Equilibrium, Stability, and Robustness in Underactuated Grasping

This paper aims to develop a performance measure for underactuated grasping devices, which is useful in making design decisions to obtain an optimally performing device. Underactuated fingers, defined as having more degrees of freedom than degrees of actuation, intrinsically adapt their shape to the object. However, the equilibrium configuration and grasp forces of these fingers are not fully controllable, which may limit their performance. The grasp performance measure defined in this paper consists of three aspects: (1) the ability to grasp objects, which is limited by the equilibrium conditions and constraints of both the underactuated fingers and the freely movable object; (2) the grasp stability, which takes the passive compliance of the fingers into account; (3) the ability to oppose disturbance forces on the grasped object by passively adapting the frictional grasp forces. This measure was applied to optimize a planar grasping device with two underactuated fingers, each consisting of two phalanges, able to grasp freely moving circular objects.

Reverse Kinematic Analysis of the Spatial Six Axis Robotic Manipulator With Consecutive Joint Axes Parallel

This paper introduces a reconfigurable one degree-of-freedom spatial mechanism that can be applied to repetitive motion tasks. The concept is to incorporate five pairs of noncircular gears into a six degree-of-freedom closed-loop spatial chain. The gear pairs are designed based on the given mechanism parameters and the user defined motion specification of a coupler link of the mechanism. It is shown in the paper that planar gear pairs can be used if the spatial closed-loop chain is comprised of six pairs of parallel joint axes, i.e. the first joint axis is parallel to the second, the third is parallel to the fourth, …, and the eleventh is parallel to the twelfth. This paper presents the detailed reverse kinematic analysis of this specific geometry. A numerical example is presented.

Design of a High-Speed Spherical Four-Bar Mechanism for Use in a Motion Common in Assembly Processes

In this paper, we present the mechanical design of a spherical four-bar mechanism for performing a motion common in manufacturing and assembly processes. The mechanism is designed to create, in a single, smooth motion, the combined rotation of a body by 90 degrees about one axis with a 90 degree rotation about an axis perpendicular to the first. A spherical four-bar mechanism is pursued as the basis for the design because the reorientation is produced mechanically rather than via a control scheme typical when higher degree of freedom systems are utilized. The design initiates with the kinematic synthesis of the spherical mechanism to guide a body through two orientations. The next step in the design is to refine the spherical fourbar based on manufacturing and operational concerns. As one of the challenges of utilizing these four-bars is tuning the starting and ending angle for the mechanism’s motion, a sensitivity analysis is performed to gauge the needed accuracy. Finally, there are details and a discussion of the proposed mechanical design.

Modal Characterization of the Instantaneous Mobility of Manipulators

In this paper, a computational approach suitable to compute the instantaneous mobility of manipulators in any kind of configuration (either singular or nonsingular) using a general purpose software is presented. Although the procedure is applicable to any formulation of the velocity equation, in this paper authors have used a point-based jacobian formulation of the manipulator. The end-effector’s instantaneous mobility is analyzed, first discriminating among its rotational, translational and passive freedoms, and then computing its principal screws. Then, either its instantaneous screw systems or certain instantaneous pitch surfaces can be depicted. The approach is illustrated with its application to the 3-URU DYMO parallel manipulator.

Structural Vibration Control of a Moving 3-PRR Flexible Parallel Manipulator With Multiple PZT Actuators and Sensors

This paper addresses the control of structural vibrations of a 3-PRR parallel manipulator with three flexible intermediate links, bonded with multiple lead zirconate titanate (PZT) actuators and sensors. Flexible intermediate links are modeled as Euler-Bernoulli beams with pinned-pinned boundary conditions. A PZT actuator controller is designed based on strain rate feed control (SRF). Control moments from PZT actuators are transformed to force vectors in modal space, and are incorporated in the dynamic model of the manipulator. The dynamic equations are developed based on the assumed mode method for the flexible parallel manipulator with multiple PZT actuator and sensor patches. Numerical simulation is performed and the results indicate that the proposed active vibration control strategy is effective. Frequency spectra analyses of structural vibrations further illustrate that deformations from structural vibration of flexible links are suppressed to a significant extent when the proposed vibration control strategy is employed, while the deflections caused by inertial and coupling forces are not reduced.

Optimal Reduction Ratio Selection for the Driving System of a Novel High-Speed Parallel Manipulator

The reduction ratio of the driving system plays a very important role in the accelerating and decelerating capacity for a parallel manipulator. In this paper, the virtual work principle was employed to develop the inverse dynamics model of a novel high-speed parallel manipulator. A new S-curve speed profile was introduced and adopted to plan the trajectory of the end-effecter of the manipulator in the operation space. Aiming at the minimal operation time, a reduction ratio optimal selection method of the driving system was presented, which can make full use of the advantages of the AC servomotor and consequently reduce the cost of the manipulator.

HLPR Chair: A Novel Indoor Mobility-Assist and Lift System

This paper describes a novel Home Lift, Position, and Rehabilitation (HLPR) Chair, designed at National Institute of Standards and Technology (NIST), to provide independent patient mobility for indoor tasks, such as moving to and placing a person on a toilet or bed, and lift assistance for tasks, such as accessing kitchen or other tall shelves. These functionalities are currently out of reach of most wheelchair users. One of the design motivations of the HLPR Chair is to reduce back injury, typically, an important issue in the care of this group. The HLPR Chair is currently being extended to be an autonomous mobility device to assist cognition by route and trajectory planning. This paper describes the design of HLPR Chair, its control architecture, and algorithms for autonomous planning and control using its unique kinematics.

Dynamics Design of a Planar Controllable Five Bar Mechanism Based on Genetic Algorithm

A hybrid five bar mechanism is a typical planar parallel robot. It is a configuration that combines the motions of two characteristically different motors by means of a five bar mechanism to produce programmable output. Hybrid five bar mechanism is the most representative one of hybrid mechanism. In this paper, considering the bond graph can provide a compact and versatile representation for kinematics and dynamics of hybrid mechanism, the dynamics analysis for a hybrid five-bar mechanism based on power bond graph theory is introduced. Then an optimization design of hybrid mechanism is performed with reference to dynamic objective function. By the use of the properties of global search of genetic algorithm (GA), an improved GA algorithm is proposed based on real-code. Optimum dimensions are obtained assuming there are no dimensional tolerances or clearances. Finally, a numerical example is carried out, and the simulation result shows that the optimization method is feasible and satisfactory in the design of hybrid mechanism.

Robustness and Controllability Analysis for Autonomous Navigation of Two-Wheeled Mobile Robots

This work deals with the robustness and controllability analysis for autonomous navigation of two-wheeled mobile robots. The analysis of controllability of the systems at hand is conducted using both the Kalman rank condition for controllability and the Lie Algebra rank condition. We show that the robots targeted in this work can be controlled using a model for autonomous navigation by means of their dynamics model: kinematics will not be sufficient to completely control these underactuated systems. After having proven that these autonomous robots are small-time locally controllable from every equilibrium point and locally accessible from the remaining points, the uncertainty is modeled resorting to a multiplicative approach. The dynamics response of these robots is analyzed in the frequency domain. Upper bounds for the complex uncertainty are established.

Design and Development of a Novel Infant Surgical Table for 4-DOF Patient Manipulation

Retinopathy of Prematurity, caused by abnormal blood vessel development in the retina of premature infants, is a leading cause of childhood blindness. It is treated using laser photocoagulation. Current methods require the surgeon to assume awkward standing positions, which can result in injury to the surgeon if repeated often. To assist surgeons in providing quality care and prevent occupational injury, a new infant surgical table was designed. The engineered solution is an attachment to a standard surgical table, saving cost and space. This takes advantage of the adjustable height and tilt provided by the standard table, while 360° rotation designed into the attachment allows the surgeon to sit during surgery. The critical cords and tubes are routed through the attachment to avoid pulling and kinking. A four-bar locking mechanism allows easy attachment to standard medical railing. Finally, a straight line mechanism provides positive locking of the rotation, allowing precise positioning of the infant.