Abstract:
A method and device for calculating ski-jump lengths and the speed of travel of a skier along a ski-jump course comprises a shock sensitive radio transmitter attached to the skier&#39;s ski, a stationary radio receiver, a plurality of optical sensors, means for determining a skiers speed and an electronic unit for calculating ski-jump length. Upon impact, a signal transmitted by the radio transmitter is received by the radio receiver together with signals from the optical sensors which detect passage of the skier on the ski-jump course; said signals are then entered into the electronic unit and the means for determining the skier&#39;s speed. The electronic unit and the means for calculating the skier&#39;s speed respectively calculate the ski jump length and the skier&#39;s speed.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a method and a device for objectively measuring jump-lengths on a ski-jump. 
     In many sporting competitions the results now are measured by means of objective measuring methods. Such methods result in accurate and correct data values so that there is practically no possibility that a competitor will be placed inaccurately due to measuring errors within acceptable statistical margins of error. At slalom racing events, for example, the time of a competitor&#39;s speed is measured by one-hundredths of a second. At ski-jumping events, however, it is necessary to determine by manual means the landing point of a skier. In the use of manual measurement methods, measurement errors of several meters are not unusual and, due to the high speed of the ski-jumper at the landing moment (more than 20 m/s), such measurement errors are statistically unavoidable. There is, thus, a need for an objective and correct measuring method at ski-jumping events. Several objective measuring methods have been proposed and tested, but so far none has met the requirements of providing correct measuring values while simultaneously being technically and economically realizable. 
     SUMMARY OF THE INVENTION 
     The invention provides a method for objectively measuring jump-lengths of a skier from a ski-jump with high precision. The method is based upon use of shock-sensitive means mounted on the jumper&#39;s ski which transmits radio signals to time determination means to start said time determination means at the moment of the skier&#39;s landing. Thereafter, the time elapsed from the moment the jumper lands until he crosses and interrupts an optic beam trained across the direction of the jumper&#39;s travel is recorded. The said optic beam is located at a known distance along the course of the jumper&#39;s travel. This data, together with data acquired from means measuring the jumper&#39;s speed at or immediately after the moment of landing, is used for automatic calculation and display of the skier&#39;s jump-length. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective, partially diagrammatic view of a ski-jump course with the device of the invention provided thereon and a skier moving along said course; and 
     FIG. 2 is a side elevational view of the course shown in FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The method is now described in greater detail, with reference to the accompanying drawing. Every jumper is equipped with a small landing transducer package which contains shock-sensitive means and a miniradio transmitter with short range. The package is positioned on the ski just in front of the ski-binding. The package further may include code means which both feeds the transmitter with information on the start number of the skier and delivers a pre-programmed pulse code to &#34;open&#34; a radio receiver, thereby protecting the receiver against interference from foreign transmitters. 
     The radio receiver is placed stationary and connected to an electronic unit. The antenna of the receiver preferably is a loop antenna laid about the landing area. At the moment of the skier&#39;s landing from the jump, the radio transmitter emits a signal to the electronic unit, which signal may consist of either an interruption of an ongoing broadcast during the flight of the ski-jumper, or of the start of a broadcast at the moment of the skier&#39;s landing. The first alternative is preferred because an interruption of an ongoing broadcast is considered to be a safer signalling method. If the landing transducer is provided with code means, the information with respect to the start number of the skier then is transmitted to the electronic unit for automatic display while the jumper is in the air. 
     The time determination means of the electronic unit preferably consists of a pulse generator emitting pulses of a frequency in the range of 1-30 kc/s and a counter with memories. The landing signal emitted by the radio transmitter at the moment of the skier&#39;s landing starts the counter, and when the ski-jumper passes a first optic beam, trained across the skier&#39;s course of travel, which may for example be a laser beam, the pulse counting is interrupted and the number of pulses is stored in one memory of the counter. In the landing area, a plurality of optical units are placed uniformly and spaced at known distances. Each optical unit includes an optical transmitter and a receiver for a beam trained across and normal to the ski-jumper&#39;s jumping direction 10-25 cm above the ground. The receivers may have either wire connections with the electronic unit, or may actuate the same by radio signals and radio receivers. In view of its more dependable operation, wire connection is preferred. The distance between each optical unit (s) can be chosen optionally and be adjusted to different types of ski-jumps. When the ski-jumper passes the first optical unit after the landing, the number of pulses (n x ) are recorded in the memory of a first counter of the electronic unit, i.e. the number of pulses produced by the pulse generator when the ski-jumper covers the distance (x) in the Figures. 
     For calculating the distance (x), the speed at and immediately after the skier&#39;s landing must be determined. This can be carried out in different ways. One way is to emit sound-waves from a fixed point at one end of the landing area and to record the Doppler-effect therefore by a receiver on the jumper&#39;s ski. 
     Alternatively, of course, the transmitter can be mounted on the ski. According to an especially advantageous embodiment of the invention, the skier&#39;s speed, however, is measured by means which have been described, i.e. the optical units and the counters of the electronic unit. 
     This special embodiment, which is shown in the drawing, is based on the assumption that the skier&#39;s speed can be considered constant from the point of landing to the point where the skier&#39;s has passed two subsequent optical units. This assumption has been proved by practical experiments. At the time that the skier&#39;s passes the first optical unit, the counter is reset to zero and thereafter records the number of pulses (n s ) emitted until the second optical unit is passed at the distance (s) from the first unit. 
     A ski-jumper often lands with one leg ahead of the other. Since the skier&#39;s point of landing then is considered to have taken place in the middle between the skier&#39;s spread-apart legs, a correction must be made. This can be carried out by a separate counter counting the pulses (n k ) produced by the pulse generator from the moment when the skier&#39;s front leg breaks the first optical beam after the landing to the moment when the rear leg breaks the same beam. In the memory of the counter a number of pulses are recorded for automatically calculating the correction, which quite simply is n k  /2. 
     When the ski-jumper passes the next optical unit, this unit emits a signal to the electronic unit to stop the first counter. In the first memory of this counter now the number of pulses (n x ) is stored, which were produced until the first optical unit was passed, and in a second memory the number of pulses (n s ) are stored which were produced between the two optical units having been passed first. 
     Prior to the start of the ski-jumping, a reference measure (r) is fed into the logic of the electronic unit, which measure, for example, may be the distance from the take-off point of the skier to the first optical unit, and a reference measure (s), which is the distance between two optical units. The skier&#39;s jump-length immediately is calculated in the fixed-programmed logic for data processing and presentation of the electronic unit. The data also may be calculated together with skier&#39;s start information, and may be transmitted to an external result panel for display of the data. 
     The above referred to calculations may be made in the following manner: 
     r = reference measure for the distance between the skier&#39;s take-off and the point at which he passes the first optical unit 
     n x  = number of pulses between the skier&#39;s landing and his passage of the forward leg past the first optical unit after the landing 
     n k  = number of pulses between the passage of the skier&#39;s forward and rearward leg past the first optical unit 
     n s  = number of pulses between the passage of the skier&#39;s between the first two optical units 
     N = figure calculated from the identification code from the optical unit passed first, it being here assumed that the optical units in turn from the distance r render the figures 0, 1, 2 . . . etc. 
     L = jump-length of the skier 
     s = distance between two subsequent optical units ##EQU1## 
     The apparatus for carrying out the method of the invention includes a device for objectively measuring jump-lengths of a skier on a ski-jump. The device includes a landing-transducer package adapted to be mounted on the ski of a ski-jumper. The package has a radio transmitter and shock-sensitive means, which means are intended to start time determination means by emission of a signal from the radio transmitter at the moment of landing of the skier. The device also includes a radio receiver and a plurality of optical units which are mounted at precisely defined spacings within the skier&#39;s landing area. Each optical unit includes an optical transmitter for emitting an optical beam which may be located 10-25 cm above the ground and across the path of the skier in the landing area normal to the jumping direction. The optical beams emitted are received by respective optically sensitive transducers. Means are provided for determining the jumper&#39;s speed at or immediately after his landing. Also included is an electronic unit having the time determination means for calculating the time between the moment of the skier&#39;s landing and a first signal generated from the optical unit which is first passed by the skier when he lands in the landing area and the time between the first signal generated and a second signal generated from the same optical unit. A logic is provided for feed-in of speed data from the speed measuring means, and another logic is provided for the feed-in of reference measures of the ski-jump and distances between the optical units. There also is a code converter for identification codes from each optical unit, and a fixed-programmed logic for data processing and display of said data. 
     The landing transducer package containing shock-sensitive means, a radio transmitter and, if desired, code means for start information, may be of small size as determined by the size of a battery which must be included in and constitutes the greater part of the package. The shock-sensitive means preferably comprises two permanent magnets, one being fixed and one being spring-suspended. The spring-suspended magnet is locked by a set-screw (for force adjustment) against the terminal point of the fixed magnet. Said spring-suspended magnet, therefore, reacts to forces from only one side, and changes in the magnetic field at very small movements can be used as an accurate indication that the ski-jumper has hit the ground. 
     Immediately prior to the landing moment, the ski-jumper possibly may &#34;dip&#34; the rear end of the ski with the landing transducer on the ground, creating the risk of a false release of the landing signal. This risk, however, will be small when the aforedescribed shock-sensitive means is used, because the force in this case has a direction other than the direction of the force, by which the spring-suspended magnet is actuated at the landing. For safety reasons, nevertheless the landing transducer may be provided with a protective contact, which renders release impossible as long as the ski is in horizontal or upward inclined position. The protective contact may be a mercury switch. 
     The optical unit, as shown in the Figures, preferably may consist of a laser, which together with an optical receiver, for example a phototransistor, is positioned on one side of the landing area, and of a vertically positioned reflector means on the other side of the landing area to reflect the laser beam to the receiver. The laser and receiver advantageously are manufactured in one and the same package. 
     In order to manually test the entire measuring operation prior to a competition, the electronic unit preferably should be equipped with simulator means. 
     The device of the invention enables very good measuring accuracy is obtained. The electronic unit records an interruption exceeding hundred microseconds as a landing, and the jump-length error referred to the radio-emitted landing signal lies within ± 0.25 mm. When a frequency of about 10 kc/s is chosen for the pulse generator, the pulse counting does not give rise to a jump-length error greater than ± 3 mm. When the skier&#39;s speed is measured according to the method based on the assumption that the speed can be regarded being constant between the skier&#39;s landing and his movement past the first two optical units passed, the additional increase in error due to a possible acceleration is not greater than that of the total measuring error which lies within ± 5 cm.