Abstract:
A caliper for measuring the thickness of collated printed products and which has a lever arm which is pressed into engagement with each of a plurality of printed products as they are serially conveyed past a measurement station. The lever arm is actuated by a servo motor which includes an encoder, and when the lever arm is pressed into engagement with each product, the position of the lever arm is sensed by the encoder which then delivers a signal to a controller where the thickness is calculated and compared with a predetermined correct value. A method of calibrating the caliper is also disclosed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a caliper for measuring the thickness of each of a plurality of collated printed products, such as books, magazines, signatures, and the like, so as to determine whether the printed products contain the proper number of sheets.  
           [0002]    In collating conveyor systems, it is common to incorporate a caliper along the path of travel of the products to check the thickness of each product and thereby verify that there has not been a malfunction in the collating process resulting in either missing sheets or excessive sheets. If a malfunction is detected, the caliper issues a signal which causes the non-complying product to be rejected or otherwise identified to permit the error to be corrected.  
           [0003]    Calipers used with such systems in the past have typically comprised a lever arm which is moved into contact with the advancing products by means of an actuator, such as an air cylinder or a linear electric transducer, and a microswitch is provided which issues a go/no-go signal depending upon whether or not the lever arm has been pivoted by the actuator into the product to an elevation which indicates the proper number of sheets. Such prior devices require several mechanical linkages, and it is difficult to obtain highly accurate readings.  
           [0004]    It is accordingly an object of the present invention to provide an improved caliper of the described type, which is highly accurate and reliable, and which is readily programmable to facilitate its initial set up and operation.  
         SUMMARY OF THE INVENTION  
         [0005]    The above and other objects and advantages of the invention are achieved by the provision of an apparatus and method which includes an endless conveyor configured for serially conveying the printed products along a path of travel, and a lever arm mounted above the conveyor at a measurement station and for pivotal movement about a pivot axis which is transverse to the path of travel of the conveyor. An electric motor is provided with its output spindle connected to the lever arm so that the lever arm pivots about the pivot axis of the lever arm upon rotation of the output spindle. An encoder is connected to the output spindle for sensing the rotational position of the output spindle and thus the pivotal position of the lever arm, and a controller is provided which is responsive to a signal from the encoder for calculating the thickness of a printed product upon the lever arm being pivoted by the electric motor into pressing engagement with the upper surface of the product. The controller also compares the calculated thickness with a predetermined correct value, and issues a reject or other signal whenever the calculated thickness varies from the predetermined correct value by more than a permissible tolerance.  
           [0006]    In a preferred embodiment, the apparatus further comprises a lifting member positioned to engage and lift the undersurface of each product as it is conveyed past the lever arm, and so that at least a portion of each product is lifted when it is engaged by the lever arm. The lifting member preferably comprises an eccentric roller which is rotated about an axis which is traverse to the direction of the conveyed products and a second electric motor for rotating the roller about its axis at a peripheral speed which is substantially equal to the conveying speed of the products on the conveyor.  
           [0007]    The electric motor which is connected to the lever arm preferably comprises a servo motor of the type wherein its rotational torque may be controlled by the level of the power supplied thereto. In this case, the servo motor may be operated at a relatively high power level so as to pivot the lever arm about its pivot axis to press or bias the lever arm into the product and squeeze the product between the lever arm and the underlying eccentric roller, until a predetermined resistance is reached. The encoder senses the rotational position at this point, and the thickness may be accurately calculated in the controller.  
           [0008]    Subsequent to the sensing step, the power level to the motor may be reduced to a level where the lever arm may be easily pivoted. This facilitates the continued advance of the measured product and the receipt of a trailing product at the measurement station.  
           [0009]    The conveyor may take the form of a mail table having a flat upper surface with a pair of transversely spaced drive chains. This embodiment is particularly suitable for processing complete books or other printed products which lie flat on the table as they are advanced by the conveyor. Also, in such embodiment, the lever arm, the electric motor, and the encoder may be mounted to a subassembly which is mounted for movement transversely across the path of travel of the products on the conveyor. Also, the lifting member may comprise a pair of transversely spaced apart eccentric rollers which are mounted below the upper surface of the table for rotation about a common axis which is transverse to the path of travel. The subassembly may be selectively moved transversely so that the lever arm may be positioned to cooperate with either one of the rollers. This configuration permits different areas of the products to be sensed by the caliper, which can be of significant benefit in instances where a card is inserted in each product and it is not desired to measure through the card. Thus the subassembly can be shifted to measure at a location where the card is not present. In other cases, it may be desired to measure through the card, and the ability to laterally shift the subassembly also permits this function.  
           [0010]    The caliper may be initially calibrated by positioning a product with the correct number of sheets and thus with the correct thickness at the measurement station. The motor is then actuated to move the lever arm downwardly to squeeze the product until the predetermined resistance is reached. The encoder then senses the position of the lever arm, and the controller calculates and stores the correct thickness value.  
           [0011]    The caliper of the present invention is able to continuously process differing versions of products having differing thicknesses. In this embodiment, the host machine controller can be taught the thickness of several different product versions, and the host machine controller is then able to tell the caliper controller which version is at the measurement station and how thick it should be. The caliper can then evaluate the thickness based upon the correct thickness for that version.  
           [0012]    The conveyor may also take the form of a “saddle” conveyor wherein the products straddle the conveyor. This embodiment may utilize only a single eccentric roller to lift the products at the measurement station, and it measures half the thickness of each product, but it is otherwise similar in its calibration and operation to the above described mail table embodiment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The present invention now will be described more fully with reference to the accompanying drawings, in which:  
         [0014]    [0014]FIG. 1 is a fragmentary perspective view of a conventional mail table with one embodiment of the caliper of the present invention attached thereto;  
         [0015]    [0015]FIG. 1A is a fragmentary view of the eccentric roller and lever arm of the caliper shown in FIG. 1;  
         [0016]    [0016]FIG. 2 is a perspective view of the caliper of FIG. 1 with parts broken away;  
         [0017]    [0017]FIG. 3 is a sectional view taken along the line  3 - 3  of FIG. 2;  
         [0018]    [0018]FIG. 4 is a sectional view similar to FIG. 3 and illustrating the lifting of a printed product by the eccentric roller;  
         [0019]    [0019]FIG. 5 is a perspective view of a saddle conveyor with a second embodiment of the caliper of the invention;  
         [0020]    [0020]FIG. 6 is a sectional view taken along the line  6 - 6  of FIG. 5;  
         [0021]    [0021]FIG. 7 is a perspective view of the eccentric roller as used in the caliper of FIG. 5; and  
         [0022]    [0022]FIG. 8 is an exploded perspective view of the caliper of FIG. 5. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    [0023]FIGS. 1-4 illustrate an embodiment of the caliper  10  of the present invention which is used in association with a mail table  11  or the like. As is conventional, the mail table  11  is positioned downstream of a collating assembly line or trimmer and it incorporates two feed chains  12 ,  13  which carry the collated products P serially along the table and past a measurement station which is defined by the location of the caliper  10 . As further described below, the caliper  10  serves to measure the thickness of the individual products to determine whether the proper number of sheets are present in each product.  
         [0024]    The caliper  10  includes a pair of end plates  15 ,  16  which are fixed to opposite sides of the table, and a pair of parallel upper guide rods  18 ,  19  which are fixed to the end plates so as to extend transversely across and above the table  11 . The two upper guide rods  18 ,  19  in turn mount a subassembly  20  which is slideable along the rods in the manner further described below. A pair of lower rods  22 ,  23  are fixed to extend between the end plates so as to extend below the upper surface of the table.  
         [0025]    The subassembly  20  comprises a front mounting plate  25  having a pair of side plates  26 ,  27  mounted to the back side thereof, and a servo motor  28  is also mounted to the back side of the plate  25  so that the output spindle of the motor extends through an opening in the plate  25 . The output spindle of the servo motor mounts a radial pivot arm  30 . Also, a position block  32  is secured to the side plate  27  and is releasably fixed to the guide rod  19  so as to permit the subassembly  20  to slide between a rearward position as shown in FIGS. 1-2 and a forward position as further described below when the block  32  is loosened on the guide rod  19 .  
         [0026]    A motor mount  34  is fixed to the pair of lower rods  22 ,  23  so as to depend in a plane parallel to that of the front plate  25 . The motor mount  34  mounts a second servo motor  35  which has an output spindle which is rotatably connected to a shaft  36  via a timing belt and pulley assembly  37 . The shaft  36  extends parallel to and is rotatably supported from the lower rod  22  by a pair of swing arms  38 ,  39 . Also, the shaft  36  is rotatably connected to a pair of pulleys  41 ,  42  via the timing belt and pulley assemblies  43 ,  44  respectively. The pulleys  41 ,  42  are mounted via bearings so as to be rotatable about the axis of the lower rod  23 , and each of the pulleys  41 ,  42  mounts an eccentric roller  46  as best seen in FIG. 4.  
         [0027]    Each of the eccentric rollers  46  is generally circular but slightly eccentric in its peripheral outline, in that it has a generally circular outline but with a raised arcuate segment of increased radius along about ¼ of its periphery. In the specific embodiment illustrated in FIG. 4, the lower ¾ of the periphery of the roller  46  is defined by a radius R 1 , and the upper ¼ of the periphery, which defines the raised arcuate segment, is defined by a radius R 2 . The radius R 2  is centered on the axis of the rod  23 , while the radius R 1  is centered at a point slightly above the axis of the rod  23  to define an offset  48 , when the roller is rotated to the position shown in FIG. 4. Thus the portion of the outer periphery defined by the radius R 1  is in the nature of a relief.  
         [0028]    The radius R 2  is dimensioned to define a circumference which equals the distance between the products being conveyed along the table  11 , and the rollers  46  are mounted so that the raised arcuate segment of each roller extends through an opening in the upper surface of the table  11  and to a point slightly above the upper surface of the table. The radius R 1  is dimensioned so as to lie flush with or slightly below the upper surface of the table, and the offset  48  is typically about {fraction (1/16)} inch. Also, the raised arcuate segments of the two rollers are transversely aligned.  
         [0029]    The servo motor  28  may comprise for example Model No. MPL-A310P-HK22AA, manufactured by the Allen/Bradley Company, and the servo motor  35  may comprise for example Model No. MPL-310P-SJ22AA also manufactured by the Allen/Bradley Company. Also, the motor  28  includes a high resolution encoder, which is in turn connected to a controller  50 . The motor  35  also includes an encoder and is also connected to the controller  50 . The controller  50  for the caliper is in turn connected to a host machine controller  51  which includes a master encoder and controls the operation of the mail table  11  and supplies signals to the caliper controller  50  as further described below.  
         [0030]    As shown in FIGS. 1 and 2, the subassembly  20  is positioned in its rearward position, where it is held by the position block  32  which is locked to the rod  19 . In this position, the pivot arm  30  is aligned with the eccentric roller  46  which is mounted to the pulley  41 . Upon releasing the position block  32 , the subassembly  20  may be moved forwardly to a position (not illustrated) wherein the pivot arm  30  is aligned with the eccentric roller  46  which is mounted to the pulley  42 . The position block  30  may then be re-secured to hold the subassembly in the advanced position.  
       Calibrating the Caliper  
       [0031]    The caliper  10  as illustrated in FIGS. 1-4 may be initially calibrated for operation by the following steps:  
         [0032]    a. A product P with the correct number of sheets, and thus with the correct thickness, is placed on the mail table at the measurement position.  
         [0033]    b. The eccentric rollers  46  are rotated so that the roller which is aligned with the arm  30  lifts the product toward the arm.  
         [0034]    c. The controller  50  actuates the servo motor  28  at a relatively high power level, such as about 30 amps, to move the arm down to squeeze the product until a predetermined resistance is reached, and the controller  50  then calculates and stores the “correct” thickness, using an appropriate trigonometric function.  
         [0035]    d. The controller  50  adjusts the power to the motor  28  to a relatively low power setting such as about 2 amps, where the motor holds the arm  30  with a force which is easily overcome.  
         [0036]    e. The product P is advanced from the measurement station, and with the easily moveable arm  30  providing no significant resistance.  
       Operating Sequence  
       [0037]    After the calibration as described above is completed, the caliper is ready for operation, as follows:  
         [0038]    a. The mail table  11  is operated by the host machine controller  51  to serially convey the products P past the measuring station, and the servo motor  35  is operated at a speed monitored by the encoder of the motor  35  so that the peripheries of the eccentric rollers  46  have a speed which is in a one to one relationship with the advancing speed of the products along the table. Also, the raised arcuate segments of the eccentric rollers  46  are timed by a signal from the host machine controller so as to lift at least a portion of each product as it moves through the measurement station.  
         [0039]    b. With the servo motor  28  at the low power setting as indicated above, the lifted product engages the lever arm  30  and the lever arm is slightly lifted.  
         [0040]    C. The caliper is instructed to take the thickness reading based upon the position of the product as signaled by the host machine controller  51 . Shortly before that position is reached, e.g. about one inch before, the controller  50  turns on the full power to the servo motor  28  to move the arm  30  back downwardly, so as to squeeze the lifted portion of the product to the same predetermined power level achieved during the calibration sequence.  
         [0041]    d. While the product is being squeezed, the rotational position is noted by the encoder associated with the motor  28  and signaled to the controller  50 .  
         [0042]    e. The controller  50  calculates from the encoder signal the thickness of the particular product which is engaged, again using an appropriate trigonometric function.  
         [0043]    f. The calculated thickness is then compared with the predetermined correct value as determined during the calibration sequence, and a reject or other signal is issued whenever the calculated thickness varies from the predetermined correct value by more than a permissible tolerance.  
         [0044]    g. The controller  50  acts to reduce the power level to the motor  28  to the indicated low level, to minimize any resistance caused by the arm  30  to the continued movement of the product being measured and the arrival of the next product.  
         [0045]    In some applications, a card C, flyer, or other insert is inserted in each product which occupies only a portion of the area of the product, note FIG. 1A. Also, in such cases, it is often preferred not to measure through the area which contains the insert since erroneous thickness readings become more likely. With the embodiment of the caliper shown in FIGS. 1-4, this problem can be avoided by permitting the subassembly  20  to be shifted to operate with the eccentric roller  46  which is aligned with an area of the products where the insert is not present. In other cases, it may be desired to measure through the card, and the ability to laterally shift the subassembly also permits this function.  
         [0046]    Thus the test location of the products can be shifted between the left and right sides of the products by reason of the mobility of the subassembly, and it can also be shifted between the front and back edges of the products by the timing of the measurement sequence as signaled by the host machine controller.  
         [0047]    In an embodiment which does not include the eccentric rollers  46 , the caliper  10  is calibrated without lifting the products, and during operation, the products lift the lever arm  30  by reason of their own thickness while the arm is relaxed, i.e. under the low power setting. Thereafter, the power to the servo motor  28  is increased to lower the arm  30  and squeeze the product as described above.  
         [0048]    However, the lifting of the products at the measurement station is preferred since it avoids the need to move the arm  30  through the thickness of each product. Thus lifting the products permits the necessary pivotal movement of the lever arm  30  to be minimized, and the speed of operation may be increased.  
         [0049]    The caliper  60  of FIGS. 5-8 is designed for use with a “saddle” conveyor  61  wherein the collated products straddle a conveyor chain  62  having the form of an inverted V in transverse cross section, note FIG. 6. The caliper  60  includes a mounting base  64  mounting a pair of vertical side plates  65 ,  66  and a front plate  68 . The upper ends of the side plates  65 ,  66  are vertically slotted at  70 , and they mount a guide plate  72  which lifts the left half of the products as seen in FIG. 6 and supports the lifted half at about a 45° incline as it moves into the measurement station defined by the caliper  60 .  
         [0050]    A servo motor  74  and encoder are mounted to a motor mount  75 , which is in turn mounted between the two side plates  65 ,  66  so that the axis of the output spindle of the motor  74  is inclined at an angle of about 45° as seen in FIG. 6.  
         [0051]    A second servo motor  76  is mounted to the front plate  68  so that the motor  76  is positioned between the side plates  65 ,  66 , and the second motor  76  includes an output spindle which extends forwardly from the front plate  68  and mounts a drive pulley  77 . The front plate  68  also fixedly mounts a fixed shaft  78 , which in turn mounts a timing pulley  80  via a suitable bearing, such as a double row angular contact bearing. The drive pulley  77  and the pulley  80  are rotatably interconnected by a timing belt  81 , and the timing pulley  80  is fixed to an eccentric roller  82 , as best seen in FIG. 7. The eccentric roller  82  includes an inclined or conical outer periphery  83  which generally matches the inclination of the axis of the motor  74  where viewed in cross section, note FIG. 6.  
         [0052]    The output spindle of the motor  74  mounts a pivot arm  85  which, by reason of the inclined orientation of the motor, is aligned to oppose the inclined periphery  83  of the eccentric roller  82 .  
         [0053]    The eccentric roller  82  used in the embodiment of FIGS. 5-8 includes a raised arcuate segment  86  which is concentric to the reminder of the periphery and serves to lift each product into the lever arm at the measurement station. For this purpose, the roller  82  is positioned so that the raised segment  86  extends above the plane defined by the guide plate  72 , and the second motor  76  rotates the pulley  80  and eccentric roller  82  at a one to one timed relationship with the conveyor chain  62 , so that the raised segment  86  lifts each product as it moves through the measurement station.  
         [0054]    The calibration and operation of the caliper  60  of FIGS. 5-8 is essentially the same as that described above with respect to the caliper  10  of FIGS. 1-4. However, the caliper  60  includes only a single eccentric roller, and it is programmed to measure only one half the thickness of each product.  
         [0055]    Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.