FEATURE INSPECTION & MEASUREMENT
CONFOCAL SENSOR PERFORMS precision alignment to 2 micron accuracy
A non-contact confocal chromatic sensor installed on an automated machine measures the alignment of a precision disc pin assembly to within a clearance of 2 microns
U
K-based engineering and test company Curtis Assemble & Test Ltd
has installed a non-contact confocal chromatic sensor from Micro-Epsilon on an automated assembly and test machine that checks the alignment of a precision disc pin assembly, part of an automotive fuel injector valve. These high precision confocal displacement sensors are able to measure the alignment of the valve disc pin assembly to within a clearance of 2 microns. Testing and measuring customers’ products requires a very high level of cleanliness so the company has developed in-process and clean room high-pressure wash units specialising in hydraulic, pneumatic and leak testing, selective high precision assembly techniques and vision systems. “The high level of precision required by our customers means that in terms of measurement technologies our machines and test rigs must be equipped with the very best sensors and measurement devices,” comments works director Steve House. “Recently, one of our customers required us to check the mechanical alignment of an automotive fuel injector valve pin assembly to within a few microns. Basically, the assembly machine that we’ve developed presses the two parts together – a 15mm diameter valve disc onto a 2mm diameter injector pin – and checks that these parts are mechanically aligned to a set clearance of +/- 2 microns which is critical in order to ensure that the valve moves freely. We therefore required a displacement sensor that was even more accurate than this.” Prior to this the customer had been checking the alignment using a high end, clean room-mounted laser measuring device which took around 10 minutes per component to complete the necessary alignment check – which was too long. “We were therefore asked by the customer to develop a special purpose test and assembly machine that would reduce the time taken for alignment checks. Now we transfer the valve, disc and pin assembly into the special purpose automatic assembly machine using a robot handling system. In order to avoid any measurement interference due to vibration from the moving robot we mounted Micro-Epsilon’s confocal
16 MARCH 2015 | FACTORY EQUIPMENT
displacement sensor on a separate frame and stand in close proximity to the parts to be measured. The machine is now fully tested and proven, enabling us to check the alignment within 25 seconds.” “Alternative displacement sensors
including laser-based versions were prone to interference from the thin film of oil present on the metal components that were being measured as well as the wet environment the sensors needed to operate in,” explains House. “With the confocal sensor we don’t have any of these issues. In addition, it works well on highly reflective, polished metal parts. “We had trialled some of the company’s confocal sensors on a previous assembly machine and knew they could do the job and meet the very high levels of precision required for this particular project.” Micro-Epsilon recommended its confocalDT IFS 2405-3 non-contact confocal displacement sensor which is able to measure on shiny, highly reflective metal surfaces and provide the extremely high measurement precision required for the machine. “We’ve learned a great deal about
Micro-Epsilon’s confocal displacement sensors on this project,” concludes House. “The experience and knowledge that
The non-contact confocal displacement sensor is able to measure on shiny, highly reflective metal surfaces and provide the extremely high measurement precision required for the machine
we’ve gained from this will stand us in very good stead for future customer projects, particularly where high precision measurements on shiny, highly reflective metal components are required.”
CONFOCAL MEASURING PRINCIPLE The confocal chromatic measuring principle works by focusing polychromatic white light onto the target surface using a multi-lens optical system. The lenses are arranged so that the white light is dispersed into a monochromatic light by controlled chromatic deviation (aberration). A certain deviation (specific distance) is assigned to each wavelength by a factory calibration. Only the wavelength that is exactly focussed on the target surface or material 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. Both diffuse and specular surfaces can be measured using the confocal chromatic principle.
Micro-Epsilon T: 0151 355 6070
www.micro-epsilon.co.uk Enter 314
/ FACTORYEQUIPMENT
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