Page 158 - Sensors and Control Systems in Manufacturing

Classification and Types of Sensors
mirror to become the output laser beam. A low-power laser may 119
require an output mirror reflectivity as high as 98 percent, leaving
only 2 percent to be transmitted. The output mirror that is designed
to transmit a given percentage of the laser light in the cavity between
the feedback mirrors is called the output coupler.
2.12.3 Semiconductor Displacement Laser Sensors
Semiconductor displacement laser sensors, consisting of a light-meter-
ing element and a position-sensitive detector (PSD), detect targets by
using triangulation. A light-emitting diode or semiconductor laser is
used as the light source. A semiconductor laser beam is focused on the
target by the lens. The target reflects the beam, which is then focused
on the PSD, forming a beam spot. The beam spot moves on the PSD as
the target moves. The displacement of the workpiece can then be
determined by detecting the movement of the beam spot.

2.12.3.1 Industrial Applications of Semiconductor
Displacement Lasers
The laser beam emitted from the laser diode in the transmitter is con-
verged into a parallel beam by the lens unit. The laser beam is then
directed through the slit on the receiver and focused on the light-receiv-
ing element. As the target moves through the parallel laser beam, the
change in the size of the shadow is translated into the change in received
light quantity (voltage). The resulting voltage is used as a comparator
to generate an analog output voltage.
2.12.4 Industrial Applications of Laser Sensors*

Electrical and electronics industries:
• Warpage and pitch of IC leads. The visible beam spot facilitates
the positioning of the sensor head for small workpieces.
Warpage and pitch can be measured by scanning IC leads
with the sensor head (Fig. 2.112).
• Measurement of lead pitch of electronic components. The sensor
performs precise noncontact measurement of pitch using a
laser beam (Fig. 2.113).
• Measurement of disk head movement. The laser sensor is con-
nected to a computer in order to compare the pulse input to the
disk head drive unit with actual movement. The measurement
is done on-line, thus increasing productivity (Fig. 2.114).
• Detection of presence/absence of resin coating. The laser displace-
ment sensor determines whether a resin coating was formed
after wire bonding (Fig. 2.115).

∗ A few nonlaser optical sensors are included, as indicated.