Sensor for machine guidance made available to all

Originally developed to enable feature location and machine guidance in aircraft production, a high speed, non-contact position sensor is broadly applicable to production of large components.

Originally developed by Meta Vision Systems for Boeing's factory in Long Beach, California, to enable feature location and machine guidance in aircraft production, a high speed, non-contact position sensor that is broadly applicable to production of large components throughout manufacturing industry has been launched by Meta.

Employing a pair of laser stripes at right angles to each other, the new Digital MXS sensor is able to identify the position of a feature to within a few microns and use the feedback signal to send offsets to the control driving a robot or machine tool.

In this way, the exact location of the feature is known as well as the orientation of the often-complex surface at that particular point.

So countersinking or tapping a hole, for example, can be performed accurately and normal to the surface.

Were this not the case, a skewed countersink could compromise the strength of a subsequent riveting operation, while if tapping is not co-linear the tool might break and the component may have to be scrapped.

Where components are of relatively modest size, such a system is not needed.

The part is fixtured in a known position on the table of the machine tool and the program controlling its axes always presents the tool at the exact position and correct orientation.

However, for big and sometimes flexible components such as are found in the aerospace industry, machine tools are very large and expensive and so too are the fixtures for clamping the parts.

There is also a considerable cost associated with storing and periodically calibrating the large number of fixtures needed.

Moreover, batch runs are often short, so set-ups can consume a large proportion of production time.

It is not surprising, therefore, that manual production methods are still widely used, as they do not require the part to be fixtured accurately - merely supported.

One way to combine such versatility with the productivity benefits of automated CNC machining, and so achieve an agile production environment, is to use a robot equipped with a spindle and fit a Digital MXS sensor, or similarly equip a conventional machining centre.

This approach eliminates the need for precise location of the part in an expensive fixture; only simple, low cost clamps are needed to hold the workpiece.

With a contact probe there is always a risk of damage due to collision with the component, but this is eliminated with a non-contact sensor.

For the same reason, the latter can safely approach the component more quickly than is possible with a touch sensor, eliminating the cycle time penalty of slow-approaches.

Absolute reliability of operation is assured, as the Digital MXS includes filters to remove light wavelengths other than those of the laser, so changes in the ambient lighting conditions have no effect on sensor operation.

An additional advantage of using this vision technique is that in-process measurement may be incorporated as a matter of course.

When the sensor locates a hole centre, for instance, the data fed back to the machine control includes, in addition to its position, such information as hole diameter, size of countersink, angle of the component surface and the height of the sensor (and hence of the tool) from it.

The latter information can further speed productivity by over-riding the CNC program to enable faster rapid infeed to the next cut.

Two versions of the Digital MXS sensor are available with 10mm and 20mm field of view, having nominal stand-off distances of 30mm and 63.5mm respectively.

The former is the most accurate, enabling height, centre detection and tool angle measurement to within +/-4.3 microns, +/-3.6 microns and +/-0.3 degree of arc.

Accuracy of hole diameter measurement is +/-7.6 microns and that of countersink depth is +/-22 microns.

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