Abstract:
A handwriting pen used in a tablet type handwriting entry device comprises a pen tip, a pen tip position sensor, and a pressure sensor. The pen tip position recognizer captures a main position coordinates as the pen tip taps on a tablet panel, and generates a main position data. The pressure generator senses a press by the pen tip on the tablet, and generates a pressure value. The handwriting pen connects to a main system by a signal transmission line, and the acquired information is transferred to the main system. The main system has a pen stroke simulation apparatus that manipulates the main position data and the pressure value for simulating different pen strokes.

Description:
[0001]     This application claims priority of Taiwanese application no. 092125437 and 092125435, filed on Sep. 16, 2003.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a handwriting pen and more particularly relates to a handwriting pen capable of simulating different pen strokes.  
         [0004]     2. Description of the Prior Art  
         [0005]     Recently, handwriting entry devices emerge to form a new generation of input devices. In general, a handwriting device comprises a handwriting tablet and a handwriting pen, supports user handwriting with a stylus directly on the tablet, and features an alternative means to replace the keyboard mode of input. Popularly seen handwriting devices are categorized into the following two types: Tablet PC, consisting of a flat-screen LCD panel and an electromagnetic sensitive touch-control pen; and WACOM digitizer or graphics tablet, consisting of a pressure sensitive graphics tablet or digitizing tablet, and a pressure sensitive pen. Moreover, the users have to install recognition software; for instance, Photoshop and the like graphics software in the computer system, for the recognition of what the users write or draw by means of the handwriting entry devices.  
         [0006]     The recognition software has to recognize a position that the handwriting pen taps on the handwriting tablet, an (X, Y) coordinates; and pressing force with the handwriting done by an individual user, a pressure value Z, to simulate pen strokes of distinct styles. However, due to the deficiency in acquiring enough data, the existing graphics software; for instance, Photoshop, CorelDraw, Painter, etc, have tremendous deficiency in the simulation of the pen strokes.  
       SUMMARY OF THE INVENTION  
       [0007]     Therefore, the main purpose of the present invention is to offer a handwriting pen an attribute of simulating different pen strokes, to accomplish the simulation of distinct styles of individual pen strokes according to the distinguishing feature of the hand press, and to further enhance the power of simulating the pen strokes by the graphics software.  
         [0008]     The handwriting pen of the present invention comprises a pen tip; a pen tip position recognizer, capturing a main position coordinates of the pen tip on the handwriting tablet to generate a main position data; a pressure generator, sensing a value of pressure exerting by the pen tip on the handwriting tablet panel to generate a pressure value. The handwriting pen connects to main system by a signal transmission line through which the main position data and the corresponding pressure value are sent to the main system. The main system has a pen stroke simulation apparatus, which manipulates the main position data and the pressure value, and simulates the pen strokes of distinct styles. The pen stroke simulation apparatus comprises a pressure-radius transformation module, which receives the pressure value, and converts it into a radius data; a positive vector generation module, receiving the main position data through which a positive vector data is generated; a density location generation module, connecting to the pressure-radius. transformation module and the positive vector generation module, for generating a plurality of density locations to represent a plurality of density location coordinates in the direction of the positive vector at the main positions, according to the radius and the positive vector data; and a pen stroke generation module, drawing a main line of trajectory according to the pen tip sliding across the main positions over time, and drawing a plurality of density lines according to the density location data, wherein each main position data corresponds to a plurality of the density location data. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention featuring its novelty, can be readily understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein:  
         [0010]      FIG. 1  shows a handwriting pen accompanying a handwriting tablet in the usage of the present invention;  
         [0011]      FIG. 2  shows a relationship between radiuses of circles and pressure values;  
         [0012]      FIG. 3  is a schematic diagram of the present invention showing the handwriting pen connecting to a main system;  
         [0013]      FIG. 4  shows a plurality of density location coordinates;  
         [0014]      FIG. 5  shows a main line and density lines;  
         [0015]      FIG. 6  is a flow diagram showing a pen stroke forming method of a pen stroke generation module;  
         [0016]      FIG. 7  is a schematic diagram showing a pen stroke formed by the pen stroke generation module;  
         [0017]      FIG. 8  is a block diagram of the pen stroke generation module;  
         [0018]      FIG. 9  shows dispersion position coordinates;  
         [0019]      FIG. 10  is a schematic diagram of different pen strokes;  
         [0020]      FIG. 11  is a schematic diagram of the handwriting pen of the present invention;  
         [0021]      FIG. 12  is a system structure diagram of the handwriting pen;  
         [0022]      FIG. 13  is a schematic diagram of the handwriting pen undergoing a deformation at its pen head;  
         [0023]      FIG. 14  is a schematic diagram of a gear and a rotation velocity detector of the handwriting pen  
         [0024]      FIG. 15  is a circuit block diagram of the handwriting pen;  
         [0025]      FIG. 16  shows a bending angle of a pen head;  
         [0026]      FIG. 17  shows a variation relationship between the bending angle of the pen head and the pressure value by the handwriting pen; and  
         [0027]      FIG. 18  is a schematic diagram of another example of the handwriting pen of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     Please refer to  FIG. 1 .  FIG. 1  is an exterior view of the present invention, showing the usage of a handwriting pen  10  (detail structure will be described in the next paragraph) and an accompanying handwriting tablet  12 . As shown in the figure, the handwriting pen  10  comprises a pen tip  11 , where a user employs the handwriting pen  10  writing on the handwriting tablet  12  to accomplish a pen stroke  14  which is composed of a plurality of circles  16 , where the center of the circle  16  is represented by O and the radius ω.  
         [0029]     Please refer to  FIG. 2 .  FIG. 2  shows a relationship between the radius ω of circle  16  and pressure value Z. As shown in the figure, the harder the user presses down on the pen tip, the larger the pressure value Z of the handwriting pen  10  is, and hence the radius ω of the circle  16  becomes lengthy. In other words, according to a variety of pressure values Z, the handwriting pen  10  over time generates a lot of circles  16  varied in size on the handwriting tablet to form the pen stroke  14 , where Maxω is a preset maximum value of radius.  
         [0030]     Please refer to  FIG. 3 .  FIG. 3  is a schematic diagram of the present invention showing the handwriting pen  10  connecting to a main system  21 . The handwriting pen  10  comprises a pen tip position sensor  18  and a pressure sensor  20 . The pen tip position sensor  18  is used to capture a main position coordinates O i , where the pen tip  11  taps on the handwriting tablet  12 , for generating a main position data. The main position coordinates O i  is the center of the circle  16  that the handwriting pen  10  generates over time t i , which can be denoted as a coordinates (X i , Y i ) . The pressure sensor  20  is used to sense the pressure that the pen tip  11  presses down on the handwriting tablet  12  to form a pressure value Z.  
         [0031]     The handwriting pen  10  connects to the main system  21  by a signal transmission line (not shown) through which the main position data and corresponding pressure values are sent to the main system  21 . The main system has a pen stroke simulation apparatus  23 ; for instance, graphics software or recognition software that manipulates the main position data and the pressure values, for simulating different pen strokes.  
         [0032]     The pen stroke simulation apparatus  23  comprises a pressure—radius transformation module  22 , a positive vector generation module  24 , a density location generation module  26 , and a pen stroke generation module  28 . The pressure-radius transformation module  22  is used to acquire a pressure value Z, and through applying a pressure-radius transformation equation, the pressure value Z is thus transformed to a radius value ω. The pressure-radius transformation equation is established by the relationship between the radius ω and the pressure value Z in  FIG. 2 , and represented as:  
       {             ϖ   =       f   ⁡     (   z   )       =       (     Max   ⁢           ⁢   ϖ     )     *     (         e   z     -   1       e   -   1       )                   where               f   ⁡     (   0   )       =   0                 f   ⁡     (   1   )       =     Max   ⁢           ⁢   ϖ                 0   ≤   Z   ≤   1           .         
 
         [0033]     The positive vector generation module  24  is used to acquire the main position data through which a positive vector data is generated. The positive vector generation module  24  first acquires an instantaneous direction of the pen tip  11  at the main position coordinate O i , according to the main position data, and the equation is expressed as:  
           V   i     =         O   i     -     O     i   -   1                  O   i     -     O     i   -   1                  ;       
 
 where V i  represents the instantaneous direction of the pen tip  11  over time t i ; O i , the main position coordinates of the pen tip  11  over time t i ; and O i−1 , the main position coordinates of the pen tip  11  over time t i−1 . Suppose V i =(x, y), the positive vector data N i =(−y, x) 
 
         [0035]     The density location generation module  26 , connects to the pressure-radius transformation module  22  and the positive vector generation module  24 , employs the radius data ω and the positive vector data N i  to generate a plurality of density location data, in the direction of the positive vector over the main position coordinate O i , and represents a plurality of density location coordinates b ij .  
         [0036]     Please refer to  FIG. 4 .  FIG. 4  shows a plurality of density location coordinates b ij . The density location generation module  26  employs a density location generation equation to generate a plurality of density location data b ij . The equation is represented as:  
         b     i   ,   j       =       O   i     +       ϖ   ⁡     (       j   n     -   1     )       ·     N   i             
 
 where O i  represents the main position coordinates of the pen tip over time t i ; ω, the radius; N i , the positive vector; n, a preset system value, used to decide the number of density locations; and b ij  the j th  density location coordinates of the i th  main position coordinates. On the other hand, the pen stroke  14 , drawn by the handwriting pen  10 , comprises m main positions, and each main position corresponds to n density locations. As shown in the diagram, the main position coordinate O i  corresponds to a plurality of density location coordinates b ij . 
 
         [0038]     Please refer to  FIG. 5 .  FIG. 5  shows a main line L and density lines l 1 ˜l 10 . The pen stroke generation module  28  is used to draw the main line L according to the pen tip  11  sliding across the main position coordinates O i−1 , O i , and O i+1  over time t i−1 , t i , and t i+1 , and to draw the density lines l 1 ˜l 10  based on the density location coordinates b i−1,j , b i,j , and b i+1,j . As shown in the figure, each main position coordinate corresponds to  10  density location coordinates.  
         [0039]     Please refer to  FIG. 6 .  FIG. 6  is a flow diagram showing a pen stroke forming method  30  of the pen stroke generation module  28 . The pen stroke generation module.  28  employs the pen stroke forming method  30  to form the main line L and the related density lines l 1 ˜ 10 . Suppose the main line L is formed by m main position coordinates and each main position coordinates corresponds to n density location coordinates, the example shown in  FIG. 5  has m=3 and n=10.  
         [0040]     In step  32 , the pen stroke generation module  28  computes the tangent vectors, T i  and T i+1 , of the i th  and (i+1) th  position coordinates. The equation is as follows:  
       {                 ⁢       T     i   +   1       =     a   *     (       P     i   +   1       -     P   i       )                         ⁢     a   ∈     [     0   ,   1     ]               ;         
 
 where P i+1  is the (i+1) th  position coordinate, and P i  is the i th  position coordinate. 
 
         [0042]     In step  34 , the pen stroke generation module  28  employs Blending functions to estimate the interpolating value between the i th  and the (i+1) th  position coordinates. The Blending functions are shown as follows:  
       {                 ⁢         h   1     ⁡     (   s   )       =       2   ⁢     s   3       -     3   ⁢     s   2       +   1                       h   2     ⁡     (   s   )       =         -   2     ⁢     s   3       +     3   ⁢     s   2                         h   3     ⁡     (   s   )       =       s   3     -     2   ⁢     s   2       +   s                     h   4     ⁡     (   s   )       =       s   3     -     s   2                       ⁢     0   ≤   s   ≤   1             .         
 
         [0043]     In step  36 , the pen stroke generation module  28  acquires a Cardinal Splines Curve, and the equation is: 
 
 {overscore (P)}={overscore (P)}   i   *h   1   +{overscore (P)}   i+1   *h   2   +{overscore (T)}   i   *h   3   +{overscore (T)}   i+1   *h   4 . 
 
         [0044]     Finally, in step  38 , the pen stroke generation module  28  computes the medium coordinate position between the i th  and the (i+1) th  position coordinates, and links the entire coordinate positions to form a smooth curve. The equation of the medium coordinate position is: 
 
 P=S*h*C  ; where 
 
       S   =         [           s   3               s   2               s   1             1         ]     ⁢           ⁢   C     =         [           P   i               P     i   +   1                 T   i               T     i   +   1             ]     ⁢           ⁢   h     =       [         2         -   2         1       1             -   3         3         -   2           -   1             0       0       1       0           1       0       0       0         ]     .             
 
         [0045]     Please refer to  FIG. 7 .  FIG. 7  is a schematic diagram showing a pen stroke formed by the pen stroke generation module  28 . After the pen stroke generation module  28  employs the pen stroke forming method  30  to link all the main position coordinates into the main line, and links all the density location coordinates into density lines, the pen stroke shown in  FIG. 7  is obtained.  
         [0046]     Moreover, the pen stroke generation module  28  consists of a variety of parameter generation modules, used for allocating various parameters for simulating different styles of pen strokes.  
         [0047]     Please refer to  FIG. 8 .  FIG. 8  is a block diagram of the pen stroke generation module  28 . The pen stroke generation module  28  comprises a color parameters generation module  40 , a speed parameters generation module  42 , a speed-color parameters generation module  44 , a shade parameters generation module  46 , a dispersion parameters generation module  48 , a pause parameters generation module  50 , and a stroke-color parameters generation module  52 .  
         [0048]     The color parameters generation module  40  generates color parameters relative to the main position data and the density location data by a random number generator (not shown) , for determining the color of each position at the main line L and the density lines l 1 ˜l 10 . The color parameters generation module employs a color parameters generation equation to form the color parameters ρ i . The equation is as follows:  
         {               ⁢       ρ   i     =       ρ   1     +            rand   (   )          ⁢   %   ⁢     (       ρ   2     -     ρ   1     +   1     )                     where               ρ   1     ≤     ρ   i     ≤     ρ   2                     ⁢       ρ   1     ,       ρ   2     ∈     [     0   ,   255     ]                       ;       
 
 where ρ 1  and ρ 2  are preset system values. 
 
         [0050]     In general, the values of ρ 1  and ρ 2  are set rather closer to each other to avoid considerable difference.  
         [0051]     The speed parameters generation module  42  generates speed parameters, relative to the main position data and the density location data, to represent the instantaneous speed of the handwriting pen  10  at each position. The speed parameters generation module  42  employs a speed parameters generation equation to generate the speed parameter V. The equation is as follows  
         V   =       f   ⁡     (   v   )       =     (         v   max   3     -     3   ⁢     v   max     ⁢     v   2       +     2   ⁢     v   3           v   max   3       )         ;       
 
 where ν represents the instantaneous speed of the handwriting pen  10  at the main position coordinates, and ν max  represents a maximum preset speed value. 
 
         [0053]     During writing, due to the varying of the instantaneous speed, the ink presents a different degree of density. In general, the faster the instantaneous speed, the paler in color of the ink is. Therefore, the speed-color parameters generation module  44  generates speed-color parameters according to the color parameters and the speed parameters, for exhibiting the above relationship between the instantaneous speed and the density of the ink. The speed-color parameters generation module  44  employs a speed-color parameters generation equation to generate the speed-color parameter ρ i . The equation is as follows: 
 
ρ i =ρ i   *V  
 
         [0054]     The shade parameters generation module  46  generates shade parameters according to the pressure value Z, relative to the main position data and the density location data. Writing or drawing with a soft pen such as a writing brush or a watercolor pen, usually makes the ink paler by the repeated depictions. Therefore, the main position data would possess a maximum value of the shade parameters, and the farther the distance from the main position coordinates, the smaller the shade parameter value of the density location data is; such that the main line L is the deepest, while a density line appears paler as it separates farther from the main line L, exhibiting a situation of shade gradient.  
         [0055]     In general, the pressure gets lower; that is, a gentle pressing on writing, it is obvious that the shade of a pen stroke gets paler, and the shade changing is less obvious while reversely. For instance, with a harsh pressing on writing, the shade of the stroke is usually thick and homogeneous, and it is rare to be a tint. Therefore, according to the above description, the shade parameters generation module  46  generates the shade parameters based on the pressure value Z.  
         [0056]     Besides, the shade parameters generation module  46  employs a shade parameters generation equation to form shade parameter λ. The equation is as follows: 
 
λ=(1−λ 0 )(1− e   −az )+λ 0 ; 
 
 where a is a user defined constant; z, the pressure value; and λ 0 , a present value of the shade parameters. 
 
         [0058]     As a harsh pressing on writing, the shade of the pen stroke is especially thick and extremely homogeneous, and it is not likely to be in a tint; therefore, as the value of the pressure in the above equation exceeds a certain predefined value, the shade parameter would be a constant.  
         [0059]     In general, the writing or drawing by writing brush or a watercolor pen usually appears a phenomenon of being dispersed or diffused; therefore, each pen stroke exhibits a different degreee in width. The longer the pen tip stays, the considerable the degree of being dispersed, and the dispersion parameters generation module  48  is used to simulate the phenomenon of dispersion.  
         [0060]     The dispersion parameters generation module  48  generates a plurality of dispersion positions according to the main positions and the radii ω, for representing a plurality of dispersion position coordinates.  
         [0061]     Please refer to  FIG. 9 .  FIG. 9  is a schematic diagram of the dispersion position coordinates q i . Each main position corresponds to a plurality of dispersion positions, which means that each main position coordinates O i  corresponds to a plurality of dispersion position coordinates q i . The dispersion parameters generation module  48  consists of a dispersion parameters D, which is used to decide the distance between every two of the dispersion position coordinates q i , and employs a dispersion position generation equation to generate dispersion positional coordinates, such that the farther the distance from the main position coordinates O i , the shorter the distance between the dispersion positional coordinates q i  is. The equation is as follows:  
             ∂   q       ∂   t       =     D   ⁢       ∇   2     ⁢   q         ⁢           ;       
 
 where the equation is expanded by employing the finite difference method:  
         ⇒         q     i   +   1       -     q     i   -   1           2   ⁢   t         =         D   ·     (       q     i   +   1       -     2   ⁢     q   i       +     q     i   -   1         )       ⁢     
     ⇒     q     i   +   1         =           q     i   -   1       +     2   ⁢     Dt   ·     q     i   +   1           -     4   ⁢     Dtq   i       +     2   ⁢     Dtq     i   -   1           ⁢     
     ⇒     q     i   +   1         =       (     1     1   -     2   ⁢   Dt         )     ⁢       (         -   4     ⁢     Dtq   i       +       (     1   +     2   ⁢   Dt       )     ⁢     q     i   -   1           )     .               
 
         [0063]     As in the foregoing description, the extend, beyond the radius ω, would confront a plurality of the dispersion position coordinates, and the distance falls between the dispersion position coordinates is gradually decreasing, and eventually approaching zero. Therefore, as a pen stroke is being formed, it tends to stretch outward, and the stretching rate would gradually decrease, eventually approaching zero. According to the different values assigned to the dispersion parameters D, the variations of the stretching rate also vary, and further exhibiting a different degree of dispersion.  
         [0064]     The foregoing description is about simulating the variations in position for the phenomenon of dispersion; as for the variations in color, it is available to apply it in the above equation to obtain the variations in color for the phenomenon of dispersion. Therefore, each dispersion position data mentioned above corresponds to a dispersion color data, while the dispersion parameters generation module  48  utilizes the dispersion parameters D too, for determining the variations in color between every two of the dispersion color data, and employs the foregoing equation to generate the dispersion color data; such that the farther the dispersion position from the main position, the smaller the variance between the dispersion color data is. Hence, it appears an effect of dispersion that the shade of color gets paler gradually.  
         [0065]     Furthermore, the pen stroke  14  may encounter a pause, subject to the different materials of the brush pen or watercolor pen; that is, certain portions of the pen stroke  14  are vacant, and the pause parameters generation module  50  is used to simulate the phenomenon of the pauses herein.  
         [0066]     The pause parameters generation module  50  generates pause parameters, mapping to the main position and the density locations, for determining whether the main position and the density locations are to be seen. The pause parameters generation module  50  consists of a pause parameters preset table, possessing a plurality of the pause parameters, for corresponding to the main position data and the density location data. As a pause parameter is set to a first value, the corresponding position will be shown up; otherwise, a setting of a second value will disable the appearance of the corresponding position.  
         [0067]     Therefore, through the pause parameters setting, certain portions of the pen stroke  14  are vacant, which makes the line an aspect of pauses. The pause parameters d can be represented as: 
 
 d=d Table( i ); 
 
 where d ε[0, 1]. 
 
         [0069]     If pause parameters equal 0, the actual point location of the corresponding position data is blank; otherwise, a value of 1 enables the appearance of the actual point location.  
         [0070]     In addition to the generation of each parameter setting by the above parameters generation modules respectively, the pen stroke generation module  28  yet includes a stroke-color parameters generation module  52 , and combines a couple of the above parameters to produce a stroke-color parameters.  
         [0071]     The stroke-color parameters generation module  52  generates the stroke-color parameters according to the color parameters ρ i , by the color parameters generation module 40; the rate parameters V, by the rate parameters generation module  42 ; the shade parameters λ, by the shade parameters generation module  46 ; and the pause parameters d, by the pause parameters generation module  50 . The stroke-color parameters generation module  52  employs a stroke-color parameters generation equation to compute the stroke-color parameters C i,j . The equation is represented by: 
 
 C   i,j   =λ*C   i,j−1   *d*V;  
 
         [0072]     As described in the above, the pen stroke  14 , drawn by the handwriting pen  10 , comprises m main position data, and each main position data corresponds to n density location data, where C i,j  represents the stroke-color parameters to which the j th  density location coordinates of the i th  main position coordinates corresponds.  
         [0073]     Please refer to  FIG. 10 .  FIG. 10  is a schematic diagram of different pen strokes. By applying the handwriting pen  10  of the present invention, it is available to simulate a variety of pen strokes of which the figure shows only two kinds, and the main system  21  puts the simulated pen strokes on the connecting screen.  
         [0074]     Please refer to  FIG. 11 .  FIG. 11  is a schematic diagram of the handwriting pen  100  of the present invention. The handwriting pen  100  connects to the main system (not shown) by a signal transmission line  120 ; for instance, a computer, and the usage of the handwriting pen  100  is associated with a handwriting tablet  140 . As shown in the figure, the handwriting pen  100  comprises a pen stick  160 , and a pen head  180  fixed at one end of the pen stick  160 . The pen head  180  is made of soft materials, such as rubber or plastic; a common trait of them is their shapes deformed under pressure, and restoring as the pressure releases. As shown in  FIG. 11 , the shape of the pen head  180  imitates the geometrical outline of the brush pen, and simulates the pen stroke of the brush pen.  
         [0075]     Please refer to  FIG. 12 .  FIG. 12  is a systemstructure diagram of the handwriting pen  100 . The handwriting pen  100  again comprises a gear  200 , a rotational velocity detector  220 , a pen tip  240 , and a central stick  260 . The central stick  260  comprises a first stick  280 , extending from the pen stick  160  into the pen head  180 ; a second stick  300 , locating inside the pen head  180 ; and a spring  320 , joining the first stick  280  to the second stick  300 . The spring  320  could be a torsion one or an extension one, such that the handwriting pen  100  bends under pressure, and restores at pressure diminishing.  
         [0076]     As shown in  FIG. 12 , the pen tip  240  is fixed at one end of the second stick  300 , extending beyond the pen head  180 ; and the gear  200  is fixed at the lateral of the central stick  260 , located in between the first stick  280  and the second stick  300 . The rotational velocity detector  220  is fixed at the lateral of the first stick  280 , and located on the top of the gear  200 . The rotational velocity detector  220  detects the variation of magnetic force during the rotation of the gear  200 , and-computes the instantaneous velocity of rotation according to diameter and length of cog of the gear  200 . The rotational velocity detector  220  can be realized by adopting Philips manufactured KMI22/1 apparatus, which not only detects the rotational velocity of gear  200 , but computes its rotational direction.  
         [0077]     Please refer to  FIG. 13 .  FIG. 13  is a schematic diagram of the handwriting pen  100  undergoing a deformation at its pen head  180 . Since the pen head  180  of the handwriting pen  100  is made of soft material, it will come across a degree of deformation, subject to the different pressing force of individuals. As shown in the figure, once the pen head  180  deforms, the spring  320  would bend under that force. Due to the spring  320  joining the first stick  280  to the second stick  300 , as the spring  320  confronts a degree of bending by a variant force, the angle between the first stick  280  and the second stick  300  varies proportionally too. Besides, since the gear  200  is located between the first stick  280  and the second stick  300 , the changing of the angle between the two sticks causes the gear  200  rotating a proportion, which consists of variations both in speed and direction. In other words, as the pen head  180  deforms, the gear  200  undergoes a proportion of rotation accordingly.  
         [0078]     Please refer to  FIG. 14 .  FIG. 14  is a schematic diagram of the gear  200  and the rotational velocity detector  220  of the handwriting pen  100 . The rotational velocity detector  220  is located on the top of the gear  200 . The gear  200  has a plurality of cogs  520 . As the gear  200  rotates, the rotational velocity detector  220 , on the top of the gear  200 , detects its rotation, and counts a rotational velocity and a rotational direction according to the diameter and the length of the cog of the gear  200 .  
         [0079]     Please refer to  FIG. 15 .  FIG. 15  is a circuit block diagram of the handwriting pen  100 . The handwriting pen  100  further comprises a pen tip position sensor  340 , fixed in the pen tip  240 , for sensing the position coordinates (X, Y) of the pen tip  240  on the handwriting tablet  140 ; and a pressure generator  360 , connected to the rotational velocity detector  220 , for receiving the rotational velocity data and the rotational direction data of the gear  200 , and generating a pressure value Z according to the rotational velocity data and the rotational direction data. The position coordinates (X, Y) accompanying the pressure value Z, are transferred to the main system by the signal transmission line  120 .  
         [0080]     As shown in  FIG. 15 , the pressure generator  360  comprises a signal processor  380 , for receiving the rotational velocity data and the rotational direction data of the gear  200 , and generating a tangential velocity of the gear  200  according to the rotational velocity data and the rotational direction data; and a pressure signal transformer  460 , connected to the signal processor  380 , for receiving the tangential velocity, and generating the pressure value Z according to the tangential velocity.  
         [0081]     The signal processor  380  comprises a gear position sensor  400 , a direction sensor  420 , and a tangential velocity generator  440 . The gear position sensor  400  is used to sense rotational position of the gear  200 . As the gear position sensor  400  senses a cog  520  of the gear  200 , it will signal a position. The direction sensor  420  is used to sense rotational direction of the gear  200  and to signal a direction. Once the rotational direction of the gear  200  is clockwise, the direction signal is 1; otherwise, −1 for a counterclockwise rotational direction.  
         [0082]     The tangential velocity generator  440  connects to the position sensor  400  and the direction sensor  420 , for receiving the position signal and the direction signal. The tangential velocity generator  440 , employs a quotient, dividing perimeter of the gear  200  by the number of cogs to compute distance between two cogs  520 ; employs another quotient, dividing the distance between cogs by time interval of two position signals to compute the tangent rotational speed of the gear  200 ; and applies the direction signal, determining the direction of the tangent rotational speed, and obtaining the resulting tangential velocity. The equation of calculating the tangential velocity is as follows: 
 
 V   t =±1× P/N   c ×1 /T   i ; 
 
 where 
        V t : tangential velocity     P: perimeter of the gear     N c : number of cogs     T i : time interval.        
 
         [0088]     As shown in  FIG. 15 , the pressure signal transformer  460  comprises an angle calculator  480  and an angle-pressure transformer  500 . The angle calculator  480  is used to receive the tangential velocity, generated by the tangential velocity generator  440 , and to compute bending angle θ 2  of the pen head  180  according to the tangential velocity; while the angle-pressure transformer  500  is connected to the angle calculator  480 , used to receive the bending angle θ 2 , and to generate the pressure value Z according to the bending angle θ 2 .  
         [0089]     Please refer to  FIG. 16 .  FIG. 16  is a schematic diagram of the bending angle of the pen head  180 . As shown in the above, as the pen head  180  deforms into a bend, the angle between the first stick  280  and the second stick  300  varies proportionally. In the current example, the bending angle θ 2  is defined as the angle θ in  FIG. 6 .  
         [0090]     To compute the bending angle θ 2  of the pen head  180  over time t+Δt, the angle calculator  480  has to have the following known parameters: r represents the length of the pen head  180 ; θ 1 , the bending angle of the pen head  180  over time t; ∂ 1 , the angular acceleration of the gear  200  rotates over time t; ω 1 , the angular velocity of the gear  200  rotates over time t; and Δt, a unit time.  
         [0091]     The tangential velocity, received by the angle calculator, is represented by ν 2 , which is the tangential velocity of the gear 200 over time t+At. The equation of the angular velocity ω 2  of the gear  200  rotates over time t+Δt is:  
         ϖ   2     =         v   2     r     .         
 
 Also, the equation of the angular acceleration ∂ 2  of the gear  200  rotates over time t+Δt is:  
         ∂   2     ⁢     =         (       ϖ   2     -     ϖ   1       )       Δ   ⁢           ⁢   t       .           
 
 The bending angle θ 2  is:  
         θ   2     =       θ   1     +       ϖ   1     *   Δ   ⁢           ⁢   t     +       1   2     *       ∂   2     ⁢     *   Δ   ⁢           ⁢       t   2     .                 
 
         [0094]     Please refer to  FIG. 17 .  FIG. 17  is an angle-pressure variation graph showing the relationship between the bending angle θ of the pen head  180  and the pressure value Z exerting on the handwriting pen  100 . The angle-pressure variation table is preset, and stored in the angle-pressure transformer  500 . The angle-pressure transformer  500  employs the preset table to generate a pressure calculation formula, and substitutes the bending angle θ 2  of the pen head  180  over time t+αt into the formula to compute the pressure value Z. The formula is as follows:  
       Z   =     {                 ⁢         K   1     *   θ     ,                 ⁢       if   ⁢           ⁢   0     ≤   θ   ≤     θ   a                         K   2     *     (     θ   -     θ   n       )       +       K   1     *     θ   a         ,             if   ⁢           ⁢     θ   a       ≤   θ   ≤     θ   b                     ⁢           K   3     *     (     θ   -     θ   b       )       +       K   2     *     (       θ   b     -     θ   a       )       +       K   1     *     θ   a         ,                 ⁢       if   ⁢           ⁢   θ     ≥     θ   b               ;           
 
 where K 1 , K 2 , and K 3  are preset slopes, and θ a  and θ b  are preset angles. 
 
         [0096]     Please refer to  FIG. 18 .  FIG. 18  is a schematic diagram of another example of the handwriting pen  540  of the present invention. The shape of the pen head  560  of the handwriting pen  540  imitates the geometrical outline of the watercolor pen, for simulating the stroke of the watercolor pen.  
         [0097]     As a result, the pen heads,  180  and  560 , of the handwriting pens,  100  and  540 , are made of soft materials, and their shapes imitate the geometrical outlines of the brush pen and watercolor pen; moreover, the handwriting pens,  100  and  540 , will compute the pressing force by individuals according to deformation of the pen heads,  180  and  560 , to simulate the strokes of the brush pen and the water color pen respectively.  
         [0098]     While the present invention has been shown and described with reference to a preferred embodiment thereof, and in terms of the illustrative drawings, it should not be considered as limited thereby. Various possible modifications, omissions, and alterations could be conceived of by one skilled in the art to the form and the content of any particular embodiment, without departing from the scope of the present invention.