I have just been on site at a customers IRB340 Flexpicker installation where we have a some problems with placement.
Firstly when the flexpicker has picked an item from a moving conveyor it goes to place the item in a moving tray on a second conveyor. But instead of placing the item straight into the tray the flexpicker follows the tray in the x direction but is not correct in the y direction. The flexpicker follows the moving tray for about 100mm then corrects the y position and deposits the item in the tray corrrectly.
Secondly the placement of the items in the moving tray is bad when the flexpicker goes to place the item in the tray just as the conveyor is stopping (using conveyor start/stop) and the flexpicker overshoots the tray as it places the item. I have some adjustment on the acceleration/deceleration rates of the conveyor, but is their any paramaters that can be adjusted in the S4C to allow better tracking of the speed changes of the placement conveyor during acceleration/deceleration.
The second question can be answered yes. You can make some adjustments with the two parameters described. Be careful using them if you notice that the robot is jerking then you should adjust the parameters so that this is avoided.
When PickMaster is used some modifications might be done in the PROC.cfg and MOC.cfg files. These files can be located in the system directory of the robot.
The following modifications must be done in the PROC.cfg file.
a -correction_vector_ramp_length 5. This parameter shall be entered under the CONVEYOR section. This is the correction start filter ramp that is used when connecting to a moving conveyor. This is by default set to 5 steps. This parameter should be tuned if higher accuracy is needed. A lower value gives better accuracy but the manipulator may jerk whenconnecting to the moving object.
a -correction_vector_stop_ramp 5. This parameter shall be entered under the CONVEYOR section. This is the correction stop filter ramp that is used when disconnecting from amoving conveyor. This is by default set to 5 steps. A lower value gives better accuracy when leaving the conveyor. This parameter shall be tuned to eliminate manipulator jerks when leaving the moving object.
Have a read of the Conveyor Tracking Application Manual. In there it describes a parameter called IIRFFP, stored in the EIO file under FieldBus Command. The book recommends setting this filter to 10 - 15 Hz (I think the default is 2 Hz) for good accuracy during stop and start. You need to apply this to each conveyor affected.
This certainly improved the inaccuracy I had picking or placing during acceleration or deceleration of the conveyors, however I still do get some lag and overshoot. The overshoot is causing me grief at the moment which is particularly bad when the placement conveyor is just stopping. Use a linear ramp profile as well.
I tried the parameters suggested by Milun, but it didn’t fix my problem.
ABB have also introduced a new parameter called -use_kinematic_corvec in RobotWare 5.06.02 I have no idea what this means, it is supposed to improve accuracy during conveyor tracking as I understand it, but it didn’t fix my problem, yet. Apparently version 5.07 makes some improvements on this function. I don’t know about S4CPlus though.
The FlexPicker I am working on at the moment does a few strange twitches after a placement. Any ideas?
The IIRFFPeriod should be set to the same value (in ms) as the poll rate of the DSQC377(A)
encoder board. This poll value is by default 20ms for both S4C+ and IRC5. We have however
discovered that this value is incorrectly set to 10ms when PickMaster is used. This will
be corrected in the next release of both IRC5 and S4C+.
The -use_kinematic_corvec parameter will increase accuracy during continous conveyor
operation and will not have any affect during start/stop of the conveyor.
If the conveyor is accelerating/decelerating just when the robot has picked/placed
and is about to leave the pick/place target it may happen that the robot performs a
“jump”/twitch/shake. This is usually caused by a steep acceleration/deceleration of
the conveyor in conjunction with low robot speed and/or reduced robot acceleration
(PathAccLim or AccSet). It might be worth a try to increase the zone-size on the last
movement (the up stroke, i.e. the last TriggL instruction in the Pick or Place procedure).
This will however only make a difference if the pick/place elevation is large enough
(as a zone between two points never can be larger than half the distance inbetween them).
Of course, if the application allows it, lower acceleration/deceleration on the conveyor,
higher robot speed and higher robot acceleration/deceleration will usually improve the
situation.