并联机构动力学性能评价指标的研究

利用向量范数和矩阵范数理论,导出了机构主动关节驱动力或力矩相对变化量与动平台速度加速度相对变化量之间的解析关系式,提出并联机构速度加速度性能的量化指标,并且它们在工作空间分别趋近于雅可比矩阵和惯量矩阵的奇异位形轨迹,以这两条奇异位形轨迹为边界确定机构工作空间,它们的公共部分可以作为机构动力学性能优良的工作空间。分析了主动关节的速度和加速度引起的耦合作用,提出评定主动关节之间耦合程度的度量指标,为机构的关节解耦控制提供了依据。结合实例,分析了机构速度加速度性能和主动关节之间的耦合性。

226B某客运版柴油机的性能优化研究

226B某客运版柴油机在使用中普遍存在加速性差的现象,本文针对这一现象,以226B4缸某客运版柴油机为例,结合试验,从增压系统、供油系统进行了分析和研究,并提出了有效的解决方案。经试验证明,这些方案都是行之有效的。

6-TPS并联机构动力学分析

建立了6-TPS并联机构全部构件和关节与动平台速度加速度的解析关系。用凯恩法建立机构运动微分方程,该方程采用了机构输出速度作为独立变量,可作为动力学控制模型对机构进行完全闭环控制。利用矩阵范数导出了主动关节驱动力相对变化量与惯量矩阵以及加速度相对变化量之间的摄动关系,提出量化机构加速度性能和动力学优化的指标。通过实例得出机构加速度性能指标是以惯量矩阵在工作空间的奇异轨迹为极限的结论,这可以用来选取动力学性能优良的工作空间。

Performance of Dual-throat Supersonic Separation Device with Porous Wall Structure

In this paper, a dual-throat supersonic separation device with porous wall has been proposed to solve the starting problem of supersonic separator, and the feasibility of the proposed device has been tested numerically and experimentally. Its flow characteristics have been investigated and the effect of some important parameters includ-ing nozzle pressure ratio(RNP), inlet temperature and swirl intensity were examined. In the device, the supersonic flow state and strong centrifugal acceleration of 240000g can be obtained, which are necessary for the condensation and separation of water vapor. The supersonic region in the device enlarged and the shock wave shifted downstream along with the increasing RNP. The separation performance was improved with the increasing RNP and the inlet temperature. The best separation performance in this study was obtained with ΔTd? 28 K.

Effects of sliding velocity and normal load on tribological behavior of aged Al-Sn-Cu alloy

The tribological behavior of aged Al-Sn-Cu alloy rubbed in the presence of lubricant over a range of sliding velocities and normal loads was investigated. The results showed that peak-aged （PA） alloy had a better tribological behavior than under-aged （UA） and over-aged （OA） alloys, which could be attributed to the optimized strength-ductility matching and a better hardness under PA condition. Wear rate and friction coefficient showed great sensitivity to applied sliding velocity and normal load. The wear rate and friction coefficient of the alloy exhibited a reduction trend with the increase in sliding velocity. The low wear rate and friction coefficient of alloy at high velocities were due to the effectively protected film and homogeneous Sn on surface. However, an increase in normal load led to an obvious increment in wear rate. The friction coefficient exhibited a fluctuant trend with the increase of normal loads. The seriously destroyed film and abraded Sn resulted in poor tribological behavior at high normal loads. The Sn particles and lubricant film which includes low shear interfacial lubricating layer and oxide tribolayer are the key to the tribological behavior of Al-Sn-Cu alloy.

Influence of Carbonation on Mechanical Properties of Concrete

As one of the most important factors that determine the lifespan of a reinforced concrete structure, carbonation not only corrodes the reinforcing steel, but also changes the mechanical properties of concrete. For better understanding the performance of carbonated concrete structure, it is necessary to study the mechanical properties of carbonated concrete. The strees strain relationship of carbonated concrete was analyzed on the basis of experiments. The specimens were made by means of accelerated carbonation and then compressed on the testing machine. Some very important characteristics of carbonated concrete were revealed by the testing results. In addition, a useful constitutive model of carbonated concrete, which proved to be suitable for analyzing carbonated concrete members, was established in this research.

Dissymmetrical 3×3 Coupled Optical Accelerometer

Without adding feedback to modulate light path system, the dissymmetrical 3×3 coupled optical accelerometer reduces the complexity of the design of light path system. Experiments prove that it can attain good demodulation effects. As carrier is not needed in this system, the frequency range of input signal is diminished so as to decrease the sampling frequency of accelerometer. This makes for the system on programmable chip(SOPC) design of digital demodulating system. The upper limit of accelerometer working frequency can reach 3 500 Hz. But affected by the inherent frequency of sensitive components, its working frequency is 10 Hz^1 000 Hz, and the sensitivity is 8.718 0 V/(m·s-2). This accelerometer can detect the dynamic range of acceleration signal real-timely, steadily and accurately, solving the dissymmetrical problem of light path caused by circumstances and the complexity of process.

Extreme Dynamics on Electronic Cam Linear Drive

One of the requirements for modem production machine is versatility and easy reconfiguration to produce new products. The production machines use fixed gearing and mechanical cams in history. The cams were used for specific stokes and cam switches were used for commissioning of technological process. This solution has disadvantages in lower production speed and no flexibility of production. This article summaries practical steps for machine modernization and highlight practical problems in modernization of older production machine. The electronic cam with direct linear drive was used for traversal motion with high peak acceleration. This paper discusses cam stoke curve design, redesign and fitting.

一种含闭环结构单元的新型2R1T并联机构运动性能优化

提出了一种含闭环结构单元的新型2R1T并联机构—3-PPaS。推导获得了解析形式的机构位置正逆解,便于后续的运动规划及控制;采用数值搜索方法求解机构的可达空间,考察确定了机构转动能力与关键尺度参数的影响。进一步,应用雅可比矩阵条件数求解了反映机构转动能力的机构角速度性能全域指标和角加速度性能全域指标,并基于这两种性能指标,优选出了尺度参数的合理取值范围。相关成果为混联高效数控加工中心的研究奠定了理论基础。