Design and motion control of an under-actuated snake arm maintainer

This study presents an under-actuated snake arm maintainer (SAM) for complex and extreme environments such as nuclear power plants. The structure adopts the layered cable drive principle, whereby a single drive layer drives multiple joints. This design significantly reduces the complexity of the control system while increasing the spatial curvature. The traction of multiple wire ropes with a composite capstan drives the synchronous angular motion of several adjacent joints. By changing the number of joints in the single driver layer of the snake arm, the arm can be adapted to various complex environments. The trajectory planning and trajectory tracking motion control methods of the under-actuated SAM are established based on the improved backbone method and the variable rod length algorithm. Finally, a 10-joint prototype with an arm length of 2300 mm is designed for nuclear reactor maintenance. Trajectory experiments confirmed the rationality of the under-actuated SAM, the correctness of the inverse kinematics, and the effectiveness of the motion control methods.

Numerical Modeling of Mine Hoist Disc Brake Temperature for Safer Operation

The sustainable exploitation of raw materials, with improved safety and increased productivity, is closely linked to the development of mechanical mining installations. Mine hoists are designed for the transport of material, equipment and personnel between the mine surface and the underground. The mine hoist braking system is of paramount importance in its safe operation. Thus, for both drum and disc brake systems, the temperature of the friction surfaces is important for ensuring efficient braking, as exceeding the temperature threshold causes a decrease in the braking capacity. In this paper we present a numerical calculation model for the temperature of the braking disc of a mine hoist in the case of emergency braking. A real-scale model was built, based on the cable drive wheel and disc brake system of a hoisting machine used in Romania. Real material characteristics were imposed for the brake discs, the cable drive wheel and the brake pads. The simulation was performed for decelerations of 3, 3.5, 4 and 4.5 m/s2. The analysis shows that regardless of the acceleration and time simulated, the disc temperature reaches its maximum after 1.35 s of emergency braking. This value does not exceed the 327 °C limit where, according to previous studies, the braking power starts to fade. It means that the emergency braking is safe for the acceleration and masses under consideration, in the case of the studied mine hoist.

Design and Analysis of Synchronous Joint for SAR Antenna Deployable Mechanism

Synchronous joints are an important part of the SAR antenna deployment mechanism. They are the key to the synchronized deployment of antenna. By means of mechanism combination and deformation, a new type of synchronous joint with a precise cable drive system is designed in order to meet the requirements of SAR antenna deployment mechanism. This study mainly focuses on the design of the synchronous joint, including the system design and the precise cable drive system design. By applying a preload to the drive cable, the transmission gap is reduced, and the accuracy and efficiency of transmission are improved. This paper focuses on the theoretical calculation and analysis of the preload and system stiffness of the precise cable drive system. Based on the Euler equation of the flexible friction drive, the stiffness formula of the cable drive system is derived. In addition, the main design parameters affecting the stiffness of the cable drive system are analyzed parametrically. The comparison between the results obtained from the system stiffness experiment and the theoretical calculation result indicates that the experimental values are slightly smaller than the theoretical values, and the trend of change is basically consistent. This experiment therefore verifies the validity of the stiffness calculation formula and theoretical analysis.

Analytical and experimental research on transmission backlash in precise cable drive for an electro-optical targeting system

Due to transmission backlash of precise cable drive in electro-optical targeting system, it is difficult to predict force and pointing precisely during target detection. This article aims to develop a rigorous model for predicting the cable tension and transmission backlash of precise cable drive in electro-optical targeting system to better evaluate the performance in the preliminary design stages. The model of transmission backlash in different phase is established by satisfying the system’s geometric and equilibrium constraints, which is applicable to cable drive systems with any external load, pretension, and motion trajectories. Simulations are conducted to reveal the changes of cable deformation, cable tension, and deflection angles. The model is validated by experiments using a suitable experimental setup, predicting transmission backlash with the error level of 8.27%. The sensitivities of the preload force and external load are tested, and corresponding results are in good agreement with the theoretical ones. The backlash plunges dramatically when the preload force is small and flattens out when the preload force is larger than the threshold value. A proper preload force should be applied to keep the backlash in stable state. The threshold value could be predicted by the proposed model. The method presented in this article could provide a theoretic guide for system design and nonlinearity compensation.