POSITION DETECTION DEVICE, MAGNETIC RESONANCE STYLUS AND POSITION DETECTION SYSTEM

Abstract

[Task] Ability to transmit data from an electromagnetic resonant stylus to a position sensing device while the position sensing device excites its loop coils. [Solution] An electromagnetic resonant stylus 2 according to the present invention includes a resonant circuit comprising a coil L and a capacitor C, a switching element SW connected in parallel with the capacitor C, and a processing circuit 23 for transmitting data to a position sensing device 3 by performing on / off control on the switching element SW based on the data to be transmitted to the position sensing device 3.

Description

Technical area

[0001] The present invention relates to a position detecting device, an electromagnetic resonance stylus and a position detecting system. background

[0002] A position detecting device for detecting the position of an electromagnetic resonance stylus based on the principle of electromagnetic resonance (EMR) has been known. Patent Document 1 discloses an example of a position detecting device of the described type. The position detecting device described in the patent document includes a plurality of X-side loop coils arranged along an X-axis and Y-side loop coils arranged along a Y-axis, and is configured to detect induced currents developed in the respective Y-side loop coils and sequentially excite the X-side loop coils one by one (supply predetermined drive currents to the X-side loop coils). An electromagnetic resonance stylus described in the patent document includes a resonant circuit including a coil and a capacitor.

[0003] When the position detection device energizes a specific X-side loop coil, it detects a significant induced current from a Y-side loop coil that crosses the X-side loop coil at a location near the electromagnetic resonance stylus. The position detection device described in Patent Document 1 derives the coordinates of the electromagnetic resonance stylus based on the nature of such an induced current. State of the art documentPatent specification

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. H05-019164 SUMMARY OF THE INVENTIONTechnical Problems

[0005] However, the technology disclosed in Patent Document 1 is problematic in that the electromagnetic resonance stylus is unable to transmit data to the position detecting device.

[0006] Regarding this point, provided a period is established in which the position detecting device does not energize the X-side loop coils, it is possible for the electromagnetic resonance stylus to transmit data to the position detecting device during the period. Specifically, when the position detecting device supplies the X-side loop coils with drive currents, an alternating magnetic field generated at a touch surface thereof charges the capacitor of the resonance circuit in the electromagnetic resonance stylus. Thereafter, when the position detecting device stops supplying the drive currents to the X-side loop coils, the coil of the resonance circuit in the electromagnetic resonance stylus transmits a reflected signal according to the electric power stored in the capacitor.At this time, the electromagnetic resonance stylus can change the frequency of the reflected signal to be transmitted by controlling the resonance frequency of the resonance circuit based on the data to be transmitted. The position detection device can acquire the data transmitted by the electromagnetic resonance stylus by detecting an induced current flowing through an X-side loop coil or a Y-side loop coil as a reflected signal and by detecting a change in the frequency of the reflected signal.

[0007] Data transmission according to controlling the frequency of the reflected signal is disabled while the position detection device energizes the X-side loop coils. This is because while the position detection device energizes the X-side loop coils, the frequency of the reflected signal is forcibly adjusted to match the frequency of the drive currents.

[0008] Although the electromagnetic resonance stylus can transmit data to the position detection device during a period in which the position detection device is not energizing the X-side loop coils, the period in which the position detection device is not energizing the X-side loop coils results in a reduction in the position detection rate. Consequently, there has been a demand for an electromagnetic resonance stylus capable of transmitting data to a position detection device while the position detection device is energizing its X-side loop coils.

[0009] It is therefore one of the objects of the present invention to provide a position detecting device, an electromagnetic resonant stylus, and a position detecting system capable of transmitting data from the electromagnetic resonant stylus to the position detecting device while the position detecting device energizes its loop coils. Technical solution

[0010] A position detecting device according to the present invention includes a plurality of first loop coils arranged in a first direction, a plurality of second loop coils arranged in a second direction perpendicular to the first direction, and a sensor control device that detects induced currents in the second loop coils respectively while one of the first loop coils is energized, wherein the sensor control device derives a position of an electromagnetic resonance stylus in at least the second direction based on a distribution of levels of the detected induced currents and acquires data acquired from the electromagnetic resonance stylus by performing on-off keying modulation on the detected induced currents.

[0011] An electromagnetic resonance stylus (resonance pen) according to the present invention includes a resonance circuit including a coil and a capacitor, a switching element connected in parallel with the capacitor, and a processing circuit that transmits data to a position detection circuit by performing on-off keying modulation on the switching element according to the data to be transmitted to the position detection circuit, wherein the processing circuit detects an alternating current generated in the resonance circuit by an alternating magnetic field intermittently transmitted from the position detection circuit, and detects a timing at which the position detection device again transmits the alternating magnetic field based on a result of detection of the alternating current and performs on / off control on the switching element based on the detected timing.

[0012] A position detecting system includes an electromagnetic resonance stylus and a position detecting device, wherein the electromagnetic resonance stylus includes a resonance circuit including a coil and a capacitor, a switching element connected in parallel with the capacitor, and a processing circuit that transmits data to the position detecting circuit by performing on / off control on the switching element according to the data to be transmitted to the position detecting circuit.The position detecting device includes a plurality of first loop coils arranged in a first direction, a plurality of second loop coils arranged in a second direction perpendicular to the first direction, and a sensor control device that detects induced currents in the second loop coils respectively while one of the first loop coils is energized, and the sensor control device derives a position of an electromagnetic resonance stylus in at least the second direction based on a distribution of levels of the detected induced currents and collects data collected from the electromagnetic resonance stylus by performing on-off keying modulation on the detected induced currents. Beneficial effect

[0013] According to the present invention, it is possible for the electromagnetic resonance stylus to transmit data to the position detecting device while the position detecting device excites the loop coils by causing the electromagnetic resonance stylus to switch between a state in which the resonance circuit exists and a state in which no resonance circuit exists. SHORT DESCRIPTION OF DRAWINGS [ Fig. 1] Fig. 1 is a diagram illustrating a configuration of a position detection system 1 according to a first embodiment of the present invention. [ Fig. 2] Fig. Figure 2 is a diagram explaining the relationship between transmission of an alternating magnetic field AM and reception of a stylus signal PS. [ Fig. 3] Fig. Figure 3 is a diagram illustrating simulation results of waveforms of a driving current Tx, an electromagnetic force PE, and induced currents Rx. [ Fig. 4] Fig. 4 is a diagram explaining a process of deriving a position by a sensor control device 31. [ Fig. 5] Fig. 5 is a diagram explaining results of simulating the waveforms of a drive current Tx, an electromagnetic force PE, and induced currents Rx in a case where an electromagnetic resonance stylus 2 performs on-off keying modulation on the stylus signal PS. [ Fig. 6] Fig. Figure 6 is a diagram showing results of a simulation of amplitudes of induced currents R x1 to R x3 illustrated, each in loop coils LC x1 to LC X3 in a case where a coil L is located above a loop coil LCx2 is positioned. [ Fig. 7] Fig. 7 is a diagram illustrating difference detection performed by a sensor control device 31 according to a second embodiment of the present invention. [ Fig. 8] Fig. Figure 8 is a diagram illustrating results of a simulation of the waveforms of ground noise generated in loop coils S c1 to LC x7 which are located in the first to seventh positions from one end in an x-direction among a plurality of loop coils LCx of a position detecting device 3. [ Fig. 9] Fig. Figure 9 is a diagram showing results of a simulation of distributions in the x-direction of respective amplitudes of induced currents R x1 to R x7 and differences DR x1 to DR x7obtained in a case where the coil L of the electromagnetic resonance stylus 2 is arranged above the loop coil LC x4 is positioned. [ Fig. 10] Fig. 10 is a diagram illustrating difference detection performed by a sensor control device 31 according to a third embodiment of the present invention. [ Fig. 11] Fig. 11 is a diagram of amplitudes of the noise floor shown in Fig. 8, which are plotted along a horizontal axis as the x-direction. [ Fig. 12] Fig. 12 depicts diagrams explaining a local sensing process performed by a sensor control device 31 according to a fourth embodiment of the present invention. EMBODIMENTS OF THE INVENTION

[0014] Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.

[0015] Fig. 1 is a diagram illustrating a configuration of a position detection system 1 according to a first embodiment of the present invention. As shown in Fig. As illustrated in Figure 1, the position detection system 1 comprises an electromagnetic resonance stylus 2 and a position detection device 3, each compatible with the EMR principle. The electromagnetic resonance stylus 2 includes a pin-shaped device including a core 20, a pressure sensor 21, a side switch 22, a processing circuit 23, a coil L, a capacitor C, and a switching element SW. The position detection device 3 includes a device including a plurality of loop coils LC, a switching unit 30, a sensor control device 31, and a host processor 32. The loop coils LC include a plurality of loop coils LCx (second loop coils) arranged in an x-direction (second direction) and a plurality of loop coils LCy (first loop coils) arranged in a y-direction (first direction) perpendicular to the x-direction.According to a typical example, the position detection device 3 includes a tablet or laptop computer having a display surface that also serves as a touch surface. However, the position detection device 3 can be implemented by a digitizer without a display surface.

[0016] Before describing the configurations of the electromagnetic resonance stylus 2 and the position detecting device 3 in detail, the present invention will be briefly outlined below. The sensor control device 31 has a function of intermittently transmitting an alternating magnetic field AM through the loop coils LCy from the touch surface of the position detecting device 3. When the coil L of the electromagnetic resonance stylus 2 enters the alternating magnetic field AM, an electromotive force PE is generated across the coil L, and a stylus signal PS is transmitted as a reflected signal from the coil L. During the transmission of the alternating magnetic field AM, the position detecting device 3 detects the position of the electromagnetic resonance stylus 2 by having the loop coils LCx detect the stylus signal PS.

[0017] During the transmission of the stylus signal PS, the processing circuit 23 of the electromagnetic resonance stylus 2 turns the switching element SW on and off based on data to be transmitted to the position detection device 3, thereby performing on-off keying modulation on the stylus signal PS. The reason why the switching element SW can perform on-off keying modulation on the stylus signal PS by turning it on and off will be described in detail below. When the processing circuit 23 performs on-off keying modulation and the position detection device 3 demodulates the stylus signal PS, data is transmitted from the electromagnetic resonance stylus 2 to the position detection device 3 while the sensor control device 31 transmits the alternating magnetic field AM.The respective configurations of the electromagnetic resonance stylus 2 and the position detecting device 3 for realizing such data transmission will be described in detail below.

[0018] First, attention is drawn to the position detection device 3. The loop coils LC are arranged in the touch surface and include the loop coils LCx and LCy referred to above. Each of the loop coils LC has one end connected to the switching unit 30 and another element connected to ground. The switching unit 30 refers to a circuit for connecting one or more of the loop coils LC to the sensor control device 31 under the control of the sensor control device 31.

[0019] The sensor control device 31 refers to an integrated circuit having a function of detecting the position of the electromagnetic resonance stylus 2 in the touch surface, collecting data transmitted from the electromagnetic resonance stylus 2 as the stylus signal PS, and sequentially delivering the detected position and the provided data to the host processor 32. To perform these processing activities, the sensor control device 31 is configured to sequentially excite the loop coils LCy (i.e., sequentially supply drive currents Tx to the respective loop coils LCy) and receive induced currents Rx developed in the loop coils LCx as the stylus signal PS.

[0020] Fig. Figure 2 is a diagram explaining the relationship between the transmission of the alternating magnetic field AM and the reception of a stylus signal PS. If, as in Fig. 2, the sensor control device 31 supplies a drive current Tx to one of the loop coils LCy, it generates an alternating magnetic field AM around the loop coil LCy. Since the generated alternating magnetic field AM is parallel to the loop coils LCx, as shown in Fig. 2, the alternating magnetic field AM alone almost fails to cause the loop coils LCx to generate induced currents Rx. However, if the electromagnetic resonance stylus 2 is positioned near a point where the loop coil LCy, which is supplied with the drive current Tx, crosses a particular loop coil LCx, then, insofar as the resonance circuit of the electromagnetic resonance stylus 2 disturbs the magnetic field, a significant induced current Rx flows through the loop coil LCx. The sensor control device 31 is configured to detect the induced current Rx thus flowing through the loop coil LCx as a stylus signal PS.

[0021] Fig. Figure 3 is a diagram illustrating results of a simulation of waveforms of a drive current Tx, an electromagnetic force PE, and induced currents Rx. The illustrated induced currents Rx include an induced current Rx flowing through the loop coil LCx positioned near the electromagnetic resonance stylus 2 and an induced current Rx flowing through a loop coil LCx located away from the electromagnetic resonance stylus 2. The vertical axis of the Fig. 3 represents the amplitude of the waveforms, and its horizontal axis represents time (µs). Fig. 3 illustrates an example in which the sensor control device 31 starts to excite a certain loop coil LCy at the time point of 0 µs.

[0022] If, as in Fig. 3 illustrates, when the sensor control device 31 begins to supply a drive current Tx, an electromotive force PE is generated in the electromagnetic resonance stylus 2, causing a large induced current Rx to be observed in the loop coil LCx positioned near the electromagnetic resonance stylus 2. On the other hand, only a small induced current Rx is observed in the loop coil LCx located away from the electromagnetic resonance stylus 2. The small induced current Rx is directly induced by the alternating magnetic field AM transmitted from the loop coil LCx and is hereinafter referred to as "noise floor." On the other hand, only a small induced current Rx is observed in the loop coil LCx located away from the electromagnetic resonance stylus 2.

[0023] The position detection system 1 therefore detects a significant difference between the amplitudes of the induced currents Rx developing in the loop coil LCx located near the electromagnetic resonance stylus 2 and the loop coil LCx located away from the electromagnetic resonance stylus 2. The sensor control device 31 derives the position of the electromagnetic resonance stylus 2 while the loop coil LCy is energized based on the difference.

[0024] Fig. Fig. 4 is a diagram explaining a process of deriving a position by the sensor control device 31. The derivation process of the position of the electromagnetic resonance stylus 2 by the sensor control device 31 while the loop coil LCy is excited is specifically described below with reference to Fig. 4 described.

[0025] First, the sensor control device 31, which has not yet detected the electromagnetic resonance stylus 2, performs a global scan to detect the electromagnetic resonance stylus 2 again. Specifically, the sensor control device 31 performs a process of supplying an excitation current Tx to one of the loop coils LCy of the position detection device 3 and detecting induced currents Rx (stylus signals PS) in the loop coils LCx of the position detection device 3, one after another, with respect to each of the loop coils LCy. Then, the sensor control device 31 derives the positions of the electromagnetic resonance stylus 2 in the x-direction and the y-direction, respectively, based on a distribution in the touch surface of the levels of the induced currents Tx detected in the process.

[0026] Once the sensor controller 31 has detected the position of the electromagnetic resonance stylus 2 according to the global scan, the sensor controller 31 performs a local scan to update the position of the electromagnetic resonance stylus 2. Specifically, the sensor controller 31 selects predetermined numbers of loop coils LCx and LCy according to the most recently detected position. The sensor controller 31 should preferably select predetermined numbers of loop coils LCx and LCy sequentially closer to the most recently detected position. The sensor controller 31 then performs a process similar to the global scan by using only the selected loop coils LCx and LCy.

[0027] Specifically, the sensor control device 31 performs a process of supplying an excitation current Tx to one of the selected predetermined number of loop coils LCy and detecting induced currents Rx (stylus signals PS) in each of the selected predetermined number of loop coils LCx, one after another, with respect to each of the selected predetermined number of loop coils LCy. Then, the sensor control device 31 derives the positions of the electromagnetic resonance stylus 2 in the x-direction and the y-direction, respectively, based on a distribution in the touch surface of the levels of the induced currents Tx detected in the process, and updates the detected position with the derived position.

[0028] While performing the above-mentioned local sampling, the sensor control device 31 also performs a collection process of the data transmitted from the electromagnetic resonance stylus 2. Since the electromagnetic resonance stylus 2 performs on-off keying modulation on the stylus signal PS as described above, the induced currents Rx detected by the sensor control device 31 are also keyed on-off. The sensor control device 31 collects the data transmitted from the electromagnetic resonance stylus 2 by demodulating the on-off keyed induced currents Rx according to on-off keying modulation.

[0029] The sensor control device 31 is also configured to provide a period of a predetermined duration during which it does not supply excitation currents Tx to the loop coils LCy before starting to supply excitation currents Tx to the loop coils LCy. Consequently, the alternating magnetic field AM generated by the position detection device 3 is intermittently transmitted from the touch surface. The predetermined duration referred to above is not long enough to allow data to be transmitted by controlling the frequency of reflected signals, but may be extremely short enough for the electromagnetic resonant stylus 2 to be able to detect a pause in the alternating magnetic field AM.

[0030] The electromagnetic resonance stylus 2 detects the timing to restart the transmission of the alternating magnetic field AM through the sensor control device 31 by detecting a pause in the alternating magnetic field AM caused by intermittent transmission of the alternating magnetic field AM, and performs on-off keying modulation on the stylus signal PS based on the detected timing. The sensor control device 31 also demodulates the stylus signal PS based on the timing to start the transmission of the alternating magnetic field AM (i.e., the timing to start energizing one of the loop coils LCy). In this way, it is possible to transmit data from the electromagnetic resonance stylus 2 to the sensor control device 31 while they are synchronized.

[0031] With further reference to Fig. 1, the host processor 32 performs a process of moving a cursor displayed on the display surface and generating stroke data indicating a path followed by the electromagnetic resonance stylus 2 on the touch surface, using positions and data supplied from the sensor controller 31. Regarding the stroke data, the host processor 32 also performs a process of rendering and displaying the generated stroke data, a process of generating and recording digital ink including the generated stroke data, and a process of sending the generated digital ink to an external device according to the user's instructions.

[0032] Now, attention is drawn to the electromagnetic resonance stylus 2. The core 20 includes a rod-shaped member that forms a stylus tip of the electromagnetic resonance stylus 2 and is movable in the axial directions of the stylus. The core 20 has a rear end that is held in abutment against the pressure sensor 21. The pressure sensor 21 refers to a sensor for detecting a pressure applied to the stylus tip by detecting a pressing force from the rear end of the core 20 and is configured to provide the processing circuit 23 with a value (stylus pressure value) representing the detected pressure.

[0033] The side switch 22 includes an on / off switch mounted on a surface of the electromagnetic resonance stylus 2 and is configured to supply the processing circuit 23 with information (on / off information) representing its own on or off state. Although the electromagnetic resonance stylus 2 is Fig. 1 as having a side switch 22, the electromagnetic resonance stylus 2 may have a plurality of side switches 22. The electromagnetic resonance stylus 2 may have a similar switch on a surface (e.g., terminal end portion) other than a side surface of the electromagnetic resonance stylus 2.

[0034] The coil L refers to an inductor located near the stylus tip and magnetically coupled to the loop coils LC in the position detecting device 3. The coil L is connected in parallel with the capacitor C and forms a resonant circuit together in cooperation with the capacitor C. When the coil L enters the alternating magnetic field AM generated by the position detecting device 3, the electromotive force PE is developed across the coil L due to electromagnetic induction, which generates an alternating current in the resonant circuit and stores electrical energy in the capacitor C. At this time, induced currents Rx (stylus signal PS) develop as a reflected signal in the loop coils LC in the position detecting device 3 and are detected by the sensor control device 31.

[0035] The switching element SW includes a single-pole double throw switch connected in parallel with the capacitor C. When the switching element SW is turned off, the coil L and the capacitor C function as a resonant circuit, and when the switching element SW is turned on, the coil L and the capacitor C do not function as a resonant circuit because the capacitor C is short-circuited. Since, when the coil L and the capacitor C do not function as a resonant circuit, the magnetic field disturbance described above with reference to Fig. 2 does not occur, no induced currents Rx, which would otherwise be caused by a resonance circuit, flow in the loop coils LCx in the position detecting device 3. In other words, when the switching element SW is turned on, no stylus signal PS is transmitted from the electromagnetic resonance stylus 2 to the position detecting device 3.

[0036] The processing circuit 23 includes an integrated circuit for transmitting data to the position detecting device 3 by performing on / off control on the switching element SW based on data to be transmitted to the position detecting device 3. Examples of the data to be transmitted include a stylus ID uniquely assigned to the electromagnetic resonance stylus 2, the stylus pressure value, and the above-mentioned on / off information.

[0037] According to one example, for transmitting data "0," the processing circuit 23 may control the switching element SW to turn on to cause the amplitude of the stylus signal PS to have a minimum value (low), and for transmitting data "1," the processing circuit 23 may control the switching element SW to turn off to cause the amplitude of the stylus signal PS to have a maximum value (high). This is nothing other than performing on-off keying modulation on the stylus signal PS by performing on / off control on the switching element SW. When the processing circuit 23 performs such a process, the position detection device 3 demodulates the received stylus signal PS according to on / off control, thereby making it possible to collect the data transmitted from the electromagnetic resonance stylus 2.

[0038] Fig. Figure 5 is a diagram illustrating the results of simulating the waveforms of a drive current Tx, an electromagnetic force PE, and induced currents Rx in a case where an electromagnetic resonance stylus 2 performs on-off keying modulation on the stylus signal PS. The symbol Rx n , which induced a current in Fig. 5, represents an induced current Rx which flows through an n-th (called “loop coil LCx n “) of the loop coils LCx is observed from one end in the x-direction. Fig. Figure 5 illustrates the waveforms at the time when the coil L of the electromagnetic resonance stylus 2 is placed over a loop coil LC x3 is positioned.

[0039] In Fig. 5, a state in which the amplitude of the electromotive force PE is relatively small corresponds to a state in which the processing circuit 23 turns on the switching element SW to transmit data "0". A state in which the amplitude of the electromotive force PE is relatively large corresponds to a state in which the processing circuit 23 turns off the switching element SW to transmit data "1". When the processing circuit 23 turns the switching element SW on and off, the amplitude of the electromotive force PE undergoes large changes, which are reflected in an induced current Rx developed in a loop coil LCx. Since in the Fig. In the example illustrated in Figure 5, when the coil L of the electromagnetic resonance stylus 2 is positioned above the loop coil LCx3, the induced current Rx3 is larger than the amplitudes of the other induced currents Rx, and the induced current Rx3 reflects the changes in the amplitude of the electromotive force PE. The position detection device 3 is configured to collect the data transmitted from the electromagnetic resonance stylus 2 by demodulating the induced current Rx3 whose amplitude is larger.

[0040] The processing circuit 23 is configured to detect an alternating current generated in the resonant circuit and performs a detection process of the timing at which the position detection device 3 should restart transmitting the alternating magnetic field AM based on the result of the detection of the alternating current. Then, the processing circuit 23 performs on / off control on the switching element SW based on the detected timing. In this way, it is possible to transmit data from the electromagnetic resonant stylus 2 to the sensor control device 31 while maintaining synchronization as described above.

[0041] In the position detection system 1 according to the present embodiment, as described above, when the switching element SW is turned off (i.e., in a state where the resonance circuit exists), the position detection device 3 detects induced currents Rx, and when the switching element SW is turned on (i.e., in a state where no resonance circuit exists), the position detection device 3 does not detect the induced currents Rx. Therefore, performing on / off control on the switching element SW based on data to be transmitted to the position detection device 3 is equivalent to performing on-off keying modulation on an induced current Rx, i.e., the stylus signal PS.Consequently, with the position detecting system 1 according to the present embodiment, it is possible to transmit data from the electromagnetic resonance stylus 2 to the position detecting device 3 while the position detecting device 3 excites the loop coils LCy.

[0042] Furthermore, the sensor control device 31 with the position detection system 1 according to the present embodiment is configured to intermittently develop the alternating magnetic field AM, and the processing circuit 23 is configured to perform on-off keying modulation on the stylus signal PS based on the timing at which the position detection device 3 should restart developing the alternating magnetic field AM. Consequently, it is possible to transmit data from the electromagnetic resonance stylus 2 to the sensor control device 31 while maintaining synchronization.

[0043] Furthermore, the position detection system 1 according to the present embodiment is also advantageous in that the signal-to-noise ratio of the stylus signal PS is higher than in a case where data is transmitted by frequency control of reflected signals. This advantage will be explained below with reference to Fig. 6 described.

[0044] Fig. Figure 6 is a diagram showing simulation results of amplitudes of induced currents Rx1 to Rx3 observed in loop coils LCx1 to LCx3, respectively, in a case where the coil L is arranged above the loop coil LC x2 is positioned. In Fig. 6, an amplitude W1 represents the amplitudes of the induced currents Rx1 to Rx3 gated on-off according to the present embodiment (average values ​​of the amplitudes observed when the switching element SW is turned off), and an amplitude W2 represents the amplitudes of the induced currents Rx1 to Rx3 modulated according to a comparative example in which data is transmitted by frequency control of reflected signals (average values ​​of the amplitudes observed after the position detecting device 3 stops supplying excitation currents Tx until the electromagnetic resonance stylus 2 stops transmitting data by frequency control of reflected signals). Fig. 5 also illustrates respective amplitudes W1 and W2 at the time when the distance between the stylus tip of the electromagnetic resonance stylus 2 and the touch surface is 0 mm, 5 mm, 10 mm, 15 mm, and 20 mm.

[0045] As in Fig. 6, the amplitudes W1 are noticeably larger than the amplitudes W2 regardless of the distance between the stylus tip of the electromagnetic resonance stylus 2 and the touch surface. This is because while the position detecting device 3 energizes the loop coils LCy, the electric power for maintaining the amplitudes of the induced currents Rx is constantly supplied from the sensor control device 31, but after the position detecting device 3 stops energizing the loop coils LCy, the electric power for maintaining the amplitudes of the induced currents Rx is provided solely by the electric power stored in the capacitor C. As the remaining charged energy in the capacitor C gradually decreases, the amplitudes of the induced currents Rx are gradually attenuated.

[0046] As described above, with the position detection system 1 according to the present embodiment, since the electromagnetic resonance stylus 2 is configured to transmit the stylus signal PS while the position detection device 3 excites the loop coils LCy, the electromagnetic resonance stylus 2 is capable of transmitting the stylus signal PS with larger amplitudes than in a case where the electromagnetic resonance stylus 2 is configured to transmit data by frequency control of reflected signals. Accordingly, it is possible to make the signal-to-noise ratio of the stylus signal PS higher than in the case where the electromagnetic resonance stylus 2 is configured to transmit data by frequency control of reflected signals.

[0047] A position detection device 1 according to a second embodiment of the present invention will be described below. The position detection system 1 according to the present embodiment differs from the position detection system 1 according to the first embodiment in that the sensor control device 31 performs differential detection of induced currents Rx. Since the position detection system 1 according to the present embodiment is similar to the position detection system 1 according to the first embodiment in other details, the position detection system 1 will be described below with emphasis on the difference from the position detection system 1 according to the first embodiment.

[0048] Fig. Fig. 7 is a diagram illustrating differential detection performed by a sensor control device 31 according to the present embodiment. As shown in Fig. As illustrated in Figure 7, the sensor control device 31 according to the present embodiment is configured to derive the position of the electromagnetic resonance stylus 2 using the differences between the levels of the induced currents Rx from two adjacent loop coils LCx and to demodulate the stylus signal PS. Specifically, the sensor control device 31 derives a difference DRx k between an induced current Rx k , which in a loop coil LCx k is detected (k is an integer from 1 to n-1, n is the total number of loop coils LCx) and an induced current Rx k+1 , which in a loop coil LCx k+1 and detects the positions of the electromagnetic resonance stylus 2 and demodulates the stylus signal PS using the differences DRx1 to DRx n-1 than the stylus signal PS.

[0049] The process described above makes it possible to reduce the negative impact of the aforementioned background noise. This feature is described in detail below.

[0050] Fig. Fig. 8 is a diagram showing the results of simulation of the waveforms of the ground noise observed in the loop coils LCx1 to LCx7 located in the first to seventh positions from one end in an x-direction among the plurality of loop coils LCx of a position detecting device 3, respectively. Since, as Fig. As illustrated in Figure 8, the phases of the noise floor observed in the respective loop coils LCx are equal, the noise floor can be canceled by deriving the differences between the induced currents Rx. Therefore, the above-described process performed by the sensor control device 31 makes it possible to reduce the negative effect of the noise floor.

[0051] Fig. Figure 9 is a diagram illustrating simulation results of distributions in the x-direction of respective amplitudes of induced currents Rx1 to Rx7 and differences DRx1 to Drx7 obtained in a case where the coil L of the electromagnetic resonance stylus 2 is positioned above the loop coil LCx4. The distribution W3 shown in Fig. 9, refers to the amplitudes of the differences DRx1 to DRx7, and the distribution W4 refers to a distribution of the amplitudes of the induced currents Rx1 to Rx7. The position of the peak of the distribution W3 is shifted from the position of the peak of the distribution W4 by half of a loop coil LCx because the induced currents Rx k and the differences DRx k at the same positions on the horizontal axis of the Fig. 9. The sensor control device 31 according to the present embodiment is configured to derive the positions of the electromagnetic resonance stylus 2 while correcting such a phase shift.

[0052] As from Fig. As can be seen from Figure 9, the distribution W4 is wider than the distribution W3 except for the peak. This means that the process performed by the sensor control device 31 according to the present embodiment effectively cancels the background noise. From the results shown in Fig. 9, it can also be seen that the process performed by the sensor control device 31 according to the present embodiment is effective for increasing the peak value of the distribution.

[0053] As described above, with the position detection system 1 according to the present embodiment, since the sensor control device 31 is configured to derive the position of the electromagnetic resonance stylus 2 and demodulate the stylus signal PS using the differences between the levels of the induced currents Rx from two adjacent loop coils LCx, it is possible to reduce the adverse effects of the background noise on the derivation of the position of the electromagnetic resonance stylus 2 and the demodulation of the stylus signal PS. The position detection system 1 according to the present embodiment also makes it possible to increase the peak value of the amplitude distribution of the stylus signal PS.

[0054] A position detection system 1 according to a third embodiment of the present invention will be described below. The position detection system 1 according to the present embodiment differs from the position detection system 1 according to the second embodiment in that the sensor control device 31 performs differential detection of induced currents Rx only with respect to loop coils LCx positioned at ends in the x-direction. Since the position detection system 1 according to the present embodiment is similar to the position detection system 1 according to the second embodiment in other details, the position detection system 1 according to the present embodiment will be described below with emphasis on the difference from the position detection system 1 according to the second embodiment.

[0055] Fig. 10 is a diagram illustrating differential detection performed by a sensor control device 31 according to a third embodiment of the present invention. As shown in Fig. 10, the sensor control device 31 according to the present embodiment performs differential detection only on the loop coils LCx1 and LCx n positioned at one end in the x-direction, and loop coils LC x2 and LCx n-1 , which are adjacent thereto. In particular, the sensor control device 31 derives the position of the electromagnetic resonance stylus 2 and demodulates the stylus signal PS using a current obtained by subtracting an induced current Rx n from an induced current Rx1 is calculated as an induced current Rx1, a current obtained by subtracting an induced current Rx n-1from a reduced current Rx2 as an induced current Rx2 of a current obtained by subtracting the induced current Rx2 from the induced current Rx n-1 as an induced current Rx n-1 and a current calculated by subtracting the induced current Rx1 from the induced current Rx n as an induced current Rx n is calculated.

[0056] The above process makes it possible to reduce the negative effects of background noise at both ends in the x-direction, where the background noise is particularly strong. This feature is described in detail below.

[0057] Fig. 11 is a diagram of the amplitudes of the noise floor shown in Fig. 8, which are plotted along a horizontal axis as the x-direction. As in Fig. 11, the amplitude of the background noise at the loop coils LCx1 and LC x2near one end in the x-direction and small at the other end of the loop coils LCx. It is assumed that this, as Fig. 2, is due to the fact that at the end in the x-direction the loop coils LCy include short sections extending in the x-direction and an alternating magnetic field AM generated by these sections is received by the loop coils LCx.

[0058] The increased noise floor at the end occurs essentially the same way at both ends in the x-direction. It is therefore possible to effectively cancel the noise floor by reducing the induced currents Rx at the ends from each other, as described above.

[0059] As described above, in the position detection system 1 according to the present embodiment, the sensor control device 31 performs differential detection on induced currents Rx at the x-direction ends. Therefore, it is possible to infer the position of the electromagnetic resonance stylus 2 and reduce the negative effects of the noise floor on the demodulation of the stylus signal PS at the x-direction ends where the noise floor is particularly strong.

[0060] According to the present embodiment, differential detection is performed on two loop coils LCx at each of the ends in the x-direction. However, differential detection may be performed on one loop coil LCx at each of the ends in the x-direction or on three or more loop coils LCx at each of the ends in the x-direction.

[0061] A position detection system 1 according to a fourth embodiment of the present invention will be described below. The position detection system 1 according to the present embodiment differs from the position detection system 1 according to the first embodiment in that the specific process of local sensing is different. Since the position detection system 1 according to the present embodiment is similar to the position detection system 1 according to the first embodiment in other details, the position detection system 1 will be described below with emphasis on the difference from the position detection system 1 according to the first embodiment.

[0062] Fig. 12 depicts diagrams explaining a local sensing process performed by a sensor control device 31 according to a fourth embodiment of the present invention. Fig. Figure 12 illustrates a situation in which the last detected position of an electromagnetic resonance stylus 2 is near an intersection point of a loop coil LCx a and a loop coil LCy b is positioned. Fig. Fig. 12 also illustrates the manner in which the sensor control device 31 controls five loop coils LCy (in particular, the loop coils LCx a-2 up to LCx a+2 and the loop coils LCy b-2 to LC yb+2 ) for local sampling. The number of selected loop coils is not limited to 5, but can be greater or less than 5.

[0063] The sensor control device according to the present embodiment first selects one loop coil LCx and one loop coil LCy in addition to the five loop coils LCx a-2 up to LCx a+2 and the five loop coils LCy b-2 to LCy b+2based on the last detected position. For such a selection, the sensor control device 31 is configured to control the loop coils LCx a , LCy b that are closest to the last detected position. The loop coils LCx a-2 up to LCx a+2 and the loop coils LCy b-2 to LCy b+2 , which are also selected for local scanning according to the first embodiment, may be referred to hereinafter as “receiving loop coils”, while the loop coils LCx a and LCx b which are closest to the last detected position, hereinafter referred to as “transmission loop coils”.

[0064] Then the sensor control device 31 supplies the loop coil LCy b , which is selected as a transmission loop coil, with an excitation current Tx, as in Fig. 12A, and while the loop coil LCyb supplied with the excitation current Tx, it detects induced currents Rx in each of the five loop coils LCx a-2 up to LCx a+2 which are selected as receiving loop coils. Then, the sensor control device 31 determines the position of the electromagnetic resonance stylus 2 in the x-direction based on the distribution (distribution in the x-direction) of the levels of the five induced currents Rx a-2 to Rx a+2 (stylus signal PS) obtained in this way.

[0065] Then the sensor control device 31 supplies the loop coil LCx a , which is selected as a transmission loop coil, with an excitation current Tx, as in Fig. 12B, and while the loop coil LCx a supplied with the excitation current Tx, it detects induced currents Tx in the five loop coils LCy b-2 to LCy b+2which are selected as the receiving loop coils. Then, the sensor control device 31 determines the position of the electromagnetic resonance stylus 2 in the y-direction based on the distribution (distribution in the y-direction) of the levels of the five induced currents Rx b+2 to Rx b+2 (stylus signal PS) obtained in this way.

[0066] When the sensor control device 31 performs the local sampling according to the above process, the time required for one local sampling is shortened compared to the first embodiment. Specifically, in the example shown in Fig.12, for deriving a position using five loop coils LCx and five loop coils LCy, excitation currents Tx are supplied five times in the local scanning according to the first embodiment, but the excitation currents Tx are supplied only twice in the local scanning according to the present embodiment. Therefore, the time required for one local scanning is shortened.

[0067] As described above, the position detection system 1 according to the present embodiment makes it possible to shorten the time required for local scanning.

[0068] The preferred embodiments of the present invention have been described above. However, the present invention is not limited to these embodiments and can be reduced to practice in various forms without departing from the scope of the invention. DESCRIPTION OF REFERENCE SYMBOLS 1 position detection system 2 Electromagnetic resonance stylus 3 Position detection device 20 core 21 Pressure sensor 22 side switches 23 Processing circuit 30 switching unit 31 Sensor control device 32 host processors AM alternating magnetic field C capacitor L coil LC, LCx, LCy loop coil PE Electromotive force PS stylus signal Rx Induced Current SW switching element Tx excitation current QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 05-019164

[0004]

Claims

[1] Position detecting device comprising: a plurality of first loop coils arranged in a first direction; a plurality of second loop coils arranged in a second direction perpendicular to the first direction; and a sensor control device which detects induced currents in each of the second loop coils during the excitation of one of the first loop coils, wherein the sensor control device derives a position of an electromagnetic resonance stylus in at least the second direction based on a distribution of levels of the detected induced currents and collects data transmitted from the electromagnetic resonance stylus by performing on-off keying modulation on the detected induced currents. [2] The position detecting device according to claim 1, wherein the sensor control device performs demodulation on the induced currents based on a timing for starting the energization of the one of the first loop coils. [3] Position detecting device according to claim 1 or 2, wherein the sensor control device is configured to a global scan to detect the electromagnetic resonance stylus that is undetected, and to perform a local scan to detect the electromagnetic resonance stylus that has been detected, the global sensing includes a process of supplying one of the first loop coils with an excitation current and detecting the induced currents in the second loop coils respectively sequentially with respect to the first loop coils and deriving the position of the electromagnetic resonance stylus in each of the first direction and the second direction based on a distribution in a touch surface of the levels of the detected induced currents, and local scanning is a process for Selecting a predetermined number of the first loop coils and a predetermined number of the second loop coils as receiving loop coils and one of the first loop coils and one of the second loop coils as transmitting coils based on the position of the detected electromagnetic resonance stylus, Detecting the induced currents respectively in the predetermined number of the second loop coils selected as the receiving loop coils while supplying the excitation current to a first loop coil selected as a transmitting loop coil, and deriving the position of the electromagnetic resonance stylus in the second direction on the basis of the distribution in the second direction of the levels of the detected induced currents, and Detecting the induced currents respectively in the predetermined number of the first loop coils selected as the receiving loop coils while supplying the excitation current to a first loop coil selected as a transmitting loop coil, and deriving the position of the electromagnetic resonance stylus in the first direction based on the distribution in the first direction of the levels of the detected induced currents. [4] A position detecting device according to claim 1 or 2, wherein the sensor control device derives the position of the electromagnetic resonance stylus and collects the data transmitted from the electromagnetic resonance stylus by using differences between the induced currents respectively detected in two adjacent ones of the second loop coils. [5] Position detecting device according to claim 1 or 2, wherein the sensor control device derives the position of the electromagnetic resonance stylus and collects the data transmitted by the electromagnetic resonance stylus, by using a current calculated by subtracting an induced current detected in a second loop coil positioned at one end in the second direction among the second loop coils from an induced current detected in a second loop coil positioned at another end in the second direction among the second loop coils as the induced current detected in a second loop coil positioned at the end in the second direction among the second loop coils, and by using a current calculated by subtracting the induced current detected in the second loop coil positioned at the end in the second direction among the second loop coils from the induced current detected in the second loop coil positioned at the other end in the second direction among the second loop coils as the induced current detected in the second loop coil positioned at the other end in the second direction among the second loop coils. [6] Electromagnetic resonance stylus, comprising: a resonant circuit containing a coil and a capacitor, a switching element connected in parallel with the capacitor; and a processing circuit that transmits data to a position detection circuit by performing on / off control of the switching element according to the data to be transmitted to the position detection circuit, where the processing circuit detects an alternating current generated in the resonant circuit by an alternating magnetic field transmitted intermittently by the position detecting circuit, and detects a timing so that the position detecting circuit again transmits the alternating magnetic field based on a result of detecting the alternating current and performs on / off control on the switching element based on the detected timing. [7] Position detection system, comprising: an electromagnetic resonance stylus and a position detecting device, wherein the electromagnetic resonance stylus comprises: a resonant circuit including a coil and a capacitor, a switching element connected in parallel with the capacitor, and includes a processing circuit that transmits data to a position detection circuit by performing on / off control on the switching element according to the data to be transmitted to the position detection circuit, the position detection device a plurality of first loop coils arranged in a first direction, a plurality of second loop coils arranged in a second direction perpendicular to the first direction, and a sensor control device which detects induced currents in each of the second loop coils during the energization of one of the first loop coils, the sensor control device derives a position of the electromagnetic resonance stylus in at least the second direction based on a distribution of levels of the detected induced currents and collects data transmitted from the electromagnetic resonance stylus by performing on-off keying modulation on the detected induced currents.

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