Game ball monitoring method and apparatus

Abstract

A method and apparatus for determining in a ball game (for example, tennis) the position, relative to a service reference lines ( 12 ), of the first contact of the ball ( 14 ) with the playing surface. In play, the ball passes through a collimated light beam to intercept light directed at a light sensing array, which comprises many closely spaced sensors ( 46 ) arranged in column and row formation. A signal storage means includes one storage device for each of the sensors, so that the position of the ball may be tracked in the storage means as it passes through the light beam. The said position is determined by tracking in the storage means the front of the ball ( 14 F), and for each sensed position of the ball front determining the then height (H) of the top of the ball, at a position displaced rearwardly one half the ball diameter. The detected height of the top of the ball is compared for each position of the ball front with a ball reference height to ascertain the said ball position at the moment the height of the top of the ball equates with the ball reference height. Alternatively, real-time comparisons of detected and reference ball heights may be made by a computer operating on the interrupt principle, thus obviating the need for the storage devices in the making of comparisons.

1 . A method of monitoring in a ball game the position, relative to a reference line extending linearly between near and far ends thereof, of the first contact of a game ball with a playing surface carrying said reference line, which method includes the following steps: 
 (a) from said near end of the reference line directing a collimated radiation along and parallel with the reference line to irradiate a predetermined field at said far end of the reference line and lying adjacent the reference line, said field being such as will be materially but not wholly shaded by the passage of a game ball through the radiation when in play near the reference line;    (b) at said far end of the reference line sensing the game ball's presence in the radiation by detecting the shadow cast at that end by the game ball;    (c) when the game ball is in flight through said field detecting from said shadow the passage of the front of the game ball through successive closely-spaced positions in the direction of flight of the game ball;    (d) for each such closely-spaced position, determining the height of the top of the game ball at a position spaced one half the diameter of the game ball rearwardly of the front of the game ball;    (e) for each such closely-spaced position, comparing the detected height of the top of the game ball with a stored game ball diameter reference height stored in a storage means; and    (f) determining as the position of first contact of the game ball with the playing surface the game ball position at which the reducing height of the top of the game ball has become equal to the stored game ball diameter reference height.    
     
     
         2 . A method according to  claim 1 , wherein the stored game ball diameter reference height is determined by detecting the height of said shadow when the game ball lies stationary on the playing surface at the reference line.  
     
     
         3 . A method according to  claim 1  or  2 , which method includes the following steps: 
 (a) from said near end of the reference line directing a collimated radiation along and parallel with the reference line to irradiate a predetermined field at said far end of the reference line and lying adjacent the reference line, said field being such as will be materially but not wholly shaded by the passage of the game ball through the radiation when in play near the reference line;  
 (b) at the far end of the reference line, receiving at closely spaced locations in said field respective elements of said radiation, which locations are disposed uniformly in vertical column and horizontal row formation;  
 (c) converting the respective received radiation elements into corresponding electrical signals;  
 (d) storing the respective electrical signals in respective signal storage elements of a storage means for retention therein until set by the passage of the game ball through the radiation, each said storage element when storing a said electrical signal representing a radiation element that has not been interrupted by the game ball, and each said storage element when not so storing a said electrical signal representing a radiation element which has been interrupted by the game ball;  
 (e) defining in said storage means a game ball diameter reference height;  
 (f) tracking in said storage means the front of the game ball as it moves forwardly through the radiation, by following the first shading by the game ball of sensors in successive next columns of sensors in the direction of ball flight;  
 (g) for each of successive positions of the front of the game ball, determining in said storage means the height of the top of the game ball at a position disposed one half of the diameter of the game ball rearwardly from the front of the ball—by determining in the column of sensors at said rearwardly disposed position the height of the uppermost sensor not receiving radiation;  
 (h) determining the instant at which the reducing detected height of the top of the ball equates to the game ball diameter reference height; and  
 (i) determining the position of the game ball at that instant, which position is the position of first contact of the game ball with the playing surface relative to said reference line.  
 
     
     
         4 . A method according to  claim 3 , wherein said game ball diameter reference height is defined by determining the lowest row of sensors in which all of the sensors in the row continue to receive radiation when the game ball lies stationary on the playing surface at the reference line.  
     
     
         5 . A method according to  claim 3  or  4 , wherein in step 
 (f) the shading of at least one sensor in a next vertical column of sensors (referred to hereinafter as a ‘trigger column’) in the direction of ball flight causes the transmission of a staticising signal for retaining in step  
 (g) (until reset) the status of the respective sensor signals in a vertical column of sensors (referred to hereinafter as a ‘controlled column’) disposed rearwardly a distance corresponding to one half of the game ball diameter.  
 
     
     
         6 . A method according to  claim 5 , wherein the position of first contact of the game ball with the playing surface relative to said reference line is determined in said storage means by comparing the game ball reference height as determined in step (e) with successive detected heights of the top of the game ball as determined in step (g).  
     
     
         7 . A method according to  claim 3  or  4 , wherein the position of first contact of the game ball with the playing surface relative to said reference line is determined in said storage means, directly or indirectly, by scanning along each row of sensors in the direction of game ball flight in turn starting from the top row to find the row in which a sequence of sensors not receiving radiation is interrupted temporarily by one or more sensors receiving radiation.  
     
     
         8 . A method according to  claim 3  or  4 , wherein step (h) comprises scanning in the storage means, directly or indirectly, the respective sensor states (‘shaded’ or ‘unshaded’) of corresponding sensors comprising a given row, and repeating the scanning progressively in successively lower rows of sensors to find the row in which a sequence of ‘shaded’ sensors is interrupted temporarily by one or only a few ‘unshaded’ sensors.  
     
     
         9 . A method according to  claim 3  or  4 , wherein step (h) comprises scanning horizontally, in the storage means, directly or indirectly, and in the direction of ball flight, the respective storage states (‘shaded’ or ‘unshaded’) of respective sensors of the row of sensors defining the game ball height reference level, and determining in that row the sensor column at which a ‘shaded sensor’ status is followed by an ‘unshaded sensor’ status.  
     
     
         10 . A method according to  claim 3  or  4 , wherein step (h) comprises scanning vertically, in the storage means, directly or indirectly, and in the direction of ball flight, successive columns of sensors to find that column in which a change from a ‘shaded’ sensor to an ‘unshaded’ sensor occurs at the game ball diameter reference height.  
     
     
         11 . A method according to any one of the  claims 3  to  9 , wherein the detected position of first contact of the game ball with the playing surface is adjusted, in order to allow for squash-back of the game ball, in dependence upon the angle relative to the playing surface at which the game ball approaches the playing surface.  
     
     
         12 . A method according to any one of the  claims 3  to  7 , wherein the radiation comprises visible light, or infra-red radiation.  
     
     
         13 . Apparatus for monitoring in a ball game the position, relative to a reference line extending linearly between near and far ends thereof, of the first contact of a game ball with a playing surface carrying the reference line, which apparatus comprises: 
 (a) at said near end of the reference line, radiation emitting means for directing a collimated radiation along and parallel with the reference line to irradiate a predetermined field at said far end of the reference line and lying adjacent the reference line, said field being such as will be materially but not wholly shaded by the passage of the game ball through the radiation when in play near the reference line;    (b) at said far end of the reference line, radiation receiving means comprising a plurality of radiation sensors for receiving at closely spaced locations in said field respective elements of said radiation, which locations are disposed uniformly in vertical column and horizontal row formation, which radiation receiving means is arranged to sense the game ball's presence in the radiation by the shadow cast at said far end by the game ball; (c) means for detecting when the game ball is in flight through said field the passage of the front of the game ball through successive closely-spaced positions in the direction of flight of the game ball; and    (d) means for determining, each such closely-spaced position, the height of the top of the game ball at a position spaced one half the diameter of the game ball rearwardly of the front of the game ball;    (e) means for comparing, for each such closely-spaced position, the detected height of the top of the game ball with a stored game ball diameter reference height; and    (f) means for determining as the position of first contact of the game ball with the playing surface the game ball position at which the reducing detected height of the top of the game ball has become equal to the stored game ball diameter reference height.    
     
     
         14 . Apparatus according to  claim 13 , including means for determining from said shadow when the game ball lies stationary on the playing surface at the reference line said game ball diameter reference height for retention in a storage means.  
     
     
         15 . Apparatus according to  claim 13  or  14 , which apparatus comprises: 
 (a) at said near end of the reference line, radiation emitting means for directing a collimated radiation along and parallel with the reference line to irradiate a predetermined field at said far end of the reference line and lying adjacent the reference line, said field being such as will be materially but not wholly shaded by the passage of the game ball through the radiation when in play near the reference line;  
 (b) at the far end of the reference line, radiation receiving means comprising a plurality of radiation sensors for receiving at closely spaced locations in said field respective elements of said radiation, which locations are disposed uniformly in vertical column and horizontal row formation;  
 (c) converting means for converting the respective received radiation elements into corresponding electrical signals;  
 (d) electrical signal storage means for storing the respective electrical signals in respective signal storage elements of the storage means for retention therein until set by the passage of the game ball through the radiation, each said storage element when storing a said electrical signal representing a radiation element that has not been interrupted by the game ball, and each said storage element when not so storing a said electrical signal representing a radiation element which has been interrupted by the game ball;  
 (e) means for determining as a game ball diameter reference height, the lowest row of sensors in which all sensors in the row continue to receive radiation when the game ball lies stationary on the reference line;  
 (f) means for tracking the front of the game ball as it moves forwardly through the radiation, by reference to the first shading by the game ball of sensors in successive next columns of sensors;  
 (g) means for determining for each of successive positions of the front of the game ball the height of the top of the game ball at a position disposed one half of the diameter of the game ball rearwardly from the front of the game ball—by determining in the column of sensors at said rearwardly disposed position the height of the uppermost sensor not receiving radiation;  
 (h) means for determining the instant at which the reducing detected height of the top of the game ball equates to the game ball diameter reference height; and  
 (i) means for determining the position of the game ball at that instant, which position is the position of first contact of the game ball with the playing surface relative to said reference line.  
 
     
     
         16 . Apparatus according to  claim 15 , including for use in step (f) means responsive to the shading of at least one sensor in a next vertical column of sensors (referred to hereinafter as a ‘trigger column’) in the direction of ball flight for transmitting a staticising signal for retaining (until reset) the status of the sensor signals generated in a vertical column of sensors (referred to hereinafter as a ‘controlled column’) disposed rearwardly a distance corresponding to one half of the game ball diameter.  
     
     
         17 . Apparatus according to  claim 16 , wherein said means for determining the position of first contact of the game ball with the playing surface relative to said reference line comprises means for comparing with the said game ball reference height successive sets of said sensor signals retained in respective controlled columns.  
     
     
         18 . Apparatus according to  claim 15 , wherein said means for determining the position of first contact of the game ball with the playing surface relative to said reference line comprises means for scanning, in said storage means, directly or indirectly, and in the direction of game ball flight, along each row of sensors in turn starting from the top row to find the row in which a sequence of sensors not receiving radiation is interrupted temporarily by one or only a few sensors receiving radiation.  
     
     
         19 . Apparatus according to  claim 15 , including means for scanning ‘horizontally’, in the storage means, directly or indirectly, and in the direction of ball flight, the respective sensor states (‘shaded’ or ‘unshaded’) of respective sensors of the row of sensors defining the game ball height reference level, and determining in that row the sensor column at which a ‘shaded sensor’ status is followed by an ‘unshaded sensor’ status.  
     
     
         20 . Apparatus according to  claim 15 , including means for scanning ‘vertically’ in the storage means, directly or indirectly, successive columns of sensors in the direction of ball flight, to find that column in which a change from a ‘shaded’ sensor to an ‘unshaded’ sensor occurs at the game ball diameter reference height.  
     
     
         21 . Apparatus according to any one of the  claims 15  to  20 , including means for measuring the angle relative to the playing surface at which the game ball approaches that surface, and means for adjusting the detected position of first contact of the game ball with the playing surface, in order to allow for ‘squash-back’ of the game ball, in dependence upon the said angle relative to the playing surface.  
     
     
         22 . Apparatus according to any one of the  claims 13  to  21 , wherein the radiation comprises visible light, or infra-red radiation.  
     
     
         23 . A method according to any one of the  claims 1  to  12 , substantially as hereinbefore described with reference to and as illustrated by the accompanying diagrammatic drawings.  
     
     
         24 . Apparatus according to any one of the  claims 13  to  22 , substantially as hereinbefore described with reference to and as illustrated by the accompanying diagrammatic drawings.