Online force control of a shape-memory-alloy-based 2 degree-of-freedom human finger via inverse model and proportional–integral–derivative compensator

In this work, a model-based controller is developed to track the force at fingertip of an artificial hand. To do so, shape-memory-alloy wires are implemented as an actuator in the finger. Besides, different aspects of modeling, including force relations, kinematics, and heat transfer analysis, are investigated. A modified version of Brinson’s model is used to capture thermomechanical behavior of shape-memory-alloy wires. A controller is designed to control the applied potential difference between shape-memory-alloy wires and consequently control the electrical current in these wires based on the shape-memory-alloy wires model. The main goal of the proposed controller is force controlling of a 2-degree-of-freedom hand finger. This controller contains shape-memory-alloy constitutive model used for compensating system uncertainties. Furthermore, a proportional–integral–derivative controller/compensator is included in the closed-loop system. The compensator acts only on the derivative-type states, and this is one of the differences of this work compared to that of similar literature. The results of three arbitrary reference input signals are reported confirming the model prediction and simulation results are in good agreement with experimental tests. The analysis of the relative tracking error for an arbitrary reference signal is 11% in experimental test and 4% in the simulation.

REALISMO E INDETERMINATEZZA NEI FONDAMENTI DELLA MATEMATICA

Two of the most influential foundational approaches in the philosophy of mathematics of the past thirty years, i.e. neologicism and ante rem mathematical structuralism, suffer from metaphysical and semantic indeterminacy. My present aim is to offer an explanation of this phenomenon and provide a solution in terms of arbitrary reference.

Posture Control of Two Link Torque Unit Manipulator Considering Influence of Viscous Friction on Joints

In this research, we consider a posture control problem of a planar two-link torque unit manipulator under a viscous friction condition. The torque unit is a module that consists of an electric motor and a reaction wheel. The friction caused by the presence of a viscous environment cannot be ignored in the real system. In this report, we first clarify the relation between the angle of links and the angular momentum of the reaction wheels under the viscous friction condition. Next, we try to control the first link at an arbitrary reference position without taking into consideration the angle of the second link. The angle of the first link can be controlled by changing the viscous friction condition between the first link and the base. Moreover, we attempt to control the second link at an arbitrary reference position by using the residual angular momentum of the reaction wheel at the second link. Finally, we demonstrate the feasibility of the proposed method by conducting a verification experiment.

Structuralist Neologicism†

ABSTRACT Neofregeanism and structuralism are among the most promising recent approaches to the philosophy of mathematics. Yet both have serious costs. We develop a view, structuralist neologicism, which retains the central advantages of each while avoiding their more serious costs. The key to our approach is using arbitrary reference to explicate how mathematical terms, introduced by abstraction principles, refer. Focusing on numerical terms, this allows us to treat abstraction principles as implicit definitions determining all (known) properties of the numbers, achieving a key neofregean advantage, while preserving the key structuralist advantage, which objects play the number role does not matter.