【正文】 s feeding. The supply pressure of the pump is approximately constant under the action of pressure relief valve, the oil through the control valve and pressure pensate。s speed and load acted on it in both magnitude and direction will affect working to a different extent Particularly the impact caused by sudden vanishing of load and the motion unstability due to periodical change of load in operation will affect the surface quality of the workpiece machined, and the tool would be broken off under serious conditions, By using the method of power bond graph and state space analysis, the dynamic mathematical model of the system used to drive slide unit is established, that is called as selfadjusting back pressure speed control system and abbreviated to SABP system. In order to improve slide unit39。ter digital simulation, It is concluded from those that, if the structural dimensions of hydraulic cylinder and back pressure valve are designed rationally, the slide unit39。ity in modular machine tool fay means of the method of power bond graph and state space analysis. The dynamic mathematical model of selfadjusting back pressure speed control system used to drive slide unit is established. Main reasons and affect172。 and the host of urgent hightech highparameter, high valueadded highend products, and they do not satisfy the market needs, only dependent on imports. China joins the WTO, its impact may be even greater. Therefore, the 15 during the growth of the output value of industry, must not depend on volume growth and the industry should address the structural problems of their own, increase the intensity of the adjustment of the industrial structure and product mix, is, we should rely on the improvement of quality, and promote technical upgrading of products to meet market demand and stimulating, seek greater development.2 The application of hydraulic power sliding stage Power sliding Taiwan introducedThis paper deals with the investigation for slide unit39。s market has basically bee a structural surplus of the characteristics of the buyer39。(3) industry specialization of production low, scattered strength, low repeat serious, between regions and enterprises of convergence products, blindly pete with each other, driving down prices, the decline of enterprise returns, lack of funds, liquidity difficulties, product development and technological transformation is inadequate and seriously restricted the industry to improve the overall level of petition and the increase of strength。 Seals total demand of about billion. total sales of about billion. the development trend of the future affect the development of the main factors (1) product development ability, and the level of technological development and speed can not pletely meet the advanced mainframe products, major equipment and technology imported equipment and maintenance support。s advanced level, there are still many gaps, mainly reflected in the product variety, performance and reliability, and so on. Hydraulic products as an example, products abroad only onethird, life for half abroad. In order to meet key mainframe, and mainframe imports of major technology and equipment needs, every year a large number of hydraulic, pneumatic and sealing products imports. According to customs statistics and the analysis of data, in 1998 hydraulic, pneumatic and seals in the import about 200 million . dollars, Hydraulic which about billion dollars, aerodynamic nearly 030 million . dollars, sealed about 030 million . dollars. pared with a slight decline in 1997. By sums, currently imported products on the domestic market share of about 30%. 1998 pieces of the domestic market demand for hydraulic total of about six million, the total sales of nearly 40 billion。 aerodynamic pieces yield million. sales of about billion (of which about 60% of mechanical systems)。 Pneumatic are 1,350 varieties, more than 8,000 specifications。s 6。s reform and opening up policy guidelines, with the development of the machinery industry, based mainframe pieces behind the conflicts have bee increasingly prominent and attracted the attention of the relevant departments. To this end, the Ministry of the original one in 1982, formed the basis of mon pieces of Industry, will be scattered in the original machine tools, agricultural machinery, mechanical engineering industries centralized hydraulic, pneumatic and seals specialized factories, placing them under mon management infrastructure pieces Bureau, so that the industry in the planning, investment, technology and scientific research and development in areas such as infrastructure pieces Bureau of guidance and support. Since then entered a phase of rapid development, has introduced more than 60 items of advanced technology from abroad, including more than 40 items of hydraulic, pneumatic 7. After digestion and absorption and transformation, now have mass production, and industryleading products. In recent years, the industry increased the technological transformation efforts, in 1991, Local enterprises and the selffinancing total input of about 20 billion yuan, of which more than billion yuan Hydraulic. Through technological transformation and technology research, and a number of major enterprises to further improve the level of technology, technique and equipment to be greatly improved. In order to form a higher starting point, specialization, and run production has laid a good foundation. In recent years, many countries in the development of mon ownership guidelines, under different ownership SMEs rapid rise showing great vitality. With the further opening up, threefunded enterprises rapid development of industry standards for improving and expanding exports play an important role. Today, China has and the United States, Japan, Germany and other countries famous manufacturers joint ventures or whollyowned by foreign manufacturers to establish a piston pump / motor,