Background Art A cutting blade is a strip-shaped member having a sharp edge at an upper portion thereof, and a body adapted to support the edge at a lower portion thereof.

Such a cutting blade is used in a state of being attached to a pattern. When a sheet material is laid on the pattern, and then downwardly pressed, it is cut to conform to the shape of the cutting blade. In such a manner, a variety of articles such as blanks of boxes, receipt sheets, and puzzle products can be manufactured.

In order to manufacture such articles, in particular, articles having small and complex shapes, it is necessary to accurately form a desired bending angle of the cutting blade. For correct and accurate formation of the bending angle, the configuration of the associated bending machine is important. However, it is most important to control the bending angle of the cutting blade in an automatically-controlled manner, that is, a software manner.

U. S. Patent No. 5,461, 893 to Tylor discloses a method for performing bending angle correction in an automatically-controlled manner using a computer.

However, this patent discloses only the general procedure without describing any concrete process. Furthermore, the method disclosed in this patent uses a method of picking up, by a camera, an image indicative of the shape of a cutting blade obtained after being completely subjected to a bending process, and comparing the picked-up image with an image of the final product previously stored in a computer in order to increase or decrease the drive force required for the bending of the cutting blade based on the result of the comparison. However, this method is complex while involving a number of errors, similarly to a manual correction

method.

Disclosure of the Invention Therefore, a main object of the invention is to provide a method for automatically correcting the bending angle of a cutting blade, which is capable of accurately setting a desired bending angle of the cutting blade.

Another object of the invention is to provide a cutting blade bending machine for implementing the automatic bending angle correction method.

Another object of the invention is to provide a method for automatically correcting the bending angle of a cutting blade, which is capable of accurately controlling the feeding amount of the cutting blade having an accurately-corrected bending angle.

In accordance with the present invention, these objects are accomplished by providing a method for automatically correcting a bending angle of a cutting blade, comprising the steps of : (1) bending the cutting blade, based on basic bending data stored in a memory; (2) picking up a profile of the cutting blade bent based on the basic bending data, and transmitting the picked-up profile to a computer; (3) measuring an actual bending angle based on the profile of the bent cutting blade; (4) deriving a difference between an ideal bending angle and the actual bending angle; and (5) correcting the basic bending data stored in the memory based on the derived difference.

Preferably, the correction step in the cutting blade bending angle correcting method of the present invention comprises a primary correction step of correcting the basic bending data based on the measured error or difference, and a secondary correction step of adjusting a value by which the correction value derived at the primary correction step is to be increased or reduced. Where there is an error after the secondary correction, the secondary correction step is repeated at least one time to re-correct the basic bending data. This correction method is applicable to all bending processes forming a bent portion with an optional angle, a right-angled shape, or an arc shape.

Brief Description of the Drawings The above objects, and other features and advantages of the present invention will become more apparent after a reading of the following detailed description when taken in conjunction with the drawings, in which: Fig. 1 is a perspective view illustrating an apparatus for carrying out an automatic bending angle correcting method according to the present invention; Fig. 2 is a flow chart illustrating the processing steps of the automatic bending angle correcting method according to the present invention; Fig. 3a illustrates a bending data table for linear bending processes stored in the memory of a computer control unit in accordance with the present invention; Fig. 3b is a conceptual plan view illustrating an error generated in a primary bending process for forming a right-angled bent portion; Fig. 3c is a conceptual plan view illustrating an error generated in a secondary bending process for forming a right-angled bent portion; Fig. 3d is a conceptual plan view illustrating a method for standardizing a profile of a bent cutting blade with reference to a central line; Fig. 4a illustrates an angle data table for bending processes adapted to form an arc-shaped bent portion, the table being stored in the memory of the computer control unit in accordance with the present invention; Fig. 4b illustrates an equal-division data table for bending processes adapted to form an arc-shaped bent portion, the table being stored in the memory of the computer control unit in accordance with the present invention; Fig. 4c is a conceptual plan view illustrating an error generated in a primary bending process for forming an arc-shaped bent portion; Fig. 4d is a conceptual plan view illustrating an error generated in a secondary bending process for forming an arc-shaped bent portion; Fig. 5a is a plan view illustrating the profile of a cutting blade ideally bent to have a right-angled structure; Fig. 5b is a plan view illustrating the case in which the cutting blade is fed

by a feeding length calculated taking into consideration an elongation amount of the cutting blade; Fig. 5c is a plan view for explaining a correction amount required for formation of a second portion of the cutting blade; Fig. 5d illustrates a leading length correction table for linear bending processes stored in the memory of the computer control unit in accordance with the present invention; Fig. 5e illustrates a trailing length correction table for linear bending processes stored in the memory of the computer control unit in accordance with the present invention; and Fig. 6 illustrates a feeding length correction table for bending processes adapted to form an arc-shaped bent portion, the table being stored in the memory of the computer control unit in accordance with the present invention.

Best Mode for Carrying Out the Invention Now, a method for correcting the bending angle of a cutting blade in accordance with an embodiment of the present invention will be described in detail with reference to the annexed drawings.

Fig. 1 is a perspective view illustrating a bending machine for implementing the cutting blade bending angle correcting method according to the embodiment of the present invention. Referring to Fig. 1, a cutting blade A reaches a bending region after passing through a guide unit 100 along a guide groove formed at the guide unit 100, and then emerging from an outlet groove provided at a detachable bending nozzle 200. At the bending region, the cutting blade A is bent by a desired angle in accordance with rotation of a bending member 300. An image detecting unit 20, which may comprise a camera, is attached to a support plate (not shown) over the cutting blade A in order to detect an image of the cutting blade A during a bending process. The image detecting unit 20 picks up a bending profile of the cutting blade A emerging from the bending nozzle 200, images the picked-up bending profile, and sends the resultant

image to a computer control unit 10. The computer control unit 10 manages all operations associated with the automated cutting blade bending machine. This computer control unit 10 includes a CPU, a memory, application programs, an input/output unit, and an I/O board. The computer control unit 10 performs bending angle correction in accordance with a method described hereinafter in association with the correction method of the present invention.

Fig. 2 illustrates processes involved in the bending angle correction method carried out by the computer control unit 10. The processes indicated by phantom lines correspond to processes executed by the cutting blade bending machine and image detecting unit arranged outside the computer control unit 10.

Bending angle data corresponding to each of various cutting blade bending angles is stored in the memory of the computer control unit 10. The computer control unit 10 reads out an angle by which the cutting blade is to be bent, and externally sends a command for rotating the bending member 300 based on the read-out data (S10). In response to the command, the cutting blade bending machine is controlled to rotate the bending member 300 by a desired angle corresponding to the read-out data in accordance with operations of a servo motor, pulleys, and a rotating member supporting the bending member (Sll). The image detecting unit 20 picks up a planar profile of the cutting blade obtained after being completely subjected to a bending process by the bending member 300, images the picked-up profile, and sends the resultant image file to the computer control unit 10 (S12). The computer control unit 10 measures an actual bending angle, based on the image file received thereto (S13). Thereafter, the computer control-unit 10 determines whether or not the measured actual bending angle corresponds to the desired bending angle (su4). Of course, the desired bending angle at this step is identical to the initial read-out bending angle data. When the actual bending angle corresponds to the desired bending angle, this desired bending angle is fixed as bending data. However, when the actual bending angle does not correspond to the desired bending angle, the bending data should be corrected, based on correction data derived in accordance with a difference

between the actual bending angle and the desired bending angle (S15). In the latter case, the processing steps S10 to S14 are repeatedly executed to determine again whether or not the re-measured actual bending angle corresponds to the desired bending angle. Typically, a satisfactory result is obtained when these processes are repeated three times or less. It is preferred that the critical range of the bending angle to be used at step S14 be set in such a manner that the set bending angle is determined as satisfying the given forming condition when the angle difference is, for example, about 0. 5°.

All bending data values are sequentially updated in a manner as described above. The updated bending data values are then automatically and correctly written in respective corresponding boxes of the bending data table. These data values are used as optimum bending data meeting diverse thicknesses, heights, and physical properties of cutting blades to be bent, respectively. Accordingly, it is possible to bend the cutting blade with a correct and accurate bending angle.

Figs. 3a to 3d illustrate an example of the bending method where the desired bending angle is 90°. Fig. 3a shows a bending data table 30 stored in the memory of the computer control unit 10. The numerals described in the leftmost column 31 of the table 30 represent bending angles with the unit of 10°, and the numerals described in the uppermost row 32 of the table 30 represent bending angles with the unit of 1°. For example, the bending angle of 90° corresponds to a point 33 where"9"in the leftmost column 31 crosses"0"in the uppermost row 32. In this case, the procedure of Fig. 2 is carried out in the same manner as described above. That is, the computer control unit 10 reads out the bending angle data"90"at the point 33, and then externally transmits a command for rotating the bending member 300 by an angle based on the read-out data (S10).

In response to the command, the bending member 300 is controlled to rotate 90 ° (S11). Thereafter, the image detecting unit 20 sends, to the computer control unit 10, an image file produced by picking up the planar profile of the cutting blade obtained after being completely subjected to a bending process, and imaging the picked-up profile (S12). The computer control unit 10 measures an actual

bending angle, based on the image file received thereto (S13).

The procedure of step S13 will be described in more detail. The image transmitted from the image detecting unit 20, which represents an actual planar shape of the cutting blade, as shown in Fig. 3d, has a thickness and a width which may be variably determined. The computer control unit of the present invention defines a central line of the width (indicated by a double-dotted line), and measures an actual bending angle with reference to the central line. For the automation and standardization of bending processes, it is important to determine the correction angle amount and feeding amount of a workpiece with reference to the central line of the width of the workpiece, and to measure data of diverse shapes of the workpiece with reference to the central line, thereby building a database having a broader application.

Thereafter, the computer control unit 10 determines at step S14 whether or not the measured actual bending angle corresponds to the desired bending angle, that is, 90°. When the actual bending angle corresponds to the desired bending angle, the desired angle is fixed as bending data. However, when the actual bending angle does not correspond to the desired bending angle, a routine for calculating the difference between the actual bending angle and 90°, that is, step S 15, is executed. Where the cutting blade is bent by an angle of 90°, it is difficult, after only one bending process, to obtain the result in which the actual bending angle corresponds to the desired bending angle. This is due to errors caused by a spring back phenomenon, in addition to general reasons such as frictional forces or inertial forces generated due to the use of a motor or gears. The spring back phenomenon is caused by the tendency of the cutting blade to return to its original state by virtue of the plasticity of the cutting blade incompletely removed in the bending (forming) process. For this reason, in most cases, although the bending member bends the cutting blade as it rotates 90°, the actual bending angle of the cutting blade does not reach 90° after one bending process because the cutting blade springs back in a small amount in a direction opposite to the original bending direction.

The difference calculating routine of step S15 will be described in more detail. Where the actual bending angle measured on the basis of the reference line is 75°, as shown in Fig. 3b, a value of"x"satisfying a proportional expression "90: 75 = x: 90" (x = 108) is derived as corrected bending data. This value"x" is temporarily written in a box of the table 30 corresponding to 90°. Based on the corrected bending data, the bending process is carried out again by repeating the procedure of steps S10 to S13. Subsequently, it is determined again at step S14 whether or not the actual bending angle corresponds to the desired bending angle, that is, 90°. In most cases, however, the actual bending angle obtained after the secondary bending process exceeds a desired bending angle, due to the following reasons. Generally, when the cutting blade is bent by an angle exceeding about 80°, there is no spring back phenomenon because the resilience of the cutting blade is completely removed (in this case, the angle of 80° is referred to as a critical angle). Since the correction value obtained after the primary bending process is a value calculated taking into consideration a certain parameter, that is, the error caused by spring back, the bending carried out in a correction angle range exceeding the critical angle (the correction angle range corresponds to a range of 80 to 108° when the critical angle is 80°) is considered as being made taken into consideration the factor of"spring back". As a result, the bending angle obtained after the secondary bending process slightly exceeds a desired bending angle.

In order to compensate for such an error, therefore, desired correction data is applied to the difference calculating routine of step S 15. This correction data is derived by calculating a value of"x"satisfying a proportional expression"18 : 35 = x: 15" ("Correction Angle Increase: Actual Angle Increase = x: Target Angle Increase for Obtaining 90°") in the case in which the actual bending angles based on the reference line is 110° (x = 7. 71). This value"x"is added to 90°. The resultant value"97. 71" is then written in the box 33 of the table 30. Based on the resultant corrected bending data, the procedure of step S10 to S13 is repeated.

That is, the bending process is executed by rotating the bending member 300 by an angle of 97. 71°. Thereafter, it is determined again at step S14 whether or not the

actual bending angle corresponds to 90°. In most cases in which the bending process is carried out to form a right-angled bent portion, it is possible to obtain an accurate bending angle, using the correction angle corrected as described above.

In this case, therefore, the correction angle is fixed as basic data. However, where an excessive error is generated due to a high thickness or height of the cutting blade, or it is necessary to form a very accurate right-angled bent portion, the routine of step S10 and steps following step S10 is further repeated until the actual bending angle accurately corresponds to a desired bending angle.

The above example is associated with the case in which the primary actual angle is less than the critical angle. However, where the actual angle measured after the primary bending process is more than the critical angle (for example, in the case of 85°), it may be possible to derive an accurate bending angle by performing the data correction process only one time.

The above described method is based on the principle of deriving an estimated bending angle at a primary correction step, and increasing or reducing the difference of the estimated bending angle from a desired bending angle at a secondary correction step, thereby gradually tracing an accurate bending angle.

Accordingly, it can be understood that this method is generally applicable to optional linear bending processes in which the actual angle measured after a primary bending procedure exceeds a critical angle.

Now, a preferred embodiment of the present invention associated with an arc-forming bending process will be described in detail.

Figs. 4a and 4b are basic data tables for an arc-forming bending process.

In an equal-division data table of Fig. 4b, the leftmost column 51 represents the radius R of an arc to be formed at a bending region under the condition in which the arc has an arc angle of 180°, and the uppermost row 52 represents the value below the decimal point of the radius R. The numeral described in each box where the leftmost column 51 crosses the uppermost row 52 represents the number of bending times (count value). For example, where an arc having a radius R of 10.0 and an arc angle of 180° is to be formed in accordance with a bending process,

the count value is"28. 00" as described in the box 53.

Hereinafter, the meaning of the count value will be more concretely described for better understanding of the present invention. The basic principle of the arc-forming bending process is to bend the cutting blade A to have a polygonal shape approximating a desired arc shape by repeatedly striking the cutting blade A while advancing the cutting blade A by a predetermined length after every striking, thereby bending the cutting blade A by a predetermined angle after every striking. In order to achieve this arc-forming bending process, it is necessary to calculate the arc length of the arc, based on the radius R and arc angle of the arc. In accordance with the calculated arc length and a predetermined number of bending times, the feeding length of the cutting blade A required for every bending time is automatically determined. For example, where the length of a circle having a radius R of 10 mm is 62.8 mm (10 * 2 * 3.14 = 62.8), an arc corresponding to a part of the circle while having an arc angle of 180° has an arc length of 31.4 mm (62.8/2 = 31. 4). Where the count value indicated in Fig. 4b is set to be"28", the feeding amount of the cutting blade A for every bending time is about 1.12 (31.4/28 = 1. 12). That is, when the cutting blade advances about 1.12 mm, the bending member rotates by a predetermined angle to bend the cutting blade. This process is continuously repeated 28 times, thereby causing the cutting blade to have a shape approximating an arc having a radius R of 10 mm and an arc angle of 180°. Of course, the arc angle set in the computer control unit 10 and the count value of Fig. 4b are freely variable because they are inputted by <BR> <BR> the user (A higher arc-forming accuracy is obtained at a higher count value. ). For example, where an arc corresponding to a quarter of a circle is formed, the feeding amount of the cutting blade is reduced by 1/2. In this case, it may be unnecessary to vary the count value.

The leftmost column 41 and uppermost row 42 of an angle data table shown in Fig. 4a have the same meanings as those of the equal-division data table shown in Fig. 4b. The angle data described in each box where the leftmost column 41 crosses the uppermost row 42 represents the rotating angle of the

bending member in the arc-forming bending process. For example, "6. 43" described in the box 43 represents the angle by which the bending member should rotate for each of 28 bending times (At each bending time, the cutting blade <BR> <BR> advances about 1.12 mm. ) in order to form an arc having a radius R of 10 mm and an arc angle of 180°.

In the above described embodiment of the present invention, the method for correcting the values described in the angle data table of Fig. 4a is proposed.

The processes associated with this method are the same as those described in conjunction with Fig. 3a. Accordingly, the description of these processes is omitted, and only the routine for finally determining angle data, for example, after two correction times, will be described.

Fig. 4c shows an error generated when a bending process is carried out, based on the data of"6. 43" and"28. 00" read out from the tables of Figs. 4a and 4b.

Referring to Fig. 4c, it can be seen that the actual bending angle of the cutting blade obtained after being completely subjected to a bending process is 165°, which is less than a desired bending angle of 180° by 15°. In order to compensate for the angle of 15°, a method for increasing the bending angle of the bending member achieved at every striking time is adopted in accordance with the present invention. That is, a value of"0.53" (15/28 = 0.53) (corresponding to an angle by which the bending member should further rotate at every bending time, as compared to the previous case) is added to the basic data value, that is, 6.43, in order to form an arc having an arc angle increased from the previous arc angle by 15° after 28 bending times. The data value of"6. 96" derived in the above calculation is written in the box 43 of the table 40 as corrected data. Thus, the process for rotating the bending member by an angle of 6. 96° is repeated 28 times.

Fig. 4d shows an error generated when a secondary bending process is carried out, based on the data of"6. 96" and"28. 00" derived as described above.

Referring to Fig. 4c, it can be seen that the actual bending angle of the cutting blade obtained after the bending process is 200°, which is more than a desired bending angle of 180°. In this case, the bending data is adjusted using a desired

angle increase"x". The value of"x"is derived using a proportional expression "0.53 : 35 = x: 15" ("Angle Data Value Increase: Actual Bending Angle Increase = x : Target Angle Increase for Obtaining 180°"). The value"x"of"0.22" derived as described above is added to the original data value"6.43". The derived data of"6. 65" is bending angle data obtained after the secondary correction. The above described routine is then repeated. When a correct radius and a correct arc angle are obtained in accordance with the execution of the above described routine, they are fixed as angle data, and written in the associated box 43 of the table 40.

The above described arc-forming bending angle correcting method is also applicable to the case in which the arc angle is an optional angle other than 180°, in the same manner as described above.

Furthermore, it is possible to collectively set data meeting diverse sizes and physical properties of cutting blades in association with an arc-forming bending process by automatically correcting each angle data value of the table 40 for optional arc angles and optional radii R. This table is stored in the memory of the computer control unit 10 so that it is used in a practical bending process.

Thus, formation of an accurate and correct arc can be achieved.

Where the radius R is not indicated in the table of Fig. 4a, but exists within a certain range between two radius values indicated in that table, for example, where the radius R is 12 mm existing within a range between 10 mm and 15 mm, a desired bending angle is derived in accordance with a well-known proportional expression, based on the bending angles respectively corresponding to 10 mm and 15 mm.

In addition to correction of the bending angle, it is also necessary to correctly control the feeding length of the cutting blade in order to correctly form the cutting blade. This will be described in brief.

Fig. 5a is a plan view illustrating an ideal cutting blade bent to have a right-angled structure having two portions 61 and 62 each having a length of 10 mm. The length measurement is carried out with reference to the central line of

the width. The cutting blade A is fed by a length (10 mm) corresponding to the length of the portion 61, and then bent in accordance with rotation of the bending member, thereby forming the portion 61. Thereafter, the cutting blade A is fed again by a length (10 mm) corresponding to the portion 62, and then cut using a cutting device (not shown). Thus, a bent cutting blade product is obtained. This is an ideal bending process. However, when the cutting blade is bent, it is longitudinally elongated at its bending portion. For this reason, the practical bending process is carried out under the condition in which the cutting blade is fed by a length less than the ideal length (10 mm) for forming the portion 61. Data for this bending process is provided by a leading length correction table illustrated in Fig. 5d. For example, data"0. 28" described in the table of Fig. 5d in association with a bending angle of 90° is a value deducted from the ideal length (10 mm). In this case, therefore, the practical feeding length of the cutting blade for forming the portion 61 corresponds to"9. 72 mm" (Fig. 5b). When the bending member is rotated under this condition, a blade portion having a length of 10 mm is formed. In order to form, as the portion 62, a portion having a length of exactly 10 mm when measured from a reference point 63, the cutting blade should be fed by a length obtained by deducting, from 10 mm, 1/2 of the width of the cutting blade (d/2). Thus, the portion 62 has a length of exactly 10 mm with reference to the central line. Fig. 5e illustrates an example of a trailing length correction table showing such data.

Fig. 6 is a table for correcting the feeding length of the cutting blade in the arc-forming bending process. Where the radius and count values described in conjunction with Fig. 4 correspond to"10"and"28", respectively, the numeral "0. 01"indicated in the box 61 of Fig. 6 is a value deducted from an ideal length of the cutting blade to be fed for every bending time, that is, 1.12 mm (this length can be calculated in the above described manner). Accordingly, the total length to be reduced for the formation of a desired arc is 0.28 mm (28 * 0.01 = 0.28).

The above described feeding length correction table is read out by the computer control unit 10 in a process for feeding the cutting blade before the

process for practically bending the cutting blade.

Industrial Applicability As apparent from the above description, in accordance with the automatic cutting blade bending angle correction method and apparatus of the present invention, values written in the angle adjusting table stored in the memory included in the computer control unit are automatically corrected in cope with a bending process forming a bent portion with an optional angle, a right-angled shape, or an arc shape, so as to calculate bending angles meeting diverse sizes and physical properties of cutting blades to be bent, respectively. Accordingly, it is possible to bend the cutting blade with a correct and accurate bending angle. In particular, the present invention exhibits superior effects in the case of bending workpieces involving a precise and complicated bending process.

Moreover, the processes of measuring and correcting a bending angle for forming a bent portion with ah optional angle or an arc shape are carried out in a sequential fashion. Accordingly, it is possible to automatically construct a desired database in the computer control unit, and automatically update the database, so that very efficient effects are provided.