PT LBG


PT LBG

Table 1. Basic Load Balance Setup Items

ITEM DESCRIPTION
Name

This is a 21 character name.

A unique name for the LBG, ex: LBG 1. Press Enter to be able to bring up the alpha key editor.
Conveyor Select the Conveyor to which the LBG belongs. (A conveyor can have more than one LBG). This is selected from the [CHOICE] menu.
OTol

Range: –9999.99 to 9999.99

You need to specify the Overlap Tolerance in order to avoid duplicate or ghost part detection by a sensor. It is most commonly used with vision sensors but can also be used with DI sensors. In case of a vision sensor, when a workpiece is found in more than one snap as it travels through the field of view, this tolerance is used to help determine if it is the same already found workpiece or a new workpiece. If it is determined that the found workpiece has already been found in an earlier snap then it is not put into the queue multiple times. During runtime, if the robot tends to pick the same part multiple times, raise the overlap tolerance.

With DI sensors, you would sometimes want to use overlap tolerance when you have flighted conveyors and you wish to use only every alternate or third flight, etc. Or, your tray on the conveyor is such that it would be detected twice by the sensor but you do not want PickTool to think that there are two trays.

LoadBal

Range: YES/NO/LB-NFB/FIX-FB/FIX-NFB.

Load Balance algorithms:

  • ON: In this mode, PickTool attempts to strictly maintain quotas. Quotas are entered in the PT LBG LD_BAL sub-menu. If a part goes through the end of the conveyor untouched by any robot, feedback is sent by downstream CStns in the LBG to the upstream CStns. When the feedback is received, the actual quota of the robot is readjusted to reflect the missed part at the end of the line. This impacts which part is allocated to the CStn after the feedback. A leading part in its track window may be allocated which may otherwise have been reserved for a downstream CStn. Vice-versa, it is also possible that the leading part(s) in the track window may not be allocated which would otherwise have been allocated if not for the feedback.

  • OFF: The leading robot in the LBG attempts to pick as many as possible. The ones it can't pick, will be passed on to the next robot and it will try to pick as many as possible. Qutoas are not used at all.

  • LB-NFB: It stands for Load Balance No FeedBack. In this mode, the upstream CStn's quotas are not re-adjusted as in the standard ON when unpicked parts cross the downstream boundary of the last CStn in the LBG. You choose this because you don't want the upstream robot to simply skip a part that it could have picked to a downstream robot just so that it can make up its quota for missing a part at the end of the line.

  • FIX-FB: It stands for Fixed with FeedBack. If a part goes through the end of the line untouched by any robot, feedback is sent by downstream robots to the upstream robots like in ON. However, after the feedback when the next GETQ request comes in, a check is made to determine the number of parts Q that have crossed the CStn. Usually, in multiple robot systems, each robot should pick P parts and skip S parts to the downstream robots. If the check determines that Q >= S, then the leading part in the CStn is allocated. If despite the feedback, Q < S, then the leading S-Q are not allocated, but the S-Q+1 part is allocated. Therefore, this algorithm guarantees that the in two consecutive pick cycles, the robot will never pick parts that are at least S apart. Whereas in the ON or the LB-NFB it is possible that the in two consecutive pick cycles, the robot will pick parts that are less than S apart.

  • FIX-NFB: It stands for Fixed with No Feedback. In this mode, everything is the same as with FIX-FB, except that when unpicked parts cross the end of the line, the downstream CStns don't send feedback to the upstream CStns.


Table 2. PT LBG MODIFY Items

ITEM

DESCRIPTION

LBG Object A LBG object can only be a sensor or a Conveyor Station. You cannot choose the item in this column. When you select an LBG object while in the LBG_ObjName column, the type of object is updated automatically in the LBG_Object column. The first object in the LBG must be a sensor.
Sensor A sensor must be the first item in a LBG. Select Sensor in the LBG_ObjName column. Use the [CHOICE] key to select a defined sensor in the right hand column. Example: Cam 1. The choice sub-window contains all the defined sensors and conveyor stations.
CStn Once you define the sensor as the first object for the LBG, then enter the CStns in the same sequence as a part would flow from the sensor downstream to each CStn. You cannot compromise the order. It must be correct.

Table 3. Load Balance (Quota) Items

ITEM

DESCRIPTION

Stn In the Load Balance menu you specify the ratios or percentages of the each Model_id (quotas) you want to see the robot pick at each conveyor station in the LBG. When you enter the menu, you will see the Stn column already populated with the same sequence of Conveyor stations that you created in the LBG – Modify menu. This column is auto-filled with all the Conveyor Stations specified for the LBG in the LBG setup, in sequential order.
M1...M8

Model Ids that would be detected at each conveyor station. A Model ID defines a part that satisfies certain conditions in the iR Vision menu (for example: the part found by vision is model id 1 if its rotation angle is –45 <= R <= 45). For each model ID, specify the utilization rate or quota at the selected station (row).

For example, if you only had one model id M1, and you wanted the robots at each conveyor station pick this part equally, then you could enter

Stn	       M1
CS1     1
CS2     1
CS3     1
CS4     1

This tells PickTool that you want equal allocation of Model id M1 to all 4 of the conveyor stations. If you wish CS2 and CS4 to pick twice as many Model id M1’s as CS1 and CS4, you would enter:

Stn	       M1
CS1     1
CS2     2
CS3     1
CS4     2

In order to enter the Model Ids which you defined while doing the Vision Process setup, press the MODEL_ID function key to display the Model_id menu shown below. If you have more than one model_id in your vision process, you should actually visit the Model_id menu prior to setting up the Load Balance data in the LD_BAL menu.


Table 4. Model ID Items

ITEM

DESCRIPTION

Name This column is auto-filled with pre-named model_ids. PickTool supports upto 8 Model_ids per LBG.
Value Enter the values of the Model_ids you defined in the vision process and note the corresponding name (M1, M2, etc.) in the Name column. When done, press PREV to go back to the Load Balance menu to complete the setup of Load balance data.