Patent Publication Number: US-2018050832-A1

Title: Method for wrapping plastic film on a load and wrapping machine

Description:
This international application claims priority to and the benefit of Finland Patent Application No. 20155083, filed on Feb. 9, 2015, the entire contents of which are incorporated herein by reference. 
     The present invention relates to wrapping of a plastic film web on a load. 
     Various types of wrapping machines for wrapping a web type plastic film around an article being packaged are previously known. The article to be packaged is typically a pallet-mounted load, sail load being usually an entity in the form of a rectangular parallelepiped. 
     The plastic film web is wrapped around a load either by rotating rolls of plastic film web around a pallet or by rotating a pallet with respect to rolls of plastic film web, or by conducting both at the same time, whereby the rolls of plastic film web are also simultaneously shifted in vertical direction. Wrapping machines are also typically fitted with elements for providing a piece of film web for covering a top surface of the load to be wrapped. 
     During the wrapping process the film is usually also pre-stretched to a certain degree prior to wrapping the film around the load. The stretched film provides secure protection of the wrapped load and helps to keep the wrapped products at their places on the pallet. The stretching of the film also lowers the thickness of the film and thus less film material is used in the wrapping of the load. 
     One way of moving rolls of film web around a stationary pallet and a load thereon is to provide the wrapping machine with a horizontally placed, ring-shaped circular guide, said circular guide being fitted with one or more film supply carriages comprising a roll of film web. Such a circular guide structure can be formed for example from a circular guide ring mounted on a frame of the wrapping machine in a vertically movable manner, and from a circular guide ring capable of rotating relative to the stationary circular guide ring, said rotating circular guide ring being fitted with film supply carriages. Alternatively, the circular guide structure of a wrapping machine may consist of just one circular guide ring, which is mounted on a frame of the wrapping machine either rotatably or nonrotatably, as well as to be movable in vertical direction. One wrapping machine solution based on the use of circular guides is known from patent publication U.S. Pat. No. 4,587,796. 
     The wrapping process in the known machines is generally carried out so, that the wrapping process is started either from the bottom portion of the load and the wrapping proceed upwards along the load, or from the top portion of the load and the wrapping proceeds downwards along the load, until the whole load is wrapped. With some machines it is possible to carry out double layer wrapping, where the load is wrapped twice, for example from bottom to top and back to bottom. 
     The present invention provides a wrapping method, and a wrapping machine implementing this kind of method, where the wrapping characteristics can be preset so that they are charged during the wrapping process at predefined points or locations and/or between these predefined points or locations. This allows for proper wrapping also for loads that have varying characteristics at different locations along the load to be wrapped, so that the whole load does not need to be wrapped the same way. Further, the present invention also allows the operator of the wrapping machine to freely set the points and locations together with the wrapping characteristics for the load to be wrapped which makes it possible to form many different kinds of wrapping modes and ways without the need to change the program controlling the wrapping machine. 
     In the method of the invention for wrapping a plastic film web from at least one roll on a load with a wrapping machine, at least one roll of plastic film web in relation to at least the height of the load to be wrapped is detected and monitored during wrapping, a plurality of points or locations along the height of the load to be wrapped are preset before starting of the wrapping, at which preset points or locations and/or between said preset points or locations the wrapping characteristics are changed during wrapping. 
     In an embodiment of the method of the invention the said wrapping characteristics include wrapping height, number of plastic film web layers wrapped, tension of the plastic film web, wrapping speed, amount of overlap of subsequent wrapping rounds and/or overlap tension. 
     In an embodiment of the method of the invention the points or locations and/or the wrapping characteristics are set by an operator of the wrapping machined through user interface prior to starting of the wrapping of the load. This allows changing of the wrapping characteristics whenever the loads to be wrapped vary in type or composition, for example, by the operator, even for each single load to be wrapped if necessary. 
     In an embodiment of the method of the invention the load to be wrapped is stationary and a film web roll is rotated around the load during the wrapping. 
     In an embodiment of the method of the invention the plastic film web is pre-stretched before wrapping it around the load. 
     The present invention also provides a wrapping machine for wrapping a plastic film web on a load comprising at least one roll of plastic film web, a device for detecting and monitoring the location of the at least one roll of plastic film web in relation to at least the height of the load to be wrapped during wrapping, a device for defining preset points along the height of the load, and a device for changing the wrapping characteristics at and/or between the preset points during wrapping. 
     In an embodiment of the wrapping machine of the invention the said devices comprise at least one processor or processing unit and at least one memory including computer program code, wherein the at least one memory and the program code are configured to, with the at least one processor or processing unit, control the motors of the wrapping machine moving the at least one roll of plastic web in relation to the load to be wrapped and/or a motor for feeding the plastic film web. 
     In an embodiment of the wrapping machine of the invention the at least one memory and the program code are configured to, with the at least one processor or processing unit, control the wrapping characteristics during the wrapping so that wrapping height changes, number of wrapped plastic film web layers changes, tension of the plastic film web changes wrapping speed changes, amount of overlap of subsequent wrapping rounds changes and/or overlap changes. 
     In an embodiment of the wrapping machine of the invention the device for detecting and monitoring the location of the at least one roll of plastic film web in relation to at least the height of the load to be wrapped during wrapping comprises an encoder arranged in connection of a motor moving the at least one roll of plastic film in vertical direction, and a photocell. 
     In an embodiment of the wrapping machine of the invention the wrapping machine comprises an automatic control system for controlling the wrapping machine and the said devices, with a user interface for setting the preset points and/or the wrapping characteristics before wrapping. 
     In an embodiment of the wrapping machine of the invention the wrapping machine comprises a device for rotating the at least one roll of plastic film web around a stationary load. This device preferably comprises a circular guide along which the roll or rolls of plastic film web are moved, and the circular guide is connected vertically adjustably on a frame of the wrapping machine. 
     In an embodiment of the wrapping machine of the invention the wrapping machine also comprises a device for pre-stretching the plastic film before it is wrapped on a load. 
     The features defining a method of the invention are more precisely disclosed in claim  1 , and the features defining a wrapping machine of the invention are more precisely disclosed in claim  6 . Dependent claims disclose advantageous features and embodiments of the invention. 
    
    
     
       In the following an exemplifying embodiment of the invention is discussed in greater detail in the sense of example and with reference to accompanying drawings, where, 
         FIG. 1  shows schematically an embodiment of a wrapping machine utilizing the present invention, and 
         FIG. 2  shows schematically the principle of controlling and setting of the wrapping process of the invention. 
     
    
    
       FIG. 1  shows schematically a wrapping machine  1 , which comprises a frame  2 , a circular guide  3  connected to the frame vertically adjustably, and a carrier  4  for roll of plastic film web  9 , which carrier is movable along the circular guide. 
     Load to be wrapped is brought, usually on a suitable pallet, under the circular guide  3  in the area inside the circular guide with a suitable forklift or conveyer belt passing though the wrapping machine  1 , for example. Once the wrapping process is started, the circular guide  3  is first lowered downwards until the load to be wrapped cuts a light beam from a photocell connected to the circular guide, at which moment the vertical position of the circular guide is registered and used to determine the height of the load to be wrapped by an automatic control system controlling the wrapping machine and its wrapping process. 
     The wrapping machine  1  also comprises a user interface  5 , which is used to input data, or select corresponding setting, relating to the type of pallet into the automatic control system on which the load to be wrapped in located, so that the automatic control system knows the level from which the wrapping is to be started or at which is to be ended at the lower end of the load to be wrapped. 
     The vertical position of the circular guide  3 , and thus also the vertical location of the roll of plastic film web  9  located in a carrier  4  connected to the circular guide, is defined and monitored with an encoder arranged in the motor  6  moving the circular guide vertically along the frame  2 . The encoder forwards the location data to the automatic control system of the wrapping machine  1 . 
     Another encoder is arranger in the motor  7  which rotates the carrier  4  along the circular guide  3 , which also forwards data of the location of the carrier  4  on the circular guide to the automatic control system of the wrapping machine  1 . 
     Based on the data obtained from the two encoders, the automatic control system, which comprises suitable data processing means and devices, such as data processors or processing units, memories and computer program codes, determines and follows the location of the roll of plastic film web  9  in relation to the load to be wrapped. 
     The automatic control system also controls a motor  8  for feeding the plastic film web from the carrier  4 , which motor is located in the carrier, so that the feeding of the plastic film web is adjusted accordingly with the changes in the other wrapping characteristics during wrapping. 
     The user interface  5  also allows the operator of the wrapping machine  1  to input different settings and changes to the automatic control system of the wrapping machine before the wrapping process is stated, so that suitable wrapping for different kinds of loads to be wrapped can be obtained. This is discussed in more detail below in connection to  FIG. 2 . 
       FIG. 2  shows schematically the principle of controlling and setting of the wrapping process of the invention. 
     At the start of the setting process the user sets the points or locations along the height of the load to be wrapped, which are shown in  FIG. 2  as numbered circles. The location of points can be defined as distance from the pallet top surface or from the top of the load to be wrapped, for example. The amount of the set points or locations may be between 1-5, preferably 3-5. 
     Once the points are set, the user defines wrapping characteristics to be applied at the set points or between the set points. The wrapping characteristics may include:
         wrapping height,   number of plastic film web layers wrapped,   tension of the plastic film web,   wrapping speed,   amount of overlap of subsequent wrapping rounds, and/or   overlap tension.       

     Once the set setting of points and wrapping characteristics is done, the user starts the actual wrapping process, which is the carried out by the wrapping machine, such as one shown in  FIG. 1 , in accordance with the settings. 
     The user may freely set the points and locations along the height of the load to be wrapped as well as the related wrapping characteristics, which allows the same wrapping machine to be used in multitude of different wrapping modes and ways without the need to make changes to the programmable logic, i.e. the automatic control system, controlling the wrapping machine. 
     The selected settings may also be saved into the automatic control system of the wrapping machine, so that the saved settings can be retrieved to be used again. 
     The changes to the wrapping characteristics during the wrapping process are carried out by the automatic control system of the wrapping machine based on the location information of the roll of plastic film web and controlling of the motors moving the roll of plastic film web. 
     The specific exemplifying embodiments of the invention shown in figures and discussed above should not be construed as limiting. A person skilled in the art can amend and modify the embodiments in many evident ways within the scope of the attached claims. Thus the invention is not limited merely to the embodiments described above.