| 1. |
- Riazi, Sarmad, 1986, et al.
(författare)
-
Energy Optimization of Multi-robot Systems
- 2015
-
Ingår i: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. - 9781467381833 ; 2015-October, s. 1345-1350
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Konferensbidrag (refereegranskat)abstract
- This paper presents an optimization algorithm that has been able to save up to 45% of the energy consumption of an industrial multi-robot system. The tool Sequence Planner now includes these algorithms, focusing on minimizing energy consumption. The goal has been to reduce the energy consumption of individual robots and robots interacting in a work station, without changing the original paths or the total cycle time. The presented algorithms are based on an efficient and rapid nonlinear model for optimizing the sequences of operations and the motion trajectories. Smart simplification of the optimization problem together with innovative tools for logging data and executing the optimized trajectories on real robots has resulted in 18% to 45% saving of the energy consumption in the presented test scenarios.
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| 2. |
- Lennartson, Bengt, 1956, et al.
(författare)
-
Modeling and Optimization of Hybrid Systems
- 2015
-
Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 48:27, s. 351-357
-
Konferensbidrag (refereegranskat)abstract
- In this paper a predicate transition model for discrete event systems is generalized to include continuous dynamics, and the result is a modular hybrid predicate transition model. Based on this model a hybrid Petri net, including explicit differential equations and shared variables, is also proposed. It is then shown how this hybrid Petri net model can be optimized based on a simple and robust nonlinear programming formulation. The procedure only assumes that desired sampled paths for a number of interacting moving devices are given, while originally equidistant time instances are adjusted to minimize a given criterion. This optimization of hybrid systems is also applied to a real robot station with interacting devices, which results in about 30\% reduction in energy consumption.
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| 3. |
- Lennartson, Bengt, 1956-, et al.
(författare)
-
Modeling and Optimization of Hybrid Systems for the Tweeting Factory
- 2016
-
Ingår i: IEEE Transactions on Automation Science and Engineering. - 1545-5955 .- 1558-3783. ; 13:1, s. 195-205
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a predicate transition model for discrete-event systems is generalized to include continuous dynamics, and the result is a modular hybrid predicate transition model. Based on this model, a hybrid Petri net including explicit differential equations and shared variables is also proposed. It is then shown how this hybrid Petri net model can be optimized based on a simple and robust nonlinear programming formulation. The procedure only assumes that desired sampled paths for a number of interacting moving devices are given, while originally equidistant time instances are adjusted to minimize a given criterion. This optimization of hybrid systems is also applied to a real robot station with interacting devices, which results in about 30% reduction in energy consumption. Moreover, a flexible online and event-based information architecture called the Tweeting Factory is proposed. Simple messages (tweets) from all kinds of equipment are combined into high-level knowledge, and it is demonstrated how this information architecture can be used to support optimization of robot stations.
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| 4. |
- Riazi, Sarmad, 1986, et al.
(författare)
-
A Column Generation-Based Gossip Algorithm for Home Healthcare Routing and Scheduling Problems
- 2019
-
Ingår i: IEEE Transactions on Automation Science and Engineering. - 1558-3783 .- 1545-5955. ; 16:1, s. 127-137
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Tidskriftsartikel (refereegranskat)abstract
- Home healthcare (HHC) is a service that dispatches caregivers to people in need of healthcare who live in the home. The task assignment and route generation for caregivers can be formulated as an extension of the well-known vehicle routing problem with time windows (VRPTW). Currently, the most successful exact algorithms for VRPTW are based on a framework combining column generation (CG) and branching. Although such methods could be successful for HHC routing and scheduling problem (HHCRSP) as well, fast approximate algorithms are appealing, especially for large problems. In an early version of this paper, we employed a heuristic distributed gossip algorithm to solve HHCRSP. In this paper, we integrate the gossip algorithm with a local solver based on CG, which makes it an effective algorithm for larger problem instances. As it will be shown with extensive numerical experiments, for large problem instances, gossip-CG performs better than the pure CG. Note to Practitioners-The task of routing and scheduling caregivers for HHC providers can be formulated as a mathematical problem that is theoretically challenging to solve to optimality for large-scale problems involving many clients and caregivers. Although extensive research and tools for tackling this problem already exist, in practice, even in developed countries, it is still common to rely on schedules generated manually by staff. What we present in this paper is the summary of our theoretical work on tackling such problems. The benefit of the framework that we propose, the CG-based gossip method, is that it can be preempted at any time if the staff requires to obtain a good schedule as soon as possible. If ample time is available, one can let our algorithm to run for a longer period of time to generate even shorter routes.
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| 5. |
- Riazi, Sarmad, 1986, et al.
(författare)
-
A Gossip Algorithm for Home Healthcare Scheduling and Routing Problems
- 2014
-
Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. - 9783902823625 ; 19, s. 10754-10759
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Konferensbidrag (refereegranskat)abstract
- Many people in need of care still live in their homes, requiring the caretakers to travel to them. Assigning tasks to nurses (or caretakers) and scheduling their work plans is an NP-hard problem, which can be expressed as a vehicle routing problem with time windows (VRPTW) that includes additional problem-specific constraints. In this paper, we propose to solve the Home Healthcare Scheduling and Routing Problem (HHCRSP) by a distributed Gossip algorithm. We also apply an extended version called n-Gossip, which provides the required flexibility to balance optimality versus computational speed. We also introduce a relaxation on the optimality of the underlying solver in the Gossip, which speeds up the iterations of the Gossip algorithm, and helps to quickly obtain solutions with good quality.
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| 6. |
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| 7. |
- Riazi, Sarmad, 1986, et al.
(författare)
-
Decomposition and distributed algorithms for home healthcare routing and scheduling problem
- 2017
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Ingår i: IEEE International Conference on Emerging Technologies and Factory Automation, ETFA. - 1946-0759 .- 1946-0740. ; , s. 1-7
-
Konferensbidrag (refereegranskat)abstract
- Many people in need of care still live in their homes, requiring the caretakers to travel to them. Assigning the people to caretakers and generating their schedules can be formulated as a mixed integer linear programming problem (MILP) that inherits many features of the well-known vehicle routing problem with time windows (VRPTW). Currently, the most successful exact algorithms for VRPTW are based on branch and price framework, which combine column generation (CG) and branching. While these methods could be successful for Home Healthcare Routing and Scheduling Problem (HHCRSP) as well, fast approximate algorithms are appealing, especially for large problems. We recently employed a heuristic distributed gossip algorithm to solve HHCRSP. The method had the potential to provide approximate solutions for relatively large problem instances, but its effectiveness was limited to the performance of its local MILP solver. In this paper, we integrate the gossip algorithm with a local solver based on CG, which makes it an effective algorithm for larger problem instances. We also provide numerical experiments and complexity evaluations of the improved gossip algorithm (gossip-CG) with the standard gossip (gossip-MILP) and CG, and show that gossip-CG outperforms the pure CG in case of large problems.
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| 8. |
- Riazi, Sarmad, 1986, et al.
(författare)
-
Energy and peak-power optimization of existing time-optimal robot trajectories
- 2016
-
Ingår i: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. - 9781509024094 ; 2016-November, s. 321-327
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Konferensbidrag (refereegranskat)abstract
- This paper, as an outcome of the EU project AREUS, heralds an optimization procedure that reduces up to 30% of energy consumption and up to 60% of peak-power for the trajectories that were tested on a real industrial robot. We have evaluated a number of cost functions and examined our algorithm for a variety of scenarios such as varying cycle times and single/two-robot cases. The significance of our work is not only in the impressive savings, simplicity of implementation and preserving path and cycle time, but also in the effort made to carry out the optimization and experiments in as realistic conditions as possible.
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| 9. |
- Riazi, Sarmad, 1986, et al.
(författare)
-
Energy and Peak Power Optimization of Time-Bounded Robot Trajectories
- 2017
-
Ingår i: IEEE Transactions on Automation Science and Engineering. - 1558-3783 .- 1545-5955. ; 14:2, s. 646-657
-
Tidskriftsartikel (refereegranskat)abstract
- This paper, as an outcome of the EU project AREUS, heralds an optimization procedure that reduces up to 30% of energy consumption and up to 60% in peak power for the trajectories that have been tested on real industrial robots. We have evaluated a number of cost functions and tested our algorithm for a variety of scenarios such as varying cycle times, payloads, and single/multirobot cases in both ac- and dc-operated robot cells. The significance of our work is not only in the impressive savings, simplicity of implementation, and preserving path and cycle time, but also in the variety of test scenarios that include different kinds of KUKA robots. We have carried out the optimization and experiments in as realistic conditions as possible.
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| 10. |
- Riazi, Sarmad, 1986, et al.
(författare)
-
Energy and Peak-power Optimization of Time-bounded Robot Trajectories
- 2017
-
Ingår i: 2017 13TH IEEE CONFERENCE ON AUTOMATION SCIENCE AND ENGINEERING (CASE). - 2161-8070. - 9781509067817 ; , s. 1301-1301
-
Konferensbidrag (refereegranskat)abstract
- This paper, as an outcome of the EU project AREUS, heralds an optimization procedure that reduces up to 30% of energy consumption and up to 60% in peak-power for the trajectories that were tested on a real industrial robot. We have evaluated a number of cost functions and tested our algorithm for a variety of scenarios such as varying cycle times, payloads, and single/two-robot cases. The significance of our work is not only in the impressive savings, simplicity of implementation and preserving path and cycle time, but also in the effort made to carry out the optimization and experiments in as realistic conditions as possible, and the guidelines we provide to achieve this.
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| 11. |
- Sundström, Nina, 1980, et al.
(författare)
-
On the conflict between energy, stability and robustness in production schedules
- 2016
-
Ingår i: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. - 9781509024094 ; 2016-November, s. 1263-1269
-
Konferensbidrag (refereegranskat)abstract
- In this paper, a novel contribution to highlight the conflict between energy efficiency, robustness and stability is presented. Energy optimization is combined with robust scheduling techniques to analyze the trade-off. In rescheduling, slack is often used in order to protect a schedule from disruptions. However, results from the literature on energy minimization show that a reduction in energy consumption is achieved by extending the execution time of operations. Thus, slack in schedules is eliminated on behalf of longer execution times. A continuous-time formulation is proposed using a mixed-integer nonlinear programming model including a multi-objective corresponding to energy, robustness, stability and makespan. Surrogate slack-based measures are used to evaluate robustness and stability. Previous work connecting the two research fields use simulation for analyzing the impact of disruptions in order to generate robust production schedules. Our results show that an increase in energy efficiency comes at a cost of reducing stability and robustness and hence becoming more sensitive to disruptions.
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| 12. |
- Wigström, Oskar, 1986, et al.
(författare)
-
Computationally efficient energy optimization of multiple robots
- 2017
-
Ingår i: Proc. 13th IEEE Conference on Automation Science and Engineering (CASE 2017). - 2161-8089.
-
Konferensbidrag (refereegranskat)abstract
- This paper presents convex modeling techniques for the problem of optimal velocity control of multiple robots on given intersecting paths. The optimal control problem is formulated as a nonlinear program, which generates predictive state and control trajectories that avoid collisions among the robots and minimize a certain performance index, such as operation time, energy dissipation and actuator usage. Advantages and disadvantages of two modeling approaches are discussed, involving a variable change with square of velocity, or alternatively inverse of velocity. The performance of the two approaches is evaluated in a case study with an industrial robot.
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| 13. |
- Boger, Elin, et al.
(författare)
-
A Partial Differential Equation Approach to Inhalation Physiologically Based Pharmacokinetic Modeling
- 2018
-
Ingår i: CPT: Pharmacometrics and Systems Pharmacology. - : Wiley. - 2163-8306. ; 7:10, s. 638-646
-
Tidskriftsartikel (refereegranskat)abstract
- CPT: Pharmacometrics & Systems Pharmacology published by Wiley Periodicals, Inc. on behalf of the American Society for Clinical Pharmacology and Therapeutics. The heterogeneous nature of the lungs and the range of processes affecting pulmonary drug disposition make prediction of inhaled drugs challenging. These predictions are critical, as the local exposure cannot be measured and current inhalation physiologically based pharmacokinetic (PBPK) models do not capture all necessary features. Utilizing partial differential equations, we present an inhalation PBPK model to describe the heterogeneity in both lung physiology and particle size. The model mechanistically describes important processes, such as deposition, mucociliary clearance, and dissolution. In addition, simplifications are introduced to reduce computational cost without loss of accuracy. Three case studies exemplify how the model can enhance our understanding of pulmonary drug disposition. Specific findings include that most small airways can be targeted by inhalation, and overdosing may eradicate the advantage of inhalation. The presented model can guide the design of inhaled molecules, formulations, as well as clinical trials, providing opportunities to explore regional targeting.
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| 14. |
- Hagebring, Fredrik, 1985, et al.
(författare)
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Comparing MILP, CP, and A* for Multiple Stacker Crane Scheduling
- 2016
-
Ingår i: Proc. 13th International Workshop on Discrete Event Systems (WODES’16), Xi’an, China, May. - 1550-5227. - 9781509041909 ; , s. 63-70
-
Konferensbidrag (refereegranskat)abstract
- This paper describes an optimisation model for the scheduling of a system consisting of three stacker cranes that are restricted to the same track. To improve the efficiency of the solution methods, a novel simplification of the model is presented, which has a low impact on the quality of the solution but greatly decreases its complexity. This model is then used to benchmark several popular solution methods, including both optimal and approximate methods. Some are based on monolithic models, whereas others solve the problem in phases by using sub-problem formulations. The result presented in this paper shows that evaluated solution methods have complementary strengths and weaknesses. Constraint Programming (CP) is very efficient on small scale problems, while Mixed Integer Linear Programming (MILP) scales much better when the number of movement orders increases. However, none of these methods are able to solve large instances of the problem to optimality. To handle the complexity of the problem, approximate solution methods are the only viable option. In this paper we show that promising results can be obtained even with simple methods using well known search algorithms such as A* and Tabu-search. However, preliminary results on more advanced search algorithms show that further improvements may be achieved, allowing the solution of very large problem instances.
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| 15. |
- Jorge, Emilio, 1992, et al.
(författare)
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Reinforcement learning in real-time geometry assurance
- 2018
-
Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 72, s. 1073-1078
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Konferensbidrag (refereegranskat)abstract
- To improve the assembly quality during production, expert systems are often used. These experts typically use a system model as a basis for identifying improvements. However, since a model uses approximate dynamics or imperfect parameters, the expert advice is bound to be biased. This paper presents a reinforcement learning agent that can identify and limit systematic errors of an expert systems used for geometry assurance. By observing the resulting assembly quality over time, and understanding how different decisions affect the quality, the agent learns when and how to override the biased advice from the expert software.
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| 16. |
- Lennartson, Bengt, 1956, et al.
(författare)
-
Optimization of hybrid Petri nets with shared variables
- 2015
-
Ingår i: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. - 9781467381833 ; 2015-October, s. 1395-1396
-
Konferensbidrag (refereegranskat)abstract
- A generalized modeling framework for hybrid systems, including both discrete event and continuous-time dynamics, is presented in this paper. It is based on a new type of hybrid Petri nets, involving both modular structures, discrete shared variables and flexible transition predicates. The continuous-time dynamics is given by local differential equations, in a style similar to hybrid automata. This can be compared with existing hybrid Petri nets, where also the continuous-time dynamics is represented graphically, but then in reality limiting the continuous-time behavior to simple flow processes. The hybrid Petri net proposed in this paper works well for any type of continuous-time dynamics, including even differential inclusions, and the result is a compact, flexible and readable mix of graphical and equation based representations. The proposed modeling framework is also applied to a physical robot cell, where the energy consumption of the robot motions is minimized based on a hybrid Petri net model, easily transformed to a mixed integer nonlinear programming problem. The resulting optimization procedure is shown to reduce the energy consumption of the real robot cell by approximately 50%.
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| 17. |
- Lennartson, Bengt, 1956, et al.
(författare)
-
Unified model for synthesis and optimization of discrete event and hybrid systems
- 2014
-
Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. ; 12, s. 86-92
-
Konferensbidrag (refereegranskat)abstract
- A recently proposed generic discrete event model is further developed and exemplified in this paper. Since every transition is expressed as a predicate on the current and next values of a set of variables, the model is called Predicate Transition Model (PTM). It is briefly illustrated how a number of well known discrete-event models, including automata and Petri nets extended with shared variables, can be formulated and synthesized in the PTM framework. More specifically modular Petri nets with shared variables (PNSVs) are shown to be significantly more readable compared to ordinary Petri nets. PTMs are also naturally extended to hybrid systems, and finally it is shown how easy and efficiently PNSVs can be optimized concerning performance based on Constraint Programming. To summarize, the proposed modeling framework unifies and simplifies both synthesis, optimization and implementation of discrete event systems.
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| 18. |
- Sundström, Nina, 1980, et al.
(författare)
-
Conflict Between Energy, Stability, and Robustness in Production Schedules
- 2017
-
Ingår i: IEEE Transactions on Automation Science and Engineering. - 1558-3783 .- 1545-5955. ; 14:2, s. 658-668
-
Tidskriftsartikel (refereegranskat)abstract
- A systematic method to evaluate the conflict between robustness, stability, and energy consumption is proposed in this paper. Energy optimization is combined with robust scheduling techniques to analyze the tradeoff. In rescheduling, slack is often used to protect a schedule from disruptions. However, results from the literature on energy minimization show that a reduction in energy consumption is achieved by extending the execution time of operations. Thus, slack in schedules is diminished on behalf of longer execution times. The proposed method, which quantitatively shows this conflict, is based on a multiobjective optimization formulation where efficient computation of the involved criteria is developed. This includes a convex surrogate stability measure that makes it possible to evaluate different operation sequences by a mixed-integer nonlinear programming formulation. Previous works connecting the two research fields use simulation for analyzing the impact of disruptions in order to generate robust production schedules. Our results show that an increase in energy efficiency comes at a cost of reducing stability and robustness and hence becoming more sensitive to disruptions.
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| 19. |
- Sundström, Nina, 1980, et al.
(författare)
-
Optimization of operation sequences using constraint programming
- 2012
-
Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. - 9783902661982 ; 14:1, s. 1580-1585
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we connect the dots: design and optimization of production systems. A possible link between these two areas, is a previously presented modeling language, Sequence Planner Language (SPL). It has been demonstrated how relevant information can be extracted from production systems modeling applications, and converted into SPL. We show how the SPL model can be converted into a constraint programming model for optimization. Also, a useful abstraction concept, work-equivalence, is introduced to enable alternative model formulations. A case study consisting of an aero engine structure assembly plant is presented, in which the efficiency of the resulting constraint programs is investigated. The formulations enabled by abstraction are shown to perform better than the standard formulation.
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| 20. |
- Sundström, Nina, 1980, et al.
(författare)
-
Robust and energy efficient trajectories for robots in a common workspace setting
- 2019
-
Ingår i: IISE Transactions. - : Informa UK Limited. - 2472-5862 .- 2472-5854. ; 51:7, s. 766-776
-
Tidskriftsartikel (refereegranskat)abstract
- A method, incorporating robustness into trajectory planning, is proposed in this article. In the presence of delays, the suggested approach guarantees collision-free scenarios for robots with predefined paths and overlapping workspaces. Traditionally, only the time at which a robot can enter a common workspace is constrained so as to avoid collisions. If the shared zone becomes available later than planned, collisions can potentially occur if the robot is unable to stop before entering the shared space. In this work, a clearance point is introduced where the occupancy of the common workspace is evaluated. The velocity is constrained at this point such that, if necessary, the robot is able to stop at the boundary of the shared space. The closer to the boundary the evaluation is performed, the more restricted is the velocity. The problem formulation is stated in space assuming a predefined path, where robot dynamics and robust constraints are included. Multiple objectives corresponding to final time and energy consumption are considered. The impact on the system performance concerning the position and timing related to the clearance point is analyzed. An example is presented, where the optimal clearance point position is determined, based on the time at which the shared space is assumed to become available.
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| 21. |
- Sundström, Nina, 1980, et al.
(författare)
-
Robust and Energy Efficient Trajectories in a Stochastic Common Workspace Setting
- 2018
-
Ingår i: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. ; 2018-August, s. 77-83
-
Konferensbidrag (refereegranskat)abstract
- A trajectory planning formulation incorporating robustness is proposed in this paper, where uncertainties in the availability of a common workspace for robots are present. By introducing a clearance point where the occupancy of the shared space is evaluated and restricting the velocity and arrival time at this point, collision free paths are guaranteed. The expected final time and energy consumption are derived and sensitivity analysis are performed to study how changes in clearance point position and arrival time impact these measures. A simulation study is presented where the stochastic time at which a common workspace becomes available follows a uniform, normal and exponential distribution. The optimal clearance point, arrival time and expected values for final time and energy consumption are obtained and compared for the different distributions. For the uniform and normal distribution, the results show that the expected final time is robust to uncertainties, while energy savings are possible for the uniform and exponential distribution when redundant time is available.
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| 22. |
- Wigström, Oskar, 1986, et al.
(författare)
-
An Integrated CP/OR Method for Optimal Control of Modular Hybrid Systems
- 2014
-
Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. - 9783902823618 ; 12:3, s. 485-491
-
Konferensbidrag (refereegranskat)abstract
- This paper concerns the optimal control of modular hybrid systems synchronized by shared variables. Instead of synchronizing the discrete dynamics of the system into one global mode before optimization, Constraint Programming (CP) is used to model the discrete dynamics of each modular system separately. Integrated in the CP solver are also classic Operations Research (OR) models in the form of Nonlinear Programs (NLPs) approximating the continuous dynamics of the system. Using CP considerably decreases the number of NLPs which must be solved, compared to that of using a traditional mixed integer nonlinear programming approach.
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| 23. |
- Wigström, Oskar, 1986
(författare)
-
Energy efficient multi-robot coordination
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When multiple systems work in the same physical environment, it is important to ensure that no collisions occur. This thesis is focused on the centralized offline coordination of such collaborating systems, with the condition that the spatial path each system travels along is known before hand. In addition to collisions, dynamic constraints as well as optimization of a performance criterion are considered.The problem is decomposed into two parts, a sequencing problem and coordination subproblem. For the sequencing problem, an algorithmic improvement is proposed, where constraint propagation methods from the computer science community are introduced to improve existing mixed integer nonlinear programming methods used in mathematical programming. The coordination subproblem on the other hand is approached from a modeling perspective. By applying state space discretization and variable changes, two models are derived, one which is entirely convex. Also, a two stage abstraction approach is introduced, where dynamic programming is used to parameterize part of the problem, resulting in a much simpler model at the next stage.The above methods can be used for minimum energy coordination of industrial robots. Experimental results from the two robot case study are presented. In addition, the one robot case is also studied, where the execution time, robot payload and minimization criteria are varied. Furthermore, the application of the presented methods to hybrid systems is also discussed.Finally, the slightly different problem of minimum time stacker crane scheduling is considered. In the stacker crane problem, a number of tasks should be allocated to a set of robots moving along the same one dimensional track. Although the exact spatial path is unknown in the stacker crane problem, it is shown that in a minimum time setting, it is still possible to use state space discretization.
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| 24. |
- Wigström, Oskar, 1986, et al.
(författare)
-
Energy optimization of trajectories for high level scheduling
- 2011
-
Ingår i: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. - 9781457717307 ; , s. 654-659
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Konferensbidrag (refereegranskat)abstract
- Minimization of energy consumption is today an issue of utmost importance in manufacturing industry. A previously presented technique for scheduling of robot cells, which exploits variable execution time for the individual robot operations, has shown promising results in energy minimization. In order to slow down a manipulator's movement the method utilizes a linear time scaling of the time optimal trajectory. This paper attempts to improve the scheduling method by generating energy optimal data using dynamic time scaling. Dynamic programming can be applied to an existing trajectory and generate a new energy optimal trajectory that follows the same path but with another execution time. With the new method, it is possible to solve the optimization problem for a range of execution times in one run. A simple two-joint planar example is presented in which energy optimal dynamic time scaling is compared to linear time scaling. The results show a small decrease in energy usage for minor scaling, but a significant reduction for longer execution times.
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| 25. |
- Wigström, Oskar, 1986, et al.
(författare)
-
High-Level Scheduling of Energy Optimal Trajectories
- 2013
-
Ingår i: IEEE Transactions on Automation Science and Engineering. - 1558-3783 .- 1545-5955. ; 10:1, s. 57-64
-
Tidskriftsartikel (refereegranskat)abstract
- The reduction of energy consumption is today addressed with great effort in manufacturing industry. In this paper, we improve upon a previously presented method for robotic system scheduling. By applying dynamic programming to existing trajectories, we generate new energy optimal trajectories that follow the same path but in a different execution time frame. With this new method, it is possible to solve the optimization problem for a range of execution times for the individual operations, based on one simulation only. The minimum energy trajectories can then be used to derive a globally energy optimal schedule. A case study of a cell comprised of four six-link manipulators is presented, in which energy optimal dynamic time scaling is compared to linear time scaling. The results show that a significant decrease in energy consumption can be achieved for any given cycle time.
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| 26. |
- Wigström, Oskar, 1986, et al.
(författare)
-
Integrated OR/CP Optimization for Discrete Event Systems with Nonlinear Cost
- 2013
-
Ingår i: Proceedings of the IEEE Conference on Decision and Control. - 2576-2370 .- 0743-1546. - 9781467357173 ; , s. 7627-7633
-
Konferensbidrag (refereegranskat)abstract
- Optimization of a discrete event systems including (non)linear cost in local states is mainly solved either byheuristic search methods or mathematical programming. Inthis paper the second approach is further elaborated, including guarantees on both optimal performance and logicalcorrectness. An integrated algorithm is developed utilizing both Operations Research (OR) and Constraint Programming (CP). The majority of integrated approaches have up till now focused on solving linear problems. In this paper we use our integrated algorithm to optimize discrete event systems with nonlinear cost and logical constraints. We present a straightforward method to incorporate OR functionality into an existing CP algorithm such that it can process nonlinear expressions, otherwise too complex for the CP algorithm to handle. Evaluation of the algorithm’s performance is done by comparison to that of state of the art Mixed Integer Nonlinear Programming (MINLP) methods. The benchmark shows that our integrated approach finds the optimal solution in roughly the same time as existing MINLP methods. However, when also proof of optimality is required, the integrated algorithm outperforms the best MINLP algorithm by roughly a factor of ten.
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| 27. |
- Wigström, Oskar, 1986, et al.
(författare)
-
Model-free approaches for the energy minimization of robot trajectories
- 2014
-
Ingår i: Reglermöte 2014.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Energy eciency is increasingly important for robotic manufacturing systems. An energy minimal schedule may be generated given that the energy consumption for each robotoperation may be parameterized as a function of execution time. Existing approaches rely heavily on the use of models to generate functions describing energy consumption. We are interested in solving the problem using model-free approaches, such as Iterative Learning Control, model-free/iterative Dynamic Programming and derivative free optimization.
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| 28. |
- Wigström, Oskar, 1986, et al.
(författare)
-
Optimization of Hybrid Systems with Known Paths
- 2012
-
Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. ; 45:9, s. 39-45
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Konferensbidrag (refereegranskat)abstract
- In this paper we study a subset of hybrid systems and present a generalized method for their optimization. We outline Hybrid Cost Automata (HCA), an extension to Hybrid Automata, where discrete and continuous cost expressions are added. The class of hybrid systems with known spatial paths is dened in the context of HCA. This type of system is common in industry where for example AGVs transport goods from one location to another, or manipulators move between joint coordinates. The optimization is performed using Dynamic Programming as a preprocessing step, whereafter Mixed Integer Nonlinear Programming is used for scheduling. A case study of a four robot cell is presented with energy consumption used as a minimization criterion.
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| 29. |
- Wigström, Oskar, 1986, et al.
(författare)
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Scheduling model for systems with complex alternative behaviour
- 2012
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Ingår i: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. - 9781467304290 ; , s. 587-593
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Konferensbidrag (refereegranskat)abstract
- In this paper we propose a flexible model for scheduling problems, which allows the modeling of systems with complex alternative behaviour. This model could for example facilitate the step from process planning model to optimization model. We show how automatic constraint generation can be performed for both Constraint Programming and Mixed Integer Linear Programming (MILP) models. Also, for the MILP case, a new formulation for mutual exclusion of resources is proposed. This new formulation works well for proving optimality in systems with multiple capacity resources. Some benchmarks for such job shop scheduling problems as well as systems with a large number of alternatives are also presented.
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| 30. |
- Wigström, Oskar, 1986, et al.
(författare)
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Sustainable production automation - Energy optimization of robot cells
- 2013
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Ingår i: Proceedings - IEEE International Conference on Robotics and Automation. - 1050-4729. - 9781467356411 ; , s. 252-257
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Konferensbidrag (refereegranskat)abstract
- This paper concerns the reduction of energy use in manufacturing industry. If individual robot movements in a system are preprocessed using Dynamic Programming, one can attain a Mixed Integer Nonlinear Program (MINLP) which models the energy consumption of the complete system. This model can then be solved to optimality using mathematical programming. We have previously shown proof of concept for this energy reduction method. In this paper, we apply state of the art MINLP methods to a number of problems in order benchmark their effectiveness. Algorithms used are Nonlinear Programming based Branch and Bound (NLP-BB), Outer Approximation (OA), LP/NLP based Branch and Bound (LP/NLP-BB) and Extended Cutting Plane (ECP). Benchmarks show that the NLP-BB does not perform well for nonlinear scheduling problems. This is due to the weak lower bounds of the integer relaxations. For scheduling problems with nonlinear costs, ECP and in particular LP/NLP-BB are shown to outperform both NLP-BB and OA. The resulting energy optimal schedules for the examples show a significant decrease in energy consumption.
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| 31. |
- Wigström, Oskar, 1986, et al.
(författare)
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Towards Integrated OR/CP Energy Optimization for Robot Cells
- 2014
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Ingår i: Proceedings - IEEE International Conference on Robotics and Automation. - 1050-4729. ; , s. 1674-1680
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Konferensbidrag (refereegranskat)abstract
- This paper concerns the energy optimization of systems with interacting robots. Pseudo spectral optimal control is used to collocate the continuous time dynamics of each robot. The resulting model is a multi stage, multi robot, trajectory planning problem with timing constraints. In the case of a given task sequence, the mathematical formulation is that of a Nonlinear Programming problem. We present two example problems where three 3-DoF robots work together. For the case the problem consists of undetermined sequences, we outline an algorithm which integrates Operations Research methods with those of Constraint Programming.
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