Note: Descriptions are shown in the official language in which they were submitted.
20379~7
CONTROLLER FOR RIVETTING MACHINE
This invention relates to a controller for a rivetting
machine which makes it possible to carry out rivetting
automatically simply by inputting data on machining.
A rivetting machine is known which comprises a motor-
drlven spindle extending through and journaled to a piston
shaft of a hydraulic cylinder connected to a hydraulic
power source, a rivet head forming tool having a forming
shaft and secured to the bottom end of the spindle. The
spindle is lowered by extending the hydraulic cylinder to
press the bottom end face of the forming shaft against the
top end face of a work rivet by the hydraulic force acting
on the piston shaft and at the same time the spindle is
rotated by the motor. Thus a rivet head is formed on the
work rivet.
Since the work rivets placed on the work table are of
various heights according to the products to be formed, it
is necessary to adjust the length of stroke of the
hydraulic cylinder. For this purpose, a mechanical stroke
adjusting structure was used. Such a structure may be a
stopper plate provided around the piston shaft of the
hydraulic cylinder so that its vertical position will be
adjustable by use of an index motor or the like. In this
arrangement, the lower limit of the stroke of the piston
- 2037947
shaft is set by abutting a member fixed to the piston shaft
against the stopper plate when the piston shaft is moved
down. Also, such a structure may comprise a disc member
provided around the piston shaft and having stopper pins of
different heights protruding upwardly therefrom, and a
plate-like member integral with the piston shaft and
provided with a pin extending downwardly. As the piston is
lowered, the pin at the side of the piston shaft will abut
one of the stopper pins selected by turning the disc
member. Thus the lower limit of the stroke of the piston
shaft is set.
In order to position a work rivet with respect to the
forming shaft by moving a work table placed on a plane (X-Y
plane) perpendicular to the hydraulic cylinder in X-Y
directions relative to the forming tool, a manual or
motor-driven ball-thread type table moving mechanism was
used.
~ ut the above-described prior art mechanical stroke
adjusting structure not only required e~tra parts such as
an index motor and stopper means but the stroke adjustment
was very troublesome. These problems have been big
obstacles to full automation of rivetting work. Also,
since stepless adjustment of stroke was difficult, a
special stopper had to be prepared when forming an off-
specification work rivet. This incurs extra labor and
` 2037947
cost.
Further, the ball-thread type mechanism for moving the
X-Y table had a problem that its moving speed was slow. If
the moving speed is increased, the positioning accuracy
worsens. Further, since wear on the ball-thread can also
lower the positioning accuracy, frequent lubrication and
exchange of parts were necessary. This also increases the
cost.
Further, the setting of caulking pressure had to be
carried out by manually adjusting the working pressure of
the relief valve according to the diameter of each rivet
and its material. This is also troublesome and has been
another obstacle to automation of rivetting work.
An object of the present invention is to provide a
controller for a rivetting machine which is capable of
adjusting the stroke of the hydraulic cylinder with high
accuracy by controlling the hydraulic pressure, which is
capable of relative positioning between the work table and
the hydraulic cylinder, i.e. X-Y axis control with high
accuracy, and which permits automatic setting of caulking
pressure and thus automation of rivetting work.
In the controller for a rivetting machine of this
invention, the control unit automatically calculates the
length of stroke of the hydraulic cylinder according to the
data on a work rivet to be formed such as its length and
2037947
actuates the servo valve to lower the piston shaft of the
hydraulic cylinder until the output of the linear encoder
indicates that the piston shaft is at the lower limit of
stroke (extension mode). When the piston shaft reaches its
lower limit, the control unit switches the servo valve to
reverse position to raise the piston shaft (shrinkage
mode). When the output of the linear encoder indicates the
upper limit of stroke, the servo valve is switched back to
its neutral position to stop the hydraulic cylinder in
preparation for the forming of the next work rivet.
With the controller for a rivetting machine according
to this invention, since the hydraulic pressure for
pressing a work rivet through the forming shaft of the
rivet head forming tool mounted on the bottom end of the
spindle shaft is controlled according to the output signals
of the linear encoder, it can be used for the positioning
of the spindle shaft. This eliminates the need for any
mechanical stroke adjusting means.
With the controller for a rivetting machine of this
invention, the working pressure of the electromagnetic
pressure control valve is set automatically by the control
unit depending upon the diameter of the work rivet and its
material. Thus, the rivetting can be done automatically at
a caulking pressure suitable for each work rivet. It can
be checked whether or not there is a work rivet at a
2037947
predetermined machining position. This further improves
the accuracy of rivet forming.
With the controller for a rivetting machine of this
invention, the control unit not only controls the stroke in
the direction of e~tension and shrinkage (in the directiOn
of Z-axis), but also controls the positioning of the work
table by controlling the hydraulic cylinders for the
respective shafts with the X-axis servo valve and the Y-
axis servo valve while feeding back the position
information from the X- and Y- axis linear encoders. This
allows a quick positioning of the wor~ table without the
need for a limit switch or a stopper.
According to this invention, the stroke of the spindle
shaft of a rivetting machine can be variably set simply by
inputting machining data. Further, the machining can be
done automatically according to the setting with high
accuracy. Thus the rivetting efficiency and the quality of
the rivets thus made improve greatly. Also, the work table
can be positioned quic~ly and accurately utilizing
hydraulic pressure. This permits fully automated, labor-
saving rivetting operation. Its maintainance is also less
troublesome because no ball-thread i~ used.
, ~ .,
20379~7
Accordlng to one aspect of the present lnventlon,
there ls provlded a controller of a rlvettlng machlne havlng a
hydraullc cyllnder, and a motor and a hydraullc power source
connected to sald hydraullc cyllnder, the cyllnder lncludlng a
plston shaft, a splndle extendlng through and ~ournaled to
sald plston shaft and drlven by sald motor, a rlvet head
formlng tool secured to the bottom end of sald splndle, and a
formlng shaft supported by sald rlvet head formlng tool,
whereby sald splndle ls lowerable by sald hydraullc cylinder
to cause abuttlng contact between the bottom end face of sald
formlng shaft and the top end face of a work rlvet and at the
same tlme sald splndle ls rotatable by sald motor to form a
rlvet head on the work rlvet wlth sald formlng shaft, sald
controller comprlslng: a llnear encoder ln operatlve
assoclatlon wlth sald plston shaft so as to detect the axlal
posltlon of sald plston shaft; an electrlc/hydraullc servo
valve provlded ln a hydraullc clrcult between sald hydraullc
power source and sald hydraullc cyllnder so as to control the
flow of hydraullc fluld to and from sald hydraullc cyllnder,
sald hydraullc clrcult lncludlng a hydraullc llne extendlng to
sald hydraullc cyllnder; an electromagnetic pressure control
valve operatlvely hydraullcally connected in said hydraulic
line so as to control the pressure of hydraulic fluid flowing
therethrough to said cylinder; a control unit programmable to
receive machinlng data for rivets to be worked by the
rivetting machine, said control unit being operatlvely
5a
2037947
connected to sald linear encoder so as to recelve the output
of said llnear encoder, sald control unlt belng operatlvely
connected to hydraulic cyllnder vla sald electrlc/hydraullc
servo valve so as to control sald hydraullc cyllnder by
controlllng the posltlon of sald electrlc/hydraullc servo
valve based on the machlnlng data and the output of sald
llnear encoder, and sald control unlt belng operatlvely
connected to sald electromagnetlc pressure control valve so as
to control sald electromagnetlc pressure control valve to
regulate the pressure of hydraullc fluld flowlng through sald
hydraullc llne to be no hlgher than a predetermlned pressure
establlshed by the machlnlng data for a rlvet to be worked.
Accordlng to another aspect of the present
lnventlon, there ls provlded a controller of a rlvettlng
machlne havlng a hydraullc cyllnder, and a motor and a
hydraullc power source connected to sald hydraullc cyllnder,
the cyllnder lncludlng a plston shaft, a splndle extendlng
through and ~ournaled to sald plston shaft and drlven by sald
motor, a rlvet head formlng tool secured to the bottom end of
sald splndle, and a formlng shaft supported by sald rlvet head
formlng tool, whereby sald splndle ls lowerable by sald
hydraullc cyllnder to cause abuttlng contact between the
bottom end face of sald formlng shaft and the top end face of
a work rlvet and at the same tlme sald splndle ls rotatable by
sald motor to form a rlvet head on the work rlvet wlth sald
formlng shaft, sald controller comprlslng: a linear encoder
5b
'-J
20379 17
in operative assoclatlon wlth said plston shaft so as to
detect the axlal posltlon of sald plston shaft; an
electric/hydraulic servo valve provlded ln a hydraulic clrcuit
between said hydraulic power source and sald hydraulic
cylinder so as to control the flow of hydraulic fluid to and
from sald hydraullc cyllnder, sald hydraullc clrcult lncludlng
a hydraullc llne extendlng to sald hydraullc cyllnder; a
pressure sensor operatlvely connected to sald hydraullc llne
so as to sense the pressure of hydraullc fluld ln sald
hydraulic line; and a control unit programmable to recelve
machinlng data for rivets to be worked by the rlvetlng
machine, said control unit belng operatlvely connected to said
linear encoder so as to receive the output of sald llnear
encoder, said control unit belng operatlvely connected to said
hydraulic cylinder via at least said electrlc/hydraullc servo
valve so as to control sald hydraullc cyllnder by controlllng
tne position of said electrlc/hydraulic servo valve based on
the machining data and the output of sald llnear encoder, and
sald control unlt also being operatively connected to sald
pressure sensor so as to monitor the pressure in sald
hydraullc llne and effect a control of sald electrlc/hydraullc
servo valve, based on sald monltorlng of the pressure ln sald
hydraulic line during an extenslon of sald plston shaft, whlch
causes sald plston shaft to retract when sald plston shaft has
moved a predetermined stroke wlthout the pressure ln said
hydraulic line having increased thereby detectlng that a rlvet
5c
, -
2037947
- ls not dlsposed in a posltlon to be worked by sald forming
shaft.
Other features and ob~ects of the present invention
wlll become apparent from the following descrlptlon taken
with reference to the accompanylng drawlngs, in whlch:
/ 5d
203~9~7
Fig. 1 is a block diagram of one embodiment of the
controller for a rivetting machine according to this
invention;
Fig. 2 is a sectional view showing one example of the
Z-axis hydraulic cylinder.
Fig. 3 is a hydraulic circuit diagram showing one
example of the hydraulic system of the above embodiment;
Fig. 4 is an explanatory view of one e~ample of the
work table; and
Fig. 5 is a block diagram showing the loop structure
of the control system of another embodiment.
Now, one embodiment of the controler for a rivetting
machine according to this invention will be described with
reference to the drawings.
Fig. 1 shows the basic structure of this embodiment in
which the controller shown comprises a control unit 1, a
Z-axis linear encoder S mounted on a Z-a~is hydraulic
cylinder 2 for moving a rivetting spindle S (Fig. 2) in the
direction of Z-a~is (vertically) to detect the position of
the spindle S in the direction Z-a~is, and an X-a2is linear
encoder 6 and a Y-axis linear encoder 7 provided parallel
to an X-axis hydraulic cylinder 3 and a Y-agis hydraulic
cylinder 4 for moving, respectively, in the directions of
X-a~is and Y-a~is, a work table W placed on a plane
perpendicular to the spindle S and adapted to support a
~037947
work rivet, so as to detect the position of the work table
in the directions of X-axis and Y-axis. The controller
further comprises a Z-axis servo valve 8, an X-axis servo
valve 9 and a Y-axis servo valve 10 for controlling the Z-
axis hydraulic cylinder 2, the X-axis hydraulic cylinder 3
and the Y-a~is hydraulic cylinder 4, respectively. In the
drawings, M indicates a driving motor for the spindle S, P
is a hydraulic pump as a hydraulic power source, and R is
an oil reservoir.
The control unit 1 of this embodiment comprises a host
computer 11, an interface 12, a motor control circuit 13
for controlling the driving motor M and a Z-axis control
circuit 14, an X-axis control circuit 15 and a Y-axis
control circuit 16 for controlling the Z-, X- and Y-axis
servo valves 8, 9 and 10, respectively.
Fig. 2 shows the detailed structure of an example of
the Z-axis hydraulic cylinder 2. It has a piston shaft 20
moved up and down under the action of the hydraulic oil
supplied and discharged through ports C and D, and a
spindle S extending through the piston shaft 20 and
journaled thereto. The spindle S is provided at its bottom
end with a rivet head forming tool 21 having a forming
shaft 22 secured to the bottom thereof. The forming shaft
22 has its bottom end as a forming surface aligned with the
axis of the spindle S and its top end offset therefrom.
2037947
In this arrangement, when the forming tool 21 is
rotated by the spindle S, the forming shaft 22 is rotated,
forming an inverted cone with the forming surface as its
apex. A driving motor M is mounted on the Z-axis hydraulic
cylinder 2 through a spacer 23. It has its output shaft 24
connected with the spindle S through a universal joint 25.
But it may be connected not through the universal joint 25
but through an ordinary joint so that the motor M will move
up and down together with the spindle S.
When rivetting with the Z-axis hydraulic cylinder 2,
as shown in Fig. 4 by way of example, rivets B (work
rivets) are placed on the work table W with their heads
received in holes formed in a product sheet A. In this
st~te, the work table W is moved in the X and Y directions
to bring the rivets into alignment with the spindle S one
after another. Then the spindle S is lowered by a
predetermined stroke together with the piston shaft 20.
The bottom end face of the forming shaft 22 will come into
abutment with the top end face of the work rivet B at a
point slightly higher than the lower limit of the stroke.
As the spindle S is turned in this state by the driving
motor M while pressing the work rivet B by the hydraulic
force transmitted to the spindle S through the piston shaft
20, the head of the work rivet B will be caulked, so that
when the piston shaft 20 has reached the lower end of
`- 2037947
stroke, a rivet head of a required size is formed. In this
state, the piston shaft 20 is raised and the work table W
is-moved for the forming of the next work rivet B.
In this embodiment. the order of forming of a
plurality of work rivets B and their heights (lengths) are
preset in the host computer 11 in the control unit 1. The
host computer 11 calculates the stroke of the spindle S and
the movement of the work table W according to these preset
data and give the results of calculation to the Z-, X- and
Y-axis control circuits 14, 15 and 16 through the interface
12. Also, it gives a command on the timing for actuating
the driving motor M to the motor control circuit 13. The
driving motor M may be kept activated e.g. throughout the
period while the spindle 20 is moving down (it may be
driven continuously) or it may be activated immediately
before the bottom end face of the rivet forming tool 21
comes into abutment with the top end face of the work rivet
B and kept activated until its stroke reaches its iower
limit.
When the X-a~is control circuit 15 and the Y-axis
control circuit 16 receive the command from the host
computer 11, they will electrically control the X-axis
servo valve 9 and the Y-axis servo valve 10, respectively,
to activate the X-axis cylinder 3 and the Y-axis cylinder
4, while detecting the position of the work table W in the
2037947
X- and Y-axis directions by means of the X- and Y-axis
linear encoders 6 and 7. Thus, the work table W is moved
to the designated position by the host computer 11, so that
the target work rivet B will be brought into alignment with
the axis of the spindle S in the Z-axis cylinder 2. Then,
the Z-axis control circuit 14 will electrically control the
Z-axis servo valve 8 to activate the Z-axis hydraulic
cylinder 2, while feeding back the position Or the spindle
S through the Z-axis linear encoder 5, so that the spindle
S will be lowered to the lower end of its stroke as
commanded by the host computer 11.
During this downward stroke, the bottom end face of
the forming shaft 22 will come into abutment with the top
end face of the work rivet B. In this ~tate, the spindle
20 is rotated by the driving motor M, while pressing the
work rivet B by the hydraulic force transmitted to the
spindle S through the piston shaft 20. Thus, when the
spindle S reaches the lower limit of its stroke, a rivet
head of a desired size will be formed. The information
that the spindle S has reached its lower limit is fed back
by the Z-axis linear encoder 5. In response to this
information, the driving motor M is stopped by the motor
control circuit 13 and the Z-agis servo valve 8 is switched
to a position reverse to the descent position by the Z-axis
control circuit 14 to actuate the Z-axis hydraulic cylinder
20379~7
2 so as to raise the spindle S. In Fig. 1, arrows in thin
solid lines indicate the flow of electrical signal and the
thick lines indicate the flow of hydraulic oil.
Fig. 3 shows the detailed structure of an example of
the Z-axis system. In the illustrated hydraulic system.
the Z-axis servo valve 8 is a double-coil type 4-port, 3-
position servo valve. It is adapted to change over the
state of energization of the coil energized by the output
current from the Z-axis control circuit 14 to which the
signal representing the piston of the spindle S is fed back
by the Z-axis linear encoder 5. Thus, it is determined
which one of the ports C and D in the Z-axis hydraulic
cylinder 2 is used to introduce the oil pressure from the
oil pump P, in other words, which one is used to discharge
the pressure oil into the oil reservoir R. During the
rivetting operation, the control unit 1 controls the Z-axis
servo valve 8 in such a way as to extend the Z-axis
hydraulic cylinder 5 quickly (fast feed) until it
approaches the head of the work rivet, extend it at a
suitable predetermined speed (slow ~eed) while caulking the
head, and move it backward (shrink) at a high speed again
after caulking. In this case, the feed speed can be
controlled in a stepless manner.
In this embodiment, the pipe line in the pressure
increase system extending from the Z-axis servo valve ~ to
2~37S~7
the port C in the Z-a~is hydraulic cylinder 2 contains a
pressure sensor 31 for converting the pressure in the pipe
line (numeral 30 indicates a pressure gauge) into electric
signals to supply them to the Z-a2is control circuit 14,
and an electromagnetic pressure control valve (relief
valve) 32. The working pressure of the valve 32, i.e. the
caulking pressure of the Z-axis hydraulic cylinder 2 is set
automatically by a program through the Z-a~is control
circuit 14 according to the respective rivets. Also, the
pressure in the pressure increase system of the Z-axis
hydraulic cylinder 2 is monitored by the controller 1
through the pressure sensor 31. If the oil pressure fails
to increase even when the piston 20 reaches its
predetermined stroke during the pressure increase mode of
the Z-axis hydraulic cylinder, the controller 1 will Judge
that the work rivet is missing. In this way, it can be
checked whether or not a work rivet is in each rivet hole
formed in the product sheet A at a predetermined point.
Numeral 33 designates a relief valve, 34 and 35 are filters
and PM designates a pump motor. The X- and Y-a~is systems
may be of the same structure as the Z-axis system e~cept
that there are not provided the spindles, the driving motor
M and the solenoid relief valve 32. Thus, their detailed
description is omitted.
The rivet head forming tool 21 may be detachably
2~37947
mounted (Fig. 2) so that a press jig (not shown) for
press-fitting a work rivet B in a rivet hole in the product
sheet A can be mounted in place of the rivet head forming
tool. With this arrangement. the controller for a
rivetting machine according to this invention can also be
used as a controller for a rivet press.
According to this invention, a servo loop for the
electric system and the hydraulic system comprising
electric and mechanical elements as shown in Fig. 5 may be
used to carry out the position control as an acceleration-
load control. This arrangement makes it possible to
control the servo hydraulic cylinder in a PLL (phase locked
loop) state without any delay in position and thus to
remarkably improve the accuracy of rivetting work.
