Electricity: motive power systems – Braking
Reexamination Certificate
2000-07-10
2002-04-09
Ip, Paul (Department: 2837)
Electricity: motive power systems
Braking
C318S437000, C068S012020, C068S012040
Reexamination Certificate
active
06369538
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for braking a washing machine. More particularly, the present invention relates to a method for braking a washing machine by controlling a revival voltage in a motor braking system by adjusting a pulse phase and a pulse duty ratio when a revival voltage is at or below a predetermined level, and using a minimum capacity dynamic braking resistor when a revival voltage reaches over a predetermined level.
2. Description of the Related Art
Referring to
FIG. 1
, a conventional braking system for a washing machine comprises: a rectifier
101
which converts the AC power of the system to the DC voltage; a capacitor filter
102
which smoothes the rectified DC voltage; a motor driver
103
which drives a motor by using a smoothed DC voltage; a voltage detector
104
for detecting a voltage of the system when a motor M is suddenly braked; a voltage comparator
105
for comparing a detected voltage of the voltage detector
104
and a reference voltage pre-set in the system; a switch element
106
for determining on/off status of the dynamic brake resistor R
1
according to the comparison result of the voltage comparator
105
; a sensor
107
for detecting a revolution position and the speed of a motor M; a microcomputer
108
for controlling an overall operation to resolve the over-voltage in the system; and a signal output device
109
for generating a control signal according to the control of the microcomputer
108
.
The dynamic braking resistor R
1
converts the revival voltage into thermal energy to protect the system when the inertia energy of the motor or the load transforms into electric energy causing the level of the revival voltage charged in a capacitor filter
102
to increase.
The overall operation of the conventional braking system for a washing machine as described above is illustrated hereinafter with reference to FIG.
1
.
Firstly, the rectifier
101
converts the commercial AC power supplied from the outer power source to the DC voltage, and then the DC voltage is smoothed by the capacitor filter
102
before being supplied to a motor driver
103
.
The washing machine is operated as the motor driver
103
and converts the DC voltage smoothed by the capacitor filter
102
to drive the motor M.
However, in the event that a lid of the washing machine is opened during a dehydrating process or an unbalance state of the tub is detected, the rapidly rotating motor M must be braked quickly in order to make sudden stop of the tub.
Since the motor M is a brushless DC motor and it becomes the load during the normal washing operation, current flows in a discharging direction from the capacitor filter
102
to the motor M.
However, when the rapidly rotating motor M is suddenly braked, the motor M becomes a power generator and current flows in a charged direction, from the motor M to the capacitor filter
102
, due to the induction electromotive power generated from the motor M causes increase in the voltage level of the capacitor filter
102
.
If the revival voltage charged in the capacitor filter
102
is not discharged, then the voltage level exceeds the inner voltage of the designed circuit thereby damaging the peripheral circuit and the device.
Therefore, the voltage detector
104
, the voltage comparator
105
and the dynamic braking resistor R
1
are provided in order to discharge the over-flown voltage in the system during braking of the motor M.
In the event that the motor M is braked while washing or dehydration process, the voltage detector
104
measures the voltage between the capacitor filter
102
and the motor M thereof, and delivers the detected voltage measurement to the voltage comparator
105
.
The voltage comparator
105
then compares the reference voltage Vref and the detected voltage Vdc delivered from the voltage detector
104
, and sends the result of comparison to the switching element
106
. The switching element
106
operates on/off control functions based on the compared result sent from the voltage comparator
105
.
If it is determined that the detected voltage Vdc exceeds the reference voltage Vref, then the dynamic braking resistor R
1
is activated as the switch is turned to on state through a power output from the voltage comparator
105
.
As a result, the over-flown voltage between the capacitor filter
102
and the motor M flows to the dynamic braking resistor R
1
instead of capacitor filter
102
, thereby the system is sustained at the regular voltage-level as the over-flown voltage is discharged into thermal energy.
If the detected voltage Vdc between the capacitor filter
102
and the motor M is lower than the reference voltage Vref level, then the dynamic braking resistor R
1
is turned off by the switching element
106
during the discharge process of the over-voltage. Then, the motor M operates as the current flows only to the capacitor filter
102
, and not to the dynamic braking resistor R
1
.
However, when the motor M decelerates quickly or the load inertia of the motor M is massive, the revival energy generated in the motor M becomes more massive. As a result, the revival energy is revived to the motor driver
103
, and the voltage charged to the capacitor filter
102
increases. And, when the DC voltage reaches over 380V, the dynamic braking resistor R
1
is turned on to discharged the revival energy into thermal energy.
However, one of the disadvantages of the conventional method is that the detected voltage is compared only with one reference level, and the switching element
106
is operated to start the dynamic braking resistor R
1
only in the event that the detected voltage exceeds the reference level which results in difficulty in dealing appropriately with the revival voltage according to the motor braking, and also the problem of the motor not being operated rapidly or smoothly.
Another disadvantage of the conventional method is that the size and the capacity of the dynamic braking resistor R
1
installed on the outer part of the system is large making the system more complicated and increase the cost of the system.
SUMMARY OF THE INVENTION
Accordingly, it is an object present invention to provide a method for rapidly and smoothly braking a washing machine by treating a revival voltage of the motor braking with hardware and software.
Another object of this invention is to reduce the size and capacity of a dynamic braking resistor in order to reduce the system capacity and the cost.
These and other objects are satisfied by a method for braking a washing machine comprising the steps of: determining whether or not a motor is braking; transmitting a PWM (Pulse Width Modulation) control signal by setting up the initial phase and the duty ratio according to the voltage flows in the system when an operation mode determined by the previous step as a braking mode; comparing a capacity and a variance of the detected voltage with a reference voltage predetermined by the previous step; and controlling a motor driver by re-establishing the control phase and the duty ratio until the motor is stopped when the comparison result of the previous step indicates that the capacity and the variance of the voltage are lower than the predetermined reference level.
REFERENCES:
patent: 5325677 (1994-07-01), Payne et al.
patent: 5647232 (1997-07-01), Boldt et al.
patent: 5778703 (1998-07-01), Imai et al.
patent: 5913952 (1999-06-01), Kim
patent: 5979194 (1999-11-01), Matsumoto et al.
patent: 6014004 (2000-01-01), Hamaoka et al.
patent: 6041625 (2000-03-01), Nagai et al.
patent: 6060851 (2000-05-01), Imai et al.
patent: P2001-46782 (2001-02-01), None
Lee Chul Woong
Lee Joo Hwan
Ra In Hwan
Youn Sang Chul
Fleshner & Kim LLP
Ip Paul
LG Electronics Inc.
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