What is Z-Dynamic and how it works
One of the crucial aspects in the manipulation of a laser beam is the control of the focus point. This control can be achieved through the use of different optical lenses, allowing the beam to be tailored to the specific needs of their applications.
Optical lenses are critical to the manipulation of a laser beam. They can converge or diverge the beam, directly affecting its focus point.
One of the most effective techniques for varying the focus point of a laser beam is the combination of different lenses such as concave or convex lenses
Convex lenses are designed to converge the beam, while concave lenses have the opposite effect, defocusing the beam.
The fundamental law of refraction, enunciated by Snell, describes how light behaves when it passes through a medium with different index of refraction.
This law is essential for understanding how optical lenses can focus or defocus a laser beam.
When light passes through a converging lens, the rays will converge toward a focal point. Conversely, a diverging lens will cause the rays to diverge, simulating the origin from a virtual focal point.
The mathematical relationship associated with image formation through a lens emphasizes the relationship between Snell’s law and the optical properties of lenses:
The combination of these lenses provides a synthesis of focal power, enabling precise and adjustable focus points.
When you have three lenses in series, you can calculate the total focal distance of the lens system using the formula of the reciprocal sum of focal distances.
This formula is given by:
In more complex applications, lenses can be conveniently combined to allow for focus variations even over long distances.
Parameters such as spot quality, shape,M2, and MTF are all crucial in assessing the effectiveness and reliability of an engineered optical system. Optimization of these aspects is critical to ensure high-precision and consistent results in advanced laser applications.
- A very good spot quality is characterized by a smooth and concentrated intensity profile.
- The shape of the spot refers to the geometry of the area illuminated by the laser beam. In many applications, an attempt is made to obtain as symmetrical and uniform a spot as possible to ensure accurate results.
- In the vast world of optics and particle physics, the shape of laser spots plays a crucial role in practical applications from industry to scientific research. These spots, often described with Gaussian distributions.
The Gaussian function, expressed mathematically as:
where A is the maximum amplitude, μ is the mean value and σ is the standard deviation, accurately describes the shape of energy distributed in space.
The Gaussian histogram shape equation allows calculation of the value of f(x) at any point in space, providing a complete mathematical description of the laser spot. Integration of the equation over the whole space provides the total energy.
Poprieties of the Gaussian curve are:
- Symmetry: The Gaussian is symmetrical with respect to its mean value μ, implying that the distribution is equal to the left and right of the peak.
- Area under the curve: The area under the Gaussian curve is proportional to the total energy of the spot.
- The parameter M², or beam quality factor, is an indicator of the quality of a laser beam. It measures how far the beam profile deviates from that of an ideal Gaussian beam. An M² value of 1 indicates a perfectly Gaussian beam. Higher values indicate a deviation from the ideal pattern. The M² factor is particularly relevant when considering beam propagation performance over long distances or when precise collimation is crucial.
- The modulated transfer function (MTF) is an indicator of an optical system’s ability to reproduce image details.
Limitations and solutions of 3D markings/engravings
Laser markings on three-dimensional solids can be made within two limits:
The first limitation is physical and is given by the tilt of the laser beam.
In fact, at perpendicularity the laser beam is characterized by a spot of circular size having the maximum amount of energy and consequently the maximum incisivity on the material; moving away from such perpendicularity conditions later, the laser spot gradually becomes more elliptical in size, reducing the energy density and thus the incisivity on the material.
The second limitation is mechanical and is given by the maximum possible travel of the Z-Dynamic.
This travel depends on the optical design used and generally takes values of 35/40mm.
Depending on the case, these limitations can sometimes be circumvented by the use of, for example, a marking/engraving spindle on entire cylindrical surfaces:
Wrapping and Projection and Example of 3D Markings
We have developed technologies that enable us to mark or engrave on complex surfaces with very high geometric precision.
In fact, in addition to simple planar projection, we are able to wrap any flat graphic onto any three-dimensional solid, thus achieving results that are geometrically extremely faithful to what was envisioned at the design stage, thus producing markings/engravings in which geometric distortions are absent.
This type of complex marking/engraving is made possible by the coexistence of two different technologies:
- 3D wrapping à Which allows us to mark geometrically perfect three-dimensional designs
- Z-Dynamic à Which allows us to maintain focus on all points of the surface under consideration.
Below are some examples of 3D marking:
Comparative examples between projection and wrapping of a grid on a truncated cone surface:
Example of marking on a hemispherical surface
Example of 3D de-painting on a car rim
Example of 3D engraving of textures and lettering inside a bottle mold
3-axis head for 3D marking: When to use it?
Considering that a three-axis scanning head has a much higher cost than the traditional two-axis system, it is appropriate to understand when we actually need it and when it is only being offered for economic reasons.
As mentioned earlier, the substantial difference between the two systems relates to the different focal tolerance, that is, the ability to mark a part that, due to its geometric characteristics, is not always at the same focus distance from the laser head.
Considering a marking area of 100×100 mm, a three-axis head usually has a focus tolerance of about 40mm, while the conventional one is limited to a tolerance of about 2mm. It should be specified that larger marking fields allow for a larger focus tolerance.
