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In order to meet the needs of intensive mechanized picking in trellised pear orchards, this paper designed a pick-place integrated end-picker based on the analysis of agronomic characteristics of trellised pear gardens and fruit. In order to realize the accurate positioning of pears in picking, based on the kinematic analysis of robot arms and the construction of a private dataset, the YOLOv5s object detection algorithm was used in conjunction with a depth camera to achieve fruit positioning. The hand–eye system calibration was carried out. Aiming at solving the problems of redundancy, inefficiency, and uneven distribution of task volume in the conventional multiple robot arms algorithm, a simulated annealing algorithm was introduced to optimize the picking sequence, and a task allocation method was proposed. On the basis of studying several key parameters affecting the performance of the algorithm, the picking efficiency was greatly optimized. And the effectiveness of the proposed multi-robot collaborative picking method in a trellised pear orchard environment was demonstrated through experiments and simulation verification. The experiments showed that the picking efficiency of the integrated end-picker was increased by about 30%, and the success rate was significantly higher than that of the flexible grippers. The results of this study can be utilized to advance robotic pear-picking research and development. [ABSTRACT FROM AUTHOR]

Soft robots have drawn a lot of attention due to their soft materials that make them highly flexible and adaptable to complex environments. However, these also make soft robots not suited to high-load tasks, and achieving controllable material stiffness variation is still a challenge. Herein, we designed a soft structure with variable stiffness based on electrorheological fluids, which presented the advantages of continuously variable stiffness and fast response. The structure exhibited a stiffness of up to 1065 mN mm−1 when the electric field strength was 4.5 kV mm−1 (displacement of 1 mm). When varying the electric field strength (0 to 4.5 kV mm−1), the rate of stiffness variation was over 1500%. According to the load cycle experiments, it was shown that the structure's response time to a change in load was less than 65 ms, and that the structure changes could be made repeatedly. In addition, we demonstrated the functions of stiffness adjustment, shape memory, and motion locking of the structure. This work has potential applications in the fields of soft robotics and artificial muscles. [ABSTRACT FROM AUTHOR]

Based on cores from tight oil reservoirs in Ordos Basin, water flooding experiments with both low and high displacement pressures were carried out. Combined with NMR, quantitative analysis approaches for produced oil under different microscopic effects were established for quantitative research of the microscopic mechanism of water flooding in tight reservoirs. The research indicated that under low displacement pressure, oil recovery mechanisms of hydrophilic cores mainly include displacement, imbibition, and denudation, and those of wetting cores mainly include displacement and imbibition. After increasing the displacement pressure, both hydrophilic and neutral wetting cores have a certain increase in oil recovery. The common point is that both oil controlled by small throats and remaining oil droplets controlled by traps in large pores have been activated, while the discrepancy is that the oil film of the neutral wetting core boundary layer becomes thinner, which improves oil recovery ratio, and these mechanisms have less effect on hydrophilic cores. The amount of oil produced by each type of oil recovery mode was quantitatively analyzed. Percentages of produced oil in hydrophilic cores by flooding and imbibition and denudation are 15% and 12%, respectively, which are the main oil recovery mechanisms; percentages of produced oil in neutral wetting cores by displacement and imbibition are 25% and 2%, respectively, with displacement as the main oil recovery mechanism. After increasing the displacement pressure, oil produced by hydrophilic and neutral wetting cores increased by 6% and 9%, respectively, indicating that with increasing the displacement pressure, a part of the boundary layer of oil could be produced in neutral wetting cores. [ABSTRACT FROM AUTHOR]

Based on rock samples of tight oil reservoirs in the buried hills of North China, conventional gas flooding and high-speed centrifugal experiments at different pressures were carried out. Combined with nuclear magnetic resonance experiments, an evaluation method of oil production potential in fractured porous media was established to quantitatively study the gas flooding potential of target reservoirs. Results indicated that the "gas fingering phenomenon" is serious in conventional gas flooding experiments of fractured cores even under low pressures because of fractures. With an increase in flooding pressure, the changes of T2 (T2 relaxation time) spectrum and displacement percentage are relatively small, which means that the displacement efficiency has not been improved significantly (the flooding pressure for these three cores increased from 0.014 MPa to 2.6 MPa, with an average increase in displacement percentage of 6.3%). High-speed centrifugation can realize "homogeneous displacement" of the cores and overcome the influence of gas channeling. With an increase in the displacement pressure, the T2 spectrum and percentage of displaced oil varied obviously, and the displacement efficiency improved greatly (the flooding pressure for these three cores increases from 0.014 MPa to 2.6 MPa, with an average percentage of displaced oil being increased to 16.16%). Using the method of this study, 13 cores of the target reservoir were evaluated for gas flooding potential. The percentage of available pores in the target reservoir ranges from 17.64% to 58.54%, with an average of 33.84%. Movable fluid controlled by microthroats in the reservoirs larger than 0.1 mD is about 20%, while that in the reservoirs smaller than 0.1 mD is about 5%. This study indicates that the development of fractures and microfractures controls the physical properties and fluid productivity of reservoirs. [ABSTRACT FROM AUTHOR]

In order to increase single well control area, producing degree and production of single well, a pilot test of bi-lateral horizontal well acidizing was conduced in K oilfield, Kazakhstan. First, clean self-diverting-acid system was chosen as the main acid, which has self-diverting and little formation pollution, based on the characteristics of the reservoir, lithology and physical properties of this oilfield. Besides, nitrogen and liquid nitrogen were used to temporarily block high permeability layers and make the acidizing more uniform. They can also accelerate flowing back velocity of residual acid. Treating pressure, pumping rate, and coiled tubing drawback velocity were optimized. The analysis after acidizing shows that acidizing worked in plugging removal and productivity restoration in both branches, and the production of single branch equals to its neighbour well separately. This means that bi-lateral horizontal well acidizing can get good application effect in this oilfield. [ABSTRACT FROM AUTHOR]

In Zanazour oilfield, wells feature long perforation interval, multiple perforation stages, large difference between layers and uneven production profile. In order to acidize uniformly, improve oil production profile and increase the producing degree of low permeability layers, selective acid systems, which can temporary block high-permeability layers and divert acid to low-permeability layers, have been researched and used in Kazakhstan Zanazour oilfield carbonate reservoirs. First, according to the reservoir, lithology and physical properties of this oilfield, three acid systems were chosen as the main acid, which have better blocking, diversion and low damage and good compatibility with the reservoir. Besides, their performances have been evaluated by experimental tests. Furthermore, selective foam acidizing and self diverting-emulsified acid system were utilized to achieve synergy diverting and better uniformity of acidizing, speed up flowing back rate and increase acidizing penetration depth. Field application results show that the technology can increase production significantly, and have a promising application prospect in this field. [ABSTRACT FROM AUTHOR]

To improve the producing reserves and well production of the sub-salt carbonate reservoirs in Kenhkiak, segregated acid fracturing pilot tests were taken on 5 openhole wells in the reservoir. The host acid was determined to be the clean steering acid with good formation compatibility and ability of stimulating deeply and uniformly. Then the integrated pipe structure of gas lifting, completion, and acid fracturing was optimized. The field operation was completed with obvious stimulation effect through optimizing section amounts, packer positions, and technical parameters. The technique provided valuable experience for stimulating the same type of reservoirs. [ABSTRACT FROM AUTHOR]

Brain-computer interface (BCI) based on speech imagery can decode users' verbal intent and help people with motor disabilities communicate naturally. Functional near-infrared spectroscopy (fNIRS) is a commonly used brain signal acquisition method. Asynchronous BCI can response to control commands at any time, which provides great convenience for users. Task state detection, defined as identifying whether user starts or continues covertly articulating, plays an important role in speech imagery BCIs. To better distinguish task state from idle state during speech imagery, this work used fNIRS signals from different brain regions to study the effects of different brain regions on task state detection accuracy. The imagined tonal syllables included four lexical tones and four vowels in Mandarin Chinese. The brain regions that were measured included Broca's area, Wernicke's area, Superior temporal cortex and Motor cortex. Task state detection accuracies of imagining tonal monosyllables with four different tones were analyzed. The average accuracy of four speech imagery tasks based on the whole brain was 0.67 and it was close to 0.69, which was the average accuracy based on Broca's area. The accuracies of Broca's area and the whole brain were significantly higher than those of other brain regions. The findings of this work demonstrated that using a few channels of Broca's area could result in a similar task state detection accuracy to that using all the channels of the brain. Moreover, it was discovered that speech imagery with tone 2/3 tasks yielded higher task state detection accuracy than speech imagery with other tones.