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INTRODUCTION
By originally pioneering
"light reflection-diffraction interference method,"
We were able to achieved ultra-compact size and high
linear precision with micro linear encoders.
The Canon Micro Linear Encoder ML Series uses LED
as its light source and is equipped with the optimum
optical technology. It is not a traditional encoder;
rather, it is a linear encoder of the next generation
with super-high precision and ultra-compact size.
Combined with an interpolator, it is capable of achieving
a high resolution of 0.8 nm.
FEATURES
- Since an optimum optical system
detecting the interference of reflected and diffracted
beams, alignment and adjustment are easier than
on a permeable type.
- The use of a scale makes it more
stable with respect to changes in the ambient environment
conditions compared with the traditional laser interference
length-measuring instruments that use laser wavelengths
as the standard for measurement.
- Since an LED is used as the light
source, the expected life is significantly improved
over the type that uses semiconductor laser.
- Since the relay box contains an
electrically partitioned HIC in its interior, making
this system more compact.
THEORY
As shown in the figure,
the light beams emitted by an LED are made into parallel
light beams by a collimator lens, separated into three
optical beams (orders 0, +1, and -1), and are irradiated
to a scale. Two of these optical beams (diffracted
beams of orders 0 and -1) are used for the encoder
while the other beam (diffracted beam of order 1)
is used for the initial point.
The theory behind encoder
measurement is as follows: first, the diffracted beam
of order 0 and the diffracted beam of order 1 are
irradiated to the scale placed opposite from the head,
as shown in the figure. The diffracted beams of orders
+1 and -1 generated here are composed by a diffraction
grating (on the head side) divided into 4 parts and
then injected into a lightreceptor element.
The optical beams diffracted
by the scale here have the property that their phase
slides by ±2π
when the scale slides by one pitch. As a result, if
the scale moves by one pitch at the light-receptor
element, two sinusoidalcurve signals are obtained;
further, because the grating that composes the light
beams is divided into 4 parts, each with a 1/2 pitch
interval, four signals are sent with a phase difference
of 90 degrees. The ML-08 type has a scale pitch of
1.6µm and sends output signals with a period of 0.8µm
from the head; the ML 16 type has a scale pitch of
3.2µm and sends output signals with a period of 1.6µm
from the head; and the ML-20 type has a scale pitch
of 4.0µm and sends output signals with a period of
2.0µm from the head. The theory of initial-point measurement
functions as follows. Light beams are diffracted on
the initial-point sensor side with respect to the
light source. These beams do not enter the light-receptor
element when an end of the scale is reached but rather
follows the light path shown with the dotted line
in the figure. The output from the light-receptor
element becomes small as a result, and this helps
detect the initial point.
APPLICATION
EXAMPLES
- Sensor for
Linear Motor Stages
- Hard Disc
Detectors
- Semiconductor
Measuring Instruments
- Three-Dimensional
Measuring Instruments
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