Methods for calibration and automatic alignment in friction drive apparatus

Abstract

A friction drive apparatus includes an edge detection system for determining a lateral position of a strip material advancing in a longitudinal direction. The edge detection system includes a first sensor and a second sensor for monitoring the lateral position of the strip material. The friction drive apparatus also includes instructions for automatically aligning the strip material as the strip material is advanced a predetermined aligning distance and instructions for calibrating the second sensor with respect to the first sensor to compensate for any potential discrepancies therebetween. The apparatus and methods of the present invention ensure that the strip material is properly aligned in the friction drive apparatus and limit waste of strip material during those operations.

We claim:  
     
         1 . A friction drive apparatus for feeding a strip material in a longitudinal direction along a feed path for printing, plotting, or cutting, said strip material having a first longitudinal edge and a second longitudinal edge, said friction drive apparatus comprising: 
 a first friction wheel associated with said first longitudinal edge of said strip material;    a second friction wheel associated with said second longitudinal edge of said strip material;    a first motor drive for rotating said first friction wheel;    a second motor drive for rotating said second friction wheel;    a processor for controlling said first motor drive and said second motor drive independently; and    a first sensor for monitoring lateral position of said strip material, said first sensor disposed behind said first friction wheel and said second friction wheel with respect to direction of motion of said strip material, said first sensor generating a first sensor signal being received by said processor to automatically align said strip material with respect to said feed path at an onset of an operation.    
     
     
         2 . The friction drive apparatus according to  claim 1  wherein said apparatus further comprises: 
 means for limiting longitudinal displacement of said strip material to a predetermined aligning distance.  
 
     
     
         3 . The friction drive apparatus according to  claim 1  wherein said apparatus further comprises: 
 a second sensor disposed on an opposite side of said friction wheels from said first sensor, said second sensor generating a second sensor signal being received by said processor to automatically align said strip material with respect to said feed path when feed direction of said strip material is reversed.  
 
     
     
         4 . The friction drive apparatus according to  claim 3  wherein said apparatus further comprises: 
 first means for limiting longitudinal displacement of said strip material to a predetermined aligning distance when said strip material is advanced in a forward X-direction; and  
 second means for limiting longitudinal displacement of said strip material to said predetermined aligning distance when said strip material is advanced in a reverse X-direction.  
 
     
     
         5 . The friction drive apparatus according to  claim 3  wherein said first sensor is calibrated with respect to said second sensor to compensate for any discrepancies therebetween.  
     
     
         6 . The friction drive apparatus according to  claim 1  wherein said apparatus further comprises: 
 means for including instructions to automatically align said strip material within said apparatus by advancing said strip material a predetermined distance in a forward X-axis direction while steering said strip material to cover substantially a half of said first sensor.  
 
     
     
         7 . The friction drive apparatus according to  claim 6  wherein said means further comprises instructions to calibrate said first sensor with respect to a second sensor disposed on an opposite side of said friction wheels from said first sensor.  
     
     
         8 . The friction drive apparatus according to  claim 1  wherein said apparatus further comprises a second sensor being spaced away from said first sensor, said second sensor generating a second sensor signal to determine in cooperation with said first sensor signal lateral deviation of said strip material at a steering point disposed on an opposite side of said first and second friction wheels for automatically aligning said strip material when feed direction of said strip material is reversed.  
     
     
         9 . The friction drive apparatus according to  claim 1  wherein said first sensor is positioned along said first longitudinal edge of said strip material.  
     
     
         10 . The friction drive apparatus according to  claim 1  wherein said first sensor is positioned along an edge of a stripe disposed on the underside of said strip material.  
     
     
         11 . The friction drive apparatus according to  claim 1  wherein said processor in response to said first sensor signal received from said first sensor commands said first motor drive and said second motor drive to rotate said first friction wheel and said second friction wheel, respectively, independently at different speeds to properly align and position said strip material.  
     
     
         12 . The friction drive apparatus according to  claim 1  wherein said first sensor is a linear array digital sensor.  
     
     
         13 . The friction drive apparatus according to  claim 1  further comprises a sensor stop for positioning said first longitudinal edge of said strip material over said first sensor when said strip material is placed into said friction drive apparatus  
     
     
         14 . A method for aligning a strip material in a friction drive apparatus, said method comprising the steps of: 
 placing a strip material into said friction drive apparatus;    moving said strip material a predetermined aligning distance in a forward X-axis direction while steering said strip material with respect to a first sensor to align said strip material in said X-axis direction.    
     
     
         15 . The method according to  claim 14  further comprising a subsequent step of: 
 moving said strip material said predetermined aligning distance in a reverse X-axis direction while steering said strip material with respect to a second sensor spaced away from said first sensor.  
 
     
     
         16 . The method according to  claim 15  wherein said first sensor and said second sensor are disposed along a first longitudinal edge of said strip material.  
     
     
         17 . The method according to  claim 15  wherein said first sensor and said second sensor are associated with a stripe disposed on the underside of said strip material.  
     
     
         18 . The method according to  claim 15 , further comprising subsequent steps of: 
 incrementing a counter by one after determining that said strip material has not been aligned; and    repeating above steps until said counter reaches a fixed predetermined number.    
     
     
         19 . The method according to  claim 15 , further comprising a subsequent step of: 
 calibrating said first sensor with respect to said second sensor to compensate for any discrepancies between outputs of said first sensor and said second sensor when said strip material is aligned within said friction drive apparatus.    
     
     
         20 . The method according to  claim 19  wherein said step of calibrating further comprises the steps of: 
 moving said strip material a predetermined calibration distance in said forward X-axis direction;  
 establishing a first sensor forward position of said strip material;  
 establishing a second sensor forward position of said strip material;  
 calculating a first difference between said first sensor forward position and said second sensor forward position; and  
 adjusting a center reference position of said first sensor to calibrate said first sensor with respect to said second sensor.  
 
     
     
         21 . The method according to  claim 14  wherein said step of moving said strip material in said reverse X-axis direction further comprises the step of: 
 determining whether said second sensor is half covered; and  
 further steering said strip material to position said strip material to cover half of said second sensor.  
 
     
     
         22 . The method according to  claim 14 , wherein said step of placing said strip material into said friction drive apparatus further comprises the step of: 
 placing a first longitudinal edge of said strip material against a plurality of sensor stops.    
     
     
         23 . The method according to  claim 14 , further comprising the step of: 
 saving an initial X-axis aligning position of said strip material subsequent to said step of placing said strip material into said friction drive apparatus.    
     
     
         24 . The method according to  claim 14  wherein said step of moving said strip material in said forward X-axis direction further comprises the step of: 
 determining whether said first sensor is half covered; and  
 further steering said strip material to position said strip material to cover half of said first sensor.  
 
     
     
         25 . A method for calibrating an edge detection system in a friction drive apparatus, said method comprising the steps of: 
 moving a strip material a predetermined calibration distance in a forward X-axis direction;    establishing a first sensor forward position of said strip material with respect to a first sensor;    establishing a second sensor forward position of said strip material with respect to a second sensor;    calculating a first difference between said first sensor forward position and said second sensor forward position to define a sensor adjustment; and    adjusting a center reference position of said second sensor by said sensor adjustment to calibrate said second sensor with respect to said first sensor so as to compensate for differences between outputs of said first sensor and said second sensor when said strip material is aligned.    
     
     
         26 . The method according to  claim 25  further comprising subsequent steps of: 
 incrementing a counter after determining that said first difference is substantially zero; and  
 repeating above steps until said counter reaches a fixed predetermined number.  
 
     
     
         27 . The method according to  claim 25  further comprising the steps of: 
 incrementing said center reference position of said second sensor when said first difference is positive.  
 
     
     
         28 . The method according to  claim 25  further comprising the steps of: 
 decrementing said center reference position of said second sensor when said first difference is negative.  
 
     
     
         29 . The method according to  claim 25  further comprising a preceding step of: 
 saving an initial X-axis calibration position of said strip material.  
 
     
     
         30 . The method according to  claim 25  further comprising the steps of: 
 moving said strip material said predetermined calibration distance in reverse X-axis direction;  
 establishing a first sensor reverse position of said strip material with respect to said first sensor;  
 establishing a second sensor reverse position of said strip material with respect to said second sensor;  
 calculating a second difference between said first sensor reverse position and said second sensor reverse position; and  
 calculating an average of said first difference and said second difference to define said sensor adjustment prior to said step of adjusting said center reference position of said second sensor.  
 
     
     
         31 . The method according to  claim 30  further comprising the steps of: 
 incrementing a counter after determining that said first difference and said second difference are substantially zero; and  
 repeating above steps until said counter reaches five.  
 
     
     
         32 . The method according to  claim 30  further comprising the steps of: 
 incrementing said center reference position of said second sensor when said first difference and said second difference are positive.  
 
     
     
         33 . The method according to  claim 30  further comprising the steps of: 
 decrementing said center reference position of said second sensor when said first difference and said second difference are negative.  
 
     
     
         34 . An edge detection system in a friction drive apparatus for feeding a strip material in a longitudinal direction along a feed path for printing, plotting, or cutting, said strip material having a first longitudinal edge and a second longitudinal edge, said edge detection system comprising: 
 a first sensor for monitoring lateral position of said strip material, said first sensor generating a first sensor signal being received by a processor to automatically align said strip material with respect to said feed path at an onset of an operation; and    a second sensor spaced apart from said first sensor, said second sensor generating a second sensor signal being received by said processor to automatically align said strip material with respect to said feed path when feed direction of said strip material is reversed.    
     
     
         35 . The edge detection system according to  claim 34  further comprising: 
 a first light source associated with said first sensor; and  
 a second light source associated with said second sensor.  
 
     
     
         36 . The edge detection system according to  claim 34  further comprising: 
 a first sensor stop associated with said first sensor for positioning said first longitudinal edge of said strip material over said first sensor when said strip material is placed into said friction drive apparatus; and  
 a second sensor stop associated with said second sensor for positioning said first longitudinal edge of said strip material over said second sensor when said strip material is placed into said friction drive apparatus.  
 
     
     
         37 . The edge detection system according to  claim 34  wherein each said first and said second sensors comprises: 
 an inner edge disposed inward from said feed path of said strip material;  
 an outer edge outward from said feed path of said strip material; and  
 a center reference position disposed between said outer edge and said inner edge.  
 
     
     
         38 . The edge detection system according to  claim 37  wherein said sensor further comprises: 
 a plurality of pixels arranged in a linear array extending from said outer edge to said inner edge.  
 
     
     
         39 . The edge detection system according to  claim 37  wherein said center reference position of said second sensor is adjusted to compensate for discrepancies between outputs of said first sensor and said second sensor when said strip material is aligned.  
     
     
         40 . A method for aligning a strip material in an apparatus for performing a work operation on said strip material, said strip material being advanced in an X-axis direction in a course of a work operation, said method comprising the steps of: 
 placing a strip material into said apparatus without precisely aligning said strip material in said X-axis direction;    establishing an initial Y-axis position of said strip material at an initial X-axis position;    displacing said strip material a predetermined aligning distance forward in said X-axis direction;    establishing a second Y-axis position of said strip material at a second X-axis position; and    moving said strip material within said apparatus to reduce misalignment of said strip material in said X-axis direction.    
     
     
         41 . The method according to  claim 40  further comprising subsequent steps of: 
 determining whether said strip material is aligned in said X-axis direction within said apparatus; and  
 repeating said steps of establishing, displacing, establishing, and moving if said strip material is not properly aligned in said X-axis direction within said apparatus.  
 
     
     
         42 . The method according to  claim 40  further comprising subsequent steps of: 
 displacing said strip material said predetermined aligning distance in a reverse X-axis direction; and  
 again moving said strip material within said apparatus to further reduce misalignment of said strip material in said Y-axis direction.  
 
     
     
         43 . The method according to  claim 40  wherein said step of moving further comprising a step of: 
 shifting said strip material such that one longitudinal edge of said strip material travels a greater distance than another longitudinal edge of said strip material.  
 
     
     
         44 . A method of aligning sheet material in an apparatus, the apparatus having a drive mechanism for engaging and shifting the strip material in the course of a work operation performed by the apparatus on the strip material, comprising the steps of: 
 positioning the strip material in the apparatus in engagement with the drive mechanism without regard to a precise alignment of the strip material with the longitudinal direction;    moving the strip back and forth in the longitudinal direction by means of the drive mechanism;    measuring the lateral movement of the strip material at a given point in the apparatus, the lateral movement resulting from misalignment of the strip material and movement in the longitudinal direction; and    correcting the misalignment by shifting the strip material with the drive mechanism to reduce the lateral movement resulting from the misalignment during movement in the longitudinal direction.    
     
     
         45 . The method according to  claim 44  wherein the step of moving the strip material back and forth in the longitudinal direction moves the strip material a predetermined amount with each movement.  
     
     
         46 . The method according to  claim 44  wherein the step of moving back and forth is performed a limited number of times and the step of correcting is performed with each movement in one direction or the other.