Yuan-Fang Zheng

Strategies for automatic assembly of deformable objects

Strategies for automatic assembly of deformable objects are presented. A flexible beam mating with a rigid hole is taken as the target of investigation. The deflection behavior of a deformable beam is studied. The geometric and force conditions for successful assembly of rigid parts are reviewed. Based on these conditions, strategies for assembling deformable beams are proposed. The strategies are defined by the motion trajectory of the tool which handles the beam. It is found that when the clearance between the beam and the hole is loose, the desired trajectory should be the same as the curve formed by the deformed beam. When the clearance is tight, the position and orientation of the tool should be adjusted, following the involute of the deformed beam curve.<<ETX>>

Dynamics and Control of Motion on the Ground and in the Air with Application to Biped Robots

The dynamics of a multi-linkage model of natural or man-made systems with arbitrary holonomic and non-holonomic constraints at the joints are formulated. The formulation is equally applicable to movements on the ground or in the air. Nonlinear control strategies for postural balance and rhythmic motion are presented. A predictive algorithm to compensate for computation or transmission delay is proposed. Digital computer simulations are presented to demonstrate the effectiveness of the control strategy for a five-link three-dimensional biped.

Control of the heel-off to toe-off motion of a dynamic biped gait

A mechanism for the control of the heel off to toe off motion of a dynamic biped gait is presented in this paper. It is argued that the reaction force between the ground and the biped foot is an important factor in a satisfactory implementation of dynamic gait. This force must be properly controlled while the foot is in the heel off to toe off phase. Since the foot rolls over the ground surface in this phase, and the global description of the surface is unknown, the foot has to execute a nonholonomic constraint motion. The formulations of nonholonomic constraints and system dynamics under the constraints are derived for the roll-over motion. A feedback control mechanism is designed based on the formulations.<<ETX>>

Pattern generation using coupled oscillators for robotic and biorobotic adaptive periodic movement

In this study, a coupled pattern generator is used to achieve rhythmic gait movements by a planar five-link musculoskeletal biped model. In particular, five coupled oscillators are designed which provide the biped with the desired joint angles while a controller tracks the specified trajectories. The system is adaptive in that a high-level parameter controller can adjust the parameters of the pattern generator to change the frequency of the desired joint trajectories. Simulations show the biped walking while changing frequency of the gait as its joint angles track the pattern generator.

Muscle Dynamics, Size Principle, and Stability

A mathematical model of skeletal muscle activation during small or isometric movements is discussed with the following attributes. A direct relationship between the stimulus rate and the active state is established. A piecewise linear relation between the length of the contractile element and the isometric force is considered. Hills characteristic equation is maintained for determining the actual output force during different shortening velocities. A physical threshold model is proposed for recruitment which encompasses the size principle and its manifestations and also exceptions to the size principle. Finally, the role of spindle feedback in stability of the model is demonstrated by studying a pair of muscles.

Coordinating multilimbed robots for generating large Cartesian force

The coordination of the arm and main body of multilimbed robots to generate large Cartesian forces is discussed. Two methods are developed. In the first method, motions for the arm and main body are separately considered. For a given Cartesian force, an optimal configuration is determined for the arm. Based on the arm configuration, the main body is adjusted to satisfy the constraints of the position and orientation of the end-effector. To reduce the energy consumption, the nonlinear programming techniques could be further applied to the main body to obtain an optimal configuration. The second method treats the multilimbed robot as a single system and directly applies the nonlinear programming technique to the arm and main body with the arm torque limitation as an added set of constraints. Since the multilimbed robot is considered as a single system, the method had the least sense of coordination and is computationally more complicated than the first method.<<ETX>>

Vibration-free movement of deformable beams by robot manipulator

Passive approaches for vibration-free handling of deformable beams are investigated. Dynamic equations are formulated. Trajectory plannings of the end-effector which lead to a small vibration of the beam in three-motion patterns are specified. Since vibrations cannot be totally eliminated, another passive approach, which uses a rubber pad in parallel with a spring installed on the fingers of the end-effector, is suggested. To understand the effectiveness of this passive approach, damped vibration and optimal damping are studied. Two experiments are conducted to verify the above methods.<<ETX>>

Experimental study of a cable-driven suspended platform

We present the design of an experimental prototype cable-driven suspended platform for robotic applications, and the feasibility of using this platform in certain industrial applications is considered. In order to study and improve dynamic stability, the point-to-point motion of the platform is observed and analyzed in a laboratory environment. To focus the study, the domain of experiments is restricted to only two-dimensional space. At the starting point, or departure, the platform displays a lag and at the destination, or terminal point, the platform has a significant overshoot which causes a large settling time. Certain methods are suggested and implemented for damping the oscillation and decreasing the settling time. In the three-dimensional domain, two experiments are performed: one experiment is devoted to drilling holes in a piece of wood and another to loosening a nut.

Performance analysis of token bus LAN in coordinating multiple robots

Using Local Area Network (LAN) to coordinate multiple industrial robots in a multi-robot system (workcell) is studied in this paper. The properties of the multiple robot coordination task are first discussed. Then, a method is proposed to evaluate a pre-defined task decomposition and allocation scheme for the coordination task, In this method, a parameter called effective token passing ratio is defined to measure how efficient the scheme is when the token bus LAN is used as the communication medium. A lower bound of the effective token passing ratio is analytically determined based on time constraints imposed on the task. By using this method, one does not need to determine the communication delay and computation time of individual tasks (or subtasks) decomposed from the ccordination task, Instead, one can compare the effective token passing ratio of the network with the lower bound. From the comparison, it can be determined whether the task decomposition and allocation scheme is appropriate. The probability that real-time coordination is successful is also computed.

A three-link module for modular dynamics and control of high-dimensional humanoids

Modeling complicated dynamics of humanoids is considered in this paper. It is proposed that the three-link module is a pivotal element in formulation of high-dimensional humanoids. The equations of motion of the module are first derived by projection of the free body equations of motion onto the space of the translation of an arbitrary point and Bryant angles and angular velocities. It is then shown that the formulation can be used as a construction module for systems with a larger number of segments. Holonomic and nonholonomic constraints are included to show the feasibility and versatility for representing other parts of the humanoid system. Digital computer simulations are presented to test the modules formulation and demonstrate its behavior in two maneuvers, jumping and sway.