Method and apparatus for detecting container movement by a crane

A method of operating an apparatus having a tag that can receive first and second wireless signals respectively defining first and second fields of transmission that overlap, comprising:

• generating, by a first transmission device, the first wireless signal defining the first field of transmission;
• generating, by a second transmission device, the second wireless signal defining the second field of transmission, the second field of transmission overlapping the first field of transmission in a region of overlap;
• moving a tag between at least the first field of transmission and the second field of transmission;
• detecting a location of the tag as it moves between at least the first field of transmission and the second field of transmission;
• and
• transitioning only once from recognizing that said tag is in the first field to recognizing that said tag is in the second field when said tag is moving from the first field to the region of overlap and into the second field.

An apparatus comprising:

• a crane having a first portion and a second portion, the first portion being supported for movement relative to the second portion;
• a first signpost supported on the first portion of the crane, the first signpost transmitting a first wireless signal defining a first field of transmission;
• and
• a second signpost supported on the second portion of the crane at a vertical separation from the first signpost, the second signpost transmitting a second wireless signal defining a second field of transmission, the second wireless signal being different from the first wireless signal, wherein
• the first field of transmission weakens when the first portion moves away from the second portion.

A method comprising:

• transmitting a first wireless signal from a first signpost supported on a first portion of a crane, the first wireless signal defining a first field of transmission;
• transmitting a second wireless signal from a second signpost supported on a second portion of the crane, vertically spaced from the first signpost, the second wireless signal being different from the first wireless signal and defining a second field of transmission;
• and
• moving the first portion of the crane relative to the second portion of the crane, wherein
• the first field of transmission weakens as the first portion is moved away from the second portion.

An apparatus comprising:

• a first signpost that transmits first wireless signals defining a first transmission field;
• a second signpost, spaced apart from the first signpost, that transmits second wireless signals defining a second transmission field;
• a tag that can move relative to the first signpost and the second signpost, and that can receive the first and second wireless signals transmitted by the first signpost and the second signpost when said tag is within the first transmission field or the second transmission field, respectively;
• and
• a system having structure for sensing positional information regarding said tag, said system using said positional information to determine a location of said tag in relation to said first transmission field and the second transmission field, wherein
• the system disables the first signpost when the location of the tag is determined to be out of the first transmission field and disables the second signpost when the location of the tag is determined to be out of the second transmission field.

A method comprising:

• transmitting, by a first signpost, a first wireless defining a first transmission field;
• transmitting, by a second signpost, a second wireless signal defining a second transmission field;
• sensing positional information regarding a tag that can move relative to the first transmission field and the second transmission field, and that can receive the first and second wireless signals when said tag is within the first transmission field or the second transmission field;
• using said positional information to determine a location of said tag in relation to the first transmission field and the second transmission field;
• and
• disabling the first signpost when the location of the tag is determined to be out of the first transmission field;
• and
• disabling the second signpost when the location of the tag is determined to be out of the second transmission field.