Web cutting control system

Abstract

A web cutting control system controlling the speed of a rotary cutter for automatic, continuous and precise cutting of a web fed at a constant speed into predetermined lengths or on the marks on the web. Two transducers generate pulses the number of which corresponds to the web feed length and the rotating angle of the rotary cutter, respectively. Three sensors detect the marks on the web, the completion of cutting, and the arrival of the cutter blades, respectively, to control the flow of signals. A desired cutting length or the distance between the mark detection point and the point of completion of cutting is preset. A reversible counter receives the pulses from these two transducers and the difference signal between the preset value and a reference signal and performs reversible counting thereof, the result of which is used to control the speed of motor for the rotary cutter to bring its speed into synchronization with the web feed speed for accurate cutting.

What is claimed is: 
     
       1. A control system for cutting a web fed .[.at a constant-speed.]. by means of a rotary cutter driven by a motor selectively either into predetermined lengths or at fixed positions thereof, said control system comprising in combination: a. first transducer for generating pulses, the number thereof being proportional to the length of the web which has been fed;   b. a second transducer for generating pulses, the number thereof being proportional to the angle through which said rotary cutter has rotated;   c. a first setting means for setting reference pulses, the number thereof being predetermined by a fixed rotating angle of said rotary cutter;   d. a first sensor for detecting the marks put beforehand on the web to give a mark detection signal,   e. a second sensor for detecting completion of each cutting operation to give a cutting completion detection signal;   f. a third sensor for giving a mark distance discriminating signal for discrimination whether the detection of the next mark occurs before or after the completion of cutting on the last mark;   g. a second setting means for digitally setting selectively either a desired cutting length or the distance between the mark detection point and the cutting completion detection point;   h. a first reversible counting means responsive to a detection signal from said first sensor for counting any difference between the value preset on said first setting means and the value preset on said second setting means;   i. an addition/subtraction discriminating means for comparing the value from said first setting means with the value from said second setting means to couple said difference between said two values to said first reversible counting means as a signal to be added or a signal to be subtracted according to the result of comparison;   j. .[.said first.]. .Iadd.a second .Iaddend.reversible counting means receiving the pulses from said first transducer as a signal to be subtracted and the pulses from said second transducer as a signal to be added as well as the difference between said two values and performing reversible counting thereof;   k. a .[.differentiating.]. .Iadd.differencing .Iaddend.means for obtaining any difference between the result of said reversible counting by said .[.first.]. .Iadd.second .Iaddend.reversible counting means and a voltage proportional to the web feed speed;   l. a motor speed control means for discriminating the polarity of the output voltage from said .[.differentiating.]. .Iadd.differencing .Iaddend.means and controlling the speed of the motor for driving the rotary cutter according to the polarity and quantity of said output voltage; and   m. .[.a second.]. .Iadd.said first .Iaddend.reversible counting means .Iadd.further being .Iaddend.for subtracting from the preset value on said .[.first sensing.]. .Iadd.second setting .Iaddend.means a value corresponding to the length of the web which has been fed from the instant of detection by said first sensor to the instant of detection by said second sensor, in case the mark detection signal from said first sensor arrives .[.inn.]. .Iadd.in .Iaddend.advance of the cutting completion detection signal from said second sensor after the mark distance discriminating signal has come from said third sensor. .Iadd. 2. A control system for controlling the cutting of a web into predetermined lengths by means of a rotary cutter driven by a motor; said control system comprising in combination;   (a) a first transducer means for generating pulses, the number thereof being proportional to the length of the web which has been fed;   (b) a signal generator means for generating a signal proportional to the web speed;   (c) a second transducer means for generating pulses, the number thereof being proportional to the angle through which said rotary cutter has rotated;   (d) means for providing a first reference value, the magnitude thereof being related to the swept circumference of said rotary cutter;   (e) a sensor for establishing a knife position datum signal during each cutting cycle;   (f) a setting means for providing a second value representative of a desired predetermined cutting length;   (g) a combining means for combining said first and second values for obtaining a third value representative of the difference therebetween;   (h) a reversible counting means which receives the third value from said combining means in response to each datum signal and which subtracts therefrom the pulses from said first transducer means and adds thereto the pulses from said second transducer means to achieve a resultant count and producing a signal proportional to the resultant count;   (i) a differencing means for obtaining a signal proportional to any difference between said signal proportional to said resultant count and said signal proportional to the web speed; and   (j) motor control means responsive to the signal from said differencing means for controlling the operation of the motor to cut the web into said predetermined lengths. .Iaddend..Iadd. 3. A control system as claimed in claim 2 which is also capable of controlling the rotary cutter for cutting the web at points according to preapplied marks on the web, further comprising:   (a) a further sensor for detecting marks on the web at which the web is to be cut and for giving a mark detection signal;   said setting means having means for providing the second value which, when the system is operating to cut the web at points according to preapplied marks on the web, provides the second value having a magnitude being determined by the distance between the mark detection point and the knife position datum detection point, said distance being a distance from said mark detection point and measured along the path of web travel and around the swept circumference of the cutter to a position which lies in the range from the cutting point to a point spaced around the swept circumference of the cutter from said cutting point;   said combining means having means which, when the system is operating to cut the web at points according to preapplied marks on the web,   (1) when said further sensor detects a mark according to which a cut is to be made no earlier than the occurrence of the knife position datum signal for the next preceding cut, operates in a long-size mode for combining said first and second values to provide a third value representative of the difference between said first and second values, and   (2) when said further sensor detects a mark according to which a cut is to be made before the occurrence of the knife position datum signal for the next preceding cut, operates in a short-size mode for combining said first value, said second value and a value corresponding to the length of web which has been fed from the instant of detection by said further sensor to the occurrence of the knife position datum signal for obtaining the difference between the first and second values reduced by said value corresponding to the length of fed web to obtain a third value;   said reversible counting means having means which, when the system is operating to cut the web at points according to preapplied marks on the web,   (1) when said combining means operates in said long-size mode, during each cutting cycle receives said third value and which receives pulses from said second transducer means as a signal to be added and which on generation of a mark detection signal by said further sensor receives pulses from said first transducer means as a signal to be subtracted to achieve a resultant count and producing a signal porportional to said resultant count, and   (2) when said combining means operates in said short-sized mode, on generation of each datum signal by said firstmentioned sensor receives said third value and which also receives pulses from said second transducer means as a signal to be added and pulses from said first transducer means as a signal to be subtracted to achieve a resultant count and producing a signal proportional to said resultant count. .Iaddend..Iadd. 4. A control system as claimed in claim 3 further comprising more sensing means for determining whether the detection of a mark occurs before or after the occurrence of said knife position datum signal for the next preceding mark and for controlling the operation of said combining means and said reversible counting means in the appropriate one of said long-size mode and said short-size mode. .Iaddend..Iadd. 5. A control system for controlling the cutting of a web at points according to preapplied marks thereon by means of a rotary cutter driven by a motor, comprising:   (a) a first sensor for detecting marks on the web at which the web is to be cut and giving a mark detection signal;   (b) a second sensor for establishing a knife position datum signal during each cutting cycle, the distance between consecutive marks being greater than the distance between said first sensor and said second sensor, the latter distance being a distance from said first sensor and measured along the path of the web and around the swept circumference of the cutter to a position which lies in the range from the cutting point to a point spaced around the swept circumference of the cutter from said cutting point;   (c) a first transducer means for generating pulses, the number thereof being proportional to the length of the web which has been fed;   (d) a signal generator means for generating a signal proportional to the web speed;   (e) a second transducer means for generating pulses, the number thereof being proportional to the angle through which said rotary cutter has rotated;   (f) a first means for providing a first reference value, the magnitude thereof being related to the swept circumference of said rotary cutter;   (g) a second means for providing a second value, the magnitude thereof being determined by the distance between the mark detection point and the knife position datum detection point;   (h) a combining means for combining said first and second values for providing a third value representative of the difference therebetween;   (i) a reversible counting means which, during each cutting cycle, receives said third value and which receives pulses from said second transducer means as a signal to be added and which on generation of a mark detection signal by said first sensor receives pulses from said first transducer means as a signal to be subtracted to achieve a resultant count and producing a signal proportional to said resultant count;   (j) a differencing means for obtaining a signal proportional to any difference between said signal proportional to said resultant count and said signal proportional to the web speed; and   (k) motor control means responsive to the signal from said differencing means for controlling the operation of said motor to cut the web on said   
     
     
        marks. .Iaddend..Iadd. 6.  A control system as claimed in claim 5 in which the distance between consecutive marks can also be less than the distance between said first sensor and said second sensor, and said combining means, when the first sensor detects a mark according to which a cut is to be made no earlier than the occurrence of the knife position datum signal for the next preceding cut, operating in a long-size mode for combining said first and second values to provide the third value representative of the difference between said first and second values, and further having means which, when the first sensor detects a mark according to which a cut is to be made before the occurrence of the knife position datum signal for the next preceding cut, operates in a short-size mode for combining said first value, said second value and a value corresponding to the length of web which has been fed from the instant of detection by said first sensor to the occurrence of the knife position datum signal for obtaining the difference between the first and second values reduced by said value corresponding to the length of fed web to obtain a third value;   said reversible counting means when said combining means operates in said long-size mode, during each cutting cycle receives said third value and which receives pulses from said second transducer means as a signal to be added and which on generation of a mark detection signal by said first sensor receives pulses from said first transducer means as a signal to be subtracted to achieve a resultant count and producing a signal proportional to said resultant count, and further having means which, when said combining means operates in said short-size mode, on generation of each datum signal by said second sensor receives said third value and which also receives pulses from said second transducer means as a signal to be added and pulses from said first transducer means as a signal to be subtracted to achieve a resultant count and producing a signal proportional to said resultant count. .Iaddend..Iadd. 7. A control system as claimed in claim 6 further comprising mode sensing means for determining whether the detection of a mark occurs before or after the occurrence of said knife position datum signal for the next preceding mark and for controlling the operation of said combining means and said reversible counting means in the appropriate one of said long-size mode and said short-size mode. .Iaddend..Iadd. 8. A control system for controlling the cutting of a web at points according to preapplied marks thereon by means of a rotary, cutter driven by a motor, comprising:   (a) a first sensor for detecting marks on the web at which the web is to be cut and giving a mark detection signal;   (b) a second sensor for establishing a knife position datum signal during each cutting cycle, the distance between consecutive marks being smaller than the distance between said first sensor and said second sensor, the latter distance being a distance from said first sensor and measured along the path of the web and around the swept circumference of the cutter to a position which lies in the range from the cutting point to a point spaced around the swept circumference of the cutter from said cutting point;   (c) a first transducer means for generating pulses, the number thereof being proportional to the length of the web which has been fed;   (d) a signal generator means for generating a signal proportional to the web speed;   (e) a second transducer means for generating pulses, the number thereof being proportional to the angle through which said rotary cutter has rotated;   (f) a first means for providing a first reference value, the magnitude thereof being related to the swept circumference of said rotary cutter;   (g) a second means for providing a second value, the magnitude thereof being determined by the distance between the mark detection point and the knife position datum detection point;   (h) a combining means for combining said first value, said second value and a value corresponding to the length of web which has been fed from the instant of detection by said first sensor to the occurrence of the knife position datum signal for obtaining the difference between the first and second values reduced by said value corresponding to the length of fed web to obtain a third value;   (i) a reversible counting means which on generation of each datum signal by said second sensor receives said third value and which also receives pulses from said second transducer means as a signal to be added and pulses from said first transducer means as a signal to be subtracted to achieve a resultant count and producing a signal proportional to said resultant count;   (j) a differencing means for obtaining a signal proportional to any difference between said signal proportional to said resultant count and said signal proportional to the web speed; and   (k) motor control means responsive to the signal from said differencing means for controlling the operation of said motor to cut the web on said marks.