Automatic Blast Gates

[Jonathan Spool]

Is Ecogate the only electric automatic blast gate available, or are there other automatic electric options available?

[Roger Jensen]

I got mine at Grizzly. I don't see the model I bought on their site, but I didn't look too hard. It has the switched gate that turns on the unit when you open the gate. Not sure if if that is what you are looking for. If so, you may want to call them to see if they still carry it.

Roger

[Alan Schaffter]

Is Ecogate the only electric automatic blast gate available, or are there other automatic electric options available?

I assume you mean blast gates that open automatically when you turn on a machine, not the ones with a micro switch that turns on the DC when you manually open the gate.

If so I have never seen any. All the other commercial ones, like those from Norfab (http://www.nordfab.com/index.cfm/do/pages.view/id/57/p/1/page/Nordfab-Products~Automatic-Blast-Gates), etc. are electro-pneumatic (as are my homemade ones). I know of one woodworker who made gates with electric solenoid actuators. While he hasn't had problems I would not recommend that approach for a couple of reasons.

The problem with electric ones are the motors (and solenoid actuators) are typically not very strong and without special control circuits there is a very real danger they will stall, overheat, and cause a fire, especially when you try to operate them with the blower going. Electrically controlled or triggered, but pneumatically operated blast gates are safer and more reliable. My system (http://videos.americanwoodworker.com/video/Automatic-Dust-Collection) uses current sensor switches at each outlet to control 24V solenoid air valves which port low pressure (15 psi) shop air to dual acting cylinders that open and close my blast gates. 15 PSI allows me to use small, cheap vinyl fish tank type air hose. Even at only 15 PSI, however, I needed flow restrictors to slow down the speed of the gate slide to protect it. If I removed the restrictors, sharpened the edge of the slide, and upped the pressure to 20 PSI or more, I would have auto-guillotines!!! They are so strong they could easily sever a finger!

[Jonathan Spool]

Great video of your system Alan. I wish I had your engineering skills, and were retired to have the time to invest in such a system. I really like that your activators are alongside the gate rather than mounted like a lollypop. Much cleaner and compact.

[Jeffrey Makiel]

Electric solenoids are better suited for use with a pivoting damper blade arrangement vs. a sliding gate. With a damper blade, very little force is needed to rotate the damper even when the dust collector is on. And the blade in the air stream has never been a problem regarding clogging.

Should a damper bind, electrical protection is provided by a 1 amp fuse.

The problem with pneumatic is cost. Unless you luck-out on Ebay, pneumatic actuators and air valves are very costly. When I built mine 20+ years ago, Ebay did not exist.

-Jeff :)


http://i3.photobucket.com/albums/y84/Beff2/1-1.jpg?t=1286160070

[Alan Schaffter]

I seriously considered Jeff's system because, with the exception of the solenoids, I could build them with parts on hand, but other considerations took me in another direction.

First and foremost, most of my blast gates were already built, leftover from my previous shop. These were the same design as the new ones so easily adapted to autogates by adding a slightly longer slide and the pneumatic cylinders. I was patient, which paid off with good prices for stuff on Ebay. There are still tons of new and used Bimba cylinders and used SMC solenoids at good prices on Ebay still. Additionally, I felt the damper gates were too big, would take up too much space where I didn't really have it, and since they are rectangular and have the damper in the air stream, would result in more static pressure resistance than I wanted to give up, possibly have dust clogs in the corners, and be much harder to get a good seal, especially along the long sides of the damper blade. The current sensor switches I used are only rated for 120 mA at 24V which was perfect for my pneumatic solenoids but mechanical solenoids would have required a much heavier duty switch or an additional mechanical or solid state relay operated by the current sensor switch. I didn't want to run another 120V circuit to all the gates. Light gauge bell wire carries my 24V, and made it easy to add local buttons for manual control as well as the automatic control.

It basically comes down to what you can get and what you want to do. Neither option is for the rookie.

[Jonathan Spool]

I think the Ecogate system, which is electric, utilizes a screw drive to open an arched, gear edged gate, rather than a solenoid. Interesting approach I think. My local Woodcraft has utilized them in their shop for the last 6 months. I am curious as to their longivity.

[Dan Friedrichs]

Alan and Jeff,

A thought: instead of a damper on a pivot, or a pneumatic cylinder, couldn't you use a small low-voltage motor to spin a lead screw?

I'm thinking that very small stepper motors are cheap enough that you could put one on each side of the gate, and you'd never have any binding. Or just some very cheap little reversible DC motors.

[Alan Schaffter]

Alan and Jeff,

A thought: instead of a damper on a pivot, or a pneumatic cylinder, couldn't you use a small low-voltage motor to spin a lead screw?

I'm thinking that very small stepper motors are cheap enough that you could put one on each side of the gate, and you'd never have any binding. Or just some very cheap little reversible DC motors.

That is certainly an option. You don't need a stepper motor though for something like this. You need a motor like the newer generation of small, low voltage gear motors that have replaced the large ones used with electric car windows and also have replaced the solenoids in electric door locks. You would also need to decide how to do it- with a direct drive leadscrew and follower or worm gear, cog wheel, and linkages. You would also need mechanical or magnetic limit switches, or a current sensing circuit and possibly a clutch assembly to prevent over-travel and protect the gate and the motor- so it starts to get complicated and expensive. As you can see, I spent a lot of time mulling over all these options.

[Dan Friedrichs]

That is certainly an option. You don't need a stepper motor though for something like this.

No, but I think the stepper avoids all the problems you mentioned. Put one on each side, and you'd never bind, and you wouldn't need limit switches. Just measure how many steps, and take that many steps each time. One low voltage wire to each blast gate, and one chip to run the steppers and read the current sensors on the equipment, and time the blower on/off.

Cheap little motors might be less expensive, but the limit switches make it more complicated than I'd like.

I'm curious if a stepper motor + lead screw has has any disadvantage over pneumatic cylinders. I have a few steppers laying around, so I'm going to try to build one and see how it turns out. I've been contemplating building a pneumatic one (like yours, Alan), and even have some nice SMC solenoids, but I kind of like this all-electric idea better.

[Alan Schaffter]

No, but I think the stepper avoids all the problems you mentioned. Put one on each side, and you'd never bind, and you wouldn't need limit switches. Just measure how many steps, and take that many steps each time. One low voltage wire to each blast gate, and one chip to run the steppers and read the current sensors on the equipment, and time the blower on/off.

Cheap little motors might be less expensive, but the limit switches make it more complicated than I'd like.

I'm curious if a stepper motor + lead screw has has any disadvantage over pneumatic cylinders. I have a few steppers laying around, so I'm going to try to build one and see how it turns out. I've been contemplating building a pneumatic one (like yours, Alan), and even have some nice SMC solenoids, but I kind of like this all-electric idea better.

That controller presents a number of problems. You either need a separate controller for each gate or a central master PLC unit for all gates. Then you end up with something like the Ecogate system. While an individual controller might not be expensive, a larger PLC might be, it can be a real pain to program. You can't just tell the stepper to start, stop, reverse, etc.- you need to program a ramp up/ramp down or you will lose steps each activation. You may also need a power supply and a motor driver- due to stepper motor voltage and current requirements the processor may not be able to control the stepper motor directly, but require a motor driver. Another issue with steppers, is that they can lose steps and get out of sync if stalled or over-stressed. So, you still need the limit indicators. My brother just finished converting a huge Bridgeport mill to full three axis CNC with 4th axis quill feed and these are just some of the issues he had to address. They are also some of the issues that I considered when I made a stepper-driven router lift proposal to Rich Hummel at Woodpeckers- the stepper motor was the the cheapest component in the unit.

The force of the pneumatics and my easy-slide gate design allow operation of the gate when the blower is running. Timing the blower on/off, isn't really necessary. My blower comes up to speed quickly, well before I would ever start making dust, and if I am on my second operation the blower is already running. As far as shut down delay- at approx 4000 fpm (typical velocity for air flow in a DC) it takes less than 1/2 second for dust to go from my furthest machine to the cyclone- I don't turn off a machine that quickly, even if I could.

Cylinder rods are smooth, self cleaning, and stay that way, but lead screws, especially nicely greased ones can be dust magnets. A leadscrew requires a good follower which must be well aligned or it will bind and it can wear out. They can be expensive unless you go with less expensive "all thread" hardware story threaded rod.

I think, once designed and produced in volume, an electric gate system might be cheaper than a pneumatic one, but I found for my limited installation the pneumatics were simpler and cheaper. Look at the price of the Ecogates and that system! Of course look at the cost of pnuematic gates from Norfab and others.

[Alan Lightstone]

Does a pneumatic system need to be hooked up to an air compressor for the air source? If so, even more complexity, and the need for the compressor. To me, that would be an advantage of an electric system.

[Alan Schaffter]

Does a pneumatic system need to be hooked up to an air compressor for the air source? If so, even more complexity, and the need for the compressor. To me, that would be an advantage of an electric system.

Anyone who has shop large enough and/or well equipped enough to consider a complex DC system with automatic blast gates would already have a compressor, don't you think? Anyway, all that is needed for a pneumatic system is a VERY small compressor. The pneumatic gates need only about 15 psi and minimal CFM. Since the pressure is so low, the hose running to each gate can be very lightweight and very flexible 1/8" or 3/16" vinyl or PE fish tank tubing which is easily run where you need it.

Remember, we are not talking about adding automatic blast gates to a portable, rolling, single stage, bag "dust collector." Something like that doesn't need nor justify the complexity or cost of autogates. We are talking about a fixed "dust collection system" with a fair amount of ducting and blast gates at every machine.

[kenneth wilkinson]

Great video of your system Alan. I wish I had your engineering skills, and were retired to have the time to invest in such a system. I really like that your activators are alongside the gate rather than mounted like a lollypop. Much cleaner and compact.
do you have plans &material list

[Alan Schaffter]

do you have plans &material list

Sorry, no. Plans and a materials list wouldn't be much use since I got all my stuff from Ebay and other surplus sources so those parts may or may not be available. Purchased retail they would have been prohibitively expensive. Also, in the case of the solenoid air valves, a number of different models will work- I used 3 different models- they were all 24VDC 5/2 valves (five ports, 2 direction). Send me a PM if you have any specific questions about what I did or a particular part I used.

[Anthony Whitesell]

No, but I think the stepper avoids all the problems you mentioned. Put one on each side, and you'd never bind, and you wouldn't need limit switches. Just measure how many steps, and take that many steps each time. One low voltage wire to each blast gate, and one chip to run the steppers and read the current sensors on the equipment, and time the blower on/off.

Cheap little motors might be less expensive, but the limit switches make it more complicated than I'd like.

I'm curious if a stepper motor + lead screw has has any disadvantage over pneumatic cylinders. I have a few steppers laying around, so I'm going to try to build one and see how it turns out. I've been contemplating building a pneumatic one (like yours, Alan), and even have some nice SMC solenoids, but I kind of like this all-electric idea better.

I also think trying to keep two motors in sync (as you mention to avoid binding) would cause really bad binding if they got out of step.

[Anthony Whitesell]

That controller presents a number of problems. You either need a separate controller for each gate or a central master PLC unit for all gates. Then you end up with something like the Ecogate system. While an individual controller might not be expensive, a larger PLC might be, it can be a real pain to program. You can't just tell the stepper to start, stop, reverse, etc.- you need to program a ramp up/ramp down or you will lose steps each activation. You may also need a power supply and a motor driver- due to stepper motor voltage and current requirements the processor may not be able to control the stepper motor directly, but require a motor driver. Another issue with steppers, is that they can lose steps and get out of sync if stalled or over-stressed. So, you still need the limit indicators.

With the stepper motor controller chips that are available they are not that complicated to build. There are chips available that will produce a stepper voltage pattern based on forward and reverse inputs. So just one chip per motor. I also think you need limit switches, so the step counting would not be needed. In 30 seconds thinking about this layout. The stepper driver chip would reside on the gate. A 4 conductor cable would be required to send power, ground, forward (open), reverse (close) to each gate. The wiring would get more complicated if there were distributed control stations, probably a 2 conductor cable to each station (power/ground) and then 4 conductors to each gate. Or 4 conductor cables from a central point and a 2 conductor cable from each station to the controller. This last option would allow for wireless remote operation to be integrated as well.

I am working as hard as I can on my setup (lead screw design), but I have been interrupted by car repairs. We've (LOML and I) have had at least 8 different things break and require repair on her car and the truck. Some day I'll get out of the driveway and back into the shop.

[Jerome Hanby]

I haven't worked it out on paper (yet), but wouldn't a two stroke arrangement work well with a solenoid? First stroke (solenoid fires then retracts) would slide the gate open. Next stroke would slide it closed. No power needed to hold it in either state and no lead screws to get fouled. Also no fancy control circuitry to operate it, just a momentary contact switch (possibly with a capacitor to de-bounce it)...

[Alan Schaffter]

I'm sure it is mechanically possible, but I suspect the mechanism might be pretty complicated unless you did it with two solenoids- complicated enough to make it difficult to assemble so it works reliably. Again, this is where pneumatics shines.

In any case I don't think that would work due to the limited throw of a solenoid which is typically less than an inch. To operate a 6" gate you need a travel of more than 6" so would need a linkage with significant mechanical advantage and that would limit the force available by the same mechanical advantage factor- If you had a solenoid with 1" throw, the mechanical linkage would need to expand it almost 7 fold for a 6" gate. Likewise the force applied would then be less than 1/6 of the original solenoid power. If the DC was running gate slide might not move at all. Unless you had some sort of over-center cam or linkage, it would be possible for the gate slide to stop only partially open or closed. It might work on gates made like mine which have slides and inside faces of the gate body lined with smooth, high pressure laminate - minimal friction and the gate moves effortlessly, but it still takes considerable additional force when the DC is running.

If you could come up with a working linkage, you would still need some sort of control circuitry- to provide an "open" then "closed" pulse. And it can't just be a pulse or else the solenoid won't fire or extend fully- it would need to be a looooong pulse .

All this isn't rocket science, but it can get pretty complicated.

[Jerome Hanby]

Rocker science had some rough going at the start. Initially all the rockers just went back then fell over. After a while the market for testers all but dried up. The development of the rock back forward revolutionized the field.

[Dan Hintz]

Didn't the County Appraiser's Taskforce and Tribunal Against Improper Legislative Services (CATTAILS) also have a problem with the progression of Rocker science? If memory serves, they were crushed more than once...

[Alan Schaffter]

Tough crowd! What rocker? :D