Abstract:
A distributed array of force sensors disposed in the inner lining of a safety helmet measure forces between the inner periphery of the helmet and a user&#39;s head, and a microcontroller responsive to the force measurements and other sensor data determines if the helmet fits the user properly. The force sensors are preferably provided at the front, back, sides and top of the inner lining, and the microcontroller compares the measured forces to calibrated threshold values to evaluate and indicate the fit of the helmet.

Description:
TECHNICAL FIELD 
   The present invention relates to an electronic monitoring apparatus incorporated into a safety helmet for detecting and alerting the user of improper helmet fit. 
   BACKGROUND OF THE INVENTION 
   Safety helmets are routinely worn for various vehicle-related and sport-related activities. Although the helmet is designed to protect the user from head injury, the user remains at risk if the helmet is not worn properly. For example, the helmet may not fit properly, the restraining strap(s) may be unfastened or improperly tensioned, and so forth. The U.S. Pat. No. 6,157,298 to Garfinkel et al. addresses some of these concerns with a safety helmet electronic control module that alerts the user with a prerecorded voice message or warning signal if the chin strap is not fastened or is fastened incorrectly, or if the helmet is situated on the user&#39;s head in an unsafe manner. However, a safety helmet can fit improperly even when fastened with a chin strap, and the user may not know what constitutes a proper fit. Accordingly, what is needed is a monitoring apparatus for detecting and alerting the user of improper helmet fit. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an improved safety helmet apparatus for monitoring safety-related parameters including helmet fit and alerting the user of any detected improper usage or fit. A distributed array of force sensors disposed in the inner lining of the helmet monitor the helmet attachment force, and a microcontroller responsive to the force sensors and other sensor data determines if the helmet fits the user properly. In a preferred embodiment, force sensors are provided at the front, back, sides and top of the inner lining, and the microcontroller compares the measured forces to pre-established threshold values to evaluate the fit of the helmet. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a bottom inside view of a safety helmet including an array of force sensors according to this invention; 
       FIG. 2  is a circuit diagram of the force sensors of  FIG. 1  and a microcontroller responsive to the sensors; and 
       FIG. 3  is a diagram depicting a logic operation carried out by the microcontroller of  FIG. 2  according to this invention; 
       FIG. 4  is a flow diagram of a software routine carried out by the microcontroller of  FIG. 2  according to this invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , the reference numeral  10  generally designates a safety helmet such as a cycling or sports helmet. The helmet  10  has a hard outer shell  12  covering a layer  14  of energy absorbing material such as polystyrene foam and a fabric lining  16  that contacts the head of a person wearing the helmet  10 . An array of thin pressure or force-responsive sensors designated in  FIG. 1  as S 1 , S 2 , S 3 , S 4  and S 5  are mounted between the energy absorbing layer  14  and the liner  16  for measuring contact forces between the inner periphery of helmet  10  and the front, back, sides and top of the user&#39;s head. In the illustrated embodiment, the sensors S 1 -S 5  are in the form of variable resistive sensor pads having characteristic electrical resistances that vary with the amount of compressive force applied thereto. Alternatively, piezo-resistive or capacitive sensors can be utilized. It is also possible to implement the invention with a multi-chamber fluid-filled bladder and a set of capacitive or pressure-responsive sensors for indicating the force applied to each chamber. Also, it will be understood that the sensors S 1 -S 5  may be different in number and/or placement than shown in  FIG. 1 . 
   In the circuit diagram of  FIG. 2 , the sensors S 1 , S 2 , S 3 , S 4  and S 5  are represented by the variable resistors  20 ,  22 ,  24 ,  26  and  28 , respectively. In general,  FIG. 2  is a circuit diagram of a control module mounted in a cavity of the energy absorbing layer  14 , for example. The module includes a number of small components mounted on a rigid or flexible circuit board, including a battery (not shown), a microcontroller  30 , an alarm or indicator  32  that is visible or audible to the user, and a number of passive elements for interfacing the sensors  20 - 28  with microcontroller  30 . A regulated voltage VCC is coupled to one terminal of each sensor  20 - 28  via a current-limiting resistor  34 , and a set of interface circuits generally designated by the reference numerals  36 ,  38 ,  40 ,  42  and  44  couple the other terminal of each sensor  20 - 28  to analog-to-digital input ports AD 1 -AD 5  of microcontroller  30 . In general, each interface circuit  3644  includes passive voltage dividing and filtering elements selected to optimize pressure or force sensing range and noise rejection. Of course, the control module may include additional components such as acceleration-responsive sensors, a low battery indicator and so forth; likewise, the helmet  10  may be equipped with additional sensors for detecting proper use and tensioning of head straps and chin straps, and sensors for detecting the orientation of the helmet  10  on the user&#39;s head, for example. 
     FIG. 3  depicts an easily implemented processing technique utilized by microcontroller  30  in respect to the sensors  20 - 28 . Prior to analog-to-digital conversion, each sensor input is an analog voltage that varies over the range of 0-5 VDC in proportion to the respective sensed pressure. The microcontroller  30  establishes a pair of calibrated thresholds THRmin and THRmax for each sensor location defining a range of input signal variation (shaded in  FIG. 3 ) for which the contact force between the user&#39;s head and the energy absorbing layer  14  is consistent with proper fit of the helmet  10 . In general, if the sensor input voltage exceeds THRmax, the contact force is too high for a proper fit, indicating that the retaining strap(s) should be loosened or that the helmet  10  is simply too small for the user; and if the sensor input voltage is less than THRmin, the contact force is too low for a proper fit, indicating that the retaining strap(s) should be tightened or that the helmet  10  is simply too large for the user. 
   The flow diagram of  FIG. 4  represents a software routine that is executed by microcontroller  30  according to this invention. The sensors and control module circuitry are powered up at block  70  in response to a user-activated switch or motion sensor. The blocks  72 ,  74  and  76  are then executed before the helmet  10  is placed on the user&#39;s head to measure a bias voltage indicative of the sensors&#39; state of health (SOH) and to indicate a sensor malfunction with warning indicator  32  if the measured bias voltage is out of range. If operability of the sensors S 1 -S 5  is confirmed, the user is prompted (by indicator  32 , for example) to put on the helmet  10 , and the microcontroller  30  executes the remainder of the routine to compare the sensor readings to the calibrated minimum and maximum thresholds THRmin and THRmax to determine if the helmet fit is proper. 
   First, the blocks  78 - 84  check for conditions indicative of a helmet that is too small to adequately protect the user. When the helmet  10  is too small, it will be too snug laterally to provide adequate pressure vertically (i.e., to the top of the user&#39;s head), even when the chin strap is fastened and properly tensioned. The block  78  determines if the inputs for front and rear sensors S 1  and S 2  exceed THRmax, or if the inputs for the side sensors S 3  and S 4  exceed THRmax. If either or both conditions are true, the block  80  is periodically executed to determine if the input for the top sensor S 5  is also less than THRmin. If block  80  is answered in the affirmative, the helmet  10  is considered to be too small to provide adequate protection to the user, and the blocks  82 - 84  are executed to provide a warning to that effect via indicator  32 . 
   Second, the blocks  86 - 92  check for conditions indicative of a helmet that is too large to adequately protect the user. When the helmet  10  is too large, it will be too loose laterally even when the chin strap is fastened and properly tensioned, and at the same time too snug vertically, assuming that the chin strap is fastened and properly tensioned. The block  86  determines if the inputs for front and rear sensors S 1  and S 2  are less than THRmin, or if the inputs for the side sensors S 3  and S 4  are less than THRmin. If either or both conditions are true, the block  88  is periodically executed to determine if the input for the top sensor S 5  is also greater than THRmin. If block  88  is answered in the affirmafive, the helmet  10  is considered to be too large to provide adequate protection to the user, and the blocks  90 - 92  are executed to provide a warning to that effect via indicator  32 . 
   If blocks  78  and  86  are both answered in the negative, the block  94  is executed to determine if the helmet  10  is properly sized for the user. In this case, all of the sensor readings will be within the shaded portion of the diagram of FIG.  3 —that is between THRmin and THRmax. If block  94  determines that this condition is true, the block  96  is executed to provide a suitable indication via indicator  32 . 
   In summary, the present invention provides a simple and convenient way of monitoring for improper fit of a safety helmet, and alerting the user when an improper fit is detected. As mentioned herein, the illustrated apparatus may be used in conjunction with other sensors to provide comprehensive helmet fit and usage monitoring. It will be recognized that numerous additional modifications and variations will occur to those skilled in the art. For example, the described functionality of microcontroller  30  may be performed with discrete circuitry, additional indicators or different types of indicators (a dual-color indicator, for example) may be provided, and so on. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.