Harvesting of delicate products

Abstract: Apparatus for harvesting delicate produce - but particularly mushrooms - includes a picking head 26 which is controlled to be positioned over an item 53 of produce to be harvested, by means of a camera 17 which scans a tray of said items and a control unit 19 operating on a camera output to determine the co-­ ordinates of those items found to be suitable for picking. The picking head 26 includes a bellows-like produce gripper 41 through which air is drawn to hold an item of produce securely but gently against an engagement face at the free end of the gripper. Once the item has been securely held, it is pulled free by means of a twisting and lifting action, imparted to the picking head 26. The stalk is then cut away by a cutter 29, and the item is deposited in a box carried on a conveyer 28.

Description: This invention relates to methods of and apparatus for the harvesting of mushrooms, which have a delicate character and so which might easily be bruised or damaged by an automated harvesting procedure. The harvesting of many kinds of fruits and vegetables is most often performed manually. A human operator can with experience rapidly determine whether any particular item of produce is ready for harvesting and, in the case of delicate fruits and vegetables, the likelihood of damage can be minimised. The costs of harvesting produce can represent a significant proportion of the ultimate retail price of the produce, though since harvesting is often considered to be low- level poorly-paid work of a seasonal character, it can be difficult for growers to obtain sufficient staff at the required times. In view of the above difficulties, attempts have been made to automate the harvesting of various kinds of produce, but so far these have met with only limited success, especially in the case of the harvesting of delicate produce such as mushrooms. The capital cost of the equipment tends to be very high and yet the productivity relatively low, particularly if the produce requires delicate handling. In US-A-4843561, there is described a machine for selectively harvesting items of fruit or vegetable, dependent upon certain detectable characteristics of the items. The machine is relatively large-scale and is driven on ground-wheels over a field where the items are grown. The actual picking of the items is achieved by grasping the items between robotic fingers. Such an arrangement is wholly unsuitable for the harvesting of delicate items such as mushrooms or kiwi fruits, for these items are readily damaged and rendered worthless. EP-A-0053994 describes a robot asparagus picker, where asparagus shoots are detected by video cameras, and then grasped by side-gripping fingers. Though the tip of an asparagus shoot is more delicate than, say, a cabbage, the height of a shoot is not material when the generally cylindrical shaft of that shoot is to be grasped some way below the tip, the harvesting then being performed merely by pulling the shoot vertically out of the ground. Again, this asparagus picker is not suitable for the harvesting of delicate items such as mushrooms or kiwi fruits, as these items cannot be gripped in the described manner. In NL-A-8600887, there is a proposal for an automated mushroom harvester having a relatively massive harvesting head including a mushroom holder adapted to grip the top surface of a cap. The entire head has to be positioned with the holder just above a cap to be picked; a ring in the lower part of the holder is inflated until it contacts the cap; the interior of the holder is evacuated; the holder is rotated to break the mushroom stem away from the growing medium; and then the entire assembly is lifted away from the growing medium, carrying the cap with it. Such an arrangement is hardly practical; apart from the inevitably slow speed of operation in view of the separate steps of inflating the ring and evacuating the holder interior, the accurate positioning of the holder above a cap is a problem which cannot be overcome. Mushrooms do not grow regularly, and the height of the upper surface of a cap above the growing medium is most variable. In any practical installation, to operate at a sensible rate, the assessment of the height of a cap followed by the positioning of a massive assembly just above that cap cannot be achieved - and NL-A-8600887 gives absolutely no guidance as to how this could be done. As the harvester of NL-A-8600887 requires an operator for the positioning of the head, the productivity of that operator together with the harvester would be significantly lower than could be expected for the operator working purely manually. It is an aim of the present invention to provide practical, automatic harvesting apparatus for the picking of mushrooms and which may operate reliably, rapidly and with very low damage rates, notwithstanding the irregularity with which mushrooms grow. According to the present invention, there is provided an automatic method of harvesting mushrooms grown in a growing bed and using a video camera to yield an image of the bed, which image is analysed thereby to control a harvesting head including a soft resilient suction gripper for holding a mushroom, in which method the gripper of the harvesting head is moved towards a mushroom until the gripper makes contact with the upper surface of a mushroom cap and holds by suction that mushroom, the gripper is twisted whilst maintaining the hold of the gripper on the mushroom, the gripper is moved away from the contact position, so as to pick said mushroom from the growing bed, and the mushroom is subsequently released by removing the suction from the gripper; the growing bed is mounted on a conveyor and is thereby moved relative to the video camera arranged to scan the growing bed to produce said image; the image is analysed to determine the co-ordinates relative to a pre-set datum of each mushroom assessed to be suitable for harvesting on the basis of a characteristic analysed from said image; the growing bed is advanced by said conveyor to pass through a harvesting zone, said co-ordinates being utilised to control the positioning of the harvesting head over the bed as the bed is advanced, with the line of action of the head intersecting the co-ordinates of a mushroom selected for harvesting; and after the gripper of the harvesting head has gripped a selected mushroom, the gripper is moved away from the contact position with said mushroom substantially simultaneously with the twisting of the gripper; and subsequent to picking of said mushroom, the harvesting head is moved to a discharge position whereat said mushroom is released; the mushroom harvesting steps all being performed on an on-going automatic basis. It will be appreciated that in the present invention, a video camera is used to derive an image of a growing bed (for example, a growing tray) for mushrooms. The image is then analysed to determine which mushrooms should be harvested (for example, mushrooms of a size falling within a preset range of diameters) and the co-ordinates of those mushrooms are determined, relative to some datum. Next, a harvesting head having a highly flexible suction gripper is used to grip the upper surface of a mushroom cap, whereafter the mushroom is harvested by pulling the mushroom away from the growing area whilst at essentially the same time imparting thereto a twisting motion. This is achieved by twisting and raising the gripper relative to the harvesting head. The harvesting head may then carry the mushroom to a convenient point for its discharge, for example into a box. The use of a video camera to produce an image which conveniently is analysed by a computer running a suitable program allows the method to be performed at a relatively high speed and it is found that a single video camera may be able to control a plurality of harvesting heads all operating simultaneously over different parts of the same growing bed. In the case of the harvesting of mushrooms, it is essential that the stalk is broken away from the mycelium without greatly disturbing the mycelium or the layer of growing medium in which the mycelium lies. This is achieved by twisting the mushroom essentially simultaneously as it is lifted away from the growing medium. It is highly preferred to use a line-scan camera which performs a plurality of scanning operations on the growing area to build up the image one line (of the image) at a time as the camera and growing bed are moved relatively; in this way a complete image is built up gradually and can be analysed as the scanning takes place. Depending upon the analysing program, it may not be necessary at any one time to have a complete image of the growing area; it could be sufficient for no more than an image of a narrow band to be stored for analysis at any instant. Each time a mushroom is determined to be suitable for harvesting, the centre co-ordinates of that mushroom may be assessed, and then stored for subsequent recall to control the harvesting head. It is preferred for the growing bed to be defined by a tray including a growing medium for the mushrooms, and for the scanning to be performed by moving the tray past the field of view of the camera, the tray being mounted on a suitable conveyor which is then driven to carry the tray through the field of view of the camera and towards a position where the harvesting head operates. In this case, it is preferred for the harvesting head to be mounted for movement in a direction transverse to the direction of movement of the tray, and for the alignment of the line of action of the head and the co-ordinates of a mushroom to be harvested to be achieved by the combined movement of the tray in one direction and the head in a direction substantially at right angles thereto. In addition, the harvesting head may be movable forwards and backwards in a direction parallel to the direction of advancement of the tray. According to a further aspect of the present invention, there is provided apparatus for harvesting mushrooms, and including a video camera arranged to scan a growing area for the mushrooms and a harvesting head controlled on the basis of an analysis of the camera output, which apparatus includes a harvesting head including a soft resilient suction gripper; means to rotate the gripper; means to position the harvesting head over a mushroom to be harvested, and control means to analyse the output of the video camera to allow appropriate positioning of the harvesting head; the apparatus including a conveyor to support and advance in one direction past the video camera a growing bed for the mushrooms, so that the camera scans the bed to produce said image, the conveyor then advancing the bed through a harvesting zone at which the harvesting head is located; means to move the harvesting head together with the growing bed in one direction; means relatively to move the harvesting head to the growing bed in a second direction substantially at right angles to said one direction; means mounting the gripper on the harvesting head for vertical movement with respect thereto, in addition to said rotation of the gripper; said control means operating automatically to analyse said image and to position the harvesting head accordingly, taking into account the advancement of the bed by the conveyor, and then to cause said gripper to move to contact a mushroom selected for harvesting dependent upon the results of the analysis of the image, the control means being arranged to cause substantially simultaneous rotation of the gripper and movement thereof away from the growing bed after contact with an item to be picked has been achieved. Most preferably, the conveyor is adapted to support a growing bed in the form of a tray containing growing medium, whereby the tray may be moved through the field of view of the camera. The speed of movement of the conveyor may be variable, to facilitate positioning of the harvesting head. The harvesting head may be mounted on a guide extending transversely to the direction of advancement of the tray, drive means being arranged to effect movement of the head along the length of the guide. By the combined movement of a supported tray and of the head on the guide, the line of action of the head may be located to pass through any point on the tray. In this arrangement, the guide may form a part of a carriage which is arranged for forward and backwards movement in a direction parallel to that of the conveyer, to facilitate positioning of the harvesting head thereby to optimise the picking rate. Moreover, the carriage may support more than one harvesting head; a plurality of heads may be provided, each separately movable transversely of the tray, or movable in pairs or in other groupings transversely of the tray. All of the heads may however be controlled by the analysis of an image derived from a single video camera. The control means may include a processing unit operating in accordance with a predetermined program, and a memory in which the co-ordinates of each mushroom to be harvested are stored. The determined co- ordinates are then used to control the positioning of the or each harvesting head, with one co-ordinate corresponding to the movement of the support and the other to the position of a head on its guide. Each harvesting head may include a pneumatic ram, the gripper for the mushrooms being mounted on one part of that ram and the other part being mounted on a suitable sub-frame associated with the guide. Advantageously the whole ram is mounted on the sub-frame for rotational movement, so that the twisting action may be imparted to the gripper by turning the ram, as a whole. A further ram may be provided for this purpose, appropriately coupled to the first-mentioned ram. The gripper for holding items of produce must be capable of securely holding a mushroom without significantly bruising or otherwise damaging that mushroom. To that end, the gripper may be in the form of a cylindrical impervious bellows containing a porous block through which air is drawn, the bellows having at its free end a resilient contact face adapted to contact and effect a seal against the upper surface of a mushroom cap. The contact face may be defined by a replaceable resilient washer adhered to the bellows. By way of example only, one specific embodiment of apparatus constructed in accordance with this invention and arranged to operate according to a method thereof will now be described in detail, reference being made to the accompanying drawings, in which:- Figure 1 is a diagrammatic plan view of the embodiment of automatic mushroom picking apparatus of this invention; Figure 2 is a diagrammatic side view of the apparatus of Figure 1; Figure 3 is an end view on the picking head used in the apparatus of Figures 1 and 2; and Figure 4 is an enlarged view on a mushroom gripper forming a part of the picking head of Figure 3. Referring to the drawings, the embodiment of apparatus comprises a main frame 10 supporting a tray conveyor having two pairs of sprockets 11 and 12 around which extend two endless conveyer chains 13, a variable-speed motor 14 being coupled to one pair of sprockets 11 to effect driving of the chains. An encoder 15 is connected to the motor shaft to give an indication of the conveyor advancement. The conveyer chains 13 are arranged to support conventional mushroom-growing trays one of which is shown at 16, to advance the trays in direction 'A'. A line-scan camera 17 is mounted above the frame on a bracket 18, so as to produce a linb image of that part of a tray of mushrooms for the time being below the camera. Operation of the conveyer advances a tray along the length of the frame, so allowing a complete image of the tray to be built up. The camera line-image output signal may be analysed by an on-board processor in the camera, or by a separate computer control unit 19 including a monitor and keyboard. The analysis is performed by a predef ined program to yield the co-ordinates of mushrooms in the tray which are of a size suitable for harvesting, the co-ordinates then being stored in the control unit 19, which also receives the output from the encoder 15 and controls the operation of the motor 14. A pair of rails 20 are mounted above the main frame 10, the rails supporting a carriage 21 arranged for sliding movement parallel to the direction 'A' under the action of two screw actuators 22 controlled by the control unit 19. The carriage has three cross-members 23 on each of which is mounted a slide 24, each slide being movable along the length of its associated cross-member by means of a respective actuator 25. Each slide 24 supports two individual and separately-operable mushroom picking heads 26. The carriage 21 spans the tray conveyor and also a parallel-running stalk conveyer 27 and a parallel-running box conveyor 28, and each crossmember supports a stalk-cutter 29 at a fixed position over the stalk conveyer 27. The picking heads 26, actuators 25 and stalk cutters 29 are all controlled by the control unit 19. The frame 10 further supports a pneumatic controller (not shown) including a low-pressure source and connected to the picking heads 26, the operation of which controller is in turn controlled by the control unit 19. Referring now to Figures 3 and 4, each picking head 26 is illustrated in greater detail. The picking head includes a mounting plate 30 secured to the slide 24 by means of bolts 31, there being an opposed pair of right-angle brackets 32 attached to the plate 30, and between which is mounted the cylinder 33 of a pneumatic ram 34, for rotational movement about the ram axis. A second pneumatic ram 35 is pivoted to the plate 30, and the free end of the ram piston rod 36 is pivoted to an arm 37 projecting radially from the cylinder 33. Operation of the ram 35 will thus rotate the cylinder 33. The piston rod 40 of the cylinder 33 is non-rotatably disposed with respect to that cylinder and has a mushroom gripper 41 mounted at its free end. The rod 40 is hollow and allows communication between the gripper 41 and a suction pipe 42 coupled to the pneumatic controller by means of a flexible pipe 43. Further pneumatic control pipes from the pneumatic controller are provided as required to allow raising and lowering of the piston rod 40, and operation of the second ram 35. The gripper 41 comprises a boss 45 screw-threaded on to the free end of the rod 40, the boss 45 having an internal annular groove 46 in which is located a bead formed around a neck 47 of a cylindrical flexible bellows 48, a block 49 of relatively soft, resilient open-cell foamed plastics material being positioned within the bellows, against the end face of the boss 45, to act as an air filter. The free end of the bellows has adhered thereto a replaceable washer 51 of a soft resilient material for contacting a mushroom to be harvested and effecting a seal thereagainst. The apparatus described above operates in the following manner. The motor 14 is operated to drive the tray conveyer in direction 'A', and a tray 16 of mushrooms 53 to be harvested is fed on to the conveyor, to be advanced slowly to the right (Figure 2) so as to pass below the field of view of the camera 17. An image of the tray is built up from a combination of the outputs from the encoder 15 and the camera 17, scanning the tray by one line at a time. As this image is being produced and analysed by the camera on-board processor or by the control unit 19, it is stored in a memory in the control unit, operating in accordance with a predetermined program. The analysis observes the contrast between a mushroom cap (more or less white) with the growing medium (more or less black), and an assessment of the diameter of each cap on the bed can be made. If a mushroom suitable for harvesting is found, because its size falls within a preset range, then a further analysis is performed to find the approximate geometric centre thereof, and the co-ordinates of that centre relative to a datum (for instance, a corner of the tray) are stored in memory. Further advancing of the tray brings it to beneath the carriage 21; as soon as a mushroom ready for harvesting is under the line of movement of a slide 24, the appropriate actuator 25 is controlled to bring the line of action of a picking head 26 on that slide into alignment with the centre of the mushroom. It will here be appreciated that the advancement of the tray corresponds to one stored co-ordinate of a mushroom and the transverse movement of the head corresponds to the other stored co-ordinate. Then, the pneumatic controller is operated by the control unit 19 to cause the piston rod 40 of the ram 34 to be lowed until the washer 51 of the bellows 48 contacts the upper surface of the cap of the mushroom to be picked. At the same time, the low-pressure source applies suction to pipe 42, and so also to the hollow piston rod 40, to draw air through the foam block 49. The contact of the washer 51 of the bellows 48 with the upper surface of the mushroom cap effects at least a partial air-seal which serves to draw the bellows 48 into close engagement with the mushroom cap, but the resilient washer 51 cushions the mushroom so as to prevent any significant bruising or other damage. As the gripping action is perfected, there is a consequent change in pressure within the rod 40, and this is detected by the pneumatic controller. The movement of the rod 40 is then reversed and at the same time, the ram 34 is operated to twist the cylinder 33. Thus, a mushroom held against the washer 51 is both twisted and lifted away from the supported tray. Immediately thereafter, the slide 24 is moved laterally to overlie the stalk conveyer 27, and the associated stalk cutter 29 is operated to remove the lower portion of the stalk of the held mushroom. The stalk cutter 29 may operate with a scissor-like cutting action, or may utilise rotary cutting discs, in a manner understood in the art, so that the cut stalk 54 falls away on to the stalk conveyer 27. The held mushroom is then moved laterally further, so as to overlie the box conveyer 28. There, the mushroom .pa is deposited within a box 55 on that conveyer, by allowing the pressure within the rod 40 to increase and, if appropriate, lowering the gripper at the same time. The slide 24 is then moved back to overlie the tray of mushrooms, to harvest another mushroom using co-ordinate data stored by the control unit 19. If there are many mushrooms to be harvested, the three slides 24 may operate simultaneously, the two picking heads on each slide being used sequentially. Productivity is increased by driving the carriage by actuators 22, to minimise 'wait-time' for a mushroom to be in a position where it may be harvested by a picking head. The software controlling the operation should optimise the sharing of the picking between all six heads and the operation of the carriage 21 to enhance productivity. In the embodiment of apparatus described above, a mushroom is harvested by a twisting and pulling action which to some extent simulates a manual harvesting operation, and yet the mushroom is held only by the upper surface of the cap. However, the cushioning effect of the bellows 48 and washer 51 in association with the low-pressure gripping technique allows the mushroom to be harvested without significant bruising or other damage. The apparatus may however operate at relatively high speeds, with the picking rate enhanced by providing more than one picking head on each of three slides. By enabling very high picking rates in this way, the apparatus becomes most viable, commercially.

Claims: An automatic method of harvesting mushrooms grown in a growing bed and using a video camera to yield an image of the bed, which image is analysed thereby to control a harvesting head (26) including a soft resilient suction gripper (41) for holding a mushroom, in which method the gripper (41) of the harvesting head (26) is moved towards a mushroom (53) until the gripper (41) makes contact with the upper surface of a mushroom cap and holds by suction that mushroom (53), the gripper (41) is twisted whilst maintaining the hold of the gripper on the mushroom (53), the gripper (41) is moved away from the contact position, so as to pick said mushroom (53) from the growing bed, and the mushroom is subsequently released by removing the suction from the gripper; the growing bed (16) is mounted on a conveyor (11,12,13) and is thereby moved relative to the video camera (17) arranged to scan the growing bed to produce said image; the image is analysed to determine the co-ordinates relative to a pre-set datum of each mushroom (53) assessed to be suitable for harvesting on the basis of a characteristic analysed from said image; the growing bed (16) is advanced by said conveyor (11,12,13) to pass through a harvesting zone, said co-ordinates being utilised to control the positioning of the harvesting head (26) over the bed (16) as the bed is advanced, with the line of action of the head (26) intersecting the co-ordinates of a mushroom (53) selected for harvesting; and after the gripper of the harvesting head has gripped a selected mushroom, the gripper (41) is moved away from the contact position with said mushroom (53) substantially simultaneously with the twisting of the gripper (41); and subsequent to picking of said mushroom (53), the harvesting head (26) is moved to a discharge position whereat said mushroom is released; the mushroom harvesting steps all being performed on an on-going automatic basis. A method according to Claim 1, wherein said image is analysed to assess the effective diameter of the mushrooms found in said image, and the assessment of the suitability for harvesting is made on the basis of the effective diameter. A method according to Claim 1 or Claim 2, wherein a plurality of harvesting heads (26) is controlled by the output of a single video camera (17), the harvesting heads operating simultaneously over different parts of the same harvesting zone. A method according to any of the preceding Claims, wherein the centre co-ordinates of mushroom (53) determined to be suitable for harvesting are assessed and stored for subsequent recall to control the harvesting head. A method according to any of the preceding Claims, wherein the growing bed is defined by a tray (16) containing a growing medium in which the produce is grown, the conveyor (11,12,13) being arranged to feed a succession of such trays (16) past the video camera (17) and the harvesting zone. A method according to Claim 5, wherein the harvesting head (26) is movable in a direction transverse to the direction of movement of the tray (16), whereby the alignment of the line of action of the head and the co-ordinates of a mushroom to be harvested are achieved by the combined movement of the tray (16) in one direction and the movement of the head (26) in a direction substantially at right-angles thereto. A method according to Claim 6, in which the harvesting head (26) is additionally movable forwards and backwards in a direction parallel to the direction of advancement of the tray (16). Apparatus for harvesting mushrooms and including a video camera arranged to scan a growing area for the mushrooms and a harvesting head controlled on the basis of an analysis of the camera output, which apparatus includes a harvesting head (26) including a soft resilient suction gripper (41); means (35) to rotate the gripper (41); means to position the harvesting head (26) over a mushroom to be harvested; and control means to analyse the output of the video camera to allow appropriate positioning of the harvesting head (26); the apparatus including a conveyor (11,12,13) to support and advance in one direction past the video camera (17) a growing bed (16) for the mushrooms, so that the camera (17) scans the bed to produce said image, the conveyor (11,12,13) then advancing the bed (16) through a harvesting zone at which the harvesting head (26) is located; means to move the harvesting head together with the growing bed in one direction; means relatively to move the harvesting head (26) to the growing bed (16) in a second direction substantially at right angles to said one direction; means mounting the gripper (41) on the harvesting head (26) for vertical movement with respect thereto, in addition to said rotation of the gripper; said control means operating automatically to analyse said image and to position the harvesting head accordingly, taking into account the advancement of the bed (16) by the conveyor (11,12,13), and then to cause said gripper (41) to move to contact a mushroom (53) selected for harvesting dependent upon the results of the analysis of the image, the control means being arranged to cause substantially simultaneous rotation of the gripper and movement thereof away from the growing bed after contact with a mushroom to be picked has been achieved. Apparatus according to Claim 8, wherein the conveyor (11,12,13) is arranged to carry a succession of trays past the video camera and through the harvesting zone, the conveyor (11,12,13) having variable speed drive means. Apparatus according to Claim 8 or Claim 9, wherein the harvesting head (26) is mounted on a guide (23) extending transversely of said one direction, drive means (25) being arranged to effect movement of the head along the length of the guide. Apparatus according to Claim 10, wherein the guide (23) is a part of a carriage (21) which is arranged for forward and backward movement in a direction parallel to said one direction. Apparatus according to any of Claims 8 to 11, wherein a plurality of heads (26) are provided, each head or group of heads being separately movable transversely of said one direction. Apparatus according to any of Claims 8 to 12, wherein the or each harvesting head (26) includes a pneumatic ram (34), the gripper (41) for the mushrooms being mounted on one part of that ram and the other part being mounted on a sub-frame (24) of the head. Apparatus according to Claim 13, wherein said ram (34) is mounted on the sub-frame (24) for rotational movement, whereby the twisting action of the gripper (41) is imparted to the gripper by turning the ram as a whole. Apparatus according to any of Claims 8 to 14, wherein the gripper (41) for holding mushrooms comprises a cylindrical impervious bellows (48) having at its free end a resilient contact face (51) adapted to contact and effect a seal against the upper surface of a mushroom cap.

Inventors: WHEELER GEOFFREY CHARLES, WHEELER, GEOFFREY CHARLES
Applicants: PRIORLUCKY LTD, PRIORLUCKY LIMITED
Application year: 1990
Main classification: A01D45
IPC codes: A01D91, G01N21, A01D46, A01D45, H04N7, G05D1, G06T1, A01G1