Integral Resonant Control for vibration damping and precise tip-positioning of a single-link flexible manipulator

Peer reviewedPostprin

HUMAN SANITARY WASTES AND WASTE TREATMENT IN NEW YORK CITY

Henry Hudson first sailed toNew Yorkharbor 400 years ago. Since then,New York Cityhas both affected and been affected by water quality in greaterNew YorkHarbor. In this paper, we focus on sewers, sewerage, and sewage treatment inManhattanand their effects on theHudson River. It is clear that feedbacks among drinking water quality and quantity, population, public perceptions, regulations, and estuarine water quality exist, although their strength and character have varied over time. Early land uses damaged local water supplies found on ManhattanIsland. New Yorkthen began to exploit the large fresh water resources available to its north, which helped the City to expand more rapidly. Water availability also allowed for water carriage sanitary practices, increasing discharges of wastes through a growing sewer network into local waters. The discharge of wastes degraded water quality, affecting natural resources in the harbor. Untreated wastes led to disease from contaminated seafood, and also more generalized effects on public health. Overall, New Yorklifestyles became largely detached from its shoreline, partly due to the industrial character of the waterfront, and partly because of odors and visual blight from pollution. Growing public distaste over poor harbor water quality, especially in the early 20th century, led to some sewage treatment. More and more comprehensive treatment followed regulatory and legal actions, beginning in mid-twentieth century. Concurrently, maritime commerce declined, and the waterfront became underutilized. However, in the twenty-first century, natural resources are recovering, andNew York City citizens once again flock to the shores of theHudson River, to new and revitalized parks, new areas of development and older areas undergoing transformation, and into the harbor, now largely cleaned of its fouling from sanitary waste disposal. Today New York City public life has a much greater orientation toward the waterfront, which certainly was fostered by improved harbor water quality, and the opportunities for growth that were available with the disappearance of the City’s maritime industries. Thus, there has been a complicated relationship between the City and its rivers and harbor. One aspect has been continuing use of local water bodies as receptacles for wastes, which has benefitted those living in the City. Gaining these benefits has had continuing costs, however. Marine resources were damaged and some were lost, and quality of life on land was affected. Trying to undo the impacts, which has required great effort and much capital, has been hampered by technology decisions that appear suboptimal with the advantage of more than 100 years of hindsight. Still, modern sewage treatment, initiated by local efforts and concerns, but spurred on to completion by the forces unleashed by the great environmental awakening of the 1960s and 1970s, has made it possible for the citizens of New York to again fish, boat, and even swim in City waters

Achieving high-bandwidth nanopositioning in presence of plant uncertainties

In the absence of plant parameter uncertainties, inversion-based feedforward techniques have been known to deliver accurate tracking performance. Due to changes in operating conditions like ambient temperature, humidity and loading, piezoelectric-stack actuated nanopositioning platforms can undergo significant changes in their system parameters. Nonlinear effects of hysteresis, an inherent property of a piezoelectric actuator, are also present; charge actuation is applied to reduce the effects of hysteresis. In this work, a suitable feedback controller that reduces the effects of parameter uncertainties is integrated with the inversion-based feedforward technique to deliver accurate nanopositioning over a large bandwidth. It is shown experimentally that by integrating closed-loop damping, inversion-based feedforward and charge actuation, the tracking bandwidth of the platform from can be increased significantly from 310 Hz to 1320 Hz

Loop-shaping H ∞-control of a 2-DOF piezoelectric-stack actuated platform for nanoscale positioning

Piezoelectric-stack actuated platforms are utilized in many nanopositioning applications. Their performance is limited by their low-frequency resonance due to the mechanical construction as well as piezoelectric nonlinear effects. We propose a hybrid control scheme comprising a loop-shaping H∞ controller and an inversion-based feedforward control scheme, capable of delivering accurate nanopositioning performance at relatively high speeds, upto 40 Hz. It is shown that the implemented control strategy is robust in the presence of uncertainty in resonance frequency due to loading. It is also shown that by employing charge actuation on the fast axis and integral tracking control on the slow axis, accurate raster scans can be obtained. Experimental results that show resonance damping, integral tracking action as well as the robustness of the implemented control scheme to resonance frequency uncertainty are presented. Finally, raster scans recorded at 10 Hz, 20 Hz and 40 Hz are presented to show the achievable positioning performance

A new robust damping and tracking controller for SPM positioning stages

This paper demonstrates a simple second-order controller that eliminates scan-induced oscillation and provides integral tracking action. The controller can be retrofitted to any scanning probe microscope with position sensors by implementing a simple digital controller or op-amp circuit. The controller is demonstrated to improve the tracking bandwidth of an NT-MDT scanning probe microscope from 15 Hz (with an integral controller) to 490 Hz while simultaneously improving gain-margin from 2 dB to 7 dB. The penalty on sensor induced positioning noise is minimal. For the Scanning Probe Microscope considered in this paper, the noise is marginally increased from 0.30 nm RMS to 0.39 nm RMS. Open- and closed-loop experimental images of a calibration standard are reported at speeds of 1 and 10 lines per second (with a scanner resonance frequency of 290 Hz). Compared to traditional integral or PID controllers, the proposed controller provides a bandwidth improvement of approximately ten times. This allows faster imaging and less tracking lag at low speeds

Design, analysis and control of a fast nanopositioning stage

We present a fast flexure-based, piezoelectric stack-actuated XY nanopositioning stage which is suitable for high-speed, accurate nanoscale positioning applications. The performance of the design are analyzed using finite-element-analysis software. Experiments demonstrate that the design has a high first resonant mode at 2.7 kHz, a low cross-coupling of -35 dB and a relatively large traveling range of 25x25 mum. These results are in close agreement with the predicted FEA results. Non-linearities due to hysteresis of the piezoelectric stack actuators are present in the stage. The hysteresis effect is minimized using charge actuation. The Integral Resonant Control (IRC) method is applied to damp the first resonant mode. By implementing feedforward inversion technique, high-speed and accurate scanning performances, up to 400 Hz, are achieved

A closed-loop approach to reducing scan errors in nanopositioning platforms

Piezoelectric stack-actuated parallel-kinematic nanopositioning platforms have their first resonant mode at relatively low frequencies and also suffer from nonlinearities such as hysteresis and creep, resulting in a typically low-grade positioning performance. Closed- loop control algorithms have shown the potential to eliminate these problems and achieve robust, repeatable nanopositioning. In this work, the performance of three commonly used damping controllers is compared based on their closed-loop noise characteristics. The best one is combined with an integrator to produce accurate raster scans of large areas while imparting substantial damping to the system and minimizing inherent nonlinearities. A scanning resolution of approximately 8nm, over a 100μm × 100μm area is achieved

Minimizing scanning errors in piezoelectric stack-actuated nanopositioning platforms

Piezoelectric stack-actuated parallel-kinematic nanopositioning platforms are widely used in nanopositioning applications. These platforms have a dominant first resonant mode at relatively low frequencies, typically in the hundreds of hertz. Furthermore, piezoelectric stacks used for actuation have inherent nonlinearities such as hysteresis and creep. These problems result in a typically low-grade positioning performance. Closed-loop control algorithms have shown the potential to eliminate these problems and achieve robust, repeatable nanopositioning. Using closed-loop noise profile as a performance criterion, three commonly used damping controllers, positive position feedback, polynomial-based pole placement, and resonant control are compared for their suitability in nanopositioning applications. The polynomial-based pole placement controller is chosen as the most suitable of the three. Consequently, the polynomial-based control design to damp the resonant mode of the platform is combined with an integrator to produce raster scans of large areas. A scanning resolution of approximately 8 nm, over a 100 μm X 100 μm area is achieved

A hybrid control strategy for vibration damping and precise tip-positioning of a single-link flexible manipulator

In this work, we propose a new control approach for a single-link flexible manipulator, based on the integral resonant control (IRC) scheme. A hybrid control scheme consisting of two nested loops by treating the joint angle and the torque measured at the base of the arm (coupling torque) as the system outputs are formulated. It is shown that the IRC scheme, a high performance controller design methodology for flexible structures with collocated actuator-sensor pairs, can be implemented in a flexible manipulator to achieve precise end-point positioning with effective vibration suppression. Experimental results are presented in order to validate the proposed control scheme. Finally, a brief discussion is included to highlight the contributions of this work in broad area of controlling single-link flexible manipulators