Conveyors: power-driven – Conveyor arrangement for selecting among plural sources or... – By loading or unloading section at selected one of a...
Reexamination Certificate
1997-11-04
2001-03-27
Valenza, Jospeh E. (Department: 3651)
Conveyors: power-driven
Conveyor arrangement for selecting among plural sources or...
By loading or unloading section at selected one of a...
C198S805000, C198S810010, C104S284000
Reexamination Certificate
active
06206170
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally to package sorting conveyors and, more particularly, to a control system for such a conveyor system.
(2) Description of the Related Art
Conveyor systems having a number of individual carrying carts have been commonly used for many years to carry and sort packages or other items, such as mail. For example, U.S. Pat. No. 5,054,601 to Sjogren et al. discloses a package sorting conveyor comprised of a train of tilt tray carriers coupled in tandem to form a continuous loop. Each carrier includes a pivotally mounted tilt tray normally maintained in an upright position. The carriers are moved around the loop by a series of motors spaced around the loop. Branching out from the loop are outfeed chutes or the like for receiving packages from the carriers. When a particular carrier holding a particular package to be sorted reaches a selected outfeed chute, an actuator tilts the tray to dump the package into the outfeed chute. Another example of a typical package sorting conveyor is disclosed in International PCT Application Number PCT/DK90/00047 of Kosan Crisplant A/S.
One significant disadvantage of conventionally designed package sorting conveyors is that conventional conveyor carriers laterally tilt only on a horizontal axis parallel to the direction of conveyor travel. While this accomplishes the objective of dumping the package from the carrier into an outfeed chute or the like, the package is often roughly tumbled or rolled, sometimes damaging the package's contents. One reason for this is that the packages typically are unloaded from the carrier while still traveling forward at the same speed as the conveyor. Thus, packages tend to slam into a forward retaining wall of the outfeed chute before sliding down the chute. Another problem with conventional laterally tilting conveyors is that because the packages are moving forward at full speed when they are unloaded into the outfeed chute, the outfeed chute must be relatively wide so that packages do not miss the chute and fall off the conveyor past the chute. This often unnecessarily increases the overall size of the conveyor system.
U.S. Pat. No. 4,744,454 and an improvement thereto, U.S. Pat. No. 5,086,905, both to Pölling, disclose previous attempts to remedy this problem of rough handling by conventional laterally tilting conveyor carriers. Both of these patents to Pölling disclose a conveyor element for a package conveyor that includes a tilting carrier tray mounted to be rotatable about two swivel axes. A first swivel shaft extends obliquely downward from the underside of the carrying tray and is in turn connected at an angle to the end of a second swivel shaft extending obliquely upwards from a base support part of the conveyor element. Together, the two swivel shafts form a “V” that points in the direction of conveyor travel. Both of the swivel shafts lie in the vertical plane of symmetry of the conveyor element when the carrier tray is disposed in its upright position.
Because the carrier tray of Pölling rotates about two oblique axes, the carrier tray can be tilted not only lateral on a horizontal axis, but is moved through a geometrically complex spatial reorientation during package discharge. This allows for more gentle placement of a package on an outfeed chute than can be accomplished using conventional conveyor trays that laterally tip on only a horizontal axis. The Pölling conveyor element more gently handles the packages by imparting some degree of rearward velocity to the packages as they are discharged, which, when added to the forward velocity of the conveyor system, results in the packages' forward velocity during discharge being less than that of the conveyor system itself.
However, the conveyor elements of both of Pölling's patents are unduly complicated and intolerant of manufacturing discrepancies. In fact, the second Pölling conveyor element (U.S. Pat. No. 5,086,905) was invented in an attempt to simplify the original design disclosed in the first Pölling patent (U.S. Pat. No. 4,744,454), which had proved to be too expensive and complicated to manufacture efficiently. As a result of this complexity and cost, the Pölling devices have not enjoyed significant commercial acceptance and success.
One solution to this problem is shown in co-pending U.S. application Ser. No. 08/632,012, filed Apr. 15, 1996, now U.S. Pat. No. 5,836,436 issued Nov. 17, 1998, the entire disclosure hereby incorporated by reference.
Another problem which is more recent has arisen from the movement of the industry from chain driven sorters to linear induction motor (LIM) driven sorters. LIM's are extremely quiet and have fewer moving parts which require maintenance. However, such systems are not trouble free and have a tendency to overheat when run at lower speeds. It is now believed that the conventional practice of using an AC inverter to control by varying frequency produces transients which contribute to this heating problem which occurs predominately in linear induction motors. In addition, in such “chain-less” systems it has proven more difficult to accurately determine the speed and position of the trays since there is no physical connection between the trays and the motor.
Thus, there remains a need for a new and improved control system for a tilting conveyor system that substantially eliminates the heating problem when the LIM is run at slower speeds while, at the same time, accurately determines the speed and position of the trays.
SUMMARY OF THE INVENTION
The present invention is directed to a control system for a sorting conveyor for transporting objects and unloading objects at one or more unloading stations adjacent the conveyor. Generally, the sorting conveyor includes: a conveyor track; a train of the tilting conveyor carts connected end-to-end; and a power source for moving the conveyor carts on the conveyor track. Each of the tilting conveyor carts includes a trailer frame base. The trailer frame includes a roller structure for engaging the conveyor track, a driven member responsive to the power source, and a hitch mechanism for connecting each tilting conveyor cart to an adjacent conveyor cart. The conveyor cart also includes a carrying tray for holding the objects and a two-axis tiltable support apparatus for supporting the carrying tray above the trailer frame base and for allowing tilting of the carrying tray towards at least one side of the conveyor to unload objects into unloading stations on at least one side of the conveyor.
The two-axis tiltable support apparatus includes an upper support structure joined to the carrying tray, a lower support structure joined to the trailer frame base, and an angled pivot structure connecting the upper support structure to the lower support structure along a pivot axis, wherein the pivot axis is disposed at an angle to a line of travel of the sorting conveyor so as to impart two axial components to the tilting of the carrying tray.
A tilting mechanism tilts the carrying tray on the tiltable support apparatus to thereby unload objects into one of the unloading stations adjacent the conveyor.
According to the present invention, the conveyor system includes a plurality of selectively energized linear induction motors for driving the train along the conveyor track. A speed control system including a fixed-frequency, variable-voltage transformer is connected to a portion of the linear induction motors for varying the speed of the train.
In the preferred embodiment, the speed control system includes a fixed frequency AC electrical power supply and a fixed-frequency, variable-voltage transformer connected to the power supply. A preselected number of the linear induction motors are connected directly to the fixed frequency AC electrical power supply and the remaining linear induction motors are connected to the transformer. A voltage controller is connected to the transformer for receiving a speed setting input signal and sending a variable voltage signal to the transformer
Fortenbery J. David
Kissel Gregory P.
Mantissa Corporation
Rhodes & Mason PLLC
Valenza Jospeh E.
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