Accuracy,Resolution & Repeatability Tests

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Ilios Photon 2 Accuracy3D Printing, just like any other way of manufacturing parts, in our opinion should be just as accurate as the parts you want to create. We take great pride in the build quality and components which are used in our 3D printers. Ilios Photon 2 is no different, with 16mm hardened steel ball bearing spindles, all metal slide joints and absolutely massive framing, which allows the 3D printer to create models with the upmost accuracy. We use these types of components and overbuilt constructions so that the end user spends no time in tinkering, upgrading or fine tuning the 3D printer and can expect the best possible outcome from the machine right out of the box.

It is however hard to explain the benefits and prove resolution as well as accuracy just with text and numbers since it may be hard to even imagine dimensions such as Microns at which the Ilios Photon 2 operates. For this reason we conducted a set of tests, using the best measuring equipment in order to demonstrate the actual final result that the 3D printer can achieve since things like Flex, Backlash and even heat can cause deformations at the micron level. The tests were conducted on 3 main areas which the 3D printer performs during its build cycle. Accuracy and resolution of the actual mechanical movement, Repeatability of the movement as it constantly going back and forth during layer creation and finally the actual Flex which occurs as the model slowly gains weight on the build area.

The Setup

To properly demonstrate the three main areas where the 3D printer should shine the most, we took a default Ilios Photon 2 setup, removed its VAT assembly and placed a Mitutoyo Micron Dial indicator with resolution of 1 micron (0.001mm) per step and accuracy of +/- 3 microns (0.003mm), Jeweled bearing for absolute accuracy and Shock proof characteristics. Have in mind that usually machine shops will use a similar measuring tool but at a 10 micron resolution.

Ilios Photon 2 Test

The measuring tool is mounted on a 7mm thick Steel plate which covers the entire build area and an aluminum extrusion with dimensions of 25 x 50mm. The above mentioned setup ensures that the measurements are as accurate as possible, without external vibrations, movement or deflection while the printer operates. The fact that the Base Plate of the Ilios Photon 2 is made from Dur-aluminium with thickness of 6mm also contributes to the overall accuracy not only during the tests but also during normal operation of the 3D printer.

Repeatability Test

One of the most overlooked functions and characteristics of a 3D printer is its repeatability accuracy. As the Lift moves up and down after each layer during the entire print cycle, this is what determines how even are the distances between each layer. Cheap spindle and slide assemblies would normally have very bad repeatability since just the backlash of inferior components would destroy any accuracy that the rest of the drive trains would have. That is without even considering the flex of a single point lift arm that common 3D printing assemblies have and other frame characteristics.

Since Ilios Photon 2 3D printer uses a dual spindle and slide assembly, mounted through metal junctions and machined for absolute accuracy, as the test shows, the deviation from that repeatability is even lower than the accuracy of the tool we used to measure it. The Lift comes to the same spot each and every time with deviations of 0.1 - 1 microns. Measurements were taken 10 times during this test to come up with an approximate overall value.

Accuracy - Resolution

Just specifying the "Theoretical" motor accuracy does not determine the actual 3D printer accuracy since the movement goes through many different assemblies with variable build quality before it reaches the model and the VAT surface. Don't forget that you also have to consider the fact that each layer adds strain to the lift during detachment and if there is any backlash in the overall assembly then the rest of the layers will follow the error to compensate.

To test the accuracy of the Ilios Photon 2 Lift we set the movement to single steps, with a resulting expected accuracy of 1.56microns (0.00156mm) since the motors operate at 1600 steps per revolution (for a reasonable mid torque) and spin the Ball Bearing spindles with a pitch of 2.5mm. This means that for a 1mm movement on the lift, the motor will actually do 640 steps.

As tests showed, the actual accuracy of the 3D printer was even higher than the specified accuracy of the tool with which we measured it. However since we are limited by the accuracy of the measuring tool, the result can only be stated to be within +/- 3 microns.

Flex

When customers choose a 3D printer by its build volume they often forget that as the build volume increases, so should the overall quality of the 3D printer. It is simple physics since the larger the model is, the heavier it will be. When building a large model, if the printer simply cannot handle it or cheap parts are used as well as simple assemblies, the model will actually drag the Lift with it and accelerate the warping since each layer will displace more resin from the curing area despite what the 3D printer thinks is actually happening. It may not sound serious but when there are more than 10000 layers in a model it really adds up at the end.

As a simple test we took a known weight of 616 grams which emulates a model that would typically use half a bottle of a 1kg material and measured the actual displacement of the Lift. Tests showed that there is a 5 micron flex displacement when force is applied at the edge of the lift where there is less supporting structures. Having in mind that normally a model would be built at the center of the Lift plate, we can assume that the 5 micron flex would not even show up at the maximum build volume of the 3D printer.

A simple test you can do to check the "Flex" of the 3D printer lift is to just try to wiggle the lift when it is static. If you see even the slightest flex then that is within the 1000 micron resolution and essentially defeats whatever claimed accuracy of the 3D printer is.

Conclusion

Based on the above proven tests, we can with ease say that the Ilios Photon 2 3D printer is well within the claimed specifications since similar equipment would be suited for laboratory and research work. Having in mind that normally a tool with 10 times the error and 10 times less resolution is used in professional machine shops, the resolution and accuracy of the main 3D printer lift is higher if not the same as the measuring tool used in our tests.

If you need more information about 3D printer quality and resolution in general, feel free to checkout our "Understanding 3D Printer Resolution" article in the Documentation section of the website.

Δημιουργηθηκε στις Παρασκευή, 21 Απριλίου 2017 16:04
Γράφτηκε από τον/την Demetris Zavorotnitsienko

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