Patent Publication Number: US-11026361-B2

Title: Linear/angular correction of pick-and-place held component and related optical subsystem

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to the following concurrently filed and commonly owned applications: 
     1. Ser. No. 13/837,727, filed Mar. 15, 2013, now U.S. Pat. No. 9,549,493, issued Jan. 17, 2017, entitled: Passive Feeder Cartridge Driven by Pickup Head; 
     2. Ser. No. 13/838,416, filed Mar. 15, 2013, now U.S. Pat. No. 9,247,685, issued Jan. 26, 2016 entitled: Multi-Component Nozzle System; 
     3. Ser. No. 13/838,762, filed Mar. 15, 2013, now U.S. Pat. No. 9,547,284, issued Jan. 17, 2017, entitled: Auto-setup Control Process; 
     4. Ser. No. 13/839,239, filed Mar. 15, 2013, now U.S. Pat. No. 9,361,682, issued Jun. 7, 2016, entitled: Virtual Assembly and Product Inspection Control Processes; and 
     5. Ser. No. 13/839,790, filed Mar. 15, 2013, entitled: Pick-and-Place Feeder Module Assembly. 
     TECHNICAL FIELD 
     The present technology relates generally to the field of material handling, and more particularly to mechanisms and methods for transporting small articles from a first location to a second location, as might be involved during precise placement of components onto a printed circuit board. 
     BACKGROUND 
     Pickup, transport and precise placement of small articles normally includes use of a vacuum head for engaging and releasing the transported article. Such apparatuses are commonly referred to as pick and place mechanisms. 
     Some pick and place mechanisms include a pneumatic cylinder which drives a spindle mounting a vacuum head on a free end thereof. The spindle is advanced and retracted as required along its own axis, to pick up or place the articles (components), and is transported in a plane normal to the axis of the spindle to move the components from one location to another. Pneumatically operated devices are accompanied by substantial disadvantages inherent in pneumatic operation. Some drawbacks are the difficulty in monitoring the spindle position along its axis, and excessive size, particularly when the component is quite small. 
     Known pick and place mechanisms include, for example, U.S. Pat. No. 5,278,634 to Skunes, U.S. Pat. No. 6,145,901 to Rich, U.S. Pat. No. 4,860,438 to Chen, U.S. Pat. No. 4,595,335 to Takahashi, U.S. Pat. No. 4,151,945 to Ragard, U.S. Pat. No. 8,068,664 to Rudd and European patent application publication 0235045 A2 to Universal Instruments Corporation. 
     SUMMARY 
     One exemplary pick-and-place machine feeds components from a supply tape cartridge advanced by a feeder gear mechanically rotated by the pickup head, thus avoiding the need for the tape cartridge to have on-board power components. The pickup head includes a pickup device (e.g., a vacuum nozzle) to pick up components from the tape as well as a rack gear to engage and drive the feeder gear of the supply tape cartridge. The pickup head also places components accurately on a substrate such as a printed circuit board (PCB). 
     The exemplary pick-and-place machine may include a component camera cooperating with a collimated light source arranged to project collimated light towards a component held by the pickup device and a diffuser screen disposed between the component and the component camera such that a shadow image of the held component is projected onto the diffuser screen. A linear correction and an angular correction of the held component position are calculated in accordance with this shadow image on the diffuser screen. 
     An exemplary pickup nozzle has an elongated hollow portion, a stop slidably disposed within the hollow portion, and a vacuum source in fluid communication with the hollow portion. The hollow portion is configured to simultaneously accommodate a plurality of picked-up components as the internal stop is adjusted in the proximal direction. A component can be ejected from the hollow portion and onto a substrate as the internal stop is adjusted in the distal direction. 
     A computer program readable storage medium may store computer program code structures including executable instructions that control at least one computer processor programmed to control a pick-and-place machine in picking up components from a feeder cartridge and then precisely placing the components onto a substrate (e.g., to assemble a printed circuit board). At least one pickup device may be selectively installed on the pickup head under such program control. Thereafter, the pickup head may be controlled to advance a selected component supply tape. A multi-purpose camera also mounted on the pickup head may read readable information on each feeder cartridge to obtain location and/or identification information for each respective feeder component and use such data to better insure correct assembly of the printed circuit board in accordance with the detected location and identification information. 
     Computer program code instructions may also control at least one processor in virtually assembling a printed circuit board with a plurality of components to be provided on a substrate at predetermined locations. Individual images of the plurality of components are overlaid on an image of the substrate in accordance with the predetermined locations. An operator may confirm the location of each virtual component placement to insure the proper location of each feeder without actually consuming any components. 
     A substrate having a plurality of components provided thereon (e.g., held on the substrate with soldering paste) can also be inspected. An imaging device may capture an image of each component on the substrate and then group the images such that images of what is supposed to be the same component type are grouped together so that one may readily detect whether in fact the components installed on the substrate (a) are the same component type; (b) are the intended component; and/or (c) were installed with the correct orientation. 
     An exemplary feeder cartridge for a pick-and-place machine may include a feeder gear which acts to feed a tape through the feeder cartridge, wherein the feeder cartridge itself is without onboard provisions of electrical, mechanical or pneumatic power. 
     An exemplary feeder module for a pick-and-place machine may be interchangeable with other feeder modules in the pick-and-place machine to reduce setup time. A user may configure in a feeder module a group of feeder cartridges for a particular job (e.g., assembly of a certain board) and leave the feeder module undisturbed until the next time that particular board assembly is needed. Such modularity may allow a user to change jobs in a matter of seconds. 
     Other aspects, features, and advantages of the present technology will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, different aspects of this technology. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings facilitate an understanding of various embodiments wherein: 
         FIG. 1  is a perspective view of an example pick-and-place machine; 
         FIG. 2  is a perspective view of an example motion system of the pick-and-place machine of  FIG. 1 ; 
         FIG. 3-1  is a perspective view of an example feeder module of the pick-and-place machine of  FIG. 1 ; 
         FIGS. 3-2   a  to  3 - 2   e  are various views of example feeder modules of the pick-and-place machine of  FIG. 1 ; 
         FIG. 4  is an enlarged detail of a portion of  FIG. 3 ; 
         FIG. 5  shows an example removable feeder cartridge of the pick-and-place machine of  FIG. 1 ; 
         FIG. 6  is a perspective view of an example removable feeder cartridge of the pick-and-place machine of  FIG. 1 ; 
         FIG. 7-1  is another perspective view of the removable feeder cartridge of  FIG. 6 ; 
         FIG. 7-2   a  is a perspective view of another example removable feeder cartridge of the pick-and-place machine of  FIG. 1 ; 
         FIG. 7-2   b  is another perspective view of the removable feeder cartridge of  FIG. 7-2   a;    
         FIG. 8  is a perspective view of an example cover film drive assembly of the pick-and-place machine of  FIG. 1 ; 
         FIG. 9  is a side view of the removable feeder cartridge of  FIG. 6 ; 
         FIG. 10  is an exploded perspective view of the removable feeder cartridge of  FIG. 6 ; 
         FIG. 11  is a perspective view of an example pickup head of the pick-and-place machine of  FIG. 1 ; 
         FIG. 11 a    is an enlarged detail of  FIG. 11  showing an example force sensing mechanism of the pick-and-place machine of  FIG. 1 ; 
         FIG. 11 b    is an exploded perspective view of the force sensing mechanism of  FIG. 11   a;    
         FIG. 11 c    is another exploded perspective view of the force sensing mechanism of  FIG. 11   a;    
         FIG. 12  is a perspective view of a lower portion of the pickup head shown in  FIG. 11 ; 
         FIG. 13  is a side view of the pickup head of  FIG. 11  engaging a feeder gear; 
         FIG. 14  is a perspective view of the pickup head of  FIG. 11  showing an example vacuum nozzle in a down position; 
         FIG. 15  is a perspective view of the vacuum nozzle shown in  FIG. 14 ; 
         FIG. 16  is a perspective view of an example vacuum nozzle changer cartridge of the pick-and-place machine of  FIG. 1 . 
         FIGS. 17 and 18  are perspective views of an example optical subsystem of the pick-and-place machine of  FIG. 1 ; 
         FIGS. 19A to 20B  are schematic representations of optical paths of the optical sub-systems of  FIGS. 17 and 18 ; 
         FIG. 21  is a perspective view of an example optional multi-component vacuum nozzle system for the pick-and-place machine of  FIG. 1 ; 
         FIG. 22  is an exploded perspective view of the multi-component vacuum nozzle system of  FIG. 21 ; 
         FIG. 23  is an exploded top view of the multi-component vacuum nozzle system of  FIG. 21 ; 
         FIG. 24  an exploded bottom view of the multi-component vacuum nozzle system of  FIG. 21 ; 
         FIGS. 25-30  are various views of a vacuum nozzle of the multi-component vacuum nozzle system of  FIG. 21 ; 
         FIG. 31  is a perspective view of an example optional multi-component vacuum nozzle system including pickup-head-mounted coils for inductive coupling with the multi-component vacuum nozzle system; 
         FIG. 32  is a side view of the multi-component vacuum nozzle system of  FIG. 31 ; 
         FIG. 33  is a perspective view of an example optional multi-component vacuum nozzle system including a pickup-head-mounted coil for inductive coupling with the multi-component vacuum nozzle system; 
         FIG. 34  is a side view of an example optional multi-component vacuum nozzle system for the pick-and-place machine of  FIG. 1 ; 
         FIG. 35  is a perspective view of an other example of a multi-component vacuum nozzle system for the pick-and-place machine of  FIG. 1 ; 
         FIG. 36  is an example electrical inductive coupling circuit for use with the nozzles of the pick-and-place machine of  FIG. 1 ; 
         FIG. 37  is a flow chart diagram of computer program code structure for an example “squaring” method used to provide linear and/or angular corrections for component placement; 
         FIGS. 38-1 and 38-2  are example graphical representations of images of a substrate and components to be placed on the substrate; 
         FIG. 39  is a schematic representation of an example virtual PCB having the component images of  FIG. 38-2  placed onto the substrate image of  FIG. 38-1 ; 
         FIG. 40  is an example image representing a computer generated pre-defined PCB; 
         FIG. 41  is representative of an example computer generated image of the virtual printed circuit board of  FIG. 39  overlaid onto the pre-defined PCB of  FIG. 40 ; 
         FIG. 42  is an example schematic representation of a virtual PCB having some component images of  FIG. 38-2  misplaced onto the substrate image of  FIG. 38-1 ; 
         FIG. 43  is representative of a computer generated image of the virtual PCB of  FIG. 42  overlaid onto the pre-defined PCB of  FIG. 40 ; 
         FIG. 44  is representative of a computer generated image of a finished PCB image overlaid onto the pre-defined PCB of  FIG. 40 ; 
         FIG. 45  is representative of an example operator display screen enabling finished product inspection; 
         FIG. 46  is representative of an example operator display screen providing information regarding components required for a PCB assembly; 
         FIG. 47  is a graph showing an example force vs. distance profile of pickup device placing a component onto a substrate; and 
         FIG. 48  is a schematic representation of a laser engraver of the pick-and-place machine of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATED EXAMPLES 
     The following description is provided in relation to several examples (most of which are illustrated) which may share some common characteristics and features. It is to be understood that one or more features of any one example may be combinable with one or more features of the other examples. In addition, any single feature or combination of features in any of the examples may constitute additional examples. 
     1.0 Pick-and-Place Machine 
     The example pick-and-place machine shown in  FIG. 1  includes an outer frame  103  and a display  105  supported by the outer frame. The machine  1000  further includes a pick and place head  200  arranged to pick up a selected component from feeder cartridges within feeder modules  300  and accurately place the component on a substrate (e.g., a printed circuit board (PCB)) (not shown in  FIG. 1 ) located there below and positioned in an area between the opposing groups of feeder modules  300 . The display provides a convenient interface for a machine operator. 
     Computerized control circuits are shown schematically in  FIG. 1  as including at least one central processing unit (CPU)  110  connected to execute computerized program code structures stored in memory  112  (e.g., possibly in conjunction with a suitable overarching operating system as those in the art will appreciate). Of course, CPU  110  also has access to any needed working memory  114 , as well as suitable input/output (I/O) circuits  116 . Indeed, display screen  105  may itself provide an I/O port for operators (e.g., using a touch sensitive screen). A mouse, keyboard and/or other conventional I/O devices  118  may also be provided as will be understood. 
     CPU  110  also has control of various light sources (e.g., LEDs) and optical sensors  120  distributed throughout the pick-and-place machine  1000  as will be described further below. In addition, the exemplary pick-and-place machine  1000  also has a multi-purpose camera  252  and a component camera  251  interfaced with CPU  110  and utilized as explained below. Inductive coupling circuits  122  are also interfaced with CPU  110  and utilized to control optical interfaces with vacuum nozzles as will be explained. X/Y motor control  124  is also coupled to the CPU  110 , as are control circuits  126  for controlling up/down pickup head motion and vacuum on/off valve control to the pickup head vacuum nozzle. 
     An X/Y motion system  400 , shown in  FIG. 2 , is used to transport pick and place head  200  between feeder modules  300  and a desired underlying substrate location. Motion system  400  provides movement in both the X and Y directions, thereby enabling pickup head  200  to be positioned adjacent any desired component pick-up locations (i.e., feeder cartridges within feeder modules  300 ) and adjacent any desired placement locations on the substrate. Once the pickup head is positioned in the correct x-y coordinate location, a crank mechanism (described later) inside pickup head  200  quickly raises or lowers the pickup head vertically to either pick up or place components. 
     Pickup head  200  is attached to a slider  455 ( 1 ) that traverses a rail  423  parallel to the X axis. A motor  403  rotates a screw shaft  413  that also extends in the X axis direction. A nut member  455  receives screw shaft  413  and is also attached to slider  455 ( 1 ) such that rotation of motor  403  causes movement of nut member  455  along the screw shaft  413 , thereby causing the pickup head to traverse the rail  423  in the X axis direction. 
     Rail  423  is attached at its ends to respective nut members  445 ,  447 . Nut members  445 ,  447  are each in turn connected to respective sliders  445 ( 1 ),  447 ( 1 ). The sliders  445 ( 1 ),  447 ( 1 ) are arranged for movement along respective parallel rails  424 ,  426  which each extend in the Y axis direction. Two parallel screw shafts  414 ,  416  are arranged along the Y axis direction such that each one of screw shafts  414 ,  416  extends through a respective nut member  445 ,  447 . Each screw shaft  414 ,  416  is connected to a respective motor  404 ,  406  such that synchronous rotation of motors  404 ,  406  causes synchronized movement of nut members  445 ,  447  along screw shafts  414 ,  416 , thereby causing rail  423  (and therefore pickup head  200 ) to move in the Y axis direction. 
     Rails  424 ,  426  may be positioned on support members  462 ,  464  to provide a stable, sturdy base for the motion system  400 . Further, stabilizers  463 ,  465  may extend between and connect support members  462 ,  464  to prevent relative movement between the support members. 
     Motors  403 ,  404 ,  406  may be conventional synchronized incrementally stepped servo motors using encoders for conventional position feedback to enable precise positioning of pickup head  200  in the X/Y directions. 
     1.1 Feeder System 
     Now, with reference to  FIGS. 3-10 , an example feeder system will be described. A feeder module  300  is shown in  FIG. 3 . Feeder module  300  includes a frame  305  which supports a plurality of removable feeder cartridges  350 , as best shown in  FIG. 4 . The feeder module frame includes two spaced-apart handle portions  307  and a front plate portion (or rail)  306  extending between handle portions  307 . A reel-retaining portion  309  is positioned below the front plate portion  306 . The reel-retaining portion  309  includes a curved section arranged to removably receive a plurality of tape-wound reels  330 . Reel upright supports  381  may be slidably disposed in the reel-retaining portion  309  so provide support to reels  330  to aid in keeping the reels upright. 
     The handle portions  307  facilitate an operator in positioning the feeder module into, or removing the feeder module from, its operable position in the pick-and-place machine  1000 . Feeder modules  300  are interchangeable. An aperture  314  in front plate portion  306  is arranged to receive an alignment pin (not shown) that protrudes from pick-and-place machine  1000 . The alignment pin serves to properly align feeder module  300  in the machine. The opposing end of front plate portion  306  may also include an aperture  314 , as shown in  FIG. 4 . Front plate portion  306  also includes a feeder module lock/ejection mechanism  311  configured to lock feeder module  300  to the pick-and-place machine, as shown in  FIG. 3 . The feeder module lock/ejection mechanism  311  may also be actuated to eject the feeder module  300  from the machine  1000 . Further, a plurality of alignment slots  398  may be formed in and extend across a top portion of front plate  306  in a spaced arrangement, as shown in  FIG. 3-1 . Each alignment slot  398  is configured to engage a mating portion of a feeder cartridge  350 . Alignments slots  398  serve to properly align and space feeder cartridges  350  in feeder module  300  which in turn ensures that feeder cartridges  350  are properly aligned in pick-and-place machine  1000 . A plurality of feeder modules  300  may be positioned in the machine at any given time. 
     Alignment slots  398  may be spaced apart by 0.25 inches. A typical 8 mm tape feeder cartridge has a width of 0.5 inches, while 12 mm and 16 mm tape feeder cartridges have a width of 0.75 mm. Thus, by spacing the alignment slots 0.25 inches apart, 8 mm, 12 mm and 16 mm tape feeder cartridges can be accommodated without gaps or wasted spaced between the feeder cartridges. 
     The modular arrangement of feeder module  300  facilitates quick setup time. For instance, a user can configure in a feeder module  300  a group of feeder cartridges  350  for a particular job (e.g., assembly of a certain board). Feeder module  300  may be left undisturbed until the next time that particular board assembly is needed. Cost impediments to such strategy are removed by the relatively low cost of feeder cartridge  350 , which is constructed from relatively inexpensive materials and designed without onboard provisions for power (as described below). In other words, a user can own significantly more feeder cartridges  350  as compared to conventional feeders without adding significantly to the cost of pick-and-place machine  1000 . A user may even dedicate a feeder cartridge for each tape-wound reel  330 . Feeder module  300  may accommodate up to 40 feeder cartridges, which may provide sufficient capacity for complex assemblies while also facilitating portability. However, feeder module  300  may be configured to accommodate more than 40 feeder cartridges depending on need. 
     An alternative feeder module  300 - 1  is shown in  FIGS. 3-2   a  to  3 - 2   e . Feeder module  300 - 1  includes a frame  305 - 1  which supports a plurality of removable feeder cartridges  350 , as best shown in  FIGS. 3-2   a  and  3 - 2   b . Frame  305 - 1  includes two spaced-apart handle portions  307 - 1 , a front plate portion  306 - 1  extending between handle portions  307 - 1  and foot portions  308  to engage a surface on which the feeder module is positioned. A reel-retaining portion  309 - 1  is positioned below the front plate portion  306 - 1  to accommodate tape-wound reels  330  below feeder cartridges  350 . Feeder module lock/ejection mechanism  311 - 1  may be configured to lock feeder module  300 - 1  to the pick-and-place machine. Frame  305 - 1  may be constructed from steel rod or other suitable materials. Front plate portion  306 - 1  may be formed from aluminum or other suitable materials. 
     Reel-retaining portion  309 - 1  may include support members (e.g., a pair of spaced support members  393  (e.g., a pair of rods)) to support reels  330 , as best shown in  FIG. 3-2   d . Support members  393  may be spaced apart by a distance relatively close to but smaller than a diameter of reels  330 . This arrangement prevents reels  330  from dropping through a space between support members  393  while also containing the reels in stable engagement with the support members. 
     Feeder module  300 - 1  may include a locking device  391  to lock reels  330  in position in reel-retaining portion  309 - 1 . Locking device  391  may include a locking member  394  (e.g., a rod or bar) positioned near a top portion of reels  330 , a pair of triggers  395  on opposite ends of the feeder module to actuate the locking device, a pair of sleeves  362 , a pair of springs  397  (e.g., a helical spring), and a pair of pivot arms  302  connecting locking member  394  to a respective trigger  395 , as shown in  FIG. 3-2   d . Each trigger  395  may include an actuating portion  395 ( 1 ) (e.g., a user engaging portion such as a U-shaped member configured to be displaced (e.g., by pulling) or otherwise actuated by the user) and an operating portion  395 ( 2 ) (e.g., an elongate portion configured to transfer movement of actuating portion  395 ( 1 ) to rotate arm  302  about pivot  399 . 
     Locking member  394  may be connected to first end portions of pivot arms  302 . Second end portions of pivot arms  302  may be rotatably connected to respective operating portions  395 ( 2 ) via an optional block  396  as those skilled in the art will understand. Each helical spring  397  may extend between block  396  and sleeve  362  such that operating portion  395 ( 2 ) extends through an inner portion of the helical spring. By this arrangement, spring  397  urges block  396  (and thus the second end portion of pivot arm  302  away from sleeve  362  (and toward front plate portion  306 - 1 ) thereby causing operating portion  395 ( 2 ) to move toward front plate portion  306 - 1  and into an inserted position. When operating portion  395 ( 2 ) is urged towards the front plate portion, locking member  394  is moved into a locking position, as shown in  FIG. 3-2   d . In the locking position, locking member  394  is positioned above reels  330  and relative to support member  393  such that the reels are prevented (by locking member  394 ) from being moved upward enough to clear the support members. Thus, reels  330  are locked inside reel-retaining portion  309 - 1  when locking member  394  is in the locked position shown in  FIG. 3-2   d.    
     Reels  330  may be easily inserted into reel-retaining portion  309 - 1  by pressing each reel against locking member  394  (when in the locked position) until locking member  394  is displaced against a restoring force of spring  397  a sufficient distance ( FIG. 3-2   e ) that the reel is positioned in place in reel-retaining portion  309 - 1  and locking member  394  snaps back into its locked position ( FIG. 3-2   d ). A bent tab  379  prevents pivot arm  302  from pivoting past a vertical position thereby preventing reels from being removed by forceful pulling. Reels  330  are locked in reel-retaining portion  309 - 1  in a manner that allows rotation of reels  330  as tape  340  is fed through feeder cartridges  350 . That is, the reels, which, e.g., are formed of plastic, may slide against support members  393  and/or locking member  394 . 
     A user may pull trigger  395  away from front plate portion  306 - 1  against a restoring force of spring  397  to cause locking member  394  to be moved to the unlocked position shown in  FIG. 3-2   e  in order to remove reels  330  from reel-retaining portion  309 - 1 . 
     It is noted that sleeve  362  may include an upright portion  362 ( 1 ). In another example, the spring  397  may extend between the upright portion  361 ( 2 ) and pivot arm  302  (e.g., via block  396 ). Those skilled in the art will understand and recognize that there are other suitable arrangements for arranging spring  397  in locking device  391 . Furthermore, other suitable locking arrangements may be used to secure reels  330  in feeder module  300 - 1 . 
     As shown in  FIG. 3-2   b , guide member  303  may extend between feeder cartridges  350  and reels  330  to guide the used tape  340  away from the reels so that the used tape does not get tangled in the reels. 
     Feeder module  300 - 1  may include rollers  301  configured to engage a surface of pick-and-place machine  1000  to facilitate insertion of the feeder module into an operative position in the pick-and-place machine. Apertures  304  (e.g., tapered bores) may be disposed at opposite end portions of the feeder module, as shown in  FIG. 3-2   b . Apertures  304  may be configured to receive a mating pin on pick-and-place machine  1000  to align the feeder module in the pick-and-place machine. 
     As shown in  FIG. 4 , a plurality of removable feeder cartridges  350  are mounted on front plate portion  306  of feeder module  300 . A tape  340  from each reel  330  is fed through a respective feeder cartridge  350 . Components to be placed on the substrate are contained on and/or in tape  340 . Feeder cartridges  350  serve to feed the component-bearing tape to a component pick-up location where the components are exposed for pick-up by pickup head  200 . Feeder cartridges  350  are passive devices (as will be described in more detail later) having no onboard provisions for power (e.g., electrical, mechanical or pneumatic power). Tape  340  may have any suitable width as needed for a given component size (e.g., 8, 12, 16, 24 mm or more). 
     The front plate portion  306  of frame  305  includes a first attachment device (e.g., a protuberance  316 , e.g., a rounded protuberance) along a top edge portion thereof and a second attachment device (e.g., a recess  317 ) along a bottom edge. It is noted that the first and second attachment devices may be partitioned (or otherwise divided) and thus each configured as a plurality of first attachment devices and a plurality of second attachment devices corresponding to a respective feeder cartridge. As mentioned above, alignment slots  398  are formed in an upper portion of front plate portion  306 . In an example, the alignment slots may be at least partially formed in protuberance  316 . Protuberance  316  and recess  317  facilitate attachment of a feeder cartridge  350  to front plate portion  306 . 
     As best shown in  FIG. 5 , a body portion  352  of the feeder cartridge includes an upper attachment portion  352 ( 1 ) which terminates in a first connecting device (e.g., receiving portion  352 ( 1 ) a ). Upper attachment portion  352 ( 1 ) includes alignment protrusion  363  on an inner surface thereof. Alignment protrusion  363  may be configured with a shape that mates with alignment slots  398 . Referring to  FIG. 7-1 , body portion  352  includes a lower attachment portion  352 ( 2 ) having a second connecting device (e.g., projection  352 ( 2 ) a ) extending across an end portion thereof. Projection  352 ( 2 ) a  has an inclined or tapered surface  352 ( 2 ) b.    
     To mount feeder cartridge  350  to frame  305 , upper attachment portion  352 ( 1 ) may be placed over front plate portion  306  such that alignment protrusion  363  fits into a respective alignment slot  398  thereby positioning receiving portion  352 ( 1 ) a  around protuberance  316 . A user may then press down upon knob  365  which causes inclined surface  352 ( 2 ) b  to engage front plate portion  306  (e.g., locating member  317 ( 1 )) which in turn causes lower attachment portion  352 ( 2 ) to flex so as to cause projection  352 ( 2 ) a  to snap into recess  317  of front plate portion  306 . The snap-fit arrangement of lower attachment portion  352 ( 2 ) and recess  317  provides ease of installation. By this arrangement, feeder cartridge  350  is supported at only one end by the front plate portion  306  of feeder module  300  thereby forming a cantilever. This arrangement allows for compact feeder cartridge and reel packaging. The cantilever mounting of feeder cartridge  350  allows access to a bottom portion of the feeder cartridge. Therefore, reels  330  may be mounted below the feeder cartridges and the tape  340  from each reel may be fed to a bottom portion of a respective feeder cartridge. Providing the feeder cartridges and the reels in a stacked arrangement helps reduce the footprint of the feeder module. In another example, feeder cartridge  350  may be connected directly to pick-and-place machine  1000  in the manner of a cantilever. Preferably, receiving portion  352 ( 1 ) a  and the protuberance have mating shapes. 
     An example snap-fit arrangement may be described as “a mechanical joint system where part-to-part attachment is accomplished with locating and locking features (constraint features) that are homogenous with one or the other of the components being joined. Joining requires the (flexible) locking features to move aside for engagement with the mating part, followed by return of the locking feature toward its original position to accomplish the interference required to latch the components together. Locator features, the second type of constraint feature, are inflexible, providing strength and stability in the attachment.”  The First Snap - Fit Handbook , Bonenberger, 2000. 
     To remove a feeder cartridge, a user may simply push upwardly upon knob  365  which causes front plate portion  306  to exert a force against lower attachment portion  352 ( 2 ) which in turn causes the lower attachment portion to flex such that projection  352 ( 2 ) a  becomes disengaged with recess  317 . 
     Referring to  FIGS. 5 to 7-2   b , a channel  365 ( 1 ) is formed in knob  365  such that an anti-tamper device may be fed through a group of feeder cartridges. This allows a group of feeder cartridges  355  (e.g., grouped in a particular feeder module for assembly of a certain board) to be “put on the shelf” until the next time they are needed while ensuring that the grouping of feeder cartridges is not changed. 
     Pick-and-place machine  1000  may include a detection device (e.g., an optical interrupter  313  provided on front plate portion  306 ) to detect the presence of feeder cartridge  350  in a properly installed position. Optical interrupter  313  includes spaced light emitting and light detecting portions as one skilled in the art will understand. A protruding portion  315  of body portion  352  is positioned to block the light transmission of optical interrupter  313  (thus triggering the optical interrupter) when feeder cartridge  350  has been inserted far enough that projection  352 ( 2 ) a  snaps into recess  317 , thus confirming proper attachment of feeder cartridge  350  to front plate portion  306 . A feeder cartridge  350  that is not inserted completely may have a raised position which may interfere with the pickup head. By the above described arrangement, feeder cartridge  350  will snap into place and be consistently positioned with respect to front plate portion  306  each time the feeder cartridge is connected to the front plate portion. 
     Optical interrupter  313  may be used to determine when a feeder cartridge  350  has been removed or when a new feeder cartridge has been added. As will be described later, the addition of a new feeder cartridge  350  may prompt pick-and-place machine  1000  to acquire information from the feeder cartridge. 
     In an alternative example shown in  FIGS. 7-2   a  and  7 - 2   b , front plate portion  306 - 1  may include a series of spaced guide channels  310  for receiving protruding portion  315  of feeder cartridges  350 . Each guide channel  310  corresponds to a respective alignment slot  398 - 1  and will further ensure that each feeder cartridge  350  is properly aligned in pick-and-place machine  1000 . As shown in  FIG. 9 , upper attachment portion  352 ( 1 ) may include a protrusion  364  to mate with alignment slots  398 - 1  on front plate portion  306 - 1 . Optical interrupter  313  may be disposed within guide channel  310 . Further, front plate portion  306 - 1  may include an inclined surface  366  upon which inclined surface  352 ( 2 ) b  of projection  352 ( 2 ) a  may engage to facilitate attachment of feeder cartridge to front plate portion  306 - 1 . That is, in referring to  FIG. 7-2   b , as the user pushes downwardly on knob  365 , feeder cartridge  350  rotates in a clockwise direction as inclined surface  352 ( 2 ) b  slides against inclined surface  366  until projection  352 ( 2 ) a  snaps into recess  317 . Additionally, as shown in  FIGS. 7-2   a  and  7 - 2   b , lower attachment portion  352 ( 2 ) may include a recessed portion to form a more pronounced catch  352 ( 2 ) c  to accommodate locating member  317 ( 1 ). 
     Body portion  352  may further include a stabilizing portion  392  disposed between upper attachment portion  352 ( 1 ) and lower attachment portion  352 ( 2 ) and configured to engage front plate portion  306 - 1  to stabilize feeder cartridge  350 . Stabilizing portion  392  may contact an engaging portion of front plate portion  306 - 1  disposed between protuberance  316  and recess  317 . Stabilizing portion  392  may include an extended flat portion configured to engage a flat portion of front plate portion  306 - 1  for stabilizing the feeder cartridge by limiting movement between feeder cartridge  350  and front plate portion  306 - 1 . Those skilled in the art will recognize that other mating surfaces may be used to limit movement. Receiving portion  352 ( 1 ) a - 1  may include an extending portion configured to engage a surface of front plate portion  306 - 1  opposite protuberance  316 . 
     Referring to  FIG. 5 , tape  340  includes a plurality of sprocket holes  341 , a plurality of component pockets  343  to accommodate components (not shown), and a cover film  344  to contain the components in pockets  343  until they are to be exposed for pickup. The cover film may be a thin transparent film lightly glued or heat sealed to tape  340  and/or the components. As tape  340  is advanced through feeder cartridge  350 , a cover film drive assembly  359  peels the cover film from tape  340  (e.g., see motion arrows on tape  340  in  FIG. 5 ) to expose the components across a pickup zone  342 . 
     A feeder gear  355  is rotatably disposed in feeder cartridge  350 . Feeder gear  355  is a passive gear relying on drive forces external of the feeder cartridge  350  for rotation. Feeder gear  355  may be exposed from body portion  352  to facilitate engagement with an external driving device. However, in another example, feeder gear  355  may be recessed into body portion  352  and accessible via a slot in the body portion. A sprocket wheel  356  ( FIG. 5 ) is rotatable about a common axis with feeder gear  355  and is locked in rotation with the feeder gear. As shown in  FIG. 10 , feeder gear  355  and sprocket wheel  356  may be rotatably disposed on shaft  360 . Pickup head  200  includes a rack gear that drives the feeder gear  355 , as will be described later. As feeder gear  355  of a given feeder cartridge  350  is driven (by pickup head  200 ), sprocket wheel  356  also rotates because of its locked arrangement with the feeder gear. Sprocket teeth  356 ( 1 ) engage sprocket holes  341  in tape  340  to advance the tape through feeder cartridge  350 . 
     Gear teeth  355 ( 1 ) of feeder gear  355  engage cover film peeling gears  357 ,  358  ( FIG. 5 ) in cover film drive assembly  359  to cause cover film  344  to be peeled away from tape  340 . Specifically, gear teeth  355 ( 1 ) of feeder gear  355  mesh with gear teeth  357 ( 1 ) of cover film peeling gear  357 . Gear teeth  357 ( 1 ), in turn, mesh with gear teeth  358 ( 1 ) of cover film peeling gear  358 . Cover film peeling gears  357 ,  358  are connected, respectively, to a pair of mating rollers  357 ( 2 ),  358 ( 2 ) which together function to pull cover film  344  and peel it from tape  340 . In another example, the feeder gear could drive cover film drive assembly  359  via a belt or other suitable device as those skilled in the art will recognize. 
     As shown in  FIGS. 6 and 7 , feeder gear  355  includes calibration marks  351  (e.g., corresponding to every other tooth), to enable the position of the feeder gear to be precisely determined by CPU  110 , as will be described in more detail later. Calibration marks  351  may be hot-stamped with a highly reflective foil (e.g., a white foil) to facilitate easy optical detection. Alternatively, the marks may be stamped with a silver or gold colored foil, for example. Calibration marks  351  may be arranged on feeder gear  355  in a manner that matches the component spacing on tape  340  such that the calibration marks may also identify a location of components on tape  340  as well. 
     Turning back to  FIG. 4 , a series of light emitting diodes (LEDs) (e.g., multi-colored LEDs  312 ) extend across front plate portion  306 . Front plate portion  306  (or another part of feeder module  300 ) may include through holes or channels to permit the LEDs to optically communicate with light pipes  354  (e.g., formed of translucent or transparent plastic) disposed on each feeder cartridge  350 . Since feeder cartridges  350  do not require electrical power, light (i.e., LEDs  312 ) produced by pick-and-place machine  1000  may be selectively fed to light pipes  354  to derive a status of each feeder cartridge  350 . The light may be visible to an operator through a button  354 ( 1 ) at a top portion of light pipe  354 . 
     Now referring to  FIGS. 6, 7 and 9 , body portion  352  of feeder cartridge  350  includes an inlet guide channel  384  through which tape  340  is guided to pickup zone  342 . Inlet guide channel  384  is formed by opposing wall portions  384 ( 1 ),  384 ( 2 ), as best shown in  FIG. 9 . Once cover film  344  is peeled from tape  340 , the remaining portion of the tape (after components are removed) is fed out of the feeder cartridge through an outlet guide channel  386 . As shown in  FIG. 9 , outlet guide channel  386  is formed by opposing wall portions  386 ( 1 ),  386 ( 2 ). Similarly, peeled back and used cover film  344  is guided out of the feeder cartridge  350  by a cover film guide channel formed by opposing wall portions  388 ( 1 ),  388 ( 2 ). 
     An alternative cover film drive assembly  370  is shown in  FIGS. 6-10 . As best shown in  FIG. 8 , cover film drive assembly  370  includes first and second cover film peeling gears  371 ,  372  having mating gear teeth  371 ( 1 ),  372 ( 1 ). First gear  371  is connected to and driven by a third gear  373 . Referring to  FIGS. 8 and 10 , third gear  373  has gear teeth  373 ( 1 ) that engage gear teeth  355 ( 1 ) of feeder gear  355  such that third gear  373  is driven by feeder gear. As best shown in  FIGS. 6 and 8 , cover film  344  is fed between mating first and second gears  371 ,  372  such that rotation of feeder gear  355  causes the peeled back cover film to be drawn between first and second gears  371 ,  372  thereby peeling the cover film from tape  340 . The mating teeth  371 ( 1 ),  372 ( 1 ) drive the cover film  344 ; however, it is noted that the cover film  344  is intended to slip at a modest force through the teeth  371 ( 1 ),  372 ( 1 ). Alternatively, one of the first and second gears  371 ,  372  may instead be a roller (e.g., a rubber roller). 
     The second gear  372  may be supported on a tensioner arm  380 . A lower portion of tensioner arm  380  includes a shaft opening  380 ( 1 ) that rotatably receives shaft  382  ( FIG. 10 ) which protrudes from body portion  352 . Second gear  372  is attached to an upper portion of tensioner arm  380 . When tape  340  is initially fed through feeder cartridge  350 , an operator may peel cover film  344  from a leading edge of tape  340  and feed a leading edge of the cover film through cover film drive assembly  370 , as an initial set-up procedure. Tensioner arm  380  enables second gear  372  to be rotated away from first gear  371 , thereby providing sufficient space to easily place the leading edge of cover film  344  between first and second gears  371 ,  372 . Once the leading edge of the cover film is in place between the first and second gears, tensioner arm  380  may be rotated toward first gear  371  to pinch the cover film between first and second gears  371 ,  372 . Tensioner arm  380  may be urged toward the cover film by a spring (e.g., a helical torsion spring (not shown) connected to the shaft  382 ). 
     The tensioner arm  380  may include a knob  380 ( 3 ) to assist the operator in pivoting tensioner arm  380 . Knob  380 ( 3 ) protrudes upwardly from body portion  352  through opening  353  in the body portion. 
     In another example, first and second gears  371 ,  372  may each include separable portions, as shown in  FIG. 10 . For instance, first gear  371  may comprise a first portion  371 ( a ) and a second portion  372 ( b ) disposed on opposite sides of body portion  352  and connected to one another through opening  352 ( 3 ) formed in body portion  352 . Similarly, second gear  372  may comprise a first portion  372 ( a ) and a second portion  372 ( b ) disposed on opposite sides of tensioner arm  380  and connected to one another through opening  380 ( 2 ) formed in the tensioner arm. A shaft portion may protrude from one portion of first and second gears  371 ,  372  to connect to the other portion. 
     Body portion  352  may include opposing curved portions  390  to assist in directing the cover film to cover film drive assembly  370 . The curved portions may be tapered to more precisely direct the path of the cover film. 
     As shown in  FIGS. 6 and 7 , a feeder cartridge  350  may include a label (e.g., on the body portion  352 ). Label  361  may include a machine readable barcode (or other machine readable markings), as well as human readable alphanumeric text (which may, of course, also be machine read and recognizable). The barcode may be read by a multi-purpose camera on pickup head  200 , as will be described later, to convey to pick-and-place machine  1000  (e.g., CPU  110 ) information (e.g., a part number) regarding the particular components being fed by that particular feeder cartridge. Additionally, as a confirmation, the operator may simply read the alphanumeric text on label  361  to ensure that the component identifying information (e.g., a part number) on the label matches the component identifying information (e.g., a part number) on reel  330  containing tape  340  being fed through feeder cartridge  350 . 
     Turning back to  FIG. 4 , in an example, four color LEDs (e.g., green blue, red and yellow LEDs  312 ) may be used. The light pipe  354  of a newly installed feeder cartridge may blink yellow until label  361  is read. If label  361  is successfully read, the light pipe may show the green or blue light. The green light may indicate that all is ready to go while the blue light may indicate that the feeder cartridge is ready but not used in the current program (assembly). Thus, the blue light might indicate an “incorrect” feeder cartridge for the current assembly or simply that the feeder cartridge is needed for a later assembly. If a feeder cartridge has no label or a label that is not readable, light pipe  354  will show red. During an assembly process, the blue light may indicate to a user which feeder cartridges  350  can be removed without affecting the current assembly. This facilitates change-over to a new assembly. 
     Further, light pipe  354  of a feeder cartridge may blink (e.g., red) when the feeder cartridge will be empty in a certain amount of time (e.g., 20 minutes) at the current rate of production. The light may blink at a faster rate as the feeder cartridge approaches an empty status (e.g., 5 minutes until empty). This may alert a user to prepare a new reel of components for reloading, or the user may simply install a backup feeder cartridge to allow the machine to revert to the backup feeder cartridge upon depletion of the primary cartridge. Light pipe  354  of the primary feeder cartridge may then show red to indicate an empty status. 
     The feeder cartridge  350  parts (e.g., body portion  352 , feeder gear  355 , sprocket wheel  356 , and cover film drive assembly  359 ,  370 ) are preferably formed of plastic (e.g., injection molded plastic). 
     1.2 Pickup Head 
     Referring to  FIGS. 11-14 , the pickup head  200  of the example pick-and-place machine  1000  is shown. Pickup head  200  includes a frame  204 . A controller (e.g., printed circuit board  202 ) for controlling the pickup head  200  is attached to the frame  204 . The frame includes opposing sidewalls  204 ( 2 ),  204 ( 3 ). Each sidewall  204 ( 2 ),  204 ( 3 ) may extend continuously or may include offset portions in the manner of sidewall  204 ( 3 ) which has an inwardly offset upper portion. A front lower wall portion  205  extends between front portions of the sidewalls  204 ( 2 ),  204 ( 3 ) and a rear lower wall portion  207  extends between rear portions of sidewalls  204 ( 2 ),  204 ( 3 ). 
     A gear driving mechanism  210  is disposed at a lower portion of pickup head  200  and is rotatably connected to the front and rear lower wall portions  205 ,  207 . As best shown in  FIG. 12 , gear driving mechanism  210  includes a pair of parallel arms  212 ,  214 . The arms  212 ,  214  are rotatably connected to lower wall portions at pivot  217 . Arms  212 ,  214  may be formed of any suitable material, but are preferably formed of aluminum, Al stainless steel or brass. 
     A rack gear  216  is connected to the free ends of arms  212 ,  214  such that the rack gear extends between the arms. Rack gear  216  may be formed of any suitable material, but is preferably formed of aluminum, Al stainless steel or brass. The rack gear has one or more gear teeth  216 ( 1 ) that mesh with the gear teeth  355 ( 1 ) of the feeder gear  355  of a particular feeder cartridge that happens to be aligned with it. That is, arms  212 ,  214  are configured to rotate downwardly to cause rack gear  216  to mesh with feeder gear  355  when the pickup head  200  is so positioned at a particular selected feeder cartridge  350 , as best shown in  FIG. 13 . Once rack gear  216  is engaged with feeder gear  355 , the pickup head may be moved in the Y axis direction by motion system  400  to drive feeder gear  355  and thereby index (i.e., move) tape  340  to bring the next component into pickup zone  342 . The motive power required for the feeder cartridges is thus supplied as needed by the pickup head  200 , avoiding the need for a drive motor in the feeder cartridge (or feeder module) itself. 
     The gear driving mechanism  210  includes an optical sensing system (e.g., reflective sensors) to read the calibration marks  351  on the engaged feeder gear  355 . In the illustrated example of  FIG. 12 , gear driving mechanism  210  includes two sensors (e.g., LED/phototransistor sensors)  218  on opposing ends of rack gear  216 . The two sensors  218  are also disposed on opposite sides of rack gear  216 . The sensors  218  include an LED arranged to emit light toward feeder gear  355 . A phototransistor element is also included in each sensor  218  to detect whether or not the emitted light is reflected, as one skilled in the art will understand. As such, sensors  218  are able to precisely detect the rotary position of feeder gear  355 . As shown, sensors  218  are oppositely directed thus permitting one to be used when the feeder gear is on one side of pickup head  200  and the other sensor  218  to be used when the feeder gear is on the other side of pickup head  200 . 
     Optical sensors  218  may also be used to measure the gear position in the lateral (x) axis direction, as determined by a distance from one of the sensors  218  to feeder gear  355 . Sensor  218  has a relatively narrow range (distance) over which the sensor can detect reflected light. The response signal amplitude peaks at a specific distance from feeder gear  355  and falls quickly at greater or lesser distances from that point thus making it possible to identify an optimal distance relative to the peak amplitude point. One skilled in the art will recognize that a “valley” instead of a peak of the signal amplitude may be used. Moving sensor  218  until the response has a predetermined amplitude relative to the peak amplitude will identify the lateral position of the gear (distance from feeder gear  355  to sensor  218 ). Since feeder gear  355 , sprocket  356  and tape  340  are connected to one another, the measured lateral position of feeder gear  355  can be used to further determine the location of pickup zone  342  as well as a component to be picked. This peak/distance sensing operation may be done on the fly. For example, the process can be performed by starting with sensor  218  in relatively close position to feeder gear  355  and then moving the sensor away from the feeder gear, or alternatively, starting with sensor  218  relatively far away and then moving the sensor closer to the feeder gear, while noting a peak in the amplitude and the position where the peak occurred—the peak being at a known distance relative to a desired optimum distance. 
     The rotary position of feeder gear  355  can be used to determine component location in the Y axis direction, while the lateral position of the feeder gear can be used to determine component location in the X axis direction. This information is used by the pick-and-place machine  1000  to refine its determined location of pickup zone  342 . Knowledge of the exact X axis location of pickup zone  342  can be used to mitigate or cancel the effects of feeder lateral location misalignment. Similarly, knowledge of the exact Y axis location of pickup zone  342  can be used to mitigate or eliminate the effects of errors caused by mechanical slop or lash in the drive gear train. 
     Sensor  218  includes an LED to emit light and a photosensor to detect the reflected light. However, one skilled in the art will understand that the LED may serve the dual functions of emitting light and sensing (now operating as a photodiode) reflected light. Such arrangement may reduce the space required by sensors  218  on the gear driving mechanism  210 . 
     An electromechanical solenoid  220  is positioned in pickup head  200 , as best shown in  FIG. 11 . Electromechanical solenoid  220  may be actuated to lower an engaging element (e.g., a roller)  222  which engages arm  214  and pushes it downwardly about its pivot to cause the gear driving mechanism  210  to be lowered. In other examples, an air cylinder or motor (e.g., a linear motor) may be used instead of electromechanical solenoid  220 . Gear driving mechanism  210  may be returned to its original position by a spring (as depicted) or other suitable device. 
     Referring to  FIGS. 11 and 14 , pickup head  200  includes a pickup device (e.g., vacuum nozzle  230 ) that functions to pick up a component from a selected tape  340  and then place that component onto the substrate (not shown) at a precisely determined location and in a precisely determined orientation. Although vacuum nozzle  230  is shown in the illustrated example, it is noted that other methods of picking up and placing a component may be used. For example, grippers may be actuated (e.g., by a vacuum pressure driven piston) to pick up components and place the components on a substrate. Magnetic components may be picked up with an electro-magnet. An adhesive could be used to pick and place components. Other examples include state change adhesion (e.g., freezing water into ice), AC magnetic induction (which may attract non-magnetic components if they are electrically conductive), jet entrainment (which may be used to pick and place components by pressure), and electro-static charge. 
     As shown in  FIG. 11 , vacuum nozzle  230  is suspended from nozzle holder  231 . Vacuum nozzle  230  is removably attached to nozzle holder  231 . Nozzle holder  231  is connected at its upper end to a shaft of nozzle rotation motor  234 . Vacuum nozzle  230  is in flexible fluid communication (e.g., a flexible tube) with a vacuum generator via nozzle holder  231  so as to provide vacuum/suction at a distal opening of vacuum nozzle  230 . The vacuum is provided so that a component may be picked up and held against the distal nozzle end by vacuum force (i.e., actually by differential air pressure forces on the top and bottom of the component caused by the vacuum at the distal end of the nozzle) while in transit between the feeder cartridge and the substrate. 
     Nozzle rotation motor  234  is positioned on a top side of platform  232  opposite nozzle holder  231 . Nozzle rotation motor  234  serves to rotate vacuum nozzle  230  so as to adjust an angular position of a component picked-up/held by vacuum nozzle  230 . Nozzle rotation motor  234  is preferably a servo step motor using a conventional position feedback encoder to provide precise rotary adjustment of vacuum nozzle  230 . 
     Vacuum nozzle  230  is quickly raised and lowered by a crank mechanism connected to platform  232 , e.g., via a force sensing mechanism  800  which will be described later. Crank arm  240  is connected to connecting rod  242  which extends downwardly to connect to platform  232 . Crank arm drive  246  (e.g., a servo-controlled rotary motor) is arranged to rotate crank arm  240 , thereby causing connecting rod  242  to raise or lower vacuum nozzle  230 . When platform  232  is raised or lowered, nozzle rotation motor  234  is also raised or lowered along with platform  232 . Platform  232  is arranged to slide along vertical guide rail  239  positioned on rear wall  204 ( 1 ) of frame  204 . Instead of a crank mechanism, vacuum nozzle  230  may be raised and lowered by other devices, such as a motor driven lead screw of a voice coil linear motor. 
     As can be seen in  FIG. 11 , the platform extends to a side portion of pickup head  200  to support a camera assembly  250 . As such, camera assembly  250  is also raised or lowered with the platform, as can be seen in  FIG. 14  where pickup head  200  is in a down position. Vacuum nozzle  230  is arranged to either pick up a component from a selected tape  340  or place a component on the substrate at a selected position when the vacuum nozzle is in the down position shown in  FIG. 14 . 
     As shown in  FIG. 15 , vacuum nozzle  230  includes flange  230 ( 1 ), neck portion  230 ( 2 ) and distal nozzle opening  230 ( 3 ). Projection  238  and notch  237  permit controlled accurate indexed positioning of the vacuum nozzle  230  on pickup head  200  and/or a nozzle changer cartridge. Specifically, projection  238  may be used to align vacuum nozzle  230  in nozzle holder  231  and the notch  237  may be used to align the vacuum nozzle in a nozzle changer  270  (discussed below). Information as to nozzle type and/or identity can be encoded by fiducial markings  233 ,  235  (e.g., reflective/non-reflective and/or color-coded markings). 
     A nozzle changer cartridge  270  is shown in  FIG. 16 . The nozzle changer cartridge may house a variety of vacuum nozzles, including differently sized vacuum nozzles. Nozzle size may correspond to the size of components contained on a particular tape  340  (e.g., a larger vacuum nozzle may be required for larger components). The nozzle changer cartridge is arranged in the pick-and-place machine  1000  in an area accessible to pickup head  200 . In this manner, pickup head  200  may be lowered at a selected position to cause nozzle holder  231  to attach to a desired vacuum nozzle (or to deposit a presently attached vacuum nozzle into an empty cavity of the nozzle changer cartridge). Then, the selected vacuum nozzle  230  may be unlocked from the nozzle changer cartridge  270  by shifting locking plate  273  from alignment of nozzles with the small opening  272  to alignment of nozzles with the large opening  274  of the nozzle changer cartridge  270 . Locking plate  273  may be driven back and forth (e.g., with a solenoid, air cylinder or motor). 
     The multi-purpose camera in pickup head  200  may be used to read the fiducial markings  233 ,  235  on vacuum nozzle  230  so as to selectively position the pickup head for pickup of a desired vacuum nozzle and/or for deposit of a vacuum nozzle in a currently empty position of the nozzle changer cartridge  270 . CPU  110  may also be programmed to maintain a table or other data to record the identity of vacuum nozzles in particular changer cartridges positions, open positions in the changer cartridge, and the like. 
     Fiducial marks  271  (e.g., round dots) on the nozzle changer cartridge  270  are used to locate the precise installed location of the changer cartridge. Other information may be encoded by fiducial size or location, such as changer type, number of positions, etc. An optical interrupter (not shown) may be positioned internally to report when a user opens the changer cartridge  270  (e.g., to change the nozzle configuration). The system will be prompted to re-read fiducial markings  233 ,  235  on the vacuum nozzles if changer cartridge  270  is opened. Once the changer cartridge is open, the system may maintain the changer cartridge in the open position for the user&#39;s convenience. 
     1.3 Dual Camera Assembly 
     The pickup head  200  employs a dual camera assembly  250  to provide for component centering and a variety of other imaging control functions. Referring to  FIGS. 17 and 19A to 20B , dual camera assembly  250  includes side-facing component camera  251  to capture a shadow image (silhouette) of a component held on vacuum nozzle  230 . Component camera  251  facilitates angular adjustment of the component as well as linear adjustment, i.e., positioning of the component. Dual camera assembly  250  also includes a down-facing multi-purpose camera  252  to capture images of the substrate, read barcode labels (e.g., on the feeder cartridges  350 ), image calibration marks (e.g., on the machine  1000 ) and perform other imaging functions. Cameras  251 ,  252  are preferably high resolution monochrome cameras. 
     Component camera  251  and the multi-purpose camera  252  share a single lens  250 ( 1 ) via beam splitter  250 ( 2 ), as best shown in  FIG. 19A . The lens  250 ( 1 ) is preferably an ordinary lens intended for ordinary (not telecentric) camera imaging. Light passing through lens  250 ( 1 ) is directed to both component camera  251  and multi-purpose camera  252  by a beam splitter  250 ( 2 ). However, in the exemplary embodiment, component camera  251  and the multi-purpose camera  252  are not required to be used at the same time. 
     The dual camera assembly  250  also comprises a conventional microprocessor/controller subsystem (not shown) and video capture hardware (not shown) to interface the cameras  251 ,  252  and the microprocessor/controller subsystem ultimately to the at least one system CPU  110 . 
     1.3.1 Component Camera 
     Referring to  FIGS. 17-19A , light from a light source (e.g., LED or laser)  253  is delivered to component camera  251  via mirror  255 , collimating lens  257 , component C, diffuser screen  259 , beam splitter  260 , lens  250 ( 1 ) and beam splitter  250 ( 2 ). Light source  253  projects light  253 ( 1 ) downwardly to mirror  255 , as best shown in  FIG. 19A . The mirror reflects the light through collimating lens  257  and then towards diffuser screen  259 . Mirror  255  and collimating lens  257  may be contained in housing  257 ( 1 ), as shown in  FIG. 18 . Additionally, support structure  259   a  may support the diffuser screen. Light  253 ( 1 ) emerging from diffuser screen  259  enters conventional beam splitter  260  and is directed upwardly to camera lens  250 ( 1 ), as best shown in  FIG. 1913 . Finally, light  253 ( 1 ) enters component camera  251  by way of beam splitter  250 ( 2 ). 
     When the component C is picked up by vacuum nozzle  230 , the vacuum nozzle is raised to the up position within pickup head  200 , as shown in  FIG. 18 . Such positioning brings the component C, which is held against the nozzle opening  230 ( 3 ), into the path of light  253 ( 1 ), as shown in  FIG. 19A . The collimated light projects a clearly focused shadow of the component C onto diffuser screen  259 . Use of a diffuser screen  259  between component C (illuminated by collimated light) and component camera  251  provides essentially an unlimited depth of field. 
     A component C as held against the distal nozzle opening  230 ( 3 ) is typically not exactly centered with respect to the nozzle opening. Thus, to ensure accurate placement of the held component on the substrate, an alignment correction must be calculated before the component is placed. The shadow image of the component on diffuser screen  259  is used to obtain this correction. 
     Squaring Method 
     In an example, a position adjustment routine, or “squaring method,” as described below with reference to  FIG. 37 , may be used to obtain alignment correction of component C. 
     The component angle as actually held by the nozzle is measured by rotating the component C to a test angle of 22.5 degrees on either side of a nominal predetermined normal angle, as represented by steps  601 ,  602 . Measurements begin with the narrow side of the component facing the camera. This orientation will result in the largest shadow length change for a given rotation. The squaring scale factor number is based on this orientation and the measurement does not work if the long dimension initially faces the camera. This problem does not exist with square symmetrical components. If the picked-up component is rotationally misaligned by 5 degrees, for example, the test rotations would yield actual orientation angles of 22.5-5 and 22.5+5 degrees, thereby resulting in component angles of 17.5 degrees and 27.5 degrees. 
     By measuring both directions a greater difference in the resulting silhouette length (angles) is available, which enhances precision. Because the ratio of these values is employed, the actual magnitude of these values, or in other words the size of the part, is irrelevant. In addition, this makes certain forms of image distortion and non-linearity self cancelling. 
     The ratio of the lengths of the horizontal shadows is related to the component angle. If the ratio is smaller than 1, the inverse of the ratio is used, and in either case, 1 is subtracted. This results in a number that increases as the component angle increases. The relationship to actual angle depends on the aspect ratio of the component (width/length), but is independent of size. The ratio is nearly proportional to angle, but has a small downward slope decreasing about 15% between 1 and 10 degrees. An equation is used to better fit the slope. For example, K-ratio*K/2.4+4.2 works well over a good range of component sizes, where K is the scale factor of a rotation of 10 degrees. The value K is typically 20-40 and may be calculated in advance if the component dimensions are known. The derivation process for K rotates the coordinates of the component as determined by the given dimensions (e.g., 10 degrees via trigonometry), then figures the ratio of the silhouette lengths and derives the scale factor that would convert the ratio to 10 degrees. 
     The component angle calculated by this procedure, as represented by step  603 , will first be used to align the component to measure its linear misalignment. In step  604 , the component is rotated back from the test angle (22.5 degrees) to the nominal predetermined normal angle (but in addition accounting for the calculated error angle) which aligns the narrower side of the rectangular component parallel to the camera. This rotational orientation is equivalent to an orientation the component would have had if the component was initially picked up with zero error. The left edge of the camera image is used as the reference point for measurements. 
     The fundamental unit of video measurement is the sensor pixel. A resolution of 0.001 inches per pixel is suitable. However, the measurement resolution is not limited to the size of a single pixel. The pixel intensity may be used to infer the actual edge position of the component, thus effectively increasing the available resolution. This is commonly known as sub pixel imaging, or sub pixel interpolation. To reduce the effect of “image noise,” measurements from several sequential lines may be averaged. In step  605 , the pixel counts from the left edge of the image to both left and right edges of the component silhouette are measured. The center of the component is found by averaging these two values, in step  606 . Center=(L+R)/2. The difference between the component center and the pickup spindle (nozzle holder) center is a linear error that must be corrected. In step  607 , the component is then rotated 90 degrees and then, in step  608 , the process is repeated to find the error on the other axis. The outcome of this process is both a linear X/Y correction and an angular correction, as represented by step  609 . This will be applied to the spindle (nozzle holder) position just prior to the component being placed. 
     Averaging may be applied to the squaring process. That is, data from other scan lines in the component image may be employed. Specifically, several values of L from sequential scan lines may be averaged to produce a “cleaner” L. This process may also be used for R. Then, a single (L+R)/2 calculation may be performed, or alternatively, several (L+R)/2 calculations may be carried out with several raw L and R values, and then the (L+R)/2 results may be averaged to produce a cleaner (L+R)/2 result. When several data points are available, artifact rejection may also improve the quality of the resulting calculations. Data points that lie relatively far away from the others may be rejected as defective so as to not contaminate the result. This process can eliminate the influence of measurement noise or physical contamination such as dust in the image. 
     In addition to the center of the component, (R−L) may be calculated to determine the component length. Also, by counting the scan lines in the silhouette, the thickness of the component may be determined. 
     1.3.2 Multi-Purpose Camera 
     Referring to  FIGS. 17, 18, 20A and 20B , light from a light source (e.g., a multi-color LED array)  254  is delivered to multi-purpose camera  252  via diffuser  256 , beam splitter  260 , lens  250 ( 1 ) and beam splitter  250 ( 2 ). Light source  254  projects light  254 ( 1 ) through diffuser  256  and into beam splitter  260  which passes part of the light and directs the other part of the light downwardly to substrate  258 , as best shown in  FIG. 20A . As can be seen in  FIG. 20B , substrate  258  reflects the light back through beam splitter  260  and then to multi-purpose camera  252  by way of lens  250 ( 1 ) and beam splitter  250 ( 2 ). 
     The light that passes through beam splitter  260  may hit diffuser screen  259  and/or its mounting frame and be reflected back to beam splitter  260  which will reflect part of the light up to multi-purpose camera  252 . The light being reflected off of diffuser screen  259  may create an undesirable ghost image on the diffuser screen which will overlay and interfere with the image of the substrate  258 . In an example, an antireflective device (e.g., an antireflective coated circular polarizer  259 ( 1 )) may be installed between diffuser screen  259  and beam splitter  260 . In the illustrated example, antireflective coated circular polarizer  259 ( 1 ) is applied (e.g., glued) to diffuser screen  259 . The antireflective coating prevents ghost reflections from its front surface as those skilled in the art will understand. The circular polarizer polarizes incoming light before it strikes diffuser screen  259 . Thus, the light reflected off of diffuser screen  259  will have an opposite polarization to that allowed through the circular polarizer, thereby suppressing reflections. 
     Unlike the component camera  251 , which may have a fixed focus due to its fixed vertical movement with the vacuum nozzle  230  (and therefore the imaged component), multi-purpose camera  252  has a variable focus due to its relative vertical movement with respect to substrate  258 . The variable focus ability of multi-purpose camera  251  enables the camera to perform a variety of imaging functions. 
     Multi-purpose camera  252  is arranged to image the substrate (or vacuum nozzles, feeder cartridges, etc. located beneath pickup head  200 ). Multi-purpose camera  252  may also provide close-up images of components placed on substrate  258 . Multi-purpose camera  252  may also image calibration marks provided on machine  1000  (e.g., on a base or support portion). Further, the camera can read barcode labels (e.g., label  361 ) on feeder cartridges  350 . The multi-purpose camera  252  may also measure feeder cartridge  350  location targets (fiducial marks) (e.g., a round or square dot) on the feeder cartridge (e.g., on upper attachment portion  352 ( 1 )) to update the system with actual feeder location values. Each of these imaging functions is likely performed at a different focus distance. 
     Additionally, with a reverse periscope mirror system (not shown), multi-purpose camera  252  may serve the function of an up-facing component camera utilized to obtain alignment correction of component C. This is particularly useful for large integrated circuit packages (e.g., greater than 0.75 inch), which are typically imaged by an up-facing camera. 
     1.4 Force Measurement 
     Utilizing control of a “touch” force of nozzle  230  when picking or placing a component (part) allows significant advantages. Particularly, with a crank driven nozzle, the below described system allows a clean, “noise” free measurement of the actual force component of the crank drive movement. The oscillatory nature of the crank provides force in a constantly changing direction. Measuring stress in the crank arm itself would produce a value contaminated by force components that do not all operate on the part being picked or placed. Indeed, some of these force components are used to accelerate the crank system. The challenge ultimately amounts to isolating the vertical component from all of the other components and identifying an amount of the force that is contributing to acceleration/deceleration of the crank structure, and further, the amount of the force that is imparted to the picked or placed part itself. 
     The vertical component of force is isolated by a flexible mechanical structure akin to a door hinge, which is described below in relation to  FIGS. 11 a  to 11 c   . A typical door hinge allows free motion of the door to allow passage in/out while not allowing the door to move up/down or side-to-side. That is, the hinge offers solid resistance to up/down, left/right forces while allowing the door to swing freely in the operative axis. Similarly, a long thin flexible structure in the crank arm terminating structure functions in this manner. Motion of this structure in the flexure axis is measured by a force sensing chip that deflects a relatively small amount (e.g., 0.0001 inch) for the forces encountered. Force magnitude is conveyed as an analog voltage. The flexible structure is spring loaded to a midscale value and forces in an upward direction on the nozzle unload the spring loaded flexible structure. Thus, in the event of an unanticipated impact with the circuit board the sensor is unloaded, rather than overloaded, to prevent damage. The force reported by this system is the sum of nozzle touch force and acceleration/deceleration forces. 
     A 3-axis accelerometer may be mounted on the moving structure to report vertical acceleration as an analog voltage. Thus, (acceleration) force may be derived from the acceleration using F=ma. The touch force is then calculated by subtracting the acceleration force from the total force. This measured force may be used to create a force-distance profile that can identify the absence or presence of solder paste, as described below in relation to  FIG. 47 . The force-distance profile may report the measured force over a traveled distance of nozzle  230 . Particularly, a force vs. distance profile may be analyzed and compared (e.g., with a control processor) to a predetermined force vs. distance profile to determine the presence or absence of solder paste. 
     An example force sensing mechanism  800  is shown in  FIGS. 11 a  to 11 c   . As best shown in  FIGS. 11 b  and 11 c   , force sensing mechanism  800  includes housing  802 , a plate (e.g., circuit board  810 ), and spring  809  connected to housing  802  and circuit board  810  in tension so as to pull them towards one another. Housing  802  includes tab  804  on a first side thereof which connects to connecting rod  242  at drive point  804 ( 1 ). A pair of wall portions  802 ( 1 ) extends from tab  804  and each includes a cutout  802 ( 2 ) therein so as to form a hinge  808  (e.g., a thin flexible hinge). Flexing wall  807  extends upwardly from hinge  808  and terminates in an attachment portion  806 . By this arrangement, force sensing mechanism  800  is flexible in response to forces in the direction of the operative axis and maintains rigidity in response to forces in the directions of the other axes. 
     Attachment portion  806  is attached to platform  232 , for example by screws extending through screw holes  806 ( 1 ). Thus, circuit board  810  and housing  802  are permitted to move relative to one another by movement of flexing wall  807  via hinge  808 . That is, for example, an upward force on nozzle  230  may cause housing  802  to move toward circuit board  810  as flexing wall  807  rotates outwardly. Such movement may be measured by force sensor  812  (e.g., a semiconductor and strain gauge on circuit board  810 ) to determine a magnitude of the upward force on nozzle  230 . An adjustable member (e.g., a screw) may be attached to housing  802  and extend through aperture  816  to a position adjacent contact point  814  such that the screw presses upon contact point  814  when housing  802  moves closer to circuit board  810  to provide a force input to force sensor  812 . Circuit board  810  may rest on a recessed portion  818  formed in attachment portion  806  such that the circuit board lies below platform  232 . 
     As the nozzle is moved downwardly, housing  802  will tend to move away from circuit board  810 , thus diminishing the measured force. On the other hand, when the nozzle is moved upwardly, housing  802  will tend to move toward circuit board  810  thereby increasing the measured force. 
     1.5 Laser Engraver 
     Pickup head  200  may also include a laser to engrave substrate  258  (e.g., PCB) with part information, date of manufacture, or other information. 
     Referring to  FIG. 48 , a laser  900  (e.g., a laser diode) may be mounted on pickup head  200 . Lens  902  may also be mounted on pickup head  200  to focus and concentrate the laser energy onto a small spot on a surface of the board. Lens  902  may include a single element, or alternatively, multiple elements. The laser wavelength may be chosen such that a portion of the laser energy is absorbed by the substrate surface. The power required is influenced by the absorption efficiency of the substrate surface. 10 watts or less of power may be suitable for most operations; however, more power may be used. Increasing the power facilitates marking at higher speeds. 
     XY motion of pickup head  200  may be coordinated with ON/OFF beam modulation to draw symbols (e.g., alphabetic, numeric and/or barcode types). The laser energy could be linearly modulated or pulse width modulated proportionally to marking speed, however simple full ON or full OFF may be suitable. 
     The laser energy absorbed by substrate  258  may be used to vaporize or scar a PCB solder mask coating, PCB ink stencil markings, or apply a label to identify the board by marking thereon, e.g., the board type, revision, serial number, manufacturing date, machine operators name, and/or production lot. Barcode marking may be applied for subsequent reading by other machinery or hand held barcode readers. 
     Symbols could also be drawn by laser motion along one axis and board motion along the other axis by means of a board conveyor or by the normal use of the board motion axis where the pick and place machine moves the board along one axis and the head moves along the other axis. Alternatively, the pick and place machine may move the board in two axis directions and the laser could remain stationary. 
     Laser  900  could be mounted outside of pickup head  200 . Additionally, the laser may be mounted on its own separate single or dual axis motion platform independent of the pickup head motion. The laser beam could be scanned with a rotating or oscillating mirror (e.g., galvanometer driven mirrors) to mark a board that is stationary or moving. 
     2.0 Operation 
     Operation of the example pick-and-place machine  1000  will now be described. 
     After the desired feeder cartridges  350  have been installed in pick-and-place machine  1000 , pickup head  200  is moved to a position adjacent a feeder cartridge  350  having a component to be picked. Sensors  218  then scan the calibration marks on the feeder gear of the selected feeder cartridge. This position information is used to locate the feeder gear so that rack gear  216  can be aligned and engaged with the feeder gear. Such position information may also be used to determine a position of the component pockets on tape  340  if the calibration marks on the feeder gear are arranged to match the component spacing on tape  340 . Next, gear driving mechanism  210  is lowered to cause rack gear  216  to engage feeder gear  355 . Taking into account the position information of the feeder gear  355 , motion system  400  then moves pickup head  200  a precise distance such that rack gear  216  drives feeder gear  355  to index (i.e., incrementally move) tape  340 , thereby causing the next component pocket  343  to enter pickup zone  342 . 
     After rack gear  216  is disengaged from feeder gear  355 , the sensors  218  again detect the position of feeder gear  350  by sensing the calibration marks on the feeder gear. This position information is used to precisely locate the rotary orientation of the feeder gear and the component pocket locations for storage by CPU  110  and later use in subsequent “pickups.” Scanning calibration marks after the feed move substantially eliminates the negative effects of backlash. That is, if there is a discrepancy in actual distance moved and the intended distance of movement, such discrepancy can be corrected by a correction move in the Y direction. Gear driving mechanism  210  is then returned to its raised position (shown in  FIG. 11 ). 
     Next, the vacuum source is turned on and vacuum nozzle  230  is lowered into pickup zone  342  to contact or nearly contact a component positioned in a component pocket  343  in tape  340 . Due to the vacuum force, the component is drawn up against distal nozzle opening  230 ( 3 ). 
     The component is then imaged by component camera  251  and the above-described squaring method is performed to obtain and effect both a linear XY correction and an angular correction of the component held against the distal nozzle opening. 
     The vacuum nozzle is then positioned over the desired placement location (with both linear and angular corrections included) and lowered to place the component (e.g., by pushing the component into solder paste) on the substrate  258 . The vacuum source is then turned off and vacuum nozzle  230  is raised leaving the component in place on the substrate. The pickup head is then moved to the feeder cartridge having the next component to be picked and placed. This process is repeated until all the desired components have been placed on the substrate. CPU  110  may store computer program code structures to carry out the example method of operation described above. 
     2.1 Control Computer Program Code Structures 
     The control program code structures  112 , when executed by CPU  110 , provide a system designed to simplify machine operation for the user. CPU  110  executes stored program code to provide advantageous set-up features. 
     2.11 Auto-Setup 
     An example automated set-up process will be described. Feeder management is often the largest part of the set-up process and an area where errors are frequently made. The disclosed exemplary auto set-up system significantly reduces set up time associated with assembling a new printed circuit board and eliminates many error-prone processes. 
     A user may install feeder cartridges  350  at any feeder module location in pick-and-place machine  1000 . The feeder cartridges may be installed in full or half slots and may be placed in the machine without concern of the particular component (part) associated with a given feeder cartridge. Each feeder cartridge has a permanent alignment target mark (e.g., on upper attachment portion  352 ( 1 )) that when measured by multi-purpose camera  252  reports an exact location of the feeder cartridge. Further, each feeder slot may include an optical sensor to confirm proper installation of feeder cartridge  350  in pick-and-place machine  1000 . 
     Multi-purpose camera  252  in conjunction with optical interrupter  313  will detect each feeder cartridge and determine the location of each feeder cartridge by its position (location information) in pick-and-place machine  1000 . The multi-purpose camera  252  may also scan a machine readable barcode on label  361  which will inform CPU  110  of the particular component (e.g., identification information such as part number) associated with that feeder cartridge. As described earlier, the operator also may simply read the alphanumeric text on label  361  to ensure that the component identifying information (e.g., part number) on the label matches the component identifying information (e.g., part number) on reel  330  containing the tape being fed through the feeder cartridge, as a confirmation. 
     The system will then provide gathered feeder cartridge information to an assembly program which will identify any missing components. Should any components be missing, the user can simply add the missing feeder cartridges. The system will organize (e.g., schedule the picking and placing of each component) the assembly of the substrate in accordance with the location of each feeder cartridge and the identification information of the components. The system may also offer optimization suggestions (e.g., to reduce assembly time). 
     In order to recognize and identify any missing components, the system may compare the gathered feeder information against pre-defined PCB information The pre-defined PCB information may include a listing of each required component and coordinates for the placement locations of the components for a given PCB assembly. This information may be provided to CPU  110  to guide the assembly process. A comparison of the gathered feeder information and the pre-defined PCB may be displayed to an operator in the manner shown in  FIG. 46 . Missing components may be highlighted to prompt the operator to add the missing feeder cartridges. 
     The system will also automatically select and install vacuum nozzles as needed. The vacuum nozzles  230  have machine readable identification information (e.g., a barcode) provided on an outer surface of the nozzles. Multi-purpose camera  252  is configured to read identification information on the vacuum nozzles and then automatically select the currently desired nozzle (e.g., from the nozzle changer cartridge  270 ) and install that nozzle on nozzle holder  231 . 
     Additionally, the system provides flexible support for partial board population and various circuit board configurations. That is, for example, the user may activate or deactivate placement of a single component, multiple components or all components of a given part number. 
     Panel arrays are easy to setup and may be built in a variety of ways. It is often more efficient to build boards several at a time. The boards may be arranged in linear or rectilinear arrays. The user need only specify the spacing of the boards in the array and the system will perform the remaining set-up procedures. In a first example, the system may build complete boards one at a time. An advantage of this method is that the user may observe and inspect a complete board before building the other boards. This affords an opportunity to correct errors before building the other boards. In another example, the system may place each component of a given type and designation on all boards in the array before proceeding to the next component. This method is potentially faster because it may reduce the frequency of nozzle changes. 
     2.12 Virtual Build 
     As part of an initial set-up procedure, the system may provide a virtual build feature that enables a user to confirm component alignment in the feeder cartridges without wasting any components. A scanned image of the board (substrate) to be assembled, having no components yet placed thereon, as shown in  FIG. 38-1 , may be uploaded to the system. The scanned image is preferably a high resolution image. The image may be used to teach coordinate locations; however, CAD centroid data is preferred for this function. The centroid data may include the component type/part number for all components, the x/y coordinate location on the board for each component, as well as the orientation of each component on the board. 
     The system may use individual stored images (C 1  to C 8 ) of the actual components in each feeder cartridge, as shown in  FIG. 38-2 . As shown in  FIG. 39 , the system may overlay component images C 1  to C 8  onto the scanned board image in accordance with predetermined locations (e.g., as contained in the centroid data) for placing each component (thereby building a virtual PCB). 
     In contrast to systems that create an image of the assembled board from imported data, the instant system does not presume a component orientation based on a user input (which if such input is incorrect results in a placement error). By using a captured image (including orientation) of the component on the tape, the possibility of user errors may be greatly reduced or even eliminated. In some machines, it is difficult to even see the component in the feeder. Further, determining an orientation of the component in such a machine may be further complicated by location (front, back, sides) of the feeder in the machine. 
     The virtual build process eliminates errors that have been common place. The results of the virtual build process may be presented to the user in a number of arrangements. In one example, a realistic view of the finished board is provided, as shown in  FIG. 39 . In another example, the system displays the components in a part number/feeder number organized mosaic with rotation correction. Thus, for example, if three capacitors were used from feeder cartridge number “17,” then three images would be linked to feeder cartridge “17” for viewing. Unlike the realistic mode, the mosaic mode would undo the component rotation so all components of a particular type should appear the same. The user can simply focus on identifying differences in the images of components of the same type (part number). 
     This system also logically facilitates the user in identifying the cause of errors. For example, if there is a problem with only a single component, the user may logically suspect that there is a problem with the CAD centroid data. If there is a problem with all of the components for a given feeder, then the user may logically suspect that the feeder cartridge data (e.g., part number, part value (e.g., 0.01 uF/20V), package number, feeder orientation, tape width/pitch, polar/non-polar(n/p)) is the likely cause. If rotation of the components appears to be correct at 0° and 180°, but wrong at all other angles, then the user may logically suspect that the rotation direction in the centroid data is backwards. If the location of some components is vastly wrong while the location of other components appears to be correct, then the user may logically suspect that the centroid data is incorrect. Further, if most or all of the component locations are off target by a considerable degree, the user may logically suspect that confusion in the unit of dimensions (e.g., inch/metric) is the cause. An advantage of the system is that these “diagnoses” are much more evident as compared to other systems. 
     Accordingly, a user may confirm placement of the various components against the pre-defined PCB data (described earlier). Unlike other systems, no components are consumed in this virtual process of confirming feeder cartridge installation and alignment. Feeder cartridge alignment may pertain to whether the cartridge in mounted in the front or back of the machine. Additionally, as described above, the virtual build process may also catch other errors such as erroneous CAD data and errors with incoming translations (e.g., unit of dimension, rotation direction, etc.). A user may correct an incoming translation error by applying a revised rule to the entire board to be assembled. 
     Additionally, the pre-defined PCB data may be represented graphically, as shown in  FIG. 40 . Placement locations P 1  to P 8  for respectively receiving components C 1  to C 8  may be disposed in accordance with the coordinate information of the pre-defined PCB data. In this manner, the graphical representation of the pre-defined PCB may be overlaid onto the virtual PCB (e.g., with the overlaid image being partially transparent to facilitate visual comparisons) to provide a more intuitive confirmation procedure, as shown in  FIG. 41 . The user need only confirm proper placement of the component images C 1  to C 8  onto corresponding placement locations P 1  to P 8 . In an example shown in  FIGS. 42 and 43 , mistakenly installed feeder cartridges and/or feeder modules, improperly placed tape reels  330 , etc., have resulted in misplaced components (e.g., C 4  and C 8 ) that may be easily recognized by the operator. 
     The system may also store the length, width and thickness of each component to later qualify each measured component as actually placed. This information may be used to test, adjust and perfect the video centering process. For instance, when a component is measured (during the linear/rotational error correction process), the component must meet dimensional specifications to prevent attempted placement of an out of position or missing component. Components identified as a “mis-pick” will be rejected and a full image of the component will be stored for troubleshooting. 
     2.13 Product Inspection 
     To facilitate finished product inspection, multi-purpose camera  252  may capture images of each component as it is actually placed on substrate  258 . These images may be acquired after each placement or acquired sequentially after the entire assembly is complete. Acquiring an image after each placement requires less pickup head motion and is faster; however, if a subsequent placement interferes with a previous placement, the image of the previous placement would not show the subsequent movement of the component. So, capturing all of the images on a completed assembly is the most error free process, but is also more time consuming. However, the inspection phase causes pickup head motion only between nearby components, so the process is reasonably fast. 
     The system then organizes the images for easy inspection. For example, the images are rotated to the same orientation and then grouped (e.g., by part number). An example of such display screen is shown in  FIG. 45 . The images are displayed in a mosaic array organized by component type feeder cartridge. Each line of the array may display components of a particular part number (i.e., component type) so that all of the images on a line should look the same. By this method, even the slightest dissimilarity is easily noticeable to the user. For instance, by analyzing a line of the array, an operator may readily detect whether in fact the components installed on the substrate (a) are the same component type; (b) are the intended component; and/or (c) were installed with the correct orientation. 
     As shown in  FIG. 45 , a component of a different type mistakenly installed in a “component-type 1” location may be easily identified as dissimilar to the other components. Additionally, a misaligned component-type 2 component may be identified by an operator due to its different orientation from the other components. Further, once the substrate solder is reflowed, the same process may be used to inspect the finished substrate. 
     As another finished product inspection procedure, the graphical representation of the pre-defined PCB (described earlier) may be overlaid onto an image of the actual finished PCB (e.g., captured by multi-purpose camera  252 ), as shown in  FIG. 44 , to ensure correct placement of the components. 
     One skilled in the art will recognize that for each of the overlay procedures described above, either image may serve as the overlaid image. Further, those skilled in the art will also recognize that providing one or both images in at least partial transparency may facilitate comparison. 
     3.0 Multi-Component Vacuum Nozzle 
     Instead of the previously described vacuum nozzle  231 , a multi-component vacuum nozzle system  500 , shown in  FIGS. 21-35 , may be used in pick-and-place machine  1000 . The multi-component vacuum nozzle system includes vacuum nozzle  502  attached to body portion  506 . Collar  502 ( 1 ) of the nozzle abuts the body portion. Vacuum nozzle  502  is configured to simultaneously carry multiple components. In this manner, multiple components may be delivered to the substrate during each trip of vacuum nozzle  502  from feeder cartridges  350  to the substrate. 
     Vacuum nozzle  502  is configured such that components enter the nozzle through distal nozzle opening  504 . Vacuum nozzle  502  has a plurality of inner walls  507  forming a hollow portion  503 , as best shown in  FIG. 35  (only two of four are shown). The components may be stacked one on top of another in hollow portion  503 . By this arrangement, the components are automatically aligned by the inner walls  507  of vacuum nozzle  502 , thus there is no requirement for a component camera to correct misalignments of the components. However, vacuum nozzle  502  may still be rotated to place components at any angle. The inner walls  507  of vacuum nozzle  502  are designed to match the shape of the components, thereby automatically aligning the components. In the illustrated example, the components are rectangular. By way of example, if the components are 0.05×0.08 inches, a suitable distal nozzle opening  504  may be 0.052×0.082 inches. Hollow portion  503  may have the same cross-sectional dimensions as the distal nozzle opening. Hollow portion  503  is made long enough to accommodate several components. A chamfer  505  may be provided at the distal nozzle opening  504  to assist component entry. 
     Stop  512  is slidably received in hollow portion  503 . Four air passages  504 ( 1 ),  504 ( 2 ),  504 ( 3 ),  504 ( 4 ) are formed along respective corners of the hollow portion  503  to allow vacuum suction to pass around stop  512 , as best shown in  FIG. 30 . It should be noted that more or fewer air passages may be provided. Further, the location of the air passages around stop  512  may vary. For instance, instead of being positioned at the corners of the stop, the air passages may be formed between the corners. One skilled in the art will further recognize that the shape of the hollow portion may vary in accordance with the shape of the component to be picked and placed; thus the air passages may be positioned in any suitable location in the hollow portion. 
     In operation, the vacuum force draws a component into hollow portion  503  via the distal nozzle opening  504  so as to abut against stop  512 . The stop  512  prevents the component from flipping. Once the component is established in place against the stop and between the inner walls  507 , the stop is retracted into hollow portion  503  by a distance equal to the thickness of one component to make room for the next component. By providing a space at the end of hollow portion  503  that is only large enough for a single component, motion of the component is fully controlled. This process may be repeated to stack as many components as desired (e.g., up to 10 or more, 2-5, 5-10, 10-20, 15-20, up to 20, 20 or more) into hollow portion  503 . 
     The stop  512  may later be moved toward distal nozzle opening  504  to push the components into the solder paste on the substrate. Stop  512  is preferably controlled by a servo step motor or a voice coil actuator with position feedback to enable precise incremental movements. Pickup head  200  may also incorporate a conventional force feedback measurement system to help guide the placement process. 
     3.1 Confirmation of Component Pickup 
     An optical sensor (e.g., LED/phototransistor sensor)  516  may be provided at an end portion of vacuum nozzle  502  to detect when a component has been successfully picked up. Sensor  516  is configured to emit a light beam from one side of the nozzle and to detect the light beam at the other side of the nozzle. When a component is successfully picked up, the component will block the light beam, thereby indicating a successful pickup. However, those skilled in the art will recognize that the sensor could depend on light reflection rather than light blockage in which case the sensor and emitter would be positioned on the same side of the nozzle. Additionally, mirrors, optical fibers, prisms, reflectors and/or light pipes may be used to transport light to/from stationary sensors/emitters on pickup head  200 , thereby eliminating the need for inductive power transfer to sensors/emitters on vacuum nozzle  502 . Further, other non-optical sensing methods may be employed. For instance, magnetic sensors that utilize induction or eddy current could be used, as well as other techniques such as ultrasonic detection, fluidic cross flow, air pressure or capacitance change. Cavity resonate frequency would change with component presence which could be detected in both acoustic and electromagnetic spectrums. 
     Further, as one skilled in the art will understand, an LED may be used both to emit light and to serve as a photodiode to sense light. Such dual function arrangement may reduce the space required by sensor  516  since an LED is typically smaller than a light-sensing photodiode or phototransistor. 
     An inductive coupling system is provided in the exemplary embodiment to provide power to illuminate the LED and to return an optical status signal over the inductive link. The inductive coupling system includes two coils that inductively couple without touching. Referring to  FIGS. 31-34 , primary coupling coil  530  is arranged to be fixed on pickup head  200  while secondary coupling coil  510  is mounted on vacuum nozzle system  500 . Secondary coupling coil  510  may be mounted on seat  508  of body portion  506  and connected to sensor  516  via a flexible printed circuit board  520 . A suitable air gap (e.g., 0.25 inches) may exist between primary coupling coil  530  and secondary coupling coil  510 . This enables vacuum nozzle  502  and sensor  516  to be easily dismounted for replacement. Further, rotation of the vacuum nozzle by nozzle rotation motor  234  is not complicated by electrical connection since primary coupling coil  530  is fixed on the Z axis and secondary coupling coil  510  is mounted on the vacuum nozzle system. A flange  509  may be arranged on an upper side of seat  508  to contain secondary coupling coil  510 . Seat  508  and flange  509  are electrically non-conductive, as one skilled in the art will understand. 
     An example of a circuit for the inductive coupling system is shown in  FIG. 36 . Primary coupling coil  530  and associated circuits are included on pickup head  200 . Secondary coupling coil  510  and associated circuits (included on flexible PCB  520 ) are mounted on vacuum nozzle system  500 . Primary coupling coil  530  is driven with a high frequency AC signal (e.g., 3.0-6.0 MHz). The signal could be a square wave, pulse train, filtered square wave or sinusoid which would radiate the least radio interference. A resistor (R 1 ) acts as a current sensing shunt allowing primary drive current to be measured. A clamp diode (left half of D 1 ) may parallel the shunt resistor (R 1 ) to reduce its impedance during an LED drive phase. When output of secondary coupling coil  510  is in a negative half phase, a diode (top half of D 2 ) and a capacitor (C 2 ) provide DC to power the LED and create an illuminative output. The capacitor (C 2 ) stores energy so that the LED light output will persist across the other (positive) half phase. 
     The positive half phase powers the light sensing system. Either a phototransistor or an LED (PHOTO1) operating in photo sensing mode provides a signal that is amplified by a suitable transistor (Q 1 ). This transistor draws more current when the sensor is illuminated and very little when the sensor is not illuminated. The magnitude of the current draw during the positive half phase reports the light/dark status of a light sensor. The shunt resistor (R 1 ) in series with primary coupling coil  530  reports the LED drive current as a negative signal and the photo current as a positive one. A simple diode (right half of D 1 ) separates the photocurrent from the LED current for easy measurement. Ultimately, the signal is conveyed as an analog level to a processor chip (e.g., CPU  110 ). The processor may note a light level just prior to beam blockage to reduce the effects of variation and drift. The processor may then set a threshold based on this value to reliably recognize small changes. 
     In another example, vacuum nozzle  502  may include a planar secondary coupling coil  522  (e.g., a planar spiral coil connected to or as part of flexible PCB  520 ) instead of the wire coil  510  for inductively coupling with primary coupling coil  530 , as shown in  FIG. 35 . The planar secondary coupling coil  522  is integrally connected and easier to assemble while the wire secondary coupling coil  510  is closer to primary coupling coil  530  and thus has greater coupling efficiency. The planar secondary coupling coil  522  may be disposed on either a distal side of flange  506 ( 1 ) as shown in  FIG. 35  or a proximal side of flange  506 ( 1 ) as shown in  FIGS. 31-34 . Further, one skilled in the art will understand that either secondary coupling coil  510  or planar secondary coupling coil  522  would be used at any given time; however, both coils may be disposed on the nozzle system. 
     In another example, a vacuum sensor (not shown), instead of the optical sensor  516 , could be provided near an end portion of vacuum nozzle  502  to confirm a successful pickup by detecting a change in pressure when a component occludes the hollow portion  503  thereby restricting vacuum flow. 
     3.2 Actuation of the Stop 
     A voice coil actuator may be employed to create a force to move stop  512  along hollow portion  503 . A rare earth magnet  514  (e.g., 0.236 inches in diameter and 0.236 inches long) is attached to a magnet-receiving portion  513  at an upper portion of stop  512 , as shown in  FIG. 22 . The stop is nonmagnetic to prevent flux from conveying down to the components (which are typically magnetic). Stop  512  and magnet-receiving portion  513  are slidably received in the body portion  506 . Referring to  FIGS. 31 and 32 , a linear drive coil  540  may be configured to be fixed on pickup head  200  for inductively coupling with magnet  514  to move stop  512 . 
     The space between linear drive coil  540  and magnet  514  may be as small as possible to optimize magnetic coupling. Linear drive coil  540  controls the position of the magnet  514  and the stop  512  with a magnetic field created by current flow in the linear drive coil, as one skilled in the art will understand. A suitable material for body portion  506  is carbon fiber. Current in linear drive coil  540  is preferably controlled by a class-D-amplifier with pulse width modulation. 
     Actuation of magnet  514  and stop  512  is preferably servo controlled to enable precise movements. The position of the magnet may be accurately determined with a magnetic field strength sensor. This technique is described in Honeywell application note AN211, which is incorporated herein by reference. The position may be reported magnetically as an analog voltage. This may be used in a proportional-integral-derivative (PID) servo loop to control the current in linear drive coil  540 . Current in linear drive coil  540  may be adjusted as necessary to keep stop  512  in a desired position. Because the static magnetic field from magnet  514  and the dynamic field from linear drive coil  540  may both influence the magnetic field strength position sensor, position measurement requires measuring the static component from magnet  514  without outside influence. In order to achieve this, current in linear drive coil  540  may be turned off briefly during position measurement intervals. Several thousand measurements per second may be taken, as one skilled in the art will understand. 
     The combination of the voice coil actuator and the magnetic position feedback sensor provides very high resolution force measurement. Because the voice coil produces a force in proportion to drive current independent of magnet position over a modest range, the voice coil acts like a nearly linear spring. Thus, the voice coil actuator combined with the position sensor is somewhat analogous to a spring scale with milligram resolution. The system is adept at measuring force vs. distance relationships, since force is easily controlled as a direct function of current and distance is measured directly with the magnetic sensor. For relatively small parts, precision force control is essential to placing the parts without damage. It is noted that other feedback systems may also be used. 
     Vibration of stop  512  may be induced to aid in picking up and aligning components in the hollow portion  503 . This vibration may be introduced as hysteresis in the servo loop to produce vibration at the update rate, or the vibration could be introduced as a separate error signal in the loop to obtain vibration at a lower frequency. The vibration may be turned on or off and the frequency and amplitude of the vibration may be changed to accommodate various components. 
     Additionally, optical sensor  516  may be used to confirm the location of the components held within hollow portion  503 . The position of the components may be relative to a reference location such as the bottom of the last component picked up by vacuum nozzle  502 . Thus, all movements of stop  512  may be relative to this reference location. This arrangement may diminish the need for accurate linearity over long travel distances of the magnet. This arrangement also mitigates variation in field strength of different magnets on different vacuum nozzles. 
     In an alternative arrangement, movement of stop  512  may be accomplished by a motor driven screw connected to the stop, as should now be appreciated by those in the art. A connection between stop  512  and the servo system is accomplished with a toroidal ring magnet on the outside of the body portion  506  that couples and captures a cylindrical magnet attached to the stop on the inside of the body portion. The stop is nonmagnetic to prevent flux from conveying down to the components. A rare earth magnet is used. The ring magnet and the cylinder magnet are magnetized along their lengths or thicknesses. These magnets are oriented so their opposing poles align and attract. While this coupling is compliant, it takes a large force to displace the magnet when captured inside the toroid. The magnetic coupling is essentially solid in the vertical displacement axis but allows friction-free rotation. The toroidal magnet is driven by a lead screw which is in turn driven by a gear and a long pinion. A servo or stepper motor may be used to control rotation of the lead screw and thus the vertical position of stop  512 . 
     3.3 Operation 
     In operation of the example multi-component vacuum nozzle system  500 , a calibration process is performed to set the position of stop  512  before a first component is picked from tape  340 . Stop  512  is first lowered to break the light beam from sensor  516  and is then raised until the light beam is restored. This position of stop  512  may be a sufficient starting position for picking thin components; however, for thicker components, the stop may be raised further. Next, the vacuum source is turned on and vacuum nozzle  502  is lowered to nearly contact tape  340  between adjacent component pockets  343 . Then, the vacuum nozzle is moved over a component pocket  343  to draw the component into the vacuum nozzle. A successful pick-up of the component is reported by sensor  516 . Instead of sensor  516 , it is noted that the previously described vacuum sensor may be used. Stop  512  is then moved up a distance equal to the thickness of a component in order to make room for the next component. Sensor  516  then reports that there is no blockage of the light beam. The vacuum nozzle is moved over the next component pocket  343  to pick the next component. This process may be repeated as necessary to pick a desired number of components. The tape may be indexed to bring the components to the vacuum nozzle  502  one at a time, or possibly, a large number of component pockets  343  may be simultaneously exposed in an elongated pickup zone so that the vacuum nozzle  502  can move across an exposed section of tape to rapidly pick up components. That is, each feed move may expose multiple components (e.g., 2-7, 7 or more, 10, 10 or more, 15-20, 5-15, 15 or more, 20, 20 or more). 
     If a component is unable to be picked by vacuum nozzle  502 , the nozzle may re-try the pickup or go on to a subsequent component instead. Further, if the component ultimately is unable to be picked up by vacuum nozzle  502 , the CPU  110  may keep track of such component and adjust the placement process accordingly so the nozzle does not attempt to place the (“missed”) component. 
     As described earlier, vibration of stop  512  may be induced to aid in picking up components. The stop may be lowered to a position near distal nozzle opening  504  and then a slight vertical vibration of stop  512  may be induced. The component would remain in motion after being drawn into hollow portion  503  due to the vibration of stop  512 . However, in another example, the vibration may be stopped once the component is picked up. The stop is then moved up to confirm the component pickup and to make room for the next component. The vibration helps components find their way into and past distal nozzle opening  504 , which for example may be a chamfered opening. 
     Once a desired number of components are loaded into hollow portion  503  of vacuum nozzle  502 , the placement process may begin. The vacuum nozzle will be positioned over the first placement location and lowered to nearly touch substrate  258 . Stop  512  is then lowered to push (or eject) a component out of nozzle opening  504  and into solder paste on the substrate. Once the component has been completely removed from vacuum nozzle  502 , the vacuum force will be smaller than the adhesive force of the solder paste thereby causing the component to remain on the substrate as the vacuum nozzle  502  is raised. Because of the high bandwidth of motion of stop  512 , components may be rapidly placed while pickup head  200  is still moving. Since slowing the pickup head to a complete stop consumes a great deal of time, keeping the pickup head moving at even a modest pace adds significantly to performance. 
     The stop positioning system can also report push force and distance with fine resolution, as described previously. Referring to  FIG. 47 , the shape characteristics of the force vs. distance curve can be used to identify the presence or absence of solder paste. Placing a component on a board without paste will report an abrupt rise in force because the component will experience no resistance until it hits the hard board. On the other hand, placing a component in paste will report a more gradual rise in force as the displacement of the paste cushions the impact. Without solder paste, the component will not connect to the board which will cause a defective assembly. Detection of absent solder paste is significant in preventing defective assemblies. A force vs. distance profile of stop  512  may be analyzed and compared (e.g., with a control processor) to a predetermined force vs. distance profile to determine the presence or absence of solder paste. 
     Additionally, sensor  516  may be used to confirm that a component was actually placed in the paste on the substrate. Stop  512  and the stack of components may be raised to confirm placement of a component by verifying that the light beam is not blocked. A component that will not remain on substrate  258  (e.g., because of missing paste) may be purged by placing the component in a dump area having an adhesive coated tape which retains the component. 
     While the examples discussed above have been described in connection with what are presently considered to be practical and preferred features, it is to be understood that appended claims are intended to cover modifications and equivalent arrangements included within the spirit and scope of these examples.