Ultrasonic Position Indicator
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Described herein is a means of locating the position of a printhead using ultrasonic sound. The time that a sound wave propagates through air is measured and that time is proportional to the distance from the transmitter to the receiver. There are several problems associated with a simple measurement of the transit time of the wave. First, the velocity of sound is 1100 feet/second at 25ŒC and one atmosphere of pressure. As the temperature increases, the velocity of sound changes by one foot/second per degree Fahrenheit. Second, the number of times per second the position can be determined is inversely proportional to the distance to be measured because, usually, only one pulse is sent and the next pulse is not transmitted until the first pulse is received. The distance to be measured is approximately 15 inches.