Crank opperated hydraulic?

One would think that pneumatics would deserve consideration? Air cylinders etc.

Why add the hydraulics?

--Winston

this also sounds like a pneumatic cyl would work to me

Tight space considerations and, air is jerky and abrupt. The application will power a shear that needs to cut smooth. Sorry I didn't mention that.

Tight space considerations and, air is jerky and abrupt. The application will power a shear that needs to cut smooth. Sorry I didn't mention that.

Here's a pix of part of the mechanical:

Might be a good idea. The benefit is that it can remove mechanical complexity away from a crowded place, leaving just a small hydraulic actuator "in the zone". They do that a lot in aircraft and missiles. Ditto automotive brakes -- small wheel cylinders do the job with comparable strokes and forces.

The force and stroke you cite are certainly compatible with readily-available hydraulic components.

There are details to consider, like effects of leakage and making sure the motion at the driven end will stay in spec if there is some leakage. Mechanical systems retain geometry, and hence expected motion, unless/until something deforms or wears. All hydraulic systems with sliding or rotational seals leak, it's merely a question of how much -- molecules per decade or ounces per hour.

"Tom Gardner" wrote in news:KOVAg.2388$ snipped-for-privacy@newssvr14.news.prodigy.com:

A cam, follower, and lever would give you everything you need.

Hi Don

What do you know about automotive anti-lock brake apparatus? It seems that the devices within the car's brake system, coupled with a pump could drive a cylinder far enough and fast enough. It seems that a anti-lock system from a wrecking yard might be modified to provide the hydraulic displacement from an electrical pulse. I'm thinking automotive valve spring for piston return.

Jerry

perfect application for a solenoid

"Tom Gardner" wrote in news:JDUAg.2377$ snipped-for-privacy@newssvr14.news.prodigy.com:

The heat is gonna kill you. Moving the fluid that fast, at that cycle rate is going to generate some serious heat in short order. A mechanical linkage or a solenoid would be a better fit I think.

That's where I'm at now. The first machine had a cam that we chanced to an eccentric roller bearing. We improved this on the second machine by optimizing the lever ratios and such. I'm thinking about the third machine...what ways I can simplify it. They take nine months to build and it's several hundred machined parts...one at a time! The more parts, the more failure!

Yep! The grey area is, can I get the speed? I know hydraulics = leaks! But, we could hard pipe it and weld everything.

Do you think I can get the power with a solenoid?

Here's a pix of part of the mechanical:

If you have a double-acting system, and it sounds like you would, you'll still have some seepage around a gland seal. No big deal, but the design would need to accomodate that -- i.e., keep working right even if a little fluid is lost over time.

Don't see why speed would be any problem. Antilock brakes are hydraulic, pulse a lot faster than a couple hundred milliseconds.

ABS systems use solenoid-actuated valves. Your setup could use that, but a simpler setup might be more like hydraulic valve lifters, where you produce the desired motion mechanically in one location and then use hydraulics to replicate that motion elsewhere in a tighter place. Speed: A change in pressure travels thru a hydraulic system at close to the speed of sound in the fluid -- which is considerably faster than it is in air. In a system with a few feet of hydraulic line, I would think that operation at frequencies up to 100 Hz (cycles per second) would be no problem.

One issue could be wear. Your hydraulic gizmos will be cycling back and forth over a short range at 90 strokes per minute, or 43,200 strokes per 8-hour shift. I don't know how many strokes hydraulic cylinders are good for before they need a rebuild.

You certainly could with a big enough solenoid. But solenoids primarily produce force, not displacement, and the force is quite nonlinear with displacement. Solenoids are more suitable for bang-bang short strokes where there are only two stable positions and slamming from one to the other is acceptable. If the driven element must have motion more determined than just slamming between two stops, I don't think a solenoid would be suitable or satisfactory.

The size and weight of a solenoid or other electromechanical actuator that could deliver the required force and displacement may be more objectionable than the mechanisms it would replace.

Electromechanical actuators (solenoids, motors, voicecoil actuators) tend to have a lot more mass/inertia than hydraulic actuators, so there would need to be enough excess force capacity to achieve the necessary accelerations and decelerations.

With this sort of intermittent reciprocating action, current-controlled excitation with considerable voltage overhead would be a must to minimize heat dissipation while achieving the rapid changes in force. No big deal, but something else to design and build or have designed and built. I don't know of any off-the-shelf solutions though there may well be some available.

If the motion must be bi-directional (both push and pull) then one would need either a heavy spring (hence twice peak actuator force), a voice-coil actuator or two solenoids where a single (considerably smaller) dual-acting hydraulic actuator would suffice.

If the plumbing is relatively unrestricted, the heat produced would be considerably less than that generated by a solenoid.

Tom, you haven't said if this motion must be somewhat deterministic, as it would be with a cam and follower, or if it can just bang between stops with no regard to speed other than "fast enough" as in wham (pause) wham.... ? Further, is it 300 lbf as against a spring, or must it both push and pull?

While you are thinking about the redesign, is there any other places where hydraulics would work well. I am thinking that if you had a hydraulic pump and accumulator, you could use a spool valve to actuate the shear. And could use hydraulics for other things as clamps.

Dan