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Actuator automates automotive component testing

Edited by the Engineeringtalk editorial team Jan 10, 2006

Ever stricter specifications for the acceptance of automotive parts have increased the pressure for 100% quality inspection of all manufacturing processes over the last few years.

Ever stricter specifications for the acceptance of automotive parts have increased the pressure for 100% quality inspection of all manufacturing processes over the last few years.

Thread inspection is no exception.

Until recently the common practice has been the use of eddy current probes, lasers, proximity sensors or a vision system.

These systems were successful to some degree in the past but today's quality-conscious end customers need to know more than just the presence of a thread.

A major automotive manufacturer has recently chosen an automated thread checking solution developed by SMAC for 100% quality inspection of tapped threads in a cylinder head.

The manufacturer's requirement included checking for: thread depth; number of threads; faults such as crossed thread, no thread; and oversize/undersized thread indicating worn or damaged tap.

Other requirements were: high throughput; objective measurement data output for each part for quality control; reliability - 24/7 operation; and a cost effective solution.

The traditional method for checking threads would have been by hand with a screw plug gauge.

This process is labour intensive, subject to human error and relies on a skilled workforce.

The SMAC solution takes this well proven manual technique and automates it allowing it to be integrated into a modern production environment.

A conventional thread gauge is mounted on a linear/rotary actuator (in this case an LAR55-100-75FS).

All of SMAC's LAR series actuators have high resolution linear and rotary encoders for precise position measurement of angle and distance.

These data are monitored by the controller and compared with pass/fail parameters to identify and reject faulty parts.

It can also be interpreted and fed back to a database for a complete quality control history.

To carry out the checking procedure, SMAC's unique softland routine is employed to find the part, landing with a controlled, low force so as not to damage the gauge.

While maintaining a low contact force, the actuator then rotates anticlockwise until the thread gauge drops into the thread (indicated by a sharp change in linear position).

It then rotates clockwise at a predetermined torque, driving the gauge into the thread (an overtorque situation indicates a fault such as crossed thread, insufficient thread depth or excessive debris).

Other checks that can be carried out include measuring linear motion during one rotation of the rotary axis confirming the pitch of the thread and a push-pull test with the rotary axis held stationary giving the play in the thread.

When combined with SMAC's controllers, the actuator is fully programmable in position, velocity, acceleration and force, and therefore can carry out a comprehensive, qualitative check of a screw thread in just a few seconds.

Part changeover is achieved simply and easily by selecting a different program (either memory-resident or downloaded via RS232) and if necessary, changing the thread gauge.