The present invention relates to an automatic depalletizer for unloading palletized blocks of material. More in detail, the invention relates to a depalletizer that is particularly suitable for unloading palletized blocks of raw rubber for industrial use.

Depalletization is a very common task in the field of material handling, essentially consisting in unloading single objects from a pallet to send them to a subsequent processing step. Different ways are known to perform this task, from manual handling to use of automatic depalletizing machines or robots. Such machines substantially work with an arm adapted to pick up the palletized objects, and transfer them to the outlet of the machine, typically on a conveyor belt; the arm is controlled by a more or less complex program (software). Most common machines normally follow preset programs, so that the pickup member is always guided in the same positions, according to a preset sequence. As a matter of fact, such machines require the palletized objects to be all the same, and positioned and aligned in an orderly manner, otherwise they cannot carry out their task. More complex applications exist, wherein the machine is required to recognise the shape or the presence of the objects too. Genuine proper robots are developed in such cases, providing complex sensor systems and image recognition algorithms.

The invention is particularly directed to the application of unloading pallets of blocks of rubber.

Rubber for industrial processes of melting, moulding, etc. , is available in the form of blocks or "batches" of about 20-30 kg each.

These blocks are generally palletized in a quite irregular manner, for some reasons including: the shape of the blocks is approximately parallelepipedon but still irregular, as the material is intended for cutting or melting; the blocks are still hot when they are stacked, so that they buckle bending the stacks in one direction or the other; the pallets have non-standard sizes, as they come from different regions of the world.

Another problem is that different grades of rubber are normally used, so that dimensions, hardness and weight of the blocks may change from one material to another. Obviously, an automatic depalletizing machine should be able to cope with this variability of the material.

For the above reasons, machines with preset standard programs are not suitable for unloading pallets of rubber. On the other hand, the solution of a robot with a very complex sensor part would be too expensive, especially for medium or medium to small applications, taking into account that the purpose is to handle raw and relatively low-cost blocks of material, still to be processed.

The consequence is that manual handling is still used, with people charged of picking up the blocks from the pallet and placing them on a conveyor belt. The drawbacks of manual handling are well known, and can be summarised as inevitably high costs, as labour is required; safety risks depending on the weight of the blocks; downstream productive cycle slown down.

The object of the invention is to provide a solution to the problem, overcoming the disadvantages of the prior art. The object, more in particular, is to provide an automatic depalletizer suitable for moving blocks of material, particularly rubber, adapted to work in a completely automatic mode on irregular pallets, also

comprising blocks with non-uniform shape and/or dimensions.

A further object is a depalletizer adapted to cope with blocks of different material, in particular of different consistency and hardness.

With reference to the rubber blocks, an object of the invention is a depalletizer adapted to manage blocks made of soft or hard rubber, particularly in the range 30 - 80 Shore.

Another purpose of the invention is a reasonable complexity and cost of the machine, taking into account the field of application.

These objects are achieved by a depalletizing machine for palletized blocks of raw material, particularly rubber, said machine comprising a loading station adapted to receive pallets and an unloading station adapted to receive single depalletized blocks, characterised in that: the machine comprises a pickup head coupled to a motion system acting on three cartesian axes longitudinal, transverse and vertical, with rotation around the vertical axis, for moving said pickup head between the loading station and the unloading station; the pickup head is provided with at least an optical sensor, suitable for detecting the presence of a block of material in front of said head and measuring the distance between the head and the block, and is further provided with grasping means for grasping said blocks of material; the machine comprises an electronic control system running an automatic working program, wherein a pallet located in the loading station is scanned by the machine, moving the pickup head in front of the pallet and detecting the arrangement of the blocks by means of said optical sensor, and the blocks are grasped and conveyed to the unloading station, by means of said pickup head.

According to preferred aspects of the invention, the machine scans the pallet to be unloaded, moving the pickup head in front of the pallet and simultaneously detecting the presence of blocks of material by means of said sensor. In particular, the maximum height of blocks is detected, and blocks are unloaded by longitudinal rows, starting from the top and moving progressively to the bottom until the pallet has been completely unloaded.

According to a particularly preferred aspect, the pickup head is made with a box structure, having a lower face where the grasping means are provided, while the optical sensor is mounted in the front of the head.

The grasping of one block of material substantially comprises the following steps: a) the pickup head is positioned so that the front portion, provided with the sensor, is aligned with the block of material; the correct alignment between the pickup head and the block is allowed by the detection of the sensor itself; b) the linear distance between the pickup head and the block is measured, by means of the same sensor; c) the pickup head is raised and positioned directly above the block; d) the pickup head is lowered and the block is grasped by operating said grasping means.

According to a preferred embodiment, the machine has an overhead- crane structure, with three linear guides according to the main axes. The head is supported by the vertical guide, by means of a rotating pneumatic actuator (or equivalent) enabling rotation of the head around the vertical axis. The motor drive on the three main axes is preferably

obtained with coaxial epicyclic reduction gears, coupled with three-phase asynchronous motors.

The head-mounted sensor is preferably a laser sensor with digital output and analogue output. The digital output means the presence or absence of the material; the analogue output is proportional to the distance in millimetres between the material and the front of the pickup head itself, thus enabling the machine to position the pickup head exactly above the block to be taken.

According to another aspect of the invention, said grasping means comprise tools adapted to penetrate through the material of the blocks, and blocks are just grasped by said tools penetrating into them. Three tools are provided, arranged like a triangle at the centre of the lower face of the head, for ensuring a secure hold of blocks which may happen to be not aligned with the main axes. The tools are, preferably, helicoidal rotating drills operated by reversible pneumatic motors. These lasts are provided to screw the drills into the material when the blocks are picked up, and unscrew them when blocks are to be relased into the unloading station.

According to another aspect of the invention, the operating time and depth of penetration of said tools are both checked, when said tools are operated. The tools are stopped after a preset maximum time, or when the maximum depth is reached. In this way, soft and hard materials are safely grasped as well, for example rubber with hardness ranging between 30 and 80 Shore. The pickup head is advantageously also equipped with position transducers, extending from the lower face of its structure and enabling the head to detect its approaching to a block. Said transducers are

preferably made by rods of pneumatic cylinders; two magnetic sensors are mounted on each pneumatic cylinder, namely a lower sensor to provide a first signal to be used as slow-down signal for the head approaching the block, and a further sensor, to provide a second signal to be used as a stop signal.

A further aspect of the invention provides a sensor located in the unloading station, for detecting the position of a block of material grasped by the pickup head, before it is released. This sensor enables the blocks to be positioned in the right way before they are released, rotating the head when necessary.

The above-mentioned purposes are achieved by the invention, substantially enabling to unload pallets in a completely automatic manner, even when the pallets are not uniform in terms of dimensions, shape and arrangement of the blocks of material; the machine can work as well with blocks of different hardness, thanks to the particular management of the grasping tools.

The purposes are achieved with reasonable costs and complexity, in particular by using only a single distance laser sensor, that provides both the digital output of the presence of material on the pallet, and the analogue output correlated to the distance between the head and the blocks. This makes possible to scan the pallets, search for material and move the head to the correct place for the grasping manoeuvre.

The machine is particularly adapted to work with palletized blocks of rubber, for the above explained reasons. The invention is now disclosed with reference to a preferred embodiment, shown by way of non-limitative example, with the help of the figures, in which:

Fig. 1 is a side view of a depalletizing machine, or depalletizer, according to the invention;

Fig. 2 is a plan view of the machine of Fig. 1 ;

Fig. 3 is a front view of the main components of the pickup head of the machine of Fig. 1 ;

Fig. 4 is a schematical plan view of the head of Fig. 3, showing the arrangement of the main parts, and

Figs 5 - 8 refer to a block diagram of the machine's operating logic.

With reference to the figures, a depalletizing machine (or depalletizer) is shown, with a motion unit 1 , a pickup head 2 and a belt conveyor 3 as basic parts. The machine comprises a loading station 4, that corresponds to an area intended to receive palletized blocks of raw material, and an unloading station 5, where each single block can be released onto the conveyor 3. Fig. 1 shows two pallets of material in the loading station 4, in particular formed by blocks (or balls) of rubber; the pallets are shown as P1 and P2.

The machine also comprises a control panel 6 housing an electronic board, storing a program for operation in automatic mode. The motion system 1 consist of a cartesian robot with 3+1 degrees of freedom for the pickup head 2. It gives the head 2 a free linear movement on the three axes X, Y and Z respectively longitudinal, transverse and vertical (as shown); it is furthermore able to rotate the head 2 around the vertical axis Z. Said motion system 1 , in greater detail, has an overhead-crane structure with longitudinal beams 10 and uprights 11. The beams 10 carry X-oriented linear guides 12.

The overhead-crane structure comprises a movable crosspiece, consisting of an Y-oriented linear guide 14 mounted on sliding shoes 13

(Fig. 2); a motor-driven carriage 15 is running on said linear guide 14 and supports a third, vertically-oriented linear guide 16, which is sliding in the vertical direction with respect to said carriage 15.

The movement of the carriage 15 and the vertical guide 16 according to the X, Y and Z axes is substantially obtained with drive belt wheeled runners, following the aforesaid guides.

The motors are epicyclic coaxial reduction gears, coupled with three- phase asynchronous motors; the X, Y and Z motors are shown in Fig. 2 respectively as 18x, 18y and 18z. The motor 18x is mounted on the overhead-crane structure; the motor 18y is mounted on the guide 14 and the motor 18z on the carriage 15. These linear motion systems pertain to known technique, and thus they will not be further described. The head 2 is mounted on the lower end of the vertical guide 16, coupled to a pneumatic actuator 17 enabling 90-degree rotation of said head 2 around the Z axis.

The head 2 comprises an optical sensor 20, mounted in a central and frontal position, and three helicoidal-tip tools 21 , mounted on a lower face of the head 2.

The optical sensor 20 has a digital output and an analogue output; said sensor then provides a digital signal, stating the presence of material in front of the head and enabling to scan the pallets, and an analogue signal proportional to the distance on the Y axis between a block and the head. The analogue signal is used for positioning the head right above the blocks, as will be explained below. The sensor 20 is preferably an infrared laser sensor.

The tools 21 are arranged, in a preferred embodiment, at the tops of a triangle, as illustrated in Fig. 4.

Each tool 21 is operated by a reversible pneumatic motor 22.

The unit formed by tools 21 and motors 22 is mounted on a moving plate 23; said moving plate 23 can be extended and retracted in the vertical direction, by dual-effect pneumatic actuators 24.

The head 2 also comprises two pneumatic cylinders 25, each fitted with a rod 26 extending downwards below the plate 23, and acting as a probe and position transducer. Each cylinder 25 is equipped with two magnetic proximity sensors 27a and 27b, mounted at different heights to provide a sequence of two outputs when rod 26 is moving. Said two signals can be used for slowing down and stopping the head 2. Two probe cylinders 25 are provided, one for each side, arranged as in Fig. 4.

The frame structure of the head is substantially a box structure formed by bolted aluminium alloy plates. More in detail, the structure of the head consists essentially of a plate 60 fixed to the shaft of the pneumatic motor 17, and two side plates 61 supporting a central bracket 62. A protective guard (not shown) can be mounted.

The actuators 24 are fixed to the side plates 61 ; the pneumatic cylinders 25 and the sensor 20 are fixed to the bracket 62. The pneumatic motors 22 are fixed to the moving plate 23 by suitable clamping collars 63; the drills 21 are locked on the shafts of the motors

22 by means of a sleeve 64, having one end fixed to the motor shaft by a key, and the other end supporting the tip 21 inserted and locked by a bolt acting as a plug. The plate 23 has an octagonal shape, with two passing slots 65 (Fig. 4) corresponding to the probe cylinders 25.

The motors and pneumatic cylinders are controlled by a pneumatic

circuit with solenoid valves that open and close the compressed-air supply using prior-art techniques. The components of the pneumatic circuit are not shown.

In the example, the belt conveyor 3 has a first belt 30, about three metres long, and a second belt 31 about 1 metre long and acting as a magazine. The conveyors are provided with a smooth PVC belt and the respective drive rollers are rotated by screw-feed motor-driven reduction gears.

A photoelectric cell sensor 32 is positioned at the starting point of the belt 30, with upwards orientation.

The loading station 4 comprises two substations, made in particular by two steel bases 40 and 41. These bases constitute a reference for positioning the pallets loaded with blocks of material, to allow a precise execution of the machine's working program. The unloading station 5 corresponds to the portion of space above the end of the belt 30, where the sensor 32 is also located.

The machine is also provided with suitable safety guards, both passive to prevent access to the zones in which the moving members operate, and active, to stop the machine in case of an emergency. These guards may, for example, include welded mesh panels around the moving zone of the pickup head 2; an access gate with microswitch that stops the machine if the gate is opened whilst the machine is running; a photoelectric safety barrier at the front pallet-loading side.

The control panel 6 controls the position of the axes, operation of grasping means and movement of the conveyors. The user interface consists of a switch panel through which commands can be given to the machine, and a display showing operating parameters, and can also be

used for manual operation mode.

In particular, the control panel 6 houses the electronic control system that provides automatic operation of the machine. The automatic wotking program substantially carries out the steps of scanning the pallet by means of the sensor 20 mounted on the head 2 and progressively unloading the pallets from top to bottom, by horizontal rows.

More in particular, the blocks are transferred with the following steps: a) the pickup head 2 is positioned with the front part aligned with one block of material; b) the linear distance between the pickup head 2 and said block is measured by means of the same sensor 20; c) the pickup head 2 is raised and positioned directly above the block; d) the head 2 is lowered and the block is grasped, by drills 21 penetrating through the material of the block itself.

The control of motors 22 provides a double stop condition, that is i) limit switch reached by movable plane 23 or ii) operating timeout (e.g. 2.5 s) reached. This double stop condition enables a secure pickup of both soft and hard materials: in case of a soft block, the drills 21 can easily penetrate through the block itself and motors are stopped by the plate 23 reaching the limit switch; with a hard material, the action of drills 21 is more difficult and the stop occurs because of timeout. Further insistence with action of the drills 21 , in fact, would be a loss of time and may even be harmful. The logic of the working program, in a preferred embodiment, is shown in greater detail by block diagram of Figs. 5 to 8.

Step 100: motion system 1 quickly takes the pickup head 2 to a

scanning start position. This scanning start position is in front of the pallet, leaving a free path (corridor) for the head 2 along the X-direction, for the purposes of scanning.

Step 110: the guide 16 descends slowly downwards, taking the head 2 towards the pallet.

Step 120: the laser sensor 20 provides the digital output "yes/no" indicating whether there is some material in front of the pickup head 2 or not; in order to avoid false readings, the digital response is preferably adjusted to exclude reports above a given threshold distance (greater than the depth of the pallet).

Steps 130 to 132: in the event of a negative signal, the head 2 continues to descend slowly along the Z axis (step 130), seeking for bottom blocks of material. If the head reaches a maximum descent position (step 131) the system considers that the pallet has been completely unloaded (step 132).

Step 140: the head 2 is raised for a distance equivalent to the average height of one of the blocks of material. As an example, for balls of rubber this height is typically 160 mm.

Steps 150 - 160: the machines rotates the head 2 by 90°, by means of the motor 17. This rotation enables the sensor 20 to perform complete scanning of the horizontal plane in the area where the pallet is located. The machine can in this way locate blocks of material that are not aligned in front of the head: it can typically be the case of an isolated block above the others, or a partially unloaded pallet. Steps 161 to 165: this sequence is followed if the previous horizontal plane scan gives a positive result: the pickup head 2 is rotated in the opposite direction by 90°, realigning the sensor 20 with Y (step 161); it is

then slowly moved along X, performing horizontal scanning (step 162). The machine seeks material along a continuous length that is the equivalent of half of the average width of a block, in order to avoid false reports. At this point, the machine has selected the next block to unload, which may be the block detected with the first vertical scan, or the first block detected with the next horizontal scan.

Step 170: the pickup head 2 is moved in front of the selected block of material. The system acquires the distance of the block from the head (according to Y) by means of the analogue output provided by the sensor 20.

Step 180: the head 2 is quickly raised by a preset safety height, that is sufficient to pass over the pallet. In normal applications, this height may be approximately 700 mm. Step 190: the head 2 is moved along Y, for a distance corresponding to the sum of three amounts: the distance between the head and the block, measured by the sensor 20, plus the distance between the "zero" point of the sensor and the centre C (Fig. 4) of the pickup head, plus half the average width of the blocks on which the machine is working. In this way, the pickup members 21 is moved correctly above the central portion of the selected block.

Step 200: the pickup head 2 is quickly lowered towards the block.

Step 210: one or both rods 26 of the probe cylinders 25 touch the block. As soon as the piston of one of the cylinders reaches the first, lower proximity sensor, said sensor gives a first signal to the system causing the head 2 to slow down.

Step 220: after the above slow-down signal has been received, the

system commands slow descent of the pickup head 2, slowing down the motor 18z of the guide 16.

Step 230: the piston of one of the cylinders 25, normally the same one that supplied the slow-down signal, reaches the second, higher sensor, thus providing the stop signal. At this point, the head 2 is in the grasping position, just above the block.

Step 240: the same stop signal is also used to start operation of the grasping members. Referring to the shown embodiment, the stop signal gives consent to operate the motors 22 and the pneumatic cylinders 24, lowering the plate 23 towards the block.

Step 250: the drills 21 are screwed into the material, realizing the grasping function. Normally, when the block is aligned with axes X and Y, all the drills can penetrate through the block, thanks to the head positioning procedure disclosed above. The triangular arrangement of the tips 21 nevertheless ensures that at least one or two of them can grasp the block, even if it is not aligned with X and Y axes.

Steps 260 - 270: the system checks whether the full stroke of the cylinders 24 has been reached; in the meantime, the time elapsed from start of the grasping means, i.e. the motors 22, is checked. The motors 22 are stopped when one of these two conditions (full stroke or timeout) is reached.

Steps 280 - 300: the selected block has now been grasped; the head 2 is quickly moved to the unloading station 5; the guide 16 is lowered to take the block close to the belt 30. Steps 310 - 311 : the sensor 32 enables the machine to check whether the position of the block is right. If the position is not as desired, a 90° rotation of the head 2 is imparted by means of the pneumatic

motor 17. The blocks are normally parallelpipedons with a long side and a short side, and the right unloading position is that with the long side parallel to the X axis, that is parallel to the belt 30. In case the long side of the block is parallel to Y axis, the cell 32 is covered and the resulting signal is used to operate the motor 17 accordingly.

Step 320: the head 2 continues its descent to the belt 30, until it reaches the unloading position.

Step 330: the block of material is released from the head 2. The motors 22 are driven with inverted rotation, to unscrew the drills 21 from the material. In this step, the moving plate 23 is in "neutral", i.e. the corresponding air solenoid valve are open.

Steps 340 - 360: after releasing the block, the head 2 is raised and the plate 23 reascends. The head 2 is returned to the pallet scanning start position and to the material pickup height in the cycle that has just concluded.

Steps 370 - 380: an X-scan is perfomed by the head 2, searching for other blocks of material. In the positive case, the cycle is repeated from step 170. In the negative, the machine goes to following step 390.

Steps 390: The head 2 is taken back to the scanning start X- coordinate, through the guide 14.

Steps 400 and 410 to 413: A vertical Z-scan is made by the head 2. If blocks are found, the system returns to step 170, in practice unloading one layer below. If blocks are not found, the guide 16 continues to descend along Z until some material is found; when the bottom Z position is reached, the pallet has been fully unloaded (step 413).