James K. Mills

Microassembly of 3-D microstructures using a compliant, passive microgripper

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 /spl times/ 410 /spl mu/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.

Robotic Cell Injection System With Position and Force Control: Toward Automatic Batch Biomanipulation

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 ldquoout-of-planerdquo 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.

A PZT actuator control of a single-link flexible manipulator based on linear velocity feedback and actuator placement

This paper describes an approach for the use of smart materials, specifically, piezoelectric materials (PZT), in control of a single-link flexible manipulator. It is investigated by a Lyapunov approach that a combined scheme of PD feedback and command voltages applied to segmented PZT actuators, which are bonded to the surface of the flexible link, can effectively control the rigid body motion and at the same time, damp link vibrations. The unique features of the proposed PZT actuator control are twofolds: First, it utilizes linear in contrast to angular velocities of particular points on the link, signals which are readily available. Second, the actuator placement is examined based on the analysis of mode shape functions. Stability of the system with the proposed PZT actuator control is analyzed using a virtual joint model. Simulation and experimental results confirm these theoretical predictions.

Control of Robotic Manipulators During General Task Execution: A Discontinuous Control Approach

In this article, a control methodology is proposed that ad dresses the problem of control of robotic manipulators during a general class of task that requires the manipulator to make a transition from (I) noncontact motion to contact motion and (2) contact motion to noncontact motion. Specifically, the problem of control of a general n-degree-of-freedom rigid-link robotic manipulator during a general class of tasks, as described ear lier, is treated. It is assumed that during the contact phase of the assumed task, frictionless point contact is made with fixed objects in the manipulator work environment, which is modeled as a linear mechanical impedance. Furthermore, it is assumed that exact knowledge of the manipulator and work environment kinematic and dynamic parameters is available. The following closed-loop behavior is achieved with the pro posed control law: (1) the closed-loop system exhibits global asymptotic stability; (2) asymptotic trajectory tracking of gen eralized force and position inputs is achieved; and significantly, (3) on inadvertent loss of contact by the manipulator, contact is reestablished, and generalized forces and positions are again asymptotically achieved. This closed-loop behavior is achieved in the presence of collisions between the manipulator and ob jects in the manipulator work environment; such collisions may include multiple impacts as a result of bouncing on initial contact. A general mathematical framework is established to prove that the closed-loop robotic system, with a discontin uous control applied, is asymptotically stable. Experimental results performed on a two-degree-of-freedom direct-drive robot support the theoretical claims made in this work.

Visual-Based Impedance Control of Out-of-Plane Cell Injection Systems

In this paper, a vision-based impedance control algorithm is proposed to regulate the cell injection force, based on dynamic modeling conducted on a laboratory test-bed cell injection system. The injection force is initially calibrated to derive the relationship between the force and the cell deformation utilizing a cell membrane point-load model. To increase the success rate of injection, the injector is positioned out of the focal plane of the camera, used to obtain visual feedback for the injection process. In this out-of-plane injection process, the total cell membrane deformation is estimated, based on the X-Y coordinate frame deformation of the cell, as measured with a microscope, and the known angle between the injector and the X-Y plane. Further, a relationship between the injection force and the injector displacement of the cell membrane, as observed with the camera, is derived. Based on this visual force estimation scheme, an impedance control algorithm is developed. Experimental results of the proposed injection method are given which validate the approach.

Energy Management Control of Microturbine-Powered Plug-In Hybrid Electric Vehicles Using the Telemetry Equivalent Consumption Minimization Strategy

This paper presents a novel approach to the solution of the energy management problem of a microturbine-powered plug-in hybrid electric vehicle (PHEV). A series hybrid midsize sedan, utilizing a microturbine and a chargeable Li-ion battery stack as its primary energy source and energy storage system, respectively, is modeled in this paper. The equivalent consumption minimization strategy (ECMS) is utilized to minimize the driving cost based on Pontryagins minimum principle. To identify the equivalent factor (EF), a new concept called the energy ratio is defined, which is demonstrated to be closely related to the EF over all possible trips. By detecting the vehicle position with a telemetry system and measuring the battery state of charge (SOC), the EF is updated in real time and is used as an input for the computation of the ECMS. Simulation results demonstrate that the proposed ECMS exhibits driving cost and diesel consumption equivalent to that determined from numerical dynamic programming. Significantly, the proposed approach reduces the driving cost from 7.7% to 21.6%, compared with a baseline control over both urban and highway cycles. In addition, through numerical simulations, the computational cost of the proposed strategy is demonstrated to be acceptable for industrial applications. Furthermore, because this strategy uses the feedback of the battery SOC, the control performance is insensitive to the control parameter errors.

Dynamic Modeling and Experimental Validation of a 3-PRR Parallel Manipulator with Flexible Intermediate Links

This paper presents the development of structural dynamic equations of motion for a 3-PRR parallel manipulator with three flexible intermediate links, based on the assumed mode method. Lagrange’s equation is used to derive the dynamic model of the manipulator system. Flexible intermediate links are modeled as Euler–Bernoulli beams with pinned–pinned boundary conditions. Dynamic equations of motion of a 3-PRR parallel manipulator with three flexible links are developed by adopting the assumed mode method. The effect of concentrated rotational inertia at both ends of intermediate links is included in this model. Numerical simulations of vibration responses, coupling forces and inertial forces are presented. The corresponding frequency spectra analysis is performed using the Fast Fourier Transform (FFT). Experimental modal tests are performed to validate the theoretical model through comparison and analysis of modal characteristics of the flexible manipulator system.

Manipulator transition to and from contact tasks: a discontinuous control approach

The stability and control of robotic manipulators during the execution of tasks that require the manipulator to make a transition from noncontact motion to contact motion, or vice versa, are investigated. A dynamic model of the manipulator during noncontact and contact motion is developed. This model includes the effect of the inevitable collision that occurs between the manipulator end effector and the work environment during the transition from noncontact to contact motion. The work environment that the manipulator comes into contact with is modeled as a very still surface. The dynamic model of the robot during this transition is transformed through a nonlinear coordinate transformation into a new set of generalized coordinates in which the form of the dynamics is greatly simplified. A discontinuous control is proposed for the robotic manipulator system. It is shown that with this discontinuous control applied to the system, the closed-loop system can be treated as a generalized dynamical system. Using the theory associated with generalized dynamical systems, it is possible to extend Lyapunov stability analysis to systems with discontinuous controls. The system dynamics is written as a contingent equation to which a set valued control function is applied. Within this mathematical framework, the uniform asymptotic stability in the larger of the closed-loop systems is proved. The controller has several desirable properties, including the ability to return to contact motion if the manipulator end effector inadvertently leaves the surface due to some external disturbance acting on the system.<<ETX>>

Development of a 6 degree of freedom robotic micromanipulator for use in 3D MEMS microassembly

This paper describes the design and development of a 6 degree of freedom robotic manipulator used in the assembly of three-dimensional MEMS (micro electromechanical systems) microstructures. The robot employs a highly innovative mechanical design for the rotational axes to provide unprecedented access to a microchip substrate for microassembly operations. The first three axes of the robotic manipulator are orthogonally mounted linear stages providing Cartesian positioning of the chips beneath the end effector (microgripper). A rotational stage (alpha) mounted on the distal end of these three Cartesian axes allows the MEMS chip to be rotated. Two more degrees of freedom (beta and gamma) are serially mounted to the base frame, allowing for two degrees of rotation of the end effector. This configuration permits assembly of micro-parts on the surface of a MEMS chip at any orientation angle to the surface, within the limits of the workspace of the manipulator and the resolution of the motors. The end effector employs a standard tungsten probe with a passive microgripper bonded to it, which is used for grasping micro-parts. A software system has been developed to allow automatic operation of the manipulator. Preliminary assembly tests confirm the usefulness of the proposed design

Synchronous Tracking Control of Parallel Manipulators Using Cross-coupling Approach

This paper presents a cross-coupled control approach to the tracking control of parallel manipulators in a synchronous manner. Based on the synchronization goal, the position synchronization error is investigated by considering motion synchronization between each actuator joint and its adjacent ones. A decentralized trajectory tracking controller is then developed with feedback of both position and synchronization errors, formed with a combination of feedforward, feedback and a saturation control. It is proven that this tracking controller can asymptotically stabilize both position and synchronization errors of the system. The proposed controller does not require the explicit use of the system dynamic model. Experiments performed on a 3-DOF parallel manipulator demonstrate improved performance with the proposed synchronous control design.