JPH05126532A - Method for measuring unit picture element length - Google Patents

Abstract

PURPOSE:To obtain a simple method for measuring the unit picture element length of a visual sensor. CONSTITUTION:By using at least one object 2 having dimensions which come in sight of a visual sensor 1 and a moving means which can move the object 2 and sensor 1 in two orthogonal directions without relatively rotating them against each other, the object 2 and sensor 1 are relatively moved against each other in the two directions by the same moving amount and the positions of the object 2 before and after the movement are calculated from the measured results of the sensor 1 and moved amount. The unit picture element of the sensor 1 can be obtained from a simple calculation formula and, since it is not necessary to make the measured position of the object 2 obtained by means of the sensor 1 to coincide with a known position on a coordinate system in the working space, the degree of freedom the object can be increased in its shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when measuring an object using a visual sensor, uses the information obtained in the coordinate system of the image captured by the visual sensor to determine the coordinates of the space where the actual work is performed. The present invention relates to a method of obtaining a unit pixel length which is one of the parameters for coordinate conversion necessary for conversion into a system.

[0002]

2. Description of the Related Art A visual sensor attached to a mechanical device such as an industrial robot determines the type of work, inspects whether the work is good, measures dimensions, etc., and selects the work corresponding to the result to operate the robot. Teaching is widely practiced.

For example, when measuring the size of an object with a visual sensor, the size of the object is first measured in the coordinate system of the image captured by the visual sensor and converted into the size in the coordinate system of the space in which the work is performed. By doing so, the actual size of the object can be known.

In order to perform the above-mentioned conversion, some coordinate conversion parameters are necessary. If the coordinate conversion parameters are not obtained in advance, the measurement result of the object by the visual sensor is used. You cannot continue working. This parameter has a unit pixel length that is a value that represents the size of one pixel in the vertical and horizontal directions, which is the unit of the image coordinate system, in the unit of the actual working space coordinate system. If this unit pixel length is obtained, the measurement result of the size and shape of the object by the visual sensor can be converted into a value in the working space coordinate system.

The conventional method for obtaining the unit pixel length is for teaching in which an object whose position and dimensions are known in the working space coordinate system is prepared, and the object is grasped by a visual sensor and measured in the image coordinate system. It is calculated from the relationship between the position and size of the object and the position and size of the teaching target in a known work space coordinate system.

For example, in Japanese Unexamined Patent Publication No. 61-132805, the marker is positioned so that the center of gravity of the marker coincides with at least two known distances in the visual field of the sensor, and the marker is then positioned at that time. There is presented a method of calculating the center of gravity of the sign, and then calculating the unit pixel length of the visual sensor from the calculated center of gravity of at least two points and the known distance.

[0007]

However, in the above-mentioned conventional method, the shape of the object to be taught is defined by a point (for example, the position of the center of gravity of the object image) that can be specified based on the measurement by the visual sensor. Must be a shape that can be positioned mechanically, and its position must be known in the workspace coordinate system. Further, it is necessary to bring a plurality of objects into the visual field of the visual sensor at the same time. Therefore, the work for obtaining the unit pixel length is complicated and troublesome.

Therefore, the present invention does not require the shape of the object and the alignment to the absolute position in the working space coordinate system, and obtains the unit pixel length by a single object and a simple calculation formula. The purpose is to provide a method.

[0009]

In order to achieve the above object, according to the present invention, at least one object whose position is stably measured by the visual sensor and at least one object on the imaging plane of the visual sensor. A moving means for relatively moving the visual sensor is prepared, and relative movement between the visual sensor and the object is performed by an equal amount of movement in two directions orthogonal to each other in the work space coordinate system, and movement is performed in each case. The unit pixel length is calculated from the relationship between the position and the movement amount of the object measured in the image coordinate system using the visual sensor before and after the movement.

At this time, the condition is that the object fits within the visual field of the visual sensor, and the dimension is such that it does not protrude from the visual field due to the relative movement of the object and the visual sensor. Further, the moving means can know the moving amount by the value of the same unit as the working space coordinate system, can move in two directions which are orthogonal to each other, and do not involve relative rotation at the time of moving. On the condition.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below with reference to the drawings. FIG. 1 shows a visual sensor 1 above the workspace coordinate system.
3 is a perspective view showing a state in which the visual sensor 1 is measuring the object 2 that is fixed and is installed on the upper surface of the XY stage 3. FIG. In this case, the XY stage 3 is a moving unit that gives relative movement between the visual sensor 1 and the object 2, and the imaging plane of the visual sensor 1 is the upper surface of the XY stage.

FIG. 2 and FIG. 3 show that, according to the procedure of the present invention, relative movement between the visual sensor 1 and the object 2 is performed in two directions which are at right angles to each other by an equal amount of movement, in each case. Shows the geometrical relationship of the position of the object 2 when the position of the center of gravity of the object 2 is measured by the visual sensor 1 before and after the movement. FIG. 2 shows the case where each movement is projected on the x-axis. It is a figure which shows, and FIG. 3 is a figure which shows the case where it projects on ay axis.

The visual sensor 1 captures the movements Px and Py of the object which are at right angles to each other, and the movement amounts are both equal to p.

[Equation 1]

For the movements Px and Py, the projections on the x-axis of the image coordinate system are Vxx and Vxy, respectively. Here, the inclination of the movement Px with respect to the x-axis of the image coordinate system is α, and the unit pixel length in the x-axis direction is Ux.

[Equation 2]

From equation (4) showing the relationship of trigonometric functions for one angle, equations (2) and (3) can be summarized in the form of equation (5).

[Equation 3]

Therefore, the unit pixel length Ux in the x-axis direction is calculated from the equation (6). Further, in the same manner, the equation (7) for calculating the unit pixel length Uy in the y-axis direction is obtained.

[Equation 4]

The above-described embodiment is an application example in which the visual sensor is fixed and only the object is moved. However, there is no relative rotation between the visual sensor and the object, and they are perpendicular to each other. If the relative movement between the visual sensor and the object in one direction is possible, the object is fixed and the visual sensor is moved, or both the visual sensor and the object with respect to the workspace coordinate system. The present invention can be widely applied to the case of moving the.

In order to specify the position of the object in the image coordinate system from the image captured by the visual sensor, the center of gravity of the image of the object is used in the above-mentioned embodiment, but the specific vertex of the object,
The center of the hole or the like can be used, and in the present invention, the method of measuring the position of the object is arbitrary.

[0019]

As described above, according to the present invention, the equations (6) and (7) for calculating the unit pixel length do not include the absolute position of the object in the workspace coordinate system, and the visual sensor Since it is not necessary to match the measured position of the object with the known position in the work space coordinate system, the degree of freedom of the shape of the object is high and the alignment work is unnecessary.

Equations (6) and (7) are the amounts of movement of two relative movements of the visual sensor and the object at right angles to each other, and the object in the image coordinate system measured before and after each movement. Since this is a simple calculation formula composed only of the values of the positions, it is possible to obtain a highly reliable value in which unnecessary error factors are less likely to enter.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a geometrical relationship of an object moving in an image coordinate system according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a geometrical relationship of an object moving in an image coordinate system according to an embodiment of the present invention.

[Explanation of symbols]

 1 Visual sensor 2 Object 3 XY stage

Claims (1)

[Claims] 1. A horizontal direction, which is necessary when a measurement result of an object measured by a visual sensor and obtained in a unit of an image coordinate system is converted into a unit of a working space coordinate system in which an actual work is performed and used. In the method of measuring the unit pixel length, which is a value that represents the size of one pixel in the vertical direction in units of the working space coordinate system, the size and shape are within the visual field of the visual sensor, and the position can be stably measured by the visual sensor. It is possible to provide relative movement in two directions at right angles to each other on the imaging plane of the visual sensor without any relative rotation between the at least one possible object and the visual sensor. By using a moving means capable of knowing the amount of movement in units of the working space coordinate system, relative movement is performed between the visual sensor and the object with the same amount of movement in each of the two directions, and before and after each movement. Visual A method for measuring a unit pixel length, which is calculated from a relationship between a position of an object measured in a unit of an image coordinate system using a sensor and the movement amount.