Task sequence planning in a robot workcell using AND/OR nets

An approach to task sequence planning for a generalized robotic manufacturing or material handling workcell is described. Given the descriptions of the objects in this system and all feasible geometric relationships among these objects, an AND/OR net which describes the relationships of all feasible geometric states and associated feasibility criteria for net transitions is generated. This AND/OR net is mapped into a Petri net which incorporates all feasible sequences of operations. The resulting Petri net is shown to be bounded and have guaranteed properties of liveness, safeness, and reversibility. Sequences are found from the reachability tree of the Petri net. Feasibility criteria for net transitions may be used to generate an extended Petri net representation of lower level command sequences. The resulting Petri net representation may be used for on-line scheduling and control of the system of feasible sequences. A simulation example of the sequences is described

Task planning with uncertainty for robotic systems

In a practical robotic system, it is important to represent and plan sequences of operations and to be able to choose an efficient sequence from them for a specific task. During the generation and execution of task plans, different kinds of uncertainty may occur and erroneous states need to be handled to ensure the efficiency and reliability of the system. An approach to task representation, planning, and error recovery for robotic systems is demonstrated. Our approach to task planning is based on an AND/OR net representation, which is then mapped to a Petri net representation of all feasible geometric states and associated feasibility criteria for net transitions. Task decomposition of robotic assembly plans based on this representation is performed on the Petri net for robotic assembly tasks, and the inheritance of properties of liveness, safeness, and reversibility at all levels of decomposition are explored. This approach provides a framework for robust execution of tasks through the properties of traceability and viability. Uncertainty in robotic systems are modeled by local fuzzy variables, fuzzy marking variables, and global fuzzy variables which are incorporated in fuzzy Petri nets. Analysis of properties and reasoning about uncertainty are investigated using fuzzy reasoning structures built into the net. Two applications of fuzzy Petri nets, robot task sequence planning and sensor-based error recovery, are explored. In the first application, the search space for feasible and complete task sequences with correct precedence relationships is reduced via the use of global fuzzy variables in reasoning about subgoals. In the second application, sensory verification operations are modeled by mutually exclusive transitions to reason about local and global fuzzy variables on-line and automatically select a retry or an alternative error recovery sequence when errors occur. Task sequencing and task execution with error recovery capability for one and multiple soft components in robotic systems are investigated

Human Health Risk Assessment of Toxic Elements in Farmland Topsoil with Source Identification in Jilin Province, China

The presence of toxic elements in agricultural soils from anthropogenic activities is a potential threat to human health through the food chain. In this study, the concentration of toxic elements in 122 agricultural topsoil composite samples were determined in order to study the current status, identify their sources and assess the level of pollution and human health risk. The results showed that the mean concentrations of Zn, Cu, Pb, Cd, Hg and As in the farmland topsoil were 21.72, 15.09, 36.08, 0.2451, 0.0378 and 4.957 mg·kg−1, respectively. The spatial distribution showed that the soils were mainly contaminated by Cd, Pb and Hg in midwest Jilin but by Cu and As in the east. According to the pollution index (Pi), Nemerow integrated pollution index (PN) and Geo-Accumulation Index (Igeo), Cd and Pb were the main pollutants in the soils. The occurrence of these elements was caused by anthropogenic activities and they were concentrated in the Songyuan-Changchun-Siping economic belt. There is limited non-carcinogenic and carcinogenic health risk to humans. Principal component analyses suggest the Pb, Cd and Hg soil contamination was mainly derived from anthropogenic activities in the Midwest, but all examined toxic elements in the east were mainly due to geogenic anomalies and came from atmospheric deposition

The Tradeoff between Maintaining Maize (<i>Zea mays</i> L.) Productivity and Improving Soil Quality under Conservation Tillage Practice in Semi-Arid Region of Northeast China

Conservation tillage has received strong support globally to achieve food security and minimize environmental impacts. However, there are comprehensive debates on whether it can achieve the synergy between maintaining crop yields and improving soil quality. To this end, a field experiment under continuous maize (Zea mays L.) cropping was conducted in northeast China. The treatment included rotary tillage with straw removal (CK, conventional tillage) and rotary tillage, subsoiling tillage, and no tillage with straw retention (CR, CS, and CN, respectively). Maize yield and a set of soil physio-chemical indicators in relation with soil quality were measured during 2017 to 2021. Results showed that CN significantly reduced the maize yield by 24.9%, 23.1%, and 19.5% on average compared to that with CR, CK, and CS treatments, respectively. CN and CS significantly increased the ratio of >2 mm soil aggregates and soil geometric mean diameter (GMD) in the 0–20 cm soil layer compared those of CK and CR treatments. However, CN and CS treatments had a higher soil bulk density and soil compaction in the 0–20 cm layer compared to those with CK and CR treatments. Soil organic carbon and total nitrogen in the 0–20 cm layer under CN and CS were higher than those with CK by 5.1–15.0% and 8.5–15.7%, whereas soil NH4+ was lower by 9.1–13.9% correspondingly. CN also reduced the soil temperature during the early-growth stage of maize. Importance analysis indicated that soil temperature, bulk density, and available nitrogen were the key factors affecting maize yield. Overall, no tillage with straw mulching could improve soil stability and soil fertility but reduced maize yield. Alternatively, minimum tillage (e.g., subsoiling tillage) with straw mulching might be a suitable practice as it maintains the maize yield and improves soil quality compared to those with conventional tillage practices in the semi-arid region of northeast China in the short term

Decomposition of potent greenhouse gas sulfur hexafluoride (SF6) by kirschsteinite-dominant stainless steel slag

In this investigation, kirschsteinite-dominant stainless steel slag (SSS) has been found to decompose sulfur hexafluoride (SF6) with the activity higher than pure metal oxides, such as Fe2O3 and CaO. SSS is mainly made up of CaO·FeO·SiO2(CFS)/ MgO·FeO·MnO(RO) phase conglomeration. The SF6 decomposition reaction with SSS at 500-700 C generated solid MF 2/MF3 and gaseous SiF4, SO2/SO 3 as well as HF. When 10 wt % of SSS was replaced by Fe 2O3 or CaO, the SF6 decomposition amount decreased from 21.0 to 15.2 or 15.0 mg/g at 600 C. The advantage of SSS over Fe2O3 or CaO in the SF6 decomposition is related to its own special microstructure and composition. The dispersion of each oxide component in SSS reduces the sintering of freshly formed MF 2/MF3, which is severe in the case of pure metal oxides and inhibits the continuous reaction of inner components. Moreover, SiO 2 in SSS reacts with SF6 and evolves as gaseous SiF 4, which leaves SSS with voids and consequently exposes inner oxides for further reactions. In addition, we have found that oxygen significantly inhibited the SF6 decomposition with SSS while H2O did not, which could be explained in terms of reaction pathways. This research thus demonstrates that waste material SSS could be potentially an effective removal reagent of greenhouse gas SF6

Decomposition of Potent Greenhouse Gas Sulfur Hexafluoride (SF₆) by Kirschsteinite-dominant Stainless Steel Slag

In this investigation, kirschsteinite-dominant stainless steel slag (SSS) has been found to decompose sulfur hexafluoride (SF₆) with the activity higher than pure metal oxides, such as Fe₂O₃ and CaO. SSS is mainly made up of CaO·FeO·SiO₂(CFS)/MgO·FeO·MnO­(RO) phase conglomeration. The SF₆ decomposition reaction with SSS at 500–700 °C generated solid MF₂/MF₃ and gaseous SiF₄, SO₂/SO₃ as well as HF. When 10 wt % of SSS was replaced by Fe₂O₃ or CaO, the SF₆ decomposition amount decreased from 21.0 to 15.2 or 15.0 mg/g at 600 °C. The advantage of SSS over Fe₂O₃ or CaO in the SF₆ decomposition is related to its own special microstructure and composition. The dispersion of each oxide component in SSS reduces the sintering of freshly formed MF₂/MF₃, which is severe in the case of pure metal oxides and inhibits the continuous reaction of inner components. Moreover, SiO₂ in SSS reacts with SF₆ and evolves as gaseous SiF₄, which leaves SSS with voids and consequently exposes inner oxides for further reactions. In addition, we have found that oxygen significantly inhibited the SF₆ decomposition with SSS while H₂O did not, which could be explained in terms of reaction pathways. This research thus demonstrates that waste material SSS could be potentially an effective removal reagent of greenhouse gas SF₆