Latest Papers

ASME Journal of Mechanisms and Robotics

  • Design of Rolling Motion for Snake-Like Robots Using Center-of-Gravity Shift
    on January 20, 2025 at 12:00 am

    AbstractThe snake-like robot can travel over environments that are difficult for wheeled mobility mechanisms. However, undulating locomotion requires high power consumption. We propose an efficient method that integrates the center-of-gravity (COG) shifting for the navigation of the robot to address the aforementioned problem. The proposed method allows the use of rolling motion with high traveling efficiency on level ground and undulating locomotion in water as well as other uneven surfaces. In this paper, we present a design method using the multi-objective genetic algorithm in terms of the traveling velocity of the robot, load, and energy consumption of the servomotor. The results of the motion design show that the COG shift motion mode was obtained as the optimal solution. It was observed that the COG shift motion with the designed parameters can achieve high traveling efficiency compared to that with conventional undulating locomotion by experiment.

  • Point-Based Models: A Unified Approach for Geometric Constraint Analysis of Planar n -Bar Mechanisms With Rotary, Sliding, and Rolling Joints
    on January 20, 2025 at 12:00 am

    AbstractKinematic simulation of planar n-bar mechanisms has been an intense topic of study for several decades now. However, a large majority of efforts have focused on position analysis of such mechanisms with limited links and joint types. This article presents a novel, unified approach to the analysis of geometric constraints of planar n-bar mechanisms with revolute joint (R-joint), prismatic joint (P-joint), and rolling joint. This work is motivated by a need to create and program a system of constraint equations that deal with different types of joints in a unified way. A key feature of this work is that the rolling joint constraints are represented by four-point models, which enables us to use the well-established undirected graph rigidity analysis algorithms. As a result, mechanisms with an arbitrary combination of revolute-, prismatic joints, and wheel/gear/wheel-belt chains without any limitations on their actuation scheme can be analyzed and simulated efficiently for potential implementation in interactive computer software and large-scale data generation.

  • On the Use of Tension Transition Zones for Kinematic and Compliance Performance Analysis of Wire-Actuated Continuum Robots
    on January 20, 2025 at 12:00 am

    AbstractWire-actuated/tendon-actuated mechanisms suffer from discontinuity in their performance measures stemming from the limitation of unilateral actuation due to tendon actuation (pull-only actuation). Using traditional Jacobian-based performance measures ignores these limitations and can underestimate the expected position/orientation (pose) uncertainty for a given design. In this paper, we put forth the notion of wire-tension transition zones, and we illustrate how these tension transition zones can be used to modify the definition of the traditional Jacobian when calculating the expected robot performance in terms of dexterity, end-effector pose uncertainty and compliance. We use wire-actuated continuum robots as an illustrative robot architecture. We compare the expected performance of three-wire versus four-wire designs while considering somewhat realistic design parameters drawn from surgical robotics as an application domain. The results of our simulation studies emphasize the importance of carefully using the reduced Jacobin with tension transition zones to capture the performance measure discontinuities due to wires/tendons going slack. Furthermore, the results show that the traditional approach underestimates the uncertainty in the position of the end-effector by as much as 50% (effects of joint-level uncertainty) and 206% (compliance performance analysis) in the case of a three-wire design alternative. We believe that this contribution supports medical robotic system designers in architecture selection and comparative design performance analysis while avoiding unpleasant surprises that would otherwise be encountered if traditional performance measures were used.

  • Cable Force Distribution and Motion Control for a Cable-Driven Super-Redundant Robot Under Stiffness Constraints
    on January 20, 2025 at 12:00 am

    AbstractCable-driven super-redundant robots (CDSSR) with slender and flexible bodies have wide application potential in narrow spaces. However, the control accuracy of the robot is affected by the instability of the operating stiffness during motion, which is related to the diversity of the cable tension distribution solutions. To solve this problem, an analytical stiffness model of the cable-driven super-redundant robot is first constructed based on the virtual work principle. Then, an optimal cable tension distribution model based on energy optimization and stiffness constraint is proposed. Third, a motion control framework of cable-driven super-redundant robot with stiffness constraints is proposed. Finally, constant stiffness control experiments and repeated positioning accuracy experiments of robot end under different end stiffness conditions are carried out on a 21-DOF cable-driven super-redundant robot. The results show that the proposed control strategy can achieve constant stiffness control. When the stiffness of the robot is adjusted from 200 N/m to 300 N/m, the repeated positioning accuracy in the X, Y, and Z directions is increased by 40.00%, 27.62%, and 53.09%, respectively. When the end stiffness is adjusted from 300 N/m to 400 N/m, the repeated positioning accuracy in the X, Y, and Z directions is increased by 40.81%, 58.08%, and 64.99%, respectively. The experimental results show that the proposed cable force distribution model and control strategy are effective.

  • An Undulating Kirigami Pattern With Enhanced Tear Strength
    on January 20, 2025 at 12:00 am

    AbstractKirigami, the cutting and folding of sheets, can create useful three-dimensional shapes from flat sheets of material. Some kirigami patterns self-deploy from their flat state when tension is applied; we call these tension-activated kirigami (TAK) patterns. A new TAK pattern has been proposed that produces ribbons of material that undulate out of the plane of the kirigami sheet when deployed with tension. In the planar state, this pattern comprises staggered rows of multiple slits, so we call it the multi-slit pattern. The multiple slits can include two, three, or more slits in place of the widely studied single-slit kirigami pattern, with an increased number of undulations produced with additional slits. An enhancement is also proposed that increases the tear strength of this pattern by adding multiple beams to carry the tension forces that deploy and hold the structure. This multi-beam enhancement to the multi-slit pattern has been investigated with experiments and duplicated with finite element analysis simulations. A good correlation was found, and a broader design space was also investigated with additional simulations. It is proposed that the multi-slit undulating kirigami pattern, with or without the multi-beam enhancement, produces a compelling new deployed structure with increased interlocking and the potential for many applications.

Flexible-Joint Humanoid Balancing Augmentation via Full-State Feedback Variable Impedance Control

Abstract

This paper attempts to address the quandary of flexible-joint humanoid balancing performance augmentation, via the introduction of the Full-State Feedback Variable Impedance Control (FSFVIC), and Model-Free Compliant Floating-base VIC (MCFVIC) schemes. In comparison to rigid-joint humanoid robots, efficient balancing control of compliant bipeds, powered by Series Elastic Actuators (or harmonic drives), requires the design of more sophisticated controllers encapsulating both the motor and underactuated link dynamics. It has been demonstrated that Variable Impedance Control (VIC) can improve robotic interaction performance, albeit by introducing energy-injecting elements that may jeopardize closed-loop stability. To this end, the novel FSFVIC and MCFVIC schemes are proposed, which amalgamate both collocated and non-collocated feedback gains, with power-shaping signals that are capable of preserving the system’s stability/passivity during VIC. The FSFVIC and MCFVIC stably modulate the system’s collocated state gains to augment balancing performance, in addition to the non-collocated state gains that dictate the position control accuracy. Utilization of arbitrarily low-impedance gains is permitted by both the FSFVIC and MCFVIC schemes propounded herein. An array of experiments involving the COmpliant huMANoid reveals that significant balancing performance amelioration is achievable through online modulation of the full-state feedback gains (VIC), as compared to utilization of invariant impedance control.
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