DE1135689B - Optical testing device - Google Patents

Description

The invention relates to an optical testing device for quality control of the printing on recording media with means of comparison for those supplied by the optical scanning device Pulses with normal voltages.

In the production of recording media, such as. B. punch cards, a continuous tape of suitable Paper stock fed into a high speed rotary printing press, in that the desired printing process takes place before the individual cards are cut from the tape will. The form of printing and the amount of printed characters can vary depending on the intended use Change the use of cards from one run to another.

Various factors can adversely affect the pressure to be applied to the cards. One the main cause of misprints is fluctuations in the ink supply. Because of the high The operating speed of the printing press creates a great deal of scrap, if not all but exceptions of a temporary nature must be identified and remedied immediately. Of course, also need temporary Defects that lead to one or a few defect cards are detected so that the defect cards can be eradicated. So far the maps have been examined in various ways, z. B. also by manual inspection after cutting from the tape.

An arrangement for checking paper money is already known which uses a light gap for scanning is used, the length of which is equal to the width of the section to be tested. The bills will be passed in the longitudinal direction under the light gap, so that the notes are scanned column by column will. The evaluation device connected to the photocell counts the printed lines and compares the result with a normal value.

However, this arrangement is not suitable for checking the printing on recording media the printing machines operating at high speed, as they are e.g. B. in the production of Punch cards are common.

Punch cards od. Ä. Recording media are made from paper of various colors and are provided with different colored imprint. It is therefore the object of the invention to provide a test device to create that can cope with these diverse variations.

The invention is used in an optical testing device for quality control of the imprint on recording media with a device for comparison Optical test device

Applicant:
IBM Germany
International office machines

Gesellschaft mb H.,
Sindelfingen (Würit.), Tübinger Allee 49

Claimed priority:
V. St. v. America, June 30, 1958 (No. 745 401)

Maxwell Richards Cannon, Endwell, N.Y.

(V. St. A.),
has been named as the inventor

for the pulses with normal voltages supplied by the optical scanning device, and at the scanning through a fixed, narrow band of light with continuously moving recording media takes place, seen in the fact that the pulses supplied by the photocell in an integrator over a map area can be integrated and the integrating voltage via a minimum comparator and set a maximum comparator a bistable multivibrator.

Because of the different imprints and the different colored paper of the individual card versions it is necessary to use the test facility at the start of printing a different card version reset. An advantage of the present invention is that it can be easily adjusted it can be made to account for the difference in the signal obtained in different print runs. In the embodiment described, the setting can be made that the integrated signal derived from one properly printed card is that of another Map, although the color intensity varies within certain limits.

An important feature of the invention is the use of a photosensitive device, which is more sensitive to infrared light than to other parts of the spectrum. In order to the discovery is exploited that for six

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3 4

possible printing colors with one exception in combination are in the following description and the nation with any of nine possible drawings:

High contrast paper colors are available. Fig. 1 is a schematic representation of a

due to the large difference in the spectral pressure test system according to the invention; Reflectance of Unprinted Material 5 Figure 2 is a graphical representation of the spec the spectral reflectivity of the central response of the arrangement in use Printing dyes in that part of the spectrum whose one silicon photocell;

Wavelengths between about 0.7 and 1 μ are. A Fig. 3 is a graphic representation of the spec-

Satisfactory red ink response has occurred with assembly response in use with one of the different card material colors erio a selenium photocell;

if held with a photosensitive device, Fig. 4 shows in schematic form the preferred one

which represents its highest sensitivity to light embodiment of the invention. possesses whose wavelength is less than 0.6 μ or As far as the drawings are concerned in detail, so

is approximately equal to 0.4 to 0.6 μ. Fig. 1 shows in schematic form a pressure test

In the exemplary embodiment described, a system according to the invention is represented, which comprises a lamp 10 contains the light coming from an elongated lamp with an elongated heating wire, preferably through a cylinder lens and a filter passed so that wise with a reduced width on the running paper long, narrow beam of light that is projected from the belt 11. For use in this Rotary printing cylinder of the press coming band arrangement is well suited to a lamp that one material is projected. The length of the light beam is 20 clear quartz bulb with a spiral-shaped incandescent equal to the width of the tape material, and because of the thread, the illuminated length of which is 10.2 cm Movement of the belt will carry this in continuously. As shown schematically in Fig. 1, Scanned lengthways. From the surface of the light from the lamp 10 falls through a longitudinal strip of material reflected light falls on an elongated cylindrical lens 12 through onto a filter 13 loaned photo tents, the length of which is also the width of the 25 elongated photocell 14 is placed so that they light Band material corresponds. The scanning speed receives that only from that of the light beam 15 is determined by the speed at which the scanned area of the tape 11 is reflected, A lens holder 16 in conjunction with passes through the th illuminated area. Through the lens 12 a corresponding focusing of the Fluctuations in the light beam incident on the photocell in such a way that an illuminated Be light an electrical signal is created, which is amplified and has a width of 0.5 mm. By attacks and then passed to an integrator, where at the edges of the tape is the length of the abdie delimited from a single map area derived tactile strip.

Pulses are integrated to form a signal, the photocell 14 generates an electrical signal,

which reproduces the total amount of dye on the scanned area of the individual map area of the radiant energy that has just been captured. This signal is proportional. Preferably, a light sensor is fed through a buffer store to a comparatively sensitive semiconductor device in the form of a silicon circuit, where it uses a zium photovoltaic cell with a reference signal. This cell has to be compared, which represents the acceptable minimum greatest sensitivity to light with an amount of dye on a card of this kind, 40 wavelength between 0.8 and 0.9 μ and is compared with and with a reference signal which the assumed Filter 13 is used, the transferable maximum amount of dye represents. By a speed a steep peak for light with a wavelength output pulse from the comparison circuit is of 0.8 μ has to be actuated to a desirable overall effect on a bistable multivibrator. In the test device that is described in more detail for all normally encountered standing, 45 printing colors with the exception of red are reached, the bistable toggle switch at the beginning of a scanning cycle is switched to the "bad" state. To is represented by the line A in Fig. 2 and has been when the entire area of the band, spectral transmission capability of the filter is determined by the form of a card is scanned, the reset time line B in Fig. 2. If the lamp filament a provides If the flip-flop has a bad card at a temperature of around 1890 ° K, the entire signal will be displayed if it has not been switched to its "good" state before the reset time of the response of the filter and the silicon cell and line C shown in FIG. This arrangement for the remaining part of the circulation in this state provides a good contrast between the remains. In each work cycle, when the reflectivity of the empty strip material and the output voltage of the integrator reaches a minimum of printing ink printed on it with many different values, the comparison circuit switches the toggle switch color combinations. Of the various changes from the "bad" to the "good" state. Reversible inks have all except when the output voltage of the integrator before that of red has a relatively low reflectivity for the completion of the scanning of this card an infrared light with a wavelength below 1 μ. If the correct maximum value is reached, the toggle switch is switched back to its "bad" state. wisely usable tape material colors a high at the reset time, ie when the cut-off line of the reflectivity for infrared light with a currently checked map area of the scanning before wavelength between about 0.7 and 1 μ. direction is reached, then determines the condition. If the tape material is loaded with red dye

the toggle switch, whether an acceptance or an imprint is 65, you get the desired results, Instruction signal is generated. if the total spectral response of the system

Further features of the invention are in the areas at the blue end of the visible spectrum; H. Contain sayings. An embodiment of the Er- under about 0.6 μ. A selenium photovoltaic cell leads to

5 6

good results at the blue end of the visible for most unacceptable maps smaller than the spectrum and even into the adjacent ultra-minimum reference voltage of the comparator 23. Any violet part of the spectrum into it. The relative when during the scan cycle for normal sensitivity, the transmission capacity and the map areas and most bad map composite relative response of the selenium cell, 5 areas with excess dye increases the output of the filter used with it and that with an output voltage of the integrator above the minimum reference temperature of 2120 ° K operating lamp are live, and the bistable flip-flop 25 is represented by the lines / i, B and C in FIG. 3, respectively. switched to its other or "good" state. From Fig. 3 it can be seen that the highest response for normal card areas does not reach the output when using the system for measuring the quantity io voltage of the integrator equal to the red printing dye in a card area about the maximum reference voltage, so that the bistable around 0.51 µ in the blue area of the spectrum around toggle 25 at reset time in its »good is where the reflectivity of the card or state is. On the other hand, if the integrator chip tape material is relatively high compared to that of the red color because of the scanning of an area with a cloth. As the block diagram in Fig. 1 shows, if a tension or more increases, any suitable amplifier 20 is used to switch the bistable flip-flop 25 back and the relatively low output energy of the photocell is found at the reset time in its "bad" increase, and the amplified signal becomes the interest.

grator 21, where it is integrated over each card length in a suitable manner

is grated to provide an indication of the amount of dye attached to photoelectric device 26

to deliver in the map area. With the exception of a timing pulse delivered with the arrival

Background noise coinciding on the mottling of the clipping line 22 on the light beam.

At the time of receipt of this timing pulse, an empty or un- at the time of receipt of this timing pulse can be delivered printed card area a zero signal, and the coincidence circuit 27 gives the output voltage

Markings printed in the map area reveal the state of the from the comparators 23, 24

Signal pulses, their amplitude and duration of the scanned area act again, and only if

the density of the dye and the size of the mark, this output voltage corresponds to that of a bad card

speak. The working cycle of the integrator 21 is equivalent to an output pulse from the Koinzibeliebiger Way generated with the movement of the belt 11 to 30 denzschalt, which is a suitable evaluation

the light beam 15 synchronized over so that the processing device can be fed which the

Integrator - as will be described in more detail - refuses or otherwise with unacceptable work

Simultaneously with the arrival of the rear trimming process.

line of the scanned area (22 in Fig. 1) at Now a preferred embodiment is the Light beam is reset. 35 control circuit of this arrangement in more detail in connection Output voltage of the integrator 21, which is described with Fig. 4 manure. The in amplifier 20 through the buffer 28 the minimum and amplified output voltage of the photocell 14 becomes Maximum comparators 23 and 24 is fed to one side of the capacitor 30 in the manner represents the amount of dye at the recovery time that is applied so that positive pulses are a measure of the up the scanned map area is printed on. 40 print on the card to be checked. Of the The integration speed of the integrator 21, the most negative part of the signal, is therefore unreacted pre-set to produce a pre-printed portion of the card. The other side certain output voltage for the optimal of the capacitor 30 is across the resistor 31 on Print quality on a card during a counter- a negative voltage source 34 (-48VoIt) and on level press run. At the comparator 23 45 the base of an N-P-N transistor 32 becomes collector the circuit coming through the buffer is connected. The common connec output voltage of the integrator with a reference point of the capacitor 30, the resistor compared voltage, which represents the minimum amount of dye 31 and the transistor 32 is over a limit, which is used to generate an acceptable diode 33 to a constant negative voltage source Card is necessary. In addition, the output voltage 50 35 (ζ. B. -40VoIt) is connected, whereby the tion of the integrator through the buffer store 28 signal level for unprinted cards to -4OVoIt fed to the comparator 24, where it is held with a span, while all the impulses by benung is compared, which the maximum dye-printed areas on the card can be generated, to this represents amount that lead to a map area that the base of transistor 32 is more positive than and still becomes an acceptable card at 55-40 volts. The emitter of transistor 32 is on leads. The output voltage of the comparators 23, 24, the voltage source 35 over a relatively small is fed to the bistable multivibrator 25, the resistor 36 and a variable resistor joins that of their 37 at the beginning of each orbit. The collector of transistor 32 is both states is the one bad or unacceptable directly to the emitter of an N-P-N transistor 38 Showing map. The cut-off line for 60 is closed, which - as will be explained in more detail - a card area is effective in the present embodiment as an integration transistor. The connection example the starting line for the next following connection point of the collector of transistor 32 with Map area. Since so when reaching the emitter of the transistor 38 is grounded via a cutting line of the integrator into its output resistor 39, which forms a high impedance to earth, status is reset, is during the initiation. 65 The emitter of transistor 32 retains almost the same Part of the scan cycle for a given same potential is at as its base, and therefore is Map range, the output voltage of the integrator emitter current of transistor 32 is approximately zero for for all acceptable cards and usually a signal corresponding to an empty area of the card,

and proportional to the voltage of the input signal when a printed area is scanned. Of the The collector current of transistor 32 is directly proportional to its emitter current and is equal to the emitter current of transistor 38 to which it is directly connected. Hence the emitter current of the transistor 38 directly proportional to the voltage of the input signal from amplifier 20.

The base of the transistor 38 is connected directly to a board 46 that the voltage of the collector's Transistor 44 is approximately equal to the voltage of voltage source 40 (approximately -20 volts). Since the Voltage source 40 supplied voltage is the same as that supplied by voltage source 41, but reversed Has sign, its negative voltage biases the diode 43 inversely, so that the Capacitor 42 can be recharged in the negative direction according to the coming from amplifier 20-

voltage source 40 (-20VoIt) connected, and io the input signal. The resistor 50 in the collector

its collector is connected to a voltage source 41 (+20 volts) via the capacitor 42. The output signal of the integrator 21 is via the capacitor 42 of its connection point with the

The circuit of the transistor 45 limits the energy consumption of this transistor when it drives the power transistor 44 into the fully conductive state.
In the present embodiment, the cons

Collector of transistor 38 removed. This 15 stood 37 a 50,000 ohm potentiometer, and with the connection point is also connected to the intermediate setting of its wiper, the proportional memory 28 and a diode 43 with
a reset circuit, which consists of a PNP

Power transistor 44 and a P-N-P driver trans-

constant between the charging current of the capacitor 42 and that applied to the transistor 32 Signal voltage set. If the potential

sistor 45 exists. The emitter of transistor 44 is 20 tiometer 37 is adjusted so that its resistance connected to voltage source 41, and being zero, creates a relatively small input collector is at the connection point of the diode 43 signal from the amplifier 20 a large charge and a resistor 46 connected, the grounding current for the capacitor 42. If on the other hand is connected to the bias source 40. On the one hand, the potentiometer 37 is set so that The base of transistor 44 is effective over a relatively small 25 of its full 50,000 ohms in the circuit Current limiting resistor 47 at the emitter of the will create a relatively large input driver transistor by itself 45 connected. The emitter of the voltage pulse is a small capacitor-charging driver transistor 45 is also about a reverse current. By setting the stand 48 with a voltage source 49 of about potentiometer 37, the integration speed +120 volts connected. The collector circuit of the 30 speed of the circuit 21 can be controlled so that ent

Transistor 45 is connected through a resistor 50 having a relatively low value equal to that of the Resistance 47 can be built to earth. The bias for the base of transistor 45 becomes

neither a flawlessly printed good card of a passage or one printed with weak ink good map of another pass to the same output voltage at the integrator output, d. H.

leads from the +24 volt voltage source 51 via a 35 at the collector of transistor 38. This is very resistor 52 supplied while the input signal is advantageous because then the same sawtooth voltage is fed through a capacitor 53, its
a clamp to the common connection point
connected between resistor 52 and the base.

During normal operation of the integrator 21, the resistor 48 maintains the emitter-base connection.

at the output terminal of the integrator for cards from different passages and with the same Print quality appears even if these cards are printed with completely different amounts of dye. The negative sawtooth output voltage of the integrator 21 is fed to the buffer 28.

tion of the transistor 44 is inversely biased, and led, which has the purpose of reducing the load on the

transistor 44 is non-conductive. Because of the under capacitor 42 to keep as low as possible, and the

The high blocking resistance existing under these circumstances enables a relatively large current to be obtained for the same

When the diode 43 is in position, the current of the capacitor can achieve voltage, i. H. without potential changes

42 equal to the collector current of transistor 38, the tion. The buffer 28 consists of one in turn independent of the collector voltage P-N-P transistor 56 and an N-P-N transistor 57, and arranged as a double emitter follower circuit proportional to the emitter current of the transistor 38 is. Hence the current of the capacitor 42 is pro- 50. The output voltage connected to the portional the voltage of the input signal across the common terminal of the emitter of transistor 57 Blank card level, the terminal received from amplifier 20 and its load resistor 58 connected will catch. That is taken from the photoelectric device 55 is sent to two comparators 23 device 26 coming timing pulse has the form and 24 applied, where it is with tolerance or reference negative voltage pulse and is compared to the 55 voltages. Actually compares Base of transistor 45 via capacitor 53 to the comparator circuit together with the bistage. This leads to the application of a negative constant flip-flop 25, the time integral of the pulses through resistor 47 to the emitter-base scan of each successive printed Junction of transistor 44, the thereby derived signal voltage in map with a span forward direction is biased to transistor 60 voltage, which is the value of a good card. the 44 to make it highly conductive. When transistor 44 has reference voltages with which the output of the Intestark is conductive, when its collector potential reaches a grators 21 is compared, set the desired Value corresponding to that of voltage source 41 (approximately maximum and minimum dye tolerances. + 20 volts) comes very close, and any existing voltage comparison circuits 23 and 24 Charging of the capacitor 42 is via the diode 65, each form a regenerative, emitter-coupled

43 derived. Differential amplifier of conventional design. The termination of the negative pulse from the comparator 23 comprises a P-N-P transistor 63,

photoelectric device 26 causes the counter- whose base via a winding 60 a of a transformer

mators 60 is connected with three windings to the potentiometer 61, one side of which is grounded and the other side of which is connected to a voltage source 62 of a suitable positive reference voltage (here 5 volts). A second winding 60 b of the transformer 60, which functions as a primary or input winding, is located in the collector circuit of the PNP transistor 64. The base of the transistor 64 is connected to the terminal 55.

As shown in FIG. 4, the comparator 24 preferably has the same structure as the comparator 23, namely one winding 66 a of the transformer 66, which is also provided with three windings, is connected between the base of the PNP transistor 67 and the potentiometer 68 one end of which is grounded and the other end of which is connected to a voltage source 69 of a suitable negative reference voltage (here 5 volts). A second winding 66 b of the transformer 66 is connected to the collector circuit of the PNP transistor 70, the base of which is also connected to the output terminal 55.

At the potentiometers 61 and 68, positive and negative reference voltages for the comparators 23 and 24 are tapped, which can be set according to the desired minimum and maximum printing ink tolerances. When the negative sawtooth voltage from the terminal 55 reaches the reference voltage of the comparator 23, the conductive state is transferred from the transistor 63 to the transistor 64, and an output signal in the form of a sharp pulse appears in the third winding 60c of the transformer 60 of this comparator. As will be described in more detail, the winding 60 c together with the third winding 66 c of the transformer of the comparator 24 controls the operation of the bistable multivibrator 25. If the output voltage from the integrator 21 is the result of scanning a bad card on which a too large amount of dye is located, the negative sawtooth voltage of terminal 55 reaches the reference voltage of comparator 24, and therefore the conductive state is transferred from transistor 67 to transistor 70, and a pulse appears in the third winding 66 c of the transformer 66, the comparator 24 with one side of the bistable trigger circuit 25 couples.

The bistable multivibrator 25 is a circuit of a known type in which the P-N-P transistors 73 and 74 are resistively cross coupled. At the beginning of a scan cycle, what about the At the beginning of an integrating cycle of the integrator 21 coincides, the bistable multivibrator 25 is in FIG that of its two stable states that is a bad card. The transistor 73 is then conductive and the transistor 74 switched off.

The coincidence circuit 27 consists of a PNP transistor 77, the base of which is connected to the collector of the transistor 74 via a diode 75. The common terminal of the collector of the transistor 74 and the diode 75 is connected to the voltage source 40 via a load resistor 76. The common terminal 78 of the base of the transistor 77 and the diode 75 is also connected to the voltage source 40 via a resistor 79. Resistor 79 is preferably ten times the value of resistor 76. A further diode 80 is shown connected between terminal 70 and photoelectric device 26 to receive a pulse simultaneously with capacitor 53 of the integrator reset stage. When the negative ramp voltage drops from the integrator 21 to the level of the reference voltage of the comparator 23 and a Ausgangsinipuls appears in the transformer winding 60 c, the transistor 73 is off and the transistor 74 turned on. This causes the diode 75 to be forward biased. Assuming that a good card is being scanned and that the sawtooth output voltage of the integrator never drops to the level of the reference voltage of comparator 24, transistor 74 of flip-flop 25 will conduct upon arrival of clipping line 22 at the scan area. At this point the pulse from photoelectric device 26 is applied to diode 80 to sense the state of flip-flop 25, and because diode 75 is conducting, the sense pulse does not appear across load resistor 81 in the collector circuit of transistor 77. Indeed the sense pulse is blocked and that indicates a good card. On the other hand, if a bad card is sensed and the integrator output voltage does not drop to the level of the reference voltage of comparator 23 or, after reaching this level, continues to drop to or below the reference voltage of comparator 24 before the scan of the card area is completed, transistor 74 will turn off. and the transistor 73 is turned on when the pulse from the photoelectric device 26 arrives. Under these circumstances, the diode 75 is non-conductive and the sensing pulse is sent to a suitable evaluation device which has the purpose of rejecting the bad cards.

The pulse from the photoelectric device 26 is also used to set the flip-flop 25 to its "bad" state, in which the transistor 73 is conductive and the Transistor 74 are turned off. This is done by a delay circuit 85 which is a P-N-P transistor 86 includes whose base via a capacitor 87 to the common terminal of the diode 80 and the photoelectric device 26 is connected. The common terminal of the base of the Transistor 86 and capacitor 87 are connected to the voltage source via a bias resistor 88 40 connected. The collector of transistor 86 is through a relatively small resistor 89 with the Voltage source 40 and directly through resistor 90 to the common terminal between the base of the transistor 73 and the transformer winding 60 c connected. The delay circuit 85 effects a sufficient delay before the reset pulse is applied to the flip-flop 25 to allow it to pass the sensing pulse on before going into the "bad" state is postponed. The effect of the delay circuit 85 is to provide the The rear edge of the pulse applied to the capacitor 87 is differentiated.

As already described, the setting of the potentiometer 37 controls the ratio of the to the integrator capacitor 42 applied charging current to the signal voltage obtained by amplifier 20.

This can be achieved manually by measuring the output voltage of the integrator 21 via a peak voltmeter 92 (Fig. 1) is applied to a measuring device 93 with a zero point in the center of the scale. To

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Time, the operator observes the first new cards produced by the printing press, and when a good card is delivered, the potentiometer 37 is adjusted to the Measuring device 93 has reached zero. The potentiometer 37 is preferably set by the application of the output signal from the peak voltmeter 92 to a servo controller 94, the in turn controls a direct current motor 95 with a permanent magnetic field, which is connected to the wiper of the potentiometer 37 is connected via a corresponding reduction gear. If the Printing press starts delivering good cards, operator only needs a switch (not shown) which connects the servo control 94 to ig the peak voltmeter 92. While During normal operation, the voltmeter 93 provides a visual indication of the print quality. If the The amount of ink applied to the cards begins to deviate, the amount on the voltmeter gives way 93 applied voltage accordingly, and this shows in the state of the measuring device. A single one badly printed card leads to a corresponding rejection signal from the coincidence circuit 27, but the fact that a single bad card has been scanned is shown on the Meter 93 not displayed.

While the system shown and described here always sends an output pulse to a Evaluation device sends when a bad card has been scanned and the lack of a pulse shows a good map, the arrangement up to the comparators is secured against failure. That that is, in the event of a failure in the circuit the “bad card” signal from the evaluation device is fed to the comparators. As desired the whole system can be secured against failure by adding an output pulse to the Collector circuit of transistor 77 is supplied when good cards are scanned, and that the lack of a pulse indicates the occurrence of a bad card. This is done by breaking the connection between the diode 75 and the common terminal of the collector of the transistor 74 with his Load resistor 76 and connect this terminal of diode 75 to the collector of transistor 73 its connection with its load resistance.

In the preferred embodiment described, the reset stage of the integrator functions as a switch that closes to the parallel capacitor 42 when the pulse from the photoelectric device 26 is received, whereby the capacitor 42 is quickly discharged. Other arrangements for resetting the integrator can of course be used if other effects are desired.

Claims (6)

Patent claims 1. Optical testing device for quality control of the print on the recording medium with a device for comparison for the pulses supplied by the optical scanning device with normal voltages, and in which the scanning takes place through a fixed narrow light band with continuously moving recording media, characterized in that the photo cell (14) delivered pulses are integrated in an integrator (21) over a map area and set the integrating voltage over a minimum comparator (23) and a maximum comparator (24) a bistable multivibrator (25). 2. Device according to claim 1, characterized in that the narrow band of light (15) and the photocell (14) extend over the entire width of the recording medium (11). 3. Device according to claims 1 and 2, characterized in that the reference voltages for the minimum and maximum comparators (23, 24) can be set. 4. Device according to claims 1 to 3, characterized in that between the integrator (21) and the comparators (23, 24) a buffer (28) is arranged. 5. Device according to claims 1 to 4, characterized by an adjusting member (37) for Adjustment of the charging speed of a storage capacitor (42) in the intermediate storage (28) for the pulses supplied by the integrator (21). 6. Device according to claims 1 to 5, characterized in that the scanning with Light either in the wavelength range between 0.7 and 1.0 μ or in the wavelength range between 0.4 and 0.6 μ takes place. Documents considered: German Patent No. 646 658; Austrian Patent No. 122,267; British Patent Nos. 741687, 748 204; U.S. Patent No. 2731621. For this purpose 2 sheets of drawings © 209638/200 8.62