Apparatus for detecting tag movements and wireless tag reader

Patent metadata

Field	Value
Publication number	US-11030424-B2
Application number	US-201916352408-A
Country	US
Kind code	B2
Filing date	Mar 13, 2019
Priority date	Mar 13, 2018
Publication date	Jun 8, 2021
Grant date	Jun 8, 2021

Abstract

A configuration which can easily discriminate a moving wireless (radio) tag from a stationary wireless (radio) tag. The configuration uses an antenna to measure phases of response waves received from a wireless tag. Based on the measurements, the configuration measures changes in distance from the wireless tag to the antenna and detects travel of the wireless tag. Based on the measurements, the configuration measures changes in velocity of the wireless tag relative to the antenna. A wireless tag having a rate of changes in signs of the velocity, of not less than a predetermined value in the measured velocity changes, is detected as being a stationary tag.

First claim

What is claimed is:

1. A wireless tag reader that detects a moving tag and a stationary tag based on phase values of response waves received from a wireless tag, comprising:
a total number calculation unit that calculates a total number of phase values throughout an angle range of detecting phase values;
a sum calculation unit that calculates a most frequent sum by calculating a sum of phase values for each angle in every predetermined angle range throughout the angle range of detecting phase values;
a calculation unit that calculates a phase bias, that is, whether phase values are biased in the predetermined angle range of the most frequent sum, by comparing the total number with the most frequent sum; and
a selecting unit that selects tags with a low phase bias as being moving tags and selects tags with a high phase bias as being stationary tags.

2. The wireless tag reader according to claim 1 , comprising:
a phase variation calculation unit that calculates a phase variation as an index of a moving state of a wireless tag by cumulatively adding phase differences, each of which is a phase difference between a previous cycle and a present cycle, based on phases of response waves received from a wireless tag, wherein
the selecting unit determines thresholds using the phase bias and the phase variation to select tags as moving tags and stationary tags.

3. The wireless tag reader according to claim 2 , wherein the phase variation calculation unit smooths a phase sum graph prepared by the cumulative addition, then acquires inflection points based on change of gradient, and calculates the phase variation based on a sum of phase variation values between inflection points, including a starting point and an end point.

4. The wireless tag reader according to claim 3 , wherein
the selecting unit determines a first threshold for reliably determining a tag as being a stationary tag and a second threshold for reliably determining a tag as being a moving tag, based on the phase bias and the phase variation, and reliably selects tags which fall into moving tags and stationary tags; and
the wireless tag reader includes a determination unit that calculates a third threshold by using at least one of phase variation, velocity or acceleration, distance or angle data, period from first reading to last reading, and reception intensity of one or more tags reliably determined to be moving tags, and uses the third threshold as a basis for determining whether tags, other than the tags reliably selected as moving tags and stationary tags, are moving tags or stationary tags.

5. The wireless tag reader according to claim 4 , wherein a moving velocity of each of the moving tags is estimated to correct the phase variation.

6. The wireless tag reader according to claim 4 , wherein velocity of each of the moving tags is estimated to correct the third threshold.

7. The wireless tag reader according to claim 4 , wherein a distance from an antenna to each of the moving tags is estimated to correct the third threshold.

8. The wireless tag reader according to claim 5 , wherein a moving velocity of each of the moving tags is estimated based on tag reading period data of tags reliably determined to be moving tags.

9. The wireless tag reader according to claim 8 , wherein a moving velocity of each of the moving tags is estimated based on tag reading period data of a tag having a maximum phase variation among the tags reliably determined to be moving tags.

10. The wireless tag reader according to claim 5 , wherein a moving velocity of each of the moving tags is estimated based on an average of estimated moving velocities of a predetermined number of tags having high-order phase variations among the tags reliably determined to be moving tags.

11. The wireless tag reader according to claim 5 , wherein a moving velocity of each of the moving tags is estimated based on an average of estimated moving velocities of a predetermined number of tags having high-order velocities exceeding the second threshold.

12. The wireless tag reader according to claim 7 , wherein a distance from an antenna to a moving tag is estimated based on data of the tags reliably selected as being moving tags.

13. The wireless tag reader according to claim 12 , wherein a distance from the antenna to a moving tag is estimated based on reception intensities of the tags reliably determined to be moving tags.

14. The wireless tag reader according to claim 12 , wherein a distance from the antenna to a moving tag is estimated based on a reception intensity of a tag having a maximum phase variation among the tags reliably determined to be moving tags.

15. The wireless tag reader according to claim 12 , wherein a distance from the antenna to a moving tag is estimated based on an average of estimated distances of a predetermined number of tags having high-order phase variations among the tags reliably determined to be moving tags.

16. The wireless tag reader according to claim 12 , wherein a distance from the antenna to a moving tag is estimated based on an average of estimated velocities of a predetermined number of tags having high-order velocities exceeding the second threshold.

17. The wireless tag reader according to claim 4 , wherein when the phase bias is large, the first threshold and the second threshold are increased as criteria for the phase variation.

18. The wireless tag reader according to claim 1 , wherein the selecting unit selects tags with a low phase bias as being moving tags from which direct waves have been received, and selects tags with a high phase bias as being stationary tags from which direct waves and reflected waves have been received.

Assignees

• Denso Wave Inc

Inventors

• Ogawa Masayuki
• Enomoto Kohei
• Masuda Yusuke

Classifications

• G01S13/84

  for distance determination by phase measurement · CPC title

• G01S1/38

  using comparison of [1] the phase of the envelope of the change of frequency, due to Doppler effect, of the signal transmitted by an antenna moving, or appearing to move, in a cyclic path with [2] the phase of a reference signal, the frequency of this reference signal being synchronised with that of the cyclic movement, or apparent cyclic movement, of the antenna · CPC title

• G06K7/10108 Primary

  interrogating only those RFIDs that fulfill a predetermined requirement, e.g. selecting all RFIDs having the same speed and moving in a cloud like fashion, e.g. on the same train; interrogating only RFIDs having a certain predetermined temperature, e.g. in the same fridge, another possibility being the active ignoring of a group of tags that fulfill a predetermined requirement, equivalent to the Boolean NOT operation · CPC title

• G06K17/0032

  Apparatus for automatic testing and analysing marked record carriers, used for examinations of the multiple choice answer type (teaching apparatus working with questions and answers G09B7/00) · CPC title

• H04W4/33

  for indoor environments, e.g. buildings · CPC title