Metal detection apparatus for an agricultural harvester

Abstract: An agricultural harvesting machine (10) having feed rolls (18-22) for feeding crop material along a feed path (57) to a cutterhead (23) which chops the crop material, is provided with a metal detector (42) for detecting ferrous metal objects passing along the feed path (57). The metal detector (42) comprises a plurality of magnets (54-64) and a plurality of generally planar Hall effect sensing elements (84). The magnets (54-64) collectively produce a detection field which extends into the crop feed path (57). Each sensing element (84) is disposed such that the magnetic field produced by two adjacent magnets (e.g. 54, 58) is normal to the plane (P1) of the sensing element (84). In addition the sensing elements (84) are disposed in a plurality of planes (P1, P2) all normal to the crop feed path (57). However, the sensing elements (84) are disposed in planes oriented at different angles (α, β) relative to the direction of crop feed. When a ferrous metal object passes through the detection field it varies the density of the magnetic field at one or more of the transducers (74-82) and the Hall effect causes an output voltage signal to be developed across the output leads (88). The output signal is applied through processing circuitry (92, 94, 96) to a stop apparatus (98) to stop the feed rolls (18-22). The transducers (74-82) are mounted on a circuit board (66) which surmounts the magnets (54-64) inside a housing (43, 44) within one of the feed rolls (20). An encapsulating material (49) fills the interior of the housing (43, 44).

Description: The present invention relates to metal detectors and more particularly to metal detectors for detecting ferrous material in crop harvesting machines. A typical harvesting machine, such as a forage harvester, may include an attachment mounted on the front end of the harvester for cutting and/or gathering crop material and feeding it into a basic processing unit. The basic unit includes feed rolls for advancing the crop material, compressing it into a mat, and feeding it into a cutterhead. The cutterhead generally comprises a plurality of knives mounted on a rotating reel, the knives cooperating with a stationary shear bar to chop the crop material. The crop material is then discharged from the harvester. Tramp metal such as fencing stakes, nuts and bolts detached from other equipment, tools which have been left in the field or bounced out of moving machines, etc. is frequently picked up from the field with the crop material. The tramp metal, if it reaches the cutterhead, damages the shear bar and cutterhead knives. The problem of tramp metal in crop material being processed by agricultural harvesting equipment moving across farm fields is well known and much time and money has been expended in efforts to solve the problem. One conventional way to alleviate the problems caused by tramp metal has been to provide a magnetic metal detector within one of the feed rolls which feeds the crop material toward the cutterhead. Metal passing in proximity to the feed roll varies a magnetic field generated by the detector and circuits are provided for detecting variations in the magnetic field and stopping the feeder mechanism when a variation is detected, thereby preventing metal objects from being fed into the cutterhead. Many types of magnetic metal detectors have been devised in efforts to obtain a detector which is inexpensive and easily manufactured, at the same time being small enough to be located within a feed roll and sensitive enough to detect smaller metal objects such as nails, nuts and bolts anywhere over the lateral extent of the crop feed path. Various forms of prior art metal detectors are disclosed in US-A-3 972 156, US-A-3 757 501, US-A-3 889 249, US-A-4 290 255, US-A-4 433 528, US-A-5 070 682, US-A-5 078 645, US-A-5 092 818, US-A-4 344 074 and US-A-4 788 813. These detectors typically include a plurality of electromagnets or permanent magnets for producing a magnetic detection field and sensing coils for sensing changes in the magnetic field produced by metal objects passing through the crop feed path. Each coil may comprise a thousand turns of insulated wire. The coils are bulky and only limited space is available within the feed roll to accommodate them. Furthermore, to prevent wear of the coil insulation due to rubbing as a result of harvester vibrations, insulating pads are required between the coils and the magnets and between the coils and the housing enclosing the detector. It is an object of the present invention to provide a magnetic metal detector for a harvesting machine, the metal detector requiring less space than prior art detectors. The replacement of plural turn sensing coils with smaller sensing elements results in a magnetic metal detector which is easily accommodated within a feed roll of a harvester. The smaller volumes of the new sensing elements permit the raising of the magnets, such that they may be located closer to the crop feed path for improved sensing action. According to the invention an apparatus is provided for detecting the passage of ferrous metal objects through the crop feed path of an agricultural harvester, having feed means for feeding crop material along said crop feed path, said apparatus comprising: magnets means disposed adjacent said crop feed path such that a magnetic field produced by said magnet means is traversed by crop material and any ferrous material objects therein being fed along the crop feed path, said ferrous metal objects causing variations in said magnetic field; and sensing means operable to produce an output signal when a ferrous metal object traverses said magnetic field. Such an apparatus is known from US-A-4 433 528. Said detection apparatus is characterized in that said sensing means comprises at least one generally planar Hall sensing element, disposed in said magnetic field and said detection apparatus further comprises means for causing a direct current to flow through said Hall sensing element. Preferably the magnet means comprises a first group of permanent magnets having South poles facing the crop feed path and a second group having North poles facing the same. Hall sensing elements may be disposed between each magnet of the first group and an adjacent magnet of the second group in planes normal to the crop feed path and extending at a substantial angle relative to the direction of crop feed. The sensing elements may be mounted on a circuit board mounted between the magnets and crop feed path. Magnets and circuit board may be disposed in an enclosed housing, filled with encapsulating material, within a feed roll of the feed means. The signal from the sensing elements when the passage of a ferrous object is detected, can be used for stopping the feed means. Fig. 1 is a schematic view of a forage harvester in which the invention may be used; Fig. 2 is a part sectional view taken along the line 2-2 of Fig. 1 and illustrating the mounting of a metal detector inside a feed roll; Fig. 3 is a sectional view taken along the line 3-3 of Fig. 2 and illustrating the mounting of a metal detector and a circuit board inside of a feed roll; Fig. 4 is a schematic plan view of a circuit board surmounting a plurality of permanent magnets, the view also illustrating magnetic lines of flux produced between sets of the magnets; Fig. 5 is a diagrammatic elevation view illustrating the relationship between the detection field generated by the metal detector and the crop feed path; and, Fig. 6 is a perspective view of a transducer module, the view including a block diagram of a signal processing circuit for processing the output signal from the module. Fig. 1 illustrates an improved forage harvesting machine of the kind in which the present invention may be employed. It is apparent that the invention may also be employed with benefit for the protection of other types of farm machinery. The representative farm machine illustrated in Fig. 1 may be similar to the forage harvester in US-A-3 523 411 and US-A-3 959 953. The forage harvester, generally designated by reference numeral 10, comprises a base unit 11 and an attachment 12 for gathering crop material and feeding it to the base unit 11 for processing. Attachment 12 directly cuts crop material in the field and feeds it to base unit 11 where it is chopped and eventually conveyed to a trailing forage wagon (not shown). A direct cut attachment is shown for exemplary purposes but in actual practice any type of attachment, e.g. a row crop unit or a windrow pick-up, could be used with a base unit of the type shown insofar as the present invention is concerned. More particularly, the attachment shown includes a reel 13, depicted in phantom outline, which operates in a conventional manner to guide material over a cutter bar 14 and up an inclined floor 15 to a consolidating auger 16, also depicted in phantom outline. Attachment 12 is pivotally mounted to base unit 11 at 17 and is adapted to feed crop material to the space between upper and lower front feed rolls 18, 20 and then on to upper and lower rear feed rolls 21, 22 which in turn feed material to a cutterhead 23 (shown in phantom) which chops the crop material and guides it rearwardly to conveyor means 24 in a well known manner. The conveyor 24 commonly comprises an auger mounted transversely for feeding the chopped crop material to a blower unit which conveys it upwardly via a vertical spout 25 (partially shown) and then rearwardly to a trailing forage wagon. The front and rear pairs of upper and lower feed rolls 18, 20, 21, 22 compress into a mat-like configuration the crop material which has been gathered by the attachment and consolidated by auger 16. The mat of material is fed rearwardly across the top surface of a shearbar 26 which is operatively associated with a series of cutting elements 27 (one of which is shown in phantom) on a rotating cutterhead 23 journaled for rotation by a mounting assembly 28 in sidewall 30 of base unit 11. The present invention is directed to apparatus for detecting ferrous metal objects in the crop material being fed to cutterhead 23, and more particularly, it is concerned with detection means mounted in the lower front feed roll 20 for detecting metal objects in the compressed mat and initiating a control signal in response thereto for discontinuing transport of the crop material prior to introduction of the sensed object into the area at which the shearbar 26 and cutterhead 23 cooperatively engage and cut the crop. Lower front feed roll 20, shown in detail in Fig. 2, includes a stationary shaft 31 on which the feed roll is journaled for rotation in bearing assemblies 32, 33 suitably mounted in feed roll end caps 34, 35. A generally tubular non-ferrous outer wall 36 of the feed roll is secured to end caps 34, 35 by fastening means 37, 38. A series of radial aggressive non-ferrous flange elements 39 are provided for engaging and feeding the mat of crop material in the usual manner. A splined stub drive shaft 40 is contained by a collar 41 forming an integral part of end cap 35. When drive shaft 40 is rotated by a feed drive mechanism (not shown) of the forage harvester, the drive force rotates feed roll end caps 34, 35 and the tubular outer wall 36 of the feed roll. Bearings 32, 33 permit rotation of the end caps even though the shaft 31 remains stationary. In this regard, the left end of shaft 31, as viewed in Fig. 2, may be keyed to a support block affixed to the frame of the forage harvester as shown in US-A-4 353 199. Referring to Figs. 3 and 4, a metal detector assembly 42 is mounted on the stationary shaft 31 as described in US-A-4 433 528. The detector assembly 42 includes a cover plate 43, preferably made of aluminum or another non-ferrous material, and a mounting frame 44 which serve to support and cover a plurality of magnets 54, 56, 58, 60, 62 and 64 and a printed circuit board 66. Mounting frame 44 is secured to fixed shaft 31 by a series of bolts 46 and nuts 47 spaced by spacers 48, 50 disposed between the inner surface of frame 44 and shaft 31. Cover plate 43 is secured to, and aligned with, the outer surface of mounting frame 44 by a series of metal screws 51. The printed circuit board 66 carries a plurality of Hall effect transducers 74, 76, 78, 80 and 82 and circuitry for the processing of signals generated by the metal detector. The magnets 54, 56, 58, 60, 62 and 64 are mounted on surfaces 52 and 53 of mounting frame 44. The printed circuit board 66 surmounts the magnets. Cover plate 43 and mounting frame 44 form an enclosed region which is filled with an encapsulating material 49 such as an epoxy or urethane. For the sake of clarity, only a portion of the encapsulating material is shown in Fig. 3. A cable 55 extends from the printed circuit board 66 through an axial opening in stationary shaft 31. The cable 55 includes leads for supplying voltages to the circuits on board 66 and leads for conveying output signals from the circuits on the board to circuits external to the feed roll. Fig. 4 is a top view showing the arrangement of magnets 54, 56, 58, 60, 62 and 64 and the transducers 74, 76, 78, 80 and 82. The magnets may be electromagnets or permanent magnets, permanent magnets being shown to avoid the necessity of showing energizing windings. The number of magnets may vary depending on the application. The magnets are arranged in two rows extending traverse to the crop feed path represented by arrow 57 (Fig. 4) the magnets of one row having a North pole adjacent board 66 and the magnets of the second row having a South pole adjacent the board as best seen in Fig. 5. The transducers 74, 76, 78, 80, 82 may be pluggable modules such as the model 3503 ratiometric, linear Hall effect sensor sold commercially by Allegro Microsystems, Inc. These pluggable units include a Hall sensing element, linear amplifier and an emitter-follower output stage. Fig. 6 includes a perspective view of a module 82 having a sensing element 84 which is a planar conductive film. According to Hall effect theory, when sensing element 84 is placed in a magnetic field perpendicular to its plane, and a direct current is caused to flow through the sensing element from one side to the opposite side, an electric field is produced in the plane of the sensing element in a direction perpendicular to current flow, the intensity of the electric field being proportional to the magnetic field density. The placement of the magnets is such that flux lines are established between a magnet in one row and the two magnets closest thereto in the second row. This is illustrated in Fig. 4 where flux lines are shown extending from the magnet 58 to the magnets 54 and 56. Fig. 5 is a schematic elevation of magnets 54 and 58 and shows that the flux lines between these magnets extend outwardly into the crop feed path represented by arrow 57. Each transducer 74, 76, 78, 80, 82 is disposed such that its sensing element intercepts flux lines extending between the magnets of a set, that is, between the North pole of a magnet in one row and the South pole of a magnet in the other row. Each sensing element should be in a plane perpendicular to the flux lines passing through it, or as nearly perpendicular as possible. Assuming that the magnets in a given row are equally spaced this results in the sensing elements of alternate transducers 74, 78, and 82 being disposed in parallel planes P1 which are at a substantial angle α on the order of 45 degrees relative to the direction of crop feed with the remaining transducers 76 and 80 being disposed in generally parallel planes P2 which are at a substantial angle β on the order of 45 degrees relative to the direction of crop feed. While equal spacing between the magnets of a set is preferred, it is not essential and in the case of non-uniform spacing the planes P1 or planes P2 may not be parallel. The transducers, in addition to being positioned so that their sensing elements 84 are at an angle with respect to the direction of crop feed as shown in Fig. 4, are oriented such that the planes of the sensing elements are normal to the crop feed path as shown in Fig. 5. When the magnets and the transducers are disposed as described above, the magnets create a magnetic detection field extending into and across the crop feed path, the detection field comprising a plurality of magnetic fields with each field extending between a set of magnets which includes a magnet in each row. Each field of the plurality of fields has flux lines extending through a transducer in a direction generally normal to the plane of the Hall sensing element therein. Thus, when a ferrous metal object being fed along the crop feed path passes through one or more of the plurality of magnetic fields, the flux density through one or more of the sensing elements is varied and it or they produce output signals. In Fig. 6, a typical transducer module 82 has three pins 88 which are inserted into board 66. One pin is connected to ground and a second pin 88 is connected to a current source 90 which causes direct current flow through the sensing element 84 in the transducer. The third pin or signal output pin 88 is connected to an amplifier 92 in a signal processing channel which also includes a low-pass filter circuit 94 and a threshold detector 96. After the output signal from transducer 82 is amplified by amplifier 92 it is applied to the filter circuit 94 which is designed to filter from the transducer output signal the higher frequency noise caused by movement of ferrous machine parts such as gear teeth near the region of the detection field. The filtered signal is then applied to a threshold detector which compares the filtered signal with a reference voltage V R . The threshold detector is set so that noise generated by moving machine parts will not cause the detector to produce an output signal. When tramp metal passes through the magnetic field in which sensing element 84 is disposed, it varies the magnetic field so that the sensing element produces an output signal. After amplification by amplifier 92 and filtering by filter circuit 94, the output signal triggers threshold detector 96 and the detector produces an output signal to energize a feed stop mechanism 98. The feed stop mechanism is conventional and may, for example, be of the type disclosed in US-A-5 078 645. Although Fig. 6 shows only one signal processing channel, it will be understood that a signal processing channel is provided for each of the transducers 74, 76, 78, 80 and 82, the channels all having outputs connected to the feed stop mechanism 98. From the foregoing description it is seen that the present invention provides a metal detector which requires less space than prior art detectors used to detect tramp metal in the crop feed path of an agricultural harvester. Since the magnets may be mounted underneath the printed circuit board and no space is required above the board for bulky sensing coils, the printed circuit board may be raised considerably, limited only by the circuitry and transducers mounted thereon. Thus, even though the magnets are mounted below the circuit board, they may in effect be located closer to the internal periphery of the feed roll so that their detection fields may extend further into and across the crop feed path. It is not essential that the magnets be located below the circuit board. They may be located on the top surface of the circuit board or even on a separate support. However, mounting of the magnets below the board has an advantage in that the board may then provide the support for the transducer elements. Furthermore, the magnets and transducer elements need not be mounted within a feed roll although this location has the advantage of protecting the detecting apparatus while permitting the disposition of the magnets closely adjacent the crop feed path. However, the present invention is suitable for use in other positions such as under a floor plate adjacent the crop feed path as suggested in US-A-4 344 074.

Claims: Apparatus (42) for detecting the passage of ferrous metal objects through the crop feed path (57) of an agricultural harvester (10), having feed means (18, 20, 21, 22) for feeding crop material along said crop feed path (57), said apparatus (42) comprising: magnets means (54, 56, 58, 60, 62, 64) disposed adjacent said crop feed path (57) such that a magnetic field produced by said magnet means (54, 56, 58, 60, 62, 64) is traversed by crop material and any ferrous material objects therein being fed along the crop feed path (57), said ferrous metal objects causing variations in said magnetic field; and sensing means (74, 76, 78, 80, 82) operable to produce an output signal when a ferrous metal object traverses said magnetic field; said detection apparatus (42) being characterized in that: said sensing means (74, 76, 78, 80, 82) comprises at least one generally planar Hall sensing element (84), disposed in said magnetic field; and said detection apparatus (42) further comprises means (90) for causing a direct current to flow through said Hall sensing element (84). An apparatus (42) according to claim 1, characterized in that said at least one Hall sensing element (84) is disposed, such that the magnetic field produced by said magnet means (54, 56, 58, 60, 62, 64) extends through the Hall sensing element (84) in a direction normal to the plane (P1, P2) of the Hall sensing element (84). An apparatus (42) according to claim 1 or 2, characterized in that: said magnet means comprises a first group of magnets (54, 56, 62) having South poles facing generally toward said crop feed path (57) and a second group of magnets (58, 60, 64) having North poles also facing generally toward said crop feed path (57); and said at least one Hall sensing element (84) is disposed between a magnet (56) of said first group of magnets (54, 56, 62) and an adjacent magnet (58) of said second group of magnets (58, 60, 64). An apparatus (42) according to claim 3, characterized in that said first group of magnets (54, 56, 62) and second group of magnets (58, 60, 64) are disposed transverse to the direction of crop feed and arranged such that magnetic lines of flux extend between each magnet of said first group (54, 56, 62) and at least one magnet of said second group (58, 60, 64). An apparatus (42) according to claim 4 characterized in that said at least one Hall sensing element (48) is disposed in a plane (P1, P2) normal to the crop feed path (57). An apparatus (42) according to claim 5, characterized in that said plane (P1, P2) extends at a substantial angle (α, β) relative to the direction of crop feed. An apparatus (42) according to any of the preceding claims, characterized in that said at least one Hall sensing element (84) is mounted on a circuit board (66). An apparatus (42) according to claim 7, characterized in that said circuit board (66) is disposed between the magnet means (54, 56, 58, 60, 62, 64) and the crop feed path (57). An apparatus (42) according to claim 7 or 8, characterized in that the feed means (18, 20, 21, 22) comprises at least one feed roll (20) and said circuit board (66) and said magnet means (54, 56, 58, 60, 62, 64) are disposed within said at least one feed roll (20). An apparatus (42) according to claim 9, characterized in that said circuit board (66) and said magnet means (54, 56, 58, 60, 62, 64) are supported within an enclosed housing (43, 44) within said at least one feed roll (20). An apparatus (42) according to claim 10, characterized in that said enclosed housing (43, 44) is filled with an encapsulating material (49). An apparatus (42) according to any of the preceding claims, characterized in that said magnet means comprises permanent magnets (54, 56, 58, 60, 62, 64). An apparatus (42) according to any of the preceding claims, characterized in that it comprises means (92, 94, 96, 98) responsive to the output signal from said at least one Hall sensing element (84) for stopping the feed means (18, 20, 21, 22) when the passage of a ferrous metal object through the magnetic field is detected.

Inventors: CHOW MARK K, STROSSER RICHARD P, WEAVER MARVIN G JR, CHOW, MARK K., STROSSER, RICHARD P., WEAVER, MARVIN G., JR.
Applicants: FORD NEW HOLLAND NV, NEW HOLLAND BELGIUM N.V.
Application year: 1995
Main classification: A01D75
IPC codes: A01D75