CN107704788B - A Calligraphy Copying Method Based on RF Technology - Google Patents

Abstract

The invention discloses a calligraphy copying method based on an RF technology, which comprises the steps of setting an RFID tag on a writing brush, deploying antennas on three dimensions to receive RSS and phase information of a pen moving process, dividing the writing process according to strokes, extracting key characteristics influencing calligraphy, and calculating a calligraphy copy of each stroke; the difference between the learner and the calligrapher is found by utilizing the calligraphy copy, so that the learner is guided to improve.

Description

A Calligraphy Copying Method Based on RF Technology

technical field

The invention relates to the technical field of indoor positioning, in particular to a calligraphy copying method based on RF technology.

Background technique

Brush calligraphy is a method of writing Chinese characters and a visual art, which is the essence of traditional Chinese culture. In recent years, with people's attention to Chinese traditional culture, the art of calligraphy, as the best way to learn to appreciate Chinese culture, has also been widely followed by learners. The mastery of calligraphy skills is indispensable to copying and comparing the works of calligraphy masters, accumulating years of practice, and guiding the correct essentials. Some existing methods are based on pixel points to track the differences between the works of learners and calligraphers, but in brush calligraphy, the three essential elements are the way of the brush, the structure of the frame and the characteristics of the strokes. How to improve to reduce the difference, it still requires learners to spend a lot of time and energy to practice and figure out, in order to improve.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for copying calligraphy based on RF technology, which can redraw the writing process of calligraphy with millimeter-level precision, and provides a traditional method for the copying practice of calligraphy learners Guidance for precise positioning that cannot be achieved.

For realizing above-mentioned task, the present invention adopts following technical solution:

A calligraphy copying method based on RF technology, comprising the following steps:

其中，a表示天线的标号，a＝1,2,3，j表示RFID标签的标号，j＝1,2，i表示信道的标号，i＝1,2,...,N，N表示信道的个数,t表示笔移动过程中的时刻；Step 1, write calligraphy with a pen, and use the antenna to obtain the RSS value S _{a, j, i} (t) and phase information of the tag set on the pen holder of the pen during the movement of the pen.

Among them, a represents the label of the antenna, a=1, 2, 3, j represents the label of the RFID tag, j=1, 2, i represents the label of the channel, i=1, 2,..., N, N represents the channel The number of , t represents the moment during the movement of the pen;

进行预处理得到预处理后的相位信息

预处理包括相移校准、噪声抑制和多径处理，预处理后的相位信息

对应的RSS值为S_a,j,m(t)，其中，m表示干净信道的标号， m＝1,2,...,M,M表示干净信道的个数；Step 2, for phase information

Perform preprocessing to obtain the preprocessed phase information

Preprocessing includes phase shift calibration, noise suppression and multipath processing, and the preprocessed phase information

The corresponding RSS value is Sa _,j,m (t), where m represents the label of the clean channel, m=1,2,...,M,M represents the number of clean channels;

对RFID标签的相位信息

进行相移校准的过程，就是在相位信息

中去除相移

Among them, the method used for phase shift calibration is as follows: in the same environment as writing calligraphy, the real distance between the tag and the antenna is measured; according to the real distance between the tag and the antenna, the relationship between distance and phase is used to obtain The real phase value of the tag; obtain the measured phase value of the tag; find the difference between the real phase value of the tag and the measured phase value of the tag, which is the phase shift that needs to be removed

Phase information for RFID tags

The process of performing phase shift calibration is to

remove phase shift

中选出属于干净信道对应的相位信息，即为经过多径处理后的相位信息

干净信道的确定方法为在撰写书法的环境中，RFID阅读器跳过不同频率的信道接收数据，在每个信道获取标签的相位信息序列，求每个信道中所有相位信息的平均值，即相位均值；以信道标号为横坐标，以相位均值为纵坐标，所有相位均值连接形成曲线，通过观察曲线的走向，保留呈线性关系的相位均值，这些相位均值对应的信道即为干净信道；Among them, the method used in multipath processing is as follows:

Select the phase information corresponding to the clean channel, that is, the phase information after multipath processing

The method for determining the clean channel is that in the writing environment, the RFID reader skips the channels of different frequencies to receive data, obtains the phase information sequence of the tag in each channel, and obtains the average value of all phase information in each channel, that is, the phase. Mean value; take the channel label as the abscissa and the phase mean as the ordinate, all the phase mean values are connected to form a curve, and by observing the trend of the curve, the phase mean values in a linear relationship are retained, and the channels corresponding to these phase mean values are clean channels;

和RSS值S_a,j,m(t)，求任一时刻t, 信道m对应的天线a与标签j的距离d_a,j,m(t)；采用的公式如下：Step 3, according to the phase information

and the RSS value S _a,j,m (t), find the distance d _a,j,m (t) between the antenna a and the tag j corresponding to the channel m at any time t; the formula used is as follows:

Among them, f _m represents the frequency of the mth clean channel, and c represents the speed of light;

Among them, k is an integer. In the environment of writing calligraphy, set up a tag and an antenna, change the distance between the tag and the antenna, and use the RFID reader to obtain the phase information and RSS information of the tag; the RSS value is obtained with the difference between the tag and the antenna. The graph of the change of the distance between the tags; when the distance between the tag and the antenna is in the range of (0, λ/2), k=1, when the distance between the tag and the antenna increases λ/2, the value of k increases by 1 , according to each distance range between the tag and the antenna, the range of the RSS information can be determined; according to the RSS value, the range to which it belongs can be determined, and the value of k can be determined; where λ represents the wavelength;

Step 4: Screen all the distance values obtained in Step 3 according to the linear relationship characteristics of the phase information received by the adjacent frequency channels and the relationship of the side length of the triangle; for the screened distance values, calculate any time t Next, the average value of the distance between the a-th antenna and the j-th tag corresponding to all channels, and the average value obtained is taken as the distance value between the a-th antenna and the j-th tag at this moment da _,j (t) ;

Step 5, utilizes the distance value d _{a, j} (t) adopts the trigonometric function method to calculate in the pen movement process, under any moment t, the vertical height h (t) of the pen holder midpoint position; According to the vertical height h of the pen holder midpoint position (t) variation law between strokes, the moments in the writing process are segmented, and each segment corresponds to a stroke;

The distance value d _a,j (t) is used to calculate the vertical height h(t) of the midpoint of the pen at any time t during the movement of the pen by using the trigonometric method. The formula used is as follows:

其中，α1表示天线A1与标签1的连线与垂直方向的夹角；α2表示天线A1与标签2 的连线与垂直方向的夹角；

Among them, α1 represents the angle between the connection line between the antenna A1 and the tag 1 and the vertical direction; α2 represents the angle between the connection line between the antenna A1 and the tag 2 and the vertical direction;

Wherein, h ₁ (t) represents the vertical height of the tag 1; h ₂ (t) represents the vertical height of the tag 2; d ₁₁ represents the distance between the antenna A1 and the tag 1; d ₂₁ represents the distance between the antenna A2 and the tag 1 distance; d ₁₂ represents the distance between the antenna A1 and the tag 2; d ₂₂ represents the distance between the antenna A2 and the tag 2; a represents the distance between the antenna A1 and the antenna A2;

Wherein, the strokes in the writing process are segmented according to the change of the vertical height h(t) of the midpoint position of the pen; the adopted method is as follows: set the threshold h _p + η as the sign of the end of the stroke, if h(t _e ) is greater than the threshold , indicating that the pen is lifted off the writing plane, a stroke is completed, and the moment t _e is the moment when a stroke ends; a threshold h _p -n is set as the sign of the beginning of a stroke, if h(t _s ) is less than the threshold, it indicates that the pen is in writing Plane, channel strokes begin to form, time t _e is the moment when a stroke ends; h _p is the distance from the midpoint of the pen to the tip of the pen; η is a constant; according to time _te and time t _s , the time in the writing process is segmented , each paragraph corresponds to a stroke;

Step 6, for each moment in each stroke, seek its corresponding multiple key characteristic quantities, and multiple key characteristic quantities form the template feature matrix corresponding to this stroke; key characteristic quantities include elevation angle, pen tip length variation, pen tip movement speed and nib position;

b表示标签1与标签2之间的距离；Among them, the formula used to calculate the elevation angle is as follows:

b represents the distance between label 1 and label 2;

L是笔杆上标签1到笔尖的距离；Among them, the formula used to calculate the change in the length of the pen tip is as follows:

L is the distance from label 1 on the barrel to the tip of the pen;

Among them, the formula used to calculate the moving speed of the pen tip is as follows: the distance from the antenna A1 to the pen tip T0:

Δt表示t+1时刻到t时刻的时间间隔；T1' and T2' are the projections of the labels T1 and T2 on the barrel of the pen, respectively; d _11' is the distance from the antenna A1 to T1'; d _12' is the distance from the antenna A1 to T2'; the pen tip moving speed:

Δt represents the time interval from time t+1 to time t;

Among them, to calculate the pen tip position T0(x(t), y(t)), the formula used is as follows:

x(t)=d _11' (t) sinβ ₁ +Lcosθ(t)sin(β ₂ +β ₁ );

y(t)=d _11' (t)cosβ ₁ +Lcosθ(t)cos(β ₂ +β ₁ ); β ₁ represents the angle between A1A3 and A1T1', β ₂ represents A1T1' and T1'T2' the angle between

The four key feature quantities at all the above moments (t,...t+t'...t+s) constitute the feature matrix of the stroke, namely:

；

;

Step 7: Repeat steps 1 to 6 to obtain the copying feature matrix corresponding to each stroke, compare it with the template feature matrix, and use the difference result to guide the gap between calligraphy learners and calligraphers.

Specifically, the noise suppression in step 2 adopts the following method:

Given a threshold, if the phase deviation between the phase values of two consecutive moments in the phase information exceeds the set threshold, the adjusted phase value is equal to the previous phase value; then the Kalman filter method is used to smooth the phase information.

Compared with the prior art, the present invention has the following technical effects:

By setting RFID tags on the pen, deploying antennas in three dimensions to receive the RSS and phase information of the pen movement process, dividing the writing process by strokes, extracting the key features that affect calligraphy, and calculating the calligraphy copy of each stroke; use the calligraphy copy to find The difference between the learner and the calligrapher can guide the learner to improve and improve. The invention can estimate the tag-antenna distance at the millimeter level, so as to realize the redrawing of the writing process of calligraphy.

Description of drawings

Figure 1 is the location map of three different experimental environments;

Figure 2 is a detailed deployment diagram of the system in an office environment;

Fig. 3 is the result graph of the phase information after phase shift calibration and noise suppression; wherein, (a) represents the result graph after phase shift calibration, and (b) represents the result graph of noise suppression;

Figure 4 is a graph of phase data received in a hall environment for 16 different frequency channels;

Figure 5 is a graph of phase data received by 16 different frequency channels in a library environment;

Figure 6 shows the relationship between the RSS value and the antenna-tag distance.

FIG. 7 is a schematic diagram of the height change of the brush and the division of the strokes during the writing process.

Fig. 8 is the geometrical relation diagram that obtains the brush elevation angle;

Fig. 9 is a schematic diagram of changing the length of the brush tip;

Fig. 10 is a geometrical relationship diagram when estimating the position of the pen tip;

Figure 11 is a coordinate diagram of the position of the pen tip;

12 is a schematic diagram of screening the distances between antennas A1 and A2 and tags 1 and 2 by using the relationship of the side lengths of the triangles;

Figure 13 is a tracking effect diagram for different calligraphy levels;

FIG. 14 is a schematic diagram of screening the distance between the antenna A3 and the tags 1 and 2 with the side length relationship of the triangle;

Fig. 15 is a schematic diagram of calculation of the distance from antenna A1 to T1', the distance from antenna A1 to T2', and the distance from antenna A2 to T1';

The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

Detailed ways

Referring to Fig. 1, the method for copying calligraphy based on RF technology of the present invention, the adopted system includes an RFID reader, two Alien tags and three directional antennas with a gain of 5dBi, wherein the two Alien tags are stuck on the upper and lower ends of the pen barrel , the distance b=16cm, the three directional antennas are connected to the reader, the antenna 1 is located at the origin of the coordinates, the antenna 2 is located on the Z axis, the antenna 3 is located on the Y axis, and the distance from antenna 1 to antenna 2 is equal to the distance from antenna 1 to antenna 3 Distance a, a=40cm. Deploy the system on the table to form a monitoring area with a size of 50cm×50cm. The writing area of calligraphy is 40cm×40cm of rice paper. The pen used can be an ordinary brush or a pen with a soft tip. In this embodiment, the sampling brush , the total length is 29.8cm, and the length of the pen head is 5.5cm. When the pen enters the monitoring area and just vertically touches the paper surface, the height of the midpoint of the pen holder from the paper surface is h=16cm; during the writing process, the maximum change in the length of the pen tip is about is 4cm. Move the pen at a speed of 1-2cm/s.

Among them, the RFID reader is compatible with the EPC Gen2 standard and works in China's legal UHF frequency band, that is, the range of 920.625MHz to 924.375MHz; in the process of data collection, the reader jumps 16 different frequency channels, and the frequency interval between adjacent channels is 500KHz.

The calligraphy copying method based on RF technology of the present invention comprises the following steps:

其中，a表示天线的标号，a＝1,2,3，j表示RFID标签的标号，j＝1,2，i表示信道的标号，i＝1,2,...,N，N表示信道的个数，此实施例中,N＝16,t表示毛笔移动过程中的时刻。Step 1, calligraphy uses a brush to write calligraphy. During the movement of the brush, multiple channels of the RFID reader obtain the RSS value S _a,j of the RFID tag at each moment during the movement of the brush through three antennas (A1, A2 and A3). _{, i} (t) and phase information

Among them, a represents the label of the antenna, a=1, 2, 3, j represents the label of the RFID tag, j=1, 2, i represents the label of the channel, i=1, 2,..., N, N represents the channel The number of , in this embodiment, N=16, t represents the moment during the movement of the brush.

进行预处理，得到预处理后的相位信息

其中，m表示干净信道的标号， m＝1,2,...,M,M表示干净信道的个数；预处理包括相移校准、噪声抑制和多径处理。Step 2, the phase information of the RFID tag obtained in step 1

Perform preprocessing to obtain the preprocessed phase information

Among them, m represents the label of the clean channel, m=1,2,...,M,M represents the number of clean channels; the preprocessing includes phase shift calibration, noise suppression and multipath processing.

Among them, the method used for phase shift calibration is:

Place a tag and an antenna in the environment where the calligrapher writes the calligraphy, place the tag close to the antenna to reduce the number of multipaths; measure the true distance between the tag and the antenna with a laser meter; measure the tag by The real distance between the antenna and the antenna, according to the relationship between the real distance and the real phase, as shown in formula (1), the real phase value of the tag can be calculated. The RFID reader can obtain the measured phase value of the tag through the antenna. Find the difference between the real phase value and the phase value of the tag obtained by the RFID reader, which is the phase shift that needs to be removed

进行相移校准的过程，就是在相位信息

中去除相移

Phase information for RFID tags

The process of performing phase shift calibration is to

remove phase shift

The methods used for noise suppression are:

针对同一信道，同一天线、同一标签下的相位信息，给定阈值＝2,如果相位信息中两个连续时刻的相位值之间的相位偏差超过设定阈值，则调整后一相位值与前一相位值相等；再采用卡尔曼滤波方法对相位信息进行平滑。After removing the constant phase shift, a large peak in the phase information is still observed due to random phase noise

For the phase information of the same channel, the same antenna, and the same label, the given threshold=2, if the phase deviation between the phase values of two consecutive moments in the phase information exceeds the set threshold, the latter phase value is adjusted to the previous one. The phase values are equal; then the Kalman filter method is used to smooth the phase information.

The multipath process is implemented based on a multi-channel approach for the following reasons: (1) Although commercial RFID readers use directional antennas for transmission, the number of multipaths is much smaller compared to Wi-Fi; (2) Since the written tracking area is smaller, the tag-antenna distance is also smaller. Therefore the direct path signal is strongly dominant, reducing the effect of multipath; (3) commercial RFID readers can skip channels of different frequencies during normal operation, by using a considerable number of available channels (16), certain Individual channels (dominated by direct path signals) with little interference from multipath can be identified. If there is no multipath interference, given a tag location, the center frequency difference between the two channels is known to be Δf, and their phase difference Δφ can be expressed as:

Among them, c is the speed of light, Δδ is the phase noise, mod is the modulo function, and the phase values of different channels are linearly related. Once which channel is dominated by multipath signals, the linear relationship with other channels is broken. However, due to the use of directional antennas and the small scope of system deployment, this linear relationship still exists for most of the channels, which we refer to as "clean channels". That is, only the direct path signal propagates in these clean channels, and the corresponding phase readings can be used for distance estimation.

The method for determining the clean channel is that, in the same environment as this embodiment, one antenna and one RFID tag are set up, and the RFID reader skips 16 channels of different frequencies to receive data, and obtains the data of the tag in each channel. Phase information sequence, find the average value of all phase information in each channel, that is, the phase mean value; take the channel label as the abscissa and the phase mean as the ordinate, all phase mean values are connected to form a curve, and by observing the trend of the curve, the retention is linear. The phase averages of the relationship, the channels corresponding to these phase averages are clean channels.

中选出属于干净信道对应的相位信息，即为经过多径处理后的相位信息

多径处理后的相位信息

对应的RSS值为S_a,j,m(t)；The realization method of multipath processing is: in the phase information

Select the phase information corresponding to the clean channel, that is, the phase information after multipath processing

Phase information after multipath processing

The corresponding RSS value is Sa _,j,m (t);

以及与相位信息

对应的RSS值S_a,j,m(t)，求在时刻t，信道m对应的天线a与标签 j的距离d_a,j,m(t)；采用的公式如下：Step 3, according to the preprocessed phase information

and with phase information

The corresponding RSS value S _a,j,m (t), find the distance d _a,j,m (t) between the antenna a and the tag j corresponding to the channel m at time t; the formula used is as follows:

Among them, f _m represents the frequency of the mth clean channel, c represents the speed of light; k is an integer;

The method of determining k is as follows:

In the environment of this embodiment, a tag and an antenna are set, the distance between the tag and the antenna is changed, and the RFID reader is used to obtain the phase information and RSS information of the tag; the RSS value obtained varies with the distance between the tag and the antenna. Graph; experiments show that the signal strength value decreases with increasing antenna-to-tag distance. When the distance changes by λ/2, where λ represents the wavelength, the corresponding phase is rotated by one 2π period but the reading does not change, but the RSS value change will be easily detected. We set the corresponding RSS value variation range for all possible phase rotation numbers k, as shown in Figure 6, the corresponding relationship between RSS value and distance; when the distance range between the tag and the antenna is (0, λ/2), k=1; when the distance range between the tag and the antenna is (λ/2, λ), k=2; through the above relationship, the value of k can be obtained when the RSS value is in a certain range. In this embodiment, the value of k may be 1 or 2.

In step four, through different frequency channels, multiple estimates of distance are obtained, these estimates are theoretically similar to each other, so we exclude the values that do not meet the similarity relationship. Then, according to the geometrical relationship restriction between the positions of the antenna and the tag, the distance d _{a, j, m} (t) between all the antennas and tags obtained in step 3 is screened by using the relationship of the side length of the triangle, and the filtered The distance between the antenna and the tag; for the distance between the filtered antenna and the tag, calculate the average value of the distance between the a-th antenna and the j-th tag corresponding to all channels at a certain time t, and take the average value obtained as the time. The distance value da _,j (t) between the a-th antenna and the j-th label.

The specific filtering methods are as follows:

Referring to Figure 12, using the side length relationship of the triangle, at time t1, the distance d _2,1,i (t1) between the antenna A2 corresponding to the channel i and the tag T1, according to the triangles A2, T1 and T2, a set of relationships is obtained Mode:

Fixed d _2,1,i (t1), d _2,2,m (t1) represents any one of the distance values between the antenna A2 and the label T2 corresponding to all channels, select d _2,2,m ( t1) Substitute into the above formula for calculation, if more than half of the calculation results of d _2,2,m (t1) satisfy the above formula, keep the d _2,1,i (t1); otherwise, remove d _{2,1, i} (t1), that is, the value is an error value;

For the time t1, the distance d _2,2,i (t1) between the antenna A2 corresponding to the channel i and the label T2, according to the triangles A2, T2 and T2, a set of relational expressions are obtained:

Fixed d _2,2,i (t1), d _1,2,m (t1) represents any one of the distance values between the antenna A1 and the label T2 corresponding to all channels, select d _1,2,m ( t1) Substitute into the above formula for calculation, if more than half of the calculation results of d _1,2,m (t1) satisfy the above formula, keep the d _2,2,i (t1); otherwise, remove d _{2,2, i} (t1), that is, the value is an error value;

For the time t1, the distance d _1,2,i (t1) between the antenna A1 corresponding to the channel i and the label T2, according to the triangles A1, T1 and T2, a set of relational expressions are obtained:

Fixed d _1,2,i (t1), d _1,1,m (t1) represents any one of the distance values between the antenna A1 and the label T1 corresponding to all channels, select d _1,1,m ( t1) Substitute into the above formula for calculation, if more than half of the calculation results of d _1,1,m (t1) satisfy the above formula, keep the d _1,2,i (t1); otherwise, remove d _{1,2, i} (t1), that is, the value is an error value;

For the time t1, the distance d _1,1,i (t1) between the antenna A1 corresponding to the channel i and the label T1, according to the triangles A1, A2 and T1, a set of relational expressions are obtained:

Fixed d _1,1,i (t1), d _2,1,m (t1) represents any one of the distance values between the antenna A2 and the tag T1 corresponding to all channels, select d _2,1,m ( t1) Substitute into the above formula for calculation, if more than half of the calculation results of d _2,1,m (t1) satisfy the above formula, keep the d _1,1,i (t1); otherwise, remove d _{1,1, i} (t1), that is, the value is an error value;

Referring to Fig. 14, for the time t1, the distance d _3,1,i (t1) between the antenna A3 corresponding to the channel i and the tag T1, according to the triangles A1, A3 and T1, a set of relational expressions are obtained:

Fixed d _3,1,i (t1), d _1,1,m (t1) represents any one of the distance values between the antenna A2 and the label T1 corresponding to all channels, select d _1,1,m ( t1) Substitute into the above formula for calculation, if more than half of the calculation results of d _1,1,m (t1) satisfy the above formula, keep the d _3,1,i (t1); otherwise, remove d _{3,1, i} (t1), that is, the value is an error value;

Average the distances between all antennas and a tag at a certain moment, and use the average value as the distance value da _,j (t) between the antenna and the tag at that moment.

Step 5: Calculate the vertical height h(t) of the midpoint position of the pen at each moment during the movement of the brush; corresponds to a stroke;

The vertical height of the label 1 on the pen holder at each moment during the movement of the writing brush is h ₁ (t), and the vertical height of the label 2 on the pen holder at each moment during the movement of the writing brush is h ₂ (t);

Among them, α1 represents the angle between the connection line between the antenna A1 and the tag 1 and the vertical direction; α2 represents the angle between the connection line between the antenna A1 and the tag 2 and the vertical direction; d ₁₁ represents the distance between the antenna A1 and the tag 1; d ₂₁ represents the distance between the antenna A2 and the tag 1; d ₁₂ represents the distance between the antenna A1 and the tag 2; d ₂₂ represents the distance between the antenna A2 and the tag 2; a represents the distance between the antenna A1 and the antenna A2.

According to the change of the vertical height h of the brush, the writing process is divided into strokes. Theoretically, the movement of the brush between each stroke in the writing process is related to the height h: h increases when the pen is lifted, remains basically unchanged when the pen is moved, and decreases when the pen is down. Because when writing with a brush, due to the softness of the nib, the range of raising and dropping the pen is relatively large, and the length of the nib may change by 2-3cm, so the change range of h is obvious, which can be detected and used to segment strokes.

Referring to Figure 7, the movement of the brush between each stroke in the writing process is related to the height h: h increases when the pen is lifted, remains basically unchanged when the pen is moved, and decreases when the pen is down. As shown in Figure 7, the timestamp te of the end of each _stroke and the timestamp t _s of the beginning of the stroke are found, and the phase sequence is divided into small segments at these positions.

Set the threshold h _p +η as the sign of the end of the stroke, if h(t _e ) is greater than the threshold, it indicates that the writing brush is lifted off the writing plane, a stroke is completed, and the moment t _e is the moment when a stroke ends; set the threshold h _p − η is the sign of the beginning of the stroke, if h(t _s ) is less than the threshold, it indicates that the writing brush is on the writing plane, the channel stroke begins to form, and the moment t _e is the moment when a stroke ends; h _p is the distance from the midpoint of the pen barrel to the tip of the pen; η is a constant; set parameter n=5mm in the present embodiment; thus find the time stamp of the end and the beginning of each stroke, segment the phase sequence with the time stamp, and each segment obtained after the division is the writing process of a single stroke .

Step 6: For each moment in each stroke, obtain a plurality of corresponding key feature quantities, and the plurality of key feature quantities form a template feature matrix corresponding to the stroke.

The nib of the brush is different from ordinary pens, its texture is soft, and the nib is dipped in ink for writing, so the writing effect will be greatly affected by the strength and speed of the brush stroke, for example: (1) The different inclination angles of the brush and the degree of depression of the nib cause handwriting Changes in width; (2) The appearance of handwriting written at different speeds by the nib varies greatly; (3) The position and movement direction of the nib determine the spatial layout of each stroke in a word. If the relative position of each stroke is inappropriate, then even if each stroke is beautifully written, the whole character will not look beautiful. Therefore, these feature quantities are quantized.

(1) Elevation angle

The elevation angle is the angle between the brush and the writing plane, which represents the inclination of the brush during writing. We denote the elevation angle as θ, θ∈(0,90°), when θ=90°, the brush is perpendicular to the writing plane. The higher the elevation angle, the smaller the width of the ink blot. The calculation formula of the elevation angle θ(t) at each moment in the stroke is as follows:

(2) Change in pen tip length Δh

因此，只要算出毛笔的垂直高度h，就能算出笔尖长度变化量Δh；The change in the length of the nib indicates the degree of depression of the nib when writing, and is another important indicator of the width of the handwriting. The greater the change in the length of the pen tip, the larger the area where the brush tip touches the writing area, which means the wider the handwriting; when the brush touches the writing area lightly at an elevation angle θ, L is the distance from the label 1 on the pen holder to the pen tip T0, Then, when the pen tip is not pressed down, the vertical distance between the midpoint of the brush and the paper surface is

Therefore, as long as the vertical height h of the brush is calculated, the length change Δh of the pen tip can be calculated;

The formula for calculating Δh(t) at each moment in the stroke is as follows:

Among them, L is the distance from the label 1 on the pen holder to the tip T0;

(3) Pen tip moving speed v

As shown in Figure 10, T1' and T2' are the projections of the labels T1 and T2 on the brush barrel, respectively. When the brush touches the writing area lightly at an elevation angle θ, L is the distance from the label 1 on the pen holder to the pen tip T0, and the distance d ₁₀ (t) from the antenna A1 to the pen tip T0, the calculation formula is as follows:

d _11' is the distance from the antenna A1 to T1'. In triangle A1T1'T2',

Therefore, the distance from the tip T0 to the antenna 1 at time t is expressed as:

Among them, the calculation method of d _11' is as follows: refer to Figure 15, in the triangle A1A2T1, the lengths of the three sides are known, the inverse function can be used to calculate the size of α ₁ , and then d _11' is calculated. In the triangle A2A1T2, the three sides The length of is known, and the inverse function can be used to calculate the size of α ₂ , and then d _12' can be calculated.

Then, the movement speed of the pen tip is calculated as:

Among them, Δt represents the time interval from time t+1 to time t.

(4) Pen tip position T0

Referring to Figure 11, the calculation formula of the pen tip position T0 (x(t), y(t)) at each moment in the stroke is as follows:

x(t)=d _11' (t)sinβ ₁ +Lcosθ(t)sin(β ₂ +β ₁ )

y(t)=d _11' (t)cosβ ₁ +Lcosθ(t)cos(β ₂ +β ₁ ) (15)

Among them, β ₁ represents the angle between A1A3 and A1T1', and β ₂ represents the angle between A1T1' and T1'T2';

The calculation method of β ₁ is as follows: in the triangle A1A3T1', A1A3, A1T1' are known, the solution method of A3T1' is: replace A1 in Figure 15 with A3, in the triangle A3A2T1, the lengths of the three sides are known , the size of the included angle α ₃ between A2A3 and A3T1 can be calculated by the inverse function, d _{31 ′} =d ₃₁ ·sinα ₃ ; the angle β ₁ can be calculated by the inverse function.

The calculation method of β ₂ is as follows: in the triangle A1T1'T2', A1T1', A1T2' are known, the distance between T1' and T2' can be obtained as bcosθ; the angle β ₂ can be calculated by the inverse function.

The four key feature quantities at all the above moments constitute the feature matrix of the stroke, namely:

Wherein, the moment in the stroke is t,...t+t'...t+s.

Step 7, the calligraphy learner writes calligraphy, according to the method of the above-mentioned steps 1 to 6, obtains the copying feature matrix of each stroke of the calligraphy learner, compares it with the feature matrix of the calligraphy expert, and the difference result obtained is used to guide. The learner finds the gap with the calligrapher, improves the copying, and improves the level of calligraphy.

Ask experts and learners to write the same Chinese character "大". The system is then applied to monitor the writing process and extract the feature matrix. By comparing the feature matrices of experts and learners, it is possible to obtain where learners are underperforming. The written track is shown in Figure 13. The learner's trajectory is coarse and incorrect compared to the expert's trajectory. First, the relative positions between different strokes in the learner's calligraphy characters are not correct, which we can improve by correcting the pen tip position T0(x,y) of each stroke according to the difference between the learner and the expert. Second, the strokes are uneven due to the non-smooth writing speed. The learner can imitate the expert's movement speed v to improve. Finally, the stroke width is different, let's take the horizontal stroke "horizontal" as an example. For strokes written by experts, the width is moderate and widens from left to right along the stroke, but the width of the strokes written by the learner is random. Therefore, we can compare the elevation angle θ and the length change Δh of the pen tip between the two works. These differences instruct the learner to reduce the inclination of the brush and reduce the pressure exerted on the writing surface, thereby improving the problem of stroke width.

Claims (2)

1. A calligraphy copying method based on RF technology is characterized by comprising the following steps:

writing calligraphy with a pen, and obtaining calligraphy with an antennaRSS value S of label arranged on pen holder of pen in pen taking moving process_a,j,i(t) and phase information

Wherein, a represents the label of the antenna, a is 1,2,3, j represents the label of the RFID tag, j is 1,2, i represents the label of the channel, i is 1,2, N represents the number of the channels, and t represents the time in the moving process of the pen;

step two, phase information is corrected

Preprocessing the phase information to obtain preprocessed phase information

The preprocessing includes phase shift calibration, noise suppression and multipath processing, and the preprocessed phase information

Corresponding RSS value is S_a,j,m(t), wherein M denotes the number of clean channels, and M is 1, 2.., M denotes the number of clean channels;

the method for phase shift calibration specifically comprises the following steps: measuring the real distance between the tag and the antenna in the same environment as writing calligraphy; according to the real distance between the tag and the antenna, the real phase value of the tag is obtained by using a distance and phase relation; acquiring a measurement phase value of the tag; calculating the difference value between the real phase value of the tag and the measured phase value of the tag, namely the phase shift to be removed

Phase information for RFID tags

The phase shift calibration is performed on the phase information

Removing phase shift

The multipath processing method specifically comprises the following steps: in phase information

Selecting the phase information corresponding to the clean channel, namely the phase information after multipath processing

The method for determining the clean channel comprises the steps that in a calligraphy writing environment, an RFID reader skips channels with different frequencies to receive data, phase information sequences of labels are obtained in each channel, and the average value of all phase information in each channel, namely the phase average value, is solved; taking the channel label as an abscissa and the phase mean value as an ordinate, connecting all the phase mean values to form a curve, and keeping the phase mean values in a linear relation by observing the trend of the curve, wherein the channels corresponding to the phase mean values are clean channels;

step three, according to the phase information

And RSS value S_a,j,m(t) determining the distance d between the tag j and the antenna a corresponding to the channel m at any time t_a,j,m(t); the formula used is as follows:

wherein f is_mThe frequency of the mth clean channel is indicated, c represents the speed of light;

setting a tag and an antenna under the calligraphy writing environment, changing the distance between the tag and the antenna, and acquiring phase information and RSS information of the tag by using an RFID reader; obtaining a curve graph of RSS values changing along with the distance between the tag and the antenna; when the distance between the tag and the antenna is in the range of (0, λ/2), k is 1, when the distance between the tag and the antenna is increased by λ/2, the value of k is increased by 1, and the range section of the RSS information can be determined according to each distance range section between the tag and the antenna; determining the range interval to which the RSS value belongs according to the RSS value, namely determining the value of k; wherein λ represents a wavelength;

step four, screening all the distance values obtained in the step three according to the linear relation characteristics of the phase information received by the adjacent frequency channels and the side length relation of the triangle; calculating the average value of the distances between the a-th antenna and the j-th label corresponding to all channels at any time t according to the screened distance values, and taking the obtained average value as the distance value d between the a-th antenna and the j-th label at the time_a,j(t)；

Step five, utilizing the distance value d_a,j(t) calculating the vertical height h (t) of the midpoint position of the penholder at any time t in the moving process of the pen by adopting a trigonometric function method; segmenting the moment in the writing process according to the change rule of the vertical height h (t) of the midpoint position of the penholder among strokes, wherein each segment corresponds to one stroke;

wherein the distance value d is used_a,j(t) calculating the vertical height h (t) of the midpoint position of the penholder at any time t in the moving process of the pen by adopting a trigonometric function method, wherein the formula is as follows:

α 1 shows the angle between the line connecting antenna A1 and tag 1 and the vertical direction, α 2 shows the angle between the line connecting antenna A1 and tag 2 and the vertical direction;

wherein h is₁(t) represents the vertical height of the label 1; h is₂(t) represents the vertical height of the label 2; d₁₁Represents the distance between antenna a1 and tag 1; d₂₁Shows antennas A2 andthe distance between the tags 1; d₁₂Represents the distance between antenna a1 and tag 2; d₂₂Represents the distance between antenna a2 and tag 2; a represents the distance between antenna a1 and antenna a 2;

wherein, the strokes in the writing process are divided according to the change of the vertical height h (t) of the midpoint position of the penholder; the method adopted is as follows: setting a threshold h_p+ η as the end of stroke marker if h (t)_e) Above the threshold, it indicates that the pen is lifted off the writing surface and a stroke is complete, at time t_eNamely the time when one stroke ends; setting a threshold h_p- η as a marker for the start of a stroke if h (t)_s) Less than the threshold, indicating that the pen is in the writing plane, channel strokes begin to form, at time t_eNamely the time when one stroke ends; h is_pDistance from the middle point of the pen holder to the pen point, η is constant, according to the time t_eAnd time t_sSegmenting the time in the writing process, wherein each segment corresponds to one stroke;

step six, aiming at each moment in each stroke, solving a plurality of corresponding key characteristic quantities, and forming a template characteristic matrix corresponding to the stroke by the plurality of key characteristic quantities; the key characteristic quantity comprises an elevation angle, pen point length change, pen point moving speed and pen point position;

the formula for calculating the elevation angle is as follows:

b represents the distance between tag 1 and tag 2;

wherein, the length change of the pen point is calculated by the following formula:

l is the distance from the label 1 on the penholder to the pen point;

wherein, calculate nib moving speed, the formula of adoption is as follows: distance from antenna a1 to pen tip T0:

t1 'and T2' are projections of labels T1 and T2 on the shaft of the pen, respectively; d_11'Is the distance of antenna a1 to T1'; d_12'Is the distance of antenna a1 to T2'; moving speed of the pen point:

Δ t represents the time interval from time t +1 to time t;

the pen tip positions T0(x (T), y (T)) are calculated by the following formula:

x(t)＝d_11'(t)sinβ₁+Lcosθ(t)sin(β₂+β₁)；

y(t)＝d_11'(t)cosβ₁+Lcosθ(t)cos(β₂+β₁)；β₁represents the angle between A1A3 and A1T1', β₂Represents the included angle between A1T1' and T1' T2 ';

the four key feature quantities at all the above time instants (t,. t + t.. t + s) form a feature matrix of the stroke, that is:

；

and step seven, repeating the method from the step one to the step six to obtain a copy feature matrix corresponding to each stroke, comparing the copy feature matrix with the template feature matrix, and using the obtained difference result to guide the difference between the calligraphy learner and the calligraphy writer.

2. The method for calligraphy copying based on RF technology as claimed in claim 1, wherein the noise suppression in step two is performed by:

a threshold value is given, and if the phase deviation between the phase values of two continuous moments in the phase information exceeds the set threshold value, the subsequent phase value is adjusted to be equal to the previous phase value; and smoothing the phase information by adopting a Kalman filtering method.

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