Conveyors: power-driven – Conveyor section – Having means to enhance the friction or adherence between...
Reexamination Certificate
2000-09-26
2002-11-19
Bidwell, James R. (Department: 3651)
Conveyors: power-driven
Conveyor section
Having means to enhance the friction or adherence between...
Reexamination Certificate
active
06481565
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to a belt conveyor system, and in particular to a conveyor system incorporating pneumatic transfer.
2. Description of the Prior Art
Belt conveyors for transferring articles are widely used in industry, including incorporation as integral parts of production lines, for a wide range of products,. Such production lines frequently have work stations at spaced intervals, at which the conveyor is required to stop, to enable working upon the conveyed article. In such instances the precise monitoring of the displacement of the conveyor belt along its path becomes very important. Present systems, which monitor travel of the conveyor belt for such location purposes by encoding the revolutions of the driving motor, suffer from inaccuracy, due to belt slippage which generates discrepancies between rotation of the driving motor and the actual travel of the belt. Inconsistencies in belt tension, with consequent variations in the rates of belt slippage, exacerbate this problem.
Certain types of article, for example lightweight articles having relatively large surface areas, such as plastic sheets, sheets of thin metal, cardboards, including cardboard blanks and blocks generally have smooth, low friction surfaces that make their transfer and handling most difficult. In some instances, such problems are accentuated, due to the relative fragility of the articles, or other factors such as a susceptibility to becoming marked on their surfaces, as a consequence of transfer to or passage along a conveyor, including encounter with hard stops and position sensing mechanical feelers.
The use of pneumatic transfer with conveyor systems is well known, and widely practiced, both in regard to belt conveyors and for agricultural purposes, such as the blowing of grain along pipes.
In the case of belt conveyors with pneumatic transfer many existing systems are characterized by their use of wide-area suction chambers, with associated unduly large air-mass displacement requirements, in the form of generated vacuum, or of compressed air. The response times of such systems is unduly slow, while the necessary air displacement is large, and excessive forces may be generated against system components, including the associated friction drag upon the belt. In other systems, the large size of certain vacuum system components necessitates unduly large belt turning radii, with correspondingly large end pulleys and related space requirements.
It should be noted that the size of a conveyor system per se, both in height and width, can bear significant economic implications, with down-sizing being most desireable. This has particular bearing on the size and location of the necessary anciliary systems associated with the conveyor. The driving systems for conveyors usually employ a chain or other transmission acting upon the end roller of the conveyor, usually at the oncoming end. Certain disadvantages associated with these earlier arrangements include unsatisfactory frictional tractive effort between the pulley and the belt, due to the limited (180 degree or less) wrap of the belt on the pulley, and shortage of space at the conveyor end, where the motor and reduction gear are located. Also, this system limits and complicates the belt tensioning arrangements, as tractive transfer at the pulley is dependent upon the extent of belt wrap about the pulley, and belt tension.
Inadequate belt tensioning also results in excessive lost motion when the drive is reversed, in order to reverse the conveyor. This exacerbates the problems encountered in achieving accurate registry of the conveyor with the associated workstations.
The handling of ferritic sheet metal production lines has involved magnetic conveyors, which employ magnets to secure the sheet to the conveyor. There is a requirement to handle sheets of different thickness, and to permit precise manipulation of them for purposes such as the welding together of two adjoining sheets of different thickness, to form welded blanks for automotive stampings, for which operations the characteristics of magnetic attachment are not well suited. Magnetic conveyors are also ineffective for handling aluminum or stainless steel sheet.
SUMMARY OF THE INVENTION
The present invention provides a modular pneumatic transfer system for conveyors, the conveyor system consisting of a plurality of individual transfer blocks, over which a perforated conveyor belt runs.
The aligned transfer blocks occupy the top of a beam that extends the length of the conveyor. The subject modular system incorporates a transfer suction block for operation with a belt conveyor, the system incorporating an air driven, reaction sensing means to determine the presence of an article upon the conveyor above the block; air-driven vacuum generation means; and a pneumatic control actuated by the sensing means to operate the vacuum generation means, to apply vacuum by way of the suction block, through the perforated belt to the over-lying section of the conveyor, in response to the sensed presence of an object upon that section of the conveyor.
The vacuum generation means consists of a multi-stage air-driven venturi, having a high pressure air jet or jets discharging through convergent-divergent nozzles, serving as an air ejector, to thereby provide a source of high volume air flow, generating a correspondingly rapid rate of high vacuum, which is applied to the suction block of a module.
In one embodiment, each module may have its respective vacuum generator. However, it will be understood that a larger vacuum generator may be used to service a number of modules, the respective object-sensing sensors being used to switch the vacuum to the related module.
The reaction sensing means consists of low pressure air jet means having an escape flow path immediately adjacent an edge of the conveyor belt, the partial blocking of which flow path by the presence of an overlying object causes a build-up in back-pressure in the air supply circuit of the sensor, sufficient to actuate an air servo-valve, thereby admitting supply air to the air displacement (vacuum generation) means. This action causes rapid displacement of air from the transfer block, and applies suction to the block, which suction is transferred through the perforated belt to the overlying object, causing it to be drawn down to the belt, and transferred.
In the preferred system embodiment the subject suction blocks are each part of an individual module, each module being essentially self contained, with its own sensing means and associated air displacement unit. This enables the provision of exceedingly compact system elements, the modular nature of which enable the provision of conveyors of virtually any desired length.
The suction blocks are selectively located to provide a desired presence-sensing and air displacement pattern in conjunction with the adjoining, superposed perforated conveyor belt. In the preferred embodiment the low pressure sensing jet forms a part of the suction block. However it will be understood that this is not imperatively the case, as the sensor may be physically located independent of the suction block.
The suction blocks are of generally small size, being made of hardened, Teflon (T.M.) coated a aluminum, or of plastic or ceramic, and being further characterized by having a shallow top groove for passage of a conveyor belt therealong. The belt fits closely in the groove, the groove sides serving to guide the belt in its passage along the beam, and to complement the sealing of the belt to the block with substantially no increase in wear or drag upon the belt or the block.
The conveyor has a series of the subject suction blocks mounted in mutual, substantially end-to-end relation upon a hollow beam extending the length of the conveyor, portions of the beam interior serving as air passages for the conveyor air system.
In operation, a respective suction block only comes into operation when the belt portion passing over that block is carrying something that obstructs the sen
Bidwell James R.
Eggins D. W.
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