The Basics of Multisensor Metrology Technology with OGP UK
OGP UK’s offering is diverse and aims to provide manufacturers, no matter the measurement need, with the right inspection solution. Over the years metrology has evolved enormously allowing for the use of multiple sensors to assign to data point collection of any part feature. Here are the basics in multisensor metrology technology and the most suitable uses for each various sensor and probe, brought to you by OGP UK.
Optical sensors, such as video, collect measurements without touching the component. This is suitable if the part is delicate, flexible, too small to easily handle or physically inaccessible (such as the filament in a lightbulb). Optical measurement is the only technology that can quickly and accurately measure edges directly, and can also be much faster than tactile measurement (touch) systems, particularly since large numbers of data points can be gathered simultaneously by video.
There is a wide variety of tactile measurement methods, this involves a probe physically touching the component, and that point of contact is then registered as a data point. Contact probes can reach areas that are inaccessible to optical methods, collectively allowing more measurements in a single setup.
While optical measurement machines offer versatility and efficiency, tactile measurement can be used to gather data that is unattainable to optical methods. To combine both methods of measurement it is suggested as best to add tactile sensors to an optical measurement machine because optical measurement systems have a larger amount of technical requirements to satisfy than tactile probes, and it would be best suited to start with a system designed for optical metrology, rather than optics being grafted on to a CMM measurement machine.
Optical sensors are noncontact technologies for fast, accurate measurement. These technologies include lasers, video measurement, and white light interferometry.
Lasers: When scanned, laser sensors collect points from the component and can be used to make faster contour and dimensional measurements on a variety of materials and surfaces. A measurement machine that is equipped for lasers is capable of supporting multiple laser configurations that may be necessary in order to accurately collect data from specular and diffuse components. Lasers can also provide accurate measurement of part features that are inaccessible by other measurement methods, including tactile probes.
Video Measurement Systems: Video systems can measure images of a component, taken by an in-built camera. This method can collect large amounts of data based on image contrast and edge detection. Multiple small parts can be identified and measured simultaneously in one field of view. Accuracy and speed for this technology rely on innovative video system illumination, technology advancements have allowed integration of cooler, brighter LED configurations, providing backlighting, oblique lighting, strobing and co-axial surface lighting.
Modern advancements in camera and optic technology makes video measurement a pragmatic choice when considering a multi-sensor solution that is both fast and accurate. Video measurement systems today offer telecentric optics, high resolution cameras, through-the-lens laser scanning, and supplemental tactile probes to provide full measurement capability ranging from compact, benchtop systems to high capacity models. Combining both optical and tactile measurement methods would be a sound strategy for creating future benefits, by minimising the need for multiple measurement systems.
White Light Devices: Chromatic white light sensor technology analyses the optical spectrum of reflected light to measure surface height changes to nanometre resolutions, allowing ease of measurement especially of transparent and translucent subtrates, which may be beyond the capability of most other measurement tools. Applications where white light interferometry would be beneficial are contoured surfaces, such as turbine blades or orthopaedic medical devices, where many measurement points are needed to accurately define complex shapes. Whether it is white light interferometry or chromatic aberration analysis, white light devices can provide unique solutions for specialised applications.
Touch Trigger Probes: Touch trigger devices make contact with the part, retract, move and repeat, collecting one point at a time. There are many combinations of styli length and tips that will allow access to the feature being measured, but this method of measurement may be limited to the physical reach of the measuring tip, along with room to trigger and back off. Styli tips are often made of ruby, tungsten, or even a soft Teflon material, depending on the nature of the part material. With an optimal stylus and tip combination, touch trigger probes can register measurement data points with as little as 0.08N of trigger force.
Scanning Probes: Scanning probes look similar to touch trigger probes and are designed to slide across a surface contour, collecting hundreds or thousands of measurement data points as they move. System software drives the probe, rapidly following the component contour and collecting the data points at a user defined velocity and data sampling rate.
Micro-probes: Micro-Probes are a variant of the touch trigger probe. Micro-probes have similar contact measurement method, but with a much higher sensitivity trigger that can allow data point acquisition with less than 0.04mN of trigger force. Micro-probes might be required when a part to be measured is delicate and could be easily deformed. This type of probe would be appropriate for accurately measuring part features as small as 0.15mm.