Learning Motor Skills of Reactive Reaching and Grasping of Objects

Reactive grasping of objects is an essential capability of autonomous robot manipulation, which is yet challenging to learn such sensorimotor control to coordinate coherent hand-finger motions and be robust against disturbances and failures. This work proposed a deep reinforcement learning based scheme to train feedback control policies which can coordinate reaching and grasping actions in presence of uncertainties. We formulated geometric metrics and task-orientated quantities to design the reward, which enabled efficient exploration of grasping policies. Further, to improve the success rate, we deployed key initial states of difficult hand-finger poses to train policies to overcome potential failures due to challenging configurations. The extensive simulation validations and benchmarks demonstrated that the learned policy was robust to grasp both static and moving objects. Moreover, the policy generated successful failure recoveries within a short time in difficult configurations and was robust with synthetic noises in the state feedback which were unseen during training

Learning Pregrasp Manipulation of Objects from Ungraspable Poses

In robotic grasping, objects are often occluded in ungraspable configurations such that no pregrasp pose can be found, eg large flat boxes on the table that can only be grasped from the side. Inspired by humans' bimanual manipulation, eg one hand to lift up things and the other to grasp, we address this type of problems by introducing pregrasp manipulation - push and lift actions. We propose a model-free Deep Reinforcement Learning framework to train control policies that utilize visual information and proprioceptive states of the robot to autonomously discover robust pregrasp manipulation. The robot arm learns to first push the object towards a support surface and establishes a pivot to lift up one side of the object, thus creating a clearance between the object and the table for possible grasping solutions. Furthermore, we show the effectiveness of our proposed learning framework in training robust pregrasp policies that can directly transfer from simulation to real hardware through suitable design of training procedures, state, and action space. Lastly, we evaluate the effectiveness and the generalisation ability of the learned policies in real-world experiments, and demonstrate pregrasp manipulation of objects with various size, shape, weight, and surface friction.Comment: 8 pages open access version for ICRA2020 6 pages acceptance pape

Research progress of neuromodulation in the treatment of Parkinson's disease

Parkinson's disease (PD) is a common degenerative neurological disorder, characterized by static tremor, bradykinesia, myotonia and postural abnormalities. Dopaminergic drugs are the main drugs in the treatment of PD, but long-term use will lead to drug efficacy loss, and even cause some adverse reactions such as dyskinesia and "on-off" phenomenon. Neuromodulation is a kind of biomedical engineering technology that can stimulate or inhibit the activity of brain neurons and regulate the changes of neuroplasticity by means of electric energy, magnetic field, ultrasound and other methods, so as to achieve treatment and improvement of diseases. In the non-drug treatment of PD, neuromodulation, as a new therapeutic means, has shown good efficacy, and has the advantages of small adverse reactions and easy tolerance. Based on this, this article reviews the research progress of several common neuromodulation in PD, including deep brain stimulation, transcranial magnetic stimulation, transcranial direct current stimulation and transcranial focused ultrasound

The distribution and concentration of particulate biogenic silica in surface waters of Prydz Bay, Antarctica, during the austral summer of 2011

The concentrations and distributions of particulate biogenic silica (PBSi) in the upper surface waters of Prydz Bay, Antarctica, were investigated during the 27th Chinese National Antarctic Research Expedition cruises of January 2011. We aimed to characterize the correlations between PBSi and plankton, nutrients and particulate organic carbon. The results showed that the concentrations of biogenic silica ranged from 0.76—19.72 μmol∙dm-3 and the average concentration of biogenic silica was 6.06 μmol∙dm-3. The distribution of surface PBSi had significant regional characteristics: The concentrations were higher south of 67°S than to the north. The distribution of PBSi, chlorophyll a and particulate organic carbon showed similar patterns, and PBSi distribution had a negative correlation with that of silicate. In the vertical direction, the mole ratio of PBSi and POC (Sibio/Corg) decreased with increasing depth. This trend indicated a higher rate of PBSi dissolution, or a lower rate of organic matter remineralization rate, in the upper 200 m

Phytoplankton community changes indicated by biomarker from sediment in Prydz Bay, Antarctica

Biomarkers including brassicasterol, dinosterol and alkenone in sediments are used as indicators to reconstruct changes to the phytoplankton community in surface and sub-aerial sediments of Prydz Bay, Antarctica. The results indicate that the biomarker records in surface and core sediment samples changed with time and space. The total content of phytoplankton biomarkers ranges from 391.0—1 470.6 ng∙g-1. The phytoplankton biomass has increased in Prydz Bay over the past 100 years. This variation may be mainly related with climate change in the region. The total biomarker contents in surface sediments from 5 stations in Prydz Bay are in the range of 215.8—1 294.3 ng∙g-1. The phytoplankton biomass in Prydz Bay is higher than that outside of the bay. This is similar to the distributions of chlorophyll a, organic carbon and biogenic silica in surface waters determined through in situ investigation. Such consistency indicates a coupling between the bottom of the ocean and biogeochemical processes in the upper water

Contents and benthic fluxes of nutrients in sediment pore water of Southern Ocean

The concentration and profile characters of nutrients in sediment pore water of the South Ocean, sampled during the cruise of CHINARE218 of the austral summer 2001 /02 were determined. The results show that the content of SiO3-Si and NH4-N were much higher than other nutrients. The profile of SiO3-Si was characterized with sharp gradients near the sediment-water interface, profile distribution of silicate show that during the diagenetic reaction of silicate, dissolution was the main part. The organic matter decomposition was occurred under the anaerobic condition. Benthic fluxes of SiO3-Si, NH4-N were from pore water to overlying water, and regeneration of silicate and ammonium were the main part of the nutrient regeneration from the pore water of the study area

The content and distribution of Ge in the sediments of Prydz Bay, Antarctica

The content and distribution of Ge is investigated in sediments from the Southern Ocean (Prydz Bay, Antarctica). The content of Getotal in the sediments ranges from 1.14×10-6 to 2.35×10-6 (average of 1.71×10-6) and the highest value occurs at station P3-9 where water depth is > 1 000 m. The lowest value occurs at station P4-13 which is near the edge of the Amery ice shelf. The surface sediments have 16%–68% Gebio within Getotal. The distribution trends of Gebio and Getotal are generally similar, and the values outside Prydz Bay are higher than within the bay, bounded at 67°S. The vertical distribution of Ge in sediment cores presents higher values at the surface than in underlying sediments. Values of Gebio appear to positively correlate with biogenic silica (BSiO2) in surface sediments from non-polynyas sea. The vertical distribution of Gebio and BSiO2 is similar in sediments of station P3-16

Concentrations and distribution of biogenic barium in surface sediments of Prydz Bay, Antarctica

Concentrations of biogenic barium were investigated in surface sediments of Prydz Bay, Antarctica, during the 21st and 27th CHINARE cruises. Factors controlling the observed distribution are explored. Biogenic barium concentrations obtained from a sequential extraction procedure are compared with total concentrations obtained from the normative calculation based on a total digestion, and differences in the results are examined. Concentrations of biogenic barium, calculated by the normative calculation, were much higher than the concentrations obtained through sequential extraction; this discrepancy is the result of the occurrence of barium associated with Mn/Fe oxides, which represents an important component of total barium in these sediments. Concentrations of biogenic barium obtained from the sequential extraction range from 104 to 445 μg∙g-1, and the average concentration was 227 μg∙g-1. The highest concentrations of biogenic barium occur in the central area of the bay, where the seawater is more stable, while lower values occur in the bank and the ice shelf. Biogenic barium is significantly linearly correlated with biogenic barium and organic carbon, and similar in distribution of Chl a, which may indicate that primary productivity of phytoplankton in the surface water column is the main environmental factor regulating barium concentration and distribution