Racer911

because I am not using flying shears or rotating knives. the web needs to stop to be sealed, then drawn and stopped again for the next bag to be sealed. This document is very helpful and relevant to me. Thanks for that. .

Hi. thanks for this. This article is actually not mildly but fully related to my application. Such bag making machines is exactly what we manufacture. Am just trying to upgrade control techniques to make the machine logic control more self sufficient and reduce operator skill and intuition required to run these.

The only problem with real time analogue response is that there is always a certain degree of continuous acceleration deceleration scenario. While this is absolutely comfortable with reels that are not extremely heavy or large in diameter, in this particular area the problem arises that unless an expensive eletronically controlled breaking or tension creating mechanism is not applied, the reel maintains its angular momentum even as the motor slightly decelerates causing the web between the reel and the rubber rolls pulling the web to loosens effectively causing them to first loose their traction, as in the line of the web starts shifting, not an acceptable scenario, second, when the motor accelerates again, it will always create a jerk, kind of a sudden tug on the web once the motor speed gets higher than the reel rotation speed that it has maintained due to its inertia. So with lighter reels, a slightly lower line speed, an extremely low cost and time proven solution is to just hang a friction belt over the reel so that keeps a certain amount of breaking in check. and its a wonderful system because its hanging around the circumference of the reel, so as the reel diameter reduces, so does the effect of breaking caused by the belt, effectively creating a self adjusting mechanism of reduction in breaking as the reel gets lighter and lighter. This will even work wonderfully in my application, it already is on one of my machines from China, the only problem is when the machine needs to Estop. So basically, if the PID can smoothen out the rising and falling graph of input signal, and basically output an averaged speed reference that would match the total distance of reel unwound, that would be the perfect solution.

Guys, off topic. Wanted some information on PID Control Loop for Motor Speed Control. Can PID Control Loop help in averaging out or say smoothen the motor speed output when the input speed reference is continously oscillating. Again, the oscillation being caused by the part mentioned in the earlier query. the Dancing roller which is connected with a potentiometer that gives a 0 to 10VDC signal to a VFD. Normally, cheaper machine manufacturers just dont care about fine tuning. Motor speed keeps on oscillating with the oscillating input reference. Some level of averaging in actual speed is achieved by increasing acceleration and deacceleration time parameters on the VFD or inverter which basically creates a scenario where the output is oscillating just as much but the motor acceleration times and de acceleration times are increased to a higher value, the variation in speed is kind of averaged to an extent because by the time the motor can achieve the high point reference speed, the dancer comes down again causing the motor to begin to de accelerate and vice versa. But again, this is a very very inefficient solution as when a machine needs to be emergency stopped or stopped in general, the motor will not come to a complete stop in the required time as the de acceleration time is quite high. I hope you guys dont mind such elaborate explanations. Its just that you guys caught on so fast to the earlier problem, I felt I can throw all my queries at you and have them solved to my satisfaction.

No No. Much Simpler. Its a actually a plastic bag on roll making machine. so theres basically a reel of plastic at the unwind side, the servo motor draws lengths as per the operator setting and seal and perforate at that point, and then those bags are rewound into smaller rolls, say 10 bags per roll or 20 bags per roll for consumer use. This is where the above dancing roller swingarm comes into effect. as the servo motor starts and stops to draw the appropriate length and seal the bag, the rewind process is a continuous one and it is neither feasible nor efficient to stop the rewind process everytime the servo motor stops. so this swingarm goes up and down, effectively creating a buffer of extra web while the web draw and sealing cycle continuously repeats itself. just search youtube for garbage bag or trash bag on roll making machine, you'll know what I'm talking about. Thanks very much for the help. WATCH THIS. https://www.youtube.com/watch?v=Sn50vV_ilvw

Ok. So the point of 70N force is 520mm away from the rotational axis. and each consequent point is at a distance of 100mm. The only reason I want to get a rough estimate of the weight or force exerted on the tape when all 5 rollers are engaged, is because this particular machine will involve processing a web with perforations at certain intervals and if the force exerted is beyond a certain accepted limit, the web or tape will tear from the perforation causing the machine to stop, create lots of wastage and loss of production. Plus the machine runs at about a 120 metres per minute, its not a lot by any definition from industrial standards, but still repeated breakages are never desirable. @GAHD, if the exerted force is even roughly near what you've calculated, 15N, I think I am good to move forward because the perforated web easily lifts up 2 to 2.5 kgs of weight in a soft manner if no jerking is present. @oceanbreeze have written the measurements as you requested. Will be waiting for your calculation too. Fingers crossed. I am hoping I dont have to make design changes

Yes. I absolutely understand the mechanical disadvantage part, albeit practically, as we use this kind of a lever in our industrial machines everyday. So with every rise in the level above 90 degrees, the effort to lift it increases as the web will require more and more tension to lift the lever further because it doesnt stay in a vertical 90 degree rise and fall situation. But, quite frankly, that is something way too theoretical and not really required in the calculation in the concerned practical application as the use of this kind of lever in our machines, though absolutely necessary, is not of a highly critical nature. Although, I appreciate and am impressed you already figured that out by this diagram alone. What I basically want to get at is, If I pass the web through all of the rollers as shown in the diagram, how much force will have to be applied by the web at the exit point where I've pointed the arrow upwards, so that the lever starts rising up. I am only asking this question because right now I am assuming the answer wont be 70N as that is downward force when the lever is suspended from Point E alone, and similarly for all other Points. And in my daily use, we observe that with each roller that we engage the web with, the force or muscle strength required to lift the lever reduces. This is basically used to create a buffer for a servo start stop application because the servo starts and stops at the given length, while the unwind and rewinding of the web reel is a continuous process. So this lever keeps dancing up and down, hence the name dancing roller, to keep the tension maintained and unwinding process continuous while the servo motor starts again to draw the next length. In the application for which I want to use this lever, I can safely ignore the mechanical disadvantage factor that is caused once the lever starts rising upwards. Is there a simple way to get at an approximation?? Again apologies for such long and probably confusing explanation.

Hi guys, I have not had a formal education in physics. But I am designing a machine which involves the use of dancing rollers. i.e. rollers fixed to a swingarm that rotates on an axis at one end. multiple rollers are attached through which a flexible web. eg. paper, plastic film etc will pass through. I want to know how much force would be required to lift the swingarm up. I am attaching a diagram with the weights the swingarm exerts downward at each point through which the web will pass. I am attaching a file which marks the rotational axis, as well as the weight in Newtons exerted by the swingarm if it is only suspended from a single point. What I would like to calculate or know the answer to is, how much force will be required to lift the swingarm up from the farthest point from the axis, which is exerting a weight of 70 Newtons if the web is run through as shown like a pulley. Sorry if my explanation is very confusing