[SOLVED] Electrostatic force in gripping small objects

[CataM]

I am reading about MicroRobotics in an article from Robotics & Automation Magazine, IEEE.
They are saying that making smaller the objects, then forces created by an Electrostatic field, Magnetic field, Surface Tension of fluids or Van der Waals forces became significant and could be used to manipulate those objects.

They gave me an example but the Electrostatic part I do not understand it very well. I have highlighted that part (see picture).



By "grounding the charge" they are referring to place the object on the ground ? But then I do not understand how the electrostatic field will stop if the "capacitor" is charged...

How an electric schematic for "realising the charge" as they say would look like ?

Is this the electric schematic in figure "e" of the article?

 

[BradtheRad]

By ground they mean to connect to earth. It drains away the static charge, just like the wrist strap in common use.

I don't believe a capacitor is really the component used, although the diagram implies it is there in principle. Static charge can be retained by items which act like one plate of capacitor. The same things used in parlor experiments: plastic items, balloons, electroscopes, etc.

 

[CataM]

I don't believe a capacitor is really the component used, although the diagram implies it is there in principle.

Yes, the principle of the capacitor I was referring.

But what are the steps in order to grip the object? I mean: First connect power supply. And then they can remove power supply and moving the upper bar(grey in the picture) (also means one plate of the capacitor) are able to move the round object?

And to release the part just place the round object on the ground without any electrical or whatelse connection on the upper bar(grey one), I mean the upper bar standing in air?

 

[c_mitra]

You need to have two components: the holder and the holdee.

1. Charge the holder to a high potential. This can be tricky because the holder must be insulated otherwise. You need to provide a high voltage switch.
2. Bring the holder close to the object (holdee). Charges are induced and the object gets attached (stuck) by electrostatic forces.
3. Move to holder to the desired location.
4. Release the object by discharging the holder. Just touching (grounding) the conducting part will do- the charge will disappear and the object will be released.

If you want an analogy with the capacitor, the other plate of the capacitor is the ground.

 

[c_mitra]

But then I do not understand how the electrostatic field will stop if the "capacitor" is charged...

I believe it is the voltage source (battery) and not a capacitor. The electric field will be maximum once the hollow rectangular object will be fully charged. The electric field will induce an induced dipole in the object which will therefore get attracted to the rectangular object just above.

If the hollow circle is conducting, it will still get attracted, then take away some charge from the upper plate (or whatever that may be) and get repelled.

Laser printers work in a similar fashion.

 

[CataM]

I believe it is the voltage source (battery) and not a capacitor. The electric field will be maximum once the hollow rectangular object will be fully charged.

Ok. So it only charges up with charge the rectangular object.

I thought the rectangular object is 1 plate and the round object is the other plate and together form a capacitor.

Then they are referring to remove the battery from the rectangular object and hence the electrostatic field will disappear ?

 

[c_mitra]

Then they are referring to remove the battery from the rectangular object and hence the electrostatic field will disappear ?

Not quite so. Removing the battery will not remove the charge from the rectangular object. Just like a capacitor: once it is charged, removing the source of charge will not remove the charge from the capacitor. You need to short the two plates. In this case, you need to ground the object so that the charge goes to the ground (discharge to zero potential).