Abstract:
The present invention features a method whereby each vacuum nozzle in a multi-spindle component placement machine is inspected placement cycle. This process also allows for updating calibration of the nozzle position as well as immediate feedback regarding the condition of the vacuum nozzle. A chipped orifice or otherwise damaged nozzle is detected using a vision system and comparing the currently acquired image of each nozzle with the image of an “ideal” nozzle. Likewise, contamination such as adhesive on the nozzle is detected before that contamination can affect placement accuracy. Because of the nozzle inspection during the placement cycle, there is no slowdown of the placement machine cycle rate.

Description:
RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Patent Application Ser. No. 60/338,820, filed Nov. 30, 2001. 

   FIELD OF THE INVENTION 
   This invention relates to component placement machines and, more particularly to a method for inspecting vacuum nozzles to ensure accurate and reliable component placement. 
   BACKGROUND OF INVENTION 
   The use of sophisticated placement machines in manufacturing printed circuit or similar cards, boards, panels, etc. is well known. The term printed circuit board (PCB) is used herein is to refer to any such electronic packaging structure. Typically, reels of tape-mounted circuit components are supplied to the placement machine by multiple feeders, each feeder holding a reel of components. Components are provided at a pick station by each feeder assembly. A pick/place head, having a vacuum spindle equipped with a vacuum nozzle, may be moved in the Z-axis as well as along the X and Y axes. The vacuum nozzle is sized and otherwise configured for use with each different size and style of component to be placed by the machine. In operation, the pick/place head is moved to the pick station and the nozzle positioned over the tape-mounted component. The vacuum nozzle is lowered to a point where, upon application of vacuum, the component is removed from its backing tape, centered, and held tightly against the nozzle orifice. The pick/place head is then moved to a point over the printed circuit board being assembled and the component deposited on the printed circuit board at a predetermined location. 
   Several problems must be addressed in this seemingly simple operation. First, as component sizes have shrunk, the accuracy of placement of the vacuum nozzle over the component for picking has become more critical. Typically, calibration routines are performed upon machine setup or periodically as required for operation of the machine. With micro-miniature components, small variations occurring over time can quickly lead to inaccurate picking and/or placement of these components. 
   Vacuum nozzles have also shrunk commensurately to maintain compatibility with these shrinking component sizes. Consequently, the vacuum nozzles have become more fragile and more readily damaged. Damage may occur while a nozzle is being installed on a pick/place head or during the actual pick/place operation of the component placement machine. 
   A third problem is that the adhesive typically used to hold surface mount and similar components in place until a solder reflow operation may contaminate the nozzle. Likewise, small particles of dirt or debris may lodge in the nozzle. As nozzle orifice sizes have shrunk, the effects of these contaminants have become more critical to reliable operation of the placement machine. 
   Currently, component placement machines utilize multi-spindle pick/place heads to improve assembly speed. Each head contains multiple vacuum spindles, each having its own vacuum nozzle. With multi-spindle machines, the need for real-time monitoring of the vacuum nozzle condition becomes even more critical. One damaged or contaminated nozzle can be difficult to locate based on intermittent placement problems on the printed circuit boards being assembled. 
   SUMMARY OF THE INVENTION 
   The present invention is a method whereby each vacuum nozzle is inspected during each component placement cycle. This process also allows for updating calibration of the nozzle position as well as immediate feedback regarding the condition of the vacuum nozzle. A chipped orifice or otherwise damaged nozzle is detected using a vision system and comparing the currently acquired image of each nozzle with the image of an “ideal” nozzle. Likewise, contamination such as adhesive on the nozzle is detected before that contamination can affect placement accuracy. Adhesive on the nozzle can cause a component to stick to the nozzle when the component should be placed on the printed circuit board. When the inspection process is applied to a multi-spindle head, each nozzle can be inspected during each component placement cycle. Therefore the inspection process in multi-spindle heads allows no slowdown of the placement machine cycle rate for this process to occur. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when taken in conjunction with the detail description thereof and in which: 
       FIG. 1  is a side, schematic view of a multi-spindle pick/place head showing a plurality of vacuum spindles disposed thereupon; 
       FIG. 2  is a simplified schematic block diagram of a portion of a component placement machine adapted to practice the method of the invention; 
       FIG. 3  is a timing diagram of nozzle image acquisition and processing during the placement cycle time; and 
       FIG. 4  is a simplified flow chart of the method of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention pertains to inspection of vacuum nozzles on the multi-spindle pick/place head of a component placement machine for assembling printed circuit boards. 
   Referring first to  FIG. 1 , there is shown a schematic view of a multi-spindle, rotatable pick/place head, generally at reference number  100 . A plurality of vacuum spindles  102  is disposed on head  100 . It will be recognized by those skilled in the component placement machine arts that a head  100  may carry any number of vacuum spindles  102  disposed radially about its perimeter. For purposes of this disclosure, a general case of n vacuum spindles  102  is discussed. A vacuum nozzle or chuck  104  is disposed at the end of each vacuum spindle  102 . Multi-spindle pick/place heads  100  are known and the concept forms no part of the present invention and are described in U.S. Pat. No. RE. 35,027 and German Patent No. EP 0 315 799. 
   It is also known to use a vision system as a process station, as described in U.S. Pat. No. RE. 35,027, in component placement machines to process images of components to facilitate identifying, positioning and manipulating or orienting the components held against a vacuum nozzle  104  of a vacuum spindle  102 .  FIG. 2  shows a schematic block diagram  200  of a typical image acquisition arrangement for use in a component placement machine. At least one camera  202  is used to capture images, often at different magnifications or with different lighting conditions. A pick station  203  and a place stations  204  are shown. 
   The output of camera  202  is connected to electronic signal processing and control circuitry  214 . Circuitry  214  controls camera  202  and provides image capture functions. The output of electronic signal processing and control circuitry  214  is connected to a vision system  216 . The present invention expands the use of such vision systems  216  to perform nozzle inspection during each pick cycle or place cycle performed by each vacuum nozzle  104  of the component placement machine. The inventive method is operative with any number of vacuum spindles  102  and is not considered limited to any particular number thereof. It will also be recognized that the timing data used for purposes of disclosure may vary depending on the actual design of the pick head  100 . 
   Reference images of good nozzles (not shown) are stored using methods not a part of the instant invention. At least one reference image is provided for each nozzle size and/or type in use on the component placement machine. These reference images are available to the vision system  216  in a suitable memory or library, so that image compare algorithms and technology may be used to compare the nozzle image captured during each pick or place cycle of machine operation with an appropriate reference image. Any significant deviation is immediately flagged and, depending upon the severity of the defect, the placement machine may be stopped. In alternate embodiments, a defective nozzle  104  on a head  100  could be logically disabled (i.e., removed from active service) without stopping the placement machine with the remaining good nozzles operating at a slightly reduced efficiency. 
   In the embodiment chosen for purposes of disclosure each active nozzle  104  on each spindle  102  of the head  100  is imaged during each pick or place cycle. 
   At inspection time, the exact position of the nozzle  104  may be recorded, thereby re-calibrating the position of the nozzle. The position calibration data is typically placed in a lookup table, so that the most recent position data may be utilized by the placement machine for the next pick or place cycle involving that particular nozzle. While methods other than lookup tables could be used for storing nozzle calibration information, a fixed table of nozzles associated with a position on the pick/place head  100  has been found to be satisfactory. In addition to verifying the exact, current nozzle position, the inventive method inspects the physical condition of each nozzle  104 . In the embodiment chosen for purposes of disclosure, data from the same lookup table is used to set up and initiate each nozzle inspection. It will be recognized that other data storage formats could be used. 
   Referring now to  FIG. 3 , there is shown a timing diagram for image acquisition and processing within a pick or place cycle. As may be seen, image acquisition and processing (inspection) for each spindle are always completed within a pick or place cycle. 
   Referring now to  FIGS. 2 and 4 , there is shown a flow chart  400  of the steps of the inventive method ( FIG. 4 ). It is assumed that initial placement machine setup, nozzle installation and calibration have previously been performed. The pick/place head is moved to a pick station  203 , a particular spindle is lowered and a component  212  is picked, step  402 . This step is repeated for the number of spindles in the multi-spindle pick/place head. The pick/place head is then moved under program control to the desired X-Y coordinates over the printed circuit board being assembled at the place station  204 . The spindle is lowered and the component  212 , picked in step  402 , is placed onto the printed circuit board, step  404 . After component placement begins, the empty nozzles  104  proceed to camera  202 . As components  212  are continued to be placed or when the head  102  returns to the component pick station  203  and the previously inspected nozzles  104  begin to acquire new components  212 , the remaining uninspected nozzles  104  move to camera  202  where they are inspected. Therefore, either during the placement cycle or the pick cycle all nozzles  104  are inspected at camera  202 . This step is repeated for all components  212 . Details of the nozzle inspection process, step  406 , are provided in more detail hereinbelow. 
   Assuming that the inspection process, step  406 , finds no nozzle integrity problem and no significant contamination at or near the nozzle orifice, step  408 , the placement cycle continues, step  402 . If, however, a problem with nozzle integrity or contamination is discovered, step  408 , the operator is alerted, step  410 . In addition, depending upon the severity of the problem, the component placement machine could be stopped automatically or the problem spindle removed from active service until the problem is resolved. 
   After image acquisition is complete, the image or images are processed, step  406 . Processing involves comparing the newly-acquired image(s) with stored ideal images of the nozzle being inspected and using vision algorithms to infer whether any image differences constitute either a nozzle integrity or a nozzle contamination problem. 
   It will be recognized that an inspection of a particular vacuum nozzle  104  associated with a particular vacuum spindle  102  need not be performed. If a nozzle  104  is not currently in active service, for example, inspection is skipped. It would also be possible to define algorithms for periodically skipping inspection of a nozzle  104  if placement machine speed placed an undue burden on the vision system, particularly image processing. The invention, therefore, is not considered limited to a method wherein each nozzle is inspected during each placement cycle. 
   Having thus described the invention, what is desired to be protected by Letters Patent is presented in the subsequently appended claims.