text: <s>[INST] Driven Unwind for Web Tension Control Summary: Please recommend a motor / drive combination Hi, I am trying to pick out a motor / drive combination to handle a driven unwind on a piece of web handling equipment. This unwind will feed a spool of web through a series of rollers that guide it through a machine for processing. One of these rollers acts as a tension load cell. The tension load cell provides a signal that corresponds to actual web tension to an automatic tension controller. The automatic tension controller allows the operator to enter a tension set point and uses a PID control loop to regulate a -10 to +10 VDC control signal that can be used to regulate tension. The automatic tension controller manufacturer recommended that I use a permanent magnet DC motor for my Unwind Shaft with a 4 quadrant regenerative DC drive board. Wiring the -10 to +10 VDC signal from the tension controller into the drive board would allow the tension controller to maintain tension at set point by controlling the motor speed. They say that this is a common use of their tension controllers and it works great. I ran into some confusion though when I started thinking about what motor to use. My requirements are such that my line speed can be anywhere between 1 - 25 feet per minute (25:1 speed ratio). This unwind can accommodate spools of material anywhere between 3-1/2 to 18 diameter (5.14:1 diameter ratio). The way I see it, this means that the required speed ratio for my unwind shaft is 128.5:1. After speaking to a few of my suppliers, I think that this speed ratio is too much to ask from a permanent magnet DC motor. I have been told that the typical constant torque speed range for a permanent magnet DC motor is 60:1. (Please correct me if this is wrong, or if you think I might be able to find a DC motor with a greater speed range). Yesterday, I was advised by someone that my best best was to first pick out a motor that meets my 128.5:1 speed range requirement. He said this would most likely be some sort of AC vector motor. After choosing my motor, I would then have to find a drive that not only support this speed range but that also could follow the -10 to +10 VDC signal from the tension controller. He suggested that I should look for some type of AC Inverter drive and that it would need to have regenerative capabilities. He mentioned that I would probably need a drive that can make use of encoder feedback, although I don't fully understand this suggestion because I am trying to do closed loop tension control rather than speed control. Although I am controlling tension by controlling speed, I don't care or need to know what the actual speed is. I just want the drive to do what the tension controller tells it to. Based on the recommendations of the tension controller manufacturer, the motor power that I would be looking for would be 1/4 HP. If anyone here can recommend a motor and drive that might suit my needs, I would really appreciate it. Thanks in advance, Paul [/INST] Take a look at the new PowerFlex 525 drives. Your application is extremely small and the AC drive/motor will offer excellent speed control (even though you're controlling tension). We use the PowerFlex drives in many web applications but much larger (150HP and up). You can use the DriveLogix inside the drive to fine-tune the loop, which essentially is what you have. On a small scale you're talking about, a drive on the unwind stand running slower should suffice without having to look to regenerative drives. Can't completely spec a motor but a small inverter-duty motor will work fine. I typically upsize the unwind stand drive to accomodate for any heat generated by the drive. \\n </s>