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Search Results (3)

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Keywords = cam pitch curve synthesis

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19 pages, 7933 KiB  
Article
Rigid-Body Guidance Synthesis of Noncircular Gear-Five-Bar Mechanisms and Its Application in a Knee Joint Rehabilitation Device
by Chennan Yu, Kun Yao, Yanyu Zong, Jun Ye and Jianneng Chen
Machines 2022, 10(12), 1110; https://doi.org/10.3390/machines10121110 - 22 Nov 2022
Cited by 6 | Viewed by 2764
Abstract
At present, the research objects of rigid-body guidance synthesis are mostly limited to pure linkages, and there is little research on the combined mechanisms of gears or cams and linkages. In order to expand the research objects of rigid-body guidance and improve the [...] Read more.
At present, the research objects of rigid-body guidance synthesis are mostly limited to pure linkages, and there is little research on the combined mechanisms of gears or cams and linkages. In order to expand the research objects of rigid-body guidance and improve the kinematic mapping theory, this paper proposes a rigid-body guidance method of noncircular gear-five-bar combined mechanisms. A noncircular gear-five-bar mechanism can be regarded as a combination of a 2R (two revolute joints) open chain, a 3R (three revolute joints) open chain and a pair of noncircular gears. Firstly, the circle point curves and circle center point curves of the 2R and 3R open chains are obtained by using kinematic mapping, and they are formed into a double crank five-bar linkage. Secondly, the B-spline curve is used to fit the rotation angle relationship of the gear pair to obtain the pitch curves of noncircular gears. Finally, aiming at correcting patients’ abnormal gait, a noncircular gear-five-bar exoskeleton knee joint rehabilitation device is designed based on four task poses. The prototype is developed and the wear test is carried out. The test results verify the correctness of the rigid-body guidance synthesis method and the effectiveness of rehabilitation training. Full article
(This article belongs to the Section Machine Design and Theory)
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18 pages, 6425 KiB  
Article
A Novel Cam-Based Variable Stiffness Actuator: Pitch Curve Synthetic Approach for Reconfiguration Design
by Fanghua Mei, Shusheng Bi and Bianhong Li
Mathematics 2022, 10(21), 4088; https://doi.org/10.3390/math10214088 - 2 Nov 2022
Viewed by 2034
Abstract
Variable stiffness actuators (VSA) have attracted much attention because of their potential for human-like interaction behaviors. This paper devotes to improving the VSA’s versatility. VSA with different characteristics can be obtained by shape reconfiguration of its internal driving cams. The proposed VSA mainly [...] Read more.
Variable stiffness actuators (VSA) have attracted much attention because of their potential for human-like interaction behaviors. This paper devotes to improving the VSA’s versatility. VSA with different characteristics can be obtained by shape reconfiguration of its internal driving cams. The proposed VSA mainly includes a variable stiffness module and a cam-based driven module. A common node connects the two modules. It is placed in the common grooves of the dual cams. Kinematically, the radial position of the node can be changed for stiffness adjustment by cam differential motion. Mechanically, the driven force on this node can be resolved into two orthogonal directions by cam groove, one for stiffness adjustment and another for position balance., The paper establishes the analytical relationship between the pressure angle of the cam pitch curve, stiffness adjustment speed and accuracy, and load distribution. Furtherly, the pitch curve synthetic approach for VSA reconfiguration is provided. A special cam shape with a favorable load distribution is proposed to verify the method. The correctness of the design was effectively proved by experiments in the virtual model and physical prototype. Full article
(This article belongs to the Special Issue Advanced Mathematical Modeling and Numerical Solutions in Applied Mechanics and Engineering)
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23 pages, 6157 KiB  
Article
Design and Experiment Evaluation of Load Distribution on the Dual Motors in Cam-Based Variable Stiffness Actuator with Helping Mode
by Fanghua Mei, Shusheng Bi, Yueri Cai and Hanjun Gao
Actuators 2022, 11(6), 153; https://doi.org/10.3390/act11060153 - 8 Jun 2022
Viewed by 2834
Abstract
This paper presents a novel cam-based variable stiffness actuator (VSA). It significantly differs from its counterparts in that the external load distributes on its two motors with a small difference. It is a feasible method to improve VSA’s output power, especially in compact [...] Read more.
This paper presents a novel cam-based variable stiffness actuator (VSA). It significantly differs from its counterparts in that the external load distributes on its two motors with a small difference. It is a feasible method to improve VSA’s output power, especially in compact joints, such as rehabilitation devices. The stiffness adjustment involves a spring-balanced crank-slider mechanism with a variable-length base frame. Its tunable node is the common node for force decomposition, synthesis, stiffness adjustment, and position control by setting it at the common groove of two differential variable-pitch cams. The paper establishes analytical expressions among the pressure angle of the cam pitch curve, load distribution, and its crucial design indexes and constraints. Based on this, the pitch curve synthesis method is put forward to optimize the load distribution. In addition, a reasonable tradeoff can be easily made by locally adjusting the cam pressure angle. So, the dual motors can work against the output load together in the same direction with a close amount. In the fabricated prototype, current stratification caused by the unstable friction direction has been observed. The estimation results of motor frictionless current matched the designed load distribution behavior. Full article
(This article belongs to the Special Issue Actuation Solutions for Wearable Robots)
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