US 3508591 A
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United States Patent O 3,508,591 CONTROL SYSTEM FOR SOLIDS SLICING Robert L. Johnson, Greenwich, Conn., and Edward L.
Ralston, Flossmoor, Ill., assignors to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Filed Jan. 4, 1968, Ser. No. 695,746 Int. Cl. B26d 4/56 US. Cl. 146-222 9 Claims ABSTRACT OF THE DISCLOSURE A system for obtaining a preselected number of slices from a solid to provide a batch having a desired weight. The partial batch weight is measured after each slice is added and based on the number of slices and partial batch weight a predicted terminal error signal is calculated. The predicted terminal error signal is employed in one of a number of control algorithms and control effected to vary the feed rate of the solid into the slicing mechanism such that the thickness of each slice is regulated to minimize deviation fro-m the desired batch weight.
BACKGROUND OF THE INVENTION Field of the invention This invention relates to the slicing of solids in general and more particularly to a system in which control is effected during the slicing of a batch to regulate the thickness of the slices of the batch.
Description of the prior art US. Patent 3,099,304 to Monsees et a1. provides a system in which the speed of a ram feeding a solid into a slicer is varied in accordance with whether the total weight of a previously sliced batch exceeds or is under the desired batch weight.
The system of Monsees is directed primarily to the control of a slicing operation in which slices are taken from a loaf of material which is substantially uniform along its length in both density and dimensions. The success of the control effected by Monsees is predicated on the relative uniformity of the loaf. That is, the weight of slices of a given thickness will not vary significantly from slice to slice. Monsees, therefore, can effect control of the thickness of slices of a batch being sliced based on a measurement of the weight of a previously sliced batch due to the relative uniformity of the loaf. The control system of Monsees, however, would be totally unsatisfactory where solids are to be sliced from a loaf which varies significantly along its length in either density or dimensions. Thus, this system, which relies on the uniformity of the solid being sliced, could not satisfactorily be adapted to the slicing of, for instance, bacon.
Not only does a slab of bacon vary significantly in its dimensions along its length, but additionally, the density of the bacon varies. Additionally, while loaves of materials such as ham loaves have recently been marketed which are substantially uniform dimensionally along their length, they, as in the case of bacon, still vary considerably in density. Referring to FIGURE 1, it can be seen that if a solid of the dimensions yz is sliced into pieces of thickness T, the weight of each slice is affected by the relative amounts of density A and B materials present in the slice. As illustrated in FIGURE 1, if the density of the material B is greater than that of the material A, lice S will weigh more than slice S Several systems have been devised which attempt to take into consideration variations in dimensions along the length of a solid. US. Patent 3,010,499 to Dahms et al.
utilizes a finger which gauges the thickness of the solid being sliced and modifies the feed rate of the system in accordance with variations in the thickness of the solid. However, this manual feeler cannot take into consideration variations in density and, consequently, while it may modify the thickness of the slice in a batch currently being sliced in accordance with gross variations in the dimensions of a solid, variations in density are only corrected for by adjusting the feed of the ram based on the error in terminal weight of the previous batch. That is, the weight of the partial batch is not continuously monitored and corrections made only after the previous batch has been weighed, and the assumption is therefore made that the density of the subsequent batch will be equal to that of the previous batch. Therefore, when using the Dahms system, as well as any other currently available system, the weight of each batch must still be monitored to assure that its weight equals or exceeds the desired weight. The most common method of modifying an underweight batch is to add a partial slice of solid. No adjustment is usually attempted in the case where an overweight is noted with the result that often significant amounts of solid in excess of the desired weight are given away. The net result of the Dahms system is that the frequency of occurrence of significant amounts of giveaway, as well as occurrences of underweights, is alleviated but not prevented, and the monitoring operation and attendant operator are still required.
SUMMARY Briefly, there is provided a control system for a solids slicing operation in which the partial batch weight is taken after each slice is added and a predicted terminal weight error is calculated. This predicted terminal weight error is then employed in a control algorithm to effect a change in the thickness of the next slice. In the preferred embodiment the thickness of slices is varied by varying the velocity of the feed of the solid to the slicer.
BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a view illustrating the variations in density of a dimensionally uniform block of solid;
FIGURE 2 is a plot illustrating the error which would result if the slices of the block of FIGURE 1 in a given batch were made uniform in thickness as compared with a system in which control is effected from slice to slice in accordance with the actual weight of each slice; and
FIGURE 3 is a block schematic view illustrative of the subject system.
DESCRIPTION OF THE PREFERRED EMBODIMENT Refer first to FIGURE 1. As previously discussed, not only are variations in dimensions significant along the length of a solid to be sliced, but as illustrated in FIG- URE 1, variations in density also affect the weight of a slice. It can be seen that while the loaf in FIGURE 1 is substantially uniform dimensionally, the ratio of solid A to that of B will decrease as slicing progresses. In FIG- URE 2, the solid line plot represents the resultant weight of the slices of solid in FIGURE 1 which would result if slices of uniform thickness are taken with the assumption being made that the density of material B is greater than that of material A. As illustrated by the solid line plot of FIGURE 2, the slices, while being of uniform thickness, increase in weight from slice to slice such that after the 10th or final slice is made, a significant amount of product is given away. The dotted line plot of FIGURE 2, on the other hand, is illustrative of the result which would be obtained if the deviations in weight of each slice are noted during a slicing operation and the feed rate of the solid into the slicing mechanism vatied to vary the thickness of each slice in accordance with its predicted weight. Thus, as illustrated by the dotted line plot, very little giveaway will result.
Refer next to FIGURE 3 which illustrates a typical slicing line. In FIGURE 3 a solid 10 to be sliced is moved by means of a piston 11 into a slicing mechanism generally designated as 12. The piston 11 is caused to move by application of hydraulic fluid to cylinder 32. For purposes of simplicity, the slicer 12 is illustrated as having a knife 13 which is moved reciprocally in a vertical direction. A slicer driver 14 is operative by means of shaft 15 to move the knife 13 in a vertical direction. Slices from the solid 10 fall onto a conveyor scale generally designated as 16 which is operative to provide, along line 17, a signal indicative of the Weight of the partial batch as each slice is added. The conveyor scale 16 is further operative to transport the slices of solid 18 onto a conveyor 19 for subsequent packaging. A counter 20 is shown in operative association with the slicing means 13 and is operative to provide an indication along line 21 of the number of slices of a batch which have been deposited on the conveyor scale 16. The partial batch weight signal w and the number of slices signal n appearing on lines 17 and 21 respectively, are fed into a controller 25. The controller 25 also receives input signals from an operator along lines 33 and 34. Thus, the operator selects the desired number of slices N and the desired weight W and inputs this information into controller 25. The output of the controller 25 is applied along line 26 to control the hydraulic valve 27 such that the amount of fluid flowing through line 28 from hydraulic motor 29 to cylinder 32 is regulated by controller 25. A reservoir of hydraulic fluid 30 is shown connected to hydraulic motor 29 along hydraulic line 31.
The system illustrated in FIGURE 3 is purposely made illustrative for the sake of simplicity. It should be understood that conventional components are herein contemplated for each of the components shown in the slicing line. Thus, for instance, the hydraulic system which drives the piston 11 under control of the hydraulic valve 27 is conventional. Likewise, many slicing mechanisms and conveyor scales are available. For instance, in the above mentioned Patent 3,099,304 to Monsees et al., a system is provided in which an orifice in a hydraulic flow control valve 64 is varied in accordance with the weight of a previously sliced batch such that the feed rate of the solid to the slicing mechanism is varied (col. 8, lines 19-33). The system of Monsees could be utilized in the subject system with very minor modifications, the primary one being that the weight of the partial batch must be available after each slice is added rather than being available only after the desired number of slices in a batch have been added.
The essence of applicants invention lies in the calculation of a predicted terminal error based on the deviation in weight of a partially sliced batch from a partial ideal weight. In the subject system, the operator, as above mentioned, enters the predetermined number of slices N which are to make up a complete batch and the desired batch weight W into the controller 25. The controller will initiate the feed of the solid to the slicing mechanism by opening the hydraulic valve 27 and the slicing operation begins. The initial velocity of the solid V may likewise be set by the operator. After the first slice is deposited on scale 16, its weight W is sensed and fed to the controller along line 17 and the signal indicative of the number of slices on the scale 16 is fed along line 21 to the controller. In the controller the ratio N /n is formed and this ratio is multiplied by the weight w of the partially sliced batch and the product subtracted from the desired finished batch weight W to generate an error signal e. Thus,
This error signal is a calculated prediction of the deviation in weight from the desired finished batch weight which will exist at the conclusion of the slicing operation based upon the present trend. This error signal is generated after each slice is added. This terminal weight error signal can then be employed in one of several different types of control algorithms to produce the control action V which will produce a change in the velocity with which the solid is fed to the slicer. The desired velocity of the solid to the slicing mechanism may be defined as V: V +AV (2) where:
V =the initial velocity and AV=the required velocity change to obtain substantially uniform slice weight.
AV may be calculated in several dilferent ways. AV may be defined as follows:
where K is the desired average weight per slice. Thus, Equation 1 can be rewritten as:
v=vi+vi (NHL) where:
g g=e e (since At is constant) P=the proportional gain term D=the derivative gain term.
These gain terms are determined in a well known manner by use, for instance, of the Nichols/Ziegler technique described in a publication entitled Optimum Settings for Automatic Controller, Transactions of A.S.M.E., November 1942.
While the predicted terminal Weight error e may be used directly in Equation 5, it might be desirable to filter 2 through a weighting exponential filter. The weighted trend of the weight per slice would then be the controlling factor in determining the amount of control action implemented at each step of the slicing operation. The predicted terminal weight error e would be filtered as follows:
ef th filtered error term to be used in the control equation a=the exponential filter constant (a=( 1) (as a increases, the relative weighting applied to previous values of the filtered error signal increases).
The advantage of filtering is in preventing the noise in the instantaneous predicted terminal weight error signal from imposing a control action on the slicing system in the absence of an actual trend in slice weight. Filtering of this type permits the use of larger magnitude gain terms (D and P) without inducing instability in the slicing system. Obviously, however, filtering could result in a larger terminal error.
The resulting control algorithm derived from Equations 5 and 6 would, therefore, become:
It will be obvious to those skilled in the art that the calculation of the control algorithms herein presented is straightforward and may be readily performed on various apparatus. Either analog or digital apparatus may be used. The present invention is concerned with performing a number of steps and the specific details of the apparatus used to perform these steps are not particularly relevant to the invention so long as the apparatus used is suitable for performing the various steps.
It will be further appreciated by those skilled in the art that the control algorithms presented herein in which the predicted terminal error e may be used are exemplary and that other algorithms may be derived therefrom which employ e in a different manner where different results are desired. Thus, for example, while in the control algorithms herein presented the prime concern is to provide a preselected number of slices having a total weight closely approximating a desired batch weight, in other applications it may be desirable to control not only the weight of the individual slices but additionally to control the thickness of the slices. That is; in some applications, the thickness of the slices may be monitored and action taken to prevent large variations in slice thickness regardless of weight.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.
What is claimed is:
1. A method of providing a batch of preselected number of slices from a solid which varies along its length dimensionally and/or in density, each individual slice being substantially equal in weight and the total Weight of the preselected number of slices being substantially equal to a desired batch weight, said method comprising the steps of:
continuously feeding said solid, beginning at an initial velocity, into a slicing mechanism which is operative to provide slices of a thickness proportional to the feed velocity;
obtaining a partial batch weight during said feeding by weighing a number of said slices less than said preselected number, calculating the predicted terminal deviation from the desired batch weight based on said partial batch weight and the ratio of said number of slices in said partial batch to said preselected number of slices, and
adjusting the feed velocity of said solid to said slicing mechanism during the completion of the slicing of said batch to reduce said predicted terminal deviation.
2. The method of claim 1 in which said partial batch weight is obtained, said terminal deviation calculated and said feed velocity adjusted after each slice is cut.
3. The method of claim 1 in which the terminal deviation (a) is calculated in accordance with the following equation:
4. The method of claim 2 in which said terminal deviation (e) is calculated in accordance with the following equation:
N ws where:
W =the desired batch weight,
6 N =the desired number of slices in the batch, n =the number of slices in the partial batch, w =the partial batch weight.
5. The method of claim 3 in which the feed velocity (V) of said solid to the slicing mechanism is adjusted in accordance with the following control equation:
V =the initial feed velocity,
e=the calculated predicted terminal error, k=the desired average weight per slice, N =the desired number of slices in the batch, n =the number of slices in the partial batch.
6. The method of claim 4 in which the feed velocity (V) of said solid to the slicing mechanism is adjusted in accordance with the following control equation:
V =the initial feed velocity,
e=the calculated predicted terminal error, k the desired average weight per slice, N =the desired number of slices in the batch, n the number of slices in the partial batch.
7. The method of claim 3 in which the feed velocity (V) of said solid to the slicing mechanism is adjusted in accordance with the following control equation:
V V, +Pe D 3% where:
V =the initial velocity, P=the proportional gain term, D=the derivative gain term.
8. The method of claim 4 in which the feed velocity (V) of said solid to the slicing mechanism is adjusted in accordance with the following control equation:
V=V +Pe+DZ Z where:
V =the initial velocity, P=the proportional gain term, D=the derivative gain term.
9. The method of claim 8 in which the calculated predicted terminal error signal (e) is filtered to provide a filtered error term e, prior to its use in the control equation as follows:
r= r-1+( where: e =the terminal error filtered oc=tl16 exponential filter constant (oc=0- 1) and the filtered terminal error signal is then used in the control equation as follows:
References Cited UNITED STATES PATENTS 3,010,499 11/1961 Dahms et al. 146-94 3,204,676 9/1965 Gillman 14694 3,379,234- 4/ 1968 Kasper 146-94 ANDREW R. JUHASZ, Primary Examiner Z. R. BILINSKY, Assistant Examiner US. Cl. X.R. 146-94, 158, 241