Background reference level system and method for document scanners

Claim 2

In an apparatus for reading a document containing a plurality of data response areas arranged in columns and rows by measuring the intensity of light transmitted from said areas on the document, a system for establishing a basic reference level for measuring said light intensity, said system comprising a plurality of data channels corresponding in number to at least the number of data columns to be read, each data channel including a light sensitive device that produces an analog signal corresponding to the intensity of the light transmitted to it, means providing for the simultaneous scanning by all data channels of an area of the document containing no data, means for averaging the analog signals produced by all data channels during the scanning of said area containing no data, said averaging taking place prior to scanning of the data response areas, means for setting a reference level based upon said averaging of the analog signals from all of the data channels, detection means for detecting a reference level above or below predetermined limits, said detection means being connected to the output of the means for setting said reference level, comparative means in each data channel for comparing said reference level with the analog signal produced by the light sensitive device in each data channel, said comparative means providing an output indicating the magnitude of the analog signal as compared to said reference level, and means for manipulating the output from each of said comparative means to produce an indication of the light intensity detected.

Claim 3

The system of claim 1 in which said means for averaging the analog signals produced by the light sensitive devices in said data channels includes a series averaging resistor in each data channel through which said analog signal is fed, a summing resistor connected to said series resistors for averaging the analog signals, a capacitor for storing the average signal, and switching means for selectively connecting said summing resistor to said capacitor or for connecting said capacitor to said means for setting the reference level.

Claim 4

The system of claim 2 in which an amplifier is connected to the output of each light sensitive device in each data channel, the output of each amplifier being connected to a respective one of the series resistors and to a respective one of said comparative means, and said means for setting the reference level includes a gain adjustable amplifier, the input of which is connected to said capacitor through said switching means and the output of which is connected to each of said comparative means.

Claim 5

The system of claim 3 in which said switching means provides for connection of said summing resistor to said capacitor simultaneously with disconnecting said capacitor from the input of said gain adjustable amplifier, and for connection of said capacitor to the input of said gain adjustable amplifier simultaneously with disconnecting said capacitor from said summing resistor.

Claim 6

In an apparatus for reading a document containing a plurality of data response areas arranged in columns and rows by measuring the intensity of light transmitted from said areas on the document, a system for establishing a basic reference level for measuring said light intensity, said system comprising a plurality of data channels corresponding in number to at least the number of data columns to be read, each data channel including a light sensitive device that produces an analog signal corresponding to the intensity of the light transmitted to it, means providing for the simultaneous scanning by all data channels of an area of the document containing no data, means for averaging the analog signals produced by all data channels during the scanning of said area containing no data. said averaging taking place prior to scanning of the data response areas, means for setting a reference level based upon said averaging of the analog signals from all of the data channels including switching logic for setting a test reference level both above and below the typical analog signal of a data channel when scanning the area of said document containing no data, comparative means in each data channel for comparing said reference level with the analog signal produced by the light sensitive device in each data channel, said comparative means providing an output indicating the magnitude of the analog signal as compared to said reference level, said comparative means also comparing each of said test reference levels with the analog signal produced by the light sensitive device when scanning said no data area thereby producing an output from each said comparative means indicative of the performance of each data channel, and means for manipulating the output from each of said comparative means to produce an indication of the light intensity detected.

Claim 7

In an apparatus for reading a document containing a plurality of data response areas arranged in columns and rows by measuring the intensity of light transmitted from said areas on the document, a system for establishing a basic reference level for measuring said light intensity, said system comprising a plurality of data channels corresponding in number to at least the number of data columns to be read, each data channel including a light sensitive device that produces an analog signal corresponding to the intensity of the light transmitted to it, means providing for the simultaneous scanning by all data channels of an area of the document containing no data, means for averaging the analog signals produced by all data channels during the scanning of said area containing no data. said averaging taking place prior to scanning of the data response areas, means for setting a reference level based upon said averaging of the analog signals from all of the data channels including switching logic for setting a test reference level both above and below the typical analog signal of a data channel when scanning the area of said document containing no data, comparative means in each data channel for comparing said reference level with the analog signal produced by the light sensitive device in each data channel, said comparative means providing an output indicating the magnitude of the analog signal as compared to said reference level, said comparative means also comparing each of said test reference levels with the analog signal produced by the light sensitive device when scanning said no data area thereby producing an output from each said comparative means indicative of the performance of each data channel, and means for manipulating the output from each of said comparative means to produce an indication of the light intensity detected.

Claim 8

The system of claim 5 in which said means for averaging the analog signals from said data channels includes a series resistor in each data channel through which the analog signal is fed, a summing resistor connected to said series resistors for averaging the analog signals, a capacitor for storing the average analog signal, and switching means for selectively Connecting said summing resistor to said capacitor or for connecting said capacitor to said means for setting a reference level.

Claim 9

The system of claim 6 in which an amplifier is connected to the output of each light sensitive device in each data channel, the output of each amplifier being connected to a respective one of said series resistors and to a respective one of said comparative means, and said means for setting a reference level includes a gain adjustable amplifier the input of which is connected to said capacitor through said switching means and the output of which is connected to each of said comparative means, said gain adjustable amplifier being connected to said switching logic.

Claim 10

They system of claim 7 in which said switching means provides for connection of said summing resistor to said capacitor simultaneously with disconnecting said capacitor from the input of said gain adjustable amplifier and for connection of said capacitor to the input of said gain adjustable amplifier simultaneously with disconnecting said capacitor from said summing resistor.

Claim 13

The method of claim 9 in which the comparison of the analog output of the data channels produced during the no print area with the test reference levels takes place between the lead edge of the document and the data response area of the document.

Claim 14

The method of claim 9 in which said test reference levels and comparisons with the analog output signal of each data channel produced from a no print area are made more than once during the reading of a single document.

Claim 15

The method of claim 11 in which the comparison of the analog output signal of each data channel produced from a no print area with each of said test reference levels occurs between the last data response area and the trailing edge of the document.