Abstract:
A pointing device of a computer includes a sensing module and a button. The sensing module has two magnetism detectors, each detector having a unique sensing axis. The magnetism detectors generate signals according to the relative changes of the sensing axes with respect to the geomagnetic field. The sensing signals and button signal are processed and transmitted to the computer for use in controlling the function of the computer.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a pointing device of a computer. More specifically, the present invention discloses a pointing device for generating a displacement signal according to the displacement of the pointing device with respect to a geomagnetic field. 
     2. Description of the Prior Art 
     In modern computer systems, a graphical user interface (GUI) has become the main method of interaction for a computer, user. GUIs are typically user-friendly and have simple and intuitive designs. In cooperation with the GUI, a pointing device has become a necessary peripheral device of the modern computer system by allowing the user to both operate the movement of the on-screen cursor and execute commands. It is therefore an important research objective of the information industry to develop an ergonomic and user-friendly pointing device. 
     The typical and commonly used pointing device is a mouse. The prior art mouse comprises a rolling ball mechanism disposed at the bottom of the mouse. When the user moves the mouse across a plane, the roller ball is caused to roll. The displacement of the mouse is measured by sensing the rolling action of the roller ball. This displacement measurement is translated into a displacement of the cursor on the computer screen. In other words, the cursor on the computer screen makes a corresponding movement when the user moves the mouse. As a result, the user may operate the GUI of the computer system with the mouse. 
     The drawback of the prior art mouse is that the mechanical mechanism of the roller ball is vulnerable to particles (such as dust), which results in wear of the mechanical mechanism. Because of this, periodic cleaning and maintenance are necessary. In addition, the user must operate the prior art mouse directly on a flat surface so that the roller ball contacts the flat surface. Consequently, the user can feel tired and strained due to these repetitive plane-limited movements. Furthermore, there is the possibility of serious injury with continued use. 
     SUMMARY OF INVENTION 
     It is therefore a primary objective of the claimed invention to provide a pointing device to sense displacement with respect to the geomagnetic field to solve the above-mentioned problems. 
     According to the claimed invention, the pointing device comprises a housing, at least a button installed on the housing for generating a control signal when a user presses the button, and a sensing module installed inside the housing. The sensing module further comprises a first magnetism detector comprising a first sensing axis, a second magnetism detector comprising a second sensing axis, an amplifier and a decoder. The first magnetism detector generates a first sensing signal according to a relative change of the first sensing axis with respect to a geomagnetic field. The second magnetism detector generates a second sensing signal according to a relative change of the second sensing axis with respect to the geomagnetic field. The amplifier is connected to the first magnetism detector and the second magnetism detector for amplifying the first sensing signal and the second sensing signal. The decoder is connected to the amplifier for generating a two-dimensional displacement signal according to the amplified first sensing signal and the amplified second sensing signal. The first sensing axis is not parallel with the second sensing axis and forms a predetermined angle with the second sensing axis. The first magnetism detector and the second magnetism detector respectively sense changes of the first sensing axis and the second sensing axis with respect to the geomagnetic field when the user moves the pointing device such that the decoder generates the corresponding two-dimensional displacement signal accordingly. 
     It is an advantage of the claimed invention that the pointing device utilizes an entirely electronic means to measure the displacement of the pointing device. Furthermore, the pointing device references the geomagnetic field. Therefore, the user feels less tired or strained after extended use of the pointing device. 
     These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of a mouse for utilizing as a pointing device according to the present invention. 
     FIG. 2 is a schematic diagram of an internal structure of the mouse in FIG.  1 . 
     FIG. 3 is a functional block diagram of the mouse depicted in FIG.  2 . 
     FIG.  4 A and FIG. 4B are diagrams to show the operating method of a magnetoresistor detector under different magnetic fields. 
     FIG. 5 is a schematic diagram to show the principle of utilizing an electromagnetic inductance detector as a magnetism detector. 
    
    
     DETAILED DESCRIPTION 
     Please refer to FIG.  1 . FIG. 1 is a perspective view a mouse  10  for utilizing as a pointing device according to the present invention. The mouse  10  is encased in a housing  12 . Buttons  14  are installed on the housing. When a user presses the button  14 , the button  14  will generate a corresponding control signal. 
     Please refer to FIG.  2  and FIG.  3 . FIG. 2 is a schematic diagram of an internal structure of a mouse  10  according to the present invention. FIG. 3 is a functional block diagram of the mouse  10  depicted in FIG.  2 . As shown in FIG. 2, a first magnetism detector  16 A, a second magnetism detector  16 B, an amplifier  18 , a decoder  22  and a first wireless transmission module  24 A are installed inside the housing. An arrow  19 A represents the direction of a first sensing axis of the first magnetism detector  16 A. An arrow  19 B represents the direction of a second sensing axis of the second magnetism detector  16 B. As shown in FIG.  2  and FIG. 3, the direction of the arrow  19 A is perpendicular to the direction of the arrow  19 B. The first magnetism detector  16 A and the second magnetism detector  16 B operate under the same principle. The first magnetism detector  16 A senses the change of the first sensing axis with respect to the geomagnetic field and generates a corresponding first sensing signal  17 A. Similarly, the second magnetism detector  16 B senses the change of the second sensing axis with respect to the geomagnetic field and generates a corresponding second sensing signal  17 B. The first sensing signal  17 A and the second sensing signal  17 B are first amplified by the amplifying circuits  26 A and  26 B (shown in FIG. 3) in the amplifier  18  respectively, and are then sent to the decoder  22 . Since the sensing axis of the first magnetism detector  16 A is perpendicular to the sensing axis of the second magnetism detector  16 B, the relative displacement with respect to the geomagnetic field, resulting from moving the mouse  10 , is divided into two perpendicular components. These two components are contained in the first sensing signal  17 A and the second sensing signal  17 B respectively. The decoder  22  then analyzes the amplified first sensing signal  17 A and the amplified second sensing signal  17 B to determine the two perpendicular displacement components, which reflect the actual displacement of the mouse  10 , and generates a two-dimensional displacement signal  23 A. In the preferred embodiment of the present invention, a first wireless transmission module  24 A is installed inside the mouse  10  for transmitting the two-dimensional displacement signal  23 A through radio communication. In addition, a control signal  23 B generated by a user by pressing the button  14  is transmitted from the first wireless transmission module  24 A through radio communication. As the mouse  10  is a pointing device of a computer system  30 , the control signal  23 B and the two-dimensional displacement signal  23 A transmitted from the first wireless transmission module  24 A through radio communication are received by a second wireless transmission module  24 B located in the computer system  30 . 
     The operating procedure of the present invention mouse  10  is described as follows. When the user moves the mouse  10 , the first and second magnetism detectors  16 A and  16 B fixed inside the mouse  10  and their corresponding first and second sensing axis move as well. The first sensing axis and the second sensing axis respectively form different angles with reference to the geomagnetic field of fixed orientation as the user moves the mouse  10 . The first and the second magnetism detectors  16 A and  16 B sense such changes and respectively generate the corresponding first and second sensing signals  17 A and  17 B. Since the first sensing axis is perpendicular to the second sensing axis, the corresponding first and second sensing signals,  17 A and  17 B, are equivalent to the two perpendicular components obtained by decomposing the displacement vector of the mouse  10 . After the corresponding first and second sensing signal  17 A and  17 B are processed by the amplifier  18  and the decoder  22 , a two-dimensional displacement signal  23 A is thus generated to represent the two-dimensional displacement of the mouse  10 . In addition, the user can press the button  14  to generate a corresponding control signal  23 B. The two-dimensional displacement signal  23 A and the control signal  23 B are transmitted to the second wireless transmission module  24 B in the computer system  30  from the first wireless transmission module  24 A inside the mouse  10  through radio communication. The computer system  30  receives the two-dimensional displacement signal and the control signal that are then used to move the cursor and execute functions correspondingly such that the user can operate the computer system  30  by utilizing the mouse  10 . 
     The first and second magnetism detectors  16 A and  16 B in the present invention may be realized by using magnetoresistor detectors. The working principle of a magnetoresistor detector  36  under the influence of different magnetic fields is illustrated in FIGS. 4A,  4 B. The magnetoresistor detector  36  is realized by a magnetoresistor  34  and a resistor measurement circuit  32 . The magnetoresistor  34  behaves like a typical electrical resistor except that the resistance of the magnetoresistor changes as the external magnetic field changes. Furthermore, the resistance of the magnetoresistor  34  depends on the angle between the magnetic field and the direction of a current I passing through the magnetoresistor. The resistor measurement circuit  32  is utilized to measure the resistance of the magnetoresistor  34 . As shown in FIG. 4A, the magnetoresistor  34  has its own induced magnetic field Mo. When there is no external magnetic field, the angle between the current I and the magnetic field M 0  is A 0 . As shown in FIG. 4B, when there is an external magnetic field M 1  applied on the magnetism detector  36 , the external magnetic field M 1  would add to magnetic field M 0  and create a magnetic field M 2 . The angle between the magnetic field M 2  and the current I becomes A 1  and the resistance of the magnetoresistor  34  changes as angle A 1  is changed. The resistor measurement circuit  32  measures the resistance change of the magnetoresistor  34  and generates a corresponding sensing signal that reflects the change of the external magnetic field. As known by those skilled in the arts and illustrated in FIG. 4B, when the direction of the external magnetic field M 1  changes the angle A 1  between the current I and the total magnetic field M 2  changes causing the resistance of the magnetoresistor  34  to change. In practical application, the direction of the current I or the direction of the induced magnetic field M 0  of the magnetoresistor  34  could be regarded as the sensing axis of the magnetoresistor detector. 
     In addition, the present invention magnetism detector can be created by employing the principle of electromagnetic inductance. Please refer to FIG. 5, which is a schematic diagram showing the principle of utilizing an electromagnetic inductance detector  40  as a magnetism detector. The electromagnetic inductance detector  40  is formed by a conductive ring  46  and a potential measurement circuit  42 . As known from Faraday&#39;s law, when the conductive ring  46  moves across the a static magnetic field M, such as the geomagnetic field, with a velocity V, a potential difference (the so-called flux-cutting electromotive force) is produced between a node  48 A and a node  48 B in the conductive ring  46  due to the electromagnetic inductance effect. This potential difference, as measured by the potential measurement circuit  42 , is proportional to velocity V. In practical application, the electromagnetic inductance detector  40  is fixed in the mouse. The conductive ring  46  moves across the geomagnetic field, as the mouse is moved, and produces the potential difference. The potential measurement circuit  42  can cooperate with a high frequency clock pulse to periodically measure the potential difference. Since the period of the clock pulse is fixed, the displacement of the mouse can be obtained by comparing the potential differences measured. The direction  47  of the conductive ring  46  can be regarded as the sensing axis of the electromagnetic inductance detector  40 . 
     In contrast to the prior art, the present invention mouse utilizes an entirely electronic means to measure the displacement of the mouse. Since the present invention mouse has no mechanical parts, as the prior art rolling ball type mouse, the problem of mechanical wear is eliminated. Furthermore, the present invention mouse need not be operated on a flat planar surface as it references the geomagnetic field. This results in the user feeling less tired or strained after extended use of the mouse, and the possibility of long-term serious injury can be avoided. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.