Working Principle of a Laser Barcode Scanner

When the user activates the barcode scanner by turning on the power switch or the corresponding device, the VLD (Visible Laser Diode) emits a red laser beam, which passes through the beam-expanding lens and is widened. The laser is then reflected onto the barcode from a movable mirror. As the mirror swings, the position of the laser spot on the barcode changes. When the mirror continuously swings, a red laser line appears on the barcode due to the visual persistence effect. The barcode surface is relatively rough, and the laser spot reflected from the barcode will vary in intensity between the bars and the spaces. The diffuse light from the barcode is directed onto the mirror, which then reflects it onto a light collector. The collector gathers the light, and a filter removes stray natural light before it enters the photodiode, generating a photoelectric signal. This signal is amplified, shaped, and decoded into useful information, which is then transmitted to the host computer.

Types of Laser Scanners

Laser scanners come in two types: handheld and fixed.

• Handheld Laser Scanners are easy to connect and use flexibly.
• Fixed Laser Scanners are ideal for reading large or small barcodes and are suitable for freeing up hands during work.

Advantages of Laser Scanners

1. Non-contact Scanning: Laser scanners are excellent for non-contact scanning. In most cases, laser scanners are the only choice when the scanning distance exceeds 30 cm.
2. Wide Barcode Density Range: Laser scanners can read irregular barcode surfaces or scan through glass or transparent tape. Since they are non-contact, they do not damage the barcode labels.
3. High First-Time Read Rate: Due to advanced scanning and decoding systems, laser scanners have a high first-read success rate, faster recognition speeds than pen-type or CCD scanners, and better performance when dealing with poorly printed or blurred barcodes.
4. Low Error Rate: The error rate is extremely low (about one in three million).
5. Shock and Drop Resistance: Laser scanners are robust and can withstand drops. For example, the Symbol LS4000 series scanners can survive drops from 1.5 meters onto concrete.

Disadvantages of Laser Scanners

The main disadvantage of laser scanners is their relatively high price. However, when considering both purchase costs and operational costs, they are not much more expensive than CCD scanners.

Common Failure Causes and Troubleshooting

1.Barcode Scanning Function Not Enabled:

The scanner might not be able to scan certain barcodes if the necessary function is not enabled.

2.Barcode Not Compliant:

The barcode may be problematic due to:

oMissing necessary blank spaces

oLow contrast between bars and spaces

oIncorrect ratio between bar width and space width

3.Sunlight Interference:

Direct sunlight can saturate the photodetector, causing the scanner to fail.

4.Barcode Covered by Transparent Material:

If the barcode is covered by a material with too high reflectivity (e.g., plastic or shiny film), the scanner may not be able to read it, even though it is visible to the human eye.

5.Hardware Malfunction:

If there is a hardware issue, contact your dealer for repair.

6.Barcode Scanner Not Working with Laptop Keyboard Interface

Barcode Scanner Not Working with Laptop Keyboard Interface

A barcode scanner connected to a laptop keyboard interface is essentially treated as an external keyboard. If there are problems with the keyboard interface, you might experience the following:

• Scenario 1: The original keyboard becomes inoperative, and the barcode scanner works, but the keyboard does not.
• Scenario 2: The laptop’s keyboard works, but the external keyboard does not. The barcode scanner may fail to work.

Solution:

1. Set the BIOS to automatically enable the external keyboard.
2. Reconnect the barcode scanner to the keyboard interface.
3. Connect the barcode scanner to the external keyboard.
4. Alternatively, use a barcode scanner with a serial interface.

Barcode Scanner Freezes After Reading a Barcode

1. Protection Function: If the barcode scanner's protection function is triggered due to incorrect data transmission, it will automatically enter a protective state to prevent data loss. After unsuccessfully transmitting data, the scanner can be used again once the unsuccessful data is cleared.
2. Solution: Check the connection and protocol carefully. After confirming everything is correct, turn off the barcode scanner and turn it back on to restore normal operation.

Barcode Scanner Does Not Power On

1. Loose Power Connection: Check the power connection.
2. Blown Fuse: Replace the fuse if necessary.
3. Power Circuit Failure: The barcode scanner’s power circuit may be faulty and require repair.

Faults Requiring Professional Repair

1. Abnormal Indicator Lights: If the indicator lights are not functioning properly, the device will not work.
2. Unusual Sounds: If the scanner is emitting abnormal sounds, this indicates a problem.
3. No Laser Line: If the laser line is not visible, the scanner may be malfunctioning.
4. Scanning Range Becomes Very Short: If the scanning distance becomes unusually short, the device may need to be repaired.