Linear or Rotary Actuator

The type of tracker, I am talking about can be seen in the link below,

http://www.google.com/patents/US20140053825

Thanks,

- NTR

ntr,

Using a patent to describe the workings of a mechanical drive is just about meaningless.

While patents are written to disclose how things work to "those well schooled in the art" they rarely depict the actual workings of such a device.

Think screw drive garage door openers. Simple, and when they stop the driven device can't move.

Or automatic gate openers as JE said.

The mechanicals in that patent basically show how a rotary system can be implemented and still have the desirable features of a linear actuator, except maybe cost, but that can be debatable because of the parts coming out of China.

While in the truest sense rotary motion is not converted to linear, if you look at the closely it actually does create linear motion in a loose sense, at least in the most desirable configuration of a worm drive. With many mentions of a worm drive using different nomenclature, as well as the fact that it is kinda obvious, I'm surprised the patent was issued.

You've got a small motor driving a worm gear which is basically a screw. Instead of a screw that turns and moves a non rotating nut along the screw, the worm gear turns and the ring gear rotates. At any snapshot in time the portion of the ring gear engaging the worm is moving linearly. While not as easy to visualize, you could think of this system in terms of a rack and pinion. A rack is just a ring/spur gear with an infinite radius.

The patent describes a system in which multiple rows of panels can be driven with one device. Each rotation axis has a beam or whatever rigidly attached to it, and the other end pinned to a piece that spans the length between the first and last rows of panels.

This construction forms a 4 bar linkage between any 2 rows. The 4th (pinned but stationary) bar doesn't physically exist, but it would tie the 2 rows together at their rotation points. So you have one motor and a mechanical element that rotates one row of panels, this rotation is transferred through the rigidly attached bar to the piece that runs the length of the rows.

Think oof the panels as the slats on a shutter that can be opened or closed with the piece of wood that runs from top to bottom of the slats.

The work gear creates a ton of torque in the ring, and it's virtually impossible for the ring to back drive the worm. So just like a linear actuator, a small motor with no brake can be used. The patent allows for many different motor/drive combos. There is cost/benefit associated just like there is with a linear actuator. This will likely replace linear actuators, although mostly on large arrays.

So what advantage does the rotary drive have over the linear drive described as "prior art" in the patent application?

Smaller motor for the same size array. Linkages are much more simple, although a linear actuator could be used to operate one row which then transfers to a 4 bar. Most efficient rotary to linear motion conversion with a force multiplier is a ball screw with a clearance nut. To get large angle swings you need a long screw, and even with the cheapest rolled screw you are still getting micron accuracy which you definitely don't need, and don't need to pay for. Of you are dealing with a large system then a larger diameter and higher priced screw is needed. Every gear in the reduction drive robs power.

Probably the biggest advantage will a rotary system is the ability to rotate the panels a full 360 degrees, although 180 is all you need to flip the panels for whatever reason (protection/maintenance/etc). Worm and matching spur gear with no accuracy requirements are incredible easy to make. A lathe will live tooling and a Y axis could knock them out very quickly, or a basic lathe and a basic mill with a 4th axis. No need to find a hobbing machine which is pretty difficult, if you do find one that will make your parts your back account will get a lot smaller, or you're buying stock gears. Both cases you're getting accuracy that isn't needed.

All that can be tossed if you use a harmonic drive or planetary reduction, or any other simple gear reduction, these would likely need a brake which doesn't really as too much to the cost of a motor. Gear reductions here will have the same problem of robbing power in a linear drive.

Worm gear setup needs practically no maintenance as it simply sits in an oil bath. At most an oil change and possibly resetting the spur periodically to create even wear, although I'm not sure that would even be a problem. However, with a ball screw, there are automatic grease products available which have replaced most oil systems for ballscrews and linear guides in machine tools. Just change the cartridge when needed. In this application they would likely last quite awhile.

I'm pretty sure you already know all of this. Cost/benefit analysis at the time of design is required, just like it is when designing anything else.

How about looking at the picture of "prior art" in the patent application? It's the SAME LINKAGE, dammit!

I mixed up the figures, and technically the prior art doesn't match the new embodiment.

Regardless, what I said about using a linear actuator is valid. Motor mounting and actuator to linkage mounting is going to be more complex than if a rotary is used.

Besides that, everything else still holds.

Perhaps you are a patent attorney?

They seem to subscribe to the philosophy of why use 20 words when you can use 200?

LOL. I'd probably kill myself. Just getting the patent process started as an engineer is painful enough!

I know my posts tend to be long. Unfortunately my brain isn't made for forums. I'm always in "report to the boss and higher ups" or "teach" mode. When I see a one liner question I tend to get pretty verbose and try to explain everything very clearly. But this is a forum, not work. At work I might write exactly what I did in response to that patent, but then I'd go over it a few times to edit and trim. Actually, considering my profession that post would never hit paper. We design and manufacture machine tools, including a crap load of rotary tables in which all but the smallest use ultra precision worm drives that are hobbed on ridiculously expensive Studers. That post would be t reduced to a 60 second conversation with my boss.

Well, it's fine to be thorough. Especially if you know what you're talking about.

The teacher mode would have been my second guess.

I'm sure many here welcome completeness and competence.

I tend to go the other way and assume that everyone knows what I mean after a sentence or two.

If not more words are just wasted.

More compact?

Simpler?

Better holding torque?

Longer 'throw'?

Self-deleted.

John... you seem to have miss spelled "deluded"
Del

Now you misspelled bright spark!

Probably boils down to cost, but a lot of these linear actuators are simply a DC motor that is geared down to turn a jackscrew.

The advantage is both cost and high torque.

A small motor geared way down can produce huge amounts of torque and the speed of the reduction ratio does not need to be fast at all.

Thank you all,,

John I didn't understand, why you deleted your post.

Please let me know, if there is anything more to understand.

Thanks,

- NTR

My reply was too simplistic; it only held true for the same type of motor. As AH pointed out, a small, low-torque high speed motor could be used vs. a high torque low speed type.

Then there is this new development, which if successful, may eliminate the need for such actuators.

http://cr4.globalspec.com/blogentry/25080/Half-Price-Solar-Power

Also gear reduction adds enough friction that the motor does not have to hold a position.

Most linear actuators are powered by motors. These motor are they not rotary actuators being used for linear motion. The amount of work it takes to move the panel doesn't change. If the motor is on a gear reducer to apply the rotational force. Comparable torque would for both ways be about the same.

Linear actuator is a simpler design.

A high-torque gearbox simply costs more than a jackscrew.

I think it all depends on the design...

Whether it's electric or pneumatic or hydraulic, the size, and off the shelf parts available....

linear actuators are better suited for the job. plain and simple.

Look at automatic gates. the majority of them are installed using linear actuators.

There are a few models that use either large external rotary actuators with a long scissor hinge, as well as some crap models that try to work directly at the hinge point.

By far the most reliable, simple and cost effective way to position a panel is with a linear actuator.

Nearly all the actuators are have rotary drivers... they just incorporate a linear element to transfer the movement over a longer distance. To do that with rotary components needs a lot of cogs or very big ones. A belt or chain would do it, but you have backlash and wear problems. It's all about choosing the most suitable drive for an application.
If you are building something yourself, the most suitable is whatever you happen to have lying about in your junk stash.
Del

(anyone ever noticed that Application has "cat" in it?)

Linear actuators have been around for many years, they are cheap and reliable. Now if you track in both altitude and azimuth, the altitude will be controlled with a linear actuator and the azimuth with a really big ball bearing with a ring and worm gear drive like this:

...and the completed install looks like this: