Please note, due to essential maintenance online transactions will not be possible between 02:30 and 04:00 BST, on Tuesday 17th September 2019 (22:30-00:00 EDT, 17 Sep, 2019). We apologise for any inconvenience.
To send this article to your account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send this article to your Kindle, first ensure email@example.com is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
The importance of verifying safety-critical systems has been highlighted recently when the Embedded Systems Group (SEN2) and the Systems Validation Group (VASY) launched a collaboration agreement. Called SENVA, which represents System Engineering and Validation, this joint research team will add strength to this important area of endeavour.
This paper presents a Q-learning approach to state-based planning of behaviour-based walking robots. The learning process consists of a teaching stage and an autonomous learning stage. During the teaching stage, the robot is instructed to operate in some interesting areas of the solution space to accumulate some prior knowledge. Then, the learning is switched to the autonomous learning stage to let the robot explore the solution space based on its prior knowledge. Experiments are conducted in the RoboCup domain and results show a good performance of the proposed method.
This paper reports on the use of a particular actuator in the field of legged robots. The proposed actuator, the Pleated Pneumatic Artificial Muscle, has some interesting characteristics which makes it suitable for machines which move by means of legs. An important issue is the actuator's adaptable passive behaviour which allows the stiffness of a joint that is actuated by two antagonistically coupled muscles, to be varied online. The natural frequency of the system can thus be changed in order to reduce control efforts and energy consumption. The idea of changing this natural frequency in combination with trajectory control will be implemented on a two-dimensional leg model. It will be shown that an appropriate choice of compliance can strongly reduce the amount of needed control activity and energy consumption while tracking a given trajectory.
In this paper a framework is proposed for the adaptive control of robotic manipulators which combines parametric adaptive control with Artificial Neural Network (ANN)-based compensation of dynamic uncertainties like friction. The proposed method utilizes a passivity-based parametric adaptive control approach and makes use of the ANN models as generic identifiers to compensate for unmodelled friction effects. Unlike many approaches for ANN based control in the literature, parameter update equations for the ANN model and for the parametric adaptive model are driven by both the tracking error and the system identification error. A stability analysis is given based on the passivity properties of the manipulator dynamics. The methodology is successfully tested for the control of a Direct Drive SCARA arm and performance is compared with standard adaptive control schemes.
In this paper, we study the base placement problem for a two-degree-freedom-robot. The feasible area for the robot base is described, and its manipulability measure is formulated. To find the optimal base location of the robot, we develop a genetic algorithm (GA) to search for the valid solution in the reachable area of the robot base. To speed up the evolutionary process, we keep the elitists from one generation to the next generation according to certain elitist rate. The genetic algorithm approach is beneficial because it can also be extended to trajectory planning for robots with more degrees-of-freedom. We demonstrate the algorithm with some examples.
This paper presents a new haptic device based on a parallel structure that can be used as a master interface in a teleoperation or haptic control architecture. The basic idea of a haptic device is to serve force and/or position reflection to the operator; at the same time that is being used by the human operator to input the required commands. The original mechanical structure of the presented system implies important advantages over other existing devices. The mechanism is a modification of the 6-d.o.f. Gough platform where the linear actuators have been replaced by cable-driven pantographs. Avoiding the use of reduction gears by means of cable transmission allows a wide sensing bandwidth. Some experimental indices comparing the performance of the presented device are presented. The paper shows the geometrical model and the kinematic analysis used on the control algorithms of this interface. The hardware and software architectures used on the system, and the control schemes implemented on a multi-axis board, are detailed. This setup provides an open control architecture that allows the implementation and experimentation of several bilateral control schemes. The integration of the haptic device in a teleoperation simulator is shown. This simulator includes virtual robotic slaves and its dynamic interaction with the virtual environment. Finally, the results obtained in the virtual objects manipulation experiments are shown. A classical force-position bilateral control scheme was used for these experiments.
This paper extends the models developed previously by the authors for simulating tip-over stability of mobile manipulators, to include the friction of the contact between the base and the ground. Thus, the present model takes into account the detailed dynamics of the base that can rock back and forth during the movement of the manipulator, the combined vehicle suspension and ground-tire compliance and, the friction between the wheels and the ground. ‘LuGre’ tire friction model is employed, which along with the novel method of virtual links transforms the system into a fixed base manipulator with single degree of freedom at each joint. The model is then used to simulate planar movements of a 215B Caterpillar excavator-based log-loader machine. The results are also compared to those obtained by the simplified model, which was developed previously based on the assumption that the friction between the base and the ground is high enough to prevent the base from skidding forward or backward. The results clearly show that the friction properties between the wheels and the ground affect machine stability. Thus, one has to include the frictional effect in order to accurately predict the tip-over behavior of mobile manipulators.
Structural flexibility is an inherent characteristic of a class of macro-micro manipulators consisting of a rigid micro manipulator mounted on a long-reach (flexible) macro manipulator. Vibrations caused by flexibility make it difficult to achieve accurate control of the end-point of the micro manipulator. In this paper, we develop a control strategy that can be applied to such a system. An experimental test-bed has been developed in which a 6 DOF PUMA 560 manipulator is mounted on a compliant platform. The control strategy consists of a rigid body inverse dynamics controller together with a neural network based strategy for damping out the oscillations due to the flexible base. Experimental results obtained from the test-bed are presented to show the effectiveness of the proposed control scheme.
A new solution of the inverse kinematics task for a 3-DOF parallel manipulator with a R-P-S joint structure is obtained for a given position of end-effector in the form of simple position equations. Based on this the number of the inverse kinematics task solutions was investigated, in general, equal to four. We identify the size of the manipulator feasible area and simple relationships are found between the position and orientation of the platform. We prove a new theorem stating that, while the end-effector traces a circular horizontal path with its centre at the vertical z-axis, the norm of the joint coordinates vector remains constant.
In this paper, the kinematics and inverse dynamics of a novel kind of mechanism called a general 3-PRS parallel mechanism is investigated. In the kinematics study, the inverse kinematics solution is derived in closed form, and the forward kinematics problem is resolved by the Newton iterative method seeking for an on-line solution to this issue. The inverse dynamics analysis is approached with two methods: Lagrangian formulations and principle of virtual work. After deriving the dynamic model by a Lagrangian formulation approach, the simulation results of two introduced examples quantitatively and qualitatively verify the accuracy of the derived dynamic equations. By introducing a simplifying hypothesis, a simplified dynamic model is set up using principle of virtual work, also a computer simulation is performed on this reduced model. The simulation results demonstrate that the simplified dynamic model is reasonable under such kind of assumptions through comparison with the precise model derived from the Lagrangian formulation. The inverse dynamics analysis provides a sound basis to develop controllers for controlling over a general 3-PRS parallel robot.
This paper proposes a general method to develop n-DOF serial isotropic manipulators. The parameters of 6-DOF isotropy generators are used as the initial values in a numerical method to obtain redundant isotropic generators. Additional constraint equations are then added, with the parameters of the obtained generators as initial values, to obtain the isotropy generators with special parameters. Each generator can be developed into many isotropic designs with special or desired link parameters. Two different approaches for developing isotropic manipulators are also investigated.
Motion coupling is one of the typical characters of parallel robots. This makes it complicated to control the parallel robots. Therefore, the design of parallel mechanisms with decoupled motions is an important and challenging issue in the parallel robotic field. However, research in this field, including the definition and type synthesis theory, is weak or lacking. In this paper, the reducible correlation between the input and the output of 3-DOF translational mechanisms with decoupled motions is investigated and the definition of this topic is presented. A new parameter named Gf coordinate is propsed for the synthesis of 3-DOF reducible translational mechanisms. The type synthesis theory for this kind of mechanisms is obtained and some reducible mechanisms are synthesized.
This paper describes a software tool to automate a design method for robotic fuzzy force control. The original method was developed to ensure robust and stable force control in situations where environmental stiffness at the robot/task interface is unknown, obviating the use of fixed-gain controllers. It did, however, involve a manual design process requiring significant knowledge of control theory and fuzzy logic. This process has been automated in the form of a Windows-based application, requiring minimal user inputs and incorporating an automatic tuning technique for improved performance in the final controller application. Results obtained from an experimental robot are presented.
This paper concerns the proposal and analysis of HANA, a novel spatial parallel manipulator with over constraint. The parallel manipulator consists of a base plate, a movable platform, and three connecting legs. The moving platform has three degrees of freedom (DoFs), which are two degrees of translational freedom and one degree of rotational freedom, with respect to the base plate. The new parallel manipulator is very interesting for the reason of a lack of singularity in its workspace, single-DoF joint architecture and high rotational capability of its moving platform. The inverse and forward kinematics problems are described in closed-forms. The velocity equation of the new parallel manipulator is given. Three kinds of singularities are presented. The workspace for the manipulator is analyzed systematically. Especially, the index to evaluate the rotational capability of the manipulator is defined and discussed in detail. The proposed manipulator has a wide application in the fields of industrial robots, simulators, micro-motion manipulators, and parallel kinematics machines.