Using the Novel X-Ray Digital Detectors to Enhance Tire Quality Controls

Table of Content

Introduction
Working Principle of a Typical X-ray Tire Inspection System
Development Trends of X-ray Inspection Systems in Tire Industry
Novel X-ray Detectors for Tire Inspection – DT’s U-Shaped LDA Products

Introduction

In the tire industry, X-ray linear detector arrays (LDAs) have been ideal choices for in-line and off-line non-destructive testing (NDT). To improve tire quality controls, novel digital X-ray detectors have recently been developed.

These new detectors are based on a new intelligent digital platform, aiming to increase the maximum scanning speed, enhance image quality, and save the overall system cost with both electronics and software designs. Additionally, it enables remote firmware upgrade, diagnostics, and other advanced features.

This article presents the working principles of a standard industrial X-ray imaging system in the tire industry. It also discusses the new U-shaped detector and explains the improvements in the production efficiency and detection abilities in X-ray tire inspection systems. The article presents examples of applications in X-ray tire inspection systems for different types of tires.

Working Principle of a Typical X-ray Tire Inspection System

There are several standard designs of X-ray inspection systems based on the types of tires and the requirements of inspection systems. The most common X-ray inspection in the tire tread and protruding wire inspections is the X-ray LDA used with standard X-ray source.

The X-ray LDA captures a single line at a time (horizontal), and creates the vertical direction of the image when the tire is moved or rotated. The LDA is shaped to approximate the contour of a tire from bead to bead as a U-shaped detector for large commercial truck and bus tires and some passenger and light truck tires, in order to provide the best image quality and production efficiency.

A complete tire image can be quickly collected in a single pass with the U-shaped detector by placing a panoramic X-ray source inside the tire and rotating the tire during inspection. Therefore, this is currently a popular usage in X-ray in-line production testing. Figure 1 displays the operating principle of a typical imaging system with a U-shaped detector.

Figure 1. The operating principle of a typical imaging system.

To reduce the overall system cost, a single long X-ray linear detector is used for extra-large off-the-road tires. Three or five rotations of the tire are required by the tire X-ray inspection systems to collect the necessary information to generate an image by moving the long X-ray linear detector with the contour of a giant tire. For analysis, the image is generated for a minimum of three sections: upper sidewall, tread, and lower sidewall.

Development Trends of X-ray Inspection Systems in Tire Industry

The tire industry is promoting X-ray tire inspection system development to offer maximum precision and reliability and to improve production efficiency, because of the high demand of the in-line production testing. The X-ray inspection systems are usually operated at an in-line basis and are a part of a large production line, where every idle minute costs money. Therefore, the aim is always to maintain maximum uptime and decrease cycle time.

The conventional quality inspection process is mostly carried out by human inspection, leading to undetected and inaccurate inspection results caused by visual fatigue. This also leads to low efficiency and high labor costs.

Today's tire manufacturers produce tires that are complex and need high-level testing to verify the overall quality of the final product. The computer-vision-based automatic defect recognition (ADR) technique has emerged as a result of this. ADR is an efficient and important tool to improve product quality and increasing manufacturing efficiency.

Novel X-ray Detectors for Tire Inspection – DT’s U-Shaped LDA Products

Based on the development trend of X-ray inspection systems of tire inspection, the requirements for X-ray detectors can be easily summarized as:

  • Easy for maintenance
  • Improved X-ray imaging quality for ADR
  • Ultra-high throughput and speed to improve production efficiency
  • Flexible design to support various tire sizes
  • Robustness for external noise, and reliability for high temperature and humidity
  • Multi-view system support for dual-station inspection system

An enhanced product family of U-shaped X-ray LDAs developed and optimized specifically for high-speed digital tire inspection utilizing panoramic X-ray sources is the recently developed X-Scan U01 series. Figure 3 displays the block diagram of X-Scan U01 series products.

Figure 2. The X-Scan U01 series products.

Figure 3. The block diagram of X-Scan U01 series products

The novel intelligent digital read-out platform forms the basis for X-Scan U01 series products, which bring substantial advances in image quality and speed for industrial in-line and off-line NDT of tire. New features include user-friendly design for maintenance, including remote firmware upgrade, automatic diagnostics together with updated compact mechanics.

The gigabit Ethernet (GigE) interface and digital parallel readout structure enable achieving a maximum of 1.8 m/s of scanning speed, which helps to reduce the cycle time to about 20 seconds for up to 20% improvement of production efficiency. The novel platform supports dual-station system by using the GigE interface to allow several U-Shaped detectors to be simultaneously controlled by a single computer.

It is optimized with a robust and dependable design for high temperature (0 °C - 65 °C), humid and contaminated surroundings of a tire production factory, as it satisfies the CE requirements and the dust and water resistant standard (IP43). The lifetime cost of X-ray systems is minimized as the novel platform improves the radiation hardness and lifetime of the detector. Figure 4 shows the improvement of X-ray response drop with absorbed radiation dose.

Figure 4. Comparison of X-ray response drop with absorbed radiation dose

The standard series is ideal for quality inspection of different types of tires, including passenger car tires, truck tires, and off-the-road tires. The series has active lengths from 1382 mm to 3379 mm, and covers tire bead sizes of 12-35 inches.

Due to the latest design of DT’s ultra-low noise front-end ASIC and the digital readout platform, it substantially reduces dark noise and enables the highest sensitivity level with 0.75pC gain. The series satisfies the high scanning speed requirement and provides the industry leading image quality to meet the tightest quality needs. The dynamic range of the U-shaped detectors is doubled as shown in Figure 5.

Figure 5. Dynamic range comparison

A stringent hardware assembly control process ensures less than 0.25 mm mechanical gap along the entire 0.4 mm pitch LDA, in order to satisfy the demanding image quality requirements for in-line ADR. Additionally, as the discontinuity issue on some detector array joints can disturb in-line ADR for tire carcass and belt structure integrity, an advanced pixel discontinuity correction algorithm is developed to obtain an edgeless image.

To recalculate the pixel positions of each pixel, the pixel discontinuity correction algorithm utilizes actual measured physical gaps in between detector arrays. The algorithm inserts a new pixel to each physical gap and calculates the correction values. These values are stored in a flash memory of the detector hardware as factory configuration for each U-shaped detector.

Figure 6. Pixel discontinuity correction

Figure 7 displays an example of image quality improvement by comparing the difference with the application of the advance pixel discontinuity correction to the 0.4 mm pitch U-shaped detector.

Figure 7. Example of high resolution tire X-ray scan without and with pixel discontinuity correction

An upgraded software library stores up to 256 offset and gain correction tables depending on the optimized configurations for various types of tires, in order to optimize the image quality further. New software functions such as dead pixel correction, advanced non-linear calibration, multiple detectors support, and automatic troubleshooting procedure are also ideal for tire inspection.

Figure 8 presents an instance of X-ray tire image with 0.4 mm U-shaped detector.

Figure 8. Example of project image of tire x -ray image with 0.4 mm U-shaped detector

References

1. Valavanis, I and Dimitrios Kosmopoulos, Multiclass defect detection and classification in weld radiographic images using geometric and texture features, 2010 Expert Systems with Applications, 37 7606

2. Anouncia S M and Saravanan R, Non-destructive testing using radiographic images a survey, 2006 Insight - Non-Destructive Testing and Condition Monitoring, 48 592

This information has been sourced, reviewed and adapted from materials provided by Detection Technology, Inc.

For more information on this source, please visit Detection Technology, Inc.

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