Printing Fast Part 1, Jerk and Acceleration

As I put this machine together from a kit and have been customizing since I have often wondered how fast it could really print. There are many articles about the limits of printing, I have always liked experience through trial and error.

When you crank up the speed you start to run in to the physical limitations of your printer. These limitations can be tuned in the firmware of your printer. They are typically called acceleration, and jerk. Acceleration is a fairly common term, it is how fast you reach a target speed. Jerk is a little bit more esoteric, but it is an important value to take in to consideration when trying to reach the fastest speed possible. Jerk is how fast you reach a target acceleration value or how fast the acceleration can change.

When the print head is stopped, your acceleration is at zero. The printer is then commanded to move to a certain position. Jerk is then used to determine how long it takes to get to the maximum acceleration value. Once it is at that acceleration value, the print head will accelerate constantly until it reaches the maximum speed setting. It will then start slowing down at a certain point, calculated by the firmware, for the next move.

It is important to use a firmware that has a look-ahead feature. It can then calculate using the Acceleration and Jerk values quicker movements that allow the print head to maintain speed while remaining within the limits that are programmed into the firmware. Determining these values takes trial and error and are limited by the physical characteristics of your machine. As you print faster, you will have more errors in your print.

The most common error that you will see is called ringing. It is when an axis oscillates when changing directions. It is caused by having either a too fast acceleration speed, or a too fast jerk speed. One axis comes to a stop, but it doesn’t really stop it bounces. The firmware doesn’t wait for it to stop bouncing before it makes the next move. So as the next move is happening, you get an damped oscillation visible in the side of your piece.

This can be reduced in several ways. One method is to adjust the Jerk and Acceleration settings. By slowing down the jerk setting you can increase the acceleration for longer print distances. The drawback with this method is that when you are making smaller details with a slow jerk speed, the overall print speed will be slower. A better way would be able to have a jerk and maximum speed setting for varying print distances. It could be linearlly varied to maintain the fastest print speed at various print distances. I cannot think of seeing this in a firmware existing out there yet. If you have seen this, or are willing to pay me to implement this in your firmware, please contact me at brian@briansblog.net

Another method is to print the outer shell at a much slower speed. This will reduce the momentum and the force that the belts need to resist when the print head stops, the same as lowering the jerk speed. The part that is not visible still contains errors, but the outer part that is visible is of higher quality. This quality is great for pieces intended for display only, as the interior may be too inaccurate for applications that require very low errors.

In the end, the quality of your parts determines your maximum speed. A lightweight carriage reduces momentum and inertial allowing faster movement speeds. Stiffer components, stronger belts and motors allow faster, more precise movements and faster print speeds. Physical movement limitations are not the only thing you run in to when trying to print fast. Physics will get in your way in other ways. My next blog will go into detail about another issue that you will run into when trying to print fast.

Finally the resulting prints at this speed. The Monterey Bay and the local area in the mountains I live in.

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