Inline profile thickness measurement systems for plastics

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 plastics processing applications, including systems for measuring thickness and profile of blown film, extruded plastic sheet, strip and plates.

Chris Jones, Managing Director at Micro-Epsilon UK comments: "Many plastics processing 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 distinct 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.

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 plastics, 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," adds Jones.

Micro-Epsilon's range of measurement systems for plastics comprises the following:

Inline thickness profile measurement

Part of Micro-Epsilon's thicknessCONTROL family, the FTS 8102 is a C-frame system that measures the thickness profile of plastic strip and sheet. C-frame systems are modular in their design, offering flexibility and high performance. These systems can be installed in plastic extrusion and calendar lines, providing reliable, high-precision measurement results that create 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 to +/- 1um. These systems are therefore suitable for use in extrusion lines for cast film or deep drawn film; blown film lines after collapsing; melting calendar lines; and extrusion lines for plastic profiles and plates.

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 plastics industry, 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. 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 1250mm and strip thickness from 10um up to 50mm.

Thickness profile measurement of larger material widths

For larger material widths up to 4000mm, Micro-Epsilon's FTS 8101 O-frame systems are able to measure plastic thicknesses from

O-frame systems measure differentially and incorporate many of the same features, functionality and software as C-frame systems. An application-specific displacement sensor is mounted on a mechanical carriage in the upper and lower flanges of the O-frame, which detects the upper side of the target material. This works in combination with an eddy current sensor in a housing, which detects the underside of the opposite target via a measuring roll. The thickness of the target material is the difference between the two sensor signals. This provides the advantage of ensuring a "true thickness' measurement of the product irrespective of rollers and bearing wear, which would cause errors in conventional measurement systems. In addition, a sophisticated thermal compensation algorithm corrects for changes in the measured thickness, by compensating for thermal expansion of mechanical parts.

Reverse frame systems for blown film

Micro-Epsilon's thicknessCONTROL BTS 8104 system measures profile thickness of non-conductive blown film, including film used for packaging, agricultural applications, waste bin liners, carrier bags, freezer bags and shrink covers.

Designed as reversing systems, the BTS 8104 is based on capacitive measuring technology. Capacitive sensors are mounted directly behind the calibration cage on the film bubble, therefore offering very fast, efficient control of the production process. Adaptive reversing speed enables measurements to be adjusted according to each stage of the extrusion process.

For example, the BTS 8104.NC system is based on a patented pneumatic positioning control system that utilises non-contact air bearing technology. These bearings enable very precise positioning and compensate for any movement on the film bubble. The system is suitable for measuring highly adhesive surface protection films on the bubble very close to the blow head.

The BTS 8104 system measures film widths from 255mm up to 3600mm (double flat) and film thicknesses from 5um up to 300um.

Follow the link for more information about Micro-Epsilon's range of measuring and inspection systems for plastics or email [email protected].