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DOI: 10.1186/s10033-019-0389-8
A Review on Lower Limb Rehabilitation Exoskeleton Robots
Di Shi, Wuxiang Zhang, Wei Zhang & Xilun Ding
Abstract: Lower limb rehabilitation exoskeleton robots integrate sensing, control, and other technologies and exhibit the characteristics of bionics, robotics, information and control science, medicine, and other interdisciplinary areas. In this review, the typical products and prototypes of lower limb exoskeleton rehabilitation robots are introduced and state-of-the-art techniques are analyzed and summarized. Because the goal of rehabilitation training is to recover patients’ sporting ability to the normal level, studying the human gait is the foundation of lower limb exoskeleton rehabilitation robot research. Therefore, this review critically evaluates research progress in human gait analysis and systematically summarizes developments in the mechanical design and control of lower limb rehabilitation exoskeleton robots. From the performance of typical prototypes, it can be deduced that these robots can be connected to human limbs as wearable forms; further, it is possible to control robot movement at each joint to simulate normal gait and drive the patient’s limb to realize robot-assisted rehabilitation training. Therefore human–robot integration is one of the most important research directions, and in this context, rigid-flexible-soft hybrid structure design, customized personalized gait generation, and multimodal information fusion are three key technologies.
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https://cjme.springeropen.com/articles/10.1186/s10033-019-0389-8
DOI: 10.1186/s10033-019-0382-2
Optimal Design and Force Control of a Nine-Cable-Driven Parallel Mechanism for Lunar Takeoff Simulation
Wangmin Yi, Yu Zheng, Weifang Wang, Xiaoqiang Tang, Xinjun Liu & Fanwei Meng
Abstract: Traditional simulation methods are unable to meet the requirements of lunar takeoff simulations, such as high force output precision, low cost, and repeated use. Considering that cable-driven parallel mechanisms have the advantages of high payload to weight ratio, potentially large workspace, and high-speed motion, these mechanisms have the potential to be used for lunar takeoff simulations. Thus, this paper presents a parallel mechanism driven by nine cables. The purpose of this study is to optimize the dimensions of the cable-driven parallel mechanism to meet dynamic workspace requirements under cable tension constraints. The dynamic workspace requirements are derived from the kinematical function requests of the lunar takeoff simulation equipment. Experimental design and response surface methods are adopted for building the surrogate mathematical model linking the optimal variables and the optimization indices. A set of dimensional parameters are determined by analyzing the surrogate mathematical model. The volume of the dynamic workspace increased by 46% after optimization. Besides, a force control method is proposed for calculating output vector and sinusoidal forces. A force control loop is introduced into the traditional position control loop to adjust the cable force precisely, while controlling the cable length. The effectiveness of the proposed control method is verified through experiments. A 5% vector output accuracy and 12 Hz undulation force output can be realized. This paper proposes a cable-driven parallel mechanism which can be used for lunar takeoff simulation.
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https://cjme.springeropen.com/articles/10.1186/s10033-019-0382-2
DOI: 10.1186/s10033-019-0386-y
Research on the Error Averaging Effect in A Rolling Guide Pair
Yanbing Ni, Haiyang Zhou, Cuiyan Shao & Jinhe Li
Abstract: By studying the effects of geometric precision on kinematic accuracy, an error mapping model has been established, based on the hypothesis that a motion pair and its installation surface are rigid. However, when using this assumption, there is a significant error induced in high-precision computer numerical control (CNC) machine tools as compared with reality. One of the most important reasons for this error is failing to consider the error averaging effect of motion pair elements. Therefore, this work examines a high-precision horizontal machining center as its research object, and analyzes the error averaging mechanism of a rolling guide pair under a deformation of the rolling elements. The carriage bearing forces caused by guideway straightness errors are obtained by constructing a geometric error model of a single carriage. The relationship between guideway straightness errors and carriage bearing forces is described by a transfer function in the spatial frequency domain, and its characteristics are analyzed. It quantifies the so-called error averaging effect of the rolling guide system and, on this basis, a static model for four carriages is established to reflect the error averaging effect of the rolling guide pair on the position and orientation errors of the motion pair. In addition, it is found that the wavelengths and phase differences of guideway errors affect this error averaging mechanism, but the amplitude and preload have little influence thereon. The experiment result shows that the kinematic straightness errors in the x- and y-directions were approximately 1/3 to 1/2 of the guideway straightness errors in the corresponding directions. The results can be used to guide the precision design and assembly of machine tools.
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https://cjme.springeropen.com/articles/10.1186/s10033-019-0386-y
DOI: 10.1186/s10033-019-0381-3
Effects of Prestressing of the Ring Gear in Interference Fit on Flexural Fatigue Strength of Tooth Root
Shiping Yang, Yixing Ji, Yulin Mo & Tianyu Xia
Abstract: When the gearbox body interference is connected to the ring gear, prestressing occurs in the ring gear, which has a significant impact on the strength and life of the gear. Research on the prestressing of the inner ring gear is in the preliminary stage, and the distribution rule of the prestressing and the influence of each parameter on the interference prestressing have not been derived. In this paper, based on the method of calculating the prestressing of the thick cylinder in interference fit, the ring gear is found to be equivalent to a thick cylinder, and the distribution rule of prestressing of the ring gear in the interference fit is inferred. Then, by modeling and analyzing the gearbox body and ring gear in the interference fit using ABAQUS, the distribution rule of prestressing the ring gear in the interference fit is obtained through a numerical simulation. Finally, the prestressing of the ring gear in the interference fit is measured using X-ray diffraction, and the distribution rule of prestressing of the ring gear in the interference fit is obtained through analysis. Compared with the distribution rule of prestressing in theory, numerical simulation, and experiment, the theoretical distribution rule of prestressing is amended through a statistical method, and a more accurate formula of prestressing is obtained. Through the calculation of the stress and bending moment in the dangerous section of the ring gear through prestressing, the formula for checking the tooth root flexural fatigue strength in the interference fit prestressing is inferred. This research proposes a tooth root bending strength conditional formula for the inner ring gear of the interference fit, which serves as a guide for the design and production of the actual interference joint inner ring gear.
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https://cjme.springeropen.com/articles/10.1186/s10033-019-0381-3
DOI: 10.1186/s10033-019-0385-z
Influence of Axial Loads to Propagation Characteristics of the Elastic Wave in a Non-Uniform Shaft
Yimin Wei, Zhiwei Zhao, Wenhua Chen & Qi Liu
Abstract: The vibration propagates through the shaft in the form of elastic waves. The propagation characteristics of the elastic waves are affected by the axial loads. The influence of the axial loads to the propagation characteristics of the elastic waves is studied in this paper. Firstly, the transfer matrix of the elastic waves for the non-uniform shaft with axial loads is deduced by combining the transfer matrix without axial load and the additional equation caused by the axial load. And then, a numerical method is used to study the influence of the axial load, non-uniformity and the rotating speed to the propagation characteristics of the elastic waves. It’s found that a new Stop Band will appear due to the axial force, and the central frequency of which will decrease as the increase of the force, while the band width of which remains the same. The central frequency of the new Stop Band will also increase as the increase of the cross-section area ratio; however, the rotating speed of the shaft doesn’t affect the propagation characteristics of the elastic waves obviously. Finally, an experimental rig is built up for further study, even though there are some small local errors, the results of experiments match well with the numerical ones, which indicates the validation of the theoretical results. The result can help to study the influence of the axial load to the dynamics of a non-uniform shaft and help to reveal the vibration propagating mechanism in such a shaft.
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https://cjme.springeropen.com/articles/10.1186/s10033-019-0385-z
DOI: 10.1186/s10033-019-0387-x
Design and Experimentation of Automatic Tidying and Sorting Mechanism for Blood Collection Needles in Stacking State
Junhua Tong, Yingpeng Zhu, Leiying He, Chuanyu Wu & Peilin Cheng
Abstract: Disposable blood collection needles become severely intertwined and hooked during stacking, and thus individually feeding disposable blood collection needles during mechanical packaging is difficult. Based on the physical characteristics of the blood collection needles during the stacking state, this study designed an automatic tidying and sorting mechanism by combining compound vibration, sorting, and conveying. During the feeding process, the compound vibration-type material-tidying mechanism tidies 20‒30 blood collection needles first; then, the material sorting and conveying mechanism transports the tidied blood collection needles individually. The orthogonal testing of the automatic material tidying process shows that various experimental factors are ranked by the significance level of the effect on the tidying process and the significance ranking is as follows: vertical vibration frequency > horizontal amplitude > vertical amplitude > horizontal vibration frequency. Experiments were performed after analyzing the optimal combination. The results demonstrate that when the horizontal vibration frequency is 1.7 Hz, the horizontal amplitude is 150 mm, vertical vibration frequency is 1.3 Hz, vertical amplitude is 30 mm, and material length after tidying is 265 mm. The automatic sorting and conveying experiment shows the effect of various experimental factors on the feed rate of the material, where the significance level of the effect is ranked as follows: vibration frequency > material quantity > channel dip angle. The experimental results show that when the number of materials is 25, the channel dip angle is 12°, and vibration frequency is 52.5 Hz. The material delivery efficiency reaches 0.51 s/root, meeting the requirement of five channels for 80000 root/day feeding efficiency. The study can provide reference for the realization of automatic feeding of large aspect ratio flexible materials in similar stacking state.
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https://cjme.springeropen.com/articles/10.1186/s10033-019-0387-x
DOI: 10.1186/s10033-019-0384-0
Grinding Burn Detection Based on Cross Wavelet and Wavelet Coherence Analysis by Acoustic Emission Signal
Zheyu Gao, Jing Lin, Xiufeng Wang & Yuhe Liao
Abstract: Grinding burn monitoring is of great importance to guarantee the surface integrity of the workpiece. Existing methods monitor overall signal variation. However, the signals produced by metal burn are always weak. Therefore, the detection rate of grinding burn still needs to be improved. The paper presents a novel grinding burn detection method basing on acoustic emission (AE) signals. It is achieved by establishing the coherence relationship of pure metal burn and grinding burn signals. Firstly, laser and grinding experiments were carried out to produce pure metal burn signals and grinding burn signals. No-burn and burn surfaces were generated and AE signals were captured separately. Then, the cross wavelet transform (XWT) and wavelet coherence (WTC) were applied to reveal the coherence relationship of the pure metal burn signal and grinding burn signal. The methods can reduce unwanted AE sources and background noise. Novel parameters based on XWT and WTC are proposed to quantify the degree of coherence and monitor the grinding burn. The grinding burn signals were recognized successfully by the proposed indexes under same grinding condition.
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https://cjme.springeropen.com/articles/10.1186/s10033-019-0384-0
DOI: 10.1186/s10033-019-0383-1
Characteristics of Vibration and Sound Radiation of Metro Resilient Wheel
Xin Zhou, Jian Han, Yue Zhao, Bing Wu, Gong Cheng, Shenghui Xu & Xuesong Jin
Abstract: Resilient wheels are extensively used in urban rail transit, especially for tramway systems, owing to its advantages in noise reduction. A new type of resilient wheel for a metro is designed, and its characteristics of vibration and sound radiation, including the rolling noise of a resilient single wheel coupled with a track, are studied in this paper. A two-step research is presented. Firstly, laboratory experiments were conducted to obtain the vibration response of the designed resilient wheel under the radial excitation on its tread. Secondly, the rolling noise model of the resilient wheel coupled with a slab track used in a metro line is developed. The wheel model is based on the 3D finite element and boundary element methods and verified by using the experimental results obtained from the laboratory. The track vibration model is based on the wavenumber finite element method, and the track sound radiation is calculated by using an efficient frequency-domain Rayleigh method. The interaction of the resilient wheel and the slab track is analyzed considering the measured wheel/rail roughness of the metro. The contribution of the resilient wheel to the reduction of wheel/rail system noise is analyzed. The results show that the resilient wheel can effectively reduce the wheel/rail rolling noise by approximately 2 dB(A) to 3 dB(A), mainly because the radiated noise by the rail is reduced. In addition, the elastic modulus of the rubber has an important influence on the noise reduction of resilient wheels.
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https://cjme.springeropen.com/articles/10.1186/s10033-019-0383-1
DOI: 10.1186/s10033-019-0380-4
Friction and Wear Study on Friction Pairs with a Biomimetic Non-smooth Surface of 316L Relative to CF/PEEK under a Seawater Lubricated Condition
Yingna Liang, Dianrong Gao, Bo Chen & Jianhua Zhao
Abstract: Current studies of a seawater axial piston pump mainly solve the problems of corrosion and wear in a slipper pair by selecting materials with corrosion resistance, self-lubrication, and wear resistance. In addition, an appropriate biomimetic non-smooth surface design for the slipper pair can further improve the tribological behavior. In this paper, 316L stainless steel and CF/PEEK were selected to process the upper and bottom specimens, and the biomimetic non-smooth surface was introduced into the interface between the friction pair. The friction and wear tests were performed on a MMD-5A tester at a rotation speed of 1000 r/min and load of 200 N under seawater lubricated condition. The results indicate that the main friction form of the smooth surface friction pair corresponds to abrasive wear and adhesive wear and that it exhibits a friction coefficient of 0.05–0.07, a specimen temperature of 56 °C, a high wear rate, and surface roughness. Pits on the non-smooth surface friction pairs produced hydrodynamic lubrication and reduced abrasive wear, and thus the plowing effect is their main friction form. The non-smooth surface friction pairs exhibit a friction coefficient of 0.03–0.04, a specimen temperature of 48 °C, a low wear rate, and surface roughness. The study has important theoretical significance for enriching the lubrication, friction, and wear theory of a seawater axial piston pump, and economic significance and military significance for promoting the marine development and the national defense military.
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https://cjme.springeropen.com/articles/10.1186/s10033-019-0380-4
DOI: 10.1186/s10033-019-0379-x
Experimental and Computational Analysis of the Unstable Flow Structure in a Centrifugal Compressor with a Vaneless Diffuser
Xiang Xue & Tong Wang
Abstract: The unstable flow phenomena in compressors, such as stall and surge, are closely related to the efficiency and the operating region. It is indispensable to capture the unstable flow structure in compressors and understand the mechanism of flow instability at low flow rates. Cooperated with the manufacturer, an industrial centrifugal compressor with a vaneless diffuser is tested by its performance test rig and our multi-phase dynamic measurement system. Many dynamic pressure transducers are circumferentially mounted on the casing surface at seven radial locations, spanning the impeller region and the diffuser inlet region. The pressure fields from the design condition to surge are measured in details. Based on the multi-phase dynamic signals, the original location of stall occurring can be determined. Meanwhile, the information of the unstable flow structure is obtained, such as the circumferential mode and the propagating speed of stall cells. To get more details of the vortex structure, an unsteady simulation of this tested compressor is carried out. The computational result is well matched with the experimental result and further illustrates how the unstable flow structure in the impeller region gradually affects the stability of the total machine at low flow rates. The dynamic mode decomposition (DMD) method is applied to get the specific flow pattern corresponding to the stall frequency. Both experimental and computational analysis show that the flow structure at a particular radial location in the impeller region has a great impact on the stall and surge. Some differences between the computational and experimental result are also discussed. Through these two main analytical methods, an insight into the unstable flow structure in an industrial compressor is gained. The result also plays a crucial role in the guidance of the compressor stabilization techniques.
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