Patent Publication Number: US-6209426-B1

Title: Magnetically attractive driver bit assembly

Description:
FIELD OF THE INVENTION 
     The present invention relates to a magnetically attractive driver bit assembly. 
     BACKGROUND OF THE INVENTION 
     Conventionally, when driving a screw, devices such as one disclosed in the Japanese Utility Model Publication No. Sho 46-35987, wherein air attraction is employed to attract a screw to the tip of a driver bit, have been utilized. Also, for example, the Publication of Unexamined Japanese Utility Model Application No. Sho 57-202669 discloses a device, wherein magnetic force is employed to attract a screw to the tip of a driver bit by magnetizing the driver bit using one or more permanent magnets. 
     In the case where air attraction is employed, however, it is necessary to fit a device adapted for air attraction around a driver bit. Therefore, when driving a screw into an object having a counterbore, the driver bit with such a device cannot be used because the outside diameter thereof is relatively large. Moreover, since the weight of the end portion of a screwing robot is increased, it is impossible to convey a screw attracted to the driver bit from a screw supply position to a screwing position at high speed. 
     Prior art for magnetizing a driver bit itself has the disadvantage that the magnetic attraction of the driver bit for a screw is not strong enough to securely hold the screw. As a result, high-speed movement of a screwing robot arm from a screw supply position to a screwing position may cause the screw to drop off the driver bit and, therefore, speed-up of the screwing operation is prevented. 
     SUMMARY OF THE INVENTION 
     Wherefore, a principal object of the invention is to provide a novel driver bit assembly which comprises a driver bit and a magnetically attractive device and shows a strong magnetic attraction when applied to a screwing robot and the like so that the operating speed of the robot arm can be increased. Another object of the invention is to provide a driver bit assembly which can prevent breakage of the magnetically attractive device even when the driver bit is broken. 
     To attain these and other objects, there is provided a magnetically attractive driver bit assembly capable of magnetically attracting a screw, the driver bit assembly comprising: a driver bit made of a magnetic body having a tip for engaging with the screw and a peripheral portion extending from the tip to a position at a predetermined distance; a cylindrical spacer made of a magnetic body fitted around the peripheral portion of the driver bit; a fixing means for fixing the cylindrical spacer around the driver bit; and a ring magnet fixed to an end of the cylindrical spacer by means of its magnetic attraction and adapted for magnetically attracting the screw. 
     The fixing means is preferably another ring magnet, which is disposed between the cylindrical spacer and a step located between the above peripheral portion and a large diameter portion, and magnetically attracts both the step and the cylindrical spacer. 
     Alternatively, the fixing means may be an O-ring fitted on the inner surface of the cylindrical spacer, which has an annular in cross-section larger than the clearance between the inner surface of the cylindrical spacer and the outer surface of the peripheral portion of the driver bit, and which is elastically deformed to fix the cylindrical spacer on the driver bit. 
     Preferably, the length of the cylindrical spacer is such that, when a screw is magnetically attracted to the tip of the driver bit, the head of the screw and the ring magnet do not contact each other with a narrow gap therebetween. 
     In the case where an O-ring is employed as a fixing means, the length of the cylindrical spacer is such that even when the cylindrical spacer is positioned away from the step of the driver bit, the above described gap occurs between the head of the screw and the ring magnet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIGS. 1 and 2 are front views, partly in cross-section, of a magnetically attractive driver bit assembly according to a first embodiment of the present invention; and 
     FIG. 3 is a front view, partly in cross-section, of a magnetically attractive driver bit assembly according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Preferred embodiments of the invention will be described referring to drawing figures as follows. 
     As shown in FIGS. 1 and 2, a magnetically attractive driver bit assembly  1  according to a first embodiment includes an iron driver bit  3  having a step  7 , at a predetermined distance from the pointed edge of a tip  15  of the driver bit  3 , from which a larger diameter portion  5  extends. A first ring magnet  9  having approximately the same outside diameter as the larger diameter portion  5  is firstly fitted around the driver bit  3  from the direction of the pointed tip thereof, and an iron cylindrical spacer  11  having approximately the same outside diameter as the first ring magnet  9  is then fitted. A second ring magnet  13  similar to the first ring magnet  9  is then fitted to the end of the cylindrical spacer  11 . From the end surface of the second ring magnet  13  is exposed a portion of the tip  15  (a Phillips screwdriver tip) of the driver bit  3 , so that a screw  17  engaging with the tip  15  of the driver bit  3  is attracted by the second ring magnet  13 . 
     In the magnetically attractive driver bit assembly  1 , the length of the cylindrical spacer  11  is determined such that when the screw  17  is engaged with and attracted to the tip  15  of the driver bit  3 , a narrow gap g (about 0.3 mm) is formed between the head  19  of the screw  17  and the second ring magnet  13  instead of allowing direct contact thereof with each other. 
     Also, respective outside diameters of the larger diameter portion  5 , the first ring magnet  9 , the second ring magnet  13 , and the cylindrical spacer  11  are approximately the same and smaller than the diameter of even a deep counterbore formed on an object in which the screw is to be installed. 
     Rare earth magnets (neodymium magnets) are employed as the first and the second ring magnets  9 ,  13  to provide a strong magnetic force to allow fast operation of a screwing robot. 
     The above described constitution enables the magnetically attractive driver bit assembly  1  of the first embodiment to attract the screw  17  in securely engaging relation to the tip  15  of the driver bit  3  by the magnetic attraction of the second ring magnet  13  disposed near the tip  15  of the driver bit  3 . As a result, when applied to a screwing robot, the magnetically attractive driver bit assembly  1  enables the movement of the robot arm from a screw supply position to a screwing position to be quickened. Also, the first ring magnet  9  is attracted to the step  7  of the driver bit  3 , the cylindrical spacer  11  is attracted to the first ring magnet  9 , and the second ring magnet  13  is attracted to the cylindrical spacer  11 , and ring magnets  9 ,  13  can be easily detached. Furthermore, even when fatigue failure of the driver bit  3  occurs, the first and the second ring magnets  9 ,  13  and the cylindrical spacer  11  can be used again by removing them from the broken driver bit and fitting them around a replacement driver bit. 
     By providing a narrow gap g between the second ring magnet  13  and the head  19  of the screw  17 , as described above, the second ring magnet  13  and the head  19  of the screw  17  do not directly contact with each other, and thus wear or damage thereof due to rubbing against each other during a screwing operation is prevented. In the first embodiment, wherein desired magnetic attraction is effected by the first and the second ring magnets  9 ,  13  and the length of the cylindrical spacer  11  therebetween, by changing the length of the cylindrical spacer  11 , similar operation can be achieved regardless of the size of a screw (i.e. the depth of the cross-shaped slot of its screw head) by adjusting the length of the spacer  11  or adjusting the position of the magnets and spaces away from the steps to adjust the gap g. 
     As shown in FIG. 3, a magnetically attractive driver bit assembly  21  according to a second embodiment includes an iron driver bit  23  having a step  27 , at a predetermined distance away from the pointed edge of a tip  43  of the driver bit  23 , from which a larger diameter portion  25  extends in the direction opposite to the pointed end. Firstly, fitted to the driver bit  23  from the direction of the pointed end thereof is an iron cylindrical spacer  33 , whose outside diameter is approximately the same as that of the larger diameter portion  25 , and which has a recess  29  formed on its inner surface and contains rubber O-rings  31 , 31  that have previously been fitted therein and which elastically engage the bit  23 . Secondly fitted, to the end of the cylindrical spacer  33  is a ring magnet  35  whose inside and outside diameters are approximately the same as those of the cylindrical spacer  33 . From the end surface of the ring magnet  35  is exposed a predetermined portion of a tip  43  of the driver bit  23 , so that a screw  37  engaging with the tip  43  of the driver bit  23  is attracted by the ring magnet  35 . 
     The cylindrical spacer  33  includes a thinner portion  39  configured to form the recess  29  housing the O-rings  31 ,  31  therein while leaving the remaining of the spacer  33  portion to be attracted by the ring magnet  35 . An open end of the thinner portion  39  is plugged by a ring-shaped cap  41  made of synthetic resin after installation of the O-rings  31 ,  31 . 
     The cylindrical spacer  33  has an inside diameter such that a gap of about 0.05 mm occurs between the driver bit  23  and itself, and therefore can be easily fitted around the driver bit  23  from the direction of the pointed end thereof. 
     Also, respective outside diameters of the larger diameter portion  25 , the cylindrical spacer  33  and the ring magnet  35  are approximately the same and smaller than the diameter of even a deep counterbore formed on the object in which the screw is to be installed. 
     A rare earth magnet (neodymium magnet) is employed as the ring magnet  35  for the same reason as in the first embodiment. 
     In the magnetically attractive driver bit assembly  21 , the length of the cylindrical spacer  33  is determined such that a predetermined space is secured between the step  27  and the cylindrical spacer  33 . As a result, if a pressure is imposed on the cylindrical spacer  33  and the ring magnet  35  from the direction of the tip  43  of the driver bit  23 , the cylindrical spacer  33  and the ring magnet  35  can slidingly move a little in the direction of the larger diameter portion  25 , so that a heavy load is prevented from being applied to the ring magnet  35 . 
     The above described construction enables the magnetically attractive driver bit assembly  21  of the second embodiment to attract the screw  37  in securely engaging relation to the tip  43  of the driver bit  23  by the magnetic attraction of the ring magnet  35  disposed near the tip  43  of the driver bit  23 . As a result, when applied to a screwing robot, the magnetically attractive driver bit assembly  21  enables the movement of the robot arm from a screw supply position to a screwing position to be quickened. Also, due to the structure that the cylindrical spacer  33  is fitted around the driver bit  23  via the O-rings  31 , 31  and the ring magnet  35  attracts the cylindrical spacer  33 , the ring magnet  35  can be easily detached. Furthermore, even when fatigue failure of tip  43  of the driver bit  23  occurs and a heavy load is likely to be applied to the ring magnet  35 , the cylindrical spacer  33  and the ring magnet  35  can move a little in the direction of the larger diameter portion  25  owing to the resilience of the O-rings, so that damage to the ring magnet  35  by a heavy load applied thereto is prevented. Therefore, the ring magnet  35  and the cylindrical spacer  33  can be used again by removing them from the broken driver bit and fitting them around a replacement driver bit. 
     It is preferable to provide a narrow gap between the ring magnet  35  and the head  45  of the screw  37  in the same way as in the first embodiment. By this, the ring magnet  35  and the screw  37  do not directly contact with each other, and wear or damage thereof due to rubbing against each other during screwing operation is prevented. 
     While the description above refers to particular embodiments of the invention, it will be understood that the invention is not restricted to the above described embodiments and any modification may be made without departing from the spirit and the scope of the invention. 
     For example, rare earth magnets other than a neodymium magnet may be employed and the ring-shaped cap made of synthetic resin in the second embodiment may be made of iron.