【正文】 nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。s agricultural exports to America. Through the analysis, we are going to determine the dominant impact factor, to provide basis reference for decision making on promoting China39。s agricultural exports to America, using constant market share (CMS model) analysis, discuss of China39。s agricultural exports to the United States, and with what characteristics? What are the factors that affect the fluctuate of China39。s second largest trading partner after the European Union , the agricultural trade plays a very important role in SinoUS economic and trade relations. With those social and political factors, trade in agricultural products often bees the focus of SinoUS trade friction, therefore, the study on the impact factors of China39。 br /Abstractbr /Since the year 2004, China39。s Agricultural Products Export to America and Countermeasuresamp。 CMS模型br /br /Influential Factors Analysis of Chinaamp。 美國amp。br /【關(guān)鍵詞】農(nóng)產(chǎn)品出口amp。中美兩國的農(nóng)產(chǎn)品貿(mào)易以互補(bǔ)性為主，競爭性為輔，中國對(duì)美國的農(nóng)產(chǎn)品出口的現(xiàn)狀如何，具有哪些特征?影響中國對(duì)美國農(nóng)產(chǎn)品出口額波動(dòng)的因素是什么?本文將通過對(duì)中國對(duì)美農(nóng)產(chǎn)品出口的現(xiàn)狀及影響因素進(jìn)行分析，運(yùn)用恒定市場份額(CMS模型)分析方法，研究中國對(duì)美農(nóng)產(chǎn)品出口，量化影響中國對(duì)美國農(nóng)產(chǎn)品出口變動(dòng)的不同因素。而目前，美國已經(jīng)成為繼歐盟之后的中國第二大貿(mào)易伙伴，農(nóng)產(chǎn)品貿(mào)易在中美經(jīng)貿(mào)關(guān)系中占有十分重要的地位。Aqk90639。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。低功率有利于電池供電的應(yīng)用場合，而高速度非常適用于對(duì)電動(dòng)機(jī)實(shí)時(shí)監(jiān)控。DSP具有低功率和高速度的特點(diǎn)，工作電壓33v，單指令周期最短為25ns。nbsp。nbsp。nbsp。為了使電動(dòng)機(jī)的轉(zhuǎn)子轉(zhuǎn)起來，必須使定子電樞各相繞組不斷的換相通電，這樣才能使定子磁場隨著轉(zhuǎn)子的位置不斷的變化，使定子磁場與轉(zhuǎn)子永磁磁場始終保持90 左右的空間角，產(chǎn)生轉(zhuǎn)距推動(dòng)轉(zhuǎn)子旋轉(zhuǎn)。br /無刷直流電動(dòng)機(jī)為了去掉電刷，將電樞放到定子上去，而轉(zhuǎn)子做成永磁體，這樣的結(jié)構(gòu)正好與普通直流電動(dòng)機(jī)相反。br /無刷直流電動(dòng)機(jī)的工作原理br /普通直流電動(dòng)機(jī)的電樞在轉(zhuǎn)子上，而定子產(chǎn)生固定不動(dòng)的磁場。 detectionbr /amp。/p br /Key Words: Brushless DC motor。br /br /關(guān)鍵詞：無刷直流電動(dòng)機(jī)；數(shù)學(xué)信號(hào)處理器(DSP)；檢測br /br /The Design of the Control of Brushless DC Motor br /Based on DSPbr /Abstractbr /Brushless DC Motor AC motor with both the simple structure, reliable operation, easy maintenance, long life, etc, are also mon DC motor to run with high efficiency, large torque, speed convenient, and fast dynamic performance advantages while overing the mon DC motor mechanical mutation spark caused by interference, maintenance is difficult, and many other shortings, which bines the DC motor and AC motor has the merit of a new generation of direction of development of electric driveIn this paper, the structure of brushless DC motor starting, in order to detail its working principle, the use of threephase brushless DC motor, for example, to analyze the process of its rotationThen describes the performance characteristics of brushless DC motor and transfer functionIt discusses the threephase PWM rectifier circuit and control method and starconnected fullbridge driving principleIn this paper,the DSPTMS320LF2407 is chosen as control chip of the Motor According to the characteristic of BLDCM and the function of the chip, sensored and senseless control solutions which are based on DSP technology are presented respectively Then, the hardware design of the system according to the preceding solutions are discussed in detailed For the hardware part, after a dissertation on the whole design, the design of several chief circuits such as peripheral circuit of DSP, the unit of driver，the unit of position signal detecting is expounded p class=39。然后針對(duì)所設(shè)計(jì)的控制方案對(duì)控制系統(tǒng)硬件設(shè)計(jì)作了詳細(xì)論述。最后論述三相PWM整流電路及控制方法和星形聯(lián)結(jié)全橋驅(qū)動(dòng)原理。本文從無刷直流電動(dòng)機(jī)的結(jié)構(gòu)出發(fā)，為了詳細(xì)說明其工作原理，利用三相無刷直流電動(dòng)機(jī)為例，來分析它的轉(zhuǎn)動(dòng)過程。Gzb59739。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。Gzb59739。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。Gzb59739。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。nbsp。Gzb59739。nbsp。br /(12)調(diào)高范圍要大，照明和通信方便。br /(10)要易于拆卸，結(jié)構(gòu)要簡單。而每個(gè)綜采工作面平均需要安裝100臺(tái)以上液壓支架。br /br /設(shè)計(jì)目的br /采用綜合機(jī)械化采煤方法是大幅度增加煤炭產(chǎn)量、提高經(jīng)濟(jì)效益的必由之路。br /（6）要易于拆卸，結(jié)構(gòu)要簡單。br /（4）支架的穩(wěn)定性要好，底座最大比壓要小于規(guī)定值。推溜力一般為100kN左右；移架力按煤層厚度而定，厚煤層一般為300kN～ 500kN。br /要求：br /（1）為了滿足采煤工藝及地質(zhì)條件的要求，液壓支架要有足夠的初撐力和工作阻力，以便有效地控制頂板，保證合理的下沉量。nbsp。nbsp。nbsp。 Fourbar linkage；Coal mining。Gzb59739。s coal industry determinants. Mechanized mining equipment is not only large output, high efficiency, low cost, and can significantly reduce casualties and improve the working environment. Stent cover 70 years of the last century there products, its notable features is the roof beams are attached between the base terminal and the shield. Shield is generally inclined, hinged at the top between the beam and base. From the kinematic sense, it is stable, this is the best in the box cover stent stent and stent stack point shield is fully closed mined area, which can fall into the support to prevent the broken roof rock face . Therefore, the general said, face shield support bracket is relatively clean.br /This paper expounds the great mining height shield hydraulic support the design process. Design elements include: selection frame type, general design, the main ponents of the design, and hydraulic system design, 3D modeling and simulation, the main ponents of the check. As the coal seam thickness, use the cover of hydraulic support. Between 110m thick coal seam between the coal seam thickness greater range of choice to increase the resistance level is larg