Control system for booster type belt conveyor

A control system for a booster type belt conveyor having one or more booster belts spaced at intervals along a conveyor belt with the upper, driving run of each booster belt frictionally engaging the underside of the conveyor belt carrying run. Each belt has a driving pulley connected to a driving unit including one or more electric motors, engageable and disengageable fluid couplings, and a gear box. The conveyor is for heavy duty service, in long lengths of several miles. There is an electrical control assembly for each drum or pulley driving unit. These automatically start the motors in sequence while the couplings are disengaged, each being started in response to a signal from a previously started motor that it has reached running speed. An electrical loop interconnects all the control assemblies and contains relays which, when the loop is energized to actuate the relays, cause the fluid couplings to engage. The electrical loop is conditioned responsive to a running condition signal from the last-started motor, and is then energizable by a switch to engage all the fluid couplings and cause the motors to rotate the drive pulleys.

BACKGROUND OF THE INVENTION 
This invention relates generally to belt conveyors and particularly to 
heavy duty mining and industrial type conveyors characterized by a very 
long conveying run extending in a single reach with one or more 
frictionally engaged auxiliary booster drive belts augmenting the head end 
conveyor drive. 
Belt type conveyors are widely used for example in moving coal and ore, 
both underground from the face to a cleaning and sizing operation, and 
aboveground from the mine to a loading point. Even in underground 
applications, some of these are miles long. 
There are three general types of these long belt conveyors: 1. cascade; 2. 
cable belt; and 3. booster type belt. 
Cascade conveyors are a series of individual, separately powered conveyors 
arranged in "cascade" relationship, with one discharging onto another. 
Although extensively used in the past for conveyors longer than were 
practical for a single length of conveyor belt, they have several 
drawbacks including degradation of conveyed material and dust generation 
at each transfer point, and, when used underground, they require extra 
brushing to remove overhead rock at transfer points. 
Cable belt conveyors have a belt supported between a pair of moving steel 
cables. Although adaptable to very long lengths of many miles, they are 
complex, expensive, not easily extended, and require substantial head room 
limiting their use underground. 
Booster type belt conveyors are relatively new, the first believed 
developed for heavy duty use in a British coal mine about 1976 by Hu Wood, 
Limited. It was originated as a means of uprating an existing 
half-mile-long conveyor, but did not address problems of applying the 
booster concept from the outset as a means of providing a long distance 
transport system which could be extended to a length of several miles as 
needed. 
The booster type belt conveyor offers economic and operational advantages 
for materials handling over long distances both underground and 
aboveground. It comprises a conveyor belt having conveyor and return runs 
trained for orbital movement between driving and idler pulleys located 
respectively at head and tail ends. One or more intermediate booster belts 
are trained for orbital movement between driving and idler pulleys with 
their driving runs in frictional driving engagement with the upper, 
carrying run of the conveyor belt. Drive motors are connected to the 
driving pulleys. 
In a typical coal mining operation, a booster type belt conveyor may 
initially be a few hundred or a few thousand feet long. As it is extended, 
for example, to follow an advancing mine face, it may become several miles 
long with booster drive belts spaced apart at intervals of a mile or so. 
Starting such a long conveyor involves many problems. The motor or motors 
in each driving unit will often require hundreds of horsepower and the 
booster driving units will be located beyond the sight and hearing of the 
operator at the main control station. Because the motors take six or more 
times full load current to start from rest, the power to start all the 
motors at once could place an unacceptable load on an electrical power 
source. 
Sequential starting is therefore essential. This however can introduce 
localized stretching of the conveyor belt at the driving point, and severe 
stress differentials on opposite sides of the drive pulley. This can 
produce an undesirable "ripple" or wave effect moving along the conveyor 
as one driving unit after another is powered, and require special, costly, 
high tensile strength belting, and complex, costly, takeup loop structures 
for absorbing surplus or stretched belting. 
SUMMARY OF THE INVENTION 
Because the driving pulleys are widely separated and may be as much as a 
mile apart, the electrical control and coordination of the complete 
conveyor poses some unusual problems. 
A general object of the present invention is to provide in a booster type 
belt conveyor an improved electrical control system for sequentially 
starting the drive motors and then coupling them to the driving pulleys or 
drums in a timed sequence in a progressive manner. 
An important objective of the present invention is to provide overall 
control of a booster conveyor system in a manner which is reliable, safe 
and economic. In practical terms this means sequenced starting of the 
motors, under conditions where it is safe to do so, followed by 
synchronized or time related operation of the couplings to tension the 
conveyor belt progressively to insure smooth, uniform acceleration along 
the carrying run of the belt. It is also necessary to have a means of 
stopping the conveyor by the simulataneous removal of power from the 
separate drives, either in normal operation or because of some hazardous 
development or occurrence at one of the drive stations. 
Because of the length of the conveyor, the expense of multi-conductor 
cables running between drive stations is a serious consideration in the 
economic evaluation of a booster conveyor system. The present invention 
seeks to minimize cabling costs by reducing the required number of 
conductors to four, of a relatively small gauge, while at the same time 
using simple circuits which are easy to understand and maintain. 
Another object is to provide, in a booster type belt conveyor having a 
pulley driving unit with electrical motor means for each driving pulley, 
an improved electrical starting and control system comprising: engageable 
and disengageable coupling means in each driving unit between the 
corresponding motor means and driving pulley or drum; a plurality of 
control assemblies, one for each driving unit; means in each control 
assembly for sensing a running condition of the corresponding motor means 
and generating a running condition signal in response thereto; means 
effective after a first motor means has been started for automatically 
sequentially starting each of the remainder of the motor means in response 
to a running condition signal from a previously started motor means; a 
coupling-controlling electrical loop common to all of the control 
assemblies; a plurality of electrically energizable, coupling actuating 
means in the loop, one for each control assembly, each effective when 
energized to engage the corresponding coupling means; and means responsive 
to the running condition signal from the last motor means started to 
connect the electrical loop to an electrical power source and thereby 
condition the loop to engage all of the couplings. 
Another object is to provide a switch in the electrical loop for energizing 
the coupling actuating means after the loop has been conditioned as stated 
above. 
Another object is to provide, in the control assembly for each one of the 
motor means except the last to be started, a motor starting circuit 
including: a relay responsive to a running condition signal from said one 
motor means to connect an electrical power source to a motor starting 
relay in the control assembly for the next of the motor means started; and 
a coupling engaging circuit including part of an electrical loop common to 
the control assemblies for all the motor means, the coupling-engaging 
circuit having a relay responsive to electrical energization of the loop, 
when the last motor means is started, to engage the coupling means for 
said one motor means. 
Another object is to provide, in the control assembly for the last motor 
means started, means to condition the above-described electrical loop for 
energization including a relay responsive to a running condition signal 
from said last motor means started to connect an electrical power source 
to the electrical loop; and a coupling-engaging circuit including part of 
the electrical loop having a relay responsive to electrical energization 
of the loop to engage the coupling means for said last motor means 
started. 
Another object is to provide in one of the control assemblies a switch 
controlling energization of the electrical loop to simultaneously actuate 
the relays controlling engagement of the couplings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the specific embodiment of the invention shown in the 
drawings, a booster type belt conveyor generally designated 20 is 
diagrammatically shown in FIG. 1. It comprises a main conveyor belt 22 
having conveying and return runs 24 and 26 trained for orbital movement 
between drive head and return end drums 28 and 30 located respectively at 
head and tail ends 32 and 34. The conveying or carrying run will 
preferably have a troughed configuration (not shown) for heavy duty mine 
service and the like, and both runs will be supported on conventional 
troughing and return rollers (not shown). 
A plurality (in this case four) of booster belts 36 are located 
intermediate the conveyor belt drive head and return end drums. Each 
booster belt has driving and return runs 38 and 40 trained for orbital 
movement between drive head and return end drums 42 and 44, with each 
driving run in frictional driving engagement with the underside of the 
conveyor carrying run 24. As an indication of scale, one specific 
prototype on which this description is based is 20,000 feet long, the 
booster belts are 700 feet long spaced on 4,000-foot centers, and the 
conveyor and booster belting are reinforced rubberlike materials about 42" 
wide. 
The conveyor drive head drum 28 and the booster drive head drums 42 are 
connected by drive shafts 46 and 48 to drum driving units 50, 52, 54, 56 
and 58 respectively. These are located at control assemblies 60, 62, 64, 
66 and 68 respectively, and interconnected by a cable 70 to integrate the 
individual control assemblies into a unitary, cooperative system. The drum 
driving units 50-58 are illustrated as identical except for addition of 
start and stop buttons on starter 78 in driving unit 50. Each unit 
comprises a gear box 72 with output drive shaft 46 or 48. Each unit has 
electrically engageable and disengageable coupling means 74 and electric 
motor means 76 controlled by a starter 78. Although a single, larger 
coupling, and a single, larger motor could be used, they are arranged in 
pairs in the specific prototype described. Each motor means is here shown 
comprising two individual, 250-horsepower induction motors 76A, 76A. While 
any suitable electrically operated coupling means may be used, the 
specific coupling means 74 used in the prototype described comprises two 
electrically controllable fluid couplings 74A, 74A, known in the trade as 
"scoop controlled fluid couplings" and are available in a wide variety of 
horsepower and speed ratings. They are externally electrically 
controllable in that they engage or close to a selected degree when 
terminals 80 and 82 are interconnected. The control assemblies 60-68 will 
preferably be provided in readily replaceable module form to facilitate 
installation and maintenance of the system. 
The internal workings of the motors, couplings and starters form no part of 
this invention so will not be described in detail. While, in practice, the 
entire system will be completely controlled and monitored by computer 
means, not shown, relatively simple controls are illustrated to facilitate 
a description and understanding of the invention. The starters 78 are 
substantially identical, except that the starter for the main conveyor 60 
has "start" and "stop" buttons while those in the booster control 
assemblies are actuated automatically through input terminals 134, 136. 
Each starter, irrespective of the actuating means, starts the 
corresponding pair of motors 76A sequentially in a conventional manner and 
energizes starter output terminals 88, 90 to place a running condition 
signal across terminals 92, 94 in the corresponding control assembly, via 
a connecting cable 96, to indicate that the corresponding pair of motors 
have been brought up to proper running speed. 
The control assemblies 60-68 are generally similar in that each has a 
motor-starting circuit generally designated 98 and a coupling-engaging 
circuit 100 consisting of a portion of an electrical loop generally 
designated 102. The loop extends the entire distance between the main Type 
A control assembly 60 and the last Type B booster control assembly 68 via 
conductors 174, 176 which will be described. 
In the main control assembly 60, the motor-starting circuit comprises a 
power source consisting of an isolation transformer 104 and a relay 106. 
Transformer input terminals 108, 110 are connected to a conventional 
120-volt alternating current control circuit supply. The relay has a coil 
112 with terminals 92, 94 connected through cable 96 to output terminals 
88, 90 of the corresponding starter 78. The transformer output is 
connected through relay contacts 114 to output terminals 116, 118. This is 
repeated in each of the booster control assemblies 62, 64, 66 and 68. 
In addition, the motor starting circuit for each of the booster control 
assemblies has a relay 120 with a coil 122 between input terminals 124, 
126, and contacts 128 between output terminals 130, 132, the latter being 
connected to corresponding starter input terminals 134, 136 via a 
connecting cable 138. 
Turning attention now to the coupling-engaging control circuit 100, this 
comprises the pair of conductors 174, 176 connected at the far end via 
jumpers 178, 180 to terminals 116, 118 in the last booster control 
assembly 68. They extend all the way across the control assemblies (in 
cable 70) back to the main control assembly 60 where they are 
interconnected by jumper 140. 
Portions of the circuit 100 in the individual control assemblies will now 
be described. The main control assembly 60 and each of the booster control 
assemblies 62, 64, 66 and 68 has a relay 142 with a coil 144 and contacts 
146. The coil 144 in each of the main and booster control assemblies is in 
series with contacts 148 between terminals 150, 152. In addition, the main 
control assembly 60 has contacts 166 between the respective contacts 148 
and coil 144. Contacts 146 and a programmable time delay unit 154 are 
connected between a pair of terminals 156, 158, these being connected to 
corresponding fluid coupling terminals 80, 82 via a connecting cable 160. 
A signal monitor comprising a high input impedance voltage detector 162 is 
connected across terminals 152, 153 in opposite legs of the loop 102 in 
each booster control assembly. In the main control assembly it is 
connected between terminals 153 and 164, a terminal 164 being provided in 
one of the legs of each control assembly as shown in FIG. 2. Safety switch 
means including safety contacts 148 in each of the control assemblies are 
the master contacts for all automatic or manually operated safety devices 
(not shown) associated with each driving unit. Contacts 148 are repeated 
in all the control assemblies. These are normally open but under safe 
conditions they will be closed. In the main control assembly 60 contacts 
166 are associated with relay means (not shown) which stops the conveyor 
belts 22 at times when an outbye tipple, conveyor, or railway car, which 
normally receives material, is inoperable. 
In addition to the above components which are common to the loop 100 in all 
the control assemblies, the main control assembly 60 has a coupling 
control switch 168 and rectifying means, namely a diode 169, in parallel 
with the signal monitor 162. 
It will be understood that the coupling control switch 168 and rectifier 
diode 169 are not necessarily physically within the main control assembly 
60. The motor starters are usually located as near to the motors as 
practicable, but the first driving unit (50 in this case) may be 200 feet 
or so back from the delivery end of the conveyor. In such cases, it is 
convenient to mount the coupling control switch 168, rectifier 169, and 
associated signal monitor 162 near the delivery end of the conveyor where 
an operator would be stationed to watch material being discharged from the 
conveyor. Positioning the rectifier as near to the switch as practicable 
provides maximum protection against dangerous maloperation due to a short 
in the control circuit. 
Because of the length of the conveyor, the multiconductor cable 70 may 
extend as much as a mile between control assemblies. Cable cost therefore 
can be a serious consideration in the economic assessment of any booster 
conveyor system. The present invention minimizes cabling costs by reducing 
the number of conductors required to four, namely those numbered 170, 172, 
174 and 176 between control assemblies. These may be light conductors in 
the order of 14-gauge. The fact that the system requires only four 
conductors between control assemblies has a further advantage by enabling 
use of the well-known "quad" cable relationship. Thus conductors 170 and 
172 are selected to be diametrically opposed, likewise conductors 174 and 
176 are diametrically opposed in the four conductor cable. This 
configuration ensures that the inductive coupling between the separate 
circuits is negligible. 
The complete loop circuit involving all four control assemblies and booster 
drives as shown in FIGS. 2 and 3 may be several miles long, approximately 
four miles in the present example. The conductor cross section initially 
selected for the loop 100 should be suitable for the maximum specified 
distance to which the conveyor would eventually be extended. In the early 
stages of development, when there are less than the maximum number of 
booster drives in service and the installed loop length is less than the 
maximum, it is necessary to compensate for the reduced impedance of the 
circuit by adding selected values of resistance. The resistor values for 
the various reduced lengths of conveyor are shown in FIGS. 5, 6, 7 and 8. 
For example, as shown in FIG. 2, where all four booster drives are used in 
the present example, jumpers 178 and 180 will interconnect terminals 118, 
150 and terminals 116, 164 respectively in the last booster control 
assembly. Where only three booster drives are used, FIG. 5 shows a single 
50-ohm, 100-watt resistor 182 will be substituted for the jumper between 
terminals 116 and 164. Where there are only two booster drives, FIG. 6 
shows two such resistors used in the jumper. Where only one booster drive 
is used, FIG. 7 shows three such resistors. And where no booster drive is 
used, FIG. 8 shows four such resistors. 
The basic coupling-engaging loop circuit 100 described above has some 
special features to ensure safe and convenient operation. To prevent 
inadvertent energization of one or more fluid-coupling-engaging relays 142 
due to a short circuit between conductors 174, 176, the relays 142 are of 
a special design which permits operation on half wave rectified 
alternating current but not on normal full wave alternating current. While 
any suitable relay may be used, one such relay which has been successfully 
used in the present invention is known as a "slugged" relay, in which the 
iron core carries a heavy "shorted turn" which enables it to function as 
described. Under normal conditions the series diode 169 provides the half 
wave rectification required. A short circuit at any point between 
conductors 174 and 176 will result in all the relays 142 being deenergized 
thereby disengaging the corresponding fluid couplings and shutting down 
the conveyor. The signal monitor units 162 provide an effective way of 
locating an open circuit in the loop. For instance if there is an open 
circuit fault in conductor 174 between booster control assemblies 64 and 
66, the signal monitors at booster control assemblies 66 and 68 will 
detect the alternating current voltage at the output of the last isolation 
transformer 104 while the signal monitors at the main control unit 60 and 
at control assemblies 62 and 64 will not detect an alternating current 
voltage. 
The signal monitor 162 connected across the diode 169 at the main control 
assembly 60 has a broader application. After the "start" button on the 
main unit starter 78 has been actuated, the signal monitor 162 will show 
when all the motors up to and including those in the last booster drive 
have started and reached proper running speed, so the operator will know 
when he can actuate coupling control switch 168 to initiate the engagement 
procedure for the fluid couplings. As noted by the "5 SEC. T.D.C." legend 
associated with coupling control switch 168, there will preferably be a 
time delay of five seconds or so in the system between closing of the 
switch and actual engagement of the fluid couplings to start the conveyor. 
The particular time delay circuitry is not shown but may be incorporated 
as a safety feature allowing time for warning sirens and flashing lights 
to be actuated along the complete length of the conveyor before it starts. 
The programmable time delay units 154 represent tension control devices and 
techniques which may be employed to control conveyor belt tension during 
start up. Because the conveyor belt may be many miles long, it should not 
be started by sudden, full engagement of all five pairs of fluid 
couplings. This would create severe tension gradients on opposite sides of 
the driving pulleys with very high tensioning behind them and considerable 
slack ahead of them, and wave-like distortion rippling along the conveying 
run for an initial period until the tension could equalize. To prevent 
this and enable the belt to start smoothly without such ripple effect, 
time delay units 154 may be programmed to energize the fluid couplings in 
two stages a few seconds apart: an initial stage in which the couplings 
are only partially engaged to apply limited driving tension to the 
conveyor belt simulataneously through all five driving pulleys and prevent 
development of slack in localized portions of the conveying run; followed 
a few seconds later by full engagement of the fluid couplings to bring the 
conveyor smoothly up to maximum rated speed. 
As stated, the plurality of sets of safety contacts 148 are important to 
the safe operation of the system. They are normally open, but each set 
will be part of a relay means (not shown) which will monitor various 
electrical and mechanical functions in the respective drives and controls. 
If all functions are safe and proper, the safety contacts 148 will be 
closed as shown in FIG. 2. If there is any detectable electrical or 
mechanical defect at any drivehead the related contacts 148 will be opened 
to prevent the conveyor from starting or to immediately stop it if it is 
already running. The overall control system is such that, in the latter 
case, all the couplings 74 are disengaged immediately and simultaneously, 
to quickly stop the conveyor, no matter where the defect may be located. 
The signal monitors 162 enable the open contact to be identified and hence 
the cause investigated. 
Starting and stopping procedures will now be described. In general, the 
electrical motor means are sequentially started beginning with the main 
conveyor motors in the conveyor driving unit 50 and progressing in a 
cascade manner inbye along the conveyor to the motor means in the last 
booster drive unit 58. Each motor means is started only after the previous 
one is brought up to proper no load running speed. After the motors are 
running, the fluid couplings are engaged in a suitable progressive manner 
as described. 
To start the conveyor, the "start" button on the main conveyor starter 78 
is pressed. By conventional starter cicuitry (not shown) the pair of main 
motors 76A, 76A will be started sequentially and brought up to no load 
running speed, it being understood that the fluid couplings 74A, 74A in 
driving unit 50 will remain disengaged at this time in the absence of a 
coupling engaging signal in cable 160. At this time, a running condition 
signal appears on starter output terminals 88, 90 of unit 50 and is 
communicated through cable 96 to terminals 92, 94 of relay 106 in main 
control assembly 60. This closes contacts 114 and energizes relay 120 in 
the first booster control assembly 62 closing contacts 128 therein and 
transmitting a start signal through cable 138 to the starter in driving 
unit 52. Relays 120 in successive booster control assemblies are energized 
in the same way as the separate motor means are brought up to running 
speed until all five pairs of motors 74A are running. When the last 
booster motor means, in control assembly 68, reaches running speed, loop 
100 is conditioned for energization through jumpers 178 and 180 by the 
closing of the last set of contacts 114. 
At that time, the operator can confirm that all the motors are running by 
means of signal monitor 162 in main control unit 60. He then presses 
coupling control switch 168 to energize the loop. After a suitable time 
delay of 5 seconds or so (by the "T.D.C." means) to provide time for 
warning signals to be broadcast along the conveyor, then, under control of 
the programmed time delay units 154, the fluid coupling means will be 
engaged to bring the conveyor belt 22 up to proper conveying speed. 
Stopping procedure for the conveyor is the reverse of the above. As a first 
step, the couplings are disengaged by opening coupling control switch 168. 
This stops the belt. Normal shut-down of the motor means is initiated by 
pressing the "stop" button in the starter of main driving unit 50 which 
results in an automatic cascade shut-down of the motors, first the main 
motor means in unit 50 followed one at a time by those in booster driving 
units 52, 54, 56 and 58. 
The embodiments described and shown to illustrate the present invention 
have been necessarily specific for purposes of illustration. Alterations, 
extensions and modifications would be apparent to those skilled in the 
art. The aim of the appended claims, therefore, is to cover all variations 
included within the spirit and scope of the invention.