A TRAIN LOADING SYSTEM

SYSTEME DE CHARGEMENT DE TRAIN

English Abstract

A system comprises a bin for supplying material to cars of a train that travels relative to the bin. The flow of material from the bin is controllable. The system comprises a device arranged to produce a measured freeboard value indicative of a front and/or rear freeboard of a car. The system is arranged to determine a car mass error value representing an error between a car mass value indicative of a mass of material in a car and a defined car mass set point, and to use the mass error value to produce a freeboard set point indicative of desired front and rear freeboard values. The system determines a freeboard error value indicative of an error between a measured freeboard value and a freeboard set point and to control timing of flow of material based on the freeboard error value.

French Abstract

Il est décrit un système comprenant une caisse visant à fournit du matériel aux voitures d'un train se déplaçant par rapport à la caisse. Le débit de matériel de la caisse est gérable. Le système comprend un appareil servant à produire une valeur de franc-bord mesurée indiquant le franc-bord à l'avant et/ou à l'arrière d'une voiture. Le système peut déterminer une valeur d'erreur de la masse d'un véhicule représentant une erreur entre la valeur de la masse d'un véhicule indiquant qu'une masse de matériel se trouve dans un véhicule et un point de consigne défini pour la masse d'un véhicule. Le système peut également utiliser la valeur de l'erreur de masse pour produire un point de consigne franc-bord indiquant les valeurs francs-bords souhaitées à l'avant et à l'arrière. Le système détermine une valeur d'erreur de franc-bord indiquant une erreur entre une valeur de franc-bord mesurée et un point de consigne de franc-bord. Le système contrôle également la synchronisation du flux de matière en fonction de la valeur d'erreur de franc-bord.

Claims

23
CLAIMS:
1. A train loading system for loading material onto cars of a train, the
system
comprising:
a surge bin arranged to receive material and supply material to cars of a
train
that travels relative to the surge bin, wherein flow of material from the
surge bin is
controllable to prevent or permit flow of material from the surge bin and
thereby control
the volume of material loaded into a car of the train; and
at least one freeboard measuring device arranged to produce at least one
measured freeboard value indicative of a front and/or rear freeboard of a car;
the system arranged to determine a car mass error value representing an error
between a car mass value indicative of a mass of material in a car and a
defined car
mass set point, and to use the car mass error value to produce at least one
freeboard
set point indicative of desired front and rear freeboard values; and
the system arranged to determine at least one freeboard error value indicative
of an error between a measured freeboard value and a freeboard set point and
to
control timing of flow of material from the surge bin based on the freeboard
error value
so as to control the mass and volume of material loaded into the car.
2. A train loading system as claimed in claim 1, wherein the car mass value
is
indicative of a mass of a car after the car has been loaded with material.
3. A train loading system as claimed in claim 2, wherein the system
includes a
weighing device arranged to produce the car mass value after the car has been
loaded
with material.
4. A train loading system as claimed in claim 1, comprising a mass
estimator,
wherein the car mass value is indicative of an estimated car mass before or as
the car
is loaded with material from the surge bin.
5. A train loading system as claimed in any one of the preceding claims,
comprising at least one car detection sensor arranged to detect presence of a
car and
determine a train location reference usable to determine a position of the car
relative to
the surge bin as the car moves relative to the surge bin, the system
controlling the

24
timing of flow of material from the surge bin according to the determined
position of the
car relative to the surge bin.
6. A train loading system as claimed in claim 5, wherein the at least one
car
detection sensor comprises a first car detection sensor arranged to detect
presence of
a car and determine a first train location reference before the surge bin, the
first train
location reference usable to determine a front slider position indicative of a
position of
the car relative to the first train location reference, the system controlling
the timing of
commencement of ore flow according to the determined front slider position.
7. A train loading system as claimed in claim 6, wherein the at least one
car
detection sensor comprises a second car detection sensor arranged to detect
presence of a car and determine a second train location reference after the
surge bin,
the second train location reference usable to determine a rear slider position
indicative
of a position of the car relative to the second train location reference, the
system
controlling the timing of cessation of ore flow according to the determined
rear slider
position.
8. A train loading system as claimed in claim 7, wherein the first and/or
second
car detection sensor comprises a photoelectric cell.
9. A train loading system as claimed in any one of the preceding claims,
wherein
the at least one freeboard measuring device comprises a front freeboard
measuring
device arranged to produce a front freeboard value indicative of a front
freeboard of a
car.
10. A train loading system as claimed in any one of the preceding claims,
wherein
the at least one freeboard measuring device comprises a rear freeboard
measuring
device arranged to produce a rear freeboard value indicative of a rear
freeboard of a
car.
11. A train loading system as claimed in any one of the preceding claims,
wherein
the at least one freeboard measuring device is disposed at a location at least
one car
away from the surge bin.

25
12. A train loading system as claimed in any one of the preceding claims,
wherein
the at least one freeboard measuring device comprises at least one laser
measuring
device.
13. A train loading system as claimed in any one of the preceding claims,
wherein
the at least one freeboard measuring device is arranged to produce a raw
freeboard
value and the system comprises at least one filter arranged to filter the raw
freeboard
value to produce a filtered freeboard value.
14. A train loading system as claimed in claim 13, wherein the at least one
filter
comprises a low pass filter.
15. A train loading system as claimed in claim 14, wherein the at least one
filter is a
discrete filter arranged to implement the following filter algorithm:
<IMG>
where F i is the new filtered freeboard measurement, F i-1 is the previous
filtered
freeboard measurement, L i is the raw measurement signal received from the
laser and
f is a filter constant.
16. A train loading system as claimed in any one of the preceding claims,
wherein
the system comprises an overload controller arranged to cause cessation of
flow of
material from the surge bin when the car mass value exceeds a defined value.
17. A train loading system as claimed in claim 16, wherein if the overload
controller
has caused flow of material from the surge bin to cease, the system is
arranged to use
a new filtered rear freeboard measurement if the new filtered freeboard
measurement
is below the freeboard set point, and to use a previous filtered rear
freeboard
measurement if the new freeboard measurement is above the freeboard set point.
18. A train loading system as claimed in any one of the preceding claims,
wherein
the at least one freeboard set point includes a front freeboard set point
associated with
a measured front freeboard value and a rear freeboard set point associated
with a

26
measured rear freeboard value, the front freeboard set point being
substantially the
same as the rear freeboard set point.
19. A train loading system as claimed in any one of the preceding claims,
wherein
the system comprises a mass controller arranged to use the car mass error
value to
produce the at least one freeboard set point.
20. A train loading system as claimed in claim 19, wherein the mass
controller is a
discrete controller.
21. A train loading system as claimed in claim 20, wherein the mass
controller
comprises a proportional-integral (PI) controller.
22. A train loading system as claimed in claim 21, wherein the proportional-
integral
(PI) controller is in in velocity form.
23. A train loading system as claimed in any one of claims 20 to 22,
wherein the
mass controller is arranged to implement the following algorithm:
m i=m i-1+K c(e i-e i-1)+K cK iE i
where m i is the new controller output corresponding to a new freeboard set
point, m i-1
is the previous controller output, K c is an overall controller gain constant,
K i is an
integral gain constant, e i is a constant error value between the current mass
set point
value and the current car mass, and e i-1 is a previous error value between
the previous
mass set point value and the previous car mass.
24. A train loading system as claimed in any one of the preceding claims,
wherein
the system is arranged to define maximum and minimum values for the freeboard
set
point.
25. A train loading system as claimed in any one of the preceding claims,
wherein
the system comprises at least one freeboard controller arranged to control
timing of
flow of material from the surge bin by controlling the front and/or rear
slider position
based on the at least one freeboard error value.

27
26. A train loading system as claimed in claim 25, wherein the system
comprises a
front freeboard controller and a rear freeboard controller, the front
freeboard controller
arranged to use a front freeboard error value indicative of an error between a
measured front freeboard value and the freeboard set point to control timing
of
commencement of flow of material from the surge bin based on the front
freeboard
error value, and the rear freeboard controller arranged to use a rear
freeboard error
value indicative of an error between a measured rear freeboard value and the
freeboard set point and to control timing of cessation of flow of material
from the surge
bin based on the rear freeboard error value
27. A train loading system as claimed in claim 25 or claim 26, wherein the
or each
freeboard controller is a discrete controller.
28. A train loading system as claimed in claim 27, wherein the or each
freeboard
controller comprises a proportional-integral-derivative (PID) controller.
29. A train loading system as claimed in claim 28, wherein the proportional-
integral-derivative (PID) controller is in velocity form.
30. A train loading system as claimed in claim 29, wherein the PID
controller is a
PID-gamma controller.
31. A train loading system as claimed in claim 27, wherein the or each
freeboard
controller comprises a proportional-integral-derivative (PID) controller.
32. A train loading system as claimed in any one of claims 25 to 31,
wherein the or
each freeboard controller is arranged to implement the following algorithm:
m i=(1+a)m i-1-am i-2+e i(K p+K i+b)-3 i-1(K p[1+a]+aK i+2b)+e i-2(K pa+b)
(3)
where:
m i is the new controller output, that is, the new slider position in mm;

28
m i-1 is the current slider position;
m i-2 is the previous slider position;
e i is the new freeboard error (mm);
e i-1 is the current freeboard error (mm);
e i-2 is the previous freeboard error (mm);
K p is a proportional gain parameter;
K i is an integral gain parameter;
b is a Kd/gamma control parameter;
a is an exp(-1/gamma) control parameter.
33. A train loading system as claimed in any one of the preceding claims,
wherein
at commencement of loading of a train and prior to obtaining at least one
measured
freeboard value indicative of a front and/or rear freeboard of a car, the
system is
arranged to set an initialisation freeboard set point value, the
initialisation freeboard set
point value being used until the at least one measured freeboard value is
obtained.
34. A train loading system as claimed in claim 33, wherein the system is
arranged
such that when front and rear measured freeboard values are obtained after
initialisation, a freeboard set point is determined based on the front and
rear freeboard
values.
35. A train loading system as claimed in any one of the preceding claims,
wherein
the system is arranged to adjust the rear slider in response to an adjustment
to the
front slider so as to compensate for a change to the rear freeboard caused by
a
change to the front slider.
36. A train loading system as claimed in any one of the preceding claims,
wherein
the system is arranged to facilitate manual adjustment of the timing of flow
of material
from the surge bin by an operator.
37. A method of loading material onto cars of a train at a mine operation,
the
method comprising:
receiving material to be loaded onto cars in a surge bin;
supplying material to cars of a train as the train travels relative to the
surge bin,
wherein flow of material from the surge bin is controllable to prevent or
permit flow of

29
material from the surge bin and thereby control the volume of material loaded
into a car
of the train;
producing at least one measured freeboard value indicative of a front and/or
rear freeboard of a car;
determining a car mass error value representing an error between a car mass
value indicative of a mass of material in a car and a defined car mass set
point;
using the car mass error value to produce at least one freeboard set point
indicative of desired front and rear freeboard values;
determining at least one freeboard error value indicative of an error between
a
measured freeboard value and a freeboard set point; and
controlling timing of flow of material from the surge bin based on the
freeboard
error value so as to control the mass and volume of material loaded into the
car.
38. A method as claimed in claim 37, wherein the car mass value is
indicative of a
mass of a car after the car has been loaded with material.
39. A method as claimed in claim 38, comprising producing the car mass
value
after the car has been loaded with material using a weighing device.
40. A method as claimed in claim 37, wherein the car mass value is
indicative of an
estimated car mass before or as the car is loaded with material from the surge
bin.
41. A method as claimed in any one of claims 37 to 40, comprising detecting
presence of a car and determining a train location reference usable to
determine a
position of the car relative to the surge bin as the car moves relative to the
surge bin,
and controlling the timing of flow of material from the surge bin according to
the
determined position of the car relative to the surge bin.
42. A method as claimed in claim 41, comprising using a first car detection
sensor
to detect presence of a car and determine a first train location reference
before the
surge bin, the first train location reference usable to determine a front
slider position
indicative of a position of the car relative to the first train location
reference, and
controlling the timing of commencement of ore flow according to the determined
front
slider position.

30
43. A method as claimed in claim 42, comprising using a second car
detection
sensor arranged to detect presence of a car and determine a second train
location
reference after the surge bin, the second train location reference usable to
determine a
rear slider position indicative of a position of the car relative to the
second train location
reference, and controlling the timing of cessation of ore flow according to
the
determined rear slider position.
44. A method as claimed in claim 43, wherein the first and/or second car
detection
sensor comprises a photoelectric cell.
45. A method as claimed in any one of claims 37 to 44, comprising using a
front
freeboard measuring device to produce a front freeboard value indicative of a
front
freeboard of a car.
46. A method as claimed in any one of claims 37 to 45, comprising using a
rear
freeboard measuring device to produce a rear freeboard value indicative of a
rear
freeboard of a car.
47. A method as claimed in any one of claims 37 to 46, comprising producing
a raw
freeboard value and filtering the raw freeboard value to produce a filtered
freeboard
value.
48. A method as claimed in claim 47, wherein the filtering comprises using
a low
pass filter.
49. A method as claimed in claim 48, wherein the low pass filter is a
discrete filter
arranged to implement the following filter algorithm:
<IMG>
where F i is the new filtered freeboard measurement, F i-1 is the previous
filtered
freeboard measurement, L i is the raw measurement signal received from the
laser and
f is a filter constant.

31
50. A method as claimed in any one of claims 37 to 49, comprising causing
cessation of flow of material from the surge bin when the car mass value
exceeds a
defined value.
51. A method as claimed in claim 50, wherein if flow of material from the
surge bin
is caused to cease, using a new filtered rear freeboard measurement if the new
filtered
freeboard measurement is below the freeboard set point, and using a previous
filtered
rear freeboard measurement if the new freeboard measurement is above the
freeboard
set point.
52. A method as claimed in any one of claims 37 to 51, wherein the at least
one
freeboard set point includes a front freeboard set point associated with a
measured
front freeboard value and a rear freeboard set point associated with a
measured rear
freeboard value, the front freeboard set point being substantially the same as
the rear
freeboard set point.
53. A method as claimed in any one of claims 37 to 52, comprising providing
a
mass controller arranged to use the car mass error value to produce the at
least one
freeboard set point.
54. A method as claimed in claim 53, wherein the mass controller is a
discrete
controller.
55. A method as claimed in claim 53, wherein the mass controller comprises
a
proportional-integral (PI) controller.
56. A method as claimed in claim 55, wherein the proportional-integral (PI)
controller is in in velocity form.
57. A method as claimed in any one of claims 53 to 56, wherein the mass
controller
is arranged to implement the following algorithm:

32
where m i is the new controller output corresponding to a new freeboard set
point, m i-1
is the previous controller output, K c is an overall controller gain constant,
K i is an
integral gain constant, e i is a constant error value between the current mass
set point
value and the current car mass, and eo is a previous error value between the
previous
mass set point value and the previous car mass.
58. A method as claimed in any one of claims 37 to 57, comprising defining
maximum and minimum values for the freeboard set point.
59. A method as claimed in any one of claims 37 to 58, comprising providing
at
least one freeboard controller arranged to control timing of flow of material
from the
surge bin by controlling the front and/or rear slider position based on the at
least one
freeboard error value.
60. A method as claimed in claim 59, comprising providing a front freeboard
controller and a rear freeboard controller, the front freeboard controller
arranged to use
a front freeboard error value indicative of an error between a measured front
freeboard
value and the freeboard set point to control timing of commencement of flow of
material from the surge bin based on the front freeboard error value, and the
rear
freeboard controller arranged to use a rear freeboard error value indicative
of an error
between a measured rear freeboard value and the freeboard set point and to
control
timing of cessation of flow of material from the surge bin based on the rear
freeboard
error value
61. A method as claimed in claim 59 or claim 60, wherein the or each
freeboard
controller is a discrete controller.
62. A method as claimed in claim 61, wherein the or each freeboard
controller
comprises a proportional-integral-derivative (PID) controller.
63. A method as claimed in claim 62, wherein the proportional-integral-
derivative
(PID) controller is in velocity form.
64. A method as claimed in claim 63, wherein the PID controller is a PID-
gamma
controller.

33
65. A method as claimed in claim 61, wherein the or each freeboard
controller
comprises a proportional-integral-derivative (PID) controller.
66. A method as claimed in any one of claims 59 to 65, wherein the or each
freeboard controller is arranged to implement the following algorithm:
m i=(1 + a)m i-1-am i-2 + e i(K p+K i+b)-e i-1(K p[1 + a]+ a K i+2b)+e i-2(K p
a + b) (3)
where:
m i is the new controller output, that is, the new slider position in mm;
m i-1 is the current slider position;
m i-2 is the previous slider position;
e i is the new freeboard error (mm);
e i-1 is the current freeboard error (mm);
e i-2 is the previous freeboard error (mm);
K p is a proportional gain parameter;
K i is an integral gain parameter;
b is a Kd/gamma control parameter;
a is an exp(-1/gamma) control parameter.
67. A method as claimed in any one of claims 37 to 66, comprising setting
an
initialisation freeboard set point value at commencement of loading of a train
and prior
to obtaining at least one measured freeboard value indicative of a front
and/or rear
freeboard of a car, the initialisation freeboard set point value being used
until the at
least one measured freeboard value is obtained.
68. A method as claimed in claim 67, comprising determining a freeboard set
point
based on the front and rear freeboard values when front and rear measured
freeboard
values are obtained after initialisation.

34
69. A method as claimed in any one of claims 37 to 68, comprising adjusting
the
rear slider in response to an adjustment to the front slider so as to
compensate for a
change to the rear freeboard caused by a change to the front slider.
70. A method as claimed in any one of claims 37 to 69, comprising
facilitating
manual adjustment of the timing of flow of material from the surge bin by an
operator.

Description

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1
A TRAIN LOADING SYSTEM
Field of the Invention
The present invention relates to a train loading system for loading mined
material onto
a train at a mine operation.
Background of the Invention
It is known to provide a mine operation such as a mine site with a train
loading facility
arranged to facilitate loading of material onto dedicated material transport
trains by
train loadout operators.
Typically, ore is carried by a conveyor from a reclaimer to a surge bin, and
ore flows
out of the surge bin and into cars of the train as the train continuously
moves under the
bin. Ore flow from the surge bin is determined by an operator by controlling
the
opening and closing times of a clam, with the aim being to load material into
a car such
that the volume and mass of material in the car are close to but do not exceed
defined
limits.
Summary of the Invention
It will be understood that in the present specification a mine operation means
any
operation or facility associated with extracting, handling, processing and/or
transporting
bulk commodities in a resource extraction environment or part of such a
process, for
example mine sites, rail facilities, port facilities, and associated
infrastructure.
In accordance with a first aspect of the present invention, there is provided
a train
loading system for loading material onto cars of a train, the system
comprising:
a surge bin arranged to receive material and supply material to cars of a
train
that travels relative to the surge bin, wherein flow of material from the
surge bin is
controllable to prevent or permit flow of material from the surge bin and
thereby control
the volume of material loaded into a car of the train; and
at least one freeboard measuring device arranged to produce at least one
measured freeboard value indicative of a front and/or rear freeboard of a car;

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the system arranged to determine a car mass error value representing an error
between a car mass value indicative of a mass of material in a car and a
defined car
mass set point, and to use the car mass error value to produce at least one
freeboard
set point indicative of desired front and rear freeboard values; and
the system arranged to determine at least one freeboard error value indicative
of an error between a measured freeboard value and a freeboard set point and
to
control timing of flow of material from the surge bin based on the freeboard
error value
so as to control the mass and volume of material loaded into the car.
In an embodiment, the car mass value is indicative of a mass of a car after
the car has
been loaded with material.
In an embodiment, the system includes a weighing device arranged to produce
the car
mass value after the car has been loaded with material. The weighing device
may be
disposed at a location at least one car away from the surge bin, for example 4
cars
away from the surge bin.
In an embodiment, the system includes a mass estimator, wherein the car mass
value
is indicative of an estimated car mass before or as the car is loaded with
material from
the surge bin.
In an embodiment, the system includes at least one car detection sensor
arranged to
detect presence of a car and determine a train location reference usable to
determine
a position of the car relative to the surge bin as the car moves relative to
the surge bin,
the system controlling the timing of flow of material from the surge bin
according to the
determined position of the car relative to the surge bin.
In an embodiment, the system includes a first car detection sensor arranged to
detect
presence of a car and determine a first train location reference before the
surge bin,
the first train location reference usable to determine a front slider position
indicative of
a position of the car relative to the first train location reference, the
system controlling
the timing of commencement of ore flow according to the determined front
slider
position.

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In an embodiment, the system includes a second car detection sensor arranged
to
detect presence of a car and determine a second train location reference after
the
surge bin, the second train location reference usable to determine a rear
slider position
indicative of a position of the car relative to the second train location
reference, the
system controlling the timing of cessation of ore flow according to the
determined rear
slider position.
In an embodiment, the first and/or second car detection sensor comprises a
photoelectric cell.
In an embodiment, the at least one freeboard measuring device comprises a
front
freeboard measuring device arranged to produce a front freeboard value
indicative of a
front freeboard of a car.
In an embodiment, the at least one freeboard measuring device comprises a rear
freeboard measuring device arranged to produce a rear freeboard value
indicative of a
rear freeboard of a car.
In an embodiment, the at least one freeboard measuring device is disposed at a
location at least one car away from the surge bin, for example 3 cars away
from the
surge bin.
The at least one freeboard measuring device may comprise at least one laser
measuring device.
In an embodiment, the at least one freeboard measuring device is arranged to
produce
a raw freeboard value and the system comprises at least one filter arranged to
filter the
raw freeboard value to produce a filtered freeboard value. The at least one
filter may
comprise a low pass filter. The at least one filter may be a discrete filter
and may be
arranged to implement the following filter algorithm:
µ),
F r=1 _______________________________
= I " +1

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where F, is the new filtered freeboard measurement, F1_1 is the previous
filtered
freeboard measurement, L, is the raw measurement signal received from the
laser and
f is a filter constant.
In an embodiment, the system comprises an overload controller arranged to
cause
cessation of flow of material from the surge bin when the car mass value
exceeds a
defined value.
In an embodiment, if the overload controller has caused flow of material from
the surge
bin to cease, the system is arranged to use a new filtered rear freeboard
measurement
if the new filtered freeboard measurement is below the freeboard set point,
and to use
a previous filtered rear freeboard measurement if the new freeboard
measurement is
above the freeboard set point.
In an embodiment, the at least one freeboard set point includes a front
freeboard set
point associated with a measured front freeboard value and a rear freeboard
set point
associated with a measured rear freeboard value, the front freeboard set point
being
substantially the same as the rear freeboard set point.
In an embodiment, the system comprises a mass controller arranged to use the
car
mass error value to produce the at least one freeboard set point. The mass
controller
may be a discrete controller, and may comprise a proportional-integral (P1)
controller
that may be in velocity form. The mass controller may be arranged to implement
the
following algorithm:
where m, is the new controller output corresponding to a new freeboard set
point, mo
is the previous controller output, K, is an overall controller gain constant,
K, is an
integral gain constant, e, is a constant error value between the current mass
set point
value and the current car mass, and eo is a previous error value between the
previous
mass set point value and the previous car mass.
In an embodiment, the system is arranged to define maximum and minimum values
for
the freeboard set point.

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In an embodiment, the system comprises at least one freeboard controller
arranged to
control timing of flow of material from the surge bin by controlling the front
and/or rear
slider position based on the at least one freeboard error value.
5
In an embodiment, the system comprises a front freeboard controller and a rear
freeboard controller, the front freeboard controller arranged to use a front
freeboard
error value indicative of an error between a measured front freeboard value
and the
freeboard set point to control timing of commencement of flow of material from
the
surge bin based on the front freeboard error value, and the rear freeboard
controller
arranged to use a rear freeboard error value indicative of an error between a
measured
rear freeboard value and the freeboard set point and to control timing of
cessation of
flow of material from the surge bin based on the rear freeboard error value
In an embodiment, the or each freeboard controller is a discrete controller,
and may
comprise a proportional-integral-derivative (PID) controller that may be in
velocity form.
In an embodiment, the or each freeboard controller is a PID-gamma controller.
In an embodiment, the or each freeboard controller is arranged to implement
the
following algorithm:
(1 (3)
where:
m, is the new controller output, that is, the new slider position in
mm;
mo is the current slider position;
m12 is the previous slider position;
e, is the new freeboard error (mm);
eo is the current freeboard error (mm);
e12 is the previous freeboard error (mm);
Kp is a proportional gain parameter;
K, is an integral gain parameter;

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b is a Kd/gamma control parameter;
a is an exp(-1/gamma) control parameter.
In an embodiment, at commencement of loading of a train and prior to obtaining
at
least one measured freeboard value indicative of a front and/or rear freeboard
of a car,
the system is arranged to set an initialisation freeboard set point value, the
initialisation
freeboard set point value being used until the at least one measured freeboard
value is
obtained.
In an embodiment, the system is arranged such that when front and rear
measured
freeboard values are obtained after initialisation, a freeboard set point is
determined
based on the front and rear freeboard values, for example by averaging the
front and
rear freeboard values.
In an embodiment, the system is arranged to adjust the rear slider in response
to an
adjustment to the front slider so as to compensate for a change to the rear
freeboard
caused by a change to the front slider.
In an embodiment, the system is arranged to facilitate manual adjustment of
the timing
of flow of material from the surge bin by an operator.
In accordance with a second aspect of the present invention, there is provided
a
method of loading material onto cars of a train at a mine operation, the
method
comprising:
receiving material to be loaded onto cars in a surge bin;
supplying material to cars of a train as the train travels relative to the
surge bin,
wherein flow of material from the surge bin is controllable to prevent or
permit flow of
material from the surge bin and thereby control the volume of material loaded
into a car
of the train;
producing at least one measured freeboard value indicative of a front and/or
rear freeboard of a car;
determining a car mass error value representing an error between a car mass
value indicative of a mass of material in a car and a defined car mass set
point;
using the car mass error value to produce at least one freeboard set point
indicative of desired front and rear freeboard values;

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determining at least one freeboard error value indicative of an error between
a
measured freeboard value and a freeboard set point; and
controlling timing of flow of material from the surge bin based on the
freeboard
error value so as to control the mass and volume of material loaded into the
car.
Brief Description of the Drawings
The present invention will now be described, by way of example only, with
reference to
the accompanying drawings, in which:
Figure 1 is a diagrammatic perspective representation of a train loading
system
according to an embodiment of the present invention;
Figure 2 shows timing diagrams representing open and close distances
associated with opening and closing of a clam of a surge bin;
Figure 3 is a diagrammatic representation of a loaded car of a train
illustrating
front and rear freeboards;
Figure 4 is a block diagram of a control system of the train loading system
shown in Figure 1; and
Figure 5 is a schematic diagram illustrating functional components of the
control
system shown in Figure 4.
Description of an Embodiment of the Invention
An embodiment of a train loading system will now be described with reference
to mine
operations in the form of mine sites, although it will be understood that
other mine
operations wherein train loading operations occur are envisaged.
An example train loading system 10 is shown diagrammatically in Figure 1.
The train loading system 10 is arranged to load material 12, in this example
ore, onto
cars 14 of a train 16.
During train loading, ore flows out of a surge bin 20 and into cars 14 of the
train 20 as
the train continuously moves under the surge bin 20 in the direction of arrow
18. The
ore flow from the surge bin 20 is controlled by opening and closing a clam 22.

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In order to fill a car 14 to a volume of material that corresponds closely to
a desired car
mass level and does not cause material to overflow from the car 14, the clam
must be
controlled to open and close at the correct times relative to movement of the
train 16.
However, given that variations may exist between cars, for example because the
density of material loaded into each car varies, the optimum clam open and
close times
may vary for each car 14.
In order to control the timing of clam opening and closing, the system 10
includes a
first car detection sensor 24, arranged to provide a first train location
reference usable
to define the timing of clam opening; and a second car detection sensor 26,
arranged
to provide a second train location reference usable to define the timing of
clam closing.
In this example, the first train location reference is indicative of the
location of a front
edge of a car 14 prior to movement of the car 14 to a location under the surge
bin 20,
and the second train location reference is indicative of the location of a
rear edge of a
car 14 after the car 14 has moved from a location under the surge bin 20,
although it
will be understood that other arrangements are possible. In this example, each
of the
first and second car detection sensors 24, 26 includes a photoelectric cell
arranged to
detect presence of an object in a field of view of the cell, although it will
be understood
that any suitable sensor capable of detecting presence of a car is envisaged.
Using the determined first and second train location references, the system 10
defines
a timing relationship 28 for opening the clam 22 and a timing relationship 30
for closing
the calm 22, as shown in Figure 2.
As shown in Figure 2, the open timing relationship 28 defines an open distance
offset
32 corresponding to the distance of train movement between detection of a car
14 by
the first car detection sensor 24 and opening of the clam 22, the open
distance offset
32 including a fixed front base component 34 and a front slider component 36
that is
variable. It will be understood that the distance defined by the front slider
component
36 therefore determines the location of a car 14 relative to the clam 22 when
the clam
opens, and in this way the front slider component 36 is a variable component
that can
be used to control the amount of material loaded into the car 14.

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Similarly, the close timing relationship 30 defines a close distance offset 38
corresponding to the distance of train movement between detection of a car 14
by the
second car detection sensor 26 and closing of the clam 22, the close distance
offset 38
including a fixed rear base component 40 and a rear slider component 42 that
is
variable. It will be understood that the distance defined by the rear slider
component
42 therefore determines the location of a car 14 relative to the clam 22 when
the clam
closes, and in this way the rear slider component 42 is a variable component
that can
be used to control the amount of material loaded into the car 14.
Setting the open and close distances by setting the front and rear slider
components
36, 42 in order to modify the amount of material loaded into a car 14 will be
referred to
in this specification as controlling the "sliders".
During use, the system 10 is capable of adjusting the sliders 36, 42
automatically as
necessary in order to account for process variation (such as ore density or
variations in
flow properties) and thereby control the mass and volume of ore in each car
14.
Figure 3 shows an example fully loaded car 14 of a train 16. As shown, when
material
12 is loaded into the car 14, the material forms a mound that may extend above
upper
edges 43 of the car at a location generally central of the car 14, and may
extend below
the edges 43 of the car 14 at front and rear ends of the car 14. The distance
measured in a generally horizontal direction between a front upper edge of the
car 14
and the material 12 is termed the "front freeboard" 44. Similarly, the
distance
measured in a generally horizontal direction between a rear upper edge of the
car 14
and the material 12 is termed the "rear freeboard" 46.
It will be appreciated that the front and rear freeboards 44, 46 are
indicative of the
amount of material in the car 14 in the sense that an increase in the front
and/or rear
freeboard 44, 46 corresponds to a reduction in the volume of material in the
car 14,
and a decrease in the front and/or rear freeboard 44, 46 corresponds to an
increase in
the volume of material in the car 14.
It will also be appreciated that the front and rear freeboards 44, 46 are
dependent on
the front and rear sliders 36, 42, and therefore by controlling the front and
rear sliders,

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the front and rear freeboards 44, 46 can be controlled and thereby the mass
and
volume of material in the car 14 controlled.
As shown in Figure 1, the system also 10 includes a weighing device 45
arranged to
5 determine a net weight value of each car 14 as the car moves forwards, a
front
freeboard measuring device 47 arranged provide a measured value for the front
freeboard 44 of a car 14, and a rear freeboard measuring device 49 arranged
provide a
measured value for the rear freeboard 46 of the car 14.
10 In this example, the weighing device 45 comprises track scales, although
any suitable
device for weighing a car 14 is envisaged.
In this example, each of the front and rear freeboard measuring devices 47, 49
includes a laser based measuring device, although it will be understood that
any
suitable measuring device capable of providing a value indicative of the front
and rear
freeboards 44, 46 is envisaged.
It will be appreciated that in this example the measured values for the front
and rear
freeboards 44, 46 are delayed by three cars 14, and the net weight value
produced by
the weighing device 45 is delayed by four cars.
The system 10 is arranged to automatically adjust the sliders 36, 42 with a
view to
controlling the mass and volume in a car 14 so that the mass in the car is
maintained
at a desired mass set point, whilst ensuring that the ore does not overflow
from the car
14.
For this purpose, the system 10 implements a cascade control arrangement
wherein a
desired set point for the front and rear freeboards 44, 46 is determined based
on a
determined error between a desired mass set point and a measured car mass
value
indicative of an actual car mass (for example provided by the weighing device
45).
The desired mass set point is indicative of a desired net mass of a car 14 and
the
desired set point for the front and rear freeboards 44, 46 is a set point for
the front and
rear freeboards that is considered to correspond to the desired net mass for
the car 14.
Based on the determined freeboard set point, values for the front and rear
sliders 36,
42 are then set.

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In this example, the front and rear freeboard set points are the same; that
is, the same
freeboard set point is used for both the front and rear freeboards 44, 46,
which ensures
that the mass of material in a car 14 is correctly balanced between the front
and rear of
the car 14.
A block diagram representing a control system 50 of the train loading system
10 is
shown in Figure 4, the control system 50 implementing the cascade control
arrangement.
The control system 50 includes a mass controller 56 that receives a measured
mass
value 52 (for example, from the weighing device 45) and a mass set point value
54,
and based on the measured mass value 52 and the mass set point value 54
calculates
a freeboard set point value 58. The freeboard set point value 58 is for both
the front
and rear freeboards 44, 46 and as such is provided to a front freeboard
controller 60
and a rear freeboard controller 62 which also respectively receive a front
freeboard
measurement and a rear freeboard measurement from respective front and rear
freeboard measuring devices 47, 49. Using a front freeboard error value
representing
a difference between the freeboard set point 58 and the front freeboard
measurement,
the front freeboard controller 60 calculates a front adjustment value for an
open slider
adjuster 64. Similarly, using a rear freeboard error value representing a
difference
between the freeboard set point 58 and the rear freeboard measurement, the
rear
freeboard controller 60 calculates a rear adjustment value for a close slider
adjuster
66. The open slider adjuster 64 controls the front slider 36 in order to
adjust the
location of the car 14 relative to the clam 22 when the clam opens. Similarly,
the close
slider adjuster 66 controls the rear slider 42 in order to adjust the location
of the car 14
relative to the clam 22 when the clam closes.
It will be understood that since the system 10 operates on the basis of the
mass of
each car 14, the mass controller 56, and the front and rear freeboard
controllers 60, 62
are of discrete controller type that operate on the basis of individual cars,
not time.
Functional components 70 of the train control system 10 are shown in more
detail in
Figure 5.

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The functional components 70 include mass control components 72 arranged to
produce the freeboard set point value 58 using measured and desired car mass
values, and slider control components 74 arranged to use the freeboard set
point value
58 to determine the front and rear freeboard adjustment values for the open
and close
slider adjusters 64, 66.
The mass control components 72 show a mass estimator 76 and the car weighing
device 45, one of which provides a car mass value indicative of the mass of a
car 14 to
an overload controller 78 arranged to generate a close clam instruction 80
when the
car mass value exceeds a defined value. The car mass value is also provided to
a
mass error determiner 86 that calculates a mass error between the mass set
point 54
and the car mass value, in this example, the mass set point 54 being defined
based on
current mass loading statistics 82 and a desired overload rate 84. The mass
control
components 72 also include the mass controller 56 and auto/manual mass control
switch 100.
In this example, the mass controller 56 is a proportional-integral (P1)
feedback
controller implemented as a discrete controller. As such, the controller does
not
produce an output until a new railcar mass measurement arrives, either from
the car
weighing device 45 or the mass estimator 76. When this occurs, a new freeboard
set
point 58 for the front and rear freeboard controllers 60,62 is calculated. The
mass
controller 56 is implemented in velocity form, thus allowing for bumpless
transfer with
operator actions.
As shown in Figure 5, the mass controller 56 may use either a trackscale
measurement from the car weighing device 45 or a car mass estimate from the
mass
estimator 76 as input. The trackscale measurement is more accurate, but
includes a
delay which the mass estimator 76 does not. Both reduced accuracy and feedback
delay will limit the tunability and performance of the mass controller 56, so
the best
choice will depend on the relative error of the mass estimator 76 and the
distance
between the surge bin 20 and the car weighing device 45 for a given site.
Testing has shown that for some cars 14, a total freeboard change of 100mm
causes a
change in mass of about 2 tonnes, and therefore changing each of the front and
back
freeboards by about 25 mm will cause about 1 tonne mass change. For other cars
14,

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changing each of the front and back freeboards by 25 mm will cause about 2.2
tonnes
change in mass.
The auto/manual mass control switch 100 is arranged to enable an operator to
place
the mass controller 56 in manual mode or automatic mode. When the mass
controller
56 is in manual mode, the freeboard set point 58 must be initialized to an
appropriate
value before automatic mode can commence.
At commencement of loading of a train 16, no freeboard measurements have yet
been
provided by the front and rear freeboard measuring devices 47, 49, and
consequently
the mass controller 56 cannot be placed in automatic mode and instead
commences in
manual mode. With the mass controller 56 in manual mode, the mass controller
output
- the freeboard set point 58 - is manually set to an initialisation freeboard
set point
value. The initialisation freeboard set point value is used until freeboard
measurements are provided by the front and rear freeboard measuring devices
47, 49
(after a delay corresponding to 3 cars). When this occurs, the auto/manual
mass
control switch 100 is set to automatic and the output of the mass controller
56 set to a
value corresponding to the current, filtered, freeboard measurements obtained
using
the front and rear freeboard measuring devices 47, 49.
In an example during use with the mass controller 56 in automatic mode, the
following
parameters exist:
i) the current car mass set point 54 is 120 tonnes;
ii) cars are used wherein a change to each of the front and back
freeboards 42, 46 by about 25 mm will cause about 1 tonne mass
change in the car;
iii) based on the current car mass set point 54 and the current car mass,
the current mass controller output defines a freeboard set point of 50
mm (that is, each of the front and rear freeboards have a freeboard set
point of 50 mm);
iv) the mass of a new car is measured and weighs 117 tonnes net, and
therefore the mass error for the new car is therefore 117-120 = -3
tonnes; and

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v) the previous car weighed 118 tonnes so the previous car mass
error
was -2 tonnes.
In this example, the velocity form of the PI discrete control algorithm
implemented by
the mass controller 56 to produce a controller output m, corresponding to the
freeboard
set point 58 is given by:
(1)
where m, is the new controller output, mo is the previous controller output,
K, is an
overall controller gain constant, K, is an integral gain constant, e, is a
constant error
value between the current mass set point value 54 and the current car mass,
and e1_1 is
a previous error value between the previous mass set point value 54 and the
previous
car mass.
In simulations, values of 1.8 for K, and 0.333 for K, have been found to give
reasonable
results.
zo Therefore, based on the above parameters, the new controller output m,
is 50 + 1.8*(
3+2) + 1.8*0.333*(-3) = 46.4 mm.
If another car then arrives with mass of 122 tonnes, the next controller
output m, would
be 46.4 + 1.8*(2-(-3)) + 1.8*0.333*2 = 56.6mm.
It will be appreciated that in this example the calculated controller output
values that
define the freeboard set point value 58 are constrained to appropriate maximum
and
minimum freeboard set point values 58 so as to avoid the possibility of the
mass
controller 56 producing an inappropriate outlier freeboard set point value 58.
The raw freeboard measurements produced by the front and rear freeboard
measuring
devices 47, 49 are noisy. As a consequence, the raw measurement signals
produced
by the freeboard measuring devices 47, 49 are filtered prior to providing the
freeboard
measurements to the freeboard controllers 60, 62. Since the raw freeboard

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measurement signals arrive intermittently - when a car 14 arrives at the front
and rear
freeboard measuring devices 47, 49 - a discrete filter algorithm is used.
In the present example, the following discrete filter algorithm is used:
5
= ___________________________________ F ____________ (2)
jic +1
where F, is the new freeboard measurement, Fo is the previous freeboard
10 measurement, L, is the raw measurement signal received from the laser
and f is a filter
constant.
If the overload controller 78 has closed the clam 22 early on a car 14, the
rear
freeboard 46 will potentially be relatively large compared to the freeboard
set point. In
15 order to compensate fora falsely large rear freeboard 46 and thereby
avoid the rear
freeboard controller 62 winding up in response to intervention by the overload
controller 78, the system 10 is arranged to use the new freeboard measurement
F, if
the new freeboard measurement F, is below the freeboard set point, and to use
the
previous freeboard measurement F1_1 if the new freeboard measurement F, is
above the
freeboard set point.
In an example during use, a previous front freeboard measurement F, was 10mm,
a
previous rear freeboard measurement F, was 25mm, a new raw laser measurement
L,
of 60mm is received for the front freeboard of the next car, and a new raw
laser
measurement L, of 80mm is received for the rear freeboard of the next car. The
set
point for both the front and rear freeboard was 30mm, and f is 0.5.
Using equation (2) above, the new front freeboard measurement F, corresponding
to
the new front freeboard raw laser measurement L, is given by (0.5/1.5)*10 +
60/1.5 =
43.33 mm.
However, since the overload controller 78 closed the clam 22 prematurely on
this car,
the rear freeboard measurement is falsely large, and since the new freeboard
estimate
F, is above the set point, the previous freeboard measurement Fo of 25mm is
used for
the new rear freeboard measurement F,.

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It will be appreciated that selection of the filter constant f is important
and will affect the
tuning of the front and rear freeboard controllers 60, 62.
The slider control components 74 include a front low pass filter 92 for
filtering the raw
front freeboard measurement 93 received from the front freeboard measuring
device
47, in this example by applying the discrete filter algorithm shown in
equation (2), and
a rear low pass filter 94 for filtering the raw rear freeboard measurement 95
received
from the rear freeboard measuring device 49, in this example by applying the
discrete
filter algorithm shown in equation (2).
The filtered front freeboard measurement and the freeboard set point 58 are
provided
to a front freeboard error determiner 88 that calculates a front freeboard
error indicative
of the difference between the filtered front freeboard measurement and the
freeboard
set point 58. Similarly, the filtered rear freeboard measurement and the
freeboard set
point 58 are provided to a rear freeboard error determiner 90 that calculates
a rear
freeboard error indicative of the difference between the filtered rear
freeboard
measurement and the freeboard set point 58.
The front freeboard error is provided to the front freeboard controller 60
that uses the
front freeboard error to produce the front slider adjustment value for the
open slider
adjuster 64. Similarly, the rear freeboard error is provided to the rear
freeboard
controller 62 that uses the rear freeboard error to produce the rear slider
adjustment
value for the close slider adjuster 66.
The slider control components 74 also include a front manual adjustment
control 102
and rear manual adjustment control 104 usable to facilitate manual adjustment
of the
front and rear sliders respectively by an operator and thereby override the
automatic
slider control provided by the system 10.
In this example, the outputs of the front and rear freeboard controllers 60,62
are
constrained to appropriate maximum and minimum values to prevent windup.
In this example, the front and rear freeboard controllers 60, 62 are
proportional-
integral-derivative (PID) controllers that are implemented as discrete
controllers. As

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such, the front and rear sliders 36, 42 are only updated by the front and rear
freeboard
controllers 60, 62 when additional measurements arrive. In addition, the front
and rear
sliders 36, 42 are only allowed to be updated if the clam is closed.
In this example, the front and rear freeboard controllers 60, 62 are
implemented in
velocity form, thus simultaneously allowing discrete operation and making
bumpless
transfer from manual adjustments simpler.
It will be understood that changing the timing of opening of the clam 22
changes the
rear freeboard 46 in addition to the front freeboard 44, because the amount of
material
that is initially loaded into the car, including a rear portion of the car 14,
will change by
changing the front slider 36. As a result, in order to compensate for changes
to the
rear slider 42 because of changes to the front slider 36, an adjustment is
made to the
rear slider 42. In the present example, a rear freeboard compensation value 96
corresponding to at least a portion of the calculated changes to the front
slider 36 is
subtracted from the calculated changes to the rear slider 42, as shown in
Figure 5.
However, if the mass overload controller 78 has closed the clam 22 early to
the extent
that the current rear freeboard 46 is below the freeboard set point 58, the
rear
freeboard compensation value 96 is not passed on to the rear freeboard
controller 62.
Without this, the rear freeboard controller could wind up.
The front and rear freeboard controllers 60, 62 operate on a discrete basis
and need to
cope with the time delay imposed by the freeboard measuring devices 47, 49, as
well
as the lag imposed by the low pass filters 92, 94. For this reason, in this
example PID-
gamma controllers are used for the front and rear freeboard controllers 60,
62.
In this example, the discrete velocity form of a PID-gamma controller is as
follows:
1 COM K,+13)¨e (K,[1 c] _ (3)
where:
m, is the new controller output, that is, the new slider position in
mm;

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rni_i is the current slider position;
m1-2 is the previous slider position;
ei is the new freeboard error (mm), noting that the error sense is
reversed for front
and rear freeboard.
e1_1 is the current freeboard error (mm);
e1_2 is the previous freeboard error (mm);
Kp is the proportional gain ¨
a controller tuning parameter;
K1 is the integral gain ¨ a controller tuning parameter;
b is Kd/gamma ¨ a controller tuning parameter
a is exp(-1/gamma) ¨ a controller tuning parameter
This control form can be coded into a PLC as an algorithm that only executes
when a
new freeboard measurement arrives from a freeboard measuring device 47, 49.
Internal model control (IMC) tuning rules for the PID-gamma controller have
provided
the following suggestions for initial controller tuning parameters:
Kp = 0.05
K = 0.066
a = 0.434
b = -0.01167
In an example during use, the following parameters exist:
Parameter 'Value
.Current open slider pOSbri, m 5 mm
Previous open s4der posibon, m 90 mm
Front freeboard ..set oblnt 50 mm
New Mtered front freeboard measurement 47 mm
Current fiitered front freeboard rri E0,"33irement 4 mm
previous filtered front freebo.ard measurem4,-Jnt 40 mm
,Curcen :.bse s$ider taositon, ni 55 mm
Previous dose s4der position, im.7 50 ram
Rear freeboard set pat 50 ram
New fitered rear freeboard measurement t,/ ram
Current fiftered rear freeboar-d measurement 60 ram
Previous filtered Mai': freabOaUl rieserner 2mfit
Table 3

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Based on these values, the error values ei, ei_i, e1_2 are calculated, as
follows:
Front Rear
= 47-50 - -3
E=i_; = 45-50 - -5i=6O-5O= 10
Table 4
Using the values in Table 3 and Table 4, the new front slider mi is calculated
as
follows:
m1 (front) = (1+0.434)*95 - 0.434*90 - 3*(0.05+0.066-0.01167) +
5*(0.05*(1+.434) +
0.434*0.066 - 2(0.01167)) - 10*(0.434*0.05-0.01167) = 97.1 mm
Similarly, the new rear slider mi is calculated using the values in Table 3
and Table 4
as follows:
m, (rear) = (1+0.434)*55 - 0.434*50 + 7*(0.05+0.066-0.01167) -
10*(0.05*(1+0.434) +
0.434*0.066 - 2(0.01167)) + 12*(0.434*0.05-0.01167) = 57.3 mm
Accordingly, in this example it can be seen that with successive cars, the
front and rear
freeboard controllers 60, 62 cause the freeboards 44, 46 to trend towards the
freeboard set point and the front slider to gradually increase in order to
effect a gradual
reduction in the front freeboard.
As discussed above, the overload controller 78 is arranged to close the clam
22 early
in response to a high likelihood of mass overload of a car 14. Closing the
calm early
has the effect of increasing the rear freeboard and reducing the mass of ore
loaded
into the car 14. Frequent intervention by the overload controller 78 has the
potential to
cause wind up in the rear freeboard controller 62 and the mass controller 56.
The impact of the overload controller 78 on the rear freeboard controller 62
can be
reduced by estimating what the rear freeboard 46 would have been if the
overload
controller 78 had not intervened. This can be done by subtracting the "early
close
distance" (the distance between the rear slider 42 and the actual position of
the car

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when the overload controller 78 caused the clam 22 to close) from the measured
rear
freeboard measurement 95 for the car. The adjusted value is then used as an
input to
the rear freeboard filter 94.
5 The impact of the overload controller 78 on the mass controller 56 can be
reduced by
adding a "tonnes removed" mass value corresponding to the early close distance
multiplied by a constant of approximately 13 tonnes per metre to the measured
mass
for the car. The adjusted value of mass is then used as an input to the mass
controller
56 so that the current mass value input to the mass error determiner 86 more
10 accurately represents the car mass value that will have occurred if the
overload
controller 78 had not intervened.
The averaged value of the current filtered front and rear freeboard
measurements
should be used as the initial output of the mass controller 56 when the mass
controller
15 56 is first switched to automatic mode.
In the example above, the current front and rear filtered freeboard
measurements mo
are 47mm and 57mm respectively. If the mass controller 56 is currently in
automatic
mode, switching the mass controller 56 to manual mode then immediately back to
20 automatic mode would cause the set point for the front and rear
freeboard controllers
60, 62 to be set to (47+57)/2 = 52mm. In this circumstance, 52mm would also be
the
value used by the mass controller 56 for the values in equation (1) for the
new and
current freeboard set points mõ
Because the velocity form of the PID controllers has been used, transfer
between
automatic and manual modes is straightforward for the freeboard controllers
60, 62.
When the freeboard controllers 60, 62 are in manual mode, the control
calculation
defined in equation (3) is not executed, and the latest (manual) value for m,
is used for
the current and previous slider positions mo, m12. Similarly, the current
value for the
new freeboard error e, is used and the current and previous freeboard error
values eo,
e12 are also set to this value. This ensures that there is no "bump" and the
controller
restarts normally.
The operator is able to adjust the sliders 36, 42 while the controllers are in
automatic
mode, and any adjustment made is treated as a brief transition into manual
mode and

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21
back to automatic mode such that the mass and freeboard controllers 56, 60, 62
are
reset as described above.
Controller tuning, and particularly freeboard controller tuning, is important
to the
reliability of the system 10. The freeboard controllers 60, 62 should be tuned
first
before tuning the mass controller 56. The initial tuning process may follow a
procedure
according to the following:
= Establish stable loading conditions with the mass and freeboard
controllers 56,
60, 62 in manual mode;
= Put the rear freeboard controller 62 in automatic mode, with both the
mass
controller 56 and the front freeboard controller 60 in manual mode;
= Make a step change to the freeboard set point 58, observe the effect on
the
rear freeboard controller 62 and tune as normal.
= Leave the rear freeboard controller 62 in automatic mode and tune the front
freeboard controller 60, verifying that the decoupling of the front and rear
controllers 60, 62i5 effective;
= Load several cars 14 with the front and rear freeboard controllers 60, 62
in
automatic mode, but providing manual step set point changes to the freeboard,
and verifying that the combined performance is acceptable; and
= Place the mass controller in automatic mode with appropriate controller
gains
as set by the observation of the response to the manual set point changes.
In order for the system to perform safely and well, it is important that the
freeboard
measuring devices are operating reliably. A permissive should be installed
such that
the freeboard controllers 60, 62 cannot be put into automatic mode unless the
freeboard measuring devices are running properly.
Once the system 10 is operating in automatic mode, if a valid freeboard signal
has not
been detected for five cars, then the system 10 may be arranged so as to place
the
controllers 56, 60, 62 in manual mode with the system not allowing the
controllers 56,
60, 62 to move to automatic mode until at least one valid freeboard signal has
been
received.

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It is to be understood that, if any prior art publication is referred to
herein, such
reference does not constitute an admission that the publication forms a part
of the
common general knowledge in the art, in Australia or any other country.
In the claims which follow and in the preceding description of the invention,
except
where the context requires otherwise due to express language or necessary
implication, the word "comprise" or variations such as "comprises" or
"comprising" is
used in an inclusive sense, i.e. to specify the presence of the stated
features but not to
preclude the presence or addition of further features in various embodiments
of the
invention.
Modifications and variations as would be apparent to a skilled addressee are
deemed
to be within the scope of the present invention.

Representative Drawing