Abstrict A control system for a rock crusher in a rock crushing plant operates
the crusher at optimum efficiency for increasing the throughput
of the crusher. The horsepower of the motor that drives the crusher
is sensed, and the level of rock within the crusher bowl is sensed,
and these sensed conditions are inputted into a programmable logic
controller. The programmable logic controller correspondingly adjusts
the feed rate of a feeder that supplies rock to the crusher. The
controller also commands a bypass component positioned between the
feeder and crusher adjacent the mouth of the crusher for providing
an immediately responsive control of the feed rate being delivered
to the crusher.
Claims I claim:
1. A control system for a rock crusher operating in a rock crushing
plant, comprising:
the plant having a feeder, and first conveyor means for conveying
rock from the feeder to a mouth of a crusher;
the crusher having a motor for driving the crusher;
a horsepower sensor for sensing the horsepower output of the motor
driving the crusher;
a programmable logic controller having means for controlling the
output of the feeder;
a level sensor mounted in the crusher for sensing the level of
rock within a crusher bowl of the crusher;
second conveyor means for receiving rock discharged from the crusher
and for returning the discharged rock to the first conveyor means;
a bypass chute means component located between said first conveyor
means and the mouth of the crusher for diverting a selectable portion
of the flow of rock intended to be delivered to the mouth of the
crusher from said first conveyor means and for delivering said diverted
rock onto said second conveyor means;
said programmable logic controller further having means for controlling
the amount of rock diverted from the flow of rock intended to be
delivered leaving said first conveyor means and intending to be
delivered into the mouth of the crusher; and
said programmable logic controller having means for receiving the
sensed horsepower signal and level signal from the horsepower sensor
and the level control device respectively, and commanding the feeder
and bypass chute component respectively to correspondingly increase
or decrease the feed rate of rock entering the mouth of the crusher.
2. The crusher control system according to claim 1 further comprising:
said bypass chute component having an extendible chute and a stationary
chute, wherein said extendible chute is positioned within said stationary
chute, and said chutes are positioned such that their longitudinal
direction is perpendicular to the flow of rock being conveyed from
said first conveyor means into the mouth of the crusher.
3. The crusher control system as claimed in claim 2 wherein said
bypass chute component further includes a column means and arms
pivotally mounted on said column means at one end of each of said
arms and pivotally mounted at the other end of each of said arms
to said extendible chute for supporting said extendible chute within
said stationary chute; and
linear actuator means having opposite ends, one of said ends being
pivotally mounted to one of said arms, and the other of said ends
being mounted to push against one of said column structures for
moving said arms and said extendible chute outwardly into the flow
of rock relative to said stationary chute.
Description FIELD OF THE INVENTION
This invention relates to the production of aggregates, and particularly
to a system for controlling the throughput of size reduction equipment,
such as crushers in a rock crushing plant.
BACKGROUND OF THE INVENTION
Rock crushing plants are used for the production of aggregates.
Within a rock crushing plant there are usually three stages of crushing:
primary crushing, secondary crushing, and tertiary crushing. Quarry
rock is fed to a primary crusher in order to reduce the size of
the rock to below a given maximum size. Typically a Jaw crusher
or Gyratory crusher is used in the primary crushing stage. The size
of the quarry rock is reduced to 8 inches in diameter or less (minus
8 inches) by the primary crusher, and is then conveyed to a stockpile.
The stockpile generated by the primary crusher is transferred onto
a conveyor by a feeder, delivered to screens for classifying the
rock, and then to a secondary crusher. In ordinary plant operations,
only one secondary crusher is required. The secondary rock crusher
is capable of reducing the size of the rock to less than a given
size normally minus 4 inches. It is not possible to control the
minimum particle size that will be produced. The desired maximum
diameter of the rock being crushed depends upon the intended use
of the rock, whether it be for concrete aggregate, roadstone, or
a finer product, such as sand. Some of the rock leaving the primary
and secondary stages will be reduced in size enough so that no further
crushing is required. The remainder of the rock will need to be
crushed in the secondary and tertiary crushers respectively. Accordingly,
the output of the primary, secondary and tertiary crushing stages
go through classifying screens so that only the larger diameter
rock is crushed in the secondary and tertiary crushers respectively.
The smaller diameter rock that is the size of the desired product
is temporarily stored and later transported out of the plant as
a final product.
The output of the secondary crusher is classified to remove the
dust and smaller diameter rock with screens. The larger diameter
rock is conveyed to a surge pile and then fed to a tertiary crusher.
Cone crushers are usually used in the tertiary stage, and for very
fine tertiary crushing, Gyradisc crushers are used. The maximum
size of the tertiary crusher output can be chosen by setting a desired
gap dimension between the crushing surfaces of the crusher. As with
the secondary crushers, the product of the tertiary crushers needs
to be classified to obtain the desired final product.
In a rock crushing plant, each of the primary, secondary and tertiary
stages is operated independently of the other. That is, the feed
to the secondary crusher is obtained from a stockpile. Likewise,
the feed to the tertiary crusher is obtained from a bin or surge
pile. As a result, the focus of optimizing overall plant throughput
is divided into optimizing the throughput for each of the crushing
stages with priority being given to the least productive stage.
The difficulty in optimizing the efficiency of the crushers in
a rock crushing plant relates to the extremely hazardous environment
in which the process control equipment must operate and the constantly
changing variables that must be accounted for. Sensing equipment
that is intended to contact the rock, such as a level sensor or
the like, must withstand occasional, severe impacts and also withstand
the penetration and build-up of fine particulate matter, such as
rock dust. Further, the system must be able to accommodate changes
in operating parameters that are frequently changed by the operators
in accordance with their needs.
The variables that are subject to change during a run include differences
in hardness, size, and moisture content. For example, the feed at
the beginning of a run will have a smaller average diameter than
at the end of the run due to segregation of the rock in the surge
pile from which the rock is fed. Also, the rock at the bottom of
a pile will have a different moisture content than the rock that
has been laying on the surface of the pile. Therefore, effective
throughput control systems for rock crushers have been slow in development.
Modern size reduction equipment has been designed to operate more
efficiently in accordance with the recognized need to increase throughput.
Replacing equipment in a rock crushing plant, however, is ordinarily
one of the least viable alternatives to the owner, because the equipment,
such as the crushers, is so expensive. As a result, a great need
has developed for process control systems that can optimize the
crusher efficiency and thereby increase the crusher throughput of
existing crushers. Some of the variables that affect the operation
of a crusher during a given run can be assumed to be fixed to a
certain extent. For example, the hardness of the rock in a given
run will remain substantially the same. Other variables cannot be
fixed with such certainty, however, because they change as the length
of the run continues. For example, the size of the rock and its
moisture content changes as the surge pile is reduced. As another
example, the setting of the gap between the crushing surfaces of
the crusher will widen as the surfaces wear, and the rate of wear
will depend upon the hardness of the rock being crushed. Therefore,
for a control system to operate a crusher efficiently, it must take
into account all of the variables, and deal with them whether they
are fixed or subject to change.
The most controllable and result effective variable is the feed
rate of rock delivered to the crusher. For cone crushers, the feed
rate should be increased until the crushing cavity is filled, but
not increased so much that the rock overflows the crusher. This
results in the most efficient operation of a cone crusher. When
the feed rate is such that the crushing cavity is always full, then
the crusher is being choke fed. To ensure that the choke fed condition
is maintained, the crusher bowl can be kept full and the feed rate
controlled so that no overflow condition occurs. As the crushing
cavity fills, the horsepower requirement for the prime mover of
the crusher increases. When the crushing cavity is completely full
and the crusher is operating under a choke fed condition, the motor
driving the crusher operates within a peak range, and the feed rate
can thereafter be controlled by monitoring the horsepower of the
motor and adjusting the feed rate accordingly. As the crushing surfaces
of the crushing cavity wear, however, the horsepower decreases and
a control system operated by sensing horsepower alone would increase
the feed rate and eventually overflow the crusher bowl, without
timely intervention by an operator. To alleviate the overflow problem,
and to signal an operator to reset the crushing cavity gap, a level
control device, such as a level probe, can be used to signal the
control system that adding feed will cause an overflow condition.
If the gap is not then reset, the crusher can continue to operate
by simply increasing the feed rate when the level control device
indicates that the crusher bowl is below a predetermined level,
and decreasing the feed rate when the level control device indicates
that the crusher bowl is filled above that level.
Control systems of the type mentioned are known. A programmable
logic controller has been used to vary the feed rate to the crusher
in accordance with signals received from a horsepower sensor and
a level sensor so that an optimum feed rate for the present conditions
is delivered to the crusher. Accordingly, the control system automatically
accounts for changes in moisture content, rock size, and the wearing
of crushing surfaces. This type of control system, in theory, therefore
is adequate to increase crusher throughput by ensuring that the
crusher cavity is always filled and therefore that the crusher is
operated in a choke fed condition.
In practice, however, this type of control system is barely workable
for many crushers presently operating in rock production plants.
The secondary and tertiary crushers of these plants are fed from
a stockpile or surge pile located a significant distance away from
the mouth of the crusher. The rock must travel a long way from a
feeder at a surge pile along a series of conveyor belts to the mouth
of the crusher. As a result, when a control system commands the
feeder to increase or decrease the feed rate in accordance with
a sensed condition of the prime mover, or level sensor, the response
time is too long and the unwanted condition occurs anyway. Locating
the feeder closer to the crusher in order to alleviate this problem
is impractical, if not impossible, because of the fixed constraints
of the overall plant design. Also, the conveyors for transporting
the rock cannot be eliminated or shortened, because the maximum
slope of the conveyors cannot be increased. As a result, many of
the secondary and tertiary cushers operating in rock production
plants are being operated at less than 50 percent of their maximum
efficiency, which represents the fact that most crushers in present
use are not being choke fed.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a control system for
rock crushers in a rock crushing plant that can be retrofit to existing
crushers for optimizing the efficiency of the crusher and increasing
its throughput without having to make capital intensive replacements
of existing equipment.
It is an object of the invention to provide a control system that
can maintain a choke feed condition for a crusher by varying the
feed rate to the crusher mouth even though the feeder and surge
pile or bin are remotely located with respect to the crusher.
It is a further object of the invention to provide a crusher control
system that responds to a level control probe within a crusher bowl
and a horsepower sensor that senses the horsepower of the prime
mover during crushing, and that controls the feed rate to the crusher
mouth with a bypass component positioned adjacent or near to the
crusher entrance for diverting a portion of or all of the flow of
the rock intended to be fed into the crusher, and with a variable
rate, feeder.
It is an object of the invention to provide a bypass component
that can be adjusted to divert a portion of the flow of the rock
destined for the crusher mouth to an existing return conveyor that
is ordinarily provided for classifying the crusher output. The amount
of rock diverted from the flow of rock destined for the crusher
by the bypass component can be controlled by a programmable logic
controller that also controls the feeder. Therefore the response
time can be quickened when it is determined that the rate of feed
being delivered to the crusher must be changed.
It is an object of the invention to provide a bypass component
that can divert a portion of the rock destined for the crusher that
can continuously function without the need for frequent maintenance
in the harsh environment of a rock crushing plant. Further, it is
an object to add the bypass component to the existing size reducing
equipment of the rock crushing plant without the need to replace
existing equipment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of the control system of the invention applied
to a cone crusher;
FIG. 2 is a detailed perspective view of the upper portion of the
bypass component of the invention diverting a portion of the flow
of rock away from the mouth of the cone crusher of FIG. 1;
FIG. 3 is a top view of the bypass component of FIG. 2;
FIG. 4 is a section view of a probe designed for use with the control
system of FIG. 1; and
FIG. 5 is a partial end view of the bypass component of FIG. 2
shown pivotally mounted to a conveyor support structure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The crusher control system of the invention is illustrated as it
would be applied to a cone crusher in a secondary or tertiary crushing
stage of a rock crushing plant. The crusher controls are applicable
to Gyradisc crushers and other types of crushers that can be choke
fed. For purposes of explanation, it is assumed that cone crusher
10 is operating in a tertiary crushing phase.
Cone crusher 10 is shown schematically to include a crusher bowl
11 and a crushing cavity 12 located between an outer crushing surface
or mantle 13 and a rotating inner crushing surface or cone head
14. This design allows the crushed material to spread out as it
works its way downwardly through the crusher.
Rock is fed from the output of a secondary crushing stage of the
plant to a hopper 20 where it is temporarily stored. The rock in
hopper 20 is delivered to a conveyor 24 by a vibratory feeder 22.
The rock is conveyed along conveyor 24 to screens 26. The larger
diameter rock that does not fall through the screens is fed into
the crusher as indicated by arrow 27.
A bypass component 30 is located between screens 26 and the mouth
28 of crusher 10. An extendible chute 34 of the bypass component
is extendible into the flow of rock 27 being delivered from screens
26 to mouth 28 of the crusher, as shown in FIG. 2. The rock that
is diverted from flow 27 slides downwardly by gravity in chute 34
into a larger stationary chute 32 and then onto a conveyor 38 that
transports the diverted rock upwardly back onto conveyor 24 for
return of the rock to screens 26.
The rock that is fed to the mouth of crusher 28 strikes a distributor
plate 15 in the crusher. The rock is distributed evenly around crusher
bowl 11 and falls into crushing cavity 12. If the feed rate is sufficient,
the crushing cavity and bowl can be kept full. The crushed material
of crusher 10 is discharged at 29 onto a conveyor 37 which is an
existing conveyor in an ordinary plant. Conveyor 37 conveys the
crushed rock to return conveyor 38 for return on conveyor 24 to
the screens 26. The crushed rock must be returned to the screens,
because it is an unclassified product when it is discharged from
the crusher. Therefore, component 30 can be added to cooperate with
the existing flow of rock within the plant without having to re-design
or add to the existing conveyors.
The bypass component 30 is shown in FIGS. 2 3 and 5. In FIG. 2
a detailed perspective view of the upper portion of the bypass component
30 is shown. The support structure for extendible chute 34 includes
two vertical columns 39a, 39b and 40a, 40b. Stringer 41a, 41b are
connected between columns 39a, 40a and 39b, 40b respectively, Arms
42 43 and 46 47 are pivotally connected to stringers 41a, 41b
at 44a, 45a and 44b, 45b respectively. Arms 46 and 47 are partially
shown in FIG. 2 for clarity. Arms 42 43 and 46 47 are pivotally
mounted to the extendible chute side walls 51 and 52 respectively
by pins, bolts, or the like 54-57. Therefore, extendible chute 34
is hung between the columns and stringers by arms 42 43 and 46
47 so that it swings within stationary chute 32.
Extending across from column 39a to column 39b on the other side
of chute 32 is a cross support 58 that is welded to each of the
columns. The cross support has a pair of flanges 59a, 59b for pivotally
connecting one end of an actuator 48 by a pin or bolt 49. The opposite
end 50 of the actuator is also pivotally mounted between like flanges
64a, 64b by a pin or bolt 67. Flanges 64a, 64b are fixed to a cross
support 65 that extends between arms 43 and 47.
Actuator 48 may be electrically, pneumatically, or hydraulically
driven. As the actuator extends, one end of the actuator pushes
on cross support 65 and the other end pushes on cross support 58.
Cross support 58 is fixed between the columns and is immovable,
so chute 34 swings outwardly. When the actuator is retracted, the
arms swing inwardly until they hang in a vertical position. The
weight of chute 34 aids the actuator during retraction of the chute,
but the movement of the chute is always under control of the actuator
in both the extending and retracting directions.
The chute is driven into the flow of rock 27 upwardly at a steep
angle, for example at about 45 degrees. The leading edge of extendible
chute 34 is driven into the rock and the steepness of the chute
causes the rock to be diverted into the extendible chute and slide
further downwardly into the stationary chute 32 and onto conveyor
38. Therefore, this construction relies upon the geometry of the
plant design to allow for a steep pick-off angle of the rock by
extendible chute 34. On the other hand, if the plant design prevented
a chute from being constructed at such a steep angle, the rock might
get jammed in the chute. In this situation, chute 34 could be replaced
with a self-propelled conveyor belt that would be supported by arms
42 43 and 46 47 in the same manner as chute 34 is supported. Alternatively,
chute 34 could be replaced by a vibratory feeder if the plant design
prevented the steep pick-off angle that is necessary to enable chutes
32 and 34 to work as gravity conveyors. Likewise, chute 32 could
be replaced with a conveyor belt or vibratory feeder if necessary.
The extendible chute 34 must be capable of being continuously driven
into and pulled out of rock flow 27 without jamming. Accordingly,
the width of extendible chute 34 is much less than the width of
stationary chute 32 and similarly the depth of extendible chute
34 is much less than the depth of stationary chute 32. This results
in a clearance between the side walls 51 52 of extendible chute
34 and side walls 61 62 of chute 32. Similarly, a clearance between
bottom wall 53 of chute 34 and bottom wall 63 of chute 32 is maintained.
The dimension of these clearances exceeds the diameter of the largest
rock occurring in rock flow 27. Accordingly, any rock diverted from
flow 27 that works its way in between extendible chute 34 and stationary
chute 32 will not cause the extendible chute to jam within the stationary
chute. Appropriate adjustment is made to allow extendible chute
34 to swing outwardly into the flow of rock 27 and back without
compromising the minimum clearance that must be maintained between
the two chutes to prevent jamming.
As shown in FIG. 5 one embodiment of a pivoting support for mounting
stationary chute 32 to the framework of conveyor 38 is shown. Conveyor
38 has a belt 100 that is supported by idler rollers 101-103. The
idler rollers ar supported on a frame structure that includes vertical
side frame members 104 and 105 and a horizontally extending cross
beam 106. Fixed to frame members 104 and 105 are side plates 106
107 and 108 109 respectively. These side plates may be welded or
bolted to the frame members. Foot portions 110 and 111 that are
connected to the side walls 61 and 62 of chute 32 are received within
the space between the respective side plates 106 107 and 108 109.
The feet 110 111 are pivotally supported between each respective
set of side plates by pins 114 115. This allows the chute to be
pivoted away from the crusher when access to the crusher is desired.
Additional structure shown schematically in FIG. 1 is provided to
limit the extent of pivoting movement of the bypass component in
the direction toward the crusher.
In order to optimize the efficiency of the cone crusher 10 it
is necessary to ensure that the crushing cavity is choke fed, or
completely filled. To accomplish this result, the crushing bowl
11 is kept full, but not so full that there is a danger of overflowing
the crushing bowl and spilling rock onto the ground. In order to
prevent the rock from overflowing, a level sensor 70 is provided
that includes an actuator 71 which extends down into the crusher
bowl 11 at any desired height.
Level sensor 70 is mounted for free swinging movement on a chain
72 from a structural support 73 which can be of any conventional
design. As shown in FIG. 4 actuator 71 is connected to microswitch
74. The switch is tripped when the level of rock within the bowl
reaches the tip of the actuator, and causes it to move. When the
trip is switched, a control signal is sent out over line 75 that
the switch has been tripped. As the level sensor is subject to being
impacted by the rock entering crusher 10 it is housed within a
cylindrical steel housing 76. Within the housing 76 is a mounting
frame 77 to which the microswitch 74 is attached. Frame 77 is fixed
to a chase nipple 78 which is in turn fixed to a lower extension
79 having an opening 80 through which actuator 71 protrudes. Opening
80 must be small enough to prevent stray rock from bouncing up inside
the housing, and must be large enough to allow for movement of the
actuator in order to trip the microswitch. A suitable seal between
the extension 79 and housing 76 is provided at 81 to prevent the
accumulation of dust between the frame and housing. Chain 72 can
be attached to an eyehook 82. The free swinging movement of the
probe reduces the shock that occurs should a stray rock impact the
level sensing probe.
The cone crusher 10 is driven by a prime mover or motor 16 through
a transmission 17 shown schematically. A horsepower sensor 90 provides
a digital output signal proportional to a range of the operating
horsepower of motor 16. Any conventional horsepower sensing device
can be used. For an electric prime mover, the current supplied to
motor 16 can be used to sense the horsepower of the motor. First,
the current is transformed to a lower AC voltage and rectified to
provide a DC signal. The DC signal thus produced is proportional
to the horsepower of the motor 16. As the level of the DC signal
changes, the horsepower sensor provides a stepped output or digital
signal indicative of the range of horsepower in which the motor
is operating.
The digital output signal of the horsepower sensor is transmitted
along line 91 and input to a programmable logic controller 92. Also,
the digital signal from line 75 of the level sensor is provided
as an input to the programmable logic controller. The programmable
logic controller is capable of sending command signals over lines
93 and 91 to the vibrator feeder 22 and bypass component 30 respectively
in accordance with the sensed level and horsepower conditions. The
programmable logic controller functions as follows. When the horsepower
sensor indicates that the motor 16 is no driving the crusher at
near peak horsepower, the flow rate to the crusher is increased
by sending a signal along line 93 to the vibratory feeder 22 to
increase the amplitude of oscillation of the feeder and thereby
increase the amount of rock being delivered onto conveyor 24. When
the horsepower sensor detects that motor 16 is driving the crusher
within a maximum range of the motor's horsepower rating, then the
rate of feed added to conveyor 24 by feeder 22 is stabilized. Accordingly,
so long as the horsepower of the motor 16 is maintained within a
peak range of the rated performance, then the feeder will continue
to feed the same amount of rock to the crusher.
In order to adapt the control system of the invention to existing
equipment, a motor driven potentiometer may be used in conjunction
with the existing vibratory feeder controls to increase and decrease
the rate of oscillation of the feeder. The signal from PLC 92 to
vibratory feeder 22 along line 93 need only be of the correct time
duration and polarity to drive the motorized potentiometer to increase
the vibratory feed control knob or lever, or decrease it.
In some instances, the PLC is unable to efficiently control the
feed rate to the crusher by only changing the vibration of feeder
22 because the rock must travel all the way from the feeder 22
to the mouth 28 of the crusher before any difference in feed rate
is realized by the crusher 10 and motor 16. This situation may result
at start-up or after a change has been made to the setting of the
cone crusher, or when a new feed of rock is being fed to the crusher.
In order to establish an optimum throughput quickly, the bypass
component of the control system is utilized.
Bypass component 30 is commanded to extend and retract in order
to change the feed rate entering the crusher through mouth 28. The
PLC 92 commands the bypass component to divert a larger or smaller
portion of the rock flow away from the mouth of the crusher by moving
extendible chute 34 into and out of the flow of rock 27. The linear
actuator expands or contracts in accordance with the polarity of
the signal received. The signal is applied for a predetermined time
duration that is correlated to the desired amount of expansion or
contraction. The extendible chute 34 moves accordingly a predetermined
distance. As a result of chute 34 being driven perpendicularly into
the flow of rock 27 from one side, the further the chute is extended
into the flow of rock, the greater the amount of rock is diverted
from the mouth 28 of crusher 10. Accordingly, the duration and polarity
of the signal applied to the linear actuator from the PLC is proportional
to the amount of rock that will be diverted from the flow 27 of
rock and returned to the screens 26 by conveyors 38 and 24.
It is particularly advantageous, although not mandatory that conveyor
38 deliver the rock diverted through component 30 onto conveyor
24 about midway of conveyor 24. By this arrangement, the excess
diverted rock is added to conveyor 24 at a point where the feed
rate has already been reduced in accordance with a signal sent to
the vibratory feeder 22 by the PLC. In this way, as a steady state
feed rate is established, the extendible bypass chute 34 is retracted
as the oscillation of the vibratory feeder is decreased a compensating
amount.
The level sensor 70 completes the control system by intervening
when the steady state flow rate condition is changed and an overflow
condition is threatened. This steady state condition can be changed
in a number of ways. For example, an operator of the plant may change
the setting of the gap between the crushing surfaces of the cone
crusher in order to achieve a coarser or finer product. Also, if
a continuous run of rock is being crushed, then the crushing surfaces
may begin to wear resulting in a widening of the gap. For hard granite
based rock, this wear condition can occur within a day's time. When
the latter type of change occurs, the horsepower sensor senses a
drop in horsepower as the gap is widened and the PLC responds by
increasing the feed rate of feeder 22. In other words, the system
believes that the crushing cavity is no longer being filled at the
present feed rate, so the feed rate should be increased. If the
feed rate increases significantly, the crusher will not be able
to keep up and so a spillover condition would occur. Level sensor
70 is provided to prevent this type of occurrence. If the gap is
not reset, then the system will continue to operate under the primary
control of the level sensor, by signaling the feeder to increase
the feed when the rock in the crusher bowl is below the actuator
71 of level sensor 70 and to slow feeder 22 when the level sensor
70 has been tripped. Therefore, control of the system is maintained
even though a variable in the system has been significantly changed.
To install the process control system, it is not necessary to re-design
the plant. The bypass component can be a self-standing structure
having a discharge that feeds directly onto a return conveyor 38
which is ordinarily provided adjacent an output conveyor 37 for
conveying the crusher output to the screens. The probe 70 can be
mounted on a frame 73 fixed to the outer housing of crusher 10.
The horsepower sensor 80 is of a conventional nature and needs only
be connected to the current supply for motor 16. The PLC is a small
component that can be added to the plant operator's control room.
As explained above, the vibratory feeder is typically provided with
a control knob for adjusting the feed rate. In the preferred embodiment,
a motorized potentiometer is attached to the control knob so that
automatic adjustment of the control knob can be performed by providing
the correct polarity signal along line 93 from the PLC 92 for power
adjustment of the control knob of the vibratory feeder. Similarly,
the control of linear actuator 48 can be achieved by supplying the
appropriate signal from PLC along line 94. Therefore, the entire
control system can be added to an existing plant, of conventional
design, without requiring the replacement of expensive crushing
equipment or changing the design layout of the conveyors.
It can be appreciated that the foregoing invention can be practiced
by modifying the bypass chute structure in any number of ways so
that a portion of the rock is diverted away from the flow of rock
entering the mouth of the crusher in incremental amounts. The significance
of the preferred embodiment illustrated in FIG. 2 is that it will
operate continuously without jamming, because the clearance between
the inner and outer chute is maintained in excess of the largest
diameter rock found in the flow of rock 27. Accordingly, it is understood
that within the scope of the appended claims the invention may be
practiced as described.
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