Shredding machine

Abstract

A shredding machine for domestic or office use having a feed passage 3 leading to a cutting mechanism 10, 11 powered by an electric motor, has a thickness measuring device 15 for measuring the thickness of bundles of paper fed through the feed passage and the machine is controlled by a microprocessor which receives signals from the thickness measuring device and prevents the cutting mechanism from being energised if the thickness measured is above a threshold determined by the microprocessor. The microprocessor varies the threshold in accordance with electrical supply voltage, the electric motor temperature and the electric current drawn by the motor during a previous shredding operation, so that the maximum thickness the shredder will accept can be reduced automatically when motor temperature increases or as the effectiveness of the machine deteriorates throughout its working life.

1 . A shredder comprising:
 a housing having a throat for receiving at least one article to be shredded;   a shredder mechanism received in the housing and including an electrically powered motor and cutter elements, the shredder mechanism enabling the at least one article to be shredded to be fed into the cutter elements and the motor being operable in a shredding direction to drive the cutter elements to shred the articles fed therein;   a thickness detector configured to detect a thickness of the at least one article to be shredded being received by the throat; and   a controller coupled to the motor and the thickness detector, the controller being configured to determine, prior to operation of the motor, whether the thickness detector detects that the thickness of the at least one article to be shredded being received by the throat is below or at or above a predetermined maximum thickness threshold, and in response:   (a) prevent operation of the motor if the thickness detector detects that the at least one article to be shredded being received by the throat is at or above predetermined maximum thickness threshold, and   (b) operate the motor in the shredding direction to drive the cutter elements to shred the at least one article being received by the throat if the thickness detector detects that the at least one article is below the predetermined maximum thickness threshold, without preventing the operation of the motor in the shredding direction in response to the thickness detector detecting during the operation of the motor that the thickness of the at least one article is at or above the predetermined maximum thickness threshold to thereby prevent unnecessary motor shut-off due to fluttering of the at least one article being shredded.   
     
     
         2 . A shredder according to  claim 1 , wherein the thickness detector is a variable thickness detector for detecting and outputting varying amounts of detected thicknesses. 
     
     
         3 . A shredder according to  claim 2 , wherein said thickness detector includes a contact member in the throat movable by engagement of the article being received in the throat, and a sensor for measuring an amount of displacement of the contact member. 
     
     
         4 . A shredder according to  claim 3 , wherein said sensor is an optical sensor. 
     
     
         5 . A shredder according to  claim 4 , wherein said thickness detector comprises a marker member provided with a series of markers movable with the contact member, said optical sensor detecting the markers moving past the optical sensor to measure the amount of displacement of the contact member. 
     
     
         6 . A shredder according to  claim 5  wherein said optical sensor comprises two optical sensors disposed at different positions to allow said controller to determine the direction of displacement of the marker member as well as the extent of such movement. 
     
     
         7 . A shredder according to  claim 2 , further comprising a presence sensor, separate from the thickness detector, in the throat for determining whether the at least one article has been inserted into the throat. 
     
     
         8 . A shredder according to  claim 1 , wherein the controller comprises a microcontroller. 
     
     
         9 . A shredder according to  claim 1 , wherein the controller is configured to monitor a motor operating condition during the operation of the motor in the shredding direction to determine whether to prevent operation of the motor in the shredding direction. 
     
     
         10 . A shredder according to  claim 1 , wherein said thickness detector includes a contact member in the throat movable by engagement of the at least one article being received in the throat, and a sensor for detecting movement of the contact member. 
     
     
         11 . A shredder according  10 , wherein said sensor is an optical sensor. 
     
     
         12 . A method for operating a shredder comprising a housing having a throat for receiving at least one article to be shredded, a thickness detector for detecting a thickness of the at least one article to be shredded inserted in the throat, and a shredder mechanism received in the housing and including an electrically powered motor and cutter elements, the shredder mechanism enabling the at least one article to be shredded to be fed into the cutter elements and the motor being operable in a shredding direction to drive the cutter elements to shred the articles fed therein; the method comprising:
 prior to operation of the motor, determining whether the thickness detector detects that the thickness of the at least one article to be shredded being received by the throat is below or at or above a predetermined maximum thickness threshold; and   operating the motor in the shredding direction to drive the cutter elements to shred the at least one article being received by the throat if the thickness detector detects that the at least one article is below the predetermined maximum thickness threshold, without preventing the operation of the motor in the shredding direction in response to the thickness detector detecting during the operation of the motor that the thickness of the at least one article is at or above the predetermined maximum thickness threshold to thereby prevent unnecessary motor shut-off due to fluttering of the at least one article being shredded.   
     
     
         13 . A method according to  claim 12 , wherein the shredder further comprises a controller coupled to the motor and the thickness detector, and the method is performed by the controller. 
     
     
         14 . A method according to  claim 13 , further comprising monitoring a motor operating condition during the operation of the motor in the shredding direction to determine whether to prevent operation of the motor in the shredding direction. 
     
     
         15 . A shredder comprising:
 a housing having a feed passage for receiving material to be shredded;   a shredding machine received in the housing and including an electrically powered motor and cutters, the shredding machine enabling the material to be shredded to be fed into the cutters and the motor being operable in a shredding direction to drive the cutters to shred the material fed therein;   a thickness gauging device configured to detect a thickness of the material to be shredded received by the feed passage; and   a processor coupled to the motor and the thickness gauging device, the processor being configured to determine, prior to operation of the motor, whether the thickness gauging device detects that the thickness of the material to be shredded received by the feed passage is less than or greater than a capacity threshold thickness, and in response,   (a) prevent operation of the motor if the thickness gauging device detects that the material to be shredded received by the feed passage is greater than the capacity threshold thickness; and   (b) operate the motor in the shredding direction to drive the cutters to shred the material received by the feed passage if the thickness of the material is less than the capacity threshold thickness, without preventing the operation of the motor in the shredding direction in response to the thickness gauging device detecting during the operation of the motor that the thickness of the material is greater than the capacity threshold thickness to thereby prevent unnecessary motor shut-off due to flapping of the material being shredded.   
     
     
         16 . A shredder according to  claim 15 , wherein the thickness gauging device is a variable thickness gauging device for detecting and outputting varying amounts of detected thicknesses. 
     
     
         17 . A shredder according to  claim 16 , wherein said thickness gauging device includes a actuating arm in the throat movable by engagement of the material being received in the feed passage, and a sensor for measuring an amount of displacement of the actuating arm. 
     
     
         18 . A shredder according to  claim 17 , wherein said sensor is an optical sensor. 
     
     
         19 . A shredder according to  claim 18 , wherein said actuating arm comprises a disc provided with a series of slots movable with the actuating arm, said optical sensor detecting the slots moving past the optical sensor to measure the amount of displacement of the actuating arm. 
     
     
         20 . A shredder according to  claim 19  wherein said optical sensor comprises two optical sensors disposed at different positions to allow said processor to determine the direction of displacement of the disc as well as the extent of such movement. 
     
     
         21 . A shredder according to  claim 16 , further comprising a presence sensor, separate from the thickness gauging device, in the feed passage for determining whether the material has been inserted into the feed passage. 
     
     
         22 . A shredder according to  claim 15 , wherein the processor comprises a microprocessor. 
     
     
         23 . A shredder according to  claim 15 , wherein the processor is configured to monitor for a jam during the operation of the motor in the shredding direction to determine whether to prevent operation of the motor in the shredding direction. 
     
     
         24 . A shredder according to  claim 15 , wherein said thickness gauging device includes an actuating arm in the feed passage movable by engagement of the material being received in the feed passage, and a sensor for detecting movement of the actuating arm. 
     
     
         25 . A shredder according  24 , wherein said sensor is an optical sensor. 
     
     
         26 . A method for operating a shredder comprising a housing having a feed passage for receiving material to be shredded, a thickness gauging device for detecting a thickness of the material to be shredded inserted in the feed passage, and a shredding machine received in the housing and including an electrically powered motor and cutters, the shredding machine enabling the material to be shredded to be fed into the cutters and the motor being operable in a shredding direction to drive the cutters to shred the material fed therein; the method comprising:
 prior to operation of the motor, determining whether the thickness gauging device detects that the thickness of the material to be shredded received by the feed passage is less than or greater than a capacity threshold thickness; and   operating the motor in the shredding direction to drive the cutters to shred the material received by the feed passage if the thickness gauging device detects that the material is less than the capacity threshold thickness, without preventing the operation of the motor in the shredding direction in response to the thickness gauging device detecting during the operation of the motor that the thickness of the material is greater than the capacity threshold thickness to thereby prevent unnecessary motor shut-off due to flapping of the material being shredded.   
     
     
         27 . A method according to  claim 26 , wherein the shredder further comprises a processor coupled to the motor and the thickness gauging device, and the method is performed by the processor. 
     
     
         28 . A method according to  claim 27 , further comprising monitoring for a jam during the operation of the motor in the shredding direction to determine whether to prevent operation of the motor in the shredding direction.