Abstract:
A labeling system employs a multi-processing computer control system for a servo motor which drives a label-carrying web. The system is responsive to the physical position of the labels and the physical position of containers or similar objects to which the labels are applied. The label application motion controller identifies the machine position and performs the mathematical calculations needed to create a piecewise continuous function motion profile required to achieve label contact at a predefined contact point on the surface of each container. Multiple functions may be used to construct a motion profile, which smoothly accelerates the label at a calculated acceleration needed to cause a label to arrive at the defined contact position on a container and to decelerates the carrier web after application. Correction for measured label registration error is provided for. Because the position of the label is based on the position of the container and a motion profile is calculated for each application, a fixed initial staging position of the label prior to application is not needed.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to control of container labeling equipment. More specifically, the invention relates to procedures and apparatus for accurately applying labels, such as pressure sensitive labels, to containers, utilizing continual monitoring of the absolute positions of the container and label in order to correctly apply the labels at high container speeds. 
     Currently-used label applicator systems frequently use a type of motion control system referred to as “velocity slaving”. Such systems start a predefined move of the label initiated by a stimulus and wherein the velocity of the label is dictated by the ratio-metric velocity of the container. The feedback as to the container velocity is generated by a main container-handling portion of the machine. Additionally, the end point for the application of the labels carried by a carrier web, to a particular container may be advanced or retarded based on a registration stimulus incorporated into the system. 
     One example of such a system is that which is described in U.S. Pat. No. 4,294,644. In that patent a servomotor is controlled pursuant to input of information relating to the relative velocities of the container and labels. One important limitation of such systems relates to the inability of many such systems to accelerate the velocity of a web carrying the labels to the linear velocity of the containers. This problem is particularly acute with respect to short labels. 
     In the &#39;644 patent there is described a control system for a servomotor which is responsive to the rate of feed or speed of the surface to be labeled as it is advanced to the labeler. One aspect of this previous system is to bring the servomotor up to a determined speed which is then held constant based on a assumption that conveyor speed is constant, so that the pulse output derived from a servomotor encoder will match the pulse output derived from the conveyor encoder. Such control systems are an essential feature of speed matching, i.e., “velocity slaving”. 
     Another significant limitation of the velocity slaved labeling process is due to the fact that it is linear in nature. Such linearity is manifested by the direct speed match between the master encoder and predictable linear acceleration and deceleration ramps controlling movement of the labels. By utilizing the linear properties of the velocity profile, basically a trapezoid, the label placement position is derived. Such devices are limited by the fact that very complex requirements may be needed to match the label velocity to the container surface velocity but the master encoder still runs at a constant rate thereby ruling out complex moves. One situation where such applicators fail is where the length of the material available to accelerate to the surface velocity of the container is too short. In this condition there is a requirement that the label carrier web must first be backed up before acceleration begins, which backup move would be a low acceleration, deceleration move in order to maintain necessary web tension, but a simple velocity slaved servo system cannot perform such a function. Limitations are also caused due to unusual shapes of some containers or due to unusual geometry of the labels which may require complex move profiles, which velocity slaved system cannot perform. 
     SUMMARY OF THE INVENTION 
     It is a principal object of the present invention to provide a new labeling control system which overcomes the foregoing limitations by utilizing a position slaved motion control system. An important aspect of the present invention is to provide a position slaved system which incorporates sufficient mathematical power to generate the necessary move profiles to control high speed labeling equipment. Such mathematical power is provided by the provision of high speed microprocessors used in conjunction with appropriate mathematical algorithms. 
     A further important aspect of the present invention involves the intimate coupling of the slave motion control system, which controls a label carrier web&#39;s position, to the position of the master feedback device, i.e., an encoder or a resolver, and thus to the position of the containers. In accordance with this aspect, an ability to offset the commanded position of the container (or other specific object on a container) is provided. This offset, in the form of an electronic signal received from a sensing device, identifies the absolute location of the container or object such as a previously applied label, which, in effect, produces an absolute position independent of the main container handling portion of the machine but which is relative to each container or object on the container. Further, in accordance with this aspect, a high precision position control results in the ability to provide very complex motion even at speeds of 750 labels per minute. Further, in accordance with this aspect, the motion of the label-carrying web is not linear with respect to the position of the master, i.e., the container handler. Further, even though accurate label placement cannot be predicted by means of velocity in complex non-linear situations, the use of position slaving, in accordance with the invention, overcomes this limitation. 
     In accordance with a further aspect of the invention a mathematical algorithm is provided for each specific container configuration or shape to allow for the ability to generate complex move profiles. In connection with such algorithms the position of the label carrier web is related mathematically to the position of each container as it travels and possibly rotates past the label application head. In a general sense the position of the slave carrier web is a function of the position of the master as follows: 
     
       
         Slave_position=f(master_position) 
       
     
     The function of the slave web position must be continuous throughout all master-feedback positions. Therefore, in the case of multiple functions, the first derivative of each function at the endpoint must equal the first derivative of the next function at its start point. That is, for successive functions ƒ 1 (i) and ƒ 2 (i), where i 0 &lt;i&lt;iƒ and iƒ&lt;i&lt;jƒ respectively for functions ƒ 1 (i) and ƒ 2 (i) we have: 
     
       
           d ƒ 1 ( i   ƒ )/ di=d ƒ 2 ( i   ƒ )/ di   
       
     
     This is adhered to so that a step change in velocity does not occur which could be detrimental to the label placement and damaging to the web material. 
     Briefly, the invention provides a method of labeling containers which includes providing a container handling machine such as conveyor in the case of an inline labeling machine, and a rotary bottle table in the case of a rotary labeling machine, for successively transporting containers past a label application station. The container handling machine i.e., “machine base” has an associated position signaling device such as a rotary encoder for providing data in electronic form identifying the position of the machine. In the preferred embodiment the encoder makes one revolution each time the container handling machine translates a distance equal to the center-to center distance between successive containers. As will be appreciated by those skilled in the are, the encoder could be set to make more than one revolution per machine pitch, if desired. 
     A label applicator is driven by a servomotor with said servomotor being controlled by a microprocessor-based slave position motion controller. The label applicator includes an electronic signal generator identifying the motion controller position of each successive label dispensed by the label applicator. 
     A machine base position control or identifying microprocessor is operatively connected to the label applicator&#39;s motion controlling microprocessor and to the machine base encoder. An electronic signal generator identifying the physical position of the container or object such as a previously applied label on the container surface is operatively connected to the position control microprocessor. The machine base position control microprocessor generates signals to the label applicator&#39;s motion controlling microprocessor that relates the position of the container to be labeled. 
     The label applicator servomotor contains an associated position identifying device such as an encoder that provides electronic data to the motion control microprocessor that relates to servo motor position and velocity. The motion control microprocessor is operatively connected to a label applicator servo amplifier, the servo motor encoder and to the machine base encoder. The label applicator servo amplifier is operatively connected and provides power to the label applicator servomotor. The motion control microprocessor generates a move profile for each successive label, using mathematical algorithms, and electronically controls the label applicator servo amplifier to vary the torque applied by the servomotor. Electronic feedback signals from the servo motor encoder and machine encoder to the motion control microprocessor provide the electronic position and velocity feedback data needed to control the torque applied by the servo amplifier and servo motor. Typically in accordance with the invention, such signals are continually generated and processed at a rate of at least once each 125 th  microsecond. 
     In accordance with a further aspect of the invention, a host microprocessor generates a pitch based electronic shift register that contains information on the labeling processes that need to be performed on a container. The host microprocessor provides the labeling commands and is operatively connected to a label position motion control microprocessor. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a simplified diagram showing a synchronous infeed rotary, dual application station pressure sensitive labeling machine that employs the invention; 
     FIG. 2 is a top view of a simplified diagram showing a random infeed linear or inline, dual application station pressure sensitive labeling machine that employs the invention; 
     FIG. 3 a  is a top view and FIG. 3 b  is an elevational view of the label application head assemblies shown in FIG.  1  and FIG. 2; 
     FIG. 4 a  is top,  4   b  bottom and  4   c  elevational view of the servo driven actuator sub assembly shown in FIGS. 3 a  and  3   b;    
     FIG. 5 a  is a side elevational and  5   b  is a front view of an unwind station sub assembly; 
     FIG. 6 is a simplified elevational view of a rotary machine base; 
     FIG. 7 is a simplified fragmentary perspective view showing a label position detector on a rotary-labeling machine; 
     FIG. 8 is a simplified overhead view of a container position detector on an inline-labeling machine; 
     FIG. 9 is a simplified top view of the label transfer contact point on a rotary-labeling machine; 
     FIG. 10 is a schematic diagram of a positioning servo system feedback loop; 
     FIG. 11 is a 6 function piecewise continuous function motion profile plot showing, web position vs. machine position; 
     FIG. 12 is a 6 function piecewise continuous function motion profile plot of, web velocity vs. machine position; 
     FIG. 13 shows a plot of the axis velocity vs. master feedback index; 
     FIG. 14 shows a plot of the axis position vs. master feedback index; 
     FIG. 15 shows plots of the master feedback index vs. time; and, 
     FIG. 16 shows plots of the axis velocity vs. time. 
     FIG. 17 is a simplified labeler system functional diagram; 
     FIG. 18 is a simplified block functional diagram of an encoder processing system, consisting of a hardware processing system, a micro processor which provides software based encoder signal processing, and an interface to a host system bus; and, 
     FIG. 19 is a simplified block diagram of the encoder processing hardware. 
    
    
     DETAILED DESCRIPTION 
     A pressure sensitive label application system consists of equipment that applies pressure sensitive labels which are coated with a adhesive, successively, to the surfaces of a series of containers. A system of this invention is capable of supporting at least from 1 to 4 label application stations, thus applying from one to four separate labels to one container or similar object, in independent mode, and two combinations of the same label on 4 stations in redundant mode. The most general configuration  20  of this system is shown in FIG.  1 . This two label application station machine  20  is defined as a synchronous “rotary” machine because the position of each container is governed by the position of the machine. 
     Containers moving down a conveyor  26  are captured and spaced apart by infeed screw  24 . Infeed screw  24  is driven by a gear train that originates at the bottle table  32 . As a container travels down the feed screw  24  it is detected by an electronic sensing device, i.e., a “bottle present sensor”  25 . The infeed screw  24  will transfer containers in a synchronous fashion and in mechanical coordination with pockets in an infeed star  28 . The infeed star  28  is geared to the bottle table  32 . As the infeed star  28  rotates, each container will travel along the radius of the centering guide  30  to transfer, in mechanical coordination, to a bottle support plate  34 . 
     As the bottle table  32  rotates on its main bearing  44 , containers on bottle plates  34  are carried to the first label application station  36  (“head #1”). In the event that the application station  36  is to apply a label, as a container passes the application station, a label will be applied while the container continues to travel with the bottle table  32 . After label application, the container continues through an outside brush station  37  and an inside brush station  39 . The brush stations  37  and  39  wipe the label down onto the surface of the container. To assist in the wipe down of the labels, the bottle table  32  contains a mechanical cam track with cam followers attached to the bottle plates. The cam track will cause the bottle plates to rotate during label wipe down through the brush stations. After label application and wipe down, the containers continue to travel to application station  38  (“head #2”). After the label application process is complete at label application station  38  and related wipe down brush stations  37  and  39 , the container continues onto discharge star  40 . As the container approaches the discharge star  40 , which is geared to the bottle table  32 , the container is captured by the centering guide  30  to be transferred synchronously to the discharge star  40 . The container will travel along the radius of the centering guide  30  to transfer from the discharge star  40  to a discharge conveyor  22 . 
     The position of the bottle turntable  32  is monitored by encoder  274  (FIG. 6) which serves as a position feedback device. Such devices , generally include encoders and resolvers, as will be recognized by those skilled in the art. Such devices are, for convenience and by way of example, rather than by way of limitation, referred to herein as “encoders.” 
     A second general configuration  49  of a labeling system is shown in FIG.  2 . This machine  49  is defined as a non-synchronous “inline” machine. Such inline machines are considered non-synchronous because the position of the container is random with respect to known pre-defined positions of the machine. The container-handling portion of machine  49  consists of a conveyor 50 and, usually, container-engaging timing belts  51 , which are not part of this invention. It will be noted that the machine base encoder  53  is geared to the conveyor drive motor  54  and its gearbox  52  and conveyor  50 , such that the encoder  53  will make at least 1 revolution per container. 
     Containers travel down the conveyor  50  in the direction indicated by the arrow  56  near the infeed of the machine  49 . The timing belts  51  capture the containers  58  upon entry to the machine. The timing belts  51  turn traveling generally in the same direction as conveyor  50 , and maintain position control of the containers. If desired, the timing belts  51  may be used to manipulate the containers  58 , for example, by rotating them, if required in a particular labeling sequence. Containers  58  continue to travel into the machine  49  where the leading edge of each container  58  is detected by an electronic sensing device, which is usually a photoelectric cell, i.e., the bottle present sensor  60  and its retroreflector  62 . The electronic bottle present sensor  60  will electronically identify the position of the container with respect to the machine base encoder  53 . Such identification or “position stamping” of the leading edge of the container establishes the physical position of the container within the machine  49 . 
     As container  58  continues into the machine towards the application station  68  (“head #1”), an electronic sensing device, the “position latch sensor”  64 , detects the leading edge of the container  58  and identifies or “position stamps” its location with respect to the machine encoder  53 . This new position stamp enables correction of position error of the container  58  prior to labeling. Such errors may be caused by irregularities in the container configuration or dimensions, positioning on the machine base, etc. The container will then continue on to the label application station  68  (“head #1”). In the event that the application station  68  is to apply a label as a particular container that passes the application station, a label will be applied while the container continues to travel with the conveyor  50 . After label application, the container continues through the brush station  70  which wipes the label down onto the surface of the container  58  as the container rotates across a brush. 
     On inline machines of this type, each label application head  68  or  78  applies the same label, with one head being active and the other in standby. If label application  78  (“head #2”) is active, while label application head  68  is inactive, the sequence of operation remains the same. 
     The label application head  68  or  78  is responsible for the motion of the web  80  and the transfer of the leading edge of a label  306  to the surface of a container. As shown in FIGS. 3 a  and  3   b , web  79  which carries labels  80  enters a push-pull actuator assembly  82  shown in detail in FIG. 4 c . The web  79  with labels  80  passes around a first idler roller  180  and then proceeds around the smooth “push” capstan roller  160 . The web  79  with labels  80  leaves the push-pull unit and proceeds to spender arm assembly  81 . The spender arm assembly  81  of a type know to the art, is composed of the spender arm mounting bracket  88 , spender arm pivot bracket  90 , spender arm pivot groove  92 , spender arm upper rod  94 , and lower rod  95 , spender plate  96 , spender plate foot  98 , web guide assembly  100 , and sensor mounting assembly  102 . 
     The web  79  with labels  80  will pass across the front of the spender arm to and around the edge of the spender plate  96  thereby causing the labels to separate from the web, in know fashion. The web  79  without labels will then continue on to and around another idler roller  180  to the “pull” capstan  158 . The web continues around the “pull” capstan  158  and continues on to the rewind dancer assembly rollers  108 . After the web passes through the rewind dancer assembly  109 , the web is rewound onto the rewind capstan  130 , as a roll  146 . 
     The rewind dancer is constructed of a series of rollers. One set of rollers are stationary, with the other set mounted to a dancer arm  134  connected to a pivot shaft that is in turn connected to the rewind proportioning disk  110 . An electronic signal generator  112  monitors the position of the proportioning disk  110 . As material leaves the push-pull assembly  84 , the dancer arm  134  moves toward an open position to provide for storage of the material due to the force applied by the spring tension device  111 . The electronic signal generator  112  monitors the position change of the proportioning disk  110  and outputs an analog electronic signal to the motor drive  114  that feeds power to the DC unwind motor  116 . The DC unwind motor  116  drives its gearbox  118  through a right angle shaft adapter  120  to drive the rewind capstan  130  and disk  126 . As the rewind capstan  130  rewinds material, the dancer arm  134  will move towards a closed position thus causing the electronic signal generator  112  to reduce the analog signal to the rewind drive  114 , thus reducing the speed of the motor  116 . 
     The smooth “push” capstan  160  is attached to its drive gear  156  (FIG. 4 b ), with the knurled “pull” capstan  158  being also attached to a drive gear  154 . The servomotor  150  through the servomotor drive gear  152  drives the gears  160  and  156 . 
     Rubber coated nip rollers  164  and  162  have eccentric shafts that are actuated by the nip pressure actuation levers  166  and  170 . Spring  172  applies tension to the “push” capstan nip pressure actuator lever  170 . This actuation causes the rubber coated nip roller  164  to apply pressure to the smooth “push” capstan  160 . Spring  168  applies tension to the “pull” capstan nip pressure actuation lever  166 . This actuation causes the rubber coated nip roller  162  to apply pressure to the knurled “pull” capstan  158 . The nips between the capstans  160  and  156  and the rubber coated nip rollers  164  and  162 , respectively, pinch the web  80  such that there is no web slip across the knurled capstan  158 , and there is nip pressure controlled slip across the smooth capstan  160 . The circumference of the smooth capstan  160  is slightly less than the circumference of the knurled capstan  158 . The drive gears for the capstans  160  and  158  are the same size. As the servomotor  150  drives the capstans  158  and  160  which move the web material across the spender plate  96 . The mismatch in circumference between the two capstans causes the web to acquire tension. Web tension is dictated by the frictional component of the web  80  to the surface of the smooth capstan  160 . The applied pressure of the rubber nip roller  164  dictates the quantity of friction to the smooth capstan  160 . The web tension controls the peel angle of the label as it leaves the web, as the web is pulled around the sharp edge of the spender plate  96 . 
     The unwind station shown in FIGS. 5 a  and  5   b  is a stand-alone system that functions to provide web material  79  with labels  80  to the label application head  68  or  78  from a roll of label material. The unwind station also provides an inertia buffer between the high acceleration web drive assembly  84 , FIGS. 4 a ,  4   b  and  4   c , and the large inertial load of the material reel  204 . A supply roll of unused label material  204  is mounted onto the unwind hub  202  and fixtured between the unwind disks  206 . The web material  79  with labels  80  is pulled from roll  204  by the nip  212  created by the nip roller assemble  214  and a rubber coated unwind drive roller  216 . The unwind drive roller  216  is connected to the DC motor  219  and controlled by the electronic signaling device  220 . As the label application head dispenses labels, the web inertia buffer gravity loop bobbin  220  will move up as web material is pulled from the buffer zone  218 . An electronic signaling device  222  signals the motor  219  to turn on. The motor  219  drives the unwind drive roller  216  which in turn pulls web material across the web guide idler roller  208  and from the material roll  204 . As the unwind drive roller  216  pulls material from the material roll  204  into the buffer zone  218 , the bobbin  220  will move down until the electronic sensing device  222  detects the bobbin  220  thus turning the motor  219  off. The web tension brushes  234  and  240  apply tension to the web  80  to stabilize the web path. 
     The machine base  20 , shown, in elevation in FIG. 6, is responsible for the flow of containers and their positions with respect to the application heads  36  and  38 . A rotary encoder  274  geared to the bottle table  258  through main bull gear  260 . The main bull gear  260  is driven by main drive gear  262 , which in turn is driven by gearbox  264  and the main drive motor  266 . The master encoder  274  is geared to the machine such that it makes one revolution per container. This is accomplished by the correct selection of intermediary encoder gears  271  and  272 . The master encoder  274  provides feedback to the computer control systems on each containers physical location on the machine. 
     Bull gear  260  drives main bearing shaft  261 , which in turn drives the rotating components including the bottle table assembly  258  and carrier assembly  286 . The main bearing housing  254  supports the rotating components and the non-rotating bottle table cam housing assembly  268 . The containers in the machine are fixtured by the bottle plates  270  and the centering bells  282  which are connected to the spring loaded centering head  284 , that is affixed to the carrier assembly  286 . As containers are processed through the machine, cam segments in the bottle table cam housing assembly  268 , turn the containers to the correct kinematic positions that relate to the needs of the appropriate process. The kinematics include presentations and motion for labeling, label wipe down and other process such as inspection or coding. FIG. 6 includes examples of the wipe down brush stations including the outside brush station mount  269 , the outside brush mount assembly  292 , the wipe down brush  290  and the inside brush mount  298 , with its associated inside wipe down brush  296 . The support columns  255  affix the non-rotating portions of the machine head  280  and cam carrier housing  256 . The brush station bearing  294  is affixed to the outside of the machine base table plate  250  and affix the inside brush stations to the non-rotation machine base. The table plate support assembly  252  supports the machine table plate  250 . 
     The correlation of the encoder  274  to the machine base position is defined as the machine master axis. On rotary machines, the centerline distance between two containers is defined as one pitch. 
     Label application control is accomplished with a multiprocessor computer controlled servo system or motion control system. See FIG.  17 . The motion control processor  520  with its corresponding servo amplifier  524  and servomotor  526  are responsible for the actual motion of the label carrying web  80 . Computer host processor  536  is responsible for the system background tasks, internal machine process shift register and process rules. The container tracking processor  528  is responsible for all machine position controls. 
     As a container enters the machine an electronic signaling device the bottle present sensor  538  signals the container tracking processor  528  that a container is entering the machine. The container tracking processor  528  electronically notifies the computer host processor  536  that a container is present. The computer host processor  536  enters a valid container into the internal labeling process shift register. As the machine continues to rotate the z axis pulse of the master encoder  522  providing electronic position signals to the container tracking processor  528 , indicates the beginning of the next pitch cycle. The container tracking processor  528  will electronically indicate to the computer host processor  536  that a new pitch has started. The computer host processor  536  will increment the internal labeling process shift register. 
     The labeling process shift register pitch increment process will continue as the container moves through the machine, until the container reaches the label application head or a container/label position correction sensor  534 . In the event that the machine incorporates the use of the optional container/label position correction sensor  308 , the position of a surface artifact such as a surface embossment on a container or a previously applied label  306  (FIG.  7 ), may be used as a position reference for a container  58  which is, thus, independent of the container fixtures  34  of the bottle table  32 . When the beam  310  of the electronic signaling device  308  is interrupted by the leading edge of the label  306  a signal is generated. 
     As seen in FIG. 17, the electronic signal generated by the container/label position correction sensor  308  provides a position locating electronic signal or “stamp” to the container tracking processor  528  which relates to the exact position of the master encoder  274 . The stamped position of the master encoder  274 , is then electronically compared to a preset application parameter in the container tracking processor  528 , which specifies the predicted position of the tracked artifact thus generating a label contact point position offset. 
     The label contact point position offset is turn used to edit, electronically, the preset label contact point position parameter which dictates the position on the container to which the label is to be applied. 
     As the container proceeds to the position on the machine where the label is to be applied, the computer host processor  536  indicates electronically to the container tracking processor  528  that a container is to be labeled. As the container enters the labeling zone the container tracking processor  528  electronically signals the motion control processor  520  to begin the labeling process. 
     Referring to FIG. 10, the correlation of the motion control system&#39;s internal position feedback; that is the servo loop closed around the web drive motor feedback  411 , with respect to the label carrying web position feedback  410 , is defined as the labeling axis. To successfully complete the labeling process, the leading edge of each label must applied to a precise position on the associated container and the velocity of the label during application must match the surface velocity of the container. 
     Between label applications, the motion profile is required to prepare itself for the next labeling process as well as to correct for any registration error which may have occurred. The means of performing the label application motion is through a position slaved move profile. That is, a move profile where the labeling axis position is based on the position of the master axis encoder  400 , of the machine base. 
     The servo loop of the labeling axis  412  is also a closed position loop with the label&#39;s leading edge used as a registration mark where and in feedback is provided by electronic signaling device  414 , the registration sensor, which electronically position stamps the labeling axis position at the point of the registration mark. This correction can only be allowed to occur when the actual labeling process is not being performed in order to reduce label-to-container surface velocity mismatch which would result from attempted position correction during label application. 
     The process of motion control referred to as position slaving relies fundamentally on the use of a master axis and a slave axis. The master axis indicated by encoder  274  provides feedback for computing the commanded position of the servo system of the slave or labeling axis. For each master position feedback unit or count, the slave axis is assigned a corresponding position. In the preferred example, the master feedback relates to the position of the machine base and is mechanically geared such that the feedback period is one machine pitch in length. Note that the period is measured in distance instead of time since this is not a time based motion controller, but a position based controller. 
     Using a position slaved servo loop can be described, in general, by means of a block diagram of the basic components of the servo loop. Referring again to FIG. 10, we see that the main reference bench mark that dictates the motion is the position of the machine base encoder  400 . This position is signaled to processor  528  which utilizes a profile-generating algorithm  402  such that the desired position of the label web is directly related to the machine base position based on the algorithm&#39;s mathematical equation. The resulting motion profile ideally can be generated and updated continually if the processing power of the servo controller is sufficient. If this is not possible, the motion profile could also be generated, only upon receiving new setup information relating to the geometry of the label, web, container, or machine which is stored in a look up table. The position slaved servo system would then generate its motion profile by referencing the look up table and utilizing the master feedback as an index to the table. Then, only the servo loop update and registration correction algorithm calculation are performed in real time. 
     The remaining blocks in the diagram FIG. 10, describe a general type of high performance positioning servo system. The system utilizes the torque controlled servo amplifier  404  closed around a proportional, integral, derivative (PID) servo loop  406  utilizing velocity and acceleration feedforward terms  408  to essentially eliminate following error in the system. 
     The position slaved motion profile, illustrated graphically in FIGS. 11 and 12, will implement a piecewise continuous function comprised of a minimum of three separate functions. These functions are represented by mathematical equations wherein the mathematical expression is a function of master feedback counts. The three basic portions of the illustrated complete function are: 
     the label application function, which is based on the geometry of the machine and the container. 
     the pre-labeling move which primarily is the portion of the move that accelerates the web so that it has reached labeling velocity at the precise position of label placement on the surface of the container while making a smooth transition to the label application function; 
     the post-labeling move which handles the deceleration, the recording of any registration error, and the preparation of the web position for the next label application, taking into account any observed registration error. It should also be noted that each of the basic portions of the function may be comprised of multiple sub-functions. The total function of the move profile, f T (i), is expressed as follows:            f   T          (   i   )       =       ∑     s   =   1     n            f   s          (   i   )                                
     The plots shown in FIG.  11  and FIG. 12 illustrate such a motion profile, which is comprised of 6 functions pieced together to form a single continuous function. 
     The functions shown in FIGS. 11 and 12 of the curve denoted as f s (0)  420  or  432  and f s (5)  430  or  442  are regions where the label web axis is in servo lock but no motion is commanded. This would represent the position between containers where no labeling action is required. 
     The function denoted as f s (1)  422  or  434  is the region of acceleration of the web. The function denoted as f s (2)  424  or  436  represents a region of the curve where the labeling process is occurring. As can be clearly seen in FIG. 12, the illustrated curve in this case is a constant velocity function. This is not, however, generally the case for applications with complicated container geometry or special labeling requirements. Referring again to FIGS. 11 and 12, the function denoted as f s (3)  426  or  438  is the region of deceleration of the web. The example shown utilized a sinusoidal profile generator in both the position (FIG. 11) and velocity (FIG. 12) domain of the profile. 
     The function denoted as f s (4)  428  or  440  is optional as shown. Function f s (4)  428  or  440  would be used to back the web up to allow for more web material to be made available in the event that the servo system does not have the acceleration capabilities to achieve the surface velocity of the container within the constraints of the label application travel distance. The label application travel distance is comprised of the label length plus the gap between adjacent labels on the web. A situation requiring f s (4) presently occurs on pressure sensitive labeling machines where the application requires short labels on high surface velocity machines. Note that these functions can not be performed on prior art velocity slaved system. 
     The example shown utilizes a sinusoidal profile generation utilizing a half period in the position domain as shown in FIG.  11 . Region f s (4)  428 ,  440  or f s (5)  430 ,  442  will also be utilized as the regions where registration error correction is accomplished. This is necessary to account for the outer position loop  410 , FIG. 10 to be closed around the web material itself. It is desirable to perform the correction here since the label application has been completed and the system is simply preparing for the next application. 
     The concept of a position slaved motion control system has been defined and its benefits have been explained. Next, the manner in which this motion control system relates to a pressure sensitive labeling process on a machine, will be explained. There are several basic building blocks in the motion control system which are necessary for position slaved control. They are shown in FIG. 17 as follows: 
     A motion control processor  520  that incorporates the use of microprocessors capable of performing math intensive functions at a very high rate is provided. Recent technological advances in microprocessor architectures has made available today, devices that provide the needed computational speed to perform complex mathematical position loop closure. This technology includes digital signal processors such as the advanced or modified Harvard architecture processor. 
     Because microprocessor technology continues to advance, the nature of the microprocessor is not directly a part of the invention except in so far as the ability to process and calculate complex mathematical equations that relate to the position of a label to be applied to a container has been made possible by the present level of computer technology. 
     The motion control processor  520  must perform at a rate of at least one position loop update every 125 microseconds for the pressure sensitive label application. This is necessary to maintain the placement accuracy of the labels at very high linear web speeds and accelerations. 
     An encoder  274  or, alternatively, a rotary resolver, which serves as a feedback device on the machine base serves as the master feedback position index. This provides the index through which the motion control processor  520  produces the position-slaved motion profiles. 
     A high performance web drive servomotor and amplifier  150 ,  404 . The system must have a very high torque to inertia ratio to achieve the necessary accelerations for a machine running in excess of 750 cycles per minute. 
     A high speed input  532  into the motion controller  520 , which performs a hardware capture of the slave axis position is necessary. This input should be able to identify the axis position in less than 20 microseconds. This input is connected to the electronic signal device  530  utilized for registration error correction of the labels on the web material. 
     The container tracking processor  528  is responsible for identifying the container position and the computer host processor  536  is responsible for the process overhead, diagnostics, and rules. The container tracking processor  528  and the computer host processor  536  will be discussed in detail later. 
     The manner in which these components of the system operate together in the system is as follows: 
     A known parameter, The point  362  on the container  58  where the label  306  must initially make contact for accurate placement is a known parameter see FIG. 9 362 . This is referred to herein as the contact point. This point is a predetermined position on the surface of a container that is subject to customer quality placement specifications. The drawing FIG. 9 illustrates a method to coordinate the selected label contact point to a fixed object that exists on the container  58 . With respect to the application of multiple labels to a single container, using the example of a front label and back label application to a single container, as indicated in FIG. 9, a problem exists with machines that use a master index machine reference position of the machine bottle table  350 , with containers in pre-positioned holders  34  to determine the placement of the labels  306  and  358 . 
     Customer specifications on label placement generally refer to the distance, edge to edge, between the two labels. Because the motion control system incorporates the use of the machine master index signaled by encoder  274  to indicate the contact point  362  of the second label  358 , tolerance stackup occurs between the 2 labels during application. To achieve high accuracy placement between two labels on a container  58 , the position of the first label applied  306  must be determined and used to reference the position of the application of the second label  358 . 
     The secondary position detection system shown in FIG. 7 adds an important feature to the system. This function allows the label application system to reference the position of an object such as label  306  on the surface of the actual physical container  58 , not a theoretical position on the container surface of a container positioned on the machine base, as is the case with other labelers. 
     The bottle table  32  is connected to the master encoder  274 . The bottle  58  is captured by the bottle plate  34 . The label  306  leading edge  310  is detected by an electronic signal generator  308 . The electronic signal is used to identify a corrected first label position which thus identifies any deviation or offset from the machine master index position prior to label application. 
     FIG. 8 indicates this function on an inline machine with respect to container position. Inline machines generally have problems with accurate container handing due to the fact that there are no fixtures to hold the container positions. In the case of timing belts, container slip for any reason results in position error with respect to the master encoder position. 
     Containers are moving in the machine on conveyor  320 . Bottle present sensor  60  will electronically signal the master index position of a container  72  when the container breaks the sensor beam  65 . The containers as they move through the system may develop error as to their position. The containers leading edge  72  is detected by an electronic signal generator  64  when the container breaks sensor beam  65 . The electronic signal is used to identify or “position stamp” a corrected first container position offset from the container&#39;s machine master index position just prior to label application. 
     The motion control processor uses the master encoder counts as an index. This index acts as a time component which a non-position slaved motion control algorithm uses to generate the move profile. In the position slaved motion control algorithm, the motion control processor does not have any time component in the move profile algorithm. This unique feature enables the contact point to be consistent through all speed ranges. This is accomplished by virtue of the fact that the position feedback index acts as a variable time component resulting in variable acceleration of the slave axis, which is driving the label web. As the machine speeds up, the feedback counts enter the motion control processor at a higher rate, which in turn results in a higher acceleration rate. This variable acceleration in the position slaved motion control system is crucial to repeatable label placement accuracy of the pressure sensitive labeling head. This is because the master and the slave axes are linked together by an exact function relating the position of the master to the position of the slave. Accuracy is thus maintained at any machine speed up to the physical constraints detected by maximum achievable acceleration. 
     As an example, we will utilize a simple move profile, which is trapezoidal as to velocity since this is a very common move. Because this is a position-based system, the profile will be defined as position of the slave as a function of the master feedback index. For the example, we will limit the scope to the first portion of the move, the acceleration, up to the constant velocity portion. If we integrate the trapezoidal function shown in FIG. 13 with respect to the master index, the position profile is readily shown to be a second order polynomial where the acceleration occurs and a positive sloping line during constant velocity as shown in FIG.  14 . Note that the units of the vertical axis is position of the slave axis and the units of the horizontal axis is position of the master feedback index. 
     The following graph, FIG. 15, shows the relationship between the machine speed in containers per minute and the number of index counts of the master feedback versus time. We note the linear relationship of the two. 
     This relationship is fairly obvious, and is the reason why the position slaved system works so well for the labeling process. The relationship between the master feedback index and the slave position is a constant, and the relationship between machine speed and the master feedback index is constant. Therefore, the relationship between the machine speed and the slave, or labeling axis, is constant as illustrated in FIG.  16 . 
     This results in the application of a pressure sensitive label by the labeling head to an actual position, rather than to a theoretical point in space. 
     To develop a position slaved move profile for an axis we have four distinct constraints. These constraints are: 
     1. The initial position. 
     2. The final position. 
     3. The initial velocity. 
     4. The final velocity. 
     To solve for such a system, the system need to be mathematically represented by four coefficients 50 that there are enough constraints to explicitly solve the equation. 
     To have the four coefficients a third order equation is used to represent the position of the profile. The velocity of the profile is then the first derivative of the position profile. Since the system will have an upper limit on the acceleration, the second derivative will eventually be used in determining the viability of the specific application. 
     
       
           pos ( i )= a·i   3   +a·i   2   +c·i+d   
       
     
     
       
           vel ( i )= d/di ( a·i   3   +b·i   2   +c·i+d )→ vel ( i )=3· a·i   2 +2· b·i+c   
       
     
     Boundary conditions are as follows: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 vel(0) = v 0   
                 Velocity at start of profile 
               
               
                   
                 vel(N) = v f   
                 Velocity at end of profile 
               
               
                   
                 pos(0) = 0 
                 Initial position 
               
               
                   
                 pos(N) = accel_length 
                 Final position 
               
               
                   
                   
               
             
          
         
       
     
     These boundary condition result in four equations and four unknowns. Therefore the coefficients may be solved explicitly.            [             v   0     =       3   ·   a   ·     0   2       +     2   ·   b   ·   0     +   c                   v   f     =       3   ·   a   ·     N   2       +     2   ·   b   ·   N     +   c                 0   =       a   ·     0   3       +     b   ·     0   2       +     c   ·   0     +   d                     accel   —        length     =       a   ·     N   3       +     b   ·     N   2       +     c   ·   N     +   d             ]                   solve     ,                            [         a           b           c           d         ]     →     [             root   ·     v   0       =     root   ·   c                   root   ·     v   f       =     root   ·     (       3   ·   a   ·     N   2       +     2   ·   b   ·   N     +   c     )                   0   =     root   ·   d                     root   ·     accel   —          length     =     root   ·     (       a   ·     N   3       +     b   ·     N   2       +     c   ·   N     +   d     )               ]                              
     Given 
     
       
           v   0   =a· 0 2   +b· 0 +c   equation 1: 
       
     
     
       
           v   f   =a·N   2   +b·N+c   equation 2: 
       
     
      0 =a/ 3·0 3   +b/ 2·0 2   +c· 0 +d   equation 3: 
     
       
         accel_length= a/ 3 ·N   3   +b/ 2 ·N   2   +c·N+d   equation 4: 
       
     
     
       
         
           
             
               Find 
                
               
                   
               
                
               
                 ( 
                 
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                   c 
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                   d 
                 
                 ) 
               
             
             → 
             
               [ 
               
                 
                   
                     
                       3 
                       · 
                       
                         
                           ( 
                           
                             
                               
                                 
                                   - 
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                                   accel 
                                   — 
                                 
                               
                                
                               length 
                             
                             + 
                             
                               
                                 v 
                                 0 
                               
                               · 
                               N 
                             
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                               N 
                               · 
                               
                                 v 
                                 f 
                               
                             
                           
                           ) 
                         
                         
                           N 
                           3 
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         - 
                         2 
                       
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                           ( 
                           
                             
                               N 
                               · 
                               
                                 v 
                                 f 
                               
                             
                             - 
                             
                               
                                 3 
                                 · 
                                 
                                   accel 
                                   — 
                                 
                               
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                               length 
                             
                             + 
                             
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                               · 
                               
                                 v 
                                 0 
                               
                               · 
                               N 
                             
                           
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                           N 
                           2 
                         
                       
                     
                   
                 
                 
                   
                     
                       v 
                       0 
                     
                   
                 
                 
                   
                     0 
                   
                 
               
               ] 
             
           
         
                 
         
             
         
      
     
     The boundary conditions are entered into the system. 
     v 0 :=0 
     v f :=36 
     accel_length:=1273 
     n:=38 
     In general purpose applications we ensure that the velocity never goes negative, we will solve for the ‘b’ coefficient to be zero. 
     Given        0   =       -   2     ·       (       n   ·     v   f       -       3   ·     accel   —          length     +     2   ·     v   0     ·   n       )       n   2                                
     counts:=Find(n) 
     N:=counts 
     N=106.08333333 
     Given 
     
       
           v   0   =a· 0 2   +b· 0 +c   equation 1: 
       
     
     
       
           v   f   =a·N   2   +b·N+c   equation 2: 
       
     
      0= a/ 3·0 3   +b/ 2·0 2   +c· 0 +d   equation 3: 
     
       
         accel_length= a/ 3· N   3   +b/ 2· N   2   +c·N+d   equation 4: 
       
     
     
       
         
           
             
               [ 
               
                 
                   
                     A 
                   
                 
                 
                   
                     B 
                   
                 
                 
                   
                     C 
                   
                 
                 
                   
                     D 
                   
                 
               
               ] 
             
             := 
             
               
                 Find 
                  
                 
                     
                 
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                   ) 
                 
               
               → 
               
                 [ 
                 
                   
                     
                       
                         6 
                         · 
                         
                           
                             ( 
                             
                               
                                 - 
                                 1273 
                               
                               + 
                               
                                 18 
                                 · 
                                 counts 
                               
                             
                             ) 
                           
                           
                             counts 
                             3 
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           - 
                           6 
                         
                         · 
                         
                           
                             ( 
                             
                               
                                 12 
                                 · 
                                 counts 
                               
                               - 
                               1273 
                             
                             ) 
                           
                           
                             counts 
                             2 
                           
                         
                       
                     
                   
                   
                     
                       0 
                     
                   
                   
                     
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                 ] 
               
             
           
         
                 
         
             
         
      
     
     The registration portion of the profile is then calculated 
     
       
           i   reg :=0,1 . . .  N   
       
     
     
       
         pos_cam( i   reg ):=⅓ ·A ·( i   reg ) 3 +½ ·B ·( reg ) 2   +C ·( i   reg )+ D   
       
     
     
       
                 
         
             
             
         
      
     
     The physical properties of the move profile are calculated in the time domain to determine if the required acceleration can physically be performed by the selected motion control system. For now, we will use the standard encoder with 1000 counts per pitch and let us use 300 containers per minute to start. 
     enc_res:=1000 
     machine base encoder resolution 
     mach_speed:=300 
     desired machine base run speed 
     roller_dia:=20 
     drive roller diameter 
     motor_res:=8000 
     web drive motor encoder resolution            pos   —          cam   —        m                   m        (     i   reg     )         :=           pos   —            cam        (     i   reg     )       ·     roller   —          dia         motor   —        res       ·   π                            
     pos_cam_mm(N)=9.99811862                           
     The velocity of the profile is calculated by taking the first derivative of the position profile and then the acceleration of the profile by taking the second derivative of the position profile. The functions are graphed out below.            vel   —          cam        (     i   reg     )         :=                 i   reg              pos   —            cam        (     i   reg     )       ·     enc   —            res   ·         mach   —          speed   ·     roller   —            dia   ·   π           60   ·     motor   —          res                                                                      accel   —          cam        (     i   reg     )         :=                 i   reg              vel   —            cam        (     i   reg     )       ·     enc   —            res   ·         mach   —        speed     60                                 
     accel_cam(N)=133264.73157412 Maximum acceleration (mm/sec 2 )                           
     As was previously discussed, the position of the applied label to the surface of a container in many customer applications is subject to specified placement tolerances. A typical placement tolerance is plus/minus 0.5 millimeters. 
     The design specification for this machine exceeds 100,000 millimeters per minute maximum container surface velocity. If the time domain is calculated for the placement tolerance, we find that the maximum system accumulated latency equals 300 microseconds per 0.5 millimeter of surface travel. To accomplish the final placement tolerance, it is found that the control system can contribute no more than 50% of the maximum allowable error. The remaining error will come from material and mechanical system sources. 
     The two systems susceptible to critical time issues are the motion control system, FIG. 10, (also shown in component blocks  521 ,  522 ,  524 ,  526 ,  530  in FIG. 19) and the position control processor  522 ,  528 ,  534 . The timing issues are critical for the digital signals connecting the position control processor to the motion control processor. The specification for the maximum accumulated interrupt service routine latency of the motion control processor  520 , FIGS. 17 and 19, which includes high speed input reaction time, and motion algorithm “math intensive task” completion is 125 microseconds. The specification for the position control processors position command latency is 25 microseconds. Because of the demanding requirements of this system, the following details relating to the position control processor  520  are included herein. 
     With reference to FIG. 18 there is shown an PLS/Encoder FPGA  446  which accepts signals from a quadrature encoder  464  and various sensors  466 , processes these signals, and in conjunction with a micro processor  456 , generates a set of control outputs  468 . 
     The PLS/Encoder FPGA  446  takes advantage of the fact that although a mechanical device may be operating at a high rate of speed the time required for an encoder to move from one discrete position to the next is relatively long when compared to the clock rate capability of high speed logic devices. The PLS/Encoder FPGA  446  uses the time between encoder steps to manipulate a set of control outputs  468  and to warn the system microprocessor  456  of impending significant events by use of an interrupt signal  470 . A more detailed description of the operation of the PLS/Encoder FPGA  446  will follow. 
     The PLS/Encoder FPGA  446  is responsible for driving the outputs,  472  and  474 , which are scheduled to occur within the next full rotation (pitch) of the encoder. The system microprocessor is responsible for scheduling output events that must be delayed for one or more full encoder rotations. The PLS/Encoder FPGA can provide multiple interrupts  470  to the system micro processor  456  during a single encoder rotation such that the microprocessor  456  will have ample opportunity to configure the output control circuits of the PLS/Encoder FPGA when delayed output events now falls within the current encoder rotation (pitch). Splitting the responsibility for the inter and intra pitch events between the microprocessor  456  and the PLS/Encoder FPGA  446  greatly reduces the processing requirements imposed on the microprocessor  456  and increases the achievable system performance. 
     All of the signals which are input to the PLS/Encoder FPGA  446  are connected at a header  440  and are sensed and ESD protected by an input buffer  444 . All of the signals which are output from the PLS/Encoder FPGA  446  are buffered and ESD protected by an output buffer  442  and are made available at a header  440 . 
     Also shown in FIG. 18 is a general-purpose microprocessor system which consists of a microprocessor IC  456 , FLASH type program memory  452 , and SRAM data memory  454 . The microprocessor  456  works in conjunction with the PLS/Encoder FPGA  446  to generate the various control signals  468 . The micro processor  456  also generates a clock signal  450  which is used by the PLS/Encoder FPGA  446  to sample and filter the sensor inputs  466  and the encoder inputs  464 . 
     As shown in FIG. 18 a host system bus interface consisting of an interface IC  458 , the board address select switch  460 , and a bus interface connector  462  is provided. The interface IC  458  provides a bridge between the host system bus and the native bus protocol of the microprocessor  456 . Although an ISA bus is indicated in FIG. 18, any host bus could be utilized by simply reconfiguring the function provided by the interface IC  458 . In addition to the bus bridge function, the interface IC  458  also implements a direct connection  448  to the PLS/Encoder FPGA  446 , this provides high speed access to hardware based information, such as encoder position, without requiring intervention by the system micro processor  456 . 
     FIG. 18 provides a more detailed view of the PLS/Encoder FPGA  446 , in order to simplify this diagram all address decoding and chip select functions which are performed in order to access the various hardware resources have been omitted. 
     As shown in FIG. 18, all sensor  466 , and encoder  464  signals which are input to the PLS/Encoder FPGA  446  are digitally filtered. The signals are filtered in order to minimize the detection of false signal transitions due to the noise inherent in most installations. The Digital Filter  480  consist of an N bit shift register connected to each input, where N is typically a small integer. The input signal is continuously shifted on the active edge of the filter clock  450 , when all N bits of the shift register are at the same logic level the digital filter output is switched to that level. The output level is held until all N bits of the shift register are detected to be at the opposite logic level. The filter clock used by the Digital Filter is sourced from the system microprocessor  456  (FIG.  18 ). The Digital Filter  480  also synchronizes the filtered outputs to the high frequency clock that drives all of the remaining logic of the PLS/Encoder FPGA  446 . 
     The three encoder signals  464  that have been filtered  478  are passed to the Encoder Processor  482 . The Z_ph input is a reference pulse from the encoder which is active once during every rotation (pitch) of the encoder. The other two inputs, (A_ph &amp; B_ph), are the quadrature signals from the encoder, the phase relationship between these two signals is used to determine the direction of encoder rotation, the edge transitions of these two signals are used to derive an absolute angular position measurement. 
     The Encoder Processor  482  tracks the A_ph and B_ph inputs, and monitors the Z_ph input  478  in order to generate control signals for a Position Counter  484  which tracks the absolute angular position of the encoder shaft. The operation of the control signals depends on the direction of rotation, when the A_ph signal leads the B_ph signal by 90 degrees the encoder is considered to be rotating in the forward direction, when B_ph leads A_ph by 90 degrees the direction of rotation is considered to be backwards. 
     The Encoder Processor  482  also contains a Z delay register, which is loaded by the on board microcontroller  456 . This function allows the set of position referenced system parameters to remain constant when a new encoder is installed. The new encoder will almost certainly be installed with a rotational offset relative to the old encoder. The rotational offset is compensated for by delaying the reset of the encoder position count by ‘n’ A_ph and B_ph edges after a Z_ph  478  input is detected, ‘n’ is the value stored in the Z delay register. It should be noted that up to one complete revolution of the encoder is required for a new Z delay to become effective. 
     As previously noted, the filtered encoder signals  478  are used to generate control signal to a Position Counter  484  which tracks the absolute angular position of the encoder shaft. In order to track the angular position the counter  484  must be capable of counting up, counting down, clearing to zero, and loading to the maximum count value. The maximum count value is defined to be equal to the number of counts per revolution of the encoder times 4 A_ph and B_ph edges per encoder count. For example a 1000 count encoder will have a maximum count of 4000 edges per revolution. The specific operation of the counter control signals generated by the Encoder processor  482  is as follows: 
     The Encoder Processor will issue a DOWN, or a LOAD if the Z delay has expired, when one of the following is true: 
     B_ph is logic 0 and A_ph has a high to low transition. 
     B_ph is logic 1 and A_ph has a low to high transition. 
     A_ph is logic 0 and B_ph has a low to high transition. 
     A_ph is logic 1 and B_ph has a high to low transition. 
     The Encoder Processor will issue an UP, or a CLEAR if the Z delay has expired, when one of the following is true: 
     B_ph is logic 0 and A_ph has a low to high transition. 
     B_ph is logic 1 and A_ph has a high to low transition. 
     A_ph is logic 0 and B_ph has a high to low transition. 
     A_ph is logic 1 and B_ph has a low to high transition. 
     The Encoder Processor  482  will issue a one system clock cycle wide NEW_COUNT signal  512  on any change in count, this is essentially a logical ‘OR’ of LOAD, CLEAR, UP, and DOWN. 
     A DIRECTION signal  524  is maintained by the Encoder Processor  482 , the signal will be at a logic low when the rotation direction is forward and logic high when the rotation direction is backward. 
     The Input Filter  480  and the Encoder Processor  482  provide a set of signals  478  which allow external motion control systems to have access to the angular position information generated by the PLS/Encoder FPGA  446 . The A, B, and Z outputs are copies of the encoder inputs delayed by the Digital Input Filter  480 , the Z_CLEAR output will go active approximately  100  nS before an A or B output edge at which the Encoder Position Counter will be reset. The Z_CLEAR output is required since the use of the Z delay feature precludes the use of the three encoder phases to determine the zero reference point of the system. 
     As previously noted the control signals output from the encoder processor  482  are used to control a Position Counter  484  which maintains a value which represents the absolute angular position of the encoder shaft. Since the Position Counter  484  is changed at every edge transition of both the A_ph and B_ph signals the angular position measurement resolution is equal to one fourth of an encoder count. For example the angular position of a 1000 count per revolution encoder can be tracked down to {fraction (1/4000)} of a revolution which is 0.0016 radians (0.09°). 
     Since the number of counts per revolution of an encoder is typically not a power of two the Position Counter  484  must be designed to count down from zero to the maximum count and count up from the maximum count to zero. As previously noted the maximum count is four times the number of counts per revolution of the encoder. This maximum count values can either be hard wired into the hardware design or implemented as a configurable register located within the Position Counter  484  circuit. 
     The absolute angular position output  504  from the position counter  484  is used by the Clock Gen circuit  486  to generate a set of position based periodic signals. All of the signals output from the Clock Gen circuit  486  are driven to logic 0 when the absolute angular position  504  equals 0. 
     Two of the signals  476  generated by the Clock Gen circuit  486  are used by external control systems as position references, the pitch_clk signal provides one cycle per encoder revolution while the fine_clk signal provides 10 cycles per revolution. 
     Two of the signals issued by the Clock Gen circuit  486  are used to interrupt the system micro controller  456  at various reference positions within one revolution of the encoder. One of the signals  526  will provide two interrupts per revolution while the second signal  528  will provide five interrupts per revolution. 
     In addition to the two position based signals,  526  and  528 , generated by the Clock Gen circuit  486 , the PLS/encoder FPGA  446  can generate an interrupt to the micro processor  456  whenever the encoder position  504  changes and when an active edge is detected at any of the sensor inputs  466 . The interrupt signal  470  is generated by the Transition Detect circuit  488  when an active edge transition is detected at any of the inputs  516 . A status register is maintained within the Transition Detect circuit  488 , the register  506  can be read by the system microprocessor  456  so that the source of the interrupt can be determined. Any of the inputs to the Transition Detect circuit  488  can be masked in order to block the activation of the interrupt  470  for that source, this register is written by the system microprocessor  456 . 
     When the system micro processor  456  reads data from the PLS/Encoder FPGA  446  the Data Buffer  494  routes the desired data from the PLS/Encoder FPGA&#39;s internal data bus to the system processor&#39;s data bus based on the address used for the access. The system microprocessor can either read the state of the Transition Detect  488  status register  506 , or the current encoder position  504  and the current encoder rotation direction  524 . 
     Whenever the Encoder Processor  482  issues a NEW_COUNT signal  512  to indicate that the encoder position has changed the List Select circuit  490  will sequence though a series of  24  addresses  518 . The time required to scan through the  24  addresses and perform the operations associated with each determines the encoder resolution and rotational speed, which can be handled by the PLS/Encoder FPGA  446 . For example if the PLS/Encoder FPGA  446  is operating at 25 Mhz and each address requires 8 clock cycles to process the address scan will take 7.7 uS, so a 4000 edge encoder (1000 cnts/rev) can be processed in abut 31 mSec which correlates to a rotational speed of about 1900 RPM. The preceding example assumes no software over head for scheduling output events, it is expected that the actual obtainable rotational velocity will be about one half of the base hardware speed or 950 RPM for a 4000 edge encoder (1000 cnts/rev). 
     Each List Select address  518  will simultaneously select: 
     The output group, PLS  496  or One Shot  498 , to operate on. 
     The specific output within the selected group, one of  472  or  474 . 
     The state to which a selected PLS output  472  is to be driven. 
     The on time (dwell) for a selected One Shot output,  474 . 
     The encoder position  508  at which the output operation is to occur. 
     The encoder position at which the output event is to occur  508  is read from a List of Target Counts  492  and compared to the current encoder position  504  by the Equality Compare circuit  500 . If the current position  504  is equal to the target position  508 , as indicated by signal  521  becoming active, the selected output event will occur. 
     Each PLS output  472  is associated with two List Select addresses  518  which access target encoder positions  508  stored in the List of Target Counts  492 . One address selects the target encoder position  508  at which the output  472  is to be driven active, the second address selects the target encoder position  508  at which the output is to be driven inactive. 
     Each One Shot output  474  is associated with a single List Select Address  518 , this address selects the encoder position at which the output  474  is to be driven active from the List of Target Counts  492 . The same address  518  also selects the on time (dwell) for the output from the List of Target Counts  492 . 
     The List of Target Counts  492  is stored in on chip dual port RAM. The write port is connected to the on board micro controller  456  bus, the values in the RAM can be updated on a random access basis at any time. The read side of the dual port RAM is controlled by the List Select circuit  490 , as previously described. 
     The One Shot Outputs control circuit  498  shown in FIG. 19 requires that the an output be rearmed after each operation, this is accomplished by having the system micro processor  456  rewrite the on time (dwell) value for the particular one shot output  474 . This was done to allow the system microprocessor to make adjustments to the firing position and on (dwell) time for these outputs  474  while operating at full speed. 
     The Ksa  16  Reg circuit  502  provides for direct access to the encoder position and several mailbox registers from the host backplane interface  458 . This direct access scheme allows the host system to quickly access the most frequently required data without impacting the performance of the system processor  456 .