US3261284A - Non-impact electrostatic printer - Google Patents

Description

July 19, 1966 J. J. LYNOTT ETAL NON-IMPACTELECTROSTATIC PRINTER 5 Sheets-Sheet 1 Filed March 26, 1962 EEEE $2 596% H6583 INVENTOR. JOHN J. LYNOTT BY REYNOLD BJOHNSON 9% XS W,

ATTORNEY July 19, 1966 J. J. LYNOTT ETAL 3,251,284

NON-IMPACT ELECTROSTATIC PRINTER Filed March 26, 1962 5 Sheets-Sheet 2 7 BINARYLEVEL 0; 1 2 5 4 5 6 7 8 9 1O 11 12 13 14 15 Hm mm mu um um um um 1111+ {nnnunuunnnunuunnjz nuununnununuuuum ununnnj HIGH VOLTAGE CONTROLLER AMPLIFIER July 19, 1966 5 Sheets-Sheet 5 Filed March 26, 1962 FIG.6

United States Patent 3,261,284 NON-IMPACT ELECTROSTATIC PRINTER John J. Lynott, Los Gatos, and Reynold B. Johnson, Palo Alto, Calif., assignors to International Business M..-

chines Corporation, New York, N.Y., a corporation of New York Filed Mar. 26, 1962, Ser. No. 182,258 1 Claim. (Cl. 101-114) This invention relates to printing mechanisms in general, and more particularly to a non-impact printer of the electrostatic type.

Intensive efforts in research and development in recent years have resulted in many significant improvements in printing devices. For instance, instead of the usual type of key-moving carriage arrangement utilized in most typewriters, one typewriter now utilizes a rotatable print ball which moves transverse to the paper to be printed upon, thereby eliminating carriage movement. Likewise, developments have been made which have resulted in quieter typewriters, as well as typewriters which are less complex mechanically which provides greater reliability. However, while recent improvements have resulted in highly improved printing mechanisms, certain shortcomings still exist.

For instance, while as previously mentioned great strides forward have been made toward developing a less noisy type of printing mechanism, they are still relatively noisy since some impact mechanism must usually strike the paper or other printing medium employed. Thus, in those applications where numerous typewriters are simultaneously used, background noise often rises to a relatively high level which adversely affects both the quality and quantity of the work output of the employees subjected to it. Likewise, while the reliability of typewriters has been greatly increased, a relatively large number of moving parts are still employed. This relatively large number of moving parts not only results in a less reliable machine but, additionally, increases maintenance and repair costs since often machines which malfunction must be taken off premises for repair. Furthermore, since these typewriters are of the impact type and must, therefore, cause a print carrier such as a type key, to impact on the print medium with sufficient force to print'and return it out of the Way before the next key arrives, wear, due to acceleration and impact involved, substantially limits the life of the machine.

Other shortcomings attendant to the use of most present day typewriters are that eraser particles tend to clog print faces, and most employ a moving carriage. Moreover, due to their mechanical complexity they are heavy and are relatively expensive. Additionally, all require a carbon or similar ribbon which has a relatively short life and, consequentially, must be frequently changed. While engineering advances have simplified the ribboon changing operation, it still must be changed with a resultant loss of time.

It is, therefore, an object of the present invention to provide a novel printing mechanism employing nonimpactprinting;

Another object of the present invention is to provide a printing mechanism which is extremely quiet, has relatively few moving parts, and is highly reliable;

Another object of the present invention is to provide a typewriter which does not require a ribbon and which has a fixed carriage;

Another object of the present invention is to provide a typewriter which is relatively inexpensive, lightweight and not subject to clogging by erasure particles;

Another object of the present invention is to provide a novel printing mechanism employing electrostaic patterns for character formation;

Another object of the present invention is to provide a printing mechanism employing electrostatic techniques to form visible toner characters on a print medium.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which: a

FIG. 1 is a partially cutaway isometric view of one embodiment of the herein disclosed printing mechanism which utilizes a plurality of selectively energizable electrodes in combination with a character drum for character formation.

FIG. 2 is a blown up portion of the character drum of the mechanism of FIG. 1.

FIG. 3 is a graphic representation of strips illustrating the principle of operation of a permutation unit for use in character selection.

FIG. 4 is a partial isometric view of the character drum of the device of FIG. 1.

FIG. 5 is a combination block-isometric structural view of another embodiment of a printing mechanism which may be constructed in accordance with the present invention which utilizes a single electrode and an endless steel aperture tape in combination with a character drum for character formation.

FIG. 6 is a side view of another embodiment of a printing mechanism which may be constructed in accordance with the present invention which utilizes a dielectric web as the printing medium.

FIG. 7 is a side view illustrating another embodiment of the present invention which illustrates an endless dielectric web arrangement used for contact printing onto a print medium.

FIG. 8 is still another embodiment of the present invention which utilizes a single character wheel for printing onto a dielectric strip for pressure transfer to a print medium.

Briefly, the preferred embodiment of the present invention comprises a thin character drum or mask having a plurality of openings therein in the configuration of print characters. A micromesh screen is contained on the inner surface of the character drum. Means are provided for applying toner to the micromesh screen, such that toner print characters are formed. A plurality of electrostatic probes or electrodes are disposed adjacent to and parallel the axis of the character drum, and paper or other material to beprinted upon is passed therebetween. Energization of the electrodes will cause toner to be pulled from the character drum to the paper in the configuration of the particular print character which was in alignment with the probe upon energization. Means for selectively energizing the plurality of probes to accomplish printing responsive to an input keyboard or other external input means is provided.

Refer first to FIG. 1 wherein is shown the preferred embodiment of the subject invention. In FIG. 1 is shown a thin character drum ormask 1 which may be, for instance, .004 thick, made of conductive material. Disposed on the inner surface of thecharacter drum 1 is amicromesh screen 2. Formed completely through the the character drum are a plurality ofopenings 3 in the configuration of print characters. As shown in FIG. 1, theprint characters 3 on thecharacter drum 1 are disposed around it in circumferential columns. All circumferential columns are identical such that, considering a line parallel to the axis of rotation of the character drum, it can be seen that all Zs are in alignment, all As are in alignment, etc. Means of applying toner to the character drum-mesh screen configuration are provided comprising avelvet toner roll 4 andmohair loading roll 5. Toner is applied to themohair loading roll 5 which rotates at the same speed as thevelvet toner roll 4 which in turn rotates at a speed slightly slower than thecharacter drum 1. Thevelvet toner roll 4 rotates at a speed slower than thecharacter drum 1 to produce a scrubbing action between them. In this manner toner is applied to the character drum-mesh screen configuration. It should be noted that the toner does not adhere to thecharacter drum 1, but adheres only to themicromesh screen 2, such that print characters of toner are formed. This attraction of toner only to and retention of toner by the micromesh screen can be assured in several ways. For instance, as shown in FIG. 1, acenter electrode 6 is provided having a potential applied thereto which causes the toner to be drawn toward it and thereby retained by themicroswitch screen 2. In those areas other than theopen areas 3 of thecharacter drum 1, thecharacter drum 1 acts as a shield and toner does not adhere thereto. Obviously, to act as an electrostatic shield the character drum, which is made of a conductive material, is grounded.

In FIG. 1 it should be obvious that themohair loading roll 5, thevelvet toner roll 4, thecharacter drum 1 and the printmedium feed sprocket 7 are rotated by conventional rotating means (not shown). Also, while in FIG. 1 there is shown a print mediumsprocket feed mechanism 7, it will of course be apparent that any other type of feed mechanism such as a conventional roller feed, would be suitable.

Contained within thepaper guide 8 are a plurality of selectively energizableelectrostatic probes 9. Oneelectrostatic probe 9 is provided for each print station. Eachprobe 9 is connected byleads 10 to the electrode decoder andamplifier 11. Thepaper guide 8 comprises not only the probe section, but also comprises aheater section 12. As is well known, toner is contained within resin and to make it adhere to the material which is to be printed on, the toner in almost all instances must be heat set. While other methods of heat setting the toner can be provided, it has been found that incorporation of the heating element in the paper guide has provided suitable heat setting.

Rotatably mounted onshaft 13 about whichcharacter drum 1 is rotated and afiixed to drum 1 is aphotoelectric cell arm 14 having mounted on the outer extremity thereof aphotoelectric cell 15. Thephotoelectric cell 15 is electrically connected to the slip ring 16, which in turn is electrically connected by means of leads 17 to the electrode decoder andamplifier 11. A plurality of permutation disks 18-1811 are rotatably mounted on theshaft 13 and free to rotate with respect thereto. Each permutation disk 18-18n is connected by means of an arm 19-19n to a solenoid armature 20-2011 which moves a predetermined distance upon energization of the solenoids 21-- 21. The solenoid-permutation disk unit is the character selection means in that it enables selection of a particular row of print characters across thedrum 1 by means of a binary input. For instance, if there are to be 128 different characters in each circumferential column disposed oncharacter drum 1, there would be 8 permutation disks and associated solenoids 21. The solenoids 21 are energized by striking the keys of theinput keyboard 22, which provides a parallel binary output to the solenoids to accomplish energization of selected solenoids to select the particular character which is to be printed as will hereinafter become apparent from the following discussion. The electrode decoder andamplifier 11 may be of any conventional design. One such electrode and electrode decoder and amplifier is shown in US. Patent 2,726,940 to Buhler entitled Xerographic Printer.

Disposed on the opposite side of thepermutation disks 18 from thephoto cell 15 is aring light source 23. As thephotocell 15 rotates about theshaft 13 only one set of openings in the permutation disks will be in alignment, such that light is passed from thelight source 23 to thephotocell 15. It is at this instance that thephotocell 15 emits an output pulse which is amplified and furnished to the particularelectrostatic probe 9 involved. This operation will hereinafter become more clear.

In FIG. 3 are shown four straight strips, each corresponding to a binary level, i.e., 1, 2, 4, and 8. While these strips are shown for simplicity of operational description as straight in FIG. 3, it will become apparent that these strips could be formed in a circular configuration to form a circular disk member as is the actual case in FIG. 1. Each of the strips is selectively movable into one of two positions by a moving mechanism (not shown) which corresponds to the solenoids 21 of FIG. 1. Each of the strips are divided into 16 cells numbered 015. A rectangular shaped opening 27 is located in each cell either in the right or lift hand portion thereof. For instance, considering the uppermost strip labeledBinary Level 1 incell 0, it can be seen that an opening is conin the right hand half, whereas the opening is contained in the left hand half ofcell 1. As will hereinafter become obvious, the placing of the openings in either the left hand or right hand half of the cells will determine at which position the openings are in alignment, such that if there were a light source-photocell arrangement as shown in FIG. 1, alignment would exist and light would pass through all the strips and strike the photocell to cause an output pulse. The movement of each strip upon actuation of its associated binary mechanism is to the right for approximately one-half of the cell width. The permutation strips of FIG. 3 are shown in their initial or deenergized position with none of the binary positioning mechanisms corresponding tolevels 1, 2, 4 or 8 energized. Thus, the output from the keyboard in this instance would be 0000 to each solenoid. It can readily be seen that ifbinary positioning mechanisms 4, 2 and 1 were energized, the openings in the strips would be in alignment such thatposition 7 would pass light. Likewise, it can be seen that ifbinary positioning mechanisms 8, 4 and 1 were energized,position 13 would pass light. Thus, if a photocell-light source combination were to pass along the strips on opposite sides thereof, an output pulse would be emitted from the photocell upon encountering the particular position at which the openings of the strips are in alignment, and this particular position is selected as heretofore explained by selectively activating the binary positioning mechanisms corresponding tobinary levels 1, 2, 4 and 8. While to facilitate the description of operation of the permutation unit, only four permutation strips have been shown, it will, of course, be apparent that any number of permutation strips or disks could be employed; the limiting factor is the number of rows of print which can be physically placed on thecharacter drum 1.

In FIG. 4 is shown a partial isometric view of the character drum of FIG. 1. In FIG. 4 ablank space 28 is shown on the periphery of thedrum 29. During positioning of the permutation disks '18 responsive to energization of solenoids 21, it is possible that erroneous alignment through the disks may temporarily take place with the result that a pulse may be applied to aprobe 9. To

prevent this occurrence, the blank space is provided in the character selection mask, and positioning of the permutartion disks 21 takes place during the time that the blank space of the character selection drum is adjacent theprobes 9. Other types of muting devices could, of course, be provided to prevent the generation of pulses during alignment of the permutation disks, but this method has been found to be quite simple. Positioning of thepermutation disks 18 at the moment that the blank space on thecharacter drum 1 is adjacent the row ofelectrostatic probes 9 is accomplished by having thepermutation units 18 always in alignment when the blank space is adjacent theprobes 9 such that a pulse is emitted by the photocell which is gated with the binary code set up in the keyboard. Thus, only during the time that the blank space of thecharacter drum 1 is adjacent theprobes 9 can the code "be fed to the solenoids of the permutation unit.

The electrode decoder and amplifier III, which is the print station selector means, receives pulses from the slip ring 16, amplifies them and feeds them to a selectedelectrostatic probe 9. The electrode decoder andamplifier 11 has contained therein a progression or other similar type switch, such that as the code is entered from thekeyboard 22 to thepermutation disks 18, the switch is stepped forward one position allowing thenext probe 9 in the line to be energized. Thus, theprobes 9 are selectively energized across theprint medium 24 to print a line at a time. In the event that no code is set up during a revolution, the stepping switch, of course, does not advance.

The number of output lines from thekeyboard 22 is dependent upon the number ofkeys 25 on the keyboard. For instance, if 64 keys were on the keyboard, a 6 level binary code would be required. By striking a particular key 25 on the keyboard, a binary input code is set up on the lines leading from the keyboard, which in this instance are the leads to the solenoids 21 of the permutation unit. The keyboard must have the feature that even though a key has been struck the output from the keyboard is delayed pending acceptance of a read or print signalfrom a computer, or as in this case, the permutation unit indicating that the blank portion of thecharacter mask 1 is in alignment with the row ofelectrostatic probes 9. Thus, energization of the solenoids of the permutation unit is accomplished under control of the input keyboard.

As heretofore described, thepermutation disks 18 are aligned such that when the desired line of print characters on therotating character drum 1 are in alignment with the row ofelectrostatic probes 9, light is received through the disks .18 from the light 23 source by thephotocell 15. Thephotocell 15 at this time emits an output pulse which is fed along lines 17 from slip ring 16 to the electrode decoder and amplifier .11. Theelectrode decoder 11 amplifies the pulse received from thephotocell 15 to a level such that when it is applied to aprobe 9, sufficient electrostatic force will exist between the probe and the character mask to draw toner from the particular print character in alignment with it to theprint medium 24 disposed between thecharaoter drum 1 andprobe 9. Theelectrode decoder 11 also as heretofore described acts as a controller to the probes in that it channels the amplified .phototube pulse to theproper probe 9.

It will be obvious then that upon energization of one of the plurality ofprobes 9, toner will be pulled from thecharacter drum 1 onto thepaper 24 from the particular print character involved. The toner will be pulled onto the paper in the configuration that it was on the character drum mesh screen combination as shown for example in FIG. 2 which shows a mesh screen FIGURE 26. Thus, by selective energization of the plurality ofelectrostatic probes 9, a line the width of thecharacter drum 1 can be printed line by line upon apaper 24 or other medium to be printed upon. When one line of printing has been completed, the paper as in conventional typewriters is stepped up one line and printing on the next line commenced.

Refer next to FIG. 5 which is another embodiment of the subject invention wherein is shown aprinter controller 30 connected along line .31 to acharacter selector 32. Thischaracter selector 32 corresponds to the heretofore described permutation unit of FIG. 1 comprising solenoids, disks, light source and photocell and is mechanically tied to the shaft on which thecharacter drum 38 is mounted. It should also be understood that theprinter controller 30 of FIG. 5 correspond-s to theinput keyboard 22 of FIG. 1. Printer controller merely being a term which is intended to encompass not only input keyboard-sot the type of FIG. 1, but is intended to encompass any other type of controller which may be used to control the printing operation. In FIG. 5 thecharacter drum 38 is constructed the same as the character drum-mesh screen configuration of FIG. 1. As illustrated in FIG. 5 however, toner is contained within thecharacter drum 38 rather than applied externally, and there is no electrode in the character drum 3-8 as in the embodiment of FIG. 1. Likewise, as shown in FIG. 5, there is ahigh voltage electrode 39 adjacent to and extending the entire length of and parallel to the axis of rotation of thecharacter drum 38. Disposed between thehigh voltage electrode 39 and the character drum is anendless steel tape 40. Contained in thissteel tape 40 is anaperture 41 the size of the largest print character on the character drum 3-8. Thesteel tape 40 thus acts as a shield allowing electrostatic forces to pass from thehigh voltage electrode 39 upon energization only through theaperture 41. Thus, if a sheet of paper orother print medium 42 to be printed upon is disposed bet-ween thecharacter drum 38 and theendless steel tape 40, upon energization of thehigh voltage electrode 39 toner will be pulled from thecharacter drum 38 to thepaper 42 only from the print character which is in alignment with theaperture 41.

There is also shown a conventionalhigh voltage amplifier 34 connected to receive an input from the character selector-32 by means ofline 33 as well as to thehigh voltage electrode 39 by means ofline 43. Theprinter controller 30 is connected alongline 31 to the character selector and also is connected alongline 36 to a tape position control 35. The tape position control 35 may be of a conventional type such as a rotary stepping switch which imparts a stepping movement to thesteel tape 40 under control of theprinter controller 30 or of the ratchet and pawl type.

Thus, in operation thecharacter selector 32, similar to the permutation unit of FIG. 1, under control of theprinter controller 30 sets up the particular transverse row of characters on thecharacter drum 38 which are to be adjacent thesteel tape 40 upon energization of theelectrode 39. Likewise, theprinter controller 30, as thepermutation unit 32 is set up, sends a pulse alongline 36 to the tape position control 35 which steps thetape 40 forward one position. Thus, theaperture 41 is caused to step forward one position across thecharacter'drum 38. When proper alignment exists in the disks of thecharacter selector 32, an output pulse is emitted by the photocell to thehigh voltage amplifier 34. The amplified pulse is then applied to theelectrode 39 thereby drawing toner through the character drum and mesh screen to theprint medium 42 disposed between thecharacter drum 38 and theendless steel tape 40 only from the print character in alignment with theaperture 41. Again, as in the embodiment of FIG. 1, the toner is drawn onto thepaper 42 or other medium to be printed upon in the configuration of the particular print character involved.

Refer next to FIG. 6 wherein is shown another embodiment of the subject invention which is particularly suited for use in those applications in which extremely high speed printing is required. From a consideration of the embodiments of FIGS. 1 and 5, it can be seen that the character drum cannot be rotated at extremely high speeds since toner would be flung from the character drum. Thus, for high speed applications the embodiment of FIG. 6 is provided which does not require toner to be placed on or in the extremely high speed rotatingcharacter drum 40.

In FIG, 6 thecharacter drum 77 has along center electrode 78 which is grounded by means of awiper 79. Disposed parallel to the axis of rotation of thecharacter drum 77 is a plurality of selectively energizablehigh voltage electrodes 80, as in FIG. 1, or the steel tape-single electrode arrangement of FIG. 5. A material 47 having dielectric characteristics is fed from thereel 44 over thepaper guide 46 which is disposed between thecharacter drum 77 and the plurality of selectivelyenergizable electrodes 80. The dielectric 47 then passes by a toning station comprising toner rolls 48 and 49, through a heat fixing station comprisingheat platens 50 and 51 and onto the take-up reel 45. Not shown in FIG. 6, but which is obviously necessary, are the permutation unit and method of selectively energizing the high voltage electrodes.

In operation as the probes are selectively energized, an electrostatic pattern is printed upon the dielectric 47 by thecharacter drum 77 acting as a shield such that an electrostatic pattern in the form of the particular print character involved is formed on the dielectric which, upon application of toner, provides a visible image. The developed dielectric then passes through the heat fixing station 5051 and then on to the take-up reel 45. Thus, as is obvious from a consideration of this embodiment, relatively high printing speeds can be obtained since toner is applied to the dielectric, not from therotating character drum 77 but from the external toner applicator.

Refer next to FIG. 7, which like the embodiment of FIG. 6, is particularly suited for use in those applications wherein relatively high speed printing is required. In FIG. 7 is shown a dielectric 52 fed between a character drum 53 and the plurality of selectivelyenergizable electrodes 54, or the single electrode and steel tape arrangement of FIG. 5. The dielectric 52 is also fed past a. toner station 5556 and past a contact printing station comprising twopressure rollers 57 and 58 and afeed reel 61 and take-up reel 62 for feeding paper orother material 64 which is to be printed upon in rolling contact with the dielectric 52. While in FIG. 7 the dielectric 52 is shown to be an endless belt which is erased by thedischarge unit 63 prior to being returned to the print operation station, it is, of course, obvious that the dielectric 52 need not be an endless belt, but may be for instance a web which is fed to a take-up reel.

The operation of the embodiment of FIG. 7 as far as the printing of the latent electrostatic images is identical to that of FIG. 6. The dielectric 52 then passes the toning station 5556 where toner is applied to develop the electrostatic image, but then passes to the contact printing station 57-58. At the contact printing station 57-58 the web ofpaper 64 is brought into rolling pressure contact with the dielectric 52 to thereby transfer the toner image on the dielectric 52 to thepaper 58. Thus, as is obvious, the embodiment of FIG. 7 like the embodiment of FIG. 6 is ideally suited for those applications where high speed printing is required. Further, the embodiment of FIG. 7 provides a method of inexpensively providing high speed printing without the necessity of printing directly onto a dielectric and utilizing the dielectric for storage as is necessary in the embodiment of FIG. 6.

Refer next to FIG. 8 wherein is shown another embodiment which is admirably suited for use in those applications where a relatively inexpensive printing mechanism is required. In FIG. 8 is shown a strip ofdielectric material 65 which is fed from afeed reel 66 to a take-up reel 67 in tangential relationship past acharacter wheel 68. Afirst electrode 69 is disposed on one side of the character wheel and asecond electrode 70 is disposed on the opposite side of the dielectric tape at the point of tangency between thecharacter wheel 68 and thedielectric tape 65. A permutation unit consisting ofpermutation disks 71,light source 72,photocell 73 tied to the rotation ofcharacter wheel 68, and high voltage amplifier (not shown) is provided. The operation of this permutation unit and high voltage amplifier is as heretofore described in conjunction with FIGS. 1 and 5. Thus, latent electrostatic images are formed on the dielectric 65 which is then fed by conventional drive means (not shown) past a toningroller 74. Thedielectric tape 65 is then fed past apaper 75 or other medium to be printed upon, and is brought into alignment therewith one line at a time. Apressure transfer roller 76 is then caused to move along thedielectric tape 65 causing it to be brought into pressure contact with thepaper 75. Theroller 76 is then returned to its original position and another line is printed on the dielectric tape and again pressure transferred. This embodiment, as is obvious, is quite inexpensive and simple in operation and is admirably suited for those applications where extremely high speed printing is not required and medium speed printing can be tolerated. The embodiment of FIG. 8 is also quite inexpensive in that only one electrode is utilized and thus the output pulse furnished by thephotocell 73 can be amplified and fed directly to the electrode without the necessity of selecting a particular electrode as in the embodiment of FIG. 1.

In the above described manner there has been provided a novel non-impact printer employing electrostatic techniques which is not only relatively quiet, but which is mechanically simple, highly reliable, and relatively inexpensive. Additionally, there has been provided a printing mechanism which does not require a moving carriage and which does not require a conventional type ribbon. Moreover, while the non-impact printer herein presented is capable of extremely high speed operation, it unlike normal impact printing mechanisms, is not subject to increased wear or unreliability due to the high speed operation.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

Apparatus for printing on a print medium comprising:

a rotatable cylindrical character member containing a plurality of circumferential columns of character forming openings,

toner retaining means in said character forming openings,

means for applying toner to said toner retaining means,

a single electrode in electrostatic relationship with said cylindrical character member extending substantially parallel to the axis of rotation thereof and separated therefrom to allow said print medium to pass therebetween,

shielding means including an aperture for selectively shielding portions of said single electrode disposed between said electrode and said cylindrical character member,

and means for sequentially stepping said aperture of said selective shielding means along said single electrode.

References Cited by the Examiner UNITED STATES PATENTS 1,278,964 9/1918 MacGill 346-74 2,586,047 2/1952 I-Iuebner 118637 X 2,643,753 6/1953 Wohlgemuth 197-18 2,676,100 4/1954 Huebner 118-637 X 2,726,940 12/1955 Buhler 101 (Other references on following page) 9 UNITED STATES PATENTS Gundlach 118-637 X Bolton 118-637 X Green et a1. 101 Hickerson 197-16 Hickerson 1971 X Bolton 118637 Schwertz 101 Hoffman 101 Schwartz 101 Shull 101-93 10 3,081,698 3/1963 Childress 101 3,160,091 12/1964 Schwertz 101 3,161,544 12/1964 Berry 101 FOREIGN PATENTS 81,920 9/1956 Denmark. 1,051,870 3/1959 Germany.

DAVID KLEIN, Primary Examiner.

10 ROBERT E. PULFREY, Examiner.

ERNEST R. WRIGHT, Assistant Examiner.

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