Sensor system detects beads, bulges and bumps

Written by: Tom Shelley | Published:

Dean Palmer reports on a unique, non-contact laser line sensor and integrated controller that offer high speed, accurate inspection and that requires no special programming skills to set up

Dean Palmer reports on a unique, non-contact laser line sensor and integrated controller that offer high speed, accurate inspection and that requires no special programming skills to set up

A non-contact, laser line profile measurement system has been developed that enables end user manufacturers, systems integrators and machine builders to detect beads (ie. bulges or bumps) of adhesive, weld seams, grooves, channels, gaps and edges on components, in a variety of industrial applications.

The system, which is referred to as a '2D/3D laser sensor' by its developer, has standalone plug-and-play capability, and is easy to set up, configure and adapt for different applications. More importantly, engineers require no special software programming skills to change measurement parameters and to get the system up and running quickly.

The 'scanCONTROL 2810', Micro-Epsilon's latest version of its 'scanCONTROL' range of sensor systems, was unveiled at last year's Hanover Fair in Germany and was officially launched in Autumn 2005.

The system builds on the success of the company's 'scanCONTROL 2800' 2D/3D laser line sensor, but goes even further and is capable of measuring up to 256,000 points per second up to 4kHz.

The 2810 uses the same laser line triangulation measurement principle as the 2800. The sensor has an integrated, highly-sensitive CMOS array, which enables measurements of almost any shiny, reflective or transparent surface, independent of the reflection from the target. "This means excellent accuracy, resolution and reliability are achieved, even at high measurement speeds," explained Chris Jones, managing director at Micro-Epsilon UK.

The sensor works using a line optical system, which projects a laser line onto the surface of the object being measured. The back scattered light from the laser line is registered on a CMOS matrix by a high quality optical system. Along with distance information (z-axis), the controller calculates the true position along the laser line (x-axis) from the camera image and outputs both values in the sensor's 2D coordinate system. A moving target or traversing sensor generates a 3D representation of the object being measured.

The 2810 is capable of measuring up to 256,000 points per second and so is ideal for real time quality inspection or online process guidance. Depending on the resolution and size of the measurement range, a profile frequency of up to 4,000 profiles per second can be attained.

As Jones stated: "Customers are using the sensor for detecting weld seams, beads of adhesive, edges, angles and for detecting grooves, channels and gaps. In the automotive industry, VW and BMW are using the system to check the height, width and integrity of glue beads. In the drinks industry, Syscona is using the system to verify the position of barrel cups on its production lines. Qion is using the system to check the position of a welding seam on its pipelines, and in the aircraft sector, DLR is checking the angle of helicopter rotor blades for calibration in an engine test cell."

The system itself comprises a sensor and integrated controller, which calculates the dimensions of the bead or groove. The system works in two ways: either in a stationary mode, with the sensor fixed and looking at moving targets, or in a scanning mode, where the sensor works in combination with a motion control device or robot. The sensor uses an innovative CMOS array with a real time, high speed electronic shutter (rather than conventional rolling shutters), which captures the entire profile and processes the information instantaneously.

The controller evaluates the measurement data and provides control signals via analogue or digital outputs. The system can be easily configured using the parameter software included within the sensor package. Parameters that can be configured include area, height and width of the bead. The user simply connects a laptop or PC to the controller and configures the sensor via easy-to-use software. Triggers and alarms can also be set up using the software, so that when limits or tolerances are exceeded, users are alerted.

"We are selling the system to machine builders, systems integrators and direct to end users, because it is so easy to adapt the system to different applications," said Jones. "It is also easy to set up and configure for different measuring fields and no special software programming skills are required to do this. The system also offers very high speeds and accuracies, enabling end users to inspect their products in-process in real time."

According to Jones, typical applications for the sensor system include: welding seam inspection; glue bead inspection; door edge detection; angle measurement; step and height measurement; planarity and surface control on PCBs; robot guidance and positioning; and groove width and depth measurement.

The predecessor of the 'scanCONTROL 2810', the 'scanCONTROL 2800' is already being used by manufacturers around the globe.

Continental Tyres, a leading manufacturer of tyres, has solved an inline inspection problem using the sensors, which detect the slightest bulge, recess or other surface defect that may affect the performance of the tyre.

Continental is using three scanCONTROL 2800 2D/3D laser profile sensors on a test rig developed by machine builder/systems integrator MicroStep of the Czech Republic. The test rig inspects individual tyres in less than one second, enabling Continental to carry out 100% inspection of tyres from its production line.

Rather than using multiple laser-based point sensors or capacitive sensors, the scanCONTROL 2800 sensors measure the profile of the tyre using a non-contact laser line, on which multiple measurement points (up to 250 per second) can be acquired and analysed.

Previously, Continental used capacitive sensors and laser-based optical point sensors to inspect tyres. Compared to the laser line method, capacitive sensing detects over a relatively large measurement spot and so patterns, symbols or legends on the tyre could not be distinguished from genuine surface defects such as bulges.

With laser point or spot sensors, not only would multiple sensors have to be used to acquire the same surface defect data, but the sensors could not cope with the high throughput rates of tyres on the test rig. The sensors also had problems with the reflection properties of newly-produced, black, shiny rubber tyres.

Similar to the 2810, the scanCONTROL 2800 sensor has an integrated, highly-sensitive CMOS array, which enables measurements of almost any shiny, reflective or transparent surface, independent of the reflection from the target. Using special software algorithms, logos and symbols on the tyre can be removed from any analyses of the acquired data.

MicroStep's test rig receives tyres automatically from the production line. These are held in place by a fixture or gripper, which rotates the individual tyre through 360° in less than one second. During this time, the three scanCONTROL 2800 sensors inspect the three sides of the tyre walls for defects, taking measurements in real time.

The measurement system consists of three scanCONTROL 2800 sensors and a controller. The measurement data is output from the controller via a Firewire interface to the manufacturer's in-house developed analysis/evaluation software.

Potential applications for scanCONTROL 2800 include contour measurement, robot guidance, door gap alignment, position measurement, rail profile, groove measurement, co-planarity measurement and flatness measurement.

Eureka says: Manufacturers are now demanding sensor systems that can measure and inspect fast-moving components or products on high speed production lines. The 2810 represents a step-change in laser optical sensing

Pointers

* The 2810 offers high speed measurements of up to 256.000 points per second, up to 4kHz

* The 'plug-and-play' system is easy to set up and integrate with existing factory automation systems, and also requires no special software programming skills

* Typical applications include weld seam and glue bead inspection; door edge detection; angle measurement; step and height measurement; planarity and surface control on PCBs; groove width and depth measurement; and robot guidance


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