## 1 Introduction  
Coal has always been the main energy source in China, accounting for more than 70% and 60% of primary energy production and consumption [1]. The world's energy picture and the real economic and social demands determine that coal will remain the main energy source in China for a long time to come. Taking the advantage of scientific and technological progress to eliminate the drawbacks in the production and utilization of coal and realize safe and efficient green mining and clean and efficient utilization is the direction of coal development [2, 3]. China has proposed the strategy of \"Made in China 2025\" with the development of intelligent manufacturing, intelligent equipping, and intelligent producing as its main content. Building intelligent coal mines and developing intelligent mining technology is in line with the national strategy and is an inevitable choice for the development of China's coal industry [4]. With the intelligent mining technology, the production equipment at the coal mine working face can be remotely monitored and intelligently controlled on the ground or in the mining roadway, so the miners can move from the dangerous working face to the roadway or the ground during the mining process, reducing the occurrence of safety accidents and casualties greatly, and the production efficiency and safety level will also be significantly improved [5]. At present, intelligent mining technology and equipment have been successfully applied in some mines, but the overall level of coal mine intelligence is far from the expected effect due to the complex and variable coal seam occurrence conditions in China. A series of key technical problems during intelligent mining need to be solved urgently, includingthe precise positioning and navigation of the mining equipment at underground working face [6], the intelligent sensing of the mining environment information at working face [7], the adaptive control of the support system and surrounding rock, the cooperative control of the mining equipment [8], the intelligent prediction and early warning of the mining hazards on mining site, etc. [9].  
It is one of the keys to realizing intelligent mining at a working face to accurately perceive the attitude of the shearer [10]. Shearer, hydraulic support, and scraper conveyor are called \"three machines\" at the working face. The shearer undertakes the task of cutting and loading coal at the working face. The track of the scraper conveyor provides a movement path for the shearer to perform reciprocating coal cutting. The cutting path of the bottom plate of the shearer drum determines the attitude of the scraper conveyor. The cutting path of the top plate determines the support height of the hydraulic support, and its movement track indirectly reflects the straightness bending state of the scraper conveyor. All of these production state elements of the intelligent working face can be obtained by constructing the information on position and attitude and geometric characteristics of the shearer during operation. The accurate attitude information of the shearer is the key to ensuring its automatic coal cutting and the automatic moving of hydraulic supports [11], and it is also the basis for realizing the adaptive cutting by the shearer [12]. The research on real-time and accurate shearer attitude sensing can not only provide a way to detect and predict the production state of the intelligent working face, but also supply basic information for the shearer's independent height adjustment, coal cutting, and other intelligent decision-making to realize intelligent control.