Lasers are truly extraordinary devices, especially when they're used in production processes to measure moving products. Have you ever wondered how they work and how they're being used in industrial applications? Here's a primer that gives you an inside look.
The Need for Measuring Length and Speed
Over the years, non-contact laser length and speed technology has gained a wide acceptance in a broad scope of industries. In businesses where customers buy by length, it's important for manufacturers to know the exact length of the product being shipped in order to avoid costly product overages or shortages. (Typically, a manufacturer will ship a certain amount of extra product to avoid shortage situations.) In applications where speed control is critical, manufacturers process materials to meet unique customer product specifications and quality requirements. Any problems with achieving these demands, translates into costly rework, material waste or product returns.
Accurate length and speed measurements are important for many different industry sectors and process applications.
- Building Materials
- Pipe & Tube
- Plastic Film & Sheet
- Wire & Cable
- And other sectors
Applications include continuous length, cut control, speed control, stretch/draw control, product positioning, product marketing/printing, quality control and other operations.
Common Measurement Approaches
Currently, most length and speed measurements are made using contact methods. All contact length and speed measurements are indirect measurements relying on physical contact between the product surface being measured and the instrument surface which turns an encoder counter. Length is calculated from the amount of rotation of a contact wheel as measured by the encoder. However, contact wheel encoder systems by their very nature have several fundamental flaws that make them prone to measurement errors. These include:
- The amount of slippage or jitter between the wheel and the measurement surfaces
- Day-to-day wear of the contact wheel, causing the radius to change
- Build-up of product material, debris or other material between the wheel and product
Many different contact measurement systems have been designed to reduce these measurement errors. They include contact tachometers using two-wheel, three-wheel and four-wheel tracking systems. However, many of the problems mentioned above still exist to some degree. In general, most tachometer systems provide a length error of 0.5% or higher; greater than 1.0% error is common. A contact encoder attached to the drive roller or capturing pulses of the drive has the same problems. From a quality standpoint, contact tachometers have the potential to mark the product, thereby creating a defect. From a maintenance perspective, contact measurement systems require periodic calibration and service. The ideal length and speed measurement technique is a non-contact approach.
Non-Contact Laser Technology Comes to the Rescue
The latest solutions for non-contact measurement use the long-established Laser Doppler Velocimetry (LDV) technology to provide highly accurate and repeatable product length and speed measurements. This technology eliminates the length and speed measurement errors associated with mechanical contact encoders. For instance, NDC’s LaserSpeed Pro non-contact gauge provides length and speed measurements with better than ±0.03% accuracy and ±0.02% repeatability.
How Non-Contact Laser Measurement Works
Let’s take a close look at how LDV measurement technology works. In this example, we’ll look at NDC’s LaserSpeed Pro gauge. The LaserSpeed Pro gauge uses advanced, laser-based technology to project a unique pattern on the product’s surface. The pattern is created when the two laser beams converge to create a measurement region called the “depth of field”. As the product moves through the depth of field, light is scattered back to the gauge. This information is translated into product speed and pulses are produced to determine the product length. Length and speed measurements are captured with the highest accuracy. Gauge pulses are then used to control a wide range of critical process functions, as mentioned earlier in this blog.
The Good News is that the Payback is Fast
The Return on Investment (ROI) from accurate length and speed measurements is significant.
You can expect savings from:
- Minimizing product waste
- Reducing product shortages and overages
- Increasing product quality
- Eliminating maintenance
- Minimizing downtime
- Lowering the cost of ownership
The following is a good example that illustrates the savings:
Depending on the application, length and speed inaccuracies in a manufacturing process (such as in converting a roll of paper or plastic material) may be as much as 2% or more. A 2% inaccuracy on a 20,000-foot roll translates into 400 feet of uncertainty. If that inaccuracy produces an excess in the quantity delivered, each roll is costing the manufacturer significantly. If the roll is 400 feet short, this can cost the manufacturer in customer bill backs.
The LaserSpeed Pro gauge has been verified to be 20 to 40 times more accurate than a contact encoder. As mentioned earlier, LaserSpeed Pro has a measurement accuracy of 0.03%. This degree of accuracy provides a fast payback from the savings. Instead of an uncertainty of 400 feet per every 20,000 feet with the contact method, the LaserSpeed Pro gauge lowers the possible error to a maximum of six (6) feet on a 20,000-foot roll. In addition, the LaserSpeed Pro gauge is permanently calibrated, resulting in significant time and money savings related to maintenance and downtime issues. The LaserSpeed Pro gauge can literally pay for itself in a matter of weeks.
Are You Ready to Adopt Non-Contact Laser Measurement?
If you’re like other manufacturers, you’re probably also facing numerous challenges to produce quality products faster, better and most cost efficiently. Non-contact length and speed gauging technology can help. It is highly accurate and reliable and has been proven on all types of manufacturing processes. If you want to learn how this technology can give you the competitive advantage, just reach out us. We’re ready to help.