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abeachy_HG24
Posts: 79 Handy
Normal and reduced mode settings |
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abeachy_HG24
Posts: 79 Handy
in Robot Safety
What does everyone typically have the normal and reduced mode safety settings set at whenever they are not using light curtains, area scanners, or pressure mates for a UR 10? I have a unique challenge with my project. We want each robot to perform their tasks in ideally 20 second cycles, but our absolute max time is 23 or 24 second cycles. I was doing well with this originally but my boss didn't like how hard the UR would hit you before it stopped, the way I originally had it set up it met the guidelines laid out in ISO/TS 15066. So it was safe to work around but he is afraid people will see how fast it is moving and be afraid to work with it. I played around with the all of the settings and came up with a pretty good combination that stops quickly, but now the issue is with the changes the UR is significantly slower so we won't meet our cycle times for most of the stations. Right now this is what my settings look like, Normal Mode: Force 100 N, Power 80 W, Speed 3000 mm/s, and Momentum 10 kg m/s. Reduced Mode: Force 100 N, Power 80 W, Speed 2800 mm/s, and Momentum 7 kg m/s. Any thoughts on how I can make it stop with little force but move quicker?
Thanks!
Thanks!
this is a really good challenge that you are facing. We ran into the same issue in the past with light curtains on a robot cell. Operators were constantly walking through the robot zone, making the robot go into reduced mode. However, the operator did not have to go next to the robot that often, the robot cell was simply just to close to a walking trail where operators would walk and take a shortcut that was entering the robot's safe zone. If like us, the operator does not have to work to much close to the robot, you can do like we did, we added a simple Danger plastic fence just to make sure people did not take the shortcut that was crossing the robot's zone.
Otherwise, I know this may sound silly, but if you look at the variables that you need to address if you want to reduce force of the impact would be to increase impact time and dissipate impact force. Have you considered adding some sort of padding material on the UR like we see on the green Fanuc CR35iA? I did not see this anywhere else but I think it would be an idea.
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We have considered that, but my boss did not like that idea very much. He believes people would see that and think that it was too dangerous to begin with so we gave it sort of a "bandaid" to cover up the issue instead of actually fixing it.
We we just had a physical demarcation between the robot and the human/robot zones so the employees knew where the robot would slow down.
Our operators will be stocking the parts within the pink box so this is where the robots and operators are most likely to come in contact with each other. It is possible that they could reach past and interfere with the other operations, they shouldn't but they could. Right now I have a horizontal safety plane set up about 6 inches above where the robots are picking the parts and the safety plane triggers reduced mode. What I have been considering trying is removing that safety plane and putting a vertical safety plane in right at the edge that is furthest from the operator. That way any time the robot is behind the safety plane it can run faster, but whenever it is over any of the parts it would be in reduced mode. Not sure if this would gain us the cycle time, but it might.
Just an observation, I recommend being careful using cable ties to hold the cables to the robot. We have had issues where the cable gets in a bind and we have cut the outer sheath on the cable and rendered the cable non operational. We were fortunate that it was not the pigtail coming from the gripper so it was an easy fix. We use 2 sided Velcro to hold the cables in place of our new cable management system we designed.
Yeah we don't necessarily like the cable ties, they work but they are definitely not the best way to go about it. We have been talking about trying to come up with something different for the cable management. Do have a specific brand of the velcro that you guys like to use?
for I went ahead with his approach first.
@matthewd92
I tried your suggestion of defining safety planes by defining two simple way-points(one before the safety plane and one after)and it worked like a charm (by keeping same and different values in the general limit of safety configuration for normal and reduced mode). Thank you!
But then, I tried to implement the same in my ongoing project at my university and the robot seizes to enter the safety plane altogether. It stops before entering the safety plane and gives me a protective stop message. I thought the General limits (in safety configuration) that I had defined for normal and reduced modes posed a problem. I was wrong there, as I tried to keep all the 4 values in the General limits (both normal and reduced mode in safety configuration) same and yet again the robot seized to enter the safety plane zone. Any inputs/ideas/suggestions as to why my UR is behaving so?
Note: All the joints are well within their respective extreme limits
@meeksy we are using the Omron safety scanner as well, we generally just due safeguard stop as soon as they enter the danger area, we don't have any cells where we are using a safety scanner where the robot should slow before stopping. We don't have issues with resuming operation coming out of the safeguard stop. The robot goes right back to 100% immediately. Where we do occasionally have protective stops when entering the safeguard stop is points where the motion is blended. Its not every time that it enters safeguard during those moves that it faults but I would say its better then a 7/10 chance that it will fault.
@meeksy at this point Universal Robots does not have a fix to the potential "jerky" motion seen at the TCP when entering/exiting safety planes but there are some work around: The first I believe @matthewd92 mentioned already- set a waypoint just before the safety plane and just after with a slower speed going into the plane and a faster speed exiting the plane so that during each trajectory the TCP is a bit more controlled entering/exiting reduced or full stops. The second involves controlling the speed slider programmatically so ideally the scanner would first trigger this event in your program which will slow the robot to say 50% then it will enter the reduced mode then upon exiting the safety zone you can put the slider up to 75% or 100% just before it exits the plane and it will smooth out the motion. Further information and examples on this can be read here https://www.universal-robots.com/how-tos-and-faqs/how-to/ur-how-tos/setting-the-speed-slider-from-a-program-15293/
Thank you so much for your respective suggestions. It is working fine now. Another question on the same grounds is as follows:
Is it a bad idea to define a safety plane (with Trigger Reduced Mode) closer to the home position of my robot in my project? Sometimes, it so happens that the robot gives a protective stop pop-up if I tend to define the safety plane close to the home position in my project. Is it so, that the UR robot needs time to trigger and change the speed from normal to reduced mode? And, too close a distance refrains the robot from doing so? Any leads here would be helpful.
Let me put my question a little more in detail.
I currently have a Universal robot and a conveyor belt as a part of my project. The task of the robot is to pick a certain workpiece and place it on the conveyor belt. The home position of the robot (which is also my 1st waypoint and is pretty away from the base) is around 40-50cm diagonally away from the conveyor belt. My 2nd waypoint is 30cm straight above the conveyor belt. My 3rd waypoint is few centimeters straight above the conveyor belt. I have built a safety plane say around 10-15cm above the conveyor belt. The waypoints are such that my 2nd waypoint is above the safety plane and my 3rd waypoint is below the safety plane. The safety plane is set to 'Trigger reduced speed'. My normal speed value is 500 and reduced speed is 250. So my robot starts from waypoint 1, goes to waypoint 2 and then drops the workpiece after reaching waypoint 3. The safety plane is constructed between waypoint 2 and waypoint 3 (so as to make sure the robot drops the piece carefully!). But the problem is, my robot gives me a protective stop as soon as it touches my safety plane and seizes to enter further (which should not happen in the 'Trigger reduced mode'). I thought that the speed values (keeping in mind the speed change and jerk problems) could pose a problem and so I tried with the same speed values in the normal and reduced mode (just to test whether my robot at least enters the safety plane). Unfortunately, the robot did not enter the safety plane and stopped as soon as the gripper touched the safety plane. Whereas, a safety plane with 'Trigger reduced mode' constructed elsewhere in the same project works absolutely fine. Why is the Universal robot behaving this way with the safety plane, just close to the home position?
If safety planes feature cannot solve my need of dropping the workpiece slowly on the conveyor, what other things can I possibly do to achieve the same aim? Any suggestions/ideas/inputs would be highly appreciated.
P.S:
1. I tried to play around by changing the speed and distance values as per the basic formula of speed but none worked on the robot and it seized to enter the safety plane near the conveyor belt.
2. Just to assure you all, none of my robot joints enter the safety plane. It is just the gripper and the workpiece that enters the safety plane near the conveyor belt.
3. My robot works absolutely fine and performs all the tasks as required near the conveyor belt if I disable the safety plane on the conveyor (Just that it drops my workpiece little harshly).