Electronic compensation for optical system focal length variation

Claim 2

In an optical scanning system of the type having optical means for focusing incident light enErgy on an object, said optical means having a predetermined actual focal length, the value of said focal length lying within a fixed range about some prescribed value and wherein deviations from said prescribed focal length result in fixed and proportional system scanning errors, means for receiving scanned light energy and for transducing said light energy into a representative electronic signal, and also means for electronically converting said representative electronic signal into digital form, wherein the improvement comprises: means for electronically correcting for fixed and proportional scanning errors resulting from any difference between the value of the actual focal length in said optical means and said prescribed value.

Claim 3

In an optical scanning system of the type having optical means for focusing incident light energy on an object and scanning said light energy across said object, said optical means having a predetermined actual focal length, the value of said focal length lying within a fixed range about some prescribed value and wherein deviations from said prescribed focal length result in fixed and proportional system scanning errors, means for receiving scanned light energy and for transducing said light energy into a representative electronic signal, and means for converting said representative electronic signal into digital form, wherein the improvement comprises: means for providing a digitizing signal to effect said digital conversion, said signal having a frequency causing said fixed scanning error for said optical means to be always either greater than or less than the error corresponding to a reference focal length value lying outside of said fixed range; and means responsive to said digitizing signal for electronically correcting said digital form of electronic signal for fixed and proportional system scanning errors resulting from any difference between the value of said actual focal length and the value of said prescribed focal length.

Claim 4

In an optical scanning system of the type having optical means for focusing incident light energy on an object and scanning said light energy across said object, said optical means having a predetermined actual focal length, the value of said focal length lying within a fixed range about some prescribed value and wherein deviations from said prescribed focal length result in fixed and proportional system scanning errors, means for receiving scanned light energy and for transducing said light energy into a representative electronic signal, and means for converting said representative electronic signal into digital form, wherein the improvement comprises: means for providing a digitizing signal to effect said digital conversion, said signal having a frequency causing said fixed scanning error for said optical means to be always either greater than or less than the error corresponding to a reference focal length value lying outside of said fixed range; and means responsive to said digitizing signal for electronically correcting said digital form of electronic signal for fixed and proportional system scanning errors resulting from any difference between the value of said actual focal length and the value of said prescribed focal length.

Claim 5

The optical scanning system of claim 2, wherein said digitizing signal frequency is selected to correspond to a particular focal length to achieve a desired system scale factor and said digitizing signal frequency is chosen to be higher than the frequency which corresponds to the minimum focal length of said fixed range whereby the fixed system error will always be positive.

Claim 6

The apparatus of claim 2, including means for disabling the correcting means so that the necessary fixed and proportional correction factors may be measured.

Claim 7

The scanning system of claim 4, wherein said digitizing signal is a train of pulses and the correcting means includes a proportional correction circuit for periodically deleting pulses of said digitizing signal to provide a corrected digitizing signal which is compensated for proportional system scanning errors.

Claim 8

The scanning system of claim 4, wherein the correcting means also includes a fixed correction circuit and an output gate each responsive to said corrected digitizing signal, said fixed correction circuit providing a delayed output signal for blocking said gate from transmitting the corrected digitized signal to main system counters for a duration of time corresponding to the offset error in digital form so that the offset error may be compensated for.

Claim 9

The apparatus of claim 5, wherein the proportional correction circuit includes means for manually inserting signals corresponding to the measured correction factor.

Claim 10

The apparatus of claim 6, wherein the fixed correction circuit includes means for manually inserting signals corresponding to the measured correction factor.

Claim 11

The apparatus of claim 8, wherein said measured correction factor signals are in digital form and wherein said fixed correction circuitry includes a presettable reverse counter, said counter being preset at a predetermined time by said measured correction factor signals in digital form, said counter being supplied with said corrected digitizing signal so that the couNter may read out, said counter output acting to block said output gate until said counter reads zero.

Claim 12

The apparatus of claim 7, wherein the proportional correction circuitry includes a forward counter responsive to said digitizing signal for producing a plurality of lower frequency signals and also includes a plurality of gates responsive to said lower frequency signals, to said digitizing frequency and to said manually inserted measured correction factor signals, said gates operating to block the transmission of digitizing pulses at appropriate times corresponding to the amount of proportional correction required so that the proportional correction is effected by the reduction of the average frequency of the digitizing signal.