in a folding (advantage 5-8% of the pulse).
This is because in a folding chair of propulsion energy is lost in the movement structure for the articulation points. Other advantages of the rigid frame is easy to handle and is somewhat lighter than a similar fold. However the folding chair is more comfortable to carry and store folded to occupy less space overall.
Currently there are chairs that presenting behavior rigid frame allows a very compact folding.
The composition of the frame is a key factor in the functionality of the chair. Steel being the most common, is the heaviest but also the cheapest. A chair with aluminum frame is much lighter and therefore easier to propel, but also more expensive. Can also find frameworks made in very light materials such as titanium and carbon. Commonly used in rigid frame chairs and have a very high price.
1 – Size
The smaller are the front wheels have less friction and greater ease of rotation, being suitable for indoor use. So for example 75 mm and 125 mm are recommended track chairs for sports like basketball. It also depends on the seat height you need.
The large wheels (200 mm) are more suitable for outdoor use, and uneven ground, as it is easier to overcome obstacles and do not dig into the ground.
The intermediate commitment to outer and inner wheel is 150 mm. Whenever variemos size front wheel fork adjustment is necessary. The axis of rotation of the fork must always be at 90 ° to the ground.
2 – Covers
Pneumatic: damp ground imperfections but require maintenance (you can click and you have to hincharlas).
Solid: are tougher driving to not weaken but do not require maintenance.
1 – Size
The most common is the rear wheel of diameter 600 mm. (24 “). Wheels smaller than 22 “(550 mm) or 20” (500 mm) in child seats for people with limited movement in the shoulders or hemiplegic are used so they can reach the ground and propel the foot. The smaller wheel lets you apply less effort to propel, but also requires greater number of pulses. Wheels 650 mm (26 “) are used for very high and for sports persons.
• Massive: offer less rolling resistance and require no maintenance, but are heavier and harder to not dampen driving terrain features. Have worse grip on wet surfaces.
• Solid Insert: are intermediate between the solid and pneumatic. They require no maintenance, have better grip than solid in the wet, but not as much as the pneumatic cushion and weigh more than these.
• Pneumatic: They are more comfortable driving accidents as damping off and have a good grip on most surfaces. They are the lightest. One drawback have to require more force to propel them to be softer and require maintenance (you can click, and you have to hincharlas and monitor the air pressure to maintain performance).
• Tubular: Very lightweight, and low rolling resistance. Disadvantages: A puncture resistance and high maintenance. Used Wheelchair ramp sport like basketball.
• High pressure: They are used in sports and aluminum chairs (active). Are very light tires, high performance camera that bringing allow repair is cheaper (only the camera is changed).
• Soft Beds: With a similar tire weight, have lower rolling resistance than these. They are more durable than solid insert and they are cheaper.
• Plastic Wheels: virtually maintenance, but heavier than spoked wheels.
• spoke aluminum rim: It lighter than plastic and better absorb the roughness of the terrain. The Crusaders radios offer a stronger fabric.
For sport straight spokes, giving greater rigidity to the structure are preferred, but the rings and reel should be especially strong.
THRUST RING (DRIVE):
They can be aluminum, steel (which is heavier but slips less), titanium (very light), or plastic coated. Besides the material, there are rings with projections to facilitate gripping by people with limited mobility in his hands.
The most common brakes are the brake caliper. Assembly are high (the tube that is below the seat are anchored), and can be of two types, according to activate pushing forward or pulling back.
For very light or sports chairs are often used scissor brakes. This type of brakes can be high or low mounting assembly (as anchored in the upper or lower frame tube).
These brakes are collected under the seat when not in use, so they are more protected from impacts and not bother transfers.
A hand brake: To hemiplegic persons only propel one hand, there is a kind of brake that defuses the two wheels with one hand.
Brakes with extension: Extension cord brake is an accessory that is used to facilitate access to the brake users with little movement of the arms or hands, and thus facilitate braking.
Drum brakes: They are brakes that are not activated by the user but by the passenger. To do this, press the levers (bicycle brakes type) located under the handles of the wheelchair. This type of brake is the only one that also serves to lock the wheels when the chair is stopped, to reduce the speed of the chair when it is running.
There are several types of armrests. They may be removable or folding backwards. With different lengths (normal or long) padding.
Height adjustable: the padding can be located at various heights to suit user needs.
Desktop: shape that allows the approach to tables.
Tubular: weigh less but has lower support surface.
For very active people tend to remove the armrests and place a side shields to prevent the wheels dirty clothes to splash.
FOOTRESTS and PLATFORMS:
They can be fixed or removable. To shorten the length of the chair in confined spaces such as elevators, you better be removable. If no space problems is more advisable that the footrests are fixed. The ideal anatomical position of the footrest is 90 °. However feet adults can interfere with the rotation of the front forks, so that the angle tends to be reduced. The most common angles are 90 °, 70 ° and 60 °.
Elevating: Elevate the leg assembly to adopt more comfortable positions. They are widely used in chairs with reclining backrest.
Footrest platforms are usually composite. They can be double or a single platform, with or without heel straps. Typically the angle between the footrests and the platforms is 90 °, but there are platforms that have the possibility of adjusting this angle, to suit specific needs of some users.