|Year : 2017 | Volume
| Issue : 2 | Page : 68-71
Study on the relationship of continuous laser printing and the distance of trace on the OPC
Xingzhou Han1, Yuanli Han2, Xiaoguang Wang3
1 QD Examination Division, Institute of Forensic Science, Ministry of Public Security, Beijing 100038; QD Laboratory, Criminal Police University, Shenyang 1110035, China
2 Collaborative Innovation Center of Judicial Civilization, University of Political Science and Law, Beijing 100088, China
3 QD Examination Division, Institute of Forensic Science, Ministry of Public Security, Beijing 100038, China
|Date of Web Publication||30-Jun-2017|
Institute of Forensic Science, Ministry of Public Security, Beijing 100038
Source of Support: None, Conflict of Interest: None
This thesis aims to seek the relationship between photosensitive drum cyclical trace distance of two pages (shorted for L') and continuity printing of laser printers. Characteristics quantification, statistics are chosen to evaluate the data and results. It is indicated that the regularity is existed between L' and continuity printing, and regular performance between different models of HP and Canon printers are consistent. According to the data, L' of continuous printing are summed up, the probability of replacing the front page and the middle page which can meet the continuity regularity are analyzed. The numerical interval is given of noncontinuous printing. The study can enhance the scientificity of printing document examination and have innovation and practical significance in civil disputes, criminal cases, and social community.
Keywords: Continuous printing, printing document examination, statistical, trace
|How to cite this article:|
Han X, Han Y, Wang X. Study on the relationship of continuous laser printing and the distance of trace on the OPC. J Forensic Sci Med 2017;3:68-71
|How to cite this URL:|
Han X, Han Y, Wang X. Study on the relationship of continuous laser printing and the distance of trace on the OPC. J Forensic Sci Med [serial online] 2017 [cited 2017 Oct 23];3:68-71. Available from: http://www.jfsmonline.com/text.asp?2017/3/2/68/209286
| Introduction|| |
Nowadays, printing is one of the most important and common documents forming method in our daily life and work, and printing document examination has been to an indispensable branch of questioned document (QD) examination. Among all kinds of printing methods, as we all known, laser printing occupied the largest market share all over the word after 2000, as the continuing developments in the quality of impression, combined with the ever reducing cost of toner printers, especially after 2007. Laser printing documents are easy to be a criminal or economy fraud for its fast characteristics. As far as laser printing documents concerned, usually multi-page documents are printed by one laser printer, but in fact, the suspects often replaced one or some pages of it to change the original meaning of a contract or other legal documents. Document examiners should have the ability to identify whether the documents were altered or not. The common types of altered documents are as followed: (a) replaced by different principle printers, for example, using inkjet printing pages to replace. (b) Replaced by the same principle but different brands printers, for example, using HP to replace Canon printing pages. (c) Replaced by the same principle, brand but different models printers, for example, using HP 3030 to replace HP P1106 printing pages. (d) Replaced by the same principle, brand and model but not the same printer. (e) Replaced by the same printer. For the four types of cases above, it is easy to examine, microscopic investigation at large magnifications to examine the surface aspect of the printing, component analysis,, and trace features  can be used. For the last one, it is difficult, although the documents are printed by the same printer, it may be also altered actually, the front one may be replaced by the back ones. Now, document examiner is troubling to face the continuous printing.
| Materials and Methods|| |
Organic photoconductor drum
Now, most of the laser printers are using organic photoconductor drum (OPC) in China, which is organic photoconductor shorted. In general, OPC is made of the coating layer and the aluminum substrate. Coating layer has three kinds of layers: metal oxide blocking layer, charge generation layer, and anti-reflection layer. The most important feature of the OPC drum is exposed conductivity, insulation when no light. The working process of OPC contains charging, exposure, development, transfer, fixing, and cleaning.
The shortcoming of OPC is avoiding fire, high temperature, dirty, and scraped. If the surface is clashed, a trace will be formed on it, then the trace will affect the imaging and appeared on the printing papers [Figure 1]. The trace is a very important feature to examine the documents whether printed by the same printer, and examiners summed many successful cases in China. Moreover, the researcher found that OPC is easily destroyed  and appeared the trace on its surface, Deng Hailong, a QD examiner in China found that after using 2 years of 11 different brands and models laser printers, and there are 6 appeared the trace on its OPC, the appearing rate is 55%.
|Figure 1: Cyclical trace features of OPC. (a) Black traces, (b) white traces|
Click here to view
Laser printer belongs to page printing, so the trace features appear regularly. Moreover for common A4 laser printer, the distance between two adjacent trace points in one page is about 76 mm, L = 76 mm, as shown in [Figure 2]. This paper wants to discuss the relationship of the distance L' and bn, tn+1 [Figure 2], bn is the bottom page margin of the n th page, tn+1 is the top page margin of the (n + 1) th page.
L' = bn + tn+1
If two pages are continuous printed, whether L' meet some certain regularity? If we use the x th (x > n+1) page to replace the n th page, then L' =bx + tn+1 whether also meets the continuous printing regularity.
- Equipment: Shengong–Caliper, use it to calculate bn, tn+1
- Laser printer: HP P1106, HP 3030, Canon LBP 2900
- Software: Matlab 6.0, Photoshop 7.01, Microsoft Excel 2007
- Paper: 70 g/m2 A4 Pure White Copy Paper, UPM Classic Jet-set.
Ideas and methods
- Study the regularity of L' in the condition of normal continuous printing. Every printer print 500 pages, measure bn and tn+1 of every page and calculate the sum of them by Microsoft Excel
- Statistical calculate the regularity of L' of replacing the front page. For the 500 pages, if the 1st and 2nd page are a file, for example, a contract, we can choose the 3rd, 4th, 5th…500th to replace the 1st, there have 498 kinds of possibilities, then separately calculate the sum L' of t2 and b3, b4, b5, …b500, which is the bottom page margins of the 3rd, 4th, 5th…500th. In the same way, if the 2nd and 3rd page are a file, we can choose the 4th, 5th…500th to replace the 2nd, there are 497 possibilities, then gain 497 L'. And so on, if the 498th and 499th page are a file, we can only choose the 500th to replace the 498th, there is one possibility, then gain only one L'. Above all, replacing the front page when typing out 500 pages, the possibility (X) is:
X = 498 + 497 + 496 + 495 +… + 1==124251
There are 12,451 possibilities, just like an orderly 498*498 matrix.
- 3.Statistical calculate the regularity of L' of replacing the middle page. For the 500 pages, if the 1st, 2nd, and 3rd page are a file, we can choose the 4th, 5th…500th to replace the 2nd, there are 497 possibilities, then separately calculate the sum L' of t3 and b4, b5,…b500. In the same way, if the 2nd, 3rd, and 4th page are a file, we can choose the 5th, 6th…500th to replace the 3rd, there are 496 possibilities, then gain 496 L'. And so on, if the 497th, 498th and 499th page are a file, we can use only the 500th to replace the 498th, there is only one possibility. Above all, replacing the front page, and printing 500 pages, the possibility (X) is just like an orderly matrix, 497*497. Meanwhile, replacing the middle page, we also calculate the top page margin of the replacing page and the bottom page margin of the front page, we also gain an orderly matrix, 497*497. Then, the possibility (X) equal to two 497*497 orderly matrix, that is 247,506.
Regularity of normal continuous printing
Regularity of HP P1106-1
Measure all the bn, tn+1 by caliper, and calculate the L' accordingly, the data are shown in [Figure 3]. It is showed that most of the L' distribution in two areas: (3.4, 12.3), (78, 88.1), there are three discrete points.
Regularity of HP P1106-2
Using the same brand and model laser printer, but not the same one, and measure bn, tn+1 by caliper, and calculate the L', the data from small to large order are shown in [Figure 4]. It is showed that all the L' distribution in two areas: (3.7, 11.9), (76.1, 87.3), there are no discrete points.
Regularity of HP 3030
Measure all the bn, tn+1 by caliper, and calculate the L', the data from small to large order are shown in [Figure 5]. It is showed that most of the L' distribution in two areas: (3.5, 10.5), (78.3, 88), there are seven discrete points.
Regularity of Canon 2900
Measure all the bn, tn+1 by caliper, and calculate the L', the data from small to large order are shown in [Figure 6]. It is showed that all the L' distribution in two areas: (33.3, 41.4), (106.7, 116.5), there are no discrete points.
To calculate the possibility of replacing the front page and the middle page, due to there are so many data, Microsoft Excel did not work, a program must be written by MATLAB to the statistic. Two program are separately written to calculate the possibility of replacing the front page and the middle page.
| Results and Conclusions|| |
Through the program written above and sum up all the data are shown in [Table 1].
|Table 1: Data of L' and successful possibility in the condition of replacing front and middle page|
Click here to view
It can be seen that four printers are all perform a certain regularity when continuously printing, and replacing the front-page, the successful possibility in the interval range of (11.6–13.4), replacing the mid-page, the successful possibility in the interval range of (6.7–9.1). From the data, we also can see that the regularity of Canon 2900 is better than HP P1106 and 3030. For HP laser printer, no matter P1106 or 3030, it exist an interval range that could not give a definite conclusion, but for Canon 2900, the data are perfect and the regularity is best. Maybe it is the difference of printing principle and process working.
Aggregated data of three HP printer, [Figure 7]a. The distribution, scope of the three HP printers data curve is similar, in addition to a very few points. It is also proved that the regularity of normal continuous printing is exist and better. From [Figure 7]b, it can be seen that, (1) stands for the area of (12.3, 68.2), (2) stands for the area of (95.5, ∞), there are no point in the two area, that is to say, if the value of L' of two pages lie in this two area, we can gain the conclusion that the two pages are not continuous printed by the same printer.
Aggregated data of Canon 2900 printer are shown in [Figure 8]. It can be seen that (1) stands for the area of (0, 33.3), (2) stands for the area of (41.4, 106.7), (3) stands for the area of (116.5, ∞), there are no one point in the three areas, that is to say, if the value of L' lie in this areas, we can gain the conclusion that the pages are not continuous printed by the same printer.
Above all, this study discussed the relationship of the trace on OPC and continuously printing, and gained some useful conclusion through the data and program calculation. It is difficult to give a definite conclusion whether two or three pages are printed continuously, because the data showed that choosing the back pages to replace the front, there exist about 10% successful possibility. It demonstrates that the results have big meaningful, especially to a negative conclusion, in some certain areas, there is even no one L' point existing. Furthermore, in our work, negative conclusion have great value to the evidence of a case. Due to time limited, the author only choose four black and white laser printer and only print 500 pages each for discussion and research, it is just only tentative for feasibility study. If it is want to be an examination method, more brand and model printers are needed to choose and more pages are needed to type out to give further investigation.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]