PRINTING BARCODES

Electrical Apparatus, Sep 2008 by Tryling, David P

Several methods exist, each suited to different conditions

IN THE JULY ISSUE OF ELECTRlcal Apparatus, we discussed barcode types and reading them. But the other half of the barcoding process is the printing or marking of the products and packages with the barcodes.

To quickly review, barcodes are a series of lines and spaces. The thickness of the lines and the thickness of the spaces translate into patterns that are recognizable by a light sensitive array or CCD imager. The light-sensitive arrays are usually laser-based, projecting a light across the length of the barcode and the reflected light is then read by the array.

This type of barcode is referred to as a Picket Fence Barcode. The characters in the lines and spaces are translated into numbers or alphabetic characters. These barcodes are used for many different applications in industrial, commercial, and retail settings for product identification. There are a number of different types of barcodes specific to retail, military, and manufacturing applications.

A manufacturer that wants to mark its products will want to establish certain criteria for that marking. This will probably include the kind of data that needs to be encoded, the amount of that data, and the type of barcode to be used. Once this plan is established, the method of marking the product with the barcode must be determined. There are various methods of doing this; for the sake of space, we cannot cover them all here. For this discussion we will be looking at methods of high speed direct barcode application.

Applying the barcode

One of the first decisions regarding barcoding is how the barcode will be applied to the product or package. Certainly the most prevalent method of applying a barcode remains the attachment of a label. The labels can be generated and then directly applied to the product. Labels can also be pregenerated with the barcodes and arrive on the manufacturing floor in a roll to be applied to the product or package as part of the process. This is an indirect printing method.

Direct printing of barcodes is a process of applying the barcode onto the actual surface of the part or package. In this way the barcode becomes part of the product and is not generally removable as a sticker would be.

The next decision regarding barcode printing equipment will be the speed of the print. The faster the barcodes need to be applied to the end product, the more the requirements for printing will vary. The easiest method for applying a code is direct contact printing. This is the same method by which a label is generated. This requires, however, that the print head can be in actual contact with the product without either damaging the product or being damaged itself by the surface characteristics of the product. Further, many manufacturers choose not to have direct contact printing because allowing the product to actually touch the print head requires much tighter control and orientation of the product during the printing process.

For these reasons, most manufacturers have tended to move toward a noncontact printing method. Some noncontact methods also provide the ability to produce at higher speed for larger-volume manufacturing applications. Here are three of the most prevalent methods.

Piezo jet printing

Piezo jet printing is an ink-based print method. An ink is provided in a reservoir that is gravity-fed to a print head. The print head has a series of Piezo-controlled jets.

A Piezo is a device that emits a magnetic field. The ink is retained by the orifice. When the field is applied, the ink releases. This is an extremely small orifice that the Piezo controls; therefore, the amount of ink is in minute amounts. By using an array in the Piezo jets and by controlling them electrically, the ink can be released in a pattern.

The product in turn must be moved under the print head. The Piezos will turn the ink on and off, and as the product moves by, the lines and spaces of the barcode can be defined. When the ink is released from the Piezo head, it falls to the surface of the product, where it adheres and dries.

The Piezo heads must be controlled by a microprocessor-based product that determines the process of converting the customer number to the appropriate lines and spaces. The head controller must know the speed at which the product is traveling underneath the head in order to turn the ink jets on and off at the appropriate time, thereby creating the lines and spaces at the correct intervals.

This is accomplished either by inputting the correct speed to the controller or, in some applications, by adding an encoder to monitor the speed of the product as it passes under the print head.

Piezo print systems are generally very cost effective. However, they are a gravity-fed system, and the ink falling from the head to the product is also controlled by gravity. This means that Piezo printing can be subject to ambient air movement and ink starvation from the gravity-fed system. A properly working system should be quite sufficient for continuous product marking.