Identification of printout devices

Forensic Science International, 19 (1982) 11 - 38 0 Elsevier Sequoia S. A., Lausanne --- Printed in The Netherlands

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IDENTIFICATION OF PRINTOUT DEVICES*

A. G. LESLIE and T. A. STIMPSON

Questioned Document Section, R. C. M. Police, Crime Detection Laboratory, Ottawa, Ontario (Canada)

(Received August 23, 1980; in revised form February 24, 1981; accepted May 13,198l)

Summary

Some of the aspects that will assist in the identification of printout devices have been explored. More research must be done particularly with the ink jet and laser printers to facilitate identification of the documents printed by these devices. Further technological changes in printout devices are imminent. Prototypes of printing devices activated by the human voice have been devised. Research and development in the identification of printout devices must continue so that the expertise of the document examiner is not dwarfed by technological changes.

Introduction

The identification of texts on documents produced by printout devices presents a challenge to the document examiner because the technological advances in printout devices are constantly changing. This requires that the document examiner keep abreast of these changes so that when the examiner is presented with questioned documents, he/she has a solid base of data to work with.

I.B.M. Electronic Typewriters

The I.B.M. Electronic Typewriter is a desktop typewriter that combines the capabilities of modern electronics with familiar I.B.M. single-element typewriter technology. The I.B.M. Electronic Typewriter has many features normally found in more sophisticated, multi-console word processing systems. One of the features of the Model 50 is its function as a ten-pitch, twelve-pitch or proportional spacing typewriter by simply positioning the selection lever and choosing the proper element. A feature of the Model 60 is a 736 -character memory storage [l] .

The single elements with 88 characters and color labelled white for the I.B.M. Selectric I and II typewriters are not interchangeable with the I.B.M. Selectric III and I.B.M. Electronic typewriter 10 and 12 pitch single elements with 96 characters (different character grouping) and color labelled yellow, or vice versa. There is a difference in the mould which does not permit proper mounting nor do the wire clips of the element clasp the upper ball socket. The element will eject when the keylever is depressed.

*Presented at the American Society of Questioned Document Examiners Meeting, Vancouver, B. C., Canada, August 1980.

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Microscopic examination of a number of 96 character single elements has revealed that some elements have randomly placed raised beads on a few characters similar to beads found on the 88 character single elements. Figures 1 and 2 show raised beads on the staff of the upper case ‘R’ and period dot. Figure 3 shows the corresponding punctures in the paper of the two characters in sequence.

Word Processor Printwheels

“In the narrow technological sense, word processing is the process of producing written communication, at higher speed and lower cost, with more accuracy and less work, through the use of improved technology.” [2] .

Electronics permits various makes of console keyboards to be interchangeable with various printers. The Micon console keyboard together with the Qume printer is an example of a working unit. Such arrangements are used to meet the needs of the customer.

“A key element of the word processing system is the output printer, which, typically, has been an impact printer.” [3] .

The printwheel characters are impacted against the ribbon and the paper by a hammer directly behind the character in the print position. Figure 4 is an overall view of the hammer/printwheel mechanism on an AES printer with the ribbon removed. Figure 5 is a platen view of the hammer behind the character ‘N’ in the print position.

The adjustment of the hammer intensity is quite critical. If the hammer applies too much pressure it breaks the character spoke and usually renders the printwheel useless. The hammer striking the ribbon, when the broken character spoke is in the print position, simply leaves a black smudge. The wording of the text will indicate which character has been broken off. Figure

Fig. 1. IBM Courier 96 type style.

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Fig. 2. IBM Courier 96 type style. Fig. 3. IBM Courier 96 type style.

Fig. 4. AES Printhead. Fig. 5. AES Printwheel,

Fig. 6. Prestige Elite 12 type style. Fig. 7. Qume Prestige Elite 12 type style.

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6 illustrates a broken underscore character and Fig. 7 is the resulting example using the broken underscore character.

Some printwheels are interchangeable with different manufactured units. For example Qume printwheels are compatible with a number of systems including the AES printers. The Diablo and Xerox metal printwheels can be used on all systems utilizing the metal printwheel mode including the Wang WP 10, 20 and 30. The Diablo plastic printwheels can also be used on Qume printers. Plastic printwheels cannot be substituted for metal printwheels, and vice versa, due to the weight difference.

Most printwheels are daisy shaped but may have varying terminology by different manufacturers. There are exceptions like the NEC Spinwriter printer which is thimble shaped.

Printwheels are available in various horizontal spacings (monospace) including 10 and 12 pitch and proportional spacing. The printwheels are available in plastic, plastic with glass-tipped characters, or metal spoked with the nonmetal characters being electroplated. Micon is introducing a teflon coated printwheel. Higher print speeds are possible with the plastic printwheels.

The characters on a printwheel will eventually show wear through use. Figure 8 shows excessive wear on the ‘en’ combination and the printed result is illustrated in Fig. 9. Figure 10 is an example of a twisted ‘$’ symbol spoke on a metal printwheel. The printed result shows lateral misalignment in Fig. 11. Note also the shadowing at the top of the symbol inside the top down- stroke where it meets the S curve.

Through use, the electroplating on the characters of a metal printwheel will begin to peel. This is probably due to deterioration of the underlying nonmetal -material from repeated hammering of the character. Figure 12 shows peeling of the electroplating on the lower case ‘i’ and the printed result is illustrated in Fig. 13.

Microscopic examination of metal printwheels has revealed that some printwheels have randomly placed raised beads on the surface of a few characters [4] . Figures 14 and 15 show a raised bead and corresponding puncture in the paper from a ‘?’ symbol. The size and height of the raised beads will determine whether or not the bead will puncture the paper. Figure 16 shows an elongated bead on the left arm (platen view) of the upper case ‘W’. The elongated bead did not puncture the paper when printed, as illustrated in Fig. 17, even using greater pressure and also testing the printwheel on two printers. The type of ribbon medium may also be a factor in cushioning the printed impression, Our experience to date indicates that the raised beads on printwheels are somewhat less prone to puncturing the paper when printing as opposed to the single element on typewriters. The weight of the single element ball striking the paper versus the hammer strike on the back of the spoke of the printwheel character combined with the cushioning effect of the ribbon medium may account for this occurrence.

Figure 18 is an illustration of the damage through wear on an upper case ‘M’ and Fig. 19 illustrates the corresponding impression. The damage of this character on the used printwheel occurred during a two week period.

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P

i

Fig. 8. Qume Prestige Elite 12 type style. Fig. 9. Qume Prestige Elite 12 type style.

Fig. 10. Xerox Gothic P. S. type style. Fig. 11. Xerox Gothic P. S. type style.

Fig. 13. Xerox CDN - Roman P.S. type Fig. 12. Xerox CDN - Roman P.S. type style. style.

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Fig. 14. Wang Madeleine P.S. type style. Fig. 15. Wang Madeleine P.S. type style.

Fig. 16. Xerox CDN - Roman P.S. type style. Fig. 17. Xerox CDN - Roman P.S. type style.

Fig. 18. Wang Madeleine P.S. type style. Fig. 19. Wang Madeleine P.S. type style

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I.B.M. Ink Jet Printer

As mentioned earlier the output printer in the word processing system, typically, has been an impact printer. Ink jet printing is, in effect, non impact matrix printing which can achieve greater printing speeds as compared to character impact printers in the word processing system.

“In ink jet printing, characters are formed from small ink drops. Basi- cally, in the printing process conductive ink under pressure is forced through a small nozzle to form a jet. The jet would normally break up into a stream of drops of quasi-random size and spacing, but drop formation can be controlled by vibrating the ink within the nozzle cavity at a fixed ultrasonic frequency. The pressure waves cause the jet to break up into a stream of drops of uniform size and spacing at a well defined distance from the nozzle.” [ 51 .

The section of the print head that causes the ink stream to form the drops is called the crystal

“A voltage applied to an electrode surrounding the breakup point in- duces an electrical charge of a specific, predetermined magnitude on the forming drop. This charge is retained by the drop throughout its flight to the paper.” [ 51.

The charge electrode assembly is mounted on the upper deflection plate to the rear of the nozzle.

“The stream of drops passes through an electrostatic field formed by a fixed high voltage across a pair of horizontal deflection plates.” [ 51.

Figure 20 is an overview of the high voltage deflection plates with gutter assembly and Fig. 21 is a bird’s eye view of the separation of the deflection plates.

“Because the charge on each drop of ink is controlled individually, a drop can be deflected vertically a desired amount.”

In the I.B.M. printer, “the drops are deflected from bottom to top, and one column of dots

and/or spaces is referred to as a scan. If, in forming a character a particular space in a scan is to be left white, it is blanked by leaving the drops un- charged. These undeflected drops are intercepted by a gutter and recycled to the ink reservoir.”

“AS drops are deflected vertically, the printhead is driven horizontally at constant speed. Thus, drops are deposited in appropriate positions within a raster area to form the desired character.” [ 51.

“Each character is printed within a character matrix 40 drops high and 12 - 28 drops wide, according to the pitch and the typestyle used. The vertical position of the drops is controlled by the electronics.”

“The pump (part of the print mechanism) provides the vacuum necessary to draw ink from the bottle and to supply the head assembly with a constant flow of ink at the correct pressure for printing.”

“By adjusting the voltage on the pump its operating pressure can be changed. This will change the speed of the drops, which is seen as a change in

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drop spacing and will affect the height the drops are deflected. This is because the time the drops are in the deflections field will be changed.” [6].

Figures 22, 23 and 24 illustrate three different heights of the same text printed by three separate printers as measured with a scale of l/35 of an inch.

The print quality depends on “the accuracy with which the individual dots are placed on paper.

Vertical placement errors are primarily caused by the ink jet system and horizontal errors by printhead velocity variations. Dot placement errors fall into two general classes: those that affect all dots uniformly (either vertically or horizontally), causing size variations either in height or width of the character being printed, and those that affect the placement of individual dots relative to neighbouring dots.”

“Misplacement of dots relative to adjacent drops can cause raggedness of the edges, voids, and loss of optical density (failure to achieve necessary ink overlap for solid fill). In some cases, dots may be grossly misplaced, but even relatively small placement errors can cause noticeable degradation in print quality.” [ 71.

Figure 25 shows a split in the dot of the diacritic over the lower case ‘i’. The most probable cause is an improper crystal drive voltage.

When splitting in the characters occurs the most probable causes are (1) the charge electrode is off centre, (2) crystal needs adjustment, or (3) increased drop spacing.

Another factor resulting in poor print quality is the drop misplacement in the character (excess splatter surrounding characters). The most probable cause being: (1) crystal adjustment, (2) increased drop spacing or (3) charge electrode off centre. A vertical white space or lateral misalignment in the text will probably be caused by a restricted carrier motion [ 81.

The left hand margin on the ink jet printer is constant once it has been set and should remain constant until it is adjusted by a technician. Since the adjustment is manual, all left hand margins are unlikely to be set in the exact same position. Figure 26 illustrates three left hand margins of the same text printed by three separate printers.

Any appreciable change in the print quality is likely to be noticeable and technical adjustments effected. It is, therefore, incumbent that standards produced at a time as close as possible to any questioned text prior to technical adjustments, be made available for comparison purposes.

policies Fig. 25. IBM (ink jet) prestige elite type style.

Fig. 26. IBM (ink jet) prestige elite type style.

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Drum Printer

The drum printer is an impact line printer. This printer consists of a steel drum spinning on a horizontal axis on which are located 132 vertical columns of raised characters across the length of it. Each column makes up a complete character set of up to 64 characters. Figure 27 illustrates a character drum. Parallel to the drum is a hammer bank, as illustrated in Figure 28, consisting of a corresponding number of hammers, or one hammer for every one of 132 separate columns. Some models feature one hammer for two de- signated columns. The paper (next to the hammer bank) and inked cloth run between the hammer banks and the rotating drum. The paper is advanced by means of tractors, illustrated in Fig. 28. The individual hammers strike the paper against a character on the rotating drum at the instant the character is in the print position, leaving an impression on the paper. As the drum is revolving in a clockwise direction at speeds in excess of 1800 rpm it is imperative that the hammer strikes at the exact instant the character on the drum is aligned with the hammer. A fraction of a second difference in the hammer strike, or a misalignment between the hammer and character results in an im- perfect character impression on the paper. The following is a list of some of the defective impressions as they appear on the printout together with their possible sources:

Character Printing Low In the case where the hammer strike mechanism is delayed, all the

printed characters in the column corresponding to that particular hammer will be low as illustrated by the column of A’s in Fig. 29. As this delay becomes greater the defective impression becomes more obvious until the lower portion of the character is eventually cut off, as illustrated by the column of V’s in Fig. 30. If this delay becomes even longer the character impression is not only cut off, but a partial impression of the next step character becomes visible above the cut off character impression as illustrated in the left hand column in Fig. 31.

Character Printing High In this case the hammer strike is premature. All the characters in the

column corresponding to that particular hammer will be high as illustrated in the column of characters ‘D’, ‘T’, ‘C’, and “/” in Fig. 32.

Uneven (off the feet) impression across the face of the letter There is some lateral play between each hammer of the hammer bank.

If any particular hammer becomes misaligned it will not strike the characters on the drum evenly resulting in an off the foot impression, as illustrated in the column of H’s in Fig. 33. The character will print heavier on the right side or on the left depending on which direction the misalignment occurs. If the hammer is severely misaligned a partial impression of the character will be the result as is illustrated in the characters ‘F’ and ‘H’ of the top line in Fig. 34.

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Fig. 27. Print drum, drum printer.

HAMMERS

TRACTORS

Fig. 28, Hammer & tractor, drum printer.

Fig. 29. Drum Printer. Fig. 30. Drum Printer.

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Fig. 31. Drum Printer. t 1y aLI 1 rlr** * 1

Fig. 32. Drum Printer.

Fig. 33. Drum Printer. Fig. 34. Drum Printer.

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Ghosting If the hammer is so severely misaligned that it also partially strikes the

character in the adjacent column, a partial impression (ghosting) of the character will result as illustrated between the ‘L’ and ‘+’ sign of line 2 in Fig. 34. Ghosting is also caused when the activated hammer causes the hammer adjacent to it to be dragged forward, to such an extent that it too strikes the paper causing a light impression in the next lateral column.

Ghosting of characters above or below the line, for all characters across the page

This is caused by all hammers in the bank striking the character drum prematurely or late. The resulting printout will feature ghosting of characters or vertical ‘off the foot’ impressions for all print positions as illustrated in Fig. 35. This feature is of insignificant identifying value as the problem can be simply alleviated by the operator. This feature could mask more significant defects.

Light impressions The character drum consists of a steel drum with as many as 132 col-

umns of characters surrounding it. The most frequently used characters may eventually wear out. The resulting impression will be less intense, surrounded by a vague outline of the hammer face as illustrated by the left parenthesis in Fig. 36.

Misalignment of a whole line The paper in a drum (and train printer) is advanced by means of two

sets of tractors situated on either side of the printer. The perforations along the edges of the paper are threaded into these tractors. If the tractors are not perfectly aligned, the resulting print line will not be parallel to the lined paper. On the train printer this feature may also be caused by misalignment of the swing gate. Figure 37 illustrates whole line misalignment from a train printer. This misalignment is usually so slight that it will not be observed un- less the printing is on lined paper. The examiner, of course, should ensure that the lines on the paper are not in themselves misaligned thus creating the illusion that the printer tractor mechanism is defective.

Dark to light (or vice versa) printing across a sheet of paper could be due to a number of causes

(1) The inked cloth may be worn only on one end due to previous printing requirements which use a set number of lateral columns. This feature has insignificant evidential value.

(2) The cause is usually an uneven bearing of the hammer bank in re- lation to the drum.

As in cases of typewriter examinations, there may be some apparent defects in the drum printer that have little or no identifying significance, but serve only to mask other more significant defects:

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Smudging of characters on the paper due to a dirty character drum should not be confused with worn characters. Worn characters are rare and are usually surrounded by the outline of a print hammer. Smudging of characters is more frequent and the hammer outline surrounding the character will not be as distinct (Fig. 38).

Blank impressions (a) Non-inked impressions at the extreme ends of the paper due to a

misaligned ink cloth is usually observed at the extreme right or left sides of the paper as in Fig. 39.

(b) Blank impressions in the printer may be due to a disc of paper getting caught between the ribbon and paper during printing or a tear or hole in the cloth.

The Train or Chain Printer

These line printers are impact printers which incorporate either a character slug bearing chain or train. The train surrounds one drive wheel and one idler gear mounted on the same plane. As these wheels turn the attached train advances carrying the characters past 132 print positions. When a character passes a selected print position, a hammer, mounted in the hammer bank, strikes the paper against the ribbon and slug to produce a desired impression. Usually there is one hammer for each of up to 132 print positions. Rather than travelling vertically, the train of slugs travels horizontally. Thus a single character could be impressed on all 132 columns or print positions. Figure 40 illustrates the character slug bearing train and Fig. 41 illustrates the hammer bank assembly.

The timing of the hammer strike against the character is critical. Any malfunction of the hammers, revolving train or the interaction between the two, results in a defective impression on the paper. Some of these defects and their probable causes are:

(1) Inconsistent horizontal misalignments down a column of printing is evidence of a chain or train printing device malfunction

This feature will appear as a wavy line of print when viewed down one column. The sources of this defect are numerous:

a) Between each slug (bearing 3 or 4 characters) on the train there is a small gauged space. After continual use this gap may vary along some portions of the train due to a buildup of dirt between the slugs or crowding or jamming somewhere along the train. This will cause all the characters on one slug to pass by the striking hammers slightly early or late depending on the degree of space between slugs. If the space is excessive a partial impression will be the result. Figure 42 illustrates misalignments resulting from mis- spaced character slugs.

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Fig. 40. Print train.

Fig. 41. Train printer, hammer bank.

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(b) Erratic spacing along the train may be due to a break in the character slug at the spot where it is attached to the train. This causes jamming of characters along the train especially as the broken slug rounds the drive wheel or idler gear. Figure 43 illustrates a broken character slug.

(2) Consistent horizontal misalignment down a column of printing a) There is some play between each hammer in the hammer bank. When

the hammers are adjusted they print the characters so that they appear evenly spaced. If the space between two adjacent hammers increases due to the wear in the comb that separates each hammer a fixed distance the result will be an excessively wide space between two printed columns as is illustrated between the F and G columns in Fig. 44. Any increase in space between two hammers will cause a corresponding decrease in space with the misaligned hammer and its other adjacent hammer which will naturally reflect as two columns of print crowding, as illustrated in the G and H columns in Fig. 44.

(b) Delayed ‘fly’ time which causes a delay in the hammer strike will also result in misaligned columns.

(3) Ghosting is the faint impression of a second character appearing immediately before or after the impression of the intended character This is caused by either a premature or late strike of a hammer or by

the striking hammer dragging an adjacent hammer partially into print position.

(4) Cut off Eeft or cut off right impressions are due to early or late hammer strikes that do not result in complete

contact with the characters as illustrated in Fig. 45.

(5) Whole column not printing refers to an obvious white line down a column in the printout. This

defect is caused by an electrical problem which prohibits the hammer from striking. The width of the blank column in the text should distinguish it from a horizontal misalignment caused by malaligned hammers. Figure 46 illustrates a blank column.

(6) Indis tint t impressions result from a worn character on the slug. Figure 47 illustrates the worn

characters P and Q. Figure 48 illustrates character impressions, D, E, and F on lines one and six produced from worn slugs. Worn slugs containing 3 or 4 characters are eventually replaced. The impressions from the characters on the replacement slug will then be sharp and distinct when compared to other impressions from moderately worn characters. Figure 49 illustrates printing resulting from a train consisting of both unworn and worn character slugs.

(7) Consistent vertical crowding of whole lines of prin t as illustrated in Fig. 50 is an indication of a line feed malfunction. If

this defect is not readily noticeable it may go unrepaired.

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Fig. 42, Train printer.

Fig. 44. Train printer.

Fig. 46. Train printer.

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(8) Some groups of columns consistently print lighter or darker than other columns This can be attributed to uneven wear of the cloth due to past printing requirements.

(9) Heavy to light printing or vice versa along the width of a page is due to uneven bearing of the chain or train of slugs to the hammers.

The uneven bearing is due to the maladjusted swing gate that carries the chain or train assembly.

Features such as smudging and blank impressions due to worn ribbons, dirty printing mechanisms and paper discs have no identifying significance but only serve to mask other significant defects.

The Dot Matrix (impact) Printer

In this printing technique a character image is formed by printing selected dots in a matrix usually consisting of five columns by seven rows. Figure 51 illustrates a matrix print head and Fig. 52 illustrates the impact wires of the same print head. (Note the two missing wires and two other wires not in the home position). The print head consists of a vertical column of seven wires which are activated, usually electro-magnetically or hydrau- lically to strike the paper through an inked ribbon to produce dots. This column of pins then moves horizontally to the next print position in the character matrix and continues to strike the paper in this lateral movement until all five horizontal print positions for a character have been completed. Dot matrix printing techniques can be utilized in both serial (character) and line printing.

Malfunctions that result directly in defective print quality can usually be attributed to the print head. The following are print defects:

(1) Gaps in letters caused by the failure of wires to strike the paper through the inked

ribbon are due to broken wires or malfunction of the wire actuating mechanism.

(2) Matrix characters printing heavy on the top and light on the bottom or vice versa are attributable to an improper platen-print head bearing.

(3) Differences in intensity among ink dots in the matrix that are consistent for all the dots corresponding to a

specific wire are related to impact differences among the print head wires. Figure 53 illustrates upper case printing where the lst., 2nd., 3rd., 5th. and 6th. wires are printing heavy and the 4th. and 7th. wires are printing lighter. Figure 54 illustrates lower case letters produced by the same print head.

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Fig. 53. Dot matrix printer. Fig. 54. Dot matrix printer.

Fig. 55. Dot matrix printer. Fig. 56. Dot matrix printer.

Fig. 57. Thermal matrix printer.

Fig. 58. Thermal matrix printhead.

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I Fig. 62. Thermal matrix printer.



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(4) Dots running together Through use the wire tips become blunt or burred producing unevenly

inked printed dots, Heavily burred wires produce dots that run into each other on certain letters as illustrated in Fig. 55.

(5) Light impressions that occasionally occur throughout the printout, as illustrated in Fig. 56

are indicative of sporadic binding of the wires in the print head and thus the wire does not impact the paper as forcefully as it does under normal con- ditions.

(6) Consistently faint impressions throughout the whole of the document are likely to be attributable to a

worn or dry ribbon and are of insignificant evidential value. This occurrence may mask the more significant defects.

Thermal Matrix Printer

This printer utilizes a matrix print head consisting of five columns and seven rows of tiny heat elements. As the print head moves across heat sensitive paper stopping at each print position, selected elements are electrically heated. These heated elements are recorded on the paper as the printed character. Figures 57 and 58 illustrate an overall view and close up of a print head in the print position. Figure 59 illustrates the 5 X 7 element print matrix. There are a number of malfunctions of this printer, some of which by their very severity result in a complete shut down of the machine. For example, when the line feed mechanism malfunctions the paper is continually fed through the machine.

Most observable defects in the printing can be attributed to the print head. The print head is composed of three main parts, as illustrated in Fig. 60, the circuit module, the wire band and the dot matrix. Malfunction in the circuit module, breaks in the wire band or burned out matrix elements result in portions of the matrix consistently not recording. This is illustrated as breaks in the characters ‘T’, ‘R’ and ‘W’ in Fig. 61.

Unequal power supply to the various heating elements in the matrix causes some elements to become consistently hotter than others. These elements are recorded as darker spots or impressions on the paper than those impressions resulting from elements receiving less current. Figure 62 illustrates a complete matrix impression featuring dark and light dots and blank areas corresponding to a burned out element. Excessively hot elements will bum minute holes in the surface of the paper as illustrated in Fig. 63.

If the current to all the heating elements is excessive the resultant impressions will be very dark as is illustrated in Fig. 64.

A distinct line impression above the print line is caused by a poorly adjusted bearing of the print head on the paper (Fig. 65).

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Laser Printer

Prior to 1978 the technological advances in the data handling ability of computer systems stood like a giant beside the technological development in output printing devices. The mechanical impact printers appeared to be operating at their maximum output potential which was incompatible with the data processing capability. As a result, a printer using the electrophotographic principle of producing images in conjunction with laser technology was developed. The non impact matrix style laser printer achieved a capacity to print up to 80 cm/second on normal width paper.

In a general sense the laser printer operates on principles similar to a bond paper indirect electrostatic photocopier. A large drum circumscribed

Fig. 67. Laser printer.

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with a flexible photoconducting material rotates at a constant speed. The negatively charged material is exposed by a modulating beam from a low- powered laser which creates a latent image on the drum of the text to be printed. Flashing the image of a forms overlay negative onto the drum permits printing of forms simultaneously with the data.

The latent image is then coated with toner composed of a thermoplastic material permeated with lamp black [ 91. This surface then comes in contact with paper carried on a smaller drum. Thus the negatively charged toner (image) on the drum is transferred to the positively charged paper by means of an electric charge. The paper then passes the fuser station where the developed image is melted into the paper. The photoconductor drum then goes through a cleaning and neutralizing process before it begins another rotation cycle.

If the surface of the photoconductor drum becomes scratched, these markings will be transferred to the paper on each rotation of the drum. Figure 66 illustrates a mark across the surface of the drum with the corre-

10 JUN 1980

JUL

Fig. 68. Laser printer. Fig. 69. Laser printer.

Fig. 70. Laser printer. Fig. 7 1. Laser printer.

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sponding printed mark shown in Fig. 67. A scratch of this magnitude is un- acceptable and will be eliminated by the technician who simply advances the roll of sensitive material that circumscribes the drum. Figures 68 and 69 illustrate less prominent random markings that may go uncorrected over a period of time. Figure 70 is a white gap in the printed line resulting from an imperfection in the forms overlay negative. Because markings on the photoconductor drum surface can be advanced and thus removed from the printed paper, it is imperative that specimens printed as close as possible to any questioned text be submitted to permit a meaningful comparison.

Print quality problems can occur. One of the problem areas is in image formation. Figure 71 illustrates the wavy staffs on the upper case ‘M’. This problem was remedied when the mirror motor in the printer was replaced.

Acknowledgements

The authors wish to thank the following persons for their cooperation and assistance:

C/M’s Doug Howes and Gerry Beiko, Photography Section; Peter Labranche, Audio Visual Section; RCMP “L” Directorate, Ottawa, Ontario.

Mr. Don Turcotte, CN/CP Telecommunications, Ottawa, Ontario.

Miss Donna Hooper, Canadian Word Processing Supply, Ottawa, Ontario.

Miss Trish Morin, Computer Media Group (Qume), Ottawa, Ontario.

Mr Colin Brodie, Manager, Office Products Division; Mr Bob Ford, Advisory Systems Engineering Representative, Data Processing Division; Mr Paul Morrissette, Mr Jim Stephens, Mr Brian Terrance, IBM Canada Ltd., Ottawa, Ontario.

Mr Ron Harrison, Industry, Trade and Commerce; Miss Susan Moore, Depart- ment of Finance; Government of Canada, Ottawa, Ontario.

Mr Alex Ball, Northern Telecom Systems Limited, Ottawa, Ontario.

Mr Hak Kim, Telex (Tulsa Computer Products), Ottawa, Ontario.

To all those persons that contributed to this article who prefer to remain anonymous but share a common view with the police community.

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ted at the Annual Meeting of the American Society of Questioned Document Exam- iners, August, 29, 1977, San Francisco, CA.

References

1 I.B.M. Corp. OPD Adv. Form No. G540-3005 2 Gilbert J. Konkel and Phyllis J. Peck, The Word Processing Explosion, Office Publica-

tions Inc., Stamford, Conn., 1976, p. 3. 3 W. L. Buehner et al., Application of ink jet technology to a word processing output

printer, IBM J. Res. Develop., (January) (1977) 2. 4 A. G. Leslie, Identification of the single element typewriter and type element. Part I -

Type elements. Can. Sot. Forensic Sci. J., 10 (3) (1977). 5 W. L. Buehner et al., Application of ink jet technology to a word processing output

printer. IBM J. Res. Develop., (January) (1977) 3. 6 IBM Office System 6 Service Manual Form No. 241-6201-0, 1978, p. 535 - 536. 7 W. L. Buehner et al., Application of ink jet technology to a word processing output

printer. IBM J. Res. Develop., (January) (1977) 4. 8 IBM Office System 6 Maintenance Analysis Procedures Manual. 9 IBM 3800 Printing Subsystems Maintenance Library Map.

Documents

Identification of printout devices