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Time-varying loads, manufacturing errors, and assembly errors are the main factors leading to the performance degradation of the planetary roller screw mechanism. This paper proposes a comprehensive analysis method for the performance degradation of the planetary roller screw mechanism caused by time-varying loads and manufacturing and assembly errors. Firstly, a simulation analysis model of the planetary roller screw mechanism was established and its effectiveness was verified. A quantitative analysis was conducted on the influence of manufacturing and assembly errors on the load distribution, revealing the load-bearing mechanism under the influence of errors. Secondly, loading experiments were conducted on the planetary roller screw mechanism, and the degradation of its load-bearing performance was divided into the normal degradation stage, the accelerated degradation stage, and the failure stage. The experimental results prove that the initial transmission accuracy has a significant impact on the degradation of the load-bearing performance, determining the occurrence of the node where the accelerated degradation stage appears in the load-bearing performance. Thirdly, the wear status of the threads and gears was examined, and the results showed that material peeling was the main factor causing the degradation of load-bearing performance. [ABSTRACT FROM AUTHOR]

This paper proposes a load distribution model for the ball screw feed system with the assembly errors of the guide rails, which is used to predict the variation law of the load distributions for the ball screws and carriage-guide rail systems. Firstly, under the action of the contact loads of the ball screws, the bending deformation of the screw axis corresponding to each ball is derived. Secondly, a static model of the machine tool bearing system with the assembly errors is established. Then, the load distribution model of the ball screw feed system is proposed based on the load balance and deformation compatibility equation, and the solution process of the proposed model including judging the ball-raceway contact state is given. In addition, the results are compared with those of the existing models to demonstrate the validity of the proposed model. Finally, the relation between the curve shape of the load distribution and the bending of the screw shaft axis is explored, and the variation law of the load distributions for the feed system under the effects of the axial, radial loads, and assembly errors is discussed. [ABSTRACT FROM AUTHOR]

To research the vibration problem caused by bearing assembly errors in machine tool spindles, a special test rig for rolling bearing misalignment is designed and built. The dynamic model of the spindle-bearing-pedestal system of the test rig is established, and the characterization method for bearing parallel and angular misalignments is given through the Hertz contact theory. The effect rule of the misalignment level on spindle vibration response is studied by simulation and experiment, and the system dynamic model and bearing misalignment model are verified. On this basis, the vibration characteristics of the spindle system under the joint effect of raceway misalignment and waviness are further analyzed. The numerical and experimental results show that when the bearing is in the misalignment state, the excitation of bearing variable compliance increases. The assembly errors of the bearing raceway lead to the deviation of the centroid motion trajectory of the spindle tool end, which seriously affects the machining accuracy of the machine tool. In the case of severe angular misalignment, the system shows chaotic motion, indicating that the instability of the system is enhanced. The impact of angular misalignment on system vibration is greater than parallel misalignment, so bearing ring tilt should be avoided as far as possible in practice. In addition, it is also found that the variation of excitation amplitude of bearing waviness caused by raceway tilt is related to the relationship between the number of waviness and ball number. [ABSTRACT FROM AUTHOR]

Based on the spatial position relationship of spiral bevel gear, mathematical model and mesh model applied with finite element analysis (FEA) approach has been established. The influence of axial position errors of pinion and wheel, offset error, and shaft angle error on the meshing characteristics has been investigated. A method has been proposed to compensate the gear assembly errors by the axial displacement of the pinion and wheel, and the correctness of this method verified by numerical examples. The performed results indicate that the existence of assembly errors can cause contact pattern on the tooth surface to deviate from its design position, resulting in poor meshing quality and having a certain impact on transmission error (TE) and peak-to-peak transmission error (PPTE). The pinion and wheel's axial positioning errors can be offset by each other, whereas the offset error and shaft angle error can be mitigated by the interplay between the axial positioning of the pinion and wheel. By compensating for assembly errors with axial displacement, the position of the contact pattern can be precisely controlled, and TE will not significant changes. [ABSTRACT FROM AUTHOR]

Abstract Background Transcriptomic studies involving organisms for which reference genomes are not available typically start by generating de novo transcriptome or supertranscriptome assembly from the raw RNA-seq reads. Assembling a supertranscriptome is, however, a challenging task due to significantly varying abundance of mRNA transcripts, alternative splicing, and sequencing errors. As a result, popular de novo supertranscriptome assembly tools generate assemblies containing contigs that are partially-assembled, fragmented, false chimeras or have local mis-assemblies leading to decreased assembly accuracy. Commonly available tools for assembly improvement rely primarily on running BLAST using closely related species making their accuracy and reliability conditioned on the availability of the data for closely related organisms. Results We present ROAST, a tool for optimization of supertranscriptome assemblies that uses paired-end RNA-seq data from Illumina sequencing platform to iteratively identify and fix assembly errors solely using the error signatures generated by RNA-seq alignment tools including soft-clips, unexpected expression coverage, and reads with mates unmapped or mapped on a different contig to identify and fix various supertranscriptome assembly errors without performing BLAST searches against other organisms. Evaluation results using simulated as well as real datasets show that ROAST significantly improves assembly quality by identifying and fixing various assembly errors. Conclusion ROAST provides a reference-free approach to optimizing supertranscriptome assemblies highlighting its utility in refining de novo supertranscriptome assemblies of non-model organisms.

Rotary laser scanning measurement systems, such as the workshop measurement positioning system (wMPS), play critical roles in manufacturing industries. The wMPS realizes coordinate measurement through the intersection of multiple rotating fanned lasers. The measurement model of multi-laser plane intersection poses challenges in terms of accurately evaluating the system, making it difficult to establish a standardized evaluation method. The traditional evaluation method is based on horizontal and vertical angles derived from scanning angles, which are the direct observation of wMPS. However, the horizontal- and vertical-angle-based methods ignore the assembly errors of fanned laser devices and mechanical shafts. These errors introduce calculation errors and affect the accuracy of angle measurement evaluation. This work proposes a performance evaluation method for the scanning angle independent of the assembly errors above. The transmitter of the wMPS is installed on a high-precision turntable that provides the angle reference. The coordinates of enhanced reference points (ERP) distributed in the calibration space are measured by the laser tracker multilateration method. Then, the spatial relationship between the transmitter and the turntable is reconstructed based on the high-precision turntable and the good rotational repeatability of the transmitter. The simulation was carried out to validate the proposed method. We also studied the effect of fanned laser devices and shaft assembly errors on horizontal and vertical angles. Subsequently, the calibration results were validated by comparing the residuals with those derived from the space-resection method. Furthermore, the method was also validated by comparing the reference and scanning angles. The results show that the maximum angle measurement error was approximately 2.79″, while the average angle measurement error was approximately 1.26″. The uncertainty (k = 1) of the scanning angle was approximately 1.7″. Finally, the coordinate measurement test was carried out to verify the proposed method by laser tracker. The results show that the average re-scanning error was 2.17″. [ABSTRACT FROM AUTHOR]

Assembly errors may change contact state of gear pairs, then induce failure and vibration. To reveal the effects of assembly errors and tooth modification on the meshing characteristics, the loaded tooth contact analysis (LTCA) is conducted through an improved algorithm. The time-varying meshing stiffness (TVMS), static transmission error (STE) and contact stress (CS) are calculated considering assembly errors and tooth modification. Then, sensitivity of meshing characteristics to coupling assembly errors are investigated based on the design of orthogonal experiment (DOE). The meshing characteristic analysis results show that assembly errors have a significant effect on mesh characteristics of the gear pair. The results of sensitivity analysis indicate that the meshing characteristic is the most sensitive to axial deviation for the model used in this paper. [ABSTRACT FROM AUTHOR]

Rotary laser scanning measurement systems, such as the workshop measurement positioning system (wMPS), play critical roles in manufacturing industries. The wMPS realizes coordinate measurement through the intersection of multiple rotating fanned lasers. The measurement model of multi-laser plane intersection poses challenges in terms of accurately evaluating the system, making it difficult to establish a standardized evaluation method. The traditional evaluation method is based on horizontal and vertical angles derived from scanning angles, which are the direct observation of wMPS. However, the horizontal- and vertical-angle-based methods ignore the assembly errors of fanned laser devices and mechanical shafts. These errors introduce calculation errors and affect the accuracy of angle measurement evaluation. This work proposes a performance evaluation method for the scanning angle independent of the assembly errors above. The transmitter of the wMPS is installed on a high-precision turntable that provides the angle reference. The coordinates of enhanced reference points (ERP) distributed in the calibration space are measured by the laser tracker multilateration method. Then, the spatial relationship between the transmitter and the turntable is reconstructed based on the high-precision turntable and the good rotational repeatability of the transmitter. The simulation was carried out to validate the proposed method. We also studied the effect of fanned laser devices and shaft assembly errors on horizontal and vertical angles. Subsequently, the calibration results were validated by comparing the residuals with those derived from the space-resection method. Furthermore, the method was also validated by comparing the reference and scanning angles. The results show that the maximum angle measurement error was approximately 2.79″, while the average angle measurement error was approximately 1.26″. The uncertainty (k = 1) of the scanning angle was approximately 1.7″. Finally, the coordinate measurement test was carried out to verify the proposed method by laser tracker. The results show that the average re-scanning error was 2.17″.

The performance of the milling head is affected by the machining and assembly process of the parts. The key to improving machining accuracy and reliability of swing angle milling head is to establish the precision prediction model. Therefore, a precision prediction model of swing angle milling head under the influence of multiple errors' sources is built. The transmission and accumulation of machining and assembly errors along the assembly sequence path for the transmission system are carried out. All essential components on the assembly sequence path are considered. In addition, the secondary impact of the bearing seat hole is also taken into account. The source of the gear assembly errors is explained. The predicted range of transmission error based on the coupling relationship between assembly errors and transmission error is obtained. A precision experiment is carried out, and the result is within the predicted range. This research demonstrates that the errors' coupling relationship considered in this paper does exist and has an effect on transmission error, which provides a new idea for calculating transmission error of other gear systems. [ABSTRACT FROM AUTHOR]

A major challenge for manufacturing companies today is to manage a huge amount of product variants and build options at the same time in manufacturing engineering and in production. The overall complexity and risk of quality errors in manual assembly will increase placing high demands on the operators who must manage many different tasks in current production. Therefore, methods for decreasing and controlling assembly complexity are urgent because managing complex product and installation conditions will result in distinct competitive advantages. The objective of this paper is to present a method for predictive assessment of basic manual assembly complexity and explain how included complexity criteria were arrived at. The verified method includes 16 high complexity and 16 low complexity criteria to aid designers in preventing costly errors during assembly and create good basic assembly conditions in early design phases of new manufacturing concepts. [ABSTRACT FROM AUTHOR]

Automation is a high priority in manufacturing today. In particular, the conditions required to automate assembly by means of bolts and screws are of interest. In devising an assembly process, the goal is to obtain the final product in the shortest time at minimal cost. As an example, attention focuses on the possibility of automating assembly on the basis of boundary conditions such that components are satisfactorily combined by means of bolts and screws. [ABSTRACT FROM AUTHOR]

For the accurate calculation of the time-varying mesh stiffness (TVMS) of helical gear pairs, a novel method is proposed in this paper. This proposed method can predict the TVMS based on the gear accuracy grade or the measurement coordinates of the tooth surface. The abnormal meshing phenomena caused by manufacturing errors (MEs), assembly errors (AEs), and tooth modifications (TMs), such as the loss of contact of tooth pairs, out-of-line meshing, and eccentric loads, are considered in the calculation process. The proposed method was verified to be effective for both spur and helical gear pairs. The effects of MEs, AEs, and TMs on the TVMS of helical gear pairs were also investigated. The results showed that the pitch, helix, and misalignment deviations were the main influencing factors of the TVMS in MEs and AEs. Both profile modification and lead crowning reduced the mean of the TVMS. The proposed method is expected to provide accurate TVMS excitation data of gear transmission systems for dynamic analysis. [ABSTRACT FROM AUTHOR]

Abstract Background Advances in whole genome sequencing strategies have provided the opportunity for genomic and comparative genomic analysis of a vast variety of organisms. The analysis results are highly dependent on the quality of the genome assemblies used. Assessment of the assembly accuracy may significantly increase the reliability of the analysis results and is therefore of great importance. Results Here, we present a new tool called NucBreak aimed at localizing structural errors in assemblies, including insertions, deletions, duplications, inversions, and different inter- and intra-chromosomal rearrangements. The approach taken by existing alternative tools is based on analysing reads that do not map properly to the assembly, for instance discordantly mapped reads, soft-clipped reads and singletons. NucBreak uses an entirely different and unique method to localise the errors. It is based on analysing the alignments of reads that are properly mapped to an assembly and exploit information about the alternative read alignments. It does not annotate detected errors. We have compared NucBreak with other existing assembly accuracy assessment tools, namely Pilon, REAPR, and FRCbam as well as with several structural variant detection tools, including BreakDancer, Lumpy, and Wham, by using both simulated and real datasets. Conclusions The benchmarking results have shown that NucBreak in general predicts assembly errors of different types and sizes with relatively high sensitivity and with lower false discovery rate than the other tools. Such a balance between sensitivity and false discovery rate makes NucBreak a good alternative to the existing assembly accuracy assessment tools and SV detection tools. NucBreak is freely available at https://github.com/uio-bmi/NucBreak under the MPL license.

Abstract A recent article in BMC Genomics describes a new bioinformatics tool, HumanMycobiomeScan, to classify fungal taxa in metagenomic samples. This tool was used to characterize the gut mycobiome of hunter-gatherers and Western populations, resulting in the identification of a range of fungal species in the vast majority of samples. In the HumanMycobiomeScan pipeline, sequence reads are mapped against a reference database containing fungal genome sequences only. We argue that using reference databases comprised of a single taxonomic group leads to an unacceptably high number of false-positives due to: (i) mapping to conserved genetic regions in reference genomes, and (ii) sequence contamination in the assembled reference genomes. To demonstrate this, we replaced the HumanMycobiomeScan’s fungal reference database with one containing genome sequences of amphibians and reptiles and re-analysed their case study. The classification pipeline recovered all species present in the reference database, revealing turtles (Geoemydidae), bull frogs (Pyxicephalidae) and snakes (Colubridae) as the most abundant herpetological taxa in the human gut. We also re-analysed their case study using a kingdom-agnostic pipeline. This revealed that while the gut of hunter-gatherers and Western subjects may be colonized by a range of microbial eukaryotes, only three fungal families were retrieved. These results highlight the pitfalls of using taxon-specific reference databases for metagenome classification, even when they are comprised of curated whole genome data. We propose that databases containing all domains of life provide the most suitable option for metagenomic species profiling, especially when targeting microbial eukaryotes.

The investigation of the influence of different errors of alignment on the mesh behavior of hypoid gears with low crossing shaft angle has been carried out. As a result, a simplified methodology of compensation of errors of alignment and correction of the contact pattern by controlled axial displacements to the pinion and wheel of the hypoid gear set has been proposed. The shaft angle error and the offset error mainly influence the position of the contact pattern in profile direction. The pinion and wheel axial position errors influence the position of contact pattern along the tooth trace direction and change the position slightly along the tooth profile direction. All the assembly errors increase the peak-to-peak value of transmission errors, except positive values of the pinion axial position error that allows decreasing the peak-to-peak transmission error slightly in an appropriate range. Finite element analysis has been performed to verify the compensating ability of the developed methodology. [ABSTRACT FROM AUTHOR]

Transmission error (TE) and backlash are important parameters used to evaluate the transmission accuracy of cycloid-pin drives. Existing calculation methods are mostly based on two-dimensional tooth profile models, and these methods ignore the influence of some abnormal meshing phenomena caused by profile modifications (PMs), manufacturing errors (MEs), and assembly errors (AEs), such as the instantaneous mesh-apart of tooth pairs and the eccentric load on the tooth surface. To fill this gap, a novel approach to accurately calculating the TE and backlash of a cycloid-pin gear pair based on the error tooth surfaces is proposed, and its feasibility and effectiveness are validated by comparison with the theoretical analyses and the results from the literature. Based on this, the effects of the PMs, MEs, and AEs on the transmission accuracy are studied, which will be helpful in optimizing the tooth profile design of a cycloid gear and the tolerance allocation during the installation of a gear pair. The proposed method is also expected to provide accurate error excitation data for the dynamic analysis of cycloid-pin drives. [ABSTRACT FROM AUTHOR]

Featured Application: For photoelectric detection devices based on unmanned aerial vehicles, the analysis results are used as standards of manufacturing process improvements. A photoelectric detection system is a typical type of device widely used for detecting purposes based on unmanned aerial vehicles (UAV). Stability accuracy is the key performance index. Compared to traditional analysis methods aimed at unpredictable error-causing sources, assembly errors can be easily controlled during the manufacturing processes. In this research, an analysis method of assembly error effect on stability accuracy is proposed. First, by using kinematics analysis of homogeneous coordinate transformation, stability accuracy is comprehensively modeled and simulated. Then, by analyzing the manufacturing process, assembly errors of axis perpendicularities, run-outs and gyroscopes are defined and modeled. By simulating different carrier movements, the effects caused by assembly errors under various environments are studied. Finally, error sensitivity is proposed by using standard deviation analysis. Results show that the most sensitive assembly errors are identified, and ranked in order of sensitivity as follows: x-component of pitch axis perpendicularity, y-component of the azimuth gyroscope assembly, and z-component of the pitch gyroscope assembly. In conclusion, the results can be used as standards of manufacturing process improvements, and the proposed methods can be used to provide valuable references for real application scenarios. [ABSTRACT FROM AUTHOR]

A recent article in BMC Genomics describes a new bioinformatics tool, HumanMycobiomeScan, to classify fungal taxa in metagenomic samples. This tool was used to characterize the gut mycobiome of hunter-gatherers and Western populations, resulting in the identification of a range of fungal species in the vast majority of samples. In the HumanMycobiomeScan pipeline, sequence reads are mapped against a reference database containing fungal genome sequences only. We argue that using reference databases comprised of a single taxonomic group leads to an unacceptably high number of false-positives due to: (i) mapping to conserved genetic regions in reference genomes, and (ii) sequence contamination in the assembled reference genomes. To demonstrate this, we replaced the HumanMycobiomeScan's fungal reference database with one containing genome sequences of amphibians and reptiles and re-analysed their case study. The classification pipeline recovered all species present in the reference database, revealing turtles (Geoemydidae), bull frogs (Pyxicephalidae) and snakes (Colubridae) as the most abundant herpetological taxa in the human gut. We also re-analysed their case study using a kingdom-agnostic pipeline. This revealed that while the gut of hunter-gatherers and Western subjects may be colonized by a range of microbial eukaryotes, only three fungal families were retrieved. These results highlight the pitfalls of using taxon-specific reference databases for metagenome classification, even when they are comprised of curated whole genome data. We propose that databases containing all domains of life provide the most suitable option for metagenomic species profiling, especially when targeting microbial eukaryotes. [ABSTRACT FROM AUTHOR]

Background: Advances in whole genome sequencing strategies have provided the opportunity for genomic and comparative genomic analysis of a vast variety of organisms. The analysis results are highly dependent on the quality of the genome assemblies used. Assessment of the assembly accuracy may significantly increase the reliability of the analysis results and is therefore of great importance. Results: Here, we present a new tool called NucBreak aimed at localizing structural errors in assemblies, including insertions, deletions, duplications, inversions, and different inter- and intra-chromosomal rearrangements. The approach taken by existing alternative tools is based on analysing reads that do not map properly to the assembly, for instance discordantly mapped reads, soft-clipped reads and singletons. NucBreak uses an entirely different and unique method to localise the errors. It is based on analysing the alignments of reads that are properly mapped to an assembly and exploit information about the alternative read alignments. It does not annotate detected errors. We have compared NucBreak with other existing assembly accuracy assessment tools, namely Pilon, REAPR, and FRCbam as well as with several structural variant detection tools, including BreakDancer, Lumpy, and Wham, by using both simulated and real datasets. Conclusions: The benchmarking results have shown that NucBreak in general predicts assembly errors of different types and sizes with relatively high sensitivity and with lower false discovery rate than the other tools. Such a balance between sensitivity and false discovery rate makes NucBreak a good alternative to the existing assembly accuracy assessment tools and SV detection tools. NucBreak is freely available at https://github.com/uio-bmi/NucBreak under the MPL license. [ABSTRACT FROM AUTHOR]

Assembly errors can occur in a robotic assembly system. In this paper, a method that predicts an assembly error is proposed. It considers that assembly errors occur under the condition that the geometric trajectory of a mated part and the relational position and orientation of a base part are outside the allowable tolerance. A certain point, which is determined by using a physical light reflectance model of a mated part, is followed with two high-speed cameras. A statistical pattern recognition method in which explanatory variables are tracked points in a three-dimensional space is then employed to predict an assembly error. The proposed method is applied to a peg-in-a-hole assembly by a selective compliance assembly robot arm (SCARA)-type robot and its potential value is discussed. [ABSTRACT FROM AUTHOR]

Transmission error (TE) and backlash are important parameters used to evaluate the transmission accuracy of cycloid-pin drives. Existing calculation methods are mostly based on two-dimensional tooth profile models, and these methods ignore the influence of some abnormal meshing phenomena caused by profile modifications (PMs), manufacturing errors (MEs), and assembly errors (AEs), such as the instantaneous mesh-apart of tooth pairs and the eccentric load on the tooth surface. To fill this gap, a novel approach to accurately calculating the TE and backlash of a cycloid-pin gear pair based on the error tooth surfaces is proposed, and its feasibility and effectiveness are validated by comparison with the theoretical analyses and the results from the literature. Based on this, the effects of the PMs, MEs, and AEs on the transmission accuracy are studied, which will be helpful in optimizing the tooth profile design of a cycloid gear and the tolerance allocation during the installation of a gear pair. The proposed method is also expected to provide accurate error excitation data for the dynamic analysis of cycloid-pin drives.

• A new approach for calculating the NLSTE based on measured tooth surfaces. • Manufacturing errors, profile modifications and assembly errors have been considered. • A new tooth contact analysis algorithm is formulated. • The numerical results are verified by comparing with the experimental results. No-load static transmission error (NLSTE) is widely recognized as the main source of vibration excitation. A novel approach for calculating NLSTE based on measured discrete tooth surfaces is proposed, with profile modifications, manufacturing errors and assembly errors considered. In modeling the measured discrete tooth surfaces, Delaunay triangulation is utilized to process the point data of tooth surfaces obtained by Coordinate Measuring Machines (CMMs), causing the tooth surfaces to be divided into multiple triangles. A new tooth contact analysis algorithm based on the principle of triangle intersection judgment is formulated to calculate the NLSTE of the gear pair. The NLSTE of a crowned spur gear pair with different assembly errors is computed by the proposed approach, and the numerical results are verified by comparing with the experimental results. The new approach is applicable to all types of gears. [ABSTRACT FROM AUTHOR]

A photoelectric detection system is a typical type of device widely used for detecting purposes based on unmanned aerial vehicles (UAV). Stability accuracy is the key performance index. Compared to traditional analysis methods aimed at unpredictable error-causing sources, assembly errors can be easily controlled during the manufacturing processes. In this research, an analysis method of assembly error effect on stability accuracy is proposed. First, by using kinematics analysis of homogeneous coordinate transformation, stability accuracy is comprehensively modeled and simulated. Then, by analyzing the manufacturing process, assembly errors of axis perpendicularities, run-outs and gyroscopes are defined and modeled. By simulating different carrier movements, the effects caused by assembly errors under various environments are studied. Finally, error sensitivity is proposed by using standard deviation analysis. Results show that the most sensitive assembly errors are identified, and ranked in order of sensitivity as follows: x-component of pitch axis perpendicularity, y-component of the azimuth gyroscope assembly, and z-component of the pitch gyroscope assembly. In conclusion, the results can be used as standards of manufacturing process improvements, and the proposed methods can be used to provide valuable references for real application scenarios.

We present a method for analyzing the transmission error of helical gear system with errors. First a finite element method is used for modeling gear transmission system with machining errors, assembly errors, modifications and the static transmission error is obtained. Then the bending-torsional-axial coupling dynamic model of the transmission system based on the lumped mass method is established and the dynamic transmission error of gear transmission system is calculated, which provides error excitation data for the analysis and control of vibration and noise of gear system. [ABSTRACT FROM AUTHOR]

Due to the existence of assembly errors, the dynamic characteristics of planetary gear system could be changed compared with the original ideal design. Considering the assembly errors of component, a bending-torsional-pendular coupled vibration model of the 1st helical planetary gear system in wind turbine gearbox was built using lumped parameter method. Then the variable step Runge–Kutta algorithm was applied to solve the dynamic model of helical planetary gear system. The effects of carrier horizontal assembly error, carrier axis assembly error and carrier spatial assembly error on the dynamic characteristics were investigated. Results show that the influence of carrier assembly error along the z -axis on the variations for DTE response of the system is worse than other axis error cases. The carrier assembly errors along the different directions tend to make the dynamic responses for dynamic mesh forces (DMFs) larger. The frequency responses for DMFs of helical planetary gear system are influenced comprehensively by carrier assembly errors along the different directions. The frequency positions of DMFs are reduced under carrier spatial assembly errors (< 2000 Hz). [ABSTRACT FROM AUTHOR]

The dynamics of the ball screw feed system is very important in high-precision machining of CNC machine tools. However, the existing literatures rarely study the dynamic behaviors of the coupled feed system and didn't take the influence of the assembly error of the guide rails into consideration. Because the stiffness of the feed system is mainly affected by the ball screw, linear guide and ball bearings, this paper presents the fourteen degree-of-freedom dynamic model of the feed system by deriving the nonlinear restoring force functions of the screw nut, linear guide and ball bearings and the screw shaft's stiffness. An algorithm of combining the Newmark Method and the Monte Carlo simulation is proposed to numerically solve for the vibration responses of the feed system, and the proposed dynamic model is experimentally verified. Based on the established dynamic model, the effects of the excitation amplitude, system parameters and assembly error on the dynamic characteristics of the feed system are discussed by means of the amplitude-frequency curve and 3-D frequency spectrum, which demonstrate that the vibration responses of the feed system for the fourteen degrees of freedom influence each other, and the assembly error affects the nonlinear dynamic characteristics of the feed system. [ABSTRACT FROM AUTHOR]

In the last research [S. Li, Effects of machining errors, assembly errors and tooth modifications on load-carrying capacity, load-sharing rate and transmission error of a pair of spur gear, Mech. Mach. Theory 42 (2007) 698–726], effects of machining errors, assembly errors and lead crowning on tooth surface contact stresses (CS), root bending stresses, load-sharing ratios (LSR) and transmission errors of a pair of spur gears were investigated through performing loaded tooth contact analysis (LTCA) with developed finite element method (FEM) programs. But this research couldn't investigate the effects of tooth profile modification and lead relieving on tooth engagements. Also, the effects of machining errors, assembly errors and tooth modifications on tooth mesh stiffness (MS) couldn't be investigated. So, as a continuous study of the last research, this paper investigates the effects of tooth profile modification and lead relieving on tooth engagements of a pair of spur gears and the effects of misalignment error of gear shafts on the plane of action, tooth lead crowing and transmitted torque on tooth MS. An arc curve is used to modify tooth profiles of a pair of spur gears in this paper. This is because this method is used very popularly for the spur gears. Methods used in the last research are also used here to investigate the effects of the tooth profile modification, lead relieving and transmitted torque on tooth engagements. Based on the results, it is found that the tooth profile modification and lead relieving have significant effects on tooth CS, LSR and MS. It is also found that transmitted torque has a little effect on tooth MS, but has no effect on LSR of the gears. For the lead-relieved gears, calculation results show that edge-loads happened at the joint parts of the relieved part and the non-relieved part of tooth lead when the lead is relieved with straight lines. Since the edge-loads resulted in greater contact stresses at the joint parts and weakened tooth contact strength, attention must be paid to the lead relieving. It is necessary to reduce the edge-loads as small as possible through making the joint part smooth when the lead relieving is made. [ABSTRACT FROM AUTHOR]

A novel design for skew conical involute gear drives in approximate line contact is proposed. Such a drive has a contact ellipse with a large major-to-minor-axis ratio, which allows it to overcome the weakness of conical gear drives for application in power transmission. This gearing design approach is characterized by reduced edge contact sensitivity and increased surface durability. The edge contact sensitivity that can arise with this kind of gear drive due to assembly or manufacturing errors is evaluated by analysing the value of the shift of the line of action caused by such errors. The surface durability is evaluated by calculating the Hertz stress. Some guidelines are developed based on the analysis of the influence of the gearing parameters on the edge contact sensitivity and the surface durability made possible using this design approach for conical gear drives in the approximate line contact. The guidelines are summarized and, finally, a practical example is given to demonstrate the feasibility of the approximate line contact design. [ABSTRACT FROM AUTHOR]

Abstract: This paper quantitatively investigates effects of machining errors (ME), assembly errors (AE) and tooth modifications (TM) on loading capacity, load-sharing ratio (LSR) and transmission error (TE) of a pair of spur gears by using special-developed finite element method (FEM) software in a personal computer. Tooth surface contact stress (TSCS) and tooth root bending stress (TRBS) of a pair of spur gears with ME, AE and TM are analyzed by the FEM software. Effects of ME, AE and TM on TSCS and TRBS are also defined as “Influence factors” and the influence factors of ME, AE and TM on TSCS and TRBS are calculated quantitatively. It is found that misalignment error of gear shafts on the plane of action of the spur gears exerts great effects on TSCS and TRBS while misalignment error of gear shafts on the vertical plane of the plane of action almost exerts no effects on TSCS and TRBS. It is also found that ME and lead crowning have greater effects on TSCS and TRBS. When the maximum tooth surface machining error is 40μm, influence factor of ME on TSCS and TRBS are about 2.2 and 1.5. When quantity of lead crowning is 40μm, influence factor of lead crowning on TSCS and TRBS are about 2.0 and 1.4. These influence factors can be used as references when ISO standards are used for tooth surface contact strength and root bending strength calculations of a pair of spur gears with ME, AE and TM. Methods for LSR calculation of a pair of spur gears with ME, AE and TM are also presented in this paper. Effects of ME, AE and TM on LSR are analyzed quantitatively. It is found that ME has greater effect on LSR. When the maximum tooth surface machining error is greater than 10μm, double pair tooth-contact shall become single pair tooth-contact for sake of the effect of ME. This means that when ME on tooth surface is large, outer limit of the single pair tooth-contact area can not be used as the so-called “worst load position”. It is safe and reasonable to use tooth tip as the “worst load position” when to perform tooth bending strength calculation. Methods for TE calculation of a pair of spur gears with ME, AE and TM are also presented in this paper. Effects of ME, AE and TM on TE of the gears are analyzed quantitatively. It is found that ME not only changes waveform of TE easily, but also makes TE greater and greater when ME is increased. AE and TM also make TE greater and greater when they are increased, but do not change waveform of TE. [Copyright &y& Elsevier]

Abstract: This paper presents three-dimensional (3-D), finite element methods (FEM) to conduct surface contact stress (SCS) and root bending stress (RBS) calculations of a pair of spur gears with machining errors (ME), assembly errors (AE) and tooth modifications (TM). In this paper, firstly positions of a pair of parallel-shaft spur gears with ME, AE and TM are defined in a 3-D coordinate system. Then tooth contact of the pair of gears is assumed on a reference face around the geometrical contact line. This tooth contact on the reference face is called face-contact model of the gears. With this face-contact model, contact reference points on the reference face of one gear are assumed firstly, then a geometrical method that can consider the effects of ME, AE and TM on tooth contact is presented to find the responsive contact reference points on tooth surface of the second gear (the mating gear). Deformation influence coefficients of the pairs of contact points are calculated by 3-D, FEM and loaded tooth contact analysis (LTCA) of the pair of gears with ME, AE and TM is conducted by mathematical programming method. FEM programs are developed to do LTCA, tooth load, SCS and RBS calculations of the pair of spur gears with ME, AE and TM automatically in a personal computer. Tooth contact lengths of a pair of spur gears with lead crowning are calculated by the programs and compared with the measured results. Also, tooth contact pattern and root stains of a pair of spur gears with AE are analyzed by the programs and compared with experimental results. It is found that the calculated results are agreement with the measured ones well. Finally, an example of calculating the real SCS and RBS of a pair of spur gears with ME, AE and TM is given in the paper. It is found that ME, AE and TM exert great effects on SCS and RBS of the gears. SCS and RBS of the same pair of gears are also calculated by ISO and JGMA standards for comparing with the FEM results. [Copyright &y& Elsevier]

• The pure kinematic error model with machining and assembly errors is proposed. • Tooth error has a larger effect on kinematic error than wave generator misalignment. • The effects of wave generator structure and shape on kinematic error are discussed. • Kinematic error is affected by modulus, pressure angle, and wave generator width. Harmonic drives are widely used in the precision positioning systems due to their attractive attributes. However, kinematic error is the most fundamental problems in these drives. In this work, we present a method for analyzing the pure kinematic error of harmonic drive with machining and assembly errors. The pure kinematic error is decomposed into two parts including nonuniform motion component and lag component. The beat frequency phenomenon of the pure kinematic error is revealed. The explanation of the mechanism of pure kinematic error is verified by the experimental data from a specialized harmonic reducer test device. The influences of the wave generator structure (automatic alignment and integral structures) and shape on the pure kinematic error of harmonic drive are discussed and quantitatively evaluated, and the one possible new configuration of the wave generator is presented, which can improve the transmission performance of the drive. The results of this paper are believed to be useful for the design of harmonic drive. [ABSTRACT FROM AUTHOR]

Recombinant inbred lines (RILs) derived from bi-parental populations are stable genetic resources, which are widely used for constructing genetic linkage maps. These genetic maps are essential for QTL mapping and can aid contig and scaffold anchoring in the final stages of genome assembly. In this study, two Lotus sp. RIL populations, Lotus japonicus MG-20 × Gifu and Gifu × L. burttii, were characterized by Illumina re-sequencing. Genotyping of 187 MG-20 × Gifu RILs at 87,140 marker positions and 96 Gifu × L. burttii RILs at 357,973 marker positions allowed us to accurately identify 1,929 recombination breakpoints in the MG-20 × Gifu RILs and 1,044 breakpoints in the Gifu × L. burttii population. The resulting high-density genetic maps now facilitate high-accuracy QTL mapping, identification of reference genome mis-assemblies, and characterization of structural variants., (© The Author 2016. Published by Oxford University Press on behalf of Kazusa DNA Research Institute.)