Compact optical sensors offer high precision
Micro-Epsilon's new range of miniature confocal displacement measurement sensors have a diameter of just 4mm (standard sensor diameters are 27mm) and are therefore suitable for measuring inside confined spaces such as narrow cavities, drilled holes and bores.
As well as axial measurement, the new range of sensors also includes a 90-degree version that enables users to measure (radially) the inner surfaces of small components. The sensor head can be rotated inside the bore, so users can measure surface defects inside and check the concentricity or roundness of bores or drilled holes.
Other potential applications include: the checking of liquid fill levels in medical test tube racks and trays; inspecting drilled holes and recesses; measuring grooves inside pipes; measuring the thickness of transparent materials, including glass and film; and mirrored or highly reflective surfaces (which are difficult to measure with laser sensors) can also be measured easily and with very high stability.
The sensor is targeted at a range of industry sectors, including medical, biotechnology, pharmaceuticals, aerospace component inspection, electronics components and PCB measurement, machine gauging/inspection and general engineering.
The new optoNCDT 2402 sensors, developed and manufactured by Micro-Epsilon, are confocal miniature displacement sensors based on the company's patented lens design. Manufactured using Micro-Epsilon's own special optical production technology, the sensors are currently claimed to be the smallest diameter confocal displacement sensor available on the market.
At a measuring range of 1.5mm, the sensor has a resolution of 0.06um at 0.004 per cent FSO (full scale output). Measuring rate is from 30Hz up to 30kHz and the operating temperature is 10-50 degrees C.
With a titanium housing, the optoNCDT 2402 sensor weighs just 50g and is suitable for machines that require a lightweight, miniature displacement sensor. The sensor head comprises precision optical parts without any electrical components that enable a very high level of stability that is not possible with other laser optical devices.
Micro-Epsilon's complete measurement system consists of a sensor, an optical cable and a controller. Up to six different sensors can be factory-calibrated for one corresponding controller.
The optoNCDT2402 sensor is the latest in Micro-Epsilon's optoNCDT 2400 range of confocal displacement sensors. All sensors in the range have no moving parts and can therefore be considered wear-free. The sensors work on the confocal measurement principle in which polychromatic white light is focused onto the target surface by a multi-lens optical system. The lenses are arranged such that the white light is dispersed into a monochromatic light by controlled chromatic aberration. A specific distance is assigned to each wavelength by factory calibration. Only the wavelength that is exactly focused on the target is used for the measurement. This light reflected from the target surface is passed through a confocal aperture onto a spectrometer, which detects and processes the spectral changes.
The spot size of the device is very small, in the region of 7-10 microns, depending upon measurement range, and is always constant in diameter. This measuring principle enables displacements and distances to be measured with high precision and exact spatial resolution. Both diffuse and specular surfaces can be measured. With transparent materials such as glass, a one-sided thickness measurement can be achieved along with the distance measurement. Shadowing is also avoided because the emitter and receiver are arranged in one axis.
The white light technology is also said to give greater stability than laser-based technologies when used with shiny metal, transparent and mirrored surfaces.
