Distance sensor is not confused by colour

17 Jun 2002

Engineers in Italy have developed an electro-optic distance detector that does not depend on the surface colour or reflectivity being uniform. This could have industrial applications such as in car assembly lines, where the colour can vary, or in checking the packaging of cakes that have been cooked for different lengths of time.

The device, created by Eureka Engineering, consists of three parallel plastic optical fibres connected to standard red LED light sources and light detectors. Light from the device hits a surface and the angle of the diffused light is recorded so that the distance can be calculated.

Vincenzo Arrichiello, the company's president, commented that most distance sensing devices on the market have one transmitter and one detector and measure intensity of the light diffused from a surface. This means that the reflectivity of the surface must be known to determine the distance and the surface must have a uniform reflectivity. The new device intrinsically compensates for differences in colour.

The signal varies almost linearly with distance so an accuracy of approximately 5% can be obtained with simple computations. Better resolution is possible if a linearity correction is applied to the signal.

The range of distances over which the device works can be changed readily with beam shaping lenses. Arrichiello says that, in theory, the device could measure any distance. However, at long distances it is hard to get a great enough intensity of light to overcome the interference from ambient light so the device works best from millimetres to tens of centimetres. It is expected to have a similar cost to currently available devices as it employs 'off the shelf' components.

The device has been patented in Italy and a European patent is pending. The company, mainly involved in technical consultancy, is now seeking partners who might be interested in a license agreement.

SH