The International Journal of Robotics Research current issue

Analytic Characterization of a Class of Three-contact Frictional Equilibrium Postures in Three-dimensional Gravitational Environments

Or, Y., Rimon, E. — Wed, 13 Jan 2010 09:43:41 PST

Quasistatic legged locomotion over uneven terrains requires characterization of the mechanism’s feasible equilibrium postures. This paper characterizes the feasible equilibrium postures of mechanisms supported by three frictional point contacts in a three-dimensional gravitational environment, for a subclass of contact arrangements, called tame, for which the friction cones lie above the plane spanned by the contacts. The kinematic structure of the mechanism is lumped into a single rigid body B having the same contacts with the environment and a variable center of mass. The equilibrium postures associated with a given set of contacts become the center-of-mass locations of B that maintain a feasible equilibrium with respect to gravity. The paper establishes the relations between the feasible equilibrium region and the classical support polygon principle. For tame 3-contact arrangements, the paper identifies and characterizes geometrically three types of boundary curves of the feasible equilibrium region, where two of them are obtained is closed-from, and the third is given implicitly as a solution of a set of nonlinear equations, which can be traced numerically. The three types of boundary curves are then associated with the onset of three different modes of non-static contact motions. Finally, the paper reports on experimental results that verify the theoretical predictions by using a 3-legged prototype.

Pneumatic Control of Robots for Rehabilitation

Wolbrecht, E. T., Reinkensmeyer, D. J., Bobrow, J. E. — Wed, 13 Jan 2010 09:43:41 PST

Pneumatic actuators are attractive for robotic rehabilitation applications because they are lightweight, powerful, and compliant, but their control has historically been difficult, limiting their use. In this paper we present the pneumatic control system developed for Pneu-WREX: a pneumatically actuated, upper extremity orthosis for rehabilitation after stroke. The developed pneumatic control system combines several novel components to make the entire system stable, reliable, and backdrivable. These components, which are described in this paper, include: (1) a unique two-valve force control subsystem that keeps chamber pressure low (to reduce friction and energy consumption) and adaptively compensates for leakage; (2) a new servovalve characterization approach that uses experimentally measured data in a combined non-linear and least-squares regression to obtain a linear relationship between mass flow and valve voltage; and (3) a new approach to state estimation using accelerometers and a Kalman filter to obtain clean signals for use in a non-linear adaptive feedback control law. Experimental testing of the device demonstrates the efficacy of the developed pneumatic control system.

A Planar Symmetric Walking Cancellation Algorithm for a Foot--Platform Locomotion Interface

Yoon, J., Park, J., Ryu, J. — Wed, 13 Jan 2010 09:43:41 PST

In this paper we describe a planar symmetric walking cancellation algorithm for generating smooth and collision-free turning motions on the foot—platform locomotion interface, the Virtual Walking Machine that has two three-degree-of-freedom (DOF) planar and three-DOF footpad parallel manipulators connected in series. This solves the problem of the asymmetric walking velocity profile of the swing and stance feet in the existing constant-velocity walking cancellation method. The proposed symmetric walking cancellation method cancels the stance foot motion with the opposite swing foot motion. In addition, the proposed walking cancellation method was extended to a planar walking algorithm that uses constraint motions of curvatures to avoid mechanical collisions between the two foot platforms. Walking simulations, experiments, and user evaluations showed that the proposed symmetric walking cancellation algorithm is better than the previous constant-velocity algorithm in terms of smoothness, absence of delay, and walking stability. For planar motions, the device can generate a maximum turning angle of 20 ^° and a maximum turning velocity of 45 ^° per second for one step with a minimum available curvature of 1 m. Navigation experiments in a virtual environment were performed to show the effectiveness of the suggested planar walking algorithm.

Mimesis Model from Partial Observations for a Humanoid Robot

Lee, D., Nakamura, Y. — Wed, 13 Jan 2010 09:43:41 PST

This paper proposes a new mimesis scheme for partial observations, consisting of two strategies; (1) motion understanding from partial observations and (2) proto-symbol-based motion duplication. With the proposed method, whole-body motion imitation is possible even when observing partial motion data. The scheme enables a humanoid robot to imitate a new observed motion by utilizing its own prior knowledge, without learning the demonstrated motion. Evaluation factors, such as inheritance coordinate and matching error, are introduced to evaluate imitation performance. The feasibility of the proposed scheme is demonstrated by an evaluation for a 20-degree-of-freedom humanoid robot.

The Epi.q-1 Hybrid Mobile Robot

Quaglia, G., Maffiodo, D., Franco, W., Appendino, S., Oderio, R. — Wed, 13 Jan 2010 09:43:41 PST

In this paper we propose an innovative solution for a small size hybrid mobile robot called Epi.q-1. Overall dimensions are about 160 mm x 360 mm x 280 mm (height x length x width). The Epi.q-1 robot moves on flat, steep or uneven ground. It can climb over obstacles or steps, even if they are non-uniform in size. Its operating mode adapts to ground conditions and changes accordingly: from rolling (on wheels) to stepping (on legs); thanks to its great mobility it can follow complex routes. It is easy to control with just a few actuators. Robot locomotion drive-generating units employ an original driving mechanism, where degrees of freedom (DOFs) can be limited to some extent according to the operating conditions or thanks to a switching device. Locomotion units consist of a motor linked to a gear (double epicyclical chain) and an axial device (mini-motor and lead screw system) able to lock or unlock some DOFs of the kinematic chain. Moreover, the robot locomotion unit can change its size, from small to large and vice versa, in order to be able to reach restricted spaces and to overcome even quite tall obstacles. It was experimentally tested on flat ground and slopes. It can overcome 90 mm obstacles, that are 72% of the height of the locomotion unit, and climb stairs.

Distributed Kinematic Motion Control of Multi-Robot Coordination Subject to Physical Constraints

Kim, Y., Minor, M. A. — Wed, 13 Jan 2010 09:43:41 PST

This paper presents a kinematic motion control strategy for an n-axle Compliant Framed Modular wheeled Mobile Robot (CFMMR). This robot is essentially a passive-joint active-wheel snake robot where coordinated motion of the robot modules is critical for maximizing mobility and minimizing traction forces. A distributed master—slave kinematic motion control structure is proposed where the front axle module of the robot is the master and subsequent axle modules are slaves. An existing path manifold based controller is used to guide the motion of the master. Two steering algorithms with different specializations are then proposed for the slave modules. Performance of the steering algorithms is characterized based upon their capability to reduce traction forces, control final robot posture, and maneuver in a limited space. It is shown that these algorithms satisfy the physical constraints of the robot, which are characterized by path curvature and velocity limitations. Simulation and experimental results validate and characterize the performance of the algorithms.

Robotic Routers: Algorithms and Implementation

Tekdas, O., Wei Yang, , Isler, V. — Wed, 13 Jan 2010 09:43:41 PST

Mobile robots equipped with wireless networking capabilities can act as robotic routers and provide network connectivity to mobile users. Robotic routers provide cost-efficient solutions for the deployment of a wireless network in a large environment with a limited number of users. In this paper, we present motion planning algorithms for robotic routers to maintain the connectivity of a single user to a base station. We consider two motion models for the user. In the first model, the user’s motion is known in advance. In the second model, the user moves in an adversarial fashion and tries to break the connectivity. We present optimal motion planning strategies for both models. We also present details of a proof-of-concept implementation.