Method and apparatus for measuring a weight of a stirring fluid

A stirring apparatus according to the present invention detects a weight of a stirring fluid, such as water or some other fluid, by using a hall sensor. The present invention, a method and apparatus for measuring a weight of a stirring fluid, detects the number of revolutions of a stirring motor, which varies according to the amount of an object fluid, by using a hall sensor to compute a weight of the fluid corresponding to the revolutions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a technique for measuring a weight of a 
stirring fluid, such as water or some other fluid, in stirrers applicable 
to a refrigerator, etc. More particularly this invention relates to a 
method and apparatus for measuring the weight of the fluid (hereinafter 
referred to as an "object fluid") which reduces measurement errors by a 
simple structure including a hall sensor. 
2. Description of the Prior Art 
FIG. 1 shows a schematic diagram of a stirrer adopting a conventional 
weight measuring apparatus. As shown, this apparatus includes an 
instruction input section 2 for accepting a user's instruction; a 
microcomputer 3 for computing a weight of an object fluid on the basis of 
an output frequency from a weight detecting section 1 and for providing a 
control signal pertinent to a load computed by the weight; a stirring 
motor driving section 4, driven by the control signal from the 
microcomputer 3, for driving the following stirring motor M; and a display 
section 5 for displaying an operation of a system under the control of the 
microcomputer 3. 
FIG. 2 is a simplified view showing a general stirrer. In construction, it 
is composed of a driving section 7, in which a driving magnet 6 
(specifically a circular permanent magnet) is assembled to a shaft of the 
stirring motor M, for generating a rotational power to stir an object 
fluid; a stirring magnet 8, assembled in the lower part of a container 10, 
for stirring an object fluid by interaction with the driving magnet 6; and 
a weight sensor 9, positioned under the container 10, for sensing a weight 
of an object fluid. 
An operation of the above-constructed apparatus will be discussed with 
regard to FIG. 3. 
When a user turns on a start switch SW1, the microcomputer 3 recognizes 
that a start instruction is offered through its input port P2 and drives 
the stirring motor driving section 4. Also, the microcomputer 3 computes 
the weight of an object fluid to be stirred, by using a frequency of an 
oscillating signal provided through its input port P1. 
The weight sensor 9 constitutes two electrode plates facing each other. The 
electrostatic capacity between the plates can be used to measure a weight 
of an object fluid. Pressed by the weight of an object fluid, as shown in 
FIG. 3, the two electrode plates become closer, and the electrostatic 
capacity of the weight sensor 9 increases as follows: 
EQU C1=.di-elect cons..sub.o .di-elect cons..sub.r .times.S/d, 
where "S" denotes the area of each metal plates; "d" the distance between 
the electrode plates; and ".di-elect cons..sub.o .di-elect cons..sub.r " 
the dielectric constant of a material within the plates. 
In addition, an oscillation frequency (F) of an oscillation circuit 1A in 
the weight sensing section 1 is in inverse proportion to the electrostatic 
capacity C1 as shown the following formula: 
EQU F.varies.1/(R1+R2)C1. 
It follows that, as a result, as the weight of an object fluid increases, 
the oscillation frequency of the oscillation circuit 1A decreases, and 
vice versa. 
The microcomputer 3 checks the weight of an object fluid on the basis of 
the oscillation frequency. If it checks that the weight is less than a 
given value, it outputs a low-level signal through its output port P4 to 
turn on a light-emitting diode for an object fluid supply display LED1; if 
greater, it outputs a high-level signal through its output port P3 for a 
given time to drive the stirring motor M. 
The driving magnet 6 rotates by the stirring motor M, and accordingly the 
stirring magnet 8 rotates by magnetic power from the driving magnet 6. An 
object fluid in a container will be stirred. 
At this moment, the microcomputer 3 outputs a low-level signal through its 
output port P5 to turn on a light-emitting diode for operation display 
LED2. Thus a user can learn that stirring is being performed. 
After a prescribed time, the microcomputer 3 turns off a relay for driving 
a motor RY1 by outputting a high-level signal through its output port P3, 
and accordingly the stirring motor M stops stirring. At the same time, the 
microcomputer 3 also outputs a low-level signal through its output port P6 
to turn on a light-emitting diode for completion display LED3. 
However, in such a conventional apparatus for measuring a weight, if an 
object fluid is contained all the time in a container, two electrode 
plates of a weight sensor are continuously kept pressed. This results in 
poor elasticity of electrode plates and accordingly the force of 
restitution is compromised. Measurement error therefore increases. 
Besides, a variable resistor, added to compensate a tolerance of resistors 
and a variable capacitor (in this case, a weight sensor) which both 
constitute an oscillation circuit, makes the circuit complicated and 
adjustment difficult. Complexity in construction, in addition, raises cost 
of production. Especially, when a human or an animal approaches the weight 
sensor, electrostatic capacity variation increases the measurement error. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method and apparatus 
for measuring a weight of an object fluid which detects, by using a hall 
sensor, the number of revolutions of a driving magnet driven by a stirring 
motor so as to compute a real weight of an object fluid by the detected 
revolutions. 
According to one aspect of this invention, there is provided a method for 
measuring a weight of a stirring fluid, which stirs an object fluid by a 
stirring motor, by a driving magnet which rotates in accordance with a 
rotation of said stirring motor, and by a stirring magnet which rotates by 
magnetic power transferred from said driving magnet, the method comprising 
the steps of: detecting, by a hall sensor, the number of revolutions of 
said stirring motor by sensing magnetic power emanating from said driving 
magnet; computing a weight of an object fluid by using the detected number 
of revolutions of said stirring motor; and driving said stirring motor by 
said computed weight. 
According to another aspect of this invention, there is provided an 
apparatus for measuring a weight of a stirring fluid, having a stirring 
motor for stirring an object fluid, a driving magnet which rotates in 
accordance with rotation of said stirring motor and a stirring magnet 
which rotates by magnetic power transferred from said driving magnet, the 
apparatus comprising: means for detecting the number of revolutions of 
said stirring motor by using magnetic power emanating from said driving 
magnet; control means, computing a weight of an object fluid corresponding 
to said detected number of revolutions of said stirring motor, for 
stopping, if said computed weight of an object fluid is equal to or less 
than a prescribed value, said stirring motor rotating, and for driving, if 
said computed weight of an object fluid is greater than the prescribed 
value, said stirring motor during a stirring time corresponding to said 
weight of an object fluid; means for controlling said stirring motor under 
a control of said control means; and means for accepting a user's 
operation instruction and for displaying an operation by said control 
means.

DETAILED DESCRIPTION OF TEE PREFERRED EMBODIMENTS 
FIG. 4 is a schematic diagram of one preferred embodiment of the present 
invention. As shown, it is composed of a weight detecting section 11 for 
detecting and outputting as a square wave the number of revolutions of the 
following stirring motor to measure a weight of an object fluid; an 
instruction input section 12 for accepting a user's operation instruction; 
a microcomputer 13 for computing a weight of an object fluid on the basis 
of an output frequency from the weight detecting section 11 and for 
providing a control signal pertinent to the computed weight; a stirring 
motor driving section 14, driven by the control signal from the 
microcomputer 13, for driving the stirring motor M; and a display section 
5 for displaying an operation of a system under the control of the 
microcomputer 13. 
FIG. 5 is a block diagram of a hall sensor section 11A in the weight 
detecting section 11 depicted in. FIG. 4. In construction, it is composed 
of a voltage regulator 16 for regulating a source voltage; a hall sensor 
17, working by the voltage from the voltage regulator 16, for providing a 
square pulse whose period corresponds to the revolutions of the following 
driving magnet 20; an amplifier 18 for amplifying the output pulse from 
the hall sensor 17 to such an extent that it is suitable to be treated to; 
a hysteresis buffer 19 for shaping accurately a level of the output from 
the amplifier 18; and a transistor Q11 which is switched in accordance 
with the output signal from the hysteresis buffer 19. 
An operation of such a constructed apparatus of the present invention will 
be discussed with reference to FIGS. 4 to 9. 
Under the condition that the stirring motor M illustrated in FIG. 6 
reposes, the microcomputer 13 outputs high-level signals from its output 
ports P4-P6 to keep all of the light-emitting diodes in the displaying 
section 15, i.e., a light-emitting diode for object fluid supply display 
LED11, a light-emitting diode for operation display LED12, and a 
light-emitting diode for completion display LED13 in being turned off. 
If a user activates a start key SW11, containing an object fluid in a 
container 22, the microcomputer 13 recognizes that a start instruction is 
offered through its input port P2. Then it controls a relay for driving a 
stirring motor RY2 by outputting a low-level signal through its output 
port P3 to drive the stirring motor M. At the same time, it turns on the 
light-emitting diode for operation display LED12 by outputting a low-level 
signal through its output port P5. 
The driving magnet 20 rotates by the stirring motor M, and accordingly a 
stirring magnet 21 remotely rotates by the magnetic power from the driving 
magnet 20. Because a load imposed on the stirring motor M varies according 
to a weight of an object fluid in the container 22, the number of 
revolutions of the stirring motor M varies, as shown in FIG. 7, in 
accordance with the amount of a load. 
The number of revolutions of the stirring motor M is detected by the hall 
sensor 17 and applied to the microcomputer 13. 
As to the principle of revolution detection of a hall sensor, if a current 
appears in a hall sensor when the magnetic power of the driving magnet 20 
is applied to the hall sensor 17, a hall voltage is created, which the 
direction of the voltage is perpendicular to the direction of both the 
magnetic power and the current. As the driving magnet 20 rotates, the 
magnetic power is rotatively stirred. Thereby the hall voltage appears in 
accordance with the revolutions of the stirring motor M, i.e., the weight 
of an object fluid, as is shown in FIG. 8. 
The hall voltage, the output voltage of the hall sensor 17, is amplified by 
the amplifier 18 to such an extent that it can be suitably treated to and 
is thereafter level-shaped by the hysteresis buffer 19. Switched by the 
output of the hysteresis buffer 19, the transistor Q11 provides a pulse 
voltage to the input port P1 of the microcomputer 13. 
The microcomputer 13 thereafter judges, on the basis of the period of the 
pulse signal from the hall sensor section 11A, how much an object fluid is 
in the container 20. If the amount is less than a given valve, the 
microcomputer 13 stops the stirring motor M rotation and turns on the 
light-emitting diode for object fluid supply display LED11; if greater, 
the microcomputer 13 rotates the stirring motor M during a stirring time 
pertinent to the amount of an object fluid and turns on the light-emitting 
diode for operation display LED12. After the stirring time elapses, the 
microcomputer 13 stops the stirring motor M rotation and turns on the 
light-emitting diode for completion display LED13. 
FIG. 10 shows a structural view indicating another preferred embodiment of 
the present invention. As shown, a stirring blade 33 instead of the 
stirring magnet 21 stirs directly an object fluid in the container 22. 
FIG. 9 is a flowchart showing the operation of the embodiment of FIG. 4. 
If a user activates a start instruction (step S1), the stirring motor M 
rotates and the light-emitting diode for operation display LED12 is turned 
on. Thereafter the revolutions of the stirring motor M detected by the 
weight detecting section 11 is provided as a weight of an object fluid to 
the microcomputer 13 (steps S2 to S4). 
The microcomputer 13 compares the revolutions of the stirring motor M, 
i.e., a weight of an object fluid, with a reference amount (step S5). If 
the revolutions are less than a given amount, the microcomputer 13 stops 
the stirring motor M rotation (step S6) and turns on the light-emitting 
diode for object fluid supply display LED11 to urge a user to supply the 
container 22 with an aiming fluid (step S7). In this embodiment, it was 
set to display an object fluid supply when the amount of an object fluid 
is less than one-sixth (1/6) of the capacity of the container 22. 
In the mean time, if the revolutions are greater than a given amount, the 
microcomputer 13 computes a stirring time pertinent stepwise to a weight 
of an object fluid (steps S8 to S8') and rotates the stirring motor M 
during this stirring time. 
If the stirring time elapses (step S9), the microcomputer 13 stops the 
stirring motor M rotation and turns on the light-emitting diode for 
completion display LED13 (step S10). A sequence of an operation cycle of 
the present invention is done as the above steps. 
From the foregoing, the present invention measures a weight of an object 
fluid by detecting the number of revolutions of a driving magnet attached 
to a stirring motor, using a hall sensor rather than a mechanical sensor. 
Not having mechanical fatigue which is susceptible to be imposed upon a 
conventional mechanical weight sensor, the present intention can prevent 
errors caused by physical modification. In addition, this intention 
provides simple construction and unnecessary adjustment.