kamenges said:
Do I really need a pneumatic nailer if I am only driving one nail? Some of the nailgun salesmen will say I do. I tend to disagree.
I think allscott's bus/sports car analogy is a bit off. The plc/motion controller question is more like comparing a Porsche to a Toyota Corrola. They will both work in the low to mid performance area.
I think the nail gun analogy is off too. One nail can be driven quickly either way.
There are obviously some things a Porsche can do that a Corrola can't. And if I am only buying one I will probably buy a Porsche. I know it will do anything I need to do no matter what the performance required.
Again I think this analogy is off. Two people can start at the same place in a Corrola and a Porsche and legal get to the same place at the same time.
The motion controller saves time and is insurance because it is loaded with diagnostics that PLCs can't match. I had one customer call it his get out of jail free card because the motion controller allowed him to finish the project and go home.
But now, what if I am buying a fleet of cars? It is fiscally irresponsible of me to buy the Porsches if the Corrola will do the job. My purchase isn't just a one-time thing. It is a 100-time or 1000-time thing. So even if it takes me a little more to make the lower performance item work it makes sense to do it.
This brings up a good point. OEMs that use 100s or thousands don't user commercially available motion controllers. They bring it in house and make their own controller with just the features they need to bring the cost down.
We have hit this wall many times. We could make motion controllers for a lot less. We can just strip out the diagnostics and the setup software and just mount a 4x20 LCD on the controller. This would be fine for a OEM application where a simple motion controller is required for dump trucks or lifting wheel chair platforms. In these cases the motion controller would always use the same parameters and once one controller was setup one could copy the parameters for the next project. Extensive procedures can be written for debugging and trouble shooting because these controllers would be sold by the hundreds each year.
We would lose our shirts if we sold a controller like this to the average application. All profits would be gone on the first tech support call and there would be no graphs to provide a clue as to what is wrong. Tech support is hard enough even with the graphs and all the tools.
The reality is that we have no customers that sell 100s of controllers. The closest thing is some large sawmill OEMs. These OEMs are always pushing the performance envelope. They also want documentation, diagnostics, auto tuning and polish, that no PLC PID based motion system can match. Down time is expensive. Good diagnostics is the key to getting up and running. This can save the cost of the controller. These OEMs also like having access to someone that knows the math and physics of motion.
Most of our customer buy less than 10 units a year. It isn't wise to write your own PID motion any more than it makes sense to write your own HMI in VB. It is better to buy WonderWare or something like it. You can't justify the time and support. That doesn't mean it can't be done, but it is kind of like re-inventing a wheel and not a very round one. Even if you can do it there is the PLC law about creeping features and usually these causes the code to be too complicated.
There are some guys around, Peter being one of them, that can analyse and model a system accurately enough to be able to tell you if a plc is good enough or a motion controller is required.
I don't count. There is only one of me and my time is best spent doing other things than installing motion controllers. One of them is making motion control easy for others to install and maintain. It has to be so easy that our salesmen, student business major ( cave man ) and distributors can do it. If a salesman can do it, an engineer, good PLC programmer or one of our application/tech support people engineers should be able to do it too.
I hate to say "motion control for dummies". I would prefer to say that we require as little mental energy as possible so there is plenty left for the rest of the application. Some applications out there are very sophisticated.