A variable-fractional order admittance controller for pHRI

In today’s automation driven manufacturing environments, emerging technologies like cobots (collaborative robots) and augmented reality interfaces can help integrating humans into the production workflow to benefit from their adaptability and cognitive skills. In such settings, humans are expected to work with robots side by side and physically interact with them. However, the trade-off between stability and transparency is a core challenge in the presence of physical human robot interaction (pHRI). While stability is of utmost importance for safety, transparency is required for fully exploiting the precision and ability of robots in handling labor intensive tasks. In this work, we propose a new variable admittance controller based on fractional order control to handle this trade-off more effectively. We compared the performance of fractional order variable admittance controller with a classical admittance controller with fixed parameters as a baseline and an integer order variable admittance controller during a realistic drilling task. Our comparisons indicate that the proposed controller led to a more transparent interaction compared to the other controllers without sacrificing the stability. We also demonstrate a use case for an augmented reality (AR) headset which can augment human sensory capabilities for reaching a certain drilling depth otherwise not possible without changing the role of the robot as the decision maker

The effect of stand structure on litter decomposition in Pinus sylvestris L. stands in Turkey

center dot Key message Canopy closure and stand age significantly affected the litter decomposition. Therefore, stand-specific decomposition constants (k) should be calculated in forest carbon models for more accurate carbon budget estimation. Furthermore, to reduce the carbon release from decomposing litter, regeneration cutting should be carried out at later ages, and heavy thinning should not be implemented in mature as well as overmature stands. center dot Context Decomposition of litter has an important role in primary production with its influence on nutrient release for plant uptake and carbon flux in forest ecosystems. Thus, understanding the effects of the intervention on litter decomposition is crucial for carbon management in forestry. center dot Aims The effects of stand structure and exposure on litter decomposition rate in Pinus sylvestris stands were investigated. center dot Methods Samples were taken from young to overmature stands with open to dense canopy. The litterbag method was used to measure the mass loss of the litter. The k values were calculated from the mass loss of decaying litter. Carbon and nitrogen contents of the litter were determined. center dot Results Cutting caused the decomposition to accelerate at a rate of up to 58% depending on its intensity. The k values were found to fluctuate over time from 0.189 in moderately dense-canopied stands to 0.317 in open-canopied overmature stands. Stand basal area, incubation time, and remaining carbon concentration of the litter accounted for 75% of the variation in the k value. center dot Conclusion Changes in the stand structure affect the litter decomposition rate in forest ecosystems. Heavy thinning can alter the litter decomposition process drastically, while moderate thinning may not have a clear effect in the long run