US 5,959,568 A · Measuring distance

Abstract

An object in a storage area or moving vehicle is monitored by attaching an electronic tag to the object. An electronic device detects the presence of the object by communicating with the tag while the object is in storage or is being moved by the vehicle. The tags may also determine the location of an attached object and may reroute the object if it deviates from a given shipping schedule. A group of objects is monitored by two electronic tags, each attached to an object in the group. Each tag has circuitry for communicating information relating to an object in the group to a second tag. Each tag also includes a memory connected to the circuitry that is capable of storing the information, and a controller connected to the memory and the circuitry. A distance is measured by transmitting multiple symbols from one object to another object, having the symbols returned such that the symbols' measured round-trip times are not all identical, and calculating the distance using the measured round-trip times.

Claims31

Dependent claims

A system for monitoring and affecting actions on behalf of a group of objects, comprising:

a first electronic tag attached to an object in the group, comprising:
circuitry for communicating with a second tag, the circuitry communicating at least information pertaining to an object in the group, and
a memory connected to the circuitry and capable of storing the information, and
a second electronic tag attached to an object in the group, comprising
circuitry for communicating the information with the first tag,
a memory connected to the circuitry in the second tag and capable of storing the information,
wherein the information comprises a distance between the first tag and the second tag.

4 more elements

A method of measuring a distance between two objects, said method comprising the steps of:

transmitting from one of said objects a first symbol;
transmitting from said one of said objects a second symbol, said transmission of said second symbol being separated from said transmission of said first symbol by a time interval which is a multiple of a first clock period;
receiving said first symbol at the other of said objects and re-transmitting said first symbol back to said one of said objects;
receiving said second symbol at said other of said objects and re-transmitting said second symbol back to said one of said objects, said re-transmission of said second symbol being separated from said re-transmission of said first symbol by a second time interval which is a multiple of a second different clock period;
measuring a first round-trip time corresponding to detection of receipt from said other of said objects of said first symbol, said first round-trip time being a multiple of said first clock period;
measuring a second round-trip time corresponding to detection of receipt from said other of said objects of said second symbol, said second round-trip time being a multiple of said first clock period;
if said round-trip times are not different by at least one first clock period, repeating said transmitting, said receiving, said re-transmitting, and said round-trip measuring of said second symbol until said round-trip times are different by one first clock period;
and
determining the distance between said objects using a velocity of the symbols, the clock periods, the time intervals, and the round-trip times.

6 more elements

A method of measuring a distance between two objects, said method comprising the steps of:

transmitting from one of said objects a plurality of symbols, said transmissions occurring in a first series in which consecutive transmissions are separated by a first time interval which is a multiple of a first clock period, said symbols having a constant velocity;
receiving each of said symbols at the other of said objects and re-transmitting each of said symbols back to said one of said objects, said re-transmissions occurring in a second series in which consecutive re-transmissions are separated by a second time interval, said second time interval being different from the first time interval, said second time interval being a multiple of a second clock period which is different from the first clock period, each said re-transmission thus occurring after a delay, said delay being different for each re-transmission and constituting the period of time between arrival of each said symbol at said other of said objects and re-transmission of each said symbol, said delay having a nominal length which is a multiple of a delay unit, said delay unit being equal to the product of the number of first clock periods corresponding to the first time interval and the difference between the clock periods, said delay unit also being equal to the second clock period divided by the number of symbols in the plurality of symbols, said delay having an actual length which is within one delay unit of said nominal length;
measuring a round-trip time corresponding to detection of receipt from said other of said objects of each of said symbols, each said round-trip time being a multiple of said first clock period;
and
determining said distance between said objects by multiplying said velocity of said symbols by half of the difference between the average of all of said round-trip times and the first clock period.

2 more elements

A method of measuring a distance between two objects, said method comprising the steps of:

transmitting from one of said objects a plurality of symbols, said transmissions occurring in a series in which consecutive transmissions are separated by a time interval which is a multiple of a first clock period, said symbols having a constant velocity;
detecting said transmissions using a second clock period, said second clock period being different from said first clock period, each said transmission detection thus occurring after a delay, said delay being different for each said detection and constituting the period of time between each said transmission and said detection of each said transmission, said delay having a nominal length which is a multiple of a delay unit, said delay unit being equal to the product of the number of first clock periods corresponding to the time interval and the difference between the clock periods, said delay unit also being equal to the second clock period divided by the number of symbols in the plurality of symbols, said delay having an actual length which is within one delay unit of said nominal length;
returning each of said symbols from the other of said objects back to said one of said objects;
detecting the arrivals of said returning symbols back at said one of said objects using said second clock period, each said arrival detection thus occurring after a second delay, said second delay being different for each said detection and constituting the period of time between each said arrival and said detection of each said arrival, the nominal length of said second delay being a multiple of said delay unit, said second delay having an actual length which is within one delay unit of said nominal length of said second delay;
measuring a round-trip time corresponding to detection of receipt from said other of said objects of each of said symbols, each said round-trip time corresponding to a multiple of a second clock period;
and
determining said distance between said objects by multiplying said velocity by half of the average of the round-trip times.

4 more elements

Dependencies are inferred from the claim text.

Measuring distance

Life of this patent

Measuring distance

Life of this patent

Abstract

Claims31