Working Area of Wheelchairs

Details about Some Dimensions that are specified in ISO 7176-5

FIOT Wien, Austria

Ing. Johann Ziegler

Working group WG1 of Sub Committee SC1 of Technical Committee TC173 of the International Organization for Standardization ISO focuses on

Test Methods for Wheelchairs.

A great number of standards has been developed during the past years. They all are listed in the ISO 7176 series. At present the WG1 is revising the following document:

ISO 7176-5 Wheelchairs - Determination of dimensions and mass.

Even if not yet a ready standard (CD stage) the content and structure are clearly comprised.

The purpose of this International Standard is to provide technical definitions together with appropriate test procedures for measuring important dimensions and masses of manual wheelchairs as well as electrically powered wheelchairs including scooters.

Under the headline Required measurements, the wheelchair features that are most important for the user are listed. Their values will be disclosed in the specification sheets to inform the user before purchase whether the wheelchair will fit to its specific requirements and needs.

Under the headline Architectural considerations, the wheelchair dimensions that are most important for its use in narrow places are listed.

Annexes give typical values and recommended limits for the Required measurements and for the Architectural considerations and specify supplementary dimensions, which are of higher influence to good performance of the wheelchair (driving, steering, tracking etc.) as well as it explains some theoretical details about reversing width, turning diameter, wheelchair longitudinal axis and wheelchair centre-point.

Out from this standard ISO 7176-5 with a total of 36 items, the most relevant ones for the topic of this workshop are explained in deeper detail. These 11 selected items are:

1 Occupied length;

2 Occupied width;

3 Occupied height;

4 Minimum space;

5 Turning diameter;

6 Reversing width (type 1);

7 Reversing width (type 2);

8 Required width of angled corridor;

9 Required doorway entry depth;

10 Required corridor width for side exit; and

11 Ramp angle.

1 Occupied length

Distance between the most forward and most rearward point of the occupied wheelchair including user (see Figure 1).

2 Occupied width

Horizontal distance across the wheelchair including user (see Figure 1).

3 Occupied height

Vertical distance from the test plane to the uppermost point of the head of the user when occupying the wheelchair (see Figure 1).

Figure 1 - Dimensions of the wheelchair when occupied

The standard ISO 7176-5 provides the following typical values and recommended limits.

Typical values (in mm)

	Manual wheelchair	Electrically powered wheelchair
		Class A	Class B	Class C
Occupied length	1200	1240	1300	1300
Occupied width	740	620	680	700
Occupied height	1500	1500	1530	1590

Recommended maximum limits (in mm)

	Manual wheelchair	Electrically powered wheelchair
		Class A	Class B	Class C
Occupied length	1300	1300	1300	1300
Occupied width	800	700	700	700
Occupied height	1600	1600	1600	1600

4 Minimum space

4.1 Definition

Minimum cylindrical space in which a wheelchair can be used in narrow places without excessive need of repeated reversing movements (see Figure 2).

Required minimum space is expressed as diameter x height in mm.

NOTE This dimension is used to help architects to provide space in toilets, baths, aisles and other narrow places that is minimally acceptable. Rooms need to be large enough to leave the required minimum space free even when the room is fitted with appropriate furniture.

Figure 2 - Required minimum space

4.2 Technical details

Minimum space is not measured but derived from long term experience. But it need to be said, that this dimension is very poor.

When turning a typical wheelchair about a single point (Figure 3 a) not more than 90° are achieved.

When executing a turn with the front part of the wheelchair sliding along the limiting wall (Figure 3 b) the angle can extended to only 145°.

And when executing a 360° turn with several reversing manoeuvres (Figure 3 c) almost 7 backing operations are necessary.

Since the minimum space only specifies the circle around which the walls are arranged and sanitary equipment and furniture are located, some extra space might be available in real life. But since one cannot guarantee this extra space, you should be aware of this effect.

Figure 3 – Wheelchair manoeuvres in a circle of 1500 mm (minimum space)

The standard ISO 7176-5 provides the following recommended limits.

Recommended limits of required minimum space (in mm)

Manual wheelchair	Electrically powered wheelchair
	Class A	Class B	Class C
1500Æ x 2000	1500 Æ x 2000	1500 Æ x 2000	1800 Æ x 2000

5 Turning diameter

5.1 Definition

The diameter of the smallest cylindrical envelope in which the unloaded wheelchair can drive in a circle through 360° (see Figure 4).

NOTE 1 The midpoint of turning will always lie on the axis of the fixed wheels. It will be more or less close to the wheelchair centre-point. Some wheelchairs can turn about a very near midpoint of turning while others only can turn about a more remote point. Wheelchairs with full differential steering can turn with the midpoint of turning lying at the wheelchair centre-point. Wheelchairs with direct steering have their midpoint of turning at the point of intersection between axis of fixed wheels and axis of steering wheels when the steering wheels are in their most extreme steering position.

NOTE 2 The turning diameter is intended as a theoretical dimension when comparing manoeuvrability of different wheelchairs.

Key:

a manual wheelchair

b electrically powered wheelchair with rear wheel drive and direct steering

c electrically powered wheelchair with front wheel drive and direct steering

d electrically powered wheelchair with rear wheel drive and full differential steering

e electrically powered wheelchair with mid wheel drive and full differential steering

f electrically powered wheelchair with scooter design and direct steering

Figure 4 - Turning diameter (examples for various wheelchair types)

5.2 Technical details

5.2.1 Wheelchair with direct steering

When a wheelchair has:

· direct steering;

· symmetrical construction without any wheel misalignment; and

· pivot wheels or pivot drive wheels which are vertical and pivot about vertical axes

and when all dimensions are projected to the test plane, the minimum turning diameter (TD_DIR) is calculated from:

where

TD_DIR is the turning diameter for wheelchairs with direct steering, equal to the double distance between M and W, see Figure 5);

M is the midpoint of the turn;

W is that point of the wheelchair which is most remote from M;

y is the distance between W and wheelchair longitudinal axis;

h is the distance between G and wheelchair longitudinal axis ;

G is the ground contact point of the inner pivot wheel when the steering angle is at its maximum with the front in the lateral direction;

g is the distance between G and the axis of the fixed wheels;

a is the maximum steering angle of the inner pivot wheel (in degrees) with the front in the lateral direction; and

x is the distance between W and the axis of the fixed wheels.

Figure 5 - Turning diameter, wheelchair with direct steering (TD_DIR)

5.2.2 Wheelchair with differential steering

When a wheelchair has:

· limited differential steering;

· symmetrical construction without any wheel misalignment;

· castor wheels which are vertical and pivot about vertical castor axes

and when all dimensions are projected to the test plane, the minimum turning diameter (TD_DIF) is calculated from:

where

TD_DIF is the minimum turning diameter for a wheelchair with limited differential steering, equal to the double distance between M and W, see Figure 6);

M is the midpoint of the turning circle;

W is the point of the wheelchair that is most remote from M;

t is the wheel track of the manoeuvring wheels;

v is the speed of each manoeuvring wheel (indices: o...outer wheel, i...inner wheel);

y is the distance between W and wheelchair longitudinal axis; and

x is the distance between W and axis of manoeuvring wheels.

For a wheelchair with full differential steering the situation is much simpler. In this case the forward speed of one manoeuvring wheel equals the rearward speed of the other manoeuvring wheel (+ v_o = - v_i). Hence, the formula given above simplifies to

because the midpoint M of the smallest turning circle coincides with the wheelchair centre point.

Figure 6 - Turning diameter, wheelchair with differential steering (TD_DIF)

The standard ISO 7176-5 provides the following typical values and recommended limits.

NOTE No matter of steering type.

Typical turning diameter (in mm)

Manual wheelchair	Electrically powered wheelchair
	Class A	Class B	Class C
1650	1780	1795	2700

Recommended maximum limits of turning diameter (in mm)

Manual wheelchair	Electrically powered wheelchair
	Class A	Class B	Class C
2000	2000	2300	2800

6 Reversing width (type 1)

6.1 Definition

Minimum distance between two vertical and parallel walls between which an occupied wheelchair with full differential steering can turn around for 180° with one single and smooth turning manoeuvre (see Figure 7).

NOTE The reversing width (type 1) is intended as a clinical dimension to estimate the space needed in real live situations.

Figure 7 - Reversing width (type 1)

6.2 Technical details

Reversing width (type 1) is applicable for wheelchairs with full differential steering only.

The shape of the footprint (all dimensions are projected to the test plane) of a typical wheelchair is known from field experience. The footprint of a typical manual wheelchair with typical dimensions is shown in the left sketch of Figure 8 as an example. It is symmetrical and the greatest width of the wheelchair is at the drive wheels, while at the footrests the wheelchair is narrower. Its typical overall length and overall width are known from A.1 and A.3. The feet of the user are represented by the two bows at the front end, 200 mm apart and adding 100 mm to the length. The sketch also shows three distances of importance:

Distance R reaches from the wheelchair centre point C to that point of the footprint, which is to the rear and to the right of C and most remote from it. Its length is 432 mm and it will be perpendicular to the walls after the wheelchair has turned for 44°. This distance is shown in bold lines intermitted by small squares;

Distance D is located between the two points of the footprint that are furthest apart from each other. Its length is 1267 mm and it will be perpendicular to the walls after the wheelchair has turned for 71°. This distance is shown in bold lines intermitted by circles.

Distance F reaches from C to that point of the footprint, which is in front and to the left of C and most remote from it. Its length is 901 mm and it will be perpendicular to the walls after the wheelchair has turned for 83°. This distance is shown in bold lines intermitted by asterisks; and

NOTE 1 The end points of distances R and F usually are very close to but not identical with those of distance D

When an experienced user executes a turning manoeuvre between limiting walls, the front part of the wheelchair will swing around without any visible deviation from a smooth and unidirectional move. Meanwhile, without spending so much attention to this fact, the user will correct the position of the wheelchair intuitively by using micro steering manoeuvres. This is needed in order to adapt the position of the wheelchair between the walls.

The turning manoeuvre is performed as follows:

NOTE 2 It is assumed the distance between the adjustable walls is already reduced to the reversing width (type 1).

The wheelchair is placed between and parallel to the walls.

The turning manoeuvre can be started at any point, but it will need some drive to reach the best starting position from which it can be executed with a minimum of travel.

The right sketch of Figure 8 illustrates the path of the wheelchair when starting from the best starting position.

The best starting position is with C the distance R away from the right wall to allow as much as possible free space for the turn (C is at location 1 which is shown in the middle of the right sketch and in magnified view below). This position is shown in bold line near the word “start”.

The wheelchair turns about C (with C still on location 1) allowing its right rear end to pass by very closely at the right wall after a turn of 44° (distance R is perpendicular to the wall). This position and distance R are shown in bold lines intermitted by squares.

The wheelchair continues to turn about point C (with C still on location 1) until the left front end hits the left wall. This position is shown in bold lines intermitted by plus signs.

During the following turning manoeuvre, C needs to drive along the V-shaped line (which is shown in the middle of the sketch and in magnified view below) while the front part of the wheelchair slides along the left wall.

This turning manoeuvre is continued until C reaches location 2 and after the wheelchair has turned for 71°. The end points of distance D of the wheelchair will touch both walls at one time. This position and distance D are shown in bold lines intermitted by circles.

NOTE 3 If the walls are further apart so that the wheelchair cannot touch both walls at one time, the reversing width (type 1) is not yet achieved.

Hence, the reversing width (type 1) is equal to the distance D.

The turning manoeuvre continues with C driving along the V-shaped line and with the front end of the wheelchair sliding along the left wall until C reaches location 3 after a turn of 83°. The wheelchair will be the distance F away from the left wall. The front part of the wheelchair is no longer restricted from turning freely by the wall. This position and distance F are shown in bold lines intermitted by asterisks.

A further turn of the wheelchair about C (with C still on location 3) will bring it to a position that is perpendicular to the walls. This position is shown in bold lines intermitted by triangles. The first half of the turning manoeuvre (90°) is completed.

Since a symmetrical pattern of the turning manoeuvre is used, its first half only needs to be mirrored to receive the respective positions of the wheelchair during its second half. These positions and distances are shown in thin lines intermitted by their respective mirrored symbols.

During the second half of the turning manoeuvre C drives from location 3 via 4 to 5.

Since the sum of distance R plus distance F is 66 mm greater than distance D, the distance between location 1 and location 3 is 66 mm when measured perpendicular to the walls.

At the end of the turning manoeuvre the wheelchair again is parallel to the walls but turned around for 180°.

To demonstrate the whole drive pattern of the wheelchair when executing reversing width (type 1) in a way that is easier to imagine, also the total paths of two prominent wheelchair points is shown:

The wheelchair centre point C moving along the V-shaped line from location 1 via 2, 3 and 4 to 5; and

the middle of the foot support moving along the bowed line between “start” and “end”. This path is shown with a bold dash-dot line.

NOTE 4 The flat section in the middle of this bowed line indicates one important difference between the reversing width (type 1) and part of the turning diameter of a wheelchair with full differential steering (which is twice the distance F).

Figure 8 - Reversing width (type 1) (example)

The standard ISO 7176-5 provides the following typical values and recommended limits.

NOTE Class C wheelchairs and scooters usually do not have differential steering.

Typical reversing width (type 1) (in mm)

Manual wheelchair	Electrically powered wheelchair
	Class A	Class B	Class C
1270	1250	1310