High-precision transmission shaft torque measurement method based on phase difference characteristic

Abstract

The invention relates to a phase difference characteristic-based high-precision transmission shaft torque measurement method, and belongs to the technical field of transmission shaft torque measurement by utilizing a grating sensor. According to the technical scheme, pulse counting switch signals are generated according to phase difference signals by means of the phase difference relation of periodic changes between pulse signals f1 and f2 output by a transmission shaft grating sensor and medium pulse signals f0 controlled by a small frequency difference. Through the arrangement of the pulse sampler, the phase difference of counting starting signals is the same as the phase difference of counting ending, it is guaranteed that the number of intermediate pulse signals in the counting switch is an integer, the counting error of + / -1 pulse is greatly eliminated, pulse counting is conducted on a pulse signal f1 and an intermediate pulse signal f0 in the counting switch, and the counting accuracy is improved. And the phase difference between the pulse signal f1 and the pulse signal f2 is solved, so that an accurate phase difference value is provided for solving the torque, and high-precision torque measurement is realized.

Description

Technical Field

[0001] The present invention relates to a high-precision torque measurement method for a drive shaft based on phase difference characteristics. By using the periodic phase difference relationship between the pulse signal output by the grating sensor of the drive shaft and the pulse signal controlled by a small frequency difference, the phase difference detection and extraction between signals are carried out to achieve high-precision torque measurement of the drive shaft, belonging to the technical field of using grating sensors for torque measurement of drive shafts. Background Art

[0002] Torque measurement is applied in the field of intelligent manufacturing such as motors, automobiles, aerospace, and military industries. As a key component of the power transmission system, torque is the core dynamic parameter of the drive shaft and a typical indicator for measuring the safety and reliability of the power mechanical transmission system. The principle of photoelectric torque measurement is that when the drive shaft rotates, the relative rotation angle of the grating sensor on the drive shaft changes with the torque, and the relationship is:

[0003]

[0004] In the above formula, T is the torque, G is the shear modulus of elasticity, I p is the polar moment of inertia, L is the length of the drive shaft between the two gratings, and Δα is the relative rotation angle at both ends of the drive shaft.

[0005] The change in the twist angle causes the output electrical signal of the grating sensor to change, that is, the grating sensor outputs a periodically changing signal during the rotation of the drive shaft. After amplification, shaping and other processing, a periodically changing pulse signal is finally output. The relationship between the relative rotation angle Δα at both ends of the drive shaft and the phase difference Δβ between the two gratings is:

[0006]

[0007] In the above formula, Δα is the relative rotation angle at both ends of the drive shaft, Δβ is the relative rotation angle at both ends of the drive shaft, and n is the number of pulses generated when the grating rotates one circle.

[0008] According to formulas (1) and (2), it can be seen that the torque measurement of the drive shaft can be converted into the measurement of the phase difference between the two gratings at both ends of the drive shaft, that is, the phase difference between the pulse signals output by the two grating sensors is measured. The phase difference between the two gratings is commonly measured by the high-frequency pulse filling counting method, that is, using the detected phase difference between the two gratings as the counting gate. High-frequency pulse signals are filled within this counting gate, and then the number of high-frequency pulse signals is measured. Then the phase difference between the two gratings is the single-period value of the high-frequency pulse signal multiplied by the number of pulses. However, the counting error of a general counter is ±1 pulse, introducing a large counting error, that is, there is a ±1 pulse counting error in the number of high-frequency pulses included in the phase difference between the two gratings at both ends of the drive shaft, especially the impact on high-precision torque measurement of the drive shaft is greater. Summary of the Invention

[0009] The object of the present invention is to provide a high-precision torque measurement method for a drive shaft based on the phase difference characteristic. By using the periodically changing phase difference relationship between the pulse signal output by the drive shaft grating sensor and the pulse signal controlled by a small frequency difference, the phase difference detection and extraction between the signals are carried out to achieve high-precision torque measurement of the drive shaft. By introducing an intermediate pulse signal, the frequency value of this intermediate pulse signal has a small frequency deviation from the frequency value of the pulse signal output by the drive shaft grating sensor. At this time, the phase difference between the two pulse signals has the characteristic of periodic change. Using this phase difference signal to generate a pulse counting gate can greatly eliminate the counting error of ±1 pulse. The measurement of the present invention has high precision and the circuit is easy to implement, solving the problem of low precision of drive shaft torque measurement caused by the ±1 pulse counting error in the background art.

[0010] The technical solution of the present invention is as follows:

[0011] A high-precision torque measurement method for a drive shaft based on the phase difference characteristic, comprising the following steps:

[0012] ① Use the pulse signals f1 and f2 output by the same grating sensors at both ends of the drive shaft to measure the initial frequency value of the f1 signal.

[0013] The grating sheets at both ends of the drive shaft are the same and the grating is uniform. The torque of the drive shaft brings about a change in the rotation angle. Through the grating type sensor, the same-frequency pulse signals f1 and f2 are output. Then the phase difference between the two pulse signals is the relative rotation angle at both ends of the drive shaft. As Figure 1 shown, assuming that the two ends of the drive shaft are the A end and the B end respectively, the grating sensor at the A end of the drive shaft outputs the pulse signal f1, and the grating sensor at the B end outputs the pulse signal f2. Using the rising edges of the two pulses as the phase comparison trigger signal, the phase difference between the two pulse signals is Therefore, the measurement of the drive shaft torque is the measurement of the phase difference . The commonly used high-frequency pulse filling counting method is to fill the high-frequency pulse signal into the phase difference , use the rising edge of the phase difference as the counting start signal, and the falling edge as the counting end signal to count the high-frequency pulse signal. However, generally, the high-frequency pulse signal is not an integer number of cycles within the phase difference , which is the problem of the counting error of ±1 pulse mentioned in the background art. The present invention can greatly eliminate the counting error of ±1 pulse.

[0014] ② According to the initial frequency value of the pulse signal f1, generate an intermediate pulse signal f0 under the control of a small frequency deviation value. The frequency values of f1, f2, and f0 have the same nominal value and a small deviation.

[0015] The present invention introduces an intermediate pulse signal, so that a periodically changing phase difference signal is generated between the two end pulse signals and the intermediate pulse signal, and a counting gate is generated by using this periodically changing phase difference signal. For the sake of simple introduction, as Figure 1 shown, taking the change of the phase difference θ between the pulse signal f1 output by the grating sensor at the A end of the transmission shaft and the intermediate pulse signal f0 as an example, when the pulse signals f1 and f2 have the same frequency, the phase difference change between the pulse signal f2 and the intermediate pulse signal f0 also has the same periodic characteristics.

[0016] For example, the frequency value of the pulse signal f1 is 10 Hz, and the frequency value of the pulse signal f0 is (10 + 1 = 11) Hz, that is, the nominal values of f0 and f1 are 10 Hz, and there is a small deviation of 1 Hz. The rising edge is the phase comparison moment of the two signals. Assuming that f1 and f0 are in phase coincidence at the initial moment, that is, the phase difference is 0, and the subsequent phase difference is until f1 and f0 are in phase coincidence again. As Figure 1 shown, the phase difference changes of f1 and f0 are θ1, θ2, θ3, θ4, …, and this phase difference sequence appears periodically. This law applies to the case where the frequency values of the pulse signals f1, f2 output by the grating sensors at both ends of the transmission shaft and the intermediate pulse signal f0 have the same nominal value and a small deviation.

[0017] ③ Use a phase discriminator to detect the phase relationship between the pulse signals f1, f2 and the intermediate pulse signal f0 respectively, and generate two groups of periodically changing phase difference sequences.

[0018] After the preliminary measurement of the pulse signal f1, the system generates an intermediate pulse signal f0 through micro frequency control. The pulse signals f1 and f2 have the same frequency, and the phase difference change between the pulse signal f2 and the intermediate pulse signal f0 also has the same periodic characteristics, that is, Figure 1 the θ1, θ2, θ3, θ4, … shown.

[0019] ④ In the two groups of periodically changing phase difference sequences, use a pulse sampler to obtain the phase difference signal with the most sensitive width.

[0020] The sampling value of the pulse sampler can be set, and the sensitivity of the device is a limited value. That is to say, the minimum phase difference between the pulse signals should meet the sensitivity limit value of the pulse sampler so that it can be captured by the pulse sampler. Most importantly, the minimum phase difference between the pulse signal f1 and the intermediate pulse signal f0 is the same as the minimum phase difference between the pulse signal f2 and the intermediate pulse signal f0, which eliminates the phase difference detection error, that is, eliminates the inconsistency error between the pulse counting start signal and the end signal in the subsequent steps.

[0021] ⑤In the phase difference signal with the most sensitive width obtained, the phase difference signal between the pulse signal f1 and the intermediate pulse signal f0 serves as the pulse counting start signal, and the phase difference signal between the pulse signal f2 and the intermediate pulse signal f0 serves as the pulse counting end signal.

[0022] As Figure 1 shown, by using the counting start signal and end signal formed by the phase difference of the same most sensitive width with such periodic changes, the counting error of ±1 pulse is overcome, and the number of cycles of the intermediate pulse signal f0 is an integer.

[0023] ⑥Within the pulse counting start and end signals, a counter is used to respectively count the pulses of the pulse signal f1 and the intermediate pulse signal f0. The number of pulses of the pulse signal f1 is counted as N1, and the number of pulses of the intermediate pulse signal f0 is counted as N0.

[0024] ⑦According to the single - cycle value T1 of the pulse signal f1 and the single - cycle value T0 of the intermediate pulse signal f0, the phase difference of the drive shaft torque is calculated as N0T0 - N1T1.

[0025] As Figure 1 shown, within the pulse counting start and end signals, the number of pulses of the intermediate pulse signal f0 is an integer N0, and the number of pulses of the pulse signal f1 is an integer N1. Then, the phase difference between the pulse signals f1 and f2 output by the same grating sensors at both ends of the drive shaft is accurately measured as

[0026] The main innovation of the present invention is: using the phase difference signal with periodic changes between the pulse signals output by the grating sensors at both ends of the drive shaft and the intermediate pulse signal to form a counting switch. Through the setting of the pulse sampler, the phase difference of the counting start signal is the same as that of the counting end. In this way, it is ensured that the number of intermediate pulse signals within the counting switch is an integer. And precisely because of the consistency of these two phase difference signals, as Figure 1 shown, the integer number of cycles of the pulse signal f1 starts to be counted at the counting start moment, and the non - integer - cycle value of the pulse signal f1 at the counting end moment is the phase difference between the pulse signals f1 and f2. Within this counting switch, the pulses of the pulse signals f1 and f0 output by the grating sensors are respectively counted, and then the phase difference between the pulse signals f1 and f2 is obtained, providing an accurate phase difference value for the calculation of torque.

[0027] The positive effect of the present invention is: the circuit system has a simple structure, and the setting of electronic device parameters is easy to implement. By using frequency preliminary measurement to quickly generate the intermediate pulse signal f0, and controlling the pulse counting switch by detecting the phase difference signal between pulse signals, the counting error of ±1 pulse is greatly eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the change in the phase difference between the pulse signals of the transmission shaft of the present invention;

[0029] Figure 2 It is a block diagram of the phase difference measurement structure of the transmission shaft torque of the present invention. Specific embodiments

[0030] The present invention will be further described below through embodiments

[0031] As Figure 2 shown:

[0032] In this phase difference measurement system of the transmission shaft torque, the microcomputer controls the signals of the grating sensors at both ends of the transmission shaft and shapes and outputs the pulse signals f1 and f2. The frequency of the pulse signal f1 is preliminarily measured, and after calculating the small frequency deviation value, the intermediate pulse signal f0 is synthesized by DDS. The phase difference signals between the pulse signals f1 and f2 and the intermediate pulse signal f0 are detected by the phase discriminator digitally edited by the CPLD. The microcomputer detects the change of the phase difference and adjusts the small frequency deviation value according to the periodic change of the phase difference. Then, the sensitivity limit value of the pulse sampler is set by the CPLD, and the minimum phase difference signal is extracted to form the start signal and the end signal of the pulse counter, that is, the same phase difference value forms the gate of the counter. Counter 1 counts the pulse signal f1, and counter 2 counts the intermediate pulse signal f0. During the counting period, the number of pulses of the intermediate pulse signal f0 is an integer, and the non-integer value of the pulse signal f1 is the phase difference value between the pulse signals f1 and f2. Subsequently, the number of pulses of the pulse signal f1 is counted as N1, and the number of pulses of the intermediate pulse signal f0 is counted as N0. Finally, the torque phase difference is calculated by the microcomputer. Since the number of pulses of the detected pulse signal f1 and the reference pulse signal f2 are both integers during the counting period, the counting error of ±1 pulse is greatly eliminated, thereby improving the measurement accuracy of the torque phase difference.

[0033] Through the present invention, by utilizing the periodic change characteristics of the phase difference between the pulse signals f1 and f2 of the grating sensors at both ends of the transmission shaft and the intermediate pulse signal f0, and extracting the same phase difference signal, the present invention can reduce the relative error at the start and end moments of counting. During the counting time, the number of pulses of the intermediate pulse signal f0 is an integer, and the non-integer value of the pulse signal f1 is the phase difference to be obtained, greatly eliminating the counting error of ±1 pulse. Therefore, the measurement accuracy of the torque phase difference is higher and the measurement range of the torque phase difference is wider.

Claims

1. A high-precision transmission shaft torque measurement method based on phase difference characteristics: ① Use the same grating sensors at both ends of the transmission shaft to output pulse signals f1 and f2, and measure the initial frequency value of the f1 signal; ② According to the initial frequency value of the pulse signal f1, an intermediate pulse signal f0 is generated under the control of a small frequency deviation value. The frequency values ​​of f1, f2 and f0 have the same nominal value and a small deviation; ③ Use the phase detector to detect the phase relationship between the pulse signals f1 and f2 and the intermediate pulse signal f0, and generate two sets of periodically changing phase difference sequences; ④ In two sets of periodically changing phase difference sequences, the phase difference signal with the most sensitive width is obtained by using a pulse sampler; ⑤ In the phase difference signal with the most sensitive width, the phase difference signal between the pulse signal f1 and the intermediate pulse signal f0 is used as the pulse counting start signal, and the phase difference signal between the pulse signal f2 and the intermediate pulse signal f0 is used as the pulse counting end signal; ⑥ In the pulse counting start and end signals, the counter is used to count the pulses of the pulse signal f1 and the intermediate pulse signal f0 respectively, and the number of pulses of the pulse signal f1 is counted as N1, and the number of pulses of the intermediate pulse signal f0 is counted as N0; ⑦ According to the single cycle value T1 of the pulse signal f1 and the single cycle value T0 of the intermediate pulse signal f0, the phase difference of the transmission shaft torque is calculated as N0T0-N1T1.

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