JP4078764B2 - Coordinate reader - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  This inventionseatThe present invention relates to a mark reader.
[0002]
[Prior art]
  Conventionally, a coordinate reading apparatus shown in FIG. FIG. 20A is an explanatory diagram showing a configuration of a conventional coordinate reading apparatus.
  The coordinate reading apparatus shown in FIG. 20A is a coordinate input sheet having X1-Xm sense coils (conductors) for detecting X coordinates and Y1-Yn sense coils (conductors) for detecting Y coordinates. 91, a scanning circuit 92 that sequentially scans the sense coil of the coordinate input sheet 91, and a detection circuit 90 that detects an induction signal generated in the sense coil and calculates a position coordinate.
[0003]
  When a pen (writing means) 100 having a coil 101 that generates an alternating magnetic field comes into contact with the coordinate input sheet 91, the sense coil near the pen 100 is in contact with the alternating magnetic field generated from the coil 101 by magnetic coupling. An induction signal 97 is induced, and the induction signal 97 is input to the detection circuit 90. The induction signal 97 input to the detection circuit 90 is amplified by the amplifier 93 and subjected to amplitude detection, for example, by the detection circuit 94. Next, the A / D conversion circuit 95 measures the amplitude of the detected induction signal and outputs the measured value to the CPU 96. Then, the CPU 96 calculates the position coordinates of the pen 100 based on the input digital value. For example, a calculation method is used in which a position coordinate table corresponding to a digital value is selected with reference to a position coordinate table in which a digital value is associated with a position coordinate.
[0004]
  By the way, in the case of using a plurality of types of pens in the coordinate reading apparatus as described above, attribute information indicating attributes such as pen types is transmitted from the pen by a code string, and the attribute information is transmitted on the coordinate input sheet side. What is recognized is known (Japanese Patent Laid-Open No. 5-233127). FIG. 20B is an explanatory diagram illustrating a code string transmitted from the pen.
  The code G is composed of a total of 10 bits including a start bit of 2 bits, an attribute information bit of 7 bits indicating the attribute information of the pen, and a stop bit of 1 bit, and is superimposed on the alternating magnetic field from the pen according to the operation clock F. Is output.
  Then, the coordinate input sheet side reads the code string superimposed on the signal generated in the sense coil by the alternating magnetic field transmitted from the pen, and recognizes the attribute information of the pen.
[0005]
[Problems to be solved by the invention]
  However, the conventional coordinate reading apparatus (Japanese Patent Laid-Open No. 5-233127) cannot recognize pen attribute information without receiving a plurality of cycles from a start bit to a stop bit.
  Further, the pen attribute information cannot be recognized unless the operation clock on the pen side and the operation clock on the coordinate input sheet side are synchronized.
  Furthermore, if detection is started by the sense coil from the middle of the start bit to the stop bit, it waits until the next start bit is transmitted, and if it does not receive from the start bit to the stop bit again, the pen attribute information is displayed. It cannot be recognized.
  That is, the conventional coordinate reading apparatus has a problem that it takes time to recognize the attribute information of the pen.
[0006]
  Accordingly, the present invention has been made to solve the above-described problem, and can reduce the time required to identify information.seatAn object is to realize a mark reader.
[0007]
[Means for solving the problems, functions and effects of the invention]
[0008]
[0009]
[0010]
[0011]
  In order to achieve the above object, the present inventionClaim1 and claim 2In the invention described in (2), a main body having a coordinate input sheet in which a plurality of conductors magnetically coupled to an alternating magnetic field are laid under the writing surface, and a writing means for generating the alternating magnetic field,eachConductorIs detected by detecting the lead wire that generated the signal.Occurs indidIn the coordinate reading device that reads the position coordinates of the writing means on the writing surface based on a signal, the writing means is set for each of the coil that generates an alternating magnetic field having a predetermined period and the attribute information of the writing means. Single cycleTheAnd transmitting means for transmitting an alternating magnetic field generated from the coil by angle-modulating the signal using the signal having,DetectedOccurs on conductordidsignalThe position coordinate of the writing means on the writing surface is read based on and the signal used for the readingOf the signal transmitted from the writing means.1 cycle length every half cycleDetect and its detectedLength for one cycleOn the basis of the above, the technical means that the receiving means for recognizing the attribute information of the writing means is provided.
[0012]
  In other words, the cycle of the signal transmitted from the writing means to the main bodyIsSingle and periodic according to the attribute information of the writing meansButSince they are different, the main body can recognize the attribute information of the writing means only by detecting one period of the signal.
  Therefore, the time required for recognizing attribute information can be shortened compared with the conventional case of recognizing attribute information indicated by using a plurality of cycles from a start bit to a stop bit.
In particular, the length of one cycle of the signal transmitted from the writing means can be detected every half cycle, and the attribute information of the writing means can be recognized based on the detected length of one cycle.
In other words, even when the conductor is scanned in the middle of one cycle of the signal generated on the conductor, there is no need to wait for the start of the next one cycle, and one cycle from the next half cycle. Since the attribute information of the writing means can be recognized based on the length of the minute, the attribute information can be recognized at high speed.
  Also, the signal cycleButThe attribute information can be recognized with a slight difference. For example, the cycleButThe attribute information can be recognized only by a difference of at least one cycle of the system clock of the main body.
  Therefore, very many types of attribute information can be transmitted and the attribute information can be recognized in a short time.
  Further, the attribute information is transmitted by angle-modulating the alternating magnetic field generated from the coil of the writing means, and the signal generated from the conductive wire laid on the coordinate input sheet is demodulated, so that the signal transmitted from the writing means is simply transmitted. One cycleTheDetect and its detected periodInBecause the attribute information is recognized based on this, even if the alternating magnetic field intensity changes, the period or phase that indicates the attribute information is not affected, so the attribute information can be transmitted and received accurately. it can.
[0013]
  Claim2In the invention described in claim1In the coordinate reading apparatus described in item 3, the transmission unit uses a technical unit that repeatedly transmits the signal for a predetermined time.
[0014]
  That is, when the signal from the writing means is repeatedly transmitted for a predetermined time, the timing at which the alternating magnetic field is generated from the writing means and the timing at which the coordinate input sheet side detects the signal generated on the conductor does not match. However, since the coordinate input sheet side can detect a signal generated in the conductor after a predetermined time, the attribute information can be recognized.
  The coordinate input sheet includes a sheet-like or plate-like sheet having no flexibility, or a sheet-like or plate-like sheet having flexibility.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
  Hereinafter, according to the present inventionseatA first embodiment of a mark reading apparatus will be described with reference to the drawings.
  In the first embodiment, as a coordinate reading apparatus according to the present invention, a so-called electronic blackboard that electrically reads handwritten characters or figures drawn on a coordinate input sheet will be described as an example.YouThe An example using frequency modulation, which is a kind of angle modulation, will be described.
[Main configuration]
  First, the main configuration of the electronic blackboard according to the first embodiment will be described with reference to FIGS. 1 and 2.
  FIG. 1 is an external perspective view showing the main configuration of the electronic blackboard, and FIG. 2 is an explanatory view showing a state in which a personal computer (hereinafter abbreviated as a PC) and a printer are connected to the electronic blackboard shown in FIG. is there.
[0016]
  The electronic blackboard 1 includes a writing panel 10, a pen 60 for writing on the writing surface 21 a, and an eraser 40 for erasing the written locus and data indicating the locus. The writing panel 10 is provided with a frame-like frame 11, and the writing panel body 20 is incorporated in the frame 11. A plate-like table 12 is attached to the front lower end of the frame 11 so as to protrude from the front surface along the lower end. A concave portion 12a having a semicircular cross section for accommodating the pen 60 is formed on the upper surface of the table 12, and a flat surface portion 12b for placing the eraser 40 and the like is formed on the right side of the concave portion 12a. .
[0017]
  An operation unit 30 is provided on the front right side of the frame 11. The operation unit 30 includes a speaker 31 that reproduces sounds such as operation sounds and warning sounds, and the number of pages in which data indicating the contents written on the writing surface 21a (hereinafter abbreviated as writing data) is stored in 7 segments. LED page number display LED 32, page return button 33 that returns one page each time it is pressed, page feed button 34 that feeds one page each time it is pressed, and one page that is erased each time the stored writing data is pressed An erasing button 35 to be pressed, a printer output button 36 to be pressed to output the stored writing data to the printer 200 (FIG. 2), and a PC to be pressed to output the stored writing data to the PC 100 (FIG. 2). In order to start or stop the output button 37, the battery exhaustion notification LED 39 for notifying the battery of the pen 60, and the electronic blackboard 1. A power button 38 is pressed is provided.
[0018]
  A battery case 14 is provided at the lower front portion of the frame 11 to accommodate four AA dry batteries 14a serving as a power source for the electronic blackboard 1. A lid 14b is attached to the front surface of the battery case 14 so as to be openable and closable. It has been. A volume adjustment knob 13c for adjusting the volume of the speaker 31 is provided on the right side of the battery case 14, and connectors 13b and 13a are provided on the right side thereof. As shown in FIG. 2, a plug 202 of a connection cable 201 connected to the printer 200 is connected to the connector 13b, and a plug 102 of a connection cable 101 connected to the PC 100 is connected to the connector 13a.
  That is, writing data indicating the contents written on the writing surface 21 a of the electronic blackboard 1 can be output to the PC 100, and the contents written on the electronic blackboard 1 can be viewed on the monitor 103 provided in the PC 100. It is also possible to output writing data to the printer 200 and print the contents written on the electronic blackboard 1 on the printing paper 203.
[0019]
  Further, metal fittings 15 for attaching the electronic blackboard 1 to the wall are attached to both ends of the upper end of the back surface of the frame 11.
  In the first embodiment, the writing surface 21a has a height H1 of 900 mm and a width W1 of 600 mm. Moreover, the frame 11 and the base 12 are formed lightly by a synthetic resin such as polypropylene, and the total weight of the electronic blackboard 1 is 10 kg or less. Further, the eraser 40 includes a coil that generates an alternating magnetic field, an oscillation circuit, a battery, and the like.
[0020]
[Network configuration]
  Next, the configuration of a network when data communication is performed between the electronic blackboard 1 and another electronic blackboard 1 will be described with reference to FIG.
  Here, a case where communication is performed between a plurality of rooms provided with the electronic blackboard 1 or between companies in the company will be described as an example.
  The room 3 in the company 2 includes an electronic blackboard 1, a PC 100 connected to the electronic blackboard 1, and a LAN board 103 connected to the PC 100. The room 4 includes the electronic blackboard 1 and A PC 100 connected to the electronic blackboard 1 and a modem 108 connected to the PC 100 are provided. The LAN board 103 provided in each room 3 is connected to the HUB 105 by a LAN cable 104. The HUB 105 is connected to a server 106, and the server 106 can be connected to another company 5 via the Internet 300. The modem 108 provided in the room 4 can be connected to another company 5 from the telephone line 109 via the public communication switching network 301.
  Although not shown, in the other company 5, as in the company 2, an electronic blackboard 1 that can communicate via a PC is provided.
[0021]
  Here, a data flow in the network will be described.
  The writing data stored in the electronic blackboard 1 provided in a room 3 is transmitted from the PC 100 to the PC 100 in the designated room 3 via the LAN board 103 and the HUB 105. The person who receives the data displays the received data on the monitor 103 provided in the PC 100 (FIG. 2) or prints the received data on the sheet 203 by the printer 200 connected to the PC 100. (FIG. 2), the contents of the received data can be viewed.
  Moreover, handwritten data can be attached as an image file to an electronic mail in a TIFF (Tag Image File Format) format, for example, and transmitted from the server 106 to another company 5 via the Internet 300. As a result, the other company 5 can view the contents of the written data by decoding the image file attached to the electronic mail transmitted from the company 2.
[0022]
[Structure of writing panel body 20]
  Next, the structure of the writing panel body 20 will be described with reference to FIG.
  FIG. 4 is an explanatory diagram showing each component of the writing panel body 20.
  The writing panel body 20 has a structure in which a writing sheet 21 having a writing surface 21a, a plate-like panel 22, a frame-shaped mounting panel 24 on which a sense coil 23 is laid, and a plate-like back panel 25 are laminated in order. It is.
  In this embodiment, the writing sheet 21 is formed with a thickness of 0.1 mm by a bonded PET (polyethylene terephthalate) film, and the panel 22 is made of acrylic resin, ABS (acrylonitrile-butadiene-styrene copolymer). , PC (polycarbonate) or the like to a thickness of 3.0 mm. Further, the mounting panel 24 is formed to a thickness of 40 mm from a foamed resin material such as polystyrene foam, and the back panel 25 is formed to a thickness of 1.0 mm from a conductive material such as aluminum. Furthermore, the entire thickness of the frame 11 that holds each end of the writing panel body 20 is 50 mm.
[0023]
[Configuration of Sense Coil 23]
  Next, the configuration of the sense coil 23 will be described with reference to FIG.
  FIG. 5A is an explanatory diagram showing a part of the configuration of the sense coil 23 shown in FIG. 4 with a part omitted, and FIG. 5B shows the width and overlap of the sense coil 23 shown in FIG. It is explanatory drawing which shows a pitch.
  In the following description, a sense coil arranged in the X-axis direction among the sense coils 23 is referred to as an X coil, and a sense coil arranged in the Y-axis direction is referred to as a Y coil.
  As shown in FIG. 5A, m X coils X1 to Xm for detecting the X coordinates of the (X, Y) coordinates of the pen 60 and the eraser 40 are arranged in the X-axis direction. In the Y axis direction, n Y coils Y1 to Yn for detecting the Y coordinate are arranged orthogonal to the X coil. The X coil and Y coil are each formed in a substantially rectangular shape, and the lengths of the long sides of the rectangular portion are P2X and P2Y, respectively.
[0024]
  As shown in FIG. 5B, the X coils are each formed to have a width (the length of the short side of the rectangular portion) P1, and the adjacent X coils are overlapped at a pitch of P1 / 2. . Each Y coil is also formed with a width P1, and adjacent Y coils are overlapped with each other at a pitch of P1 / 2. Each terminal 23a of the X coil is connected to the X coil switching circuit 50a, and each terminal 23b of the Y coil is connected to the Y coil switching circuit 50b (FIG. 9).
  In the first embodiment, P1 = 50 mm, P2X = 680 mm, and P2Y = 980 mm. Further, m = 22 and n = 33. Furthermore, both the X coil and the Y coil are formed of a copper wire having a diameter of 0.35 mm having an insulating coating layer (for example, enamel layer) on the surface.
  In FIG. 5A, the sides of the coils are drawn so as not to overlap in order to make the arrangement of the coils easy to understand. However, in practice, for example, each Y coil is placed on the long side of the X coil X1. The short sides of Y1, Y2, Y3. Further, the terminals 23a and 23b are configured with a minimum interval.
[0025]
[Position coordinate table]
  Next, a position coordinate table for detecting the position coordinates of the pen 60 on the writing surface 21a will be described with reference to FIGS.
  FIG. 6A is an explanatory diagram showing a part of the X coils X1 to X3, and FIG. 6B shows the voltage generated in the X coils X1 to X3 shown in FIG. 6A and the distance in the width direction. FIG. 6C is a graph showing a voltage difference between adjacent sense coils of the X coils X1 to X3 shown in FIG. 6A. FIG. 7A is an explanatory diagram showing the position coordinate table in a graph, FIG. 7B is an explanatory diagram of the position coordinate table, and FIG. 7C is a storage of detected values detected from each X coil. It is explanatory drawing which shows a state.
[0026]
  In FIG. 6, the center lines of the X coils X1, X2, and X3 are C1, C2, and C3, respectively, and the voltages generated in the X coils X1, X2, and X3 are ex1, ex2, and ex3, respectively. As shown in FIG. 6B, the voltages ex1 to ex3 are maximal at the centers C1 to C3 of the sense coils, respectively, and exhibit a single peak property that decreases as the end in the longitudinal direction is approached. Each coil is overlapped at P1 / 2 so that its own null point, that is, the point where the voltages ex1 to ex3 are 0, is outside the center of the adjacent coil.
  In addition, as shown in FIG. 6C, the voltage difference between the adjacent sense coils of the X coils X1 to X3 has a maximum value on the center C1 to C3 of the sense coil, The graph becomes zero at the midpoint of the long side portion of the sense coil, that is, the midpoint of the portion where the adjacent sense coils overlap.
[0027]
  For example, in FIG. 6C, the right half (portion indicated by the solid line) of the graph indicating (ex1-ex2) is the distance from the center C1 of the X coil X1 to the intermediate point Q2 of the portion where the X coil X2 is overlapped. The relationship between (1/2 of the overlapping pitch, that is, P1 / 4) and (ex1-ex2) is shown. Now, if the pen 60 is present at the point Q2, the distance ΔX1 from the center C1 to the point Q2 can be detected by detecting (ex1-ex2), so that the X coordinate of the point Q2 can be obtained.
  In this embodiment, since the coil width P1 is 50 mm, P1 / 4 = 12.5 mm. For example, when the part (part drawn with a solid line) showing the characteristic of (ex1-ex2) in FIG. 6C is converted into 8-bit digital data, the graph shown in FIG. 7A is obtained. When this graph is converted into a table format, a position coordinate table 58a shown in FIG. 7B is obtained. The position coordinate table 58a is stored in the ROM 58 (FIG. 9) or the like and used for calculating the position coordinates of the pen 60.
[0028]
  Next, the main configuration of the pen 60 will be described with reference to FIG.
  8A is an explanatory diagram showing the internal structure of the pen 60, and FIG. 8B is an explanatory diagram showing the electrical configuration of the pen 60 shown in FIG. 8A.
[Internal structure of pen 60]
  The pen 60 includes a cylindrical body portion 61a and a lid 61c detachably attached to the rear end of the body portion 61a. Inside the body portion 61a, the coil L1, the ink cartridge 63 that can be taken out in the direction indicated by the arrow F2, the pen tip 62 inserted into the ink cartridge 63, and an oscillation for generating an alternating magnetic field from the coil L1. A circuit board 69 on which a circuit or the like is mounted and a battery 70 for supplying power to the circuit board 69 are provided.
  Further, a push button type switch 67 is provided between the ink cartridge 63 and the circuit board 69 for supplying and shutting off power to the oscillation circuit and the like. The switch 67 presses the pen tip 62 against the writing surface 21a (FIG. 1) and turns ON when the ink cartridge 63 moves in the direction indicated by the arrow F1, and turns OFF when the ink cartridge 63 returns in the direction indicated by the arrow F2. That is, an alternating magnetic field is generated from the coil L1 when writing is performed on the writing surface 21a by the pen 60.
[0029]
[Electric configuration of pen 60]
  As shown in FIG. 8B, the circuit mounted on the circuit board 69 includes a CR oscillation circuit 69e in which a different modulation frequency is set for each attribute of the pen such as the color of the ink and the thickness of the pen tip. An LC oscillation circuit 69c that oscillates a carrier wave that carries a signal oscillated from the CR oscillation circuit 69e, and an FSK circuit 69d that modulates the oscillation frequency of the LC oscillation circuit 69c by FSK (Frequency Shift Keying) by the modulation frequency of the CR oscillation circuit 69e. It consists of. The oscillation frequency of the carrier wave is determined by the inductance L1 and the capacitors C1, C2, and C3 constituting the LC oscillation circuit 69c, and the modulation frequency is determined by the capacitor C5 and the resistors R2 and R3 that constitute the CR oscillation circuit 69e. Further, the frequency deviation of the oscillation frequency of the carrier wave is determined by the capacitance of the capacitor C4 of the FSK circuit 69d.
[0030]
  The relationship between the attribute of the pen 60 and the modulation frequency fm is set as shown in FIG. 10A, “thin” indicates that the pen tip 62 (FIG. 8A) is thin, and “thick” indicates that the pen tip 62 is thick. For example, black thick indicates a pen that has a thick nib and uses black ink.
  Note that the eraser 40 also has a built-in coil. In order to calculate the erase range by the eraser 40 based on the signal generated in the sense coil by the alternating magnetic field generated from the coil, the eraser 40 is also assigned a modulation frequency fm, 60.
[0031]
  When the switch 67 is turned on, the power of the battery 70 is supplied to each circuit, the output of the integrated circuit IC3 of the CR oscillation circuit 69e switches the gate of the MOS FET of the FSK circuit 69d, and the carrier wave oscillated from the LC oscillation circuit 69c. Is frequency-modulated by the signal oscillated from the CR oscillation circuit 69e.
  In the first embodiment, the center frequency of the carrier wave is 410 kHz, and the frequency deviation is ± 20 kHz. In the first embodiment, the integrated circuit IC1 is a TC7SLU04F made by Toshiba, and the integrated circuits IC2 and IC3 are both U04 made by Toshiba. The MOS FET is 2SK2158. The resistors R1 and R2 are both 1 MΩ, and the variable range of the variable resistor R3 is 0Ω to 1MΩ. Capacitors C1, C4, and C5 are 0.1 μF, 0.0015 μF, and 100 pF, respectively, and capacitors C2 and C3 are both 0.0033 μF. Furthermore, the battery 70 is LR44, and a voltage is about 1.5V.
[0032]
[Main electrical configuration and control contents of electronic blackboard 1]
  Next, main electrical configurations and control contents of the electronic blackboard 1 will be described with reference to FIGS. 9, 10 </ b> B, and 11.
  FIG. 9 is an explanatory diagram showing the electrical configuration of the electronic blackboard 1 in blocks, FIG. 10B is an explanatory diagram showing signals at points A, B, and C in FIG. 9, and FIG. 6 is a flowchart showing main control contents executed by the CPU 56 shown in FIG.
  When the CPU 56 provided in the control device 50 shown in FIG. 9 detects that the power button 38 (FIG. 1) is turned on (step (hereinafter abbreviated as S) 100: Yes), the control program stored in the ROM 58 is stored. The initial setting such as loading the position coordinate table 58a (FIG. 7B) into the work area of the RAM 59 is performed (S200), and coordinate reading / pen information detection processing is executed (S300).
[0033]
[Coordinate reading process]
  Here, the coordinate reading process will be described with reference to the flowchart of FIG.
  The CPU 56 outputs a coil selection signal A (FIG. 10B) for selecting the X coils X1 to Xm in order to the X coil switching circuit 50a via the input / output circuit (I / O) 53, whereby the X coil X1. Scan of ~ Xm is performed (S302). Subsequently, the signal generated by the magnetic coupling between the alternating magnetic field generated from the coil L1 of the pen 60 and one of the X coils is amplified by the amplifier 50c (FIG. 9), and the amplified signal (FIG. 10B) is The unnecessary band is filtered by the band pass filter (BPF) 50 d and the amplitude is detected by the amplitude detection circuit 51. Subsequently, the amplitude-detected signal (FIG. 10B) is converted into a digital signal corresponding to the amplitude, that is, the voltage value by the A / D conversion circuit 52 and input to the CPU 56 via the input / output circuit 53. .
[0034]
  Subsequently, the CPU 56 determines that the pen 60 has been detected (S304: Yes), and scans the X coils X1 to Xm to indicate voltage values e1 to em indicated by the input digital signals as shown in FIG. 7C. Next, it is sequentially stored in the voltage value storage area 59a of the RAM 59 in association with the coil number of the X coil (S306). Subsequently, the CPU 56 calculates the X coordinate of the pen 60 according to the following procedure based on each voltage value stored in the voltage value storage area 59a (S308).
  First, the maximum voltage value emax is selected from the voltage values e1 to em stored in the voltage value storage area 59a, and the coil number (hereinafter referred to as max) of the X coil that generated the voltage value emax is selected in the RAM 59. To remember.
  For example, as shown in FIG. 6, when the pen 60 is present at the position Q3 and the voltage values e1, e2, e3 are generated from the X coils X1, X2, X3, respectively, as shown in FIG. The maximum voltage value e2 is selected, and the coil number 2 of the X coil that generated the voltage value e2 is stored in the RAM 59 as max.
  Then, the CPU 56 determines the larger one of the voltage values emax ± 1 on both sides of emax, and stores the coil number (hereinafter referred to as max2) of the X coil that generated the determined voltage value in the RAM 59.
[0035]
  In the example shown in FIG. 6, the larger e3 of the voltage values e3 and e1 adjacent to e2 is determined, and the coil number 3 of the X coil that generated e3 is stored in the RAM 59 as max2.
  Subsequently, the CPU 56 compares the coil numbers max and max2 stored in the RAM 59 to determine whether the coil number max2 is present in the + direction or the − direction of the X axis from the coil number max. If max2 ≧ max, the variable SIDE is set to 1, and if max2 <max, the variable SIDE is set to -1. In the example shown in FIG. 6, since max = 2 and max2 = 3, max2> max and the variable SIDE is set to 1.
  Subsequently, the CPU 56
[0036]
  DIFF = e (max) −e (max2) (1)
[0037]
And the position coordinate closest to the calculated DIFF is read from the position coordinate table 58a stored in the ROM 58, and set as OFFSET. Subsequently, the CPU 56
[0038]
  X1 = (P1 / 2) × max + OFFSET × SIDE (2)
[0039]
To obtain the X coordinate X1. Here, (P1 / 2) × max indicates the X coordinate of the center of the coil number max. In the example shown in FIG. 6, the equation (2) is X = (P1 / 2) × 2 + (e2−e3) × 1, and the X coordinate of the position Q3 is + X of the X axis from the center line C2 of the X coil X2. The distance is a distance corresponding to (e2-e3) in the direction, for example, coordinates separated by ΔX2.
  Then, the CPU 56 scans each Y coil (S310), and stores the voltage value detected from each Y coil in the voltage value storage area for the Y coil in the RAM 59 (S312). Subsequently, the CPU 56 calculates the Y coordinate of the pen 60 using the same method as the calculation of the X coordinate in S308 described above (S314).
[0040]
[Determination of pen attributes]
  Next, an electrical configuration and control for the CPU 56 to determine the pen attribute will be described with reference to FIGS.
  FIG. 13 is an explanatory diagram showing an electrical configuration of the FSK demodulator circuit 55 (FIG. 9), and FIG. 14 is an explanatory diagram showing signal waveforms appearing at each part of the FSK demodulator circuit 55 shown in FIG.
  FIG. 15A shows an output signal from the CR oscillation circuit 69e (hereinafter referred to as a CR signal), an output signal from the LC oscillation circuit 69c (hereinafter referred to as a carrier signal), and an output signal from the limiter circuit 54 (hereinafter referred to as a limiter). It is explanatory drawing which shows the relationship between a count value by a count circuit 55a (FIG. 13) and an output signal. FIG. 15B is an explanatory diagram showing how the count value stored in the shift register 55b (FIG. 13) is shifted.
  FIG. 16A is an explanatory diagram showing the relationship between the threshold value determination output by the absolute value comparator 55f (FIG. 13) and the determination period of the CPU 56, and FIG. 16B shows the movement of the count value by the counter 55g. It is explanatory drawing which shows a mode. FIG. 17 is a flowchart showing the flow of processing (pen attribute detection processing 1) from the count circuit 55a constituting the FSK demodulating circuit 55 to the absolute value comparator 55f, and FIG. 18 shows the processing (pen attribute) of the counter 55g and the adder 55i. It is a flowchart which shows the flow of a detection process 2).
  Note that the carrier signal shown in FIG. 15A has a center frequency of 410 kHz and a frequency shift of ± 20 kHz as described above, for example, but in FIG. The shift is exaggerated.
[0041]
  First, characteristics of the FSK demodulating circuit 55 for detecting pen attributes will be described with reference to FIG.
  In the example shown in FIG. 15A, the carrier signal is modulated at a high frequency (for example, 430 kHz) during the low level of the CR signal, and is modulated at a low frequency (for example, 390 kHz) during the high level. . Therefore, if the period of the limiter output signal while the CR signal is at the low level is TB, the period of the limiter output signal while the CR signal is at the high level is TC longer than TB.
  Therefore, the count value k for one cycle of the limiter output signal by the count circuit 55a increases when the CR signal changes from the low level to the high level, and decreases when the CR signal changes from the high level to the low level.
[0042]
  That is, the rising or falling timing of the CR signal can be detected by detecting the timing at which the count value k is changed by the count circuit 55a. Since the time from when the count value k changes until the next change corresponds to a half cycle of the CR signal, if one cycle of the time when the count value k changes is measured, the cycle of the CR signal Can be obtained, so that the pen attribute can be detected.
  Here, the outline of the operation of each component of the FSK demodulating circuit 55 will be described. The count circuit 55a measures the count value k, shift register 55b, first weighted average circuit 55c, second weighted average circuit 55d, subtractor. 55e and the absolute value comparator 55f detect the change timing of the count value k, and the counter 55g, the register 55h, and the adder 55i measure the cycle in which the count value k changes. Then, the CPU 56 determines a pen attribute based on the added value output from the adder 55i (S318).
[0043]
  Next, the operation of the FSK demodulation circuit 55 will be described in detail.
  The signal output from the band pass filter 50 d is converted into a square wave limiter output signal shown in FIG. 15A by the limiter circuit 54 and output to the FSK demodulation circuit 55. When the rising edge of the limiter output signal is detected (S10: Yes in FIG. 17), the FSK demodulating circuit 55 starts counting the period of the limiter output signal using the system clock (CLK) (S12), and the limiter output signal When the next rising edge is detected (S14: Yes), the count value k is output to the shift register 55b (S16), and the count value k is reset (S18).
  That is, the count circuit 55a measures the length TB or TC of one cycle of the limiter output signal.
[0044]
  In this embodiment, as shown in FIG. 15B, the shift register 55b stores the count value k for one period of the limiter output signal for eight periods k1 to k8, and takes in the newest count value k. The oldest count value k is discarded, and each count value k is shifted one by one.
  The first weighted average circuit 55c calculates the weighted average value from the newest count value stored in the shift register 55b to the third newest count value, and the weighted average value (hereinafter referred to as the first weighted average value). ) Is output to the subtractor 55e. The second weighted average circuit 55d calculates a weighted average value from the oldest count value stored in the shift register 55b to the third oldest count value, and the weighted average value (hereinafter referred to as the second weighted average value). Is output to the subtractor 55e.
[0045]
  In this way, since the count values counted apart in time are weighted and averaged by the weighted average circuit, even if a certain count value is affected by noise, the influence can be reduced.
  The subtractor 55e calculates a difference Δm between the first weighted average value and the second weighted average value, and outputs the difference Δm to the absolute value comparator 55f (S20 in FIG. 17).
  For example, in FIG. 15A, when the first weighted average circuit 55c calculates the weighted average value of the count values k1 to k3, and the second weighted average circuit 55d calculates the weighted average value of the count values k6 to k8, Among the count values k6 to k8, the count values k7 and k8 are obtained by counting the cycle TC longer than the cycle TB of the limiter output signal, and therefore the second weighted average value is larger than the first weighted average value.
  Therefore, if it is detected that the second weighted average value is larger than the first weighted average value, the changing point of the CR signal cycle can be detected.
  That is, if the period of the change point of the CR signal period is detected, the CR signal period can be detected, so that the attribute information of the pen 60 can be recognized.
  The first weighted average circuit 55c and the second weighted average circuit 55d are determined on the basis of the ratio between the carrier frequency (the oscillation frequency of the LC oscillation circuit 69c) and the modulation frequency, and the complexity of the circuit. Further, the count value held by the shift register 55b, that is, the number of periods of the limiter output signal is determined by the ratio of the system clock frequency and the frequency of the carrier wave, and the system clock frequency is set to a size that can sufficiently discriminate the change in frequency. To do.
[0046]
  Next, processing from the absolute value comparator 55f to the adder 55i will be described with reference to FIG.
  In FIG. 16, (1) to (8) indicate count values by the counter 55g.
  The absolute value comparator 55f compares the difference Δm with a preset threshold value m1, and determines whether or not the difference Δm is equal to or greater than the threshold value m1 (S22 in FIG. 17). If it is determined that the threshold value is greater than or equal to the threshold value m1 (S22: Yes), the threshold value determination output is changed from the low level to the high level (S24).
  That is, it is determined that the cycle of the limiter output signal has changed (the rising edge of the CR signal has been detected).
  For example, if the count value by the count circuit 55a of the shorter cycle TB of the limiter signal shown in FIG. 15A is 10, the count value of the cycle TC is 16, and the threshold value m1 is 2, the count values k1 to k6 are Since both are 10, the first weighted average value = (k1 + k2 + k3) / 3 = 10. Since the count values k7 and k8 are both 16, the second weighted average value = (k6 + k7 + k8) / 3 = 42/3 = 14, and the difference Δm = 10−14 = −4.
[0047]
  Accordingly, since (absolute value of difference Δm = 4)> (threshold value m1 = 2), the threshold determination output changes from the low level to the high level (S24). This high level state is maintained until the absolute value comparator 55f next determines that the absolute value of the difference Δm is greater than or equal to the threshold value m1.
  When the calculation range of the first weighted average circuit 55c and the second weighted average circuit 55d reaches the portion that has passed the edge of the CR signal, the period of the limiter output signal becomes constant, so both weighted average circuits are the same. Since the weighted average value of the count value of the period is calculated, the subtraction value by the subtractor 55e becomes 0, and the threshold judgment output continues to be in the high level state.
[0048]
  On the other hand, when the counter 55g detects that the threshold judgment output has changed from the low level to the high level (S30: Yes in FIG. 18), the time during which the judgment output is at the high level, that is, the half cycle of the judgment output. Is counted using the system clock (CLK) (S32). The count value is (1) ((B1) in FIG. 16B).
  When the absolute value comparator 55f again determines that the difference Δm is greater than or equal to the threshold value m1 (S22: Yes in FIG. 17), the threshold value determination output is changed from the high level to the low level (S24).
  That is, it is determined that the cycle of the limiter output signal has changed (the falling edge of the CR signal has been detected).
  Thereby, the counter 55g detects that the threshold judgment output has changed from the high level to the low level (S34: Yes), and the count value (1) as shown in (B2) of FIG. Is output to the register 55h (S36). Subsequently, the counter 55g resets the count value (1) (S38), and counts the time during which the threshold judgment output is at the low level, that is, the half cycle of the threshold judgment output (S32). Let the count value be (2).
[0049]
  Subsequently, when the adder 55i determines that it is the timing at which the counter 55g and the register 55h hold the count value, that is, the addition timing (S50: Yes), the counter 55g holds the count value (2) and the register. The count value (1) held by 55h is added (S52), and the addition values (1) and (2) are output to the CPU 56 (S54). At this time, the counter 55g outputs the count value (2) to the register 55h as shown in (B3) of FIG. 16B (S36 in FIG. 18).
  Then, the CPU 56 reads the addition value (1) (2) (S316 in FIG. 12), and determines the pen attribute based on the read addition value (1) (2) (S318). For example, when the addition values (1) and (2) are 245, it is determined that the pen attribute is black thick as shown in FIG. Further, the CPU 56 stores the pen attribute and the XY coordinates in the RAM 59 in association with each other. The writing data stored in such a form is output to the printer 200 (FIG. 2), for example, and printed with thick black. Further, it is output to the PC 100 and displayed on the monitor 103 (FIG. 2) in black.
  That is, the written data can be reproduced according to the attribute of the pen 60.
[0050]
  Subsequently, the adder 55i adds the count value (2) of the register 55h and the count value (3) of the counter 55g, and outputs it to the CPU 56 ((B3) in FIG. 16B).
  Thereafter, every time the threshold judgment output changes, the count value by the counter 55g is output to the register 55h, and the adder 55i adds the count value by the counter 55g and the count value held in the register 55h, The cycle of outputting the added value to the CPU 56 is repeated.
  That is, as shown in FIG. 16B, the adder 55i adds the latest count value counted by the counter 55g and the previous count value held in the register 55h, and adds it to the CPU 56. As shown in FIG. 16A, the CPU 56 determines the pen attribute based on the latest count value and the added value of the previous count value for each half cycle of the threshold determination output. To do.
  Therefore, even if the sense coil 23 is scanned during the threshold determination output, for example, between the times t0 and t1 in FIG. Even if the added value of (t2 to t4) is not taken in, the time t0T after half a cycle from1~ T3Therefore, the pen attribute can be determined at high speed.
[0051]
  Returning to the description of FIG. 11, the CPU 56 returns or sends the stored writing data in units of pages when the page return button 33, the page feed button 34 and the delete button 35 are pressed. Page processing such as erasure is performed (S400). Further, the CPU 56 takes in switching signals generated by the operation of various buttons (FIG. 1) provided on the operation unit 30 via the I / F circuit 57 (FIG. 9), and acquires the position coordinate data stored in the RAM 59. A page process such as sending or returning the page to be stored, or deleting the position coordinate data in page units is executed (S400). Further, the CPU 56 executes a data output process of converting the position coordinate data of the target page out of the position coordinate data stored in the RAM 59 into an appropriate format and outputting it to the PC 100 or the printer 200 (FIG. 2) ( S500).
[0052]
  Furthermore, the CPU 56 operates the audio circuit 31a based on switching signals generated when various buttons are pressed, and executes an audio output process for generating operation sounds such as “Peep” and “Pip” from the speaker 31. (S600). Further, the CPU 56 calculates the wiping locus of the eraser 40 based on the voltage generated in the X coil and the Y coil by the alternating magnetic field generated from the coil built in the eraser 40, and the position coordinate data in the calculated wiping locus is stored in the RAM 59. The eraser process for erasing from FIG. 9 is executed (S700).
[0053]
  As described above, when the electronic blackboard 1 of the first embodiment is used, a CR signal having a period corresponding to the attribute of the pen 60 is transmitted from the pen 60 to the writing panel body 20, and one period of the CR signal is measured. Thus, since the attribute of the pen 60 can be recognized, the time required for recognizing the attribute of the pen 60 can be shortened as compared with the conventional case of transmitting the code string in a plurality of cycles.
  For example, when the modulation frequency of the CR oscillation circuit 69e is 5 kHz, one period of the CR signal, that is, the time required for recognizing the pen attribute is 1 / 5,000 = 200 (μs) at the shortest. Further, in the conventional coordinate reading apparatus shown in FIG. 20, if the frequency for transmitting the code string is 5 kHz, 200 (μs) is required to transmit 1 bit, and a total of 10 bits are transmitted. The time required to transmit the code string is 200 (μs) × 10 = 2,000 (μs).
  That is, if the electronic blackboard 1 of the first embodiment is used, the time required for recognizing the pen attribute can be shortened to the conventional 200 / 2,000 = 1/10.
[0054]
  Moreover, even if the CR signal cycle changes small, the change appears as a change in the cycle of the limiter output signal. The change is detected by the FSK demodulating circuit 55 and further detected by the CPU 56. Even if the period of the CR signal is set finely every time, the attribute of the pen 60 can be recognized.
  For example, when the periods TB and TC of the limiter output signal are counted using the system clock as in the first embodiment described above, the count value is determined if the period of the limiter output signal changes by at least one period of the system clock. Changes so that the pen attribute can be recognized. Therefore, the attribute may be set for each pen 60 so that the cycle of the CR signal differs by at least one cycle of the system clock.
  Therefore, a very large number of pen attributes can be set.
  Furthermore, since the pen attribute can be recognized based on the measurement result of the CR signal cycle, it is not necessary to synchronize the operation clock on the pen side and the operation clock on the coordinate input sheet as in the prior art. Since there is no need to provide a frequency divider or the like that generates the above, the circuit configuration of the pen 60 can be simplified.
[0055]
  In addition, since the CR signal can be repeatedly transmitted in a single cycle, the pen attribute can be recognized by measuring the next cycle even when scanned in the middle of one cycle of the CR signal. Therefore, unlike the prior art, it is not necessary to wait until the next start bit is transmitted and receive a plurality of cycles from the start bit to the stop bit, so that the time required for recognizing the pen attribute can be reduced.
  Further, since the carrier wave by the LC oscillation circuit 69c is frequency-modulated by the CR signal, even if the amplitude of the carrier wave changes, the CR signal period does not change, so the pen attribute indicated by the CR signal period is There is no change. For example, even when the voltage of the battery 70 built in the pen 60 decreases and the strength of the alternating magnetic field generated from the coil L1 decreases, the attribute information of the pen 60 can be transmitted accurately.
[0056]
[Second Embodiment]
  Next, a second embodiment of the present invention will be described with reference to FIG.
  The electronic blackboard of the second embodiment is characterized in that the XY coordinates can be read at high speed by scanning every other X coil and Y coil.
  FIG. 19 is a flowchart showing the flow of the coordinate reading process executed by the CPU 56 provided in the electronic blackboard of the second embodiment. In the second embodiment, the processing executed by the CPU 56 other than the coordinate reading processing and the other configurations are the same as those of the electronic blackboard of the first embodiment described above. Only the flow of the reading process will be described. Moreover, the same code | symbol is used about the same structure as the electronic blackboard of 1st Embodiment.
[0057]
  The CPU 56 scans every other X coil (S330) and detects the pen 60 (S332: Yes), and sequentially stores the voltage value of each X coil in the voltage value storage area 59a of the RAM 59 (S334). . Subsequently, the CPU 56 detects the X coil Xi that has generated the maximum voltage value emax among the voltage values e1 to em stored in the voltage value storage area 59a (S336), and the X coil (B) adjacent to the X coil Xi ( Xi-1) and (Xi + 1) are scanned (S338).
  That is, since every other X coil is scanned, one of the X coils (Xi−1) and (Xi + 1) adjacent to the X coil Xi may have a higher voltage value than the X coil Xi. The X coils (Xi−1) and (Xi + 1) adjacent to the X coil Xi are scanned.
[0058]
  Subsequently, the CPU 56 obtains the X coil having the maximum voltage among the three X coils of the X coils (Xi-1), Xi, and (Xi + 1), and stores the coil number of the X coil (hereinafter referred to as max) in the RAM 59. Store (S340). Subsequently, the CPU 56 selects the larger one of the voltage values of the X coils adjacent to max, and stores the coil number (hereinafter referred to as max2) of the X coil that generated the selected voltage value in the RAM 59.
  Subsequently, the CPU 56 compares the coil numbers max and max2 stored in the RAM 59 to determine whether the coil number max2 is present in the + direction or the − direction of the X axis from the coil number max. If max2 ≧ max, the variable SIDE is set to 1, and if max2 <max, the variable SIDE is set to -1.
[0059]
  Subsequently, the CPU 56 calculates DIFF using the equation (1) described in the first embodiment, reads out the position coordinate closest to the calculated DIFF from the position coordinate table 58a stored in the ROM 58, and calculates it. Set to OFFSET. Then, CPU56 calculates | requires X coordinate X1 using Formula (2).
  Then, the CPU 56 scans every other Y coil and calculates the Y coordinate Y1 by the same method (S332 to S344) as the X coordinate calculation described above.
  For example, when there are 22 X coils, every other X coil is scanned, the number of scans in S330 is 22/2 = 11, and the number of scans in S338 is 2, so the total number of scans Is 11 times + 2 times = 13 times.
  Therefore, since the scan of 22 times is sufficient for 13 scans, the scan time for 9 times (= 22-13 times) can be shortened.
  Even if the scan time is shortened,
[0060]
  As described above, if the electronic blackboard of the second embodiment is used, the time required for recognizing the pen attribute can be shortened, and the scan time of the sense coil 23 can also be shortened. Can be realized.
[0061]
  In each of the embodiments described above, the pen attribute is recognized based on the length of one cycle of the CR signal. However, when the duty ratio of the CR signal is constant 50%, the pen attribute is determined based on the half cycle of the CR signal. It can also recognize attributes. In this case, the time required for recognizing the pen attribute can be shortened to ½ that of each embodiment.
  Furthermore, in addition to changing the length of one period of the CR signal for each pen attribute and setting the duty ratio, more pen information can be set.
  In addition, by setting the duty ratio of the CR signal for each user of the pen 60 and storing the user name and the duty ratio in association with each other in an EEPROM or the like, it is possible to print writing data with the user name. Can be displayed. Note that phase modulation may be used instead of frequency modulation.
[0062]
  Further, each of the embodiments described aboveTechnology described inIsTheFor example, it can be applied to a security device. For example, a transmission device having the same function as the pen 60 is attached to the output of a sensor attached to a place to be monitored such as a doorway or window of a building, and a reception device is provided in a management room or the like. In this case, the period of the CR oscillation circuit provided in the transmission device is set to a different period for each sensor. When a certain sensor is turned on, a transmission device connected to the sensor is activated to transmit a signal to the reception device. Subsequently, the receiving apparatus demodulates the transmitted signal by the demodulation means described in each of the above-described embodiments, and identifies which sensor the sensor that transmitted the signal is.
  Therefore, a sensor can be identified by slightly changing the period of the CR oscillation circuit, so that a great number of sensors can be attached.
[0063]
  By the way, the pen 60 corresponds to the writing means of the present invention, the sense coil 23 corresponds to the conducting wire, and the mounting panel 24 corresponds to the coordinate input sheet. Further, the electrical configuration of the pen 60 shown in FIG.SendingThe electronic configuration of the electronic blackboard 1 shown in FIG.ReceivingIt functions as a communication means.
[Brief description of the drawings]
FIG. 1 is an external perspective view illustrating the main configuration of an electronic blackboard according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a state in which a PC and a printer are connected to the electronic blackboard shown in FIG.
FIG. 3 is an explanatory diagram showing in block form the configuration of a network when data communication is performed between the electronic blackboard 1 and another electronic blackboard 1;
FIG. 4 is an explanatory view showing each component of the writing panel body 20;
5A is an explanatory diagram showing a part of the configuration of the sense coil 23 shown in FIG. 5 with part omitted, and FIG. 5B is a width of the sense coil 23 shown in FIG. 5A. It is explanatory drawing which shows an overlap pitch.
6A is an explanatory diagram showing a part of the X coils X1 to X3, and FIG. 6B is a voltage generated in the X coils X1 to X3 shown in FIG. 6A and the width direction. 6C is a graph showing the voltage difference between the adjacent sense coils of the X coils X1 to X3 shown in FIG. 6A.
FIG. 7A is an explanatory diagram showing a graph of the position coordinate table, FIG. 7B is an explanatory diagram of the position coordinate table, and FIG. 7C is detected from each X coil. It is explanatory drawing which shows the memory | storage state of a voltage value.
8A is an explanatory diagram showing the internal structure of the pen 60, and FIG. 8B is an explanatory diagram showing the electrical configuration of the pen 60 shown in FIG. 8A.
FIG. 9 is an explanatory diagram showing the electrical configuration of the electronic blackboard 1 in blocks.
10A is an explanatory diagram showing the relationship between the attributes of the pen 60 and the modulation frequency fm, and FIG. 10B is an explanatory diagram showing signals at points A, B, and C in FIG. FIG.
11 is a flowchart showing main control contents executed by a CPU 56 shown in FIG. 9;
FIG. 12 is a flowchart showing a flow of coordinate reading processing in the first embodiment.
FIG. 13 is an explanatory diagram showing an electrical configuration of an FSK demodulator circuit 55 (FIG. 9).
FIG. 14 is an explanatory diagram showing signal waveforms appearing at each part of the FSK demodulating circuit 55;
FIG. 15A is an explanatory diagram showing the relationship between the CR signal, the carrier signal, the limiter output signal, and the count value by the count circuit 55a (FIG. 13), and FIG. It is explanatory drawing which shows a mode that the count value stored in the register | resistor 55b (FIG. 13) shifts.
FIG. 16A is an explanatory diagram showing the relationship between the threshold value determination output by the absolute value comparator 55f (FIG. 13) and the determination period of the CPU 56, and FIG. 16B shows the count by the counter 55g. It is explanatory drawing which shows a mode that a value moves.
FIG. 17 is a flowchart showing a flow of processing (pen attribute detection processing) from the count circuit 55a constituting the FSK demodulating circuit 55 to the absolute value comparator 55f.
FIG. 18 is a flowchart showing a processing flow of a counter 55g and an adder 55i.
FIG. 19 is a flowchart showing a flow of coordinate reading processing in the second embodiment.
FIG. 20A is an explanatory diagram illustrating a configuration of a conventional coordinate reading apparatus, and FIG. 20B is an explanatory diagram illustrating a code string transmitted from a pen.
[Explanation of symbols]
    1 Electronic blackboard (coordinate reader)
  21a Writing surface (coordinate input surface)
  23 Sense coil (conductor)
  24 Mounting panel (coordinate input sheet)
  30 Operation unit
  55 FSK demodulator
  56 CPU
  58a Position coordinate table
  60 Pen (Writing means)
  69c LC oscillator circuit
  69d FSK circuit
  69e CR oscillator circuit
  L1 coil

Claims (2)

A main body having a coordinate input sheet in which a plurality of conductive wires magnetically coupled to an alternating magnetic field are laid at the bottom of the writing surface;
Writing means for generating the alternating magnetic field, scanning each of the conductors to detect a conductor that has generated a signal, and based on the signal generated in the detected conductor , the writing means on the writing surface In a coordinate reader that reads position coordinates,
The writing means is:
A coil that generates an alternating magnetic field with a predetermined period;
Using a signal having a single period set for each attribute information included in said writing means, and a transmitting means for transmitting the alternating magnetic field generated from the coil angle modulation to,
The body is
One cycle of the signal transmitted from the writing means by reading the position coordinates of the writing means on the writing surface based on the signal generated on the detected conductor and demodulating the signal used for the reading A coordinate reading apparatus comprising: a receiving unit that detects a minute length every half cycle and recognizes attribute information of the writing unit based on the detected length of one cycle . The transmission means includes
The coordinate reading apparatus according to claim 1 , wherein the signal is repeatedly transmitted for a predetermined time.

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