Fans in the background have left messages wanting to understand the knowledge of galvo control. To start from the end, let’s first discuss its acceleration control.Below is a galvo, an XY galvo consists of two such components.
Essentially, a galvo can be viewed as: a mirror + a motor. This motor is a deflection motor, operating on the same principle as a galvanometer.When powered, due to the inertia generated by components like the mirror and motor rotor, there are issues of “braking” and “deceleration”.This issue is easy to understand and very important. In the FDM sub-industry, TuoZhu Company has solved this problem well, creating a giant.—-Technical Principles—–Consider the following path: the laser marks sequentially from 1-2-3, with 2 being the turning point. The galvo must first decelerate and then accelerate upon reaching this point; how can we ensure that it does not stop here and that the spot moves uniformly?
This is what sky writing aims to achieve; essentially, it is an algorithm. Note that sky writing has been around for two to three decades.There are three processing methods, which we will explain according to the SCANLABS manual (as only their manual can be obtained from the official website without registration).Most manufacturers provide three modes: Mode1, Mode2, Mode3 –>The meaning of the dashed line in the figure: The laser is off, only the galvo is moving (jumping) –>The meaning of the solid line in the figure: The laser is on, and the galvo is also on (marking)Mode1: (1) Marks along 1-2 at a constant speed, turns off the laser at point 2, and the galvo begins to brake. Therefore, it will travel a bit further and then return to 2; (2) After returning to 2, the laser is still off, and the galvo moves backward in the opposite direction along the next segment (2-3), starting to accelerate until it reaches the predetermined speed at point 2, then turns on the laser to mark the next segment.Remember: this method requires “four segments” of extension + retraction on the paper.Mode2: (1) Marks along 1-2 at a constant speed, turns off the laser at point 2, and the galvo begins to brake. This means it will travel a bit further until it completely stops at 3; (2) At this point, the laser is still off, allowing the galvo to move to 4, which is a point on the reverse extension line of the next line. From 4, it starts to accelerate until it reaches the predetermined speed at 2, then turns on the laser.Mode3: This mode operates exactly like Mode2, with the only difference being: it allows setting an angle a, and only when angle a is less than a certain value will it initiate forward and backward movements.Because when the angle is large (180 degrees is a straight line), the inertia effect is minimal (gentle), and there is no need to waste time.Thus, Sky Writing is a method for handling the acceleration and deceleration of the galvo, with several points to note: (1) Sky Writing is aimed at high-precision scenarios; low precision is unnecessary. With the rise of 3D printing, it has developed rapidly. Its biggest issue is time overhead.[Domestic galvos and imported galvos are not significantly different in most performance aspects, but in terms of acceleration and deceleration performance (time overhead), there may be a difference of 20% or more, which is an area where domestic manufacturers need to improve] (2) Its control is pre-written on the control board, requiring only configuration; (3) It can be seen that Mode1 has a larger time overhead compared to Mode2 and Mode3, so the vast majority of 3D printing only chooses Mode3 (Mode3 covers Mode2).Regarding debugging:Debugging Sky Writing is very complex; without knowledge of galvo programming control, it is nearly impossible to start. Even through some “hard testing” methods, such as using photo paper, it is not possible to understand its operating mechanism.Those who do not know programming cannot debug the galvo effectively.There will be a dedicated detailed chapter on debugging Sky Writing later, but this involves complex program design and algorithm design, requiring extensive foundational knowledge, which may need to be divided into many chapters. Interested parties should stay tuned.Further updates on galvo control methods will follow.