Triangular and CCD technology boost displacement sensor capability

Citation

(1998), "Triangular and CCD technology boost displacement sensor capability", Sensor Review, Vol. 18 No. 2. https://doi.org/10.1108/sr.1998.08718baf.002

Triangular and CCD technology boost displacement sensor capability

Triangular and CCD technology boost displacement sensor capability

Keywords Displacement sensors, Keyence, Sensors

Monitoring the depth of a golf ball's dimples or the depth and shape of a tyre's tread; measuring the shape or the size of a product; ensuring the presence or absence of a small component; controlling the thickness of solder paste on a PCB; checking the width and thickness of plate and sheet materials after rolling; monitoring coating thickness ­ wet or dry; checking the shape of biscuits: these are just a few of the industrial applications for which the LK Series laser displacement sensors from Keyence have demonstrated their suitability, it is claimed.

The two members of the LK Series (LK-031 and LK-081 ) use triangulation measurement technology and are designed around a newly developed CCD (charge coupled device) and a 32-bit processor for the precise measurement of height, width and position, measurements that are unaffected by the colour or surface texture of the target or by stray light.

Conventional displacement sensors employ a position sensitive detector (PSD) as the light receiving element. The CCD in the LK Series provides previously unobtainable resolution coupled with high accuracy and minimum interference.

Technical note

Whereas conventional displacement sensors employ a position sensitive detector (PSD) as the light-receiving element, the LK Series uses a charge coupled device (CCD). In both types the light reflected by the target passes through the receiver lens and is focused onto the PSD or CCD. The PSD uses the light quantity distribution of the entire beam spot entering the light element to determine the beam spot centre and identifies this as the target position. The distribution of light quality is affected by the surface condition of the target causing variations in the measured values. The CCD detects the peak value of the light quality distribution of the beam spot for each pixel and identifies this as the target position. Therefore, the CCD enables stable highly accurate displacement measurement, regardless of the light quantity distribution of the beam spot.

Several other in-built benefits help to maximise the customer advantages of the LK Series. For instance, the sensors include laser flash time control (LFTC) circuit that can automatically control the laser emission time according to the target surface condition. This facilitates the stable measurement of glossy metal targets, low reflective black rubber targets, and those with various colours with no reduction in measurement accuracy.

Another feature, Auto Gain, automatically adjusts the amplification factor of the light receiving signal according to the received light quality and is thus able to rationalise the signals from glossy and low reflective targets. Response speed selection is a function used to switch the measurement averaging time between 0.5 and 4ms (1 and 8ms for the LK-081) for the measurement of targets with wide colour differences. It also allows the sensor to ignore sporadic changes in measurement data.

Plate 2 LK diagram

An LED indicates the operation condition. It flashes yellow when the target is outside the measuring range, or if the amount of the received light is too small or too great, and it lights yellow when the target enters the measuring range. The LED lights green when the target approaches the centre of the measuring range. These features are combined in the LK series to deliver a small yet rugged instrument with a resolution of 1µm and a linearity of only ± 0.1 per cent of full scale regardless of target surface properties. Because the LK Series offers a minimum beam spot diameter of 30µm it can be used for extremely accurate measurement of surface contours such as the pin alignment on ICs and the presence or absence of rings and washers on mechanical assemblies.

Two models are available: the high-precision LK-031 (with a reference distance of 30mm) and the long-distance LK-081 which has a reference distance of 80mm. Weighing only 260g and 385g they measure only 85 x 76 x 26mm and 95 x 76 x 26mm respectively. Enclosed in an IP-67 housing, they are rugged enough for the industrial environments in which they are used and, because they are so small, they can easily be retrofitted to existing machinery. The controller, which is located remotely, measures only 140 x 10 x 89mm, is just as easily sited.

For further information contact: Keyence UK Limited, 504-510, Elder House, Station Square, Milton Keynes, Buckinghamshire MK9 1LR, UK. Tel: +44 (0) 1908 696900; Fax: +44 (0) 1908 696777.