JPH04293B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a coordinate input device that is effective when inputting information such as handwritten characters or figures into an electronic device such as a computer using an input pen or the like.

2. Description of the Related Art Structure and Problems There has recently been an increasing demand for coordinate input devices that input handwritten characters and graphic information into a computer or the like as coordinate information.

There are various possible principles for detecting coordinates.
Among them, the electromagnetic induction method is widely used because of its high precision and reliability.
However, in this method, a magnetic field is generated or detected by a detection coil built into the input pen or cursor, and therefore, coordinate detection errors often occur if the relative distance between the input board and the detection coil is too large. Therefore, the detection coil must be placed at the very tip of the input pen,
Problems include the thick pen tip, which makes it difficult to use, and the inability to place thick menu sheets, protective sheets, etc. on the input board.

OBJECTS OF THE INVENTION An object of the present invention is to provide a coordinate input device that can detect coordinates with high precision even if there is a relative distance between an input board and a detection coil.

Structure of the Invention The coordinate input device of the present invention has a plurality of conductors arranged in a matrix at predetermined intervals in the X direction and the Y direction, and two of the conductors in the X or Y direction are arranged in a matrix. an input board configured to sequentially select the conductors of and supply current from the outside; a detection coil for coordinate input movably positioned on the surface of the input board; and the two selected conductors. detecting means for independently detecting the induced voltage induced in the detection coil by the current flowing through the two conductors; The value of the current flowing through the two conductors is relatively changed so that the sum of the values of is constant, and the magnetic field generated by each conductor in the detection coil placed between the two conductors. The position of the detection coil is determined based on the current value of one conductor when the ratio of the values of the induced voltages induced in the input board and the detection coil reach a predetermined value. Detection error of the above position due to relative distance,
The relative distance or the diameter of the aperture of the detection coil is set so that the detection error at the position due to the diameter of the aperture of the detection coil is mutually corrected. This enables highly accurate coordinate detection even if there is a relative distance from the

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be specifically described based on the drawings. FIGS. 1A and 1B are a schematic diagram showing the position detection principle of the coordinate input device of the present invention and a graph showing the magnetic field strength distribution. In FIG. 1A, 1 and 1 are conductors arranged in parallel, and 2 is a detection coil placed on the same plane as the conductor 1. This is, for example, provided at the tip of an input pen. .

In Figure 1A, when a current is passed through each conductor,
A concentric magnetic field is generated around the conductor, but
On a plane surrounded by conductors, the magnetic field is perpendicular to this plane, and the magnetic field strength is expressed by the following equation.

H ₁ = I ₁ /2πx ...(1) H ₂ = I ₂ /2π(d-x) ...(2) However, the current flowing through one conductor is I ₁ , the resulting magnetic field is H ₁ , and the other conductor is Let I ₂ be the current flowing through the conductor, and H ₂ be the magnetic field caused by this. d is the distance between both conductors.

This can be illustrated as shown in the magnetic field strength distribution graph in FIG. 1B. Next, when the detection coil 2 is placed at the position where x=x _p as shown in Fig. 1, the voltage induced in the detection coil 2 is as follows: V ₁ is the specified voltage due to H ₁ and V ₂ is the induced voltage due to H ₂ . Then, V ₁ = K・H ₁ = K・I ₁ /2πx _p ...(3) V ₂ = K・H ₂ = K・I ₂ /2π(d−x _p ) ...(4) ( However, K is a constant). Therefore, when the position x _p of the detection coil 2 is determined using both equations (3) and (4), it is expressed as equation (5).

x _p = d・I ₁ /I ₂ /V ₁ /V ₂ +I ₁ /I ₂ ...(5) Here, V ₁ /V ₂ = 1, I ₁ + I ₂ = I ₀ (I ₀ is constant) Then, the position x _p of the detection coil 2 is expressed as x _p =d/I ₀ ·I ₁ (6).

That is, by checking the value of I 1 when the ratio of the values of induced voltages V ₁ and _{V 2 induced} in the detection coil 2 by the currents I ₁ and I ₂ is 1, the position x of the detection coil 2 _p can be found.

FIG. 2 is a block diagram showing an embodiment of the coordinate input device of the present invention embodying the above principle, in which 1 is a conductor arranged in a matrix with a pitch d on the input board 3, and 2 is an input pen. This is a detection coil attached to the The diameter of the opening of the detection coil 2 is set as will be explained later. 6 is a D/A (digital-analog) which sets _I1 and _I2 to the current values corresponding to the binary code from the counter 8a and maintains the sum of the currents _I1 and _I2 to a constant value _I0 . ) conversion circuit,
5 is a switch circuit for distributing currents I ₁ and I ₂ in the X direction or Y direction; 4a and 4b are multiplexers for distributing currents I ₁ and I ₂ to conductor 1 according to the binary code from counter 8b; It is.
9 is two induced voltages induced in the detection coil 2
Detecting that the ratio between V ₁ and V ₂ is 1, and
a detection circuit 11 that determines whether the detection coil 2 is present between conductors through which current flows and controls a latch circuit 10 that temporarily stores coordinate data;
is a modulation circuit for obtaining a high frequency current equal to the currents I ₁ and I ₂ ; 7 is a counter 8a; a modulation circuit 11;
A clock pulse generation circuit 12 is used to drive the D/A conversion circuit 6, and a preset circuit 12 provides preset data to the counter 8a.

The operation of the coordinate input device of this embodiment configured as described above will be explained below. First, the output code of the counter 8b is sent to the multiplexer 4a,
4b and select the two conductors through which the current will flow. In this case, it is assumed that every other two conductors are selected. Therefore, the interval between the two selected conductors is d, and in order to seamlessly detect coordinates across the entire input board 3,
It is sufficient to use a range between d/4 and 3d/4 between two conductors.

Counter 8a sends its carry output to counter 8b at the full count number "48". However, the counter 8a is given a preset value of "16" by the preset circuit 13, and this preset value is made to correspond to the current value of d/4. Therefore,
When the clock pulse generator 7 counts 32 clock pulses, the counter 8a outputs a carry signal. That is, the range between d/4 and 3d/4 is broken down into 32 steps. When the carry output from the counter 8a is given to the counter 8b, the output code of the counter 8b changes, the next two conductors are selected, and the same operation is repeated.

On the other hand, in the detection coil 2, induced voltages are generated from each conductor, but current flows through the conductors on both sides of the detection coil 2, and the two induced voltages V ₁ and V ₂ induced in the detection coil 2 are When the ratio becomes 1, the detection circuit 9 outputs a control signal and the counter 8a
and 8b are stored in the latch circuit 10. Since the output codes of the counters 8a and 8b correspond to the coordinate values of the input surface 3, the latch circuit 10
The position of the detection coil 2 can be known from the output code.

By the way, the relationship in equation (6) applies when the detection coil 2 is located closely on the plane composed of the input board, that is, the conductor 1, but when there is a relative distance between the input board and the detection coil 2 (i.e. If the detection coil 2 is located at a certain height above the input board), there will be a difference between the actual position of the detection coil 2 and the position determined by equation (6).

FIG. 3 is a sectional view when the detection coil 2 is located at a height h above the input board. For conductor 1,
Assume that currents I ₁ and I ₂ are flowing, respectively. The magnetic field at the position of the detection coil 2 is expressed as follows.

If the elevation angles at which the detection coil is viewed from the conductor 1 are α ₁ and α ₂ , respectively, the magnetic field detected by the detection coil 2 is expressed as follows.

H″ ₁ = H′ ₁・cosα ₁ ……(9) H″ ₂ = H′ ₂・cosα ₂ ……(10) On the other hand, Therefore, the voltage induced in the detection coil 2 is
Corresponding to each current, it is expressed as follows.

V′ ₁ =K・H″ ₁ =K・x _p・I ₁ /2π(x _p ² + h ² )……(1
3) V′ ₁ =K・H″ ₂ =K・(d−x _p )・I ₂ /2π{(d−x
_p ) ² + h ² }...(14) According to the principle of coordinate detection, the coordinates will be read out by I ₁ when V′ ₁ = V′ ₂ , so let this read coordinate be x _p ′. Then, x′ _p can be found as follows.

From V′ ₁ = V′ ₂ , x _p ′=d/I ₀・I ₁ = x _p + (d−2x _p )h ² /x _p (d−x _p )+ ² ……(15) That is, The second term in equation (15) is the error in coordinate detection. Rewriting equation (15) results in equation (16).

(x _p ′ / d) − (x _p / d) = {1-2 (x _p / d)} (h / d) ² / (x _p / d)
{1-(x _p /d)}+(h/d) ² (16) FIG. 4A is a graph showing the relationship between the position of the detection coil and the detection error calculated by equation (16).
Figure 4A only shows the range 1/4≦x _p /d≦3/4, but in practice, this area will be connected sequentially to configure a wide input board, so within this range. Just think about it. According to FIG. 4A, the detection error has a negative slope.

Incidentally, the relationship in which the magnetic field strength is inversely proportional to the distance from the conductor, as shown in equations (1) and (2), does not hold true unless the opening area of the detection coil is sufficiently small. In reality, in order to obtain a sufficient induced voltage, the diameter of the aperture surface becomes large to some extent, resulting in a detection error.

Now, when the shape of the aperture of the detection coil is a circle and the radius is r, the detection error of the coordinates due to the radius r is determined as follows.

FIG. 5 is a position diagram of a detection coil on a plane between two conductors. In FIG. 5, the center of the detection coil is assumed to be the true position coordinate x _p . In Figure 5,
The area ΔS of the minute portion is given by the following formula.

ΔS=Δx{√ ² −(− _p ) ² } ...(17) Therefore, since the magnetic field generated by the current I ₁ flowing through the conductor 1 is H ₁ in equation (1), the magnetic field in this minute part is expressed as equation (18), and therefore, the magnetic field φ ₀ across the entire aperture surface of the detection coil is expressed as equation (19).

μ・H ₁・ΔS=μI ₁ /2πx {√ ² −(− _p ) ² }・
Δx ……(18) φ ₁ =2∫μH ₁・ΔS μI ₁ /π∫ ^xp+r _xp-r √r ² − (x−x _p ) ² /xdx = μI ₁ (x _p −√ _p ² − ² ) ...(19) However, μ is magnetic permeability and x ₀ > r.

Similarly, the magnetic flux φ ₂ that crosses the aperture of the detection coil due to the current flowing through the conductor 1' can be calculated as follows.

φ ₂ = μI ₂ {(d−x _p )−√(− _p ) ² − ² } The voltage induced in the detection coil is (19), (20)
It is proportional to the magnetic field of Eq. According to the principle of coordinate detection, when the two induced voltages are equal, the coordinates can be found by equation (6), so if this coordinate is x' _p , φ ₁ = φ ₂ ... (21) x' _p = d/I ₀ · I ₁ ...The following relationship can be obtained from both equations (22).

(x' _p /d) - (x _p /d) = 1 - (1 + A) (x _p /d)
/1+A...(23) However FIG. 4B is a graph showing the relationship between the position of the detection coil and the detection error calculated from equation (24).
4B has a positive slope, contrary to FIG. 4A, so the polarities are complementary. Therefore, h/d
If r/d, that is, the diameter of the aperture of the detection coil is appropriately selected, it is possible to correct the error caused by the height h of the detection coil. Conversely, when the diameter of the aperture of the detection coil is determined, it is of course possible to correct it by appropriately setting h.

Effects of the Invention As is clear from the above description, even if there is a relative distance between the detection coil and the input board, the coordinate input device of the present invention can correct the error caused by the relative distance between the detection coil and the input board by adjusting the diameter of the aperture of the detection coil appropriately. It can be corrected according to the setting, and highly accurate coordinate detection is possible. Moreover, conversely, it is also possible to correct the error due to the diameter of the detection coil by appropriately setting the above-mentioned relative distance. Therefore, there is a large degree of freedom in designing the input board detection coil, and it is possible to provide a device with high precision and good operability.

[Brief explanation of drawings]

Figures 1A and B are conceptual diagrams and graphs showing magnetic field strength distribution for explaining the position detection principle of the coordinate input device of the present invention, and Figure 2 is a coordinate input device of the present invention embodying the principle of Figure 1. A block diagram showing one embodiment of the device, FIG. 3 is a sectional view when the detection coil is located on the input board, FIGS. 4A and B are graphs showing the relationship between the position of the detection coil and detection error, and FIG. The figure is a positional relationship diagram of detection coils on a plane between two conductors. DESCRIPTION OF SYMBOLS 1... Conductor, 2... Detection coil, 3... Input board, 4a, 4b... Multiplexer, 5... Switch circuit, 6... D/A conversion circuit, 7... Clock pulse generation circuit, 8a, 8b... …counter,
9...Detection circuit, 10...Latch circuit, 11...
Modulation circuit, 12... preset circuit.

Claims (1)

[Claims] 1. It has a plurality of conductors arranged in a matrix at predetermined intervals in the X direction and Y direction, and two conductors are sequentially selected from each of the conductors in the X or Y direction and a current is applied from the outside. an input board configured to supply coordinates; a detection coil for coordinate input movably positioned on the surface of the input board; The selected two
In the two conductors, the value of the current flowing through the two conductors is relatively changed so that the sum of the value of the current flowing through one conductor and the value of the current flowing through the other conductor is constant. The above is determined by the current value of one conductor when the ratio of the values of each induced voltage induced by the magnetic field generated by each conductor in the detection coil placed between the conductors reaches a predetermined value. The detection coil is configured to determine the position of the detection coil, and a detection error of the position due to the relative distance between the input board and the detection coil and a detection error of the position due to the diameter of the aperture of the detection coil are eliminated. A coordinate input device characterized in that the relative distance or the diameter of the aperture of the detection coil is set so as to correct each other.