Mechanism to allow change of inclination angle.

[jimmybobshortpants]

Howdy all,

I'm working on a little project that I need some help with. My objective is to hold a flat plate, but, using a stepper motor and encoder, be able to change the angle that this plate is at.

My rig will consist of a motor (at the top, shaft pointing down). There will be a casing from here that extends ~300mm down, then a right angle bend and another 100mm or so. (forming a large L). At the end of the short arm of this L I will place my plate (on some form of hinge to allow motion from 15deg (from the horizontal) to 90deg (perpendicular to the short arm of the L).

Now this is all easy enough, but I need some way of controlling the angle of the plate. I can place shafts and gears and whatnot inside the casing to join the motor to the plate, but I need some way of using gears to control it. I thought of having a bevel gear at the corner of the 'L' to change the orientation of the motion, then at the end of the second shaft I could put a thread, converting this rotation into translation. And from this I could fix a linkage to the plate. I don't think this solution will provide enough of a range in rotation angles, however. I've attached a (very) rough sketch of what I've just described.

Any help would be greatly appreciated.

 

[jimmybobshortpants]

 

[jimmybobshortpants]

I'm not sure if the picture worked so here it is as an attachment.

 

[EngineerErrant]

What sort of moment load are you expecting at the hinge, and how fast does it need to move?

"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." -Scott Adams

 

[jimmybobshortpants]

Speed is not an issue at all. I just want to move it into place and it'll stay there for a while.

As for moments, the plate will be ~200mm wide by ~100mm high and immersed in flowing water. The moment will, of course, vary with the angle, but I don't imagine it will be too high.

 

[rb1957]

agree with the question about load.

are you trying to close the arms of the L as it rotates ? (the two arrows confused me ... not especially difficult to do)

i don't think that bevel gear will work well, won't it bind as you get to either extreme ?
why not a gas spring actuator ?
or a link that extends mechanically (like a worm-drive) ?

 

[jimmybobshortpants]

The arrows were just to describe the rotation of the shaft in the housing. The red arrows were representing the translation of the 'internally-threaded' piece.

And yes I had thought of a worm-drive, but thought that I would need more gearing to achieve this.

My main concern is to make the whole thing as compact as possible as the larger the housing the more influence it will have on the flow of the water and hence the more disruptive it will be to my tests.

 

[rb1957]

i got that the red arrows represented the drive thread. ok, so you just want to rotate the L about the pivot.

does it need to be something driven, ie operated remotely, or could you use a simple telescoping rod with pins to maintain a length (once set) ?

do you have access to the RH side of the blue box ? the support for the red link ? could you have a simple cable attached to the L, running up to the red link attachment and through to the other side of the blue box ? taking in or paying out the cable would rotate the L. but this'd only work with down acting loads.

 

[jimmybobshortpants]

The green (the L) is fixed. The blue plate is what I want to be able to adjust the angle of.

And yes it needs to be remotely operated so I can automate it.

I doubt I'll be able to use cables as the forces will be fluctuating and I need a rigid connection.

 

[hydtools]

Can you use a worm to drive a gear attached to one end of the pivot shaft? Direct and reasonably stiff.

Ted

 

[jimmybobshortpants]

DO you think that will allow for enough motion (75 degrees?).

The pivot shaft was just an initial idea so if there is a better solution I'm happy to change it.

 

[rb1957]

"The green (the L) is fixed. The blue plate is what I want to be able to adjust the angle of." ... boy, the arrows didn't make that clear ! oh, i see now, the arrows are showing a worm drive rotating.

if the L is the space you want to work within, to control the blue plate, how about attaching a pair of rods to the blue plate, pivoting them about a fulcrum. then a linear actuator (or worm drive) to drive it ? this'd give you twice the movement (at the cost of twice the vibration/slop, there will be slop in a worm drive). or would it ... if you had two barrels (moving on the worm drive) in opposite directions, then wouldn't they be driven to opposive sides of the worm thread and so be stable(r) ?

 

[hydtools]

Use a push-pull control cable. You could time a repeater indicator at the control end to directly indicate the plate angle.
To reduce worm gear play, use a zero-play gear.

Ted

 

[IRstuff]

The picture implies that you want to use the motor that's not shown to tilt the plate?

One obvious option is to use a threaded sleeve to which the red line is attached with a hinge, then, as the sleeve moves left/right, the red line would be forced to tilt the plate.

The most compact solution would be to use gear motor that replaces the fixed part of the hinge, and gear motor drive shaft replaces the hinge pin, assuming the mass and load are not huge.

TTFN
faq731-376

 

[zekeman]

Can you give us an idea of the mass of the plate and the accuracy needed for the the plate angles?

Why all the complication for simply trying to rotate a plate? or am I missing something?

Might not Irstuff's gear motor with a high gear ratio be a good solution ?


Or a stepper, or a servo?

 

[jimmybobshortpants]

The complication comes from two parts, one is that everything is under water (except the motor). Secondly, because I'm trying to look at the flow structures around this plate, it's pretty important that whatever holds the plate is influencing the flow as little as possible. That's the reason for the strange request.

Also the plate will be stainless steel and be up to ~200mm x ~100mm. Though the main force will be due to the water flow rather than the weight.