1 INTRODUCTION
As a extensive technology, the sorting robot based on
machine vision has been used increasingly in express
industry including sorting packages on the conveyer which
makes a significant contribution to reducing the burden on
workers.
The whole sorting system is made up of the vision module
and the motion control module. On automatic sorting lines,
machine vision is used to obtain and identify images of the
moving target so as to conduct manipulators completing
sorting tasks. The machine arm control is a complex task
because it is hard to achieve the pick-and-place operation
for the manipulator in a high-speed sorting process
instantly.
Ref.
[1-5]
present the general structure and working principle
of the sorting robot system. Ref.
[6]
proposes a new theory
of describing serial-link manipulators. Ref.
[7-8]
uses
Denavit- Hartenberg representation method to model
manipulator. Ref.
[9-10]
mentioned the dead-zone and
limitation of the manipulator. Ref.
[11-13]
indicates that
genetic algorithm is applied to accomplish the optimization
of path planning with the optimizing index including shift
distance and path length. Ref.
[14-16]
researches on the
optimal control of the arbitrary serial-link manipulator. Ref.
[17]
came up with the time-optimal algorithm for robot based
on kinematic constraints. Ref.
[18-22]
introduces the Robotics
Toolbox for MATLAB in tutorial form with examples
chosen to account for a range of capabilities.
Most scholars focus on how to fulfill grabbing objects
precisely but pay little attention to analysis the influence on
specific grabbing position on the conveyer. Actually,
different picking positions result in different rotation angles
of the manipulator and it will spend more time and consume
more energy on large rotation angle at the same velocity for
the robot system during the sorting operation. Thus, it is a
significant research on the optimal picking point of sorting
robots.
In this paper, the optimal picking point would be
investigated by kinematic equations for SCARA sorting
manipulators based on the Denavit-Hartenberg method.
Then, a new idea aimed at the multi-solution of the inverse
kinematics has been proposed after the introduction of
traditional algorithm. Because of the precise functional
relationship between any position on the conveyer and
rotation angle of manipulators, the selection of optimal
grabbing point converts into another issue that analyze
optimal rotation angle according to the minimum sorting
time. Further, the concept called the optimal sorting line
and the optimal picking point database aimed at the
real-time sorting operation would be proposed. Moreover,
simulation demonstrates that it spends the minimum time
and less energy picking the object on the optimal sorting
line.
2 ROBOT KINEMATIC MODELING
D-H representation method, proposed by Denavit and
Hartenberg in 1955, is utilized to research the modeling of
manipulator. It is the basis of kinematic and dynamic
analysis.
Generally, the geometrical relations of robot joints are
described by the D-H parameter list. The parameters of the
D-H method are shown in the following Fig.1 and table1.
Fig.1 D-H parameter description
Research on a high-speed picking-placing motion of the sorting robot
based on the optimal picking point
Zeqiang He, Zonglin Li, Jiachen Ma
Harbin Institute of Technology, Harbin 150001, China
E-mail: zqhe_mail@126.com
Abstract: In this paper, a new method to determine the optimal picking point on automation sorting pipeline operations is
proposed. Kinematic equations for SCARA sorting manipulators are established based on the Denavit-Hartenberg representation
method. Algebraic and geometric algorithms to the inverse kinematic problem for sorting manipulators are introduced and a new
idea that establishes an optimal picking point database has been proposed to solve the same issue efficiently by contrast. In the
same angular velocity conditions,
the position costing minimum time to fetch the object for the manipulator would be obtained by
optimal angle objective function customized. The corresponding coordinate position namely is the optimal picking point and then
the optimal grab line is obtained. The simulation conducted on robotics toolbox demonstrates the efficiency and validity of the
proposed optimal grab point algorithm.
Key Words: Optimal picking point, D-H method, Inverse kinematic, Simulation
5310
978-1-4673-9714-8/16/$31.00
c
2016 IEEE
