Measurement system used for calibrating mechanical parameters of robot

Patent metadata

Field	Value
Publication number	US-10035268-B2
Application number	US-201615263967-A
Country	US
Kind code	B2
Filing date	Sep 13, 2016
Priority date	Sep 14, 2015
Publication date	Jul 31, 2018
Grant date	Jul 31, 2018

Abstract

A measurement system able to perform measurement by a simpler manner when performing measurement a plurality of times for a plurality of targets. The measurement system utilizes the light receiving device to measure targets fastened to the machine tool. The robot is moved so that the difference between a target on a light receiving surface of the light receiving device and an image acquired by the light receiving device in the state where the machine tool is stopped at each stop position and the robot is placed in the measurement position and posture becomes within a predetermined error. A plurality of stop positions and a plurality of end point positions and postures after the movement are used as the basis to simultaneously find the error of the mechanical parameters of the robot and the relative relationship between the robot coordinate system Σb and the machine tool coordinate system Σm.

First claim

What is claimed is:

1. A measurement system comprising:
a multi-articulated robot including a light receiving device at a front end of an arm; and
a machine tool that is provided inside a range of operation of the robot and utilizes the light receiving device to measure a target fastened to the machine tool, wherein
the target has a geometric feature enabling identification of information on a position of an image of the target formed on a light receiving surface of the light receiving device and information on a length relating to a distance between the light receiving device and the target, and
the measurement system further comprises:
a measurement position/posture determining part determining a plurality of stop positions of the machine tool and a plurality of measurement positions and postures of the robot whereby when the machine tool is at the plurality of stop positions, the target is included in a field of vision of the light receiving device,
a positioning part successively positioning the machine tool at the plurality of stop positions and successively positioning the robot at the plurality of measurement positions and postures corresponding to the plurality of stop positions,
a target detecting part forming the image of the target on the light receiving surface of the light receiving device and using information on the position of the target and information on the length as the basis to detect information on the distance between the light receiving device and the target,
a robot moving part moving the robot so that in a state where the machine tool is at a stop position and the robot is at a measurement position and posture, a difference between a position of the target on the light receiving surface of the light receiving device and a predetermined location of the image acquired by the light receiving device becomes within a predetermined error and a difference of information on the distance and a predetermined value becomes within a predetermined error,
a robot end point storing part storing positions and postures of the robot after being moved by the robot moving part as end points linked with the stop positions of the machine tool and the measurement positions and postures, and
a calculating part using the plurality of end points corresponding to the plurality of stop positions and the plurality of measurement positions and postures and the plurality of stop positions as the basis to simultaneously find error of the mechanical parameters of the robot and a correspondence between the coordinate system of the robot and the coordinate system of the machine tool.

2. The measurement system according to claim 1 , wherein the measurement position/posture determining part is configured to determine the plurality of measurement positions/postures so that a distance between the light receiving device and a predetermined point of the target is constant and a slant of a line of sight of the light receiving device passing through the predetermined point differs.

3. The measurement system according to claim 1 , wherein the measurement position/posture determining part is configured to determine the plurality of measurement positions/postures so that a posture of a line of sight of the light receiving device passing through a predetermined point of the target is constant and a distance between the light receiving device and the predetermined point of the target differs.

4. The measurement system according to claim 1 , wherein the measurement position/posture determining part is configured to automatically generate the plurality of measurement positions and postures.

5. The measurement system according to claim 1 , wherein the calculating part is configured to utilize nonlinear optimization including the Newton-Raphson method, a genetic algorithm, and a neural network so as to find the error of the mechanical parameters of the robot.

6. The measurement system according to claim 1 , wherein the light receiving device is a CCD camera configured to capture a 2D image.

7. The measurement system according to claim 1 , wherein the target has a circular mark and wherein the information on length includes a long axis length of an oval corresponding to the image of the mark formed on the light receiving surface of the light receiving device.

8. The measurement system according to claim 1 , wherein the light receiving device is a PSD configured to find a center of gravity of distribution of the amount of light received.

9. The measurement system according to claim 8 , wherein the target is a light emitting device.

10. The measurement system according to claim 1 , wherein the calculating part is configured to use the error between the position of a point of interest of the light receiving device and the position of a predetermined point of the mark formed on the target as the basis to find the error of the mechanical parameters of the robot.

11. A calibration method for calibrating mechanical parameters of a robot using a measurement system comprising a multi-articulated robot including a light receiving device at a front end of an arm and a machine tool provided inside a range of operation of the robot, the calibration method comprising
determining a plurality of stop positions of the machine tool and a plurality of measurement positions and postures of the robot whereby when the machine tool is arranged at the plurality of stop positions, a target fastened to the machine tool is included in a field of vision of the light receiving device,
successively positioning the machine tool at the plurality of stop positions and successively positioning the robot at the plurality of measurement positions and postures corresponding to the plurality of stop positions,
forming the image of the target on the light receiving surface of the light receiving device and using information on the position of the target and the information on length as the basis to detect information on the distance between the light receiving device and the target,
moving the robot so that in a state where the machine tool is at a stop position and the robot is at a measurement position and posture, a difference between a position of the target on the light receiving surface of the light receiving device and a predetermined location of the image acquired by the light receiving device becomes within a predetermined error and a difference of information on the distance and a predetermined value becomes within a predetermined error,
storing positions and postures of the robot after being moved based on the error as end points linked with the stop positions of the machine tool and the measurement positions and postures, and
using the plurality of end points corresponding to the plurality of stop positions and the plurality of measurement positions and postures and the plurality of stop positions as the basis to simultaneously find error of the mechanical parameters of the robot and a correspondence between the coordinate system of the robot and the coordinate system of the machine tool.

12. The calibration method according to claim 11 further comprising, when finding error of the mechanical parameters of the robot, using an error between a position of a point of interest of the light receiving device and a position of a predetermined point of a mark formed on the target as the basis to find error of the mechanical parameters of the robot.

Assignees

• Fanuc Corp

Inventors

• Murata Yuusuke

Classifications

• B25J9/1653

  parameters identification, estimation, stiffness, accuracy, error analysis · CPC title

• G05B2219/39045

  Camera on end effector detects reference pattern · CPC title

• B25J9/1664

  characterised by motion, path, trajectory planning · CPC title

• B25J9/1671

  characterised by simulation, either to verify existing program or to create and verify new program, CAD/CAM oriented, graphic oriented programming systems · CPC title

• G01B11/14

  for measuring distance or clearance between spaced objects or spaced apertures (G01B11/26 takes precedence; rangefinders G01C3/00) · CPC title