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Tiling Options for Extended Ultrasonic Positioning Coverage

The current design for the Bristol Ultrasonic Positioning System (BUPS) was intended for use in small areas e.g. up to 8m x 8m. It has been extended using additional ultrasonic transducers to cover areas as large as 10m x   20m. In order to provide coverage over larger areas using the same basic design we have two options - we either identify additional zones with 'slave' r.f. pingers or by providing signature chirps from a nominated ultrasonic transducer in each zone.

The drawings in the table below illustrate a 40m x 40m area with coverage provided by nine zones of nine transducers. Each zone is configured using a standard ping followed by nine chirps 50ms apart as in the original design, but with an additional five transmitting transducers.

Master/Slave Pingers

Ultrasonic Identifiers

In this option a master r.f. ping transmitter, centrally located, sends synchronising pulses to eight slave transmitters. The synchronising pulse is a standard ping which is used to ensure that the slave transmitters do not conflict (see timing diagram below). The receiver listens for the ultrasonic chirps and then locks on to the appropriate ping. For this to work effectively there must be a clear separation - either free space containing no ultrasound, or a wall - to separate the zones. In this option, each zone is identified by signature chirps following the positioning chirps. A central transducer is selected to produce up to four additional chirps at the end of the positioning sequence. The first three of these chirps identify which of the eight zones the receiver is located in. The final chirp is used to verify that the identifier chirps are valid (not reflections), and that the receiver is not in the central zone. The timing diagram illustrates this.

tile1.gif

Fig. 1 - Coverage of 40m x 40m using slave pingers.

tile2.gif

Fig. 2 - Coverage of 40m x 40m using identifier chirps.

key:
Normal ultrasonic tx. us_norm.gif (704 bytes)
Master ping with usonic tx us_mastr.gif (906 bytes)
Slave ping with usonic tx us_slave.gif (967 bytes)
'Dead' space between usonic txs us_bar.gif (881 bytes)
key:
Normal ultrasonic tx. us_norm.gif
Usonic tx with ident chirps us_ident.gif
Master ping with usonic tx us_mastr.gif
us_white.gif
timing diagram:

us_ms_t.gif

cycle time = 940ms

timing diagram:

us_id_t.gif

cycle time = 728ms

Both techniques are scalable and could provide coverage of even larger areas, however the cycle times will increase correspondingly. A combination of the two techniques could cover an area of 120m x 120m using a single master ping.

The specification for a particular installation will depend on the actual configuration of the interior space and would need to be customised accordingly.

Cliff (with thanks to Richard Hull, John Honniball and Henk Muller).
June 2002

 

 


This page last updated June 19, 2002
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