タイトルまたは説明

Laser Marking Heads (Laser Scanners, Optical Scanners, Scan Heads)

A whole laser marking head (or called laser scanner) consists of two scan mirrors, two galvanometers (or called galvo-scanner motor) & drive cards, a XY mount, a scanning lens (f-theta lens), an interface card (or called D/A card), a set of marking software and a DC power supply. Two types of scanning optics for CO2 and Nd:YAG lasers are available.

Basics of *-axis laser scanners

Field of scan

The laser beam will be scanned over an angle q, equal to twice the mirror deflection angle. So, the typical scanned field might be q=±*0° in both X and Y directions. (q=±*5° would be the usual maximum scanned field). The field size is then approximately 2Ftanq? in both X and Y.

The approximation arises because:

1) it is usually desirable to have a deliberate distortion characteristic in the scanner lens design so that the field position is proportional to q, not tanq.
2) scanning in two axes produces a geometrical distortion which is unrelated to the lens properties.

Focused spot size

The lower limit on spot size ‘d’ (1/e2 intensity diameter) for a laser beam of diameter ‘D’ (1/e2) is:

d = *3.5QF/D mm

Example: A TEM*0 beam (Q=1) of *3.5mm (1/e2) diameter, focused by a perfect lens of **0mm focal length, will form a focused spot of **0mm diameter. (Taking a more realistic value of Q=1.5, the spot size would be **0mm).

Beam clipping and optical aberrations can lead to focused spot sizes which are larger than the minimum diffraction limited value found from the equation above.

Large field sizes demand the use of lenses of long focal length. In turn, this leads to increased focused spot size unless the beam diameter, mirror sizes, and lens diameter are all increased.