JPH0315204B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a coordinate reading device for an electromagnetic induction tablet.

(Conventional technology) A conventional coordinate reading device will be explained with reference to FIG.

In Fig. 1, 1 is a coordinate input device, 2 is a laminated board, x ₀ , x ₁ , x ₂ , _. . . Has a potential. y ₀ , y ₁ , y ₂ ...,
The same applies to y _o . X ₀ , X ₁ , ...X _n-2 is the X-axis sense coil, X ₀ is x ₀ and x ₂ , X ₁ is x ₁ and x ₃
The same applies hereafter. Also, Y ₀ , Y ₁ ,
..., Y _o-2 is the Y-axis sense coil, Y ₀ is y ₀ and y ₂ ,
Y ₁ is composed of y ₁ and y ₃ , and so on. The X-axis sense coil group and the Y-axis sense coil group are insulated. 3X is an X-axis scanning circuit which selects x ₀ and x ₂ and selects the sense coil X ₀ , and selects x ₁ and x ₃ as the sense coil X ₁ . The same applies below. Also,
3Y is a Y-axis scanning circuit which selects y ₀ and y ₂ and selects the sense coil Y ₀ , and selects y ₁ and y ₃ to become the sense coil Y ₁ . The same applies below. 16 is a decoder, which connects the sense coils to X ₀ , X ₁ , ..., X _n-2 , Y ₀ , Y ₁ , ...
Scan in the order of Y _o-2 . Reference numeral 4 denotes a coordinate indicator, which has an excitation winding and a capacitor attached to its pen-shaped tip, and generates an alternating magnetic field of a constant frequency by a signal obtained by amplifying an oscillator 6 with an amplifier 5. Also, a pen switch (not shown) is built in, and is configured to close when a certain amount of writing pressure is applied. 7 is an amplifier, 8 is a rectifier circuit, 9 is a low frequency filter, 10 is an A/
The D converter 11 is an arithmetic control section.

Next, its operation will be described.

An output line K, an amplifier _{7 , a} rectifier circuit 8, _...
When input to the arithmetic controller 11 via..., the arithmetic controller 11 recognizes the X-axis sense coil and Y-axis sense coil that are above a certain level and have the maximum induced voltage, and also recognizes the Coil P and adjacent sense coils P+1, P-1
Recognize.

Next, to find the position of the coordinate indicator 4, as shown in Fig. 3, find the position A on the panel surface shown in Fig. 2 from the position of the sense coil that generates the maximum induced voltage v _p , and then It is now determined by calculating A±Δa. However, Δa is calculated using the following formula.

Δa=v _p+1 −v _p-1 /v _p ×C... Note that v _p-1 is the induced voltage of sense coil P-1,
v _p+1 is the induced voltage of the sense coil P+1, and C is a constant. The induced voltages v _p , v _p-1 , v _p+1 are amplified by the amplifier 7, and the voltages are expressed as V _p , V _p-1 , V _{p+1 ,} respectively.
Then, Δa can be found by the formula.

Δa=v _p+1 −v _p-1 /v _p ×C... (Problem to be solved by the invention) Since the output voltage of the amplifier 7 has an offset voltage V _OFF , the denominator in the equation is V _OFF There is an error corresponding to , and there is a drawback that Δa cannot be determined accurately.
Although V _OFF is added to V _p+1 and V _p-1 , they are canceled out and the numerator of the equation has no effect from V _OFF .

The present invention solves the above drawbacks and provides a coordinate input device with high detection accuracy.

(Means for Solving the Problems) In order to solve the problems of the prior art, the present invention provides that when a value exceeding a predetermined slice level cannot be obtained during scanning of all sense coils, The offset voltage value is repeatedly detected, and the equation is corrected based on the detected offset voltage, so that coordinates can be detected with high accuracy.

(Example) In order to prevent the denominator from causing an error due to the offset voltage of the amplifier 7 in the formula,
When V _p is zero or very small, detect the output voltage of the amplifier 7 and set it as V _OFF to find Δa from the formula Δa=V _p+1 −V _p-1 /V _p −V _OFF ×C …… A specific example is shown below.

FIG. 1 is a block diagram of a coordinate reading device showing an embodiment of the coordinate input device of the present invention. As shown in the figure, the coordinate input device 1 includes a sense coil group laminated board 2
The X-axis sense coil x ₀ is installed on the upper side of the
x ₁ , . . . , x _n and Y-axis sense coils y ₀ , y ₁ , . . . _yo provided below with an insulating plate in between. Two of these sense coils form a set and form sense coils X ₀ , X ₁ , ..., X _n-2 , Y ₀ ,
They form Y ₁ and Y _o-2 . X consisting of selectors
The axis scanning circuit 3X and the Y-axis scanning circuit 3Y are connected to each sense coil, respectively, and perform switching operations for each sense coil based on the decoder 16. The scanning circuits 3X and 3Y are selected by the control line I, and X ₀ →X ₁ ...→X _n-2 , Y ₀ →Y ₁ ...
The induction signals of each sense coil are outputted to the common output line K in the order of ...→Y _o-2 .

An excitation winding and a capacitor are attached to the tip of the pen-shaped coordinate indicator, and an alternating magnetic field of a constant frequency is generated by the output signal of the oscillator 6 through the amplifier 5. The coordinate indicator 4 also has a built-in pen switch, which closes when a certain amount of pen pressure is applied.

The X-axis and Y-axis induced signals are inputted to the arithmetic control section 11 via the output line K, the amplifier 7, the rectifier circuit 8, the low frequency converter 9, and the A/D converter 10. The arithmetic control unit 11 is composed of a microprocessor 12, a memory 13, and interfaces 14 and 15, and outputs the scanning address of the sense coil to the decoder 16 to control the scanning circuits 3X and 3Y, as well as controlling the pen switch of the coordinate indicator 4. It is configured to send the calculated coordinate signal to an external device according to the output signal. To show the basic operation of each part above in a procedural manner, when the sense coil induction signal exceeds a predetermined slice level, that value is set as a temporary maximum value V _p ,
It is stored in the memory 13 along with the scan address of the sense coil, and if the next sense coil signal is higher than the level detected immediately before, that value is set as a temporary maximum value and rewritten together with the sense coil address. Repeat this one after another, and then
The respective maximum value signals and the addresses of their sense coils for the axes are stored in the memory 13. At this time, the values of the signal values V _p-1 and V _p+1 before and after V _p can also be stored.

Here, if a value exceeding a predetermined slice level cannot be obtained, scan the first and last sense coils of the X-axis and Y-axis, that is, X ₀ , X _n-2 , Y ₀ , and _Yo-2. The obtained signals are compared and the lower signal value is stored in the memory 13 as the offset voltage value V _OFF .

When the sense coil induced voltage does not exceed a predetermined slice level, the coordinate indicator 4 is far from the sense coil, and in this state, X ₀ ,
If the lowest induced voltage among X _n-2 , Y ₀ , and Yo _-2 is selected as V _OFF , V _OFF becomes a value that is not affected by the coordinate indicator. The sense coil is scanned again, and if a value exceeding the predetermined slice level is not obtained, the offset voltage value V _OFF is rewritten using the same procedure as described above. Let this V _OFF be V _OFF in the formula.

With the above, the sense coil is scanned to obtain the maximum value V _p
If , the tip position of the coordinate indicator 4 is calculated using the coordinates in the sense coil according to the formula and the corresponding calculated value, and the coordinates are specified using the sense coil number N and sense coil pitch l from which the maximum value V _p is obtained. Find position X. The coordinate indicated position X is determined as follows: X=(N+1)・l+x... Here x is equal to Δa in the formula.
For V _OFF in the formula, use the value of V _OFF determined by the above method. The Y coordinate is also found in the same way.

The offset voltage value V _OFF is repeatedly and automatically adjusted by the above-described procedure, and the offset voltage value always takes into account the environmental conditions, making it possible to detect coordinates in consideration of the environmental conditions. Even if the sense coil is formed by a method other than the method shown in FIG. 1 or FIG. 2, the present invention can be applied to any method in which the coordinates can be calculated using an equation.

(Effects of the Invention) As described in detail above, the present invention has the effect of eliminating position detection errors because the position detection calculation is always corrected using an automatically adjusted offset voltage value. Since the lower of the first and last signal values of the sense coil is set as the offset voltage value, the offset voltage value is not influenced by the coordinate indicator and highly accurate coordinate detection is possible. Also, when scanning all sense coils, scan all sense coils to find the minimum value using the same method as the method used to find the maximum value,
It is also possible to use that value as the offset voltage value, but in this method, (m-1) is required to find the minimum value.
+(n-1) sense coils need to be scanned, whereas the method applied in the present invention
It is only necessary to scan two sense coils for each axis, which has the effect of shortening the scanning time.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a coordinate reading device showing one embodiment of the coordinate input device of the present invention, and FIGS. 2 and 3 are diagrams illustrating its operation. 1... Coordinate input device, X ₀ , X ₁ ...X _n-2 , Y ₀ ,
Y ₁ ...Y _o-2 ...Sense coil, 2...Sense coil group multilayer board, 3X, 3Y...Scanning line, 4...
...coordinate indicator, 5...amplifier, 6...oscillator, 7
... Amplifier, 8 ... Rectifier circuit, 9 ... Low frequency converter, 10 ... A/D converter, 11 ... Arithmetic control section, 12 ... Microprocessor, 13 ... Memory, 14, 15...Interface.

Claims (1)

[Claims] 1. A coordinate indicator for generating an alternating magnetic field, a plurality of sense coils that induce force through the linkage of magnetic flux generated from the coordinate indicator, a group of switches for selecting the sense coils, and a group of switches for selecting the sense coils. It has a circuit for identifying the tip position of the coordinate indicator by detecting the induced voltage, and when a value exceeding a predetermined slice level cannot be obtained during scanning of all sense coils, the circuit is installed at a sufficient distance from the coordinate indicator. Means for appropriately reading the output voltage of the amplifier 7 while amplifying the induced voltage of the unaffected sense coil, setting it as the offset voltage of the amplifier 7, and updating and storing the voltage value in the memory of the arithmetic control section as appropriate. and the ratio of the difference between the induced voltages of the two sense coils on both sides of the sense coil where the maximum induced voltage is generated and the maximum induced voltage corrected by the offset voltage of the amplifier 7 set by the above method. A coordinate input device characterized in that the coordinates of the tip position of the coordinate indicator are determined based on .