Inline profile thickness measurement for rubber and tyres

Micro-Epsilon's Systems Group specialises in the development, manufacture and installation of a comprehensive range of non-contact, inline and offline measurement and inspection systems for process monitoring and quality control applications. These include specific measurement systems for rubber processing applications, including systems for measuring strip thickness, length, width and profile of rubber strip and sheet.

Specific systems are also available for the measurement of tyres for passenger, truck and commercial vehicles. These include systems for measuring the thickness profile of tyres, tyre treads, sidewalls and inner tube linings, as well as systems for measuring other critical dimensions of tyres and for colour coding or marking of tyre treads. Micro-Epsilon also provides a retrofit and upgrade service for tyre uniformity (TU) machines.

Chris Jones, Managing Director at Micro-Epsilon UK comments: "Many rubber processing and tyre manufacturing companies prefer to outsource to a third party specialist in non-contact measurement. Over the past 12 years, Micro-Epsilon's Systems Group has developed a range of innovative, robust, complete turnkey measurement systems that offer distinct technical advantages in terms of measurement accuracy, thermal stability and reliability. This is backed up by installation, servicing, maintenance, technical support with guaranteed response times, retrofitting and upgrade services."

These technical advantages include fully automatic calibration. The system periodically re-measures against a known reference. The system also has integrated measurement sensors in the framework and mechanical parts, which measure the thermal expansion of the system. The software then compensates accordingly.

Developed in-house

Jones continues: "We manufacture the sensor technology and all other critical parts including the electronics and software. The mechanical design is also developed in-house, which enables us to guarantee measurement performance and take ownership of the complete system. All electrical hardware including the PCs are industrial grade with solid state memory.

"As well as offering our comprehensive range of inline, non-contact thickness and profile measurement systems for rubber and tyres, we are providing a dedicated service to UK-based customers, including a 24/7 technical support hotline and a guaranteed on-site, rapid response service. We understand how critical it is for these companies to minimise production downtime and improve their product quality and so our engineers will be on call to assist the customer at all times. We can also provide customers with dial-in communications and remote diagnostics for measurement systems, which speed up our response times, enabling our engineers to quickly rectify any issues that arise on site."

Micro-Epsilon's range of measurement systems for rubber strip and tyres comprises the following:

Inline & offline profile measurement of strip thickness

Part of Micro-Epsilon's thicknessCONTROL family, the RTP 8302 is a C-frame system that measures the thickness profile of rubber strip and sheet. C-frame systems are modular in their design, offering flexibility and high performance. These systems can be installed in tyre production lines, extruders, rollerheads, calendar lines and inspection rooms, providing reliable, high precision measurement results that creates a basis for controlling the production process and product quality.

C-frame systems measure differentially. An application-specific (confocal, capacitive or laser triangulation) displacement sensor is integrated in the upper and lower flanges of the C-frame. The thickness of the target material is derived from the distance between the two sensors and the resulting signals. By combining highly efficient signal processing algorithms and visualisation software, the system is able to achieve accuracies in the sub-micrometre range.

The C-frame can be used as a traversing thickness measurement system on linear axes in order to ensure full width measurements of the target. The control and analysis software is developed in-house by Micro-Epsilon specifically to match the needs of the rubber processing and tyre manufacturing industries, providing all the required functions in order to continuously record and evaluate production quality. This includes graphical user interfaces and the ability to store multiple product libraries. Also, the software supports and displays Statistical Process Control (SPC) parameters and other "Process Capability' analysis and reporting methods such as Six Sigma PK and PM. Various fieldbus interfaces are available, which enable integration to the customer's production control systems.

Fully automatic calibration ensures that measurements are not affected by temperature, enabling the system to be installed as a fixed, inline measurement system in harsh production environments, without the need for calibration or manual adjustments. All sensor technologies used are non-contact, wear-free and do not use isotopes or X-rays. The C-frame system provides long-term measurement reliability at an affordable price. C-frame systems can be used to measure strip widths up to 1m and strip thickness from

Thickness profile measurement of inner tube liners

For larger strip widths up to 4000mm, Micro-Epsilon's O-frame systems are able to measure rubber thicknesses from 1mm up to 20mm at accuracies of +/- 5um.

O-frame systems measure differentially and incorporate many of the same features, functionality and software as C-frame systems, but also incorporate high speed gauging sensors, which are mounted to a mechanical linear guidance system that measures by traversing along the complete width of the rubber strip.

Thickness profile measurement of tyre treads and side walls

In tyre production, measuring the thickness profile of treads and sidewalls is critical to the quality of the end product. Micro-Epsilon's TTP 8301 system operates on the light intersection method and laser triangulation (line or point) sensors. Based on an O-frame system, TTP 8301 systems measure differentially i.e. the thickness of the material calculated from two distance measurement signals.

In the case of the TTP 8301.l, a laser line is projected onto the rubber surface, which is then detected by a camera. In the TTP 8301.T system, one displacement sensor is installed on the upper and lower flanges of the O-frame on a mechanical carriage or slide. The thickness of the target material is determined by the distance from the sensor and cameras to one another and the amount of signals.

Measuring tyre geometries

Systems are also available to measure a variety of dimensions and parameters of a tyre. These systems measure tyre widths of 100mm up to 460mm at resolutions of up to 640 points per profile, with measuring cycles of up to 60 tyres per minute. Measurement repeatability is less than 0.04mm (3-Sigma).

Micro-Epsilon's dimensionCONTROL TGI 8302.LLT system, for example, is a C-frame system that incorporates three application-specific triangulation laser line scanners. These are set up to reliably detect the radial and axial imbalance of the tyre, as well as any bulges or indentations on the surface of the tyre. The sensors on the upper and lower flange, as well as the tread sensor, are controlled automatically according to the size of the tyre being inspected. The actuators can be operated by either servo or stepper motors.

The three laser scanners measure the complete surface area of the tyre, detecting angles, lateral size and depth of any tyre defects. Special signal processing software algorithms also ensure that any letters or numbering on the surface of the tyre is detected and disregarded from any subsequent measurements.

Systems for colour coding in extrusion lines

The dimensionCONTROL TLS 8303.l system can be installed in rubber extrusion lines immediately after the cutting operation. The system incorporates two cameras that inspect the profile and length of rubber strip for tyre production. The cameras record synchronously the cutting edge of the strips and detect any deviations from the nominal cutting edge. This enables evaluation of the length of the strips by the distance of the two cameras from each other and the dimensions of the cut surface.

In order to ensure stable, reliable measurements, the system uses special signal processing algorithms and filters to avoid any interference from vibrations or external light.

Using the TCS 8303.l system, tyre treads can be colour-coded. The cartridges for the marking of treads are inserted in a special holder. Pneumatic height adjustment and servo-controlled horizontal positioning ensure straight line, optimal positioning of code lines, which are verified by an image processing system, which detects missing, incorrect or incomplete lines. Whilst marking, the system can simultaneously measure strip width.

The TCS 8303.l system measures strip widths from 200mm up to 550mm, strip lengths from 1,500mm up to 2,500mm and strip thicknesses up to 50mm, and material feeds of up to 30m/min.

Retrofit of tyre uniformity machines

Micro-Epsilon also offers retrofitting and upgrading of tyre uniformity (TU) machines. Akron D70, Meyer Beulenprfmaschinen, and Hoffmann RGM-E machines can be retrofitted with Micro-Epsilon's TRP 8309.M system, which utilises standard products and special sensors that have been used in hundreds of TU applications.

Micro-Epsilon also offers upgrading of TU machines, including the upgrade of electrical components, control system (either a Siemens or Beckhoff-based system), bead moistening station, marking station (with optical inspection if required), sorting unit, safety gate, software-controlled pressure filling station, as well as geometrical and uniformity measurement systems.

For more information on Micro-Epsilon's range of measurement systems for rubber strip and tyres, please email [email protected], or visit the website at www.micro-epsilon.co.uk.