Tension Control

I've used a small dc motor with a chain (the cheap plastic ones) holding the reel at a constant torque while I just pull past that torque (which, at constant radius translates into constant tension). Just make sure the motor will run 100%. You can also run a Prony brake if you can live with constant force with more variance. There are also some mechanical tensioners available from people who supply coil winding equipment if you want to pay more.

Belay that answer. After posting, I realized you probably need to go from a full reel to an empty one with constant tension. In that case, use a sheave on the dc motor with the material wrapped once or twice (till it doesn't slip) around it.

I have seen apllications where 3 rollers are used.Two rollers are mounted at some distance apart, and free to rotate, not driven.The center roller between them is mounted on a rack gear, like a rack and pinion, with the pinion gear being mounted on the moving roll.The material is threaded over the first roller, under the middle roller, and over the third roller.The center roller has a potentiometer attached, or an LVDT to transmit a signal based upon the position of the center roller in the rack.This signal is used to control a drive motro downstream which pulls the material form the main roller.As the center roller floats up and down, the speed varies on the drive motor, controlling the sag at the desired point.The tension is adjusted by adding or subtracting weight or pneumatic pressure to the center roll.

Hope this explantion was not to muddy.If you need more info, let me know.

Get a hold of Converter Accessory Corporation. Talk with Jeff Damour. 610-863-6008 They are specialists in this area and furnish tension control systems to all of the big boys.

One thing that you did not mention was the type of material that you will be unwinding or the amount of tension that you will require. Is this wire, or are we dealing with a web of paper or film? If this is some type of wide web application at the slow speeds you indicated an open loop system may not provide the accuracy that you are after. A mechanical solution would be to use some type of dancer roller that is providing the feedback. One novel and relatively inexpensive way to do this would be to load the dancer roller using pneumatics and then from the pivot point of the roller arm control the master cylinder from a automotive disk brake system. This takes a bit to get the system tuned so plan for it during your build. A much easier and quicker solution to the application would be the use of a load cell roller for the feedback element. At this point you can create any algorithm you need to control the torque on a motor to hold back the unwind roll. My personal favorite is the eddy current drive. This drive gives you direct control of the slip of the motor.

Using a dancer is probably the simplest way to go, we have used pneumatic braked pneumatically controlled systems with some success but have found the control hunts. Our preference now is to use linear potentiometers/encoders to have feedback from the dancer position back into the control system (PLC or direct to VF drive). We either use the weight of the dancer roll, a physical weight, or a pneumatic cylinder/airbag with an I/P transmitter. If the dancer has the ability to move a reasonable distance then delay in start, stopping or speed control doesn't affect the tension.

Cheers,

Trevor.

please check website www.dynaspede.net for all tension control applications. They have hundreds of specific solutions on torque-speed-tension controls.-wellwisher

Fit a positive hydraulic pump geared onto your reel with a closed loop circuit feeding oil through a volume restrictor valve , this can be adjusted via a feedback link driven from your reel to correct for reducing diameter of the material being fed off from the reel.

Alternatively if your pump is a variable volume type have the feed back link alter the swash plate delivery angle to reduce the amount of oil being fed into the loop.

It will need some experimentation to work out the correct ratios for the links but once set it will require very little attention.

Magnetic hysterisis brake, or maybe a pneumatic clutch with with an arm that rides on the reel of material to control an adjustable regulator thereby changing the air pressure on the clutch as the material roll gets smaller. We use both successfully.

Magnetic hysterisis brake, or for purely mechanical solution, a pneumatic clutch with a variable air regulator controlled by an arm riding on the reel of material. The air pressure to the clutch will change as the diameter of the product roll changes.

I,ve worked in the textile Ind for a while and found that speed control is the best way to handel this issuse. you would have the reel mounted to one motor driven and another drive roll with a nip for line speed control. the reel motor drive or inverter will need to have programming feature to be able to calculate ratio. this would set your reel speed. you then can fine tune the process with neg current limit. contact Allen bradly or any other major drive manufacture.

Hi Ablevins

All of our coater/laminators use load cells fed into amplifier cards which, in turn, are fed to a PLC. On each coater, there are two sets of load cells; one set to measure the tension between the coating head and the laminator and the other measures the tension between the laminator and the rewind stand. Tension control is achieved by varying the speeds of the coater and rewind motors around each of their respective set-points (dial setting on the front panel).

The feed rolls (unwind) tensions are manually controlled by pneumatic disk brakes.

You could do a couple of things, depending on how accurate & how much $$$ you can spend.

(1) Pneumatic disk brakes on the unwind roll - manual adjustment of air regulator - $100 - $500 (WAG)

(2) IF YOU HAVE A VARIABLE-SPEED WINDER MOTOR, a load cell-based system will work. You would need a pair of load cells with amplified signal, an extra idler to mount the load cells on, a potentiometer, and a small PLC (needs to have 2 analog inputs - one for the setpoint signal from the pot and one for the load cell signal - and 1 analog output - to control the winder motor speed). A little programming of the PLC plus calibrating the load cells and voilla, you're there! This would take more time and I reckon the cost would be ~ $1000.

I could go into a lot more detail and will, if it sounds like something you would be interested in. Let me know.

Mike

Hi, I am D.Ramakrishna Naidu, a recent Member.

Since presently, " currently controlled by the winding reel", the winding reel will be continuously increasing in diameter with the incoming material riding over the already wound up material. This increase in dia will cause increase in tension for a constant RPM of the winding reel. For maintaining constant tension, the speed (RPM) of the winding reel has to be continuously adjusted (appropriately reduced in real-time- as it is happening) to compensate the increase in tension.

This can be achieved by monitoring the Diameter of the winding reel with material and adjusting the speed of the winding reel driver, as a continuous feed back loop.

On getting a Current (analog) feedback signal, this can be fed to a PID controller as converted Voltage. The output Voltage of the PID will be the input to the speed controller of the winding reel driver. Of course, you have to set a "Reference" (Voltage) valuefor the PID controller-which you can vary as per optimal results obtained after a few trial runs. The PID controller also needs to be fine tuned (Trained) with the "gain" values for the P (Proportional), I (Integral), and D (Derivative) outputs which are summed and given out as a single output signal. This signal can be used by any amplifier of the winding reel driver.

Please visit www.artecrobotics.com to know me better and to refer the problem as a proper Statement of requirements for a directly usable set of hardware/software system.

Rubber roller against feed reel. Roller to be held against reel with spring tension. Tension adjustable to increase load on the rollers bearing. Which will allow you to adjust to the tension you need. A device that you can look at that incorporates this device is a dispenser for banding on a banding machine.

Have you got room for a 10" or 12" disc brake on this reels axle? If so, hydralic or electric controls are both available at your Truck/Trailer Sales. Either can also be controlled by a slave relay, tuned to your pulling source. If the brake disc &/or the brake pads don't last very long, go to the next size larger, both in thickness & diameter to cope with greater heat dissapation. C.O.H.

My first reply, #3 is in fact a dancer roll.I did not think the guest was familiar with that term, so I simply described it.The take up roll can be powered by a DC motor, and the back roll can be powered likewise.

If more tension is desired, the take up motor is simply run a a slightly higher speed than the unwinding roll.This in effect provides a magnetic drag on the roll, which has no fricitonal parts to wear out.

The position of the dancer roll is an indicator of tension, and as previously stated, can be monitored by an LVDT(Linear Voltage Differential Transformer) which will provide a voltage output proportional to position of the roller, or a potentiometer can be driven from the dancer roll.This voltage can be scaled to provide feedback control for the motors, with local fine tune trimming at both motors.

Another speed control option is a PIV gearbox.Primitive, but very rugged and relaible.This has a variable drive chain sheave and a speed adjusting motor that varies the ratio of input/output.Clockwise rotation changes speed in one direction, and the opposite of course changes speed in the other direction.

At the top end of the technology heap is servo-control of both rolls, with tachometer input from surface of both rolls,a sag detector, and computer interface for conversion to engineering units and display of position in either numerical or iconic display, or both.

Hope this helps.

We have been using 500 lb reels with wire layer wound on them for coating it with another material and find that the pull of the roll forming machine does the pulling and we use a flat 2 inch face pully with a diameter of 12 inches with an adgustable band brake to control the tension and it has worked fine for over ten years of service. Try this, the tension on the brake will depend on the speed you want. Our speed is about 31 feet per minute aproximately.

Hope this will help you

vshwn7@aol.com

This is classic control problem in Steel /paper/textile mills:
see this commercial http://www.avtron.com/metals_coldroll.htm

Dear Mr.Mukulmahant,

You have a very impressive industrial record with highly standardised products.

The thread "Tension control" is a very localised micro problem compared to the vast array of your products and services. I am happy to see that there is a concurrence with my suggetion of REGULATING WINDING ROLLER SPEED BASED ON DIAMETER VARIATION AS "TENSION" (control parameter) IS HAVING A DIRECT CORELATION with "DIAMETER" (monitored parameter) with "SPEED" (controlled parameter).

Thank you anyway for making visible your company AVTRON and its products/services. Similarly, please visit my website www.artecrobotics.com for identifying potential of synergy.

Sincerely

D.Ramakrishna Naidu

Founder Managing Director

Artec Sriman Controlls Private Limited

49 Vijayaraghava Road

Chennai-600017

Ph: +914428151157

Mo.09884008810