Facing some special operating environments or conditions, existing control methods for the peg-in-hole assembly guided by robots always have their own disadvantages, for example, low efficiency or poor adaptability. For the above problem, in this article, a new circular peg-in-hole assembly control strategy is proposed for the 6-Degree of Freedom (DOF) robot based on hybrid visual measurements, avoiding peg-in-hole contacts during the robotic operation. In the strategy, the pose of the monocular camera mounted at the end-effector is adaptively adjusted to improve the image quality through an algorithm based on the rough pose measurement of the target hole by the binocular camera; the accurate 3-D pose of the hole is determined by an algorithm based on processing of high-quality images and the compensation of the orientation error. Combined with the robotic collision-free path planning, the automatic peg-in-hole assembly can be implemented in real setting. The assembly precision of the robotic system based on the proposed method is validated and discussed based on experimental results. Then, the minimal peg-in-hole interval relative to the alignment error is modeled through the spatial relation analysis to analyze the applicable condition of the robotic system with the control strategy. Also, the reliability of the proposed strategy is verified through experimental tests under some applicable conditions. Finally, suggestions and plans of future works are discussed for further extension of the application area of the proposed strategy, such as fields of precision and ultraprecision manufacturing. This contribution has the major significance on the automatic peg-in-hole assembly under 3-D operating environment.

In this article, the experimental investigation and analysis of the effect of rheological properties on the starting torque of the magnetic fluid seal are reported. The change of the starting torque with a standing time for perfluoropolyether-based magnetic fluid seal and diester-based magnetic fluid seal, as well as the viscosity of magnetic fluids under the relevant magnetic field and shear rate, were measured. It was observed that the magnetic fluid with higher viscosity correspondingly exhibited higher starting torque. The starting torque of seals with two different magnetic fluids exhibited the same variation tendency. The starting torque was exponentially increased with the standing time and then tended to be a stable state with small scale fluctuation. The average maximum starting torque of PFPE-based ferrofluid seal after standing five days was ten times as large as the value of the initial standing, whereas that of diester-based ferrofluid seal was 3.5 times as large the value of the initial standing. The rheological behavior was the key factor influencing the starting torque of the magnetic fluid seal. Particle agglomeration and shear thinning were the main microscopic mechanisms leading to the change of starting torque with a standing time. The correlation between macroscopic rheological properties and starting torque was established based on the microstructure variation.

Magnetic fluids, as smart nanomaterials, have been successfully used in sealing applications and other fields. However, the temperature of magnetic fluids in the sealing gap is a key factor affecting sealing performances, limiting their application in high-speed sealing fields. Since obtaining a direct measurement of the magnetic fluid’s temperature is difficult, due to the small clearance, accurately calculating the maximum temperature of the magnetic fluid layer in high-speed seals is crucial. Herein, a mathematical model for calculating the maximum temperature of the magnetic fluid layer was established, by using a reasonable simplification of high-speed sealing conditions, and the calculation formula was modified by studying the rheological properties of the diester-based magnetic fluid. The results suggest that the calculation of the maximum temperature is influenced by viscous dissipation, and both are related to the rheological characteristics of magnetic fluids. When the influence of rheological properties is ignored, the calculation results are not accurate for higher-velocity seals, but the calculation model applies to lower-velocity seals. When the influence of rheological properties is considered, the calculation results obtained by the corrected formula are more accurate, and they are applicable to both lower- and higher-velocity seals. This work can help us more accurately and conveniently estimate the maximum temperature of magnetic fluids in high-speed seal applications, which is of theoretical and practical research significance for determining sealing performances and thermal designs.

Magnetic fluids, a new type of energy transfer fluid with tunable properties, have garnered significant interest from researchers worldwide. Hybrid magnetic fluids prepared by adding different types of nanoparticles exhibit superior thermophysical properties and functional characteristics. In this paper, we prepared a water-based magnetic fluid loaded with multi-walled carbon nanotubes (MCNTs), silver (Ag), and copper (Cu) to enhance thermal conductivity. Using a transient double hot-wire method, we designed and built an experimental measurement system for the thermal conductivity of magnetic fluids with an average measurement error of less than 5%. We studied the thermal conductivity of hybrid magnetic fluids under different conditions and evaluated the advantages and disadvantages of various models, including the Maxwell model, H&C model, Tim model, Y&C model, and Evans model. Our results show that MF+MCNTs, MF+Ag, and MF+Cu nanofluids can all improve the thermal conductivity of the carrier fluid, with MF+MCNTs exhibiting the best improvement effect of 10.93%. Among the five models evaluated, the Evans model had the best predictive effect with a deviation range within 5%. This work provides theoretical and practical reference for enhancing the thermal conductivity of magnetic fluids and provides a more accurate theoretical model for calculating the thermal conductivity of hybrid magnetic fluids.