Abstract:
A position sensing apparatus and method includes a targeting device with a plurality of infrared transmitters or photodiode receivers attached to the targeting device and with corresponding receivers or transmitters mounted near a display monitor. The transmitters emit light signals that are received by the photodiode receivers. Receiver circuitry converts the light signals into signals representing the distance of the transmitters from the receivers. A processor then calculates the three-dimensional position and vector of the targeting device relative to the display monitor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to position sensors and more specifically to an apparatus for detecting the position coordinates and orientation of a targeting device. 
     2. Description of the Related Art 
     Conventional optical coordinate detection in most video game systems makes use of the vertical and horizontal synchronizing signals in the video signal generated by a game device. In order to define the location of an object on a video screen, the game device is provided with a horizontal counter for counting the columns on a display screen, a vertical counter for counting the number of scanning lines, and a real, user manipulated device, such as a model gun, sword, paint brush, boxing glove, shield, etc. for interacting with images on the display screen. The device is provided with a photosensor which receives light from the scanning lines shown on the display screen, and which has a certain degree of directionality. In other words, the device does not emit a light ray, but rather it actually receives a portion of the light emitted from the display. 
     Presently known shooting game machines may include an object such as a gun, and function such that the display screen turns white for one frame when the game controller detects that the player has pulled a trigger on the model gun. Starting at the next vertical blanking period following the “shot”, white pixels are displayed and counted starting from the upper left along a scan line. As each scan line is filled and counted, the system looks for where the shot from the gun would have impacted the screen by continuously looking for an illumination detection by a photosensor in the gun, and thus the targeted position is detected based on the pixel and scan line count at which the photosensor receives light from the raster scanning screen. 
     Unfortunately, the display screen turns white every time the trigger of the model gun is pulled. This may be used as a benefit in simulating a gun flash and giving the player instant feedback, but the intensity of the light from the white screen can be also annoying to the player. Further, when using a rapid-fire gun, the display screen is constantly flickering and reduces the quality of the display screen image. Also, this places an extra stress on the power supply of the monitor. Putting up a screen of white is a big jolt to the power supply and has been known to cause power supply failure. 
     Additionally, because NTSC is displayed at 59.9 Hz (60 Hz.), the fastest one can update the pointer value is 60 Hz/2. This allows for one screen frame of video to be interlaced between one white position finding frame. Actual games include more frames of video between successive white frames, since the image quality is unsatisfactory with so many white screens. However, there are many times when it would be desirable to have a faster update, such as when tracking rapid movements or simulating rapid gun-fire, such as with a machine gun. 
     Furthermore, with the advent of digital displays, the conventional method does not work in a straightforward manner because digital displays do not normally display the scanning lines. Additionally, the conventional method only determines the location on the display screen to which the model gun is pointing. The position coordinates of the model gun and the vector in which the model gun is pointed are not determined. Accordingly, input into the shooting game cannot generate scenes from the user&#39;s perspective and generate simulated bullet traces because the position of the gun is not known. Also, known shooting games cannot take advantage of the increased computer processing speeds and more realistic digital displays. In view of the above, it would be a significant improvement in the technology to provide a targeting system that does not depend on a raster scanning display screen and also one that can detect and input the position of the targeting device and the direction it is pointing into the video game system. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, there is disclosed an apparatus and a method for determining a targeting device&#39;s position coordinates and orientation in such a way as to be unrelated to the video being displayed. 
     In one embodiment, a position sensing apparatus includes a targeting device, a plurality of transmitters for transmitting light signals, a plurality of receivers capable of detecting the light signals from the transmitters, and a receiver circuit connected to the receivers. The receiver circuit develops distance signals representative of the distance of the transmitters from the receivers and sends the signals to a processor to determine the three-dimensional coordinate position and orientation of the targeting device with respect to a display monitor. 
     Another embodiment is a targeting game machine including a display monitor for displaying a target and at least one targeting device. The game machine includes at least three transmitters for emitting infrared light signals, wherein at least three transmitters are mounted on the at least one targeting device, and at least three photodiode receivers capable of detecting the light signals from said transmitters, wherein the receivers are mounted about the display monitor. The game machine also includes a receiver circuit electrically connected to said receivers, wherein the receiver circuit generates signals in relation to the intensity of the infrared light signals detected by the receivers, the generated signals representing the distance of the transmitters from the receivers, and a processor for processing the signals to determine the three-dimensional coordinate position and orientation of the targeting device with respect to the display monitor. 
     Another embodiment is a method of detecting a targeted position of a targeting device relative to a display monitor for use in a targeting game machine. The targeting device and the display monitor have a plurality of transmitters and a plurality of receivers fixedly mounted thereto. The method includes emitting light signals from the transmitters, detecting light signals emitted from the transmitters at the receivers, and calculating the three-dimensional position and orientation of the targeting device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the invention will become more fully apparent from the following description and appended claims taken in conjunction with the following drawings, where like reference numbers indicate identical or functionally similar elements. 
     FIG. 1 is a perspective view of a shooting video game machine that includes an embodiment of the position sensor system of the invention; 
     FIG. 2 is a block diagram of the IReye board; 
     FIG. 3 is a block diagram of the Eyecon board; 
     FIG. 4 is a flow chart of a method of operating the position sensing system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following presents a detailed description of certain specific embodiments of the present invention. However, the invention can be embodied in a multitude of different ways as defined and covered by the claims. The invention is best understood by reference to the figures wherein like parts are designated with like numerals throughout. 
     FIG. 1 illustrates a perspective view of a video game machine  100  that includes an embodiment of a position sensor system of the invention. Although the embodiment of the position sensor system described in the following figures and description is presented as a shooting video game, one skilled in the art will recognize that the position sensor system can be used in any application where the position and orientation of an article visible to a control unit is desired. 
     The shooting game machine  100  comprises a housing  102  within which a video display monitor  104  is located facing toward a player (not shown). The video display monitor  104  may be a raster scan or digital display monitor. The housing  102  includes a holder  106  in which a targeting device such as a model gun  110  is received. The model gun  110  is connected to an internal circuit in the housing  102  through a cable  112 . Alternatively, the model gun  110  can be cordless. 
     When the player stands in front of the display with the gun  110 , a game scene is displayed on the video display monitor  104 . The player can aim the gun  110  at targets successively displayed on the video display monitor  104  and pull a trigger  114  on the gun  110  to simulate shooting the targets. The appearance of the shooting game machine of FIG. 1 is basically similar to that of the conventional shooting game machines except that the housing  102  has three infrared photo receivers  120 A-C positioned at spaced locations on the housing  102  and adjacent the edge of the monitor  104 . The gun  110  has three infrared LED transmitters  130 A-C positioned on the gun  110  as will be explained below. 
     In one embodiment, the housing  102  can have three infrared photo receivers  120 A-C positioned about the periphery of the monitor  104 . The receivers  120 A-C can be positioned in a right triangle formation about the monitor  104  so that the base line between receivers  120 A and  120 C forms one leg of the right triangle and the base line between receivers  120 A and  120 B forms the second leg of the right triangle. In one embodiment, the receivers are positioned in the housing  102  so that the base line between receivers  120 A and  120 C and the base line between receivers  120 A and  120 B are 32 inches in length. This distance becomes a calibration distance as discussed below. Alternatively, other receiver orientations and distances between the receivers may be used. 
     An embodiment of the gun  110  is illustrated as including three infrared led transmitters  130 A-C positioned on the gun  110 . Although the depicted embodiment describes the transmitters  103 A-C mounted on the gun and the receivers  120 A-C mounted on the housing  102 , it is also understood that embodiments of the invention can have the transmitters mounted on the housing and the receivers mounted on the gun. The transmitters  130 A-C can be positioned on the gun  110  so that they are located at the corners of an equilateral triangle. In one embodiment, the transmitters  130 A-C are positioned so that each side of the equilateral triangle formed by the three transmitters  130 A-C is six inches in length. Alternatively, distances greater than or less than six inches and orientations other than an equilateral triangle can be used. The transmitters  130 A-C can be commercially available transmitters such as a model PDI-E804 from Photonic Detectors, Inc., which have the desirable optical qualities of broadcasting light over a wide and even pattern. 
     The transmitters  130 A-C are positioned on the gun  110  and the gun  110  is located for use in such a manner that there is no obstruction between the transmitters  130 A-C and the receivers  120 A-C. The transmitters  130 A-C can be positioned on the gun  110  so that each is recessed in a respective beveled hole in the body of the gun (not shown). The beveled holes can be of sufficient depth so as to prevent contact by the player with the transmitters  130 A-C. However, the transmitters  130 A-C should be close enough to the surface of the beveled holes on the gun  110  so that the light from the transmitters  130 A-C does not reflect off the interior surfaces of the holes. 
     The transmitters  130 A-C emit a modulated, infrared light signal over a tightly controlled bandwidth. In one embodiment, the transmitters  130 A-C emit a square wave with a 50% duty cycle at about 31k Hz. As explained below, the transmitters  130 A-C receive a control signal dictating when to transmit. In one embodiment, each transmitter  130 A-C is time sequenced to transmit for ⅙ th  of the total transmit time. In one embodiment, the shooting game machine  100  can include two guns  110 A and  110 B, each gun  110 A,  110 B having three transmitters  130 A-C. Therefore, in this embodiment, there are six transmitters  130 , making it desirable that each transmitter  130  be active for ⅙ th  of the total transmit time. This allows the transmitters  130 A-C on gun  110 A and the transmitters  130 A-C on gun  110 B to be sequenced so that the three receivers  120 A-C will receive a signal from only a single transmitter  130  at any given time. Alternatively, one skilled in the art will recognize that code division multiplexing can be used enabling two transmitters to emit signals at the same time, with their modulation in quadrature. 
     FIG. 2 is a block diagram showing receiver  120 A mounted on an IReye board  122 A. Receivers  120 B-C (not shown) are similarly mounted on identical IReye boards  122 B-C, respectively. The receivers  120 A-C are photo diode receivers such as model LTR-516AD available from LITE-ON, Inc. The receivers  120 A-C are receptive to an AC signal at a wide range of frequencies. The receivers  120 A-C convert the amount of light received at all amplitudes within the bandwidth of the circuit into an analog signal proportional to the amount of light received. Each of the IReye boards  122 A-C amplifies the signal using a low noise op-amp  126  and then a differential driver op-amp  128  and then outputs the signal. The IReye boards  122 A-C gather light energy, for example, square-wave modulated light. Alternatively, other forms of modulation, such as sine-wave modulation or triangle-wave modulation can be used. It is preferable that the IReye boards  122 A-C do not gather DC light sources such as sunlight or flash light. 
     FIG. 3 is a block diagram illustrating an Eyecon board  140  located in the housing  102  (FIG. 1) and shows that the analog signal from each IReye board  122 A-C is received by a differential input amplifier  142  on the Eyecon board  140 . The signals are then sent to an inverter buffer  144 . The signals are then sent to a multiplexer (MUX)  146  that switches at the transmission frequency. This method of signal reconstruction is known as a synchronous detector (code-division-multiplexing) and is known in the art. The resulting polarized analog signal is sent from the MUX  146  to a low pass filter buffer  148 . The signal is then sent to an analog-to-digital converter (A/D)  150 . In this system, the signal, plus its inversion, when read synchronously will add up to the original signal, minus interference noise. A serial control connects the A/D converter  150  to a control EPLD  152  which provides a convenient parallel connection to a game-control processor (not shown), as well as providing timing signals to the gun  110 , receivers,  120 A-C and other auxiliary input/output devices such as flashing lights (not shown). 
     The control EPLD  152  is also electrically connected to the gun  110  through the cable  112 . The control EPLD  152  controls the timing cycle of the transmitters  130 A-C on the gun  110  so that only one transmitter is active at a time. A processor  160  located in the housing  102  is connected to the control EPLD  152 . The ELPD synchronizes the signals with the corresponding transmitter and sends the data to the processor  160 . The processor  160  converts the signals into position data for each of the transmitters  130 A-C. 
     As discussed above, in one embodiment the receivers  120 A-C are positioned around the display monitor  104  to define a right triangle configuration. Referring back to FIG. 1, in one embodiment, the base line distance between the receivers  120 A and  120 B and between receivers  120 A and  120  C is 32 inches. This distance of 32 inches is defined as D or one light scale unit (LSU). Of course, it is conceived that other distances can be selected for this reference unit. 
     The three transmitters  130 A-C are calibrated by noting the light amplitude for each transmitter  130 A-C while placed directly over each receiver  120 A-C at a distance of one LSU. Noting that the intensity of light varies as the inverse square of the distance the light travels (assuming a spreading light source), the distance can be calculated by dividing a proportionality constant by the square root of the light reading. The distance then defines a sphere centered on the respective receiver with the radius of the sphere equal to the distance of the transmitter  130  from the receiver  120 . 
     The distances calculated from the light readings then can be used to calculate position of the transmitters  130 A-C as now discussed. The distance a first transmitter, for example  130 A, is from receiver  120 A defines a first sphere centered on the receiver. Likewise, the distance from receiver  120 B defines a second sphere and the distance from  120 C defines a third sphere. The intersection of the first two spheres defines a circle. Then, the intersection of the third sphere and the above-defined circle defines two points. One of the points will be located behind the housing  102  and can be eliminated. 
     The distances to the other two transmitters  130 B and  130 C are similarly determined. This allows the calculation of the positions of the points of the three transmitters  130 A-C in three dimensional space, thereby defining a plane on which the transmitters  130 A-C are located. 
     Referring back to FIG. 1, the geometry of the transmitters  130 A-C positioned on the gun  110  is illustrated. The three-space coordinates of the transmitters determined above now define a triangle in space. A “weighted average” of those coordinates can be used as the (x,y,z) of the tip of the gun-muzzle  162 . In one embodiment where the transmitters  130 A-C are positioned in an equilateral triangle as described above, the weights of the coordinates are the same, simplifying the calculation. 
     The midpoint of the plane and the perpendicular vector pointing in the direction of the three receivers  120 A-C can now be calculated. The cross-product of two of the vectors defined between the transmitters  130 A-C will give the normal vector to the plane defined by the three transmitters. For example, the cross-product of the vector from transmitter  130 A to transmitter  130 B and the vector from transmitter  130 B to transmitter  130 C defines a vector normal to the plane containing the three transmitters. Using the position and orientation of the triangle of transmitters, the position and orientation of the gun  110  is calculated. For example, the muzzle of the gun  110  would be within the triangle, and the barrel of the gun is parallel to the normal vector calculated above. 
     The receivers  120 A-C are located around the monitor  104  in a right triangle configuration to promote the least obstructed pathway between transmitters  130 A-C and receivers  120 A-C (taking into account players of various sizes and/or pedestals that may be added to the configuration of the housing  102 ). Since the output from this system will be mapped onto a rectangular monitor  104  with coordinates that align with horizontal and vertical, the data must be rotated 45 degrees counter clockwise from the XYZ coordinate system of transmitter  120 A to that of the monitor  104 . This is easily accomplished by rotating the data around a known point, such as the center of the monitor  104 . This point, though virtual, is well defined and scales with both the size of the monitor  104  and the length of the legs of the right triangle formed by the receivers  120 A-C. 
     A method  400  of operating of the position sensor system will now be described with reference to FIG.  4 . In step  402 , a signal is generated by the Eyecon board  140  directing the first transmitter  130  to emit a light signal. The system then moves to a step  404 , wherein the light signal is received by the receivers  120 A-C. The system then moves to a step  406 , wherein the light received from the transmitter  130  is converted into an analog signal, which is amplified and sent to the Eyecon board  140 . Next, in step  408 , the Eyecon board  140  uses code-division multiplexing to remove noise and then converts the analog signals into digital signals as explained above. In one embodiment, the transmission time period for any one transmitter is enough to allow more than one conversion of the analog signal by the A/D converter  150  on the Eyecon board  140 . For example, the time period can be such that six signals are generated for each transmitter. Multiplying these six signals by three receivers  120 A-C, it can be seen that a total of eighteen sets of raw data are passed to the processor  160  during this step. 
     The system then moves to a step  410 , wherein the processor  160  takes the six sets of data from each of the three receivers  120 A-C, sums and averages the data, and produces three averaged values, (one for each receiver from the one transmitter of that time period), which are stored by the processor  160 . The sequence then proceeds to the next transmitter  130 . In an embodiment with one gun  110 , this sequence continues until each of the three transmitters  130 A-C have been activated for their period of time, producing nine averaged values. In the embodiment having two guns  110 A and  110 B, this sequence would proceed through all six transmitters  130  to produce a total of eighteen averaged values. The process then starts over again with the first transmitter  130 . In one preferred embodiment, one cycle through all six transmitters  130  can be completed in less than {fraction (1/60)} of a second. 
     In step  412 , the processor  160  uses the eighteen sets of averaged data to determine the XYZ coordinates of the six transmitters  130 . In step  414 , the plane of the three transmitters  130 A-C on each gun  110 A and  110 B is calculated and the vector normal to the plane through the midpoint is calculated. These values are then sent to the video game software to be used by the processor  160  in the generation of the three-dimensional scenes displayed on the display monitor  104 . 
     The three-dimensional coordinates and the orientation of the gun  110  as calculated are input to the processor  160  and used to generate three-dimensional scenes displayed on the display monitor  104 . The position and vector can be used to project a virtual vector into the scene of the game depicting the targeted position of the gun  110  or to display the trajectory of gunfire or laser shots from the gun  110  into the displayed scene. 
     Specific blocks, sections, devices, functions and modules have been set forth. However, a skilled technologist will realize that there are many ways to partition the system of the present invention, and that there are many parts, components, modules or functions that may be substituted for those listed above. Although the above detailed description has shown, described and pointed out fundamental novel features of the invention as applied to various embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated may be made by those skilled in the art, without departing from the spirit of the invention.