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 5 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 10 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 15 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 20 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 5 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 magnitude of light received at the light 10 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 15 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 20 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 5 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.

10 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.

15 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 20 sensor is much higher than that of load cell.

Secondly, many hinges having a thickness of about O. lmm 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 5 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 xlOOmmDx50mmH, 10 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.

15 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, 20 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.

5 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, LVDT (Linear Variation Differential Transformer), eddy current displacement meter, condenser displacement meter, magnetic lattice sensor, optical displacement sensor, 10 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 15 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 20 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.

5 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 10 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.

15 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 20 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 5 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 10 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 is provided.

15 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.

20 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.

5 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 10 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.

15 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 20 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.

5 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 10 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.

15 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 20 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.

5 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.

10 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 15 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.

20 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 1-1.

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.

5 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 10 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 15 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 20 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, LVDT (Linear Variation Differential Transformer), eddy current displacement meter, condenser displacement meter, magnetic lattice sensor, optical displacement sensor, laser sensor, LED displacement 5 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 10 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 15 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 20 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.

5 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.

10 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.

15 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.

20 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 5 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 10 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 15 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.

20 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 5 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, 10 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 15 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 20 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 5 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.

10 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 15 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, 20 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 5 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 10 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.

15 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 14 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 20 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 5 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 10 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.

15 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 20 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.

5 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.

10 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.

15 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 20 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.

5 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 10 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 15 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 20 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 5 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 10 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 15 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 20 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.

5 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 10 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 15 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 20 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.