## 4 Shearer Pick Forces during Coal-Rock Cutting
### Load Spectrums of the Pick
Considering computer simulation methods of shearer pick force, there are the finite element method [96; 97], discrete element method [62; 98; 99] and Matlab simulation method [100; 101]. In the finite element method, the finite element model of coal seam cutting by shearer is established using Ansys/LS-DYNA. The forces are exerted on the drum and picks during cutting, and the load spectrums of the picks are obtained. Meanwhile, the effects of the structural parameters of the shearer cutting unit, kinematic parameters of the shearer, and shearer cutting condition on the load spectrums are investigated, respectively. In the discrete element method, EDEM software is employed to establish the discrete element model of the drum and coal rock through the settings of the mechanical parameters of particles and contact parameters between drum and coal rock, which can induce pick forces during cutting and load spectrum of the pick. In the Matlab simulation, the input is the pick structure, kinematic parameters and coal-rock characteristics, and the simulation angle and step size are determined. Afterwards, the loop variables of the rotation angle and pick number are set to calculate the pick position and pick force. When the pick number is larger than the total pick number and rotation angle larger than 360\({}^{\circ}\), the pick and drum load spectrums are the output. Typical load spectrums of the pick during coal rock mining of thin coal seams under different working conditions are investigated [107; 108; 109]. The pick force shows the large impact as the shear drum cuts into the coal wall; the pick forces during coal-rock cutting change periodically, and pick forces along three directions exhibit different evolutions. In cases of different coal-rock types, the overall pick force during coal rock cutting decreases in the order of mudstone, hard coal and soft coal [108; 109]. In coal seams with dirt bands, the pick force exhibits the largest value at the middle locations of coal seam. Meanwhile, the thickness of dirt bands greatly affects the ranges of vibration time and vibration amplitude. [PERSON] et al. [110] thought that the parameters of the cutters and their spatial orientation relative to the end of the blade of the screw executive body had a significant impact on the power and energy performance of coal-mining combines. They have identified the extent to which the spatial orientation of the cutter affects the power and energy parameters of the cutting process. It was found that small values of the angle of inclination of the cutter were optimum for the cutting forces, and the lateral component of the load on the cutter decreased with increasing angle of inclination. [PERSON] [111] compared results of theoretical investigations into the external forces acting on the cutter drum of a shearer with results obtained using strain gauge measurements taken on the cutter picks using a reduced-scale surface test rig. He found external forces to be random in nature and to have similar properties to those of white noise, which did not contradict the results of strain gauge measurements taken underground. \begin{table}
\begin{tabular}{c c} \hline
**Measurement Methods** & **Research Results** \\ \hline Cutting current of drum & Random load of cutting unit [102] \\ Pin shaft strains of shearer rocker & Drum load spectrum of drum load [103; 104] \\ Drum torque & Pick forces at different transversal positions [105] \\ Equivalent pick holder load & Pick forces at different transversal positions [105] \\ Strain of pick seat and torque of rocker arm idler shaft & Three-dimensional force and torque of the pick [88] \\ Tooth sleeve rear end force sensor. Rear end force transducer of pick sleeve & Cutting resistance of the pick [96] \\ Three-dimensional load cell & Normal and tangential forces of the pick [106] \\ \hline \end{tabular}
\end{table} 
Table 5: Field tests of shearer pick forces.