A Multiscale Accuracy Degradation Prediction Method of Planetary Roller Screw Mechanism Based on Fractal Theory Considering Thread Surface Roughness

The wear problems are vital to the planetary roller screw mechanism (PRSM) as they have a great influence on transmission accuracy, working efficiency, and service life. However, the wear characteristics of the PRSM have been rarely investigated in the past. In this paper, a multiscale adhesive wear model is established by incorporating the effective wear coefficient and considering the thread surface roughness. The variation of surface roughness is characterized by the two-dimension Majumdar–Bhushan (MB) function. The multi-asperity contact regimes are used to estimate microcontact mechanics of the rough interface. Moreover, the influences of surface roughness, material properties, and working conditions on the wear depth and precision loss of the PRSM are studied in detail. The results reveal that as the surface roughness increases, the total actual contact area, wear depth, and precision loss rate rise. In addition, the adhesive wear increases with the growth of the axial load, and decreases with the increase in the material hardness and material elastic modulus ratio to a certain extent. The investigation opens up a theoretical methodology to predict the wear volume and precision loss with regard to thread surface roughness, which lays the foundation for the design, manufacturing, and application of the PRSM.

Rams Analysis for Different XT Technologies

This paper analyses the probability of failure on demand of different subsea christmas tree actuation principles and their related control system architectures. The all-electric technology has limited or insufficient field data available. This means that the reliability and availability analysis is based on theoretical analysis from data provided in reliability handbooks for mechanical and electronic components. The analysis includes the probability of failure on demand to isolate the well and the availability of each equipment type until a first failure causes the need for repair. The following different actuator and system designs were chosen for this analysis: – Spring based hydraulic actuator – Spring based electric actuator – Electric power screw actuator – Electric planetary roller screw actuator All Electric Systems (except the spring based electric actuator) utilize a battery to provide the energy for the valve operation. The reliability analysis provides detailed information about the major contributors that limit the reliability of the actuators and systems. With this knowledge, qualification activities can focus on the improvement of the reliability of the critical components and the actuator elements within the system. The power screw actuator and the corresponding system provides the best reliability and availability compared to other systems. The electric with spring design provides better results than the hydraulic with spring design. Generally, the battery-based systems provide a better reliability than spring-based designs. The most critical elements are the mechanical springs, sealings, brakes and the spindle mechanisms. Another aspect is the analysis of an optimized operation strategy in order to utilize the redundant components to improve the availability and reduce the number of interventions by analysis of the second and third failure in the system.

Lagrange-method-based dynamic analysis of multi-stage planetary roller screw mechanism

A rigid-body dynamic model of multi-stage planetary roller screw mechanism (multi-stage PRSM) is proposed in this paper. The structure of multi-stage PRSM is introduced and the motion analysis is presented. The total kinetic energy of the mechanism is calculated. The rotation of the screws and carriers is chosen as generalized degrees of freedom. The generalized forces and motion equations of multi-stage PRSM are derived using the Lagrange method. The transient and steady-state behaviours of multi-stage PRSM are simulated, followed by an analysis of the influence of friction coefficients and thread pitches on the motion and forces acting on the multi-stage PRSM. Taking a two-stage PRSM as an example, the simulation results show that the friction coefficient between screw #1 and screw #2 has a slight effect on efficiency and rotational velocity ratios of carriers to screws. When the sum of the pitches of screws is a constant, the axial component of contact force between screw #1 and roller #1 decreases with the increase in the pitch of screw #1.

Open Source 3D-Printable Planetary Roller Screw for Food Processing Applications

Historically, open source agriculture (OSA) was based on grassroots technology generally manufactured by hand tools or with manual machining. The rise of distributed digital manufacturing provides an opportunity for much more rapid lateral scaling of open source appropriate technologies for agriculture. However, the most mature distributed manufacturing area is plastic, which has limited use for many OSA applications. To overcome this limitation with design, this study reports on of a completely 3D-printable planetary roller screw linear actuator. The device is designed as a parametric script-based computer aided design (CAD) package to allow for the easy adaption for a number of applications such as food processing at different scales. The planetary roller screw is fabricated in dishwasher-safe polyethylene terephthalate glycol (PETG) on an open source machine and tested using an open source testing platform to determine if it could maintain a constant load without slipping and the maximum force. Then, this output is compared to a direct screw press using the same materials. The results found that the maximum force is more than doubled for the roller screw actuator using the same materials, making them adequate for some food processing techniques. Future work is outlined to improve the performance and ease of assembly.

Dynamic Modeling of the Double-Nut Planetary Roller Screw Mechanism Considering Elastic Deformations

With the rising application of double-nut Planetary Roller Screw Mechanism (PRSM) into industry, increasing comprehensive studies are required to identify the interactions among motion, forces and deformations of the mechanism. A dynamic model of the double-nut PRSM with considering elastic deformations is proposed in this paper. As preloads, inertial forces and elastic deformations have a great influence on the load distribution among threads, the double-nut PRSM is discretized into a spring-mass system. An adjacency matrix is introduced, which relates the elastic displacements of nodes and the deformations of elements in the spring-mass system. Then, the compressive force acting on the spacer is derived and the equations of load distribution are given. Considering both the equilibrium of forces and the compatibility of deformations, nonlinear equations of motion for the double-nut PRSM are developed. The effectiveness of the proposed model is verified by comparing dynamic characteristics and the load distribution among threads with those from the previously published models. Then, the dynamic analysis of a double-nut PRSM is carried out, when the rotational speed of the screw and the external force acting on the nut #2 are changed periodically. The results show that if the external force is increased, the preload of the nut #1 is decreased and that of the nut #2 is increased. Although the nominal radii of rollers are the same, the maximum contact force acting on the roller #2 is much larger than that of the roller #1.