Kira Barton

A Cross-Coupled Iterative Learning Control Design for Precision Motion Control

This paper presents an improved method for precision motion control by combining individual axis iterative learning control (ILC) and cross-coupled ILC (CCILC) into a single control input. CCILC is a new method in which a multi-axis cross-coupled controller (CCC) is reformatted into a single-input single-output (SISO) ILC format. Applying the techniques of ILC to CCC enables learning of the cross-coupled error which leads to a modified control signal and subsequent improvements in the contour trajectory tracking performance. In this paper, performance of the combined ILC and CCILC system is compared to standard feedback control through computer simulations and experimental testing on a Cartesian robotic system. Sufficient stability and convergence properties for the combined system are presented along with a modified approach for determining monotonic convergence of systems that are computationally challenging. The combined design is shown to enhance the precision motion control of the robotic system through performance improvements in individual axis tracking and contour tracking.

High-speed and drop-on-demand printing with a pulsed electrohydrodynamic jet

We present a pulsed dc voltage printing regime for high-speed, high-resolution and high-precision electrohydrodynamic jet (E-jet) printing. The voltage pulse peak induces a very fast E-jetting mode from the nozzle for a short duration, while a baseline dc voltage is picked to ensure that the meniscus is always deformed to nearly a conical shape but not in a jetting mode. The duration of the pulse determines the volume of the droplet and therefore the feature size on the substrate. The droplet deposition rate is controlled by the time interval between two successive pulses. Through a suitable choice of the pulse width and frequency, a jet-printing regime with a specified droplet size and droplet spacing can be created. Further, by properly coordinating the pulsing with positioning commands, high spatial resolution can also be achieved. We demonstrate high-speed printing capabilities at 1 kHz with drop-on-demand and registration capabilities with 3–5 µm droplet size for an aqueous ink and 1–2 µm for a photocurable polymer ink.

A Norm Optimal Approach to Time-Varying ILC With Application to a Multi-Axis Robotic Testbed

In this paper, we focus on improving performance and robustness in precision motion control (PMC) of multi-axis systems through the use of iterative learning control (ILC). A norm optimal ILC framework is used to design optimal learning filters based on design objectives. This paper contains two key contributions. The first half of this paper presents the norm optimal framework, including the introduction of an additional degree of design flexibility via time-varying weighting matrices. This addition enables the controller to take trajectory, position-dependent dynamics, and time-varying stochastic disturbances into consideration when designing the optimal learning controller. Explicit guidelines and analysis requirements for weighting matrix design are provided. The second half of this paper seeks to demonstrate the use of these guidelines. Using the design details provided in the paper, norm optimal learning controllers using time-invariant and time-varying weighting matrices are designed for comparison through simulation on a model of a multi-axis robotic testbed.

Patterned Hydrogel Substrates for Cell Culture with Electrohydrodynamic Jet Printing

Cells respond to and are directed by physiochemical cues in their microenvironment, including geometry and substrate stiffness. The development of substrates for cell culture with precisely controlled physiochemical characteristics has the potential to advance the understanding of cell biology considerably. In this communication, E-jet printing is introduced as a method for creating high-resolution protein patterns on substrates with controlled elasticity. It is the first application of E-jet printing on a soft surface. Protein spots as small as 5 µm in diameter on polyacrylamide are demonstrated. The patterned hydrogels are shown to support cell attachment and spreading. Polyacrylamide substrates patterned by E-jet printing may be applied to further the study of cellular mechanobiology.

A multimaterial electrohydrodynamic jet (E-jet) printing system

Electrohydrodynamic jet (E-jet) printing has emerged as a high-resolution alternative to other forms of direct solution-based fabrication approaches, such as ink-jet printing. This paper discusses the design, integration and operation of a unique E-jet printing platform. The uniqueness lies in the ability to utilize multiple materials in the same overall print-head, thereby enabling increased degrees of heterogeneous integration of different functionalities on a single substrate. By utilizing multiple individual print-heads, with a carrousel indexing among them, increased material flexibility is achieved. The hardware design and system operation for a relatively inexpensive system are developed and presented. Crossover interconnects and multiple fluorescent tagged proteins, demonstrating printed electronics and biological sensing applications, respectively.

Cross-coupled iterative learning control of systems with dissimilar dynamics: design and implementation

Cross-coupled iterative learning control has previously been applied to contour tracking problems with planar manufacturing robots in which both axes can be characterised as similar systems; having similar dynamics and identical hardware. However, there are many repetitive applications in which dynamically dissimilar systems cooperate to pursue a primary performance objective. This article introduces a novel framework to couple dynamically dissimilar systems while applying iterative learning control, showing the ability to noncausally compensate for a slow system with a fast system. In this framework, performance requirements for a primary objective can more readily be achieved by emphasising an underutilised fast system instead of straining a less-capable slow system. The controller is applied to a micro-robotic deposition manufacturing system to coordinate a slow extrusion system axis and a fast positioning system axis to pursue the primary performance objective, dimensional accuracy of a fabricated part. Experimental results show a 14% improvement in fabrication-dimensional accuracy with only marginal changes in actuator effort, as compared to independently controlled axes.

Norm optimal Cross-Coupled Iterative Learning Control

In this paper, we focus on improving contour tracking in precision motion control (PMC) applications through the use of Cross-Coupled Iterative Learning Control (CCILC). Initially, the relationship between individual axis errors and contour error is discussed, including insights into the different reasons for implementing CCILC versus individual axis ILC. A Norm Optimal (N.O.) framework is used to design optimal learning filters based on design objectives. The general N.O. framework is reformatted to include the contour error, as well as individual axis errors. General guidelines for tuning the different weighting matrices are presented. The weighting approach of this framework enables one to focus on individual axis or contour tracking independently. The performance benefits of N.O. CCILC versus ILC are illustrated through simulation and experimental testing on a multi-axis robotic testbed.

High Precision Electrohydrodynamic Printing of Polymer Onto Microcantilever Sensors

We report electrohydrodynamic jet printing to deposit 2-27 μm diameter polymer droplets onto microcantilever sensors. The polymer droplets were deposited as single droplets or organized patterns, with sub-μm control over droplet diameter and position. The droplet size could be controlled through a pulse-modulated source voltage, while droplet position was controlled using a positioning stage. Gravimetry analyzed the polymer droplets by examining the shift in microcantilever resonance frequency resulting from droplet deposition. The resonance shift of 50-4130 Hz corresponded to a polymer mass of 4.5-135 pg. The electrohydrodynamic method is a precise way to deposit multiple materials onto micromechanical sensors with greater resolution and repeatability than current methods.

A Numerical Method for Determining Monotonicity and Convergence Rate in Iterative Learning Control

In iterative learning control (ILC), a lifted system representation is often used for design and analysis to determine the convergence rate of the learning algorithm. Computation of the convergence rate in the lifted setting requires construction of large N×N matrices, where N is the number of data points in an iteration. The convergence rate computation is O(N2) and is typically limited to short iteration lengths because of computational memory constraints. As an alternative approach, the implicitly restarted Arnoldi/Lanczos method (IRLM) can be used to calculate the ILC convergence rate with calculations of O(N). In this article, we show that the convergence rate calculation using IRLM can be performed using dynamic simulations rather than matrices, thereby eliminating the need for large matrix construction. In addition to faster computation, IRLM enables the calculation of the ILC convergence rate for long iteration lengths. To illustrate generality, this method is presented for multi-input multi-output, linear time-varying discrete-time systems.

A field shaping printhead for high-resolution electrohydrodynamic jet printing onto non-conductive and uneven surfaces

High-resolution electrohydrodynamic jet printing is a cost effective, flexible, multi-material, high-resolution (sub 10 μm) additive manufacturing process. In this paper, we present an electric field shaping printhead capable of controlled high-resolution (sub 10 μm) e-jet printing and demonstrate printhead capabilities by creating patterns with both an optical adhesive and silver nanoparticle ink material with equivalent accuracy to state-of-the-art e-jet printing. Importantly, we demonstrate controlled printing onto non-conductive and height varying surfaces without the use of a grounded substrate at a previously unattainable length scale. This ability to print onto highly varied non-conductive substrates will enable the generalization of the 2D process to a controlled 3D printing technology at the micro-scale.