I have a large Voice Coil Actuator (VCA) in my toolbox with an integral quadrature encoder. It has a 1" stroke, 55lbs force, and 2400 Hz response. I've powered it and it is pretty neat. I have no method of controlling this closed loop.



Mine is made by BEI Kimco. This might work for your application, but would definitely be pricy.

EDIT: this is a very large one. Lots of smaller, lower force options are available online. These are very fast, but other linear motion options are possible too.

 

BEI Kimco.

but this one has only 1 stroke, no? I need 3 as I described in the beginning of the thread, unless they have options with position stoke, the force I need is not much could be 5 to 10N but the speed is important, 20ms max

 

 

but this one has only 1 stroke, no? I need 3 as I described in the beginning of the thread, unless they have options with position stoke, the force I need is not much could be 5 to 10N but the speed is important, 20ms max

The whole point of these is that it has feedback so you can move it to any position within its stroke length. It has an electronic controller so you program the position and speed. You need one with enough stroke to fit all your positions inside and enough force + overhead to allow for wear in the machine and reliable operation.

Edit: You need a minimum of a 25Hz bandwidth at full stroke. I definitely think you need a VCA. Traditional motor actuators are not going to get this fast.

 

The whole point of these is that it has feedback so you can move it to any position within its stroke length. It has an electronic controller so you program the position and speed. You need one with enough stroke to fit all your positions inside and enough force + overhead to allow for wear in the machine and reliable operation.

yup, right... but like you said before, this is going to be pricy... I was looking this: https://www.tds-pp.com/uploads/tx_tdsproducts/Hubmagnet__3_Position_01.pdf

But I still think I ll need to build myself, I ll need something like 2400 solenoids, so $$$

I really liked the - Lower Cost Voice Coil Positioning Stage - VCS20-020-LB-12 you posted, I'm digging more on that

 

yup, right... but like you said before, this is going to be pricy... I was looking this: https://www.tds-pp.com/uploads/tx_tdsproducts/Hubmagnet__3_Position_01.pdf

But I still think I ll need to build myself, I ll need something like 2400 solenoids, so $$$

I really liked the - Lower Cost Voice Coil Positioning Stage - VCS20-020-LB-12 you posted, I'm digging more on that

There might be something to be said about this. 2400 channels of independent motion control (with variable position and high speed) is no small feat. Perhaps the added cost of doing this is the reason nobody has done it before. Not saying it can't be done, but is the cost savings in the form of reduced cycle time going to offset the significant cost increase of moving each needle individually rather than all together. I would not expect to be able to build a full size prototype cheaply.

Something to think about and certainly not trying to hold you back from trying. I'll be following this to see where you get.

 

There might be something to be said about this. 2400 channels of independent motion control (with variable position and high speed) is no small feat. Perhaps the added cost of doing this is the reason nobody has done it before. Not saying it can't be done, but is the cost savings in the form of reduced cycle time going to offset the significant cost increase of moving each needle individually rather than all together. I would not expect to be able to build a full size prototype cheaply.

Something to think about and certainly not trying to hold you back from trying. I'll be following this to see where you get.

I agree 100% with what you said, it is not a trivial problem to solve and involves several variables to put in this equation, while I am in the research phase I am also building a simulation in solid works to measure the advantages that individual channels will have in comparison with a simpler approach as currently used in the most modern machines

 

I agree 100% with what you said, it is not a trivial problem to solve and involves several variables to put in this equation, while I am in the research phase I am also building a simulation in solid works to measure the advantages that individual channels will have in comparison with a simpler approach as currently used in the most modern machines

One thing to keep in mind is the solenoid's inertia. In the case of the multi-coil (or coils in tandem) once activated, they won't immediately stop at whatever coil you've energized, but will bounce back and forth until they stabilize their position. It would be best if you considered mechanical stops positioned at different lengths for them instead.

A couple of questions
- Do you want to change the stroke lengths individually for each solenoid? Or would all soleniod's strokes change at the same time to a uniform length?
- When changing strokes, do you want to do it on the fly, or on a per-run basis?

 

One thing to keep in mind is the solenoid's inertia. In the case of the multi-coil (or coils in tandem) once activated, they won't immediately stop at whatever coil you've energized, but will bounce back and forth until they stabilize their position. It would be best if you considered mechanical stops positioned at different lengths for them instead.

A couple of questions
- Do you want to change the stroke lengths individually for each solenoid? Or would all soleniod's strokes change at the same time to a uniform length?
- When changing strokes, do you want to do it on the fly, or on a per-run basis?

Let's imagine 100 needles lined up side by side - in a given cycle from needle 1 to needle 100, I may want to activate all other needles with a 10mm stroke... second cycle, I may want to activate all other needles again, but now 15 mm, but in the third cycle only the first 30 needles will be activated 5mm stroke and so on... there's no fixed rule of how many needles are activated, what is defined by each cycle is the stroke length.

I think a voice coil motor is an overkill/pricey solution but if I could lower the price of production would make sense, found a simple example here: https://www.instructables.com/Electromagnetic-Actuator/ but I still need to check the response time, I would like something like 20ms

 

Let's imagine 100 needles lined up side by side - in a given cycle from needle 1 to needle 100, I may want to activate all other needles with a 10mm stroke... second cycle, I may want to activate all other needles again, but now 15 mm, but in the third cycle only the first 30 needles will be activated 5mm stroke and so on... there's no fixed rule of how many needles are activated, what is defined by each cycle is the stroke length.

I think a voice coil motor is an overkill/pricey solution but if I could lower the price of production would make sense, found a simple example here: https://www.instructables.com/Electromagnetic-Actuator/ but I still need to check the response time, I would like something like 20ms

And what's the maximum speed of each cycle? That is, at what maximum frequency are you planning on activating each needle?

 

hmmm. interestingggg how accurate do you think this can be?

Nobody knows. It needs to be prototyped and tested.

do you think i can buy it somewhere or do i need to build it myself?

Idea is new, such solenoids not exist in a market, but you can fabricate and sell them.

Force of this solenoid is more uniformly along stroke:



Force of conventional solenoid:


Design of a Solenoid Actuator with a Magnetic Plunger for Miniaturized Segment Robots

Solenoid Actuator Design for Improvement of Response Speed

 

And what's the maximum speed of each cycle? That is, at what maximum frequency are you planning on activating each needle?

Im planning to obtain these numbers with a simulation, the cycle is dynamic because, as I mentioned, during a given cycle I may want to activate only x number of needles, I think 80,000Hz is doable, but to be honest, I still don't know

 

Im planning to obtain these numbers with a simulation, the cycle is dynamic because, as I mentioned, during a given cycle I may want to activate only x number of needles, I think 80,000Hz is doable, but to be honest, I still don't know

That’s 80 . 000 Hz right? You mentioned a stroke time above that resulted in a 25 Hz max cycle.

Also understand the solenoid will actuate much more slowly under load than in free air.

 

I think your solution has to be electro-mechanical. Solenoids are not very good actuators. They are slow, difficult to drive and only have useful force at close to one end of their travel.

I'm thinking you have a continuously spinning shaft with cams. These operate followers which drive horizontal bars. You need 3 positions then you have 3 bars. Also, the shaft has a position sensor that detects 0deg (position 0).
So:

• Bar #1 oscillates between position 0 and position 1
• Bar #2 oscillates between position 0 and position 2
• Bar #3 oscillates between position 0 and position 3

The cams are arranged so that all the bars are at position 0 at the same time (0deg of the drive shaft).
They will get to maximum travel at 180deg of the shaft.

Each of your 3000 (was it that many?) actuators has 3 small cup electromagnets mounted on top.
When all the bars are at position 0, these electromagnets are either all off or only 1 of the 3 is on.
If on, it sticks to its bar and is lifted up and down for a 360deg of the shaft rotation.
When it gets back to 0deg, the electromagnet is switched off and another electromagnet (or none) is selected.

Whole heap of problems here, least of all is the requirement to have 9000 electromagnets! Also not reliable to have flexible wires to the electromagnets.

What I'm trying to say is you need to use the solenoids or electromagnets as selectors only. They need to be as small and weak as possible. The actual movement is powered separately.

 

I think your solution has to be electro-mechanical. Solenoids are not very good actuators. They are slow, difficult to drive and only have useful force at close to one end of their travel.

I'm thinking you have a continuously spinning shaft with cams. These operate followers which drive horizontal bars. You need 3 positions then you have 3 bars. Also, the shaft has a position sensor that detects 0deg (position 0).
So:

• Bar #1 oscillates between position 0 and position 1
• Bar #2 oscillates between position 0 and position 2
• Bar #3 oscillates between position 0 and position 3

The cams are arranged so that all the bars are at position 0 at the same time (0deg of the drive shaft).
They will get to maximum travel at 180deg of the shaft.

Each of your 3000 (was it that many?) actuators has 3 small cup electromagnets mounted on top.
When all the bars are at position 0, these electromagnets are either all off or only 1 of the 3 is on.
If on, it sticks to its bar and is lifted up and down for a 360deg of the shaft rotation.
When it gets back to 0deg, the electromagnet is switched off and another electromagnet (or none) is selected.

Whole heap of problems here, least of all is the requirement to have 9000 electromagnets! Also not reliable to have flexible wires to the electromagnets.

What I'm trying to say is you need to use the solenoids or electromagnets as selectors only. They need to be as small and weak as possible. The actual movement is powered separately.

@Marley ~2400 yea, I know it sounds a little crazy but for a v-bed knitting machine with a gauge 7 for example, that's the amount of needles - I partially got the idea, I'm trying to picture what you said....

Something like this?



or are you thinking of an unique spinning shaft for the whole thing? what I didn't understand is, if the mechanism is in continuous rotation, how are the bars/selectors positioned? horizontally?
If I'm following correctly this will increase the amount of channels (that's not a problem, im already planning to use a Siemens micro controller) and require more solenoids but simpler ones, something like https://www.aliexpress.com/item/4000082585106.html

 

I was thinking of one spinning shaft for the whole machine. Therefore all actuators will operate in sync.

Another possible way might be to have 1 cam operated actuator traveling the maximum distance.
Each channel would have only 1 electromagnet which would be switched on at 0deg if movement is required.
The magnet would be switched off after a certain time depending how much travel is required. The channel would have a spring return. Accuracy would depend on timing.

The shaft would have a position sensor to detect 0deg and another sensor (say a toothed wheel) so that the amount of rotation since 0deg could be measured. This would be used to accurately time the switch off point using a micro-controller. Therefore the speed of the shaft would not be so important.

This is kind of how diesel injectors work on modern engines with ECU's. A solenoid times the cut-off point of the injector. The fuel is pumped mechanically.

Of course you could have a single oscillating bar and mount all the electromagnets on the bar instead of the channels. You could even have the drive electronics on the bar minimizing the amount of wires flexing.

BTW: to energize and de-energize an electromagnet or solenoid very fast means handling high voltages due to the inductance and stored energy in the magnetic field. Even if the drive voltage is quite low.

Lots of engineering however you do it!

 

2400 yea, I know it sounds a little crazy but for a v-bed knitting machine with a gauge 7

Have you done the math on this yet? Gauge 7 is only 3.628mm or .143 inch center to center. That is going to be one very small solenoid! Look at the PDF Danko posted and see how big those solenoids are.

 

Have you done the math on this yet? Gauge 7 is only 3.628mm or .143 inch center to center. That is going to be one very small solenoid! Look at the PDF Danko posted and see how big those solenoids are.

@shortbus you are absolutely right about the space, I did not mention this restriction because I have a solution, no solenoid or anything else would fit in the space I have between needles anyway, so I'm more concerned with getting the actuation mechanism right first

 

I was thinking of one spinning shaft for the whole machine. Therefore all actuators will operate in sync.

Another possible way might be to have 1 cam operated actuator traveling the maximum distance.
Each channel would have only 1 electromagnet which would be switched on at 0deg if movement is required.
The magnet would be switched off after a certain time depending how much travel is required. The channel would have a spring return. Accuracy would depend on timing.

The shaft would have a position sensor to detect 0deg and another sensor (say a toothed wheel) so that the amount of rotation since 0deg could be measured. This would be used to accurately time the switch off point using a micro-controller. Therefore the speed of the shaft would not be so important.

This is kind of how diesel injectors work on modern engines with ECU's. A solenoid times the cut-off point of the injector. The fuel is pumped mechanically.

Of course you could have a single oscillating bar and mount all the electromagnets on the bar instead of the channels. You could even have the drive electronics on the bar minimizing the amount of wires flexing.

BTW: to energize and de-energize an electromagnet or solenoid very fast means handling high voltages due to the inductance and stored energy in the magnetic field. Even if the drive voltage is quite low.

Lots of engineering however you do it!

@Marley, I like your line of thought, but it can add considerable complexity, since it is just a "dumb" linear positioning system of 3 stages... lot engineering

 

lot engineering

I'm afraid that'll be a consequence of any path you choose to take... yours is not a trivial problem.