Touch positioning system and method

Abstract

The application provides a touch positioning system and method, which can effectively realize accurate positioning of a touch pen and improve positioning accuracy; the system comprises a transmitting end and a receiving end, a signal transmitting module is arranged in the transmitting end, a signal receiving module is arranged in the receiving end, and a positioning module connected with the signal receiving module is further arranged in the receiving end; wherein the signal transmitting module is used for transmitting ultrasonic signals and infrared synchronous signals simultaneously; the signal receiving module is used for obtaining an infrared synchronous digital signal and an ultrasonic complex signal containing amplitude information and phase information of the ultrasonic signals according to the received signals, and then sending the ultrasonic complex signal and the infrared synchronous digital signal to the positioning module; and the positioning module is used for obtaining the distance from the transmitting end to the signal receiving module according to the received signals, and then determining the positioning coordinates of the transmitting end according to the obtained distance information.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic touch and positioning technology, specifically a touch positioning system and method. Background Technology

[0002] Currently, the main types of touchscreens used in the market include capacitive touchscreens, infrared touchscreens, and capacitive touchscreens. These screens offer high positioning accuracy and are therefore widely used in electronic devices such as televisions, computers, and mobile phones. However, these types of touchscreens are all contact-based, requiring the object to touch the screen for positioning. They cannot function properly when the object is suspended in the air. In recent years, with the rise of motion-sensing games and virtual reality games, the demand for touchscreens that can be controlled remotely has become increasingly strong.

[0003] Ultrasonic touch technology uses a stylus that emits ultrasonic waves as the touch object, and then measures the distance between the stylus and the microphone to locate the coordinates of the ultrasonic transmitter. Ultrasonic touch technology can achieve three-dimensional coordinate positioning, thus enabling touch operation of the display screen without the touch object touching the screen. However, current ultrasonic touch technology measures the distance between the stylus and the microphone based on time delay difference. Its measurement accuracy is affected by sampling point errors or external environmental factors, making it difficult to achieve a stylus coordinate positioning accuracy of 1mm. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a touch positioning system and method that can effectively achieve accurate positioning of the stylus and improve positioning accuracy.

[0005] The technical solution is as follows: a touch-screen positioning system includes a transmitter and a receiver. The transmitter includes a signal transmitting module, and the receiver includes a signal receiving module. The system is characterized in that the receiver further includes a positioning module connected to the signal receiving module.

[0006] The signal transmitting module is used to simultaneously transmit ultrasonic signals and infrared synchronization signals;

[0007] The signal receiving module is used to obtain an infrared synchronous digital signal and an ultrasonic complex signal containing amplitude and phase information of the ultrasonic signal based on the received signal, and then send the ultrasonic complex signal and the infrared synchronous digital signal to the positioning module.

[0008] The positioning module is used to obtain the distance from the transmitter to the signal receiving module based on the received signal, and then determine the positioning coordinates of the transmitter based on the obtained distance information.

[0009] Furthermore, the transmitting end uses a stylus, and the receiving end uses a display screen; the signal transmitting module includes an ultrasonic transmitter and an infrared transmitter; the signal receiving module includes a microphone and an infrared receiver, the microphone is provided with four microphones, the four electrically connected microphones receive the ultrasonic signals emitted by the ultrasonic transmitter, and the infrared receiver receives the infrared synchronization signals emitted by the infrared transmitter;

[0010] Furthermore, the ultrasonic transmitter converts the sweep frequency signal into an ultrasonic signal and transmits it to the microphone; the initial frequency of the sweep frequency signal is -1.5kHz, the termination frequency is 1.5kHz, the sampling frequency is 48kHz, and the duration of the sweep frequency signal is 5ms.

[0011] A touch positioning method, characterized in that it includes:

[0012] The transmitter synchronously transmits ultrasonic signals and infrared synchronization signals to the receiver at a preset frequency.

[0013] The ultrasonic signal is demodulated and filtered to obtain an ultrasonic complex signal containing the amplitude and phase information of the ultrasonic signal.

[0014] The distance from the transmitter to the receiver is obtained based on the ultrasonic complex signal and the infrared synchronization signal, and the positioning coordinates of the transmitter are determined.

[0015] Furthermore, the ultrasonic transmitter in the signal transmitting module converts the swept frequency signal into an ultrasonic signal and then transmits it to the microphone of the signal receiving module. The signal conversion includes the following steps:

[0016] S1.1 The mathematical expression for the pulse function of the swept frequency signal is as follows:

[0017]

[0018] in, The pulse duration is represented by f1, which represents half the pulse spectral width, and t represents time. Represents the imaginary unit;

[0019] S1.2, the pulse function by To obtain the ultrasound baseband signal through periodic repetition, the mathematical expression for the ultrasound baseband signal is as follows:

[0020]

[0021] Where m takes values ​​in the range [1, +inf];

[0022] S1.3. Take the real and imaginary parts of the ultrasonic baseband signal respectively, and compare the real part signal with... Multiplication, imaginary part signal and Multiply,

[0023] Finally, the two multiplied signals are added together to obtain the final ultrasonic signal. , ultrasonic signal The mathematical expression is:

[0024]

[0025] in, The modulation frequency; This represents the real part of the ultrasonic baseband signal. Represents the imaginary part of the ultrasound baseband signal;

[0026] Furthermore, the ultrasonic signal demodulation and filtering includes the following steps:

[0027] S2.1, the four microphones at a sampling frequency Ultrasonic signals are obtained by sampling ultrasonic signals. , Indicates the microphone number. ;

[0028] S2.2, Ultrasonic signal respectively with and Multiplying them yields two signals. ;

[0029] S2.3, the pulse function conjugate inverse sequence As a matched filter, respectively with the signal Convolution is performed to obtain the signal ;

[0030] S2.4 Obtain the ultrasonic complex signal according to the formula. ;

[0031] Furthermore, the infrared receiver samples the infrared synchronization signal at a sampling frequency of 48kHz to obtain an infrared synchronization digital signal. By calculating the infrared synchronization digital signal and ultrasonic complex signals The peak value is taken as the modulus to obtain the time difference between the two signal peaks. ;

[0032] in Represents ultrasonic complex signals The time corresponding to the peak value after modulo;

[0033] Indicates infrared synchronization digital signal The time corresponding to the peak;

[0034] This indicates the time difference between the arrival of the ultrasonic signal and the infrared synchronization signal at the signal receiving module;

[0035] Furthermore, according to the formula The distance from the stylus to the display screen is obtained. ,

[0036] in, Indicating from stylus to microphone An ultrasonic signal passes through n wavelengths. As a parameter;

[0037] This indicates that the ultrasonic signal has reached the microphone. Phase of time, ;

[0038] Indicates modulation frequency The corresponding wavelength;

[0039] Indicates that the stylus has reached the microphone. The estimated transmission distance, i.e. ; The speed at which sound travels;

[0040] Further, determining the positioning coordinates of the stylus includes the following steps:

[0041] S3.1 Obtain the estimated distance difference between the stylus and each microphone according to the formula:

[0042]

[0043] This indicates the stylus to microphone. With microphone Distance difference estimate; through This will cancel out the phase shift caused by the frequency shift;

[0044] S3.2, Assume the spatial coordinates of the stylus are... Select the three microphones labeled i, j, and k. Spatial coordinates are ,microphone Spatial coordinates are ,microphone Spatial coordinates are Substituting into formula (4), we get:

[0045]

[0046]

[0047] Simplifying formulas (5) and (6) yields:

[0048]

[0049]

[0050]

[0051] in, , ;

[0052] A is The matrix, for ;

[0053] S3.3, Using the least squares method, we obtain:

[0054]

[0055] Furthermore, the optimal coordinates for the obtained stylus positioning coordinates are selected, including:

[0056] The four microphones obtain 3^4 = 81 distance combinations, and the stylus is then positioned using these 81 distance combinations. Subsequently, the following formula is used:

[0057]

[0058]

[0059] After substituting the 81 positioning coordinates into formulas (11) and (12), select The coordinate with the smallest value is used as the final positioning coordinate of the stylus;

[0060] in, This indicates that the ultrasonic signal has reached the microphone. Phase of time;

[0061] It is an intermediate variable representing the phase difference from the estimated ultrasonic transmitter coordinates to microphone i and to microphone j;

[0062] It is the final error calculation function.

[0063] The beneficial effects of this invention are that it obtains the distance from the stylus to the display screen based on the ultrasonic complex signal and the infrared synchronous digital signal, and then determines the coordinate positioning of the stylus based on the distance information. By introducing amplitude information and phase information in the process of positioning the touch point coordinates, the accuracy of ultrasonic positioning is greatly improved. The accuracy of ultrasonic positioning can be improved to 1mm, and the influence of phase shift caused by frequency shift on positioning accuracy can be avoided, which has good application value. Attached Figure Description

[0064] Figure 1 This is a structural block diagram of the present invention;

[0065] Figure 2 This is a flowchart of the transmitting end in this invention;

[0066] Figure 3 This is a flowchart of the receiving end in this invention;

[0067] Figure 4 This is the autocorrelation curve of the ultrasonic pulse signal used in this invention. Detailed Implementation

[0068] like Figures 1-4 As shown, a touch positioning system includes a transmitter and a receiver. The transmitter is equipped with a signal transmitting module, and the receiver is equipped with a signal receiving module. The receiver is also equipped with a positioning module connected to the signal receiving module. The signal transmitting module is used to simultaneously transmit ultrasonic signals and infrared synchronization signals.

[0069] The signal receiving module is used to demodulate and filter the received ultrasonic signal to obtain an ultrasonic complex signal containing amplitude and phase information of the ultrasonic signal, and then send the ultrasonic complex signal and the infrared synchronous digital signal to the positioning module.

[0070] The positioning module is used to obtain the distance from the transmitter to the signal receiving module based on the received signal, and then determine the positioning coordinates of the stylus based on the obtained distance information.

[0071] The transmitter uses a stylus, and the receiver uses a display screen. The signal transmission module includes an ultrasonic transmitter and an infrared transmitter; the signal receiving module includes microphones and an infrared receiver. Four microphones are electrically connected to receive the ultrasonic signals emitted by the ultrasonic transmitter, and the infrared receivers receive the infrared synchronization signals emitted by the infrared transmitter. The ultrasonic transmitter uses a swept frequency signal as a pulse function, converting the swept frequency signal into an ultrasonic signal before transmitting it to the microphones. The initial frequency of the swept frequency signal is -1.5kHz, the termination frequency is 1.5kHz, the sampling frequency is 48kHz, and the duration of the swept frequency signal is 5ms. The ultrasonic baseband signal is generated by periodically repeating the swept frequency signal at 5ms intervals. The modulation frequency is... The ultrasonic baseband signal is modulated to the ultrasonic frequency band at kHz, and the ultrasonic wave is emitted using a stylus, while an infrared signal is emitted as an infrared synchronization signal; four microphones sample the ultrasonic signal at a sampling frequency of 48kHz; and an infrared receiver samples the infrared synchronization signal at a sampling frequency of 48kHz.

[0072] A touch positioning method, comprising:

[0073] First, the stylus, which includes an ultrasonic transmitter and an infrared transmitter, synchronously transmits ultrasonic signals and infrared synchronization signals to the display screen at a preset frequency.

[0074] Specifically, the ultrasonic transmitter in the signal transmitting module uses a swept frequency signal as the ultrasonic pulse signal, and then converts the swept frequency signal into an ultrasonic signal before transmitting it to the microphone of the signal receiving module. The signal conversion includes the following steps:

[0075] S1.1 The mathematical expression for the pulse function of the swept frequency signal is as follows:

[0076]

[0077] in, The pulse duration is represented by f1, which represents half the pulse spectral width, and t represents time. Represents the imaginary unit

[0078] The impulse function has a very strong autocorrelation property, and its mathematical expression is as follows:

[0079]

[0080] in This represents the convolution operation. pulse function The conjugate inverse sequence;

[0081] Figure 4 (I) is The waveform of the signal shows that the signal has a very high amplitude near the peak time, while the amplitude of the signal is almost 0 at other times.

[0082] Figure 4 Figure (II) demonstrates that after adding Gaussian white noise to a pulse signal, the signal-to-noise ratio is 0 dB. The waveform of the signal after filtering by the matched filter shows that the signal near the peak moment still has a high amplitude, that is, a high signal-to-noise ratio. Using the above pulse signal can ensure that the signal near the peak moment still has a very high signal-to-noise ratio even under strong noise.

[0083] S1.2, the pulse function by To obtain the ultrasound baseband signal through periodic repetition, the mathematical expression for the ultrasound baseband signal is as follows:

[0084]

[0085] Where m takes values ​​in the range [1, +inf]; g(t-mT) represents delaying the signal g(t) by m T time intervals; s(t) is the continuous repetition of g(t);

[0086] If T = 25ms, and g(t) is transmitted 100 times to obtain a signal s(t) of 2.5s, then the range of m is 1~100. Then s(t) is equal to the sum of g(tT), g(t-2T), g(t-3T), …, g(t-100T), and m represents which g(t) signal is repeatedly transmitted.

[0087] S1.3. Take the real and imaginary parts of the ultrasonic baseband signal respectively, and compare the real part signal with... Multiplication, imaginary part signal and Multiply,

[0088] Finally, the two multiplied signals are added together to obtain the final ultrasonic signal. , ultrasonic signal The mathematical expression is:

[0089]

[0090] in, The modulation frequency; This represents the real part of the ultrasonic baseband signal. Represents the imaginary part of the ultrasound baseband signal;

[0091] Next, the display clock synchronously receives the ultrasonic signal and the infrared synchronization signal, that is, the clocks of the four microphones and the infrared receiver are synchronized and can work simultaneously. The four microphones are used to receive the ultrasonic signal, and the infrared receiver is used to receive the infrared synchronization signal. Then the ultrasonic signal is demodulated and filtered to obtain an ultrasonic complex signal containing the amplitude and phase information of the ultrasonic signal.

[0092] Specifically, ultrasonic signal demodulation and filtering includes the following steps:

[0093] S2.1, four microphones at sampling frequency Ultrasonic signals are obtained by sampling ultrasonic signals. , Indicates the microphone number. ;

[0094] S2.2, Ultrasonic signal respectively with and Multiplying them yields two signals. and ;

[0095] S2.3, the pulse function conjugate inverse sequence As a matched filter, respectively with the signal and Convolution is performed to obtain the signal and ;

[0096] S2.4 Obtain the ultrasonic complex signal according to the formula. ;

[0097] It is a complex signal, which contains not only the amplitude information of the received ultrasonic signal but also the phase information of the received ultrasonic signal.

[0098] The infrared receiver samples the infrared synchronization signal at a sampling frequency of 48kHz to obtain the infrared synchronization digital signal. By calculating the infrared synchronization digital signal and ultrasonic complex signals The peak value is taken as the modulus to obtain the time difference between the two signal peaks. ;

[0099] in Represents ultrasonic complex signals The time corresponding to the peak value after modulo;

[0100] Indicates infrared synchronization digital signal The time corresponding to the peak;

[0101] This indicates the time difference between the arrival of the ultrasonic signal and the infrared synchronization signal at the signal receiving module;

[0102] Considering that the infrared synchronization signal propagates at the speed of light, its transmission time can be approximated as 0. This can be represented as an ultrasonic signal traveling from the stylus to the microphone. Transmission time;

[0103] Finally, the distance from the stylus to the display screen is obtained based on the ultrasonic complex signal and the infrared synchronization signal, and the positioning coordinates of the stylus are determined.

[0104] Specifically, according to the formula To obtain the distance from the stylus to the display screen ,

[0105] in, Indicating from stylus to microphone An ultrasonic signal passes through n wavelengths. ; parameters The introduction of is due to There is an error, therefore, an error is introduced. expand Scope;

[0106] This indicates that the ultrasonic signal has reached the microphone. Phase of time, ;

[0107] Indicates modulation frequency The corresponding wavelength;

[0108] like: hour, , Acquire ultrasonic complex signals The phase corresponding to the peak value;

[0109] Indicates that the stylus has reached the microphone. The estimated transmission distance, i.e. ; The speed of sound propagation; if using The distance from the stylus to the display screen, but limited by the sampling frequency. , The estimated value The minimum precision is Take c = 340 m / s, ,but The accuracy is 7mm, but because ultrasonic signals introduce noise when passing through the air, it can cause... The peak time will fluctuate, which will further reduce [the data]. The measurement accuracy.

[0110] The above will and Substitute into the formula From which can be obtained Its measurement accuracy is Phase error express The phase error, when the phase error When the temperature is below 10 degrees Celsius, The measurement accuracy is 0.4mm, compared to With an accuracy of 7mm, the above formula significantly improves the accuracy of distance estimation.

[0111] Furthermore, in practice, the center frequency and modulation frequency of the ultrasonic signal from the signal receiving module... The presence of a frequency offset introduces a phase shift in the received signal that increases linearly with time. This phase shift affects the range. The calculation will be affected by the phase shift, therefore the distance calculation can no longer be used. Coordinate positioning is used for stylus stylus. However, the distance difference between the stylus and each microphone is not affected by frequency shift. Therefore, this invention uses distance difference estimation for coordinate positioning.

[0112] Determining the stylus's positioning coordinates involves the following steps:

[0113] S3.1. Obtain the estimated distance difference between the stylus and each microphone according to the formula:

[0114]

[0115] Indicates stylus to microphone With microphone Distance difference estimate; through This will cancel out the phase shift caused by the frequency shift; It can be used for coordinate positioning with a stylus; similarly The measurement accuracy is When phase error When the temperature is below 10 degrees Celsius, The measurement accuracy is within 0.4mm;

[0116] S3.2, i, j, k all represent microphone numbers, and the three numbers i, j, k cannot be the same at the same time;

[0117] Then assume the spatial coordinates of the stylus are Select three microphones, i.e., microphones Spatial coordinates are ,microphone Spatial coordinates are ,microphone Spatial coordinates are Substituting into formula (4), we get:

[0118]

[0119]

[0120] Simplifying formulas (5) and (6) yields:

[0121]

[0122]

[0123]

[0124] in, ;

[0125] ;

[0126] By permuting the four microphones using the formulas (i, k, j), we can obtain four sets of formulas (8) and (9). Combining these four sets of formulas, we get A as follows: The matrix, for ;

[0127] S3.3, Using the least squares method, we obtain:

[0128]

[0129] because The accuracy can reach within 0.4mm, and the coordinate accuracy obtained by the above formula can reach within 1mm;

[0130] S3.4 Optimal coordinate selection is performed on the obtained stylus positioning coordinates, including:

[0131] Due to the distance between the stylus and the microphone There will be three estimates, corresponding to... ,

[0132] The four microphones will thus obtain 3^4 = 81 distance combinations. Substituting these 81 distance combinations into formulas (5)-(10), we can obtain 81 positioning coordinates for the stylus. Then, according to the formula:

[0133]

[0134]

[0135] Only one of the 81 positioning coordinates is the most accurate. Therefore, after substituting the 81 positioning coordinates into formulas (11) and (12), the most accurate coordinate is selected. The coordinate with the smallest value is used as the final spatial coordinate of the stylus;

[0136] in, This indicates that the ultrasonic signal has reached the microphone. Phase of time;

[0137] It is an intermediate variable representing the phase difference from the estimated ultrasonic transmitter coordinates to microphone i and microphone j;

[0138] It is the final error calculation function.

[0139] This invention uses a swept frequency signal as the ultrasonic transmission signal, and utilizes the autocorrelation characteristics of the swept frequency signal to improve the signal-to-noise ratio of the signal received by the display screen and reduce sampling point errors. At the same time, it measures the phase information of the signals received by the four microphones, and introduces phase information in the process of locating the touch point coordinates, reducing the impact of sampling point errors. In addition, the touch point coordinates are calculated by the distance difference between the touch point and each microphone, avoiding the impact of phase shift caused by frequency shift on positioning accuracy, and improving the coordinate positioning accuracy of ultrasonic touch technology to 1mm.

[0140] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0141] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A touch positioning method, characterized in that: A touch-screen positioning system includes a transmitter and a receiver. The transmitter includes a signal transmitting module, and the receiver includes a signal receiving module. The receiver also includes a positioning module connected to the signal receiving module. The signal transmitting module is used to simultaneously transmit ultrasonic signals and infrared synchronization signals; The signal receiving module is used to obtain an infrared synchronous digital signal and an ultrasonic complex signal containing amplitude and phase information of the ultrasonic signal based on the received signal, and then send the ultrasonic complex signal and the infrared synchronous digital signal to the positioning module. The positioning module is used to obtain the distance from the transmitter to the signal receiving module based on the received signal, and then determine the positioning coordinates of the transmitter based on the obtained distance information; The method includes: The transmitter synchronously transmits ultrasonic signals and infrared synchronization signals to the receiver at a preset frequency. The ultrasonic signal is demodulated and filtered to obtain an ultrasonic complex signal containing the amplitude and phase information of the ultrasonic signal. The distance from the transmitter to the receiver is obtained based on the ultrasonic complex signal and the infrared synchronization signal, and the positioning coordinates of the transmitter are determined. The transmitting end uses a stylus, and the receiving end uses a display screen; the signal transmitting module includes an ultrasonic transmitter and an infrared transmitter; the signal receiving module includes a microphone and an infrared receiver, the microphone is provided with four microphones, the four electrically connected microphones receive the ultrasonic signals emitted by the ultrasonic transmitter, and the infrared receiver receives the infrared synchronization signals emitted by the infrared transmitter; Determining the positioning coordinates of the stylus includes obtaining an estimated distance difference between the stylus and each microphone. The estimation of the distance difference between the stylus and each microphone is obtained by introducing the phase difference when the ultrasonic signal reaches each microphone to cancel out the phase shift caused by the frequency shift.

2. The touch positioning method according to claim 1, characterized in that: The ultrasonic transmitter converts the swept frequency signal into an ultrasonic signal and transmits it to the microphone; the initial frequency of the swept frequency signal is -1.5kHz, the termination frequency is 1.5kHz, the sampling frequency is 48kHz, and the duration of the swept frequency signal is 5ms.

3. The touch positioning method according to claim 1, characterized in that: The ultrasonic transmitter in the signal transmitting module converts the swept frequency signal into an ultrasonic signal and then transmits it to the microphone of the signal receiving module. The signal conversion includes the following steps: S1.1 The mathematical expression for the pulse function of the swept frequency signal is as follows: ； in, The pulse duration is represented by f1, which represents half the pulse spectral width, and t represents time. Represents the imaginary unit; S1.2, the pulse function by To obtain the ultrasound baseband signal through periodic repetition, the mathematical expression for the ultrasound baseband signal is as follows: ； Where m takes values ​​in the range [1, +inf]; S1.

3. Take the real and imaginary parts of the ultrasonic baseband signal respectively, and compare the real part signal with... Multiplication, imaginary part signal and Multiply, Finally, the two multiplied signals are added together to obtain the final ultrasonic signal. , ultrasonic signal The mathematical expression is: ； in, The modulation frequency; This represents the real part of the ultrasonic baseband signal. This represents the imaginary part of the ultrasound baseband signal.

4. The touch positioning method according to claim 3, characterized in that: Ultrasonic signal demodulation and filtering includes the following steps: S2.1, the four microphones at a sampling frequency Ultrasonic signals are obtained by sampling ultrasonic signals. , Indicates the microphone number. ; S2.2, Ultrasonic signal respectively with and Multiplying them yields two signals. and ; S2.3, the pulse function conjugate inverse sequence As a matched filter, respectively with the signal and Convolution is performed to obtain the signal and ; S2.4 Obtain the ultrasonic complex signal according to the formula. .

5. A touch positioning method according to claim 4, characterized in that: The infrared receiver samples the infrared synchronization signal at a sampling frequency of 48kHz to obtain the infrared synchronization digital signal. By calculating the infrared synchronization digital signal and ultrasonic complex signals The peak value is taken as the modulus to obtain the time difference between the two signal peaks. ; in Represents ultrasonic complex signals The time corresponding to the peak value after modulo; Indicates infrared synchronization digital signal The time corresponding to the peak; This indicates the time difference between the arrival of the ultrasonic signal and the infrared synchronization signal at the signal receiving module.

6. The touch positioning method according to claim 5, characterized in that: According to the formula The distance from the stylus to the display screen is obtained. , in, Indicating everything from stylus to microphone An ultrasonic signal passes through n wavelengths. ; As a parameter; This indicates that the ultrasonic signal has reached the microphone. Phase of time, ; Indicates modulation frequency The corresponding wavelength; Indicates that the stylus has reached the microphone. The estimated transmission distance, i.e. ; The speed at which sound travels.

7. The touch positioning method according to claim 6, characterized in that: Determining the positioning coordinates of the stylus includes the following steps: S3.1 Obtain the estimated distance difference between the stylus and each microphone according to the formula: ； This indicates the stylus to microphone connection. With microphone Distance difference estimate; through This will cancel out the phase shift caused by the frequency shift; S3.2, Assume the spatial coordinates of the stylus are... Select the three microphones labeled i, j, and k. Spatial coordinates are ,microphone Spatial coordinates are ,microphone Spatial coordinates are Substituting into formula (4), we get: ； ； Simplifying formulas (5) and (6) yields: ； ； ； in, ; ； A is The matrix, for ; S3.3, Using the least squares method, we obtain: 。 8. The touch positioning method according to claim 7, characterized in that: Optimal coordinate selection is performed on the obtained stylus positioning coordinates, including: The four microphones obtain 3^4 = 81 distance combinations, and the stylus is positioned using these 81 distance combinations. Then, according to the formula: ； ； After substituting the 81 positioning coordinates into formulas (11) and (12), select The coordinate with the smallest value is used as the final positioning coordinate of the stylus; in, This indicates that the ultrasonic signal has reached the microphone. Phase of time; It is an intermediate variable representing the phase difference from the estimated ultrasonic transmitter coordinates to microphone i and to microphone j; It is the final error calculation function.

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