Process Control and Verification for 1D and 2D Symbologies

Performing true ISO verification requires proper ISO algorithms, ISO lighting, and ISO calibration. The MicroHAWK contains the correct algorithms. It can also be used with the ISO calibration card, but it does not have the correct lighting. External lights must be used. Without ISO lighting, the MicroHAWK can only be used for “code validation”.

 

This section describes the differences between process control and true verification of symbols, as well as detailed verification requirements, hardware configuration, and lighting suggestions.

 

Process Control

Simple process control requires you to decide what is necessary for your application so you can produce marks that can be read reliably.

 

To use the camera for process control:

 

 

Process control can help ensure that you create reliable marks. They do not, however, ensure that the mark is certified against a standard.

 

Process control is best used to produce a grade of “Good”, “Fair”, or “Poor” to indicate when the marking process is out of spec for your application.

 

Verification

Verification ensures that a mark is certified against a specific standard. The camera must be calibrated and must have correct optics and lighting. The algorithm fully conforms to the ISO standards. All verification parameters must be enabled. Marks that are verified with a fully conforming system can be sent out with a report certifying them.

 

To achieve true verification, the following must be observed:

 

 

Additional suggestions to ensure true verification:

 

 

Lighting

Optics and lighting are the key to successful 1D/2D verification. Omron Microscan offers a number of light setups that can be used for 1D/2D verification. The choice of the light depends on the size of the mark.

Pharmalite Option

For symbols up to 50 mm long, Omron Microscan offers Pharmalite. It consists of two 100 mm long rows of white LEDs and a bracket that can be mated to any Omron Microscan camera.

 

Pharmalite kit and cable required to power the Pharmalite using a QX-1:

 

98-000228-01 KIT, SMART SERIES PHARMA, WHITE, DARK FIELD

 

61-000204-01 CABLE, POWER, SMART SERIES-TO-QX-1, CONTINUOUS

 

Edge-to-Edge Backlight Option

Intended for symbols up to 100-125 mm long. The 50 x 200 mm Edge-to-Edge diffuse backlight kit consists of a light, extension cable, and power supply. Red, white, blue and infrared options are available.

 

 

Red LED option:

 

NER-011659600G NERLITE, 50 x 200 MM, RED, BACKLIGHT, 24V CONTINUOUS, 150 MM, M12

 

Extension cable and power supply:

 

NER-011504100 DSP60, 24VDC, 2.5A, DIN MOUNT, POWER SUPPLY

 

NER-030029100 CABLE, NERLITE, M12 CONNECTOR, 5 PIN-TO-FLYING LEADS

 

MAX 300 Option

For even larger symbols up to 200 mm long, Omron Microscan offers the MAX 300. This is a 300 mm large area array light. Its kit consists of a light, extension cable, and power supply. Red, white, and blue options are available.

 

Red LED option with cable required to power the light using a QX-1:

 

NER-011660300G NERLITE, MAX 300, RED, NARROW, M12 CONNECTOR

 

61-000204-01 CABLE, POWER, SMART SERIES-TO-QX-1

 

Proper Camera and Light Configuration

Below is the required setup for 1D/2D verification as detailed in the ISO 15416 specification.

 

The correct ISO 15416 symbol verification setup includes an illumination source that is uniform across the symbol area at a 45 degree angle to the surface, and in a plane containing the illumination source that is perpendicular to the surface and parallel to the bars of the 1D/2D symbol. The configuration also includes a camera whose axis is perpendicular to the symbol surface.

 

The light reflected from a circular sample area of the symbol surface is collected in a cone formation with a vertex angle of 15 degrees, centered on the perpendicular to the surface, through a circular measuring aperture with a diameter of 1:1 magnification which is equivalent to that of the sample area (the area containing the 1D/2D symbol).

 

The angles of the configuration described above minimize specular reflection and maximize diffuse reflection from the symbol. This configuration is intended to provide a reference for measurement consistency.

 

 

1 = Image Sensor

2 = Aperture at 1:1 Magnification (such that measurement A is equal to measurement B)

3 = Light Baffle

4 = Symbol Surface

5 = Illumination Source

 

Resolution Requirements

Of all verification parameters, the most difficult test to pass using machine vision is Modulation. This is because the scan brightness profile typically shows narrow spaces as being less bright than wide spaces, and narrow bars as being less dark than wide bars. The reasons for this have to do with resolution, optics, focus, and lighting used for verification.  

 

The first figure below demonstrates this problem. Gray values for wide white bars are 210-230 where they are only 150 for narrow white bars. Gray values for wide black bars are 20, while they are 60-70 for narrow black bars.

 

 

The second figure below shows how adequate resolution resolves this. Gray values for both wide and narrow white bars are 210-230. Gray values for wide and narrow black bars are 20-30.