Electricity and Control February 2020

SENSORS + SWITCHES

At a glance ■  In this application, relating to the process of fine sanding of veneer surfaces for large table tops, photoelectric sensors have replaced mechanical switches. ■  The sensors detect the contour and cut-outs of the furniture panel and control the up and down movements of the individual pressure shoe segments of the sanding machine accordingly, via a PLC, to ensure precise edges.

The controller receives an image of the workpiece from the sensors and controls the lowering of the individual sanding segments.

Small sensors, high performance Sensor specialist ifm electronic’s 06H201 diffuse reflection sensors feature an adjustable range from 2 to 200 mm. The maximum range is colour independent. It applies, for example, to white surfaces with 90% remission and to black surfaces with just 6% remission. The sensors do not need to be adjusted for surfaces of different reflectivity. The diffuse reflection sensors suppress background interference effectively. Depending on the distance and the degree of remission of the object surface, distances of only a few millimetres can be differentiated reliably. In addition, the background suppression is immune to interference even from highly reflective backgrounds such as stainless steel, or reflections caused by moving machine parts. The clearly limited round light spot, only 8 mm in diameter (at maximum range), provides a homogeneous light distribution in the light cone. This ensures additional reliability, especially in this application where the sensors are mounted close to each other. The high-performance 06 photoelectric sensors ensure optimum sanding results.

Optical contour detection Now 51 compact ifm 06 diffuse reflection sensors detect the contour and cut-outs of the furniture panel from the front and another 51 from the back, as each panel is moved forward and backwards underneath the sanding belt. Depending on the workpiece geometry and the individual cut-outs, the sensors control the up and down movements of the individual pressure shoe segments via a PLC. This avoids excessive pressure on the edges by neighbouring pressure shoe segments. The results are precise, right- angled edges. The requirements on the photoelectric sensors that are aligned like a scanner strip are high. Different veneers with light, dark, matt or glossy top surfaces have to be verified reliably without the sensors needing to be adjusted. Simultaneously, the background – that is – the contact area has to be suppressed. Depending on the thickness of the furniture panel this can mean a range of a few millimetres, so sensors with precise background suppression are required.

In the sanding process 53 lowerable pressure shoe segments adapt to the surface of the workpiece geometry to prevent unwanted rounding of the edges.

Ifm’s 06 diffuse reflection sensors are mounted inline to detect the contour and cut-outs of the furniture panels and control the movements of the pressure shoe segments via the PLC.

Electricity + Control

FEBRUARY 2020

29