extra pulses

Hey everyone,

Heres a problem that I have been working on. I am tracking and controlling parallel drive systems that move in unison. The tracking could be for any number of drives that you would like to keep together. I am currently controlling 3. I am using a custom cable control system which moves the table in or out over about 25'. All three tables are to end up in the same location regardless of differences in loads. If a move out signal is sent, than the drives are to move 2 pulses. Once the 2 pulses are sensed the drive stops and sends an "all okay" signal to the plc. Once all the "all okay" signals are received from all the individual drives, the drives are once again able to move should there be a signal to do so. This checks system prevents one drive from getting to far ahead of the other drive systems and ensures that all three drives are moving. If one doesn't move within the presribed time allowed than the complete system stops until it is checked.
The problem I am having is sometimes the drives are under loaded. If the drive is under loaded than the drive continues to rotate after power is removed from the motor(free wheeling) This free wheeling is sometimes far enough to activate another pulse. This extra pulse messes up the system.
Another problem is under heavy load. This time the load stops while the flag is still under the sensor ( a prox) This problem is that when the drive is told to move again it counts the pulse it is sitting under. Does any one have any good ideas on how to work through these? I know I am cheating by asking here but what the heck, maybe we will all learn something here.
Thanks.

Working hard and moving slow, Bitsnpieces.

bitsnpieces said:

Hey everyone,

Heres a problem that I have been working on. I am tracking and controlling parallel drive systems that move in unison. The tracking could be for any number of drives that you would like to keep together. I am currently controlling 3. I am using a custom cable control system which moves the table in or out over about 25'. All three tables are to end up in the same location regardless of differences in loads. If a move out signal is sent, than the drives are to move 2 pulses. Once the 2 pulses are sensed the drive stops and sends an "all okay" signal to the plc. Once all the "all okay" signals are received from all the individual drives, the drives are once again able to move should there be a signal to do so. This checks system prevents one drive from getting to far ahead of the other drive systems and ensures that all three drives are moving. If one doesn't move within the presribed time allowed than the complete system stops until it is checked.
The problem I am having is sometimes the drives are under loaded. If the drive is under loaded than the drive continues to rotate after power is removed from the motor(free wheeling) This free wheeling is sometimes far enough to activate another pulse. This extra pulse messes up the system.

Click to expand...

Drives do that. You will need to keep track of the overshoot and correct by not asking the drive to move as much next time.l

bitsnpieces said:

Another problem is under heavy load. This time the load stops while the flag is still under the sensor ( a prox) This problem is that when the drive is told to move again it counts the pulse it is sitting under. Does any one have any good ideas on how to work through these? I know I am cheating by asking here but what the heck, maybe we will all learn something here.
Thanks.

Working hard and moving slow, Bitsnpieces.

Click to expand...

Can you set a bit to remember that you are at that flag and ingore other activations until the actuator has left that flag. Clear this bit when you get to the next flag or when you tell the actuator to move to the next flag. This bit will keep track of what state ( flag ) the actuator is at.

The easy way to do this would be to user servo motors and a motion controller. The motion controller would then keep track of all three servo motors positions and would make sure they were at the same position at the same time.

The problem I am having is sometimes the drives are under loaded. If the drive is under loaded than the drive continues to rotate after power is removed from the motor(free wheeling)

Click to expand...

You did not say what kind of drive system you are using to power these motors. One would assume that you are using just across the line starters to operate the motors. The "free wheeling" you describe is built in. If you are using a standard motor starter arrangement, you might consider using a DC brake by applying some DC to one of the motor windings when it is not being powered from the line. This is a little on the cheap and dirty side but it does work. Now, if you were using a VFD, you could tell the drive to go to zero speed and stop rather than just turn off. Setting an appropriate deceleration value would help as well. Also, as Peter mentioned, you would do well to use servos on this app if you had the option.

Another problem is under heavy load. This time the load stops while the flag is still under the sensor ( a prox)

Click to expand...

Another thought on this angle would be to use a one-shot on your prox input bit in the program. That way the bit only gets seen once and will not be re-examined until after it moves out from under the prox and back under another.