1756-M02AE connected to Variable speed drive

[Donovanr 0]

I have a large XY gantry crane that needs to be positioned via a PLC, using existing 3 phase induction motors. External encoders will be mounted to both axis X and Y. Originally i was going to control both ABB ACS550 variable speed drives using a 1756-HSC and 1756-OF4. Simply by setting up a target position. Starting the drive at A speed then changing to B speed within a window of the target position, then stopping on target. However i thought of the 1756-M02AE module Can this be used for this type of application using a variable speed drive? or is its purpose only servo? Has anyone used M02AE to control VSD? Positioning tolerance needs to be +/- 5mm

[mercedes98 0]

1756-M02AE module is used for controls server drives. Do these motors that you are using have brakes? For motor speed control you can use analog input cards and power flex drives. With external encoders and limit proxi. switches you can control when to stop the motors. I suggest that you use motors with brakes. Hope this helps you.

[paulengr 44]

Yes, you can use a VSD. A servo drive just offloads the motion control stuff from the PLC to the drive itself so that you'd just send positioning commands instead of dealing with the motion control loop itself. If you read the AB documentation, I believe they explain fairly well how to do motion control with a CLX processor. You might have to resort to building your own motion control algorithms if necessary. Switched-speed controls are equivalent to bang-bang by the way and are fraught with all kinds of control problems. You have continuous speed control so this is unnecessary. By the way, for a variety of reasons, I built a complete motion control algorithm in a PLC-5 with hydraulic drives (even poorer response) in the past. Here's how it worked: 1. The main program would just execute "moves". The move commands would be sent to a trajectory calculator. 2. The trajectory calculator would use a 3rd degree spline polynomial (but you are welcome to just use trapezoids...I only used a spline to eliminate jerk at the end points where acceleration theoretically goes to infinity) to calculate points. It had a maximum speed limit to determine what to do and essentially projected forwards into the future over the next 100 ms (that was my step size but you have better control so you can use much smaller time increments) where the machine SHOULD be. 3. A feed forward/backward loop. Effectively I took the signals from the trajectory calculator which provided a speed requirement (delta between last and new positions from the trajectory calculation). This was multiplied by a constant (the feed forward gain). In addition, I ran the standard AB PID loop with clamping limits on the absolute outputs and adjusted the gains as needed. These two inputs were added together and provided the speed command to the valve (or VSD in your case). The feedback signal goes to the PID loop only (feedback). Other than some bells and whistles (they do both speed AND acceleration in the feedforward loop while I only did the speed portion), and a lot of gain calculation math, this describes the algorithm that most motion controllers do. There's clearly a lot of work involved but you could theoretically do it yourself. If you want to save a lot of time and effort though, I strongly suggest you just get a servo controller/drive or figure out how to use the one in CLX (I haven't had access to a CLX processor long enough to do this yet) because writing your own motion controller is not an easy task and took me about 2 weeks to get it working well.

[Gerry 13]

That is all in the MO2AE firmware - you will need to tune the axes though.The RSLogix 5000 software enables easy co-ordinated x-y moves (i.e. along a vector) - may or may not be appropriate for your application.

[widelto 0]

I know this is not exactly what you´re looking for, but this AOI will help you, you can find it at AB web page. Take a look at the attached file. Bill AOI_PF700_VR_AXIS_SC_Information.pdf

[Donovanr 0]

Thanks to all your replys.. My reason to use the MO2AE is to simplify the control.. Edited 1 Mar 2009 by Donovanr

[Donovanr 0]

Hi Gerry On your application with ACS800 did you have a braking resistor connected to the drive? What size drive did you use? Was there a lot of inertia? Cheers

[Gerry 13]

The largest motors were 25 KW and had regen drives. Smaller drives had brake resistors and chopper modules. I can imagine that with 0.4 KW motors and a heavy gantry, you would be worried about inertia. I guess with high gearing you can get a stable and precise system - it just won't be fast. I foresee problems with your arrangement of 2 motors for each axis. Unless you're paying a lot for gearboxes, getting their output speeds & accelerations to match will be difficult. If they are attached to a common shaft, they will fight each other. If they drive opposite sides independently, there is the likelihood of skewing (and jamming) - most noticeable on long moves.

[Donovanr 0]

I am still waiting on gearbox ratios etc from the gantry supplier... From what i know they are independent motors on each of the axis, without a common shaft.. A traditional two motor gantry using DOL to control motors could also have the chance of racking (skewing) if one motor slips or the other has friction. Controlling two motors from the one VSD should have the same affect as control with DOL Edited 5 Mar 2009 by Donovanr

[bryan372002 0]

We have 2 Gantry systems that are using MO2AE cards with PF700 Drives and SEW Gear motors. using "MAG" (motion axis gear) command one motor is the master and the other is the slave. It actually works very well and travels constantly 12 hr/day 7 days/week

[Donovanr 0]

Do you have 2x motors with encoders on one gantry axis using master/slave? Or are the two gantries geared together? That way if you ever had mechanical issues you could independently jog one of the axis? Edited 6 Mar 2009 by Donovanr