Strap tensioning apparatus

Abstract: A strap tensioning means for a strapping device, comprises pulling means (4, 6) for pulling strap (13) from a strap coil (9), and connection means (5, 10, 11) for connecting the strap coil (9) to the pulling means (4, 6) for pulling strap (13) from the strap coil (9) so that the pulling means (4, 6) are drivable by rotation of the strap coil (9) independently of any other power supply. In this way any overrun of the strap coil (9) causes the pulling means (4, 6) to pull further strap (13) from the strap coil (9) to maintain tension in the strap (13) extending between the strap coil (9) and the pulling means (4, 6).

Description: The present invention relates to strap tensioning means for use with strapping machines for positioning and securing a binding strap around an object or objects. Strap being pulled off of a strap coil of a strapping machine must be maintained at a particular tension for proper functioning of the strapping machine. In the past, as shown for example in document GB-A-1 161 827, several apparatuses and methods have been proposed for maintaining tension on the strap. One prior art device requires a dancer arm with a spring clutch to apply a force to a strap segment, and belt brakes to stop coil rotation after cessation of strap pulling from the strap coil, in order to prevent slack and insufficient strap tension. Another prior art device requires electrical or electromagnetic brakes to stop coil rotation. Other prior art devices require electrical brakes to stop coil rotation and also require constantly rotating pull off wheels which constantly slip on the strap. All of these prior art systems typically work only in the forward direction of strap pull, where strap is fed off of the strap coil. The prior art tensioning devices do not function in the reverse, or rewinding direction. All of the prior art systems are hampered by a general mechanical complexity. Dancer arms which function properly for various strap speeds and varying strap acceleration and deceleration conditions are difficult to design, and difficult to keep in adjustment. Also, the braking systems are generally complex, particularly the sensing and signalling systems for application and removal of the braking action against the coil. The present invention solves the problem of maintenance of proper strap tension by providing an inertial system, eliminating the need for complex dancer arm and braking systems. According to this invention a strap tensioning means for a strapping device, comprises a pulling means for pulling strap from a strap coil, and connection means for connecting the strap coil to the pulling means for pulling strap from the strap coil so that the pulling means are drivable by rotation of the strap coil independently of any other power supply. Thus any overrun of the strap coil causes the pulling means to pull further strap from the strap coil to maintain tension in the strap extending between the strap coil and the pulling means. The strap is held in a substantially constant tension condition, and so the formation of strap loops which would otherwise fall off of the strap coil is prevented. Strap cross-over on the strap coil is also avoided. Additionally, slack is removed from the strap gently, eliminating abrupt forces which would otherwise be applied to the strap and machine components during conventional strap tensioning. Embodiments of the invention also solve the problems associated with stoppage of rotation or the rotating elements of the strapping machine, and rewinding strap out of the machine and back onto the coil. In the preferred embodiment the inertia of the rotating elements of the strap coil are used to drive the drive motor shaft after electric power to the drive motor is stopped. The inertia of the previously electrically motor driven rotating strap coil is transferred by a pulley and belt arrangement back through the drive motor shaft, turning the drive motor shaft in the forward direction, thereby continuing to maintain tension on the strap end. Friction and other restrictive forces in the system will cause the rotating members to rotate at a decreasing rate, and eventually come to a gradual stop. Electrically powering the drive motor in the reverse direction moves the belt in the reverse direction. A one-way clutch preferably connects the belt to the strap coil, reversing the rotation of the strap coil in order to withdraw the strap from the strapping machine and rewind it onto the strap coil. A preferred embodiment of a strapping machine in accordance with this invention will now be described with reference to the accompanying drawings; in which:- FIGURE 1 is a front view; FIGURE 2 is a side view. Referring to Figure 1 the strapping machine includes a frame 15 and drive motor 1 having a first motor shaft 2. A driven wheel 4 is attached to the first motor shaft 2. A pinch roller 6 is attached to a pinch roller arm 16 is matable with the driven wheel 4. The force by which the pinch roller arm 16 and pinch roller 6 are urged against the driven wheel 4 may be adjusted by a pinch roller spring 17. Supplying electric or other power to the drive motor to drive it in the forward direction causes forward rotation of the first motor shaft 2. Driven wheel 4 is thereby driven in the forward direction. A strap 13 having a strap loose end 14 is pulled off of a strap coil 9, by the physical connection of the strap with the rotating driven wheel 4 and the pinch roller 6. Unwinding of the strap 13 causes the strap coil 9 to rotate in a forward direction. Referring now to Figure 2, a first pulley 5 is connected with a second motor shaft 3. The first pulley 5 and second motor shaft 3 are connected through a drive belt 11, chain or other means to a second pulley 10. The second pulley 10 is attached to a flange set fixed shaft 8 by means of a one-way clutch 12. Flange set 7 cooperates to form a strap coil 9 for holding an amount of strap in a coil arrangement. In operation, the strap loose end 14 is mechanically held between the driven wheel 4 and the pinch roller 6. The pinch roller 6 is movable with respect to the driven wheel 4 in a direction generally along a line connecting their two centers, in order to exert an appropriate force against the strap 13 through the urging of the pinch roller spring 17 in connection with the pinch roller arm 16 against the pinch roller 6. Electric power supplied to the drive motor 1 causing it to rotate in the forward direction also causes rotation of the first motor shaft 2 and the driven wheel 4 in the forward direction. The strap 13 is thereby pulled from the strap coil 9, causing rotation of the strap coil 9, flange set 7, and flange set fixed shaft 8 in the forward direction. The flange set fixed shaft 8 is connected by a one-way clutch 12, in one embodiment a roller-type clutch, to a large second pulley 10. The flange set fixed shaft 8 and the second pulley 10 may share a common central axis. A drive belt 11 or other means such as a chain connects the second pulley 10 to a first pulley 5 which is mounted on a second motor shaft 3 of the drive motor 1. In one embodiment, the first pulley 5 shows a common central axis with the driven wheel 4. In one embodiment, the ratio of the first pulley 5 pitch diameter and the second pulley 10 pitch diameter is greater than the ratio of the maximum strap coil 9 diameter and the driven wheel diameter 4. As strap 13 is pulled from the strap coil 9, the diameter of the strap coil 9 decreases. The strap coil 9 therefore rotates at a correspondingly increasing speed. However, due to the constant speed of the driven wheel 4 and the pinch roller 6, the speed of the strap coil 9 rotation does not affect the speed at which the strap 13 is taken off of the strap coil 9. Because of the one-way clutch 12, the second pulley 10 is overrunning on the flange set fixed shaft 8 during forward rotation of the drive motor 1. Strap tension is maintained during this phase of operation as strap 13 is being pulled from the strap coil 9 by the driven wheel 4. When electric power to the drive motor 1 is discontinued, the inertia of the strap coil 9 and flange set 7 will continue to drive the drive motor 1 in the forward direction. This driving force is provided from the rotating strap coil/flange set system through the flange set fixed shaft 8, to the one-way clutch 12, to the second pulley 10, to the drive belt 11, to the first pulley 5, to the second motor shaft 3, and eventually to the drive motor 1 itself. Rotation of the drive motor 1 in this forward direction causes the driven wheel 4 to continue to pull strap 13 under tension from the strap coil 9. Friction and other resistant forces eventually cause the rotation members to cease rotating, whereby the system comes to a rest position. However, the strap loose end 14 is as a consequence maintained under constant tension. Removal of the strap 13 from the strapping machine and rewinding of the strap 13 onto the strap coil 9 may be accomplished by electrically or otherwise powering the drive motor 1 in the reverse direction after releasing tension of the pinch roller 6 form the strap 13 and driven wheel 4. The drive motor 1 will now drive the first pulley 5, which drives the drive belt 11, the second pulley 10, the one-way clutch 12 and the flange set fixed shaft 8, thereby driving the flange set 7 and the strap coil in the reverse direction, causing the strap 13 to be removed from the strapping machine and rewound onto the strap coil 9.

Claims: Strap tensioning means for a strapping device, comprising pulling means (4, 6) for pulling strap (13) from a strap coil (9), and connection means (5, 10, 11) for connecting the strap coil (9) to the pulling means (4, 6) for pulling strap (13) from the strap coil (9) so that the pulling means (4, 6) are drivable by rotation of the strap coil (9), independently of any other power supply, and so that any overrun of the strap coil (9) causes the pulling means (4, 6) to pull further strap (13) from the strap coil (9) to maintain tension in the strap (13) extending between the strap coil (9) and the pulling means (4, 6). Strap tensioning means according to claim 1, further comprising an externally powered drive means (1) for driving the pulling means (4,6). Strap tensioning means according to claim 2, wherein the externally powered drive means is a drive motor (1), the drive motor (1) having a first motor shaft (2) and a second motor shaft (3), a driven wheel (4) attached to the first motor shaft (2), a first pulley (5) attached to the second motor shaft (3), the pulling means comprising a pinch roller (6) acting in cooperation with the driven wheel (4), a strap loose end (14) being firmly held between the driven wheel (4) and the pinch roller (6), wherein forward rotation of the drive motor by application of external power rotates the first motor shaft (2) and the driven wheel (4) in a forward direction, the action of the driven wheel (4) and the pinch roller (6) against the strap (13) causing strap to be pulled under tension from the strap coil (9). Strap tensioning means according to claim 2 or 3, wherein the strap coil (9) has a flange set fixed shaft (8) fixed to and rotatable with the strap coil (9), a one-way clutch (12) attached to the flange fixed shaft (8), and a second pulley (10) fixed to the one-way clutch (12) wherein the one-way clutch (12) is overrunning the flange set fixed shaft (8) when the driven wheel (4) is rotated in the forward direction by the externally powered drive motor (1). Strap tensioning means according to claim 4, wherein the connection means includes a drive belt (11) connecting the second pulley (10) with the first pulley (5), the drive belt being drivable in the forward direction by rotation of the strap coil (9), the flange set fixed shaft (8), and the one-way clutch (12), wherein, upon cessation of external power application to the drive motor (1), the inertial rotation of the strap coil (9) through the one-way clutch (12) drives the belt (11), the first pulley (15), the second motor shaft (3), the first motor shaft (2) and the driven wheel (4), the driven wheel (4) acting with the pinch roller (6) to continue pulling strap under tension from the strap coil until rotational motion ceases. Strap tensioning means according to claim 5, wherein the drive motor (1) is drivable in a reverse direction by an external power source, the strap coil (9) is drivable in a reverse direction by an external power source, the strap coil (9) is drivable through the second motor shaft (3), the first pulley (5), the drive belt (11), the second pulley (10), and the flange set fixed shaft (8) through the action of the one-way clutch (12), wherein upon operation of the drive motor (1) in the reverse direction, the strap coil (9) is driven in the reverse direction and rewinding strap (13) onto the strap coil (9). A strapping machine including a strap tensioning means in accordance with any one of the preceding claims.

Inventors: ABRAMS JACK, GURAK RONALD, PEARSON TIMOTHY, ABRAMS, JACK, GURAK, RONALD, PEARSON, TIMOTHY
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS INC.
Application year: 1996
Main classification: B65B13
IPC codes: B65H49, B65B13, B65H16