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Control Systems, IEEE

Issue 3 • Date June 1997

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Displaying Results 1 - 9 of 9
  • 1996 IEEE Control Systems Award

    Page(s): 112 - 115
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    Freely Available from IEEE
  • Variable structure control of shape memory alloy actuators

    Page(s): 80 - 88
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    A shape memory alloy (SMA) actuator consisting of a number of thin NiTi fibers woven in a counter rotating helical pattern around supporting disks is first described. This structure accomplishes a highly efficient transformation between force and displacement overcoming the main mechanical drawback of shape memory alloys, that being limited strain. Time domain open loop experiments were then conducted to determine the intrinsic properties of the actuator. From these experiments and from the knowledge of the underlying physics of SMAs, a multiterm model, including linear and nonlinear elements, was proposed. After further investigation and simulation, it was found that most of these complexities did not need to be considered in order to explain the reported results, and that the model could be reduced to that of a single integrator. A variable structure controller was then applied to a pair of antagonist actuators. The feedback switches between the two actuators according to the sign of the displacement error. A further improvement was added to compensate for known gross nonlinearities by modulating the current magnitude in a discrete manner as a function of the state space position. It was therefore possible to realize smooth and robust control with very little cost in complexity View full abstract»

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  • Design and experimentation of a jump impact controller

    Page(s): 99 - 106
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    An impact/force controller known as jump impact controller (JIC) is designed and evaluated experimentally. JIC is derived by representing dynamics of collision in terms of a jump linear system where the jumps of system dynamics can be described by a state-dependent stochastic process. Thus, JIC provides robustness to the uncertainties in the environment dynamics as well as the location of the collision surface. The experimental results not only demonstrate the robustness of JIC but also help explain and interpret how robustness is associated with the JIC theory in terms of such known concepts as approach velocity and control system bandwidth View full abstract»

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  • Motion planning of a pneumatic robot using a neural network

    Page(s): 89 - 98
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    Integration of sensing and motion planning plays a crucial role in autonomous robot operation. We present a framework for sensor-based robot motion planning that uses learning to handle arbitrarily configured sensors and robots. The theoretical basis of this approach is the concept of the perceptual control manifold that extends the notion of the robot configuration space to include sensor space. To overcome modeling uncertainty, the topology-representing-network algorithm is employed to learn a representation of the perceptual control manifold. By exploiting the topology-preserving features of the neural network, a diffusion-based path planning strategy leads to flexible obstacle avoidance. The practical feasibility of the approach is demonstrated on a pneumatically driven robot arm (SoftArm) using visual sensing View full abstract»

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  • 300 years of optimal control: from the brachystochrone to the maximum principle

    Page(s): 32 - 44
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    An historical review of the development of optimal control from the publication of the brachystochrone problem by Johann Bernoulli in 1696. Ideas on curve minimization already known at the time are briefly outlined. The brachystochrone problem is stated and Bernoulli's solution is given. Bernoulli's personality and his family are discussed. The article then traces the development of the necessary conditions for a minimum, from the Euler-Lagrange equations to the work of Legendre and Weierstrass and, eventually, the maximum principle of optimal control theory View full abstract»

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  • An elliptic friction drive element using an ICPF actuator

    Page(s): 60 - 68
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    The ionic conducting polymer gel film (ICPF) actuator, which has advantages such as low driving voltage, high speed, and underwater motion, was discovered in 1992. This article presents a new actuator element using the ICPF which generates an elliptic motion, as used in ultrasonic motors, to drive objects by friction. A method of forming a pattern of ICPF on a membrane was developed for production of the element. Some robotic applications are proposed. Experimental elements effectively functioned as driving devices and successfully drove a rotary motor as a testimony. Experiments and modeling revealed the relationship of the resultant elliptic motion to control signals and design parameters View full abstract»

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  • Robust control prevents car skidding

    Page(s): 23 - 31
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    The author discusses a system of robust unilateral decoupling of car steering dynamics. Its effect is that the driver has to concern himself much less with disturbance attenuation. The important quick reaction to disturbance torques is done by the automatic feedback system. The yaw dynamics no longer interfere with the path-following task of the driver. The safety advantages have been demonstrated in experiments with a test vehicle. By empirical improvements, we have modified the controller such that it preserves the robust decoupling advantages for the first 0.5 seconds after a disturbance and then returns the steering authority gradually back to the driver View full abstract»

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  • Nonlinear design of active suspensions

    Page(s): 45 - 59
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    This article develops a new nonlinear backstepping design for the control of active suspension systems, which improves the inherent tradeoff between ride quality and suspension travel. The novelty is in the use of a nonlinear filter whose effective bandwidth depends on the magnitude of the suspension travel. This intentional introduction of nonlinearity, which is readily accommodated by backstepping, results in a design that is fundamentally different from previous ones: as the suspension travel changes, the controller smoothly shifts its focus between the conflicting objectives of ride comfort and rattlespace utilization, softening the suspension when suspension travel is small and stiffening it as it approaches the travel limits. Thus, our nonlinear design allows the closed-loop system to behave differently in different operating regions, thereby eliminating the dilemma of whether to use a soft or stiff suspension setting. The improvement achieved with our design is illustrated through comparative simulations View full abstract»

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  • Modeling piezoelectric stack actuators for control of micromanipulation

    Page(s): 69 - 79
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    A nonlinear lumped-parameter model of a piezoelectric stack actuator has been developed to describe actuator behavior for purposes of control system analysis and design, and, in particular, for microrobotic applications requiring accurate position and/or force control. In formulating this model, the authors propose a generalized Maxwell resistive capacitor as a lumped-parameter causal representation of rate-independent hysteresis. Model formulation is validated by comparing results of numerical simulations to experimental data. Validation is followed by a discussion of model implications for purposes of actuator control View full abstract»

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Richard D. Braatz
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