the chipping blades of the machine 9. The sensing coil 32 is embedded in a truncated pyramid-shaped insulator matrix 13. The insulator matrix 13 mounts the sensing coil 32 to a wall of the chute 10 and insulates the sensing coil 32 from the wall of the chute 10.
FIG. 3 shows a hydraulic pump 1, and a reservoir 8 for hydraulic fluid is coupled to the pump. Feed valve 2, when in the position shown, allows the pump 1 to supply fluid to safety diverter solenoid valve 3. The valve 2 may be moved to its other position, in which case fluid from the pump is diverted to a return filter 7 and then fed back into the reservoir 8.
Valve 3 includes a coil which, when energised, moves the valve from the position shown to its second position. In the position shown, fluid passes through valve 3 and is returned to the filter 7 and then to the reservoir 8 because the manual feed roller directional valve 4 is in its intermediate position.
The solenoid valve 3 is normally in the position shown when its associated coil is de-energised.
Feed roller directional valve 4 is manually operable and may be moved either to the left or to the right of its intermediate position. When valve 4 is moved to its left hand position, fluid may be supplied to flow divider/combiner 5 and by that device to feed roller hydraulic motors 6 to cause the motors to drive the feed rollers 11 in a first direction. When the valve 4 is moved into its right hand position, fluid may be supplied to the motors 6 via flow divider/combiner 5 to cause the rollers 11 to be driven in a direction opposite the first direction.
The safety solenoid valve 3 is normally energised and is de-energised whenever the hands of machine operator are detected close to an area within the feed chute 10 of the chipping machine 9. When valve 3 is de-energised, it returns to the position shown in FIG. 3 and motors 6 no longer rotate and the feed rollers 11 cease their rotation.
FIG. 4 shows further details of the safety system of the invention. Alarm circuit 40 has the sensing coil 32 coupled to it. Coil 32 is positioned extending in a plane along the wall of the feed chute 10. The passive sensor coils worn by the machine operator function to modify the electromagnetic field produced by coil 32 whenever the passive sensor coils are close enough to the coil 32. This modification of the field of coil 32 is sensed by circuit 40 which provides an output as a consequence of this sensed proximity. That output is used to drive a switching circuit consisting of transistors Ql, Q2 and Q3 and a relay having a coil Rl and a contact CI. With relay Rl de-energised, contact CI is in the position shown.
An emergency stop switch SW1 is present in series with contact CI and switch SW1 is normally closed.
A second relay has a coil Rl and two contacts C2 and C3. Contacts C2 and C3 are in the positions shown when relay coil R2 is energised. Coil R3 is the coil of solenoid valve 3 in FIG. 3. With FIG. 4 in the state shown coil R3 is energised and the valve in its left hand position.
When coil 32 detects the proximity of a passive sensor coil, Rl is de-energised and contact CI moves to its normally closed position. This de-energises coil R2, and contacts C2 and C3 move to normally closed positions and coil R3 is de-energised.
A start/reset switch SW2 is in series with emergency switch SW1. Once the passive sensors move away from coil 32, coil Rl is energised and contact CI returns to the position shown in FIG. 4. Coil R2 is de-energised and contacts C2 and C3 are in the opposite (NC) positions to that
shown in the figure and coil R3 is de-energised and the motors 6 (in FIG. 3) which drive the feed rollers 11 are not operating.
The start switch SW2 is momentarily moved to the
5 position opposite to that shown in FIG. 4, and thus allows coil R2 to be energised to move contacts C2 and C3 into the positions shown. The coil R3 is then energised and switch SW2 is released and returns to the position shown. Coil R2 is held in and coil R3 remains energised until coil 32 once
10 again detects the proximity of a passive sensor.
FIG. 5 shows a detailed circuit block diagram of a control circuit for the system of the invention. The circuit has four inputs, ANT1, ANT2, ANT3 and ANT4 and only one of these is used. Coil 32 (FIG. 4) has one of its ends connected
15 to input ANT1 and its other end is connected to ground. The circuit of FIG. 5 energises the coil 32 and also monitors that coil to detect field changes in that coil produced by the proximity of a passive sensor. An output at line 50 may be used to operate an alarm and is the output supplied to
20 transistor Ql in FIG. 4.
The control circuit illustrated in FIG. 5 also includes a microprocessor 51, power supply 52, sync comparators 53, function switch 54, system control 55, alarm buzzer 56, digitizer 57, receiver 58, receive switches 59 to 62, trans
25 mitter oscillator 63, phase splitter 64, phase switch 65, first transmitter 66, second transmitter 67, output switch 68, and transmitter switches 69 to 72.
The use of passive sensors like that shown in FIG. 1 means that no power supply need be carried by the machine
30 operator. As the passive sensors do not require power, their function is not dependent on the presence of a power supply to them and thus give rise to operational advantages.
The invention has been described by way of example with reference to its use with a wood chipping machine 9. In that
35 example application solenoid valve 3 in FIG. 3 is necessary to ensure that drive to the feed rollers 11 is discontinued.
If the system of the invention were used with equipment other than the wood chipping machine 9, a coil like coil 32, passive sensors and other components would still be neces
40 sary but a solenoid valve 3 would not. The system of the invention would be used to control some other device to achieve activation and deactivation of the equipment being controlled.
What is claimed is:
45 1. A wood chipping machine comprising a safety system, said wood chipping machine including:
chipping blades that rotate to chip material delivered to the machine;
5q a feed rollers that grip and feed the material to the chipping blades; a feed chute that guides material to the feed rollers, the feed chute having walls defining a passage, an open front end for receiving the material and an open rear 55 end adjacent the feed rollers; and
a motor that drives the feed rollers and the chipping blades;
said safety system comprising:
at least one passive sensor incorporated in a band worn by 60 a user of the wood chipping machine;
at least one sensing coil mounted on one of the walls of the chute, the sensing coil generating a signal when the passive sensor is in the passage; and means for stopping the chipping blades and/or the feed 65 rollers in response to the signal.
2. The wood chipping machine of claim 1 wherein the at least one passive sensor consists of a tuned circuit.