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US 6,850,023 B2Granted
Method of measuring motor speed
AssigneeJohnson Electrics S.A.
InventorJames Ching Sik Lau
Life of this patent
Estimating the term…
Abstract
A speed sensor for an electric motor detects the variation in the electric field of the armature due to commutation to produce an output signal indicative of the speed of rotation of the motor.
Claims13
A method of producing a signal indicative of rotational speed of a PMDC motor having a wound rotor, comprising the steps of:
- producing a raw signal by measuring the electromagnetic emission of the motor;
- producing a second signal by filtering the raw signal to isolate electromagnetic activity of the wound rotor, including spikes associated with commutation events;
- and
- producing an output signal by processing the second signal to change the spikes into square pulses.
1 more element
A PMDC motor comprising:
- a permanent magnet stator;
- a wound rotor confronting the stator;
- a speed sensor comprising a sensor coil located spaced from the rotor but in an electromagnetic field produced by the rotor and producing a raw input signal when the motor is in use;
- and
- a signal processing circuit connected to the coil for receiving the raw input signal and producing an output signal indicative of motor speed, the circuit including a filter for filtering the input signal and a signal modifier to convert the filtered signal into the output signal,
- wherein the signal modifier comprises a square pulse generator triggered by spikes in the filtered signal to produce a pulse train as the output signal.
3 more elements
Dependencies are inferred from the claim text.