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By originally pioneering "light reflection-diffraction interference method," We were able to achieve 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

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