US3606954A - Control system for stacking equipment - Google Patents

Abstract

A NOVEL BED BLENDING SYSTEM IS DISCLOSED WHICH PRODUCES UNIFORM THICKNESS LAYERS IN THE BED. A CONVEYOR FEEDS A CONVENTIONAL TRAVELING STACKING BOOM WHICH DEPOSITS MATERIAL ON THE BED AS IT TRAVELS. THE BED IS FORMED, LAYER BY LAYER, ON SUCCESSIVE PASSES OF THE STACKER. THE CONTROL SYSTEM MONITORS THE FEED RATE AND CONTROLS THE STACKER SPEED TO PROVIDE FOR CONTROLLED LAYER THICKNESS IN THE BED AS CONVEYOR SPEED AND MASS FEED VARY. THE CONTROL SYSTEM IS SO DESIGNED THAT A LAYER OF THE BED IS UNIFORM ALONG THE BED BUT IS CAPABLE OF PROVIDING VARIATIONS IN BED LAYER THICKNESS FROM ONE LAYER TO THE NEXT.

Description

Sept. 21,, 1971 s. c'. MAYER 1 5 3 CONTROL SYSTEM FOR sucxmc mumu'an'r Filed Nov. 24, 1969 gsheets-sheet 1 INVENTOR. erald C. Mayer agan Sept. 21, 1971 e. c. MAYER CONTROL SYSTEM FOR STACKING EQUIBIENT 2 Sheets-Sheet 2 Filed Nov. 24; 1969 INVENTOR.

W M W& m .M a? M y QB United States Patent Office Int. Cl. B65g 57/00 US. Cl.' 214-10 4 Claims ABSTRACT OF THE DISCLOSURE A novel bed blending system is disclosed which produces uniform thickness layers in the bed. A conveyor feeds a conventional traveling stacking boom which deposits material on the bed as it travels. The bed is formed, layer by layer, on successive passes of the stacker. The control system monitors the feed rate and controls the stacker speed to provide for controlled layer thickness in the bed as conveyor speed and mass feed vary. The control system is so designed that a layer of the bed is uniform along the bed but is capable of providing variations in bed layer thickness from one layer to the next.

BACKGROUND This invention relates to an improvement in bed blending systems. Systems of this type have been in use for some sixty years all over the world. U. S. Pat. No. 677,677 issued July 2, 1901 to Messiter is an example of the early systems.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a plan view of the layout of a modern bed blending system;

FIG. 2 is an elevation view of the system illustrated in FIG. 1;

FIG. 3 is a plan view of an early bed blending system;

FIG. 4 is an elevation view of the system illustrated in FIG. 3;

FIG. 5 is a cross section of FIG. 4;

FIG. 6 illustrates the stacker conveyor; and

FIG. 7 is a schematic diagram of the control system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Today, bed blending is used for a variety of purposes. In one application, it can be used to average out raw ore taken from a mine so as to obviate the necessity for expensive and wasteful selective mining. In another type of use, a bed blending system can be used to mix a plurality of ingredients to a particular recipe in preparation for further processing. Such a recipe allows the processing plant to be operated for efi'icient processing with a minimum of maintenance and adjustment. This also allows use of highly efli cient and, if desired, automated processing plants with further savings in costs.

The Messiter patent, mentioned above, provides a good showing of the theory behind bed blending which will now be explained. FIGS. 3, 4 and 5, reproduced from Messiter, show respectively plan, elevation and cross section views of a bed blending system. The material, such as iron ore, coal, cement, etc., is fed into the system on conveyor b. FIGS. 3, 4, and 5 show diagrammatically how the material travels down the conveyor to the tripper device a and is laid onto the pile f. The continous back and forth travel of the tripper device results in a plurality of layers being formed. FIG. shows that as the material is deposited, a roughly triangular pile is formed. As the pile grows, the material is deposited at the apex and falls down both sides of the pile. If now the pile is sliced transversely of its length, an accurate sample of all the material 3,606,954 Patented Sept. 21, 1971 in the pile is obtained. That is, the slice represents a weighted average of that which went into the pile. Although perfect blending is not usually achieved, a Well engineered system will approach this figure, within commercial tolerances. The remaining element of the system provides a device which performs the slicing operation to reclaim the desired result. The Messiter patent employs plow-like blades, g, connected to a chain to continuously slice the pile at its base. As the resulting product is reclaimed, the plow-chain combination moves down the bed. The resulting mix, which is now blended so that particle size and chemical analysis are uniform, is carried out on conveyor k.

A modern bed blending system is shown in FIGS. 1 and 2.. A plurality of beds 1 are shown. Raw material is brought in by distributing conveyor 2. The material can then be switched to one of the stacking and reclaiming conveyors 3, 4, or 5 from distributing conveyors 2, 6, or 7. The illustration shows the incoming material on stacking conveyor 4. Tripping trailers 8 and 9 are provided for discharging material from conveyor 4 onto the stacker conveyors 19. As illustrated, trailer 8 is not in use and trailer 9 is operatively associated with the stacker 11. The stackeris capable of feeding one or both piles directly adjacent its path. As stacker 11 moves back and forth along the bed, the material ejected forms the piles 1. Once the bed is built up and it is determined to be ready for reclaiming, the reclaimer 12 is put into operation. The reclaimer 12 may be of the bucket wheel type shown, for example, in Dischinger, US. Pat. 3,069,027, issued Dec. 18, 1962. As explained in that patent, the reclaimer continuously slices the pile and carries off the resulting blended product. FIG. 1 illustrates reclaiming conveyor 3 carrying off the blend to collecting conveyor 13 for subsequent use.

As can be seen, the theoretical basis of bed blending depends on the transverse slice accurately portraying, in physical size and chemical content, the material comprising the entire bed. Since the very objective of these systems is to blend materials, one begins with at least two different materials to be blended. Each is, in turn, fed to the stacker and laid on the bed. In order for each transverse slice to be an accurate cross section of the material in the entire bed, rigid control must be exercised to ensure that the layers do not vary longitudinally. The three variables that control layer thickness are (a) belt loading, that is the density of material on the conveyor; (b) belt speed; and (c) stacker speed. The product of belt loading and belt speed is mass flow, which, when divided by stacker speed results in density in the bed. Since the area of the bed is fixed, this is directl proportional to the layer thickness. And, in fact, the prior art does show attempts at control of these factors. The only prior alternative was manual control of both stacker speed and belt speed. In the present invention, a bed blending system is disclosed which is capable of coping with situations in which the belt loading is variable and not susceptible to control. Furthermore, applicant has recognized that the only requirement for effective blending is unvarying layer thickness along the length of the bed and that, in fact, variations of layer thickness from one layer to the next are not only immaterial but such variations may serve to obviate still another problem.

This problem relates to non-integral numbers of layers. I

in most cases is within acceptable commercial tolerances.

However, when blending to a recipe, which may call for the equivalent of 3 layers, a problem is present which the prior art could not cope with. Discarding the non-integral portion will throw off the recipe by 14%.

Using the material as /2 layer will result in a 33 /2% I variation in slices. Either variation is too great to be 7 commercially acceptable. The control system of the present invention solves this problem by assuring longitudinal uniformity, yet providing for variations in layer thickness between layers. In the example given above, the excess /2 layer would be spread out over the entire bed at /2 normal thickness. This will provide the proper recipe and proper blending.

Another advantage of the present invention is the fact that the control system readily lends itself to remote operation which, in turn, is capable of automation if desired.

FIG. 6 shows the stacker 11 used in the present invention. The stacker 11 travels on rails 14. A conventional frame 15 supports the operating elements on wheels 16. Preferably each wheel 16 is driven by a separate AC. motor, however, only one motor 16 is shown in FIG. 7 for the sake of clarity. The stacker trailer 9 supports a conveyor 4 so as to discharge ontostacker conveyors 19 mounted on boom arms 20. Boom arms 20 may be raised or lowered by conventional cable haulage systems 21 so as to clear the top of the bed as the bed increases in height. It should be recognized that conventional stackers can often have only one arm which pivots about a vertical axis so as to serve beds on either side of the stacker. Likewise, an automatic stacker can be made in the form shown in FIGS. 3 through 5 wherein material is simply discharged onto the stockpile by a conveyor which extends over the center of the pile and wherein the conveyor is provided with a powered tripper for discharging material from the conveyor and which tripper is adapted to move back and forth between the ends of the pile. Thus, for the purpose of this invention, it is immaterial what type of stacker is employed. Regardless of the type of stacker that is employed, this invention requires that the Weight of the material being discharged therefrom be monitored by a scale such as indicated by reference numeral 22. Thus, scale unit 22 is shown on both boomsof stacker 11 as well as also being indicated in the vicinity of the discharge point of the stacker shown in FIG. 4. For the systems shown in FIGS. 1, 2, 6 and 7, the scales 22! are mounted near the outer edge of the booms 20 and measure the material being fed by stacker conveyors 19. Since boom arm 20 is not always horizontal, any gravity scale must be compensated for deviations from the horizontal to give accurate readings. For this reason, and others, applicant prefers to use a nuclear scale. Scales of this type are available commercially. One

scale that could be used is available from Ohmart, Inc. of Cincinnati, Ohio.

FIG. 7 shows the control system of the present invention. The nuclear scale 22 comprises sensing heads 32 and 33. Power is supplied by supply 31 and the signal from sensing head 33- is amplified and linearized by amplifier 23. Sensing heads 32 and 33 are positioned so that the material on stacker conveyor 19 is measured. The output of scale amplifier 23 is connected to one input of analog multiplier 24. Tachometer 30 is mechanically coupled to stacker conveyor 19 and senses the speed thereof. The tachometer 30 produces an electrical analog signal proportional to the speed of the conveyor 19. This signal provides the second input to analog multiplier 24. The output of analog multiplier 24 is fed to potentiometer 25. Wiper 34 of potentiometer 25 picks off a selected portion of the signal fed to the potentiometer by the multiplier 24. The signal picked off by Wiper 34 is fed as one input to the error amplifier 26. Tachometer 29 is mechanically coupled to one of the stacker driving motors 28. This tachometer provides an output signal proportional to the speed of the stacker 11. The signal from tachometer 29 provides the other input to error amplifier 26. Amplifier 26 comprises the two input signals and the output is proportional to the difference of these signals. The output of error amplifier 26 is fed to variable frequency control 27. This converts the error signal into a suitable form for controlling the stacker drive motors 28. One suitable form of variable frequency control 28 is commercially available from Ramsey Controls, Inc., Mahwah, NJ. Although FIG. 7 illustrates only one motorwheel combination, it should be understood that the stacker 11 is normally provided with at least four or more driving wheels. Usually each driving wheel is associated with a separate motor, so generally four motorwheel combinations will be present.

In operation, the stacker conveyor 19, operatively associated with the stacker trailer 9 delivers material to the bed. The material passes between sensing heads 3233- of the nuclear scale 22. The scale relies on the reduction in transmission of radiation between sensors 32-33 to indicate the mass or weight of material. Power supply 31 and amplifier and linearizer 23- provide a signal proportional to the mass or weight of material on the belt. This signal may be quantized in terms of pounds per feet. Analog multiplier 24 multiplies this by the conveyor speed signal from tachometer 30. The output of multiplier 24 is a signal proportional to mass flow which can be expressed as pounds per minute. The output from multiplier 24 is then applied to potentiometer 25. The potentiometer 25 is calibrated in terms of bed layer thickness as a reciprocal function of its resistance. That is, maximum layer thickness corresponds to minimum resistance or the lower end of the potentiometer as shown in FIG. 7. With the wiper 34 at the midpoint, the result would be a layer twice as thick as if the wiper were in the upper or position.

At any one setting of potentiometer 25, the control system operates as follows. The nuclear scale output indicates the belt loading factor. Tachometer 30 indicates belt speed. The output of analog multiplier 24 is proportional to mass flow which can be expressed in pounds per minute. The setting of potentiometer 25 corresponds to a preselected layer thickness. This selected portion of the output of multiplier 24 is compared with a signal proportional to the speed of the stacker 11 as developed by tachometer 29. The comparison is effected by error amplifier '26 in a conventional manner. Variations in the amplitude of either or both inputs will vary the amplitude of the output of error amplifier 26. In order to provide for direct motor control, this amplitude signal is converted into a variable frequency signal by variable frequency control 27. The output of variable frequency control 27 consists of a signal whose frequency is related to the output of error amplifier 26. This variable frequency signal is suitable to control motors 28. This mode of operation will cause the stacker speed to compensate for changes in mass flow so as to maintain constant layer thickness. However, as explained above, it is sometimes desirable to vary layer thickness from one layer to the next. For instance, assume it is desired to provide a layer of /2 normal thickness. If normal thickness corresponds to the lower quarter point of the potentiometer, that is the 25% point, a layer of half this thickness can be provided by raising the potentiometer to the 50% point. In effect, this will double the voltage delivered by the potentiometer to the comparison circuit. In order to drive the error voltage to zero, which corresponds to the output of amplifier 26, the stacker speed will have to double. With other factors being equal, this doubling of stacker speed will produce a layer which is /2 the thickness of the standard layer. Of course, if either of the other factors vary the control system will compensate for such variation by adjusting stacker speed to nullify the effect of any such unwanted variation.

Potentiometer 25 then presents the operator with a readilly controlled parameter which renders control of layer thickness a simple matter. Inasmuch as the only connections between the control system and the blending system itself are electrical, this is readily adaptable to remote operation. Automation can also be provided for simply. A program can be written out in advance specifying which materials are to be delivered on particular passes of the stacker. A counter would then control the supply of material to conform to the program. If layer thickness were desired to vary, relays could be used to pick the proper layer thickness off of potentiometer 25 in response to the program and the count stored in the counters. Such a system would completely eliminate the operators.

The present system provides for remote operation of of the bed blending system. With one setting, choosing predetermined layer thicknes, the operator sets in motion the system. Variations in mass flow, which are unavoidable are automatically compensated for by the system by varying the stacker speed. The layer thickness then is unvarying longitudinally which is the sine qua non of the bed blending system. The control system also provides for readily variable layer thickness if necessary or desirable when blending to a particular recipe.

I claim:

1. In a bed blending system including a conveyor system for feeding material to a stacker,

said stacker feeding said material to a bed,

a control system for controlling the speed of said stacker comprising,

means to determine the rate of flow of material from the stacker,

means to measure the sped of said stacker traveling along said bed, and

means for comparing said speed with said rate of flow and control means for adjusting the speed of said stacker in accordance with said comparison.

2. The control system of claim 1 wherein said means to determine the rate of flow of material from said stacker comprises a nuclear scale mounted on said stacker producing a first electrical signal proportional to the mass of material passing a point on said stacker,

means for producing a second eletrical signal proportional to the speed of a conveyor on said stacker, and

multiplier means for multiplying said first two electrical signals to produce a third electrical signal proportional to said rate of material flow from said stacker.

3. The control system of claim 2 in which said means to measure said stacker speed produces a fourth electrical signal proportional to said stacker speed and where said means for comparing comprises a difference amplifier which produces a signal proportional to the difference between said third and fourth electrical signals.

4. In the control system of claim 3 which includes means to vary the thickness of the layer of material in the bed, said means comprises a potentiometer across which said third electrical signal is produced, said potentiometer being calibrated in terms of layer thickness, the wiper of said potentiometer feeding a selected portion of said third electrical signal to said difference amplifier, the selected portion being in inverse proportion to said selected layer thickness.

References Cited UNITED STATES PATENTS 2,750,023 6/1956 Meissner 198--36 3,43 0,751 3 /1969 Bateson 19=8--39 3,441,039 4/1969 Rawson 239- GERALD M. FORLENZA, Primary Examiner J. MANNIX, Assistant Examiner US. Cl. X.R. 19 8-486

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