WO2005064292A1 - Device and method for measuring weight - Google Patents

Device and method for measuring weight Download PDF

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Publication number
WO2005064292A1
WO2005064292A1 PCT/KR2004/003437 KR2004003437W WO2005064292A1 WO 2005064292 A1 WO2005064292 A1 WO 2005064292A1 KR 2004003437 W KR2004003437 W KR 2004003437W WO 2005064292 A1 WO2005064292 A1 WO 2005064292A1
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WO
WIPO (PCT)
Prior art keywords
board
weight
elastic body
displacement
sensor
Prior art date
Application number
PCT/KR2004/003437
Other languages
French (fr)
Inventor
Eui-Jung Lee
Original Assignee
Eui-Jung Lee
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eui-Jung Lee filed Critical Eui-Jung Lee
Publication of WO2005064292A1 publication Critical patent/WO2005064292A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01G—WEIGHING
    • G01G3/00—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances
    • G01G3/12—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01G—WEIGHING
    • G01G23/00—Auxiliary devices for weighing apparatus
    • G01G23/18—Indicating devices, e.g. for remote indication; Recording devices; Scales, e.g. graduated
    • G01G23/36—Indicating the weight by electrical means, e.g. using photoelectric cells
    • G01G23/37—Indicating the weight by electrical means, e.g. using photoelectric cells involving digital counting
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01G—WEIGHING
    • G01G7/00—Weighing apparatus wherein the balancing is effected by magnetic, electromagnetic, or electrostatic action, or by means not provided for in the preceding groups
    • G01G7/02—Weighing apparatus wherein the balancing is effected by magnetic, electromagnetic, or electrostatic action, or by means not provided for in the preceding groups by electromagnetic action
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/14—Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators

Definitions

  • the present invention relates to a device and method for measuring weight
  • weight measuring device such as electronic scale and so on.
  • FIG. 1 is a cross sectional view of the conventional load cell
  • FIG. 2 is an
  • FIG. 3 is a lower part plane
  • the load cell comprises an elastic body, strain
  • gauges 10, 12, 14, 16 which are attached to the lower part and upper part of the load cell
  • strain gauges are connected electrically, and they are transformed
  • FIG. 4 is a state change of the load cell when weight is applied. Referring to FIG. 4, when weight is applied, the elastic body is transformed and
  • strain gauges .10, 12, 14, 16 are also transformed.
  • FIG. 5 is a circuit configuration of the strain gauges.
  • the circuit configuration of the strain gauges is whaetstone
  • the strain gauges attached to the load cell expand or
  • load cell measures weight by measuring transforming rate which is displacement per
  • FIG. 6 is an enlarged cross sectional view of the strain gauge attached to.
  • a bond layer 32 is formed on upper part of the load cell and
  • the high polymer layer 34 is formed on the bond layer.
  • the polymer layer is formed using
  • a resistance layer is formed on the
  • polymer layer and resistance value of the resistance layer varies with transformation of the elastic body.
  • a polymer film is deposited on the resistance layer, the polymer film
  • the load cell has generally accuracy of 1/3,000. the load cell can be
  • the load cell cannot be used as a weight sensor
  • the elastic body when weight is applied to the elastic body, the elastic body is
  • strain gauge used for adhering the strain gauge is a polymer material which has heterogeneous
  • strain gauge itself is hard to provide high accuracy.
  • the polymer layer made of phenol and polyamide, etc. is formed under
  • strain gauge material which is the most important in the strain gauge consists of a grid of wire
  • FIG. 7 is a cross sectional view of the conventional magnetic weight sensor.
  • the magnetic weight sensor uses the principle of leverage.
  • An object to be measured for weight is placed on the plate 40 of the magnetic
  • the receiving part is in one side of the beam 42, if force is applied to the beam 42, the
  • the magnitude of light of the light receiving part reaches to the upper
  • the beam 42 moves to the downward direction, the magnitude of light reaches to the
  • the repeating time will be relatively long. That is, the
  • magnetic weight sensor measures weight through a time period repeating the upper limit and the lower limit.
  • the beam moves not only vertically but
  • the magnetic weight sensor includes a parallel
  • the parallel guide includes many hinge structures.
  • Electronic circuit 62 calculates weight of the object using a repeating period
  • Aforementioned magnetic weight sensor has relatively higher accuracy
  • the magnetic weight more than 1/100,000, 1/1,000,000, 1/5,000,000. Therefore, the magnetic weight
  • the magnetic weight sensor is much more expensive than load cell.
  • the magnetic weight sensor uses the principle of leverage, many revision means
  • the magnetic weight sensor has
  • the magnetic weight sensor is frequently damaged.
  • the magnetic weight sensor cannot be applied to various industries
  • the weight sensor is not only used for scale but used in measuring a heavy weight
  • the magnetic weight sensor is also applied to
  • the magnetic weight sensor can be applied only to limited field because of aforementioned problems.
  • the present invention is for overcoming the aforementioned problems, an
  • object of the present invention is to provide a device and method for measuring weight
  • Another object of the present invention is to provide a device and method for
  • Still another object of the present invention is to provide a device and method
  • Still another object of the present invention is to provide a device and method
  • a device for measuring weight comprising an elastic body which is transformed according to weight of an object; a displacement sensor for detecting
  • a protrusion part or an identifier can be formed on the center of the elastic body
  • the displacement sensor is one selected from group consisting of inductosyn,
  • LNDT Linear Variation Differential Transformer
  • radar radar, holography sensor, image sensor, semiconductor magnetic resistance element,
  • the displacement sensor includes inductosyn, and detects displacement of the
  • the displacement sensor comprises a fixed first board where electric pattern is
  • the second board is coupled to the center of the lower part of the elastic body
  • first board and the second board are manufactured by a PCB process or
  • the inductosyn is one of electric capacity inductosyn and electromagnetic
  • the weight measuring device is cylindrical or square pillar form, and cavity is
  • At least one transforming groove is further formed on the upper part or lower
  • At least one hole is further formed on the elastic body, so that the elastic body
  • the signal transforming part comprises an amplifier for amplifying induction
  • an AC/DC signal converter for converting output signal of the amplifier into DC signal
  • an active filter for converting active filter
  • the weight measuring device includes a microprocessor, and calculates weight
  • weight comprising the steps of applying weight to the upper part of an elastic body
  • FIG. 1 is a cross sectional view of the conventional load cell.
  • FIG. 2 is an upper part plane view of the conventional load cell.
  • FIG 3 is a lower part plane view of the conventional load cell.
  • FIG. 4 is a state change of the load cell when weight is applied.
  • FIG. 5 is a circuit configuration of strain gauges.
  • FIG. 6 is enlarged cross sectional view of the strain gauge attached to the
  • FIG. 7 is a cross sectional view of the conventional magnetic weight sensor.
  • FIG. 8 is a block diagram of the weight measuring device according to a
  • FIG. 9 is perspective view of the external appearance of the weight sensor
  • FIG. 10 is a cross sectional view of the weight sensor of FIG. 9 for the direction
  • FIG. 11 is a cross sectional view of the weight sensor of FIG. 9 for the
  • FIG 12 is an example of electric pattern formed on the first board and the
  • FIG. 13 is another example electric pattern formed on the first board and the
  • FIG. 14 is a cross sectional view of the weight sensor according to another
  • FIG. 15 is a pattern formed on the first board and the second board according to
  • FIG. 16 is a perspective view of the external appearance of the weight sensor
  • FIG. 17 is a cross sectional view of the weight sensor of FIG. 16 for direction of
  • FIG. 18 is a cross sectional view of the weight sensor of FIG. 16 for
  • FIG. 19 is a perspective view of the external appearance of the weight sensor
  • FIG. 20 is a cross sectional view of the weight sensor of FIG. 19 for direction of
  • FIG. 21 is a cross sectional view of the weight sensor of FIG. 19 for
  • FIG 22 is a perspective view of the external appearance of the weight sensor
  • FIG. 23 is a cross sectional view of the weight sensor of FIG. 22 for direction of
  • FIG. 24 is a cross sectional view of the weight sensor of FIG. 22 for
  • FIG. 25 is a perspective view of the external appearance of the weight sensor
  • FIG. 26 is a cross sectional view of the weight sensor of FIG. 25 for direction of
  • FIG. 27 is a cross sectional view of the weight sensor of FIG. 25 for
  • FIG. 28 is a perspective view of the external appearance of the weight sensor
  • FIG. 29 is a cross sectional view of weight sensor of FIG. 28 for direction of F-F.
  • FIG. 30 is a cross sectional view of the weight sensor of FIG. 28 for
  • FIG. 31 is perspective view of the external appearance of the weight sensor
  • FIG. 32 is a cross sectional view of the weight sensor of FIG. 31 for direction of
  • FIG. 33 is cross sectional view of the weight sensor of FIG. 31 for perpendicular
  • FIG. 34 is a perspective view of the external appearance of the weight sensor
  • FIG. 35 is a cross sectional view of the weight sensor of FIG. 34 for direction of
  • FIG 36 is a cross sectional view of the weight sensor of FIG. 34 for perpendicular direction of G-G.
  • FIG. 37 is a perspective view of the external appearance of the weight sensor
  • FIG. 38 is cross sectional view of weight sensor of FIG. 37 for direction of I-I.
  • FIG. 39 is a cross sectional view of the weight sensor of FIG. 37 for
  • FIG. 40 is a block diagram of the signal transforming part and weight
  • FIG. 41 is a flow chart of the method for measuring weight according to a
  • FIG. 8 is a block diagram of the weight measuring device according to a
  • the weight measuring device according to a preferred embodiment
  • embodiment of the present invention may comprise a weight sensor 500, a signal
  • the weight sensor 500 may comprise an elastic body 508 and a displacement sensor 510.
  • weight of the object was measured using a
  • the object was measured using force applied to a beam.
  • the object was measured using force applied to a beam.
  • weight is measured using displacement of the elastic body.
  • the displacement sensor 510 included in weight sensor 500 detects
  • the displacement sensor is configured to:
  • the displacement sensor 510 is not physically contacted to the elastic body. Because the displacement sensor 510
  • the displacement sensor 510 may include all elements which detect
  • magnetic lattice sensor optical displacement sensor, laser sensor, LED displacement
  • the displacement sensor 510 outputs electric signal or optic signal according to
  • the signal transforming part 502 transforms the displacement detection signal
  • detection signal outputted from the weight sensor 500 is general analogue signal and
  • the signal transforming part 502 transforms analogue signal
  • the circuit design of the signal transforming part 502 may be implemented
  • the weight calculating part 504 calculates weight of the object using output
  • the weight calculating part 504 may be implemented as microprocessor.
  • the display part 506 displays weight calculated by the weight calculating
  • the display part 506 may be implemented using various digital display
  • the output signal of the LCD means or analogue display means such as LCD, LED and so on. According to an embodiment of the present invention, the output signal of the LCD, LED and so on.
  • Look-Up table can be also used in order to calculate weight of the object
  • FIG. 9 is a perspective view of the external appearance of the weight sensor
  • the weight sensor may be cylindrical form and may include
  • the elastic body 60 a side wall 62 and bottom surface 72. In center of the elastic body
  • the material of the elastic body may include a metal material with elasticity such as aluminum, steel,
  • the protrusion part 64 of the elastic body 60 plays a role of an indicator which
  • the elastic body 60 is transformed proportional to the weight of the
  • the protrusion part 64 is formed for indication of center.
  • the protrusion part 64 does not affect mechanical operation, and the
  • protrusion part 64 may not be formed. Instead of the protrusion part, identification
  • the side wall 62 supports the elastic body 62. According to a preferred embodiment
  • the side wall is also the same material with the same material with the same material
  • the bottom surface need not be the same
  • FIG. 10 is a cross sectional view of the weight sensor of FIG. 9 for the direction
  • FIG. 11 is a cross sectional view of the weight sensor of FIG. 9 for the
  • the cavity 70 is formed in the weight sensor so
  • the board 68 is moved and the first board is fixed. As shown in FIG. 11, the first board 66
  • the second board 68 is coupled to the center of the elastic
  • second board moves not only to longitudinal direction but also to the lateral direction
  • the second board 68 is coupled to the center of the elastic
  • FIG. 12 is a diagrammatic representation of Electric pattern. Electric pattern is formed on the first board and the second board.
  • FIG. 12 is a diagrammatic representation of Electric pattern. Electric pattern is formed on the first board and the second board.
  • an identification number 900 is pattern formed on the first board
  • an identification number 902 is pattern formed on the second board.
  • the pattern 900 may be formed on the
  • second board and the pattern 902 may be formed on the first board.
  • the part (a) is state before the weight is applied and the part
  • An alternating current source is coupled to the pattern 900 formed on the first
  • the alternating current is provided to the pattern 900 through the alternating
  • FIG. 12 As shown in FIG. 12, the phase of the first board and the second is same
  • phase of patterns formed on the two boards changes. As the first board is adjacent to
  • the second board if the second board moves, the magnetic field generated by the first board changes amplitude of induction current which is generated on the second board.
  • the amplitude of the induction current depends on location relation between the first
  • the present invention detects displacement of the elastic
  • the second board moves.
  • the weight sensor of the present invention detects displacement in the •
  • the weight sensor of the present invention is more than 1/100,000.
  • the displacement detection method described referring to FIG. 12 is a method
  • inductosyn are produced by a sputtering process(thin film deposition process).
  • first board and the second board can be produced by a PCB process. If the boards are
  • the displacement sensor used for measuring weight does not require very high accuracy.
  • FIG. 13 is another example electric pattern formed on the first board and the
  • FIG. 12 is electric capacity inductosyn pattern and the FIG. 13 is
  • an identification number 1000 is electric pattern-formed on the first
  • the pattern 1000 can be formed on the second board and the
  • the electric pattern formed on the first board is same as FIG. 12, the
  • the second board are cut with phase difference of 90°. Unlike electromagnetic induction
  • FIG. 14 is a cross sectional view of the weight sensor according to another
  • the displacement is detected by amplitude
  • FIG. 15 is pattern formed on the first board and the second board according to
  • an identification number 1200 is pattern formed on the second board
  • an identification number 1202 is pattern formed on the first board.
  • the pattern moves to the longitudinal direction, the amplitude of the induction current
  • FIG. 12 and FIG. 13 Particularly, the length of the weight sensor can be smaller in the embodiment of FIG. 14 and FIG. 15.
  • the embodiment of FIG. 14 and FIG. 15 is
  • FIG. 16 is a perspective view of the external appearance of the weight sensor
  • FIG. 17 is a cross
  • FIG. 18 is a
  • transforming groove 65 is larger than that of the first transforming groove 63.
  • second transforming groove 65 make transformation of the elastic body more sensitive.
  • FIG. 19 is a perspective view of the external appearance of the weight sensor
  • FIG. 20 is a cross
  • FIG. 21 is a
  • FIG. 19 cross sectional view of the weight sensor of FIG. 19 for perpendicular direction of C-C.
  • a first transforming groove 63 is formed on the upper surface of the elastic
  • transforming groove 63 is larger than that of the second transforming groove 65.
  • FIG. 22 is a perspective view of the external appearance of the weight sensor
  • FIG. 23 is a cross
  • FIG. 24 is cross
  • half-circular holes 80 are formed at both sides of the
  • the holes 80 make the elastic body 60 transform
  • FIG. 25 is a perspective view of the external appearance of the weight sensor
  • FIG. 26 is a cross
  • FIG. 27 is a
  • groove 63 are formed on the upper surface of the elastic body, and the second
  • transforming groove 65 is formed on the lower surface of the elastic body.
  • holes and transforming grooves are
  • the diameter of the second transforming groove is larger than that of
  • FIG. 28 to FIG 30 is illustrated in FIG. 28 to FIG 30.
  • FIG. 25 to FIG. 30 are same as aforementioned embodiments.
  • FIG. 31 is a perspective view of the external appearance of the weight sensor
  • FIG. 32 is a cross sectional view of the weight sensor of FIG. 31 for direction of G-G
  • FIG 33 is a
  • FIG. 31 to FIG. 33 are same as embodiment of FIG. 9 to FIG.
  • FIG. 34 is a perspective view of the external appearance of the weight sensor
  • FIG. 35 is a cross
  • FIG. 36 is a
  • the form of the weight sensor is a square pillar
  • the first transforming groove 63 is formed on the upper surface of the elastic body 60
  • the transforming grooves 63, 65 make
  • first transforming groove is formed closer to the center.
  • FIG. 40 is a block diagram of the signal transforming part and weight
  • the signal transforming part and the weight calculating part according to a preferred embodiment of the present invention. Referring to FIG. 40, the signal transforming part and the weight calculating
  • the amplifier 370 amplifies detection signal output from the weight sensor.
  • the amplifier 370 is an
  • the current applied to the pattern of the board is alternating current
  • the detection signal outputted from the weight sensor is also alternating current.
  • AC/DC signal converter 372 converts the detection signal into DC signal, which is
  • the AC/DC signal converter may be implemented as
  • the detection signal which is converted into DC signal is inputted to the active
  • the active filter 374 performs filtering for serge signal, etc. in order to get
  • the output signal of the active filter is inputted to the A/D converter 376
  • the A/D converter 376 converts the inputted signal to the digital signal.
  • the converted digital signal is inputted to the microprocessor 378, the
  • microprocessor 378 calculates weight of the object material corresponding to amplitude
  • FIG. 41 is a flow chart of the method for measuring weight according to a preferred embodiment of the present invention.
  • weight is applied to the elastic body when the object is
  • the first board and the second board are overlapped in the lateral direction, by which the
  • the generated induction current is inputted to the amplifier, the
  • amplified induction current is transformed into DC signal by the AC/DC signal
  • the active filter After the signal is rectified, the active filter performs filtering for the serge
  • the filter is transformed into digital signal by the A/D converter S394.
  • the weight calculating part which is implemented using microprocessor, etc. calculates weight of the object material using the transformed digital signal S396, As
  • the weight can be calculated using predetermined algorithm or Look ⁇
  • the calculated weight is displayed to the users through a display device
  • the present invention can be applied to measure light weight measuring

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)

Abstract

The present invention relates to a device and method for measuring weight, the device of the present invention comprises an elastic body which is transformed according to weight of an object; a displacement sensor for detecting displacement of the elastic body; a signal transforming part for transforming output signal of the displacement sensor; and a weight calculating part for calculating weight of the object using output signal of the signal transforming part. According to the present invention, production cost can be reduced and high accuracy such as magnetic weight sensor can be achieved.

Description

Title of the invention
DEVICE AND METHOD FOR MEASURING WEIGHT
Field of the invention
The present invention relates to a device and method for measuring weight,
more particularly to a device and method for measuring weight by detecting
displacement of an elastic body which is transformed depending on weight.
Background of the invention Conventionally, a load cell or a magnetic weight sensor has been used for
weight measuring device such as electronic scale and so on.
FIG. 1 is a cross sectional view of the conventional load cell, and FIG. 2 is an
upper part plane view of the conventional load cell, and FIG. 3 is a lower part plane
view of the conventional load cell. Referring to FIG. 1 to FIG. 3, the load cell comprises an elastic body, strain
gauges 10, 12, 14, 16 which are attached to the lower part and upper part of the load cell
using polymer bond.
The strain gauges are connected electrically, and they are transformed
corresponding to transformation of the elastic body when weight is applied. FIG. 4 is a state change of the load cell when weight is applied. Referring to FIG. 4, when weight is applied, the elastic body is transformed and
the strain gauges .10, 12, 14, 16 are also transformed.
FIG. 5 is a circuit configuration of the strain gauges.
Referring to FIG. 5, the circuit configuration of the strain gauges is whaetstone
bridge circuit, and in initial state, the output value is set to be 0. The strain gauges
operate as resistors 10, 12, 14, 16 in the circuit.
When weight is applied, the strain gauges attached to the load cell expand or
shrink. As the resistance is a function of cross sectional area of wire and length of
wire, the resistance changes as the strain gauges expand or shrink, which invites
breaking of equilibrium state of the whaetstone bridge circuit. Therefore, the
whaetstone bridge circuit outputs voltage and weight is measured by measuring
amplitude of electric signal which is outputted when weight is applied. That is, the
load cell measures weight by measuring transforming rate which is displacement per
unit length when the elastic body is transformed. The FIG. 6 is an enlarged cross sectional view of the strain gauge attached to.
the load cell.
Referring to FIG. 6, a bond layer 32 is formed on upper part of the load cell and
high polymer layer 34 is formed on the bond layer. The polymer layer is formed using
polymer material such as phenols or polyamides. A resistance layer is formed on the
polymer layer and resistance value of the resistance layer varies with transformation of the elastic body. A polymer film is deposited on the resistance layer, the polymer film
prevents moisture or dust from penetrating into the resistance layer.
The load cell has generally accuracy of 1/3,000. the load cell can be
manufactured with low cost by employing simple and various structure designs, and
thus used in various ways. However, the load cell cannot be used as a weight sensor
which requires a high accuracy. Demand for high-density integration and ultra
miniaturization is rapidly increased in recent industry, and accuracy higher than
1/100,000, 1/500,000, 1/1,000,000, 1/5,000,000 is frequently required, and many
devices using a magnetic weight sensor for achieving high accuracy have been
manufactured and used. The reason why the load cell does not provide high
accuracy is as follows.
Firstly, when weight is applied to the elastic body, the elastic body is
transformed and its transforming rate of the elastic body should be transmitted to the
strain gauge without being distorted. However, bond by which the strain gauge is
adhered to the load cell, distorts the transforming rate of the strain gauge. As the bond
used for adhering the strain gauge is a polymer material which has heterogeneous
amorphous structure and irregular mechanical property, it is hard to predict mechanical
property of the bond. Further, it is difficult to make an even bond layer between
structure and the strain gauge to have regular thickness during the manufacturing
process. Furthermore, it is difficult to make a bond layer have regular property while hardening bond, and many bubbles exist if the bond layer is magnified, which
deteriorates mechanical property.
Secondly, the strain gauge itself is hard to provide high accuracy. Similarly to
the first reason, the polymer layer made of phenol and polyamide, etc. is formed under
resistance material of the strain gauge, and therefore, there is irregularity on account of
distortion when transformation of the elastic body is transmitted to the resistance
material of the strain gauge. Further, the polymer film for preventing penetration of
moisture is formed on the resistance material, which prevents elongation operation of
the resistance material. All of the aforementioned phenol, polyamide and polymer
film for preventing penetration of moisture have amorphous structure. The resistance
material which is the most important in the strain gauge consists of a grid of wire
filament, but the cross sectional form of the grid is not uniform, which prevents regular
elongation operation corresponding to the transformation. Therefore, an electric signal
depending on the elongation operation becomes irregular, which means accuracy of the
load cell is not high enough.
By aforementioned reasons, the load cell cannot be applied to a weight sensor
which requires high accuracy. Although getting higher accuracy in the load cell has
been studied and developed, the highest accuracy of the load cell is not higher than
1/12,000. FIG. 7 is a cross sectional view of the conventional magnetic weight sensor. The magnetic weight sensor uses the principle of leverage.
Referring to FIG. 7, operation of the magnetic weight sensor is described
hereinafter.
An object to be measured for weight is placed on the plate 40 of the magnetic
weight sensor. If the object is placed on the plate 40, downward force is applied to the
plate 40 due to weight of the object. The force is transmitted to a beam 42. A light
receiving part is in one side of the beam 42, if force is applied to the beam 42, the
magnitude of light received at the light receiving part changes with movement of the
beam 42. Upper and lower limit is set for the magmtude of light received at the light
receiving part. The magnitude of light of the light receiving part reaches to the upper
limit when the force applied to the beam 42 is transmitted, at this moment current is
generated in a coil 46 so that the magnitude of light returns to an initial value. If
current flows on the coil, a magnetic force is generated and the generated magnetic
force moves the beam to the downward direction by interaction with a magnet 48. If
the beam 42 moves to the downward direction, the magnitude of light reaches to the
lower limit and generation of current is stopped at this time. Above processes are
repeated continuously, therefore the magnitude of light repeats between the upper limit
and the lower limit. If the applied weight is heavy, the repeating time will be short.
If the applied weight is light, the repeating time will be relatively long. That is, the
magnetic weight sensor measures weight through a time period repeating the upper limit and the lower limit.
When weight is applied by an object, the beam moves not only vertically but
also slightly horizontally. Therefore, the applied weight may not be fully transformed
into movement of the beam. Therefore, the magnetic weight sensor includes a parallel
guide 50 so that the beam does not have horizontal movement. As shown in FIG. 7,
the parallel guide includes many hinge structures.
Electronic circuit 62 calculates weight of the object using a repeating period
between the upper and lower limit, and the calculated weight is displayed on a display
panel 54. Aforementioned magnetic weight sensor has relatively higher accuracy
compared with the load cell. Generally, accuracy of the magnetic weight sensor is
more than 1/100,000, 1/1,000,000, 1/5,000,000. Therefore, the magnetic weight
sensor is widely used when high accuracy is required. However, in order to achieve
desired high accuracy, following problems have occurred. Firstly, the magnetic weight sensor is much more expensive than load cell. As
the magnetic weight sensor uses the principle of leverage, many revision means
including a parallel guide are required in order to transfer force only to the vertical
direction. By the revision means, an operation mechanism of the magnetic weight
sensor is very complicate, and therefore, the manufacture cost of the magnetic weight
sensor is much higher than that of load cell. Secondly, many hinges having a thickness of about 0.1mm are required for the
complicate mechanism. As the thickness of the hinge is very thin, the hinge is very
frail when external impact or heavy weight is applied. The magnetic weight sensor has
been actually used for an object having weight of below 6kg. In particular cases, the
magnetic weight sensor just endures tens of kg. Further, much caution is required
when the magnetic weight sensor is conveyed, moved or treated. By incautious
treatment, the magnetic weight sensor is frequently damaged.
Thirdly, miniaturization is difficult on account of size limit of sensor. The size
of the magnetic weight sensor actually being used is lOOmmW xl00mmDx50mmH,
and it is extremely difficult to have smaller size than aforementioned size. The main
reason is a complicate mechanism. As industry progresses rapidly, high density
integration and super ultra miniaturization is a very important object in every device and
technique. However, the object cannot be achieved due to large size of the magnetic
weight sensor. Fourthly, the magnetic weight sensor cannot be applied to various industries
due to its complicate mechanism, frail structure, and large size. In an actual industry,
the weight sensor is not only used for scale but used in measuring a heavy weight
device such as hopper. Further, the magnetic weight sensor is also applied to
automatic devices and very small devices and demand therefore is very high. However,
the magnetic weight sensor can be applied only to limited field because of aforementioned problems.
Detailed description of the invention
Technical objects The present invention is for overcoming the aforementioned problems, an
object of the present invention is to provide a device and method for measuring weight
with high accuracy such as magnetic weight sensor and low cost.
Another object of the present invention is to provide a device and method for
measuring weight by employing a displacement sensor which measures displacement of
an elastic body .
Still another object of the present invention is to provide a device and method
for measuring weight which can be applied from light weight to heavy weight with high
accuracy.
Still another object of the present invention is to provide a device and method
for measuring weight with high accuracy and a simple mechanism and thus being
suitable for miniaturization.
Technical solution
To achieve aforementioned objects, according to one aspect of the present
invention, a device for measuring weight comprising an elastic body which is transformed according to weight of an object; a displacement sensor for detecting
displacement of the elastic body; a signal transforming part for transforming output
signal of the displacement sensor; and a weight calculating part for calculating weight
of the object using the output signal of the signal transforming part is provided. A protrusion part or an identifier can be formed on the center of the elastic body
for indicating center.
The displacement sensor is one selected from group consisting of inductosyn,
LNDT (Linear Variation Differential Transformer), eddy current displacement meter,
condenser displacement meter, magnetic lattice sensor, optical displacement sensor,
laser sensor, LED displacement sensor, supersonic displacement sensor, microwave
radar, holography sensor, image sensor, semiconductor magnetic resistance element,
magnetron, thermal electron beam pipe, magnetic diode, optic application sensor, and
optic fiber displacement sensor
The displacement sensor includes inductosyn, and detects displacement of the
elastic body through induction current which changes depending on the displacement of
the elastic body.
The displacement sensor comprises a fixed first board where electric pattern is
formed; a second board where electric pattern is formed, the second board being
coupled to lower part of the elastic body, wherein the second board moves
corresponding to the displacement of the elastic body, and change of induction current occurs in one of the first board and the second board.
The pattern formed on the second board and the pattern formed on the first
board are overlapped in a lateral direction, and thus change of induction current occurs,
as the second board moves. The pattern formed on the second board and the pattern formed on the first
board are overlapped in a longitudinal direction, and thus change of induction current
occurs as the second board moves.
The second board is coupled to the center of the lower part of the elastic body,
and the first board and the second board are manufactured by a PCB process or
sputtering process.
The inductosyn is one of electric capacity inductosyn and electromagnetic
induction inductosyn.
The weight measuring device is cylindrical or square pillar form, and cavity is
formed inside the weight measuring device so that the elastic body can be transformed. At least one transforming groove is further formed on the upper part or lower
part of the elastic body, so that the elastic body can react more sensitively.
At least one hole is further formed on the elastic body, so that the elastic body
can react more sensitively.
The signal transforming part comprises an amplifier for amplifying induction
current outputted from one of the first board and the second board; an AC/DC signal converter for converting output signal of the amplifier into DC signal; an active filter
for deriving valid component of output signal of the AC/DC signal converter; an A/D
converter for converting output signal of the active filter into digital signal.
The weight measuring device includes a microprocessor, and calculates weight
using output signal of the signal transforming part according to a predetermined
algorithm.
According to another aspect of the present invention, a method for measuring
weight, comprising the steps of applying weight to the upper part of an elastic body;
detecting displacement of the elastic body which is transformed proportional to weight
using a displacement sensor; outpurting detection signal corresponding to the detected
displacement; amplifying the detection signal and converting the amplified signal into
digital signal; and calculating weight by a predetermined algorithm by inputting the
converted digital signal to a microprocessor is provided.
Brief description of the drawings
FIG. 1 is a cross sectional view of the conventional load cell. FIG. 2 is an upper part plane view of the conventional load cell. FIG 3 is a lower part plane view of the conventional load cell. FIG. 4 is a state change of the load cell when weight is applied. FIG. 5 is a circuit configuration of strain gauges.
The FIG. 6 is enlarged cross sectional view of the strain gauge attached to the
load cell.
FIG. 7 is a cross sectional view of the conventional magnetic weight sensor. FIG. 8 is a block diagram of the weight measuring device according to a
preferred embodiment of the present invention.
FIG. 9 is perspective view of the external appearance of the weight sensor
according to a preferred embodiment of the present invention.
FIG. 10 is a cross sectional view of the weight sensor of FIG. 9 for the direction
ofA-A.
FIG. 11 is a cross sectional view of the weight sensor of FIG. 9 for the
perpendicular direction of A- A.
FIG 12 is an example of electric pattern formed on the first board and the
second board. FIG. 13 is another example electric pattern formed on the first board and the
second board.
FIG. 14 is a cross sectional view of the weight sensor according to another
embodiment of the present invention.
FIG. 15 is a pattern formed on the first board and the second board according to
the embodiment of FIG. 14. FIG. 16 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention.
FIG. 17 is a cross sectional view of the weight sensor of FIG. 16 for direction of
B-B. FIG. 18 is a cross sectional view of the weight sensor of FIG. 16 for
perpendicular direction of B-B .
FIG. 19 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention.
FIG. 20 is a cross sectional view of the weight sensor of FIG. 19 for direction of
C-C.
FIG. 21 is a cross sectional view of the weight sensor of FIG. 19 for
perpendicular direction of C-C.
FIG 22 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention. FIG. 23 is a cross sectional view of the weight sensor of FIG. 22 for direction of
D-D.
FIG. 24 is a cross sectional view of the weight sensor of FIG. 22 for
perpendicular direction of D-D.
FIG. 25 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention. FIG. 26 is a cross sectional view of the weight sensor of FIG. 25 for direction of
E-E.
FIG. 27 is a cross sectional view of the weight sensor of FIG. 25 for
perpendicular direction of E-E. FIG. 28 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention.
FIG. 29 is a cross sectional view of weight sensor of FIG. 28 for direction of F-F. FIG. 30 is a cross sectional view of the weight sensor of FIG. 28 for
perpendicular direction of F-F. FIG. 31 is perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention.
FIG. 32 is a cross sectional view of the weight sensor of FIG. 31 for direction of
G-G.
FIG. 33 is cross sectional view of the weight sensor of FIG. 31 for perpendicular
direction of G-G.
FIG. 34 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention.
FIG. 35 is a cross sectional view of the weight sensor of FIG. 34 for direction of
H-H. FIG 36 is a cross sectional view of the weight sensor of FIG. 34 for perpendicular direction of G-G.
FIG. 37 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention.
FIG. 38 is cross sectional view of weight sensor of FIG. 37 for direction of I-I. FIG. 39 is a cross sectional view of the weight sensor of FIG. 37 for
perpendicular direction of I-I.
FIG. 40 is a block diagram of the signal transforming part and weight
calculating part according to a preferred embodiment of the present invention.
FIG. 41 is a flow chart of the method for measuring weight according to a
preferred embodiment of the present invention.
Mode of invention
Hereinafter, the preferred embodiment of the present invention will be
described with accompanying drawings.
FIG. 8 is a block diagram of the weight measuring device according to a
preferred embodiment of the present invention.
Referring to FIG. 8, the weight measuring device according to a preferred
embodiment of the present invention may comprise a weight sensor 500, a signal
transforming part 502, a weight calculating part 504 and a display part 510, and the weight sensor 500 may comprise an elastic body 508 and a displacement sensor 510.
In FIG. 8, when an object is placed on the weight sensor, the weight sensor
detects weight of the object by measuring displacement of the elastic body 508 which is
transformed depending on the weight of the object. In case of conventional load cells, weight of the object was measured using a
transforming rate of the elastic body, and in case of magnetic weight sensor, weight of
the object was measured using force applied to a beam. However, according to the
present invention, weight is measured using displacement of the elastic body.
The displacement sensor 510 included in weight sensor 500 detects
displacement which varies according to weight of the object, and outputs detection
signal to provide detection signal to the signal transforming part 502.
According to an embodiment of the present invention, the displacement sensor
510 detects displacement of the elastic body in the state that the displacement sensor
510 is not physically contacted to the elastic body. Because the displacement sensor 510
is not physically contacted to the elastic body, the displacement of the elastic body is not
distorted, and therefore the weight can be measured with higher accuracy compared
with the case that the weight is measured in the state that sensor is physically contacted
to the elastic body.
However, it would be apparent to those skilled in the art that weight can also be
measured in the state that the sensor is physically contacted to the elastic body. The displacement sensor 510 may include all elements which detect
displacement, for example, inductosyn, LNDT (Linear Variation Differential
Transformer), eddy current displacement meter, condenser displacement meter,
magnetic lattice sensor, optical displacement sensor, laser sensor, LED displacement
sensor, supersonic displacement sensor, microwave radar, holography sensor, image
sensor, semiconductor magnetic resistance element, magnetron, thermal electron beam
pipe, magnetic diode, optic application sensor, and optic fiber displacement sensor, etc.
The displacement sensor 510 outputs electric signal or optic signal according to
the detected displacement, and the output signal is inputted to the signal transforming
part 502.
The preferred embodiment of the mechanical configuration of the weight sensor
500 is described in more detail referring to another figures.
The signal transforming part 502 transforms the displacement detection signal
so that the weight can be measured using the displacement detection signal. The
detection signal outputted from the weight sensor 500 is general analogue signal and
may include much noise. The signal transforming part 502 transforms analogue signal
into digital signal and removes noise component.
The circuit design of the signal transforming part 502 may be implemented
variously depending on the element of the displacement sensor. The detailed
embodiment of the signal transforming part 502 is described in more detail referring to another figure.
The weight calculating part 504 calculates weight of the object using output
signal of the signal transforming part 502. According to an embodiment of the present
invention, the weight calculating part 504 may be implemented as microprocessor.
However, it would be apparent to those skilled in the art that the weight calculating part
may be implemented using various processing means.
The display part 506 displays weight calculated by the weight calculating
means 504. The display part 506 may be implemented using various digital display
means or analogue display means such as LCD, LED and so on. According to an embodiment of the present invention, the output signal of the
signal transforming part is inputted to the microprocessor, and the microprocessor
calculates weight of the object using the predetermined algorithm. If high accuracy is
not required, Look-Up table can be also used in order to calculate weight of the object
material. FIG. 9 is a perspective view of the external appearance of the weight sensor
according to a preferred embodiment of the present invention.
Referring to FIG. 9, the weight sensor may be cylindrical form and may include
the elastic body 60, a side wall 62 and bottom surface 72. In center of the elastic body
60 is a protrusion part 64 formed. In FIG. 9, as the object is placed on the elastic body 60, the material of the elastic body may include a metal material with elasticity such as aluminum, steel,
stainless and so on. If the object is placed on the elastic body 60, the elastic body is
transformed according to weight of the object material.
The protrusion part 64 of the elastic body 60 plays a role of an indicator which
indicates center of the elastic body 60. If the object is placed on the center of the
elastic body 60, the elastic body 60 is transformed proportional to the weight of the
object more exactly. Therefore the protrusion part 64 is formed for indication of center.
Therefore, the protrusion part 64 does not affect mechanical operation, and the
protrusion part 64 may not be formed. Instead of the protrusion part, identification
mark can be indicated in the center of the elastic body.
The side wall 62 supports the elastic body 62. According to a preferred
embodiment of the present invention, the side wall is also the same material with the
elastic body 60, so that the elastic body is transformed with higher accuracy according
to weight of the object material. However, the bottom surface need not be the same
material with the elastic body 60, and the material of the bottom surface 72 may be
various including plastic, metal, etc.
FIG. 10 is a cross sectional view of the weight sensor of FIG. 9 for the direction
of A-A, FIG. 11 is a cross sectional view of the weight sensor of FIG. 9 for the
perpendicular direction of A-A. An example where inductosyn is used as the displacement sensor is illustrated in FIG. 9 to FIG. 11. However, it would be apparent to those skilled in the art that
other various displacement sensors can be used.
Referring to FIG. 9 and FIG. 11, the cavity 70 is formed in the weight sensor so
that the elastic body 60 can be transformed, and a first board 66 is coupled to the upper
part of the bottom surface 72 and a second board 68 is coupled to the lower part of the
elastic body 60.
As the second board 68 is coupled to the elastic body, the location of the second
board 68 is moved and the first board is fixed. As shown in FIG. 11, the first board 66
and the second board 68 is placed with predetermined interval so that they are not
bumped.
In FIG. 11, an example that the second board 68 coupled to the elastic body is
moved to the downward direction as the weight is applied to the elastic body 60 is
illustrated.
It is preferable that the second board 68 is coupled to the center of the elastic
body. If the second board 68 is not coupled to the center of the elastic body, the
second board moves not only to longitudinal direction but also to the lateral direction,
which means all weight of the object material is not reflected to the displacement of the
second board 68. Therefore, the second board 68 is coupled to the center of the elastic
body, so that the all weight of the object material is reflected to the longitudinal
displacement. Electric pattern is formed on the first board and the second board. FIG. 12 is
an example of the electric pattern formed on the first board and the second board.
Referring to FIG. 12, detailed method for detecting displacement of the elastic
body is described hereinafter. In FIG. 11, an identification number 900 is pattern formed on the first board,
and an identification number 902 is pattern formed on the second board. However, it
would be apparent to those skilled in the art that the pattern 900 may be formed on the
second board and the pattern 902 may be formed on the first board.
Further, in FIG. 12, the part (a) is state before the weight is applied and the part
(b) is state after the weight is applied.
An alternating current source is coupled to the pattern 900 formed on the first
board, the alternating current is provided to the pattern 900 through the alternating
current source. If alternating current flows on the pattern of the first board, magnetic
field is generated. If weight is applied to the elastic body, the location of the second board changes,
location relation between the first board and the second board changes like part (b) of
FIG. 12. As shown in FIG. 12, the phase of the first board and the second is same
before weight is applied to the elastic body. If the weight is applied to the elastic body,
phase of patterns formed on the two boards changes. As the first board is adjacent to
the second board, if the second board moves, the magnetic field generated by the first board changes amplitude of induction current which is generated on the second board.
The amplitude of the induction current depends on location relation between the first
board and the second board. The present invention detects displacement of the elastic
body by detecting amplitude of the induction current generated on the second board as
the second board moves.
That is, the weight sensor of the present invention detects displacement in the •
state that the first board is not physically contacted to the second board, and therefore,
distortion caused by physical contact can be prevented, by which weight can be
measured with higher accuracy. For example, while accuracy of the load cell is 1/3000,
the weight sensor of the present invention is more than 1/100,000.
The displacement detection method described referring to FIG. 12 is a method
for detection displacement using inductosyn which is a representative displacement
sensor.
The first board and the second board with electric pattern which is used in
inductosyn are produced by a sputtering process(thin film deposition process). The
board with more delicate pattern can be produced by the sputtering process.
However, according to more preferred embodiment of the present invention, the
first board and the second board can be produced by a PCB process. If the boards are
produced by the PCB process, production cost and time can be saved. Although
delicate pattern cannot be formed, the displacement sensor used for measuring weight does not require very high accuracy.
FIG. 13 is another example electric pattern formed on the first board and the
second board.
FIG. 12 is electric capacity inductosyn pattern and the FIG. 13 is
electromagnetic induction inductosyn pattern.
In FIG. 13, an identification number 1000 is electric pattern-formed on the first
board and an identification number 1002 is electric pattern formed on the second board.
Like case of the FIG. 12, the pattern 1000 can be formed on the second board and the
pattern 1002 can be formed on the first board. In FIG. 13, the electric pattern formed on the first board is same as FIG. 12, the
pattern formed on the second board is different from FIG. 12. The patterns formed on
the second board are cut with phase difference of 90°. Unlike electromagnetic induction
inductosyn, if all currents of each pattern are summed, the amplitude of the induction
current caused by movement of the second board does not change and only the phase of
the induction current changes. Therefore, the displacement of the elastic body is
detected through phase change of the induction current.
FIG. 14 is a cross sectional view of the weight sensor according to another
embodiment of the present invention.
Referring to FIG. 14, direction of the pattern is reverse compared with FIG. 10,
and other parts are same as FIG. 10. In embodiment of FIG. 10 to FIG. 13, the displacement is detected by amplitude
change or phase change of the induction current which is cause by lateral movement
distance of the pattern (or phase difference between two patterns) as weight is applied. However, in FIG. 14, the displacement is detected by change of induction
current caused by longitudinal movement distance of the pattern.
FIG. 15 is pattern formed on the first board and the second board according to
the embodiment of FIG. 14.
In FIG. 15, an identification number 1200 is pattern formed on the second board,
an identification number 1202 is pattern formed on the first board. Likewise, the
sequence can be changed.
Referring to FIG. 15, as the pattern is formed in reverse direction, the pattern
moves to longitudinal direction, not to lateral direction, as weight is applied. Although
the pattern moves to the longitudinal direction, the amplitude of the induction current
generated in the second board changes. As part where patterns are overlapped is larger, the amplitude of the induction
current becomes larger, and the larger current indicates heavier weight.
When the reverse directional pattern is formed like the embodiment of FIG. 1
and FIG. 15, more delicate pattern can be formed so that whole resistance of the patterns
matches, and smaller weight sensor can be produced compared with the embodiment of
FIG. 12 and FIG. 13. Particularly, the length of the weight sensor can be smaller in the embodiment of FIG. 14 and FIG. 15. The embodiment of FIG. 14 and FIG. 15 is
applied to electric cpacity inductosyn, and is not applied to electromagnetic induction
inductosyn which detects change of phase.
FIG. 16 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention, and FIG. 17 is a cross
sectional view of the weight sensor of FIG. 16 for direction of B-B, and FIG. 18 is a
cross sectional view of the weight sensor of FIG. 16 for perpendicular direction of B-B.
Referring to FIG 16 to FIG. 18, a first transforming groove 63 with circular
form is formed on the upper surface of the elastic body, and a second transforming
groove 65 which is concentric circle with the first transforming groove is formed on the
lower surface of the elastic body. In FIG 16 to FIG. 18, the diameter of the second
transforming groove 65 is larger than that of the first transforming groove 63.
In embodiment of FIG. 16 to FIG. 18, the first transforming groove 63 and the
second transforming groove 65 make transformation of the elastic body more sensitive.
Therefore, when the transforming grooves are formed like FIG. 16 to FIG. 18, the
weight can be measured with higher accuracy.
The principle that weight is measured using change of the induction current
generated by movement of the second board is same. Further, the pattern same as FIG.
12 is illustrated in FIG. 17, however, it would be apparent to those skilled in the art that
the pattern same as FIG. 15 can also be formed. FIG. 19 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention, and FIG. 20 is a cross
sectional view of the weight sensor of FIG. 19 for direction of C-C, and FIG. 21 is a
cross sectional view of the weight sensor of FIG. 19 for perpendicular direction of C-C. Referring to FIG. 19 to FIG. 21, according to another embodiment of the present
invention, a first transforming groove 63 is formed on the upper surface of the elastic
body 60 and a second transforming groove 65 is formed on the lower surface of the
weight sensor. Unlike embodiment of FIG. 18 to FIG. 20, diameter of the first
transforming groove 63 is larger than that of the second transforming groove 65.
Regardless of diameter length of the transforming groove, if the transforming grooves
are formed on the upper and lower part of the elastic body, transformation of the elastic
body becomes more sensitive, which enables measuring weight more precisely.
Besides transforming grooves, other operational parts are same as aforementioned
embodiments. FIG. 22 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention, and FIG. 23 is a cross
sectional view of the weight sensor of FIG. 22 for direction of D-D, and FIG. 24 is cross
sectional view of weight sensor of FIG. 22 for perpendicular direction of D-D.
Referring to FIG. 22, half-circular holes 80 are formed at both sides of the
elastic body 60. Although the half-circular hole is illustrated in FIG. 22, it would be apparent to those skilled in the art that the form of holes can be changed variously.
Like the transforming groove, the holes 80 make the elastic body 60 transform
more sensitively depending on the applied weight. Besides holes, other parts of FIG.
22 to FIG. 24 are same as aforementioned embodiments. FIG. 25 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention, and FIG. 26 is a cross
sectional view of the weight sensor of FIG. 25 for direction of E-E, and FIG. 27 is a
cross sectional view of the weight sensor of FIG. 25 for perpendicular direction of E-E. Referring to FIG. 25 to FIG 27, holes 80 as well as the first transforming
groove 63 are formed on the upper surface of the elastic body, and the second
transforming groove 65 is formed on the lower surface of the elastic body.
In embodiments of FIG. 25 to FIG. 27, holes and transforming grooves are
formed together, by which transformation of the elastic body can be more sensitive. In
FIG. 25 to FIG 27, the diameter of the second transforming groove is larger than that of
the first transforming groove, and the embodiments where the diameter of the first
transforming groove is larger is illustrated in FIG. 28 to FIG 30.
Besides that holes and transforming grooves are formed together, other parts of
embodiments of FIG. 25 to FIG. 30 are same as aforementioned embodiments.
FIG. 31 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention, and FIG. 32 is a cross sectional view of the weight sensor of FIG. 31 for direction of G-G, and FIG 33 is a
cross sectional view of the weight sensor of FIG. 31 for perpendicular direction of G-G.
In the embodiment shown in FIG. 31 to FIG. 33, the form of the weight sensor
is a square pillar. Besides that form of the weight sensor is square pillar, other parts of
the embodiment shown in FIG. 31 to FIG. 33 are same as embodiment of FIG. 9 to FIG.
11. It would be apparent to those skilled in the art that the form of the weight sensor can
be various besides cylindrical pillar and square pillar.
FIG. 34 is a perspective view of the external appearance of the weight sensor
according to another embodiment of the present invention, and FIG. 35 is a cross
sectional view of the weight sensor of FIG. 34 for direction of H-H, and FIG. 36 is a
cross sectional view of the weight sensor of FIG. 34 for perpendicular direction of G-G.
Referring to FIG. 34 to FIG 36, the form of the weight sensor is a square pillar,
the first transforming groove 63 is formed on the upper surface of the elastic body 60
and the second transforming groove 65 is formed on the lower surface of the elastic
body 60. Like aforementioned embodiments, the transforming grooves 63, 65 make
elastic body react more sensitively for the applied weight. In FIG. 34 to FIG. 36, the
first transforming groove is formed closer to the center. The embodiment that the
second transforming groove is formed closer to the center is shown in FIG. 37 to FIG. 39.
FIG. 40 is a block diagram of the signal transforming part and weight
calculating part according to a preferred embodiment of the present invention. Referring to FIG. 40, the signal transforming part and the weight calculating
part according to an embodiment of the present invention may comprise an amplifier
370, an AC/DC signal converter 372, an active filter 374, an A/D converter 376 and a
microprocessor 378. The amplifier 370 amplifies detection signal output from the weight sensor.
According to a preferred embodiment of the present invention, the amplifier 370 is an
OP amp which performs differential amplification for the detection signal.
As the current applied to the pattern of the board is alternating current, the
detection signal outputted from the weight sensor is also alternating current. The
AC/DC signal converter 372 converts the detection signal into DC signal, which is
function of rectifier circuit. The AC/DC signal converter may be implemented as
diodes or integrated circuit where elements like diodes are integrated.
The detection signal which is converted into DC signal is inputted to the active
filter 374, the active filter 374 performs filtering for serge signal, etc. in order to get
valid signal. The output signal of the active filter is inputted to the A/D converter 376
and the A/D converter 376 converts the inputted signal to the digital signal.
The converted digital signal is inputted to the microprocessor 378, the
microprocessor 378 calculates weight of the object material corresponding to amplitude
of inputted signal using predetermined algorithm. FIG. 41 is a flow chart of the method for measuring weight according to a preferred embodiment of the present invention.
Referring to FIG. 41, weight is applied to the elastic body when the object is
placed on the elastic body S380.
If weight is applied to the elastic body, the elastic body is transformed
according to the direction where weight is applied S382.
As the elastic body is transformed, the second, board coupled to the center of
lower surface of the elastic body moves S384.
As the location of the second board changes, the induction current of the pattern
formed on the board changes S386. As shown in FIG. 12 and FIG. 13, the patterns of
the first board and the second board are overlapped in the lateral direction, by which the
induction current changes. As shown in FIG. 15, the patterns of the first board and the
second board are overlapped in the longitudinal direction, by which the induction
current changes. The generated induction current is inputted to the amplifier, the
amplifier performs differential amplification for the inputted current S388. The
amplified induction current is transformed into DC signal by the AC/DC signal
converter S390.
After the signal is rectified, the active filter performs filtering for the serge
component and valid component can be obtained S392. The output signal of the active
filter is transformed into digital signal by the A/D converter S394. The weight calculating part which is implemented using microprocessor, etc. calculates weight of the object material using the transformed digital signal S396, As
described above, the weight can be calculated using predetermined algorithm or Look¬
up table. The calculated weight is displayed to the users through a display device
S398.
Industrial applicability
As aforementioned, according to the present invention, production cost can be
reduced and high accuracy such as magnetic weight sensor can be obtained. Further, the present invention can be applied to measure light weight measuring
as well as heavy weight and can be manufactured with a simple mechanism.
Furthermore, as the weight measuring device of the present invention is
manufactured through the PCB process, production cost can be reduced, and as the
pattern direction is reverse compared with the conventional inductosyn, smaller weight
sensor can be manufactured.
Although the present invention is described with reference of the preferred
embodiments, those who skilled in the art will understand that many changes and
equivalent embodiments can be made without departing from the spirits and scope of
the present invention.

Claims

Claims
1. A weight measuring device comprising: an elastic body which is transformed according to weight of an object; a displacement sensor for detecting displacement of the elastic body; a signal transforming part for transforming output signal of the displacement
sensor; and a weight calculating part for calculating weight of the object using output signal
of the signal transforming part.
2. The device of claim 1, wherein said displacement sensor is one selected from
group consisting of inductosyn, LVDT (Linear Variation Differential Transformer), eddy
current displacement meter, condenser displacement meter, magnetic lattice sensor,
optical displacement sensor, laser sensor, LED displacement sensor, supersonic
displacement sensor, microwave radar, holography sensor, image sensor, semiconductor
magnetic resistance element, magnetron, thermal electron beam pipe, magnetic diode,
optic application sensor, and optic fiber displacement sensor.
3. The device of claim 1, wherein said displacement sensor includes inductosyn,
and said displacement sensor detects displacement of the elastic body through induction
current which changes depending on the displacement of the elastic body.
4. The device of claim 1, wherein said displacement sensor comprises, a fixed first board where electric pattern is formed; a second board where electric pattern is formed, the second board being
coupled to lower part of the elastic body, wherein the second board moves corresponding to the displacement of the
elastic body, and change of induction current occurs in one of the first board and the
second board.
5. The device of claim 4, wherein said pattern formed on the second board and
said pattern formed on the first board are overlapped in the lateral direction, and change
of induction current occurs, as the second board moves.
6. The device of claim 4, wherein said pattern formed on the second board and
said pattern formed on the first board are overlapped in the longitudinal direction, and
change of induction current occurs as the second board moves.
7. The device of claim 4, wherein said second board is coupled to the center of
the lower part of the elastic body.
8. The device of claim 4, wherein said first board and said second board are
manufactured by a PCB process.
9. The device of claim 4, wherein said first board and said second board are
manufactured by a sputtering process.
10. The device of claim 3, wherein said inductosyn is one of electric capacity
inductosyn and electromagnetic induction inductosyn.
11. The device of claim 1, wherein said weight measuring device is a
cylindrical or square pillar form, and cavity is formed inside said weight measuring
device so that the elastic body can be transformed.
12. The device of claim 11, at least one transforming groove is further formed
on the upper part or lower part of the elastic body, so that the elastic body can react
more sensitively.
13. The device of claim 11, at least one hole is further formed on the elastic
body, so that the elastic body can react more sensitively.
14. The device of claim 1, wherein said signal transforming part comprises: an amplifier for amplifying induction current outputted from one of the first
board or the second board; an AC/DC signal converter for converting output signal of the amplifier into
DC signal;
• an active filter for deriving valid component of output signal of the AC/DC
signal converter; and an A D converter for converting output signal of the active filter into digital
signal.
15. The device of claim 1, wherein said weight measuring device includes a
microprocessor, and calculates weight using output signal of the signal transforming
part according to predetermined algorithm.
16. A method for measuring weight, comprising the steps of: applying weight to the upper part of an elastic body; detecting displacement of the elastic body which is transformed proportional to
weight using a displacement sensor; outputting detection signal corresponding to the detected displacement; amplifying the detection signal and converting the amplified signal into digital signal; and calculating weight by a predetermined algorithm by inputting the converted
digital signal to a microprocessor.
17. The method of claim 16, wherein the displacement sensor is one selected
from group consisting of inductosyn, LVDT (Linear Variation Differential Transformer),
eddy current displacement meter, condenser displacement meter, magnetic lattice sensor,
optical displacement sensor, laser sensor, LED displacement sensor, supersonic
displacement sensor, microwave radar, holography sensor, image sensor, semiconductor
magnetic resistance element, magnetron, thermal electron beam pipe, magnetic diode,
optic application sensor, and optic fiber displacement sensor.
18. The method of claim 17, wherein said displacement sensor includes
inductosyn and outputs induction current corresponding to displacement of the elastic
body as the detection signal.
19. The method of claim 18, wherein said displacement sensor comprises: a fixed first board where electric pattern is formed; a second board where electric pattern is formed, the second board being
coupled to the lower part of the elastic body, wherein the second board moves corresponding to the displacement of the
elastic body, and change of induction current occurs in one of the first board or the
second board.
20. The method of claim 19, wherein said first board and said second board are
manufactured by PCB process.
PCT/KR2004/003437 2003-12-26 2004-12-24 Device and method for measuring weight WO2005064292A1 (en)

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