A film free end control device and method for a stretch winding machine

Abstract

This invention discloses an apparatus and method for stretch winding palletized goods, using film tension feedback from a film tension control load sensor to control film distribution. The load sensor measures film tension, and the film release speed is determined by the film tension. The film tension value is used to determine when an out-of-range condition occurs, i.e., when film breakage occurs, when film breakage is likely, or when the film is cut at the end of the winding cycle. To prevent tangling of the free end of the film due to breakage, a clamp engages with the film, thereby controlling the film tail and eliminating the risk of retraction. The broken film tail can then be quickly and reliably reattached to the desired position of the rotating goods.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for wrapping goods, and more specifically, to a stretch wrapping machine for wrapping palletized goods with stretch wrapping material, wherein the stretch wrapping machine includes components for controlling the tail of a free film to prevent the tail of the film from inadvertently engaging with components of the stretch wrapping machine. Background Technology

[0002] Stretch wrapping is a common method for protecting palletized goods during transport. Generally, stretch wrapping involves wrapping a specialized film around a stack of items, such as boxes already arranged on a pallet. The film is wrapped around the boxes under tension, thus stabilizing the stack and minimizing the risk of damage during transport. Tension can be provided by the memory recovery of the pre-stretched film, or it can be generated by the resistance between the goods and the film dispenser, or a combination of both.

[0003] Automatic or semi-automatic stretch wrapping machines come in various styles and designs, many working in conjunction with automated palletizers for building palletized goods. A stretch wrapping machine provides relative rotation between the palletized goods and a distributor containing a roll of stretch wrapping film. Typically, the pallet and goods are stationary, with the distributor rotating around the goods, or the pallet and goods rotating relative to a fixed distributor. In either case, the stretch wrapping film spirally wraps around the goods under tension to stabilize them.

[0004] Stretch wrapping machines are used in highly automated production and packaging lines and must be able to keep up with the throughput of other equipment used in palletizing operations so that the stretch wrapping operation does not slow down overall production. Accordingly, these machines typically operate at relatively high productivity. However, stretch wrapping is not always a simple operation. For example, it is well known that when there are rectangular goods on a pallet, the demand for stretch wrapping film changes as the corners of the goods pass the film dispensing point: the demand for film release increases as the corners of the goods pass the dispensing point and decreases as the film is dispensed to one side of the goods between the corners. In addition to the payout rate, the tension on the film also directly affects the stability of the fully wrapped goods. Many stretch wrapping machines use tensioning devices to control the film tension. However, tension varies with rotational position, so maintaining proper tension is often difficult at high throughput rates. When the film breaks for various reasons, including excessive tension, the stretch wrapping operation may stop or slow down, and the film may automatically or with operator intervention reattachment to the goods.

[0005] U.S. Patent 10,604,284, the entire disclosure of which is incorporated herein by reference, describes a stretch-winding apparatus for winding palletized goods placed on a rotating turntable. A stretch-winding head supplies a pre-stretched wrapping film to the rotating goods, and an air jet blows the tail of the film onto the goods. A relative rotational motion is generated between the wrapping head and the goods, with the free end of the film unsupported by any mechanical structure and guided to the goods solely by air from the jet. The free end of the film adheres to the outer surface of the goods, and the wrapping head moves vertically so that the goods are spirally wound. The film is dispensed at a certain speed to provide film release consistent with demand, as each goods corner varies based on a calculated interval through its relative distance to the dispensing point. Sensors detect changes in the film's optical properties—defects—to determine out-of-range conditions such as film breakage.

[0006] Free film ends, sometimes referred to herein as "film tails," are generated in three different situations. First, when the free end of the film is distributed to the cargo before the film tail is attached to the cargo. Second, when the wrapping operation is completed and the film has been cut. Third, when the film breaks during the wrapping operation. In stretch wrapping machines, such as those described in U.S. Patent 10,604,284, where the film tail is blown toward the cargo, it has been found that positive control of the film tail is necessary to ensure that the film tail does not become entangled with the stretch wrapping head. Therefore, in any of the three situations described above where film tails are generated, it is desirable to prevent the film from becoming entangled in the stretch wrapping machine. If entanglement occurs, the wrapping operation will slow down, and if the entanglement is severe enough, operator intervention may be required.

[0007] In the first scenario described above, the film tail is distributed to the rotating cargo before the film is bonded to the cargo. Forward control of the film tail holds the film in the desired position relative to the cargo so that it will be blown toward the cargo for bonding, as described in U.S. Patent 10,604,284. In the second scenario, when the winding operation is complete and the film has been cut, forward control of the film before or simultaneously with cutting prevents the film tail from springing back and the risk of tangling due to cutting the film under tension, and holds the film in the ideal position so that it can be blown toward the next cargo to be wound. In the third scenario, when the film breaks during the winding operation, the risk of the film becoming entangled with the stretch winding head is most severe. Because the film is under tension during winding, when a break occurs, the film tail resulting from the break may retract or spring back, thus becoming entangled with the stretch winding head. The film tail may also be relatively long, sometimes between 20 and 40 inches, depending on the equipment setup, and the film tail may droop downwards under gravity. This can cause several problems. First, the drooping tail may become entangled with other equipment. Secondly, long, uncontrolled, and drooping film tails can be difficult to engage with the blower for reattachment to the cargo. More problematic, in the event of film breakage, the uncontrolled film tails can engage with film already dispensed by the pre-stretch rollers, causing the film tails to become entangled in the pre-stretch roller system when it is powered on for the next blow. This can quickly damage the pre-stretch roller system and may result in downtime and costly repairs.

[0008] Known stretch wrapping machines that do not use a blower to attach the film to the goods employ clamps mounted in a fixed position relative to the rotating equipment and the goods, rather than relative to the stretch wrapping head. For example, a turntable may have clamps to control the film and allow it to be attached to the next item. Alternatively, in the case of stationary goods with a stretch wrapping head rotating around the goods, a fixed clamp adjacent to the stationary goods is used to control the film. None of these arrangements allow for control of the film tail caused by film breakage and do not account for or prevent film tail tangling.

[0009] There is a continued need for improved stretch winding equipment to balance the demands and challenges of keeping up with productivity while winding goods with appropriate film tension to properly stabilize them. Improved stretch winding equipment is also needed to prevent the aforementioned problems regarding uncontrolled film tails, and to incorporate the use of blown film as a method of goods attachment, which is accomplished by blowing film onto (a) goods already partially wrapped with broken film tails to prevent tangling until reattachment is completed by blowing out the film, (b) goods constructed without film, where the film tail is managed and controlled between previous film cutting and film attachment to new goods, (c) goods not yet started, where film is blown onto empty pallets before the first layer is placed (where stacking and winding are performed simultaneously), or (d) blowing film between already placed layers and the next layer (e.g., where stacking and winding are performed simultaneously). The reattachment of blown film contrasts with current industry practice of film tail clamps, which are fixed relative to the cargo during differential rotation. For the blown film described herein, the tail clamp is fixed relative to the film distribution position rather than the cargo, thus preventing tangling caused by retraction. Summary of the Invention

[0010] This invention includes an improved apparatus and method for the automated stretch wrapping of palletized goods. The apparatus utilizes film tension feedback parameters from a film tension control load sensor. The load sensor continuously monitors and measures the film tension during the wrapping operation, and based on the film tension, the film payout rate is determined by the film tension measured by the load sensor. The film is released according to the film tension, and the film payout rate or film speed is adjusted by reaction during relative rotation; no active film speed calculation is performed. The tension value is monitored and used to determine when a film overshoot occurs, i.e., film breakage occurs, when film breakage is likely, or when the film is cut at the end of the wrapping cycle. When any of these overshoots occur, the film clamp engages the film before, simultaneously with, or slightly after the overshoot occurs. The relative rotation of the goods relative to the film dispenser can continue, thus achieving controlled film breakage if the overshoot is a predicted film breakage. That is, with the clamp engaging the film, film delivery stopping, and relative rotation between the dispenser and the goods continuing, the film breaks in a relatively controlled manner downstream of the clamp, eliminating the risk of retraction and tangling. The broken film tail can then be quickly and reliably reattached to the desired position on the rotating cargo. For example, the vertical position of the stretch wrapping head can be changed after the breakage, causing the film tail to be blown toward the cargo and reattached, so that the film re-covers the broken free end of the film on the cargo. When the stretch wrapping head is in the desired vertical position, the clamp is released, the film is blown out, and film feeding is resumed to automatically continue wrapping without interruption.

[0011] Therefore, the sensitivity of the load sensor allows for control of predicted film breakage (in addition to actual film breakage) and allows for reattachment when the film dispensing speed increases to match the relative rotation speed as relative rotation continues.

[0012] This disclosure provides an apparatus for preventing film tangling in a stretch wrapping machine for wrapping goods, comprising: a vertically movable dispensing head having at least one pair of pre-stretch rollers adapted to dispense film; a first drive mechanism for driving the at least one pair of pre-stretch rollers to dispense film; a compressed air source for blowing compressed air through an air jet aligned with the film after the film has been dispensed from the at least one pair of pre-stretch rollers, thereby blowing the film toward the goods; a second drive mechanism adapted to provide relative rotation between the goods and the dispensing head; and a film clamp mounted to the dispensing head between the dispensing head and the goods, wherein the film clamp is adapted to hold the film in the event of a film breakage event.

[0013] The apparatus includes a film tension device for continuously measuring film tension to generate a film tension value and transmitting the film tension value to a controller.

[0014] According to the device, when a film breakage event occurs, the controller stops the film dispensing and simultaneously causes the film clamp to hold the film.

[0015] According to the device, an acceptable tension value range is stored in the controller, and a film breakage event is defined as a film tension value that is higher or lower than the acceptable tension value range.

[0016] According to the device, the film clamp holds the film before it breaks.

[0017] According to the device, the film breakage is caused by a film clamp holding the film.

[0018] According to the device, the film clamp holds the film after it breaks.

[0019] According to the device, the film has a free end after it breaks, and the free end of the film is prevented from retracting and tangling after the film clamp is holding the film.

[0020] According to the device, the film is dispensed at a speed responsive to the film tension value.

[0021] This disclosure also provides a method for preventing film tangling in a stretch wrapping machine for wrapping goods, comprising the following steps:

[0022] a) Provides relative rotation between the film conveyor head and the cargo;

[0023] b) Install a film clamp at a fixed position on the film conveying head;

[0024] c) Dispensing film from the film conveying head and attaching the film to the goods;

[0025] d) Measure the tension in the film;

[0026] e) If the measured tension is higher than the upper limit or lower than the lower limit, the clamp is closed to hold the film, and film dispensing is stopped.

[0027] The method includes blowing air into the film at least intermittently during relative rotation.

[0028] The method includes the step of closing the clamp to hold the film after the film breaks.

[0029] The method includes the step of closing the clamp to hold the film before the film breaks.

[0030] According to the method, closing the clamp to hold the film causes the film to break.

[0031] According to the method, the relative rotation does not stop, and the method includes reattaching the film to the cargo after step e) by:

[0032] a) Blow air into the film;

[0033] b) Open the clamp and simultaneously resume film dispensing from the film delivery head.

[0034] According to the method, the film is distributed at a speed determined by the measured film tension.

[0035] This disclosure also provides an apparatus for preventing film tangling in a stretch wrapping machine for wrapping goods, comprising: a dispensing head for dispensing film; a film holder mounted on the dispensing head and located between the dispensing head and the goods, the film holder being movable between a film holding position and a film non-holding position; a controller communicating with a film tension measuring device adapted to measure film tension, such that a film tension value from the film tension measuring device is transmitted to the controller, wherein the controller is programmed to have an acceptable range of film tension values, having an upper limit and a lower limit; a drive mechanism for dispensing film from the dispensing head at a speed determined by the film tension value; wherein if the film tension value is outside the acceptable range of film tension values, the film holder moves to the film holding position.

[0036] According to the device, a pressurized air source is included, which blows air at least intermittently through an air jet aimed at the film after the film is dispensed from the dispensing head.

[0037] According to the device, a film breakage event is defined as a film tension value outside the acceptable range of film tension values.

[0038] According to the device, the film breakage event occurs before the film breaks.

[0039] According to the device, the film breakage event occurs after the film breaks. Attached Figure Description

[0040] The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, and its many objects and advantages will become apparent.

[0041] Figure 1This is a top perspective view of the stretch winding apparatus according to the invention, including palletized goods located on a turntable adjacent to the stretch winding apparatus, and including a portion for the housing of the apparatus; Figure 1 In the middle, the film clamp is in the clamping position, and the film is firmly clamped by the clamping arm.

[0042] Figure 2 yes Figure 1 The top perspective view of the stretch winding device shown is only... Figure 2 The film in it is broken or cut.

[0043] Figure 3 This is a top perspective view of the stretch winding apparatus according to the invention, wherein the goods have been removed from the turntable and the clamps are in the clamping position, clamping the film.

[0044] Figure 4 This is a top perspective view of the stretch wrapping head of the present invention, shown separately, with the clamp in an unclamped (or open) position, and showing the film tail, which will be dispensed onto palletized goods.

[0045] Figure 5 yes Figure 4 A top perspective view of the stretch winding head, shown separately again, shows the clamp in the clamped (or closed) position and the tail of the film when it has been cut or broken.

[0046] Figure 6 yes Figure 5 The stretch winding head is viewed from above at another angle, with the clamps in a clamped (or closed) position, and the tail of the film is shown when the film has been cut or broken.

[0047] Figure 7 This is a top perspective view of the stretch wrap head according to the invention, located near palletized goods, with some of the outer casings removed from the stretch wrap head to show the components.

[0048] Figure 8 Is it like this? Figure 1 The side view of the stretch wrapping apparatus shown illustrates the film attached to palletized goods during the wrapping operation.

[0049] Figure 9 Is it like this? Figure 7 The side view of the stretch winding apparatus shown illustrates a film in a broken or cut state.

[0050] Figure 10 This is an upper axonometric view of a stretch winding apparatus according to the invention, including palletized goods placed on a turntable adjacent to the stretch winding apparatus, wherein the film clamp is in a clamped position, the film is intact or uncut, and the film cutting assembly is in an extended position. Detailed Implementation

[0051] First, the main structural components of the stretch winding device 10 are described with reference to the accompanying drawings. Then, its operating characteristics and functions are described.

[0052] The stretch winding device 10 typically includes a stretch winding head assembly 12 mounted to a bracket assembly 14, which is vertically and reciprocally mounted on a frame 16. A turntable 100 is located adjacent to the stretch winding head assembly 12. Figure 1 As shown, pallet 101 is operatively positioned on turntable 100 and carries a stack of palletized boxes 152. Frame 16 includes a column 18 interconnected with top guide rail 20. A bracket assembly 14 defines a movable bracket, on which a stretch winding head assembly 12 is mounted and includes guide rollers 22 conventionally housed in vertical tracks formed in the column 18. A bracket lifting drive motor, housed in motor housing 24, is mounted on bracket assembly 14 and drives the vertical reciprocating motion of the bracket assembly with a conventional bracket lifting chain assembly or other suitable lifting mechanism.

[0053] exist Figure 1 The housing 500 shown in the middle section is typically used to isolate and protect components of the device 10, and for safety purposes.

[0054] The stretch winding head assembly 12 includes components mounted to a horizontal support member 28, which is mounted to a bracket assembly 14, such that vertical movement of the bracket assembly directly moves the stretch winding head assembly. A spool 30 of the stretch winding film 200 is mounted on a spindle (not shown) operably adjacent to the winding head assembly 12, the longitudinal axis of the spool being perpendicular to the ground plane, and allowing the film 200 to be fed into the winding head assembly 12 as described below. A film pre-stretching assembly, generally indicated by 32, is adjacent to the spool 30 and includes a pre-stretch drive motor contained within a cover or housing 34; the drive motor is operably connected to and drives a pair of vertically mounted pre-stretch rollers 36. Film guide rollers are located between the pre-stretch rollers 36. In some cases, and in some devices, more than one pair of pre-stretch rollers 36 may be used, and additional guide rollers may be used.

[0055] The pre-stretch roller 36 defines the active film dispensing mechanism for dispensing the film 200. The film 200 is fed on the film guide rollers and then passes through the pre-stretch roller 36. During pre-stretch film dispensing, the pre-stretch rollers rotate at different speeds, which pre-stretches the film between adjacent rollers. Non-pre-stretch dispensers typically use a single drive roller or the relative motion between the cargo and the dispenser to pull the film directly from a reel, which usually has some type of friction clutch to generate film tension.

[0056] Downstream of the film pre-stretch roller 36 are a pair of opposing and vertically arranged film outlet guide rollers 202 and 204. These guide rollers 202 and 204 are mounted to an upper mounting bracket 206 and a lower mounting bracket 208. As detailed below, the film 200 is fed from the pre-stretch roller 36 through the film outlet guide rollers 202 and 204. The tangent between the film outlet guide rollers 202 and 204 defines the film outlet point from the pre-stretch assembly 32 to the cargo. Pressurized air is supplied through one or more air pipes to deliver compressed air to two vertically arranged and parallel film-aligning air jets 44 and 46. These air jets 44 and 46 include multiple air jets 48, which are openings through which pressurized air is guided by the film 200, as detailed below, so that the film is blown onto the box 152 on the pallet 101. Air jets 44 and 46 are arranged adjacent to each other, one on each side of the membrane outlet guide rollers 202 and 204, such that the membrane 200 supplied and passing through the outlet guide rollers is guided between the two air jets, and air discharged from the air jetter 48 is directed onto the membrane. Plant gas is the preferred air source for supplying to the air jets 44 and 46 because it is more economical than, for example, a blower motor, and plant gas is readily available, whereas pressurized air from a blower motor typically requires acceleration time. That is, in some cases, a blower motor can be successfully used and can be installed, for example, in a housing 42.

[0057] Fixture assembly 120 is mounted onto upper bracket 206, see Figure 4 and 5 It is worth noting that the clamp assembly 120 is fixedly mounted to the film pre-stretch assembly 32, and the clamp (described below) is in a fixed position relative to the point where the film leaves the pre-stretch assembly. The clamp assembly 120 is defined by two L-shaped clamping arms 122 and 124, each clamping arm having a gear base 126. Figure 4 and 5The gears 126a and 126b are pivotally mounted to the bracket 206, the 90-degree bend 207, and the downwardly suspended clamp portions 128 and 130, respectively. L-shaped clamping arms 122 and 124 are mounted on the bracket 206 such that the gear at the base 126a of clamping arm 122 meshes with the gear at the base 126b of clamping arm 124. The drive cylinder 132 has a cylinder barrel 133 with a proximal end 134 mounted to the bracket 206 and a reciprocating drive piston 136 that translates within the cylinder barrel, its distal end 138 pivotally mounted to the L-shaped clamping arm 122, located between the 90-degree bend 207 and the pivot point from the base 126a to the bracket 206. The drive cylinder 132 can be of any suitable type, such as pneumatic, hydraulic, electric, or other types. It should be understood that the operation of the drive cylinder 132 in the first direction causes the drive piston 136 to extend from the cylinder barrel 133, thereby causing the clamping arm 122 to rotate about the pivot connection between the clamping arm and the support 206. Simultaneously, since the gear base 126a of the clamping arm 122 meshes with the gear base 126b of the clamping arm 124, when the clamping arm 122 rotates due to the extension of the cylinder barrel 133, the clamping arm 124 rotates in the opposite rotational direction of the pivot connection between the clamping arm and the support 206. Therefore, when the piston 133 is in... Figure 4 When extended, as shown, clamping arms 122 and 124 are in the open position, thereby defining a gap 140 between clamping portions 128 and 130 and allowing the film 200 to be conveyed through the gap to palletized goods.

[0058] like Figure 5 As shown, the actuating drive cylinder 132 operates directly in the reverse direction, that is, the drive piston 133 retracts into the cylinder, causing the two clamping arms 122 and 124 to rotate in opposite directions, thereby closing the gap 140 and thus firmly clamping or gripping the film 200 between the clamping arms. This is the closed position of the clamping arms. Optional grippers, such as elastic bands 142, may be included on the clamping portions 128 and 130 to provide a more secure grip between the clamp and the film.

[0059] Now refer to Figure 7 The stretch winding head assembly 12 is shown with the cover 34 removed, revealing the internal components. Notably, a load sensor 150 is mounted to the winding head assembly 12 and is operable to continuously monitor the tension in the film 200 during winding of goods. The load sensor 150, along with other controllable components of the stretch winding device 10, is under the control of a programmable controller 5, which... Figure 7 The diagram is shown below. The load sensor 150 does not control or change the film tension, but only measures and monitors the tension, providing input to the controller 5, which adjusts the film dispensing speed based on the film tension data from the load sensor 150.

[0060] The stretch wrapping head assembly 12 also includes a film cutting assembly 50, which includes a linearly extendable and retractable arm 52, at its distal end, i.e., an end that extends toward the palletized goods, having a pressure pad 54, a pair of vertical rollers 56a and 56b, and a film cutting hot wire 58 suspended between the rollers 56a and 56b such that the hot wire coincides with the external tangent between the two rollers 56. Considering the direction of rotation of the goods on the turntable 100 (i.e., arrow A), Figure 1 Roller 56a is considered the downstream roller and roller 56b is therefore the upstream roller. The film cutting assembly actuation cylinder (not shown), under the control of the programmable controller 5, operates to drive arm 52 from its retracted position (e.g., Figure 4 (As shown) to the extended position, as Figure 7 As shown. The operation of the thin film cutting assembly 50 is described in detail below.

[0061] Refer again Figure 1 The turntable 100 includes a plurality of drive rollers 102 mounted on a rotatable base 104. An encoder, shown schematically at 106, is mounted to the turntable 100. The turntable 100 moves along... Figure 1 Rotation occurs in the direction of arrow A, with a turntable drive motor (not shown); encoder 106 can be mounted to the drive motor instead of directly to the turntable. The turntable rotation speed and position are known based on encoder feedback. Other types of position indicators can be used in place of encoder 106.

[0062] As previously stated, the stretching and winding device 10, all its components, and the turntable 100 are under the control of the programmable controller 5. The operation of the device 10 will now be described in detail.

[0063] Certain operating parameters and standards are programmed into controller 5 for each item, i.e., each pallet of the box 152 being stretched and wound by device 10 or to be stretched and wound. These operating parameters and standards include:

[0064] a. The film dispensing point—that is, the film outlet point as defined above—maintains a known distance from the center point of the turntable 100;

[0065] b. The entangled goods are located in the center of the turntable;

[0066] c. The dimensions of the finished goods are known, based on existing data available from the palletizer controller that is assembling the goods;

[0067] d. Once the turntable 100 begins to rotate, the rotational speed is determined by data from the encoder 106, and the corner position of the cargo begins to change relative to the distribution point. The controller 105 begins to distribute the film to the cargo, the clamping arms 122 and 124 of the clamp assembly 120 open, and pressurized air is blown to the free end of the film through the air jet 48;

[0068] e. When the film is attached to the goods, the film tension is continuously measured and monitored by the load sensor 150, and the film tension data is transmitted to the programmable controller 5;

[0069] f. As the turntable rotates, the film is distributed at a certain speed—the release speed—determined by the film tension data provided to the controller 5 by the load sensor 150, ensuring that the film release is consistent with and appropriate to the measured film tension. Therefore, the required film release speed is determined by and responds to the film tension.

[0070] g. The film dispensing speed can be varied with offset or other factors to slightly increase or decrease the dispensing relative to the tension value;

[0071] h. When the bracket assembly 14 moves vertically relative to the cargo, the auger is compensated by tracking the change in the height of the film head relative to the height of the film when the film is engaged with the cargo;

[0072] i. If the palletizer or other system does not know the size characteristics of the goods, sensors can be used to determine the size of the goods and their position on the turntable, or operator input from the operator interface station can be used.

[0073] After setting the above parameters, the stretching and winding process begins. Stacked boxes 152 are placed on pallet 101, and the pallet moves to the center of turntable 100 with the help of drive rollers 102. It was previously noted that the dimensions of the goods have been known by controller 5.

[0074] like Figure 3As shown, the free end 212 of the film 200 is held by the clamping assembly 120. That is, the clamping arms 122 and 124 are in their engaged clamped position, with the film clamped between them. This is the normal situation when winding is not yet complete. When the clamps engage and hold the free end 212 of the film, the air blowing is preferably turned off, so no air is blown onto the film. The arm 52 of the film cutting assembly 50 is in the retracted position. The turntable rotation is initiated, and as the turntable rotates and the vertical position of the stretch winding head 12 is set to the desired position, the airflow through the air jet 48 is briefly initiated so that the free end 212 of the film is controlled. Then the clamping arms 122 and 124 move to their open position to release the clamp on the film and film blowing begins (i.e., pressurized air is blown onto the tail of the film). Shortly after the clamping arms 122 and 124 open, or optionally simultaneously with the clamp opening, film dispensing begins, and the film is dispensed through the pre-stretch roller 36 and through the dispensing point between the air tubes 46 and 48. Before the film is attached to the cargo, and with the clamping arms 122 and 124 in the open position, the free or loose end 212, i.e., the "tail" 212 of the film 200, has no support other than the "support" provided by pressurized air aligned with the film. The tail of the film is thus blown toward the cargo. Air is blown onto the traveling film until it is attached to the cargo, but once attachment occurs, the pressurized airflow can be stopped for the remainder of the winding cycle.

[0075] During pre-attachment, the pre-stretch roller 36 dispenses the film at a speed at which it would be dispensed if it were to adhere to the cargo. As the film is released from the pre-stretch roller 36, the tail 212 of the film contacts the surface of the cargo rotating on the turntable—the surface in contact with the film may be a side, an upper corner surface, or some other location, as described below. The contact between the film and the cargo is maintained by a continuous airflow blown onto the film, and the film adheres to the cargo directly or by means of the continuous contact between the film and the cargo after contact. In some cases, depending on various factors such as environmental factors, the nature of the cargo, etc., the cargo may rotate one or more revolutions before the film is attached to the cargo. However, given the continuous and consistent airflow from the blower pushing the film toward the outer surface of the cargo, the film will adhere reliably, such that the film remains in continuous contact with the cargo as it rotates. Once the film is attached to the cargo, film tension data is measured by the load sensor 150 and transmitted to the controller 5. As described above, the speed at which the film is dispensed from the stretch winding head assembly 12 is controlled by the controller 5 and reacts to the film tension data from the load sensor 150, as well as shutting off the pressurized airflow.

[0076] The vertical position of the bracket assembly can initially be located near the upper limit of the cargo so that the tail 212 of the film 200 attaches to the top of the box 152 or one of the upper corners. The film is then spirally wound downwards; the bracket assembly 14 moves downwards as the turntable rotates. Similarly, the tail of the film 200 can be blown to one side of the cargo, and in most cases the film tail is quickly captured to begin the winding operation; the bracket assembly 14 is vertically repositioned as needed to wind the cargo. Regardless of where the film tail contacts the cargo—i.e., on the side, upper corner surface, or other locations—the film adheres because it is continuously blown by air from the blower to contact the outer surface of the cargo. This contrasts with the prior art, in which the film is blown toward stationary cargo and the film is secured to the cargo by capturing the film between the box and pallet or between layers of the box. In other words, previously, using air to blow the film toward the cargo required the weight of the cargo to secure the film between one inner surface (e.g., the upper surface of the middle layer of the pallet or box) and another inner surface (e.g., the lower surface of the box layer).

[0077] The wrapping continues until the goods are completely wrapped. Once the goods are completely wrapped, the film 200 is cut by the operation of the film cutting assembly 50. The cutting arm assembly 50... Figure 1 The center is shown in the retracted or original position. This is the position used during the winding operation. When the goods are fully wound, the rotation of the turntable 100 is when the goods are in the retracted or original position. Figure 1 Stop at the indicated position. The blower operation is turned off, and the diaphragm is held by clamping arms 122 and 124. Controller 5 activates arm 52 to extend to... Figure 7 and 10 The extended position is shown. In this position, the pressure pad 54 contacts the side of the palletized and wrapped goods, and the downstream roller 56a contacts the film 200; the upstream roller 56b may or may not contact the goods. After the goods are wrapped, the pressure applied to the film by the pressure pad 54 serves as a method of pressing the film against the goods to secure the film.

[0078] like Figure 10 As shown, when the pad 54 contacts the cargo, the cutting hot wire 58 is energized, heating the wire and thus cutting the film when the telescopic arm 52 is in its extended position. At this time, the film 200 deflects through the upstream and downstream rollers 56a and 56b; the hot wire 66 is close to the film, causing it to be cut even without actual contact between the film and the wire. Furthermore, avoiding direct contact between the wire and the film helps prevent residual molten film from accumulating on the wire. The pad 54 contacts the cargo and thus presses the cut edge of the film onto the cargo, preventing loose film ends.

[0079] Once the film 200 is cut, the arm 52 retracts to its original position and the wrapped goods are removed from the turntable.

[0080] The operation of the stretch winding apparatus 10 under conditions of film breakage, anticipated or predicted film breakage, and other operating conditions will now be described in detail. As used herein, the term "film breakage event" refers to a condition that leads to film breakage. As described below, a film breakage event can be an unpredictable breakage of the film, or a film breakage event may be caused by conditions intentionally leading to film breakage, such as predicted film breakage, and intentional film cutting, such as occurring at the end of a winding cycle.

[0081] Throughout the entire process of attaching the film 200 to palletized goods and distributing the film 200 to the goods, the load sensor 150 monitors and detects film tension information, and this information is transmitted to the controller 5, which communicates with the load sensor 150. The load sensor 150 also monitors and detects film tension information when the film is not attached to the goods, in which case the measured cargo tension may be zero. The controller 5 is programmed with operating specifications for film tension, referred to here as X (i.e., film tension = X), which may depend on the type of film and its specific characteristics (e.g., film type, film thickness, film manufacturer, etc.), but in all cases includes the following parameters:

[0082] a. Nominal film tension range. This is the range of values ​​for the film tension X, within which the film tension is considered satisfactory, and therefore winding is considered to be proceeding as expected. This range has an upper limit Z and a lower limit Y, and can be expressed as [Z,Y] or Z≥X≥Y. Depending on the conditions and film type, the difference between the upper limit Z and X, and the difference between the lower limit Y and X, need not be equal within the range. In other words, the numerical range between X and the upper limit Z can be greater than the numerical range between X and the lower limit Y, and vice versa.

[0083] b. Out-of-range film tension. Based on the film tension X detected by the load sensor 150 and as programmed in the controller 5, there are two basic out-of-range conditions.

[0084] 1) If the film tension X detected by the load sensor 150 is greater than the upper limit value Z, then the film tension X is considered to have exceeded the upper limit value of the film tension. This situation is considered out of range because it is an accurate prediction of impending film breakage. Impending film breakage can be predicted by a film tension X higher than the upper limit value Z because it is well known that for a particular film in use, when the film tension exceeds the upper limit value, the film will typically break.

[0085] 2) If the film tension X detected by the load sensor 150 is less than the lower limit value Y. If this situation exists, the film tension X is considered to be below the lower limit value of the film tension. This situation is also considered out of range because it indicates an impending film breakage or that a breakage has already occurred. When the detected film tension X drops below the lower limit value Y, it is known that the film has broken, or for example, the elasticity of the film has been compromised, resulting in insufficient tension applied to the film during winding, which is a prediction of impending film breakage. When a winding cycle is completed and the film has been cut, the detected film tension X equals zero.

[0086] As detailed below, there are multiple operating sequences applicable to the conditions detected by the load sensor 150.

[0087] a. Film Breakage. As mentioned above, when a film breaks during the winding operation, there is a danger that the newly generated film tail may retract towards the shrink wrap head and become entangled in the equipment. The operating procedure described below is designed to control the film tail generated by the breakage to prevent entanglement. When the film breaks during the winding operation, the tension value X detected by the load sensor 150 immediately drops below the lower limit value Y. When the tension value X is below the lower limit value Y, the programmable controller 5 immediately moves the clamping arms 122 and 124 of the clamping assembly 120 to the clamping position. At the same time, the controller stops feeding the film through the shrink wrap head. The film tail is captured between the clamping arms, and the palletized goods continue to rotate on the turntable. The film breakage event of the nature just described is an unintentional film breakage.

[0088] As the clamping arms capture and interrupt film dispensing, the system is ready to reattach the film to the cargo in the same manner as described above regarding the initial attachment of the film to unwound cargo. In this case of film breakage, the only difference is that the vertical position of the shrink wrapping head can move vertically up or down, such that when the film is reattached, the area of ​​the partially broken cargo is wrapped with the reattached film. This ensures a secure wrapping of the cargo and prevents any loose film tails from hanging on the cargo. Furthermore, a blower may not be necessary during the reattachment process, depending on, for example, the type of film used.

[0089] b. Predicted or anticipated film breakage. As described above, there are two possible scenarios where the controller 5 is programmed to determine that film breakage is anticipated and thus initiate corrective operations to prevent film tail tangling that may accompany breakage. The first scenario is that the film tension X detected by the load sensor 150 is greater than the upper limit value Z. The second scenario is that the film tension X is less than the lower limit value Y. In both cases, the film may be intact, but the detected film tension is a precursor to impending breakage. Therefore, corrective measures are taken to prevent uncontrolled breakage and possible film tail retraction caused by film tangling accompanying the breakage. When either scenario occurs, and upon detection, the controller 5 immediately moves the clamping arms 122 and 124 of the clamp assembly 120 to the clamping position. Simultaneously, the controller stops feeding the film through the shrink wrapping head. The turntable 100 continues to rotate. If the film remains intact, the clamps firmly hold the film, and film dispensing stops, the film breaks between the clamps and the cargo. In this scenario, the film breakage is caused by the clamp gripping the film, but the breakage is controlled; retraction of the film tail and potential entanglement with other components of the shrink wrap assembly are prevented. The type of film breakage event described in this paragraph is intentional because the film does not actually break until a predicted or anticipated breakage is detected by tension measurement, and the clamp is moved to the closed position to induce actual film breakage, thereby controlling retraction.

[0090] c. For the purposes of this description, another type of film breakage event occurs at the end of the winding cycle, when the goods are fully wound and the film is intentionally cut by the film cutting assembly 50 as described above. Similar to the predicted or anticipated film breakage described above, film breakage events caused by intentional cutting of the film after the winding cycle are intentional film breakage.

[0091] The film is reattached in the same manner as described above regarding the reattachment of the film after it has broken, by adjusting the vertical position of the shrink wrapping head so that when film reattachment occurs, the area on the broken goods is wrapped with the reattached film.

[0092] Some palletizing operations offer parallel cargo building and stretch wrapping. In other words, cargo is built on pallets and stretch wrapped while the cargo is being built. The principles of the invention described above also apply to this palletizing / stretch wrapping machine configuration, for example, using the pre-stretch assembly and clamping assembly described above, the film can be blown onto an empty pallet on the turntable before the first layer of boxes is placed onto the pallet; typically, the film is captured under the first layer of boxes. Stretch wrapping occurs simultaneously as the stacking process continues. The clamping assembly 120 provides greater reliability when blowing the film onto an empty pallet because the tail of the film is always controlled by the clamping arms 122, 124 before being blown onto the pallet, thus eliminating the risk of film tangling. This also applies to cases where the film is first blown onto pallets that have already been built one or more layers. In this case, the film is blown onto the existing one or more layers of boxes, and stretch wrapping and palletizing occur simultaneously. Again, the risk of film tail tangling is eliminated or greatly reduced because the clamps manage and control the film tail before joining. Therefore, it should be understood that, as used herein, the term "cargo" can refer to an empty pallet, a partially loaded pallet, or a fully loaded pallet.

[0093] In one embodiment of the invention, the stretch winding apparatus 10 may include an optional optical thin-film sensor located downstream of the film pre-stretch roller 36. The sensor detects the presence (or absence) of the film and, optionally, the relevant conditions of the film, as detailed below. The sensor is connected to the stretch winding head assembly 12 to detect whether the film 200 has not left the pre-stretch assembly 32 due to a momentary change in the film's properties. As previously described, the sensor is an optical sensor that can detect the presence of the film 200 and, optionally, the position or characteristics of the film 200. If the sensor detects that the film is no longer leaving the pre-stretch assembly, it indicates that the film 200 on the roll 30 may have been used up, or there may be other malfunctions. Alternatively, a different type of sensor may be used instead of the original sensor to detect whether the film is actually being distributed through the pre-stretch roller, or to detect defects such as partial film tears or holes in the film based on optical characteristics. For example, when the film is broken, it vibrates. This causes a change in the optical characteristics "seen" by the sensor, indicating an out-of-range condition. Furthermore, the sensor can be adapted to sense the film tail-to-cargo bonding by continuously monitoring the integrity of the film web between the pre-stretched assembly 32 and the cargo. If the integrity of the film web is compromised, the sensor detects the problem (again, through changes in optical properties), and the controller 5 automatically takes action to ensure cargo containment by distributing additional film in the cargo area where the film defect is located, for example, to wrap the broken cargo section, ensuring complete film wrapping of the entire cargo. The sensor described above is an optical sensor, but other sensor technologies, such as ultrasound, can be used as alternatives.

[0094] Those skilled in the art will readily understand that the invention described herein and illustrated in the accompanying drawings can be modified in certain ways to produce equivalent devices without departing from the spirit of the invention. For example, while the invention is described using a turntable on which palletized goods are placed, the desired relative rotational motion between the goods and the stretch wrapping head can also be generated by keeping the goods stationary and rotating the stretch wrapping head about the stationary goods. Therefore, the term rotation axis herein describes the central point of these different methods of generating relative rotation between the goods and the wrapping head, namely, (a) in which the stationary wrapping head is used in conjunction with the rotating goods, and (b) in which the stationary goods are used in conjunction with the rotating wrapping head.

[0095] As another example, the pre-stretch assembly 32 can be modified such that the last pre-stretch roller (i.e., the most downstream roller in terms of film dispensing direction) is positioned so that the film exits the roller without a downstream idler roller. This is accomplished by tilting the assembly so that the film can be fed directly from the last pre-stretch roller into the space between air jets 44 and 46. Pressurized air can be supplied in many other ways, such as via a pressurized air tank. Other modifications will be apparent to those skilled in the art.

[0096] The present invention has been described with reference to preferred and exemplary embodiments, but it should be understood by those skilled in the art that the spirit and scope of the invention are not limited to these embodiments, but extend to various modifications and equivalents, as defined in the appended claims.

Claims

1. A device for preventing film tangling in a stretch wrapping machine for wrapping goods, comprising: A vertically movable dispensing head having at least a pair of pre-stretched rollers suitable for dispensing films; A first drive mechanism is used to drive the at least one pair of pre-stretched rollers to dispense the film; A compressed air source blows compressed air through an air jet aimed at the film after the film is dispensed from the at least one pair of pre-stretch rollers, thereby blowing the film toward the cargo. A film tension device for continuously measuring film tension to generate film tension values ​​and transmitting the film tension values ​​to a controller, wherein an acceptable tension value range is stored in the controller, and a film breakage event is defined as a film tension value that is higher or lower than the acceptable tension value range; A second drive mechanism is adapted to provide relative rotation between the cargo and the dispensing head; A film clamp is mounted to the dispensing head between the dispensing head and the cargo, wherein the film clamp is adapted to hold the film in the event of a film breakage event, and wherein the film clamp is adapted to hold the film before the film breaks.

2. The apparatus according to claim 1, wherein, When a film breakage event occurs, the controller stops film dispensing and simultaneously causes the film clamp to hold the film.

3. The apparatus according to claim 1, characterized in that, The film breakage is caused by the film clamp that holds the film.

4. The apparatus according to claim 1, characterized in that, The film has a free end after it breaks, and the free end of the film is prevented from retracting and tangling after the film clamp holds the film.

5. The apparatus according to claim 1, characterized in that, The film is dispensed at a rate responsive to the film tension value.

6. A method for preventing film tangling in a stretch wrapping machine for wrapping goods, comprising the following steps: a) Provides relative rotation between the film conveyor head and the cargo; b) Install a film clamp at a fixed position on the film conveying head; c) Dispensing film from the film conveying head and attaching the film to the goods; d) Measure the tension in the film; e) If the measured tension is higher than the upper limit or lower than the lower limit, the clamp is closed to hold the film before film rupture occurs, and film dispensing is stopped simultaneously. In this case, closing the clamp to hold the film causes the film to break.

7. The method of claim 6, comprising blowing air onto the film at least intermittently during relative rotation.

8. The method according to claim 6, wherein, The relative rotation does not stop, and the film is reattached to the cargo after step e) by: a) Blow air into the film; b) Open the clamp and simultaneously resume film dispensing from the film delivery head.

9. The method of claim 6, wherein the film is dispensed at a speed determined by the measured film tension.

10. A device for preventing film tangling in a stretch wrapping machine for wrapping goods, comprising: A dispensing head for dispensing thin films; A film holder is mounted on the dispensing head and located between the dispensing head and the cargo; the film holder is movable between a film holding position and a film non-holding position. A controller communicates with a film tension measuring device suitable for measuring film tension, such that a film tension value from the film tension measuring device is transmitted to the controller, wherein the controller is programmed to have an acceptable range of film tension values ​​with upper and lower limits. A drive mechanism for dispensing a film from the dispensing head at a speed determined by the film tension value; If the film tension value is outside the acceptable range, the film holder moves to the film clamping position, and A film fracture event is defined as a film tension value outside the acceptable range of film tension values, and the film fracture event occurs before the film fractures.

11. The apparatus of claim 10, comprising a pressurized air source, wherein after the film is dispensed from the dispensing head, air is blown at least intermittently through an air jet aimed at the film.

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