FIELD OF THE INVENTION

The invention generally relates to wrapping loads with packaging material through relative rotation of loads and a packaging material dispenser.

BACKGROUND OF THE INVENTION

Various packaging techniques have been used to build a load of unit products and subsequently wrap them for transportation, storage, containment and stabilization, protection and waterproofing. One system uses wrapping machines to stretch, dispense, and wrap packaging material around a load. The packaging material may be pre-stretched before it is applied to the load. Wrapping can be performed as an inline, automated packaging technique that dispenses and wraps packaging material in a stretch condition around a load on a pallet to cover and contain the load. Stretch wrapping, whether accomplished by a turntable, rotating arm, vertical rotating ring, or horizontal rotating ring, typically covers the four vertical sides of the load with a stretchable packaging material such as polyethylene packaging material. In each of these arrangements, relative rotation is provided between the load and the packaging material dispenser to wrap packaging material about the sides of the load.

A primary metric used in the shipping industry for gauging overall wrapping effectiveness is containment force, which is generally the cumulative force exerted on the load by the packaging material wrapped around the load. Containment force depends on a number of factors, including the number of layers of packaging material, the thickness, strength and other properties of the packaging material, the amount of pre-stretch applied to the packaging material, and the wrap force or tension applied to the load while wrapping the load. An insufficient containment force can lead to undesirable shifting of a wrapped load during later transportation or handling, and may in some instances result in damaged products. On the other hand, due to environmental, cost and weight concerns, an ongoing desire exists to reduce the amount of packaging material used to wrap loads, typically through the use of thinner, and thus relatively weaker packaging materials and/or through the application of fewer layers of packaging material. As such, maintaining adequate containment forces in the presence of such concerns can be a challenge.

In particular, wrappers have historically suffered from packaging material breaks and limitations on the amount of wrap force applied to the load (as determined in part by the amount of pre-stretch used) due to erratic speed changes required to wrap loads. Were all loads perfectly cylindrical in shape and centered precisely at the center of rotation for the relative rotation, the rate at which packaging material would need to be dispensed would be constant throughout the rotation. Typical loads, however, are generally box-shaped, and have a square or rectangular cross-section in the plane of rotation, such that even in the case of square loads, the rate at which packaging material is dispensed varies throughout the rotation. In some instances, loosely wrapped loads result due to the supply of excess packaging material during portions of the wrapping cycle where the demand rate for packaging material by the load is exceeded by the rate at which the packaging material is supplied by the packaging material dispenser. In other instances, when the demand rate for packaging material by the load is greater than the supply rate of the packaging material by the packaging material dispenser, breakage of the packaging material may occur.

When wrapping a typical rectangular load, the demand for packaging material typically decreases as the packaging material approaches contact with a corner of the load and increases after contact with the corner of the load. When wrapping a tall, narrow load or a short load, the variation in the demand rate is typically even greater than in a typical rectangular load. In vertical rotating rings, high speed rotating arms, and turntable apparatuses, the variation is caused by a difference between the length and the width of the load, while in a horizontal rotating ring apparatus, the variation is caused by a difference between the height of the load (distance above the conveyor) and the width of the load. Variations in demand may make it difficult to properly wrap the load, and the problem with variations may be exacerbated when wrapping a load having one or more dimensions that may differ from one or more corresponding dimensions of a preceding load. The problem may also be exacerbated when wrapping a load having one or more dimensions that vary at one or more locations of the load itself. Furthermore, whenever a load is not centered precisely at the center of rotation of the relative rotation, the variation in the demand rate is also typically greater, as the corners and sides of even a perfectly symmetric load will be different distances away from the packaging material dispenser as they rotate past the dispenser.

The amount of force, or pull, that the packaging material exhibits on the load determines in part how tightly and securely the load is wrapped. Conventionally, this wrap force is controlled by controlling the feed or supply rate of the packaging material dispensed by the packaging material dispenser. For example, the wrap force of many conventional stretch wrapping machines is controlled by attempting to alter the supply of packaging material such that a relatively constant packaging material wrap force is maintained. With powered pre-stretching devices, changes in the force or tension of the dispensed packaging material are monitored, e.g., by using feedback mechanisms typically linked to spring loaded dancer bars, electronic load cells, or torque control devices. The changing force or tension of the packaging material caused by rotating a rectangular shaped load is transmitted back through the packaging material to some type of sensing device, which attempts to vary the speed of the motor driven dispenser to minimize the change. The passage of the corner causes the force or tension of the packaging material to increase, and the increase is typically transmitted back to an electronic load cell, spring-loaded dancer interconnected with a sensor, or to a torque control device. As the corner approaches, the force or tension of the packaging material decreases, and the reduction is transmitted back to some device that in turn reduces the packaging material supply to attempt to maintain a relatively constant wrap force or tension.

With the ever faster wrapping rates demanded by the industry, however, rotation speeds have increased significantly to a point where the concept of sensing changes in force and altering supply speed in response often loses effectiveness. The delay of response has been observed to begin to move out of phase with rotation at approximately 20 RPM. Given that a packaging dispenser is required to shift between accelerating and decelerating eight times per revolution in order to accommodate the four corners of the load, at 20 RPM the shift between acceleration and deceleration occurs at a rate of more than once every half of a second. Given also that the rotating mass of a packaging material roll and rollers in a packaging material dispenser may be 100 pounds or more, maintaining an ideal dispense rate throughout the relative rotation can be a challenge.

Also significant is the need in many applications to minimize acceleration and deceleration times for faster cycles. Initial acceleration must pull against clamped packaging material, which typically cannot stand a high force, and especially the high force of rapid acceleration, which typically cannot be maintained by the feedback mechanisms described above. As a result of these challenges, the use of high speed wrapping has often been limited to relatively lower wrap forces and pre-stretch levels where the loss of control at high speeds does not produce undesirable packaging material breaks.

Therefore, a significant need continues to exist in the art for an improved manner of reliably and efficiently controlling a wrapping machine.

SUMMARY OF THE INVENTION

The invention addresses these and other problems associated with the art by providing a method, apparatus and program product that control a dispense rate of a packaging material dispenser at least in part by utilizing a combination of a sensed rate of dispensed packaging material and a predicted geometric relationship between the packaging material dispenser and the load.

Therefore, consistent with one aspect of the invention, a method is provided for wrapping a load with packaging material using a wrapping apparatus of a type including a packaging material dispenser for dispensing packaging material to the load. The method may include generating relative rotation between the packaging material dispenser and the load about a center of rotation, sensing a rate of the packaging material exiting the packaging material dispenser, and controlling a dispense rate of the packaging material dispenser during the relative rotation based at least in part on a geometric relationship between the packaging material dispenser and a calculated location of at least one corner of the load within a plane perpendicular to the center of rotation, and further based at least in part on the sensed rate of the packaging material exiting the packaging material dispenser.

In some embodiments, the at least one corner includes a first corner, and the method further includes calculating the position of the first corner based at least in part upon one or more dimensions of the load. Also, in some embodiments, the one or more dimensions includes a length and a width. Further, in some embodiments, the one or more dimensions are input by an operator, while in some embodiments, the one or more dimensions are sensed by one or more sensors directed at the load. In addition, in some embodiments, the one or more dimensions are retrieved from a wrap profile stored in the wrapping apparatus.

In some embodiments, the one or more dimensions are based at least in part upon a standard load type representative of the load, and the one or more dimensions are determined without sensing the one or more dimensions from the load and without receiving input from an operator or a wrap profile specific to the load. In addition, in some embodiments, calculating the position of the first corner is further based at least in part upon an offset of the load from the center of rotation. Moreover, in some embodiments, the offset is based at least in part upon a standard load type representative of the load, and the offset is determined without sensing the offset from the load and without receiving input from an operator or a wrap profile specific to the load.

In some embodiments, the at least one corner of the load includes a first corner, and controlling the dispense rate of the packaging material dispenser includes determining a demand at a first rotational position about the center of rotation using a curve fit between second and third rotational positions that are respectively before and after the first rotational position about the center of rotation and for which predicted demands are determined. Moreover, in some embodiments, controlling the dispense rate of the packaging material dispenser further includes determining the predicted demands for the second and third rotational positions based at least in part upon the calculated position for the first corner. In some embodiments, the curve is a demand curve defining a demand at each of a plurality of rotational positions between the second and third rotational positions, and controlling the dispense rate further includes determining the first dispense rate by scaling a demand from the demand curve based at least in part upon a wrap force parameter. In addition, in some embodiments, the curve defines, for each of a plurality of rotational positions, a percentage of a girth of a standard load type representative of the load.

In some embodiments, the curve defines, for each of a plurality of rotational positions, a percentage of a girth of the load, where the girth of the load is based upon input of one or more dimensions of the load. Moreover, in some embodiments, the curve includes a portion of a sinusoidal curve fit between the second and third rotational positions. In addition, some embodiments may further include determining the first dispense rate at the first rotational position further by applying a rotational data shift to offset system lag. In some embodiments, the rotational data shift is variable based at least in part upon a rate of relative rotation between the packaging material dispenser and the load.

In addition, in some embodiments, the curve includes a plurality of segments spanning a full revolution about the center of rotation, each segment fit between two or more rotational positions for which predicted demands are determined. Also, in some embodiments, each segment includes a sine curve fit between two or more rotational positions for which predicted demands are determined. Moreover, in some embodiments, the plurality of segments includes eight segments, each of the eight segments spanning between a rotational position associated with a local minimum in demand and a rotational position associated with a local maximum in demand.

Further, in some embodiments, the packaging material dispenser includes a pre-stretch assembly, and sensing the rate of the packaging material exiting the packaging material dispenser includes sensing rotation of an idle roller disposed downstream of the pre-stretch assembly. Also, in some embodiments, the idle roller forms an exit point for the packaging material dispenser.

Further, in some embodiments, controlling the dispense rate of the packaging material dispenser based at least in part on the sensed rate of the packaging material exiting the packaging material dispenser includes generating a signal from the sensed rate that varies based upon an actual girth of the load at an elevation at which the packaging material dispenser is dispensing packaging material to the load. In some embodiments, controlling the dispense rate of the packaging material dispenser based at least in part on the geometric relationship between the packaging material dispenser and the calculated location of at least one corner of the load includes determining a demand at a first rotational position about the center of rotation. Also, in some embodiments, controlling the dispense rate of the packaging material dispenser based at least in part on the sensed rate of the packaging material includes scaling the determined demand based at least in part upon the generated signal.

In some embodiments, controlling the dispense rate of the packaging material dispenser based at least in part on the geometric relationship between the packaging material dispenser and the calculated location of at least one corner of the load further includes determining a percentage of girth of the load from the determined demand, and controlling the dispense rate of the packaging material dispenser based at least in part on the sensed rate of the packaging material includes scaling the generated signal by the determined percentage of girth. Further, in some embodiments, controlling the dispense rate of the packaging material dispenser based at least in part on the geometric relationship between the packaging material dispenser and the calculated location of at least one corner of the load includes generating a curve for a plurality of rotational positions about the center of rotation.

In some embodiments, the curve is a demand curve defining a demand for each of the plurality of rotational positions, and controlling the dispense rate of the packaging material dispenser based at least in part on the sensed rate of the packaging material includes scaling the curve based at least in part upon the generated signal. Further, in some embodiments, the curve is a curve defining a percentage of girth for each of the plurality of rotational positions, and controlling the dispense rate of the packaging material dispenser based at least in part on the sensed rate of the packaging material includes scaling the generated signal based at least in part upon the curve.

Also, in some embodiments, the at least one corner of the load includes a first corner, and controlling the dispense rate of the packaging material dispenser includes determining a first demand at a first rotational position about the center of rotation using the curve, and the curve is fit between second and third rotational positions that are respectively before and after the first rotational position about the center of rotation and for which predicted demands are determined.

In addition, in some embodiments, generating the signal includes sampling the sensed rate of the packaging material exiting the packaging material dispenser at a plurality of intervals and applying a filter to the samples. In some embodiments, generating the signal includes sampling the sensed rate of the packaging material exiting the packaging material dispenser at a plurality of intervals and, at each interval, summing a first percentage of the sampled sense rate with a second percentage of value calculated during a prior interval.

Consistent with another aspect of the invention, a method may be provided for wrapping a load with packaging material using a wrapping apparatus of the type including a packaging material dispenser for dispensing packaging material to the load. The method may include generating relative rotation between the packaging material dispenser and the load about a center of rotation, sensing a rate of the packaging material exiting the packaging material dispenser, and controlling a dispense rate of the packaging material dispenser during the relative rotation. Controlling the dispense rate includes generating a curve that varies over at least a portion of a relative revolution about the center of rotation based at least in part upon one or more dimensions of the load within a plane perpendicular to the center of rotation, at a first rotational position, generating a dispenser control signal by combining a value of the curve corresponding to the first rotational position with the sensed rate of the packaging material exiting the packaging material dispenser, and using the dispenser control signal to control the dispense rate of the packaging material dispenser.

In addition, in some embodiments, the curve defines a plurality of values each representing a percentage of a girth of the load at an associated rotational position, and where combining the value of the curve corresponding to the first rotational position with the sensed rate of the packaging material exiting the packaging material dispenser includes scaling the sensed rate of the packaging material exiting the packaging material dispenser by the value of the curve corresponding to the first rotational position. In addition, some embodiments may further include generating the sensed rate of the packaging material exiting the packaging material dispenser by sampling a rate of rotation of an encoder coupled to an idle roller downstream of a pre-stretch assembly of the packaging material dispenser at each of a plurality of intervals and averaging sampled rates captured over multiple intervals.

In addition, in some embodiments, controlling the dispense rate further includes applying a wrap force parameter such that the dispenser control signal is scaled by the wrap force parameter. In some embodiments, controlling the dispense rate further includes applying a rotational data shift such that the dispenser control signal is shifted to offset system lag.

Consistent with another aspect of the invention, a method may be provided for wrapping a load with packaging material using a wrapping apparatus of the type including a packaging material dispenser for dispensing packaging material to the load during relative rotation between the packaging material dispenser and the load about a center of rotation. The method may include, prior to initiating a wrap cycle for the load, receiving operator input specifying one or more dimensions of the load within a plane perpendicular to the center of rotation, determining a wrap model for the load based upon the one or more dimensions specified by the received operator input, the wrap model being representative of a demand for the packaging material dispenser over at least a portion of a revolution between the packaging material dispenser and the load based upon the one or more dimensions specified by the received operator input, initiating the wrap cycle for the load and generating relative rotation between the packaging material dispenser and the load about the center of rotation, sensing a rate of the packaging material exiting the packaging material dispenser with a sensor during the relative rotation and generating a signal representative thereof, and controlling the dispense rate of the packaging material dispenser during the relative rotation by scaling the generated signal at a first rotational position based upon the wrap model.

Further, in some embodiments, the wrap model represents demand in terms of percentage of load girth over the at least a portion of the revolution. In addition, in some embodiments, the wrap model defines a curve including a plurality of values, each representing a percentage of a girth of the load at an associated rotational position, and scaling the generated signal at the first rotational position based upon the wrap model includes scaling the generated signal by the value of the curve corresponding to the first rotational position. Some embodiments may further include generating the signal by sampling a rate of rotation of an encoder coupled to an idle roller downstream of a pre-stretch assembly of the packaging material dispenser at each of a plurality of intervals and averaging sampled rates captured over multiple intervals.

Moreover, in some embodiments, controlling the dispense rate further includes applying a wrap force parameter such that the dispense rate is scaled by the wrap force parameter. Further, in some embodiments, controlling the dispense rate further includes applying a rotational data shift such that the dispense rate is shifted to offset system lag.

Some embodiments may also include an apparatus for wrapping a load with packaging material including a packaging material dispenser for dispensing packaging material to the load, a rotational drive configured to generate relative rotation between the packaging material dispenser and the load about a center of rotation, and a controller coupled to the packaging material dispenser and the rotational drive and configured to perform any of the aforementioned methods. Similarly, some embodiments may include a program product including a computer readable medium, and program code configured upon execution by a controller in an apparatus that wraps a load with packaging material using a packaging material dispenser adapted for relative rotation with the load about a center of rotation, with the program code configured to perform any of the aforementioned methods.

Consistent with another aspect of the invention, an apparatus for wrapping a load with packaging material may include a packaging material dispenser for dispensing packaging material to the load, the packaging material dispenser including a pre-stretch assembly and an idle roller downstream of the pre-stretch assembly, a rotational drive configured to generate relative rotation between the packaging material dispenser and the load about a center of rotation, an encoder configured to sense rotation of the idle roller and output a signal representative thereof, and a controller coupled to the packaging material dispenser, the rotational drive and the sensor. The controller may be configured to control a dispense rate of the packaging material dispenser during the relative rotation by generating a filtered rate signal at least in part by averaging together a plurality of samples of the encoder signal, and scaling the filtered rate signal by a value determined based at least in part on a geometric relationship between the packaging material dispenser and a calculated location of at least one corner of the load within a plane perpendicular to the center of rotation.

In some embodiments, the controller is further configured to determine the value by accessing a wrap model that defines a curve representative of a demand for the packaging material dispenser over at least a portion of a revolution between the packaging material dispenser and the load based upon one or more dimensions of the load. Moreover, in some embodiments, the wrap model represents demand in terms of percentage of load girth over the at least a portion of the revolution. Further, in some embodiments, the wrap model includes a rotational data shift to offset system lag. In addition, in some embodiments, the controller is further configured to control the dispense rate further by applying a wrap force parameter such that the dispense rate is scaled by the wrap force parameter.

These and other advantages and features, which characterize the invention, are set forth in the claims annexed hereto and forming a further part hereof. However, for a better understanding of the invention, and of the advantages and objectives attained through its use, reference should be made to the Drawings, and to the accompanying descriptive matter, in which there is described example embodiments of the invention.

