The dynamic movement primitives framework in its original form is constrained to the kinematic aspects of the movement. In this paper we bridge the gap to dynamic behavior by extending the framework with force/torque feedback. We propose and evaluate a modulation approach that allows interaction with objects and the environment. Through the proposed coupling of originally independent robotic trajectories, the approach also enables the execution of bimanual and tightly coupled cooperative tasks. We apply an iterative learning control algorithm to learn a coupling term, which is applied to the original trajectory in a feedforward fashion and thus modifies the trajectory in accordance to the desired positions or external forces. A stability analysis and results of simulated and realworld experiments using two KUKA LWR arms for bimanual tasks and interaction with the environment are presented.
COBISS.SI-ID: 27524135
In this paper we present a novel method to obtain the basic frequency of an unknown periodic signal with an arbitrary waveform, which can work online with no additional signal processing or logical operations. The proposed method uses a Fourier series representation in the feedback loop combined with a single oscillator. In this way it can extract the frequency and the phase of an unknown periodic signal. For demonstration several highly nonlinear and dynamic periodic robotic tasks are shown, including also a task where an electromyography (EMG) signal is used in a feedback loop.
COBISS.SI-ID: 25108775
This paper describes a methodology that enables the generalization of the available sensorimotor knowledge. New actions are synthesized by the application of statistical methods, where the goal and other characteristics of an action are utilized as queries to create a suitable control policy, taking into account the current state of the world. The proposed approach enables the generation of a wide range of policies without requiring an expert to modify the underlying representations to account for different taskspecific features and perceptual feedback. The paper also demonstrates that the proposed methodology can be integrated with an active vision system of a humanoid robot. While 3D vision on humanoid robots with complex oculomotor systems is often difficult due to the modeling uncertainties, we show that these uncertainties can be accounted for by the proposed approach.
COBISS.SI-ID: 23918375
Recent studies are reviewed, concerning the in vivo wall stiffness of arteries and arterioles in healthy humans, and how these properties adapt to iterative increments or sustained reductions in local intravascular pressure. A novel technique was used, by which arterial and arteriolar stiffness were determined as changes in arterial diameter and flow, respectively, during graded increments in distending pressure in the blood vessels of an arm or a leg. Pressureinduced increases in diameter and flow were smaller in the lower leg than in the arm, indicating greater stiffness in the arteries/arterioles of the leg. A 5wk period of intermittent intravascular pressure elevations in one arm reduced pressure distension and pressureinduced flow in the brachial artery by about 50%. Conversely, prolonged reduction of arterial/arteriolar pressure in the lower body by 5 wks of sustained horizontal bedrest, induced threefold increases of the pressuredistension and pressureflow responses in a tibial artery. Thus, the wall stiffness of arteries and arterioles are plastic properties that readily adapt to changes in the prevailing local intravascular pressure. The discussion concerns mechanisms underlying changes in local arterial/arteriolar stiffness as well as whether stiffness is altered by changes in myogenic tone and/or wall structure. As regards implications, regulation of local arterial/arteriolar stiffness may facilitate control of arterial pressure in erect posture and conditions of exaggerated intravascular pressure gradients. That increased intravascular pressure leads to increased arteriolar wall stiffness also supports the notion that local pressure loading may constitute a prime mover in the development of vascular changes in hypertension.
COBISS.SI-ID: 27299623
This study tests the hypothesis that moderate exercise alleviates chronic hypoxia induced oxidative stress. Our obtain results confirm the proposed hypothesis and show the ability of daily, moderate intensity exercise training to reduce the oxidative stress levels and improve redox equilibrium. These findings also have significant applied value, since moderate training can be used to blunt oxidative stress induced by health/disease related chronic hypoxic exposures as experienced by patients with pulmonary disease, obesity etc.
COBISS.SI-ID: 26881063