Sewn Products Plotters 101

Offshore outsourcing in the apparel industry is now the norm. As a result, the need to transfer production data electronically becomes critical to reducing costs and reducing lead times. However, establishing business partnerships with offshore contractors must take into consideration the data compatibility of the CAD systems of both the producer and offshore contractors.

Fortunately, producers and contractors can now select the plotter that is right for their production needs instead of purchasing plotters based on CAD data compatibility. This article is intended to give an introduction to the types of plotters available, how data can be transferred from various CAD systems to third-party plotters, and how to make the right choice when purchasing a sewn products plotter.

A sewn products plotter is a wide-format, one-to-one scale production-printing device used to print out markers or nests that are used to identify pattern pieces cut out from material goods. It is also used to print out pattern pieces for design quality control. The printing paper comes in rolls of up to 600 yards and the width can vary from 36 to 100 inches or more. Note: there are many different types of wide-format printing devices used in engineering, sign making, fabric printing, etc. that have not been included for discussion here.

Plotter Types

Pen Plotters

Pen plotters use a pen to draw the lines making up the pattern pieces in the marker. They are also referred to as vector plotters. There are two types of pen plotters:

Upright Pen Plotter

The pen and the penholder only move in one direction, namely the Y-direction (a movement to the left and right sides of the plotter, horizontal to the floor). Drawing onto the paper is achieved by a coordination of the pen movement in the Y-direction with the movement of the paper in the X-direction (a movement up and down, vertical to the floor). The paper moves across a platen (a thin curved horizontal surface), upon which the pen draws.

Examples: Ioline 600 Ae, 28Ae, StylistAe and StudioA; Polygon Avion series.

Flatbed Pen Plotters

The pen and the penholder are attached to a beam horizontally above a table of a certain width and length. The pen can be moved in the Y-direction (a movement along the length of the beam). The beam itself can be moved in the X-direction (a movement of the beam along the length of the plotter). Drawing onto the paper is achieved by a coordination of the beam and pen movements in the X- and Y-directions respectively. The paper is pulled across the table for plotting.

The drawing of text or annotation requires a lot of pen movements and can slow down the plotting. Therefore, some flatbed models incorporate an inkjet head exclusively for printing text. For example Gerber Technology AccuJet 520.

Some flatbed plotters have different tool heads such as routing/milling (the cutting of thicker and harder materials, such as Masonite® and Plexiglas®, by using a spinning cylindrical piece of metal with cutting edges), knife cutting (normally used with fabric-based materials and cardboard).

Examples: Assyst-Bullmer’s Zünd S,M,L,XL-Line series; Gerber Technology Microjets, AccuPlot 300 & 700 series; Graphtec FC2230 series; Investronica INVESPLOT 2000 VECTOR series; Lectra Flypen Plotter series.

The Graphtec is an example of a static flatbed plotter that uses sheets of paper or cardboard instead of rolls of paper.

In both pen and inkjet plotters, the paper comes from the feed roll and the printed paper is rolled onto the take-up roll. If the plot-out length is long, several frame plot-outs will be performed. This means that the plotting is divided up into several frames or windows. Each frame is plotted completely and the paper is advanced to the take-up roll so that the next frame can be plotted. Alignment between frames is very important to maintain the continuity of the lines making up the entire plot-out.

Inkjet Plotters

Also referred to as raster plotters, inkjet plotters and are typically upright in design. The vector information (the lines making up the pattern piece in the marker) are rasterized or converted to a bitmap (a series of horizontal lines where a pixel is set to zero (do not draw a dot) or one (draw a dot). The print head is not a pen but rather an inkjet head that sprays ink on the paper, without touching the paper. The plot-out is achieved by the head moving in the Y-direction (a movement to the left and right sides of the plotter, horizontal to the floor). The plot-out is constructed from a series of horizontally printed strips. However, unlike pen plotters, no frame advance is required. This is a significant time saving because the frame advance is dead time, where no printing is occurring. The paper comes off the feed roll and is moved in the X-direction (a one-way movement either up or down, vertical to the floor) and is rolled onto the take-up roll. A disadvantage to inkjet plotters is that they require more technical attention (i.e. cleaning and alignment) of the inkjet head than pens on pen plotters.

Examples: Assyst-Bullmer’s Algotex StreamJet, WindJet, WaveJet, PowerJet series; Gerber Infinity and Infinity II; Investronica INVESPLOT PARTNER, JOKER, and P-2000; Lectra ALYS; HP DesignJet Series.

How Data goes from a Computer System to a Plotter

A CAD software program running on a computer converts the pattern piece data or marker data into a plotfile - a data file containing a series of commands instructing the plotter on how to plot the data. The normal plotfile format is HPGL/2, a vector-based description of the geometry of the pieces. However, some plotter vendors use there own proprietary formats, use variations of HPGL/2, or even support the conversion of ANSI/AAMA 274 (now known as ASTM D6672-01) NC cutfiles to run on plotters.

For those interested in sewn product automation standards, especially for pattern piece, marker, and plotfile data exchange, you can obtain details from ASTM D13.66 subcommittee chairman James Hiegel at jhiegel@keller.edu or by visiting the ASTM web site at www.astm.org.

A Plotter Management Program is used to read the plotfile and prepare it to be sent to the plotter. This program may be responsible for converting the plotfile into a format that the plotter can understand or configuring the plotter settings. In the case of inkjet plotters, the plotter management program is usually responsible for rasterizing a vector-based plotfile format, such as HPGL/2, into the raster format that the plotter understands. Examples of plotter management programs includes: Algotex AlgoJet; Assyst-Bullmer RemPlot; Gerber Technology WinPlot; Lectra VigiPrint; Ioline 601.

Typically, an RS-232 serial cable is used to connect the computer to the plotter, although parallel cable connections are also common (most home PC printers use a parallel cable). The plotter management program sends the data to another program called the Plotter/Printer Driver. The plotter/printer driver is responsible for establishing and maintaining the communication of the computer with the plotter while the plotfile data is transferred over the cable.

Sending Plot Data from a CAD System to an Offsite Plotter

It is not always necessary for the contractor to have the same CAD system and plotter as the producer when plot marker data needs to be sent. First determine from the User Manual of the CAD system, or by calling the CAD vendor support line, to find out how to create a plotfile or what plotfile formats are supported. This plotfile can be sent as an e-mail attachment or some other more secure electronic method to the contractor. Secondly, determine if the contractor has a plotter with plotter management software that can read and process the plotfile you are sending. The contractor may also need to consult their User Manual or call the CAD/plotter vendor support line.

Many plotter vendors offer standalone solutions with a PC running plotter management software to drive the plotter, independent of the CAD system. Such independent plotters with PCs are called remote plotting solutions. A number of plotter vendors have also written their plotter management software and printer/plotter drivers to support different plotfile formats.

Making the Right Plotter Choice

Price and Plotter Type Considerations

Generally speaking, the wider the plotter, the more expensive it is. Therefore, purchase a plotter that has the right piece goods width for current and future needs. You cannot upgrade a plotter to a larger width; it must be replaced! The more throughput you require, the more expensive the plotter is. Therefore, purchase a plotter that meets current and future needs. Normally the return on investment for a faster plotter is justified through savings in overtime costs when operators no longer need to stay back and oversee the plotter production.

Depending on the width, an upright plotter will cost $8,000 – $15,000. A flatbed plotter will cost $15,000-$50,000 (depends on robust nature of such plotter’s, size, and tool-head choice). Inkjet plotters will cost $10,000-$40,000 depending on the width and speed of plotting.

The biggest problem with comparing the speed of a pen plotter to an inkjet plotter is that you must run tests with your specific markers to compare them. You cannot use the manufacturer’s specifications as these are based on ideal circumstances. The speed of a pen plotter is severely affected if the pen must draw a lot of small lines or text. (This may not be an issue for upholstery goods due to the large size of the pieces but would be an issue for an intimate apparel producer).

Unlike pen plotters, inkjet plotters do have a constant rate of plotting, regardless of the size of the pieces and the amount of text in the marker. Inkjet plotters plot in strips, across the width of the plot-out. This is a disadvantage when plotting large piece goods (e.g. upholstery) because there is a lot of head movement across the paper where nothing is plotted. Pen plotters, however, actually draw only the lines making up such large pieces. All plotter vendors are now offering inkjet plotters as the latest technology.

Inkjet speeds are rated in square feet per hour because the marker width also affects the speed. When comparing inkjets, either compare the square feet printed per hour or request a test in linear yards per hour given a typical marker width (e.g. 60 inches).

A big advantage of pen plotters over inkjet plotters is that the pen is much cheaper to replace than an inkjet print head. Although an inkjet head uses replaceable inkjet cartridges or ink reservoirs, the head itself is subject to constant use. The head can last anywhere from 1-3 years on average, depending on usage and maintenance. Check the warranty on the head, the exchange price on refurbished heads and the cost of new heads.

Another price consideration is to check the actual cost of service, parts and consumables. A plotter may be cheap to purchase but expensive to maintain. Always try to obtain an unbiased reference.

Data Compatibility Considerations

If your entire CAD system is from one CAD vendor, you need not be forced to purchase their plotters too. Simply run some tests by generating marker plotfiles from the CAD system you have, and have the plotter vendor demonstrate that such plotfiles work on their plotter.

Ask the plotter vendor to verify (by example) what type of plotfile formats their plotter management software supports. All vendors will say HPGL/2, but only a few plotter vendors have robust plotter management software that can support plotfile data from many CAD vendors. Remember: always request tests to be performed with example plotfiles you expect to use in production.

A big consideration in choosing a plotter is the type of material you are plotting on. For example, Tyvek® requires a pen plotter. Combined plotting/milling/cutting will require a flatbed plotter. Cardboard cutouts will require a static flatbed plotter. Check the type of paper you need to use and make sure the plotter supports that type of paper.

The location of the plotter in the factory is also important. You need to ensure the correct humidity to avoid calibration issues with the paper. Therefore, it is recommended that the plotter be placed in a climate-controlled room with air-conditioning and humidifier. This will add additional cost if such a room must be built. Removing the paper roll from the shipping materials 24 hours before it is needed (lay roll horizontally) allows the paper to adjust to local environmental conditions. This will reduce calibration issues when plotting.

A plotter is a critical piece of production equipment. Therefore, you need to consider the cost of downtime. Compare this to the cost of purchasing a spare parts kit, training your plant mechanic to do repairs; and the ease of parts and consumable replacement/reordering. In some circumstances, it makes sense to split the production over two slower plotters instead of running it on a faster one. In this way, if one plotter fails, there is a backup plotter.

Check the on-board fault diagnosis and resolution functionality of the plotter and its ability to get around problems. For example, most inkjet plotters come with one inkjet head. If it fails, the plotter is down. However, some inkjet plotters come with two or even four heads and can operate even if one head is down (e.g. Assyst-Bullmer Algotex series). However, a two- to four-head plotter will cost between $5,000 to $30,000 more than a single-head inkjet plotter.

The paper on the take-up roll will need to be removed and used when cutting the material goods. Ask the plotter vendor how the paper roll is removed and unrolled. Do they have optional add-ons to help in this task?

After Sales Service and Support Considerations

The most critical aspect in choosing a plotter, besides the overall reliability, is service and support.

The warranty provides a level of coverage after installation. Compare warranty periods and coverages. At a minimum, expect parts to be included in the warranty. Look also for on-site labor and travel to be included.

Parts need to be in stock and deliverable the next day. A plotter technician needs to be local, or at least available in a guaranteed response time. If you intend to sign up for a service contract after the warranty period, compare service contract terms and conditions.

Conclusion

There is a limited choice of upright pen plotters and flatbed plotters unless you purchase pre-owned equipment. This choice is not likely to increase in the future. There is a wider range of vendors providing inkjet plotters, and the prices are likely to come down in the near future. Although the future plotter technology is based around inkjet solutions, there will always be a need for pen plotters due to specific material constraints that inkjet plotters are not currently designed to overcome. Combinations of pen and inkjet technologies are also feasible in the future.

Richard Downham has over 10 years of experience in the sewn products industry. He has worked 6 years in the software development of CAD/CAM solutions and over 4 years in service and support . He is currently Support Manager for Assyst-Bullmer in the United States. Richard is an active member of the ASTM D13.66 subcommittee on sewn products automation. He can be contacted at r.downham@att.net.