a handy simulator for motion control ...

I've just picked up a nifty new tool that might be interesting to some of our readers ...

background ...

last week I had a couple of students coming in who not only needed a five-day course on SLC-5/04 systems – but were also desperate for some basic-level training in motion control ... oops! ... motion control is something that I hadn't dealt with in over 15 years – and I had ZERO hardware in my lab equipment to put together any hands-on lab experiments for these guys ...

I easily found enough stuff on eBay to take care of the PLC end of the rope – a 1746-HSRV Servo Control Module; a 1746-HT Termination Panel; and a 1746-HCA Cable ... all together about $250 ... no problems – yet ...

but ...

I still needed some type of "motor" - and a suitable "drive" – and a suitable "encoder" ... trying to get all of THOSE pieces of the puzzle matched up and pulled together quickly became both challenging – and expensive ...

the point of this post:

I called up a friend of mine (Tim at TWControls) hoping that he'd have some spare gear lying around that I could borrow for a few weeks ... turned out he had a perfect solution to my problem – available for sale for about $70 – a Servo Axis Simulator ...

https://www.theautomationstore.com/...age_images.tpl&option=com_virtuemart&Itemid=2

this dandy little item is about the size of a BIC lighter – and it pretends that it's a drive, a motor, and an encoder ...

within an hour or so in the workshop I had everything that I needed neatly mounted on a breadboard - and wired up ... then I burned some midnight oil to work through some experiments on my own – and was able to pull together enough "motion control" material to make my customers very happy with the results ...

true – we didn't need to get into "torque" and "acceleration" and topics like that – but that's not what they were interested in anyway ... basically they just needed an understanding of how their existing SLC-5/04 programs use all of those mysterious "COPY" rungs to control the movements of their servo axes ... in their plant troubleshooting this type of stuff had always required outside contractors – and now they have enough understanding to start tackling some of that work on their own ...

suggestion:

if you're interested in this subject, I highly recommend that you start by programming in the sample rungs located at the back of Allen-Bradley's user manual for the 1746-HSVR module (linked below) ... these are uncommonly good examples – and (with the hardware available) I was able to make the little simulated axis tool perform all of the different types of moves that we needed to cover in the class ...

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1746-um613_-en-p.pdf

shown below is the breadboard arrangement with the Servo Axis Simulator connected to the 1746-HT Termination Panel ...

continued in next post ...

.

and shown below is a quick trend line graph to demonstrate just a few of the moves that we were able to develop in the lab ...

we started from HOME position, and then at Point A we began an ABSOLUTE move to 32 inches – by ramping the velocity (green) up to 64 inches per minute ... this sent an actual voltage over to the simulator – and it responded (bless its little heart) by sending back the proper encoder counts to indicate the simulated motion (yellow) ...

at Point N the axis completed the move to 32 inches – and notice that the velocity began dropping off at Point C ... the move from Point M (zero/home position) to Point N (32 inches) took 0.5 minutes – due to the 64 inches per minute velocity that we had specified for this particular move ...

note that we were purposefully keeping the simulated movements very slow – in order to be able to watch and discuss their progress on the graph ...

then beginning at Point E we started an INCREMENTAL move of negative 24 inches – at a velocity of 24 inches per minute ... the graph shows that the system sent a negative voltage to the simulator – causing the axis to move from its position at 32 inches (at Point O) to a position of 8 inches (at Point P) ... compare the green trace between Points B and C – and between Points F and G - to account for the slower ramping of the yellow trace between Points O and P – when compared to the faster ramping between Points M and N ...

at Point P the axis completed the incremental move of negative 24 inches – settling down at an axis position of 8 inches ... and notice how the velocity began ramping off at Point G ... the move from Point O (32 inches) to Point P (8 inches) took 1.0 minute – due to the 24 inches per minute velocity that we had specified for this particular move ...

finally at Point I we began one more ABSOLUTE move – this time to 20 inches – by ramping the velocity (green) to 12 inches per minute ... the voltage sent to the simulator caused it to respond by sending back encoder counts to indicate its simulated motion – as shown in yellow between Points Q and R ...

consider that for this particular move, we had changed the system's ACCELERATION setting from its default value of 1.0 – to a much reduced setting of 0.0002 ... the effect of this reduced acceleration can be seen by comparing the rate of change (the "slope") between Points I and J – with the rates of change between Points A and B – and between Points G and H ... looking closely will show a smoother "take off" at Point Q when compared to the "take off" at Point M ...

at Point R the axis completed the move to 20 inches – and notice that the velocity began dropping off Point K ... this was in advance of arrival of the axis at Point R – in order to allow for the smoother "landing" required by the reduced acceleration setting (0.0002) that we had specified for this particular move ...

based on the outcome of these "bench top" lessons, my students and I were able to analyze their existing SLC programs – and to identify specific examples of how the same types of moves are being done by their own plant's motion control equipment ...

summing up ...

the Servo Axis Simulator definitely saved my neck on this project ... I'm grateful to Tim - and to his "team" - for making this handy little tool available ... and since I wasn't even aware that it existed – I wanted to post a little demonstration of how it works in case other forum members might be able to use it ...

.

Thank you once again Ron!!

gas said:

Thank you once again Ron!!

Click to expand...

Ditto

As usual, well presented, interesting, and useful.

Thank Ron!

Stu....

Thanks for your evaluation of the servo simulator Ron. It is now our second most popular product behind the analog simulators and is our fastest growing.

One question that came up over email that I thought I would share is "How do you configure the encoder resolution?" You can configure the z marker period (encoder resolution), z marker width, engineering units scaling, deadband, and command offset all via a Window's applet. You can find a download either the installer package or the exe that can be ran without any installation at the bottom of this page.
https://www.theautomationstore.com/...&category_id=3&option=com_virtuemart&Itemid=2

Interesting, I forwarded this off to our training and tech support guy.