US1958885A - Facsimile printer - Google Patents

Description

1934- R. w. CARLISLE 1,958,885

FACSIMILE PRINTER Filed Sept. 15, 1931 INVENTOR A I'TO EY Richard 14 GarZz'sZeQ Patented May 15, 1934 FACSIMILE PRINTER Richard Wallace Carlisle, Audubon, N. 1., assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania.

Application September 15, 1931, Serial No. 562,877

10 Claims.

My invention relates to printing apparatus designed for the reproduction of pictures, printed matter and the like wherein the apparatus is made responsive to electric currents of intensities which vary with the degree of intensity of the elements comprising the matter to be reproduced. Apparatus of this type is generally referred to as facsimile printers. More particularly, my invention is limited to improvements in apparatus of the above type, these improvements centering about the printing element and its associated structure.

Prior art discloses facsimile printing or reproducing apparatus of many types, the majority of them operating upon the same broad general principles, the main distinguishing characteristics centering around the means whereby the modulated currents may be converted into intelligence. Broadly speaking, these printing means may opt-rolytlc changes produced by the received current impulses, or by reason of physical impressions made upon a wax or other suitable surface.

My invention is particularly adapted to an apparatus of yet another type well known in the art wherein the received current pulses are transformed into interpretive symbols by means of pressure brought to bear upon message paper which is maintained in contact with transfer paper of the coated-carbon species or the like. In apparatus employing this mode of reproduction, message paper in contact with carbon is caused to travel over a rotatable drum upon the surface of which is provided a helical rib. In close proximity thereto, is mounted a printing member which customarily assumes the form of a knife-edged bar of a length suflicient to span the width of the paper which is usually fed over the drum from rolls. In response to current impulses received by the apparatus from a transmitter, the printing element is caused to vibrate and strike the paper, at each vibrationQagainst the helical rib, resulting in an impression being registered thereon from the carbon paper at the point defined by the intersection of the helix and the printing member at that moment. In this manner, subject-matter being sent out from some transmitting source, may be duplicate of the original.

Great difllculty has been experienced with apreproduced as a paratus constructed according to the prior art in obtaining clear and sharply defined reproductions of material which is being transmitted from some distant location. The important causes of these relatively poor results have been traced to the erate or function by reason of chemical or elecprinting element and its associated apparatus. As constructed according to the prior art, the printing member, comprising a bar extending across the width of the message paper and means,

in the form of a magnetic driving unit or a pluraiity of the same, are provided at spaced locations along the bar for the purpose of causing the bar to vibrate toward the paper in response to received current impulses. It was found that,

if the bar were too flexible the effect of striking the paper in response to a current impulse would result in bouncing of the printing member, thereby causing the development of ghost images. Attempts have been made to overcome this defeet by increasing the stifiness of the printing member. While this change serves to overcome,

to some extent, the rebound efiects, its large mass prevented it from actually following the motion of the motor armatures at the higher speeds.

It is very desirable, to the extent of being necessary, in apparatus of this type that, for the production of clear images, the amplitude response of the printing member shall be uniform and independent of the range of frequencies to which the apparatus is designed to respond. The structure described above, as constituting prior art, is obviously too insensitive for the successful operation of the same; that is, from the viewpoint of obtaining uniform amplitude response to the frequencies received in apparatus of the type referred to.

It is also customary, according to the priorart, to provide means for framing the received message or picture. This is accomplished by providing a framing angle on the drum of approxi- .0 mately 20, that is, a portion of the drum within an angle of 20 is maintained free from the helical rib which extends around the remainder of the drum surface. During periods of reception, very often, the printing member may be influenced into vibrating during a moment when the framing-angle portion of the drum is passing beneath it. When the helix then begins its passage beneath the printing member, the mem her is thereupon caused to bounce upon the helix and have considerable rebound on the same, thereby producing undesired marks on the message paper. The above outlined defects and disadvantages, arising by reason of the construction of apparatus, as defined by prior art and noted above, have been cured in the apparatus constructed according to my invention.

It is, accordingly, one object of my invention to provide facsimile recorders or printing appa- 1m an apparatus, of the type described, which shall member.

have uniform frequency-response characteristics throughout the receiving range of frequencies.

Another object of my invention is to provide in a printing apparatus of the type referred to, a printing member which shall be free from reflected waves normally produced in a vibrating member.

Another object of my invention resides in the provision of means for limiting the striking distance of the printing member in an apparatus of the type described to eliminate the undesired results normally obtained by reason of the printing member bouncing upon the helical rib.

In the apparatus constructed, according to my invention, wherein the above objects may be obtained, I provide a specially designed printing member and caused it to be operated by means of a driving motor associated with the printing member at one of its extremities, through the instrumentality of a specially designed coupling The location of the driver at one extremity of the printing member is designed to transmit the vibrational energy through the printing member by a torsional twisting of the same.

In designing mechanical members which shall be adapted to respond to certain predetermined frequencies, itis possible to consider the physical characteristics of the members as being analogous to the constants of an equivalent electrical circuit. Having done this, it becomes possible to so design the rnember that it will be responsive to frequencies within a certain range in much the same manner as with electrical circuits. In analyzing the characteristics of the member, we may consider the printing member as analogous to an electrical transmission line or filter circuit. Such a line has inductance and capacitance per unit length and, similarly, the mechanical member may be considered as having a moment of inertia and a torsional compliance per unit length. Deriving an equation for frequency involving analogous constants of the metallic member it becomes possible to design the member to have a certain moment of inertia per unit length and a definite torsional compliance, so that the member will be equally responsive to a definite band of frequencies and have an impedance which will match the drivers and the damping effect of the pa er.

I have, therefore, according to my invention, so designed the printing member that its response will be uniform over the desired range and have also similarly so designed the vibrating mechanism of the driving motor as to be equally responsive to the same range of frequencies. In other words, to obtain minimum resistance to the vibrational energy produced by the driving member and thereby to obtain the maximum output from the apparatus, I have matched the impedance of the printing member with that of the driving member, and the impedance of the printing member with the apparent impedance of the paper. For more detailed discussion of the apparatus, reference will be made to the drawing wherein:

Figure 1 is a view, in perspective, of that much 1of a printing apparatus wherein lies my invenion.

Fig. 2 is a bottom plan view of the structure illustrated in Fig. 1.

Fig. 3 is a plan view of the driving mechanism.

Fig. 4 is a plan view of the driving mechanism, the armature-restoring-spring holder being removed.

Fig. 5 is a side elevational view of the driving mechanism.

Fig. 6 is a view, in perspective, of the vibrating mechanism of the driving motor, showing the manner of connection to the printing member.

Referring more particularly to Fig. 1, the apparatus comprises a drum 1 mounted on a shaft 3, the ends of the drum being provided with sprocket teeth 5 to engage message paper 7 in contact with carbon paper 9 and cause the same to be carried at a slow velocity underneath the printing member or bar 11 which is maintained in close proximity to the drum. The papers may alternatively be pulled through by rubber rollers as in a typewriter. A pinion 13, mounted on the shaft 3 adjacent to one end of the drum, is coupled to a driving motor (not shown) to cause rotation of the drum at a predetermined speed. Mounted upon a surface of the drum is a helical rib 15 which extends around the surface of the drum except for an angular portion of approximately 20 which is maintained free for framing purposes. The rib 15 is of suflicient height to make contact with the paper as it is drawn around under the printing member by rotation of the drum and may consist of a steel wire .010 to .030 inch diameter. The printing member 'or printer bar 11 comprises a small strip of hard metal of a length sufiicient to span the width of the paper and is quite stiff.

The printer bar is mounted upona hinge member 17 which comprises a very thin strip of spring metal attached, preferably, along the full length of the bar and may be soldered or otherwise integrally united thereto. The printing member is permanently aflixed to a rigid bracket 19 of L-shape, extending parallel thereto, by screws or other connecting means extending through the hinge and engaging the bracket. A bracket 21 of U-shape, to which the L- shape bracket is affixed, constitutes means, by reason of it being mounted upon a shaft or axle 23, whereby the printing member 11 may be lifted from its position in close proximity to the drum, so that the message paper may readily be inserted or removed.

The short arm of the L-shape bracket 19 provides supporting means whereby the driving unit 25 may be mounted in the desired position relative to the printing member 11. The driving means comprises a vibrator assembly mounted upon. a base plate 2'1, this base plate being attached to the bracket 19 in the position illustrated. A magnetic circuit comprises a horseshoe magnet 29, preferably of the permanentmagnet type, having removable pole pieces 31 and 33 of U-shape, the whole metallic structure being clamped to the base plate 27 by means of bolts or other suitable attaching means. Between the pole pieces .is provided an armature 35 and suspension means 36 surrounded by a plurality of coils 37 and 39 which are maintained in fixed position by spacing elements 41 of insulating material. be fed by the incoming current impulses; and by means of the resulting reactions with the flux of the permanent magnet, they are adapted to cause the armature to vibrate in response to the incoming current.

The coils are adapted to A means is provided for damping the vibration of the armature for the purpose which will be more clearly described subsequently. The damping means comprises a pad 43 of resilient material, such as rubber, mounted in a holding member 45 which is flxedly mounted on the magnetic structure. The armature 35 comprises a substantially rectangular metallic member having an extended projection 47 which is designed to extend to and be embedded in, the damping pad 43. The armature may be suspended by a flexible spring member 49 which is supported from an adjustable supporting means 51 mounted upon one of the magnetic pole pieces. This member comprises an element provided with a groove 53 on its under surface which is in slidable engagement with a ribbed member 55, also mounted on the pole structure. One end of the adjustable member 51 is slit, the slit 57 terminating in a circular opening 59 through the member into which may be inserted the armaturesuspension means 36 which may be clamped therein by means of a clamping bolt 61 engaging the split ends of the adjustable member in such manner as to draw them together, when desired.

The adjustable means just described may be employed for centering the armature in its correct position relative to the coils and the pole pieces. A driving motor is shown mounted on the bracket in such position as to bring the armature and its suspension means in substantially axial alignment with the printing member, to which member the suspension element may be permanently connected. As stated above, the printing member is so designed as to have characteristics analogous to that of a transmission line, and the armature and its suspension means are designed to have characteristics to match this line.

The respective impedance of the pertinent elements may be determined as follows:

If the inertia of the armature is Ia and the torsional compliance of the stem is Ca, the characteristic impedance of the driver is The inertia per unit length of the line is for a strip, ,1

where M=mass per unit length h :width of strip The compliance per unit length is the ratio of the angular deformation in radians to the apwhere G=modulus of shear in dynes per sq. cm.

0 :thickness of strip g :empirical constant depending on ratio of width to thickness, i. e.,

The characteristic impedance of the line is The velocity of propagation along the line may be calculated from the following formula:

Respective elements therefore having matched impedances, will be capable of responding equally to all frequencies within a predetermined range. However, at certain frequencies, the vibrational waves set up in the printing member will be reflected back and either coincide with or oppose the starting of another wave. This phenomenon, known as reflection, will have the effect of changing the apparent impedance of the member for the various frequencies to which it is designed to be resonant. In order to reduce the undesirable effect caused by reflections, it is necessary to provide means for absorbing the excess energy which is normally embodied in the reflected wave. This might be done by extending the length of the printing member to such an extent that energy of the impressed wave would have been dissipated by the time the wave should reach the end of the bar, but this scheme is impracticable because of the limits imposed by the design of the apparatus. The squeezing action of the printer bar upon the paper acts as a partial damper on the bar.

Additional damping effect may be accomplished by adding damping means to the vibrating structure. This damping means may take the form of a pad of.resilient material, such as rubber, similar to that disclosed in the description of the driver, and may be mounted at the extremity of the printing member farthest from the driving motor. When a damping member is employed for the purpose described, it may be considered as comprising a portion of the total impedance of the printing member, in which case, the impedance of the printing member may be reduced by an amount equal to the impedance offered by the damping member.

Therefore, in the preferred embodiment of my invention, the impedance of the driving unit will be made to match with the combined impedances of the printing member and damping means. If desired, the rubber damping member may be loaded with particles of heavy foreign material, such as powdered tungsten, lead oxide or the like, to increase the damping effect, prevent rebound, and prevent the printing member from over shooting the helix in case it be set in vibration during the time when the angular framing portion of the drum is passing beneath the printing member. The impedance of the printing assembly is sufiioiently high, so that its path of travel will be just sufficient to reach the edge of the helix.

In designing apparatus of this type to obtain the results set forth in the objects of my invention, I first determine the force which must be exerted to obtain a clear impression on the message paper. The printer bar is then made stifl enough to produce a satisfactory impression at the end remote from the driven, when twisted at the driven end. Its flexibility is called the compliance of the printing member. It should be constructed no stiffer than necessary in order to allow it to vibrate like a transmission line rather than as a rigid mass which would be diflicult to move at high frequency. The air gap of the driving motor will depend upon the deformation of the printing member required to obtain a clear image. The range of frequencies to which the apparatus must be capable of responding with equal efiiciency is determined from the size of the picture and the number of scanning lines and dots per second desired. Knowing this, the moment of inertia of the armature and the compliance of the suspension stem may be calculated, placing the natural period of the stiflly suspended armature at the upper end of the frequency range desired. Suitable dimensions may be chosen for the armature which will give light weight consistently with good magnetic efliciency, as well known in the art of designing magnetic drivers for loud speakers.

I have, accordingly, disclosed, in detail, the improvements in printing apparatus which constitute my invention. I provide means, in the form of a simple structure, whereby well defined reproductions of transmitted views may be obtained by reason of the fact that, in the apparatus described by me, I have eliminated the causes of the poor results obtained in apparatus of the prior art.

While I have disclosed my invention in detail, various changes within the scope of my invention will suggest themselves to those skilled in the art. I, therefore, do not desire to be limited to the exact details shown, except insofar as is necessitated by the claims and the prior art.

I claim as my invention:

1. In a facsimile printing apparatus, a still printer bar, a fixed member, and means yieldably connecting said bar to said member substantially along the entire length of said bar and means for driving said bar.

2. In a facsimile printing apparatus, a stiff printer bar, a fixed member and means yieldably connecting said bar to said member substantially along the entire length of said bar, and means for driving said bar in the printing direction only.

3. In a printing apparatus, a printing bar and means for actuating said bar comprising an armature, said armature being substantially coaxial with said bar.

4. In a printing apparatus, a printing bar, an armature assembly associated therewith, the mechanical impedance of said bar being substantially equal to the mechanical impedance of said assembly.

5. In a printing apparatus, a printing bar, damping means therefor, an armature assembly associated with said bar for actuating the same, the mechanical impedance of said bar and damping means being substantially equal to the mechanical impedance of said armature assembly.

6. In a printing apparatus, a printing bar, means for actuating said bar in response to direct current and current at audio frequencies, the mechanical impedance of said bar being substantially constant over a wide range of frequencies.

7. In a printing apparatus, a printing bar, means for actuating said bar in response to current at audio frequencies, and damping means associated with said bar and actuator for preventing resonances and reflections from establishing themselves therein.

8. In a printing apparatus, a printer bar, a drum, a, helix thereon for movement relative to said bar and in close proximity thereto, means for actuating said bar toward said helix, the impedance of said bar being of such value as to prevent overshooting with the helix removed.

9. In a printing apparatus, a printing element and actuating means therefor, said actuating means operating at one end of said printing element to set up torsional stresses in said printing element.

10. In a printing apparatus, a printing bar and means for causing said bar to vibrate by reason of torsional stresses set up directly in said 5 printing bar.

RICHARD WALLACE CARLISLE.

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