Direct digital design of computed torque controllers

Direct digital design of computed torque controllers for a robot manipulator is discussed in this article. A simple discrete-time model of the robot manipulator obtained by Euler's method is used for the design. Taking account of computation delay in the digital processor, we propose predictor-based designs of the PD and PID type controllers. The PID-type controller is designed based on a modified version of the discrete-time integral controller proposed by Mita. For both controllers, the feedback gains can be determined easily by using simple formulas. A simulation example is presented to illustrate the relevance of the proposed designs and the robustness of PID-type controller against physical parameter variations. © 1994 John Wiley & Sons, Inc.     

A Technique to Eliminate Redundant Inter-Processor Communication on Parallelizing Compiler TINPAR

Optimizing inter-processor (PE) communication is crucial for parallelizing compilers for message-passing parallel machines to achieve high performance. In this paper, we propose a technique to eliminate redundant inter-PE messages. This technique utilizes data-flow analysis to find a definition point that corresponds to a use point where the definition and the use occur in different PEs. If several read accesses occurred in the same PE use the data defined at the same definition point in another PE, redundant inter-PE messages are eliminated as follows: only one inter-PE communication is performed for the earliest read access and the previously received data are used for the following read. In order to guarantee the consistency of the data, a valid flag and a sent flag are provided for each chunk of received data. The control of these flags is equivalent to the coherence control by the self invalidation on a compiler aided cache coherence scheme.     

Buoyancy engine developed for underwater gliders

A buoyancy engine with a swashplate-type axial piston pump was developed. Its oil extrusion and drawing properties under high hydraulic pressure were evaluated. This buoyancy engine is now installed in an underwater glider that will achieve long-term monitoring of ocean environments up to 2100 m depth in a designated area with lower operational costs. This bidirectionally functioning pump can control the amount of oil in extrusion and draw operations. When drawing oil under high pressure, the hydraulic pump and the electric motor, respectively, act as a hydraulic motor and an electric generator. The generated electric power is absorbed by a damping resistor. The oil-drawing and extrusion properties were measured using a large hyperbaric chamber that is able to produce an almost identical environment to that of actual operations. Results confirmed stable oil extrusion operations up to 21 MPa. Regarding oil-drawing properties, although it was measured only up to 10 MPa in the hyperbaric chamber, it can be inferred that the system can draw the oil and can control the buoyancy precisely up to 21 MPa by replacing the two-way ball valve with an electromagnetic latching solenoid valve.     

Output feedback of Markov jump linear systems with no mode observation: An automotive throttle application

The note presents an output feedback control strategy for Markov jump linear systems with no mode observation. Based on minimizing a finite‐time quadratic cost, we derive an algorithm that generates output feedback gains that satisfy a necessary optimality condition. These gains can be computed off‐line relying only on the initial condition of the system. This result expands a previous one from the literature that considered state‐feedback only. To illustrate the usefulness of the approach, real‐time laboratory experiments were performed to control an automotive electronic throttle valve subject to Markov‐driven voltage fluctuations. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimal initial production control period based on a quality growth model

The initial production phase of new products or the initial installation phase of new manufacturing facilities is often unstable because of inexperienced workers and many defective products. An initial production process control, in which the defects in design, production technologies and products are fully fixed and removed, is switched to a normal process control whenever it is ready for actual mass production. This paper discusses a method of deciding the optimal initial production control period, based on a quality growth model. It is determined by the number of products with the minimum expected total quality control cost. Finally a penalty cost due to unattainable loss to the quality goal is introduced in the quality control cost: the realized stabilization level of the initial production process control is lower than the original quality objective. Numerical illustrations of the optimal policy are also presented. Copyright © 1999 John Wiley & Sons, Ltd.     

Scalability of hybrid programming for a CFD code on the Earth Simulator

The Earth Simulator (ES) is an SMP cluster system. There are two types of parallel programming models available on the ES. One is a flat programming model, in which a parallel program is implemented by MPI interfaces only, both within an SMP node and among nodes. The other is a hybrid programming model, in which a parallel program is written by using thread programming within an SMP node and MPI programming among nodes simultaneously. It is generally known that it is difficult to obtain the same high level of performance using the hybrid programming model as can be achieved with the flat programming model.

In this paper, we have evaluated scalability of the code for direct numerical simulation of the Navier–Stokes equations on the ES. The hybrid programming model achieves the sustained performance of 346.9 Gflop/s, while the flat programming model achieves 296.4 Gflop/s with 16 PNs of the ES for a DNS problem size of 256³. For small scale problems, however, the hybrid programming model is not as efficient because of microtasking overhead. It is shown that there is an advantage for the hybrid programming model on the ES for the larger size problems.     

Stationary policies for lower bounds on the minimum average cost of discrete‐time nonlinear control systems

The paper deals with the control problem of discrete‐time nonlinear systems. The main contribution of this note is to present conditions that assure the existence of stationary policies that generate lower bounds for the minimal long‐run average cost. These lower bounds coincide with the optimal solution when a mild convergence assumption holds. To illustrate the results, the paper presents an application for the simultaneous state‐feedback control problem, and the derived strategy is used to design a real‐time simultaneous control for two direct current motor devices. The dynamics of these two devices are written in terms of a nonlinear algebraic matrix recurrence, which in turn represents a particular case for our general nonlinear approach. The optimal gain for the corresponding simultaneous state‐feedback problem is obtained, and such a gain was implemented in a laboratory testbed to control simultaneously the two direct current motors. Copyright © 2013 John Wiley & Sons, Ltd.     

Tracking a Sea Turtle by an AUV with a Multibeam Imaging Sonar: Toward Robotic Observation of Marine Life

International Journal of Control, Automation and Systems - This paper proposes a method for autonomous underwater vehicles to chase sea turtles without attaching any tag to them, toward efficient...     

Analysis of magnetic fields of a delta type shunt reactor

A model is given and a periodic boundary condition is adopted to analyze magnetic fields of a delta type shunt reactor. An approximate three-dimensional finite-element method that combines some axisymmetric fields and a two-dimensional field is then applied. It is found that the flux in the yoke concentrates on the part that is near the legs. The flux density heightens as the legs is approached, and rotational magnetic flux occurs in the parts joined by a leg and the yoke. All flux density waveforms contain mainly third harmonics. It is found that there is rotating flux in the yoke, which causes increased core losses     

Relationship between crystallinity and device characteristics of In‐Sn‐Zn oxide

We have reported that the transistors having the c‐axis‐aligned crystalline (CAAC) In‐Ga‐Zn oxide (IGZO) show good performance. Recently, In‐Sn‐Zn Oxide (ITZO) has attracted much attention because of its high electron mobility, as well as IGZO. However, it has been reported that ITZO field effect transistors (FET) tend to have positive Vth (normally‐on characteristics) and poor reliability compared with IGZO‐FETs. We have reported that high‐performance and high‐reliability OS‐FETs can be fabricated by using CAAC‐IGZO, which has high crystallinity and has no clear grain boundaries, as an active layer. Therefore, we have fabricated CAAC‐ITZO thin films to improve performance of ITZO‐FETs by using CAAC‐ITZO as an active layer. In addition, FETs employing CAAC‐ITZO have better characteristics and reliability than FETs using nano‐crystal ITZO. Furthermore, constant photocurrent method (CPM) measurement was carried out in order to estimate density of deep‐level defect states caused by oxygen vacancies in oxide semiconductors. The results show that CAAC‐ITZO has lower density of deep‐level defect states than nano‐crystal ITZO. We attribute the improvement in reliability of ITZO‐FETs to a decrease in deep‐level defect states of an ITZO active layer, as is the case with IGZO.