Mechanism Selection for Multi-Robot Task Allocation

There is increasing interest in fielding multi-robot teams for applications such as search and rescue, warehouse automation, and delivery of consumer goods. Task allocation is an important problem to solve in such multi-robot settings. Given a mission that can be decomposed into discrete tasks, the Multi-Robot Task Allocation (MRTA) problem looks for an assignment of tasks to robots that ultimately results in efficient execution of the mission. There is a range of approaches to this optimisation problem, from centralised solvers to fully distributed methods that involve no explicit coordination between team members. Somewhere in the middle of this range lie market-based approaches, where tasks can be treated as goods, robots as "buyers" who can compute and express their own preferences for tasks in a virtual marketplace, and some clearing mechanism exists to match tasks to robots according to these preferences. The most common type of market-based mechanism for multi-robot task allocation is an auction, in which tasks are announced to the team, robots compute and place bids that encode some measure of cost or utility of performing the tasks, and tasks are awarded to robots over a number of rounds, according to the particular rules of the mechanism. Many different auction mechanisms exist, and they vary in the trade-offs that they make between computation time and space on the one hand, and performance of the execution of the mission on the other. In addition, the performance that results from a mechanism's allocation can be greatly affected by properties of task environments---the spatial and temporal arrangements of tasks, as well as other properties like precedence constraints, whether tasks require the simultaneous cooperation of multiple robots, and so on---in which it is employed. A simple mechanism that is inexpensive to compute and scales well may perform well in some environments, but not in others. The work presented in this thesis focuses on this relationship between auction-based task allocation mechanisms and properties of task environments, with the goal of developing a method of selecting, from a portfolio, a mechanism that is appropriate for a given task environment. The first part of this work is an empirical performance evaluation of a range of mechanisms employed in a series of environments of increasing complexity. The second part of this work uses results from this evaluation to develop and train a data-driven method of mechanism selection using properties of environments that can be measured at the start of a mission. The results show that, under certain conditions, this method of mechanism selection can lead to significant performance improvements compared to using a single mechanism alone

Auction-based Task Allocation Mechanisms for Managing Fruit Harvesting Tasks

Multi-robot task allocation mechanisms are de-signed to distribute a set of activities fairly amongst a set of robots. Frequently, this can be framed as a multi-criteria optimisation problem, for example minimising cost while maximising rewards. In soft fruit farms, tasks, such as picking ripe fruit at harvest time, are assigned to human labourers. The work presented here explores the application of multi-robot task allocation mechanisms to the complex problem of managing a heterogeneous workforce to undertake activities associated with harvesting soft fruit

Multi-agent Task Allocation for Fruit Picker Team Formation (Extended Abstract)

Multi-agent task allocation methods seek to distribute a set of tasks fairly amongst a set of agents. In real-world settings, such as fruit farms, human labourers undertake harvesting tasks, organised each day by farm manager(s) who assign workers to the fields that are ready to be harvested. The work presented here considers three challenges identified in the adaptation of a multi-agent task allocation methodology applied to the problem of distributing workers to fields. First, the methodology must be fast to compute so that it can be applied on a daily basis. Second, the incremental acquisition of harvesting data used to make decisions about worker-task assignments means that a data-backed approach must be derived from incomplete information as the growing season unfolds. Third, the allocation must take “fairness” into account and consider worker motivation. Solutions to these challenges are demonstrated, showing statistically significant results based on the operations at a soft fruit farm during their 2020 and 2021 harvesting seasons

Towards the application of multi-agent task allocation to hygiene tasks in the food production industry.

The food production industry faces the complex challenge of scheduling both production and hygiene tasks. These tasks are typically scheduled manually. However, due to the increasing costs of raw materials and the regulations factories must adhere to, inefficiencies can be costly. This paper presents the initial findings of a survey, conducted to learn more about the hygiene tasks within the industry and to inform research on how multi-agent task allocation (MATA) methodologies could automate and improve the scheduling of hygiene tasks. A simulation of a heterogeneous human workforce within a factory environment is presented. This work evaluates experimentally different strategies for applying market-based mechanisms, in particular Sequential Single Item (SSI) auctions, to the problem of allocation hygiene tasks to a heterogeneous workforce

Multi-agent task allocation for harvest management

Multi-agent task allocation methods seek to distribute a set of tasks fairly amongst a set of agents. In real-world settings, such as soft fruit farms, human labourers undertake harvesting tasks. The harvesting workforce is typically organised by farm manager(s) who assign workers to the fields that are ready to be harvested and team leaders who manage the workers in the fields. Creating these assignments is a dynamic and complex problem, as the skill of the workforce and the yield (quantity of ripe fruit picked) are variable and not entirely predictable. The work presented here posits that multi-agent task allocation methods can assist farm managers and team leaders to manage the harvesting workforce effectively and efficiently. There are three key challenges faced when adapting multi-agent approaches to this problem: (i) staff time (and thus cost) should be minimised; (ii) tasks must be distributed fairly to keep staff motivated; and (iii) the approach must be able to handle incremental (incomplete) data as the season progresses. An adapted variation of Round Robin (RR) is proposed for the problem of assigning workers to fields, and market-based task allocation mechanisms are applied to the challenge of assigning tasks to workers within the fields. To evaluate the approach introduced here, experiments are performed based on data that was supplied by a large commercial soft fruit farm for the past two harvesting seasons. The results demonstrate that our approach produces appropriate worker-to-field allocations. Moreover, simulated experiments demonstrate that there is a “sweet spot” with respect to the ratio between two types of in-field workers

Towards full-scale autonomy for multi-vehicle systems planning and acting in extreme environments

Currently, robotic technology offers flexible platforms for addressing many challenging problems that arise in extreme environments. These problems’ nature enhances the use of heterogeneous multi-vehicle systems which can coordinate and collaborate to achieve a common set of goals. While such applications have previously been explored in limited contexts, long-term deployments in such settings often require an advanced level of autonomy to maintain operability. The success of planning and acting approaches for multi-robot systems are conditioned by including reasoning regarding temporal, resource and knowledge requirements, and world dynamics. Automated planning provides the tools to enable intelligent behaviours in robotic systems. However, whilst many planning approaches and plan execution techniques have been proposed, these solutions highlight an inability to consistently build and execute high-quality plans. Motivated by these challenges, this thesis presents developments advancing state-of-the-art temporal planning and acting to address multi-robot problems. We propose a set of advanced techniques, methods and tools to build a high-level temporal planning and execution system that can devise, execute and monitor plans suitable for long-term missions in extreme environments. We introduce a new task allocation strategy, called HRTA, that optimises the task distribution amongst the heterogeneous fleet, relaxes the planning problem and boosts the plan search. We implement the TraCE planner that enforces contingent planning considering propositional temporal and numeric constraints to deal with partial observability about the initial state. Our developments regarding robust plan execution and mission adaptability include the HLMA, which efficiently optimises the task allocation and refines the planning model considering the experience from robots’ previous mission executions. We introduce the SEA failure solver that, combined with online planning, overcomes unexpected situations during mission execution, deals with joint goals implementation, and enhances mission operability in long-term deployments. Finally, we demonstrate the efficiency of our approaches with a series of experiments using a new set of real-world planning domains.Engineering and Physical Sciences Research Council (EPSRC) grant EP/R026173/