In this article and video, Brad Vorrie walks you through the process of sizing a motor for your Omron NJ and using the motor sizing software.
The first question you will typically ask when designing a servo system is what size motor do I need? Let’s just get the biggest motor available and slap it on right? Well unless you have an unlimited budget and large floor space to put this machine in you may want to reconsider!
To start, there are two main categories to think about. What am I moving and how fast do I need to get there?
For example, let’s say you have a turn table and you need to rotate it 20 degrees in ½ a second.
You will need to know things like diameter of the turn table and weight? The product that will be on this turn table at its weight? As wells as any offset loads or external forces?
So once you get that info, take the diameter of the table – times pi – multiply that by the circumference of a circle, divide by the weight – times the coefficient of aluminum – oh yeah, then there's is friction so I think you add that – and there is this off balance thing….. How much does that dog food weigh again? You getting all of this?
Neither am I!
How about I tell you a much easier way of doing this! The Omron Sysmac family of products has developed an easy method of sizing your servo that will even interact with Sysmac Studio programming software!
Using Sysmac’s Motor Sizing Tool the software will help you determine the correct size of servo for your application. Using the previous example of a turn-table, enter in inner and outer diameter of the turntable, thickness, and material. It will automatically calculate the inertia.
The next step is to enter in the move profile. For this application we are moving 20 degrees in half a second with a 2 second dwell. We have a force of 2 NM at this point in the cycle. This force represents any load or weight on the turn table.
As you can see at the bottom of the screen the program is giving us an indication of an acceptable motor and its utilization of that motor. If you want to see if a gearbox will help, simply enter in a reduction ratio and the suggested motors will change based on the gearbox selection.
Once you have selected a motor you can print off a report that will give you a complete list of part numbers to give to your distributor! By the way… it’s Ramco. That’s R – A – M – C – O
One of the coolest features of this program is that you can export this information and then import it into Sysmac Studio and it will automatically add the program to your EtherCat network and add the appropriate axis in your program using the values entered in the sizing software.