JP2002148127A - Weight sensor containing magnetostrictive element, and washing machine having weight sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a weight sensor containing a magnetostrictive element of high detection precision. SOLUTION: A flowing current quantity is increased in a pick-up coil 6 provided to surrounding the magnetostrictive element 2. To attain this, a push- pull circuit is connected to the coil 6 by an H-bridge system. Concretely saying, the first paired transistors 41 are connected to an upper end side of the pick-up coil 6, and the second paired transistors 42 are connected to a lower end part of the coil 6. ON-conditions for the transistor pairs 41, 42 are switched using comparators 43, 44, 45. The pick-up coil 6 is repeatedly charged and discharged alternatively thereby, and a current flows not only in the charge also in the discharge. A variation of an inductance of the pick-up coil 6 to a variation of external force applied to the magnetostrictive element 2 is increased to enhance the detection precision of the weight sensor 1 by increasing the current quantity flowing in the coil 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a weight sensor including a magnetostrictive element. Further, the present invention relates to a washing machine having such a weight sensor.

[0002]

2. Description of the Related Art A fully automatic washing machine is provided with a weight sensor for measuring the weight of the laundry in the washing / dewatering tub so that the laundry can be operated according to the amount of laundry in the washing / dehydrating tub. There is something. The conventional weight sensor is provided on a suspension rod that connects the washing dehydration tub and the casing, and a coil spring that is compressed and deformed by a force applied to the suspension rod, a magnet attached to the coil spring, and a magnet can be moved forward and backward inside. It has a coil.

[0003] Since such a weight sensor includes a movable part called a coil spring, there have been problems in that the detection accuracy is reduced due to aging, and that the coil spring may amplify the vibration of the washing and dewatering tub. .

[0004]

SUMMARY OF THE INVENTION Accordingly, the applicant of the present application
A washing machine capable of measuring the weight of laundry and water in a washing and dewatering tub with a weight sensor using a solid element called a magnetostrictive element has been previously proposed (Japanese Patent Application No. 11-96130).
issue). In a weight sensor using a magnetostrictive element, when an external force is applied to the magnetostrictive element, the magnetic permeability of the magnetostrictive element changes due to the stress generated in the magnetostrictive element. Since it is difficult to directly detect a change in magnetic permeability, the change in magnetic permeability is detected as a change in inductance of the pickup coil, and a force (weight) applied to the magnetostrictive element is calculated based on the detection result. It has become.

By the way, the change in magnetic permeability of the magnetostrictive element is small with respect to the change in weight given to the magnetostrictive element, and therefore the change in inductance of the pickup coil is also small. For this reason, the weight sensor using the magnetostrictive element has a problem that it is difficult to improve the detection accuracy. In particular,
When a weight sensor using a magnetostrictive element is used in a washing machine, a power supply voltage used in a control circuit of the washing machine must be used, and there is a problem that it is difficult to improve detection accuracy of the weight sensor. Was.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has as its main object to provide a weight sensor including a magnetostrictive element having high detection accuracy. Another object of the present invention is to provide a washing machine having a weight sensor including a magnetostrictive element capable of accurately detecting the weight of a washing dewatering tub or the like.

[0007]

Means for Solving the Problems and Effects of the Invention An invention according to claim 1 is a weight sensor for detecting a load, wherein a magnetostrictive element whose magnetic permeability is changed by a stress generated when an external force is applied is provided. A pickup coil provided around the magnetostrictive element, the inductance of which varies according to the magnetic permeability of the magnetostrictive element; an oscillating section including the pickup coil, wherein the oscillation frequency changes with a change in the inductance of the pickup coil; and a pickup coil. And a current supply circuit connected so as to allow current to flow to the pickup coil alternately from two directions during one cycle of oscillation of the oscillation section. It is a weight sensor.

According to a second aspect of the present invention, the oscillating section has two terminals for current input / output, and the current supply circuit includes a first switching circuit for supplying a current from one end of the oscillating section;
2. The weight sensor according to claim 1, further comprising a second switching circuit for supplying a current from the other end of the oscillating unit, and a switching circuit for selectively conducting both switching circuits. The invention according to claim 3 is the weight sensor according to claim 2, wherein the switching circuit switches the state of the two switching circuits based on the voltage at any one end of the oscillation unit.

According to a fourth aspect of the present invention, the oscillating section includes a pickup coil, and a capacitor and a resistor connected in parallel to the pickup coil.
A weight sensor according to claim 1. According to a fifth aspect of the present invention, there is provided a washing machine employing the weight sensor according to any one of the first to fourth aspects, wherein a weight of a washing dehydration tub of the washing machine is given to the magnetostrictive element. Washing machine.

According to a sixth aspect of the present invention, in the washing machine, the washing machine includes a hanging rod for suspending the washing and dewatering tub with respect to the housing, and the magnetostrictive element is provided at a connecting portion between the hanging rod and the housing. The washing machine according to claim 5, wherein the weight of the washing and dewatering tub is given to the magnetostrictive element via the washing machine. According to the configuration of the first aspect, the current supply circuit for supplying the current to the pickup coil employs, for example, an H-bridge connection configuration. Therefore, during one cycle in which the oscillation unit including the pickup coil oscillates, current can be alternately applied to the pickup coil from two directions, one direction and the other direction. Therefore, the current flows through the pickup coil of the oscillating unit not only during charging but also in the opposite direction during discharging. That is, a current twice as large as that in the conventional case flows through the pickup coil. When the current flowing through the pickup coil increases, the detection accuracy of the sensor improves.

Next, the reason why the detection accuracy is improved when the amount of current flowing through the pickup coil is increased will be described. The magnetic permeability of a magnetostrictive element (or a giant magnetostrictive element) changes due to a stress generated when an external force is applied. Changes in permeability are difficult to detect directly. Therefore, a coil is provided around the magnetostrictive element in order to detect a change in the magnetic permeability. The inductance of this coil changes due to a change in the magnetic permeability of the magnetostrictive element.

Therefore, when an oscillator including a coil (inductance) is formed, the oscillation frequency of the oscillator changes due to the change in inductance. In other words, the oscillation frequency changes as a function of the external force applied to the magnetostrictive element. Therefore,
In order to increase the detection accuracy, it is necessary to make the change in inductance larger with respect to the change in applied external force. By the way, if the current flowing through the coil is increased, the magnetostrictive element surrounded by the coil is magnetized more, the magnetic permeability is increased, and the inductance of the coil is increased. Therefore, to increase the detection accuracy of the weight sensor, the amount of current flowing through the coil should be increased.

The present invention has been made based on the above considerations, and improves the detection accuracy of a weight sensor by increasing the amount of current flowing through a pickup coil. The amount of current flowing through the pickup coil can be increased by increasing the power supply voltage.
However, when the weight sensor according to the present invention is to be incorporated in a washing machine, it is not preferable to create a new power supply for the weight sensor because the cost of the washing machine is increased. Therefore, the existing power supply circuit used for the control circuit of the washing machine is used. In order to receive the current supply from the existing power supply circuit and increase the current flowing through the pickup circuit, the present invention employs, for example, a current supply circuit of a push-pull circuit connected in an H-bridge system.

[0014] The current supply circuit may be configured as follows.
A configuration including a first switching circuit for supplying current from one end of the oscillation circuit, a second switching circuit for supplying current from the other end of the oscillation circuit, and a switching circuit for selectively conducting both switching circuits; By doing so, it is possible to stably supply a current to the pickup coil. According to a third aspect of the present invention, the switching circuit switches the state (conduction) of the two switching circuits based on the voltage at one end of the oscillation circuit, so that the current flows in synchronization with the charging and discharging of the oscillation circuit. Can be satisfactorily switched.

The oscillation circuit including the pickup coil preferably has a pickup coil, and a capacitor and a resistor connected in parallel to the pickup coil. By doing so, it is possible to absorb a surge that may occur when the direction in which the current flows to the pickup coil is switched. As described in claim 5, by employing the weight sensor according to the present invention in a washing machine, the weight of the washing and dewatering tub can be accurately detected by using a solid element called a magnetostrictive element.

According to the sixth aspect of the present invention, a simple mounting structure can be realized by arranging the position of the magnetostrictive element in relation to the hanging rod that hangs the washing and dewatering tub from the housing.

[0017]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is an external view of a weight sensor 1 according to an embodiment of the present invention, and FIG. 2 is a vertical cross-sectional view of the weight sensor 1 cut along AA in FIG. 1 and 2, a current supply circuit (push-pull circuit) and the like are omitted. The weight sensor 1 has a cylindrical magnetostrictive element or a giant magnetostrictive element.
The magnetostrictive element is an element having a small magnetic permeability and a large resistance, and the giant magnetostrictive element has an improved performance. Below,
It is referred to as the magnetostrictive element 2.

On top of the magnetostrictive element 2, a cylindrical upper pin 3 is provided.
However, a cylindrical lower pin 4 is arranged below the magnetostrictive element 2, and a central shaft portion is formed by the magnetostrictive element 2 and the upper pin 3 and the lower pin 4 sandwiching the same. A bobbin 5 is fitted on the shaft portion, and a pickup coil 6 is wound around the central shaft portion via the bobbin 5. And a cross section U extending to the bottom and both sides of the bobbin 5
A letter-shaped yoke (case) 7 is provided, and an upper portion of the yoke 7 is connected with a lid 8. A hole is formed in the center of the lid 8 to contact the upper pin 3, and the head of the upper pin 3 protrudes from this hole.

With the above configuration, a magnetic loop is formed around the magnetostrictive element 2, the upper pin 3, the lid 8, the yoke 7, and the lower pin 4. When the magnetostrictive element 2 receives an external force such as mechanical compression, expansion, or twist, a stress corresponding to the external force is generated inside, and the magnetic permeability changes according to the speed and magnitude of the stress. Therefore, in the weight sensor 1 shown in FIGS. 1 and 2, when an external force (weight) is applied to the head of the upper pin 3, the magnetic permeability of the magnetostrictive element 2 changes, and the inductance of the pickup coil 6 surrounding the magnetostrictive element 2 ( (Self-inductance) changes.

FIG. 3 is a graph showing an example of the relationship between the magnitude of the external force (weight) applied to the weight sensor 1 and the inductance taken out of the pickup coil 6.
As is clear from FIG. 3, in the weight sensor 1, as the external force is smaller, the amount of change in inductance with respect to the same amount of external force change is larger. That is, it has a characteristic that the detection sensitivity is high. Further, in the case of the same magnetostrictive element 2, the inductance increases as the number of turns of the pickup coil 6 increases, and as shown in FIG. 3, the slope of the curve showing the characteristic becomes steeper. Therefore, the weight sensor 1 having the magnetostrictive element 2
Is adopted in the washing machine, it is possible to detect both the weight of the laundry stored in the washing and dewatering tub and the weight of the water stored in the washing and dewatering tub.

The inductance of the pickup coil 6 can also be increased by increasing the current flowing through the pickup coil 6. FIG. 4 is a graph showing the relationship between the current flowing through the pickup coil 6 and the inductance of the coil 6. As shown in FIG. 4, the weight sensor 1 has an external force of L ₀ (weight 0 kg), L ₅ (weight 5
kg), L ₁₀ (weight 10 kg), L ₁₅ (weight 15 kg)
, The inductance of the pickup coil 6 changes. It can be seen that the larger the amount of current flowing through the pickup coil 6, the larger the change in the inductance.

Therefore, in this embodiment, a current is applied to the pickup coil 6 by the circuit shown in FIG. 5 to constitute the weight sensor 1 having good detection accuracy. FIG. 5 is a circuit configuration diagram of the weight sensor 1. In FIG. 5, a pickup coil 6 is shown at the center. A series circuit of a capacitor and a resistor is connected in parallel to the pickup coil 6 to form an oscillating unit 60. Oscillator 60
These capacitors and resistors are for absorbing a surge that may occur when the direction of the current flowing to the pickup coil 6 is switched. A first switching transistor pair 41 is connected to an upper end of the pickup coil 6, and a second switching transistor pair 41 is connected to a lower end of the pickup coil 6.
Are connected.
Both transistor pairs 41 and 42 each include an upper power supply transistor and a lower ground transistor, and are turned on / off in a reverse state. These two transistor pairs 41 and 42 have comparators 43 and 44, respectively.
Output is given. Further, the potential on the lower end side of the pickup coil 6 is compared with a predetermined reference potential by a comparator 45, and the output of the comparator 45 is given to the + input of the comparator 43 and
4 to the-input. As a result, the comparator 4
The reference numerals 3 and 44 derive outputs of opposite polarities based on a change in the potential of the lower end of the pickup coil 6. As a result, the first switching transistor pair 4
1 is conductive (the power supply transistor is on and the ground transistor is off), the second switching transistor pair 42 is not conductive (the power supply transistor is off and the ground transistor is on). When one switching transistor pair 41 is non-conductive, the second switching transistor pair 42 is conductive.

When the first transistor pair 41 is conducting, a current from the power supply voltage flows from the upper end of the pickup coil 6 to the pickup coil 6 via the power supply side transistor, and the ground side transistor of the second transistor pair 42 Through to ground potential. Conversely, when the second switching transistor pair 42 is in a conductive state, the current from the power supply voltage flows to the pickup coil 6 from the lower end side of the pickup coil 6 through the power supply side transistor, and the ground of the first switching transistor pair 41 is grounded. It flows to the ground potential via the side transistor.

The pickup coil 6 performs charging when current is supplied through the first switching transistor pair 41, for example, and discharges when no current is supplied. That is, the pickup coil 6 oscillates by alternately repeating charging and discharging. In this embodiment, when the pickup coil 6 performs a discharge, a current flows through the second switching transistor pair 42 in a direction in which the current flows at the time of the discharge.

As a result, twice as much current flows through the pickup coil 6 as compared with the case where current flows only in one direction. Thereby, the amount of change in the inductance of the pickup coil 6 with respect to the amount of change in the external force (weight) increases (see FIG. 4), and the detection accuracy of the weight sensor 1 improves. A first transistor pair 41, a second transistor pair 42, and comparators 43, 44, and 4 shown in FIG.
5 is generally called a push-pull circuit. In particular, the configuration shown in FIG. 5 is called an H-bridge connection push-pull circuit. The H-bridge type push-pull circuit allows current to flow alternately from two directions to the pickup coil 6 in one cycle of its oscillation, thereby using the current from the existing power supply circuit to achieve a weight with high detection accuracy. A sensor can be configured.

FIG. 6 is a side sectional view showing the configuration of a fully automatic washing machine according to one embodiment of the present invention. Inside the casing 10 of the washing machine, four outer tubs 11 are suspended by four (only two are shown in FIG. 6) hanging rods 12, and a large number of outer tubs 11 The inner tub 13 having the dehydration hole is rotatably supported about the main shaft 15. A pulsator 14 for stirring the laundry is arranged at the bottom of the inner tub 13. The rotational power of a motor 16 attached to the lower surface of the outer tub 11 is a motor pulley 17, a V-belt 18, a main pulley 19, and a power switch. It is transmitted to the inner tank 13 and the pulsator 14 via the mechanism 20.

The lower end of the suspension rod 12 penetrates a mounting piece 21 projecting outward from the bottom wall of the outer tub 11, and a vibration isolator 22 provided with a compression coil spring is provided at the tip thereof.
The upper end of this coil spring is fixed to the mounting piece 21,
When the load of the outer tub 11 is applied to the vibration isolator 22 via the mounting piece 21, the coil spring contracts and absorbs the vibration of the outer tub 11. On the other hand, the upper end side of the suspension rod 12 is provided with a vibration-proof spring seat 24 engaged with a mounting piece 23 projecting inward from the casing 10.
Thus, it is held movably in the vertical direction. The weight sensor 1 that receives a load applied to the hanging bar 12 is installed on a holding member 24 that holds at least one of the four hanging bars 12.

A tap water supply pipe 26 provided with a water supply valve 25 in the middle thereof as a water supply mechanism is disposed behind the upper part of the casing 10. Water supplied from outside through the tap water supply pipe 26 is injected into the inner tub 13 from a water inlet 27 provided with a detergent container, a softener container and the like. FIG. 7 is an electrical configuration diagram of a main part of the washing machine. The oscillation / current supply circuit 31 is connected to the pickup coil 6 of the weight sensor 1 provided on the vibration isolation spring seat 24, as described with reference to FIG. The oscillation / current supply circuit 31 supplies a current to the pickup coil 6 to generate an oscillation having a frequency corresponding to the inductance L1 of the pickup coil 6. This oscillation frequency is
The frequency is detected by the frequency detector 32, and the result is
0 is given.

The control unit 30 includes a CPU and the like, receives an operation signal from the operation unit 33, and controls the operation of the motor 16, the opening / closing operation of the water injection valve 25 and the drain valve 34, and the like. FIG. 8 is a flowchart showing the control operation of the washing machine. The operation from the start of washing to the start of washing operation will be described with reference to FIG. When the user puts laundry into the inner tub 13 and instructs the start of washing with the operation unit 33, the control unit 30 first executes a load amount detection process (step S1). That is, when the laundry is put into the inner tub 13, the weight applied to the hanging bar 12 increases by the weight of the laundry, so that the external force received by the upper pin 3 of the weight sensor 1 increases. Then, the inductance L1 changes, and the oscillation frequency in the oscillation / current supply circuit 31 changes. The control unit 30 reads the oscillation frequency from the frequency detection unit 32 and calculates the weight by referring to, for example, a table indicating the relationship between the frequency and the weight. Such a table can be experimentally checked in advance and stored in a memory in the control unit 30.

The controller 30 determines the washing water level and the strength of the water flow according to the detected weight (step S2), opens the water injection valve 25, and starts supplying water to the outer tub 11 (step S3). . When water accumulates in the outer tub 11, the external force applied to the upper pin 3 of the weight sensor 1 further increases due to the weight of the water. If the oscillation frequency read from the frequency detection unit 32 becomes a frequency corresponding to the weight of water corresponding to the washing water level (YE in step S4),
S), the water supply valve 25 is closed to stop water supply (step S5). Then, the motor 16 is rotationally driven so as to have a rotational speed corresponding to the water flow determined as described above,
The pulsator 14 is rotated to start washing.

As described above, in the washing machine, the weight of the laundry is detected by using the weight sensor 1, and the water level is also detected by converting the amount of water into the weight. Therefore,
The installation of a water level sensor becomes unnecessary. Normally, the weight of the laundry is at most about 7 to 8 kg, but when the washing water level is high, the amount of water is as high as several tens of liters. It is much larger than the weight and its required detection range is wide. Although the accuracy of detecting the weight of water may be coarse, the accuracy of detecting the weight of laundry is required to be as high as about 0.5 to 1.5 kg.
As shown in FIG. 3, the characteristics of the weight sensor 1 have higher detection sensitivity as the external force is smaller. That is, a high sensitivity is obtained when detecting the weight of the laundry, and the detection sensitivity is low when the water level is detected. It can be seen that this is suitable for detecting the water level.

The present invention is not limited to the embodiment described above, and various changes can be made within the scope of the claims.

[Brief description of the drawings]

FIG. 1 is an external view of a weight sensor according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of the weight sensor cut along AA in FIG. 1;

FIG. 3 shows the magnitude of an external force (weight) applied to a weight sensor,
It is a graph which shows an example of the relation with the inductance taken out from a pickup coil.

FIG. 4 is a graph showing a relationship between a current flowing through a pickup coil and an inductance of the coil.

FIG. 5 is a circuit diagram of a weight sensor.

FIG. 6 is a side sectional view showing a configuration of a fully automatic washing machine according to one embodiment of the present invention.

FIG. 7 is an electrical configuration diagram of a main part of the fully automatic washing machine according to the embodiment of the present invention.

FIG. 8 is a flowchart showing a control operation of the fully automatic washing machine according to one embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 Weight sensor 2 Magnetostrictive element (giant magnetostrictive element) 6 Pickup coil 41, 42 Switching transistor pair 43, 44, 45 Comparator 60 Oscillator

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) G01G 3/15 G01G 3/15 H01F 5/00 H01F 5/00 E H01L 41/08 H01L 41/12 41 / 12 41/08 Z (72) Inventor Minoru Nakanishi 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term in Sanyo Electric Co., Ltd. 3B155 AA10 BB19 CB06 DD04 HC05 KA02 KB10 KB17 MA01 MA02 MA05 MA09

Claims (6)

[Claims] 1. A weight sensor for detecting a load, comprising: a magnetostrictive element whose magnetic permeability changes due to a stress generated when an external force is applied; and a weight sensor provided around the magnetostrictive element, wherein A pick-up coil whose inductance changes, an oscillating unit including the pick-up coil and whose oscillation frequency changes due to a change in the inductance of the pick-up coil, and a circuit for flowing a current to the pick-up coil,
A current supply circuit connected so that current can flow to the pickup coil alternately from two directions during one cycle of oscillation of the oscillating unit. 2. The oscillating section has two terminals for inputting and outputting a current. The current supply circuit includes a first switching circuit for supplying a current from one end of the oscillating section, and a 2. The weight sensor according to claim 1, further comprising a second switching circuit for supplying a current, and a switching circuit for selectively conducting both switching circuits. 3. The weight sensor according to claim 2, wherein the switching circuit switches the states of the two switching circuits based on a voltage at one end of the oscillating unit. 4. The weight sensor according to claim 1, wherein the oscillating unit includes a pickup coil, and a capacitor and a resistor connected in parallel to the pickup coil. 5. A washing machine employing the weight sensor according to claim 1, wherein a weight of a washing dehydration tub of the washing machine is given to the magnetostrictive element. . 6. The washing machine has a hanging rod for suspending the washing and dewatering tub with respect to the housing, wherein the magnetostrictive element is provided at a connecting portion between the hanging rod and the housing, and the washing and dewatering tub is connected via the hanging rod. The washing machine according to claim 5, wherein the weight of the washing machine is given to the magnetostrictive element.