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  • CONFERENCE PAPER
    Pardo F, Tavakoli A, Levdik V, Kormushev Pet al., 2018,

    Time limits in reinforcement learning

    , International Conference on Machine Learning, Pages: 4042-4051

    In reinforcement learning, it is common to let anagent interact for a fixed amount of time with itsenvironment before resetting it and repeating theprocess in a series of episodes. The task that theagent has to learn can either be to maximize itsperformance over (i) that fixed period, or (ii) anindefinite period where time limits are only usedduring training to diversify experience. In thispaper, we provide a formal account for how timelimits could effectively be handled in each of thetwo cases and explain why not doing so can causestate-aliasing and invalidation of experience re-play, leading to suboptimal policies and traininginstability. In case (i), we argue that the termi-nations due to time limits are in fact part of theenvironment, and thus a notion of the remainingtime should be included as part of the agent’s in-put to avoid violation of the Markov property. Incase (ii), the time limits are not part of the envi-ronment and are only used to facilitate learning.We argue that this insight should be incorporatedby bootstrapping from the value of the state atthe end of each partial episode. For both cases,we illustrate empirically the significance of ourconsiderations in improving the performance andstability of existing reinforcement learning algo-rithms, showing state-of-the-art results on severalcontrol tasks.

  • CONFERENCE PAPER
    Saputra RP, Kormushev P, 2018,

    ResQbot: A Mobile Rescue Robot for Casualty Extraction

    , Pages: 239-240
  • CONFERENCE PAPER
    Saputra RP, Kormushev P, 2018,

    Casualty Detection from 3D Point Cloud Data for Autonomous Ground Mobile Rescue Robots

    , SSRR 2018
  • CONFERENCE PAPER
    Saputra RP, Kormushev P, 2018,

    Casualty Detection for Mobile Rescue Robots via Ground-Projected Point Clouds

  • CONFERENCE PAPER
    Saputra RP, Kormushev P, 2018,

    ResQbot: A Mobile Rescue Robot with Immersive Teleperception for Casualty Extraction

  • CONFERENCE PAPER
    Tavakoli A, Pardo F, Kormushev P, 2018,

    Action Branching Architectures for Deep Reinforcement Learning

    Discrete-action algorithms have been central to numerous recent successes ofdeep reinforcement learning. However, applying these algorithms tohigh-dimensional action tasks requires tackling the combinatorial increase ofthe number of possible actions with the number of action dimensions. Thisproblem is further exacerbated for continuous-action tasks that require finecontrol of actions via discretization. In this paper, we propose a novel neuralarchitecture featuring a shared decision module followed by several networkbranches, one for each action dimension. This approach achieves a linearincrease of the number of network outputs with the number of degrees of freedomby allowing a level of independence for each individual action dimension. Toillustrate the approach, we present a novel agent, called Branching DuelingQ-Network (BDQ), as a branching variant of the Dueling Double Deep Q-Network(Dueling DDQN). We evaluate the performance of our agent on a set ofchallenging continuous control tasks. The empirical results show that theproposed agent scales gracefully to environments with increasing actiondimensionality and indicate the significance of the shared decision module incoordination of the distributed action branches. Furthermore, we show that theproposed agent performs competitively against a state-of-the-art continuouscontrol algorithm, Deep Deterministic Policy Gradient (DDPG).

  • CONFERENCE PAPER
    Wang K, Shah A, Kormushev P, 2018,

    SLIDER: A Bipedal Robot with Knee-less Legs and Vertical Hip Sliding Motion

  • CONFERENCE PAPER
    Wang K, Shah A, Kormushev P, 2018,

    SLIDER: A Novel Bipedal Walking Robot without Knees

  • CONFERENCE PAPER
    Kanajar P, Caldwell DG, Kormushev P, 2017,

    Climbing over Large Obstacles with a Humanoid Robot via Multi-Contact Motion Planning

  • CONFERENCE PAPER
    Pardo F, Tavakoli A, Levdik V, Kormushev Pet al., 2017,

    Time Limits in Reinforcement Learning

    , Deep Reinforcement Learning Symposium (DRLS), 31st Conference on Neural Information Processing Systems (NIPS 2017)

    In reinforcement learning, it is common to let an agent interact with its environment for a fixed amount of time before resetting the environment and repeating the process in a series of episodes. The task that the agent has to learn can either be to maximize its performance over (i) that fixed period, or (ii) an indefinite period where time limits are only used during training to diversify experience. In this paper, we investigate theoretically how time limits could effectively be handled in each of the two cases. In the first one, we argue that the terminations due to time limits are in fact part of the environment, and propose to include a notion of the remaining time as part of the agent’s input. In the second case, the time limits are not part of the environment and are only used to facilitate learning. We argue that such terminations should not be treated as environmental ones and propose a method, specific to value-based algorithms, that incorporates this insight by continuing to bootstrap at the end of each partial episode. To illustrate the significance of our proposals, we perform several experiments on a range of environments from simple few-state transition graphs to complex control tasks, including novel and standard benchmark domains. Our results show that the proposed methods improve the performance and stability of existing reinforcement learning algorithms.

  • CONFERENCE PAPER
    Rakicevic N, Kormushev P, 2017,

    Efficient Robot Task Learning and Transfer via Informed Search in Movement Parameter Space

  • CONFERENCE PAPER
    Tavakoli A, Pardo F, Kormushev P, 2017,

    Action Branching Architectures for Deep Reinforcement Learning

  • BOOK CHAPTER
    Ahmadzadeh SR, Mastrogiovanni F, Kormushev P, 2016,

    Visuospatial Skill Learning for Robots

    A novel skill learning approach is proposed that allows a robot to acquirehuman-like visuospatial skills for object manipulation tasks. Visuospatialskills are attained by observing spatial relationships among objects throughdemonstrations. The proposed Visuospatial Skill Learning (VSL) is a goal-basedapproach that focuses on achieving a desired goal configuration of objectsrelative to one another while maintaining the sequence of operations. VSL iscapable of learning and generalizing multi-operation skills from a singledemonstration, while requiring minimum prior knowledge about the objects andthe environment. In contrast to many existing approaches, VSL offerssimplicity, efficiency and user-friendly human-robot interaction. We also showthat VSL can be easily extended towards 3D object manipulation tasks, simply byemploying point cloud processing techniques. In addition, a robot learningframework, VSL-SP, is proposed by integrating VSL, Imitation Learning, and aconventional planning method. In VSL-SP, the sequence of performed actions arelearned using VSL, while the sensorimotor skills are learned using aconventional trajectory-based learning approach. such integration easilyextends robot capabilities to novel situations, even by users withoutprogramming ability. In VSL-SP the internal planner of VSL is integrated withan existing action-level symbolic planner. Using the underlying constraints ofthe task and extracted symbolic predicates, identified by VSL, symbolicrepresentation of the task is updated. Therefore the planner maintains ageneralized representation of each skill as a reusable action, which can beused in planning and performed independently during the learning phase. Theproposed approach is validated through several real-world experiments.

  • JOURNAL ARTICLE
    Jamisola RS, Kormushev PS, Roberts RG, Caldwell DGet al., 2016,

    Task-Space Modular Dynamics for Dual-Arms Expressed through a Relative Jacobian

    , JOURNAL OF INTELLIGENT & ROBOTIC SYSTEMS, Vol: 83, Pages: 205-218, ISSN: 0921-0296
  • BOOK CHAPTER
    Kormushev P, Ahmadzadeh SR, 2016,

    Robot Learning for Persistent Autonomy

    , Handling Uncertainty and Networked Structure in Robot Control, Editors: Busoniu, Tamás, Publisher: Springer International Publishing, Pages: 3-28, ISBN: 978-3-319-26327-4
  • CONFERENCE PAPER
    Maurelli F, Lane D, Kormushev P, Caldwell D, Carreras M, Salvi J, Fox M, Long D, Kyriakopoulos K, Karras Get al., 2016,

    The PANDORA project: a success story in AUV autonomy

    , OCEANS Conference, Publisher: IEEE, ISSN: 0197-7385
  • JOURNAL ARTICLE
    Palomeras N, Carrera A, Hurtos N, Karras GC, Bechlioulis CP, Cashmore M, Magazzeni D, Long D, Fox M, Kyriakopoulos KJ, Kormushev P, Salvi J, Carreras Met al., 2016,

    Toward persistent autonomous intervention in a subsea panel

    , AUTONOMOUS ROBOTS, Vol: 40, Pages: 1279-1306, ISSN: 0929-5593
  • CONFERENCE PAPER
    Ahmadzadeh SR, Paikan A, Mastrogiovanni F, Natale L, Kormushev P, Caldwell DGet al., 2015,

    Learning Symbolic Representations of Actions from Human Demonstrations

    , IEEE International Conference on Robotics and Automation (ICRA), Publisher: IEEE COMPUTER SOC, Pages: 3801-3808, ISSN: 1050-4729
  • JOURNAL ARTICLE
    Bimbo J, Kormushev P, Althoefer K, Liu Het al., 2015,

    Global estimation of an object's pose using tactile sensing

    , ADVANCED ROBOTICS, Vol: 29, Pages: 363-374, ISSN: 0169-1864
  • JOURNAL ARTICLE
    Carrera A, Palomeras N, Hurtos N, Kormushev P, Carreras Met al., 2015,

    Cognitive system for autonomous underwater intervention

    , PATTERN RECOGNITION LETTERS, Vol: 67, Pages: 91-99, ISSN: 0167-8655

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