Maus L V0.05 - VikOlliver/RepRapMicron GitHub Wiki

The V0.05 "Maus L" is an interim development that uses the Axis Drivers from the upcoming V0.05 PIKA μRepRap. The V0.05 Axis Driver uses flexures that give the Axis Drivers linear (the "L" in "Maus L") movement on all axes rather than relying on pivoting flexure joints that approximate linear movement over short arcs.

Linear Movement Benefits

The benefits of this system are:

• No software compensation is required for accurate positioning, allowing existing CNC hardware and software to be used over the full working volume.

• The Drive Screw used is always the same horizontal distance from the central flexure. This reduces load on the motor allowing the mechanism to move at greater acceleration and speed.

• The compound nature of the flexure mechanism adds more constraint perpendicular to the axis of motion in one plane perpendicular to the axis of motion.

• One of the X or Y axes can be directly connected to the Axis Driver with a rigid link rather than a flexible one as prior.

Pantograph Flexures

The flexures used are in an arrangement similar to an artist's pantograph, but with three points of contact on the driven and driving ends to keep them parallel. Thus it is a form of parallel bar linkage. The assembly instructions are here.

As this allows motion in two axes, the Z Axis Driver is fitted with complementary flexures to limit motion to only the Z direction. This also substantially reduces vibration on the Z Probe and results in greater precision. Assembly details for the Z Axis can be found here.

Because of the rigid link to the Y axis, a complementary flexure is now needed to link the Axis Driver to the X axis.

Improvements to XY Table

While the Axis Drivers are theoretically capable of 8mm of movement, this was limited by the dimensions of the V0.04 XY Table. This has been improved, and relevant clearance on other parts added.

These changes handily provide the second degree of constraint needed by the X and Y Axis Drivers. It also requires other redesigns as it had no constraint over rotation,though this is not a major issue. Modifications to fit a larger stage with greater frame rigidity and reduced rotation are implemented in the PIKA design.

Bed Levelling

Another improvement is the addition of simple hardware bed levelling. This is achieved by placing spring washers between the Stage and XY Table on the four securing screws. Levelling is achieved by touch probing several locations to determine an average slope for the X and Y directions, and tightening or losening the relevant securing screws until sufficient consistency is achieved.

A potential improvement for PIKA is to make the securing screws more readily accessible, and more widely spaced.

The Stage assembly has been significantly simplified, and combined with a Complementary Flexure for the X Axis Driver allowing X and Y to move independently. The Ground Probe has been replaced with a wired connection to a magnetic slide clamp, providing a larger and clearer working area, and more clearance on the Z Touch Ground Probe.

It is hoped to produce a version of the frame as a single piece print for PIKA, integrating the Z Tower in the process.

X & Y Driver Supports And Z Tower

The X and Y Driver Supports have been moved 10mm up the XY Table Frame because of the new Axis Driver geometry.

The Z Tower also needed a redesign, and its stability was increased. Note that the 3mm acrylic baseplate used was too flexible, and a 10-unit square Metriccano beam was bolted on to add rigidity as a temporary measure. PIKA will not require a baseplate.

Change of Resin Type

While V0.04 demonstrated the principle of depositing 3D printer resin, this comes with the problem of oxygen inhibition. Thin films of resin absorb atmospheric oxygen which reacts with the catalyst before it can completely solidify the resin. UV Curing nail art resin is designed to solidify in air in thin films and appears to be a more suitable material. Experiments have already shown that curing standard deposited resin in a box of oxygen-free gas will not prevent absorbtion of oxygen sufficiently to reliably cure the resin without exotic additives.

"Jelly" and "Top Coat" nail art resins have been tested. Top Coat forms sheets that are sufficiently robust to be manually manipulated with a probe tip when deposited approximately 30-40μm thick.

Jelly appears to be extremely viscous and is difficult to place accurately with current hardware.

Attempts to stack layers ranging from 1-3μm are ongoing and have had some success.

Slicer Filter

The filter used to turn PrusaSlicer gcode into printable voxels has been upgraded to move faster, link voxels more smoothly, automatically manage UV curing, and most importantly deposit 3D layered prints.

Probe Design

It was found that an oxidizing electrolyte such a dilute nitric acid would roughen the probe body, if the wire were immersed ~15mm. This retains significantly more resin than a smooth probe allowing over 100 voxels to be deposited in one pass.

The probe point could then be sharpened by briefly touching it to the meniscus until the desired point size was achieved. An ogival point offered a convenient compromise between precision and durability.

Angling the probe tip such that it makes perpendicular contact to the slide gave a more consistent width to deposited lines.