Speed Control on Hydraulic Driven Conveyor

Foreman174

Member
Join Date
Nov 2005
Location
Ames, Iowa
Posts
2
The speed control of my hydraulic belts currently consists of a 6-tooth sprocket affixed to the the shaft of the belt drive opposite of the hydraulic drive, and a prox switch witch counts drive revolutions. I have a program which times, individually, 4 complete revolutions of the shaft. Those times are then averaged to come up with a belt speed and then object dwell time. Does anybody else use this technique for speed control??? If so, do you have any advice for attaining more accurate speed readouts?
 
Last edited:
Your application isn't that clear and I don't know what is driving your question. Are you having problems now? What are your accuracy criteria? How is "dwell time" defined? etc...

That being said, here are some possibilities without sufficient data to back them up.
Why not just put an encoder on the shaft? You will get much better accuracy if that is what you are worried about. Alternatively, if you don't want to spend much money, I would suggest adding more teeth and/or reducing the averaging.
 
Any application where we want motion feedback(speed, or direction, or position, or all three) we alway use an encoder. Always.
 
Please define the system in more detail. If you have fixed speed thru gearing then technically it should not change...exactly how do you control the speed?

An encoder can offer more accurate resoulution but if you do not have a means to use the information it is worthless.
 
Foreman174 said:
The speed control of my hydraulic belts currently consists of a 6-tooth sprocket affixed to the the shaft of the belt drive opposite of the hydraulic drive, and a prox switch witch counts drive revolutions.

I have a program which times, individually, 4 complete revolutions of the shaft. Those times are then averaged to come up with a belt speed and then object dwell time.

Does anybody else use this technique for speed control??? If so, do you have any advice for attaining more accurate speed readouts?

So what your saying is you actually get a speed sample for every 4 revolutions.

Serious details are missing, like the speed of the shafts, (RPM) & your current display update rate. Right away you can likely update your speed reading by timing ONE revolution of the shaft; but that depends on the actuall RPMs and your program scan time & your timers resolution (1/10 or 1/100sec). Maybe Maybe Maybe??

If you really need to improve the speed update, then post the details on your equipment and we'll see?
 
Are you saying that the Sprocket is used just for the Prox to count teeth. Cheep way of making incoder, I've done that before in the past. Now incoder don't cost that much, The trick is to connect the incoder to the shaft.
 
I have done the same thing before, but have used a 15 tooth sprocket on a shaft that turns 500-600 rpm. Cheap and resonably robust in the sort of environment and with the millwrights I work with (the only tools they own are a hammer, a bigger hammer and an adjustable wrench:)

An encoder would just not last on the end of the shaft of a hammer hog.

Willpower
 
Why use hydraulic, in this case, remote location, the customer has (3) Cat 3206 Diesels he uses as power packs. From there he drives multiple pump combinations, he can then have individual speed control on the conveyors and screens. With the price of Diesel right now, he wishes he had paid the $300K to bring electrical service into the area, he may do that yet. With all of the hydraulics it keeps me busy anyway.
 
Peter Nachtwey said:
More teeth!!

Why use hydraulics?

Hydraulice is a lot of power in a small package. Slow speed is its plus. There are a lot of advantages useing hydraulics in some applications over other power sources.
The one big disavantage when it failes, oil everywhere.
 
I still think Foreman174 just needs an extra tooth on his sprocket.

Where did Foreman174 go? Until then.....

Rich1955 said:
Hydraulice is a lot of power in a small package.
How is a 5 HP motor pumping hydraulic oil any smaller than a 5 HP motor geared to a conveyor?

Rich1955 said:
Slow speed is its plus.
Why?

Rich1955 said:
There are a lot of advantages useing hydraulics in some applications over other power sources.
Name a few.

Rich1955 said:
The one big disavantage when it failes, oil everywhere.
What fails? Failures happen with any system that is poorly designed or maintained.
 
I know I will get flamed for this one....

One of the differences with hydraulics and strictly electrical systems is that, you can put an electric motor in and have it run well for 30 years or longer with minimal maintenace. Try doing that with a hydraulic system.

They both have advantages and disadvantages. With the advent of better and cheaper variable speed electrical motor systems, it can be both easier and cheaper to put in a VFD over a variable output speed hydraulic circuit.

Where the advantage lays with hydraulics is in linear motion, and especially large press and compactor systems. Although there are advances in electrical linear positioner systems, they can not yet rival the tonnage developed in large hydraulic systems.

On that note, whats the largest strictly electrical linear motion system that you folks have seen. I have personally not seen very many but know they are around. The largest hydraulic press system, in tonnage would have to be one that I worked on a few years ago, used for forming, pressing, and cooking multipel 4X8 sheets of particle board. And the OSB presses, they are pretty cool too.

Willpower
 
Ames Iowa...Having spent some time down on the farm, & a LOT of time on construction sites; I get the picture that this may be a peice of portable farm or construction equipment. If so it's likely driven by a PTO.

The other possability is that's it's in a hazardous enviorment.
 
How is a 5 HP motor pumping hydraulic oil any smaller than a 5 HP motor geared to a conveyor?

I was speaking of the size of the Hydraulic motor. When space is limited it is easer to install with no gearing and still matain alot of torque at slow speed.

There are a lot of advantages useing hydraulics in some applications over other power sources.

How about several Hydraulic motors and cylinders with the same Pump.
Starting under a load
Match a phunamic cylinder to a hydraulic cylinder (size and power)

The one big disavantage when it failes, oil everywhere.

Failures really can not be perdicted even maintained properly and desined. New parts can fail right out of the box.
 
The reasons I give for using Fluid Power Motors (Air or Hydraulic) in my basic Fluid Power training book. Many are stated in this thread already.

The main reason cited for using air or hydraulic motors is they have high torque in a small package. Air drills of ½- 3 HP for many rotation speeds and torque take less than a third of the space a comparable electric motor setup. This means space at the work is less cluttered and/or more units can be applied. Hydraulic motors are even more compact especially in higher horsepower units. The main reason for the small size is no reduction gearing is required for hydraulic motors and small planetary units work well with air motors.

Other reasons for choosing fluid motors are:

Ø Instant or almost instant reversing capabilities. Since these motors are so compact and have little inertia to overcome they can reverse rotation quickly without damage. Some motors act as oscillators that never make a full revolution.

Variable speed capabilities of fluid motors is simple and results in little change in torque when it is a low speed high torque hydraulic motor. A change in flow with flow controls or variable volume pumps requires little sophistication when minor RPM changes can be tolerated. Sophisticated servo controls allow speed changes and can maintain tight control of speed at any RPM.

Ø Overload protection is part of any fluid power system and motors have the same ability. When a motor circuit meets resistance it cannot overcome it stalls and holds torque without damage to the circuit or machine.
Ø
Along with overload protection is a fluid motors capability of stalling for long periods without over heating or damaging itself. There is some internal leakage while stalled but this can be minimized with the right motor selection.

Another place where fluid motors shine is in wet or explosive atmospheres. These motors have no electrical input so they pose no threat from sparks or over heating. A hydraulic motor can operate under water with bio-degradable fluids without any of the problems electric motors have in this application
 

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