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In this article, we combine nonlinear estimation and control methods for precise bending angle control in soft pneumatic actuators driven by a pressure source and single low-cost on/off solenoid valve. First, a complete model for the soft actuator is derived, which includes both the motion and pressure dynamics. An unscented Kalman filter (UKF) is used to estimate the velocity state and filter noisy measurements from a pressure sensor and an embedded resistive flex sensor. Then, a feedback linearization approach is used with pole placement and linear quadratic regulator (LQR) controllers for bending angle control. To compensate for model uncertainties and improve reference tracking, integral action is incorporated to both controllers. The closed-loop performance of the nonlinear estimation and control approach is experimentally evaluated with a soft pneumatic network actuator. The simulation and experimental results show that the UKF provides accurate state estimation from noisy sensor measurements. The results demonstrate the effectiveness and robustness of the proposed observer-based nonlinear controllers for bending angle trajectory tracking. [ABSTRACT FROM AUTHOR]

The article describes two new methods for driving piezoelectric tube scanners. The first method aims to maximize horizontal and vertical scan range by driving the internal electrode rather than grounding it. This approach eliminates the need for a circumferential Z-electrode, which permits longer quadrant electrodes that develop greater deflection and vertical scan range. Experimental results demonstrate a 62% increase in lateral scan range and an 87% increase in vertical scan range. The second method aims to eliminate mechanical cross-coupling between the lateral deflection, tilt angle, and vertical extension. This method involves splitting the piezoelectric tube into eight external electrodes and a driven internal electrode, similar to the first method. This configuration results in less lateral deflection but significantly reduces the tilting and vertical motion induced by lateral deflection. Experimental results demonstrate an 44% increase in vertical displacement, 96% reduction in tilting, and 62% reduction in vertical cross-coupling. [ABSTRACT FROM AUTHOR]

Positive velocity and position feedback (PVPF) is a widely used control scheme in lightly damped resonant systems with collocated sensor actuator pairs. The popularity of PVPF is due to the ability to achieve a chosen damping ratio by repositioning the poles of the system. The addition of a tracking controller, to reduce the effects of inherent nonlinearities, causes the poles to deviate from the intended location and can be a detriment to the damping achieved. By designing the PVPF and tracking controllers simultaneously, the optimal damping and tracking can be achieved. Simulations show full damping of the first resonance mode and significantly higher bandwidth than that achieved using the traditional PVPF design method, allowing for high-speed scanning with accurate tracking. Experimental results are also provided to verify performance in implementation. [ABSTRACT FROM AUTHOR]

This paper explores the possibility of piezoelectric actuators with integrated high-voltage power electronics. Such devices dramatically simplify the application of piezoelectric actuators since the power electronics are already optimized for the voltage range, capacitance, and power dissipation of the actuator. The foremost consideration is the thermal impedance of the actuator and heat dissipation. Analytical and finite-element methods are described for predicting the thermal impedance of a piezoelectric bender. The predictions are compared experimentally using thermal imaging on a piezoelectric bender with laminated miniature power electronics. [ABSTRACT FROM PUBLISHER]

The resolution is a critical performance metric of precision mechatronic systems such as nanopositioners and atomic force microscopes. However, there is not presently a strict definition for the measurement or reporting of this parameter. This article defines resolution as the smallest distance between two non-overlapping position commands. Methods are presented for simulating and predicting resolution in both the time and frequency domains. In order to simplify resolution measurement, a new technique is proposed which allows the resolution to be estimated from a measurement of the closed-loop actuator voltage. Simulation and experimental results demonstrate the proposed techniques. The paper concludes by comparing the resolution benefits of new control schemes over standard output feedback techniques. [ABSTRACT FROM AUTHOR]

Many popular modes of scanning probe microscopy require a vertical feedback system to regulate the tip-sample interaction. Examples include constant-current scanning tunneling microscopy and constant-force atomic force microscopy. Due to the control of tip-sample interaction, these modes of microscopy provide precise topographic information and result in drastically reduced sample damage, hence their popularity. Unfortunately the vertical feedback controller also imposes a severe limit on the scan-speed of scanning probe microscopes. In this paper, the foremost bandwidth limitation is identified to be the low-frequency mechanical resonances of the scanner. To overcome this limitation, a dual-stage vertical positioner is proposed. This comprises the original scanner, plus an additional high-speed stage. The improved bandwidth provided by the high-speed stage allows a vast improvement in feedback gain and bandwidth. In this work, the bandwidth is increased from 83 Hz to 2.7 kHz. This improvement allows image quality to be retained with a speed increase of 33 times, or alternatively, feedback error can be reduced by 33 times if scan speed is not increased. The techniques proposed are mechanically and electrically simple and can be retrofitted to any scanning probe microscope. [ABSTRACT FROM AUTHOR]

Many forms of scanning probe microscopy require a piezoelectric actuator to vary the probe-sample distance. Examples include constant-force atomic force microscopy and constant-current scanning tunneling microscopy. In such modes, the topography of the sample is reconstructed from the voltage applied to the vertical piezoelectric actuator. However, piezoelectric actuators exhibit significant hysteresis which can produce up to 14% uncertainty in the reproduced topography. In this work, a charge drive is used to linearize the vertical piezoelectric actuator which reduces the error from 14% to 0.65%. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new sensor arrangement and feedback controller for hysteresis, creep and vibration in piezoelectric actuators. A piezoelectric force sensor is combined with a resistive strain gage to provide both extremely low noise and high stability. The use of a force sensor also results in a system transfer function that exhibits zero-pole ordering. Such systems allow a simple integral controller to provide excellent tracking and damping performance with guaranteed stability. The proposed technique is demonstrated on a nanopositioning platform with a range of 10 m and a resonance frequency of 2.4kHz. In closed-loop, the controller damps the resonance by 33dB and provides a tracking bandwidth of 1.8kHz. Excellent tracking of a 130Hz triangular reference and reduction of hysteresis to 0.46% at 10Hz is also demonstrated. The closed-loop positioning noise, predicted from the sensor noise density, was approximately 0.67nm peak-to-peak, or 0.0067% of the 10 m range. [Copyright &y& Elsevier]

Due to their high stiffness, small dimensions, and low mass, piezoelectric stack actuators are capable of developing large displacements over bandwidths of greater than 100 kHz. However, due to their large electrical capacitance, the associated driving amplifier is usually limited in bandwidth to a few kilohertz or less. In this paper the limiting characteristics of piezoelectric drives are identified as the small-signal bandwidth, output impedance, cable inductance, and power dissipation. A new dual amplifier is introduced that exhibits a small-signal bandwidth of 2 MHz with a 100 nF capacitive load. The dual amplifier is comprised of a standard high-voltage amplifier combined with a fast low-voltage amplifier to improve performance at higher frequencies. Experiments demonstrate a 300 kHz sine wave of 20 Vp-p amplitude being applied to a 100 nF load with negligible phase delay and a peak-to-peak current of 3.8 A. With a voltage range of 200 V and peak current of 1.9 A a standard amplifier would require a worst-case power dissipation of 380 W. However, the dual-amplifier arrangement has a worst-case power dissipation of only 30 W. The penalty is reduced range at high frequencies and slower operation from the high-voltage stage. [ABSTRACT FROM AUTHOR]

The difficulties imposed by actuator limitations in a range of active vibration and noise control problems are well recognized. This paper proposes and examines a new approach of employing model predictive control (MPC). MPC permits limitations on allowable control action to be explicitly included in the computation of an optimal control action. Such techniques have been widely and successfully applied in many other areas. However, due to the relatively high computational requirements of MPC, existing applications have been limited to systems with slow dynamics. This paper illustrates that MPC can be implemented on inexpensive hardware at high sampling rates using traditional online quadratic programming methods for nontrivial models and with significant control performance dividends. [ABSTRACT FROM AUTHOR]

This Note describes a new technique for estimating the resolution of nanopositioning systems. By recording the voltage applied to an actuator and performing a filtering operation, the position noise and resolution can be estimated. This technique is simple to apply in practice and does not require any additional sensors or specialized equipment. [ABSTRACT FROM AUTHOR]

Charge drive circuits can significantly reduce piezoelectric nonlinearity; however, they are rarely used in practice because of their limited low-frequency performance, their dependence of voltage gain on the load capacitance, and their requirement for time-consuming tuning procedures. In this report, a new charge drive circuit is proposed that uses a controlled current source with voltage feedback to stabilize the low-frequency behavior. This approach eliminates many of the present difficulties and allows extremely low transition frequencies without a long transient response. Experimental results demonstrate that the proposed charge amplifier can effectively reduce piezoelectric hysteresis and creep to less than 1.3% at scan-rates of 10, 1, and 0.1 Hz. [ABSTRACT FROM AUTHOR]

Soft robots have been developed for a variety of applications including gripping, locomotion, wearables and medical devices. For the majority of soft robots, actuation is performed using pneumatics or hydraulics. Many previous works have addressed the modeling of these fluid-driven soft robots using static finite element simulations where the pressure inside the actuator is assumed to be constant and uniform. The assumption of constant internal pressure is a useful simplification but introduces significant errors during events such as pressurization, depressurization, and transient loads from a liquid environment. Applications that use soft actuators for locomotion or propulsion operate using a sequence of transient events, so accurate simulation of these events is critical to optimizing performance. To improve the simulation of soft fluidic actuators and enable the modeling of both internal and external fluid flow in underwater applications, this work describes a fully-coupled, three-dimensional fluid–structure interaction simulation approach, where the pressure and flow dynamics are explicitly solved. This approach provides a realistic simulation of soft actuators in fluid environments, and permits the optimization of transient responses, which may be due to a combination of environmental fluid loads and non-uniform pressurization. The proposed methods are demonstrated in a number of case studies and experiments for a range of actuation and both internal and external inlet flow configurations, including bending actuators, a soft robotic fish fin for propulsion, and experimental results of a bending actuator in a high-speed fluid, which correlate closely with simulations. The proposed approach is expected to assist in the design, modeling, and optimization of bioinspired soft robots in underwater applications. [Display omitted] • 3D fluid–structure interaction simulations (FSI) for soft fluidic actuators are developed. • This approach is used to model both internal and external flow and pressure dynamics. • Realistic simulation of soft actuators in fluid environments such as underwater. • A series of comparison experiments and FSI analysis are presented and discussed. [ABSTRACT FROM AUTHOR]

This article describes a monolithic nanopositioner constructed from in-plane bending actuators which provide greater deflection than previously reported extension actuators, at the expense of stiffness and resonance frequency. The proposed actuators are demonstrated by constructing an XY nanopositioning stage with a serial kinematic design. Analytical modeling and finite-element-analysis accurately predicts the experimental performance of the nanopositioner. A 10 μ m range is achieved in the X and Y axes with an applied voltage of +/-200 V. The first resonance mode occurs at 250 Hz in the Z axis. The stage is demonstrated for atomic force microscopy imaging. [ABSTRACT FROM AUTHOR]

• Integration of strain gauges into piezoelectric bender electrodes. • Deflection sensing in response to applied voltages and external applied tip forces. • Model based tip force sensing. • Applications include micro-grippers and pneumatic valves. This article derives design guidelines for integrating strain gauges into the electrodes of piezoelectric bending actuators. The proposed sensor can estimate the actuator tip displacement in response to an applied voltage and an external applied tip force. The actuator load force is also estimated with an accuracy of 8% full scale by approximating the actuator response with a linear model. The applications of this work include micro-grippers and pneumatic valves, which both require the measurement of deflection and load force. At present, this is achieved by external sensors. However, this work shows that these functions can be integrated into the actuator electrodes. [ABSTRACT FROM AUTHOR]