Structural changes in samples cryofixed by contact with a cold metal block

A common method of cryofixation is to bring a specimen rapidly in contact with a cold metal block. It is usually thought that during this process the surface of the specimen suffers little distortion since it freezes rapidly. Whether this is likely depends on the rate at which samples freeze compared with the speed at which the sample hits the cold block. There is some discrepancy between the published experimentally and theoretically determined freezing rates. As a contribution to this debate the distortion in cryofixed, freeze-substituted, striated muscle fibres has been investigated. In transverse sections, compression can be detected by deviations of the filament lattice from the hexagonal and used to estimate the time of freezing. Some specimens were frozen using a Gatan Cryosnapper, which freezes by catching the specimen between two nitrogen-cooled copper jaws. In addition, the speed with which the jaws close has also been determined. The results suggest that freezing of the well-preserved areas occurs in substantially less than 1 ms. This conclusion is supported by results obtained using metal-mirror apparatus in which the cushioned specimen was dropped onto a nitrogen- or helium-cooled copper block. All the specimens frozen against a cold block have a flat edge whereas muscle fibres are round. At the very edge there is evidence of structural damage as well as the more general lattice distortion.     

基于形状记忆合金弹簧阵列的人工肌肉设计与研究

针对形状记忆合金（SMA）丝、SMA弹簧驱动力和输出位移小的缺陷,提出了基于SMA弹簧阵列的人工肌肉设计方法。利用仿生学原理,设计了SMA弹簧阵列的空间串并联结构,推导了人工肌肉驱动力计算公式,对其输出模拟量用组合学方法进行了分析。利用UG和ADAMS建立了人工肌肉的多体动力学模型,同时,在Simulink上建立了人工肌肉的激活控制模型,在这些基础上,模拟仿生手臂弯曲伸展运动的工作过程,分析该人工肌肉的驱动和控制特性。仿真结果表明,SMA弹簧阵列结构能显著增大SMA驱动器输出位移和驱动力,并简化模拟量输出的控制。     

Stroboscopic near-field imaging for the analysis of contraction of muscle cells

We have developed a stroboscopic near-field optical microscope for observation of biological specimens and observed glycerinated muscles before and after muscle contraction with the developed system. In the system, the optical field distribution localized near the specimen is recorded as the surface topographic distribution of a photosensitive film surface. Our system is very useful for observing living biological specimens with high resolutions, because it is possible to get stroboscopic image by using a photosensitive film as detecting optical distributions instead of a scanning of probes. We have succeeded in observing inner structures of muscle cells with sub-wavelength resolution and achieved higher contrast than an ordinary optical microscope.     

基于改进J-A模型的气动肌肉迟滞建模及其补偿控制

 针对气动肌肉非对称迟滞现象,采用改进Jiles-Atherton(J-A)模型来对其进行描述,并利用自适应权重粒子群来对模型所需参数进行辨识;通过与实验数据进行对比,对所建模型精度进行验证。基于所建迟滞模型,进而提出一种积分逆迟滞补偿器,通过将其引入到PID控制系统中,实现对气动肌肉的迟滞补偿控制。仿真结果表明,引入迟滞补偿器后显著提高了对气动肌肉的控制精度,验证了所提迟滞补偿器的有效性。     

踝关节章动式康复运动轨迹规划

作为一种常见的骨骼损伤方式,踝关节损伤的康复过程十分漫长。现有研究中规划的踝关节康复轨迹模式较单一、且容易造成踝关节的二次损伤。为避免踝关节的二次损伤,需要对其康复运动轨迹进行精心规划。有鉴于此,提出一种混联式踝关节康复装置,并提出一种基于章动原理的康复运动轨迹规划方法。结合踝关节康复运动的安全性要求,借助生物力学软件AnyBody分析了不同位姿下相关肌肉的活动度,进而确定了章动式踝关节康复运动轨迹的章动角。在此基础上,通过运动学推导,给出了混联式踝关节康复装置中各推杆的位移。最后,以所提混联式踝关节康复装置为对象搭建系统的运动控制平台,并通过激光跟踪仪对动平台上的运动参考点进行跟踪。理论和实测数据对比表明,所提章动式踝关节康复运动轨迹能实现跖屈/背屈、内翻/外翻的复合运动,并满足康复安全性要求。所设计的混联式踝关节康复装置及章动式康复运动轨迹可为踝关节患者的康复训练提供有效的解决方案。     

高速开关阀驱动的气动肌肉关节的滑模变结构跟踪控制

建立了PWM高速开关阀控制的气动人工肌肉单关节的4阶SISO动态数学模型，针对实现轨迹跟踪目标，采用输入输出线性化方法得到相对阶数为3的等价系统，该等价系统零动态渐近稳定。由于系统具有参数不确定性和未建模动态特性，采用了带积分的滑模变结构控制。实验结果表明，采用基于等效降阶模型的鲁棒控制，当模型存在误差时，能在关节的整个运动范围内实现较高精度的轨迹跟踪，且对气源压力和负载变化等外加干扰具有良好的鲁棒性。     

气动人工肌肉并联机器人平台

提出一种基于气动人工肌肉的新型3自由度并联机器人平台,该机器人平台结构简单,具有3转动自由度。在对该新型3自由度并联机器人平台运动学和动力学特性理论分析的基础上,采用模糊变结构控制策略设计了新型3自由度并联机器人平台的两层滑模模糊变结构控制器,并建立了试验系统,开展了新型3自由度并联机器人平台的试验研究,其最大位置跟踪误差0．3 mm,当气源压力改变后,最大跟踪误差仍小于0．6 mm。试验结果表明,采用气动人工肌肉作为驱动装置设计的3自由度并联机器人平台是可行的,两层滑模模糊变结构控制策略对于该系统是适合的。     

Finite element modelling of skeletal muscles coupled with fatigue

In this study, Hill's muscle theory coupled with fatigue was proposed to describe mechanical behaviours of skeletal muscles. The force developed by a fatigued muscle was described by a muscle fatigue formula which was a time function of the activation α_a and the stretch λ. The modified Hill's muscle theory was hence incorporated into a three-dimensional (3D) finite element model using the PAK finite element code. In this paper, the theoretical derivation of the 3D muscle model was firstly described. After presenting the method of establishing the finite element programme, a case example of studying the mechanical response of a frog gastrocnemius muscle was used to illustrate the applicability of the proposed methodology. The effects of the muscle fatigue on the deformation as well as the stress and strain distribution of the frog muscle subject to a cyclic activation function have been determined. An experiment capturing the real-time shape change of a frog muscle was also conducted to assess the applicability of the proposed method. A comparison between the deformed shapes of the predictive model and the frog muscles was also made. It was shown that the method is capable of providing a reasonable model for describing the mechanical behaviour of skeletal muscles.     

一种混合驱动式多关节双机械臂的设计与实验

基于机器入学和仿生学,设计了一种基于气动人工肌肉和步进电机混合驱动的多关节双机械臂,结构上兼具柔顺性和紧凑性,完成了多关节双机械臂气动回路和控制系统硬件的设计.基于VC+ +编程,开发了相应的控制系统软件和实现了用计算机对多关节双机械臂的位置协调控制.样机实验验证了多关节机械臂具有良好的位置精度和协调运动能力.     

气动肌肉质量项动力学建模及仿真

单独考虑气动肌肉的质量项并在动力学推导中将其看成沿圆柱体均匀分布的质点系,利用拉格朗日方程建立了气动肌肉质量项动力学模型。利用ANSYS对气动肌肉柔性体进行了网格划分,并将生成的模态中性文件导入ADAMS进行了动力学仿真,仿真结果验证了动力学模型的正确性。