Title:
INSTALLATION FOR HANDLING BULK MATERIALS
United States Patent 3556317


Abstract:
The invention provides a dragline for use in maintaining the slope of bulk materials such as for concrete making stored on the ground in compartments radiating from a distribution tower. A bucket suspended from a carriage running on a horizontal girder moves parallel to the girder until a stop on a return cable connected to the bucket abuts a front stop on the girder. Continued forward travel of the carriage causes the bucket to move in an ascending trajectory. The return cable is wound on a return winch which is connected by a clutch to winches on which are wound cables connected to the carriage and the bucket respectively and the clutch is operated to disconnect the return winch from the other winches when the latter rotate to wind-on their cables and to drive the return winch when they rotate in the opposite direction to pay out their cables.



Inventors:
Lucien Rene, Vidal Domaine De La Pimpine 33
, FR.
Application Number:
04/826211
Publication Date:
01/19/1971
Filing Date:
05/20/1969
Assignee:
LUCIEN RENE VIDAL
Primary Class:
Other Classes:
37/396, 172/26.5
International Classes:
E02F3/46; B66C11/16; B66C11/18; E02F3/54; (IPC1-7): E02F3/46
Field of Search:
214/17.84,10 198
View Patent Images:
US Patent References:
1748931Bank grader1930-02-25Lehman et al.
1002732N/A1911-09-05Morris



Foreign References:
SE416419B1980-12-22
Primary Examiner:
Gerald, Forlenza M.
Assistant Examiner:
Frank, Werner E.
Attorney, Agent or Firm:
Robert, Burns Emmanuel Lobato E. J.
Claims:
1. An installation for handling bulk materials comprising a compartmented distributor tower, a substantially horizontal girder rotatable about the vertical axis of the tower at the upper end thereof, a carriage movable along said girder, a bucket suspended below said carriage, a first winch, a traction cable connected at one end of said carriage and at the other end to said first winch, a second winch integrally connected to said first winch, a scraper cable connected at one end to the leading edge of said bucket and at the other end to said second winch, a third winch rotatable independently of said first and second winches, a return cable connected at one end to the rear of said bucket passing over a pulley on said carriage and a pulley on said girder and connected at the other end to said third winch, two fixed stops on said girder, a mobile stop carried by said return cable and movable between said fixed stops and means to connect said first and second winches to said third winch when they rotate in a direction to pay out their cables and to disconnect the third winch from said first and second winches when they rotate in the opposite

2. An installation as claimed in claim 1 wherein said means comprises a clutch disconnecting the third winch from the first two winches when the latter rotate in the direction corresponding to the winding-on of their cables, and connecting the third winch to the first two winches when the latter rotate in the direction corresponding to the unwinding of their

3. An installation as claimed in claim 1 wherein said three winches are coaxial and comprising a friction ring carried by said third winch, a friction band surrounding said friction ring, a spindle carried by one of said other winches, to which one end of said band is connected, a bellcrank pivoted on said other winch, one arm of said crank acting on said spindle, the other arm of said crank being connected to the other end of said friction band, a disc loosely mounted coaxial with said other winch, a finger projecting from said disc into a slot in said other arm of said bellcrank and friction pads engaging said disc to brake rotation

4. An installation as claimed in claim 1 comprising a series of peripheral teeth on said third winch, a double pawl adapted to cooperate with said teeth, an electromagnet adapted to rotate said pawl in one direction to engage said teeth to control the lifting of said bucket and a second electromagnet adapted to rotate said pawl in the opposite direction to

5. An installation as claimed in claim 1 including means for detecting the tension in the cable connected to the carriage and to emit a signal to

6. An installation as claimed in claim 1 wherein said that means for connecting the first two winches to the third winch comprise a

7. An installation as claimed in claim 6 wherein said unidirectional drive

8. An installation as claimed in claim 6 wherein said unidirectional drive mechanism comprises a pawl mounted on a spindle borne by the first two winches and resiliently applied against a ratchet wheel connected to a bush freely mounted on the shaft of the third winch and bearing a clutch

9. An installation as claimed in claim 1 wherein the direction of winding-on of the cables on to the first and second winches is opposite to the direction of winding-on of the return cable on to the third winch.

10. An installation as claimed in claim 1 wherein said three winches are mounted on a platform disposed at the top of the tower distributor, said platform bearing a shaft of which the lower portion is mounted on a plinth associated with the tower distributor and comprising means for regulating

11. An installation as claimed in claim 1 wherein the bucket is formed by two lateral plates interconnected at the rear by a plate covering only the upper portion, the lower portion being formed by a pivoted flap which is resiliently loaded and moves in the opposite direction from scraping.

Description:
An arrangement for concrete-preparing installations is known which enables the various aggregates stored on the ground to be distributed to a weighing hopper adapted to feed a cement mixer. For instance, an arrangement of this kind comprises a tower behind which the storage area is divided into a number of sectors, in which the various aggregates are stored, by partitions extending out from the tower. The aggregates flow by gravity into the weighing hopper after passing through a distributing hood associated with each of the sectors.

One of the problems to be solved in an installation of this kind is to build up an adequate reserve of aggregates again above the particular hood associated with each sector; various installations, one of which is known as a dragline, have been suggested to reform a slope at that place.

The present invention is concerned with a dragline of the kind comprising a bucket so suspended from a carriage running along a substantially horizontal girder that the bucket moves substantially parallel with the ground.

According to the invention, a dragline of the kind specified is mainly characterized in that the carriage is driven by a traction cable wound on to a first winch permanently connected to a second winch on which is wound a scraper cable connected to the leading edge of the bucket, whilst the bucket is driven at the rear by a return or lifting cable running over a reversing pulley borne by the carriage and incorporating a mobile stop adapted to cooperate with two fixed stops borne by the girder, this return cable being wound on to a third winch, and in that means are provided to connect the first two winches to the third winch when they rotate in the direction of unwinding or paying-out (reverse movement) and to disconnect them when they rotate in the direction of winding-on their cables (forward movement).

In one embodiment of the invention, these means comprise a clutch disconnecting the third winch from the first two winches when the latter rotate in the direction corresponding to the winding-on of their cables (forward movement, and connecting the third winch to the first two winches when the latter rotate in the direction corresponding to the unwinding of their cables (reverse movement).

Advantageously, the three winches are coaxial, and the third winch bears a friction ring cooperating with a friction band one end of which is connected to a spindle which is borne by the scraper winch and on which there acts one of the arms of a bellcrank pivoted on a spindle borne by the scraper winch, the other arm of the bellcrank bearing a spindle, to which the other end of the friction band is connected, and being formed with a slot through which there freely extends a finger carried by a disc loosely mounted on the scraper winch and rotation of which is slightly braked by brakeshoes borne by a yoke unitary with the frame.

The movements of the carriage over the girder can thus be automatically controlled.

In a variant of the invention, the band brake control mechanism is associated with the carriage cable winch instead of being associated as stated hereinbefore, with the scraper cable winch.

In an advantageous embodiment of the invention, the winch for the lifting cable is provided with a series of peripheral teeth with which cooperates a double pawl whose rotation clockwise or anticlockwise is controlled by two electromagnets, one of which is adapted to control the lifting of the bucket and the other the lowering thereof.

The lifting of the bucket can be controlled manually, by energizing the corresponding electromagnet, or automatically, if the bucket is "planted" in the pile of aggregates.

To control the lifting of the bucket in this way, the scraper cable runs, upstream of its winch, over a return pulley having means for detecting the tension of the cable and to emit a signal for energizing the electromagnet controlling the lifting of the bucket.

Advantageously, the bucket is formed by two lateral plates interconnected at the rear by a plate covering only the upper portion, the lower portion being formed by a pivoted flap which is resiliently loaded and moves in the opposite direction from the scraping direction.

In a second embodiment of the invention, the means for connecting or disconnecting the third winch (return winch) to or from the first two winches (carriage control and scraper winches) are formed by a unidirectional mechanism which can be associated with a clutch means.

Preferably, the unidirectional drive mechanism comprises a pawl mounted on a spindle borne by the first two (carriage and scraper) winches and resiliently applied against a ratchet wheel connected to a bush freely mounted on the shaft of the third winch (carriage return winch) and bearing a clutch disc cooperating with clutch pads associated with the return winch.

In this embodiment, the three winches and the bush are mounted on the same shaft and the three winches are mounted on a platform disposed at the top of the distributor, the platform bearing a shaft whose lower portion is mounted on a plinth associated with the distributor and comprising means for regulating the angular position of the horizontal girder.

Other parts of the invention are embodied in the preferred forms which will now be described by way of example with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a diagrammatic elevation of a first embodiment of the dragline according to the invention;

FIG. 2 is a diagrammatic view showing the disposition of the cables in the dragline shown in FIG. 1;

FIG. 3 is a diagrammatic perspective view of the clutch of the dragline shown in FIG. 1;

FIG. 4 is a diagrammatic side elevation of the second embodiment of the dragline according to the invention;

FIG. 5 is a partial plan view of FIG. 4;

FIG. 6 is a partially sectioned perspective view of the mechanism connecting the three winches of the dragline shown in FIG. 4, and

FIG. 7 is a diagrammatic perspective view of the dragline shown in FIG. 4, the carriages and bucket being shown in an intermediate position during the operational cycle.

Referring to FIGS. 1 and 2, a pyramidical distributor 1 has surfaces such as, 2 and 3, provided with detectors 4, 5 which are known devices to detect the level of the pile of aggregates reformed in the radial sectors associated with the sides 2, 3. The part played by the detectors 4, 5 is disclosed in French Pat. application No. P.V. 105 109 filed in the name of Societe PROMAT on 30th May, 1967, now French Pat. No. 1,528,871.

Mounted at the top of the distributor 1 is a pivoting base 6 having a platform 7. Mounted on the platform 7 are an electric motor or a geared reduction motor 8 driving a sprocket wheel 10 through a chain 9, and also an assembly of common spindles 11 associated with a winch 12 for a carriage cable 13, a winch 14 for a scraper cable 15, a winch 16 for a lifting of return cable 17, and a clutch 78 by means of which the winch 16 can be connected to the two winches 14 and 12, which always rotate together and could therefore be replaced by a single winch.

Also attached to the platform 7 is a girder 18 on which runs a carriage 19 on rollers 20, 21, the carriage 19 bearing a return pulley 22.

Disposed on the girder 18 are a front fixed stop 23, a rear fixed stop 24, and a return pulley 25; the platform 7 also bears a return pulley 26 and a return pulley 27 is mounted on the lower surface of the platform 7.

A bucket 28 is connected at a place 29 to a scraper cable 15 which runs over pulleys 27, 26 and is wound on to the winch 14. The carriage cable 13, driving the carriage at a place 30, is wound on to the winch 12.

At its rear portion, the bucket 28, which will be described in greater detail hereinafter, is connected to the lifting cable 17 which runs over the return pulleys 22, 25 and is wound on to the winch 16 in the opposite direction from that in which the scraper cable is wound on to the winch 14. As can be seen in FIG. 1, the lifting cable 17 includes a mobile stop 31 which can cooperate with the carriage 19 and with the two stops 23, 24 borne by the girder 18.

The dragline described hereinbefore operates as follows: let us suppose that the various members are situated in the positions shown in FIG. 1. If the reduction geared motor 8 is started to rotate clockwise the winches 14 and 12 rotate in the same direction, so that the scraper cable 15 and the carriage cable 13 are wound on to the winches 14 and 12.

Consequently, the carriage 19 moves to the right as shown in FIG. 1 and the bucket 28 moves in the same direction, following a path which is substantially parallel with the ground; as the clutch 78 is released, the lifting cable 17 is unwound from its winch 16 by a pull exerted by the return pulley 22 on this cable. The mobile stop 31 remains applied against the carriage 19, due to the weight of the bucket which keeps the cable 17 tensioned.

When the carriage 19 reaches the fixed stop 23 beneath which the bucket 28 also comes into position, the mobile stop 31 is stopped by the fixed stop 23. As the carriage cable and the scraper cable continue to be wound on to the winches 14 and 12, the carriage 19 continues to be moved to the right and leaves the stop 31, thus causing the bucket 28 to be lifted as a result of the progressive shortening of the vertical arm of the lifting cable, the ascending path of the bucket being inclined at about 45° to the horizontal. When the bucket reaches its top position it conventionally actuates a microcontact which cuts out the supply to the geared reduction motor.

If the bucket 28 and the carriage 19 are to be returned to their starting positions, with the motor 8 still inoperative, the clutch 78 is moved into its operative position in which the winch 16 is connected to the winches 14 and 12; the first result is that for the time being the bucket 28 cannot descend.

The geared reduction motor 8 is then reversed, i.e., so that it rotates anticlockwise. The result is that the lifting cable 17 is wound on and pulls at the carriage 19 to move it to the left as shown in FIG. 1, this movement being possible since the carriage cable 13 and the scraper cable 15 are unwound at the same speed from their winches 12 and 14.

When the mobile stop 31 abuts the fixed stop 24, the cable 17 can no longer be wound on to the winch 16 and the clutch slips. On the other hand, the carriage and scraper cables 13 and 15 continue to be paid-out from their respective winches and acquire slack so that under the weight of the bucket, the carriage 19 continues to move to the left, thus causing the bucket to be lowered due to the increase in the length of the vertical run of the lifting cable 17.

When the carriage reaches the end of its travel against the rear stop, the motor is stopped and a fresh cycle can start.

A convenient way of stopping the motor 18 when the carriage 19 abuts the fixed stop 24 is to associate the carriage cable 13 with a sensing roller 32 operating a microswitch 33 when the carriage cable 13 acquires slack.

Although the clutch 78 can be of any kind, provided that it can slip to some extent, FIG. 3 shows a particularly advantageous embodiment which can be used in the dragline according to the invention.

FIG. 3 shows diagrammatically the geared reduction motor 8, the transmission chain 9 and the gearwheel 10; the latter is keyed to the shaft 11 bearing the winch 12 on to which the carriage cable 13 is wound, the winch 14 on to which the scraper cable 15 is wound and the winch 16 on to which the return and lifting cable 17 is wound, it being understood that the two winches 12 and 14 can be replaced by a single winch on which the cables 13 and 15 are wound.

The winch 14 has an attachment 34 bearing a spindle 35 to which one end 36 of a friction band 37 is connected, its other end 38 being connected to a spindle 39 borne by a bellcrank 40. The bellcrank 40 is pivoted on a spindle 41 parallel with the spindle 35 and borne by the attachment 34. One of the arms 42 of the bellcrank engages below the spindle 35, while the other arm 43 is formed with a slot 44 in which the end of a spindle 45 engages. This spindle 45 is borne by a disc 46 (shown broken away for reasons of convenience) loosely mounted on the winch 14 with which it can rotate, due to the mechanical connection formed by the bellcrank 40. Pads 47 bear on the sides of the disc 46; each of the pads 47 forms a friction pad and is supported by a yoke 48 attached to the frame in a manner not shown.

Lastly, the winch 16 has a friction surface 49 cooperating with a friction band 37.

The device described hereinbefore operates as follows: let us suppose, that at first the reduction geared motor 8 is inoperative, so that both the winches 12 and 14 are immobile.

If the reduction geared motor 8 is connected to rotate clockwise or in the direction indicated by the arrow AR shown in FIG. 3, it will drive the two winches 12 and 14 in the same direction. The spindle 35 is driven in the same direction and via its end 36 the band 37 is applied against the friction surface 49; as the disc 46 is braked by the pads 47, the bellcrank 40 is tilted anticlockwise around its spindle 41, thus displacing in the same direction the end 38 of the friction band 37 which is applied over its whole surface against the friction surface 49; the winch 16 is therefore engaged with the winches 12 and 14 and the whole assembly, including the disc 46, rotates clockwise, i.e., in the direction indicated by the arrow AR; if during the displacement of the carriage 19 to the left as shown in FIG. 1, the stop 31 abuts the fixed stop 24 to prevent any further winding of the cable 17 on to the winch 16 connected to the winches 12 and 14, the clutch can slip for the purpose indicated hereinbefore in the description of the operation of the dragline, with reference to FIGS. 1 and 2.

If the geared reduction motor 8 is connected to rotate anticlockwise, i.e., in the direction indicated by the arrow AV in FIG. 3, the winches 12 and 14 rotate in the same direction. The front portion (FIG. 3) of the band 37 is disengaged from the friction surface 49 and the bellcrank tilts clockwise and is entrained in the direction indicated by the arrow AV by the spindle 41 and retained by the slot 44, the disc 46 being stopped and braked by the pads 47, untensioning the other portion of the band so that the disengaged position is reached. Arm 42 of the bellcrank 40 abuts the spindle 35 and the disc 46 is rotated in the direction indicated by the arrow AV; the band 37 being disengaged from the friction surface 49, the winch 16 is released.

From the foregoing it can be seen that clutching is so performed as to be engaged whenever the winches 14 and 12 rotate in the direction indicated by the arrow AR and released whenever the winches rotate in the direction AV.

The lifting and releasing of the bucket 28 during "planting" is performed by mechanism associated with the winch 16.

This mechanism comprises a number of peripheral teeth 50--52 etc. which are uniformly spaced and which cooperate with a double pawl 53 which pivots around a spindle 54 fixed in relation to the frame and has engaging claws 55, 56; the rotation of the pawl is controlled by two electromagnets 57, 58.

The lifting of the bucket is controlled by the electromagnet 57 which can be energized either by a supply circuit controlled by a pushbutton, or automatically during the "planting" of the bucket 28, it being understood that one or the other control methods for lifting the bucket is brought into operation when the carriage moves forwards, i.e., towards the distributor 1.

When the electromagnet 57 is energized by the pushbutton which closes its supply circuit, the armature 59, which is connected to the upper portion of the double pawl 53, tilts the pawl 53 clockwise and brings its claw 56 into abutment with one of the teeth 50--52. This step locks the winch 16 against rotation in the direction AV and completely prevents the lifting cable 17 from being paid-off from the winch 16, while the cables 13 and 15 continue to be wound on to their respective winches, causing the bucket to rise.

Control of the release of the bucket 28 during "planting" in a pile of materials is also performed by the energization of the electromagnet 57 and results in the operation described hereinbefore. However, in this case the energization of the electromagnet 57 is initiated by a signal obtained by means of a mechanism associated with the return pulley 26 which detects overtensioning of the scraper cable. This mechanism can be formed by a spring associated with the shaft of the return pulley to produce resilient suspension of the shaft. When overtensioning is felt on the scraper cable, the return pulley 26 can move in opposition to the spring (not shown) and close a contact inserted in the supply circuit of the electromagnet 57.

The electromagnet 58 enables the lowering of the bucket to be controlled at any time during operation by manual control, but only during the return travel of the carriage. When the carriage is making its return travel, the cable 17 is wound on to the winch 16 and the cables 13 and 15 are paid-off from their winches 12 and 14, since the clutch 78 is in the engaged position. If the electromagnet 58 is energized, the double pawl tilts anticlockwise and its operational claw 55 abuts one of the teeth 50--52 stopping the rotation of the winch 16. The clutch slips, but the carriage 19 continues to move to the left as seen in FIG. 1 as a result of the weight of the descending bucket, such descending movement being produced by the paying-off of the cables 13 and 15.

Note should also be taken of the special embodiment of the bucket 28 as shown in FIG. 1.

The bucket is formed by two plates interconnected by pivots 29 and 60, the bucket also having a rear plate 61 which covers only the upper portion of the bucket. Articulated on the pivot 60 is a flap 62 which is directed downwardly and towards the front of the bucket 28 and is continued at the rear by claws 63, a spring being disposed between the claws 63 and a flange 64 of the plate 61.

When during scraping the bucket comes up against resistance in the pile of aggregates, the flap 62 is withdrawn by rotating clockwise and the bucket can jump over the obstacle. When the bucket is "planted" in the pile of aggregates, the flap 62 is withdrawn in the same manner, thus reducing the forces of resistance caused by the "planting." It should be noted that when there is "planting," causing lifting of the bucket by the action described hereinbefore, the lifting force of the cable 17 acting on the claws 63 facilitates the rotation of the flap 62.

In a variant embodiment the clutch 78 described hereinbefore can be of the electromagnetic, pneumatic or hydraulic kind. Similarly, the double pawl 53 can be replaced by an electromagnetic, pneumatic, hydraulic or mechanical brake.

In the second embodiment illustrated in FIGS. 4--7, the installation according to the invention mainly comprises a platform 101 connected to a vertical pivot 102 whose lower portion 102' is mounted in bearings 103, 112 forming part of a plinth 104 disposed on a known distributor (not shown in FIG. 4).

The lower surface of the platform 101 bears a motor 105 whose shaft 106 bears a pinion 107 meshing with a chain 108 whose ends are attached at points 109, 110 to a circular plate 111 connected to the plinth 104. This device enables the angular position of the platform 101 to be controlled.

The mechanism shown in detail in FIG. 6 is mounted on the platform 101.

This mechanism comprises a geared reduction motor 113 whose shaft 114 bears a toothed pinion 115 and also comprises two bearings 116, 117 in which a shaft 118 is mounted. Mounted on the shaft 118 are two connected winches 119, 120, one of which, the winch 119, bears a toothed disc 121 connected to the pinion 115 via a chain 122. Also mounted on shaft 118 is a ratchet wheel 123 with which a pawl 124 cooperates. The wheel 123 bears a bush 125 bearing a clutch disc 126 disposed between two clutch linings 127, 128, one of which is borne by a winch 129 loosely mounted on the shaft 118, and the other by a disc 130 coaxial with the shaft 118 and urged towards the winch 129 by return springs 131, 132. Applied to the cylindrical surface of the winch 129 is a brakeshoe 133 on which a compression spring 134 acts.

Attached to the platform 101 is a horizontal girder 135 retained in place by guys, as 136, attached to the upper end of the shaft 102.

Running on rollers 138, 139 on the horizontal girder 135 is a bucket carriage 137. A stop carriage 140 also runs on the girder on rollers, 141, 142.

At the outer end, the horizontal girder 135 bears a stop 143 adapted to cooperate with the stop carriage 140. A second stop 144 is mounted in the upper portion of the girder and is also adapted to cooperate with the stop carriage. The upper portion of the bucket carriage is disposed at a lower level than the second stop 144, while the height of the stop carriage 140 is adequate for it to abut this stop which, on the other hand, allows the bucket carriage 137 to pass in the direction of the platform.

The horizontal girder also bears at its free end a return pulley 145.

The bucket 146 is suspended by its rear portion from a bucket cable 147 which runs over a return pulley 148 and is attached at 149 to the stop carriage. Attached at a place 150 thereof is a return cable 151 which runs over the return pulley 145 and is wound on to the return winch 129.

The bucket carriage 137 is connected at 152 to one end of the carriage cable 153 which is wound on to the winch 119 to which its other end is attached. At its front portion the bucket 146 is connected at 154 to a scraper cable 155 which runs over a return pulley 156 and is wound on to the winch 120 to which the other end of the scraper cable is attached.

It should be noted that the direction in which the carriage cable 153 and the scraper cable 155 are wound on to their respective winches 119 and 120 is opposite from the direction in which the return cable 151 is wound on to its winch 129 (cf. FIG. 7 for this direction of winding-on).

The operation of this device is as follows:

FIG. 4 shows the various members in their respective starting positions.

If the geared reduction motor 113 is rotated anticlockwise the toothed wheel 121 rotates in the direction indicated by the arrow 157 and simultaneously drives the two winches 119, 120 in the same direction. The pawl 124 resiliently articulated on the spindle 158 borne by the winch 120 can slide over the teeth of the ratchet wheel 123, so that the rotation of the two winches 110, 120 is not transmitted to the winch 129.

As a result of the rotation of the two winches 119, 120, the scraper cable 155 and the carriage cable 153 are respectively wound on to the winches 119, 120. The bucket carriage 137 moves in the direction of the platform 101 and the bucket 146 describes a substantially horizontal trajectory, i.e., skims over the ground. During these movements, due to its weight the bucket retains, via the bucket cable 147, the stop carriage against the bucket carriage 137, so that while the latter moves towards the platform 101 the stop carriage is displaced in the same direction as a result of the winch 129 rotating freely on the shaft 118 and enabling the return cable to be paid-out, the pad 133 maintaining a certain degree of tensioning of this cable to prevent any slack.

During its movement in the direction of the platform 101, the bucket carriage 137 passes freely beneath the stop 144, but the latter stops the stop carriage 140.

From that moment onwards, the carriage cable 153 and the scraper cable 155 continue to be wound on to their respective winches 119, 120 and the distance between the bucket carriage 137 and the stop carriage 140 increases, so that the bucket 146, whose cable 147 is connected to the stop carriage 140 describes an ascending trajectory until it is disposed just below the girder 135, a limit switch (not shown) then cutting off the supply to the geared reduction motor 113 and reversing its direction of rotation.

The geared reduction motor 113 then rotates clockwise and the toothed wheel 121 rotates in the same direction, driving the two winches 119, 120 in the direction indicated by the arrow 159. The pawl 124 driven by the spindle 158 rotates in the same direction and drives the ratchet wheel 123 and also the clutch disc 126, so that the winch 129 is also entrained and rotates in the same direction as the two winches 119, 120.

The return cable 151 is wound on to its winch 129, while the carriage cable 153 and the scraper cable 155 are paid-out at the same speed as the winches 119, 120.

Due to the winding of the return cable 151 on to its winch 129, the stop carriage 140 is displaced towards the stop 143.

The pull exerted on the stop carriage 140 is transmitted, via the bucket cable 147 running over the return pulley 148, to the bucket carriage 137 and to the bucket 146, which are both also displaced towards the stop 143, the distance between the stop carriage 140 and the bucket carriage 137 beneath which the bucket 146 is situated being maintained, so that the bucket is withdrawn in its raised position without being able to descend, the clutch 126 exerting adequate torque.

When during its return travel the stop carriage 140 is stopped by the stop 143, the return cable 151 stops and the winch 129 is immobilized. The winches 119, 121 continue to rotate driven by the geared reduction motor 113 and force the clutch 126 to slip.

The weight of the bucket 146 acting on its bucket cable displaces the bucket carriage 137 until it bears against the stop carriage 140, the bucket 146 descending to its starting position, when a limit contact reverses the supply to the geared reduction motor 113, thus starting a fresh operational cycle.