Raising and lowering pen with servo?

Yes it sounds easy, but what I want is the pen to apply slight pressure to the paper. This is a bit tricky as I can't just tell the servo to move a few degrees extra, as this wouldn't be good for the servo (I think). Has anybody got an Idea how I can do this? I guess what I need is a good suggestion for a pen holder...

This is usually done with a spring loaded mechanism.

Yes I have been doing this recently and it is difficult. I have made a pen holder from a small piece of plastic U channel that is used to make a seal on a piece of glass acting as a shower screen when you mount a shower head in a bath. I have attached the servo horn to the bottom and cut two slots for the rim of the pen. Then I have put a bit of sugru between the pen and the bottom of the U channel to give a solid base for the pen to go on. By carefully adjusting the servos angle I have applied a bit of pressure due to the flexing of the components.

Attached are two views of the holder.

What is "sugru" ?

The closest I can think is "Sugrue" which is a surname.
(I'm not trying to take the piss - just in case it is a typo)

...R

What is "sugru" ?

It is a flexible compound a bit like putty that sets into a hard rubber in about 24 hours.

Some version of this:

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Maybe instead of the servo pushing the pen down the servo only lifts the pen and let gravity (might need some added weight) push (pull) the pen down.

Grumpy_Mike:
It is a flexible compound a bit like putty that sets into a hard rubber in about 24 hours.

Thanks. Looks like it could be very useful - I have bookmarked it.

...R

justone:
Maybe instead of the servo pushing the pen down the servo only lifts the pen and let gravity (might need some added weight) push (pull) the pen down.

I do like this Idea... It seems to be a lot easier to make something like that yourself. Maybe I could use a tube which I put the pen in. The pen could move up and down the tube freely, but would have a blocker so it couldn't fall out. The problem is getting a tube which has exactly the same diameter as the pen, because I obviously don't want it moving to the side. I guess I won't find a tube like that and anyway, I want to be able to replace the pen with another one of a different diameter. Maybe I could use a too big tube with a screw in it or so... Any Ideas on how I could do this?

Here in the states hobby shops have a brass tubing rack that has varying sizes that slide over or inside of each other kind of like a telescoping antenna. The fit of these tubes is pretty good. The wall of the tube is thin so as the sizes vary the diameter doesn’t drastically change. Just went online and they are pretty easy to find.

Don’t know how much movement is needed but maybe make a holder using 2 hinges so as to keep the pen vertical as it moves up and down. That way there is no sliding to worry about just the friction of the 2 hinges which should be slight. The hinges could be made from joining 2 hinges together.

pen1.pdf (71.6 KB)