The application of Petri Net to the design and operation of sequential control systems is widely devoloped. It is considered that Petri Net may be automatically generated by computer. Especially, in recent years, the possibility of utilization of ES(Expert System) has been explored, as ES is effective in acquiring and using the knowledge of experts. On the other hand, there are two points to solve in approaching the usual knowledge engineering, that is, (1) the management and utilization of knowledge, and (2) the reconstruction of knowledge. In order to cope with these two points, we provide “multi-purpose knowledge base”, which highly abstracts the knowledge, and “problem-oriented knowledge base”, which stores the necessary knowledge to solve a concrete problem. Based on the above knowledge bases, we construct ES with a knowledge-management module, which canmanage knowledge and reconstruct the later base. It is pointed out that the knowledge-management module may be applied to ES of designing type domain. This paper gives an example to show the management and utilization of the knowledge in our ES.

View full abstract

This paper describes a low current magnetic rotary encoder which is characterized by MR elements (Magneto Resistive elements) with current sources.
A magnetic encoder consists of a magnetic drum, MR elements, and a volatge comparator. The magnetic drum is mult-magnetized. The MR elements are connected to a bridge circuit and trans-form a magnetic signal into a voltage signal. However, this bridge type arrangment has less flexibility for pattern design.
Next, we propose a new drive method of MR elements. It replaces the MR elements connected to the ground by current sources. Comparing it to the conventional type, we have found that the new type has more flexibility in pattern design. Therefore, we can connect many MR elements in series, and achieve low current.
We made this encoder in which twelve MR elements are connected in series. It has a bi-phase rectangular wave at its output. It spends the current of 3.3mA, where the output voltage of power supply is 4.2V. This is an allowable value for the absolute encoder.

View full abstract

Inverter systems are now being applied as the power source in large scale equipment. In the present paper, a highly reliable configuration of a large capacity inverter control system is proposed.
In order to make the inverter system highly reliable, enhanced reliability of its control system is a necessity. This control system consists of triple redundant controllers and signal selection circuits which select the most reasonable control signals. The number of signal selection circuits corresponds to that of switching elements in an inverter. Each signal selection circuit consists of a majority voting gate in which any stuck faults can be excluded by eliminating the DC-power supply. Since the control system controls the switching elements, the control signals should be synchronized. Then, each controller has a synchronous circuit. Synchronizing signals are produced by voting trigger signals from the controllers themselves. By applying the above synchronizing method, even if one synchronous circuit fails, the controllers connected to the other synchronous circuits are able to generate normal control signals.
Therefore the reliability of the inverter system is enhanced, and mean time between failures (MTBF) on the system is three times longer than that on an inverter system consisting of conventional triple redundant controllers.

View full abstract

General purpose inverters have been widely used for driving induction motor. In this type of inverter, V/f ratio constant control has been utilized. However, this control does not always satisfy all sorts of the specification required from the user side. For example, deterioration of torque in low speed range or large driving speed regulation etc. are problems to be solved. Although to improving this problem, vector control without speed sensor-so-called PG-less control-has been proposed, the system needed complicated observer.
In this paper, PG-less vector control system with the estimating functions of the motor parameters is proposed. If the rating parameters of the motor are given, the system automatically estimates the optimum constants for control, and the stable vector control is achieved. This system is also constructed simple control equations.
In this paper, system construction, performance characteristics and the principal of estimating motor parameters are discussed. The simulation and the experimental results of the tested machine shows that this method can be expected for the general purpose inverter.

View full abstract

By using the vector control strategy, PWM inverter-fed induction motor drive system is used in various fields. In this case, a conventional PI speed control is widely used as the major feedback loop. In this paper, the application of model following servo (MFS) control to the vector controlled induction motor drive system is studied to achieve superior performance compared with the PI controller.
At first, by assuming ideal vector control, a MFS controller is designed to minimize a specified performance index. Secondly, in order to study the influence of machine parameter change, a linear model is derived by using a small displacement theory. Finally, the computed and the experimental results are discussed from the viewpoints of the trajectories of poles and zeros, and the transient responses. As the result of the analysis, the pole of induction motor is close to the zero by choosing the large value of the weighting constant in spite of the change of rotor resistance. And the superiority of the MFS control as compared with the PI control is maintained when the rotor resistance is changed.

View full abstract

It is important to measure the growth of plant for analyzing the physiological phenomenon of plant. As the growth of plant is usually measured by the sensor that touches on plant, it is influenced by touching pressure. Especially, there is no literature about measuring a little young plant just after germination.
The equipment measuring stem diameter is made by the combination the Linear DC Motor(LDM) and optical sensor. It can measure stem diameter without touching on it at arbitrary periodin long term. This LDM has a new type linear suspension and flat type linear variable differential transformer (LVDT). As the mover of the LDM is held by the special spring suspension, that is driven to only one direction without friction and displacement to other direction. The new LVDT, composed in the LDM, is constructed of four fixed detective coils and magnetic driving coil, that is used as both the thrust coil of the mover, So that the LDM can detect fine position.
The optical probe, that is the beam of a LED and a photo diode, is drived for 20.48mm by the mover, and the apparatus can detect the maximam diameter 20mm of growth of plant stem for fine displacements less than 5 μm errors.

View full abstract

This paper describes a brushless DC motor system without position or speed sensor. The brushless DC motor consists of a permanent magnet synchronous motor and a voltage-source inverter which is capable of controlling the amplitude and frequency of voltage. The rectangular-shaped stator current with a conducting interval of 120° (electrical) is controlled to be in phase with the trapezoidal back electromotive force. This results in producing maximum torque. Variable speed is achieved by adjusting the average motor voltage, just like chopper control of DC motors.
In this paper, two sensorless position detecting methods, “indirect method” suited at lower speed range and “direct method” suited at higher speed range, are proposed. The combination of the two makes it possible to detect the rotor position over a wide speed range. Furthermore, a speedsensorless PLL control is proposed, applying the principle of the direct method. Experimental results obtained from a prototype brushless DC motor are shown to confirm the validity of the sensorless drive. The starting procedure of the motor is also discussed because it is impossible to detect the rotor position at a standstill.

View full abstract

Not a few types of d-and q-axis equivalent circuits for analysis of electrical transients of synchronous machines have been proposed. However these circuits, in general, have the same structure fundamentally except the rotor circuit composed of field and damper circuits. Therefore these several types of d-and q-axis circuits may be considered to have some properties in common. This paper investigates the fundamental properties of d-and q-axis equivalent circuits and basic equations by using the generalized d-and q-axis circuits whose rotor circuits are expressed by two-port networks.
At first, the generalized d-and q-axis equivalent circuits are shown and the basic equations for analysis of electrical transients are derived from them. And the basic properties of the four transfer functions (d-and q-axis operational inductances, and two armature-to-field transfer functions) appearing in the basic equations are analyzed. Next, some problems encountered on constructing d-and q-axis circuits by using these transfer functions are noted. Finally, the fundamental theory of three test methods which are based on the determination of the transfer functions (frequency response method, three-phase short circuit test and stator decrement test) are developed by using the basic equations derived here, and their fundamental meanings are clarified.

View full abstract