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Energy field-assisted machining technology has the potential to overcome the limitations of machining difficult-to-machine metal materials, such as poor machinability, low cutting efficiency, and high energy consumption. High-speed dry milling has emerged as a typical green processing technology due to its high processing efficiency and avoidance of cutting fluids. However, the lack of necessary cooling and lubrication in high-speed dry milling makes it difficult to meet the continuous milling requirements for difficult-to-machine metal materials. The introduction of advanced energy-field-assisted green processing technology can improve the machinability of such metallic materials and achieve efficient precision manufacturing, making it a focus of academic and industrial research. In this review, the characteristics and limitations of high-speed dry milling of difficult-to-machine metal materials, including titanium alloys, nickel-based alloys, and high-strength steel, are systematically explored. The laser energy field, ultrasonic energy field, and cryogenic minimum quantity lubrication energy fields are introduced. By analyzing the effects of changing the energy field and cutting parameters on tool wear, chip morphology, cutting force, temperature, and surface quality of the workpiece during milling, the superiority of energy-field-assisted milling of difficult-to-machine metal materials is demonstrated. Finally, the shortcomings and technical challenges of energy-field-assisted milling are summarized in detail, providing feasible ideas for realizing multi-energy field collaborative green machining of difficult-to-machine metal materials in the future.

Robots with transformable tracked mechanisms are widely used in complex terrains because of their high adaptability, and many studies on novel locomotion mechanisms have been conducted to make them able to climb higher obstacles. Developing underactuated transformable mechanisms for tracked robots could decrease the number of actuators used while maintaining the flexibility and obstacle-crossing capability of these robots, and increasing their cost performance. Therefore, the underactuated tracked robots have appreciable research potential. In this paper, a novel tracked robot with a newly proposed underactuated revolute‒revolute‒prismatic (RRP) transformable mechanism, which is inspired by the sit-up actions of humans, was developed. The newly proposed tracked robot has only two actuators installed on the track pulleys for moving and does not need extra actuators for transformations. Instead, it could concentrate the track belt's tension toward one side, and the unbalanced tension would drive the linkage mechanisms to change its configuration. Through this method, the proposed underactuated design could change its external shape to create support points with the terrain and move its center of mass actively at the same time while climbing obstacles or crossing other kinds of terrains, thus greatly improving the climbing capability of the robot. The geometry and kinematic relationships of the robot and the crossing strategies for three kinds of typical obstacles are discussed. On the basis of such crossing motions, the parameters of links in the robot are designed to make sure the robot has sufficient stability while climbing obstacles. Terrain-crossing dynamic simulations were run and analyzed to prove the feasibility of the robot. A prototype was built and tested. Experiments show that the proposed robot could climb platforms with heights up to 33.3% of the robot's length or cross gaps with widths up to 43.5% of the robot's length.

The deployable telescopic boom, whose mass and stiffness play crucial roles, is extensively used in the design of space-deployable structures. However, the most existing optimal design that neglects the influence of the locking mechanisms in boom joints cannot raise the whole stiffness while reducing the boom mass. To tackle this challenge, a novel optimization model, which utilizes the arrangement of the locking mechanisms to achieve synchronous improvement of the stiffness and mass, is proposed. The proposed optimization model incorporates a novel joint stiffness model developed based on an equivalent parallel mechanism that enables the consideration of multiple internal stiffness factors of the locking mechanisms and tubes, resulting in more accurate representations of the joint stiffness behavior. Comparative analysis shows that the proposed stiffness model achieves more than at least 11% improved accuracy compared with existing models. Furthermore, case verification shows that the proposed optimization model can improve stiffness while effectively reducing mass, and it is applied in boom optimization design.

The planetary roller screw mechanism (PRSM) is a novel precision transmission mechanism that realizes the conversion between linear and rotary motions. The contact characteristics of helical surfaces directly determine PRSM’s performance in load-carrying capacity and transmission accuracy. Therefore, studying the contact characteristics of PRSM forms the fundamental basis for enhancing its transmission performance. In this study, a three-dimensional parametric analysis method of contact characteristics is proposed based on the PRSM meshing principle and PyVista (a high-level API to the Visualization Toolkit). The proposed method considers the influence of machining errors among various thread teeth. The effects of key machining errors on contact positions and axial clearance, as well as their sensitivities, are analyzed. With excellent solution accuracy, this method exhibits higher calculation efficiency and stronger robustness than the analytical and numerical meshing models. The influence of nominal diameter and pitch errors of the screw, roller, and nut on the axial clearance follows a linear relationship, whereas flank angle errors have negligible effects on the axial clearance. The corresponding influence coefficients for these three machining errors on the axial clearance are 0.623, 0.341, and 0.036. The variations in contact positions caused by individual errors are axisymmetric. Flank angle errors and roller diameter errors result in linear displacements of the contact points, whereas pitch errors cause the contact points to move along the arc of the roller diameter. Based on the proposed three-dimensional parametric contact characteristics analysis method, the Fuzzy C-Means clustering algorithm considering error sensitivity is utilized to establish a component grouping technique in the selective assembly of critical PRSM components, ensuring the rational and consistent clearances based on the given component’s machining errors. This study provides effective guidance for analyzing contact characteristics and grouping in selective assembly for PRSM components. It also presents the proposed method’s potential applicability to similar calculation problems for contact positions and clearances in other transmission systems.

The failure types in gear systems vary, with typical ones mainly including pitting, cracking, wear, and broken teeth. Different modeling and stiffness calculation methods have been developed for various gear failure types. A unified method for typical gear failure modeling and stiffness calculation is introduced in this study by considering the deviations in the time-varying meshing stiffness (TVMS) of faulty gears resulting from the use of different methods. Specifically, a gear tooth is discretized into a large number of microelements expressed with a matrix, and unified models of typical gear failures are built by adjusting the values of the matrix microelements. The values and positions of the microelements in the tooth failure model matrix have the same physical meaning as the parameter variables in the potential energy method (PEM), so the matrix-based failure model can be perfectly matched with PEM. Afterward, a unified method for TVMS is established. Modeling of healthy and faulty gears with pitting, wear, crack, and broken tooth is performed with the matrix equation, and the corresponding TVMS values are calculated by incorporating the matrix models with PEM. On the basis of the results, the mechanism of typical fault types that affect TVMS is analyzed, and the conclusions are verified through the finite element method. The developed unified method is a promising technique for studying the dynamic response characteristics of gear systems with different failure types because of its superiority in eliminating stiffness deviations.

The plastic gear is widely used in agricultural equipment, electronic products, aircraft, and other fields because of its light weight, corrosion resistance, and self-lubrication ability. However, it has a limited range of working conditions due to the low modulus and thermal deformation of the material, especially in high-speed and heavy-duty situations. A compensation modification method (CMM) is proposed in this paper to restrain the heat production of the plastic gear tooth surface by considering the meshing deformation, and the corresponding modification formulas are derived. Improving the position of the maximum contact pressure (CP) and the relative sliding velocity (RSV) of the tooth surface resulted in a 30% lower steady-state temperature rise of the modified plastic gear tooth surface than that of the unmodified plastic gear. Meanwhile, the temperature rise of plastic gear with CMM is reduced by 19% compared with the traditional modification of removal material. Then, the influences of modification index and the segment number of modification on the meshing characteristics of plastic gear with CMM are discussed, such as maximum CP and steady-state temperature rise, RSV, transmission error, meshing angle, and contact ratio. A smaller segment number and modification index are beneficial to reduce the temperature rise of plastic gear with CMM. Finally, an experiment is carried out to verify the theoretical analysis model.

End worm gear drives are characterized by their multi-tooth contact, compact contour, and theoretical potential to overcome some inherent flaws of cylindrical worm drives. However, quantitative basic research on end worm gear drives is currently inadequate, which hinders the development of this transmission. This work focuses on the computational design of end worm gear drives and proposes a new Niemann-type design. Meshing models of the proposed drive are established, and its engagement theory is deduced systematically. Based on the derived tooth surface equations, an innovative research methodology for the tooth curve geometry of the end worm gear is created, and the tooth curve in the worm gear reference plane is proved to be a spiral. An improved formula for the lubrication angle is developed, which can provide more rational numerical results for the angle. Theoretically, the modified formula is universally applicable for line contact drives and can be used to quantitatively investigate the lubrication level between the teeth for the proposed drive. Simulation outcomes demonstrate the favorable characteristics of the transmission, including broad conjugate areas, even contact lines, and fine global lubrication state.

Planet pin position errors significantly affect the mechanical behavior of planetary transmissions at both the power-sharing level and the gear tooth meshing level, and its tolerance properties are one of the key design elements that determine the fatigue reliability of large aviation planetary systems. The dangerous stress response of planetary systems with error excitation is analyzed according to the hybrid finite element method, and the weakening mechanism of large-size carrier flexibility to this error excitation is also analyzed. In the simulation and analysis process, the Monte Carlo method was combined to take into account the randomness of planet pin position errors and the coupling mechanism among the error individuals, which provides effective load input information for the fatigue reliability evaluation model of planetary systems. In addition, a simulation test of gear teeth bending fatigue intensity was conducted using a power flow enclosed gear rotational tester, providing the corresponding intensity input information for the reliability model. Finally, under the framework of stress-intensity interference theory, the computational logic of total formula is extended to establish a fatigue reliability evaluation model of planetary systems that can simultaneously consider the failure correlation and load bearing time-sequence properties of potential failure units, and the mathematical mapping of planet pin positional tolerance to planetary systems fatigue reliability was developed based on this model. Accordingly, the upper limit of planet pin positional tolerance zone can be determined at the early design stage according to the specific reliability index requirements, thus maximizing the balance between reliability and economy.

Servo-hydraulic actuators (SHAs) are widely used in mechanical equipment to drive heavy-duty mechanisms. However, their energy efficiency is low, and their motion characteristics are inevitably affected by uncertain nonlinearities. Electromechanical actuators (EMAs) possess superior energy efficiency and motion characteristics. However, they cannot easily drive heavy-duty mechanisms because of weak bearing capacity. This study proposes and designs a novel electromechanical-hydraulic hybrid actuator (EMHA) that integrates the advantages of EMA and SHA. EMHA mainly features two transmission mechanisms. The piston of the hydraulic transmission mechanism and the ball screw pair of the electromechanical transmission mechanism are mechanically fixed together through screw bolts, realizing the integration of two types of transmission mechanisms. The control scheme of the electromechanical transmission mechanism is used for motion control, and the hydraulic transmission mechanism is used for power assistance. Then, the mathematical model, structure, and parameter design of the new EMHA are studied. Finally, the EMHA prototype and test platform are manufactured. The test results prove that the EMHA has good working characteristics and high energy efficiency. Compared with the valve-controlled hydraulic cylinder system, EMHA exhibits a velocity tracking error and energy consumption reduced by 49.7% and 54%, respectively, under the same working conditions.

For hundreds of years, water mills have supported the local economies of Piedmont by contributing to the production of flour, textile fibres, timber, and metal agricultural tools. Since the beginning of the last century, and in particular after the 1950s, many artefacts have been abandoned. Nonetheless, hundreds of mills are still present in southern Piedmont, both in the plains and in the mountains, sometimes in an excellent state of conservation. This work presents a hammer forge, the La Pianca mill in Busca, Cuneo, Italy, as a significant, detailed case study. The socio-economic context in which exists is analysed, its history is reconstructed, and the functioning of the machinery, including the water wheels, the motion transmission systems, and the various utilities consisting of tilt hammers, grinding wheels, and drills, is analysed in detail. Beyond the historical interest, concerning both the territory and the architecture, as well as the machines and mechanisms, this work aims to make a contribution to the prefiguration of effective scenarios for the reconversion of similar productive artefacts.