kamenges
Member
As you can see from the equations that are being referenced, the hard part about caculating diameter based on caliper is not the baseline equations. Even the equations that Peter linked to are just tweaks on the equations for the area of a roll face. The hard part is coming up with caliper.
But, you say, the operator enters that. But, alas, the operator will enter a spec value. The caliper will not be exactly that number. If the operator happened to enter the exact average AND the error distibution is Gaussian there isn't much of a problem. However, it is more likely that the actual caliper will spend significant time on one side or the other of the setpoint. All this time the caliper error will be integrating with respect to wraps, producing an accumulating diameter error.
In a torque based system this isn't a huge deal. However, in a velocity based system this can be completely unacceptable. Without some method of correcting for caliper variation the systems that count solely on caliper integration will not work effectively in a velocity based system. And, as Peter inferred, if the transmission losses are great enough a torque based system gets hard to implement. From past experience, anything over about a 25:1 gear ratio gets pretty hard to do purely in torque unless you have a very small build ratio (say 2:1 or 3:1). This all assumes you need a tension that stays within about +/-30%.
Peter, given the right options the PowerFlex 700S is more than capable of doing the job. The 700S can be optioned with the Logix control engine onboard, so it's just like programming a CLX processor. I have yet to use one but I've seen some demos and I think I like.
Keith
But, you say, the operator enters that. But, alas, the operator will enter a spec value. The caliper will not be exactly that number. If the operator happened to enter the exact average AND the error distibution is Gaussian there isn't much of a problem. However, it is more likely that the actual caliper will spend significant time on one side or the other of the setpoint. All this time the caliper error will be integrating with respect to wraps, producing an accumulating diameter error.
In a torque based system this isn't a huge deal. However, in a velocity based system this can be completely unacceptable. Without some method of correcting for caliper variation the systems that count solely on caliper integration will not work effectively in a velocity based system. And, as Peter inferred, if the transmission losses are great enough a torque based system gets hard to implement. From past experience, anything over about a 25:1 gear ratio gets pretty hard to do purely in torque unless you have a very small build ratio (say 2:1 or 3:1). This all assumes you need a tension that stays within about +/-30%.
Peter, given the right options the PowerFlex 700S is more than capable of doing the job. The 700S can be optioned with the Logix control engine onboard, so it's just like programming a CLX processor. I have yet to use one but I've seen some demos and I think I like.
Keith