## 3 Principle of the Shearer Attitude Sensing System
### Principle of the Shearer Attitude Sensing System  
SINS is a navigation system in which inertial sensors (including such sensors as accelerometers and gyroscopes) are directly fixed onto a running carrier, and the acceleration and the angular velocity of the carrier are measured by the accelerometers and gyroscopes, respectively. The initial position, velocity, acceleration, and angular velocity of the carrier are used together to obtain various navigation parameters such as position, velocity, and running attitude of the running carrier through integration calculation [22]. The SINS is applied onto a shearer to sense its attitude. In fact, the acceleration and angular velocity of the shearer relative to the inertial space are measured with the accelerometer and gyroscope and then the attitude information of the shearer is obtained through iterative calculation [23]. In other words, the three-dimensional coordinates and motion parameters of the shearer in a coordinate system at a time point are determined. This process is realized in the carrier coordinate system (\(b\) system) and cannot be directly used to solve  
Figure 1: Layout of three machines at a typical fully mechanized mining face; (a) front view; (b) top view. for the shearer attitude [24] as the shearer attitude needs to be solved for in the navigation coordinate system (\(n\) system). Accordingly, when the shearer attitude is solved for, transformation between the carrier coordinate system and the navigation coordinate system is needed [25]. The orientation relationship between the above two coordinate systems is shown in Figure 2, and it gives the attitude angles of the shearer, including heading angle, pitch angle, and roll angle, which are \(\varphi\), \(\theta\), and \(\gamma\), respectively. It is defined that the transformation between the \(n\) system and the b system is  
shearer attitude sensing will be significantly reduced. Therefore, it is necessary to make effective compensation for the various errors from SINS. The errors affecting the SINS accuracy mainly include initial alignment error, installation error, measurement error by the inertial sensor, calculation error, etc. 1. Initial alignment error If no effective error elimination is performed during the initial alignment process, the typical values of various initial alignment errors will be superimposed onto the final attitude, velocity, and position parameters at the beginning of navigation, thus affecting the output value of the navigation system. 2. Installation error Installation errors include installation deviation angle error and lever arm effect error. In the SINS of the shearer, the installation deviation angle error means that there is an included angle between the sensing axis of the inertial navigation assembly and the coordinate axis of the shearer body due to the installation process and the working state of the shearer, causing the output of the inertial sensor not to be the real navigation parameter of the shearer. The lever arm effect error means that the non-coincidence of the mass center of the inertial navigation assembly and that of the shearer body causes an interference acceleration, which affects the output value of the accelerometer and thus influences the shearer positioning accuracy. 3. Inertia sensor error The inertial sensor error refers to the errors caused by gyroscopes and accelerometers themselves, mainly including accuracy error, zero bias error, scale factor error, random noise error, etc. These errors are mainly determined by the processing technology and assembly level of the sensor itself. 4. Calculation error It includes the solution algorithm approximation error, computer algorithm error, processor calculation error, etc. [27], and it is basically negligible. It has been proved through long-term theoretical studies and numerous practice operations that the errors affecting the accuracy of the SINS are mainly the initial alignment error, installation error, and inertial sensor error [28].