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IMOVE Rules Tips & Techniques

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IMOVE Rules Tips & Techniques for Single Zone Portals

 

Establishing IMOVE rules are relatively straightforward to setup as detailed in this section. The reality when using passive RFID is that even with the best planning, read accuracy may not always be 100% especially when hundreds of tags are involved passing through a read zone/portal at the same time. Tuning a read zone is always a balance of transmit power (TX) and RSSI cut-off that is detailed in this topic.  Even with known physical factors that can influence a read event, there is always the 'human' factor that can change that balance. For example, the average person is 60% water and RF is absorbed by aqueous substances (e.g. water, liquids, gels, etc).  When a person or persons get between antennas and the tags, their body mass alone can change the read field (for which UHF is sensitive to). As an example, when pushing a cart with many tagged items, the exact position of the persons body (legs, arms, hands) relative to the tags during passage can have an affect on the read zone performance.

 

For these reasons, IMOVE rules need to be setup to be a little forgiving and account for missed reads that invariably will happen from time to time.

 

There are two scenarios where a missed read can cause a problem with a typical IMOVE rule setup as shown below in Figure 1

 

 

Scenario 1. Tag is missed on leaving a given room

1.Tag location does not change to INTRANSIT and is still in that last room (e.g. RM01). 

2.When tagged object arrives at a another room (e.g. RMO2), it does not meet any IMOVE rule (as above) and thus stays in its previous room location

3.When tag eventually leaves that target room (RM02), it still does not meet any IMOVE rule and thus stays in its previous room location (e.g. RM01)

this will never be corrected unless the Tag returns to is prior room (e.g. RM01) to ‘reset’ back to INTRANSIT. Even with this it will now ping-pong in reverse order unless the user stays within the read zone (past the dwell) to get it back in sync. Unlikely scenario as they may have no PEV to know when it has been adjusted correctly.

 

Scenario 2. Tag is missed on arriving at a given room

1.Tag location does not change from INTRANSIT to RM02.  Location is still INTRANSIT.

2.When tag leaves same room (e.g. RM02) it now executes LTC_RM02_ARRIVE and moves to RM02 incorrectly as its last location was INTRANSIT.

Same situation as with Scenario 1.3 comment in red.

 

Corrective Approach

IMOVE rules are processed alphabetically as setup when comparing the reader location (e.g. XXXXX_ ARRIVE is ahead of XXXX_LEAVE).

Create a ‘Wildcard’ IMOVE rule that doesn’t care what the previous location was upon arriving. To do this the LEAVE must be ahead of the ARRIVE

If the rule is not met that the tag is leaving the room, then it will execute the wildcard which will imply 'anything else'.

 

 

Shown below are the same two scenarios where a modified approach can provide more forgiveness for missed reads

 

Scenario 1. Tag is missed on leaving a given room

1.Tag location does not change to INTRANSIT and is still in that last room (e.g. RM01).

2.When tagged object arrives at a another room (e.g. RMO2), it meets the WILDCARD rule and moves to its target Room location (e.g. RM02)

 

Scenario 2. Tag is missed on arrival at a given room

1.Tag location does not change from INTRANSIT (or any other location) to target room RM02 

2.When tag leaves same room (e.g. RM02) it now moves to RM02 if its last location was INTRANSIT.

This will self-correct upon arrival at next room with new WILDCARD rule as it coming from 'anywhere else'.

3.When tag eventually leaves that target room (RM02), and its target location was missed at other end and still in that previous room (e.g. RM01), it will execute WILDCARD Rule and now move to RM01 (while it is technically ‘In-transit’).

This will self-correct on arrival at next room with new WILDCARD rule as it coming from anywhere else.

 

 


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