Hindawi Publishing Corporation
Advances in Mechanical Engineering
Volume , Article ID , pages
http://dx.doi.org/.//
Research Article
Reference Sphere Positioning Measurement Based on
Line-Structured Light Vision Sensor
Bin Wu and Yuan Zhang
State Key Laboratory of Precision Measuring Technology & Instrument, Tianjin University, Tianjin 300072, China
Correspondence should be addressed to Bin Wu; wubin@tju.edu.cn
Received June ; Accepted September
Academic Editor: Fuqiang Zhou
Copyright © B. Wu and Y. Zhang. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
e line-structured light vision sensor has been used widely in industrial vision measuring elds due to its simple structure, small
volume, light weight, low cost, convenient calibration, and high accuracy of measurement. To locate the reference sphere precisely
with line-structured light vision sensor, a mathematical model based on the measuring principle of line-structured light vision
sensor is established in the paper. en, the positioning measurement error is analyzed in detail. e experimental results show
that the method is valid and correct. In addition, an accurate measurement area which is from
0
× sin 45
∘
to
0
× sin 75
∘
away
from the center of reference sphere is delimited through the statistical analysis of the experimental data. For the robot temperature
compensation and calibration of exible vision measurement system, this method eectively solves the positioning measurement
problems about reference sphere with line-structured light vision sensor and has been applied in the industrial exible online
measurement systems successfully.
1. Introduction
e line-structured light vision sensor consists of a line
structured light projector (linear laser) and a camera [].
is type of sensor has many advantages, such as simple
structure, small volume, light weight, low cost, convenient
calibration, and high accuracy of measurement. Hence, it is
widely used in the industrial vision measuring elds [, ].
In particular in the exible measurement system based on
industrial robots [], the line-structured light vision sensor
has more prominent advantages at the aspect of exibility and
spatial accessibility than the stereo visual sensor (binocular or
multi-camera vision sensor).
In the exible online vision measurement system, each
robot is congured with one line-structured light vision
sensor generally. In principle, just the point in the structured
light plan can be a positioning measurement. However, there
are various types of the measured characteristics, such as
edge (inection point) [], round hole (or ellipse hole) [, ],
square hole (or rectangular hole), and sphere. Liu et al. []
studied seam tracking based on a line-structured light vision
sensor. Wu et al. []proposedatwo-stepmethodforspatial
circle orientation with a line-structured light vision sensor
and analyzed the orientation errors in detail. eoretically,
this method can also realize the spatial measurement of the
symmetrical features, such as elliptical hole, square hole,
and rectangular hole. However, few scholars have researched
about the reference sphere positioning measurement with the
line-structured light vision sensor.
Industrial robot is the motion platform in the exible
online measuring system. It is well known that industrial
robot has high position repeatability but low absolute posi-
tioning accuracy []. In addition, every joint motor can
generate a large amount of heat with the robot moving, which
leads to the signicant changes of robot joint length and other
robot parameters []. Due to the extreme complexity of the
joint temperature distribution, it is dicult to establish an
accurate temperature distribution model for the calculation
of parameters that change. e external auxiliary devices are
generally introduced into the system for robot parameters
calibration and temperature compensation []. e reference
sphere is a spatial geometry symmetrical object. So there is
no strict posture requirement for the vision sensor during
the positioning measurement. During the robot parameters
calibration and temperature compensation, the sphere is an
idealauxiliaryobject,anditscenteractsasthephysical