Created Date: December 10,2019

Created by: z28z34man

I have an application where I need to adjust the width of a side trimmer. We currently have a 3 phase motor and a reversing starter and measure the width with a tape measure. My original plan was a 1kw servo setup with a precision limit switch for the home position and normal limit switches for over travel. now i am considering a stepper motor for this application as the motor should have plenty of torque, the Productivity 3000 at the line should be able to handle the motion commands, and the backlash in the width adjust current setup would never allow an absolutely perfect precision.

The only issue I can see is that the servo motor has a brake and the stepper does not but the stepper naturally has some holding power.

What are your thoughts on this?

Created Date: December 10,2019

Created by: Cap

An Energized Servo or Stepper will have a Holding Torque.. Steppers are SIMPLE and Cheep.. Servos get more complicated.. and you only need it for a Stepper Application Anyway.. Pulse and Direction I'm thinking..

I'd size up a stepper, and see how it fits in the Scheme of things.. Drop it into some sort of a Gear box and hook all that to the Drive Components that move the Slide.. See how it all fits..

Cap

Created Date: December 10,2019

Created by: MikeN

For me it always comes down to 2 things: What speed do I need, and what torque do I need.

If I have to be over 1000rpm, I always choose servo. Steppers just loose too much torque as speed rises.

Also if the torque I need is more than a stepper of the size I need can produce, then I move up to a servo.

I dont really know your application, but to me width adjustment sounds like the motor will move a little bit and relatively slowly and then stop and hold location there and not do any more moves. If that is correct, speed is probably not a concern at all in your calculations. The question then becomes will a stepper have the torque needed to move your load?

You should look at the torque curve of the stepper motors and see if it will work. For instance the largest stepper says 9N-m holding torque, however when it is running with 70v and at only a measly 450RPM, it is down at 3.8N-m. At 900RPM, you drop all the way to 1.9N-m. Servo on the other hand maintains full torque output all the way out to 3000RPM. Which for 1kw is about 3.25N-m continuous, and 10N-m intermittently

So will the stepper have enough torque at the speed you need/want?

Created Date: December 10,2019

Created by: z28z34man

speed rely isn't of much concern as long as it complete its move of 6 in or less 30 seconds or so it will be fine. The vast majority of time it will be sitting still it only needs to move in changeovers.

now it has a 1 HP 1725 RPM motor, a 15 to 1 right angle gear box, and a 4 TPI lead screw that moves both sides of the head so 2 revs of the lead screw would move the head 1 in closer together. With that gearing it moves way faster than i would want it to move.

If I go with a stepper i am thinking a STP-MTRAC-34156D that has approximately 720 oz in at 10 rps. for a gear box i am thinking the PGCN34-2550 gear box at 25 to 1 ratio. If my math is correct i should have about double the torque and it will be wight at the 6 in in 30 seconds.

Created Date: December 10,2019

Created by: MikeN

10 revolutions per second is 600RPM. With 25:1 gearbox that is 24RPM after the gearbox. With 4 turns per inch, that is 6 inches per minute.

You will have an insane resolution, meaning you can move the tiniest of increments thats for sure. It is a bit slow though.

15:1 gearbox would give you 10 inches per minute. 10:1 gearbox would give you 15 inches a minute.

Technically speaking, that stepper motor is higher power than the 1HP motor. 340v DC to the motor at 2.5 amps is 850watts. 1HP into wattage is 750w (ish). If you can use a 1HP and 15:1 gearbox now, you could probably use that stepper and a 15:1 gearbox. That would give you 5.5inches of movement in 30 seconds which is pretty close to what you want.

If you actually use a home switch with either an inductive sensor (since they are nice and accurate and repeatable) or a precision mechanical home switch, then you could set up your moves in an HMI and tell it to move specific distances. That way you aren't just velocity mode jogging to "eyeball correct ", you could move to exact distances you need.

Created Date: December 11,2019

Created by: z28z34man

The lead screw moves 2 slitter heads with the same shaft one side is threaded clockwise and the other is counterclockwise so the speed is double.

I calculated 45.67 ft lbs out of the current setups 15 to 1 gear box currently. HP = ( torque* rpm ) / 5252

With the stepper and a 25 to 1 I calculated 93.75 ft lbs.

The plan was using regular limit switches for over travel and a precision limit switch for home. I was going to use simple move instructions in the P3000 and have an encoder on the back of the motor for position feedback. If backlash becomes too much of a problem I might use a dual magnet temposonic for position feedback.

Created Date: December 11,2019

Created by: Tinker

Since you already have the motor and drive train you might consider putting an inverter variable speed drive and an encoder on it, might seem kind of funky/old school, but since you don't need a lot of speed it might be an option. We have an old Wysong metal shear that drives the back gauge that way (using a big box full of old TTL chips, I would probably use a BRX now). It can do a 30 inch move in probably less than ten seconds, and the display shows increments of one thousandth of an inch (I think they may be a bit optimistic there, when "calibrating " it (one point calibration) I call it good if it is within couple of thousandths (and that is only at that one point, but repeatability going back to that one point is generally not worse than a couple thousandths, closer than I can measure with a tape measure :).)

"Technically speaking, that stepper motor is higher power than the 1HP motor. 340v DC to the motor at 2.5 amps is 850watts. "

Well, more like the stepper is a bigger heater than the induction motor, electrical power in doesn't necessarily match mechanical power out (and with a stepper there can be a significant difference). Also you'd need the RMS voltage if you are going to try to get power by multiplying voltage time current, 340V is peak, after chopping RMS will be less, my guess is much less. That said, 1 hp is probably far more than needed anyway.

Created Date: December 11,2019

Created by: Cap

Since you already have the motor and drive train you might consider putting an inverter variable speed drive and an encoder on it, might seem kind of funky/old school, but since you don't need a lot of speed it might be an option. We have an old Wysong metal shear that drives the back gauge that way (using a big box full of old TTL chips, I would probably use a BRX now). It can do a 30 inch move in probably less than ten seconds, and the display shows increments of one thousandth of an inch (I think they may be a bit optimistic there, when "calibrating " it (one point calibration) I call it good if it is within couple of thousandths (and that is only at that one point, but repeatability going back to that one point is generally not worse than a couple thousandths, closer than I can measure with a tape measure :).)

"Technically speaking, that stepper motor is higher power than the 1HP motor. 340v DC to the motor at 2.5 amps is 850watts. "

Well, more like the stepper is a bigger heater than the induction motor, electrical power in doesn't necessarily match mechanical power out (and with a stepper there can be a significant difference). Also you'd need the RMS voltage if you are going to try to get power by multiplying voltage time current, 340V is peak, after chopping RMS will be less, my guess is much less. That said, 1 hp is probably far more than needed anyway.

I like Tinkers Idea.. The Drive stuff is already installed.. it's just a few wires and the same amount of Programing

Cap

Created Date: December 11,2019

Created by: z28z34man

The current motor is an odd ball 575 V brake motor that we do not have a spare for. If I go with an inverter drive I would probably replace the motor as well so i can use 480V drives that we keep in stock. it is something i am considering though.

is it possible to run a 575V motor with a 460V drive if i never intend on running the motor at more than 1/2 speed? that is something i never even thought about until now