Abstract: In a forage harvester having a metal detector positioned within a first feed roll and a second feed roll whose displacement from the first feed roll varies with the bulk of crop material passing between the feed rolls, the sensitivity of the metal detector is adjusted according to the displacement of the second feed roll from the metal detector to provide a more uniform detection of tramp metal with varying crop bulk. The sensitivity is increased as the inherent noise component induced in the metal detector output signal by the second feed roll decreases as the second feed roll is displaced from the metal detector by crop bulk.

Abstract: Under the control of a microprocessor first and second motors alternately drive first and second ends of a shear bar for adjusting the position of the shear bar relative to cutter head. The shear bar is adjusted so that it is substantially parallel to the cutter head even though the cutter head and shear bar may not be parallel at the time the adjustment is initiated. A knock sensor is provided for sensing impacts between the cutter head and shear bar, the knock sensor output signal being converted to a digital value for controlling the adjusting sequence. A knocker is provided for inducing vibrations in the shear bar to thereby test the operability of the knock sensor and its output circuitry. The sensitivity of the adjustment system to the output of the knock sensor is set automatically before an adjustment sequence begins to account for variations in the knock sensor, its output circuitry, and "noise" vibrations induced in the shear bar by normal machine operation.

Abstract: In a forage harvester having a metal detector with permanent magnets located within a crop feed roll, additional permanent magnets are positioned beyond the ends of the feed roll and at a distance greater than the radius of the feed roll from the axis of rotation of the feed roll. The additional magnets cooperate with magnets within the feed roll to provide a more uniform flux density across the width of the feed roll, even in regions near ferrous side sheets defining the lateral limits of the harvester feed path. Tramp metal is thus detected with equal facility regardless of its trajectory past the feed roll.

Abstract: The metal detector circuitry for a forage harvester is provided with a socket for receiving a pluggable unit, the arrangement being such that a resistor in the pluggable unit is connected into the detection circuitry of a metal detector whereby the sensitivity of the metal detector may be changed by inserting into the socket a pluggable unit containing a resistor of a different value. A metal detector test assembly connected to the metal detector through the socket, provides a means for testing the sensitivity of the metal detector and its associated circuitry. The test assembly includes a signal unit which is placed adjacent the metal detector sensing unit and generates a magnetic field that is sensed by the sensing unit, and a test box with circuitry, indicators and switches for selectively checking the sensitivity of the metal detector and correct operation of its associated circuitry.

Abstract: The unpredictability of the actual characteristics of spurious sounds has resulted in the use of electronic filtering or comparator circuits being less than satisfactory in certain cases, such as for distinguishing between machinery sounds and foreign objects in the machinery. An acoustically based stone detector is provided for use on a field harvesting machine. A piezoelectric acoustic detector is attached to the central support web of a feed roll within the frame of the harvester, and a rotating transformer is used to transmit the signal from the feed roll to the frame. The air core rotating transformer is built with one coil rotating with the feed roll and the other coil stationary on the frame. Electronic circuitry is used to process the signal and control the harvester action to protect the cutter blades from damage by detected stones, either by stopping the machine or mechanically ejecting the stones.

Abstract: Metal detectors having parallel magnetic fields produce signals which vary depending upon the shape and orientation of a metal object passing through the field. An improved metal detector sensor includes a magnet of special configuration having a multi-directional magnetic field resulting in a detector which is insensitive to orientation of the detected metal. One embodiment of the magnet is a pattern of cylindrical poles with the opposing pole central to the cylinder, thus creating a multiplicity of radially extending magnet fields. An alternate embodiment of the invention is an offset pattern of opposite poles which create two groups of fields, each at an angle to the general direction of movement of the material fed into the machine.