Friction Properties of Crystalline Cellulose Sliding on Chromium under Water Lubrication Based on Molecular Dynamics Simulations.

This work studies the friction and wear behaviors of chromium (hard material) and crystalline cellulose (soft material) under water lubrication considering the loading and sliding velocity on friction force, temperature of contact interfaces, and worn atoms from the atomic view. The change of friction force with sliding velocity is greater than that with loading, and it is easier to obtain a stable friction at high velocity. The average friction force in the stabilization gradually increases with loading and velocity, and the growth rate decreases with loading, while it increases with velocity. The temperature of contact interfaces at the beginning of sliding changes rapidly and gradually becomes stable. The temperature at the stabilization increases distinctly with velocity, while it does not change much with loading. Both the loading and sliding velocity have an important influence on the wear of soft material; it is noticed that the amount of worn atoms increases close to exponentially with velocity and linearly with loading. However, the wear of hard material changes less with increasing loading and sliding velocity.

Force-Free Control for Direct Teaching of a Surgical Assistant Robot End Effector with Wire-Driven Bidirectional Telescopic Mechanism.

This paper shows the design and modeling of an end effector with a bidirectional telescopic mechanism to allow a surgical assistant robot to hold and handle surgical instruments. It also presents a force-free control algorithm for the direct teaching of end effectors. The bidirectional telescopic mechanism can actively transmit force both upwards and downwards by staggering the wires on both sides. In order to estimate and control torque via motor current without a force/torque sensor, the gravity model and friction model of the device are derived through repeated experiments. The LuGre model is applied to the friction model, and the static and dynamic parameters are obtained using a curve fitting function and a genetic algorithm. Direct teaching control is designed using a force-free control algorithm that compensates for the estimated torque from the motor current for gravity and friction, and then converts it into a position control input. Direct teaching operation sensitivity is verified through hand-guiding experiments.

Mechanical properties and physicochemical characteristics of cotton fibers during combing process.

This study employs a combination of experiments and molecular dynamics to analyze the mechanical properties and surface damage characteristics of cotton fibers during the combing process. Additionally, it investigates the alterations in physical and chemical properties at the atomic scale resulting from mechanical damage. Raw cotton (RC) is combed to 1st combed cotton (1st CC), 2nd combed cotton (2nd CC) and 3rd combed cotton (3rd CC). It was found that the mechanical properties and crystallinity showed an increasing and then decreasing trend with the process of combing, and the degree of surface tearing increased, and the binding energy of C and O shifted to a lower position. The breaking strength of cotton fibers first increased by 7.4 % and then decreased by 11 % and 7.7 % respectively, and the crystallinity was CrI (RC) = 70.8 %, CrI (1st CC) = 75.3 %, CrI (2nd CC) = 72.7 %, and CrI (3rd CC) = 71.8 % respectively. The C-O bond and the C-C bond at the amorphous regions are broken after combing lead to the cellulose chain to break, resulting in a decrease in the breaking strength of the fibers. The C-O bond as well as the C-O-C bond angles changes significantly during stretching, and the increase in ordering of the amorphous regions causes an increase in crystallinity.

Investigation of the microscopic damage mechanisms in cotton fibers induced by mechanical friction.

For the problem of friction damage in cotton fiber processing, a multi-scale combination of investigation methods is proposed. The surface of damaged cotton fiber is detected by relevant test means with damage features such as dislocations, defects and cracks. The internal pyranose ring and glycosidic bond fail, the crystallinity decreases, and the number of hydrogen bonds decreases. Anisotropy exists in the frictional properties of the microscopic surface of the cotton fiber. The results of molecular dynamics simulation showed that the cellulose main chain failed mainly at the glycosidic bond, and the side chain failed mainly at the hydroxymethyl functional group. Its interchain hydrogen bond O3H…O5 was the least damaged. The cellulose crystal (200) surfaces had poor abrasion resistance, and the frictional properties of each crystal surface were anisotropic. The results of the study provide a theoretical basis for improving friction and wear problems in cotton fiber processing.

Soft tissue surgical robot for minimally invasive surgery: a review.

Purpose: The current state of soft tissue surgery robots is surveyed, and the key technologies underlying their success are analyzed. State-of-the-art technologies are introduced, and future directions are discussed. Methods: Relevant literature is explored, analyzed, and summarized. Results: Soft tissue surgical robots had rapidly spread in the field of laparoscopic surgery based on the multi-degree-of-freedom movement of intra-abdominal surgical tools and stereoscopic imaging that are not possible in conventional surgery. The three key technologies that have made surgical robots successful are wire-driven mechanisms for multi-degree-of-freedom movement, master devices for intuitive remote control, and stereoscopic imaging technology. Recently, human-robot interaction technologies have been applied to develop user interfaces such as vision assistance and haptic feedback, and research on autonomous surgery has begun. Conclusion: Robotic surgery not only replaces conventional laparoscopic surgery but also allows for complex surgeries that are not possible with laparoscopic surgery. On the other hand, it is also criticized for its high cost and lack of clinical superiority or patient benefit compared to conventional laparoscopic surgery. As various robots compete in the market, the cost of surgical robots is expected to decrease. Surgical robots are expected to continue to evolve in the future due to the need to reduce the workload of medical staff and improve the level of care demanded by patients.

Research on an intelligent diagnosis method of mechanical faults for small sample data sets.

The difficulty of feature extraction and the small sample size are two challenges in the field of mechanical fault diagnosis for a long time. Here we propose an intelligent mechanical fault diagnosis method for scenario with small sample datasets. This method can not only diagnose bearing faults but also gear faults, and has strong generalization performance. We use convolutional neural network to realize automatic feature extraction. Through sliding window scanning, one sample set is expanded to three sub-sample sets with different scales to meet the needs of deep learning training. Three convolutional networks are used to extract the features of the subsets respectively to ensure that their useful features are fully extracted. After feature extraction, the feature is reconstructed through feature splicing. Because of the unique advantages of SVM in dealing with small sample sets, we use SVM to classify the reconstructed features. We use the bearing data set collected by Case Western Reserve University in the United States, the bearing fault data set collected by Xi'an Jiaotong University in China, and the gearbox fault data collected by the University of Connecticut in the United States to conduct experiments. The experimental results show that the accuracy of training, validation and testing of the proposed method on the three data sets all reach 100%. This proves that our method can not only tackle the two challenges, but also has high fault diagnosis accuracy and strong generalization performance. It is hoped that our proposed method can contribute to the development of mechanical fault diagnosis.

Na⁺/K⁺ Hybrid Battery Based on a Sulfurized Polyacrylonitrile Cathode.

Sulfurized polyacrylonitrile (SPAN) nanocomposites were synthesized and used as a cathode in a novel rechargeable Na⁺/K⁺ hybrid battery with high performance for the first time. When 0.9 mol NaPF6 and 0.1 mol KPF6 were dissolved in ethylene carbonate (EC)/dimethyl carbonate(DMC)/ethyl methyl cabonate(EMC) (4:3:2, v/v/v), used as hybrid electrolyte, Na foil was used as the anode, and SPAN composites were used as the cathode, a hybrid ion system was created via composition⁻decomposition between Na⁺/K⁺ and SPAN and stripping⁻depositing of Na⁺ with suppressed dendrites by taking advantage of the self-healing electrostatic shield effect. As a result, a highly reversible calculated capacity of 1405.5 mAh gsulfur-1 with a coulombic efficiency approaching 100% after 100 cycles was obtained at a current density of 35 mA g-1. This environmentally benign, low-cost Na⁺/K⁺ hybrid battery shows promise as a new future flexible energy storage system (ESS) technology.

Mechanical interlocking of cotton fibers on slightly textured surfaces of metallic cylinders.

Mechanical interlocking is widely applied in industry and general lives of human beings. In this work, we realized the control of locking or sliding states of cotton fibers on the metal surfaces with slightly different textures through traditional machining. Three types of sliding states, i.e., locking, one-way sliding, and two-way sliding have been achieved. It is found that the locking or sliding of the cotton fibers on the metallic cylinder depends on the friction coefficient and the ratio of cotton fiber diameter, 2r, to the height of the rough peaks, h, of metal surfaces. When the critical ratio h/r exceeds 1, the cotton fibers could tightly attach to the metallic surface through mechanical interlocking. This work provided a convenient and universal method for the control of interlocking or sliding of fiber-based materials on textured surfaces.