JP2021089224A - Position detection method, encoder unit, and robot - Google Patents

Abstract

To provide a position detection method and an encoder unit that can easily improve detection accuracy, and to provide a robot including the encoder unit.SOLUTION: A method using an encoder having a scale unit having a plurality of marks and image pick-up devices, and includes the steps of: acquiring a first template image and first reference coordinates when the scale unit is at a first position; acquiring first matching coordinates of the marks by template matching based on the first template image when the scale unit is at a second position; determining the correlation relationship established between the first position, second position, first reference coordinates, and first matching coordinates; acquiring measurement matching coordinates of the marks by the template matching based on the first template image; and determining a measurement position on the basis of the first position, first reference coordinates, measurement matching coordinates, and correlation relationship.SELECTED DRAWING: Figure 9

Description

The present invention relates to a position detection method, an encoder unit and a robot.

An optical rotary encoder is known as a kind of encoder. The rotary encoder detects a rotation state such as a rotation angle, a rotation position, a rotation speed, and a rotation speed of a joint portion in a robot including a robot arm having a rotatable joint portion, for example. The detection result is used, for example, for driving control of a joint portion.

The encoder described in Patent Document 1 reads a code plate on which a numerical pattern such as a Gray code and a striped pattern are formed by an image pickup device, and detects a position from the read numerical pattern and the striped pattern.

Japanese Unexamined Patent Publication No. 63-187118

In the encoder described in Patent Document 1, in order to realize high detection accuracy, it is necessary to form a high-definition pattern on the cord plate and to position the encoder with high accuracy when installing the cord plate. Therefore, the encoder described in Patent Document 1 has a problem that it is not easy to realize high detection accuracy.

The position detection method according to the application example of the present invention is
The position of the scale unit is detected by using an encoder having a scale unit having a plurality of marks and an image sensor that images the mark, and the scale unit moves relative to the image sensor. It is a position detection method
When the scale unit is in the first position, the mark is imaged by the image sensor to generate a first reference image, and the first template image and the first reference coordinates of the mark in the first reference image are obtained. Steps to get and
When the scale unit is in the second position, the mark is imaged by the image sensor to generate a second reference image, and template matching based on the first template image results in the first template in the second reference image. The step of acquiring the first matching coordinates of the mark that matches the image, and
A step of finding a correlation established between the first position, the second position, the first reference coordinate, and the first matching coordinate.
When the scale unit is at the measurement position, the mark is imaged by the image sensor to generate a positioning image, and the positioning matching coordinates of the mark in the positioning image are acquired by template matching based on the first template image. Steps and
A step of obtaining the measurement position based on the first position, the first reference coordinate, the positioning matching coordinate, and the correlation.
It is characterized by having.

It is a side view which shows the robot which concerns on embodiment. It is sectional drawing which shows the encoder unit which concerns on 1st Embodiment. It is a functional block diagram which shows the encoder of FIG. It is a figure for demonstrating the scale part provided in the encoder of FIG. It is an enlarged view of E part of the scale part shown in FIG. It is a partially enlarged view of the scale part shown in FIG. It is a flowchart which shows the position detection method which concerns on 1st Embodiment. Of the position detection methods shown in FIG. 7, it is a flowchart showing step S1 in detail. It is a figure for demonstrating step S1 shown in FIG. It is a list which shows the calibration angle, the template image, the reference coordinate, and the coefficient acquired by the position detection method shown in FIG. It is a figure for demonstrating the image capture image of the image pickup element included in the encoder shown in FIG. It is a figure for demonstrating the template matching in the search area set in the captured image shown in FIG. It is a figure which shows the state which deviated by 1 pixel from the state which the correlation value becomes the maximum or the minimum at the time of template matching. It is a figure which shows the state which the correlation value becomes the maximum or the minimum at the time of template matching. It is a figure which shows the state which deviated by 1 pixel from the state which the correlation value becomes the maximum or the minimum at the time of template matching to the side opposite to the state shown in FIG. It is a flowchart which shows step S1 in detail in the position detection method which concerns on 2nd Embodiment. It is a list which shows the calibration angle, the template image, the reference coordinate, and the coefficient acquired by the position detection method shown in FIG.

Hereinafter, preferred embodiments of the position detection method, encoder unit, and robot of the present invention will be described in detail with reference to the accompanying drawings.

1. 1. Robot FIG. 1 is a side view showing a robot according to an embodiment. In the following, for convenience of explanation, the upper side in FIG. 1 is referred to as “upper” and the lower side is referred to as “lower”. Further, the base side in FIG. 1 is referred to as a "base end side", and the opposite side is referred to as a "tip side".

The robot 100 shown in FIG. 1 is a so-called horizontal articulated robot (SCARA robot), and is used, for example, in a manufacturing process for manufacturing precision equipment and the like, and can grip and transport precision equipment and parts. ..

As shown in FIG. 1, the robot 100 has a base 110, a first arm 120, a second arm 130, a work head 140, an end effector 150, and a wiring routing portion 160. Hereinafter, each part of the robot 100 will be briefly described in sequence.

The base 110 is fixed to, for example, a floor surface (not shown) with bolts or the like. The first arm 120 is connected to the upper end of the base 110. The first arm 120 is rotatable around the first axis J1 passing through the base 110.

A motor 111 that generates a driving force for rotating the first arm 120 and a speed reducer 112 that reduces the driving force of the motor 111 are installed in the base 110. The input shaft of the speed reducer 112 is connected to the rotation shaft of the motor 111, and the output shaft of the speed reducer 112 is connected to the first arm 120. Therefore, when the motor 111 is driven and the driving force is transmitted to the first arm 120 via the speed reducer 112, the first arm 120 rotates around the first axis J1 with respect to the base 110.

Further, the base 110 and the first arm 120 are encoders that are first encoders that detect the rotational state of the first arm 120 with respect to the base 110 by detecting the rotation angle of the output shaft of the speed reducer 112. 1 is provided.

A second arm 130 is connected to the tip of the first arm 120. The second arm 130 is rotatable around the second axis J2 with respect to the first arm 120. Although not shown, a second motor that generates a driving force for rotating the second arm 130 and a speed reducer that reduces the driving force of the second motor are installed in the second arm 130. Then, the driving force of the second motor is transmitted to the first arm 120 via the speed reducer, so that the second arm 130 rotates around the second axis J2 with respect to the first arm 120. Further, although not shown, the second motor is provided with an encoder different from the encoder 1 described above, which detects the rotational state of the second arm 130 with respect to the first arm 120.

A work head 140 is arranged at the tip of the second arm 130. The working head 140 has a spline shaft 141 inserted through a spline nut (not shown) and a ball screw nut (not shown) coaxially arranged at the tip of the second arm 130. The spline shaft 141 can rotate around the third axis J3 with respect to the second arm 130, and can move (up and down) in the vertical direction.

Although not shown, a rotary motor and an elevating motor are arranged in the second arm 130. The driving force of the rotary motor is transmitted to the spline nut by a driving force transmission mechanism (not shown), and when the spline nut rotates forward and reverse, the spline shaft 141 rotates forward and reverse around the third axis J3 along the vertical direction. Further, although not shown, the rotary motor is provided with an encoder different from the encoder 1 described above, which detects the rotational state of the spline shaft 141 with respect to the second arm 130.

On the other hand, the driving force of the elevating motor is transmitted to the ball screw nut by a driving force transmission mechanism (not shown), and when the ball screw nut rotates in the forward and reverse directions, the spline shaft 141 moves up and down. The elevating motor is provided with an encoder different from the encoder 1 described above, which detects the amount of movement of the spline shaft 141 with respect to the second arm 130.

An end effector 150 is connected to the tip end portion (lower end portion) of the spline shaft 141. The end effector 150 is not particularly limited, and examples thereof include those that grip an object to be transported, those that process an object to be processed, and the like.

A plurality of wirings connected to each electronic component arranged in the second arm 130, for example, a second motor, a rotary motor, an elevating motor, each encoder, etc., are tubular connecting the second arm 130 and the base 110. It is routed to the base 110 through the wiring route 160 of the above. Further, such a plurality of wirings are grouped in the base 110, and together with the wirings connected to the motor 111 and the encoder 1, are installed outside the base 110 to a control device (not shown) that controls the robot 100 in an integrated manner. Be routed.

The configuration of the robot 100 has been briefly described above. As described above, the robot 100 has a base 110 which is a first member and a first arm which is a second member which rotates with respect to the base 110. A 120 and an encoder unit 10 are provided. Here, the encoder unit 10 according to the present embodiment is a speed reducer 112 having an output shaft that rotates around a rotation shaft and outputs a driving force, and an encoder 1 that detects the rotation angle of the output shaft of the speed reducer 112. And have. A speed reducer 112 is installed in the base 110, and the output shaft of the speed reducer 112 is connected to the first arm 120. According to such a robot 100, as will be described later, the rotation angle of the first arm 120 can be detected with high accuracy, and the drive control of the first arm 120 can be performed with high accuracy based on the detection result. ..

2. First Embodiment 2.1. Encoder Unit Hereinafter, the encoder unit 10 according to the first embodiment will be described. The encoder unit 10 is incorporated in various devices, but the case where the encoder unit 10 is incorporated in the robot 100 will be described below as an example.

FIG. 2 is a cross-sectional view showing an encoder unit according to the first embodiment. FIG. 3 is a functional block diagram showing the encoder of FIG. FIG. 4 is a diagram for explaining a scale unit included in the encoder of FIG. FIG. 5 is an enlarged view of the E portion of the scale portion shown in FIG. FIG. 6 is a partially enlarged view of the scale portion shown in FIG. In addition, in FIG. 2 and FIGS. 4 to 6, the scale of each part is appropriately changed for convenience of explanation, the structure shown does not necessarily match the actual scale, and the illustration of each part is simplified as appropriate. ing.

As shown in FIG. 2, the base 110 of the robot 100 described above has a support member 114 that supports the motor 111 and the speed reducer 112, and houses the motor 111 and the speed reducer 112. With respect to such a base 110, the first arm 120 is rotatable around the first axis J1.

The first arm 120 has an arm main body 121 extending to the left and right in FIG. 2 and a shaft portion 122 protruding downward from the arm main body 121, and these are connected to each other. The shaft portion 122 is rotatable around the first shaft J1 with respect to the base 110 via the bearing 115, and is connected to the output shaft of the speed reducer 112. Further, the input shaft of the speed reducer 112 is connected to the rotation shaft 1111 of the motor 111. The speed reducer 112 is not particularly limited, and examples thereof include a wave speed reducer, a planetary gear speed reducer, a cyclo speed reducer, and an RV speed reducer.

Here, the base 110 is a structure to which a load due to its own weight or another mass supported by the base 110 is applied. Similarly, the first arm 120 is also a structure to which a load due to its own weight or another mass supported by the first arm 120 is applied. The constituent materials of the base 110 and the first arm 120 are not particularly limited, and examples thereof include a metal material.

In the present embodiment, the outer surfaces of the base 110 and the first arm 120 form a part of the outer surface of the robot 100. An exterior member such as a cover or a shock absorbing material may be mounted on the outer surfaces of the base 110 and the first arm 120.

Such a relatively rotating base 110 and the first arm 120 are provided with an encoder 1 for detecting these rotating states. The encoder 1 may be a linear encoder, but in the following description, an example in which the encoder 1 is a rotary encoder will be described. The rotary encoder detects the rotation angle of the scale unit 2, while the linear encoder detects the position of the linearly moving scale unit.

The encoder 1 has a scale unit 2 provided on the first arm 120, a detection unit 3 provided on the base 110, and a circuit unit 4 electrically connected to the detection unit 3. The circuit unit 4 includes a processing unit 5 and a storage unit 6.

As shown in FIG. 2, the scale portion 2 is provided on a portion of the arm main body portion 121 facing the base 110, that is, a portion on the lower surface of the arm main body portion 121 that surrounds the shaft portion 122. As shown in FIG. 4, the scale portion 2 has a dot pattern arranged around the first axis J1 at a position different from that of the first axis J1.

The scale portion 2 is provided on the surface of the first arm 120, for example. As a result, it is not necessary to provide a member for providing the scale portion 2 separately from the first arm 120. Therefore, the number of parts can be reduced. The scale portion 2 is not limited to the case where it is provided directly on the surface of the first arm 120, and may be provided on, for example, a sheet-like member attached to the surface of the first arm 120. However, it may be provided on a plate-shaped member provided so as to rotate together with the first arm 120. That is, the member provided with the scale portion 2 may be a member that rotates around the first axis J1 with respect to the base 110 together with the first arm 120.

As shown in FIGS. 4 to 6, the scale unit 2 has a plurality of marks 21 in which a plurality of dots 20 are arranged in a row. The plurality of marks 21 are arranged at substantially equal intervals along the circumference centered on the first axis J1. In the following description, the direction in which the radius of the circle centered on the first axis J1 extends is referred to as "radial DR", and the direction orthogonal to the radial DR is referred to as "circumferential DC".

As shown in FIG. 5, the mark 21 has a shape in which the length in the radial direction DR is longer than the length in the circumferential direction DC. As shown in FIG. 6, the mark 21 has a plurality of dots 20 arranged in a row along the radial DR, and the rows are arranged in four rows along the circumferential direction DC. In each column, the dots 20 are displaced along the circumferential DC, and the pattern of the deviation of the dots 20 functions as a unique identifier that uniquely identifies the mark 21. In the present embodiment, a row formed by four dots 20 arranged in the radial direction DR is set as one unit, and 16 dots 20 in which the units are arranged in four rows in the circumferential direction DC are used in template matching described later. An array pattern that can be a template image is configured. Therefore, each mark 21 contains an arrangement pattern different from that of the other marks 21.

Then, when the scale portion 2 having such a mark 21 is rotated around the first axis J1, the same array pattern does not appear more than once in a predetermined region in the captured image G described later. In the specification of the present application, having such distinctiveness is referred to as "unique", and a unique pattern is referred to as "unique pattern UP". If the unique unique pattern UP included in each mark 21 can be identified, the absolute position of the scale portion 2 in the circumferential direction can be identified.

Further, it is preferable that the unique pattern UP is repeatedly included in the radial DR of the mark 21. As a result, even when the imaging region RI shown in FIG. 5 is displaced in the radial direction DR, the unique pattern UP can be captured in these regions.

The positions, sizes, numbers, arrangement patterns, and the like of the dots 20 shown in FIG. 6 are examples, and are not limited thereto. Further, contrary to FIG. 2, the scale unit 2 may be arranged on the base 110 side, and the detection unit 3 may be arranged on the first arm 120 side.

The mark 21 shown in each figure is configured by uniquely arranging a plurality of black dots 20 on a white background. The shape of the dot 20 is circular in the drawing, but is not limited to this, and may be, for example, an ellipse, a quadrangle, or an irregular shape. Further, the mark 21 is not limited to a dot pattern composed of a plurality of dots 20, and for example, a pattern composed of linear lines, a pattern composed of curved lines, dots, linear lines, and the like. The pattern may be composed of a combination of at least two of the curved lines. Further, the mark 21 may be a pattern in which the white background and the black dots or lines of the above-mentioned pattern are inverted, that is, a pattern of the black background and the white dots or lines. Further, the dots 20 may be formed of, for example, an ink such as a dye or a pigment, or may have an uneven shape.

Further, the mark 21 is not limited to the one using a pattern such as a dot 20, and may include, for example, a number, a character such as a Roman character, an Arabic character, or a Chinese character, or a character. Other symbols, codes, marks, marks, designs, one-dimensional barcodes, QR codes (registered trademarks) and the like may be included.

The detection unit 3 shown in FIG. 2 includes an image pickup element 31 provided in the base 110 and an optical system 32 provided in the opening of the base 110, and the image pickup element 31 is an optical system 32. A part of the circumferential direction DC of the scale unit 2, specifically, the image pickup region RI of FIG. 5 is imaged via the image sensor. The angle of view of the imaging region RI is preferably set to an angle at which a plurality of marks 21 can be captured in the same image. If necessary, a light source that illuminates the image pickup region RI of the image pickup device 31 may be provided.

Examples of the image sensor 31 include CCD (Charge Coupled Devices), CMOS (Complementary Metal Oxide Semiconductor), and the like. Such an image sensor 31 converts the captured image into an electric signal for each pixel and outputs the image. The image sensor 31 may be either a two-dimensional image sensor (area image sensor) or a one-dimensional image sensor (line image sensor). It is desirable that the one-dimensional image sensor is arranged in a direction in which the arrangement of pixels is in contact with the swirling circle of the arm. When a two-dimensional image sensor is used, a two-dimensional image having a large amount of information can be generated, and it is easy to improve the detection accuracy of the dot 20 by template matching described later. As a result, the rotational state of the first arm 120 can be detected with high accuracy. When a one-dimensional image sensor is used, since the image sampling cycle, that is, the frame rate, is high, it is possible to increase the detection frequency, which is advantageous during high-speed operation. In the present embodiment, the image sensor 31 is a two-dimensional image sensor.

The optical system 32 is an imaging optical system arranged between the scale unit 2 and the image pickup device 31. It is preferable that at least the object side (scale portion 2 side) of the optical system 32 is telecentric. As a result, even if the distance between the scale unit 2 and the image sensor 31 fluctuates, the change in the imaging magnification on the image sensor 31 can be reduced, and as a result, the decrease in the detection accuracy of the encoder 1 is reduced. can do. In particular, when the optical system 32 is telecentric on both sides, even if the distance between the lens of the optical system 32 and the image sensor 31 fluctuates, the change in the imaging magnification on the image sensor 31 can be reduced. Therefore, there is an advantage that the optical system 32 can be easily assembled.

Here, as shown in FIG. 5, the image pickup region RI of the image pickup device 31 is set so as to overlap a part of the scale unit 2 in the circumferential direction DC. As a result, the image sensor 31 can image the dots 20 in the image pickup region RI. Therefore, by reading the dot 20 in the circuit unit 4, the rotational state of the first arm 120 can be known.

The circuit unit 4 shown in FIGS. 2 and 3 includes a processing unit 5 (processor) which is a processing device, and a storage unit 6 (memory) such as a ROM (Read only memory) and a RAM (Random Access Memory). Here, the storage unit 6 stores instructions and information that can be read by the processing unit 5, and the processing unit 5 realizes various functions by appropriately reading and executing the instructions and information from the storage unit 6. To do. Such a circuit unit 4 can be configured by using, for example, a microcomputer, an ASIC (application specific integrated circuit), an FPGA (field-programmable gate array), or the like. In particular, by hardwareizing the circuit unit 4 using an ASIC or FPGA, it is possible to increase the processing speed, reduce the size, and reduce the cost of the circuit unit 4. At least a part of the circuit unit 4 may be incorporated in the control device of the robot 100 described above.

The processing unit 5 estimates the relative rotational state of the base 110 and the first arm 120 based on the detection result of the detection unit 3. Examples of the rotation state include a rotation angle, a rotation speed, a rotation direction, and the like.

In particular, the processing unit 5 recognizes the unique pattern UP by template matching the image captured by the image sensor 31 using the template image, and uses the recognition result of the first arm 120 with respect to the base 110. Estimate the relative rotation state.

Further, the processing unit 5 has a function of estimating the relative rotation angle of the first arm 120 with respect to the base 110 in more detail based on the position of the unique pattern UP in the captured image of the image pickup device 31. Further, the processing unit 5 obtains the rotation speed based on the time interval in which the unique pattern UP is detected and the movement amount of the unique pattern UP, and determines the rotation direction based on the order of the types of the detected unique pattern UP. It also has a function to estimate. Then, the processing unit 5 outputs a signal corresponding to the above-mentioned estimation result, that is, a signal corresponding to the relative rotation state of the first arm 120 with respect to the base 110. This signal is input to, for example, a control device (not shown) and used to control the operation of the robot 100.

In addition, the processing unit 5 has a function of cutting out a part of the captured image of the image pickup device 31 to generate a template image. The generation of this template image is prior to estimating the rotational state of the first arm 120 relative to the base 110, or as needed, relative to the first arm 120 relative to the base 110. It is performed at each predetermined calibration angle in the rotation angle. Then, the generated template image is stored in the storage unit 6 corresponding to each calibration angle. Then, the processing unit 5 performs template matching using the template image stored in the storage unit 6. The template matching and the estimation of the rotation state using the template matching will be described in detail later.

The processing unit 5 may be configured to include both a device (internal device) provided inside the base 110 and a device (external device) provided outside the base 110. In this case, the external device is composed of, for example, a personal computer. The external device preferably has a function of cutting out a part of the captured image to generate a template image. By assigning this function to the external device, the function of the internal device can be simplified, and it becomes easy to reduce the size and cost of the base 110.

In addition to instructions (programs) that can be read by the processing unit 5, various information (data) that can be read by the processing unit 5 is stored in the storage unit 6. Specifically, in the storage unit 6, the above-mentioned captured image relates to the coordinates (reference coordinates) of the unique pattern UP in the captured image for each relative rotation state of the first arm 120 with respect to the base 110. It is stored together with the information and the information (angle information) regarding the rotation angle of the first arm 120. Such a storage unit 6 may be either a non-volatile memory or a volatile memory, but can hold a state in which information is stored without supplying power, and power saving can be achieved. From the viewpoint of being able to do so, a non-volatile memory is preferable.

2.2. Position detection method Next, the position detection method according to the first embodiment will be described.

The position detection method according to the first embodiment includes a step S1 for acquiring a template image and information related thereto, and a step S2 for detecting the rotation angle of the scale unit 2 based on the acquired template image. According to such a position detection method, the detection accuracy can be improved even when the shaft runout is involved.

FIG. 7 is a flowchart showing a position detection method according to the first embodiment. FIG. 8 is a flowchart showing step S1 in detail among the position detection methods shown in FIG. 7. FIG. 9 is a diagram for explaining step S1 shown in FIG. 7. FIG. 10 is a list showing calibration angles, template images, reference coordinates, and coefficients acquired by the position detection method shown in FIG.

Step S1 includes steps S101 to S114, as shown in FIG. Hereinafter, each step will be described.

2.2.1. Acquisition of template image, etc. In step S1 shown in FIG. 7, a template image used for template matching and related to the template image are used prior to estimating the relative rotation state of the first arm 120 with respect to the base 110 using template matching. Get a dataset that contains information. The acquisition of the template image or the like may be performed only once before the first template matching, but may be performed after that as needed. In that case, the template image used for template matching can be updated with the newly acquired template image.

In step S1, first, as step S101, the rotation shaft of the encoder 1 and a calibration encoder (not shown) are mechanically connected. The calibration encoder is an angle calibration encoder that detects the rotation angle of the rotation shaft of the encoder 1, that is, the position of the scale unit 2 with sufficiently high accuracy. As a result, highly accurate angle information can be added to the template image.

Next, in step S102, the rotation shaft of the encoder 1 is rotated to align the scale portion 2 with the start angle. The start angle is not particularly limited, but is a rotation angle when one of the plurality of marks 21 included in the scale unit 2 is captured in the image captured by the image sensor 31.

Here, the rotation angle of the rotation shaft of the encoder 1 detected by the calibration encoder, that is, the rotation angle of the scale unit 2 is defined as the calibration angle θ [i]. The variable i is a value corresponding to the number assigned to the mark 21 along the circumferential direction DC, and takes an integer from 0 to n corresponding to the number n + 1 of the marks 21 provided in the scale unit 2.

Next, in step S103, the variable i is set to 0. When the rotation axis of the encoder 1 is at the start angle described above, one of the marks 21 is captured in the image captured by the image sensor 31.

Next, as step S104, the storage unit 6 stores the calibration angle θ [i] (first position). Here, since 0 is set as the variable i, the calibration angle θ [0] is stored.

Next, in step S105, the image sensor 31 of the encoder 1 is made to image the mark 21. As a result, the captured image [i] (first reference image) is generated. Here, since 0 is set as the variable i, the captured image [0] is generated. In the captured image [0], the unique pattern UP included in the mark 21 corresponding to the calibration angle θ [0] is captured. The generated captured image [0] is temporarily stored in the storage unit 6.

Next, in step S106, it is determined whether or not the variable i is larger than 0. If the variable i is larger than 0, the process proceeds to steps S107 and S108. If the variable i is 0, the process proceeds to steps S109 to S114. Since the variable i is 0 at this point, steps S109 to S114 will be described first, and steps S107 and S108 will be described later.

In step S109, it is determined whether or not the variable i is n or less. If this variable i is n or less, it is necessary to continue to acquire the template image described later, so the process proceeds to step S110. When the variable i is larger than n, that is, when it is n + 1, it means that the acquisition of the template image is completed for all the marks 21, so the step flow for acquiring the template image and the like is completed. Since the variable i is 0 at this point, step S110 and the like will be described first in the following description.

In step S110, the captured image [i] (first reference image) is read from the storage unit 6, and the cutout position of the captured image [i] is determined so that the unique pattern UP is included without being chipped. Here, since 0 is set as the variable i, the cutout position of the captured image [0] is determined.

In step S111, the coordinates of the upper left end of the cutout position in the captured image [i] are set as the reference coordinates [i] (first reference coordinates). Here, since 0 is set as the variable i, the coordinates of the upper left end of the cutout position in the captured image [i] are set as the reference coordinates [0].

In step S112, an image of the unique pattern UP is cut out based on the reference coordinate [i] of the captured image [i]. As a result, the template image [i] (first template image) is acquired. Here, since 0 is set as the variable i, the template image [0] is acquired. The acquired template image [0] and reference coordinates [0] are stored in the storage unit 6. On the other hand, the temporarily stored captured image [i] is subsequently overwritten when it is discarded at an arbitrary timing or when a new captured image is generated.

As described above, in the present embodiment, when the template image [i] is acquired, a region including the unique pattern UP is selected as the cutout position from the captured image [i] having a size larger than that of the unique pattern UP. The method of adopting the image cut out from is adopted as the template image [i] is used. As a result, the template image [i] can be acquired without increasing the formation accuracy of the unique pattern UP more than necessary. Therefore, the scale portion 2 can be easily formed and the formation cost can be reduced. In other words, even when the scale portion 2 having a low forming accuracy is used, the low forming accuracy can be made unquestioned when the template image [i] is acquired.

FIG. 9 shows an example of an captured image [0] captured when the rotation axis of the encoder 1 is at the calibration angle θ [0]. Among the plurality of marks 21 captured in the captured image [0], the one close to the center of the image is selected, the unique pattern UP is specified from the mark 21, and the region including the mark without being chipped is set as the cutout position. Then, the coordinates of the upper left end of the cutout position are obtained from the captured image [0], and this is obtained as the reference coordinate [0]. Further, the image of the unique pattern UP included in the cutout position is cut out as a template image [0] as shown in FIG.

Next, in step S113, the rotation axis of the encoder 1 is advanced by a predetermined angle. The predetermined angle is, for example, an angle corresponding to the arrangement interval of the marks 21. At the calibration angle θ [i], the mark 21 captured near the center of the captured image [i] and the mark 21 adjacent thereto are separated from each other. It is an angle corresponding to an angle. As a result, the image sensor 31 can capture the adjacent mark 21, that is, the mark 21 corresponding to the calibration angle θ [i2] described later, in the field of view.

Next, in step S114, i + 1 is set as the variable i (the variable i is updated). Here, in order to distinguish between the variable i before the update and the variable i after the update, the variable i after the update is referred to as “i2”. In each flowchart, the variable i is used without distinguishing between before and after the update for convenience of illustration.

Immediately before this step S114, 0 was set as the variable i, so in this step S114, 1 is set as the variable i2. When step S114 is completed, the step flow returns to step S104.

Also in the second step S104, the storage unit 6 stores the calibration angle θ [i2] (second position). Here, since 1 is set as the variable i2, the calibration angle θ [1] is stored.

Also in the second step S105, the image sensor 31 is made to image the mark 21. As a result, the captured image [i2] (second reference image) is generated. Here, since 1 is set as the variable i2, the captured image [1] is generated. In the captured image [1], the unique pattern UP included in the mark 21 corresponding to the calibration angle θ [1] is captured. The generated captured image [1] is temporarily stored in the storage unit 6.

Also in the second step S106, it is determined whether or not the variable i2 is larger than 0. If the variable i2 is larger than 0, the process proceeds to steps S107 and S108. In the example of this explanation, since the variable i2 is 1 at this point, steps S107 and S108 will be described below.

In step S107, the template image [i2-1] (first template image) is read out from the storage unit 6, and template matching is performed on the generated captured image [i2] (second reference image). Then, in the captured image [i2], the unique pattern UP that matches the template image [i2-1] is captured. Therefore, the coordinates of the upper left end of the captured unique pattern UP are set to the matching coordinates [i2-1] (first match). Coordinates). Here, since 1 is set as the variable i2, the template image [0] is read out, and template matching is performed on the generated captured image [1]. Then, the matching coordinates [0] are obtained.

In step S107, a process called sub-pixel estimation may be performed when performing template matching. According to the sub-pixel estimation, when the position of the unique pattern UP is estimated by template matching, the position can be estimated in units of one pixel or less. As a result, the matching coordinates [i2-1] (first matching coordinates) can be obtained with higher accuracy.

Hereinafter, template matching and sub-pixel estimation will be described.
FIG. 11 is a diagram for explaining an image captured by an image pickup device included in the encoder shown in FIG.

When the first arm 120 rotates around the first axis J1 with respect to the base 110, for example, as shown in FIG. 11, a unique image of the unique pattern UP reflected in the image G of the image sensor 31. The pattern image 22A moves in the captured image G along the arcs C1 and C2. Here, the arc C1 is a locus drawn by the lower center of FIG. 11 of the unique pattern image 22A with the rotation of the first arm 120 with respect to the base 110, and the arc C2 is the rotation of the first arm 120 with respect to the base 110. It is a locus drawn by the upper end in FIG. 11 of the unique pattern image 22A with the movement. Further, FIG. 11 illustrates a case where three unique patterns UP belonging to different marks 21 are included in the imaging region RI shown in FIG. In addition to the unique pattern image 22A, the captured image G shown in FIG. 11 includes a unique pattern image 22B located on one side of the unique pattern image 22A in the circumferential direction DC. The unique pattern image 22X located on the other side is included.

Here, the captured image G obtained by imaging by the image sensor 31 has a shape corresponding to the imaging region RI, and extends along the two sides extending in the X-axis direction and the Y-axis direction. It forms a rectangle with two sides. Further, the two sides extending along the X-axis direction of the captured image G are arranged so as to be along the arcs C1 and C2 as much as possible. Further, the captured image G has a plurality of pixels arranged in a matrix in the X-axis direction and the Y-axis direction. Here, the pixel positions are represented by a pixel coordinate system (X, Y) represented by "X" indicating the position of the pixel in the X-axis direction and "Y" indicating the position of the pixel in the Y-axis direction. expressed. Further, the pixel at the upper left end in the figure of the captured image G is set to the origin pixel P0 (0,0) of the image coordinate system (X, Y).

For example, when generating the template image TA corresponding to the unique pattern image 22A, the first arm 120 is appropriately rotated with respect to the base 110, and the unique pattern image 22A is placed at a predetermined position in the captured image G, for example, FIG. , Positioned on the center line LY set in the center of the captured image G in the X-axis direction.

By trimming the captured image G shown in FIG. 11 in a rectangular pixel range that is the minimum necessary range including the unique pattern image 22A, a template image TA for detecting the unique pattern UP can be obtained. obtain. The obtained template image TA is stored in the storage unit 6. At this time, the template image TA is stored in association with the coordinate information related to the reference coordinates (XA0, YA0) which are the coordinates of the upper left pixel of the template image TA of FIG. As a result, the template image TA, the angle information, and the coordinate information become one template set used for template matching.

FIG. 12 is a diagram for explaining template matching in the search region set in the captured image shown in FIG. FIG. 13 is a diagram showing a state in which the correlation value is deviated by one pixel from the state in which the correlation value is the maximum or the minimum at the time of template matching. FIG. 14 is a diagram showing a state in which the correlation value becomes the maximum or the minimum during template matching. FIG. 15 is a diagram showing a state in which the correlation value is deviated by one pixel from the state in which the correlation value is maximum or minimum during template matching to the side opposite to the state shown in FIG.

As shown in FIG. 12, when the unique pattern image 22A exists in the captured image G, template matching is performed on the image of the captured image G using the template image TA. In the present embodiment, the entire area of the captured image G is set as the search area RS, the template image TA is superimposed on the search area RS, and the template image TA is shifted by one pixel from the search area RS, and the search area RS and the template image TA are combined. Calculate the correlation value of the overlapping part. Here, the template image TA moves its pixel coordinates from the start coordinate PS (origin pixel P0) to the end pixel PE one by one, and for the pixels in the entire search area RS, the overlapping portion of the search area RS and the template image TA. Correlation value is calculated for each pixel coordinate of the template image TA. Then, the calculated correlation value is associated with the pixel coordinates of the template image TA and temporarily stored in the storage unit 6.

Next, the maximum correlation value is selected from the plurality of correlation values stored in the storage unit 6 for each pixel coordinate, and the pixel coordinates (XA1, YA1) of the template image TA that becomes the selected correlation value. ) Is determined as the pixel coordinates of the unique pattern image 22A. In this way, the position of the unique pattern image 22A in the captured image G can be detected. Then, the pixel coordinates (XA1, YA1) become the above-mentioned "matching coordinates".

Here, when obtaining the pixel coordinates of the unique pattern image 22A, it is preferable to use the sub-pixel estimation method. In the vicinity where the correlation value is maximum, the template image TA overlaps with the unique pattern image 22A, as shown in FIGS. 13 to 15. The state shown in FIG. 14 has a larger correlation value and the largest correlation value than the state shown in FIGS. 13 and 15, that is, the state deviated by one pixel from the state shown in FIG. However, as in the state shown in FIG. 14, when the template image TA does not completely match the unique pattern image 22A and overlaps with each other, the state shown in FIG. 14 is the same as the pixel coordinates of the unique pattern image 22A described above. If it is judged as the coordinates, the deviation becomes an error. This deviation is the field of view size BX per pixel at the maximum. That is, when the sub-pixel estimation method is not used, the field of view size BX per pixel is the minimum resolution (accuracy). On the other hand, when the sub-pixel estimation method is used, the correlation values for each field size BX per pixel are fitted by a parabola, an equiangular straight line, or the like, and the correlation values (between pixel pitches) are complemented (approximate). be able to. Therefore, the pixel coordinates of the unique pattern image 22A can be obtained with higher accuracy. In the above description, the case where the pixel coordinate having the maximum correlation value is the pixel position of the unique pattern image 22A has been described as an example, but the pixel coordinate having the minimum correlation value is the pixel position of the unique pattern image 22A. It is also possible to perform template matching so that

In the next step S108, the calibration angle θ [i2-1] (first position), the calibration angle θ [i2] (second position), and the reference coordinates [i2-1] (first reference coordinates) are matched. The correlation established between the coordinates [i2-1] (first matching coordinates) and the coordinates [i2-1] is obtained. Here, since 1 is set as the variable i2, the correlation established between the calibration angle θ [0], the calibration angle θ [1], the reference coordinate [0], and the matching coordinate [0]. Ask for. This correlation shows the correlation between the rotation angle of the scale unit 2 and the distance in the captured image G, and may be expressed in any form, but in step S2 described later. , The rotation angle θ can be calculated back from the matching coordinates [i2-1] and the reference coordinates [i2-1] by template matching.

As a specific form of the correlation, for example, the calibration angle θ [with respect to the amount of movement from the reference coordinate [i2-1] (first reference coordinate) to the matching coordinate [i2-1] (first matching coordinate). The coefficient [i2-1] obtained as the ratio of the amount of change from the i2-1] (first position) to the calibration angle θ [i2] (second position) can be mentioned. As a form of correlation, for example, a list (calculation table) obtained by back-calculating the rotation angle θ from the matching coordinates and the reference coordinates can be considered, but in this case, when it takes time to calculate the rotation angle θ. There is also. On the other hand, by calculating such a coefficient [i2-1] and storing it in the storage unit 6, when the rotation angle θ is back-calculated in step S2 described later, the calculation speed can be increased. it can.
This coefficient [i2-1] is as follows when formulated.

After the end of step S108, the process proceeds to the second step S109.
Also in the second step S109, as described above, it is determined whether or not the variable i2 is n or less. Here, since the variable i2 is 1, the process proceeds to step S110.

In the second step S110, the captured image [i2] (second reference image) is read from the storage unit 6, and the cutout position of the captured image [i2] is determined so that the unique pattern UP is included without being chipped. Here, since 1 is set as the variable i2, the cutout position of the captured image [1] is determined.

In the second step S111, the coordinates of the upper left end of the cutout position in the captured image [i2] are set as the reference coordinates [i2] (second reference coordinates). Here, since 1 is set as the variable i2, the coordinates of the upper left end of the cutout position in the captured image [i2] are set as the reference coordinates [1].

In the second step S112, an image of the unique pattern UP is cut out based on the reference coordinates [i2] of the captured image [i2]. As a result, the template image [i2] (second template image) is acquired. Here, since 1 is set as the variable i2, the template image [1] is acquired. The acquired template image [1] and reference coordinates [1] are stored in the storage unit 6.

FIG. 9 shows an example of the captured image [1] captured when the scale unit 2 is at the calibration angle θ [1]. Then, the coordinates of the upper left end of the cutout position are obtained from the captured image [1], and this is obtained as the reference coordinate [1]. Further, the image of the unique pattern UP included in the cutout position is cut out as a template image [1] as shown in FIG.

Next, also in the second step S113, the rotation axis of the encoder 1 is advanced by a predetermined angle.
Next, in the second step S114, i2 + 1 is set as the variable i2 (the variable i2 is updated). Here, in order to distinguish between the variable i2 before the update and the variable i2 after the update, the variable i2 after the update is referred to as "i3". In each flowchart, the variable i is used without distinguishing between before and after the update for convenience of illustration.

Immediately before this step S114, 1 was set as the variable i2, so that 2 is set as the variable i3 in this step S114. When step S114 is completed, the step flow returns to step S104.

Also in the third step S104, the storage unit 6 stores the calibration angle θ [i3] (third position). Here, since 2 is set as the variable i3, the calibration angle θ [2] is stored.

Also in the third step S105, the image sensor 31 is made to image the mark 21. As a result, the captured image [i3] (third reference image) is generated. Here, since 2 is set as the variable i3, the captured image [2] is generated. In the captured image [2], the unique pattern UP included in the mark 21 corresponding to the calibration angle θ [2] is captured. The generated captured image [2] is temporarily stored in the storage unit 6.

Also in the third step S106, it is determined whether or not the variable i3 is larger than 0. If the variable i3 is larger than 0, the process proceeds to steps S107 and S108. In the example of this explanation, since the variable i3 is 2 at this point, steps S107 and S108 will be described below.

In the second step S107, the template image [i3-1] (second template image) is read out from the storage unit 6, and template matching is performed with the generated captured image [i3] (third reference image). Then, in the captured image [i3], the unique pattern UP that matches the template image [i3-1] is captured. Therefore, the coordinates of the upper left end of the captured unique pattern UP are set to the matching coordinates [i3-1] (second match). Coordinates). Here, since 2 is set as the variable i3, the template image [1] is read out, and template matching is performed on the generated captured image [2]. Then, the matching coordinates [1] are obtained. The obtained matching coordinates [1] are temporarily stored in the storage unit 6.

In the second step S108, the calibration angle θ [i3-1] (second position), the calibration angle θ [i3] (third position), the reference coordinates [i3-1] (second reference coordinates), and the like. The correlation established between the matching coordinates [i3-1] (second matching coordinates) and the matching coordinates is obtained.

As a specific form of the correlation, for example, the calibration angle θ [with respect to the movement amount from the reference coordinate [i3-1] (second reference coordinate) to the match coordinate [i3-1] (second match coordinate). The coefficient [i3-1] obtained as the ratio of the amount of change from the i3-1] (second position) to the calibration angle θ [i3] (third position) can be mentioned.
This coefficient [i3-1] is as follows when formulated.

After the completion of the second step S108, the process proceeds to the third step S109.
Also in the third step S109, as described above, it is determined whether or not the variable i3 is n or less. Here, since the variable i3 is 2, the process proceeds to step S110. After that, the step flow is advanced in the same manner as in steps S110 to S114 described above, and then the process returns to step S104. In step S114, i3 + 1 is set as the variable i3 (the variable i3 is updated). The updated variable i3 is referred to as "i4".

Subsequently, in the same manner, the fourth steps S104 to S106 and the third steps S107 and S108 can be performed to obtain the coefficient [i4-1].

After that, the coefficient [i5-1], the coefficient [i6-1], ..., The coefficient [i (n + 1) -1] can be obtained in the same manner. As a result, for all the marks 21, the correlation by the coefficient can be obtained and stored in the storage unit 6. Then, by using these correlations, it is possible to obtain a highly accurate rotation angle in step S2, which will be described later, regardless of the rotation angle of the rotation shaft of the encoder 1.

After that, the process proceeds to step S109 again. In step S109, as described above, it is determined whether or not the variable i (n + 2) is n or less. After obtaining the correlation for all the marks 21 (all calibration angles θ [i]), since n + 1 is set as the variable i (n + 2), the step flow shown in FIG. 8 ends. At this time, since the calibration encoder is unnecessary, the calibration encoder is removed after the determination in step S109 (step S120).

As described above, it is possible to obtain a data set composed of the calibration angle, the template image, the reference coordinates, and the coefficients necessary for detecting the rotation angle in step S2 described later.

2.2.2. Detection of Rotation Angle In step S2 shown in FIG. 7, the rotation angle of the rotation shaft of the encoder 1 is detected using the data set acquired in step S1.

Step S2 includes steps S201 to S203, as shown in FIG. Hereinafter, each step will be described.

In step S2, first, in step S201, when the rotation axis of the encoder 1 is at an unknown rotation angle θ (measurement position), the image sensor 31 is made to image the mark 21. As a result, an angle measurement image (positioning image) is generated. The generated angle measurement image is stored in the storage unit 6.
The rotation angle θ is assumed to be between the calibration angle θ [i] and the calibration angle θ [i2].

In the next step S202, the angle measurement image and the template image [i] acquired in step S1 are read out from the storage unit 6, and template matching is performed on the angle measurement image. At the time of template matching, sub-pixel estimation is performed as necessary. By performing template matching, the unique pattern UP that matches the template image [i] is captured in the angled image, so the coordinates of the upper left end of the captured unique pattern UP are set as the angled matching coordinates. The obtained angle measurement matching coordinates are stored in the storage unit 6.

In the next step S203, the angle measurement matching coordinates are read from the storage unit 6. Further, the reference coordinates [i] and the coefficients [i] acquired in step S1 are read out. Then, the rotation angle θ is calculated by the following formula.
Rotation angle θ = Calibration angle θ [i] + (angle measurement matching coordinates-reference coordinates [i]) × coefficient [i]

As described above, the rotation angle θ can be calculated. The calculated rotation angle θ is output from the circuit unit 4, and is used, for example, in the control device of the robot 100 for driving control of the arm. In the present embodiment, an example is shown in which the angle measurement image generated in S2 is stored in the storage unit 6 and then the angle measurement matching coordinates are acquired by using template matching, but the processing unit 5 has a plurality of processing devices. It is preferable that the processing unit 5 performs template matching processing every time the angle measuring pixel is transferred from the image sensor 31 to the processing unit 5, and causes the generation of the angled image and the acquisition of the angled matching coordinates to be processed in parallel.

As described above, the position detection method according to the present embodiment is a method of detecting the position of the scale unit 2, for example, the rotation angle of the scale unit 2 by using the encoder 1 having the scale unit 2 and the image sensor 31. is there. Of these, the scale unit 2 has a plurality of marks 21. The image sensor 31 is an element that captures the mark 21. The encoder 1 is configured such that the scale unit 2 moves relative to the image sensor 31.

Such a position detection method includes a step S1 including the above-mentioned steps S101 to S114 and a step S2 including the above-mentioned steps S201 to S203.

Of these, in steps S104, S105, and S110 to S112, when the scale unit 2 is at the calibration angle θ [i] (first position), the image sensor 31 is made to image the mark 21 and the captured image [i] (first position). This is a step of generating a reference image) and acquiring the template image [i] (first template image) and the reference coordinates [i] (first reference coordinates) of the mark 21 in the captured image [i].

In steps S104, S105, and S107, when the scale unit 2 is at the calibration angle θ [i2] (second position), the image sensor 31 is made to image the mark 21 to generate an image [i2] (second reference image). Then, by template matching based on the template image [i2-1] (first template image), the matching coordinates [i2-1] (first) of the mark 21 that matches the template image [i2-1] in the captured image [i2]. It is a step to acquire the matching coordinates).

In step S108, the calibration angle θ [i2-1] (first position) and the calibration angle θ [i2] (second position) are correlated with the rotation angle of the scale unit 2 and the distance in the captured image G. In the step of finding the correlation that holds between the reference coordinate [i2-1] (first reference coordinate) and the matching coordinate [i2-1] (first matching coordinate), for example, the coefficient [i2-1]. is there.

In steps S201 and S202, when the rotation angle of the encoder 1 is at the rotation angle θ (measurement position), the image sensor 31 is made to image the mark 21 to generate an angle measurement image (positioning image). Then, it is a step of acquiring the angle measurement matching coordinates (positioning matching coordinates) of the mark 21 in the angle measurement image by template matching based on the template image [i2-1] (first template image).

Then, in step S203, the calibration angle θ [i2-1] (first position), the reference coordinates [i2-1] (first reference coordinates), the angle measurement matching coordinates, and the correlation (coefficient [i2-1]). This is a step of obtaining the rotation angle θ (measurement position) based on.

In such a position detection method, since the rotation angle θ is calculated by using the template image acquired in advance and template matching at the time of measurement, the positional deviation of the mark 21 at the time of forming the scale portion 2 is the rotation angle θ. It does not easily affect the accuracy of. Therefore, the encoder unit 10 which can easily improve the detection accuracy, is easy to manufacture, and is low in cost can be obtained.

Further, in the conventional image pickup type rotary encoder, in order to detect the rotation angle θ, parameters such as the image pickup magnification of the image sensor (camera) and the distance between the rotation axis of the rotating scale portion and the mark are measured in advance. It is necessary to keep it. If the measured values of these parameters deviate from the actual values, the error of the detected rotation angle θ becomes large. However, it is difficult to measure these parameters exactly, and individual differences due to manufacturing variations cannot be ignored.

On the other hand, in the present embodiment, the rotation angle θ is calculated based on the image in which these parameters are reflected by using the correlation between the rotation angle and the distance in the captured image and template matching. The rotation angle θ can be detected with high accuracy without actually measuring these parameters in advance. Further, since the proofreading work of acquiring the template image and deriving the above-mentioned correlation is also performed by using template matching, it can be performed in a relatively short time. Therefore, according to the present embodiment, it is possible to realize a position detection method capable of detecting the rotation angle θ with high accuracy even by using the encoder unit 10 which is easy to manufacture and can reduce the cost.

As described above, the encoder according to the present invention can also be applied to a linear encoder, but the encoder 1 according to the present embodiment is a rotary encoder. As a result, the encoder unit 10 capable of detecting the rotation angle θ with high accuracy can be realized.

Further, the encoder unit 10 according to the present embodiment includes an encoder 1, a processing unit 5, and a storage unit 6. Of these, the encoder 1 has a scale unit 2 and an image sensor 31, and the scale unit 2 is configured to rotate (move) relative to the image sensor 31. The scale unit 2 has a plurality of marks 21. The image sensor 31 is an element that captures the mark 21. The processing unit 5 executes a process of obtaining the position of the scale unit 2, for example, the rotation angle of the scale unit 2 based on the image pickup result of the image sensor 31. The storage unit 6 stores an instruction that can be read by the processing unit 5.

In such an encoder unit 10, when the scale unit 2 is at the calibration angle θ [i] (first position), the image sensor 31 is made to image the mark 21 to generate an captured image [i] (first reference image). Then, the template image [i] (first template image) and the reference coordinates [i] (first reference coordinates) of the mark 21 in the captured image [i] are acquired.

Further, when the scale unit 2 is at the calibration angle θ [i2] (second position), the encoder unit 10 causes the image pickup element 31 to image the mark 21 to generate an image pickup image [i2] (second reference image). , Matching coordinates [i2-1] (first matching) of the mark 21 that matches the template image [i2-1] in the captured image [i2] by template matching based on the template image [i2-1] (first template image). Coordinates).

Further, the encoder unit 10 has a calibration angle θ [i2-1] (first position) and a calibration angle θ [i2] (first position) as a correlation between the rotation angle of the scale unit 2 and the distance in the captured image G. 2 positions), the reference coordinates [i2-1] (first reference coordinates), and the matching coordinates [i2-1] (first matching coordinates), for example, the coefficient [i2-1]. Ask.

Further, when the rotation angle of the encoder 1 is at the rotation angle θ (measurement position), the encoder unit 10 causes the image pickup element 31 to image the mark 21 to generate an angle measurement image (positioning image). Then, by template matching based on the template image [i2-1] (first template image), the angle measurement matching coordinates (positioning matching coordinates) of the mark 21 in the angle measurement image are acquired.

Further, the encoder unit 10 has a calibration angle θ [i2-1] (first position), reference coordinates [i2-1] (first reference coordinates), matching coordinates [i2-1] (first matching coordinates), and The rotation angle θ (measurement position) is obtained based on the correlation (coefficient [i2-1]).

In such an encoder unit 10, since the rotation angle θ is calculated by using the template image acquired in advance and template matching at the time of measurement, the positional deviation of the mark 21 at the time of forming the scale portion 2 is the rotation angle θ. It does not easily affect the accuracy of. Therefore, the encoder unit 10 which can easily improve the detection accuracy, is easy to manufacture, and is low in cost can be obtained.

Further, the robot 100 according to the present embodiment includes a base 110 which is a first member, a first arm 120 which is a second member which moves with respect to the base 110, and an encoder unit 10. The scale unit 2 is provided on the first arm 120, and the image sensor 31 is provided on the base 110.

According to such a robot 100, since the accuracy of the rotation angle of the first arm 120 detected by the encoder unit 10 is high, the first arm 120 can be controlled with high accuracy. As a result, it is possible to realize a highly reliable robot 100 capable of performing more accurate and delicate work.

3. 3. Second Embodiment Next, the position detection method according to the second embodiment will be described.

FIG. 16 is a flowchart showing step S1 in detail in the position detection method according to the second embodiment. FIG. 17 is a list showing calibration angles, template images, reference coordinates, and coefficients acquired by the position detection method shown in FIG.

Hereinafter, the second embodiment will be described, but in the following description, the differences from the first embodiment will be mainly described, and the same matters will be omitted. Further, in FIGS. 16 and 17, the same reference numerals are given to the same configurations as those in the first embodiment.

The second embodiment is the same as the first embodiment except that the coefficients are different. Specifically, in the first embodiment described above, a coefficient is calculated for each calibration angle and used for calculating the rotation angle θ. On the other hand, in the second embodiment, the average coefficient is calculated at a plurality of calibration angles and used for calculating the rotation angle θ regardless of the calibration angle.

3.1. Acquisition of template image and the like The position detection method shown in FIG. 16 includes step S108A instead of step S108 shown in FIG.

In step S108A, as in step S108 according to the first embodiment, first, all the marks 21, that is, all of the calibration angles θ [i] from i = 0 to i = n, are respectively.
Movement amount [i] = Match coordinates [i] -Reference coordinates [i]
Calculate the movement amount [i] defined in.
Then, these movement amounts [i] are added up by the following equation to obtain the cumulative movement amount.

In the above equation, m is an arbitrary integer of m ≦ n.
Then, the average coefficient defined by the following equation is obtained.

The average coefficient thus obtained replaces the coefficient set for each calibration angle θ [i] in the first embodiment in common with all calibration angles θ [i] as shown in FIG. be able to. As a result, it is not necessary to calculate individual coefficients for each calibration angle θ [i] and store them in the storage unit 6, and only one average coefficient needs to be stored. As a result, it is possible to save labor in calculation and reduce the amount of use of the storage unit 6.

The above-mentioned average coefficient is calculated using the cumulative movement amount obtained by adding the movement amounts [i] for all the calibration angles θ [i], but is not limited to all, and the cumulative movement is limited to only a part. You may ask for the quantity. That is, the integer m when calculating the above-mentioned average coefficient may be less than n. Further, the above-mentioned cumulative movement amount may be calculated after obtaining all the movement amounts [i], but the cumulative movement amount is updated by accumulating the movement amount [i] at any time as described below. It may be calculated by a method.

Here, the step flow of the position detection method according to the present embodiment will be described with reference to FIG.

First, in step S103, the variable i is set to 0, and the cumulative movement amount is also reset to 0.

In the first step S108A, since the variable i is updated to the variable i2, the calibration angle θ [i2-1] (first position), the calibration angle θ [i2] (second position), and the reference coordinates. [I2-1] (first reference coordinates) and matching coordinates [i2-1] (first matching coordinates) are obtained. Then, the cumulative movement amount is updated by the following formula.
Cumulative movement amount after update = Cumulative movement amount before update + Match coordinates [i2-1] -Reference coordinates [i2-1]

Here, since 1 is set as the variable i2, the calibration angle θ [0], the calibration angle θ [1], the reference coordinate [0], and the matching coordinate [0] are obtained. Since the cumulative movement amount before the update is 0, the cumulative movement amount after the update is obtained by the matching coordinate [0] -reference coordinate [0].

In the second step S108A, since the variable i2 has been updated to the variable i3, the calibration angle θ [i3-1] (second position), the calibration angle θ [i3] (third position), and the reference coordinates. [I3-1] (second reference coordinates) and matching coordinates [i3-1] (second matching coordinates) are obtained. Then, the cumulative movement amount is updated by the following formula.
Cumulative movement amount after update = Cumulative movement amount before update + Match coordinates [i3-1] -Reference coordinates [i3-1]

Here, since 2 is set as the variable i3, the calibration angle θ [1], the calibration angle θ [2], the reference coordinate [1], and the matching coordinate [1] are obtained. Then, the cumulative movement amount after the update is obtained by the cumulative movement amount before the update + the matching coordinate [1] -reference coordinate [1].

Then, each time the variable is updated, the cumulative movement amount can be updated at any time by repeating step S108A as described above. Then, the above-mentioned average coefficient can be obtained from the cumulative movement amount finally obtained.

Specifically, in the first embodiment, the step flow is terminated after the transition of the final step S109, but in the present embodiment, the step S115 is added after the final step S109.

In step S115, first, the total amount of change from the first calibration angle θ [0] to the last calibration angle θ [m + 1] when the template image is acquired is set to the calibration angle θ [m + 1] − calibration angle θ [0]. Obtained by. Then, the average coefficient is calculated by the above-mentioned formula. At this time, since the calibration encoder is unnecessary, the calibration encoder is removed after step S115 (step S120).

3.2. Detection of rotation angle In the first embodiment described above, the rotation angle θ is determined by using the coefficient [i] peculiar to the calibration angle θ [i] and the difference between the positioning matching coordinates and the reference coordinates [i]. calculate. On the other hand, the reference image and the angle measurement image captured by the image sensor 31 are used for the calculation of each coefficient [i], and these images include random noise that is inevitably generated. Therefore, each coefficient [i] includes a measurement error due to random noise.

On the other hand, in the present embodiment, the average coefficient is obtained from the cumulative amount of movement, and the rotation angle θ is calculated using this. Specifically, the rotation angle θ is calculated by the following formula.
Rotation angle θ = Calibration angle θ [i] + (angle measurement matching coordinates-reference coordinates [i]) × average coefficient

Here, it is known that the above-mentioned random noise follows a normal distribution. Therefore, the process of calculating the average coefficient of obtaining the cumulative movement amount in step S1 has an effect of converging the measurement error caused by the random noise following the normal distribution to the average value of zero. Therefore, in the rotation angle θ calculated by the above formula, the occurrence of measurement error due to random noise is suppressed. Therefore, according to the present embodiment, the measurement error is smaller than that of the first embodiment, and the rotation angle θ can be detected with higher accuracy.

As described above, in the position detection method according to the present embodiment, the total change amount of at least two calibration angles and the cumulative movement amount obtained by accumulating at least two movement amounts are obtained, and the average coefficient which is the ratio of these is obtained. In other words, it can be rephrased as a method of calculating the rotation angle θ using.

Specifically, in the first steps S104, S105, and S110 to S112, when the scale unit 2 is at the calibration angle θ [i] (first position), the image sensor 31 is made to image the mark 21 and the captured image [ i] (first reference image) is generated, and the template image [i] (first template image) and the reference coordinates [i] (first reference coordinates) of the mark 21 in the captured image [i] are acquired.

Further, in the second steps S104, S105, and S110 to S112, when the scale unit 2 is at the calibration angle θ [i2] (second position), the image sensor 31 is made to image the mark 21 and the captured image [i2] ( The second reference image) is generated, and the template image [i2] (second template image) and the reference coordinates [i2] (second reference coordinates) of the mark 21 in the captured image [i2] are acquired.

Further, in the third step S104, S105, S110 to S112, when the scale unit 2 is at the calibration angle θ [i3] (third position), the image sensor 31 is made to image the mark 21 and the captured image [i3] ( Third reference image) is generated. The mark 21 included in the captured image [i3] is located on the opposite side of the mark 21 included in the captured image [i2] to the mark 21 included in the captured image [i]. Then, by template matching based on the template image [i3-1] (second template image), the matching coordinates [i3-1] (second) of the mark 21 that matches the template image [i3-1] in the captured image [i3]. Match coordinates) is acquired.

The position detection method according to the present embodiment has the above steps. Then, the total change amount of at least two calibration angles is obtained as the total change amount from the calibration angle θ [i] (first position) to the calibration angle θ [i3] (third position). Further, the cumulative movement amount obtained by accumulating at least two movement amounts is obtained as the cumulative movement amount from the reference coordinate [i] (first reference coordinate) to the matching coordinate [i3-1] (second matching coordinate). Then, in the present embodiment, as the correlation used for back-calculating the rotation angle θ, the average coefficient obtained as the ratio of the total change amount to the cumulative movement amount is used.

According to such a method, as described above, it is not necessary to calculate individual coefficients for each calibration angle i and store them in the storage unit 6, and only one average coefficient needs to be stored. It is possible to save labor in calculation and reduce the amount of use of the storage unit 6. Further, as compared with the first embodiment, the influence of the measurement error due to the random noise can be reduced.
In the second embodiment as described above, the same effect as that of the first embodiment can be obtained.

Although the position detection method, the encoder unit, and the robot of the present invention have been described above based on the preferred embodiments shown in the drawings, the present invention is not limited thereto, and the configuration of each part is arbitrary having the same function. Can be replaced with the one of the configuration of. Moreover, other arbitrary components may be added.

Further, the encoder unit of the present invention can be applied to both absolute type and incremental type.

Further, in the above-described embodiment, the case where the base of the robot is the “first member” and the first arm is the “second member” has been described as an example, but the present invention is not limited to this, and the robot rotates relatively. One of any two members can be referred to as a "first member" and the other can be referred to as a "second member". That is, the location where the encoder is installed is not limited to the joint between the base and the first arm, and may be the joint of any two arms that rotate relative to each other. Further, the installation location of the encoder is not limited to the joint portion of the robot.

Further, in the above-described embodiment, the number of robot arms is one, but the number of robot arms may be two or more. That is, the robot of the present invention may be a multi-arm robot such as a dual-arm robot, for example.

Further, in the above-described embodiment, the number of arms possessed by the robot arm is six, but the number of arms is not limited to this, and may be one, or two or more and five or less or seven. The above may be sufficient.

Further, the installation location of the robot is not limited to the floor surface, and may be, for example, a ceiling surface, a side wall surface, or a moving body such as an AGV (Automatic Guided Vehicle).

1 ... Encoder, 2 ... Scale unit, 3 ... Detection unit, 4 ... Circuit unit, 5 ... Processing unit, 6 ... Storage unit, 10 ... Encoder unit, 20 ... Dot, 21 ... Mark, 22A ... Unique pattern image, 22B ... Unique pattern image, 22X ... Unique pattern image, 31 ... Image sensor, 32 ... Optical system, 100 ... Robot, 110 ... Base, 111 ... Motor, 112 ... Reducer, 114 ... Support member, 115 ... Bearing, 120 ... No. 1 arm, 121 ... arm body, 122 ... shaft, 130 ... second arm, 140 ... work head, 141 ... spline shaft, 150 ... end effector, 160 ... wiring routing, 1111 ... rotation axis, BX ... field of view Size, C1 ... Arc, C2 ... Arc, DC ... Circumferential, DR ... Radial, G ... Image, J1 ... 1st axis, J2 ... 2nd axis, J3 ... 3rd axis, LY ... Centerline, P0 ... Origin pixel, PE ... End pixel, PS ... Start coordinate, RI ... Image area, RS ... Search area, S1 ... Step, S101 ... Step, S102 ... Step, S103 ... Step, S104 ... Step, S105 ... Step, S106 ... Step , S107 ... step, S108 ... step, S108A ... step, S109 ... step, S110 ... step, S111 ... step, S112 ... step, S113 ... step, S114 ... step, S115 ... step, S120 ... step, S2 ... step, S201 ... step, S202 ... step, S203 ... step, TA ... template image, UP ... unique pattern

Claims (7)

The position of the scale unit is detected by using an encoder having a scale unit having a plurality of marks and an image sensor that images the mark, and the scale unit moves relative to the image sensor. It is a position detection method
When the scale unit is in the first position, the mark is imaged by the image sensor to generate a first reference image, and the first template image and the first reference coordinates of the mark in the first reference image are obtained. Steps to get and
When the scale unit is in the second position, the mark is imaged by the image sensor to generate a second reference image, and template matching based on the first template image results in the first template in the second reference image. The step of acquiring the first matching coordinates of the mark that matches the image, and
A step of finding a correlation established between the first position, the second position, the first reference coordinate, and the first matching coordinate.
When the scale unit is at the measurement position, the mark is imaged by the image sensor to generate a positioning image, and the positioning matching coordinates of the mark in the positioning image are acquired by template matching based on the first template image. Steps and
A step of obtaining the measurement position based on the first position, the first reference coordinate, the positioning matching coordinate, and the correlation.
A position detection method comprising. The correlation is the coefficient obtained as a ratio of the amount of movement from the first reference coordinate to the first matching coordinate, and the amount of change from the first position to the second position, according to claim 1. Position detection method. When the scale portion is in the second position, the step of acquiring the second template image and the second reference coordinates of the mark in the second reference image, and
When the scale unit is in the third position, the mark is imaged by the image sensor to generate a third reference image, and template matching based on the second template image results in the second template in the third reference image. The step of acquiring the second matching coordinates of the mark that matches the image, and
Have,
The correlation is an average coefficient obtained as a ratio of the cumulative movement amount from the first reference coordinate to the second matching coordinate and the total change amount from the first position to the third position. The position detection method according to 1. The position detection method according to any one of claims 1 to 3, wherein the template matching is a process of estimating sub-pixels. An encoder having a scale unit having a plurality of marks, an image pickup element for capturing the mark, and the scale portion moving relative to the image pickup element.
A processing unit that executes a process of obtaining the position of the scale unit based on the image pickup result of the image sensor, and a processing unit.
A storage unit that stores instructions that can be read by the processing unit,
Have,
The processing unit is based on the instruction stored in the storage unit.
When the scale unit is in the first position, the image sensor is made to image the mark to generate a first reference image, and the first template image and the first reference coordinates of the mark in the first reference image are obtained. Acquired,
When the scale unit is in the second position, the image sensor is made to image the mark to generate a second reference image, and template matching based on the first template image is performed to obtain the first template in the second reference image. Obtain the first matching coordinates of the mark that matches the image,
The correlation established between the first position, the second position, the first reference coordinate, and the first matching coordinate is obtained.
When the scale unit is in the measurement position, the image sensor is made to image the mark to generate a positioning image, and the positioning matching coordinates of the mark in the positioning image are acquired by template matching based on the first template image. ,
An encoder unit characterized by executing a process of obtaining the measurement position based on the first position, the first reference coordinate, the positioning matching coordinate, and the correlation. The encoder unit according to claim 5, wherein the encoder is a rotary encoder. The first member and
A second member that moves with respect to the first member,
The encoder unit according to claim 5 or 6, and the encoder unit.
With
A robot characterized in that the scale portion is provided on the second member and the image pickup element is provided on the first member.

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