Highly reliable strip width gauge

Claim 2

Apparatus for measuring the width of a strip comprising: means for illuminating each edge of the strip with radiant energy of a frequency other than the frequency of the background illumination; photodetecting means positioned adjacent each edge of the strip for generating an edge signal indicative of the portion of radiant energy permitted to reach each photodetecting means by the adjacent edge of the strip; summing means responsive to the edge signal from said photodetecting means at each edge of the strip for summing the two edge signals whereby a width signal is generated; width detecting means for detecting variations in the width signal and thereby variations in the width of the strip; coupling means responsive to said summing means for limited frequency coupling of the width signal to said width detecting means whereby only width-signal frequency components representative of radiant energy from said illuminating means are coupled to said width detecting means; second photodetecting means positioned adjacent said illuminating means for generating a reference signal proportional to the radiant energy emitted by said illuminating means; second coupling means responsive to said second photodetecting means for limited frequency coupling of the reference signal to said width detecting means whereby only reference-signal frequency components representative of radiant energy from said illuminating means are coupled to said width detecting means; difference amplifying means in said width detecting means for taking the difference between the width signal and the reference signal whereby the reliability and sensitivity of the width measurement is enhanced.

Claim 3

The apparatus of claim 1 and, in addition: balance adjustment means in said width detecting means for adjusting the amplitude and phase of the reference signal relative to the width signal so that for normal strip width said difference amplifying means will have a null output.

Claim 4

The apparatus of claim 1 and, in addition: rectifying means in said width detecting means for rectifying the width signal and the reference signal before they are applied to said difference amplifying means whereby the output of said difference amplifying means is substantially a DC level having low frequency variations reflecting variations in strip width.

Claim 5

Apparatus for gauging the width of magnetic tape comprising: a pair of light emitting diodes; a photodiode associated with each light emitting diode and positioned on the opposite side of the tape from its associated light emitting diode for generating an edge signal based upon the intensity of the light reaching the photodiode from its associated light emitting diode; an AC signal source for driving said light emitting diodes so that they emit light that varies in intensity at a frequency different from the background illumination of the tape; means for directing the light from each light emitting diode past the edge of the tape to its associated diode whereby the amount of light reaching each photodiode is indicative of the position of the edge of the tape; means for summing the edge signals from the pair of photidiodes to thereby produce a width signal; means responsive to said summing means for filtering the width signal so that it contains frequency components which are substantially only the frequency of said AC source; means responsive to a filtered width signal for detecting variations in the width of the tape from variations in the amplitude of the filtered width signal; a reference photidiode associated with each light emitting diode for generating a signal whose amplitude is proportional to the light emitted from its associated light emitting diode; second means for summing the signals from the pair of reference photodiodes to thereby produce a reference signal; second filtering means responsive to said second summing means for filtering the reference signal whereby the frequency components of the reference signal are substantially only the frequency of said AC source; means responsive to said filtered reference signal and said filtered width signal for subtracting the two signals to produce an absolute filtered width signal for passage to said detecting means.

Claim 6

Apparatus for gauging the width of magnetic tape comprising: a pair of light emitting diodes; a photodiode associated with each light emitting diode and positioned on the opposite side of the tape from its associated light emitting diode for generating an edge signal based upon the intensity of the light reaching the photodiode from its associated light emitting diode; an AC signal source for driving said light emitting diodes so that they emit light that varies in intensity at a frequency different from the background illumination of the tape; means for directing the light from each light emitting diode past the edge of the tape to its associated diode whereby the amount of light reaching each photodiode is indicative of the position of the edge of the tape; means for summing the edge signals from the pair of photidiodes to thereby produce a width signal; means responsive to said summing means for filtering the width signal so that it contains frequency components which are substantially only the frequency of said AC source; means responsive to a filtered width signal for detecting variations in the width of the tape from variations in the amplitude of the filtered width signal; a reference photidiode associated with each light emitting diode for generating a signal whose amplitude is proportional to the light emitted from its associated light emitting diode; second means for summing the signals from the pair of reference photodiodes to thereby produce a reference signal; second filtering means responsive to said second summing means for filtering the reference signal whereby the frequency components of the reference signal are substantially only the frequency of said AC source; means responsive to said filtered reference signal and said filtered width signal for subtracting the two signals to produce an absolute filtered width signal for passage to said detecting means.

Claim 7

The apparatus of claim 4 and, in addition: means for adjusting the amplitude and phase of the filtered reference signal relative to the filtered width signal prior to the application of both signals to said subtracting means.

Claim 8

The apparatus of claim 4 and, in addition: means for converting the filtered reference signal and the filtered width signal into substantially DC signals before application to said subtracting means.

Claim 9

Method for measuring the width of strips with radiant energy of a frequency other than the frequency of background illumination, said radiant energy being produced by radiant energy source and being monitored by radiant energy detector, said method comprising the steps of: modulating the radiant energy with variations in the strip width by positioning the strip to partially block the radiant energy path from the radiant energy source to the radiant energy detector; filtering the modulated radiant energy signal from the detector so that the filtered signal does not contain frequency components due to radiant energy from sources other than the radiant energy source; monitoring the radiant energy emitted from the radiant energy source and thereby generating a reference signal; subtracting the reference signal from the modulated filtered signal whereby only the modulation of the filtered signal remains and is indicative of the width of the strip.

Claim 10

Method for measuring the width of strips with radiant energy of a frequency other than the frequency of background illumination, said radiant energy being produced by radiant energy source and being monitored by radiant energy detector, said method comprising the steps of: modulating the radiant energy with variations in the strip width by positioning the strip to partially block the radiant energy path from the radiant energy source to the radiant energy detector; filtering the modulated radiant energy signal from the detector so that the filtered signal does not contain frequency components due to radiant energy from sources other than the radiant energy source; monitoring the radiant energy emitted from the radiant energy source and thereby generating a reference signal; subtracting the reference signal from the modulated filtered signal whereby only the modulation of the filtered signal remains and is indicative of the width of the strip.