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1、Introduction to Modern Control TheorySeveral factors provided the stimulus for the development of modern control theory: a. The necessary of dealing with more realistic models of system.b. The shift in emphasis towards optimal control and optimal system design. c. The continuing developments in digi
2、tal computer technology. e. Recognition of the applicability of well-known methods in other fields of knowledge.The transition from simple approximate models, which are easy to work with, to more realistic models, produces two effects. First, a large number of variables must be included in the model
3、s. Second, a more realistic model is more likely to contain nonlinearities and time-varying parameters. Previously ignored aspects of the system, such as interactions with feedback through the environment, are more likely to be included. Mechanism of Surface Finish Production There are basically fiv
4、e mechanisms which contribute to the production of a surface which have been machined. There are: (1) The basic geometry of the cutting process. In, for example, single point turning the tool will advance a constant distance axially per revolution of the work piece and the resultant surface will hav
5、e on it, when viewed perpendicularly to the direction of tool feed motion, a series of cusps which will have a basic form which replicates the shape of the tool in cut. (2) The efficiency of the cutting operation. It has already been mentioned that cutting with unstable built-up-edges will produce a
6、 surface which contains hard built-up-edge fragments which will result in a degradation of the surface finish. It can also be demonstrated that cutting under adverse conditions such as apply when using large feeds small rake angles and low cutting speeds, besides producing conditions whichcontinuous
7、 shear occurring in the shear zone, tearing takes place, discontinuous chips of uneven thickness are produced, and the resultant surface is poor. This situation is particularly noticeable when machining very ductile materials such as copper and aluminum. (3) The stability of the machine tool. Under
8、some combinations of cutting conditions: work piece size , method of clamping, and cutting tool rigidity relative to the machine tool structure, instability can be set up in the tool which causes it to vibrate. Under some conditions the vibration will built up and unless cutting is stopped considera
9、ble damage to both the cutting tool and work piece may occur. This phenomenon is known as chatter and in axial turning is characterized by long pitch helical bands on the work piece surface and short pitch undulations on the transient machined surface.(4) The effectiveness of removing sward. In disc
10、ontinuous chip production machining, such as milling or turning of brittle materials, it is expected that the chip (sward) will leave the cutting zone either under gravity or with the assistance of a jet of cutting fluid and that they will not influence the cut surface in any way. However, when cont
11、inuous chip production is evident, unless steps ate taken to control the swarf it is likely that it will impinge on the cut surface and mark it. Inevitably, this marking beside a looking unattractive, often results in a poorer surface finishing, (5) The effective clearance angle on the cutting tool.
12、 For certain geometries of minor cutting edge relief and clearance angles it is possible to cut on the major cutting edge and burnish on the minor cutting edge. This can produce a good surface finish but, of course, it is strictly a combination of metal cutting and metal forming and is not to be rec
13、ommended as a practical cutting method. However, due to cutting tool wear, these conditions occasionally arise and lead to a marked change in the surface characteristics.玉米剥皮机简介下列几方面为玉米剥皮机发展的促进因素: 1.处理更多的现实模型系统的必要性2.强调向最佳的控制和最佳的系统设计的升级3.当前技术的不成熟.众所周知的方法在其它知识领域的适用性得到承认.从容易解决的简单近似的模型到更多的现实模型的转变产生了两种效果
14、：首先，模型必须包括很多的变量。其次，一个十分逼真的模型是尽可能的包括非线性和随时间变化的参数。早先的忽略了系统的一些方面，例如很有可能的一方面就是在环境中有着反馈的交互作用。表面粗糙度的技术在已经进行机械加工过的表面，有五种基本的影响其表面粗糙度的技术。1、切断过程的基本几何学. 例如，在单点车削时，工件每转一周，刀具就沿轴线方向进给一个固定的距离。从垂直刀具进给的方向观察，所得到的表面上有很多尖角，这些尖角的形状与切削刀具的形状相同。2、切断操作的效率. 已经提过的用不稳定的切削瘤切削将会加工出包含有坚硬的切削瘤碎片在上面的表面，而这些将会导致表明粗糙度的等级降低。已经证明，在采用进给量大
15、，前角小，切削速度低的不利情况下，除了产生不稳定的切削瘤外，切削过程也会不稳定。同时，在切削区里进行的也不再是切削，而是撕裂，导致厚度不均匀，不连续的切削，加工出的表面质量差。在切削加工延展性良好的金属材料，如铜和铝时，这种情况就尤为突出。3、机械工具的稳定性。在许多联合切削的情况下：工件的大小，夹紧的方法，和切断工具相对于机床结构的坚硬度，不稳定性是建立在使其变化的工具上的。在某些情况下，这种变化将达到并保持很长一段时间，在另外一些情况下，这种变化将会产生，除非切断停止，否则，将肯定会同时对切断刀具和工具产生破坏。这种现象就是知名的刀振，在轴向转动被描述为在工件表面的长间距螺旋状带和段间距波
16、动在机械加工的过渡表面。4、刀刃的移动效率。在不连续的产品加工过程中例如易碎材料的磨或旋转，我们期望碎片在重力作用或在冷却液的喷射作用下将离开切削面域。而且怎么也不会影响切削表面。然而，在连续切削时，产品是明显的，除非逐步控制刀刃，否则他很有可能中级切削表面并在其上留下记号。不可避免，这记号在旁边样子不美的, 时常导致差的表面粗糙度。5、切断工具的有效清除角。由于副切削刃的某种几何特征减轻和清除了角，使得在主切削面上主切削刃切削和副切削刃打磨变得可能。这样能加工出良好的表面粗糙度，但是，当然，它严格来讲，是一种金属切削和金属成型的综合，而不失被认为的一种实际的切削方法。然而，归功于切削工具的表面处理，这些情况偶尔才会出现，并导致了表面特性的标志性改变。
