Patent Application
20120085204
1. Field
The present technology relates to mechanisms for fastening and releasing a bit with respect to a mandrel.
2. Description of the Related Art
Screwdrivers have removable bits for engaging and driving screws into a workpiece. These screwdrivers typically have an elongate mandrel having an end into which a screw bit is removably coupled. Screws have a wide variety of screw drives in the head of the screw, including for example slotted, Phillips head, Robertson (square) and hex to name but a few. Each time a different type of screw drive is used, the screw bit of the screwdriver needs to be changed out.
In many screwdrivers, the bit is coupled to the mandrel by threads. For example, in a power screwdriver disclosed in U.S. Pat. No. 4,146,071 to Mueller et al., issued Mar. 27, 1970, the bit has a reduced diameter externally threaded male portion to be received within an internally threaded female socket in the mandrel. Threaded couplings have the disadvantages that the mandrel and bits are both expensive and it is also difficult and time consuming to change the bit.
The power screwdriver of U.S. Pat. No. 4,146,071 utilizes a system in which the head of a screw is located and retained in coaxial alignment with the mandrel and bit by the head of the screw engaging a part-cylindrical guideway member having a diameter approximately equal to the diameter of the head of the screw. In such a configuration, it is necessary that the mandrel and bit be of a sufficiently small diameter that the mandrel and bit may reciprocate axially through the part-cylindrical guideway member. The constraints of the mandrel and bit being of a diameter not greater than the diameter of the screw head renders replacement of the threaded coupling of the bit to the mandrel with another system difficult.
Other bit to mandrel coupling systems are known in which the mandrel carries a split-ring in a deep groove in a socket in the mandrel. A split-ring is a ring of resilient material, typically metal, where the ring is split so that it can expand around larger diameter objects and contract back to its original size when in an unbiased position. One such example is shown in prior art
The bit 26 for use with mandrel 20 also includes an annular groove 28 around an outer circumference of the bit 26. When the bit 26 is inserted into the mandrel 20, the split-ring 22 retains the bit 26 in the mandrel 20 by the split-ring 22 being partially received in the groove 24 in the mandrel and partially within the groove 28 around about the bit. Such known systems suffer the disadvantage that the coupling may generally hold the bit too loosely so that it may come off the mandrel too easily, or hold the bit too tightly so that it is difficult to remove. Furthermore, as parts wear over time, the force required to remove the bit may decrease. Thus, even if the correct balance (not too loose, not too tight) is provided initially, over time, this balance may shift to a situation where the bit is held too loosely.
Embodiments of the present technology relate to a mandrel for securely holding a screw bit during use, but allowing easy removal of the screw bit for replacement. The mandrel includes a cylindrical socket for receiving a screw bit and a cylindrical cover translationally mounted over the socket. A chamber is defined within an interior of the socket having a first, cylindrical section with a constant diameter and a second, conical section where the walls taper inward toward a distal tip of the socket. A locking mechanism is housed within the chamber and is capable of moving between the first and second sections of the interior chamber. In embodiments, the locking mechanism is a resilient split-ring.
A bit for use with the mandrel of the present technology may include an annular bit groove around its circumference. The split-ring expands to accept the bit, and then contracts into the bit groove when the bit is fully inserted into the mandrel. If attempt is made to remove the bit by pulling on it distally, the split-ring moves distally with the bit until the split-ring contacts a conical wall of the second section of the interior chamber. At that point, the split-ring is wedged in the bit groove by the conical wall and is prevented from being removed from the socket.
In one embodiment, the socket further includes a pair of spaced apart slots extending proximally from a distal tip of the socket. The slots extend through the first and second sections of the interior chamber. The cover includes a release mechanism capable of biasing the split-ring away from the conical wall back into the first section so that the bit may be removed. In one embodiment, the release mechanism may be a pair of ears formed on the translating cover. When the cover is moved proximally relative to the socket, the ears move the split ring into the first, cylindrical section, where the split-ring has room to expand out of the bit groove as the bit is pulled distally out of the socket.
In one example, the present technology relates to a mandrel including: a socket for receiving the bit, the socket including a locking mechanism mounted within a chamber in an interior of the socket, the locking mechanism moving between a first position where the locking mechanism binds between the bit groove of the bit and a wall of the socket as the bit is pulled distally to prevent distal withdrawal of the bit, and a second position where the locking mechanism may be removed from the bit groove as the bit is pulled distally; and a release mechanism translationally mounted to the socket, the release mechanism capable of moving the locking mechanism from the first position to the second position as the bit is pulled distally.
In another example, the present technology relates to a mandrel including: a socket for receiving the bit, the socket including an annular split-ring mounted within a chamber in an interior of the socket, the split-ring moving between a first position where the split-ring binds between the bit groove of the bit and a sloped wall of the chamber as the bit is pulled distally to prevent distal withdrawal of the bit, and a second position where the split-ring may expand and be removed from the bit groove as the bit is pulled distally; and a release mechanism translationally mounted to the socket, the release mechanism including at least one ear capable of moving the split-ring from the first position to the second position as the bit is pulled distally.
In another example, the present technology relates to a method of releasably holding a bit within a distal end of a screwdriver, the bit including a bit groove, the method comprising: (a) defining a chamber within a socket of the mandrel, the chamber including a first section with cylindrical walls and a second section with conical walls having a smaller diameter than the cylindrical walls of the first section; (b) positioning an annular split-ring in the chamber, the annular split ring capable of moving between the first and second sections, and the annular split-ring capable of fitting snugly within the bit groove when the bit is inserted into the socket through the split-ring; (c) binding the bit within the socket by the split-ring engaging the bit groove and a conical wall of the second section upon attempted removal of the bit from the socket in the distal direction; and (d) moving the split-ring from the second section of the socket to the first section of the socket to allow expansion and removal of the split ring from the bit groove and removal of the bit from the socket upon a force in the distal direction.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
The present technology will now be described with reference to the following drawings.
The present technology will now be described with reference to
A release mechanism in the form of the cylindrical cover 114 fits over a portion of the cylindrical base 112 so that the base 112 and cover 114 are fixed with respect to each other. The base 112 and cover 114 are both circumjacent around the outer periphery of socket 118 with an end 118a of socket 118 being generally coplanar with an end 114a of cover 114. This relationship is shown more clearly for example in
The socket 118 may for example be formed of steel, and may have a central bore sized to receive a bit as explained below. The socket 118 may have a second end, opposite end 118a, with a bore to securely affix socket 118 to shaft 110 so that torque and translational force on shaft 110 are transmitted to socket 118. The walls of the socket may for example be 0.072 inches thick. The material from which socket 118 is formed, and the wall thicknesses of socket 118, may both vary from that described above in further embodiments.
Cylindrical cover 114 includes a biasing mechanism which in embodiments may be a pair of ears 130 in end 114a. The ears 130 may be oriented 180° apart from each other in end 114a and may extend inward toward axis 122 of cover 114, generally at a right angle to the cylindrical walls forming the cover 114. In further embodiments, there may be more than two ears 130, such as for example four ears oriented 90° from each other. When assembled as explained below, the ears 130 are received within slots 126. The base 112 and cover 114 may be pinned to the shaft 110 by a fastener (not shown) so as to be able to translate over the socket 118, along axis 122, a distance generally equal to the length of slots 126 in socket 118. A spring 132 biases the base 112 and cover 114 to a distal position where the end of cover 114 is generally coplanar with the end of socket 118. As used herein, “distal” is closer to socket end 118a and “proximal” is further way from socket end 118a.
The base 112 may for example be formed of steel, and may have a central bore sized to fit snugly over the socket 118 while still being capable of freely translating over socket 118 along the central axis 122. The cover 114 may for example be formed of aluminum, and may have a central bore sized to fit snugly over the base 112. The walls of the cover 114 may for example be 0.027 inches thick. The material from which the base 112 and cover 114 are formed, as well as the wall thicknesses of these components, may both vary from that described above in further embodiments. In other embodiments, the base 112 and cover 114 may be formed of a unitary construction.
Annular chamber 142 includes a first cylindrical section 142a and a second conical section 142b. The cylindrical section 142a is defined along its axial length (parallel to central axis 122) by constant-diameter interior walls of the socket 118. The conical section 142b is defined along its axial length (parallel to central axis 122) by decreasing-diameter interior walls of the socket 118. Thus, the diameter of conical section 142b gets smaller closer to the distal end 118a of socket 118. The slots 126 are formed in the socket end 118a so as to extend through both the conical section 142b and the cylindrical section 142a as shown.
The cylindrical section 142a is sized so that the split-ring 120 fits therein as explained below. The conical section 142b has a range of diameters along its axial length so that, at some point along the axial length, the diameter is smaller than the diameter of split-ring 120 when engaged within a slot in the bit. These size relationships of the portions of the chamber 142 to the diameters of the split-ring 120 are also explained below.
An operation of the mandrel 104 according to the present technology will now be explained with reference to the perspective and cross-sectional views of
The perspective and cross-sectional views of
When the bit 150 is inserted to its full extent, the bit groove 152 aligns with the split-ring 120 within the cylindrical portion 142b of chamber 142. This is the position shown in
Once the split-ring 120 engages the conical sidewall of conical section 142b, any further distal force on screw bit 150 wedges the split-ring 120 more tightly within the bit groove 152, and further prevents the bit from being withdrawn from the mandrel 104.
A split-ring has been described above as the locking mechanism which moves within chamber 142 so as to bind the bit 150 within the mandrel 104 (when the ring is in a distal position), and to allow removal of the bit 150 from the mandrel (when placed in the proximal position by the ears 130). In further embodiments, it is understood that other locking mechanisms may be provided within the socket 118 to affect the same operation. For example, instead of split-ring 120 in an annular chamber 142, the locking mechanism may be a ball-lock mechanism where a ball is mounted in an annular chamber. Instead of an annular chamber, which extends radially 360° around the central axis 122, a notch may be provided, which extends for example 10°-20° around the central axis 122, big enough to house the ball-lock. In this example, the ball-lock would reside in the slot. If attempt to pull the screw bit out is made without the secondary action, the ball-lock would wedge in the bit groove 152 and against the conical wall of conical section 142b. However, upon the secondary action of moving the cover proximally, an ear 130 can engage the ball and move it back to a larger diameter section, whereupon the screw bit 150 may be removed. Other mechanisms are contemplated.
In the embodiments described above, the release mechanism (cover 114) was affixed to the axial drive assembly 102. However, in a further embodiment shown in
The shape of plate 160 may vary in embodiments, with the provision that it include ears 130, or similarly defined structures, that are capable of engaging within slots 126 to bias the split-ring 120 distally.
The foregoing detailed description of the technology has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the technology to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen in order to best explain the principles of the technology and its practical application to thereby enable others skilled in the art to best utilize the technology in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the technology be defined by the claims appended hereto.
