Patent Application
20240199262
The present invention relates to apparatus and methods for wrapping a load, and more specifically, a stretch wrapping machine for wrapping a palletized load of items with stretch wrapping material, in which the machine includes components for controlling a free film tail to prevent unintentional engagement of the film tail with components of the stretch wrapping machine.
Stretch wrapping is a commonly used method of protecting palletized loads of material for shipping. Described generally, stretch wrapping involves wrapping a specialized film around a stack of items such as cases that have been arranged on a pallet. The film is wrapped around the cases under tension and thereby stabilizes the stack to minimize the risk of damage during shipping. Tension can be provided by the memory recovery of pre-stretched film, and tension may also be created by resistance between the load and film dispenser or a combination of the two.
There are many styles and designs of automated or semi-automated stretch wrapping machines, many of which work in cooperation with automated palletizing machines that build the palletized loads. The stretch wrapping machines provide relative rotation between the palletized load and a dispenser that holds a roll of stretch wrapping film. Typically, either the pallet and load are stationary with the dispenser rotating around the load, or the pallet and load are rotated relative to a stationary dispenser. Either way, the stretch wrapping film is wrapped helically up and down the load under tension to stabilize it.
Stretch wrapping machines are used in highly automated production and packaging lines and must be able to keep up with throughput rates of the other equipment used in the palletizing operation so that the stretch wrapping operation does not slow the overall production. As such, the devices often operate at relatively high production rates themselves. But stretch wrapping is not always a simple operation. For example, it is known that with a rectangular load on a pallet the demand for the stretch wrapping film varies as the corners of the load pass by the film dispensing point: the payout demand for film increases as the corner of the load passes the dispensing point and decreases as the film is being dispensed across the side of the load between corners. In addition to the payout rate, the amount of tension on the film has a direct impact on the stability of the load when completely wrapped. Many stretch wrapping machines use tensioning devices to control the tension on the film. However, tension forces vary with rotational position and as a result, proper tensioning is often difficult to maintain with high throughput rates. When the film breaks for any number of reasons (including excessive tension), the operation of the stretch wrapping device may be stopped or slowed while the film is reattached to the load, either automatically or with operator intervention.
U.S. Pat. No. 10,604,284, the entire disclosure of which is incorporated herein by this reference, describes a stretch wrapping apparatus that wraps a palletized load that is placed on a rotating turntable. A stretch wrapping head feeds pre-stretched wrapping film toward the rotating load and air jets blow the tail of the film onto the load. Relative rotational movement is created between the wrapping head and the load and the free end of the film is unsupported by any mechanical structure and is directed toward the load only with air from the jets. The free end of the film attaches to an outer surface the load and the wrapping head moves vertically so that the load is helically wrapped. Film is dispensed at a rate to provide payout of film that is consistent with the demand as each load corner transitions through its relative distance change from the dispensing point based on calculations intervals. A sensor detects changes in the optical character of the film—defects—to determine an out of bounds condition such as a film break.
A free film end, also referred to at times herein as a “film tail” is created in three different situations. First, when the free end of the film is being dispensed toward a load prior to attachment of the film tail to the load. Second, when a wrapping operation is complete and the film has been cut, and third, when a film break occurs during wrapping operations. In a stretch wrapping machine such as that described in U.S. Pat. No. 10,604,284, which blows the film tail toward the load, it has been found that positive control of the film tail is necessary to insure that the film tail does not become entangled with the stretch wrapping head. Thus, in any of the three conditions described above where a film tail is created, it is desirable to prevent the film from becoming entangled in the stretch wrapping machine. If entanglement occurs, wrapping operations are slowed and if the entanglement is serious enough, operator intervention may be required.
In the first situation described above, where the film tail is being dispensed toward the rotating load prior to engagement of the film to the load, positive control of the film tail retains the film in a desired position relative to the load so that the film will be blown toward the load for engagement as described in U.S. Pat. No. 10,604,284. In the second situation, that is, when a wrapping operation is complete and the film has been cut, positive control of the film prior to or concurrent with film cutting prevents film tail spring-back and the risk of entanglement from cutting the film under tension, and also retains the film in an ideal position for it to be blown toward the next load to be wrapped. The third situation, namely, when there is a break in the film during wrapping operations, presents the most serious risk of film entanglement with the stretch wrapping head. Because there is tension on the film as it is being wrapped, when a break occurs the film tail created by the break may recoil or snap back and thereby be entangled with the stretch wrapping 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 drape downwardly under the force of gravity. This can cause a couple of problems. First, the draping tail may become entangled with other equipment. Second, a long, uncontrolled, and draping film tail may be difficult for the blower to engage for reattachment to the load. More problematically, when a film break occurs an uncontrolled film tail may become engaged with film that is already being dispensed through the pre-stretch rollers, causing the film tail to wrap up with the in pre-stretch roller system when it is powered up for the next blow out. This can quickly damage the pre-stretch roller system and can lead to downtime and expensive repairs.
Known stretch wrapping machines that do not use a blower to attach film to a load use a clamp that is mounted in a position that is fixed relative to the rotation device and the load, not in a position that is fixed relative to the stretch wrapping head. For instance, a turntable may have a clamp to control film and allow attachment of the film to the next load. Or in the case of a fixed load with a stretch wrapping head that rotates around the load, a fixed clamp adjacent to the stationary load is used to control film. Neither of these arrangements allow for control of film tail resulting from a film break, and do not contemplate or prevent entanglement of the film tail.
There is an ongoing need for improved stretch wrapping devices that balance the needs and challenges of keeping up with production rates while wrapping loads with proper film tension to correctly stabilize the loads. There is a further need for improved stretch wrapping apparatus that prevents the problems described above with respect to uncontrolled film tails in combination with the use of blown film as a method of load attachment that is achieved by blowing film towards (a) an already partially wrapped load with broken film tail managed to prevent entanglement until reattachment is accomplished with film blow, (b) to a load built without film with film tail managed and controlled between the prior film cut and film attachment to new load, (c) an un-started load where the film is blown onto an empty pallet prior to first layer deposit (where concurrent palletizing and wrapping is being done), or (d) film blown between an already positioned layer and the next layer deposit (for instance, where concurrent palletizing and wrapping is occurring). Blown film reattachment may be contrasted with current industry practice of a film tail clamp that is in a fixed position relative to the load while differential rotation occurs; with blown film as described herein, the tail clamp is in a fixed position relative to the film dispensing position rather than the load and thereby prevents entanglement caused by recoil.
The present invention comprises an improved apparatus and method for automated stretch wrapping of a palletized load. The apparatus utilizes a film tension feedback parameter derived from a film tension control load cell. The load cell continuously monitors and measures film tension during wrapping operations and based on the film tension and the film payout rate is determined by the film tension as measured by the load cell. The film is paid out in reaction to the film tension and film payout rate, or film speed, is adjusted in a reactionary manner during relative rotation; no proactive film speed calculations are performed. The tension values are monitored and used to determine when a film out of bounds condition occurs, namely, a film break has occurred, or when a possible film break is about to occur or when the film has been cut at the end of a wrapping cycle. When any of these out of bounds conditions occur, film clamps engage the film prior, concurrent with or slightly after the out of bounds conditions occur. Relative rotation of the load to film dispenser may continue, so if the out of bounds condition is a predicted film break, a controlled film break is accomplished. That is, with the clamps engaging the film, with film delivery stopped, and relative rotation between the dispenser and the load continuing, the film breaks downstream of the clamps in a relatively controlled manner, eliminating the risk of recoil and entanglement. The broken film tail may then be quickly and reliably reattached to the rotating load in a desired position. For example, the vertical position of the stretch wrapping head may be changed subsequent to the break so that the film tail is blown toward the load, and reattached to the load such that the film overwraps the broken, free end of the film that is on the load. When the stretch wrapping head is in the desired vertical position, the clamps are released, film blow is enabled and film delivery is resumed to continue wrapping automatically without interruption.
The sensitivity of the load cell thus allows for control of predictive film break (in addition to actual film break) and for reattachment when relative rotation continues with an increase in film dispensing rate to match relative rotation speed.
The invention will be better understood and its numerous objects and advantages will be apparent by reference to the following detailed description of the invention when taken in conjunction with the following drawings.
The primary structural components of stretch wrapping apparatus 10 are described first with reference to the drawings. Operational characteristics and functions are then described.
Stretch wrapping apparatus 10 generally comprises a stretch wrapping head assembly 12 that is mounted to a carriage assembly 14 that is vertically reciprocally mounted on a frame 16. A turntable 100 is located immediately adjacent stretch wrapping head assembly 12. As seen in
An enclosure 500, shown partially in
Stretch wrap head assembly 12 comprises components described below, which are mounted to a horizontal support member 28 that is mounted to carriage assembly 14 so that vertical movement of the carriage assembly directly moves the stretch wrap head assembly. A roll 30 of stretch wrap film 200 is mounted on a mandrel (not shown) operatively adjacent to the head assembly 12 with the longitudinal axis of the roll vertically oriented relative to the ground plane and such that the film 200 may be fed into the head assembly as described below. A film pre-stretch assembly shown generally at 32 is adjacent the roll 30 and includes a pre-stretch drive motor contained in a cowling or enclosure 34; the drive motor is operatively connected to and drives pair of vertically oriented pre-stretch drive rollers 36. A film guide roller 38 is located between the drive rollers 36. In some instances, and in some installations more than one pair of pre-stretch rollers 36 may be used and additional guide rollers 38 may be utilized.
The driven rollers 36 define the active film payout mechanism for dispensing the film 200. Film 200 is fed over the film guide roller 38 and then through driven rollers 36. When pre-stretch film dispensing occurs, the drive rollers rotate at different speeds which pre-stretches film between the adjacent rollers. Non pre-stretch dispensers generally use one driven roller or using relative motion between the load and dispenser, film is pulled directly from the roll that usually has some type of friction clutch to create film tension.
Directly downstream of the film drive rollers 36 are a pair of oppositely mounted and vertically oriented film exit guide rollers 202 and 204. The guide rollers 202 and 204 are mounted to upper and lower mounting brackets, 206 and 208. As detailed below, the film 200 is fed from the drive rollers 36 through the film exit guide rollers 202 and 204. A tangent line between the film guide exit rollers 202 and 204 defines the film exit point for film delivered from the pre-stretch assembly 32 toward the load. Pressurized air is delivered via one or more air tubes to feed compressed air to two vertically oriented and parallel film training air jet tubes 44 and 46. The air jet tubes 44 and 46 include plural air jets 48, which are openings through which pressurized air is directed onto film 200, as detailed below, as the film is blown toward the boxes 152 on pallet 101. The air jet tubes 44 and 46 are positioned adjacent and one on each side of the film exit guide rollers 202 and 204 such that film 200 being fed through and traveling through the exit guide rollers is fed between the two air jet tubes and the air expelled from the air jets 48 is directed onto the film. Plant air is the preferred source of air for delivery to the air jet tubes 44 and 46 because it is more economical than, for example, an air blower motor, and plant air is available instantaneously while pressurized air from a blower motor typically requires spool up time. That said, in some situations an air blower motor may be utilized successfully, and could be mounted, for example, in enclosure 42.
A clamp assembly 120 is mounted to upper bracket 206 as best illustrated in
Operation of drive cylinder 132 in the opposite directly, namely, to retract driven piston 133 into cylinder barrel causes the two clamp arms 122 and 124 to rotate the opposite directions and to thereby close gap 140 and to thus securely clamp or grip the film 200 between clamp arms as shown in
With reference now to
Stretch wrap head assembly 12 further comprises a film cut assembly 50 that comprises a linearly extensible and retractable arm 52 that has on its distal end, that is, the end that may be extended toward a palletized load, a pressure pad 54, a pair of vertical rolls 56a and 56b, and a film cut hot wire 58 strung between the rolls 56a and 56b such that the hot wire is coincident with the outer tangent between the two rolls 56. Considering the direction of load rotation on turntable 100 (i.e., arrow A,
With returning reference to
As noted previously, the stretch wrap apparatus 10 and all components, and turntable 100, are under the control of a programmable controller 5. Operation of apparatus 10 will now be described in detail.
Certain operational parameters and criteria are programmed into controller 5 for each load, i.e., each pallet of boxes 152 that is or will be stretch wrapped by apparatus 10. Those operational parameters and criteria include
With the foregoing parameters being set, the stretch wrapping procedure begins with a pallet 101 having a completed stack of boxes 152 positioned thereupon is moved onto the center of turntable 100 with the assistance of driven rollers 102. The load dimensions are known by controller 5 as indicated previously.
The free end 212 of film 200 is retained by clamp assembly 120 as seen in
During pre-attachment, the film is dispensed by the pre-stretch rollers 36 at the rate at which the film would be dispensed if the film were attached to the load. As the film is paid out by the pre-stretch drive rollers 36 the tail 212 of the film makes contact with a surface of the load that is rotating on the turntable—as noted below, the surface that the film contacts may be a side surface, an upper corner surface, or some other location. Contact between the film and the load is sustained by the continuous flow of air being blown onto the film and the film attaches to the load after it makes contact, either directly or by virtue of sustained contact between the film and the load. In some instances, depending upon a variety of factors such as environmental factors, the nature of the load, etc., the load may rotate through a complete rotation or more before the film attaches to the load. However, the film will positively attach given the sustained and continuous air stream from the blower that pushes the film against an outer surface of the load, such that the film makes sustained contact with the load as it rotates. Once the film attaches to the load, film tension data is measured by load cell 150 and transmitted to controller 5. As indicated above, the rate at which film is dispensed from stretch wrapping head assembly 12 is controlled by controller 5 and is reactive to the film tension data from load cell 150, and the flow of pressurized air is off.
The vertical position of the carriage assembly may be initially located near the upper limit of the load so that the tail 212 of the film 200 attaches near the top or on one of the upper corners of the boxes 152. The film is then wrapped in a downward helix; the carriage assembly 14 is moved downward as the turntable rotates. Equally well, the tail of the film 200 may be blown onto a side of the load where it catches quickly in most instances to begin the wrapping operation; the carriage assembly 14 is repositioned vertically as required to wrap the load. Regardless of the position at which the film tail contacts the load, i.e., on a side surface, an upper corner surface, or another location, the film attaches because it is continuously blown into contact with an outer surface of the load by the air from the blower. This may be contrasted with the prior art, where film was blown toward a stationary load and where the film was secured to the load by virtue of capturing the film between the cases and the pallet, or between layers of the cases. In other words, prior uses of air to blow film toward a load required the weight of the load to secure the film between one inner surface (e.g., the pallet or an upper surface of an intermediate layer of cases) and another inner surface (e.g., the lower surface of layer of cases).
Wrapping continues until the load has been completely wrapped. Once the load is completely wrapped the film 200 is cut by operation of film cut assembly 50. The cut arm assembly 50 is shown in the retracted or home position in
When the pad 54 makes contact with the load as shown in
Once the film 200 has been cut the arm 52 is retracted to its home position and the wrapped load is transported off the turntable.
Operation of the stretch wrap apparatus 10 in the case of a film break, anticipated or predicted film break, and other operational conditions are now described in detail. The term “film break event” as used herein refers to conditions that result in a break of the film. As detailed below, a film break event may be an unanticipated break of the film, or a film break event may arise from conditions that result in an intentionally-caused break of the film, as in a predicted film break, and also a film cut that is intentional, such as occurs at the end of a wrapping cycle.
At all times during which the film 200 is attached to a palletized load and the film 200 is being dispensed toward the load, load cell 150 monitors and detects the film tension information and that information is transmitted to controller 5, which is in communication with the load cell 150. Load cell 150 also monitors and detects film tension information when the film is not attached to a load, in which case the load tension measured may be a zero value. Controller 5 is programmed with operational specifications for film tension, referred to herein as X (i.e., film tension=X), which may be dependent upon the type of film and its specific characteristics (such as type of film, film thickness, film manufacturer, etc.), but in all cases which include parameters for:
As detailed below, there are a variety of operational sequences that apply to the conditions recited above as detected by the load cell 150.
With the film captured between the clamp arms and the film dispensation discontinued, the system is ready for reattachment of the film to the load in the same manner as described above with respect to the initial attachment of film to an unwrapped load. The only difference in this situation with a film break is that the vertical position of the shrink wrap head may be moved vertically, up or down, so that when film reattachment occurs the area where the break occurred on the partially-wrapped load is overwrapped with the reattached film. This ensures a secure wrap for the load and prevents any loose film tails hanging from the load. Moreover, during reattachment use of the blower may not be necessary depending on, for instance, the type of film being used.
Reattachment of the film proceeds in the same manner as described above with respect to the reattachment of film to after a film break, with adjustment of the vertical position of the shrink wrap head so that when film reattachment occurs the area on the load where the break occurred is overwrapped with the reattached film.
Some palletizing operations provide for concurrent load building and stretch wrapping. Said another way, the load is built on the pallet and stretch wrapping occurs as the load is being built. The principles of the invention described above are equally applicable in this type of a palletizing/stretch wrapping machine configuration, For example, using the pre-stretch assembly and clamp assembly described above, film may be blown onto an empty pallet that is on the turntable prior to the first layer of boxes being deposited onto the pallet; typically, the film is captured under the boxes of the first layer. As the layer-building continues, stretch wrapping occurs simultaneously. The clamp assembly 120 provides for much greater reliability in blowing the film onto the empty pallet because the tail of the film is always controlled by clamps 122, 124, prior to blowing onto the pallet, thereby eliminating the risk of film entanglement. The same is true where the film is first blown onto a pallet that has one or more layers already built. In that case, the film is blown onto the existing layer or layers of boxes and stretch wrapping is simultaneous with palletizing. Again, film tail entanglement risk is either eliminated or greatly reduced because the clamps manage and control the film tail prior to engagement. It will be appreciated therefore that as used herein, the term “load” may refer to an empty pallet, a partially loaded pallet, or a fully loaded pallet.
In an embodiment of the invention, stretch wrap apparatus 10 may include an optional, optical film sensor 40 is positioned downstream of the film drive rollers 36. Sensor 40 detects the presence (or absence) of film and optionally, the relative condition of the film, as detailed below. Sensor 40 is attached to the stretch wrapping head assembly 12 to sense if film 200 is not exiting the pre-stretch assembly 32 because the character of the film momentarily changes. As noted, sensor 40 is an optical sensor that can detect presence and optionally the position or character of film 200. If sensor 40 detects that film is no longer exiting the pre-stretch assembly, it indicates it is likely that the film 200 on roll 30 has run out, or there is some other failure. Optionally, a different type of sensor can be used in place of sensor 40 to detect if the film is actually being dispensed through the pre-stretch rollers, or detect defects such as partial film tears or holes in the film based on optical characteristics described below. When there is, for example, a break in the film the film flutters. This causes changes in the optical characteristics “seen” by sensor 40 and this is indicative of an out of bounds situation. Further, the sensor 40 may be adapted to sense engagement of the tail of the film to the load by continuous monitoring of the integrity of the film web between the pre-stretch assembly 32 and the load. If film web integrity has been compromised, the problem is detected by sensor 40 (again, by optical characteristic changes) and action will automatically be taken via controller 5 to insure load containment by dispensing additional film in the area of the load where the film defect was encountered in order to, for example, overwrap the portion of the load where the break occurred to insure complete film wrapping of the entire load. Sensor 40 is described above as an optical sensor, but other sensor technologies exist that may be used instead, such as ultrasonics.
Those of skill in the art will readily appreciate that invention described herein and illustrated in the drawings may be modified in certain manners to create equivalent equipment without departing from the nature of the invention. For example, while the invention has been described as used with a turntable on which a palletized load is positioned, it is equally possible to create the required relative rotational motion between the load and the stretch wrapping head by keeping the load stationary and by rotating the stretch wrapping head around the stationary load. Accordingly, the term rotational axis is used herein to describe the center point for both a of these different methods of creating relative rotation between the load and the head, i.e., (a) where a stationary head used in combination with a rotating load, and (b) where a stationary load used in combination with a rotating head.
As another example, the pre-stretch assembly 32 may be modified such that the last pre-stretch roller (i.e., the most downstream roller in terms of film dispensing direction) is positioned such that film exits the roller without a downstream idler roller. This is done by canting the assembly so that film is fed directly off the last pre-stretch roller into the space between the air tubes 44, 46. Pressurized air may be supplied in numerous additional ways, for instance, a canister of pressurized air to name but one of many examples. Other modifications will be apparent to those of skill in the art.
The present invention has been described in terms of preferred and illustrated embodiments, it will be appreciated by those of ordinary skill that the spirit and scope of the invention is not limited to those embodiments, but extend to the various modifications and equivalents as defined in the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2020/063101 | 12/3/2020 | WO |
