U.S. patent application number 10/692246 was filed with the patent office on 2004-05-06 for laundry machine.
This patent application is currently assigned to Fisher & Paykel Limited. Invention is credited to Cheyne, Neil, Taylor, Samuel John Selwyn.
Application Number | 20040084640 10/692246 |
Document ID | / |
Family ID | 19927016 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040084640 |
Kind Code |
A1 |
Cheyne, Neil ; et
al. |
May 6, 2004 |
Laundry machine
Abstract
An optocoupler drive circuit for the high side of a totem pole
power transistor pair in a bridge circuit for commutating a motor
includes an optocoupler output device being directly connected to
the upper power transistor in the totem pole, and series resistor
of selected value for controlling the drive current to said upper
power transistor to reduce its speed of turn on.
Inventors: |
Cheyne, Neil; (Auckland,
NZ) ; Taylor, Samuel John Selwyn; (Auckland,
NZ) |
Correspondence
Address: |
TREXLER, BUSHNELL, GIANGIORGI,
BLACKSTONE & MARR, LTD.
105 WEST ADAMS STREET
SUITE 3600
CHICAGO
IL
60603
US
|
Assignee: |
Fisher & Paykel Limited
Auckland
NZ
|
Family ID: |
19927016 |
Appl. No.: |
10/692246 |
Filed: |
October 23, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10692246 |
Oct 23, 2003 |
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09856412 |
Aug 28, 2001 |
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09856412 |
Aug 28, 2001 |
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PCT/NZ99/00193 |
Nov 17, 1999 |
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Current U.S.
Class: |
250/551 |
Current CPC
Class: |
D06F 2103/48 20200201;
D06F 39/085 20130101; Y02B 40/00 20130101 |
Class at
Publication: |
250/551 |
International
Class: |
G02B 027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 17, 1998 |
NZ |
332836 |
Claims
1. In an optocoupler drive circuit for the high side of a totem
pole power transistor pair in a bridge circuit for commutating a
motor the improvement comprising: the optocoupler output device
being directly connected to the upper power transistor in the totem
pole, and means for controlling the drive current to said upper
power transistor to reduce its speed of turn on.
2. An optocoupler drive circuit as claimed in claim 1 wherein said
means for controlling said drive current is a series resistor of
selected value.
Description
TECHNICAL FIELD
[0001] This invention relates to laundry machines. In particular it
relates to laundry machine drain pump control, power supplies,
electronically commutated permanent magnet motor drives and motor
braking during spin dry cycles.
BACKGROUND ART
[0002] Most laundry machine drain pumps use an AC induction motor
or synchronous motor, operating off the mains frequency, which is
typically 50 or 60 Hz. This fixed frequency, along with the mains
voltage, determines the design of the pump, and hence the flow rate
and maximum head height that can be obtained.
[0003] There are numerous disadvantages of a fixed mains-frequency
pump motor. These are: (a) the starting torque is typically low,
making the pump susceptible to being blocked, (b) separate pump
designs are needed for countries having differing mains voltage and
frequency, (c) the noise level during "ventilation" is high,
particularly when running at a supply frequency of 60 Hz, (d) the
torque varies with the mains voltage and (e) there is no feedback
to indicate if the pump is faulty.
[0004] By the nature of the washing process debris, including
strands of textile, is removed from the wash load and flushed into
the sump of the washing machine. This debris is then pumped out
along with the dirty wash water. Occasionally the pump impeller
will catch or the debris, or will start accumulating textile
strands and then stop pumping.
[0005] Problems of this nature have been solved in other industries
such as sewage handling, by having powerful motors driving pumps,
with large clearances and large flow passages. Home appliances,
however, do not have the space available to utilise large flow
passages. One small volume solution in use is the vortex impeller,
where the impeller has a shroud around it that eliminates the
jamming point between vane end and the `cutwater`. Unfortunately
this pump has the disadvantage that it can still become blocked by
bundles of fibres that become twisted "ropes" in the centre of the
vortex. Traditionally a laundry washing machine is turned off by
employing one of two methods. In the first power to the washer is
isolated using an expensive mains rated switch which de-energises
it and makes power consumption negligible. The switch must be
capable of carrying and breaking the total current required at the
required voltage. In the second method the machine is made to
appear it has been switched off by removing all power on
indications on its control panel. In reality the machine's power
usage is the same when it appears to be switched off as when it is
switched on. These methods have the respective disadvantages that
either a high current and/or voltage rated switch is required or
power is consumed unnecessarily when the laundry machine is not in
use.
[0006] The use of permanent magnet rotor three winding stator
motors with electronic commutation of the windings is known. A
common way of driving an electronically commutated three phase
motor is to configure it in an H-Bridge between two dc rails, as
shown in FIG. 5. The six power transistors Q1 to Q6 energise the
motor windings by switching in a particular pattern. It is possible
to have a high level of control over the speed and torque of the
motor if feedback on the position of the rotor is available to the
drive circuit logic which controls the switching pattern. The
transistors are switched on by applying a voltage, usually 15 V,
from gate to source. Because the source voltage varies from 0 V to
the DC rail voltage, some technique is required to get the signal
from the driving logic, which is referenced to 0 V, to the high
side gate which is referenced to the phase output (A, B, and
C).
[0007] Common techniques are to use pulse transformers,
purpose-designed ICs such as the IR2111, or optocouplers. A typical
prior art circuit which employs an optocoupler for driving the high
side transistor is shown in FIG. 6. When transistor Q2 switches
off, noise is generated which tends to pull the optocoupler off. A
logic inverter q4 ensures that turn off to the optocoupler means
turn off of Q1. Since Q1 should always be off during turn off of
Q2, correct operation of the circuit is not compromised. The
disadvantage of this conventional optocoupler drive design is that
high quality and therefore high cost devices are required.
[0008] During laundry machine spin dry cycles the spin tub is
rotated at relatively high speed. At the termination of the spin
cycle it is desirable to brake the motor to minimise spin tub run
down speed. Conventionally this has been achieved by connecting
resistors across the motor windings. This technique has the
disadvantage that relatively high power resistors are required and
these add to the cost of the laundry machine.
DISCLOSURE OF THE INVENTION
[0009] It is therefore an object of the present invention to
provide a laundry machine having drain pump control, a power
supply, a motor drive, and a motor braking system which overcomes
the respective disadvantages outlined above.
[0010] In a first aspect the invention consists in a method of
operating a drain pump in a laundry washing machine during the
drain phase of the wash cycle to reduce pump blockages
characterised in that:
[0011] (a) the pump is started and run for a first period of
time,
[0012] (b) the pump is stopped for a second period of time which is
less than 10% of said first period of time, and
[0013] (c) steps (a) and (b) are repeated for the duration of said
drain phase.
[0014] In a second aspect the invention consists in a method of
braking a top loading laundry washing machine spin tub wherein said
spin tub is driven by an electronically commutated DC motor,
wherein the commutation devices are connected to a DC power supply
and have free-wheeling diodes connected in parallel therewith, and
wherein said washing machine includes other components having
inductive windings,
[0015] characterised in that:
[0016] commutation of power to the motor windings is
terminated,
[0017] the voltage of the DC power supply is monitored,
[0018] and when the DC power supply voltage exceeds a
pre-determined value the inductive winding of an unused component
in said machine is connected across said DC power supply until the
DC power supply voltage reduces below said pre-determined
value.
[0019] In a third aspect the invention consists in a method of
powering on and off a laundry washing machine where power is
consumed in the form of direct current using a switched mode power
supply of the type described in Australian Patent 651408
characterised in that:
[0020] an active switching device connected between the base of the
lower switch in the motor bridge drive used as part of said
switched mode power supply and the lower voltage rail is switched
on by a latching circuit to cause the DC power supplies in said
machine to be disabled,
[0021] the latching circuit comprises a capacitor charged from the
high voltage rail for said laundry machine motor in parallel with a
transistor biased from the switched mode power supply low voltage
rail, and
[0022] a push button normally off switch connected in parallel with
said capacitor is used to discharge said capacitor to disable said
latching circuit to thereby enable the laundry machine DC power
supplies.
[0023] In a fourth aspect the invention consists in an optocoupler
drive circuit for the high side of a totem pole power transistor
pair in a bridge circuit for commutating a motor characterised in
that the optocoupler does not use a logic inverter on the output
side and the optocoupler transistor is controlled to limit the
speed of turn off and thus the speed of turn on of the upper power
transistor in the totem pole.
[0024] In a fifth aspect the invention consists in a laundry
washing machine including a wash bowl drain pump characterised in
that:
[0025] said pump is driven by a variable speed motor which in turn
is driven by a variable frequency pulse width modulated
inverter,
[0026] and the pump motor frequency is decreased at low bowl water
levels to reduce the effects of ventilation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 shows a plan view of a laundry machine sludge
pump,
[0028] FIG. 2 shows alternative impellers for the sludge pump.
[0029] FIG. 3 shows a voltage waveform for a laundry machine sludge
pump controlled in accordance with the present invention,
[0030] FIG. 4 shows a circuit for a laundry machine power supply
derived from the laundry machine motor drive,
[0031] FIG. 5 shows a totem pole switching circuit for a three
phase motor drive,
[0032] FIG. 6 shows a high side drive circuit using an optocoupler
for the circuit of FIG. 5,
[0033] FIG. 7 shows a high side optocoupler drive circuit according
to the present invention, and
[0034] FIG. 8 shows a braking circuit for a laundry machine
motor.
BEST MODES FOR CARRYING OUT THE INVENTION
Pump Stopping to Clear Lint and Thus Prevent Pump Blocks
[0035] In a first embodiment of this invention there is provided a
method of drain pump motor control that will flush through bundles
of fibres before they become large enough to jam the pump.
Typically the pump motor will be an ac induction motor which may be
of the shaded pole type. FIG. 1 shows the plan view of a laundry
machine sludge pump, with the impeller 1 having two, backwardly
inclined vanes 2, 3, with large clearances, especially to the
cutwater 4. FIG. 2a shows a perspective view of sludge impeller 1.
An alternative vortex impeller 5 (FIG. 2b) may be used to reduce
pump noise. It has vane recessed into the impeller.
[0036] The method of operation involves stopping the pump very
quickly for a short period of time every few seconds. The sudden
stop of the pump means that there is no more energy put into the
vortex, and the momentum of the water flowing down the discharge
pipe sucks the vortex and any fibres entrapped in the vortex out
the pump exit. The pump is started again before the velocity in the
discharge pipe reduces to zero so that the trapped fibres carry on
out into the drain. If the pump off time is too long the discharge
flow will stop and then reverses returning the fibres to the
pump.
[0037] To achieve the sudden stop, a direct current is applied to
the shaded pole (asynchronous) motor for 200 mS. This current
produces a stationary flux that acts as a brake. It has beer found
experimentally that a stop for 200 mS every 10 seconds gives the
best results.
[0038] In one embodiment of this invention the shaded pole motor
has half wave rectified voltage applied to produce the stationary
flux. FIG. 3 shows the voltage history of this half wave rectified
version, with interval 6 the first 200 mS stop interval, then a ten
second (full wave) pumping period, 7 followed by a second 200 mS
stop period 8.
Variable Speed Induction Motor Drain Pump
[0039] The laundry machine drain pump motor 15 of the present
invention is driven from four switching devices 11 to 14 in an
"H-bridge" configuration as shown in FIG. 4 to switch a 230 V/50 Hz
AC induction motor for the above described drain pump from a 325 V
DC rail (peak value of 230 volt RMS mains voltage), under the
control of a microprocessor (not shown). The switching signals are
pulse width modulated with a variable duty cycle. This allows the
frequency and RMS voltage being applied to the pump to be
controlled.
Variable Speed Pumping During Drain
[0040] When the water level in the laundry machine bowl is above a
pre-determined height--the "bowl float level" in a machine of the
type described in New Zealand patent 215389/217623/218356--the pump
speed is set to 60 Hz, to maximise the flow rate. This is achieved
by programming the microprocessor which controls the switching
frequency of the H bridge switching devices. When water level is
below this pre-determined height, "ventilation" will occur. The
microprocessor is programmed to drive 50 Hz at such water levels.
This reduction in speed reduces the noise level of the pump
considerably, but still allows pumping over an acceptable head
height.
[0041] The variable speed pumping described has three main
advantages over fixed speed pumps:
[0042] (a) the drain time at 60 Hz is approximately 15% less than
at 50 Hz, due to the higher flow rate to reduce a typical cycle
time by about 1-2 minutes,
[0043] (b) audible noise is greatly reduced during "ventilation" by
slowing the pump to 50 Hz, and (c) the same 230 VAC/50 Hz pump
design can be used irrespective of country in which the laundry
machine is used.
Low Frequency, High Torque Pump Startup
[0044] To overcome the problem of the starting torque of AC
induction motors being increases when the supply frequency is
decreased in the present invention, when the pump starts, the drain
pump microprocessor switches the H bridge devices 11 to 14 to
produce a 30 Hz drive current to the pump motor but with an
increased PWM duty cycle, for the first four revolutions (ie. 80 ms
at 50 Hz). This provides a high torque "kick", which will attempt
to dislodge anything which is impeding the pump impeller.
[0045] The microprocessor subsequently controls the H bridge
devices to produce a drive current at the target frequency (50 or
60 Hz), but with a high PWM duty cycle, for the next 150
revolutions (3 seconds at 50 Hz). This helps to initially get the
water over the required head height.
[0046] After these two "startup" phases, the microprocessor causes
the PWM duty cycle to revert to the "normal" duty cycle for the
desired drive frequency.
[0047] By programming the microprocessor to control the frequency
and duty cycle during pump startup in this manner a reduction in
pump blockage can be achieved.
Variable Pump PWM Depending on Mains Voltage
[0048] The nominal AC mains RMS voltage has a typical tolerance of
10%, which for nominal 230 V AC, equates to a range of 207 to 253
volts. In rural areas, this variation can be even greater. This
mains voltage variation has an effect on the current supply to the
drain pump and thus the torque of the drain pump. The maximum head
height and flow rate of the pump can therefore vary depending on
the location of the laundry machine.
[0049] In this invention, the microprocessor is also caused to
measure the DC rail voltage, and from this determine the mains
voltage. The microprocessor is programmed to compensate for
differing mains voltages by adjusting the duty cycle of the drive
signal supplied to the pump motor. If the AC mains voltage is
reduced, the duty cycle is increased, and vice versa, thereby
ensuring a constant torque in the drain pump over a wide range of
mains conditions.
[0050] When driving the pump at 60 Hz, the maximum torque available
is less than when driving at 50 Hz. If the pump is operating at 60
Hz, and the mains voltage drops below a pre-determined level (200 V
for nominal 230 V), the flow rate will drop to an unacceptable
level. In the present invention the microprocessor is programmed to
reduce the frequency of the pump drive current to 50 Hz, and 60 Hz
operation disabled until the microprocessor is reset.
[0051] By using variable duty cycle that is caused to vary as a
function of mains voltage, a constant drain pump performance is
maintained over a wider range of actual mains voltages than is
normally possible. Secondly, by disabling the 60 Hz mode of
operation when the mains drops below a pre-determined voltage, the
problem of very low flow rates is avoided when attempting to drain
at 60 Hz under low mains conditions.
Pump Over-Current Detection
[0052] Washing machine drain pumps are susceptible to water damage
if they leak. This water damage eventually causes electrical
shorting of the pump windings increasing the winding current and
causing the pump it to overheat and fail, due to the change in
winding resistance and inductance characteristics. As well as being
a potential fire/smoke risk, this overheating and failure can also
damage the hardware that is driving the pump, unless additional
protection is provided.
[0053] Conventionally, there is no feedback indicative of current
in the pump windings, so there is no "early warning" that the pump
is being damaged in such circumstances. In the present invention
the current peaks in the pump windings are monitored by the
microprocessor. The current may typically peak at approximately 1.1
A (rms=650 mA). If the microprocessor detects two consecutive
current peaks of greater than 2.6 A, it is programmed to flag a
"pump overcurrent" fault to the pump motor controller
microprocessor.
[0054] Since the change in electrical characteristics from water
damage is gradual, this fault condition will occur and be detected
before any other parts of the circuit are damaged, and before the
pump becomes a potential fire/smoke hazard. It allows the
replacement of a water-damaged pump before any other subsequent
damage occurs.
Power Supply ON-OFF
[0055] In a third embodiment the invention provides a means of
allowing a laundry machine power supply to power down automatically
and power up via a low voltage, low current switch. This eliminates
the need for a high current and/or voltage rated switch and ensures
negligible power consumption when the laundry machine is not in
use.
[0056] Referring to FIG. 4 power supply for the machine is produced
by employing a simple switch mode power supply (SMPS) topology that
is controlled by a microprocessor 17 and makes use of the main
motor windings 15 and motor drive circuit 11 to 14. This general
form of laundry machine power supply is described in the
applicant's Australian Patent 651408. The power supply is disabled
by a hardware circuit (fourth wire circuit). Power down functions
are initiated by the micro processor and locked by the fourth wire
circuit. Power up functions are initiated by the user via a low
voltage, low current push button SWI.
Power Down
[0057] When the machine has finished a task and has received no
further instructions for some defined time period, the
microprocessor simply reduces the power output of the SMPS to zero
hence powering down the machine. The fourth wire circuit is then
enabled to ensure the SMPS does not power up until the user presses
the appropriate push button on the control panel. This dramatically
reduces the power consumption of the machine compared to that
required by hardware lockout circuitry.
Power Up
[0058] The user presses a power button which disables the fourth
wire circuit that is disabling the SMPS. The SMPS then starts up
and brings alive the microprocessors. The machine is now ready for
use.
[0059] In FIG. 4 a buck converter is inherent in the H-bridge
topology of the motor drive. Assuming that A+ and B- devices 11 and
14 are off when the circuit is run as a buck converter, then the A-
device 12 is latched on and B+ device 13 is driven by a PWM signal
to control power output. The circuit can be modified by adding the
"hardware lock off" circuitry to provide shutdown and start up
functions.
Power Down
[0060] To shut down the SMPS the microprocessor simply turns off
the A- device 12 by turning on transistor Tx2. The nominal 15 v
rail 16 (produced by the SMPS) will drop in voltage and transistor
Tx1 previously biased on by the 15 v, will turn off allowing
capacitor C1 to charge from the high voltage DC rail 18. C1 then
latches transistor Tx2 on hard so that the A- device 12 is latched
off. Thus the buck converter is disabled.
Power Up
[0061] The user presses Sw1 which short circuits and discharges
capacitator C1 thus turning off transistor Tx2 allowing the A-
device 12 to turn on. The SMPS is then able to start up and produce
the 15 v rail 16 required to latch transistor Tx1 on. The machine
is now ready for use.
[0062] The employment of the described microprocessor controlled
SMPS has the following advantages:
[0063] (a) a cheap low current, low voltage switch to be used to
provide power up functions, (b) the power switch can be referenced
to the SMPS zero volt rail allowing it to be used for other
functions, (c) allowing the SMPS to shut down extends the life time
of components and reduces any emissions from the product (i.e. RFI,
EMI), (d) provides very low power consumption when not in use, and
(e) eliminates transients caused by mains power interruption.
ECM Motor Drive
[0064] In a fourth embodiment the present invention provides a low
cost high side drive for an H bridge switching circuit for an
electronically commutated motor. Such a switching circuit is shown
in FIG. 5 for commutating a three winding motor.
[0065] The present invention provides a more cost effective circuit
to that shown in FIG. 6. This is shown in FIG. 7. Here, turn off of
Q2 tends to turn on Q1. The value of resistor R is selected to
limit the turn on speed of Q1 so there is no risk of overlap.
Because this causes a slewed turn on for Q1, this circuit is only
appropriate for switching Q1 at low frequency. Therefore the motor
must be energised at audible switching frequencies.
[0066] The optocoupler can have relatively low gain and slew rate,
which allows the use of a more cost effective device. There is also
no need for an inverter such as q4 in FIG. 6.
[0067] Configuring at least one high side drive as in FIG. 7 is
necessary to facilitate the power supply ON-OFF concept described
in relation to FIG. 4.
Braking the Wash Tub Motor
[0068] In a fifth embodiment the invention provides a low cost
method of braking a laundry machine motor.
[0069] One of the functions of a top loading vertical axis washing
machine is to spin the wash tub at high rpm to remove excess water
from the clothes at the end of the wash cycle. A spinning tub is
unsafe for a user to touch so many machines have a brake function
that quickly stops the spinning tub if the access lid is opened.
This brake function can be done by different techniques and one
technique that is becoming more common is to use regenerative
braking from the main drive motor. Using this technique the drive
motor effectively acts as a generator during brake and converts the
energy from the spinning tub into electrical energy which is
typically then converted into heat and dissipated via a dump
resistor.
[0070] The present invention connects a motor or solenoid installed
in the machine for some other purpose across the DC voltage rails
for the motor so that the electrical energy generated during
braking of the spinning tub can be dissipated in this
motor/solenoid impedance saving the cost of additional components
needed for a dump resistor or equivalent. The power dissipation
component chosen must not be in operation for its primary purpose
during braking of the spin tub.
[0071] The circuit shown in FIG. 8 has a 3 phase brushless DC main
motor 21 for driving a laundry machine agitator (not shown) and or
spin tub and a water pump powered by an AC induction motor 22 both
driven from the HVDC bus. The tree winding motor 21 is driven from
the six transistor bridge 29 to 34. The pump motor 22 is driven
from a four transistor H bridge 23 to 26 which in turn is switched
by current steering circuitry 27 under the control of
microprocessor 28. When main motor 21 is driven by the angular
momentum of the spin tub as a generator, during a brake phase when
switching devices 29 to 34 are off, electrical energy is fed back
into the HVDC bus through free wheeling diodes 35 to 40 which
results in an increase in the bus voltage. The bus voltage is
sensed by microprocessor 28. When the bus voltage exceeds 400 V DC,
the microprocessor through current steering circuity 27 switches
transistors 23 and 26 of the pump H bridge hard on until the bus
voltage falls below 390 V. In this way the regenerative braking
energy is dissipated as heat in the pump motor windings. This heat
is dissipated in the pump as power according to the equation:
P.sub.pump=I.sup.2.sub.pump.times.R.sub.pump (1)
[0072] For a pump of this type the motor windings typically have a
resistance of approximately 34 ohms. Therefor for a braking power
of say 600 W, from equation 1, the pump winding current is around
4.2 amps during braking.
[0073] The following advantages are achieved by this embodiment of
the present invention: (a) a dump resistor and control circuit are
eliminated, (b) by turning the pump on after a braking phase the
braking energy (heat) can be quickly dissipated by the pump fan,
(c) the heat rise due to the energy (heat) being dissipated in the
pump windings is remote to the usually enclosed main motor
electronics area where it can be difficult to ventilate and hence
cool, and (d) the motor winding inductance reduces the peak
currents that would flow in a purely resistive load, and hence the
switching transistors.
[0074] It should be appreciated that other existing laundry machine
resistive/inductive components could be utilised in place of the
drain pump motor as a means of dissipating power. For example the
solenoid in a solenoid controlled valve or other actuator could be
used.
* * * * *