Cutting device for a plotter

Abstract: The invention refers to a cutting device for a plotter for automatic cutting of a paper band on which markings are formed by marking means, the plotter comprising a marker carriage for receiving the marking means and for moving the marking means in a direction transverse to the movement of the paper band, with the cutting device comprising a cutting element and in which the cutting element -23- is arranged on a cutter carriage -6-, means -13, 14- being provided for the selective engagement or disengagement of the cutter carriage -6- to or from the marker carriage -1-. During a cutting operation the cutter carriage -6- is engaged to the marker carriage -1- and moved across the paper band due to the movement of the marker carriage. The marking means comprise a pen which can be disengaged from the marker carriage -1- during a cutting operation. The driving means for the engagement and disengagement of the cutter carriage -6- are the same as those for raising or lowering the drafting pens.

Description: This invention refers to a cutting device for a plotter for carrying out the cutting of the paper band at the end of a plotting cycle. The application of this invention is foreseen for plotters which have a continuous paper band consisting of a roll of paper incorporated on the plotter, so that at the end of each plotting cycle, a paper band length has to be cut which comprises the graphic representation drawn by the plotter. According to the present state of the art, a number of devices have been disclosed for cutting the paper band in plotters and printers. To obtain high quality cuts of the paper band, sliding carriages are usually provided to cut the paper. Such cutter carriages are independent of the plotting carriage or printing device, having independent motors and transmission systems to produce the displacement of the cutting carriage along straight guides in order to carry out the cutting of the paper band usually by means of a rotating cutter. Thus, as an example, German Patent DE3119998 discloses a device for the cutting of a continuous paper band comprising a carriage which may slide along specific guides and which has a motor to operate a toothed belt which is connected to a wheel incorporated on the shaft carrying the rotating cutter. This prior disclosure shows as well a couple of angle shaped plates for the guidance of the continuous paper band in the vicinity of the cutter carriage. In other cases, straight cutters are provided to act on the whole width of the continuous paper band, practically with a single stroke. An example of this technique is disclosed in USA Patent 4 617 577, which shows a device for the cutting of paper sheets by means of a rotating cutter which has a swiveling movement from a rest position up to a cutting position, coming back to the starting position after each cutting cycle. In this case, there is no movable carriage as the cutting is carried out in only one stroke on the whole width of the paper sheet. This system does not permit to obtain high quality cuts on the paper band as the cutting action is simply carried out by compression between the swiveling cutter and the fixed cutter. Besides, the system is not appropriate for great paper band widths. In EP-A-0172319 there is disclosed a cutting device for paper and foils webs, particularly for printers, plotters, copiers and similar machines, where a cutting wheel rotatably supported in a cutting carrier is movable along a cutting rail over which the web is moved, the effectivity of which cutting device is increased with the well-known operating principle being maintained, in that the cutting wheel is kept under the force of a spring acting axially against the cutting rail and supported, from a neutral starting position plane parallel to the cutting rail pivoting by an angle corresponding to the maximum admissible angle between cutting wheel and cutting rail, round the axis extending rectangularly to the cutting wheel axis and the cutting rail. In US-A-3951252 there is disclosed an electromechanical writing device comprising a writing head, a writing head carrier for carrying the writing head, a guide along which the carrier is movable during a writing operation, a writing platen over which a recording medium is moved during the writing operation, a shearing edge forming part of the writing platen, the shearing edge extending in a direction parallel to the direction of movement of the writing head, and a roller knife mounted for movement along the guide and cooperating with the shearing edge to permit the recording medium to be cut. It is the object of the invention to provide a cutting device for a plotter for automatic cutting of a paper band, in which the frictional force between the external periphery of the resilient ring and the border of the surface for guiding the paper band is effective independent of the wear of the material of the resilient ring. This problem is solved in a cutting device according to claim 1. According to a preferred embodiment of the present invention, an engageable cutter carriage has a rotating cutter which overlaps on a fixed cutter blade. The rotating cutter is incorporated by means of a floating assembly on the engageable cutter carriage and has means to produce the rotation of the cutter as a result of the straight displacement of the cutter carriage, without the need of specific transmission means or independent driving motors for the cutting device. According to the present invention, the cutter carriage stays in a rest or parking position on one end of the guideways for the pen carriage, which supports the pens used for plotting the graphic representation, while such pen carriage is being operated during a plotting cycle. At the end of the plotting cycle, when the graphic representation has been completed, the pen carriage will grab the cutter carriage from its parking position by means of a mechanical engagement system, drawing the cutter carriage along its guideways, such straight travel being transformed in a cutting action of the rotating cutter. After the cutting operation, when the pen carriage comes back to the position in which the engagement with the cutter carriage has taken place, the pen carriage disengages again the cutter carriage, which will stay again in the parking position. Then, the pen carriage may perform its normal duty in a new plotting cycle. The engagement and disengagement of the pen carriage relatively to the cutter carriage is carried out according to the present invention by means of a hook which forms part of a swiveling lever which is assembled with rotating capacity on a shaft of the pen carriage, so that the swiveling of the lever defines two positions for the same, one of which corresponds to the engagement of the cutter carriage and the other corresponds to the disengagement after parking the cutter carriage in the rest position. The operation of the swiveling lever which incorporated the engagement hook is carried out, according to the present invention, by means of a magnet which coil is excited in a direct or reversed sense, according to the engagement and disengagement of the cutter carriage. Both raising and lowering actions of the magnet will be used as well for raising and lowering the drafting pen. The invention is preferably used in plotters of the type known from Hewlett-Packard Journal, November 1981, wherein the drafting pen is moved forward and backwards in a first direction and the paper is moved in a second direction perpendicular to the first direction. The present invention will allow to obtain a number of important advantages over the previous art, among which: Suppression of independent motors and driving means for the cutter, with the subsequent gains in simplicity and reliability of the paper cutting device; Great simplicity, hence reliability and low cost of the cutting means, which allows at the same time to obtain high quality cuts on many different types of paper band without need of any mechanisms to secure the paper. Lower weight of the pen carriage, specially during its normal operation as drafting means, allowing faster acceleration and stoppage and all inherent advantages related with a lower inertia; The same carriage will perform both drafting and paper cutting functions; The same driving means will be used for operating the engagement/disengagement of the cutter carriage as well as the raising and lowering of the pens. The design of the cutting device is adapted to the structure of the plotter and not vice-versa. It will use the existing guideways and may be easily applied to upgrading existing plotters which donnot have any automatic cutting system. Very simple assembly/disassembly, for an easy maintenance. The invention will be explained in more detail in the following making reference to a preferred execution of the same. In the drawings: Figure 1 shows a side view of the pen carriage resting on its guides. Figure 2 is an upper view showing in higher detail the pen carriage of figure 1. Figure 3 is an exploded view of the elements comprising the cutter carriage showing its positioning relatively to the pen carriage. Figure 4 shows a section along IV-IV of figure 1 showing the pen carriage and the cutter carriage disengaged from each other. Figure 5 shows a view similar to figure 4 with the pen carriage and the cutter carriage in the first step of its mutual engagement. Figure 6 is a similar view to figures 4 and 5 showing the pen carriage and the cutter carriage mutually engaged. Figure 7 shows a section along VII-VII of figure 2 corresponding to the cutter carriage. According to the figures 1-3, the cutting device for plotters, for the automatic cutting of a paper band, according to this invention, may be applied to a plotter in which the marker carriage or pen carriage, which has been designated with reference numeral -1-, rests on an upper guiding rail -2- on which it may travel on rollers - 3- and -4-, resting as well as on a lower angled guide - 5. The carriage -1- may travel from one end to the other of its stroke sliding on the above mentioned guideways carrying out the drawing of the graphic representation according to the control instructions which govern the operation of the pen carriage. The graphic representation is conventionnaly drawn on a continuous paper band which has not been shown in the figures. The paper band progressively advances during the operation of the plotter, combining the straight displacement of pen carriage -1- on its straigth guides with the displacement of the paper sheet on a direction which is perpendicular to such guides. The cutting of the paper band has to take place after the graphic representation has been completed. According to this invention, the cutting of the paper band at the end of the plotting operation is carried out by means of a cutter carriage shown by means of reference number -6-, which will rest, when not in operation, in a parking position on one of the ends of the straight guide -5-, which in the case of the figures corresponds to the left end. The cutter carriage -6- will be engaged by the pen carriage -1- at the moment in which the cutting of the paper band has to be carried out. The cutter carriage -6- will be parked again in its rest position at the end of the cutting operation. The engagement between the pen carriage -1- and the cutter carriage -6- may be obtained by any convential method known in this technique. According to the present invention, such connection will be made in a mechanical way by means of swiveling lever -7-, figure 3, which has a central hub -8- which may rotate on shaft -9-incorporated to the pen carriage -1-. Lever -7- has in one end the arm -10- which will receive the operating stroke of a pusher to be explained later. Said lever has at the other end, opposed to such arm -10-, a hook constituted by a second arm -11- parallel to the straight displacement guide for pen carriage -1-, ending such arm in a head portion -12- which has a lower angled protrusion -13-which may engage a similar mating hook -14- which the cutter carriage -6- incorporates on its upper part. The head portion -12- is connected to antagonistic helical spring -20-. The position in which the engagement between the portions -13- and -14- may be effected corresponds to one of the two stable positions for lever -7- corresponding to the vertical displacement of a pusher -15- vertically guided on pen carriage -1-, preferably by means of a vertical axis which upper end has been shown by reference numeral -16- in figure 3. To activate pusher -15- a magnet -17- will be preferably provided in the present invention, which magnet will be assembled on pen carriage -1-, being able to activate the descent of pusher -15- against the action of spring -18-. The straight edge -19- of pusher - 15- acts on the lower portion of arm -10- of lever -7- in a way that the descent of pusher -15- will release lever -7-, allowing its rotation under the action of spring - 20-. When the driving action of pusher -15- is inverted, the spring -20- will return the hook's arm -11- to its rest position. The driving action of magnet -17- on pusher -15- will be used also for raising and lowering the drafting pen, associated to clamping means -36-. The pen will be removed from cutter carriage -6- during each cutting operation. When pen carriage -1- travels towards the end of the guideways in which the cutter carriage -6- is parked in its rest position having hook -13- in the position to engage the mating portion -14- of the cutter carriage after the activation of lever -7- as above explained, the cutter carriage will be drawn by the pen carriage along the guideways for the same, activating the cutting action of the rotating cutter on the paper band in a way that will be explained in the following. Cutter carriage -6- has a main body -21- with an upper engaging portion or hook -14-. At the same time it receives the swiveling shaft -22- on which the rotating cutter -23- is assembled. As shown in figures 6 and 7, the shaft -22- is assembled with rotating capacity on carrier block -24-, which has two end protrusions or pins -25- and -26- lodged inside holes of body -21- which holes have side openings, one of which has been shown with reference number -27-. Flat springs -28- and -29- are assembled on carrier block -24- acting against the inside surface of body -21- and exerting an antagonistic action against the upwards swiveling of shaft -22-. A rotating cutter -23- is assembled on shaft -22-by means of a supporting body or block -30- which has sliding and rotating capacity on shaft -22-. On the same supporting body -30- an elastic ring -31- is pressured fitted, which ring will contact the edge -32- of the guide for the paper band, under the pressure of springs -28- and -29-. Thus, the sliding of the cutter carriage on its guideways, originates, because of the friction between ring -31- and the surface -32-, the rotation of the supporting body -30- and therefore the rotation of the cutter -23- which overlaps stationary blade -33-, which is secured to the border of the surface -32- for guiding the paper band. An helical spring -34-assembled on shaft -22- effects a pushing action against the carrying body -30- on the shaft -22-, which has in its end a washer -35- against which the carrying body -30-abuts when the cutter carriage is out of the plotter, that is, in the case when the cutter carrying shaft has to be manually disassembled to change the cutter blade. It is obvious that the cutter carriage according to the present invention is very simple and it does not require any independent devices for driving the rotating cutter, for which reason the cutter carriage dispenses with the traditionnal independent driving motors for the cutter or toothed belts to operate the cutter as well as other devices usually bringing higher mechanical complication and higher costs in known paper cutters. On the other hand, and given the fact that the paper band in cut between a rotable cutter and a fixed blade cutter, the cut made on the paper band is of high quality in the whole width of the paper band.

Claims: Cutting device for a plotter for the automatic cutting of a paper band on which markings are formed by marking means, the plotter comprising a marker carriage for receiving the marking means and for moving the marking means in a direction transverse to the movement of the paper band, with the cutting device comprising a cutting element (23) which can be moved across the paper band, characterized in that: the cutting element (23) is arranged on a cutter carriage (6), and comprises a rotating blade (23) arranged on a shaft (22), wherein the cutter carriage (6) supports the rotatable cutter shaft (22) with swiveling capacity, which rotatable cutter is incorporated on a supporting block (30) freely sliding on said shaft, which supporting block (30) brings in its external periphery a resilient ring (31) which is able to contact the border of the surface (32) for guiding of the paper band, so that the friction originating between said ring (31) and the guiding surface (32) for the paper band provokes the rotation of the supporting block (30) when the cutter carriage (6) is drawn by the pen carriage along its guideways, and which cutter carriage (6) has a main body (21), resting with sliding capacity on one of the guideways for the pen carriage (1), said main body (21) receiving the swiveling shaft (22) for the rotating cutter (23), by means of carrier block (24) which receives the action of flat springs (28, 29) which limit the upwards swiveling travel of said carrier block (24), providing the elastic support of such block (24) against the main body (21) of the cutter carriage, means (13, 14) are provided for the selective engagement or disengagement of the cutter carriage (6) to or from the marker carriage (1), and during a cutting operation, the cutter carriage (6) is engaged to the marker carriage (1) and moved across the paper band due to the movement of the marker carriage. Cutting device for a plotter, according to claim 1, wherein the marking means comprise a pen which can be disengaged from the marker carriage (1) during a cutting operation, and wherein the driving means for the engagement/disengagement of cutter carriage (6) are the same as those for raising and lowering the drafting pens. Cutting device for a plotter, according to claim 1, characterized in that the connection between the pen carriage (1) and the cutter carriage (6) is mechanically established by the engagement of a hook (14) of the cutter carriage (6), with a mating hook (13) of the pen carriage (1), which has two predetermined stable positions, one of which corresponds to the engagement with the hook of the cutter carriage (6) and the other position corresponds to the disengagement between both carriages. Cutting device for a plotter according to claim 3, characterized in that the hook (13) in the pen carriage (1) is integral with a swiveling lever (7) assembled with rotating capacity on the same pen carriage and having an arm (10) which may be selectively operated by a pusher (15) of the pen carriage, such pushing action determining one of the two stable positions for the engagement hook (13) while the other stable position is determined by a spring (20). Cutting device for a plotter, according to claim 4, characterized in that the pusher (15) in the pen carrier (1) for the operation of the swiveling lever (7) is driven by a magnet (17) incorporated on the same pen carriage , also used for raising and lowering drafting pens. Cutting device for a plotter, according to claim 1, characterized in that the shaft (22) for the rotating cutter receives an helical spring (34) to push the supporting block (30) towards the front end of the shaft, in which end a washer (35) acts as abutment to prevent the disassembly of the supporting block (30) in the situation corresponding to the removal of the cutter assembly from the cutter carriage. Cutting device for a plotter, according to claim 4, characterized in that the carrier block (24) for cutter shaft (22) is articulated on the cutter main body (21) in holes which have side openings (27) and which receive opposed protrusions (25, 26) of said carrier block (24) which determine the rotation center and which are easily disengageable by hand pressure through said side openings, to remove the cutter shaft (22).

Inventors: AGRAFOJO VENTURA CAAMANO, AGRAFOJO, VENTURA CAAMANO
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1991
Main classification: B41J11
IPC codes: G01D15, B43L13, B41J11, B26D7