FIELD OF INVENTION
The present invention relates to a universal motor speed control device more particularly to a device for speed control of a universal motor used in home appliances including refrigerators, washing machines, mixers and food processors.
PRIOR ART
US Patent 6,854,299 discloses a rotary speed control in which a power switch is switched on an off electronically to conduct in mains relationship over variable periods of time from before the end of a mains half-period to after the beginning of the following mains half-period. The motor current remains unchanged during the switching gaps by way of a freewheeling diode.
US Patent 6,016,041 discloses a rotary speed control circuit for feeding a dc universal motor for driving a washing machine. A rectifier and a smoothing capacitor derive the operating voltage of the motor from the mains ac voltage and provided for control of the rotary speed is a regulating device which controls a power stage for the motor, the power stage including a power switch and a commutation diode in the topology of a low-setting device. The power stage feeding the motor includes a high-setting inductor and can be switched over from the topology of a low-setting device to the topology of a high-setting device.
In US Patent 5,530,325, a control circuit is proposed, which can be used for the phase-shift control of an electric motor in an a.c. voltage supply line. The ground connector of the control circuit, together with the cathode of a semiconductor switch (triac), is directly connected with load current circuit. Because of this, it is possible to do without potential-separating means when it is intended to feed signals at the load current circuit directly into the control circuit. An auxiliary voltage source is connected between the synchronization input and the ground connector to maintain the function of the synchronization input.
In US Patent 5,495,161, a series universal AC/DC motor is controlled by switching the phase angle of an AC signal with a triac power switch in response to a motor control providing a phase-locked loop velocity control. A speed command circuit provides a deference frequency corresponding to a selected motor speed. The reference frequency is compared to a feedback frequency representing actual motor speed. An error signal representing the
phase difference between the reference and feedback frequencies is compared to a ramp signal produced by the AC power source, and a resulting trigger pulse is used to control the triac power switch, thereby regulating the speed of the motor.
US Patent 4,673,860 discloses a speed variator for an AC motor included preferably in a food processing apparatus. The variator comprises a controllable switching member, such as a triac, and an RC circuit for regulating the motor speed to a predetermined speed. A current compensating circuit is provided, connected across the terminals of capacitors in the regulating circuit and to a terminal of the variator for compensating a current increase to maintain the predetermined motor speed regardless of the fluctuations of the load torque on the motor during motor operation.
But none of the prior documents discloses an IR sensor based speed control device which controls the speed to preselected speed based on feed back received by IR sensor.
OBJECTS OF THE INVENTTON
The primary object of the invention is to propose an IR based universal motor speed control device.
Another object of the invention is to propose a device which enables the user to select the speed.
Yet another object of the invention is propose a device to control the speed of motor as selected by the user.
Further objects and the advantages of the invention will be more apparent from the ensuing description.
STATEMENT OF INVENTION
According to the present invention there is provided a speed control device for a single phase moor used in home appliances comprising:
an IR source to produce an infra red rays;
a motor provided with means for periodically directing infra red rays to generate a sensor output;
an IR sensor provided along the path of infra red rays to sense the IR rays, periodically transmitted by said source and provide a pulsed output to the electronic control board;
an electronic control board for receiving the signal from the sensor, conditioning and providing signal to motor for controlling the speed;
a user interface electrically connected with the motor to select the required speed of the universal motor;
a power supply unit to supply power to said speed control device;
a motor driver circuit to drive the said motor; and
a computing means to compare the pulsed output with required speed, to calculate the firing angle of the motor driver circuit and supply the required power pulse to motor driver circuit.
DESCRIPTION OF ACCOMPANYING DRAWINGS
Fig. 1 shows the block diagram of the present invention.
Fig. 2 shows the arrangement of opaque blades, IR source and IR sensor.
Fig. 3 shows the arrangement of reflectors, IR source and IR sensor.
DETAILED DESCRIPTION WITH REFERENCE TO DRAWINGS
According to the invention, the IR sensor universal motor speed control device essentially comprises a universal motor provided with means for periodically transmitting IR energy; an IR source to radiate IR energy towards the means for periodically transmitting IR energy; a
means to sense the IR energy by the means for periodically transmitting IR energy and to provide pulsed output; a user interface to input the required speed; a power supply; a motor driver circuit; and a computing means to compare the pulsed output with required speed to calculate the firing angle of the motor driver circuit and supply the required power pulse to motor driver circuit.
In accordance with one embodiment of invention the means for periodically transmitting IR energy may be plurality of bands of reflecting material provided on the shaft of the motor which reflect IR energy radiated by IR source towards means to sense IR energy.
In an embodiment of invention the means to sense IR energy comprises a photo diode or photo transistor or a photo Darlington.
Accordingly to another embodiment, the means for periodically transmitting IR energy comprise a plurality of opaque blades mounted on the motor shaft, the blades being configured to periodically obstruct the IR energy radiated by the IR source so that IR energy is periodically transmitted towards the means to sense IR energy, when not obstructed by a blade.
In an embodiment the computing means comprises a microcontroller provided with an input capture circuit to measure the time period of each reflected IR energy pulse, an rpm calculator to calculate the rpm of motor, an rpm compare circuit to compare the rpm of the motor with the required speed, a firing angle calculator to estimate time when microprocessor is to give pulse to the triac, and pulse width modulator output generator to generate said output pulse.
In another embodiment the motor driver circuit comprises a device wherein the motor driver circuit comprises zero line cross detector to synchronize the trigger pulse with zero crossing of the AC power supply and a triac driver circuit to receive said trigger pulse and supply required power to the motor.
In another embodiment means to sense and provide the input to the computing means comprises a wave shaping circuit to convert the sensor output to a pulsed output.
The constructional and functional features of a various units of the preferred embodiment are described hereunder:
IR LED (3) (Infra Red Light Emitting Diode) emits light in the Infra Red light spectrum. IR components are manufactured either to work with wavelength of 940nm or 880nm.
IR Sensors (4) are of different types. They can be any one of the following types:
Photo Diode Photo Transistor Photo Darlington
Depending on the sensitivity of the sensor required, any one of the above types are used. In the above types, Photo diode will be less sensitive and a Photo Darlington will be highly sensitive hence providing amplified output single. Sensors are also available to detect wavelength of ether 940nm or 880nm.
The IR LED and IR Sensor are placed adjacent to each other such that, if a surface (Reflector) (2) comes in the path of this IR light or the blade of the fan is'not obstructing the IR light, then the IR sensor receives the IR light and gives a change in output voltage.
The reflector is connected to the rotor of motor. Due to the construction of the reflector, while the shaft rotates, the reflector interrupts the IR rays and reflects it to the IR sensor. So the sensor gives an output voltage whenever the reflector comes facing the IR LED and Sensor. In alternative arrangement, opaque blades of fan mounted on shaft of the motor, periodically blocks the IR light such that when blade is not in line with IR rays, the IR sensor receives the IR energy and given on output voltage.
The output of sensor is converted into a pulsed output by using a wave shaping circuit (16). This circuit usually contains a transistor which biased for saturation. This converts the weak signal coming from the signal to a digital pulse which a Microcontroller can detect.
The Microcontroller (8) plays a vital role in controlling the whole application. The different modules/functions incorporated in the Microcontroller are explained below.
Input pulses from the IR Sensor are captured by input capture (9) and the Time Period (T) of each pulse is measured.
This Time Period (T) captured by the Input Capture module (9) is related to RPM by the RPM calculator (10) as follows:
RPM = 60 * N / T
wherein N = Number of reflections per revolution.
T = Time period between two reflections (Time period of each pulse).
RPM = Revolutions per minute.
Using the above relation, RPM is calculated.
Required target rpm is given by user to micro through an User Interface (5). User Interface consists of Keys and LEDs.
RPM Compare Module (11) calculates the deviation of Measured Present Motor RPM from the Required Target RPM.
RPM = Target RPM - Measured RPM
The speed control is achieved by using the PI (Proportional Integral) Control Algorithm. This Control System Algorithm requires the following parameters:
> Target RPM
> Measured RPM
> Previous cycle RPM
> Previous cycle Power Output
to provide a correction to Output Power to Motor to control the speed.
The below PI algorithm is used for the speed control in this application:
Toff(n) = Toff(n-l) - Kp x RPM(n) - Ki {RPM(n) - RPM(n-l)}
Where Toff(n) = Triac Firing Angle Output of present cycle.
Toff(n-l) = Triac Firing Angle Output provided in previous cycle.
Kp = Proportionality Constant.
Ki = Integration Constant.
RPM(n) = Difference in RPM in present cycle.
RPM(n-l) = Difference in RPM in previous cycle.
The output of the above equation is given to Firing angle Calculator (12) where it is synchronized with Zero cross pulse.
To implement the Firing Angle Control, the Microcontroller output to trigger Triac, should be synchronized with AC Line Zero Crossings. Hence, a Zero Cross Detector circuit (14) is used which gives a pulse during every AC Line zero cross to the micro.
The firing angle calculator estimates at which time the micro has to give output pulse to triac module. This module takes input from PI Module and synchronizes the output with Zero cross input and provides the Timer value to PWM Output Generator.
The Pulse Width Modulator (PWM) Module (13) generates output pulse at the instant specified by the Firing Angle Calculator.
The microprocessor is fed to Triac based motor Driver Circuit (7), wherein it drives a transistor which drives the Triac (15) in Quadrant 1 and Quadrant 3. This controls the voltage provided to the motor (1) and hence controls the speed of the motor (1).
It is to be understood that the features and concepts of the invention can be adapted to various embodiments by making changes, adaptations, modifications by those skilled in the art. Such varient embodiments are intended to be within the scope of the present invention.

WE CLAIM:
1. A speed control device for a single phase motor used in home appliances comprising:
an IR source to produce an infra red rays;
a motor provided with means for periodically directing infra red rays to generate a sensor output;
an IR sensor provided along the path of infra red rays to sense the IR rays, periodically transmitted by said source and provide a pulsed output to the electronic control board;
an electronic control board for receiving the signal from the sensor, conditioning and providing signal to motor for controlling the speed;
a user interface electrically connected with the motor to select the required speed of the universal motor;
a power supply unit to supply power to said speed control device;
a motor driver circuit to drive the said motor; and
a computing means to compare the pulsed output with required speed, to calculate the firing angle of the motor driver circuit and supply the required power pulse to motor driver circuit.
2. A speed control device as claimed in claim 1, wherein the electronic control board comprises a signal conditioning circuit, a micro controller, and a triac firing module.
3. A speed control device as claimed in claim 2, wherein the said micro controller comprising a speed measurement module & a speed algorithm module placed along the path of the signal.
4. A speed control device as claimed in claim 1, wherein said means for periodically directing IR rays comprise a plurality of bands of reflecting material provided on shaft of the motor.
5. A speed control device as claimed in claim 1, wherein said means for periodically directing IR rays comprise a plurality of opaque blades of a fan mounted on the shaft of the motor, said blades configured to periodically block and transmit IR rays.
6. A speed control device as claimed in claim 1, wherein the said IR sensor is a photo diode or a photo transistor or a photo Darlington.
7. A speed control device as claimed in claim 1, wherein the said IR source is an IR light emitting diode.
8. A speed control device as claimed in claim 1, wherein the user interface comprises a set of keys and light emitting diodes.
9. A speed control device as claimed in claim 2, wherein the signal conditioning circuit receives the signal from the sensor and converts it into digital pulses which is proportional to motor rpm and given to micro controller.
10. A speed control device as claimed in claim 2, wherein the micro controller comprises a software to measures the rpm from the pulse input from signal conditioning circuit to control the speed of motor by controlling the power output to the motor.
11. A speed control device as claimed in claim 2, wherein the micro controller gives the input to triac firing module to turn the motor on.
12. A speed control device as claimed in claim 2, wherein triac firing angle is controlled to vary the power to motor which in turn the speed.
13. A speed control device as claimed in claim 1, wherein said computing means comprise a microcontroller provided with an input capture circuit to measure the time period of each reflected IR energy pulse, an rpm calculator to calculate the rpm of the motor, an rpm compare circuit to compare the rpm of the motor with the
required speed, a firing angle calculator to estimate time when microprocessor is to give pulse to the triac, and pulse width modulator output generate said output pulse.
14. A speed control device as claimed in claim 1, wherein the motor driver circuit comprises zero line cross detector to synchronize the trigger pulse with zero crossing of the AC power supply.
15. A speed control device as claimed in claim 13, wherein the motor driver circuit comprises a triac driver circuit to receive said trigger pulse and supply required power to the motor.
16. A speed control device as claimed in claim 2, wherein said sensor comprises a wave shaping circuit to convert the sensor output to a pulsed output.
17. A speed control device for a single phase motor used in home appliances, substantially as hereinbefore described with reference to the accompanying drawings.