Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~9353
The present invention relates to a method of dis-
criminating fitting pressure during an assembly operation of
articulated track links on a track press and more particularly
to a method of discriminating whether or not each of the links
constituting a line of track chain is press fitted onto a pln
rotatably held in a bushing within a properly determined range
of fitting pressure when the track chain is assembled for
tractor or the like track vehicles.
As is well known, fitting pressure for links is
specified for each of the kinds of track vehicles such as a
tractor. For this reason, pressure fitting is achieved within
the specified pressure range when a line of articulated track
chain is assembled.
Discriminating of fitting pressure is hitherto
achieved by visually confirming that a pressure gauge for
indicating ram pressure in a track press indicates the exist-
ing pressure higher than the minimum value or lower than the
maximum value. However, the conventional method of discrimi-
nating fitting pressure has drawbacks in that discriminating20
is achieved at a lower operational efficiency and an lntensity
of press fitting fluctuates from link to link because the
pressure gauge fails to indicate actual fitting pressure
because it indicates also instantaneous peak pressure.
When the conventional simple method of discriminat-
ing fitting pressure is employed, a link is determined unac-
ceptable if the press pressure detected by the pressure gauge
instantaneously exceeds a predetermined upper limit but in
practical press working there tends to be instantaneously gen-
erated excessively high pressure due to existence of the burr30
or small projection on t~e fitting surface. However, experi-
ences illustrate that the link which is subjected to press
fitting with normal fitting pressure after removal of a burr
$
-- 1 --
~L29~353
or small projectlon is different from the case when a link is
press fitted with excessively high f:Ltting pressure and there-
fore the first mentioned link mainta:Lns a normal intensity of
the press fitting.
The present invention is adapted not to detect that
press pressure used for an assembly operation is held at a
level higher than the upper limit value or lower than the
lower limit value but to make a decision as to whether the
applied fitting pressure is acceptable or unacceptable in
lo dependence on the fact that the time in which pressure kept in
the specified range of pressure is loaded within a predeter-
mined pushing ti~e T or the press fitting distance is longer
than a predetermined time. Further, the present invention is
intended not to determine as unacceptable a press fitting
immediately when it is found that pushing or press time is
shorter than the predetermined time even when press pressure
exceeds the upper limit value whereby an average intensity of
press fitting or fitting pressure is utilized as a standard
for making a decision.
Specifically, a basic principle of the present
invention is such that the case where a predetermined press
fitting time T, as measured from the point of time when the
end faces of pins or bushings come in engagement to the fit-
ting holes in a link to start a fitting operation or a sum
Sta of press loading time for which press pressure is main-
tained within a range, as defined between both the predeter-
mined lower and upper limit pressures while press fitting is
achieved by a press fittlng distance, is longer than a prede-
termined value relative to the predetermined fitting time is
determined acceptable and in the case where the same is
shorter than the aforesaid value is determined unacceptable.
In addition to the fact that press fitting is deter-
-- 2
~2~93~i3
mined acceptable or unacceptable in accordance with the prin-
ciple of the invention as described above, the case where tlme
tb in which fitting pressure exceeds the upper limit pressure
level is longer than a predetermined time R is as detected
unacceptable.
According to the invention fitting time T is deter-
mined in dependence on the length of the link fitting holes
provided that an operational speed of the ram is maintained
constant, and it has a certain relation relative to the dis-
tance of press fitting of the links. For this reason either
of the fitting time and fitting distance may be employed as a
standard for carrying out the method of the invention. How-
ever, the description will be made below as to the case where
fitting time is employed as the standard for the purpose of
simplification of illustration and description.
Predetermlned value S ls represented ln the form of
percentages relative to fittlng time T and it ls normally
determined ln the range of 55 to 88%.
Now, time ta in which press pressure exceeds the
lower limit pressure value or lt is maintained within the
range of pressure higher than the lower limit pressure and
lower than the upper limit pressure during the step of press
working, that is, for the period of fitting time T has a cer-
tain relation relative to the fitting time T when the relation
is represented in the form of ratio (Q%) as follows.
Q = ( ~ ta X 100 ) % --- (1)
Thus, discrimination is carried out by comparing processing
result Q with predetermined value S.
Further, according to the invention time R ln whlch
pressure in excess of thè upper limit value PH is permissively
loaded is experientially determined in dependence on the sur-
~Z49353
face condition of the pin and other components. In practice,
it is normally determined in the range of 0.3 to 0.5 second.
Thus according to the present invention there is
provided a method of discriminating fltting pressure during an
assembly operation for articulated track links on a track
press essentially comprising the steps of: detecting loadtng
pressure in a ram during assembly operation of a link, compar-
ing the detected loading pressure with a lower limit pressure
value as well as an upp~r limit pressure value both of which
are predetermined with reference to a range of fitting pres-
sure specified for the link, predetermining allowable time in
which loading pressure in excess of the predetermined upper
limit pressure value can be loaded, and carrying out discrimi-
nation in dependence on whether or not a sum of pressure load-
ing time at a level of loading pressure higher than the prede-
termined lower limit pressure value during the pushing opera-
tion of the track press is longer than a predetermined time,
while excess pressure appearing within the allowable time dur-
ing the pushing operation of the track press is neglected.
Suitably fitting of a link is determined acceptable when a sum
of press loading time is longer than a predetermined value
while press pressure is maintained within the range between
the predetermined lower and upper pressure values and fitting
of the link is determined unacceptable when the sum of press
loading time is shorter than the predetermined one. Desirably
fitting of a link is determined unacceptable when time in
which press pressure exceeds the upper limit pressure value is
longer than a predetermined time during a fitting operation.
The present invention will be further illustrated by
way of the accompanying drawings, in which:-
Fig. 1 is a fràgmentary plan view of a track press,illustrating how assembly is successively effected for links;
~L2~93~3
Fig. 2 is a block diagram illustrating electrical
circuits for controlling operation o:E the fitting pressure
discriminating apparatus; and
Fig.s 3 to 6 are each a graph illustrating a rela-
tion of fitting pressure versus time, respectively.
Referring flrst to Fig. 1, a line of track chaln 1
is successively assembled by way of the steps of causing fit-
ting holes 7a and 7b on an opposing pair of track links 6 to
come in fitting engagement onto both the end parts of pins 3
rotatably held in bushings ~ which are placed on the jaw
insert 2 and repeating the foregoing operation for other llnks
to be assembled articulated on the track chain 1.
In the drawing reference numeral 8 designates a
pushing ram. AS is apparent from the drawlng, two pushing
rams 8 are mounted in symmetrical relation relative to the ~aw
lnsert 2 and they are actuated separately to move back and
forth. Further, reference numeral 9 designates a pressure
sensor which is disposed mldway of the hydraulic circuit for
each of the rams 8.
An example of discrlminating apparatus to which the
present invention is applied is illustrated in Fig. 2. An
electrical output form the pressure sensor 9 is applied into a
meter relay 10 in the illustrated embodiment.
The meter relay 10 includes a switching circuit 11
adapted to output ON signals after the pressure changing point
tl is detected, outputting of ON signals is effected irrespec-
tive of how the pushing pressure varies, a lower limit level
switch 12 is adapted to output ON signals only when the input
is compared with a predetermined lower limit value PL and lt
is found that the former exceeds the latter and an upper limit
level switch 13 is adapted to generate an output when it is
found that the input exceeds a predetermined upper limit level
~Z~9353
switch 13. Output from each of the above-mentioned switches
becomes a corresponding gate signal for respective pulse coun-
ters 14, 15 and 16.
Incidentally, the gate signal for the pulse counter
15 may be a logic output comprising the output from the lower
limit level switching circuit 12 and the output from the upper
limit level switching circuit 13. Alternatively, it may be an
output only from the lower limit level switching circuit 12,
because the predetermined allowable time R is short and an NG
signal is outputted in such a manner as described later when
an inequality R<tb is established.
In the drawing reference numeral 17 designates a
clock pulse generator adapted to be activated by means of a
pressure swltch 18 which serves to detect the pushing opera-
tion of the ram and stop its operation in response to a signal
output from a position switch 19 which serves to output a sig-
nal which represents the completion of pushing operation (the
extreme end of the fitting operation).
Further, in the drawing reference numeral 20 desig-
nates a processing and discriminating circuit. This clrcuit
20 is adapted to calculate the time Ta in which an inequal-
ity PH>PL is established during time T of the step of the
pushing operation or in which the input exceeds PL and more-
over carry out processing in accordance with the formula (1)
to generate an OK signal when an inequality S<Q is established
as a result of comparing Q (result of processing) with S
(predetermlned value) and generate an NG signal when an
inequality S>Q is established in the same way whereby an alarm
device such as buzzer, lamp or the like means is activated.
Specifically, when the press pressure varies prop-
erly as illustrated in F~g. 3, this operating state is natu-
rally represented by an OK signal but when time ta = tal +
1'~49353
ta2 + ~~~ in which press pressure is maintained within a spec-
ified pressure range during time T of the step of the pushlng
operation is short and the processing result Q is smaller than
predetermined value S as illustrated in Fig. 4, an NG signal
is outputted.
The counter 16 outputs a pulse signal equivalent to
excessive time tb when press pressure exceeds PH. Further,
the comparing circuit 21 makes a comparison between the excess
time tb and the predetermined time R so that it outputs an NG
signal when an inequality tb>R is established and at the same
time interrupts feeding of pressurized hydraulic oil to the
ram cylinder. However, when an inequality tb_R is estab-
lished, a signal is generated which clears the content con-
tained in the counter 16.
For this reason the NG signal is generated in the
case as illustrated in Fig. 5 but no NG signal is outputted in
the case as illustrated in Fig. 6.
The position switch 19 disposed in the discriminat-
ing apparatus as described above can be utilized as a limit
switch for limiting press fitting length for a certain link,
wherein the press fitting length varies in dependence on the
type of track press used for the above-mentioned purpose.
It should, of course, be understood that the meter
relay 10 may be fully replaced with an electronic circuit.
