Exploring Development Methods for Reactive Synthesis Specifications

This paper proposes a novel version of the vehicle routing problem (VRP). Instead of servicing all the customers, feasible solutions of the VRP instance are forced to satisfy a set of complex high-level tasks given as a metric temporal logic (MTL) specification, which allows complex quantitative timing constraints to be incorporated into the problem. For the resulting vehicle routing problem with metric temporal logic specifications (VRPMTL), a mixed-integer linear programming (MILP) based algorithm is provided that solves the problem to optimality. Examples for optimal multi-UAV mission planning are provided where MTL is used as a high level language to specify complex mission tasks.

In automobile panel manufacturing, the design of a feasible trimming line is crucial in obtaining an accurate edge profile after flanging. In this study, an effective method which combines the robust incremental development method and finite element inverse method is presented. The finite element inverse method is used to analyze the flanging process. In using the finite element inverse method, the main obstacle is the generation of the initial guess. An improved incremental development method is presented to handle badly-shaped element, various element sizes, and undercut parts. This method incrementally develops a 3D triangular mesh onto the drawing tool surface by layer-wise development and smoothing technique. The effectiveness of this method is verified by two numerical examples.

Reactive synthesis is the process of generate correct con- trollers from temporal logic specifications. Typically, synthesis is restricted to Boolean specifications in LTL. Recently, a Boolean abstraction technique allows to translate LTLT specifications that contain literals in theories into equi-realizable LTL specifications, but no full synthesis procedure exists yet. In synthesis modulo theories, the system receives valuations of environment variables (from a first-order theory T ) and outputs valuations of system variables from T . In this paper, we address how to syntheize a full controller using a combination of the static Boolean controller obtained from the Booleanized LTL specification together with on-the-fly queries to a solver that produces models of satisfiable existential T formulae. This is the first synthesis method for LTL modulo theories. Additionally, our method can produce adaptive responses which increases explainability and can improve runtime properties like performance. Our approach is applicable to both LTL modulo theories and LTLf modulo theories.

In this paper, we investigate fully-automated controller synthesis of coordination strategies for multi-robot warehouse robotic systems. We consider the scenario where a group of automated guided vehicles (AGVs) deliver goods from starting locations to destinations in a grid-abstracted workspace. We propose a distributed framework with prioritized-based coordination strategy to fulfill the entire planning task. Specifically, the task of each AGV is specified by a Linear Temporal Logic (LTL) specification. The local control strategies are obtained by solving the corresponding LTL reactive synthesis problems. In order to avoid conflicts, we use the prioritized-based coordination strategy to guarantee that the overall systems is safe and live, i.e., AGVs will collide with each other and there is no deadlock and livelock. The proposed design methodology is correct-by-construction with the formal guarantee and is amenable to handle temporal tasks in a flexible manner. Furthermore, the proposed framework is distributed; hence computationally more efficient than the centralized approach. Finally, we demonstrate the proposed distributed framework by simulation examples.

Reactive synthesis is an automated procedure to obtain a\ncorrect-by-construction reactive system from a given specification. GR(1) is a\nwell-known fragment of linear temporal logic (LTL) where synthesis is possible\nusing a polynomial symbolic algorithm. We conducted a case study to learn about\nthe challenges that software engineers may face when using GR(1) synthesis for\nthe development of a reactive robotic system. In the case study we developed\ntwo variants of a forklift controller, deployed on a Lego robot. The case study\nemploys LTL specification patterns as an extension of the GR(1) specification\nlanguage, an examination of two specification variants for execution\nscheduling, traceability from the synthesized controller to constraints in the\nspecification, and generated counter strategies to support understanding\nreasons for unrealizability. We present the specifications we developed, our\nobservations, and challenges faced during the case study.\n

In this paper, we study the problem of learning to satisfy temporal logic specifications with a group of agents in an unknown environment, which may exhibit probabilistic behaviour. From a learning perspective these specifications provide a rich formal language with which to capture tasks or objectives, while from a logic and automated verification perspective the introduction of learning capabilities allows for practical applications in large, stochastic, unknown environments. The existing work in this area is, however, limited. Of the frameworks that consider full linear temporal logic or have correctness guarantees, all methods thus far consider only the case of a single temporal logic specification and a single agent. In order to overcome this limitation, we develop the first multi-agent reinforcement learning technique for temporal logic specifications, which is also novel in its ability to handle multiple specifications. We provide correctness and convergence guarantees for our main algorithm – ALMANAC (Automaton/Logic Multi-Agent Natural Actor-Critic) – even when using function approximation. Alongside our theoretical results, we further demonstrate the applicability of our technique via a set of preliminary experiments.

The normal operation of synchronous modules may be temporarily suspended or finally aborted due to requests of their environment. Hence, if a temporal logic specification has already been verified for a synchronous module, then the available verification result can typically only be used if neither suspension nor abortion will take place. Also, the simulation of synchronous modules has to be finally aborted so that temporal logic specifications referring to infinite behaviors cannot be completely answered. In this paper, we therefore define transformations on temporal logic specifications to lift available verification results for synchronous modules without suspension or abortion to refined temporal logic specifications that take care of these preemption statements. This way, one can establish simulation and modular verification of synchronous modules in contexts where preemptions are used.KeywordsModel CheckTransition SystemTemporal LogicLinear Temporal LogicLinear Temporal Logic FormulaThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The fundamental idea of this work is to synthesize reactive controllers such that closed-loop execution trajectories of the system satisfies desired specifications that ensure correct system behaviors, while optimizing a desired performance criteria. We define the correctness of a system's behavior according to the system's relation to the environment, for example, the output trajectories of the system terminate in a goal set without entering an unsafe set. Using Metric Temporal Logic (MTL) specifications we can capture complex system behaviors and timing requirements, such as the output trajectories must pass through a number of way-points within a certain time frame before terminating in the goal set. Given a Mixed Logical Dynamical (MLD) system and system specifications in terms of MTL formula or simpler reach-avoid specifications, our goal is to find a closed-loop trajectory that satisfies the specifications, in non-deterministic environments. Using an MILP framework we search over the space of input signals to obtain such valid trajectories of the system, by adding constraints to satisfy the MTL formula only when necessary, to avoid the exponential complexity of solving MILP problems. We also present experimental results for planning a path in real-time for a mobile robot through a dynamically changing environment with a desired task specification.

Manipulation planning from high-level task specifications, even though highly desirable, is a challenging problem. The large dimensionality of manipulators and complexity of task specifications make the problem computationally intractable. This work introduces a manipulation planning framework with linear temporal logic (LTL) specifications. The use of LTL as the specification language allows the expression of rich and complex manipulation tasks. The framework deals with the state-explosion problem through a novel abstraction technique. Given a robotic system, a workspace consisting of obstacles, manipulable objects, and locations of interest, and a co-safe LTL specification over the objects and locations, the framework computes a motion plan to achieve the task through a synergistic multi-layered planning architecture. The power of the framework is demonstrated through case studies, in which the planner efficiently computes plans for complex tasks. The case studies also illustrate the ability of the framework in intelligently moving away objects that block desired executions without requiring backtracking.

We present an energy storage controller synthesis method for power systems with respect to metric temporal logic (MTL) specifications. The power systems with both constant impedance loads and constant power loads are modeled as a set of differential–algebraic equations. After a fault is cleared, with uncertainties in the fault clearing time, the generator machine angles and rotor speed deviations will enter a set of postfault initial states. We use the robust neighborhood approach to cover this set using the initial robust neighborhoods of finitely many simulated postfault trajectories. These simulated postfault trajectories meet the frequency regulation requirements specified in MTL as they are driven by the optimal control input signals obtained through a functional gradient descent approach. In this way, all the possible postfault trajectories with the given uncertainties in the fault clearing time are guaranteed to satisfy the MTL specification. Furthermore, we learn a piecewise linear control law from the data of the simulated trajectories to generate a feedback controller.

Graph-based games are an important tool in computer science. They have applications in synthesis, verification, refinement, and far beyond. We review graph-based games with objectives on infinite plays. We give definitions and algorithms to solve the games and to give a winning strategy. The objectives we consider are mostly Boolean, but we also look at quantitative graph-based games and their objectives. Synthesis aims to turn temporal logic specifications into correct reactive systems. We explain the reduction of synthesis to graph-based games (or equivalently tree automata) using synthesis of LTL specifications as an example. We treat the classical approach that uses determinization of parity automata and more modern approaches.

In recent years, event and self-triggered control have been proposed as energy-aware control strategies to expand the life-time of battery powered devices in Networked Control Systems (NCSs). In contrast to the previous works in which their control objective is to achieve stability, this paper presents a novel energy-aware control scheme for achieving high level specifications, or more specifically, temporal logic specifications. Inspired by the standard hierarchical strategy that has been proposed in the field of formal control synthesis paradigm, we propose a new abstraction procedure for jointly synthesizing control and communication strategies, such that the communication reduction in NCSs and the satisfaction of the temporal logic specifications are guaranteed. The benefits of the proposal are illustrated through a numerical example.

In control theory, models of physical processes, such as systems of differential equations, are usually checked against specifications, such as stability and set invariance. In formal methods, rich specifications, such as languages and formulae of temporal logics, are checked against models of software programs and digital circuits, such as finite transition graphs. With the development and integration of cyber physical and safety critical systems, there is an increasing need for computational tools for verification and control of complex systems from rich, temporal logic specifications. The formal verification and synthesis problems have been shown to be undecidable even for very simple classes of infinitespace continuous and hybrid systems. However, provably correct but conservative approaches, in which the satisfaction of a property by a dynamical system is implied by the satisfaction of the property by a finite over-approximation (abstraction) of the system, have received a lot of attention in recent years. Some classes of systems allowing for computationally efficient verification and control from temporal logic specifications are reviewed. For continuous and discrete-time linear systems and continuous-time multi-linear systems, it is shown that finite abstractions can be constructed through polyhedral operations only. By using techniques from model checking and automata games, this allows for verification and control from specifications given as Linear Temporal Logic (LTL) formulae over linear predicates in the state variables. A connection between the existence of Lyapunov functions and finite bisimulations is established for discrete-time linear and switched linear systems. Finally, optimality and correctness requirements are combined in a model predictive approach to generate control strategies for discrete-time linear systems. The usefulness of these computational tools is illustrated with various examples such as verification and synthesis of biological circuits in synthetic biology and motion planning and control in robotics.

In this paper, a motion planning system based on predictive control and temporal logic specifications is established for the welding dual-arm robot with gantry. Firstly, based on the spatial structure of the dual-arm robot with gantry, a novel mathematical model is presented between the joint variables and the terminal attitude and the quaternion replaces the Euler Angle to describe the posture for avoiding gimbal lock. Then a constraint model predictive controller is constructed for the multi-variable, nonlinear and coupling model of the robot and the constraints of the environment. Meanwhile, the temporal logic formula is used for describing the complex welding tasks and reducing the workload of repeated programming. Next the expectation values and constraints are converted by the temporal logic formula will be sent to the predictive controller one by one. Finally, the simulation result shows that the system can effectively solve the problem of motion planning for the welding dual-arm robot with gantry.

This paper presents an approach for building SoftWareImplemented Fault Injection (SWIFI) tools for real-time systems starting from temporal logic specifications. Temporal logic formulas are provided describing the behavior of the main SWIFI mechanisms, both for the injection of faults and for the observation of the target system. Besides conventional fault injectors (i.e., that flip bits in memory and in system calls’ parameters), we have also considered fault injectors based on the notion of saboteur. Concerning the observation mechanisms, we have defined on-line software probes aimed at observing not only the failure modes of the system under test, but also the real-time behavior of both the application and the underlying operating system. The specifications of all such mechanisms are then translated into programs that are executed on-line by a virtual machine. This approach was applied to the development of MAFALDA-RT, a SWIFI tool for real-time systems. A case study exemplifies how the proposed approach allows for the SWIFI mechanisms to be defined and applied.