Pair Of Threads Research Articles

A comprehensive sliding wear prediction method for planetary roller screw mechanism

The thread-pairs wear has a significant role in the transmission accuracy, operational stability and service life of planetary roller screw mechanism (PRSM). Nevertheless, the previous literatures still lack the investigation on the wear evolution of roller, nut and screw. Hence, an accumulative wear depth (AWD) prediction model is proposed for PRSM with reciprocating motion. The presented model is validated by the measured wear phenomena of thread pairs and the experimental results in the literature. The equivalent sliding wear experiment of PRSM is designed and the sliding wear coefficient of PRSM material is obtained by the equivalent sliding wear experiment. Considering the thread profile error caused by AWD of roller, nut and screw, the load distribution (LD) and sliding velocities on screw-roller (SR) and nut-roller (NR) sides are calculated. More importantly, the interactions between the AWD, LD and sliding velocity are investigated. Furthermore, the effects of axial load on the AWD, sliding velocities in contact regions and load distribution coefficient are analyzed.

Study on calculation method for dynamic load distribution of thread pair of planetary roller screw mechanism

To reveal the dynamic load distribution characteristics of planetary roller screw mechanism under the high-speed operating conditions, based on the spiral surface equation and deformation coordination relationship, a static contact force calculation method of the roller-screw and roller-nut thread at the contact point is proposed, and a formula for calculating the contact angle after bearing is derived. On this basis, further considering the inertial force generated by using high-speed operation, a dynamic load distribution model for planetary roller screw mechanism thread was established. By comparing with the finite element contact model of planetary roller screw mechansim, the error is below 5%, which verifies the correctness of the model established. Finally, the influence of the parameters such as screw speed, axial load, pitch, and tooth flank angle on the distribution of dynamic load was analyzed. The results show that the inertia force causes the roller to have a tendency to move closer to the nut and away from the screw resulting in a decrease in dynamic contact force on the roller screw side and an increase in dynamic contact force on the roller nut side. The degree of uneven distribution of dynamic load is positively correlated with the screw speed and pitch, and negatively correlated with the tooth side angle. The size of axial load has a significant impact on the distribution of dynamic load.

Studies on meshing clearance of thread pairs of planetary roller screw mechanism in different directions

The helix surface model of planetary roller screw mechanism (PRSM) is established by utilizing the parametric equations of space surface according to the structural features of screw, roller and nut. The helix surface model of PRSM is improved in consideration of the PRSM assembly relationship. The normal vector equations of helix surfaces are obtained based on the helix surface model. The meshing clearance models of PRSM in axial, radial and circumferential directions are built considering the movement direction of parts utilizing surface meshing conditions. The influence of structural parameters on the meshing clearance of PRSM is also analyzed. The results show that the meshing points between the roller and the screw in three directions are not in the middle diameter. The meshing points in the three directions of the roller and the nut are in the middle diameter of the roller. The pitch, tooth angle and tooth thickness of the thread all have an influence on the meshing clearance of PRSM. Only by increasing the tooth thickness of the thread can the meshing clearance in the three directions be reduced at the same time. The pitch and tooth angle should be selected properly to meet the practical requirements.

Effects of Eccentric Errors on Sliding Velocity and Accumulative Wear Depth of Planetary Roller Screw Mechanism

Abstract The eccentric errors of planetary roller screw mechanism (PRSM) affect the contact kinematic characteristics and exacerbate the cumulative wear of thread pairs, which will reduce its transmission accuracy and reliability. Hence, it is significant to investigate the cumulative wear of PRSM with the eccentric errors. In this work, based on the conjugate surface contact condition and Archard wear theory, the sliding speed and cumulative wear depth of PRSM with eccentricity errors are modeled, respectively. The effects of eccentric errors on the sliding velocities and cumulative wear depth of PRSM are investigated. It has been determined that the eccentric errors of the screw and nut do not cause the sliding motion in the nut–roller contact region (NRCR). However, there are noticeable variations in sliding velocity and cumulative wear depth in the screw–roller contact region (SRCR). The eccentric errors of the screw and nut have a combined effect on the sliding velocity and wear between the screw and roller. This investigation and finding can provide a valuable reference for the processing and assembly of PRSM.

Steel–aluminum screw–thread pair tightening mechanism and fastening axial force conversion efficiency

During the tightening of bolted connection, the tightening torque of the bolt is converted into its fastening axial force. The magnitude of the fastening axial force significantly affects the reliability and fatigue strength of bolted connections. Herein, a theoretical analysis of the tightening process of bolt connection is conducted using a power exponent hardening constitutive model, and the expressions of the tightening angle–fastening axial force and tightening angle–tightening torque during the tightening process are derived. A fine finite element model of steel–aluminum thread connections that can be used to simulate the actual tightening process considering the detailed thread structure is established. The accuracy of the theoretical formula is verified by finite element method and experiment, respectively. Through finite element simulation and experiment, the correctness of the formula is verified. Further, the conversion efficiency of the fastening axial force of the steel–aluminum screw–thread pair is analyzed by combining finite element analysis and theory. The results show that under the same tightening torque, the conversion efficiency of the fastening axial force can be increased by 6.8%–9.3% by appropriately reducing the friction coefficient of the steel–aluminum threaded connection pair. By controlling the fluctuation range of the friction coefficient, the dispersal error of the fastening axial force can be reduced by 26.9%–36.7%. The angle method is more conducive to improving the connection reliability of the steel–aluminum screw–thread pair than the torque method.

Modeling of End Face Perpendicularity Error and Its Influence Mechanism on Thread Assembly Clamping Force

The precise control of thread clamping force is the main means to achieve the assembly performance of electromechanical systems. The end face perpendicularity error generated in thread machining causes changes in the meshing contact stress and end face stress after thread fitting, which makes the variations of the relationship between tightening torque and clamping force during the thread tightening process. As a result, the dispersion of the final clamping force is increased after the thread assembly, and the fit of the mounting edge becomes worse, which affects the overall performance of the electromechanical systems. In terms of the above issues, this paper takes a M5 bolt as an example to accurately represent and simulate the end face perpendicularity error and connection performance of the bolting using a computer. A digital twin model for thread clamping is established and the study of thread clamping is conducted. Firstly, the 3D point cloud data considering the perpendicularity error of the end face is obtained, and the NURBS surface numerical model is applied to developing the surface models of thread and end face. Then, a geometric digital twin model of the bolt with perpendicularity error is established using CAD. Furthermore, a physical digital twin model of the tightening process of bolting is established using finite element method. Based on the numerical simulation results, the effect of different perpendicularity errors on the stresses of the thread pair and end face are analyzed, and the variation law of tightening accuracy is determined. The influence mechanism of end face perpendicularity error on the clamping force of bolt assembly is revealed. Finally, by comparing the tightening process with M5 standard bolts, the effect of perpendicularity error on the error in the clamping force prediction is investigated, which provides a theoretical basis for achieving precise control of thread clamping force.

Investigation on fatigue life of HAp and rGO hybrid coating on the PEEK artificial screws for dental implant

The mechanical behaviour of dental implants is crucial to their long-term endurance. Despite the demonstrated efficacy of dental implants, mechanical and biological concerns revealed in long-term follow-up studies continue to be a cause for concern. Screw loosening, which is usually caused by masticatory pressures when chewing, and peri-implantitis owing to microleakage are two of them, and if left untreated, they can lead to gradual loss of the supporting crestal bone. This study investigated the influence of hydroxyapatite (HAp) and reduced graphene oxide (rGO) hybrid coatings on the threads of a dental implant retention screw made of polyetheretherketone (PEEK). HAp with different concentrations of rGO (0.25, 0.5, 0.75, and 1%) coatings were investigated. The clamping force (CF) and coefficient of friction (COF) of the screw thread pair, as well as the single load fracture and dynamic fatigue life tests, were assessed to determine the integrity of the implant thread connection. The screw fracture mechanism and screw thread surface erosion morphology were also studied. The results revealed that C4 (HAp/rGO) coating might minimize COF, improve CF, and reduce fracture load. Furthermore, it demonstrated better anti-loosening properties under dynamic load. Most screw fractures happen on the screw's initial thread. The fracture end of a C3 combination coated screw was easily removed, but not that of a C4 combination coated screw.

New design method of unequal taper thread (UTT) pairs and its application in API NC38 thread improvement

New design method of unequal taper thread (UTT) pairs and its application in API NC38 thread improvement

Checking Just Pairs of Threads for Efficient and Scalable Incremental Verification of Multithreaded Programs

Many techniques of automated verification target multithreaded programs, because subtle interactions between threads may trigger concurrency errors such as deadlocks and data races. However, techniques and tools involving systematic exploration of the whole space of possible thread interleavings do not scale to large software systems, despite various clever algorithmic optimizations. A viable approach is to use incremental verification techniques that, in each run, focus just on the recently modified code and the relatively small number of affected execution traces, and therefore can provide results (bug reports) very quickly. In this paper we present a new algorithm for incremental verification of multithreaded programs based on the pairwise approach, whose key idea is systematic exploration of all possible thread interleavings just for specific relevant pairs of threads. We implemented the algorithm with Java Pathfinder as the backend verification tool, and evaluated it on several multithreaded Java programs. Results show that our incremental algorithm (1) can find errors very fast, (2) greatly reduces time needed for complete safety verification, and (3) it can find the same errors as full verification of the whole state space.

Design of point-type heavy load connection and low impact separation mechanism based on energy flow analysis

In this paper, based on the development of the non-pyrotechnic low impact connection and separation device for heavy load connection of large space vehicles, the design method of connection and separation device is studied. The traditional heavy load connection separation device has a strong loading capacity, but the release of system energy will cause a huge impact during separation. This paper considers the transfer of impact energy in the mechanism design process, reduces separation impact based on energy flow analysis. Based on the analysis of the DOF (Degree of Freedom) constraint function of the separation system and the working requirements of the separation mechanism, the movability model of separation system was established. According to the research on DOF constraints and release, the key of force constraints in DOF constraints of the separation mechanism is obtained, and the separation mechanism that can implement the force constraints and release is analyzed. Furthermore, based on the energy flow analysis of the separation mechanism, the design method of the low impact separation mechanism is proposed, obtained a non-self-locking thread pair connection separation mechanism. The effectiveness of the design method was verified by the energy conversion analysis of the separation mechanism.

Research on the Modeling of Bending-Torsional Coupling and Vibration Characteristics of Planetary Roller Screw Mechanism

A general bending-torsional coupling dynamic model of the planetary roller screw mechanism is developed by the lumped mass method in this paper to analyze the vibration characteristics. Firstly, the components of the planetary roller screw mechanism are treated as lumped mass, and the meshing relationships are expressed by the spring element. Secondly, the natural vibration characteristics of the planetary roller screw mechanism are analyzed, and four vibration modes based on the bending-torsional coupling dynamic model are summarized: carrier mode, torsional mode, transverse mode and roller mode. This reveals the vibration characteristics when the two kinds of meshing pairs (thread pair and gear pair) come into meshing synchronously. Then, the relationships between the structural parameters and the natural frequency of each vibration mode are discussed. Finally, the matrix equation is simplified according to the characteristics of vibration mode, and the analytic expressions of natural frequency under carrier mode and roller mode are obtained.

Design and test of electromechanical disc brake controller for mine hoist

Electromechanical braking technology is an effective way to improve the braking response of mine hoist. Through the analysis of the mine hoist electromechanical mechanical disc brake, a mathematical model including the motor, reducer and thread pair is established. The control process is analyzed in detail, and then the control strategy is obtained. An automatic control system based on linear quadratic regulator and PI controller is proposed. The braking goal of self-adaptive adjustment of braking clearance and on-line adjustment of braking force is realized. Compare the simulation and test results, discuss the performance of the controller. The results of the experiment indicate that the brake gap adjustment time is less than 10 s, stable within 1±0.2 mm, and the steady-state error is less than 2%. The positive pressure of the brake has a linear relationship with the motor voltage, with a slope of 920.4 and an intercept of −1298.88. It can replace the existing hydraulic brakes without the problem of low degree of automation and high pollution, which provides a new way for the control system of electromechanical brake.

Modeling of the draping textile on a curved surface

sThis paper presents algorithm for draping 2D textile fabric on curved surface. Using computer analyze to predicting strength and stiffness of textile reinforced composite details allows to achieve better characteristics of received parts. Part of this task is stacking initial cloth on the surface. Modeling of draped fabrics on surface produced by representation initial cloth by pin-jointed net model, which are describes position of each thread. This algorithm also provides to analyses angles between each pair of threads in considered object. It is used to find areas with critical tension, or places of formation of folds of fabrics. In this paper threads of fabrics are inextensibility.

Effect of Pitch Difference on Stress Distribution of Thread Pair and Preload

Effect of Pitch Difference on Stress Distribution of Thread Pair and Preload

Methodology for Studying the Wear of Drill Pipe Threads during Repeated Making up and Holding under Load

Purpose of reseach is to develop a methodology for studying the wear of drill pipe threads during repeated making up and holding under load. Methods. For the research, stand “IRS-1” was used. This stand is a device for creating a torque of up to 80 kNm and transferring it to a made-up pipe. It is equipped with a make-up torque sensor and a control system that performs make-up until the specified tightening torque is achieved or periodically applies the torque to the made-up thread pair. The test procedure for IRS-1 stand consists of the following sequence of actions: before starting the tests, the threaded protectors are removed; the threads on the nipple and sleeve are cleaned of the preservative grease and traces of corrosion by dry wiping and subsequent degreasing; the thread on the nipple is measured according to the measurement chart using a gauge. The gauge is made on the basis of the threaded surface impression and is a plate with cutouts in the form of a cross-section of four threads. The gap between the gauge and the thread is measured using a set of probes from 0.01 to 0.09 mm in increments of 0.01 mm, over 0.1 mm to 0.45 mm in increments of 0.05 mm, over 0.5 mm to 1 mm in increments of 0.1 mm. Results. A new tribotechnical stand of IRS-1 model was designed and created, which allows implementing various techniques for studying the wear of drill pipe threads during repeated making-up and holding under load. An important feature of the designed stand is a make-up torque sensor and a control system that perform make-up until the specified tightening torque is achieved or periodically applies the torque to the made-up threaded pair. The maximum torque generated by the stand is 80 kNm. A particular technique was developed. The technique includes the requirements of the API 7G-2 standard and has shown its effectiveness in the study of thread wear of steel drill pipes. To implement the technique, a special gauge was developed on the basis of the threaded surface impression and is a plate with cutouts in the form of a cross-section of four threads. Within this technique, a measurement chart with two selected measurement areas was developed. An algorithm for making up a pipe at a uniform speed was created. The algorithm includes three stages. There was developed an algorithm of measurements using reference marks, providing measurements at four points in each selected area. Conclusion. The results obtained can be used to create resource-saving technologies for processing ingot, powder, and nanocomposite materials with different dispersion of phase and structural components that are operated under extreme conditions and states.

Atomic shell structure from an orbital-free-related density-functional-theory Pauli potential

Polymer self-consistent field theory techniques are used to find radial electron densities and total binding energies for isolated atoms. Quantum particles are modelled as Gaussian threads with ring-polymer architecture in a four dimensional thermal-space, and a Pauli potential is postulated based on classical excluded volume implemented in the thermal-space using Edwards/Flory-Huggins interactions in a mean-field approximation. Other approximations include a Fermi-Amaldi correction for electron-electron self-interactions, a spherical averaging approximation to reduce the dimensionality of the problem, and the neglect of correlations. Polymer scaling theory is used to show that the excluded volume form of Pauli potential reduces to the known Thomas-Fermi energy density in the uniform limit. Self-consistent equations are solved using a bilinear Fourier expansion, with radial basis functions, for the first eighteen elements of the periodic table. Radial electron densities show correct shell structure, and the errors on the total binding energies compared to known binding energies are less than 9% for the lightest elements and drop to 3% or less for atoms heavier than nitrogen. More generally, it is suggested that only two postulates are needed within classical statistical mechanics to achieve equivalency of predictions with static, non-relativistic quantum mechanics: First, quantum particles are modelled as Gaussian threads in four dimensional thermal-space and, second, pairs of threads (allowing for spin) are subject to classical excluded volume in the thermal-space. It is shown that these two postulates in thermal-space become the same as the Heisenberg uncertainty principle and the Pauli exclusion principle in three dimensional space.

Ionic spiderwebs

Spiders use adhesive, stretchable, and translucent webs to capture their prey. However, sustaining the capturing capability of these webs can be challenging because the webs inevitably invite contamination, thus reducing its adhesion force. To overcome these challenges, spiders have developed strategies of using webs to sense prey and clean contaminants. Here, we emulate the capturing strategies of a spider with a single pair of ionic threads based on electrostatics. Our ionic spiderwebs completed consecutive missions of cleaning contamination on itself, sensing approaching targets, capturing those targets, and releasing them. The ionic spiderwebs demonstrate the importance of learning from nature and push the boundaries of soft robotics in an attempt to combine mutually complementary functions into a single unit with a simple structure.

Experimental evaluation for internal trapezoidal thread with axial ultrasonic vibration cutting of Ti–6Al–4V

Renewal of the manufacturing process for thread is important in a variety of products and industry applications. Especially for machining the internal trapezoidal thread, the cutting edge is in a semi-closed state, three cutting edges and two cutting tips are in contact with the workpiece, resulting the heat is not easy to spread out. At the same time, the narrow space of the internal thread leads to the poor rigidity of the tool, the instability of the machining state, which seriously affects the surface machining quality of the parts. Here, a new precision processing device of axial ultrasonic-assisted turning (AUAT) is designed, which can achieve the industrial application of machining internal thread parts. The device can work stably at a working frequency of about 28.8 kHz. Secondly, considering that the bottom and flank of the thread need to be machined at the same time, the contact mode of the tool is different between them. The main cutting edge of the tool contacts the workpiece intermittently on the flank tooth, forming the texture surface which is conducive to the transmission of the thread pair. On the bottom teeth, the main cutting edge is always in contact with the workpiece and carries out the axial sawing movement. The high-frequency axial vibration damping effect is obvious, which suppresses the unstable machining state such as chatter and improves the machining surface quality of the bottom teeth. Finally, Ti–6Al–4V trapezoid thread is selected in the verification, in which the separation effect of ultrasonic vibration cutting is verified, the cutting force is tested, and the machined surface topography of the workpiece is analyzed. Experimental results show that the quality of thread was significantly improved in AUAT.

Contact Analysis of Thread Pairs in a Planetary Roller Screw Based on Finite Element Method

This paper investigates the contact characteristics of the thread pairs in the planetary roller screw mechanism. Firstly, the analytical model of thread contact based on Hertz contact theory is established. Secondly, the contact models of the screw and roller threads and of the roller and nut threads based on FE method are developed. The correctness of the numerical results is verified via the comparison with analytical results, the relative error between the two sets of results is less than or equal to 2%. Lastly, according to FE model, the contact state, contact positions and contact stresses of thread pairs at the screw-roller interface and at the roller-nut interface are derived.

Effect of PEEK and PTFE coatings in fatigue performance of dental implant retaining screw joint: An in vitro study

ObjectivesMechanical complications play a key role in failure of dental implants. Retaining screw loosening was one of the most commonly encountered. This study investigated the effect of PEEK and PTFE coatings on dental implant screw thread joint. MethodsRetaining screws were coated with PEEK and PTFE in thickness of 30 μm and 60 μm. Friction coefficient and clamping force of screw thread pair were measured, single load-to-fracture (SLF) test and dynamic fatigue life (DFL) test were done to test the stability of implant thread connection. After that, screw fracture mode and erosion morphology of screw surface and implant internal thread were observed. ResultsThe results showed that both PEEK and PTFE coatings could reduce friction coefficient, and consequently increase clamping force, especially PTFE coatings. PEEK coatings had no significant effect on fracture load, while 30 μm PTFE coating reduced fracture load. PEEK coatings also elongated fatigue life and improved the anti-loosening property under dynamic load, while 30 μm PTFE coating shortened fatigue life. Most of the screw fracture happened at the first thread of the retaining screws. The fracture-end of PEEK coated screws were loosed and could easily remove, but fracture-end of PTFE screws could not. Internal thread observation showed that both PEEK and PTFE coatings could reduce wear of implant internal thread. ConclusionPEEK coatings could effectively improve the stability of implant threaded connection, and reduce wear of implant internal thread. PEEK coating may be a suitable way to prevent screw loosening.