US2947972A

US2947972A - Method and apparatus for determining the position of a printed or written item with respect to an identification mark applied thereto

Info

Publication number: US2947972A
Application number: US668502A
Authority: US
Inventors: Steinbuch Karl
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1956-07-07
Filing date: 1957-06-27
Publication date: 1960-08-02
Anticipated expiration: 1977-08-02

Description

Aug. 2, 1960 K. STEINBUCH 2,947,972

METHOD AND APPARATUS FOR DETERMINING THE PQSITION OF A PRINTED OR WRITTEN ITEM WITH RESPECT TO AN IDENTIFICATION MARK APPLIED THERETO Filed June 27, 195'! lengfh dimension of letter G? 4 3 low Pa. F/lfer I -0 v law Pass FI/zJer my Pass Fi/te'r 3 5 6 2 INVENTOR K. fitenbuck ATTORNEY United States Patent METHOD AND APPARATUS FOR DETERMINING THE POSITION OF A PRINTED OR WRITTEN ITEM WITH RESPECT TO AN IDENTIFICATION MARK APPLIED THERETO Karl Steinbuch, Fellbach, Wurttemberg, Germany, as-

signor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed June 27, 1957, Ser. No. 668,502

- Claims priority, application Germany July 7, 1956 2 Claims. (Cl. 340-149) The present invention relates to a method of and apparatus for determining the position or orientation of a printed or written item with respect to an identification mark applied thereto. This problem especially arises e.g. with letters, bank accounting cheques, bank notes and the like, which are required to be sorted with respect to their places of destination or receipt. A particular need for such a method exists in a post ofiice for the sorting of mail items. The description of the instant invention therefore, is particularly directed to a method of recognizing the position of mail items, but the invention is not restricted to such application.

in order to enable a sorting of items it is required that the respective letters, cards or the like are led past the sorting operator in a readable manner. However, since the items on the conveyor belt, on which they are led past the operator, may be lying in different positions it is rendered necessary to turn the non-readable items accordingly. The number of possible positions is limited to four assuming that a suitable device ensures that the longest edges of the items on the conveying system always lie horizontally, so that turns of 90 are practically excluded.

lostage stamps may be regarded as a characteristical identification mark for letters. Furthermore, it may be assumed that in the readable position of the letters the stamps are stuck to the front of the envelope in the right-hand upper corner. For determining the position of the letters it is, therefore, necessary to examine the right-hand upper corner of the letter. The result of such an examination is then utilized for controlling the following operation, in the course of which the letters, etc. are sorted in accordance with their respective positions.

it is possible to carry out the examination with respect to identification marks on written or printed items by means of various methods employing a photo-electric scanning or sensing. One method consists in transporting the items past a scanning or sensing device continuously on a conveyor belt systems, e.g. of the edgewise type, and moving a scanning beam up and down vertically in relation to the direction of movement. As soon as the identification mark is hit by the beam, intensity fluctuations will be caused in a photocell which then, via amplifiers, can be used to produce a control pulse. Depending on whether the fluctuations of intensity appear when sweeping over the upper or lower half of the letter this pulse is utilized for a sorting operation with a subsequent turning of the item or letter, or for a sorting operation without involving a turning of the letter.

Such examination methods, however, are easily liable to mistakes or errors, because on the items there may also be other markings or signs, such as remarks with respect to the address or sender, or the like, and which, under certain circumstances, may cause a similar intensity An object of the present invention is to avoid such" faulty evaluations. According to the instant invention the mean value of a signal portion, derived from the identification mark, is compared with a fixed or predetermined threshold value which is determined in such a way that when exceeding the threshold value, there can be made certain conclusions as to the location of the identification mark. For the scanning of the examination range there may be used a plane-like exploring photocell. However, since in some cases the scanning device will also have to serve the evaluation of narrow ranges, such as at the evaluation of the white edges of the postage stamps in the case of dark-colored letters, it is of advantage to employ a gap-type photocell. In such a case, however, it is necessary to provide for means enabling the examination of a complete identification-mark range. On the other hand, also in the case of gap scanning, all transitions in brightness, which are caused by recordings, such as writing, are evaluated as well, so that there arises the additional problem of how to exclude or suppress the larger signals resulting from the scanning of writing or the like.

According to the present invention the above problem is solved by feeding the signals coming from the photocell simultaneously to a highpass and a low-pass filter with parallel-connected inputs. The output signals from the high-pass filter are rectified and are fed to a second low-pass filter and the output signals from the two lowpass filters are then subtracted one from the other. This may be accomplished in that the rectifier only permits the passage of the negative signal portions and in that these negative signals, after having passed through the second low-pass filter, are added to the positive signals from the first low-pass filter. in this way the signals resulting from the scanning of the writing, etc., will be completely or almost completely compensated, while an unambiguous identification signal will remain, which is capable of being well compared with a predetermined threshold value.

in the following, the invention will be particularly described with reference to the accompanying drawings and the example of determining the location of a postage stamp on a letter (envelope).

in the drawings: I

Fig. 1 shows a photocell signal produced by the scanning of a letter in readable position;

Fig. 2 shows a circuit arrangement for carrying out the method according to the invention, and

Pig. 3 shows three diagrams of the signals produced in the individual stages of the arrangement according to Fig. 2.

The letters travel continuously past the scanning device of an edgeway conveyor belt, whereby a photocell signal is produced as is shown in Fig. l. The intensity peaks in front of the wide or broad signal, which corresponds to the postage stamp, are caused by the writing or other markings on the front of the letter. (In all of the wave form diagrams it is assumed that the abscissa corresponds to the white-value, and that with an increasing ordinate value the signal approaches the black-value.)

The postage stamp signal, as will be seen from Fig. 1, consists of a relatively large direct-current portion, whilst over the remaining parts of the letter the peaks are much narrower. This difference, therefore, may be used for identifying the location of the stamp. A simple expedient is to fix a value lying between the two directcurrent values to be expected, so that when this value is exceeded, this indication may be used to deduce the location of the stamp. The threshold value can be determined the better the greater the difference is between the two direct-current portions. Therefore, care should be taken that the signals produced by the writing or other extraneous markings are suppressed as far as possible, whereby the direct-current portion of these parts of the letter becomes substantially smaller and, in certain cases,

even zero.

Referring to Fig. 2 there is shown an arrangement for forming the peak value by simultaneously excluding the signals produced by the writing or the like. The photocell signal produced by the scanning operation of the gap photocell 1, after being amplified in the amplifier 2, is simultaneously fed to the high-pass filter 3 and to the low-pass filter 4. The low-pass filter is adapted to smooth the curve, so that the signals caused by the writing on the letter are largely suppressed. The output signal of the low-pass filter 4 is shown in Fig. 3a. Actually this signal could itself be used for comparison with the threshold value, but the difference between the stamp portion and the remaining portions of the letter is too small, and may even entirely disappear in some specially unfavorable cases. For this reason the scanning signal is simultaneously fed to the high-pass filter 3, at the output of which there appear the higher-frequency signals, as shown in Fig. 3b of the drawings. These signals are then rectified by the rectifier 5, so that only the negative portion of the signal is permitted to pass. The thus rectified signals are then fed to another low-pass filter 6, similar to the low-pass filter 4, and thereby smoothed. The output signals of the low-pass filter 6 are shown in Fig. 3c. Thereupon the output signals from the two lowpass filters 4 and 6 are algebraically added in the combining circuit 7. An illustration of this adding circuit is shown on page 458 of Reference Data for Radio Engineers, 4th edition, copyrighted by I.T.&T., 1956. As will be seen from the Figs. 3a and 3c the signals produced by the writing will be compensated either entirely or almost completely on account of the combining process, so that one of the direct-current portions will disappear. In this way there will remain a distinctly wide signal for identifying the stamp location, the direct-current value of which can be well defined with respect to a predetermined threshold value. An example of this threshold comparator is shown on page 329 Fig. 9.3a in volume 19 of the Radiation Laboratory Series. The difference signal is fed to a comparing device 8 (comparator), in which it will be compared with the said threshold value. By noting when the threshold value is exceeded, conclusions may be drawn as to the position of the postage stamp. When the threshold value is thus exceeded there is produced a control signal which may be used to initiate the required controlling operations for handling the scanned letter. Four photocells may be used which simultaneously scan both sides of the letter and the upper and lower halves of each side. In this case that particular photocell which locates the postage stamp then produces the control signal which initiates the desired controlling operation to direct the letter into a filing compartment, or the like.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

What is claimed is:

1. System for determining the position of a written or printed item with respect to the location thereon of an identification mark applied thereto, comprising photoelectric scanning means, the item being moved relative to said scanning means whereby at least a portion of the surface of said item is scanned, means for deriving a signal current from said scanning means, threshold circuit means including a reference source of current having a predetermined value for comparing said signal current with said reference current, said threshold circuit comprising a parallel branch circuit intermediate said scanning means and said means for deriving a signal current from said scanning means, said branch circuit comprising means for cancelling signals derived from markings on said item not corresponding to said identification mark, whereby the location of said identification mark may be deduced when the current derived from said threshold circuit differs from said reference current by a predetermined amount.

2. System according to claim 1, wherein said parallel branch circuit comprises a first low-pass filter and a high-pass filter the inputs of which are connected in parallel, means for applying said signal current to said inputs, a rectifier, a second low-pass filter, means for serially connecting said high-pass filter, said rectifier and said second low-pass filter in the order named, a combining circuit, means connecting the outputs of both said low-pass filters to said combining circuit, and means connecting the output of said combining circuit to said comparator.

Hansell Apr. 23, 1940 Zworykin Nov. 4, 1952