GB1602475A - Improvements in and relating to anagricultural implement for harvesting crop - Google Patents

Description

(54) IMPROVEMENTS IN AND RELATING TO AN AGRICULTURAL IMPLEMENT FOR HARVESTING CROP (71) We, NATIONAL RESEARCH DE VELOPMENT CORPORATION, of Kingsgate House, 66-74 Victoria Street, London, S.W. 1., a British Corporation established by Statute, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to agricultural implements for use in harvesting crops, and is concerned in particular, but not exclusively, with forage harvesters. The present invention is an improvement in, or modification of, the invention claimed in UK Patent No. 1,447,026.

It is a well known hazard of forage harvesters, particularly of the precision chop type, that objects differing from the crop, for example stones, pieces of metal, and like objects heavier than the crop, tend to be fed to the chopping mechanism along with the cut crop. This may occur both when the crop is cut by the forage harvester, and when the crop has been cut previously and is merely picked up by the forage harvester, for example, after a period of field wilting. For example, where a flail or double-chop forage harvester is used either to cut and collect crop or to pick up previously cut crop, the cup shaped or S-shaped flails tend to pick up stones and the like and fling them into the chopping mechanism.

It is one object of the present invention to provide an agricultural implement for collecting crop which has either been previously cut and is lying on the ground, or which is a standing crop to be cut by the implement itself, in which means are provided to reduce the risk of damage to crop processing machinery present in the implement by the passage of the stones and the like into the machinery.

According to the present invention there is provided an agricultural implement for use in harvesting crop comprising a rotor for collecting crop by rotation about a horizontal axis, hood means extending over the rotor, means for driving the rotor in rotation in a sense such that crop collected by the rotor is carrid upwardly and rearwardly over the axis of the rotor, detection means for detecting objects differing from the crop picked up by the rotor with the crop, moveable deflector means for deflecting such objects out of the normal crop path, and control means for moving the deflector means into the path of such an object when the object is detected by the detection means.

The detection means may comprise means for detecting vibrations in the hood means caused by impact on the hood means of objects differing from the crop, for example stones or like objects. More than one detection means may be provided and may be positioned at different locations. Conveniently, the or each detection means may comprise an accelerometer, microphone, or other vibration or acoustic sensor fixed on or near the hood means. The output of such detection means may conveniently be coupled by way of a high-pass filter to a comparator circuit. A reference signal source may be connected to the comparator circuit so that output signals from the detection means due to vibrations in the hood means, having frequencies above the cut-off frequency of the filter and having an amplitude above a predetermined level determined by the reference signal, indicate the impact on the hood means of objects differing from the crop, for example, stones and like objects.

Preferably, the control means includes a first timing circuit which ensures that, after actuation, the deflector means remains in the path of the detected object for the period of a typical deflection and for a predetermined interval thereafter before being restored to a position outside the crop path. Preferably a second timing circuit is also provided to ensure that after the deflector means has been returned to its position outside the crop path it remains in that position for a second predetermined time interval. The purpose of this second interval is to prevent vibrations caused by the restoration of the deflector means from operating the detection means.

The control means may comprise an actuator (preferably a solenoid actuator for a hydraulic ram) coupled to the moveable deflector means and having two stable positions, the actuator being arranged to be set in one stable position in which the deflector means is in the path of a detected object when the detector means output indicates that an object has been detected, and the actuator being coupled to the timing circuits to be reset to its other stable position at the end of the first timing interval determined by the first timing circuit. Means may be provided for inhibiting the triggering of the actuator again to its said one position until the end of the second timing interval of the second timing circuit.

Thus, the output of the detection means may be coupled to a comparator circuit which is also coupled to a reference signal source, the arrangement being such that signals originating from the detection means due to vibrations in the hood means having an amplitude above a level determined by the reference signal source indicate the impact of objects on the hood means.

The output of the detection means may be supplied to the comparator circuit by way of a band-pass or high-pass filter, the arrangement being such that signals originating from the detection means due to vibrations in the hood means having frequencies within the bandpass or above the cut-off frequency, of the filter having an amplitude above the level determined by the reference signal, indicate the impact on the hood means of objects differing from the crop.

Alternatively, or in addition, the detection means may be coupled to a peak detector circuit for indicating signals from the detector which originate from the impact of an object on the hood means.

Preferably the rotor and the hood means co-operate to effect a degree of separation between the crop and the stones and like objects heavier that the crop by concentrating the stones and the like in a peripheral path around the inside of the hood means.

An agricultural implement according to the invention may include crop processing machinery for processing crop coming from the rotor, the deflector means being arranged for deflecting objects differing from the crop clear of the crop processing machinery after movement of the deflector means by the control means into the path of such an object.

Preferably the hood means defines a crop flow channel for crop collected by the rotor, and the rotor driving means is adapted to rotate the rotor at a speed sufficient to thin out the crop and propel it across the space between the rotor and the crop processing machinery, the deflector means being positioned, when actuated by the control means, to deflect objects differing from the crop downwardly towards the ground through the space between the rotor and the crop processing machinery.

Preferably the deflector means comprises a deflector plate positioned across the underside of the hood means to the rear of the axis of the rotor.

Preferably the rotor comprises an array of discrete elements distributed axially along the rotor, each element comprising at least one arm extending outwardly from the axis of the rotor and each element having a shape and inclination such as to tease out the crop and free stones and the like from the crop, and such as to tend to fling stones and the like outwardly against the hood means. Thus the stones may be concentrated in the said peripheral path by being driven outwardly by the rotor elements and then maintained in the path by bouncing between the inside of the hood means and the tips of the rotor elements.

Preferably each outwardly extending arm has a length at least four times its width taken in a direction along the axis of the rotor. Each element may include arms disposed in the form of a V with the apex of the V form directed towards the axis of the rotor.

Alternatively, the rotor may comprise a conventional tedder.

The said rotor may comprise a pick up rotor adapted to collect previously cut crop lying on the ground. Alternatively, there may be provided cutting means for cutting a crop during forward travel of the harvester, the rotor being positioned to engage crop cut by the cutting means before or after the cut crop falls to the ground.

The cutting means may comprise a reciprocatory cutter-bar, an endless, horizontal driven belt with knives attached thereto, or a rotary cutter having at least one cutting element arranged to rotate about a vertical axis. The rotary cutter may comprise a drum mower having at least two drums rotating about vertical axes in opposite senses and carrying cutting elements on the rotary drums. Alternatively, the crop may be cut by the rotor itself, which may comprise a flail mower rotor having a plurality of cutting elements extending outwardly from the rotor for cutting crop by rotation about the horizontal axis of the rotor.

The said crop processing means may include means for chopping crop coming from the rotor, and there may be included a device for delivering chopped crop from the chopping means to a container for transport.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a side view, partly in section, of an agricultural implement for use in harvesting crop and embodying the invention; Figure 2 is a perspective view of a rotor element suitable for use in the implement of Figure 1; Figure 3 is a block circuit diagram of means for detecting stones and like objects and for controlling a deflector means shown in Fig. 1; and Figure 4 shows an alternative arrangement of a front end to the implement shown in Figure 1.

Referring first to Figure 1, an agricultural implement 11 embodying the invention comprises a main body 12 mounted on land wheels 13 and drawn behind a tractor (not shown) to which it is coupled by a drawbar or three point linkage and by the power-takeoff of the tractor. Mounted in the main body 12 is a chopping means shown diagrammatically at 14, and a delivery chute 15. The chopping means 14 delivers the chopped crop up the chute 15 and may conveniently be of conventional design. For example the chopping means 14 may comprise an intake auger 16 comprising two oppositely handed auger portions leading towards the centre of the harvester, and a central tined portion for feeding crop into a pair of compaction rollers 17. The compaction rollers 17 may be arranged to feed the crop to a rotary precision chopper 18 which impels the chopped crop to the delivery chute 15.

Mounted at the front end of the main body 12 is a rotor 19 comprising an array of discrete rotor elements 20 distributed axially along the rotor. A hood means 21 curves over the rotor 19 and may comprise a curved sheet metal housing diverging slightly from the path of the tips of the elements 20 and extending back to the chopping means 14 as a substantially flat overhead housing. At the rear end of the curved part of the hood means 21 is positioned a deflector means comprising a deflector plate 22 extending transversely across the underside of the hood means 21. The deflector plate 22 is pivoted at 23 and can pivot downwardly to a position shown in dotted lines and indicated at 22'.

The movement of the deflector member 22 is controlled by a control means 24 mounted on the rear of the hood means 21. Also mounted on the hood means 21 is a detector means 25 for detecting the presence of stones and the like in the crop flowing around the underside of the hood means 21. The detector means 25 is connected, as will be described hereinafter, to the control means 24, which is arranged to actuate the deflector plate 22 in response to the output of the detector means 25.

There will next be described the basic manner of operation of the mechanical components of the agricultural implement 11. In use the implement is drawn by a tractor and the rotor 19 and chopping means 14 are driven by the power-take-off of the tractor. The rotor 19 is rotated in a sense (clockwise in Fig. 1) such as to pick up cut crop lying on the ground and to convey it upwardly and rearwardly through the space between the rotor axis and the underside of the hood means 21. The crop travels not only between the tips of the elements 20 and the hood means 21, but also through the outer space occupied by the elements 20. The elements 20 penetrate and move through the crop while it is being conveyed by the rotor.

It is found that known pick-up rotors for harvesters such as forage harvesters tend to pick up stones, pieces of metal, timber or other extraneous hard objects with the crop.

Similarly some stones, pieces of metal and the like may be picked up by the rotor 19.

However, it is a feature of the type of rotor described that the rotor 19 tends to tease out the crop layer and to free the stones and the like trapped therein. Many of these objects will fall on to the ground where they may be passed over or are ejected sideways. Other objects may be carried up by the rotor 19 and tend to be flung outwardly from the rotor axis by the elements 20 and to be concentrated in a peripheral path around the inside of the hood means 21. One object of the embodiment shown is to reduce the likelihood of stones and the like entering the chopping means 14. To this end the deflector plate 22 is positioned above the peripheral path of the crop, and when moved down wardly to the position 22', deflects the material downwardly to the ground clear of the chopping means 14.

Preferably there is provided behind the main rotor 19 a stripper rotor 19' having the purpose of recovering downwardly directed stray crop and directing the stripped crop towards the auger 16. The stripper rotor 19' rotates in the same sense as the main rotor 19. The stripper rotor 19' may have rubber paddle-like blades which deflect under the impact of heavy objects and do not direct extraneous objects into the chopping mechanism 14.

Conveniently the rotor elements 20 may be of the general form shown in our published UK Specification No. 1447026, and conveniently may be mounted in damage resisting resilient mountings such as are described in our published UK Patent No. 1493574. In Figure 2 there is shown one example of a convenient form of a conditioning element 20, which in this case is taken from our copending British Patent Application No.

20373/75 (1548889). Referring to Figure 2, the conditioning element 20 comprises two outwardly directed arms 41 and 41' which diverge from each other in the outward direction, the arms 41 and 41' being pivoted by a bolt 42 to outwardly directed lugs 43 and 43' protruding from a rotor 44. A resilient mounting is provided by a U-shaped bracket 45 which houses a rubber block 46.

The block 46 holds the arms 41 and 41' in the required outward direction, but provides a degree of pivoting movement when the arms 41 and 41' strike a heavy object.

There will now be described one example of the detector means 25 and control means 24, shown diagrammatically in Fig. 1, for detecting solid objects and for operating the deflector plate 22.

Referring to Figure 3, the detector means 25 may comprise as one particular example a strain gauge accelerometer which may for example be the Bell and Howell type CEC 4/202 (plus or minus 5g range). Alternatively, the detector means 25 may comprise a microphone of the piezo-electric type, or other acoustic or vibration sensors may be used. The detector means 25 is fixed to the exterior of the hood means 21 at a selected point where a considerable amount of vibration would be caused by a stone, for example on or above the centre line at the front of the hood means 21.

The detector means 25 is coupled by way of an amplifier 36 and a high-pass or bandpass filter 34, with a cut-off or centre-pass frequency of several hundred Hz, to the input of a voltage comparator 35. The filter 34 is not essential, but its presence is preferred. By way of example, the filter 34 may be a high pass filter having a pass frequency of 300 Hz. Signals indicative of vibrations are therefore passed through the amplifier 36 to the voltage comparator 24. If a filter 34 is included, frequency components characteristic of normal running of the harvester are attenuated whilst those high frequency components produced by the impact of solid objects are further amplified, so improving the discrimination between frequency components.

The voltage comparator 35 is tripped by signals of sufficiently high amplitude and these appear at the output of the high-pass filter 34. The voltage comparator 35 is a circuit known in itself in which a very high gain differential amplifier without feedback is connected to receive the output from the high-pass filter 34 at one input terminal while a unidirectional adjustable reference voltage is applied to the other input terminal. The effect is that the output of the comparator 35 switches from low to high as soon as the instantaneous voltage of signals from the filter 34 exceeds the reference voltage. Since no feedback is applied to the differential amplifier, it saturates in one direction or the other depending upon the sum of the instantaneous input signals. The comparator 35 then has an output signal which always takes up one of two values depending on whether the amplitude of the signals from the filter 34 is smaller or greater than a predetermined value. The construction of a suitable voltage comparator is described in the book "Applications of Operational Amplifiers" (The Burr Brown Co.), published by McGraw Hill in 1973 and edited by Graham Gehar AEME; and also in the "Non-linear Circuits Handbook" published in 1974 by Analogue Devices Incorporated and edited by Sheingold.

gold.

When this predetermined value of input to the comparator 35 is exceeded, a monostable timing circuit 26 is triggered to its unstable state by a signal passing from the comparator 35 by way of an AND gate 27 (enabled at this time as is explained below). The signal from the AND gate 27 also passes to a driver amplifier 29 and thence to a solenoid actuator 30.

The actuator 30 has two stable positions in a first of which hydraulic fluid passing by way of hydraulic lines indicated schematically at 31 passes in one direction to a hydraulic ram 32 moving the deflector plate 22 into the crop path. In the second actuator position fluid passes in the other direction to the ram 32 and the deflector plate 22 is restored to its position out of the crop path.

When a signal reaches the actuator 30 from the amplifier 29, the actuator takes up its first position and the deflector plate 22 moves into the path of the crop. After a time which is sufficient for a solid object to pass, after detection, through the machine as far as the deflector plate 22, the timing circuit 26 reverts to its stable state (unless a further solid object is detected, whereupon the timing circuit is triggered again). On retun to its stable state the timing circuit 26 triggers a further monostable timing circuit 28 to its unstable state in which a signal is applied to reset the actuator 30 by way of a driver amplifier 33. Hydraulic fluid now flows in the opposite direction in the lines 31 restoring the detector plate 22 to its position outside the crop path.

The timing circuit 28 when in its unstable state also applies an inhibiting signal to the AND gate 27 to prevent re-triggering by vibration when the deflector plate 22 is restored. As soon as the timing circuit 28 returns to its stable state the inhibiting signal is removed and any impacts by solid objects again cause the deflector plate 22 to be moved. The timing circuit 28 therefore has an unstable interval which is sufficient to allow vibrations caused by impact of the deflector plate 22 to subside before the AND gate 27 is opened. The output of the timing circuit 28 is "high" when in its stable state, so that only when it enters its unstable state is the AND gate 27 closed. A "low" input to the driver amplifier 33 resets the actuator 30. The timing circuits 26 and 28 may for example be R.C.A. CMOS type CD.4528 integrated circuits. Typically the timing circuit 26 is set up by means of an external resistor to have an unstable interval of about one second, while the circuit 28 is set up to have an unstable interval of about half a second. These intervals may, of course, be set differently depending on the type of agricultural machine and the position of the vibration detector.

While a specific embodiment of the invention has been described, it will be appreciated that the invention can be put into practice in many other ways. For example the circuit described in connection with Fig.

3 may use different component circuits in which for example the accelerometer described may be replaced by other forms of vibration detector such as a microphone or a piezoelectric device, and the position of the vibration detector on the hood may be varied so long as it is in a position where vibrations due to hard objects can be detected and it is sufficiently forward of the deflector plate 22 in the crop path to allow the deflector plate 22 to be moved after the objects are detected.

The high-pass filter may be replaced by a band-pass filter or in some arrangements may be omitted. The voltage comparator may be in a different form and other circuits may be used to control, and to time the operations of, the actuator.

Although the harvester shown in Figure 1 is illustrated with the rotor 19 for collecting previously cut crop lying on the ground, the machine can be modified if required to collect standing crop by incorporating a cutter in the machine. In the machine shown in Figure 1, the cutter can conveniently be a reciprocatory cutter bar positioned substantially immediately below the rotor 19. This may be arranged as in the general manner shown in our published UK Patent No.

1447026. Moreover, to aid detection of heavy objects the front housing may be more angular, as shown in our UK Patent No.

1322165.

In an alternative arrangement shown diagrammatically in Fig. 4, the rotor 19 may be positioned behind a known rotary drum mower indicated generally at 37. The cutter 37 comprises a pair of vertical drums 38 positioned side by side and carrying outwardly directed cutting knives 39 mounted upon horizontal domed discs 40. The rotor 19 is positioned to the rear of the drums 38 at a position between the gap between the two drums 38 so as to collect the crop transferred by the discs 40 and drums 38 between the drums 38. In Fig. 4 the diagrammatic representation is shown partly in cross section, the drum 38 which is shown being the right hand drum of a pair of drums, taken when facing in the direction of forward movement of the machine. The remainder of the harvester following the deflector plate 22 may be the same as is shown in Fig. 1.

In another modification, the deflector plate 22may be spring loaded into the downward position 22' and may be retained in the raised position by a catch mechanism. Upon detection of an extraneous object, the control means may be arranged to release the catch mechanism so that the deflector plate is propelled into the downward position by its spring loading. Conveniently the deflector plate may be arranged to be returned to the spring-biassed, loaded position by a pull rope operated by the driver or by automatic means.

Conveniently the piezoelectric crystal microphone or other detector may be mounted in a separate resonance box which is mounted on the hood means with an air gap between the detector and the hood means in order to protect the detector from mechanical damage.

Preferably the rotor is a high speed rotor in the sense that it picks up the crop by elements having a tip speed sufficient to tease out the crop into a fast moving stream which is propelled towards the chopping mechanism. A convenient tip speed is a speed at least about 4 times the normal, forward ground speed of the implement and preferably greater than 10 times the ground speed of the implement. By way of example, for a rotor having a diameter in the range 550 to 600 mm, the speed of rotation is proferably in the range 500 to 1000 r.p.m.

Conveniently more than one detector means may be used, the detectors being positioned at different locations on the hood means or adjacent structure.

WHAT WE CLAIM IS: 1. An agricultural implement for use in harvesting crop, comprising a rotor for collecting crop by rotation about a horizontal axis, hood means extending over the rotor, means for driving the rotor in rotation in a sense such that crop collected by the rotor is carried upwardly and rearwardly over the axis of the rotor, detection means for detecting objects differing from the crop picked up by the rotor with the crop, movable deflector means for deflecting such objects out of the normal crop path, and control means for moving the deflector means into the path of such an object when the object is detected by the detection means.

2. An agricultural implement according to Claim 1 in which the detection means comprises means for detecting vibrations in the hood means caused by impact on the hood means of objects differing from the crop.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (21)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   that only when it enters its unstable state is the AND gate 27 closed. A "low" input to the driver amplifier 33 resets the actuator 30. The timing circuits 26 and 28 may for example be R.C.A. CMOS type CD.4528 integrated circuits. Typically the timing circuit 26 is set up by means of an external resistor to have an unstable interval of about one second, while the circuit 28 is set up to have an unstable interval of about half a second. These intervals may, of course, be set differently depending on the type of agricultural machine and the position of the vibration detector.

   While a specific embodiment of the invention has been described, it will be appreciated that the invention can be put into practice in many other ways. For example the circuit described in connection with Fig.

   3 may use different component circuits in which for example the accelerometer described may be replaced by other forms of vibration detector such as a microphone or a piezoelectric device, and the position of the vibration detector on the hood may be varied so long as it is in a position where vibrations due to hard objects can be detected and it is sufficiently forward of the deflector plate 22 in the crop path to allow the deflector plate 22 to be moved after the objects are detected.

   The high-pass filter may be replaced by a band-pass filter or in some arrangements may be omitted. The voltage comparator may be in a different form and other circuits may be used to control, and to time the operations of, the actuator.

   Although the harvester shown in Figure 1 is illustrated with the rotor 19 for collecting previously cut crop lying on the ground, the machine can be modified if required to collect standing crop by incorporating a cutter in the machine. In the machine shown in Figure 1, the cutter can conveniently be a reciprocatory cutter bar positioned substantially immediately below the rotor 19. This may be arranged as in the general manner shown in our published UK Patent No.

   1447026. Moreover, to aid detection of heavy objects the front housing may be more angular, as shown in our UK Patent No.

   1322165.

   In an alternative arrangement shown diagrammatically in Fig. 4, the rotor 19 may be positioned behind a known rotary drum mower indicated generally at 37. The cutter 37 comprises a pair of vertical drums 38 positioned side by side and carrying outwardly directed cutting knives 39 mounted upon horizontal domed discs 40. The rotor 19 is positioned to the rear of the drums 38 at a position between the gap between the two drums 38 so as to collect the crop transferred by the discs 40 and drums 38 between the drums 38. In Fig. 4 the diagrammatic representation is shown partly in cross section, the drum 38 which is shown being the right hand drum of a pair of drums, taken when facing in the direction of forward movement of the machine. The remainder of the harvester following the deflector plate 22 may be the same as is shown in Fig. 1.

   In another modification, the deflector plate 22may be spring loaded into the downward position 22' and may be retained in the raised position by a catch mechanism. Upon detection of an extraneous object, the control means may be arranged to release the catch mechanism so that the deflector plate is propelled into the downward position by its spring loading. Conveniently the deflector plate may be arranged to be returned to the spring-biassed, loaded position by a pull rope operated by the driver or by automatic means.

   Conveniently the piezoelectric crystal microphone or other detector may be mounted in a separate resonance box which is mounted on the hood means with an air gap between the detector and the hood means in order to protect the detector from mechanical damage.

   Preferably the rotor is a high speed rotor in the sense that it picks up the crop by elements having a tip speed sufficient to tease out the crop into a fast moving stream which is propelled towards the chopping mechanism. A convenient tip speed is a speed at least about 4 times the normal, forward ground speed of the implement and preferably greater than 10 times the ground speed of the implement. By way of example, for a rotor having a diameter in the range 550 to 600 mm, the speed of rotation is proferably in the range 500 to 1000 r.p.m.

   Conveniently more than one detector means may be used, the detectors being positioned at different locations on the hood means or adjacent structure.

   WHAT WE CLAIM IS: 1. An agricultural implement for use in harvesting crop, comprising a rotor for collecting crop by rotation about a horizontal axis, hood means extending over the rotor, means for driving the rotor in rotation in a sense such that crop collected by the rotor is carried upwardly and rearwardly over the axis of the rotor, detection means for detecting objects differing from the crop picked up by the rotor with the crop, movable deflector means for deflecting such objects out of the normal crop path, and control means for moving the deflector means into the path of such an object when the object is detected by the detection means.
2. 2. An agricultural implement according to Claim 1 in which the detection means comprises means for detecting vibrations in the hood means caused by impact on the hood means of objects differing from the crop.
3. 3. An agricultural implement according

   to Claim 2 in which the output of the detection means is coupled to a comparator circuit which is also coupled to a reference signal source, the arrangement being such that signals originating from the detection means due to vibrations in the hood means having an amplitude above a level determined by the reference signal source indicate the impact on the hood means of objects differing from the crop.
4. 4. An agricultural implement according to Claim 3 in which the output of the detection means is coupled to the comparator circuit by way of a band-pass or high-pass filter, the arrangement being such that signals originating from the detection means due to vibrations in the hood means having frequencies within the band-pass, or above the cut-off frequency, of the filter and having an amplitude above the level determined by the reference signal, indicate the impact on the hood means of objects differing from the crop.
5. 5. An agricultural implement according to any preceding claim in which the output of the detection means is coupled to a peak detector circuit for indicating signals from the detector which originate from the impact on the hood means of objects differing from the crop.
6. 6. An agricultural implement according to any preceding claim in which the control means includes a first timing circuit which ensures that, after actuation, the deflector means remains in the crop path of the detected object for the period of a typical deflection and for a predetermined interval thereafter before being restored to a position outside the crop path.
7. 7. An agricultural implement according to Claim 6 in which a second timing circuit is also provided to ensure that after the deflector means has been returned to its position outside the crop path it remains in that position for a second predetermined time interval to prevent vibrations caused by the restoration of the deflector means from operating the detection means.
8. 8. An agricultural implement according to Claim 6 or 7 in which the control means comprises an actuator coupled to the movable deflector means and having two stable positions, the actuator being arranged to be set in one stable position in which the deflector means is in the path of a detected object when the detector means output indicates that an object has been detected, and the actuator being coupled to the timing circuits to be reset to its other stable position at the end of the first timing interval determined by the first timing circuit.
9. 9. An agricultural implement according to Claim 8 including means for inhibiting the triggering of the actuator again to its said one position until the end of the second timing interval of the second timing circuit.
10. 10. An agricultural implement according to Claim 8 or 9 in which the said actuator comprises an hydraulic ram.
11. I 1. An agricultural implement according to any preceding claim in which the rotor and the hood means cooperate to effect a degree of separation between the crop and stones and like objects heavier than the crop by concentrating the stones and the like in a peripheral path around the inside of the hood means.
12. 12. An agricultural implement according to any preceding claim including crop processing machinery for processing crop coming from the rotor, the deflector means being arranged for deflecting objects differing from the crop clear of the crop processing machinery after movement of the deflector means by the control means into the path of such an object.
13. 13. An agricultural implement according to Claim 12 in which the crop processing means includes means for chopping crop coming from the rotor.
14. 14. An agricultural implement according to any preceding claim in which there is provided a flow channel for crop collected by the rotor, and the rotor driving means is adapted to rotate the rotor at a speed sufficient to thin out the crop and propel it across a space between the rotor and crop processing machinery, the deflector means being positioned, when actuated by the control means, to deflect objects differing from the crop downwardly towards the ground through the space between the rotor and the crop processing machinery.
15. 15. An agricultural implement according to any preceding claim in which the deflector means comprises a deflector plate positioned across the underside of the hood means to the rear of the axis of the rotor.
16. 16. An agricultural implement according to any preceding claim in which the rotor comprises an array of discrete elements distributed axially along the rotor, each element comprising at least one arm extending outwardly from the axis of the rotor and each element having a shape and inclination such as to tease out the crop and free stones and the like from the crop, and such as to tend to fling stones and the like outwardly against the hood means.
17. 17. An agricultural implement according to Claim 16 in which each discrete element includes arms disposed in the form of a V with the apex of the V form directed towards the axis of the rotor.
18. 18. An agricultural implement according to any preceding claim in which the said rotor comprises a pick-up rotor adapted to collect previously cut crop lying on the ground.
19. 19. An agricultural implement according to any of Claim 1 to 5 in which there is provided cutting means for cutting a crop during forward travel of the harvester, the rotor being positiond to engage crop cut by the cutting means.
20. 20. An agricultural implement according to any of Claims 1 to 17 in which the rotor comprises a flail mower rotor having a plurality of cutting elements extending outwardly from the rotor for cutting crop by rotation about the horizontal axis of the rotor.
21. 21. An agricultural implement for use in harvesting crop substantially as hereinbefore described with reference to Figures 1,2 and 3 or Figures 2, 3 and 4 of the accompanying drawings.