Skip filling apparatus and method

A material handling system in which a skip is filled with material from a loading flask. The skip moves downwardly during filling and the flask, which is supported by at least one ram, is caused to move downwardly in unison with the skip, to minimize material spillage.

BACKGROUND OF THE INVENTION 
This invention relates generally to the handling of material and more 
particularly to the handling of material such as ore or rock in mines. 
It is commonplace on mines to transfer ore or rock from an underground 
loading flask to a skip which is then hoisted to surface. In modern 
installations the transference of the material is effected substantially 
automatically. 
The skip referred to is suspended from a cable in a shaft and the loading 
station may be a considerable distance below surface. In the loading 
process a rapid transference of material takes place and this may be 
likened to an impulse loading of the skip. As a consequence the skip is 
subjected to oscillations and eventually settles at a point which, 
depending on its final load, can be in the order of metres below the 
position at which loading commenced. The flask on the other hand is 
stationary and consequently a substantial gap can be formed between the 
mouth of the skip and the discharge end of the flask. Material destined 
for the skip may, in this way, not enter the mouth and instead fall down 
the shaft. This material is highly hazardous to personnel and any 
installation or equipment at a lower level. 
To counteract the danger of falling material use has been made of a 
spillage bin immediately below the skip. It does happen however that the 
spillage bin can be filled with waste material in which event the skip may 
inadvertently be brought to rest on the top of this material. This can 
lead to a slack cable condition which in turn can result in cable failure. 
Various approches to the problem are to be found in the disclosures in 
German Pat. Nos. 1215884, 718546, 876901 and 392005, and in U.S. Pat. Nos. 
3,702,140, 1,708,925, 2,737,308 and 3,767,074. 
The first mentioned specification describes an arrangement wherein an 
intermediate funnel, which moves together with the skip, is used to 
transfer material from a primary bunker to the skip. The primary bunker 
does not move. This arrangement, in practice, leads to considerable 
spillage of ore down the shaft and is not satisfactory. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method of filling a 
skip which at least partly counters problems of the type described. 
The invention provides a method of filling a skip with material from a 
loading flask which includes the steps of discharging material from the 
flask into the skip and causing or permitting the flask to move downwardly 
to a limited extent during at least part of the discharge. 
The downward movement of the flask may be initiated on the opening of a 
discharge door of the flask or within a predetermined time interval of 
such opening. 
The method of the invention may include the step of controlling the 
movement of the flask in a manner which is dependent on the movement of 
the skip. 
The flask may be permitted to move in a predetermined manner. The nature of 
the movement of the flask may be determined at least partly by prior 
measurements taken of the skip movement during its filling. This data is 
then used to control the movement of the flask in subsequent filling 
operations. 
Alternatively the skip movement may be tracked during each filling 
operation and the flask may be caused or permitted to move in a manner 
which is dependent on the tracked movement of the skip. 
The flask movement may be controlled so that it is substantially asymptotic 
relatively to a reference location. The reference location may be 
substantially the lowermost position of the skip when it has come to rest 
after a filling operation. 
The method of the invention may include the step, after the skip has been 
filled, or restoring the flask to its initial position i.e. to the 
position it had before its downward movement. 
The method of the invention may include the step of supporting the flask on 
means which permits downward and upward movement of the flask. Such means 
may be actuated hydraulically or in any other suitable manner. In the 
former case the method may include the step of varying the rate of 
hydraulic fluid flow from or to the support means in a manner which is 
dependent on the movement of the skip. 
During the filling operation the skip may oscillate. The oscillation may be 
substantially undamped or more generally be underdamped. Under these 
conditions the method of the invention may include the step of controlling 
the movement of the flask so that its position is not lower at any time 
relatively to the skip than an optimum filling position. 
The method of the invention may also include the step of damping the 
movement of the skip. Preferably the skip oscillations are critically 
damped. 
The invention further extends to a material handling installation which 
includes a loading flask, a skip which is movable by means of a hoist and 
which is filled with material from the flask, and means for causing or 
permitting movement of the flask in a downwards direction while the skip 
is being filled. 
The said means may include at least one ram for supporting the flask. The 
ram may be hydraulically actuated. The ram may be movable to permit the 
flask to move downwardly, under its own mass, in a controlled manner while 
the skip is being filled. 
The hydraulic fluid flow rate may be varied to control the rate of downward 
movement of the flask. 
Use may be made of one or more control orifices or valves for regulating 
the hydraulic fluid flow rate. For example use may be made of one or more 
fixed or variable orifices or multiple independently operable valves for 
regulating the hydraulic fluid fluid flow. 
In one form of the invention the said means may be designed to react in a 
predetermined manner. For example the control orifices or valves may be 
operated in such a way that the flask is caused or permitted to move along 
a predetermined path. This path may be determined from a plurality of 
measurements of the movement of the skip during prior filling operations. 
In an alternative form of the invention use may be made of sensors for 
tracking the position of the skip and for controlling the movement of the 
flask accordingly. 
Means may be provided for damping the oscillations of the skip during the 
filling operation. For example use may be made of a braking mechanism 
which permits the skip to descend at a controlled rate while it is being 
filled. This is equivalent to a critical damping situation. With this form 
of the invention, i.e. where there are no upward movements of the skip in 
the filling operation, the downward movement of the skip can be accurately 
tracked and the downward movement of the flask can be accurately varied so 
that the skip and the flask are maintained within predetermined limits of 
each other.

DESCRIPTION OF PREFERRED EMBODIMENT 
FIG. 1 illustrates a material handling installation according to the 
invention at an underground location. The installation includes a skip 10 
which is movable vertically, upwardly and downwardly, in a shaft 12. The 
skip is suspended from a cable 14 which is movable by means of a hoist, 
not shown. When the skip is to be filled it is brought to a loading 
station 16 in the shaft; the loading station normally being located near 
or at the bottom of the shaft. 
The loading station includes a loading flask 18 and one or more conveyors 
20 for discharging material e.g. rock or ore into the flask 18. The flask 
includes a discharge chute 22 and a mechanism 24 for controlling the 
opening and closing of a door of the flask which leads onto the chute 22. 
The flask is supported by one or more vertically extending rams 26. 
FIG. 2 is a graph which illustrates the movement of the skip 10 when it is 
filled with material from the flask 18. The filling operation is effected 
substantially automatically and is initiated in a known manner when a 
sensor on the flask detects that the skip 10 has been brought to a loading 
position relatively to the flask. At this position a mouth 28 at the upper 
end of the skip is substantially adjacent and opposing the chute 22. The 
sensor transmits a signal to a control device which causes the mechanism 
24 to operate so that the door of the flask is opened. Material is then 
discharged under the action of gravity from the flask through the mouth 28 
into the skip 10. The discharge takes place rapidly and is over within a 
period of about 2 seconds. After the discharge the door of the flask is 
closed by the mechanism 24. 
The sudden inrush of material into the skip imparts a shock loading, or an 
impulse loading, to the skip. The cable 14 undergoes a degree of stretch 
and the skip oscillates whilst generally sinking lower in the shaft. This 
process is illustrated in FIG. 2 where a continuous line 30 represents the 
movement of the skip 10, during the filling operation, as it descends from 
its loading position designated by the numeral 32 to a rest position, 
designated by the numeral 34, at which the skip is fully loaded. The 
movement of the skip may thus, referring to the curve 30, be described as 
an underdamped oscillatory movement. 
In this embodiment of the invention it is an objective to cause the flask 
18 to be moved along a path shown in FIG. 2 by a dotted line and 
designated by the numeral 36. This path coincides with the peaks of the 
oscillatory skip movement and approaches the rest position 34 in a manner 
which can be described as being substantially asymtotic or, otherwise, as 
a critically damped movement. The point is that if the flask follows the 
path 36 the discharge chute 22 is never below the mouth 28 of the skip. On 
the other hand the distance between the chute and mouth is at all times 
kept to a practical minimum and spillage of material down the shaft is 
minimised as well. 
The movement of the flask 18 during the skip filling operation is 
controlled by means of the ram 26. In general it may be said that as the 
flask discharges material into the skip hydraulic fluid is permitted to 
escape from the ram so that the flask settles downwardly in a 
predetermined manner under its own mass. 
Various control circuits may be employed for regulating the movement of the 
ram 26. Examples of these circuits are illustrated in FIGS. 3 to 6. 
In the circuit of FIG. 3 a solenoid valve 38 is opened at the same time as 
material discharge from the flask is started. The valve 38 permits fluid 
from the ram 26 to flow to a receiving tank 40 through a fixed orifice 42. 
The size of the orifice is calculated to give a desired hydraulic fluid 
flow rate. During discharge of the flask the mass of the flask decreases 
and the pressure of the hydraulic fluid therefore also decreases. It may 
be seen from an examination of FIG. 2 that initially a high rate of flask 
movement is required and that the rate of movement decreases as the skip 
is filled. Since the fluid flow rate through the fixed orifice 42 is 
pressure dependent it will be possible under certain conditions to obtain 
flask movement which approximates the line 36 of FIG. 2. As pointed out in 
this way spillage of material is kept to a minimum. Once the ram 26 is 
fully settled, and this will normally take place as the skip is completely 
filled, the valve 38 is closed and a pump 44 is actuated to return fluid 
to the ram and extended so that the flask 18 is raised to its initial 
position. 
In the circuit of FIG. 4 use is again made of a solenoid valve 38 which is 
opened when filling of the skip is started. In this case the fluid flows 
from the ram through an orifice the size of which is varied by means of a 
linkage mechanism 46 which is responsive to movement of the flask 18. When 
the valve 38 is opened the flask immediately starts descending but its 
rate of movement is determined, via the linkage, by the position of the 
flask relatively to its initial position. The fluid is returned to a tank 
and, after the skip has been filled, pumped back to the ram to restore the 
flask to its initial position. 
In the circuit of FIG. 5 the hydraulic fluid flows through a variable 
orifice or valve 48. The operation of the valve i.e. its opening and 
closing is determined by means of a cam follower 50 which rides on a cam 
52 which is movable by means of the flask 18. Thus, as with the circuit of 
FIG. 4, the setting of the valve 48 is dependent on the position of the 
flask 18. 
With the circuit of FIG. 6 fluid from the ram 26 is permitted to flow 
through a solenoid valve 38 and then through parallel paths designated 54 
with each of the paths including a separate valve 56. The respective 
valves 56 are initially all opened but are closed separately at 
predetermined intervals after the valve 38 is opened. In this way the flow 
rate is varied and the flask movement is controlled so that it 
approximates the curve 36. 
Other control techniques may of course be employed for determining the 
movement of the flask. For example the flask may be supported by 
electrically actuated means such as motors which drive gear trains. It is 
also possible to control the operation of the ram by means of sensors 
which are responsive to the position of the skip during its filling. The 
sensors determine the rate of movement of the skip and its position and 
generate a control signal which is used to open or close a valve so that 
the rate of hydraulic fluid flow from the ram 26 is controlled as desired. 
In yet another form of the invention use is made of a brake mechanism on 
the skip which effectively dampens its oscillatory movement during the 
filling operation. The braking mechanism is installed on the shaft 
superstructure and is actuated at the same time as the door of the flask 
is opened. The braking mechanism permits the skip to move downwardly as it 
is loaded, at a controlled rate, and in this way minimizes oscillations of 
the skip. Thus there are no, or no substantial, upward movements of the 
skip. The flask can therefore track the downward movement of the skip far 
more accurately and the chute 22 and the mouth 28 can be maintained within 
a predetermined distance of one another with a greater degree of 
precision. This variation of the invention lends itself particularly to 
the use of sensors which track the position of the skip during each 
loading operation and which control the movement of the ram 26, or any 
other supporting device, accordingly.