JPH04213007A - Method and apparatus for measuring shape of circular body - Google Patents

Abstract

PURPOSE:To make it possible to perform more positive and highly accurate measurement in comparison with conventional measurements and to improve the selecting ability for coins and the like by constituting a new means for measuring the shape of a circular body. CONSTITUTION:The picture-element addresses of two critical parts of a shade formed on a light receiving part 5 of an image sensor with the shielding of a coin are detected with a shift register H 7a, a NAND circuit 8s, a shift register L 7b, a NAND circuit 8b, a counter 9 and a latch circuit 10. The diameter of the coin is judged based on the maximum value of the difference in picture- element addresses. The outer diameter and the presence or absence of the hole or its inner diameter are judged based on the difference in plural sets of the picture-element addresses. The roundness is judged based on the time change in difference of the picture-element addresses. These judgments are performed with a CPU 14, respectively.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for detecting the diameter and other shapes of circular objects such as coins and sorting the circular objects, and an apparatus using this method. The present invention relates to a technique for measuring the shape of a circular object by signal processing an output signal of a photoelectric conversion means that detects a state of blocking light when irradiating the object.

0002

2. Description of the Related Art Conventionally, as a method for optically measuring the outer diameter of a circular object, an image sensor having a large number of pixel arrays including photodiodes arranged in a direction perpendicular to the direction in which the circular object passes is used. is installed, irradiates light from above a circular object onto the pixel row, detects the number of pixels in the shadow part formed above the pixel row when the light is blocked by the circular object, and detects this number of pixels. The outer diameter of a circular object was measured from the total number of pixels.

0003

[Problems to be Solved by the Invention] However, in the conventional outer diameter measuring method described above, the outer diameter of a circular object is determined based on the total number of pixels in the part where the circular object blocks light. When a hole is formed, there is a problem in that the total number of pixels is reduced due to the hole, making accurate outer diameter measurement impossible.

In addition, it is impossible to detect the presence or absence of a hole in a circular object and its inner diameter, and it is impossible to detect defects, distortions, and irregularities on the outer edge of a circular object to select defective products. could not. Therefore, it is difficult to distinguish the type of circular object, and there are also problems in that it is impossible to detect and sort out small abnormalities.

[0005] Therefore, the present invention solves the above-mentioned problems, and the problem is not to determine the number of pixels in the shadow area formed by the light shielding of the circular object, but to determine the pixel position at the boundary of the area. To provide a method and device that enables accurate outer diameter measurement of a circular object regardless of the presence or absence of a hole, and further detects the presence or absence of a hole in a circular object, its inner diameter, and roundness. There is a particular thing.

[0006]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention adopts a method of measuring the shape. A photoelectric conversion means detects as an electrical signal whether or not light is irradiated to a plurality of pixels arranged in a predetermined direction orthogonal to the first pixel, and the light changes from a non-shielding part to a shielding part along the predetermined direction. The first pixel existing in the critical region of
and a second address of a pixel existing in a second critical region where light changes from a light shielding area to a non-shielding area along the same predetermined direction, and detecting the first address that changes as the circular object passes. The diameter of the circular object is calculated based on the maximum value of the difference between the address and the second address.

In this case, it is detected whether or not a hole exists in the circular object based on whether or not a plurality of sets of first addresses and second addresses are detected; When an address and a second address are detected, the outer diameter of the circular object is measured based on the maximum value of the difference between the first address and the second address that are the most distant among the multiple sets. be.

[0008] Furthermore, a plurality of sets of first addresses and second addresses are detected, and the outer diameter of the circular object is calculated from the first address and second address that are the most distant among these sets. one or more sets of first address and second address of
The inner diameter of a circular object is calculated based on the difference in addresses.

[0009] Here, when the roundness of a circular object is determined by comparing the difference between a plurality of first addresses and second addresses, which change as the circular object passes, with a reference value of the perfect circular chord length. There is. In this case, the standard value of the perfect circular chord length is determined by the function F(x
)=y·sin(cos-1(2x/y)).

[0010] In each of the above means, the circular object may be a coin.

On the other hand, as a shape measuring device for a circular object,
A photoelectric conversion means is provided on the path through which the circular object passes, and this photoelectric conversion means has a plurality of pixels arranged to detect light in a predetermined direction orthogonal to the direction of passage of the circular object, The first part changes from the non-shielded part to the shielded part towards the
Address detection for detecting a first address of a pixel located in a critical region of and a second address of a pixel located in a second critical region that changes from a shielding portion to a non-shielding portion in the same predetermined direction. and calculation means for calculating the diameter of the circular object based on the maximum value of the difference between the first address and the second address.

In this case, the address detection means detects whether or not a hole exists in the circular object based on whether or not a plurality of sets of first and second addresses are detected, and also performs a calculation. In the case where there are a plurality of sets of first addresses and second addresses, the means calculates the outer diameter of the circular object based on the difference between the first address and the second address that are the most distant from each other. be.

Further, the address detecting means detects a plurality of sets of first addresses and second addresses, and the calculating means detects a plurality of sets based on the difference between the most distant first address and second address. In addition to calculating the outer diameter of the circular object, the inner diameter of the hole formed in the circular object is calculated based on the difference between the first address and the second address of one or more other sets.

[0014] Here, the calculation means compares the difference between the first address and the second address, which changes as the circular object passes, with a reference value of the perfect circular chord length, and determines the circularity of the circular object. In this case, the calculation means uses the calculated diameter y of the circular object and the distance x from the diameter to calculate the function F(x)=y・sin(cos−1(2x/y)) It is desirable to calculate the value of F(x) and use this value as a reference value for the perfect circular chord length.

[0015] In each of the above devices, the circular object may also be a coin.

[0016]

[Operation] According to this means, when a circular object passes, the shadow of the circular object falls on the plurality of pixels of the photoelectric conversion means, so that the light reaches the parts not covered by the circular object, and the parts covered by the shadow are Light does not reach those parts. Therefore, on the photoelectric conversion means, along one direction of the pixel column, there is a critical area where the area where light reaches (non-shielding area) changes to an area where light does not reach (shielding area), and vice versa. Part (shielding part)
A critical region is formed in which the light reaches a portion (non-shielding portion). Detect the first and second addresses of pixels existing in both of these critical regions, calculate the difference between them, and calculate the outer diameter of the circular object using the maximum value of the difference that changes as the circular object passes. You can ask for it.

According to this method and the measuring device using this method, unlike the conventional method of detecting the diameter based on the total number of pixels in the shaded area, even when a hole is formed in a circular object, , the outer diameter can be accurately determined without providing any auxiliary means and without being affected by the presence of the hole.

[0018] Furthermore, if one or more holes are formed in a circular object, there will be multiple sets of first and second addresses. Based on the presence or absence of the first and second addresses, it is possible to detect whether a hole exists in the circular object. In this case, the outer diameter can be determined based on the difference between the first address and the second address, which are the farthest apart, but the outer diameter can be detected based on the other first and second addresses. It is calculated independently of the address, and the outer diameter can be determined with high accuracy completely independently of whether or not there is a hole in the circular object.

Furthermore, when there are multiple sets of first and second addresses, the difference between the first and second addresses of the sets other than the set of first and second addresses that are the most distant from each other is Based on this, the inner diameter of a hole formed in a circular object can be detected.

[0020] In each of the above means, since the first address and the second address are detected separately, it is possible to prevent errors in measuring the outer diameter and inner diameter calculated based on the difference between the two addresses. It is possible to improve the reliability and accuracy of measurement.

[0021] Next, when comparing the difference between the first address and the second address, which fluctuates as a circular object passes, with the reference value of the perfect circular chord length, the difference between the two addresses to be compared is constant. If the value exceeds the value, it is possible to determine the deviation of the shape of the circular object from a perfect circle, and it is possible to know that irregularities, chips, scratches, or distortions have occurred on the outer periphery. Therefore, it is possible to grasp the overall shape of these outer peripheral edges, and it is possible to discover minute abnormalities.

[0022] When using F(x) obtained from the outer diameter value obtained by the first method as the reference value for the perfect circular chord length, there is no need to set a reference value in advance for knowing the shape. , it can handle circular objects with arbitrary diameters.

When each of the above means is used as a coin sorting method or a sorting device, there is no need to provide a separate means for sorting out coins with holes formed therein, and it is not necessary to provide a separate means for sorting out coins with holes formed therein. It is possible to accurately detect the presence or absence of holes, irregularities on the inner diameter and outer periphery, scratches, chips, distortions, etc., and even small abnormalities can be detected, greatly increasing the coin sorting ability than before.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of a method for measuring the shape of a circular object and a shape measuring device using this method according to the present invention will be described with reference to the accompanying drawings.

(First Embodiment) FIG. 1 is a block diagram showing the overall configuration of a device according to a first embodiment of the present invention. This first embodiment is for detecting the outer diameter, inner diameter, etc. of a coin. The detection unit 1 includes an LE installed above the path of the circular object 2.
D3 and an image sensor drive circuit 4 are provided, and the image sensor drive circuit 4 includes a light receiving section 5 provided with a plurality of pixels 5a arranged in a direction perpendicular to the path direction. has been done. As shown in FIG. 3, the circular object is moved on a path by a conveyor belt 40, and when the circular object approaches the light receiving section 5, the shadow formed only by the conveyor belt 40 is replaced by the circular object. When it expands and its diameter portion passes through, a shadow with the maximum width is formed on the light receiving section 5.

The image sensor driving circuit 4 outputs a clock signal VDCLK for scanning each pixel 5a arranged in the light receiving section 5, and serial data scanned based on this clock signal VDCLK as a video signal VDS. . This video signal VDS is input to the shift register H7a and shift register L7b, while the clock signal VDCLK is input to the delay circuit 6 to form a delayed clock CLKC.
KC is also input to shift register H7a and shift register L7b. The output signals of these shift registers H7a and L7b are sent to two NAND circuits 8.
a and 8b, and the rising edge signal UFLG
and is introduced into the latch circuit 10 as a falling edge signal DFLG. This latch circuit 10 inputs a delayed clock CLKC and receives a signal from a counter circuit 9 to specify a pixel address, and receives a rising edge signal UFLG.
and the address signal corresponding to the falling edge signal DFLG are transferred to the input port 11, and this address signal is
The data is sent to the CPU 14 via the data bus 12 and is subjected to arithmetic processing. This arithmetic processed data is stored in RAM13.
The data is sent to the CPU 14 for temporary storage, and is sent again to the CPU 14 for arithmetic processing.

In FIG. 2, the circular object 2 has a total effective number of pixels of 25.
The signal waveforms at each of the above components are shown in a state in which a shadow is formed in the range from pixel address 0112 to pixel address 2521 on the light receiving section 5 having 92. When the scan start signal SSTART shown in FIG. 2(a) is input to the image sensor circuit 4, the pixel 5a is synchronized with the video signal transfer clock signal VDCLK shown in FIG. 2(b).
are scanned in the order of arrangement, and as shown in FIG. 2(c), the rising edge is set at the point corresponding to pixel address 0112
At the time when the falling edge corresponds to the pixel address 2521, the respective video signals VDS are output. The light receiving state of each pixel 5a included as serial data in this video signal VDS is determined by the shift register H7a,
Input to shift register L7b and delay clock CLK
It is output as parallel data in synchronization with C, but the rising edge and falling edge are respectively shown in Figure 2(e).
At the timing when the state shown in is reached, the rising edge flag UFLG shown in FIG. 2(f) is outputted from the NAND circuit 8a, and the falling edge flag DFLG shown in FIG. 2(g) is outputted from the NAND circuit 8a. . At the pulse timing of this rising edge flag UFLG and falling edge flag DFLG, the delay clock CLK
Counter circuit 9 that receives C and displays the pixel address
The output signal is latched and sent to the input port 11. This signal corresponds to the pixel addresses 0112 and 2521 mentioned above.
The data content is sent to the CPU 14 through the data bus 12.

By the way, for example, when the conveyor belt 40 is arranged at the center of the passage route as shown in FIG. It is sent to the CPU 14 and is in a standby state, so to speak. Here, when the coin approaches the light receiving section 5, the rising edge flag UFL
Since the pulse timing of G and the falling edge flag DFLG changes, the pulse timing of the edge detection report signal also changes, and this change triggers the CPU 14 to measure the outer diameter based on the data introduced via the input port 11. Start. That is, the difference between the two pixel addresses (2521-0112=2409) obtained from the data is calculated as a temporary outer diameter value, and the outer diameter value is stored in the RAM.
13 and stored. As the circular object moves, this outer diameter value is replaced with a larger outer diameter value, or is accumulated in order, and finally when the circular object passes, the maximum value among them is Stored as the true outer diameter value of the object.

Note that the OR circuit 15 in FIG.
) The latch circuit 10 receives the edge detection report signal EDGE shown in
and is output to the CPU 14 to determine latch timing. Further, the NAND circuit 16 is used to transmit the time when counting the total number of pixels is finished to the CPU 14, and to clear the output of the counter circuit 9.

As shown in FIG. 4, when measuring a circular object 2' in which a hole 41 is formed, the conveyor belt 40 is
By installing the hole 41 at a position away from the center of the passage, a non-shielding part based on the hole 41 is formed on the light receiving part 5,
This unshielded portion generates another set of rising and falling edges in the video signal VDS.
The detected pixel addresses are B, C, as shown in FIG.
, D, and E, making a total of four. In this case, the outer diameter of the circular object can be calculated based on the difference between the minimum value B and the maximum value E of the pixel addresses, and the inner diameter of the circular object can be calculated from the difference between the intermediate pixel addresses C and D. can.

If the conveyor belt 40 is arranged so as not to overlap the light receiving section 5, the presence or absence of a hole and its inner diameter can always be measured regardless of the position of the hole formed in the circular object.

According to this embodiment, the outer diameter of a circular object is always calculated based on the difference between the farthest pixel addresses, so even if a hole is formed in the circular object, it is not affected by the existence of the hole. It is possible to measure the outer diameter of a circular object without having to do so. Additionally, since the rising edge and falling edge of the video signal VDS are detected separately, errors in outer diameter calculation can be prevented, and outer diameter measurement can be performed more reliably than before. .

Furthermore, when a hole is formed in a circular object, in addition to one set of pixel addresses corresponding to the outer diameter, one of the pixel addresses
Since one or more sets of pixel addresses are detected between the sets of pixel addresses, it is easy to know whether there is a hole or not.
Furthermore, the inner diameter of one or more holes can be calculated from the one or more sets of pixel addresses.

Since the inner diameters of these holes are also obtained based on the falling edges and rising edges of the video signal VDS which are taken out separately, it is possible to avoid misidentification and confusion with other sets of pixel addresses, and eliminate inner diameter calculation errors. can be prevented.

Regarding the structure of the detecting section 1, in addition to the structure according to the above embodiment, an equal-magnification lens array 5 as shown in FIG.
It is also possible to use 0.

When this embodiment is used as a coin sorting method or a sorting device, regardless of whether a coin has a hole or not, the outer diameter and the presence or absence of a hole or inner diameter can be determined by the same means. It is possible to improve the reliability and responsiveness of coin sorting. Furthermore, in this case, it is also possible to detect abnormalities such as holes formed in the coin due to mischief. In this coin sorting, it is of course possible to use this embodiment in combination with other sorting means such as a material sensor.

(Second Example) Next, a second example according to the present invention will be described. This second embodiment is for determining the roundness of the outer periphery of a coin, etc., and the overall configuration of the device is the same as that shown in FIG. 1, similar to the first embodiment. In this embodiment, all or part of the differences in pixel addresses that are sequentially obtained as the circular object passes are stored in the RAM 13, and when the maximum value of the pixel address differences is obtained, this is stored in the RAM 13. is determined as the outer diameter value y. Using the time point at which the outer diameter value y is obtained as a reference, a plurality of symmetrical time intervals are set before and after the time point, and the difference between the pixel addresses obtained at each time point is extracted. This situation is shown in Table 1.

[0038]

[Table 1]

[0039] Here, the distance x is calculated from the time point when the pixel address difference is obtained and the coin conveyance speed, and is the amount of movement of the coin from the position at the time point when the outer diameter value y is obtained. This shows that.

Next, using the above outer diameter value y, the value of F(x) is calculated from the following equation.

F(x)=y·sin(cos−1(2x/y)) Here, the distance x of the data shown in Table 1 taken earlier is substituted for x in the formula. In this formula, F(x) is, as shown in Figure 7, in a perfect circle with diameter y, parallel to this diameter and distance x
It represents the length of the strings apart. As a result, each distance x
The chord length of a perfect circle is calculated for the value of , and is shown in Table 2 below.

[0042]

[Table 2]

By comparing the chord length of the perfect circle calculated in this way with the difference between the actually detected pixel addresses, it is possible to determine the deviation of the shape of the passed coin from the perfect circle. For example, 5 with an outer diameter value y of approximately 26.5 mm.
When passing a 100 yen coin, in this example, 1 pixel is 1
Since it has a width of 1 μm, the maximum value of the difference in pixel address is 2409 pixels, but if you calculate the chord length +/-5 mm and +/-10 mm away from the diameter using this value as a reference, it will be a perfect circular chord. The length F(x) is as shown in FIG. On the other hand, a decagon, an ellipse, which has a similar outer diameter value y,
When passing three types of 500 yen coins with chipping and protrusions formed on the outer periphery, the difference between detected pixel addresses and this The value S(x
) is obtained. Since it is possible to determine whether a coin is good or bad based on the absolute value and variance of this S(x), it is possible to sort coins much more precisely than before, and to detect and reproduce the shape itself with high precision. can do. The number of comparison data used for this determination can be increased without making any special changes to the circuit configuration or calculation program. It is also possible to determine the presence or absence of jagged edges.

In this embodiment, the roundness is determined based on the detected outer diameter value, and it is possible to grasp the shape of an object with an arbitrary diameter. Instead of calculating the perfect circular chord length based on the obtained outer diameter value, data on the perfect circular chord length having one or more types of diameters is stored in advance, and the difference between these data and the pixel address is calculated. You can also compare. Further, in this case, it is also possible to select one data from among a plurality of types of data based on the outer diameter value obtained by the maximum value of the difference between the pixel addresses, and to compare with this data.

[0045]

As explained above, the present invention detects the shadow of a circular object using the pixel array of the photoelectric conversion means, and detects the first pixel address and the second pixel address of the critical portion of the shadow. By doing so, the present invention is characterized in that the outer diameter of the circular object, the presence or absence of a hole, the inner diameter, and other shapes of the circular object are determined from the one or more sets of first and second addresses, so that the following effects are achieved.

■ Calculate the outer diameter of a circular object based only on the first address and the second address in a method that is independent of the presence or absence of a hole, and furthermore, the first address and the second address are distinct. Since it is possible to detect the diameter separately, it is possible to improve the accuracy of outer diameter measurement and prevent calculation errors.

■ It is possible to determine the presence or absence of a hole in a circular object and its inner diameter at the same time as measuring the outer diameter without providing a separate means. It can be done reliably.

[0048] By comparing data on differences in pixel addresses measured sequentially with data on perfect circular chord length, information on the entire image of a circular object can be obtained, and irregularities, chips, scratches, deformations, etc. on the outer periphery can be obtained. can be detected in detail to improve sorting accuracy. Here, when calculating and comparing the data of the perfect circular chord length based on the measured outer diameter value, it becomes possible to perform the determination for an object having an arbitrary diameter.

[0049] When each of the above means is used as a coin sorting method or a sorting device, for example, it is possible to detect holes, chips, scratches, deformations, and other small abnormalities caused by mischief, and the reliability of sorting can be improved. and improve responsiveness.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of a method or apparatus for measuring the diameter of a circular object according to the present invention.

FIG. 2 is a waveform diagram for explaining the operation of each block in FIG. 1;

FIG. 3 is a plan view showing a state in which a circular object moves along a passage.

FIG. 4 is a plan view showing a state in which a circular object with a hole is moved through a passage.

FIG. 5 is a conceptual diagram showing a state in which detection data is stored in a RAM.

FIG. 6 is a perspective view showing another example of the detection section.

FIG. 7 is an explanatory diagram for explaining a formula for calculating the chord length F(x) of a perfect circle from the measured outer diameter value.

FIG. 8 is an explanatory diagram showing the value of the perfect circular chord length F(x) to be compared with the measurement data when a 500 yen coin is passed.

[Fig. 9] (a) is a 500 yen coin with a decagonal shape, (b)
) is a 500 yen coin with an elliptical shape, and (c) is a 500 yen coin with a chip and a protrusion on the outer periphery, and the perfect circular chord is calculated from the difference between the measured pixel addresses and the difference between this pixel address. It is an explanatory view showing a value S(x) obtained by subtracting the length F(x).

[Explanation of symbols]

1 Detection section 2. Circular object (coin) 3 LED 4 Image sensor drive circuit 5 Light receiving section 6 pixels 7a Shift register H 7b Shift register L 8a, 8b NAND circuit 9 Counter circuit 10 Latch circuit 11 Input port 13 RAM 14 CPU.

Claims (12)

[Claims] 1. A path through which a circular object passes is irradiated with light, and a photoelectric conversion means converts an electric signal into an electric signal indicating whether or not the light is irradiated onto a plurality of pixels arranged in a predetermined direction orthogonal to the path. a first address of the pixel existing in a first critical region where light changes from a non-shielding part to a shielding part along the predetermined direction; a second address of the pixel existing in a second critical region that changes to A method for measuring the shape of a circular object, the method comprising: calculating the diameter of the circular object. 2. The method for measuring the shape of a circular object according to claim 1, wherein the presence of a hole in the circular object is determined based on whether or not a plurality of sets of the first address and the second address are detected. If a plurality of sets of the first address and the second address are detected, the first address and the second address which are the most distant among the plurality of sets are detected. A method for measuring the shape of a circular object, characterized in that the outer diameter of the circular object is measured based on the maximum value of the difference in addresses. 3. The method for measuring the shape of a circular object according to claim 1, wherein a plurality of sets of the first address and the second address are detected, and the first address that is the most distant among the plurality of sets is detected. The outer diameter of the circular object is calculated from the address and the second address, and the diameter of the hole formed in the circular object is calculated based on the difference between the first address and the second address of one or more other sets. A method for measuring the diameter of a circular object, characterized by calculating the inner diameter. 4. The method for measuring the shape of a circular object according to claim 1, wherein the difference between the plurality of first addresses and the second address, which changes as the circular object passes, is calculated as a perfect circular chord length. A method for measuring the shape of a circular object, comprising determining the roundness of the circular object by comparing it with a reference value. 5. In the method for measuring the shape of a circular object according to claim 4, the reference value of the true circular chord length is determined by a function F using the calculated diameter y of the circular object and the distance x from the diameter.
A method for measuring the shape of a circular object, characterized in that the value is obtained by calculating (x)=y·sin(cos-1(2x/y)). [Claim 6] Any one of claims 1 to 5
2. The method for measuring the shape of a circular object according to item 1, wherein the circular object is a coin. 7. A photoelectric conversion means is provided on a path through which the circular object passes, and the photoelectric conversion means includes a plurality of pixels that detect light in a predetermined direction orthogonal to the direction in which the circular object passes. a first address of the pixel located in a first critical region arranged in the predetermined direction from the non-shielding part to the non-shielding part; a second address of the pixel located in a critical region of the pixel; and address detection means to detect the second address of the pixel located in a critical region of the pixel, and calculate the diameter of the circular object based on the maximum value of the difference between the first address and the second address. 1. An apparatus for measuring the shape of a circular object, characterized in that it has a calculation means for determining the shape of a circular object. 8. The shape measuring device for a circular object according to claim 7, wherein the address detecting means determines whether the shape of the circular object is determined based on whether or not a plurality of sets of the first address and the second address are detected. The calculation means detects whether or not a hole exists in the object, and when a plurality of sets of the first address and the second address exist, the calculation means determines whether the first address and the second address are the most distant. A shape measuring device for a circular object, characterized in that the outer diameter of the circular object is calculated based on the difference between two addresses. 9. The shape measuring device for a circular object according to claim 7, wherein the address detecting means detects a plurality of sets of the first address and the second address, and the calculating means detects a plurality of sets of the first address and the second address, and the calculating means detects a plurality of sets of the first address and the second address. Calculate the outer diameter of the circular object based on the difference between the first address and the second address, and calculate the outer diameter of the circular object based on the difference between the first address and the second address of one or more other sets. A shape measuring device for a circular object, characterized in that the inner diameter of a hole formed in the circular object is calculated. 10. The shape measuring device for a circular object according to claim 7, wherein the calculation means calculates the difference between the first address and the second address, which changes as the circular object passes, into a perfect circle. A shape measuring device for a circular object, characterized in that the roundness of the circular object is determined by comparing it with a reference value of chord length. 11. The shape measuring device for a circular object according to claim 10, wherein the calculation means calculates a function F(x
)=y・sin(cos−1(2x/y)),
A shape measuring device for a circular object, characterized in that the value of F(x) is used as a reference value for a perfect circular chord length. 12. The shape measuring device for a circular object according to claim 7, wherein the circular object is a coin.