Burns, Doane, Swecker & Mathis
Film manufacturing apparatus with bubble controlling sensor
 A film manufacturing apparatus includes a circular die having a lip-shaped circular outlet for extruding a molten plastic in an annular form and an air passage for blowing air into the annular molten plastic to form a bubble. A water containing cooling ring cools the bubble and restrains the bubble so as to form a tubular plastic film below the cooling ring. An ultrasonic sensor is arranged near the circular die and extends substantially downwardly obliquely toward the center of the bubble for detecting the distance between the surface of the bubble and the ultrasonic sensor, and a controller controls an air supply regulating valve arranged in a line leading to the air passage to control the size of the bubble. Also, an ambient temperature sensor is arranged for correcting the speed of the ultrasonic signal, and a receiving time selecting device is arranged for correcting the time period during which an ultrasonic signal reflected from the bubble can be received. 
Nippon Petrochmicals Company, Limited
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Hideo Masao
Yamanaka Saito