EP0806349A1 - Tensioning device - Google Patents

Abstract

The outer wrapping on a package is secured by a strap wrapped around the package. The ends are clamped (6) together and joined. The clamp (6) incorporates a transport device (11) which takes up slack in the strap and subjects the strap to a pre-set and controlled tension value while the strap ends are joined. The clamp and tensioning is acted by a lever (3). The drive may be exclusively for the use of transport movement in the future of transport units. The capture units value of the parameters is gripped on the transport mechanism.

Description

The invention relates to a device for applying a tension force to a strapping, which is provided with a guide for the strapping, a transport device with which the strapping can be moved, and a drive for the transport device.

Various machines are already known for applying a band or several bands with which an open or packaged good is held together. Such machines are used to tension the band around the goods, to connect them at the ends of the band and to separate them from a supply roll. The application of the tape around the material to be wrapped around and the introduction of the tape with the required overlap of the tape ends into the machine can be carried out manually or automatically. However, the clamping and subsequent connection process is usually carried out mechanically in machines which are provided with a generic device.

For example, it is already known to carry out and deflect the belt between at least two rubberized wheels, plastic wheels and / or belt drives, the belt being tensioned with the help of the frictional forces thereby created. Such a device is described in CH-PS 662 791. With this tensioning system, however, it is disadvantageous that the wheels or the belt drives wear out relatively quickly as a result of the friction, and the functional reliability is thereby impaired. It cannot then be ensured that a certain target tensioning force is actually applied to the belt.

Other previously known tensioning systems that use a slotted drum to fix a tape end when applying the required tape tension can also not satisfy. In such tensioning systems, it is necessary to fix a band section in the drum which is still connected to the band located on the storage drum. In particular, if high band tensions are to be applied, the band is deformed by the slotted drum through plastic buckling. It has been shown that such deformations have a detrimental effect on the functionality, such as, for example, the clamping force that can be applied.

Furthermore, it is also not possible with such clamping systems to compensate for the deviations from the target clamping force that occur due to interference. It is also disadvantageous that band sections deformed in this way can no longer be safely transported in guides of clamping and closing heads. Since the deformed band section is the end of the next strapping and still has to be transported through the entire guide, the only way to help is to separate this band section before the next strapping cycle.

In another already known tensioning system, there is a relative movement between a tensioning lever and a so-called bell curve. A bell curve is to be understood as the contour of an end face of a rotatable cylinder on which one end of the tensioning lever is located. The stroke of the tensioning lever resulting from the rotary movement of the cylinder is used to tension the belt. However, it is disadvantageous that the path covered by the tension lever through the bell curve is fixed. Since the tension applied to the tape depends on several factors, such as the length, the material or the cross-section of the tape, it is almost impossible to apply a predetermined tension to the respective tape under different operating conditions.

The invention is therefore based on the object To further develop the device of the type mentioned at the outset such that a predetermined, in particular a predetermined, high tension can always be reliably applied to the respective band, even under different operating conditions.

The object is achieved according to the invention in a device mentioned at the outset by a clamping device for fixing a band section during a tensioning phase, and by the transport device by means of which the clamping device and the band section fixed therein can be moved along a path to apply the tensioning force during the tensioning phase, wherein the device is provided with a means for detecting a value of a parameter corresponding to the clamping force, and wherein the detection means is connected to a control device which, when a predetermined limit value of the parameter is reached, causes the transport device to stop.

A first basic aspect of the invention thus consists in using a parameter for the application of the desired tensioning force to the tape, which parameter can be determined during the tensioning process and allows a conclusion to be drawn about the tensioning force already applied to the tape. By limiting the maximum permissible actual value of the parameter (limit value), which also corresponds to the target clamping force, it can be determined whether the latter has already been reached. Alternatively, the respective actual, actual value of the parameter can be determined and compared with the limit value. The drive of the device according to the invention moves the transport device further as long as the actual value of the parameter is smaller than the limit value or the limit value has not yet been reached. It is preferable to use a parameter that can be tapped or detected on the drive.

The device according to the invention is thus not, as is the case, for example, with the solution described above the bell curve, the path covered rigidly by the clamping device during the tensioning phase. Rather, the tensioning path is variable and depends on the tension force actually present, which is why, with the described control or regulation, regardless of, for example, the length or the elasticity of the band, a predetermined tension force can be applied repeatedly.

Another aspect of the invention is the application of tension to the belt using a clamping device arranged on a pivoting lever, which fixes the belt and transports it along a path. It is preferred in this case that - while the band is fixed in the clamping device - a band section pulled out of a closing station to apply the tension from the clamping or transport device is aligned essentially in a straight line. An essentially rectilinear alignment of the band is an arrangement in which the band is not plastically deformed by deflections. This alignment can be achieved in a particularly simple manner in that the band section fixed in the clamping device travels an essentially straight tension path, which lies at least approximately along the alignment of the band section between the closing station and the clamping device before the band is fixed in the clamping device. This measure also supports tensioning the strap without plastically deforming it. The transport route can be completely straight. Likewise, during this movement, the belt can also cover a path that deviates slightly from a linear movement, for example an arc-shaped path or a path that is curved in some other way. Such movements can be generated with relatively small devices. So that the linear movement described above and its purpose are at least approximately realized, a radius of curvature should be used that is at least so large that the elastic limit on the outer radius of any resulting band curvature is not exceeded.

By realizing both aspects in the device according to the invention, a predetermined, in particular a constantly high tensioning force can thus be achieved without thereby deforming the fixed band section.

This type of application of the tensioning force can also be supported by the band also being clamped in the clamping device without kinks. This means that the tape itself does not experience any deforming deflection in the clamping device itself. As a result, after tensioning the tape and opening the clamping device, the tape essentially returns to its original shape and assumes its original orientation.

In principle, almost any drive principle (for example electrical, hydraulic or pneumatic) can be used to drive the transport device of the device according to the invention. However, it is preferred to provide an electric drive that only drives the transport device. With such a drive it is possible with relatively little design effort to provide suitable parameters which are essentially only dependent on the belt tension and not also on other components of the machine. In a preferred embodiment of the invention, the torque applied to the shaft of the drive is used as a parameter for determining the belt tension. It is particularly preferred to use the motor current as a parameter dependent on the clamping force. Such a control or regulating device for monitoring the belt tension can be provided both with direct current and with alternating current motors. By limiting the maximum current consumption of the motor, it can be ensured that, on the one hand, the fixed belt section is transported until the motor reaches the predetermined current and thereby the predetermined clamping force is reached. On the other hand, the transport device is stopped when the predetermined clamping force is reached. This avoids overloading the belt or damaging the packaged goods.

Fig. 1

eine Seitenansicht eines Spann- und Verschliesskopfes, an dem eine erfindungsgemässe Vorrichtung angeordnet und in zwei verschiedenen Positionen gezeigt ist;

Fig. 2

eine dreidimensionale Darstellung der erfindungsgemässen Vorrichtung aus Fig. 1;

Fig. 3

eine Schnittdarstellung des in den Fig. 1 und 2 dargestellten Kugelumlaufgetriebes.

The invention is explained in more detail with reference to the exemplary embodiments shown schematically in the figures; show it:

Fig. 1

a side view of a clamping and closing head, on which a device according to the invention is arranged and shown in two different positions;

Fig. 2

a three-dimensional representation of the inventive device from FIG. 1;

Fig. 3

a sectional view of the ball screw shown in Figs. 1 and 2.

The device according to the invention shown in FIGS. 1 and 2 is part of a so-called tensioning and closing head 1, with which a steel or plastic band, not shown, is placed around a packaged product, also not shown. For this purpose, the clamping and closing head 1 rests on the packaged goods with a base area 2. The device has a transport device 11, which is provided with a swivel lever 3, a drive 4, a gear 5 and a clamping device 6.

The fork-shaped pivot lever 3 is pivotally articulated on a housing 7 of the clamping and closing head 1. For this purpose, the pivot lever 3 is provided with a roller bearing 8. Following a curvature of the pivot lever 3, the latter is provided with two legs 9, 9 'arranged in a fork shape, of which only one is shown in the illustration in FIG. 1 can be seen.

The gear 5 is attached to the legs 9, 9 '. On the other hand, the gear 5 is also pivotally articulated on the housing 7 about a further bearing 10. The gear 5 essentially has an enveloping drive 13 and a recirculating ball gear 14, shown in particular in FIG. 3. The latter is fastened with a nut 15 to the legs 9, 9 'in a rotationally fixed manner. The roller 15 is supported by roller bearings 16, 17, 18 on transmission sleeves 19, 20 arranged essentially coaxially in it. The transmission sleeve 19 is rotatably connected with screws to a gear 23. The second transmission sleeve 20 lies on balls, not shown, of a threaded spindle 24 of the ball screw mechanism 14 which are arranged in threads. Furthermore, a bearing plate 25, which is only partially shown, is arranged in a rotationally fixed manner around the threaded spindle 24.

The threaded spindle 24, which is secured against rotational movements, is fastened at its two unthreaded ends in brackets 26, 27, respectively. The bracket 26 is provided with a bearing pin 28 for the pivotable arrangement of the ball screw 14 on the housing 7. Furthermore, the threaded spindle 24 is located between the holder 26 and the nut 15 and the holder 27 and the gear 23 in a rotationally fixed bellows 29, 30, which is each provided with spacers 33. The two bellows 29, 30 are each arranged in a rotationally fixed manner, for which purpose the bellows 30 is mounted on a further ball bearing 34.

In addition to the toothed wheel 23 and a toothed belt 35, the enveloping drive 13 also has a pinion 38 arranged on a drive shaft 36 of a direct current electric motor 37. The diameters of the gear 23 and the pinion 38 are coordinated with one another in such a way that the rotational movement of the shaft 36 is translated into small dimensions.

The electric motor 37, which is arranged with its drive shaft 36 essentially parallel to the threaded spindle 24, is fastened to the non-rotatably arranged bearing plate 25. The position of the electric motor 37 is thus fixed in relation to the threaded spindle 24. The electric motor 37 is connected to a power source (not shown) and a control device via electrical lines 39, only one of which is shown. The maximum current to be output to the electric motor 37 is infinitely variable and repeatable adjustable as a limit value on the control device. An electrical circuit designed as a detection means determines the current actual value of the motor current and compares this value with the predetermined limit value. Such circuits for limiting the current are known per se to the person skilled in the art. There is therefore no need to discuss the structure of such circuits in more detail.

The previously mentioned clamping device 6 is attached to the legs 9, 9 'in the region of their ends below the nut 15. The clamping device 6 has a clamping plate 40 with a contoured bearing surface 43, above which a pivotable clamping cam 44 is arranged, which is provided with a correspondingly contoured pressure surface 45. The clamping cam 44 can be pivoted about a bearing 46 in such a way that the pressure surface 45 comes to rest on the bearing surface 43. Since the surfaces 43, 45, between which the band can be clamped, are contoured, the band can be held particularly securely. The contouring, which essentially consists of mutually congruent curvatures, is however carried out in such a way that the orientation of the band is essentially not influenced by the fixation.

In order, for example, to place a steel or plastic band around a packaged product (not shown in the figures), the band is introduced between the clamping plate 40 and the clamping cam 44 into a guide 47 of the tensioning and closing head 1, which is only shown schematically (FIG. 1). The tape inserted into a first guide rail 48, placed around the packaged goods and given into the second guide rail 49 of the guide 47. The required withdrawal of the tape from a supply roll, not shown, is carried out by a transport roller 50. The end of the band is then fixed in a clamping station (not shown) of the tensioning and closing head. As a result, a section of the belt that is already guided around the packaged goods and a second section of the belt that is located between the transport roller 50 and the first guide rail 48 overlap below a merely schematically illustrated closing station 53.

In order to provide the band with the intended tensioning force, a band section is now clamped between the clamping plate 40 and the clamping cam 44, so that this clamped section cannot make any relative movements with respect to the clamping device 6.

Thereafter, the control of the device, by means of which the latter can be controlled separately from the other components of the tensioning and closing head 1, causes the electric motor 37 to be supplied with current. The rotational movement of the shaft 36 of the electric motor 37 is then transmitted from the pinion 38 and the toothed belt 35 of the enveloping drive 13 to the gear 23. The transmission sleeves 19, 20 which are also set in rotation as a result, since they are operatively connected to the threaded spindle 24, also perform a translatory movement in the direction of the holder 27. Furthermore, the rotationally fixed nut 15, which is operatively connected to the transmission sleeves 19, 20, is taken along with the pivot lever 3 during this movement.

Thus, on the one hand, there is a pivoting movement of the lever 3 around the bearing 8 from a first end position into a second end position. On the other hand, the ball screw 14 leads one Pivotal movement around the bearing 10. Because of these two movements, the components of the gear 5 arranged on the threaded spindle 24 are shifted in a straight line relative to the latter. Since the clamping device 6 is also carried along during this movement, the band section clamped in it travels a path corresponding to a circular arc, as a result of which the band is tensioned. 1 shows a distance covered by the clamping device approximately as the distance s between the two positions of the clamping device. As can also be seen from the illustration in FIG. 1, the transport section of the belt which is pulled out of the closing station 53 by the transport device 11 in the tensioning direction during the tensioning phase is essentially always aligned in a straight line. The section of the belt which is becoming longer and longer during the tensioning phase and is located between the closing station 53 and the clamping device 6 is regarded as the transport section. Depending on how long the tensioning path is, the transport section of the belt can at most experience a slight deflection by the transport roller 50. However, this deflection is so small that the stress on the belt caused thereby is below its elastic limit. Ideally, the transport section is thus essentially only subjected to tensile stress during the tensioning phase.

After the actual value of the current of the electric motor 37 determined by the detection means has reached the limit value, this current value is kept constant by the control until the overlapping ends of the strip are connected to one another. Alternatively, it can also be provided that when the limit value is reached, the pivot lever 3 is locked and the electric motor 37 is switched off. In Fig. 1, the device according to the invention is partially shown in its position when a limit value is reached with dash-dotted lines. The components of the device shown in this position are each with provided with an index "a".

In contrast to previously known tensioning systems, the length of the path covered by the belt during the tensioning phase is of no importance for the application of the tensioning force in the device according to the invention. It only has to be ensured that the maximum stroke of the ball screw mechanism is sufficient for reaching the limit value of the current and thus for the clamping force to be applied.

After the desired tension force has been applied to the belt, the closing device 53 is used. This attaches a seal to the two above-mentioned sections of the band lying one above the other, or closes the band in some other way, for example by friction welding or thermal welding. Other sealless closures, e.g. notches possible. The strapping process is now complete.

For each belt, the functional dependency between different values of the belt tension and the motor current required for this can be determined on the basis of simple tests. Every interim value can thus be determined by an interpolation. This functional relationship between the respective (mechanical) tension of a certain type of strip and the respective value of the current is expediently stored in an electronic storage unit of the control. Of course, this relationship can also be stored in a storage unit for several different tape types. This means that any desired value for the tensioning force or tension can be set on the control system for each belt that can be used.

Claims (10)

Device for applying a tension force to a strapping, comprising a guide for the strapping, a clamping device (6) in which a section of the band can be fixed during a tensioning phase, a transport device (11) which is provided with a swivel lever (3) on which the clamping device is arranged, so that the belt section which can be fixed in the clamping device can be moved along a path during the tensioning phase, a drive for the transport device, a means for detecting a value of a parameter corresponding to the clamping force, and a control device connected to the detection means which, when a predetermined limit value of the parameter is reached, causes the transport device (11) to stop. Device according to Claim 1, in which the drive is provided exclusively for generating the transport movement of the transport device. Device according to one or both of the preceding claims, in which the detection means taps values of the parameter at the drive (4). Apparatus according to claim 3, wherein the detection means determines a value of a parameter which is dependent on the torque of the drive (4). Device according to one or more of the preceding claims, in which the detection means determines the current consumption of an electric motor (37) as a parameter. Device according to one or more of the preceding claims, in which the limit value of the parameter is infinitely adjustable. Device according to one or more of the preceding claims, in which the transport device (11) aligns the belt to be tensioned in a substantially straight line on its transport path. Device according to one or more of the preceding claims, in which the drive (4) is operatively connected to the swivel lever (3) by means of an enveloping drive (13). Device according to one or more of the preceding claims, in which the drive (4) is operatively connected to a ball screw mechanism (14) Apparatus according to claim 9, wherein the ball screw mechanism (14) is pivotally arranged.

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