JPH04294B2 - - 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.

Conventional Structure and Problems There has recently been an increasing demand for coordinate input devices that input handwritten characters and graphic information into computers 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 has to be placed very close to the tip of the input pen, and the tip of the input pen becomes thick, making it difficult to operate.Also, there is no need to place a too thick menu sheet or protector on the input board. There is a problem with not being able to place sheets etc.

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 of the conductors when the ratio of the values of the induced voltages induced in the coil reaches a predetermined value, and a bias current is superimposed on each of the conductors. The value of the bias current is set so as to correct the detection error in the position of the detection coil.This allows highly accurate coordinate detection even if there is a relative distance between the input board and the detection coil. This makes it possible to

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 circular 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 as follows.

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 x=x _p as shown in Figure 1, the voltage induced in the detection coil 2 is the induced voltage due to H ₁ , V ₁ , H ₂
If the induced voltage is V 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) (where 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, 1 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. The relationship of the above equation (6) is illustrated in FIG. 2. Therefore, when it is desired to output the position of the detection coil in a digital code, the digital code, for example, a binary code, corresponding to the above-mentioned position coordinate x is converted into _I1 , This can be easily achieved by creating I ₂ .

The relationship in equation (6) applies when there is a detection coil in close proximity to the input board, that is, on a plane composed of conductor 1, but when there is a relative distance between the input board and the detection coil (i.e., when the detection coil is (at a certain height on the board), the actual coil position and
There is a difference between the position calculated by equation (6).

Figure 3 shows that the detection coil is at a height h above the input board.
FIG. It is assumed that currents I ₁ and I ₂ are flowing through the conductor 1, respectively. The magnetic field at the position of the detection coil is expressed as follows.

If the elevation angles at which the detection coil is viewed from the two conductors 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′ ₂ =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, it can be found as x′ _p .

From V′ ₁ = V′ ₂ , x′ _p = d/I ₀・I ₁ = x _p + (d−2x _p )h ₂ /x _p (d−x _p )+h ₂ ……(15
) In other words, this is the error in coordinate detection in the second term of equation (15).

Figure 4 shows the relationship between the position coordinates of the detection coil and the current value when a bias current I _B is commonly applied to I ₁ and I ₂ for the above error correction.
FIG. In this case, in equation (7),
I ₁ + I _B instead of I ₁ , I _{2 +} instead of I 2 in equation (8)
I _B , by replacing I ₀ in equation (15) with I ₀ +2I _B ,
By performing a similar calculation, the read coordinate x″ _p can be obtained as follows.

x _{″ p} = _d /I _{0 ・ I 1 = x p} + _d ⁻ ₂ ² }] ...(16) The condition for the error term to be zero in equation (16) is
Assuming that the second term is 0, the equation becomes as follows.

I _B /I ₀ =h ² /x _p (d−x _p )−h ² (17) Since this condition is a relation of x _p , it only holds true for a certain x _p . However, in practice, o~
It is appropriate not to use the entire area of d for coordinate detection, but to use the range of d/4 to 3d/4 as described later. Therefore, x _p (d
−x _p ) is 0.19 (when x _p = d/4, 3d/4) ~
There is only a variation of 0.25 (when x _p = d/2), and the correction effect is sufficient. Note that since the second term of equation (16) has a coefficient of (d-2x _p ), the second term naturally becomes small near x _p =d/2. Therefore, I _B is set so as to satisfy equation (17) at the end of the usable area, that is, when x _p =d/4.

FIG. 5 is a block diagram of a coordinate input device according to an embodiment of the present invention.
The conductors are arranged in a matrix, and 2 is a detection coil attached to the tip of the input pen. 6 is the current corresponding to the binary code from the counter 8a _.
and _I2 , and maintains the sum of currents _I1 and _I2 to a constant value _I0 , 12 is a D/A (digital-analog) conversion circuit for currents _I1 and _I2 , Bias circuit providing bias current for error correction, 5
is a switch circuit for distributing currents I ₁ and I ₂ in the X direction or Y direction, 4a and 4b are counters 8
A multiplexer for distributing the currents I ₁ and I ₁ to conductor 1 according to the binary code from b. 9
are the two induced voltages V ₁ induced in the detection coil 2
detects that the ratio _between detection circuit. 11 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, and a D/A
A clock pulse generation circuit 13 is used to drive the conversion circuit 6, and a preset circuit 13 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 set to "16" by the preset circuit 13.
A preset value is given, and this preset value is made to correspond to a 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, between d/4 and 3d/4
It will be broken down into 32 steps. counter 8a
When more carry output is given to the counter 8b, the output code of the counter 8b changes and the next two
Select the book conductor and repeat the same operation.

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 counters 8aa and 8b correspond to the coordinate values of input surface 3, latch circuit 1
The position of the detection coil 2 can be known from the output code of 0.

Effects of the Invention As is clear from the above description, the coordinate input device of the present invention applies a bias current of a value derived from the relative distance between the detection coil and the input board to the currents I ₁ and I ₂ flowing through the conductors. With the simple operation of adding
Detection errors in the position of the detection coil due to this relative distance can be corrected, allowing highly accurate coordinate detection.

[Brief explanation of drawings]

1A and 1B are schematic diagrams and graphs showing the magnetic field strength distribution for explaining the position detection principle of the coordinate input device of the present invention, and FIG. 2 is a graph showing the relationship between theoretical formulas based on the above position detection principle. , Figure 3 is a cross-sectional view when the detection coil is located on the input board, and Figure 4 is a cross-sectional view when the detection coil is located on the input board.
The figure is a characteristic diagram showing the relationship between position coordinates and current value when a bias current is applied, and FIG. 5 is a block diagram of a coordinate input device according to an embodiment of the present invention. 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... bias circuit, 13... 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 device is configured to determine the position of the detection coil, and a bias current is superimposed and passed through each of the conductors, and the value of the bias current is set so as to correct a detection error in the position of the detection coil. Coordinate input device.