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Need to be able to firmly lift about 110Lbs (~50Kgs) weight, through a distance of upto 12 inches. The weight can be considered to be a flat & square wooden board, hinged to a flat platform, with the lifting action applied to the free end, s.t. the wooden board slopes at an angle, when a signal is applied.

Also, I need that the lift should be proportional to signal duration or strength (voltage), ideally not be jerky (or be minimally be so), and it should be possible to reduce the lifted height as well.

Would like to understand the potential options available for the required mechanical action, on application to electrical current. Few things on my mind are electronically-controlled pneumatic lifts, gear-and-pully with stepper motor. An indication of the relative costs (amongst alternatives), would be of great value.

bdutta74
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    How "firmly" does it need to be? Pneumatic is a very good option, but it will be "springy" in the lifted position. If it needs to be more "locked" into position, a leadscrew driven by a motor might be a better idea. Are there any constraints on the speed of lifting/lowering? – Dave Tweed Oct 18 '12 at 15:34
  • Have you considered [Air Muscles](http://www.shadowrobot.com/airmuscles/overview.shtml)? – Rocketmagnet Oct 18 '12 at 16:33
  • @DaveTweed, an excellent point there. Slightly springy is acceptable, although I am unable to quantify (by how-much) exactly. Also, another excellent question is the speed of lifting/lowering is important. full lift / full lowering (12") should ideally be attainable in 5 seconds. For lead-screw driven by motor type of actuator, the speed seems to be constraint. – bdutta74 Oct 19 '12 at 06:15
  • @Rocketmagnet, had not heard of Air-Muscles until I saw your response. Thanks for the link. – bdutta74 Oct 19 '12 at 06:15

2 Answers2

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A fairly simple pneumatic actuator is the Air Muscle.

Air muscle

It consists of a rubber tube surrounded by a plastic braid. You start out with the muscle stretched out, and when you pressurise it, it contracts with considerable force.

Muscle extended Muscle contracted

The one problem is that they only contract about 30% of the braided length, which means you'll need a muscle about 3 foot long. However, you can have muscles custom made to your required length.

It's possible to use them for precision control, e.g. in a robotic application:

Robot arm with Air Muscles

If the weight of the platform is constant, then you simply need to control the pressure in the muscle to control the height of the platform.

If the weight of the platform can vary, then you'll need to control it's position directly. Add a position sensor to the platform, and use a microcontroller running a PID controller to adjust the muscle pressure.

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Rocketmagnet
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    Shameless Plug, Shameless Plug, Shameless Plug, Shameless Plug – Connor Wolf Oct 19 '12 at 03:21
  • Very interesting (and impressive) technology. Wondering however, if the Air-Muscles are indeed "Lower Cost" as in "cheaper to buy and install than other actuators and pneumatic cylinders" as claimed. For Muscle-30 at 95 GBP, (without the pneumatic pump, I believe) seems to be significantly more expensive than linear-actuators for instance, unless I am missing a subtle point here. – bdutta74 Oct 19 '12 at 06:08
  • @FakeName - Correct. I'm not ashamed at all to offer one of our products to solve someone's problem. – Rocketmagnet Oct 20 '12 at 09:18
  • @Rocketmagnet - To be clear, I (at least imagined) the "Shameless Plug, Shameless Plug, Shameless Plug, Shameless Plug" statement to be in a monty-python-esque announcer voice. It was intended to be jocular, not insulting. – Connor Wolf Oct 20 '12 at 10:45
  • Yet another situation where the medium (text) doesn't properly carry the intended overtones, and I failed to make them explicit. – Connor Wolf Oct 20 '12 at 10:47
  • @FakeName - Oh no worries. You're right, a lot of meaning gets lost in the comments. – Rocketmagnet Oct 20 '12 at 20:43
  • And of course, because I mentioned monty python I wound up watching the parrot sketch on youtube, Which eventually resulted in an hour of watching various monty python sketches. – Connor Wolf Oct 21 '12 at 06:30
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It's going to be difficult to get a pneumatic system to stop exactly where you want it to. Hydraulics could be used, but would be complex. The simplest concept I can think of that can be moved to specific positions would be an electrical actuator, perhaps with an encoder if you needed that level of precision. Basically it's a leadscrew with a lead nut and a shaft driven by an electric motor. The screw provides significant gearing, so the mechanical advantage of the motor is increased. They're used a lot for garden tractors and riding mowers. Surplus Center is a good place to look if you're not planning on going into production with these. This 107 lb actuator looks like it may be close to what you want

lyndon
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  • Wow, that seems to be incredibly close to my requirements. Also, it's price is close to what I consider as "affordable" for my application. Need to spend some time understanding it's mechanics more thoroughly. The only thing that could be bettered is the "extension" speed. 30sec's for full-extension at full-load, is higher than what I was hoping for. Thanks for this sharing this. A strong "accepted answer" candidate for me. – bdutta74 Oct 19 '12 at 06:03