The present invention relates to a method and an apparatus for controlling an unloader for unloading bulk material from the hold of a ship, said unloader comprising a tower rotatable about a vertical axis, a horizontal conveyor which is rotatably mounted in said tower about an axis perpendicular to its longi¬ tudinal direction and the axis of rotation of the tower, and a vertical conveyor hingedly suspended at the end of the horizontal conveyor facing away from the tower, said vertical conveyor being swingable relative to said horizontal conveyor at least in a plane common to said horizontal conveyor and said vertical conveyor.

Unloaders of this type which are previously known from, for example, Swedish patents 377,099 and 390,157, may be mounted on the ship which is to be unloaded, on a quay, or on a floating platform separate from the ship, or on another ship. Unloaders for handling longer ships with several holds are preferably mounted on a carriage travelling in the fore and aft direction of the ship. In order to achieve greater freedom of movement of the vertical conveyor in the hold, the unloader, in some cases, is so arranged that the said common plane is tiltable about an axis perpendicular to the axis of rotation of the tower.

To control the movement of the unloader while unloading is in progress, use is made traditionally of control means in a cabin or a portable control unit by which an operator who may be standing on deck at the hold which is being unloaded, can manually control the rotation of the tower, the swinging of the horizontal conveyor in the vertical plane, the pendulum

movement of the vertical conveyor relative to the horizontal conveyor and, where applicable, the travelling movement of the unloader, i.e. the tower, in the fore and aft direction of the ship as well as the tilting of the vertical conveyor.

When unloading is begun, the operator lowers the horizontal conveyor by means of a first control lever on the control unit so that the lower end of the vertical conveyor, which is operatively connected with a separate feeding device, is lowered into the material to the desired depth. During the subsequent unloading of the hold, the operator activates a second and a third control lever on the control unit to rotate the tower and imitiate the pendulum movement. of the vertical conveyor so that the feeding device is moved in the fore and aft direction of the ship and from port to starboard. When a certain volume of material has been unloaded, the horizontal conveyor is further lowered, and this procedure is repeated until but a small volume of bulk material remains in the hold. The above-mentioned primary or rough unloading normally takes from 50 to 70% of the total unloading time, the final unloading and clean-up accounting for the remaining 30-50% of the unloading time. The unloading capacity during primary unloading may be in the order of, for example, 600 tons/hour, while the final unloading capacity may be, for example, 125 tons/hour. In consideration of the relatively high ship's cost a day, it will be obvious that a reduction of the final ^' unloading and clean-up time is an object to be desired.

One important aspect contributing to the compara¬ tively long final unloading time is the fact that, when the vertical conveyor makes a pendulum movement, the feeding device is moving along an arc of circle, not along a straight line. This means that, during final unloading, the feeding device will constantly

bump against the bottom of the hold when the operator changes the pendulum position of the vertical conveyor, and the operator will then be obliged to compensate manually for the circular movement of the feeding device by raising or lowering the horizontal conveyor from which the vertical conveyor is suspended.

To solve this problem, it has been suggested to connect the control unit with a control system which, in broad terms, operates in such a manner that, during pendulum movement of the vertical conveyor, an automatic compensation is effected by raising or lowering the horizontal conveyor, such that the "cir¬ cular movement" on the feeding device is converted into a rectilinear movement in the horizontal plane. Swinging of the tower or travelling with the entire unloader along the ship has required no compensation in this respect.

The above-mentioned prior art control system which compensates for the circular movement of the feeding device during pendulum movement is sufficient if the bottom plane of the hold is horizontal, but this is not always the case. Furthermore, if the un¬ loader is separate from the ship, also a bottom plane parallel to the plane of the deck may tilt in relation to the horizontal plane because the ship is inclining in the longitudinal and/or transverse direction. The longitudinal inclination is especially pronounced when the ship is unloaded by means of a single un¬ loader travelling from hold to hold. This longitudinal e. inclination which is due to unbalance of the ship may, however, be reduced somewhat if two or more un¬ loaders are employed.

If, for example, the unloader is working from the quayside, and if the ship has both a longitudinal inclination and a transverse inclination, additional compensation is required during unloading if the un¬ loader is moved along the quayside, if the tower is

rotated, if the unloader is tilted, and if the pendulum angle of the vertical arm in relation to a vertical axis is changed.

It is the object of the invention to provide a method and an apparatus by which the feeding device can be simply and manually moved in planes parallel to the bottom plane of the hold, even though the bottom plane is inclined in relation to the horizontal plane. This object is achieved by means of a method and an apparatus having the characteristic features indicated in the appended claims.

According to the invention, each horizontal move¬ ment of the feeding device, due to manual control of the unloader movement, thus brings about an automatic compensation of the vertical position of the feeding device, such that the feeding device is made to follow a plane parallel to the bottom plane of the hold.

This brings the advantage that, during primary unloading, the material can be unloaded in layers parallel to the bottom plane, such that the material thickness relative to the bottom plane is the same throughout the hold when final unloading is begun. This makes it possible to extend the primary unloading time so that a smaller volume of material remains for final unloading, and this means that the final unloading time can be shortened, while preventing the feeding device from repeatedly bumping against the bottom of the hold.

The invention is particularly useful when the lower feeding end of the vertical conveyor has a spe¬ cially designed clean-up device which is suspended, via a universal joint, from the lower end of the verti¬ cal conveyor and whose construction is disclosed in SE 8600805-9 which has the same applicant as the present application and which relates to such a clean-up device. By combining the method which is specific to the present invention and by which the lower end of the vertical

conveyor is made to follow the bottom of the hold, with such a clean-up device, a highly efficient final unloading is achieved which, in some instances, may reduce the final unloading time by a factor 3 as com- pared with traditional unloading technique.

The principle by which the height of the feeding device of the unloader is compensated for in accordance with the present invention, as well as an exemplifying embodiment of the apparatus according to the invention, will now be described in more detail, reference being had to the accompanying drawings in which

Fig. 1 illustrates a quayside unloader of known construction and a cross-section of a ship moored adjacent the unloader; Fig. 2 is a schematic view of the unloader ac¬ cording to Fig. 1 and illustrates the magnitude of the height compensation required because of the pendulum movement of the feeding device;

Fig. 3 illustrates schematically the longitudinal inclination of a ship;

Fig. 4 illustrates schematically the magnitude of the height compensation which, because of a longi¬ tudinal inclination of the ship, is required for a horizontal movement of the feeding device in the longi- tudinal direction of the ship;

Fig. 5 illustrates schematically the transverse inclination of a ship;

Fig. 6 illustrates schematically the magnitude of the height compensation which, because of a trans- verse inclination of the ship, is required for a hori¬ zontal movement of the feeding device in the transverse direction of the ship;

Fig. 7 is a schematic top plan view of the un¬ loader according to Fig. 2 and illustrates the magni- tude of the horizontal movement of the feeding device that is achieved by rotating the tower when the ver¬ tical conveyor is vertically directed;

Fig. 8 is a schematic top plan view of the unloader according to Fig. 2 and illustrates the magnitude of the horizontal movement of the feeding device which is achieved by a pendulum movement of the vertical conveyor after the tower has been rotated such that the horizontal conveyor will assume a given angle to the transverse direction of the ship; and

Fig. 9 is an exemplifying block diagram of a control apparatus according to the invention. Fig. 1 illustrates a quayside unloader 1 of known construction and a cross-section of a hold 2 in a ship 4 moored along a quay 3. The unloader 1 substan¬ tially comprises a carriage 5 travelling in the longi¬ tudinal direction of the ship 4, a tower 6 supported by said carriage and mounted on a gear rim 7 for rotation about a vertical axis, a horizontal conveyor 8 which is hingedly suspended from the tower 6 and whose end 9 facing away from the tower 6 therefore can be raised and lowered and moved back and forth along a"circular arc with its center on the gear rim 7, and a vertical conveyor 10 which is swingably suspended from the end 9 of the horizontal conveyor 8 facing away from the tower 6 and which, in the embodiment illustrated, is swingable with respect to the horizontal conveyor 8 in a plane common to the horizontal conveyor and the vertical conveyor, as shown by the arrow A in Fig. 1. To adjust the pendulum angle between the verti- cal and the horizontal conveyor, a longitudinally adjustable device 11, such as a hydraulic piston and a. cylinder assembly, is connected with the conveyors

8 and 10 at a distance from their interconnected ends

9 and 12, respectively. The vertical conveyor 10 is provided at its lower feeding end 13 with a separate feeding device 14 of known construction. Bulk material carried in the hold 2 can be fed by means of the feeding device 14 into the lower end 13 of the vertical conveyor 10 and is conveyed via

said vertical and horizontal conveyors to a discharge location on the quay 3.

By means of a control unit (not shown) for manual control of the unloader 1, an operator can move the feeding device 14 to the desired position in the hold 2, as is shown at positions I and II in Fig. 1. In position I, the horizontal conveyor 8 is directed in the transverse direction of the ship 4, and the vertical conveyor 10 is angled such that the feeding device 14 can take up material lying on the bottom of the holder 2 below the deck area 16 on the seaward side. In position II, the carriage 5 - as compared with position I - has been laterally displaced and the tower 6 has been rotated, as indicated by the arrow B in Fig. 1, and the horizontal conveyor 8 has been slightly lowered, such that the feeding device 14 can unload material below the deck area 17 facing the unloader 1.

As mentioned by way of introduction, it is al- ready known, during manual control of the pendulum movement of the vertical conveyor 10, to automatically control the vertical position of the horizontal con¬ veyor 8, such that the feeding device 14 is moved along a horizontal straight line instead of along a circular arc.

Fig. 2 which is a schematic view of the unloader 1 and the hold 2 according to Fig. 1, illustrates how this known compensation for the circular movement of the feeding device 14 is carried out. In Fig. 2, it is assumed that the horizontal conveyor 8 is di¬ rected in the transverse direction of the ship, i.e. in the y direction according to the coordinate system shown in this Figure. Assuming that the point of sus¬ pension PI of the vertical conveyor 10 at the vertically movable end 9 of the horizontal conveyor initially is at a distance H directly above the feeding device 14 at a point P2. An angular change φ of the vertical

conveyor 10 would entail - if the angle θ of the hori¬ zontal conveyor 8 were unchanged - that the feeding device 14 would move from the point P2 along the dash- dot circular arc 18 to the position P2" which lies at a vertical distance ΔH _p from position P2. However, this circular movement is compensated for by the prior art control of the angular position Θ of the horizontal conveyor 8, such that during the pendulum movement the feeding device 14 is moved to the point P2' lying in the same horizontal plane as the point P2. With the designations in Fig. 2, the height compensation for the circular movement of the feeding device 14 is given by

ΔH = L (1-cosφ) (1)

wherein L is the pendulum length of the vertical con¬ veyor 10 and the displacement in the y direction be¬ tween points PI and Pi ¹ has been neglected. As has been mentioned by way of introduction, this compensation for the circular movement of the feeding device 14 is sufficient if the bottom plane 19 of the hold 2 is horizontal. If, on the other hand, the ship is inclined, for example in the transverse direction, the operator, during the manoeuver described with reference to Fig. 2, is obliged to constantly compensate for the transverse inclination in order to prevent that the feeding device 14 either departs from the desired horizontal plane or that it bumps against the bottom 19 of the hold.

Moreover, the above-mentioned prior art compen¬ sation is unsatisfactory for unloading ship holds where the bottom plane is inclined with respect to the deck plane of the ship. The manner in which these problems are solved in accordance with the present invention will now be described in more detail by means of simple calcu-

lations which, however, in no way are to be taken as restrictions on the invention.

Fig. 3 is a schematic side view of a ship having a positive longitudinal inclination β_ . Fig. 4 illu- strates a part of the hold bottom 19 which is inclined at an angle β_ in relation to the horizontal plane. If the feeding device 14 of the unloader initially is at point P2 and then, by manual operation of the unloader, is moved in the x direction through a di- stance ΔX to a point P2' , the longitudinal inclination must be compensated for by raising the feeding device 14 through a distance Δh _τ wherein

Δh_ = ΔX tanβ, (2)

Fig. 5 is a schematic cross-section of a ship having a positive transverse inclination β_,. Fig. 6 shows a part of the hold bottom 19 which -is inclined at an angle β_ in relation to the horizontal plane. If the feeding device 14 of the unloader initially is at the point P2 and then, by manual operation of the unloader, is moved in the y direction through a distance ΔY to a point P2 ' , the transverse inclination must be compensated for by raising the feeding device 14 through a distance Δh_, wherein

Δh _τ = ΔY • tanβ-, (3)

In the following, it is assumed that the ship 4 has both a longitudinally inclination β_ and a trans¬ verse inclination β_. The ship's inclination is com¬ pensated for by raising and lowering the free end 9 of the horizontal conveyor 8. The partial compen¬ sations necessitated by the ship's inclination for the individual operations "travelling with the carriage 5", "rotation of the tower 6", and "pendulum movement of the vertical conveyor 10" will now be briefly re-

viewed .

Fig. 7 is a schematic top plan view of the unloader 1 and a travelling path 20 for the carriage 5. The Figure illustrates the magnitude of the horizontal movement of the feeding device 14 which is accomplished by rotating the tower 6 through an angle α, in the event that the vertical conveyor 10 has no amplitude pendulum swing φ and is directed straight down. If the feeding device 14 initially is at the point P2 and, by rotation of the tower 6, is moved along the dash-dot circular arc 21 having the radius R to the point P2', the x coordinate of the feeding device 14 is changed by a value ΔX , and its y coordinate by a value ΔY . Because of the longitudinal inclination β_ of the ship, rotation of the tower 6 thus necessitates a compensation ΔH in the vertical direction of the feeding device 14, a compensation which according to formulae (2) and (3) is given by

ΔHα = Rsinα • tanβ,L + R(l-cos ) • tanβT_, (4)

If, furthermore, the unloader shown in Fig. 7 is moved, by travelling with the carriage 5, through a distance x , the ship's longitudinal inclination will require a compensation ΔH :

ΔH _v = x _v - tanβ _L ^" (5)

Fig. 8 is a top plan view of the unloader, corre¬ sponding to Fig. 7, and illustrates the magnitude of the horizontal movement of the feeding device 14 which, because of the ship's longitudinal and trans¬ verse inclination, is required for pendulum movement of the vertical conveyor 10 in the event that the horizontal conveyor 8 forms an angle α with the y axis. If the feeding device initially is in the position

P2 directly below the point of suspension of the vertical conveyor 10 and then, while retaining the same angle of rotation α of the tower 5, is moved to the point

P2', this will change the x coordinate of the feeding device 14 by a value ΔX , and its y coordinate by a value ΔYφ. Thus, ^pendulum movement of the vertical conveyor 10 will necessitate, because of the ship's longitudinal and transverse inclination, a compensation

ΔHφ in the vertical direction of the feeding device 14, a compensation which according to formulae (2) and (3) is given by

ΔH = (Lsinφsinα) • tanβ _τ J_l + (Lsinφcos ) • tanβ_i, (6)

If ΔH represents the total automatic height com¬ pensation necessitated by the control for the point of suspension of the vertical conveyor 10 in the hori¬ zontal conveyor 8, there is obtained from formulae (1), (4), (5) and (6) the relationship

ΔH = ΔHα + ΔHv + ΔHcp - ΔHp (7)

Besides the described pendulum movement of the vertical conveyor 10 in the plane common to the hori- zontal conveyor and the vertical conveyor, the verti¬ cal conveyor 10 may also be tiltable in a direction perpendicular to the pendulum movement, i.e. the un- loader may be arranged such that the said common plane can be tilted in relation to the vertical plane. In this case, further compensation is required if the vertical conveyor is tilted. This compensation will be analogous to the above-mentioned compensation for the circular movement of the vertical conveyor in the common plane upon pendulum movement, i.e. the compensation ΔH and ΔH .

P Φ Furthermore, in order to carry the above-mentioned method into effect, the present invention provides

a control device which is coupled with the operating unit and whose fundamental function will now be described in more detail, reference being had to Fig. 9 which illustrates an exemplifying block diagram of such a device. It should be pointed out in this connec¬ tion that the block diagram as shown in no way must be considered to restrict the apparatus according to the invention which is solely restricted by the statements of the appended claims. The control device shown in Fig. 9 comprises two angle sensors 30 and 31 of the water level type adapted to continuously transmit, during the entire unloading operation, signals corresponding to the ship's longitudinal inclination β_ and transverse inclination β in relation to the horizontal plane. The sensors 30 and 31 may preferably be mounted at the upper edges of the hold 2 and aligned along two straight intersecting lines lying- in a plane parallel to the bottom plane 19 of the hold. The sensors 30 and 31 are connected to a radio transmitter 32 on the ship which transmits radio signals corresponding to the ship's inclination and picked up by a receiver 33 on the quayside or the like. However other means, such as a cable, may also be used for the signal trans- mission. The received signals representing the ship's inclination are fed to a first calculating unit 34 which determines the relative inclination between the bottom plane 19 of the hold 2 and a reference plane, for example the horizontal plane, for the un- loader 1. If the bottom plane 19 of the hold, because of the ship's construction, is inclined in relation to the plane with which the sensors 30 and 31 are aligned, the first calculating unit 34 also receives information B representing the said inclination of the bottom plane 19.

In some cases, the unloader may be utilised for transferring material from one ship to another, in which case the inclination of the ship on which the

unloader is mounted must also be determined in order to calculate the relative inclination between the reference plane of the unloader and the inclination of the bottom plane in the hold from which unloading is carried out. This additional inclination information is designated F in Fig. 9 and is fed to the first calculating unit 34.

The first calculating unit 34 supplies inclination information LI corresponding to the relative inclination between the reference plane of the unloader and the bottom plane of the hold. The inclination information LI is fed to a second calculating unit 35 which con¬ tinuously receives information about the rotation of the tower 6, the travelling ^ movement xv of the carriage 5, the amplitude pendulum swing φ in the said common plane and, where applicable, information about the tilting of the vertical conveyor 10. In response to the inclination information LI and the information about the actual state of movement of the unloader, the second calculating unit 35 generates signals corresponding to the part compensations ΔH ,

ΔHv, ΔHφ and ΔHp, which are fed to a third calculating^ unit 36 transmitting a resulting control signal e for compensating for the vertical position of the feeding device 19.

The control system as described above may be realised for example by means of a microprocessor or the like coupled to the manual operating unit.