Timothy C. Burg

A redesigned DCAL controller without velocity measurements: theory and demonstration

A link position tracking controller is formulated for an n-link, rigid, revolute, serially-connected robot. The controller generates torque commands to the individual robot links based on adaptive estimates of the system parameters and measurements of only link positions. A filtering technique, based on the link position signal, is used to alleviate the need for velocity measurements. A complete development of the controller is presented along with a proof of semiglobal asymptotic link position-velocity tracking performance. Experimental validation of the proposed controller on the Integrated Motion Inc. (IMI) two-link direct drive robot is also presented. Several extensions to the basic controller are described that consider the use of fixed parameter estimates.

Adaptive position/force control of robot manipulators without velocity measurements: theory and experimentation

In this paper, we design an adaptive position/force controller for robot manipulators during constrained motion. The proposed controller can compensate for parametric uncertainty while only requiring measurements of link position and end-effector force. A filtering technique is utilized to produce a pseudo-velocity error signal and thus, eliminate the need for link velocity measurements. The control strategy provides semiglobal asymptotic tracking performance for the end-effector position and the interaction force between the constraint and the end-effector. An experimental implementation of the proposed controller on a two-link planar robot is also presented.

Nonlinear control of an overhead crane via the saturating control approach of Teel

Presents a control strategy for the horizontal position control of a two degree-of-freedom overhead crane. The approach transforms the underactuated crane dynamics into a form similar to the well known ball-and-beam dynamics. A controller is then developed based on the work of Teel (1992, 1995) for the transformed dynamics using a saturation control design technique. The control approach is based on a crane model which includes the typically neglected, higher-order nonlinearities. The resulting controller provides for asymptotic positioning of the crane payload from a large set of initial conditions. Experimental trials demonstrate the performance of the proposed controller while a computer simulation is used to suggest the benefit of the proposed saturation controller over a standard linear controller.

Output Feedback Tracking Control of an Underactuated Quad-Rotor UAV

This paper proposes a new controller for an underactuated quad-rotor family of small-scale unmanned aerial vehicles (UAVs) using output feedback (OFB). Specifically, an observer is designed to estimate the velocities and an output feedback controller is designed for a nonlinear UAV system in which only position and angles are measurable. The design is performed via a Lyapunov type analysis. A semi- global uniformly ultimate bounded (SGUUB) tracking result is achieved. Simulation results are shown to demonstrate the proposed approach.

Robust tracking control of an underactuated quadrotor aerial-robot based on a parametric uncertain model

In this paper, the tracking control of a underactuated quadrotor aerial vehicle is presented where position and yaw trajectory tracking is achieved using feedback control system. The control design is complicated by considering parametric uncertainty in the dynamic modeling of the quadrotor aerial-robot. Robust control schemes are then designed using a Lyapunov-based approach to compensate for the unknown parameters in each dynamic subsystem model. Lyapunov-type stability analysis suggests a global uniform ultimately bounded (GUUB) tracking result.

A redesigned DCAL controller without velocity measurements: theory and experimentation

In this paper, a link position tracking controller is formulated for an n-link, rigid, revolute robot. The controller generates torque commands to the individual robot links based on adaptive estimates of the system parameters and measurements of link positions only. A filtering technique, based on the link position signals, is used to remove the need for velocity measurements. A complete development of the controller is presented along with a proof of semi-global asymptotic link position-velocity tracking performance. Experimental validation of the proposed controller on the Integrated Motion Inc. (IMI) two-link direct drive robot is also presented.<<ETX>>

Adaptive tracking control of an underactuated aerial vehicle

In this paper, adaptive tracking control of an underactuated quadrotor is addressed. Position and yaw trajectory tracking is designed using state feedback control system and an integrator backstepping approach is applied to this coupled and cascaded dynamic system. The control design is further complicated by considering the parametric uncertainty of the dynamic modeling of the quadrotor aerial-robot vehicle. Projection-based adaptive control schemes are then designed to estimate the unknown parameters. Lyapunov-type stability analysis and numerical simulation results which yields a bounded tracking result are shown to demonstrate the initial validity of the proposed controllers.

Building off-the-shelf tissue-engineered composites

Rapid advances in technology have created the realistic possibility of personalized medicine. In 2000, Time magazine listed tissue engineering as one of the ‘hottest 10 career choices’. However, in the past decade, only a handful of tissue-engineered products were translated to the clinical market and none were financially viable. The reality of complex business planning and the high-investment, high-technology environment was not apparent, and the promise of tissue engineering was overstated. In the meantime, biologists were steadily applying three-dimensional benchtop tissue-culture systems for cellular research, but the systems were gelatinous and thus limited in their ability to facilitate the development of complex tissues. Now, the bioengineering literature has seen an emergence of literature describing biofabrication of tissues and organs. However, if one looks closely, again, the viable products appear distant. ‘Rapid’ prototyping to reproduce the intricate patterns of whole organs using large volumes of cellular components faces daunting challenges. Homogenous forms are being labelled ‘tissues’, but, in fact, do not represent the heterogeneous structure of the native biological system. In 2003, we disclosed the concept of combining rapid prototyping techniques with tissue engineering technologies to facilitate precision development of heterogeneous complex tissue-test systems, i.e. systems to be used for drug discovery and the study of cellular behaviour, biomedical devices and progression of disease. The focus of this paper is on the challenges we have faced since that time, moving this concept towards reality, using the case of breast tissue as an example.

EDTA enhances high-throughput two-dimensional bioprinting by inhibiting salt scaling and cell aggregation at the nozzle surface

Tissue‐engineering strategies may be employed in the development of in vitro breast tissue models for use in testing regimens of drug therapies and vaccines. The physical and chemical interactions that occur among cells and extracellular matrix components can also be elucidated with these models to gain an understanding of the progression of transformed epithelial cells into tumours and the ultimate metastases of tumour cells. The modified inkjet printer may be a useful tool for creating three‐dimensional (3D) in vitro models, because it offers an inexpensive and high‐throughput solution to microfabrication, and because the printer can be easily manipulated to produce varying tissue attributes. We hypothesized, however, that when ink is replaced with a biologically based fluid (i.e. a ‘bio‐ink’), specifically a serum‐free cell culture medium, printer nozzle failure can result from salt scale build‐up as fluid evaporates on the printhead surface. In this study, ethylene diamine tetra‐acetic acid (EDTA) was used as a culture medium additive to prevent salt scaling and cell aggregation during the bioprinting process. The results showed that EDTA, at a concentration typically found in commercially available trypsin solutions (0.53 mM), prevented nozzle failure when a serum‐free culture medium was printed from a nozzle at 1000 drops/s. Furthermore, increasing concentrations of EDTA appeared to mildly decrease aggregation of 4T07 cells. Cell viability studies were performed to demonstrate that addition of EDTA did not result in significant cell death. In conclusion, it is recommended that EDTA be incorporated into bio‐ink solutions containing salts that could lead to nozzle failure. Copyright

Adaptive control of redundant robot manipulators with sub-task objectives*

In this paper, adaptive control of kinematically redundant robot manipulators is considered. An end-effector tracking controller is designed and the manipulators kinematic redundancy is utilized to integrate a general sub-task controller for self-motion control. The control objectives are achieved by designing a feedback linearizing controller that includes a least-squares estimation algorithm to compensate for the parametric uncertainties.