Do You Know The Performance Indicators Of Single-line Lasers in Industrial Applications?

Search a word line laser on the network, a variety of manufacturers and pictures are dazzling, it can be said that it is quite rich, but many technicians in the field of machine vision equipment manufacturing still often hurt their brains, why?

We can find that all are a line, the linear look is very "word", then why bother people? See the following:

The first kind of trouble: is the mystery of uniformity indicators, see the figure above to find problems, can find:

Bright at both ends or bright in the middle, uneven thickness, uneven brightness

It's broken at the ends, but it's good in the middle

The background stray light is more

The second kind of trouble: easy to break, it becomes dark when used, the laser is still alive but only shimmering

Installation and commissioning are good one day, the next day is broken

Put it on the client side, it breaks in a few days

Over time, gradually change.

The third kind of trouble: red, green, blue, and purple, the price from tens of dollars to tens of thousands of dollars, how to choose?

Why do people say blue light is good? Should I use blue light?

Why does one cost 8~9 thousand yuan or even tens of thousands of yuan, while the other only 300 yuan?

The following share our experience in developing industrial machine vision lasers one by one, and hope to contribute to you as a little knowledge!

[Basic] How is a line laser generated?

The devices that can generate one-line laser include column mirror/wave mirror, Powell prism, and DOE diffraction element, which are common. The device materials are plastic and glass. Among them, the first two methods belong to the content of geometric optics, DOE belongs to the technology of diffraction optics, they each have advantages and disadvantages. We focus on the Powell prism-based line laser, and other methods to generate line products, and do not recommend or even oppose the use of industrial machine vision, especially in the field of 3D measurement.

Online circulation of the Powell prism to achieve the principle diagram of the beamline, you can see that the Powell prism has a curved ridge, the ridge curve processing quality will determine the quality of the line laser. If you are familiar with Zemax, simulate the distribution function of the ridge curve and compare it with the column mirror to understand the difference. It does not matter if you are not familiar with it, remember that in the three methods, the Powell prism is the king, and choosing it is the first step not to worry.

Problem-solving of the first kind

The core of the first kind of trouble is the mismatch of the quality of the device that generates the first line, such as the natural characteristic of the column mirror is that the edge will slowly darken, and the wave mirror can be understood as a plurality of column mirrors connected together to improve the degree of edge darkening, but there is still an uneven. Therefore, such devices generated a word line, its uniformity index is difficult to reach more than 85%, such as easy to appear at both ends of the broken line, but such products in the linear indication such as line guidance and other scenes, enough to meet user needs, coupled with a huge amount of cheap, happy to see, is the most common class of first-line laser.

DOE type line, the advantage is super thin, also cheap, but prone to central zero light spots, and easy to appear on the dark object discrete breakpoints, such devices are also indicative of the light source, to show people can do an indicator light, can not be used as a machine vision 3D measurement information light source.

The first-line laser generated by Powell prism is the only choice to meet high-end industrial needs, but it will also appear at both ends of the light or dark situation. The Powell prism, whose processing quality meets the design requirements, can achieve more than 95% uniformity of Gaussian beam shaping into a type of beam, and the best case can achieve a 99% uniformity index.

The reason for the above problems depends on the matching degree between the design parameters of the Powell prism and the parameters of the incident beam. Simply put: Assuming that the Powell prism design incident light spot diameter D=3 mm, if the actual incident light beam diameter R= 3.2mm, then there will be dark at both ends, if the actual incident light spot is 2.8mm, there will be bright at both ends, the greater the deviation, the greater the degree of unevenness. The figure below shows that in debugging, the difference of 0.1 mm between D and R can distinguish the obvious non-uniformity.

The second kind of trouble is solving puzzles

This is annoying, but the reason is very simple: the current over the threshold causes the LD to be broken down or the LD to work at the Max upper limit in the specification for a long time. A lot of drive circuit schematics on the Internet can be used, but the devil is hidden in the details.

This can happen if the circuit is designed in a bad way, there is no ESD protection, or an inappropriate capacitor is used. LD laser diode is an electrostatic sensitive device, very fragile and delicate fear of static electricity. A lot of constant current source design circuit is analyzed, there is PWM signal regulation there is overshoot current, just on the moment peak current spike, external current leakage, and other problems, and even some drive board for A plant LD is very stable, B plant LD is prone to problems. If the circuit with these problems is sealed as a finished product by a manufacturer without an external control card, it is not easy to expose the problem, but the field of machine vision always needs an external control card to synchronize with the camera, which will expose the limitations of such products.

How to solve and avoid this kind of thing? The installation and commissioning environment must be well grounded, personnel must wear ESD rings, and electrostatic discharge devices must be added to avoid installation and commissioning problems. At the same time, the choice of a reasonable design is also very critical, the core is the device standard and must use industrial standard components, any small device quality that is not up to standard will lead to design quality failure. In terms of detection, it is very important for the laser module to pass the ESD4KV electrostatic test and voltage surge detection, which requires the joint grinding of the manufacturer's design and assembly process, and the lack of design ability can not solve such problems from the root.

When this kind of thing is encountered, from the user's point of view, you can only pay close attention to changing manufacturers and choosing professional industrial machine vision laser manufacturers. From the perspective of the manufacturer, we must pay close attention to reviewing the design and testing out hidden dangers, and find out the design defects through high-intensity testing and verification, including the circuit and structure. Because of the strange user scenarios, the only thing to do is to accumulate experience and iterate quickly to improve quality.

The third kind of trouble puzzle

This kind of thing is purely inexperienced, I hope to read this little knowledge can be solved. The choice of wavelength depends on the application scenario, red light has good recognition on the surface of non-metallic materials such as plastics, and the response curve of many cameras is better in the red band. So you'll see a lot of machine vision projects with red light. Blue light has better recognition on the surface of metal materials. The wavelength of green light is between red and blue, and the human eye is the most intense perception, the power is very small green light human eye perception will feel the brightness is very high, hope that the human eye's perception of strong scenes green light is, of course, the first choice, but do not want the human eye to perceive the scene, then choose 800~940 nm such as the invisible laser. Therefore, the core factor is the application scenario and the camera configuration, which two factors determine the wavelength of the laser should be selected.

As for whether the price is annoying, different people have different opinions. 10,000 yuan laser, can be accepted by the market is the reason: the line width is very thin 10~100 μm, the consistency is very high, the deviation of thousands of indicators can be maintained within 5%, the uniformity of more than 95%, the straightness is not more than one thousandth, plus the brand premium, the essence is to spend money to buy peace of mind, spend money with the strengths of others to increase the competitiveness of their products. Putting aside the brand premium, a thousand yuan laser, its performance indicators are definitely much higher than hundreds of lasers, therefore, out of the performance indicators to discuss the price, is the source of trouble. The solution is to return to the first and second kinds of problems to study carefully, figure out the reasons and technical principles, and then choose the right product, make a reasonable budget according to the indicators, and naturally will not be troubled by price.

Contact information:

If you have any ideas, feel free to talk to us. No matter where our customers are and what our requirements are, we will follow our goal to provide our customers with high quality, low prices, and the best service.