Automatic release device for automatically releasing the hold-on setting of an outside line call, and transfer method for an outside line call

An automatic release device for automatically releasing hold-on setting of an outside line call wherein a first telephone when having an outside line call from a second telephone and set to the hold-on state can be released from the hold-on setting by use of a sensing means detecting signals based on the hook-down at the second telephone slde. Further a transfer method for an outside line call, by using a conference call system served by Telegraph and Telephone Corporations wherein a running outside line call received from a second telephone by a first telephone through outside line wire is set to enable the conference call and the first telephone is set to the hold-on state so as to allow persons at the second and third telephones to talk with each other, wherein a sensing means for detecting signals based on hook-down of either of the second and third telephones is used to release the first telephone from the hold-on state.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The invention relates to an automatic release device for automatically 
releasing the setting of hold-on of a first telephone holding an outside 
line call from a second telephone by means of "hook-down" of the second 
telephone (replacement of the telephone receiver on its cradle), and also 
to a transfer method for transferring an outside line call received from a 
second telephone by a first telephone to any other lines by use of the 
hold-on setting automatic release device together with a "conference call" 
system (in which a plurality of persons can talk together using the same 
and single line) served by a Telegraph and Telephone Corporation. 
A hold-on setting device for setting a first telephone to the hold-on state 
holding an outside line call from a second telephone has been provided for 
various telephone sets or users telephone exchange apparatuses (called 
"business main exchange" in Japan) and is used when the first telephone is 
to be temporarily off with the outside line call being kept alive, causing 
the transmitting person (the second telephone) to hold on the line while 
an aimed speaker is gotten or the call is transferred to any other lines. 
The hold-on setting device is operated at the call-receiving side, usually 
by the receiving person (the person first picked up the telephone receiver 
of the first telephone) through his depressing the hold-on setting button 
on the telephone or other manners and may be released from the hold-on 
setting state at the call-receiving side. 
The conventional type of outside line call hold-on setting device is 
operated of the hold-on setting and its release only by the telephone at 
the call-receiving side. Release of the hold-on setting is forgettable 
after the hold-on setting is kept for hours, for example, when the 
receiving person takes time in getting the aimed speaker after setting the 
telephone to the hold-on state or such aimed speaker inadvertently fails 
to be on the line. The transmitting person has to merely hold on the line, 
having nothing to do in this case and will often hang up after kept 
waiting long, leading to the problem that the telephone at the 
call-receiving side is kept in the hold-on set state and cannot use the 
outside line on which the call has been off. 
Another case having the problem that the hold-on setting on the telephone 
at the receiving side is not released but kept to thereby cause the line 
to be kept unusable is seen under such circumstance that an outside line 
call is transferred to any other lines by use of the conference call 
system served by Telegraph and Telephone Corporations, for example, 
Trio-phone service by Nippon Telegraph and Telephone Corp., Japan, 
(telephoning function that three persons can talk together using the same 
and single line). In this case, a call-receiving person receives an 
outside line call from a transmitting person, calls up a third person (to 
whom the outside line call is to be transferred) to establish a three 
persons call and then set the call-receiving person's telephone to the 
hold-on state, thereby allowing that transmitting person and the third 
person (the one to whom the outside line call is to be transferred) to 
talk with each other. In the above case of transferring the outside line 
call by use of the conference call system, when the call between that 
transmitting person and that third person ends, the hold-on setting on the 
telephone at the call-receiving person is not released but kept to thereby 
cause the line to be kept unusable. 
Also, when the call-receiving person (the subscriber for the Trio-Phone 
service) merely replaces the telephone receiver on the cradle (the usual 
hanging up state), all the telephone communication above is broken. The 
call-receiving person necessarily needs to have the hold-on setting or 
keep "on" the telephone by picking up the telephone receiver for the 
purpose of providing the transfer as abovesaid. But, in the former (by the 
hold-on setting), hold-on tones hinders the call between that transmitting 
person and that third person, and in the latter, the telephone receiver 
picked up is a bother and does not keep secret any confidential 
conversation between those persons. Hence, the trio-phone service may be 
usable only for the three-persons call but is practically unreasonable to 
be applied for the aforesaid transfer of outside line call. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an automatic release 
device for automatically releasing the hold-on setting of an outside line 
call, by which device a first telephone when having at least one outside 
line call from a second telephone and set to the hold-on state can be 
automatically released from the hold-on setting through hook-down (or 
replacement) of the telephone transmitter/receiver on a cradle at the 
second telephone side, thereby allowing that outside line to be off and 
enabling the first telephone to receive any other calls from any other 
persons through the outside line. 
The present invention is characterized in an automatic release device for 
automatically releasing the hold-on setting of an outside line call 
wherein a first telephone when having an outside line call from a second 
telephone and set to the hold-on state can be released from the hold-on 
setting by use of a sensing means detecting signals based on the hook-down 
at the second telephone side. 
The present invention is also characterized in an automatic release device 
for automatically releasing the hold-on setting of an outside line call, 
the automatic release device being connected between outside line wires 
and outside line input terminals at a first telephone having an outside 
line call from a second telephone through the outside line wire, the 
automatic release device being provided with: a hold-on relay which is 
actuated by DTMF signals sent by the first or second telephone during the 
outside line call to set the first telephone to the hold-on state in 
relation to the outside line call and a release relay which is actuated by 
the DTMF signals to release the first telephone from the hold-on state, 
and a sensing means for detecting signals based on hook-down of the second 
telephone when the first telephone is in the hold-on state, the sensing 
means being adapted to actuate the release relay to cut a hold-on loop for 
the outside line call formed by the hold-on relay. 
The present invention is further characterized in a transfer method for an 
outside line call, by using a conference call system served by Telegraph 
and Telephone Corporations wherein a running outside line call received 
from a second telephone by a first telephone through outside line wire is 
set to the hold-on state in the conference call system by a Telephone 
Exchange while any other third line is called up, then, that outside line 
call is released from the hold-on state by the Telephone Exchange to 
enable the conference call, and also using a hold-on relay, which is 
connected between the outside line wire and outside line input terminals 
at the first telephone and to be actuated by DTMF signals sent by the 
first telephone or the third telephone subjected to the conference call, 
in order to set the first telephone to the hold-on state in relation to 
the outside line wire so as to allow persons at the second and the third 
telephones to talk with each other, wherein a sensing means for detecting 
signals based on hook-down of either of the second and third telephones is 
used to actuate a hold-on setting release relay, which is adapted to cut a 
hold-on loop formed by the hold-on relay, to release the first telephone 
from the hold-on setting in relation to the outside line wire. 
DETAILED DESCRIPTION OF THE INVENTION 
The "telephones" referred to in the specification may be general telephone 
sets commercially available from any makers of communication apparatuses 
or Telegraph and Telephone Corporations and are not limited to any 
particular devices. The hold-on setting for the telephones is carried out 
by depressing the hold-on button when the telephone has therein the 
hold-on function. The hold-on setting for the telephones may alternatively 
be carried out by actuation of any device having the hold-on function and 
connected to the telephones. The hold-on function is to catch the outside 
line when a corresponding telephone has a call thereon, so that when the 
receiver of such telephone is replaced on (hook-down) on the cradle, it 
does not cut the running outside line but keeps the hold-on setting 
therefor. In case of using a general telephone set, the hold-on setting is 
carried out by depressing the hold-on button on the telephone to actuate 
the hold-on relay (H relay) in the local line circuit to form a hold-on 
loop. Alternatively, a separate hold-on relay may be provided to be 
actuated by DTMF signals from telephones or actuated by an electrically 
connected switch. 
The "sensing means" is that when a first telephone has an outside line call 
from a second telephone and is set to the hold-on state in relation to the 
outside line, the sensing means detects signals based on the hook-down of 
the receiver at the second telephone to release the first telephone from 
the hold-on setting, leading to clear-down state. Release of the hold-on 
state may be carried out by the sensing means itself or in such manner of 
actuating the hold-on setting release relay by outputs from the sensing 
means, or cutting the hold-on loop by logical circuit. The signals based 
on the hook-down at the second telephone side are, for example, reversal 
of polarity or interrupted tone of 400 Hz forming busy-back tone. Means 
for sensing the signals may use thyristor or photocoupler IC which 
instantly cuts the hold-on loop correspondingly to reversal of polarity 
due to the hook-down. Also, means for sensing the interrupted tone of 400 
Hz may be touch-tone decoder. These means may be used solely, or together 
with a sensing means for detecting busy-back tone of 400 Hz in 
consideration of such case that polarity is not reversed upon the 
clear-down state because of free-line at the call-receiving side. The 
sensing means may be assembled in the telephone body or separately formed 
and connected thereto. 
The "DTMF signals" represent numbers by combinations of 2 frequencies in 
voice frequency band and are usually used in pushbutton phones. Also, a 
telephone having function of PB conversion tone may provide the DTMF 
signals. The DTMF signals to be used in the present invention should not 
be limited to any particular features but may be preferably a combination 
of two or more DTMF signals to prevent malfunction. The DTMF signals may 
be so set that two pushbuttons 7 and # are depressed to actuate the 
hold-on relay and the hold-on setting release relay. 
The "hold-on relay" is that when actuated forms a hold-on loop to provide 
the hold-on state. The "hold-on setting release relay" is that cuts the 
hold-on loop formed by the hold-on relay to allow a corresponding 
telephone to return to the state enabling the telephone talk. The relays 
may be actuated by the DTMF signals in such manner as actuated alternately 
with flip-flap (FF) using the same signals or actuated by separate 
signals. 
The "A.C. relay" is to be connected with a transmitting circuit which 
inputs signals of required frequency to call signal of telephones. The 
frequency is generally 16 Hz and preferably 15-20 Hz, and selected 
accordingly to have separate ring tone for the call signal of telephones 
from that of an outside line call. The A.C. relay may be adapted to 
transmit signals to provide ringing intervals with different cycles. The 
A.C. relay is actuated by the DTMF signals from a telephone at a 
transmitting side in an outside line call, and the DTMF signals are to be 
different from those for actuating the hold-on relay. 
The "Conference Call system" (the Trio-Phone service in Japan) is to be 
served by Telegraph and Telephone Corporations to their subscribers, 
allowing more than three persons with their respective telephones to talk 
together using a single line.

EMBODIMENTS 
Next, the present invention will be further detailed with referring to 
examples shown in the attached drawings. 
FIG. 1 is a schematic diagram showing connection of the automatic release 
device 1 of hold-on setting of outside line call according to the present 
invention. The automatic release device 1 is connected between outside 
line wire 2 (L1, L2) and outside line input terminals at a local telephone 
3. When the telephone 3 (a first side) receives an outside line call 
through the outside line wire 2 or transmits an outside line call through 
the outside line wire 2, and is set to the hold on state in relation to 
the outside line call, the automatic release device 1 will automatically 
release the hold-on setting when a transmitting or receiving side (a 
second side) of that outside line call replaces (hook-down) the telephone 
receiver on the cradle, thereby ending the outside line call. 
FIG. 2 shows an example of the present invention, wherein provided are a 
hold-on relay 4, hold-on setting release relay 5 and two thyristors 6. 
Hold-on setting or release of the hold-on setting can be performed by DTMF 
signals from the telephone 3. Also, hold-on setting can be released 
automatically by clear-down signals from the outside line wire 2 which 
clear-down signals are generated through the hook-down of telephone 
receiver at the second side. In detail, when a person talks over the 
telephone 3 with the second side and depresses two pushbuttons on the 
telephone, for example, 7 and *, this actuates the hold-on relay 1 and 
causes electric current to flow in the gate G of the thyristor 6 in a 
short time, so that properties of the thyristor 6 forms a loop of the 
outside line wire L1, L2 to provide the state of hold-on setting. When the 
pushbuttons 7 and * on the telephone 3 are depressed again, the hold-on 
setting release relay 5 is actuated in a short time to cut the formed loop 
of the outside line wire and release the hold-on setting. Operation of the 
hold-on relay 4 and the hold-on setting release relay 5 is controlled by a 
DTMF receiver 7 connected to the outside line wire. When the push buttons 
7 and * are first depressed, the hold-on relay 5 is actuated and when the 
pushbuttons are depressed again, the hold-on setting release relay 5 is 
actuated. These operations are alternately repeated by flip-flap IC 
(FF.IC). 
When the second side makes the hook-down in the state of hold-on setting, 
polarity of the outside line wire 2 is reversed. The hold-on loop held by 
the thyristor 6 is cut by the thyristor 6 itself, leading automatically to 
the clear-down state. In detail, cathode (K) of the thyristor 6 is applied 
with backward voltage to cut the hold-on loop, thereby releasing the 
hold-on setting. Hence, the telephone 3 even in the state of hold-on 
setting is automatically ended of the call to be able to receive any other 
calls from others. The example provides two thyristors 6 as having 
opposite polarity to each other since polarity of the outside line wire 2 
is not fixed when the automatic release device 1 is connected to the 
telephone 3 and either of the two thyristors 6 may perform the above 
function. A single thyristor 6 may be used when connected in conformity 
with a specific polarity of the outside line wire 2. Also, the example is 
so constructed not to emit hold-on tone in the state of hold-on setting 
because in use of the conference call, i.e., the Trio-Phone service 
provided by Telegraph and Telephone Corporations enabling three-persons 
call, when the first side (the first telephone) sets the telephone to the 
hold-on state without participating in the three-persons call, the hold-on 
tone if provided will bother the conference call between the second and 
third sides. Without use of the conference call service, the hold-on tone 
may be provided. The hold-on tone is preferable to be adjustable in volume 
in consideration of possibilities of use of the conference call service. 
FIG. 3 is a circuit diagram of IC to be actuated by DTMF signals, showing 
operation of a DTMF receiver 7 connected to the outside line wire 2 (L1, 
L2). The pushbuttons 7 and * on the telephone 3 are depressed to cause the 
DTMF receiver 7 to emit two DTMF signals and input them to a flip-flap 
(FF) IC 8 from which outputs related to the two DTMF signals can be 
extracted alternately. Data (Q,Q) output alternately by the FFIC 8 
actuates alternately the hold-on relay 4 and the hold-on setting release 
relay 5 in the circuit shown in FIGS. 4(a) and 4(b) in a short time. 
FIG. 5 shows a modified example of the present invention wherein a A.C. 
relay 9 is added in the circuit shown in FIG. 2. The A.C. relay 9 is 
provided for allowing a person at the second side to ring the bell of the 
telephone 3 at the first side when the second side waits long in the state 
of hold-on setting of the telephone 3. As shown in FIGS. 6 and 7, the 
second side depresses two pushbuttons 0 and # to actuate the A.C. relay 9 
with DTMF signals through the outside line wire to send bell voltage (AC 
75 V, 15-20 Hz) to the telephone 3, thereby ringing the bell of the 
telephone 3 at the first side. The A.C. relay 9 is controlled by the DTMF 
receiver 7 and actuated by the signals from depression of 0 and # 
pushbuttons to ring the bell every few seconds intermittently. 
FIG. 8 shows a further modified example of the present invention, providing 
a touch-tone decoder 10 which detects busy-back tone (interrupted tone, 
400 Hz in Japan), i.e., catches for few seconds the intermittently emitted 
busy-back tone 400 Hz when the second side makes the hook-down of the 
second telephone in the state of hold-on setting of the first telephone, 
and actuate the hold-on setting release relay 5 shown in FIGS. 2 or 5 to 
release the hold-on setting. The decoder 10 is preferably used together 
with the foregoing thyristor 6 to ensure the detection of the hook-down of 
the second side telephone. The example uses a counter IC 11 to count the 
intermittently emitted busy-back tone 400 Hz to actuate the hold-on 
setting release relay 5 with any numbers set by the counting, thereby 
preventing malfunction of the relay 5 based on any other tone 400 Hz than 
the busy-back tone. 
The present invention may use a photo-coupler 12 as shown in FIG. 9 to 
detect reversal of polarity upon ending of call. The feature is so 
constructed that first transition or last transition due to reversal of 
polarity from the hook-down at the second side telephone is caught in the 
form of pulse signals by which the hold-on setting release relay 5 shown 
in FIGS. 2 or 5 is actuated. 
The aforesaid example uses the thyristor 6 for forming the hold-on loop and 
releasing the hold-on state. This feature may be modified as the circuit 
shown in FIG. 10, wherein pushbuttons 7 and * are depressed to actuate a 
hold-on setting startup relay 13 and allow electric current to flow 
through the gate C of the thyristor 6, thereby actuating the hold-on relay 
4 to provide the hold-on state. Releasing the hold-on state is carried out 
by actuating the hold-on setting release relay 5. The hold-on setting 
release relay 5 is actuated by inputting to the part A the DTMF signals 
given when the pushbuttons 7 and * are depressed again, or signals to be 
emitted when the photocoupler IC 12 detects pulses due to polarity 
reversal from the hook-down at the second side telephone or the touch-tone 
decoder 10 detects busy-back tone 400 Hz, so that the hold-on relay 4 is 
reset to cause the hold-on state to be automatically released. 
FIG. 11 shows a further modified example of the present invention, showing 
a circuit which when the telephone 3 is set to the hold-on state by 
depressing a hold-on button on the telephone 3, the circuit detects 
hook-down at the second telephone side to release the hold-on state. 
Generally, when the telephone is set to the hold-on state in relation to 
an outside line by use of the hold-on button on the telephone, electric 
potential on H line becomes middle level by Zener diode. The potential 
level is detected by a level sensing circuit to actuate the hold-on relay 
(H relay) 14 and cause the relay 14 to self-hold, so that the H relay 14 
causes the outside line wire L1, L2 to connect the hold-on resistance 
R.sub.O to provide the hold-on state. Hence, the present example provides 
the hold-on setting release relay 5 on a part of the hold-on loop formed 
by the H relay 14, so that the hold-on setting release relay 5 is actuated 
by the foregoing touch-tone decoder 10 and photo-coupler IC 12 to release 
the hold-on state and automatically end the call, i.e., providing the 
clear-down state. 
FIG. 12 shows a transfer method of an outside line call by providing the 
automatic release device 1 of the hold-on setting of outside line call 
according to the present invention and using the foregoing conference call 
system, such as Trio-Phone service, served by Telegraph and Telephone 
Corporations. The example shows the case that a subscriber X having the 
automatic release device 1 of the hold-on setting of outside line call and 
subscribed for the conference call system receives an outside line call 
from a transmitting person Y and transfers the outside line call to a 
third person Z (to which such call is to be transferred). This is, for 
example, such case that when the transmitting person Y telephones the 
subscriber (the receiving person) X (FIG. 12(a)), the person Z with whom 
the transmitting person Y want to talk is absent due to going out and 
required to be called up with any local telephones near the person Z or a 
portable telephone set he may carry with so as to cause him to talk with 
the transmitting person Y. First, the outside line call from the 
transmitting person Y is set to the hold-on state with the conference call 
system by Telephone Exchange 15 (FIG. 12(b)). This is carried out, for 
example, by depressing the plunger on the cradle for an instant (about 700 
mmsec) (or depressing once a special "hook button" on a telephone). Then, 
the receiving person (subscriber) X calls up the third person Z (FIG. 
12(c)) to inform him of the call from the transmitting person Y, and 
depresses the hook button again to have the state of three-persons call 
(FIG. 12(d)). In this instance, the receiving person X actuates the 
automatic release device 1 of hold-on setting of outside line call and 
sets the telephone 3 to the hold-on state, so that the call from the 
transmitting person Y is substantially transmitted to the third person Z 
(FIG. 12(c)). That is, in this state, when the person X is replaced the 
telephone receiver to the cradle, the call between the persons Y and Z can 
be continued and the person X is kept out of the call. After transfer of 
the call as above, when the transmitting person Y and the third person Z 
end talking and either of them replaces (hook-down) the receiver on the 
cradle, signals from the hook-down is detected by the sensing means to 
cause the hold-on state of the telephone 3 (at the receiving person X 
(subscriber)) to be automatically released. 
In this case, when the A.C.relay 9 is provided as foregoing, either of the 
transmitting person Y and the third person Z can ring the bell of the 
telephone 3 to call back the receiving person X. Also, operation in 
relation to the conference call system is generally to depress the plunger 
on the cradle of the telephone 3 but alternatively may use the aforesaid 
special hook button provided on the telephone for the purpose of the 
conference call system. 
The above examples refer to the case the receiving person X possesses one 
telephone set. The automatic release device 1 according to the present 
invention can, as seen in FIG. 13, be incorporated in a system including a 
telephone facility 17 comprising users telephone exchange apparatus 16 
(main exchange) controlling a plurality of extension telephones 3A (three 
telephones shown in the drawing) and a plurality of outside lines 2 (three 
lines shown in the drawing) connected to the telephone facility 17. In 
this case, the automatic release devices 1 are disposed before outside 
line input terminals of the users telephone exchange apparatus 16 (i.e., 
the devices 1 are located at the side of the telephone facility 17 nearer 
Telephone Exchange). 
Also, to provide actuation of the automatic release device 1 according to 
the present invention in every kind of call including the foregoing 
transfer of outside line call using the Trio-Phone Service, the automatic 
release devices 1 are to be connected to every outside line wires 2. When 
the automatic release device 1 is integrally assembled in the users 
telephone exchange apparatus, the above connecting work can be carried out 
simply and the users telephone exchange apparatus can be added with 
values. 
As seen from the above, the automatic release device of hold-on state of 
outside line call according to the present invention has the following 
excellent advantages. 
(1) The hold-on state can be released by the clear-down signals emitted by 
the second (or third) side telephone. Hence, when the person at the first 
side happens to forget to release the first side telephone from the 
hold-on state, that the line is kept busy uselessly can be avoided and a 
corresponding telephone to the line can receive other calls. 
(2) The automatic release device can be operated simply and be readily 
connected to commercially available telephone sets. 
(3) The automatic release device when assembled in the telephone body 
provides a telephone having function of automatically releasing the 
hold-on setting as an added value to the telephone. 
(4) When a first telephone is set to be called up by a second side 
telephone's operation for ringing the bell of the first telephone in the 
state of hold-on setting, the second side's intention can be indicated to 
the first side, such as urging release of the hold-on state or leaving a 
message with any other person than an objective one. 
(5) In the case using the conference call system (The trio-phone service in 
Japan) served by Telegraph and Telephone Corps., after the first side 
person is set to provide the state enabling three-persons call on the 
outside line, when he does not participate in the three-persons call (or 
wants to transfer the call on the line to the other), the first side 
person's actuation of the hold-on relay for setting the hold-on state 
enables the remaining persons to talk together on the outside line even 
when he replaces the receiver on the cradle. Also, when the talk between 
that remaining persons ends, the hold-on state can be automatically 
released and that outside line can be automatically vacant. Also, use of 
the function of ringing the bell of the first side telephone causes the 
first side telephone to be called up by ringing of the bell through 
emission of DTMF signals from either of the second and third sides related 
to the outside line call, thereby allowing the first side person 
(telephone) to return to the three-persons call, 
(6) The transfer method of outside call using the conference call system 
(Trio-Phone service) may be usable even with a single line (outside line) 
and can largely reduce running cost in comparison with the conventional 
transfer method requiring two lines (two outside lines).