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Large Solenoid Actuator driven Display

Hello, I am new to this site so I hope you won’t mind if I ask a few questions that I am sure are going to sound quite amateurish to most of you. 

I am an American living in Berlin working on a collaboration between two art research institutes here.  I have been given the task of putting together a proposal for a dynamic moving display. That will be featured next year as part of a conference on kinesthesia. 

My back ground is not in computing or robotics, I am simply putting together a list of materials (and their cost) that would be necessary to make this project work.  And I am responsible for finding collaborators that can help put it together. 

I found this website when I was researching solenoids.  If you have any experience with solenoids I would greatly appreciate any advice or knowledge that you would care to pass on.

So let me try to explain what we would like to do and what I think I might have figured out so far – please be patient and bear with me.

The dynamic display I spoke of can be thought of as a much larger version of this pin-art-clock

http://gadgets.boingboing.net/2008/11/25/1980sstyle-pin-clock.html 

However the display would not be used for numbers but instead for larger art-related images.  Instead of metal pins the display would use much larger plastic knobs (for lack of a better word).  The idea was to use individual actuators to individually lift up each of these knobs so that you could create a series of unique images , symbols, impression, etc.  I hope this makes sense the way I am describing it.  In theory it should be able to handle quick successive displays resulting in a seamless image concept.  To get a better idea of what I mean take a look at the following youtube vid. 

 http://www.youtube.com/watch?v=KRCeKkcTjWw&feature=related

Each knob would have to be able to be raised and lowered independently of the others and in quick succession because the images would in effect be streaming across the display.  The display would be quite large (2 to 3 meters in length and width) with several hundred knobs and corresponding actuators in order to achieve higher resolution.   The knobs would be constructed out of light weight plastic.

I located these companies for solenoids:

http://www.dormeyersolenoids.com/solenoids.html

http://www.ledex.com/

http://www.solenoids.com.tw/about.htm

I thought a small, electric - AC, linear, pull-type solenoid should suit the purpose.  The only problem is that the shaft extension length on most of them is quite short.  I was thinking that for best resolution it would be good to have a difference between the raised and lowered knobs/pixels of at least 2 to 4 cm.  However, most of the solenoids that are capable of achieving that are far too powerful (and thus expensive) for our needs.  I realize that it would be possible to devise a lever of sorts to amplify the small movement but that would result in more moving parts and thus a greater chance of breakdown and higher maintenance.  I also looked at the possibility that I saw recommended of a camshaft with suspension spring but I think this would be too bulky to place side by side and would not possess sufficient speed.

And  I thought that this microcontroller, or something like it, that I found on this forum might be what  would be needed to independently control the solenoid actuators.

http://www.societyofrobots.com/axon/

So what I would like to know is what kind of solenoid would you recommend for something like this (does not require large force, does require large shaft movement of 2 to 4cm)?  How do I determine how long it can remain on (in a contracted position) and how long it has to rest (heat dissipate) before it can be activated again.  Is is possible to get an electric solenoid that is able to be activated in quick succession (1 to several times per second) for several hours without damage?  What would be the best means of control several hundred solenoid actuators independently?  Would the microcontroller I posted above work, and if so would I need several of them to control a large number of solenoids or is one scalable – if I do need several is there a way to link them to create a seamless image? What should I take into account when deciding on an operation voltage?  Finally what would you expect to pay for the type of solenoid that I described above?  Also any suggestions on the best way to hook up a power supply would be appreciated.

I will definitely have more questions, but I thought this would be a good place to start.   I hope you will be able to help – and patient enough to make it to the end of this long posting J

Cheers,

Ryan

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I still haven't seen a definitive answer regarding the 'value' or 'shade' each pixel will need to be capable of. Both solenoids and pneumatics are notoriously difficult to control in any situation that requires more than a simple on/off, or in your case, black/white system.
To make a pneumatic or solenoid actuator loiter mid-stroke with even low accuracy typicaly requires a significant investment in feedback hardware and software.

Well before I was not actually considering giving each pixel a shade.  I thought black and white would only be necessary and not really grey(s), so to speak.  I thought the best way to go would not to have a static image but one that quickly moves across the screen.  

Imagine this: you have a vertical screen in front of you.  It has 100 of these pixels that are able to move up and down.  Each pixel is is a ball (choose your color) connected to a linear actuator.  Unless you have a very large range of movement I am not sure that the eye would be able to distinguish very well between balls that were not completely elevated or at rest.  If you have a ball at 75% maximum height and an adjacent one at 65% I am not sure the eye would be able to distinguish the difference (of course that might depend on lighting as well)  

But I did not think it would be necessary to have anything more then a simple on/off when producing waves or image silhouette that were moving across the screen.  For example in the youtube vid I posted earlier there is no shading.  You have a signal that propagates out from the center.  As one pixel is in mid stroke the next one start up, and when it is mid stroke the next one starts up.  THis works because the image moves fast enough that your eye is able to perceive the over all movement of the piece.  If you were to have a static image that remained on the screen then I think you would have to have some sort of shading.  But if you did have a static piece (even a very simple image) you would need many more pixels.  Again in the you tube video I think there is something like 2,500 pixels just for a moving wave.  In the kinetic sculpture piece you have something like 800 to 900.  I think cost wise 500 to a 1000 might be feasible (might be) but to get really good resolution where shades of grey would be required would greatly exceed what is feasible.  I think. 

Does that make any sense?  

 

It really comes down to the level of detail the images need to have. 2 level imaging restricts you to basic silhouettes, lettering characters, etc.

The "Box Dance" video does in fact use graded values for height; you can see this by observing the pixels near the center - many of them never reach the full height of the other pixels. If you were to attempt a smoothly propogating wave with binary pixel values you'd need to carefully match the wave speed to the rise/fall time of each pixel.
For an actual image to move across the screen without blurring the edges you'd need to ensure the movement period (seconds per pixel) was sufficiently below the rise/fall time of each pixel.

If you use micro servos, geared motors, or similar then there is virtually no overhead involved with adding shading. With other designs there will be significantly more added cost and complexity.

As far as the Bernoulli effect design goes you'd need to ensure that each ball was isolated from the surrounding ones, otherwise the venting of adjacent valves would disturb the ball's stability. For the balls to become trapped in the air stream the valves must also open and close gradually, otherwise inertial effects will shoot to ball out of the stream, or at the very least generate excessive turbulence. The only way I can see this working effectively is if the balls are either contained in transparent tubes, or if they have a small area of open space around them and they are securely tethered to the valve, preferably with an elastic cord. The second of the above options will require a significant amount of extra air pressure compared to the first option, due to various turbulence and loss effects.

Just a thaught why not use Micro servos with a linkage to produce linear motion, then you can control extentsion level, plus they are small, light and cheap :)

 

Just my two cents.

So instead of using a solenoid you would suggest using a servo like they suggest here ( http://letsmakerobots.com/node/5581#comment-18056 See: OddBot -To imitate a pneumatic ram)

This would allow you to create a range of motion as well, correct?  Do you know how fast the servo's are?  I ask because the whole idea would be to have a fluid image moving across the "screen".  This is why I was staying away from the thread mounted motor with because of the time it would take to adjust them up and down.  If they are fast, and able to handle a moderate load (the load being the ball or knob that is used as the "pixel), and cheap this might be a nice solution.  

 

Are there any other problems that might arise from this?  

Servos typically rotate at about 60degrees in 0.1 - 0.16 seconds depending on the model. By using appropriate leverage such as a 200mm lever then the servo may be able to move your "knob" far enough with less rotation thus increasing the speed.

The main problem I see with thius idea is that whatever system you use, each knob will have to move 1000's of times a day. Only a servo that has metal gears and ball bearings has any chance of lasting any length of time and even then, the pot used to monitor the servos position probably wont last.

Air based methods such as pneumatics or solenoids are still your best bet.

I saw the video - interesting too, my suggestion would be more along the video..  What about of an air nozzle vs a pneumatic solenoid?  You could put a plastic ball on a small plastic air nozzle.  The air goes on the ball goes up on a jet of air.  The Bernoulli effect would keep each of the balls in place.  This probably does not match your requirements for the display, yet I would imagine that the air nozzle / ball approach is :

1. cheap (needle air nozzle)

2. and light - (all plastic and air hoses & control wires)

needle_air.jpg

I would want each nozzel to be connected to a PWM output - so you could get a range of motion vs only ON/OFF of a typical solenoid - this could add to dramatic effect as a wave turned into a static wave.. etc

 Good Luck - dang this looks fun :)

Hmm. I really like the idea of using air to move the display. Excuse us for hijacking the thread to continue down this path even if you don't follow it. ; j

Those valves look like you adjust them with a set screw that turns. So depending on if a half turn is enough, you could just hook up a servo. Or use servos attached to a gear set to get more range of motion.

There is an advantage to an electrically controlled valve. You could run flexible tubing to the back of the display, so as long as you have access to space behind the display, you aren't limited to very small valves. That would give you more flexibility on choosing parts that work and are cost effective.

For a vertically mounted display, having both a vacuum tank and pressurized tank along with a three-way valve would be a cool set up. The valve connects each pixel to either vacuum or pressure. Even if the valve is either "on" or "off", you could switch rapidly to set the balls at varying positions. More complex programming if you go that way, though.

You'd need to re-pressurize and re-vacuum the reserve tanks periodically, but you wouldn't need a full time air compressor and vacuum running all the time. That plus remoting the valves could make the display nice a quiet. You can and speakers for sound effects sych'd with the display.

Cool idea. Thanks for bringing it to LMR to kick around.

Yah,

this has potential - you don't need to use a servo - but directly connect the electrical output (plus BJ Transistor) to the needle valve.  If you pulse the the needle valve with PWM - you can get an analog pressure from the needle valve.  Air, water, or electricity - pulsed can provide a gradient of pressure if you can vary the duty cycle.

I have heard of really cool fountains regulated with air pressure, which in turn is regulated by a needle valve.  With computer control segments of water fly from one nozzle to another giving the impression of bouncing water segments....

Then there is the BMW kinetic sculpture -I have not read the details but I imagine this works on servos and wire.

I think they pulled it off very well.  Balls on air would not probably have the range - but they would be potentially quicker.

Thanks for the link GroG!  That was great.  So you guys are suggesting a sort of inverted version of that kinetic sculpture piece – instead of the balls hanging from the ceiling they would be pushed up from the floor via a controlled air current.  If this was a horizontal piece then you would not need the 3-way valve that ignoble suggested you would just let gravity do the work.

I liked GroG’s idea of creating analog air pressure pulse for controlling the balls that seems to be the easiest way instead of opening and closing the air valves with a servo – and much faster and more responsive .  But correct me if I am wrong you would need an air tank per valve/ball it you went this way.  Imagine you have a small grid (thus low resolution) of 100 balls in parallel (10x10) Each ball would have a corresponding valve.  There would be no way to direct and control the air pressure from a single tank.  Correct me if I am wrong but as some point you would have to have a mechanism (individuals servos perhaps) that would redirect/modulate the air flow from the single tank to each valve.    

If you have a tank per valve or if go with ignoble’s idea of a three valve system with servos and a single tank wouldn’t you create a piece that would almost or more expensive then something that uses a solenoids?  Also the amount of space that would be required for the valves, airtank(s) and tubbing (three types in ignoble example plus a plastic casing for the balls) would make the whole structure quite large.

What do you think about this? Let me know.