	Optical Micrometers

Operating Principle

High-accuracy CCD method

The light emitted from a high-intensity GaN green LED transform into uniform parallel light by passing through the special diffusion unit and collimator lens before being irradiated on the measuring target object. At this time, the image of a shadow created by the measuring target object is projected with high accuracy on the HL (High Speed Linear) - CCD via the telecentric optical system. Based on the received light output sent from the HL-CCD, the D. E. processor (Digital Edge-detection Processor) in the controller and the CPU carry out an operation, and then the dimensions of the target object are displayed and output.

Explanatory image of "High Accuracy CCD Method"

High-intensity GaN green LED + special diffusion unit

The safe and uniform light of the highly reliable GaN green LED with short wavelengths was combined with the special diffusion unit. With this combination, ideal and even illumination light is irradiated on the measuring target object. Thus, a highly accurate image is formed on the CCD and high-resolution is achieved.

Telecentric optical system

The optical system which eliminates unnecessary light and forms only parallel light does not require lens magnification correction even if the position of an object is changed, resulting in highly accurate measurement.

HL-CCD

The CCD comes with the HL-CCD which constantly exposes received light, allowing ultrahigh-speed sampling. Even temporal changes are captured because the mean value is constantly measured within exposure time.

D.E. processor

The edge of the image of the measuring object formed on the HL-CCD is detected through digital signal processing, which is rarely affected by a change of light intensity caused by contamination on the window, foreign matter, or dust. Moreover, by changing the threshold, even transparent objects can be detected.

Detection of glass board by changing the threshold

Changing the threshold affects detection

Scanning method

The beam emitted from the semiconductor laser is reflected by a 12-surface polygon mirror and a planar mirror. The beam passes through a collimator (Fθ lens).
After scanning the target, the beam is converged through the receiver lens and converted to an electronic signal proportional to the received light intensity. Based on the timing of the shadow produced due to laser beam interruption by the target, the target dimension is calculated.
*What is an Fθ lens?
An Fθ corrects the scanning rate of the laser beam so that the rate is constant.

When using an Fθ lens

An Fθ lens is designed to make the scanning rate at the periphery of the lens equal to the rate at the center of the lens, by combining two lenses with different curvatures.
Using an Fθ lens enables the outer dimension of a target to be measured based on the timing of the shadow produced due to laser beam interruption by the target.

When using an ordinary convex lens

A polygon mirror makes the emitted laser beam scan through angle θ, making length A longer than length B.
The parallel beam scanning the target shifts more quickly closer to the periphery of the lens and more slowly closer to the center of the lens. Since the laser thrubeam sensor measures based on the timing of the shadow produced due to laser beam interruption by the target, using an ordinary convex lens for the instrument causes measurement error.

CCD method

The visible beam emitted from the semiconductor laser diode in the transmitter converges into a parallel beam through the transmitter lens and is transmitted. The parallel beam passes through the band-pass filter in the receiver, and is received by the one-dimensional CCD image sensor in the receiver.
When the laser beam is interrupted by a target, a shadow with an area proportional to the target size is projected onto the receiver. The CCD image sensor scans and calculates the shadow area and position at a 780 c/s sampling rate to measure target dimension or position.

What is a CCD image sensor?

"CCD" is the abbreviation for a Charge Coupled Device.
The CCD image sensor consists of multiple minute photodiodes, or picture elements, forming a line, and is constructed so as to detect how much electrical charge accumulates when light is projected.

As shown below, when light is projected onto a CCD, an electrical charge proportional to the light intensity accumulates on each photodiode. The electrical charge accumulated on each picture element is sequentially detected, and binarized to "bright" or "dark", enabling position information on each picture element to be obtained.

VG Series CCD image sensor

The VG Series receiver uses a CCD image sensor. The dimension of each element in the CCD image sensor is 7 µm 0.28 Mil and the image sensor consists of 5,000 elements, making the detecting range 35 mm 1.38" (7 µm 0.28 Mil x 5,000 bits).

Two-dimensional CCD Method

The illumination light which was uniformly irradiated from the ultra high-intensity green LED is transformed into a highly-accurate parallel light by the optical system, which will be irradiated on the measuring object.
The shape of the object obtained by the irradiation is formed on the high-precision measurement, a 1.3 million-pixel CCD by the dual telecentric optical system.
The dimension of the measuring object which was formed on the CCD is measured through computation. Because the image of the measuring object formed on the CCD is displayed on the PC monitor, edge definition and measurement details can be easily specified on the monitor.

Uniform Diffusion, Ultra High-intensity Green LED

The ultra-intensity green LED with a wavelength of 520mm was adopted. One of the unique features of this LED is that the light volume is large and accurate edge detection is enabled by a highly sensitive CCD. In addition, even illumination light allows highly accurate measurement of wide areas.

Dual Telecentric Lens

One of the features of telecentric lens is that the size of the image on the CCD does not change even if the position of work is moved up or down, maintaining the same precision at all time. Moreover, a high-resolution lens allows highly accurate measurement.

2/3 Type 1.3 Million-pixel CCD for High-precision Measurements

The number of pixels of height x width is 1280 x 1024. A pixel is a tetragonal lattice, 6.7 µm on a side. According to the scale of the optical system, 1 pixel is equivalent to 40µm, and this will be further processed to achieve higher resolution, called sub pixel processing.

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