Organizational Unit:
Biorobotics and Human Modeling Lab

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Publication Search Results

Now showing 1 - 10 of 17
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    Piezoelectric Self-Sensing Technique for Tweezer Style End-effector
    (Georgia Institute of Technology, 2011-12) McPherson, Timothy ; Ueda, Jun
    This paper presents the application of a piezoelectric self-sensing technique based on discharged current to robotic tweezers incorporating a rhombus strain amplification mechanism driven by serially connected piezoelectric stack actuators. Connecting a shunt resistor in series with a piezoelectric element allows it to be used simultaneously as an actuator and a sensor by measuring the current generated by the piezoelectric element. This allows the displacement and force to be measured without extra sensors or the loss of actuation capability. Applying an inverse model of the nested structure allows the force and displacement at the tip of the tweezers to be determined. The accuracy of this method is then examined by experiment for the case of free displacement.
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    Design of an MRI Compatible Haptic Interface
    (Georgia Institute of Technology, 2011-12) Turkseven, Melih ; Ueda, Jun
    This paper proposes an MRI-compatible, 1-axis force sensing unit which is designed to be used as a haptic interface on an MRI compatible robot. Recently, it became a popular research direction to enable MRI in surgical operations and brain studies with the help of robotic devices. However, due to high magnetic field in MRI environment, conventional sensors and robots cannot be used in MRI rooms. Existing MRI-compatible force sensors have limited number of degrees of freedom or they do not offer compact solutions for multiple-axis sensing. In this paper, a compact 1-axis force sensing unit which employs a compliant displacement amplification mechanism is introduced and then analyzed for better sensitivity and accuracy. A combination of multiple proposed sensing units can be assembled to have a force sensor with desired number of degrees of freedom. Prototypes made of delrin and ABS-plastic are tested. Experiments indicated that the proposed sensor is suitable for force sensing and fully compatible to MRI. Also, the sensor made of delrin is superior in mechanical performance and MRI compatibility to ABS-plastic sample.
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    Piezoelectric Tweezer-type End-effector with Force- and Displacement-Sensing Capability
    (Georgia Institute of Technology, 2011-06) Kurita, Yuichi ; Sugihara, Fuyuki ; Ueda, Jun ; Ogasawara, Tsukasa
    This paper presents the design and development of robotic tweezers with a force- and displacement-sensing capability driven by piezoelectric stack actuators. In order to satisfy sufficient stroke and tip-force for future medical operations, a rhombus strain amplification mechanism is adopted. One of the serially-connected piezoelectric stack actuators nested in the end effector is used as a force sensor. The force-displacement characteristics at the outer-most layer with respect to the forces of the inner-most PZT actuators (i.e., forward model) is obtained from a lumped parameter model of the rhombus strain amplification mechanism and a Bernoulli-Euler beam model of the tweezerstyle end-effector. The end-effector tip force and displacement is measured using an inverse model of the nested multi-layer structure relating these quantities to an induced voltage across the inner-most PZT actuator. The prototype end-effector has the size of 69 (length) × 14 (height) × 13 (width) [mm]. The performance test shows that the prototype has 1.0 [N] force and 8.8 [mm] displacement at the tip. The sensing accuracy was also evaluated through experiments. The experimental results show that the prototype has mean error of 0.086 [N] for force and 0.39 [mm] for displacement, which are equivalent to 11% of their maximum measurable values.
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    Wearable Sensorimotor Enhancer for a Fingertip based on Stochastic Resonance
    (Georgia Institute of Technology, 2011-05) Kurita, Yuichi ; Shinohara, Minoru ; Ueda, Jun
    This paper reports the initial experimental results of a wearable sensorimotor enhancer for a fingertip. A shorttime exposure of tactile receptors to sub-sensory white-noise vibration is known to improve the tactile sensitivity. This phenomenon, called “noise-enhanced tactile sensation” or stochastic resonance (SR) in the somatosensory system, is expected to enhance the sense of touch when white-noise vibration is applied to a fingertip, and thereby improve associated motor skills. A prototype sensorimotor enhancer has been developed in this research. This wearable device is to stimulate tactile receptors by applying vibration from a compact lead zirconate titanate (PZT) piezoelectric stack actuator attached at the radial side of the fingertip. This design keeps the palmar region free and maintains the wearer’s manipulability. Sensory and motor tests have been conducted for health subjects to confirm the efficacy of the device. Statistical significance has been observed in most of the tests.
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    Experimental Verification of Discrete Switching Vibration Suppression
    (Georgia Institute of Technology, 2011-01-20) Schultz, Joshua ; Ueda, Jun
    Control system design for flexible robotic systems requires special care with regard to the control system design to prevent oscillation in the system's resonant modes. If the resonant frequencies of such a system are known, it is possible to determine a switching command that delivers comparable actuation without exciting these natural modes of vibration. If there is redundancy in actuation, it can be exploited to suppress vibration with a reduced amount of actuator changes in state. Minimum switching discrete switching vibration suppression (MSDSVS) involves choosing a switching function with integer amplitudes and continuously variable switch timings to force the root of the residual oscillation function with respect to frequency to be at a resonance. By minimizing the one norm of the vector of amplitudes, we obtain several desired properties. Such a vibration suppression command is developed for a flexible robotic actuator, and experimental results are presented. The proposed command reduces residual oscillation by 73% (rms) and 74% (largest Fourier component) and represents a 37% energy savings over vibration suppression commands that do not exploit the redundancy in actuation.
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    A fingerprint method for variability and robustness analysis of stochastically controlled cellular actuator arrays
    (Georgia Institute of Technology, 2011) MacNair, David L. ; Ueda, Jun
    This paper presents a “Fingerprint Method” for modeling and subsequently characterizing stochastically controlled actuator arrays. The actuator arrays are built from small actuator cells with structural elasticity. These cells are controlled using a bistable stochastic process wherein all cells are given a common input probability (control) value which they use to determine whether to actuate or relax. Arranging the cells in different networks gives different actuator array properties, which must be found before the actuator arrays can be applied to manipulators. The fingerprint method is used to describe and automatically generate every possible stochastic actuator array topology for a given number of cells, and to calculate actuator array properties such as: travel, required actuator strength/displacement, force range, force variance, and robustness for any array topology. The properties of several illustrative examples are shown and a discussion covers the importance of the properties, and trends between actuator array layouts and their properties. Finally, results from a validation experiment using a stochastically controlled solenoid array are presented.
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    Large Effective-Strain Piezoelectric Actuators Using Nested Cellular Architecture with Exponential Strain Amplification Mechanisms
    (Georgia Institute of Technology, 2010-10) Ueda, Jun ; Secord, Thomas ; Asada, H. Harry
    Design and analysis of piezoelectric actuators having over 20% effective strain using an exponential strain amplification mechanism are presented in this paper. Piezoelectric ceramic material, such as lead zirconate titanate (PZT), has large stress and bandwidth, but its extremely small strain, i.e., only 0.1%, has been a major bottleneck for broad applications. This paper presents a new strain amplification design, called a “nested rhombus” multilayer mechanism, that increases strain exponentially through its hierarchical cellular structure. This allows for over 20% effective strain. In order to design the whole actuator structure, not only the compliance of piezoelectric material but also the compliance of the amplification structures needs to be taken into account. This paper addresses how the output force and displacement are attenuated by the compliance involved in the strain amplification mechanism through kinematic and static analysis. An insightful lumped parameter model is proposed to quantify the performance degradation and facilitate design tradeoffs. A prototype-nested PZT cellular actuator that weighs only 15 g has produced 21% effective strain (2.5 mm displacement from 12-mm actuator length and 30 mm width) and 1.7 N blocking force.
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    Large Effective-Strain Piezoelectric Actuators Using Nested Cellular Architecture with Exponential Strain Amplification Mechanisms
    (Georgia Institute of Technology, 2010-10) Ueda, Jun ; Secord, Thomas W. ; Asada, H. Harry
    Design and analysis of piezoelectric actuators having over 20% effective strain using an exponential strain amplification mechanism are presented in this paper. Piezoelectric ceramic material, such as lead zirconate titanate (PZT), has large stress and bandwidth, but its extremely small strain, i.e., only 0.1%, has been a major bottleneck for broad applications. This paper presents a new strain amplification design, called a “nested rhombus” multilayer mechanism, that increases strain exponentially through its hierarchical cellular structure. This allows for over 20% effective strain. In order to design the whole actuator structure, not only the compliance of piezoelectric material but also the compliance of the amplification structures needs to be taken into account. This paper addresses how the output force and displacement are attenuated by the compliance involved in the strain amplification mechanism through kinematic and static analysis. An insightful lumped parameter model is proposed to quantify the performance degradation and facilitate design tradeoffs. A prototype-nested PZT cellular actuator that weighs only 15 g has produced 21% effective strain (2.5 mm displacement from 12-mm actuator length and 30 mm width) and 1.7 N blocking force.
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    Pinpointed Muscle Force Control Taking Into Account the Control DOF of Power-assisting Device
    (Georgia Institute of Technology, 2010-09) Ding, Ming ; Kurita, Yuichi ; Ueda, Jun ; Ogasawara, Tsukasa