Existing practice
The envisaged application for the invention is in manufacturing production lines where parts are often transported around the factory from station to station, sometimes with an overhead system. In this, hoists are used to raise the parts from the station, the hoist and parts are moved via overhead rail to the next station, and the hoist lowers the parts to where they are required. In one type of assembly the hoist carries a support platform suspended by six hoist cable connected to three points on the platform. The support platform is adapted to grasp the parts or a container holding the parts.
In hoist assemblies of this design the cables are all reeled up and down simultaneously over the same distance, at the same rate. They have been shown not to be subject to side-to-side sway and twisting, and so are applicable to where delicate parts are involved and/or high location precision required, such as in the semiconductor industry.
The problem with such systems however, say the inventors, is that the cable can easily develop kinks or could unravel from internal tension fatigue failure. As a result, the platform could tilt and the reels bind, making it difficult to deliver parts precisely and perhaps damaging the production parts. Rectification by replacing the hoist cables is expensive and time consuming.
The invention tackles these problems with a new cable retention assembly aimed at improving hoist cable life.
The patent covers three embodiments and aspects of the invention covering a hoist cable attachment assembly, a hoist system for lifting and lowering a payload, and a transportation system for lifting and lowering a payload, and providing sideways movement.
Construction
In Fig 1 the hoist system includes a lifting mechanism (105) and a payload gripping mechanism (110) connected by hoist cables (115). The lifting mechanism includes a frame (120) with three winches (125) arranged at angles of about 120 degrees to each other around a central axis about which the frame is rotatable. Each winch includes a motor (135) to turn a pair of cable drums (140) on opposite sides of the motor with a common longitudinal axis. Each hoist cable passes through a slot in the frame.
The payload gripping mechanism includes a frame (155) to which are attached three hoist cable attachment assemblies (160). These are arranged at angles of about 120 degrees to each other, similar to the orientation of the winches, and they also carry a pair of cables from each winch. Each hoist cable attachment is connected to the frame by a bracket – a main pivot pin (170), allowing free pivoting. Each attachment has an adjustment screw (175) to set the rotational resistance about the pivot pin.
The hoist cables are under tension and provide six horizontal force components in three non-parallel planes. The motors rotate all six cables simultaneously to raise or lower frame 155 relative to frame 120. Alternatively a single motor may be adapted to drive all six cable drums.
Fig 1 shows the hoist system in conjunction with a rail transport system. Frame 120 is attached to the transport system’s rails (180) by a bracket (185) through dollies (190).
Frame 155 has payload grippers (195) and, in this example, location sensors (200) to locate the payload and position the grippers.
If the hoist cables comprise wire rope with a plastics costing, they are electrically conductive and can be used to carry signal between the lifting mechanism and payload gripping mechanism. If this is the case a transceiver is also mounted on frame 155, connected electrically by wires (210) to the hoist cables and clamps. The hoist cable drums can be fitted with conductive and isolated rings and brushes adapted so that the hoist cables can be coupled electrically to the corresponding wires (220) and transceiver. The transceiver is used to communicate with the system controller for positioning purposes. Signals can be analogue, digital or power-based.
In Fig 2 the hoist cable attachment assembly (160) includes front and back plates held apart by a spacer. The main pivot pin (170) passes through and is fixed to bracket 165. This structure holds a pair of hoist cable pivot assemblies (245) using cable pivot pins (250A and 250B). Each assembly includes a hoist cable pivot body (255) and a hoist cable retainer (260). Each assembly’s pivot pin extends into and are fixed in the hoist cable pivot body. Screws (265) hold together the whole attachment assembly, which is free to pivot about the axis 265. Also, each hoist cable pivot assembly is free to pivot about its respective axis 270. Axes 265 and 270 are parallel to each other.
Each hoist cable is free to rotate about the axis 275 through a hoist cable retainer (260). Axes 275 are perpendicular to axes 265 and 270.
As shown in Fig 3, the hoist cable retainer (260) fits into a chamber in the hoist cable pivot body. The upper part of the hoist cable retainer extends through a hole in the pivot body. The hoist cable retainer also incorporates a chamber. The hoist cable passes through the hoist cable retainer, through thrust washers (300A and 300B), and into a hole in the hoist cable stop (305). The chamber in the hoist cable retainer contains the thrust washers and hoist cable stop, with the hoist cable stop swaged onto the cable but free to rotate about axis 275. The hoist cable retainer can either rotate freely along this axis or is press fitted, pinned or otherwise restrained from rotating along this axis.
The hoist cable pivot body can be made from aluminium or stainless steel, and the retainer made from nylon polyfluoroethylene, or other polymers or resins. The thrust washers can be made from stainless steel, oil-filled bronze, nylon, polyfluoroethylene, or similar plastics. Any number of thrust washers may be employed, or one. Other types of thrust bearings such as ball and roller pin types can also be used.
Other designs of hoist cable pivot body can be employed, including forms using slots to make hoist cable replacement easier.
For assembly, the hoist cable retainer (260) comprises two identical halves. In one form the thrust washes are slipped over the end of the hoist cable, and then the hoist cable stop is slipped over the hoist cable and swaged, leaving an indent in the cable stop. The mating surfaces of the two halves of hoist cable retainer are brought together to enclose the end of the hoist cable etc within the chamber formed by the two semi-cylindrical notches. The assembled hoist cable retainer can then be placed into a hoist cable pivot body, and two hoist cable pivot body assemblies placed in a hoist cable attachment assembly.
TestsAbout the patent
This article is an edited version of patent WO/2007/051783, published May 10 2007, and resulting from US patent application number 11/163,835. The inventors are Ray Reyes, David Schmoke and Uldis Ziemins, all of New York State, for the applicant International Business Machines Corp. (IBM) headquartered in Armonk, New York. Disclaimer
This article is an edited version of the patent and may omit legally or technically important text. To see the full patent go to www.hoistmagazine.com/patents
Fig 3 – Cross-section through the hoist cable pivot assembly Fig 3 Fig 2 – Isometric view of the hoist the hoist cable attachment assembly Fig 2 Fig 1b – A side view of the preferred embodiment of hoist system Fig 1b Fig 1a – The top (plan) view of the preferred embodiment of hoist system Fig 1a
