Difference between revisions of "Improving precision"
From Evil Mad Scientist Wiki
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If you are producing sloppy drawings, or good ones that you want to be better, you may need to do one or more of the following: | If you are producing sloppy drawings, or good ones that you want to be better, you may need to do one or more of the following: | ||
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* '''Check egg alignment.''' Make sure that the object (which we'll call an "egg" even if it's a light bulb or a golf ball) being plotted is very well centered on the egg axis. Use the "Raise pen, turn off motors" setup mode to turn your object by hand, and make sure that it is as concentric as possible. | * '''Check egg alignment.''' Make sure that the object (which we'll call an "egg" even if it's a light bulb or a golf ball) being plotted is very well centered on the egg axis. Use the "Raise pen, turn off motors" setup mode to turn your object by hand, and make sure that it is as concentric as possible. | ||
* '''Check pen alignment.''' The pen should point ''directly towards'' the egg-motor axis, and directly towards the pen-motor axis as well. There are a number of places that you can make adjustments to ensure that these are correct. For example, the screw at the top of the proximal pen arm can be used to adjust the angle between the pen point and the pen-arm axis. | * '''Check pen alignment.''' The pen should point ''directly towards'' the egg-motor axis, and directly towards the pen-motor axis as well. There are a number of places that you can make adjustments to ensure that these are correct. For example, the screw at the top of the proximal pen arm can be used to adjust the angle between the pen point and the pen-arm axis. | ||
| − | * '''Check contact.''' The "egg" needs to make good contact with the egg-motor. There should not be any slippage between the two, or the egg will gradually work its way out. It may help to clean and dry the "egg" and/or the polyurethane egg cup. For super-precision work you may want to experiment with different egg cup designs, or even screw down or glue your object to the egg-motor shaft. | + | * '''Check contact.''' The "egg" needs to make good contact with the egg-motor. There should not be any slippage between the two, or the egg will gradually work its way out. Even if there is not slippage, there can be apparent "backlash" (direction-dependent lag) when the egg-motor turns back and forth. It may help to clean and dry the "egg" and/or the polyurethane egg cup. For super-precision work you may want to experiment with different egg cup designs, or even screw down or glue your object to the egg-motor shaft. |
* '''Check for drag on the plunger.''' If the plunger is not able to turn easily, then it will provide drag to the "egg." If the tension is too high, the O-ring is rubbing on the back bushing, or the thin nylon washer is not present, there can be increased drag. | * '''Check for drag on the plunger.''' If the plunger is not able to turn easily, then it will provide drag to the "egg." If the tension is too high, the O-ring is rubbing on the back bushing, or the thin nylon washer is not present, there can be increased drag. | ||
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* '''Slow down the pen speed.''' The faster the pen is moving, the more vibration (and thus slop) you'll have when the pen stops moving. By slowing the speed at which the motors turn, or the servo lifts/drops the pen, you'll improve your drawings. The correct speed will depend upon your medium (egg shells, glass, etc) and your pens -- you'll need to experiment. Often you can raise the pen much faster than you can lower it. | * '''Slow down the pen speed.''' The faster the pen is moving, the more vibration (and thus slop) you'll have when the pen stops moving. By slowing the speed at which the motors turn, or the servo lifts/drops the pen, you'll improve your drawings. The correct speed will depend upon your medium (egg shells, glass, etc) and your pens -- you'll need to experiment. Often you can raise the pen much faster than you can lower it. | ||
| + | |||
| + | * '''Use a smoother toolpath.''' If your pen travels in a path with sharp corners, you may see ringing at the corners, where the ben vibrates after quickly changing direction. Using a smooth path that provides built-in deceleration and acceleration can prevent this. For example, when [[Creating_filled_regions|filling regions]] the plots made with the "hatch" method generally provide excellent toolpaths with minimum ringing. | ||
* '''Use a smaller/shorter pen.''' The pen arm grips your pen very close to the bottom of the pen. While this generally gives better precision, gripping the pen below the center of mass means that there will be more sway, particularly when the pen has been lifted or is being lowered. | * '''Use a smaller/shorter pen.''' The pen arm grips your pen very close to the bottom of the pen. While this generally gives better precision, gripping the pen below the center of mass means that there will be more sway, particularly when the pen has been lifted or is being lowered. | ||
| − | * '''Clean your medium before plotting.''' If you remove surface dust and oils before drawing, you'll get a sharper plot. | + | * '''Clean your medium before plotting.''' If you remove surface dust and oils before drawing, you'll get a sharper plot. In particular, certain types of pens will show fingerprints-- areas where the pen does not make as strong as a mark, where the object has been handled. |
* '''Maintain your pen(s).''' Clean them frequently, and don't let them dry out. | * '''Maintain your pen(s).''' Clean them frequently, and don't let them dry out. | ||
Revision as of 11:49, 7 October 2010
If you are producing sloppy drawings, or good ones that you want to be better, you may need to do one or more of the following:
- Check egg alignment. Make sure that the object (which we'll call an "egg" even if it's a light bulb or a golf ball) being plotted is very well centered on the egg axis. Use the "Raise pen, turn off motors" setup mode to turn your object by hand, and make sure that it is as concentric as possible.
- Check pen alignment. The pen should point directly towards the egg-motor axis, and directly towards the pen-motor axis as well. There are a number of places that you can make adjustments to ensure that these are correct. For example, the screw at the top of the proximal pen arm can be used to adjust the angle between the pen point and the pen-arm axis.
- Check contact. The "egg" needs to make good contact with the egg-motor. There should not be any slippage between the two, or the egg will gradually work its way out. Even if there is not slippage, there can be apparent "backlash" (direction-dependent lag) when the egg-motor turns back and forth. It may help to clean and dry the "egg" and/or the polyurethane egg cup. For super-precision work you may want to experiment with different egg cup designs, or even screw down or glue your object to the egg-motor shaft.
- Check for drag on the plunger. If the plunger is not able to turn easily, then it will provide drag to the "egg." If the tension is too high, the O-ring is rubbing on the back bushing, or the thin nylon washer is not present, there can be increased drag.
- Increase tension. Compressing the plunger spring further pushes the "egg" against the egg-cup of the egg-motor, improving contact. This generally helps up until the tension starts to create excess drag-- for example when the spring is fully compressed.
- Reduce lateral play in the plunger. See Appendix B of the assembly instructions for hints on how to do this.
- Check for drag on the pen. The pen should only lightly touch the surface that it's drawing on. If you use a stiff hinge, or otherwise arrange things such that there's heavy downward force, it can create excess drag at the egg-pen interface.
- Slow down the pen speed. The faster the pen is moving, the more vibration (and thus slop) you'll have when the pen stops moving. By slowing the speed at which the motors turn, or the servo lifts/drops the pen, you'll improve your drawings. The correct speed will depend upon your medium (egg shells, glass, etc) and your pens -- you'll need to experiment. Often you can raise the pen much faster than you can lower it.
- Use a smoother toolpath. If your pen travels in a path with sharp corners, you may see ringing at the corners, where the ben vibrates after quickly changing direction. Using a smooth path that provides built-in deceleration and acceleration can prevent this. For example, when filling regions the plots made with the "hatch" method generally provide excellent toolpaths with minimum ringing.
- Use a smaller/shorter pen. The pen arm grips your pen very close to the bottom of the pen. While this generally gives better precision, gripping the pen below the center of mass means that there will be more sway, particularly when the pen has been lifted or is being lowered.
- Clean your medium before plotting. If you remove surface dust and oils before drawing, you'll get a sharper plot. In particular, certain types of pens will show fingerprints-- areas where the pen does not make as strong as a mark, where the object has been handled.
- Maintain your pen(s). Clean them frequently, and don't let them dry out.
