Patent Application
20190256232
The present invention concerns a method for actuating a belt drive mechanism of a strapping machine during a loss of a strapping band in its shooting and retrieval unit, where the strapping machine includes a shooting and retrieval unit with at least a first pair of rollers, between which the band can be driven through by at least one of the rollers in and against the shooting direction of the band, a detector for detecting a leading end of the band at an end of the shooting trajectory, and a back tensioning unit arranged behind the shooting and retrieval unit in regard to the shooting direction with a second pair of rollers, between which the band can be tensioned by at least one of the rollers against the shooting direction around an item being strapped in the strapping machine, as well as a strapping machine with a correspondingly controlled band drive mechanism.
A strapping machine is known, for example, from DE 196 02 579 A1. Besides the familiar parts that are present in such machines, such as machine frame, work bench, and band guide frame for leading the strapping band around the object being strapped as a loose loop, it has a band drive unit placed underneath the work bench. This comprises a combined shooting and retrieval unit for shooting the strapping band into the band guide frame and retrieving the strapping band from the band guide frame until the strapping band bears against the object being strapped. Moreover, a back-tensioning mechanism is often present for tightening the strapping band about the object, being dependent on the stack height.
The shooting and retrieval unit has at least one pair of rollers, between the gap of which the strapping band is led through by one of the rollers in the shooting and retrieval direction. The back-tensioning unit has another pair of rollers, between the gap of which the strapping band is likewise fed and can be clamped around the item being strapped in the machine by at least one of the rollers in the retrieval direction.
Finally, guide channel sections are provided to guide the strapping band through the band drive mechanism, which lead the strapping band brought up from a supply roll or a temporary storage device to the back-tensioning mechanism, between the latter and the shooting and retrieval unit, and from the latter in the direction of the band frame on the work bench. The guide channel sections are formed by cheeks which guide the strapping band on either of its flat sides, being configured as webs or side surfaces of larger prismatic bodies.
A typical problem in the operation of such a strapping machine sometimes occurs due to a faulty handling of the strapping band. Thus, for example, the leading end of the band cannot reach the welding head due to obstacles in the band guide frame and therefore the detector situated here, for example, in the form of an end switch, is not activated to detect the leading end of the band at the end of its shooting trajectory in the band guide frame. The control system of the strapping machine recognizes this and it then arranges for a retrieval of the strapping band, usually until it emerges backward from the pair of drive rollers of the band drive mechanism opposite the shooting direction.
This fault situation is normally monitored by a sensing mechanism, which detects the condition when the strapping band emerges from the shooting and retrieval unit opposite the shooting direction.
To remedy the fault in the strapping machines known thus far it was necessary to open the band drive mechanism and manually thread the strapping band into the shooting and retrieval unit, so that the shooting process can start over again. This leads to a substantial down time for the strapping machine, which is basically undesirable and in an extreme case can lead to a shutdown of the entire production line when the strapping machine is integrated as part of a continuous production process for print products, for example.
In EP 1 489 005 A2 a corresponding method is indicated for actuating a band drive mechanism that can eliminate the described fault situation without manual intervention in substantially less time. According to this, the back-tensioning mechanism can be reversed in its drive direction so that when a fault is detected—that is, a band loss in the shooting and retrieval unit—the strapping band is transported back almost automatically to the shooting and retrieval unit.
A drawback with this control method is the fact that the fault situation and the driving of the band must be detected by means of a suitable sensor, e.g., an incremental encoder on the pressing roller of the shooting and retrieval unit. This signal is then further processed in. the control program and incorporated into the control sequence. This requires additional expense for control technology and apparatus.
This drawback is even more glaring for the strapping machine of DE 603 18 160 T2, which is different in its design makeup of shooting, retrieval and back-tensioning unit. Here, the band length that was shot out and retrieved in the fault situation is detected and the band is pulled back with two different band speeds to the starting position before being threaded once again.
Accordingly, the problem to which the invention is directed is to provide a simplified yet reliable actuation method for the band drive mechanism of a strapping machine to eliminate the above described fault situation.
This problem is solved by the steps of the method indicated below:
Thanks to the method of the invention, it is possible to eliminate the separate detector in the area of the shooting and retrieval unit, since it is no longer necessary to actively detect the presence of the strapping band in the pair of rollers there. Instead, the timing control of the retrieval of the strapping band with a defined retrieval speed assures the reliable emergence of the strapping band from the pair of driving rollers. Since the back tensioning unit is opened and thus inactive during the retrieval of the strapping band with the aid of the shooting and retrieval unit, the strapping band also stops as soon as it has left the shooting and retrieval unit. This occurs regardless of whether the latter is still being driven. Thus, the strapping band is available with certainty for reintroducing into the shooting and retrieval unit with the aid of the back tensioning unit, which runs in its driving direction opposite the tensioning direction.
As is evident from the foregoing, the described fault situation is reliably corrected without manual intervention in the band drive mechanism by means of a simplified design for the drive engineering.
Features, details and benefits of the method of actuation of the invention and a corresponding band drive mechanism will emerge from the following description of an exemplary embodiment.
As is shown by
On the work bench 2 is arranged a vertically upright band guide frame 6, by means of which the strapping band 7 can be led as a loose loop around the object 4 on the work bench 2. For this, the strapping band 7 stored on a supply roll not otherwise depicted at the side of the machine frame 1 is shot by the band drive mechanism 5 shown only schematically in
Guide channel sections 10, 11, 12 are provided to form a defined transport path for the strapping band 7 through the band drive mechanism 5. A first guide channel section 10 leads the strapping band 7 from the supply roll or interim storage (neither being shown) to the back tensioning unit 9. A second guide channel section 11 connects the back tensioning unit 9 and the shooting and retrieval unit 8. A last guide channel section 12 goes from the shooting and retrieval unit 8 in the direction of the welding head 3 and to the point of entry of the strapping band 7 into the band guide frame 6.
The shooting and retrieval unit 8 has a drive roller pair 13 with a roller 14 driven by a motor (not shown) and a non-driven pressure roller 15.
For the shooting of the strapping band 7, the roller 14 of the drive roller pair 13 is set turning in the proper direction via the actuation of the drive motor by a control unit (not shown) and the strapping band 7 is taken around in the band guide frame 6 until its leading end 40 with detection by the end switch 16 comes to lie in the region of the welding head 3 and is fixed there. After this, the drive roller pair 13 is activated in the opposite direction and in this way the strapping band 7 is retrieved, as described above, until it is laid basically with no tension about the object 4 being strapped.
The back tensioning unit 9 has a tension roller pair 17 with interconnected rollers 18, 19, which then applies a large tractive force with the aid of its drive motor (not shown) for the back tensioning of the strapping band 7 about the object 4 being strapped.
The guide channel sections 10, 11 are formed by web-like cheeks 20, 21 jointly led away across the rollers 18, 19, which are fixed by projecting support feet 22, 23 in a manner to be explained below in the band drive mechanism 5. The rollers 18, 19 reach through recesses in the cheeks 20, 21, not otherwise shown in the drawing.
The guide channel section 12 is likewise formed by cheeks 24, 25 on either side, the one cheek 24 being formed by the side surface of a prismatic body 26 that is roughly T-shaped in top view. The other cheek 25 is formed to be curved in a curved section corresponding to the outer circumference of the roller 14 by a strapping angle for the strapping band 7 and then continues in a straight section. It is formed as a side surface on a corresponding elongated prismatic body 27.
In what follows, the above mentioned fault situation will be explained by means of a sample embodiment. The triggering event is the fact that the end switch 16 does not respond in the time defined for the shooting of the strapping band 7 in the machine control unit, of say 0.2 seconds. This is a signal that the strapping band 7 has not reached the welding head 3 with its leading end 40. Based on this fault recognition, the shooting and retrieval unit 8 is activated so that the strapping band 7 is transported back against the shooting direction E with a substantially lower retrieval speed than for the shooting process. The retrieval time is defined so that the strapping band 7 is pulled with certainty completely out of the shooting path and the shooting and retrieval unit 8. In this way, the strapping band 7 stops with its leading end 40 between the latter and the back tensioning unit 9.
The retrieval time can also be defined variably by a kind of self-learning system, in that the retrieval time is determined by deriving the required time from the previous shooting in direct proportionality to the reduced retrieval speed.
The control system of the strapping machine, not otherwise described, then activates the back tensioning unit 9 against its normal back tensioning direction, which is opposite the shooting direction E. For this, the roller 18 of the tension roller pair 17 is set moving counterclockwise, so that the strapping band 7 is again transported in the shooting direction E from the position shown in.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 075 629.9 | May 2011 | DE | national |
This patent application is a continuation of, claims priority to and the benefit of U.S. patent application Ser. No. 14/117,027, filed on Dec. 5, 2013 as a 371(c) Application of PCT/EP2012/058027, filed on May 2, 2012, which claims priority to and the benefit of German Patent Application No. 10 2011 075 629.9, filed on May 11, 2011, the entire contents of each of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14117027 | Dec 2013 | US |
| Child | 16400409 | US |
