466 research outputs found
Adaptive Passivity-Based Pose Tracking Control of Cable-Driven Parallel Robots for Multiple Attitude Parameterizations
The proposed control method uses an adaptive feedforward-based controller to
establish a passive input-output mapping for the CDPR that is used alongside a
linear time-invariant strictly positive real feedback controller to guarantee
robust closed-loop input-output stability and asymptotic pose trajectory
tracking via the passivity theorem. A novelty of the proposed controller is its
formulation for use with a range of payload attitude parameterizations,
including any unconstrained attitude parameterization, the quaternion, or the
direction cosine matrix (DCM). The performance and robustness of the proposed
controller is demonstrated through numerical simulations of a CDPR with rigid
and flexible cables. The results demonstrate the importance of carefully
defining the CDPR's pose error, which is performed in multiplicative fashion
when using the quaternion and DCM, and in a specific additive fashion when
using unconstrained attitude parameters (e.g., an Euler-angle sequence)
Simultaneous Position-and-Stiffness Control of Underactuated Antagonistic Tendon-Driven Continuum Robots
Continuum robots have gained widespread popularity due to their inherent
compliance and flexibility, particularly their adjustable levels of stiffness
for various application scenarios. Despite efforts to dynamic modeling and
control synthesis over the past decade, few studies have focused on
incorporating stiffness regulation in their feedback control design; however,
this is one of the initial motivations to develop continuum robots. This paper
aims to address the crucial challenge of controlling both the position and
stiffness of a class of highly underactuated continuum robots that are actuated
by antagonistic tendons. To this end, the first step involves presenting a
high-dimensional rigid-link dynamical model that can analyze the open-loop
stiffening of tendon-driven continuum robots. Based on this model, we propose a
novel passivity-based position-and-stiffness controller adheres to the
non-negative tension constraint. To demonstrate the effectiveness of our
approach, we tested the theoretical results on our continuum robot, and the
experimental results show the efficacy and precise performance of the proposed
methodology
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High-performance series elastic actuation
textMobile legged robots have the potential to restructure many aspects of our lives in the near future. Whether for applications in household care, entertainment, or disaster response, these systems depend on high-performance actuators to improve their basic capabilities. The work presented here focuses on developing new high-performance actuators, specifically series elastic actuators, to address this need. We adopt a system-wide optimization approach, dealing with factors which influence performance at the levels of mechanical design, electrical system design, and control. Using this approach and based on a set of performance metrics, we produce an actuator, the UT-SEA, which achieves leading empirical results in terms of power-to-weight, force control, size, and system efficiency. We also develop general high-performance control techniques for both force- and position-controlled actuators, some of which were adopted for use on NASA-JSC's Valkyrie Humanoid robot and were used during DARPA's DRC Trials 2013 robotics competition.Electrical and Computer Engineerin
Shared control of an aerial cooperative transportation system with a cable-suspended payload
This paper presents a novel bilateral shared framework for a cooperative aerial transportation and manipulation system composed by a team of micro aerial vehicles with a cable-suspended payload. The human operator is in charge of steering the payload and he/she can also change online the desired shape of the formation of robots. At the same time, an obstacle avoidance algorithm is in charge of avoiding collisions with the static environment. The signals from the user and from the obstacle avoidance are blended together in the trajectory generation module, by means of a tracking controller and a filter called dynamic input boundary (DIB). The DIB filters out the directions of motions that would bring the system too close to singularities, according to a suitable metric. The loop with the user is finally closed with a force feedback that is informative of the mismatch between the operator’s commands and the trajectory of the payload. This feedback intuitively increases the user’s awareness of obstacles or configurations of the system that are close to singularities. The proposed framework is validated by means of realistic hardware-in-the-loop simulations with a person operating the system via a force-feedback haptic interface
Performance of modified jatropha oil in combination with hexagonal boron nitride particles as a bio-based lubricant for green machining
This study evaluates the machining performance of newly developed modified jatropha oils (MJO1, MJO3 and MJO5), both with and without hexagonal boron nitride (hBN) particles (ranging between 0.05 and 0.5 wt%) during turning of AISI 1045 using minimum quantity lubrication (MQL). The experimental results indicated that, viscosity improved with the increase in MJOs molar ratio and hBN concentration. Excellent tribological behaviours is found to correlated with a better machining performance were achieved by MJO5a with 0.05 wt%. The MJO5a sample showed the lowest values of cutting force, cutting temperature and surface roughness, with a prolonged tool life and less tool wear, qualifying itself to be a potential alternative to the synthetic ester, with regard to the environmental concern
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