Using variable modulus to modify a rack cutter and generate a gear pair

In this paper, two normal imaginary helical rack cutters were first established. One of these cutters is a skewed-rack cutter with an asymmetrical straight edge. The other is a rack cutter with an asymmetric parabolic profile. Second, the gear’s tooth surface of the asymmetric parabolic rack cutter is modified to be barrel-shaped based on a variable modulus. The tooth thickness of the gear is gradually reduced along the face width of the tooth from the middle of the tooth surface. Then the coordinate relationship between the gears’ blanks and the imaginary helical rack cutters was established. Through the differential geometry, crowned and uncrowned helical gear pairs were generated. Because of human factors, when the gear pair is installed, it is easy to cause the gear pair edge contact. It is necessary to add artificial assembly error settings through the tooth contact analysis to investigate the kinematic errors and contact conditions of the crowned and uncrowned helical gear pair. The mathematical models and analysis methods proposed for the crowned imaginary rack cutter using variable modulus should be useful for the design and production of double crowned helical gears with asymmetric parabolic teeth.

Fast Optimization Design of the Flexure for a Space Mirror Based on Mesh Deformation

According to the requirements of high force-thermal stability and high performance of a space telescope, a space mirror assembly must not be influenced by environmental factors. In this study, a space mirror assembly under load conditions, such as gravity, thermal, and assembly error, is considered. After the mirror is optimized, the surface shape error is reduced by 22%, and the mass is increased by 0.113 kg. In order to improve the efficiency of integration optimization, we present a fast optimization method using mesh deformation to be applied to the flexure. The size parameters of flexure and axial mount position are obtained by optimization. With our method, the single optimization time reduces from 10 min to 40 s, which can improve the efficiency of multi-objective optimization. The mirror assembly is fabricated and assembled based on optimization results. Finite element analysis (FEA) and test results for the space mirror assembly confirm the validity and feasibility of the fast optimization method, and we believe that the flexure based on fast optimization meets the requirements of a space mirror assembly for space applications.

Novel application of mapping method from small displacement torsor to tolerance: Error optimization design of assembly parts

The manufacturing/assembly error of machine parts is a key factor that influences the performance and economy of mechanical systems. To achieve high assembly precision and performance on the basis of low manufacturing accuracy and cost, this study primarily optimizes the assembly error of machine parts. First, the small displacement torsor is used to characterize the small deformation between the mating surfaces of parts. Subsequently, to realize the combination of small displacement torsor and tolerance, the small displacement torsor with manufacturing error and assembly deformation is mapped to the tolerance domain. Second, based on the relationship between small displacement torsor and tolerance, an assembly error optimization model is established on the basis of the conventional tolerance-cost model, considering the emergence of manufacturing error and assembly deformation. Third, aiming at the high-pressure rotor for aeroengines, the error optimization design of assembly is carried out developed with the assembly accuracy requirement as the constraint condition, and the total costs of the manufacturing and assembly processes as the objective. The optimization results indicate that the manufacturing error range of each mating surface after optimization changes, from small to large, under the premise of ensuring the product’s performance, which verifies that the difficulty in processing parts is reduced, and that the efficiency of parts processing is also improved. Meanwhile, the relative manufacturing cost after optimization is reduced by 6.79%, which reflects the economic requirements to a certain extent. The content of this article provides the necessary design basis and reference for the realization of high assembly accuracy of mechanical systems, under low cost requirements from the design perspective.

Poka Yoke Meets Deep Learning: a Proof of Concept for an Assembly Line Application

In this paper we present the re-engineering process of an assembly line that features speed reducers and multipliers for agricultural applications. The product operates as an interface between an input torque, typically supplied by an agricultural vehicle, and an output torque, generally moving specific equipment placed on a trolley equipped with a tow hook. The "as-is'' (initial version) line was highly inefficient due to several critical issues, including the high age of the machines, a non-optimal arrangement of them in the shop floor, and the absence of controls and process standards. These critical issues were analysed with the tools offered by Lean Manufacturing, which made it possible to identify irregularities and operations that require effort (Mura), overload (Muri), and waste (Muda). The definition of the "to-be'' (new version) assembly line included actions to update the department layout, to modify the assembly process and to design the line feeding system in compliance with the well-known concepts of Golden Zone and Strike Zone. The whole process addressed, in particular, the problem of the incorrect assembly of the oil seals. The registered error was mainly caused by the difficulty in visually identifying the correct side of the assembled oil seal, and by the mental fatigue of operators at the end of the shift. The solution studied in this paper resulted in a Poka-Yoke solution, which, leveraging the modern technologies and methods of deep learning and computer vision, monitors the process flow of the operators through a camera, preventing its completion in the event of an assembly error.

A New Method to Focus SEBs Using the Periodic Magnetic Field and the Electrostatic Field

In this paper, a novel method, named PM-E, to focus the sheet electron beam (SEB) is proposed. This new method consists of a periodic magnetic field and an electrostatic field, which are used to control the thickness and width of the SEB, respectively. The PM-E system utilizes this electrostatic field to replace the unreliable By,off, which is a tiny transverse magnetic field in the PCM that confines the SEB’s width. Moreover, the horizontal focusing force of the PM-E system is more uniform than that of the conventional PCM, and the transition distance of the former is shorter than that of the latter. In addition, the simulation results demonstrate the ability of the PM-E system to resist the influence of the assembly error. Furthermore, in the PM-E system, the electric field can be conveniently changed to correct the deflection of the SEB’s trajectory and to improve the quality of the SEB.

Modeling and Analyzing of Nonlinear Dynamics for Linear Guide Slide Platform Considering Assembly Error

In this study, a novel five degrees-of-freedom nonlinear dynamic model of linear guide slide platform is proposed, the model considers the effect of assembly error. The assembly errors are modeled as five types including: straightness assembly errors along x and y axes and rotation assembly error around x, y and z axes. The assembly error induced displacement of platform is considered. The restoring force and moment of the carriages is equal to zero when no dynamic or static load applied on the platform with considering the influence of assembly error. The influence of assembly error on the static and dynamic characteristics are investigated. The results indicate that the assembly error can cause uneven load distribution, change the dynamics of the system. In addition, the stability of the system cannot be improved by simply increasing the preload. Moreover, a series of experiments are conducted on a specialized platform to estimate the parameters of the system and verify the proposed model.

Analysis of Assembly Tolerance Based on Assembly Constraint Information Model

Mechanical products are composed of two or more parts. The geometric tolerance and dimensional tolerance of each feature in part will affect the assembly performance of the product, which are accumulated and propagated between assembly fit and parts. In this paper, through the secondary development of CAD software, the B-rep model of parts is obtained. The model information is decomposed and simplified based on geometric features to obtain the key information of parts in the assembly process, simplify the operation, and improve the accuracy. Through a directed graph network, the transmission model of assembly error information based on geometrical and dimensional tolerances (GD&T) on the surface of parts is established. Combined with the error transfer characteristics of different geometric surfaces and different error sources, guided by the breadth-first search algorithm and the shortest path theory, the search and establishment of a three-dimensional assembly chain are realized. Finally, the three-dimensional chain is simulated by the Monte Carlo method. The calculation results are compared with the error range obtained by the traditional method to prove the effectiveness of the method.