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Biological cell injection is laborious work that requires lengthy training and suffers from a low success rate. In this paper, a robotic cell-injection system for automatic injection of batch-suspended cells is proposed. To facilitate the process, these suspended cells are held and fixed to a cell array by a specially designed cell-holding device, and injected one by one through an "out-of-plane" cell-injection process. A micropipette equipped with a polyvinylidene fluoride microforce sensor to measure real-time injection force is integrated in the proposed system. Through calibration, an empirical relationship between the cell-injection force and the desired injector pipette trajectory is obtained in advance. Then, after decoupling the out-of-plane cell injection into a position control in the X-Y horizontal plane and an impedance control in the Z-axis, a position and force control algorithm is developed to control the injection pipette. The depth motion of the injector pipette, which cannot be observed by microscope, is indirectly controlled via the impedance control, and the desired force is determined from the online X-Y position control and cell calibration results. Finally, experimental results demonstrate the effectiveness of the proposed approach. Index Terms--Batch biomanipulation, cell-holding device, position and force control, robotic cell injection.

In this paper, we propose a visual-servo-control approach and a two-stage grasping strategy and, then, develop control software to perform micrograsping tasks, i.e., to control a passive microgripper to automatically grasp a micropart, in a 2-D plane with high accuracy. In the proposed control scheme, we employ closed-loop control with the use of two position feedback signals: relative positions of the micropart with respect to the microgripper measured by the vision-control system and absolute displacements of the micropart measured by linear encoders. To improve the grasping efficiency and success rate, a two-stage grasping strategy is employed: 1) the bonded microgripper is controlled to directly reach a specific position adjacent to the mating edge of a designated micropart with the same y coordinate, by matching the patterns of the microgripper and the micropart only once, and 2) finely align the micropart with the microgripper along the x and y translation axes of the microassembly robot in the horizontal plane by employing the proposed visual servo control, until the micropart is completely grasped. Experiments conducted with a 6-DOF microassembly robot demonstrate the efficiency and validity of the proposed control approach and grasping strategy. Index Terms--Microassembly, visual servo control, 2-D.

Arm-free paraplegic standing via functional electrical stimulation (FES) has drawn much attention in the biomechanical field as it might allow a paraplegic to stand and simultaneously use both arms to perform daily activities. However, current FES systems for standing require that the individual actively regulates balance using one or both arms, thus limiting the practical use of these systems. The purpose of the present study was to show that actuating only six out of 12 degrees of freedom (12-DOFs) in the lower limbs to allow paraplegics to stand freely is theoretically feasible with respect to multibody stability and physiological torque limitations of the lower limb DOE Specifically, the goal was to determine the optimal combination of the minimum DOF that can be realistically actuated using FES while ensuring stability and able-bodied kinematics during perturbed arm-free standing. The human body was represented by a three-dimensional dynamics model with 12-DOFs in the lower limbs. Nakamura's method (Nakamura, Y., and Ghodoussi, U., 1989, 'Dynamics Computation of Closed-Link Robot Mechanisms With Nonredundant and Redundant Actuators,' IEEE Trans. Rob. Autom., 5(3), pp. 294-302) was applied to estimate the joint torques of the system using experimental motion data from four healthy subjects. The torques were estimated by applying our previous finding that only 6 (6-DOFs) out of 12-DOFs in the lower limbs need to be actuated to facilitate stable standing. Furthermore, it was shown that six cases of 6-DOFs exist, which facilitate stable standing. In order to characterize each of these cases in terms of the torque generation patterns and to identify a potential optimal 6-DOF combination, the joint torques during perturbations in eight different directions were estimated for all six cases of 6-DOFs. The results suggest that the actuation of both ankle flexion/extension, both knee flexion/extension, one hip flexion/extension, and one hip abduction/adduction DOF will result in the minimum torque requirements to regulate balance during perturbed standing. To facilitate unsupported FES-assisted standing, it is sufficient to actuate only 6-DOFs. An optimal combination of 6-DOFs exists, for which this system can generate able-bodied kinematics while requiring lower limb joint torques that are producible using contemporary FES technology. These findings suggest that FES-assisted arm-free standing of paraplegics is theoretically feasible, even when limited by the fact that muscles actuating specific DOFs are often denervated or difficult to access. [DOI: 10.1115/1.2800767] Keywords: functional electrical stimulation, inverse dynamics, paraplegia, perturbed standing, torque estimation

In this paper, we develop a new control method, termed adaptive synchronized (A-S) control, for improving tracking accuracy of a P-R-R type planar parallel manipulator with parametric uncertainty. The novelty of A-S control, a combination of synchronized control and adaptive control, is in the application of synchronized control to a single parallel manipulator so that tracking accuracy is improved during high-speed, high-acceleration tracking motions. Through treatment of each chain as a submanipulator; the P-R-R manipulator is thus modeled as a multi-robot system comprised of three submanipulators grasping a common payload. Considering the geometry of the platform, these submanipulators are kinematically constrained and move in a synchronous manner. To solve this synchronization control problem, a synchronization error is defined, which represents the coupling effects among the submanipulators. With the employment of this synchronization error, tracking accuracy of the platform is improved. Simultaneously, the estimated unknown parameters converge to their true values through the use of a bounded-gain-forgetting estimator. Experiments conducted on the P-R-R manipulator demonstrate the validity of the approach. [DOI: 10.1115/1.2363200]

This paper presents a novel method for the scheduling and control of flexible manufacturing cells (FMCs). The approach employs automata, augmented by time labels proposed herein, for the modeling of machines, transportation devices, buffers, precedence constraints, and part routes. Ramadge-Wonham's supervisory-control theory is then used to synthesize a deadlock-free controller that is also capable of keeping track of time. For a given set of parts to be processed by the cell, A* search algorithm is subsequently employed using a proposed heuristic function. Three different production configurations are considered: Case 1) each part has a unique route; Case 2) parts may have multiple routes, but same devices in each route; and Case 3) parts may have multiple routes with different devices. The proposed approach yields optimal deadlock-free schedules for the first two cases. For Case 3, our simulations have yielded effective solutions but in practice, optimal deadlock-free schedules may not be obtainable without sacrificing computational time efficiency. One such nontime-efficient method is included in this paper. The proposed approach is illustrated through three typical manufacturing-cell simulation examples, the first adopted from a Petri-net-based scheduling paper, the second adopted from a mathematical-programming-based scheduling paper, and the third, a new example that deals with a more complex FMC scenario where parts have multiple routes for their production. These and other simulations clearly demonstrate the effectiveness of the proposed automata-based scheduling methodology. Index Terms--Automata, deadlock-free scheduling, heuristic search, supervisor) control.

High-precision motion of parallel manipulators depends not only on the position accuracy of each actuator, but also on the position synchronization of all actuators. This paper presents a simple synchronized control algorithm for the setpoint position control of parallel manipulators, by incorporating cross-coupling technology into a common proportional-derivative (PD) control architecture. An integrated controller is developed, consisting of a PD control and a saturated proportional-integral (S-PI) control with feedback of the differential position errors amongst actuators (defined as the synchronization errors). The controller can stabilize the motion of each actuator, and meanwhile synchronize all actuators' motions so that both position and synchronization errors converge to zero. The control algorithm dues not use the modeling parameters in the controller formulation, and thus permits easy implementation in practice. It is proved that the proposed method can guarantee global asymptotical stability of the system. Experiments conducted on a planar three-degree-of-freedom parallel manipulator demonstrate the effectiveness of the proposed approach. Index Terms--Cross-coupling control, parallel manipulators, proportional-derivative (PD) control, saturated proportional-integral (S-PI) control, synchronization.

In this paper, a new integrated design method, referred to as the extended multiple simultaneous specification (EMSS) method, is proposed to solve simultaneous mechanical structure and control system design problems in which a set of n multiple closed-loop performance specifications must be simultaneously satisfied. To utilize this approach, all closed-loop performance specifications considered must have the property that they are convex with respect to the closed-loop system transfer matrix. With the proposed approach, a simply implemented two-stage design approach is used to determine a set of open-loop mechanical system design parameters and a closed-loop controller which simultaneously satisfies a set of n closed-loop performance specifications. In the first stage, for each closed-loop performance specification, one 'sample system,' i.e., the closed-loop system with one set of mechanical design parameters with a closed-loop controller chosen from the set of all linear controllers, is determined by trial and error, such that the specification is satisfied. In the second stage, the transfer matrix of the final system, which satisfies all n performance specifications, is determined through the convex combination of the transfer matrices of n sample systems. A linear programming problem is solved to give the combination vector for this convex combination. With the closed-loop transfer matrix given, the mechanical design parameters, the closed-loop controller structure and its gains, are solved algebraically. In this paper, we establish conditions for the existence of a solution to this integrated design problem as well as prove that the EMSS approach retains the stability properties of the sample systems. Experimental results of the EMSS method, carried out on a linear positioning system are given, verifying the effectiveness of the proposed method. We note that the proposed EMSS method works well when the number of design parameters to be determined is small. Further, the proposed EMSS method also has some utility as a controller design method, to determine a closed-loop controller that satisfies a set of n multiple closed-loop performance specifications, given a fixed mechanical system structure. Keywords: Simultaneous Design, Integrated Design, Integrated System Design, Convex Approach, Mechanical Structure, Control Design, Multiple Closed-Loop Performance Specifications

This paper describes a novel microassembly system that can be used to construct out-of-plane three-dimensional (3-D) microstructures. The system makes use of a surface-micromachined microgripper that is solder bonded to a robotic manipulator. The microgripper is able to grasp a micropart, remove it from the chip, reorient it about two independent axes, translate it along the x, y and z axes to a secondary location, and join it to another micropart. In this way, out-of-plane 3-D microstructures can be assembled from a set of initially planar and parallel surface micromachined microparts. The microgripper is 380 x 410 [micro]m in size. It utilizes three geometric features for operation: 1) compliant beams to allow for deflection at the grasping tips; 2) self-tightening geometry during grasping; and 3) 3-D interlocking geometry to secure a micropart after the grasp. Each micropart has three geometric features built into its body. The first is the interlock interface feature that allows it to be grasped by the microgripper. The second is a tether feature that secures the micropart to the substrate, and breaks away after the microgripper has grasped the micropart. The third is the snap-lock feature, which is used to join the micropart to other microparts. [1061] Index Terms--Compliant, joint, microelectromechanical systems (MEMS), microgripper, microassembly, microstructure, micropart, snap-lock microjoint, three-dimensional (3-D).

Coordination of multirobot systems has received extensive studies in the past decade. The majority of previous approaches require a complex setup of the hybrid position/force-control architecture, and have not fully addressed the coordination problem when the robots are not kinematically constrained but perform a common task. In this paper, we propose to use a new coordination scheme that is more straightforward and easier to implement and is applicable to a wider area. The basic idea of the new coordination strategy is to use the concept of motion synchronization, since the problem of coordinating multiple manipulators is basically the problem of maintaining certain kinematic relationships amongst robots. The key to the success of the new method is to ensure that each manipulator tracks its desired trajectory while synchronizing its motion with other manipulators' motions, so that differential (or synchronization) position errors amongst manipulators converge to zero. The controller, designed by incorporating the cross-coupling technology into an adaptive-control architecture, successfully guarantees asymptotic convergence to zero of both position tracking and synchronization errors simultaneously. Experiments and simulations on multirobot assembly systems demonstrate the effectiveness of the approach. Index Terms--Adaptive control, coordination, cross-coupling, multirobot, synchronization.