Degree Of Freedom Configuration Research Articles

Structural design and performance analysis of an auxiliary dining robot

An auxiliary dining robot is designed in this paper, which implements the humanoid feeding function with theory of inventive problem solving (TRIZ) theory and aims at the demand of special auxiliary nursing equipment. Firstly, this robot simulated the motion function of human arm by using the tandem joints of the manipulator. The end-effector used a motor-driven spoon to simulate the feeding actions of human hand. Meanwhile, the eye in hand installation style was adopted to instead the human vision to realize its automatic feeding action. Moreover, the feeding and drinking actions of the dining robot were considered comprehensively with the flexibility of spatial movement under the lowest degree of freedom (DOF) configuration. The structure of the dining robot was confirmed by analyzing its stresses and discussing the specific application scenarios under this condition. Finally, the simulation results demonstrate high-flexibility of the dining robot in the workspace with lowest DOF configuration.

Noncommutative black holes of various genera in the connection formalism

We consider black hole interiors of arbitrary genus number within the paradigm of non-commutative geometry. The study is performed in two ways: One way is a simple smearing of a matter distribution within the black hole. The resulting structure is often known in the literature as a "model inspired by non-commutative geometry". The second method involves a more fundamental approach, in which the Hamiltonian formalism is utilized and a non-trivial Poisson bracket is introduced between the configuration degrees of freedom, as well as between the canonical momentum degrees of freedom. This is done in terms of connection variables instead of the more common ADM variables. Connection variables are utilized here since non-commutative effects are usually inspired from the quantum theory, and it is the connection variables that are used in some of the more promising modern theories of quantum gravity. We find that in the first study, the singularity of the black holes can easily be removed. In the second study, we find that introducing a non-trivial bracket between the connections (the configuration variables) may delay the singularity, but not necessarily eliminate it. However, by introducing a non-trivial bracket between the densitized triads (the canonical momentum variables) the singularity can generally be removed. In some cases, new horizons also appear due to the non-commutativity.

Obstacle-crossing strategy and formation parameters optimization of a multi-tracked-mobile-robot system with a parallel manipulator

Multiple robots collaborative transportation is a new trend of robotic research in unmanned logistics area. Existing researches focus on the collaborative transportation on the flat ground, but usually neglect the obstacle-crossing problems in real-world environments. This paper designs a novel multi-robotsystem composed of tracked mobile robots used for collaborative transportation and investigatesits stairs climbing process. The robots are combined with each other by a parallel manipulator which is implemented to carry payloads. Meanwhile, actuated by the robots, the manipulator could achieve a 6 degrees of freedom configuration. A cable-driven unit is designed to provide extratension among these robots to improve the climbing capability. The statics model of the stair climbing process of a monorobot is analyzed. The climbing orientation of the robot is optimized and the stair climbing capabilityis improved by changing the climbing yaw angle. Based on the optimized mono robotclimbing process, the stair climbing formations of the multi-robot system are analyzed and the formationparameters are optimized with the maximal support angle.The climbing strategy is proposed according to the mass of payload and the height of the stair. The effectiveness of the climbing strategy is validated by the stair climbing experiments.

Collision Avoidance of Redundant Robotic Manipulators Using Newton’s Method

This study investigates the application of Newton method to the problems of collision avoidance and path planning for robotic manipulators, especially robots with high Degrees of Freedom (DOF). The proposed algorithm applies to the potential fields method, where the Newton technique is used for performing the optimization. As compared to classical gradient descent method this implementation is mathematically elegant, enhances the performance of motion generation, eliminates oscillations, does not require gains tuning, and gives a faster convergence to the solution. In addition, the paper presents a computationally efficient symbolic formula for calculating the Hessian with respect to joint angles, which is essential for achieving realtime performance of the algorithm in high DOF configuration spaces. The method is validated successfully in simulation environment. Results for different methods (Newton, gradient descent and gradient descent with momentum) are compared in terms of quality of the path generated, oscillations, minimum distance to obstacles and convergence rate.

Quantum Cosmology and Varying Physical Constants

The main task of this review is to discuss quantum cosmology minisuperspace models based on the Wheeler–DeWitt equation, which apart from the standard matter and 3-geometry configuration degrees of freedom, allow those related to the variability of physical constants—varying speed of light (VSL) c and varying gravitational constant G. The tunneling probability of the universe “from nothing” to the Friedmann phase will be given for such varying constants minisuperspace models.

Effective temperatures and the breakdown of the Stokes-Einstein relation for particle suspensions.

The short- and long-time breakdown of the classical Stokes-Einstein relation for colloidal suspensions at arbitrary volume fractions is explained here by examining the role that confinement and attractive interactions play in the intra- and inter-cage dynamics executed by the colloidal particles. We show that the measured short-time diffusion coefficient is larger than the one predicted by the classical Stokes-Einstein relation due to a non-equilibrated energy transfer between kinetic and configuration degrees of freedom. This transfer can be incorporated in an effective kinetic temperature that is higher than the temperature of the heat bath. We propose a Generalized Stokes-Einstein relation (GSER) in which the effective temperature replaces the temperature of the heat bath. This relation then allows to obtain the diffusion coefficient once the viscosity and the effective temperature are known. On the other hand, the temporary cluster formation induced by confinement and attractive interactions of hydrodynamic nature makes the long-time diffusion coefficient to be smaller than the corresponding one obtained from the classical Stokes-Einstein relation. Then, the use of the GSER allows to obtain an effective temperature that is smaller than the temperature of the heat bath. Additionally, we provide a simple expression based on a differential effective medium theory that allows to calculate the diffusion coefficient at short and long times. Comparison of our results with experiments and simulations for suspensions of hard and porous spheres shows an excellent agreement in all cases.

Experimental Implementation of a Nonlinear Dynamic Inversion Controller with Antiwindup

A recently proposed nonlinear antiwindup compensation scheme is implemented and tested on a scaled BAe Hawk jet trainer wind-tunnel model, mounted in a one degree of freedom configuration. The Hawk is modeled as a nonlinear affine system subject to input amplitude constraints. The primary control system consists of an inner-loop nonlinear dynamic inversion controller and an outer-loop linear proportional integral derivative controller. The input constraints are addressed by supplementing this nominal controller with two types of nonlinear antiwindup schemes: a nonlinear variant of the well-known internal model control scheme and a suboptimal norm-based antiwindup compensator. Wind tunnel results are presented which demonstrate the usefulness of the antiwindup schemes in preventing performance deterioration due to the input constraints and the flexibility of the proposed approach from a practical perspective.

Adaptive complementary filtering algorithm for mobile robot localization

As a mobile robot navigates through an indoor environment, the condition of the floor is of low (or no) relevance to its decisions. In an outdoor environment, however, terrain characteristics play a major role on the robot's motion. Without an adequate assessment of terrain conditions and irregularities, the robot will be prone to major failures, since the environment conditions may greatly vary. As such, it may assume any orientation about the three axes of its reference frame, which leads to a full six degrees of freedom configuration. The added three degrees of freedom have a major bearing on position and velocity estimation due to higher time complexity of classical techniques such as Kalman filters and particle filters. This article presents an algorithm for localization of mobile robots based on the complementary filtering technique to estimate the localization and orientation, through the fusion of data from IMU, GPS and compass. The main advantages are the low complexity of implementation and the high quality of the results for the case of navigation in outdoor environments (uneven terrain). The results obtained through this system are compared positively with those obtained using more complex and time consuming classic techniques.

Adaptive complementary filtering algorithm for mobile robot localization

Abstract As a mobile robot navigates through an indoor environment, the condition of the floor is of low (or no) relevance to its decisions. In an outdoor environment, however, terrain characteristics play a major role on the robot’s motion. Without an adequate assessment of terrain conditions and irregularities, the robot will be prone to major failures, since the environment conditions may greatly vary. As such, it may assume any orientation about the three axes of its reference frame, which leads to a full six degrees of freedom configuration. The added three degrees of freedom have a major bearing on position and velocity estimation due to higher time complexity of classical techniques such as Kalman filters and particle filters. This article presents an algorithm for localization of mobile robots based on the complementary filtering technique to estimate the localization and orientation, through the fusion of data from IMU, GPS and compass. The main advantages are the low complexity of implementation and the high quality of the results for the case of navigation in outdoor environments (uneven terrain). The results obtained through this system are compared positively with those obtained using more complex and time consuming classic techniques.

Re-analysis of the degree-of-freedom configuration of the platforms in spatial parallel mechanisms with constraints spaces

The degree-of-freedom (DoF) configuration of a mechanism, which is an important concept in the field of mechanisms and is the key problem to be solved before mechanisms are designed, has been discussed in our previous article [1]. In this paper, we will further analyze the DoF configuration of the platforms of spatial parallel mechanisms with constraints spaces. According to the physical meaning of reciprocal screws, we can solve the constraints spaces spanned by reciprocal screws, and then solve the free mobility spaces of the platform and its DoF configuration. With this methodology, not only can we differentiate the system from its members, but we also extend the concept of DoF configuration, which should have the attributes of number, type, and direction.

A theory of degrees of freedom for mechanisms

In this paper, we put forward a stricter and more complete theory of degrees of freedom (DOF) for mechanisms, especially for the complex spatial mechanisms, which may not be solved correctly with traditional theories. We also point out that it is more appropriate to calculate the DOF of the mechanism with an output member rather than that of the whole mechanism. Furthermore, the new concept of configuration degrees of freedom (CDOF) in this theory can form a more complete and reasonable theoretical base for analyzing the mobility, singularity and stability of the mechanisms.

Analysis of Multiaxis Vibration Simulators

A mathematical procedure that quantitatively addresses issues critical to the design and operation of multiaxis vibration simulators is presented. Both kinematic and dynamic issues are considered. The analysis is applied to both 3 and 6 degrees of freedom configurations. The existence of singular configurations is mentioned and appropriate corrective measures are recommended. A methodology for determining the required actuator commands is also presented.

Analysis of Multiaxis Vibration Simulators

A mathematical procedure that quantitatively addresses issues critical to the design and operation of multiaxis vibration simulators is presented. Both kinematic and dynamic issues are considered. The analysis is applied to both 3 and 6 degrees of freedom configurations. The existence of singular configurations is mentioned and appropriate corrective measures are recommended. A methodology for determining the required actuator commands is also presented. © 1995 John Wiley & Sons, Inc.

Feedforward Controllers for Perfect Tracking that does not Invert Plant Zeros Outside the Unit Disc

In this paper we look at synthesizing feedforward controllers for the explicit purpose of assuring perfect tracking (in the absence of plant uncertainty) of a prespecified class of time varying signals. Proposed is a technique that cancels all the closed loop poles and only the minimum phase zeros. The non-minimum phase zeros are not cancelled but are taken into account in a unique way. These results complement the notion of zero phase error tracking (ZPET) introduced by Tomizuka (1987). The essential point of ZPET is to try and make the overall gain approximately equal to 1 over a desired frequency range while maintaining the overall phase at 0° for all frequencies. While in ZPET the desired output can be an arbitrary time signal the method proposed here relies on the fact that the function to be tracked is known apriori. A complete formulation of the problem in the discrete time domain for the perfect model case is given. Also formulated is a robust version of the problem statement. The latter is accomplished by embedding the controller synthesis in a standard two degree of freedom configuration

New approach to the application of redundant robots

The problem of a heavy robot performing highly accelerated motion is discussed. Since the original six degree of freedom configuration could not solve the task, a suitable redundancy was added to improve the acceleration capabilities. This redundant configuration equipped with the DPS (distributed positioning system) software was able to perform the motion required. The theoretical background and simulation results are presented.

The dynamics of offshore gravity platforms: Some insights afforded by a two degree of freedom model

AbstractThis paper presents some findings of an investigation into the dynamic behaviour of offshore gravity platforms excited by waves. Results obtained from a finite element model are presented in the form of dynamic magnification factor curves for two structures typical of current concrete platform designs. In order to facilitate interpretation of these results a simple two degree of freedom model is developed and the equivalent results presented. These are found to be very similar to those obtained from the more detailed idealization, and it is therefore concluded that the principal mechanisms involved in the dynamic behaviour of offshore gravity structures are adequately represented in the simple model. Several useful insights into this behaviour are then achieved by closer examination of the two degree of freedom configuration.