BACKGROUND OF THE INVENTION
This invention refers to a drive system for working tools like drawing
and ruling utilized e.g. in draughting machines, known as plotters and, in particular
for a flat plotter type. These tools are of two types: the first is in contact
with a strip material with a fluid released during contact, while the second penetrates
the strip material, leaving its mark as a result of the penetration. Both types
of tools are moved over the strip material, parallel and at right angles to the
surface in socalled X- and Y-directions, in response to signals delivered from
a controller to the associated transmission devices.
Especially the present invention relates to a working head assembly
for a plotting or ruling apparatus and the like, supported by a carriage for positioning
the assembly over a strip material in a x-y plane parallel to the surface of that
strip material, a support for mounting at least one actuating device to move a
tool up and down between a resting position and a working position in a z-direction
orthogonal to the x-y plane, said actuating device comprising a housing, a core
for supporting the tool in an axially bore, and a solenoid coil, all arranged
coaxially to each other, which solenoid coil acts against the force of a first
spring, when driving core and tool into their working position, said actuating
device further comprising a second spring for coupling said tool to the actuating
Such a working head assembly with an actuating device to move up
a draughting tool or pen in a resting position and to move down that pen in a working
position is shown in United States Patent No. 4,426,783 issued to Gerber et al.
Gerber et al. teach to use a first compression spring for moving
up the pen. This first spring acts between the upper end of a pressure foot and
a shaft spacer of the pen body. Therefore the force of the spring is permanently
transmitted by the presser foot onto the surface of the strip material. Moving
the working head assembly in a x-y plane the presser foot will be all times in
engagement with the strip material independent of the pen position.
Due to this fact the strip material can be destroied by the load
of the presser foot and its sliding on the surface of the strip material. A second
problem are difficulties for service especially when changing the strip material.
Another working head assembly for a rotating ruling tool is shown
in the EP A 02 65 957 issued to Muramaya et al.
This working head assembly includes an actuating device driven by a socalled "linear
motor". The actuator of said linear motor is rigidly connected with the tool at
its upper end. Therefore the tool moving in the working position on an uneven
surface will jump up against the force of the linear motor.
Sicking teaches in US Patent No. 3,384,965 an actuating device, which
is driven by a "pushing down" type of solenoid. That solenoid drives down a first
plunger upon a second plunger supported by the force of a scribing pressure adjusting
spring. The main function of this spring is to hold both plungers in contact to
move back the first plunger into the solenoid, when the tool supporting means
are moved up in the resting position driven by the force of a lifting coil.
SUMMARY OF THE INVENTION
Accordingly, it is a principal object of the invention to provide
a novel working head assembly for a draughting or a ruling tool and the like which
is allowed to follow any unevennes of the strip material, wereby the strip material
is at least in the resting position free from the means supporting or guiding a
It is another object of the invention to provide a compact covered
working head assembly with a minimum number of elements which are supported by
the carriage in a vibration-free manner.
It is a further object of the invention to provide minimal adjustment
requirements for adjust the tool.
The aforementioned main objects are accomplished by the present invention,
with a working head assembly which whole actuating device is mounted above the
support, which first spring is located under tension between an upper surface
of said housing and a cap, which is connected with the core, which cap has a recess
to cover the upper end of said tool and which second spring is located in the
recess of the cap.
Using a working head assembly according to the invention the strip
material at least in the resting position is free from means supporting or guiding
a tool. Furthermore penetrating the core and being covered at its upper end by
the cap the tool is only at its downside end outside of guiding and supporting
means. Therefore and in due to the coaxially arrangement of pen, housing, solenoid
coil and springs the working head assembly can be built in a compact manner comprising
a minimum number of elements. So such a compact working head assembly is mountable
above only the one support supported by the carriage.
According to a first embodiment of the present invention the tool
is a draughting tool, the axially bore of the core is a stepped through hole, the
second spring is located under tension between the cap and the upper end of the
draughting tool for keeping the draughting tool in the resting position against
a surface of the stepped through hole of the core, whereby in the resting position
the second spring is most relaxed, and the second spring is compressed in the working
position for loosening the draughting tool from the surface of the stepped axially
bore and to allow the draughting tool to move along its own axis to follow any
unevenness of the surface of the strip material without losing contact with said
surface. Using a working head assembly according to this embodiment the strip material
all times is free from means supporting or guiding a tool. Here an adaption of
implement to surface irregularities is done by the spring strength loading the
housing mounted by the support and therefore the carriage.
According to a second embodiment of the present invention the tool
is a punch, the whole actuating device is mounted above the support, the first
spring is located under tension between an upper surface of said housing and a
cap, which is connected with the core, the cap has a recess to cover the upper
end of said punch, the core has a recess and the second spring rests in the recess
of said core for pressing the punch against said cap. In this embodiment an adaption
of implement to surface irregularities is done by the spring of the engaged solenoid
For a preferred embodiment of a working head assembly with a ruling
tool in the working position the lower end of the core is moved down until a face
of the core rests on the strip material, whereby the core can turn on its axis
to follow any unevenness of the surface of the strip material especially deformations
created by the ruling tool penetrating a sheet material.
The last object of the invention is solved by a cap which is screwed
upon the core, whereby the tool is adjustable by turning the cap. So the tool is
adjustable against the core resp. the surface of the strip material in such an
BRIEF DESCRIPTION OF THE FIGURES
A DETAILED DESCRIPTION OF THE INVENTION
- FIG. 1
- is a perspective view of an automatically controlled draughting plotter,
- FIG. 2
- is an elevated general view of the working head comprising a draughting and
a ruling tool for a plotter according to Figure 1,
- FIG. 3
- is a cross-section elevated view of Figure 2, according to section 3-3, of
the draughting tool assembly,
- FIG. 4
- is a cross-section of the ruling tool assembly in Figure 2, seen according
to section 4-4,
- FIG. 5
- is a perspective view of the carriage drive for the plotter in Figure 1,
- FIG. 6
- is a view of the draughting tool's position when in operation,
- FIG. 7
- is a view of the ruling tool's position when in operation,
- FIG. 8
- is a detail of the ruling tool assembly, seen from below and
- FIG. 9A and B
- are further details of the ruling tool assembly.
Referring now to the Figures a draughting machine 1 incorporating
features of the present invention is illustrated in Figure 1 as an example to
facilitate the understanding of this invention.
In particular, this invention refers to the drive system for the
working tools used in a draughting machine, and normally referred to as flat plotters,
which generates graphic information on a sector of strip material. The head assembly
includes a working instrument for drawing and/or ruling 4 which reacts to the
commands sent from a controller 5 to generate graphic information on the strip
material like drawing paper 6. The controller 5 is the unit which transforms the
draughting program into command signals for the motors which move the working head,
and for the devices which move the working tools.
This draughting machine has a working area and is automatically operated
from said controller 5; the instruments for drawing and/or ruling includes one
or more marker instruments or tools which are carried on said carriage 2 which
makes up the socalled working head 3. This carriage is the unit which permits
the correct positioning of the marking tools over the strip material 6 secured
on the stationary working surface 7 of the draughting machine 1.
FIG. 5 shows diagrammatically the flat plotter transmission system
with servo-motors 55 for the movement of the X-axes and 51 for the Y-axes and the
associated gear systems 54 and 50 which transmit the movement through pulleys 53
and 49 as well as the belts 52 and 48 to the X- and Y-axis carriages.
The working head assembly 3 is fitted on the Y-carriage 4 which moves
alternately along the direction marked YY; this unit is fitted on X-carriage 2
which moves alternately along the XX direction indicated in Figure 1. This allows
the working head to shift to any position on the table with the combined movement
of the X- and Y-carriages. The machine has been fitted with a discrete advance
system for the strip material, so that it can generate traces which are longer
than the table as such.
FIG. 2 shows an elevated view of the working head for the flat plotter.
This specific working head comprises one or more working tools, namely the drawing
tool 17 and the ruling tool 10, which are secured on a support 16 which, in turn,
is fixed onto the Y-carriage 14.
The tools 10 and 17 are parts of a single unit with a support 16
which, in turn, is part of the Y-carriage 14 - in Figure 1 indicated by Numeral
4 - so that when the carriage moves over the working surface, the tools move with
it. The support has slots 15 so that it can be adjusted with respect to the working
surface towards or away; this adjustment is done on the machine so that, from the
highest point of the working surface 7 to the lower face 8 of the tool support,
the minimum clearance can be changed to allow the strip material on which the
machine is to operate to pass through. The support 16 has two reference surfaces
13 which are complemented by others on the Y-carriage 14 so that when the support
is adjusted, it can move only along direction Z, at right angles to the working
surface; this is because the axis of the working tools is at right angles to the
base 8 of the support 16, which, in turn, is at right angles to the seating face
28 (see Fig. 3) of the support on the Y-carriage 14. The support 16 has a base
with rounded zones 9 which make it easier for the working head to enter over the
FIG. 3 shows an elevation view of the drawing tool 17 seen through
cross-section 3-3 of Figure 2. Here, the elements can be seen which make up said
drawing tool. The tool consists of an electromagnet housing 22 secured at the bottom
to the support 16; there are two openings 30 and 24 through said housing in which
friction bushings 31 and 23 are arranged through which the electromagnet core 21
can slide, constituting the main body of the draughting tool having a stepped
through hole 60. There is a coil 19 inside the solenoid housing 22 which is designed
to move the magnetic core 21 of the solenoid downwards against the force of a
spring 27 until a coaxially arranged plastic stroke limiter 25 comes up against
the housing 22 of the solenoid, as shown in Figure 6. Thus the draughting tool
is raised when the coil 19 is not charged. All of the above described components
are arranged coaxially to the core 21.
The presence of the plastic limiter 25 has the advantage of preventing
the sharp knock against the housing 22 so that the unit operates more silently.
When the core 21 of the solenoid moves to its bottom position it takes a ball-point
20 - by through hole 60 coaxially arranged - with it, because a spring 26 keeps
it compressed against the surface 10 of the stepped through hole 60 of the solenoid
Fig. 6 shows a side view of the draughting tool 20 in its working
position, i.e. in operation. It shows how the limiter 25 is in contact with the
housing of the electromagnet 22, and the ball-point 20 can move along its own axis
without losing contact with the surface of the strip material, adapting to any
possible unevenness in it, thanks to the effect of the spring 26 acting against
the ball-point as seen in Fig. 3 also.
In some cases, the ball-point may have an additional ink container
11 as shown in Figure 2; this tank is under air pressure since, once the ink has
been added, it is pressurized by means of the one-way valve 12.
The ball-point 20 rises when the coil 19 (Figure 3) ceases to operate;
the compressed spring 27 pushes the limiter 25 then upwards, taking the core, and
therefore the ball-point, with it, until a coaxial plastic stroke limiter 29 on
the core comes into contact with the housing of the electromagnet 22.
This type of drive has obvious advantages; on the one hand, there
is the fact that the system is highly compact, since all the elements are coaxial
with the line of the working instrument itself. Similarly, this means that, when
drive stresses are applied, symmetry is exact. A further significant advantage
is in the economics of the design: it is cheaper than the traditional indirect
drive systems, and this benefit is clearly to do with the small number of components
Furthermore, there is the additional advantage that the system requires
virtually no adjustments in its operation, the only thing required being the overhead
positioning of the carriage (the working head); this is done only when the carriage
must be replaced, and that is an infrequent occurrence.
FIG. 4 shows an elevated view of the ruling tool 34, seen along section
4-4 of Figure 2. In Figure 4, the elements making up this tool can be seen. The
tool consists of an electromagnet housing 36 secured at the bottom to support 16;
as in the previous described case, this housing has two openings 32 and 39 which
house friction bushings 33 and 38 each, inside which the electromagnet core 37
which has a stepped through hole 61 making up the main body of the ruling tool
34 can slide. Inside said housing 36, there is also a coil 35 which is designed
to move the electromagnet core 37 downwards until the face 46 of said electromagnet
core 37 rests on the strip material 6 which is to be ruled. This means that, when
the coil is activated, the ruling tool or punch 34 which rules the line is introduced
into the strip material by the same amount as said punch 34 emerges from the face
46 of the electromagnet core 37. The penetration of the punch into the strip material
can be adjusted by turning a threaded cap 42 which is in permanent contact with
the punch under the influence of a spring 41 which rests in a recess 63 of the
electromagnet core 37 and presses the punch against the said cup 42. All components
described above are arranged coaxially to the core 37.
Once this adjustment is made as required for the protrusion of the
punch from the electromagnet core 37, this position is fixed by tightening a nut
40 against said cap 42. The ruling tool is raised when the coil 35 is not charged,
because of the effect of the spring 44 which presses the limiter 43 upwards, taking
the whole tool with it. The upward movement is limited by the plastic stroke limiter
45 when it comes into contact with the electromagnetic housing 36.
The limiter 43 is adjusted so that surface 46 always comes into contact
against the strip material before said limiter 43 touches the electromegnet housing
36. Discharges 57 can be seen on the bottom surface 46 of the ruling tool for the
removal of any possible shavings, at the same time as permitting correct and even
support on the strip material, so ensuring that deformations which may be caused
to said material in the area of the marking line do not remove the point of the
punch from the material.
The advantages listed in the explanation of the embodiment according
to Figure 3, referring to the drawing tool, are also existent for the ruling tool,
and for the same reasons - compactness, low cost, symmetry and uniformity in the
application of forces, the low number of parts, and the minimal adjustments.
FIG. 7 shows the ruling tool in its operating position, with the
detail of how the surface 46 referred to above is supported on the strip material
56 (in Figure 1 strip material 6) while the part of the punch 34 protruding from
the surface 46, is inside the strip material which is to be ruled.
FIG. 8 in connection with Figures 9A and 9B show the shape of said
discharges 57 on the surface 46 of the ruling tool core. As was explained in connection
with Figure 4 these discharges make it possible to remove any shavings at the same
time as guiding the ruling tool with respect to the marking line, so that the
axis of each of the discharges is aligned with said marking line.
As shown especially in FIG. 9B during the ruling operation the ruling
tool generates shavings or chips 81 and the discharges 57 allow these shavings
or chips to be removed from the operating area. Without such discharges the shavings
cannot be removed and rest between the ruling tool 34 and the surface of sheet
material until cavity 85 between ruling tool 34 and core 37 is filled up. Then
new shavings push up the core 37, this produces a clearance between the ruling
tool 34 and the surface of sheet material, this behaviour changes the depth of
Also, during the ruling operation when the tool 34 penetrates into
the sheet material, the tool creates deformations 82 in the area of the marking
line. These deformations increase the thickness of the material and change the
distance between tool and material surface, but the core 37 can turn on its axis
when the deformations contact the walls of discharges 57 and this allows an alignement
of discharges and marking line. In this way, the ruling tool rests correctly onto
the sheet material, like drawing paper 6.