Communication apparatus

A communication apparatus for carrying out a communication operation in accordance with a remote command from another communication apparatus sharing one line with the another communication apparatus comprises a communication unit, line switching unit for selectively connecting the line to the another communication apparatus or the communication unit a power supply for supplying a power to the another communication apparatus to form a current loop with the another communication apparatus, a detector for detecting a status of formation of the current loop of the another communication apparatus, and a control unit for carrying out the communication operation in accordance with the detection signal of the detector.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a communication apparatus which shares a 
single line with another communication apparatus and performs a 
communication operation in accordance with a remote command from the 
another communication apparatus. 
2. Related Background Art 
A facsimile apparatus which shares a single telephone line with a telephone 
set and performs a facsimile Communication in accordance with a remote 
command from the telephone set has been known in the art. Such a facsimile 
apparatus is installed remotely from the telephone set and is connected 
through a network control unit (NCU). A user responds to a call signal 
from the line, and if the calling station is a facsimile terminal, the 
user manipulates a hook switch of the telephone set or a dialing ten-key 
to switch the line from the telephone set to the facsimile apparatus so 
that the facsimile reception is carried out (remote reception). 
The NCU of the facsimile apparatus is configured as shown in FIG. 4. 
In FIG. 4, a telephone line is connected to terminals L1 and L2, and a 
telephone set is connected to terminals T1 and T2. Numeral 1 denotes a CML 
relay which switches the telephone line between the telephone set and a 
modem. In a non-communication status, the CML relay 1 is connected to a so 
that the line is connected to the telephone set. 
When a remote reception is to be carried out, a user depresses a hook 
switch of the telephone set for hooking to temporarily (usually less than 
one second) open the line. When the user does the hooking, a control unit 
of the facsimile apparatus detects the hooking by a current sensor 2 and 
switches the CML relay 1 to the modem (b) to carry out the communication. 
Another configuration is shown in FIG. 5. In FIG. 5, when the user off 
hooks the telephone set in response to a call signal from the line and 
recognizes the calling station is a facsimile terminal, he/she manipulates 
the telephone set to dial a predetermined number (output a DTMF signal) in 
order to remotely receive the facsimile communication. The DTMF signal is 
sent from the terminals T1 and T2 to a terminal A through a transformer 8. 
A DTMF receiver is connected to the terminal A and the control unit 
recognizes the number outputted by the telephone set based on the output 
of the DTMF receiver. If it is the number for the remote reception, the 
control unit switches the CML relay 1 to b to carry out the communication. 
In this manner, the remote reception is attained. 
However, in the switching by the hooking described above, the hooking is 
generated by the user by depressing the hook switch of the telephone set 
for a short period. Accordingly, depending on the duration of hooking, a 
switching unit may determine it as the opening of the line and disconnect 
the line, or the hooking of a given duration may be determined as the 
opening of the line or may not be determined depending on the switching 
unit. Thus, the remote reception is very unreliable. 
Further, even if the remote reception normally operates, the user can hear 
nothing from the telephone set and cannot confirm whether the remote 
reception is successful or not. 
Where the CML relay is switched by the DTMF signal, the DTMF detector may 
misoperate by a DTMF signal due to crosstalk on the line so that the CML 
relay may be switched during the speech communication to break off the 
speech. 
Further, if the number for the remote reception is included in the number 
dialed by the user to call a destination, the CML relay is switched and 
the user cannot call. In order to solve the above problem, it has been 
proposed to limit the remote reception to a predetermined period after the 
reception of the call, but it is still not perfect because it does not 
permit the start of polling by the remote control and because of 
malfunction due to crosstalk from other lines. 
The control of the facsimile apparatus by the remote telephone set is 
disclosed in U.S. patent application Ser. Nos. 372,622 (filed on Jun. 28, 
1989); 453,364 (refiled on Dec. 20, 1989); 659,463 (refiled on Feb. 25, 
1991); and 670,461 (refiled on Mar. 13, 1991). 
However, no proposal to solve the above problems has been made. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to improve a communication 
apparatus in the light of the above problems. 
It is another object of the present invention to provide a communication 
apparatus which is free from malfunction when it is remotely operated by 
an external terminal. 
It is a still another object of the present invention to provide a 
communication apparatus which functions to form a current loop with 
another terminal which shares the same line, detects the status of 
formation of the current loop by the another terminal and carries out the 
communication in accordance with the detected status. 
It is a still another object of the present invention to provide a 
communication apparatus which detects the status of formation of the 
current loop of the line-by the another terminal, disconnects the another 
terminal from the line in accordance with the detected status and carries 
out the communication in accordance with the remote control signal from 
the another terminal. 
Other objects of the present invention will be apparent from the following 
detailed description of the preferred embodiments and the accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments of the present invention are now explained in 
detail with reference to the accompanying drawings. 
FIG. 1 shows a block diagram of a configuration of a facsimile apparatus in 
accordance with one embodiment of the present invention. Numeral 101 
denotes a control unit comprising a microprocessor which includes a CPU 
113, a read-only memory (ROM) 114, a random access memory (RAM) 115, a 
buffer memory 112, a line memory 110 and an encoder/decoder 111. It 
controls-the image input/output and the entire communication process. 
The ROM 114 stores a control program to be described later and the RAM 115 
is used as a work area for the CPU 113. 
The image input and output are carried out by a reader 100 and a recorder 
102, respectively. 
Document image data is read by the reader 100 which comprises a CCD (charge 
coupled device) sensor and a document feeder. Received image data or image 
data read by the reader 100 in a copy mode is recorded by the recorder 102 
which comprises a thermal printer or an ink jet printer. 
The input/output of the image data between the reader 100 or the recorder 
102 and the encoder/decoder 111 is carried out through a line memory 110 
one line at a time. The data input/output between the encoder/decoder 111 
and a communication line is controlled through a buffer memory having more 
than one line of processing unit (for example, a predetermined number of 
pages). 
The encoder/decoder 111 encodes and decodes to suppress redundancy and it 
may comprise software of the CPU 113. 
The connection with a center line N such as a telephone line and the data 
input/output are carried out by a modem 106 and a network control unit 
(NCU) 107. A telephone set or an auto-response telephone set 16 for speech 
communication and manual control is connected to the NCU 107. 
A console panel 103 comprises a ten-key for entering a telephone number and 
various function keys. A display 104 for displaying a telephone number and 
time is mounted on the console panel 103. 
FIG. 2 shows the NCU of the present embodiment. Numeral 1 denotes a CML 
relay, and numeral 2 denotes a current sensor which comprises a coil and a 
Hall element arranged in the vicinity of the coil and insulated from the 
coil. The coil generates a magnetic field which is proportional to a 
current flowing through the coil and the Hall element converts the 
magnetic field to a current which is proportional to the magnetic field so 
that an output current which is proportional to the coil current is 
generated. The output of the current sensor 2 is supplied to a comparator 
3 which produces a DCDET signal indicating the presence or absence of the 
current. 
The DCDET signal is supplied to the control unit 101. 
Numeral 7 denotes a power supply for supplying a DC voltage to the 
telephone set, numeral 6 denotes a constant current circuit for increasing 
an AC. impedance of the power supply 7, numeral 5 denotes a relay for 
connecting the telephone line to the line or the DC power supply, and 
numeral 8 denotes a transformer. 
A remote reception operation in the above configuration is now explained 
with reference to FIG. 3 which shows the operation of the control unit 101 
(CPU 113). This process is stored in the ROM 114. 
In FIG. 3, when the telephone set 16 is off-hooked by the DCDET signal, the 
control unit 101 advances a control process to a step S1. The status of 
the relays is shown in FIG. 2. In the step S1, the DCDET signal is further 
monitored, and if a DC current is detected, the process loops in the step 
S1. When the DC current disappears, the process proceeds to a step S2 to 
determine off-hooking or on-hook. In the step S2, a software timer T1 (as 
which a counter provided in the RAM L15 is used) for counting a line open 
time is initialized and the counting is started. Where the line is opened 
and the timer T1 does not reach 70 ms, the process loops in steps S3 and 
S4. The count 70 ms corresponds to a break time of a dialing pulse of 10 
pps having a make factor of 33% (the line open time 67 ms) plus a margin. 
If a DC current flows before the elapse of 70 ms, the line opening is 
regarded as a non-significant signal such as a dialing pulse or a noise 
and the process returns to the step S1. If the line opening continues for 
longer than 70 ms, the process proceeds to a step S5 to switch the CML 
relay 1 to b to again capture the line. Since the line is not opened for 
longer than 70 ms, the line which is not disconnected when the dialing 
pulse is sent will not be disconnected. The relay 5 is switched to c so 
that a DC voltage is applied to the telephone set 16 from the DC power 
supply 7 through the constant current circuit 6. Whether the hook switch 
is depressed or not is detected by the current sensor 2. A confirmation 
sound generated by a confirmation sound generator 117 is applied to the 
telephone set 16 through a transformer 8 and a DC blocking capacitor 9. 
The process then proceeds to a step S6 and loops in the step S6 and S7 
until the DC current disappears and the timer T1 reaches one second. If 
the DC-current is detected before the timer T1 reaches one second, it is 
regarded as the hooking and the process proceeds to a reception step 
(remote reception). If the timer T1 exceeds one second, it is regarded as 
the on-hook of the handset and the control returns to the stand-by state. 
Thus, the remote reception is attained when the user depresses the hook 
switch of the telephone set 16 within one second, and substantially within 
the same break of line as that caused by the dialing pulse takes place. 
In the present embodiment, the facsimile communication is started by the 
hooking of the telephone set 16. Another embodiment in which the facsimile 
communication is started by the DTMF signal from the telephone set is 
explained below. 
FIG. 6 shows a block diagram of a configuration of the facsimile apparatus 
of the other embodiment. In FIG. 6, the like numerals to those shown in 
FIG. 1 designate the like elements and the explanation thereof is omitted. 
In FIG. 6, a DTMF receiver 118 is added to the configuration of FIG. 1 and 
it is connected to the terminal A of the network control unit 107 (FIG. 
2). 
The remote reception operation in the above configuration is explained with 
reference to FIG. 7, which shows an operation of the control unit 101 (or 
the CPU 113). The process shown in FIG. 7 is stored in the ROM 114. 
In FIG. 7, when the telephone set is off hooked by the DCDET signal, the 
control unit 101 proceeds its control to a step S11. The status of the 
relays is shown in FIG. 2. The DTMF receiver is disconnected from the line 
at the terminal C of the relay 5 so that the remote reception is not 
started by the DTMF signal generated by the telephone set for the call. 
In the step S11, the DTDET signal is further monitored, and if no current 
is detected for 0.5-1.5 second, it is regarded as the hooking and the 
process proceeds to a step S12. If there is no hooking, the process loops 
in the step S11. In a step S12, the relay 5 is switched to c so that the 
DC current is supplied to the telephone set 16 from the DC power supply 7 
through the constant current circuit 6. In a step S13, the control unit 
monitors the output of the DTMF receiver 117 to check if the digit "5" for 
the DTMF is dialed. If it is dialed, the telephone set is connected to the 
DTMF receiver but since the line is disconnected at the terminal d of the 
relay 5, there is no risk of malfunction due to the crosstalk. When the 
user dials "5" from the telephone set, the "5" in the DTMF signal appears 
at the terminal A of the NCU from the terminals T.sub.1 and T.sub.2 
through the contact c of the relay 5, a capacitor 9 and the transformer 8 
and it is supplied to the DTMF receiver. When the control unit recognizes 
it, it proceeds to the reception so that the remote reception is attained. 
Accordingly, the remote reception is attained in either calling mode or 
called mode without risk of malfunction due to the crosstalk. 
While the remote reception has been described above, other functions of the 
facsimile apparatus may also be remotely controlled such as the outputting 
of a communication control report by the remote control or the 
transmission of the image stored in the memory to other facsimile 
apparatus. 
while the facsimile apparatus which carries out the facsimile communication 
in accordance with the remote command from the telephone set has been 
described, the remote command need not be sent by the telephone set but 
may be sent by other unit. Further, the communication apparatus to be 
remotely communicated is not limited to the facsimile apparatus but it may 
be other apparatus such as a teletex apparatus.