US2311803A - Reciprocating facsimile apparatus - Google Patents

Description

Feb. 23, 1943. R. J. WISE ETAL 2,

RECIPROCATING FACSIMILE APPARATUS Filed Nov. 15, 1940 s'sneets-shee'c 1 INVENTORS RLJ.WISE R. D. FARROTT RECIPROGATING FACSIMILE APPARATUS Filed Nov. 15, 1940 3 Sheets-Sheet 2 TRANS.

' INVENTORS R.J. WISE BY R. 0. ARROTT Feb. 23, 1943.

FIG. I s

R. J. WISE EII'AL' 2,311,803

RECIPROGA'IING FACSI MILE APPARATUS 3 Sheets-Sheet 3 Filed Nov. 15, 1940 INVENTORS R. J. WISE R. D. PARROTT Patented Feb. 23, 1943 NITED STAT ES PATENT OFFICE RECIPROCATINGFACSI'MILE APPARATUS corporation .of New York Application November 15, 1940, Serial No. 365,772

12 Claims.

This invention relates to facsimile apparatus and more particularly to receiving apparatus for recording subject matter on a continuous web.

Some of the novel features of the invention pertain to recording mechanisms operating on the start-stop principle of synchronization, while other of the novel features pertain to recordin mechanisms employing reciprocating scanning elements irrespective of the type of synchronization employed. The invention constitutes improvements on continuous sheet recorders utilizing reciprocating scanning elements, of which numerous examples may be found in the prior art. These prior art devices have certain limitations which the present invention seeks to obviate or, at least, to minimize. One of the objectiona'blefeatures of most prior art recorders of this type is the mass of the movable scanning member. One of the desirable attributes of the movable scanning member is that it can be returned to its starting position in the shortest possible time. It is evident, therefore, that the lighter the movable member, the more nearly the achievement of this result is approached. Also, the means by which some of the prior art recorders effect the movement of the movable scanning member from the end of its scanning stroke to the beginning of the succeeding stroke do not lend themselves to high speed operation. In one type of prior art recorder the movable scanning member is drawn from one edge of the recordin surface to the other by means of a cord which is Wound upon a drum. At the completion of the scanning stroke the drum is rotated in the opposite direction, permitting the cord to be unwound and thereby to return the scanning member to its starting position. Here again the mass of the drum in unwinding the cord appreciably retards the operation of the recorder.

It is one of the major objects of the invention to obviate wherever possible or, at least, to minimize the above enumerated disadvantages of the prior art continuous sheet recorders.

Another object of the invention is to provide novel means for returning the movable scanning member of a facsimile recorder to its starting position.

Still another object of the invention is to provide, in a facsimile recorder employing a drum upon whch a cord is wound to effect a scanning stroke, novel means for disengaging the cord from the drum upon the completion of the scanning stroke whereby the scanning element may be returned to its starting position.

A further object of the invention is to provide a carriage for the movable scanning member which is light in weight and which embodies means for automatically disengaging the movable and stationary scanning members during the return stroke of the movable member.

A still further object of the invention 'is'to provide, in a facsimile recorder operating on the start-stop system of synchronization under the control of signals sent from the transmitting apparatus, means for preserving a definite cyclic relationship between the gear teeth engaged and any particular recording position of the scanning member throughout the length of the scanning stroke in apparatus which employs reduction gearing between the driving motor and the scanning member.

Still another object of the invention is to provide, in a facsimile recorder in which the scanning member is driven by means of a relatively high speed motor through the medium of reduction gearing and operating on the start-stop system of synchronization, means for applying the start-stop synchronization to the motor shaft in response to signals sent from the transmitting apparatus.

The foregoing and other more specific objects will become apparent from the following detailed description of a facsimile recorder embodying the invention, which is taken in conjunction with the accompanying drawings, of which:

Fig. 1 is a perspective view of a facsimile recorder embodying some of the features of the invention;

Fig. 2 is a fragmentary view of the carriage supporting the movable scanning member;

Fig. 3 is a sectional View taken on the line 3-3 of Fig. 2;

Fig. 4 is a fragmentary view of the drum upon which is wound the line attached to the carriage, together with a circuit diagram illustrating the operation of the scanning apparatus on the start-stop system of synchronization; and

Fig. 5 is a perspective view of a facsimile recorder illustrating the application of the startstop synchronization at the high speed shaft of the driving motor.

Reference is made first principally to Fig. 1 which shows a continuous sheet of sensitized recording paper I l which is supplied from a roll l2 and is passed around a metallic roll or platen l3 which preferably should be of good electrical conductivity and is passed between two feed rolls l4 and I5. The feed rolls are arranged to :grip the recording sheet H between them with sufficient pressure to draw the paper from the roll I2 when the feed rolls are rotated in the directions indicated by the arrows. Part of this pressure is exerted by means of a spring I6 which is arranged to press down upon the shaft of the roll I4. It will be understood that the left hand end of the feed roll I4 is provided with a similar spring so that the pressure may be exerted uniformly over the entire width of the recording sheet. The feed rolls I4 and I5 are provided with gears I! and I8 respectively, by means of which the roll I4 is driven by the rotation of the roll I5. The latter roll is connected by means of a clutch I9 to a pinion gear 2| which is driven by a worm 22 secured to an intermediate shaft 23. Also secured to the intermediate shaft is a pinion gear 24 which is driven by means of a worm gear 25 attached to the shaft of a driving motor 26. Normally, the feed roll I5 is driven slowly by the rotation of the gear 2!. However,

the roll I5 is provided with a knob 21 so that it may be rotated manually at a more rapid rate in order to feed out blank paper between recordings if desired. The clutch I9 permits this type of manipulation of the paper feed mechanism to be effected independently of the motor driven paper feed mechanism.

A disc 28 is coupled by a friction clutch 29 to the intermediate shaft 23. Secured to this disc is a drum 30 and also a deflecting member 3| which is provided with a sloping surface as illustrated in the drawings. A line 32 is attached to the deflecting member 3| and also to a lug 33 which forms part of a movable carriage 34. The line 32 may comprise a stout thread or string, a cord. a light flexible wire, or the like, the only requirements being that it be light, flexible and substantially inextensible. The details of the carriage are best illustrated in Figs. 2 and 3. It is arran ed for sliding movement in a pair of guide rails 35 which have forms approximatin channels and are arranged with the open sides thereof facing one another. A cylindrical member 36 is attached to the carria e 34 adjacent the left hand end thereof as viewed in Fig. 2 and is arran ed to move along the track provided by the guide rails 35. A stylus 3'! is secured to the underpart of the carriage so that it is in a position to engage the surface of the recording sheet II. The carriage 34 is also provided with a second lu 33 located adiacent the left hand end thereof for the attachment thereto of a retractile line 39. This line is passed around a light guide pulley M and is attached to one end of a resilient extensible member 53 which may be 'an elastic band. The other end of the extensible member 43 is secured to any convenient fixed part of the apparatus.

The carriage 34 is arran ed so that when it is subjected solely to the influence of the retractile line 39, it is held against a stop 45 at the left handend of the recording a paratus. Also, while it is held in this position it is arranged to pivot about the cylindrical member 36 in such a manner that the stylus 3'! is lifted from the recording sheet II. The carriage is also provided with a stop member 45 which is adapted to engage the upper surface of one of the'guide rails 35 when tension is applied to the line 32 in an amount sufficient to overcome the moment produced by the elastic band 43 acting through the line 39 and to pivot the carriage in the opposite direction. This position of the carriage is best illustrated in Fig. 2 where it may be seen that the stylus 31 is brought into contact with the surface of the recording sheet II.

During a recording operation the intermediate shaft 23 rotates at a rate equal to one revolution per scanning line. However, when the apparatus of Fig. 1 is employed in a start-stop system, the intermediate shaft continues to rotate as the scanning apparatus is periodically stopped for synchronizing purposes. Hence, in a complete recording operation the shaft will make a greater number of revolutions than there are scanning lines. The ratio of the gears 2| and 22 is such that during one revolution of the intermediate shaft 23 the feed rolls I4 and I5 are rotated sufficiently to advance the recording sheet I I a distance equal to the separation of two adjacent scanning lines at the transmitter. At the beginning of each scanning operation the drum 3!] is rotated from the position shown in Fig. 1 in the direction of the arrow, thereby drawing the carriage 34 to the right. Continued rotation of the shaft 23 causes the line 32 to be wound upon the drum 3!) until the carriage 34 has been moved to its extreme right hand position. At this time the line 32 will have been wound upon the drum 30 to substantially the extent shown in Fig. 4 that is, approximately one complete turn of the cord will have been made upon the drum. The continued rotation of the disc 28 in the direction of the arrow brings the line 32 into engagement with the sloping surface of the de fleeting member 3|. This surface is so designed that as the disc continues to rotate, the one wrapping of the line 32 about the drum 20 will be dislodged from the drum. The carriage 34 is then influenced solely by the retractile line 39 which pivots the carriage about the cylindrical member 36 in the manner described, thereby lifting the stylus 31 from the surface 01' the recording sheet I I and, substantially instantaneously, drawing the carriage to its extreme left hand starting position. The line '32 is attached to the member 3| in such a manner that it has a swivel action. A simple and convenient manner of effecting this attachment is to pass the end of the line through a suitable hole in the member 3|, and to place a knot near the end of the line. There is also provided a guard 41 in the form of a wire bent as illustrated in Fig. 1 and mounted adjacent the right hand end of the guide rails 35 for the purpose of damping lateral movements of the line 32 which has a tendency to whip when it is dislodged from the drum 30 at the end of a scanning stroke.

When it is desired to maintain synchronism between the transmitting and the recording apparatus by means of the start-stop principle, a stop arm 48 is attached to the disc 28. A latch 49 is also provided and positioned so that it may be moved into or out of the path of the stop arm 48. A start magnet 5| controls the operation of the latch to withdraw it from the path of the stop arm. The stop arm 48 is positioned on the disc 28 relative to the deflecting member 3| so that it is in a position to be engaged by the latch 49 at substantially the same time that the deflecting member completes the dislodgement of the line 32 from the drum 3!]. Thus, further scanning is prevented until the scanning apparatus is released by energizing the start magnet 5|. However, during the time that the scanning apparatus is stopped, the intermediate shaft 23 continues to rotate by reason of the frictional coupling between the disc 21 and the shaft. Hence, the feed rollers I4 and I5 continuev to. operatev but, normally. the scanning:

apparatus; is. stopped for sucha, short: time that the: infinitesimal distance throughv which the recording sheet II is moved during the stoppagev to, Figs. 3 and 4. The facsimile signals may be generated in any well-known manner: For example, thesubject matter to betransmitted may be; applied to a sheet 52 which is wrapped; around a cylinder 53. This cylinder isrotated and moved axially in any well-known manner. An optical scanning system may be; employed comprising a source of light 54, the light from which is condensed by means of a lens 55- to a point impinging upon the surface of the sheet 52. Depending upon the nature of the subject mat:- ter' to be transmitted, light variations will be reflected from the sheet 52 and concentrated by means of another lens 56 to a point which falls within the plane of a shutter 51 which may be any conventional light chopper such as. a. perforated or notched disc. The interrupted light beam is then directed to aphotocell 58 by means of which alternating currents of varying amplitudes are generated and subsequently amplified by means of a transmitting amplifier 59- and transmitted over line conductors L to the re.- ceiving station.

At this point the line conductors are connected to a signal inverter 6|, since 'in the type of scanning system described a negative copy of the transmitted subject matter would be made if the line signals were used directly; The: inverted facsimile signals are impressed upon the primary of a transformer 62', the secondary winding of which is connected to excite a pair of amplifier vacuum tubes 63 and 64 arranged in push-pull connection for class operation. The output circuits of the vacuum tubes 63 and 64 are connected to the primary of a coupling transformer 65, the secondary winding of which is connected to one of the guide rails 35 by means ofwhich connection is made tothe recording stylus 31. Plate current for the amplifier tubes 63 and 64 is supplied by abattery 66 which is connected through a contact 8.? which is normally closed during a scanning operation to the mid-point of the primary winding of the transformer 65.

The contact 61 is connected to. short circuit the Winding of a relay 6.8 during; the. scanning operations. One. of the contact. springs 69. is extended, to a point where it may be engaged by a pin, 'Il projecting from the. rear face of the. disc 28. Ihe. pin ll is, positioned on the disc sothat it engages the contact spring 69 substantially simultaneously with the engagement. of the stop arm 48 with the latch 49. Thus, at the time therotation of the disc 28 is arrested the contact 6.! is opened, thereby removing the short circuit from the winding of relay 68. Hence, it is seen that the facsimile signals which are received from the line L are normally ineffective. tocause operation of the relay 68.

At the transmitting station facilities. are provided for transmitting a synchronizing signal after the completion of the scanning of each line. One way in which this may be accomplished is to provide a mark 12 along one edge. of the sheet 52 containing the subject matter to be transmitted. Thus, once per revolution of the transmitter drum 53, the mark 12 is scanned and a facsimile signal corresponding to this mark; is transmitted to the receiving station. The response to. this signal produced by the amplifying tubes 63 and G4. is such that the maximum plate current is drawn from the battery 66. The time atwhich the synchronizing signal is received corresponds to the time at which the disc 28 is in its stopped position and the contact 61 is open. Consequently, the plate current drawn by the amplifier is. employed to energize the relay 68 which effects the closure of its make contact to energize the stop magnet 5! through an obvious circuit, The latch 49 is withdrawn, thereby permitting the disc 28 to start upon another revolution, thereby actuating the movable scanning member to scan the succeeding line. the disc 28 is rotated through a small angle from the stop position, the pin H is disengaged from the contact spring 69, thereby permitting the contact 6'! to again short circuit the winding of relay 68- so that the succeeding group of facsimile signals will not affect the relay.

The apparatus described up to this point has been found to give satisfactory results provided that certain precautions are taken, such as the ratio of the reduction gearing being properly chosen and a high degree of precision employed in cutting the necessary gears. character where an accurate reproduction of the subject matter is desired, it has been found that such results may be obtained only if an even gear ratio is chosen so that a definite cyclic relationship is maintained between each recording position of the stylus throughout the entire length of the scanning stroke and the particular gear teeth engaged at the time. That is, every time that the stylus reaches any given position the same teeth of each pair of gears are in mesh. By observing these precautions any eccentricity or other imperfections present in the driving gears do not produce a jagged reproduction.

However, when the start-stop principle of synchronization is employed, the angular position of; the disc 28 and, consequently, the recording stylus Si is constantly being shifted with respect to cooperating elements of the driving gears, since the scanning apparatus is periodically stopped while the gears continue to rotate. Thus, it is seen that the above described cyclic relationship no longer exists, and if satisfactory reproductions are to be obtained, the gears must be cut with such a high degree of precision that manufacturing costs may become too great for commercial use of the apparatus. 'In addition, even where high precision methods are employed in manufacturing the gears, imperfections developed through operation of the apparatus will produce the undesirable jagged reproductions.

The present invention contemplates an arrangement for obviating all of the aforementioned limitations of the apparatus described previously. Fig. 5 shows in perspective a. facsimile recorder embodying this feature of the invention. The recording sheet H is fed through the recorder in substantially the same manner as. that described in connection with the apparatus of Fig. 1. Similarly, the scanning apparatus is identical to that previously described. In this case, however, the disc 28 is rigidly attached to the intermediate shaft 23, and the worm gear 25 is coupled to the shaft of the motor 26 through a friction clutch '53. A stop arm 14 is also secured to the shaft supporting the gear 25 for the purpose of stopping the scanning, and

As soon as- In work of this.

sheet-feeding apparatus in a manner to be described. V

For this purpose a latch 15 is mounted on the armature 16 of a stop magnet 11. The supporting structure of the stop magnet includes a bracket 18 which is rigidly secured to any convenient stationary portion of the supporting structure of the recording apparatus. The latch 15 is pivotally mounted on a supporting member 19 in such a manner that the impact of the stop arm 14 with the latch 15, when the latter is operated to intercept the stop arm, is absorbed to an appreciable extent. One way of accomplishing this result is to mount the latch supporting member 19 between two resilient members, such as the pads 80, which may be formed of rubber or its equivalent. The latch 15 extends between the two upstanding spaced arms of a retaining bracket 8! so that the hinge or pivot 82 normally rests against the vertical arms of the bracket. In this way the latch and its supporting member 19 are free to move away from the vertical arms of the bracket 8| to abso1b the shock of the stop arm 74 striking the latch. The resiliency of the rubber pads 80, however, restores the hinge 82 to its contact with the vertical arms of the bracket 8| as soon as a state of equilibrium is reached.

Normally, during a scanning operation the latch 15 is kept out of the path of the stop arm 14 by means of a retractile spring 83, one end of which is attached to the latch and the other end of which is attached to a stationary member 84 which i secured to the bracket 18 and is provided with an opening for the latch, the latter serving also to limit movements of the latch. The energization of the windings of the stop magnet 11 attracts the armature 16 to move the latch downward against the pull of the spring 83 so that it is in a position to intercept the stop arm 14 on the revolution thereof following the actuation of the stop magnet.

The cooperation between the scanning apparatus and the synchronizing apparatus is subtantially the same as that described in connection with Fig. 1. The stop magnet 11 is connected in the synchronizing circuit in precisely the same manner as the stop magnet of Fig. 4. During a scanning operation a contact similar to contact 67 renders the stop magnet 11 inoperative by short circuiting the control relay 68. Following the scanning of each line, the contact 61 is opened, thereby placing the relay 68 under the control of the signals transmitted over the line conductors L. This occurs substantially simultaneously with the scanning at the transmitting station of the line 12 which produces at the receiving station a marking signal. The relay 68 is operated to energize the stop magnet 11 and thereby move the latch 15 into a position to intercept the stop arm 14. It will be remembered that substantially coincidentally with the opening of the contact 61, the movable carriage 34 hearing the stylus 13 is returned to its extreme left hand position. Consequently, when the stop magnet 11 is energized, the scanning operation of the recording apparatus is momentarily interrupted. This condition exists until the completion of the scanning of the synchronizing line 12 at the transmitting station. Before encountering the next portion of the subject matter to be transmitted the transmitting apparaus scans a blank space which produces at the receiving station a non-marking signal. Hence, the stop magnet 1'! is deener- Therefore, it is not possible to employ a latch which normally lies in a position to intercept the stop arm, such as in the case of the apparatus of Fig. 1. Incidentally the arrangement of the synchronizing apparatus shown in Fig. 5 may also be employed with the recording apparatus of Fig. 1.

It should be noted that while Fig. 5 discloses the application of the start-stop synchronizing apparatu to a shaft which is arranged to be driven directly from the driving motor, it is not contemplated that the invention be limited to this specific arrangement. is necessary, in order to get proper speed reduction, to employ one or more intermediate shafts between the driving motor and the scanning apparatus, the start-stop apparatus may be connected to any of the intermediate shafts. Of course, the maximum benefits to be derived from applying the start-stop synchronization to a shaft which rotates at a relatively higher speed than the scanning apparatus shaft are obtained by stopping and starting the shaft which is driven at the same speed as the driving motor shaft. However, it has been found that a large proportion of the defects introduced by gear eccentricities where the gears are allowed to rotate during the stop interval of the scanning apparatus may be eliminated by stopping one of the intermediate shafts which rotates at a speed which is higher than that of the scanning apparatus and lower than the motor shaft.

The nature of the invention may be ascertained from the foregoing description of two illustrative embodiments, it being understood that changes in the invention herein disclosed may be made within the scope of what is claimed without departing from the spirit of the invention.

What is claimed is:

1. In facsimile apparatus, a recording surface, a guideway disposed transversely of said surface and substantially parallel thereto, means for moving said recording surface continuously in a direction normal to said guideway, a scanning v electrode mounted for reciprocable movement along said guideway and for pivotable movement into and out of operative recording relation to said surface about an axis normal to said guideway and substantially parallel to said surface, means operable initially to move said electrode on the pivotal mounting into operative recording relation to said recording surface and subsequently to effect a relatively slow scanning movement of said electrode along said guideway in one direction, means to render said electrode moving mean inoperative at the end of said scanning movement, and means effective during the inoperativeness of said electrode moving means to move said electrode on the pivotal mounting out of operative recording relation to said recording surface and subsequently to efiect Obviously, where it with a recording surface of a track disposed par- 'allel to said recording surface, a stylus bearing carriage adapted to be moved along said track, said carriage being pivotable about an axis normm to said track and substantially parallel 'to said surface to move said stylus into or out of engagement with said surface, means for urging said carriage toward one end of said track and said stylus out of engagement with said surface, means operable to move said carriage to the opposite end of said track and said stylus into engagement with said surface, and means for periodically rendering said carriage moving means inoperative whereby said carriage urging means is rendered effective to return said carriage to said one end of said track with said stylus out of engagement with said surface.

3. In facsimile apparatus, the combination with a recording surface of a plurality of spaced guide rails disposed parallel to said recording surface, a movable carriage, a cylindrical member attached to said carriage and in engagement with said guide rails, a recording stylus carried by said carriage, said carriage being pivotable about the rotational center of said cylindrical member to move said stylus into or out of engagement with .said recording surface, a retractile line attached to said carriage, means including said retractile line for urging said carriage toward one end of said guide rails and tending to disengage said stylus from said recording surface, an actuating line, and means including said actuating line operable to move said carriage toward the other end of said guide rails and said stylus into engagement with said recording surface.

4. In facsimile apparatus, a carriage supporting a scanning member and movable between two extreme positions, means for constantly urging said carriage toward one of said positions, a line attached to said carriage, means operable invariably in the same direction for winding said lllne to draw said carriage toward the other of said positions, and means controlled by said winding means for periodically releasing the wound line from the winding means.

5. In facsimile apparatus, a carriage supporting a scanning member and movable between two extreme positions, means for constantly urging .said carriage toward one of said positions, a rotating drum, a line attached at one end to said carriage, means for causing said line to be wrapped around said drum to effect a movement of said carriage toward the other of said positions, and means rotatable with said drum for dislodging the line from said drum concurrently with the arrival of said carriage at said other position.

6. In facsimile apparatus, a reciprocable scanning element, a linear track along which said scanning element is adapted to be moved, a rtating member carrying a drum, a line attached at one end to said scanning element and at the other end to said rotating member, said drum being disposed to cause said line to be wrapped around the drum, thereby producing a forward linear movement of said scanning element, a deflecting member attached to said rotating member and having a surface inclined to the rotational plane of said drum, said deflecting memher being disposed to cause the inclined surface thereof to divert the line sufficiently to dislodge the wrapped portion from the drum, and a retractile'line attached atone'end to said scanning element to produce a backward linear movement transmitter which comprises, periodically transmitting a plurality of successive synchronizing signals, stopping said driving member in response to one of said synchronizing signals, and starting said driving member in response to a succeeding one of said synchronizing signals.

8. In a facsimile telegraph system employing a. continuously operating transmitter of facsimile signals and a recorder of said facsimile signals having a scanning electrode adapted to make one scanning traverse of a recording surface for a plurality of revolutions of its rotary driving member, the method of synchronizing said recorder with said transmitter which comprises, transmitting after each scanning traverse of the subject matter being transmitted two successive signals having substantially opposite characteristics, stopping said driving member in response to the first of said successive signals, and starting said driving member in response to the second of said successive signals.

9. In start-stop facsimile apparatus, scanning apparatus including a recording electrode, a constantly running driving motor, speed reducing mechanism coupling said motor and said scanning apparatus, whereby said electrode is operated at a relatively low speed by said relatively high speed motor, means for effecting an invariable cyclic relation between cooperating elements of said speed reducing mechanism and successive recording positions of said electrode during a scanning movement, means for transmitting in succession a start signal and a stop signal, and means responsive to said signals for stopping and starting said scanning apparatus without altering said cyclic relation.

10. In start-stop facsimile apparatus, a scanning member, a constantly running driving motor, speed reducing mechanism comprising, a plurality of shafts, gears attached to said shafts and serving to drive one shaft from another at different rates of speed, said scanning member being actuated from a relatively low speed shaft and said motor being connected to drive a relatively high speed shaft, a clutch comprising a driving member and a driven member and having the driven member secured to said relatively high speed shaft, a stop arm attached to said relatively high speed shaft, a latch operable to engage said stop arm, means for transmitting a group of synchronizing signals, means responsive to one of said synchronizing signals, and means controlled by said low speed shaft coacting with said signal responsive means to operate said latch to its stop engaging position.

11. In a start-stop facsimile system, a recorder having a retractile scanning member, means operable at a relatively low speed to effect a scanning movement of said scanning member against a retractive force, said low speed means embodying mechanism for disabling the low speed means at the end of a scanning movement whereby said scanning member is returned by said retractive force, means operable at a relatively high speed for driving said low speed means, means operable in response to a first synchronizing signal to stop said high speed means substantially concurrently with the disabling of said low speed means, and means controlled by a second synchronizing signal and said low speed means to restart said high speed means.

12. In a start-stop facsimile system, a recorder having a retractile scanning member, a relatively low speed shaft, a relatively high speed shaft, a winding drum attached to said low speed shaft, a cord attached at one end to said scanning member and at the other end to said drum whereby rotation of said drum causes the cord to be wound thereon and to effect a scanning movement of said scanning member against a retractive force, said drum having means for dislodging said wound cord at the end of a scanning movement whereby said scanning member is returned by said retractive force, a stop member attached to said relatively high speed shaft, a latch operable in response to a first synchronizing signal to engage said stop member substantially concurrently with the dislodgement of said cord, and a release mechanism controlled by a second synchronizing signal and said stopped drum to disengage said latch from said stop member.

RALEIGH J. WISE.

ROBERT D. PARROTT.

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