Method for measuring subdivision angle of rotating shaft of robot servo system

Abstract

The invention relates to a rotating shaft subdivision angle measurement method of a robot servo system, and belongs to the technical field of digital rotating shaft subdivision angle measurement by using an analog-to-digital converter and a sine-cosine encoder. According to the technical scheme, a computer adjusts frequency values between sampling signals of an analog / digital converter and sinusoidal signals output by an encoder to be in a multiple and deviation relation, and a phase discriminator detects the phase difference between the two signals and stores phase difference information and sine and cosine signal sampling values. And according to the phase difference information of the periodic linear change and the sampling unit of the periodic change, the computer rapidly extracts the final sine and cosine signal sampling value of the analog / digital converter and the sampling value of the next moment, digitally corrects the sine and cosine signal value finally output by the encoder, and further solves the subdivision angle. The method is high in measurement precision and simple in circuit structure, and solves the problems that in the prior art, the circuit cost is large, and the angle subdivision precision highly depends on the line number of an encoder and the digit number of an analog-to-digital converter, so that the measurement speed is affected.

Description

Technical Field

[0001] The invention relates to a method for measuring the subdivided angle of a rotating shaft of a robot servo system. The method utilizes the linear variation characteristic of the phase difference corresponding to each periodic sampling value of the sine and cosine signals of an encoder in the rotating shaft angle measurement to perform high-precision digital correction on the sampling value, thereby realizing high-precision measurement of small angles of the rotating shaft of the robot. The method belongs to the technical field of digital rotating shaft angle measurement using an analog / digital converter and a sine and cosine encoder. Background Art

[0002] The robot servo system has higher and higher requirements for the positioning accuracy and angle measurement accuracy of the rotating shaft position. The accuracy of angle measurement in the servo system greatly affects the response bandwidth and control accuracy of the servo. The incremental sine-cosine encoder is a precision sensor for measuring angular displacement and angular velocity, and is often used for rotating shaft angle measurement in servo systems. The tangent direct calculation method based on the sine-cosine encoder is one of the commonly used rotating shaft angle measurement methods. The sine-cosine encoder is based on the grating moiré fringe technology. When the encoder code disk rotates with the working shaft, the light signal becomes a periodically changing sinusoidal wave signal after photoelectric conversion. Each change in the signal indicates that the measured object has moved an angle θ. The size of the measured angle can be obtained by recording the output sinusoidal wave signal. The sinusoidal wave signal in the recording process includes the full cycle part and the non-full cycle part. For example, when the measured angle is Mθ+θ′, M is the number of cycles of the sine wave signal, and the angle less than one cycle is θ′. If the sine signal moves less than one cycle, the tangent direct calculation method is often used for high-precision phase angle subdivision. The sine signal output by the encoder is U s , the cosine signal is U c , the expressions are:

[0003] U s =Usin(θ′) (1)

[0004] U c =Ucos(θ′) (2)

[0005] The θ′ in the above formula represents the subdivision angle, which refers to the phase of the sine and cosine waves. The sine and cosine signals output by the encoder are sampled by the analog / digital converter at the same time. s and U c The sampling value of θ′ can be obtained as:

[0006]

[0007] As mentioned above, the key technology in the direct tangent calculation method based on the sine-cosine encoder is the determination of the subdivision angle, and the calculation of the subdivision angle depends on the high-precision sampling of the encoder sine-cosine signals. The conventional design of angle subdivision is highly dependent on the increase in the number of encoder lines and the increase in the number of bits of the analog / digital converter, and does not give full play to the phase difference change characteristics of the sampling value in digital measurement. The present invention proposes a new angle subdivision measurement method, in which the stable phase difference relationship between the sampling signal and the sine-cosine signal is controlled, and a new idea for digital correction of the sampling value in the rotation axis angle subdivision measurement is established. Summary of the invention

[0008] The purpose of the present invention is to provide a method for measuring the subdivision angle of a rotating axis of a robot servo system, wherein the sine and cosine signals output by the encoder are of the same frequency, and the relationship between the sampling clock signal frequency value of the analog / digital converter and the frequency value of the sine signal output by the encoder is adjusted so that the phase difference corresponding to the sampling value of the sine and cosine signals presents a linear variation characteristic, and the linear variation characteristic of the phase difference is utilized to digitally correct the sampling value to improve the angle subdivision accuracy. The present invention has high measurement accuracy, a simple circuit structure, and is easy to implement, and solves the problems existing in the background technology that the circuit cost is high, the angle subdivision accuracy is highly dependent on the increase in the number of encoder lines and the increase in the number of bits of the analog / digital converter, and affects the measurement speed.

[0009] The technical solution of the present invention is:

[0010] A method for measuring the subdivision angle of a rotary axis of a robot servo system comprises the following steps:

[0011] ① The frequency value of the sampling clock signal is adjustable, so that the frequency value of the sampling clock signal of the analog / digital converter is a multiple of the frequency value of the encoder output sinusoidal signal with a slight deviation.

[0012] When the frequency values ​​of two signals are multiples and have a slight deviation, the phase difference generated by the phase comparison of the two signals has the characteristic of linear change, and this linear change is periodic. For a simple example, a pulse signal f1 with a frequency value of 13Hz and a pulse signal f2 with a frequency value of 40Hz, 40Hz=13Hz×3+1Hz, that is, the frequency value of the f2 signal is 3 times the frequency value of the f1 signal, and there is a slight deviation of 1Hz. The rising edge of the pulse signal is used as the comparison moment of the phases of the two frequency signals, and the phase coincidence is used as the first comparison, followed by the second phase comparison. Since signal f2 needs 3 cycles to be compared with signal f1, the phase difference during the second phase comparison is By analogy, the phase difference is 0, The 0 here means the two signals are in phase with each other. The phase difference between the pulse signal f1 and the pulse signal f2 will appear periodically according to the above order.

[0013] ② Use CPLD to generate a phase detector to detect the phase difference between the sampling clock signal and the pulse signal generated by the sinusoidal signal, and adjust the sampling clock signal frequency value so that the phase difference within one rotation of the encoder with the rotating shaft is periodic. The computer then stores the phase difference information of the periodic characteristics.

[0014] The sinusoidal signal is passed through a shaping circuit to generate a pulse signal, and the phase of this pulse signal is compared with the sampling clock signal in order to store the periodically changing phase difference, because each sampling signal of the analog / digital converter moves linearly according to the phase difference, such as Figure 1 As shown, the sampling signal of the analog / digital converter corresponding to the a0 sampling point moves to the a1 sampling point in the next sinusoidal signal, and the phase difference between the a0 sampling point and the a1 sampling point is Δt. Similarly, the sampling signal of the analog / digital converter corresponding to the a1 sampling point moves to the a2 sampling point in the next sinusoidal signal, and the phase difference between the two sampling points is 2Δt. The reason for this linear change in phase difference is that the relationship between the two signal frequencies mentioned above exists.

[0015] Further analysis shows that all sampling points in a periodic sinusoidal signal move linearly according to the phase difference, such as Figure 1 As shown, point b0 moves to point b1, and point b1 moves to point b2, and the corresponding phase differences are Δt and 2Δt respectively. By utilizing the characteristic that the sampling signal moves according to the linear change of the phase difference, more sampling points can be generated under the same hardware conditions. This sampling method reduces the dependence on high-frequency sampling devices, reduces hardware costs, and improves the sampling speed. Each change in the phase difference means that the sampling point moves once. When the phase difference appears periodically, it means that the sampling point is repeatedly sampled. The encoder will generate multiple sinusoidal signals when the rotating shaft rotates one circle. These sinusoidal signals are called sinusoidal signal groups. Let the sampling point complete the mobile sampling in this sinusoidal signal group. When the rotating shaft rotates in the next circle, the sampling point starts to repeat the sampling, which improves the sampling efficiency. As mentioned above, by adjusting the numerical relationship between the sampling clock signal frequency value of the analog / digital converter and the frequency value of the encoder output sinusoidal signal, high-efficiency repeated sampling can be completed.

[0016] ③ The analog / digital converter samples the sine and cosine signals output by the encoder. The sampling value of each cycle of the sine and cosine signals is a sampling unit, and each sampling unit corresponds to a phase difference information. The computer stores the sampling unit.

[0017] The tangent direct calculation method requires sampling of sine and cosine signals. The frequency value of the sine signal output by the encoder is the same as that of the cosine signal. The cosine signal changes synchronously with the sine signal. The linear change characteristics of the phase difference mentioned above and the characteristics that the sampling point moves according to the linear change of the phase difference also apply to the cosine signal. Each sampling unit corresponds to a phase difference information, such as Figure 1 As shown, the sampling units [a1, b1, ...] correspond to the phase difference Δt, the sampling units [a2, b2, ...] correspond to the phase difference 2Δt, and the sampling units [a3, b3, ...] correspond to the phase difference 3Δt. When the phase difference repeats, the sampling units also repeat, which means that the mobile sampling is completed.

[0018] ④ The rotating shaft stop signal and the sampling clock signal act together on the phase detector. The effective value output by the phase detector indicates that the sine and cosine values ​​finally output by the encoder linked to the rotating shaft have not been sampled, and the sine and cosine values ​​finally output need to be obtained digitally.

[0019] The encoder rotates with the rotation of the rotating shaft, and then the encoder outputs sine and cosine signals. When the rotating shaft stops rotating, the encoder also stops outputting sine and cosine signals. The moment the rotating shaft stop signal is generated is the moment when the encoder stops outputting sine and cosine signals. In general, the last stored sampling value is not the final value of the sine and cosine signal output by the encoder, that is, the sampling clock signal of the analog / digital converter is difficult to synchronize with the rotating shaft stop signal, and the phase detector detects this asynchronous situation. Figure 1 As shown, the encoder's sinusoidal signal stops at b x The sampling point b3 of the analog / digital converter does not coincide with the sampling point b3 of the analog / digital converter because the sine signal of the encoder stops and the sampling point b3 of the analog / digital converter is not sampled. The last sampling point generated by the analog / digital converter is b x Point a3 before point b, that is, the encoder's sinusoidal signal stops at point b x The point falls between the sampling point a3 generated by the analog / digital converter and the sampling point b3 not generated. Due to the periodicity of the sampling unit, the sampling point b3 can be extracted from the sampling unit of the previous cycle.

[0020] ⑤ Through the stored phase difference information and the rotation axis stop signal, the computer quickly locks the sampling unit where the sine and cosine signal value output by the encoder is located, and extracts the last sine signal sampling value U of the analog / digital converter in the locked sampling unit. a and its next sampling value U b , extract the final cosine signal sampling value U of the analog / digital converter c and its next sampling value U d , the final sinusoidal signal value U output by the encoder s Take (U a +U b) / 2, the final cosine signal value U output by the encoder c Take (U c +U d ) / 2. The computer uses the sine value U s and cosine value U c Find the subdivision angle.

[0021] As mentioned above, the subdivision angle in the tangent calculation method is arctan(U s / U c ), the present invention realizes U s and U c Low-cost fast sampling. Through analog / digital converter sampling, each sine and cosine signal output by the encoder has its own sampling unit, and each sampling unit corresponds to a phase difference value, such as Figure 1 The [a1, b1, ...] sampling units correspond to the phase difference Δt, and the [a2, b2, ...] sampling units correspond to the phase difference 2Δt, etc. Because the phase difference changes linearly and appears periodically, the sampling units also appear periodically. Therefore, the sampling unit where the sine and cosine signal value output by the encoder is located at the end, the computer locks the same sampling unit of the previous cycle. The reason for locking the sampling unit of the previous cycle is that the sampling unit of the previous cycle contains the complete information of the last sine and cosine signal sampling value output by the analog / digital converter and its sampling value at the next moment.

[0022] The main innovation of the present invention is: by utilizing the relationship between the sampling clock signal frequency value of the analog / digital converter and the frequency value of the sine and cosine signals output by the encoder, the phase difference corresponding to the sampling value of the sine and cosine signals presents a linear change characteristic and periodicity, and the sampling unit composed of the sampling value also presents periodicity, and the sampling value can be obtained quickly and at low cost. The present invention has a wide measurement range and can perform high-precision dynamic measurement of the subdivision angle of the rotating shaft of a servo system with a changing speed.

[0023] The positive effects of the present invention are: the instrument structure is simple and easy to implement; under the same sampling hardware conditions, the sampling points of the sine and cosine signals are more; by using the phase difference information with stable periodic changes and the sine and cosine signal sampling unit, the sine and cosine signal values ​​finally output by the encoder are quickly digitally corrected; and the periodic linearly changing phase difference is computer controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of encoder signal sampling of the present invention;

[0025] Figure 2 It is a block diagram of the rotary axis subdivision angle measurement system of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described below by way of examples.

[0027] like Figure 2 As shown:

[0028] In the rotary axis subdivision angle measurement system of this robot servo system, because the sine signal and cosine signal output by the encoder have the same frequency, the system's operation process on the sine signal is also applied to the cosine signal. The following is an illustration of the measurement system's operation on the sine signal.

[0029] The computer adjusts the sampling clock signal of the analog / digital converter, so that the frequency value of the sampling clock signal of the analog / digital converter is a multiple of the frequency value of the encoder output sinusoidal signal with a small deviation, and the phase difference within one rotation of the encoder with the rotating shaft is periodic.

[0030] The sine signal is converted into a pulse signal to provide a pulse comparison signal for generating a periodic linear phase difference. The CPLD in the system performs two functions: one is to compare the rising edge of the pulse signal with the sampling clock signal to perform phase detection and extract the phase difference after phase detection; the other is to perform phase detection on the rotating shaft stop signal and the sampling clock signal. The effective value of the phase detection output indicates that the final sinusoidal signal value output by the encoder linked to the rotating shaft needs to be digitally corrected.

[0031] The computer is used to observe the periodic changes of the phase difference information. If no periodic phenomenon occurs, the computer adjusts the sampling clock signal of the analog / digital converter. This process is equivalent to the closed-loop control process of the phase difference. After the phase difference changes periodically, the computer stores the phase difference information and the sampling values ​​of the sinusoidal signal. The stored sampling values ​​have the periodic characteristics of the sampling unit. This method of generating a periodic linear change of the phase difference by controlling the frequency value relationship between the sampling clock signal of the analog / digital converter and the output sinusoidal signal of the encoder can efficiently obtain a large number of sampling points without increasing the sampling hardware cost, or can obtain more sampling points under the same hardware conditions.

[0032] When the encoder stops rotating shaft, the final sinusoidal signal outputted by the encoder does not occur at the same time as the sampling signal. In this case, the system needs to use a computer to define the sampling interval where the rotating shaft stop signal falls. That is, the computer locks the sampling unit. This sampling unit contains important sampling value information, among which the final sampling value is closest to the final sinusoidal signal value outputted by the encoder.

[0033] According to the periodic characteristics of the sampling unit and phase difference, the computer locks the same sampling unit as the previous cycle and extracts the required sampling value in the sampling unit of the previous cycle. Based on the last sampling value and the sampling value of the previous cycle, the computer obtains the last sinusoidal signal value output by the encoder, and then applies the tangent algorithm to obtain the subdivision angle of the rotating axis.

[0034] In the process of subdivided angle measurement of the present invention, since the relationship between the sampling clock signal frequency value and the sinusoidal signal frequency value is controllable, a periodic linearly changing phase difference and a periodic sampling unit can be generated. The computer uses the phase difference information and the sampling unit information to perform fast and efficient digital correction, and then obtain the subdivided angle of the rotating axis of the robot servo system.

Claims

1. A method for measuring the subdivision angle of the rotary axis of a robot servo system: ① The frequency value of the sampling clock signal is adjustable, so that the frequency value of the sampling clock signal of the analog / digital converter is a multiple of the frequency value of the encoder output sinusoidal signal with a slight deviation; ② Use CPLD to generate a phase detector to detect the phase difference between the sampling clock signal and the pulse signal generated by the sine signal, and adjust the sampling clock signal frequency value so that the phase difference within one rotation of the encoder with the rotating shaft is periodic. Then the computer stores the phase difference information of the periodic characteristics. ③ The analog / digital converter samples the sine and cosine signals output by the encoder. The sampling value of each cycle of the sine and cosine signals is a sampling unit, and each sampling unit corresponds to a phase difference information. The computer stores the sampling unit; ④ The rotation axis stop signal and the sampling clock signal act together on the phase detector. The effective value output by the phase detector indicates that the sine and cosine values ​​finally output by the encoder linked to the rotation axis have not been sampled, and the sine and cosine values ​​finally output need to be obtained digitally; ⑤ Through the stored phase difference information and the rotation axis stop signal, the computer quickly locks the sampling unit where the sine and cosine signal value output by the encoder is located, and extracts the last sine signal sampling value U of the analog / digital converter in the locked sampling unit. a and its next sampling value U b , extract the final cosine signal sampling value U of the analog / digital converter c and its next sampling value U d , the final sinusoidal signal value U output by the encoder s Take (U a +U b ) / 2, the final cosine signal value U output by the encoder c Take (U c +U d ) / 2; the computer uses the sine value U s and cosine value U c Find the subdivision angle.

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