A 17-in. video rate full color Ferroelectric Liquid Crystal Display (FLCD) with 720•~916 dots, using r-Vmin mode was developed. The full color moving images with 256 gray levels for each color was displayed by the digital gray scale method combining 2 bits spatial dither and 4 bits temporal dither. The response speed of FLC material is very fast (12 ps/line) and the 4 bits temporal dither with video rate scanning was realized. The FLCD shows a contrast ratio of 60 : 1, a wide viewing angle due to the in-plane switching, and strong shock stability (20 kg/cm2) due to the spacer walls structure. This paper presents a high potential of FLCD for the large-size direct-view video-rate full-color simple-passive-matrix flat panel display.
A lot of brushless DC motors are adopted in the compressor of the air conditioner and the refrigerator because of the maintenance-free and highly effective. And, sensorless drive using back electromotive force (EMF) is widely used for these motor controls.However, it is very difficult to apply the sensorless drive at the start sequence because the EMF is too low to detect. Therefore, an open loop drive that controlled by fixed switching pattern is used at the start sequence. After acceleration up to the appropriate speed, the drive method switches to the sensorless drive from the open loop drive.This start sequence has some problems. The motor output torque and the rotational speed change greatly when the motor is driven by an open loop control, and it causes the vibration. Furthermore, it is important to adjust the switching patterns of the open loop appropriately. If it is not adjusted appropriately, the switch to the sensorless drive may fail.In this paper, we propose new start method suitable for sensorless brushless DC motor drive systems. The proposed method introduces new switching patterns at the start point. The switching patterns are determined by motor parameters. Using this method, the open loop drive sequence can be eliminated. Fig. 1 shows the simulation result of the motor output torque and the rotational speed of conventional open loop start method.The motor output torque and rotational speed change greatly and the vibration occurs after the start. Fig. 2 shows the simulation result of the motor torque output and the rotational speed of new start method.The motor output torque and the rotational speed are smooth from the start. Fig. 3 shows the experimental result that shows applied voltage and the motor current waveform at the start. The smooth acceleration is obtained using the proposed method. As mentioned above, we has proposed new start method for brushless DC motors. Rapid acceleration and high performance can be achieved. The simulation and experimental results demonstrated the validity of the proposed method.
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