637 research outputs found
Chat-PM: A Class of Composite Hybrid Aerial/Terrestrial Precise Manipulator
This paper concentrates on the development of Chat-PM, a class of composite
hybrid aerial/terrestrial manipulator, in concern with composite configuration
design, dynamics modeling, motion control and force estimation. Compared with
existing aerial or terrestrial mobile manipulators, Chat-PM demonstrates
advantages in terms of reachability, energy efficiency and manipulation
precision. To achieve precise manipulation in terrestrial mode, the dynamics is
analyzed with consideration of surface contact, based on which a cascaded
controller is designed with compensation for the interference force and torque
from the arm. Benefiting from the kinematic constraints caused by the surface
contact, the position deviation and the vehicle vibration are effectively
decreased, resulting in higher control precision of the end gripper. For
manipulation on surfaces with unknown inclination angles, the moving horizon
estimation (MHE) is exploited to obtain the precise estimations of force and
inclination angle, which are used in the control loop to compensate for the
effect of the unknown surface. Real-world experiments are performed to evaluate
the superiority of the developed manipulator and the proposed controllers
Locomotion training of legged robots using hybrid machine learning techniques
In this study artificial neural networks and fuzzy logic are used to control the jumping behavior of a three-link uniped robot. The biped locomotion control problem is an increment of the uniped locomotion control. Study of legged locomotion dynamics indicates that a hierarchical controller is required to control the behavior of a legged robot. A structured control strategy is suggested which includes navigator, motion planner, biped coordinator and uniped controllers. A three-link uniped robot simulation is developed to be used as the plant. Neurocontrollers were trained both online and offline. In the case of on-line training, a reinforcement learning technique was used to train the neurocontroller to make the robot jump to a specified height. After several hundred iterations of training, the plant output achieved an accuracy of 7.4%. However, when jump distance and body angular momentum were also included in the control objectives, training time became impractically long. In the case of off-line training, a three-layered backpropagation (BP) network was first used with three inputs, three outputs and 15 to 40 hidden nodes. Pre-generated data were presented to the network with a learning rate as low as 0.003 in order to reach convergence. The low learning rate required for convergence resulted in a very slow training process which took weeks to learn 460 examples. After training, performance of the neurocontroller was rather poor. Consequently, the BP network was replaced by a Cerebeller Model Articulation Controller (CMAC) network. Subsequent experiments described in this document show that the CMAC network is more suitable to the solution of uniped locomotion control problems in terms of both learning efficiency and performance. A new approach is introduced in this report, viz., a self-organizing multiagent cerebeller model for fuzzy-neural control of uniped locomotion is suggested to improve training efficiency. This is currently being evaluated for a possible patent by NASA, Johnson Space Center. An alternative modular approach is also developed which uses separate controllers for each stage of the running stride. A self-organizing fuzzy-neural controller controls the height, distance and angular momentum of the stride. A CMAC-based controller controls the movement of the leg from the time the foot leaves the ground to the time of landing. Because the leg joints are controlled at each time step during flight, movement is smooth and obstacles can be avoided. Initial results indicate that this approach can yield fast, accurate results
Real-time biped character stepping
PhD ThesisA rudimentary biped activity that is essential in interactive evirtual worlds, such as
video-games and training simulations, is stepping. For example, stepping is fundamental in everyday terrestrial activities that include walking and balance recovery.
Therefore an effective 3D stepping control algorithm that is computationally fast
and easy to implement is extremely valuable and important to character animation
research. This thesis focuses on generating real-time controllable stepping motions
on-the-fly without key-framed data that are responsive and robust (e.g.,can remain
upright and balanced under a variety of conditions, such as pushes and dynami-
cally changing terrain). In our approach, we control the character’s direction and
speed by means of varying the stepposition and duration. Our lightweight stepping
model is used to create coordinated full-body motions, which produce directable
steps to guide the character with specific goals (e.g., following a particular path
while placing feet at viable locations). We also create protective steps in response
to random disturbances (e.g., pushes). Whereby, the system automatically calculates where and when to place the foot to remedy the disruption. In conclusion,
the inverted pendulum has a number of limitations that we address and resolve
to produce an improved lightweight technique that provides better control and
stability using approximate feature enhancements, for instance, ankle-torque and
elongated-body
Review article: locomotion systems for ground mobile robots in unstructured environments
Abstract. The world market of mobile robotics is expected to increase substantially in the next 20 yr, surpassing the market of industrial robotics in terms of units and sales. Important fields of application are homeland security, surveillance, demining, reconnaissance in dangerous situations, and agriculture. The design of the locomotion systems of mobile robots for unstructured environments is generally complex, particularly when they are required to move on uneven or soft terrains, or to climb obstacles. This paper sets out to analyse the state-of-the-art of locomotion mechanisms for ground mobile robots, focussing on solutions for unstructured environments, in order to help designers to select the optimal solution for specific operating requirements. The three main categories of locomotion systems (wheeled - W, tracked - T and legged - L) and the four hybrid categories that can be derived by combining these main locomotion systems are discussed with reference to maximum speed, obstacle-crossing capability, step/stair climbing capability, slope climbing capability, walking capability on soft terrains, walking capability on uneven terrains, energy efficiency, mechanical complexity, control complexity and technology readiness. The current and future trends of mobile robotics are also outlined
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