Laser sensor application in the tire industry

As tire specifications become more stringent, tire production poses a new challenge for suppliers, requiring faster, more cutting-edge development and a more accurate measurement and inspection system for both online and offline applications. .

What manufacturers need is a device that can reliably detect tires at a cost that is at the expense of accuracy and higher yields, as well as high sampling rates and longer intervals.

For the tire industry, production and production mean everything. They can only promise little or no downtime, and backup stocks must be kept to a minimum. At the same time, manual review of defective products must also be minimized.

In these applications, the non-contact laser measurement sensor is superior to the traditional contact/mechanical follow-up, and the earlier the capacitance sensor that changes the repeatability and yield per measurement.

The biggest disadvantage of contact or mechanical followers is that such sensors require continuous measurement of the channels that are cleaned on the tires.

The lettering or pattern on the tire destroys the contact probe when the tire speed is 60 revolutions per minute (rpm). These letterings and patterns can also seriously reduce their repeatability due to unnecessary rebound. In contrast, the design of a suitable laser measurement sensor is not affected by surface texture, color, speed or conditions of light in different environments. Compared to contact sensors, laser sensors are independent of probe wear or bounce and can collect data at higher rates.

Performance requirements in rubber applications

Since the rubber is black, it absorbs almost all of the light on the surface, so in order to obtain a high-quality laser spot image and quickly adjust the surface reflectance, the measuring device needs sufficient optical power.

Generally, even if the laser has the best sensor performance, the spot size of the laser is required to be small, and the frequency response is fast, so that reliable data can be obtained from a cross section such as a tread or a side wall having various shapes and shapes.

The raw material of the rubber to be processed, typically from an extruder, a calender or an unprocessed or unvulcanized material during the tire building process, is generally hot and viscous, having a black shiny surface while releasing smoke. The measured data must reflect the true form factor and contour.

It should not be affected by heat, the environment or surface of the smoke, nor should it be affected by the measured angle or texture, brightness, bevel, speed or temperature of the material.

When measuring a rotating tire on a high speed TUO (tire uniformity) machine, the non-contact sensor must provide a sample quickly to ensure that no defects are detected.

Since contactless laser measurement can quickly react to process changes, it is ideal for this type of application, allowing high-speed, uninterrupted measurements throughout the entire production process.

How to carry out triangulation

Most non-contact sensors in the rubber and tire industry use optical laser triangulation to accurately measure objects or surfaces.

In this technique a beam of light is emitted from the sensor to the surface being measured. It is equivalent to an automatic light section microscope, sometimes referred to as a structured light. On the surface, the laser emits a spot at one point. At a certain angle with the laser, a lens is used to form an image or a photo of the spot on the image plane, and a position sensing detector is placed on the image plane. If the surface is further widened, the spot of the detector changes to a different point. The sensor-to-surface spacing can be determined by determining the position of the spot and the angle associated with the measurement.

There are two main types of detectors for non-contact triangulation sensors. They are all solid-state, integrated with circuit chips with a rough structure, and as long as the sensor housing is properly assembled, it has reliable performance even in harsh environments.

The first type of sensor is a PSD or a position sensitive detector; the second is a CCD, also known as a charged coupling device.

PSD is a simple element detector that converts incoming light into continuous position data. Essentially it is an analog device. PSD sensors are used in the rubber and tire industries when applied to high data requirements. PSD sensors are designed for high frequency response, rapid control of light power and small spots. They provide a very rapid compensation for changes in the level of light, a feature that is important in rubber applications.

The CCD detector is essentially a form of digital camera, done in one and two dimensions. Usually one-dimensional CCD arrays are used for single point measurement. The two-dimensional style is used in conjunction with a laser linear sensor that measures a two-dimensional shape in a simple image frame. The primary disadvantage of CCD detectors is related to the speed of manipulation, which is generally smaller than that obtained from PSD.

PSD-based laser sensors are ideal for tire and rubber applications, and are gradually replacing dial indicators, linear variable differential transformers, capacitors, induction and ultrasonic sensors.

Production application

PSD triangulation sensors are widely used in the tire industry in both semi-finished and production lines. It has a smaller spot than most other sensing technologies and is ideal for measuring small changes and sections. The following are some examples of production applications.

Measurement of calendered rubber thickness

Most thickness measurements are done at a fixed location, using two opposite lasers, one on top of the material and one below.

With differential sensor products, thickness variations can be accurately and correctly measured for any type of material. Due to the high sample rate and small spot size, any change in the passing line or vibration of the material will not affect the measurement of the thickness.

In some cases, the two sensors are mounted in a mechanical slide and "C" shaped frame where they can be scanned back and forth to monitor changes in the width of the material. This framework must be strictly prevented from introducing measurement errors due to vibration.

Other applications require one or more mounted sensors that are referenced by rollers or the like. This method is simple and straightforward, but its correctness depends on the precision roller used. There must be compensation for bearing wear and dirt build up on precision balls. Moreover, the use of expanded materials at high speeds at high speeds is also dangerous.

Extrusion and orientation

Due to its long range and durability, this type of measuring laser sensor is ideal. This measurement is also independent of the speed and temperature of the extruded rubber.

The extruded rubber forms a specific shape through the mold, such as the tread portion of the tire. The on-line measurement of the profile during the extrusion process promises to control the machining to form the appropriate profile by correcting some parameters such as thickness, width and profile. Surface features such as ridgelines, centerlines and edges can also be detected. It mainly gives the operator how the mold is worn and when it changes.

The extruded profile of the tread can usually be accomplished by mechanical scanning during the extrusion process. In many applications, the speed required is higher than that achieved by mechanical scanning.

In order to meet this need, some producers have developed a high-speed optical scanning point triangulation sensor. This sensor can quickly adjust the laser power with each point on the 2D scan line. This ensures that each data point is properly illuminated.

Overlap and seam detection

The reason for tire non-uniformity is generally the incorrect layer overlap and side joints in the stacking operation of the tire. By on-line inspection in tire manufacturing machines, such as the rapid detection of errors and trends, the elimination of large quantities of vulcanized tires is avoided. In this application, the laser sensor is more accurate than other types of sensors.

Detecting radial and lateral curved surfaces of environmentally friendly tires

In order to reduce waste, it is necessary to monitor the curved surface of the product early in the production process and measure it during tire building; it also provides the necessary information to perform the correct handling. When measuring environmentally friendly tires in the manufacture of tire machinery, the inner layer, sidewall or tread joint overlap can be analyzed and measured. By identifying and correcting the problem prior to curing and testing, a more uniform end product can be guaranteed. The accuracy and repeatability provided are key factors in creating a good benchmark for statistical calculations such as roundness.

Ultimate inspection application

Tire sidewall inspection

When it is necessary to minimize the elimination rate or the possibility of downgrading a high-grade tire, the sidewall inspection process must detect all suspicious products, such as sunken and protruding tires. This process involves a lot of manual testing, which takes a lot of time and money.

Many tire manufacturing is affected by the measurement limits of the sensor, so the sensitivity of their sidewall embossing system must be enhanced, which requires expensive manual testing. Some measurement systems can't even distinguish the sag or stand out.

The latest measurement accuracy and advanced software analysis overcome most of these limitations. For example, the PSD laser triangulation sensor provides accurate and reliable data with high resolution and high speed.

Tire protrusion is a weak point created by a small joint of sidewall material during tire production. Usually, if the joints do not have enough overlap, when the tire is under pressure, it will burst like a balloon. This protrusion can be anywhere from 0.3mm to 3.0mm in height and from 5.0mm to 7.0mm in width.

The PSD laser sensor can quickly detect protrusions or other deformations at a tire speed of 60 rpm, and the accuracy of the measurement can reach ±0.0254 mm.

The effective protruding height is approximately 0.3 mm. Since many of the highlights are not related ropes but bubbles, customers can now request a height limit of 0.2mm.

The laser sensor can also be measured on a slope, with no data loss and no need for pre-reset angle. It provides protrusions, depressions, and X/Y points and locations on the sidewalls. It can also be measured by black lettering, oil or any other obstacle.

The sensor has a small spot that also filters out high frequency signals and statically detects and measures the active frequency of the bump.

Incorrect positive experiments, often referred to as alpha errors, can also be minimized by laser sensors. Geometric testing is performed using a capacitive probe or a clean channel that does not have a sidewall on the tire, and this alpha error rate becomes large. Usually, an undetected protrusion of the tire is unacceptable, which causes the entire batch to be recycled or invalid.

The industry is also interested in providing a complete range of tire coverage and a linear laser sensation that effectively analyzes the sidewalls. Its disadvantages are high price and complex structure.

Uniform tire machine

Many sensors are used in tire uniform machines (TUO). Although many TUOs, such as the TTOC-II and TSOS systems, use lasers, most systems still use very large spot capacitance probes, which can sometimes lead to product divergence.

Other machines use contact probes that cause errors on the surface of a rotating tire, or use low-end sensors that are not as high-sample-rate and high-grade lasers as light-controlled circuits.

The combination of a laser sensor and a TUO machine provides a much more accurate and fast cycle than traditional contact measurement and capacitive sensor systems.

For example, some microprocessor systems have a spot size greater than 6.0 mm, while a precision laser sensor is only 0.02 mm. Large spots can affect the accuracy of the reading and limit the application. Due to the slow measurement sampling rate, some CCD sensors require additional cycle time to process unrelated data.

In a typical TUO application, the non-contact sensor is mounted on an aluminum C-frame arm. This TUO system monitors the signal through sensors and identifies the type of recess, the width of the bottom, the size of the ramp and other geometric parameters. When the tire rotates at 60 revolutions per second, it can read and write more than 4,000 times on each side. In comparison, up to five sides are tested with standard uniformity.

Tire uniform system

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