Micrologix 1500 and stepper


Thread Starter


Hi. I'm new with AB PLC's, for this reason I'm looking for information about the manner of connecting a Micrologix 1500 with a stepper motor. I know that Micrologix generate pulses, but what more I need?



The MicroLogix 1500 provide a couple of different ways to connect up to a pair of steppers. First off, the ML1500 supports 2 physical stepper channels. FET outputs on the base of the ML1500 allow the connectivity of 2 motors. These outputs can also be used for general purpose so they cannot conflict with other functional requirements.

Since the FET outputs on the base of the ML1500 module are limited to about 1 or 2 Amps (not sure off hand, see manual), the connection wiring often requires the use of a stepper amplifier which may take the output pulses and boost, condition, turn them into a PWM train, or fan them out for the motor in question. Another potential limiting factor is the fact that the FET is basically of the 24VDC variety (within a range) -- your motor may be quite different.

Basically, either try to design your motor around the characteristics of the ML1500 (which are of the general purpose variety) or add a suitable Amp for the motor. You can usually buy these for around $100 at the low power end. They typically come with step and direction input channels. Send the output Pulse signals to Step and a discrete output to direction.

Once you have the wiring, the ML1500 firmware supports 2 kinds of pulse generators to each of these 2 channels. These are "Pulse Train Output" (PTO) and "Pulse Width Modulation" (PWM). The PTO is the most commonly used stepper output instruction and outputs a uniform series of steps to the motor (or via amplifier). The PWM allows you to do more precise manipulation of the output wave form with 'duty cycle'. This can fine tune a wave to better dance with a specific motor and load. One can save serious hardware in that case provided the motor characteristics line up with that of the controller.

For PTO and PWM instructions, there are about 20 and 10 configurable parameters respectively which include the ability to use an S-Curve velocity profile or a Trapezoidal velocity profile. The S-Curve will better preserve your machinery at the cost of thruput. See the "Knowledge Base" launchable/Searchable from www.ab.com for the best default configuration of the PTO and PWM in the ML1500. This will get you past any abiguities of a first time setup and can save you time in the first implementation.