Method and system for determining occurrence of slips leading to falls

• US 20050222807A1
• Filed: 04/06/2004
• Published: 10/06/2005
• Est. Priority Date: 04/06/2004
• Status: Active Grant

• Current Assignee: Batterman Engineering LLC
• Original Assignee: Batterman Engineering LLC
• Inventors: Batterman, Steven C., Batterman, Scott D.
• Granted Patent: US 7,089,151 B2
• Time in Patent Office: Days
• US Class Current: 702/181
• CPC Class Codes: G06F 2111/08 Probabilistic or stochastic CAD
• CPC Class Codes: G06F 2111/10 Numerical modelling
• CPC Class Codes: G06F 30/20 Design optimisation, verification or simulation optimisation, verification or simulation of circuit designs G06F30/30

Abstract

The present invention provides a system and method for the prediction of macroslip on walkway surfaces. The slip prediction is based on a viscous shear model and incorporates anthropometric characteristics of an individual or substantially similar grouping of individuals as well as properties of the walkway surface. In the shear model, the prediction of slip is a function of walking speed, stride length and other anthropometric factors which affect gait, as well as the friction (shear) forces that develop at the shoe-floor interface. Mathematical relationships are developed relating the forward walking speeds to the stride lengths necessary for the onset of macroslip. Curves are then plotted which enable the prediction of macroslip for various footwear and walkway surface combinations under both wet and dry conditions.

Claims

1. A method for predicting a macroslip on a walkway surface, comprising:

determining a characteristic of the walkway surface;

determining an anthropometric constant;

determining a relationship between a walking speed and a stride length in terms of the characteristic of the walkway and the anthropometric constant; and

plotting a curve of the relationship between the walking speed and stride length, wherein the macroslip is predicted to occur at a position on or above the curve of the relationship between the walking speed and stride length.

2. The method of claim 1, wherein determining an anthropometric constant includes determining the Anthropometric Gait Index (AGI), or indices, for specific anthropometric groupings.

3. The method of claim 2, wherein the anthropometric group includes group members related by age, height, weight, and gender.

4. The method of claim 2, wherein plotting the curve of the relationship between the walking speed and stride length is done for the anthropometric group.

5. The method of claim 4, further comprising:

determining the walking speed and stride length for an individual; and

plotting the walking speed and stride length for the individual on the curve of the relationship between the walking speed and stride length of the anthropometric group, wherein the macroslip is predicted to occur at a position on or above the curve of the relationship between the walking speed and stride length.

6. The method of claim 1, wherein the characteristic of the walkway surface includes a dry walkway surface.

7. The method of claim 6, wherein the onset of macroslip occurs when

${\mu }_{}$

i = C di ⁢

V 2 gL ,

wherein μ

_i is a relevant coefficient of friction, C_di is the anthropometric constant (AGI) for the dry surface, V is a forward walking speed of a center of mass of an individual, L is the stride length of the individual, and g is an acceleration due to gravity.

8. The method of claim 7, wherein for determining slip at push-off the relevant coefficient of friction μ

_i is a static coefficient of friction.

9. The method of claim 7, wherein the anthropometric constant C_di is determined from:

$C_{\mathrm{di}}=\frac{{\mathrm{\mu <br><br>}}_i<br><br>\mathrm{gL}}{V^2}$

wherein μ

_i is the slip resistance at a walking speed and stride length at which slip commences.

10. The method of claim 7, wherein the anthropometric constant C_di is experimentally determined.

11. The method of claim 7, wherein the relationship between the walking speed and stride length is determined from:

$V=\sqrt{\frac{{\mathrm{\mu <br><br>}}_i<br><br>\mathrm{gL}}{C_{\mathrm{di}}}}.$

12. A method for determining a slip at heel strike on a dry walkway surface, comprising:

determining an anthropometric constant, C_di, for the dry walkway surface;

determining the occurrence of macroslip, wherein the macroslip occurs when

$\frac{C_{\mathrm{di}}<br><br>V^2}{\mathrm{gL}}\ge <br><br>{\mathrm{\mu <br><br>}}_i,$

wherein V is a forward walking speed of a center of mass of an individual, L is a stride length of the individual, g is an acceleration due to gravity, and μ

_i is a relevant dynamic coefficient of friction.

13. The method of claim 12, further comprising:

determining a relationship between the forward walking speed and the stride length of the individual, wherein the relationship between the forward walking speed and stride length is determined from

$V=\sqrt{\frac{{\mathrm{\mu <br><br>}}_i<br><br>\mathrm{gL}}{C_{\mathrm{di}}}};<br><br>$

and

plotting a curve of the relationship between the forward walking speed and stride length, wherein the macroslip is predicted to occur at a position on or above the curve of the relationship between the forward walking speed and stride length.

14. A method for determining a slip on a wet walkway surface having a fluid contaminant thereon, comprising:

determining an anthropometric constant, C_wi, for the wet walkway surface;

determining the occurrence of slip, wherein the slip occurs when

$\frac{C_{\mathrm{wi}}<br><br>{\mathrm{Mh}}^{*}<br><br>\stackrel{.}{x}}{A_c<br><br>L}-\frac{{\mathrm{\tau <br><br>}}_y<br><br>h^{*}}{\stackrel{.}{x}}\ge <br><br>\mathrm{\eta <br><br>}$

wherein M is a mass of an individual, h* is a depth of the fluid contaminant at a point of maximum pressure, {dot over (x)} is a horizontal shoe (foot) speed, τ

_y is a shear stress necessary to commence shearing in the fluid contaminant, A_c is an area of shoe contact with the interface at the commencement of macroslip, L is a stride length of the individual, and η

is an absolute viscosity of the fluid contaminant.

15. The method of claim 14, further comprising:

determining a relationship between a forward walking speed and the stride length for the individual;

wherein the horizontal shoe speed, {dot over (x)}, is equal to V, the forward walking speed at a center of mass of the individual at heel strike, and the relationship between the forward walking speed at a center of mass of the individual and stride length is determined from

$\frac{C_{\mathrm{wk}}<br><br>{\mathrm{Mh}}^{*}<br><br>V^2}{A_c<br><br>L}-\mathrm{\eta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>V-{\mathrm{\tau <br><br>}}_y<br><br>h^{*}=0;<br><br>\mathrm{and}$

plotting a curve of the relationship between the forward walking speed and stride length, wherein the slip is predicted to occur at a position on or above the curve of the relationship between the forward walking speed and stride length.

16. The method of claim 14, wherein τ

_y is determined from;

${\mathrm{\tau <br><br>}}_y=S_{\mathrm{fi}}<br><br>{\mathrm{\mu <br><br>}}_i<br><br>\frac{W}{A_c},$

wherein μ

_i is a relevant coefficient of friction, S_fi is a measure of the surface-footwear interaction represented as a fraction of the coefficient of friction, and W is a weight of the individual.

17. The method of claim 16, wherein for determining slip at push-off the relevant coefficient of friction μ

_i is a static coefficient of friction.

18. The method of claim 16, wherein for determining slip at heel strike the relevant coefficient of friction μ

_i is a dynamic coefficient of friction.

19. The method of claim 14, wherein the anthropometric constant C_wk for the wet surface is related to an anthropometric constant C_dk for the dry surface and determined from

$C_{\mathrm{wk}}=\frac{V^2}{{\stackrel{.}{x}}^2}$

C dk

wherein V is a forward walking speed at a center of mass of the individual.

20. The method of claim 14, wherein the anthropometric constant C_wi is experimentally determined.