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Position Detection Device Using Amplitude Modulation

IP.com Disclosure Number: IPCOM000075959D
Original Publication Date: 1971-Dec-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Walewski, LG: AUTHOR [+2]

Abstract

Described is a system for determining the position of a moving chain associated with a chain printer and utilizes an inductive probe or sensing element, for detecting the metallic spaced fingers comprising the chain printing element. An oscillator provides a signal of constant amplitude and frequency. This signal is amplitude modulated in a variable-voltage divider network. The divider includes the electromagnetic probe, the admittance of which is a function of its proximity to metallic material. The probe in conjunction with a capacitor, forms a circuit resonating near the oscillator frequency. The resonant circuit admittance variation is much greater than that of the probe alone.

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Position Detection Device Using Amplitude Modulation

Described is a system for determining the position of a moving chain associated with a chain printer and utilizes an inductive probe or sensing element, for detecting the metallic spaced fingers comprising the chain printing element. An oscillator provides a signal of constant amplitude and frequency. This signal is amplitude modulated in a variable-voltage divider network. The divider includes the electromagnetic probe, the admittance of which is a function of its proximity to metallic material. The probe in conjunction with a capacitor, forms a circuit resonating near the oscillator frequency. The resonant circuit admittance variation is much greater than that of the probe alone.

In this application, the passage of the moving chain printer consisting of metallic fingers spaced a fraction of an inch apart causes the probe to have a periodically varying admittance. The amplitude-modulated signal, developed by the probe voltage divider network, is nearly sinusoidally modulated with one amplitude extreme corresponding to the center of the print finger, while the other amplitude extreme corresponds to the center of the air gap between adjacent print fingers. The amplitude-modulated signal is demodulated and phase shifted 90 degrees; therefore, the sinusoidal amplitude peaks of the input to the phase-shifting circuit correspond to the zero-signal crossings of the output of the phase shifter. The output of the phase...