Thomas W. Secord

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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(More)
A new approach to a variable stiffness actuator with tunable resonant frequencies is presented in this paper. Variable stiffness actuators have become increasingly important to meet safety requirements and achieve adaptive manipulation or locomotion. For cyclic motion, exploiting dynamic resonance can lead to high power transmission, high energy efficiency,(More)
The demand for high-force and compact actuators with large strain is increasing in robotics. PZT is known as one of the promising materials for this purpose with respect to bandwidth, stress, and reliability. However, the most critical drawback of PZT is its extremely small strain, i.e. only 0.1 %. This paper presents a nested rhombus structure for strain(More)
A static lumped parameter model is proposed for the design and analysis of nested piezoelectric cellular actuators with exponential strain amplification mechanisms. 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(More)
A simple and efficient approach for varying the inherent stiffness and impedance of a muscle-like actuator is presented. The basic architecture of PZT cellular actuators has already achieved a large effective strain (10–20%). This architecture is modified and extended so that each cellular unit can be switched between a zero compliance state and(More)
This paper presents the dynamic analysis of an artificial muscle actuator designed for high-bandwidth, power- law strain amplification. The actuator is based on a nested cellular architecture of PZT stack actuators. Most smart material actuators have seen limited use in mobile robotic applications because of their small strain, low stress capacity, low(More)
This paper presents the design and analysis of a novel variable stiffness and variable resonance actuator based on a cellular arrangement of piezoelectric devices. The cellular muscle actuator design concept is presented followed by a general dynamic model for establishing the theoretical bounds on achievable resonant frequencies. A model that is specific(More)
Experiments were performed using commercially available, self-contained, multilayer polypyrrole (PPy) actuators to develop low-order lumped parameter models of actuator electrical, mechanical, and electromechanical behavior. Experimental data were processed using system identification techniques. Both grey box and black box models were identified. The grey(More)
This paper describes the design and analysis of a humanoid foot constructed using polypyrrole (PPy) conducting polymer (CP) actuators. The compliance and damping of natural muscles plays an important role in natural human gait. Conducting polymers actuators and other smart structure actuators can store energy by means of inherent mechanical compliance that(More)
Variable stiffness actuation and energy harvesting have been important yet separate challenges in robotics. Both functions are needed, however, for mobile robots on extended missions when actuators and generators must be used together. In this paper, we present a unique piezoelectric cellular system that combines motion generation and energy harvesting(More)