Frequency base knife control systems

Claim 2

In a knife control apparatus for providing accurate control of the length of pieces cut off from a high-speed, continuously moving elongated stock material, the apparatus having a main motor and means clutched thereto for moving the stock material past a cyclic cutoff knife, means comprising a variable speed drive mechanism powered by the main motor for driving the cutoff knife and being adjustable to control the speed of the cutoff knife relative to the stock material speed, and a reversible correction motor for adjusting the variable speed drive mechanism, the improvement comprising: a frequency-based control system for providing an error signal at any time during operation of the apparatus that a variation in a preselected operating condition of the knife relative to movement of the stock material is detected comprising: reference pulse generating means for providing a train of pulses of a frequency proportional to the stock material speed; feedback pulse generating means for providing a fixed number of pulses per cycle of the cutoff knife and having a frequency proportional to the speed thereof; means for continuously comparing during a given cutoff knife cycle the reference and feedback pulse trains to detect a difference therein that occurs whenever the knife operation varies from proper synchronism with the advancement of the piece of stock material to be cut off; means responsive to detection of such difference for providing an error signal during such given cycle; and means responsive to said error signal for operating the correction motor during such given cycle to adjust the variable speed drive mechanism in an amount and direction to bring the knife cycle Into said proper synchronism thereby to afford accurate control of the length of the pieces that are cut off.

Claim 3

The invention defined in claim 1 together with: manually settable means for selecting a desired length for the pieces to be cut off; and means responsive to said manually settable means when set for a given length for passing a number of feedback pulses proportional thereto and for deleting the remainder of the fixed number of pulses per cycle of knife operation.

Claim 4

The invention defined in claim 1, wherein said reference pulse generating means comprises: a preset reference pulse generator driven by the main motor for generating one pulse per simulated unit length of stock material; a cutting reference pulse generator driven by the moving material for generating one pulse per unit length of moving material; means for connecting said preset reference pulse generator to the frequency based control system to preset the cutoff knife cycle as near as possible into said proper synchronism before any stock material is moved; and means operable upon initiation of movement of stock material for disconnecting said preset reference pulse generator and for connecting said cutting reference pulse generator to the frequency based control system.

Claim 5

The invention defined in claim 1, wherein said means for continuously comparing the reference and feedback pulse trains comprises: speed control means for adjusting the speed of the cutoff knife as a function of the frequency difference between the reference and feedback pulses; and position control means for adjusting the phase of the knife cycle with respect to a properly corresponding point on the moving piece to be cut for proper synchronism therebetween.

Claim 6

The invention defined in claim 1, together with: manually settable means for selecting a desired number of pieces to be cut for a single order; a counter for automatically counting the pieces as they are cut; means operable to transfer the setting of said manually settable means to said counter; means responsive to operation of said frequency based control system for causing said counter to count once for each cycle of the cutoff knife; and means responsive to said counter counting out for stopping the apparatus from cutting any further pieces for that order.

Claim 7

The invention defined in claim 5, together with: an add-on counter manually settable to add a desired number of pieces to the order previously registered in the first-mentioned counter; and means for temporarily substituting said add-on counter in place of said first-mentioned counter for counting pieces until it counts out and then transferring back to said first-mentioned counter to resume counting of the balance of the order after the add-on pieces have been cut.

Claim 8

The invention defined in claim 1, together with: a sheet length readout device for displaying the length of the sheets being cut; means responsive to movement of the stock material for operating said sheet length readout device; and means responsive to cyclic operation of said cutoff knife for cycling said sheet length readout device to display the length of alternate sheets.

Claim 9

The invention defined in claim 1, together with: a footage counter for displaying the total length of stock material that has been used; and means responsive to movement of said stock material for operating said footage counter.

Claim 10

The invention defined in claim 1, wherein said means for continuously comparing the reference and feedback pulse trains comprises: means for shaping said pulses of both the reference and feedback pulse trains to uniform widths; and said means responsive to detection of a difference in the reference and feedback pulse trains comprises integrator means responsive to the difference in the frequencies of the uniform width pulse trains for providing said error signal.

Claim 11

The invention defined in claim 9, wherein said meaNs responsive to said error signal comprises: means for operating the correction motor and the variable speed drive mechanism to adjust the speed of the cutoff knife for accurate cutoff of the correct length of piece.

Claim 12

The invention defined in claim 1, wherein said means for continuously comparing the reference and feedback pulse trains comprises: means for cancelling coincident pulses in the two trains, that is, pulses whose leading edges are within a predetermined time limit of each other, and for passing the pulses outside such time limit for position control; a position pulse generator responsive to the trains of out of phase pulses passed by said cancelling means for providing a first pulse train output when the reference pulses lead the feedback pulses or to provide a second pulse train when the feedback pulses lead the reference pulses, said first and second pulse trains having a pulse width proportional to their phase displacement and a frequency proportional to the stock material speed; and said means responsive to detection of a difference in the reference and feedback pulse trains comprises integrator means responsive to said first or said second pulse train for providing said error signal.

Claim 13

The invention defined in claim 11, wherein said means responsive to said error signal comprises: means for rotating the correction motor to adjust the variable drive mechanism and to adjust the position of the cutoff knife relative to the position of the moving stock material for accurate cutoff of the correct length of piece.

Claim 14

In a knife control apparatus for providing accurate control of the length of sheets cut off from a high-speed, continuously moving web, the apparatus having web forming and moving means, a main motor and a clutch operable to couple the main motor to the web moving means to move the web past a cyclic cutoff knife, the combination comprising: a variable speed drive mechanism driven by the main motor for driving the cyclic cutoff knife; a correction motor coupled to said variable speed mechanism; motor control means responsive to an error signal for operating said correction motor in the proper direction to adjust the variable speed drive mechanism thereby to adjust the cutoff knife cycle relative to the web speed and control the cutoff length of the sheets; and a frequency based control system for continuously monitoring the cutoff length of the sheets and for providing an error signal whenever a variation from a preselected sheet length is detected comprising: reference pulse generating means for providing a train of pulses having a frequency proportional to the stock material speed; feedback pulse generating means for providing a fixed number of pulses per operating cycle of the cutoff knife having a frequency proportional to the cutoff knife speed; cutoff length selecting means settable for a desired length of sheets to be cut thereby selecting a portion of said fixed number of feedback pulses and deleting the remainder thereof per cycle of the cutoff knife; means for comparing the reference pulses and selected portion of feedback pulses to detect a difference thereon indicative of a deviation between web movement and knife operation that will produce an incorrect length if left uncorrected; and means responsive to detection of such difference for providing a directional error signal for operating said motor control means to correct such deviation.

Claim 15

In a knife control apparatus for providing accurate control of the length of sheets cut off from a high-speed, continuously moving web, the apparatus having web forming and moving means, a main motor and a clutch operable to couple the main motor to the web moving means to move the web past a cyclic cutoff knife, the combination comprising: a variable speed drive mechanism driven by the main motor for driving the cyclic cutoff knife; a correction motor coupled to said variable speed mechanism; motor control means responsive to an error signal for operating said correction motor in the proper direction to adjust the variable speed drive mechanism thereby to adjust the cutoff knife cycle relative to the web speed and control the cutoff length of the sheets; and a frequency based control system for continuously monitoring the cutoff length of the sheets and for providing an error signal whenever a variation from a preselected sheet length is detected comprising: reference pulse generating means for providing a train of pulses having a frequency proportional to the stock material speed; feedback pulse generating means for providing a fixed number of pulses per operating cycle of the cutoff knife having a frequency proportional to the cutoff knife speed; cutoff length selecting means settable for a desired length of sheets to be cut thereby selecting a portion of said fixed number of feedback pulses and deleting the remainder thereof per cycle of the cutoff knife; means for comparing the reference pulses and selected portion of feedback pulses to detect a difference thereon indicative of a deviation between web movement and knife operation that will produce an incorrect length if left uncorrected; and means responsive to detection of such difference for providing a directional error signal for operating said motor control means to correct such deviation.

Claim 16

The invention defined in claim 13, wherein said means responsive to detection of such difference for providing a directional error signal comprises: dead band providing means whereby said directional error signal providing means provides an error signal only when said difference is above a predetermined adjustable value thereby to stabilize the corrective action.

Claim 17

The invention defined in claim 13, wherein said cutoff length selecting means comprises: a counter for counting said feedback pulses haviNg a plurality of outputs providing pulse trains of a plurality of frequencies indicative of a plurality of progressive percentages, respectively, of the total length of sheet for a given web speed; manual switches connected to said outputs operable to select the sheet length in terms of small fractions of an inch by closing the proper contacts thereby deleting the pulses coming to the contracts left open; and a scaler connected to said switches for receiving a plurality of different frequency pulse trains of noncoincident pulses and providing a single train of pulses equal to the sum thereof for comparison with said reference pulses.

Claim 18

The invention defined in claim 15, wherein said cutoff length selecting means also comprises: a second set of like manual switches connected in series to the outputs of said counter in parallel with the first-mentioned switches; and means for switching either the first or the second set of switches into operative connection in the system to control the length of sheet whereby when one set of such switches is in use, the other set of switches can be preset and switched in at the appropriate time to change the length of sheets that are cut.

Claim 19

The invention defined in claim 15, wherein said means for comparing the reference pulses and selected portion of feedback pulses comprises: means for making a first comparison of said reference pulses and selected portion of feedback pulses to detect a difference in their frequencies; and means for making a second comparison of said reference pulses and selected portion of feedback pulses to detect a difference in their phases for knife position regulation; and said means for providing a directional error signal comprises: means responsive to the difference in their frequencies for providing a knife speed error signal having a polarity according to which frequency is higher and a magnitude proportional to the frequency difference; and means responsive to the difference in phases for providing a knife position error signal having a polarity according to which pulses are leading and a magnitude proportional to the phase difference.

Claim 20

The invention defined in claim 17, wherein said means for making a second comparison comprises: a pair of frequency dividers for the reference pulses and selected portion of feedback pulses, respectively, affording selection of the gain for best performance of the knife position regulation; and a pulse canceller connected to said frequency dividers for cancelling pulses whose leading edges coincide within a predetermined time limit and for passing both reference pulses and feedback pulses whose leading edges are displaced more than said limit; and a reversible shift register connected to said pulse canceller for providing one or another pulse output according to which pulses have a leading phase and having a pulse width proportional to the phase difference.

Claim 21

In a frequency based knife control system for providing accurate control of the length of pieces cut off from a high-speed continuously moving elongated stock material, the system having a main motor and means powered thereby for driving the stock material past a rotary cutoff knife, and means comprising a variable speed drive mechanism powered by the main motor for driving the cutoff knife and being adjustable to control the speed thereof, the improvement comprising: reference pulse generating means for generating pulses of a frequency proportional to the speed of the stock material; feedback pulse generating means for generating a fixed number of pulses per cycle of the cutoff knife; cutoff length selecting means settable for a desired length of pieces to be cut thereby selecting a portion of said fixed number of feedback pulses and deleting the remainder thereof; a reversible correction motor coupled to the variable speed drive mechanism for adjusting it to increase or decrease the speed of the cutoff knife relative to the speed Of the main motor; control means for said correction motor operable to run it in the forward or reverse direction; pulse integrator means for controlling said motor control means comprising speed control means responsive to said reference pulses or the selected portion of said feedback pulses having the higher frequency for controlling said motor control means in a manner to run the correction motor in the proper direction to adjust the speed of the cutoff knife and to reduce the frequency difference of the reference and feedback pulses; pulse canceller means for cancelling reference and feedback pulses that have a phase coincidence within a predetermined time limit and for passing reference and feedback pulses that have a larger phase difference; means responsive to the pulses passed by said pulse canceller means for producing position faster or position slower control pulses according to whether the reference or the feedback pulses have a leading phase, these pulses having a width proportional to such phase difference and a frequency proportional to the speed of the stock material; and said pulse integrator means also comprising position control means responsive to said position or said position slower control pulses for controlling said motor control means in a manner to rotate the correction motor in the proper direction to adjust the rotary position of the cutoff knife into correct phase with a given point on the piece of advancing stock material to be cut and to reduce the noncoincidence of the phases of the reference and feedback pulses.

Claim 22

In a frequency based knife control system for providing accurate control of the length of pieces cut off from a high-speed continuously moving elongated stock material, the system having a main motor and means powered thereby for driving the stock material past a rotary cutoff knife, and means comprising a variable speed drive mechanism powered by the main motor for driving the cutoff knife and being adjustable to control the speed thereof, the improvement comprising: reference pulse generating means for generating pulses of a frequency proportional to the speed of the stock material; feedback pulse generating means for generating a fixed number of pulses per cycle of the cutoff knife; cutoff length selecting means settable for a desired length of pieces to be cut thereby selecting a portion of said fixed number of feedback pulses and deleting the remainder thereof; a reversible correction motor coupled to the variable speed drive mechanism for adjusting it to increase or decrease the speed of the cutoff knife relative to the speed Of the main motor; control means for said correction motor operable to run it in the forward or reverse direction; pulse integrator means for controlling said motor control means comprising speed control means responsive to said reference pulses or the selected portion of said feedback pulses having the higher frequency for controlling said motor control means in a manner to run the correction motor in the proper direction to adjust the speed of the cutoff knife and to reduce the frequency difference of the reference and feedback pulses; pulse canceller means for cancelling reference and feedback pulses that have a phase coincidence within a predetermined time limit and for passing reference and feedback pulses that have a larger phase difference; means responsive to the pulses passed by said pulse canceller means for producing position faster or position slower control pulses according to whether the reference or the feedback pulses have a leading phase, these pulses having a width proportional to such phase difference and a frequency proportional to the speed of the stock material; and said pulse integrator means also comprising position control means responsive to said position or said position slower control pulses for controlling said motor control means in a manner to rotate the correction motor in the proper direction to adjust the rotary position of the cutoff knife into correct phase with a given point on the piece of advancing stock material to be cut and to reduce the noncoincidence of the phases of the reference and feedback pulses.