Spreader Control

This invention is directed generally to material distribution apparatus and more particularly to a novel and improved control system for a mobile material distribution apparatus such as a vehicular spreader.

Mobile material distribution apparatus such as vehicular spreaders for distributing "solid" or granular material and vehicular sprayers for distributing liquid products are known in the art. In such material distribution apparatus, it is generally desired to control the rate, usually by weight, of material distribution per unit area. Accordingly, as the vehicle travels along the ground at a given speed, the rate of distribution of material will be dependent upon both the vehicle speed and the rate at which material is delivered to distribution apparatus of the vehicular sprayer or spreader.

The rate of distribution achieved will further vary in accordance with the relative density of the product being distributed, as well as the width of the spread or spray pattern achieved by the spray nozzle or nozzles or by the "solid" or granular spreading apparatus utilized. In this regard, it will be appreciated that the control systems and variables to be considered in both liquid and solid material application are analogous. Liquid distribution may include such applications as the spraying of liquid fertilizers, weed control products or the like upon a field. Similarly, "solid" or granular material spreading may find application in the distribution of granular fertilizer or similar materials over a field as well as in the distribution of ice control chemicals in granular form upon a road or highway.

While the present invention is not so limited, the description will be facilitated by specific reference to a solid or granular material distribution apparatus or spreader. Generally speaking, control systems for such material distribution apparatus have heretofore controlled the rate of delivery of material to a spinner or similar material distribution device in accordance with the speed of the vehicle to achieve a desired spread or application rate. Such control systems take into account not only the rate of material delivery to this distribution device and the speed of the vehicle, but also the density of material being distributed and the width of the spread pattern. The foregoing variables are utilized in achieving suitable control of the rate of delivery of material to the distribution device, usually in weight per unit time. Such control assures distribution of material to a field or highway at the desired weight per unit area.

There is room for improvement in such systems, however. For example, it is generally desirable in such systems to avoid excessive "hunting" in the operation of the control system in achieving corrections of the material delivery rate. In this regard, it is generally desirable to maintain a relatively smooth operation of mechanical control members in achieving any corrections or variations in the material delivery rate. This in turn maintains the distribution or application rate substantially constant at the desired rate.

In this regard, a conveyor is generally utilized to deliver material from a hopper or other supply of material to one or more distribution devices, such as "spinners" commonly utilized in the spreading of granular material. This conveyor is provided with a variable speed motor, which is often hydraulically controlled. The hydraulic control system may further be provided with a movable member or flow control valve which controls the flow of hydraulic fluid to the conveyor drive motor and hence the speed thereof. This hydraulic control valve may be manually adjusted. However, it is the practice in such control systems to further provide an electric motor for controlling the position of the hydraulic valve remotely, for example, from the operator's station of the vehicle.

Prior art automatic control systems have generally devised various means for effecting automatic control of the position of the valve in accordance with the desired application rate of material. The aim is to achieve a substantially constant, desired application rate irrespective of changes in the speed of the vehicle. It will be recognized, however, that the hydraulic valve and associated drive motor have some inertia or resistance which prevents reliable response thereof to control signals below a certain threshold level. Hence, relatively fine adjustments thereof are often difficult to obtain.

Moreover, the hydraulic, electrical and mechanical components of such a system will experience various tolerances or variations from their nominal operating characteristics. These variations should be taken into account in achieving accurate control of material distribution or application rate.

Accordingly, it is a general object of the present invention to provide a novel and improved automatic control system for material distribution apparatus.

A more specific object is to provide such an automatic control system which controls changes in the rate of material delivery for distribution substantially in proportion to the amount of correction required so as to substantially avoid hunting.

A further object is to provide an automatic control system in accordance with the foregong objects which is capable of integrating or accumulating relatively small or fine corrections or adjustments until the sum of such accumulated corrections is of sufficient magnitude to achieve a reliable adjustment in the rate of material delivery.

A related object is to provide an automatic control system in accordance with the foregoing objects which is further capable of achieving correction of material delivery rates over a relatively broad range while maintaining a relatively fine incremental control of the corrections achieved within this range.

Briefly, and in accordance with the foregoing objects, the invention provides a novel and improved control system for a mobile material distribution apparatus. The material distribution apparatus includes ground speed sensor means for developing a signal corresponding to the ground speed thereof, distributing means for distributing the material as the apparatus moves along a given path of travel, variable rate delivery means for delivering material at a controllably variable rate to said distributing means, delivery rate sensor means for developing a signal corresponding to the actual rate of delivery of material to said distributing means, and desired distribution rate control means for developing signal corresponding to a desired distribution rate of material per unit area. The control system comprises: control circuit means responsive to said ground speed signal, to said actual delivery rate signal and to said desired distribution rate signal for periodically calculating a desired delivery rate of material to the distributing means necessary to achieve said desired distribution rate and for periodically developing a difference signal corresponding to the difference between said desired delivery rate and said actual delivery rate; and control signal producing means responsive to each said difference signal for developing a control signal. The variable rate delivery means is responsive to said control signal for varying the delivery rate of material to said distributing means in the amount necessary to achieve said desired material delivery rate, so as to achieve and thereafter maintain said desired distribution rate. The control signal producing means is further responsive to values of said difference signal within a predetermined range of values for developing said control signal as a cyclical signal having a duty cycle which varies in a predetermined fashion in accordance with the value of said difference signal. The control signal producing means is further responsive to values of said difference signal which are below said predetermined range of values for accumulating said periodically developed difference signals until the sum of the values of the accumulated difference signals is within said predetermined range of values and for thereafter developing said cyclical, variable duty cycle control signal in accordance with the value of said sum.

The foregoing as well as other objects, features and advantages of the invention will be more readily understood upon reference to the following detailed description of the illustrated embodiment together with reference to the accompanying drawings, wherein:

FIG. 1 is a diagramatic illustration of portions of a vehicular spreader with which the control system of the invention may be advantageously utilized;

FIG. 2 is a front elevation of an exemplary control panel for the control system of the present invention;

FIG. 3 is a functional block diagram illustrating the operation of the control system of the invention;

FIGS. 4A and 4B, taken together, form a schematic circuit diagram of a preferred embodiment of the control system of the invention; and

FIG. 5 is a graphical illustration of the operation of the control circuits of FIGS. 4A and 4B.

Referring now to the drawings, and initially to FIG. 1, portions of a vehicular spreader with which the control system of the invention may be utilized are illustrated. In this regard, such a vehicular spreader generally includes a material distribution apparatus which often takes the form of one or more spinners 10. This spinner 10 is provided with an inlet 12 for receiving material to be distributed thereby, and a rotatable blade-like member 14. This spinning or rotating blade 14 ejects the material through suitable apertures 15 to be spread along the path of travel of the vehicular spreader. The spinner blade 14 is preferably mounted to a rotatable axis 16 which may be driven by a suitable motor 18.

Preferably, the motor 18 forms part of a hydraulic drive system (not shown). The material supplied to the inlet 12 of the spinner or distribution member 10 is normally provided by way of a material delivery structure such as a conveyor designated generally by the reference numeral 20. In accordance with conventional practice, the conveyor 20 includes an endless member or belt 22 which is advanced by means of a suitable driveshaft 24. This driveshaft 24 is preferably driven from a suitable hydraulic motor (not shown), which forms part of the hydraulic system previously mentioned.

It will be noted that the conveyor 22 receives a supply of material from a suitable hopper or other material supply 26 (partially illustrated in FIG. 1). Additionally, in accordance with conventional practice an adjustable height outlet gate 28 may be provided for the hopper 26.

In operation, the foregoing structure distributes material over a path of travel of a mobile spreader in accordance with the ground speed of the mobile spreader and in accordance with the rate of material delivery from the conveyor 20 to the material distribution apparatus or spinner 10. Preferably, the rotation of the shaft 16 of the spinner blade 14 is held at a substantially constant or optimum rate. Hence, the amount of material by weight or volume delivered over a path of travel of the mobile spreader per unit area or per unit distance may be controlled by controlling the rate of material delivery from the conveyor 20 to the spinner 10. Such control is preferably achieved by controlling the rate of rotation of the driveshaft 24 and hence the rate of motion of the conveyor 20.

The operation of the control system of the invention will be better understood upon reference to FIG. 2 wherein an exemplary control console 40 is illustrated. This control console 40 includes a rotary function selector dial or switch 42 which is rotatable to one of a plurality of positions for selecting a corresponding function. The dial 42 functions in conjunction with the position of a SYSTEM SETUP/OPERATE toggle switch 44. When the SETUP/OPERATE toggle switch 44 is actuated to the SETUP position, a plurality of functions for setting up the control system are available for selection by the rotary dial 42, as indicated on the outer ring of function names. Similarly, when the SETUP/OPERATE switch 44 is actuated to its OPERATE position a plurality of operating functions indicated on the inner ring about the selector dial 42 are available for selection thereby. Moreover, a display panel 46 displays a numeric value corresponding to the selected function when the switch is either in the OPERATE or SETUP mode. In the illustrated embodiment, this display panel 46 includes four, seven-segment display characters. The display 46 also displays various malfunction indications when in the OPERATE mode.

A SPREAD toggle switch 48 may be left in its center or AUTOMATIC position for automatically controlled spreading operation, or alternatively may be switched to its OFF position or CHANGE DECIMAL PT. position so as to manually control the speed of the conveyor 20. In conjunction with this latter operation of the toggle switch 48 a further CONTROL MANUAL/NORMAL toggle switch 50 is provided for selecting either manual or automatic operation of the control system. A final toggle control switch 52 is designated a DIGIT SELECT/SET/RESET switch and is utilized to set the values of certain set-up functions selected by the rotary selector dial 42. These selected values are indicated on the display 46 to accomplish setup or calibration of the control system.

Having briefly described the control panel 40, the operation thereof for setting up or calibrating of the control system of the invention and thereafter in monitoring the spreading operation will now be described. Initially, with the control toggle 44 in the SETUP position, the selector dial 42 may be rotated to its first, APPL. RATE position (on the outer ring), whereupon the operator may enter the desired application rate in pounds per acre (or kilograms per hectare) which is simultaneously shown on the digital display 46. The right-most digit of the display will be automatically energized when the toggle 52 is placed in the SELECT position. This digit will advance incrementally when the toggle 52 is held at the SET position. When the right-most digit of the display 46 has advanced to the desired number the toggle 52 is again moved to the SELECT position to hold the digit at this number. The process may be repeated using the toggle 52 to individually SELECT and then SET each successive digit to the left in the display 46 until the desired application rate is displayed in the format XX.XX hundreds of pounds per acre. The CHANGE DECIMAL PT. position of the SPREAD switch 48 is used to place the decimal in the position indicated for the application rate selection function. The displayed number is set into the system when the dial 42 is moved to another position.

The next position of the selector 42 (moving in a clockwise direction) is designated APPL. RATE, accompanied by upwardly and downwardly directed arrows. This position is utilized to permit changes, while in operation, of the application rate previously set by some desired increments in pounds per acre. For example, if the operator wishes to have the option of increasing or decreasing the previously set application rate by 50 pounds per acre increments, while spreading, the DIGIT switch 52 is utilized as described above to enter 0050 in the display 46. No decimal point is utilized in conjunction with this setting.

It will be noted that the DIGIT switch also includes upwardly and downwardly facing arrows adjacent the SELECT and SET positions thereof. When the SYSTEM switch is in the OPERATE position, each operation of the digit switch 52 to the "up" position indicates that the incremental change (e.g. 50 pounds per acre) set in as just described is added to the application rate previously set in the application rate position. Conversely, each time the digit switch is moved to the "down" position, this increment is subtracted from the application rate previously selected.

The SPREADER CONSTANT position of the dial 42 is utilized to set in a gate flow constant for various heights of the gate 28 described above. The appropriate number or constant for a given spreader apparatus will be provided by the spreader manufacturer. For example, if the spreader constant is 32.72, the digits 3272 are entered in the display 46 using the DIGIT switch as described above and the decimal point is placed in the correct position using the SPREAD switch as described above.

Next, a conversion factor corresponding to the density of the product to be spread in pounds per cubic foot entered on the digits of the display 46 in the same fashion, in the format XXX.X using the DIGIT and SPREAD switches. The next position (outer ring) of the dial 42 is designated TEST SPEED. With the dial 42 in this position a value is entered on the display 46 in the same fashion described above. This value indicates in miles per hour the value of an internally generated ground speed signal which is utilized as described later in making stationary system checks or troubleshooting the system. The operator may enter the nominal or expected ground speed of the mobile spreader to be used during the spreading operation.

With the dial 42 in the SPREAD WIDTH position, the width of the spread pattern being used is entered in the display 46 in feet. This entry is in the format XXX.X, using the DIGIT and SPREAD switches as described above.

The next position of the dial 42 (outer ring) is designated FINE TUNE. In this position, the operator may make percentage adjustments in application rate to compensate for overall spreader tolerances or variations from nominal characteristics. This will normally be done after observing operation of the spreader at a given application rate setting. The allowable range of adjustment is plus or minus 9 percent. Hence, only a single digit is entered in the display 46 in the fashion described above.

When the dial 42 is in the DIST CAL position, the toggle 52 may be utilized as before to set the display 46 to the number of pulses per unit distance produced by a particular ground speed sensor to be used with the mobile spreader. Alternatively, the vehicle may be driven over a measured course (400 feet in the illustrated embodiment) and the toggle 48 actuated to AUTOMATIC at the start of the course and to OFF at the end of the course, to achieve automatic setting of this number. The control system will now correctly calculate the ground speed from the pulses received from the particular ground speed sensor associated therewith.

During the spreading operation, the toggle 44 is moved to the OPERATE position, the toggle 50 is moved to the NORMAL position, and the toggle 48 is set to the AUTOMATIC position. The dial 52 is now operative for selecting the operating functions indicated on the inner ring thereof, as described below.

When the dial 42 is moved to the APPL. RATE position (inner ring), the current application rate, based upon the present vehicle speed and present speed of the conveyor 20 will be displayed in pounds per acre on the display 46. This figure should match the application rate selected in the setup mode, absent transient conditions.

The SPEED position of the selector 42 causes the display 46 to indicate the current vehicle or spreader ground speed in miles per hour. Rotation to the next clockwise position TOTAL APPL. displays a cumulative count of the total quantity of material, in pounds, applied by the spreader since the last resetting of an associated accumulator. Similarly, the next or AREA position of the selector 42 causes the cumulative area covered in acres to be displayed. Either of the foregoing accumulators may be reset to zero by moving the selector 42 to the associated TOTAL APPL. or AREA positions while in the OPERATE mode, and holding the DIGIT switch 52 in the lower or RESET position. This will cause an audible alarm, to be described later, to sound. When the audible alarm ceases, the selected accumulator has been reset to zero.

With the toggle 44 still in the OPERATE mode, the remaining positions of the selector dial 42 are for system test purposes. When the spreader vehicle is stationary, the dial 42 may be rotated to the TEST SPEED position to verify the test speed value set in during the SETUP mode. With the selector dial 42 in the TEST APPL. RATE position the digits of the display 46 indicate the application rate in pounds per acre, based upon the test speed and other constants entered during the SETUP mode. It will be recognized that the application rate actually achieved during operation may vary from this TEST APPL. RATE due to variations in the actual density of the product, or in the tolerances in the operation of the conveyor 20, gate 28 and spinner 10. All of these factors may vary somewhat in operation from the nominal values thereof.

With the selector in the TEST RPM position, the actual speed of the monitored drive component of the conveyor 20, which may be the shaft 24 previously described, or some other convenient monitoring location, is indicated in RPM. Finally, with the selector 42 in the TEST COUNTS position the revolutions of the conveyor speed monitored shaft are counted and accumulated. Both the TEST RPM and TEST COUNTS indications are selected while the spreader vehicle is stationary and are based upon the test speed and other constants entered during the SETUP mode.

The TEST APPL. rate switch is used in the OPERATE mode to initially set the control system to the desired application rate. With the spreader vehicle stationary, the desired operating speed is first entered in the SET UP mode with the selector switch in the TEST SPEED position. Thereafter the switch 44 is placed in the OPERATE position and the selector 42 in the TEST APPL. RATE position. The spread switch 48 is then moved between the OFF and CHANGE DEC. PT. positions until the desired application rate is displayed in the display 46. Once the desired application rate is displayed, the selector dial 42 is placed in the SPEED position and spreading may be commenced. If it is desired to operate with the control 50 in the MANUAL position, a constant operating speed must be maintained. However, with the control 50 set to the NORMAL position, the control system achieves the desired application rate, taking into account any incremental adjustments or percentage variations entered as described above, without regard for changes in the ground speed of the spreader vehicle.

As briefly indicated above, the SPREAD CONTROL switch 48 may also be utilized to achieve manual control of the operation of the conveyor 20. In this regard, movement of this switch 48 to the AUTOMATIC position normally causes the control system to automatically regulate the speed of the conveyor 20 to achieve the desired application rate set in during the SETUP procedure, (with switch 44 set to OPERATE and switch 50 set to NORMAL). The control system also takes into account any variations desired in conjunction with the APPL. RATE "up/down" setting or the FINE TUNE PERCENT setting as described above. Spreading of material may be halted by moving the SPREAD switch 48 to its OFF position.

However, the switch 50 is moved to the MANUAL position, the SPREAD switch functions to directly control an electric motor for opening and closing of a hydraulic valve. As mentioned previously, this hydraulic valve controls the speed of a hydraulic motor which drives the conveyor 20. Movement of the switch 48 to the OFF position causes the valve to be moved toward its closed position, decreasing the conveyor speed. Movement of the switch 48 to the CHANGE DEC. PT. position causes the valve to be moved toward its open position, increasing the speed of the conveyor. If the switch 48 is left in its center or AUTOMATIC position, the valve remains in the position to which it was last set.

In addition to the foregoing, as mentioned above, the display 46 is capable of displaying a number of failure or malfunction messages. The message LoHP is displayed when in the OPERATE mode if the contents of the hopper 26 are below a predetermined level. In this regard, a suitable level sensor is provided. This message will be displayed for approximately three seconds accompanied by sounding of an audible alarm. The audible alarm may be eliminated by actuating the SPREAD switch 48 to the OFF position.

The message APEr (application error) is displayed in the OPERATE mode when a hydraulic control valve which regulates the speed of the conveyor 20 is fully opened and the control system can no longer further regulate the speed of the conveyor 20. This message is also accompanied by sounding of the audible alarm and will alternate with the readout of the selected function.

The message ShCr (short circuit) is displayed in either of the SETUP or OPERATE modes should a short circuit occur in the control system. The message is accompanied by a continuous audible alarm.

The message FAIL is displayed in the OPERATE mode if all of the required constants have not been entered by the operator as described above. Additionally, failure of the internal memory components, to be described later, or removal thereof from the required power source, or other electrical malfunctions effecting memory will cause display of the FAIL message. This message is also accompanied by a continuous audible alarm. Additionally, the FAIL message may also be displayed if the constants entered in the SETUP mode are beyond the operational parameters of the control system.

Referring now to FIG. 3, a functional block diagram indicates functional aspects of the operation of the control system of the invention. In this regard, various means and functions are accomplished by the use of a microprocessor or microcomputer component and associated memories and registers to be described with reference to FIGS. 4A and 4B. It will be understood that various means, functions, calculations and signals produced, to which reference is made herein, are embodied in such processor or computer components and in various memories, registers and programming, associated therewith.

As illustrated in FIG. 3, a ground speed signal fg comprises a signal produced by any of a plurality of conventional ground speed sensors 58 as known in the art. This ground speed signal fg is fed to a counter/summer 60 which in the illustrated embodiment accumulates pulses from the ground speed sensor 58 and reads the total of the accumulated pulses at 2.5 millisecond intervals. The counter/summer 60 then determines the sum of 50 such counter readings, which is fed out as a signal f'g to a further summer block 62. This latter summer block 62 sums the last eight digital words produced by the counter/summer 60 at 125 millisecond intervals.

A first multiplier 64 multiplies the output of the summer 62 by a factor Kg which represents the number of pulses produced by the particular sensor utilized per unit distance travelled. This factor was entered during the SETUP mode, in the distance calibration procedure described above. This product is here designated Vg.

A further similar multiplier 66 multiplies the foregoing by a factor, K which represents the net result of the remaining constants set in during the SETUP mode. These constants will be remembered to include the desired application rate, the spreader gate constant, the material density and the spread width. Any percent variation of application rate, entered as previously described, is also factored in to this constant K. The output of the multiplier 66 is applied to one side of an error junction 68. This resultant output from multiplier 66 comprises a signal corresponding to a desired speed of conveyor 20. Stated alternatively, this signal corresponds to a desired rate of delivery of material from conveyor 20 to spinner 10 for achieving the desired application rate.

Rotation sensor 30 produces a signal at a frequency Fc in response to rotation of the driveshaft 24 or other monitored part of the conveyor 20. This signal Fc includes the effect of a sensor constant Kc which represents the number of pulses produced by the sensor 30 per revolution of the driveshafts 24. The signal Fc is fed to a counter/summer block 72, which like the similar block 60 described above, reads the counted sensor pulses at 2.5 millisecond intervals and sums 50 such readings. The output of the counter/summer 72 is designated as fc and is fed to a multiplier block 74 which multiplies by a factor of 4 to produce an output signal here designated as f'c, which is fed to the opposite side of the error junction 68. This signal f'c corresponds to the actual speed of conveyor 20 and hence to the actual rate of delivery of material to spinner 10. An additional summing block 75 sums eight successive counts/sums of fc from counter/summer 72, for use in the display functions previously described.

Accordingly, the error junction 68 produces an error or difference signal as illustrated in block 76 and here designated as En. This difference signal En therefore corresponds to the difference between the desired rate of material delivery and the actual rate of material delivery to the spinner 10. In accordance with a preferred embodiment, a further resultant error signal Eout is produced in a block 78 by adding to a calculated error En the immediately previously calculated error En-1 divided by four. This block 78 then also updates the value of error En-1 by adding to it the value of the present error En.

The resultant signal Eout is further modified in a functional block 80 to produce a resultant output drive signal M, which is derived by multiplying Eout by additional factors P and Km.

As illustrated in block 82, the factor Km is chosen to be equal to the output of sensor 30 in response to rotation of the shaft 24 when under full drive condition. The factor P is a gain factor and as also illustrated in block 82, is a function of Vg, the product of fg and Kg, which is the output of block 64 described above. It will be noted that the factor Km is the inverse of the constant or characteristic of the system associated with a given spreader vehicle.

In this regard, as diagrammatically illustrated in FIG. 3, and as previously described, the conveyor shaft 24 is preferably driven by a suitable hydraulic motor 84 at a speed controlled by a suitable hydraulic valve 86. The position of this hydraulic valve 86 is in turn controlled by an electric motor 88 which receives drive signals from a suitable power driver circuit 90. The output signal M derived by the block 80 feeds the power drive circuit 90.

It will be recognized that any given combination of the components including the conveyor shaft 24 the hydraulic drive motor 84, hydraulic valve 86 and electric motor 88 and power driver circuit 90 will in the aggregate respond with a given characteristic or constant to a given signal M produced by the output block 80. This constant is here designated as the inverse of the constant Km when operating under a full or maximum drive signal M to the power driver 90. That is, causing any chain of components from the power driver 90 to the shaft 24 to operate at a maximum rate of change will produce a repeatable, measurable result. Hence, the constant comprising the inverse of Km may be readily determined by producing this full drive condition to the foregoing component. Accordingly, addition of constant Km as a factor in the output signal M eliminates the effect of this constant which will of course vary from one set of drive components to another.

The addition of the gain factor P recognizes that it is desirable to change or correct the speed of the conveyor 24 at a somewhat faster rate as the spreader vehicle speed decreases, to achieve a relatively constant application rate.

In operation, the conveyor sensor 30 develops a signal corresponding to the actual rate of delivery of material from the conveyor 20 to the distributing apparatus or spinner 10 (see FIG. 1). The ground speed sensor 58 develops a signal corresponding to the actual ground speed of the mobile spreader vehicle or other apparatus. Functional blocks 60, 62, 64 and 66 form a portion of a calculating circuit for periodically calculating the desired delivery rate of material by the conveyor to achieve the desired distribution or application rate of material in weight per unit area.

Functional blocks 72 and 74, the error junction 68 and functional block 76 (representing the function of error junction 68) form a further portion of calculating means for periodically calculating the difference between the desired delivery rate and developing a corresponding difference or error signal En. Remaining functional blocks 78 and 80 form a control signal producing means responsive to the error or difference signal En for developing a control signal.

The variable rate conveyor drive system comprising hydraulic motor 84, hydraulic valve 86, electric motor 88 and power driver 90 is then responsive to the control signal developed by blocks 78 and 80 for varying the rate at which material is delivered from the conveyor 22 the distributing means or spinner 10 to achieve and maintain the desired distribution rate.

As will be more fully described with reference to FIG. 5, when the error or difference signal En is of a value within a predetermined range of values, the blocks 78 and 80 develop the control signal as a cyclical signal having a duty cycle which varies substantially proportionately with the value of the difference or error signal En. This is referred to as the "proportional" control range. However, when the error or difference signal En is below this predetermined range of values, the block 78 and 80 function to accumulate the periodically developed error or difference signal until their sum is within the predetermined range of values. Thereafter, the blocks 78 and 80 develop the cyclical, variable duty cycle control signal in accordance with the value of the sum of error or difference signals obtained.

The foregoing summing of error or difference signals can be referred to as an integral control procedure. This procedure is especially useful in cases where the error or difference signal developed is not of sufficient magnitude to cause a reliable effect upon the operation of the control system comprising the hydraulic motor 84, valve 86, electric motor 88 and power driver circuit 90.

Additionally, when the error or difference signal En reaches a value above the predetermined range of values for "proportional" control described above, the control signal producing blocks 78 and 80 produce a constant, maximum level control signal output rather than a cyclical signal. This predetermined maximum level output signal is maintained until the value of the error or difference signal En falls back within the predetermined "proportional" control range of values.

Reference is next invited to FIG. 5 wherein the details of operation of the block 80 in producing the cyclical, control duty cycle or proportional control signal is illustrated in graph form. In accordance with a preferred form of the invention, a periodic, proportional error correction cycle is designated generally by a time interval indicated by arrows 100 along a time axis or scale 102. This interval 100 is further subdivided into five equal intervals 104, along the time axis or scale 102. Each interval 104 is further subdivided into ten equal sub-intervals 106.

In accordance with the preferred form of the invention, the time length of the overall time interval 100 is 125 milliseconds. Accordingly, the interval 104 is 25 milliseconds in duration and the sub interval 106 is 2.5 milliseconds in duration.

Referring also to FIG. 4, the resultant output control signal M to the power driver 90 produced by the block 80, when in the proportional control range, is a series of pulses of controlled duty cycle, one pulse in each of the five intervals 104. Accordingly, the block 80 further acts to divide the value of signal M by five, so as to produce in each interval 104 a pulse signal of width or duty cycle equal to substantially 1-5th of the value of the signal M. The pulse widths of these signals are further capable of being subdivided into incremental values in increments of the sub-interval 106.

Hence, in each interval 104 a pulse signal is produced of a pulse width or duty cycle equal to the number of increments 106 obtained by dividing the value of M by five, or in other words the integer part of the quotient M/5. Any fractional part of the quotient results in the addition of one additional increment 106 to the pulse width or duty cycle of the pulse produced in one or more of the successive periods or intervals 104, starting with the first interval 104 and in as many additional successive intervals as required to include this fractional part. In other words, one increment 106 is added to the duty cycle of the control signal in each of the periods or intervals 104 up to the number of added increments equal to the dividend of the fractional part of the quotient defined by the value of the signal M divided by the number of intervals or periods, which in the illustrated embodiment is the quotient M/5.

Referring now to FIGS. 4A and 4B a microcomputer and associated circuits comprising the control system functionally illustrated in FIG. 3 are shown in circuit schematic form.

Referring initially to FIG. 4A, a suitable power supply circuit for the remaining circuits of the invention is designated generally by the reference numeral 110. This power supply circuit produces a plurality of regulated DC voltages as generally indicated at various outputs thereof. Additionally, the power supply circuit is provided with three monitored terminals 112, 114 and 116, which as will be presently described, provide means for monitoring of the power supply by the microcomputer component illustrated in FIG. 4B.

The power supply 110 is coupled with a suitable power source such as a twelve volt DC vehicle battery at terminals 118, 120 thereof. Additionally, the power supply may be coupled for energization from the vehicle ignition switch (IGN.) at a terminal 122. This terminal 122 is also coupled with a terminal 124 which runs to the function selector switch 42 as will presently be seen in FIG. 4B. The function selector switch 42 includes a "power off" position. Accordingly, a return terminal 126 from the function selector 42 is provided to the power supply 110. Preferably, however, suitable regulated DC voltages are maintained from the power supply 110 to microcomputer memory and other related circuit components of FIG. 4B without regard for the position of the selector switch 42.

Suitable inputs from the conveyor sensor 30, ground speed sensor 58 and a suitable hopper level sensor (not shown) for the hopper 26 as mentioned above are also illustrated in FIG. 4A. These signal inputs provide suitable filtering for respective signals Fc, fg and Hlev (hopper level), which are fed to the like-labeled inputs in FIG. 4B, to which reference is now invited.

The majority of the functions illustrated and described above with reference to the diagram of FIG. 3 are carried out by a microcomputer component 200. In the illustrated embodiment this microcomputer 200 comprises a single chip microcomputer of the type generally designated MK3875/42. However, the counting functions of the respective counter/summer components 60 and 72 of FIG. 3 are carried out by a pair of integrated circuit counter components 202 and 204 which are coupled to receive the respective Fc and fg input signals from the input circuits of FIG. 4A. The inputs to the respective counters 202 and 204 are provided with suitable buffering and voltage pull-up components as well.

In the illustrated embodiment the counters 202 and 204 comprise seven-stage ripple carry binary counters of the type generally designated CD4024BE. The respective Q outputs of the respective counters 202 and 204 feed respective input terminals or ports of the microcomputer 200 which are designated by their respective port numbers and bit numbers as indicated in FIG. 4B.

Three additional inputs of the microcomputer 200 immediately below the counter 204 receive inputs for indicating the positions of the respective switches 44 and 52 which are again illustrated in circuit schematic form. Two additional inputs therebelow may be left in an open circuit condition or jumpered to circuit ground to indicate whether English or metric units are to be utilized in the control system and to indicate whether granular material such as fertilizer or ice control material such as salt are being distributed or applied by the associated spreader vehicle.

The previously mentioned power supply monitoring terminals 112, 114 and 116 are coupled to suitable terminals for monitoring by the microcomputer 200 as indicated at the lower right-hand portion thereof. The function selector switch 42 is again illustrated in FIG. 4B and the position thereof is determined by the microcomputer 200 by way of inputs fed therefrom to suitable input ports 1-0, 1-1 and 1-2. Additionally, the power supply terminals 124 and 126 from the ignition input 122 of FIG. 4A and circuit ground are coupled to suitable points of the selector switch 42. The hopper level sensor signal Hlev will be seen to feed an input 1-6 of the microcomputer 200 by way of a suitable pull up and buffering circuit.

The microcomputer 200 also receives at port 1-4 a monitored lead from the electric motor 88, which is again illustrated in FIG. 4B. Additionally, the power drive circuit 90 is illustrated in circuit schematic form, as are the circuit connections of the respective switches 48 and 50 of FIG. 1. The circuit of motor 88 is additionally provided with a double pole, double throw control switch 206 for selectively taking the motor 88 out of circuit, whereby the hydraulic control valve 86 (see FIG. 3) may be operated manually if desired. The operation of this further switch 206 is detected by the microcomputer 200 at "motor monitor" input 1-4 thereof. Additional inputs 5-2 and 5-3 of the microcomputer 104 detect operation of the respective switches 48 and 50.

It will be seen that the control signal output from the microcomputer 200 to the power drive circuit 90 comprises a pair of outputs 0-4 and 0-5 of the microcomputer 200. These outputs feed the non-inverting input terminal of each of a pair of operational amplifiers (op amp) 208, 210. The inverting input terminals of the respective op amps 208 and 210 are coupled to a suitable DC reference voltage.

In operation it will be recognized that the op amp 208 and associated output 0-4 will be operative when it is desired to rotate the motor in one direction, whereas the opposite direction of rotation of motor 88 is obtained by energization of the output 0-5 and associated op amp 210.

The respective directions of rotation of motor control movement of the hydraulic valve 86 (see FIG. 3), in two directions for opening and closing thereof, respectively. Respective opening and closing of the hydraulic valve 86 in turn respectively increases or decreases the speed of hydraulic motor 84 which drives the conveyor 20.

The display 46 in the illustrated embodiment comprises a liquid crystal display panel and is energized by the microprocessor by way of a suitable liquid crystal display driver component 220, which in the illustrated embodiment comprises a circuit component of the type generally designated HLCD0438.

In order to fully illustrate a specific embodiment of the invention, an exemplary program for the microcomputer 200 is reproduced on the following pages.

While the invention has been illustrated and described herein above with reference to specific embodiments, the invention is not limited thereto. Those skilled in the art may devise various alternatives, changes and modifications upon reading the foregoing descriptions. The invention includes such alternatives, changes and modifications insofar as they fall within the spirit and scope of the appended claims. ##SPC1## ##SPC2## ##SPC3## ##SPC4## ##SPC5## ##SPC6## ##SPC7## ##SPC8## ##SPC9##