Non-contact Thread Detection

This application specific configuration of Kaman's KD-2440 system
provides an adjustable analog signal to differentiate between a tapped
hole and one that has only been tap drilled.

Eddy current sensors produce an electro-magnetic field that emanates from
the sensor to a diameter equal to approximately 3 times the sensor diameter.
This oscillating field induces eddy currents in the surface of a conductive
material that engages the field. The influence of the resulting eddy current field
on the coil field is proportional to the distance between the coil and the
conductive 'target' material.

By inserting an appropriately sized eddy current sensor into a tapped hole, an
analog voltage proportional to the radial distance between the sensor and the
tapped hole surface is produced. As the surface of a tapped hole is not flat, the
output of the system is in fact an average of the peaks and valleys of the thread.
Thus the output is indicating the pitch diameter of the thread.

If the hole were not tapped, the output of the system would indicate the tap drill,
or minor diameter of the thread.

The KD-2440 sensor inserted into a tapped hole can distinguish between the
tap drill diameter of an untapped hole, and the pitch diameter of a tapped hole!

With the "Side View" sensor the KD-2440 can be used in conjunction with
waveform analysis tools to provide thread quality

Features & Benefits
* High resolution for fine pitch threads
* Adjustable gain analog output
* Adjustable switched output
* 10KHz frequency response
* Low switch point hysteresis
* 12-24 Vdc input

Thread detection is becoming a critical QC check in many industries today. Manufacturers not only want to determine if the hole in question was tapped,
in some cases they want an indication of the actual quality of the threads
cut into the component. Given the shear volume of tapped holes in metal
components, the only cost effective, competitive way to go beyond SPC
methodologies is to automate the inspection process.

Take as an example a flange with 4 tapped holes used for mounting. The holes
are tapped simultaneously at a rate of 6 flanges per minute. While it was easy
to pull one flange every half hour and check the threads with a thread gage,
this is not a method that is feasible when the penalties from the customer for
a bad part on the line clearly indicate 100% inspection is required.

A clear solution is to utilize 4 channels of Kaman's KD2440 systems.
With the sensors gang mounted onto an air cylinder driven flange, all four
holes can be checked simultaneously as the air cylinder positions the
sensors into the tapped hole while the flange is momentarily stopped,
and properly oriented on the transport belt.

Automation is achieved by inputting the analog output of the KD-2440 into
the control system. The controller is programmed to compare the analog
output of each KD2440 system to a predetermined value. If the values do
not match within the programmed tolerance, the part is rejected. A diverter
plate downstream of the inspection location ensures that bad parts never
reach the end of the transport belt.

For more information contact:-

Malcolm Read at Ixthus Instrumentation

March 2002

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