Abstract:
Instrument set for fitting an intervertebral prosthesis, comprising a guide device ( 4 ) for an instrument or a prosthesis part, which guide device ( 4 ) is to be secured on at least one vertebral body ( 2 ). To be able to attach the guide device ( 4 ) precisely on the vertebral bodies despite the difficult operating conditions, an adjustment instrument ( 10 ) is provided which positions the guide device when this is being arranged on the vertebral body ( 2 ). This adjustment instrument ( 10 ) expediently comprises an intervertebral plate ( 11 ) which is fitted into the intervertebral space so as to be positioned exactly in relation to the vertebral bodies.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to an electronic component mounting apparatus for picking electronic components up by suction nozzles from component feeding units and mounting the electronic components on a printed board.  
           [0003]    2. Description of the Related Art  
           [0004]    A conventional electronic component mounting apparatus of this type employs a fiber sensor for detecting presence or absence of a suction nozzle. As described in the Japanese Patent Application Publication No. 2001-102799, a standing component detection sensor (line sensor) is used for a correction of a lower end level of the suction nozzle after picking up a component.  
           [0005]    However, the fiber sensor, which is used as a detection sensor for detecting presence or absence of the suction nozzle, can not be used for detection of an electronic component mistakenly held by the suction nozzle even after a component mounting operation or for a correction of a lower end level of the suction nozzle (a height of a pickup position) because the suction nozzle wears out with time.  
           [0006]    Furthermore, since the standing component detection sensor is used for a correction of the lower end level of the suction nozzle after picking up the component, the correction can not be performed during running of the mounting apparatus so that the mounting apparatus is forced to stop mounting operation.  
         SUMMARY OF THE INVENTION  
         [0007]    The invention provides an electronic component mounting apparatus that includes a component feeding unit feeding an electronic component, a suction nozzle picking up the electronic component from the component feeding unit and mounting the electronic component on a printed board, and a position sensor measuring a vertical position of a lower end of the suction nozzle after the suction nozzle releases the electronic component to the printed board.  
           [0008]    The invention also provides an electronic component mounting apparatus that includes a plurality of component feeding units feeding electronic components, a plurality of suction nozzles provided on a mounting head for picking up the electronic components from the component feeding units and mounting the electronic components on a printed board, and a line sensor unit comprising a first light source and a light receiving device. The line sensor is configured to measure a vertical position of a lower end of each of the suction nozzles after the suction nozzles release the electronic components to the printed board. The apparatus also includes a second light source provided in the line sensor unit in addition to the first light source, and a decision device judging that a suction nozzle is about to fall when the amount of light received by the light receiving device from the first and second light sources is below a predetermined amount. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic plan view of an electronic component mounting apparatus of a first embodiment of this invention.  
         [0010]    [0010]FIG. 2 is a partially cutaway side view of the electronic component mounting apparatus of FIG. 1.  
         [0011]    [0011]FIG. 3 is an schematic perspective view of an electronic component feeding unit of the electronic component mounting apparatus of FIG. 1.  
         [0012]    [0012]FIG. 4 is a front view of a vertical shifting mechanism of a mounting head of the electronic component mounting apparatus of FIG. 1.  
         [0013]    [0013]FIG. 5 is another front view of the vertical shifting mechanism of the mounting head of the electronic component mounting apparatus of FIG. 1.  
         [0014]    [0014]FIG. 6 is a side view of the vertical shifting mechanism of the mounting head of FIG. 4.  
         [0015]    [0015]FIG. 7 is a block diagram of the electronic component mounting apparatus of FIG. 1.  
         [0016]    [0016]FIG. 8 is a table of a component library data of the electronic component mounting apparatus of FIG. 1.  
         [0017]    [0017]FIG. 9 is a view showing an operation of a line sensor unit of the electronic component mounting apparatus of FIG. 1.  
         [0018]    [0018]FIG. 10 is a cross-sectional view of the line sensor unit of a electronic component mounting apparatus of a second embodiment of this invention.  
         [0019]    [0019]FIG. 11 is a cross-sectional view of the line sensor unit of FIG. 10 with schematic movements of suction nozzles. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    An electronic component mounting apparatus of a first embodiment of the invention will be described with reference to FIGS. 1-9. As shown in FIGS. 1 and 2, in an electronic component mounting apparatus of high-speed type  1 , a feeding system  3  for feeding electronic components A and a mounting system  4  for mounting the electronic components A on a printed board B are disposed in parallel with each other with a main body  2  interposed therebetween. The feeding system  3  includes an electronic component feeding device  3 A.  
         [0021]    The main body  2  has an index unit  6  as a main body of a drive system, a rotation table  7  connected to the index unit  6 , and a plurality (for example, twelve) of mounting heads  8  mounted on an outer circumference of the rotation table  7 . The rotation table  7  intermittently rotates by a predetermined pitch corresponding to the number of the mounting heads  8  each provided with a plurality of suction nozzles  9 , driven by the index unit  6 . By intermittent rotation of the rotation table  7 , any one of the suction nozzles  9  mounted on each of the mounting heads  8  moves to the feeding system  3  or the mounting system  4  as appropriate. That is, the suction nozzle  9  moves to the feeding system  3  in order to pick up the electronic component A fed by the feeding system  3 , and then moves by rotating to the mounting system  4  in order to mount the electronic component A on the printed board B conveyed to the mounting system  4 .  
         [0022]    As shown in FIG. 3, the electronic component feeding device  3 A of the feeding system  3  has a base  11  extending in a lateral direction, four slide bases (unit bases)  12  slidably mounted on the base  11 , many component feeding units  13  attachably mounted on each of the slide bases  12 , and a linear motor  14  provided between the base  11  and the slide bases  12 . Two pairs of the slide bases  12  are each disposed on left and right sides of the base  11 . Two groups of the component feeding units  13  are alternately moves to the main body  2  by each of the two pairs of the slide bases  12 . That is, while one pair of slide bases  12  on one side, which has the component feeding units  13  thereon, slides to a front of the main body  2  to feed the electronic components A, another pair of slide bases  12  at an original position on another side performs a replacement operation of the component feeding units  13  for a next feeding operation.  
         [0023]    The component feeding units  13  are formed thin, and aligned in a lateral direction at narrow intervals on the slide bases  12 . Each of these component feeding units  13  is positioned on the slide base  12  and mounted thereon being attachable by a lever. Each of the mounting heads  8  (suction nozzles  9 ) of the main body  2  moves to each end of the component feeding units  13  mounted on the slide bases  12  to pick the electronic component A up by suction. In each of the component feeding units  13 , a carrier tape having the electronic components A therein at predetermined pitches is wound around a tape reel  16 . Each of the electronic components A stored in the carrier tape is exposed by peeling a cover tape off the carrier tape fed from the tape reel  16  (the cover tape winding around a cover tape reel  15 ) and is picked up by the suction nozzle  9 .  
         [0024]    The slide base  12  has a base block  22  on an upper side and a slide block  23  on a lower side, which are positioned and fixed by left and right connecting members  21   a  and  21   b . The component feeding units  13  are mounted on an upper surface of the base block  22 , and a pair of left and right sliders  24   a  and  24   b  is provided on a lower surface of the slide block  23 . The base block  22  includes a horizontal portion  26  and a sloped portion  27 . The horizontal portion  26  has the component feeding units  13  mounted thereon and the sloped portion  27  is located keeping off the tape reel  16 .  
         [0025]    The slide block  23  includes an upper horizontal portion  29 , a vertical portion  30 , and a lower horizontal portion  31 , and is formed into a crank shape in its cross-section. A plurality of ribs  32 , which is formed by cutting in order to form a radiating fin, is provided on an outer side of the vertical portion  30  to the lower horizontal portion  31 . The upper horizontal portion  29  supports the horizontal portion  26  of the base block  22  through one connecting member  21   a , and the ribs  32  supports the sloped portion  27  of the base block  22  through other connecting member  21   b . The first slider  24   a  is fixed on a lower surface of an outer end of the upper horizontal portion  29 , and the second slider  24   b  is fixed on a lower surface of an outer end of the lower horizontal portion  31 .  
         [0026]    The base  11  includes a base body  41  and a vertical block  42 . A first slide rail  43   a  engaged with the first slider  24   a  is attached on an upper end surface of the vertical block  42 , and a second slide rail  43   b  engaged with the second slider  24   b  is attached on an upper end surface of the base body  41 . An upper magnet base  44  is attached to an upper surface of the vertical block  42 , extending in a horizontal direction. A lower magnet base  45  is attached to an upper surface of the base body  41 , facing toward the upper magnet base  44 .  
         [0027]    The linear motor  14  has a pair of upper and lower stationary members  47   a  and  47   b  fixed on the base  11 , and a moving member  48  fixed on the slide base  12 . The stationary members  47   a  and  47   b  include the upper and lower magnet bases  44  and  45 , and upper and lower magnets  49 . The upper magnets  49  are fixed on a lower surface of the upper magnet base  44  downward, and the lower magnets  49  are fixed on an upper surface of the lower magnet base  45  upward. The moving member  48  has substantially the same length as that of the slide base  12 , and fixed on a side of the vertical portion  30  of the slide block  23 . An upper surface and a lower surface of the moving member  48  face the upper stationary member  47   a  and the lower stationary member  47   b  respectively with gaps (air gaps) therebetween. That is, the moving member  48  and each of the upper and lower stationary members  47   a  and  47   b  face each other, to operate as the linear motor  14  as a whole.  
         [0028]    The moving member  48  fixed on the slide block  23  is formed by winding an exciting coil around a magnetic core (not shown), while the upper and lower stationary members  47   a  and  47   b  are formed by aligning many magnets  49  in a longitudinal direction on the upper and lower magnet bases  44  and  45 .  
         [0029]    The printed board B is fixed on an XY table  52  which is movable in the X and Y directions driven by an X axis drive motor  50  and a Y axis drive motor  51  shown in FIGS. 1 and 7, and receives the component A from the suction nozzle  9  at the mounting station III.  
         [0030]    Each of the mounting heads  8  is attached to a lower portion of a head vertical shifting shaft  53 . The head vertical shifting shaft  53  is fixed on a roller attached body  54  on its upper portion. The upper and lower cam followers  55  and  56  are rotatably attached to an upper portion of the roller attached body  54 , protruding inside the roller attached body  54 .  
         [0031]    A numeral  57  designates a support for rotatably supporting the rotation table  7  in a horizontal direction from above. A cylindrical cam is fixed protruding on the support  57  around a rotation axis of the rotation table  7  supported by the support  57 . The cam follower  55  contacts an upper surface of the cylindrical cam to suspend the roller attached body  54 , thereby supporting the mounting head  8 . The lower cam follower  56  pushes a lower surface of the cylindrical cam, being pulled by a compression spring (not shown).  
         [0032]    Accordingly, the cylindrical cam is interposed between the cam followers  55  and  56 . By rotation of the rotation table  7 , the cam followers  55  and  56  move rotating on the upper and lower surfaces of the cylindrical cam. Since the cylindrical cam moves upward and downward, the mounting head  8  moves with rotating and moving upward and downward.  
         [0033]    A numeral  63  is a vertical shift block formed into a horseshoe shape at its cross section. The vertical shift block  63  is disposed in a cut-off portion of the cylindrical cam at the pickup station I. An upper end of the vertical shift block  63  is attached to a vertical shift board  65  which is vertically movable along a guide  64  attached on the support board  62 .  
         [0034]    A protrusion  67  at a lower portion of the vertical shift block  63  is placed at a position extending from the cylindrical cam when the vertical shift block  63  rises. Therefore, by rotation of the rotation table  7 , the cam followers  55  and  56  shift to positions on and under the protrusion  67  respectively, the protrusion  67  being interposed between the cam followers  55  and  56 .  
         [0035]    As shown in FIGS.  4  to  6 , a rail  110  is attached to an upper end of the vertical shift board  65 , and a guide  111  is provided movable in a horizontal direction along the rail  110 , so that a moving body  66  can move in vertical and horizontal directions along the guide  111 . A pair of rollers  112  is rotatably attached to a front surface of the moving body  66 . A vertical guide piece  114  is formed on the stroke adjustable plate  113 , being interposed between the rollers  112 . Therefore, the moving body  66  vertically moves along the guide piece  114 . By this movement, the rail  110  and the vertical shift board  65  move vertically.  
         [0036]    A numeral  115  designates a stroke motor for rotating a ball screw  116  engaged with a nut  117  to move the stroke adjustable plate  113  attached to the nut  117  along a guide  118  in a lateral direction. By movement of the stroke adjustable plate  113 , the moving body  66  moves along the rail  110  through the rollers  112  interposing the guide piece  114  therebetween to positions as shown in FIGS. 4 and 5.  
         [0037]    A numeral  119  designates a cam for turning a cam lever  121 , being engaged with a cam follower  122  pivotally supported on one end of the cam lever  121  which is rotatable around an axis  120 . When the cam  119  rotates to turn the cam lever  121 , a vertical turning lever  124  which is rotatably supported on one end of a link lever  123  turns around an axis  125  through the link lever  123  which is rotatably supported on another end of the lever  121 .  
         [0038]    An engagement piece  126  formed in the vertical turning lever  124  is engaged with a cam follower  127  rotatably attached to a back surface of the moving body  66 , the cam follower  127  being pulled by a pulling spring  128  stretched between the rail  110  and the support  57 . Therefore, the moving body  66  moves vertically along the guide piece  114  by turning of the turning lever  124 , the guide  114  being positioned by moving in a lateral direction by rotation of the stroke motor  115 .  
         [0039]    By rotation of the cam  119 , the engagement piece  126  turns between a position drawn by a solid line and a position drawn by a chain line shown in FIGS. 4 and 5. A surface of the engagement piece  126  which is engaged with the cam follower  127  is horizontal at the position drawn by a solid line which is at a top in a turning range. At this position drawn by a solid line, the moving body  66 , i.e., the vertical shift block  63 , does not change at its height at any position which the guide piece  114  moves to by rotation of the stroke motor  115 . Therefore, the cam followers  55  and  56  can shift between the cylindrical cam and the vertical shift block  63 . At the position drawn by a dotted line where the surface of the engagement piece  126  slants to a right side in FIGS. 4 and 5, a lowest position of the moving body  66 , i.e., the vertical shift block  63 , changes depending on a position of the guide piece  114  which moves in a lateral direction, so that an amount of a vertical stroke of the suction nozzle  9  changes.  
         [0040]    A lowest position of the engagement piece  126  is the same any time at a position drawn by a chain line of FIGS. 4 and 5, and a surface of the engagement piece  126  which the cam follower  127  contacts has a linear surface. Therefore, an amount of a descending stroke of the moving body  66  generated by a turn of the engagement piece  126  with the cam follower  127  placed at a certain position increases by movement of the moving body  66  in a lateral direction by rotation of the stroke motor  115 , proportionally to a lateral moving distance of the moving body  66 . This facilitates a control of a vertical stroke of the suction nozzle  9 .  
         [0041]    The rotation of the cam  119  makes the vertical shift block  63  keep the mounting head  8  at a high position until the mounting head  8  reaches the pickup station I from a previous station, descend the mounting head  8  at the pickup station I, and raise the mounting head  8  when the rotation table  7  starts rotating again. The same structure as above is provided in the mounting station III.  
         [0042]    Next, a block diagram of a control in FIG. 7 will be described. A numeral  90  designates an interface which is connected with an index motor  101  for intermittently rotating the X axis drive motor  50 , the Y axis drive motor  51 , the linear motor  14 , and the rotation table  7 , a stroke motor  115 , a touch panel switch  91 , a CRT  92 , a component recognition processing device  89 , and so on. These are controlled by a CPU  93 , which serves as a control device for totally controlling a mounting operation, according to mounting programs stored in a ROM  94 .  
         [0043]    The touch panel switch  91  is attached to a screen of the CRT  92  using fixtures (not shown). The touch panel switch  91  is made of a glass substrate which is coated with a transparent conductive film on its whole surface and printed with electrodes on its four edges. When an operator touches the surface of the touch panel switch  91  in a state where minimal electric currents flow on the surface of the touch panel switch  91 , current flows change at the four electrodes and coordinates of a touched position are calculated by a circuit board connected with the electrodes. If the calculated coordinates correspond to one of coordinates originally stored in the RAM  95  as a switch for executing a certain operation, the operation is executed.  
         [0044]    The component recognition processing device  89  takes an image of a lower surface of a component A within a predetermined visual field by a component recognition camera  88 , and performs recognition processing of the taken image to recognize a position of the component A in order to detect a shift amount of the component A attached to the suction nozzle  9  from a proper position.  
         [0045]    A first measuring station IV at a second position from the mounting station III is provided with a line sensor unit  96 , which is formed into a horseshoe shape at its cross section, as a level detection sensor for measuring a level of a lower portion of the suction nozzle  9 . The line sensor unit  96  has a floodlight  97  (on one side wall) for emitting light beams in a horizontal direction, and a light receiving device  98  (on another facing side wall) for receiving the emitted light beams, which is formed of many CCD elements linearly aligned in a perpendicular direction. The floodlight  97  can emit parallel light beams by a lens condensing lights from LEDs, or by a laser. In the light receiving device  98 , for example, there are aligned about one-thousand CCD elements vertically in a vertical width of 10 mm. Each of the CCD elements can detect an amount of received lights so that each can be used as an ON/OFF sensor by setting a threshold value in a received light amount. By ON or OFF outputs, a portion shaded by the electronic component A or the suction nozzle  9  can be detected so that a level of a lower end of the electronic component A or the suction nozzle  9  can be detected.  
         [0046]    The RAM  95  stores mounting data on component mounting, such as position data of X and Y directions (indicated by X and Y respectively) and an angle (indicated by Z) in the printed board, alignment numbers of the component feeding units  13  (indicated by FDR), and so on, in a mounting order. Furthermore, the RAM  95  stores component disposition data, i.e. data of each type of the electronic components (component ID) corresponding to each alignment number of the component feeding units  13 . Furthermore, the RAM  95  stores component library data having component feature data, as described below.  
         [0047]    An ON or OFF output of the line sensor unit  96  is performed at each of the CCD elements. A border between a shaded portion and an illuminated portion is calculated as a peak value of a lower end position by the CPU  93 . The RAM  95  includes a bring-in memory to store a lower end position every time it is measured and a hold memory to store the lowest measured end position during an operation. The bring-in memory stores values of lower end levels of the suction nozzle  9  (or the electronic component A) calculated at intervals of predetermined moving distances, i.e., at intervals of predetermined time from one outputs of the line sensor unit  96 . The hold memory stores the largest value during an operation, i.e., every time a newly measured value of the lower end position which is stored in the bring-in memory is larger (lower) than that stored in the hold memory, the new value replaces the value stored in the hold memory.  
         [0048]    Furthermore, the RAM  95  has component library data on component size etc as shown in FIG. 8, the data being classified into component types. For example, data on a lower end level of the suction nozzle  9  is stored in the RAM  95 , as a standard for comparing with a value of a detected lowest end level stored in the hold memory.  
         [0049]    A select and switch station at a second position from the first measuring station IV is provided with a nozzle selecting and switching device  102  for selecting and switching to the suction nozzle  9  to be used for a next component picking-up operation after a mounting operation on the printed board P. At this select and switch station, the nozzle selecting and switching device  102  raises the suction nozzle  9  which completes mounting, and lowers the suction nozzle  9  to be used next from the mounting head  8 .  
         [0050]    An operation under the above-described structure will be described hereafter. First, when power is applied to the electronic component mounting apparatus  1 , the CRT  92  displays an initial screen. An operator touches a “manufacturing running” operation switch enclosed by double boxes on the screen and then touches a start key. Then, automatic running of a mounting operation of a chip component A starts.  
         [0051]    When a printed board B is conveyed and mounted on the XY table  52  by a mounting device (not shown), the CPU  93  drives a linear motor  14  to have the predetermined component feeding unit  13  on the slide base  12  move to a component picking-up position by the suction nozzle  9  according to the mounting data (NC data) corresponding to the target printed board B stored in the RAM  95 .  
         [0052]    During this operation, the rotation table  7  intermittently rotates to move the mounting head  8  to the pickup station I, and the suction nozzle  9  already selected by the nozzle selecting and switching device is positioned above the component picking-up position. The roller attached body  54  moves along the cylindrical cam with the movement of the mounting head  8 , and the cam followers  55  and  56  which interpose the cylindrical cam therebetween shift to a position where the cam followers  55  and  56  can interpose the protrusion  67  of the vertical shift block  63  therebetween.  
         [0053]    During the movement of the mounting head  8 , a cam (not shown) rotates by rotation of the index motor  101  so that the vertical shift bar descends to push a turn lever (not shown) of the component feeding unit  13  down. Then, the tape wound around the tape reel  16  is forwarded by a predetermined pitch, and the cover tape reel  15  rotates to peel the cover tape off the tape.  
         [0054]    The CPU  93  rotates the stroke motor  115  through the interface  90 , moves the stroke adjustable plate  113  along the guide  118  through the ball screw  116  and the nut  117 , and moves the moving body  66  along the rail  110  through the vertical guide piece  114  and the rollers  112 . Accordingly, the cam follower  127  provided on the moving body  66  is positioned at a position where a descending stroke of calculated amount can be generated.  
         [0055]    The cam  119  rotates by rotation of the index motor  101  to push the cam follower  122 , turn the cam lever  121 , and then the link lever  123 , so that the vertical turning lever  124  turns downward around the axis  125 . Then, by pulling force of the pulling spring  128 , the rollers  112  rotate along the vertical guide piece  114  and the moving body  66  and the rail  110  descend so that the vertical shift board  65  integrally attached to the rail  110  descends along the guide  64 . Accordingly, the vertical shift block  63  already interposed between the cam followers  55  and  56  descends to lower the roller attached body  54 , so that the suction nozzle  9  descends to an upper surface of the chip component A and picks the component A up by suction. Then, the cam  119  further rotates to turn the turning lever  124  counterclockwise in FIG. 3 so that the suction nozzle  9  rises up to an original position with the component A attached thereto.  
         [0056]    Next, the rotation table  7  intermittently rotates so that the cam followers  55  and  56  rotate along the cylindrical cam, thereby moving the mounting head  8  holding the component A toward a next station.  
         [0057]    The rotation table  7  intermittently rotates further so that the mounting head  8  reaches the component recognition station II. At the component recognition station II, the component recognition camera  88  takes an image of the lower surface of the component A and the recognition processing device  89  performs recognition processing of the taken image so that a shift amount of the component A attached to the suction nozzle  9  from a proper position is recognized.  
         [0058]    The mounting head  8  moves to an angle adjustment station, and a head rotation device rotates the mounting head  8  by a rotation angle calculated by adding an original angle data and an angle to be corrected based on a recognition result by the component recognition device  89 .  
         [0059]    Next, the mounting head  8  reaches the mounting station III by intermittent rotation of the rotation table  7 . During this intermittent rotation of the rotation table  7 , the CPU  93  calculates an amount of a descending stroke, and rotates the stroke motor  115  to adjust the position of the moving body  66  in order to make a descending stroke of calculated amount, in a manner similar to the case in the pickup station I. Accordingly, the mounting head  8  descends in a manner similar to the case in the pickup station I, and the component A picked up by the suction nozzle  9  is mounted on the printed board B mounted on the XY table  52  which is positioned by moving by an amount to be corrected by rotation of the X axis drive motor  50  and the Y axis drive motor  51 , the amount to be corrected being calculated out based on the recognition result of the component recognition processing device  89 .  
         [0060]    At the first measuring station IV at a second position from the mounting station III, the line sensor unit  96  detects a lower end level of the suction nozzle  9  after the component mounting operation. First, when the CPU  93  detects a timing of a start of detection, that is, a little before the mounting head  8  stops at the station, the floodlight  97  emits light beams and the line sensor unit  96  starts outputting. At this timing, data for a previous component in the bring-in memory and the hold memory are cleared, and the CPU  93  calculates a border between the shaded portion and the illuminated portion as the vertical position of the lower end of the suction nozzle using outputs of the line sensor unit  96  and stores the value in the bring-in memory. The origin for measuring the value of the vertical position of the lower end is set above any of possible lower end position of the suction nozzle. Thus, the lower the vertical position of the lower end of the suction nozzle is, the larger the measured value becomes.  
         [0061]    The CPU  93  compares the value of the lower end in the bring-in memory with a value in the hold memory which is “0” at first. The suction nozzle  9  keeps moving during this process and the CPU  93  repeats the same measuring process until a timing of terminating of the detection. Normally, the suction nozzle  9  does not hold the electronic component A after completing a mounting operation of the electronic component A on the printed board B. When the suction nozzle  9  comes to a position shown in a fourth vertical dotted line from a left side of FIG. 9 where light beams emitted by the floodlight  97  of the line sensor unit  96  are applied, the CPU  93  reads outputs of the line sensor unit  96 , calculates a value of a lower end position shown by a filled circle on the dotted line of FIG. 9, stores the value of the lower end position in the bring-in memory, and compares that value with the value in the hold memory. Since the value in the bring-in memory is larger than that in the hold memory, the value in the bring-in memory is written in the hold memory. Note that FIG. 9 also shows an electronic component, denoted by the dotted line, which is inadvertently held by the suction nozzle after a completion of a mounting cycle.  
         [0062]    The suction nozzle  9  keeps moving during this process, and the CPU  93  reads outputs of the line sensor unit  96  on a fifth vertical dotted line from a left side of FIG. 9 next time, and calculates a value of a lower end position shown by a filled circle on the line, and stores the value in the bring-in memory. If that value in the bring-in memory is larger than the value written in the hold memory, the value written in the hold memory is updated to the value stored in the bring-in memory. When the CPU  93  completes reading of outputs by the line sensor unit  96  on each of vertical dotted lines of FIG. 9 accordingly and detects a timing of terminating of the detection, the CPU  93  stops reading and compares the value written in the hold memory, for example, 4.95 mm with the lower end level of the suction nozzle  9 , for example, 5.00 mm stored in the RAM  95  for comparison, in a case of a component type shown in FIG. 8. Since a difference of the values, i.e., 0.05 mm is within a range of permissible values of the nozzle level (between plus and minus 0.1 mm), the suction nozzle  9  is not worn beyond a limit. Therefore, the CPU  93  does not inform (warn) the operator of wearing, but stores the difference value of 0.05 mm in the RAM  95 . In this case, when the difference value is out of the range of the permissible values (between plus and minus 0.1 mm), the CPU  93  informs the operator that the suction nozzle  9  is worn by an informing device (not shown). However, there is a case where the suction nozzle  9  itself is not attached to the mounting head  8 , i.e. missing. Furthermore, when a value of a lower end level stored in the bring-in memory is too large, there may be a case where the suction nozzle  9  is about to fall from the mounting head  8 . In those cases, the CPU  93  controls and stops the electronic component mounting apparatus  1 .  
         [0063]    At the select and switch station, the nozzle selecting and switching device  102  replaces the suction nozzle  9  used for the current mounting with the suction nozzle  9  for a next mounting operation. When the selecting and switching device  102  selects the suction nozzle  9  which is already in use and has its lower end position measured, the CPU  93  calculates an amount of a descending stroke of the suction nozzle  9  at the pickup station I and the mounting station III, corresponding to the above-described difference value of 0.05 mm read out from the RAM  95 , and rotates the stroke motor  115  to move the moving body  66  to a position where the suction nozzle  9  can descend by the amount. Accordingly, even if the suction nozzle  9  is worn with time or changes its lower end level by thermal expansion, the electronic component A can be picked up and mounted properly by controlling a descending amount of the suction nozzle  9 , corresponding to changes in the suction nozzle  9 .  
         [0064]    However, there also occurs a case where the suction nozzle  9  keeps holding the electronic component A even after completing the mounting operation of the electronic component A. In this case, the CPU  93  reads outputs of the line sensor unit  96  when the suction nozzle  9  and the electronic component A come to a position shown by a second vertical dotted line from a left side of FIG. 9 where light beams emitted by the floodlight  97  of the line sensor unit  96  are applied. Then, the CPU  93  calculates a value of a lower end position shown by an open circle on the dotted line of FIG. 9, stores the value in the bring-in memory, and compares the value with the value in the hold memory. Since the value in the bring-in memory is larger than the value in the hold memory, the value in the bring-in memory is written in the hold memory. The suction nozzle  9  keeps moving during this process, and the CPU  93  reads outputs of the line sensor unit  96  at a position shown by a third dotted vertical line from the left side of FIG. 9, calculates a value of a lower end position shown by an open circle on the dotted line of FIG. 9, and stores the value in the bring-in memory. Since the value in the bring-in memory is larger than the value written in the hold memory, the value written in the hold memory is updated to the value in the bring-in memory.  
         [0065]    When the CPU  93  completes reading of outputs by the line sensor unit  96  on each of dotted vertical lines of FIG. 9 accordingly and detects a timing of terminating of the detection, the CPU  93  stops reading and compares the value stored in the hold memory, for example, 5.55 mm with the lower end level of the suction nozzle  9 , 5.00 mm, stored in the RAM  95  for comparison, in a case of a component type shown in FIG. 8. Since a difference of the values, i.e., 0.55 mm is out of a range of permissible values (between plus and minus 0.1 mm) of the nozzle level, the CPU  93  decides that the suction nozzle  9  keeps holding the electronic component A. Therefore, the CPU  93  makes the suction nozzle  9  discharge the electronic component A in an exhaust box disposed at a predetermined station between the first measuring station IV and the pickup station I, for example. When the CPU  93  decides that the suction nozzle  9  holds the electronic component A, the CPU  93  can stop the electronic component apparatus  1  or inform the operator of that by an informing device (visual or audio), alternatively.  
         [0066]    Next, an electronic component mounting apparatus of a second embodiment of the invention will be described with reference to FIGS. 1, 10, and  11 . A second measuring station is provided at a next position of the select and switch station, being disposed with the line sensor unit  96 , which is formed into a horseshoe shape at its cross section, as a level detection sensor for measuring a lower end level of the suction nozzle  9  in a manner similar to the case in the first measuring station IV. As described above, the line sensor unit  96  includes the floodlight  97  (on one side wall) for emitting light beams in a horizontal direction, and the light receiving device  98  (on another facing side wall) for receiving the emitted light beams, which is formed of many CCD elements linearly aligned in a perpendicular direction. Furthermore, in addition to the floodlight  97 , floodlights  99  formed of LEDs (light emitting diodes) are disposed on both sides of the floodlight  97  on a side wall of the line sensor unit  96 . Two large circles shown in FIG. 11 show ranges covered by the floodlights  99 .  
         [0067]    At the select and switch station, the nozzle selecting and switching device  102  selects the suction nozzle  9  to be used for a next electronic component picking-up operation, the suction nozzle  9  used in the current mounting operation is released, and the suction nozzle  9  to be used for the next mounting operation is attached to the mounting head.  
         [0068]    At the second measuring station, a lower end level of the selected and switched suction nozzle  9  is measured by the line sensor unit  96  as described above. At the pickup station I and the mounting station III, the CPU  93  calculates a descending amount of the suction nozzle  9 , and rotates the stroke motor  115  to move the moving body  66  to a position where the suction nozzle  9  can descend by the amount. Accordingly, even if the suction nozzle  9  is worn with time or changes at its lower end level by thermal expansion, the electronic component A can be picked up and mounted properly by controlling a descending amount of the suction nozzle  9 , corresponding changes in the suction nozzle  9 . In this case, when a difference between the value of the lower end level in the hold memory and the value stored in the RAM  95  is out of the range of the permissible values, the CPU  93  informs the operator that the suction nozzle  9  is worn by an informing device (not shown). However, there is a case where the suction nozzle  9  itself is not mounted on the mounting head  8 , i.e. missing. Furthermore, when a value of a lower end level stored in the hold memory is too large, there can be a case where the suction nozzle  9  is about to fall from the mounting head  8 . In those cases, the CPU  93  controls and stops the electronic component mounting apparatus  1 .  
         [0069]    At the second measuring station, suction nozzles  9 B, except for a suction nozzle  9 A which is selected by the nozzle selecting and switching device  102  for a next picking-up operation, may not be raised at all or high enough before it descends into the line sensor unit  96  for the lower end detection. If this happens, the design of the mounting head dictates that the nozzles  9 B are bound to fall. When the nozzles  9 B are not raised high enough, lights from the floodlights  99  are partially shaded by the suction nozzle  9 B so that an amount of lights received at the light receiving device  98  from the floodlights  97  and  99  becomes smaller. In this case, the CPU  93  decides that the suction nozzles  9 B except for the suction nozzle  9 A are about to fall so that the CPU  93  stops the electronic component mounting apparatus  1  or informs the operator of that by an informing device (visual or audio), as appropriate.  
         [0070]    In the second embodiment, although the floodlights  99  are provided in the line sensor unit  96  at the second measuring station, the floodlights  99  can be provided in the line sensor unit  96  at the first measuring station described in the first embodiment. This enables detecting of presence or absence of the suction nozzles  9 , except for the suction nozzle  9  used for component mounting, and detecting of the suction nozzles which is about to fall.  
         [0071]    The invention is not limited to the above-described electronic component mounting apparatus of high-speed type, but can be applied to an electronic component mounting apparatus where electronic component feeding devices does not move but mounting heads move in a plane direction.  
         [0072]    Although particular preferred embodiments of the invention have been disclosed in detail, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, are possible and lie within the scope of the invention.