Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR SIMULATING HEAD
IMPACTS FOR HELMET TESTING
FIELD OF THE INVENTION
[0001] The present invention relates to a method and apparatus for
simulating head
impacts for helmet testing.
BACKGROUND
[0002] Various activities, such as for example contact sports or military
operations,
require the use of helmets to attempt to protect participants from injury to
their heads
due to impact forces that may be sustained during such activities. As helmets
protect
against head injury, it follows that the science of head injury should
underlie the
development and testing of helmets to achieve the greatest effectiveness.
[0003] Concussion science is not well understood. Holborn, in 1943 and
1945,
proposed rotational acceleration as the primary concussive mechanism.
Gurdjian,
Lissner, and others in the 1950's and 60's however thought that deformation of
the skull
and pressure waves that propogated through the cranial vault were the most
offending
agents. In the 1970's and 80's experiments by Gennarelli, Ommaya, Thibault,
Adams
and others produced head injuries in monkeys and concluded that rotational
acceleration injuries produced diffuse, deep brain injury and that linear
acceleration
produced focal, superficial damage: concussive injury was more easily produced
with
rotational acceleration. Recent experiments by Hardy using high-speed bi-
planar x-ray
imaging to track the displacement of neutral-density radio-opaque markers in
the brain
of cadavers during impacts have shown that all head impacts produce a figure
of eight
movement within the brain involving both linear and rotational components.
Bayly et al
used human volunteers and MRI imaging to measure brain deformation and found
that
angular acceleration and rotation occurs with linear acceleration forces.
[0004] Helmet testing in sport became formalized with motor vehicle racing.
The
British Standards Institute produced documents in 1952 and 1954 pertaining to
the
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testing of motor vehicle helmets. They dropped a wooden block onto a helmeted
headform made of horizontally laminated birch, with a moisture of 12% and that
the
wood be straight, without defect or "dote" (Neuman). In 1956 the Sport Car
Club of
America asked George Snively to investigate helmet performance. He put helmets
on
cadavers and subjected them to severe impacts recording the presence or
absence of a
skull fracture. He improved his technique and in 1969 put helmets on a 12 lb.
K-1A
magnesium alloy head form and measured the acceleration to impact. In 1966 the
American Standards Association published standards using Snively testing
techniques
of impacting. a mobile metal head form but suggested that there should be time
limits
placed upon the impact. In 1969 the National Operating Committee for Athletic
Equipment (NOCSAE) published a standard for football helmets incorporating a
more
lifelike head form and a drop test paradigm. The helmeted head form is dropped
from a
prescribed distance onto an anvil and the central accelerometer measures the
deceleration. Maximum values of deceleration are used for certification. These
values
typically range from 275-300 x g (force of gravity). This has been a standard
method of
helmet testing ever since.
[0006] It has been recognized for some time that helmet testing has not taken
rotational acceleration into account and that helmets may protect against
certain types
of severe injury but may not be protecting against concussive injury. Science
has found
that a rotational force component is present in every impact but this is has
not been
properly accounted for in present helmet standards and certification.
Biokinetics and
Associates Ltd. is an engineering firm that was employed by the National
Football
league for helmet testing and developed a pendulum impact test onto a mobile
helmeted head form. Pellman Neurosurgery 58:78-96, 2006 reported that data
from this
has been used to update the NOCSAE drop test by placing the impactor and
helmeted
mobile head form in a horizontal plane. Results from these recent attempts
have been
questioned as to their reproducibility and clinical relevance.
[0006] A need exists for an improved method and apparatus for testing helmets.
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SUMMARY OF THE INVENTION
[0007] In accordance with an aspect of the present invention, there is
provided an
apparatus comprising: a frame; an impact delivery unit for delivering an
impact force; at
least one head form adapted to be mounted to said frame such that said impact
delivery
unit can deliver an impact force to a designated location on said at least one
head form;
said head form being configured to have a helmet installed thereon; said at
least one
head form being operable to be: (i) selectively rotated about a first axis of
rotation of a
plurality of axes of rotation such that when selected to be rotated about said
first axis of
rotation, the rotation of said at least one head form is constrained so that
said at least
one head form is only capable of rotation about said first axis of rotation of
said plurality
of axes; (ii) selectively rotated about a second axis of rotation of said
plurality of axes of
rotation such that when selected to be rotated about said second axis of
rotation, the
rotation of said at least one head form is constrained so that said at least
one head form
is only capable of rotation about said second axis of rotation; a measuring
system for
providing an indicator of the rotational acceleration of said at least one
head form when
rotated about each of said plurality of axes; wherein said system is operable,
when said
impact delivery unit delivers a plurality of impact forces to said designated
location on
said at least one head form, such that said at least one head form can be
selectively
constrained to rotate separately about each axis of rotation of said plurality
of axes, said
measurement system is operable to provide indicators of rotational
accelerations about
each of said plurality of axes of rotation of said at least one head form
during separate
rotations about each axis of said plurality of axes of rotation.
[0008] In accordance with an aspect of the present invention, there is
provided a
method of testing a helmet, the method comprising: providing an impact
delivery unit
having a force actuator for delivering an impact force; providing at least one
head form
such that said impact delivery unit can deliver an impact force to said at
least one head
form; impacting said at least one head form with said force actuator so as to
rotate said
at least one head form about a plurality of different axes of rotation in
sequence;
selectively rotating said at least one head form about a first axis of
rotation of said
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plurality of axes of rotation such that when selected to be rotated about said
first axis of
rotation, the rotation of said at least one head form is constrained so that
said at least
one head form is only capable of rotation about said first axis of rotation;
selectively
rotating said head faun about a second axis of rotation of said plurality of
axes of
rotation such that when selected to be rotated about said second axis of
rotation, the
rotation of said at least one head form is constrained so that said at least
one head form
is only capable of rotation about said second axis of rotation; obtaining an
indicator of
each acceleration of said at least one head form when rotated about each of
said
plurality of axes; from the indicators of acceleration, determining the
rotational
acceleration of each said head form during rotations about each of said
plurality of axes
of rotation.
[0009] In accordance with an aspect of the present invention, there is
provided a
method for testing a helmet, the method comprising: selecting a first head
form from a
plurality of head forms, each of said plurality of head forms each being
configured to
rotate only about a different axis of rotation of a plurality of axes of
rotation; installing a
helmet on said first head form; exerting a force against said helmet at a
designated
location to thereby cause said selected first head form to rotate about a
first axis of
rotation, wherein said first head form is constrained so that it is only
capable of rotation
about said first axis of rotation; measuring an indicator of rotational
acceleration about
said first axis of rotation of said selected first head form; determining a
rotational
acceleration of said selected first head form about said corresponding first
axis of
rotation; selecting a second head form from a plurality of head forms;
installing said
helmet on said second head form; exerting a force against said helmet at a
designated
location to thereby cause said selected second head form to rotate about said
second
axis of rotation, wherein said second head form is constrained so that it is
capable only
of rotation about said second axis of rotation; measuring an indicator of
rotational
acceleration about said second axis of said selected second head form;
determining a
rotational acceleration of said selected second head form about said second
axis of
rotation.
[0010] In accordance with an aspect of the present invention, there is
provided a
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method for testing a helmet, the method comprising: i. selecting a head form
adapted
and constrained to rotate about a first axis of rotation of a plurality of
axes of rotation; ii.
impacting the head form at a first designated location with a force actuator
operable to
exert a constant force against the head form to thereby cause the selected
head form to
rotate about the one axis of rotation; iii. measuring an indicator of
rotational acceleration
in relation to the first axis of the head form; iv. determining a baseline
rotational
acceleration in relation to the first axis of the head form; v. installing a
helmet on the
head form; vi. impacting the helmet installed on the head form at the first
designated
location with a force actuator operable to exert the constant force against
the head form
to thereby cause the selected head form to rotate about the one axis of
rotation; vii.
measuring an indicator of rotational acceleration in relation to the first
axis of the head
form; viii. determining a rotational acceleration of the selected head form
when the
helmet is installed on the head form; and ix. determining a degree of
protection against
rotational acceleration in relation to the first axis afforded by the helmet
for the impact
point; x. selecting a head form adapted and constrained to rotate about a
second axis of
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rotation of a plurality of axes of rotation; xi. impacting the head form at a
second
designated location with a force actuator operable to exert a constant force
against the
head form to thereby cause the selected head form to rotate about the second
axis of
rotation; xii. measuring an indicator of rotational acceleration of the head
form; xiii.
determining a baseline rotational acceleration in relation to the second axis
of the head
form; xiv. installing the helmet on the head form; xv. impacting the helmet
installed on
the head form at the second designated location with a force actuator operable
to exert
the constant force against the head form to thereby cause the selected head
form to
rotate about the one axis of rotation; xvi. measuring an indictor of
rotational acceleration
in relation to the second axis of the head form; xvii. determining a
rotational acceleration
in relation to the second axis of the selected head form when the helmet is
installed on
the head form; and xviii. determining a degree of protection against
rotational
acceleration in relation to the second axis afforded by the helmet for the
impact point.
[0011] In accordance with an aspect of the present invention, there is
provided a
method for testing a helmet, the method comprising: providing a head form
adapted and
constrained to rotate separately about a first axis of rotation and a second
axis of
rotation; generating a baseline rotational acceleration in relation to the
first axis of the
head form; generating a rotational acceleration in relation to the first axis
when the
helmet is installed on the head form; determining a degree of protection
against
rotational acceleration in relation to the first axis afforded by the helmet;
generating a
baseline rotational acceleration in relation to the second axis of the head
form;
generating a rotational acceleration in relation to the second axis when the
helmet is
installed on the head form; and determining a degree of protection against
rotational
acceleration in relation to the second axis afforded by the helmet.
[0012] In accordance with an aspect of the present invention, there is
provided a
method for comparing first and second helmets, the method comprising:
providing a
head form adapted and constrained to rotate separately about a first axis of
rotation and
a second axis of rotation; generating a rotational acceleration in relation to
the first axis
when the first helmet is installed on the head form; generating a rotational
acceleration
in relation to the first axis when the second helmet is installed on the head
form;
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comparing the rotational acceleration in relation to the first axis and the
second axis
between when the first and second helmets are installed on the head form.
[0013] In accordance with an aspect of the present invention, there is
provided a
method for comparing first and second helmets, the method comprising: i.
selecting a
first head form adapted and constrained to rotate about a first axis of
rotation of a
plurality of axes of rotation; ii. installing a first helmet on the first head
form; iii. exerting
a first force on the first helmet installed on the first head form at a first
designated
location to thereby cause the first head form to rotate about the first axis
of rotation; iv.
measuring an indicator of rotational acceleration in relation to the first
axis of the first
head form; v. determining a rotational acceleration in relation to the first
axis of the first
head form when the first helmet is installed on the first head form; and vi,
installing a
second helmet on the first head form; vii. exerting the first force on the
second helmet
installed on the first head form at the first designated location to thereby
cause the first
head form to rotate about the second axis of rotation; viii. measuring an
indicator of
rotational acceleration in relation to the second axis of the first head form;
ix.
determining a rotational acceleration in relation to the second axis of the
first head form
when the second helmet is installed on the first head form; and x. comparing
the
rotational accelerations in relation to the first axis between the first and
second helmets;
xi. selecting a second head form adapted and constrained to rotate about a
second axis
of rotation of a plurality of axes of rotation; xii. installing the first
helmet on the second
head form; xiii. exerting a second force on the first helmet installed on the
second head
form at a second designated location to thereby cause the second head form to
rotate
about the second axis of rotation; xiv. measuring an indicator of rotational
acceleration
in relation to the second axis of the second head form; xv. determining a
rotational
acceleration in relation to the second axis of the second head form when the
first helmet
is installed on the second head form; xvi. installing a second helmet on the
second head
form; xvii. exerting the force on the second helmet installed on the second
head form at
the second location to thereby cause the second head form to rotate about the
second
axis of rotation; xviii. measuring an indicator of rotational acceleration in
relation to the
second axis of the second head form; xix. determining a rotational
acceleration in
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relation to the second axis of the second head form when the second helmet is
installed on the head form; )oc. comparing the rotational accelerations in
relation to the
first axis between the first and second helmets.
[0014] In accordance with an aspect of the present invention, there is
provided an
apparatus comprising: at least one head form; a helmet configured for
attachment to
said at least one head form; an impact delivery unit for delivering an impact
force to said
helmet at at least one designated location when said helmet is attached to
said at least
one head form; said at least one head form being operable to be: (i)
selectively rotated
about a first axis of rotation of a plurality of axes of rotation such that
when selected to
be rotated about said first axis of rotation, the rotation of said at least
one head form is
constrained so that said at least one head form is only capable of rotation
about said
first axis of rotation of said plurality of axes; (ii) selectively rotated
about a second axis
of rotation of said plurality of axes of rotation such that when selected to
be rotated
about said second axis of rotation, the rotation of said at least one head
form is
constrained so that said at least one head form is only capable of rotation
about said
second axis of rotation; a measuring system for providing an indicator of the
acceleration of said at least one head form when rotated about each of said
plurality of
axes; wherein when said impact delivery unit delivers an impact to said at
least one
head form, said measurement device associated with each said head from
measures
the acceleration of each said head form during rotations about each of said
plurality of
axes of rotation.
[0015] Other aspects and features of the present invention will become
apparent to
those ordinarily skilled in the art upon review of the following description
of specific
embodiments of the invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In the figures which illustrate embodiments of the invention by
example only,
[0017] FIG. 1 is a front top perspective view of an apparatus in a first
configuration
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exemplary of an embodiment of the present invention;
[0018] FIG. 2 is an
enlarged partial front top perspective view of the apparatus of
FIG. 1 in the first configuration;
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[0019] FIG. 3 is an enlarged partial front top perspective view of the
apparatus of
FIG. 1 in the first configuration;
[0020] FIG. 4 is an enlarged partial rear top perspective view of the
apparatus of
FIG. 1 in the first configuration;
[0021] FIG. 5 is a rear top perspective view of the apparatus of FIG. 1 in
the first
configuration;
[0022] FIG. 6 is an enlarged partial side view of the apparatus of FIG. 1
in the first
configuration;
[0023] FIG. 7 is a top view of the apparatus of FIG. 1 in the first
configuration;
[0024] FIG. 8 is a rear side perspective view of the apparatus of FIG. 1 in
the first
configuration;
[0025] FIG. 9 is a front bottom perspective view of the apparatus of FIG. 1 in
the first
configuration;
[0026] FIG. 10 is a rear top perspective view of the apparatus of FIG. 1 in a
second
configuration;
[0027] FIG. 11 is an enlarged partial rear top perspective view of the
apparatus of
FIG. 1 in the second configuration;
[0028] FIG. 12 is an enlarged partial front top perspective view of the
apparatus of
FIG. 1 in the second configuration;
[0029] FIG. 13 is an enlarged partial side perspective view of the
apparatus of FIG. 1
in the second configuration;
[0030] FIG. 14 is a top view of the apparatus of FIG. 1 in the second
configuration;
[0031] FIG. 15 is a front top perspective view of the apparatus of FIG. 1
in a third
configuration;
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[0032] FIG. 16 is an enlarged partial front top perspective view of the
apparatus of
FIG. 1 in the third configuration;
[0033] FIG. 17 is a rear top perspective view of the apparatus of FIG. 1 in
the third
configuration;
[0034] FIG. 18 is an enlarged partial rear view of the apparatus of FIG. 1
in the third
configuration;
[0035] FIG. 19 is a top view of the apparatus of FIG. 1 in the third
configuration;
[0036] FIG. 20A is a diagram of a head form of the apparatus of FIG. 1;
[0037] FIG. 20B is a diagram of a head form of the apparatus of FIG. 1;
[0038] FIG. 20C is a diagram of a head form of the apparatus of FIG. 1;
[0039] FIG. 21A is a partial cutaway view of a head form and an impact
delivery unit
of the apparatus of FIG. 1;
[0040] FIG. 21B is a partial cutaway view of a helmeted head form and an
impact
delivery unit of the apparatus of FIG. 1;
[0041] FIG. 22 is a flow diagram illustrating steps in a method exemplary
of an
embodiment of the present invention;
[0042] FIG. 23 is a diagram illustrating motion of a head form of the
apparatus of
FIG. 1;
[0043] FIG. 24A is a diagram illustrating impact locations on a head form
of the
apparatus of FIG. 1;
[0044] FIG. 24B is a diagram illustrating impact locations on a helmeted head
form
of the apparatus of FIG. 1;
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[0045] FIG. 25 is a graph illustrating exemplary mean peak accelerations
measured
by the apparatus of FIG. 1;
[0046] FIG. 26A is a graph illustrating exemplary acceleration tracings for
axial
impacts measured by the apparatus of FIG. 1;
[0047] FIG. 26B is a graph illustrating exemplary acceleration tracings for
coronal
impacts measured by the apparatus of FIG. 1;
[0048] FIG. 26C is a graph illustrating exemplary acceleration tracings for
sagittal
impacts measured by the apparatus of FIG. 1;
[0049] FIG. 27 is a flow diagram illustrating steps in a method exemplary
of an
embodiment of the present invention;
[0050] FIG. 28A is a graph illustrating exemplary percent reductions in
axial
rotational acceleration for each of ten test helmets as measured by the
apparatus of
FIG. 1;
[0051] FIG. 28B is a graph illustrating exemplary percent reductions in
corona'
rotational acceleration for each of ten test helmets as measured by the
apparatus of
FIG. 1;
[0052] FIG. 28C is a graph illustrating exemplary percent reductions in
sagittal
rotational acceleration for each of ten test helmets as measured by the
apparatus of
FIG. 1;
[0053] FIG. 29A is a graph illustrating exemplary percent reductions in
axial
rotational acceleration at each of three impact locations for each of four
test helmets as
measured by the apparatus of FIG. 1;
[0054] FIG. 29B is a graph illustrating exemplary percent reductions in
coronal
rotational acceleration at each of six impact locations for each of four test
helmets as
measured by the apparatus of FIG. 1;
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[0055] FIG. 29C is a graph illustrating exemplary percent reductions in
sagittal
rotational acceleration at each of three impact locations for each of four
test helmets as
measured by the apparatus of FIG. 1; =
[0056] FIGS. 30A and 30B are diagrams illustrating motion of a head form of
the
apparatus of FIG. 1; and
[0057] FIG. 31 is a partial cutaway cross-sectional view of an
interconnection
mechanism of the apparatus of FIG. 1.
DETAILED DESCRIPTION
[0058] With reference to FIGS. 1-19 in which like reference designators refer
to like
elements, a test apparatus 100 exemplary of an embodiment of the present
invention is
shown in three configurations, wherein FIGS. 1-9 show apparatus 100 in a first
configuration, FIGS. 10-14 show apparatus 100 in a second configuration, and
FIGS.
15-19 show apparatus 100 in a third configuration.
[0059] As shown, test apparatus 100 may generally comprise a frame 102 formed
of
a plurality of support frame members 103 arranged substantially in a cuboid
shape.
Support frame members 103 may be made from one or more suitable materials such
as
a metal like steel or aluminium, so as to be able to withstand the loads
generated by
test apparatus 100. Also support members may include generally vertically
oriented
frame members 103a that are positioned to be able to also maintain test
apparatus in a
stable orientation and resist any significant movement while test apparatus
100 is being
operated. Frame 102 may also include pairs of vertically spaced upper and
lower
transverse frame members 103b and pairs of vertically spaced upper and lower
longitudinal frame members 103c. Together frame members 103a, 103b and 103c
are
interconnected together by suitable means such as for example nuts and bolts
to form a
rigid, strong and stable platform for other components of test apparatus 100.
[0060] In some embodiments, frame 102 may include pairs of leg extension
members 101a, 101b and a pair of wheels 105 mounted for rotation to frame 102
which
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can provide mobility for test apparatus 100. More specifically, as shown,
while leg
extension members 101b at one end of apparatus 100 may be just integral
extensions
of frame members 103a, leg extension members 101a at the opposite end of
apparatus
100 may be releasably attached plates that can be connected to the lower
portions of
frame members 103a in any suitable manner, such as by nuts and bolts. When it
is
desired to move apparatus 100, leg extensions 101a may be removed from
connection
with frame members 103a so that a pair of wheels 105 mounted on shafts secured
to
frame 102, may be lowered into contact with the floor surface. The opposite
end of
apparatus 100 may then be lifted so that the most of the weight of apparatus
100 can be
taken by the wheels 105. Test apparatus 100 can thus be made mobile when it is
desired to move test apparatus 100 from one location to another. When test
apparatus
100 is to be operated, frame 102 may be configured with leg extensions 101a,
101b
engaging the ground to provide a stable base for test apparatus 100.
[0061] Mounted to frame 102 may be two separate units: (1) an impact
delivery unit
generally designated as 199 and (2) a head form assembly unit 166.
[0062] Impact delivery unit 199 may include a piston assembly unit 104 mounted
to
the frame 102. Head form assembly unit 166 may include head form assemblies
106,
107 which may be interchangeably mounted to the frame 102. Head form
assemblies
106, 107 may comprise three separate head forms 120a, 120b and 120c. Head
forms
120a, 120b, and 120c may respectively each have a measurement device for
measuring acceleration, such as accelerometers 142a, 142b, 142c (see for
example
FIGS. 20A-20C and collectively designated as accelerometers 142). Impact
delivery
unit 199 including a piston assembly unit 104, as well as head form assembly
166, may
be configured on frame 102 and positioned in relation to each other, in such a
manner
that a force actuator (e.g. a piston device) 110 of piston assembly unit 104
is able to
exert impact forces on head forms 120a, 120b and 120c of head form assemblies
106,
107 as described in detail hereinafter.
[0063] Test apparatus 100 also includes a measuring system consisting of a
data
acquisition device 140 (FIG. 1) and suitable electronics, such as electrical
wiring or a
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wireless transmitter, for communicating signals from accelerometers 142
disposed
within the head form assemblies 106,107 to data acquisition device 140 for
processing,
also as described below.
[0064] As best shown in FIGS. 3 and 4, head form assembly 106 may include
first
and second head forms 120a, 120b with each being mounted on a respective neck
attachment member 121a, 121b. Each neck attachment member 121a, 121b may be
attached to a respective freely rotatable shaft 122a, 122b with each shaft
122a, 122b
being freely rotatably mounted to a respective bearing housing 185a, 185b
containing a
bearing to retain the shafts 122a, 122b, and permit the free rotation of the
shafts 122a,
122b. Each bearing housing 185a, 185b is mounted to one of two opposed
vertically
and longitudinally oriented base plates 123a, 123b. As shown, base plates
123a, 123b
may be interconnected to each other with transversely oriented tubular support
members 155a-d to form a rigid base support unit 156 that maybe supported on
and
releasably attachable to a rigid rectangular support frame unit 175. Frame
unit 175 may
have longitudinally oriented members 175b that are configured to rest on top
of and be
aligned with frame members 103c. Frame unit 175 may also include cross members
175a that span across frame members 103c. Base plates 123a, 123b, may each be
provided with notches to provide flanges that allow the base unit 156 to rest
upon top of
and be secured to frame 175. Base unit 156 can be secured to frame 175 using
nuts
and bolts or other suitable means. Although it may be possible to remove base
unit
from frame 175 in some embodiments, base unit 156 is not intended to be
removed
from frame unit 175 during normal operations. Interchange of neck attachments
is done
by exchanging or moving frame units 175 with a base unit attached. Frame unit
175
may be secured to frame members 103c of frame 102 in any suitable manner, such
as
by nuts and bolts.
[0065] As can be appreciated, head form 120a is adapted to simulate rotational
neck
movement in the direction of a sagittal plane (such as mid-sagittal plane P1
in FIG. 20A)
about the shaft 122a that is oriented and rotates about an axis Al (FIG. 14)
that is
perpendicular to such a sagittal plane of head form 120a. Similarly head form
120b is
adapted to simulate rotational neck movement in the direction of a coronal
plane (such
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as the mid-coronal plane P2 in FIG. 20B) about the shaft 122b that is oriented
and
rotates about an axis A2 (FIG. 7) of head form 120b.
[0066] Head
forms 120a, 120b may be held in the near vertical orientation shown in
FIGS. 1 to 14 by any suitable mechanism. For example, as illustrated only in
FIGS. 2
and 30A,B in relation to head form 120a, a steel plate 174 may have one end
attached
to shaft 122a by welding or other known attachment mechanisms, and positioned
such
that in the orientation shown in FIGS. 2 and 30A, the opposite end of plate
174 is able
to abut against a cross member 175a of frame unit 175, thus allowing head form
120a
to rest in a near vertical orientation and slightly leaned towards piston 110.
Impacts
may be kept perpendicular by elevating the vertical angle of piston 110
slightly to
compensate for the slight lean of head form 120a. As will now be appreciated,
subsequent to impact plate 174 will be lifted away from cross member 175a due
to
rotation of head form 120a, as shown in FIG. 30B. A similar mechanism may be
used
to hold head form 120b in the near vertical orientation shown in FIGS. 1 to
14.
[0067] While head forms 120a and 120b are shown to share a single common base
unit 156, it will be appreciated that head forms 120a and 120b may be
constructed
separately with each head form 120a, 120b having its own base unit so that
each head
form 120a, 120b may be individually and separately mounted to frame 102.
[0068] As best shown in FIG. 15, the other head form assembly 107 may include
a
single head form 120c mounted on a shaft 122c, with shaft 122c being freely
rotatably
mounted to a respective bearing housing 185c containing a bearing to retain
the shaft
122c and permit the free rotation of the shaft 122c. Bearing housing 185c may
be
suitably mounted such as with nuts and bolts to a base plate 124. Base plate
124 may
be removably attached to the same rigid rectangular frame 175 as unit 156 can
be
attached to. Alternatively head form assembly 107 may utilize an alternate
rectangular
frame constructed like frame 175, to enable the head form assembly 107 to be
releasably secured to rectangular support frame 175 using any suitable manner,
such
as by nuts and bolts. As can be appreciated, head form 120c is adapted to
simulate
rotational neck movement in an axial plane (such as axial plane P3 in FIG.
20C) about
14
CA 02735615 2011-03-31
the shaft 122c that is oriented and rotates about a vertical axis A3 (see FIG.
18) that is
perpendicular to such an axial plane of head form 120c. Head form 120c is
positioned
with face anterior prior to each impact as shown in FIG. 15. The rotation of
head form
120c about the vertical axis (in or in alignment with an axial plane) is
unconstrained.
[0069] Head forms 120a, 120b, 120c (collectively, head forms 120) may be sized
and shaped to simulate a human head and, as described in more detail below,
head
forms 120 are adapted to receive various types of helmets for testing. Each
head form
120 may be, for example, A NOCSAE (National Operating Comittee on Standards
for
Athletic Equipment) standard anthropometric humanoid head form, medium size,
corresponding to an average adult head.
[0070] As shown in FIGS. 20A-20C, disposed within head forms 120 may be
accelerometers 142 for measuring acceleration in head forms 120. Apparatus 100
may
include suitable electronics, such as electrical wiring, or a wireless
transmitter, for
communicating signals from accelerometers 142 to data acquisition device 140
that is
adapted to receive the signals and then conduct the processing of the data
contained in
the signals. In some embodiments accelerometers 142 are standard uni-axial
digital
accelerometers, such as Model 2260-100 accelerometers manufactured by Silicon
Designs Inc. having a differential output range of +/- 4V and a sensitivity of
40mV/g.
Though each head form 120 is shown having only one accelerometer 142, it will
be
appreciated that additional accelerometers may be used for obtaining
acceleration
measurements. Data acquisition device 140 may be, for example, a computer
having a
USB-1208LS digital I/O module manufactured by Measurement Computing
Corporation
connected thereto. Accelerometers 142 are operable to be able to measure a
linear
acceleration imparted in a particular linear direction. When mounted in the
head form,
the accelerometer may be positioned so that it measures the linear
acceleration in a
direction that is aligned with its respective direction of rotational motion.
For example, as
shown in FIGS. 20A, 20B, 20C, each accelerometer 142a, 142b, 142c is aligned
with
one of the respective planes Pi, P2 or P3 of rotation of its corresponding
head form
120a, 120b, 120c. As shown, each accelerometer 142 may be positioned to
correspond to a point of maximum tangential linear acceleration of its
corresponding
CA 02735615 2011-03-31
head form 120. Thus, for axial rotation accelerometer 142c may be positioned
in the
forehead region of head form 120c, whereas for sagittal and coronal rotations,
accelerometers 142a and 142b may be positioned in the crown region of head
forms
120a and 120b, respectively.
[0071] Having described the head form assembly unit 166, the impact
delivery unit
generally designated as 199 is now described. Impact delivery unit 199 may
include a
force actuator, such as a pneumatic piston device 110, mounted to a
positioning and
support apparatus 189.
[0072] Piston device 110 may be a standard pneumatic piston device
configured to
propel a piston housed in a cylinder outwardly in an axial direction at a
predetermined
rate of acceleration. For example, piston device 110 may include a PARKER
pneumatic
cylinder with a 2.00 inch bore housing a stainless steel piston with a 6.00
inch stroke
length, with model number 2.00DSRY06.00 that can be propelled forward by air
pressure. A stainless steel impacting weight, weighing 1.3 kg may be attached
to the
end of the piston may be used as an impact surface and may provide a increased
mass
to enhance the impact force exerted by the piston. Compressed air to drive the
piston
may be supplied from a compressor (not shown), and the motion of the piston
may be
controlled by a dual action unrestricted flow valve (not shown) which, when
activated
using an electrical switch (not shown), causes the piston to be propelled
forward and
subsequently retract.
[0073] Positioning and support apparatus 189 may be configured to support
piston
device 110 and may be operable to move the position and orientation of piston
device
110 relative to the head forms 120 of head form assembly unit 166 when the
head
forms 120a, 120b, 120c are in turn mounted to frame 102.
[0074] Positioning and support apparatus 189 will now be described with
particular
reference to FIGS. 2, 3 and 7. As shown, positioning apparatus 189 includes an
angle
alignment support plate 112 to which piston device 110 is mounted with nuts
and bolts
or other known attachment mechanisms. Angle alignment plate 112 is pivotally
16
CA 02735615 2011-03-31
mounted to a height (z-direction) alignment plate 113. More specifically,
plate 112 is
pivotally connected at one end to a shaft 183a passing through a transverse
aperture in
the plate 112. Shaft 183a is fixed against translational movement relative to
plate 113,
but permits plate 112 to be able to pivot around shaft 183a relative to plate
113. Plate
112 is connected at an opposite end to a shaft 183b that passes through
another
transverse aperture in plate 112. Shaft 183b has a first end extending out
from plate
112 and an opposite end that is received into a curved slot 181 through plate
113. Thus
plate 112 with piston 110 mounted thereto can pivot about a transverse axis in
the Y-
direction so that the vertical angle of piston 110 can be varied.
[0076] An inner end of each shaft 183a, 183b may be received in respective
height
alignment tracks 114 mounted to a longitudinally and vertically oriented
surface 115a of
a piston support structure 115 of the positioning apparatus 189 to allow the
vertical
direction Z position of plates 113, 112 and piston 110 to be adjusted. Piston
support
structure 115 may include a hand crank 111a attached to a threaded rod 171.
Threaded rod 171 may be fed through a threaded block (not shown) affixed to a
rear
surface of plate 113. By manual adjustment of crank lila the position of
height
alignment plate 113 in the vertical Z direction along height alignment tracks
114 can be
varied.
[0076] FIG. 31 is a cross-section view illustrating an exemplary
interconnection
mechanism 186 that may be used to interconnect plate 113 and tracks 114 in a
manner
that allows both for sliding movement of plate 113 on tracks 114 and for
securing the
position of plate 113 relative to tracks 114. As shown, an inner end of shaft
183a is
disposed with a flange 182 adapted to slide inside a track 114 and to hold the
inner end
of shaft 183a inside the track 114. Shaft 183a passes through apertures in
plates 113
and 112, and terminates at an outer end disposed with a handle 119. Shaft 183a
has a
threaded portion 184 around which a threaded nut 188 (see also FIG. 3) is
received.
Threaded nut 188 may be manually tightened such that nut 188 will exert a
force
against plate 112 to thereby hold plate 112 against plate 113 and plate 113
against
tracks 114. Thus, interconnection mechanism 186 may be used for releasably
securing
the angular position of plate 112 and piston 110 relative to plate 113 as well
as the
17
CA 02735615 2011-03-31
vertical position of plates 113, 112 and piston 110 along tracks 114. It will
be
appreciated however that the configuration and interconnection of plate 113
and tracks
114 may be accomplished by any other suitable mechanism that allows for
sliding
movement of the plate 113 on tracks 114.
[0077] Positioning apparatus 189 also includes a longitude (x-
direction) alignment
plate 116 slidably mounted to x-direction tracks 117 and a hand crank 111b
attached to
a threaded rod 151. The configuration and connection between plate 116 and
tracks
117 can be similar or the same as that with plate 113 and tracks 114. Piston
support
structure 115 is mounted to longitude alignment plate 116, which as shown may
be in a
generally transverse and longitudinal orientation. Threaded rod 151 may be fed
through
a threaded block (not shown) affixed to a bottom surface of alignment plate
116. This
allows manual adjustment of the position of longitude alignment plate 116
along the x-
direction tracks 117.
[0078] Positioning apparatus 189 also includes a latitude (y-
direction) alignment
plate 130 slidably mounted to y-direction tracks 118 and a hand crank 111c
attached to
a threaded rod 161. The configuration and connection between plate 130 and
tracks
118 can be similar or the same as that with plate 113 and tracks 114. Tracks
117 are
mounted to latitude alignment plate 130. Threaded rod 161 may be fed through a
threaded block (not shown) affixed to a bottom surface of alignment plate 130.
This
allows manual adjustment of the position of latitude alignment plate 130 along
the y-
1 direction tracks 118. Tracks 118 are mounted to frame 102.
[0079] As will now be appreciated, piston assembly 104 is adapted such that
the x-,
y- and z-direction coordinates of piston 110 may be manually adjusted using
hand
cranks 111a,111b,111c (collectively, hand cranks 111), and the vertical angle
of piston
110 may be manually adjusted by pivoting angle alignment plate 112 relative to
height
alignment plate 113. Although in this embodiment the horizontal angle of
piston 110 is
not adjustable, in other embodiments it would be possible to have this angle
be
adjustable instead of or in addition to the vertical angle. A plurality of
manual clamps
119 (FIGS. 4, 8 and 10) are manually operable to secure the various alignment
plates in
18
=
CA 02735615 2011-03-31
position once an adjustment is complete, for example by a mechanism similar to
interconnection mechanism 186 hereinbefore described in relation to plates
112, 113
and alignment tracks 114.
[0080] As best shown in FIGS. 6 and 7, piston assembly unit 104 also includes
an x-
direction digital scale 108a, a y-direction digital scale 108b, and a z-
direction digital
scale 108c (collectively, digital scales 108) configured to provide x, y and z
position
measurements, respectively, to a display 109 (FIG. 5). Display 109 is a
standard display
such as a liquid crystal display (LCD) model Positron 3A by Lathemaster or the
like.
Display 109 is configured to display the x, y and z coordinates received from
digital
scales 108 through a connection provided for example by hardwire, between each
digital scale 108 and display 109. The angle of piston 110 can also be
measured for
example manually using a protractor. The x, y and z coordinates and the angle
can be
appropriately recorded such as by entering them manually into device 140.
[0081] The components of frame 102, piston assembly unit 104, and head form
assemblies 106,107 may be made of any suitable material having the requisite
strength
and durability characteristics to function in test apparatus 100, and are
preferably
formed of metal such as steel, aluminium, or the like.
[0082] In the first configuration shown in FIGS. 1-9, head form assembly
106 is
mounted to frame 102 and is oriented so that head form 120b is aligned with
piston
device 110, where activation of piston 110 results in an impact of the piston
against
head form 120b.
[0083] In the second configuration shown in FIGS. 10-14, head form assembly
106 is
mounted to frame 102 and is oriented so that head form 120a is aligned with
piston 110,
where activation of piston 110 results in an impact of the piston against head
form 120a.
[0084] In the third configuration shown in FIGS. 15-19, head form assembly
107 is
mounted to frame 102 and is oriented so that head form 120c is aligned with
piston 110,
where activation of piston 110 results in an impact of the piston against head
form 120c.
19
CA 2735615 2017-03-31
[0085] Accordingly, the first configuration of apparatus 100 may be used
for impact
tests with simulated rotational neck movement limited to movement along or in
alignment with a coronal plane, the second configuration of apparatus 100 may
be used
for impact tests with simulated rotational neck movement limited to movement
along or
in alignment with a sagittal plane, and the third configuration of apparatus
100 may be
used for impact tests with simulated rotational neck movement limited to
movement
along or in alignment in an axial plane. Further, the position of the point of
impact on
the head form and the angle of impact may be adjusted with precision using
positioning
apparatus 199 to appropriately position piston 110. The actual position in 3-D
space of
the piston 110 can be displayed on display 109 for each impact. In this way
testing can
be standardized between helmets and multiple impact positions can be
accurately
calibrated for each helmet to provide a complete characterization of the
helmet's force
attenuation properties.
[0086] The energy produced by the piston 110 will depend in part upon the
weight of
the piston being driven by the cylinder, the amount of air pressure used to
propel the
piston, and the length along the piston stroke at which the impact occurs. By
keeping
these variables constant the impact force exerted upon each helmet can be
maintained
substantially consistent. For example, with a piston having a weight of about
1.3kg, air
pressure at 125 psi and impact occurring at 4.75 inches along the piston
stroke length,
with the angle of the piston set such that the piston travels perpendicularly
to the impact
surface of the head form, the piston may produce a suitable force against head
forms
120. These values, and the subsequent accelerations produced in head forms
120, are
expected to be consistent with concussion level forces in prior experimental
situations,
such as those disclosed in Zhang, Yang, King, "A Proposed Injury Threshold for
Mild
Traumatic Brain Injury", Journal of Biomechanical Engineering, April 2004
(hereinafter
"Zhang et al."); Halstead PD, Alexander CF, Cook EM, Drew RC, "Hockey headgear
and the adequacy of current designs and standards", Ashare AB, Safety in Ice
Hockey,
American Society for Testing and Materials, Philadelphia: 1998:93-101; and in
McIntosh
A, McCrory P, Comerford J, ''The dynamics of concussive head impacts in rugby
and
Australian rules football", Med Sci Sports Exerc 2000, 32(12): 1980-1984. An
CA 2735615 2017-03-31
exemplary set of test data that may be generated by apparatus 100 from impact
tests
configured according to these values is depicted in FIGS. 25 26A-C, 28A-C and
29A-C,
as described in more detail below.
[0087] In order to maintain the length along the piston stroke at which
impact occurs
consistent between impacts against an unhelmeted head form versus impacts
against a
helmeted head form, the position of piston 110 can be adjusted to account for
the
thickness of the helmet. For example, as shown in FIGS. 21A and 21B, impacts
against unhelmeted head form 120a may occur at a length L1 along the piston
stroke,
and impacts against helmeted head form 120a may occur at length L2 along the
piston
stroke. As shown, with helmet 150 having a thickness T, the longitudinal
position of
piston 110 can be adjusted away from head form 120a by a distance Tin order to
ensure L2 is equal to L1. The longitudinal position of piston 110 can be
similarly
adjusted to account for variances in thicknesses of different helmets. It
should be noted
that, while adjustment of the longitudinal position of piston 110 allows the
length along
the piston stroke at which impact occurs to be maintained consistent, there
may be
variations in the angle of impact to the helmet surface, due to variances in
sizes and
shapes of different helmets. While it will be appreciated that some of these
variations
can be accounted for by adjusting the angle and position in 3-D space of
piston 110, in
the presently disclosed embodiment these variations are not accounted for as
the shape
of the helmet is considered to contribute to the overall effect of the helmet
in potentially
reducing rotational accelerations when an impact force is directed to one or
more
particular locations on the head form.
[0088] Broadly, a helmet impact test using apparatus 100 may be performed
according to the steps shown in FIG. 22. Specifically, at one time, one of the
three
head forms 120 may be selected (step 201) for the test and mounted to frame
102
(step 202). A helmet 150 (FIG. 23) to be tested may then be installed onto the
mounted
head form 120 (step 203). A designated impact location 152 on helmet 150 may
then
be configured by adjusting the x, y and z coordinates and the angle of travel
of piston
110 (step 204). The air pressure for the piston may be generated by a canister
compressor, with the air pressure entering the pneumatic system being
displayed on an
21
CA 02735615 2011-03-31
analog gauge. Once the piston is in the desired position and the system is at
the
desired air pressure, the piston 110 may then be activated such as for example
by a
manual switch to thereby cause the piston 110 to accelerate toward the helmet
and
impact the helmet at the designated impact location (step 205), causing
helmeted head
form 120 to swing about shaft 122 and thereby generate a degree of
acceleration in the
mounted head form 120. An accelerometer 142 disposed within the mounted head
form
120 measure the level of acceleration resulting from the impact (step 206) and
communicate those measurements to data acquisition device 140 and then to a PC
for
processing (step 207). Steps 201 to 207 may be repeated multiple times for
each of the
three head forms 120 and for each of a number of desired impact points, as
described
in more detail below.
[0089] Rotational acceleration of a head form 120 during impact may be
ascertained
from measurements obtained by a corresponding accelerometer 142. It will be
appreciated that the accelerometer may be able to deliver acceleration
readings over a
period of time during the rotation of the head form and will during that time
period
deliver a series of measurements of acceleration, which will include a maximum
acceleration.
[0090] As noted above, in some embodiments accelerometers 142 may be uniaxial
digital accelerometers. Specifically, the maximum linear acceleration of a
head form 120
may be measured by placing a uni-axial accelerometer 142 at a point on the
head form
120 furthest away from the axis of rotation, i.e. a point furthest away from
the axis of
shaft 122a, 122b or 122c, as the case may be. For example, as shown in FIGS.
20A,
20B, and 20C, each accelerometer 142 is positioned to correspond to a point of
maximum tangential linear acceleration of its corresponding head form 120.
Thus, for
axial rotation accelerometer 142c is positioned in the forehead region of head
form
120c, whereas for sagittal and coronal rotations, accelerometers 142a and 142b
are
positioned in the crown region of head forms 120a and 120b, respectively. It
will be
appreciated however that accelerometers 142 may be placed in any other
suitable
position within head forms 120. In some embodiments, accelerometers may be
placed
on an outer surface of the head form.
22
CA 02735615 2011-03-31
[0091] The orientation of the accelerometers can be selected such that they
measure an acceleration that is tangential to the curve defined by the radius
from the
axis of rotation. The linear accelerations can be directly converted to
rotational
acceleration (e.g. at data acquisition device 140) by dividing the linear
acceleration by
the radius from the centre of rotation to the location of measurement of the
linear
acceleration (e.g. a location on the accelerometer):
aT
=- ¨
r
where:
a = angular acceleration
aT = tangential acceleration
r = radius of curvature
[0092] As will now be appreciated, multiple points of impact may be tested for
any
given helmet. For example, the points of impact may be chosen according to
research
published in Pellman E.J., Viano D.C., Tucker A.M., Casson I.R., "Concussion
in
professional football: location and direction of helmet impacts ¨ Part 2",
Neurosurgery
2003; 53:1328-1341, the contents of which are incorporated by reference
herein.
Pellman et al. analysed video footage of severe impacts during National
Football
League (NFL) games between 1996 and 2002, and catalogued 182 impacts based on
the location of initial contact on the players' helmets. Although Pellman et
al. only
looked at head impacts in the context of football helmets, the Pellman et al.
impact
location classification scheme may be used for all helmet types to be tested.
For
example, impact locations depicted in FIGS. 24A and 24B may be used for
standardized testing. Specifically, and as described in more detail below,
impact
locations illustrated by arrows 1, 2 and 3 may be used for impact tests
relating to
accelerations occurring in or along a sagittal plane, impact locations
illustrated by cross-
hatched circles 1, 2, 3, 4, 5 and 6 may be used for impact tests relating to
accelerations
occurring in or along a coronal plane, and impact locations illustrated by
clear circles 1,
2 and 3 may be used for impact tests relating to accelerations occurring in or
along an
axial plane. Advantageously, use of a universally applicable classification
system such
23
CA 02735615 2011-03-31
as the one established by Pellman et al. allows test results to be reported in
a
standardized fashion.
[0093] In order to be concordant with established scientific literature,
apparatus 100
is preferably adapted to meet concussive level rotational accelerations as
reported by
Zhang et al. An angular acceleration of 4.6x103 rad/s2 was found by Zhang et
al. to be
sufficient to produce 25% chance of a concussion. When testing sports helmets
in
particular, impact forces simulated should not be so high as to be clinically
irrelevant for
the usual type of impact/injury experienced during amateur level play. It will
be
appreciated that impact velocities produced by apparatus 100 may be adjusted
by
varying the piston acceleration and/or velocity and/or the weight/mass of
piston 110.
[0094] Prior to testing one or more helmets, apparatus 100 may be
calibrated in
each of the three axes (in each of the three orthogonal planes) and in
different impact
locations by consecutively impacting each unhelmeted head form 120 at each
impact
location with varying piston air pressures and with different piston impact
weights until
peak angular accelerations of 4000 rad/s2 are achieved. The resulting
pressures and
weights for each plane that produces peak angular accelerations of 4000 rad/s2
may
subsequently be used during testing of one or more helmets.
[0095] Five consecutive impacts, for example, may be used in order to reach a
level
of accuracy wherein variability in peak acceleration falls within +/- 2g's.
This level of
accuracy was chosen as an arbitrary measure, and the accuracy may be increased
by
increasing the number of consecutive impacts performed. However, five impacts
can
provide an acceptable level of accuracy and allow efficient testing of
helmets.
Exemplary mean peak accelerations for five consecutive impacts at each impact
location of FIG. 24A are illustrated by the bar graph shown in FIG. 25.
Specifically, bars
Al, A2 and A3 represent mean peak accelerations in an axial plane for five
consecutive
impacts at each of the impact locations on the head forms illustrated in FIG.
24A by
clear circles 1, 2 and 3, respectively; bars Cl, C2, C3, C4,C5 and C6
represent mean
peak accelerations in a corona' plane for five consecutive impacts at each of
the impact
locations illustrated in FIG. 24A by cross-hatched circles 1, 2, 3, 4, 5 and
6,
24
CA 02735615 2011-03-31
respectively; and bars S1, S2 and S3 represent mean peak accelerations in a
sagittal
plane for five consecutive impacts at each of the impact locations illustrated
in FIG. 24A
by arrows 1, 2 and 3, respectively. The repeatability of the acceleration
response of
head form 120 to five separate impacts is illustrated by the exemplary axial,
coronal,
and sagittal tracings shown in FIGS. 26A, 26B and 26C, respectively.
[0096] Test apparatus 100 may be used to measure and compare the degree of
protection against rotational acceleration afforded by different helmets
according to the
steps shown in FIG. 27. As shown, initially one of the three head forms 120 is
selected
for testing and is mounted to frame 102 (step 302). Next, a designated impact
location,
or impact point, is configured (step 304) and a baseline acceleration profile
for the
designated location on the unhelmeted head form 120 is recorded (steps 306 to
307).
Specifically, the unhelmeted head form 120 is impacted multiple times (e.g.
five times)
at the configured designated location (step 306), with other impact variables
(e.g. air
pressure, piston stroke length, and piston head weight) being kept constant.
For each
impact, a peak acceleration produced by the impact as measured by an
accelerometer
142 of mounted head form 120 is received and recorded by data acquisition
device 140
(step 307). The degree of variance in the impact measurements indicates the
precision
of apparatus 100 for that impact point, and may in some embodiments fall in
the range
of +/- 2 g's. Next, one of a group of helmets being compared is selected and
installed
onto the mounted head form 120 (step 308), and an acceleration profile for the
helmet is
recorded (steps 310 to 312). Specifically, the helmeted head form 120 is
impacted
multiple times (e.g. five times) at the configured designated location (step
310), with
other impact variables (e.g. air pressure, piston stroke length, and piston
head weight)
being kept constant. For each impact, a peak acceleration produced by the
impact as
measured by an accelerometer 142 of mounted head form 120 is received and
recorded
by data acquisition device 140 (step 312).
[0097] Steps 308 to 312 are repeated for each helmet in the group of helmets
being
compared (step 314) so that an acceleration profile for each helmet in the
group of
helmets being compared is recorded.
CA 02735615 2011-03-31
[0098] Steps 304 to 314 are repeated for each impact location of a
predetermined
set of impact locations (step 316) so that, for each helmet being compared, an
acceleration profile for each location is recorded. As will now be
appreciated, the
impact locations illustrated in FIG. 23A may be used as the predetermined set
of impact
locations.
[0099] Steps 302 to 316 are repeated for each head form 120 (step 318) so
that, for
each helmet being compared, acceleration profiles for each axis of rotation
are
recorded.
[00100] Once acceleration profiles for each helmet have been determined, a
degree of protection against rotational acceleration afforded by each helmet
may be
calculated and compared for each impact location (step 320). Specifically, for
any given
impact location, any change in acceleration between the unhelmeted (baseline)
acceleration profile and the acceleration profile for the helmeted head form
may be
attributed to protection afforded by the helmet itself. Thus, protection
afforded by the
helmet at each impact location is characterized. More specifically, mean peak
acceleration measurements for each impact location taken from both the
baseline
profile and the helmet profile may be compared. Similarly, mean peak
acceleration
ratios for a given impact location between any two helmets may be compared
using the
same approach. By repeating the calculations, it is possible to contrast
helmet
protection afforded by all of the helmets tested. As noted, this process can
be repeated
for each of the three head forms 120a, 120b, 120c to provide mean peak
acceleration
measurements for each of the three axes (and corresponding sagittal, coronal
and axial
planes).
[00101] It should also be noted that mean peak rotational accelerations
between
different helmets could be compared directly with each other instead of
comparing
percentage reductions relative to a baseline.
[00102] To determine whether certain classes of helmets provide better
rotational
acceleration protection, the tested helmets may be divided into categories,
and
26
CA 02735615 2011-03-31
Spearman rank correlations may then be used to determine if some categories
offer
better rotational protection. For example, to determine whether higher priced
helmets
provide better rotational acceleration protection, the tested helmets may be
divided into
four categories according to price: low, medium, high, and elite. One can then
compare
rotational acceleration protection afforded by a particular helmet, as
evidenced by the
reduction of mean peak acceleration from the unhelmeted baseline, and analyse
whether higher priced helmets have a tendency towards better impact
protection.
[00103] Once measurements have been gathered, a one-way analysis of
variance
(ANOVA) may be conducted to compare the overall effect of each test helmet at
reducing rotational acceleration compared to the unhelmeted head form. This
can be
done by comparing the mean peak acceleration at a particular impact location
for a
particular helmet to the unhelmeted mean peak acceleration at the same impact
location with the same impact parameters. Since all impact variables are kept
constant,
the effect of any reduction in mean peak acceleration is due to the protective
qualities of
the helmet.
[00104] A post hoc comparison using Dunnett's HSD test may be used to
analyse
whether each test helmet provides a statistically significant reduction in
rotational
acceleration at each location when compared to the unhelmeted head form. An
exemplary set of data that may result from tests conducted on an exemplary set
of test
helmets H1 through H10 is shown in FIGS. 28A, 288, and 28C. Specifically, the
data
can be presented in graph form as the percent reduction in rotational
acceleration for
each test helmet. In this exemplary set of data, it is shown that all test
helmets
significantly reduced rotational acceleration compared to the unhelmeted head
form.
[00105] Similarly, acceleration differences between test helmets in each of
the
planes and impact locations may be assessed. Specifically, a one-way ANOVA may
be
conducted to compare the percent reduction in rotational acceleration between
each
test helmet at each impact location and plane. A post hoc comparison using
Tukey's
HSD test may be used to analyze whether there are statistically significant
differences
in rotational acceleration between test helmets at each impact location within
a given
27
CA 02735615 2011-03-31
plane. In this way the protective qualities of a helmet can be dissected to
specific impact
locations to allow specific design and construction improvements and enhance
helmet
safety.
[00106] An exemplary set of data that may result from tests conducted on an
exemplary set of test helmets H1 through H4 is shown in FIGS. 29A, 29B, and
29C.
Specifically, the data is presented in graph form as the percent reduction in
rotational
acceleration for each test helmet at specific impact locations and planes,
where each
graph represents one of the three planes and the impact locations Al, A2, A3,
Cl, C2,
etc represent the impact locations shown in FIGS. 24A and 24B.
[00107] In addition, acceleration differences within a particular test
helmet at each
plane may also be assessed. Specifically, a one-way ANOVAs may be conducted to
compare the percent reduction in rotational acceleration provided by a
particular test
helmet at each impact location in each plane.
[00108] In general, helmets consist of a shell, foam padding, and a chin
strap. It is
widely believed that the shell disperses the impact force over a larger
surface area and
the foam padding reduces acceleration forces. The ideal shell should be: 1)
light, 2)
crack resistant, 3) allow proper ventilation, 4) disperse the impact force
over a larger
surface area, and 5) have a low level of friction to reduce rotational forces.
It is known
that helmet foam reduces linear acceleration forces. Therefore, a thicker and
denser
foam within the shell, provides greater protection. Thus, a preferred helmet
should
contain a light, smooth, round shell and very thick foam. Practicalities
intervene as
foam thickness is limited by weight and volume in the design of a wearable
sport
helmet. Various manufacturers produce helmets of varying shells, contours, and
ventilation spaces. They also have different foam types and arrangements
within the
shell.
[00109] It will be also appreciated that when a given force is exerted on
the
impacted head form with a helmet attached, the acceleration of the actual head
form
with the helmet mounted thereon, will also be dependent upon several factors
including
28
CA 02735615 2011-03-31
the total mass of the head form and helmet as well as the amount of cushioning
effect of
the force that occurs in the interaction between the piston, outer helmet
shell, inner
foam cushioning and head form. The precise impact and absorption interactions
that
occur with the helmet and head form are difficult to precisely analyse.
However it will be
expected that all other factors being equal, the heavier a helmet is, the
lower will be the
resultant acceleration of the helmet and head form combination (when the
helmet is
secured to the head form). When testing as between several different helmets,
the
mass of each head form will remain constant between different helmets during
testing
but the mass of the different helmets may vary. Therefore, a heavier helmet
can be
expected to have a lower acceleration than a lighter helmet. The foregoing
test
apparatus and methods only measure the actual accelerations experienced by the
head
form when cushioned by the helmet. The apparatus and methods do not
distinguish
between or identify the actual basis or mechanism why the head forms may have
experienced different accelerations when protected by each of the helmets.
Advantageously, the apparatus and methods disclosed herein allow helmet
testing and
evaluation to be accomplished by breaking down each event into specific
isolated
movements, and thus producing quantifiable, accurate, reliable and
reproducible
measurements of rotational acceleration at injury-relevant impact locations
and planes
with various degrees of impact force. Such measurements allow comparison of
differences in rotational force protection at specific locations in
commercially available
helmets, and enables modifications to be made and retested to produce more
focused
and measurable improvements. Knowing the importance of rotational acceleration
in
concussion causation and the fundamental lack of reliable and reproducible
test
procedures that simulate rotational impacts to helmets, the methods and
apparatus
described above bridge the fundamental gap that exists between the science of
concussion biomechanics and the engineering of helmet testing.
[00110] While apparatus 100 has been described as including three head
forms
120, it will be appreciated that in other embodiments fewer head forms may be
used.
For example, a single head form 120 may be used in conjunction with a suitable
mechanism for selectively limiting rotational movement of the single head form
120 to
29
CA 02735615 2011-03-31
three separate axes each perpendicular to one of a sagittal, a coronal and an
axial
plane, respectively.
[00111] Other modifications will be apparent to those skilled in the art
and,
therefore, the invention is defined in the claims.
[00112] Although not specifically described in detail herein, suitable
modifications
may be made to the embodiments described by persons skilled in the art
depending on
a particular application. Of course, the foregoing embodiments are intended to
be
illustrative only and in no way limiting. The described embodiments of
carrying out the
invention are susceptible to many modifications of form, arrangement of parts,
details
and order of operation. The invention, rather, is intended to encompass all
such
modification within its scope, as defined by the claims.
[00113] When introducing elements of the present invention or the
embodiments
thereof, the articles "a," "an," "the," and "said" are intended to mean that
there are one
or more of the elements. The terms "comprising," "including," and "having" are
intended
to be inclusive and mean that there may be additional elements other than the
listed
element.
