Automatic paper bail actuator

Abstract: Automatic paper bail actuator for a printer having a rotating platen (1) or equivalent means for feeding a printing support consisting in an helicoidal spring (16) wound on the platen shaft and having two end arms (13,14), a first arm (13) being elongated to interfere with the bail and a first reference stop (15), the spring coil (16) being clamped on the shaft (2) by interference with the bail and opening the bail when the shaft (2) rotates in the direction opposite to the one providing normal forward feeding of a printing support, closing the bail when the shaft (2) rotates in the direction providing normal forward feeding until the first arm interferes with the first reference stop (15) and releases the spring coils; the second arm (14) interfering with a second reference stop (17) for a rotation of the shaft (2) in the direction opposite to the normal one and releasing the spring coils for a predetermined angular position of the spring and the first arm, hence for a predetermined open position of the bail.

Description: The present invention relates to an automatic paper bail actuator for printers or electronic typewriters. It is know that in modern computer printers and electronic typewriters, single paper sheets are fed by a rotating platen which cooperates with pressure rollers to convey the paper sheet to a zone where printing devices (generally a printing head reciprocating along guiding bars) perform the printing of a character row. To assure a good printing quality it is required that the paper sheet be kept adherent to the platen in the printing zone. To this purpose pressure rollers are provided located along a generatrix of the rotating platen, downstream the printing zone. These rollers press the paper against the platen. The rollers are idle mounted on a rod, parallel to the platen axis and provided with two ending arms, perpendicular to the rod and hinged to the printer side plates, so that the rod and the rollers mounted thereon can be moved far from the platen and again brought in contact with the platen. In other words this structure, known as "bail", can be opened and closed. The rod is normally pushed against the platen by resilient means. For the correct insertion of a sheet in the printer, the bail must be opened so that a sheet may be wrapped around the platen up to the line of contact between platen and paper bail rollers. Then the bail must be closed so that the pressure rollers keep the sheet in contact with the platen. In the past, bails were manually operated. In the modern printers automatic actuators are provided, consisting in control electromagnets or mechanical devices actuated by motor members already present in the printer, such as the carriage motor or the paper feeding motor which rotates the platen. An example of such devices is described in the EP-AS-0216394. All these devices are very complex and expensive. The present invention overcomes these disadvantages and provides an automatic paper bail actuator which is reliable, extremely simple and unexpensive. The automatic paper bail of the invention uses the platen movement as a motion source. The automatic paper bail of the invention essentially consists in a coil spring wrapped around the platen shaft and having two ending arms. When the platen shaft rotates, the spring follows the shaft rotation until the upstream arm (upstream with reference to the shaft direction of rotation) interferes with a stopping member. Owing to such interference the spring coils tend to increase their diameter and release their gripping action on the shaft, which is free to rotate. As long as the coil spring is gripping the shaft the downstream arm may exert a driving torque on other elements and namely the bail, thus opening it. For a rotation of the shaft in the reverse direction, an opposite action occurs and the bail may be closed. According to a further aspect of the invention a suitable hysteresis of the bail movement relative to the platen shaft movement is obtained by means of a second coil spring wrapped around a fixed post, or by means of a cam. The features and the advantages of the invention will become more readily apparent from the following description of a preferred form of embodiment and the enclosed drawins where: Figure 1 is a perspective view of a portion of a printer provided with a preferred embodiment of automatic paper bail actuator according to the present invention. Figures from 2 to 5 shows in sketched side view and in sequence the several operative phases of a paper bail provided with the automatic actuator of fig. 1. Figure 6 shows in sketch side view a paper bail provided with the automatic actuator of fig. 1 as a device in support of the "zero tear off" functionality. Figure 7 shows in perspective view a portion of a printer provided with another embodiment of automatic paper bail actuator in accordance with the present invention. Figure 8 shows in sketched side view a further embodiment of automatic paper bail actuator in accordance with the present invention. Figure 1 shows in perspective view a portion of a printer provided with the automatic paper bail actuator of the invention. A rotating platen 1 is keyed on a shaft 2, pivoting on two side plates. Only one of such side plates, referenced by numeral 3 is shown in fig. 1. A motor 4 drives shaft 2, directly or through suitable gearing, and controls rotation of the platen. The bail consists in a rod 5 parallel to the platen axis and having one end 6 fixed to a free end of an arm 7. Arm 7 is hinged at the other end on a pivot 8, fixed to side plate 3. The other end of rod 5, not shown in fig. 1, is fixed to a free end of another arm similar to arm 7 and hinged o a pivot fixed to the other side plate. Paper pinching rollers, one of which is shown and referenced by numeral 9 are idly mounted on rod 5. A pull spring 10 (or other equivalent means) having an end fixed to arm 7 and the other end hooked to a pin 11, on side 3, urges the rod 5 towards the platen, so that the pinching rollers are in contact with the platen. The normal rotational direction of the platen, for feeding a printing support, is the one indicated by arrow 12. With reference to the view of fig. 1 this rotation is clockwise. According to the invention a coil spring 16 is wrapped around shaft 2. The spring coils have an inner diameter equal or slighty lesser than the shaft diameter, so as to grip the shaft and follow it in rotation, owing to friction. The spring 16 is ended with two arms 13,14 which approximately extend radially from shaft 2. Arm 13, extends from the spring in the normal or direct rotational direction of the platen and has a length sufficing for interferenece with rod 5, in the course of its rotation around shaft 2. Arm 14 extends from the spring 16 in the revers rotational direction of the platen. A first pin 15, fixed to side plate 3, or other equivalent element, provides a stop and rest point for arm 13 and prevents rotation of coils 16 and arm 13 in the direct direction beyond the predetermined point established by pin 15. A second pin 17, fixed on side plate 3, at a suitable position, provides a stop and rest point for arm 14 and prevents rotation of coil 16 and arm 14 in the reverse direction, beyond the predetermined limit established by pin 17. When shaft 2 rotates in the direct direction, the spring 16 follows the shaft movement until arm 13 interferes with pin 15. At this point the resisting torque exerted by arm 13 on spring 16 tends to widen the coils and the spring stops its rotation and slides on the shaft without preventing its rotation. When shaft 2 rotates in the reverse direction, spring 16 follows the shaft movement until arm 13 interferes with rod 5. At this point the resisting torque exerted by arm 13 on spring 16 tends to grip the spring coils. The spring continue to turn with shaft 2 and by so doing, it drives rod 5 away from the platen and opens the bail. The opening action continues until arm 14 interferes with pin 17. At this point resisting torque exerted by arm 14 on spring 16 tends to widen the spring coils and spring 16 stops from rotating and slides on shaft 2 without preventing its reverse rotation. Owing to the combined action of arms 14 and 13 the spring rests in a stable position in which the bail is kept open. Bail remains open even if reverse rotation of shaft 2 is stopped. If shaft 2 is rotated in the forward direction, the action of arm 14 on the spring is ended, not the action of arm 13. Therefore the spring 16 turns steady with the shaft 2 and the bail is allowed to go back in its closed position. It is therefore clear that by rotating shaft 2 and the platen in the reverse and forward direction, the bail may be open and closed in automatic way and the operation may be controlled by a suitable energization control routine for motor 4. Figures from 2 to 5 show in sketch side view the operative sequence for loading a sheet in the printer and the automatic actuation of the bail. In figure 2 the platen 1 is ready to receive a paper sheet 18, which is inserted, manually or by means of automatic feeding devices, not shown, between a feeding guide 19 and platen 1, until the leading edge of the sheet rests on pressure rollers 20, always in contact with the platen 1. By rotating the platen in the forward direction, the sheet 18 is pinched between rollers 20 and platen 1 and driven up to the printing line defined by the location of printing members 21 (generally the platen generatrix defined by a vertical plane tangent to the platen.). By continuing to forward rotate the platen (Fig. 3) the paper sheet rises vertically and rigidly up to the height of the bail rollers 9, which is in closed position. The paper forward feeding is continued until the leading edge 22 of the paper sheet is substantially at the same distance from the printing elements which has the axis of the rollers from the printing elements. Since the bail is closed and the rollers 9 are in contact with the platen, the rollers are interposed between platen and paper sheet. At this point (Fig. 4) the platen is rotated in the reverse direction of a predetermined angle. Owing to such rotation the paper sheet is drawn back and the leading edge 22 is lowered. At the same time, thanks to the automatic bail actuator, the bail is opened and takes the position shown in fig. 4, before the vertical plane in which the paper sheet leading edge is located. In the course of the bail opening, a certain interference may occur between the leading edge of the sheet and the rollers 9. Due to such interference the leading edge is temporarily bent far from the platen. The interference ends as soon as the sheet is drawn back of a predetermined amount. At this point (Fig. 5) the platen is rotated in the forward direction of the same angle of reverse rotation or even of a greater angle. Due to such rotation the paper sheet is feed forward and raises vertically again. At the same time the bail is closed again. The two combined movements cause a new interference of the leading edge with the rollers. However in this case the rollers acts by bending the paper and pushing the leading edge against the platen. When the bail is completely closed, the sheet is correctly interposed between the platen and the pressure rollers. It is clear that the automatic paper bail actuator of the invention is usefull not only for the automatic loading of single meets in the printer, but even for obtaining the so called "zero tear off" functionality. This functionality is needed when continuous forms are used, instead of single meets, and consists, as shown in Fig. 6 in advancing a continuous form portion, where printing has been performed, beyond a cutting ruler 23. Thereafter the cutting ruler 23 may be actuated thus severing the printed module portion 24 from the module portion 25 located upstream ruler 23. To avoid paper waist, it is of advantage to perform printing operation even on the printing module portion which is just upstream of the ruler 23. This is obtained by drawing back the module, by reverse rotation of the platen, until the upper edge of the module is aligned with the printing line. By this operation the bail is automaticallly open and is closed again when the module is forward fed again (between the printing operation of a line and the next one). When the bail is closed, the module is again correctly interposed between platen and pressure rollers 9. Without developing complex considerations of geometrical nature, it may be noted that the automatic paper bail of the invention is effective in a very broad range of platen diameters, roller 9 diameters, distant of the rollers from the printing line and lever arm length of rod 5. It is further possible to broaden the range by simple arrangements which introduce some hysteresis in the paper bail movement as to platen rotation. Figure 7 shows in perspective view an embodiment for the automatic actuator of Fig. 1 which includes a preferred form of hysteresis element. In Fig. 7, in addition to the several elements already consider with reference to Fig. 1., which in Fig. 7 are identified by the same reference numerals, there is provided a sleeve 26, steady with side plate 3 and acting as a bush for shaft 2. A second coil spring 27 is wound on sleeve 26. Coil spring 27 has two suitably shaped ending arms 28,29. Arm 28 is bent so as to interfere with arm 13 for a predetermined angular position of arm 28 on sleeve 26 and of arm 13 on shaft 2 respectively. Arm 28 is further capable of interference with bail rod 5. Arm 29 is bent so as to interfere with arm 14 for a predetermined angular position of the two arms on sleeve 26 and shaft 2 respectively. The angle formed by two arms 28 and 29, relative to the axis of spring 27 differs from the one formed by the two arms 13,14 and is such that when the two arms 13,28 interfere, the arm 29 is leading as to arm 14 in the direction of a forward rotation of spring 16. The position of pin 15, which defines the maximum forward rotation of spring 16 is established so that arm 13 exerts its opening action on the bail only after a suitable reverse rotation of the platen. The operation of the described actuator is very simple. A forward rotation of the platen causes rotation of spring 16 until arm 13 interferes with pin 15, preventing any further rotation of spring 16. Rotation of spring 16, hence of arm 14, causes interference of arm 14 with arm 29 and imposes a rotation of spring 27 and arm 28. Arm 28 takes a rest position in which arm 28 is in contact with rod 5 and the bail is closed. A first phase of reverse platen rotation brings arm 13 to interfere with rod 5 and arm 28 without opening the bail. A second phase of reverse platen rotation causes the bail opening and at the same time (due to interference of arm 13 with arm 28) a reverse rotation of spring 27 on sleeve 26. This rotation is allowed because the coils of spring 27 tend to be widened. The maximum reverse rotation of spring 16 and consequently of spring 27 is determined by the position of pin 17. Once the bail is open, the closing occurs in two phases. In a first phase of forward platen rotation, spring 16 rotates with the platen and arm 13 moves far from rod 5. However the bail does not close because rod 5, by pushing on arm 28 tends to grip the coils of spring 27 on sleeve 26. Thus spring 27 is locked in position and arm 28 prevents the bail closing. In a second phase of forward platen rotation, the arm 14 of spring 16 interfereres with arm 29 of spring 27 and tends to widen the coils of spring 27. Thus spring 27 yields and rotates it too in the forward direction. The bail, which is no more hindered by arm 28, closes and springs 27,16 take the position of maximum forward rotation allowed by pin 15. Therefore the opening and the closing of the bail occurs with a delay as to the platen rotation. By this delay the interference of the rollers with the paper sheet previously fed at the same height of the rollers, or more, is prevented in the opening phase. In the closing phase the delay assures that the bail is closed when the paper sheet has been already fed forward and is interposed between platen and rollers. It is clear that figure 1 and 7 show preferred form of embodiments and that several changes can be made. For instance, the arms 15 and 28 of the springs may act on arm 7 of the bail. The spring 27 may be wrapped around a sleeve or a post fixed to side plate 3 and not necessarily coaxial to shaft 2. In particular by suitable shaping of arms. 28,29 the spring 27 may be wrapped around pin 8, which acts as pivot for bail arm 7. The hysteresis between platen rotation and bail closing may be further obtained with means other than the described ones. Figure 1 shows, inserted on bail rod 5 a spacer 30, free to rotate on rod 5. Spacer 30 has the shape of a cylindrical segment, having a diameter greater than the one of the pressure rollers 9 and a chord at a distance from the segment axis, lesser than the radius of the rollers 9. The spacer is juxtaposed to an end portion of the platen and its flat surface is normally oriented towards the platen surface. In this state, a platen rotation in either the forward or reverse direction does not cause any change in the position of the spacer. However if the rod 5 is moved away from the platen (because actuated by spring 16) the spacer rotates by gravity and its flat surface orientates upward. In this position the spacer rests against the platen and prevents the bail closing. If the platen is rotated, the friction between spacer and platen causes a rotation of the spacer until the flat surface orientates again towards the platen and allows the bail to close. The bail closes with a delay as to rotation of the platen. It is clear that the shape of the spacer may be changed and may take the form of a cylindrical sector or lunette and more generally of revolving cam, normally inactive and capable of taking an active position when rod 5 is moved apart from the platen. Figure 8 shows a further embodiment of automatic paper bail actuator with hysteresis: an idle cam 31 is inserted on shaft 2 and has two notches 32,33 for insertion of the arms 13,14 respectively of spring 16, in mutually exclusive way. Cam 31 pushes with its active profile, against bail arm 7. When shaft 2 rotates in the reverse direction, the ending arm 13 inserts in notch 32 and causes rotation of the cam 31, which acts on arm 7 and open the bail with some delay. When arms 14 interferes with pin 17, spring 16 yields and the cam 31 is in a stable position which prevents the bail from closing. During a first phase of forward rotation of shaft 2, spring 16 rotates with the shaft, without causing rotation of the cam 31 until arm 14 engages with notch 33. Then spring 16 starts to rotate the cam which moves from the stable position to an instable one, thus allowing the bail to close. In the preceding description reference has been made, for sake of clearness, to a printer having a rotating platen, where the members which act on the printing media to move it, provide a surface against which the printing operation is performed. It is however clear that the two functions can be performed by two distinct elements, for instance a steady platen and one or more feeding rollers located downstream the platen (having regard to the normal advancement direction of the printing support) and cooperating with pressure rollers mounted on a bail which must be opened and closed for an easier insertion of the printing support. It is clear that the automatic actuator of the invention may be used in this case too. In addition the automatic actuator of the invention may be advantageously used not only for the loading and positioning of single sheets or for the "zero tear off" functionality, but even for the handling of fanfolded continuous forms. It is known that fanfolded continuous forms, in case of multiple copy forms or supports for labels are relatively rigid. In this case when the folded zone approaches to the pressure rollers of the bail the form has difficulty in inserting between the platen and the rollers. By temporarily releasing the bail the insertion is made easier and further enables for the recovery of relative offsetting among the several copies of the form.

Claims: Automatic paper bail actuator for a printer having a frame and at least one paper feeding roller coupled to a driving shaft, said feeding roller cooperating with pressure rollers mounted on a bail rod for guiding the movement of a printing support downstream a printing line comprising: a first helicoidal spring having coils wound on said shaft and having an inner diameter not exceeding the diameter of said shaft so that a rotation of said shaft normally causes a corresponding rotation of said coil, said coil having a first and a second ending arm, a first stop member mounted on said frame, interfering with said first arm and causing the release of said spring coils when said shaft rotates in a first direction such as to cause a forward feeding of said printing support, a second stop member mounted on said frame, interfering with said second arm and causing the release of said spring coils when said shaft rotate in the reverve direction opposite to said first direction, said first and second member being located on said frame so as to allow a predetermined rotation of said coil in both said directions, owing to rotation of said shaft, said first arm acting on said bail to cause the opening of said bail when said shaft rotates in said reverse direction and acting on said bail to enable its closing when said shaft rotates in said first direction. Automatic paper bail actuator as claimed in claim 1 comprising hysteresis means, said hysteresis means comprising a second helicoidal spring having coils wound on a cylindrical member steady with said frame and having axis parallel to said shaft, the coils of said second spring having an inner diameter not exceeding the diameter of said cylindrical member so as to be normally steady with said cylindrical member, said second spring having a first and a second ending arm, said second spring first arm interfering with said first spring first arm and causing the release of said second spring coils when said first spring rotates in said reverse direction, said second spring second arm interfering with said first spring second arm when said first spring rotates in said first direction, said second spring first arm further interfering with said bail and preventing its closing until said first coil second arm interferes with said second spring second arm causing the release of said second spring coils and enabling rotation of said second spring on said cylindrical member. Automatic bail actuator as claimed in claim 1 comprising hysteresis means consisting in a cam idly mounted on said bail rod, said cam having an active profile and an inactive profile, said cam facing said paper feeding roller, and being sized so as to enable the closing of said bail and the contact of said bail pressure rollers with said paper feeding roller, when said inactive profile is interposed between said bail rod and said paper feeding roller, said bail being kept open by the interferene of said cam with said paper feeding roller, when said active profile is interposed between said bail rod and said paper feeding roller, a rotation of said paper feeding roller causing a rotation of said cam, as long as said cam interferes with said paper feeding roller. Automatic bail actuator as claimed in claim 1, comprising hysteresis means consisting in a cam idly mounted on said shaft and having a first and second interference surface respectively with said first and second arm, the interferene of said first arm with said first surface, owing to rotation of said shaf in said reverse direction causing rotation of said cam in said reverse direction, the interference of said second arm with said second surface, owing to rotation of said shaf in said first direction, causing rotation of said cam in said first direction, said first arm acting on said bail through intermediation of said cam.

Inventors: FARE CARLO, FARE, CARLO
Applicants: BULL HN INFORMATION SYST, BULL HN INFORMATION SYSTEMS ITALIA S.P.A.
Application year: 1990
Main classification: B41J13
IPC codes: B41J13