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Help with a stuttering air cylinder

Help with a stuttering air cylinder

Help with a stuttering air cylinder

I am designing basic manual lift using hydraulic cylinders with air as the power.  It works pretty well but the cylinder stutters when it isn’t being run full throttle.  So far I have tried to use an ail to oil reservoir to address this issue but I know that must be a better solution.  Would a balance controller be a better option?

RE: Help with a stuttering air cylinder

I would take a second look at the hydraulic seals.  You may have to change out the hydraulic seals for ones intended for pnuematic operations.

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RE: Help with a stuttering air cylinder

A few questions:

Is the cylinder/s Pulling or Pushing the load?

Is the load always the same?

Are the cylinder piped double acting or single acting?

Are you metering air in or out to control speed?

Are the cylinder/s new or broken in?

What is a "balance controller?"

Air-Oil is a reasonable solution. You could use the tank idea you mentioned or what some companies call Dashpots, Self contained cylinders with oil in them that transfers from one end to the other thru a flow control and hold back against a driving force.

Bud Trinkel CFPE
fluidpower1 @ hotmail.com

RE: Help with a stuttering air cylinder

Is there one or two cylinders involved? If two, could it be a synchronization problem?

David Baird
Sr Controls Engineer
EET degree.
Journeyman Electrician.

RE: Help with a stuttering air cylinder

The load is being pushed and is not always the same weight.  The cylinders are double action and are broken in.  There is a air pressure regulator on the air input.  
A balance controller is a device I ran across recently.  It seems that is primarily used with PLC's but there is some mention that it can be used manually.  The manufacturer that I found is SMC.  From my understanding the device monitors and adjusts the air pressure in the lines to insure there is a constant motion by the cylinder.   

RE: Help with a stuttering air cylinder

The Balance Controller is a new for me. ARO has a similar device but it is not as sophisticated as SMC's appears.

With changing loads the circuit I was thinking about would not work well unles the change was intermittent and someone couls adjust pressure when it happened.

With fixed loads I use a 5-Way with dual inlet pressure and regulate the Cylinder Cap End to say 80 PSI and the Rod End regulated to a lower pressure so the load takes off quickly and usually operates smoothly. This works well for fixed loads only and pressure to the Rod End must be changed with any load change to eliminate start pause and lunging.

You didn't say if you are using Meter In or Meter Out flow controls. Meter in can cause lunging or chatter since pressure must build to breakaway force and often expands to running force plus a little more and tries to stop. Then pressure builds again and the whole scenario starts over.

If it were my call I would use air oil tank on the extend with a meter in and meter out flow control on the cap end and no flow control on the rod end. Throw full pressure to both ends and if it has a pause before extending then put a Quick Exhaust on the rod end port.

Bud Trinkel CFPE
fluidpower1 @ hotmail.com

RE: Help with a stuttering air cylinder

You may want to double-check that you are not getting a side-load or binding condition, and/or that the piston has a teflon bearing ring on it.  "Stuttering" is caused by stick/slip friction; minimize the friction forces and you'll reduce the speed/load at which it starts to happen.

RE: Help with a stuttering air cylinder

I read your request for a solution to two cylinders having unequal loading.

In the 70s I had to design around a similar problem. In any application having two cylinders operating in parallel powered by a common hydraulic or pneumatic source one of the cylinders will always move first and continue to move until the total load on that cylinder exceeds the total load on the other cylinder. This total load is the external load on the cylinder plus the frictional load in the cylinder. This process is also duplicated in the pistons in flow controls people try to use to correct the unbalanced cylinder loading. Multiple cylinders connected to a common pressure supply will always produce some jerky motion when lifting a load.

Try this: Replace each cylinder with a ball bearing jack screw. Secure the ball bearing nut in a sprocket. Thread the sprocket and nut assembly on the ball screw. Insert the ball screw through a thrust bearing having a thrust load capacity equal or exceeding the cylinders you are presently using. Thread a roller chain around the sprockets on the ball screws and an idler sprocket or sprockets.

Add one more device to the roller chain system. It will consist of a sprocket mounted on a air-to -release clutch. The clutches with mating toothed plates work best. The clutch must have a spring capacity exceeding the total maximum total load the lifting assembly will ever encounter.

The elevator (cylinder) drive shaft is connected  through a pressure-engaged load clutch to a loop of driving chain. A pressure-released load brake holds the drive shaft when the clutch is disengaged. A power cylinder and its smaller bore, stroke reset cylinder are connected to opposite sides of the driving chain loop. The power cylinder moves the chain to rotate the drive shaft with an action similar to a rotary actuator.

When an elevator (cylinder) lower signal is present, the clutch engages, the brake releases, and the power cylinder extends. The extended reset cylinder on the opposite side of the chain is pushed mechanically to a retracted position by the larger power cylinder.

The full stroke of the power cylinder does not have to drive the elevator for the height of a complete extension. Therefore provision is made to reset the power cylinder to continue lowering or raising.

If the power cylinder reaches the end of its extension stroke and the controls signal that the elevator must lower further, the clutch disengages and the brake engages to hold the load. The power cylinder is exhausted and the reset cylinder extends to drive the chain loop in reverse and retract the power cylinder mechanically. When fully retracted, the system is back in initial condition.

Versatility: To make these machines adaptable to a wide variety of operating requirements, individual pressure regulators are included in most control and power branch circuits. Efficient dual pressure circuits are used extensively. A multi-station machine pressure monitor can give readings for any branch. Flow control valves set individual cylinder speeds.

Separate  visual indicators monitor each step on the control panel and on individual logic elements. All power valves have manual overrides for start up and system checking.

To make it possible to trouble-shoot by telephone, if necessary, component and conductor numbers are dedicated consistently on three types of machine. Pneumatic tubing in the power air circuits is color-coded, and logic tubing has burned-in identification numbers.

This reply is a hasty prepared adaptation of fluid power configuration I designed many years ago. It has many fail safe components. It has been controlled by only air-logic components without any electrical power to machine for either control or lifting operations. It has also been adapted to fluidic control,  PLC and relay control. The air-logic control provides a minimum of electrical wiring at most and uses the control system air to provide power both to the controls and cylinders.

I'll be happy to talk with you further if any of this would help you with your problem.

Bill Bowdry, P.E
Carowill Services

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