Safety system for machinery
A safety system for a machine having a danger zone includes an induction coil having one or more turns extending along the periphery of a part of a worker's body as, for example, extending alone the fingers of a glove worn by the worker. A drive circuit applies a time-varying current having an identifiable characteristic such as the frequency of an alternating current. A magnetic field having the characteristic of the time-varying current is induced in an omnidirectional magnetic field sensor mounted adjacent the danger zone. The magnitude of this field is monitored. When the magnitude exceeds a threshold, a warning signal is issued and protective action may be taken, such as stopping or reversing the machine.
1. A safety system for a machine having a danger zone comprising:
(a) units including a sending unit having an inductor and a receiving unit having a magnetic field sensor with one or more transducers arranged to provide one or more transducer signals representing the strength of a magnetic field induced in the sensor, a first one of units being adapted for mounting to a body part, a second one of units being adapted for mounting adjacent to the machine adjacent the danger zone, at least one of the units being operative to send or receive magnetic fields omnidirectionally;
(b) a drive circuit connected to the inductor, the drive circuit being operative to apply an time-varying current in the inductor having a drive characteristic such that the inductor emits a time-varying magnetic field having the drive characteristic; and
(c) a detector circuit connected to the magnetic field sensor, the detector circuit being operative to provide a warning signal when the one or more transducer signals indicate that the magnitude of a magnetic field in the sensor varying with the drive characteristic exceeds a threshold value.
2. A system as claimed in claim 1 wherein the second one of the units includes a ferromagnetic body and a set of three orthogonal, unidirectional transducers, the body and orthogonal transducers being adapted for mounting to the machine.
3. A system as claimed in claim 2 wherein each of the transducers includes a sensor coil extending around the ferromagnetic body.
4. A system as claimed in claim 2 wherein the ferromagnetic body is elongated.
5. A system as claimed in claim 2 wherein the first unit includes a first coil having one or more turns adapted to extend along one or more digits of a hand when the first one of the pair is mounted on the hand.
6. A system as claimed in claim 4 wherein the each turn of the first coil includes one or more digit sections, each said digit section having a tip and a base, a pair of elongated runs spaced apart from one another and a bend connecting the runs at the tip ends, each said turn also including one or more main sections continuous with the one or more digit regions, each of the digit regions being arranged to extend along a digit of the hand with the tip of the digit region disposed adjacent the tip of the digit, the one or more main sections being arranged to extend along a periphery of the body of the hand.
7. A system as claimed in claim 5 wherein each turn of the first coil includes five digit regions.
8. A system as claimed in claim 6 wherein the one or more turns of the first coil include a plurality of turns alongside one another, the turns being electrically connected in series with one another.
9. A system as claimed in any of claims 5 to 8 wherein the first unit is the sending unit, the first coil being connected to the drive circuit, the second unit being the magnetic field sensor, the three orthogonal transducers being connected to the detector circuit to provide the one or more transducer signals as three transducer signals, each representing a magnetic field in one of three orthogonal directions.
10. A system as claimed in claim 9 wherein the detector circuit includes a calculator operative to calculate the magnitude of the magnetic field responsive to the transducer signals.
11. A system as claimed in claim 1 wherein the drive circuit is operative to apply an alternating current in the inductor at a drive frequency, and the drive characteristic includes the drive frequency.
12. A system as claimed in claim 11 wherein the drive frequency is between 1 KHz and 200 K Hz.