High-precision assembly automation based on robot compliance

Industrial robots can be made compliant to the environment when the control loop gains are reduced, creating a so-called soft servo capability. This allows industrial robots to be used for assemblies with limited contact requirements. In this paper, we propose an assembly method using soft servo to perform certain assembly tasks where part location errors typically require the use of force control or remote center of compliance (RCC) methods. A typical industrial application, valve body assembly, was used to validate the developed method. This assembly was chosen because it is simple, yet requires compliance in all directions. Lab experiments were performed and the assembly operations were consistently successful enough to show that the developed soft servo strategy can perform certain assembly tasks with small part location errors. Therefore, the soft servo strategy may open a new door for low-cost industrial assembly. Experiments with force control were also performed to compare the performance between soft servo and force control. We found that the force control method is much more sensitive to environmental contact, that the contact forces can be controlled directly, and that greater part location errors can be tolerated. Conversely, assembly with soft servo may either fail to assemble the parts or generate bigger contact forces than allowed. Thus, applications of soft servo are more limited while force control can be successfully used in most all applications. Further investigation is needed to determine the practical industrial use of soft servo for particular types of precision assembly.     

透水性混凝土路面砖路面现场的长期渗透性能研究

因为混凝土路面砖的渗透性能是道路排水和排污体系设计的一个指标,所以它对道路工程的使用寿命有着重大意义.由于矿物或有机物的细颗粒会进入多孔混凝土路面砖的孔洞中,或进入接缝料中,所以可以认为混凝土路面砖路面的渗透性能将会有不可逆转的衰减趋势.研究结果表明,使用几年以后,路面渗透性以近10的幂次方下降.采用一种专用渗透测量仪在现场进行的实测试验,证实了这一结果.这种仪器考虑局部条件(如龄期、交通荷载等)后,可立即准确地测得其放置处的渗透量.渗透曲线则以所测的平均渗透值的回归曲线来表示.可连续地重复进行试验,以观察路面的长期性能.这些试验表明,渗透性与龄期之间有着重要联系.而且研究还表明,长期的现场渗透性及其观察到的降低程度,由填缝的颗粒尺寸所决定.此外,有别于多孔混凝土砌块孔洞尺寸的透水性路面的开孔率,也会部分地使渗透性下降.总之,虽然透水性混凝土路面砖路面不能完全排干整个交通路面上的水,但它们仍对整个集水区的径流过程起着极大的作用.由于部分雨水将被保留下来,所以这部分水不会加入到总径流量中,使径流峰值由于延时而被消减.对于一个过载的排污体系来说,由于透水性混凝土路面砖路面可减低这种过度荷载,因此在生态学上具有极其重要的作用,而且还可避免排入伴有污染物的水.根据表面径流与实际渗透量之间的关系,可为确定排水体系的尺寸提供更精确的设计方法.由于透水性路面砖路面的渗透性能会不断下降,所以要求精确地设计、使用和保养透水性路面,使渗透性能长期保持在一个较高的水平,使低成本的排水及排污体系可持续运作,且具有有效的环境管理方法.     

Controlled Growth of Platinum Nanoparticles on Strontium Titanate Nanocubes by Atomic Layer Deposition

With an eye toward using surface morphology to enhance heterogeneous catalysis, Pt nanoparticles are grown by atomic layer deposition (ALD) on the surfaces of SrTiO₃ nanocubes. The size, dispersion, and chemical state of the Pt nanoparticles are controlled by the number of ALD growth cycles. The SrTiO₃ nanocubes average 60 nm on a side with {001} faces. The Pt loading increases linearly with Pt ALD cycles to a value of 1.1 × 10^?6 g cm^?2 after five cycles. Scanning electron microscopy images reveal discrete, well‐dispersed Pt nanoparticles. Small‐ and wide‐angle X‐ray scattering show that the Pt nanoparticle spacing and size increase as the number of ALD cycles increases. X‐ray absorption spectroscopy shows a progression from platinum(II) oxide to metallic platinum and a decrease in Pt? O bonding with an increase in Pt? Pt bonding as the number of ALD cycles increases.     

Controlling Protein Enrichment in Lipid Sponge Phase Droplets using SNAP-Tag Bioconjugation

All cells use organized lipid compartments to facilitate specific biological functions. Membrane-bound organelles create defined spatial environments that favor unique chemical reactions while isolating incompatible biological processes. Despite the fundamental role of cellular organelles, there is a scarcity of methods for preparing functional artificial lipid-based compartments. Here, we demonstrate a robust bioconjugation system for sequestering proteins into zwitterionic lipid sponge phase droplets. Incorporation of benzylguanine (BG)-modified phospholipids that form stable covalent linkages with an O⁶-methylguanine DNA methyltransferase (SNAP-tag) fusion protein enables programmable control of protein capture. We show that this methodology can be used to anchor hydrophilic proteins at the lipid-aqueous interface, concentrating them within an accessible but protected chemical environment. SNAP-tag technology enables the integration of proteins that regulate complex biological functions in lipid sponge phase droplets, and should facilitate the development of advanced lipid-based artificial organelles.     

Potential contamination of shipboard air samples by diffusive emissions of PCBs and other organic pollutants: implications and solutions

Air samples were taken onboard the RRS Bransfield on an Atlantic cruise from the United Kingdom to Halley, Antarctica, from October to December 1998, with the aim of establishing PCB oceanic background air concentrations and assessing their latitudinal distribution. Great care was taken to minimize pre- and post-collection contamination of the samples, which was validated through stringent QA/QC procedures. However, there is evidence that onboard contamination of the air samples occurred,following insidious, diffusive emissions on the ship. Other data (for PCBs and other persistent organic pollutants (POPs)) and examples of shipboard contamination are presented. The implications of these findings for past and future studies of global POPs distribution are discussed. Recommendations are made to help critically appraise and minimize the problems of insidious/diffusive shipboard contamination.     

Highly Extensible Bio‐Nanocomposite Films with Direction‐Dependent Properties

The structure and mechanical properties of bio‐nanocomposite films made from poly(ethylene oxide) (PEO) that is physically cross‐linked with silicate nanoparticles, Laponite, are investigated. Direction‐dependent mechanical properties of the films are presented, and the effect of shear orientation during sample preparation on tensile strength and elongation is assessed. Repeated mechanical deformation results in highly extensible materials with preferred orientation and structuring at the nano‐ and micrometer scales. Additionally, in vitro biocompatibility data are reported, and NIH 3T3 fibroblasts are observed to readily adhere and proliferate on silicate cross‐linked PEO while maintaining high cell viability.