Continuous, non-contact splice width measurement for calendered products.

Today, companies incorporating calendered material products into their manufacturing processes continue to focus on improving operating efficiencies to gain or extend competitive advantage by minimizing process variation and improving finished product quality. Many manufacturers have experienced significant savings through the implementation of extremely precise product and process measurement solutions from component extrusion through finished tire sidewall inspection.

Now, calendered rubber manufacturers can further improve operating efficiency in the material preparation area. Utilizing precise, non-contact laser triangulation technology, a splice width monitor provides real-time product and process quality feedback for both automatic and manual calendered rubber, steel or fabric bias cutting/splicing operations without affecting process cycle time.

The initial installation of a splice width monitor is integrated into the calendered body ply cutting/splicing operation in the tire manufacturing process. However, the solution extends well beyond tire manufacturing to any application where rubber material is spliced together. After over one year of production operation, the monitor is yielding impressive results. All overlap splices, including open splices, are accurately identified, providing valuable process control and product trend data, resulting in vastly improved quality of fabric ply material delivered to downstream processes.

Why measure calendered material splices?

In the tire manufacturing industry, overlap splices in calendered fabric body ply material have several important effects on finished tire quality:

* Sidewall appearance;

* sidewall structural integrity;

* tire radial uniformity.

Excessively large (wide) overlap splices in the fabric body ply material result in a local strong point in the tire sidewall that does not expand to the same degree as the rest of the sidewall when inflated. This condition produces a visually objectionable dent or indentation in the inflated tire sidewall profile (figure 1).

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A below-tolerance overlap splice width or an open splice in the body ply may result in a structural sidewall defect. A local weak point is created by the lack of fabric cords, which appears as a bump or bulge in the inflated tire sidewall (figure 2). This condition is especially significant in single-ply tire constructions.

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The overlap splice width also has a significant effect on finished tire radial uniformity. Inconsistent fabric cord spacing around the circumference of the tire contributes to unacceptable radial run-out, which is often observed by the customer as a vehicle ride disturbance. Precise monitoring of the fabric body ply splice in the bias cutting process ensures improved material preparation efficiencies and results in reduced rates of finished tire scrap and downgrades.

In non-tire rubber manufacturing industries, calendered material splices represent structural seams that must be able to accommodate the loads that will be applied. The splice width monitor ensures the structural integrity of such critical junctions in the finished product.

Principle of operation

The splice width monitor provides continuous, real-time measurement of calendered component splice widths in an automatic or manual bias cutting/splicing process. Precise, non-contact, laser triangulation sensors are positioned to allow the calendered rubber material to pass between two laser sensors. Laser measurement data are collected in digital format directly from the sensor head, which provides a distinct signal at the leading and trailing edge of a material splice. The lasers continuously monitor the thickness of the material, detecting instances where the thickness exceeds a user-defined threshold for a specified duration. The splice width is defined as the length of the distinct change in material thickness that exceeds the threshold. Figure 3 illustrates the physical operation of a single splice width channel.

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The system is typically offered with two or three pairs of laser sensors referred to as system channels. A typical three-channel installation measures the overlap splice at both ends and in the middle of the calendered material.

The system utilizes a dedicated controller running a commercially available real-time operating system, which is integrated with custom process control logic processing laser measurement data for each channel. Two of the three channels must register a detected splice or an alarm is generated. Alarms are also generated for gaps in the material (open splice) and excessive distance passed without a measured thickness exceeding the user-defined threshold (butted splice). Figure 4 illustrates the system architecture of a typical three-channel system.

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The dedicated controller operating the splice width monitor system is equipped with an Ethernet port that enables communication with host software via TCP/IP. This architecture allows remote monitoring of the system, as well as easy access to process trend data from anywhere on the local or wide area network.

Laser triangulation sensor technology

In an automatic splicing process, manufacturers have traditionally used contacting probes to measure overlap splice widths. Contacting probes often require that the calendered material stop or slow down in order to measure the overlap splice. This results in additional cycle time and negatively affects operating efficiency. In a manual splicing process, overlap splice widths are often not measured at all.

The splice width monitor utilizes industry-proven Selcom SLS laser triangulation sensors that have been optimized to meet the demanding requirements of in-line process measurement. The high-speed lasers accurately measure overlap splice widths in an automatic or manual process without affecting process cycle time. In addition, the digital signal produced by the SLS sensor enables the detection of a distinct leading and trailing edge of an overlap splice. This feature produces much more repeatable splice width measurements relative to contacting probes that locate overlap splices based only on the material thickness deviation detected on the material surface in contact.

The laser triangulation sensors have been selected for this application due to their relative insensitivity to signal variations caused by drastic surface contrast changes. In addition, the sensors remain accurate and repeatable throughout the entire measurement range, which is important considering the calender material flutter that often occurs due to the constant starting and stopping motion during an automatic or manual cutting and splicing process.

Automatic and manual splicing process

Incorporating in-line measurement in material preparation not only improves operating efficiency by providing real-time process feedback and/or control, but also ensures a higher quality product is delivered to downstream production processes. With the lack of a reliable measurement system in upstream processes, such as bias cutting/splicing, tolerances must often be set to minimize the greatest risk in downstream processes.

For example, splice width tolerances are generally set to a large percentage on the high side of the actual target to minimize the occurrence of open splices that have the greatest risk of product defect downstream. Automatic splicers are set up to avoid the narrow splice and operators are trained to err toward the wide splice in manual splicing operations. The result is often excessive splices that result in finished product defects and excessive material costs.

In-line splice width measurement is capable of improving material preparation operating efficiencies in both automatic and manual splicing processes. In the automatic splicing process, the in-line laser splice width measurement provides real-time process trends and analog or digital signal outputs for automatic process control. In the manual splicing process, the same laser splice width measurement configuration provides the operator with real-time feedback and trends for making appropriate adjustments to his/her splicing techniques.

The initial production installation of the three-channel splice width monitor has provided the opportunity to bring the automatic splicing process into control and deliver improved product quality to downstream processes. For a material line speed of approximately 1 meter/second (3 ft./sec.), the system has produced the following results:

* Encoder resolution - 0.10 mm (0.004 in.);

* splice width accuracy - [+ or -] 0.15 mm (0.006 in.);

* splice width repeatability - [+ or -] 0.15 mm (0.006 in.).

Similar results are obtainable for significantly faster material line speeds by utilizing laser sensors with faster sampling frequencies.

Powerful software tools

For monitoring each overlap splice, a software utility can be run on any PC workstation on the plant network. As illustrated in figure 5, the splice width viewer software shows the results of the splice width measured in real-time at each system channel, as well as the average of all channels. Splice width trend results are also displayed to provide process control information or operator feedback.

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As previously described, a valid splice (or open splice) is detected when the material thickness exceeds a user-defined threshold for a specified duration. In figure 6, the overlap splice profile for each system channel is displayed. The user-defined material thickness threshold that constitutes a splice is defined in laser units on the vertical axis. The duration that the material exceeds the thickness threshold is displayed along the horizontal axis in inches or millimeters. The ability to view each splice profile is valuable in determining the consistency of the splice across the width of the material.

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The main benefit of in-line splice width measurement is the ability to receive real-time process feedback for automatic process control or manual process correction. Figure 7 illustrates the splice width viewer display of splice width trends over time. The actual splice width for each channel and the average of all system channels is displayed relative to the overlap splice width target. Wide splices are shown above the target width line and narrow splices are shown below the target width line on the vertical axis. Splice width results move from left to right on the trend summary display with the most recent splice displayed on the extreme left.

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Benefit summary

The splice width monitor provides the opportunity for significant improvements in operating efficiencies in the material preparation area. Reliable in-line splice measurement enables automatic or manual process control and improves the quality of product delivered to downstream processes without affecting process cycle time. Finally, powerful software tools enable the capture of valuable process knowledge through real-time feedback and historical process trend data.