da in digital printing - puc-rio€¦ · represents the offset printing (about 60% of all printing...

Noam Shaham 7/8/2005

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Distributed “Veto” algorithm in production digital

printing machines

The market The high volume digital printing arena is an increasingly growing market. Dramatic improvements in print quality, reliability and total cost of ownership accelerate the acceptance of these technologies in what used to be a very conservative market during more then 500 years. While black and white digital printing is already an established fact with moderate market growth, the color business is growing rapidly replacing older technologies such as offset printing and entering in market niches that traditionally used offset technology to create high quality promotional or publishing material. The fierce competition between the leading companies and between the different technologies makes production digital printing technologies very cost effective. The special features that the digital equipment delivers to the users are:

• Print on Demand – print low quantity just-in-time, when it is needed. Printers can afford to print small quantities at affordable cost without having to deal with stock. This is not possible in traditional technologies where high set-up time and cost of printing plates dictates a high premium per job and therefore achieves low cost only when printing high quantities. The break-even point between color digital job and an offset job is around 1000-2000 copies.

• Variable Data Printing – the ability to change content of the printed pages in a job can be done only with digital equipment. This is a steady growing segment with many applications in the customer relationship management area, beside the more traditional statement printing market.


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• Fast turn-around – the ability to produce jobs and to change them rapidly. Cannot be done in offset printing due to high setup time.

• Distributed Print on Demand – with the wide acceptance of the internet, replacing the old “print and distribute” model, by sending the digital copies and printing them at distribution centers.

While Variable Data Printing and Distributed Printing may apply to high-end users, the Print-On-Demand feature driven by the cost effectiveness of small quantities printing is a feature of great importance. It makes printing available to anyone who wishes to publish. Even a high quality book can be done in 1000 copies, while at traditional technology; a 30,000 copies minimum is a well established standard. The print-on-demand feature liberates the user from maintaining high stock of printed material that may become outdated before distributed. There are market segments in other areas of the printing industry such as industrial printing, packaging, labels, textile and security printing. These segments are also rapidly growing and in some of them, like the labels market, there is already a dominance of digital technologies over the traditional technologies. The following table shows the evolution of the printing market in the last three decades with a rough forecast into the next ten years:

The lower end of the graph describes the market share of industrial printing, the middle represents the offset printing (about 60% of all printing market in the 1990s) and the upper represents gravure technologies for very high volume high-quality printing. The triangle on the right shows the market share for “non-impact printing”, This is a technology-oriented general name for “digital printing”. As can be seen from the graph, these technologies are expected to continue to rapidly gain market share over the traditional technologies. This market share comes mostly from the following fact: “Digital printing technologies are becoming more and more cost effective and can compete with costs of the traditional technology”. The whole struggle of this industry is for continuing improvements in cost. As we will see in this paper, this struggle dictates modular system solutions and technological solutions based on distribution of job processing.


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The products The black and white digital print market is dominated by Xerox with a long line of products covering the whole range from desktop printers and copiers to production machines at rates reaching 180 pages per minute. The color market, although still smaller, is growing much faster then the black and white market. In this market there are a number of big companies including Xerox, Canon, HP, Kodak and others. There is also a variety of technologies including toner xerography, liquid ink and inkjet. The heart of the product is the print engine, the actual part of the machine that can make toner stick to paper. Most of these machines use a Xerography process (see image on the right) involving imaging through laser beam on a charged electro-photo-conductor surface creating an image of charged and discharged areas. The toner is transferred to the discharged areas while rejected by the charged areas and then been transferred to the paper and fixed on it by heat. Although this is the heart – a high volume printing machine needs much more than a print engine to serve the market it is targeted to. The other missing pieces of the puzzle are:

• Digital Front End – a server that processes the jobs and creates the images to be printed while taking care of job structure, job prioritization, color calibration, signatures, variable data printing, job tracking, etc.

• Paper delivery system – Storing paper, delivering it to the print engine, taking the printed pages from the print engine, processing them into booklets, books, etc. and sorting and storing them at the output.

These parts are as essential to the success of the product as the print technology itself. A capable paper delivery system reduces the number of manual operations and increases the productivity by a factor that cannot be overlooked. At many of these products, the competitive edge offered by one product over the other is not in print quality or print speed put in the capabilities of the paper delivery system. A transactional printer may


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have the same print engine as a copier, but a powerful continuous paper delivery system, with finishing options such as inline folder and envelope stuffer will make a great difference. A production copier, with in-line folding and binding will reduce the number of manual operations and machine set-up times from 3 to 1 and will make it a more cost effective solution then conventional print workflow. An example of continuous-paper finishing machine:

In the digital market, where job length is much shorter then in the offset production environment, the automation is much more important. A traditional print house may print for example 10 jobs a day at volume of 300,000 copies. At the same time a digital production print house will print only 20,000 copies but from 40 different jobs. The number of finishing operations then is 4 times more then in the offset print house. Without automation of the finishing process, the production can not be cost effective. An example of a cut-sheet finishing equipment:


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Traditional Art The traditional print process is described in the following figure:

It describes the long pre-press process, followed by the print process itself and the terminal stage of “finishing” using cutters, folders, stitchers etc. Most of the transitions between one state to another are manual. A job that started at the pre-press stage, will create plates that will be manually mounted on the press machine, and the printed pages would then be manually delivered to the cutter, from there to the folder and the stitcher. This is the reason that traditional art does not require the “on-line” serial connection between the different modules. Each of them is a “stand alone” entity with input and output controlled manually in the production process.


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The Business Environment

Complexity and Design Cost The high volume printers are multi-disciplinary machines. The technologies involved in the print engine are in the areas of chemistry, material science, physics, optics, color science, mechanics and electronics, process and machine control and computer science. The implementation of a digital front end requires continuous image processing efforts, high speed electronics and networking, color science and human machine interface. The design of paper delivery system is a delicate art by itself with mechanical, electrical and control issues. The outcome of this complexity is very high development cost (Xerox for example, is investing $800 million on research and development per year). Launching a new model development is a commitment to invest a minimum of tens of millions of dollars. For this reason the company usually chooses an evolutionary product-line strategy instead of a single product design.

Evolutionary Strategy With steady evolutionary development, the company may invest in product development and marketing along years of incremental evolution financed by the sales of the first models of the line. A new product-line will be launched when new technologies are available and when the market dictates it. An incremental development may look like this: the first model of the line will be based on a print engine that can sustain print rate of 30ppm (page/minute), a two drawer feeder and a stacker. A second model will have enhanced functionality by adding a scanner connection and a binder option. The following model will have increased speed of 40ppm, and the one after that will gain a more powerful digital-front-end enabling variable data printing, and so on. The basis for all follow-up models is the original model. As an example, see the following line of DocuTechTM machines by Xerox with incremental changes. In this case, most of the changes are in print speed and monthly volume. The family grew in productivity by 75% during its current lifetime, without any change to the basic model. The development of such evolutionary product-line involves lots of engineering efforts but little technology step function challenges. However, when increasing a speed for example, the enhancement must be implemented in all the modules, not only in the print engine itself.


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Co-development

Paper Delivery There are two main paper delivery systems: continues paper feed systems in which the paper source comes on a roll, and sheet-fed feed systems in which the paper is pre-cut to standard size and sheets are fed one by one into the print engine. In both types, paper is controlled for speed, alignment, tense and other important parameters. The finishing equipment may include some or all of the following modules:

1. Binders. 2. Booklet Makers. 3. Folders. 4. Stackers. 5. Cutters. 6. Stitchers.

Paper delivery systems were and still are in use by more traditional printing technologies like offset and flexography. They started to evolve together with printing itself (Gutenberg 1436 – see the first press machine in the figure on the right), more then 500 years before the digital revolution. Many of the existing systems are being reworked and adjusted to fit into the digital arena to be connected to modern printing technologies that are replacing older machinery. The art of paper handling was developed by more traditional companies than companies involved in the digital revolution. The art is protected by patents and is maintained by number of companies that are now suppliers of paper-feed and paper finishing equipment for all kind of printing equipment, offset, flexography, commercial, industrial, digital, etc. When a company like Xerox is introducing a new machine model, with paper feeders, stackers, binders and other finishing equipment, usually the paper delivery system modules are designed and manufactured by companies specializing in that area under Original Equipment Manufacturer (OEM) agreement. For example, the Oce (www.oceusa.com) partner list for feeding and finishing equipment manufacturers contains 18 names. A printing machine design is therefore a co-development effort in which each company holds a specific core-technology. The design is done in a distributed way among the participants and a final integration stage is needed to orchestrate all modules into a machine.


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Digital Front End As in the case of paper delivery technology, digital front end implementation involves a set of technologies that came from previous products supporting more traditional printing equipment. This market is known in the industry as “pre-press” and its function is to create the image carriers for the specific printing technology in use. In most cases it would be the plates for the offset printing machines. The pre-press market has been computerized for a few decades now with first customers using computer technologies for scanning images, controlling layouts and automating the production of printing plates for the offset printing industry. Other technologies come from more recent developments and are incorporated into the pre-press tools. These technologies include color consistency and control tools, font generation tools, half-toning technologies, layout and imposition tools, variable data printing tools and others. Since pre-press is not necessarily a separate step in digital printing, the pre-press functionality is built into the digital front end and is used in job preparation. Independent pre-press technologies are still in use of course in the non-digital market, now days using laser “image-setters” for a fully digital plate-creation process. A hybrid digital-offset technology uses automatic plate creation inside an offset press with automatic plate mounting. This shortens the set-up time of the press, and enables shorter runs with traditional technology. The technology is evaluating over many years, protected by patents and has a high barrier for new companies to enter this arena. Some of these companies (CREO, AGFA, EFI and others) have already established themselves as industry standards. An EFI FieryTM color server for example, is a line of products that may drive printing equipment by the following companies: Canon, Danka, Epson, Fuji Xerox, HP, Hitachi, Lanier, Konica Minolta, Kyocera Mita, Oce, Panasonic, Ricoh, Sharp, Toshiba and Xerox. A print house is more likely to choose equipment that may be connected to an already owned color server, therefore the printing equipment companies have high motivation to cooperate with the leaders of the digital-front-end industry and co-develop new products with those companies. For these reasons, the digital printing companies are forced to use OEM servers for their digital front end solution and again, co-development and integration process between the printer modules and the digital front end module is a part of a machine development process.


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The Problem As demonstrated in previous sections, a development of a production digital printing product line is:

1. Extremely expensive. 2. Involves various companies and distributed design teams from various disciplines

and geographical locations. 3. Involves intellectual property protection issues and patent protected technologies. 4. Must be based on incremental improvements of previous models.

The products themselves are built up from modular units. Each unit may be designed and manufactured by a different company, and each unit is subjected to an upgrade process and integration process when developing the next model of the product line. In previous art, the paper-control algorithms were centralized and each of the modules was directly controlled by a central controller. This is the same concept used in smaller products such as desktop printers and copiers. In the production printers however, this caused the following problems:

1. OEM companies had to disclose their intellectual properties so that their feeders

and stackers may be controlled. 2. An incremental change in the machines speed for example, resulted in a major

software change for the control system since each and every module now needs to be adjusted to the new speed.

3. Attaching a new device to the paper-path resulted in a major software change for the same reasons.

For these reasons, a centralized control system, in which the print engine controller for example, controls each and every node, sensor and actuator of the paper delivery system, is very problematic. It requires massive software changes and long integration activities between introductions of models that are supposed to have only small incremental changes. The business environment cannot accept this situation. It causes delays in the introduction of new models and features and therefore it breaks the whole economical model of the product line. A machine designed with centralized control is too expensive to produce, and the lead time for introduction of a new model cannot compete in today’s competitive market. A better engineering solution is needed to be able to apply a real “small increment” approach and enable a modular product-line. This engineering solution is based on distributed control.


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The Solution The solution to the problem is to define each of the modules as independently controlled by a local controller. Each of the components is a “paper processor” which has paper input, output and processing capabilities. Each “paper-processor” is responsible only for its part of the whole paper path algorithm. This way we achieve the following targets:

1. Local controller done by the owner of the intellectual property is responsible for all actions of the module. No intellectual property needs to be shared with another party.

2. Attaching a new module to an existing machine does not involve dedicated software development on the main controller.

The modules communicate over a low latency local area network using dedicated protocol over standard industrial communication network. In short, this is can be described as a distributed paper-processing system.

Server

PrintEngine

PrintEngine

Feeder Feeder Binder Stacker Stacker

Distributed Paper Processing The new problem that arises is that in such a hybrid system, where paper processing is done by mechanical hardware, a buffer to store more then the currently processed paper is very expensive both in space and money. The distributed algorithm must make sure that each module that receives a paper sheet is actually ready to process it and is not currently processing another. By allowing each of the modules the right to refuse service to a paper we achieve our main goal of very small software changes for a new configuration. Even if the unit is slower then the whole paper path, it may still serve any other sheet if allowed to refuse service. Now that the local processing problem is solved we are left with the bigger problem – synchronizing the execution of distributed paper processing in such an environment.


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Distributed Veto Algorithm The following algorithm is described in United States patent number 5363175 by the Xerox cooperation. It solves the distributed paper processing modules synchronization problem and is a key to enabling the economical model that was described above. Requirements:

1. Reliable, low-latency communication. 2. All modules are aware of the machine’s structure and their location in the paper

path. 3. Each module is aware of its distance from the beginning of the paper path in

“frames”. A frame is the time period it takes to process a single page at the print engine, from start of page n to start of page n+1.

Scheduler messaging US Patent 5363175

A scheduler receives a job description and calculates the optimal print sequence and order. A list is prepared with the fastest print sequence possible from the scheduler point of view. Each page is assigned a frame in the print order. For each of the pages, the scheduler broadcasts a REQUEST(n) all modules involved. Each of the modules replies with READY(n) if capable of processing a new paper at frame n or NotREADY(n) if still busy processing a previous page. A page will be scheduled for frame n only if ALL the modules have committed to process it at the requested frame. A single VETO will inform everyone of n being a “free” frame, and the scheduler will broadcast a new request for this page at frame n+1. Note that each node needs to know its distance d in frames from the beginning of the paper path because it is committing for execution at least d frames in advance. The system will print at the maximum rate permitted by its path and will automatically adjust for introduction of a new component in the paper path. The configuration of such


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system can include more then a single print engine and a number of compatible paper feed and finishing units.

Results Two very important targets were achieved using the distributed model and the veto algorithm, and both of them drive cost down and enables higher market share for the digital equipment:

1. Lower development cost driven by shorter development period and integration between geographically distributed development teams, thus enabling the “evolutionary” approach. By lowering costs to the manufacturer, the equipment cost is also driven down and the barrier to enter into the digital production printing is lower enabling better competition with traditional technologies.

2. Lower operational costs for the end user who is now able to run fully automated jobs without manual operations between the print operation and the various finishing operations.

The elimination of the manual stages enables shorter print runs making printing more available then ever before even at small quantities.


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Example of Execution (US patent 5363175) With reference to FIG. 4, in accordance with the present invention, a print engine 202 with control 203 is illustrated with three hypothetical pieces of finishing equipment attached (finishers 204, 206, and 208) via high speed serial communications bus 210. Finisher 204 with control 205 is a multifunctional finisher that can invert, rotate, perforate, or hole punch individual sheets as they pass through the finisher paper path. Finisher 206 with control 207 is a high capacity sheet stacker with a bypass transport to allow sheets to pass through this finisher without being stacked. Finisher 208 with control 209 is a collator with an optional stitcher and a set stacker. Each finisher is distinct and may have been developed either by various finisher vendors.

To schedule a job in the printing system in accordance with the present invention, printer 202 requests permission from the affected finishers to feed each copy sheet into the paper path. Thus to produce a stitched set of sheets with each sheet perforated at finisher 208, in one embodiment, printer 202 requests and receives permission to feed sheets through finishers 204, 206 and 208 before feeding because the sheet must pass through all three finishers. If permission is granted by all three finishers, a sheet feed can be scheduled, and a second sheet can be requested in the next pitch time, and so on. If permission was denied by any of the three finishers, a skipped pitch is executed instead, and the first sheet will be requested again in the next pitch or machine clock time. For example, if printer 202 produces copies at a rate of 1 every 444 milliseconds (135 copies per minute), but finisher 204 can only perforate sheets at a rate of 1 every 666 milliseconds (90 copies per minute), finisher 204 would deny permission for the copy feed every other pitch, since the printer would attempt to feed at a rate faster than that finisher can accomplish it's finishing task. The end result would be that the printing system would execute the job at the maximum rate possible with the given configuration of printer and finishers. If finisher 204 were replaced by a new perforator that could run at the 135 CPM rate, the system would automatically run at the new rate because the new finisher would not deny the feed requests.


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Bibliography: 1. “Method and apparatus for improved job stream printing in an electronic printer with various

finishing function” United States Patent 5095369, , Xerox Corporation (Stamford, CT), Inventors: Ortiz; Pedro R. (Webster, NY);Farrell; Michael E. (Fairport, NY);Rasmussen; David L. (Fairport, NY);Austin; John C. (Rochester, NY)

2. “Distributed job scheduling with modular components” United States Patent 5363175, Xerox Corporation (Stamford, CT), Inventors: Matysek; James F. (Fairport, NY)

3. “Handbook of Print Media”, Helmut Kipphan.

da in digital printing - puc-rio€¦ · represents the offset printing (about 60% of all printing...

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