Conventional manipulators with rigid structures and sti ness actuators have poor flexibility,limited obstacle avoidance capability,and constrained workspace.Some developed flexible or soft manipulators in recent years...Conventional manipulators with rigid structures and sti ness actuators have poor flexibility,limited obstacle avoidance capability,and constrained workspace.Some developed flexible or soft manipulators in recent years have the characteristics of infinite degrees of freedom,high flexibility,environmental adaptability,and extended manipulation capability.However,these existing manipulators still cannot achieve the shrinking motion and independent control of specified segments like the animals,which hinders their applications.In this paper,a flexible bio-tensegrity manipulator,inspired by the longitudinal and transversal muscles of octopus tentacles,was proposed to mimic the shrinking behavior and achieve the variable motion patterns of each segment.Such proposed manipulator uses the elastic spring as the backbone,which is driven by four cables and has one variable structure mechanism in each segment to achieve the independent control of each segment.The variable structure mechanism innovatively contains seven lock-release states to independently control the bending and shrinking motion of each segment.After the kinematic modeling and analysis,one prototype of such bionic flexible manipulator was built and the open-loop control method was proposed.Some proof-of-concept experiments,including the shrinking motion,bending motion,and variable structure motion,were carried out by controlling the length of four cables and changing the lock-release states of the variable structure mechanism,which validate the feasibility and validity of our proposed prototype.Meanwhile,the experimental results show the flexible manipulator can accomplish the bending and shrinking motion with the relative error less than 6.8%through the simple independent control of each segment using the variable structure mechanism.This proposed manipulator has the features of controllable degree-of-freedom in each segment,which extend their environmental adaptability,and manipulation capability.展开更多
A safety mechanism capable of moving at will within the range of its whole link lengths is designed based on the link space. Sixteen extreme poses are obtained in a Stewart platform. The singular points of the extreme...A safety mechanism capable of moving at will within the range of its whole link lengths is designed based on the link space. Sixteen extreme poses are obtained in a Stewart platform. The singular points of the extreme poses are solved by using homotopy method as well as the judgment condition of singular points, and thereby the maximum link lengths are achieved. The rotation angles of joints and the distances between two neighboring links are analyzed in a calculation example in which that the mechanism moves among the extreme poses is assumed. Then an algorithm to test the safety mechanism is presented taking the constraint conditions into account. A safety mechanism having optimal properties of global movement is worked out by optimizing all structural parameters through minimizing the average condition number of extreme poses.展开更多
The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers.This paper focuses on designing a class of 2R1T(R:Rotation;T:Translation)parallel spindle...The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers.This paper focuses on designing a class of 2R1T(R:Rotation;T:Translation)parallel spindle heads and the corresponding collaborative 5-axis manipulators with 2-dimension(2D)large rotational angles.In order to construct 2D rotational degrees of freedom(DOFs),a platform with 2D revolute joints is proposed first.Based on the constraint screw theory,the feasible limbs that can be connected in the platform are synthesized.In order to provide constant rotational axis for the platform,a class of redundant limbs are designed.A class of redundant 2R1T parallel spindle heads is obtained by connecting the redundant limbs with the platform and the redundant characteristics are verified by the modified Grübler-Kutzbach criterion.The corresponding 5-axis collaborative manipulators are presented by constructing a 2-DOF series translational bottom moving platform.The inverse kinematics and the orientation workspace as well as the decoupling characteristics of this type of 2R1T parallel spindle heads are analyzed.The results show that these manipulators have large 2D rotational angles than the traditional A3/Z3 heads and can be potentially used in the application of multi-axis machine tools and the 3D printers.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.51705066,51805128)Sichuan Science and Technology Program(Grant No.2019YFG0343)Fundamental Research Funds for the Central Universities of China(Grant Nos.ZYGX2019J041,ZYGX2016KYQD137).
文摘Conventional manipulators with rigid structures and sti ness actuators have poor flexibility,limited obstacle avoidance capability,and constrained workspace.Some developed flexible or soft manipulators in recent years have the characteristics of infinite degrees of freedom,high flexibility,environmental adaptability,and extended manipulation capability.However,these existing manipulators still cannot achieve the shrinking motion and independent control of specified segments like the animals,which hinders their applications.In this paper,a flexible bio-tensegrity manipulator,inspired by the longitudinal and transversal muscles of octopus tentacles,was proposed to mimic the shrinking behavior and achieve the variable motion patterns of each segment.Such proposed manipulator uses the elastic spring as the backbone,which is driven by four cables and has one variable structure mechanism in each segment to achieve the independent control of each segment.The variable structure mechanism innovatively contains seven lock-release states to independently control the bending and shrinking motion of each segment.After the kinematic modeling and analysis,one prototype of such bionic flexible manipulator was built and the open-loop control method was proposed.Some proof-of-concept experiments,including the shrinking motion,bending motion,and variable structure motion,were carried out by controlling the length of four cables and changing the lock-release states of the variable structure mechanism,which validate the feasibility and validity of our proposed prototype.Meanwhile,the experimental results show the flexible manipulator can accomplish the bending and shrinking motion with the relative error less than 6.8%through the simple independent control of each segment using the variable structure mechanism.This proposed manipulator has the features of controllable degree-of-freedom in each segment,which extend their environmental adaptability,and manipulation capability.
文摘A safety mechanism capable of moving at will within the range of its whole link lengths is designed based on the link space. Sixteen extreme poses are obtained in a Stewart platform. The singular points of the extreme poses are solved by using homotopy method as well as the judgment condition of singular points, and thereby the maximum link lengths are achieved. The rotation angles of joints and the distances between two neighboring links are analyzed in a calculation example in which that the mechanism moves among the extreme poses is assumed. Then an algorithm to test the safety mechanism is presented taking the constraint conditions into account. A safety mechanism having optimal properties of global movement is worked out by optimizing all structural parameters through minimizing the average condition number of extreme poses.
基金The authors gratefully acknowledge the financial support of the National Nature Science Foundation of China(Grant Nos.51975039 and 51675037)the Fundamental Research Funds for the Central Universities(Grant No.2018JBZ007).
文摘The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers.This paper focuses on designing a class of 2R1T(R:Rotation;T:Translation)parallel spindle heads and the corresponding collaborative 5-axis manipulators with 2-dimension(2D)large rotational angles.In order to construct 2D rotational degrees of freedom(DOFs),a platform with 2D revolute joints is proposed first.Based on the constraint screw theory,the feasible limbs that can be connected in the platform are synthesized.In order to provide constant rotational axis for the platform,a class of redundant limbs are designed.A class of redundant 2R1T parallel spindle heads is obtained by connecting the redundant limbs with the platform and the redundant characteristics are verified by the modified Grübler-Kutzbach criterion.The corresponding 5-axis collaborative manipulators are presented by constructing a 2-DOF series translational bottom moving platform.The inverse kinematics and the orientation workspace as well as the decoupling characteristics of this type of 2R1T parallel spindle heads are analyzed.The results show that these manipulators have large 2D rotational angles than the traditional A3/Z3 heads and can be potentially used in the application of multi-axis machine tools and the 3D printers.
