Productivity Series PLCs Motion Control - Smooth Out Motion Transitions from AutomationDirect
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(VID-P2-0018)
Learn how to use the Productivity Controllers JERK feature to smooth out your systems motion. This video uses a Productivity 2000, but it applies to all members of the Productivity family of controllers.
**Software Version used in this video: Productivity Suite Programming Software Version 2.2.0(12)
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In this video we’ll pick up where the Simple Move video left off and take a look at how we can use Jerk to smooth out our motion and save wear and tear on our machines. We’re using the exact same setup as the Simple Move video so check that out if you need to see how we set all this up. What is Jerk? Well … given the absolute position, velocity is how fast the position is changing over time. And acceleration is how fast velocity is changing over time. Jerk controls how acceleration changes over time. So instead of immediately accelerating an object at a constant rate, jerk smooths out the transition. Some folks refer to this as applying an S-Curve to the motion. The smaller the jerk value is the more smoothing you get. Jerk is currently NOT enabled on this system. If I put a glass of water on the carriage, you can see the water get jerked around when the abrupt motion starts and again when it abruptly comes to a stop. Let’s enable Jerk in the forward direction only and transfer to the processor. I’ve added the Jerk t==ag to our data view so we can change it. Let’s put a small value in for Jerk – that is we want to minimize the amount of jerk on the water. And … let’s plot the carriage position and velocity on a graph in the data view. Looks Like the carriage position is currently at 20 inches and the velocity is zero. Run the carriage in the reverse direction with no jerk. And once again we see how the water jerked at the start and end of motion. Now let’s run the forward direction which does have jerk. You can see the water doesn’t move at all does it? And on the graph you can see why: In reverse direction we have no Jerk and sure enough the velocity changes linearly and the position changes abruptly. In this direction we DO have Jerk and you can see how it smooths out the positioning so the carriage doesn’t start abruptly or hit its final position abruptly. The way it does that is by changing the velocity from a simple line to a nice smooth curve. Because we used a small value for Jerk we got no motion or jerkieness of the water, right? But it took so long to ramp up, the velocity never got up to the 15 inches per second we wanted before it had to start ramping down so it took a long time for the carriage to get to its destination. So let’s try a larger value for Jerk – how about 50? Now when we run the carriage in the reverse direction where we have NO jerk– we get the same abrupt result. Wait for the water to settle. Now run it in the forward direction with Jerk set to 50. Look! The velocity did reach the 15 inches per second and the duration of the movement is much shorter, and the water still didn’t jiggle - or jerk around - did it? This little demo with a water glass isn’t real impressive, but you can see that using jerk is a great way to smooth motion on your machine because you can use it to minimize or even eliminate abrupt changes in position, which saves wear and tear on the machine and handles any fragile loads you may be controlling much more gently. All of which saves you money. You can do a lot of math to figure out what the most optimum Jerk value is for your system, but most of the time you can get what you need quickly just by experimenting a little like we did here. The good news the Productivity Series controllers make it really easy to do. If you need any help with implementing motion on the Productivity series controllers please contact AutomationDirect’s free award winning support team – they will be happy to help you. And don’t forget the forums! There are lots of folks there that love to share their years of experience. Just don’t post any questions directed at AutomationDirect’s support team there – they don’t monitor the forums on a regular basis.
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