Recently, however, several prominent OEMs have implemented a new marking technology. Referred to as Bumpy Bar CodingT (BBC) by its supplier Mecco Marking Systems, the system indents a high-integrity 3-D mark into metal, plastic and composite materials.
The mark, which is permanent, can be made through indent marking, die stamping, or roll marking on virtually any material of less than Rockwell 45C. Materials do not have to be perfectly flat or smooth-machined, however, highly reflective materials (such as polished stainless steel) are problematic. Marks can also be incorporated easily with most casting, forging, or injection molding processes. In all cases, the mark becomes a design feature of the part. BBC marking withstands annealing, heat treating, and abrasive treatments and is scannable after many coating processes as well. The service life of the mark equals the life of the part itself.
USE OF BAR CODING
Indented BBC marks are expressed by highs and lows in surface height and BBC readers use differences in height, rather than contrast, to distinguish the bars and spaces of the code being read. This allows BBCs to be read where no contrast is available (e.g., when a part is exiting a heat treating cycle and the surface is dark).
In order for BBC to be used, a given material must meet two criteria. First, it must reflect enough of the red laser light of the reader to be detected by the reader's camera. Second, the material must be capable of being formed into a suitable bar code. Bar codes can be formed by any process that results in a readable code. Some examples are molding, casting, embossing, chemical etching, laser engraving, stamping, indent marking, and milling. Table I lists some typical materials and the types of processes that are appropriate for creating Bumpy Bar Codes on them.
Bar Code TerminologyBumpy Bar Coding has much in common with traditional black-and-white bar codes. Fig. 1 shows a typical bar code, a Code 39 symbol encoding "CODE". The following paragraphs describe important features of all bar codes, including BBC codes.
The "X" dimension is the width of the narrowest bar or space in the bar coded message. "X" dimensions typically vary from 5 mils to 50 mils (0.005" to 0.050"), with most applications using "X" dimensions between 10 and 20 mils. Larger "X" dimension codes are usually read easier by scanners but require larger label area.
A specified quiet zone just to the left of the bar code that must be free from marks is referred to as the quiet zone. The quiet zone gives the scanning device time to adjust its opto-electronic measurement circuits and is needed to avoid confusion between external markings and bar code elements.
START, STOP AND CHECK CHARACTERS
Bar codes required to be read bi-directionally - from left to right or from right to left (or conversely from top to bottom or bottom to top for vertically aligned codes). To accomplish this, every symbol provides a separate start and stop character in addition to the message characters. Depending on the bar code symbolism, there may also be a check or parity character that minimizes the probability of misreading the message.
The start, stop, and check characters combined with the quiet zones constitute the bar code message overhead. The overall bar code length must take into account this overhead space in addition to the message space to achieve a successful read. Industry experts have found that insufficient quiet zones are a principal cause of poor reading performance.
The length of the bar code is directly related to the ease of reading. The taller the bar code symbol (i.e., the longer the bars), the easier it is to align the laser line across the bars. For a read range of less than 10 inches, a bar length of 20% to 50% of the total bar code symbol length is adequate. The available label space is frequently the limiting factor.
Character density is defined by the number of bar coded characters per inch (CPI) in a message. This is determined from the "X" dimension and for some codes the ratio of the narrow bar to wide bar. Dense codes (high CPI) are driven by limited space and/or a need to encode a large number of characters.
Quoted CPIs can be confusing and misleading. People often quote a CPI and include the start, stop, and parity/ check characters (overhead) in their density. A user may misinterpret this quote to only include message characters. Confusion can result in the total bar code length being longer than what the user anticipated as necessary to include all message characters and overhead.
Bumpy Bar Codes can be formed in almost any traditional symbolic pattern. Popular symbolic patterns include Code 128, Code 39, Interleaved 2 of 5, and UPC. The codes formed with these patterns must conform to all tolerances inherent within these patterns and must also conform to the specifications imposed by the reader, such as minimum depth, minimum X dimension, maximum symbol width, etc. Fig. 2 shows some of the important dimensions that must be specified for multiwidth Bumpy Bar Codes.
Traditional symbolic codes are most often usable in applications such as molding, milling, or embossing where creating multiple widths of bars accurately is not difficult. In applications such as laser engraving, chemical etching, and indent marking, control of bar widths is more difficult. Furthermore, for indent marking and laser engraving, making wider bars requires significantly more marking time. For these applications, single-width symbolic codes provide significant advantages.
PosiCode is a relatively new symbolism designed specifically to address direct part marking issues. It is in the process of becoming an international standard through AIM. The PosiCode symbolism is significantly different from most other bar code symbolism patterns. Because of this, the decision as to the best parameters to use in making a PosiCode mark is not always obvious, even to seasoned bar code users. Fig. 3 depicts a typical PosiCode bar code.
APPLICATION AT DEERESeveral advantages were noted when the BBC system was evaluated for use at Deere's Waterloo, Iowa Engine Works. The first priority was to achieve traceability for individual parts throughout the production line. It was essential that quality data be assigned to individual items. The company had always been able to correlate quality data with a particular group of parts, however, there had been no way to marry quality data with individual parts.
Deere's first application for BBC technology was connecting rods. Each connecting rod is split into two pieces (rod and cap) during machining and must be reformed as a matched set. The system allows absolute verification that each rod and cap are a matched set.
With the current system, if a problem develops with a connecting rod, the shift, production machine, quality data, and the machine operator can be identified instantly. The company can respond quickly and proactively to any problem related to the manufacturing of that part.
DESCRIPTION OF THE SYSTEM
The BBC system purchased by Deere includes a Mecco SP202 computer-controlled marking system and fixed base reader. To accommodate Deere's requirement for a very fast cycle time, the system was engineered with three stations: two marking heads and one fixed scanner, which was manufactured by Sensis Corp. The first station provides human-readable marking; the second indents the BBC marking; the third station scans and verifies the integrity of the marks. Fixturing, which was designed jointly by Deere and Mecco, includes automated parts handling.
The BBC is created by a chisel stylus that strikes the materials surface and creates a bar about 1/8" in length. The reader is unique in that it reads both Bumpy Bar Codes and traditional black and white printed barcodes, an advantage for users of both technologies. The reader is also distinctive in its use of a proprietary error detection algorithm, which makes misreading improbable.
BBC readers integrate readily with PCs, PLCs, robots and other factory equipment. They also plug into portable data terminals, which transfer data into a computer by saving it in memory for subsequent downloading or by transmission via RF link to a base station. In the assembly operation, the connecting rod number is directly linked to an engine serial number. This provides traceability from the machining data to the end user.