Note: Descriptions are shown in the official language in which they were submitted.
CONT~lOLLER FOR WORK RIVET PRESS-FITTING MACHINE
This invention relates to a controller for a work
rivet press-fitting machine for press-fitting work rivets
into holes formed in a product sheet such as a plate or a
collar.
In riveting operation, it is necessary to insert rivet
heads in holes formed in a product sheet before caulking
them. This is done by striking the rivets in with a wooden
hammer or press-fitting with a hydraulic press.
~ ut since the riveting with a wooden hammer requires
human hands, it tends to be costly. Riveting with the
hydraulic press has a problem that positioning accuracy is
low. Further, due to extremely insufficient stroke and
pressure control, when inserting work rivets of different
lengths or if the heights of the rivet holes are different,
control was impossible. Thus, efficiency was low and
automation was impossible.
An object of the present lnvention is to provide a
controller ~or a work rivet press-fitting machine which can
press-fit work rivets to predetermined heights with high
accuracy and which can position the work table carrying a
product sheet and the main hydraulic cylinder relative to
each other with high accuracy, so that the press-fitting of
work rivets can be Farrled ou= un~anned witl less power
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consump~ion and in full automation.
Other features and objects of the present invention
will become apparent from the following description taken
with reference to the accompanying drawings, in which:
Fig. 1 is a block diagram of one embodiment of the
controller 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 e~planatory view of one example of the
work table; and
Fig. 5 is a block diagram showing the loop structure
of the control system of another embodiment.
Fig. 1 shows the basic structure of preferred
embodiment in which the controller shown comprises a
control unit 1, a Z-axis linear encoder 5 mounted on a Z-
axis hydraulic cylinder 2 for moving a piston shaft 20 for
press-fitting work rivets (Fig. 2) in the direction of Z-
a~is (vertically) to detect the position of the piston
shaft 20 in the direction of Z-axis, and an X-axis linear
encoder 6 and a Y-axis linear encoder 7 provided parallel
to an X-axis hydraulic cylinder 3 and a Y-axis hydraulic
cylinder 4 for moving, respectively, in the directions of
X-a~is and Y-axis, a work table W placed on a plane
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perpendicular to the spindle S and adapted to support a
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 hydr~ulic cylinder 2, the X-axis hydraulic cylinder 3
and the Y-axis hydraulic cylinder 4, respectively. In the
drawings, P is a hydraulic pump as a hydraulic power
source, and R is an oil reservoir.
The control unit 1 of this ambodiment comprises a host
computer 11, an interface 12 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,
respectively. The piston shaft 20 is provided at its
bottom end with a rivet chuck 21.
When inserting rivets with the Z-axis hydraulic
cylinder 2, as shown in Fig. 4 by way of example, the work
table W is moved in the X and Y directions to bring rivet
holes formed in a product sheet A placed on the work table
W i~to alignment with the piston shaft 20 one after
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another. Then the piston.shaft 20 is lowered by a
predetermined stroke. The bottom end of the work rivet
held by the rivet chuck will be press-fitted into the rivet
hole at a point slightly higher than the lower limlt of the
stroke, under the hydraulic force transmitted to the
spindle S throuOh the piston shaft 20 so that when the
piston shaft 20 has reached the lower end of stroke, the
rivet chuck 21 opens and the piston shaft 20 is raised and
the work table W is moved for the treatment of the ne~t
work rivet B.
In this embodiment, the order of press-fitting a
plurality of work rivets B in ~he product sheet A and their
press-fitting heights are preset in the host computer 11 in
the controL unit 1. The host computer 11 calculates the
stroke of the piston shaft 20 and the movement of the work
table W according to these preset data and gives the
results of calculation to the Z-, X- and Y-ax1s control
circuits 14, 15 and 16 through the interface 12.
When the X-a3is 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-a2is hydraulic cylinder 3 and the Y-axis
hydraulic cylinder 4, while detectin~ the position of the
work table W in the X- and Y-axis directions by means of
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the X- and Y-axis Linear encoders 6 and 7. Thus, the work
table ~ is mo~ed to the designated position by the host
compu~er 11, so that the target work rivet ~ will be
brought in~o alignment with the axis of the spindle S in
the Z-a~is hydraulic 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 of the spindle S through the Z-
a~is linear encoder 5, so that the spindle S will be
lowered to the lower limit of its stroke as commanded by
the host computer 11.
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 Z-a2is 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 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 o~
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 ener~ization of che coil ener~ized by the outpu~
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current from the Z-axis control circuit 14 to which the
signal representing the position of the piston shaft 20 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 c~linder 2 is used to introduce the oil pressure
from the hydraulic pump P, in other words, which one is
used to discharge the pressure oil into the oil reservoir
R. During the press-fitting of work rivets, the control
unit 1 controls the Z-axis servo valve 8 in such a way as
to extend the Z-axis hydraulic cylinder 2 quickly (fast
feed) until it approaches the head o~ the work rivet,
extend it at a suitable predetermined speed (slow feed)
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 8 to
the port C in the Z-axis hydraulic cylinder 2 contains a
pressure sensor 31 for converting the pressure in the pipe
line (numeral 30 indicates a pressure gauge3 into electric
si~nals to supply them to the Z-axis control circuit 14,
and an electromagnetic pressure control valve (relief
valve) 32. The working pressure of the valve 32, i.e. the
press-fitting pressure applied by the Z-axis hydraulic
cylinder ~ is set automatically by a program through the
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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
control unit 1 through the pressure sensor 31. If the oil
pressure fails to increase even when the piston 20 reaches
its predetermined stroke durin~ the pressure increase mode
of the Z-a~is hydraulic cylinder ~, the control unit 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. Also, pressure can be checked. Numeral 33
designates a relief valve, 34 and 35 do filters and PM
designates a pump motor. The X- and Y-axis systems may be
of the same structure as the Z-axis system except that
there are not provided the piston shaft 20 and the solenoid
relief valve 32. Thus, their detailed description is
omitted.
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 riveting work.
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