How to Read Blurred Barcodes: The Synergy Between Shutter Speed and Lighting

Reading a barcode on a moving part is a race against blur. The code must be frozen sharply, or the read fails. However, the answer is not only a fast shutter. It is the synergy between shutter speed and lighting. This page explains the physics and lists the matching RODER Vision illuminators.

The Physics of Motion Blur in Barcode Reading

Motion blur grows with object speed and exposure time. Consider a barcode moving at 1 m/s with a 1 ms exposure. It travels 1 mm during that exposure. If the narrowest bar is 0.5 mm, the code shifts by two bar widths. Therefore, the result is severe smearing and a guaranteed read failure.

The acceptable blur is defined against the minimum bar width. This minimum is known as the X-dimension. ISO barcode standards set bar edge-contrast requirements for each grade. Because blur reduces edge contrast, it must stay small. For reliable reading, keep the blur below 10% to 20% of the X-dimension.

Calculating the Required Exposure Time

The required exposure follows from speed, X-dimension and the allowed blur. Take a 0.33 mm X-dimension moving at 0.5 m/s. The allowable blur is then 0.033 to 0.066 mm. Therefore, the exposure must be 0.033 mm divided by 500 mm/s, or 66 microseconds at most. On a 2 m/s conveyor with the same code, it falls to 16 microseconds.

These times are easy for modern global-shutter cameras. The real challenge is on the lighting side. Providing a correct exposure in 16 to 66 microseconds is demanding. Specifically, it needs intensities one to two orders of magnitude above standard continuous LED output.

Strobe Illumination: Peak Intensity for Short Exposure

LED illuminators run in two modes. In continuous mode, the LEDs draw a constant current. Therefore, the output is steady but limited by thermal capacity. Exceeding the maximum current raises the junction temperature and degrades the LEDs permanently.

Strobe mode changes this balance. Because the light is off between pulses, the LEDs stay cool. Therefore, the current can rise far above the continuous rating during each pulse. As a result, the peak intensity reaches the level a 16 microsecond exposure needs. In effect, the strobe compensates for the short window.

Pulse Duration and Synchronisation

The pulse must align with the camera exposure. A standard method uses the camera trigger to start the strobe. In turn, the pulse duration matches the exposure time. Moreover, the illuminator must respond quickly. Therefore, the rise time to full output must be shorter than the exposure. For 50 microsecond exposures, that means a few microseconds at most.

RODER Vision DL5 and DL6 illuminators are built for this duty. Their driver circuits reach full peak output in under 2 microseconds. The trigger input accepts both 5 V and 24 V logic. Therefore, it is directly compatible with standard cameras and frame grabbers.

Illumination Geometry for Codes on Moving Parts

Geometry affects readability beyond raw intensity. The angle, the uniformity and the direction all matter. Therefore, the geometry must suit the label surface and orientation.

Direct Illumination for Matt Surfaces

Flat barcodes on matt surfaces suit direct illumination. A bright, even field gives strong bar-to-space contrast. Therefore, the decoder reads the symbol reliably. This is the simplest and most efficient setup. As a result, it is the default for printed paper labels.

Diffuse Illumination for Gloss Surfaces

Gloss labels, metallised film and shrink-wrap need diffuse light. Otherwise, specular hotspots saturate the sensor and hide the bars. A flat dome provides diffuse light from a large solid angle. The code is imaged through the dome aperture. Therefore, reflections disappear and the symbol stays readable.

There is a trade-off in intensity. A dome spreads its output over a wide angle. Consequently, the surface intensity is lower than a direct light of equal power. Therefore, fast reflective applications combine moderate diffuse light with a very short strobe pulse. This pairing gives both contrast and motion freezing.

Datamatrix and 2D Codes

2D codes add further considerations. Datamatrix codes are often marked directly on the part. This direct part marking can be laser-etched, dot-peened or printed. Therefore, the contrast comes from surface relief, not ink. For these, low-angle or dome light brings out the cell pattern. In every case, a short strobe still freezes the motion.

Practical Guidelines for Strobe Barcode Systems

Designing a strobe system means matching several parameters. These include exposure time and peak intensity. They also include working distance, field of view and the trigger interface. The points below summarise the key steps.

• Exposure: compute it from the speed, X-dimension and allowed blur.
• Intensity: choose a strobe peak that fills the short window.
• Geometry: use direct light for matt, diffuse for gloss.
• Trigger: sync the pulse with a fast, sub-2-microsecond response.

RODER Vision Illuminator Families for Barcode Reading

The families below suit high-speed barcode and datamatrix reading. Each one supports strobe operation with high peak output. Therefore, the right choice follows the surface and the geometry.

The right choice depends on the surface and the speed. For matt labels, the DL5 and DL6 direct lights lead. Codes around the lens instead suit the DC6 ring, which gives even light. Gloss and foil call for the FD2 dome, which removes glare. In every case, RODER Vision provides engineering support to size the strobe and the geometry. Therefore, define the speed, the X-dimension and the surface first, and then choose the matching light.

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