Rocker arm inclination angle detection method based on MEMS accelerometer

Abstract

The invention relates to a rocker arm inclination angle detection method based on MEMS (micro-electromechanical systems) accelerometers, which comprises the following steps of: respectively mounting three triaxial MEMS accelerometers a, b and c in an electric cabinet of a coal mining machine and on a left rocker arm and a right rocker arm, and respectively enabling y detection axes of the accelerometers b and c to be parallel to swing axes of the left rocker arm and the right rocker arm; when the electric cabinet, the left rocker arm and the right rocker arm are all in a horizontal state, z detection axes of the accelerometers b and c are vertically upward, x detection axes horizontally extend and are far away from swing axes of the corresponding rocker arms, the corresponding detection axes of the accelerometers a and c are parallel, then original acceleration vectors output by the MEMS accelerometers a, b and c are obtained respectively, filtering processing is carried out on the original acceleration vectors, and then the MEMS accelerometers a, b and c are obtained. And respectively calculating the inclination angle values of the filtered acceleration vectors relative to the horizontal plane, and respectively calculating the included angles of the left rocker arm and the right rocker arm relative to the electric cabinet. Compared with a traditional method, the sensor is small in size, easy to install and low in cost.

Description

Technical Field

[0001] The invention relates to a method for detecting the inclination angle of a rocker arm of a coal mining machine, wherein the core sensor used is a MEMS accelerometer. Background Art

[0002] In order to control the safe mining height of the coal mining machine in underground mining conditions, it is necessary to detect the inclination of the coal mining machine rocker arm. At present, there are almost no inclination sensors that can be directly used for coal mining machine rocker arm inclination detection. Traditional rocker arm inclination detection methods include cylinder stroke displacement method and encoder potentiometer rotation distance measurement method. Among them, the cylinder stroke displacement method uses a displacement sensor, which is mainly installed inside the height adjustment cylinder. It is necessary to establish a corresponding mathematical model according to the mechanical structure of different types of coal mining machines, and calculate the relationship curve between the displacement distance and the roller height based on the displacement distance of the connecting parts. However, the calculation process of obtaining the roller height in this method is repetitive and cumbersome, and the efficiency is low. Since the sensor is installed inside the height adjustment cylinder, once it is damaged, the replacement cost is high. The encoder potentiometer rotation distance measurement method mainly uses an angle sensor, which is installed at the coal mining machine rocker arm pin. The angle sensor is used to directly obtain the swing angle value of the coal mining machine rocker arm to obtain the roller height value, but this method is affected by the underground environmental conditions and has a high failure rate. At the same time, the connecting rod mechanism at the rocker arm pin is easy to wear, which will reduce the reliability of the obtained roller height value and cause a measurement dead zone. Summary of the invention

[0003] The present invention provides a method for detecting the inclination angle of a rocker arm based on a MEMS accelerometer. Compared with the traditional method, the sensor of this method is small in size, simple to install and easy to disassemble, low in cost, and the installation position is less affected by the environment, is not prone to failure, and has strong practicality.

[0004] The main technical solutions of the present invention are:

[0005] A rocker arm inclination angle detection method based on MEMS accelerometers, wherein three triaxial MEMS accelerometers a, b, and c are respectively installed in an electric control box of a coal mining machine and on left and right rocker arms, and protective covers are provided outside the MEMS accelerometers b and c. The y detection axes of the MEMS accelerometers b and c are respectively parallel to the swing axes of the left and right rocker arms. When the electric control box and the left and right rocker arms are in a horizontal state, the z detection axes of the MEMS accelerometers b and c are vertically upward, and the x detection axes are horizontally extended and away from the swing axes of the respective rocker arms. The detection axes of the MEMS accelerometer a are parallel to the corresponding detection axes of the MEMS accelerometer c. The following measurement steps are performed:

[0006] S1. Get the original acceleration vector A output by MEMS accelerometers a, b, and c respectively a , A b , A c :

[0007] Expressed in coordinate notation, A a =(A xa , A ya , A za ), A b =(A xb , A yb , A zb ), A c =(A xc , A yc , A zc ), x, y, z represent the three detection axes of the MEMS accelerometer, A xi , A yi , A zi They are the acceleration vector A i The components on the x, y, and z axes, i represents a, b, and c;

[0008] S2. Filter the original acceleration vector to remove high-frequency and high-amplitude vibration noise and impact noise to obtain a filtered acceleration vector A′ a , A′ b , A′ c :

[0009] A′ a =(A′ xa , A′ ya , A′ za ), A′ b =(A′ xb , A′ yb , A′ zb ), A′ c =(A′ xc , A′ yc , A′ zc ),

[0010] A′ xi , A′ yi , A′ zi They are the acceleration vector A i ′ is the component on the x, y, and z axes, i represents a, b, and c;

[0011] S3. Calculate the acceleration vector A′ after filtering respectively a , A′ b , A′ c The inclination angle θ relative to the horizontal plane a ,θ b ,θ c :

[0012]

[0013] S4. Calculate the angle θ between the left and right rocker arms and the electric control box respectivelyL ,θ R :

[0014] θ L =θ b +θ a ,θ R =θ c -θ a , relative to the horizontal plane passing through the swing axis of the corresponding rocker arm, when the left and right rocker arms are in the upward swing state, θ L ,θ R When it is positive, θ is in the downward swing state. L ,θ R When the right end of the electric control box is higher than the left end, the value is θ a is positive, otherwise it is negative.

[0015] In step S2, a critical damping low-pass filter is preferably used for filtering. The amplitude square function expression of the critical damping low-pass filter in the frequency domain is:

[0016]

[0017] In the formula, n is the order, ω is the angular frequency, ω c is the low-pass filter cutoff frequency, η is a real constant,

[0018] In step S2, an eighth-order critically damped low-pass filter is used for filtering, and the transfer function of the filter is:

[0019]

[0020] in ω c is the low-pass filter cutoff frequency, ω c =2π·f c , f c is the low-pass filter cutoff frequency, f c =0.5Hz.

[0021] The sampling frequency of the MEMS accelerometer can be 26.667KHz.

[0022] In step S2, the modulus of each original acceleration vector is calculated before filtering, and all original acceleration vectors A collected at the same sampling time as the original acceleration vector with a modulus of zero are eliminated. a , A b , A c .

[0023] In step S4, the maximum and minimum inclination angles of the left and right rocker arms are calculated every second, as well as the absolute value of the algebraic difference between the maximum and minimum inclination angles, i.e., the extreme difference value R max , when the extreme value R max When it is greater than the maximum swing angle of the corresponding rocker arm per second, all data collected in that second will be discarded.

[0024] The threshold of the maximum swing angle of the rocker arm per second is set to 1°.

[0025] Furthermore, in step S3, the inclination angle values ​​θ calculated after filtering in the set sampling period are a ,θ b ,θ c Perform mean processing;

[0026] according to Calculate the average inclination value of a set sampling period And in step S4, use the formula Calculate the average angle between the left and right rocker arms and the coal mining machine body in a set sampling period The left and right rocker arm inclination angle detection values ​​are used as the actual output.

[0027] The set sampling period can be set between 0.2 and 1 seconds.

[0028] The beneficial effects of the present invention are:

[0029] MEMS accelerometer is used as the core sensor. Since the sensing part is small, flexible and low-cost, it can be installed in the appropriate position in the coal mining machine casing by fastening with screws without affecting the overall structural strength of the coal mining machine. The sensor itself is highly integrated and is not prone to failures such as water immersion and hardware damage. Therefore, the failure rate is low, and it is easy to disassemble, replace and repair, with low maintenance costs.

[0030] Since the raw data signal output by the MEMS accelerometer is filtered by critical damping low-pass filtering, the influence of high-frequency and high-amplitude vibration noise, impact noise and other interferences generated in the coal cutting process of the coal mining machine on the inclination detection of the coal mining machine rocker arm is effectively suppressed, the problem of the accuracy of the accelerometer measurement angle is solved, the accuracy of the inclination measurement is improved, and the reliability of the detection results is ensured.

[0031] For the critical damping low-pass filter adopted in the present invention, since it has poles only on the negative real axis, the pulse response cannot oscillate, and the step response can neither vibrate nor overshoot. Compared with other low-pass filters, it can reach the steady-state value at a faster response speed and without overshoot, ensuring that the coal mining machine will not cause abnormal conditions such as top cutting due to overshoot when it is automatically running, thereby ensuring the safe operation of the equipment.

[0032] The inclination measurement error of the method of the present invention is 0.3°, which is much lower than the inclination measurement error of the mining inclination sensor based on the MEMS accelerometer principle in the current market. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a flow chart of the rocker arm inclination angle detection method of the present invention;

[0034] Figure 2 A schematic diagram of the installation position of the triaxial MEMS accelerometer on the coal mining machine in a reference state;

[0035] Figure 3 The figure is a schematic diagram of the inclination angle calculation principle of the rocker arm inclination angle detection method of the present invention;

[0036] Figure 4 It is the amplitude-frequency characteristic diagram of the eighth-order critically damped low-pass filter;

[0037] Figure 5 It is the phase-frequency characteristic diagram of the eighth-order critically damped low-pass filter;

[0038] Figure 6 This is the step response diagram of the eighth-order critically damped low-pass filter. DETAILED DESCRIPTION

[0039] like Figure 1 , 2 As shown in Figure 3, the present invention discloses a rocker arm inclination angle detection method based on MEMS accelerometers, which is to install three three-axis MEMS accelerometers a, b, and c in the electric control box of the coal mining machine and on the left and right rocker arms, respectively, so that they are fixed relative to the electric control box housing and the left and right rocker arm housings, respectively. Usually, the accelerometer on the rocker arm can be directly fixed on the coal wall side end face of the rocker arm housing, and the MEMS accelerometers b and c are provided with protective covers on the outside to protect the sensor itself and the wiring from the working environment. The y detection axes of the MEMS accelerometers b and c are parallel to the swing axes of the left and right rocker arms, respectively. Since the swing axes of the left and right rocker arms are parallel, the y detection axes of the MEMS accelerometers b and c are also parallel. Figure 2 , 3 The extension direction of the swing axis of the left and right rocker arms is perpendicular to the paper direction under the viewing angle. When the electric control box (as a part of the fuselage, it can also be said to be the fuselage, the same below) and the left and right rocker arms are in a horizontal state (this state can be called a reference state, the left and right rocker arms are in a horizontal state means that the inclination angle of the left and right rocker arms relative to the horizontal plane is zero, and the electric control box is in a horizontal state means that the swing axis of the left and right rocker arms is at the same height, and the external manifestation is that the left and right ends of the electric control box are at the same height), the z detection axes of the MEMS accelerometers b and c are both vertically upward, and the x detection axes are both horizontally extended and away from the swing axis of each rocker arm, and each detection axis of the MEMS accelerometer a is parallel to each corresponding detection axis of the MEMS accelerometer c.

[0040] In summary, according to the right-hand rule, in the reference state, the z detection axes of MEMS accelerometers a, b, and c are all upward, the x detection axes are respectively to the right, left, and right, and the y detection axis is Figure 2 The viewing angles are perpendicular to the paper surface, inward, outward, and inward, respectively, that is, pointing to the coal wall side, goaf side, and coal wall side of the coal mining machine, respectively.

[0041] The installation position and direction of MEMS accelerometers a, b, and c are determined when the rocker arm and electric control box of the coal mining machine are designed. The corresponding positioning and connection structures on the rocker arm and the electric control box are processed together with the rocker arm and the electric control box body, ensuring the accurate installation position of the MEMS accelerometer.

[0042] Perform the following measurement steps:

[0043] S1. MEMS accelerometers a, b, and c work, and the original acceleration vector A output by MEMS accelerometers a, b, and c is obtained respectively a , A b , A c :

[0044] Expressed in coordinate notation, A a =(A xa , A ya , A za ), A b =(A xb , A yb , A zb ), A c =(A xc , A yc , A zc ), x, y, and z represent the three detection axes of the MEMS accelerometer. xi , A yi , A zi They are the acceleration vector A i Components on the x, y, and z axes, where i represents a, b, and c;

[0045] S2. Filter the original acceleration vector to filter out high-frequency and high-amplitude vibration noise and impact noise, and eliminate the obvious fluctuation of the accelerometer output angle value caused by the violent vibration transmitted from the rocker arm to the accelerometer, and obtain the filtered acceleration vector A′ a , A′ b , A′ c :

[0046] A′ a =(A′ xa , A′ ya , A′ za ), A′ b =(A′xb , A′ yb , A′ zb ), A′ c =(A′ xc , A′ yc , A′ zc ),

[0047] A′ xi , A′ yi , A′ zi They are the acceleration vector A i ′ components on the x, y, and z axes, where i represents a, b, and c;

[0048] S3. Calculate the acceleration vector A′ after filtering respectively a , A′ b , A′ c The inclination angle θ relative to the horizontal plane a ,θ b ,θ c :

[0049]

[0050] S4. Figure 3 As shown, the angles of the left and right rocker arms relative to the electric control box are calculated respectively (representing the angles of the left and right rocker arms relative to the coal mining machine body) θ L ,θ R :

[0051] θ L =θ b +θ a ,θ R =θ c -θ a , relative to the horizontal plane passing through the swing axis of the corresponding rocker arm, when the left and right rocker arms are in the upward swing state, θ L ,θ R When it is positive, θ is in the downward swing state. L ,θ R When the right end of the electric control box is higher than the left end, the value is θ a is positive, otherwise it is negative.

[0052] It should be noted that the installation directions of MEMS accelerometers a, b, and c are not unique. For example, some detection axes can be set in the opposite direction compared to the above directions. In this case, the positive and negative signs of the corresponding angle values ​​need to be changed when substituting them into the calculation formula. For another example, the MEMS accelerometer c can also have the x detection axis vertically upward and the y detection axis horizontally to the right. In this case,

[0053] Furthermore, in step S2, a critical damping low-pass filter is preferably used for filtering, and the amplitude square function expression of the critical damping low-pass filter in the frequency domain is:

[0054]

[0055] In the formula, n is the order, ω is the angular frequency, ω c is the low-pass filter cutoff frequency, η is a real constant,

[0056] When n=1, the critical damping low-pass filter is essentially a first-order inertia link, with poles only on the negative real axis. In this way, it can be deduced that a high-order critical damping low-pass filter is obtained by cascading and decoupling multiple identical first-order low-pass filters, or is equivalent to a cascade circuit composed of multiple real double-pole second-order low-pass filters. After the signal passes through the filter, a group delay will be generated, and the length of the delay will determine the time to return to the receiver terminal.

[0057] The critical damping low-pass filter proposed in the present application has a higher selectivity in frequency response as the filter order increases. The present application preferably uses an eighth-order critical damping low-pass filter, i.e. n=8. This order of filter can provide a steeper transition between the passband and the stopband, so that it can more effectively suppress signals above the cutoff frequency while keeping signals below the cutoff frequency almost unaffected. Compared with higher-order filters, it has higher data processing efficiency, lower latency, and lower requirements on hardware computing power.

[0058] The transfer function of the eighth-order critically damped low-pass filter is as follows:

[0059]

[0060] in ω c =2π·f c , f c is the low-pass filter cutoff frequency, f c =0.5Hz.

[0061] Figure 4-6 The amplitude-frequency characteristic diagram, phase-frequency characteristic diagram and step response diagram of the eighth-order critically damped low-pass filter are shown, and the corresponding cutoff frequency is 0.5Hz. According to the amplitude-frequency characteristic diagram, it can be seen that the eighth-order critically damped low-pass filter can more effectively suppress signals above the cutoff frequency, while keeping the signals below the cutoff frequency almost unaffected, which is very important for applications that require strict filtering of high-frequency noise or interference. It can be seen from the step response diagram that the cutoff frequency of 0.5Hz has a better response speed and has a lower delay while ensuring filtering performance.

[0062] The sampling frequency of the MEMS accelerometer can be 26.667KHz. Of course, other settings can be made according to actual needs (for example, to adapt to the processing speed of different processors and meet the needs of different scenarios) to improve the flexibility of the design. In theory, the faster the sampling frequency, the more accurate the inclination value can be obtained after the present invention.

[0063] Furthermore, the rocker arm inclination angle detection method of the present invention can be optimized in one or more of the following aspects:

[0064] 1. In step S2, the modulus of each original acceleration vector is preferably calculated before filtering, and all original acceleration vectors A obtained at the same sampling time as the original acceleration vector with a modulus of zero are eliminated. a , A b , A c For example, the original acceleration vector A obtained by calculating a certain sampling time t at , A bt , A ct The modulus lengths are L at , L bt , L ct , it is found that the module length L bt If it is equal to zero, it means that the MEMS accelerometer b is not working properly and no reliable data is collected. at , A bt , A ct All of them are eliminated to ensure the accuracy and reliability of subsequent rocker arm inclination angle calculations.

[0065] 2. In step S4, it is preferred to calculate the maximum and minimum inclination angles of the left and right rocker arms per second, as well as the absolute value of the algebraic difference between the maximum and minimum inclination angles, i.e., the extreme difference value R max , when the extreme value R max When it is greater than the maximum swing angle of the corresponding rocker arm per second, it is considered that the filter used cannot filter out all external impacts on the accelerometer (for example, large pieces of coal fall on the coal machine during the process of cutting the coal seam), resulting in errors in multiple collected data and the errors are large. Therefore, all data collected within this second are discarded, so that the data collected by the accelerometer can be more accurate, which is conducive to improving the accuracy of the subsequent calculation of the inclination angle.

[0066] Taking the sampling frequency of the accelerometer as 26.667KHz as an example, 26667 sets of data can be collected per second, and the angle calculation can obtain 26667 sets of inclination data per second. The first set of inclination data can be represented by θ1, including θ L1 ,θ R1 , the second set of inclination data can be represented by θ2, including θ L2 ,θR2 , until the 26667th set of inclination data θ is calculated 26667 , including θ L26667 ,θ R26667 If the extreme value θ of the left and right rocker arms within a certain second Lmax ,θ Rmax If one of them is greater than the maximum swing angle of the corresponding rocker arm per second, all data collected in that second will be discarded.

[0067] In practical applications, the setting of the maximum swing angle threshold of the rocker arm per second needs to be determined according to different coal mining machine models. In this embodiment, according to product requirements, the error value of the rocker arm inclination detection needs to be less than 0.3°. According to actual tests, the maximum swing speed of the rocker arm of a certain model of coal mining machine is about 0.7° per second. In other words, assuming that the rocker arm swings at the maximum speed, considering the inclination detection error, the extreme value R max The maximum is 1°, so the maximum swing angle threshold of the rocker arm per second can be set to 1°. Data greater than this threshold can be judged as invalid data and discarded.

[0068] 3. In step S3, the inclination angle values ​​θ calculated after filtering in a set sampling period can also be calculated. a ,θ b ,θ c Perform mean processing;

[0069] Specifically based on Calculate the average inclination value of a set sampling period And in step S4, use the formula Calculate the average angle between the left and right rocker arms and the coal mining machine body in a set sampling period The left and right rocker arm inclination angle detection values ​​are used as the actual output.

[0070] The set sampling period is determined according to actual needs, for example, it can be set between 0.2-1 second.

[0071] In this way, by calculating the mean of multiple groups of data, the data collected by the accelerometer can be optimized, which can reduce the random error existing in the accelerometer when collecting data, and is conducive to improving the accuracy of the subsequent height control.

[0072] The embodiments of the present invention are described in detail above, but the contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of this patent.

Claims

1. A rocker arm inclination angle detection method based on MEMS accelerometer, characterized in that: The three triaxial MEMS accelerometers a, b, and c are respectively installed in the electric control box of the coal mining machine and on the left and right rocker arms, and the MEMS accelerometers b and c are provided with protective covers. The y detection axes of the MEMS accelerometers b and c are respectively parallel to the swing axes of the left and right rocker arms. When the electric control box and the left and right rocker arms are in a horizontal state, the z detection axes of the MEMS accelerometers b and c are vertically upward, and the x detection axes are horizontally extended and away from the swing axes of the respective rocker arms. The detection axes of the MEMS accelerometer a are parallel to the corresponding detection axes of the MEMS accelerometer c. The following measurement steps are performed: S1. Get the original acceleration vector A output by MEMS accelerometers a, b, and c respectively a , A b , A c : Expressed in coordinate notation, A a =(A xa , A ya , A za ), A b =(A xb , A yb , A zb ), A c =(A xc , A yc , A zc ), x, y, z represent the three detection axes of the MEMS accelerometer, A xi , A yi , A zi They are the acceleration vector A i The components on the x, y, and z axes, i represents a, b, and c; S2. Filter the original acceleration vector to remove high-frequency and high-amplitude vibration noise and impact noise to obtain a filtered acceleration vector A′ a , A′ b , A′ c : A′ a =(A′ xa ,A′ ya ,A′ za ),A′ b =(A′ xb ,A′ yb ,A′ zb ),A′ c =(A′ xc ,A′ yc ,A′ zc ), A′ xi , A′ yi , A′ zi They are the acceleration vector A i ′ is the component on the x, y, and z axes, i represents a, b, and c; S3. Calculate the acceleration vector A′ after filtering respectively a , A′ b , A′ c The inclination angle θ relative to the horizontal plane a ,θ b ,θ c : S4. Calculate the angle θ between the left and right rocker arms and the electric control box respectively L ,θ R : θ L =θ b +θ a ,θ R =θ c -θ a , relative to the horizontal plane passing through the swing axis of the corresponding rocker arm, when the left and right rocker arms are in the upward swing state, θ L ,θ R When it is positive, θ is in the downward swing state. L ,θ R When the right end of the electric control box is higher than the left end, the value is θ a is positive, otherwise it is negative.

2. The rocker arm inclination angle detection method based on MEMS accelerometer according to claim 1, characterized in that: In step S2, a critical damping low-pass filter is used for filtering. The amplitude square function expression of the critical damping low-pass filter in the frequency domain is: In the formula, n is the order, ω is the angular frequency, ω c is the low-pass filter cutoff frequency, η is a real constant, 3. The rocker arm inclination angle detection method based on MEMS accelerometer according to claim 1, characterized in that: In step S2, an eighth-order critically damped low-pass filter is used for filtering, and the transfer function of the filter is: in ω c =2π·f c , f c is the low-pass filter cutoff frequency, f c =0.5Hz.

4. The rocker arm inclination angle detection method based on MEMS accelerometer according to claim 3, characterized in that: The sampling frequency of the MEMS accelerometer is 26.667KHz.

5. The method for detecting the inclination angle of a rocker arm based on a MEMS accelerometer according to claim 1, 2, 3 or 4, characterized in that: In step S2, the modulus of each original acceleration vector is calculated before filtering, and all original acceleration vectors A collected at the same sampling time as the original acceleration vector with a modulus of zero are eliminated. a , A b , A c .

6. The method for detecting the rocker arm inclination angle based on a MEMS accelerometer according to claim 1, 2, 3 or 4, characterized in that: In step S4, the maximum and minimum inclination angles of the left and right rocker arms are calculated every second, as well as the absolute value of the algebraic difference between the maximum and minimum inclination angles, i.e., the extreme difference value R max , when the extreme value R max When it is greater than the maximum swing angle of the corresponding rocker arm per second, all data collected in that second will be discarded.

7. The method for detecting the inclination angle of a rocker arm based on a MEMS accelerometer according to claim 6, characterized in that: The threshold of the maximum swing angle of the rocker arm per second is set to 1°.

8. The method for detecting the rocker arm inclination angle based on a MEMS accelerometer according to claim 1, 2, 3 or 4, characterized in that: In step S3, the inclination angle values ​​θ calculated after filtering in the set sampling period are a ,θ b ,θ c Perform mean processing; according to Calculate the average inclination value of a set sampling period And in step S4, use the formula Calculate the average angle between the left and right rocker arms and the coal mining machine body in a set sampling period The left and right rocker arm inclination angle detection values ​​are used as the actual output.

9. The method for detecting the rocker arm inclination angle based on a MEMS accelerometer according to claim 8, characterized in that: The set sampling period is between 0.2 and 1 second.

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