e driving sprocket matches an idler sprocket, which in turn rides on the rail track [57] made of steel peg rods [58]. Thus, the driving system of power transmission is highly efficient. The rack is made of sections that have the same length as the conveyor pan, but they are installed in such a way that the center of each section is directly above the connection line between two adjacent pans.C. Electric Haulage Shearer
Electric haulage shearers have successfully extended. Each element of the electric haulage shearer, including chainless haulage unit, two gearheads, auxiliary power pack, haulage and auxiliary control, is driven by its own electric motor with control equipment housed in a central unit [59].
The advantages of the electric haulage shearer shearer are as follows:
�� Easy maintenance: Units are readily accessible for removal from the waste side [60] without ��splitting�� [61] the machine, and are designed for easy maintenance and repair.
��Simplified transmission [62]: Simplify and direct gearing to the cutting drums and haulage drive wheels.
��No structural requirement: Units are self-contained [63] within the shearer��s mainframe and are not subject to any external forces.
The MG series AC frequency converted electric haulage [64] shearer was the first development in China. The technical performance and the reliability [65] of the product reached to a leading level in China and have been widely applied in the coal industry. At present, the product has been become a series product. The power of the product is ranging from 344 - 1020 kW and is suitable to a seam thickness ranging from 1000 mm to 4629 mm. The main features of the product are as followings:
�� A special flame proof AC frequency converted speed adjusted device [33] was developed with a wide speed adjustment, a high haulage force and less fault;
�� The product was driven with multi electric motors [66] and a flexible shaft was used to protect the cutting motor and the driven system;
�� A PLC control technology [67] was used to develop a Chinese words interface between man and machine, a operation status monitoring and control, monitoring and measuring, fault memory and display technology[68];
�� A frame structure was used for the product in order to have a easy disassembling and maintenance [69];
�� Hydraulic nut fastener [70] was used for a reliable connection.
8-4 Characteristics of Modern Shearers
A. The shearer should be designed to cut at low drum speeds with no breakdowns [71] and a minimum of maintenance. Attention should be given to visibility to enable the operator to control and manipulate the machine with ease.
B. There should be an emphasis on robustness [72] and simplicity in the design and an absolute minimum usage of hydraulics.
C. Effective dust suppression [73] has been provided by a water supply through the drum
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