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This paper presents our work on design, modeling, and control of a meso-scale shape memory alloy (SMA) actuated torsion actuator for miniature robots. This novel torsion actuator is bi-directionally activated by a pair of antagonistic SMA torsion springs through alternate Joule heating. First, we present the mechanical design and fabrication approach of this miniature actuator. Then, we present the...
In this paper, a recently suggested adaptive online optimal control algorithm for the infinite-horizon tracking problem of continuous-time non-linear systems with partially unknown system dynamics is modified and empirically evaluated. Since we lack complete systems knowledge a parameter identifier, which works simultaneously with the updating of the online optimal control algorithm, is introduced...
Robot interaction with the environment is normally described as a mass-spring-damping impedance model and the estimation of such interaction impedance parameters requires the computation of the joint (or task) space velocity and acceleration. In many cases, the velocity and acceleration are computed by numerically computing the first and second derivatives of the sensed position signal. The numerical...
This paper presents a systematic approach for experimental identification and assessment of mechanical effects on the dynamics of elastic actuators. The variable torsion stiffness (VTS) actuator is used as an example. As a basis for parameter identification, a flexible joint robot model considering friction and damping is used. To identify and assess occurring effects, a component-wise experimental...
EMY (Enhancing MobilitY) is an exoskeleton dedicated to the evaluation of Brain Machine Interface during clinical trials. This paper presents the first version of EMY restricted to upper limbs with four actuated joints per arm. Since an evaluation of a BMI controlled exoskeleton by a disabled person requires clinical trials, a risk management process should be conducted with medical standards as references...
We have developed a robot with a new control mechanism in order to collect information on flying robots in multiple fields. We aimed for a function that could rotate the tilt angle continuously and without limit and a function for flying maintaining any desired tilt angle with a structure that could efficiently use the thrust generated by the propellers. We devised a mechanism that connected two bicopter...
The Harvard Robobee is a fly-sized aerial vehicle that can perform controlled flight maneuvers. But this robot is unable to control its yaw or heading angle to a desired value. Motivated by this deficiency, we propose a new method to produce yaw-axis rotations. Termed wriggle-steering, it consists of driving body oscillations around its two other rotational axes. Because no torque is applied directly...
In this paper, the implementation of a variable stiffness joint actuated by a couple of twisted string actuators in antagonistic configuration is presented. The twisted string actuation system is particularly suitable for very compact and light-weight robotic devices, like artificial limbs and exoskeletons, since it renders a very low apparent inertia at the load side, allowing the implementation...
In this paper, a back-drivable joint mechanism for an in-pipe robot is presented. The joint mechanism consists of 2-pitch and 1-roll joint. The back-drivability of the joint mechanism is realized by using a ball-screw and a steel wire rope. When the in-pipe robot with the back-drivable joint mechanism passes through pipeline elements except the miter and the branch, the control of the joint mechanism...
Ball-balancing robots (BBRs) are endowed with rich dynamics. When properly designed and stabilized via feedback to eliminate jitter, and intuitively coordinated with a well-designed smartphone interface, BBRs exhibit a uniquely fluid and organic motion. Unlike mobile inverted pendulums (MIPs, akin to unmanned Segways), BBRs stabilize both fore/aft and left/right motions with feedback, and bank when...
This paper introduces a novel concept of an air bearing test bench for CubeSat ground testing together with the corresponding dynamic parameter identification method. Contrary to existing air bearing test benches, the proposed concept allows three degree-of-freedom unlimited rotations and minimizes the influence of the test bench on the tested CubeSat. These advantages are made possible by the use...
This paper provides an overview of the embedded joint-space control approach developed for THOR, a new series elastic humanoid. The 60 kg robot features electromechanical linear series elastic actuators (SEAs), enabling low-impedance control of each joint in the lower body via linear to rotary and parallel mechanisms. We present a distributed joint impedance control framework that leverages a custom...
The fidelity with which series elastic actuators (SEAs) render desired impedances is important. Numerous approaches to SEA impedance control have been developed under the premise that high-precision actuator torque control is a prerequisite. Indeed, the design of an inner torque compensator has a significant impact on actuator impedance rendering. The disturbance observer (DOB) based torque control...
The design of a stable and robust force controller is one of the most important and difficult tasks in rehabilitation robotics. In previous works, the Universal Haptic Pantograph (UHP) was presented as an alternative to conventional arm rehabilitation after a stroke. This robot is composed by a Series Elastic Actuator (SEA) and a Pantograph. In this work an enhanced force control for the UHP is presented...
We consider the problem of computing the inverse dynamics of a serial robot manipulator with N elastic joints in a recursive numerical way. The solution algorithm is a generalized version of the standard Newton-Euler approach, running still with linear complexity O(N) but requiring to set up recursions that involve higher order derivatives of motion and force variables. Mimicking the case of rigid...
We propose a novel control framework to demonstrate a unique foot tilting maneuver based on ankle torque control for humanoid balance recovery. The framework consists of the variable impedance regulation at the center of mass of the robot based on the ankle torque control, the virtual stoppers to prevent over tilting of the feet, and the body attitude control. The scope of our paper focuses on the...
A master and slave robot act in a teleoperation system. The master and slave angular position and velocities are sampled at integer multiples of a time step and the resulting difference errors at different sampling times are fed back both at the master and salve end after introducing appropriate feedback weights for each error sample. During the process of reading the master variables at the slave...
This paper presents an assist-as-needed method for ankle rehabilitation based on adaptive impedance control strategies. First, the dynamic contribution of the patient during the motion is estimated from robot's torque and kinematic information. Then, two robot assistance control strategies (complementary and optimal) are proposed to calculate the stiffness parameter of the impedance controller. In...
This paper presents LIGHTarm, a passive gravity compensated exoskeleton for upper-limb rehabilitation suitable for the use both in the clinical environment and at home. Despite the low-cost and not actuated design, LIGHTarm aims at providing remarkable back-drivability in wide portions of the upper-limb workspace. The weight-support and back-drivability features are experimentally investigated on...
We present a control strategy for the shoulder mechanism of an upper-body exoskeleton, called HARMONY, to assist in achieving coordinated motion at the shoulder complex. HARMONY is equipped with a novel mechanism that supports the natural mobility of the human shoulder, including the scapulohumeral rhythm, which is the coordinated motion between the upper arm (humerus) and shoulder blade (scapula)...
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