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rotary to linear converter
13

rotary to linear converter

rotary to linear converter

(OP)
I need a way to convert rotary motion to linear motion just like a rack and pinion, but it can't be a rack and pinion or a ballscrew.  Anybody have any ideas.

RE: rotary to linear converter

A drum and a piece of string?

I think you need to ask a slightly better question.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: rotary to linear converter

crank-slider?
hydraulic pump and pistons?
pulley and string?

 

RE: rotary to linear converter

I think some type of bar linkage or a disk cam with a translating follower would be the simplest, but much would depend on the loads, speeds, and what it is that you are moving and/or doing. Perhaps and electronic cam or servo system ?

A lead screw system is another fairly simple option for rotary to linear translation.



  

RE: rotary to linear converter

Need some more information on the application.

How big, how much force, how accurate, is there contamination, is there lubrication, does it need to back-drive or does it need to resist back-driving, does it need to transmit linear force in both directions, etc.

RE: rotary to linear converter

An automobile?

RE: rotary to linear converter

Sprocket/pulley & belt/chain.
Cam & pushrod.
Slider crank.
Four-bar linkage.
Drum & cable.
Hydraulic pump & cylinder.
Ratchet & pawl.
...

Don
Kansas City

 

RE: rotary to linear converter

(OP)
A few more details seem in order.  The need is based upon a valve actuator which has an approximate mass of 4 grams, needs to move .400 inch in approximately 20 msec.  Positioning accuracy should be to .001".  The killer requirement is that it must be able to return to a default position in the absence of power.  The rack and pinion is perfect except for the backlash of the gear set.  To eliminate this would require more force and consequently watts than are available for this battery driven device as well as reducing overall speed.  Power cannot exceed 10 watts.  Duty cycle may be as high as 75%.  By the way, reliability is paramount since this is a life support product.  Thanks everyone for your assistance.  I'm new to the post and appologize for any breach of protocol.

RE: rotary to linear converter

Adding to the post by BigBboris here is the Serapid push pull chain we used on our conveyer lines for 2000 lb synthetic fiber cans.  

http://serapid.com/gb/accueil1.html

RE: rotary to linear converter

Why not use a solenoid w/ spring for return on no power ? Even better, if the load trying to push the valve back is low you could use a latching valve so you're not constantly energising the coil.

RE: rotary to linear converter

The real killer requirement is the 20ms.

Takes a lot of voltage to get a solenoid up to full current in that kind of time.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: rotary to linear converter

(OP)
75% duty cycle is 20msec to position and immediately 20 msec to return then pause 12msec. The chain idea is good, but way too big, this package must be in a profile of < 2"x2" x 5".  It also can't be just a solenoid since it needs to be proportional.
 

RE: rotary to linear converter

(OP)
The rack and pinion is probably the best, however, our challenge is to not use this design if possible.

RE: rotary to linear converter

2
Voice coil actuator with servo amp. Could be expensive and steep learning curve.

RE: rotary to linear converter

How proportional must the control be, and what is the variable being controlled ?   

RE: rotary to linear converter

(OP)
No, this is most certainly not a school project--it is an actual life support device controlling low pressure flow of gas.  I am experimenting with a linear motor currently, and a voice coil is also a possible choice.

RE: rotary to linear converter

(OP)
Overall control needs to be to position to .001" and hold against varying pressures.

RE: rotary to linear converter

Out of the box,
Could you use an arragement like the tatoo machines. I know they can recipitate .250. Don't know about your requirement. If applicable you could use the needle as the piston.

http://unimaxsupply.com/tatmch/1swash1.htm

http://unimaxsupply.com/tatmch/1swiss.htm

If you didn;t need the dwell time you use a cheap PM dc with a larger shaft and an offset crank pin.

We have some production machinery that uses small PM DC motors to provide oscillating movement to a wire.They buy $1.39 motors, original $.39.  All I know about them is that they tell me the're are operating on AC. I called the inventor of this system and asked him about your problem. His response was that his design would not work due to speed requirements.  

RE: rotary to linear converter

I'm with alansimpsom, a voice coil-servo drive is the only way to get those speeds and accuracy.  There are some quite small linear optical encoders available today for position feedback.  A flexure mechanism can be used for the linear motion and would also provide the spring return to the unpowered position.

Let me add that voice coils and magnet housings are easy to design and easily built in-house.  I say this because purchased voice coil actuators are insanely expensive.

I can supply all the details you might need if you should elect to try this option.

RE: rotary to linear converter

0.4 inch in 20 ms is about +/-12 G with a peak velocity of about 20 in/sec.  Most of the accelerated mass will be in the straight line flexure and voice coil  Voice coil bobbin aluminum, flexure EDMed titanium (low mass, high strength, good fatigue resistance).  To keep the voice coil cool, ferrofluid in the voice coil-magnet housing gap.

Renishaw just came out with a self calibrating linear encoder.

RE: rotary to linear converter

(OP)
Thanks for all the suggestions and good ideas!  The voice coil is one of the leaders.  I have a valve company quoting on a custom product.  I don't know if I mentioned it but it has to control air and oxygen up to 100% oxygen at room temp.  I experimented with a linear motor today and got some very surprising result--great control and ultra fast speed.  I also have proposed a butterfly valve design which I built to a valve mfr who is considering a custom version for us.  Thanks for the concentration of brain-power on my challenge.
 

RE: rotary to linear converter

Can you use a piezo actuator?

RE: rotary to linear converter

(OP)
Piezos won't work because they don't release upon power loss.

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