Abstract:
An automatic tape feeder for use in component placement machines includes a novel sprocket wheel for driving component carrier tapes to a gross position by an electric drive motor. Before the electric drive motor reaches the final position desired, it is deactivated or turned off. A novel indexing cam is connected to the sprocket drive wheel. A spring loaded pawl or positioning cam is moved into a vee-shaped groove on the indexing cam so as to achieve an actual fine position of the indexing cam as well as the teeth on the sprocket wheel. By first achieving a gross position with the drive motor and then a fine position with an indexing cam and pawl, it is possible to achieve a positioning accuracy in a pick up station which is as accurate as the sprocket holes and component pockets in the carrier tape. The present invention has achieved accuracies of ± one 1,000 th  of one inch which exceeds positioning accuracies of devices known heretofore.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to automatic component feeders of the type used in automatic component placement machines. More particularly, the present invention relates to a tape feeder for precisely positioning a sprocketed tape having a cover tape on a carrier tape which covers a recess pocket in the base tape or carrier tape for automatically positioning it in a pick up station of a pick and place machine. 
     2. Description of the Prior Art 
     Tape feeders for pick and place machines are classified in U.S. Class 226, Subclasses 62, 122, 128, 129 to 139, et al. Covered tapes for tape feeders have become standardized to the point that reels of tapes with components may be purchased from different component vendors knowing that the covered tapes will fit into most standard tape feeders. Such tapes are made to EIA industrial standards with sprocket holes on 4-mm pitch for 8-mm tapes. Like 35 mm movie film, the sprocket holes are punched in staged die sets and are highly accurate for most purposes and have been found to be more accurate than the tape positioning mechanisms used to position the tape in the pick up station. 
     Heretofore, tape feeders have employed sprocketed wheels which have been driven by levers, escapement pawls and gears which when activated are dependent upon the accuracy of the drive mechanism. Since all of the prior art positioning devices have free play or backlash, it has been difficult if not impossible to position the sprockets as accurately as the sprocket holes in the tape would permit. 
     Accordingly, it would be desirable to provide a tape feeder that is capable of accurately positioning the sprocket holes and thus the recess pockets which hold components to an extremely high degree of accuracy when operated at high speeds over long periods of time. 
     SUMMARY OF THE INVENTION 
     It is a principal object of the present invention to provide a novel tape feeder for advancing component carrier tapes into a workstation or feed station with an extremely reliable degree of positioning accuracy. 
     It is a principal object of the present invention to provide a novel tape feeder that is interchangeable with existing tape feeders, yet provides a higher degree of positioning accuracy than prior art tape feeders. 
     It is a principal object of the present invention to provide a novel sprocket drive for a tape carrier that has gross positioning gear drive and a fine positioning cam drive. 
     It is a principal object of the present invention to provide a highly accurate cam drive for positioning a novel sprocket after introducing backlash in the sprocket gear drive. 
     It is a principal object of the present invention to provide an optical interrupter sensor for a drive motor for sensing a desired gross position of the novel sprocket drive gear. 
     It is a principal object of the present invention to provide a continuous tape path that does not reverse direction or tend to delaminate the cover tape from its carrier tape. 
     It is a principal object of the present invention to provide a novel cover tape removal station that prevents components from escaping until being positioned at the final pick up station position. 
     It is a principal object of the present invention to provide a two-stage tape positioning mechanism that eliminates high-speed overdrive positioning of the carrier tape. 
     It is a general object of the present invention to provide an economical and reliable high speed tape feeder with a minimum of wearing parts that could effect the accuracy of positioning of a tape carrier. 
     It is a principal object of the present invention to position a tape carrier in a pick up station independent of the position achieved by the drive motor. 
     It is a principal object of the present invention to finally position a carrier tape in a pick up station without using the force of a drive motor. 
     According to these and other objects of the present invention, there is provided in a tape feeder comprising a base plate and cover plates. A motor driven gear drive is mounted on the base plate and comprises a sprocketed wheel for engaging a sprocketed carrier tape and for gross positioning recess pockets in the carrier tape into a pick up position of a work station comprising an automatic cover tape stripper. The sprocketed wheel is further provided with a positioning cam that cooperates with a mating positioning cam which fine positions the sprocketed wheel after it is gross positioned by the drive motor. In the preferred embodiment of the present invention, an optical sensor controls the drive motor to a gross position and a spring actuated drive cam then cooperates with the positioning cam on the sprocket wheel to effect fine positioning of the sprocketed wheel. The sprocketed wheel and carrier tape is then positioned to the accuracy of the carrier tape of better than ± one 1,000 th  of one inch. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a right side elevation view of a prior art tape feeder with the right side cover plate removed to show the feed path of the component tape; 
     FIG. 2 is a left side elevation view of the prior art tape feeder of FIG. 1 with the left side cover plate removed to show the tape drive gearing; 
     FIG. 3 is a right side elevation view of the present invention&#39;s tape feeder with the right side cover plate removed to show the novel feed path of a component tape and the drive mechanism for the sprocketed wheel; 
     FIG. 4 is a right side elevation view of the present invention frame or base showing the path of the cover tape after being stripped from the carrier tape; 
     FIG. 4A is a right side elevation view of another preferred embodiment tape feeder showing a take up reel in place of a stuff box and a pinch roll in a changed position; 
     FIG. 5 is an exploded view of the drive gears employed to drive the sprocketed wheel to a gross position; 
     FIG. 6 is an isometric view of the tape feeder with side covers attached looking down on the pick up station as the cover tape is removed from the carrier tape; 
     FIG. 7 is an isometric view of the tape feeder of FIG. 6 taken from the right side showing access slots in the right side cover plate for positioning the cover tape; 
     FIG. 8 is an isometric view of a carrier tape showing sprocket holes and component pockets; 
     FIG. 9 is a cross-section taken through the novel sprocketed wheel; 
     FIG. 10 is an enlarged left side view of the sprocketed wheel of FIG. 9; and 
     FIG. 11 is an enlarged partial view of the sprocketed wheel of FIG. 10 showing a spring-loaded positioning actuating cam in a cam recess. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Refer now to FIG. 1 showing a right side elevation view of a prior art tape feeder  10  having a base or frame  11  with the cover plates removed (not shown). The base or frame  11  is provided with a feed path for a component two-piece tape  12  comprising a carrier tape  13  and a cover tape  14 . The tape  12  is shown entering into a slot which guides the component tape to the sprocket wheel  16 . As shown in FIG. 1, the tape  12  must pass through a reverse bend  17  and a reverse bend  18  in order to reach the sprocket wheel  16 . Since the carrier tape is stronger and thicker than the cover tape, flexing the component tape causes the cover tape  14  to delaminate from the carrier tape  13  at the reverse bends  17  and  18 . The cover tape is not tightly bonded to the carrier tape because it must be stripped or removed at the pick up station as will be explained hereinafter. 
     High speed electric motor  19  is supported by a bracket  21  mounted on the frame or base  11  and having a worm gear  22  mounted on the shaft  23  of the motor  19 . When the motor  19  is energized, the worm gear  22  drives a plurality of external spur gears (not shown) which reduce the revolutions of the motor  19  by a factor of approximately 700 to 1 to drive the sprocketed wheel  16  which positions the component tape  12  in the pick up station  24 . After the component is picked out of the pocket presented at the pick up station  24 , it continues along the tape slot  15  and exits at the bottom as shown at the numeral  13 . The carrier tape  13  is allowed to fall loose and may be collected periodically as trash and cut from the tape being driven through the tape feeder  10 . 
     At the work station  24 , the cover tape  14  is peeled back by a pulling action as it passes through the movable pinch roll  25  and a resilient drive roll  26 . The cover tape  14  being stripped from the carrier tape  13  is shown being taken up or spooled onto a reel  27  also known as a take up reel. The take up reel  27  is normally exposed and not covered by a cover plate (not shown), so that it may be easily removed and replaced without removing the cover plate. 
     Refer now to FIG. 2 showing a left side elevation view of the tape feeder  10  shown in FIG.  1 . The frame or base  11  is shown having the drive motor  19  mounted on a bracket  21  and having a shaft  23  which supports the worm gear  22  for driving a plurality of external spur gears  28 . One of the external spur gears  29  is shown having a tape take up reel drive pulley  31  which drives a resilient drive belt  32  and the take up reel pulley  33  which connects to the take up reel. In addition to driving the take up reel  27 , the external spur gears are shown engaging the drive gear for the drive roll  26  which engages the pinch roll  25  mounted on a pinch roll lever  34 . Pinch roll lever  34  is pivoted and urged into engagement with the drive roller  26  by a spring  35 . 
     The tape feeder  10  is mounted in a pick and place machine in slots especially adapted to position the tape feeder at a precise position. In order to remove the tape feeder  10  there is provided a handle  36  and a latch lever  37  which is pivoted at pivot  38  to articulate the latch  39 . Latch  39  is engagable into a support guide for releasably engaging the tape feeder  10  from the pick and place machine. 
     Refer now to FIG. 3 showing a right side elevation view of a preferred embodiment of the present invention tape feeder  10 A. In this embodiment, the component tape  12  is shown being presented into a tape slot  15 A and presented directly to the workstation  24 A. It will be observed that the component tape  12  has a direct path to the work station and does not incur any reverse bends which would cause delamination before the cover tape  14  is removed from the carrier tape  13 . It will be noted that the sprocket wheel  48  having highly precisioned sprocket teeth positions the component tape  12  in the work station at the time the component is picked from the carrier tape  13 , thus, controlling the position of the component tape  12  even while it passes through the work station  24 A. 
     Drive motor  19 A is shown having a worm gear  22 A mounted by a bifurcated bracket  41  which mounts on the base or frame  11 A. Worm gear  22 A drives an external spur gear  28 A pivoted on gear axle or shaft  42 . The external gear  28 A engages and drives an external gear  43  which has mounted thereon a sun gear  44  that moves with the gear  43 . Gear  43 ,  44  is mounted on an axle or shaft  45  and in turn simultaneously drives three planet gears  46  which engage an internal spur gear  47  which comprises a part of the novel sprocket wheel or sprocket gear  48 . In summary, the drive motor  19 A drives a sun gear  44  which causes the sprocket wheel  48  to be moved and positioned in a gross position at the workstation  24 A. 
     The novel sprocket wheel  48  comprises a positioning cam  49  mounted thereon which engages a pawl  51  which becomes a pawl shaped drive cam  51  that is mounted on a spring arm  52  which is supported by a spring block or bracket  53 . 
     In the preferred mode of operation, the drive motor  19 A takes all of the slack out of the drive gears and the pawl  51  prevents the sprocket wheel  48  from turning until all of the backlash in the gear set is removed. Once this occurs, the tape sprocket teeth on the sprocket wheel  48  will advance. As the sprocket wheel  48  advances, a sprocket index sensor  54  senses the holes  55  in the sprocket wheel  48 , thus detecting the motion of the sprocket gear by sensing the presence of a hole which is aligned radially with the teeth of the sprocket gear. Immediately upon detecting the predetermined hole, a predetermined number of pulses are counted and the motor is stopped. To provide the pulses and the exact gross position desired a tachometer wheel  56  is coupled to the drive motor  19 A and its position is sensed by pulses in the tachometer wheel  56  by tachometer sensor  57 . Thus, it will be understood that the drive motor  19 A is capable of taking all of the backlash out of the drive gears and positioning the desired sprocket teeth at the work station  24 A at a predetermined gross position. 
     As will be explained in detail hereinafter, the pawl  51  rides up on the cam  49  and moves over the crown of the cam where it becomes a positioning cam and causes the spring force in the spring  52  to now position the positioning cam  49  to a fine position which continues forward movement without conflicting with the drive of the drive motor  19 A. Stated differently, the drive motor takes all of the backlash out of the gears and pulls the component tape  12  to a gross position. When the drive motor  19 A is deactivated the positioning pawl  51  then drives the novel sprocketed wheel  48  forward again placing backlash into the gear system and positioning the novel sprocketed wheel  48  at a final fine position. 
     The latch  39 A is shown at the foot of new latch configuration latch arm  58  which terminates with a spring retainer at spring  59  and is urged toward the frame  11 A. A mounting block  62  is shown attached to frame  11 A and carries on it a pivot pin  63  for pivotally supporting a latch handle  61 . This improved latch handle enables an operator to perform latching and/or removing of a tape feeder with one hand. 
     Refer now to FIG. 4 showing a right side elevation view of the present invention frame or base  10 A showing the tape path of the cover tape  14  after being stripped from the carrier tape. Tape  12  is shown entering the guide slot  15 A. The component tape  12  remains substantially linear until it reaches the pick up station  24 A where the pockets in the carrier tape are exposed by removing the cover tape  14  which is stripped back and guided into a substantially vertical slot  66  and passes into a substantially horizontal passageway  67  and is shown at cover tape path  68  passing through a pinch roller  69  and a drive roller  71  where it exits into a stuff box which may be provided in area  72 . A stuff box door  73  is provided with a latch and a pivot to allow it to be pivoted outward and downward to have access to the stuff box area and the cover tape  14 . 
     A nozzle sensor  64 ,  65  is provided at the pick up station so that when the nozzle removes a component from the pocket in the component tape it is sensed when the nozzle rises with the component thereon so as to initiate advancement of the sprocket wheel and to bring a new component into the pick up position as will be explained in greater detail hereinafter. 
     Refer now to FIG. 4A showing a right side elevation view of another preferred embodiment tape feeder having a take up reel  73  in place of the stuff box. In this embodiment a cover plate  11 C is shown mounted onto the base or frame  11 A which is recessed at the leftmost edge to provide an open access for the take up reel  73 . The cover tape  14  is stripped from the carrier tape  13  and guided down a shallow recess or guide  66 A into the take up reel  73 . The cover tape  14  is pulled from its carrier tape  13  by pinch roll  69 A and drive roll  71 A which is actuated by the drive motor  19 A. An access area  75  is provided at the pinch rolls to feed the tape through the two rolls and an additional access area  74  is provided for access to the drive motor  19 A. The opening  75  in the cover plate  11 C leaves the take up reel  73  exposed and flush with the cover plate  11 C. This embodiment also includes the preferred embodiment latch release explained hereinbefore. 
     Refer now to FIG. 5 showing an exploded view of the drive gears employed to drive the sprocket wheel  48  to a gross position. In this embodiment, the external spur gear  43  and sun gear  44  are shown disconnected from each other but as explained hereinbefore are made as a single piece. The sprocket wheel sprocketed gear  48  is shown having an internal spur gear  47  which engages the planetary gears  46  which in turn engage the sun gear  44  which is mounted on the external spur gear  43 . Gear  28 A engages gear  43  as explained hereinbefore. There is shown a raised guide ring  60  which is part of the frame  11 A which provides the radial locating means for the sprocket wheel  48  as will be explained in greater detail hereinafter. 
     Refer now to FIG. 6 showing an isometric view of the tape feeder with side covers attached looking down on the pick up station as the cover tape is removed from the carrier tape  13 . The carrier tape  13  is shown having rectangular component pockets  13 P and round sprocket holes for mating with the teeth  48 T of the teeth on the sprocket wheel  48 . The cover tape  14  is shown emerging from a slit  70  in the stripper block  70 S. It will be understood that the components in the pockets  13 P do not emerge from under the stripper block  70 S until they are ready to emerge at the pick up station  24 A. Stated differently, the component which is positioned between the nozzle sensor  64 ,  65  will be the only exposed component in all of the component tape  12 . The cover tape  14  is shown being guided by a cover tape guide  66  where it is twisted and enters into the horizontal portion  67  of the cover tape guide. Access openings  74  and  75  are the same as those employed on FIG.  4 A and do not require additional explanation herein. 
     Refer now to FIG. 7 showing an isometric view of the tape feeder of FIG. 6 taken from the right side showing access slots in the right side cover plate. The access openings  74  and  75  in the cover plate are substantially the same as those previously shown in FIG.  4 A and do not require additional explanation. The cover tape  14  is shown passing between the pinch roll  69  and the drive roll  71 . Other numerals provided on FIG. 7 are the same as those used in previous figures and do not require additional explanation. 
     Refer now to FIG. 8 showing an isometric view of a carrier tape  13  showing the round sprocket holes  13 S which conform to the EIA specification and the component pockets  13 P therein. In the preferred embodiment shown, the sprocket teeth  48 T on the sprocket wheel  48  engage the topmost portion of their teeth in the round holes. The tape  13  is not forced down to the complete length of the tooth as will be explained hereinafter. 
     Refer now to FIG. 9 showing a cross section taken through the novel sprocket wheel  48 . Sprocket wheel  48  has teeth  48 T which have a substantially tight fit in the sprocket holes  13 S when the tape  13  is urged to the topmost portion of the tooth and not engaged fully thereon. Sprocket wheel  48  is provided with an annular recess or groove  60 G in which the aforementioned radial locator or guide ring  60  engages for maintaining its radial position. The fine positioning cam  49  and the internal spur gear  47  are numbered for purposes of coordinating FIG. 9 with the enlarged views which will now be explained. 
     Refer now to FIG. 10 showing an enlarged left side view of the sprocketed wheel  48  shown in FIG.  9 . The sprocket wheel  48  comprises teeth  48 T, sprocket holes  55 , positioning cam  49 , an annular positioning groove  60 G, and internal spur gear  47 . It will be noted that the teeth  48 T are slightly tapered and more narrow at their base to prevent the tape  13  from binding in the lower root of the tooth. 
     Refer now to FIG. 11 showing an enlarged partial view of the sprocketed wheel  48  shown in FIG.  10 . The numerals on FIG. 11 are identical to those shown in previous figures and represent the same structure and embodiment explained hereinbefore. FIG. 11 is employed to show how the fine positioning cam pawl  51  mounted on spring arm  52  is capable of advancing the sprocket wheel  48  in the direction of the arrow. In the preferred embodiment of the present invention, the sprocket wheel is moved in the direction of the arrow by the drive motor  19 A until pawl  51  passes over the apex of the cam  49 . As it starts its downward movement into the cam slot, shown as a vee-shaped cam, the sensor  54  senses the position of the sprocket holes  55  and deactivates the drive of the drive motor  19 A leaving the leftmost cam face of the drive cam pawl  51  to move the sprocket wheel  48  counter clockwise by cam action until it nests and fits tightly in the mating groove of the sprocket positioning cam  49 . 
     Having explained how the drive cam  51  is capable of exactly positioning the positioning cam  49 , it will be understood that the teeth  48 T on the sprocketed wheel are also engaged in the sprocketed tape  13  at the pick up station  24 A. By maintaining this tight position in the sprocket hole  13 S the sprocket teeth  48 T position the pockets  13 P in the pick up station  24 A as accurately as the tape can be manufactured. In the preferred embodiment of the present invention, it has been found that the carrier tape  13  can be positioned to an accuracy of ± one 1,000 th  of one inch relative to the axis of the pick up station and the pick up tool. It is believed that this increased accuracy is at least one-half of one order of magnitude greater than the accuracy available in prior art devices. 
     Having explained the preferred embodiments of the present invention, it will be understood that the novel sprocketed wheel  48  employs an entirely new and preferred mode of operation which allows the drive motor  19 A to gross position the carrier tape  13  and the drive cam pawl  51  to fine position the sprocketed wheel  48  after the drive motor has terminated its driving force so that after all backlash is taken from the gearing system the positioning pawl  51  only needs to move the sprocketed wheel forward in a counter clockwise direction again placing some backlash in the system but achieving fine positioning which can be as accurate as the sprocket holes in the carrier tape  13 .