Motor speed control circuit

• US 4,605,883 A
• Filed: 02/05/1982
• Issued: 08/12/1986
• Est. Priority Date: 02/05/1982
• Status: Expired due to Term

• Current Assignee: Sunbeam Products, Inc. d/b/a Jarden Consumer Solutions (Newell Brands Inc.)
• Original Assignee: Sunbeam Corp. (Newell Brands Inc.)
• Inventors: Cockroft, James B.
• Primary Examiner(s): Weldon, Ulysses
• Application Number:
  US06/345,972
• Time in Patent Office: 1,649 Days
• Field of Search: 318/312, 318/319, 318/326, 318/327, 318/345 C, 318/345 G, 318/345 D, 318/345 H, 318/514-516, 318/533, 318/244, 318/246, 318/249, 318/328, 318/325, 318/462, 338/48, 338/49, 338/92, 338/95, 338/120, 338/122, 338/123, 338/128, 338/129
• US Class Current: 388/815
• CPC Class Codes: H02P 25/10 Commutator motors, e.g. repulsion motors
• CPC Class Codes: Y10S 388/917 Thyristor or scr

Abstract

A motor speed control circuit for closed loop control of an electric motor of a household electric appliance is disclosed herein. The motor speed control circuit includes a coil adapted to be placed in proximity with a fan connected to an electric motor and producing a time varying signal in response to rotation thereof. A comparator connected to the coil generates a rectangular wave having a frequency proportional to the frequency of the coil signal. Additional means are provided for converting the rectangular wave signal, a D.C. signal having an amplitude which corresponds to the frequency of the rectangular wave. The D.C. signal is compared to a reference signal at an amplifier to produce an error signal which is fed through an opto-isolator to a conduction angle controlled thyrister. The thyrister is connected to the electric motor and a source of electric power to control the speed of the electric motor.

Claims

1. A motor speed control circuit for use in controlling the speed of an electric motor of a household electrical appliance comprising;

tachometer means located in proximity with a plurality of blades of a fan in driven connection with an electric motor and producing a tachometer signal when said electric motor rotates said fan blades past said tachometer means, clipping means connected to said tachometer means to produce a clipped tachometer signal having a preselected maximum amplitude, comparator means connected to said clipping means, and producing a rectangular wave signal in response to said clipped tachometer signal received from said clipping means, differentiating means connected to said comparator and receiving said rectangular wave signal therefrom and producing a differentiated pulse signal in response thereto, integrator means connected to said differentiating means and receiving said differentiated pulse signal from said differentiating means and producing a speed signal having an amplitude indicative of a speed of rotation of said electric motor, means for comparing said speed signal to a reference signal and producing an error signal indicative of a difference between said reference signal and said speed signal, isolation means receiving said error signal and producing an isolation error signal in response thereto, timing means receiving said isolation means error signal and producing a signal having a selected amplitude after a period of time proportional to a magnitude of said error signal, and a triac connected to said timing means to receive said selected amplitude signal therefrom and to change state in response thereto to control a flow of electric current received from an external power source through said electric motor of said household electric appliance.

2. A motor speed control circuit as defined in claim 1 further including means for generating said reference signal connected to said means for comparing said speed signal to a reference signal and having a first adjustable resistance adjustable between an upper reference voltage limit and a lower reference voltage limit, a lower reference limit adjustable resistance which provides a preselected low speed voltage and an upper voltage limit adjustable resistance which provides a preselected upper speed voltage, said upper and lower voltage adjustable resistances being connected to said first adjustable resistance to define a voltage range over which said first adjustable resistance operates.

3. A motor speed control circuit for use in controlling the speed of an electric motor of a household electric appliance comprising;

a pickup coil located in a spaced proxmiity with a fan of an electric motor to sense a rotational speed of a fan and produce a time-varying first motor speed signal having a frequency proportional to the rotational speed of said fan, attenuation means connected to said pickup coil to reduce a voltage of said first motor speed signal thereby producing a an attenuated first motor speed signal, a first clipping diode connected to said attenuation means and shunting a portion of attenuated first motor speed signal away from other parts of said motor speed control circuit, a comparator connected to said attenuation means to receive said attenuated first motor speed signal to produce a rectangular wave signal having a uniform amplitude and a frequency proportional to the frequency of said attenuated first motor speed signal, means for differentiating said rectangular wave signal producing a differentiated signal having a plurality of pulses, a second diode clipper receiving said differentiated signal and shunting every other pulse of said differentiated signal, means for intergrating a remaining portion of said differentiated signal, means for integrating a remaining portion of said differentiated signal to produce a second motor speed signal having an amplitude proportional to said frequency of said first motor speed signal, reference voltage generating means having a control potentiometer adjustable between an upper reference voltage limit and a lower reference voltage limit, a lower reference voltage limit potentiometer which provides a preselected low speed voltage and an upper reference voltage limit potentiometer which provides a preselected upper speed voltage, said upper and lower reference voltage limit potentiometers being connected to said control potentiometer to define a voltage range over which said control potentiometer operates, an amplifier connected to said control potentiometer to receive a speed reference voltage therefrom and also being connected to said integrating means to receive said second motor speed signal, said amplifier producing an output current having an amplitude proportional to a difference between said speed reference voltage and a voltage of said second motor speed signal, an opto-isolator connected to said amplifier and receiving said output current therefrom to control a flow of electric current received from an external source through a rectifier, timing means including a plurality of resistors and capacitors which receive a charging current from said rectifier, an amplitude of said charging current being controlled by said opto-isolator, and a triac connected to said timing means and to said electric motor to allow said electric current to flow through said electric motor when said capacitors of said timing means have charged to a predetermined level.