LCD and stepper motor question

[vomitz]

Hi. is using a 888 with a expansion card with HMI. Everything works fine but when an alarm is sounded off, some of the wordings on the LCD is changed. For example, Automatic will become Automyyic etc. Is there a problem? Would like to know how can i control servo motor with this plc as well.
regards

[AllenF]

I have used a T100MD to run an Allen/Bradley
Ultra 3000 servo drive.  The Ultra 3000 accepts
step and direction signals and runs a servo motor.

I used a high speed opto between the controller
and the drive. This setup worked very well.

[vomitz]

hi allenf. how can it be done? i'm very new to controlling a servo with plc and is trying to learn. i know a servo motor need to be driven with a servo controller right? So the plc will feed signal to the servo controller to drive the motor? What does the plc use? PWM? what's the difference between a servo motor and a stepper motor?

[AllenF]

I'm not sure about forum rules so I'll stick with
talking about the T100MD.

The T100 can supply step and direction signals that
are normally used to drive a stepper drive.  The direction
signal simply determines direction of the motor.
The step is the pulse/signal that makes the motor
move a certain amount per pulse.  
The stepper drive basically amplifies the signals
and runs a stepper motor. A stepper motor will
move a certain amount every time a signal/pulse is applied. How much it moves depends on how the drive is configured and the mechanical setup.

The T100 can send out up to 20,000 pulses per second.

Some "intelligent" servo drives can accept this step and
direction signal and use it to drive a servo motor.

Do a search on Google for the difference between servos
and steppers.  Lots of good info out there.

The T100 does not use PWM for step and direction.

Tech support will probably weigh in on this thread Monday.

Good luck,
Allen

[support]

What Allen has mentioned is a type of servo controller that combines the advantage of stepper motor and servo motor. Unlike a stepper motor which is an open loop system, this type of servo is a closed loop system with encoder feedback but the loop is closed at the driver and not at the controller.

An ordinary stepper driver translates the pulses it receives into rotating electrical phase current to turn the motor. But the stepper driver does not know if the stepper motor ACTUALLY MOVE the required number of steps.  Slippage can occur which means that there is always a possibility that the stepper motor is off position but the controller does not know about it.

For an intelligent servo, the servo accepts the pulses and directional signal from a stepper controller (such as the PLC's stepper output) but make sure that the motor DO turn the number of steps that it receive by check on the position feedback from an encoder.

Regarding your LCD display with funny characters, we would like to check with you for your configuration. Please email us your contact number to support@tri-plc.com so that we can call you for more detail info about your setup.

[KH]

Hey guys, how can I control servo motors with TMD888+? Possible  to do it with the H series PLC? How do I program the ladder program to control the Servo?
regards

[support]

The best way of using the T100MD888+ to control the servo motor is to use the "smart servo" that Allen mentioned in the last postings.  There are also servo controller that accepts RS232/RS485 serial inputs for positioning. These will work even better since all the PLC needs to do is to send out an ASCII string describing the desired position and the speed and acceleration etc and the servo controller carry out the rest.

It would not be possible for H-series PLC to control a servo or stepper since H-series are simple relay replacer and do not have the capability of interfacing to a servo motor.