Method for actuating the band driving device of a strapping machine and corresponding strapping machine

Abstract

A strapping machine configured for and method for actuating the belt drive mechanism of a strapping machine during a loss of band carrying out the following steps: (1) polling the detector as to a proper shooting of the strapping band in the shooting direction up until the end of the shooting trajectory, and (2) for an improper shooting of the strapping band, activating the shooting and retrieval unit to retrieve the strapping band with a definite retrieval speed for a defined retrieval time so that the strapping band emerges from the shooting and retrieval unit opposite the shooting direction, and (3) actuating the drive of the back-tensioning unit so that the back-tensioning unit transports the strapping band back into the shooting and retrieval unit in the shooting direction.

Claims

1. A method of operating a strapping machine, the method comprising: driving, via a first motor, a first drive roller of a shooting-and-retrieval unit to move a strapping band in a feed direction at a feed speed so a leading end of the strapping band enters a strapping band guide; and responsive to a detector failing to detect the leading end of the strapping band within a designated time period: determining a retrieval time based on a designated retrieval speed and an amount of time the first motor was actuated; and driving the first drive roller to move the strapping band in a retraction direction opposite the feed direction at the designated retrieval speed for the retrieval time so the leading end of the strapping band is withdrawn from the shooting-and-retrieval unit.

2. The method of claim 1, further comprising actuating the first motor to drive the first drive roller to move the strapping band in the feed direction and the retraction direction.

3. The method of claim 2, wherein the designated time period comprises a time period following actuation of the first motor to drive the first drive roller to move the strapping band in the feed direction.

4. The method of claim 1, wherein a controller determines the retrieval time.

5. The method of claim 1, wherein driving the first drive roller to move the strapping band in the feed direction comprises driving the first drive roller in a first rotational direction, and wherein driving the first drive roller to move the strapping band in the retraction direction comprises driving the first drive roller in a second rotational direction opposite the first rotational direction.

6. The method of claim 1, further comprising, responsive to the detector detecting the leading end of the strapping band within the designated time period: holding the leading end of the strapping band; driving the first drive roller to move the strapping band in the retraction direction to withdraw the strapping band from the strapping band guide to form an untensioned loop of the strapping band around an object; driving a second drive roller of the shooting-and-retrieval unit to tension the strapping band around the object; and attaching the leading end of the strapping band to a second portion of the strapping band to form a tensioned loop of the strapping band around the object.

7. The method of claim 6, further comprising holding the leading end of the strapping band and attaching the leading end of the strapping band to the second portion of the strapping band via a welding head.

8. The method of claim 1, further comprising, after the leading end of the strapping band is withdrawn from the shooting-and-retrieval unit, driving a second drive roller of the shooting-and-retrieval unit to move the strapping band in the feed direction so the leading end of the strapping band is received in the shooting-and-retrieval unit.

9. The method of claim 8, further comprising, after the leading end of the strapping band is received in the shooting-and-retrieval unit, driving the first drive roller to move the strapping band in the feed direction so the leading end of the strapping band enters the strapping band guide.

10. The method of claim 1, wherein the designated retrieval speed is less than the feed speed.

11. A strapping machine comprising: a frame; a strapping band guide supported by the frame; a shooting-and-retrieval unit supported by the frame and comprising a first drive roller and a first motor operably connected to the first drive roller and configured to drive the first drive roller; a back-tensioning unit supported by the frame and comprising a second drive roller and a second motor operably connected to the second drive roller and configured to drive the second drive roller; a detector configured to detect a leading end of a strapping band; and a controller configured to: actuate the first motor to drive the first drive roller to move the strapping band in a feed direction at a feed speed so a leading end of the strapping band enters the strapping band guide; and responsive to the detector failing to detect the leading end of the strapping band within a designated time period: determine a retrieval time based on a designated retrieval speed and an amount of time the first motor was actuated; and actuate the first motor to drive the first drive roller to move the strapping band in a retraction direction opposite the feed direction at the designated retrieval speed for the retrieval time so the leading end of the strapping band is withdrawn from the shooting-and-retrieval unit.

12. The strapping machine of claim 11, wherein the designated time period comprises a time period following actuation of the first motor to drive the first drive roller to move the strapping band in the feed direction.

13. The strapping machine of claim 11, wherein the first drive roller rotates in a first rotational direction to move the strapping band in the feed direction and a second opposite rotational direction to move the strapping band in the retraction direction.

14. The strapping machine of claim 11, further comprising a welding head supported by the frame, wherein the controller is further configured to, responsive to the detector detecting the leading end of the strapping band within the designated time period: control the welding head to hold the leading end of the strapping band; actuate the first motor to drive the first drive roller to move the strapping band in the retraction direction to withdraw the strapping band from the strapping band guide to form an untensioned loop of the strapping band around an object; actuate the second motor to drive the second drive roller to tension the strapping band around the object; and control the welding head to attach the leading end of the strapping band to another portion of the strapping band to form a tensioned loop of the strapping band around the object.

15. The strapping machine of claim 11, wherein the controller is further configured to, after the leading end of the strapping band is withdrawn from the shooting-and-retrieval unit, actuate the second motor to drive the second drive roller to move the strapping band in the feed direction so the leading end of the strapping band is received in the shooting-and-retrieval unit.

16. The strapping machine of claim 15, wherein the controller is further configured to, after the leading end of the strapping band is received in the shooting-and-retrieval unit, actuate the first motor to drive the first drive roller to move the strapping band in the feed direction so the leading end of the strapping band enters the strapping band guide.

17. The strapping machine of claim 11, wherein the designated retrieval speed is less than the feed speed.

18. The strapping machine of claim 17, wherein the designated retrieval speed is less than 50% of the feed speed.

19. The strapping machine of claim 18, wherein the designated retrieval speed is less than 20% of the feed speed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 a schematic side view of a strapping machine, and

(2) FIGS. 2 and 3 are schematic side views of the band drive mechanism of this strapping machine indifferent positions of the strapping band.

DETAILED DESCRIPTION OF AT LEAST ONE PREFERRED EMBODIMENT

(3) As is shown by FIG. 1, the strapping machine has a machine frame 1 mounted on rollers, on which is arranged a work bench 2. The work bench 2 has conveyor belts (not shown), by means of which the objects 4 being strapped, such as a stack of newspapers in FIG. 1, is transported into the strapping position on the work bench 2. For so-called cross strapping, a turntable can also be integrated in the work bench 2, as is found in EP 0 445 429 B1.

(4) 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 FIG. 1 underneath the work bench 2 through the welding head 3 of the strapping machine into the band guide frame 6 forming the shooting trajectory and led around it until it again arrives at the welding head 3. The detector arranged there at the end of the shooting trajectory in the form of an end switch 16 detects the proper arrival of the strapping band 7. The end of the band is fixed there and then the strapping band 7 is retrieved with the aid of the band drive mechanism 5, whereupon it emerges from the band guide frame 6 and lies around the object 4 as a still un -tensioned loop. Next, with the aid of the band drive mechanism 5, the band is tensioned and thus lies firmly about the object 4. The band layers overlapping in the welding head 3 are heat welded, for example, and the resulting product is separated from the supplied strapping band. The object 4 is now strapped and can be transported away.

(5) FIG. 2 will explain the layout of the band drive mechanism 5. The basic subassemblies are, first, the shooting and retrieval unit 8 and, secondly, the back tensioning unit 9, which perform the above mentioned band manipulations according to their designation.

(6) 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.

(7) 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.

(8) 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.

(9) 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.

(10) 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.

(11) 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.

(12) 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.

(13) 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.

(14) 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 FIG. 3 upward in the roller gap of the drive roller pair 13 of the shooting and retrieval unit 8. This takes up the leading end 40 of the strapping band 7 once again. By a corresponding activation of the drive roller 14 of the shooting and retrieval unit 8, the strapping band 7 is again shot into the band guide frame 6. Then the drive of the back tensioning unit 9 can be deactivated once more.