High speed linear actuator 2

[cenglish]

I'm looking for a low cost/high speed linear actuator. At first I started using the

http://www.firgelliauto.com/

products, but they are just too slow. Here are my requirements:
12-24 vdc
25 lbf min
4-6 in/sec rate of travel
3+ inches of travel
low cost

The system will extend/retract 3 or 4 times in 30 second, then sit idle for 3 minutes before doing it again. I will only use the device once a month, so I don't need to over-design it for long life.

I've considered trying to build my own using a lead-screw, but don't have any experience with lead-screw design/selection. I would be interested in lead-screw design guide references if you have any. I have done exhaustive research on dc motors, but need more knowlege regarding how to couple the motor shaft to the lead screw and the bearing selection etc...

Thanks in advance.

 

[MintJulep]

Positional accuracy?

Velocity vs time profile?

Pneumatic or hydraulic cylinder banging a slide against a hard stop meets your criteria.

 

[cenglish]

Positional accuracy is not a major concern. Vel vs. time is not either. I'm limited to an electric device since the application has to be setup and broken down in the same day. The cost of hydraulics is too high and i'm trying to avoid pnuematics due to complexity. I'm using a PLC to operate the linear actuator.

I am willing to consider 110 vac if I can get the speed I'm looking for.

 

[CakeMaster]

Have you checked into belt driven actuator units?

They basically consist of a mounting block fitted with linear guide bearings/rails and are driven back and forth via a timing belt and electric motor. They are capable of extremely fast speeds and have good accuracy.

I would check Nook Industries or Danaher Motion.

 

[MadMango]

3in of travel- what about an electric solenoid and a lever arm?

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[israelkk]

cenglish

You didn't specify maximum current (in Ampres).
No limit on size of motor and system?

MadMango

If you will use a lever let say 1:10 ratio the solenoid travel will be 0.3 inch and the force will be 225 lbs. I am looking forward to see that miniature solenoid.

 

[tygerdawg]

Given your requirements, I would give some variation of a crank-slider mechanism a try. This would convert the rotary motion of a motor into oscillating linear motion.

You said "low cost", but did not specify what you mean by that. You need to narrow that down a bit.

TygerDawg
Blue Technik LLC
Advanced Robotics & Automation Engineering

http://www.bluetechnik.com

 

[GregLocock]

windscreen wiper motor.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[cenglish]

CakeMaster: the Firgelli linear actuators are belt driven. This is why I was thinking of building my own with a lead screw. Then I could design it to move as fast as I want, but I've got to put the limit switches, bearing etc in place. I was hoping to find something off the self.

I have been through Nook, Danaher and a bunch of other web sites. Almost all of them are too slow and on top of that, too expensive. I was trying to keep the cost below $150, since this is a hobby project. Sourcing in another challenge. I hate to bug these big companies with one-off purchases. Going to thier distributors and then to be pointed to a local vendor is the same thing. When the local guy hears that I just want one or two, they don't want to fool with me. I can't blame them, so I've been looking for web sites that sell one-off via the web.

MadMango: Yes, in fact I have purchased a 12vdc solenoid that has 25 lbf in a 1" stroke. To get 3" of travel out of it using a simple lever, I would need a solenoid with 75lbf. I have not done an exhaustive search on high force solenoids, but I have not found one that will generate that amount of force. Any recomendations?

israelkk: At 12vdc I'm trying to keep the current under 3 amps or i'll have to get a bigger battery. I'm not opposed to using a 110vac power supply to get higher current ratings, but then my PLC will have to control relays instead of thier on-board relays. It all just increases the complexity. Again, complexity = cost and I'm trying to minimize both.

TygerDawg: What I did not tell you is that this 3" of stroke is actually driving a slider crank to yield even more movement on the output of my 4 bar linkage. There is a certain timming involved here. Extend, hold for 3 sec, retract, hold for 4 sec, extend ...

To use rotary motion as the input to a slider crank, I would have to use a stepper motor, driver and controller. Complexity = cost so I'm avoiding steppers.

GregLocock: I have purchased some surplus electric window motors for less than $20 to use on a related project and was thinking of using them as the input to a lead screw. They are cheap and have fairly high torque output.

 

[MikeHalloran]

... and their output crank can form one arm of a four-bar linkage.

Also go to the junkyard and take a look at power door lock motors. Maybe you can build an extra long screw for them.



Mike Halloran
Pembroke Pines, FL, USA

 

[prohammy]

Try Linak at the following

http://www.linak.com/

have used them before (many, many years ago) and found them reliable


Kevin

“It is a mathematical fact that fifty percent of all doctors graduate in the bottom half of their class." ~Author Unknown

"If two wrongs don't make a right, try three." ~Author Unknown

 

[cenglish]

Hi Kevin, thanks for the heads-up. I have been to the Linak web site before, but did not find anything fast enough. I just went back to it and found that they have just released an actuator that runs at 160mm/sec. This would work for me. I'm contacting them to obtain pricing. Hopefully, I can afford it...

 

[cenglish]

I just spoke to Linak and at $500 - $600 each, I think they are too expensive...

Back to the drawing board.

 

[btrueblood]

OK, so you need cheap, quick that rules out "good". McMaster-Carr has some 12- and 24-volt linear actuators that run at about 120 in/min. at 25 lbs. force, for $200 each. See page 964 in their on-line catalog. I would bet you a beer at the pub that if you needed more than 2 in/min., you could run the motors for short duty cycles at up to twice their "nameplate" voltage, getting close to double the speed output, these being (for the price) most likely brushed DC motors. Caveats: 1) the motors will overheat rapidly (note their rated duty cycle is 10 on/30 off), so adding some means of cooling would be a good idea. 2) doing this trick voids any warranty, and probably will cause the motors, gear train, bearings, and acme nuts to wear out quite quickly (the motor brushes likely will be the first thing to wear out, if you don't burn the insulation off the windings first). You might need to bypass or disable the thermal cutout on the motors also.

Try searching on Global-Spec site, you will find more than a dozen mfgrs. that can meet your specs., but be prepared to pay more than $200 for something that will meet your specs without breaking.

 

[cenglish]

btrueblood, thanks for your post. 2 in/sec is what I have now and is too slow. I've been hesitant to run my actuator at 24vdc, but the cycle time is only 1 sec on 3 sec off. The Firgelli actuators are $100, so I could burn up 6 of them for the price of one Linak.

 

[Compositepro]

It seems a used windshield wiper motor from a junk yard would work for you.