Communications: electrical – Systems – Selsyn type
Reexamination Certificate
2001-03-22
2003-07-22
Lieu, Julie (Department: 2632)
Communications: electrical
Systems
Selsyn type
C340S315000, C340S315000, C375S130000
Reexamination Certificate
active
06597282
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power-line carrier method using power transmission lines as communications lines, and more specifically, to a spread spectrum transmission system which transmits data by superimposing spread spectrum modulated signals (hereinafter called as S signals on commercial power lines.
2. Detailed Description of the Related Art
The spread spectrum transmission system is a communication system using the spread spectrum modulation method. Spread spectrum transmission was originally conventionally developed mainly for military use. The communications are encrypted by means of a spread code used as the key. Since the transmitted electric power is spread over a wide bandwidth, spectrum density can be lowered, making it possible to maintain even the existence of the communications secret. Meanwhile, since the spread spectrum transmission system transmits data by spreading it over a wide bandwidth, it is possible to transmit data even if the signal strength of the signal electric power is, in places, weaker than the noise of the transmission line. In recent years, based on these observations, a commercial spread spectrum transmission system has been developed using commercial electric power lines as signal transmission lines, for such applications as the remote control of machine tools in factories, where the generation of noise cannot be avoided.
Referring to
FIG. 3
, a conventional spread spectrum transmission system
100
, employed for such applications as the remote control of machine tools inside a factory, uses the same commercial electric power line
101
wired from outside the building to the inside of the factory via a breaker
102
. A blocking filter
103
connected downstream of the breaker
102
prevents the infiltration of external electrical noise via the breaker
102
from the transmission lines of an electric power company. Additionally, the blocking filter
103
is installed so as to prevent the external leakage of SS signals flowing along the commercial electric power lines
101
a
and
101
b
inside the factory, to be described later.
A plurality of commercial electric power lines
101
a
and
101
b
branch to each process within the factory, including assembly lines, molding lines, and the like, and to plug sockets
104
,
104
. . . The plug sockes
104
are installed at convenient locations along the power lines
101
a
/
101
b
to provide power to load devices such as machine tools and electrical apparatuses.
For example, the socket plugs of a press molding device
105
and an illuminating device
106
are connected to the plug sockets
104
,
104
. . . of the commercial electric power line
101
a
. The socket plugs of assembling devices
107
and
108
are connected to the plug sockets
104
,
104
. . . of the commercial electric power line
101
b
. Commercial alternating current power is thus supplied to each load device.
The socket plugs of a plurality of spread spectrum communication terminal apparatuses
109
a
,
109
b
,
109
c
, and
109
d
are plugged into freely selected remaining plug sockets
104
,
104
. . . of the commercial electric power lines
101
a
and
101
b
. These spread spectrum communication terminal apparatuses
109
are each equipped with an input-output portion which inputs and outputs communication signals, and a spread spectrum modem apparatus (hereinafter called as S modem) which modulates and demodulates between communication signals and SS signals. Each S modem superimposes SS communication signals onto the commercial electric power line
101
to which its socket plug is connected. In addition each S modem outputs SS signals flowing on the commercial electric power line
101
as communication signals, to or from the input-output portion.
For example, the spread spectrum communication terminal apparatus
109
a
connected to the commercial electric power line
101
a
is installed adjacent the press molding device
105
. The spread spectrum communication terminal apparatus
109
a
receives and decodes communication signals indicating operational information of the press molding device
105
. Information to and from the spread spectrum communication terminal apparatus
109
a
passes along communication cables shown as dotted lines in the drawing. This operational information is superimposed on the commercial electric power line
101
a
as SS signals, demodulated to communication signals by the spread spectrum communication terminal apparatus
109
b
similarly connected to the commercial electric power line
101
a
, and output to a personal computer (hereinafter called as PC
110
connected to the input-output portion of the spread spectrum communication terminal apparatus
109
b
. Additionally, the PC
110
can output control information for controlling the press mold
105
. Communication signals representing the control information are sent to the press molding device
105
via the commercial electric power line
101
a
, by flow in the opposite direction to that described above.
In the same way, communication signals can be transmitted between assembling devices
107
and
108
and a PC
111
installed in a freely chosen location, by means of the spread spectrum communication terminal apparatus
109
c
connected to the assembling devices
107
and
108
. These communication signals travel along the communication cables shown by the dotted lines, and a spread spectrum communication terminal apparatus
109
d
connected to the PC
111
. Moreover, if PC
110
and PC
111
are connected to another communication network
112
, all machine tools in the factory can be centrally managed from a host computer, not shown in the drawing, connected to the communication network
112
(noted as a local area network LAN).
Thus, with the spread spectrum transmission system
100
using the commercial electric power line
101
, it is possible to connect an SS modem, which modulates and demodulates SS signals between data terminal apparatuses (control-receiving apparatuses), using a commercial electric power line
101
, and transmit data between the spread spectrum communication terminal apparatuses
109
using this commercial electric power line
101
as a signal transmission line. Consequently, in an environment having ordinary power supply equipment, it is possible to easily transmit data between terminal apparatuses without preparing a new communication line.
With the above-mentioned conventional spread spectrum transmission system
100
, blocking filter
103
is required after the breaker
102
which is the lead-in for the commercial electric power line
101
from outside the facility, in order to prevent the infiltration of external noise, and to prevent external leakage of SS signals superimposed over commercial power lines inside the factory.
However, in order to serially interpose the blocking filter
103
in the commercial electric power line
101
through which all the load devices in the factory are supplied with electric power, blocking filter
103
must be an expensive, high-capacity blocking filter.
Additionally, the spread spectrum modulation method is not easily impacted by noise because it diffuses noise by back-diffusion during demodulation. However, machine tools inside a factory are prone to generate high levels of noise which can produce an outflow of electrical noise to the commercial electric power line
101
. Consequently, in order to conduct stable communications using a commercial electric power line
101
as a communication line, a noise filter is required on each load device, increasing the overall cost of the system.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present invention is to provide an inexpensive spread spectrum transmission system which prevents the infiltration of external noise, and prevents the external leakage of SS signals.
Additionally, another object of the present invention is to provide a spread spectrum transmission system which allows stable communication by means of SS signals, without installing filters on loa
Sakamoto Masahide
Takakura Tooru
Takata Hajime
Darby & Darby
Lieu Julie
SMK Corporation
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