Cable pulley

A pulley guides a cable on an overhead framework structure which is suspended from a ceiling by a threaded rod. The pulley includes a guide structure which guides the cable longitudinally through the pulley, and further includes a bracket structure which mounts the guide structure on the threaded rod. The guide structure can be mounted on the threaded rod in a first position in which a cable can be moved transversely into and out of the guide structure, and can be alternatively mounted on the threaded rod in a second position in which the cable cannot be moved transversely into or out of the guide structure.

FIELD OF THE INVENTION
 The present invention relates to a pulley for installing cables at a
 central office in a telephone system.
 BACKGROUND OF THE INVENTION
 A central office in a telephone system contains banks of batteries for
 powering the equipment in the central office upon a failure of the
 external power supply. Power cables for interconnecting the batteries and
 the telephone equipment are supported on overhead racks. The racks are
 ladder shaped structures that extend horizontally across beams defined by
 framing channels. The framing channels are suspended from the ceiling by
 threaded rods that are anchored to the ceiling.
 Pulleys are used to guide the power cables over the racks when the power
 cables are being installed. Specifically, the pulleys are clamped onto the
 racks or the framing channels at locations suitable for the particular
 installation of power cables. The pulleys are removed when the
 installation is complete.
 SUMMARY OF THE INVENTION
 The present invention comprises a pulley apparatus, and particularly
 comprises a pulley apparatus for installing a cable on an overhead
 framework structure at a central office in a telephone system. The pulley
 is configured to be mounted on a threaded rod upon which the overhead
 framework structure is suspended from the ceiling of the central office.
 Specifically, the pulley apparatus includes a guide structure which guides
 the cable longitudinally through the pulley, and further includes a
 bracket structure which mounts the guide structure on the threaded rod. In
 a preferred embodiment, the guide structure can be mounted on the threaded
 rod in a first position in which a cable can be moved transversely into
 and out of the guide structure, and can be alternatively mounted on the
 threaded rod in a second position in which the cable cannot be moved
 transversely into or out of the guide structure.

DESCRIPTION OF PREFERRED EMBODIMENTS
 A pulley 10 comprising a first embodiment of the invention is shown in FIG.
 1. The pulley 10 includes a bracket structure 12 and a guide structure 14.
 The bracket structure 12 is configured for mounting on a threaded rod 16.
 The guide structure 14 is configured to guide one or more cables 18
 longitudinally through the pulley 10.
 The cables 18 shown in FIG. 1 are power cables that interconnect batteries
 and telephone equipment, and are supported on an overhead rack 20. The
 rack 20 is a ladder shaped structure that extends horizontally across
 beams 22 defined by framing channels 24. The horizontal beams 22 defined
 by the framing channels 24 are suspended from the ceiling 25 by vertical
 threaded rods 16 (one of which is shown in FIG. 1) that are anchored to
 the ceiling 25.
 The guide structure 14 includes a pulley rod 30 in the shape of an open
 loop 32. An upper end portion 34 of the pulley rod 30 includes a hook 36
 that extends around the threaded rod 16 when the pulley 10 is mounted on
 the threaded rod 16 in the position shown in FIG. 1. The bracket structure
 12 projects from the opposite end portion 38 of the pulley rod 30. A
 plurality of rollers 40 are received over the pulley rod 30. The rollers
 40 are rotatable on the pulley rod 30 under the influence of a cable 18
 when the cable 18 is pulled longitudinally through the loop 32 defined by
 the pulley rod 30, i.e., when the cable 18 is pulled in the longitudinal
 directions indicated by the arrows shown in FIG. 1A.
 Each roller 40 in the first embodiment of the invention is an independently
 rotatable disk with a cylindrical peripheral surface 42 (FIG. 2), a flat
 side surface 44, and a frusto-conical side surface 46. Each frusto-conical
 side surface 46 faces and adjoins the flat side surface 44 of an adjacent
 roller 40. This promotes rolling contact between adjacent rollers 40 over
 a surface area that is wider than an area that might otherwise be defined
 by line contact between adjacent rollers 40.
 The rollers 40 in the first embodiment are pressed together under the bias
 of a spring 50. The spring 50 is compressed between a pair of washers 52
 and 54 that are movable along the pulley rod 30. Movement of one washer 52
 is limited by the rollers 40 when the rollers 40 are pressed into contact
 with one another under the influence of the spring 50. Movement of the
 other washer 54 is limited by a stop member 56 on the pulley rod 30. That
 washer 54 can be moved away from the hook 36 against the bias of the
 spring 50 to provide clearance as needed for removal of the hook 36 from
 the threaded rod 16 upon which the pulley 10 is mounted.
 The bracket structure 12 in the first embodiment includes a pair of bracket
 bars 60 and 62 which are vertically spaced apart from each other. Each
 bracket bar 60 and 62 has a rectangular cross section. The upper bracket
 bar 60 is shown separately in FIG. 3, and the lower bracket bar 62 is
 shown separately in FIG. 4. The upper bracket bar 60 has a pair of
 transversely extending slots 64 and 66 which are open at its opposite side
 edges 68 and 70. The first slot 64 is located directly beneath the hook 36
 (FIG. 1) at the upper end portion 34 of the pulley rod 30. The second slot
 66 is spaced horizontally from the hook 36. The threaded rod 16 hanging
 from the ceiling can fit into either slot 64 or 66.
 As shown in FIG. 4, the lower bracket bar 62 also has a pair of slots 74
 and 76 for separately receiving the threaded rod 16. However, the slots 74
 and 76 in the lower bracket bar 62 are open at the same side edge 78 of
 the lower bracket bar 62.
 The pulley 10 can be mounted on the threaded rod 16 in a either a closed
 position, as shown in FIG. 6, or in an open position, as shown in FIG. 7.
 In the closed position the threaded rod 16 extends through the hook 36 at
 the upper end portion 34 of the pulley rod 30, through the first slot 64
 in the upper bracket bar 60, and through the first slot 74 in the lower
 bracket bar 62. The open loop 32 defined by the pulley rod 30 is then
 closed by a section 110 of the threaded rod 16 that extends between the
 hook 36 and the upper bracket bar 60. This prevents the cable 18 from
 moving transversely out of the loop 32.
 The upper bracket bar 60 is fixed to the pulley rod 30, and the lower
 bracket bar 62 is pivotal about the pulley rod 30. When the pulley 10 is
 being mounted on the threaded rod 16 in the closed position of FIG. 6, the
 lower bracket bar 62 is moved pivotally into engagement with the threaded
 rod 16 after the hook 36 and the upper bracket bar 60 have been engaged
 with the threaded rod 16. The hook 36 and the two bracket bars 60 and 62
 securely block movement of the pulley 10 horizontally relative to the
 threaded rod 16. Further in accordance with this feature of the invention,
 the lower bracket bar 62 is preferably mounted loosely on the pulley rod
 30 so that it can move pivotally toward and away from the upper bracket
 bar 60 through a small range of movement. This facilitates movement of the
 lower bracket bar 62 into engagement with the threaded rod 16.
 When the pulley 10 is mounted on the threaded rod 16 in the open position
 100 of FIG. 7, the threaded rod 16 is received in the second slots 66 and
 76 in the bracket bars 60 and 62, which are spaced horizontally from the
 hook 36 at the upper end portion 34 of the pulley rod 30. The cable 18 can
 then be moved transversely into and out of the open loop 32 through a gap
 120 defined between the threaded rod 16 and the hook 36.
 As best shown in FIG. 7, the bracket structure 12 includes a pair of
 locking devices 130 and 132. The first locking device 130 secures the
 pulley 10 vertically on the threaded rod 16 in the closed position. The
 second locking device 132 secures the pulley 10 vertically on the threaded
 rod 16 in the open position.
 As further shown in FIGS. 9 and 10, the first locking device 130 includes a
 screw-threaded bore 133 which extends through the lower bracket bar 62.
 The bore 133 adjoins the first slot 74 in the lower bracket bar 62, and is
 open to the first slot 74. A locking member 134 with a screw thread 136 is
 received in the bore 133. The locking member 134 is an end portion of a
 lever 138 (FIG. 7), and is rotatable within the bore 133 in meshing
 engagement with the screw thread 140 in the bore 133. A flat 142 is
 provided on the locking member 134. When the flat 142 faces the adjoining
 slot 74 in the lower bracket bar 62 (FIG. 8), the threaded rod 16 can be
 received in the slot 74, and can be moved fully into meshing engagement
 with a screw thread 144 at the inner end of the slot 74. (A similar screw
 thread is located at the inner end of the other slot 76.) The lever 136
 can then rotate so as to move the screw thread 136 on the locking member
 134 into meshing engagement with the screw thread 146 on the threaded rod
 16, as shown in FIG. 9.
 When the locking member 134 is in a locking position as shown in FIG. 9,
 the meshing screw threads 136 and 146 securely block movement of the
 bracket structure 12 vertically relative to the threaded rod 16 under the
 weight of the pulley 10, or under the influence of forces applied to the
 pulley 10 by one or more cables 18 extending through the loop 32. In
 accordance with a particular feature of the invention, the meshing screw
 threads 136 and 144 enable the entire pulley 10 to rotate about the
 threaded rod 16. This avoids stresses that would otherwise be induced in
 the locking member 134 by the forces applied to the pulley 10 by the
 moving cables 18.
 Additionally, each screw thread 140 in the bores 133 and 154 is preferably
 slightly out of phase with the screw thread 144 in the adjoining slot 74
 or 76. This provides a fit between the meshing screw threads 136 and 146
 that is tighter than it would be if the screw threads 140 and 144 were not
 out of phase. The phase difference between the screw threads 140 and 144
 is preferably within a specified range of up to about 2.degree. to
 3.degree..
 The second locking device 132 similarly comprises a lever 150 with a screw
 threaded end portion 152 that rotates between locking and unlocking
 positions in a corresponding bore 154 in the same manner for mounting of
 the pulley 10 on the threaded rod 16 in the open position, as shown in
 FIG. 1. When the pulley 10 is mounted on the threaded rod 16 in the open
 position, the hook 36 at the upper end portion 34 of the pulley rod 30
 does not engage the threaded rod 16 to block movement of the pulley 10
 horizontally relative to the threaded rod 16. Therefore, as shown in FIG.
 3, the second slot 66 in the upper bracket bar 60 is preferably open
 oppositely relative to the second slot 76 in the lower bracket bar 62.
 This provides a secure engagement of the bracket structure 12 with the
 threaded rod 16 by enabling the bracket structure 12 to engage the
 threaded rod 16 at diametrically opposite sides of the threaded rod 16.
 Without the oppositely directed orientation of the slots 66 and 76, the
 entire pulley 10 would be movable horizontally off the threaded rod 16 by
 moving the rod 16 out of both slots 66 and 76 in a single direction.
 In accordance with more particular features of the invention, the levers
 138 and 150 are preferably long enough to reach the rollers 40 on the
 pulley 10 and 30. This blocks the levers 136 and 150 from rotating enough
 for the locking members 134 and 152 to be unscrewed from the lower bracket
 bar 62. In addition, a pair of vertically aligned apertures 161 and 163
 (FIGS. 4 and 5) in the upper and lower bracket bars 60 and 62, which may
 have internal screw threads (not shown), are provided for receiving a bolt
 or other fastener for optional mounting of the pulley 10 on a rack 20 or a
 framing channel 24 in the overhead structure of FIG. 1. Additionally, the
 second slot 66 in the upper bracket bar 60 extends transversely inward of
 the upper bracket bar 60 at an angle from a transverse centerline 155 of
 the upper bracket bar 60. This helps to limit movement of the upper
 bracket bar 60 relative to the threaded rod 16 in a direction parallel to
 the longitudinal centerline 157 of the upper bracket bar 60.
 A pulley 200 comprising a second embodiment of the invention is shown in
 FIG. 10. The pulley 200 has many parts that are substantially the same as
 corresponding parts of the pulley 10 described above. This is indicated by
 the use of the same reference numbers for such corresponding parts in
 FIGS. 1 and 10. However, the pulley 200 includes only a single bracket bar
 202, and is configured to be mounted on the threaded rod 16 in only a
 closed position, as shown in FIG. 10.
 The invention has been described with reference to preferred embodiments.
 Those skilled in the art will perceive improvements, changes and
 modifications, all of which are intended to be within the scope of the
 claims.