Abstract:
A cable attachment assembly, a hoist and a transportation system using the cable attachment assembly. The cable attachment assembly including: a plate pivotable about a first axis; first and second pivot assemblies pivotable about respective second and third axes, the first, second and third axes parallel to each other; a first cable retainer in the first pivot assembly, the first cable retainer adapted to rotateably retain an end of a first cable in the first cable pivot assembly, the first cable rotatable about a fourth axis; a second cable retainer in the second pivot assembly, the second cable retainer adapted to rotateably retain an end of a second cable in the second pivot assembly, the second cable rotatable about a fifth axis; wherein the fourth and fifth axes parallel to each other and the fourth and fifth axes are perpendicular to the first, second and third axis.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the field of hoisting apparatuses; more specifically, it relates to a multiple hoist cable, multiple attachment point hoisting apparatus. 
   BACKGROUND OF THE INVENTION 
   In manufacturing production parts are often transported around the factory from station to station. In some applications, the parts are transported using an overhead lift system. Hoists are used to raise the parts from a station and then the hoist and parts are moved by the overhead rail system to the next station, where the parts are lowered by the hoist system. In one type of hoist, a support platform is suspended by six hoist cables connected to three points on a platform adapted to grasp the parts or a container holding the parts. The hoist cables are reeled up or down simultaneously the same distance and at the same rate. Such hoist systems are not subject to side-to-side sway and twisting and are used where delicate parts and high location precision is required. However, in such systems, the hoist cables easily develop kinks or could unravel from internal tension fatigue failure which can cause the platform to tilt and the reels to bind, adversely affecting the precision of the delivery or damaging the parts. Replacement of hoist cables in such hoist systems is also expensive and time consuming. 
   Therefore, there is a need for improved hoist cable hoist systems with improved hoist cable life. 
   SUMMARY OF THE INVENTION 
   A first aspect of the present invention is a hoist cable attachment assembly for attaching a pair of hoist cables to a payload gripping mechanism, comprising: a plate pivotable about a first axis; a first hoist cable pivot assembly pivotable about a second axis and a second hoist cable pivot assembly pivotable about a third axis, the first and second hoist cable pivot assemblies disposed on opposite sides of the plate, the first, second and third axes parallel to each other; a first hoist cable retaining means in the first pivot assembly, the first hoist cable retaining means adapted to rotateably retain a first end of a first hoist cable of the pair of hoist cables in the first hoist cable pivot assembly, the first hoist cable rotatable about a fourth axis; a second hoist cable retaining means in the second pivot assembly, the second hoist cable retaining means adapted to rotateably retain a first end of a second hoist cable of the pair of hoist cables in the second hoist cable pivot assembly, the second hoist cable rotatable about a fifth axis; wherein the fourth and fifth axes are parallel to each other and the fourth and fifth axes are perpendicular to the first, second and third axis; and a bracket for attaching the hoist cable attachment assembly to the payload gripping mechanism. 
   A second aspect of the present invention is a hoist system for lifting and lowering a payload, comprising: a lifting mechanism comprising three pairs of hoist cable drums disposed on a first frame, the pairs of hoist cable drums disposed at angles of about 120° to each other, each hoist cable drum of each pair of hoist cable drums longitudinally aligned to a same axis; a payload gripping mechanism having three hoist cable attachment assemblies attached to a second frame, the hoist cable attachment assemblies disposed at angles of about 120° to each other, each hoist cable attachment assembly having a first set of three parallel axes and a second set of two parallel axes, the first set of axes perpendicular to the second set of axes, each hoist cable attachment assembly having a pair of hoist cable pivot assemblies; three pairs of hoist cables, a first end of a first hoist cable of each pair of hoist cables attached to a first hoist cable drum and a first end of a second hoist cable of each pair of hoist cables attached to a second hoist cable drum of one of the three pairs of co-joined hoist cable drums, a second end of the first hoist cable of each pair of hoist cables attached to a first hoist cable pivot assembly and a second end of the second hoist cable of each pair of hoist cables attached to a second hoist cable pivot assembly of one of the three pairs of pivot assemblies; and wherein each hoist cable attachment assembly is pivotable about a center axis of a corresponding the first set of three axes, each hoist cable pivot assembly of each pair of hoist cable pivot assemblies is pivotable about a different outer axis of the corresponding the first set of three axes, and each hoist cable of each pair of hoist cables is rotatable about a different axis of a corresponding the second set of two axes. 
   A third aspect of the present invention is a transportation system for lifting and lowering a payload, comprising: an overhead rail transportation system; a lifting mechanism coupled to the overhead rail transportation system, the lifting mechanism comprising three pairs of hoist cable drums disposed on a first frame, the pairs of hoist cable drums disposed at angles of about 120° to each other, each hoist cable drum of each pair of hoist cable drums longitudinally aligned to a same axis; a payload gripping mechanism having three hoist cable attachment assemblies attached to a second frame, the hoist cable attachment assemblies disposed at angles of about 120° to each other, each hoist cable attachment assembly having a first set of three parallel axes and a second set of two parallel axes, the first set of axes perpendicular to the second set of axes, each hoist cable attachment assembly having a pair of hoist cable pivot assemblies; three pairs of hoist cables, a first end of a first hoist cable of each pair of hoist cables attached to a first hoist cable drum and a first end of a second hoist cable of each pair of hoist cables attached to a second hoist cable drum of one of the three pairs of co-joined hoist cable drums, a second end of the first hoist cable of each pair of hoist cables attached to a first hoist cable pivot assembly and a second end of the second hoist cable of each pair of hoist cables attached to a second hoist cable pivot assembly of one of the three pairs of pivot assemblies; and wherein each hoist cable attachment assembly is pivotable about a center axis of a corresponding the first set of three axes, each hoist cable pivot assembly of each pair of hoist cable pivot assemblies is pivotable about a different outer axis of the corresponding the first set of three axes, and each hoist cable of each pair of hoist cables is rotatable about a different axis of a corresponding the second set of two axes. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1A  is top view and  FIG. 1B  is a side view of a hoist system according to the embodiments of the present invention; 
       FIG. 2  is an isometric view of a hoist cable attachment assembly according to the embodiments of the present invention; 
       FIG. 3A  is a top view of a hoist cable pivot assembly according to the embodiments of the present invention; 
       FIG. 3B  is a cross-section through line  3 B- 3 B of  FIG. 3A ; and 
       FIG. 4  is an assembly drawing of a hoist cable in a hoist cable retainer according to the embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1A  is top view and  FIG. 1B  is a side view of a hoist system  100  according to the embodiments of the present invention. In  FIGS. 1A and 1B , hoist system  100  includes a lifting mechanism  105  and a payload gripping mechanism  110  connected by hoist cables  115 . 
   Lifting mechanism  105  of hoist system  100  includes a frame  120  on which are mounted three winches  125  arranged at angles of about 120° to each other around a central axis  130 . Frame  120  is rotatable about central axis  130 . Each winch  125  includes a motor  135  for turning a pair of hoist cable drums  140  disposed on opposite side of the motor. Each pair of hoist cable drums  140  has a common longitudinal axis  145 . There is a slot  150  in frame  120  under each hoist cable drum  150  through which corresponding hoist cables  115  may pass. Hoist cable drums  140  are grooved to receive hoist cables  115  as the hoist cables are wound onto the hoist cable drums. 
   Payload gripping mechanism  110  of hoist system  100  includes a frame  155  to which are attached three hoist cable attachment assembles  160 . Hoist cable attachment assemblies  160  are arranged at angles of about 120° to each other similar to the arrangement of winches  125 . Each hoist cable attachment assembly  160  is adapted to connect a pair of hoist cables  115  from the same winch  125 . Each hoist cable attachment assembly is attached to frame  155  by a bracket  165 . Each hoist cable attachment assembly  160  is attached to each bracket by a main pivot pin  170  and is free to pivot about the main pivot pin, which has a longitudinal axis parallel to a plane defined by frame  155 . Each hoist cable attachment assembly  160  is provided with an adjustment screw  175  for adjusting the rotational resistance about main pivot pin  170 . 
   Hoist cables  115  are under tension and provide six horizontal force components in three non-parallel planes. In order to raise and lower frame  155  relative to frame  120 , all six hoist cable drums  140  are rotated simultaneously by motors  135 , thereby causing each hoist cable  115  to wind or unwind from its corresponding hoist cable drum. Alternatively, a single motor may be adapted to drive all six drums  140 . 
   Hoist system  100  is illustrated in conjunction with a rail transport system. For example, in the transport system shown, rails  180  are arranged to run to various locations or tools in a factory. Frame  120  is attached to rails  180  by a bracket  185  through dollies  190 . Such rail systems are well known, particularly in the semiconductor industry. 
   Frame  155  is fitted with grippers  195  for gripping a payload. In one example, grippers  195  are configured to grip a carrier containing semiconductor wafers, and location sensors  200  for locating the payload and positioning grippers  195  over the payload. Location sensors may be mechanical, electro-mechanical, or optical-mechanical. 
   In one example, hoist cables  115  comprise wire rope with a plastic coating. As such, hoist cables  115  are electrically conductive and may be used to transport signals between lifting mechanism  105  and payload gripping mechanism  110  of hoist assembly  100 . To such end, a transceiver  205  is mounted to frame  155  and electrically connected by electric wires  210  to hoist cables  115  by clamps  215  (after stripping away a portion of the plastic coating). Hoist cable drums  140  may be fitted with electrically conductive and isolated rings and brushes adapted to electrically couple hoist cables  115  to corresponding wires  220  and thence to a transceiver  225 . Transceiver  225  is in communication with a controller in the factory for controlling positioning of hoist system  100  relative to stations and tools in the factory. The signals applied to hoist cables  115  may be analog signals, digital signals or power. 
     FIG. 2  is an isometric view of hoist cable attachment assembly  160  according to the embodiments of the present invention. In  FIG. 2 , hoist cable attachment assembly  160  includes a front plate  230  and a back plate  235  held apart by a spacer  240 . Main pivot pin  170  passes through holes in front plate  230 , back plate  235  and spacer  240  and is fixed to bracket  165  (see  FIG. 1B ). A pair of hoist cable pivot assemblies  245  are held between front and back plates  230  and  245  by hoist cable pivot pins  250 A and  250 B (not shown, see  FIG. 3A ) on opposite sides of main pivot pin  170 . Each hoist cable pivot assembly  245  includes a hoist cable pivot body  255  and a hoist cable retainer  260 . For each hoist cable pivot assembly, respective hoist cable pivot pins  250 A extend through a circular hole in front plate  230  into hoist cable pivot body  255  and are fixed in the hoist cable pivot body. Similarly, respective hoist cable pivot pins  250 B (not shown, see  FIG. 3A ) extend through back plate  230  into hoist cable pivot body  255  and are fixed in the hoist cable pivot body. Hoist cable attachment assembly  160  is held together by screws  265 . 
   Main pivot pin  170  extends along a longitudinal axis  265  and the entire hoist cable attachment assembly  160  is free to pivot about axis  265 . Each pair of pivot pins  250 A and  250 B is aligned along a common longitudinal axis  270  running through respective hoist cable pivot pins  250 A and  250 B (not shown, see  FIG. 3A ) and each hoist cable pivot assembly  245  is free to pivot about its respective axis  270 . Axis  265  and both axes  270  are parallel to each other. In one example, axis  265  and axes  270  lie in the same plane. 
   Each hoist cable  115  is free to rotate along a respective axes  275  passing through hoist cable retainer  260 . Each axis  275  is perpendicular to axes  265  and both axes  270 . Both axes  275  are parallel to each other. 
     FIG. 3A  is a top view of hoist cable pivot assembly  245  according to the embodiments of the present invention and  FIG. 3B  is a cross-section through line  3 B- 3 B of  FIG. 3A . In  FIGS. 3A and 3B , hoist cable retainer  260  fits into a chamber  280  in hoist cable pivot body  255 . An upper portion of hoist cable retainer  260  extend through a cylindrical hole  285  in hoist cable pivot body  255 . Hoist cable retainer  260  also includes a chamber  290 . Hoist cable  115  passes through a cylindrical hole  295  in hoist cable retainer  260 , through thrust washers  300 A and  300 B and into a cylindrical hole in a hoist cable stop  305 . Thrust washers  300 A and  300 B and hoist cable stop  305  are contained within chamber  310  of hoist cable retainer  260 . Hoist cable stop  305  is swaged onto hoist cable  115 . Hoist cable  115  and hoist cable stop  305  are free to rotate about axis  275 . In one example, hoist cable retainer  260  is free to rotate along axis  275 . In one example, hoist cable retainer  260  is press fitted, pinned, or otherwise restrained from rotating along axis  275 . 
   Hoist cable pivot body  255  may advantageously be fabricated from aluminum or stainless steel. Hoist cable retainer  260  may advantageously be fabricated from nylon, polyfluoroethylene, other plastics, polymers or resins. Thrust washers  300 A and  300 B may advantageously be fabricated from stainless steel, oil filled bronze, nylon, polyfluoroethylene, other plastics, polymers or resins. While two thrust washers are illustrated in  FIG. 3B , more than two, one or none may be employed. Alternatively, various other types of thrust bearings including ball and roller pin bearing may be used in place of or in conjunction with thrust washers  300 A and  330 B. 
   The design of hoist cable pivot body  255  may be considered exemplary and other designs may be used, as for example, designs incorporating slots to make replacement of hoist cable  115  easier. 
     FIG. 4  is an assembly drawing of hoist cable  115  in hoist cable retainer  260  and according to the embodiments of the present invention. As is apparent from  FIG. 4 , hoist cable retainer  260  comprises two identical half  260 A and  260 B having respective mating surfaces  315 A and  315 B. In one example, thrust washers  300 A and  300 B are slipped over an end  320  of hoist cable  115 . Next, hoist cable stop  305  is slipped over end  320  of hoist cable  115  and swaged, leaving an indent  325  in the hoist cable stop and fixing hoist cable  115  in hoist cable stop  305 . Next mating surfaces  315 A and  315 B of respective halves  260 A and  260 B of the hoist cable retainer are brought together enclosing end  320  of hoist cable  115 , hoist cable stop  305  and thrust washers  300 A and  330 B within a chamber formed by the two semi-cylindrical notches  290 A and  290 B. 
   The assembled hoist cable retainer may then be placed into a hoist cable pivot body, and two hoist cable pivot body assemblies placed in a hoist cable attachment assembly. 
   In tests conducted by the inventors, a set of hoisting systems similar to the hoisting system of the embodiments of the present invention, except that the hoist cable was constrained from any rotation within the hoist cable pivot body experienced hoist cable failures (a kink or an unraveled wire) at the rate of about 1 hoist cable per system per year or about every 20,000 lift cycles, a cycle being one up and one down movement. A hoisting system according to the embodiments of the present invention wherein the hoist cable was free to rotate within the hoist cable pivot body experienced no hoist cable failures after four years of testing or after about 150,000 lift cycles. 
   Thus the present invention provides an improved hoist cable hoist systems with improved hoist cable life. 
   The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.