620,130. Photo-electrically con t r o l l e d hoeing-machines. MARIHART, L. A. Nov. 16, 1945, No. 30866. Convention date, Dec. 12,1944. [Class 6(i)] [Also in Group XL(b)] In an agricultural machine of the kind described in Specification 590,598, in which the operation of rotary hoeing cutters is controlled by photo-electric inspection of plants to eradicate inferior plants, or to deposit fertilizer or insecticide the photoelectric system includes colour and polarized light filters and is encircled within a resilient boot closed at its lower end by an inclined wall of light-permeable material which is in wiping contact with the plants. General description.-Photo-electricallycontrolled hoeing units B1, B2 shown in Fig. 2 are mounted in pairs in assemblies B which are attached to the underside of a tractor, and are capable of being hydraulically raised or lowered, the assembly weight being counterbalanced by a spring adjustable by a hand lever. In each unit, a continuously rotating two-bladed blocking cutter 31 is driven from the tractor transmission by shaft 37 and shaft 34 which extends longitudinally through devices 44 and 45, surrounded concentrically by a tubular shaft 33 which carries two spaced and angularly staggered fine hoeing cutters 32. Fig. 5, 6 show shafts 33, 34 carried in bearings 57, 58 in device 44, a pawl 62 tripping the clutch 59 on energization of solenoid 61, to rotate shaft 33 a quarter revolution at a time in unison with shaft 34. A friction brake 71 acts on shaft 33 to prevent backlash while a detent 73 falling into equally spaced depressions m a collar 72 retains shaft 33 in one of four stationary positions on disengagement of the clutch. A switch 64 is opened by cam ring 69 after initial rotation and closed on its cessation. The device 45, Figs. 7, 8, comprises a casting, 103 supported by a bracket on the frame of assembly B, carrying a box 106 and a dependent light-proof enclosure or huddler having sheet metal side walls 101, 102, the lower edge 102a passing through the earth bed while a flexible apron 112 passes along the shoulder of an adjacent furrow. Light is excluded from the huddler by flexible aprons 109, 111 at its front and rear ends, while a resilient boot 114 is clamped to a rib 116 of the casting 103, and is sealed at its lower end by a rectangular plate 113, the plane of which is angularly tilted with respect to the direction of motion of the machine and to the lateral contour of the earth bed. The plate is opaque except for a narrow transparent portion 113a, the leading edge of which is linear and inclined to the direction of motion. A resilient flap 121, mounted on a transverse rib 122 at an angle to the direction of motion, precedes the boot 114, within which are enclosed a lamp 123, a photocell 124, and mountings 127, 128 for lenses and for coloured and polarized light filters. The interior of the boot is vented to the atmosphere through an air filter 132 mounted on the box 106, which contains the electronic apparatus shown in Fig. 11. Cutters.-The blocking cutters 31, Fig. 3, each have two V-shaped blades comprising wings 77a, 77b; the lip 77c being sharpened. The apex of the V is the trailing edge, and edges 78, 79 are curved about shaft 34 as centre. In wet soil the wing 77b and lip 77c may be omitted. The hoeing cutters 32 each consist of two sets of four blades on arms radiating from shaft 33, the sets being angularly staggered and spaced apart. The blades may have lips similar to 77c. In adjacent units, the hoeing cutters are longitudinally staggered and the blocking cutters are angularly displaced to avoid mutual interference while rotating in opposite directions. The depth of cut of the hoeing devices and the separation between adjacent units and assemblies are adjustable while in weeding operations the blocking cutters may be removed, and in blocking operations the hoeing cutters may be disabled. Operation.-As the machine proceeds along a plant bed, the continuously rotating blocking cutters 31 divide a row into clumps of plants, which then enter the huddler, are bent backwards and towards the adjacent furrow by The flap 121, and wipe across the plate 113. The foliage is inspected through the transparent portion by the photocell and lamp, the use of a red filter distinguished the lighter stem portion from the greener leaves, while the polarized light filter minimizes unwanted reflections. The passage of a sufficiently developed plant causes the photocell to impulse the electronic device 134, Fig. 11, to reduce the current in relay 136, which opens. Pilot lamp 141 is extinguished and coil 144 is energized to attract armature 148 which holds through contact 146 and energizes solenoid 61 through contact 152. Clutch 59 is tripped by pawl 62, and the fine hoeing cutters 32 rotate one-quarter revolution, the operation of the mechanism being co-ordinated with the forward motion of the machine so that the plant selected by the photocell is preserved in the space between the cutters, which eradicate the remainder of the clump left by the blocking cutters. After a small angle of rotation, cam ring 69 opens switch 64, releasing armature 48 and de-energizing solenoid 61. A time delay may be introduced between the impulsing of the electronic amplifier and the operation of the hoeing cutters, and may be dependent on the forward speed of the machine; as described in Specification 590,598. The enclosure of the photocell system keeps it free from dust; while the transparent portion of the plate 113 is continuously wiped free of dust by the passage of the plants. Modifications.-Means may be provided for dispensing fertilizer adjacent to each plant through a hollow shoe fixed to the rear of the machine which passes through the ground adjacent to a row of plants and which is connected to a bin through a hose having a solenoid-operated valve 172. Time delay means shown in Fig. 11 are provided between the operation of solenoid 61 and the opening of valve 172, by an electromagnetic perforator 176 operating on a paper tape 182 on each energization of solenoid 61. The tape is drawn over a contact wheel 178 synchronously with the forward motion of the machine, the amount of slack corresponding to the displacement between the fine hoeing cutters and the fertilizer dispensing shoe. A brush 179 contacts the wheel 178 through each perforation and successively operates the valve 172. Fertilizer may alternatively be dispensed in accordance with the operation of the blocking cutters, and a similar arrangement may be used to deposit insecticide on each remaining plant. The device 45 may be constructed in the form of a unitary casting containing the photocell, lamp, and electrical components, readily detachable from the machine and adjustable in a vertical direction.