Showing papers on "Robot kinematics published in 2005"

Discrete abstractions for robot motion planning and control in polygonal environments

Abstract: In this paper, we present a computational framework for automatic generation of provably correct control laws for planar robots in polygonal environments. Using polygon triangulation and discrete abstractions, we map continuous motion planning and control problems, specified in terms of triangles, to computationally inexpensive problems on finite-state-transition systems. In this framework, discrete planning algorithms in complex environments can be seamlessly linked to automatic generation of feedback control laws for robots with underactuation constraints and control bounds. We focus on fully actuated kinematic robots with velocity bounds and (underactuated) unicycles with forward and turning speed bounds.

Design and implementation of a multi-section continuum robot: Air-Octor

Abstract: In this paper, we describe the design and implementation of a novel multi-section, continuous-backbone ("continuum") robot. The design is based on an innovative "hose-in-hose" concept. Its implementation is novel with respect to previous continuum robot designs in that stiffness and extension, in addition to bending, are actively controlled in each section of the robot. This requires a non-trivial extension of previously proposed kinematic models, and poses challenges for real-time control of the robot. We introduce a tangling/untangling algorithm to map between overall cable lengths and per-section cable lengths. Details of the design and its implementation are presented, along with a summary of real-time control issues and experimental results.

Dynamic Analysis of a Nonholonomic Two-Wheeled Inverted Pendulum Robot

Abstract: As a result of the increase in robots in various fields, the mechanical stability of specific robots has become an important subject of research. This study is concerned with the development of a two-wheeled inverted pendulum robot that can be applied to an intelligent, mobile home robot. This kind of robotic mechanism has an innately clumsy motion for stabilizing the robot's body posture. To analyze and execute this robotic mechanism, we investigated the exact dynamics of the mechanism with the aid of 3-DOF modeling. By using the governing equations of motion, we analyzed important issues in the dynamics of a situation with an inclined surface and also the effect of the turning motion on the stability of the robot. For the experiments, the mechanical robot was constructed with various sensors. Its application to a two-dimensional floor environment was confirmed by experiments on factors such as balancing, rectilinear motion, and spinning motion.

The human arm kinematics and dynamics during daily activities - toward a 7 DOF upper limb powered exoskeleton

Abstract: Integrating human and robot into a single system offers remarkable opportunities for creating a new generation of assistive technology. Having obvious applications in rehabilitation medicine and virtual reality simulation, such a device would benefit both the healthy and disabled population. The aim of the research is to study the kinematics and the dynamics of the human arm during daily activities in a free and unconstrained environment as part of an on-going research involved in the design of a 7 degree of freedom (DOF) powered exoskeleton for the upper limb. The kinematics of the upper limb was acquired with a motion capture system while performing a wide verity of daily activities. Utilizing a model of the human as a 7 DOF system, the equations of motion were used to calculate joint torques given the arm kinematics. During positioning tasks, higher angular velocities were observed in the gross manipulation joints (the shoulder and elbow) as compared to the fine manipulation joints (the wrist). An inverted phenomenon was observed during fine manipulation in which the angular velocities of the wrist joint exceeded the angular velocities of the shoulder and elbow joints. Analyzing the contribution of individual terms of the arm's equations of motion indicate that the gravitational term is the most dominant term in these equations. The magnitudes of this term across the joints and the various actions is higher than the inertial, centrifugal, and Coriolis terms combined. Variation in object grasping (e.g. power grasp of a spoon) alters the overall arm kinematics in which other joints, such as the shoulder joint, compensate for lost dexterity of the wrist. The collected database along with the kinematics and dynamic analysis may provide the fundamental understanding for designing powered exoskeleton for the human arm

Hybrid Controllers for Path Planning: A Temporal Logic Approach

Abstract: Robot motion planning algorithms have focused on low-level reachability goals taking into account robot kinematics, or on high level task planning while ignoring low-level dynamics. In this paper, we present an integrated approach to the design of closed–loop hybrid controllers that guarantee by construction that the resulting continuous robot trajectories satisfy sophisticated specifications expressed in the so–called Linear Temporal Logic. In addition, our framework ensures that the temporal logic specification is satisfied even in the presence of an adversary that may instantaneously reposition the robot within the environment a finite number of times. This is achieved by obtaining a Buchi automaton realization of the temporal logic specification, which supervises a finite family of continuous feedback controllers, ensuring consistency between the discrete plan and the continuous execution.

Diffusion-Based Motion Planning for a Nonholonomic Flexible Needle Model

Abstract: Fine needles facilitate diagnosis and therapy because they enable minimally invasive surgical interventions. This paper formulates the problem of steering a very flexible needle through firm tissue as a nonholonomic kinematics problem, and demonstrates how planning can be accomplished using diffusion-based motion planning on the Euclidean group, SE(3). In the present formulation, the tissue is treated as isotropic and no obstacles are present. The bevel tip of the needle is treated as a nonholonomic constraint that can be viewed as a 3D extension of the standard kinematic cart or unicycle. A deterministic model is used as the starting point, and reachability criteria are established. A stochastic differential equation and its corresponding Fokker-Planck equation are derived. The Euler-Maruyama method is used to generate the ensemble of reachable states of the needle tip. Inverse kinematics methods developed previously for hyper-redundant and binary manipulators that use this probability density information are applied to generate needle tip paths that reach the desired targets.

HapticWalker---a novel haptic foot device

Abstract: This paper presents a new haptic locomotion interface, which comprises two programmable foot platforms with permanent foot machine contact. It is designed as a scalable and modular system with unit-by-unit extensibility offering up to six plus one degrees of freedom (DOF) per foot. The basic setup comprises three DOF per foot in the sagittal plane.The machine is based on a rigid hybrid parallel-serial robot kinematics structure. It is equipped with electrical direct drive motors, enabling highly dynamic footplate motions. For contact force measurement, six DOF force/torque sensors are mounted under each foot platform. The system was developed for major application in gait rehabilitation, hence great importance was attached to the incorporation of maximum passive and active security measures for machine users and medical operating personnel.The simulator is able to perform walking trajectories with speeds of up to 5 km/h and 120 steps/min. The system is able to simulate not only slow and “smooth” trajectories like walking on an even floor, up/down staircases, but also foot motions like walking on rough ground or even stumbling or sliding, which require high system dynamics.The machine is controlled by a self-developed full-featured robot control whose soft and hardware is based on up-to-date industrial standards and interfaces. The robot control software is based on RTLinux and runs on an industrial PC. The real-time motion generator includes a newly developed Fourier-based algorithm for the interpolation of natural cyclic walking trajectories. For the implementation of asynchronous events (e.g., sliding, stumbling), the controller comprises especially developed algorithms for automatic motion override adaptation. Different modes of haptic behavior needed for gait rehabilitation, ranging from full foot support during swing phase to completely passive behavior, are currently under development.Intuitive and safe machine operation by nontechnical personnel such as clinicians and physiotherapists is achieved via a separate Windows-based graphical user interface software comprising different window areas for machine programming and operation, real-time off-line simulation and online data visualization in two and three dimensions has been developed as well.A working prototype of the system has been built and tested successfully, including all soft and hardware components. Although the machine has been designed and built for major application in gait rehabilitation, its range of applicability is not limited to this area. It could be integrated into any setup requiring a highly dynamic haptic foot interface and permanent foot machine contact if needed.

Generating natural motion in an android by mapping human motion

Abstract: One of the main aims of humanoid robotics is to develop robots that are capable of interacting naturally with people. However, to understand the essence of human interaction, it is crucial to investigate the contribution of behavior and appearance. Our group's research explores these relationships by developing androids that closely resemble human beings in both aspects. If humanlike appearance causes us to evaluate an android's behavior from a human standard, we are more likely to be cognizant of deviations from human norms. Therefore, the android's motions must closely match human performance to avoid looking strange, including such autonomic responses as the shoulder movements involved in breathing. This paper proposes a method to implement motions that look human by mapping their three-dimensional appearance from a human performer to the android and then evaluating the verisimilitude of the visible motions using a motion capture system. This approach has several advantages over current research, which has focused on copying a person's moving joint angles to a robot: (1) in an android robot with many degrees of freedom and kinematics that differs from that of a human being, it is difficult to calculate which joint angles would make the robot's posture appear similar to the human performer; and (2) the motion that we perceive is at the robot's surface, not necessarily at its joints, which are often hidden from view.

Conceptual design and dimensional synthesis for a 3-DOF module of the TriVariant-a novel 5-DOF reconfigurable hybrid robot

Abstract: This paper deals with the conceptual design and dimensional synthesis of a 3-DOF parallel mechanism module which forms the main body of a newly invented 5-DOF reconfigurable hybrid robot named "TriVariant." The TriVariant is a modified version of the Tricept robot, achieved by integrating one of the three active limbs into the passive limb. The idea leading to the innovation of the module is systematically addressed. Its kinematic performance is optimized by minimizing a global and comprehensive conditioning index subject to a set of appropriate mechanical constraints. It is concluded that the proposed hybrid system is more cost-effective and has a competitive kinematic performance in comparison with the well-known Tricept robot.

Kinematics modeling and analyses of articulated rovers

Abstract: This paper describes a general approach to the kinematics modeling and analyses of articulated rovers traversing uneven terrain. The model is derived for full 6DOF (6-degree-of-freedom) motion, enabling movements in the x,y, and z directions, as well as pitch, roll, and yaw rotations. Differential kinematics is derived for the individual wheel motions in contact with the terrain. The resulting equations of the individual wheel motions are then combined to form the composite equation for the rover motion. Three types of kinematics, i.e., navigation, actuation, and slip kinematics are identified, and the equations and application of each are discussed. The derivations are specialized to Rocky 7, a highly articulated prototype Mars rover, to illustrate the developed methods. Simulation results are provided for the motion of the Rocky 7 over several terrains, and various motion profiles are provided to explain the behavior of the rover.

Experimental Studies of a Neural Oscillator for Biped Locomotion with QRIO

Abstract: Recently, there has been a growing interest in biologically inspired biped locomotion control with Central Pattern Generator (CPG). However, few experimental attempts on real hardware 3D humanoid robots have yet been made. Our goal in this paper is to present our achievement of 3D biped locomotion using a neural oscillator applied to a humanoid robot, QRIO. We employ reduced number of neural oscillators as the CPG model, along with a task space Cartesian coordinate system and utilizing entrainment property to establish stable walking gait. We verify robustness against lateral perturbation, through numerical simulation of stepping motion in place along the lateral plane. We then implemented it on the QRIO. It could successfully cope with unknown 3mm bump by autonomously adjusting its stepping period. Sagittal motion produced by a neural oscillator is introduced, and then overlapped with the lateral motion generator in realizing 3D biped locomotion on a QRIO humanoid robot.

Proposed wall climbing robot with permanent magnetic tracks for inspecting oil tanks

Abstract: This paper presents a proposed research on the wall climbing robot with permanent magnetic tracks. A brief review about the wall climbing robot is given, different prototypes of wall climbing robot are compared, and the different application fields are introduced. A proposed wall climbing robot with permanent magnetic adhesion mechanism for inspecting oil tanks is put forward. The mechanical system architecture is detailed in the paper. By analyzing the robot's workspace, permanent magnetic adhesion mechanism is chosen for the robot. Also, tracked locomotion mechanism is applied to the robot. By static and dynamic force analysis of the robot, design parameters about adhesion and locomotion mechanism are derived. In addition, safety constraints for the robot are obtained. Finally, the electrical system architecture for the robot is offered. To improve the efficiency, hierarchy control architecture is employed in the robot system. An embedded system is used and installed in the robot to manage multiple sensors and to communicate with the master computer through the wireless link. And the Web-based teleoperation for the robot is illustrated in the paper.

Task-oriented whole body motion for humanoid robots

Abstract: We present a whole body motion control algorithm for humanoid robots It is based on the framework of Liegeois and solves the redundant inverse kinematics problem on velocity level We control the hand positions as well as the hand and head attitude The attitude is described with a novel 2-dof description suited for symmetrical problems Task-specific command elements can be assigned to the command vector at any time, such enabling the system to control one or multiple effectors and to seamlessly switch between such modes while generating a smooth, natural motion Further, kinematic constraints can be assigned to individual degrees of freedom The underlying kinematic model does not consider the leg joints explicitly Nevertheless, the method can be used in combination with an independent balance or walking control system, such reducing the complexity of a complete system control We show how to incorporate walking in this control scheme and present experimental results on ASIMO

A calibration method for odometry of mobile robots based on the least-squares technique: theory and experimental validation

Abstract: For a mobile robot, odometry calibration consists of the identification of a set of kinematic parameters that allow reconstructing the vehicle's absolute position and orientation starting from the wheels' encoder measurements. This paper develops a systematic method for odometry calibration of differential-drive mobile robots. As a first step, the kinematic equations are written so as to underline linearity in a suitable set of unknown parameters; thus, the least-squares method can be applied to estimate them. A major advantage of the adopted formulation is that it provides a quantitative measure of the optimality of a test motion; this can be exploited to drive guidelines on the choice of the test trajectories and to evaluate accuracy of a solution. The proposed technique has been experimentally validated on two different mobile robots and, in one case, compared with other existing approaches; the obtained results confirm the effectiveness of the proposed calibration method.

A Humanoid Robot Carrying a Heavy Object

Abstract: This paper studies the balance of a humanoid robot carrying a heavy object. Without knowing the mass and the position of the center of gravity of the object, the humanoid robot carries a heavy object stably by using the force sensor information attached at the wrists and the ankles. We first show how to generate the motion of a humamoid robot by taking the force sensor information into consideration. We also show the method for generating the gait pattern by taking the dynamics of the carried object. The effectiveness of the proposed method is shown by experiments.

Motion feasibility of multi-agent formations

Abstract: Formations of multi-agent systems, such as mobile robots, satellites and aircraft, require individual agents to satisfy their kinematic equations while constantly maintaining interagent constraints. In this paper, we develop a systematic framework for studying formation motion feasibility of multi-agent systems. In particular, we consider formations wherein all the agents cooperate to enforce the formation. We determine algebraic conditions that guarantee formation feasibility given the individual agent kinematics. Our framework also enables us to obtain lower dimensional control systems describing the group kinematics while maintaining all formation constraints.

Task model of lower body motion for a biped humanoid robot to imitate human dances

Abstract: The goal of this study is developing a biped humanoid robot that can observe a human dance performance and imitate it. To achieve this goal, we propose a task model of lower body motion, which consists of task primitives (what to do) and skill parameters (how to do it). Based on this model, a sequence of task primitives and their skill parameters are detected from human motion, and robot motion is regenerated from the detected result under constraints of a robot. This model can generate human-like lower body motion including various waist motions as well as various stepping motions of the legs. Generated motions can be performed stably on an actual robot supported by its own legs. We used improved robot hardware HRP-2, which has superior features in body weight, actuators, and DOF of the waist. By using the proposed method and HRP-2, we have realized a dance performance of Japanese folk dance by the robot, which is synchronized with a performance of a human grand master on the same stage.

Distributed Multi-Robot Exploration and Mapping

Abstract: Efficient exploration of unknown environments is a fundamental problem in mobile robotics. As autonomous exploration and map building becomes increasingly robust on single robots, the next challenge is to extend these techniques to large teams of robots. This talk will provide an overview of our approach to multi-robot exploration and mapping, which we developed within the CentiBots project. This project aimed at fielding 100 robots in an indoor exploration and surveillance task. A general solution to distributed exploration must consider some difficult issues, including limited communication between robots, no assumptions about relative start locations of the robots, and dynamic assignments of processing tasks. The focus of this talk will be on our current solutions to the problems of robot localization, map building, and coordinated exploration. As part of the CentiBots project, our system was evaluated rigorously by an outside team. We present results from this evaluation that demonstrate that the system is highly robust and that the maps generated by our robots are more accurate than maps generated by a human.

Humanoid motion planning for dynamic tasks

Abstract: This paper addresses an integrated humanoid motion planning scheme including both advanced algorithmic motion planning technique and dynamic pattern generator so that the humanoid robot achieve tasks including dynamic motions A two-stage approach is proposed for this goal First, geometric and kinematic motion planner first computes collision-free paths for the humanoid robot Then the dynamic pattern generator provides dynamically feasible humanoid motion including both locomotion and task execution such as object transportation or manipulation If the generated dynamic motion causes collision due to dynamic movements, the planner go back to the planning stage to remove the collision by path reshaping This iterative planning scheme enables robust planning against variation of task dynamics Simulation results are provided to validate the proposed planning method

Parameter Optimization of Simplified Propulsive Model for Biomimetic Robot Fish

Abstract: This paper is concerned with the parameter optimization for a simplified propulsive model of biomimetic robot fish propelled by a multiple linked mechanism. Taking account of both theoretic hydrodynamic issues and practical problems in engineering realization, the optimal link-length ratio is numerically calculated by an improved constrained cyclic variable method. The result is successfully applied to the 4-linked robot fish developed in our laboratory. The comparative experiments on forward swimming speed of the robot fish before and after parameter optimization verify the effectiveness of our method.

Real-time path planning for humanoid robot navigation

Abstract: We present a data structure and an algorithm for real-time path planning of a humanoid robot. Due to the many degrees of freedom, the robots shape and available actions are approximated for finding solutions efficiently. The resulting 3 dimensional configuration space is searched by the A* algorithm finding solutions in tenths of a second on lowperformance, embedded hardware. Experimental results demonstrate our solution for a robot in a world containing obstacles with different heights, stairs and a higher-level platform.

Compliance control for an anthropomorphic robot with elastic joints: Theory and experiments

Abstract: Studies on motion control of robot manipulators with elastic joints are basically aimed at improving robot performance in tracking or regulation tasks. In the interaction between robots and environment, instead, the main objective of a control strategy should be the reduction of the vibrational and chattering phenomena that elasticity in the robot joints can cause. This work takes into account working environments where unexpected interactions are experienced and proposes a compliance control scheme in the Cartesian space to reduce the counter effects of elasticity. Two theoretical formulations of the control law are presented, which differ for the term of gravity compensation. For both of them the closed-loop equilibrium conditions are evaluated and asymptotic stability is proven through the direct Lyapunov method. The two control laws are applied to a particular class of elastic robot manipulators, i.e., cable-actuated robots, since their intrinsic mechanical compliance can be successfully utilized in applications of biomedical robotics and assistive robotics. A compared experimental analysis of the two formulations of compliance control is finally carried out in order to verify stability of the two closed-loop systems as well as the capability to control the robot force in the interaction.

Analysis of stairs-climbing ability for a tracked reconfigurable modular robot

Abstract: Stairs-climbing ability is the crucial performance of mobile robot for urban environment mission such as urban search and rescue or urban reconnaissance. The track type mobile mechanism has been widely applied for its advantages such as high stability, easy to control, low terrain pressure, and continuous drive. Stairs-climbing is a complicated process for a tracked mobile robot under kinematics and dynamics constraints. In this paper, the stairs-climbing process has been divided into riser climbing, riser crossing, and nose line climbing. During each climbing process, robot's mobility has been analyzed for its kinematics and dynamics factor. The track velocity and acceleration's influences on riser climbing have been analyzed. And the semiempirical design method of the track grouser and the module length has been provided in riser crossing and nose line climbing correspondingly. Finally, stairs-climbing experiments have been made on the two-module robot in line type, and three-module robot in line type and in triangle type respectively.

An integrated path-planning and control approach for nonholonomic unicycles using switched local potentials

Abstract: In this paper, navigation and control of an autonomous mobile unicycle robot in an obstacle-ridden environment is considered. The unicycle dynamic model used has two differentially driven wheels, with the motor torques as the system input. Two novel potential-field-based controllers are derived, which stabilize the robot within a surrounding circular area (henceforth called a bubble) of arbitrary size. The first controller takes the unicycle to the center of its bubble, while the second corrects its orientation. The designed potentials also work with a kinematic model. Explicit bounds for permissible initial speeds are derived, such that maximum torque limits and/or maximum speed limits are not violated once the controller is activated. These controllers are then embedded in a navigation framework. An existing global planner is used to first create a string of variable-sized bubbles which connect the start point to the goal point, with each bubble's size indicative of the radial obstacle clearance available from its center. The robot then keeps itself within a fixed-sized bubble, which it then moves in discrete steps, according to the direction provided by the global plan, while repulsively avoiding unexpected obstacles. Hence, the gross movement is created by switching local potential-field-based controllers. This scheme is first verified in computer simulation of a single robot moving in a maze. It is then implemented on an experimental setup of robots equipped with proximity sensors. Results are presented to illustrate the effectiveness of the system.

Movement Primitives, Principal Component Analysis, and the Efficient Generation of Natural Motions

Abstract: We propose a framework for robot movement coordination and learning that combines elements of movement storage, dynamic models, and optimization, with the ultimate objective of efficiently generating natural, human-like motions. One of the novel features of our approach is that each movement primitive is represented and stored as a set of joint trajectory basis functions; these basis functions are extracted via a principal component analysis of human motion capture data. By representing arbitrary movements as a linear combination of these basis functions, and by taking advantage of recently developed geometric optimization algorithms for multibody systems, dynamics-based optimization can be more efficiently performed. Case studies with a diverse set of arm movements demonstrate the feasibility of our approach.

Comparative experiments on task space control with redundancy resolution

Abstract: Understanding the principles of motor coordination with redundant degrees of freedom still remains a challenging problem, particularly for new research in highly redundant robots like humanoids. Even after more than a decade of research, task space control with redundacy resolution still remains an incompletely understood theoretical topic, and also lacks a larger body of thorough experimental investigation on complex robotic systems. This paper presents our first steps towards the development of a working redundancy resolution algorithm which is robust against modeling errors and unforeseen disturbances arising from contact forces. To gain a better understanding of the pros and cons of different approaches to redundancy resolution, we focus on a comparative empirical evaluation. First, we review several redundancy resolution schemes at the velocity, acceleration and torque levels presented in the literature in a common notational framework and also introduce some new variants of these previous approaches. Second, we present experimental comparisons of these approaches on a seven-degree-of-freedom anthropomorphic robot arm. Surprisingly, one of our simplest algorithms empirically demonstrates the best performance, despite, from a theoretical point, the algorithm does not share the same beauty as some of the other methods. Finally, we discuss practical properties of these control algorithms, particularly in light of inevitable modeling errors of the robot dynamics.

Path Planning for Permutation-Invariant Multi-Robot Formations

Abstract: In this paper we demonstrate path planning for our formation space that represents permutation-invariant multi-robot formations. Earlier methods generally pre-assign roles for each individual robot, rely on local planning and behaviors to build emergent behaviors, or give robots implicit constraints to meet. Our method first directly plans the formation as a set, and only afterwards determines which robot takes which role. To build our representation of this formation space, we make use of a property of complex polynomials: they are unchanged by permutations of their roots. Thus we build a characteristic polynomial whose roots are the robot locations, and use its coefficients as a representation of the formation. Mappings between work spaces and formation spaces amount to building and solving polynomials. In this paper, we construct an efficient obstacle collision detector, and use it in a local planner. From this we construct a basic roadmap planner. We thus demonstrate that our polynomial based representation can be used for effective permutation invariant formation planning.

Game Theoretic Control for Robot Teams

Abstract: In the real world, noisy sensors and limited communication make it difficult for robot teams to coordinate in tightly coupled tasks. Team members cannot simply apply single-robot solution techniques for partially observable problems in parallel because they do not take into account the recursive effect that reasoning about the beliefs of others has on policy generation. Instead, we must turn to a game theoretic approach to model the problem correctly. Partially observable stochastic games (POSGs) provide a solution model for decentralized robot teams, however, this model quickly becomes intractable. In previous work we presented an algorithm for lookahead search in POSGs. Here we present an extension which reduces computation during lookahead by clustering similar observation histories together. We show that by clustering histories which have similar profiles of predicted reward, we can greatly reduce the computation time required to solve a POSG while maintaining a good approximation to the optimal policy. We demonstrate the power of the clustering algorithm in a real-time robot controller as well as for a simple benchmark problem.

Suturing in confined spaces: constrained motion control of a hybrid 8-DoF robot

Abstract: We present our work on developing and testing the high-level control for a future telerobotic system for minimally invasive surgery of the throat and upper airways. As a test-bed for these experiments, we used a hybrid 8 degrees-of-freedom (DoF) experimental robot composed of a six DoF robot and a two DoF snake-like unit. The kinematics and weighted redundancy resolution to support suturing in confined spaces, such as the throat, is developed and experimental validation in presented. The kinematics of the hybrid system is described in an 8-dimensional augmented vector space composed from the joint variables of the six DoF robot and two angles describing the configuration of the snake-like unit. Then a weighted, multi objective, optimization framework is used to perform the suturing operation under the assumption of a predefined suture geometry while satisfying joint limits, torque constraints, and minimizing extraneous motions of the system joints

Combinatorial Bids based Multi-robot Task Allocation Method

Abstract: How to coordinate several robots to cooperatively accomplish relatively complex tasks is not an easy issue. This paper presents a combinatorial bids based multi-robot task allocation method. The proposed method provides an explicit cooperation mechanism to the bidding robots so that they can form a group to bid for complex tasks. Some carefully designed simulations indicate that this method is more efficient than the typical auction based one in some situations.