A new approach for the design of robot joint transmission

Until recently the only alternative to traditional transmission techniques for robot manipulators was direct-drive (DD), and associated transmission mechanisms. These methodologies were developed to overcome the inherent problems of friction, backlash and compliance of gearboxes. The DD concept is however not ideal as the absence of a reduction ratio, means that dynamic coupling and joint interaction become important at the motor shaft. An alternative approach that keeps the directness of DD, while providing dynamic coupling and joint interaction attenuation, is the non-linear direct transmission. The new concept is applied to the prototype SPRINTA robot and its performance demonstrates the potential of the non-linear direct transmission philosophy.     

Modeling,design, and implementation of a baton robot with double-action inertial actuation

In this paper, we present a baton locomotor capable of generating tapping gait. A baton is a system that consists of two masses joined with a massless rod. We use a new double-action inertial actuation scheme to drive this system. This scheme employs two spinning pendulums at one end, turning in opposite directions with the same angular velocity. One can control the direction and magnitude of the resultant inertial force that propels the system by changing the rendez-vous angle and the angular velocity of the spinners. In this paper, we first present the modeling of the system with actuation on both ends. Then, we use a numerical approach to simulate and analyze the tapping gait of the inertially actuated baton. In addition, we developed a new prototype, Pony II robot, to establish the practicality of the concept. This prototype consists of the double-action spinners mounted on both ends of the baton. The mechanical and electronic components of the robot are also presented in full detail. Finally, we demonstrate that the robot can successfully generate periodic tapping gait.     

Optoranger: A 3D pattern matching method for bin picking applications

This paper presents a new method, based on 3D vision, for the recognition of free-form objects in the presence of clutters and occlusions, ideal for robotic bin picking tasks. The method can be considered as a compromise between complexity and effectiveness. A 3D point cloud representing the scene is generated by a triangulation-based scanning system, where a fast camera acquires a blade projected by a laser source. Image segmentation is based on 2D images, and on the estimation of the distances between point pairs, to search for empty areas. Object recognition is performed using commercial software libraries integrated with custom-developed segmentation algorithms, and a database of model clouds created by means of the same scanning system.Experiments carried out to verify the performance of the method have been designed by randomly placing objects of different types in the Robot work area. The preliminary results demonstrate the excellent ability of the system to perform the bin picking procedure, and the reliability of the method proposed for automatic recognition of identity, position and orientation of the objects.     

On the frequency bandwidth change of a servo system with a gear reducer due to backlash and motor input voltage

Summary The paper analyzes how the frequency bandwidth of a servo system is affected by the input voltage of its motor and the magnitude of the total backlash. The bandwidth of the system is defined as the set of antiresonance frequencies, which appears in the frequency-response characteristic. The change in the frequency-response characteristics is investigated depending on motor input voltage and the magnitude of the total backlash. It is shown that at infinite motor input voltage, the servo system has a bandwidth equivalent to that of a backlash-free system. The amount of the systems bandwidth reduction due to the backlash changes greatly with the motor input voltage. It becomes possible then to determine the necessary maximum input voltage of the motor and the admissible magnitude of the total backlash to satisfy the desired bandwidth for a servo system with a gear reducer.     

Computing fence designs for orienting parts

A common task in automated manufacturing processes is to orient parts prior to assembly. We consider sensorless orientation of a polygonal part by a sequence of fences. We show that any polygonal part can be oriented by a sequence of fences placed along a conveyor belt, thereby settling a conjecture by Wiegley et al. (1997), and present the first polynomial-time algorithm to compute the shortest such sequence. The algorithm is easy to implement and runs in time O(n³ logn), where n is the number of vertices of the part.     

AIS Based Distributed Wireless Sensor Network for Mobile Search and Rescue Robot Tracking

This research presents the implementation of GSCF, an AIS-based control framework, on a distributed wireless sensor network for tracking search and rescue robots in open fields. The General Suppression Control Framework (GSCF) is a framework inspired by the suppression hypothesis of the immune discrimination theory. The framework consists of five distinct components; each carries a specific function that can generate long-term and short-term influences to other components by the use of humoral and cellular signals. The goal of the research is to develop mathematical models that can assist the control and analyses of robots behavior through the use of Suppressor Cells in the Suppression Modulator. Acquire data from the physical robot will be used as simulation parameters in future search and rescue research.     

Validation of two reconfigurable wheel-track testbeds for military vehicles

The National Robotics Engineering Center has conceived a novel system that is able to reconfigure from a track to a wheel while in motion. The purpose of this device is to combine the benefits of wheels and tracks to provide performance optimization on a variety of terrain. The first stage of development resulted in two benchtop prototypes: one to test a transition from rotating hub to rotating tread and another to test a constantly-oriented shape transition from circle to triangle. This paper documents the testing of these devices including current draw, temperature change, and braking characteristics. Through experimentation with the first testbed, desired speed was shown to be consistent within +/−6% when transitioning between wheel and track modes at an approximated ground speed between 5 and 35 km/h while transitioning in 5 to 60 seconds. Testing on the second system identified asymmetry in testbed construction and showed consistent loading patterns throughout a 42 mm-change in sprocket position between wheel and track mode while transitioning between 10 and 50 mm/s. The evaluation of these testbeds informed the design of the next process of the reconfigurable wheel-track project, which resulted in a larger prototype capable of propelling a small ground vehicle.     

Energy-based approach for friction identification of robotic joints

In this paper a new open-loop (off-line) identification approach to determine the friction parameters in the joints of robotic manipulators is presented. These friction parameters are the Coulomb friction, Static friction, Stribeck velocity constant and Viscous damping coefficient, referred to as the CSSV.The new friction identification approach introduced in this paper permits the CSSV to be determined by solving a nonlinear optimization problem which is derived using work-energy principle. The corresponding nonlinear optimization problem is solved using an efficient technique which does not require iteration or any initial estimate of the parameters. This new open-loop approach, compared to the available open-loop approaches, has the advantages that do not require the values of the manipulator’s parameters; such as mass or mass moment of inertia of links. Moreover, since this new identification approach is open-loop, it has the superiority that does not require any controller, which is the vital component in the closed-loop identification approaches.The new identification approach proposed here is applicable to the joints of earth-based robotic manipulators whose corresponding links move in the horizontal plane or the joints of space manipulators. The new approach was experimentally verified on a robotic manipulator available in the Robotics Laboratory at the University of Saskatchewan.     

Learning rate free reinforcement learning for real-time motion control using a value-gradient based policy

Reinforcement learning (RL) is a framework that enables a controller to find an optimal control policy for a task in an unknown environment. Although RL has been successfully used to solve optimal control problems, learning is generally slow. The main causes are the inefficient use of information collected during interaction with the system and the inability to use prior knowledge on the system or the control task. In addition, the learning speed heavily depends on the learning rate parameter, which is difficult to tune. In this paper, we present a sample-efficient, learning-rate-free version of the Value-Gradient Based Policy (VGBP) algorithm. The main difference between VGBP and other frequently used algorithms, such as Sarsa, is that in VGBP the learning agent has a direct access to the reward function, rather than just the immediate reward values. Furthermore, the agent learns a process model. This enables the algorithm to select control actions by optimizing over the right-hand side of the Bellman equation. We demonstrate the fast learning convergence in simulations and experiments with the underactuated pendulum swing-up task. In addition, we present experimental results for a more complex 2-DOF robotic manipulator.     

A fractional order control strategy for visual servoing systems

In this paper, a control strategy based on fractional calculus for visual servoing systems is proposed. The image-based control strategy is designed using a point features based fractional-order PI controller. A real-time visual servoing system, composed of a manipulator robot with 6 degrees of freedom (d.o.f.) with an eye-in-hand camera, is used for performance evaluation of the proposed control strategy. The image acquisition and processing, together with the computing of the image-based control law are implemented in MATLAB. Using planar static objects, real-time experiments are conducted and the results reveal that the image-based fractional-order PI controller outperforms the conventional image-based integer-order PI controller.