Design of a Variable Stiffness Joint Module to Quickly Change the Stiffness and to Reduce the Power Consumption
27 Jul 2020-IEEE Access (Institute of Electrical and Electronics Engineers (IEEE))-Vol. 8, pp 138318-138330
TL;DR: By mechanically compensating the moment due to unbalanced forces at the contact points, the continuous usage of stiffness motor has been eliminated, leading to reduced power consumption.
Abstract: Variable stiffness actuators (VSA) are finding wide applications in robotics to enhance safety during interactions with stiff environments. Researchers have proposed various design architectures like antagonistic actuation, which requires both the motors to be powered simultaneously for varying the stiffness or equilibrium position. In this paper, the design of a novel joint module, named as variable stiffness joint module (VSJM), is proposed, which consists of a lead-screw arrangement for varying the stiffness range and a cam based mechanism to change the stiffness within the set range quickly. The cam profile has been synthesized to maximize the stiffness variation as well as to maintain the cam and cam follower in static equilibrium when the output link is in the equilibrium position. This was achieved by properly positioning and orienting the friction cones at the contact points. By mechanically compensating the moment due to unbalanced forces at the contact points, the continuous usage of stiffness motor has been eliminated, leading to reduced power consumption. Details of the proposed mechanism are presented along with the mathematical model for cam profile synthesis and static analysis. A simplified prototype of the proposed design has been fabricated to perform the experiments. A hammering-a-nail experiment has been conducted to show the capability of the mechanism, and the results are presented.
Citations
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TL;DR: In this paper , a planar high-compliance joint is proposed, in which the torsion spring is not an independent part but a synergy result of two adjacent parts developed from the stiffness adjustment linkage mechanism, and the flexible element is a cantilever leaf feature belongs to the rigid-flexible integral linkage.
4 citations
23 Oct 2022
TL;DR: In this article , the authors propose a new robotic gripper design, equipped with shape conformable active gripping surfaces that can act as an active or passive joint and adapt to substrates with different shapes and sizes.
Abstract: Among primates, the prehensile nature of the hand is vital for greater adaptability and a secure grip over the substrate/branches, particularly for arm-swinging motion or brachiation. Though various brachiation mechanisms that are mechanically equivalent to underactuated pendulum models are reported in the literature, not much attention has been given to the hand design that facilitates both locomotion and within-hand manipulation. In this paper, we propose a new robotic gripper design, equipped with shape conformable active gripping surfaces that can act as an active or passive joint and adapt to substrates with different shapes and sizes. A floating base serial chain, named GraspMaM, equipped with two such grippers, increases the versatility by performing a range of locomotion and manipulation modes without using dedicated systems. The unique gripper design allows the robot to estimate the passive joint state while arm-swinging and exhibits a dual relationship between manipulation and locomotion. We report the design details of the multimodal gripper and how it can be adapted for the brachiation motion assuming it as an articulated suspended pendulum model. Further, the system parameters of the physical prototype are estimated, and experimental results for the brachiation mode are discussed to validate and show the effectiveness of the proposed design.
23 Oct 2022
TL;DR: In this paper , the authors propose a new robotic gripper design, equipped with shape conformable active gripping surfaces that can act as an active or passive joint and adapt to substrates with different shapes and sizes.
Abstract: Among primates, the prehensile nature of the hand is vital for greater adaptability and a secure grip over the substrate/branches, particularly for arm-swinging motion or brachiation. Though various brachiation mechanisms that are mechanically equivalent to underactuated pendulum models are reported in the literature, not much attention has been given to the hand design that facilitates both locomotion and within-hand manipulation. In this paper, we propose a new robotic gripper design, equipped with shape conformable active gripping surfaces that can act as an active or passive joint and adapt to substrates with different shapes and sizes. A floating base serial chain, named GraspMaM, equipped with two such grippers, increases the versatility by performing a range of locomotion and manipulation modes without using dedicated systems. The unique gripper design allows the robot to estimate the passive joint state while arm-swinging and exhibits a dual relationship between manipulation and locomotion. We report the design details of the multimodal gripper and how it can be adapted for the brachiation motion assuming it as an articulated suspended pendulum model. Further, the system parameters of the physical prototype are estimated, and experimental results for the brachiation mode are discussed to validate and show the effectiveness of the proposed design.
TL;DR: In this article , a variable stiffness actuators (VSA) with different characteristics can be obtained by shape reconfiguration of its internal driving cams, and the analytical relationship between the pressure angle of the cam pitch curve, stiffness adjustment speed and accuracy, and load distribution is provided.
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 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.
References
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05 Aug 1995
TL;DR: It is proposed that for natural tasks, zero motion force bandwidth isn't everything, and incorporating series elasticity as a purposeful element within the actuator is a good idea.
Abstract: It is traditional to make the interface between an actuator and its load as stiff as possible. Despite this tradition, reducing interface stiffness offers a number of advantages, including greater shock tolerance, lower reflected inertia, more accurate and stable force control, less inadvertent damage to the environment, and the capacity for energy storage. As a trade-off, reducing interface stiffness also lowers zero motion force bandwidth. In this paper, the authors propose that for natural tasks, zero motion force bandwidth isn't everything, and incorporating series elasticity as a purposeful element within the actuator is a good idea. The authors use the term elasticity instead of compliance to indicate the presence of a passive mechanical spring in the actuator. After a discussion of the trade-offs inherent in series elastic actuators, the authors present a control system for their use under general force or impedance control. The authors conclude with test results from a revolute series-elastic actuator meant for the arms of the MIT humanoid robot Cog and for a small planetary rover.
2,309 citations
"Design of a Variable Stiffness Join..." refers background in this paper
...This was addressed in the literature by providing active or passive compliance control [2], [3], which would change the elasticity of the joint, based on the task requirement....
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TL;DR: This paper presents fast and simple algorithms for directly constructing force-closure grasps based on the shape of the grasped object, and shows that most nonmarginal equilibriumGrasps are force- closuregrasps.
Abstract: This paper presents fast and simple algorithms for directly constructing force-closure grasps based on the shape of the grasped object. The synthesis of force-closure grasps finds in dependent regions of contact for the fingertips, such that the motion of the grasped object is totally constrained. A force- closure grasp implies equilibrium grasps exist. In the reverse direction, we show that most nonmarginal equilibrium grasps are force-closure grasps.
896 citations
"Design of a Variable Stiffness Join..." refers background in this paper
...According to Nguyen’s criterion [39], if there exists a line that connects the two contact points and if that line is an interior of the friction cone, then the system of forces are balanced [40]....
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...To attain Nguyen’s criterion [39], we have imposed that one of the edges of friction cone, i....
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TL;DR: A classification based on the principles through which the variable stiffness and damping are achieved is proposed and allows for designers of new devices to orientate and take inspiration and users of VIA's to be guided in the design and implementation process for their targeted application.
876 citations
"Design of a Variable Stiffness Join..." refers background in this paper
...More information about various designs, classifications, and characteristics of VSA can be found in the review articles [5], [23]–[25]....
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TL;DR: The state of the art in the design of actuators with adaptable passive compliance is described, which is not preferred for classical position-controlled applications such as pick and place operations but is preferred in novel robots where safe human- robot interaction is required or in applications where energy efficiency must be increased by adapting the actuator's resonance frequency.
Abstract: In the growing fields of wearable robotics, rehabilitation robotics, prosthetics, and walking k robots, variable stiffness actuators (VSAs) or adjustable compliant actuators are being designed and implemented because of their ability to minimize large forces due to shocks, to safely interact with the user, and their ability to store and release energy in passive elastic elements. This review article describes the state of the art in the design of actuators with adaptable passive compliance. This new type of actuator is not preferred for classical position-controlled applications such as pick and place operations but is preferred in novel robots where safe human- robot interaction is required or in applications where energy efficiency must be increased by adapting the actuator's resonance frequency. The working principles of the different existing designs are explained and compared. The designs are divided into four groups: equilibrium-controlled stiffness, antagonistic-controlled stiffness, structure-controlled stiffness (SCS), and mechanically controlled stiffness.
772 citations
TL;DR: In this paper, the authors considered the problem of designing joint-actuation mechanisms that can allow fast and accurate operation of a robot arm, while guaranteeing a suitably limited level of injury risk.
Abstract: This article considered the problem of designing joint-actuation mechanisms that can allow fast and accurate operation of a robot arm, while guaranteeing a suitably limited level of injury risk. Different approaches to the problem were presented, and a method of performance evaluation was proposed based on minimum-time optimal control with safety constraints. The variable stiffness transmission (VST) scheme was found to be one of a few different possible schemes that allows the most flexibility and potential performance. Some aspects related to the implementation of the mechanics and control of VST actuation were also reported.
620 citations