Abstract:
A cushioning conversion machine and method for converting sheet stock material into a cushioning dunnage product and wherein the tension in the stock material is controlled to avoid problems associated with improper tension. A conversion assembly draws the stock material from a stock supply and converts the stock material into a strip of cushioning, and a controller controls the operation of the conversion assembly. The conversion assembly is powered by a motor and the controller controls the operation of the motor in response to a sensed parameter related to the tension in the paper. In another embodiment, a torque control is interposed between the feed motor and feed components that engage the stock material.

Description:
FIELD OF THE INVENTION 
     The invention herein described relates generally to cushioning conversion machines and more particularly to improvements in controlling the tension of the stock material fed into such machines for conversion into a dunnage product. 
     BACKGROUND OF THE INVENTION 
     In the process of shipping an item from one location to another, protective packaging material is often placed in the shipping container to fill any voids and/or to cushion the item during the shipping process. Some commonly used protective packaging materials are plastic foam peanuts and plastic bubble pack. While these conventional plastic materials seem to perform adequately as cushioning products, they are not without disadvantages. Perhaps the most serious drawback of plastic bubble wrap and plastic foam peanuts is their affect on our environment. Quite simply, these plastic packaging materials are not biodegradable, and therefore they cannot avoid further multiplying our planet&#39;s already critical waste disposal problems. The non-biodegradability of these packaging materials has become increasingly important in light of many industries adopting more progressive policies in terms of environmental responsibility. 
     The foregoing and other disadvantages of conventional plastic packaging materials have made paper protective packaging material a popular alternative. Paper is biodegradable, recyclable and composed of a renewable resource, making it an environmentally responsible choice for conscientious shippers. 
     While paper in sheet form could possibly be used as a protective packaging material, it is usually preferable to convert the sheets of paper into a relatively low density pad-like cushioning or dunnage product. This conversion may be accomplished by a cushioning conversion machine, such as that disclosed in commonly assigned U.S. Pat. No. 5,123,889. The conversion machine disclosed in U. S. Pat. No. 5,123,889 converts sheet stock material, such as paper in multi-ply form, into relatively low density pads. Specifically, the machine converts this stock material into a continuous unconnected strip having lateral pillow portions separated by a thin central band. This strip is connected as by coining along its central band to form a coined strip which is cut into sections, or pads, of a desired length. The stock material preferably consists of three superimposed webs or layers of biodegradable, recyclable and reusable thirty-pound Kraft paper rolled onto a hollow cylindrical tube. A thirty-inch wide roll of this paper, which is approximately 450 feet long, weighs about 35 pounds and will provide cushioning equal to approximately sixty cubic feet of plastic foam peanuts while at the same time requiring less than one-thirtieth the storage space. 
     The conversion machines known in the prior art, including the one shown in U.S. Pat. No. 5,123,889, have used a freely rotating roll from which the stock material to be converted is fed by means of the same mechanism that advances the material through the forming portion of the machine. Specifically a pair of gears that have performed a connecting operation have been used to advance the material being converted. These gears stop and start their rotation during the conversion process, and this results in the need to accelerate the stock roll every time the gears start, with resulting changes in the tension of material being fed through the conversion machine. These changes in the tension of the material can affect the quality of the dunnage product being produced. 
     Also, when the conversion process is stopped, the rotational inertia of the stock roll can cause the stock roll to overrun and form a loose loop of material at the supply end of the conversion machine. When the conversion process is resumed, initially the material will be at a relatively low tension until the loose loop of material is taken up, at which point the tension on the paper will rapidly increase, almost instantaneously, to a relatively high level until the stock roll accelerates to match the feed rate through the machine. This quick change in tension can cause the material to tear, as well as degrade the quality of the dunnage product being produced. 
     SUMMARY OF THE INVENTION 
     The present invention provides a cushioning conversion machine and method for converting sheet stock material into a cushioning dunnage product and wherein the tension in the stock material is controlled to avoid one or more of the paper tension problems associated with prior art conversion machines and methods. 
     According to one aspect of the invention, a cushioning conversion machine and method for converting sheet stock material into a cushioning dunnage product are characterized by a stock supply assembly which supplies stock material to be converted, a conversion assembly which draws the stock material from the stock supply and converts the stock material into a strip of cushioning, and a controller which controls the operation of the conversion assembly. The conversion assembly is powered by a motor and the controller controls the operation of the motor in response to a sensed parameter related to the tension in the paper. 
     In one embodiment, a tension sensor is provided to sense the tension in the stock material as it is drawn from the stock supply by the conversion assembly and to provide to the controller an output signal indicative of the sensed tension. In response to the tension sensed by the tension sensor, the controller adjusts the speed of the motor thereby to adjust the rate at which the stock material is drawn from the stock supply to maintain a prescribed and preferably substantially constant tension in the stock material. In a preferred embodiment, the stock supply assembly includes a resiliently biased member over which the stock material is trained such that movement of the resiliently biased member is related to the tension in the stock material; and the tension sensor includes a sensing device which senses movement of the resiliently biased member against a biasing force and outputs a signal related to such movement of the resiliently biased member. A preferred resiliently biased member is an idler roller journalled in mounts at opposite ends of the idler roller, and a preferred sensing device includes load cells at the roller mounts. The output signals of the load cells at the roller mounts preferably are averaged to provide an averaged value of the measured tension in the stock material. 
     In another embodiment, motor torque is sensed and fed back to the controller as a measure of the tension in the stock material. In the case of an electric feed motor, motor current is sensed and fed back to the controller for maintaining the motor current in accordance with a prescribed criteria, such as below a predetermined maximum current. 
     According to another aspect of the invention, a cushioning conversion machine and method for converting sheet stock material into a cushioning dunnage product are characterized by a stock supply assembly which supplies stock material to be converted, and a conversion assembly which draws the stock material from the stock supply and converts the stock material into a strip of cushioning. The conversion assembly includes a feed mechanism which engages the stock material and feeds it through the conversion assembly. The feed mechanism is connected to a motor by a clutch device which limits the applied torque or force to the feed mechanism to a prescribed maximum value. In a preferred embodiment, a slip clutch is used to limit the torque applied by a motor to the feed mechanism which may include cooperating rotating feed wheels which not only feed the stock material but also function to connect together overlapped portions of the stock material. 
     Further in accordance with the invention, there is provided a method of converting sheet stock material into a cushioning dunnage product which includes drawing the stock material from a stock supply and converting the stock material into a strip of cushioning, while controlling the rate at which the stock material is drawn in response to the tension in the stock material. 
     The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail one or more illustrative embodiments of the invention, such being indicative, however, of but one or a few of the various ways in which the principles of the invention may be employed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of a dunnage conversion machine constructed in accordance with the present invention, with a top cover and panel thereof removed to permit viewing of internal components of the machine. 
     FIG. 2 is a side elevational view of the machine shown in FIG. 1, with a side panel thereof removed to permit viewing of internal components of the machine. 
     FIG. 3 is a diagrammatical illustration of another embodiment of the invention. 
     FIG. 4 is a diagrammatical illustration of still another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings in detail and initially to FIGS. 1 and 2, a preferred embodiment of a cushioning conversion machine  10  according to the present invention is shown. The conversion machine  10  has a stock supply which, in the illustrated embodiment, includes an integral stock roll holder assembly  12  for supporting a roll  14  of sheet stock material  16 . Alternatively, the sheet material  16  may be supplied from a separate stand holding the sheet material, or by other suitable means. 
     The stock material  16  preferably consists of one or more, typically two or three, superimposed webs, or plies P 1 , P 2  and P 3  of biodegradable, recyclable and reusable sheet material, such as Kraft paper rolled onto a hollow cylindrical tube  18 . The machine  10  converts this stock material  16  into a crumpled strip of cushioning/dunnage (not shown). The machine  10  also has provision for severing, as by cutting, the strip to form a discrete pad of desired length, as is further discussed below. 
     The machine  10  generally comprises a housing  20  and a conversion assembly  22  that may include several sub-assemblies which form the pads. These sub-assemblies in the illustrated conversion machine include a forming assembly  24 , a feed/connecting assembly  26 , and/or a severing assembly  28 , all of which are mounted in or to the housing  20 . The illustrated forming assembly  24  includes a shaping chute  30  and a forming member  32  for forming the sheet material  16  into a relatively thicker three-dimensional strip that is then connected by the feed/connecting assembly  26  to form the cushioning strip that is cut to length by the severing assembly  28 . 
     During operation of the machine  10 , the stock material  16  is payed off of the stock roll  14  and travels over a constant entry roller  34 . After passage over the constant entry roller  34 , the plies P 1 , P 2  and P 3  are separated for passage between or around separators  35 - 37 . The constant entry roller  34  and separators  35 - 37  are mounted between brackets  38  attached to the rear end of the housing  20 . For further details of the constant entry roller and separators, reference may be had to U.S. Pat. No. 5,123,889. In the illustrated embodiment, the brackets  38  are U-shaped with the base thereof attached to the machine housing  20 , the upper legs thereof supporting the constant entry roller  34  and separators  35 ,  36 ,  37  and the lower legs thereof supporting the stock roll  14 . 
     From the separators  35 - 37 , the separated plies P 1 , P 2  and P 3  pass to the forming assembly  24 . The forming assembly  24  causes inward folding of the lateral edges of the sheet stock material  16  to form a continuous strip having lateral pillow portions and a thinner central band portion. The feed/connecting assembly  26 , which in the illustrated embodiment includes a pair of cooperating gear-like members  40  and  42 , pulls the stock material  16  downstream through the machine  10  and also connects the layers along the central band, as by coining and/or perforating in the illustrated preferred embodiment, to form a connected strip. As the connected cushioning strip travels downstream from the feed assembly  26 , the severing assembly  28  cuts the strip into pads of a desired length. For further details of the illustrated embodiment and similar cushion-producing machines, reference may be had to U.S. Pat. No. 5,123,889 and published PCT Application No. US96/09109. 
     The production of dunnage pads by the illustrated machine  10  is controlled by a controller (diagrammatically shown at  44 ) usually provided in the housing  20  or in a remote unit. For details of the general operation of the controller  44 , reference may be had to commonly assigned U.S. Pat. Nos. 4,619,635 and 5,571,067 and to published PCT Application No. PCT/US95/09275, which are hereby incorporated herein by reference in their entireties. In pertinent part, the controller  44  controls operation of a feed motor  46  which drives the feed components and particularly the rotating gear-like members  40  and  42 . The controller  44  also controls operation of a cutter motor  48  and a clutch  50  which drives the severing assembly  28 . Preferably, the cutter motor  48  is continuously operated whereas control of the clutch  50  controls the operation of the severing assembly  28 . The functions of the controller  44  may be carried out by a single processor device or by separate devices suitably interfaced to coordinate the operation of the feed motor  46 , cutter motor  48  and clutch  50 . 
     An exemplary pad produced by the illustrated machine  10  comprises the one or more plies of sheet material  16  that have side portions thereof folded over the center portions thereof to form laterally spaced-apart pillow portions extending along the length of the pad. The pillow portions are separated by a central band where lateral edge portions are brought together. The lateral edge portions, which may be overlapped and/or interleaved, are connected together, and/or to underlying center portions of the plies along the central band. In a preferred form of cushioning pad, the connecting is accomplished by a combination of coining and stitching, the stitching being effected by perforations and/or cut tabs disposed along the central band. However, it will be appreciated by those skilled in the art that other types of conversion machines may be used to produce the same or other forms of cushioning strips. For further details of an exemplary pad, reference may be had to published PCT Application No. US96/09109, which is hereby incorporated herein by reference in its entirety. 
     The housing  20  of the conversion machine  10  has a longitudinal axis corresponding to the direction of passage of the sheet material  16  downstream through the conversion assemblies from a rear or upstream end  52  to a front or downstream end  54  of the machine  10 . The housing  20  is generally rectangular in cross-section taken transverse to the longitudinal axis of the machine  10 . The machine  10  may be supported in any suitable manner, for example by a stand. 
     The machine  10  as thus far described is similar to the machine described in greater detail in U.S. Pat. No. 5,123,889 (hereby incorporated herein by reference) and reference may be had thereto for further details of the general arrangement and operation of the machine. However, it is noted that the illustrated forming assembly  24  is of the type described in pending U.S. Patent application Ser. No. 08/386,355 and similar to that shown in U.S. Pat. Nos. 5,123,889 and 5,674,172 all of which are hereby incorporated herein by reference. While the forming assembly  24  is preferably like that shown in U.S. Pat. No. 5,674,172, other forming assemblies are also usable in the practice of the present invention. 
     As depicted in FIG. 1, the conversion machine  10  also includes a web tension sensor  56  for measuring the tension in the stock material  16  as it is drawn through the forming assembly  24  and provides an output to the controller  44  which, in response to the sensed tension, adjusts the speed of the feed motor  46  to prevent the tension from increasing to a point that would cause tearing or otherwise negatively impact the strip of cushioning material being produced. The tension sensor  56  may be any suitable device for sensing the tension in the web of stock material  16 . For example, as shown in the illustrated embodiment, the tension sensor  56  may include a pair of load cells  58  and  60  integrated into the mounts  39  supporting the ends of the constant entry roller  34  (or other roller over which the stock material  16  is trained such that the tension on the stock material  16  exerts a force on the supports for the roller). The value of the measured tension is communicated as an electrical signal to the controller  44 . 
     As a further example of a tension sensing arrangement, the constant entry roller  34  (or other roller) may be supported at its ends  39  by spring biased plungers (not shown). The plungers will be depressed in relation to the tension in the stock material  16  and the extent of such depression may be determined by a sensor (such as a LVDT) or sensor array, or other suitable means, which provides a signal to the controller  44  that is representative of the tension in the stock material  16 . 
     In the illustrated preferred embodiment, the controller  44  compares the measured tension with an upper limit and optionally a lower limit. In the event the tension in the stock material  16  exceeds the upper limit, the controller  44  will reduce the motor speed from its normal operating speed until the sensed tension falls below the lower limit, at which point the controller  44  will increase the speed of the motor  46  to its normal operating value. Also, if desired, the motor speed can be increased by the controller  44  in the event the sensed tension falls below the lower limit. Provision may also be made to shut off the feed motor  46  if the tension abruptly changes, for example, drops suddenly to zero or a very low value as might arise from a tear in the stock material  16  or when the paper runs out. By controlling the maximum tension applied to the stock material  16 , tearing of the stock material can be substantially reduced or eliminated. Also, such tension control provides for production of a better pad. 
     This tension sensing arrangement is particularly useful during initial feeding of the stock material  16 . During such start-up of the stock material feeding, the tension in the sheet stock material  16  may rise rapidly in attempting to overcome the inertia of the stationary stock roll  14 . This can place the sheet material  16  under considerable tension and cause tearing, production of an undesirable pad, and/or jam the feeding/connecting assembly  26 . To prevent or reduce the likelihood of such undesirable effects, the speed of the feed motor  46  can be controllably “ramped up” during start-up. Also, the tension sensor  56  enables the controller  44  to monitor the tension in the stock material  16  and make any needed speed adjustments to keep the tension in the stock material  16  below the prescribed maximum tension. As will be appreciated, the speed and/or torque of the feed motor  46  can be gradually increased, or ramped up, while maintaining a constant tension on the paper web until the motor  46  attains a desirable steady state speed and, consequently, the conversion machine  10  attains a steady state feeding condition. Because the tension is controllably attained within a constant tension range (without an abrupt tension spike), there is little chance that the gears  40 ,  42  will tear the stock material  16  or that the stock material  16  will tear at its edges while being drawn by the feeding/connecting assembly  26 . As will further be appreciated, the tension set points may be adjusted, as desired, for stock materials having different weights, strengths, plies, etc. 
     The controller  44  may also be programmed to “ramp down” or gradually decelerate the feed motor  46  to avoid overrunning of the stock roll  14  and formation of a loose loop of stock material  16  at the supply end of the conversion machine  10 . In the absence of such a “ramp down,” when the conversion process is resumed, and the loose loop of material  16  is taken up, the tension on the stock material  16  rapidly increases and can cause undesirable effects such as those described above. Before a strip of cushioning material  16  is to be cut and before the feed motor  46  is stopped, the controller  44  progressively decreases the speed of the motor  46 . The tension in the stock material  16  may be sensed by the tension sensor  56  to inform the controller  44  that the stock roll  14  may be starting to overrun, in which case the controller  44  can reduce the deceleration rate. This ensures relatively constant tension in the web of stock material  16 . If needed, a brake  63  (shown in FIG. 2 only) may be employed to place a drag on the stock roll  14  to assist in reducing overrunning of the stock roll  14  and maintaining substantially constant tension in the stock material  16 . The brake  63  may comprise, for example, a friction roller assembly  64  to provide constant resistance to rotation of the stock roll  14 . As shown in FIG. 2, the friction roller assembly  64  includes a roller  65  mounted to a swing arm  66  which is pivotally secured to the mounting brackets  38 . Spring  67  pulls the roller  62  against the surface of the stock roll  14  to provide a continuous and preferably constant drag. Any suitable means for generating a frictional load on the stock roll may be used, such as a drum-type brake, a caliper-type brake, or even a set screw which bears down on a turning shaft. In the illustrated arrangement, the braking force will progressively decrease as the diameter of the stock roll  14 , and thus its inertial mass, decreases. 
     FIG. 3 shows another arrangement for controlling the tension in the stock material  16  whereby the motor torque or current is monitored instead of directly sensing the tension in the stock material  16 . In the FIG. 3 arrangement, a current sensor  68 , for example, an ammeter, is electrically coupled to the feed motor  46  and measures the current drawn by the feed motor  46 . The current increases when the feed motor  46  experiences a demand for more power, for example, when the tension in the web  16  increases such as when the drag (i.e. inertia) of the stock roll  14  requires additional power to be overcome. Similarly, the current drawn by the feed motor  46  decreases when the motor  46  experiences a relatively lower or no demand for power, for example, when the tension in the web  16  decreases such as when the rotational kinetic energy of the stock roll  14  urges the stock material  16  forward at a rate faster than can be drawn by the feed motor  46 . The current sensor  68  senses, or measures, the current corresponding to the amount of tension in the stock material  16  and communicates this information to the controller  44 . The controller  44 , in turn, compares the sensed current with an upper limit and optionally a lower limit. The controller  44 , as similarly described above with reference to the embodiment shown in FIG. 1, reduces or increases the feed motor speed in response to the measured tension, respectively, exceeding the upper limit or falling below the lower limit. The controller  44  and current sensor  68  provide the advantages of controlling the speed and/or torque of the feed motor  46  during start-up, thereby lessening the chances of rapid increases in tension, or during ramp down, thereby lessening the chances of overrun by the stock roll  14 . 
     FIG. 4 shows yet another arrangement for controlling the tension in the stock material  16  whereby the applied torque is limited by a clutch device  70 . In the FIG. 4 arrangement, the clutch device  70  limits the torque transferred from the feed motor  46  to the feed/connecting assembly  26  to a prescribed maximum value to prevent the tension in the stock material  16  from increasing to a point that would cause tearing or otherwise negatively impact the strip of cushioning material  16 . The clutch device  70  may be any suitable device, for example, the clutch device  70  may include a slip clutch having first and second clutch plates  72  and  74  that frictionally engage one another when the torque experienced by the feed motor  46  is below the prescribed limit and disengage, or slip, when the torque exceeds the prescribed limit. 
     Although the invention has been shown and described with respect to certain preferred embodiments, equivalent alterations and modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In particular regard to the various functions performed by the above described integers (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such integers are intended to correspond, unless otherwise indicated, to any integer which performs the specified function of the described integer (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.