Abstract:
This invention relates to a paper shredder. A first stage shredder accepts paper from a hopper. The first stage shredder includes two knife shaft assemblies with a plurality of sequentially oriented knives and spacers on hexagonal shafts. A second stage shredder accepts the output of the first stage shredder. The second stage shredder has two counter rotating shafts with saw tooth disk knives and separating spacers and cuts the paper finer than that of the first stage shredder. A third stage shredder may be connected to the second stage shredder providing even further paper size reduction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority of Canadian Patent Application No. 2,709,258 filed Jul. 8, 2010, which is incorporated herein by reference in its entirety. 
     FIELD 
     The present application relates generally to the shredding of paper. More particularly, the present application relates to the shredding of paper to a very small size so as to make the shredded remnants unreadable. 
     BACKGROUND 
     The shredding of paper is well known but with the increased awareness and legal obligations to shred confidential documents to an unreadable and non re-constructible state, there is a void. In particular, although paper shredders can be designed to achieve the results in terms of size, they tend to have much slower throughput. Conventional apparatuses for shredding paper that deliver acceptable throughput rates produce shred sizing that generally are too large to be acceptable. Conventional systems utilize a screen surrounding the cutting blades to filter paper of a certain size, the larger pieces being shredded again, the smaller pieces passing to the next stage. Once appropriately sized, the smaller pieces pass through the screen. The disadvantage to this system is that staples, paper clips, or other metal may cause sparks within the screen and ignite the paper. In addition, screened apparatus generally have unacceptably low throughput. Thus there is a need for a shredder with increased throughput that produces fine shredding and reduces the possibility of fire during the shredding process. 
     SUMMARY 
     In an aspect herein, there is provided a paper shredder, the shredder including: 
     a hopper for receiving paper; 
     a first stage shredder comprising offset blades driven by a first stage power drive; 
     a second stage shredder operatively connected to the first stage shredder, the second stage shredder comprising offset blades driven by a second stage power drive; and 
     a program logic controller adapted to control the paper shredder. 
     In a further aspect, the paper shredder further includes a third stage paper shredder operatively connected to the second stage shredder, the third stage shredder comprising offset blades driven by a third stage power drive; and a collection bin below said the third stage shredder. 
     In another aspect herein, there is provided a method for monitoring a multi-stage paper shredder the method executed by a programmable logic control to monitor motor speed for each stage and to shut down all preceding stages if a stage should jam. 
     In yet another aspect herein, there is provided a method for controlling a multi-stage paper shredder, the method executed by a programmable logic controller to monitor the amount of paper being fed to each stage, through the use of optical sensors, should too much paper arrive at any stage, shutting down said preceding stages until said too much paper is processed. 
     Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described, by way of example only, with reference to the attached Figures, wherein: 
         FIG. 1  is a perspective view of an embodiment of a paper shredder. 
         FIG. 2  is top view of a first stage shredder. 
         FIG. 3  is a side view of a first stage shredder. 
         FIG. 4  is an end view of a first stage shredder. 
         FIG. 5  is a top view of a second stage shredder. 
         FIG. 6  is an end view of a second stage shredder. 
         FIG. 7  is an end view of the cutting disks of the second stage and a third stage shredder. 
         FIG. 8A  and  FIG. 8B  are block diagrams of the components of a logic controller for a paper shredder. 
         FIG. 9  is a view of a paper shredder indicating optical sensors. 
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIG. 1 , a perspective view of an embodiment of a paper shredder is shown generally as  10 . A hopper  12  feeds paper into the shredder  10 . The shredder  10  comprises three shredder stages being first stage shredder  14 , secondary stage shredder  16  and third stage shredder  18 . First stage power drive  20  provides power to first stage shredder  14 . Second stage power drive  22  provides power to second stage shredder  16 . Third stage power drive  24  provides power to third stage shredder  15 . Each of power drives  20 ,  22  and  24  may provide power through the use of hydraulic or electric power. An example of a power drive  20  would be a hydraulic power drive, such as a planetary gear reducer provided by SAI Hydraulics, Inc. of Linwood Pa. Alternatively, Power drives  22  and  24  may not require planetary gears. 
     The first stage shredder  14  accepts paper from hopper  12 . Paper may be introduced into hopper  12  by any number of means, for example by hand, by a tipper bin or by an infeed conveyor (not shown), such as a conveyor belt. Paper is cut by first stage shredder  14  and optionally by second stage shredder  16  and third stage shredder  18 , depending upon how finely the paper is to be shredded. In the illustration of  FIG. 1  third stage shredder  18  has been removed from contact with the paper shredded by second stage shredder  16 . 
     Paper drops into collection bin  26  from which it can be removed. The paper arriving in collection bin  26  may also be compacted through the use of compactor  28 . In addition, a discharge conveyor (not shown) may be utilized to remove paper from the collection bin  26 . 
     We now refer to  FIG. 2 , which shows a top view of first stage shredder  14 . First stage power drive  20  turns drive shafts  40 , which in turn drive multiple cutting knives  42  to shred the paper. Cutting knives  42  are separated by spacers  44 . Cleaning blades  54  are mounted adjacent to cutting knives  42  to prevent the buildup of cut paper from jamming cutting knives  42 . 
       FIG. 3  shows a side view of a first stage shredder.  FIG. 3  illustrates the features of  FIG. 2 , namely: first stage power drive  20 , drive shafts  40 , cutting knives  42 , spacers  44 , and cleaning blades  54 . In addition a main drive shaft  46  is shown. 
     Referring now to  FIG. 4  an end view of a first stage shredder is shown. As shown in  FIG. 4 , each cutting knife  42  has three material capture hooks  52 , but as one skilled in the art can appreciate, any number of material capture hooks  52  may be employed. In addition cleaning blades  54  are disposed between each cutting knife  42  to scrape away paper buildup between the cutting knives  42 . Drive shafts  40  turn hexagonal shafts  50  which then turn cutting knives  42 . In one embodiment hexagonal shafts  50  and cutting knives would be manufactured from a heat treated high alloy steel, such as American Iron and Steel Institute (AISI) standards 4140 and 4340. In one embodiment the drive shafts  40  would be on the order of three inches in diameter, the hexagonal shafts on the order of 5.8 inches between a centre line and the cutting knives  42  on the order of seven inches in diameter. 
     Referring now to  FIG. 5  a top view of a second stage shredder is shown. Second stage shredder  16  comprises a pair of horizontally disposed, parallel drive shafts  60 . Drive shafts  60  are driven by second stage power drive  22  connected to a drive shaft  64  and spur gears  66 . This configuration creates a counter rotating orientation that facilitates paper capture. The drive shafts  60  have a plurality of longitudinally spaced cutting disks  62  and spacers  70 . Second stage shredder  16  is similar in construction to that of first stage shredder  14 . One difference is that cutting disks  62  have a different construction than the cutting knives  42  of first stage shredder  14 . The cutting disks  62  have a saw tooth hook profile to further reduce the sizing of the pre-shredded paper received by the second stage shredder  16 . Second stage shredder  16  may be moved in and out of operating position through the use of hydraulic piston  72 , allowing the operator to choose required shred size. 
     Referring now to  FIG. 6 , an end view of a second stage shredder is shown. Cutting disks  62  are attached to parallel drive shafts  60  and secured to them by keyholes  68 . 
     Referring now to  FIG. 7  an end view of the cutting disks of the second stage and third stage shredder are shown. The second stage and third stage shredder are identical in configuration save for the power supplied and the dimension of the cutting disks Each shredder stage has progressively smaller knives for shredding. By way of example, first stage shredder  14  would cut paper into strips approximately ⅝″ in width. Second stage shredder  16  would cut paper into approximately ⅜″ in width. Third stage shredder  18  would cut paper into approximately ¼″. Thus each shredder in the system will have progressively narrower cutters to provide a finer shred. The cutting disks  62  have a saw tooth cutting edge  74  to further reduce the sizing of the pre-shredded paper presented to it. 
     In one example, parallel drive shafts  60  would have a diameter of on the order of two inches. Cutting disks  62  would have a diameter on the order of 4.5″. In one embodiment it has been found that about 72 teeth, plus or minus, function well. A cutting disk  62  is connected to a parallel drive shaft  60  by keyholes  68 . 
     Referring now to  FIG. 8A  and  FIG. 8B  block diagrams of the components of a logic controller for a shredder are shown. 
     All shredders are controlled by Program Logic Controller (PLC  137 ). One such example being a Mitsubishi FX2N-32MR-ES. There are also included optical sensors between the first and second shredder and the second and third shredder to detect an over load of paper and stop the preceding shredders until the paper clears (see  FIG. 9 ). The shredders are also interlocked to sense power load and shaft rotation. If the second or third shredder reverses due to overload the preceding shredders will immediately stop and wait for a forward signal before commencing shredding. 
     Power for the shredders is provided by feature  82 . Examples would be 460 volts AC at 60 Hz., or 220 volts AC. Power  82  is directed to main power disconnect and fuses  84  which allows for the shutdown of the entire system. Main isolation contactor  86  is invoked if a fuse is blown and it shuts the system down. It is directly connected to features  112 ,  114 ,  116 ,  118  and  120  as shown in  FIG. 8B . Note that an infeed conveyor (not shown) and a discharge conveyor (not shown) are optional element. Control voltage transformer  88  outputs a 120 volts AC control voltage signal  89  to power motors  124 ,  128 ,  132 ,  134  and  136 . 
     Control voltage transformer  88  also provides power to 5 volt DC power supply  90  and 24 volt DC power supply  92 . Feature  90  provides power to speed feedback encoders  122 ,  126  and  130 . These encoders monitor the speed of their respective motors and provide feedback if a motor is running too slow, i.e. the shredder it drives may have become jammed. DC power supply  92  provides power to sensors for features  100 ,  102 ,  104 ,  106 ,  108  and  110 . 
     Should the operator detect that too much paper is being fed into hopper  12 , they may hit a push button (P/Bs)  98  to stop the system. In addition an optical sensor (see  FIG. 9 ) may at step  100  detect that if too much paper is being provided to first stage shredder. If either of these occurs PLC  137  will be instructed to shut down the input to first stage shredder until the paper clears the optical sensors, upon which a start signal will be provided. An optical sensor at feature  102  detects if too much flow is going from first stage shredder  14  to second stage shredder  16 . If this is the case, first stage shredder  14  is shut down until second stage shredder  18  can catch up. 
     A sensor at feature  104  indicates to PLC  137  that the second stage shredder  16  has been disengaged from the system, as it is not required for the shredding level needed. So it will not be receiving or transmitting any information while it is disengaged. In essence it is no longer part of the system. 
     Features  106  and  108  are identical in function to those of  102  and  104 , save that they apply to third stage shredder  18 . 
     Feature  94  is an emergency stop button that may be triggered by the operator which sends a signal to main isolation contactor  86  to shut down the system. Feature  96  is a system run/stop push button, which differs from feature  94  in that it is not an emergency stop button but rather a start or stop button. 
     Feature  110  is a Human Machine Interface (HMI) which allows the user to set the speed of the power drives  20 ,  22  and  24 . HMI also collects data through the use of the various sensors to record data such as: running hours, average amp draw, alarm history, and number of reversals. In general the basic operating aspects of the system 
     Features  116 ,  118  and  120  control the speed of power drives  20 ,  22  and  24 . Drives  20 ,  22  and  24  are Variable Frequency Drives (VFD). As such their speed may be adjusted as required, or their direction reversed in the case of a jam. Each of features  116 ,  118  and  120  communicate with PLC  137 . To avoid cluttering  FIG. 8B , only one set of connections has been labeled, namely features  138 ,  140  and  142  connected to feature  120 . These connections are identical to those of features  116  and  118 . Connection  138  provides status and torque monitoring. Each drive  20 ,  22  and  24  provides the torque required to maintain a preset shaft speed. When torque climbs to a pre determined high point the shredder stage  14 ,  16  or  18  respectively will stop, reverse and start again. Connection  144  provides the current speed setting and receives changes for the same. Connection  146  also provides data acquisition such as speed settings and times of shutdowns. Connection  142  provides information on when to run or stop the shredder and in which direction it should run. 
     In the case of an optional infeed conveyor being installed, speed setting  144  informs feature  114  on the speed to be utilized. Status monitoring  146  provides to PLC  137  the current operating status of the infeed conveyor, for example stopped or running. Run/Stop control  148  instructs the infeed conveyor when to start and stop. In the case of an optional discharge conveyor, status monitoring  150  provides to PLC  137  the status of the discharge conveyor. For example is it running or is it shut down. Run/Stop control  152  instructs the discharge conveyor when to run or stop. 
     Referring now to  FIG. 9  a view of a shredder indicating optical sensors is shown. Examples of optical sensors would models LT100TB58J and LR100TB58J manufactured by Telco Sensors of Charlotte N.C., U.S.A. Should optical sensors  162  and  164  become blocked by paper being fed from the first stage shredder  14  into the second stage shredder  16 , this indicates there is too much paper for second stage shredder  16  to handle. As a result first stage shredder  14  is shut down until second stage shredder  16  can catch up with the flow. 
     Should optical sensors  166  and  168  become blocked by paper being fed from the second stage shredder  16  into the third stage shredder  18 , that indicates that there is too much paper for third stage shredder  18  to handle. As a result second stage shredder  16  and first stage shredder  14  are shut down until third stage shredder  18  can catch up with the flow. 
     Embodiments of the invention disclosed herein provide a compact, unitized, multistage shredding apparatus. Due to a small physical footprint and a relatively light weight. A shredder having all three stages has exterior dimensions of approximately 75″×45″×28″ and weighs approximately. This in contrast to a single shaft screened shred with weighs approximately 5,500 pounds. This reduced size and weight allow embodiments of the shredder to be utilized in mobile installations in addition to stationary installations. The operator may selectively control the size of paper shredding at the push of a button, thus avoiding time consuming and labour intensive mechanical screen changes. This feature of selectively controlling the size of paper shredding can reduce the industry standard size of the shredded paper from ⅝″×2.5″ to ⅛″×1″. 
     The above-described embodiments of the invention are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.