1. Field of the Invention
The present invention relates to a Radio Frequency IDentifier/IDentification (RFID) reading system, an RFID reading method, an RFID reader, an RFID read control apparatus, an RFID reader control program, a computer-readable information recording medium storing the RFID reader control program, a control program for an RFID read control apparatus, and a computer-readable information recording medium storing the control program for the RFID read control apparatus. In particular, the present invention relates to an RFID reading system, an RFID reading method, an RFID reader, an RFID read control apparatus, an RFID reader control program, a computer-readable information recording medium storing the RFID reader control program, a control program for an RFID read control apparatus, and a computer-readable information recording medium storing the control program for the RFID read control apparatus, by which a predetermined reader emits a query wave, an RF tag emits a reply wave in response to the query wave, and a plurality of readers receives the reply wave such that the readers acquire information of the RF tag.
2. Description of the Prior Art
Recently, attention has been drawn to utilization of an RFID. One of the RFID applications is that RF tags are attached to items in a store so that the RF tags are read using a mobile reader to thereby provide information of items or merchandise information. There has been also proposed an RFID application in which a reader is installed on a display rack for merchandise management.
There exist conventional techniques regarding a tag information acquisition system and a tag information acquisition method as described in conjunction with prior art examples in the following paragraphs. In accordance with Japanese Patent Application Laid-Open No. 2002-60021, metallic electromagnetic shielding items are installed on lower surfaces of a plurality of shelves. According to Japanese Patent Application Laid-Open No. 2002-2917, loop antennas having mutually different characteristics are disposed in a plurality of merchandize management shelves which are adjacent to each other. Japanese Patent Application Laid-Open No. 2001-348111 has proposed a technique to control timing of supplying signals to antenna sections of a plurality of merchandize management shelves disposed adjacent to each other. In accordance with Japanese Patent Application Laid-Open No. Hei-11-345294, adjacent apparatuses such as readers and/or writers are arranged at positions at which signal phases are relatively inverted. These techniques have an object that a reply wave from an adjacent RF tag is correctly received.
However, according to a conventional tag information acquisition system adopting a plurality of readers, when a plurality of readers simultaneously emit query waves such that electromagnetic waves thereof interfere with each other, it is required to control the readers to prevent the interference so that the query waves are appropriately received.
To solve the problem, there have been proposed a method of preventing collision between radio waves. That is, a reader emits a query wave at timing at which the other readers do not emit a query wave. There is also proposed a method in which the readers use mutually different frequencies. A specific example of a technique to prevent radio wave collision is the method of preventing the collision between the fixed readers as described above. However, such technique is possible on the assumption that the reader is in a stand-still state, i.e., not moving. Therefore, if the technique is directly applied to a case including mobile readers, it will be difficult to sustain and to ensure the characteristic thereof.
Japanese Patent Application Laid-Open No. 2000-20651 describes a reader which operates with a variable communication frequency to thereby prevent collision between plural kinds of electromagnetic waves. However, there is no specific description of the procedure to determine a frequency for the operation. Additionally, timing at which the frequency is set to the reader has not been described. Although it is possible to apply a technique described in Japanese Patent Application Laid-Open No. 2003-150916 to the operation between mobile readers, there still remains a problem of interference among radio waves when a plurality of readers simultaneously emit query waves.
These techniques of the prior art are based on a restriction in which a reader desiring to acquire tag information emits a query wave and then receives a reply wave in response to the query wave to thereby acquire tag information. Consequently, some problems arise when these techniques are widely used as a system expands.
As above, when a fixed reader and a mobile reader attempt to read information from one associated module or device simultaneously, there occurs the interference. If readers are fixed, the interference can be avoided by beforehand placing the readers so as not to read the information at the same time. However, in the tag information acquisition systems of the prior art, in a situation in which mobile readers such as portable readers are employed, the interference between the readers cannot be predicted. This leads to a problem that the method in which timing to read information is beforehand set cannot be adopted.