Position detection device

Abstract

Provided is a position detection device that allows the height of an electronic pen in a hovering state from an input surface of the position detection device to be higher than conventionally possible and that makes it possible to properly detect a writing pressure.　A position detection device according to the present invention uses electromagnetic induction coupling to perform signal interaction with an electronic pen that includes a resonant circuit having a resonant frequency which changes according to an applied writing pressure, so as to detect the position on a position detection sensor instructed by the electronic pen and detect a writing pressure applied by the electronic pen. When the signal level of a feedback signal from the electronic pen is equal or greater than a prescribed threshold value, the frequency of a signal from a signal transmission circuit for the interaction with the electronic pen is switched by a control circuit from a first frequency that is equal to the resonant frequency of the resonant circuit when no writing pressure is applied to the electronic pen to a second frequency that is in a direction in which the resonant frequency changes according to the writing pressure and that is different from the first frequency.

Description

Position detection device

[0001] The present invention relates to a position detection device that is electromagnetically inductively coupled to an electronic pen to detect a position indicated by the electronic pen and detects the writing pressure applied to the electronic pen.

[0002] Electromagnetic induction type position detection devices are becoming popular, which detect the position indicated by the electronic pen on a position detection sensor by signal interaction with the electronic pen through electromagnetic induction coupling, and also detect the writing pressure applied to the electronic pen (see, for example, Patent Document 1 (JP 2012-133704 A)).

[0003] Figure 6 shows an example of the circuit configuration of an electronic pen 1 and a position detection device 2 that are an example of this electromagnetic induction method. As shown in Figure 6, the electronic pen 1 includes a resonant circuit 10R in which a coil 11, a capacitor 12 disposed on a printed circuit board, and a variable capacitor 13 that constitutes a writing pressure detection unit are connected in parallel. When writing pressure is applied to the electronic pen 1, the capacitance of the variable capacitor 13 increases and the resonant frequency of the resonant circuit 10R changes accordingly. As will be described later, the position detection device 2 detects the writing pressure by detecting this change in the resonant frequency.

[0004] On the other hand, the position detection device 2 includes a position detection sensor 21 formed by stacking an X-axis direction loop coil group 21X and a Y-axis direction loop coil group 21Y, and electromagnetically coupled to the resonant circuit 10R of the electronic pen 1.

[0005] Each of the loop coil groups 21X and 21Y is made up of, for example, n and m rectangular loop coils, respectively. The loop coils constituting each of the loop coil groups 21X and 21Y are arranged at equal intervals so as to overlap one another.

[0006] The position detection device 2 is provided with a selection circuit 22 to which the X-axis direction loop coil group 21X and the Y-axis direction loop coil group 21Y of the position detection sensor 21 are connected. The selection circuit 22 sequentially selects one or more loop coils from the two loop coil groups 21X and 21Y under the control of a processing control circuit 29, which will be described later.

[0007] The position detection device 2 is provided with an oscillator 23, a current driver 24, a switching connection circuit 25, a receiving amplifier 26, a position detection circuit 27, a writing pressure detection circuit 28, and a processing control circuit 29. The position detection circuit 27 includes a detector 271, a low-pass filter 272, a sample-and-hold circuit 273, and an A / D conversion circuit 274. The writing pressure detection circuit 28 includes a synchronous detector 281, a low-pass filter 282, a sample-and-hold circuit 283, and an A / D conversion circuit 284. The processing control circuit 29 is configured by a microprocessor.

[0008] The oscillator 23 generates an AC signal of a predetermined frequency, for example, a frequency f0 of approximately 500 kHz to 600 kHz, and supplies the generated AC signal to the current driver 24 and the synchronous detector 281 of the writing pressure detection circuit 28. The current driver 24 converts the AC signal supplied from the oscillator 23 into a current and sends it to the switching connection circuit 25. The switching connection circuit 25 switches the connection destinations (transmission terminal T, reception terminal R) to which the loop coil selected by the selection circuit 22 is connected in response to a control signal from the processing control circuit 29. Of these connection destinations, the current driver 24 is connected to the transmission terminal T, and the reception amplifier 26 is connected to the reception terminal R.

[0009] When the processing control circuit 29 connects the switching control circuit 250 to the transmitting terminal T, a signal from the signal transmission circuit 23 is supplied to the position detection sensor 21 via the current driver 24, the switching control circuit 25, and the selection circuit 22, and is transmitted from the loop coil selected by the selection circuit 220 under the control of the processing control circuit 290.

[0010] Furthermore, when the processing control circuit 29 connects the switching control circuit 250 to the receiving terminal R, the induced voltage (feedback signal from the resonant circuit 10R) generated in the loop coil selected by the selection circuit 22 is sent from the selection circuit 22 to the receiving amplifier 26 via the switching connection circuit 25. This feedback signal is a signal corresponding to the resonant frequency of the resonant circuit 10R. The receiving amplifier 26 amplifies the induced voltage supplied from the loop coil and sends it to the detector 271 of the position detection circuit 27 and the synchronous detector 281 of the writing pressure detection circuit 28.

[0011] The detector 271 of the position detection circuit 27 detects the induced voltage generated in the loop coil, i.e., the feedback signal from the resonant circuit 10R, and sends it to the low-pass filter 272. The low-pass filter 273 has a cutoff frequency sufficiently lower than the aforementioned frequency f0, and converts the output signal of the detector 271 into a DC signal and sends it to the sample-and-hold circuit 273. The sample-and-hold circuit 273 holds the voltage value of the output signal of the low-pass filter 274 at a predetermined timing, specifically at a predetermined timing during the reception period. This voltage value represents the received signal level of the feedback signal from the resonant circuit 10R. In this example, the receiving amplifier 26 and the position detection circuit 27 serve as a receiving circuit for the feedback signal from the electronic pen 100.

[0012] The sample-and-hold circuit 273 sends the held voltage value to an A / D (Analog to Digital) conversion circuit 274. The A / D conversion circuit 274 converts the analog output of the sample-and-hold circuit 273 into a digital signal and outputs it to the processing control circuit 29.

[0013] Furthermore, the synchronous detector 281 of the writing pressure detection circuit 28 synchronously detects the output signal of the receiving amplifier 26 with the AC signal from the oscillator 23, and sends a signal of a level corresponding to the frequency difference or phase difference therebetween to a low-pass filter 282. This low-pass filter 282 has a cutoff frequency sufficiently lower than the frequency f0 of the AC signal from the oscillator 23, and converts the output signal of the synchronous detector 281 into a DC signal and sends it to a sample-and-hold circuit 283. This sample-and-hold circuit 283 holds the voltage value of the output signal of the low-pass filter 282 at a predetermined timing and sends it to an A / D conversion circuit 284. The A / D conversion circuit 284 converts the analog output of the sample-and-hold circuit 283 into a digital signal and outputs it to the processing control circuit 29.

[0014] The processing control circuit 29 controls the selection of the loop coils in the selection circuit 22, the switching of the switching connection circuit 25, and the sample and hold timing in the sample and hold circuits 273 and 283. Based on input signals from the A / D conversion circuits 274 and 284, the processing control circuit 29 causes the X-axis direction loop coil group 21X and the Y-axis direction loop coil group 21Y to transmit radio waves for a fixed transmission duration (continuous transmission section).

[0015] As described above, an induced voltage is generated in each of the loop coils of the X-axis direction loop coil group 21X and the Y-axis direction loop coil group 21Y by radio waves transmitted (feedback) from the resonant circuit 10R of the electronic pen 1. The processing control circuit 29 recognizes which loop coil is selected by the selection circuit 22, and calculates the coordinate values ​​in the X-axis direction and the Y-axis direction of the position indicated by the electronic pen 1 based on the voltage value level of the induced voltage generated in that loop coil (output of the A / D conversion circuit 274). The processing control circuit 29 also detects the writing pressure based on the level of a signal corresponding to the frequency difference or phase difference between the transmitted radio waves and the received radio waves.

[0016] In this way, the electromagnetic induction type position detection device 2 transmits an AC signal of a predetermined frequency f0 to the electronic pen 1 and receives a signal returned from the resonant circuit 10R of the electronic pen 1 as a signal corresponding to that resonant frequency, thereby detecting the position indicated by the electronic pen 1 and detecting the pen pressure value applied to the electronic pen 1.

[0017] In this case, in the conventional position detection device 2, the frequency f0 of the AC signal from the oscillator 23 is selected to a predetermined frequency as follows so that it is appropriate for detecting the pointing position of the electronic pen 1 and also for detecting the writing pressure.

[0018] 7A and 7B, the resonance frequency of the resonance circuit 10R of the electronic pen 1 is not constant, but transitions from a resonance frequency fr0 when no writing pressure is applied to the electronic pen 1 (hereinafter, for convenience, this state will be referred to as the initial state) to a lower frequency as shown by the arrow in accordance with the magnitude of the writing pressure applied to the electronic pen 1. In other words, the resonance frequency fr of the resonance circuit consisting of a coil (inductance L) and a capacitor (capacitance C) is given by fr ∝ 1 / 2π(LC) １／２ The capacitance of the writing pressure detection unit increases in accordance with the applied writing pressure, and therefore, when writing pressure is applied to the electronic pen 1, the resonance frequency fr changes to be lower than the initial resonance frequency fr0 in accordance with the writing pressure, as shown by the dotted lines in Figures 7(A) and (B).

[0019] Therefore, in the position detection device 2, if the frequency f0 of the AC signal from the oscillator 23 is selected to be equal to the initial resonant frequency fr0 of the electronic pen 1 (f0 = fr0), as shown in Figure 7 (A), the signal strength of the feedback signal from the electronic pen 1 detected by the position detection device 2 will decrease as the writing pressure increases, as shown by the thick line in Figure 7 (A), resulting in a problem that the range of changes in writing pressure that can be detected by the position detection device 2 will become narrower.

[0020] Therefore, conventionally, as shown in Fig. 7(B), the frequency f0 of the AC signal from the oscillator 23 is set to a frequency frc lower than the resonance frequency in the initial state. By setting the frequency f0 of the AC signal from the oscillator 23 to a frequency frc lower than the resonance frequency fr0 in the initial state in this way, the signal strength of the feedback signal from the electronic pen 1 can be made to exhibit a maximum value of the writing pressure at that frequency frc in response to changes in writing pressure, as shown by the thick line in Fig. 7(B). This makes it possible to widen the detection range of the writing pressure in the position detection device 2 compared to when the frequency f0 of the AC signal is set to the resonance frequency fr0 in the initial state.

[0021] JP 2012-133704 A

[0022] However, when the frequency f0 of the AC signal from the oscillator 23 of the position detection device 2 is set lower than the resonance frequency fr0 in the initial state, the signal strength of the feedback signal from the electronic pen 1 in the initial state of the resonance circuit 10r of the electronic pen 1 becomes lower than when the frequency f0 of the AC signal is set equal to the resonance frequency fr0 in the initial state (see FIG. 7B). As a result, the height of the electronic pen 1 from the input surface of the position detection device 2 becomes lower, which is a so-called hover state in which the electronic pen 1 is not in contact with the input surface but signal interaction is possible through electromagnetic coupling, resulting in a problem of poor usability.

[0023] In view of this problem, conventionally, when the height of the electronic pen 1 in the hover state from the input surface of the position detection device 2 is increased, the signal strength of the AC signal with frequency f0 from the oscillator 23 of the position detection device 2 is increased. However, when the signal strength is increased, another problem occurs in that the power consumption of the position detection device 2 increases.

[0024] SUMMARY OF THE INVENTION An object of the present invention is to provide a position detection device that can solve the above problems.

[0025] In order to solve the above problem, we provide a position detection device that detects a position indicated on a position detection sensor by an electronic pen having a resonant circuit whose resonant frequency changes in response to the applied writing pressure by performing signal interaction through electromagnetic induction coupling with the electronic pen, and that detects the writing pressure applied to the electronic pen, comprising: a signal transmission circuit that outputs a signal for the interaction; a receiving circuit that receives, via the position detection sensor, a feedback signal from the resonant circuit of the electronic pen in response to a signal transmitted from the signal transmission circuit via the position detection sensor; and a control circuit that supplies to the signal transmission circuit a control signal for changing and controlling the frequency of the signal, wherein, when the control circuit detects that the signal level of the feedback signal received by the receiving circuit is equal to or higher than a predetermined threshold, the control circuit controls the frequency of the signal from the signal transmission circuit to be switched from a first frequency that is equal to the resonant frequency of the resonant circuit when no writing pressure is applied to the electronic pen to a second frequency that is different from the first frequency and in a direction in which the resonant frequency changes in response to the writing pressure,

[0026] According to the position detection device having the above-described configuration, when the signal level of the feedback signal is equal to or greater than a predetermined threshold, the frequency of the signal from the signal transmission circuit is switched from a first frequency equal to the resonant frequency of the resonant circuit when no pressure is applied to the electronic pen to a second frequency different from the first frequency in a direction in which the resonant frequency changes in response to pressure. This allows the feedback signal from the resonant circuit of the electronic pen to be received at a consistently high level. This allows the height of the electronic pen in the hover state from the input surface of the position detection device to be higher than in conventional devices. In this case, there is no need to increase the signal strength, so power consumption does not increase.

[0027] When detecting the writing pressure applied to the electronic pen, the second frequency is obtained in the direction in which the resonant frequency changes depending on the writing pressure, making it possible to detect the writing pressure within an appropriate detection range.

[0028] FIG. 1 is a diagram showing an example of the appearance of an embodiment of a position detection device according to the present invention, together with an embodiment of an electronic pen. FIG. 2 is an exploded perspective view showing an example of the internal configuration of an embodiment of a position detection device according to the present invention. FIG. 3 is a diagram showing an example of the electrical configuration of an embodiment of a position detection device according to the present invention, together with an example of the electrical configuration of an embodiment of an electronic pen. FIG. 4 is a diagram used to explain the configuration of a main part of an embodiment of a position detection device according to the present invention. FIG. 5 is a flowchart for explaining the operation of a main part of an embodiment of a position detection device according to the present invention. FIG. 6 is a diagram showing an example of the electrical configuration of a conventional position detection device, together with an example of the electrical configuration of an electronic pen. FIG. 7 is a diagram for explaining setting of the frequency of an AC signal sent to an electronic pen in a conventional position detection device.

[0029] Hereinafter, an embodiment of a position detection device according to the present invention will be described with reference to the drawings, along with an example of an electronic pen.

[0030] 1 shows an example of a position detection device 200 of this embodiment and an electronic pen 100 used together with this position detection device 200. The position detection device 200 of this embodiment has the configuration of a tablet-type information terminal.

[0031] In this example, the position detection device 200 includes an electromagnetic induction type position detection sensor 202 and a circuit board 203 housed in a flat rectangular housing 201. Fig. 2 is an exploded view of the position detection device 200, in which the position detection sensor 202 and the circuit board 203 are housed in a housing recess 201a of the housing 201, and the top of the housing recess 201a of the housing 201 is closed by a planar member 204.

[0032] The position detection sensor 202 has a configuration similar to that shown in Fig. 6, and includes an X-axis direction loop coil group 202X and a Y-axis direction loop coil group 202Y. A circuit section connected to the position detection sensor 202 is formed on the circuit board 203, similar to the example shown in Fig. 6. One surface 204a of the planar member 204 serves as an input surface when a position is specified by the electronic pen 100.

[0033] In this example, the planar member 204 has a shape that is slightly larger than the position detection area of ​​the position detection sensor 202. In the planar member 205 in Fig. 2, the area enclosed by the dotted line corresponds to the position detection area of ​​the position detection sensor 202, and this area is the area of ​​the input surface 204IN that accepts a position instruction from the electronic pen 100.

[0034] 1, in this example of electromagnetic induction type electronic pen 100, a coil 103 wound around a magnetic core, for example, a ferrite core 102, is provided on the pen tip side of a hollow portion of a cylindrical housing 101. A writing pressure detection unit 104 is provided on the opposite side of the ferrite core 102 from the pen tip side in the axial direction of the hollow portion of housing 101, and a rod-shaped core body 105 is inserted through a through-hole (not shown) provided in ferrite core 102 from the pen tip side opening of housing 101 and is fitted and attached to writing pressure detection unit 104. A tip end 105a of core body 105 protrudes to the outside from the pen tip side opening of the housing.

[0035] A circuit board 106 is disposed on the opposite side of the pen tip side of the writing pressure detection unit 104 in the axial direction of the hollow portion of the housing 101. A capacitor 107 is disposed on the circuit board 106 and is connected in parallel with the coil 103 wound around the ferrite core 102 to form a resonant circuit.

[0036] In this example, the writing pressure detection unit 104 is configured as a variable capacitance capacitor that detects the pressure (writing pressure) applied to the tip 105a of the core 105 as a change in capacitance. The writing pressure detection unit 104 is configured using a well-known configuration, such as a configuration in which the capacitance changes as the contact area between a dielectric and a conductive elastic member changes in response to the applied pressure (see, for example, Patent Document: JP 2016-126503 A), or a configuration consisting of a semiconductor device in which the distance between two electrodes facing each other via a dielectric air layer changes in response to the applied pressure (see, for example, Patent Document: JP 2013-161307 A). Therefore, a detailed description of the writing pressure detection unit 104 will be omitted in this specification.

[0037] In this example, the variable capacitance capacitor that constitutes the pen pressure detection unit 104 is connected in parallel with the coil 103 and forms part of the resonant circuit, and as described above, is configured to transmit the pen pressure detected by the pen pressure detection unit 104 to the position detection sensor 202 side as a change in the resonant frequency of the resonant circuit.

[0038] 3 shows an example of the circuit configuration of the position detection device 200 of this embodiment and an example of the circuit configuration of the electronic pen 100. The resonant circuit 100R of the electronic pen 100 is configured by connecting a capacitor 107 in parallel with the coil 103, and also connecting a variable capacitance capacitor 104C that is part of the writing pressure detection unit 104 in parallel with the coil 103. This resonant circuit 100R has exactly the same configuration as the electronic pen 1 shown in FIG. 6 described above, and has the same resonant frequency characteristics as those described above.

[0039] That is, as described above, the resonant circuit 100R constitutes an interaction unit for signal interaction with the position detection sensor 202, and operates to receive the signal sent from the position detection sensor 202 by resonance and transmit the feedback signal to the position detection sensor 202.

[0040] As described above, the resonant frequency of resonant circuit 100R is a predetermined frequency Fr0 in the initial state where core body 105 of electronic pen 100 is not in contact with input surface 204IN of position detection device 200 and no writing pressure is being applied (see FIG. 4A). In contrast, when core body 105 of electronic pen 100 is in contact with input surface 204IN of position detection device 200 and writing pressure is being applied, the resonant frequency of resonant circuit 100R changes to a low frequency equal to or lower than predetermined frequency Fr0 in accordance with a change in the capacitance of variable capacitor 104C corresponding to the writing pressure value detected by writing pressure detection unit 104 (see FIG. 4B). In this example, the resonant frequency of resonant circuit 100R is set to a frequency of approximately 500 kHz to 600 kHz, similar to the conventional frequency.

[0041] 3, the position detection device 200 of this embodiment is provided with a selection circuit 220 to which the X-axis direction loop coil group 202X and the Y-axis direction loop coil group 202Y of the position detection coil 202 are connected. The position detection device 200 of this embodiment further includes a signal transmission circuit 230, a current driver 240, a switching connection circuit 250, a receiving amplifier 260, a position detection circuit 270, a writing pressure detection circuit 280, and a processing control circuit 290.

[0042] The position detection device 200 of this embodiment is different in that a signal transmission circuit 230 is provided instead of the oscillator 23, and the frequency of the signal output from the signal transmission circuit 230 is controlled by a processing control circuit 290. Otherwise, it has the same configuration as the position detection device 2 described above and performs the same operation.

[0043] 3, the position detection circuit 270, like the position detection circuit 27, is configured to include a detector 271, a low-pass filter 272, a sample-and-hold circuit 273, and an A / D conversion circuit 274. Similarly to the pen pressure detection circuit 28, the writing pressure detection circuit 280 is configured to include a synchronous detector 281, a low-pass filter 282, a sample-and-hold circuit 283, and an A / D conversion circuit 284. Furthermore, the processing control circuit 290 is configured by a microprocessor.

[0044] The selection circuit 220 sequentially selects one or more loop coils from the two loop coil groups 202X and 202Y under the control of the processing control circuit 290. When the processing control circuit 290 connects the switching control circuit 250 to the transmission terminal T, the AC signal S from the signal transmission circuit 230 is supplied to the selection circuit 220 via the current driver 240 and the switching control circuit 250, and is transmitted from the loop coil selected by the selection circuit 220 under the control of the processing control circuit 290.

[0045] In addition, when the processing control circuit 290 connects the switching control circuit 250 to the receiving terminal R, a feedback signal from the resonant circuit 100R of the electronic pen 100 received by the loop coil selected by the selection circuit 220 under the control of the processing control circuit 290 is supplied to the position detection circuits 270 and 280 via the selection circuit 220, the switching control circuit 250 and the receiving amplifier 260.

[0046] As described above, the position detection circuit 270 supplies a digital signal indicating the received signal level of the received feedback signal to the processing control circuit 290. The processing control circuit 290 recognizes which loop coil is selected by the selection circuit 220, and calculates the coordinate values ​​in the X-axis and Y-axis directions of the position indicated by the electronic pen 100 based on the voltage level of the induced voltage generated in the selected loop coil (output of the A / D conversion circuit 274).

[0047] The writing pressure detection circuit 280 supplies a digital signal indicating a level corresponding to the frequency difference or phase difference between the transmitted signal (radio wave) and the received signal (radio wave) to the processing control circuit 290. The processing control circuit 290 detects the writing pressure applied to the tip 105 a of the core body 105 of the electronic pen 100 based on the digital signal.

[0048] The signal transmission circuit 230 of the position detection device 200 of this embodiment is composed of a variable frequency oscillator in this example, and is configured so that the frequency of the AC signal S sent from this signal transmission circuit 230 can be switched between a first frequency f01 and a second frequency f02 in response to a control signal from the processing control circuit 290.

[0049] In this embodiment, the first frequency f01 is set to a frequency equal to the resonance frequency Fr0 of the electronic pen 100 in its initial state shown in FIG. 4A. The second frequency f02 is set to a median frequency Fr1 of the writing pressure detection range D (the frequency change range (or phase change range) corresponding to the change range of the writing pressure to be detected) of the position detection device 200 in FIG. 4B. That is, as shown in FIG. 4B, the writing pressure detection range D of the position detection device 200 is a frequency equal to or lower than the resonance frequency Fr0 of the resonance circuit 100R in the initial state of the electronic pen 100 and up to the resonance frequency FrM of the resonance circuit 100R at the maximum detectable writing pressure value. Therefore, the frequency Fr1 of the median of the writing pressure detection range D is a frequency lower than the resonance frequency Fr0 by ΔF = (Fr0 - FrM) / 2, and the second frequency f02 is f02 = f01 - ΔF = Fr1. It should be noted that Fr1=(Fr0+FrM) / 2.

[0050] The processing control circuit 290 controls the frequency of the AC signal S from the signal transmission circuit 230 to be the first frequency f01 when performing a scan to detect electromagnetic induction coupling between at least the position detection device 200 (position detection sensor 202) and the electronic pen 100, and controls the frequency of the AC signal S from the signal transmission circuit 230 to be the second frequency when detecting the writing pressure applied to the electronic pen. That is, the processing control circuit 290 controls the frequency of the AC signal S from the signal transmission circuit 230 to be the first frequency f01 at least until the electronic pen 100 and the position detection sensor 202 are electromagnetically coupled and enter a hover state. Then, at least when the electronic pen 100 comes into contact with the input surface 204IN of the position detection device 200 and writing pressure is applied, the processing control circuit 290 controls the frequency of the AC signal S from the signal transmission circuit 230 to be the second frequency f02 in order to detect the writing pressure.

[0051] In this embodiment, while the signal level of the feedback signal from the electronic pen 100, represented by the digital signal output of the A / D conversion circuit 274 of the position detection circuit 270, is lower than a predetermined threshold θ, the frequency of the AC signal S from the signal transmission circuit 230 is controlled to be frequency f01 as a scan mode for detecting electromagnetic induction coupling between the position detection device 200 (position detection sensor 202) and the electronic pen 100. When the signal level of the feedback signal from the electronic pen 100 becomes equal to or higher than the threshold θ, it is determined that a hover state has been entered, and the processing control circuit 290 controls the frequency of the AC signal S from the signal transmission circuit 230 to be frequency f02.

[0052] In this example, the threshold value θ is set to a signal level at which it is detected that the electronic pen 100 has entered a hover state over the input surface 204IN of the position detection device 200. Therefore, in this example, when the electronic pen 100 enters the hover area, the frequency of the AC signal S from the signal transmission circuit 230 is switched from the first frequency f01 to the second frequency f02.

[0053] However, it is not necessary to set the threshold θ to such a value. It may be set to a value corresponding to the signal level of the feedback signal when the electronic pen 100 is at any height within the height range of the hover area. That is, when the signal level of the received signal at the height position of the electronic pen at which the position detection device 200 detects that the electronic pen 1 is not in contact with the input surface but is in a so-called hover state where signal interaction through electromagnetic coupling is possible (the position at which the electronic pen 100 is farthest from the input surface 204IN in the hover state) is La, and the signal level of the received signal at the height position at which the electronic pen 1 contacts the input surface is Lb, the threshold θ may be set to satisfy La≧θ≧Lb. In this case, it goes without saying that the threshold for detecting that the electronic pen 100 has entered the hover area may be different from the threshold for switching between the first frequency and the second frequency.

[0054] In this embodiment, the signal transmission circuit 230 is configured as a frequency synthesizer oscillator using a PLL (Phase Locked Loop) circuit, and the frequency of the AC signal S can be changed by changing the N value of the division ratio 1 / N of the variable frequency divider.

[0055] In the position detection device 200 of this embodiment, the control signal CT1 for setting the frequency of the AC signal S from the signal transmission circuit 230 to the first frequency f01 is set as follows. That is, the position detection device 200 of this example has a setting mode for setting the first frequency f01 of the AC signal S from the signal transmission circuit 230. This setting mode is set by an operator when the position detection device 200 is shipped from the factory, but can also be set by the user of the position detection device 200 at an appropriate time.

[0056] In this setting mode, with the electronic pen 200 held in a hovering state relative to the position detection device 200, the processing control circuit 290 supplies to the signal transmission circuit 230 a control signal of value N, with a frequency division ratio of 1 / N of the variable frequency divider, to gradually change the frequency of the AC signal S. The processing control circuit 290 then controls the switching control circuit 250 to switch to the terminal T side, transmits the AC signal S to the electronic pen 100 via the selection circuit 230 and the position detection sensor 202, and then controls the switching control circuit 250 to switch to the terminal R side, and supplies the feedback signal from the electronic pen 100 received by the position detection sensor 202 to the position detection circuit 270 via the selection circuit 230 and the switching control circuit 250. This operation is repeated every time the frequency of the AC signal S from the signal transmission circuit 230 is changed.

[0057] The processing control circuit 290 then detects and monitors the signal level of the feedback signal from the electronic pen 100 based on the digital signal from the position detection circuit 270. The processing control circuit 290 then finds the N value of the frequency division ratio 1 / N to set the frequency of the AC signal S at which the signal level of the feedback signal from the electronic pen 100 is maximized, and stores this N value as the control signal CT1. In this case, as shown in FIG. 4A , the frequency of the AC signal S at which the signal level of the feedback signal from the electronic pen 100 is maximized is approximately equal to the resonant frequency Fr0 of the resonant circuit 100R in the initial state of the electronic pen 100.

[0058] Therefore, the processing control circuit 290 can supply this retained control signal CT1 to the signal transmission circuit 230, thereby setting the frequency of the AC signal S from the signal transmission circuit 230 to the first frequency f01 (=Fr0).

[0059] In this example, the control signal CT2 that sets the frequency of the AC signal S from the signal transmission circuit 230 to the second frequency f02 is a division ratio of 1 / N that sets the frequency lower than the frequency corresponding to the control signal CT1 by ΔF=(Fr0-FrM) / 2, and is held in the processing control circuit 290. When this control signal CT2 is supplied from the processing control circuit 290 to the signal transmission circuit 230, the frequency of the AC signal S becomes the above-mentioned second frequency f02.

[0060] It should be noted that the frequencies f01 and f02 of the AC signal from the signal transmitting circuit 230 may not be set as described above, but may be set to frequencies that are predetermined based on the resonant frequency Fr0 of the resonant circuit 100R of the electronic pen 100.

[0061] Furthermore, the signal transmission circuit 230 does not need to be configured with a frequency synthesizer oscillator using a PLL circuit as in this example, and may be configured in any way as long as it can switch between the first frequency f01 and the second frequency f02 and output the frequency of the AC signal S. For example, the oscillation circuit included in the signal transmission circuit 230 may be configured to use a switch circuit to switch the inductance value of the coil or the capacitance of the capacitor, which are factors that change the resonance frequency.

[0062] [Explanation of Frequency Control Operation by the Processing Control Circuit 290] Next, the control operation of the signal transmission circuit 230 by the processing control circuit 290 in the position detection device 200 of this embodiment will be described with reference to the flowchart of Figure 5. The processing control circuit 290 executes this control operation based on a software program stored in its built-in memory. In the following description, the processing of each step S in the flowchart of Figure 5 will be described as being performed by the processing control circuit 290.

[0063] The processing control circuit 290 supplies a control signal CT1 to the signal transmission circuit 230 to set the frequency of the AC signal S output from the signal transmission circuit 230 to a first frequency f01 equal to the initial resonant frequency Fr0 of the resonant circuit 100R of the electronic pen 100 (step S101).The processing control circuit 290 then transmits the AC signal S of the first frequency f01 through the position detection sensor 202 and receives a feedback signal from the resonant circuit 100R of the electronic pen 100, thereby scanning to determine whether the electronic pen 100 has been brought close to the input surface 204IN of the position detection device 200 for inputting an instruction (step S102).

[0064] Next, in the scan of step S102, the processing control circuit 290 detects the received signal level of the feedback signal from the electronic pen 100 based on the digital signal from the position detection circuit 270, and determines whether the received signal level is equal to or greater than the threshold value θ (step S103). If it is determined in step S103 that the received signal level of the feedback signal is not equal to or greater than the threshold value θ, the processing control circuit 290 returns the process to step S102 and repeats the scan of step S102 and the determination process of step S103.

[0065] When it is determined in step S103 that the received signal level of the feedback signal is equal to or greater than the threshold value θ, the processing control circuit 290 changes the control signal for the signal transmission circuit 230 from the control signal CT1 to the control signal CT2, and sets the frequency of the AC signal S output from the signal transmission circuit 230 to the second frequency f02 (= f01 - ΔF) (step S104).

[0066] After step S104, the processing control circuit 290 performs scanning to detect the position indicated by the electronic pen 100 and the writing pressure (step S105). Then, the processing control circuit 290 determines whether the received signal distribution of the feedback signal is normal, such as the received signal distribution in the hover area or when the tip 105a of the core 105 of the electronic pen 100 is in contact with the input surface 204a (step S106).

[0067] If it is determined in step S106 that the received signal distribution of the feedback signal is normal, the processing control circuit 290 detects the position indicated by the electronic pen 100 using the digital signal from the position detection circuit 270, and also detects the writing pressure applied to the tip 105a of the core 105 of the electronic pen 100 using the digital signal from the writing pressure detection circuit 280 (step S107). After step S107, the processing control circuit 290 returns the process to step S105 and repeats the processes from step S105 onwards.

[0068] Furthermore, if it is determined in step S106 that the received signal distribution of the feedback signal is not normal, the processing control circuit 290 returns the processing to step S101, changes the control signal for the signal transmission circuit 230 from the control signal CT2 to the control signal CT1, and returns the frequency of the AC signal S output from the signal transmission circuit 230 to the first frequency f01 which is equal to the initial resonance frequency Fr0 of the resonance circuit 100R of the electronic pen 100. Then, the processing from step S101 onwards is repeated.

[0069] [Effects of the Position Detection Device 200 of the Embodiment] As described above, in the position detection device 200 of this embodiment, when testing at least the electromagnetic induction coupling between the position detection device 200 (position detection sensor 202) and the electronic pen 100, the frequency of the AC signal S from the signal transmission circuit 230 is controlled to be the first frequency f01, which is equal to the resonant frequency Fr0 in the initial state of the resonant circuit 100R of the electronic pen 100. Therefore, during scanning for the test, the signal level of the feedback signal from the electronic pen 100 can have a greater signal strength than in the conventional case. Incidentally, it was confirmed that the signal strength could be increased by about 30 to 40% when the frequency of the AC signal was the first frequency f01, compared to when it was the conventional frequency frc shown in FIG. 7B.

[0070] Furthermore, in the position detection device 200 of this embodiment, when detecting the writing pressure applied to the electronic pen 100, the frequency of the AC signal S from the signal transmission circuit 230 is switched from a first frequency f01, which is equal to the initial resonant frequency Fr of the resonant circuit 100R of the electronic pen 100 for detecting the electromagnetic coupling state with the electronic pen 100, to a second frequency f02 used for writing pressure detection. As described above, in the position detection device 200 of this embodiment, the second frequency f02 can be set to the median value of the writing pressure detection range D corresponding to the range of change in writing pressure to be detected, which has the effect of enabling accurate detection of the writing pressure within the writing pressure detection range D.

[0071] Therefore, according to the position detection device 200 of this embodiment, the height position detected as the hover area can be increased without increasing the signal strength of the AC signal sent out, and the writing pressure applied to the pen tip of the electronic pen 100 can be accurately detected over a desired wide range.

[0072] [Other Embodiments or Modifications] In the position detection device 200 of the above-described embodiment, the frequency of the AC signal S from the signal transmission circuit 230 is switched between the first frequency f01 and the second frequency f02 based on the signal level of the feedback signal from the electronic pen 100 when the electronic pen 100 enters a hover state relative to the position detection device 200. However, this is not limited to this. For example, the timing for switching the frequency of the AC signal S from the signal transmission circuit 230 between the first frequency f01 and the second frequency f02 may be any height position from when the electronic pen 100 enters a hover state relative to the position detection device 200 until the pen tip of the electronic pen 100 comes into contact (including contact) with the input surface 204 of the position detection device 200. In this case, the threshold value for determining the timing for switching between the first frequency f01 and the second frequency f02 is the received signal level of the feedback signal from the electronic pen 100 at each height position for the switching timing.

[0073] In addition, the writing pressure applied to the electronic pen 100 may be monitored by the position detection device 200, and the value at the time when the writing pressure value contacts the input surface 204IN, or a value slightly larger than the time of contact, may be set as a threshold value, and when the writing pressure value exceeds the threshold value, the frequency may be switched from the first frequency f01 to the second frequency f02, and when the frequency falls below the threshold value, the frequency may be switched from the second frequency f02 to the first frequency f01.

[0074] Furthermore, in the above-described embodiment, the pen pressure detection unit of the electronic pen 100 is configured to detect the applied pen pressure as a change in capacitance, but the configuration of the pen pressure detection unit is not limited to this, and it may be configured, for example, to detect the applied pen pressure as a change in inductance.

[0075] 1,100...electronic pen, 2,200...position detection device, 10R...resonance circuit, 103...coil, 104C...variable capacitor, 107...capacitor, 201...housing, 202...position detection sensor, 203...circuit board, 204...planar member, 204IN...input surface, 220...selection circuit, 230...signal transmission circuit, 250...switching control circuit, 27, 270...position detection circuit, 28, 280...pen pressure detection circuit, 29, 290...processing control circuit

Claims

1. A position detection device that detects a position indicated on a position detection sensor by an electronic pen having a resonant circuit whose resonant frequency changes in response to the applied writing pressure by performing signal interaction through electromagnetic induction coupling with the electronic pen, and detects the writing pressure applied to the electronic pen, comprising: a signal transmission circuit that outputs a signal for the interaction; a receiving circuit that receives, via the position detection sensor, a feedback signal from the resonant circuit of the electronic pen in response to a signal transmitted from the signal transmission circuit via the position detection sensor; and a control circuit that supplies to the signal transmission circuit a control signal for changing and controlling the frequency of the signal, wherein when the control circuit detects, by the control signal, that the signal level of the feedback signal received by the receiving circuit is equal to or higher than a predetermined threshold, the control circuit controls the frequency of the signal from the signal transmission circuit to be switched from a first frequency equal to the resonant frequency of the resonant circuit when no writing pressure is applied to the electronic pen to a second frequency different from the first frequency in the direction in which the resonant frequency changes in response to the writing pressure.

2. A position detection device as described in claim 1, characterized in that the control signal from the control circuit is a control signal that controls the signal transmission circuit so as to selectively output a signal of the first frequency and a signal of the second frequency.

3. A position detection device as claimed in claim 1, characterized in that said signal transmission circuit is configured with a variable frequency oscillation circuit capable of changing and controlling the frequency of the signal it outputs based on the control signal from said control circuit.

4. The position detection device according to claim 3, characterized in that the control circuit is provided with a control signal setting circuit which sequentially changes the frequency of the output signal of the signal transmission circuit in response to the control signal, monitors the signal level of the feedback signal from the electronic pen when no writing pressure is being applied, and sets the control signal at the time when the signal level of the feedback signal is at its maximum to the control signal for setting the first frequency.

5. The position detection device according to claim 1, characterized in that the second frequency is determined according to the detection width of the writing pressure applied to the electronic pen.

6. A position detection device according to claim 4, characterized in that the second frequency is set to a frequency corresponding to the center position of the detection width of the writing pressure applied to the electronic pen.

7. A position detection device as described in claim 1, further comprising a pen pressure detection circuit that detects the pen pressure applied to the electronic pen based on the frequency difference or phase difference between the signal from the signal transmission circuit and a feedback signal from a resonant circuit of the electronic pen, and when it is detected that the pen pressure detected by the pen pressure detection circuit has reached or exceeded a predetermined value, the control circuit controls the signal transmission circuit to switch from the signal of the first frequency to the signal of the second frequency.

Images