Because the host computer works underground, it is required that it should have a moisture-proof, dust-proof and explosion-proof performance。 Design of the host computer also needs to meet the principle of expansibility and compatibility。 The proceeding of hardware design demands fully considering system expansibility, which is supported by hardware interface and software performance。 The compatibility of hardware and software with the common computer is also important, so that it can utilize the technology in existence and reduce duplicated effort。 Host computer usually is realized through adopting industrial computer and explosion-proof computer which satisfy the environmental requirements, but its expansibility is poor。 So the host computer of this system adopts customized scheme with embedded PC104。

Host computer has a lot of extended interfaces, such as RS232, RS485, CAN bus, fiber interface and current loop interface and so on。 Each interface has a photoelectric isolation circuit which is in compliance with the safety standards, thus the host computer has very strong expansibility and very well compatibility。 It can connect directly to communication interfaces of the shearer, crusher, stage loader, scraper conveyor and monitor underground equipments, so as to realize the automation of full mechanized coal mining face。

Fig。 3。 The main interface of application software for hydraulic supports

The monitoring function of the host computer is achieved by application software running on the embedded operating system。 The application software consists of background data processing section and foreground display section。 Background program collects relevant data through field bus and stores in the database after processing。 Foreground program achieves the read and search of the database and displays the data in the main interface  which is shown in fig。3。

Table 1。 Operating systems compared

Item Windows Dos Vxworks Linux

Cost Not free Not free Expensive Free

Customizing not bad Bad Well Very well

Source code Not open Not open Not open Open

Real time performance Bad Bad Well Commonly

Hardware Well Well Well Well

Function Multitask Single-task Multitask Multitask

This control system uses the embedded Linux operating system。 And the comparison between Linux operating

system and other operating systems is shown in table。1。

It can be seen from the above table that the embedded Linux OS has considerable advantages such as completely free of cost, highly customizable, stable operation and a wide range of hardware support。

5。 Research on the intrinsically safe network

In field bus use, EEP Company in Germany adopts profibus technology to achieve information transfer, while MARCO Company uses the custom format open collector technology。 At present, the mature technology widely used in domestic is CAN bus technology put forward by BOTCH Company in Germany。 Communication between controllers is achieved by full-duplex RS422 technology in consideration of the vast transferred data in the actual system。