标题: 关于co2切割机的,会有帮助 [打印本页] 作者: loveme 时间: 2004-2-10 01:31 标题: 关于co2切割机的,会有帮助 How to choose the right focal length lens for your application
Cutting Applications
The first consideration to take into account when choosing a lens focal length for cutting applications (apart from some specialized cases to be covered at the end of this section) is the depth of focus requirement for the material to be cut. Two factors must be added together to determine this requirement: the thickness of the material to be cut, and the worst case vertical positional tolerances that will occur during the cutting process (the distance between the lens and material).
What is the depth of focus? The laser beam enters the lens and converges to a focus, after which it diverges. Optimal cutting occurs at the focused point. The depth of focus serves as a guide to the user as to how far from the point of focus there is still likely to be sufficient power density (laser power ÷ encompassed area) to make a cut. There are several definitions of depth of focus. For instance, one definition allows for a 50% drop in power density, yet another allows a 25% drop from the maximum value.
The true value varies from material to material, depending on its melting threshold. The depth of focus for metals, for example, is less than for plastics.
The photograph below shows the cross section of the beam around the focus point for 2.5, 4 and 5 lenses. The arrows indicate the approximate depth of focus for this material (acrylic), and the line indicates the position of focus. Note that the 5 ‘print’ extends off the sample.
These focused beam prints can be made by traversing a low power beam over an angled acrylic piece (with the paper still on).
In summary, the focal length of the lens used in a cutting application must provide a depth of focus based on the material thickness, plus any vertical height variations that may result during the cutting process through positioning or height fluctuations in the material itself.
The second consideration when choosing a lens for laser cutting applies to the cutting of thin material, where the total depth of focus requirement is less than 0.04. Because the depth of focus requirement is very small, the temptation is to select a very short focal length lens. Here, an optical rule comes into play: if the focal length ÷ beam diameter at the lens is less than 5, the focus will become seriously distorted, and processing speeds will drop. This effect is called spherical aberration, and applies to plano-convex lens, and meniscus lenses to a lesser extent.
Some helpful equations:
Focus spot diameter = Ö (depth of focus ÷ 231)
Focal length = 61.7 x beam diameter at lens x focus spot diameter
Note: All units are in millimeters. For CO2 laser only, with beam quality M2 £ 1.2. Beam diameter is taken as 1/e2 (86% of value)
How to choose the right focal length lens for your application[BR]Cutting Applications[BR]The first consideration to take into account when choosing a lens focal length for cutting applications (apart from some specialized cases to be covered at the end of this section) is the depth of focus requirement for the material to be cut. Two factors must be added together to determine this requirement: the thickness of the material to be cut, and the worst case vertical positional tolerances that will occur during the cutting process (the distance between the lens and material).
What is the depth of focus? The laser beam enters the lens and converges to a focus, after which it diverges. Optimal cutting occurs at the focused point. The depth of focus serves as a guide to the user as to how far from the point of focus there is still likely to be sufficient power density (laser power ÷ encompassed area) to make a cut. There are several definitions of depth of focus. For instance, one definition allows for a 50% drop in power density, yet another allows a 25% drop from the maximum value.
The true value varies from material to material, depending on its melting threshold. The depth of focus for metals, for example, is less than for plastics.
The photograph below shows the cross section of the beam around the focus point for 2.5, 4 and 5 lenses. The arrows indicate the approximate depth of focus for this material (acrylic), and the line indicates the position of focus. Note that the 5 ‘print’ extends off the sample.
[IMG alt= hspace=0 src=C:\Documents and Settings\TINA\My Documents\My Pictures\8-2.jpg align=baseline border=0]
[BR]These focused beam prints can be made by traversing a low power beam over an angled acrylic piece (with the paper still on).
In summary, the focal length of the lens used in a cutting application must provide a depth of focus based on the material thickness, plus any vertical height variations that may result during the cutting process through positioning or height fluctuations in the material itself.
The second consideration when choosing a lens for laser cutting applies to the cutting of thin material, where the total depth of focus requirement is less than 0.04. Because the depth of focus requirement is very small, the temptation is to select a very short focal length lens. Here, an optical rule comes into play: if the focal length ÷ beam diameter at the lens is less than 5, the focus will become seriously distorted, and processing speeds will drop. This effect is called spherical aberration, and applies to plano-convex lens, and meniscus lenses to a lesser extent.
Some helpful equations:
Focus spot diameter = Ö (depth of focus ÷ 231)[BR]Focal length = 61.7 x beam diameter at lens x focus spot diameter[BR]Note: All units are in millimeters. For CO2 laser only, with beam quality M2 £ 1.2. Beam diameter is taken as 1/e2 (86% of value) [BR]