Precision measurements of reaction wheel disturbances with frequency compensation process

The reaction wheel, an actuator for satellite attitude control, produces disturbance torque and force as well as axial control torque. The disturbances are so crucial to the pointing stability of this high precision satellite that a measurement of disturbances is necessary for such a satellite. The measurement table that is equipped with several load cells is one of the favorite types of measurement devices. The disturbance force and torque caused by the wheel's rotation, however, stimulate the elasticity of the loadcells from the measurement table and induce the vibration of the table. This then causes the measurement error, which is especially large near the resonance frequencies of the table. In order to reduce this type of error, a calibration process with frequency compensation is suggested in this paper. The “filtered” disturbance spectrum is obtained from the raw data and the degradation of data accuracy caused by the table vibration is alleviated. Since the exact measurement is made possible by this compensation process even in the resonance area, the measurement range can be expanded up to the frequency area including the resonance frequencies. The compensation method has been adopted for the HAU measurement table where three uni-directional loadcells are used. The validity of the use of uni-directional loadcells is also tested theoretically.     

Frequency effects of upstream wake and blade interaction on the unsteady boundary layer flow

Effects of the reduced frequency of upstream wake on downstream unsteady boundary layer flow were simulated by using a Navier-Stokes code. The Navier-Stokes code is based on an unstructured finite volume method and uses a low Reynolds number turbulence model to close the momentum equations. The geometry used in this paper is the MIT flapping foil experimental set-up and the reduced frequency of the upstream wake is varied in the range of 0.91 to 10.86 to study its effect on the unsteady boundary layer flow. Numerical solutions show that they can be divided into two categories. One is so called the low frequency solution, and behaves quite similar to a Stokes layer. Its characteristics is found to be quite similar to those due to either a temporal or spatial wave. The low frequency solutions are observed clearly when the reduced frequency is smaller than 3.26. The other one is the high frequency solution. It is observed for the reduced frequency larger than 7.24. It shows a sudden shift of the phase angle of the unsteady velocity around the edge of the boundary layer. The shift of phase angle is about 180 degree, and leads to separation of the boundary layer flow from corresponding outer flow. The high frequency solution shows the characteristics of a temporal wave whose wave length is half of the upstream frequency. This characteristics of the high frequency solution is found to be caused by the strong interaction between unsteady vortices. This strong interaction also leads to destroy of the upstream wake strips inside the viscous sublayer as well as the buffer layer.     

机床减振垫铁结构及其特性研究

垫铁是机床的重要附件之一,其减振性和隔振性对机床的安全高效运行有着重要作用.文章分析了机床垫铁的几种典型结构,并着重分析了弹性减振垫铁的结构特点.利用实验手段,研究了弹性减振垫铁的承载特性和垂向固有频率特性,据此提出了减振垫铁在应用中应该注意的几个问题.     

孔辐剪切应变式动态负荷传感器的研制

本文论证了剪切应变式负荷传感器更适用于动态负荷测量,推导出传感器的设计计算公式。用实测数据展示了孔辐剪切式负荷传感器优异的动态性能。     

改进压电传感器频率响应特性的措施

压电传感器的高频响应特性很好,但其低频响应特性较差,本文分析了压电传感器的高频响应特性,讨论了采用电压放大器和电荷放大器的低频响应特性,并提出了改进低频响应特性的方法。     

一种基于单片机的智能化便携振动管式液体密度计的研制

介绍了一种便携式U-型振动管液体密度计。该仪器具有使用方便、性能稳定、测量精度高且样品种类广等优点，可广泛用于各类高精度密度测量，文中介绍了振动管式液体密度传感器的组成结构和工作原理，论述了传感器安装方式对振动管振动的影响，详细阐述了密度信号频率的软同步测量方法，并简要介绍了密度计的硬件电路和软件流程及系统的低功耗设计。     

电抗器在中频熔炼设备中的应用

介绍电抗器在中频熔炼设备中的作用,并概述了电抗器的设计和计算方法。     

井下模拟信号的转换传输

油田测井中,井下的测量参数输出信号为模拟量,本文详细介绍了本设计方案中将井下模拟信号转换成频率信号的原理,通过铠装将频率信号传送到地面,以及地面频率信号还原成模拟信号的原理,对设计进行了实验室验证.     

符合多标准的泄漏电流测试系统的软件实现

介绍一种基于软件实现设计符合最新IEC、UL等多种标准的泄漏电流测试系统.首先系统地研究IEC和UL两大电气安全检测标准体系,对IEC、UL的最新标准中提出的测量泄漏电流过程中所采用的多种人体阻抗网络进行分析得出频率因数,在此基础上应用软件对测得值进行加权计算实现设计符合多标准的泄漏电流测试系统.该系统由单一模拟人体阻抗网络、信号处理电路、高速AD转换、计算机和能够实现多标准测试的软件等组成.实验表明,测试系统具有测试方法符合多种标准的测试要求,电路简单,测试精度高和测试过程自动化等特点.     

中频淬火机闭环定位控制系统改造

通过分析凸轮轴淬火机原控制系统的缺陷，提出了有效的设计方案。具体阐述了利用PLC技术结合变频技术实现位置闭环控制，使淬火定位准确，提高了淬火质量。此设计方案对国内的相同或相似设备有极好的借鉴作用。