A study on robot force control based on the GMM/GMR algorithm fusing different compensation strategies.

To address traditional impedance control methods' difficulty with obtaining stable forces during robot-skin contact, a force control based on the Gaussian mixture model/Gaussian mixture regression (GMM/GMR) algorithm fusing different compensation strategies is proposed. The contact relationship between a robot end effector and human skin is established through an impedance control model. To allow the robot to adapt to flexible skin environments, reinforcement learning algorithms and a strategy based on the skin mechanics model compensate for the impedance control strategy. Two different environment dynamics models for reinforcement learning that can be trained offline are proposed to quickly obtain reinforcement learning strategies. Three different compensation strategies are fused based on the GMM/GMR algorithm, exploiting the online calculation of physical models and offline strategies of reinforcement learning, which can improve the robustness and versatility of the algorithm when adapting to different skin environments. The experimental results show that the contact force obtained by the robot force control based on the GMM/GMR algorithm fusing different compensation strategies is relatively stable. It has better versatility than impedance control, and the force error is within ~±0.2 N.

Distribution of the existence forms of condensable particulate matter during condensation: The surface collection and the space suspension forms.

Condensable particulate matter (CPM), as an air pollutant that has received wide attention in recent years, has a high emission concentration compared to filterable particulate matter (FPM), yet there is not a well-developed removal method. Air pollution control devices (APCDs) with a condensation process have a certain effect on CPM removal, which inspired us to study the condensation behavior of CPM. During the condensation process, the condensed CPM may exist in two final forms: one was collected by the cold surface that caused the condensation; the other was converted to fine particles and suspended in the space of the flue. In a sense, the surface collection form can reflect the removal of CPM, while the CPM in the space suspension form should be further separated with the aim of removal. In this work, we adopted a CPM sampling system based on EPA Method 202 to reveal the distribution of the condensation behavior of CPM. In this sampling system, the CPM collected by all the cooling surfaces, including the cooling coil and impingers, can be counted as the surface collection form, while those collected by the terminal CPM filter can be regarded as the space suspension form. It was found that about 75 % of CPM was collected by the cooling surfaces, which suggested that CPM preferred to be in the surface collection form than the space suspension form. This preference characteristic also could be observed in the inorganic (CPMi) and organic components of the CPM (CPMo). Among the CPMi, almost all NH4+ and SO42- condensed in the form of surface collection. The preference characteristics in CPM's (and its components') condensation behavior are similar under every temperature reduction condition. In this work, the interference of CPM measurement error was resolved by the statistical method of ANOVA.

SO2 Adsorption and Kinetics Analysis during Supported Triethanolamine Acetate Ionic Liquid Desulfurization.

Ionic liquid desulfurization is an effective method for achieving green and circulating desulfurization. To overcome the negative impact of the high viscosity of ionic liquids on the desulfurization process, an economical and efficient supported ionic liquid-triethanolamine acetate ionic liquid/silica (TAIL/SiO2) was prepared in this study. TAIL is synthesized using triethanolamine and acetic acid and subsequently loaded onto silica gel particles. The effects of the reaction temperature, humidity, silica particle size, and loading ratio on SO2 adsorption are investigated using a fixed-bed reactor. The results indicate that the surface of the silica gel loaded with ionic liquid formed uneven spherical clusters, and the aggregate volume increased with an increase in the loading ratio. The TAIL/SiO2 sulfur capacity could be effectively increased by increasing the loading ratio (exceeding 0.74 is unfavorable), decreasing the silica particle size, and reducing the reaction temperature and moisture content. The maximum sulfur capacity can reach 124.98 mg SO2/(g TAIL/SiO2) under experimental conditions, which is higher than that of activated carbon. The Bangham rate model effectively predicts the kinetics of the adsorption process of SO2.

An online human-robot collaborative grinding state recognition approach based on contact dynamics and LSTM.

Collaborative state recognition is a critical issue for physical human-robot collaboration (PHRC). This paper proposes a contact dynamics-based state recognition method to identify the human-robot collaborative grinding state. The main idea of the proposed approach is to distinguish between the human-robot contact and the robot-environment contact. To achieve this, dynamic models of both these contacts are first established to identify the difference in dynamics between the human-robot contact and the robot-environment contact. Considering the reaction speed required for human-robot collaborative state recognition, feature selections based on Spearman's correlation and random forest recursive feature elimination are conducted to reduce data redundancy and computational burden. Long short-term memory (LSTM) is then used to construct a collaborative state classifier. Experimental results illustrate that the proposed method can achieve a recognition accuracy of 97% in a period of 5 ms and 99% in a period of 40 ms.

The Impact of Attention Mechanisms on Speech Emotion Recognition.

Speech emotion recognition (SER) plays an important role in real-time applications of human-machine interaction. The Attention Mechanism is widely used to improve the performance of SER. However, the applicable rules of attention mechanism are not deeply discussed. This paper discussed the difference between Global-Attention and Self-Attention and explored their applicable rules to SER classification construction. The experimental results show that the Global-Attention can improve the accuracy of the sequential model, while the Self-Attention can improve the accuracy of the parallel model when conducting the model with the CNN and the LSTM. With this knowledge, a classifier (CNN-LSTM×2+Global-Attention model) for SER is proposed. The experiments result show that it could achieve an accuracy of 85.427% on the EMO-DB dataset.

Revealing the Dynamic Characteristics of Composite Material-Based Miura-Origami Tube.

Although Miura origami has excellent planar expansion characteristics and good mechanical properties, its congenital flaws, e.g., open sections leading to weak out-of-plane stiffness and constituting the homogenization of the material, and resulting in limited design freedom, should also be taken seriously. Herein, two identical Miura sheets, made of carbon fiber/epoxy resin composite, were bonded to form a tubular structure with closed sections, i.e., an origami tube. Subsequently, the dynamic performances, including the nature frequency and the dynamic displacement response, of the designed origami tubes were extensively investigated through numerical simulations. The outcomes revealed that the natural frequency and corresponding dynamic displacement response of the structure can be adjusted in a larger range by varying the geometric and material parameters, which is realized by combining origami techniques and the composite structures' characteristics. This work can provide new ideas for the design of light-weight and high-mechanical-performance structures.

CFRP Origami Metamaterial with Tunable Buckling Loads: A Numerical Study.

Origami has played an increasingly central role in designing a broad range of novel structures due to its simple concept and its lightweight and extraordinary mechanical properties. Nonetheless, most of the research focuses on mechanical responses by using homogeneous materials and limited studies involving buckling loads. In this study, we have designed a carbon fiber reinforced plastic (CFRP) origami metamaterial based on the classical Miura sheet and composite material. The finite element (FE) modelling process's accuracy is first proved by utilizing a CFRP plate that has an analytical solution of the buckling load. Based on the validated FE modelling process, we then thoroughly study the buckling resistance ability of the proposed CFRP origami metamaterial numerically by varying the folding angle, layer order, and material properties, finding that the buckling loads can be tuned to as large as approximately 2.5 times for mode 5 by altering the folding angle from 10° to 130°. With the identical rate of increase, the shear modulus has a more significant influence on the buckling load than Young's modulus. Outcomes reported reveal that tunable buckling loads can be achieved in two ways, i.e., origami technique and the CFRP material with fruitful design freedoms. This study provides an easy way of merely adjusting and controlling the buckling load of lightweight structures for practical engineering.

Fate of chromium with the presence of HCl and steam during oxy-coal combustion: Quantum chemistry and experimental study.

Quantum chemistry combined with kinetic simulation and drop tube furnace (DTF) experiments were conducted to reveal the transformation behavior of chromium at the presence of steam and HCl under oxy-coal combustion. A completed kinetic system Cr‒O‒H‒Cl containing 107 elementary reactions was firstly proposed. The unknown microcosmic reaction paths and corresponding Arrhenius parameters were calculated via quantum chemistry. Kinetic simulations on the basis of Cr‒O‒H‒Cl system clarified that HCl promoted the oxidation of chromium to hexavalent CrO2Cl2. Coexistence of HCl and steam divided the transition of chromium into two stages. At the early stage, reaction rate between chromium and steam was faster than chromium with HCl, chromium mainly transformed to CrO(OH)2. Hereafter, HCl was dominant in the transformation of chromium, then chromium mainly presented as CrO2Cl2. Moreover, DTF experimental results indicated that introduction of HCl into combustion atmosphere induced more chromium release. Presence of steam reinforced the effect of HCl on chromium attributing to the significant transition of CrOx(OH)y to CrO2Cl2. Although CaO and Fe2O3 both exhibited good reactivity with chromium, presence of HCl largely suppressed chromium capture by CaO and Fe2O3. Moreover, the inhibition effect of HCl on Fe2O3 was stronger than CaO for Cr capture.

Desorption of CO2, SO2, and NH3 in the vacuum evaporation of desulfurization wastewater.

Mechanical vapor compression and multi-effect evaporation have been widely used in achieving zero discharge of desulfurization wastewater as they are energy-saving and efficient technologies. Solubilized weak ions, such as CO32-, SO32-, and NH4+, in the desulfurization wastewater are partly converted into CO2, SO2, and NH3, respectively, during the vacuum evaporation process, thus affecting the heat exchange and compressor performance. In this study, the migration and coupling mechanism of CO2, SO2, and NH3 desorption in desulfurized wastewater under vacuum evaporation were analyzed. The effects of temperature, pressure, reaction time, and other factors on the migration process were discussed. The hydrolysis and electrolytic equilibrium constants of the related ions were obtained for temperatures between 70 and 90 °C. The results demonstrate the relationship between the desorption capacities of CO2, SO2, and NH3 and the hydrolysis constants of their respective ions. The desorption of CO2 and NH3 increased significantly when CO32- and NH4+ coexisted, whereas the SO2 desorption capacity remained low under the same experimental conditions. The experimental results indicate that the desorption of CO2, SO2, and NH3 is controlled by chemical reactions and can be described by first-order reaction kinetics.

Efficient Removal of Elemental Mercury from Coal-Fired Flue Gas over Sulfur-Containing Sorbent at Low Temperatures.

In the work, sulfur-containing sorbents were employed to remove elemental mercury (Hg0) from coal-fired flue gas. The work used the thermogravimetric analysis, Brunauer-Emmett-Teller method, scanning electron microscopy with energy-dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy to characterize the physicochemical properties of the sorbents. The Hg0 removal performance of these used sorbents from the simulated coal-fired flue gas was evaluated by a bench-scale fixed-bed reactor. The results indicated that a generous amount of elemental sulfur covered the surface and pore structure of the used sorbent. With the rise of H2S selective oxidation temperature, both the sulfur content and specific surface area decreased rapidly. Used-Fe/SC120 could achieve the mercury removal efficiency of above 90% at 90 °C. The high temperature was not conducive to the mercury capture due to the release of surface elemental sulfur. The presence of O2 and SO2 inhibited Hg0 removal in different degrees because of the decreased active sulfur sites and competitive adsorption. Meanwhile, NO promoted the Hg0 removal efficiency by enhancing the Hg0 oxidation. The further analysis showed that the surface elemental sulfur was vital to capture the Hg0 from coal-fired flue gas, which reacted with Hg0 to form HgS.

Mechanism of the rapid mechanochemical degradation of hexachlorobenzene with silicon carbide as an additive.

Mechanochemical treatment (MCT) is a promising method for degrading hexachlorobenzene (HCB). Silicon carbide (SiC) was proposed in this study as a new additive to accelerate the reaction in MCT. The high performance of SiC was verified, and the relevant mechanism was explored. Graphite, amorphous carbon, CCl4, SiO2, and water-soluble chloride were confirmed as predominant products in the proposed method, and only trace-level low chlorinated benzenes were detected. The reaction pathway was revealed as follows: under the attack of free electrons, chlorine atoms were shed from the benzene rings of HCB to form Cl· radicals, which reacted with SiC to form SiCl4 and CCl4 and with the in situ-generated iron powder to produce Fe-based chloride. The left benzene rings were translated to graphite and amorphous carbon. As an intermediate product, SiCl4 further reacted with water vapor in the atmosphere to produce SiO2 and HCl. The in situ-generated iron powder could not remarkably accelerate the degradation reaction. The major contribution of SiC was the supply of free electrons to trigger the reaction. Two sources of free electrons were discussed. Friction heat resulting from hard SiC also contributed to the endothermic reaction of HCB degradation.

A novel on-site wheat straw pretreatment method: Enclosed torrefaction.

In this study, a novel on-site torrefaction method was proposed for the pretreatment of wheat straw, in which the wheat straw was placed in an enclosed environment for torrefaction. The effects of different torrefaction conditions on the properties of both solid and gaseous products were investigated. When the temperature of enclosed torrefaction increased from 200 °C to 250 °C, the higher heating value, fixed carbon and C content of wheat straw increased by 12.7%, 80.3% and 18.1%, respectively, and the moisture decreased by 25.0%. Enclosed torrefaction causes more mass loss due to the smoldering of wheat straw, and a strong decomposition of the hemicellulose of wheat straw during the torrefaction process. The gaseous products obtained by enclosed torrefaction have fewer acids and more esters than conventional torrefaction. Compared with conventional torrefaction, enclosed torrefaction performs similarly, or even better, in improving the properties of wheat straw.