Abstract:
In various embodiments of the invention, an improved track ball suitably includes one or more field-producing elements that produce or respond to electromagnetic fields in accordance with the Hall Effect. Hall Effect sensors in proximity to the track ball sense changes in the electromagnetic field or in the Hall Effect, and produce corresponding output signals. The output signals may be used, for example, as a control input to a digital computer for such applications as games, simulations, or control applications such as controls for an aircraft or other vehicle.

Description:
FIELD OF THE INVENTION 
     The invention relates to devices and techniques for positioning a pointer such as a cursor on a computer display. More specifically, the invention relates to a pointing device such as a track ball that is based upon the Hall Effect. 
     BACKGROUND OF THE INVENTION 
     Numerous pointing devices such as joysticks, mice, track balls, touch pads and the like are well known in the art. Such pointing devices are frequently used to position a cursor or other pointer on an electromagnetic display such as a flat panel display, cathode ray tube (CRT) display, liquid crystal display (LCD), plasma display, or the like. Pointing devices are useful in various computing applications such as games, simulations, control applications, or any other computer application. Track balls are particularly convenient for use as an input device for games, simulations, and control applications because track balls allow precise positioning of pointers, cursors or other objects on a computer display. 
     Various types of track balls have been used in the prior art. For example, mechanical track balls available from, for example, Pennie and Giles, CTI, and other manufacturers include gear-like mechanisms and switches that allow users to position objects on a display by rotating or otherwise manipulating a mechanical ball. The track ball device senses movement of the ball, and provides a corresponding control signal to the computerized display. Mechanical track balls typically exhibit a noted disadvantage, however, in that the switches and gear-like apparatus can fail or wear over time. Hence the reliability of such devices is suspect, particularly in environments that may be subject to large amounts of dust or other contaminants. 
     Optical track balls such as those available from the Logitech Corporation of Fremont, Calif. are less susceptible to dust and other contaminants, but such devices include optical guides that may wear or otherwise degrade over time. Moreover, optical track balls may be susceptible to radio frequency (RF) interference or other forms of interference. Hence even optical track balls are not suitable for all situations. 
     It is therefore desired to create a pointing device using a new sensor technology that is not susceptible to the disadvantages of prior art pointing devices. 
     SUMMARY OF THE INVENTION 
     In various embodiments of the invention, an improved track ball suitably includes one or more field-producing elements that produce or respond to electro-magnetic fields in accordance with the Hall Effect. Hall Effect sensors in proximity to the track ball sense changes in the electro-magnetic field or in the Hall Effect, and produce corresponding output signals. The output signals may be used, for example, as a control input to a digital computer for such applications as games, simulations, or control applications such as controls for an aircraft or other vehicle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     The above and other features and advantages of the present invention are hereinafter described in the following detailed description of illustrative embodiments to be read in conjunction with the accompanying drawing figures, wherein like reference numerals are used to identify the same or similar parts in the similar views and: 
     FIG. 1 is a perspective view of an exemplary track ball assembly; 
     FIG. 2 is a block diagram of an exemplary first embodiment of a track ball utilizing the Hall Effect; 
     FIG. 3 is a block diagram of a second exemplary embodiment of a track ball utilizing the Hall Effect; and 
     FIG. 4 is a flow chart of an exemplary process for monitoring movement of a track ball based upon the Hall Effect. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The present invention may be described herein in terms of functional block components and various processing steps. It should be appreciated that such functional blocks may be realized by any number of hardware and/or software components configured to perform the specified functions. For example, the present invention may employ various discreet or integrated circuit components, e.g., memory elements, processing elements, logic elements, look-up tables, and the like, that may carry out a variety of functions under the control of one or more microprocessors or other controlled devices. Similarly, the software elements of the present invention may be implemented with any programming or scripting language such as C, C++, Java, assembly language, machine language, or the like, with the various algorithms being implemented in any combination of data structures, objects, processes, routines or other programming elements. Further, it should be noted that the present invention may employ any number of conventional techniques for electronics configuration, signaling, data processing, mechanical configuration and the like. 
     It should be appreciated that the particular implementations shown and described herein are examples of the invention and are not intended to otherwise limit the scope of the present invention in any way. Indeed, for the sake of brevity, conventional electronics, software development and other functional aspects of the systems (and components of the individual operating components of the systems) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships.and/or physical or logical couplings between the various elements. It should be noted that many alternative or additional functional relationships, physical connections or logical connections may be present in a practical track ball utilizing the Hall Effect. 
     Generally speaking, when a steady current is flowing in a steady magnetic field, electromotive forces are developed that are at right angles both to the magnetic force and to the current. These electromotive forces are proportional to the product of the intensity of the current, the magnetic force, and the sine of the angle between the directions of these quantities. This phenomenon is known as the Hall Effect. Stated another way, the Hall Effect is a phenomenon that arises when an electric current and magnetic field are simultaneously imposed on a conducting material. 
     In a broad aspect of the present invention, a trackball is provided that includes a ball having embedded therein or thereon a electro-magnetic field producing element such as a magnet or a number of metallic elements. The field producing element may produce or reflect an electromagnetic field in accordance with the Hall Effect. As the ball rotates, the electro-magnetic field produced by the field-producing elements also rotates as appropriate. That is, the electro-magnetic field observed on the surface of the ball may remain fixed with respect to the ball itself, but the field observed by a relatively stationary sensor next to the ball will vary as the ball rotates. Hence, the rotation of the ball can be sensed by a detector (which may include one or more sensors), and an output signal corresponding to the ball&#39;s rotation can be prepared based upon the fields observed by the detector. The output signal may be computed and/or provided by, for example, position processing electronics as described below. 
     FIG. 1 is a perspective view of an exemplary track ball  100 . Track ball  100  suitably includes a ball  104 , a housing  102 , one or more buttons such as buttons  106 ,  108  and  110 , and a cable  112  providing a signal from track ball  100  to a digital computer (not shown) or other apparatus. To operate track ball  100 , a user rotates ball  104  in any direction. The rotation is sensed by sensors (not shown) within housing  102 , and the rotation is converted to an output signal provided via cable  112  by electronics located within housing  102 . Buttons such as buttons  106 ,  108  and  110  may be used much like the buttons on a mouse or other planing device, to select objects on a display screen, for example, or for any other purpose. Of course various configurations of track balls could be formulated in accordance with the present invention. For example, housing  102  may be configured in any manner, such as in an ergonomic manner that is tailored to accommodate a human hand, or in any other manner. Similarly, ball  104  may be formulated of plastic, metal, acrylic, or any other material. 
     FIG. 2 is a block diagram of an exemplary track ball  200  that operates in accordance with the Hall Effect. With reference now to FIG. 2, track ball  200  suitably includes ball  104  as described above, but with the addition of one or more magnets such as magnets  202  and  204 . Magnets  202  and  204  produce electro-electro-magnetic fields that are detectable by sensors  206  and  208 , respectively. Sensors  206  and  208  are any type of Hall Effect sensor such as, for example, the MRL Hall Effect sensor available from Honeywell International Inc. of Freeport, Ill. Other exemplary Hall Effect sensors include the Model LA25-NP sensor available from the LEM Corporation of Milwaukee, Wis. Alternatively, any type of Hall Effect or other electromagnetic sensor could be used to implement sensors  206  and  208 . In various embodiments, sensors  206  and  208  provide electrical signals  214  and  216 , respectively, to position processing electronics  210 . Signals  214  and  216  may be any form of electrical or optical output signal, such as a voltage or current. In an exemplary embodiment, signals  214  and  216  are voltages that are proportional to the magnitude of the Hall effect observed by the relevant sensor. Alternatively, signals  214  and  216  could be digital representations of the Hall effect observed by sensors  206  and  208 , respectively. 
     Position processing electronics  210  suitably include any hardware or software equipment for receiving.signals  214  and  216  from sensors  206  and  208 , respectively, at a producing and output signal  212  that is indicative of the rotation of ball  104 . In various embodiments, position processing electronics  210  suitably include a microprocessor or microcontroller such as any of the microcontroller products available from, for example, the Motorola Corporation of Schaumburg, Ill., the Intel Corporation of Santa Clara, Calif., or the Microchip Corporation of Chandler, Ariz. Alternatively, a digital signal processor (DSP) could be used with position processing electronics  210 . Exemplary digital signal processors include those available from, for example, the Texas Instruments Corporation of Piano, Tex., or the Lucent Corporation of Murray Hill, N.J. The various microcontrollers, microprocessors, or DSP chips may communicate with one or more digital memories (not shown) to process signals  214  and  216 . An exemplary technique for processing such signals is disclosed below in conjunction with FIG.  4 . 
     To operate track ball  200 , a user rotates ball  104  such that the electro-magnetic fields produced by magnets  202  and  204  are rotated. Note that a third magnet (not shown) could be added to ball  104  to detect movements in a third dimension, if required, or to improve resolution in two dimensions. Such a magnet may be perpendicular to magnets  202  and  204 , or may be otherwise oriented as appropriate for the particular embodiment. As the electro-magnetic fields generated by magnets  202  and  204  rotate in conjunction with rotation of ball  104 , the electro-magnetic fields detected by Hall Effect sensors  206  and  208  correspondingly vary. As such, the output signals  214  and  216  produced by sensors  206  and  208 , respectively, may vary in accordance with the electromagnetic field detected at the relevant sensor. In other embodiments, magnets  202  and  204  are arranged such that the magnets produce a unique electromagnetic field at each portion on the outer surface of ball  104 . In such embodiments, a single sensor  206  may be used to detect the portion of ball  104  in closest proximity to the sensor  206 , such that the exact position of ball  104  can be known. That is, the intensity of the electro-magnetic field associated with ball  104  and sensed at a particular position by sensor  206  is indicative of the orientation of ball  104 . Position processing electronics  210  may suitably provide an output signal  212  that corresponds to the position of ball  104 . 
     FIG. 3 is a block diagram authentic exemplary track ball  300  using a different technique for Hall Effect sensing. Ball  104  suitably includes a number of conducting elements  302 . Elements  302  may be comprised of any conducting material, such as a ferrous or non-ferrous metal or any combination of materials. In various embodiments, elements  302  are manufactured to include MU metal, which is highly responsive to electro-magnetic fields. Elements  302  may be distributed through ball  104  in any manner. For example, elements  302  may be distributed along the surface of ball  104 , or they may be distributed throughout the entirety of ball  104 . Similarly, elements  302  may be arranged in any pattern, such as a regular interspersed pattern, or a randomly placed pattern. In an exemplary embodiment, however, elements  302  are interspaced upon the surface of ball  104  in a regular pattern such that each element  302  is approximately equidistant from the other elements  302 . Hall Effect sensors  206  and  208  suitably induce electro-magnetic fields upon elements  302 , such that the passage of an element  302  in close proximity with a sensor  206  or  208  can be detected. Sensors  206  and  208  suitably provide outputs  214  and  216 , as described above, to position processing electronics  210  to indicate the passage of an element  302  in proximity with the relevant sensor  206  or  208 . Of course, various embodiments of the invention may use any number of Hall Effect sensors. For example, a simple embodiment may include a single Hall Effect sensor that is capable of detecting element movement in various directions. Similarly, additional sensors could be provided to increase resolution, or to increase sensitivity in multiple dimensions. 
     FIG. 4 is a flow chart of an exemplary technique  400  suitable for producing output signal  212  at position processing electronics  210 . Technique  400  suitably includes determining in initial position (step  402 ) of ball  104  through any technique. For example, an initial position may be determined at power up by sensoring the magnitude of the electro-magnetic field at a given point (such as at a sensor  206  or  208 ). Alternatively, an absolute position may not be necessary in embodiments requiring only relative rotation of ball  104  as an output. In such embodiments, an initial configuration may be stored in memory such that deviations from this position can be monitored and provided as output  212 . For example, a two (or more) coordinate “starting point” may be recorded in memory, or the initial position of ball  104  could be recognized as “home” (e.g. point 0,0 on a two-coordinate axis system). 
     After the initial position is determined, an interactive process  416  involves monitoring movements at each sensor  206  and  208 . Although FIG. 4 shows process  416  as being executed in a “IF-THEN” configuration, any looping or iteration scheme.could be used. For example, a practical process  416  may be implemented with a “WHILE-DO” process, a polled process, or an interrupt driven process. In the various embodiments, movement of ball  104  is tracked on various axes (steps  404  and  410 ). This movement is detected, the position of the ball is updated along the relevant axis (steps  406  and  408 ). Of course, the position may be updated in any manner, for example by updating a value stored in memory, or by providing an electrical indication to an external computer via cable  112  (FIG.  1 ). Moreover, movement could be tracked in three or more dimensions by simply adding additional decision blocks such as  404  and  410 . Movement upon a relevant axis may be sensed by any technique, but in various embodiments movement upon an individual axis is sensed at an individual sensor, such as sensor  206  or sensor  208 . For example, and with momentary reference to FIG. 2, rotation of ball  104  will create a shift in the electromagnetic field produced by magnet  202 , which may be sensed by sensor  206 . Similarly, rotation of ball  104  in a second direction will cause changes in the electro-magnetic field produced by magnet  204 . These changes may be sensed by sensor  208 . Additional sensors could detect lateral displacement of ball  104  or rotation of ball  104  in a third direction (e.g., about the axis normal to magnets  202  and  204  in FIG.  2 ). With momentary reference to FIG. 3, rotation of ball  104  may produce changes in the Hall Effect from elements  302  observed at sensors  206  and  204  dependent upon the direction of rotation. Corresponding output signals  214  and  216  may thusly contain indications of rotation in two directions. Position processing electronics  212  may then produce an output signal  212  that is indicative of the rotational displacement of ball  104  in a first or second direction. Of course output signal  212  may be updated as ball  104  continues to rotate in order to provide a continual position indication via cable  112  to an external digital computer or other device. If signal  212  indicates, for example, an X-Y coordinate corresponding to the rotational position of track ball  104 , a cursor or other item on a display screen may be correspondingly manipulated by rotating ball  104 . 
     The corresponding structures, materials, acts and equivalents of all elements in the claims below are intended to include any structure, material, or acts for performing the functions in combination with other claimed elements as specifically claimed. Moreover, the steps recited in any method claims may be executed in any order. The scope of the invention should be determined by the dependent claims and their legal equivalence, rather than by the examples given above.