US2486334A - Photoelectric scanner for register regulation - Google Patents

Description

Oct. 25, 1949.

F. SLAMAR PHOTOELECTRIC SCANNER FOR REGISTER REGULATIQN Filed Sept. 25, 1948 Fig.5.

INVENTOR Frank Siomur.

BY C W ATTOm Patented Oct. 25, 1949 PHOTOELECTRIC SCANNER FOR REGISTER REGULATION Frank Slamar, East Aurora, N. Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 25, 1948, Serial No. 51,138

6 Claims.

My invention relates to photoelectric scanners for register regulation.

Scanners of this type are used as the detecting. device of a control system for maintaining a; desired registration between a movable web material, such as paper or textile, and a printing roll, slitter, cutter'or the like machine member to operate on the Web. The scanner in such systems detects any deviation of the moving web material from a predetermined path or position relative to the machine member and controls restoring means to return the Web material to its normal path or position. The scanner operates by moving a beam of light periodically across an edge of the web material or across a line or marking on the web material and has a photoelectric cell or tube responsive to the reflected light so that a deviation of the illuminated areas on the two sides of the edge or line from a given ratio causes the phototube to issue a control stimulus which controls the restoring means to displace the Web in the direction and to the extent required to eliminate the deviation. There are scanners whose periodic scanning operation occurs many times per second, for instance, at sixty cycles per second, and that are opera-ted from an alternating-current line by a synchronous drive. My iiivention relates especially to scanners of the justmentioned kind.

It is an object of the invention to devise a scanner for register regulation that secures a reliable performance of highaccuracy with simpler apparatus and smaller space requirements than known motor-driven scanners with rotary motion of the light beam, and that also reduces or eliminates the requirements for lubrication: and for great mechanical resistance to centrifugal force peculiar to these rotary scanners.

It is also an object of the invention to provide a scanner whose light beam crosses the edge or line twice per cycle as contrasted with one per cycle in scanners of the rotary type.

Another object of the invention is to devise a scanner that permits using a larger reflecting surface than could be used with oscillatory, gal-- vanometric scanners heretofore proposed, thus reducing the gain requirements for the amplifier needed in connection with the scanner.

Another object, in comparison with previously proposed oscillatory scanners, is to devise a design of simplified construction and reduced cost that more safely stands up under continuous use.

These objects, and the means provided by my invention for achieving them, will be apparent from the following description in conjunction with the drawing, in which:

Figure 1 shows diagrammatically an example of a register regulating system equipped with a scanner according to the invention;

Fig. 2 shows afront view of the scanner and.

Fig. 3 a view onto the reflector side of the scanner;

Fig. 4 is a lateral view of the scanner and shows also the associated light source and phototube; and.

Fig. 5 is explanatory, and relates to the same scanner.

In: Figure l, a traveling web material, such as paper, is denoted; by I. The Web travels from a supply reel 2 over guide rollers 3, 4 and 5-to printing, slitting or cutting equipment (not shown), and must maintain a fixed path relative to that equipment. A guide line schematically represented at 6 ispri-ntedon the web.

In order to regulate the position of the web traveling path, the reel 2 is axially displaceable by means of adjusting equipment schematically represented by a shaft 1 which is'drivenfrom the armature 8- of areversible motor with two split field windings 9 and NJ.- The running direction of the motor,. and consequently the direction of web adjustment, depends upon which of the two field windings is energized at a time.

The motor is energized through a transformer H with a mid-tapped secondary; The two sections of the secondary are connected across the armature and in series with one of the respective field windings through a controllable rectifier tube i2 or It, for instance; ofthethyratron type. Two resistors l4and I5', each paralleled by a valve l'6' or' H, are connected across the cathodes of tubes l2 and i3i In order to prevent operation of the tube l2 or l3 until' wanted, a'normal'blocking or biasing voltage is'imposed on the grid circuitsof the-tubes from a suitable direct-current source I8. The grid circuits extends through the secondaries I 9" and 20, respectively, of a peaking transfoI'merZ I. As is-explainedbelow, the peaking transformer provides to the" grid circuits respective voltage kicks-ofmutually opposing polaritiessothat one or them causes the tube I'Z or 13 to fire, only one" tube being ignited at a time. When either tube' is conductive, the correspondingvalve t6 or I bypassesthe parallel-connected resistor M or P5 to reduce the resistance in the grid circuit of the-conductive tube, thus reducing the blocking bias for the conductive tube while the other tuberemainssafely blocked.

The peaking transformer 24'- receives its impulses under control by the photoelectric scanning equipment to be described presently. The scanning device: isattached in a normally fixed position relative to-the web portion that travels over the guide-roller 4. The scanning device has a magnetic structure 2-2 with two pole pieces.-

Two coils 23 and 24 are disposed on the respective pole pieces: and are energized fromalternatingcurrentterminals 25 which: are impressed by alternating: voltage from the source or line that energizesthe transformer l=l.- Consequently, the

voltage applied to terminals is in synchronism with that applied to the motor circuit. A rectifier 26 is disposed between the terminals 25 and the coil 24 so that this coil receives rectified excitation during voltage half-waves of only one polarity. A corresponding rectifier 21 is seriesconnected with coil 23 between terminals 25 and is poled in opposition to rectifier 26. Therefore, coil 23 receives excitation only during voltage half-waves of the other polarity. A rocking armature 28 is pivoted on the structure 22 so that it is driven by coils 23 and 24 to oscillate in synchronism with the alternating-current voltage. The middle portion of armature 28 carries a mirror or the like reflector 29 which reflects a beam of light from a source 30 onto the surface of web I. The scanner is so adjusted that the light beam crosses the guide line 6 during each oscillation, and thus illuminates areas on either side of the guiding line. The light reflected from the illuminated area impinges upon a photoelectric tube 3!. Each time the beam crosses the guiding line 6, the light reflected on tube 3| is darkened so that the tube issues an impulse.

The circuit of tube 3| comprises two seriesconnected resistors 32 and 33 as a source of direct-current voltage. The resistor 32 is energized from a suitable direct-current source 34. Connected across part of resistor 32 is an amplifying tube 35 whose plate circuit includes the primary of the peaking transformer 2|. The grid of tube 35 is connected through a resistor 36 to the negative terminal of the potentiometer resistor 32 and the grid is further connected through a capacitor 31 and a resistor 38 to a junction point between the resistor 33 and the phototube 31.

The light from source 30 is focused through a lens system, schematically shown at 52, so that the light beam reflected by mirror 29 onto the surface of web I has the desired shape, for instance, as schematically shown in Fig. 4. According to Fig, 4, the illuminated area is substantially rectangular and has two portions 4| and 42 at either side of the guide line 6, these area portions being equal when the web is in register. The oscillatory direction of movement of the light beam is indicated by an arrow 40, and the direction of travel of the web I is denoted by an arrow A.

When the photocell is illuminated, the photocell network may be considered to be balanced in such a manner that the current through the amplifying tube 35 is maintained at a substantially constant value below the knee of its saturating curve. When the illumination of the photocell is modified, the photocell network is correspondingly unbalanced to change the current through the amplifying tube. The change in the plate current momentarily energizes the primary winding of the peaking transformer 2i and causes a peaked secondary voltage to be impressed on the grids of the rectifier tubes ll, l2.

Each rectifier tube is connected so that its anode is positive and the tube able to conduct current to its associated field winding during only those half-wave periods in which that winding would correct deviation on the side of the proper path which the moving beam is scanning at that time.

Thus, when the beam is scanning the right side of the proper path, the rectifier tube whose anode would be positive at that time should be connected to that field winding of the motor that would establish restoral movement to correct deviation to the right of the proper path.

The reflector is preferably so mounted on the armature that its reflecting surface extends symmetrically to the rocking or fulcrum axis and is located so that the light beam will cross the guide line, if the guide line is in its proper location, at the end points or moments of each voltage wave. Then, if the beam strikes the guide line at the normal neutral position of the beam, the peak voltage is applied to the rectifier tubes at the instant when the voltage across the tubes is zero, and neither tube can then transmit current. The photocell will thus be fully energized by the refiected light beam until the beam strikes the guide line. At that instant, the amplifying tube is caused to vary its plate current and the peaking transformer issues peak voltages in each of the secondary windings. The peak voltages are of the same polarity in both secondary windings, but since the polarities of the two rectifier tubes are mutually opposed, only the proper tube would be energized to be conductive.

If the guide line deviates from the proper position, the scanning beam strikes the guide line off the zero position. The change in the amount of reflected light on the photocell, at that instant, changes the grid bias on the amplifying tube and, therefore, changes the plate current momentarily to establish a peak voltage in the transformer before the end of the corresponding current wave. The corresponding rectifier tube is then energized to transmit an impulse to the motor. Since the scanning action is synchronously related t the system voltage, the length of the scanning path will be related to the duration of a half wave, or 180. Consequently, when the scanning beam encounters the guide line out of its normal path, that encounter will take place before the beam reaches the end of its scanning movement which will correspond to a similar interval before the end of the current wave. The deviation as thus physically measured by the scanning beam is directly time related to the electrical space or distance ahead of the zero value at the end of the current wave. The peak voltage is thus generated when the deviation is detected and serves immediately to energize the proper rectifier tube at the same instant. The amount of energy transmitted by the rectifier tube, therefore, is a function of the deviation.

It should be understood that the above-described rectifier and amplifier system is presented only by Way of example in order to convey a complete understanding of the purpose and operation of the photoelectric scanning device which alone forms the subject-matter of the invention proper; and it will be obvious that other rectifying and amplifying systems may be used for the same scanning device.

The scanning device according t the invention is shown more in detail in Figs. 2 to 4. According to these figures, the magnetic structure denoted by 22 in Fig. 1 is composed of two angle pieces 44 and 45 and two appertaining pole pieces 46 and 41. The angular pieces 44 and 45 have adjacent legs welded or otherwise fastened together in phase-to-phase relationship. However, they may also be made of a single piece of material. The armature 28 is mounted on a fiat spring member 48 whose midposition is fastened t the frame structure by screws 49 and 50. The spring member 48 biases the armature structure normally toward th illustrated midposition and the structure is free to oscillate toward and away from the pole surface of each pole piece in opposition to the biasing force of the spring. Preferably, the natural frequency of the oscillatory armature system is kept away from the operating frequency of the drive.

Due to the rectifiers 26 and 27, only one pole piece is magnetized at a time. Consequently, the armature structure is subjected to forced oscillations which strictly coincide with the energizing alternating current. As a result, the scanning frequency is always in synchronism and a fixed phase relation to the voltage cycle of the energizing current, thereby securing a highly reliable performance of the register regulating system. It will also be recognized that the scanning de- Vice is of an extremely simple design which permits being given extremely small dimensions. The mirror or reflector of the armature system can readily be made much larger than those applicable in galvanometric devices heretofore proposed for similar purposes. The above-described mounting of the armature structure is of such nature as to require no lubrication and no maintenance adjustment. For these reasons, and as proved by experience, the scanner according to the invention maintains its satisfactor operation and stable conditions during periods of long continued application.

The optical system of the scanner may include a cylindrical lens between the reflector 29 and the web I. This has the following advantage. As the skew of the edge or guide line in the light beam is increased, a point will be reached whence the magnitude of the pulse decreases very rapidly. This is due to the fact that with such an amount of skew, the reflected light changes slowly as the light spot sweeps across the line, instead of changing rapidly as is the case when the edge or line is parallel to the light spot. However, if a cylindrical lens is inserted it can be positioned so that the light sweep is unimpaired but the light spot dimension parallel to the edge or line is diminished. In other words, the size of the light spot in the direction of web travel is then decreased while the sweep dimension remains the same.

It will be obvious to those skilled in the art that scanners according to the invention can be modified as regards details of design without departing from the objects and essential features of the invention and within the scope of the claims annexed hereto.

I claim as my invention:

1. A scanning device for register regulation, comprising an electromagnet structure with two parallel pole pieces and two coils on said pole pieces, an armature extending across said pole pieces in spaced relation thereto and being fulcrumed on said structure for rocking movement toward and away from said respective pole pieces, spring means for biasing said armature toward the mid-position of said movement, a reflector mounted on said armature oscillatorily reflecting a scanning beam of light, alternating-current terminals connected to said coils and two rectifiers connected between said respective coils and said terminals in mutually inverse polarity of connection.

2. A scanning device for register regulation, comprising an electromagnet structure with two parallel pole pieces and two coils on said pole pieces, an armature extending across said pole pieces in spaced relation thereto and being fulerumed on said structure for rocking movement toward and away from said respective pole pieces, 75

6 spring means for biasing said armature toward the mid-position of said movement, and a mirror mounted on said armature in a symmetrical position relative to said fulcrum for oscillatorily reflecting a beam of light.

3. A scannin device for register regulation, comprising a magnetic structure having a base portion and a center portion extending at a right angle to said base portion and two pole pieces extending in parallel to said center portion on both sides respectively of said center portion, two coils on said respective pole pieces, an alternatingcurrent terminal connected to said coils and having two rectifiers of mutually opposing polarities connected between said terminals and said respective coils, an armature bar, a flat spring member joined with said armature and attached to said center portion, said bar extending in front of said pole pieces so as to be capable of rocking movement toward and away from said respective pole pieces in opposition to the bias of said spring member, and a reflector mounted on said bar.

4. A scanning device for register regulation, comprising a magnetic structure having a base portion and a center portion extending at a right angle to said base portion and two pole pieces extending in parallel to said center portion on both sides respectively of said center portion, two coils on said respective pole pieces, an armature bar, a flat spring member joined with said armature and attached to said center portion, said bar extending in front of said pole pieces so as to be capable of rocking movement toward and away from said respective pole pieces in opposition to the bias of said spring member, and a mirror mounted on said bar in a position symmetrical to the rocking axis of said bar.

5. For a web register regulator, a photoelectric scanning device comprising an electromagnetic structure having two parallel pole pieces and two coils on said pole pieces, an armature extending across said pole pieces in spaced relation thereto and being fulcrumed on said structure for rocking movement toward and away from said respective pole pieces, spring means for biasing said armature toward the midposition of said movement, a reflector mounted on said armature, a source of light disposed relative to said reflector to have said reflector throw an oscillatory beam onto the web, and a photoelectric cell disposed relative to said web to respond to light from the thus illuminated area of the web.

6. A scannin device for register regulation, comprising a magnetic structure having a base portion and a center portion extending at a right angle to said base portion and two pole pieces extending in parallel to said center portion on both sides respectively of said center portion, said pole pieces being shorter than said center portion so that said center portion has an end surface farther away from said base portion than the respective pole faces of said pole pieces, a flat spring member having a middle portion firmly attached on said end surface, an armature fas- 1 tened to said spring member and extending in front of said pole pieces in spaced relation to said faces so as to be capable of rocking movement toward and away from saidrespective faces in opposition to the spring bias of said member, and a mirror on said armature bar and extending symmetrically to the fulcrum axis of said movement.

FRANK SLAMAR.

No references cited.

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