Quote
misan
The advantage of using a closed-loop system is to compensate for potential errors, that means no more missed steps.
Cost reduction is not a goal, but we are trying to get this working within a similar cost range as steppers. This solution space has been explored, tested and discarded in the past for RepRap mostly because of its high cost. That is why I am so conscious about its potential cost.
You should get better linearity from a closed-loop position control than from a stepper.
Hello both you Misan and AndrewBCN,
Misan, I do not understand why missed steps is a concern. I don't say this out of arrogance but I am fairly late to the 3d printing world - SO what I would say is that, if your 3d printer is missing steps, it is because it is not designed properly or is in need of maintenance. The only time I see my printers (Delta and a CoreXY) missing steps is when something is terribly off - Such as wrong heights so it is hitting the sides. Am I misleading my self here?
I DO realize that the potential intelligence that you can build into your system with closed loop is significant. For example if your printer hits the side you can have it go back 5 steps and then forward again and if that still does not do any good it stops moving. And more sophisticated you can implement some control schemes which handles the dynamics in high speed printing much better. Especially adaptive algorithms that based on some acceptable errors intervals can optimize the regulation parameters for perfect jerk moves. This will especially be relevant with future heavier multi-color extruders.
Finally for applications like mine and for future miniature printers where it is desirable to have very small and light motors. This could also be to solve the elasticity problem of bowden extruders. If you can cut the weight in half of the extruder then it may be more acceptable to have it together with the hotend.
Why did inkjet printers move from steppers to servos? Was it a necessity because of the demands on modern inject controls or was it simply the price?
On the same topic I found the following on [www.amci.com]
"steppers are simpler to commission and maintain than servos. They are less expensive, especially in small motor applications. They don't lose steps or require encoders if operated within their design limits. Steppers are stable at rest and hold their position without any fluctuation, especially with dynamic loads.
Servos are excellent in applications requiring speeds greater than 2,000 RPM and for high torque at high speeds or requiring high dynamic response. Steppers are excellent at speeds less than 2,000 RPM and for low to medium acceleration rates and for high holding torque.
Stepper vs. Servo: The Verdict
Servo control systems are best suited to high speed, high torque applications that involve dynamic load changes. Stepper control systems are less expensive and are optimal for applications that require low-to-medium acceleration, high holding torque, and the flexibility of open or closed loop operation."