This invention relates to apparatus for the high-speed weighing and conveying of objects, and is especially applicable to such weighing and conveying of open-topped containers of readily-flowable products.
Various forms of apparatus are known in the prior art for accomplishing the accurate yet rapid sequential weighing of objects which are moved over a weighing device in a rapidly moving train. Such high speed weighing is especially useful, for example, in connection with the mass production of products in containers, especially where it is important or necessary to be sure that each such container does in fact contain at least the weight of the product which it is represented to contain. One such type of container with respect to which the invention will be particularly described is a soup can nearly filled with soup. Other examples include, without limitation, cans of other types of food products, food packaged in containers other than cans, cans of oil, or containers of other non-food products. In some cases it may also be desirable to weigh objects other than containers of product, for example any object having a predictable exterior configuration which it will retain during normal processing and handling.
While weighing of objects one at a time at slow rates has been possible for a long time, for mass production purposes one is often interested in weighing objects at high rates such as from 300-600 objects per minute, which is 5 to 10 objects per second, and to do so reliably has presented a substantial technological challenge.
One known manner for accomplishing such high speed weighing is described and claimed in U.S. Pat. No. 3,800,893 of Joseph D. Ramsay and George R. Weaver, filed Sept. 5, 1972 and issued Apr. 2, 1974 for Weighing Apparatus and Method. In this weighing system, a pair of parallel motor-driven chains carry a train of objects to be weighed across the spring-mounted weigh platform of a weigh cell having a platform which is at all times free to oscillate or vibrate vertically in response to the weights of the objects, and which senses the instantaneous vertical displacement, vertical velocity and vertical acceleration of the vertically-vibrating weighing platform, derives the second-order differential equation of motion of the platform along the vertical direction in response to the weight of the object and chain, and from this computes the weight of each object; the vertical motion information described above may be derived over the course of a few vibrations of the platform, or in as little as 1/4 of a cycle of such vibration. The maximum vertical displacement of the weigh platform from its rest position during the weighing operations is extremely small, typically less than 0.001 inch, and less than 0.005 inch in nearly all applications of practical interest.
U.S. Pat. No. 4,151,890 of Alec B. Smith, filed Oct. 17, 1977, issued May 1, 1979 and entitled WEIGHING APPARATUS describes and claims an improved version of the high-speed weighing device of U.S. Pat. No. 3,800,893 which is simpler in form and less expensive than the embodiment of 3,800,893 and is also capable of accomplishing weighing of objects passing over it at time intervals of only a small fraction of a second and with very small vertical displacements of the weigh platform during weighing, again typically less than about 0.001 inch and in substantially all practical cases less than about 0.005 inch.
In both of the above-described previously known high-speed weighing devices, the chain passes over the weigh platform and is weighed along with the objects to be weighed; the weight of the chain is, in effect, subtracted out to produce the desired signals representing object weights. The objects may be placed at random along the chain prior to passing over the weigh platform so long as they are not placed so closely together as to interfere with their individual weighings.
While the above-described two types of high-speed small-deflection weighing devices have proved very useful and advantageous in many applications thereof, both involve the weighing of the chains which pass over the weigh platform, and this can be the source of some weighing error, particularly due to small changes in the degree of tension or slack of the chains, which can produce at least a small variation in the downward force exerted by the chain upon the weigh platform at different times.
In addition, in certain important applications it is desirable to maintain positive indexing of the positions of the objects to be weighed, so as to assure that each object to be weighed has a definite known position at any time, and usually so that the speeds and spacings between the objects are constant while traversing the weighing platform.
More particularly, in some cases it is desirable to employ, downstream or following the weighing device, apparatus which must be fed with each of the objects at precise predetermined times; as an example, the feed-time critical downstream device may be a closer for applying tops to be weighed, open-topped cans containing soup; or it may be some other device which requires operation at a predetermined periodic rate and at predetermined times, such as a labeller, a machine for marking the object, or even a packing device which presents packing positions at predetermined times and to which the weighed objects must be delivered at exactly these times. In some cases one may wish to use a rejector designed to reject from the train of weighed objects those outside of the permissible weight range, and to use for this purpose a type of rejector which anticipates when each object will reach it, and thus relies upon supply thereto of the weighed objects at predetermined predictable times. In the above-described arrangements of the prior art, if the objects to be weighed are initially placed onto the conveyor with random or non-uniform spacings, and/or become variably spaced because of the action of accelerating conveyors and/or because of slippage on the conveyor during their travel to, across or from the weighing device, then the necessary accurately-timed delivery of the objects to apparatus downstream of the weighing device will not be achieved; in some cases the objects may even "back up" and block egress of following objects from the weighing device.
What is desired, instead, is a system which will provide positive indexing in that the position of each object as it leaves the weighing device is positively maintained in known relation to the operation of the corresponding critically-timed downstream apparatus, or as it is sometimes stated, the apparatus "knows" the exact position of each object at least from the time it is leaving the weighing device to the time at which it is received by the downstream apparatus which operates with critical timing.
Further, in certain cases it is important to be able to convey the objects to be weighed to, across and from the weighing device very smoothly, i.e. without sudden acceleration in any direction and in a fixed angular orientation. A typical example of such application occurs in the high-speed weighing of open-topped containers filled, at least partially, with a flowable product, for example open-topped cans filled with soup. High-speed check-weighing of a train of such cans of soup enables automatic rejection of those cans in the train having weights outside of prescribed limits. In such case it is important that no soup be lost from any can via its open top, between filling and closing of the can, and therefore that the filled, open-topped cans be translated very smoothly from filler to closer via the high-speed weigher and via the rejector, if one is used.
U.S. Pat. No. 2,661,091 of N. G. Maloney, issued Dec. 1, 1953 and entitled APPARATUS FOR WEIGHTS CLASSIFICATION discloses a system for the balanced-beam check-weighing of cans of product, by sliding them across a weighing table in response to pushing by cross-bars extending between a pair of endless chains located on laterally opposite sides of the weighing platform. The cans are loaded into position between the cross-bars by what is referred to in the patent as a conventional conveyor, and shown in the patent as comprising a downwardly-inclined surface, without a showing of further detail. Downstream of the weigher, the cans which are out of weight specification are diverted from the train, and those which are acceptable are diverted onto another conveyor at a different angle. The weighing table is supported on a float immersed in a liquid, and its downward acceleration against the buoyancy of the float is sensed and used as an indication of weight compared to a standard. Between each such weighing, the weighing table is forced to return to a rest position flush with the delivery table and the exit table, before another can is received for weighing.
While the weighing system of the reference may be suitable for certain purposes, it appears to have inherent drawbacks for other purposes. First, it appears to be unsuitable for the high-speed weighing of open-topped cans nearly filled with a readily-flowable product such as soup, because of the spillage which would occur. Such spillage would occur because of the tilt of the cans on the inclined conveyor feeding the cross-bar conveyor, because of the mechanical shock in the transfer between these two conveyors, and because of the sudden angular diversion of the acceptable cans onto another conveyor downstream of the weigher. From this it is properly inferred that the cans in the reference must either be closed cans, or else they must not be nearly filled with a readily flowable product.
Secondly, in the system of the reference the speed of weighing is inherently slowed by the requirement that the weighing table be returned to its upward rest position and locked in this position while each new can is moved onto the weighing table.
In addition, there is no teaching in the cited reference of how transfer of the cans can be accomplished without at least momentarily relinquishing positive smooth control of the motion of the cans. There is also no teaching of how the cross-bar conveyor might be interfaced with other conveyors, for example a screw conveyor, to effect smooth, indexed delivery of cans to the cross-bar conveyor or smooth, indexed delivery of cans from the cross-bar conveyor to an exit or downstream screw conveyor.
Accordingly, it is an object of this invention to provide new and useful apparatus for the conveying and weighing of objects.
A further object is to provide such method and apparatus which provides high speed weighing of objects with a high degree of accuracy.
A further object is to provide such apparatus which accomplishes high speed, accurate weighing of objects while maintaining them in positively indexed positions.
Another object is to provide a system for receiving containers to be weighed from the output of a filler, subjecting them to high-speed weighing, and delivering them in properly timed synchronism to a container-processing device, such as a container closer, for example.
A still further object is to provide apparatus for the movement of objects to be weighed, at predetermined fixed spacings, across a high speed weighing device, while retaining the accuracy and reliability of which the weighing device itself is capable.
Another object is to provide rapid delivery to, over, and from a weighing device, of objects to be weighed while maintaining them in predetermined relative positions, and to do so with a smoothness of motion such that, even if the objects comprise open-topped containers nearly filled with flowable material, there will be no spillage of the material from the container.
Another object is to provide apparatus for the high-speed weighing of each of a train of objects, in which there is no effect exerted upon the motion of the weighing platform by the conveyor of the objects, in which the conveying of the objects to, across and from the weighing platform is smooth and without sudden accelerations, and in which the objects remain positively indexed during their conveyance to, across and from the weighing platform.
Still another object is to provide apparatus for the filling of open-topped cans with liquid product at one station, closing of the top of the cans at another station, and high speed conveying of the filled open-topped cans from the filler to the closer by way of a high-speed weigher, while moving the cans smoothly and without spillage from filler to closer, and while maintaining positive indexing of the cans throughout, and without weighing any part of the conveying apparatus.
A further object is to provide a new and useful conveyor and weigher arrangement for moving objects to be weighed across a weigh platform.
Another object is to provide the latter type of arrangement, to and from which objects can be conveyed smoothly and with positive indexing by one or more screw conveyors.