Innovative sensor technologies enable more complex, faster & higher accuracy robot inspection measurements

Author : Chris Jones | UK Managing Director | Micro-Epsilon

01 August 2019

SurfaceCONTROL detects & analyses local shape defects on surfaces that deviate by micrometres from their target measurements

Evolving sensor technologies are enabling robot measurement tasks in manufacturing, where there is growing need for high precision measurements over wide surface areas & expanding requirements for increased flexibility, says Chris Jones, UK MD at precision sensor manufacturer, Micro-Epsilon.

This article was originally featured in the August 2019 issue of EPDT magazine [read the digital issue]. Sign up to receive your own copy each month.

Such systems can provide fast, reliable 100% surface inspection that can be integrated directly into robots on processing and assembly lines.

Can non-contact sensors guide the tools or devices attached to robot arms? With the latest advanced sensor technologies, such systems certainly can. In the automotive industry in particular, these robotic sensing systems are already proving their worth.

For example, laser sensosr can be used for dynamic distance measurements when applying adhesive beads to car roof rails or windscreens. Today, windshields are much more than simple glass sheets in the car to protect drivers from headwind. This subsystem has evolved, incorporating key vehicle roles, while also having to resist shocks and high variations of temperature.

The scanCONTROL laser profile scanner serves to measure the height and position of the adhesive beading on the screen edges. The process sees a robot position the glass in front of the bodywork and after the position has been determined by light section sensors, the screen is put centrally into the bodywork. This process is performed in real time and integrated in common automotive production cycles of less than one minute. Such laser triangulation sensors are the ideal choice for these tasks. The sensors are very small with integrated electronics. Measuring ranges are from 2mm to 1,000mm, with fast measuring cycles of up to 50kHz that widen the scope of applications.

The scanCONTROL laser profile sensors are divided into three classes: Compact, High-Speed and Smart. The first two versions respectively transmit the raw profile (‘point cloud’) data to, for example, downstream customer software (software integration), whereas the Smart scanner series carries out the evaluation directly in the sensor head. The evaluation can be simple, for example, when inspecting an adhesive bead, or highly complex, thus meeting the needs of a wide range of different industrial applications, including welding, joining and installation processes.

Laser triangulation sensors & laser profile scanners are ideal choices for many robot-guided measurement tasks, as they are very compact with integrated electronics

In order to enable flexible configuration possibilities for the Smart scanner, Micro-Epsilon has developed free, user-friendly software that can be installed on any number of computers. Different software features, such as dynamic tracking and logic connection of several conditions, provide maximum flexibility for difficult tasks.

Bodywork assembly processes

But what about the vehicle’s bodywork, where during the assembly process, it is important to ensure panels are flush and that there are no gaps? For these complex measurement tasks, a Micro-Epsilon gapCONTROL sensor can be installed on a robot arm for measuring various types of gap. Here, gap measurement data is used to guide the robot along the car, making real time measurements to ensure that flushness and gaps meet manufacturers’ requirements or controlling welding robots.

For defect detection on diffuse reflective surfaces, Micro-Epsilon has developed the surfaceCONTROL measurement system. This technology uses structured light projection to detect and analyse local shape defects on surfaces that deviate by micrometres from their target measurements. The system also operates reliably on textured surfaces, such as interior automotive parts.

The surfaceCONTROL offers a variety of measurement areas ranging from 150x100mm2 to 600x400mm2 , and it takes only a few seconds to capture 3D data for a surface.

Various evaluation procedures are available, depending on the nature of the shape deviations being investigated. The 3D data can be used to calculate a flawless virtual cover, or a digital whetstone can be used, similar to a whetstone in a press shop. These methods provide repeatable, objective assessments of deviations from around 5µm to 20µm, depending on the surface. The structured light projection procedure is suitable for all surfaces that diffusely reflect at least part of the light, including steel, aluminium, plastics and ceramics.

An increasing number of sensors are being integrated with robots because these systems can complete many tasks independently

Alternatively, for detecting paintwork defects on entire car bodies, the reflectCONTROL system can be integrated into the robot. Using deflectometry, the surface is examined to micrometre accuracy. A robot continuously adjusts the position of the system to help complete measurements within a very short timeframe. The defects are measured laterally and in depth, and classified to enable follow-up work and process improvements to be performed precisely as required and easily. The technology provides objective 100% inspection of all vehicles manufactured, and enables employees to concentrate on remedying critical defects rather than identifying them.

Not only does the system reduce defects, it also means that where defects are detected, this happens immediately after the painting booth when they can still be easily reworked. This reduces costs and reduces the number of rework lines required.

An increasing number of sensors are being integrated with robots, because these systems can complete many tasks independently and travel distances are expected to be found dynamically, as the use of specified travel ranges is set to decrease over time.

A challenge for many industries

The perceived quality of smooth, defect-free surfaces is determined by the look and feel, colour and shape consistency of the surface. High quality finished surfaces are therefore a challenge for many industries, not just automotive. Aerospace components, domestic appliances, entertainment devices and consumer electronics also require high quality finished surfaces.

Although inspectors are able to recognise a high proportion of surface defects reliably and quickly, visual evaluation is often subjective and depends heavily on several factors, including tiredness, lack of concentration and varying light conditions. The aim of automated surface inspection is to achieve an objective, reproducible evaluation of surface deviations in order to quickly and reliably make decisions with respect to component tolerances.

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