Yantao Shen

Disturbance-Observer-Based Hysteresis Compensation for Piezoelectric Actuators

We present a novel hysteresis compensation method for piezoelectric actuators. We consider the hysteresis nonlinearity of the actuator as a disturbance over a linear system. A disturbance observer (DOB) is then utilized to estimate and compensate for the hysteresis nonlinearity. In contrast to the existing inverse-model-based approach, the DOB-based hysteresis compensation does not rely on any particular hysteresis model, and therefore provides a simple and effective compensation mechanism. We design and fabricate a lead magnesium niobate-lead titanate (PMN-PT) piezoelectric actuator for microscale tip-based power sintering process. Experimental validation of the proposed hysteresis compensation is performed on the PMN-PT cantilever piezoelectric actuator. The experimental results demonstrate the effectiveness and efficiency of the approach.

Integrated sensing for ionic polymer–metal composite actuators using PVDF thin films

Compact sensing methods are desirable for ionic polymer–metal composite (IPMC) actuators in microrobotic and biomedical applications. In this paper a novel sensing scheme for IPMC actuators is proposed by bonding an IPMC and a PVDF (polyvinylidene fluoride) thin film with an insulating layer in between. The insulating layer thickness is properly designed to minimize the stiffness of the composite IPMC/PVDF structure while reducing the electrical feedthrough coupling between the IPMC and PVDF. A distributed circuit model is developed to effectively represent the electrical coupling dynamics, which is then used in real-time compensation for extraction of the true sensing signal. Experimental results show that the developed IPMC/PVDF structure, together with the compensation algorithm, can perform effective, simultaneous actuation and sensing. As the first application, this sensori-actuator has been successfully used for performing and monitoring open-loop micro-injection of living Drosophila embryos. (Some figures in this article are in colour only in the electronic version)

A novel PVDF microforce/force rate sensor for practical applications in micromanipulation

This paper presents our development of a novel force and force rate sensory system to advance applications in micromanipulation using an in situ polyvinylidene fluoride (PVDF) piezoelectric sensor. To allow close monitoring of magnitude and direction of microforces acting on microdevices during manipulation, PVDF ploymer films are used to fabricate highly sensitive 1D and 2D sensors to detect real‐time microforce and force rate information during the manipulation process. The sensory system with a resolution in the range of sub‐micronewtons can be applied effectively to develop a technology on the force‐reflection microassembly of surface MEMS structures. In addition, a tele‐micromanipulation platform, which can be used to perform tele‐microassembly of the MEMS structures and tele‐cell‐manipulation with force/haptic feedback via Internet was also built successfully.

Force-guided assembly of micro mirrors

This paper aims at developing the force-guided microassembly technology with in-situ PVDF piezoelectric force sensing and control. By using the designed force sensors with the effective signal processing techniques, the micro contact force/impact signal and its derivative can be extracted and processed. Furthermore, based on a new sensor-referenced control scheme, micro mirrors can be reliably assembled by regulating the micro contact force. Experimental results verify the performance of the developed micro force sensing and control system. Ultimately the technology will provide a critical and major step towards the development of automated manufacturing processes for batch assembly of micro devices.

Closed-loop optimal control-enabled piezoelectric microforce sensors

This paper presents a closed-loop optimally controlled force-sensing technology with applications in both micromanipulation and microassembly. The microforce-sensing technology in this paper is based on a cantilevered composite beam structure with embedded piezoelectric polyvinylidene fluoride (PVDF) actuating and sensing layers. In this type of sensor, the application of an external load causes deformation within the PVDF sensing layer. This generates a signal that is fed through a linear quadratic regulator (LQR) optimal servoed controller to the PVDF actuating layer. This in turn generates a balancing force to counteract the externally applied load. As a result, a closed feedback loop is formed, which causes the tip of this highly sensitive sensor to remain in its equilibrium position, even in the presence of dynamically applied external loads. The sensors stiffness is virtually improved as a result of the equilibrium position whenever the control loop is active, thereby enabling accurate motion control of the sensor tip for fine micromanipulation and microassembly. Furthermore, the applied force can be determined in real time through measurement of the balance force

Contact and force control in microassembly

This paper aims at advancing micromanipulation technology with in-situ PVDF piezoelectric force sensing and control during microassembly and packaging process. To allow close monitoring of magnitude and direction of forces (surface, friction, and assembly force) acting on micro devices during manipulation, the polyvinylidene fluoride (PVDF) is used to fabricate highly sensitive 1-D and 2-D force sensors for assembly of micro devices. By using the designed force sensors with the effective signal processing techniques, the contact force/impact signal can be obtained desirably so that it greatly improves the reliability of force regulation in microassembly. Moreover, based on a new sensor-referenced control method, the force control had been implemented by employing a micromanipulator system equipped with the force sensor and its results verify the effectiveness of sensor model as well as the performance of force feedback and control system. Ultimately the technology will provide a critical and major step towards the development of automated manufacturing processes for batch assembly of micro devices.

Development of supermedia interface for telediagnostics of breast pathology

A robotic device with haptic, tactile, and ultrasound capabilities, which can acquire and render information of breast pathology was developed. A physician interface that can examine the human breast remotely and accurately, using such a robotic device was also developed. Such a robotic device can be used to do screening or focused breast exams for patients in remote areas without convenient access to physicians. Because of in-situ ultrasound imaging, examination by the robotic device may prove to be more accurate than examination by the physicians own hand. In addition, the robotic device can also be used to train healthcare professionals in breast pathology

High sensitivity 2-D force sensor for assembly of surface MEMS devices

This paper aims at advancing micromanipulation technology with in situ polyvinylidene fluoride (PVDF) piezoelectric force sensing during microassembly and packaging process. Based on the previously developed PVDF 1-D sensor, by employing the parallel beam structure, a novel 2-D force sensor with relatively high natural frequency and sensitivity is optimally designed. The sensor can detect micro force and force rate signals, which can be fed back so as to greatly, improve the reliability of microassembly. Preliminary calibration and experimental results on assembly of surface MEMS devices both verified the performance of the new 2-D sensor that demonstrates a high sensitivity and a resolution in the range of /spl mu/N. Ultimately the technology would provide a critical and major step towards the development of automated micro-manufacturing processes for batch assembly of micro devices.

A Humanoid Neck System Featuring Low Motion-Noise

This paper presents our recently developed humanoid neck system that can effectively mimic motion of human neck with very low motion noises. The features of low motion noises allows our system to work like a real human neck. Thus the level of acoustic noises from wearable equipments, such as donning respirators or chemical-resistant jackets, induced by human head motion can be simulated and investigated using such a system. Our low motion-noise humanoid head/neck system is based on the spring structure, which can generate 1 degree of freedom (DOF) jaw movement and 3DOF neck movement. To guarantee the low-noise feature, no noise-makers like gear and electro-driven parts are embedded in the head/neck structure. Instead, the motion is driven by seven polyester cables, and the actuators pulling the cables are sealed in a sound insulation box. Furthermore, statics analysis and motion control design of the system have been presented. Experimental results clearly show that the head/neck system can greatly mimic the motion of human head with an A-weighted noise level of 30 dB or below.

High-accuracy visual/PSD hybrid servoing of robotic manipulator

This paper presents a new and effective multisensor based control strategy for high-accuracy/precision and high-efficiency automatic robot localization and calibration. The strategy combines both coarsely visual servo and fine position-sensitive detector (PSD) servo control methods. In a large field of view, an image-based visual servo control system is developed to roughly guide the laser beam, which is from a single laser pointer mounted at the end-effector of robot, to project to the high-resolution segmented PSDs. Once the laser spot is projected onto the active area of PSD, the control will be switched to the high-resolution PSD feedback and servoing for fine positioning. The experimental results conducted on an ABB industrial robot IRB1600 verify the effectiveness of the developed visual/PSD hybrid servo controllers as well as demonstrate that the high accuracy 30 mum of robot localization can be approached. The development of the hybrid control system and method will be a major step for achieving high-performance automatic robot calibration.