BACKGROUND OF THE INVENTION

This invention relates to a method for testing personal safety accessories such as helmets. This invention also relates to associated apparatus for carrying out testing protocols.

It has been widely reported during the past 20 years that the collisions experienced by participants in contact sports and other potentially injurious endeavors are often strong enough to give rise to mild traumatic brain injuries (MTBI) such as concussions. It is a common occurrence in American football for impact speeds to exceed 20 mph (9 m/s), creating linear head accelerations exceeding 100 g's and concussion risks exceeding 70%. This has created a health hazard of epidemic proportions, with several million incidents of MTBI occurring yearly at all levels of play in all sports. (American football has the highest incidence, and it is estimated that nearly one-third of all retired NFL players will develop some level of long-term neurological disease.) In response to the MTBI epidemic, more protective helmets have been introduced and used by participants in sports and other endeavors such as car and bicycle racing, but the frequency of MTBI has remained alarmingly high. It was recently reported that a study of the brains of 111 (deceased) former NFL players revealed that 110 of them had Chronic Traumatic Encephalopathy, the degenerative MTBI caused by repeated blows to the head.

The first line of defense against MTBI for contact game participants is their protective helmet. It is therefore of the utmost importance that these helmets provide as much protection for the user as possible. This has been recognized since the early days of American football, but it was not until 1973 that a serious effort to measure the protective capability of helmets was made by the National Operating Committee on Standards for Athletic Equipment (NOCSAE). NOCSAE introduced a helmet testing method and related standard (described below) that provided a means to compare the protective performances of various helmets. This protocol, which has been updated numerous times, was a first attempt to insure that the helmets used in football games were compliant with a stated performance standard. This standard has been adopted by many sports associations and, along with sensible rule changes regarding tackling, has played an important role in the attempts to reduce MTBI. Subsequent to the introduction of the NOCSAE standard, there have been a number of other proposed helmet testing devices and protocols. It will be demonstrated below that all of these protocols are inadequate because the impacts they analyze, generated using testing laboratory (lab) equipment, differ in significant ways from the impacts experienced by game participants. Also, the existing standards only relate to head accelerations resulting from impacts, but ignore the equally important distribution of impact-created forces transmitted through helmets onto a user's head. It is believed that these limitations contribute to the continued frequent occurrence of MTBI in contact sports. (Another contributor is the inadequate protective capabilities of available helmets.)

PRIOR ART

a. Current NOCSAE Standard Drop Test Method

In this method, illustrated inFIG. 1, a helmet to be tested is affixed to a Hybred III (H3, described in humaneticsatd.com/crash-test-dummies) head-form1101attached to a rigid aluminum frame1102. The frame1102is constrained to slide, from a specified height, down a pair of vertical wires1103, so that the head-helmet1101falls onto a fixed metal anvil1104covered with a firm rubber pad (not separately depicted). The head-helmet1101is oriented on the frame1102such that the impact with the anvil1104occurs at a prescribed location on the helmet. There are three possible headform weights (9.1 lb, 10.8 lb, 13.1 lb). Accelerometers attached to the head-form record the acceleration of the head-helmet1101during the impact with the anvil target1104. The NOCSAE standard states that the severity index (SI) evaluated from the recorded acceleration profile is less than a specified upper bound when the head-helmet impacts at a specified speed. (The SI is required to be at most 300 s for a 11.34 fps impact speed (drop height of approximately 2′), and at most 1200 s for a 17.94 fps speed (drop height of approximately 5′)). (An updated complete description of the NOCSAE test method and standard is contained in NOCSAE DOC ND 001-13m14c.)

b. Proposed NOCSAE Standard Linear Impact (LI) Test Method

In this method, the helmet to be tested is affixed to a H3 head-form attached to a H3 neck and torso mounted on a translating joint attached to an adjustable table. The impactor is a hemispherical solid covered with foam padding and a urethane helmet shell. It is attached to a horizontal cylindrical piston, guided within a straight cylindrical tube by linear bearings, and propelled by a compressed air cannon. (The impactor with attached piston travels 10 cm after striking the helmet and is then stopped by a breaking cylinder and allowed to rebound backwards within the guide. The H3 dummy is instrumented with accelerometers, load cells, and potentiometers to record responses. As for the drop test standard, the linear impactor standard states that the SI evaluated from the recorded acceleration profile is less than a specified upper bound when the impactor strikes the target helmet at a specified speed. (A complete description of the NOCSAE LI test method is contained in NOCSAE DOC ND 081-04m04.)

c. Pendulum Impact Test Method

In this method, a helmeted H3 head with neck is impacted by a domed spherical surface attached to a weighted pendulum that rotates downward about a fixed horizontal axis. The head is instrumented to measure translational and rotational acceleration, and the head orientation is adjustable to enable impacts at various locations on the helmet. (Methods a-c, and related methods, are described in detail and evaluated in Pellman et al, Neurosurgery 58:78-96, 2006.)

d. Deficiencies in Prior Art Methods

The above test methods, and all others known to us that have been implemented or proposed, create impacts that are very different from those (essentially unconstrained free body) impacts that arise in the field. The most important of these differences are described below.

In the current NOCSAE method (a), the impacting head-helmet is constrained to descend down and rebound back up in a purely vertical direction. Field impact rebounds on the contrary almost always occur at angles that differ significantly from the incident angle. (SeeFIG. 2) Also, in the current NOCSAE method, the target is fixed and therefore effectively infinitely heavy and completely constrained. There are other deficiencies with this method. One issue is the limited impact speeds that are available. (A 20 mph impact would require a drop height of over 13.5′.) Another issue is the limited number of head weights that are used. The SI evaluated from impacting a 13.1 lb head could have a compliant value whereas the SI that arises from impacting a lighter head at the same speed could be non-compliant. In that case, a compliant helmet could place the player with the lighter head at risk. Another issue is the fact that the method can only measure translational but not rotational acceleration. Also, measuring only the applied accelerations (and corresponding forces) ignores the (previously unrecognized) fact that the transmitted forces applied to the head can be larger than those applied to the helmet at times during the impact, and ignores the degree to which these forces can be spread out by a helmet.

A more recent use of NOCSAE-style drop impacts is the STAR helmet rating system. The STAR rating of a helmet is the theoretical number of concussions a player using the helmet would sustain in one season. It is based on an assumed injury risk function for each measured peak acceleration and an assumed head impact exposure matrix, estimated by using published measurement data and on a number of simplifying assumptions. STAR is an innovative first attempt to quantify helmet performance in terms of a single number, it has all of the same defects as the ones stated above, and others related to the various assumptions and approximations involved.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide improved helmet testing devices and/or apparatus that generate impacts that replicate field impacts more realistically than conventional testing devices.

It is a further object of the present invention to provide improved methods for testing the safety of protective gear such as helmets.

Another object of the present invention is to provide such testing devices, apparatus and/or methods that facilitates the collection of test data pertaining to important characteristics of test impacts.

The present invention contemplates the provision of data analysis protocols that facilitate an accurately evaluation and comparison of the protective capabilities of helmets and that effectively summarize characteristics of helmet safety.

These and other objects of the present invention will be apparent from the drawings and descriptions herein. It is to be noted that any single embodiment of the invention may not achieve all of the objects of the invention, but that every object is attained by at least one embodiment.

SUMMARY OF THE INVENTION

The present invention provides devices and protocols that accurately evaluate and compare the protective capabilities of helmets, and that the present impact measurement devices may be used to closely replicate field impacts. The present devices and protocols are effectively utilized in an attempt to reduce the frequency of minor traumatic brain injury (MTBI).

The proposed NOCSAE LI method (b) described above is an improvement in that both the impactor and the target have finite weight, and large impact speeds are readily obtainable. However, the impactor is even more highly constrained. Before, during, and after the impact, the impacting element and attached piston are constrained to move in a purely horizontal direction, whereas field impact rebounds almost always occur at angles that differ significantly from the incident angle (FIG. 2). Furthermore, the impactor does not interact with the target in a natural way as a free body, but instead it is artificially forced to stop its forward motion after it travels 10 cm after striking the helmet. Also, the H3-helmet target is artificially constrained by it's attachment to a translating joint. This constraint, the horizontal direction impacting constraint, and the external impact termination render the impacts to be very different from field impacts. Also, as with the NOCSAE drop method, only a limited number of head weights are used, and transmitted forces and their distributions are not measured. (Consequences of these defects could help explain why the LI method, introduced in 2006, has yet to be incorporated into a NOCSAE standard.)

The pendulum method (c) described above, and all other reported methods, has similar issues: constrained impacts and rebounds, limited impact speeds, and limited number of head weights. Furthermore, none of these methods involve measurements of transmitted force distributions.

A method for testing a helmet for effectiveness of user protection comprises, in accordance with the present invention, (1) moving a load along a predetermined path, (2) supporting a target body at an impact location in the predetermined path, the target body including a head model and a helmet disposed on the head model, (3) impacting the target body with a force generated by the moving of the load, the impacting of the target body including contacting the target body with an impactor free to move tangentially relative to a surface of the target body, (4) at least partially reducing the supporting of the target body before or during the impact of the impactor with the target body at the location, and (5) automatically measuring forces generated during the impact of the impactor with the target body at the location.

The load may include or consist of the impactor. In that case, the moving of the load includes restraining the impactor during an initial portion of the predetermined path and further includes at least partially eliminating the restraining of the impactor at or prior to impact of the impactor with the target body at the impact location.

The moving of the impactor may comprise operating a cannon device to propel the impactor toward the impact location.

Where the impactor is a contact element resting on the helmet of the target body, the moving of the load may comprise sliding the load, or weight, down a fixed vertical rod onto a spring inserted into the contact element.

In one set of embodiments of the present invention, the impactor is connected to a rotatably supported rod. In that case, the moving of the load comprises rotating the rotatably supported rod at an accelerating angular speed. The method further comprises inserting the target body into the predetermined path at the impact location after and only after a desired impactor speed is attained.

The supporting of the target body at the impact location may include suspending the target body by elongate tensile members attached to an element configured to release the elongate tensile members. The method than further comprises operating the element to release the target body prior to the impact of the impactor with the target body or in response to engagement of the impactor with the target body.

In an alternative embodiment of the present invention, the supporting of the target body at the impact location includes supporting the head model on a rod attached to a holder or bracket via a plurality of springs each extending at least partially transversely or perpendicularly to the rod.

The automatic measuring of forces preferably includes operating a plurality of force sensors spaced from one another on the head model. The force sensors are preferably disposed between an inner surface of the helmet and an outer surface of the head model.

The method may additionally comprise operating a computer or processor to determine impact acceleration data including maximum recorded acceleration, average recorded acceleration, total impact time, severity index, and coefficient of restitution.

A target body for safety testing comprises, in accordance with the present invention, a head model, a helmet mounted to the head model, a plurality of force sensor units distributed over the head model, and a mounting plate or base platform attached to the head model, the force sensors being adjustably attached to the mounting plate or base platform.

Each of the force sensor units may comprise a tube, a post, a compression spring, and a load cell. The post is slidably inserted within the tube and rests on the compression spring, while the compression spring is in turn in operative (possibly indirect) contact with the load cell. The post has an upper section extending out of the tube and terminating in an enlarged head with a convex curved surface disposed in contact with the inner surface of the helmet. The tube may be a main tube having a threaded bottom section that screws into a threaded concentric lower tube that is attached to the mounting plate or base platform. In that event, the height of the main tube is adjustable by rotating the main tube within the threaded concentric lower tube. The location of the main tube on the mounting plate or base platform may be adjustable by sliding the threaded concentric lower tube in a slit or slot in the mounting plate or base platform.

